MECHANISM OF OXYSTEROL ACTIVATION OF MEMBRANE CHOLESTEROL

摘要 细胞胆固醇水平受到多个稳态通路的严格调控，这些通路对 膜胆固醇和在酶作用下形成的含氧胆固醇衍生物(即氧化甾醇)。 类固醇感知和转运途径的改变有助于人类先天的新陈代谢错误(例如， 尼曼-皮克C病)和获得性疾病状态(例如动脉粥样硬化)。在生理状态下 条件下，固醇调节的转录途径协同作用，抑制外源性脂蛋白的摄取 并抑制从头合成胆固醇，导致这些反应的一半最大抑制在 几个小时。相比之下，病理生理胆固醇水平，如疾病状态下的胆固醇水平， 激活不依赖转录的机制，这些机制在几分钟内对 膜胆固醇。最近对氧合甾醇对映体的研究提供了证据 相互作用是这些急性胆固醇稳态反应的基础。我们假设侧链 氧化甾醇在胆固醇稳态的急性调节中起关键作用 质膜脂环境的调节。我们认为侧链上的氧固醇会触发 膜磷脂组织和/或紊乱的转录非依赖性调控途径 增加胆固醇的可及性。这一假设将通过以下具体目标进行检验：(1) 氧化甾醇扰乱模型胆固醇-磷脂结构的机理表征 双分子膜，(2)氧化甾醇对胆固醇可及性和生理位置的影响 膜，以及(3)氧化甾醇促进质膜释放的机制的研究 到细胞内的胆固醇池。拟议的研究将进一步加深我们对微扰如何在 膜结构传递胆固醇稳态调节信号，可能识别新的药理作用 在疾病状态下操纵细胞处理胆固醇的目标。

ABSTRACT Cellular cholesterol levels are tightly regulated by multiple homeostatic pathways that respond to elevations of membrane cholesterol and to enzymatically formed oxygenated cholesterol derivatives (i.e., oxysterols). Alterations in sterol sensing and trafficking pathways contribute to human inborn errors of metabolism (e.g., Niemann-Pick C disease) and to acquired disease states (e.g., atherosclerosis). Under physiological conditions, sterol-regulated transcriptional pathways act in concert to inhibit uptake of exogenous lipoproteins and suppress de novo cholesterol synthesis, resulting in half-maximal suppression of these responses within several hours. By contrast, pathophysiological cholesterol levels, such as those present in disease states, activate transcription-independent mechanisms that respond within minutes to changes in increments in membrane cholesterol. Recent studies with oxysterol enantiomers provide evidence that sterol-membrane interactions underlie these acute cholesterol homeostatic responses. We hypothesize that side-chain oxysterols serve a critical role in acute regulation of cholesterol homeostasis through direct modulation of plasma membrane lipid environment. We propose that side-chain oxysterols trigger transcription-independent regulatory pathways by disordering membrane phospholipid organization and/or increasing the accessibility of cholesterol. This hypothesis will be tested by the following Specific Aims: (1) Characterization of the mechanism by which oxysterols perturb the structure of model cholesterol-phospholipid bilayers, (2) Examination of the efect of oxysterols on cholesterol accessibility and position in physiological membranes, and (3) Examination of the mechanism by which oxysterols promote release of plasma membrane cholesterol to intracellular pools. The proposed studies wil further our understanding of how perturbations in membrane structure relay cholesterol homeostatic regulatory signals and may identify new pharmacological targets for manipulation of the cellular handling of cholesterol in disease states.