Bile acids (BA) are signalling molecules which activate the transmembrane receptor TGR5 and the nuclear receptor FXR. BA sequestrants (BAS) complex BA in the intestinal lumen and decrease intestinal FXR activity. The BAS-BA complex also induces Glucagon-Like Peptide-1 (GLP-1) production by L-cells which potentiates β-cell glucose-induced insulin secretion. Whether FXR is expressed in L-cells and controls GLP-1 production is unknown. Here we show that FXR activation in L-cells decreases proglucagon expression by interfering with the glucose-responsive factor Carbohydrate-Responsive Element Binding Protein (ChREBP) and GLP-1 secretion by inhibiting glycolysis. In vivo, FXR-deficiency increases GLP-1 gene expression and secretion in response to glucose hence improving glucose metabolism. Moreover, treatment of ob/ob mice with the BAS colesevelam increases intestinal proglucagon gene expression and improves glycemia in a FXR-dependent manner. These findings identify the FXR/GLP-1 pathway as a new mechanism of BA control of glucose metabolism and a pharmacological target for type 2 diabetes.

OBJECTIVEBile acids (BA) participate in the maintenance of metabolic homeostasis acting through different signaling pathways. The nuclear BA receptor farnesoid X receptor (FXR) regulates pathways in BA, lipid, glucose, and energy metabolism, which become dysregulated in obesity. However, the role of FXR in obesity and associated complications, such as dyslipidemia and insulin resistance, has not been directly assessed.RESEARCH DESIGN AND METHODSHere, we evaluate the consequences of FXR deficiency on body weight development, lipid metabolism, and insulin resistance in murine models of genetic and diet-induced obesity.RESULTSFXR deficiency attenuated body weight gain and reduced adipose tissue mass in both models. Surprisingly, glucose homeostasis improved as a result of an enhanced glucose clearance and adipose tissue insulin sensitivity. In contrast, hepatic insulin sensitivity did not change, and liver steatosis aggravated as a result of the repression of β-oxidation genes. In agreement, liver-specific FXR deficiency did not protect from diet-induced obesity and insulin resistance, indicating a role for nonhepatic FXR in the control of glucose homeostasis in obesity. Decreasing elevated plasma BA concentrations in obese FXR-deficient mice by administration of the BA sequestrant colesevelam improved glucose homeostasis in a FXR-dependent manner, indicating that the observed improvements by FXR deficiency are not a result of indirect effects of altered BA metabolism.CONCLUSIONSOverall, FXR deficiency in obesity beneficially affects body weight development and glucose homeostasis.

. We report here that peripheral blood mononuclear cells (PBMC) from individuals with the CX3CR1-IM haplotype adhered more potently to membrane-bound CX3CL1 than did PBMC from homozygous CX3CR1-VT donors. Similar excess adhesion was observed with CX3CR1-IMtransfected human embryonic kidney (HEK) cell lines tested with two different methods: the parallel plate laminar flow chamber and the dual pipette aspiration technique. Suppression of the extra adhesion in the presence of pertussis toxin indicates that G-protein mediated the underlying transduction pathway, in contrast to the G-protein-independent adhesion previously described for CX3CR1-VT. Surprisingly, HEK and PBMC that expressed CX3CR1-IM and -VT were indistinguishable when tested with the soluble form of CX3CL1 for chemotaxis, calcium release, and binding capacity. In conclusion, only the membrane-anchored form of CX3CL1 functionally discriminated between these two allelic isoforms of CX3CR1. These results suggest that each form of this ligand may lead to a different signaling pathway. The extra adhesion of CX3CR1-IM may be related to immune defenses and to atherogenesis, both of which depend substantially on adhesive intercellular events.Adhesion, a critical stage in cell trafficking and migration (1, 2), requires the presence of numerous adhesion molecules, such as integrins, that need divalent ions to function. Recent studies show that two chemokines, namely, CX3CL1 and CXCL16, are not only chemoattractant as soluble molecules, but also function as adhesion molecules since they are membrane-anchored, regardless of the presence of divalent ions (3-7). The best known of these is CX3CL1, also called fractalkine. It is expressed on the surface of many types of cells, in particular interleukin-1-and tumor necrosis factor-activated endothelial (4) and dendritic cells (8), as a membrane molecule containing the classic chemokine domain, a mucin-like stalk, and a transmembrane domain tethering it to the cell membrane. CX3CL1 may be cleaved by TACE and released from cells (9, 10). In this soluble form, it behaves like a chemoattractant molecule, just as other chemokines do. The transmembrane feature of the native CX3CL1 protein, combining it with its receptor, CX3CR1, produces a strongly adhesive pair (4, 5, 11) that mediates the rapid capture and firm adhesion of leukocytes. Because this activity persists in the absence of divalent cations, it is thought to be independent of integrins (5,11,12). This adhesive feature is also independent of the G i pathway, since it is still present after pertussis toxin (PTX) 1 treatment (4, 5, 11). The CX3CR1 molecule is expressed on leukocytes, especially monocytes (4) and cytotoxic cells (13,14), on dendritic cells (15), and on neurons and microglial cells (16,17). Recently, we identified two common polymorphisms in strong linkage disequilibrium in the CX3CR1 gene: V249I and T280M (18). We also found that these mutations are associated with more rapid progression to AIDS (18,19), although two studies have failed to confirm t...