Moderate aerobic exercise prevents matrix degradation and death in a mouse model of aortic dissection and aneurysm

Abstract

Thoracic aortic aneurysm and dissection (TAAD) is a deadly disease characterized by intimal disruption induced by hemodynamic forces of the circulation. The effect of exercise in patients with TAAD is largely unknown. β-Aminopropionitrile (BAPN) is an irreversible inhibitor of lysyl oxidase that induces TAAD in mice. The objective of this study was to investigate the effect of aerobic exercise on BAPN-induced TAAD. Upon weaning, mice were given either BAPN-containing water or standard drinking water and subjected to either conventional cage activity (BAPN-CONV) or forced treadmill exercise (BAPN-EX) for up to 26 wk. Mortality was 23.5% (20/85) for BAPN-CONV mice versus 0% (0/22) for BAPN-EX mice (hazard ratio 3.8; P = 0.01). BAPN induced significant elastic lamina fragmentation and intimal-medial thickening compared with BAPN-untreated controls, and aneurysms were identified in 50% (5/10) of mice that underwent contrast-enhanced CT scanning. Exercise significantly decreased BAPN-induced wall thickening, calculated circumferential wall tension, and lumen diameter, with 0% (0/5) of BAPN-EX demonstrating chronic aortic aneurysm formation on CT scan. Expression of selected genes relevant to vascular diseases was analyzed by qRT-PCR. Notably, exercise normalized BAPN-induced increases in TGF-β pathway-related genes Cd109, Smad4, and Tgfβr1; inflammation-related genes Vcam1, Bcl2a1, Ccr2, Pparg, Il1r1, Il1r1, Itgb2, and Itgax; and vascular injury- and response-related genes Mmp3, Fn1, and Vwf. Additionally, exercise significantly increased elastin expression in BAPN-treated animals compared with controls. This study suggests that moderate aerobic exercise may be safe and effective in preventing the most devastating outcomes in TAAD.NEW & NOTEWORTHY Moderate aerobic exercise was shown to significantly reduce mortality, extracellular matrix degradation, and thoracic aortic aneurysm and dissection formation associated with lysyl oxidase inhibition in a mouse model. Gene expression suggested a reversal of TGF-β, inflammation, and extracellular matrix remodeling pathway dysregulation, along with augmented elastogenesis with exercise.

Keywords: BAPN; aortic aneurysm; aortic dissection; exercise; lysyl oxidase.

Figure 1.

Experimental scheme.

Figure 2.

LOX inhibition with BAPN causes aortic remodeling of the ascending aorta. A–F: representative histological sections of the ascending aorta (AscAo) of 8-wk-old mice without BAPN treatment (A–C) and with BAPN treatment (D–F); Verhoeff–Van Gieson (VVG) (A and D), hematoxylin and eosin (H&E) (B and E), and Masson’s Trichrome (C and F) stains. Remodeling is present in the arterial wall of BAPN-treated animals as highlighted by fragmentation of the elastin lamina (black-stained elastin layers in D compared with A) and increased collagen deposition (blue staining in F compared with C). Left panels of each subfigure are ×20 mag., right panels of each subfigure are ×40 mag. G: quantification of wall thickness in BAPN-untreated versus BAPN-treated mice (8 wk old; n = 6 BAPN-untreated, 9 BAPN-treated). *P = 0.02 by Student’s t test. H: representative dissection in a BAPN-treated mouse (8 wk old). Yellow arrow points to area of dissection; ×40 mag. I: transmission electron microscopy of AscAo section of a BAPN-treated mouse (22 wk old), demonstrating aberrant SMC cytoplasmic interaction with elastin (white arrow) and discontinuity of the elastin layer (yellow arrow). Scale bar represents 2 µm. AscAo, ascending aorta; BAPN, β-aminopropionitrile; LOX, lysyl oxidase; SMC, smooth muscle cell.

Figure 3.

LOX inhibition causes frequent aortic rupture. Top: necropsy of expired mice identified thoracic aortic ruptures as the most frequent cause of death with BAPN treatment. Bottom: thoracic cavity hematoma (left) and arch and descending thoracic aortic hematoma (right) from aortic rupture. BAPN, β-aminopropionitrile; LOX, lysyl oxidase.

Figure 4.

