BRCA2 loss triggers a downward spiral of genomic instability via ROS-dependent metabolic collapse

BRCA2 plays a central role in maintaining genome integrity through homologous recombination and replication-fork protection, yet the compensatory networks sustaining BRCA2-deficient cells remain unclear. Here we show BRCA2 enforces a homeostatic mechanism aligning mitochondrial respiration with DNA repair capacity in both cancer and non-cancer contexts. Genome-wide CRISPR screening identified glutathione metabolism and base-excision repair as the key compensatory networks sustaining BRCA2-deficient cells by detoxifying mitochondria-derived reactive oxygen species. BRCA2 loss provokes an acute mitochondrial ROS surge, causing 8-oxoguanine accumulation and a systemic metabolic crisis marked by NAD+ and glutathione depletion. PARP inhibitor targets DNA replication vulnerabilities, increasing the cellular requirement for BRCA2. The resulting oxidative burden primes cells for TP53-dependent apoptosis in G1 during olaparib treatment, which extends cytotoxicity beyond canonical S-phase stress. These findings indicate BRCA2 prevents metabolic flux from outpacing repair capacity, providing a rationale for combining PARP inhibition with redox modulation to enhance efficacy and overcome resistance. HighlightsO_LIAcute BRCA2 loss induces ROS and mitochondrial dysfunction creating a metabolic scar C_LIO_LIOxidative lesions drive PARP hyperactivation and precipitate a cellular NAD crisis C_LIO_LIPARP inhibitors provoke TP53-dependent apoptosis in G1 beyond replication stress in S phase C_LIO_LIGlutathione deficiency exacerbates bone marrow failure under BRCA2 depletion C_LIO_LIBRCA2 tightly couples mitochondrial redox homeostasis to genomic maintenance C_LI