Activation of the cAMP-PKA pathway antagonizes metformin action

 描述(申请人提供)美国有2580万人患有糖尿病，全球至少有3.87亿人患有糖尿病。2型糖尿病(T2D)占糖尿病病例的90%以上。自20世纪50年代以来，二甲双胍一直用于治疗T2D，现在全世界有超过1.5亿人在服用这种药物。2012年，在T2D的治疗指南中，美国糖尿病协会和欧洲糖尿病研究协会联合推荐二甲双胍作为T2D的首发药物。然而，二甲双胍的作用机制仍然只有部分了解和争议。我们发现，门静脉中通常存在的低浓度二甲双胍通过激活AMPK抑制原代肝细胞中葡萄糖的产生。然而，目前尚不清楚AMPKα亚基的哪一种亚型在二甲双胍抑制肝细胞葡萄糖产生中起关键作用，AMPK亚基上的二甲双胍结合位点也尚未确定。使用肝脏特异性AMPKα1、AMPKα2和联合AMPKα1/2基因敲除小鼠和AMPK亚基突变，我们将在目标1中解决这些问题。超过三分之一的糖尿病患者表现出不同程度的二甲双胍耐药。我们发现，作为糖尿病患者标志的cAMP-PKA通路的激活，通过在S485磷酸化AMPKα，直接拮抗AMPK的激活，从而降低AMPK的酶活性。这可能会导致二甲双胍耐药。我们建议研究AIM 2中导致二甲双胍耐药的机制，这对糖尿病患者使用二甲双胍具有重要的临床意义。水杨酸盐是一种常用的试剂，已知可以激活AMPK。我们将在AIM 3中测试水杨酸酯在提高二甲双胍抑制葡萄糖产生效果方面的作用。我们相信这项工作将为理解二甲双胍的作用机制提供新的证据，并为使用二甲双胍治疗T2D提供新的治疗指南。

 DESCRIPTION (provided by applicant) Diabetes affects 25.8 million individuals in the USA and at least 387 million individuals worldwide. Type 2 diabetes (T2D) accounts for more than 90% of diabetes cases. Metformin has been used to treat T2D since the 1950s, and now over 150 million people worldwide take this medication. In 2012, in guidelines for the treatment of T2D, the American Diabetes Association and the European Association for the Study of Diabetes jointly recommended metformin as the initial drug to prescribe to T2D. Yet how metformin acts remains only partially understood and controversial. We find that low metformin concentrations typically found in the portal vein suppress glucose production in primary hepatocytes through the activation of AMPK. However, it remains unclear which isoform of the AMPKα subunits is critical for the suppression of glucose production in hepatocytes by metformin, and metformin binding sites on AMPK subunits have not been characterized yet. Using liver-specific AMPKα1, AMPKα2, and combined AMPKα1/2 knockout mice and mutations of AMPK subunits, we will address these questions in Aim 1. Over one-third of diabetic patients exhibit various degrees of metformin resistance. We find that activation of the cAMP-PKA pathway, a hallmark of patients with diabetes mellitus, directly antagonizes AMPK activation by phosphorylating AMPKα at S485, which in turn reduces AMPK enzymatic activity. This could result in metformin resistance. We propose to study the mechanism leading to metformin resistance in Aim 2, which has important clinical implications for metformin usage in diabetic patients. Salicylate, a commonly used agent, is known to activate AMPK. We will test salicylate's effect on the improvement of metformin efficacy in the suppression of glucose production in Aim 3. We believe this work will provide new evidence for understanding the mechanism of metformin's action and new therapeutic guidelines for the use of metformin to treat T2D.