The Expression of Proteins Related to Serotonin Pathway in Pulmonary Arteries of Dogs Affected With Pulmonary Hypertension Secondary to Degenerative Mitral Valve Disease

Abstract

Background: Pulmonary hypertension (PH) can cause medial thickening, a hallmark of pulmonary arterial remodeling. The serotonin (5HT) pathway has been suggested as a factor associated with PH by inducing pulmonary arterial smooth muscle cells (SMCs) proliferation, a major cause of medial thickening. This study aims to demonstrate the expression of molecules in the 5HT pathway in the pulmonary artery of dogs affected with PH secondary to degenerative mitral valve disease (DMVD) compared to DMVD and healthy control dogs.Materials and Methods: The study included lung samples from the carcasses of 19 older small-breed dogs (Control n = 5, DMVD n = 7, DMVD+PH n = 7). Lung tissue sections were performed Hematoxylin and Eosin staining for measuring the percentage of medial thickness and immunohistochemistry for evaluating the expression of proteins in the 5HT pathway including serotonin transporter (SERT), serotonin 2A receptor (5HT2A), tryptophan hydroxylase 1 (TPH1), extracellular regulated kinase 1/2 (ERK1/2), and phosphorylated ERK1/2 (pERK1/2).Results: Medial thickening of the pulmonary arteries was found in the DMVD and DMVD+PH groups compared to the control. The medial thickening of the DMVD+PH group was increased significantly compared to that in the DMVD group. Intracytoplasmic expression of proteins related to the 5HT pathway was mainly presented in the medial layer of the pulmonary arteries. The control group showed a low expression of proteins related to the 5HT pathway. An intensive expression of SERT, 5HT2A, TPH1, and ERK1/2 protein was seen in the DMVD and DMVD+PH groups. Interestingly, pERK1/2 was strongly represented only in the DMVD+PH group.Conclusions: Overexpression of proteins related to the 5HT pathway including SERT, 5HT2A, TPH1, ERK1/2, and pERK1/2 was associated with medial remodeling in dogs affected with secondary to DMVD.

Investigation of Genes and Proteins Expression Associating Serotonin Signaling Pathway in Lung and Pulmonary Artery Tissues of Dogs with Pulmonary Hypertension Secondary to Degenerative Mitral Valve Disease: The Preliminary Study

“…The studies in laboratory animals have shown that 5-HT stimulated vasoconstriction and remodeling by causing contraction, proliferation and differentiation of PASMC [ 27 , 28 , 29 ]. The medial thickening associated with the expression of proteins related to the 5-HT signaling of PA was highlighted in a previous immunohistochemical study of PA in dogs with DMVD and dogs with PH due to DMVD [ 33 ]. Similarly, the present study found that the relative expression of some proteins, TPH-1 and 5-HTR2A, tended to be upregulated in the PA tissues of dogs in the DMVD and DMVD with PH groups, although this did not reach statistical significance.…”

“…The 5-HT is transported via the PAECs and PASMCs through the mediation of SERT [ 18 , 54 ]. In a previous immunohistochemical study of dogs with PH due to DMVD, SERT was expressed mainly in PASMCs, and upregulation of SERT was detected in dogs affected with DMVD with and without PH compared with normal dogs [ 33 ]. In lung tissue, the immunohistochemical study showed that SERT was expressed by pneumocytes and PAMs, similar to an investigation in rat models [ 49 , 55 , 56 ].…”

“…Previous investigations have demonstrated that an upregulation in ERK1/2 and pERK1/2 protein expression reflects 5-HT that influence the enhanced proliferation and decreased apoptosis of PASMCs via SERT and 5-HTR2A [ 27 , 28 , 29 , 70 ]. A previous immunohistochemical study in canine PA showed increased ERK1/2 and pERK1/2 expression in DMVD dogs, but only pERK1/2 increased in dogs with PH due to DMVD, suggesting that the 5-HT-ERK1/2 signaling pathway appears to be stimulated in dogs affected with DMVD and PH and is related to PA remodeling [ 33 ]. In the present study, the expression of ERK1/2 and pERK1/2 in lung tissues, as determined by immunohistochemistry, was upregulated in the pneumocytes of DMVD dogs with and without PH compared with controls, but only ERK1/2 reached a significant level.…”

“…In humans and animal models, there is evidence for the linking of 5-HT signaling to the development of PH secondary to several causes [ 31 , 32 ]. In addition, the expression of proteins related to 5-HT signaling in the pulmonary artery (PA) of PH dogs due to DMVD has been reported [ 33 ]. However, the expression of genes and proteins related to 5-HT signaling in the lung tissue of PH dogs due to DMVD has not been studied.…”

Assessment of Platelet and Plasma Serotonin in Canine Pulmonary Hypertension Secondary to Degenerative Mitral Valve Disease

“…It is then transferred to pulmonary artery smooth muscle cells via SERT and serotonin receptors to mediate the downstream effectors in the serotonin signaling pathway, causing contraction, proliferation and differentiation of pulmonary arterial walls (17)(18)(19)(20). Pulmonary arterial wall thickening has been found with overexpression of proteins related to the serotonin signaling pathway, including TPH-1, SERT, serotonin receptor 2A, extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylated ERK1/2 (pERK1/2) in dogs with PH secondary to DMVD (21). However, the association of circulating serotonin and PH secondary to DMVD in dogs has not been studied.…”