Telomeric DNA damage landscapes distinguish oxidative from inflammatory cellular stress.

Telomere dysfunction and attrition are observed in cells subjected to oxidative or inflammatory stress, largely due to DNA damage. In this study, we applied a DNA glycosylase-assisted quantitative PCR (qPCR) assay to assess telomeric DNA damage in human cells exposed to defined sources of oxidative or inflammatory stress. As a consequence of the endogenous chemistry of these stressors being different, we were able to identify distinct types of telomere DNA damage that differentiate oxidative from inflammatory stress. By selecting lesion-specific DNA glycosylases before qPCR analysis, we determined that reactive oxygen species generated under physiological bicarbonate buffering during both oxidative and inflammatory stress primarily damaged 2'-deoxyguanosine (dG) residues. In contrast, inflammatory stress increased dG oxidation sites and nitrosative DNA damage, evidenced by deamination of 2'-deoxycytosine (dC) to 2'-deoxyuridine (dU) and 2'-deoxyadenosine (dA) to 2'-deoxyinosine (dI; hypoxanthine). During inflammation, telomeric DNA contained 1.5-fold more dU than dI. These nitrosative lesions require different DNA repair enzymes compared with dG oxidation products, and they may impact telomere structure differently. Our findings suggest that beyond dG oxidation, nitrosative DNA damage can be a major source of lesions in telomeres. The profile of telomere DNA lesions can serve as a biomarker to distinguish between oxidative and inflammatory stress.