Overexpression of human catalase inhibits proliferation and promotes apoptosis in vascular smooth muscle cells

The role of reactive oxygen species, such as superoxide anions (O₂·^-) and hydrogen peroxide (H₂O₂), in modulating vascular smooth muscle cell proliferation and viability is controversial. To investigate the role of endogenously produced H₂O₂, rat aortic smooth muscle cells were infected with adenoviral vectors containing cDNA for human catalase (AdCat) or a control gene, β-galactosidase (AdLacZ). Infection with AdCat resulted in dose-dependent increases in intracellular catalase protein, which was predominantly localized to peroxisomes. After infection with 100 multiplicity of infection (MOI) of AdCat, cellular catalase activity was increased by 50- to 100-fold, and intracellular H₂O₂ concentration was reduced, as compared with control. Infection with AdCat reduced [³H]thymidine uptake, an index of DNA synthesis, in cells maintained in medium supplemented with 2% serum (0.37 ± 0.09 disintegrations per minute per cell [AdLacZ] versus 0.22 ± 0.08 disintegrations per minute per cell [AdCat], P<0.05). Five days after infection with 100 MOI of AdCat, cell numbers were reduced as compared with noninfected or AdLacZ-infected cells (157 780 ± 8413 [AdCat], P<0.05 versus 233 700 ± 3032 [noninfected] or 222 410 ± 5332 [AdLacZ]). Furthermore, the number of apoptotic cells was increased 5-fold after infection with 100 MOI of AdCat as compared with control. Infection with AdCat resulted in induction of cyclooxygenase (COX)-2, and treatment with a COX-2 inhibitor overcame the AdCat-induced reduction in cell numbers. These findings indicate that overexpression of catalase inhibited smooth muscle proliferation while increasing the rate of apoptosis, possibly through a COX-2-dependent mechanism. Our results suggest that endogenously produced H₂O₂ importantly modulates survival and proliferation of vascular smooth muscle cells.