Parkinson's Disease in Relation With Alpha-synuclein...

Neurological diseases have eluded and frustrated both scientist and
physicians for years.  Little is know about the functions of the brain,
and therefore, knowledge about neurological diseases is limited.  One
such disease, Parkinson's, has recently found its way back into the news
thanks to Michael J. Fox and is being looked at more closely.  However,
the effects of Parkinson's and its exact pathological function have been
studied for years.

Since Parkinson's disease is so elusive and difficult to diagnose
before the disease sets in, an early detection device was first looked at.
It was found that there was a genetic effect.  Genetic markers segregated
with the disease in a family study of Italians.  It was found that this
gene is located on the long arm of chromosome 4 and is the alpha-
synuclein gene.  Through familiar examinations with genetic markers, the
gene was found to be in 4q21-q22 region.  Alpha-synuclein is a
presynaptic nerve terminal protein and was originally associated with
Alzheimer's disease.

However, through further familiar studies, it was found that the majority
of phenotypes of Parkinson's disease also had the alpha-synuclein gene
of an earlier member with the disease (Polumeropoulos, Lavedan, Leroy,
et al. 1997).

Other studies were done to make sure that certain mutations in
this gene was directly associated with Parkinson's.  In zebra finches, the
homolog to synuclein, synelfin, is thought to be involved in learning
processes and memory.  Also in rats, three members of the synuclein
family have been identified at the time of this study.  These genes bear a
very close resemblance to human synuclein, 95% actually. These
proteins were also found in abundance in the olfactory bulb and tract,
hippocampus, dentate gyrus, habenula, amygdala, and piriform cortex,
and trace amounts in other areas.  This coincides directly with the loci a
Lewy bodies found in human patients (Polumeropoulos, Lavedan,
Leroy, et al. 1997).

Lewy bodies are a defining characteristic of Parkinson's disease.
They are also found in patients with Alzheimer's, but not in the same
abundance.  A study was performed in 1997 to determine if alpha-
synuclein was involved in the formation of Lewy bodies since recent
studies of the same time began linking Parkinson's to this protein.  Six
patients diagnosed with Parkinson's disease were chosen for the study.
They were injected with various antibodies, affinity purified, anti-alpha-
synuclein serum PER2 and PER1, which stained alpha-synuclein
proteins.  There was a strong immunological response in the brainstem-
type and cortical Lewy bodies in the patients with Parkinson's.  Unlike
the previous familiar studies, none of these patients were related;
therefore, the formation of Lewy bodies is not particular to one type of
alpha-synuclein, but it was still involved in all the formations.  With
these results, it is reasonable to hypothesis that Parkinson's disease is
directly related to alpha-synuclein (Spillantini 1997).

Now that it was known that alpha-synuclein is directly involved
with Lewy bodies and with Parkinson's disease, it was needed to know
what mutations of the protein caused the greatest change. One such
experiment was performed using the typical familiar variations of the
gene: the wild type, A53T, and A30P.  These variations of genes were
extracted from the human gene library and were placed in bacterial
genomes through an unnamed vector.  The genes were extracted in
cDNA and the genes were placed in the bacteria as the following: wild
type, A53T, A30P, and A53T/A30P.  The bacteria would make the
protein and carry on.  At various intervals the solutions were
centrifuged and measurements of aggregates were made.  The
aggregates were fibrillar beta-sheets, which are now known to be a
critical step in the formations of Lewy bodies (Narhi, Wood, Steavenson,
et al.  1999).

The results of this experiment produced results that confirmed the
original suspicions that mutations in alpha-synuclein led to the
formations of Lewy bodies.  There was a lag time, however, that the
proteins went through before they began to aggregate.  Under the
conditions tested, which were various times measured at 25 degrees
Celsius, the wild type lag time was 280h, the A30P was about 180h, and
A53T was about 100h.  It is obvious from this that the A53T mutation
causes the earliest aggregation and therefore, the earliest formations of
Lewy bodies.  It was also noted that shaking the test tubes made the
aggregation occur faster.  This was just noted as another possible path
for the disease, however, it was not explored further (Narhi, Wood,
Steavenson, et al.  1999).

