Hepatocellular carcinoma (HCC), the fastest rising cancer in the United States and increasing in Europe, often occurs with nonalcoholic steatohepatitis (NASH). Mechanisms underlying NASH and NASH-induced HCC are largely unknown. We developed a mouse model recapitulating key features of human metabolic syndrome, NASH, and HCC by long-term feeding of a choline-deficient high-fat diet. This induced activated intrahepatic CD8(+) T cells, NKT cells, and inflammatory cytokines, similar to NASH patients. CD8(+) T cells and NKT cells but not myeloid cells promote NASH and HCC through interactions with hepatocytes. NKT cells primarily cause steatosis via secreted LIGHT, while CD8(+) and NKT cells cooperatively induce liver damage. Hepatocellular LTβR and canonical NF-κB signaling facilitate NASH-to-HCC transition, demonstrating that distinct molecular mechanisms determine NASH and HCC development.

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Free fatty acids (FFAs) play important physiological roles in many tissues as an energy source and as signaling molecules in various cellular processes. Elevated levels of circulating FFAs are associated with obesity, dyslipidemia, and diabetes. Here we show that GPR84, a previously orphan G protein-coupled receptor, functions as a receptor for medium-chain FFAs with carbon chain lengths of 9 -14. Medium-chain FFAs elicit calcium mobilization, inhibit 3,5-cyclic AMP production, and stimulate [ 35 S]guanosine 5-O-(3-thiotriphosphate) binding in a GPR84-dependent manner. The activation of GPR84 by medium-chain FFAs couples primarily to a pertussis toxin-sensitive G i/o pathway. In addition, we show that GPR84 is selectively expressed in leukocytes and markedly induced in monocytes/macrophages upon activation by lipopolysaccharide. Furthermore, we demonstrate that medium-chain FFAs amplify lipopolysaccharidestimulated production of the proinflammatory cytokine interleukin-12 p40 through GPR84. Our results indicate a role for GPR84 in directly linking fatty acid metabolism to immunological regulation.G protein-coupled receptors (GPCRs) 3 constitute one of the largest gene families yet identified (1, 2). It has been estimated that more than half of all modern drugs target these receptors (3, 4). GPCRs contain seven transmembrane domains and are activated by a wide variety of ligand types, including light, ions, amino acids, nucleotides, lipids, peptides, and proteins. In addition to about 250 characterized receptors, over 100 human genes encode proteins that belong to this family of receptors but for which ligands and functions remain to be determined (1). These orphan receptors are expected to play important roles in the regulation of a diversity of physiological functions.In the past decade an increasing number of GPCRs have been deorphanized. Many of the identified ligands are metabolic intermediates, including succinate (ligand for GPR91) (5), ␣-ketoglutarate (ligand for GPR99) (5), fatty acids (ligands for GPR40/41/43/120) (6 -10), ketone body (ligand for HM74a) (11), bile acids (ligands for BG37) (12), and kynurenic acid (ligand for GPR35) (13). We have built a library of biochemical intermediates to test their ability to activate orphan GPCRs. In this report, we have identified medium-chain FFAs as ligands for GPR84. Short-chain and long-chain saturated and unsaturated FFAs, previously shown to activate GPR40/41/43/120 (6 -10), are inactive at GPR84. GPR84 is an orphan GPCR originally isolated using an expressed sequence tag data mining strategy (14) and as a gene differentially expressed in granulocytes (15). No close homologs of GPR84 could be identified, although GPR84 is distantly related to monoamine receptors. Expression analysis revealed significant induction of GPR84 in monocytes/macrophages upon lipopolysaccharide (LPS) stimulation, suggesting that medium-chain FFAs may regulate inflammatory responses through activation of GPR84. EXPERIMENTAL PROCEDURESCloning and Cell Culture-Human and mouse GPR84 ...

Increased expression of the chemokine CCL2 in tumor cells correlates with enhanced metastasis, poor prognosis, and recruitment of CCR2 + Ly6C hi monocytes. However, the mechanisms driving tumor cell extravasation through the endothelium remain elusive. Here, we describe CCL2 upregulation in metastatic UICC stage IV colon carcinomas and demonstrate that tumor cell-derived CCL2 activates the CCR2 + endothelium to increase vascular permeability in vivo. CCR2 deficiency prevents colon carcinoma extravasation and metastasis. Of note, CCR2 expression on radio-resistant cells or endothelial CCR2 expression restores extravasation and metastasis in Ccr2 À/À mice. Reduction of CCR2 expression on myeloid cells decreases but does not prevent metastasis. CCL2-induced vascular permeability and metastasis is dependent on JAK2-Stat5 and p38MAPK signaling. Our study identifies potential targets for treating CCL2-dependent metastasis.