Abstract
The accumulation of reactive oxygen species (ROS) is a common feature of tauopathies, defined by Tau accumulations in neurons and glia. High ROS in neurons causes lipid production and the export of toxic peroxidated lipids (LPOs). Glia uptake these LPOs and incorporate them into lipid droplets (LDs) for storage and catabolism. We found that overexpressing Tau in glia disrupts LDs in flies and rat neuron–astrocyte co-cultures, sensitizing the glia to toxic, neuronal LPOs. Using a new fly tau loss-of-function allele and RNA-mediated interference, we found that endogenous Tau is required for glial LD formation and protection against neuronal LPOs. Similarly, endogenous Tau is required in rat astrocytes and human oligodendrocyte-like cells for LD formation and the breakdown of LPOs. Behaviorally, flies lacking glial Tau have decreased lifespans and motor defects that are rescuable by administering the antioxidant N-acetylcysteine amide. Overall, this work provides insights into the important role that Tau has in glia to mitigate ROS in the brain.
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Acknowledgements
We apologize to investigators whose relevant research was not cited herein due to limits set by the journal. We thank former and present Bellen lab members for their input during investigations, particularly Z. Zou, J. Deger, J. Chang and J. Najm. We thank A. Sehgal for helpful comments during manuscript preparation. We thank H. Tricoire, A. Sehgal and N. Bonini for providing GAL4GeneSwitch fly lines. We thank L. Partridge for providing the dTau antibody. We thank S. Yamamoto and M. Wangler for the resources used during fly line development. Fly stocks were obtained from the Bloomington Drosophila Stock Center (National Institutes of Health (NIH) P40-OD018537) and Vienna Drosophila Resource Center. This work was supported by infrastructure made available by Texas Children’s Neurological Research Institute (National Institute of Child Health and Human Development (NICHD) P50-HD103555), the University of Alberta Faculty of Medicine & Dentistry Cell Imaging Core (RRID SCR_019200) and the Neurovisualization Core at Baylor College of Medicine (BCM) (NICHD U54-HD083092). This research and L.D.G. were supported by the Postdoctoral Fellowship Program in Alzheimer’s Disease Research from the BrightFocus Foundation. This research was supported by the National Institutes of Health (NIH) Common Fund to H.J.B. (National Institute on Aging (NIA R01-AG073260)). Further support to H.J.B. came from NIH awards: Office of the Director (OD R24-OD02205 and OD R24-OD031447) and National Institute of General Medical Sciences (NIGMS R01-GM067858). H.J.B. and J.M.S. received support from NIA U01-AG072439. J.M.S. received additional support from NIA RF1-AG078660. L.D.G. and M.J.M. received support from the Brain Disorders & Development Training Grant at BCM, National Institute of Neurological Disorders and Stroke (NINDS T32-NS043124-18). I.R. was supported by the Canadian Institutes of Health Research (CIHR) Doctoral Award (181551). M.S.I. was supported by a Sloan Research Fellowship from the Alfred P. Sloan Foundation (FG-2021-16349), Canada Research Chairs program (2021-00027) and a CIHR project grant (173321). K.A. received support from a Grant-in-Aid for Scientific Research on Challenging Research (Exploratory) (JSPS KAKENHI 19K21593). K.S. received support from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK R01-DK129815). The transcriptomic data were obtained from the AD Knowledge Portal (https://adknowledgeportal.org). We acknowledge the patients and their families who provided invaluable tissue samples. Rush Alzheimer’s Disease Center, Rush University Medical Center, Chicago, provided all ROSMAP data collected, which was funded by the NIA (P30-AG10161, R01-AG15819, R01-AG17917, R01-AG30146, R01-AG36836, U01-AG32984, U01-AG46152), the Illinois Department of Public Health and the Translational Genomics Research Institute. Mayo Study data were provided by the following sources: The Mayo Clinic Alzheimer’s Disease Genetic Studies, led by N. Ertekin-Taner (not certified by peer review), is made available under a CC-BY-NC 4.0 International license; Gockley et al.104 and Steven G. Younkin, Mayo Clinic, Jacksonville, FL, using samples from the Mayo Clinic Study of Aging, the Mayo Clinic Alzheimer’s Disease Research Center and the Mayo Clinic Brain Bank. Mayo Data collection was funded through the NIA (P50-AG016574, R01-AG032990, U01-58AG046139, R01-AG018023, U01-AG006576, U01-AG006786, R01-AG025711, R01-AG017216, R01-AG003949), NINDS R01-NS080820, CurePSP Foundation and the Mayo Foundation.
