Lecture 7: Parkinson's Disease

Question 1

Describe the timeline for genetic forms of P.D.

Answer 1

Tends to occur earlier in life (sometimes when the patients are in their 20s and 30s).

Question 2

How did James Parkinson describe the motor disorder of PD?

Answer 2

involuntary tremulous motion with lessened muscular power, in parts not in action and even when supported; with a propensity to bend the trunk forwards and to pass from a walking to a running pace, the senses and intellects being uninjured.

Question 3

What is PD?

Answer 3

Degeneration of dopamine producing neurons in the substantia nigra
The axons of the dopaminergic neurons project to the striatum (caudate + putamen) and synapse on medium spiny neurons).

Question 4

What are the cardinal symptoms of PD?

Answer 4

-Resting tremor (arm might shake at specific frequency)
-Slowness of movement (bradykinesia)
Rigidity Difficulty initiating movement (chronic muscle spasms).
- Paucity of spontaneous movements
-70% of patients eventually also develop dementia.

Question 5

How many people in the US are affected by PD (approximately)?

Answer 5

1.5 million Americans

Question 6

In PD there is a massive ____ in levels of the neurotransmitter dopamine

Answer 6

1) reduction

Question 7

What are some causes and risk factors of PD?

Answer 7

-Genetics
-Pesiticde exposure (example paraquat)
-Oxidative stress (byproduct of normal cell function)
-Age

Question 8

Describe the additional PD pathology of Lewy Bodies

Answer 8

Levy bodies appear as spherical masses that displace other cell components. They are primarily composed of fibrillar aggregates of the presynaptic protein alpha-synuclein
Majority of patients have Lewy bodies

Question 9

Describe a-synuclein

Answer 9

-Primary component of Lewy bodies
- A53T mutation: Alanine becomes a Threonine at position 53 of the alpha synuclein protein. A30P and E46K also causes PD
-Duplication of the a-synuclein gene can also cause PD
-a- synuclein appears susceptible to aggregation much like beta amyloid in AD.
1) Aggregate is toxic to cell
2) Aggergate stops healthy function
It is involved in dopamine signaling
1% of all proteins in the brain.
Function remains unclear.
But presynaptic locatilizaiton is associated with membranes and vesicles.
Mouse a-synuclien knockouts are relatively normal but suggest a role in synaptic vesicle recycling and dopamine signaling.

Question 10

How can we model PD?

Answer 10

• Transgenic mouse models
  -Using stem cells from patient to model PD
  -Neurotoxic lesions (6-OHDA, MPTP, Rotenone)

Question 11

Describe the frozen addicts: MPTP Story

Answer 11

In 1979 a grad student attempted to synthesize meperidine, a synthetic opiate and accidentally created an impurity: MPTP.
MPTP is metabolized in the brain to MPP+ and taken up specifically by dopaminergic neurons
MPP+ kills dopaminergic cells in the midbrain that project to the basal ganglia
Result: Highly advanced PD.

Question 12

What is the onset of symptoms like for normal PD patients vs. MPTP+ patients?

Answer 12

PD: slow onset 1-2 years before symptoms show
MPTP+: Overnight

Question 13

What are the symptoms of MPTP+ induced PD?

Answer 13

Burning sensation, frozen, inability to speak

Question 14

Why did MPTP end up becoming an useful tool for research purposes?

Answer 14

MPTP is quite specifically metabolized into toxic MPP+ and taken up by and kills dopaminergic neurons.
This was used to quickly induce PD in mice.

Question 15

Describe the 3 critical cellular functions that are affected by PD familial mutations.

Answer 15

Almost all genetic mutations and toxins associated with PD effect one or more of these 3 critical cellular functions:
Mitochondria
Proteasomes
Autophagy

Question 16

Describe the role of mitochondria.

Answer 16

-Generate energy (ATP) for all cells from glucose and oxygen.
-Neurons that are most most active need more mitochondria (ex. motor proteins).
-Create harmful reactive oxygen species (ROS) as a byproduct of energy production. ( This byproduct can damage mitochondria, proteins, DNA or RNA).
-ROS and other mitochondrial signals can induce cell death.

Question 17

Describe the role of proteasomes

Answer 17

-Degrade unwanted or misfolded proteins.
-Cells ‘tag’ unwanted or old proteins for proteasomal degradation by adding chains of the protein ubiquitin to them.
- Ex. a-synuclein is normally degraded by the proteasome.
(Issues with proteasomes = build up of alpha synuclein).

Question 18

Describe the role of autophagy.

Answer 18

• Degrades protein aggregates or old difunctional organelles.
  -Mitochondria only last about 20 days before they become damaged and need to be replaced.
• Mitophagy is another term for the degradation of mitochondria via autophagy.
  Impair ability to get rid of faulty mitochondria if problems with autophagy.

Question 19

Describe the L-DOPA therapy for PD

Answer 19

L-DOPA
Helps the brain make more dopamine but it is difficult to regulate the levels of dopamine so it often causes side effects such as Dyskinesia
-Increase efficiency to make more dopamine.
- Dyskinesia: uncontrollable movements due to L-DOPA
Over time however, L-DOPA becomes less effective.

