Hypoxia-induced mitochondrial reactive oxygen species (mtROS) differentially regulates smooth muscle cell (SMC) proliferation of pulmonary and systemic vasculature

Background: Vascular remodeling plays a pivotal role in regulation of hypoxia-mediated pulmonary and systemic hypertension via the phenotypic modulation of smooth muscle cells (SMCs) of pulmonary and systemic arteries, respectively. Mitochondria serve as putative oxygen (O₂) sensors, and consequently, adaptations to hypoxia are mediated via HIF (hypoxia-inducible factors) activation, which impinges on mitochondrial function by suppressing the mitochondrial activity. Therefore, we explored the implication of hypoxia-mediated mitochondrial stress in pulmonary and systemic arterial remodeling.

Methods: The hypoxic (10% O₂) effect on human pulmonary artery and aortic SMCs was examined in vitro by cell viability assay, proliferation index, autophagy, and comet assays. Mitochondrial ROS (mtROS), membrane potential (MMP), and mitochondrial morphology were assessed using mitochondrial-selective fluorescent probes. Further, the cell cycle distribution was analyzed by flow cytometry using propidium iodide staining.

Results: Our data indicate no significant alterations in cell viability and active proliferation of hypoxic PASMCs; however, an excessive rise in mtROS production and disrupted MMP, accompanied by enhanced DNA damage and reduced autophagy was observed, highlighting the 'apoptosis resistance' phenotype in these cells. Conversely, in hypoxia-treated hASMCs, a modest rise in mtROS levels was associated with reduced DNA damage; followed by upregulated autophagy; increased S-phase DNA content and cell viability, depicting the cytoprotective effect of hypoxia-induced autophagy against mitochondrial damage in hASMCs.

Conclusion: Our findings suggest that differential impact of mtROS on proliferative capacity may contribute to the variable hypoxic responses in pulmonary and systemic vasculature. Therefore, targeting mtROS may serve as an effective therapeutic strategy to prevent hypoxia-induced hypertension.