Facultad de Ciencias Bioquímicas y Farmacéuticas, Instituto de Fisiología Experimental, Universidad Nacional de Rosario, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.
Mol Cell Endocrinol. 2011 Jan 30;332(1-2):253-60. doi: 10.1016/j.mce.2010.10.020. Epub 2010 Nov 12.
Cumulative evidence demonstrated effective downstream metabolism of pregnenolone in renal tissue. The aim of this study was to evaluate the expression and functional activity of cytochrome P450 side chain cleavage enzyme (CYP11A1), which converts cholesterol into pregnenolone, in adult rat kidney. Immunohistochemical labeling for CYP11A1 was observed in renal cortex and medulla, on structures identified as distal convoluted tubule and thick ascending limb of Henle's loop, respectively. Immunoblotting analysis corroborated the renal expression of the protein in inner mitochondrial membrane fractions. The incubation of isolated mitochondria with the membrane-permeant cholesterol analogue 22R-hydroxycholesterol resulted in efficient formation of pregnenolone, the immediate precursor for the synthesis of all the steroid hormones. The low progesterone production rate observed in these experiments suggested a poor activity of 3β-hydroxysteroid dehydrogenase enzyme in renal mitochondria. The steroidogenic acute regulatory protein (StAR), involved in the mitochondrial import of cholesterol, was detected in renal tissue at both mRNA and protein level. Immunostaining for StAR showed similar distribution to that observed for CYP11A1. The expression of StAR and CYP11A1 was found to be higher in medulla than in cortex. This enhanced expression of steroidogenesis-related proteins correlated with a greater pregnenolone synthesis rate and higher steroid hormones tissular content measured in medulla. In conclusion, we have established the expression and localization of StAR and CYP11A1 protein, the ability of synthesizing pregnenolone and a region-specific content of sex hormones in the adult rat kidney. These data clearly show that the kidney is a steroid hormones synthesizing organ. It is proposed that the existence in the kidney of complete steroidogenic machinery would respond to a physiological significance.
累积证据表明孕烯醇酮在肾组织中有有效的下游代谢。本研究旨在评估将胆固醇转化为孕烯醇酮的细胞色素 P450 侧链裂解酶 (CYP11A1) 在成年大鼠肾脏中的表达和功能活性。在肾皮质和髓质中观察到 CYP11A1 的免疫组织化学标记，分别位于远曲小管和亨利氏环升支粗段的结构上。免疫印迹分析证实了蛋白质在内线粒体膜部分的肾表达。将分离的线粒体与膜通透的胆固醇类似物 22R-羟胆固醇孵育可有效地形成孕烯醇酮，这是所有甾体激素合成的直接前体。在这些实验中观察到的孕酮产生率低表明肾线粒体中 3β-羟甾脱氢酶酶的活性差。参与胆固醇线粒体导入的甾体生成急性调节蛋白 (StAR) 在肾组织中在 mRNA 和蛋白质水平上均被检测到。StAR 的免疫染色显示与 CYP11A1 观察到的分布相似。StAR 和 CYP11A1 的表达在髓质中高于皮质。与在皮质中相比，这种与甾体生成相关的蛋白质表达增加与在髓质中测量到的更高的孕烯醇酮合成率和更高的甾体激素组织含量相关。总之，我们已经确定了 StAR 和 CYP11A1 蛋白的表达和定位、合成孕烯醇酮的能力以及成年大鼠肾脏中特定区域的性激素含量。这些数据清楚地表明肾脏是合成甾体激素的器官。据推测，肾脏中存在完整的甾体生成机制将具有生理意义。
