2o. Brain Repair - CNS Flashcards
2 Drawbacks of the Functional Specialisation of the Brain
- Proliferative inability
- Irreversibility of intra-protoplasmic differentiation
2 Types of CNS Injury
- Ischaemic injury
- Neurodegenerative disease
Ischaemic Injury
Excitotoxic
Increased intracellular [Ca2+] that damages or kills neurones
3 Neurodegenerative Diseases
- Parkinson’s disease
Alzheimer’s disease
Multiple Sclerosis
Methods of Treating CNS Neurone Loss
- Delaying neurone loss
- Replacing lost neurones
Delaying Neurone Loss
Neuroprotection using:
- NMDA receptor blockers
- Neurotrophic factors
Trialed in neurodegenerative disease
Replacing Lost Neurones
- 3 Methods
- Neural Grafting
- Neural Stem Cells
- Stem cell grafting
Neural Grafting
- Mechanism
Grafting petal brain cells into the damaged brain
Neural Grafting
- Uses
Parkinson’s disease
Neural Grafting
- Parkinson’s Disease Method
Grafting fetal substantia nigra cells into the striatum to replace dopamine
Neural Grafting
- Parkinson’s Disease Positives (3)
- Long-term efficacy and survival
- Improved quality of life
- Improved motor function
Neural Grafting
- Parkinson’s Disease Negatives
- Most patients don’t benefit
- Ethical and logistical issues using fetal tissue
- Most grafted cells die (90%)
- Grafted tissue is not innervated or regulated
- Disease process may affect graft
- Side effects (dyskinesia)
Neural Stem Cells
- Location
Sub-ventricular zone at the anterior horn of the lateral ventricles
Neural Stem Cells
- Supply
- Olfactory bulb via the rostral migratory stream (RMS)
- Dentate gyrus granule cells in the hippocampus
Neural Stem Cells
- Location
- Role
Hippocampus
Learning and antidepressant drug action
Neural Stem Cells
- Rodents
CNS injury can induce stem cells to produce new neurones in rodents which migrate to the site of injury and differentiate
There is no evidence that such neurones have functional benefit in humans, if they are produced
Neural Stem Cells
- Use
Not useful for grafting
Stem Cell Grafting
- Induced Pluripotent Stem Cells Discovery Steps
- Cloning experiments by John Gurdon showed that a nucleus of a differentiated cell can be reprogrammed to reverse cell differentiation and produce all cells of the body
- Differentiated cells were transfected with transcription factors and formed pluripotent self-renewing cells
Stem Cell Grafting
- Pluripotent Stem Cell Differentiation in vitro vs Neural Progenitor Cell (NPC) Cell Populations in vivo
Pluripotent stem cell differentiation steps resemble neuralprogenitoy cell (NPC) populations
- Pluripotent cells resemble embryonic stem cells
- Neuroepithelial cells (NPCs) resemble neural plate cells
- Rosette-type neuroepithelial cells (NPCs) resemble neural tube cells
- Radial glial-like neural progenitor cells resemble cells in the fetal and adult brain
Stem Cell Grafting
- Parkinson’s Disease
- Embryonic stem cells
- Induced pluripotent stem cells
Triggered to differentiate into dopamine neurone progenitors and are grafted into the patient
CNS Neurone Degeneration
Distal stump of the axon degenerates following injury
CNS Neurone Regeneration In Injured CNS Environment
CNS neurones sprout after injury from the proximal stump, but CNS axons cannot regenerate >1mm
CNS neurones cannot regenerate in injured CNS environment
Experimental CNS Neurone Regeneration
CNS neurones can extend axons experimentally
CNS Neurone Regeneration in Injured CNS Environment
- 7 Reasons
- Impaired re-expression of axon growth-associated genes
- Inhibitory protein NogoA
- Astrocyte scar
- Growth inhibitors mechanisms
- Lack of growth-promoting molecules
- Lack of growth-facilitating molecules
- Axon guidance repellents
CNS Neurone Regeneration in Injured CNS Environment
- Impaired Re-Expression of Axon Growth-Associated Genes
Neurones that survive injury have impaired re-expression of axon growth associated genes
CNS Neurone Regeneration in Injured CNS Environment
- NogoA
NogoA is a myelin protein that inhibits axon branching and, by retrograde signalling, down regulates the neuronal growth programme
Anti-NogoA antibodies are shown to facilitate axon growth
CNS Neurone Regeneration in Injured CNS Environment
- Inhibitory Environment
The CNS may be an inhibitory environment for axon growth
- CNS neurones can extend their axons in vivo peripheral nerve grafts
- Axons will avoid oligodendrocytes