MECHANISM OF OXYSTEROL ACTIVATION OF MEMBRANE CHOLESTEROL

摘要 细胞胆固醇水平受到多种稳态途径的严格调节，这些途径对胆固醇水平的升高做出反应。 膜胆固醇和酶促形成的氧化胆固醇衍生物（即，氧固醇）。 固醇传感和运输途径的改变有助于人类先天性代谢缺陷（例如， 尼曼-匹克C病）和获得性疾病状态（例如，动脉粥样硬化）。在生理 条件下，甾醇调节的转录途径一致行动，以抑制摄取外源性脂蛋白 并抑制胆固醇的从头合成，导致这些反应的一半最大抑制， 几个小时.相比之下，病理生理胆固醇水平，如疾病状态中存在的胆固醇水平， 激活转录独立机制，在几分钟内响应增量变化， 膜胆固醇最近的研究与氧甾醇对映体提供的证据表明，甾醇膜 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 氧化固醇通过直接的胆固醇代谢在胆固醇体内平衡的急性调节中起关键作用。 调节质膜脂质环境。我们认为侧链氧固醇 通过扰乱膜磷脂组织和/或 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） 氧化甾醇对模型胆固醇-磷脂结构的扰动机制的表征 （2）氧固醇对胆固醇可及性和在生理性细胞中的位置的影响的检查。 （3）氧固醇促进质膜释放的机制的检查 胆固醇到细胞内池。所提出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， 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.