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Programmed cell death during neuronal development: the sympathetic neuron model

Abstract

Developing sympathetic neurons of the superior cervical ganglion are one of the best studied models of neuronal apoptosis. These cells require nerve growth factor (NGF) for survival at the time that they innervate their final target tissues during late embryonic and early postnatal development. In the absence of NGF, developing sympathetic neurons die by apoptosis in a transcription-dependent manner. Molecular studies of sympathetic neuron apoptosis began in the 1980s. We now know that NGF withdrawal activates the mitochondrial (intrinsic) pathway of apoptosis in sympathetic neurons cultured in vitro, and the roles of caspases, Bcl-2 (B-cell CLL/lymphoma 2) family proteins and XIAP (X-linked inhibitor of apoptosis protein) have been extensively studied. Importantly, a considerable amount has also been learned about the intracellular signalling pathways and transcription factors that regulate programmed cell death in sympathetic neurons. In this article, we review the key papers published in the past few years, covering all aspects of apoptosis regulation in sympathetic neurons and focusing, in particular, on how signalling pathways and transcription factors regulate the cell death programme. We make some comparisons with other models of neuronal apoptosis and describe possible future directions for the field.

Facts

  • Developing NGF-dependent sympathetic neurons are a very well characterised model of neuronal apoptosis.

  • NGF withdrawal-induced death in vitro requires de novo gene expression, as does the death of other kinds of primary neuron, including developing cerebellar granule neurons (CGNs), motor neurons and cortical neurons.

  • NGF deprivation activates the mitochondrial pathway of apoptosis, and BH3-only proteins and Bax (Bcl-2-associated x protein) are required for mitochondrial outer membrane permeabilisation (MOMP) and cytochrome c release.

  • The binding of NGF to TrkA activates the PI3K-Akt (phosphatidylinositol 3-kinase-Akt) and Raf-MEK-ERK (Raf-MAPK/extracellular signal-regulated kinase kinase-extracellular signal-regulated kinase) signalling pathways, which promote the growth and survival of sympathetic neurons.

  • NGF deprivation decreases the activity of the PI3K-Akt and Raf-MEK-ERK survival pathways, but increases the activity of the MLK-JNK-c-Jun (mixed lineage kinase-c-Jun N-terminal kinase-Jun proto-oncogene) pathway, which is required for the increased expression of BH3-only proteins and for mitochondrial cytochrome c release.

Open Questions

  • How is the PI3K-Akt pathway inactivated after NGF withdrawal and how is the JNK pathway activated?

  • How exactly do TrkA and p75NTR (p75 neurotrophin receptor) regulate NGF withdrawal-induced death?

  • How do the new NGF-regulated genes identified by gene microarray analysis contribute to the control of sympathetic neuron death and survival?

  • How do the core cell death proteins in sympathetic neurons function in axon degeneration induced by local NGF deprivation?

  • How similar are the mechanisms of cell death in sympathetic neurons and developing central nervous system neurons, such as CGNs or cortical neurons?

Apoptosis occurs extensively during the normal development of the mammalian nervous system and has been observed in populations of developing neural precursor cells, differentiated postmitotic neurons and glial cells.1, 2, 3 These cell deaths are important for establishing neuronal and glial populations of the correct size. In the case of the developing peripheral nervous system (PNS), neuronal apoptosis has been shown to be important for matching the number of innervating neurons to the size of the final targets that they innervate. Sympathetic neurons of the superior cervical ganglion (SCG) have been extensively studied as a model of naturally occurring neuronal death in the PNS. During mammalian development, one-third of these cells normally die by apoptosis during the first 2 weeks after birth.4 At this time, sympathetic neurons require nerve growth factor (NGF), synthesised by their target tissues, for survival.5 NGF is produced in limiting amounts by the targets innervated by SCG neurons, and binds to its specific tyrosine kinase receptor, TrkA, on the surface of the innervating axons.5 The NGF–TrkA complex is then retrogradely transported to the sympathetic neuron cell bodies and promotes neuronal growth. Importantly, the binding of NGF to TrkA also inhibits neuronal apoptosis. Levi-Montalcini and Booker6, 7 showed that injection of a neutralising anti-NGF antiserum into early postnatal rats or mice greatly reduced the number of SCG neurons, whereas injection of purified NGF increased their number.6, 7 In agreement with these classic studies, targeted knockout of the TrkA or Ngf genes in mice also reduces the number of SCG neurons by increasing the amount of neuronal death that occurs.5, 8, 9

Basic Features of Sympathetic Neuron Death In Vitro

Developing sympathetic neurons can be isolated from the SCGs of early postnatal rats or mice, separated from other cell types and cultured in vitro for extended periods in medium containing NGF. When deprived of NGF, sympathetic neurons die over a period of 48–72 h and this death has the classic hallmarks of apoptosis10, 11, 12 (Figure 1). After NGF withdrawal, sympathetic neurons become atrophied and their neurites fragment (Figure 1a). There is also a decrease in glucose uptake and a fall in the overall rates of protein synthesis and gene transcription.10, 11 The nuclei of NGF-deprived neurons become pyknotic (Figure 1b) and the chromosomal DNA fragments. This can be detected as a nucleosomal DNA ladder on a gel12 and visualised at the single neuron level by terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) analysis (Figure 1b). In vivo, TUNEL-positive cells can be detected in the SCGs of mice during the period of developmental neuronal death, and the number of TUNEL-positive cells per SCG is altered by mutations that change the rate of NGF withdrawal-induced death in vitro13, 14 (Figure 1c). Importantly, the NGF withdrawal-induced death of sympathetic neurons in vitro is strongly delayed by inhibitors of transcription or protein synthesis, suggesting that de novo gene expression is required for the activation of the cell death programme in these cells.10, 12 This is also true for cultured rat or mouse CGNs deprived of survival signals,15, 16 chick motor neurons deprived of trophic support17 or cortical neuron apoptosis,18 suggesting that this is often a feature of developmental neuronal death.

Figure 1
figure 1

Morphological and biochemical changes that occur in sympathetic neurons undergoing programmed cell death in vivo or following NGF withdrawal in vitro. (a) Morphology of sympathetic neurons isolated from one-day-old rats and cultured for 6 days in vitro and then in the presence and absence of NGF for 48 h. Bar, 25 μm. (b) Apoptotic chromatin condensation and DNA fragmentation in cultured sympathetic neurons visualised by Hoechst 33342 staining and TUNEL analysis. The neurons were isolated from one-day-old rats, cultured for 6 days in vitro and then in the presence and absence of NGF for 24 h. Bar, 25 μm. (c) TUNEL analysis of apoptosis in the superior cervical ganglia of one-day-old wild-type and mkp1−/− mice. The mkp1−/− knockout mutation significantly increases the number of TUNEL-positive cells per ganglion.14 Scale bar, 100 μm. (d) NGF withdrawal activates caspase-3 in sympathetic neurons. Neurons were cultured in the presence or absence of NGF for 48 h. The cleaved form of caspase-3 and nuclear morphology were visualised by staining the neurons with an anti-active caspase-3 antibody and Hoechst 33342. Bar, 25 μm. (e) Distribution of cytochrome c in normal and apoptotic sympathetic neurons visualised by immunocytochemistry with an anti-cytochrome c antibody. In the presence of NGF, cytochrome c immunoreactivity is excluded from the nuclear space and has a punctate pattern. In the absence of NGF, a fainter, diffuse staining pattern that occurs throughout the whole cell is observed. Bar, 25 μm

The timecourse of key events during NGF withdrawal-induced death has been carefully documented10, 11 (Figure 2). By 22 h after NGF withdrawal, only 50% of the neurons can be rescued by the readdition of NGF and this was defined as the commitment point for NGF withdrawal-induced death. The transcriptional commitment point is 16 h after NGF withdrawal and this is the time at which only 50% of the neurons can be rescued by the addition of inhibitors of transcription or protein synthesis (Figure 2).

Figure 2
figure 2

Key events following NGF withdrawal in sympathetic neurons. Sympathetic neurons undergo death 24–48 h after NGF withdrawal. The N-terminal phosphorylation of c-Jun, the release of cytochrome c from the mitochondria and the activation of caspase-3 are key biochemical changes seen in NGF-deprived sympathetic neurons. By 16 h after NGF withdrawal, only 50% of the neurons can be rescued by the addition of inhibitors of transcription or protein synthesis (the transcriptional commitment point) and by 22 h after NGF withdrawal only 50% of the neurons can be rescued by the readdition of NGF (the commitment point for NGF withdrawal-induced death). By 48 h, almost all of the neurons have undergone apoptosis and the nuclear and morphological changes typical of apoptosis are apparent. Images represent snapshots of NGF-deprived sympathetic neurons at the timepoints shown. Scale bars, 20 μm

NGF Withdrawal Activates the Mitochondrial (Intrinsic) Pathway in Sympathetic Neurons

