The Cyclooxygenase-2-Prostaglandin E2 Pathway Maintains Senescence of Chronic Obstructive Pulmonary Disease Fibroblasts

Rationale: Chronic obstructive pulmonary disease (COPD) is associated with lung fibroblast senescence, a process characterized by the irreversible loss of replicative capacity associated with the secretion of inflammatory mediators. However, the mechanisms of this phenomenon remain poorly defined. Objectives: The aim of this study was to analyze the role of prostaglandin E-2 (PGE(2)), a prostaglandin known to be increased in COPD lung fibroblasts, in inducing senescence and related inflammation in vitro in lung fibroblasts and in vivo in mice. Methods: Fibroblasts were isolated from patients with COPD and from smoker and nonsmoker control subjects. Senescence markers and inflammatory mediators were investigated in fibroblasts and in mice. Measurements and Main Results: Lung fibroblasts from patients with COPD exhibited higher expression of PGE(2) receptors EP2 and EP4 as compared with nonsmoker and smoker control subjects. Compared with both nonsmoker and smoker control subjects, during long-term culture, COPD fibroblasts displayed increased senescent markers (increased senescence associated-beta galactosidase activity, p16, and p53 expression and lower proliferative capacity), and an increased PGE(2), IL-6, IL-8, growth-regulated oncogene (GRO), CX3CL1, and matrix metalloproteinase-2 protein and cyclooxygenase-2 and mPGES-1 mRNA expression. Using in vitro pharmacologic approaches and in vivo experiments in wild-type and p53(-/-) mice we demonstrated that PGE(2) produced by senescent COPD fibroblasts is responsible for the increased senescence and related inflammation. PGE(2) acts either in a paracrine or autocrine fashion by a pathway involving EP2 and EP4 prostaglandin receptors, cyclooxygenase-2-dependent reactive oxygen species production and signaling, and consecutive p53 activation. Conclusions: PGE(2) is a critical component of an amplifying and self-perpetuating circle inducing senescence and inflammation in COPD fibroblasts. Modulating the described PGE(2) signaling pathway could provide a new basis to dampen senescence and senescence-associated inflammation in COPD.