The Role of Adipose H6PDH in Type 2 Diabetes and Obesity

描述（由申请人提供）：肥胖和2型糖尿病（T2DM）已经成为流行病的公共卫生问题，人们正在努力了解这些疾病发病机制的分子机制，以设计新的治疗方法。肥胖可显著增加发生2型糖尿病的风险，糖皮质激素（GC）过量（库欣综合征）的患者可产生内脏型肥胖和糖尿病，但绝大多数典型肥胖和代谢综合征（MS）患者的循环GC水平并未升高。然而，许多典型的肥胖和多发性硬化症可以解释为细胞内内质网（ER）管腔内酶在脂肪组织内异常增加的GCs再生。11ß-羟类固醇脱氢酶（11ß-HSD1）可以从无活性的可可松中产生活性的皮质醇，从而放大细胞内的GC作用，尽管肥胖和ms的血浆GC水平没有改变，但通过11ß-HSD1激活GC的受体前活化被认为是肥胖和ms的常见分子病因。然而，内质网络中的11ß-HSD1关键依赖于6-磷酸脱氢酶（H6PDH）来维持其辅助因子NADPH的可用性。在内质网内，H6PDH能够代谢葡萄糖-6-磷酸（G6P），并由NADP生成NADPH，需要G6P转运体维持其代谢底物G6P的水平。因此，H6PDH能够耦合调节细胞G6P代谢和与T2DM和肥胖发病机制相关的GC信号。事实上，我们已经证明肥胖糖尿病小鼠脂肪中H6PDH表达的增加导致11ß-HSD1的上调与T2DM患者脂肪组织中的情况相似。然而，脂肪H6PDH表达改变的功能后果尚不清楚。利用我们独特的转基因小鼠在脂肪组织中选择性过表达H6PDH，我们观察到这些小鼠的脂肪皮质酮产生和细胞G6P代谢异常增加，并表现出高血糖、内脏脂肪堆积、高脂血症和胰岛素抵抗等不良代谢表型。因此，我们假设脂肪H6PDH在肥胖和胰岛素抵抗的病理生理中起着重要作用，并且可以为ms的治疗提供潜在的策略。在本次资助中，我们将利用我们独特的现有H6PDH转基因模型，探索脂肪H6PDH对体内葡萄糖稳态和胰岛素敏感性的影响。我们还将在完整的小鼠脂肪细胞中使用siRNA技术，通过操纵H6PDH来调节细胞GC再生和G6P代谢，直接研究H6PDH表达改变在胰岛素信号传导作用中的作用。这将通过生成和评估H6PDH脂肪特异性敲除小鼠来促进。我们相信控制H6PDH对脂肪功能和体内平衡的作用和影响将为T2DM和MS患者提供新的治疗策略。

DESCRIPTION (provided by applicant): Obesity and type 2 diabetes (T2DM) have become public health problems of epidemic proportions and much effort is being undertaken to understand the molecular mechanisms underlying the pathogenesis of these conditions to design new treatments. Obesity dramatically increases the risk of developing T2DM and patients with glucocorticoid (GC) excess (Cushing's syndrome) produce visceral obesity and diabetes, but circulating GC levels are not elevated in the vast majority of patients with typical obesity and metabolic syndrome (MS). However, many typical obesity and MS can be accounted for by abnormally increased regeneration of GCs within adipose tissue by an intracellular endoplasmic reticulum (ER) lumen-resident enzyme, 11ß-hydroxysteroid dehydrogenase (11ß-HSD1) that can generate active cortisol from inactive cortisone and thus amplifies intracellular GC action despite unaltered plasma GC levels in obesity and MS. Pre-receptor activation of GCs via 11ß-HSD1 is thus regarded as a common molecular etiology for obesity and MS. However, 11ß-HSD1 within the ER is crucially dependent on the enzyme hexose-6-phosphate dehydrogenase (H6PDH) to maintain its cofactor NADPH availability. In the ER lumen, H6PDH can metabolize glucose-6-phosphate (G6P) and generates NADPH from NADP and requires the G6P transporter to maintain its metabolic substrate G6P levels. H6PDH is thus able to couple the regulation of cellular G6P metabolism and GC signaling linked to the pathogenesis of T2DM and obesity. Indeed, we have shown that the increased adipose H6PDH expression leading to up-regulation of 11ß-HSD1 in obese diabetic mice is similar to that found in adipose tissue from T2DM patients. However, the functional consequences of altered adipose H6PDH expression are unknown. Using our unique transgenic mouse overexpression of H6PDH selectively in adipose tissue, we have observed that these mice have abnormally increased adipose corticosterone production and cellular G6P metabolism and exhibited the adverse metabolic phenotypes with hyperglycemia, visceral fat accumulation, hyperlipidemia, and insulin resistance. We thus hypothesize that adipose H6PDH plays an important role in the pathophysiology of obesity and insulin resistance, and can be manipulated to provide potential strategies for the treatment of MS. In this grant, we will explore the impact of adipose H6PDH on glucose homeostasis and insulin sensitivity in vivo using our unique existing H6PDH transgenic model. We will also directly examine the role of altered H6PDH expression in insulin signaling action through manipulation of H6PDH to regulation of cellular GC regeneration and G6P metabolism by using siRNA technology in intact mouse adipocyte cells. This will be facilitated by generation and evaluation of a H6PDH fat-specific knockout mouse. We believe that manipulating the role and impact of H6PDH on adipose function and homeostasis will provide new strategies that may translate into novel therapies for patients with T2DM and MS.