Altered insulin, leptin, and ghrelin hormone levels and atypical estrous cycle lengths in two highly‐fertile mouse lines

The special phenotypic characteristics of Dummerstorf superfertile mouse lines could depend on the expression levels of IGF-axis genes

To date, animal models with reproductive phenotypes are knockout or transgenic and typically exhibit reduced fertility or infertility. This limits research to studying single-gene effects or loss of fertility. By contrast, Dummerstorf high-fertility mouse lines 1 and 2 (FL1 and FL2) are two unique outbred selection models that demonstrate exceptional reproductive performance. After approximately 50 years of selection, both lines have doubled the number of ovulated oocytes per cycle and consequently their litter size (>20 vs ∼11) compared to the unselected mice of the same founder population (Dummerstorf FZTDU, ctrl line). FL1 and FL2 exhibit atypical estrous cycle length and altered levels of hormones, such as insulin and leptin, which are associated with GnRH release and/or increased body fat content. Unlike typical cases where these factors impair fertility, they instead contribute to the FLs' high reproductive capacity: the increased ovulation rate results from an upgrade in the quality of their oocytes, influenced by different ovarian lipid profile. In the present study, we analyzed the expression of IGF-axis marker genes linked to reproductive performance and FL-specific traits in three tissues. We found that lepr, which plays a critical role in implantation, was upregulated in the FL1 uterus (1.5-fold vs. ctrl, p < 0.05). In FL1 follicles, igf1, IGF-biding proteins (IGFBP2, IGFBP4) and hsf1-which is involved in gametogenesis-were significantly upregulated (1-4-fold vs. ctrl, p < 0.05 for igf1, hsf1 and IGFBP4; p < 0.01 for igfbp2). In FL2, uterine size was reduced relatively to the body weight (∼0.2 % FL2 vs. 0.25 % in ctrl and 0.28 % in FL1, p < 0.001), indicating that uterus dimensions do not drive their increased litter size. These findings provide new insights into the molecular basis of high fertility and could serve as a foundation for further studies on genotype-phenotype relationships in reproductive biology.

Withanolide derivatives: natural compounds with anticancer potential offer low toxicity to fertility and ovarian follicles in mice

Anticancer therapy often leads to premature ovarian insufficiency (POI) and infertility due to the extreme sensitivity of the ovarian follicle reserve to the effects of chemotherapy. Withanolides are known for their cytotoxic effect on cancer cells and low cytotoxicity on non-malignant or healthy cells. Therefore, this study aimed to investigate the in vivo effects of three withanolides derivatives: 27-dehydroxy-24,25-epoxywithaferin A (WT1), 27-dehydroxywithaferin A (WT2), and withaferin A (WTA) on fertility, and the ovarian preantral follicles of young female mice. To achieve this, mice received 7 intraperitoneal doses of WT1, WT2, or WTA at a concentration of 2 mg/kg (Experiment I) and 5 or 10 mg/kg (Experiment II) over 15 alternate days. In experiment I, two days after administration of the last dose, half of the mice were mated to evaluate the effects of withanolides on fertility. The other half of the mice, as well as all mice from experiment II, were sacrificed for histological, inflammation, senescence, and immunohistochemical analyses of the follicles present in the ovary. Regardless of the administered withanolide, the concentration of 2 mg/kg did not show toxicity on the follicular morphology, ovarian function, or fertility of the mice. However, at concentrations of 5 and 10 mg/kg, the three derivatives (WT1, WT2, and WTA) increased follicular activation, cell proliferation, and ovarian senescence without affecting inflammatory cells. Furthermore, at a concentration of 10 mg/kg, the three withanolides showed intensified toxic effects, leading to DNA damage as evidenced by the labeling of γH2AX, activated Caspase 3, and TUNEL. We conclude that the cytotoxic effect of the tested withanolide derivatives (WT1, WT2, and WTA) in the concentration of 2 mg/kg did not show toxicity on the ovary. However, in higher concentrations, such as 10 mg/kg, toxic effects are potentiated, causing DNA damage.

The Imitation of the Ovarian Fatty Acid Profile of Superfertile Dummerstorf Mouse Lines during IVM of Control Line Oocytes Could Influence Their Maturation Rates

