The association between theca cells (TCs) and granulosa cells is pivotal to steroid biosynthesis in the ovary. During the late secondary follicle stage, TCs form a layer around granulosa cells, after which their steroidogenic function falls under the control of luteinizing hormone (LH) that activates the cAMP signaling pathway via a G protein-coupled receptor. In addition to perilipin-2, a marker for lipid droplets containing esters as substrates for TCs to produce steroidogenic hormones, other essential proteins, like steroidogenic acute regulatory protein (StAR), cytochrome P450 11A1, cytochrome P450c17, 3 beta-hydroxysteroid dehydrogenase/delta 5 —> 4-isomerase type 1, and 3 beta-hydroxysteroid dehydrogenase/delta 5 —> 4-isomerase type 2, play a role in the cascade after luteinizing hormone–choriogonadotropic hormone receptor (LH/CG-R) occupation by LH. The aim of the present study was to assess expression levels and corresponding amounts of LH/CG-R, perilipin-2, and enzymes involved in the steroidogenic pathway of TCs based on follicle stage. Immunohistochemical analysis of each of these proteins was therefore performed on ovarian samples from nine adult women, most (n = 8) with BRCA1 and/or BRCA2 mutations undergoing prophylactic bilateral oophorectomy. Pictures were taken of the theca layer of secondary, small (<3000 µm), and large (>3000 µm) antral follicles and corpora lutea at 100× magnification. ImageJ software was used to analyze the surface area and expression intensity of each protein at each stage, known as the staining index. Overall, our data showed that LH/CG-R, perilipin-2, and StAR expression increased in the course of folliculogenesis and luteinization. Similarly, cytochrome P450 11A1, cytochrome P450c17, 3 beta-hydroxysteroid dehydrogenase/delta 5 —> 4-isomerase type 1, and 3 beta-hydroxysteroid dehydrogenase/delta 5 —> 4-isomerase type 2 expression were substantially elevated in TCs during folliculogenesis, evidenced by their coordinated action in terms of area covered and expression intensity. This study, conducted for the first time on human ovarian tissue, contributes to localizing and quantifying expression of key steroidogenic proteins at both intracellular and tissue levels. These findings may shed new light on pathological conditions involving the human ovary, such as androgen-secreting tumors of the ovary and other disorders associated with ovarian TCs in patients with polycystic ovary syndrome.

Summary sentence

This study, conducted for the first time on human ovarian tissue, contributes to localizing and quantifying expression of key steroidogenic proteins at both intracellular and tissue levels and may shed new light on pathological conditions involving the human ovary, such as androgen-secreting tumors of the ovary and other disorders associated with theca cells in PCOS patients.