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L.D.G. designed and implemented this project and wrote the manuscript under the mentorship of H.J.B. I.R. performed rat co-culture studies under the mentorship of M.S.I. The MO3.13 studies were performed by X.L. and S.L. with feedback from L.D.G. and under the mentorship of K.S. and H.J.B., respectively. M.J.M. performed SREBP studies with L.D.G. and developed fly lines used in this study under the mentorship of H.J.B. Y.J.P. performed the Drosophila activity monitoring assays with L.D.G. P.Z. analyzed patient transcriptomic data under the mentorship of J.M.S. O.K. made the tau-CRIMIC allele. Z.G.T. provided technical assistance during tau-CRIMIC characterization under the guidance of L.D.G. J.J. provided technical assistance for rat co-culture studies under the mentorship of M.S.I. K.A. developed and provided hTau[S262] fly lines used in this study.
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Extended data
Extended Data Fig. 1 Glial lipid droplet pathway and characterization of lipid droplets in the fly retina.
(a) Elevating ROS levels in neurons causes an SREBP-dependent production of peroxidated lipids (LPOs). These lipids are exported by ABC-lipid transporters, transferred to glia via apolipoproteins (for example APOE), and endocytosed by the glia. Within the glia, the LPO are integrated into lipid droplets (LDs) via the endoplasmic reticulum (ER). LDs promote lipid β-oxidation by the mitochondria, producing energy. Thus, glial LDs remove the toxic, LPO and protect both cells from ROS-induced damage. A growing list of established and predicted AD risk genes (red text) fit into this pathway, with most genes being required for proper glial LD formation and protection against neuronal ROS5,7,8,9. Created with Biorender.com. (b) The fly retina is composed of ~800 highly structured ommatidia. Diagram: a single ommatidium with seven photoreceptor neurons (blue) surrounded by pigment glia (green). Each photoreceptor contains a lipid-rich rhabdomere (hashed circle) which can be visualized with lipid stains. (c) Elevating ROS in photoreceptors causes LDs to accumulate in surrounding glia. LDs are visualized using neutral lipid dyes, Nile red and BODIPY 493/503. (d) TEM image of the fly retina, including 4 ommatidia. Each ommatidium contains seven visible photoreceptors with the rhabdomeres (R) clustered at the center and the cell body (CB) extending distally. Photoreceptors are surrounded by retinal glia (green). (e) The genetic manipulation used to investigate regulators of glial LD formation in the fly retina. UAS-transgenes are expressed either in mature photoreceptors, using Rh1-GAL4, or in retinal glia, using 54C-GAL4. Rh:ND42 RNAi is used to induce ROS only in the photoreceptors, causing glial LDs. (f) LDs can be induced in photoreceptors either by causing neuronal ROS (Rh:ND42 RNAi) or by overexpressing the activated SREBP transcription factor (nSyb-GAL4 > UAS-SREBP). LDs produced by Rh:ND42 RNAi can be prevented by feeding flies the antioxidant NACA, consistent with5. LDs formed by neuronal SREBP upregulation in non-ROS conditions are not impacted by NACA. Lipid stain = Nile red. Data presented as mean ± SD. A datapoint represents the average LD number per ommatidium per animal (n). n = 7-10 (detailed in Supporting Data 1). Statistics: 1-way ANOVA with Tukey’s multiple comparisons test. P-values = not significant (n.s.) >0.05, **=0.004, ***=0.0002, ****≤0.0001. (g) LDs within retinas co-stain for both Nile red and BODIPY 493/503, validating that these puncta are LDs. (f-g) Retinas from 2d flies were fixed, dissected, and stained with neutral lipid dyes. Arrow = glial LD.
Extended Data Fig. 2 Additional data for hTau overexpression in flies.
(a-b) UAS transgenes were expressed in photoreceptors using Rh1-GAL4. Fixed retinas were stained with Nile red or BODIPY 493/503 to visualize LDs (white puncta, arrow) within retinal glia. (a) Few LDs were seen with UAS-Control (LacZ), UAS-Tau or UAS-TauR406W expression up to 6d. (b) Rh:ND42 RNAi was used to induce neuronal ROS and robust LD formation within glia. No change in LD number was observed when UAS-Tau or UAS-TauR406W were also expressed using Rh1-GAL4. Arrow = glial LD. A datapoint represents the average LD number per ommatidium per animal (n). n = 3-6 (detailed in Supporting Data 1). Data presented as mean ± SD. Statistics: 1-way ANOVA with Tukey’s multiple comparisons test. P-values = not significant, >0.05. (c) UAS-Control or UAS-hTau were expressed in retinal glia using 54C-GAL4 and TEM was performed. Glial cells = green. Shown are representative images for the quantification provided in Fig. 1c. (d) UAS-Ctrl (LacZ) or UAS-hTau were expressed for 10 days in adult brain glia using repoGS, starting at 2-days old (d). Both normal (total Tau) and hyperphosphorylated hTau (AT8, AT100) protein is produced in fly heads, assayed using western immunoblots (WBs). Shown are 3 replicate samples for UAS-hTau collected in parallel.
