Senescent cells are older deteriorated cells that do not function as they should, but also compromise the function of cells around them. Removal of these old dysfunctional cells has been shown to improve many features of ageing in animals such as the delayed onset of cataracts.

We still don’t fully understand why cells become senescent as we age, but damage to DNA, exposure to inflammation and damage to the protective molecules at the end of the chromosomes – the telomeres – have all been suggested.

More recently, people have suggested that one driver of senescence may be loss of our ability to turn genes on and off at the right time and in the right place.

One gene, many messages

As we age, we lose our ability to control how our genes are regulated. Each cell in the body contains all the information needed for life, but not all genes are switched on in all tissues or under all conditions. This is one of the ways that a heart cell is different from a kidney cell, despite the fact they contain the same genes.

When a gene is activated by signals from inside or outside the cell, it makes a molecular message (called an RNA) that contains all the information needed to make whatever that gene makes. We now knowthat over 95% of our genes can actually make several different types of messages, depending on the needs of the cell.

A good way to think about this is to consider each gene as a recipe. You could make either a vanilla sponge, or a chocolate cake, depending on whether you include the chocolate. Our genes can work like this. The decision as to which type of message is produced at any given time is made by a group of about 300 proteins called “splicing factors”.

As we age, the amount of splicing factors we are able to make declines. This means that aged cells are less able to switch genes on and off to respond to changes in their environment. We and others have shown that the levels of these important regulators decline in blood samples from elderly humans, and also in isolated human senescent cells of different tissue types.