A unique role for apoC-III in intestinal lipoprotein synthesis and secretion

描述(申请人提供)：载脂蛋白C-III(apoC-III)是一种由肝脏和肠道产生的可交换的脂蛋白。血浆载脂蛋白C-III浓度在1型糖尿病患者中升高，是心血管疾病的独立预测因子。载脂蛋白C-III存在于富含甘油三酯的脂蛋白和高密度脂蛋白上，通过抑制脂蛋白脂肪酶活性和干扰肝脏对脂蛋白的清除来提高血浆甘油三酯水平。虽然在了解控制这些效应的机制方面已经取得了重大进展，但载脂蛋白C-III在肠道脂蛋白合成和分泌中的作用仍不明确。我们最近观察到，在apoC-III转基因(TG)小鼠中，apoC-III的全身过表达导致肠标签的分泌受到抑制 随着游离脂肪酸(FFA)和单甘油(MAG)前体的滞留以及肠细胞内TAG的减少，肠道细胞进入淋巴。载脂蛋白C-III在肠道细胞中的这种抑制作用与在肝细胞中的研究相反，后者已将载脂蛋白C-III的表达与极低密度脂蛋白分泌增加联系起来。我们的总体假设是apoC-III在肠道和肝脏的脂蛋白合成和分泌中发挥着独特的作用。我们将测试apoC-III增加导致Tag合成受抑的3种可能机制(apoC-III直接抑制1)MGAT和/或DGAT酶活性；2)FFA转运到内质网；或3)激活FFA到脂肪酰辅酶A)，并描述apoC-III在肠道脂质吸收和分泌中的机制作用。我们还将研究载脂蛋白C-III在肠道和肝脏中的功能重要性，使用腺病毒在小鼠肝脏中敲除和过表达载脂蛋白C-III。最后，我们将研究人类载脂蛋白C-III基因多态在原代小鼠肠道培养物中对肠道标签分泌的作用。这些目标的完成将提供关于载脂蛋白-III在调节肠道脂蛋白分泌中的作用以及肠道载脂蛋白-III作为治疗靶点的潜力的关键知识。

DESCRIPTION (provided by applicant): Apolipoprotein C-III (apoC-III) is an exchangeable lipoprotein produced by both the liver and intestine. The plasma concentration of apoC-III is elevated in type 1 diabetics and is an independent predictor of cardiovascular disease. ApoC-III is found on triglyceride-rich lipoproteins and high-density lipoproteins, and acts to raise plasma triglyceride levels through the inhibition of lipoprotein lipase activity, and by interfering with lipoprotein clearance by the liver. While significant progress has been made in understanding the mechanisms that govern these effects, the role of apoC-III in intestinal lipoprotein synthesis and secretion remains undefined. We have recently observed that whole body overexpression of apoC-III in apoC-III transgenic (Tg) mice results in inhibited intestinal TAG secretion from the enterocyte into lymph coupled with the retention of free fatty acid (FFA) and monoacylglycerol (MAG) precursors and a decrease in TAG within the enterocyte. This inhibitory effect of apoC-III in the intestinal cell is in contrast to studies in hepatocytes, which have correlated apoC-III expression with increased VLDL secretion. Our overall hypothesis is that apoC-III plays a unique role in the intestine and liver in lipoprotein synthesis and secretion. We will test the 3 possible mechanisms by which increased apoC-III would lead to inhibited TAG synthesis (that apoC-III directly inhibits 1) MGAT and/or DGAT enzyme activity; 2) FFA trafficking to the ER; or 3) the activation of FFA to fatty acyl- CoA) and will delineate a mechanistic role for apoC-III in intestinal lipid absorption and secretion. We will also investigate the functional importance of apoC-III in the intestine versus the liver using adenovirus to knockdown and overexpress apoC-III in mouse liver. Finally, we will investigate the role of human apoC-III polymorphisms on intestinal TAG secretion in primary mouse enteroid cultures. The completion of these aims will provide key knowledge about the role of apoC-III in mediating intestinal lipoprotein secretion and the potential of intestinal apoC-III as a therapeutic target.