The NGF withdrawal-induced death of sympathetic neurons requires caspase activity. Activated caspase-3 can be detected after NGF withdrawal in vitro (Figure 1d) and in SCGs in vivo during the period of naturally occurring neuronal death. Caspase inhibitors, such as BAF (boc-aspartyl-(OMe)-fluoromethyl-ketone), zVAD-fmk (carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]- fluoromethylketone) or the baculovirus p35 protein protect sympathetic neurons against cell death after NGF deprivation.19, 20, 21, 22 NGF withdrawal activates the mitochondrial (intrinsic) pathway of caspase activation (Figure 3). Cytochrome c is released from the mitochondria of NGF-deprived sympathetic neurons and this can be visualised by cell fractionation and immunoblotting22 or by immunocytochemistry using an anti-cytochrome c antibody23, 24 (Figure 1e). Importantly, microinjection of a neutralising anti-cytochrome c antibody inhibits NGF withdrawal-induced death, suggesting that the released mitochondrial cytochrome c is functionally important.24 Deletion of the Apaf-1 (apoptotic protease-activating factor-1), caspase-9 or caspase-3 genes in mice prevents apoptosis after NGF deprivation, and allows the sympathetic neurons to recover and survive long-term following readdition of NGF.25 The readdition of NGF to NGF-deprived sympathetic neurons in which cytochrome c has been released leads to the refilling of the mitochondria with cytochrome c.22, 26 Sympathetic neurons are one of the few cell types in which this occurs, making this a useful model for understanding the mitochondrial death commitment point in general. Overall, these results are consistent with a model in which mitochondrial cytochrome c release promotes the formation of the apoptosome, which leads to the activation of caspase-9, which then cleaves and activates caspase-3 (Figure 3). Caspase-3 is critical for NGF withdrawal-induced death because early postnatal sympathetic neurons do not express the related executioner caspase, caspase-7.25 Another interesting feature of the sympathetic neuron model is that microinjection of purified, functional cytochrome c into sympathetic neurons cultured in the presence of NGF does not induce apoptosis.23, 24 Sympathetic neurons only become competent to die in response to cytochrome c injection when they have been deprived of NGF for several hours.23 Subsequent experiments demonstrated that after NGF withdrawal, the endogenous caspase inhibitor, X-linked inhibitor of apoptosis protein (XIAP), substantially decreases in level and that this is the molecule that protects sympathetic neurons maintained in NGF-containing medium against apoptosis induced by injection of cytochrome c27 (Figure 3).

Figure 3
figure 3

NGF withdrawal activates the mitochondrial (intrinsic) pathway of apoptosis in sympathetic neurons. After NGF withdrawal, the expression of the BH3-only proteins Dp5, Bim, Puma and Bmf increases.35, 53, 54 These promote MOMP by binding to and antagonising the antiapoptotic Bcl-2 and Bcl-xL proteins or by directly activating Bax. The multidomain proapoptotic Bax protein is activated by NGF withdrawal and essential for MOMP and mitochondrial cytochrome c release. Cytosolic cytochrome c interacts with Apaf-1 and procaspase-9 to form the apoptosome complex, which then cleaves and activates the effector caspase, caspase-3. Bim, Puma, Bax, cytochrome c, Apaf-1, caspase-9 and caspase-3 have all been shown to be essential for normal NGF withdrawal-induced death in experiments using sympathetic neurons isolated from specific knockout mice or, in the case of cytochrome c, a neutralising anti-cytochrome c antibody.23, 24, 25, 37, 41, 48, 56, 57 RAIDD and caspase-2 may function upstream of the mitochondrial pathway in sympathetic neurons and promote cell death by increasing the expression of the BH3-only protein Bim.32 In the presence of NGF, XIAP inhibits caspases in sympathetic neurons, but after NGF withdrawal, the level of the XIAP protein significantly decreases,27 allowing the intrinsic pathway to activate caspase-3 and induce cell death. During the later postnatal development of sympathetic neurons, the level of the MiR-29b microRNA increases (from P13 onwards) and this inhibits expression of the BH3-only proteins and contributes to the resistance of late postnatal (P28) sympathetic neurons to NGF deprivation-induced death54, 118

The role of another initiator caspase –caspase-2 – has also been studied in sympathetic neurons. Caspase-2 is activated after NGF withdrawal and this activation requires the adaptor protein RAIDD (RIP-associated ICH-1/CAD-3 homologous protein with a death domain).28 Knockout of the caspase-2 gene in mice does not delay NGF withdrawal-induced death in vitro.29, 30 However, caspase-9 levels are increased in the brain and in sympathetic neurons isolated from capase-2 knockout mice, compared with the same tissues from wild-type mice, suggesting that compensatory changes in caspase-9 expression have occurred.31 Knockdown of caspase-2 or RAIDD in wild-type neurons using siRNAs does reduce the rate of NGF withdrawal-induced death in vitro.28, 32 Interestingly, recent results suggest that caspase-2 may function upstream of the mitochondrial pathway in sympathetic neurons and promote cell death by increasing the phosphorylation of c-Jun and the expression of the BH3-only protein Bim (Bcl-2-interacting mediator of cell death)32 (Figure 3).

Bcl-2 (B-cell CLL/lymphoma 2) family proteins have a key role in regulating the release of mitochondrial cytochrome c after NGF withdrawal33, 34, 35 (Figure 3). Overexpression of Bcl-2 protects sympathetic neurons against NGF withdrawal-induced death36 and inhibits mitochondrial cytochrome c release.37 Conversely, sympathetic neurons from bcl-2−/− knockout mice die more rapidly after NGF withdrawal, indicating that the endogenous Bcl-2 protein promotes sympathetic neuron survival.38 The multidomain proapoptotic proteins Bax and Bak (Bcl-2-antagonist/killer) are critical for MOMP, and in many cell types, both proteins are functionally important.39 However, in the case of sympathetic neurons, only Bax is required for mitochondrial cytochrome c release and NGF withdrawal-induced death. Overexpression of Bax in sympathetic neurons is sufficient to induce cytochrome c release and apoptosis in the presence of NGF.37, 40 Importantly, sympathetic neurons isolated from bax−/− knockout mice are strongly protected against NGF withdrawal-induced death in vitro and will survive for extended periods in the absence of NGF, although the neurons still become atrophied.41 In addition, the number of sympathetic neurons isolated from the SCGs of postnatal day 1 (P1) bax−/− mice is increased by 2.5-fold compared with wild-type mice.41 On the other hand, inactivation of the bak gene in mice has no effect on the rate of NGF withdrawal-induced death.42 Interestingly, sympathetic neurons express the N-Bak transcript, which is a neuron-specific splice variant of the Bak mRNA.43 The variant Bak protein encoded by this transcript only retains the BH3 domain and lacks the other BH domains. However, the N-Bak protein is not expressed in sympathetic neurons and this is due to translational repression mediated by sequences in the 5′- and 3′-UTRs of the N-Bak mRNA.44, 45

How does NGF withdrawal regulate the activity of Bax and Bcl-2 in sympathetic neurons? Bax translocates to the mitochondria after NGF withdrawal and both this and mitochondrial cytochrome c release are inhibited by cycloheximide, suggesting that de novo protein synthesis is required for Bax translocation and MOMP.24, 46 The expression of four different BH3-only members of the Bcl-2 family – Dp5 (neuronal death protein Dp5), Bim, Puma (p53 upregulated modulator of apoptosis) and Bmf (Bcl-2 modifying factor) – increases after NGF withdrawal37, 47, 48, 49, 50, 51, 52, 53 (Figure 3). Furthermore, the BimEL (the largest isoform of Bim), Puma and Bmf proteins clearly increase in level after NGF deprivation and this starts before the transcriptional commitment point.37, 48, 50, 51, 54 Sympathetic neurons have been isolated from the SCGs of knockout mice specific for the different BH3-only protein genes and the effect of each mutation on NGF withdrawal-induced death has been studied. Knockout of bad (Bcl-2-associated agonist of cell death) or bid (BH3 interacting domain death agonist) has no effect on the rate of cell death after NGF deprivation42 and the inactivation of dp5 only has a minor effect on NGF withdrawal-induced death.55, 56 The role of the bmf gene has not been studied yet. However, knockout of either bim or puma very significantly delays cell death after NGF withdrawal, suggesting that BimEL and Puma have important roles.37, 48, 56, 57 In both cases, the protection against cell death is partial and this may be because Puma can partially compensate for the loss of Bim and vice versa. This hypothesis could be tested by culturing sympathetic neurons from bim−/− puma−/− double-knockout mice. This type of experiment has been carried out with mouse CGNs: knockout of bim or puma or bid only partially protects CGNs against apoptosis induced by survival signal withdrawal (extracellular KCl deprivation) but bim−/− puma−/− bid−/− triple knockout CGNs are highly resistant to apoptosis induced by KCl deprivation.58 The role of bim and puma has not yet been studied in developing SCG neurons in vivo, but knockout of bim has been shown to significantly reduce the number of TUNEL-positive dorsal root ganglion neurons during embryonic development, at E14.5 or E15.5.48, 59 In the case of sympathetic neurons in vivo, it would be interesting to compare the number of TUNEL-positive neurons per SCG and the total number of SCG neurons in bim −/− puma −/− double-knockout mice, bim −/− mice, puma −/− mice and wild-type mice, at the time of naturally occurring neuronal death.

