Background Previous investigations have indicated upregulation of gene expression in cellular pathways related to the biosynthesis of steroids in response to amino acids (AA) in skeletal muscle cells. This suggests AA as modulators of de novo synthesis of sex steroids for muscle growth and improved functional capacity. The aim of the present study was to investigate if increased availability of amino acids induced biosynthesis of sex steroids in skeletal muscles. Methods Confluent L6 muscle cells were cultured in media with various AA concentrations (0.3 or 9 mM AA or 2.1 mM branched-chain (BCAA) only), following pre-culture in serum-free medium. Sex steroids were quantified by gas chromatography-tandem mass spectrometry (GC-MS/MS). Mevalonate (diphospho-) decarboxylase enzyme (MVD) was quantified by Western blot. Results The experiments confirmed that estradiol and estrone increased in both L6 cell lysates and in conditioned media at the end of experiments on confluent cells, while progesterone or androgenic steroids were not detected in either cell lysates or culture media. Estradiol (+ 31 ± 3%) and estrone (+ 18 ± 4%) increased significantly in cells cultured at 9 mM AA (p < 0.001 vs. 0.3 mM AA, n = 10). Similarly, MVD protein increased at 9 mM AA (p < 0.001 vs. 0.3 mM AA, n = 17). An addition of BCAA alone to media increased MVD-protein levels to the same extent as all AA (p < 0.01 vs. 0.3 mM AA, n = 3). Conclusion Female sex steroids and MVD enzyme production increased significantly in response to amino acid availability. The results indicate a role of amino acids as modulators of local muscle estrogen synthesis in muscle cells from rats at feeding.

中文翻译：

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由氨基酸诱导的培养的骨骼肌细胞 (L6) 中的雌激素生物合成。

背景 先前的研究表明，与骨骼肌细胞中氨基酸 (AA) 响应的类固醇生物合成相关的细胞途径中的基因表达上调。这表明 AA 作为性类固醇从头合成的调节剂，可促进肌肉生长和提高功能能力。本研究的目的是调查氨基酸可用性的增加是否会诱导骨骼肌中性类固醇的生物合成。方法 在无血清培养基中预培养后，在具有各种 AA 浓度（仅 0.3 或 9 mM AA 或 2.1 mM 支链 (BCAA)）的培养基中培养融合的 L6 肌肉细胞。通过气相色谱-串联质谱 (GC-MS/MS) 对性类固醇进行量化。通过蛋白质印迹定量甲羟戊酸（二磷酸）脱羧酶（MVD）。结果 实验证实，在融合细胞实验结束时，L6 细胞裂解物和条件培养基中的雌二醇和雌酮增加，而在细胞裂解物或培养基中均未检测到孕酮或雄激素类固醇。在 9 mM AA 培养的细胞中，雌二醇 (+ 31 ± 3%) 和雌酮 (+ 18 ± 4%) 显着增加（p < 0.001 vs. 0.3 mM AA，n = 10）。同样，MVD 蛋白在 9 mM AA 时增加（p < 0.001 与 0.3 mM AA，n = 17）。在培养基中单独添加 BCAA 可将 MVD 蛋白水平提高到与所有 AA 相同的程度（p < 0.01 对 0.3 mM AA，n = 3）。结论 女性性类固醇和 MVD 酶产生显着增加，以响应氨基酸可用性。