DNA damage and mismatch repair pathway in lung ischemia and reperfusion injury

Background: Oxidative damage induced by reperfusion is responsible for increased morbidity and mortality following lung transplantation. A stable and deleterious DNA adduct, 8-oxogaunine (8-oxoG) results due to oxidative DNA damage. Mut-Y homologue (MYH) is a DNA repair enzyme promoting DNA reconstruction through the mismatch repair pathway to repair 8-oxoG lesion. We investigated the role of DNA mismatch repair pathway mediated by MYH in the setting of lung ischemia and reperfusion. Methods: Left lungs of the adult Sprague Dawley rats were subjected to 1 h ischemia and 2 and 4 h reperfusion. Un-operated animals served as controls. Quantification of 8-oxoG was performed using immunohistochemistry (IHC) and MYH was analyzed by Western blot. Apoptosis was assessed by caspase-3 levels. Results: Indices of inflammation and permeability were raised in both reperfusion groups. There was significant increase in DNA damage as reflected by positive 8-oxoG staining in 2 h (22% increase) and 4 h reperfusion (31% increase) compared to control (p < 0.01). MYH staining by IHC was significantly reduced in 2 and 4 h reperfusion compared to controls (p < 0.05). Down regulation of DNA repair enzyme (MYH) was mirrored functionally by decreased protein levels in lung tissues subjected to reperfusion compared to controls. Increasing apoptosis was detected in the reperfusion groups as reflected by caspase-3 IHC and protein estimation by Western blot. Conclusion: Reperfusion leads to increased DNA damage and down regulation of DNA mismatch repair pathway in a model of ischemia and reperfusion in lungs. Gene therapy targeted at this pathway may prove an attractive therapeutic intervention to reduce reperfusion injury in lung transplantation.