Mechanisms of diet-induced leptin resistance in ARC and VTA

描述(申请人提供)：饮食诱导肥胖(DIO)的一个潜在致病因素是瘦素抵抗。瘦素是大多数瘦肉动物体内的一种有效的厌食激素。然而，瘦素在肥胖动物身上的作用会减弱，这种折射性被称为瘦素抵抗。高脂肪和高蔗糖的饮食会导致瘦素抵抗和肥胖，但导致肥胖的饮食成分(S)仍然难以捉摸。我们的数据表明，含有高果糖的低脂肪饮食会导致瘦素抵抗，而不含果糖的饮食则不会。瘦素通过信号转导和转录激活蛋白3(STAT3)和营养感知AMP激活的激酶(AMPK)/乙酰辅酶A羧化酶(ACC)途径传递信号。瘦素通过后者促进pAMPK/pACC的去磷酸化来传递信号。我们证明果糖可以阻止瘦素介导的pAMPK/pACC去磷酸化，导致瘦素抵抗。过度营养也会导致瘦素抵抗。我们认为，导致过量摄入的饮食，被果糖加剧，会促进炎症、内质网(ER)应激和活性氧自由基(ROS)，这些都特别抑制瘦素介导的STAT3磷酸化(P-STAT3)。我们推测，饮食中高果糖，而不是葡萄糖，会损害瘦素介导的下丘脑弓状核(ARC)和腹侧被盖区(VTA)中pAMPK/pACC的去磷酸化。此外，我们假设果糖与过度营养协同作用，增加炎症、内质网应激和ROS，从而抑制pSTAT3信号转导。此外，为了促进体重增加，这两条途径的中断都是必要的。我们将通过检测摄食量和体重、全身能量平衡和大脑区域特异性瘦素信号的神经调节，在雄性Spraogue Dawley大鼠身上验证这些假设。实验1将检验与饮食葡萄糖或蔗糖相比，2周的饮食果糖是否抑制瘦素介导的pAMPK/pACC的去磷酸化，或损害STAT3的磷酸化。实验2将确定果糖是否通过中枢输注果糖或葡萄糖直接作用于中枢瘦素信号通路。EXP 3检查STAT3和AMPK瘦素信号通路的中断是否对瘦素抵抗通过特定抑制个别通路而促进体重增加至关重要。在实验4中，我们将研究过度营养加果糖(与葡萄糖相比)是否会导致更大的脑炎症/内质网应激/ROS，从而导致ARC和VTA中瘦素介导的P-STAT3信号受到更严重的抑制。实验5将研究炎症、内质网应激或ROS的产生在果糖/过度营养诱导的瘦素抵抗中的单独作用，方法是分别注入这些应激源的抑制物。我们的方法是独一无二的，因为我们认为果糖加过度营养构成了解释瘦素抵抗的两次打击模型。对这些机制的了解将为肥胖提供新的治疗策略，包括针对炎症/内质网应激/ROS的药物，以及结合低果糖饮食以恢复瘦素作用的药物。

DESCRIPTION (provided by applicant): One potential causative factor of diet-induced obesity (DIO) is leptin resistance. Leptin is a potent anorexic hormone in most lean animals. However, the effects of leptin are diminished in obese animals, and this refractiveness is known as leptin resistance. Diets high in fat and sucrose lead to leptin resistance and obesity, yet the causative dietary ingredient(s) remain elusive. Our data demonstrate that a low-fat diet with elevated fructose causes leptin resistance, whereas diets without fructose do not. Leptin signals via the signal transducer and activator of transcription protein 3 (STAT3) and the nutrient sensing AMP-activated kinase (AMPK)/acetyl CoA carboxylase (ACC) pathways. Leptin signals through the latter by promoting dephosphorylation of pAMPK/pACC. We demonstrated that fructose prevents leptin-mediated pAMPK/pACC dephosphorylation, leading to leptin resistance. Over-nutrition also leads to leptin resistance. We suggest that diets that lead to over-consumption, exacerbated by fructose, promote inflammation, endoplasmic reticulum (ER) stress, and reactive oxygen species (ROS) and these specifically inhibit leptin-mediated STAT3 phosphorylation (P-STAT3). We postulate that elevated dietary fructose, but not glucose, impairs the leptin- mediated dephosphorylation of pAMPK/pACC in the hypothalamic arcuate nucleus (ARC) and ventral tegmental area (VTA). Additionally, we postulate that fructose, in synergy with over-nutrition, increases inflammation, ER stress, and ROS, thus inhibiting pSTAT3 signaling. Furthermore, disruptions in both pathways are necessary to promote weight gain. We will test these hypotheses in male Sprague Dawley rats by examining the neural regulation of food intake and body weight, whole body energy homeostasis, and brain region-specific leptin signaling. Exp 1 will examine if 2-week dietary fructose inhibits the leptin-mediated dephosphorylation of pAMPK/pACC or impairs the phosphorylation of STAT3 compared with that of dietary glucose or sucrose. Exp 2 will determine if fructose acts directly on central leptin signaling pathways by central infusion of fructose or glucose. Exp 3 examines if disruptions in both the STAT3 and AMPK leptin signaling pathways are critical for the leptin-resistance promoted weight gain by specific inhibition of the individual pathways. In Exp 4, we will examine if over-nutrition plus fructose (vs. glucose) will induce a greater brain inflammation/ER stress/ROS, and consequently, result in more severe inhibition of leptin-mediated P-STAT3 signaling in the ARC and VTA. Exp 5 will examine the individual contribution of inflammation, ER stress or ROS production to fructose/over-nutrition-induced leptin resistance by infusion of respective inhibitors of these stressors. Our approach is unique because we suggest that fructose plus over-nutrition constitute a two-hit model explaining leptin resistance. An understanding of these mechanisms will provide new therapeutic strategies for obesity, including drugs that target inflammation/ER stress/ROS coupled with low fructose diets to resurrect leptin action.