Question 20

Describe Deep Brain Stimulation therapy for PD

Answer 20

a method of treatment in which a surgically implanted device delivers electrical pulses to particular parts of the brain. It is used to reduce tremor and to block involuntary movements in patients with motion disorders, by inhibiting overexcitement in the thalamus (especially in the treatment of multiple sclerosis) or the globus pallidus (especially in the treatment of Parkinson’s disease).
It is very effective for a subset of patients.
Typically those that are younger

Question 21

Current therapies do not halt or alter the disease progression, True or False?

Answer 21

True

Question 22

Potential uses of stem cells in PD

Answer 22

-Using stem cells to replace lost dopaminergic neurons.
- Using stem cells to protect vulnerable host dopaminergic neurons.
-Determining the placement of stem cells is an important aspect to consider as well.
-Should we put them where they belong?
-Should we put them in the target region.

Question 23

If you want a replacement of dopamine where do you put stem cells?

Answer 23

Substantia Nigra

Question 24

If you want nutrients/ more indirect effects of the stem cells where do you put them?

Answer 24

Target region

Question 25

What would you want to do for PD?

Answer 25

A) Make dopaminergic neurons or precursors in vitro
B) Transplant cells that can survive and terminally differentiate into dopaminergic neurons.
C) Have the neurons grow axons to the target
D) Form appropriate synaptic connections within the target.

Question 26

Describe the clinical trials of fetal tissue transplantation into the striatum in 1989 in Sweden.

Answer 26

-Initially it showed some promise
-Used transplantation of fetal derived mescenephalic tissue.
- Variable results some patients improved, some didn’t.
Long term effects: No improvement
50% of patients develop dyskinesia (pumping out too much dopamine).
There have also been cases in other studies of disease in fetal transplants (Lewy bodies)

Question 27

Explain how the long term effects of a-synuclein if something goes wrong.

Answer 27

A-synuclein acts like a prion. Misfolded versions of this start in the enteric system (gut) and works their way up.
4-5% grafted cell had the pathology
(Host Neuron to person getting transplant).

Question 28

Can neural stem cells be used to slow the progression of PD by protecting vulnerable host neurons? And if so, where should they be placed?

Answer 28

Substantia Nigra:
-for DA neuron replacement
-If you want to keep DA neurons alive
-May have problems with DA neuron axonal growth to striatum.
Striatum:
-Not ideal for DA neuron replacement because of uncontrolled DA production leading to dyskinesias
-Could provide target-derived growth factors to help maintain surviving neurons/connections

Question 29

Can stratal NSC transplantation improve motor or cognitive function in a transgenic model of PD?

Answer 29

Yes, as shown by the testing done on the mice which includes the rotarod and pole test

Question 30

Human wild type alpha synuclein ___ expressing transgenic mice

Answer 30

over expressing .
Brain overproduces this and gets Lewy bodies
A synuclein inclusions in the cortex, hippocampus, striatum, and substantia nigra.
Age related development of motor and cognitive deficits

Question 31

What is the rotarod test?

Answer 31

Mouse is injected with stem cells into the striatum (target region) and then placed on a spinning rod. The goal is for the mouse to not fall off the rod.
Measure time/max speed before they fall.
PD mouse falls quickly
Result: Stem Cells improved motor function.

Question 32

What is the pole test?

Answer 32

Put mouse on top of pole. It will try to hide by turning around and going down the pole.
PD mouse not good at this.
What is being measured:
1) How long to turn around
2) How long to go down
Stem cell mice also had improvements here

Question 33

Describe the novel object recognition (cortical dependent)

Answer 33

-Mouse in a cage with 2 identical objects.
- Let mouse explore and then 24 hrs later put them in a cage with one old and one new item.
-Mouse should explore new object.
PD mouse explores both equally.
Result: Stem cell mouse outperformed everyone
Neural stem cells differentiate than dopaminergic neurons.

Question 34

Describe the novel place recognition (hippocampal dependent).

Answer 34

Similar test to the other one, this one tests spatial memory.
Mouse put in a room with two objects.
Then mouse is taken out and placed again but this time one object was moved while the other stayed in place.
Normal Mouse: Mouse should look at more objects.
PD mouse: explores both equally.

Question 35

How do NSCs improve behavior?

Answer 35

NSCS predominately differentiate toward glial lineages.
More glia than neurons = not too many neurons made and they are dopaminergic.

Question 36

Do NSC translation alter alpha synuclein pathology?

Answer 36

No, because they found equivalent amount in both genes (alpha synuclein). Meaning that nothing had changed in the stem cells vs. control samples.

Question 37

Do NSCs alter dopaminergic innervation of the striatum?

Answer 37

Less axons from dopamine producing cells.
Stem cells increase survival and projection of dopaminergic neurons.

Question 38

What are the main key points of lecture 7?

Answer 38

-Fetal tissue transplants clinical trials have produced very mixed and inconclusive results.
-Stem cell based approaches could produce more pure populations of dopaminergic precursors but where should they be placed? The striatum or substantia nigra?
Striatal NSC transplantation of non dopaminergic precursors may improve cognitive and motor deficits by enhancing the connectivity and activity of endogenous dopaminergic cells.