Age changes in chromatin: accumulative or programmed?

Krebs cycle intermediates regulate DNA and histone methylation: epigenetic impact on the aging process

Many aging theories have proposed that mitochondria and energy metabolism have a major role in the aging process. There are recent studies indicating that Krebs cycle intermediates can shape the epigenetic landscape of chromatin by regulating DNA and histone methylation. A growing evidence indicates that epigenetics plays an important role in the regulation of healthspan but also is involved in the aging process. 2-Oxoglutarate (α-ketoglutarate) is a key metabolite in the Krebs cycle but it is also an obligatory substrate for 2-oxoglutarate-dependent dioxygenases (2-OGDO). The 2-OGDO enzyme family includes the major enzymes of DNA and histone demethylation, i.e. Ten-Eleven Translocation (TETs) and Jumonji C domain containing (JmjC) demethylases. In addition, 2-OGDO members can regulate collagen synthesis and hypoxic responses in a non-epigenetical manner. Interestingly, succinate and fumarate, also Krebs cycle intermediates, are potent inhibitors of 2-OGDO enzymes, i.e. the balance of Krebs cycle reactions can affect the level of DNA and histone methylation and thus control gene expression. We will review the epigenetic mechanisms through which Krebs cycle intermediates control the DNA and histone methylation. We propose that age-related disturbances in the Krebs cycle function induce stochastic epigenetic changes in chromatin structures which in turn promote the aging process.

Twenty years of ageing research at the Mill Hill laboratories

Research on ageing was carried out in the Genetics Division laboratories, Mill Hill, London, from 1970 to 1990, resulting in more than 100 publications. The work centred around the in vitro ageing of human diploid fibroblasts, but there was also research on transformed cells, rat and mouse tissues, human lymphocytes, chick cells, mice and a microbial model system. The major conclusion from all this research, together with a broad overview of the whole field of gerontology, is that ageing has multiple causes, and that adult animals become senescent through the eventual failure of several important maintenance mechanisms.