Activation of the RAS contributes to peritoneal fibrosis via dysregulation of low-density lipoprotein receptor

Peritoneal dialysis (PD)-related peritoneal fibrosis (PF) is characterized by progressive extracellular matrix (ECM) accumulation in peritoneal mesothelial cells (PMCs) during long-term use of high glucose (HG)-based dialysates. Activation of the renin-angiotensin system (Ras) has been shown to be associated with PF. The aim of this study was to explore the underlying mechanism of the Ras in HG-induced PF. We treated C57BL/6 mice and a human PMC line with HG to induce a PF model and to stimulate ECM accumulation, respectively. Ras activity was blocked using valsartan or angiotensin II (ANGII) type 1 receptor siRNA. The major findings were as follows. First, mice in the HG group exhibited increased collagen deposition and expression of ECM proteins, including α-smooth muscle actin (α-SMA) and collagen type I in the peritoneum. Consistent with the in vivo data, HG upregulated α-SMA expression in human peritoneal mesothelial cells (HPMCs) in a time- and dose-dependent manner. Second, HG stimulation led to Ras activation in HPMCs, and inactivation of Ras decreased the expression of ECM proteins in vivo and in vitro, even during HG stimulation. Finally, RAS-mediated ECM production was associated with lipid accumulation in HPMCs and depended on the dysregulation of the low-density lipoprotein receptor (LDLR) pathway. HG-stimulated HPMCs showed increased coexpression of LDLR and α-SMA, whereas blockade of Ras activity reversed the effect. Furthermore, inhibition of LDLR signaling decreased α-SMA and collagen type I expression in HPMCs when treated with HG and ANG II. In conclusion, increased intracellular Ras activity impaired lipid homeostasis and induced ECM accumulation in HPMCs by disrupting the LDLR pathway, which contributed to PF.