Telomerase overexpression in human mesenchymal stem cells offers protection against oxidative DNA damage accumulation

Abstract

Human mesenchymal stem cells (hMSCs) use in therapy often requires in vitro culture, during which the cells may reach a non differentiating replicative senescence. This condition has been linked to macromolecular damage and especially reactive oxygen species (ROS)-induced damage. The most frequently occurring oxidized DNA lesion is 8-oxoguanine (8-oxoG), the incorporation of which to the DNA can cause double strand breaks (DSB), characteristic features of cellular senescence. Recent studies, on the other hand, have demonstrated that telomerase has a telomere-length independent function that promotes cellular resistance against oxidative stress. Here, we studied the senescence as well as the response to the exposure to external acute oxidative stress of hMSCs from adipose tissue. We demonstrated that as cells senesce accumulate DNA damage (mainly 8-oxoG and DSBs) and that senescent cells are unable to repair the damage induced by exogenous oxidative stress. We also generated mesenchymal cells from adipose tissue overexpressing the telomerase catalytic subunit (hTERT) gene. Cells were engineered using the Sleeping Beauty transposon 100X system, a non-viral dual plasmid system with minimum cytotoxicity. Preliminary data indicate that hMSCs overexpressing hTERT show no difference as compared with the control cells in the amount of damage they accumulate due to the acute external oxidative exposure. Nevertheless, senescence reaching hTERT overexpressing cells show significantly lower percentages of oxidative DNA lesions and DSB as compared to control cells of the same passage. This means that hTERT offers a significant protection against the DNA damage that accumulates in the nuclei of the cells during normal cellular ageing. These results offer novel insights regarding the limitations of ex vivo amplified cell preparations for therapeutic applications.