Investigating Branched Chain Amino Acid Oxidation in Skeletal Muscle and its Contribution to Insulin Resistance

项目摘要 支链氨基酸（BCAA）是人体必需氨基酸，其催化活性受代谢速率控制。 限制性支链氨基酸脱氢酶复合物（BCKDH）及其抑制性激酶BCKDK。血浆水平升高 自20世纪60年代以来，BCAA一直与2型糖尿病有关。最近的研究表明， 支链氨基酸升高会导致胰岛素抵抗和2型糖尿病的发生。但 支链氨基酸驱动胰岛素抵抗的机制仍不清楚。我们先前已经表明 通过稳态体内重同位素示踪，发现db/db小鼠模型的胰岛素抵抗和2型 糖尿病增加了骨骼肌中的BCAA氧化，降低了肝脏和脂肪组织中的氧化。 骨骼肌中支链氨基酸的高氧化可能通过一些潜在的机制导致胰岛素抵抗，包括 促进肌肉细胞对脂肪的吸收，以及抑制脂肪分解。这两 预计这种机制会导致骨骼肌中脂质的积累，导致胰岛素分泌增加。 阻力基于这些观察，我假设骨骼肌中支链氨基酸氧化水平升高 促进胰岛素抵抗的发展。为了验证这个假设，我们开发了骨骼肌- 特异性BCKDH功能获得和功能丧失小鼠模型。我将使用各种技术，包括 稳态体内输注13 C标记的营养素和高胰岛素-正常血糖钳夹，以确定 肌肉中BCAA氧化的增加抑制脂肪氧化并促进全身胰岛素抵抗。与 这些技术和小鼠模型在我的处置，我将描绘具体的机制， 有助于胰岛素抵抗和2型糖尿病的发展，这可能会导致更好的，更多的 针对性治疗患有这种疾病的患者。

Project Summary Branched chain amino acids (BCAAs) are essential amino acids, and their catabolism is controlled by the rate- limiting BCAA dehydrogenase complex (BCKDH) and its inhibitory kinase BCKDK. Elevated plasma levels of BCAAs have been associated with type 2 diabetes since the 1960s. Recent studies have suggested that elevated BCAAs contribute to insulin resistance and the development of type 2 diabetes. However, the mechanisms through which BCAAs drive insulin resistance remain unknown. We have previously shown through steady-state in vivo heavy isotopic tracing that the db/db mouse model of insulin resistance and type 2 diabetes has increased BCAA oxidation in skeletal muscle and decreased oxidation in liver and adipose tissue. High BCAA oxidation in skeletal muscle may lead to insulin resistance by a few potential mechanisms including the promotion of fat uptake into muscle cells, as well as the inhibition of fat catabolism. Both of these mechanisms would be predicted to cause an accumulation of lipids in skeletal muscle, leading to insulin resistance. Based on these observations, I hypothesize that elevated BCAA oxidation in skeletal muscle promotes the development of insulin resistance. To test this hypothesis, we have developed skeletal muscle- specific BCKDH gain-of-function and loss-of-function mouse models. I will use a variety of techniques including steady-state in vivo infusions of 13C-labeled nutrients and hyperinsulinemic-euglycemic clamps to determine if increased BCAA oxidation in muscle suppresses fat oxidation and promotes systemic insulin resistance. With these techniques and mouse models at my disposal, I will delineate specific mechanisms by which BCAAs contribute to the development of insulin resistance and type 2 diabetes, which could lead to better, more targeted treatment of patients with this disease.