Disparity Between Functional and Structural Recovery of Placental Mitochondria After Exposure to Hypoxia

Intrauterine growth restriction (IUGR) affects 5-10% of pregnancies with placental hypoxia, playing a key role as a common pathophysiological pathway of different etiologies. Despite the high metabolic rate of the placenta and its "gatekeeper" role in protecting the fetus from hypoxia, the response of placental mitochondria to hypoxic stress is not well understood. This study tested the hypothesis that transient exposure to hypoxia leads to a loss of placental mitochondria and affects their function. Human villous trophoblastic (JEG-3) cells were cultured under normoxic and hypoxic conditions for 24 h. Mitochondrial content was determined by flow cytometry before and after hypoxic exposure and after 24 h of normoxic recovery. Parameters of oxidative phosphorylation were assessed using a respirometric analyzer before hypoxic exposure and after normoxic recovery. Mitochondrial content decreased significantly from 88.5% to 26.7% during hypoxic incubation. Although it had increased to 84.2% after 24 h of normoxic recovery, oxidative phosphorylation parameters were still significantly suppressed to 1/2 to 1/3 of the pre-incubation levels. The results underscore the ability of placental cells to adapt mitochondrial content to O₂ supply. Despite rapid recovery under normoxia, respiratory function remains suppressed, which may result in persistent impairment of adenosine triphosphate (ATP)-dependent synthetic and transport functions.