Steroid biosynthesis pathway.

A simplified version of steroid biosynthesis highlighting the specific steroidogenic enzymes investigated in this study. Filled boxes highlight the steroidogenic enzymes examined by RT-qPCR. Progesterone (P4) is highlighted as the focus of this study. First, the transport protein, steroidogenic acute regulatory protein (StAR) is needed to facilitate the movement of cholesterol from the outer to inner mitochondrial membrane. Cholesterol is then converted to pregnenolone by the action of cytochrome side-chain cleaving enzyme (P450scc). Pregnenolone can then be converted to either 17α-hydroxypregnenolone by 17α-hydroxylase (P45017α) or to P4 by 3β-hydroxysteroid dehydrogenase (3β-HSD). P4 can either be a final product in this pathway or serve as a precursor in the synthesis of glucocorticoids, androgens, or estrogens. 17β-hydroxysteroid dehydrogenase (17β-HSD) functions in the conversion of weaker and stronger androgens and estrogens and was included in this study as a marker of upstream steroid enzyme activity [4], [16].