In cultured sympathetic neurons, BimEL has been shown to be present at the mitochondria after NGF withdrawal48 and overexpression of BimEL in the presence of NGF is sufficient to trigger mitochondrial cytochrome c release and apoptosis.37 These results suggest a model in which Dp5, Bim, Puma and Bmf rapidly increase in level after NGF withdrawal and promote MOMP in sympathetic neurons, with Bim and Puma having major roles, by binding to antiapoptotic Bcl-2 family proteins, such as Bcl-2, and thereby preventing them from inhibiting Bax-dependent cytochrome c release (Figure 3). In addition, BimEL and Puma may also directly bind to and activate Bax, as suggested by work on Bax in other systems.39, 60, 61, 62

Changes in Gene Expression After NGF Withdrawal

It has been 25 years since Martin et al.10 reported that RNA and protein synthesis are necessary for neuronal death caused by NGF deprivation and proposed that de novo gene expression is required for cell death to occur. This key study contributed to the idea of apoptosis as an active form of cell death and led to the search for proapoptotic genes that are induced in NGF-deprived sympathetic neurons. Early studies based on specific hypotheses identified cyclin D1, c-jun and mkp1 (MAP kinase phosphatase 1), among others, as genes upregulated after NGF withdrawal.63, 64, 65 c-Jun is a member of the Jun and Fos family of basic/leucine zipper transcription factors, which together with activating transcription factor 2 (ATF2) constitute the transcription factor activator protein-1 (AP-1). c-Jun/c-Fos heterodimers bind to the AP-1 site (5′-TGACTCA-3′) with high affinity, whereas c-Jun/ATF2 heterodimers prefer to bind to ATF sites (5′-TGACGTCA-3′). The c-jun mRNA and protein increase in level soon after NGF withdrawal, whereas the other members of the AP-1 family do not change in level.64, 65 The microinjection of c-Jun antibodies or expression of a dominant-negative c-Jun mutant or a conditional knockout of the c-jun gene in sympathetic neurons protects the cells against NGF withdrawal-induced death64, 65, 66 and suggests that the transcriptional induction of AP-1 target genes is important for cell death following NGF deprivation. c-Jun N-terminal phosphorylation also increases after NGF withdrawal.65, 67, 68, 69 This phosphorylation increases the transcriptional activity of c-Jun and is mediated by JNKs.70

Several other NGF withdrawal-regulated genes that promote neuronal apoptosis were discovered either by looking at the expression of specific genes (bim, p63, puma) or in mRNA differential display experiments (dp5, egln3 (Egl nine homologue 3)).13, 37, 47, 48, 51, 71 For each of these genes, the mRNA and protein increases in level after NGF withdrawal and experiments with knockout mice have demonstrated that bim, puma, p63 and egln3 are required for normal NGF withdrawal-induced death.13, 37, 48, 51, 57, 71, 72, 73 The BH3-only protein genes bim and dp5 are direct targets of c-Jun,37, 52, 74, 75 and the Dp5 and Bim proteins, together with Puma and Bmf, promote MOMP after NGF withdrawal (Figure 3). However, other genes induced after NGF deprivation may be important in other aspects of NGF withdrawal-induced death, for example, the inhibition of protein synthesis and growth or the regulation of specific intracellular signalling pathways. Gene microarray technology has now been used to study the pattern of expression of all known genes in NGF-deprived sympathetic neurons.53 Using Affymetrix exon arrays, 415 up- and 813 downregulated genes were identified, including most of the genes previously known to be regulated by NGF withdrawal. One of the known induced genes was mkp1, which encodes a mitogen-activated protein kinase (MAPK) phosphatase that can dephosphorylate JNKs. Mkp1 is part of a negative feedback loop induced by the JNK-c-Jun signalling pathway, which inhibits JNK activity and thereby modulates the rate of neuronal death following NGF withdrawal.14

The expression of two members of the p53 family, ΔNp73 and TAp63, changes in sympathetic neurons following NGF withdrawal. ΔNp73, an N-terminally truncated isoform of p73, decreases in level after NGF deprivation and has been shown to promote the survival of sympathetic neurons.76 ΔNp73 may function by acting as an antagonist of p53 family transactivator proteins or by binding directly to JNKs and inhibiting their activity.77 Following NGF withdrawal, TAp63, which is a transcriptional activator closely related to p73, increases in level.13 Overexpression of TAp63 induces neuronal apoptosis in the presence of NGF and p63−/− sympathetic neurons are resistant to NGF withdrawal-induced death, suggesting that p63 has an important role in developmental neuronal apoptosis.13

The use of an MLK inhibitor, CEP-11004, which inhibits the activation of the JNK-c-Jun pathway after NGF withdrawal, has allowed the identification of NGF withdrawal-regulated genes that may be downstream targets of the JNK pathway.53, 78 However, the induction of some genes, such as egln3, which encodes a prolyl hydroxylase that destabilises hypoxia-inducible factor (HIF), is not affected by CEP-11004.53 Egln3 transcription may be regulated by other transcription factors that are activated after NGF withdrawal, but not regulated by the JNK pathway. Under normal oxygen tensions, the EglN3 protein hydroxylates specific proline residues in HIF-1α and HIF-2α. The hydroxylated proteins are then bound by the von Hippel–Lindau protein and its associated E3 ubiquitin ligase, resulting in their polyubiquitination and degradation by the proteasome. It has been proposed that EglN3 may promote the death of NGF-deprived neurons in part by suppressing a HIF-2α-mediated survival pathway.79

Receptors and Intracellular Signalling Pathways that Regulate Sympathetic Neuron Survival

NGF was the first growth factor to be discovered80 and regulates the growth, survival and differentiation of sensory and sympathetic neurons by binding to two types of cell surface receptor: the TrkA tyrosine kinase and the p75NTR, which are often present on the same cell. Binding of NGF to TrkA leads to receptor dimerisation and tyrosine residue phosphorylation of the cytoplasmic tail by adjacent Trk receptors.81 When NGF is bound to TrkA, the receptor transmits positive signals that enhance sympathetic neuron growth and survival.82 The binding of NGF to TrkA activates the small GTPase Ras, which promotes neuronal survival by activating the PI3K-Akt and Raf-MEK-ERK pathways and also by inhibiting the JNK pathway.83 The p75NTR receptor can transmit survival signals with TrkA in response to NGF, and also induces cell death upon binding BDNF (which does not bind to TrkA). Experiments with p75NTR−/− knockout mice demonstrated that p75 is required for the NGF withdrawal-induced death of sympathetic neurons and activation of p75NTR using BDNF increases the N-terminal phosphorylation of c-Jun and induces apoptosis.84 Subsequent studies showed that p75NTR can activate the JNK pathway specifically through JNK3 in sympathetic neurons.85 Recently, it was suggested that TrkA can behave as a dependence receptor and induces the death of sympathetic neurons in the absence of NGF and this TrkA-induced death requires p75NTR.86 However, the biochemical mechanism by which TrkA functions as a dependence receptor has not yet been reported.

When NGF binds to TrkA, the PI3K-Akt pathway is activated82 (Figure 4) and promotes both the survival and growth of sympathetic neurons.87 Akt can inhibit apoptosis by phosphorylating and thereby inhibiting the BH3-only protein Bad and the transcription factor forkhead box O3a (FOXO3a). FOXO3a can induce Bim expression when overexpressed and promotes the death of sympathetic neurons in a Bim-dependent manner.50 NGF withdrawal causes a rapid decrease in PI3K and Akt activity, which leads to an increase in the amount of FOXO3a in the nucleus, where it induces the transcription of proapoptotic genes such as bim. The binding of NGF to TrkA also activates the Raf-MEK-ERK signalling pathway, which can inhibit apoptosis and promote cell survival (Figure 4).67, 82 This protein kinase cascade has many effects on neurons, such as an increase in axonal growth in sympathetic neurons after ERK activation.88 The Raf-MEK-ERK pathway may suppress apoptosis by phosphorylating and inactivating the Bim protein89, 90 and by activating the protein kinase Rsk. Rsk phosphorylates and thereby activates the prosurvival transcription factor CREB91 (Figure 4). Furthermore, the Raf-MEK-ERK pathway can reduce the level of bim RNA in sympathetic neurons and inhibition of both the PI3K and ERK pathways increases the level of the bim RNA to a similar extent as NGF withdrawal.92 However, although the ERK pathway clearly regulates the activity of proteins that promote or inhibit apoptosis in sympathetic neurons, such as Bim and CREB, it appears to have a more minor role than the PI3K-Akt pathway in promoting sympathetic neuron survival in the presence of NGF.82, 92, 93

Figure 4
figure 4

Survival pathways activated by the binding of NGF to TrkA. The binding of NGF to its receptor TrkA can activate the PI3K-Akt signalling pathway, which can inhibit apoptosis and promote cell survival. The binding of NGF to TrkA triggers the activation of the small GTP-binding protein Ras. The subsequent activation of Akt through PI3K can inhibit apoptosis by phosphorylating, and therefore inactivating, proapoptotic proteins such as the BH3-only protein Bad and the transcription factor FOXO. The binding of NGF to its receptor TrkA can also activate the Raf-MEK-ERK signalling pathway. This pathway promotes survival by inhibiting the expression of Bim, and by activating Rsk, which phosphorylates and activates the transcription factor CREB, which can activate the transcription of the bcl-2 gene

In sympathetic neurons, NGF withdrawal leads to the activation of the stress-responsive MLK-JNK-c-Jun protein kinase cascade64, 65, 67, 68, 69, 94, 95 (Figure 5). NGF withdrawal has been proposed to promote the formation of a complex comprising the multidomain protein, plenty of SH3 domains (POSH), which acts as a scaffold that brings together the small G-protein Rac1, which is an activator of the JNK pathway,96 and the other elements of the JNK pathway,97 and thereby stimulates the phosphorylation of c-Jun. Recent studies showed that Sh3rf2, a homologue of POSH, acts as an inhibitor of the MLK-JNK pathway.98 Following NGF withdrawal, Sh3rf2 levels decrease, which stabilises POSH, activates JNKs and leads to cell death. The JNK-c-Jun dependent transcriptional programme is required for apoptosis induced by NGF deprivation and is initiated by the phosphorylation of the Thr-X-Tyr motif of JNKs by MAP kinase kinase 4/7 (MKK4/7).37, 64, 65, 66, 70, 99 Evidence for a role of the MLK-JNK pathway in neuronal death has come from studies using the MLK inhibitor, CEP-1347, and its derivative, CEP-11004,78, 100 and from experiments using the JNK-binding domain (JBD) of JNK-interacting protein-1. The JBD is a direct and specific inhibitor of JNKs and expression of the JBD inhibits c-Jun phosphorylation and inhibits NGF withdrawal-induced apoptosis.101, 102 JNKs phosphorylate c-Jun at serines 63 and 73 and threonines 91 and 93, which increases the ability of c-Jun to activate the transcription of its target genes,70 which include c-jun itself, bim, dp5 and mkp1 in sympathetic neurons (Figure 5).14, 52, 53, 69

