Oxysterols previously were considered intermediates of bile acid and steroid hormone biosynthetic pathways. However, recent research has emphasized the roles of oxysterols in essential physiologic processes and in various diseases. Despite these discoveries, the metabolic pathways leading to the different oxysterols are still largely unknown and the biosynthetic origin of several oxysterols remains unidentified. Earlier studies demonstrated that the glucocorticoid metabolizing enzymes, 11β-hydroxysteroid dehydrogenase (11β-HSD) types 1 and 2, interconvert 7-ketocholesterol (7kC) and 7β-hydroxycholesterol (7βOHC). We examined the role of 11β-HSDs in the enzymatic control of the intracellular availability of 7β,27-dihydroxycholesterol (7β27OHC), a retinoid-related orphan receptor γ (RORγ) ligand. We used microsomal preparations of cells expressing recombinant 11β-HSD1 and 11β-HSD2 to assess whether 7β27OHC and 7-keto,27-hydroxycholesterol (7k27OHC) are substrates of these enzymes. Binding of 7β27OHC and 7k27OHC to 11β-HSDs was studied by molecular modeling. To our knowledge, the stereospecific oxoreduction of 7k27OHC to 7β27OHC by human 11β-HSD1 and the reverse oxidation reaction of 7β27OHC to 7k27OHC by human 11β-HSD2 were demonstrated for the first time. Apparent enzyme affinities of 11β-HSDs for these novel substrates were equal to or higher than those of the glucocorticoids. This is supported by the fact that 7k27OHC and 7β27OHC are potent inhibitors of the 11β-HSD1-dependent oxoreduction of cortisone and the 11β-HSD2-dependent oxidation of cortisol, respectively. Furthermore, molecular docking calculations explained stereospecific enzyme activities. Finally, using an inducible RORγ reporter system, we showed that 11β-HSD1 and 11β-HSD2 controlled RORγ activity. These findings revealed a novel glucocorticoid-independent prereceptor regulation mechanism by 11β-HSDs that warrants further investigation.

中文翻译：

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11β-羟基类固醇脱氢酶控制 7β,27-二羟基胆固醇进入类视黄醇相关孤儿受体 γ。


氧甾醇以前被认为是胆汁酸和类固醇激素生物合成途径的中间体。然而，最近的研究强调了氧甾醇在基本生理过程和各种疾病中的作用。尽管有这些发现，但产生不同氧甾醇的代谢途径仍然很大程度上未知，并且几种氧甾醇的生物合成来源仍未确定。早期研究表明，糖皮质激素代谢酶 1 型和 2 型 11β-羟基类固醇脱氢酶 (11β-HSD) 可以相互转化 7-酮胆固醇 (7kC) 和 7β-羟基胆固醇 (7βOHC)。我们研究了 11β-HSD 在酶控制细胞内 7β,27-二羟基胆固醇 (7β27OHC)（一种视黄醇相关孤儿受体 γ (RORγ) 配体）的可用性中的作用。我们使用表达重组 11β-HSD1 和 11β-HSD2 的细胞的微粒体制剂来评估 7β27OHC 和 7-酮,27-羟基胆固醇 (7k27OHC) 是否是这些酶的底物。通过分子建模研究了 7β27OHC 和 7k27OHC 与 11β-HSD 的结合。据我们所知，首次证明了人11β-HSD1将7k27OHC立体特异性氧化还原为7β27OHC，以及人11β-HSD2将7β27OHC还原为7k27OHC的逆氧化反应。 11β-HSD 对这些新底物的表观酶亲和力等于或高于糖皮质激素。 7k27OHC 和 7β27OHC 分别是 11β-HSD1 依赖性可的松氧化还原和 11β-HSD2 依赖性皮质醇氧化的有效抑制剂，这一事实支持了这一点。此外，分子对接计算解释了立体特异性酶活性。最后，使用诱导型 RORγ 报告系统，我们证明 11β-HSD1 和 11β-HSD2 控制 RORγ 活性。 这些发现揭示了 11β-HSD 的一种新的不依赖糖皮质激素的前受体调节机制，值得进一步研究。