Beyond pressure overload: reframing right ventricular failure in pulmonary arterial hypertension

Why right ventricular decompensation remains a major unmet need

Right ventricular (RV) failure remains a major determinant of outcome in pulmonary arterial hypertension (PAH)^[1,2]. However, the transition from compensated hypertrophy to decompensated RV remodeling remains unclear. Rather than presenting RV failure solely as an inevitable consequence of progressive cardiomyocyte collapse, Zhang et al. provide a paradigm-shifting perspective by drawing attention beyond cardiomyocytes to the cardiac fibroblast-to-myofibroblast transition as a potential driver of RV failure. The authors proposed that downregulation of uncoupling protein 2 (UCP2) is a central regulator of this process and suggest that genetic variation may contribute to individual susceptibility to RV failure^[3].

A shift from cardiomyocyte-centered thinking to myofibroblast biology

Zhang et al. combined two experimental models with three human cohorts comprising 81 patients^[3]. In the monocrotaline model, decompensated RVs showed a marked increase in cardiac myofibroblasts, whereas pulmonary artery banding did not reproduce the same pattern. Unlike pulmonary artery banding, which induces isolated right ventricular pressure overload, the monocrotaline model reproduces the inflammatory and profibrotic milieu of PAH, likely explaining the greater myofibroblast expansion beyond pressure overload alone^[4-7]. The authors found decreased RV contractility in isolated decompensated RV hearts, but isolated cardiomyocyte contractility remained unchanged, suggesting a non-cardiomyocyte mechanism of failure.

The study, therefore, places cardiac fibroblasts and myofibroblasts closer to the center of RV pathobiology. Cardiac fibroblasts are not merely unidimensional matrix-producing cells. Following injury or chronic stress, they can acquire a myofibroblast phenotype characterized by enhanced contractility, extracellular matrix production, and paracrine signaling^[8,9]. Beyond extracellular matrix deposition, activated myofibroblasts amplify adverse remodeling through profibrotic paracrine signaling, including transforming growth factor-β and connective tissue growth factor, thereby perpetuating fibrosis and increasing myocardial stiffness. In addition, bidirectional cardiomyocyte-fibroblast crosstalk may further contribute to progressive right ventricular remodeling and dysfunction^[3,6,7]. These processes may initially support structural integrity, but persistent activation and expansion can lead to stiffness, impaired relaxation, disrupted mechano-electric coupling, and increased risk of arrhythmia^[9]. This interpretation should remain balanced. The data establish a strong mechanistic association across animal models, cellular experiments, and human cohorts, but do not definitively establish causality.

UCP2 and tumor necrosis factor-alpha as signals of early vulnerability

A particularly interesting aspect of the study is the proposed association between inflammation, mitochondrial calcium, pyruvate dehydrogenase (PDH) activity, and myofibroblast activation. Dromparis et al. previously implicated UCP2 in mitochondrial calcium regulation and pulmonary vascular remodeling. UCP2 deficiency can reduce mitochondrial calcium uptake, suppress mitochondrial metabolism, and create a pseudohypoxic phenotype in pulmonary artery smooth muscle cells in UCP2 knockout mice^[10]. Zhang et al. observed a progressive decline in UCP2 expression and mitochondrial calcium from control to compensated and then decompensated RV fibroblasts, while tumor necrosis factor-alpha (TNF-α) reduced UCP2 expression in RV fibroblasts but not in cardiomyocytes^[3]. Although the precise basis for this cell-type specificity remains unknown, it may reflect intrinsic differences in inflammatory responsiveness and metabolic adaptability between cardiac fibroblasts and cardiomyocytes. In the injured heart, cardiomyocytes primarily function as stress sensors that release danger-associated signals, whereas fibroblasts exhibit marked immunometabolic plasticity, rapidly adopting inflammatory and profibrotic phenotypes through metabolic reprogramming and myofibroblast differentiation^[11,12].

These findings connect two clinically relevant aspects of PAH. First, elevated inflammatory cytokines have been associated with poor prognosis in PAH and may serve as useful prognostic biomarkers^[13]. Second, the germline UCP2 single-nucleotide polymorphism rs659366 may identify patients with an intrinsic susceptibility to earlier RV decompensation. In the human cohorts, lower UCP2 levels and rs659366 were associated with worse tricuspid annular plane systolic excursion and cardiac index, even among patients with similar mean pulmonary arterial pressure^[3]. The observation is consistent with a previous report showing that genetic variation affecting mitochondrial biology, especially sirtuin 3 (SIRT3) and UCP2, may influence therapeutic response in PAH by contributing to resistance to pyruvate dehydrogenase kinase inhibition therapy^[14].

Clinical implications

The clinical implication is not that rs659366 or TNF-α should be incorporated into routine biomarker testing. Instead, the study proposes a framework to improve RV-centered phenotyping. Patients with similar pulmonary hemodynamics may have substantially different RV reserve because their ventricles differ at the stromal, inflammatory, and metabolic levels. Incorporating genetic predisposition, inflammatory signaling, and conventional RV measures could facilitate the identification of patients who require intensive surveillance or timely treatment escalation.

From a therapeutic perspective, current PAH therapies predominantly target the pulmonary circulation, while effective RV-specific therapies remain limited^[15]. The present findings suggest targeting maladaptive fibroblast activation, restoring UCP2-related mitochondrial signaling, or interrupting the inflammatory pathway. However, fibroblasts are not simply harmful cells. They play a critical role in repair and structural integrity, meaning that complete suppression of fibroblast activity may impair adaptive repair. The therapeutic goal should be selective interruption of persistent maladaptive activation while preserving the reparative functions of cardiac fibroblasts.

Several limitations should also be acknowledged. The human cohorts included a relatively modest number of patients, predominantly from a single ethnic background, which may limit the generalizability of the genetic findings. Furthermore, although the monocrotaline model reproduces many pathological features of pulmonary arterial hypertension, species-specific differences and model-dependent biology warrant caution when translating these mechanistic observations directly to human disease. Validation in larger, ethnically diverse prospective cohorts will therefore be essential.