Figure 5
figure 5

Proapoptotic signalling pathways activated in NGF-deprived sympathetic neurons. When sympathetic neurons are deprived of NGF, the MLK-JNK-c-Jun pathway is activated. MLKs phosphorylate MAP kinase kinases such as MKK4/7, which in turn phosphorylate JNKs. JNK activity increases leading to the phosphorylation of the AP-1 transcription factors c-Jun and ATF2. This increases the ability of c-Jun to activate the transcription of target genes such as bim, dp5 and c-jun itself. c-Jun can also bind to AP-1 sites in the promoter of mkp1, which encodes a MAPK phosphatase that acts as a negative regulator of the JNK pathway. The MLK inhibitor CEP-11004, which prevents JNK activation, and dominant-negative c-Jun reduce the induction of c-Jun, Bim and Dp5 and block cell death

Another protein kinase-dependent proapoptotic pathway that is activated after NGF withdrawal involves cell-cycle-related proteins. In NGF-deprived sympathetic neurons, activation of the cyclin-dependent kinases (Cdk-4 and Cdk-6) leads to the phosphorylation of retinoblastoma protein (Rb) family members, which causes the dissociation of E2F-Rb (E2 promoter binding factor-Rb) family repressor complexes and consequent derepression of E2F target genes, including b-myb and c-myb. Small-molecule Cdk inhibitors or dominant-negative forms of Cdk-4 or Cdk-6 protect NGF-deprived sympathetic neurons from death, suggesting that Cdk activation may have a role in the mechanism by which NGF withdrawal triggers neuronal death.103, 104 siRNAs that knock down the level of the b-Myb (b-myeloblastosis oncogene) and c-Myb transcription factors protect sympathetic neurons against NGF withdrawal-induced death.105 Furthermore, there are two Myb binding sites in the bim promoter and mutation of these binding sites prevents the induction of a bim promoter – luciferase reporter construct (bim-LUC) after NGF withdrawal.106

The expression of Bim in sympathetic neurons is tightly regulated at both the transcriptional and translational level.35 The bim mRNA increases in level after NGF withdrawal, but this, as well as the increase in Bim protein level, can be partially reduced by expressing dominant-negative c-Jun or by using the MLK inhibitor CEP-11004 or by the JunAA knock-in mutation in mice, which changes serines 63 and 73 in c-Jun to alanines.37, 48, 49, 51, 53 This indicates that c-Jun contributes to the increased expression of Bim after NGF withdrawal, and also suggests that other transcription factors must cooperate with c-Jun to achieve the maximal induction of Bim expression. Two conserved binding sites for FOXO transcription factors were identified in the promoter and first intron of bim and these sites are required for the induction of a bim-LUC reporter construct after NGF deprivation and FOXO activity is required for normal NGF withdrawal-induced death.50, 107 More recently, the identification of an inverted CCAAT box (ICB) in the bim promoter revealed that the trimeric transcription factor NF-Y (nuclear transcription factor Y) binds to the bim ICB and both the ICB and NF-Y activity are essential for the induction of the bim-LUC reporter after NGF withdrawal.108 Furthermore, it was shown that NF-Y and FOXO3a interact with the coactivators CBP and p300 after NGF deprivation and that CBP/p300 activity is required for the activation of the bim promoter. CBP/p300 may integrate the different signalling pathways that cooperatively activate the bim promoter after NGF withdrawal through the DNA binding transcription factors c-Jun, FOXO3a and c-Myb.50, 74, 107, 108

Other Signals that Induce Apoptosis in Sympathetic Neurons

Sympathetic neurons have been an important model for studying NGF-regulated developmental neuronal apoptosis. However, sympathetic neurons have also been very useful for studying how other signals induce neuronal death, including DNA-damaging agents, glial cell line-derived neurotrophic factor (GDNF) withdrawal, ER stress and mutant polyQ-expanded Huntingtin (Htt) protein. In experiments using the DNA-damaging agent cytosine arabinoside (araC), apoptosis is induced in sympathetic neurons via a p53-dependent JNK-independent mechanism. In this context, the inhibition of the ERK pathway increases the rate of apoptosis induced by araC in the presence of NGF, suggesting a protective role for the ERK pathway.109 GDNF is a neurotrophic factor that can promote the survival of 34% of SCG neurons isolated from 1- or 2-day-old rats.110 When these cells are deprived of GDNF, a novel non-mitochondrial caspase-dependent death pathway is activated in the neurons, which does not involve cytochrome c release, Bax, caspase-3 or caspase-9.110 Sympathetic neurons have also been used to identify the pathway of apoptosis triggered by ER stress, which is often associated with various pathological conditions. ER stress induces a neuronal apoptotic pathway that upregulates the BH3-only genes dp5 and puma and commits neurons to die before cytochrome c release, which requires Bax activation and JNK signalling. It also highlights the importance of the apoptosome as the non-redundant caspase activation pathway to execute neuronal apoptosis in response to ER stress.111 Finally, the effect of a polyQ-expanded Htt protein, which causes Huntington’s disease, has been studied in sympathetic neurons. In the presence of NGF, expression of an expanded polyQ Htt aggregating protein causes sympathetic neurons to die, but only slowly, because they express HSP70, which diverts apoptosis into slow necrosis.112

Future Directions

Our current state of knowledge of the mechanisms of apoptosis in sympathetic neurons will allow researchers in the field to investigate a number of interesting questions in the future. Although much has been learned about the role of Bcl-2 family members in this system, many important questions remain to be answered. For example, what is the consequence of knocking out both bim and puma in sympathetic neurons? And, how is the expression of these genes regulated by NGF withdrawal? Some work has been carried out on the transcriptional control of bim, but relatively little is known about puma in sympathetic neurons. In other cell types, puma is a direct target of p53113, 114, 115, 116 and also a target of FOXO3a.117 When sympathetic neurons are treated with araC, p53 is activated and the expression of Puma increases, and the resulting araC-induced apoptosis depends on p53 and puma.57 Therefore, puma might be directly regulated by p53 family members or FOXO transcription factors after NGF withdrawal. Exon microarray experiments have demonstrated that many other genes are induced after NGF withdrawal.53 Like c-jun, mkp1, dp5 and bim, some of these are likely to be downstream targets of the JNK-c-Jun pathway or FOXO transcription factors and it will be interesting to investigate their function in sympathetic neurons and study how their expression is regulated.

Sympathetic neurons depend on target-derived NGF for survival during late embryonic and early postnatal development,5 but become independent of NGF at later stages of development.118 This switch can be reproduced in vitro by culturing P1 sympathetic neurons for 28 days in NGF-containing medium. These 28 DIV neurons do not die when deprived of NGF, even though the JNK-c-Jun pathway is activated in these cells. The molecular basis for this phenomenon was investigated by Wright et al.,119 who observed that Apaf-1 expression is greatly reduced in 28 DIV neurons and P28 superior cervical ganglia owing to alterations in the chromatin structure of the apaf-1 promoter.119 In a more recent study of the changes that occur during the postnatal development of SCG neurons, Kole et al.54 reported that the microRNAs (miRs) MiR-29a, -29b and -29c greatly increase in level in SCGs from P13 onwards.54 They found that increased expression of MiR-29 may contribute to the resistance of P28 sympathetic neurons to NGF withdrawal-induced death because MiR-29 binds to the 3′-UTR regions of the mRNAs that encode Dp5, Bim, Puma and Bmf and inhibits their expression54 (Figure 3). It will be interesting to study SCG neurons in MiR-29−/− knockout mice and to determine how the expression of MiR-29a, -29b and -29c is regulated during the postnatal development of SCG neurons.118

Another important future research direction will be to understand more precisely how the signalling pathways that are regulated by NGF withdrawal are activated or inhibited by the removal of NGF. TrkA has been reported to function as a dependence receptor and induces cell death in the absence of NGF.86 It will be interesting to work out how this proapoptotic function of TrkA is linked to the activation of the MLK-JNK-c-Jun pathway. At the same time, NGF withdrawal inactivates the prosurvival PI3K-Akt pathway.82 This inactivation appears to be mediated in part by the Trib3 protein, which increases in level after NGF withdrawal.120 Trib3 inhibits Akt activity and thereby activates FOXO3a, which in turn binds to and activates the trib3 promoter.120 This constitutes a feedforward loop and it will be important to identify other molecules that function in regulatory loops that activate or inhibit the MLK-JNK-c-Jun and PI3K-Akt pathways in sympathetic neurons.

A recent study investigated the role of components of the mitochondrial pathway in axon degeneration induced by local NGF deprivation in vitro.121 In these experiments, the sympathetic neurons were cultured in microfluidic chambers so that the cell bodies and distal part of the axons were in separate compartments. Removal of NGF from the distal axons induced axon degeneration, but did not trigger apoptosis in the cell bodies, which were protected by XIAP. This axon degeneration required Bax, caspase-9, caspase-3, caspase-6 but not Apaf-1.121 This suggests that local NGF deprivation induces an alternative caspase activation pathway that is independent of the conventional apoptosome and this will certainly be an interesting area of research in the future.

Finally, some of the molecular mechanisms that were discovered using the sympathetic neuron model have also been studied in other models of developmental neuronal apoptosis and in cell culture and in vivo models of neurodegeneration. For example, the JNK-c-Jun pathway was first reported to promote cell death in sympathetic neurons and differentiated PC12 cells following NGF withdrawal.64, 65, 67 It was then found to have a proapoptotic role in some animal models of neuronal injury or neurodegeneration including the kainic acid-induced excitotoxic death of hippocampal neurons,122, 123 cerebral ischaemia-induced cortical neuron death,124 the MPTP-induced death of dopaminergic neurons, which is a model for Parkinson’s disease125 and in the optic nerve crush-induced death of retinal ganglion cells.126 It will be interesting to see which other features of NGF withdrawal-induced death are important for neuronal apoptosis in other regions of the developing and adult nervous system. In conclusion, it is likely that the sympathetic neuron model will continue to be much studied in the future and will provide further important insights that increase our understanding of the mechanisms of neuronal apoptosis during normal neural development and following injuries to the nervous system.

