Newswise, March 20, 2017—Columbia
University Medical Center (CUMC) researchers have discovered a common genetic
variant that greatly impacts normal brain aging, starting at around age 65, and
may modify the risk for neurodegenerative diseases.
The findings could point toward a novel
biomarker for the evaluation of anti-aging interventions and highlight
potential new targets for the prevention or treatment of age-associated brain
disorders such as Alzheimer’s disease.
The study was published online in the
journal Cell Systems.
“If you look at a group of seniors,
some will look older than their peers and some will look younger,” said the
study’s co-leader Asa Abeliovich, PhD, professor of pathology and neurology in
the Taub Institute for Alzheimer's Disease and the Aging Brain at CUMC.
“The same differences in aging can
be seen in the frontal cortex, the brain region responsible for higher mental
processes. Our findings show that many of these differences are tied to
variants of a gene called TMEM106B. People who have two ‘bad’ copies of this
gene have a frontal cortex that, by various biological measures, appears 12
years older that those who have two normal copies.”
Studies have identified individual
genes that increase one’s risk for various neurodegenerative disorders, such as
apolipoprotein E (APOE) for Alzheimer's disease.
“But those genes explain only a
small part of these diseases,” said study co-leader Herve Rhinn, PhD, assistant
professor of pathology and cell biology in the Taub Institute.
“By far, the major risk factor for
neurodegenerative disease is aging. Something changes in the brain as you age
that makes you more susceptible to brain disease. That got us thinking, ‘What,
on a genetic level, is driving healthy brain aging?’”
In the current study, Drs.
Abeliovich and Rhinn analyzed genetic data from autopsied human brain samples
taken from 1,904 people without neurodegenerative disease. First, the
researchers looked at the subjects’ transcriptomes (the initial products of
gene expression), compiling an average picture of the brain biology of people
at a given age.
Next, each person’s transcriptome
was compared to the average transcriptome of people at the same age, looking
specifically at about 100 genes whose expression was found to increase or
decrease with aging.
From this comparison, the
researchers derived a measure that they call differential aging: the difference
between an individual’s apparent (biological) age and his or her true
(chronological) age. “This told us whether an individual’s frontal cortex
looked older or younger than expected,” said Dr. Abeliovich.
The researchers then searched the
genome of each individual, looking for genetic variants that were associated
with an increase in differential age.
“One variant stood out: TMEM106B,”
said Dr. Rhinn. “It’s very common. About one-third of people have two copies
and another third have one copy.”
“TMEM106B begins to exert its effect
once people reach age 65,” said Dr. Abeliovich. “Until then, everybody’s in the
same boat, and then there’s some yet-to-be-defined stress that kicks in. If you
have two good copies of the gene, you respond well to that stress. If you have
two bad copies, your brain ages quickly.”
The researchers found a second
variant—inside the progranulin gene—that contributes to brain aging, though
less so than TMEM106B. Progranulin and TMEM106B are located on different
chromosomes but are involved in the same signaling pathway. Both have also been
associated with a rare neurodegenerative disease called frontotemporal dementia.
The study did not address what role
the two genetic variants might have in neurodegenerative disease. “We were
studying healthy individuals, so it is not about disease, per se,” said Dr.
Abeliovich.
“But of course, it’s in healthy
tissue that you start to get disease. It appears that if you have these genetic
variants, brain aging accelerates and that increases vulnerability to brain
disease. And vice versa: if you have brain disease, the disease accelerates
brain aging. It’s a vicious cycle.”
The study is titled, “Genetic
determinants of aging in human brain.”
The study was supported by grants
from the National Institute of Aging (AG042317), the National Institute of
Neurological Disorders and Stroke, and the Michael J. Fox Foundation for
Parkinson's Research.
Dr. Abeliovich is a co-founder of
and consultant for Alector. Dr. Rhinn is a consultant for Alector. The
researchers declare no other financial conflicts of interest.