Mitochondrial Optic Atrophy (OPA)1 expression regulates the injury response to neonatal hypoxia-ischaemia.

Mitochondrial dysfunction is a central driver of neonatal hypoxic-ischaemic encephalopathy (HIE), yet the specific vulnerabilities of mitochondrial fusion machinery in the neonatal brain remain poorly defined. Here, we investigate Optic Atrophy (OPA)1 as a critical determinant of mitochondrial resilience during hypoxia-ischaemia (HI). Human developmental transcriptomics showed stable perinatal expression of mitochondrial dynamics genes, supporting their potential utility as therapeutic targets at birth. In a neonatal mouse model, HI induced rapid proteolytic processing of OPA1 in whole brain. In vitro, exposure of primary astrocytes to oxygen-glucose deprivation (OGD) mimicked the OPA1 sensitivity observed in whole brain, with aberrant processing and loss of expression. We genetically replicated this observation by knocking down OPA1 expression in primary astrocytes. The predicted mitochondrial fragmentation and impaired bioenergetics was also accompanied by increased vulnerability to hypoxia, revealing an OPA1dependent susceptibility under moderate metabolic stress. Transcriptomics analyses of these cells highlighted an OPA1-mediated depletion of mitochondrial DNA. This mtDNA depletion was also evident in OGD-treated astrocytes and ex vivo brain samples at 24h after HI in our rodent model. In contrast, mild OPA1 overexpression enhanced astrocyte survival following OGD and OPA1 overexpression in vivo markedly reduced tissue damage after neonatal HI. MtDNA levels in OPA1-overexpressing mice before and at 7 days after HI were significantly higher than in wild-type mice. These findings position OPA1 as a key mediator of mitochondrial impairment after HI and to our knowledge, is the first study showing that loss of mtDNA is a consequence of neonatal HI. Our data highlight that maintaining OPA1 expression is a promising therapeutic strategy for protecting the neonatal brain following birth asphyxia.