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Molecular Basis of Disease(Sem 4) > Neurodegenerative Diseases > Flashcards

Neurodegenerative Diseases Flashcards

1
Q

What does Neurodegeneration mean ?

A

The progressive loss of neurons

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2
Q

What are neurodegenerative diseases ?

A

This is any disease which can cause a loss of neurons

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3
Q

What are the difference in causes based on the age of onset ?

A

Childhood-Rare
Earlier age of onset -Genetic contribution

Later age of onset -More likely a sporadic/idiopathic (Unkown cause )cause

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4
Q

What are some examples of Neurodegenerative diseases?

A 
Alzheimers -CNS
Huntingtons -CNS
Parkinsons -CNS
Motor Neurone disease (ALS) -PNS
Multiple sclerosis -CNS
Spinocerebellar ataxia -CNS (some PNS)
Spinal muscular atrophy -CN
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5
Q

Why are neurodegenerative diseases highly heterogeneous ?

A

This is because many of the disease names are usually umbrella terms

  1. Conditions with overlapping phenotypes but distinct causes
    for e.g -
    SCA has 25 types of mutations in different gene s

2.Some diseases are inherently pleiotropic:
Symptoms will manifest in different ways in different people

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6
Q

What pattern do neurodegenerative diseases follow ?

A

1.Molecular impairement somewhere within the cell

  1. Decreased transmission at synapse
    - Most likely at axon terminal
  2. Dying back at neurites -At the synapse (Axons and or dendrites
  3. Cell death

The distance between the nucleus and the synaptic terminals is a weak point because things need to be transported a long way.
“Achilles heel “

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7
Q

What are some common features of neurodegenerative diseases ?

A
  1. Protein aggregation (Porteinopathies )
  2. Lysosomal dysfunction
  3. Mitochondrial dysfunction
  4. Assosciated inflammation via activation of glia
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8
Q

What are the clinical challenges and research difficulties of neurodegenerative diseases ?

A

They rarely manifest overt (open) signs and symptoms until long after neurodegeneration has begun.
Early treatment is therefore impossible without early diagnosis

For CNS disorders studies of affected tissue is very difficult until death

They are all incurable

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9
Q

What is the most common neurodegenerative disease /dementia ?

A

Alzeihmers Disease

Onset is usually >65 years of age

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10
Q

What is dementia ?

A

This is the decline in memory and other cognitive functions that impair quality of life

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11
Q

What are pathological hallmarks ?

A

These are clear signs which indicate disease

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12
Q

Describe the pathological hallmarks of Alzheimer’s disease

A

1.Brain shrinkage
Shrinkage of hippocampus
Enlargement of ventricles
Cortex shrinks

2.Proteiopathies

Amyloid plaques

  • Extracellular protein aggregates
  • Enriched in A beta peptides

Neurofibrillary tangles
Also called paired helical filaments
Intracellular protein aggregates
Enriched in Tau protein

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13
Q

What is A beta and how does it form Amyloid plaques ?

A

A beta peptide is cleaved from a transmembrane protein called amyloid beta precursor protein (APP) by proteases.

Cleavage by Beta -Secretase and second enzyme called gamma-secretase and this release the A beta fragment which accumulates forming the Amyloid plaques.

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14
Q

What can cause rare early onset forms of Alzheimer’s?

A

Mutations in proteins involved in A beta peptide processing :

APP
PSEN1
PSEN2
These are both components of gamma-secretase

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15
Q

What is Tau and what can this protein cause ?

A

Tau is an intercellular proteinnormally binds microtubules in axons

Hyperphosphorylated by kinases.serine,tyrosine which displaces Tau:

Causes:
Tangles
Destabilisised Microtubules

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16
Q

What is the importance of microtubules in neurites ?

A

Neurites are projections from the cell body of a neuron

In post mitotic cells microtubules have three roles:

Structure/Shape of cell
Positioning of organelles
Motorways for transporting vesicular cargo

The distance between axon terminal and nucleus=Weak point

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17
Q

Outline the Tau hypothesis

A

In late onset AD, neurofibrillary tangles are:

seen before amyloid plaques
Well correlated with cell death and progression.

This therefore suggests that Tau is upstream A beta

18
Q

What are some other risk factors of Alzeihmers

A

Down syndrome (APP is on chromosome 21)

Gender

High Bp ,Cardiovascular disease, Diabetes

Low education

Head injury

Smoking /drinking

Genetic (APOE gene status)

19
Q

What are the symptoms of Parkinson’s ?

A

Movement disorder with four cardinal features

  1. Resting tremor
  2. Bradykinesia(slow movement)
  3. Rigidity
  4. Postural instability (falling over )
20
Q

What are the non-motor symptoms?

A 
Depression and Anxiety 
Loss of smell
Sleep disorders
Constipation 
Dementia 
Psychiatric complications
21
Q

Outline the pathological hallmarks of Parkinson’s disease

A

1.Loss of dopaminergic neurons of the substantia
(neurons that produce the neurotransmitter dopamine)
Substantia nigra =Part of the basal ganglia in the mid brain.

