2024 Theses Doctoral

Serotonin and Angiotensin II Mediated Signaling Pathways in Heart Valve Disease

Levine, Dov

Heart valve disease represents the second most common indication for cardiac surgery in the US, yet no therapy exists to slow down or revert its progression. Pharmacologic treatments are greatly in need for aortic and mitral valve disease and require a greater understanding of the underlying cellular mechanisms. Serotonin (5HT) dysfunction has been associated with heart valve disease, clinically observed in carcinoid syndrome or with the use of medications, such as the diet drug, Dexfenfluramine, a 5HT transporter (SERT) inhibitor and 5HT receptor (HTR) 2B agonist. Concurrently, Angiotensin II (AngII) and the renin-angiotensin system (RAS) greatly contribute to cardiac/valvular diseases.

This dissertation explores the intersecting mechanisms by which 5HT and AngII contribute to aortic and mitral valve disease with an attempt to develop therapies to mitigate their progression. Three murine models were extensively utilized, mice lacking SERT (SERT KO) and wild-type mice receiving AngII infusion or Fluoxetine, a SERT inhibitor, with/without 5HTR2B inhibitors, to characterize histopathological, hemodynamic, and cellular level changes. Valvular interstitial cells (VICs) isolated from murine and human healthy valves were treated with various stressors known to be involved in valvular remodeling/5HT signaling, including 5HT, TGFβ1, AngII, and H2O2. Patients undergoing AV and MV surgery were prospectively enrolled in our study, with their valves isolated, genotyped for SERT promotor polymorphism, and studied for 5HT-related gene expression changes.

We demonstrate that pathological, fibrotic thickening occurs to the AV and MV in response to AngII infusion, lack or inhibition of SERT in mice. AngII mice developed increased velocities and gradients across their AVs, a marker of hemodynamic compromised, and the cellular changes involved 5HT, TGFβ1 and other inflammatory pathways. Concurrent HTR2B blockade mitigated many of these changes. Most notably the MV in SERT KO mice demonstrated HTR2B upregulation and increasing levels of COL1A1. Both murine and human MVICs exposed to 5HT or TGFβ1 upregulated COL1A1, ACTA2 and/or HTR2B. Human AVICs treated with AngII in the setting of SERT downregulation displayed markers of osteogenic transdifferentiation, with these changes mitigated again by HTR2B blockade. Finally, patients with aortic stenosis and aortic insufficiency have lower levels of SERT than healthy patients, along with upregulation of various 5HT receptors. Presence of LL SERT promotor polymorphism is associated with faster progression of AI.

We then further investigated the mechanisms by which SERT downregulation may enhance mitral and aortic valvulopathy by studying the activation of mechanically sensitive calcium channel, Piezo1, and the role of mechano-transduction. ScRNAseq results of both MR and MV cells demonstrated the presence of Piezo1 expression in different cell types on the mitral valve. Mitral valve interstitial cells in culture demonstrated Piezo1 Ca++ channel activity following administration of Yoda1, a Piezo1 agonist, with associated significant downregulation of SERT and diminished SERT function and upregulation of HTR2B.

Taken together, this dissertation provides a novel and promising therapeutic target to mitigate aortic and mitral valve disease. Dysregulated AngII and 5HT, with SERT, HTR2B, and Piezo1 signaling, contribute to pathological remodeling to both valves, and preventing this signaling through Piezo1/HTR2B inhibition can prevent these changes.