EZH2-dependent myelination following sciatic nerve injury

Demyelination and remyelination have been major focal points in the study of peripheral nerve regeneration following peripheral nerve injury.Notably,the gene regulatory network of regenerated myelin differs from that of native myelin.Silencing of enhancer of zeste homolog 2(EZH2)hinders the differentiation,maturation,and myelination of Schwann cells in vitro.To further determine the role of EZH2 in myelination and recovery post-peripheral nerve injury,conditional knockout mice lacking Ezh2 in Schwann cells(Ezh2^(fl/fl);Dhh-Cre and Ezh2^(fl/fl);Mpz-Cre)were generated.Our results show that a significant proportion of axons in the sciatic nerve of Ezh2-depleted mice remain unmyelinated.This highlights the crucial role of Ezh2 in initiating Schwann cell myelination.Furthermore,we observed that 21 days after inducing a sciatic nerve crush injury in these mice,most axons had remyelinated at the injury site in the control nerve,while Ezh2^(fl/fl);Mpz-Cre mice had significantly fewer remyelinated axons compared with their wild-type littermates.This suggests that the absence of Ezh2 in Schwann cells impairs myelin formation and remyelination.In conclusion,EZH2 has emerged as a pivotal regulatory factor in the process of demyelination and myelin regeneration following peripheral nerve injury.Modulating EZH2 activity during these processes may offer a promising therapeutic target for the treatment of peripheral nerve injuries.

Spatiotemporal microRNA profile in peripheral nerve regeneration:miR-138 targets vimentin and inhibits Schwann cell migration and proliferation

While the peripheral nervous system has regenerative ability,restoration of sufficient function remains a challenge.Vimentin has been shown to be localized in axonal growth fronts and associated with nerve regeneration,including myelination,neuroplasticity,kinase signaling in nerve axoplasm,and cell migration;however,the mechanisms regulating its expression within Schwann cell（SC） remain unexplored.The aim of this study was to profile the spatial and temporal expression profile of micro RNA（mi RNA） in a regenerating rat sciatic nerve after transection,and explore the potential role of mi R-138-5 p targeting vimentin in SC proliferation and migration.A rat sciatic nerve transection model,utilizing a polyethylene nerve guide,was used to investigate mi RNA expression at 7,14,30,60,and 90 days during nerve regeneration.Relative levels of mi RNA expression were determined using microarray analysis and subsequently validated with quantitative real-time polymerase chain reaction.In vitro assays were conducted with cultured Schwann cells transfected with mi RNA mimics and assessed for migratory and proliferative potential.The top seven dysregulated mi RNAs reported in this study have been implicated in cell migration elsewhere,and GO and KEGG analyses predicted activities essential to wound healing.Transfection of one of these,mi RNA-138-5 p,into SCs reduced cell migration and proliferation.mi R-138-5 p has been shown to directly target vimentin in cancer cells,and the luciferase assay performed here in rat Schwann cells confirmed it.These results detail a role of mi R-138-5 p in rat peripheral nerve regeneration and expand on reports of it as an important regulator in the peripheral nervous system.

The proteome of distal nerves: implication in delayed repair and poor functional recovery

