Lipoprotein enhancement of ovarian theca-interstitial cell steroidogenesis: relative contribution of scavenger receptor class B (type I) and adenosine 5'-triphosphate- binding cassette (type A1) transporter in high-density lipoprotein-cholesterol transport and androgen synthesis. 
The theca-interstitial cells take up plasma high-density lipoprotein (HDL)- and low-density-lipoprotein-derived cholesterol to convert into steroid hormones.  The uptake of HDL-derived cholesterol is mediated by the scavenger receptor, class B, type I (SR-BI).  In nonsteroidogenic cells, HDL-stimulated efflux of cholesterol has been shown to be mediated by the ATP-binding cassette A1 (ABCA1) transporter.  Its expression has not been documented in steroidogenic cells.  The goal of the present study was to determine: 1) the role of SR-BI in theca-interstitial cell androgen production; 2) whether theca-interstitial cells express ABCA1 transporter mRNA; and 3) the relative roles of SR-BI and ABCA1 transporter in androgen production.  The ABCA1 transporter mRNA expression in rat theca-interstitial cells was shown using RT-PCR and Northern blot analyses.  The role of SR-BI and ABCA1 in androstenedione production was also examined by treating cells with anti-SR-BI and 2-hydroxypropyl-beta-cyclodextrin in the presence and absence of human chorionic gonadotropin and/or human HDL(3).  The treatment of theca-interstitial cells with anti-SR-BI antibody blocked more than 90% of HDL plus human chorionic gonadotropin-stimulated androstenedione production, and selective HDL-CE uptake.  On the other hand, the use of inhibitors of ABCA1 transporter function had no discernible effect on HDL-supported androgen production.  These data demonstrate that, although theca-interstitial cells express both SR-BI and ABCA1 transporter mRNA, the SR-BI pathway supplies the majority of the cholesterol required for androgen production.  Furthermore, the present study presents evidence for a crucial role for SR-BI in HDL-mediated androgen production.