Compensatory aortic remodeling in Marfan syndrome protects against sexually dimorphic rupture during a BAPN challenge

Abstract

Transmural rupture of the aorta is responsible for significant morbidity and mortality; it occurs when wall stress exceeds local wall strength. Amongst other conditions, the aortic root and ascending aorta become vulnerable to dissection and rupture in Marfan syndrome, a connective tissue disorder that results in a progressive fragmentation and degradation of the elastic fibers of the aortic wall. Whereas competent elastic fibers are critical for aortic functionality, cross-linked collagen fibers endow the aorta with its stiffness and strength. In this paper, we contrast progressive degeneration of the ascending aorta in male and female Marfan and wild-type mice, with and without chronic exposure to a potent inhibitor of lysyl oxidase (β-aminopropionitrile, or BAPN), to examine effects of extracellular matrix cross-linking in aortic dilatation and rupture. We found a strong sexual dimorphism in aortic dilatation in Marfan mice and aortic rupture in wild-type mice, but also a compensatory remodeling of the aorta that protected the Marfan aorta against lethal rupture despite a strong BAPN challenge. This compensation appears to be mediated via increased lysyl oxidase in the female and especially male Marfan aorta, resulting in improved collagen fiber stability and integrity, particularly of fibril bundles in the adventitia.

A fast, robust method for quantitative assessment of collagen fibril architecture from transmission electron micrographs

“…Most notably, that aspect ratio distributions were similar across the three specimens (Figure 8b) despite remarkable qualitative differences in fibril crosssectional shape (Figure 7) suggests that there is a need to explore alternative shape comparison metrics, including various measures of deviation between the actual fibril boundary shape and the ellipse approximation [32]. Moreover, while outside the scope of this initial proof-of-concept study, it remains important to apply and assess the pipeline presented herein to substantially larger image sets, which in practice are acquired within application studies focused on specific pathologies [23]. Future evaluation should also be performed with non-vascular samples to examine the broader applicability of this pipeline, and to modify it as needed for different tissues.…”

“…[13] for details), and one Fbn1 C1041G/+ ATA representative of Marfan syndrome (denoted as MFS; see Weiss et al . [23] for details). Specimen excision and preparation as well as image acquisition methods have been described previously [13, 23].…”

“…[23] for details). Specimen excision and preparation as well as image acquisition methods have been described previously [13, 23]. Briefly, segments were fixed in 2.5% glutaraldehyde/2% paraformaldehyde in sodium cacodylate buffer at room temperature for 2 h at 4°C.…”

“…We applied our approach to three thoracic aorta specimens excised from adult (8-14 weeks of age) male mice having a C57BL/6 genetic background to demonstrate and validate our TEM image segmentation and analysis pipeline in the specific context of vascular applications. To test our methodology against substantially different collagen fibril architectures, we show results for one wild-type control ascending thoracic aorta (ATA), one descending thoracic aorta (DTA) with disrupted TGF-β signaling (denoted as Tgfbr1r2 ; see Kawamura et al [13] for details), and one Fbn1 C1041G/+ ATA representative of Marfan syndrome (denoted as MFS; see Weiss et al [23] for details). Specimen excision and preparation as well as image acquisition methods have been described previously [13,23].…”

“…To test our methodology against substantially different collagen fibril architectures, we show results for one wild-type control ascending thoracic aorta (ATA), one descending thoracic aorta (DTA) with disrupted TGF-β signaling (denoted as Tgfbr1r2 ; see Kawamura et al [13] for details), and one Fbn1 C1041G/+ ATA representative of Marfan syndrome (denoted as MFS; see Weiss et al [23] for details). Specimen excision and preparation as well as image acquisition methods have been described previously [13,23]. Briefly, segments were fixed in 2.5% glutaraldehyde/2% paraformaldehyde in sodium cacodylate buffer at room temperature for 2 h at 4 • C. Samples were rinsed in sodium cadodylate buffer before post-fixation in 1% osmium tetraoxide for 1 h and subsequent staining using 2% uranyl acetate for 1 h. Afterward, samples were washed and embedded in resin and sections of the adventitial layer were imaged using a FEI Tecnai BioTwin transmission electron microscope.…”