StAR in Regulated Steroidogenesis

描述（由申请人提供）：受调节的类固醇生成的一个重要事件是类固醇生成细胞对营养激素的急性反应；这种反应主要反映了胆固醇底物向线粒体内膜内胆固醇侧链切割酶（Cyp11a）的传递增加。先天性脂质肾上腺增生症（lipoid CAH）患者和STAR基因敲除（STAR KO）小鼠揭示了类固醇急性调节蛋白（STAR）在胆固醇易位中的重要作用。有两种不同的StAR作用模型：它作用于线粒体外膜，可能发生构象变化，促进胆固醇易位，或者它在线粒体外膜和内膜的类固醇复合物之间运送胆固醇。我们认为，前一种模型主要基于非甾体源性COS细胞的转染研究，反映了非甾体源性细胞中StAR过表达的异常效应。我们进一步假设，在真正的类固醇生成细胞中诱导类固醇生成将需要线粒体靶向STAR。为了解决这个问题，我们将分析来自StAR KO小鼠的永生化细胞系的StAR功能。这些细胞系也将提供一个独特的系统来探索类固醇细胞背景下StAR结构和功能的其他方面。通过BAC转基因对StAR - KO小鼠进行转基因拯救，将在体内验证这些结果对StAR - KO功能的新见解。最后，最近的研究表明，脊椎动物的大脑产生一系列类固醇衍生物，称为神经类固醇，在记忆、应激反应、癫痫发作阈值和焦虑等过程中发挥重要作用；我们建议产生cns特异性的StAR KO小鼠，从而提供了一个独特的机会来定义StAR在神经类固醇产生中的作用。总的来说，这些研究将为调节类固醇生成的这一重要组成部分的功能提供新的见解。

DESCRIPTION (provided by applicant): An essential event in regulated steroidogenesis is the acute response of steroidogenic cells to trophic hormones; this response predominantly reflects increased delivery of cholesterol substrate to the cholesterol side-chain cleavage enzyme (Cyp11a) in the inner mitochondrial membrane. The essential role of the Steroidogenic Acute Regulatory protein (STAR) in cholesterol translocation has been revealed by humans with congenital lipoid adrenal hyperplasia (lipoid CAH) and by StAR knockout (STAR KO) mice. There are two divergent models of StAR action: that it acts at the outer mitochondrial membrane, perhaps undergoing a conformational change that facilitates cholesterol translocation, or that it shuttles cholesterol between the outer mitochondrial membrane and the steroidogenic complex in the inner membrane. We believe that the former model--based largely on transfection studies in non-steroidogenic COS cells--reflects aberrant effects of StAR over-expression in non-steroidogenic cells. We further hypothesize that induction of steroidogenesis in bona fide steroidogenic cells will require mitochondrial targeting of STAR. To address this question, we will analyze StAR function in immortalized cell lines derived from StAR KO mice. These cell lines also will provide a unique system to explore other aspects of StAR structure and function within the context of steroidogenic cells. Results that provide novel insights into StAR function will be verified in vivo by transgenic rescue of StAR KO mice via BAC transgenesis. Finally, recent studies suggest that the vertebrate brain produces a series of steroid derivatives--termed neurosteroids--that play important roles in processes such as memory, stress response, seizure threshold, and anxiety; we propose to generate CNS-specific StAR KO mice, thereby providing a unique opportunity to define the role of StAR in neurosteroid production. Collectively, these studies will provide novel insights into the function of this essential component of regulated steroidogenesis.