Enhanced expression of granulosa cell low density lipoprotein receptor activity in response to in vitro culture conditions

Previous studies have shown that the B/E (low density lipoprotein [LDL]) receptor pathway plays a minor role in cholesterol uptake in the intact rat ovary, but when granulosa cells are isolated and maintained in culture, the cells develop a fully functional B/E receptor system. In the current study we examined the development of the B/E receptor over time (96 h) in culture and compared its physiological function, expression of mRNA and protein levels, and morphological events to the upregulation induced in 24 h by hormone (human chorionic gonadotropin [hCG] or Bt₂cAMP). With both protocols, increased progestin production occurs and is associated with elevated binding, uptake, and degradation of LDL in the medium although the impact of Bt₂cAMP stimulation on all these measurements is several times that observed with time alone. Only the hormone‐stimulated LDL receptor response was associated with an increase in receptor protein (Western blot) or mRNA levels (RNase protection assay). We conclude that unstimulated granulosa cells show posttranslational increase in B/E receptor activity with time in culture, but transcriptional changes in B/E receptor follow stimulation with trophic hormone or its second messenger, cAMP. © 1994 Wiley‐Liss, Inc.