The Unfolded Protein Response in Sterol Cytoxicity

描述（由申请人提供）： 细胞对高水平固醇的反应对疾病过程和正常生理具有重要影响。在一种情况下，动脉粥样硬化巨噬细胞（Mfs）积聚游离胆固醇（FC）导致Mf死亡，这可能促进斑块不稳定性和急性临床事件，如心肌梗死。在另一种情况下，肠上皮细胞（IEC）暴露于高水平的潜在毒性的饮食和胆汁胆固醇和饮食植物甾醇，因此需要机制来防止肠功能障碍。PI最近发现，内质网（ER）中的一个复杂的信号转导途径-未折叠蛋白反应（UPR）-在培养的MRS对FC的反应中起着关键作用。UPR首先触发一系列适应性反应，但如果适应性反应失败，则诱导细胞凋亡。因此，UPR最初促进FC负载的Mfs中的存活，但随后在延长的FC负载后促进凋亡。由于UPR的独特分支定位于胃肠道，并且由于UPR诱导了保护IEC免受固醇细胞毒性的关键酶，因此UPR也可能在保护IEC免受高水平固醇的影响中发挥重要作用。在这种情况下，本提案的总体目标是调查的作用和机制的UPR在自适应和病理生理过程中与积累过量的甾醇的粥样硬化MFS和IEC。这一目的将通过以下方式实现：（a）确定两个关键UPR基因（一个参与适应性反应，另一个参与细胞凋亡）中的无效突变是否影响动脉粥样硬化的apoE-/-小鼠模型中的损伤性Mf死亡和斑块不稳定性;（B）确定UPR是否在暴露于过量饮食和植物甾醇的小鼠的IEC中被诱导;如果已知有助于保护IEC免受固醇的蛋白质被UPR诱导;如果UPR的破坏导致肠道功能障碍;和（c）通过检验ER膜的FC富集耗尽ER钙的假设来研究FC如何诱导UPR，其是众所周知的UPR的有效诱导剂，通过抑制肌浆网/内质网钙ATP酶或通过激活ER钙通道。Mf研究将增加我们对斑块如何变得脆弱的理解，并将提出涉及急性血管事件的新的治疗靶点，肠道研究将揭示胆固醇生理学的一个新的重要方面。

DESCRIPTION (provided by applicant): The responses of cells to high levels of sterols has important implications for disease processes and normal physiology. In one setting, the accumulation of free cholesterol (FC) by atheroma macrophages (Mfs) leads to Mf death, which likely promotes plaque instability and acute clinical events, like myocardial infarction. In another setting, intestinal epithelial cells (IECs) are exposed to high levels of potentially toxic dietary and biliary cholesterol and dietary plant sterols, and so mechanisms are necessary to prevent intestinal dysfunction. The PI has recently discovered that a complex signal transduction pathway in the endoplasmic reticulum (ER)--the Unfolded Protein Response (UPR)--plays a critical role in the response of cultured Mrs to FC. The UPR first triggers a set of adaptive response, but then induces apoptosis if the adaptive responses fail. As such, the UPR initially promotes survival in FC-Ioaded Mfs, but then promotes apoptosis after prolonged FC loading. Because a unique branch of the UPR is localized to the gastrointestinal tract, and because a critical enzyme that protects IECs from sterol cytotoxicity is induced by the UPR, the UPR may also play an important role in the protection of IECs from high levels of sterols. In this context, the overall objective of this proposal is to investigate the roles and mechanisms of the UPR in adaptive and pathophysiological processes associated with the accumulation of excess sterols by atheroma Mfs and IECs. This objective will be met by: (a) determining if null mutations in two key UPR genes--one involved in the adaptive response and the other in apoptosis--affect lesional Mf death and plaque instability in the apoE-/- mouse model of atherosclerosis; (b) determining if the UPR is induced in IECs of mice exposed to excess dietary and plant sterols; if proteins known to help protect IECs from sterols are induced by the UPR; and if disruption of the UPR leads to intestinal dysfunction; and (c) investigating how FC induces the UPR by testing the hypothesis that FC enrichment of the ER membrane depletes ER calcium, which is a well-known and potent inducer of the UPR, by inhibiting the sarco/endoplasmic reticulum calcium ATPase or by activating ER calcium channels. The Mf studies will add to our understanding of how plaques become vulnerable and will suggest novel therapeutic targets involved in acute vascular events, and the intestinal studies will reveal a new and important aspect of intestinal-sterol physiology.