Regional uterine contractility differences during pregnancy: The role of hypoxia and ferroptosis in vitro

Regional variations in uterine contractility during pregnancy have been well-documented. However, the molecular mechanisms underlying these differences remain unclear. To address this, isotonic contraction experiments were conducted on pregnant rat uteri, revealing significantly lower contractility on the placenta-attached side compared to the non-attached side. Interestingly, lactic acid accumulation was higher in the placenta-attached tissue, suggesting metabolic differences between these regions. Muscle contraction requires substantial energy, with adenosine triphosphate (ATP) serving as the direct source of energy, which is predominantly supplied by mitochondria, the cellular energy production centers. Mitochondrial energy generation relies heavily on oxygen availability. To explore the impact of oxygen conditions on uterine smooth muscle cell (USMC) contraction, we cultured these cells under hypoxic conditions. Hypoxia was found to reduce cell contraction and disrupt mitochondrial integrity. Specifically, mitochondria exhibited shrinkage and deformation, characterized by reduced cristae and a collapse of the mitochondrial membrane potential. These structural and functional changes align with hallmarks of ferroptosis. Furthermore, hypoxia stimulated the translocation of dynamic related protein 1 (Drp1) to mitochondria, a process linked to mitochondrial fragmentation. Ferroptosis was downregulated when Drp1 activity was inhibited, highlighting its regulatory role in this process. Collectively, these findings demonstrate that hypoxia induced-ferroptosis impairs mitochondria, leading to reduced energy production and cell viability. This ultimately decreases the contractility of pregnant USMC, providing new insights into the molecular mechanisms underlying regional differences in uterine contractility during pregnancy.