Alterations in Aortic Cellular Constituents during Thoracic Aortic Aneurysm Development

Abstract

The present study tested the hypothesis that changes in the resident endogenous cellular population accompany alterations in aortic collagen and elastin content during thoracic aortic aneurysm (TAA) development in a murine model. Descending thoracic aortas were analyzed at various time points (2, 4, 8, and 16 weeks) post-TAA induction (0.5 M CaCl 2 , 15 minutes). Aortic tissue sections were subjected to histological staining and morphometric analysis for collagen and elastin, as well as immunostaining for cell-type-specific markers to quantify fibroblasts, myofibroblasts, and smoothmuscle cells. Results were compared with reference control mice processed in the same fashion. Aortic dilatation was accompanied by changes in the elastic architecture that included: a decreased number of elastic lamellae (from 6 to 4); altered area fraction of elastin (elevated at 4 weeks and decreased at 16 weeks); and a decreased area between elastic lamellae (minimum reached at 4 weeks). Total collagen content did not change over time. Increased immunoreactivity for fibroblast and myofibroblast markers was observed at 8-and 16-week post-TAA-induction, whereas immunoreactivity for smooth-muscle cell markers peaked at 4 weeks and returned to baseline by 16 weeks. Therefore, this study demonstrated that changes in aortic elastin content were accompanied by the emergence of a subset of fibroblast-derived myofibroblasts whose altered phenotype may play a significant role in TAA development through the enhancement of extracellular matrix proteolysis.

Alterations in membrane type-1 matrix metalloproteinase abundance after the induction of thoracic aortic aneurysm in a murine model

“…The immunostaining results revealed that MT1-MMP was localized in a cellular pattern similar to what was seen and previously reported with DDR2 (Fig. 6, top and middle, respectively) (19,20). Fig.…”

“…Previous work from this laboratory (19) has demonstrated that endogenous fibroblasts produce MMP-9 during early aortic dilatation. In addition, degeneration of the elastic architecture was found to occur concomitantly with the emergence of a population of fibroblast-derived myofibroblasts (20). Moreover, upon isolation of aortic fibroblasts from control and TAA-induced mice, it was determined that the TAAinduced fibroblasts had undergone a significant phenotypic change during TAA formation, resulting in an enhanced proteolytic gene expression profile, including a twofold increase in MT1-MMP expression (21).…”

“…Tissue used for immunoblot analysis was immediately snap frozen and stored at Ϫ80°C (n ϭ 10 for each time point). Additionally, tissue designated for immunohistochemistry was harvested from control and 16-wk TAA-induced mice after perfusion fixation as previously described (20). The descending thoracic aorta was then carefully excised and embedded in paraffin.…”

MicroRNA-29 in Aortic Dilation: Implications for Aneurysm Formation

“…MiR-29 was additionally shown to induce apoptosis in cancer cells by targeting Mcl-1, an antiapoptotic Bcl-2 family member, 16 and by augmenting p53 levels. 17 Smooth muscle cell apoptosis is considered to favor aneurysm formation 18 and, because miR-29 is highly expressed in smooth muscle cells (Online Figure V and VII), this mechanism may contribute to miR-29 -mediated destabilization of the vascular wall. Interestingly, inhibition of miR-29 decreased the expression of matrix metalloproteinase MMP9 in the aorta (Online Figure VIII), which may additionally prevent further degradation of matrix proteins.…”

Inhibition of Transforming Growth Factor β Worsens Elastin Degradation in a Murine Model of Kawasaki Disease

“…Degradation of elastin is a key feature of aneurysm development, and extensive clinical and experimental evidence demonstrates that an imbalance between the proteinases and their endogenous inhibitors influences the development and progression of arterial aneurysms. 38 Matrix metalloproteinase 9 appears to be a key factor affecting this balance, with increased activity found in aneurysmal tissue taken from patients with an abdominal aortic aneurysm and MS, 39 in the coronary arteries of children with fatal KD, 30 and in ani- Figure 8. Inhibition of TGF-␤ increases MMP-9 activity and reduces plasminogen activator inhibitor-1 in LCWE-treated mice.…”