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Background Thoracic aortic aneurysms (TAAs) develop through an asymptomatic process resulting in gross dilatation that progresses to rupture if left undetected and untreated. If detected, TAA patients are followed over time until the risk of rupture outweighs the risk of surgical repair. Current methodologies for tracking TAA size are limited to expensive computed tomography or magnetic resonance imaging, as no acceptable population screening tools are currently available. Previous studies from this laboratory and others have identified differential protein profiles for the matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs), in ascending TAA tissue from patients with bicuspid aortic valves (BAV), versus patients with idiopathic degenerative disease and a tricuspid aortic valve (TAV). Additionally, altered microRNA (miR) expression levels have also been reported in TAAs as compared to normal aortic tissue. The objective of the present study was to identify circulating factors within the plasma that could serve as potential biomarkers for distinguishing etiological subtypes of aneurysm disease. Methods Ascending TAA tissue and plasma specimens were obtained from BAV (n=21) and TAV (n=21) patients at the time of surgical resection. The protein abundance of key MMPs (-1, -2, -3, -8, -9) and TIMPs (-1, -2, -3, -4), and microRNAs (-1, -21, -29a, -133a, -143, -145) was examined using a multi-analyte protein profiling system or by quantitative PCR, respectively. Results were compared to normal aortic tissue and plasma obtained from patients without aortic disease (n=10). Results Significant (p < 0.05) differences in standardized miR-1 and miR-21 abundance between BAV and TAV aortic tissue samples and different tissue and plasma profiles of analyte differences from normal aorta where observed between the BAV and TAV groups. Linear regression analysis significant linear relationships in plasma and tissue measurements only for MMP-8 and TIMPs -1, -3 and -4 (p < 0.05). Receiver operator curve analysis revealed specific cassettes of analytes predictive of TAA disease. Relative to normal aorta, BAV proteolytic balance was significantly increased for MMP-1, -2 and -7, and for decreased MMP-8 and -9. In contrast, TAV proteolytic balance relative to normal aorta was significantly increased only for MMP-1 and decreased for MMP-8 and -9. Conclusions Taken together these unique data demonstrate differential plasma profiles of MMPs, TIMPs, and miRs in ascending TAA specimens from patients with BAV and TAV. These results suggest that circulating biomarkers may form the foundation for a broader platform of biomarkers capable of detecting the presence of TAA using a simple blood test and may also be useful in personalized medicine strategies to distinguish between etiological subtypes of TAAs in patients with aneurysm disease.

BackgroundMaintenance of the structure and mechanical properties of the thoracic aorta contributes to aortic function and is dependent on the composition of the extracellular matrix and the cellular content within the aortic wall. Age‐related alterations in the aorta include changes in cellular content and composition of the extracellular matrix; however, the precise roles of these age‐related changes in altering aortic mechanical function are not well understood.Methods and ResultsThoracic aortic rings from the descending segment were harvested from C57BL/6 mice aged 6 and 21 months. Thoracic aortic diameter and wall thickness were higher in the old mice. Cellular density was reduced in the medial layer of aortas from the old mice; concomitantly, collagen content was higher in old mice, but elastin content was similar between young and old mice. Stress relaxation, an index of compliance, was reduced in aortas from old mice and correlated with collagen fraction. Contractility of the aortic rings following potassium stimulation was reduced in old versus young mice. Furthermore, collagen gel contraction by aortic smooth muscle cells was reduced with age.ConclusionsThese results demonstrate that numerous age‐related structural changes occurred in the thoracic aorta and were related to alterations in mechanical properties. Aortic contractility decreased with age, likely because of a reduction in medial cell number in addition to a smooth muscle contractile deficit. Together, these unique findings provide evidence that the age‐related changes in structure and mechanical function coalesce to provide an aortic substrate that may be predisposed to aortopathies.

Marfan Syndrome (MFS) and Loeys-Dietz Syndrome (LDS) represent heritable connective tissue disorders that cosegregate with a similar pattern of cardiovascular defects (thoracic aortic aneurysm, mitral valve prolapse/regurgitation, and aortic dilatation with regurgitation). This pattern of cardiovascular defects appears to be expressed along a spectrum of severity in many heritable connective tissue disorders and raises suspicion of a relationship between the normal development of connective tissues and the cardiovascular system. Given the evidence of increased transforming growth factor-beta (TGF-β) signaling in MFS and LDS, this signaling pathway may represent the common link in this relationship. To further explore this hypothetical link, this chapter will review the TGF-β signaling pathway, heritable connective tissue syndromes related to TGF-β receptor (TGFBR) mutations, and discuss the pathogenic contribution of TGF-β to these syndromes with a primary focus on the cardiovascular system.

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