The regulation of adipocyte lipolysis by insulin

描述（由申请方提供）：在禁食期间，脂肪细胞中储存的能量以甘油三酯的形式释放，供肌肉、肝脏和其他组织使用。 这一过程被称为脂解，受到激素、神经和营养输入的高度调节。 有实质性证据表明，抵抗胰岛素拮抗脂肪分解的作用是2型糖尿病和代谢综合征发展的早期和重要步骤。最常用于传递脂解增加信号的细胞内第二信使是环AMP，其响应于β-肾上腺素能药物而蓄积并激活蛋白激酶A。关于蛋白激酶A下游的信号传导，包括存在于甘油三酯脂滴上的主要底物周脂蛋白，已经知道很多。胰岛素拮抗脂肪分解的过程，有一个普遍接受的模型来解释脂肪细胞脂肪分解的急性抑制，虽然它还没有被详细研究。 胰岛素信号传导的经典模型描述了Akt（蛋白激酶B）的磷酸肌醇3 '-激酶依赖性激活，然后磷酸化并刺激磷酸二酯酶3 B（PDE 3 B），导致细胞内环AMP减少。 然而，主要研究者的实验室先前的工作已经揭示了胰岛素作用的替代途径，该途径在脂解的次最大刺激下发挥作用。 初步数据表明，这种信号级联功能独立于Akt，并且关键信号事件发生在脂滴表面。 本拨款申请中描述的研究将正式测试抗脂解信号的替代途径的假设。 实验包括使用FRET生物传感器来确定培养的脂肪细胞中PKA激活的精确细胞内位点，以及鉴定靶向脂滴调节分子的支架蛋白。 Akt和PDE 3B磷酸化在抑制脂解中的需要将首次通过遗传功能丧失实验进行测试。 最后，将通过在转基因小鼠中的体内实验评估这种抑制脂肪细胞脂解的新途径的生理相关性。

DESCRIPTION (provided by applicant): During times of fasting, energy stored in the adipocyte as triglyceride is released for use by muscle, liver and other tissues. This process, termed lipolysis, is highly regulated by hormonal, neural and nutritional inputs. There is subtantial evdence that resistance to the actions of insulin to antagonize lipolysis is an early and important step in the development of type 2 diabetes mellitus and the metabolic syndrome. The intracellular second messenger most frequently used to convey the signal for increased lipolysis is cyclic AMP, which accumulates in reponse to beta-adrenergic agents and activates protein kinase A. Much is known about signaling downstream of protein kinase A, including a major substrate, perilipin, present on the triglyceride lipid droplet. Insulin antagonizes the process of lipolysis, and there is a generally accepted model to explain the acute suppression of adipocyte lipolysis, though it has not been studied in detail. The canonical model of insulin signaling describes phosphoinositide 3'-kinase-dependent activation of Akt (protein kinase B), which then phosphorylates and stimulates phosphodiesterase 3B (PDE3B), leading to a decrease in intracellular cyclic AMP. Previous work from the laboratory of the principal investigator has revealed, however, an alternative pathway of insulin action that comes into play upon sub-maximal stimulation of lipolysis. Preliminary data indicate that this signaling cascade functions independently of Akt and that the critical signaling events occur on the surface the lipid droplet. The studies described in this grant proposal will formally test the hypothesis of an alternative pathway for anti-lipolytic signaling. Experiments include the use of FRET biosensors to determine the precise intracellular sites of PKA activation in cultured adipocytes and the identification of scaffolding proteins that target regulatory molecules ot the lipid droplet. The requirement for Akt and PDE3B phosphorylation in the suppression of lipolysis will be tested for the first time by genetic loss of function experiments. Lastly, the contribution of this novel pathway for the suppression of fat cell lipolysis will be assessed for physiological relevance through in vivo experiments in genetically modified mice.