Tu Lan N, Zhao Amy H, Hussein Mahmoud, Stocco Douglas M, Selvaraj Vimal
Department of Animal Science (L.N.T., A.H.Z., M.H., V.S.), College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853; and Department of Cell Biology and Biochemistry (D.M.S.), School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430.
Endocrinology. 2016 Mar;157(3):1110-21. doi: 10.1210/en.2015-1795. Epub 2016 Jan 7.
Translocator protein (TSPO), also known as the peripheral benzodiazepine receptor, is a highly conserved outer mitochondrial membrane protein present in specific subpopulations of cells within different tissues. In recent studies, the presumptive model depicting mammalian TSPO as a critical cholesterol transporter for steroidogenesis has been refuted by studies examining effects of Tspo gene deletion in vivo and in vitro, biochemical testing of TSPO cholesterol transport function, and specificity of TSPO-mediated pharmacological responses. Nevertheless, high TSPO expression in steroid-producing cells seemed to indicate an alternate function for this protein in steroidogenic mitochondria. To seek an explanation, we used CRISPR/Cas9-mediated TSPO knockout steroidogenic MA-10 Leydig cell (MA-10:TspoΔ/Δ) clones to examine changes to core mitochondrial functions resulting from TSPO deficiency. We observed that 1) MA-10:TspoΔ/Δ cells had a shift in substrate utilization for energy production from glucose to fatty acids with significantly higher mitochondrial fatty acid oxidation (FAO), and increased reactive oxygen species production; and 2) oxygen consumption rate, mitochondrial membrane potential, and proton leak were not different between MA-10:TspoΔ/Δ and MA-10:Tspo+/+ control cells. Consistent with this finding, TSPO-deficient adrenal glands from global TSPO knockout (Tspo(-/-)) mice also showed up-regulation of genes involved in FAO compared with the TSPO floxed (Tspo(fl/fl)) controls. These results demonstrate the first experimental evidence that TSPO can affect mitochondrial energy homeostasis through modulation of FAO, a function that appears to be consistent with high levels of TSPO expression observed in cell types active in lipid storage/metabolism.
转位蛋白（TSPO），也被称为外周型苯二氮䓬受体，是一种高度保守的线粒体外膜蛋白，存在于不同组织中特定的细胞亚群中。在最近的研究中，将哺乳动物TSPO描述为类固醇生成关键胆固醇转运蛋白的推测模型，已被体内和体外研究Tspo基因缺失的影响、TSPO胆固醇转运功能的生化测试以及TSPO介导的药理反应特异性的研究所驳斥。然而，类固醇生成细胞中TSPO的高表达似乎表明该蛋白在类固醇生成线粒体中具有另一种功能。为了寻求解释，我们使用CRISPR/Cas9介导的TSPO敲除类固醇生成MA-10睾丸间质细胞（MA-10:TspoΔ/Δ）克隆来研究TSPO缺乏导致的核心线粒体功能变化。我们观察到：1）MA-10:TspoΔ/Δ细胞在能量产生的底物利用上从葡萄糖转向脂肪酸，线粒体脂肪酸氧化（FAO）显著增加，活性氧生成增加；2）MA-10:TspoΔ/Δ细胞与MA-10:Tspo+/+对照细胞之间的氧消耗率、线粒体膜电位和质子泄漏没有差异。与此发现一致，与TSPO条件性敲除（Tspo(fl/fl)）对照相比，全身性TSPO敲除（Tspo(-/-)）小鼠的TSPO缺陷肾上腺中参与FAO的基因也出现上调。这些结果证明了第一个实验证据，即TSPO可通过调节FAO影响线粒体能量稳态，这一功能似乎与在脂质储存/代谢活跃的细胞类型中观察到的高水平TSPO表达一致。
