Ron receptor-dependent gene regulation of Kupffer cells during endotoxemia

BACKGROUND: Ron receptor tyrosine kinase signaling in macrophages, including Kupffer cells and alveolar macrophages,suppresses endotoxin-induced proinflammatory cytokine/chemokine production. Further, we have also identified genes from Ron replete and Ron deplete livers that were differentially expressed during the progression of liver inflammation associated with acute liver failure in mice by microarray analyses.While important genes and signaling pathways have been identified downstream of Ron signaling during progression of inflammation by this approach, the precise role that Ron receptor plays in regulating the transcriptional landscape in macrophages, and particular in isolated Kupffer cells, has still not been investigated.METHODS: Kupffer cells were isolated from wild-type(TK+/+)and Ron tyrosine kinase deficient(TK-/-) mice. Ex vivo, the cells were treated with lipopolysaccharide(LPS) in the presence or absence of the Ron ligand, hepatocyte growth factor-like protein(HGFL). Microarray and qRT-PCR analyses were utilized to identify alterations in gene expression between genotypes.RESULTS: Microarray analyses identified genes expressed differentially in TK+/+ and TK-/- Kupffer cells basally as well as after HGFL and LPS treatment. Interestingly, our studies identified Mefv, a gene that codes for the anti-inflammatory protein pyrin, as an HGFL-stimulated Ron-dependent gene.Moreover, lipocalin 2, a proinflammatory gene, which is induced by LPS, was significantly suppressed by HGFL treatment.Microarray results were validated by qRT-PCR studies on Kupffer cells treated with LPS and HGFL.CONCLUSION: The studies herein suggest a novel mechanism whereby HGFL-induced Ron receptor activation promotes the expression of anti-inflammatory genes while inhibiting genes involved in inflammation with a net effect of diminished inflammation in macrophages.

Ron receptor-dependent gene regulation in a mouse model of endotoxin-induced acute liver failure

BACKGROUND:Prior experimentation has shown that loss of the tyrosine kinase(TK) signaling domain of the Ron receptor leads to marked hepatocyte protection in a model of lipopolysaccharideinduced acute liver failure(ALF) in D-galactosamine(GalN)sensitized mice.The aim of this study was to identify the role of Ron in the regulation of hepatic gene expression.METHODS:Microarray analyses were performed on liver RNA isolated sequentially from wild-type(WT) and TK-/mice during the progression of ALF.Gene array data were validated using Western and immunohistochemistry analyses as well as with ex vivo culture systems.RESULTS:At baseline,101 genes were differentially expressed between WT and TK-/-livers,which regulate processes involved in hypoxia,proliferation,apoptosis and metabolism.One hour after ALF induction,WT livers exhibited increased cytokine expression compared to TK-/-livers,and after 4 hours,an induction of suppressor of cytokine signaling(SOCS) genes as well as JAK-STAT pathway activation were prominent in TK-/livers compared to controls.CONCLUSION:Our studies suggest a novel hepato-protective mechanism in Ron TK-/-mice wherein increased and sustained SOCS production and JAK-STAT activation in the hepatocyte may inhibit the destructive proinflammatory milieu and promote survival factors which blunt hepatic death and the ensuing development of ALF.