Tbx4 mutation in pulmonary arterial hypertension and right heart failure: cardiac fibroblast heterogeneity and maladaptive remodeling

Abstract Background TBX4, a T-box transcription factor essential for mesodermal and cardiopulmonary development, is increasingly recognized as a genetic determinant of pulmonary arterial hypertension (PAH). Beyond its vascular role, the contribution of TBX4 mutations to cardiac remodeling, particularly right ventricular dysfunction and HFpEF-like phenotypes, remains poorly understood. Purpose This study aimed to discover how pathogenic TBX4 mutation alter cardiac fibroblast phenotype and function, contribute to maladaptive cardiac remodeling. Combining transcriptomic, epigenetic, and functional studies, we investigated a TBX4-dependent molecular pathway driving fibroblast activation, matrix remodeling, and fibrotic responsiveness that so far link right ventricular dysfunction and HFpEF-like pathophysiology. Methods To model and understand the cellular consequences of a pathogenic TBX4 mutation we generated cardiac fibroblasts from induced pluripotent stem cells (iPSCs) carrying the mutant or wild-type TBX4 allele. Following flow cytometry-based characterization; fibroblast activation, myofibroblast markers and response to fibrotic stimulus were analyzed by immunofluorescence microscopy and quantitative PCR. Functional assays, including proliferation, migration, and contractility, were performed. RNA sequencing (RNA-seq) and ATAC-seq were performed to compare transcriptional profiles and chromatin accessibility between wild-type and mutant fibroblasts. Results TBX4-mutant cardiac fibroblasts displayed a distinct transcriptional profile, including upregulation of the activated fibroblast markers, mainly ACTA2 (αSMA), COL1A1, PDGFRA and PDGFRB. These changes indicate an enhanced myofibroblast differentiation and fibrotic phenotype. Functionally, mutant fibroblasts were more responsive to cell culture stress and TGFβ. Moreover, they were less motile but more contractile, suggesting dysregulation in fibrotic and mechanotransduction pathways. Conclusion This study discovered a previously unrecognized role of TBX4 mutation in cardiac fibroblast function and mechanosensitive remodeling. Our findings showed that TBX4 mutation role in cardiac fibroblast identity alongside pulmonary vascular resistance, and may consequently be responsible for maladaptive cardiac remodeling in TBX4-associated cardiopulmonary disease. This novel mechanistic relationship between transcriptional action of TBX4 and fibroblast mediated cardiac pathology revealed potential implications for targeted therapeutic interventions.