Maternal hyperhomocysteinemia promotes adverse pregnancy outcomes via mtDNA-cGAS-STING signaling-mediated trophoblast mitophagy.

OBJECTIVES: Hyperhomocysteinemia (HHcy) is a recognized risk factor for adverse pregnancy outcomes. However, the underlying mechanisms precipitating placental dysfunction, particularly the potential involvement of mitochondrial DNA (mtDNA), remain largely elusive. This study aims to investigate the association between maternal HHcy and adverse pregnancy outcomes mediated by reduced placental mtDNA copy number (mtDNAcn), and to elucidate the underlying molecular mechanisms driving HHcy-induced placental dysfunction. METHODS: We prospectively investigated the associations between maternal HHcy, placental mtDNA copy number (mtDNAcn), and adverse pregnancy outcomes using data from the PEOH (Prenatal Environments and Offspring Health) birth cohort. To elucidate the underlying mechanisms, human placental tissues, maternal HHcy rat placentae, and HTR-8/SVneo trophoblast cells were utilized to assess HHcy-induced mitochondrial damage, PINK1/Parkin-mediated mitophagy, and downstream inflammatory signaling. RESULTS: Epidemiological analysis revealed that maternal HHcy was significantly associated with increased risks of preterm birth and low birth weight, with reduced placental mtDNAcn serving as a critical mediator. Mechanistically, HHcy exposure induced severe mitochondrial dysfunction and excessive PINK1/Parkin-dependent mitophagy across human placentae, maternal HHcy rat placentae, and HTR-8/SVneo cells. This unrestrained mitophagic flux precipitated the leakage of mtDNA into the cytosol, which directly engaged and activated the cGAS-STING pathway, leading to placental sterile inflammation and subsequent placental dysfunction via upregulating COX-2 and pro-inflammatory cytokines. CONCLUSION: Maternal HHcy exposure contributes to adverse pregnancy outcomes by reducing placental mtDNAcn and triggering a cascade of PINK1/Parkin-mediated mitophagic disruption, cytosolic mtDNA release, and subsequent cGAS-STING-driven sterile inflammation and placental dysfunction, underscoring the need for clinical Hcy monitoring and early intervention.