Extended Data Fig. 3 Assessment of existing tau loss-of-function alleles.
(a) Schematic of the genomic region deleted in tauMR22 (green line) flies and the impacted genes. (b) Schematic of fly tau gene and isoform G. Green line = the deleted genomic region in tau∆ex6-14 (more commonly known as “dTau KO”) flies. Red shows exons known to encode microtubule binding domains (MTBDs) that are deleted. A large exon (orange) that is exclusive to isoform tau-G is intact. (c) PCR was used to confirm the deleted genomic region in tau∆ex6-14 homozygous flies. (d) qPCR was performed on control flies, tau∆ex6-14 homozygous flies, tau∆ex6-14 heterozygous flies, or transheterozygous tau∆ex6-14/Df flies to measure tau-G transcript levels. Df = deficiency allele. tau-G is significantly upregulated in response to the tau∆ex6-14 allele. Data were consistent using two independent deficiency alleles, Df-1 and Df-2. All flies are in a w[1118] background. Total RNA was extracted from 2d fly heads. A datapoint represents the relative expression per technical replicate (n). n = 4-8. Data presented as mean ± SD. Statistics: 1-way ANOVA with Tukey’s multiple comparisons test. P-values = not significant (n.s.) >0.05, *=0.0117, **≤0.01, ****≤0.0001. See Supporting Data 1 for details on n and P-values. (e) In silico analyses were performed on the protein sequence encoded by tau-G to define MTBDs. Unhighlighted text is sequence unique to tau-G and not deleted in tau∆ex6-14 flies. Pink highlighted text is sequence deleted in tau∆ex6-14 flies that is also found in tau-G. Red and green text denotes specific MTBD identified by MAPanalyzer. Italicized text denotes sequence identified as common to MT associated proteins using InterPro. Note the overlap in predictions at two MTBD within the sequence unique to tau-G (red, italicized). These predictions correctly identify established MTBD (green, italicized) within the sequence deleted in tau∆ex6-14. Overall, tau-G is likely upregulated to compensate for the loss of other tau transcripts in tau∆ex6-14 flies.
Extended Data Fig. 4 RNA analysis of tau-CRIMIC flies.
(a) Schematic of the CRIMIC cassette inserted between exons 10 and 11 of tau. This disrupts all transcripts carrying established (red) and predicted (orange) microtubule binding domains. Primer sets (blue) were designed to measure the levels of the different tau transcripts by qPCR. (b-d) qPCR data for flies including yw control, heterozygous tau-CRIMIC/+, and trans-heterozygous tau-CR/Df mutant flies carrying one copy of tau-CRIMIC and one copy of a deficiency (Df) allele. tau transcript levels were consistently decreased using two independent deficiency alleles, Df-1 and Df-2. A datapoint represents the relative expression per technical replicate (n). n = 4-10. Data presented as mean ± SD. Statistics: 1-way ANOVA with Tukey’s multiple comparisons test. P-values = not significant (n.s.) >0.05, *≤0.05, **≤0.01, ***≤0.001, ****≤0.0001. See Supporting Data 1 for details on n and P-values.
Extended Data Fig. 5 Additional data for Drosophila tau RNAi studies.
