Phospholipase A2 in Insulin Resistance and Obesity

描述（由申请人提供）：1B型磷脂酶A2（PLA 2g 1B）由胰腺的外分泌腺泡细胞和内分泌B-胰岛细胞合成。通常认为它仅作为脂解酶，促进消化道中的脂质消化和吸收。然而，我们对PLA 2 g1 B基因敲除小鼠的初步结果表明，PLA 2 g1 B在膳食脂质吸收中起次要作用。然而，在低脂肪和高脂肪饮食条件下，PLA 2 g 1 B（-/-）小鼠比PLA 2 g 1 B +/+小鼠更胰岛素敏感和葡萄糖耐受。脂肪喂养的PLA 2 g1 B（-/-）小鼠的体重增加显著低于脂肪喂养的PLA 2 g1 B（+/+）小鼠，并且与普通饲料喂养的动物的体重增加相似。该数据表明PLA 2 g1 B对饮食诱导的胰岛素抵抗和肥胖有贡献。该研究项目的目标是确定PLA 2g 1B具有这种生理作用的机制。总的假设是，PLA 2g 1B，通过其酶消化的磷脂在肠腔中，有助于餐后溶血磷脂酰胆碱（LPC）的门静脉和血浆循环和负调节胰岛素敏感组织中的胰岛素作用。具体目标1将检验以下假设：PLA 2g 1B（-/-）小鼠对饮食诱导的肥胖具有抗性，因为与类似饲喂的野生型小鼠相比，其在高脂肪饲喂后的能量消耗增加。通过在高胰岛素-正常血糖钳夹实验中测量体内脂肪酸氧化和葡萄糖摄取，比较PLA 2 g1 B（+/+）和PLA 2 g1 B（-/-）小鼠中各种组织的脂肪和葡萄糖利用。具体目标2将检验该假设，并确定磷脂的PLA 2g 1B水解产生的LPC负调节外周组织中胰岛素信号传导的机制。将使用肝细胞、肌管和脂肪细胞进行体外细胞培养实验，以测试LPC抑制UCP表达并激活JNK和/或蛋白激酶C-α，从而抑制胰岛素和胰岛素受体信号级联的可能性。目的3将在PLA 2g 1B（-/-）小鼠中产生胰腺腺泡特异性和胰岛（B细胞）特异性PLA 2g 1B转基因，以检查外分泌PLA 2g 1B与内分泌PLA 2g 1B在促成糖尿病和肥胖中的重要性。总的来说，这些研究将为饮食诱导的胰岛素抵抗和肥胖的机制提供新的见解，从而为糖尿病和肥胖的治疗提供潜在的新治疗靶点。

DESCRIPTION (provided by applicant): Group 1B phospholipase A2 (PLA2g1B) is synthesized by both exocrine acinar cells and endocrine B-islet cells of the pancreas. It is generally thought to act only as a lipolytic enzyme, facilitating lipid digestion and absorption in the digestive tract. However, our Preliminary Results in characterization of PLA2g1B knockout mice suggested that PLA2g1 B plays a minor role in dietary lipid absorption. However, the PLA2g1 B(-/-) mice are more insulin sensitive and glucose tolerant than PLA2g1B+/+ mice under both low fat and high fat dietary conditions. Weight gained by fat-fed PLA2g1B(-/-) mice was significantly lower than that of fat-fed PLA2g1 B(+/+) mice and similar to that of chow-fed animals. This data indicates that PLA2g1 B is contributory to diet-induced insulin resistance and obesity. The goal of this research project is to identify the mechanism by which PLA2g1B has this physiological role. The overall hypothesis is that PLA2g1B, through its enzymatic digestion of phospholipids in the intestinal lumen, contributes postprandial lysophosphatidylcholine (LPC) to portal and plasma circulation and negatively regulates insulin action in insulin-sensitive tissues. Specific Aim 1 will test the hypothesis that PLA2g1B(-/-) mice are resistant to diet-induced obesity due to their increased energy expenditure after high fat feeding in comparison to similarly-fed wild type mice. Fat and glucose utilization by various tissues in PLA2g1 B(+/+) and PLA2g1 B(-/-) mice will be compared by measuring fatty acid oxidation in vivo and glucose uptake in hyperinsulinemic- euglycemic clamp experiments. Specific Aim 2 will test the hypothesis and identify the mechanism by which LPC generated from PLA2g1B hydrolysis of phospholipids negatively regulate insulin signaling in peripheral tissues. In vitro cell culture experiments with hepatocytes, myotubules, and adipocytes will be performed to test the possibility that LPC inhibits UCP expression and activates JNK and/or protein kinase C-alpha, thereby inhibiting insulin and insulin receptor signaling cascade. Aim 3 will produce pancreatic acinar-specific-and islet (B-cell-specific PLA2g1B transgene in PLA2g1B(-/-) mice to examine the importance of exocrine PLA2g1B versus endocrine PLA2g1B in contributing to diabetes and obesity. Collectively, these studies will add novel insights toward mechanisms that contribute to diet-induced insulin resistance and obesity, thus offering potentially new therapeutic targets for treatment of diabetes, and obesity.