CD36 AND INTESTINAL FAT ABSORPTION

描述（由申请人提供）：CD36是一种多功能膜蛋白，我们在1993年发现它是长链脂肪酸（FA）摄取的促进剂。CD36的这一作用现在得到了我们和其他人获得的大量体内证据的支持。这项拨款最初是为了研究CD36在小肠脂质吸收中的作用，基于其高表达及其沿胃-结肠轴的分布，这与脂质转运的作用一致。我们的目的是确定CD36缺失小鼠在吸收和乳糜微粒产生方面的任何缺陷，并检查对高脂肪饮食引起的肥胖的易感性。其他研究提出要研究CD36在引导FA生成乳糜微粒中的作用，以及CD36与其他涉及FA在肠道结合和利用的蛋白质之间可能的相互作用。在这项资助期间，我们证明了CD36缺失小鼠肠道脂质处理的缺陷。淋巴中的脂质分泌也被发现有50%的抑制，乳糜微粒产生缺陷，并转向更多的VLDL减少。我们最近对原代肠细胞的研究表明，分泌缺陷是由于近端肠FA和胆固醇摄取受损造成的。最后，我们记录了CD36缺失小鼠的餐后脂蛋白清除严重受损，这干扰了在肠道水平上测量CD36缺乏对代谢影响的尝试。基于上述，目前的申请提出了检验假设，即CD36在肠细胞顶膜的存在将脂肪酸靶向甘油三酯形成的单酰基甘油途径，为乳糜微粒的产生提供营养。更具体地说，我们将研究CD36在甘油三酯转移到内质网（ER）和从内质网转移到高尔基体中的作用。我们的第二个目标是探索是否靶向肠道中的CD36，单独或联合靶向L-FABP，可以降低餐后血液甘油三酯，改善肥胖或糖尿病的预后。我们将通过在WT和L-FABP缺失背景下产生肠道特异性CD36缺失的小鼠来验证这一点。第三，我们最近的数据表明CD36在肠促胰岛素释放中的作用，我们将研究这一作用对脂肪摄入和胰岛素分泌的影响。第四，我们建议研究CD36缺乏对人体脂质吸收、餐后脂蛋白清除和肠促胰岛素释放的代谢影响。据报道，人类CD36缺乏与餐后和禁食状态的血脂异常有关。这些研究将扩大我们对乳糜微粒形成和肠促胰岛素释放的分子机制的认识。他们将深入了解肠道CD36功能障碍对人类高甘油三酯脑病病因的贡献。

DESCRIPTION (provided by applicant): CD36 is a multifunctional membrane protein we identified in 1993 as a facilitator of long-chain fatty acid (FA) uptake. This role of CD36 is now supported by a wealth of in vivo evidence obtained by us and by others. This grant was initially submitted to examine the role of CD36 in lipid absorption in the small intestine, based on its high expression and its distribution along the gastro-colonic axis, which are consistent with a role in lipid transport. Our aims were to define any defects in absorption and chylomicron production in CD36 null mice and to examine susceptibility to high fat diet-induced obesity. Other studies proposed to examine the role of CD36 in directing the FA to chylomicron production and possible interactions between CD36 and other proteins implicated in FA binding and utilization in the intestine. During the funding of this grant we demonstrated a defect in lipid processing by the intestine of the CD36 null mouse. Secretion of lipid in the ymph was also found to be 50% depressed with a defect in chylomicron production and a shift to more VLDL reduction. Our recent work with primary enterocytes indicates that the defect in secretion is consequent to mpairments in FA and cholesterol uptake in the proximal intestine. Finally, we have documented severely mpaired clearance of postprandial lipoproteins in the CD36 null mouse which interferes with attempts to measure the metabolic impact of CD36 deficiency at the level of the intestine. Based on the above the current application proposes to examine the hypothesis that the presence of CD36 at the enterocyte apical membrane targets the fatty acid to the monoacylglycerol pathway of triglyceride formation that feeds chylomicron production. More specifically we will examine the role of CD36 in transfer of triglycerides to the endoplasmic reticulum (ER) and from the ER to the Golgi. Our second goal is to explore whether targeting CD36 in the intestine, alone or in combination with targeting L-FABP, can lower postprandial blood triglycerides for improving outcome in obesity or diabetes. We will test this by generating a mouse with intestine-specific deficiency of CD36 on the WT and L-FABP null backgrounds. Third our recent data indicate a role of CD36 in the release of intestinal incretins and we will examine the implications of this role with respect to fat intake and insulin secretion. Fourth we propose to examine the metabolic impact of CD36 deficiency in humans with respect to lipid absorption, clearance of postprandial lipoproteins and incretin release. CD36 deficiency in humans has been reported to be associated with abnormalities of blood lipids in both the postprandial and fasted states. The studies will expand our knowledge of the molecular mechanisms underlying chylomicron formation and incretin release. They will provide insight into the contribution of dysfunctions in intestinal CD36 to the etiology of hypertriglyceredemia in humans.