| May 29, 2001
Science Tip Sheet Special Edition
Recent Findings on the Nature of Brain Disorders at
the Center for Neurodegenerative Disease
Below are two story ideas based on research at the
Center for Neurodegenerative Disease (CNDR) at the University
of Pennsylvania Medical Center.
The Tao of Tau: Penn Researchers Implicate Loss
of Brain Tau Protein in Newly Categorized Set of Neurodegenerative
It is fascinating
how one little protein can cause so much trouble. Medical
researchers have known that the tau protein, found in
the neurons - or nerve cells - of the brain, forms fibrous
plaques that have a role in Alzheimer's Disease and
assorted other brain disorders. Now, researchers at
CNDR have demonstrated that the loss of tau characterizes
a separate set of devastating, albeit rare, diseases
that result in the slow erosion of tissue in the frontotemporal
portion of the brain. Their findings were presented
in a recent issue of the Annals of Neurology.
Dementia lacking distinctive histopathology (DLDH) is
the common diagnosis for an array of dementias marked
by the destruction of the same portion of the brain.
First described in the 1980s, the Penn researchers have
found that these dementias, whether sporadic or inherited,
share a common trait: the lack of tau protein. The human
brain produces six forms of tau protein, which researchers
believe have a role in forming the network of microtubules
that serve as a kind of transport system within brain
cells. The lack of tau protein may cause these systems
to break down, killing off cells in the process.
The researchers are surprised by a complicating development:
the tau protein is missing but the tau gene is intact
and producing the messages necessary to create the protein.
"As in any good mystery, one solution opens up
another set of problems," Vicki Zhukareva, PhD,
and Senior Research Investigator at the Penn CNDR. "Somewhere
the tau gene's message is getting lost."
The common thread between many degenerative brain diseases
is actually a fiber, and CNDR researchers now have a
better understanding of how the building blocks of these
fibers can clump together and cause illness. The researchers
have found that a short stretch of alpha-synuclein,
a nerve cell protein, allows the proteins to bunch together
in fibrous brain deposits. These brain deposits are
indicative of a number of diseases, including Parkinson's
Disease and multiple system atrophy, collectively termed
"In these diseases, sticky regions in alpha-synclueins
allow the proteins to cling to each other and gum up
the works," said Benoit Giasson, PhD, postdoctoral
fellow in Penn's Department of Laboratory and Pathology
Medicine and the CNDR. "This is just a start, but
these regions also provide us with an opportunity for
therapeutic attack: if we can bind something to this
site then maybe the proteins won't be able to form brain
The researchers found the binding site by comparing
alpha-synculein to a closely related molecule, beta-synuclein,
which does not form fibers. The sticky region, a mere
12 amino acids out of the 140 that make up the protein,
is only found in alpha-synuclein. Their findings were
published in a recent issue of the Journal of Biological
What goes wrong to allow a-synuclein to form clumps?
According to Giasson, this is one of the "big"
questions of neurogenerative disease studies. The exact
function of either synuclein protein is not known, however,
researchers believe they play a role in the mechanism
that directs information across the space between two
neurons, called the synapse. CNDR researchers think
that plaque-forming occurs through a "seeding"
process, at least in test tube experiments.
"We are now beginning to understanding how the
protein can form clumps in a test tube under defined
conditions, but we still have much work to do to see
how they continue to form in live cells," said
Giasson. "Likely, seeding occurs when cells are
overwhelmed, and establishing the factors that overwhelm
cells - thereby leading to synuclein fiber formation
- may lead to the development of new therapeutic strategies
for Parkinson's and related disease."
# # #
Founded in 1991, the Center for Neurogenerative Disease
Research is devoted to developing better diagnostic
strategies and effective new therapies - and encouraging
the rapid translation of progress at the lab bench to
the bedside. John Q. Trojanowski, MD, PhD, and Virginia
M.-Y. Lee, PhD co-direct the CNDR, and form a focus
point for neurodegenerative research from many disciplines
throughout the University of Pennsylvania Health System.