Alpha-smooth muscle actin and serotonin receptors 2A and 2B in dogs with myxomatous mitral valve disease

Abstract Canine Myxomatous mitral valve disease (MMVD) is an age-related disease. Serotonin (5-HT) is implicated in the pathogenesis as locally-produced or platelet-derived. Involvement of the 5-HT 2A receptor (R) and 5-HT 2B R in the induction of myxomatous-mediating valvular myofibroblasts (MF) has been suggested. In an age-matched population of dogs with non-clinical and clinical MMVD, the objectives were to investigate (1) gene expression of 5-HT 2A R and 5-HT 2B R, (2) protein expression and spatial relationship of 5-HT 2A R, 5-HT 2B R and MF in the mitral valve (MV) and the cardiac anterior papillary muscle (AP) and (3) serum 5-HT concentrations. Gene expression of 5-HT 2B R was significantly higher in MV and AP among dogs with clinical MMVD. This was not found for 5-HT 2B R protein expression, though association of 5-HT 2B R with myxomatous pathology and co-localization of 5-HT 2B R and MF in MV and AP support a functional relationship, perhaps perpetuation of clinical MMVD. 5-HT 2A R-expression and serum 5-HT showed no differences between groups.