Interest in how the gut microbiome can influence the metabolic state of the host has recently heightened. One postulated link is bacterial fermentation of “indigestible” prebiotics to short-chain fatty acids (SCFAs), which in turn modulate the release of gut hormones controlling insulin release and appetite. We show here that SCFAs trigger secretion of the incretin hormone glucagon-like peptide (GLP)-1 from mixed colonic cultures in vitro. Quantitative PCR revealed enriched expression of the SCFA receptors ffar2 (grp43) and ffar3 (gpr41) in GLP-1–secreting L cells, and consistent with the reported coupling of GPR43 to Gq signaling pathways, SCFAs raised cytosolic Ca2+ in L cells in primary culture. Mice lacking ffar2 or ffar3 exhibited reduced SCFA-triggered GLP-1 secretion in vitro and in vivo and a parallel impairment of glucose tolerance. These results highlight SCFAs and their receptors as potential targets for the treatment of diabetes.

The gut endocrine system is emerging as a central player in the control of appetite and glucose homeostasis, and as a rich source of peptides with therapeutic potential in the field of diabetes and obesity. In this study we have explored the physiology of insulin-like peptide 5 (Insl5), which we identified as a product of colonic enteroendocrine L-cells, better known for their secretion of glucagon-like peptide-1 and peptideYY. i.p. Insl5 increased food intake in wild-type mice but not mice lacking the cognate receptor Rxfp4. Plasma Insl5 levels were elevated by fasting or prolonged calorie restriction, and declined with feeding. We conclude that Insl5 is an orexigenic hormone released from colonic L-cells, which promotes appetite during conditions of energy deprivation.

Changes in cytoplasmic Ca 2+ levels regulate a variety of fundamental cellular functions in virtually all cells. In nonexcitable cells, a major pathway of Ca 2+ entry involves receptor-mediated depletion of intracellular Ca 2+ stores followed by the activation of store-operated calcium channels in the plasma membrane. We have established a mouse line expressing an activating EF hand motif mutant of stromal interaction molecule 1 (Stim1), an ER receptor recently identified as the Ca 2+ sensor responsible for activation of Ca 2+ releaseactivated (CRAC) channels in T cells, whose function in mammalian physiology is not well understood. Mice expressing mutant Stim1 had macrothrombocytopenia and an associated bleeding disorder. Basal intracellular Ca 2+ levels were increased in platelets, which resulted in a preactivation state, a selective unresponsiveness to immunoreceptor tyrosine activation motif-coupled agonists, and increased platelet consumption. In contrast, basal Ca 2+ levels, but not receptor-mediated responses, were affected in mutant T cells. These findings identify Stim1 as a central regulator of platelet function and suggest a cell type-specific activation or composition of the CRAC complex. IntroductionThe regulation of intracellular Ca 2+ ([Ca 2+ ] i ) is essentially involved in signaling processes in virtually all cells. In nonexcitable cells, including hematopoietic cells, Ca 2+ is released from the ER via inositol 1,4,5-triphosphate-mediated (IP 3 -mediated) receptor activation triggered by ligand-activated plasma membrane receptors. If the limited Ca 2+ reservoir of the ER becomes exhausted, extracellular Ca 2+ enters the cytoplasm by a mechanism known as store-operated Ca 2+ entry (SOCE) (1, 2). Although electrophysiologically well defined for more than a decade, the molecular identity of the pivotal proteins undoubtedly involved in SOCE has been discovered only recently. Stromal interaction molecule 1 (Stim1) is an ER resident protein necessary for the detection of ER Ca 2+ depletion (3-6). The 4-transmembrane domain protein Orai1, or CRACM, was reported recently to confer SOC activity (4,(7)(8)(9)(10)(11)(12). In T cells, Orai1 appears to be the predominant SOC (9), despite the fact that the C-terminal region of Stim1 has been shown to also interact with other SOC candidates such as transient receptor potential channels (TRPCs) 1,

The identification of specific genetic loci that contribute to inflammatory and autoimmune diseases has proved difficult due to the contribution of multiple interacting genes, the inherent genetic heterogeneity present in human populations, and a lack of new mouse mutants. By using N-ethyl-N-nitrosourea (ENU) mutagenesis to discover new immune regulators, we identified a point mutation in the murine phospholipase Cg2 (Plcg2) gene that leads to severe spontaneous inflammation and autoimmunity. The disease is composed of an autoimmune component mediated by autoantibody immune complexes and B and T cell independent inflammation. The underlying mechanism is a gain-of-function mutation in Plcg2, which leads to hyperreactive external calcium entry in B cells and expansion of innate inflammatory cells. This mutant identifies Plcg2 as a key regulator in an autoimmune and inflammatory disease mediated by B cells and non-B, non-T haematopoietic cells and emphasizes that by distinct genetic modulation, a single point mutation can lead to a complex immunological phenotype.

IntroductionAutoinflammatory diseases are systemic conditions involving apparently unprovoked inflammation in the absence of autoantibody-and antigenic-specific T cells. A significant proportion of these diseases is caused by single gene mutations. Furthermore, the mutated gene remains to be discovered in a number of Mendelian inherited autoinflammatory diseases. 1 Identifying the genes involved is a first step toward elucidating the pathways involved in the inflammatory processes underlying these diseases. Among the genes recently identified as causal is the gene encoding the TNF receptor, which has long been recognized for its role in inflammation and immunity. TNF receptor-associated periodic syndrome (TRAPS) is caused by mutations in the extracellular domain of the 55-kDa TNF receptor that lead to a dominantly inherited periodic fever. 2 Leukocytes from some, but not all, of these patients have increased membrane TNFRS1A and impaired receptor ectodomain cleavage on in vitro stimulation, consistent with a deficiency in a normal negative homeostatic process. 3 Two autoinflammatory periodic fever syndromes in which the mutated gene has been identified recently point to a common pathway. 4 Familial Mediterranean fever (FMF) is an autosomal recessive disorder resulting from mutations in the gene encoding pyrin, which normally inhibits pro-IL-1␤ cytokine processing to the active form. It has recently been shown that mutations in the structural gene encoding Pombe Cdc15 homology (PCH) family protein, proline serine threonine phosphatase-interacting protein 1/CD2 binding protein 1 (PSTPIP1/ CD2BP1), 5 lead to an autosomal-dominant autoinflammatory disease called pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome. 6 These mutations lead to decreased binding of PSTPIP1 to a protein tyrosine phosphatase, PTP-PEST, that specifically dephosphorylates PSTPIP1. 6,7 Subsequent studies by Shoham et al 8 showed that pyrin, the protein involved in FMF, interacts with PSTPIP1, thus establishing an important biochemical link between the proteins involved in these 2 diseases. Clearly, identification of the genes mutated in autoinflammatory diseases such as TRAPS, FMF, and PAPA, coupled with increased understanding of the functions of the proteins encoded by them, promises to greatly increase our knowledge of the mechanisms that mediate leukocyte inflammatory responses.PCH proteins constitute an extensive protein family involved in the regulation of actin polymerization and actin-based processes, including membrane ruffling, formation of filopodia, cell adhesion, and cytokinesis. [9][10][11][12][13][14][15] The PCH protein, macrophage actin-associated tyrosine phosphorylated protein (MAYP), 11 closely related to PSTPIP1 and also known as PSTPIP2, 12 is expressed in macrophages and macrophage-containing tissues. 11 Like that of PSTPIP1 and the other PCH family members, its domain organization includes an amino-terminal Fes-CIP4 homology (FCH) domain For personal use only. on May 9, 2018. by guest www.bloodjournal.or...