Maternal iron deficiency remodels cardiac mitochondria and alters stress responses in hypertensive pregnancy

AimMaternal iron deficiency (ID) during pregnancy induces cardiovascular adaptations, including reduced blood pressure and improved cardiac efficiency in hypertensive pregnancy. Iron is essential for mitochondrial function, particularly oxidative phosphorylation, where it serves as a cofactor within electron transfer complexes. Given the high metabolic demands of the maternal heart and irons central role in mitochondrial metabolism, we examined how maternal ID affects cardiac mitochondrial ultrastructure, respiration, dynamics, and redox status in pregnant spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Methods and ResultsFemale SHR and WKY rats were fed iron-replete or iron-restricted diets before and throughout gestation. On gestational day 21, cardiac mitochondrial ultrastructure was assessed by transmission electron microscopy (TEM), respiration by high-resolution respirometry, and the expression of proteins involved in fusion, fission, autophagy, and apoptosis markers by immunoblotting. Antioxidant gene expression was quantified by RT-qPCR. Data were analyzed by two-way ANOVA with Holm-Sidaks post hoc test. Maternal iron restriction reduced hemoglobin levels in both strains. TEM revealed enlarged, morphologically heterogeneous mitochondria with reduced and disrupted cristae architecture in ID dams of both strains. Iron restriction reduced succinate-supported respiration and tended to reduce NADH-supported respiration, in both strains. SHR dams exhibited reduced fusion signalling, reflected by a lower L-OPA1:S-OPA1 ratio. MFN1 expression was reduced by ID in both strains, whereas MFN2 expression was lower in SHR and further reduced by ID. In contrast, DRP1 phosphorylation increased selectively in ID-WKY dams. Iron restriction increased LC3-II:I ratio and BNIP3 in SHR, and increased PINK1 in both strains, while Parkin and p62 were unchanged. Antioxidant gene expression increased in ID-SHR but decreased in ID-WKY dams. Despite these alterations, markers of oxidative damage and apoptosis were unchanged by iron restriction. ConclusionMaternal ID induces marked remodeling of myocardial mitochondrial ultrastructure and selectively constrains iron-dependent respiration in hypertensive pregnancy without overt oxidative damage or apoptosis. These mitochondrial alterations occur alongside previously observed reductions in blood pressure and improved cardiac efficiency, suggesting favorable hemodynamic adaptations may coexist with underlying bioenergetic constraints in the maternal heart. Translational PerspectiveMaternal iron deficiency anemia (IDA) may alter the course of hypertensive pregnancy in ways not evident from hemodynamic indices alone. Here, IDA was associated with abnormal myocardial mitochondrial ultrastructure, selective reductions in respiratory capacity and stress response pathways, despite previously observed improvements in blood pressure and cardiac efficiency. These findings suggest that favourable hemodynamic changes may reflect reduced metabolic demand rather than enhanced bioenergetic capacity. If confirmed in human pregnancy, management of ID in women with underlying hypertension may need closer attention to cardiac metabolic health, as cardiovascular adaptions could coexist with myocardial stress and may vary with anemia severity and duration.