Differential Insulin Secretion of High-Fat Diet-Fed C57BL/6NN and C57BL/6NJ Mice: Implications of Mixed Genetic Background in Metabolic Studies.

Many metabolic studies employ tissue-specific gene knockout mice, which requires breeding of floxed gene mice, available mostly on C57BL/6N (NN) genetic background, with cre or Flp recombinase-expressing mice, available on C57BL/6J (JJ) background, resulting in the generation of mixed C57BL/6NJ (NJ) genetic background mice. Recent awareness of many genetic differences between NN and JJ strains including the deletion of nicotinamide nucleotide transhydrogenase (nnt), necessitates examination of the consequence of mixed NJ background on glucose tolerance, beta cell function and other metabolic parameters. Male mice with NN and NJ genetic background were fed with normal or high fat diets (HFD) for 12 weeks and glucose and insulin homeostasis were studied. Genotype had no effect on body weight and food intake in mice fed normal or high fat diets. Insulinemia in the fed and fasted states and after a glucose challenge was lower in HFD-fed NJ mice, even though their glycemia and insulin sensitivity were similar to NN mice. NJ mice showed mild glucose intolerance. Moreover, glucose- but not KCl-stimulated insulin secretion in isolated islets was decreased in HFD-fed NJ vs NN mice without changes in insulin content and beta cell mass. Under normal diet, besides reduced fed insulinemia, NN and NJ mice presented similar metabolic parameters. However, HFD-fed NJ mice displayed lower fed and fasted insulinemia and glucose-induced insulin secretion in vivo and ex vivo, as compared to NN mice. These results strongly caution against using unmatched mixed genetic background C57BL/6 mice for comparisons, particularly under HFD conditions

Body weight, food intake, glycemia and insulinemia in ND- and HFD-fed NN and NJ mice.

<p>Body weight (A) and food intake (B). Glycemia and insulinemia in overnight fasted (C and E) or fed (D and F) mice. ND, normal diet; HFD, high fat diet. Results are means ± SEM of 7–9 mice in 2–3 independent experiments. *p<0.05 and **p<0.01 compared to NN mice (Student’s t-test).</p

a/b-Hydrolase Domain-6-Accessible Monoacylglycerol Controls Glucose-Stimulated Insulin Secretion

Glucose metabolism in pancreatic β cells stimulates insulin granule exocytosis, and this process requires generation of a lipid signal. However, the signals involved in lipid amplification of glucose-stimulated insulin secretion (GSIS) are unknown. Her

Insulin secretion in isolated islets from HFD-fed NN or NJ mice.

<p>Insulin secretion at 3 mM glucose plus 35 mM KCl and at 3, 8 and 16 mM glucose in the absence (3G, 8G and 16G) <b>(A)</b> or the presence <b>(B)</b> of palmitate/oleate (OP; 0.15mM each) (3G/OP, 8G/OP and 16G/OP) (n = 4–5 mice, 3–4 replicates/mouse). Insulin release was normalized for the total islet insulin content. Insulin content/10 islets <b>(C)</b>, pancreas weight <b>(D)</b> and beta-cell mass <b>(E)</b> of HFD-fed NN or NJ mice. Results are means ± SEM of 2–3 independent experiments. *p<0.05 and **p<0.01 compared to NN mice (Student’s t-test).</p

OGTT and ITT in NN and NJ mice.

<p>Glycemia <b>(A)</b> and insulinemia <b>(B)</b> were measured after glucose administration at time 0 in ND or HFD-fed NN and NJ mice and area under the curve (AUC) was calculated for glycemia <b>(D)</b> and insulinemia <b>(E)</b> curves. Glycemia during ITT and area above the curve (AAC) <b>(C and F)</b> in NN or NJ mice fed a HFD. Results are means ± SEM of 7–9 mice in 2–3 independent experiments. Glycemia was also measured after glucose administration in HFD-fed NN and NJ WT <b>(G)</b> or MCre <b>(H)</b> mice. In the same OGTT tests, insulinemia was measured in NN and NJ WT <b>(I)</b> or MCre <b>(J)</b> mice. Insets depict AUC for glycemia and insulinemia curves. Results are means ± SEM of 3 WT and 6 MCre mice/group in 2–3 independent experiments. *p<0.05 and **p<0.01 compared to NN mice under the same diet (two-way ANOVA and Bonferroni post hoc test or Student’s t-test).</p