Exercise reduces mortality in BAPN-treated mice. Survival curve in BAPN-treated mice without and with exercise (n = 85 BAPN-CONV, n = 22 BAPN-EX). The survival benefit was statistically significant (Mantel–Haenszel hazard ratio = 3.8, P = 0.01 by log-rank test). There were no deaths in mice untreated with BAPN (CONV, n = 31 or EX, n = 11). Data from CONV and EX are not shown in graph due to overlying curve with BAPN-EX. BAPN, β-aminopropionitrile; BAPN-CONV, conventional cage activity; BAPN-EX, forced treadmill exercise.

Figure 5.

Exercise reduces aortic aneurysmal dilatation in BAPN-treated mice. Quantification of aortic lumen diameters by micro-CT imaging demonstrates a decrease in AscAo and DTA lumen size in BAPN-EX mice compared with BAPN-CONV mice. Exercise did not affect lumen size in BAPN-untreated animals. Dashed lines represent 1.5× the mean diameter of the relevant aortic segment in BAPN-untreated, conventional cage activity animals. *P < 0.05, **P < 0.01 by two-way ANOVA with Tukey’s multiple comparisons test. n = 10 CONV, 5 EX, 10 BAPN-CONV, 5 BAPN-EX. AscAo, ascending aorta; BAPN, β-aminopropionitrile; BAPN-CONV, conventional cage activity; BAPN-EX, forced treadmill exercise; DTA, descending thoracic aorta.

Figure 6.

Exercise reduces aortic wall remodeling in BAPN-treated mice. A: representative section of AscAo demonstrating reduced elastin degradation in BAPN-EX mice compared with BAPN-CONV mice. Magnification in left panels (VVG) ×20 and in right panels (VVG and H&E) is ×40. B–D: quantification of intimal-medial thickness (B), adventitial thickness (C), and total wall thickness (D). E: decrease in nicks and breaks of the elastic lamina. *P < 0.05, **P < 0.01 by two-way ANOVA with Tukey’s multiple comparisons test. n = 4 CONV, 6 EX, 5 BAPN-CONV, 5 BAPN-EX. AscAo, ascending aorta; BAPN, β-aminopropionitrile; BAPN-CONV, conventional cage activity; BAPN-EX, forced treadmill exercise; VVG, Verhoeff–Van Gieson.

Figure 7.

The effect of BAPN and exercise on systemic hemodynamics. There was no difference in systolic, diastolic, mean arterial blood pressure, or pulse pressure in BAPN-treated mice as compared with BAPN-untreated mice. Exercise significantly increased the heart rate of BAPN-EX mice versus CONV mice. *P < 0.05 by two-way ANOVA with Tukey’s multiple comparisons test. n = 20 CONV, 4 EX, 8 BAPN-CONV, 5 BAPN-EX. BAPN, β-aminopropionitrile; BAPN-CONV, conventional cage activity; BAPN-EX, forced treadmill exercise.

Figure 8.

Exercise reduces circumferential wall tension in BAPN-treated mice. CWT in the ascending aorta and descending thoracic aorta was significantly reduced in BAPN-treated mice that underwent forced treadmill exercise. CWT was calculated from measured mean arterial pressures and lumen diameters on micro-CT. *P < 0.05 by two-way ANOVA with Tukey’s multiple comparisons test. n = 4 CONV, 4 EX, 4 BAPN-CONV, 5 BAPN-EX. BAPN, β-aminopropionitrile; BAPN-CONV, conventional cage activity; BAPN-EX, forced treadmill exercise; CWT, circumferential wall tension; micro-CT, microcomputed tomography.

Figure 9.

Differential gene expression in the aorta after BAPN treatment with and without exercise. Expression level (2^−ΔCT) of selected genes involved in TGFβ pathway (top row), inflammation (middle row), and vascular injury and response (bottom row) related genes in CONV, BAPN-CONV, and BAPN-EX in 10–11-wk-old mice quantified by qRT-PCR. Gene expression is analyzed with one-way ANOVA with post hoc Tukey’s tests for multiple comparisons and is normalized to GAPDH. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001. n = 4 biological replicates per group. Extreme outliers, missing data, and unamplified transcripts are excluded. BAPN, β-aminopropionitrile; BAPN-CONV, conventional cage activity; BAPN-EX, forced treadmill exercise.