Motor Neurone Disease

Question 1

What is happening in Motor Neurone
Disease?

Answer 1

• Loss of motor neurones in spinal cord, brainstem,
  motor cortex. Muscle atrophy, loss of motor function, death.
• Typical age of onset 50-60
• Average life expectancy 5 years from onset
• Incidence c. 1/100,000, 5-10% cases familial
• ca. 2000 people requiring care at any one time in UK

Question 2

What is another name for Motor Neurone Disease?

Answer 2

Amyotrophic lateral sclerosis

Question 3

Descending Corticospinal (Pyramidal) Motor Tracts?

Answer 3

Primary motor area of cerebral cortex is where the lateral and anterior corticospinal tract start and then run past the thalamus (via the internal capsule). They then pass through the medulla oblongata via the pyramid where lateral and anterior split and pass onto the cervical spinal cord where they then continue onto the lumbar spinal cord here the lateral corticospinal tract then connects with skeletal muscle.

Question 4

Explain Motor neurone loss, the pathological changes in spinal cord, Bunina bodies and other inclusions

Answer 4

Check slide 7 for histological slides

Question 5

What risk factors are associated with MND?

Answer 5

• Age
• Playing football professionally
• Smoking
• Lead exposure
• Military service

Question 6

Causes of motor neurone cell death

Answer 6

• Non-genetic (environmental?) – 90% of cases. Cause unknown
• Familial ALS accounts for about 10% of all cases
  – Mutations in SOD-1 (superoxide dismutase) 0.5% of sporadic ALS,
  20% of FALS patients,
  – Mutations in TDP43 – 1% sporadic cases, 1.5% familial cases.
  – Mutations in fus – 1% sporadic cases, 5% familial cases,
  – Repeat expansion in c9ORF72 – 7% sporadic cases, 25% of familial
  cases.

Question 7

Why do Motor Neurones die?

Answer 7

• Why do Motor Neurones degenerate selectively?
• Can we work out the processes and then create medicines to:
  – Prevent them degenerating?
  – Slow down their degeneration?
  – Reverse their degeneration?

Question 8

What is the pathogenic mechanism for MND?

Answer 8

• it’s not fully understood but these things could contribute:

1. Viral infection
2. Excess oxidation
3. Excess Glutamate
4. Abnormal structural proteins
5. Ageing mitochondria
6. Primary gene abnormalities
7. Chronic vascular insufficiency

Question 9

Explain the figure on slide 12

Answer 9

• There is impaired glutamate intake from the astrocyte causing excess glutamate to be present. This causes glutamate excitotoxicity as the pre-synatic neurones have more glutamate available to uptake.
• The astrocyte secretion toxic factors too
• Mutation of TARDBP, FUS, SOD1 genes result in TARDBP/ FUS production and a Mutant SOD1 which results in SOD1 aggregates.
• Ca2+ results in increased oxidative stress and mitochondrial dysfunction
• Neurofilament accumulation occurs
• There is dysfunction in the Na-K (sodium-potassium pump)
• Dysfunction of axonal transport systems
• Microglia release inflammatory mediators too

Question 10

What is the link between glutamate and a failure of communication?

Answer 10

Glutamate dysregulation results in excitotoxicity

Question 11

How do neurones “talk” to each other

Answer 11

via releasing chemical neurotransmitters

Question 12

Explain excitotoxicity in motor neuron disease?

Answer 12

• Excessive stimulation of calcium-permeable glutamate receptors, due to:

1. Excessive glutamate release
2. Reduced clearance of glutamate (glutamate transported)
3. Increased sensitivity of receptors

• Increased intracellular calcium
• Resulting in Excitotoxicity

Question 13

Explain excitotoxicity in motor neuron disease (in terms of a diagram)

Answer 13

1. Increase extracellular glutamate (due to release from the presynaptic neuronal terminal)
2. This causes a decreased function and expression of glutamate transporters (as they can also be taken up by perisynaptic glial cells such as astrocytes)
3. This increased expression of postsynaptic glutamate receptors such as NMDA and AMPA receptors (in the motor neurone) results in increased intracellular calcium (and sodium)
4. This increase calcium and sodium causes neuronal death of the postsynaptic neurone as it also causes a decrease in ATP

Question 14

Potential glutamate therapies in Motor Neurone Disease

Answer 14

• Reduce glutamate release (Riluzole)
• Block glutamate receptors
• Interfere in other ways with excitotoxic processes
• Improve glutamate uptake

Question 15

What happens to glutamate transporters in mice with Motor neurone disease?

Answer 15

The glutamate transporters change in spinal cord

Question 16

Describe modelleing transporter loss in simple systems

Answer 16

1. Cultured Astrocytes

Question 17

What do disease-causing SOD1 mutants do?

Answer 17

they down regulate transporters

Question 18

Can increasing glutamate transport be neuroprotective?

Answer 18

Beta-Lactam antibiotics offer neuroprotection by increasing glutamate transporter expression

Question 19

How are glutamate transporters lost? (explain via diagram)

Answer 19

1. SOD1 proteins aggregate inside astrocytes, causing ER and mitochondria to activate the targeted proteolysis of EAAT2
2. EAAT2 is usually used to prevent the conversion of Glu into iGluR

Question 20

What are the effects of mutations of SOD1?

