Supplementary Material for: Increased Energy Expenditure, Lipolysis and Hyperinsulinemia Confer Resistance to Central Obesity and Type 2 Diabetes in Mice Lacking Alpha2α-Adrenoceptors

The alpha2A-adrenoceptors (α_2A-ARs) are Gi-coupled receptors, which prejunctionally inhibit the release of norepinephrine (NE) and epinephrine (Epi), and postjunctionally inhibit insulin secretion and lipolysis. We have earlier shown that α_2A^–/– mice display sympathetic hyperactivity, hyperinsulinemia and improved glucose tolerance. Here we employed α_2A^–/– mice and placed the mice on a high-fat diet (HFD) to test the hypothesis that lack of α_2A-ARs protects from diet-induced obesity and type 2 diabetes (T2D). In addition, a high-caloric diet was combined with running wheel exercise to test the interaction of diet and exercise. HFD was obesogenic in both genotypes, but α_2A^–/– mice accumulated less visceral fat than the wild-type controls, were protected from T2D, and their insulin secretion was unaltered by the diet. Lack of α_2A-ARs is associated with an increased sympatho-adrenal tone, which resulted in increased energy expenditure and fat oxidation rate potentiated by HFD. Fittingly, α_2A^–/– mice displayed enhanced lipolytic responses to Epi, and increased faecal lipids suggesting altered fat mobilization and absorption. Subcutaneous white fat appeared to be thermogenically more active (measured as <i>Ucp1</i> mRNA expression) in α_2A^–/– mice, and brown fat showed an increased response to NE. Exercise was effective in reducing total body adiposity and increasing lean mass in both genotypes, but there was a significant diet-genotype interaction, as even modestly increased physical activity combined with lack of α_2A-AR signalling promoted weight loss more efficiently than exercise with normal α_2A-AR function. These results suggest that blockade of α_2A-ARs may be exploited to reduce visceral fat and to improve insulin secretion.

α₂A-肾上腺素能受体（alpha2A-adrenoceptors, α₂A-ARs）是Gi蛋白偶联受体，可在突触前抑制去甲肾上腺素（norepinephrine, NE）与肾上腺素（epinephrine, Epi）的释放，在突触后抑制胰岛素分泌与脂肪分解。我们此前的研究已证实，α₂A^–/–基因敲除小鼠会表现出交感神经亢进、高胰岛素血症以及糖耐量改善的表型。本研究中我们使用α₂A^–/–基因敲除小鼠，并通过高脂饮食（high-fat diet, HFD）构建模型，以验证“缺失α₂A-ARs可抵御饮食诱导的肥胖与2型糖尿病（type 2 diabetes, T2D）”这一假说。此外，我们还将高热量饮食与转轮运动相结合，以探究饮食与运动的交互作用。

高脂饮食在两种基因型小鼠中均具有致肥胖效应，但α₂A^–/–小鼠的内脏脂肪堆积量较野生型对照更少，且可抵御2型糖尿病的发生，其胰岛素分泌水平也未受高脂饮食的影响。α₂A-ARs缺失与交感-肾上腺紧张性升高相关，这一变化会使能量消耗与脂肪氧化率提升，且该效应可被高脂饮食增强。与此相符的是，α₂A^–/–小鼠对肾上腺素的脂解反应增强，粪便脂质水平升高，提示其脂肪动员与吸收过程发生改变。

α₂A^–/–小鼠的皮下白色脂肪组织的产热活性更高（以解偶联蛋白1（uncoupling protein 1, Ucp1）的mRNA表达水平作为检测指标），而棕色脂肪组织对去甲肾上腺素的响应也有所增强。运动在两种基因型小鼠中均能有效降低总体脂含量并增加瘦体重，但二者存在显著的饮食-基因型交互作用：即便是轻度增加的体力活动结合α₂A-AR信号缺失，也比正常α₂A-AR功能下的运动更高效地促进体重减轻。

本研究结果表明，阻断α₂A-ARs或可用于减少内脏脂肪堆积并改善胰岛素分泌功能。