The expression and role of tenascin C in abdominal aortic aneurysm formation and progression

Abstract

Objectives: Up-regulation of tenascin C (TNC), a matricellular protein, produced mainly by vascular smooth muscle cells (VSMC), is associated with the progression and dilation of abdominal aortic aneurysms (AAA). The aims of this study were (i) to evaluate whether serum levels of TNC in patients with AAA patients correlate with aortic diameter and (ii) to clarify the role of TNC in formation and progression of AAA in a murine model.

Methods: In 15 patients with AAA serum levels of TNC were measured and correlated with aortic diameters. Moreover, in a murine calcium chloride AAA model, the impact of TNC deficiency on AAA diameter was evaluated. Finally, human VSMC were incubated with TNC to clarify its regulating potential.

Results: In the clinical cohort, there was a trend of correlation between serum TNC levels and AAA diameter (P = 0.055). TNC knock out mice with AAA showed significantly lower diameter ratios compared to the wild-type group (WT) 3 weeks (P < 0.05) and 10 weeks (P < 0.05) after AAA induction. Immunohistochemistry revealed increased TNC expression in aortic tissue from WT with AAA as compared sham-operated mice. Furthermore, WT with AAA showed a more disrupted Elastin structure than TNC knock out mice 10 weeks after AAA induction. In human aortic VSMC, TNC incubation induced expression of remodelling associated proteins.

Conclusions: TNC might play a causative role in the formation, dilation and progression of AAA. Our results indicate that TNC might be a biomarker as well as a potential therapeutic target in the treatment of AAA.

Keywords: Abdominal aortic aneurysm; Extracellular matrix; Serum marker; Tenascin C.

Figure 1:

Correlation between aortic diameter (mm) and serum tenascin C levels (pg/ml) in patient cohort of AAA (n = 15).

Figure 2:

Representative three-dimensional reconstructed computed tomography images as well as tenascin C serum levels obtained from 2 abdominal aortic aneurysms patients.

Figure 3:

Aortic diameter ratio between the aortic size at AAA induction and during organ harvesting at 3 weeks (A) and 10 weeks (B) post-induction. Data are shown as mean plus standard deviation. *P < 0.05, for the level of significance in the comparison between WT-AAA and tenascin C KO-AAA (one-way ANOVA with Tukey-HSD post hoc test). AAA: abdominal aortic aneurysms; KO: knock out; WT: wild-type mice.

Figure 4:

Expression of TNC 3 weeks after AAA induction (A) as well as representative images of TNC immunohistochemistry of the WT-SHAM (B) and the WT-AAA group (C). Data are shown as mean plus standard deviation. ***P < 0.001, for the level of significance in the comparison between WT-SHAM and WT-AAA (unpaired T-test). WT-SHAM: n = 6, WT-AAA: n = 6. Original magnification, 200×. AAA: abdominal aortic aneurysms; TNC: tenascin C; WT: wild-type mice.

Figure 5:

Scoring of elastin structure in Elastica van Gieson staining 10 weeks after AAA induction (A). Representative images of the WT-AAA group with severe elastin degradation and inflammatory cell infiltrates (B) and the TNC KO-AAA group with mild distention (C). Data are shown as mean plus standard deviation. *P < 0.05, for the level of significance in the comparison between WT-AAA and TNC KO-AAA (unpaired T-test). WT-AAA: n = 10, TNC KO-AAA: n = 14. Original magnification, 200×. AAA: abdominal aortic aneurysms; KO: knock out; TNC: tenascin C; WT: wild-type mice.

Figure 6:

Expression matrix metalloproteinase 2 (A), Col3 (B), Elastin (C), TNC (D) as well as angiotensin-converting enzyme 1 (E) in human aortic vascular smooth muscle cells culture supernatant measured by reverse transcription and quantitative polymerase chain reaction after incubation with TNC. TNC+ TAK242 and Ang II. *P < 0.05, **P < 0.01 and ***P < 0.001, for the level of significance in the comparison between Control and TNC, TNC and TNC+TAK242 (1-way ANOVA with Tukey-HSD post hoc test) as well as Control and Ang II (unpaired T-test). TNC: tenascin C.