Epigenomic Profiling of Dorsal Root Ganglia upon Regenerative and Non-regenerative Axonal Injury.

RNA sequencing (RNA-seq), chromatin immunoprecipitation sequencing (ChIP-seq), and assay for transposase-accessible chromatin sequencing (ATAC-seq) are genome-wide techniques that provide information relative to gene expression, chromatin binding sites, and chromatin accessibility, respectively. Here we describe RNA-seq, H3K9ac, H3K27ac and H3K27me3 ChIP-seq, and ATAC-seq in dorsal root ganglia (DRG) after sciatic nerve or dorsal column axotomy, to characterize the transcriptional and epigenetic signatures of DRG upon regenerative vs non-regenerative axonal lesion.

The gut metabolite indole-3 propionate promotes nerve regeneration and repair.

The regenerative potential of mammalian peripheral nervous system neurons after injury is critically limited by their slow axonal regenerative rate1. Regenerative ability is influenced by both injury-dependent and injury-independent mechanisms2. Among the latter, environmental factors such as exercise and environmental enrichment have been shown to affect signalling pathways that promote axonal regeneration3. Several of these pathways, including modifications in gene transcription and protein synthesis, mitochondrial metabolism and the release of neurotrophins, can be activated by intermittent fasting (IF)4,5. However, whether IF influences the axonal regenerative ability remains to be investigated. Here we show that IF promotes axonal regeneration after sciatic nerve crush in mice through an unexpected mechanism that relies on the gram-positive gut microbiome and an increase in the gut bacteria-derived metabolite indole-3-propionic acid (IPA) in the serum. IPA production by Clostridium sporogenes is required for efficient axonal regeneration, and delivery of IPA after sciatic injury significantly enhances axonal regeneration, accelerating the recovery of sensory function. Mechanistically, RNA sequencing analysis from sciatic dorsal root ganglia suggested a role for neutrophil chemotaxis in the IPA-dependent regenerative phenotype, which was confirmed by inhibition of neutrophil chemotaxis. Our results demonstrate the ability of a microbiome-derived metabolite, such as IPA, to facilitate regeneration and functional recovery of sensory axons through an immune-mediated mechanism.

Reversible CD8 T cell-neuron cross-talk causes aging-dependent neuronal regenerative decline.

Aging is associated with increased prevalence of axonal injuries characterized by poor regeneration and disability. However, the underlying mechanisms remain unclear. In our experiments, RNA sequencing of sciatic dorsal root ganglia (DRG) revealed significant aging-dependent enrichment in T cell signaling both before and after sciatic nerve injury (SNI) in mice. Lymphotoxin activated the transcription factor NF-κB, which induced expression of the chemokine CXCL13 by neurons. This in turn recruited CXCR5+CD8+ T cells to injured DRG neurons overexpressing major histocompatibility complex class I. CD8+ T cells repressed the axonal regeneration of DRG neurons via caspase 3 activation. CXCL13 neutralization prevented CXCR5+CD8+ T cell recruitment to the DRG and reversed aging-dependent regenerative decline, thereby promoting neurological recovery after SNI. Thus, axonal regeneration can be facilitated by antagonizing cross-talk between immune cells and neurons.