Removing the Gβγ-SNAP25 brake on exocytosis enhances insulin action, promotes adipocyte browning, and protects against diet-induced obesity

Abstract

Negative regulation of exocytosis from secretory cells throughout the body is accomplished through inhibitory signals from Gi/o G protein-coupled receptors by G{beta}{gamma} subunit inhibition of two common mechanisms: (i) decreased calcium entry and (ii) direct interaction of G{beta}{gamma} with the Soluble N-ethylmaleimide-sensitive factor Attachment Protein (SNAP) Receptor (SNARE) plasma membrane fusion machinery. We have previously shown that disabling the second mechanism with a truncation of SNAP25 (SNAP25{Delta}3/{Delta}3) decreases the affinity of G{beta}{gamma} for the SNARE complex, leaving exocytotic fusion as well as modulation of calcium entry intact but disabling GPCR inhibition of exocytosis. Here we report significant beneficial metabolic remodeling in mice carrying this mutation. Chow-fed SNAP25{Delta}3/{Delta}3 mice exhibit enhanced insulin sensitivity and increased beiging of white fat. In response to a high fat diet, the metabolic protection was amplified in SNAP25{Delta}3/{Delta}3 mice. Glucose homeostasis, whole body insulin action, and insulin-mediated glucose uptake into white adipose tissue were improved along with resistance to diet-induced obesity. This metabolic protection in SNAP25{Delta}3/{Delta}3 mice occurred without compromising the physiological response to fasting or cold. All metabolic phenotypes were reversed at thermoneutrality, suggesting basal autonomic activity is required. Direct electrode stimulation of sympathetic neurons exocytosis from SNAP25{Delta}3/{Delta}3 inguinal adipose depot resulted in enhanced and prolonged norepinephrine release. Thus, the G{beta}{gamma}-SNARE interaction represents a cellular mechanism that deserves further exploration as a new avenue for combatting metabolic disease. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/069138v4_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@2c1fa0org.highwire.dtl.DTLVardef@d076ceorg.highwire.dtl.DTLVardef@27e351org.highwire.dtl.DTLVardef@bce219_HPS_FORMAT_FIGEXP M_FIG C_FIG