α/β-Hydrolase Domain-6-Accessible Monoacylglycerol Controls Glucose-Stimulated Insulin Secretion

International audienceGlucose metabolism in pancreatic β cells stimulates insulin granule exocytosis, and this process requires generation of a lipid signal. However, the signals involved in lipid amplification of glucose-stimulated insulin secretion (GSIS) are unknown. Here we show that in β cells, glucose stimulates production of lipolysis-derived long-chain saturated monoacylglycerols, which further increase upon inhibition of the membrane-bound monoacylglycerol lipase α/β-Hydrolase Domain-6 (ABHD6). ABHD6 expression in β cells is inversely proportional to GSIS. Exogenous monoacylglycerols stimulate β cell insulin secretion and restore GSIS suppressed by the pan-lipase inhibitor orlistat. Whole-body and β-cell-specific ABHD6-KO mice exhibit enhanced GSIS, and their islets show elevated monoacylglycerol production and insulin secretion in response to glucose. Inhibition of ABHD6 in diabetic mice restores GSIS and improves glucose tolerance. Monoacylglycerol binds and activates the vesicle priming protein Munc13-1, thereby inducing insulin exocytosis. We propose saturated monoacylglycerol as a signal for GSIS and ABHD6 as a negative modulator of insulin secretion

α/β-Hydrolase Domain-6-Accessible Monoacylglycerol Controls Glucose-Stimulated Insulin Secretion

International audienceGlucose metabolism in pancreatic β cells stimulates insulin granule exocytosis, and this process requires generation of a lipid signal. However, the signals involved in lipid amplification of glucose-stimulated insulin secretion (GSIS) are unknown. Here we show that in β cells, glucose stimulates production of lipolysis-derived long-chain saturated monoacylglycerols, which further increase upon inhibition of the membrane-bound monoacylglycerol lipase α/β-Hydrolase Domain-6 (ABHD6). ABHD6 expression in β cells is inversely proportional to GSIS. Exogenous monoacylglycerols stimulate β cell insulin secretion and restore GSIS suppressed by the pan-lipase inhibitor orlistat. Whole-body and β-cell-specific ABHD6-KO mice exhibit enhanced GSIS, and their islets show elevated monoacylglycerol production and insulin secretion in response to glucose. Inhibition of ABHD6 in diabetic mice restores GSIS and improves glucose tolerance. Monoacylglycerol binds and activates the vesicle priming protein Munc13-1, thereby inducing insulin exocytosis. We propose saturated monoacylglycerol as a signal for GSIS and ABHD6 as a negative modulator of insulin secretion

Adipose ABHD6 regulates tolerance to cold and thermogenic programs

Enhanced energy expenditure in brown (BAT) and white adipose tissues (WAT) can be therapeutic against metabolic diseases. We examined the thermogenic role of adipose α/β-hydrolase domain 6 (ABHD6), which hydrolyzes monoacylglycerol (MAG), by employing adipose-specific ABHD6-KO mice. Control and KO mice showed similar phenotypes at room temperature and thermoneutral conditions. However, KO mice were resistant to hypothermia, which can be accounted for by the simultaneously increased lipolysis and lipogenesis of the thermogenic glycerolipid/free fatty acid (GL/FFA) cycle in visceral fat, despite unaltered uncoupling protein 1 expression. Upon cold stress, nuclear 2-MAG levels increased in visceral WAT of the KO mice. Evidence is provided that 2-MAG causes activation of PPARα in white adipocytes, leading to elevated expression and activity of GL/FFA cycle enzymes. In the ABHD6-ablated BAT, glucose and oxidative metabolism were elevated upon cold induction, without changes in GL/FFA cycle and lipid turnover. Moreover, response to in vivo β3-adrenergic stimulation was comparable between KO and control mice. Our data reveal a MAG/PPARα/GL/FFA cycling metabolic signaling network in visceral adipose tissue, which contributes to cold tolerance, and that adipose ABHD6 is a negative modulator of adaptive thermogenesis