Disruption of low density lipoprotein receptor pathway is involved in peritoneal fibrosis induced by high glucose peritoneal dialysis solution

Abstract

Objective To explore the potential mechanisms of low density lipoprotein receptor (LDLr) in high glucose peritoneal dialysis solution (PDS)-induced peritoneal fibrosis. Methods Human peritoneal mesothelial cells (PMCs) were applied. In pre-experiment, human PMCs were cultured with 1.5% PDS, 2.5% PDS and 4.25% PDS for 6 h, 12 h and 24 h. 4.25% mannitol was used as high osmotic pressure control. In formal experiment, PMCs were divided into the control group(treated with phosphate buffer saline) and the high glucose PDS group (treated with 4.25% PDS for 24 h). Morphological change of PMCs was observed by inverted microscope. The mRNA and protein expressions of extracellular matrix proteins such as α-smooth muscle actin (α-SMA), fibroblast specific protein-1 (FSP-1) and collagenⅠ in PMCs were respectively measured by real-time PCR and Western blotting. The lipid accumulation was observed by oil red O staining and filipin staining, and the content of intracellular cholesterol ester was detected by high-performance liquid chromatography. The co-expression of the sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP) with golgin was observed with immunofluorescent staining. The mRNA and protein expressions of LDLr, SREBP-2 and SCAP were respectively detected by real-time PCR and Western blotting. The mRNA and protein expressions of mammalian target of rapamycin (mTOR), eukaryotic initiation factor 4E-binding protein 1 (4EBP1), and p70 S6 kinase (S6K1) were respectively detected by real-time PCR and Western blotting. Results (1) Compared with the 1.50% PDS stimulation, 4.25% PDS for 24 h intervention significantly increased the expression of LDLr in PMCs (P 0.05). (2) Compared with those in the control group, in high glucose PDS group PMCs showed notable elongation consistent with the morphology of myofibroblasts, the expressions of α-SMA, FSP-1 and collagen Ⅰ were increased (all P<0.05), and the intracellular cholesterol were enhanced (P<0.05). Meanwhile, the co-expression of SCAP with golgin was enhanced, and the mRNA and protein expressions of LDLr, SREBP-2 and SCAP were up-regulated in high glucose PDS group (all P<0.05). Further, the mRNA and protein phosphorylation of mTOR, 4EBP1 and S6K1 were increased (all P<0.05). Conclusions The disruption of LDLr feedback regulation is involved in high glucose PDS-mediated cholesterol accumulation in PMCs by mammalian target of rapamycin complex 1 (mTORC1) pathway, which promotes the accumulation of extracellular matrix and peritoneal fibrosis. Key words: Peritoneal dialysis; Receptors, LDL; Intracellular signaling peptides and proteins; Retroperitoneal fibrosis; Mechanistic target of rapamycin complex 1