Modulation of Insulin Signaling in Adipocytes

Modulation of Insulin Signaling in Adipocytes Adipose tissue is essential for normal energy homeostasis. It exerts important anti-lipotoxic effects by neutralizing free fatty acids after nutrient absorption and by releasing them through lipolysis upon systemic demand. It has been established that a dysfunctional adipocyte is tightly linked to metabolic challenges in other tissues. Aberrant insulin signaling, as observed in insulin resistance at the level of the adipocyte, is a key driver of systemic metabolic dysfunction. Our key hypothesis is that any intervention that aims to alleviate aspects of systemic metabolic dysfunction critically relies on an improvement in the insulin sensitivity of the adipocyte. How does improved adipocyte insulin sensitivity contribute to positive metabolic outcomes? We identified a number of gaps in our knowledge regarding insulin signaling in the adipocyte. We will take advantage of a multipronged approach to finetune the insulin response selectively in the adipocyte. We will deploy diverse tools to investigate the contribution of adipocyte insulin signaling to a new paradigm of insulinopenic insulin sensitization and to the effects of modern incretin and glucagon receptor agonists. We will address these questions at the cellular, tissue, and systemic level with the following Specific Aims: In Aim 1, we propose to carefully titrate insulin signaling within the adipocyte by i) inducible reduction of insulin receptor expression, ii) selective activation of an artificial insulin receptor, or iii) manipulation of the insulin signaling modulator PTEN. Many of these approaches will take advantage of recently developed models that were not previously available to the field. In Aim 2, we plan to define the consequences of a targeted reduction in β-cell insulin release on the adipocyte by i) controlled suppression of membrane depolarization or ii) induction of progressive mitochondrial dysfunction. Our new β-KIR6.2V59M and β-mitoKiller mouse models use a mouse insulin 1 promoter-based driver to achieve β- cell-specific and inducible transgene expression. In β-KIR6.2V59M mice, an activating mutant KATP channel subunit is used to suppress membrane depolarization, which, upon mild induction, results in reduced glucose- stimulated insulin secretion (GSIS) without hyperglycemia. These mice retain insulin sensitivity upon exposure to a high-fat diet. In β-mitoKiller mice, a viral protein is employed that specifically degrades mitochondrial DNA, causing mitochondrial dysfunction. This results in a lack of GSIS, progressive hyperglycemia, and deteriorated glucose tolerance while basal insulin levels are maintained. We will specifically examine the role of altered adipocyte insulin signaling in these two unique models. In Aim 3, we will determine the contribution of adipocyte insulin signaling to the beneficial effects of GLP1-R+GIP-R and GLP-1R+GIP-R+GCG-R agonists. Does increased adipocyte insulin responsiveness contribute to the effects of these drugs on weight loss and systemic metabolism? Does an insulin-resistant adipocyte prevent such improvements? Combined, our studies should provide new insights into the physiological contributions of the insulin-sensitive adipocyte.