Studying the Effect of TBX4 Loss-of-Function on Postnatal Lung Development and How it Predisposes to Pulmonary Hypertension

The term pulmonary hypertension (PH) describes a heterogeneous group of pulmonary and cardiovascular disorders and is estimated to affect 1% of the global population. The World Symposium on Pulmonary Hypertension divides patients into a five-tier classification system based on etiology and clinical findings with the aim of improving the clinical approach to patients. Group 1 PH, also known as pulmonary arterial hypertension, is a rare form of the disease with a prevalence of 15-50 cases per one million individuals. Deleterious variants within the bone morphogenetic protein receptor type 2 (BMPR2) gene are found in approximately 70-80% of the cases. However, at least twelve additional genes are known to have a definitive gene-disease relationship with PAH, including T-box 4 (TBX4). Genetic predisposition may also contribute to group 3 PH, also known as PH due to chronic lung disease or hypoxia. Heterozygous pathogenic variants within TBX4 have been reported in cases from both PH groups. Therefore, the diagnosis and classification of PH in patients with TBX4 mutations may be more challenging due to its contributions to the pathogenesis of both groups. For a decade, deleterious variants or large mutations involving TBX4 have been reported throughout the literature, but more progress has yet to be made toward understanding the mechanisms underlying the pathogenesis of PH in those patients. Therefore, in this project, using mouse genetics, we sought to disrupt Tbx4 expression and investigate if there is consistency with the diseases observed in humans. We found that Tbx4 mutant lungs have increasing alveolar simplification as confirmed by mean linear intercept (MLI) at P14 (25%), P36 (31.7%), and P180 (49.5%). The lungs also have reduced vascularization as indicated by a 39.4% reduction in the number of vWF-positive vessels. Consistent with PH, mutant mice have higher RVSP (19.4%), vascular remodeling, and mild right ventricular hypertrophy (RVH). RNA sequence analyses revealed enrichment of pathways (canonical WNT, VEGF, and BMP signaling) and genes (Lgr5, Tnc, Wnt3a, Areg, Gdf2, and Bmper) relevant to lung alveologenesis, angiogenesis, and PH. This study contributes significant knowledge that clinicians can use to diagnose, classify, and treat patients with TBX4 mutations.