Placental mitochondrial DNA mutation-related oxidative stress underlies subsequent risk of adverse prognosis in sFGR twins

BACKGROUND: Selective fetal growth restriction (sFGR), a serious complication of monochorionic diamniotic (MCDA) twin pregnancies, typically results from unequal placental sharing, especially in type II sFGR. This condition is associated with an increased risk of intrauterine death and adverse neurological outcomes in one of the twin fetuses. Mitochondria play an important role in fetal development and mitochondrial DNA (mtDNA) mutations have been implicated in the pathogenesis of singleton FGR. Mutations in the mtDNA can lead tomitochondrial dysfunction, oxidative stress, and apoptosis. However, the role of increased placental mtDNA mutations in the pathogenesis of sFGR and their potential association with fetal growth and nervous system development remain unclear. METHODS: In this study, we characterized and compared the mtDNA mutation rate (MMR) in placentas from eight pairs of type II sFGR twins and eight pairs of uncomplicated MCDA twin controls (MCDA-C). Furthermore, peripheral blood mtDNA from the mothers of both the sFGR and MCDA-C twins was sequenced to determine the differences in mtDNA heteroplasmy between the mothers and twins. The overall MMR and mutation frequencies of individual genes were analyzed separately. Mitochondrial damage, oxidative stress, and apoptosis in the placenta were investigated by immunohistochemistry. In addition, correlations between MMR, birth weight, gestational age, and brain injury were evaluated to investigate the relationship between mitochondrial defects and clinical outcomes. RESULTS: Whole mitochondrial genome sequencing identified a significantly higher MMR in sFGR placentas than in MCDA-C placentas, especially in respiratory chain genes (MT-ND3, MT-CYB, complex III, and complex V). Maternal peripheral blood MMR did not differ significantly between sFGR and MCDA-C groups. However, analysis of mtDNA heteroplasmy revealed a significantly greater mother-twin heteroplasmy difference in sFGR pairs than in MCDA-C pairs. Immunohistochemical staining showed increased PARKIN-mitochondria colocalization, 8-OHdG and cleaved caspase 3 signals in sFGR placentas, particularly in placentas from growth-restricted smaller twins (sFGR-S), suggesting increased mitochondrial damage, cellular oxidative stress, and apoptosis. In the correlation analysis, the placental MMR was negatively correlated with birth weight and gestational age at delivery. Notably, the incidence of fetal brain injury, especially periventricular leukomalacia (PVL), was higher in sFGR twins and was positively associated with the MMR. CONCLUSIONS: Placental mtDNA mutations and related oxidative stress are associated with adverse intrauterine environments in sFGR twins and may be associated with a higher frequency of fetal brain injury.