Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, CA 90089, USA.
Int J Mol Sci. 2021 Feb 18;22(4):2021. doi: 10.3390/ijms22042021.
Leydig cells contain significant amounts of constitutively produced steroidogenic acute regulatory protein (STAR; STARD1). Hormone-induced STAR plays an essential role in inducing the transfer of cholesterol into the mitochondria for hormone-dependent steroidogenesis. STAR acts at the outer mitochondrial membrane, where it interacts with a protein complex, which includes the translocator protein (TSPO). Mutations in STAR cause lipoid congenital adrenal hyperplasia (lipoid CAH), a disorder characterized by severe defects in adrenal and gonadal steroid production; in Leydig cells, the defects are seen mainly after the onset of hormone-dependent androgen formation. The function of constitutive STAR in Leydig cells is unknown. We generated STAR knockout (KO) MA-10 mouse tumor Leydig cells and showed that STAR KO cells failed to form progesterone in response to dibutyryl-cAMP and to TSPO drug ligands, but not to 22()-hydroxycholesterol, which is a membrane-permeable intermediate of the CYP11A1 reaction. Electron microscopy of STAR KO cells revealed that the number and size of lipid droplets were similar to those in wild-type (WT) MA-10 cells. However, the density of lipid droplets in STAR KO cells was drastically different than that seen in WT cells. We isolated the lipid droplets and analyzed their content by liquid chromatography-mass spectrometry. There was a significant increase in cholesteryl ester and phosphatidylcholine content in STAR KO cell lipid droplets, but the most abundant increase was in the amount of diacylglycerol (DAG); DAG 38:1 was the predominantly affected species. Lastly, we identified genes involved in DAG signaling and lipid metabolism which were differentially expressed between WT MA-10 and STAR KO cells. These results suggest that constitutive STAR in Leydig cells is involved in DAG accumulation in lipid droplets, in addition to cholesterol transport. The former event may affect cell functions mediated by DAG signaling.
间质细胞含有大量组成型产生的类固醇急性调节蛋白（STAR；STARD1）。激素诱导的 STAR 在将胆固醇转运到线粒体中以进行激素依赖性类固醇生成中起着至关重要的作用。STAR 在 外 线 粒 体 膜 上 作 用 ， 在 那 里 它 与 包 括 转 位 蛋 白 （TSPO） 的 蛋 白 复 合 物 互 作 。 STAR 的突 变 导 致 脂 质 先 天 性 肾 上 腺 过 度 活 跃 症 （lipoid CAH），这是一种以肾上腺和性腺类固醇生成严重缺陷为特征的疾病；在间质细胞中，这些缺陷主要在激素依赖性雄激素形成后出现。组成型 STAR 在间质细胞中的功能尚不清楚。我们生成了 STAR 敲除（KO）MA-10 鼠肿瘤间质细胞，并表明 STAR KO 细胞无法对二丁酰环磷酰胺和 TSPO 药物配体形成孕酮，但对 22（）-羟胆固醇没有反应，22（）-羟胆固醇是 CYP11A1 反应的膜通透中间产物。STAR KO 细胞的电镜显示，脂滴的数量和大小与 WT MA-10 细胞相似。然而，STAR KO 细胞中脂滴的密度与 WT 细胞有很大的不同。我们分离了脂滴，并通过液相色谱-质谱分析了它们的含量。在 STAR KO 细胞脂滴中，胆甾醇酯和磷脂酰胆碱的含量显著增加，但增加最多的是二酰基甘油（DAG）；DAG 38:1 是受影响最多的物种。最后，我们鉴定了 WT MA-10 和 STAR KO 细胞之间差异表达的参与 DAG 信号和脂质代谢的基因。这些结果表明，间质细胞中的组成型 STAR 除了胆固醇转运外，还参与脂滴中 DAG 的积累。前一事件可能会影响 DAG 信号转导介导的细胞功能。