Chronic denervation is one of the key factors that affect nerve regeneration.Chronic axotomy deteriorates the distal nerve stump,causes protein changes,and renders the microenvironment less permissive for regeneration.Some of these factors/proteins have been individually studied.To better delineate the comprehensive protein expression profiles and identify proteins that contribute to or are associated with this detrimental effect,we carried out a proteomic analysis of the distal nerve using an established delayed rat sciatic nerve repair model.Four rats that received immediate repair after sciatic nerve transection served as control,whereas four rats in the experimental group(chronic denervation)had their sciatic nerve repaired after a 12-week delay.All the rats were sacrificed after 16 weeks to harvest the distal nerves for extracting proteins.Twenty-five micrograms of protein from each sample were fractionated in SDS-PAGE gels.NanoLC-MS/MS analysis was applied to the gels.Protein expression levels of nerves on the surgery side were compared to those on the contralateral side.Any protein with a P value of less than 0.05 and a fold change of 4 or higher was deemed differentially expressed.All the differentially expressed proteins in both groups were further stratified according to the biological processes.A PubMed search was also conducted to identify the differentially expressed proteins that have been reported to be either beneficial or detrimental to nerve regeneration.Ingenuity Pathway Analysis(IPA)software was used for pathway analysis.The results showed that 709 differentially expressed proteins were identified in the delayed repair group,with a bigger proportion of immune and inflammatory process-related proteins and a smaller proportion of proteins related to axon regeneration and lipid metabolism in comparison to the control group where 478 differentially expressed proteins were identified.The experimental group also had more beneficial proteins that were downregulated and more detrimental proteins that were upregulated.IPA revealed that protective pathways such as LXR/RXR,acute phase response,RAC,ERK/MAPK,CNTF,IL-6,and FGF signaling were inhibited in the delayed repair group,whereas three detrimental pathways,including the complement system,PTEN,and apoptosis signaling,were activated.An available database of the adult rodent sciatic nerve was used to assign protein changes to specific cell types.The poor regeneration seen in the delayed repair group could be associated with the down-regulation of beneficial proteins and up-regulation of detrimental proteins.The proteins and pathways identified in this study may offer clues for future studies to identify therapeutic targets.

The HMGB1 signaling pathway activates the inflammatory response in Schwann cells

Schwann cells are not only myelinating cells, but also function as immune cells and express numerous innate pattern recognition receptors, including the Toll-like receptors. Injury to peripheral nerves activates an inflammatory response in Schwann cells. However, it is unclear whether specific endogenous damage-associated molecular pattern molecules are involved in the inflammatory response following nerve injury. In the present study, we demonstrate that a key damage-associated molecular pattern molecule, high mobility group box 1（HMGB1）, is upregulated following rat sciatic nerve axotomy, and we show colocalization of the protein with Schwann cells. HMGB1 alone could not enhance expression of Toll-like receptors or the receptor for advanced glycation end products（RAGE）, but was able to facilitate migration of Schwann cells. When Schwann cells were treated with HMGB1 together with lipopolysaccharide, the expression levels of Toll-like receptors and RAGE, as well as inflammatory cytokines were upregulated. Our novel findings demonstrate that the HMGB1 pathway activates the inflammatory response in Schwann cells following peripheral nerve injury.

Biopolymer-nanotube nerve guidance conduit drug delivery for peripheral nerve regeneration:In vivo structural and functional assessment

Peripheral nerve injuries account for roughly 3%of all trauma patients with over 900,000 repair procedures annually in the US.Of all extremity peripheral nerve injuries,51%require nerve repair with a transected gap.The current gold-standard treatment for peripheral nerve injuries,autograft repair,has several shortcomings.Engineered constructs are currently only suitable for short gaps or small diameter nerves.Here,we investigate novel nerve guidance conduits with aligned microchannel porosity that deliver sustained-release of neurogenic 4-aminopyridine(4-AP)for peripheral nerve regeneration in a critical-size(15 mm)rat sciatic nerve transection model.The results of functional walking track analysis,morphometric evaluations of myelin development,and histological assessments of various markers confirmed the equivalency of our drug-conduit with autograft controls.Repaired nerves showed formation of thick myelin,presence of S100 and neurofilament markers,and promising functional recovery.The conduit’s aligned microchannel architecture may play a vital role in physically guiding axons for distal target reinnervation,while the sustained release of 4-AP may increase nerve conduction,and in turn synaptic neurotransmitter release and upregulation of critical Schwann cell neurotrophic factors.Overall,our nerve construct design facilitates efficient and efficacious peripheral nerve regeneration via a drug delivery system that is feasible for clinical applications.