PD Causes and Disease Mechanisms

Question 1

What are the clinical symptoms of PD

Answer 1

Pre-Motor symptoms (constipation, loss of smell and depression) and Post Motor Symptoms (Hallucinations, Psychosis, Postural instability)
Motor symptoms - Bradykinesiia, Akinesia
Responsive to L-Dopa therapy

Question 2

What are the pathological features of PD

Answer 2

Lewy bodies (Perikyra) and Lewy neutrites (processes), these are intraneuronal inclusion bodies which invole asyn aggregates
Loss of dopaminergic neurons in the Substania Nigra
The neuropathology of PD appears to spread through anatomically connected regions of the brain in accordance to Braak's Model

Question 3

What is the Incidence of PD

Answer 3

1-5 in 1,000

Onset variable, early (~40s) or late (~65)

Question 4

What are other diseases with the histopathological features of PD?

Answer 4

MSA
Dementia with Lewy Body Disease
Incidental LBD

Question 5

Genetic Risk Factors?

Answer 5

The genetic risk factors are relatively uncommon (11 risk loci and 5 extra upon meta analysis)
Monozygotic and Dizygotic studies in twins - low concordance, except between mono with early onset

Question 6

Environmental Factors

Answer 6

Smoking, Coffee = protective
Industrialisation is associated with a higher incidence in population
P450 detoxification defects (CyP2D6) - 2.4 times higher risk
In Guam a higher incidence, associated with the type of meat they eat there
Environmental factors that are complex I inhibitors e.g. MPTP and rotenone

Question 7

What does MPTP stand for

Answer 7

N-Methyl-4-phenyl-1,2,3,6-tetrapyrimidine

Question 8

What is MPTP’s pathogenic mechanism in teh brain

Answer 8

It passes through the blood brain barrier thanks to its highly lipophilic characteristics. Here it is converted by monoamine oxidase B to MPTP+ –> MPP+ via spontaneous oxidation

Question 9

Describe Oxidative Stress in PD patients

Answer 9

• Increased Iron Levels
• Decreased reduced glutathione
• Decreased copper/zinc superoxide dismutase activity

Question 10

Describe proteasomal defects in PD patients

Answer 10

UPS

• Decreased proteasomal activity
• LB are ubiquitinated, suggesting an inhibited UPS pathway
• Decreased UPS activity in patients
• Injecting proteasome inhibitors in rats results in SN degeneration

Question 11

Describe the lysosomal defects in PD patients

Answer 11

• Decreased CMA proteins (LAMP2A and Hsc70)
• Decreased lysosome number lysosomal proteins (LAMP1 and Cathespin D)
• Increased number of autophagosomes, possibly due to decreased clearence by lysosomes

Question 12

In the Braak (2003) staging of PD where do the aggregates begin - and where do they spread to (name 6 stages)

Answer 12

1. Dorsal Motor Nucleus
2. Lower Rophe nuclei
3. Sub. Nigra (Motor Symptoms)
4. Temporal mesocortex
5. Temporal Neocortex
6. Neocortex
   - -> this notion suggested the idea of prion-like hypothesis, supported by grafting (li et al. 2008/2010) –> Hansen et al. 2011 –> Angot et al. 2012 –> Reyes et al. 2011/2013 - specifically reyes who showed that injection into olfactory and mapped for 72 hours demonstrated spread through anatomically connected regions, suggesting potential for environmental exposure

Question 13

Where is asyn phosphorylated?

Answer 13

Serine 129

Question 14

What are the pre-motor symptoms

Answer 14

Loss of smell
Depression
REM sleep disorder
Constipation (suggestive of environmental toxins orginating in the stomach) (supported by findings of LB in enteric nervous systems

Question 15

Motor symptoms?

Answer 15

Bradykinesia - slowness of movement
Akinesia - Loss of Movement
Tremor

Question 16

Post motor symptoms

Answer 16

Dementia (80% after having PD for 20 yrs)
Visual halucinations
Postural instability
Speed problems

Question 17

What did Tanner et al. 1999 describe

Answer 17

No correlation in twins (di or mono)
Except that for earlier onset PD there was a greater correlation between mono - this is supported by the fact that many AR mutations cause earlier onset, finding since been supported by improved genomic technology

Question 18

How many PD cases caused by LRRK?

Answer 18

2-40% in familial

1-2% overall

Question 19

How many PD cases caused by GBA?

Answer 19

9-18% in familal
6-8% overall
--> greater correlation with heterozygous GBA mutants
--> 31.4% in Ashenkazi jews
--> 4% in normal PD population from UK

Question 20

How many loci by GWAS?

Answer 20

11

Question 21

How many “risk loci” by meta analysis

Answer 21

5

Question 22

What is the issue with associating environmental risk with PD?

Answer 22

Tanner et al. 1989 - studies demonstrating regions of higher industrialisation rates were at greater risk. However,
Environmental studies, epidemiology is correlative with areas that are more industrialised where individuals are exposed to chemicals that mimic the structure of MPTP. Hypothesised that environmental factors contribute to the risk of developing Parkinson’s - however, this has yet to be proven as individual molecules and the mechanistic role they play in the pathophysiological development of hallmark PD features has yet to be assessed

Question 23

Describe the cytochrome p450 system

Answer 23

First enzymatic defence system against toxic compounds. In a typical defence system cytochrome p450 uses an oxygen, NADH and hydroxyl compound to detoxify the agent (typically a pharmaceutical compound) - as a consequence the product of this system is more reactive than the primary - thereby if it is not taken on to the next step (phase II) it can cause more damage unto lipids, proteins and nucleic acids. Induced phase I or reduced Phase II has been implicated in Parkinsons

Question 24

What is Beta-methylamino-L-alanine

Answer 24

It is a substance found in cyads that accumulated in the flying fox bat in guam that lead to a high incidence of disease that was similar to that of AD, PD and dementia. It was coined Lytico-Bodig.
If the villagers were westernised the disease would go away.

