FOLLICULAR ATRESIA AS AN APOPTOTIC PROCESS - ATRESIA-ASSOCIATED INCREASE IN THE OVARIAN EXPRESSION OF THE PUTATIVE APOPTOTIC MARKER SULFATED GLYCOPROTEIN-2

OBJECTIVE: To evaluate the possibility that morphologically confirmed/ hypophysectomy-induced ovarian follicular atresia, a putative apoptoti c process, is coupled to alterations in the steady-state levels of ova rian sulfated glycoprotein-2 (SGP-2) transcripts. METHODS: Hypophysect omy-induced follicular atresia in immune rats, morphologically confirm ed at the light and electron microscopic levels, was correlated with a lterations in the steady-state levels of ovarian SGP-2 transcripts as assessed by a solution hybridization/RNase protection assay. Cellular localization was accomplished by in situ hybridization technology. RES ULTS: Hypophysectomy of the 24-day-old immature rat, an established pr ecipitant of follicular atresia, led (3 days later) to a significant ( P < .05) increase (up to 3.3-fold) in the relative abundance of densit ometrically quantified ovarian SGP-2 transcripts compared with age-mat ched intact controls. Detailed time-course analysis after hypophysecto my revealed significantly (P < .05) increased ovarian SGP-2 mRNA expre ssion as early as 2 days after hypophysectomy; no further increments w ere noted on days 4 or 8. Light microscopic analysis of comparable ova rian material 4 days after hypophysectomy revealed increased numbers o f atretic follicles displaying large numbers of degenerating granulosa cells. Electron microscopic analysis of the degenerating cells of atr etic follicles (from hypopysectomized rats) disclosed nuclear condensa tion and cytoplasmic shrinkage as well as apoptotic bodies at all leve ls of the granulosa cell layer. In situ hybridization established the granulosa cell of the intact untreated rat as the somatic cell concern ed with SGP-2 gene expression. In turn, hypophysectomy led to an incre ase in SGP-2 expression at the levels of the theca-interstitial cell, an effect prevented by the concurrent provision of pregnant mare serum gonadotropin (PMSG). The hypophysectomy-induced increase in ovarian S GP-2 transcripts was similarly reversed (54% inhibition by day 27) by the concomitant provision of FSH, an established antiatretic principle . The delayed administration (day 26) of a single dose of PMSG to rats hypophysectomized on day 24 eliminated the hypophysectomy-induced inc rease in ovarian SGP-2 transcripts as assessed on day 28. Qualitativel y similar but quantitatively more pronounced increments in ovarian SGP -2 gene expression were obtained when atresia was induced by hypophyse ctomy of PMSG-primed immature rats. CONCLUSIONS: These observations es tablish the immature rat ovary as a site of SGP-2 gene expression and reveal hypophysectomy-induced follicular atresia to result in the up-r egulation of ovarian (specifically, theca-interstitial) SGP-2 gene exp ression, an effect prevented by the concurrent provision of FSH or PSM G. To the extent that SGP-2 is an acceptable apoptotic marker, the pre sent findings support the hypothesis that ovarian follicular atresia m ay be an apoptotic process.