Change in the protein level of mevalonate pyrophosphate decarboxylase in tissues of mouse by pravastatin

Estrogen biosynthesis in cultured skeletal muscle cells (L6) induced by amino acids

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.

Tissue distribution of mevalonate pyrophosphate decarboxylase in guinea pig

We previously reported that mevalonate pyrophosphate decarboxylase (MPD) is located in the cytosol and that MPD level in the liver is higher than in other rat tissues. In the present study, we further investigated the tissue distribution of MPD in guinea pigs by immunoblotting using anti-rat MPD antiserum. When immunoblot analysis was carried out using guinea pig brain, the antiserum reacted with 46-kDa protein as well as a substance with the same molecular weight of MPD in mice. Protein of 46-kDa detected in guinea pig liver treated with 0.1% pravastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor indicating a liver-specific effect, was increased 3-fold as compared with nontreated guinea pigs; however, 46-kDa protein in the brain treated with pravastatin was similar to that treated without pravastatin. When the subcellular distribution of MPD in the brain, liver, kidney, and testis, was examined by cell fractionation, MPD was mostly detected in the cytosol fraction of all tissues. From these data, the 46-kDa protein was identified as MPD. Next, when the tissue distribution of MPD was examined, MPD in the liver was higher than in other tissues. The relative amount of MPD in guinea pig kidney was higher than in rats and similar to in mice, as MPD in the liver of the same species was taken as 1. Furthermore, the correlation coefficient between guinea pigs and rats or mice in the tissue distribution of MPD was 0.69 or 0.72, respectively. These data indicate a relationship in tissue distribution between guinea pigs and rats or mice, although the tissue-specific regulator of MPD between species somewhat differed.