The Huntington's Scene In
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Drug treatment promising for halting
Huntington's-related nerve death
The study was funded by the Robert A. Welch Foundation, the Huntington's Disease
Society of America, the Hereditary Disease Foundation, and the National Institute of
Neurological Disorders and Stroke.
DALLAS – Jan. 31, 2005 – Researchers at UT Southwestern Medical Center have
discovered that drugs commonly used to treat psychiatric illnesses and blood disorders in
humans may protect the brain cells that die in people with Huntington's disease, possibly
delaying the onset and slowing the progression of the disease.
These findings, available online and in today's issue of Proceedings of the National
Academy of Sciences, may offer new treatment options for Huntington's disease, which
has no cure.
Huntington's disease is a neurological disorder in which the medium spiny striatal
neurons, the nerve cells that control movement and certain mental functions die. Patients
die within 10-15 years after onset of the disease.
The disease is caused by a mutation in the gene that makes the protein huntingtin. The
mutation creates a long chain of the amino acid glutamine at one end of the protein. The
length of the chain directly correlates with age of onset of the disease, with longer
chains leading to symptoms earlier in life.
In previous studies, Dr. Ilya Bezprozvanny, associate professor of physiology at UT
Southwestern, established that one of the defects that leads to death of nerve cells with
the mutant huntingtin protein is improper regulation of calcium due to errant signals in
the cells. Calcium is inappropriately released from its storage area in the cells, and
eventually the cells die.
"We have developed a model that links the mutation in huntingtin with degeneration of
motor neurons," Dr. Bezprozvanny said. "The model connects all the dots between
the Huntington's disease mutation, defective calcium signaling in the cell, and subsequent
degeneration of medium spiny striatal neurons."
In the current study, using the medium spiny neurons of mice that carry a copy of the
mutated human huntingtin gene, Dr. Bezprozvanny and colleagues found that treatment of the
cells in culture with the drug enoxaparin prevented inappropriate calcium
release, and prevented cell death. Enoxaparin is an anti-coagulant that is FDA-approved in
humans for use in treating blood clots.
Because the signals that lead cells to die can come from multiple pathways, Dr.
Bezprozvanny then determined which cell death pathway affected the nerve cells carrying
mutant huntingtin. He found that the nerve cells' mitochondria, the parts of the cell that
create energy, released a protein called cytochrome c through a pore just before dying.
From other studies, it was known the drugs nortriptyline and desipramine, which are
antidepressants, and trifluoperazine, an antipsychotic, block the mitochondrial pore
through which cytochrome c and other death signals are released. By treating the mouse
nerve cells containing the mutant huntingtin protein with these drugs, Dr. Bezprozvanny
was able to block the nerve cells from dying.
The next step, according to Dr. Bezprozvanny, will be to work with other researchers to
test these drugs in whole animal models of Huntington's disease, and see if cell death and
loss of motor function observed in these models can be prevented.
In addition, the researchers would like to expand their drug search beyond molecules that
block calcium release and the mitochondrial pore. "We're looking for drugs that will
prevent the pathological association of mutant huntingtin protein with the calcium
signaling proteins in striatal neurons," he said. "We have a nice model system
set up where we can easily look for cell death of Huntington's disease neurons, so we can
look for the most specific drug with the least side effects."
###
Other UT Southwestern contributors to this study were Dr. Tie-Shan Tang, assistant
instructor of physiology and Dr. Vitalie Lupu, postdoctoral researcher. In addition, Dr.
Rodolfo Llinas of New York University School of Medicine, Dr. Bruce Kristal of Cornell
University, and Dr. Michael Hayden of the University of British Columbia, who provided the
mice used in the study, and members of their laboratories also contributed.
The study was funded by the Robert A. Welch Foundation, the Huntington's Disease Society
of America, the Hereditary Disease Foundation, and the National Institute of Neurological
Disorders and Stroke.
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Link between neuronal calcium channel, mutated gene that causes Huntington's disease
identified
http://www.eurekalert.org/pub_releases/2003-07/uots-lbn071603.php
DALLAS – July 17, 2003 – Abnormally high calcium levels spurred
on by a mutated gene may lead to the death of neurons associated with Huntington's
disease, an inherited genetic disorder, characterized by mental and physical
deterioration, for which there is no known cure. This discovery by researchers at UT
Southwestern Medical Center at Dallas, published in the current issue of Neuron, sheds new
light on the process that causes the selective death of neurons in the region of the brain
called the striatum. Neurons in this area control emotions, body movements and several
other neurological processes, including addiction.
Association of inosital-(1,4,5) trisphosphate receptor with HAP 1 and Huntingtin
proteins in the brain: implications for HD
Ilya Bezprozvanny, Ph. D. (University of Texas, Southwestern Medical
Center, Dallas, Texas)
Huntington's Disease (HD) is a fatal neurodegenerative
disorder. HD is caused by mutation in protein Huntington (Htt). Htt binds to another
protein, called HAP1. Type 1 inositol (1,4,5)- trisphosphate receptor (InsP3R1) is a
neronal intracellular calcium release channels and effects the calcium levels within
cells. Normal cell function requires normal calcium levels within cells. Normal cell
function requires normal calcium levels and disturbances to these calcium levels will
disrupt function. Increased calcium levels are associated with cell death pathways. Since
previous studies have shown that InsP3R1 binds to HAP1 and Htt, this project aims to
determine the importance of InsP3R1 association with HAP1 and Htt for HD pathology.
DRUG CLASS AND MECHANISM: Enoxaparin is a low molecular weight heparin. Like heparin,
enoxaparin prevents blood clots from forming. It works by blocking the action of two of
the 12 proteins in blood (factors X and II) whose action is necessary in order for blood
to clot. The FDA approved enoxaparin in 1993.