Effects of maternal exercise intensity during pregnancy on fetal ovarian development in mice

Maternal exercise is widely regarded as beneficial for metabolic homeostasis and pregnancy outcomes; however, whether different exercise intensities are associated with distinct patterns of fetal ovarian development remains unclear. Pregnant C57BL/6J mice were assigned to control, limited exercise (LE; cage-space restriction from GD0 to GD17), moderate exercise (ME; 10 m/min treadmill running from GD9 to GD17), excessive exercise (EE; 14 m/min treadmill running from GD9 to GD17), or limited exercise with moderate exercise superimposed from GD9 to GD17 (LE&ME). The litter was used as the biological unit. Fetal ovaries collected on GD18 were assessed for morphology, proliferation and apoptosis, estradiol (E2) content, steroidogenesis-related markers, oocyte-development markers and candidate signalling pathways. Compared with controls, LE had lower ovarian volume, cumulative oocyte-profile counts, proliferative and oocyte-development indices, together with higher apoptosis-related indices, ovarian E2 content and steroidogenesis-related markers. ME increased ovarian volume, cumulative oocyte-profile counts, proliferative activity, E2 content, and several oocyte- and steroidogenesis-related markers. EE increased E2 and steroidogenesis-related markers but reduced oocyte-development markers without parallel increases in the measured morphometric or proliferative indices. LE&ME showed lower ovarian E2 content than LE and partially attenuated several LE-associated changes in proliferation, apoptosis and oocyte-development markers. Exploratory analyses identified correlations between Igf1 or Mek1 expression and selected developmental markers. Collectively, different maternal exercise intensities were associated with distinct fetal ovarian developmental profiles, with ME showing a more favourable overall profile.