MO449: Polycystins are Upregulated in Fibrotic Kidneys and Promote Renal Fibrosis

Abstract

Abstract BACKGROUND AND AIMS Mutations in PKD1 or PKD2 gene, which encodes polycystin-1 or polycystin-2, cause autosomal polycystic kidney disease (ADPKD). The development of ADPKD is associated with the progression of renal fibrosis. Whether renal fibrosis in ADPKD is a direct effect of PKD 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. METHOD Unilateral ureteral obstruction (UUO), unilateral ischemia-reperfusion injury (UIRI) and aristolochic acid nephropathy mouse models were established. Mice were treated with vehicle or triptolide. Western blotting and Masson's trichrome staining were performed to evaluate renal fibrosis. Moreover, human kidney 2 (HK2) cells and normal rat kidney 49F (NRK-49F) cells were used as in vitro models. RESULTS 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. Moreover, 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. Finally, using Pkd2 conditional knockout mice, we showed that heterozygous or homozygous deletion of Pkd2 reduced the expression of pro-fibrotic markers in UUO kidneys. Polycystin-1 was also up-regulated in three renal fibrotic models and conditional deletion of Pkd1 reduced the expression of pro-fibrotic markers in UUO or folic acid-induced fibrotic kidneys. Furthermore, conditional knockout of the methyltransferase EZH2 attenuated the anti-fibrotic responses induced by PKD1 deletion in UUO kidneys. CONCLUSION Polycystins are pro-fibrotic proteins in injured kidneys suggesting that renal fibrosis in ADPKD kidneys is not a direct effect of PKD mutation.