Regulation of Intestinal Bile Acid Absorption in Health and Cholesterol-Related Disorders

回肠尖端钠依赖型胆汁酸转运体(ASBT)在肠肝病中起着至关重要的作用。 胆汁酸的循环，在维持胆汁酸、脂肪和胆固醇平衡方面起着关键作用。 新出现的证据表明，ASBT是一种有吸引力的恢复代谢的治疗方法 功能和降低血浆胆固醇。鉴于最近的发现，这一点尤为重要。 表明有必要将高风险人群的胆固醇降至非常低的水平。 患有心血管疾病(心血管疾病)，如退伍军人。实现如此严格的目标 在许多情况下仍然具有挑战性，尽管使用了胆固醇合成抑制剂和 胆固醇吸收的阻滞剂。在这方面，已知饮食中的脂肪酸会影响 代谢功能以及脂肪和胆固醇的动态平衡。最近的一项研究表明， ASBT抑制在恢复正常代谢功能方面的有效性取决于 饮食中存在的脂肪酸。然而，不同类型的脂肪酸对ASBT的特异性影响 功能还没有完全被理解。我们最近使用树脂辅助捕获(Acyl-RAC)的新数据 而基于点击化学的代谢标记方法提供了ASBT蛋白是 受S酰化的影响，这是一种可逆的翻译后修饰，脂肪酸与 膜蛋白的半胱氨酸残基决定其膜筏的定位和功能。 我们已经证明了不饱和脂肪酸油酸盐或omega-3脂肪酸的掺入 二十碳五烯酸(EPA)进入ASBT后，其功能显著下降。 我们以前已经证明了ASBT是由转录后机制调控的 包括它与膜脂筏微域的关系。我们的初步调查结果显示 喂食富含鱼油的饲料会降低ASBT功能，并与脂筏相关 老鼠。因此，确定以S酰化为靶点的机制可能有助于抑制ASBT。 功能以及恢复正常的脂肪和胆固醇的动态平衡。ASBT活动和 在带有肠道的转基因小鼠模型(ISR2tg)中，与脂筏的相关性增加。 斯特罗尔反应元件结合蛋白(SREBP2)的特异性过度激活。我们最近 数据显示，ISR2tg小鼠出现高胆固醇血症和严重的肝脏 高脂高胆固醇饮食和阻断胆汁酸时的炎症和纤维化 胆碱胺的吸收减轻了饮食所致的肝损伤。ASBT的功能和关联 在ISR2tg小鼠中，带脂筏增加。基于这些数据，我们提议的研究将测试 假设酰化对ASBT的功能和与脂筏的关联是关键的，并且 肠道特有的机制参与调节ASBT的酰化(特定目标1)。研究 在特定的目标2中，将阐明omega-3脂肪酸对 ASBT功能和S酰化作用的体外模型，并将检验它们的影响 野生型和ASBT胆汁酸稳态及脂类和胆固醇代谢的研究 基因敲除老鼠。为了研究阻断ASBT酰化的有益效果，我们的研究将 进一步利用喂饲高脂高胆固醇饲料的ISR2tg小鼠作为独特的模型来研究 饲喂omega-3多不饱和脂肪酸对ASBT酰化及代谢的影响 功能障碍(特定目标2)。我们的发现代表着我们对 脂肪酸和胆汁酸动态平衡之间的联系。拟议的研究具有非常重要的意义 并可能揭开与阻止ASBT的潜在有益影响有关的新途径 功能和酰化在恢复代谢功能和胆固醇动态平衡中的作用。

The ileal apical sodium-dependent bile acid transporter (ASBT) is crucial for the enterohepatic circulation of bile acids and plays a key role in maintaining bile acid, lipid, and cholesterol balance. Emerging evidence suggests that ASBT is an attractive therapeutic approach to restore metabolic functions and lower plasma cholesterol. This is particularly important in light of recent findings indicating the need to lower cholesterol to very low levels in individuals with high risk for developing cardiovascular diseases (CVDs) such as the veterans. Achieving such stringent target remains challenging in many cases despite the use of cholesterol synthesis inhibitors and blockers of cholesterol absorption. In this regard, dietary fatty acids are known to influence metabolic functions as well as lipid and cholesterol homeostasis. A recent study showed that the effectiveness of ASBT inhibition in restoring normal metabolic functions depends on the types of fatty acids present in the diet. However, specific effects of different types of fatty acids on ASBT function are not fully understood. Our recent novel data using resin-assisted capture (Acyl-RAC) and click-chemistry based metabolic labeling approaches provided evidence that ASBT protein is subject to s-acylation, a reversible post-translational modification where fatty acids attach to cysteine residues of membrane proteins governing their membrane raft localization and function. We have shown that incorporation of the unsaturated fatty acid oleate or omega-3 fatty acid eicosapentaenoic acid (EPA) into ASBT was associated with a significant decrease in its function. We have previously demonstrated that ASBT is regulated by post-transcriptional mechanisms including its association with membrane lipid raft microdomains. Our preliminary findings showed that feeding a diet rich with fish oil decreased ASBT function and association with lipid rafts in mice. Thus, identifying mechanisms that target s-acylation could be beneficial in inhibiting ASBT function as well as restoring normal lipid and cholesterol homeostasis. ASBT activity and association with lipid rafts were increased in a transgenic mouse model (ISR2tg) with intestine- specific overactivation of the Sterol Response Elements Binding Protein (SREBP2). Our recent data demonstrated that ISR2tg mice develop hypercholesterolemia and severe hepatic inflammation and fibrosis when fed a high fat high cholesterol diet and blocking bile acid absorption by cholestyramine reduced the diet-induced liver injury. ASBT function and association with lipid rafts are increased in ISR2tg mice. Based on these data, our proposed studies will test the hypothesis that acylation is critical for ASBT function and association with lipid rafts and that intestine-specific mechanisms are involved in regulating ASBT acylation (Specific aim 1). Studies in Specific Aim 2 will elucidate mechanisms mediating the effects of omega-3 fatty acids on ASBT function and s-acylation in in vitro models including enteroids and will examine their effects on bile acid homeostasis as well as lipid and cholesterol metabolism in wildtype and ASBT knockout mice. To investigate the beneficial effects of blocking ASBT acylation, our studies will further utilize ISR2tg mice fed a high fat high cholesterol diet as a unique model to examine the effects of feeding dietary omega-3 poly unsaturated fatty acids on ASBT acylation and metabolic dysfunction (Specific Aim 2). Our findings represent a paradigm shift in our understanding of the link between fatty acids and bile acid homeostasis. The proposed studies are highly significant and are likely to unravel novel avenues pertaining to potential beneficial effects of blocking ASBT function and acylation in restoring metabolic functions and cholesterol homeostasis.