1These authors contributed equally to the work.Abbreviations used: 5-HT, serotonin or 5-hydroxytryptamine; CA, citric acid; CHO, Chinese hamster ovary; CV, circumvallate papillae; DB, denatonium benzoate; GLP-1, glucagon-like peptide 1; GLP-1R, GLP-1 receptor; KO, knockout; PC, proconvertase; PGP 9.5, protein gene product 9.5; PKD2 L1, polycystic kidney disease 2-like 1; TC, taste cell; WT, wild-type. AbstractIn many sensory systems, stimulus sensitivity is dynamically modulated through mechanisms of peripheral adaptation, efferent input, or hormonal action. In this way, responses to sensory stimuli can be optimized in the context of both the environment and the physiological state of the animal. Although the gustatory system critically influences food preference, food intake and metabolic homeostasis, the mechanisms for modulating taste sensitivity are poorly understood. In this study, we report that glucagon-like peptide-1 (GLP-1) signaling in taste buds modulates taste sensitivity in behaving mice. We find that GLP-1 is produced in two distinct subsets of mammalian taste cells, while the GLP-1 receptor is expressed on adjacent intragemmal afferent nerve fibers. GLP-1 receptor knockout mice show dramatically reduced taste responses to sweeteners in behavioral assays, indicating that GLP-1 signaling normally acts to maintain or enhance sweet taste sensitivity. A modest increase in citric acid taste sensitivity in these knockout mice suggests GLP-1 signaling may modulate sour taste, as well. Together, these findings suggest a novel paracrine mechanism for the regulation of taste function.

Sirt1 is an NAD+-dependent deacetylase that extends lifespan in lower organisms and improves metabolism and delays the onset of age-related diseases in mammals. Here we show that SRT1720, a synthetic compound that was identified for its ability to activate Sirt1 in vitro, extends both mean and maximum lifespan of adult mice fed a high-fat diet. This lifespan extension is accompanied by health benefits including reduced liver steatosis, increased insulin sensitivity, enhanced locomotor activity and normalization of gene expression profiles and markers of inflammation and apoptosis, all in the absence of any observable toxicity. Using a conditional SIRT1 knockout mouse and specific gene knockdowns we show SRT1720 affects mitochondrial respiration in a Sirt1- and PGC-1α-dependent manner. These findings indicate that SRT1720 has long-term benefits and demonstrate for the first time the feasibility of designing novel molecules that are safe and effective in promoting longevity and preventing multiple age-related diseases in mammals.

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Eating a “Westernized” diet high in fat and sugar leads to weight gain and numerous health problems, including the development of type 2 diabetes mellitus (T2DM). Rodent studies have shown that resveratrol supplementation reduces blood glucose levels, preserves β-cells in islets of Langerhans, and improves insulin action. Although rodent models are helpful for understanding β-cell biology and certain aspects of T2DM pathology, they fail to reproduce the complexity of the human disease as well as that of nonhuman primates. Rhesus monkeys were fed a standard diet (SD), or a high-fat/high-sugar diet in combination with either placebo (HFS) or resveratrol (HFS+Resv) for 24 months, and pancreata were examined before overt dysglycemia occurred. Increased glucose-stimulated insulin secretion and insulin resistance occurred in both HFS and HFS+Resv diets compared with SD. Although islet size was unaffected, there was a significant decrease in β-cells and an increase in α-cells containing glucagon and glucagon-like peptide 1 with HFS diets. Islets from HFS+Resv monkeys were morphologically similar to SD. HFS diets also resulted in decreased expression of essential β-cell transcription factors forkhead box O1 (FOXO1), NKX6–1, NKX2–2, and PDX1, which did not occur with resveratrol supplementation. Similar changes were observed in human islets where the effects of resveratrol were mediated through Sirtuin 1. These findings have implications for the management of humans with insulin resistance, prediabetes, and diabetes.

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The depletion of inositol trisphosphatesensitive intracellular pools of calcium causes activation of store-operated calcium (SOC) channels. Loperamide at 10-30 M has no effect on intracellular calcium levels alone, but augments calcium levels in cultured cells when SOC channels have been activated. In HL-60 leukemic cells, the apparent positive modulatory effect of loperamide on SOC channels occurs when these channels have been activated after ATP, thapsigargin, or ionomycin-elicited depletion of calcium from intracellular storage sites. Loperamide has no effect when levels of intracellular calcium are elevated through a mechanism not involving SOC channels by using sphingosine. Loperamide caused augmentation of intracellular calcium levels after activation of SOC channels in NIH 3T3 fibroblasts, astrocytoma 1321N cells, smooth muscle DDT-MF2 cells, RBL-2H3 mast cells, and pituitary GH 4 C 1 cells. Only in astrocytoma cells did loperamide cause an elevation in intracellular calcium in the absence of activation of SOC channels. The augmentation of intracellular calcium elicited by loperamide in cultured cells was dependent on extracellular calcium and was somewhat resistant to agents (SKF 96365, miconazole, clotrimazole, nitrendipine, and trif luoperazine) that in the absence of loperamide effectively blocked SOC channels. It appears that loperamide augments inf lux of calcium through activated SOC channels.The depletion of intracellular stores of calcium can result in the opening of calcium channels in the plasma membranes of cells (1). Such channels have been referred to as receptor-operated calcium channels, calcium-release-activated calcium channels, capacitative calcium entry channels, and store-operated calcium (SOC) channels. The mechanism(s) whereby depletion of inositol trisphosphate (IP 3 )-sensitive stores of calcium causes opening of SOC channels remains uncertain although several hypotheses have been advanced (2). SOC channels activate after receptor-mediated generation of IP 3 , which releases calcium from intracellular stores, or after treatment of cells with either the Ca 2ϩ -ATPase inhibitor thapsigargin, which blocks re-uptake of calcium into storage sites, or with the calcium ionophore ionomycin, which directly mobilizes calcium from storage sites. SOC channels can be blocked by imidazoles such as SKF 96365, clotrimazole, and miconazole and a small selection of other agents (3-6). Recently, loperamide was found to augment levels of intracellular calcium in HL-60 cells in which SOC channels were activated after P 2Y -receptor-mediated formation of IP 3 and release of intracellular calcium (6). The augmentation by loperamide of SOC channel-mediated elevation of intracellular calcium levels now has been shown to be a general phenomenon, occurring in several cell types after receptor-, thapsigargin-, or ionomycininduced activation of SOC channels. Loperamide appears to be a novel agent for the study of SOC channels and their functional role in cells. MATERIALS AND METHODSLoperamide, econazo...