Runx2 drives Schwann cells repair phenotype switch through chromatin remodeling and Sox2 activation after nerve injury.

Background: The states of Schwann cells undergo significant shifts during nerve regeneration. Previous studies have shown the expression of Runx2 is locally upregulated within the affected areas. However, the regulatory mechanisms underlying its epigenetic control remain unclear.

Methods: To investigate the epigenetic mechanisms through which Runx2 influences the phenotypic transition of repair Schwann cells. Runx2 siRNA fragments and Runx2 overexpression plasmids were constructed. Healthy adult Sprague-Dawley (SD) rats weighted 100-150 g, regardless of sex, were randomly selected. Following the establishment of a sciatic nerve crush injury model, samples were collected for qPCR analysis at 4 and 7 days post-injury. In vitro, the alterations in cell morphology, proliferation, apoptosis, and the ability to promote neural regeneration following the downregulation or upregulation of Runx2 in Schwann cells were assessed. A comprehensive analysis of transcriptome data, ATAC sequencing, and CUT&Tag sequencing of histones and transcription factors in SCs after Runx2 overexpression, along with single-cell RNA sequencing data from GSE216665 and Sox2 overexpression data from RSC96 in GSE94590, was conducted to elucidate the mechanism of action of Runx2, which was subsequently validated using dual luciferase assays.

Results: Runx2 expression increased locally during the early stages of injury, primarily localized within Zhu Schwann cells (Zhu SCs). Runx2-overexpressing Schwann cells, when cultured in vitro, underwent a transformation from long, spindle-shaped He Schwann cells (He SCs) to flat, rounded Zhu SCs. Multi-omics analysis indicated that Runx2-OE may positively feedback-regulate its expression by opening transcriptional regulatory regions and binding to its own gene regulatory domains. Furthermore, it could also activate transcription factors such as Sox2, transitioning them from a transcriptionally silent to an active state, thereby enhancing Sox2 expression and synergistically regulating the phenotypic transition of Schwann cells.

Conclusions: Runx2 can activate and recruit downstream stemness factors, such as Sox2, by modulating chromatin accessibility and histone modification status within Schwann cells, thereby promoting and maintaining the timely phenotypic transformation of Schwann cells following injury.