Douglas Quilty

BACKGROUND: Bronchopulmonary dysplasia (BPD) is a disease of neonatal lung development that is linked to impaired pulmonary vascularization, dysregulated TGF-β (transforming growth factor-β) signaling, and the accumulation of senescent cells. Despite the established role of TGF-β signaling in promoting vascular remodeling and suppressing the senolytic activity of natural killer (NK) cells, the contribution of NK cell TGF-β signaling to postnatal lung patterning and the pathogenesis of BPD remains unclear. METHODS: Mice bearing an NK cell-selective deletion of the type-II TGF-β receptor ( Tgfbr2 ^{NK− /−} ) were analyzed for vascular and alveolar structure, lung NK cell infiltration, senescence markers, and lung function testing across neonatal and adult time points. Lung tissue from both neonatal mice and human infants with BPD was assessed by single-cell RNA sequencing. The effects of enhanced NK cell activity in a hyperoxia-induced model of BPD were examined in Tgfbr2 ^NK−/− neonates, as well as pharmacologically, using the TGF-β ligand trap/IL-15 superagonist, HCW9218. RESULTS: Neonatal Tgfbr2 ^NK−/− mice exhibited a baseline reduction in distal arteriolar density, impaired alveolarization, and sex-specific deficits in long-term lung function. Single-cell RNA sequencing identified excessive clearance of senescent endothelial cells by TGF-β-insensitive NK cells in the lungs of Tgfbr2 ^NK−/− neonates. This enhanced NK cell activity promoted a BPD-like phenotype in naïve Tgfbr2 ^NK−/− mice but protected these animals from impaired lung development under hyperoxia. Sequencing of lung tissue from human infants with BPD confirmed excessive TGF-β signaling and cytotoxic impairment in NK cells. Treatment with HCW9218 prevented senescent cell accumulation and rescued lung development in the hyperoxia mouse model. CONCLUSIONS: TGF-β is a tunable regulator of NK cell senolytic activity that is essential for normal postnatal lung development. Excessive NK cell TGF-β signaling contributes to impaired lung development with neonatal hyperoxia and may serve as a viable therapeutic target in human BPD.

Background: Bronchopulmonary dysplasia (BPD) is a disease of neonatal lung development that is linked to impaired pulmonary vascularization, dysregulated transforming growth factor-β (TGF-β) signaling and the accumulation of senescent cells. Despite the established role for TGF-β signaling in promoting vascular remodeling and suppressing the senolytic activity of natural killer (NK) cells, the contribution of NK cell TGF-β signaling to postnatal lung patterning and the pathogenesis of BPD remains unclear. Methods: Mice bearing an NK cell-selective deletion of the type-II TGF-β receptor ( Tgfbr2 ^NK-/- ) were analyzed for vascular and alveolar structure, lung NK cell infiltration, senescence markers and lung function testing across neonatal and adult timepoints. Single-cell RNA sequencing of lung tissue from both neonatal mice and human infants with BPD was performed. The effect of enhanced NK cell activity in a hyperoxia-induced model of BPD was assessed in Tgfbr2 ^NK-/- neonates, as well as pharmacologically, using the TGF-β ligand trap/IL-15 superagonist, HCW9218. Results: Neonatal Tgfbr2 ^NK-/- mice exhibited a baseline reduction in distal arteriolar density, impaired alveolarization, and sex-specific deficits in long-term lung function. Single-cell RNA sequencing identified the excessive clearance of senescent endothelial cells by TGF-β insensitive NK cells in the lungs of Tgfbr2 ^NK-/- neonates, which served as a contributor of the BPD-like phenotype observed in naïve animals. Tgfbr2 ^NK-/- mice were protected from impaired lung development in the hyperoxia model. Sequencing from lung tissue from infants with BPD confirmed excessive TGF-β signaling and cytotoxic impairment in NK cells. Treatment with HCW9218 prevented senescent cell accumulation and rescued lung development in the hyperoxia mouse model. Conclusions: These findings identify TGF-β as a tunable regulator of NK cell senolytic activity that is essential to normal postnatal lung development. Excessive NK cell TGF-β signaling contributes to impaired lung development following exposure to neonatal hyperoxia and may serve as a viable therapeutic target for human BPD.

