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GAP JUNCTIONAL COMMUNICATION IS REQUIRED FOR ACCELERATED RATES OF OOCYTE APOPTOSIS INDUCED BY ADVANCING MATERNAL AGE BUT NOT BY CHEMOTHERAPY.
Perez, Gloria1, Tilly, Jonathan1, 1
ABSTRACT- Efforts in our center have focused on evaluating age-related changes in cell death regulatory pathways in the ovary to determine why cumulus cell (CC)-enclosed oocytes obtained from aged mice (34-35 weeks old) undergo apoptosis at significantly higher rates during in vitro culture when compared with CC-enclosed oocytes obtained from young females (7 weeks old). Importantly, we have already demonstrated that the age-dependent acceleration of apoptosis in oocytes maintained in vitro requires the CC. Here we show that cell-cell signaling through intercellular channels is required for the accelerated rates of oocyte apoptosis resulting from advanced maternal age but not from chemotherapy. Cumulus-oocyte complexes (COC) were cultured without (control; young, n=62; aged, n=30) or with two different chemicals known to uncouple gap junctions, heptanol (Hept; 10 millimolar; young, n=77; aged, n=26) or glycyrrhetinic acid (GA; 10 micromolar; young, n=71; aged, n=26). In addition, COC from aged mice were treated with doxorubicin (DXR, 200 nM), in the absence (n=30) or presence of Hept (n=20) or GA (n=10). After 24 h, oocytes were checked for changes characteristic of apoptosis. In COC from aged mice, the percentage of CC-enclosed oocytes that underwent apoptosis was greater than that of CC-enclosed oocytes from young mice (50±16% versus 18±7%, respectively; P<0.05). Heptanol or GA completely suppressed the accelerated oocyte apoptosis due to advanced maternal age, while neither compound affected the incidence of apoptosis in CC-enclosed oocytes isolated from young mice. Treatment of COC collected from aged mice with DXR further increased the mean incidence of oocyte apoptosis by 20%, but neither Hept nor GA was able to block the additional elevation in oocyte apoptosis caused by DXR. We propose that a CC-derived factor(s), or possibly an oocyte-derived factor(s) requiring direct modulation by CC and gap junctions, is essential for the elevated apoptosis in COC from aged mice. In comparison, DXR-induced oocyte apoptosis results from the direct effects of the drug on germ cells. Although aging and chemotherapy both lead to a depletion of germ cells in the ovary via apoptosis, the triggering mechanisms appear to be differentially regulated. (Supported by RO1-AG12279 and a Harvard Center of Excellence in Women's Health Grant).
KEY WORDS: oocytes, apoptosis, aging, gap junctions