PARP inhibition modulates mitochondrial morphology and metabolism under hypoxic stress in cancer cells

Hypoxia, or low oxygen availability, is one of the main factors that determine tumor growth and metastatic survival. The hypoxic response is orchestrated by HIF transcription factors, which activate genetic and metabolic programs that promote angiogenesis, metabolic reprogramming, migration, and ultimately a clinically aggressive phenotype. Mitochondria play a central role in this process, as they are not only the main consumers of oxygen but also undergo morphological and biochemical adaptations that shape how tumor cells respond to a hostile microenvironment. Because the contribution of ADP ribosylation to these mitochondrial adaptations remains unclear, we aimed to define how PARP inhibition influences mitochondrial behavior during hypoxia. To address this question, we first examined how PARP inhibitors affect mitochondrial structure and function under oxygen deprivation. We found that PARP inhibition drives a shift toward a small, globular mitochondrial phenotype characterized by membrane depolarization (ΔΨm) and enhanced fission. Given that mitochondrial morphology is tightly linked to metabolic state, we next investigated whether these structural changes altered hypoxia induced metabolic reprogramming. PARP inhibition prevented the typical shift toward anaerobic glycolysis, forcing tumor cells to activate the AMPk/mitophagy axis as an alternative survival pathway. Finally, to determine the functional consequences of this adaptive response, we assessed tumor cell fitness when mitophagy was impaired. Blocking mitophagy markedly reduced the proliferative and malignant potential of hypoxic tumor cells, thereby increasing their sensitivity to PARP inhibition. Collectively, our results uncover a previously unrecognized pathway of mitochondrial adaptation to hypoxia and reveal a therapeutically relevant crosstalk between mitochondrial dynamics and ADP ribosylation that may be exploited in future anticancer strategies.