Effects of Increased Arterial Stiffness on Atherosclerotic Plaque Amounts.

Increased arterial stiffness is associated with atherosclerosis in humans, but there have been limited animal studies investigating the relationship between these factors. We bred elastin wildtype (Eln+/+) and heterozygous (Eln+/-) mice to apolipoprotein E wildtype (Apoe+/+) and knockout (Apoe-/-) mice and fed them normal diet (ND) or Western diet (WD) for 12 weeks. Eln+/- mice have increased arterial stiffness. Apoe-/- mice develop atherosclerosis on ND that is accelerated by WD. It has been reported that Apoe-/- mice have increased arterial stiffness and that the increased stiffness may play a role in atherosclerotic plaque progression. We found that Eln+/+Apoe-/- arterial stiffness is similar to Eln+/+Apoe+/+ mice at physiologic pressures, suggesting that changes in stiffness do not play a role in atherosclerotic plaque progression in Apoe-/- mice. We found that Eln+/-Apoe-/- mice have increased structural arterial stiffness compared to Eln+/+Apoe-/- mice, but they only have increased amounts of ascending aortic plaque on ND, not WD. The results suggest a change in atherosclerosis progression but not end stage disease in Eln+/-Apoe-/- mice due to increased arterial stiffness. Possible contributing factors include increased blood pressure and changes in circulating levels of interleukin-6 (IL6) and transforming growth factor beta 1 (TGF-ß1) that are also associated with Eln+/- genotype.

Hypertension and decreased aortic compliance due to reduced elastin amounts do not increase atherosclerotic plaque accumulation in Ldlr-/- mice.

BACKGROUND AND AIMS: High blood pressure and reduced aortic compliance are associated with increased atherosclerotic plaque accumulation in humans. Animal studies support these associations, but additional factors, such as fragmented elastic fibers, are present in most previous animal studies. Elastin heterozygous (Eln+/-) mice have high blood pressure and reduced aortic compliance, with no evidence of elastic fiber fragmentation and represent an appropriate model to directly investigate the effects of these factors on atherosclerosis. METHODS AND RESULTS: Eln+/- and Eln+/+ mice were crossed with low density lipoprotein receptor knockout (Ldlr-/-) and wild-type (Ldlr+/+) mice and fed normal or Western diet (WD) for 16 weeks. We hypothesized that on WD, Eln+/-Ldlr-/- mice with high blood pressure and reduced aortic compliance would have increased atherosclerotic plaque accumulation compared to Eln+/+Ldlr-/- mice. We measured serum cholesterol and cytokine levels, blood pressure, aortic compliance, and plaque accumulation. Contrary to our hypothesis, we found that on WD, Eln+/-Ldlr-/- mice do not have increased plaque accumulation compared to Eln+/+Ldlr-/- mice. At the aortic root, there are no significant differences in plaque area between Eln+/-Ldlr-/- and Eln+/+Ldlr-/- mice on WD (p = 0.89), while in the ascending aorta, Eln+/-Ldlr-/- mice on WD have 29% less normalized plaque area than Eln+/+Ldlr-/- mice on WD (p = 0.009). CONCLUSION: Using an atherogenic mouse model, we conclude that increased blood pressure and reduced aortic compliance are not direct causes of increased aortic plaque accumulation. We propose that additional insults, such as fragmentation of elastic fibers, are necessary to alter plaque accumulation.

Elastin Insufficiency Predisposes Mice to Impaired Glucose Metabolism.

Williams-Beuren syndrome is the consequence of a large contiguous-gene deletion on the seventh human chromosome that includes the elastin gene. Elastin is an extracellular matrix protein responsible for the cardiovascular abnormalities associated with Williams's syndrome, including hypertension and aortic stenosis. A high percentage of individuals with Williams's syndrome also have impaired glucose tolerance, independent of traditional risk factors for diabetes. Here, we show that murine adipose tissue does assemble elastic fibers; however, isolated elastin insufficiency (Eln+/-) in mice does not independently influence glucose metabolism or tissue lipid accumulation. Similarly, isolated ApoE deficiency (ApoE-/-), a model of hyperlipidemia and atherosclerosis, does not impair insulin sensitivity. However, Eln+/-; ApoE-/- double mutant mice exhibit notable hyperglycemia, adipocyte hypertrophy, inflammation of adipose tissue, and ectopic lipid accumulation in liver tissue. Further, Eln+/-; ApoE-/- mutants have significant impairment of insulin sensitivity by insulin tolerance testing, independent of body weight or diet, suggesting that elastin insufficiency predisposes to metabolic disease in susceptible individuals.