TNFR2 knockdown triggers apoptosis-induced proliferation in primarily cultured Schwann cells

After sciatic nerve injury, Schwann cells in the distal segments of injury site undergo apoptosis and meanwhile proliferation. Although apoptosis-induced proliferation (AiP) has been characterized in various models, whether the proliferation of Schwann cells in the distal segments is triggered by apoptosis remains unelucidated. In this study, we used small interfering RNA to knock down the expression of TNFR1 and TNFR2 in primarily cultured Schwann cells, respectively and observed its effects on apoptosis and proliferation. The downregulation of TNFR1 or TNFR2 resulted in a remarkable decrease of cell viability and dramatically increased the apoptosis of Schwann cells. In contrast, the cell apoptosis induced by the knockdown of TNFR2, but not TNFR1, promoted the Schwann cell proliferation. Together, these observations indicated that Schwann cells can undergo AiP, and TNFR2 knockdown triggers the process. Additionally, we established the sciatic nerve injury model on TNF-α knock-out (KO) mice, and found that the Schwann cells of KO mice occurred significantly less apoptosis and proliferation than that of wild-type mice in the distal segments, which indicated TNF-α and its receptors were essential in the massive apoptosis and the apoptosis-induced proliferation of Schwann cells after sciatic nerve injury. The finding of AiP in Schwann cells may be beneficial to develop new approaches to promote axon regeneration and thereby improve the functional recovery after peripheral nerve injury.