Tenascin C promotes valvular remodeling in two large animal models of ischemic mitral regurgitation.

Ischemic mitral regurgitation (MR) is a frequent complication of myocardial infarction (MI) characterized by adverse remodeling both at the myocardial and valvular levels. Persistent activation of valvular endothelial cells leads to leaflet fibrosis through endothelial-to-mesenchymal transition (EMT). Tenascin C (TNC), an extracellular matrix glycoprotein involved in cardiovascular remodeling and fibrosis, was also identified in inducing epithelial-to-mesenchymal transition. In this study, we hypothesized that TNC also plays a role in the valvular remodeling observed in ischemic MR by contributing to valvular excess EMT. Moderate ischemic MR was induced by creating a posterior papillary muscle infarct (7 pigs and 7 sheep). Additional animals (7 pigs and 4 sheep) served as controls. Pigs and sheep were sacrificed after 6 weeks and 6 months, respectively. TNC expression was upregulated in the pig and sheep experiments at 6 weeks and 6 months, respectively, and correlated well with leaflet thickness (R = 0.68; p < 0.001 at 6 weeks, R = 0.84; p < 0.001 at 6 months). To confirm the translational potential of our findings, we obtained mitral valves from patients with ischemic cardiomyopathy presenting MR (n = 5). Indeed, TNC was also expressed in the mitral leaflets of these. Furthermore, TNC induced EMT in isolated porcine mitral valve endothelial cells (MVEC). Interestingly, Toll-like receptor 4 (TLR4) inhibition prevented TNC-mediated EMT in MVEC. We identified here for the first time a new contributor to valvular remodeling in ischemic MR, namely TNC, which induced EMT through TLR4. Our findings might set the path for novel therapeutic targets for preventing or limiting ischemic MR.

Differential gene expression of leaflet tissue in chronic ovine functional tricuspid regurgitation.

OBJECTIVES: Severe functional tricuspid regurgitation (FTR) is associated with subvalvular remodelling, but leaflet tissue alterations may also contribute. We set out to investigate molecular mechanisms driving leaflet remodelling in chronic ovine FTR. METHODS: Thirteen adult sheep (55 ± 4kg) underwent left thoracotomy, epicardial echocardiography, and pulmonary artery banding (PAB) to induce right heart failure and FTR. After 16 weeks, 13 banded (FTR) and 12 control (CTL) animals underwent median sternotomy for epicardial echocardiography and were subsequently sacrificed with each tricuspid leaflet tissue harvested for RNA-seq and histology. RESULTS: After 16 weeks, 7 animals developed severe, 2 moderate, and 4 mild tricuspid regurgitation (TR). Relative to CTL, FTR animals had increased PAP, TR, tricuspid annular diameter, and right atrial volume, while tricuspid annular plane systolic excursion (TAPSE) and RV fractional area change decreased. FTR leaflets exhibited altered constituents and an increase in cellularity. RNA-seq identified 85 significantly differentially expressed genes (DEG) with 17, 53, and 127 within the anterior, posterior, and septal leaflets respectively. RRM2, PRG4, and CXCL8 (IL-8) were identified as DEGs across all leaflets and CXCL8 was differentially expressed between FTR severity grades. RRM2, PRG4, and CXCL8 significantly correlated with TAPSE, and this correlation was consistent regardless of the anatomical location of the leaflet. CONCLUSIONS: PAB in our ovine model resulted in RV failure and FTR. Leaflet RNA-seq identified several DEGs, specifically RRM2, PRG4, and CXCL8, with known roles in tissue remodelling. These data along with an overall increase in leaflet cellularity suggest tricuspid leaflets actively remodel in FTR.

Biomechanical engineering comparison of four leaflet repair techniques for mitral regurgitation using a novel 3-dimensional-printed left heart simulator.

OBJECTIVE: Mitral valve repair is the gold standard treatment for degenerative mitral regurgitation; however, a multitude of repair techniques exist with little quantitative data comparing these approaches. Using a novel ex vivo model, we sought to evaluate biomechanical differences between repair techniques. METHODS: Using porcine mitral valves mounted within a custom 3-dimensional-printed left heart simulator, we induced mitral regurgitation using an isolated P2 prolapse model by cutting primary chordae. Next, we repaired the valves in series using the edge-to-edge technique, neochordoplasty, nonresectional remodeling, and classic leaflet resection. Hemodynamic data and chordae forces were measured and analyzed using an incomplete counterbalanced repeated measures design with the healthy pre-prolapse valve as a control. RESULTS: With the exception of the edge-to-edge technique, all repair methods effectively corrected mitral regurgitation, returning regurgitant fraction to baseline levels (baseline 11.9% ± 3.7%, edge-to-edge 22.5% ± 6.9%, nonresectional remodeling 12.3% ± 3.0%, neochordal 13.4% ± 4.8%, resection 14.7% ± 5.5%, P < 0.01). Forces on the primary chordae were minimized using the neochordal and nonresectional techniques whereas the edge-to-edge and resectional techniques resulted in significantly elevated primary forces. Secondary chordae forces also followed this pattern, with edge-to-edge repair generating significantly higher secondary forces and leaflet resection trending higher than the nonresectional and neochord repairs. CONCLUSIONS: Although multiple methods of degenerative mitral valve repair are used clinically, their biomechanical properties vary significantly. Nonresectional techniques, including leaflet remodeling and neochordal techniques, appear to result in lower chordal forces in this ex vivo technical engineering model.