(a) UAS-Control (Ctrl) RNAi or UAS-tau RNAi was expressed ubiquitously using da-GAL4. Protein extracted from 2d heads was analyzed by WB for dTau levels. A datapoint represents the relative band density per technical replicate (n). n = 6. (b) UAS-Control (LacZ), UAS-Ctrl RNAi or UAS-tau RNAi were expressed in adult flies starting at 2d using the pan-neuronal, drug inducible driver, elavGS. n = 234-325 per genotype. (c) UAS-Ctrl RNAi or UAS-tau RNAi were expressed through development and adulthood using the pan-neuronal driver, elav-GAL4, at 29 °C. Control RNAi n = 161, tau RNAi n = 125. As the GAL4/UAS system is temperature-dependent, this produces higher RNAi expression than standard 25 °C rearing temperatures (see Fig. 3e). (b-c) Survival was measured using Kaplan-Meier plots. P-value ≤ 0.0001 seen with UAS-tau RNAi versus UAS- Ctrl RNAi in b and c, with UAS-tau RNAi versus UAS-Control in c, and UAS- Ctrl RNAi versus UAS-Control in c. UAS-Ctrl RNAi and UAS-tau RNAi are in a w+ background. UAS-Control is in a w* background. (d) UAS-Control (GFP) RNAi-2 or UAS-tau RNAi-2 were expressed in retinal glia using 54C-GAL4. Rh:ND42 RNAi was used to induce neuronal ROS and glial LDs. LDs were visualized in fly retinas from 2d animals using BODIPY 493/503 (white puncta, arrows). A datapoint represents the average LD number per ommatidium per animal (n). n = 6. (e) UAS-Control RNAi or UAS-tau RNAi was expressed in retinal glia using 54C-GAL4 and TEM was performed to visualize morphological changes in the fly retina. Glial cells = green. Shown are representative images for the quantification shown in Fig. 5d. (f) UAS-Control RNAi or UAS-tau RNAi were expressed in glia of 1-2d adult flies for 10d. Fixed brains were stained for LDs using BODIPY 493/503 (white puncta, arrows). Shown are representative images for the quantification shown in Fig. 5f. (g) The total levels of triglycerides (TG) were measured in whole heads from either 10d or 26d flies expressing UAS-RNAi in adult glia using repoGS. A datapoint represents the relative TG levels per technical replicate (n). n = 8. Statistics: unpaired 2-sided student t-test (a, d), Log-rank test (b, c), 1-way ANOVA with Tukey’s multiple comparisons test (g). P-values = not significant (n.s.) >0.05, *≤0.05, **≤0.01, ***≤0.001, ****≤0.0001. Data presented as mean ± SEM. See Supporting Data 1 for details on technical replicates, n, and P-values.
Extended Data Fig. 6 Downregulating dTau in adult glia causes increased daytime sleep.
UAS-Control RNAi or UAS-tau RNAi were expressed in glia of adult animals starting at 2d using the drug-inducible glial driver, repoGS. Starting at 5d, DAM assays were used to measure fly activity over the next 3 days. (a) Average activity profiles in Control (black, n = 32) or tau RNAi (red, n = 31) expressing flies. (b-d) tau RNAi expressing flies have more recorded total and daytime sleep. A datapoint represents the mean measurement per n animal over the 3 days of analysis. Statistics: unpaired 2-sided student t-test. Data presented as mean ± SEM. P-values = not significant (n.s.) >0.05, ****≤0.0001. Experiments were performed in a w+ background.
Extended Data Fig. 7 Astrocyte monocultures require Tau for proper LD formation during stress.
(a) HBSS was used to induce stress in rat astrocytes grown in the absence (monoculture, n = 6) or presence (co-culture, n = 5) of neurons. LDs were then stained in these astrocytes using BODIPY 493/503. A datapoint represents the average LD number or size from 10 glia per experimental replicate (n). (b) WB showing GFP (control) or GFP-hTau expression in astrocyte monocultures prior to co-culturing with neurons. (c-e) LipidTox was used to assess LD number in astrocyte monocultures. CM = complete glia media (control). Glia were treated with HBSS to induce oxidative stress19. A datapoint represents the average LD number from 5-10 glia per experimental replicate (n). n = 3-4. (c) Astrocytes were transduced to overexpress GFP (control) or GFP-hTau. (d-e) Astrocytes were transduced to express RNAi targeting Mapt to a control RNAi. GFP marks cells that were successfully transduced. Statistics: unpaired 2-sided student t-test (a), 1-way Anova with Tukey’s multiple comparisons test (b and c). P-values = not significant (n.s.) >0.05, *≤0.05, **≤0.01, ***≤0.001, ****≤0.0001. Data presented as mean ± SEM. See Supporting Data 1 for details on n and P-values. All images are maximum intensity projections.
Extended Data Fig. 8 Overexpression of futsch in glia disrupts LD formation similar to hTau overexpression.
Rh:ND42 RNAi was used to induce neuronal ROS and glial LD. LDs were visualized in fly retinas of 2d animals using BODIPY 493/503 (white puncta, arrows). UAS-Control (LacZ), UAS-futsch, or UAS-ensconsin (ens) were overexpressed in glia using 54C-GAL4. A datapoint represents the average LD number per ommatidium per animal (n). n = 7-8. Statistics: 1-way ANOVA with Tukey’s multiple comparisons test. P-values = not significant (n.s.) >0.05, *≤0.05, **≤0.01, ***≤0.001, ****≤0.0001. Data presented as mean ± SEM. See Supporting Data 1 for details on n and P-values.
