Targeting p16INK4a Promotes Lipofibroblasts and Alveolar Regeneration after Early-Life Injury

Rationale: Promoting endogenous pulmonary regeneration is crucial after damage to restore normal lungs and prevent the onset of chronic adult lung diseases. Objectives: To investigate whether the cell-cycle inhibitor p16(I)(NK4a) limits lung regeneration after newborn bronchopulmonary dysplasia (BPD), a condition characterized by the arrest of alveolar development, leading to adult sequelae. Methods: We exposed p16(I)(NK4a)(-/-) and p16(I)(NK4a) ATTA C (apoptosis through targeted activation of caspase 8) transgenic mice to postnatal hyperoxia, followed by pneumonectomy of the p16(I)(NK4a)-/ - mice. We measured p16(I)(NK4a) in blood mononuclear cells of preterm newborns, 7- to 15-year-old survivors of BPD, and the lungs of patients with BPD. Measurements and Main Results: p16(I)(NK4a) concentrations increased in lung fibroblasts after hyperoxia-induced BPD in mice and persisted into adulthood. p16(I)(NK4a) deficiency did not protect against hyperoxic lesions in newborn pups but promoted restoration of the lung architecture by adulthood. Curative clearance of p16(I)(NK4a)-positive cells once hyperoxic lung lesions were established restored normal lungs by adulthood. p16(I)(NK4a) a deficiency increased neutral lipid synthesis and promoted lipofibroblast and alveolar type 2 (AT2) cell development within the stem-cell niche. Besides, lipofibroblasts support self-renewal of AT2 cells into alveolospheres. Induction with a PPAR gamma (peroxisome proliferator-activated receptor gamma) agonist after hyperoxia also increased lipofibroblast and AT2 cell numbers and restored alveolar architecture in hyperoxia-exposed mice. After pneumonectomy, p16(I)(NK4a) deficiency again led to an increase in lipofibroblast and AT2 cell numbers in the contralateral lung. Finally, we observed p16(I)(NK4a) mRNA overexpression in the blood and lungs of preterm newborns, which persisted in the blood of older survivors of BPD. Conclusions: These data demonstrate the potential of targeting p16(I)(NK4a) and promoting lipofibroblast development to stimulate alveolar regeneration from childhood to adulthood.