Breasts age faster than rest of body, DNA clock shows

A DNA-based biological clock has
shown that different parts of the body age at varying rates, with breast tissue
and tumour cells appearing older than the rest of the body.

The clock looks at DNA methylation, a natural process in which parts of the genome are altered so that
certain genes are switched on or off.

The biological age of various
organs, tissues and bodily fluids could be accurately measured by looking at
the methylation of 353 specific DNA markers, according to researcher Professor Steve
Horvath, who developed the model.

'To fight ageing, we first need
an objective way of measuring it. Pinpointing a set of biomarkers that keeps
time throughout the body has been a four-year challenge', said Horvath, professor
of human genetics at the University of California, Los Angeles, USA.

'My goal in inventing this
clock is to help scientists improve their understanding of what speeds up and
slows down the human ageing process'.

Professor Horvath's 'epigenetic clock' compares
the biological age of tissues with their chronological age. Most organs, such
as the brain, liver and lung, were seen to age at the expected rate, as did blood
cells and saliva samples. However, breast tissue was seen to age slightly
faster, and cancerous tissue was also found to be much 'older' than the
chronological age of the body.

'Healthy breast tissue is about
two to three years older than the rest of a woman's body', said Professor Horvath.
'If a woman has breast cancer, the healthy tissue next to the tumour is an
average of 12 years older than the rest of her body'.

The study also
found that induced pluripotent stem cells - adult cells that have been
reprogrammed to an embryonic state — had
effectively had their epigenetic clocks reset. 'My research shows that all stem cells are
newborns', said Professor Horvath. 'More importantly, the process of
transforming a person's cells into pluripotent stem cells resets the cells'
clock to zero'.

Darryl
Shibata, professor of medicine at the University of Southern California, who
was not involved in the study, told Forbes:
'The general idea that you can read a genome and it reflects the ageing process
is probably correct [...] No one knows how this clock works yet'.