Eects of ageing on nuclear DNA integrity and metabolism in mussel cells (Mytilus edulis L.) R. Accomando a, *, A. Viarengo b, 1 , M.N. Moore c, 2 , B. Marchi a, 3 a Istituto di Fisiologia Generale, Universita Á di Genova, C.so Europa 26, 16132 Genoa, Italy b Dipartimento di Scienze e Tecnologie Avanzate, Universita Á di Torino, sede Alessandria, C.so Borsalino 54, Alessandria, Italy c Plymouth Marine Laboratory (NERC, CCMS), Citadel Hill, Plymouth PL1 2PB, UK Received 12 February 1998; accepted 23 November 1998 Abstract As the age of a cell increases, so does the potential for DNA damage. Recent theories on ageing suggest accumulative DNA damage is the primary cause of cellular senescence, possibly due to the decreased ability of DNA to act as a template for gene expression. In this paper we investigate the eects of ageing on the level of nuclear DNA damage in tissues of wild mussels of three dierent age groups; 2±4 years (group I), 6±8 years (group II) and 10 years (group III). In the digestive gland and haemolymph cells, a signi®cant age-dependent increase of DNA damage was observed, as evaluated by the ¯uorimetric alkaline DNA unwinding technique, which is able to detect both direct single strand DNA breaks as well as alkali-labile apurinic sites. In addition, the rate of DNA polymerase activity was studied in order to determine whether DNA damage was dependent on DNA alteration, or because of a reduced rate of DNA repair. Unscheduled DNA repair synthesis in isolated nuclei of digestive gland cells in older mussels, was signi®cantly decreased in comparison to younger mussels ( 42% in group II and 37% in group III, p < 0.01). In the digestive gland, salt extraction gives a slight, but signi®cant, decrease of aphidicolin-sensitive DNA polymerase activity in age group III of 25%, p < 0.05. Finally, we looked at the age variation in relation to oxidative stress. This was evaluated by measuring malondialdehyde accumulation in mussel cells. Digestive gland cells of group III, showed a signi®cant age-related increase in malondialdehyde content of 170%, p < 0.01, indicative of enhanced peroxidative processes. Taken together, these data suggest that the accumulation of DNA damage in group II is mainly dependent on the impairment of DNA repair systems. This is contrary to group III DNA damage, where a possible relationship between oxidative stress and alteration of nuclear DNA metabolism is found, probably deriving from an antioxidant defence decline. # 1999 Published by Elsevier Science Ltd. All rights reserved. Keywords: Ageing; DNA damage; DNA repair; Oxidative damage; Mussel The International Journal of Biochemistry & Cell Biology 31 (1999) 443±450 1357-2725/99/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S1357-2725(98)00154-X PERGAMON * Corresponding author. Tel.: +3901035-38-241, fax: +3901035-38-267, e-mail: aldo@igecuniv.csita.unige.it. 1 Tel.: +3901312-83842, fax: +3901312-54410, e-mail: viarengo@al.unipmn.it 2 Tel.: +44-1017-52-633265, fax: +44-1017-52-633265, e-mail: m.moore@pml.ac.uk 3 Tel.: +3901035-38241, fax: +3901035-38267, e-mail; aldo@igecuniv. csita. unige.it Abbreviations: MDA: malondialdehyde, FADU: ¯uorimetric alkaline DNA unwinding, HPLC: high pressure liquid chromatog- raphy.