PH2113 - Neurodegenerative Disease and Epilepsy 2

Question 1

What effect do growth factors have on apoptosis?

Answer 1

Growth factors phosphorylate pro-apoptotic BAD
- inhibits ability to build or oligomerise
Bcl-2 stabilises mitochondrial function
- anti-apoptotic
Unphosphorylated/free BAD normally inhibits Bcl-2

Question 2

When are caspases activated to trigger apoptosis?

Answer 2

Pro-apoptotic Bcl members on the mitochondria increase in relation to anti-apoptotic members and oligomerise
Opening of the mitochondrial permeability transition (MPT) pore
- permeabilising the outer membrane
Permits release of pro-death proteins from mitochondrial inter-membrane space
- cytochrome c

Question 3

What is the role of Apaf-1 in apoptosis?

Answer 3

Apoptotic protease-activating factor
- exists normally in cytosol as inactive monomer
Interacts with cytochrome c released from mitochondria and caspase 9
- forms the apoptosome
- transmits apoptotic signals
- activates caspase 3
- effector caspase

Question 4

What contributes to apoptosis or necrosis in the CNS?

Answer 4

Biochemical triggers of cell death
- interlinked
- withdrawal of growth factors
- reduce phosphorylation of apoptotic proteins
- DNA damage
- increased calcium
- excitotoxicity
- oxidative stress
- mitochondrial dysfunction

Question 5

How does glutamate cause excitotoxity in NMDA receptors?

Answer 5

Major neurotransmitter in the brain
Major toxin in the brain
AMPA and NMDA
- calcium channels
High levels reached in synapse
- normally cleared rapidly
- excess glutamate leads to excess calcium influx

Question 6

What effect does glutamate have on NMDA receptors and depolarisation of nerve cells?

Answer 6

Short depolarisation
- no release of Mg2+ block
Long depolarisation
- release of Mg2+ block
- influx of Ca2+
Very long depolarisation
- release of Mg2+ block
- BIG Ca2+ influx

Question 7

How does calcium ions kill cells?

Answer 7

Wide range of functions
- originates extracellularly or from intracellular stores
- normally tightly controlled and only released in short bursts

Activates proteases
- calpain
- cleaves cytoskeletal proteins
- microtubule subunits and MAPs
- phospholipases
- hydrolyses membrane phospholipids
- may disrupt neuronal membrane

Mitochondrial dysfunction
- production of adenosine triphosphate (ATP) may be stopped
- opening of APT pore
- formation of apoptosome

Causes oxidative stress
- damage to cells or tissue when generation of reactive oxygen species (ROS) > detoxifying ability
- ROS are formed as a product of biological reactions and metabolism
- mitochondria
- free radicals
- peroxides

Question 8

What is oxidative stress?

Answer 8

Excess free radical production
- normally controlled by the cell
- enzyme - superoxide dismutase (SOD1)

In excess
- damage to DNA/cell arrest
- stops cells dividing or producing new proteins
- damage to the lipid membrane
- activate enzymes
- caspases
- Bcl-2 family proteins
- mitochondrial dysfunction

Question 9

Give examples of diseases caused by mitochondrial dysfunction

Answer 9

Parkinson’s disease
- complex I dysfunction
- Lewy bodies
Alzheimer’s disease
- impaired mitochondrial biogenesis
- defective axonal transport of mitochondria
Multiple Sclerosis
- alterations in mitochondrial DNA
- abnormal level of mitochondrial enzymes
Migraine
MADD
Complex I deficiency
Leber hereditary optic neuropathy
Alper’s syndrome
Kearns Sayre syndrome

Question 10

What are the therapeutic implications of apoptosis?

Answer 10

Caspase inhibitors
- prevent the apoptotic cascade
Growth factors
- prevent apoptosis
- stimulate survival
- outgrowth
Anti-oxidants
- reduce oxidative stress
- vitamins
- getting them to the brain?
Anti-glutamatergics
- reduce excitotoxicity

Question 11

What are the common features of neurodegenerative diseases?

Answer 11

All progressive disease states
All have specific patterns of cell death in the brain with predominately affected regions
All have ‘silent’ period before disease onset whilst degeneration is occurting
Protein deposits
- proteins aggregated
Mitochondrial changes
Most have genetic components
- familial
Most have genetic risk factors
- increased susceptibility
Most have environmental causes
No predictive testing
- except Huntington’s Disease
Symptomatic treatments only
- nothing prevents or slows disease

Question 12

Which parts of the brain are affected by Huntington’s disease?

Answer 12

Striatum and related cortical structures

Question 13

Which parts of the brain are affected by Parkinson’s disease?

Answer 13

Substantia nigra and related cortical structures

Question 14

Which parts of the brain are affected by Amyotrophic Lateral Sclerosis (ALS)?

Answer 14

Spinal cord
Precentral gyrus

Question 15

Which parts of the brain are affected by Alzheimer’s disease?

Answer 15

Hippocampus and related cortical and limbic structures

Question 16

What are the features of neurodegenerative diseases?

Answer 16

Most have protein deposits
- end stage
Before deposited, soluble monomers build up into soluble oligomers
Currently believe that these oligomers are the toxic form
- not the insoluble protein deposits shown here
- fibrils

Question 17

What are the cellular defences against protein aggregation?

Answer 17

Initially sequestered in a structure
- phagophore
- closes into a double membrane vesicle
- autophagosome
- fuses with a lysosome
Regulated process of the degradation and recycling of organelles and cellular components
- organelle turnover
- bioenergetics of starvation
Could result in cell death
- excessive self-digestion
- degradation of essential cellular constituents

Question 18

Give examples of types of autophagy

Answer 18

Macroautophagy
- autophagy
- non-selective sequestration of cytoplasmic substrates
Microautophagy
- lysosomal invagiation and ingestion of minor portions of the cytosol
Chaperone-mediated autophagy
- recognition of specific substrates by the heat shock cognate 70 (Hsc 70) machinery to remove abnormal cytoplasmic organelles and components
- stress response