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

Abstract

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^INK4a ATTAC transgenic mice to post-natal hyperoxia, followed by pneumonectomy of the p16^INK4a -/- mice. We measured p16^INK4a in blood mononuclear cells of preterm newborns and 7- to 15-year-old BPD survivors and the lungs of BPD patients. Measurements and main results. P16^INK4a levels increased in lung fibroblasts after hyperoxia-induced BPD in mice and persisted into adulthood. P16^INK4a deficiency did not protect against hyperoxia lesions in newborn pups but promoted restoration of the lung architecture by adulthood. Curative clearance of p16^INK4a-positive cells once hyperoxia lung lesions were established restored normal lungs by adulthood. p16^INK4a deficiency increased neutral lipid synthesis and promoted lipofibroblast and alveolar type 2 cell (AT2) development within the stem-cell niche. Besides, lipofibroblasts support self-renewal of AT2 cells into alveolospheres. Induction with a PPARγ agonist after hyperoxia also increased lipofibroblast and AT2 numbers and restored alveolar architecture in hyperoxia-exposed mice. After pneumonectomy, p16^INK4a-deficiency again led to an increase in lipofibroblast and AT2 numbers in the contralateral lung. Finally, we observed p16^INK4a mRNA over-expression in the blood and lungs of preterm newborns, which persisted in the blood of older BPD survivors. Conclusions. These data demonstrate the potential of targeting p16^INK4a and promoting lipofibroblast development to stimulate alveolar regeneration from childhood to adulthood.