Endothelial reactive oxygen-forming NADPH oxidase 5 is a possible player in diabetic aortic aneurysm but not atherosclerosis

Abstract

Atherosclerosis and its complications are major causes of cardiovascular morbidity and death. Apart from risk factors such as hypercholesterolemia and inflammation, the causal molecular mechanisms are unknown. One proposed causal mechanism involves elevated levels of reactive oxygen species (ROS). Indeed, early expression of the ROS forming NADPH oxidase type 5 (Nox5) in vascular endothelial cells correlates with atherosclerosis and aortic aneurysm. Here we test the pro-atherogenic Nox5 hypothesis using mouse models. Because Nox5 is missing from the mouse genome, a knock-in mouse model expressing human Nox5 in its physiological location of endothelial cells (eNOX5ki/ki) was tested as a possible new humanised mouse atherosclerosis model. However, whether just on a high cholesterol diet or by crossing in aortic atherosclerosis-prone ApoE−/− mice with and without induction of diabetes, Nox5 neither induced on its own nor aggravated aortic atherosclerosis. Surprisingly, however, diabetic ApoE−/− x eNOX5ki/ki mice developed aortic aneurysms more than twice as often correlating with lower vascular collagens, as assessed by trichrome staining, without changes in inflammatory gene expression, suggesting that endothelial Nox5 directly affects extracellular matrix remodelling associated with aneurysm formation in diabetes. Thus Nox5-derived reactive oxygen species are not a new independent mechanism of atherosclerosis but may enhance the frequency of abdominal aortic aneurysms in the context of diabetes. Together with similar clinical findings, our preclinical target validation opens up a first-in-class mechanism-based approach to treat or even prevent abdominal aortic aneurysms.

The role of oxidative stress in diabetes mellitus-induced vascular endothelial dysfunction

“…Monocyte Nox is activated by enhanced p22phox expression and p47phox translocation, which is the basis of oxidative stress in T2DM patients [ 15 ]. ROS derived from the Nox subtypes Nox1, Nox2, and Nox4 lead to vascular dysfunction in diabetic retinopathy, and Nox5-derived ROS increase the incidence of abdominal aortic aneurysms in diabetic patients [ 16 , 17 ]. Surprisingly, Nox4 has a protective role in diabetic atherosclerosis [ 18 ].…”

Structure, regulation, and physiological functions of NADPH oxidase 5 (NOX5)

“…Regarding the precise implication of NOX5 in this process, it has been described that the mRNA and protein levels of NOX5 as well as the calcium-dependent NADPH oxidase activity are significantly increased in the atherosclerotic coronary arteries from patients with coronary artery disease as compared to nonatherosclerotic vessels [ 47 ]. However, in a recent work employing a humanized Nox5 knock-in mice that expressed NOX5 in endothelial cells to test the pro-atherogenic hypothesis, Ho et al [ 50 ] found that the expression of the oxidase per se was insufficient to induce aortic atherosclerotic lesions, even in aged mice and exposed to a high cholesterol atherogenic diet. Moreover, in the same work, the authors demonstrated that the endothelial expression of NOX5 did not aggravate aortic atherosclerosis in the atherosclerosis-prone ApoE −/− mice with and without induction of diabetes [ 50 ].…”

“…However, in a recent work employing a humanized Nox5 knock-in mice that expressed NOX5 in endothelial cells to test the pro-atherogenic hypothesis, Ho et al [ 50 ] found that the expression of the oxidase per se was insufficient to induce aortic atherosclerotic lesions, even in aged mice and exposed to a high cholesterol atherogenic diet. Moreover, in the same work, the authors demonstrated that the endothelial expression of NOX5 did not aggravate aortic atherosclerosis in the atherosclerosis-prone ApoE −/− mice with and without induction of diabetes [ 50 ]. Another process related to vascular diseases in which NOX5 appears to be involved is in vascular calcification, the formation of calcium phosphate crystals in the vessel wall that promotes vascular stiffness.…”

The Role of Oxidative Stress in Atherosclerosis

“…The NOX5 gene is absent from rodent species and this has hampered our understanding of its role in atherosclerosis. A recent study using knock-in mice expressing human NOX5 in endothelial cells showed that NOX5 does not promote atherosclerosis [ 28 ], although deletion of NOX5 in New Zealand White rabbits significantly increased plaque development in the thoracic aorta, suggesting a protective role of NOX5 [ 29 ]. However, the role of NOX5 in human atherosclerosis remains unclear.…”