Mitochondria in Parkinson's disease Flashcards
What are the symptoms of PD?
bradykinesia
rigidity
tremor-4-7Hz- lost upon purposeful movements
these are the main motor symptoms
What are many mutations involved in PD?
They are associate with some part of the ubiquitin proteasome system
What has been strongly suggested to cause PD?
mitochondrial dysfunction associated with oxidative stress ad PINK1 and DJ1 seem to be involved in this
- could also be due to changes in mitophagy leading to mitochondrial dysfunction and the production of ros
- dysfunctional kinases are another suggestion as they disrupt phosphorylation
What did an experiment do to look at the bioenergetics of PD?
in post mortems they compared mitochondrial enzyme activities in the brains of control patients and PD patients
- they dissected out the substantia nigra and determined the protein content
What did the experiment show about the bioenergetics of PD?
- measured total mitochondrial activity (citrate synthase) and this was the same in both groups
- measured complex 1 and 3 activity (NADH cytochrome C reductase) and there was a significant reduction in PD patients
- measured complex 2 and 3 activity (succinate cytochrome c reductase) and this was analagous in both groups
- normalised complex 1 activity and it demonstrated a decline
Why is it important neurones receive enough energy ?
neurones are the most metabolically active cells in the body so they require a lot of energy which is provided to them by the mitochondria
- needed to maintain ionic gradients for neurotransmitter release so action potentials can be generated
What do deficiencies in the electron transport chain cause ?
generate ROS which can cause damage to the cell membrane and organelles- causes activation of apoptotic and necrotic pathways
What was seen in the frontal cortex of PD patients?
exactly the same as in the subtantia nigra
- reductions only in complex 1 activity
What toxic substances can induce PD?
MPTP
paraquat
rotenone- also used as an insecticide
What is the story of barry kidston?
- made his own recreational amphetamines- MPPP
- took a short cut one time and produced MPPP contaminated with MPTP
- when he injected this it caused burning sensations and then over 3 days he had developed severe bradykinesia
- in A&E diagnosed him with catatonic schizophrenia and gave him haloperidol which made it worse- also received ECT and the had no effect
- then diagnosed him with PD and gave him L-DOPA and this improved his mobility
What happened when they looked at traces of what kidston had taken and what did they do with it ?
found that he had contaminated his MPPP with MPTP
so they injected mice with MPTP and they initially developed bradykinesia and rigidity but it wore off so they didn’t think it was the MPTP that has given barry the PD
What happened to barry in the end?
he died of overdosing on heroine but he was also overdosing on his PD treatments
they then did post morterm analysis of his brain and it showed all the pathological signs of PD such as loss of the SN
What happened in San Jose/Watsonville USA?
6 young individiuals all developed rapid onset parkinsons
- they were all heroine addicts
- they all looked much older than they actually were
- they were given L-DOPA and it improved symptoms
- found out that the synthetic heroine was contaminated with MPPP and MPTP
What are the toxic symptoms of MPTP?
total immobility increased tone dysarthia fixed stare, lack of blinking constant drooling cogwheel rigidity pill rolling- classic tremor seen in PD
In 1983 what did they decide to do ?
they decided to inject MPTP into rhesus monkeys instead and this caused the development of a classic type of parkinson- behaviourally and anatomically - relieved by L-DOPA
What happens when MPTP is added to non-neuronal cells
MTPT added to non-neuronal cells on its own it is not toxic
What happened in vivo that causes MPTP to become toxic?
it gets converted to MPP+ which is toxic
-converted to MPP+ by MAO-B not A
What did inhibitors of MAO-A and MAO-B show?
MAO-A inhibitors had no effect whereas MAO-B inhibitors prevented toxicity so therefore oxidation of MPTP by MAO-B is fundamental
How does MPTP cause toxicity in dopaminergic neurones ?
even though dopaminergic neurones dont contain MAO-B, astrocytes do
- astrocytes uptake MPTP and convert it to MPP+ and then this is taken up into neurones by the plasmalemma DA transporter enabling it to accumulate and cause toxicity
What does mazindol do ?
it blocks DA transport and therefore prevents MPTP toxicity
Why are striatal neurones particularly sensitive to MPP+ ?
because they contain neuromelanin and the MPP+ binds to this allowing it to persist
How does MPP+ kill neurones?
it inhibits complex 1 of mitochondrial respiratory chain causing a rapid decrease in ATP synthesis leading to cell damage and death
- also causes oxidative stress and disruption of intracellular calcium homeostasis
What is another reason why MPTP is able to cause toxicity in the brain ?
because it can easily cross the BBB because it is not charged and there it can easily be converted to MPP+
What does inhibition of complex 1 cause?
- reduction in oxidative phosphorylation
- loss of calcium homeostasis
- increased ROS
- increased lipid peroxidation
