Advanced maternal age impairs spatial learning capacity in young adult mouse offspring

Effects of maternal aging on the offspring cognitive function remain controversial in population-based investigations, and information available in animal studies is very limited. We investigated the impact of a delayed first natural pregnancy on pregnancy outcomes in the mouse model. Spatial learning capacity in young adult mouse offspring was observed by step-down passive avoidance task and Morris water maze (MWM). Maternal serum α-klotho was measured by ELISA. Morphological characteristics of fetoplacental unit and offspring brain were identified by H&E and immunohistochemistry. Klotho, VDR and other related genes expression were quantified by real-time-RT-PCR and western blot. We found delayed pregnancy reduced fertility in female mice by three-fold (Young vs. Old: 5.0% vs. 20.7%), and increased adverse pregnant outcomes by eight-fold (Young vs. Old: 3.0% vs. 27.5%). Mice born to old mothers exhibited shorter retention trial latency in passive avoidance task and longer latency to find the platform in MWM, suggesting worse performance on the tests that measure learning and memory. Serum α-klotho level was lower in old female mice before pregnancy, whereas became comparable after pregnancy. Vitamin D receptor (VDR) expression, both in mRNA and protein, markedly decreased during the early stage of fetoplacental unit in old mice, especially in trophoblast giant cells when compared with that of young mice. Importantly, consistent with fetoplacental unit, VDR expression also declined in hippocampus from offspring born to old mice. These results suggest that young adult offspring from aged mothers exhibited worse cognitive function and the reduced VDR expression during fetoplacental development might play an important role.