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（T2 DM）已成为流行性的公共卫生问题，目前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。肥胖显著增加了发展为T2 DM的风险，糖皮质激素（GC）过量（库欣综合征）患者产生内脏肥胖和糖尿病，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，许多典型的肥胖症和MS可以通过细胞内内质网（ER）内腔驻留酶引起的脂肪组织内GC再生异常增加来解释，11 α-羟类固醇脱氢酶（11 β-HSD 1），其可以从非活性可的松产生活性皮质醇，因此尽管肥胖和MS中的血浆GC水平不变，但放大细胞内GC作用。因此，HSD 1被认为是肥胖和MS的常见分子病因。然而，ER内的11 β-HSD 1关键地依赖于酶己糖-6-磷酸脱氢酶（H6 PDH）以维持其辅因子NADPH的可用性。在ER腔中，H6 PDH可以代谢葡萄糖-6-磷酸（G6 P）并从NADP产生NADPH，并且需要G6 P转运蛋白来维持其代谢底物G6 P水平。因此，H6 PDH能够偶联与T2 DM和肥胖的发病机制相关的细胞G6 P代谢和GC信号传导的调节。事实上，我们已经表明，在肥胖糖尿病小鼠中导致11 β-HSD 1上调的脂肪H6 PDH表达增加与在T2 DM患者的脂肪组织中发现的相似。然而，脂肪H6 PDH表达改变的功能后果尚不清楚。使用我们独特的转基因小鼠在脂肪组织中选择性过表达H6 PDH，我们观察到这些小鼠具有异常增加的脂肪皮质酮产生和细胞G6 P代谢，并表现出不良代谢表型，包括高血糖症、内脏脂肪堆积、高脂血症和胰岛素抵抗。因此，我们假设脂肪H6 PDH在肥胖和胰岛素抵抗的病理生理学中起着重要的作用，并且可以被操纵以提供治疗MS的潜在策略。在这项资助中，我们将利用我们独特的现有H6 PDH转基因模型来探索脂肪H6 PDH对体内葡萄糖稳态和胰岛素敏感性的影响。我们还将直接检查改变H6 PDH表达在胰岛素信号传导作用中的作用，通过在完整的小鼠脂肪细胞中使用siRNA技术操纵H6 PDH来调节细胞GC再生和G6 P代谢。这将通过产生和评估H6 PDH脂肪特异性敲除小鼠来促进。我们相信，操纵H6 PDH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, 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.