MiR-503-5p mediates cell cycle arrest and fibrosis of peritoneal mesothelial cells with a high peritoneal solute transport status

Background Long-term peritoneal dialysis (PD) induces persistent inflammation and fibrosis of the peritoneal membrane (PM), altering the peritoneal solute transport rate (PSTR). We previously found elevated miR-503-5p levels in exosomes from PD effluent (PDE) in patients with high PSTR. As PSTR is strongly influenced by intraperitoneal inflammation, this study aimed to explore the relationship between miR-503-5p, inflammation, and peritoneal fibrosis and the underlying mechanisms. Methods Bioinformatics analyses were initially performed to identify the miR-503-5p target genes and determine the research subject. Real-time polymerase chain reaction (RT-PCR), miRNA RT-PCR, and western blotting were used to detect the expression levels of miR-503-5p and its targets in human MeT-5A mesothelial cells. A cell counting kit-8 assay was used to ascertain the impact of miR-503-5p on cellular proliferation, and cell cycle was evaluated using a FACScan flow cytometer. The miR-503-5p target genes were identified using mimic/inhibitor transfection and dual-luciferase reporter assays. PDE-exos labeled with PKH67 were used to observe their interactions with MeT-5A cells. Results Patients with PD who exhibited an increasing PSTR had notably elevated dialysate interleukin-6 concentrations, which demonstrated a positive correlation with the PSTR. The induction of lipopolysaccharides remarkably enhanced the expression of miR-503-5p in peritoneal mesothelial cells (PMCs). Overexpression of miR-503-5p induced cell cycle arrest in the G1/S phase and notably upregulated the expression of fibrotic indicators (alpha-smooth muscle actin and type I collagen) in PMCs. Cyclin D1 was a direct target of miR-503-5p and expressed in MeT-5A cells. Additionally, PKH67-labeled PDE-exos were internalized by MeT-5A cells. Conclusions Patients with PD who had a high PSTR exhibited an elevated inflammatory state, and the presence of inflammatory factors stimulated the upregulation of miR-503-5p expression, which led to cell cycle arrest in PMCs and promoted peritoneal fibrosis development.