Paradoxical Effects of Overexpressing Human Catalase on Vascular Function and Atherosclerotic Plaque Composition in Hypercholesterolemic Mice

Abstract

Increased oxidative stress is associated with initiation and progression of atherosclerosis. While catalase catalyzes the breakdown of hydrogen peroxide (H2O2) to water, it is unclear whether overexpression of catalase is sufficient to protect against cardiovascular dysfunction and advanced plaque formation. Therefore, we hypothesized overexpression of catalase in hypercholesterolemic mice following 3 months or 12 months of Western diet feeding will have preserved endothelial function, reduced H2O2 levels, reduced levels of osteogenic markers, and reduced calcium burden in atherosclerotic plaques. We used Ldlr−/−ApoB100/100 (LA) mice (hypercholesterolemic mice with a more “humanized” lipid profile) that were either expressed endogenous levels of murine catalase (LA‐Cat0/0) or overexpressed one copy of a human catalase construct (LA‐CatTg/0). These mice were fed a Western Diet (TD88137) for either 3 months (early disease) or 12 months (late disease). Following 3 months or 12 months on diet, we assessed endothelial function using isolated organ chambers, quantified H2O2 production (staining of frozen cross‐sections of aorta with CM‐H2DCFDA), measured changes of gene expression in aortic arch (qRT‐PCR), and performed histopathological analyses of intimal plaque calcium burden (Alizarin Red). Following 3 months on diet, endothelium‐dependent relaxation to acetylcholine (ACH) was unchanged between LA‐Cat0/0 and LA‐CatTg/0 mice, and we did not find substantive molecular or histopathological differences in aortic tissue between the two genotypes. Interestingly, and contrast to our hypothesis, endothelium‐dependent relaxation was modestly but not significantly impaired in LA‐CatTg/0 mice compared to LA‐Cat0/0 mice after 12 months of western diet feeding. Evaluation of female mice alone, however, revealed profoundly impaired endothelium‐dependent relaxation in LA‐CatTg/0. While H2O2 levels were slightly reduced in LA‐CatTg/0 at 3 months, H2O2 levels were not reduced by catalase overexpression following 12 months of Western diet feeding. In further contrast to our original hypothesis, expression of the osteogenic genes osterix and osteopontin were modestly increased in LA‐CatTg/0 mice following 3 months on diet compared to their wild‐type littermates, and further increased at the 12 month time point. Functionally, the molecular changes in 12 month animals were associated with increases in intimal plaque calcium burden in LA‐CatTg/0 (12.3% ± 2.5%) compared to their wild‐type littermates (7.8% ±1.2%). In conclusion, these data are in line with previous negative clinical trials of antioxidant treatment strategies, and suggest targeting a single antioxidant enzyme/reactive oxygen species to delay initiation or slow progression of atherosclerosis is not a viable therapeutic target, and may in fact paradoxically lead to deleterious changes in plaque composition and endothelial dysfunction.Support or Funding InformationNHLBI HL111121This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.