Question 25

What is the disease mechanism of Beta-methylamino-L-alanine?

Answer 25

Beta-methylamino-L-alanine is thought to induce exocitoxicity in glutamate receptors in neurons, it is thought, activation of the metabotropic glutamate receptor 5 is believed to induce oxidative stress in the neuron by depletion of glutathione (common symptom of PD). Additionally can incorproate itself into proteins, through replacing L-serine —> misfolding. Green Monkey subjects were feed BMAA with serine demonstrated 70% less beta-amyloid deposition, suggestive that serine acts as a neuroprotectant (Cox et al. 2015) - also first in vivo model of both beta amyloid and hyperphosphorylated tau

Question 26

What does MPP+ stand for

Answer 26

1-methyl-4-phenyl-pyridinium cation (spantaneous oxidation) enters neurones through uptake by dopaminergic transports --> SN are already susceptibile to OS thanks to the production of dopamine

Question 27

What are Rho 0 cells?

Answer 27

Cells with no mtDNA due to incubation with ethidium bromide

Question 28

What is the percent of mtDNA deleted in age-related controls?

Answer 28

>60%, cytochrome oxidase deficient cells - -> in PD not much greater - -> is PD therefore an accelerated ageing phenotype?

Question 29

What does MDA stand for

Answer 29

Malondialdehyde

Question 30

What does MDA do?

Answer 30

It is a lipid peroxidation product and acts as a signalling molecules Very recent research indicated that MDA acted as a signaling messenger and regulated islet glucose-stimulated insulin secretion (GSIS) mainly through Wnt pathway. The moderately high MDA levels (5 and 10 μM) promoted islet GSIS, elevated ATP/ADP ratio and cytosolic Ca2+ level, and affected the gene expression and protein/activity production of the key regulators of GSIS (Xang et al. 2014)

Question 31

What is an additional production of lipid peroxidation?

Answer 31

4-hydroxynonenal (4-HNE), which is highly toxic and can lead to more stress

Question 32

What is the significance of LRRK2 in serine129 phosphorylation

Answer 32

It is thought that LRRK2 can phsophorylate serine through its kinase abilitiy - with mutations causing constitutive activation

Question 33

What is the percentage of serine 129 phosphorylated in normal brains versus PD

Answer 33

4% versus 90%

Question 34

What is the proposed role of Asyn?

Answer 34

- - unknown - long-term maintenance of vesicle pools - directly implicated in release of dopamine through association with SNARE complex - its potentially multi-functional properties that have been proposed could be thanks to its conformational flexibility

Question 35

What are the apparently neuroprotective effects of asyn | Chandra et al. 2005

Answer 35

Mide studies deficient in cystein string protein a demonstrated asyn to protect against progressive degeneration, suggesting that asyn function is more predominant underconditions of stress CSPa is a co-chaperone, possibly they work together? CSPa aids SNARE assembly - this provides us a link between the two

Question 36

Describe its role in vesicle pools? Cabin et al. 2002 Chandra et al. 2002

Answer 36

- deficient mice generated through HR in ESCs - these mice couldnt release synpatic vesicles even following long-term stimulation - chandra however appears to dispute this notion, however they deleted exon 1+7 as aposed to 4+5 - however they found dopamine levels to be 20% lower, suggesting possible maintenance in pools, suggesting long term maintenance - isssue could be resolved with Cas/CRSPR

Question 37

What form does PD exist in the brain?

Answer 37

Monomeric (Fauvet et al. 2012)

Question 38

What is the issue with in vitro and in vivo work on asyn

Answer 38

still dont know the conformation

Question 39

What suggests that phosphorylation plays a role in aggregation?

Answer 39

Treatment with caesin kinase inhibitors and phophotases in transgenic mice demonstratedto prevent aggregation

Question 40

Describe li et al.'s work

Answer 40

Progressive asyn in gradts, in 12 year old graft there was 40% asyn and 1.9% LW In 16 yo graft there was 80% asyn and 5% LB (3% LB in PD)

Question 41

Describe Chu et al. 2007

Answer 41

asyn increases with age, at 65 in a normal individual there will be 4.5 X 10-4 These grafts, following the linear graph Chy et al. created should have had no asyn

Question 42

Describe Hansen et al.'s 2011

Answer 42

1. Fluorescent tags + co-culture, where the tags driving the transmission 2. Indirect staining between co-culture of mouse (dont express asyn) and human, using abs specific for human and mouse - confirmed transmisiosn - also confirmed human as donor 3. Truncated GFP and non-truncated - demonstrated seeding effect

Question 43

Describe Angot et al. 2012

Answer 43

Generated a model in hopes of recapitulating the transplantation paradigm by li et al. 1. AAV injected "host" + grafted neurons (all in mouse brain) 2. high transfer rate, with some discrepencies suggesting a dynamic process of degradation 3. Visualisation of the mouse grafted neurons demonstrated an epicentre of human and then total ab stain surrounding, seeding for both mutant and WT

Question 44

Luk et al. 2012

Answer 44

- -> confirmed spread of asyn in PFF, performed in both transgenic and non-transgenic, demosntrating the potenital for PD to be encouraged by genetic risk factors, or simply environmental exposure - -> saw pathological spread, despite injections in striatum and cortex - -> further supported by other primary culture works which demonstrated PFF to recruit endogenous asyn