Na+/K+‐ATPase coupled to endothelin receptor type B stimulates peripheral nerve regeneration via lactate signalling

We have recently demonstrated that endothelin (ET) is functionally coupled to Nax, a Na+ concentration‐sensitive Na+ channel for lactate release via ET receptor type B (ETBR) and is involved in peripheral nerve regeneration in a sciatic nerve transection–regeneration mouse model. Nax is known to interact directly with Na+/K+‐ATPase, leading to lactate production in the brain. To investigate the role of Na+/K+‐ATPase in peripheral nerve regeneration, in this study, we applied ouabain, a Na+/K+‐ATPase inhibitor, to the cut site for 4 weeks with an osmotic pump. While functional recovery and nerve reinnervation to the toe started at 5 weeks after axotomy and were completed by 7 weeks, ouabain delayed them by 2 weeks. The delay by ouabain was improved by lactate, and its effect was blocked by α‐cyano‐4‐hydroxy‐cinnamic acid (CIN), a broad monocarboxylate transporter (MCT) inhibitor. In primary cultures of dorsal root ganglia, neurite outgrowth of neurons and lactate release into the culture medium was inhibited by ouabain. Conversely, lactate enhanced the neurite outgrowth, which was blocked by CIN, but not by AR‐C155858, a MCT1/2‐selective inhibitor. ET‐1 and ET‐3 increased neurite outgrowth of neurons, which was attenuated by an ETBR antagonist, ouabain and 2 protein kinase C inhibitors. Taken together with the finding that ETBR was expressed in Schwann cells, these results demonstrate that ET enhanced neurite outgrowth of neurons mediated by Na+/K+‐ATPase via ETBR in Schwann cells. This study suggests that Na+/K+‐ATPase coupled to the ET‐ETBR system plays a critical role in peripheral nerve regeneration via lactate signalling. Endothelin (ET) activates protein kinase C (PKC) via ET receptor type B (ETBR) and promotes the coupling of Nax, a Na+‐concentration‐sensitive Na+ channel and Na+/K+‐ATPase in glial cells such as Schwann cells and satellite glial cells in the DRG and sciatic nerve. Lactate produced in glial cells is transported to DRG neurons via monocarboxylate transporter 4 (MCT4) and plays a critical role in peripheral nerve regeneration.