Degenerative mitral regurgitation (MR) due to myxomatous valve disease affects millions. The only treatment is either valve repair or replacement. This competing renewal will advance understanding of the role of the neurotransmitter, serotonin (5HT) in MR. Heart valve disease has been associated with both 5HT-secreting carcinoid tumors and medications, such as the diet drug, Dexfenfluoramine. Based on our progress in the 1ST program period, we will investigate the hypothesis that 5HT-mechanisms involving the serotonin transporter (SERT), and 5HT receptor (HTR) signaling, both in platelets and mitral valve interstitial cells (MVIC) of bone marrow origin, contribute to the pathophysiology MR, and represent promising therapeutic targets.
Specific Aim 1 : To dissect 5HT-mediated mechanisms that influence pathologic remodeling of MV leaflets in human subjects and mice Subaim 1A: To characterize 5HT-mediated MV remodeling in MR compared to normal mitral valve (MV) leaflets and human-derived MVICs. SERT-antagonists, and HTR inhibitor studies will dissect unique 5HT related transcriptome and cellular phenotypes associated with MR progression in vitro and ex vivo under TGFb, BMP4, and 5HT stimulation. Endpoints will be transcriptomic, extracellular matrix (ECM) remodeling in human MVIC and tissue from MR compared to normal leaflets exposed to 5HT-related mechanistic interrogation.
Sub aim 1 B: To investigate the role of SERT in the pathogenesis of MR: The SERT deleted mouse (SERT-/-) spontaneously develops a valvulopathy affecting the mitral and aortic valves. Mechanistic studies will compare SERT-/- to SERT+/+ . Endpoints will include valve thickness, myocardial fibrosis, and changes in the MV transcriptome, to understand disease progression in this SERT-related valvulopathy.
Specific Aim 2 : To investigate the role of 5HT in the pathogenesis of MR involving platelet mechanisms and bone marrow derived blood outgrowth endothelial cells (BOEC) that express both CD34 and HTR2B.
Sub aim 2 A: It is noteworthy that MR results in a chronic state of platelet activation, since platelets are the primary carriers of 5HT in blood, releasing 5HT upon activation. We will study the role of platelets in 5HT related MR pathophysiology in human subjects, canines with MR, and mice. Endpoints will include 5HT levels, platelet activation markers, and differences in TGF-b1 levels resulting from platelet alpha granule release.
Sub aim 2 B: To investigate the role of bone marrow derived cells in the pathophysiology of 5HT mechanisms that affect MR. BOEC will be cultivated from the study groups in Subaim 2A. The experimental designs will use flow cytometry for cell characterization, qRT-PCR studies to assess gene expression patterns, and proteomic approaches to assess HTR activity, and measurements of ECM production in vitro. It is expected that the mechanistic results of these studies will lead to therapeutic directions for MR that target platelet derived 5HT and leverage a personalized approach using BOEC to model the pathophysiology.

Public Health Relevance

This proposal will advance our studies of the previous HL131872 program period by examining the role of serotonin receptor signaling and downstream events in the pathogenesis of degenerative mitral regurgitation. The proposed experiments will investigate serotonin related platelet activity in human and canine blood, and relate this mitral valve disease. The program will also study serotonin mechanisms in human mitral valve specimens collected under approved protocols.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Cardiac Contractility, Hypertrophy, and Failure Study Section (CCHF)
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Evans, Frank
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Children's Hospital of Philadelphia
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