Search

Negative regulation of exocytosis from secretory cells is accomplished through inhibitory signals from [G.sub.i/o] GPCRs by G[beta][gamma] subunit inhibition of 2 mechanisms: decreased calcium entry and direct interaction of G[beta][gamma] with soluble N- ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) plasma membrane fusion machinery. Previously, we disabled the second mechanism with a SNAP25 truncation (SNAP25A3) that decreased G[beta][gamma] affinity for the SNARE complex, leaving exocytotic fusion and modulation of calcium entry intact and removing GPCR-G[beta][gamma] inhibition of SNARE- mediated exocytosis. Here, we report substantial metabolic benefit in mice carrying this mutation. Snap2SA3/A3 mice exhibited enhanced insulin sensitivity and beiging of white fat. Metabolic protection was amplified in Snap2SA3/A3 mice challenged with a high-fat diet. Glucose homeostasis, whole-body insulin action, and insulin-mediated glucose uptake into white adipose tissue were improved along with resistance to diet-induced obesity. Metabolic protection in [Snap25.sup.[DELTA]3/[DELTA]3] mice occurred without compromising the physiological response to fasting or cold. All metabolic phenotypes were reversed at thermoneutrality, suggesting that basal autonomic activity was required. Direct electrode stimulation of sympathetic neuron exocytosis from [Snap25.sup.[DELTA]3/[DELTA]3] inguinal adipose depots resulted in enhanced and prolonged norepinephrine release. Thus, the G[beta][gamma]-SNARE interaction represents a cellular mechanism that deserves further exploration as an additional avenue for combating metabolic disease., Introduction Metabolic diseases, such as diabetes and obesity, have an estimated annual global economic impact in the trillions of (US) dollars (1-5). Therapeutic approaches to lower metabolic risk include augmenting [...]

Cyclic nucleotides cAMP and cGMP are important second messengers for the regulation of adaptive thermogenesis. Their levels are controlled not only by their synthesis, but also their degradation. Since pharmacological inhibitors of cGMP-specific phosphodiesterase 9 (PDE9) can increase cGMP-dependent protein kinase signaling and uncoupling protein 1 expression in adipocytes, we sought to elucidate the role of PDE9 on energy balance and glucose homeostasis in vivo. Mice with targeted disruption of the PDE9 gene, Pde9a, were fed nutrient-matched high-fat (HFD) or low-fat diets. Pde9a-/- mice were resistant to HFD-induced obesity, exhibiting a global increase in energy expenditure, while brown adipose tissue (AT) had increased respiratory capacity and elevated expression of Ucp1 and other thermogenic genes. Reduced adiposity of HFD-fed Pde9a-/- mice was associated with improvements in glucose handling and hepatic steatosis. Cold exposure or treatment with β-adrenergic receptor agonists markedly decreased Pde9a expression in brown AT and cultured brown adipocytes, while Pde9a-/- mice exhibited a greater increase in AT browning, together suggesting that the PDE9-cGMP pathway augments classical cold-induced β-adrenergic/cAMP AT browning and energy expenditure. These findings suggest PDE9 is a previously unrecognized regulator of energy metabolism and that its inhibition may be a valuable avenue to explore for combating metabolic disease. [ABSTRACT FROM AUTHOR]