Targeting canonical TGFβ/SMAD3 and ERK1/2 signaling in human valve interstitial cells to modulate immune-fibrotic responses in rheumatic heart disease.

Rheumatic heart disease (RHD) is a chronic sequel of acute rheumatic fever characterized by sustained inflammation, fibrosis, and valve degeneration; however, the underlying processes remain unclear. To identify dysregulated molecular pathways, we conducted LC-MS/MS-based proteomic profiling of RHD mitral valve tissue compared with ischemic controls and validated systemic inflammation in RHD patients through peripheral blood analysis. Proteomic analysis revealed upregulation of immune response proteins, TGFβ signaling, and extracellular matrix (ECM) regulators. Notably, proteins associated with innate immune activation and macrophage-related pro- and anti-inflammatory responses were found to be enriched. Peripheral blood analysis further confirmed elevated levels of IL6, TNFα, and TIMP1, indicating systemic inflammation. To investigate the underlying mechanisms, we isolated human valve interstitial cells (hVICs) and treated them with proinflammatory stimuli (TNFα, IFNγ) and profibrotic/ anti-inflammatory (TGFβ) stimulation. TGFβ induced morphological changes within 24 h, consistent with fibrotic transformation, and upregulated fibrotic markers (ACTA2, COL1A1, COL1A2, TIMP1, CTGF, MMP2, and TGFβ) along with increased collagen deposition. In contrast, TNFα and IFNγ suppressed fibrotic gene expression while upregulating TIMP1. Notably, TGFβ induced canonical Smad3 phosphorylation, whereas TNFα and IFNγ did not find, any change. Further, macrophage-hVIC interactions were evaluated using conditioned media from M1 [LPS (100 ng/ml) + TNFα (10 ng/ml)] and M2c [TGFβ (10 ng/ml)] polarized macrophages. M2c macrophage-conditioned media enhanced profibrotic gene expression, whereas M1-conditioned media suppressed it, highlighting the role of immune-fibrotic crosstalk in valvular fibrosis. Notably, the 5-HT₂B receptor antagonist SB204741 and tadalafil effectively inhibited TGFβ-induced Smad3 phosphorylation in hVICs, thereby reducing fibrotic signaling. In addition, tadalafil selectively suppressed ERK1/2-mediated non-canonical signaling, while no significant changes were observed in the STAT3, p38 MAPK and JNK pathways. Collectively, these findings identify immune-fibrotic crosstalk and selective activation of canonical TGFβ/Smad3 and ERK1/2-mediated non-canonical signaling pathways as important contributors to valvular fibrosis in rheumatic heart disease and suggest that targeting these pathways may provide potential therapeutic approaches to limit disease progression.