Finding involving scientists at the Babraham Institute in Cambridge, shed new light on the effects of ageing on blood and the immune system. The study of haematopoetic stem cells reveals that some stem cells age faster than others. The older stem cells slowly lose the ability to produce new cells, which could go some way to explain why older people experience weaker immune systems and a greater risk of conditions such as anaemia.

The research, collaboratively led Professor Wolf Reik at the Babraham Institute and Professor Tony Green at the Department of Haematology, University of Cambridge, used recently developed techniques to examine individual haematopoetic stem cells from mice.

The findings, published in the journal Cell Reports, show that the more new cells each stem cell produces the faster it ages and the sooner it gets exhausted.

Stem cells are any group of cells in the body that are able to divide to produce several different types of new cells, therefore their correct functioning is essential. Although embryonic stem cells are well known, there are also adult stem cells in different parts of the body. Each type of adult stem cell only has a limited repertoire of cells it can produce, and usually helps to maintain specific organs or systems in the body, such as the brain, blood or digestive system.

By encouraging haematopoetic stem cells to make more new cells, the team were able to accelerate the ageing process and make more ‘old’ cells, showing that ageing of haematopoetic stem cells is linked to the number of cells they have produced in their lifetime. This also suggests that some people may have healthier stem cells than others, whilst others may be more prone to illnesses resulting from aged cells.

What the team – which also includes scientists from the Department of Haematology, University of Cambridge and the MRC Human Genetics Unit in Edinburgh – has found is an example of heterogeneity, a marked difference between individuals within a group. In haematopoetic stem cells, the oldest cells enter a state called senescence, where they no longer produce new cells.

The paper’s co–first and co–corresponding author Dr Kristina Kirschner, now based at the University of Glasgow, said: “We’ve known for some time that haematopoetic stem cells slowly lose the ability to produce new cells as they age but until now we’ve assumed this is due to a general slowing down of the whole cell population. Finding that some cells become senescent long before others means we need to rethink our approach to cell ageing.”

Although some of the cells from old mice were senescent, many more were indistinguishable from healthy cells in much younger mice. The researchers found that the older cells include high levels of activity in a biological system called JAK/STAT, which can be a key factor in certain blood cancers. As such, these aged stem cells may also help to explain the increased risk of certain leukaemias and lymphomas in older people.

As one of the senior authors on the paper, Professor Reik said, “Technology has now advanced to the point where we’re able to study the inner workings of single cells. Only through these approaches can we make sense of heterogeneity in biology and find better ways to treat disease and stay healthy as we age.”

By understanding how stem cells change throughout our lives, Professors Reik and Green hope to find ways to turn back the clock for haematopoetic stem cells. The eventual goal would be to stop the immune system from weakening with age and potentially take preventative action to remove aged cells from the body before they have an opportunity to become harmful or develop into cancer. Such interventions could help more people stay healthy for longer in their advancing years.