Tissue-specific effect of age and caloric restriction diet on mitochondrial DNA content





P. Cassano, A.G. Sciancalepore, A.M.S. Lezza, C. Leeuwenburgh, P. Cantatore, M.N. Gadaleta

Department of Biochemistry and Molecular Biology, University of Bari, via Orabona 4, 70125 Bari, Italy



The decay of mitochondrial function is considered one among the major contributors of the age-related degenerative processes. Caloric restriction (CR) diet is widely known as the only treatment able to delay aging, increasing both the mean and maximum lifespan in a wide phylogenic range of animals including rodents and non human primates. Several evidences show that CR diet is able to prevent or reduce the age-dependent accumulation of oxidative damages to mitochondrial DNA (mtDNA) in different rodent tissues, mainly reducing the OH8dG content and the number of mtDNA deleted species. As the mitochondrial function in a cell relies not only on the integrity of mtDNA molecules but also on the copy number of mitochondrial genomes we decided to investigate the effect of CR diet on age-dependent changes of mtDNA content in different rat tissues.

We evaluated by quantitative Real Time PCR the mtDNA/nuclear DNA ratio in liver, brain and soleus muscle from adults fed ad libitum (AL), old fed ad libitum (OL) and old lifelong 40% calories-restricted (OR) Fischer 344 animals. The measurement was carried out using specific primers and TaqMan probes for mitochondrial and nuclear targets represented, respectively, by the D-loop region and β-actin gene.

The data here reported show tissue-specific age-related changes of mitochondrial DNA content. In particular, we found, in liver and soleus muscle, an age-related decrease of mtDNA content (-50% and 40%, respectively) whereas in brain there is no significant change of mtDNA content during aging. CR is able to reverse the age-related loss of mtDNA in liver and soleus, while in brain it results in a significant increase of mtDNA/nDNA ratio above the OL value. This suggests that there might exist some general age-related process leading to the loss of mtDNA both in mitotic (liver) and post-mitotic (skeletal muscle) tissues, probably through prevention or reduction of mtDNA replication. This should not occur in another post-mitotic tissue (brain) where mtDNA can replicate at a normal level during aging, increasing its total amount. Therefore, this further supports the tissue-specific effect of CR, likely due to the different dependence of tissues on external nutrients uptake.

This work has been supported by funds from Ministero dell'Istruzione, dell'Universit e della Ricerca-Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale 2002 (to M.N.G.) and from the University of Bari-Progetti di Ateneo 2003 and 2004 (to A.M.S.L.). P.Cassano was supported by ESF (PON 2000-2006)




Key words: caloric restriction diet, aging, mitochondrial DNA content, Real Time PCR







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