PAR-1 mediates the thrombin-induced mesothelial cell overproduction of VEGF and PAI-1

Purpose: Thrombin mediates an excess in the production of neoangiogenetic (VEGF) and pro fibrotic (PAI-1) factors in human peritoneal mesothelial cells (HMC). The mechanisms leading to this overproduction have not been elucidated so far; in the context of peritoneal dialysis it can result in impaired peritoneal membrane function. Objectives: This study was performed to evaluate the presence of the thrombin receptor Protease-activated receptor-1 (PAR-1) in HMC and to characterize its function in the thrombin-dependent effects mentioned above. Methods: All experiments were performed using cultured primary HMC. Real-Time PCR and Western Blot were used to evaluate PAR-1; ELISA and Real-Time PCR were employed to examine PAR-1 effects on target mediators. Results: We found that cultivated primary HMC show a basal presence of PAR-1. Stimulation with IL-1 beta induced an increase of the mesothelial PAR-1 expression whereas stimulation with glycosilated human serum albumin or the ligand thrombin itself resulted in decreased PAR-1 expression. Stimulation with the specific PAR-1 ligand TFLLR-NH2 caused increased VEGF and PAI-1 levels similar to stimulation with thrombin, whereas preincubation with PAR-1 blocking antibodies ATAP2 and WEDE15 attenuated the thrombin-induced overproduction of VEGF and PAI-1. Conclusions: HMC express PAR-1 and the receptor is involved in thrombin effects on these cells. These findings may be a basis for pharmacological prevention of neoangiogenesis and adhesions in the context of peritoneal dialysis and peritonitis.