Low-intensity extracorporeal shock wave therapy promotes recovery of sciatic nerve injury and the role of mechanical sensitive YAP/TAZ signaling pathway for nerve regeneration

BACKGROUND: Histological and functional recovery after peripheral nerve injury (PNI) is of significant clinical value as delayed surgical repair and longer distances to innervate terminal organs may account for poor outcomes. Low-intensity extracorporeal shock wave therapy (LiESWT) has already been proven to be beneficial for injured tissue recovery on various pathological conditions. The objective of this study was to explore the potential effect and mechanism of LiESWT on PNI recovery. METHODS: In this project, we explored LiESWT's role using an animal model of sciatic nerve injury (SNI). Shockwave was delivered to the region of the SNI site with a special probe at 3 Hz, 500 shocks each time, and 3 times a week for 3 weeks. Rat Schwann cells (SCs) and rat perineurial fibroblasts (PNFs) cells, the two main compositional cell types in peripheral nerve tissue, were cultured in vitro, and LiESWT was applied through the cultured dish to the adherent cells. Tissues and cell cultures were harvested at corresponding time points for a reverse transcription-polymerase chain reaction, Western blotting, and immunofluorescence staining. Multiple groups were compared by using one-way analysis of variance followed by the Tukey-Kramer test for post hoc comparisons. RESULTS: LiESWT treatment promoted the functional recovery of lower extremities with SNI. More nerve fibers and myelin sheath were found after LiESWT treatment associated with local upregulation of mechanical sensitive yes-associated protein (YAP)/transcriptional co-activator with a PDZ-binding domain (TAZ) signaling pathway. In vitro results showed that SCs were more sensitive to LiESWT than PNFs. LiESWT promoted SCs activation with more expression of p75 (a SCs dedifferentiation marker) and Ki67 (a SCs proliferation marker). The SCs activation process was dependent on the intact YAP/TAZ signaling pathway as knockdown of TAZ by TAZ small interfering RNA significantly attenuated this process. CONCLUSION: The LiESWT mechanical signal perception and YAP/TAZ upregulation in SCs might be one of the underlying mechanisms for SCs activation and injured nerve axon regeneration.