Declining human fertility worldwide is an attractive research target for the search for "high fertility" genes and pathways to counteract this problem. To study these genes and pathways for high fertility, the superfertile Dummerstorf mouse lines FL1 and FL2 are two unique model organisms representing an improved fertility phenotype. A direct reason for this remarkable characteristic of increased litter size, which reaches >20 pups/litter in both FLs, is the raised ovulation rate by approximately 100%, representing an impressive record in this field. Dummerstorf high-fertility lines incarnate extraordinary and singular models of high-fertility for other species, mostly farm animals, with the aim of improving production and reducing costs. Our main goal is to describe the genetic and molecular pathways to reach their phenotypical excellence, and to reproduce them using the control population. The large litter size and ovulation rate in Dummerstorf lines are mostly due to an increase in the quality of their oocytes, which receive a different intake of fat and are composed of different types and concentrations of fatty acids. As the follicular microenvironment plays a fundamental role during the oocytes development, in the present manuscript, we tried to improve the in vitro maturation technique by mimicking the fatty acid profile of FLs oocytes during the IVM of control oocytes. Currently, the optimization of the IVM system is fundamental mostly for prepubertal girls and oncological patients whose main source of gametes to restore fertility may be their maturation in vitro. Our data suggest that the specific fatty acid composition of FLs COCs can contribute to their high-fertility phenotype. Indeed, COCs from the control line matured in IVM-medium supplemented with C14:0 (high in FL2 COCs) or with C20:0, C21:0, C22:0, and C23:0 (high in FL1 COCs), but also control oocytes without cumulus, whose concentration in long-chain FAs are "naturally" higher, showing a slightly higher maturation rate. These findings represent an important starting point for the optimization of the IVM system using FA supplementation.

Lower Plasmatic Levels of Saturated Fatty Acids and a Characteristic Fatty Acid Composition in the Ovary Could Contribute to the High-Fertility Phenotype in Dummerstorf Superfertile Mice

In recent decades, fertility traits in humans as well as in farm animals have decreased worldwide. As such, it is imperative to know more about the genetics and physiology of increased or high fertility. However, most of the current animal models with reproductive phenotypes describe lower fertility or even infertility (around 99%). The “Dummerstorf high-fertility lines” (FL1 and FL2) are two unique mouse lines selected for higher reproductive performances, more specifically for higher number of pups per litter. We recently described how those superfertile mice managed to increase their reproductive phenotype by doubling the ovulation rate and consequently the litter size compared to the unselected mice of the same founder population. FLs show an unusual estrous cycle length and atypical levels of hormones that link reproduction and metabolism, such as insulin in FL1 and leptin in FL2. Moreover, we described that their higher ovulation rate is mostly due to a higher quality of their oocytes rather than their sheer quantity, as they are characterized by a higher quantity of high-quality oocytes in antral follicles, but the quantity of follicles per ovary is not dissimilar compared to the control. In the present study, we aimed to analyze the lipid composition of the fertility lines from plasma to the gonads, as they can connect the higher reproductive performances with their metabolic atypicalities. As such, we analyzed the fat content of FLs and fatty acid composition in plasma, liver, fat, oocytes of different quality, and granulosa cells. We demonstrated that those mice show higher body weight and increased body fat content, but at the same time, they manage to decrease the lipid content in the ovarian fat compared to the abdominal fat, which could contribute to explaining their ovarian quality. In addition, we illustrate the differences in fatty acid composition in those tissues, especially a lower level of saturated fatty acids in plasma and a different lipid microenvironment of the ovary. Our ongoing and future research may be informative for farm animal biology as well as human reproductive medicine, mostly with cases that present characteristics of lower fertility that could be reversed following the way-of-managing of Dummerstorf high-fertility lines.

Higher quality rather than superior quantity of oocytes determine the amount of fertilizable oocytes in two outbred Dummerstorf high-fertility mouse lines

Dummerstorf fertility lines FL1 and FL2 represent two models of enhanced fertility characterized by the doubling of the litter size compared with an unselected control population (ctrl line, Dummerstorf FztDU). Both biodiverse FLs managed to reach this goal by increasing the ovulation rate per cycle, even showing decreased pregnancy rate and irregular oestrous cycle and metabolic hormone levels, compared with ctrl. The aim of the present study was to analyse oocytes in terms of quality and quantity by comparing the entire pool of oocytes per ovary, with those from the antral follicles within the same animal. We performed Brilliant Cresyl Blue staining as a non-invasive marker of oocyte quality in combination with an analysis of additional morphological indicators, e.g. cytoplasm clarity, cumulus cell layers, nuclear anatomy, size and shape. We compared our fertility lines with the unselected control population and with another independent line selected from the same founder population, showing lower litter size (DU6P). Our results suggest that fertility lines show decreased number of oocytes per ovary compared with DU6P but increased number of high-quality oocytes before ovulation. Hence, the raise in the ovulation rate and litter size of those super fertile mouse lines are not associated with an increased number of oocytes per ovary but rather with an increased number of higher quality fertilizable oocytes per cycle. In addition, the most conspicuous method to acquire oocytes with the highest quality in our lines is to assess their morphology, rather than their status after staining. All these discoveries together may be of fundamental importance for further studies in livestock farm animals showing some similar characteristics, e.g. irregular cycle or hormonal misbalances, to improve production while lowering costs, and in humans to increase the possibilities of successful pregnancies for couples undergoing in vitro fertilization (IVF).