Mitochondrial DNA may hold answer to why women live longer than men

Scientists working on fruit
flies say their work provides an answer to the question of why women tend to
live longer than men. The research points to mitochondria, the 'batteries'
within cells that generate energy, as hotspots for mutations that negatively
affect male health.

Researchers from Lancaster
University in the UK and Monash University in Australia studied the ageing of
13 different strains of fruit fly. They found that mutations in the mitochondrial DNA affected the how long male flies lived, and how fast they aged.

'Intriguingly,
these same mutations have no effects on patterns of ageing in females', Dr
Damian Dowling, of Monash University said.
'Our results therefore suggest that the mitochondrial mutations we have
uncovered will generally cause faster male ageing across the animal kingdom'.

Mitochondria
were already thought to play a role in ageing: in producing energy from oxygen,
they also produce free radicals, which can harm the cell. Dr Dowling and
colleagues have now found indications that this might be particularly true for
males.

'All
animals possess mitochondria, and the tendency for females to outlive males is
common to many different species', Dr Dowling explained. 'While
children receive copies of most of their genes from both their mothers and
fathers, they only receive mitochondrial genes from their mothers. This means
that evolution's quality control process, known as natural selection, only
screens the quality of mitochondrial genes in mothers'.

The idea of mitochondrial DNA in
males not being subject to natural selection and therefore leading to male-only
harmful mutations, is known among geneticists as the 'mother's curse'.

Dr
Dowling added: 'If a mitochondrial mutation occurs that harms fathers, but has
no effect on mothers, this mutation will slip through the gaze of natural
selection unnoticed. Over thousands of generations, many such mutations have
accumulated that harm only males, while leaving females unscathed'.

But
the results should be interpreted with caution. So far, the sex-specific ageing
effects of mutations in mitochondrial DNA have only been found in fruit flies
and have to be confirmed in other species.

Professor
Tim Kirkwood of Newcastle University, who was not involved in the study, told
BBC News: 'There are other things we
know also count - lifestyle, social and behavioural factors. But the biggest
difference in biology is that we have different hormones. I certainly don't
think this is a discovery that explains why women live five-to-six years longer
than men'.