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Don’t Forget It: Thrombin Related Alzheimer's Disease
Lincoln SMART Team: Eric Auchter, Vanessa Heck, Danielle Niquette, Jenna Schuh, Kira Schultz, Jen Stenson, Brandon Vance
Teacher: Mrs. Ann Hansen, Lincoln High School, Manitowoc, WI
Mentors: Dr. Sally Twining, Professor and Malathi Narayan, Graduate Student,
Department of Biochemistry Medical College of Wisconsin, Milwaukee, WI
Abstract
II.
Alzheimer’s disease is an incurable and terminal
neurodegenerative disorder and is the most common form
of dementia. There are 5.2 million people in the United
States living with Alzheimer’s and it is projected that 10
million baby boomers will eventually develop the disease.
One of the three major competing hypotheses explaining
Alzheimer’s involves hyperphosphorylation, the addition of
more than one phosphate group, to tau, an intracellular
microtubule protein. Thrombin is a serine protease involved
in the final step of blood coagulation and is normally present
in the brain’s neurons, where it cleaves tau. It is necessary
for thrombin to cleave tau in order to prevent clumping of
the microtubules for normal neuron function. In Alzheimer’s
patients, extracellular thrombin binds and cleaves PAR-1, a
protease activated receptor embedded in the cell
membrane. The interaction between thrombin and PAR-1
exposes a peptide sequence that activates kinase enzymes
adding phosphate groups to tau. This leads to tau
hyperphosphorylation and tangled microtubules because
intracellular thrombin is unable to cleave the phosphorylated
tau. Scientists are interested in studying the binding of
thrombin to PAR-1 because this interaction is a possible
therapeutic target for developing treatments for Alzheimer’s
and other neurodegenerative disorders.
I.
Introduction
Normal vs. Alzheimer’s Disease Thrombin-Tau Interactions
Tau, a microtubule
associated protein, is
normally cleaved by
intracellular thrombin.
This results in ordered
and stabilized
microtubules and normal
neuron function.
Normal
3bef.pdb
Alzheimer's Disease
Membrane
Kinase
PAR-1
Extracellular thrombin attaches
to PAR-1 and cleaves the
N-terminal peptide.
III.
The resulting exposed
peptide sequence binds
PAR-1 and activates
kinase enzymes.
Phosphate group
Kinase enzymes add
phosphate groups to tau.
Laboratory Evidence: Effect of Thrombin on Tau
Hypothesis: Excess thrombin results in tau aggregation.
Experimental Procedure:
1. Nerve cells are grown on a slide.
2. The primary antibody to tau is added
and binds each cell.
Alzheimer's disease affects the elderly,
causing memory loss and dementia.
Thrombin, a serine protease, is found in
high levels in the brains of Alzheimer’s
disease patients. There it binds PAR-1, a
membrane embedded receptor, and
triggers a multistep process that leads to
the tangling of a microtubule protein, tau.
The resulting tau tangling is one
hypothesis that explains the destruction
of neurons and progression of
Alzheimer’s disease.
Microtubules form support
structures for neurons and assist
in transporting substances into
and out of the cells.
3. A secondary antibody containing a
fluorescent label is added and binds to
the primary antibody.
Data:
Antibodies to:
Total Tau
Phosphorylated Tau
Conclusion:
• Without thrombin, tau is
not phosphorylated, as
shown by the absence of
fluorescent spots in the top
row.
• In the presence of
thrombin, tau is
phosphorylated, leading to
tangling, as shown in the
bottom row.
IV.
Thrombin is unable to cleave
phosphorylated tau because
the phosphorylated residues
mask the sites normally
recognized by thrombin.
Tangled microtubules
result in abnormal
neuron function.
Summary
Thrombin, a protein normally found in the brain’s
neurons, is present outside the brain cells in
Alzheimer’s disease. Thrombin cleaves the PAR-1
receptor and initiates a signaling process that
eventually results in hyperphosphorylation of tau.
Intracellular thrombin, normally responsible for
cleaving tau, is unable to do so. The resulting tau
tangling progressively destroys the brain’s
neurons and leads to death.
References:
• Gandhi, P.S., Chen, Z., Mathews, F.S., Di Cera, E. (2008). Structural
Identification of the Pathway of Long-range Communication in an Allosteric
Enzyme. Proceeding of the National of Academy of Science USA 105: 18321837
• www.noelderabuse.com (Section 1 Photograph)
• www.afar.com (Section 2 Photograph)
• Suo, Z., Wu, M., Citron, B.A., Palazzo, R.E., Festoff, B.W. (2003). Rapid Tau
Aggregation and Delayed Hippocampal Neuronal Death Induced by Persistent
Thrombin Signaling. The Journal of Biological Chemistry, ASBMB (Section 3
Photograph)
• 3BEF.pdb Gandhi, P.S., Chen, Z., Mathews, F.S., Di Cera, E. (2008)
Structural identification of the pathway of long-range communication in an
allosteric enzyme. Proc.Natl.Acad.Sci.Usa 105: 1832-1837
A SMART Team project supported by the National Institutes of Health (NIH) –
National Center for Research Resources Science Education Partnership Award
(NCRR-SEPA)