Role of PIK3R1 in Adipose Tissue Insulin Resistance and Inflammation in Obesity

描述(申请人提供)：肥胖及其相关的代谢性疾病是美国最大的公共卫生挑战之一。胰岛素抵抗是肥胖代谢性疾病增加的主要原因，并被认为是由于脂肪组织(AT)与巨噬细胞的渗透和促炎细胞因子产生增加而引起的继发性炎症反应。然而，令人惊讶的是，AT内启动和传播炎症表型以响应营养过剩的细胞信号在很大程度上是未知的，这突显了知识的显著差距。磷酸肌醇3-激酶(PI3K)调节关键的胰岛素、细胞因子和生长信号通路，因此是将细胞胰岛素抵抗与炎症反应联系起来的有力候选者。我们最近发现，在高脂饮食诱导的肥胖小鼠脂肪细胞中，PI3K p55α和p50α调节亚基增加了2-4倍，同时胰岛素敏感性降低。通过全球杂合性缺失编码调节亚基的Pik3r1基因，阻断高脂饮食诱导的p55α和p50α的增加，减少AT巨噬细胞的渗透，显著改善肥胖小鼠的脂肪细胞、骨骼肌和全身胰岛素敏感性。本课题组的研究发现，在营养受限的肌肉中，sirtuin 1(Sirtuin 1)和信号转导与转录激活因子3(STAT3)是p50α和p55α表达以及随后的pI3K活性的关键调节因子，这突显了胰岛素敏感性和细胞能量状态之间潜在的普遍联系。我们假设，营养过剩增加脂肪细胞p55α和p50α的丰度，1)抑制胰岛素刺激的PI3K信号，进一步抑制营养摄取，2)促进PI3K介导的NFκB激活，从而刺激细胞因子的产生和巨噬细胞的募集。与目前的范式不同，我们预测胰岛素抵抗本身通过PI3K信号促进炎症反应，而不是导致胰岛素抵抗的炎症。为了解决这一假设，我们将使用一种综合方法，将整个动物生理学与细胞和分子技术相结合。具体地说，AIM1将使用脂肪细胞特异性敲除或过度表达p55α和p50α的转基因小鼠模型来研究增加脂肪细胞p55α和p50α的丰度是否必要和足够刺激急性或慢性HFD喂养后的巨噬细胞募集。在AIM2中，我们将在体外测试脂肪细胞p55α和p50α的增加是否通过上调NFκB信号来促进巨噬细胞的趋化和/或抑制胰岛素对脂解的抑制来改变细胞因子的分泌。在AIM3中，我们将使用转基因小鼠模型在体内确定高脂血症诱导的AT p55α和p50α的增加是否位于SIRT1-STAT3轴的下游。考虑到PI3K在代谢性疾病和癌症研究中的重要作用，这些研究将为PI3K研究提供独特的新资源，拓宽我们对PI3K调控的理解，并将促进开发更有针对性的靶向PI3K的方法，PI3K具有治疗代谢并最终影响人类健康的潜力。

DESCRIPTION (provided by applicant): Obesity and its associated metabolic diseases are one of the greatest public health challenges in the United States. Insulin resistance is a primary contributor to this increase in metabolic disease with obesity and is proposed to arise secondary to an inflammatory response caused by infiltration of adipose tissue (AT) with macrophages and increased pro-inflammatory cytokine production. Surprisingly, however, the cellular signals within AT that initiate and propagate the inflammatory phenotype in response to nutrient excess are largely unknown, highlighting a significant gap in knowledge. Phosphoinosital 3-kinase (PI3K) regulates key insulin, cytokine, and growth signaling pathways, and is thus a strong candidate for linking cellular insulin resistance with the inflammatory response. We recently found a 2-4-fold increase in the PI3K p55α and p50α regulatory subunits in parallel with reduced insulin sensitivity in adipocytes from high-fat diet (HFD)-induced obese mice. Blocking HFD-induced increase in p55α and p50α through global heterozygous deletion of Pik3r1, the gene that encodes the regulatory subunits, reduced AT macrophage infiltration and significantly improved adipocyte, skeletal muscle and systemic insulin sensitivity in obese mice. Studies by our group have identify sirtuin 1 (SIRT1) and signal transducer and activator of transcription 3 (STAT3) as key regulators of p50α and p55α expression and subsequent PI3K activity in muscle with nutrient restriction, highlighting a potential universal link between insulin sensitiviy and cellular energy status. We hypothesize that nutrient excess increases adipocyte p55α and p50α abundance to, 1) inhibit insulin-stimulated PI3K signaling, further suppressing nutrient uptake and, 2) promote PI3K-mediate NFκB activation, thereby stimulating cytokine production and macrophage recruitment. In contrast to the current paradigm, we predict that insulin resistance itself, through PI3K signaling promotes the inflammatory response, rather than inflammation causing insulin resistance. To address this hypothesis, we will use an integrative approach that combines whole animal physiology with cell and molecular techniques. Specifically, AIM1 will use transgenic mouse models with adipocyte-specific knockdown or over-expression of p55α and p50α to investigate whether increased adipocyte p55α and p50α abundance is necessary and sufficient to stimulate macrophage recruitment after acute or chronic HFD feeding. In AIM2, we will test in vitro whether increased adipocyte p55α and p50α alters cytokine secretion through up-regulation of NFκB signaling to promote macrophage chemotaxis and/or inhibition of insulin suppression of lipolysis. In AIM3, we will use transgenic mouse models to determine in vivo if the HFD-induced increase in AT p55α and p50α is downstream of a SIRT1-STAT3 axis. Considering the integral role of PI3K in metabolic disease and cancer research, these studies will provide unique new resources for PI3K research, will broaden our understanding of PI3K regulation and will facilitate the development of more focused approaches for targeting PI3K, which has the potential to treat metabolic, and ultimately impact human health.