Mutations in alpha-synuclein is noted in familiar cases of Parkinson's
disease; however, in cases that are not related the disease in many times
linked with accumulations of the wild type alpha-synuclein. Because of
this, further study was done into the effects of accumulation of
alpha-synuclein, particularly on dopaminergic cells.  In an experiment
performed in February of 2000, mice were induced to display various
productivity of human wild type alpha-synuclein (the exact mechanisms
of this induction were not mentioned).  The mice with the highest
expression of human wild type aplha-synculein experienced the greatest
effect.  More cells in these mice had intraneuronal inclusions, both
nuclear and cytomplasmic, that were reactive with an antibody for human
alpha-synuclein, but not with mice.  These cells that were most effected
were also found in the regions of the brain that is most effect when a
patient has Parkinson's disease (Masliah, Rockenstein, Veinbergs, et al.
2000).

It is also known that patients with Parkinson's disease have a
degeneration of dopaminergic neurons. To test this hypothesis and see
if it correlated with the results received from the induction of wild type
human alpha-synuclein, stains were introduced for both human
alpha-synuclein and dopamine.  The concentrations of these
dopaminergic neurons were less in the mice with a higher expression
rate, and also the concentration of dopaminergic neurons was less in the
areas of the brain known to be most affected in Parkinson's disease.
These findings substantiate, again, the hypothesis that accumulation of
alpha-synuclein, in this case wild type, is directly related to Parkinson's,
and further more, the degradation of dopaminergic neurons is also
related to it (Masliah, Rockenstein, Veinbergs, et al. 2000).

These findings definitely progressed the knowledge of Parkinson's
disease, however, the exact pathway and growth of the disease is still
unknown.  Studies of this nature on humans is completely unfeasible,
not to mention inhumane.  Therefore, another method of study must be
devised for these results.  Feany and Bender looked for a new method
by inducing Parkinson's disease in Drosophila or fruit flies (Feany and
Bender 2000).

They used the previous findings and decided to induce the
mutations of alpha-synuclein in fruit flies. They used the wild type,
A30P, and A53T variations of the gene.  With inducing these genes
through the use of a vector, the scientists were only looking to see if
they could induce a disease resembling Parkinson's.  To determine this,
they ran several tests.  First, a stain was used that targeted
dopaminergic neurons and tested at intervals of 30 to 60 days.  With the
wild type, the neurons were decreased or gone, but in the A53T and
A30P mutations, the nerons were all completely gone.  They tested this
method with another marker and the same results occurred (Feany and
Bender 2000).

Other reasons they believed they induced a Parkinson's like disease in
the flies is that there were other symptoms.  There was no lose of brain
volume, therefore the neurological disorder was not caused by complete
destruction.  Also, there was no difference in any of the samples when
stained for serotonin. This means that only neurons with dopamine were
being effected.  Microscopic analysis also showed that there were
formations that appeared in every physical sense to be the same as the
Lewy bodies found in human patients.  They also ran tests for motor
skills, the speed at which the flies flew away from danger, and this
decreased as followed: A53T and wild type degenerated faster but A30P
degenerated the fastest.  All of these results concurred that the
scientist were able to create a disease that very closely resembled
Parkinson's in flies (Feany and Bender 2000).

There have been giant leaps in the study of Parkinson's disease
over the past few years.  We now know major functions of the disease
and what genes are involved, but the exact mechanism of the disease is
still not known.  With the advancements now, studies within the fruit
flies have opened the door to our understanding of the methodology
and pathology of this disease.

Works Sited

Feany, Mel B. and Bender, Welcome W.  "A Drosophila Model of
Parkinson's Disease."   Nature, 23 March 2000.

Masliah, Eliezer, Edward Rockenstein, Isaac Veinberg, et al.
"Dopaminergic Loss and Inclusion Body Formation in Alpha-Synuclein
Mice: Implications for Neurodegenerative Disorders."
Science, 18 February 2000.

Narhi, Linda, Stephen J. Wood, Shirley Steavenson, et al. "Both
Familial Parkinson's Disease Mutations Accelerate Alpha-Synuclein
Aggregation." The Journal of Biological Chemistry, 2 April 1999.

Polymeropoulos, Miheal H. Christian Lavedan, Elisabeth Leroy, et al.
"Mutation in the Alpha- Synuclein Gene Identified in Families with
Parkinson's Disease." Science, 27 June 1997.

Spillantini, Maria Grazia.  "Alpha-Synuclein in Lewy Bodies." Nature,
28 August 1997.

http://www.biol.sc.edu/~elygen/emery.html

***************

[log in to unmask]