Abbreviations

Akt:

murine thymoma viral (v-akt) oncogene homologue

AP-1:

activator protein-1

Apaf-1:

apoptotic protease-activating factor-1

AraC:

cytosine arabinoside

ATF2:

activating transcription factor 2

Bad:

Bcl-2-associated agonist of cell death

Bak:

Bcl-2-antagonist/killer

Bax:

Bcl-2-associated x protein

Bcl-2:

B-cell CLL/lymphoma 2

Bid:

BH3-interacting domain death agonist

Bim:

Bcl-2-interacting mediator of cell death

Bmf:

Bcl-2-modifying factor

Cdk:

cyclin-dependent kinase

CGN:

cerebellar granule neuron

c-Jun:

Jun proto-oncogene

CNS:

central nervous system

Dp5:

neuronal death protein Dp5

E2F:

E2 promoter-binding factor

Egln3:

Egl nine homologue 3

ERK:

extracellular signal-regulated kinase

FOXO3:

forkhead box O3

GDNF:

glial cell line-derived neurotrophic factor

HIF:

hypoxia-inducible factor

Htt:

Huntingtin protein

JNK:

c-Jun N-terminal kinase

MAPK:

mitogen-activated protein kinase

MEK:

MAPK/extracellular signal-regulated kinase kinase

Mkp1:

MAP kinase phosphatase 1

miR:

microRNA

MKK4:

MAP kinase kinase 4

MKK7:

MAP kinase kinase 7

MLK:

mixed lineage kinase

MOMP:

mitochondrial outer membrane permeabilisation

Myb:

myeloblastosis oncogene

NF-Y:

nuclear transcription factor Y

NGF:

nerve growth factor

P1:

postnatal day 1

p75NTR:

p75 neurotrophin receptor

PI3K:

phosphatidylinositol 3-kinase

PNS:

peripheral nervous system

POSH:

plenty of SH3 domains

Puma:

p53 upregulated modulator of apoptosis

RAIDD:

RIP-associated ICH-1/CAD-3 homologous protein with a death domain

Rb:

retinoblastoma protein

SCG:

superior cervical ganglion

TUNEL:

terminal deoxynucleotidyl transferase dUTP nick-end labelling

XIAP:

X-linked inhibitor of apoptosis protein

References

  1. Oppenheim RW . Cell death during development of the nervous system. Annu Rev Neurosci 1991; 14: 453–501.

    CAS  Article  PubMed  Google Scholar 

  2. Jacobson MD, Weil M, Raff MC . Programmed cell death in animal development. Cell 1997; 88: 347–354.

    CAS  PubMed  Google Scholar 

  3. Buss RR, Sun W, Oppenheim RW . Adaptive roles of programmed cell death during nervous system development. Annu Rev Neurosci 2006; 29: 1–35.

    CAS  Article  PubMed  Google Scholar 

  4. Wright LL, Cunningham TJ, Smolen AJ . Developmental neuron death in the rat superior cervical sympathetic ganglion: cell counts and ultrastructure. J Neurocytol 1983; 12: 727–738.

    CAS  PubMed  Google Scholar 

  5. Glebova NO, Ginty DD . Growth and survival signals controlling sympathetic nervous system development. Annu Rev Neurosci 2005; 28: 191–222.

    CAS  PubMed  Google Scholar 

  6. Levi-Montalcini R, Booker B . Destruction of the sympathetic ganglia in mammals by an antiserum to a nerve-growth protein. Proc Natl Acad Sci USA 1960; 46: 384–391.

    CAS  PubMed  PubMed Central  Google Scholar 

  7. Levi-Montalcini R, Booker B . Excessive growth of the sympathetic ganglia evoked by a protein isolated from mouse salivary glands. Proc Natl Acad Sci USA 1960; 46: 373–384.

    CAS  PubMed  PubMed Central  Google Scholar 

  8. Crowley C, Spencer SD, Nishimura MC, Chen KS, Pitts-Meek S, Armanini MP et al. Mice lacking nerve growth factor display perinatal loss of sensory and sympathetic neurons yet develop basal forebrain cholinergic neurons. Cell 1994; 76: 1001–1011.

    CAS  PubMed  Google Scholar 

  9. Fagan AM, Zhang H, Landis S, Smeyne RJ, Silos-Santiago I, Barbacid M . TrkA, but not TrkC, receptors are essential for survival of sympathetic neurons in vivo. J Neurosci 1996; 16: 6208–6218.

    CAS  PubMed  PubMed Central  Google Scholar 

  10. Martin DP, Schmidt RE, DiStefano PS, Lowry OH, Carter JG, Johnson EM Jr . Inhibitors of protein synthesis and RNA synthesis prevent neuronal death caused by nerve growth factor deprivation. J Cell Biol 1988; 106: 829–844.

    CAS  PubMed  Google Scholar 

  11. Deckwerth TL, Johnson EM Jr . Temporal analysis of events associated with programmed cell death (apoptosis) of sympathetic neurons deprived of nerve growth factor. J Cell Biol 1993; 123: 1207–1222.

    CAS  PubMed  Google Scholar 

  12. Edwards SN, Tolkovsky AM . Characterization of apoptosis in cultured rat sympathetic neurons after nerve growth factor withdrawal. J Cell Biol 1994; 124: 537–546.

    CAS  PubMed  Google Scholar 

  13. Jacobs WB, Govoni G, Ho D, Atwal JK, Barnabe-Heider F, Keyes WM et al. p63 is an essential pro-apoptotic protein during neural development. Neuron 2005; 48: 743–756.

    CAS  PubMed  Google Scholar 

  14. Kristiansen M, Hughes R, Patel P, Jacques TS, Clark AR, Ham J . Mkp1 is a c-Jun target gene that antagonises JNK-dependent apoptosis in sympathetic neurons. J Neurosci 2010; 30: 10820–10832.

    CAS  PubMed  PubMed Central  Google Scholar 

  15. D'Mello SR, Galli C, Ciotti T, Calissano P . Induction of apoptosis in cerebellar granule neurons by low potassium: inhibition of death by insulin-like growth factor 1 and cAMP. Proc Natl Acad Sci USA 1993; 90: 10989–10993.

    CAS  PubMed  PubMed Central  Google Scholar 

  16. Desagher S, Severac D, Lipkin A, Bernis C, Ritchie W, Le Digarcher A et al. Genes regulated in neurons undergoing transcription-dependent apoptosis belong to signaling pathways rather than the apoptotic machinery. J Biol Chem 2005; 280: 5693–5702.

    CAS  PubMed  Google Scholar 

  17. Milligan CE, Oppenheim RW, Schwartz LM . Motoneurons deprived of trophic support in vitro require new gene expression to undergo programmed cell death. J Neurobiol 1994; 25: 1005–1016.

    CAS  PubMed  Google Scholar 

  18. Wong HK, Fricker M, Wyttenbach A, Villunger A, Michalak EM, Strasser A et al. Mutually exclusive subsets of BH3-only proteins are activated by the p53 and c-Jun N-terminal kinase/c-Jun signalling pathways during cortical neuron apoptosis induced by arsenite. Mol Cell Biol 2005; 25: 8732–8747.

    CAS  PubMed  PubMed Central  Google Scholar 

  19. Martinou I, Fernandez PA, Missotten M, White E, Allet B, Sadoul R et al. Viral proteins E1B19K and p35 protect sympathetic neurons from cell death induced by NGF deprivation. J Cell Biol 1995; 128: 201–208.

    CAS  PubMed  Google Scholar 

  20. Deshmukh M, Vasilakos J, Deckwerth TL, Lampe PA, Shivers BD, Johnson EM Jr . Genetic and metabolic status of NGF-deprived sympathetic neurons saved by an inhibitor of ICE family proteases. J Cell Biol 1996; 135: 1341–1354.

    CAS  PubMed  Google Scholar 

  21. McCarthy MJ, Rubin LL, Philpott KL . Involvement of caspases in sympathetic neuron apoptosis. J Cell Sci 1997; 110: 2165–2173.

    CAS  PubMed  Google Scholar 

  22. Martinou I, Desagher S, Eskes R, Antonsson B, André E, Fakan S et al. The release of cytochrome c from mitochondria during apoptosis of NGF-deprived sympathetic neurons is a reversible event. J Cell Biol 1999; 144: 883–889.

    CAS  PubMed  PubMed Central  Google Scholar 

  23. Deshmukh M, Johnson EM Jr . Evidence of a novel event during neuronal death: development of competence-to-die in response to cytoplasmic cytochrome c. Neuron 1998; 21: 695–705.

    CAS  PubMed  Google Scholar 

  24. Neame SJ, Rubin LL, Philpott KL . Blocking cytochrome c activity within intact neurons inhibits apoptosis. J Cell Biol 1998; 142: 1583–1593.

    CAS  PubMed  PubMed Central  Google Scholar 

  25. Wright KM, Vaughn AE, Deshmukh M . Apoptosome dependent caspase-3 activation pathway is non-redundant and necessary for apoptosis in sympathetic neurons. Cell Death Differ 2007; 14: 625–633.

    CAS  PubMed  Google Scholar 

  26. Fletcher GC, Xue L, Passingham SK, Tolkovsky AM . Death commitment point is advanced by axotomy in sympathetic neurons. J Cell Biol 2000; 150: 741–754.

    CAS  PubMed  PubMed Central  Google Scholar 

  27. Potts PR, Singh S, Knezek M, Thompson CB, Deshmukh M . Critical function of endogenous XIAP in regulating caspase activation during sympathetic neuronal apoptosis. J Cell Biol 2003; 163: 789–799.

    CAS  PubMed  PubMed Central  Google Scholar 

  28. Ribe EM, Jean YY, Goldstein RL, Manzl C, Stefanis L, Villunger A et al. Neuronal caspase 2 activity and function requires RAIDD, but not PIDD. Biochem J 2012; 444: 591–599.

