Leydig cell aging: steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage enzyme.
Leydig cell aging: steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage enzyme.
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DOI：
10.1002/j.1939-4640.2001.tb02165.x
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发表时间：
2001-01
影响因子：
--
通讯作者：
L. Luo;Haolin Chen;B. Zirkin
中科院分区：
文献类型：
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作者：
L. Luo;Haolin Chen;B. Zirkin
类固醇合成的主要控制点是胆固醇从细胞内储存到线粒体膜内的运输，以及随后胆固醇侧链裂解酶(P450scc)将胆固醇转化为孕烯醇酮。研究表明，随着年龄的增长，棕色挪威大鼠的睾丸间质细胞中睾酮的产量会下降。为了更好地了解衰老间质细胞失去类固醇生成功能的机制，我们检测了衰老对Leydig细胞重要的胆固醇转移蛋白类固醇生成急性调节蛋白(STAR)和P450scc的影响。分离自中年(14个月)和老年(24个月)大鼠的间质细胞产生的睾酮明显少于年轻(4个月)大鼠的细胞。中年大鼠和老年大鼠间质细胞StAR mRNA(1.7kb)分别显著减少26%和52%。P450scc基因的稳态表达水平也显著降低，分别为29%和50%。免疫印迹结果显示，StAR蛋白和P450scc蛋白的表达显著降低，分别为47%和74%，38%和54%。在体外对黄体生成素刺激的反应中，年轻、中年和老年大鼠的间质细胞产生的睾酮分别增加了30、40和33倍，尽管年轻细胞产生的睾酮显著高于中年和老年细胞。对黄体生成素的反应，StAR蛋白分别增加了1.4倍、3倍和11倍，而P450scc蛋白保持不变。这些结果与STAR介导的胆固醇转运受损可能在与年龄相关的间质细胞类固醇生成减少中发挥关键作用的结论是一致的。然而，由于P450scc在老莱迪格细胞中被还原，在饱和胆固醇进入线粒体的情况下，这种酶催化的反应将是限速的。
Primary points of control in steroidogenesis are the transport of cholesterol from intracellular stores to the inner mitochondrial membrane, and the subsequent conversion of cholesterol to pregnenolone by the cholesterol side-chain cleavage enzyme (P450scc). Testosterone production has been shown to decline in Brown Norway rat Leydig cells as the rats age. To better understand the mechanism by which aging Leydig cells lose steroidogenic function, we examined the effect of aging on steroidogenic acute regulatory protein (StAR), an important Leydig cell cholesterol transfer protein, and on P450scc. Leydig cells isolated from middle-aged (14 months) and old (24 months) rats produced significantly less testosterone than cells from young (4 months) rats. StAR mRNA (1.7 kilobase [kb]) was significantly reduced in Leydig cells from middle-aged and old rats, by 26% and 52%, respectively. Significant reductions also were seen in the steady-state levels of mRNA for P450scc, of 29% and 50%, respectively. Western blots revealed significant reductions in StAR protein, by 47% and 74%, respectively, and in P450scc protein, by 38% and 54%, respectively. In response to LH stimulation in vitro, testosterone production by Leydig cells in young, middle-aged, and old rats increased by 30-, 40-, and 33-fold, respectively, although the amounts of testosterone produced by the young cells significantly exceeded that produced by the middle-aged and old cells. StAR protein also increased in response to LH by 1.4- , 3-, and 11-fold, respectively, whereas P450scc protein remained unchanged. These results are consistent with the conclusion that compromise of StAR-mediated cholesterol transport may play a key role in age-related reductions in Leydig cell steroidogenesis. However, because P450scc is reduced in old Leydig cells, the reaction catalyzed by this enzyme would be rate-limiting under circumstances in which saturating amounts of cholesterol entered the mitochondria.