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)对米拉贝格隆的反应， 它是一种β3肾上腺素能受体(β3AR)激动剂。β3ARs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的药物。治疗肥胖、胰岛素抵抗的人类 服用米拉贝格隆12周后，持续地诱导SC变黄，这导致了口服血糖的改善 耐受性和较低的HbA1c。改善葡萄糖稳态的机制涉及到一小部分 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 肌肉氧化类型1纤维的增加；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，米雷贝格隆对这些细胞和肌肉的有益作用 细胞可能是通过间接机制发生的。 米拉贝格隆的生理作用可能部分是通过诱导米色脂肪来实现的，而米拉贝隆 代表葡萄糖和脂类的代谢库，可能会改变脂肪重塑。此外， 脂肪组织和其他器官的变化可能会导致针对其他组织的继发性影响。 具体目的1.为了研究β-3激动剂米雷贝格隆对糖代谢的影响，我们将 综合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 为期4个月的安慰剂对照随机试验。我们将评估脂肪组织的变化，包括褐变， 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检测SC WAT中的基因表达，以确定潜在的机制，如脂肪因子谱的改变。 具体目的2.我们假设米拉贝格隆导致表达β3AR的细胞改变水平 影响外周细胞类型的分泌因素，如β细胞和肌肉。我们将使用生化和 用药理学方法鉴定米雷贝格隆处理条件培养液的机制 脂肪细胞在体外增加肌肉中Pgc1α的表达。我们将利用不偏不倚的方法确定 脂肪细胞条件培养液中脂类、代谢物和外体miRNA组成的变化。我们会 使用这些方法来识别通过米拉贝格隆治疗而改变的血浆中负责 β细胞和肌肉功能的改善。 临床相关性：米拉贝隆治疗对糖耐量的改善有积极作用 在胰岛素敏感性和β细胞功能方面。这可能被利用来防止糖尿病前期转化为 糖尿病或用作糖尿病患者的治疗药物。这个应用程序还将增加我们对 米拉贝隆的作用机制(S)，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