Answer 20

1. The main role of SOD1 is to inactivate superoxide:

2H (+ hydrogen ions) +2O2 (- oxygen ions) -> 2Oc +2H2O

However this activity is present in mutant and wild-type SOD1. Transgenic mice lacking SOD1 do not develop ALS. Therefore loss of function doesnt causes ALS.

2. SOD mutations may cause a gain of fuction.

e.g. Production of peroxynitrite. Peroxynitrite can cause inactivation of proteins (including glutamate transporter)

O2.- + NO -> ONOO- (peroxynitrite)

Question 21

What are SOD1 mutants?

Answer 21

• Aggregation prone
  – Causes proteostatic stress
• Target mitochondria – aggregate in inner mitochondrial
  membrane
  – Causes loss of energy (ATP production)
  – Oxidative stress?
  – Calcium mobilisation – activation of cell death pathways?

Question 22

TDP43 & fus

Answer 22

• Involved in RNA processing and movement of RNA in and
  out of nucleus
• Normally found in nucleus – in ALS found in aggregates
  within cytoplasm
• Is disease caused by a loss of normal function or a gain of
  toxic function?

check slide 30

Question 23

c9ORF72

Answer 23

• Repeat expansion in non-coding region of the gene
• Loss of normal function or gain of toxic function?

slide 31

Question 24

Common pathological pathways in MND/ALS

Answer 24

1. aggregates- slide 33

Question 25

Proteostasis as an abnormality in MND/ALS

Answer 25

slide 34

Question 26

TBK1

Answer 26

slide 35

Question 27

Transgenic mice allow new treatments for MND to be evaluated

Answer 27

Acrimoclomol treatment of mice which express human SOD1G93A improves survival and delays development of motor symptoms

Question 28

Problem of translation of animal data into new therapies

Answer 28

Over 200 compounds shown to work in transgenic mice. Statement up to 2016: None so far translated into positive clinical trials

Question 29

Edaravone (Radicut)

Answer 29

• Approved in US in 2017
• Proposed to work as an antioxidant, scavenger of free radicals
• 3 positive reports in transgenic animal models (SOD1 models)
• Clinical trial data published in July 2017
• MT Pharma withdraws European Marketing Application in May 2019

Question 30

Disease-modifying treatment of Motor Neuron Disease

Answer 30

• Riluzole the only licensed treatment
  – Sodium channel blocker, mechanism of action proposed to be by reducing glutamate release
  – Significant but modest benefit for survival benefit ca. 6 months on average
  – Not tolerated by everybody
  – Liver function needs monitoring.
• Discontinue if AST, ALT reach 3 x normal limits
  (AST: aspartate aminotransferase , ALT: alanine aminotransferase. Normal upper limits for ALT is 45 U/L for men and 29 U/L for women, for AST is 31 U/L for both men and women)

Question 31

Can riluzole be improved?

Question 32

Symptom management (pharmacological)- slide 42

Answer 32

Drooling:
anticholinergic drugs such as hyoscine (sublingual or transdermal), glycopyrrolate (subcutaneously), atropine (orally), tricyclic antidepressants (such as amitriptyline) and beta-blockers. Non-pharmacological approaches include
salivary gland irradiation and duct ligation.

Muscle cramps:
quinine, diazepam, phenytoin and naftidrofuryl.

Spasticity:
baclofen, dantrolene, tizanidine. Physiotherapy can be equally useful

Depression:
appropriate antidepressants include amitriptyline and SSRIs and may also relieve emotional lability and anxiety. Psychiatric guidance may also be required.

Pain:
anti-spasticity drugs, non-steroidal agents, and analgesics, using the principles of the WHO Ladder including opioids such as oral morphine or transdermal fentanyl
patches. Physiotherapy and occupational therapy interventions can help too. Symptom management

Dysphagia:
Managed in association with speech and language therapists as well as dietitians. Percutaneous Endoscopic Gastrostomy (PEG) can be used.

Communication difficulties:
Communication aids.

Limb weakness:
Splints, neck support collars, up to environmental control systems (POSSUM)

Respiratory symptoms:
Non-invasive positive pressure ventilation is recommended. Invasive ventilation (tracheostomy) is common in some countries, but not UK. Opioids can relieve dyspnoea, which is often associated with panic. This is common in the terminal stages.

Cognitive Decline:
Occurs in a substantial proportion of patients. No treatment options at present

Question 33

The Breathing Space Kit (Dyspnoea)

Answer 33

• Obtainable on medical prescription through the Motor Neurone Disease Association
• Kit includes suggestions for the management of acute respiratory symptoms and a selection of 2ml and 5ml syringes with appropriate needles. It is stocked with drugs through prescription by the GP.
  – Diazepam enema (Stesolid) 10mg x 3 (for use by carer)
  [twitching, seizure]
  – Diamorphine for injection 5mg x 3 [pain]
  – Midazolam 5mg -10mg x 3 for injection [anxiety, sedation]
  – Glycopyrronium bromide (200 micrograms X 3)
  [secretions, “death-rattle]
  – Water for injection 5mls x 3