Aged hamsters suffered from persistent sub-pleural and interstitial pulmonary fibrosis, as well as alveolar bronchiolization, until 112 dpi after a mild physical exercise. A decrease of CK8+ alveolar differentiation intermediate cells and a dominated CK14+ airway basal cells population is correlated with bronchiolization. The gene discussed is KRT14; the disease is pulmonary fibrosis.