Lipid transport in the intestine

 描述（由申请人提供）：膳食脂质在数量和质量上对人类健康都很重要，外源性脂质的肠道加工对其同化至关重要。虽然对膳食脂质的管腔消化了解很多，但对其细胞内转运和加工的了解较少。这些研究将集中在两个不同的脂肪酸结合蛋白（FABP），这是在肠上皮细胞中表达，肠-FABP和肝-FABP（IFABP和LFABP）。虽然被认为是肠上皮细胞脂质运输的关键，但这尚未得到直接证明。也不清楚为什么两种都结合FA的同源蛋白在肠上皮细胞中共表达。我们早期的动力学研究证明了蛋白质之间的显著差异，表明IFABP和LFABP可能具有不同的功能。我们现在首次比较了这些FABP缺失的小鼠，观察到的显着表型差异表明它们确实具有至少一些独特的作用，不仅在肠上皮细胞脂质代谢中，而且通过对全身能量稳态产生显著不同的影响而更是如此。具体地说，我们发现高脂肪喂养的LFABP-/-小鼠是贪食和明显肥胖的，但不显示葡萄糖耐受不良，并具有改善的运动表现，从而显示“代谢健康肥胖”（MHO）表型。IFABP-/-小鼠也比WT“更健康”，具有改善的葡萄糖耐量和更有效的肠道脂质分泌。然而，与LFABP-/-形成鲜明对比的是，高脂肪喂养的IFABP-/-小鼠比WT小鼠体重更轻，积累更少的体脂和更多的瘦体重。研究的两种无效小鼠都是整体敲除的，虽然IFABP通常仅在肠中表达，但LFABP也在肝脏中高度表达，因此我们还不知道LFABP-/-小鼠中的显著变化是否是由于肠、肝脏或两者中的LFABP。也不知道肠上皮细胞IFABP的缺失如何导致瘦型。有趣的是，我们已经发现了脂肪酸和单酰基甘油的肠代谢以及粘膜内源性大麻素（EC）（特别是MG 2-花生四烯酸甘油）水平的变化，并假设FABP消融的这些组织水平效应至少部分地促成全身表型。基于这些观察结果和问题，我们的目的是：1）确定在LFABP-/-小鼠中观察到的暴食和肥胖是否通过EC系统介导; 2）探索IFABP消融导致脂肪量和体重减少以及瘦体重增加的机制; 3）使用我们新产生的LFABP/IFABP双敲除小鼠（L/I-DKO）来确定肠细胞FABP是否是大量脂质摄取所需的;和4）确定肝LFABP与肠FABP对MHO LFABP-/-表型的贡献，以及肠FABP（L + IFABP）与肝FABP（LFABP）对肠脂质加工的下游全身效应的贡献。拟议的研究将使用L/I-DKO小鼠，通过肝脏LFABP或肠道LFABP的条件性缺失产生的小鼠，以及LFABP-/-和L/I-DKO肝脏中LFABP与IFABP的腺相关病毒替代，以提供关于肠上皮细胞脂质转运和加工及其与全身燃料代谢的关系的重要新信息。

 DESCRIPTION (provided by applicant): Dietary lipid is important both quantitatively and qualitatively to human health, and intestinal processing of exogenous lipid is central to its assimilation. While much is known about luminal digestion of dietary lipid, its intracellular transport and processing are less well understood. These studies will focus on the two different fatty acid-binding proteins (FABPs) which are expressed in the enterocyte, intestinal-FABP and liver-FABP (IFABP and LFABP). While thought to be critical for enterocyte lipid trafficking, this has not been directly demonstrated. Nor is it clear why two homologous proteins that both bind FAs, are co-expressed in the enterocyte. Our earlier kinetics studies demonstrated marked differences between the proteins, suggesting that IFABP and LFABP are likely to have distinct functions We have now compared mice null for these FABPs for the first time, and the remarkable phenotypic differences observed indicate that they indeed have at least some unique roles, not only in enterocyte lipid metabolism, but even more so by leading to markedly different effects on whole body energy homeostasis. Specifically, we find that high fat-fed LFABP-/- mice are hyperphagic and markedly obese, yet do not display glucose intolerance and have improved exercise performance, thus displaying a "metabolically healthy obese" (MHO) phenotype. The IFABP-/- mouse is also "healthier" than WT, with improved glucose tolerance and more efficient intestinal lipid secretion. However in marked contrast to the LFABP-/-, the high fat-fed IFABP-/- mouse weighs less and accumulates less body fat and more lean mass than WT mice. Both null mice studied are global knockouts, and while IFABP is normally expressed only in intestine, LFABP is also highly expressed in liver, thus we do not yet know whether the dramatic changes in LFABP-/- mice are due to LFABP in intestine, liver, or both. It is also not yet known how loss of enterocyte IFABP leads to a lean phenotype. Interestingly, we have found changes in intestinal metabolism of fatty acids and monoacylglycerols and in levels of mucosal endocannabinoids (EC), in particular the MG 2-arachidonoyl glycerol, and hypothesize that these tissue-level effects of FABP ablation contribute, at least in part, to the whole body phenotypes. Based on these observations and questions, our aims are to 1) determine whether the hyperphagia and obesity observed in the LFABP-/- mouse are mediated via the EC system; 2) explore the mechanisms by which ablation of IFABP leads to decreased fat mass and body weight and increased lean body mass; 3) use our newly generated LFABP/IFABP double knockout mouse (L/I-DKO) to definitively determine whether the enterocyte FABPs are required for bulk lipid uptake; and 4) define the contributions of liver LFABP vs. intestinal FABP to the MHO LFABP-/- phenotype, and the contributions of intestinal FABPs (L + IFABP) vs. hepatic FABP (LFABP) to the downstream systemic effects of intestinal lipid processing. The proposed studies will use the L/I-DKO mouse, mice generated by conditional deletions of liver LFABP or intestinal LFABP, and adeno-associated viral replacement of LFABP vs. IFABP in the LFABP-/- and L/I-DKO liver, to provide important new information about enterocyte lipid transport and processing, and their relationships to systemic fuel metabolism.