Up-Regulation of Local TGF-β Contributes to a Decrease in Renal Tubular Na + -K + ATPase and Hyperkalemia in a Mouse Model of Crush Syndrome

Hyperkalemia is one of the most important risk factors in patients suffering from crush syndrome with rhabdomyolysis. Glycerol-injected animals have been used as an experimental model of rhabdomyolysis-induced acute kidney injury (AKI), but little information is available for the onset and molecular mechanism of hyperkalemia. In our murine model, plasma potassium levels increased after a single injection of 50%-glycerol solution (10 ml/kg, i.m.) during the progression of muscular and renal injuries. Renal tubular Na+-K+-ATPase functions as ion-exchange pomp for potassium clearance from blood into renal tubular epithelial cells. Renal histochemistry revealed an apparent decrease in the tubular Na+-K+-ATPase expression, especially at 24 hours post-glycerol challenge in our AKI model. In contrast to the loss in active Na+-K+-ATPase, there was a significant increase in the renal levels of transforming growth factor-β (TGF-β) that is known to suppress Na+-K+-ATPase production in vitro. When anti-TGF-β antibody was administered in mice after the glycerol challenge, the suppression of renal Na+-K+-ATPase activity was partially restored. As a result, hyperkalemia was improved in the TGF-β-neutralized AKI mice, associated with a significant decrease in plasma potassium concentration. Taken together, we predict that endogenous TGF-β is a key regulator for inhibiting Na+-K+-ATPase production and, in part, enhancing hyperkalemia during progression of rhabdomyolysis-induced AKI. This is, to our knowledge, the first report to determine a critical role of endogenous TGF-β in renal potassium metabolism during crush syndrome.