MECHANISM OF OXYSTEROL ACTIVATION OF MEMBRANE CHOLESTEROL

描述(由申请人提供)：细胞胆固醇水平受到多种稳态途径的严格调控，这些途径对细胞膜胆固醇的升高和酶促形成的含氧胆固醇衍生物(即氧化甾醇)做出反应。类固醇感知和转运途径的改变有助于人类先天的代谢错误(例如，Niemann-Pick C病)和后天疾病状态(例如，动脉粥样硬化)。在生理条件下，固醇调节的转录途径协同作用，抑制外源性脂蛋白的摄取，抑制从头合成胆固醇，导致这些反应在几个小时内达到一半最大抑制。相比之下，病理生理的胆固醇水平，如那些存在于疾病状态的胆固醇，激活了转录独立的机制，这些机制在几分钟内对膜胆固醇的增加做出反应。最近对氧化甾醇对映体的研究提供了证据，证明固醇-膜相互作用是这些急性胆固醇稳态反应的基础。我们推测，侧链氧化甾醇通过直接调节质膜脂质环境，在胆固醇稳态的急性调节中起关键作用。我们认为，侧链氧合甾醇通过扰乱膜磷脂组织和/或增加胆固醇的可及性来触发转录无关的调控途径。这一假说将通过以下具体目标来检验：(1)氧化甾醇扰乱模型胆固醇-磷脂双层结构的机制的表征，(2)氧化甾醇对胆固醇在生理膜中的可及性和位置的影响的检验，以及(3)氧化甾醇促进质膜胆固醇释放到细胞内池的机理的检验。这些拟议的研究将进一步加深我们对膜结构的扰动如何传递胆固醇稳态调节信号的理解，并可能为操纵疾病状态下的胆固醇的细胞处理寻找新的药理靶点。 公共卫生相关性：虽然胆固醇对正常的细胞功能是必不可少的，但胆固醇代谢的变化可能会导致人类遗传性疾病和获得性疾病状态，如动脉粥样硬化。这项研究的目的是在分子水平上了解细胞如何应对过量的胆固醇并维持胆固醇平衡。拟议的研究可能会确定治疗胆固醇水平升高的患者的新药物靶点，这些患者有患心脏病的风险。

DESCRIPTION (provided by applicant): 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 effect of oxysterols on cholesterol accessibility and position in physiological membranes, and (3) Examination of the mechanism by which oxysterols promotes release of plasma membrane cholesterol to intracellular pools. The proposed studies will 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. PUBLIC HEALTH RELEVANCE: While cholesterol is essential for normal cellular function, alterations in cholesterol metabolism can contribute to human genetic disease and to acquired disease states, such as atherosclerosis. The goal of this study is to understand at the molecular level how cells respond to excess cholesterol and maintain cholesterol balance. The proposed studies may identify new drug targets for treatment of patients with elevated cholesterol levels, who are at risk for heart disease.