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 PKD1 (encoding polycystin-1) or PKD2 (encoding polycystin-2) gene cause autosomal dominant polycystic kidney disease (ADPKD), however high levels of polycystins are detected in renal tissues of ADPKD patients. Animal studies showed that loss and gain of function of polycystins are both pathogenic and can induce cystic phenotype in the kidney, which are associated with enhanced renal fibrosis. Recent studies showed that increased expression of polycystins contributes to organ fibrosis. However, the role of polycystins in renal tubulointerstitial fibrosis remains unclear. In this study, we demonstrated that polycystin-1 or polycystin-2 was highly expressed in the kidney of two different fibrotic mouse models and positively correlated with expression of collagen-I. Pharmaceutical inhibition of polycystin-2 with triptolide or genetic knockout of polycystin-2 reduced the expression of epithelial-mesenchymal transition (EMT) markers and deposition of extracellular matrix proteins in fibrotic kidneys. Similarly, conditional knockout of Pkd1 gene also attenuated renal fibrosis in mouse models. Thus, we further hypothesized that inhibition of polycystins delays cyst growth by mitigating renal fibrosis. Here, we showed that polycystin-1 or polycystin-2 was up-regulated in Pkd2 or Pkd1 mice respectively and tightly correlated with the growth of renal cysts and fibrosis development. Genetic deletion of both polycystin-1 and polycystin-2 retarded cyst growth in Pkd1 or Pkd2 mice. Finally, we deleted pkd1 gene in a fibrosis triggered adult ADPKD mouse model at different time point before or after the fibrotic injury. We showed that early and long-term inactivation of Pkd1 delayed fibrosis triggered renal cyst growth in adult Pkd1 mice as compared with mice with late and short-term inactivation of Pkd1 gene. We conclude that tubular obstruction induced polycystin up-regulation is pro-fibrotic and accelerates cyst growth through enhancing renal interstitial fibrosis in ADPKD mice. Our study indicates that ADPKD is caused by both loss and gain function of polycystins. Reduction of the aberrant upregulation of polycystins in cystic kidneys is a therapeutic option for ADPKD patients.