Differences in extracellular matrix proteins between Friesian horses with aortic rupture, unaffected Friesians and Warmblood horses

BACKGROUND: Unlike in Warmblood horses, aortic rupture is quite common in Friesian horses, in which a hereditary trait is suspected. The aortic connective tissue in affected Friesians shows histological changes such as medial necrosis, elastic fibre fragmentation, mucoid material accumulation and fibrosis with aberrant collagen morphology. However, ultrastructural examination of the collagen fibres of the mid‐thoracic aorta has been inconclusive in further elucidating the pathogenesis of the disease. OBJECTIVES: To assess several extracellular matrix (ECM) components biochemically in order to explore a possible underlying breed‐related systemic ECM defect in Friesians with aortic rupture. STUDY DESIGN: Cadaver study. METHODS: Tissues from affected Friesians (n = 18), unaffected Friesians (n = 10) and Warmblood horses (n = 30) were compared. Samples were taken from the thoracic aorta at the level of the rupture site, from two locations caudal to the rupture and from the deep digital flexor tendon. Total collagen content, post‐translational modifications of collagen formation including lysine hydroxylation, and hydroxylysylpyridinoline (HP), lysylpyridinoline (LP) and pyrrole cross‐links were analysed. Additionally, elastin cross‐links, glycosaminoglycan content and matrix metalloproteinase (MMP) activity were assessed. RESULTS: Significantly increased MMP activity and increased LP and HP cross‐linking, lysine hydroxylation and elastin cross‐linking were found at the site of rupture in affected Friesians. These changes may reflect processes involved in healing and aneurysm formation. Unaffected Friesians had less lysine hydroxylation and pyrrole cross‐linking within the tendons compared with Warmblood horses. No differences in the matrix of the aorta were found between normal Warmbloods and Friesian horses. MAIN LIMITATIONS: Small sample size. CONCLUSIONS: The differences in collagen parameters in tendon tissue may reflect differences in connective tissue metabolism between Friesians and Warmblood horses.