Microsomal Transfer Protein Modulates Lipoprotein Metabolism and Retinal lipid Homeostasis

脂质处理是视网膜色素上皮(RPE)最重要的功能之一 位于神经视网膜和Bruch膜脉络膜之间的非活跃细胞层。视觉功能 取决于RPE和神经视网膜之间的密切结构、功能和代谢相互作用。 在这个复合体中，脂代谢受到严格的调节，它的失调会触发过量的积累 视网膜色素上皮及邻近的Bruch膜和脉络膜血管内的脂质。在人类的视网膜中， 中性脂肪堆积是衰老的特征，是疾病相关损害的先兆。一个 值得注意的是，这种中性脂的比例不能包含在含脂蛋白的载脂蛋白B100(BLP)中 类似于心肌细胞相关的BLPS。必须处理的大量脂类 RPE，通过富含脂质的外段的循环和代谢以及循环脂蛋白的摄取， 预测为了防止脂质过载，RPE合成和分泌BLP。在这方面，RPE分享新陈代谢 与心肌细胞相似；两者都利用脂肪酸作为能量来源，都分泌独特的富含EC的BLP。 虽然已经证明MTP介导的BLPS的分泌保护心肌细胞免受脂质堆积， 关于RPE在体内组装/分泌BLP的研究很少。在这些研究中，我们将使用鼠标 破译BLP失调相关病理后果的模型和细胞培养 抑制或基因消融RPE中MTTP基因的组装和分泌途径。微粒体移植 蛋白(MTP)是MTTP基因的产物，是一种内质网驻留的脂转移蛋白 是BLP组装和分泌所必需的。在第一个特定目标中，我们将测试MTP介导的假设 BLP的分泌是一种保护RPE脂质过载的机制。测试本地化的贡献 视网膜色素上皮细胞合成和分泌BLP对视网膜脂质平衡和细胞功能代谢的影响 系统中，我们产生了rpe特异性mtp缺陷(rpemttp)小鼠。在第二个具体目标中，我们将 测试BLP装配受每日摄入的OS脂负荷调节的假设。我们将使用RPE 从人诱导多能干细胞(IPSCs)分化来研究脂类的作用机制 通过外段吞噬作用调节MTP活性和BLP的产生。使用这些细胞，我们 将确定MTP的丢失是通过基因消融(虹膜中MTP的Kd)还是药物抑制， 导致RPE脂肪变性。总体而言，这些探索性研究将探讨地方BLP的具体作用 在视网膜脂类平衡中组装。BLP功能失调可导致非自主性改变 对整个系统造成负面影响，并导致视力丧失。这些研究可能是研究的基础。 发生与年龄相关的变化的后续步骤，如炎症和退行性变 脂蛋白代谢紊乱。

Lipid handling is one of the most critical functions of the retinal pigment epithelium (RPE) a single mitotically inactive cell layer that is situated between the neural retina and the Bruch's membrane-Choroid. Visual function depends on the intimate structural, functional and metabolic interactions between the RPE and the neural retina. Within this complex, lipid metabolism is tightly regulated, and its' dysregulation triggers accumulation of excess lipids within the RPE and the adjacent Bruch's membrane and choroidal vasculature. In the human retina the accumulation of neutral lipid deposits is a characteristic of aging and precedes disease associated-lesions. A significant proportion of this neutral lipid is enclosed within apolipoprotein B100 containing lipoproteins (Blps) that resemble cardiomyocyte associated Blps. The prodigious amount of lipid that must be processed by the RPE, through the recycling and metabolism of lipid rich outer segments and ingestion of circulating lipoproteins, predicts that to prevent lipid overload the RPE synthesize and secrete Blp. In this regard, RPE shares metabolic similarity with cardiomyocytes; both utilize fatty acids as an energy source and both secrete unique EC rich Blps. While it has been shown that MTP-mediated secretion of Blps protects cardiomyocytes from lipid accumulation, there is a paucity of studies regarding Blp assembly/secretion by RPE in vivo. In these studies we will use mouse models and cell culture to decipher the pathological consequences associated with dysregulation of Blp assembly and secretion pathway by inhibiting or genetic ablation of the Mttp gene in RPE. Microsomal transfer protein (MTP), the product of the MTTP gene, is an endoplasmic reticulum-resident lipid transfer protein necessary for Blp assembly and secretion. In the first specific aim we will test the hypothesis that MTP-mediated secretion of Blp is a mechanism for protecting against RPE lipid overload. To test the contribution of localized synthesis and secretion of Blp by the RPE to retinal lipid homeostasis and cell function in a metabolically intact system, we generated the RPE-specific MTP deficient (RPEMttp) mouse. In the second specific aim we will test the hypothesis that Blp assembly is modulated by the daily load of ingested OS lipids. We will use RPE differentiated from human induced pluripotent stem cells (iPSCs) to investigate the mechanism by which lipids taken up through outer segment phagocytosis regulate MTP activity and Blp production. Using these cells, we will determine if loss of MTP, either through gene ablation (KD of MTP in iRPE) or pharmacological inhibition, contributes to RPE steatosis. Collectively, these exploratory studies will address the specific role of local Blp assembly in retinal lipid homeostasis. Dysregulation of Blp function can cause non- autonomous changes that negatively affect the entire system and lead to vision loss. These studies maybe foundational to study subsequent steps in the development of age-related changes such as inflammation and degeneration associated with dysregulation of lipoprotein metabolism.