Expression of proteins mediating pulmonary hypertension in dogs affected with degenerative mitral valve disease

Pulmonary hypertension (PH) is defined by an abnormal elevation in pressure within pulmonary vasculature, often associated with degenerative mitral valve disease (DMVD) in dogs. While histopathological changes in the pulmonary arteries, known as pulmonary arterial remodeling, have been documented in human patients with PH, these alterations in DMVD dogs with PH have not been published. Proteomics, a potent method for exploring the entire protein complement of a biological sample, has emerged as a valuable tool for identifying PH-specific proteins, potentially serving as biomarkers for diagnosis and enhancing understanding of PH pathogenesis in DMVD dogs. This study aimed to evaluate the histopathological changes in the pulmonary arteries and conduct proteomic analysis to investigate alterations in protein expression in pulmonary arteries and serum samples of DMVD dogs with PH compared to DMVD and control dogs. Lung tissues were obtained from carcasses of 19 dogs, categorized into the control (n = 5), DMVD (n = 7) and DMVD+PH (n = 7) groups. Histological staining and immunohistochemistry were performed to examine pulmonary arterial remodeling and possible associated factors. Additionally, serum samples were collected from 81 client-owned dogs divided into the control (n = 28), DMVD (n = 24) and DMVD+PH (n = 29) groups. Pulmonary arteries were collected from the same samples used in the histopathological study, with an increased number to 22 dogs divided into the control (n = 7), DMVD (n = 7) and DMVD+PH (n=8) groups. Proteomic analysis, including LC-MS/MS, phosphoproteomics and MALDI-TOF MS was performed. The study revealed evidence of pulmonary arterial remodeling in DMVD dogs both with and without PH, suggesting associations with medial thickening secondary to pulmonary arterial smooth muscle cells (SMCs) hyperplasia and hypertrophy and collagen deposition. An increase in the medial thickness of the pulmonary artery in DMVD dogs with PH may be partly associated with a decrease in the pro-apoptotic activity of pulmonary arterial SMCs. Moreover, an accumulation of perivascular inflammatory cells was found in remodeled pulmonary arteries of DMVD dogs with and without PH, suggesting that infiltration of perivascular inflammatory cells, particularly B lymphocytes and mast cells, is related to medial thickening. Proteomic analysis identified differentially expressed proteins and phosphoproteins and cluster peptide mass patterns, in both serum and pulmonary arteries among the groups, particularly in the pulmonary arteries and serum samples of DMVD dogs with PH compared to other groups. This information is essential for elucidating pathogenesis of PH in DMVD dogs and identifying potential biomarkers and peptide mass fingerprint for future application in detecting PH in DMVD dogs. In conclusion, this study provides valuable insights into histopathological changes of pulmonary arteries in DMVD dogs with PH and suggests the potential utility of proteomic techniques for selecting proteins of interest for further investigation into the pathogenesis of PH in DMVD dogs and identifying potential biomarkers and peptide mass fingerprints for diagnosis and management of PH in the future.