Department of Nutrition and Food Science, Texas A &M University, College Station, TX, USA.
USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX , USA.
J Neuroendocrinol. 2019 Jul;31(7):e12763. doi: 10.1111/jne.12763. Epub 2019 Jul 9.
Ghrelin is a gut hormone that signals to the hypothalamus to stimulate growth hormone release, increase food intake and promote fat deposition. The ghrelin receptor, also known as growth hormone secretagogue receptor (GHS-R), is highly expressed in the brain, with the highest expression in agouti-related peptide (AgRP) neurones in the hypothalamus. Compelling evidence indicates that ghrelin serves as a survival hormone with respect to maintaining blood glucose and body weight during nutritional deficiencies. Recent studies have demonstrated that AgRP neurones are involved in metabolic and behavioural adaptation to an energy deficit to improve survival. In the present study, we used a neuronal subtype-specific GHS-R knockout mouse (AgRP-Cre;Ghsr ) to investigate the role of GHS-R in hypothalamic AgRP neurones in metabolic and behavioural adaptation to hypocaloric restricted feeding. We subjected the mice to a restricted feeding regimen of 40% mild calorie restriction (CR), with one-quarter of food allotment given in the beginning of the light cycle and three-quarters given at the beginning of the dark cycle, to mimic normal mouse intake pattern. The CR-fed AgRP-Cre;Ghsr mice exhibited reductions in body weight, fat mass and blood glucose. Metabolic profiling of these CR-fed AgRP-Cre;Ghsr mice showed a trend toward reduced basal metabolic rate, significantly reduced core body temperature and a decreased expression of thermogenic genes in brown adipose tissue. This suggests a metabolic reset to a lower threshold. Significantly increased physical activity, a trend toward increased food anticipatory behaviour and altered fuel preferences were also observed in these mice. In addition, these CR-fed AgRP-Cre;Ghsr mice exhibited a decreased counter-regulatory response, showing impaired hepatic glucose production. Lastly, hypothalamic gene expression in AgRP-Cre;Ghsr mice revealed increased AgRP expression and a decreased expression of genes in β-oxidation pathways. In summary, our data suggest that GHS-R in AgRP neurones is a key component of the neurocircuitry involved in metabolic adaptation to calorie restriction.
胃饥饿素是一种肠道激素,它向下丘脑发出信号,刺激生长激素释放,增加食物摄入并促进脂肪沉积。胃饥饿素受体,也称为生长激素促分泌素受体(GHS-R),在大脑中高度表达,在下丘脑的 AgRP 神经元中表达最高。令人信服的证据表明,胃饥饿素作为一种生存激素,在营养缺乏期间维持血糖和体重。最近的研究表明,AgRP 神经元参与代谢和行为适应能量不足以提高生存能力。在本研究中,我们使用神经元亚型特异性 GHS-R 敲除小鼠(AgRP-Cre; Ghsr)来研究 GHS-R 在下丘脑 AgRP 神经元中对能量限制喂养的代谢和行为适应中的作用。我们让小鼠接受 40%轻度热量限制(CR)的限制喂养方案,其中四分之一的食物分配在光照周期的开始时给予,四分之三的食物分配在黑暗周期的开始时给予,以模拟正常小鼠的摄入模式。CR 喂养的 AgRP-Cre; Ghsr 小鼠体重、脂肪量和血糖降低。对这些 CR 喂养的 AgRP-Cre; Ghsr 小鼠进行代谢谱分析显示,基础代谢率呈下降趋势,核心体温显著降低,棕色脂肪组织中产热基因的表达降低。这表明代谢重置到较低的阈值。还观察到这些 CR 喂养的 AgRP-Cre; Ghsr 小鼠的体力活动显著增加,食物预期行为增加趋势和燃料偏好改变。此外,这些 CR 喂养的 AgRP-Cre; Ghsr 小鼠表现出较低的代偿性反应,肝葡萄糖生成受损。最后,AgRP-Cre; Ghsr 小鼠的下丘脑基因表达显示 AgRP 表达增加和β-氧化途径中的基因表达降低。总之,我们的数据表明,AgRP 神经元中的 GHS-R 是参与热量限制代谢适应的神经回路的关键组成部分。