Abstract: Peripheral nerve defect repair is a complex process that involves multiple cell types; perineurial cells play a pivotal role. Hair follicle neural crest stem cells promote perineurial cell proliferation and migration via paracrine signaling; however, their clinical applications are limited by potential risks such as tumorigenesis and xenogeneic immune rejection, which are similar to the risks associated with other stem cell transplantations. The present study therefore focuses on small extracellular vesicles derived from hair follicle neural crest stem cells, which preserve the bioactive properties of the parent cells while avoiding the transplantation-associated risks. In vitro, small extracellular vesicles derived from hair follicle neural crest stem cells significantly enhanced the proliferation, migration, tube formation, and barrier function of perineurial cells, and subsequently upregulated the expression of tight junction proteins. Furthermore, in a rat model of sciatic nerve defects bridged with silicon tubes, treatment with small extracellular vesicles derived from hair follicle neural crest stem cells resulted in higher tight junction protein expression in perineurial cells, thus facilitating neural tissue regeneration. At 10 weeks post-surgery, rats treated with small extracellular vesicles derived from hair follicle neural crest stem cells exhibited improved nerve function recovery and reduced muscle atrophy. Transcriptomic and microRNA analyses revealed that small extracellular vesicles derived from hair follicle neural crest stem cells deliver miR-21-5p, which inhibits mothers against decapentaplegic homolog 7 expression, thereby activating the transforming growth factor-β/mothers against decapentaplegic homolog signaling pathway and upregulating hyaluronan synthase 2 expression, and further enhancing tight junction protein expression. Together, our findings indicate that small extracellular vesicles derived from hair follicle neural crest stem cells promote the proliferation, migration, and tight junction protein formation of perineurial cells. These results provide new insights into peripheral nerve regeneration from the perspective of perineurial cells, and present a novel approach for the clinical treatment of peripheral nerve defects.

Key words: hair follicle neural crest stem cells, HAS2, migration, miR-21-5p, perineurial cells, proliferation, peripheral nerve injury, Smad7, small extracellular vesicles, transforming growth factor-β/SMAD signaling pathway