    CAS  PubMed  Google Scholar 

  29. Bergeron L, Perez GI, Macdonald G, Shi L, Sun Y, Jurisicova A et al. Defects in regulation of apoptosis in caspase-2-deficient mice. Genes Dev 1998; 12: 1304–1314.

    CAS  PubMed  PubMed Central  Google Scholar 

  30. O'Reilly LA, Ekert P, Harvey N, Marsden V, Cullen L, Vaux DL et al. Caspase-2 is not required for thymocyte or neuronal apoptosis even though cleavage of caspase-2 is dependent on both Apaf-1 and caspase-9. Cell Death Differ 2002; 9: 832–841.

    CAS  PubMed  Google Scholar 

  31. Troy CM, Rabacchi SA, Hohl JB, Angelastro JM, Greene LA, Shelanski ML . Death in the balance: alternative participation of the caspase-2 and -9 pathways in neuronal death induced by nerve growth factor deprivation. J Neurosci 2001; 21: 5007–5016.

    CAS  PubMed  PubMed Central  Google Scholar 

  32. Jean YY, Ribe EM, Pero ME, Moskalenko M, Iqbal Z, Marks LJ et al. Caspase-2 is essential for c-Jun transcriptional activation and Bim induction in neuron death. Biochem J 2013; 455: 15–25.

    CAS  PubMed  Google Scholar 

  33. Freeman RS, Burch RL, Crowder RJ, Lomb DJ, Schoell MC, Straub JA et al. NGF deprivation-induced gene expression: after ten years, where do we stand? Prog Brain Res 2004; 146: 111–126.

    CAS  PubMed  Google Scholar 

  34. Putcha GV, Johnson EM Jr . Men are but worms: neuronal cell death in C. elegans and vertebrates. Cell Death Differ 2004; 11: 38–48.

    CAS  PubMed  Google Scholar 

  35. Ham J, Towers E, Gilley J, Terzano S, Randall R . BH3-only proteins: key regulators of neuronal apoptosis. Cell Death Differ 2005; 12: 1015–1020.

    CAS  PubMed  Google Scholar 

  36. Garcia I, Martinou I, Tsujimoto Y, Martinou JC . Prevention of programmed cell death of sympathetic neurons by the bcl-2 proto-oncogene. Science 1992; 258: 302–304.

    CAS  PubMed  Google Scholar 

  37. Whitfield J, Neame SJ, Paquet L, Bernard O, Ham J . Dominant-negative c-Jun promotes neuronal survival by reducing BIM expression and inhibiting mitochondrial cytochrome c release. Neuron 2001; 29: 629–643.

    CAS  PubMed  Google Scholar 

  38. Greenlund LJ, Korsmeyer SJ, Johnson EM Jr . Role of BCL-2 in the survival and function of developing and mature sympathetic neurons. Neuron 1995; 15: 649–661.

    CAS  PubMed  Google Scholar 

  39. Chipuk JE, Moldoveanu T, Llambi F, Parsons MJ, Green DR . The BCL-2 family reunion. Mol Cell 2010; 37: 299–310.

    CAS  PubMed  PubMed Central  Google Scholar 

  40. Vekrellis K, McCarthy MJ, Watson A, Whitfield J, Rubin LL, Ham J . Bax promotes neuronal cell death and is downregulated during the development of the nervous system. Development 1997; 124: 1239–1249.

    CAS  PubMed  Google Scholar 

  41. Deckwerth TL, Elliott JL, Knudson CM, Johnson EM Jr, Snider WD, Korsmeyer SJ . BAX is required for neuronal death after trophic factor deprivation and during development. Neuron 1996; 17: 401–411.

    CAS  PubMed  Google Scholar 

  42. Putcha GV, Harris CA, Moulder KL, Easton RM, Thompson CB, Johnson EM Jr . Intrinsic and extrinsic pathway signaling during neuronal apoptosis: lessons from the analysis of mutant mice. J Cell Biol 2002; 157: 441–453.

    CAS  PubMed  PubMed Central  Google Scholar 

  43. Sun YF, Yu LY, Saarma M, Timmusk T, Arumae U . Neuron-specific Bcl-2 homology 3 domain-only splice variant of Bak is anti-apoptotic in neurons, but pro-apoptotic in non-neuronal cells. J Biol Chem 2001; 276: 16240–16247.

    CAS  PubMed  Google Scholar 

  44. Jakobson M, Lintulahti A, Arumae U . mRNA for N-Bak, a neuron-specific BH3-only splice isoform of Bak, escapes nonsense-mediated decay and is translationally repressed in the neurons. Cell Death Dis 2012; 3: e269.

    CAS  PubMed  PubMed Central  Google Scholar 

  45. Jakobson M, Jakobson M, Llano O, Palgi J, Arumae U . Multiple mechanisms repress N-Bak mRNA translation in the healthy and apoptotic neurons. Cell Death Dis 2013; 4: e777.

    CAS  PubMed  PubMed Central  Google Scholar 

  46. Putcha V, Deshmukh M, Johnson EM . Bax translocation is a critical event in neuronal apoptosis: regulation by neuroprotectants, Bcl-2 and caspases. J Neurosci 1999; 19: 7476–7485.

    CAS  PubMed  PubMed Central  Google Scholar 

  47. Imaizumi K, Tsuda M, Imai Y, Wanaka A, Takagi T, Tohyama M . Molecular cloning of a novel polypeptide, DP5, induced during programmed neuronal death. J Biol Chem 1997; 272: 18842–18848.

    CAS  PubMed  Google Scholar 

  48. Putcha GV, Moulder KL, Golden JP, Bouillet P, Adams JA, Strasser A et al. Induction of BIM, a proapoptotic BH3-only BCL-2 family member, is critical for neuronal apoptosis. Neuron 2001; 29: 615–628.

    CAS  PubMed  Google Scholar 

  49. Harris CA, Johnson EM Jr . BH3-only Bcl-2 family members are coordinately regulated by the JNK pathway and require Bax to induce apoptosis in neurons. J Biol Chem 2001; 276: 37754–37760.

    CAS  PubMed  Google Scholar 

  50. Gilley J, Coffer PJ, Ham J . FOXO transcription factors directly activate bim gene expression and promote apoptosis in sympathetic neurons. J Cell Biol 2003; 162: 613–622.

    CAS  PubMed  PubMed Central  Google Scholar 

  51. Besirli CG, Wagner EF, Johnson EM Jr . The limited role of NH2-terminal c-Jun phosphorylation in neuronal apoptosis: identification of the nuclear pore complex as a potential target of the JNK pathway. J Cell Biol 2005; 170: 401–411.

    CAS  PubMed  PubMed Central  Google Scholar 

  52. Towers E, Gilley J, Randall R, Hughes R, Kristiansen M, Ham J . The proapoptotic dp5 gene is a direct target of the MLK-JNK-c-Jun pathway in sympathetic neurons. Nucleic Acids Res 2009; 37: 3044–3060.

    CAS  PubMed  PubMed Central  Google Scholar 

  53. Kristiansen M, Menghi F, Hughes R, Hubank M, Ham J . Global analysis of gene expression in NGF-deprived sympathetic neurons identifies molecular pathways associated with cell death. BMC Genom 2011; 12: 551.

    CAS  Google Scholar 

  54. Kole AJ, Swahari V, Hammond SM, Deshmukh M . miR-29b is activated during neuronal maturation and targets BH3-only genes to restrict apoptosis. Genes Dev 2011; 25: 125–130.

    CAS  PubMed  PubMed Central  Google Scholar 

  55. Imaizumi K, Benito A, Kiryu-Seo S, Gonzalez V, Inohara N, Lieberman AP et al. Critical role for DP5/Harakiri, a Bcl-2 homology domain 3-only Bcl-2 family member, in axotomy-induced neuronal cell death. J Neurosci 2004; 24: 3721–3725.

    CAS  PubMed  PubMed Central  Google Scholar 

  56. Coultas L, Terzano S, Thomas T, Voss A, Reid K, Stanley EG et al. Hrk/DP5 contributes to the apoptosis of select neuronal populations but is dispensable for haematopoietic cell apoptosis. J Cell Sci 2007; 120: 2044–2052.

    CAS  PubMed  Google Scholar 

  57. Wyttenbach A, Tolkovsky AM . The BH3-only protein Puma is both necessary and sufficient for neuronal apoptosis induced by DNA damage in sympathetic neurons. J Neurochem 2006; 96: 1213–1226.

    CAS  PubMed  Google Scholar 

  58. Ren D, Tu HC, Kim H, Wang GX, Bean GR, Takeuchi O et al. BID, BIM, and PUMA are essential for activation of the BAX- and BAK-dependent cell death program. Science 2010; 330: 1390–1393.

    CAS  PubMed  PubMed Central  Google Scholar 

  59. Ghosh AP, Cape JD, Klocke BJ, Roth KA . Deficiency of pro-apoptotic Hrk attenuates programmed cell death in the developing murine nervous system but does not affect Bcl-x deficiency-induced neuron apoptosis. J Histochem Cytochem 2011; 59: 976–983.

    CAS  PubMed  PubMed Central  Google Scholar 

  60. Walensky LD, Gavathiotis E . BAX unleashed: the biochemical transformation of an inactive cytosolic monomer into a toxic mitochondrial pore. Trends Biochem Sci 2011; 36: 642–652.

    CAS  PubMed  PubMed Central  Google Scholar 

  61. Sarosiek KA, Chi X, Bachman JA, Sims JJ, Montero J, Patel L et al. BID preferentially activates BAK while BIM preferentially activates BAX, affecting chemotherapy response. Mol Cell 2013; 51: 751–765.