Extended Data Fig. 9 Characterization of 1xUAS-hTau flies.
(a) Schematic of a standard UAS construct for hTau that carries five upstream activation sequences (5xUAS). (b) Schematic of our new 1xUAS construct for hTau that carries one upstream activation sequence (1xUAS). (c) WBs comparing expression of total Tau protein in flies carrying a standard (5x)UAS-GFP-hTau transgene versus flies carrying a 1xUAS-GFP-hTau transgene. For accurate comparisons, transgenes were expressed for 4d using the drug-inducible, ubiquitous driver da-GAL4Geneswitch (daGS) starting in 2d animals. Protein was extracted from whole fly heads. (d) Viability analysis for flies expressing UAS-hTau versus flies expressing 1xUAS-hTau using the tau-CRIMIC allele. (e) WBs showing the successful production of hTau protein when 1xUAS-hTau was expressed using the tau-CRIMIC allele. Protein was extracted from 2d fly heads. Hyperphosphorylated Tau is not detected in these animals using the AT8 antibody (no data to show). Note that expression of hTau using 1xUAS-hTau and the tau-CRIMIC allele can result in secondary bands with this well-established anti-Tau antibody due to the low expression of the protein. In contrast, this same antibody does not produce secondary bands when hTau is expressed at higher levels using 5xUAS-hTau transgenes or a stronger GAL4 driver, as per c and Extended Data Fig. 3b. A datapoint represents the relative band density per technical replicate (n). n = 4. Data presented as mean ± SD. Statistics: 1-way ANOVA w/ Tukey’s multiple comparison’s test. P-values = not significant (n.s.) >0.05. (f) Expression of 1xCtrl or 1xhTau using the tau-CRIMIC allele does not induce LDs. Quantification seen in Fig. 7c.
Extended Data Fig. 10 Additional data for BODIPY-C12/ER tracker studies and expression data on PLIN2 versus MAPT in aged human brains.
(a) Human oligodendrocyte-like MO3.13 cells were transiently transfected with siRNA targeting MAPT or scrambled control. Cells were fixed and stained for total hTau levels (red) or DAPI (blue). Shown are representative images for the quantification of hTau levels provided in Fig. 8b. Note that the level of hTau downregulation varies between cells. This will make quantifications presented in Fig. 8b,c and Extended Data Fig. 10c,d underestimates as cells with intact Tau will be included. (b) Zoomed out images for those seen in Fig. 8c. Dashed square = the representative image used. (c) Total levels of BODIPY-C12 were measured in transfected cells. MAPT siRNA results in an overall increase in BODIPY-C12 levels, indicating defects in the breakdown of externally sourced lipids. (d) Total levels of ER tracker signal were measured in transfected cells, showing ER enlargement with MAPT siRNA-2. (c-d) A datapoint represents the relative fluorescence per cell in an image (n). n = 5. Statistics: 1-way ANOVA with Dunnett’s multiple comparisons test. Data presented as mean ± SD. P-values = not significant (n.s.) >0.05, *≤0.05, **≤0.01, ***≤0.001, ****≤0.0001. (e-g) Publicly available RNA-seq data from human postmortem brains was analyzed for expression levels of MAPT (encodes Tau) and the LD marker, PLIN2. Pearson r correlations were performed to define a correlation in expression between these two genes. Two analyses were performed: (1) includes all individuals independent of clinical status; (2) includes only individuals with a clinical diagnosis of AD (shown in red). (e) RNA-seq data in the MAYO cohort was obtained from temporal cortex (TCX) post-mortem tissue. This cohort includes individuals with AD, progressive supranuclear palsy, and cognitively unimpaired individuals. (f) RNA-seq data in the ROSMAP cohort was obtained from dorsolateral prefrontal cortex (DLPFC) post-mortem tissue. ROSMAP is a prospective study recruiting individuals from the community setting without known dementia who are followed longitudinally and consent for brain donation and autopsy at the time of death. See Supporting Data 1 for details on n and statistics.
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Goodman, L.D., Ralhan, I., Li, X. et al. Tau is required for glial lipid droplet formation and resistance to neuronal oxidative stress. Nat Neurosci 27, 1918–1933 (2024). https://doi.org/10.1038/s41593-024-01740-1
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DOI: https://doi.org/10.1038/s41593-024-01740-1