IL-4 expressing cells are recruited to nerve after injury and promote regeneration.

Interleukin-4 (IL-4) has garnered interest as a cytokine that mediates regeneration across multiple tissues including peripheral nerve. Within nerve, we previously showed endogenous IL-4 was critical to regeneration across nerve gaps. Here, we determined a generalizable role of IL-4 in nerve injury and regeneration. In wild-type (WT) mice receiving a sciatic nerve crush, IL-4 expressing cells preferentially accumulated within the injured nerve compared to affected sites proximal, such as dorsal root ganglia (DRGs), or distal muscle. Immunohistochemistry and flow cytometry confirmed that eosinophils (CD45+, CD11b+, CD64-, Siglec-F+) were sources of IL-4 expression. Examination of targets for IL-4 within nerve revealed macrophages, as well as subsets of neurons expressed IL-4R, while Schwann cells expressed limited IL-4R. Dorsal root ganglia cultures were exposed to IL-4 and demonstrated an increased proportion of neurons that extended axons compared to cultures without IL-4 (control), as well as longer myelinated axons compared to cultures without IL-4. The role of endogenous IL-4 during nerve injury and regeneration in vivo was assessed following a sciatic nerve crush using IL-4 knockout (KO) mice. Loss of IL-4 affected macrophage accumulation within injured nerve compared to WT mice, as well as shifted macrophage phenotype towards a CD206- phenotype with altered gene expression. Furthermore, this loss of IL-4 delayed initial axon regeneration from the injury crush site and subsequently delayed functional recovery and re-innervation of neuromuscular junctions compared to wild-type mice. Given the role of endogenous IL-4 in nerve regeneration, exogenous IL-4 was administered daily to WT mice following a nerve crush to examine regeneration. Daily IL-4 administration increased early axonal extension and CD206+ macrophage accumulation but did not alter functional recovery compared to untreated mice. Our data demonstrate IL-4 promotes nerve regeneration and recovery after injury.

Runx2 was Correlated with Neurite Outgrowth and Schwann Cell Differentiation, Migration After Sciatic Nerve Crush.

Runx2, also known as Cbfa1, is a multifunctional transcription factor essential for osteoblast differentiation. It also plays major roles in chondrocyte maturation, mesenchymal stem cell differentiation, cleidocranial dysplasia, and the growth and metastasis of tumors. The present study was performed to investigate the functions of Runx2 in the differentiation and migration of Schwann cells and outgrowth of neurites after peripheral nervous system injury. In a model of sciatic nerve crush (SNC) injury, we found a gradual increase in the expression of Runx2, which reached a peak after 1 week. Immunofluorescence revealed increased expression of Runx2 in Schwann cells and axons after SNC injury. Runx2 and Oct-6 expression trends were consistent with each other in western blotting, and colocalization of Runx2 and Oct-6 was observed in immunofluorescence. In vitro, Runx2 promoted Schwann cell differentiation by activation of the Akt-GSK3ß signaling pathway. In addition, Runx2 promoted the migration of Schwann cells and outgrowth of neurites. These findings suggest that Runx2 may be involved in neurite outgrowth and Schwann cell differentiation and migration after sciatic nerve injury.