Age-related changes in gene expression patterns of immature and aged rat primordial follicles

Women are born with millions of primordial follicles which gradually decrease with increasing age and this irreversible supply of follicles completely exhausts at menopause. The fertility capacity of women diminishes in parallel with aging. The mechanisms for reproductive aging are not fully understood. We have observed a decline in Brca1 mediated DNA repair in aging rat primordial follicles. To further understand the age-related molecular changes, we performed microarray gene expression analysis using total RNA extracted from immature (18 to 20 day old) and aged (400 to 450 day old) rat primordial follicles. The results of current microarray study revealed that there were 1,011 (>1.5 fold, p<0.05) genes differentially expressed between two groups in which 422 genes were up-regulated and 589 genes were down-regulated in aged rat primordial follicles compared to immature primordial follicles. The gene ontology and pathway analysis of differentially expressed genes revealed a critical biological function such as cell cycle, oocyte meiosis, chromosomal stability, transcriptional activity, DNA replication, and DNA repair were affected by age. This considerable difference in gene expression profiles may have an adverse influence on oocyte quality. Our data provide information on the processes that may contribute to aging and age-related decline in fertility.

Neonatal exposure to estradiol-17β modulates tumour necrosis factor alpha and cyclooxygenase-2 expression in brain and also in ovaries of adult female rats

The sexually dimorphic organization in perinatal rat brain is influenced by steroid hormones. Exposure to high levels of estrogen or endocrine-disrupting compounds during perinatal period may perturb this process, resulting in compromised reproductive physiology and behavior as observed in adult In our recent observation neonatal exposure of the female rats to estradiol-17β resulted in down-regulation of TNF-α, up-regulation of COX-2 and increase in SDN-POA size in pre-optic area in the adulthood. It is known that the control of reproductive performance in female involves a complex interplay of the hypothalamus, pituitary, and ovary. The present study was undertaken to understand the possible molecular mechanism involved in changes observed in the ovarian morphology and expression of selected genes in the ovary. Administration of estradiol-17β (100 μg) on day 2 and 3 after birth revealed up-regulation of ER-α, ER-β, COX-2 and down-regulation of TNF-α expression. Also the decrease in the ovarian weight, altered ovarian morphology and changes in the 2D protein profiles were also seen. This is apparently the first report documenting that neonatal estradiol exposure modulates TNF-α and COX-2 expression in the ovary as seen during adult stage. Our results permit us to suggest that cues originating from the modified brain structure due to neonatal exposure of estradiol-17β remodel the ovary at the molecular level in such a way that there is a disharmony in the reproductive function during adulthood and these changes are perennial and can lead to infertility and changes of reproductive behavior.