Mitochondria in Parkinson's disease

Question 1

What are the symptoms of PD?

Answer 1

bradykinesia
rigidity
tremor-4-7Hz- lost upon purposeful movements
these are the main motor symptoms

Question 2

What are many mutations involved in PD?

Answer 2

They are associate with some part of the ubiquitin proteasome system

Question 3

What has been strongly suggested to cause PD?

Answer 3

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

Question 4

What did an experiment do to look at the bioenergetics of PD?

Answer 4

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

Question 5

What did the experiment show about the bioenergetics of PD?

Answer 5

• 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

Question 6

Why is it important neurones receive enough energy ?

Answer 6

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

Question 7

What do deficiencies in the electron transport chain cause ?

Answer 7

generate ROS which can cause damage to the cell membrane and organelles- causes activation of apoptotic and necrotic pathways

Question 8

What was seen in the frontal cortex of PD patients?

Answer 8

exactly the same as in the subtantia nigra

- reductions only in complex 1 activity

Question 9

What toxic substances can induce PD?

Answer 9

MPTP
paraquat
rotenone- also used as an insecticide

Question 10

What is the story of barry kidston?

Answer 10

• 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

Question 11

What happened when they looked at traces of what kidston had taken and what did they do with it ?

Answer 11

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

Question 12

What happened to barry in the end?

Answer 12

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

Question 13

What happened in San Jose/Watsonville USA?

Answer 13

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

Question 14

What are the toxic symptoms of MPTP?

Answer 14

total immobility 
increased tone 
dysarthia
fixed stare, lack of blinking 
constant drooling 
cogwheel rigidity 
pill rolling- classic tremor seen in PD

Question 15

In 1983 what did they decide to do ?

Answer 15

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

Question 16

What happens when MPTP is added to non-neuronal cells

Answer 16

MTPT added to non-neuronal cells on its own it is not toxic

Question 17

What happened in vivo that causes MPTP to become toxic?

Answer 17

it gets converted to MPP+ which is toxic

-converted to MPP+ by MAO-B not A

Question 18

What did inhibitors of MAO-A and MAO-B show?

Answer 18

MAO-A inhibitors had no effect whereas MAO-B inhibitors prevented toxicity so therefore oxidation of MPTP by MAO-B is fundamental

Question 19

How does MPTP cause toxicity in dopaminergic neurones ?

Answer 19

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

Question 20

What does mazindol do ?

Answer 20

it blocks DA transport and therefore prevents MPTP toxicity

Question 21

Why are striatal neurones particularly sensitive to MPP+ ?

Answer 21

because they contain neuromelanin and the MPP+ binds to this allowing it to persist

Question 22

How does MPP+ kill neurones?

Answer 22

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

Question 23

What is another reason why MPTP is able to cause toxicity in the brain ?

Answer 23

because it can easily cross the BBB because it is not charged and there it can easily be converted to MPP+

Question 24

What does inhibition of complex 1 cause?

Answer 24

• reduction in oxidative phosphorylation
• loss of calcium homeostasis
• increased ROS
• increased lipid peroxidation

Question 25

What are the genetic models of PD?

Answer 25

LRRK2
PARKIN
PINK-1
DJ1

Question 26

What is alpha synucleins involvement in PD?

Answer 26

mutations in the gene were the first identified familial form
identical to sporadic forms, just earlier onset and faster progression

Question 27

What were the differences between mice expressing low levels of mutant alpha syn compared to those expressing high levels ?

Answer 27

low expression= mitochondria look normal

high expression= lower levels of mitochondria and they appear to be undergoing autophagy

Question 28

What does the A53T alpha-syn mutation cause?

Answer 28

it increases autophagy- too much mitochondrial turnover

- it can inhibit complex 1 causing changes in the mitochondria which precedes motor symptoms

Question 29

What is LRRK2?

Answer 29

leucine-rich repeat kinase 2 gene
mutations cause 7% of familial late onset autosomal dominant parkinsonsim cases
causes lewy bodies and nigrostriatial neuronal loss

Question 30

What are most mutations in LRRK2 and what did experiments show about it ?

Answer 30

most mutations cause increased kinase activity- gain of function mutations

experiments showed greater hoechst staining which is indicative of cell death in the mutant LRRK2 mice compared to WT and the cells demonstrating death colocallised with GFP labelling which was highlighting LRRK2

Question 31

What do mutations in parkin cause?

Answer 31

50% of familial autosomal recessive early onset -pre 45yrs PD
Nigral neuronal loss but no lewy bodies

prevent recognition/ubiquitination

Question 32

What does parkin do ?

Answer 32

it protects mitochondria from oxidative damage- may also have other functions
protects them from chemical toxins such as rotenone and MPTP

Question 33

What was seen in Tg parkin KO mice ?

Answer 33

they had impaired oxidative phosphorylation in striatal mitochondria

Question 34

What are the roles of parkin ?

Answer 34

important for regulating mitochondria by promoting mitophagy and by promoting mitochondrial elimination by ubiquitination

Question 35

What is PINK-1?

Answer 35

mitochondrial serine/threonine kinase - another kinase

involved in early onset PD

Question 36

What is the role of PINK1?

Answer 36

it is neuroprotective - protects against apoptotic cell death- mutants cant do this

Question 37

What can PINK1 mutants not do ?

Answer 37

they can’t

• restore mitchondrial membrane potential in PINK-1 KO SN neurones
• restore mitochondrial morphology in PINK1 KO SN neurones
• restore mitochondrial ROS handling in PINK1 KO SN neurones

Question 38

What is PINK1 involved in ?

Answer 38

membrane potential
structure
ability to handle ROS

Question 39

What is DJ1?

Answer 39

it is an anti oxidative stress sensor- neuroprotective

it is a chaperones- preventing alpha-syn aggregation

Question 40

What do mutations in DJ1 cause?

Answer 40

cause early onset autosomal recessive PD

Question 41

What happens to DJ1 when cells are exposed to oxidants?

Answer 41

it relocates to the mitochondria