Ron receptor regulates Kupffer cell-dependent cytokine production and hepatocyte survival following endotoxin exposure in mice

Abstract

Previous studies demonstrated that targeted deletion of the Ron receptor tyrosine kinase (TK) domain in mice leads to marked hepatocyte protection in a well-characterized model of lipopolysaccharide (LPS)-induced acute liver failure in D-galactosamine (GalN)-sensitized mice. Hepatocyte protection in TK2/2 mice was observed despite paradoxically elevated serum levels of tumor necrosis factor alpha (TNF-a). To understand the role of Ron in the liver, purified populations of Kupffer cells and hepatocytes from wildtype (TK1/1) and TK2/2 mice were studied. Utilizing quantitative reverse-transcription polymerase chain reaction (RT-PCR), we demonstrated that Ron is expressed in these cell types. Moreover, we also recapitulated the protected hepatocyte phenotype and exaggerated cytokine production observed in the TK2/2 mice in vivo through the use of purified cultured cells ex vivo. We show that isolated TK2/2 Kupffer cells produce increased levels of TNF-a and select cytokines compared to TK1/1 cells following LPS stimulation. We also show that conditioned media from LPS-treated TK2/2 Kupffer cells was more toxic to hepatocytes than control media, suggesting the exaggerated levels of cytokines produced from the TK2/2 Kupffer cells are detrimental to wildtype hepatocytes. In addition, we observed that TK2/2 hepatocytes were more resistant to cell death compared to TK1/1 hepatocytes, suggesting that Ron functions in both the epithelial and inflammatory cell compartments to regulate acute liver injury. These findings were confirmed in vivo in mice with hepatocyte and macrophage cell-type-specific conditional Ron deletions. Mice with Ron loss selectively in hepatocytes exhibited less liver damage and increased survival compared to mice with Ron loss in macrophages. Conclusion: We dissected cell-type-specific roles for Ron such that this receptor modulates cytokine production from Kupffer cells and inhibits hepatocyte survival in response to injury. (HEPATOLOGY 2011;53:1618-1628

MSP: An emerging player in metabolic syndrome

“…It is possible that those contradictory results are due to different target cells in the liver. This view is supported by a follow-up study by Stuart et al, which used Kupffer cells and hepatocytes from RON TK À/À mice and demonstrated that RON TK À/À Kupffer cells treated with LPS lead to remarkable up-regulation of serum TNF-a level, whereas RON TK À/À hepatocytes exhibited an increased resistance to inflammatory factors and cell death in comparison with normal genotypic hepatocytes [2]. Mechanisms behind the opposing MSP effects in hepatocytes and Kupffer cells are not clarified yet, however, it was suggested that the hepatocyte-protective effect may come from the early increase of TNF-a, since the TNF-a increase in early stage actually could be beneficial to hepatocytes [52].…”

“…RON À/À mice with LPS-induced acute endotoxemia exhibited lowered anti-inflammatory cytokine-interleukin 10 (IL-10) mRNA expression in the liver compared with wild-type mice, accompanied with deceased level of superoxide dismutase (SOD), an important antioxidant enzyme that works against oxidative stress in liver [50]. To block the intracellular signaling of MSP-RON, mice with deletion of tyrosine kinase domain of RON (RON TK À/À mice) were used in several studies [2,51,52]. In a model of acute liver failure, it was shown that RON TK À/À mice were more prone to severe inflammation showing an increased TNF-a level and a decreased IL-10 level in serum, in response to LPS and galactosamine (GalN).…”

“…MSP was later shown to be involved in inflammatory responses and following studies demonstrated MSP to be a crucial regulator of inflammation in multiple animal disease models of the liver, kidney, lung, gut and other organs [2][3][4][5]. Studies showed that homozygous MSP knockout mice (MSP À/À mice) were viable without any obvious abnormalities, however they developed hepatic steatosis even fed on normal chow diet [6].…”

Small interfering RNA-directed targeting of RON alters invasive and oncogenic phenotypes of human hepatocellular carcinoma cells

“…Also, RON has been shown to be overexpressed at mRNA and protein levels in HCC (28). Various cytokines including hepatocyte growth factor, TNF-α, IL-1 and IL-6 increase RON expression in lipopolysaccharideinduced murine model of acute liver failure and HCC cell line (28)(29)(30). Therefore, induction of RON by these cytokines may play an important role in development and progression of HCC.…”

Conditional Deletion of β-Catenin in Mammary Epithelial Cells of Ron Receptor, Mst1r, Overexpressing Mice Alters Mammary Tumorigenesis

“…qRT-PCR was performed using an ABI7900HT (Applied Biosystems by Life Technologies, Carlsbad, CA) as previously described (19,22). Briefly, independent mammary gland or tumor RNA preparations from six mice of each genotype were made at the time points indicated.…”