Enriched conditioning expands the regenerative ability of sensory neurons after spinal cord injury via neuronal intrinsic redox signaling

Francesco De Virgiliis,Vance P Lemmon,Matt C Danzi,John L Bixby,Simone Di Giovanni,Luming Zhou,Thomas H Hutson,Jian Miao,Sarah Amachree,Rositsa Todorova,Ilaria Palmisano,Ilka Wittig,Ajay M Shah,Richard Thompson

doi:10.1038/s41467-020-20179-z

Abstract

Overcoming the restricted axonal regenerative ability that limits functional repair following a central nervous system injury remains a challenge. Here we report a regenerative paradigm that we call enriched conditioning, which combines environmental enrichment (EE) followed by a conditioning sciatic nerve axotomy that precedes a spinal cord injury (SCI). Enriched conditioning significantly increases the regenerative ability of dorsal root ganglia (DRG) sensory neurons compared to EE or a conditioning injury alone, propelling axon growth well beyond the spinal injury site. Mechanistically, we established that enriched conditioning relies on the unique neuronal intrinsic signaling axis PKC-STAT3-NADPH oxidase 2 (NOX2), enhancing redox signaling as shown by redox proteomics in DRG. Finally, NOX2 conditional deletion or overexpression respectively blocked or phenocopied enriched conditioning-dependent axon regeneration after SCI leading to improved functional recovery. These studies provide a paradigm that drives the regenerative ability of sensory neurons offering a potential redox-dependent regenerative model for mechanistic and therapeutic discoveries.

Highlights

Overcoming the restricted axonal regenerative ability that limits functional repair following a central nervous system injury remains a challenge
Comparing the gene expression profiles in dorsal root ganglia (DRG) following pre-exposure to EE or sciatic nerve axotomy (SNA) based upon a previously published[30] and a recently generated dataset, we found that the two conditions generated remarkably different sets of differentially expressed (DE) genes (P-value < 0.05) (Supplementary Fig. 1A and Supplementary Data 1) and Gene Ontology (GO) pathways (Supplementary Fig. 1B and Supplementary Data 2 and 3) (Pvalue < 0.05)
When we combined EE and SNA, and performed a spinal cord T9 dorsal hemisection, we observed a significant increase in cholera toxin subunit B (CTB) traced sensory axons beyond the lesion site compared to standard housing (SH) sham, EE sham, or SH SNA (Fig. 1c–f)

Summary

Introduction

Overcoming the restricted axonal regenerative ability that limits functional repair following a central nervous system injury remains a challenge. NOX2 conditional deletion or overexpression respectively blocked or phenocopied enriched conditioningdependent axon regeneration after SCI leading to improved functional recovery These studies provide a paradigm that drives the regenerative ability of sensory neurons offering a potential redox-dependent regenerative model for mechanistic and therapeutic discoveries. Exposing rodents to environmental enrichment (EE) rather than standard housing (SH) before axonal injury enhances the regenerative ability of DRG neurons via activity-mediated CREB-binding proteindependent histone acetylation, which increases the expression of genes associated with the regenerative program[30] This increase was comparable to the one observed after performing a conditioning sciatic nerve axotomy (SNA) prior to the SCI30. Coupling EE and SNA elicited an additive effect to the regenerative potential of sensory DRG neurons, significantly enhancing axon regeneration well beyond the spinal injury site This regenerative model, which we call enriched conditioning, exhibits superior regenerative ability compared to EE or conditioning SNA alone. NOX2 overexpression in DRG neurons promotes regeneration of sensory axons and functional recovery after SCI

Methods

Results

Conclusion