Targeting p16^INK4a 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^INK4a 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^INK4a-/- and p16^INK4aATTAC (apoptosis through targeted activation of caspase 8) transgenic mice to postnatal hyperoxia, followed by pneumonectomy of the p16^INK4a-/- mice. We measured p16^INK4a 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^INK4a concentrations increased in lung fibroblasts after hyperoxia-induced BPD in mice and persisted into adulthood. p16^INK4a deficiency did not protect against hyperoxic lesions in newborn pups but promoted restoration of the lung architecture by adulthood. Curative clearance of p16^INK4a-positive cells once hyperoxic lung lesions were established restored normal lungs by adulthood. p16^INK4a 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 PPARγ (peroxisome proliferator-activated receptor γ) agonist after hyperoxia also increased lipofibroblast and AT2 cell numbers and restored alveolar architecture in hyperoxia-exposed mice. After pneumonectomy, p16^INK4a deficiency again led to an increase in lipofibroblast and AT2 cell numbers in the contralateral lung. Finally, we observed p16^INK4a 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^INK4a and promoting lipofibroblast development to stimulate alveolar regeneration from childhood to adulthood.