Follicular fluid high density lipoprotein stimulates the progesterone synthesis of human granulosa luteal cells

Abstract

OBJECTIVE: The luteal phase is marked by the dramatically increase of the capacity of granulosa luteal cells to synthesize and secrete progesterone. This change is not only regulated by gonadotrophins, but also by local ovarian factors. We previously described follicular fluid High density lipoprotein (FHDL) as a novel mediator of ovarian angiogenesis and cell proliferation; therefore we examined the effect of FHDL on the progesterone synthesis of human granulosa luteal cells. DESIGN: Laboratory study. MATERIALS AND METHODS: Human granulosa cells (HGC) were obtained from women undergoing IVF/ICSI treatment. F-HDL was separated by ultracentrifugation of follicular fluid FF. Cells were stimulated with different concentrations of FHDL for 3 days and progesterone concentrations of cell culture supernatants were determined by ELISA. Data of HGCs were compared to FHDL stimulated HGL5 cells, a human granulosa luteal cell line.Each experiment was performed in duplicates and was repeated at least three times. The obtained data were analyzed by Student's t-test. RESULTS: Increasing dose of FHDL stimulated the progesterone secretion 8 fold of HGC and 18 fold of HGL5 after 1day incubation with 2 mg/ml FHDL. Although, the dose dependently effect of FHDL sustained to 3 days, the fold induction was reduced to 5 fold after 2 days and 3 fold after 3days in both cell types. Interestingly, heat and charcoal treatment of FHDL leads only to a slightly decrease of the fold induction of progesterone secretion. With BLT-1, a specific antagonist of the SRB-I receptor, the stimulating effect of FHDL was decreased nearly to control values in HGC and HGL5 cells. CONCLUSIONS: FHDL stimulates the progesterone secretion of HGC and HGL5 cells dose dependent via the SRB-I receptor. This effect might be explained by the delivery of substrates, e.g. cholesterol for the synthesis of progesterone. These data underlines the pivotal role of FHDL during the luteal phase.