Increased expression of p21WAF1/CIP1 in kidney proximal tubules mediates fibrosis.

Tissue fibrosis is a major cause of death in developed countries. It commonly occurs after either acute or chronic injury and affects diverse organs, including the heart, liver, lung, and kidney. Using the renal ablation model of chronic kidney disease, we previously found that the development of progressive renal fibrosis was dependent on p21(WAF1/Cip1) expression; the genetic knockout of the p21 gene greatly alleviated this disease. In the present study, we expanded on this observation and report that fibrosis induced by two different acute injuries to the kidney is also dependent on p21. In addition, when p21 expression was restricted only to the proximal tubule, fibrosis after injury was induced in the whole organ. One molecular fibrogenic switch we describe is transforming growth factor-β induction, which occurred in vivo and in cultured kidney cells exposed to adenovirus expressing p21. Our data suggests that fibrosis is p21 dependent and that preventing p21 induction after stress could be a novel therapeutic target.