Adenosine concentrations are elevated in the lungs of patients with
asthma and
chronic obstructive pulmonary disease, where it balances between tissue repair and excessive
airway remodeling. We previously demonstrated that the activation of the
adenosine A2A receptor promotes epithelial
wound closure. However, the mechanism by which
adenosine-mediated wound healing occurs after cigarette
smoke exposure has not been investigated. The present study investigates whether cigarette
smoke exposure alters
adenosine-mediated reparative properties via its ability to induce a shift in the
oxidant/
antioxidant balance. Using an in vitro wounding model, bronchial epithelial cells were exposed to 5% cigarette
smoke extract, were wounded, and were then stimulated with either 10 μM
adenosine or the specific A2A receptor agonist, 5'-(N-cyclopropyl)-carboxamido-adenosine (
CPCA; 10 μM), and assessed for
wound closure. In a subset of experiments, bronchial epithelial cells were infected with adenovirus vectors encoding human
superoxide dismutase and/or
catalase or control vector. In the presence of 5%
smoke extract, significant delay was evident in both
adenosine-mediated and
CPCA-mediated
wound closure. However, cells pretreated with
N-acetylcysteine (NAC), a nonspecific
antioxidant, reversed
smoke extract-mediated inhibition. We found that cells overexpressing mitochondrial
catalase repealed the
smoke extract inhibition of
CPCA-stimulated
wound closure, whereas
superoxide dismutase overexpression exerted no effect.
Kinase experiments revealed that
smoke extract significantly reduced the A2A-mediated activation of cyclic
adenosine monophosphate-dependent
protein kinase. However, pretreatment with NAC reversed this effect. In conclusion, our data suggest that cigarette
smoke exposure impairs A2A-stimulated
wound repair via a
reactive oxygen species-dependent mechanism, thereby providing a better understanding of
adenosine signaling that may direct the development of pharmacological tools for the treatment of chronic inflammatory lung disorders.