P-253 Development of embryos from aged mothers transferred to the uterus of young mice
Authors: Gulzar H , Musson R , Krzenek J , Florencia Heber M , Ewa Ptak G 
Published: July 2024

Abstract

Study question
Is the development of embryos from advanced maternal age (AMA) mice, similar to those from young maternal age (YMA) mice when transferred to young uteri?

Summary answer
AMA mouse embryos are characterized by altered organ morphology, particularly of the brain, which may predispose to neurodevelopmental disorders.

What is known already
Human and animal studies have linked AMA pregnancy to elevated risk of neurodevelopmental disorders and behavioural alterations in offspring, primarily attributed to compromised uterine (maternal) conditions. In human, it was also suggested that postnatal care of older mother may influence offspring behaviour. Animal studies revealed that behavioural alterations of AMA offspring are programmed during pregnancy and so they persist in litters fostered by young mouse. It remains unclear whether an embryo of older mother will undergo normal development after embryo transfer to younger female’s uterus.

Study design, size, duration
Embryos for Advanced Maternal Age, AMA (n = 105) and control Young Maternal Age, YMA (n = 44) groups were collected from thirty females 8-14 months old and six females 3-5 months old, respectively and transferred to pseudo-pregnant mice for further development. At embryonic day 16 (E16) foetuses were collected, fixed for histology and evaluated using Theiler and Kaufman’s classification of mouse development, where E16 corresponds to Theiler stage 24 (TS24)

Participants/materials, setting, methods
CBA x C57BL6 hybrid mice were used throughout the experiment. At E16, embryo survival rate (number of foetuses collected / number of transferred embryos) was scored for both groups. Foetuses were assessed for visible abnormalities and underwent histological evaluation of organs accordingly to TS 24. Parameters such as size/diameter, signs of vacuolization, cell density and layers of cerebral cortex in brain of foetuses were analysed. Values were considered different when p &lt; 0.05, Mean±SD; Mann-Whitney test.

Main results and the role of chance
At E16, the survival of AMA embryos did not differ significantly from YMA control (39/105; 37% vs. 20/44; 45%, respectively) however, 5% of AMA foetuses (2/39) displayed oedema or cerebral haemorrhage. Histological analysis revealed alterations in the head/brain of AMA in comparison to YMA foetuses, such as smaller head size (head area in mid-sagittal section: 25.25±4.87 vs. 31.39±3.79 mm2, p &lt; 0.05), thinner cerebral cortex (435.78±12.95 vs. 515.22±17.78µm, p &lt; 0.005), reduced ratio of cortical plate (CP) to cerebral cortex thickness (0.20±0.03 vs. 0.26±0.009, p &lt; 0.05) and an increased ratio of ventricular zone (VZ) to cerebral cortex thickness (0.29±0.002 vs. 0.24±0.002, p &lt; 0.05). Moreover, decreased cellular density in CP layer (10378.86 vs. 12066.40 cells/mm2, P &lt; 0.05) was noted. AMA brains were characterised by high degree of cellular vacuolisation, particularly in medulla oblongata, suggestive for spongiosis (1550.27 vs. 571.92 vacuoles/mm2, p &lt; 0.05). These brain alterations may cause neurodevelopmental disorders in offspring. AMA foetuses had: smaller bronchial diameter (31.52 vs. 36.62µm, p &lt; 0.05), no ossification centres and reduced skin wrinkling, corresponding to TS23 (that is previous developmental stage). These observations may suggest a delayed development of AMA foetuses.

Limitations, reasons for caution
The results of controlled animal experiments play a key role in developing conceptual models and formulating hypothesis about target species. However, extrapolation of these results to humans requires caution because species-specific developmental features may differ.

Wider implications of the findings
Our study demonstrates that advanced maternal age (AMA) impacts oocyte/embryo programming in mice. Morphological changes in AMA-conceived foetuses suggest potential risks for neurodevelopmental and other health issues in offspring, even when carried in the uterus of a young female, emphasizing the far-reaching effects of AMA on progeny health.

Trial registration number
not applicable