Upregulated lncARAT in Schwann Cells Promotes Axonal Regeneration through Recruiting Macrophages and Inducing Macrophages M2 Polarization

Abstract Background: Axonal regeneration following peripheral nerve injury largely depends on a favorable microenvironment. Schwann cells (SCs) play a crucial role in axonal regeneration by interacting with macrophages, but the mechanisms underlying macrophages recruitment and polarization remain unclear. Methods: The total RNA of crushed sciatic nerves and intact contralateral nerves was extracted and used to RNA-sequencing (RNA-seq). The differentially expressed long noncoding RNA (lncRNA) and mRNAs were analyzed using bioinformatics analysis, and were verified using qPCR and western blot analysis. The putative role of lncRNA in nerve regeneration was analyzed in vitro and in vivo. Macrophage polarization phenotype was identified by assessing IL-10, Arg-1, and CD206.Results: Here we identified an lncRNA, termed Axon Regeneration-Associated Transcript (lncARAT), upregulated in SCs and SCs-derived exosomes after crushed sciatic nerves (CSN). LncARAT contributed to axonal regeneration and improved motor functional recovery. Mechanistically, lncARAT epigenetically activated CCL2 expression by recruiting KMT2A to CCL2 promoter, which resulted in an increased H3K4 trimethylation and CCL2 transcription in SCs. CCL2 upregulation facilitated the infiltration of macrophages into the injured nerves. Meanwhile, lncARAT-enriched exosomes were released from SCs and incorporated into macrophages. Once in macrophage, lncARAT functioned as an endogenous sponge to adsorb miRNA-329-5p, resulting in an increased SOCS2 expression, which facilitated macrophage M2 polarization through a STAT1/6-dependent pathway, thus promoted axonal regeneration. Conclusions: LncARAT may serve as a promising therapeutic avenue for peripheral nerve repair.