The Role of Adipose H6PDH in Type 2 Diabetes and Obesity

描述(申请人提供)：肥胖和2型糖尿病(T2 DM)已经成为流行比例的公共卫生问题，人们正在努力了解这些疾病发病的分子机制，以设计新的治疗方法。肥胖极大地增加了患T2 DM的风险，糖皮质激素(GC)过多的患者(库欣综合征)会导致内脏肥胖和糖尿病，但在大多数典型的肥胖和代谢综合征(MS)患者中，循环中的GC水平并没有升高。然而，许多典型的肥胖和MS可以通过细胞内内质网(ER)腔驻留酶11？-羟基类固醇脱氢酶(11？-HSD1)异常地增加脂肪组织内GCs的再生来解释，11？-HSD1可以从不活跃的皮质醇中产生活性皮质醇，从而放大细胞内GC的作用，尽管肥胖症和MS患者的血浆GC水平没有改变。因此，通过11？-HSD1激活GCs被认为是肥胖和MS的常见分子病因。然而，ER内的11？-HSD1关键依赖于己糖-6-磷酸脱氢酶(H6PDH)来维持其辅因子NADPH的可用性。在内质网中，H6PDH可以代谢葡萄糖-6-磷酸(G6P)，并由NADP生成NADPH，并需要G6P转运体维持其代谢底物G6P的水平。因此，H6PDH能够将细胞G6P代谢的调节和GC信号与T2 DM和肥胖症的发病机制联系起来。事实上，我们已经证明，肥胖糖尿病小鼠脂肪H6PDH表达增加导致11？-HSD1上调与在T2 DM患者脂肪组织中发现的相似。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H6PDH转基因小鼠选择性地在脂肪组织中过表达，我们观察到这些小鼠脂肪皮质酮的产生和细胞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的不良代谢表型。因此，我们假设脂肪H6PDH在肥胖和胰岛素抵抗的病理生理学中起重要作用，并可被操纵以提供治疗MS的潜在策略。在这项资助中，我们将利用我们独特的现有H6PDH转基因模型，在体内探索脂肪H6PDH对葡萄糖稳态和胰岛素敏感性的影响。我们还将利用siRNA技术，通过操纵H6PDH在完整的小鼠脂肪细胞中调节细胞GC再生和G6P代谢，直接检测H6PDH表达变化在胰岛素信号转导中的作用。这将通过产生和评估H6PDH脂肪特异性基因敲除小鼠来促进。我们相信，操控H6PDH对脂肪功能和体内平衡的作用和影响将提供新的策略，可能转化为T2 DM和MS患者的新疗法。

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, 11?-hydroxysteroid dehydrogenase (11?-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 11?-HSD1 is thus regarded as a common molecular etiology for obesity and MS. However, 11?-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 11?-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.