Mechanisms for activation of beige adipose tissue in humans

我们一直在研究皮下白色脂肪组织（SC WAT）对米拉贝隆的反应， 其为β3肾上腺素能受体（β3AR）激动剂。β 3 AR存在于脂肪细胞和平滑肌中，并且 米拉贝隆是FDA批准的治疗膀胱过度活动症的药物。治疗肥胖、胰岛素抵抗的人， 12周的米拉贝隆持续诱导SC WAT升高，这导致口服葡萄糖改善 耐受性和较低的HbA 1c。改善葡萄糖稳态的机制涉及小的 胰岛素敏感性的改善和β细胞功能（胰岛素分泌）的显著改善， 增加肌肉氧化1型纤维;然而，没有体重减轻或诱导棕色脂肪。 由于胰腺β细胞和肌肉不表达β3AR，因此米拉贝隆在这些细胞中的有益作用可能与β3AR有关。 细胞可能通过间接机制发生。 米拉贝隆的生理效应可能部分是通过诱导米色脂肪介导的， 代表葡萄糖和脂质的代谢库，并可能改变脂肪重塑。此外该 脂肪组织和其他器官的变化可能导致针对其他组织的继发性效应。 具体目标1。为了检查β3激动剂米拉贝隆对葡萄糖代谢的影响，我们将 全面分析糖尿病前期受试者的糖耐量、胰岛素敏感性和β细胞功能， 4个月、安慰剂对照、随机试验。我们将评估脂肪组织的变化， 炎症、纤维化和胰岛素刺激的脂肪细胞葡萄糖摄取。我们还将全面描述 通过RNA-seq在SC WAT中的基因表达，以确定潜在的机制，如改变的脂肪因子谱。 具体目标2。我们假设米拉贝隆引起表达β 3 AR的细胞改变β 3 AR的水平， 影响外周细胞类型（如β细胞和肌肉）的分泌因子。我们将使用生物化学和 药理学方法来确定米拉贝隆处理的条件培养基的机制 脂肪细胞增加体外肌肉中PGC 1 α的表达。我们将利用公正的方法来确定 脂肪细胞条件培养基中脂质、代谢物和外泌体miRNA组成的变化。我们将 使用这些方法来鉴定通过米拉贝隆治疗在血浆中改变的分子， β细胞和肌肉功能的改善。 临床相关性：Mirabegron治疗由于改善而对葡萄糖耐量产生积极影响 胰岛素敏感性和β细胞功能。这可能被用来防止糖尿病前期转化为 糖尿病或用作治疗糖尿病的药物。这个应用程序也将增加我们对 米拉贝隆的作用机制，可能揭示新的治疗靶点

We have been studying subcutaneous white adipose tissue (SC WAT) beiging in response to mirabegron, which is a β3 adrenergic receptor (β3AR) agonist. β3ARs are found in adipocytes and smooth muscle, and mirabegron is an FDA approved drug for overactive bladder. Treatment of obese, insulin resistant humans for twelve weeks with mirabegron consistently induced SC WAT beiging and this led to improved oral glucose tolerance and a lower HbA1c. The mechanism for improved glucose homeostasis involved both a small improvement in insulin sensitivity and a significant improvement in β-cell function (insulin secretion) along with an increase in muscle oxidative type 1 fibers; however, there was no weight loss or induction of brown fat. Since pancreatic β-cells and muscle do not express the β3AR, the beneficial effects of mirabegron in these cells likely occurred by an indirect mechanism. The physiological effects of mirabegron are likely mediated in part by the induction of beige adipose, which represents a metabolic sink for glucose and lipids and which may alter adipose remodeling. In addition, the changes in adipose tissue and other organs may result in secondary effects that target other tissues. Specific Aim 1. To examine the effects of the β3 agonist mirabegron on glucose metabolism, we will comprehensively analyze glucose tolerance, insulin sensitivity, and β-cell function in prediabetic subjects in a 4-month, placebo-controlled, randomized trial. We will assess changes in adipose tissue including beiging, inflammation, fibrosis, and insulin-stimulated glucose uptake by adipocytes. We will also fully characterize gene expression in SC WAT by RNA-seq to identify potential mechanisms such as altered adipokine profiles. Specific Aim 2. We hypothesize that mirabegron causes cells that express the β3AR to change the levels of secreted factors that affect peripheral cell types such as β-cells and muscle. We will use biochemical and pharmacological approaches to identify the mechanism by which conditioned medium from mirabegron-treated adipocytes increases PGC1α expression in muscle in vitro. We will utilize unbiased approaches to identify changes in lipids, metabolites, and exosome miRNA composition in the adipocyte conditioned media. We will use these approaches to identify molecules altered in plasma by mirabegron treatment that are responsible for the improvement in β-cell and muscle function. Clinical relevance: Mirabegron treatment has positive effects on glucose tolerance due to improvements in insulin sensitivity and β-cell function. This may be exploited to prevent conversion of prediabetes to diabetes or used as a therapeutic in diabetics. This application will also increase our understanding of the mechanism(s) by which mirabegron acts, which may reveal new therapeutic targets