DNA methylation of Ad4BP/SF-1 suppresses Cyp11a1 and StAR transcripts in C2C12 myoblasts

Steroidogenesis occurs locally in peripheral tissues and via adrenal and gonadal glands' biosynthesis. The C2C12 mouse myoblast cell line and rat skeletal muscles harbor a local steroidogenesis pathway for glucocorticoids, and corticosterone is biosynthesized from skeletal muscle cells. However, Cyp11a1 and StAR protein expressions are not observed in C2C12 cells or rat muscular tissues. In this context, this study investigated the relationship between DNA methylation and key steroidogenic genes. Bioinformatics analysis of methylated DNA immune precipitation showed that C2C12 myoblasts and myotubes did not have remarkable DNA methylated regions in the gene-body of Cyp11a1. However, a highly methylated region in the CpG island was detected in the intronic enhancer of Ad4BP/SF-1, known as the transcriptional factor for steroidogenic genes. After C2C12 myoblasts treatment with 5-aza-2-deoxycytidine, the gene expressions of Ad4BP/SF-1, Cyp11a1, and StAR were significantly time- and concentration-dependent upregulated. To clarify the contribution of Ad4BP/SF-1 on Cyp11a1 and StAR transcripts, we silenced Ad4BP/SF-1 during the 5-aza-2-deoxycytidine treatment in C2C12 myoblasts, resulting in significant suppression of both Cyp11a1 and StAR. Additionally, pregnenolone levels in the supernatants of C2C12 cells were enhanced by 5-aza-2-deoxycytidine treatment, whereas pregnenolone production by C2C12 myoblasts was significantly suppressed by Ad4BP/SF-1 knockdown. These results indicate that DNA methylation of Ad4BP/SF-1 might be involved in the downregulation of steroidogenic genes, such as Cyp11a1 and StAR in C2C12 myoblasts.