Post-Developmental Adipocyte Autophagy in Control of Insulin-Glucose Homeostasis

总结/摘要 肥胖、代谢综合征和2型糖尿病的特征是胰岛素抵抗， 多个组织（例如，肝脏、肌肉和脂肪）。最近的研究表明，细胞内自噬 在维持参与发病机制的组织的代谢健康方面起着重要作用。 胰岛素抵抗 自噬是细胞内的溶酶体运输途径， 体内平衡和抵消多种形式的细胞应激。此外，自噬是唯一的 细胞中线粒体降解和周转的机制。骨骼肌中的自噬功能， 肝脏、胰腺β细胞和下丘脑以维持胰岛素-葡萄糖稳态;此外， 自噬是肝脏中脂解所必需的。先前的研究检查了自噬在脂肪组织中的作用， 组织利用小鼠模型，其中脂肪细胞自噬在胚胎发生期间受损。这些 小鼠是瘦的，并且免于饮食诱导的肥胖，并且表现出增强的胰岛素敏感性， 葡萄糖耐受不良这样的观察结果导致了这样的猜测，即抑制脂肪细胞中的自噬可能 为治疗或预防肥胖症及其代谢后果提供了有希望的策略。 然而，尽管它们的代谢表型明显有利， 自噬是不健康的：他们表现出死亡率增加（12周龄时为40%）， 炎症和巨噬细胞浸润。由于脂肪细胞的极端变化 在这些小鼠中的发育和脂肪组织储库形成，它们不是用于 评估成熟脂肪细胞中自噬的发育后作用。我们假设 自噬在成熟脂肪细胞中起重要的保护作用， 脂肪细胞自噬损伤将通过已建立的 此外，我们预测“自噬应激”将导致独特的循环释放， 脂肪细胞因子通过直接作用驱动全身胰岛素抵抗和葡萄糖耐受不良 在其他器官上（例如，肝脏、肌肉和胰腺β细胞）。 该项目的总体目标是： (i)确定脂肪细胞自噬在胰岛素抵抗和葡萄糖代谢中的作用。 通过定义特定的靶组织和脂肪细胞通过其表达的分子作用， 自噬调节成人的全身代谢;和（ii）定义正常调节， 自噬在成熟脂肪细胞中的代谢功能，独立于自噬在 脂肪细胞发育/分化。我们对老鼠进行基因改造， 在成年期关闭，经过强烈的脂肪形成的发育期，通过他莫昔芬- 诱导性遗传损伤“成熟脂肪细胞自噬敲除小鼠”的初步发现 表明自噬不调节肥胖，但对健康胰岛素-葡萄糖稳态是必需的。 在拟议的工作中，我们将这些观察扩展到组织的系统评估 成熟脂肪细胞自噬损伤导致胰岛素分泌的特定机制 抵抗和葡萄糖耐受不良的小鼠体内（目标#1）;我们将利用培养的原代 脂肪祖细胞，以研究在脂肪形成过程中自噬损伤的时间 影响体外脂肪细胞的代谢表型（目标#2）。

Summary /Abstract Obesity, Metabolic Syndrome, and Type 2 diabetes are characterized by insulin resistance affecting multiple tissues (e.g., liver, muscle, and fat). Recent studies determined that intracellular autophagy plays an important role maintaining the metabolic health of tissues involved in the pathogenesis of insulin resistance. Autophagy is the intracellular lysosomal trafficking pathway that maintains energy homeostasis and counteracts multiple forms of cellular stress. In addition, autophagy is the sole mechanism for mitochondrial degradation and turnover in cells. Autophagy functions in skeletal muscle, liver, pancreatic beta cells, and hypothalamus to maintain insulin-glucose homeostasis; in addition, autophagy is required for lipolysis in liver. Prior studies examining the role of autophagy in adipose tissue utilized mouse models in which adipocyte autophagy was impaired during embryogenesis. These mice were lean and protected from diet-induced obesity, and exhibited enhanced insulin sensitivity and glucose intolerance. Such observations led to speculations that inhibiting autophagy in adipocytes might provide a promising strategy for treating or preventing obesity and its metabolic consequences. However, despite their apparently favorable metabolic phenotype, the mice with embryonic impairment of autophagy were not healthy: they exhibit increased rates of death (40% at 12 weeks of age) and inflammation and macrophage infiltration in adipose tissue. Due to the extreme alterations of adipocyte development and adipose tissue depot formation in these mice, they are not adequate models for assessing the post-developmental role of autophagy in the mature adipocyte. We hypothesize autophagy plays an important, protective function in mature adipocytes, and post-developmental impairment of adipocyte autophagy will induce intracellular stress and insulin-resistance via established signaling mechanisms; in addition, we predict "autophagic stress" will cause release of unique circulating factors from adipocytes that drive systemic insulin-resistance and glucose intolerance via direct effects on other organs (e.g., liver, muscle, and pancreatic beta cells). The Overall Objectives of this project are: (i) to determine the role of adipocyte autophagy in the pathogenesis of insulin-resistance and glucose intolerance in vivo by defining specific target tissues and molecular actions through which adipocyte autophagy regulates systemic metabolism in the adult; and (ii) to define the normal regulation and metabolic functions of autophagy in mature adipocytes, independently of the role of autophagy in adipocyte development/differentiation. We genetically engineered mice so that autophagy can be turned off in adulthood, after the developmental period of intense adipogenesis, via a tamoxifen- inducible genetic impairment. Preliminary findings with "mature adipocyte autophagy knockout mice" indicate autophagy does not regulate adiposity but is necessary for healthy insulin-glucose homeostasis. In the proposed work we will extend these observations to a systematic assessment of the tissue specific-mechanisms through which impairment of autophagy in mature adipocytes causes insulin resistance and glucose intolerance in mice in vivo (Aim #1); and we will make use of cultured primary adipocyte progenitor cells to study how the timing of autophagy impairment during adipogenesis influences the metabolic phenotype of adipocytes in vitro (Aim #2).