Nonalcoholic steatohepatitis (NASH) is a hepatic manifestation of metabolic syndrome. Although the prostaglandin (PG)I2 receptor IP is expressed broadly in the liver, the role of PGI2-IP signaling in the development of NASH remains to be determined. Here, we investigated the role of the PGI2-IP system in the development of steatohepatitis using mice lacking the PGI2 receptor IP [IP-knockout (IP-KO) mice] and beraprost (BPS), a specific IP agonist. IP-KO and wild-type (WT) mice were fed a methionine- and choline-deficient diet (MCDD) for 2, 5, or 10 wk. BPS was administered orally to mice every day during the experimental periods. The effect of BPS on the expression of chemokine and inflammatory cytokines was examined also in cultured Kupffer cells. WT mice fed MCDD developed steatohepatitis at 10 wk. IP-KO mice developed steatohepatitis at 5 wk with augmented histologic derangements accompanied by increased hepatic monocyte chemoattractant protein-1 (MCP-1) and TNF-α concentrations. After 10 wk of MCDD, IP-KO mice had greater hepatic iron deposition with prominent oxidative stress, resulting in hepatocyte damage. In WT mice, BPS improved histologic and biochemical parameters of steatohepatitis, accompanied by reduced hepatic concentration of MCP-1 and TNF-α. Accordingly, BPS suppressed the LPS-stimulated Mcp-1 and Tnf-α mRNA expression in cultured Kupffer cells prepared from WT mice. PGI2-IP signaling plays a crucial role in the development and progression of steatohepatitis by modulating the inflammatory response, leading to augmented oxidative stress. We suggest that the PGI2-IP system is an attractive therapeutic target for treating patients with NASH.-Kumei, S., Yuhki, K.-I., Kojima, F., Kashiwagi, H., Imamichi, Y., Okumura, T., Narumiya, S., Ushikubi, F. Prostaglandin I2 suppresses the development of diet-induced nonalcoholic steatohepatitis in mice.