BACKGROUND: The BMPR2 gene encodes the BMPR-II (bone morphogenetic protein receptor type-II) and is a known regulator of endothelial proliferation, apoptosis, and translational stress responses. While these effects are generally attributed to the actions of BMPR-II protein, we used circular RNA profiling to identify circ3218 and circ5078 as new BMPR2 -derived functional RNAs. METHODS: Circular RNAs were profiled by ultradeep RNA sequencing of human pulmonary artery endothelial cells. Novel BMPR2 -derived circular RNAs were assessed for their effects on endothelial proliferation, apoptosis, and translational stress responses in human pulmonary artery endothelial cells and endothelial cells from patients with pulmonary arterial hypertension with heterozygous loss-of-function BMPR2 mutations. circ5078 to linear BMPR2 mRNA ratios were quantified in cultured lymphocytes from patients with pulmonary arterial hypertension with BMPR2 mutations versus unaffected mutation carriers. RESULTS: Depletion of circ3218 enhanced human pulmonary artery endothelial cell apoptosis, whereas circ5078 silencing increased proliferation. Enhanced proliferation with circ5078 depletion was eliminated by cosilencing of circ5078 with either linear BMPR2 mRNA or the stress granule protein, Caprin-1, indicating a potential interdependence of BMPR2 transcripts in the regulation of endothelial function. Patients with pulmonary arterial hypertension with BMPR2 mutations exhibited increased circ5078 to linear BMPR2 mRNA ratios, alongside impaired stress responses in patient endothelial cells that were deficient in linear BMPR2 transcripts but not circ5078 . circ5078 depletion enhanced stress responses in human pulmonary artery endothelial cells and rescued stress granule formation in patient endothelial cells, independent of BMPR-II protein levels. Assessment of translational regulation by polysome profiling did not identify any impact of linear or circular BMPR2 transcript loss on global protein synthesis or stress-induced eIF2α (eukaryotic initiation factor 2α) phosphorylation but did identify the enhanced translational efficiency of select nuclear-encoded mitochondrial ribosome proteins with circ5078 depletion, offering a link between mitochondrial function and the circ5078 -deficient endothelial phenotype. CONCLUSIONS: The identification of circ3218 and circ5078 as novel BMPR2 -derived gene products reveals interdependent roles for coding and noncoding BMPR2 transcripts as regulators of endothelial function.

Germline loss-of-function BMPR2 mutations are the leading genetic cause of pulmonary arterial hypertension (PAH) and are strongly linked to aberrant endothelial proliferation and impaired translational stress responses. While these effects are generally attributed to a loss of the type-II bone morphogenetic protein receptor (BMPR-II), we used circular RNA profiling to identify circ5078 as a new functional RNA derived from exon 12 of the BMPR2 gene. circ5078 and linear BMPR2 mRNA exert opposing effects on endothelial proliferation and stress granule formation, driving impaired stress responses in PAH patient-derived endothelial cells that are deficient in linear BMPR2 transcripts, but not circ5078 . Rebalancing circular to linear transcript abundance by circ5078 depletion rescued stress granule formation in patient-derived endothelial cells, independent of BMPR-II protein levels. Polysome analysis demonstrated a reduction in free ribosomal subunits with the depletion of either linear or circular BMPR2 transcripts, and an accumulation of 80S monosomes exclusively with linear BMPR2 mRNA loss. These effects did not impact global protein synthesis or stress-induced eIF2α phosphorylation, but did alter the translational efficiency of multiple genes, including a group of nuclear encoded, mitochondrial ribosome proteins that were translationally enhanced with circ5078 silencing. Endothelial circ5078 depletion increased the efficiency of oxidative metabolism while reducing mitochondrial spare capacity, providing a potential link between mitochondrial function, proliferation and translational stress responses. Together, these findings reveal interdependent roles for linear and circular BMPR2 transcripts as functional contributors to the endothelial phenotype of PAH.