    CAS  PubMed  PubMed Central  Google Scholar 

  62. Vela L, Gonzalo O, Naval J, Marzo I . Direct interaction of Bax and Bak proteins with Bcl-2 homology domain 3 (BH3)-only proteins in living cells revealed by fluorescence complementation. J Biol Chem 2013; 288: 4935–4946.

    CAS  PubMed  PubMed Central  Google Scholar 

  63. Freeman RS, Estus S, Johnson EM Jr . Analysis of cell cycle-related gene expression in postmitotic neurons: selective induction of Cyclin D1 during programmed cell death. Neuron 1994; 12: 343–355.

    CAS  PubMed  Google Scholar 

  64. Estus S, Zaks WJ, Freeman RS, Gruda M, Bravo R, Johnson EM Jr . Altered gene expression in neurons during programmed cell death: identification of c-jun as necessary for neuronal apoptosis. J Cell Biol 1994; 127: 1717–1727.

    CAS  PubMed  Google Scholar 

  65. Ham J, Babij C, Whitfield J, Pfarr CM, Lallemand D, Yaniv M et al. A c-Jun dominant negative mutant protects sympathetic neurons against programmed cell death. Neuron 1995; 14: 927–939.

    CAS  PubMed  Google Scholar 

  66. Palmada M, Kanwal S, Rutkoski NJ, Gustafson-Brown C, Johnson RS, Wisdom R et al. c-jun is essential for sympathetic neuronal death induced by NGF withdrawal but not by p75 activation. J Cell Biol 2002; 158: 453–461.

    CAS  PubMed  PubMed Central  Google Scholar 

  67. Xia Z, Dickens M, Raingeaud J, Davis RJ, Greenberg ME . Opposing effects of ERK and JNK-p38 MAP kinases on apoptosis. Science 1995; 270: 1326–1331.

    CAS  PubMed  Google Scholar 

  68. Virdee K, Bannister AJ, Hunt SP, Tolkovsky AM . Comparison between the timing of JNK activation, c-Jun phosphorylation, and onset of death commitment in sympathetic neurones. J Neurochem 1997; 69: 550–561.

    CAS  PubMed  Google Scholar 

  69. Eilers A, Whitfield J, Babij C, Rubin LL, Ham J . Role of the Jun kinase pathway in the regulation of c-Jun expression and apoptosis in sympathetic neurons. J Neurosci 1998; 18: 1713–1724.

    CAS  PubMed  PubMed Central  Google Scholar 

  70. Davis RJ . Signal transduction by the JNK group of MAP kinases. Cell 2000; 103: 239–252.

    CAS  PubMed  Google Scholar 

  71. Lipscomb EA, Sarmiere PD, Crowder RJ, Freeman RS . Expression of the SM-20 gene promotes death in nerve growth factor-dependent sympathetic neurons. J Neurochem 1999; 73: 429–432.

    CAS  PubMed  Google Scholar 

  72. Bishop T, Gallagher D, Pascual A, Lygate CA, de Bono JP, Nicholls LG et al. Abnormal sympathoadrenal development and systemic hypotension in PHD3−/− mice. Mol Cell Biol 2008; 28: 3386–3400.

    CAS  PubMed  PubMed Central  Google Scholar 

  73. Schlisio S, Kenchappa RS, Vredeveld LC, George RE, Stewart R, Greulich H et al. The kinesin KIF1Bbeta acts downstream from EglN3 to induce apoptosis and is a potential 1p36 tumor suppressor. Genes Dev 2008; 22: 884–893.

    CAS  PubMed  PubMed Central  Google Scholar 

  74. Biswas SC, Shi Y, Sproul A, Greene LA . Pro-apoptotic Bim induction in response to nerve growth factor deprivation requires simultaneous activation of three different death signaling pathways. J Biol Chem 2007; 282: 29368–29374.

    CAS  PubMed  Google Scholar 

  75. Ma C, Ying C, Yuan Z, Song B, Li D, Liu Y et al. dp5/HRK is a c-Jun target gene and required for apoptosis induced by potassium deprivation in cerebellar granule neurons. J Biol Chem 2007; 282: 30901–30909.

    CAS  PubMed  Google Scholar 

  76. Pozniak CD, Radinovic S, Yang A, McKeon F, Kaplan DR, Miller FD . An anti-apoptotic role for the p53 family member, p73, during developmental neuron death. Science 2000; 289: 304–306.

    CAS  PubMed  Google Scholar 

  77. Lee AF, Ho DK, Zanassi P, Walsh GS, Kaplan DR, Miller FD . Evidence that DeltaNp73 promotes neuronal survival by p53-dependent and p53-independent mechanisms. J Neurosci 2004; 24: 9174–9184.

    CAS  PubMed  PubMed Central  Google Scholar 

  78. Maroney AC, Finn JP, Bozyczko-Coyne D, O'Kane TM, Neff NT, Tolkovsky AM et al. CEP-1347 (KT7515), an inhibitor of JNK activation, rescues sympathetic neurons and neuronally differentiated PC12 cells from death evoked by three distinct insults. J Neurochem 1999; 73: 1901–1912.

    CAS  PubMed  Google Scholar 

  79. Lomb DJ, Desouza LA, Franklin JL, Freeman RS . Prolyl hydroxylase inhibitors depend on extracellular glucose and hypoxia-inducible factor (HIF)-2α to inhibit cell death caused by nerve growth factor (NGF) deprivation: evidence that HIF-2α has a role in NGF-promoted survival of sympathetic neurons. Mol Pharmacol 2009; 75: 1198–1209.

    CAS  PubMed  PubMed Central  Google Scholar 

  80. Levi-Montalcini R, Calissano P . The nerve growth factor. Sci Am 1979; 240: 68–77.

    CAS  PubMed  Google Scholar 

  81. Kaplan DR, Martin-Zanca D, Parada LF . Tyrosine phosphorylation and tyrosine kinase activity of the trk proto-oncogene product induced by NGF. Nature 1991; 350: 158–160.

    CAS  PubMed  Google Scholar 

  82. Kaplan DR, Miller FD . Neurotrophin signal transduction in the nervous system. Curr Opin Neurobiol 2000; 10: 381–391.

    CAS  PubMed  Google Scholar 

  83. Mazzoni IE, Saïd FA, Aloyz R, Miller FD, Kaplan D . Ras regulates sympathetic neuron survival by suppressing the p53-mediated cell death pathway. J Neurosci 1999; 19: 9716–9727.

    CAS  PubMed  PubMed Central  Google Scholar 

  84. Bamji SX, Majdan M, Pozniak CD, Belliveau DJ, Aloyz R, Kohn J et al. The p75 neurotrophin receptor mediates neuronal apoptosis and is essential for naturally occurring sympathetic neuron death. J Cell Biol 1998; 140: 911–923.

    CAS  PubMed  PubMed Central  Google Scholar 

  85. Kenchappa RS, Tep C, Korade Z, Urra S, Bronfman FC, Yoon SO et al. p75 neurotrophin receptor-mediated apoptosis in sympathetic neurons involves a biphasic activation of JNK and up-regulation of tumor necrosis factor-alpha-converting enzyme/ADAM17. J Biol Chem 2010; 285: 20358–20368.

    CAS  PubMed  PubMed Central  Google Scholar 

  86. Nikoletopoulou V, Lickert H, Frade JM, Rencurel C, Giallonardo P, Zhang L et al. Neurotrophin receptors TrkA and TrkC cause neuronal death whereas TrkB does not. Nature 2010; 467: 59–63.

    CAS  PubMed  Google Scholar 

  87. Virdee K, Xue L, Hemmings BA, Goemans C, Heumann R, Tolkovsky AM . Nerve growth factor-induced PKB/Akt activity is sustained by phosphoinositide 3-kinase dependent and independent signals in sympathetic neurons. Brain Res 1999; 837: 127–142.

    CAS  PubMed  Google Scholar 

  88. Atwal JK, Massie B, Miller FD, Kaplan DR . The TrkB-Shc site signals neuronal survival and local axon growth via MEK and P13-kinase. Neuron 2000; 27: 265–277.

    CAS  PubMed  Google Scholar 

  89. Biswas SC, Greene LA . Nerve growth factor (NGF) down-regulates the Bcl-2 homology 3 (BH3) domain-only protein Bim and suppresses its proapoptotic activity by phosphorylation. J Biol Chem 2002; 277: 49511–49516.

    CAS  PubMed  Google Scholar 

  90. Ley R, Ewings KE, Hadfield K, Cook SJ . Regulatory phosphorylation of Bim: sorting out the ERK from the JNK. Cell Death Differ 2005; 12: 1008–1014.

    CAS  PubMed  Google Scholar 

  91. Riccio A, Ahn S, Davenport CM, Blendy JA, Ginty DD . Mediation by a CREB family transcription factor of NGF-dependent survival of sympathetic neurons. Science 1999; 286: 2358–2361.

    CAS  PubMed  Google Scholar 

  92. Hughes R, Gilley J, Kristiansen M, Ham J . The MEK-ERK pathway negatively regulates bim expression through the 3′ UTR in sympathetic neurons. BMC Neurosci 2011; 12: 69.

    CAS  PubMed  PubMed Central  Google Scholar 

  93. Xue L, Murray JH, Tolkovsky AM . The Ras/phosphatidylinositol 3-kinase and Ras/ERK pathways function as independent survival modules each of which inhibits a distinct apoptotic signaling pathway in sympathetic neurons. J Biol Chem 2000; 275: 8817–8824.

    CAS  PubMed  Google Scholar 

  94. Mota M, Reeder M, Chernoff J, Bazenet CE . Evidence for a role of mixed lineage kinases in neuronal apoptosis. J Neurosci 2001; 21: 4949–4957.

    CAS  PubMed  PubMed Central  Google Scholar 

  95. Xu Z, Maroney AC, Dobrzanski P, Kukekov NV, Greene LA . The MLK family mediates c-Jun N-terminal kinase activation in neuronal apoptosis. Mol Cell Biol 2001; 21: 4713–4724.

