Steve Hill

Editor’s Note: In this article, Mr. Steve Hill discusses one of the hallmarks of aging – in this case, Epigenetic Alterations. It is part of a paper published in 2013. It divides aging into a number of distinct categories (“hallmarks”) of damage to explain how the aging process works and how it causes age-related diseases [1]. This article was originally published by the Life Extension Advocacy Foundation (LEAF).

                        ~ Kenneth Alum, Director of Publication, U.S. Transhumanist Party, October 18, 2017

What are epigenetic alterations?

The DNA in every one of our cells is identical, with only small variations, so why do our various organs and tissues look so different, and how do cells know what to become?

DNA is modified by the addition of epigenetic information that changes the pattern of gene expression in a cell, suppressing or enhancing the expression of certain genes in a cell as the situation demands. This is how a cell in the liver knows that it needs to develop into a liver cell; the epigenetic instructions make sure that it is given the right orders to become the correct cell type.

At a basic level, these epigenetic instructions make sure that the genes needed to develop into a liver cell are turned on, while the instructions specific to other types of cells are turned off. Imagine if a heart cell was given the wrong instructions and became a bone cell!

How epigenetic alterations accumulate

The aging process can cause alterations to our epigenome, which can lead to alterations in gene expression that can potentially change and ultimately compromise cell function. As an example, epigenetic alterations of the immune system can harm activation and suppress immune cells, thus causing our immune system to fail and leaving us vulnerable to pathogens.

Inflammation is implicated in epigenetic alterations, and studies show that caloric restriction slows the rate of these epigenetic changes [2]. Metabolism and epigenetic alterations are closely linked with inflammation, facilitating a feedback loop leading to ever-worsening epigenetic alterations. Alterations to gene expression patterns are an important driver of the aging process. These alterations involve changes to DNA methylation patterns, histone modification, transcriptional alterations (variance in gene expression) and remodeling of chromatin (a DNA support structure that assists or impedes its transcription).

In the cell, gene expression is activated by hypomethylation (a loss of methylation) or silenced by hypermethylation (an increase of methylation) at a gene location. The aging process causes changes that reduce or increase methylation at different gene locations throughout the body. For example, some tumour suppressor genes become hypermethylated during aging, meaning that they cease functioning, which increases the risk of cancer [3]. Post-translational modifications of histones regulate gene expression by organizing the genome into active euchromatin regions, where DNA is accessible for transcription, or inactive heterochromatin regions, where DNA is compacted and less accessible for transcription. The aging process causes changes to these regions, which changes gene expression.

The aging process also causes an increase in transcriptional noise, which is the primary cause of variance in the gene expression happening between cells [4]. Researchers compared young and old tissues from several species and identified age-related transcriptional changes in the genes encoding key components of inflammatory, mitochondrial, and lysosomal degradation pathways [5].