The intrinsic prostaglandin E2-EP4 system of the renal tubular epithelium limits the development of tubulointerstitial fibrosis in mice

Inflammatory responses in the kidney lead to tubulointerstitial fibrosis, a common feature of chronic kidney diseases. Here we examined the role of prostaglandin E2 (PGE2) in the development of tubulointerstitial fibrosis. In the kidneys of wild-type mice, unilateral ureteral obstruction leads to progressive tubulointerstitial fibrosis with macrophage infiltration and myofibroblast proliferation. This was accompanied by an upregulation of COX-2 and PGE2 receptor subtype EP4 mRNAs. In the kidneys of EP4 gene knockout mice, however, obstruction-induced histological alterations were significantly augmented. In contrast, an EP4-specific agonist significantly attenuated these alterations in the kidneys of wild-type mice. The mRNAs for macrophage chemokines and profibrotic growth factors were upregulated in the kidneys of wild-type mice after ureteral obstruction. This was significantly augmented in the kidneys of EP4-knockout mice and suppressed by the EP4 agonist but only in the kidneys of wild-type mice. Notably, COX-2 and MCP-1 proteins, as well as EP4 mRNA, were localized in renal tubular epithelial cells after ureteral obstruction. In cultured renal fibroblasts, another EP4-specific agonist significantly inhibited PDGF-induced proliferation and profibrotic connective tissue growth factor production. Hence, an endogenous PGE2-EP4 system in the tubular epithelium limits the development of tubulointerstitial fibrosis by suppressing inflammatory responses.