Cardiovascular effects of uremia in apolipoprotein E-deficient mice

The purpose of this thesis work was to establish an experimental mouse model for studying the pathogenesis and therapy of accelerated atherosclerosis in uremia. Uremia was induced by surgical 5/6 nephrectomy in apolipoprotein E-deficient (apoE-/-) mice and led to development of severe aortic atherosclerosis independently of BP and plasma homocysteine levels. Also, the accelerated atherosclerosis could not be fully explained by changes in total plasma cholesterol. Morphologic and biochemical analyses of aortas suggested that accelerated initiation and expansion rather than a specific uremic lesion composition characterize atherosclerosis in the uremic mice. Increased expression of inflammatory genes in aortas of uremic mice suggests that an augmented inflammatory response in the arterial wall might be an important impetus for accelerated atherosclerosis in uremia. A marked downregulation of expression of smooth muscle cell assigned genes indicates that besides intimal atherosclerosis, uremic vasculopathy in apoE-/- mice is characterized by a uremia-specific medial smooth muscle cell degeneration. Oxidative stress could also be important for the development of atherosclerotic lesions in uremia. In the mouse model, uremia led to a marked increase of titers of antibodies against oxidized LDL (OxLDL), and increased circulating levels of the oxidized phospholipid epitope EO6. Treatment with enalapril (an ACE inhibitor) almost completely prevented the development of accelerated aortic atherosclerosis in uremic mice. This effect was parallelled by reductions of aortic expression of the proinflammatory adhesion molecule VCAM-1, and plasma titers of IgM antibodies against OxLDL, and was at least partly independent of BP-lowering. To test the involvement of the receptor for advanced glycation end products (RAGE) in development of uremic atherosclerosis, uremic mice were treated with a neutralizing RAGE-antibody. This treatment reduced the aortic plaque area fraction by 59% in parallel with reductions of the plasma levels of the oxidized phospholipid epitope EO6, and titers of IgG antibodies against OxLDL. As opposed to rats and CD-1 mice, apoE-/- mice did not have impaired cardiac structure and function (as assessed by echocardiography, histology, gene expression analysis) upon the induction of uremia. Since the uremic apoE -/- mouse is normotensive and did not develop myocardial calcifications, it is possible that these factors may be important for the development of cardiac dysfunction in uremia. In conclusion, the mice studies by Bro et al. showed that uremic vasculopathy in apoE-/- mice, besides accelerated intimal atherosclerosis, was characterized by a uremia-specific medial smooth muscle cell degeneration. Furthermore, the studies suggested that vascular inflammation and systemic oxidative stress may explain some of the proatherogenic effects of uremia in mice. Interestingly, the accelerated atherosclerosis could be prevented by RAS inhibition, or markedly reduced by RAGE blockade, probably through anti-inflammatory and antioxidative effects. The new uremic mouse model has provided a tool to identify molecular responses of the arterial wall to uremia, and may help identify new approaches for treatment and prevention of atherosclerotic disease in uremia. Also, the data obtained with the mouse model provide a platform for further studies in humans.