Short-Chain Dehydrogenases in Retinol/Sterol Metabolism

性状（由申请方提供）：视黄酸在多种胎儿和成人组织的分化和发育中起重要作用。视黄酸由视黄醇经两步产生：首先，通过可逆氧化将视黄醇转化为视黄醇醛，然后将视黄醇醛不可逆地氧化为视黄酸。视黄醇的氧化是视黄酸生产中的限速步骤，其决定了从视黄醇生物合成视黄酸的总速率。在上一个资助期间，我们已经确定了两个亚家族的人短链脱氢酶/还原酶（SDRs）超家族的蛋白质，对类维生素A有活性。当在完整细胞中表达时，RoDH样SDR赋予将视黄醇氧化为视黄醇的能力，而RalR 1样酶赋予将视黄醇还原回视黄醇的能力。基于这些观察结果，我们提出，这两组人的SDR有助于类维生素A在人体组织中的稳态调节视黄醇和视黄醇之间的平衡，从而调节视黄酸的生物合成速率。为了验证我们的假设，我们建议在人类和动物组织中，在存在和不存在RoDH和RalR 1样SDR的情况下，描述类维生素A代谢的特征。在第一个具体目标下的实验将检验以下假设：在人器官型皮肤筏培养物中RoDH样SDR基因表达的沉默导致视黄醇氧化为视黄醇的速率降低，而RalR 1样SDR基因表达的沉默导致视黄醇转化为视黄醇的速率降低。第二个具体目标下的实验将补充人皮肤筏中的离体研究与RalR 1敲除小鼠模型中的体内研究，并将测试RalR 1对小鼠组织中的视黄醇还原为视黄醇至关重要的假设。因为在体外小鼠直系同源物的RalR 1是高度活跃的中链醛类，除了视黄醇，我们还将测试是否RalR 1有助于减少中链醛。据报道，在癌细胞、酒精性肝病和胎儿酒精综合征中，类维生素A体内平衡被破坏。拟议的研究将提供一个更好的理解的分子基础基础上失调的维甲酸代谢在各种病理状态。

DESCRIPTION (provided by applicant): Retinoic acid plays an important role in differentiation and development of a wide variety of fetal and adult tissues. Retinoic acid is produced from retinol in two steps: first, retinol is converted to retinaldehyde by a reversible oxidation, and then retinaldehyde is irreversibly oxidized to retinoic acid. The oxidation of retinol is the rate-limiting step in retinoic acid production that determines the overall rate of retinoic acid biosynthesis from retinol. During the previous funding period, we have identified two subfamilies of the human short-chain dehydrogenase/reductase (SDRs) superfamily of proteins that are active toward retinoids. When expressed in intact cells, RoDH-like SDRs confer the ability to oxidize retinol to retinaldehyde, whereas RalR1-like enzymes confer the ability to reduce retinaldehyde back to retinol. Based on these observations, we propose that both groups of human SDRs contribute to retinoid homeostasis in human tissues by regulating the equilibrium between retinol and retinaldehyde, and thereby, regulating the rate of retinoic acid biosynthesis. To test our hypothesis, we propose to characterize retinoid metabolism in human and animal tissues in the presence and in the absence of RoDH- and RalR1-like SDRs. Experiments under the first specific aim will test a hypothesis that silencing of RoDH-like SDR gene expression in human organotypic skin raft culture results in a decreased rate of retinol oxidation to retinaldehyde, whereas silencing of RalR1- like SDR gene expression results in a decreased rate of retinaldehyde conversion to retinol. Experiments under the second specific aim will complement the ex vivo studies in human skin rafts with in vivo studies in RalR1 knockout mouse model and will test a hypothesis that RalR1 is essential for the reduction of retinaldehyde to retinol in mouse tissues. Because in vitro the mouse ortholog of RalR1 is highly active toward medium-chain aldehydes in addition to retinaldehydes, we will also test whether RalR1 contributes to the reduction of medium-chain aldehydes. It has been reported that retinoid homeostasis is disrupted in cancer cells, in alcoholic liver disease and in fetal alcohol syndrome. The proposed studies will provide a better understanding of the molecular bases underlying disregulation of retinoid metabolism in various pathological states.