Global Transcriptomics of Congenital Hepatic Fibrosis in Autosomal Recessive Polycystic Kidney Disease using PCK rats

Abstract

Congenital hepatic fibrosis / Autosomal recessive polycystic kidney disease (CHF/ARPKD) is an inherited neonatal disease induced by mutations in the PKHD1 gene and characterized by cysts, and robust pericystic fibrosis in liver and kidney. The PCK rat is an excellent animal model which carries a Pkhd1 mutation and exhibits similar pathophysiology. We performed RNA-Seq analysis on liver samples from PCK rats over a time course of postnatal day (PND) 15, 20, 30, and 90 using age-matched Sprague-Dawley (SD) rats as controls to characterize molecular mechanisms of CHF/ARPKD pathogenesis. A comprehensive differential gene expression (DEG) analysis identified 1298 DEGs between PCK and SD rats. The genes overexpressed in the PCK rats at PND 30 and 90 were involved cell migration (e.g. Lamc2, Tgfb2, and Plet1), cell adhesion (e.g. Spp1, Adgrg1, and Cd44), and wound healing (e.g. Plat, Celsr1, Tpm1). Connective tissue growth factor (Ctgf) and platelet-derived growth factor (Pdgfb), two genes associated with fibrosis, were upregulated in PCK rats at all time-points. Genes associated with MHC class I molecules (e.g. RT1-A2) or involved in ribosome assembly (e.g. Pes1) were significantly downregulated in PCK rats. Upstream regulator analysis showed activation of proteins involved tissue growth (MTPN) and inflammation (STAT family members) and chromatin remodeling (BRG1), and inhibition of proteins involved in hepatic differentiation (HNF4) and reduction of fibrosis (SMAD7). The increase in mRNAs of four top upregulated genes including Reg3b, Aoc1, Tm4sf20, and Cdx2 was confirmed at the protein level using immunohistochemistry. In conclusion, these studies indicate that a combination of increased inflammation, cell migration and wound healing, and inhibition of hepatic function, decreased antifibrotic gene expression are the major underlying pathogenic mechanisms in CHF/ARPKD.