OR09-01 Mini-Puberty Could Be A Key Phase Regulating Reproductive Function In Female Mice
Authors: Chester Mélanie , Devillers Marie M , Naule Lydie , Souaré Fatoumata , Corre Raphaël , Quintas Daniel , Petrovic Claire-Hélène , Cohen-Tannoudji Joelle , Mhaouty-Kodja Sakina , Guigon Celine J 
Published: October 2023

Abstract
Disclosure: M. Chester: None. M. Devillers: None. L. Naule: None. F. Souaré: None. R. Corre: None. D. Quintas: None. C. Petrovic: None. J. Cohen-Tannoudji: None. S. Mhaouty-Kodja: None. C.J. Guigon: None.
After birth, there is a transient activation of the hypothalamic-pituitary-ovary (HPO) axis, with high secretion of LH and FSH acting on the ovary to promote the secretion of sex steroids and in particular that of estradiol (E2). This period, called mini-puberty, occurs between 10-17 days postnatal (dpn) in mice. During reproductive life, E2 plays an important role on the HPO axis by regulating GnRH pulsatility and, thus, the cyclic fluctuations of gonadotropin hormone levels required for follicular development and ovulation. E2 acts on hypothalamic kisspeptin neurons of the arcuate (ARC) and the anteroventral periventricular nucleus (AVPV), which project to GnRH neurons and regulate their activity by negative and positive feedbacks, respectively. The possibility that E2 contributes, during mini-puberty, to the maturation of hypothalamic structures involved in puberty onset and reproductive function, has never been investigated. The aim of this study was to elucidate the putative roles of mini-puberty on reproduction. We developed a mouse model injected with a GnRH receptor antagonist (GonadoSTOP mice) suppressing LH and FSH surges to cause a 50% decrease in E2 levels during mini-puberty. Our results show that GonadoSTOP mice exhibited later first diestrus 2 (D2) (31.0 dpn versus 29.9 dpn in CTR; n=55-56 mice/group; P=0.0285), suggesting a possible delay in the timing of puberty. During reproductive life, GonadoSTOP mice spent a longer % of time in D2 than control mice, with no alteration in total estrous cycle time (64.4% versus 56% in CTR; n=18-19 mice/group; P=0.0350). Immunohistochemical analysis of kisspeptin neurons in ARC and AVPV of ovariectomized and hormonally-primed mice showed that their numbers were significantly lower in AVPV from GonadoSTOP mice than in control mice (n=5-6 brains/group; P=0.038). In fertility studies, we observed no difference in the time to conception or % of pregnant mice between the two groups at early reproductive life (3, 4 and 5 months). Contrary to these results, at the time of reproductive decline in control mice (11 months), a substantial % of GonadoSTOP mice could still be pregnant (47% versus 18% of CTR mice; P=0.0017). At this age, GonadoSTOP mice had lower LH levels than control mice (P=0.0074), but similar levels to young control mice at 4 months (P&gt;0.05). RT-qPCR analyses of markers reflecting ovarian activity (Cyp19a1, Inhbb, Amh, Gdf9) at 4 and 11 months revealed that ovarian aging occurred similarly in both groups, suggesting that reproductive longevity in GonadoSTOP mice does not have an ovarian origin. Taken together these data suggest that transient and sustained activation of the HPO axis at mini-puberty may regulate key aspects of reproductive function with long-term impact on fertility, possibly by acting on the hypothalamus.
Presentation: Friday, June 16, 2023