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BIOLOGICAL SCIENCES / GENETICS
Terminally differentiated muscle cells are defective in base excision DNA repair and hypersensitive to oxygen injury

Laura Narciso^*, Paola Fortini^*, Deborah Pajalunga^*, Annapaola Franchitto^*, Pingfang Liu, Paolo Degan, Mathilde Frechet^*,, Bruce Demple, Marco Crescenzi^*, and Eugenia Dogliotti^*,¶

*Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy; Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115; and Department of Translational Oncology, Istituto Nazionale per la Ricerca sul Cancro, Largo Rosanna Benzi 10, 16132 Genoa, Italy

Edited by James E. Cleaver, University of California, San Francisco, CA, and approved July 16, 2007 (received for review February 27, 2007)

The differentiation of skeletal myoblasts is characterized by permanent withdrawal from the cell cycle and fusion into multinucleated myotubes. Muscle cell survival is critically dependent on the ability of cells to respond to oxidative stress. Base excision repair (BER) is the main repair mechanism of oxidative DNA damage. In this study, we compared the levels of endogenous oxidative DNA damage and BER capacity of mouse proliferating myoblasts and their differentiated counterpart, the myotubes. Changes in the expression of oxidative stress marker genes during differentiation, together with an increase in 8-hydroxyguanine DNA levels in terminally differentiated cells, suggested that reactive oxygen species are produced during this process. The repair of 2-deoxyribonolactone, which is exclusively processed by long-patch BER, was impaired in cell extracts from myotubes. The repair of a natural abasic site (a preferred substrate for short-patch BER) also was delayed. The defect in BER of terminally differentiated muscle cells was ascribed to the nearly complete lack of DNA ligase I and to the strong down-regulation of XRCC1 with subsequent destabilization of DNA ligase III. The attenuation of BER in myotubes was associated with significant accumulation of DNA damage as detected by increased DNA single-strand breaks and phosphorylated H2AX nuclear foci upon exposure to hydrogen peroxide. We propose that in skeletal muscle exacerbated by free radical injury, the accumulation of DNA repair intermediates, due to attenuated BER, might contribute to myofiber degeneration as seen in sarcopenia and many muscle disorders.

oxidative stress | XRCC1 | DNA ligases | DNA single-strand breaks | 8-oxoguanine

Present address: Exsymol, Avenue Albert II 4, 98000 Monaco, Princedom of Monaco.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/cgi/content/full/0701743104/DC1.

^¶To whom correspondence should be addressed. E-mail: eugenia.dogliotti{at}iss.it

© 2007 by The National Academy of Sciences of the USA

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