Tubular obstruction induced polycystin upregulation is pro-fibrotic and induced a severe cystic phenotype in adult mice with autosomal dominant polycystic kidney disease: the coexistence of polycystin loss and gain function in ADPKD

Abstract

Mutations in PKD2 gene, which encodes polycystin-2, cause autosomal polycystic kidney disease (ADPKD). Development of ADPKD is associated with progression of renal fibrosis. Whether renal fibrosis in ADPKD is a direct effect of polycystin-2 mutation or a consequence of cyst growth induced tubular obstruction is currently unknown. Polycystin-2 has been identified as a direct target of triptolide, and we used triptolide as a probe to study the role of polycystin-2 in renal fibrosis. To study the expression of polycystin-2, we established unilateral ureteral obstruction (UUO), unilateral ischemia-reperfusion injury (UIRI) and aristolochic acid nephropathy mouse models. Here we showed that polycystin-2 is up-regulated in these three mouse models and tightly correlated with the expression of collagen-I in a time dependent manner. Treatment with triptolide inhibited the expression of polycystin-2 and pro-fibrotic markers in UUO and UIRI models. Moreover, triptolide dose-dependently inhibited the expression of polycystin-2 and pro-fibrotic markers in rat renal fibroblasts or in TGF-β stimulated human renal epithelial (HK2) cells. Knockdown of PKD2 reduced the expression of pro-fibrotic markers in TGF-β stimulated or unstimulated HK2 cells. Finally, we showed that knockdown of PKD2 attenuated the inhibitory effect of triptolide on the expression of pro-fibrotic markers in TGF-β stimulated HK2 cells.In conclusion, polycystin-2 is a pro-fibrotic protein suggesting that renal fibrosis in ADPKD kidneys is not a direct effect of PKD2 mutation.