Enhance Smooth Muscle Cells Apoptosis Associated With Pulmonary Arterial Remodeling in Dogs Affected With Pulmonary Hypertension Secondary to Degenerative Mitral Valve Disease

Background: Degenerative mitral valve disease (DMVD) is the most common cause of pulmonary hypertension (PH) in dogs. Medial thickening of the pulmonary artery is a major histopathological change in PH. A decrease in apoptosis of pulmonary arterial smooth muscle cells (SMCs) may be the cause of medial thickening. This study aimed to demonstrate the expression of apoptosis molecules in the pulmonary artery of dogs affected with PH secondary to DMVD (DMVD+PH) compared to DMVD without PH (DMVD) and healthy dogs (control). Lung samples were collected from three groups including control (n=5), DMVD (n=7) and DMVD+PH (n=7) groups. Masson trichrome and apoptotic proteins including Bax, Bcl2 and caspase-3 and -8, were stained. Results: The medial thickness in the DMVD and DMVD+PH groups was greater than in the control group and it was greatest in the DMVD+PH group. Bax, Bcl2 and caspase-3 and -8 were expressed mainly in the medial layer of the pulmonary artery. The percentages of Bax and caspase-3 and -8 positive cells were higher in the DMVD group compared to the DMVD+PH group, whereas the percentage of Bcl2-positive cells was increased in the DMVD and DMVD+PH groups. These findings suggested that apoptosis of pulmonary arterial SMCs occurred mainly in the DMVD group and decreased dramatically in the DMVD+PH group. Conclusions: An increase in the medial thickness in dogs affected with PH secondary to DMVD may occur due to a decrease in apoptosis of pulmonary arterial SMCs.