MiP2005: Session 11

Mitochondrial Physiology Network 10.9: 124 (2005) - download pdf

 

Mitochondrial protein modification and degradation by the Lon protease in rat liver and heart.

Bertrand Friguet, M Hamelin, J Mary, M Perichon, A Sévère, E Delaval, H Bakala

Université Denis Diderot – Paris 7, Laboratoire de Biologie et Biochimie Cellulaire du Vieillissement, 2 place Jussieu, 75005 Paris, France. –  bfriguet@paris7.jussieu.fr

    Mitochondrial matrix proteins are sensitive to oxidative inactivation, and oxidized proteins are known to accumulate during ageing. The Lon protease is believed to play an important role in the degradation of oxidized matrix proteins such as oxidized aconitase. We previously reported that an age-related accumulation of altered (i. e. oxidized and glycoxidized) proteins occurs in the liver matrix of rats and that the ATP-stimulated proteolytic activity, referred as to Lon-like protease activity, decreases considerably in 27 month-old rats, whereas no concomitant changes in the levels of Lon protein expression occur in the liver [1]. This decline is associated with a decrease in the activity of aconitase, an essential Krebs’cycle enzyme.

    Contrary to what we observed in the liver, the ATP-stimulated protease activity was found to remain constant in the heart mitochondrial matrix during ageing, and the levels of expression of the Lon protease increased in the older animals in comparison with the younger ones. Although the ATP-stimulated protease activity remained practically the same in the heart of older animals as in younger ones, a decrease in the level of aconitase activity was still observed [2]. These results indicate that matrix proteins such as the critical enzymes aconitase and Lon protease are inactivated with ageing and that the effects of ageing vary from one organ to another.

    Furthermore, analysis of glycoxidized protein pattern, monitored by western blotting with anti-carboxymethyllysine antibodies after a two-dimensional electrophoresis, revealed that only a restricted set of proteins were glycoxidized with age in rat liver mitochondrial matrix. Using LC-MS/MS analysis, we have identified proteins that are implicated in the urea cycle, especially glutamate dehydrogenase. In vitro assay of the glutamate dehydrogenase activity incubated with the glycating reagent methylglyoxal showed both an inactivation of the enzyme and alteration of its allosteric properties. These results suggest a role for glycoxidative modifications in the age-related dysfunction of mitochondria and indicate that carboxymethylated glutamate dehydrogenase could be used as a bio-marker of cellular aging.

1.  Bakala H, Delaval E, Hamelin M, Bismuth J, Borot-Laloi C, Corman B, Friguet B (2003) Changes in rat liver mitochondria with aging: lon protease-like activity and N-carboxymethyllysine accumulation in the matrix. Eur. J. Biochem. 270: 2295-2302.

2.  Delaval E, Perichon M, Friguet B. (2004) Age-related impairment of mitochondrial matrix aconitase and ATP-stimulated protease in rat liver and heart. Eur. J. Biochem. 271: 4559-4564.


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