The Contribution of the Sheep and the Goat Model to the Study of Ovarian Ageing

SIMPLE SUMMARY: Ovarian ageing is considered the major contributor to the age-related loss of fertility. Previous studies in mice evidenced the presence of a unique population of multinucleated giant cells in the stroma of the ovaries from older animals. Their presence correlated negatively with the ovarian follicle pool. The aims of the present work were to identify and characterize the presence of ovarian multinucleated giant cells in the goat and sheep ovary. The study of the ovarian morphology points to an age-related decrease in the primordial follicle pool, as observed in humans and mice. Additionally, with the aid of Sudan black B staining and autofluorescence detection, multinucleated giant cells were identified in the ovaries of mature females of both species. Implications of this research outcome are discussed, considering the presence of multinucleated giant cells in an age at which a decrease in reproductive potential is expected. Future studies should explore the potential mechanism and possible impairment on the ovarian function and, consequently, fertility. ABSTRACT: Ovarian ageing stands as the major contributor towards fertility loss. As such, there is an urge for studies addressing the mechanisms that promote ovarian ageing and new strategies aiming to delay it. Recently, the presence of a unique population of multinucleated giant cells has been identified in the ovaries of reproductively aged mice. These cells have been considered hallmarks of ovarian ageing. However, up to date multinucleated giant cells have only been described in the ovaries of the mice. Therefore, the aim of the present work was to evaluate and characterize the presence of such hallmarks of ovarian ageing in the sheep and the goat. In this study, ovaries from juvenile (6 months) and mature animals (18–24 months) were used. The hematoxylin and eosin technique was performed to describe the ovarian morphology and evaluate the ovarian follicle reserve pool. Sudan black B staining and the detection of autofluorescence emission were used to identify and characterize the presence of multinucleated giant cells. Statistical analyses were performed with GraphPad Prism 9.0.0. A decrease in the follicle reserve pool and the presence of multinucleated giant cells, with lipofuscin accumulation and the emission of autofluorescence, were observed in the ovaries of the mature animals of both species. Our results support the interest in the use of the ovine and the caprine model, that share physiological and pathophysiological characteristics with humans, in future studies addressing ovarian ageing.