Genetic deficiency of Smad3 protects against murine ischemic acute kidney injury

TGF-(β1 contributes to chronic kidney disease, at least in part, via Smad3. TGF-(β1 is induced in the kidney following acute ischemia, and there is increasing evidence that TGF-(β1 may protect against acute kidney injury. As there is a paucity of information regarding the functional significance of Smad3 in acute kidney injury, the present study explored this issue in a murine model of ischemic acute kidney injury in Smad3^+/+ and Smad3^-/-mice. We demonstrate that, at 24 h after ischemia, Smad3 is significantly induced in Smad3^+/+ mice, whereas Smad3^-/- mice fail to express this protein in the kidney in either the sham or postischemic groups. Compared with Smad3^+/+ mice, and 24 h following ischemia, Smad3^-/-mice exhibited greater preservation of renal function as measured by blood urea nitrogen (BUN) and serum creatinine; less histological injury assessed by both semiquantitative and qualitative analyses; markedly suppressed renal expression of IL-6 and endothelin-1 mRNA (but comparable expression of MCP-1, TNF-a, and heme oxygenase-1 mRNA); and no increase in plasma IL-6 levels, the latter increasing approximately sixfold in postischemic Smad3^+/+ mice. We conclude that genetic deficiency of Smad3 confers structural and functional protection against acute ischemic injury to the kidney. We speculate that these effects may be mediated through suppression of IL-6 production. Finally, we suggest that upregulation of Smad3 after an ischemic insult may contribute to the increased risk for chronic kidney disease that occurs after acute renal ischemia.