RESUMEN
A comparative biochemical study of the structural-functional peculiarities of genetic apparatus and the content of lipid peroxidation products in the liver nuclei and mitochondria of adult (4.5-5.5 months) and old (22-24 months) CBA mice was carried out. The age-related changes were found as follows: relative content of transcriptionally active and matrix-bound chromatin fractions was decreased, and that of transcriptionally low active fraction was increased; the value of protein/DNA was increased only in transcriptionally active fraction; the value of mitochondrial genome expression coefficient was diminished due to a decreased content of proteins encoded by mtDNA; the concentrations of Schiff bases were elevated both in the nuclei and mitochondria. Possible mechanisms of lipid peroxidation involvement in the above mentioned changes of the nuclear and mitochondrial genetic apparatus are discussed.
Asunto(s)
Envejecimiento/genética , Núcleo Celular/genética , Peroxidación de Lípido/fisiología , Mitocondrias Hepáticas/genética , Animales , Cromatina/genética , ADN Mitocondrial/genética , Masculino , Ratones , Ratones Endogámicos CBA , Relación Estructura-ActividadRESUMEN
We have used young (2-3 months), adult (6-8 months) and old (26-28 months) rats. Nuclear DNA (nDNA) was isolated from the liver nuclei and chromatin fractions (RCh, repressed chromatin; ACh, transcriptionally active chromatin; MCh, membrane-bound chromatin) and thereafter loaded on nitrocellulose filters. Hybridization was carried out with radioactively labelled mitochondrial DNA (mtDNA) as a probe mtDNA was first isolated from the liver mitochondria of adult rats and then labelled in nick-translation reaction with 32P-dCTP. Radioautography densitometry data have shown that the content of mtDNA-homologous sequences in the liver nDNA was decreased in adult rats (56%) and increased in the old ones (240%), as compared with the young animals. mtDNA-homologous sequences were localized in the young rats mainly in the RCh, while the adult and old rats had similar sequences in the ACh. We suggest that the age-related dynamics of mtDNA-homologous sequences was due to various factors. At the early stages cell differentiation proceeds rapidly and is accompanied by structural and functional reorganization of both nuclear and mitochondrial genomes. These changes increase the probability of contacts and integration of mtDNA fragments and whole molecules in the nuclear genome. As a result, an elevated level of mtDNA-homologous sequences is observed in the liver nuclear genome of young rats. In adult rats, repair and elimination of cells with defective nDNA and decreased proliferation of hepatocytes account for decreased amounts of mtDNA-homologous sequences in nDNA. In old animals, the repair to destruction ratio shifts towards destruction and, hence, mtDNA-homologous sequences are accumulated in the liver nDNA. Age related dynamics of mtDNA-homologous sequences in the liver chromatin fractions is characterized by accumulation of these sequences in ACh and MCh chromatin fractions during maturation and ageing. This also confirms our suggestion that integration of mtDNA-homologous sequences in the nuclear genome is due to various mechanisms operational at the early and late stages of ontogenesis.
Asunto(s)
Envejecimiento/metabolismo , Cromatina/metabolismo , ADN Mitocondrial/metabolismo , ADN/metabolismo , Hígado/metabolismo , Homología de Secuencia de Ácido Nucleico , Envejecimiento/genética , Animales , Autorradiografía , Núcleo Celular/genética , Núcleo Celular/metabolismo , Cromatina/genética , Cromatina/aislamiento & purificación , ADN/genética , ADN Mitocondrial/genética , ADN Mitocondrial/aislamiento & purificación , Femenino , Datos de Secuencia Molecular , Hibridación de Ácido Nucleico , RatasRESUMEN
The in vivo synthesis of mtDNA and mtDNA-coded proteins was studied in the whole population and in separate fractions (heavy, middle and light) of liver mitochondria from young (3-4 months), adult (6-8 months) and old (24-26 months) rats. The synthesis rate was estimated from the value of relative specific radioactivity which represented a ratio of specific radioactivity of acid insoluble fraction to that of acid soluble fraction in suspension aliquot of isolated mitochondria. It was found that the synthesis rate of mtDNA in the whole mitochondrial population was increased in the adult rats and decreased in the old animals. The same direction of changes was noticed in heavy and light mitochondrial fractions. Moreover, at any age the synthesis rate of mtDNA was higher in light fractions as compared to other fractions. In the whole mitochondrial population, the synthesis rate of proteins coded by mtDNA was also increased in adult rats and decreased in old animals. However, this decrease was less expressed than in mtDNA case. The increase in the synthesis rate of mitochondrial proteins was noted in all mitochondrial fractions too, whereas its decrease in the old age was marked in the light mitochondria only. Owing to the above peculiarities of age-related changes of the synthesis rate of mtDNA and proteins coded by mtDNA, there takes place the prevalence with age of protein synthesis over mtDNA synthesis in the whole population and in the fractions of rat liver mitochondria.