A histopathological and immunohistochemical perspective on selected aspects of valvular interstitial and valve endothelial remodeling in canine mitral valve dysplasia and myxomatous degeneration

Introduction Endothelial-to-mesenchymal transformation is a complex process previously reported in canine myxomatous mitral valve disease (MMVD) but not in congenital mitral valve dysplasia (MD) in dogs. The aim of the current study was to evaluate the endothelial-to-mesenchymal transformation in canine MD as compared to valves affected with MMVD. Animals The study was conducted on histopathological specimens obtained from 19 dogs divided into three groups: MMVD group ( n =7), MD group ( n =6) and control group ( n =6). Materials and Methods The paraffin blocks were retrieved from the archives of the Unit of Veterinary Cardiopathology and underwent histological and immunohistochemical stainings. Hematoxylin-eosin and Movat’s stains served to evaluate the histopathological changes within the valves. Immunohistochemical analysis involved antibodies against: vimentin, alpha-smooth muscle actin, fibronectin, platelet endothelial cell adhesion molecule-1, and transgelin. Scoring of the immunoreaction was performed according to the intensity and extent of staining. Results Remodelling of both valvular interstitial and endothelial cells was noted with similar extent in both examined diseases, despite differences in animals’ age, body weight, heart weight and cause of mitral valve changes. Limitations Study limitations included: relatively small number of animals in each group, a difference in the animals’ age, heart weight, and body weight between the groups, lack of detailed echocardiographic measurements, and EndMT evaluated basing on a single time point. Conclusions Despite different pathogenesis and disease course, endothelial and interstitial changes occur in both MMVD and MD. Further studies are required to evaluate the exact relationship between changes occurring in valvular endothelial and interstitial cells.