Abstract 11048: Serotonin Transporter Deficiency Leads to a Specific Fibrotic Pattern in Valvular and Myocardial Tissue

Abstract

Introduction: Increased serotonin (5HT) levels can lead to heart valve disease. This mechanism is observed in patients with 5HT-secreting carcinoid tumors and after treatment with the diet drug Dexfenfluoramine, which acts as a 5HT receptor (HTR)-2B agonist and as an inhibitor of the 5HT transporter (SERT). SERT internalizes 5HT, limiting HTR signaling (Figure 1A). We showed that SERT reduction on human mitral valve (MV) contributes to the progression of MV regurgitation. We investigated the impact of SERT deficiency on cardiac substructures in a SERT-/- murine model. Methods: SERT-/- and wild type (WT) C57BL/6J mice (n≥8/group) were sacrificed at 16 weeks of age, after echocardiography (Fig. 1B). Cardiac substructures (left ventricle (LV) apex, MV leaflets, aortic valve (AV) leaflets and aortic-mitral (AM curtain) were isolated in three animals/group (Fig. 1E). Results: Ventricular dimensions were significantly larger in SERT-/- mice vs. WT at end-systole and end-diastole (Fig. 1C). Fractional shortening was significantly reduced in SERT-/- mice vs. WT. Pricosirius staining of collagen showed that SERT-/- mice had increased MV leaflet fibrosis, MV and AV sub-valvular fibrosis at leaflet attachment points (AM curtain, Fig. 1D), and epicardial fibrosis. PCR (Fig. 1F) showed significantly increased COL1A1 expression in the LV myocardium, MV, AV and AM curtain in SERT-/- mice vs. WT. Fibrosis marker alpha smooth muscle actin (αSMA) was significantly increased in the myocardium and AM curtain of SERT-/- mice, but not in the valve leaflets. HTR2B expression was significantly increased in the MV and AM curtain of SERT-/- mice. Conclusions: SERT-/- mice have decreased cardiac function, and cardiac fibrosis that is associated with HTR2B upregulation in the MV leaflets and valve leaflet attachment points. Our results support the hypothesis that decreased 5HT clearance by SERT downregulation may increase HTR2B signaling in the MV leading to remodeling and regurgitation.