Abstract 1159: Disease Severity in a Murine Model of Kawasaki Disease is Determined By Dysregulation of Elastin Fiber Assembly
Kawasaki Disease is a leading cause of acquired heart disease in children. However, the molecular mechanisms leading to coronary aneurysms, and the host factors that determine high-risk patients are unknown. We hypothesized that:
neonatal mice with abnormal elastin production and assembly (EL+/−) would be predisposed to aneurysm following injection of Lactobacillus casei wall extract (LCWE), an inducer of coronary arteritis; and
that the mechanism involves TGF-ß, a mediator implicated in other genetic models of aneurysm.
As a surrogate for active TGF-β signaling, we measured nuclear phospho-smad2 by immunohistochemistry. We followed the expression of tropoelastin (TE), fibulin-5 (Fib-5), and lysyl oxidase (LOX-1), known TGF-β targets important in elastin fiber assembly, by qRT-PCR and western immunoblot. We evaluated morphologic changes in the elastic lamina, and aneurismal dilatation of the coronaries, by HART staining. We found that LCWE induced TGF-β signaling in the coronary endothelial and smooth muscle cells in both WT and ELN +/− mice at 48h. In the WT mice, this was followed by a coordinated induction of TE (p<0.05), Fib-5 (p<0.05) and LOX-1 (p<0.01) mRNA at 7d, followed by a repression of TE and LOX-1 expression to below baseline by 14d. This was associated with an increase in TE protein (p<0.01), but not Fib-5 or LOX-1 at 7 and 14d. In contrast, TE mRNA and protein expression was reduced in the EL+/−mice as compared to WT (p<0.01) and did not increase significantly at 7 or 14d. In the WT mice, the increase in TE protein in the absence of Fib-5 and LOX-1 was associated with the deposition of disorganized, ectopic elastin and thinning of the lamina at 42d, suggesting the induction of elastolytic activity. The EL+/− mice demonstrated more extensive pathology, including marked accumulation of ectopic elastin, widespread disruption and discontinuity of the elastic lamina, and evidence of aneurysm formation. We conclude that in response to LCWE, activation of TGF-β is associated with ectopic deposition of poorly assembled elastin in the adventitia and loss of elastin in the vessel wall. In the EL+/− mouse, compromised elastin assembly increases ectopic elastin deposition and accentuates elastin loss, thereby predisposing to aneurysm development.