    CAS  PubMed  PubMed Central  Google Scholar 

  96. Bazenet CE, Mota MA, Rubin LL . The small GTP-binding protein Cdc42 is required for nerve growth factor withdrawal-induced neuronal death. Proc Natl Acad Sci USA 1998; 95: 3984–3989.

    CAS  PubMed  PubMed Central  Google Scholar 

  97. Xu Z, Kukekov NV, Greene LA . POSH acts as a scaffold for a multiprotein complex that mediates JNK activation in apoptosis. EMBO J 2003; 22: 252–261.

    CAS  PubMed  PubMed Central  Google Scholar 

  98. Wilhelm M, Kukekov NV, Schmit TL, Biagas KV, Sproul AA, Gire S et al. Sh3rf2/POSHER protein promotes cell survival by ring-mediated proteasomal degradation of the c-Jun N-terminal kinase scaffold POSH (Plenty of SH3s) protein. J Biol Chem 2012; 287: 2247–2256.

    CAS  PubMed  Google Scholar 

  99. Harris CA, Deshmukh M, Tsui-Pierchala B, Maroney AC, Johnson EM Jr . Inhibition of the c-Jun N-terminal kinase signaling pathway by the mixed lineage kinase inhibitor CEP-1347 (KT7515) preserves metabolism and growth of trophic factor-deprived neurons. J Neurosci 2002; 22: 103–113.

    CAS  PubMed  PubMed Central  Google Scholar 

  100. Maroney AC, Finn JP, Connors TJ, Durkin JT, Angeles T, Gessner G et al. Cep-1347 (KT7515), a semisynthetic inhibitor of the mixed lineage kinase family. J Biol Chem 2001; 276: 25302–25308.

    CAS  PubMed  Google Scholar 

  101. Eilers A, Whitfield J, Shah B, Spadoni C, Desmond H, Ham J . Direct inhibition of c-Jun N-terminal kinase in sympathetic neurones prevents c-jun promoter activation and NGF withdrawal-induced death. J Neurochem 2001; 76: 1439–1454.

    CAS  PubMed  Google Scholar 

  102. Harding TC, Xue L, Bienemann A, Haywood D, Dickens M, Tolkovsky AM et al. Inhibition of JNK by overexpression of the JNK binding domain of JIP-1 prevents apoptosis in sympathetic neurons. J Biol Chem 2001; 276: 4531–4534.

    CAS  PubMed  Google Scholar 

  103. Park DS, Farinelli SE, Greene LA . Inhibitors of cyclin-dependent kinases promote survival of post-mitotic neuronally differentiated PC12 cells and sympathetic neurons. J Biol Chem 1996; 271: 8161–8169.

    PubMed  Google Scholar 

  104. Park DS, Levine B, Ferrari G, Greene LA . Cyclin dependent kinase inhibitors and dominant negative cyclin dependent kinase 4 and 6 promote survival of NGF-deprived sympathetic neurons. J Neurosci 1997; 17: 8975–8983.

    CAS  PubMed  PubMed Central  Google Scholar 

  105. Liu DX, Biswas SC, Greene LA . B-myb and C-myb play required roles in neuronal apoptosis evoked by nerve growth factor deprivation and DNA damage. J Neurosci 2004; 24: 8720–8725.

    CAS  PubMed  PubMed Central  Google Scholar 

  106. Biswas SC, Liu DX, Greene LA . Bim is a direct target of a neuronal E2F-dependent apoptotic pathway. J Neurosci 2005; 25: 8349–8358.

    CAS  PubMed  PubMed Central  Google Scholar 

  107. Gilley J, Ham J . Evidence for increased complexity in the regulation of Bim expression in sympathetic neurons: involvement of novel transcriptional and translational mechanisms. DNA Cell Biol 2005; 24: 563–573.

    CAS  PubMed  Google Scholar 

  108. Hughes R, Kristiansen M, Lassot I, Desagher S, Mantovani R, Ham J . NF-Y is essential for expression of the proapoptotic bim gene in sympathetic neurons. Cell Death Differ 2011; 18: 937–947.

    CAS  PubMed  Google Scholar 

  109. Anderson CN, Tolkovsky AM . A role for MAPK/ERK in sympathetic neuron survival: protection against a p53-dependent, JNK-independent induction of apoptosis by cytosine arabinoside. J Neurosci 1999; 19: 664–673.

    CAS  PubMed  PubMed Central  Google Scholar 

  110. Yu LY, Jokitalo E, Sun YF, Mehlen P, Lindholm D, Saarma M et al. GDNF-deprived sympathetic neurons die via a novel non-mitochondrial pathway. J Cell Biol 2003; 163: 987–997.

    CAS  PubMed  PubMed Central  Google Scholar 

  111. Smith MI, Deshmukh M . Endoplasmic reticulum stress-induced apoptosis requires bax for commitment and Apaf-1 for execution in primary neurons. Cell Death Differ 2007; 14: 1011–1019.

    CAS  PubMed  Google Scholar 

  112. King MA, Goemans CG, Hafiz F, Prehn JH, Wyttenbach A, Tolkovsky AM . Cytoplasmic inclusions of Htt exon1 containing an expanded polyglutamine tract suppress execution of apoptosis in sympathetic neurons. J Neurosci 2008; 28: 14401–14415.

    CAS  PubMed  PubMed Central  Google Scholar 

  113. Han J, Flemington C, Houghton AB, Gu Z, Zambetti GP, Lutz RJ et al. Expression of bbc3, a pro-apoptotic BH3-only gene, is regulated by diverse cell death and survival signals. Proc Natl Acad Sci USA 2001; 98: 11318–11323.

    CAS  PubMed  PubMed Central  Google Scholar 

  114. Nakano K, Vousden KH . PUMA, a novel proapoptotic gene, is induced by p53. Mol Cell 2001; 7: 683–694.

    CAS  PubMed  Google Scholar 

  115. Yu J, Zhang L, Hwang PM, Kinzler KW, Vogelstein B . PUMA induces the rapid apoptosis of colorectal cancer cells. Mol Cell 2001; 7: 673–682.

    CAS  PubMed  Google Scholar 

  116. Wang P, Yu J, Zhang L . The nuclear function of p53 is required for PUMA-mediated apoptosis induced by DNA damage. Proc Natl Acad Sci USA 2007; 104: 4054–4059.

    CAS  PubMed  PubMed Central  Google Scholar 

  117. You H, Pellegrini M, Tsuchihara K, Yamamoto K, Hacker G, Erlacher M et al. FOXO3a-dependent regulation of Puma in response to cytokine/growth factor withdrawal. J Exp Med 2006; 203: 1657–1663.

    CAS  PubMed  PubMed Central  Google Scholar 

  118. Kole AJ, Annis RP, Deshmukh M . Mature neurons: equipped for survival. Cell Death Dis 2013; 4: e689.

    CAS  PubMed  PubMed Central  Google Scholar 

  119. Wright KM, Smith MI, Farrag L, Deshmukh M . Chromatin modification of Apaf-1 restricts the apoptotic pathway in mature neurons. J Cell Biol 2007; 179: 825–832.

    CAS  PubMed  PubMed Central  Google Scholar 

  120. Zareen N, Biswas SC, Greene LA . A feed-forward loop involving Trib3, Akt and FoxO mediates death of NGF-deprived neurons. Cell Death Differ 2013; 20: 1719–1730.

    CAS  PubMed  PubMed Central  Google Scholar 

  121. Cusack CL, Swahari V, Hampton Henley W, Michael Ramsey J, Deshmukh M . Distinct pathways mediate axon degeneration during apoptosis and axon-specific pruning. Nat Commun 2013; 4: 1876.

    PubMed  Google Scholar 

  122. Yang DD, Kuan C-Y, Whitmarsh AJ, Rincon M, Zheng TS, Davis RJ et al. Absence of excitotoxicity-induced apoptosis in the hippocampus of mice lacking the Jnk3 gene. Nature 1997; 389: 865–870.

    CAS  PubMed  Google Scholar 

  123. Behrens A, Sibilia M, Wagner EF . Amino-terminal phosphorylation of c-Jun regulates stress-induced apoptosis and cellular proliferation. Nat Genet 1999; 21: 326–329.

    CAS  PubMed  Google Scholar 

  124. Borsello T, Clarke PG, Hirt L, Vercelli A, Repici M, Schorderet DF et al. A peptide inhibitor of c-Jun N-terminal kinase protects against excitotoxicity and cerebral ischemia. Nat Med 2003; 9: 1180–1186.

    CAS  PubMed  Google Scholar 

  125. Hunot S, Vila M, Teismann P, Davis RJ, Hirsch EC, Przedborski S et al. JNK-mediated induction of cyclooxygenase 2 is required for neurodegeneration in a mouse model of Parkinson’s disease. Proc Natl Acad Sci USA 2004; 101: 665–670.

    CAS  PubMed  PubMed Central  Google Scholar 

  126. Fernandes KA, Harder JM, Fornarola LB, Freeman RS, Clark AF, Pang IH et al. JNK2 and JNK3 are major regulators of axonal injury-induced retinal ganglion cell death. Neurobiol Dis 2012; 46: 393–401.

    CAS  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

Owing to space limitations, it has not been possible to review all aspects of sympathetic neuron apoptosis and we apologise to those authors whose work has not been covered in this article, although in most cases this work will have been mentioned in other recent reviews. We thank Solange Desagher and David Michod for critical reading of the manuscript and for helpful discussions. This work was partly supported by the Wellcome Trust.

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Kristiansen, M., Ham, J. Programmed cell death during neuronal development: the sympathetic neuron model. Cell Death Differ 21, 1025–1035 (2014). https://doi.org/10.1038/cdd.2014.47

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