Role of the ER stress in prostaglandin E2/E-prostanoid 2 receptor involved TGF- β 1-induced mice mesangial cell injury

This study aims to investigate the relationship between prostaglandin E2 E-prostanoid 2 receptor (EP2) and Endoplasmic reticulum (ER) stress in transforming growth factor- β 1 (TGF- β 1)-induced mouse glomerular mesangial cells (MCs) injury. We cultured primary WT, EP2 −/− MCs (EP2 deleted), and adenovirus-EP2-infected WT MCs (EP2 overexpressed). PCR, Western blot, flow cytometry, and immunohistochemical technique were used in in vitro and in vivo experiments. We found that TGF- β 1-induced PGE2 synthesis decreased in EP2-deleted MCs and increased in EP2-overexpressed MCs. EP2 deficiency in these MCs augmented the coupling of TGF- β 1 to ER stress-associated proteins [chaperone glucose-regulated protein 78 (GRP78), transient receptor potential channel 1 (TRPC1), and transient receptor potential channel 4 (TRPC4)], and upregulation of EP2 showed no significant change of GRP78, but augmented the expression of TRPC1, while TRPC4 expression was downregulated in comparison to normal MCs. In addition, EP2 deficiency in MCs augmented TGF- β 1-induced fibronectin (FN), cyclooxygenase-2 (COX2), and CyclinD1 expression. Silencing of EP2 also strengthened TGF- β 1-induced extracellular-signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Flow Cytometry showed that silencing of EP2 significantly promoted the apoptosis of MCs. In contrast, EP2 overexpression reversed the effects of EP2 deficiency. 8 weeks after 5/6 nephrectomy (N x ), blood urea nitrogen and creatinine concentrations were significantly increased in EP2 −/− 5/6N x mice as compared to those of WT 5/6N x mice. The pathological changes in kidney of EP2 −/− mice were markedly aggravated compared with WT mice. Immunohistochemical analysis showed significant augment of TRPC4 and ORP150 in the kidney of EP2 −/− mice compared with WT mice. Considering all the findings, it is suggested that increased expression of EP2 may prevent TGF- β 1-induced MCs damage through ER stress regulatory pathway.