Telomeres at chromosome ends shorten during cell division and aging in humans. Critically short dysfunctional telomeres trigger cell senescence or apoptosis, which contributes to aging-related diseases and degeneration. Oxidative stress accelerates telomere shortening, and generates reactive oxygen species (ROS), which are particularly damaging to telomeric TTAGGG repeat sequences. The goals of this proposal are to 1) measure the response of base excision repair (BER) proteins to DNA damage at telomeric regions compared with non- telomere regions;and 2) to define the impact of oxidized telomeric DNA on telomere integrity and telomere functions in preventing cell senescence and cell death. A critical barrier to investigating DNA damage and repair at telomeres has been an inability to target damage to the telomeres. To overcome this obstacle we developed a highly innovative system for confining ROS-induced DNA damage to defined regions in the genome. For this we fused KillerRed (KR) protein, a photosensitizer that generates ROS upon light irradiation, to a Tet-repressor (tetR) protein that binds to a single engineered site within condensed chromatin. We established that oxidative damage occurred only at the tetR bound site. To target telomeres we fused KR to the telomere binding protein TRF1 and showed that this restricts ROS-induced damage to the telomeres.
In Aim 1, we will combine the KR system with confocal microscopy to visualize the real time damage response of BER proteins to targeted oxidative damage in telomeric and non-telomeric genomic regions, with 3D resolution in a single cell nucleus. We will measure the mobilization kinetics of various GFP-tagged BER proteins, and the protein domains required for the response, to ROS damage at the TRF1 bound telomeric sites compared with the tetR bound non-telomeric site.
In Aim 2, we will test several endpoints of telomere damage and dysfunction, including cellular senescence and apoptosis, after ROS production by activating KR with light exposure in cells that stably express KR-TRF1, compared with cells expressing HcRed-TRF1 as a control. This study will include both bulk cell population and single cell experiments. Using the microscopy system to target KR activation to defined numbers of KR-TRF1 foci, we will measure the average number of "oxidized" telomeres required to trigger apoptosis or senescence. Successful completion of the project will provide crucial insights into how oxidative stress accelerates telomere shortening, and how telomeric oxidative base damage impacts telomere function and promotes cell senescence. The results will pave the way for future work examining how telomeric damage and repair change with age and vary with cell type, and should lead to new strategies for preserving telomere function to promote healthy aging. !

Public Health Relevance

Critically short telomeres contribute to aging-related diseases by causing cellular senescence or apoptosis. Oxidative stress accelerates telomere shortening and damages telomeric DNA. This project will advance understanding of how oxidative stress disrupts telomere structure and function, and the mechanisms for repairing damaged telomeres. This study will also establish a new platform for testing factors that influence telomere repair an promote telomere preservation to delay aging-related diseases.

National Institute of Health (NIH)
Exploratory/Developmental Grants (R21)
Project #
Application #
Study Section
Cellular Mechanisms in Aging and Development Study Section (CMAD)
Program Officer
Guo, Max
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Pittsburgh
Schools of Medicine
United States
Zip Code
Nakajima, Satoshi; Lan, Li; Wei, Leizhen et al. (2014) Ubiquitin-specific protease 5 is required for the efficient repair of DNA double-strand breaks. PLoS One 9:e84899
Benitez, Anaid; Yuan, Fenghua; Nakajima, Satoshi et al. (2014) Damage-dependent regulation of MUS81-EME1 by Fanconi anemia complementation group A protein. Nucleic Acids Res 42:1671-83
Xu, Liang; Chen, Ying-Chu; Nakajima, Satoshi et al. (2014) A Chemical Probe Targets DNA 5-Formylcytosine Sites and Inhibits TDG Excision, Polymerases Bypass, and Gene Expression. Chem Sci 5:567-574
Lan, Li; Nakajima, Satoshi; Wei, Leizhen et al. (2014) Novel method for site-specific induction of oxidative DNA damage reveals differences in recruitment of repair proteins to heterochromatin and euchromatin. Nucleic Acids Res 42:2330-45