Contusive spinal cord injury leads to a variety of disabilities owing to limited neuronal regeneration and functional plasticity. It is well established that an upregulation of glial-derived chondroitin sulphate proteoglycans (CSPGs) within the glial scar and perineuronal net creates a barrier to axonal regrowth and sprouting1,2,3,4,5. Protein tyrosine phosphatase σ (PTPσ), along with its sister phosphatase leukocyte common antigen-related (LAR) and the nogo receptors 1 and 3 (NgR), have recently been identified as receptors for the inhibitory glycosylated side chains of CSPGs6,7,8. Here we find in rats that PTPσ has a critical role in converting growth cones into a dystrophic state by tightly stabilizing them within CSPG-rich substrates. We generated a membrane-permeable peptide mimetic of the PTPσ wedge domain that binds to PTPσ and relieves CSPG-mediated inhibition. Systemic delivery of this peptide over weeks restored substantial serotonergic innervation to the spinal cord below the level of injury and facilitated functional recovery of both locomotor and urinary systems. Our results add a new layer of understanding to the critical role of PTPσ in mediating the growth-inhibited state of neurons due to CSPGs within the injured adult spinal cord.
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This work was supported by National Institute of Neurological Disorders and Stroke grant NS025713 (J.S.); the Case Western Reserve University Council to Advance Human Health; P. Jing, R. Senior and S. Poon; Unite to Fight Paralysis; The Brumagin Memorial Fund; Spinal Cord Injury Sucks; United Paralysis Foundation; and The Kaneko Family Fund. The authors thank J. Flanagan, M. Blackmore, A. Filous, S. Brady-Kalnay, R. Gardner and B. Habecker for their valuable discussion and input into the project.
A preliminary patent application (61/621,623) has been filed for ISP.
Extended data figures and tables
a, LAR expression in motile (left, on laminin) and immobilized (right, within CSPG gradient) growth cones. b, Nogo receptors in a soma and axons. Scale bars, 20 μm. c, d, PTPσ expression in the spinal cord 14 days after dorsal column crush injury. The arrowhead pointing upwards represents a labelled structure with dystrophic morphology. Scale bar, 50 μm.
a, BLAST alignment of the known sequences of mouse, rat and human LAR, PTPσ, PTPδ and PTPμ. The wedge domain of each protein is aligned within the box. b, The tandem intracellular phosphatase domains of human LAR with the previously characterized wedge domain (red)14. c, d, Pulldown of recombinant PTPσ with biotinylated (b)ISP or ILP. e, f, Eluted lysate after pulldown was probed with antibodies against either LAR or pan-NgRs. Input is 10% lysate control.
a, Purified GFAP-positive mature astrocytes (green) did not respond to ISP. b, S100-positive satellite glia were able to cross the gradient of CSPG after ISP treatment. Scale bar, 50 μm. c, d, Response of neurons and axons upon a CSPG-rich substrate to agitation after ISP treatment. Scale bar, 50 μm.
Western blot analysis revealed a significant decrease in the phosphorylation ratio of Erk1/2 in SH-SY5Y cells plated on laminin (2 μg ml−1) plus CSPGs (15 μg ml−1) compared with laminin-only substrates, which was reversed by either pre-treatment with ChABC (0.1 U ml−1) or 4 days of ISP treatment (2.5 μM). pErk1/2, phosphorylated Erk1/2; tErk1/2, total Erk1/2. Data normalized to laminin control. N = 4 independent experiments. *P < 0.05 versus all other conditions, one-way ANOVA, Tukey’s post-hoc test.
a, b, Spinal cord 1 h after subcutaneous injections of FITC-ISP or vehicle. Scale bar, 100 µM. c, Experimental design and timeline for in vivo experiment. d, e, The force and impaction velocity of all animals that received an infinite horizon contusive injury. All impactions are within 10% from the target force of 250 kdyn, with an average force of 258.2 for both ISP and vehicle.
a, b, Void frequency and average void volume at 6 weeks after injury. n = 11 naive, 21 vehicle, 10 ILP and 26 ISP. c–h, Representative smoothed metabolic cage traces of a normal animal (c) and five treated animals (vehicle (d), ILP (e) and ISP (f, h) 12 weeks after injury. Void volume is plotted (in ml) as a function of time. Scale bar, 4 h.
a, b, Average response to thermal (Hargrave’s test) and mechanical (Von Frey test) stimuli at 12 weeks after injury (n = 11 naive, 21 vehicle, 10 ILP and 26 ISP for thermal, n = 10 vehicle, 4 ILP and 10 ISP for mechanical). c–e, Correlations between recovery of each individual motor behaviour in the ISP treatment group. f–h, For each behaviour, the ISP-treated animals that recovered to two standard deviations relative to vehicle mean were separated and plotted as ‘responders’ while those that did not were plotted as ‘non-responders’. The n for the responding and non-responding group for each behaviour is listed on the graph. i, An in vivo ISP dose–response plot in a single cohort of animals. A dose-dependent increase occurred in void frequency at 12 weeks after SCI.
a–c, The individual results of five repeats of in vivo experiments are plotted as individual cohorts of animals for BBB, gridwalk and void frequency. *P < 0.05, **P < 0.01, repeated measures two-way ANOVA, Tukey’s post-hoc test (BBB); one-way ANOVA, Kruskal–Wallis post-hoc test (gridwalk and void frequency). Black indicates ISP versus control; red indicates ISP versus ILP. n for each condition is listed.
a–l, Spared tissue volume (as measured by GFAP-positive tissue) or area of spared white matter at the epicentre (as measured by eriochrome cyanine staining) were plotted against behavioural scores for vehicle- (a–f) and ISP-treated (g–l) animals. Pearson’s correlation coefficient (r value) is reported for each comparison. Only animals whose spinal cord was processed and cut coronally were included in the analysis.
a–f, Representative caudal neurofilament expression in lumbar spinal cord. Responders are ISP animals that demonstrated functional improvement (see Fig. 3n). All images were taken using identical settings. Scale bar, 500 μm.
Time lapse microscopy of motile, highly dynamic growth cones on a uniform substrate of laminin (10μg/ml) at 5d in vitro. Image taken every 30 sec. (MOV 28700 kb)
Time lapse microscopy of growth cones stabilizing and immobilized within a gradient of CSPG at 5d in vitro. Image taken every 30 sec. (MOV 28099 kb)
Time lapse microscopy of growth cones immobilized and over-adhered within a gradient of CSPG at 5d in vitro. Note that collapsed growth cones can involute into blebs, which are then transported retrogradely (part 1). 22 of the 24 growth cones analyzed at 4-6 d in vitro were partially or completely immobilized within the gradient. Image taken every 30 sec. (MOV 24668 kb)
Time lapse microscopy of adult DRG neurons which fail to immobilize and continually reform growth cones within the CSPG gradient following treatment with either ISP (2.5μM) or ILP (2.5μM) for 5d. Image taken every 30 sec. (MOV 29363 kb)
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Lang, B., Cregg, J., DePaul, M. et al. Modulation of the proteoglycan receptor PTPσ promotes recovery after spinal cord injury. Nature 518, 404–408 (2015). https://doi.org/10.1038/nature13974
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