2.Proteinopathy
Lewy bodies
Intracellular protein aggregates
Enriched in alpha-synuclein proteins
Normal role of alpha-synuclein is poorly understood -involved in neurotransmitter release
Lewy bodies are not pathogenic but an increase in alpha-synuclein is.

22
Q

What categories of PD can have genetic causes ?

A
  1. Early/juvenile onset recessive mitochondrial conditions
  2. Late/later onset autosomal dominant PD
  3. Mutations that cause PD plus conditions
23
Q

Outline the early onset mitochondrial PD

A

Mitochondira have a finite life span due to oxidative stress
Damaged mitochondria are removed by mitophagy.
Loss of function mutations in two proteins central to activating mitophagy (PINK1/Parkin) cause EO PD )
Mutations in at least 3 other genes linked to mitochondrial stress responses also linked to EO PD.

24
Q

Outline the late onset genetic PD

A

Some genetic causes found from kindred studies like EO PD but more limited :

Including
SNCA (a-synuclein) gene amplification
-confirms that a-synuclein is pathogenic

LRRK2 gain of function

VPS35 gain of function

GBA loss of function

25
Q

How has GBA been linked to a-synuclein?

A

GBA encodes GCase (beta-glucoerebroisidase ) a lysosomal enzyme

a -synuclein is degraded in the lysosome via autophages processes

26
Q

Describe what happens to the GCase enzyme in a healthy person

A

The GCase enzyme is trafficked into the lysosome from other organelles (The Golgi and ER).In the lysosome it is able to act as the final stage of autophophy where it can degrade a-synuclein meaning there isn’t accumulation and lewy bodies and parkinsons

27
Q

Describe what happens if an individual inherits a GCase mutation GBA gene mutation?

A

They will have less activity /expression of GCase. This impairs the lysosome as there is less active GCase meaning it will not serve the last step of autophagy leading to accumulation of a-synucleins.

28
Q

What happens if there is no GBA mutation but there is an increase in a-synucleins ?

A

The excess a-synucleins will inhibit the translocation of GCase into the lysosome thus also impairing the lysosome function.It will cause an increase in even more a-synucleins.Pathogenic feedforward loop.

There will be cell death

29
Q

In what way can PD affect lysosomes?

A

Consistently leads to autophogy disregulated.

Problems in autophagy will also lead to mitochondrial dysfunction-Mitophogy

30
Q

What gene found to be linked to Parkinsons disease was unexpected

A

MAPT which codes for Tau as Tau is found in Alzheimer’s.

Neurofibrillary tangles can be found in PD brains same cells as Lewy bodies.

More NFTS in brains of LRRK2 PD
Microtubules disruption long implicated in PD.

31
Q

What are some risk factors ?

A 
Gender
Red hair 
Head injury 
Not smoking /not consuming caffeine
Herbicides,pesticides,insecticides
Exposure to metal
General anaesthesia
32
Q

What is Neuroinflammation ?

A

This is the activation of the immune system within the nervous system.
In the brain this means activation of microglia (astrocytes are also involved )

33
Q

What are reactive microglia and what changes happen ?

A

It becomes a Ameboid shape (irregular shape )
More motile
Production of cytokines
Phagocytic (able to engulf cellular debris )

34
Q

How is neuroinflammation involved in neurodegenratyion ?

A

Following neurotoxic insult there is a dying/damaged neuron and this will release factors (a-synuclein and other proetins )
This will activate the microglia which will release neurotoxic factors such as (IL-1B, TNF-a, prostaglandins) and this will trigger more cell damage /cell death.
This will create a forward loop.

35
Q

What are the two types of active microglia?

A

Protective:
Anti-inflammatory e.g. TGFBeta
-Normal removal; of unhealthy cells -homeostasis

Damaging :
pro-inflammatory e.g. IL-1, TNF-alpha
-Response to pathogens etc
(ie damage to neurons =collateral damage )

36
Q

How does ageing affect the type of active microglia we have ?

A

Ageing tends to induce a shift towards a production of damaging microglia due to changes in microglia gene expression

Neuroinflammaging

37
Q

What are some other ways in which neuroinflammation triggers neurodegeneration

A

External trigger
Environmentla toxins
Pathogens
A-beta

38
Q

What are some evidence for neuroinflammation being the cause ?

A

Many Alzheimer’s risk factors cause raised levels of circulating inflammatory cytokines.

High Bp-Cardiovascular disease, Diabetes , Smoking
Effects can cross the blood brain barrier

39
Q

What is the PD gut-to-brain theory ?

A

Lewy body pathology in gut can often preced pathology in brain

evidence that gut inflammation is sufficient to cause gut Lewy bodies

May spread to brain via the vagus nerve

May be due to microbiota
(Increased constipation)

40
Q

What other ways can ageing affect neurodegeneration?

A

Shortening of telomeres in adult stem cells

Increased reactive oxygen species

Gene expression
-Altered Wnt signalling is a big focus in AD and PD
Wnts are neuroprotective and neuromodulatory
Wnt/beta-catenin is decreased in the adult brain

Deregulated Wnt in developmental and geriatric neurological conditions

Molecular Basis of Disease(Sem 4) (28 decks)

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