High serum thrombospondin-1 concentration is associated with slower abdominal aortic aneurysm growth and deficiency of thrombospondin-1 promotes angiotensin II induced aortic aneurysm in mice

Abdominal aortic aneurysm (AAA) is a common age-related vascular disease characterized by progressive weakening and dilatation of the aortic wall. Thrombospondin-1 (TSP-1; gene Thbs1) is a member of the matricellular protein family important in the control of extracellular matrix (ECM) remodelling. In the present study, the association of serum TSP-1 concentration with AAA progression was assessed in 276 men that underwent repeated ultrasound for a median 5.5 years. AAA growth was negatively correlated with serum TSP-1 concentration (Spearman's rho -0.129, P=0.033). Men with TSP-1 in the highest quartile had a reduced likelihood of AAA growth greater than median during follow-up (OR: 0.40; 95% confidence interval (CI): 0.19-0.84, P=0.016, adjusted for other risk factors). Immunohistochemical staining for TSP-1 was reduced in AAA body tissues compared with the relatively normal AAA neck. To further assess the role of TSP-1 in AAA initiation and progression, combined TSP-1 and apolipoprotein deficient (Thbs1(-/-) ApoE(-/-), n= 20) and control mice (ApoE(-/-), n= 20) were infused subcutaneously with angiotensin II (AngII) for 28 days. Following AngII infusion, Thbs1(-/-)ApoE(-/-)mice had larger AAAs by ultrasound (P=0.024) and ex vivo morphometry measurement (P=0.006). The Thbs1(-/-) ApoE(-/-) mice also showed increased elastin filament degradation along with elevated systemic levels and aortic expression of matrix metalloproteinase (MMP)-9. Suprarenal aortic segments and vascular smooth muscle cells (VSMCs) isolated from Thbs1(-/-) ApoE(-/-) mice showed reduced collagen 3A1 gene expression. Furthermore, Thbs1(-/-) ApoE(-/-) mice had reduced aortic expression of low-density lipoprotein (LDL) receptor-related protein 1. Collectively, findings from the present study suggest that TSP-1 deficiency promotes maladaptive remodelling of the ECM leading to accelerated AAA progression.