Loss of <i>Tbx4</i> Affects Postnatal Lung Development and Predisposes to Pulmonary Hypertension

Pulmonary arterial hypertension is a progressive vascular disease characterized by remodeling of the precapillary pulmonary arteries. Genomic variation within the T-box 4 (TBX4) transcription factor is the second most common genetic cause of pulmonary arterial hypertension and can also cause severe lung developmental disorders with neonatal pulmonary hypertension (PH). Currently, the effect of TBX4 loss of function on later stages of lung development and predisposition to lung disease, including PH, is not well understood. Therefore, we generated <i>Tbx4</i> conditional knockout (<i>Tbx4-</i>CKO) mice in which <i>Cre</i> recombinase deletes exon 5 of <i>Tbx4</i> within the embryonic lung mesenchyme to create a null allele. We harvested lungs from these mice at various time points to examine alveologenesis, vascularization, vascular remodeling, lung cellular composition, and disruption of transcriptional activity compared with control lungs. Right ventricular systolic pressure was measured in 6-month-old mice to evaluate for PH. <i>Tbx4-</i>CKO lungs show enlargement of airspaces, as confirmed by an increase in mean linear intercept at Postnatal Day (P)14 (24.9%), P36 (31.5%), and P180 (49.6%). These lungs also show a 39.3% decrease in von Willebrand factor-positive vessels and a 14.2% increase in vessel wall thickness. Consistent with these results, <i>Tbx4-</i>CKO mice show a statistically significant increase of 15.7% in right ventricular systolic pressure and 16.3% in the Fulton index. Bulk RNA-sequencing analysis revealed enrichment of pathways and genes relevant to lung alveologenesis, angiogenesis, and PH. Our results show that disruption of <i>Tbx4</i> expression during early lung development is sufficient to disrupt postnatal lung development and circulation.