Brain's inability to repair DNA may explain dementia, memory loss

Previously, it was thought ability to repair DNA was the same throughout the body, but new research overturns this idea and shows organs vary in the extent to which they carry out a type of DNA repair called nucleotide excision repair.

The study investigated an important type of DNA repair.

This was the finding of a new study led by Nova Southeastern University (NSU) in Fort Lauderdale, FL, that is published in the journal Photochemistry and Photobiology.

For the study, the research team investigated a type of DNA repair called nucleotide excision repair (NER). 

It is one of five types of DNA repair used by mammalian cells, primarily to repair damage caused by a range of cancer-causing agents, including ultraviolet (UV), products of organic combustion, metals and oxidative stress.

NER is a complicated process that requires a high level of metabolic investment by the cell. It mends DNA regions that contain unwanted added molecules that distort the DNA helix and interfere with DNA copying during cell division.

The researchers at the College of Pharmacy at NSU found that the heart has the greatest ability to repair DNA using NER, followed by the gut, the kidneys, the spleen, the testes and the lungs.

However, the researchers found the brain appears to have no ability to carry out this vital type of DNA repair.

One explanation could be that because they are not exposed to light, brain cells focus their energies on more essential functions.

'Brain does not prioritize DNA repair'

"The human body was not designed to live past 30 or 40 years, so our brains haven't prioritized DNA repair over other necessary functions."

"Our brains are frequently not physically prepared to last as long as medical science is now allowing our bodies to live.

"These findings could help explain a root cause behind memory loss and dementia."

For the study, the team carried out the research in mouse cell tissue cultures, but they say - because of previous work they have done on human tissue - the same will be true of humans.

The researchers used skin cells as the control to compare other cell types against. They grew cells taken from different organs and assessed their ability to repair DNA after exposing them to ultraviolet (UVC) light. UVC is a part of normal sunlight and causes extensive DNA damage.

The authors note that loss of the NER type of DNA repair also occurs in sporadic breast cancer and can influence response to therapy.

The National Cancer Institute of the National Institutes of Health and the Ruth Estrin Goldberg Foundation helped fund the study.

Meanwhile, another team of researchers suggests meditation may slow brain aging. Researchers from the University of California-Los Angeles found that people who meditate regularly had better-preserved gray matter in the brain.

Reference:

1.  Regulation and disregulation of mammalian nucleotide excision repair: a pathway to nongermline breast carcinogenesis, Jean J. Latimer, et al., Photochemistry and Photobiology, doi:10.1111/php.12387, published online 19 December 2014, abstract.
2.  Nova Southeastern University news release, accessed 10 February 2015.
3.  Genetics Home Reference nucleotide excision repair, accessed 10 February 2015.