Age-related change in the amount of ubiquitinated histones in the mouse brain

Gene Expression, Epigenetics and Ageing

As the popular adage goes, all diseases run into old age and almost all physiological changes are associated with alterations in gene expression, irrespective of whether they are causal or consequential. Therefore, the quest for mechanisms that delay ageing and decrease age-associated diseases has propelled researchers to unravel regulatory factors that lead to changes in chromatin structure and function, which ultimately results in deregulated gene expression. It is therefore essential to bring together literature, which until recently has investigated gene expression and chromatin independently. With advances in biomedical research and the emergence of epigenetic regulators as potential therapeutic targets, enhancing our understanding of mechanisms that 'derail' transcription and identification of causal genes/pathways during ageing will have a significant impact. In this context, this chapter aims to not only summarize the key features of age-associated changes in epigenetics and transcription, but also identifies gaps in the field and proposes aspects that need to be investigated in the future.

Small changes, big effects: chromatin goes aging

Aging is a complex trait and is influenced by multiple factors that are both intrinsic and extrinsic to the organism (Kirkwood et al. 2000; Knight 2000). Efforts to understanding the mechanisms that extend or shorten lifespan have been made since the early twentieth century. Aging is characteristically associated with a progressive decline in the overall fitness of the organism. Several studies have provided valuable information about the molecular events that accompany this process and include accumulation of nuclear and mitochondrial mutations, shortened and dysfunctional telomeres, oxidative damage of protein/DNA, senescence and apoptosis (Muller 2009). Clinical studies and work on model organisms have shown that there is an increased susceptibility to conditions such as neurological disorders, diabetes, cardiovascular diseases, degenerative syndromes and even cancers, with age (Arvanitakis et al. 2006; Lee and Kim 2006; Rodriguez and Fraga 2010).

Carbonyl modification in rat liver histones: decrease with age and increase by dietary restriction

We studied carbonylation, a form of oxidative modification of proteins, of histones in rat livers. Histones H1, H2B/H2A, and H3 were significantly carbonylated but the modification was almost undetectable in H4. Contrary to the generally accepted view of increased protein carbonylation with age, the modification of histones was significantly lower in old (30-month-old) than in young (5-month-old) animals. Dietary restriction of older animals for 2 months resulted in increase in carbonylation comparable to that at the young level. These findings may have physiological implications in chromatin structure/function in aging and beneficial effects of DR by influencing transcription, replication, and/or repair activities.