Abstract: 416

INDUCTION OF APOPTOSIS IN RAT OVARIAN THECA CELLS BY A PEPTIDE MIMIC OF APOLIPOPROTEIN E.

Celina Zerbinatti¹ , Robert Audet¹ , Cheryl Dyer¹
Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, USA ¹

Apolipoprotein E (apoE) has an important role in cholesterol transport and is made by all steroidogenic tissues. Within the ovary, apoE mRNA is highest in theca cells of atretic follicles and increases as degeneration of the follicle progresses. Addition of an apoE synthetic peptide that mimics apoE receptor activity at concentrations higher than 100 nM selectively inhibits androstenedione production, without affecting progesterone synthesis by theca cells in culture. This inhibition is dose dependent and is not mediated by binding of the peptide to the members of the low density lipoprotein (LDL) receptor superfamily. Here we investigated the signal transduction pathways involved in the apoE peptide-mediated inhibitory effect. The apoE-mediated inhibition of androstenedione production was significantly attenuated by phorbol-12-myristate-13-acetate (PMA) treatment, suggesting the involvement of a protein kinase C (PKC) pathway. Indeed, two PKC inhibitors with very similar amino acid sequence to the apoE peptide, a cell-permeable PKC pseudosubstrate and mastoparan (wasp venom), also caused a dose-dependent inhibition of androstenedione production without altering progesterone synthesis by theca cells. Because PKC inhibitors can induce apoptosis in other cell systems, we investigated if the apoE peptide induced apoptosis in rat ovarian theca cells. Terminal deoxynucleotidyl transferase-mediated dUTP Nick-End Labeling (TUNEL) analysis showed increasing labeling of theca cells with increasing concentrations of the apoE peptide. Confirmation of apoptosis was obtained by observing DNA ladders at the highest concentrations of the apoE peptide. These data suggest that exogenous apoE can induce apoptosis in theca cells, and selectively alter androgen production during the onset of atresia.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.