CCND1 and chronic obstructive pulmonary disease: Compared with COPD group, the expressions of cyclin D1 and TERT were significantly increased in COPD+EPCs and COPD+P5091 groups (p < 0.05), while the expression of p16 (INK4a) was markedly decreased (p < 0.001) (Figs. 3, 4, 5, 6E).