Lecture 32: Neural Repair I (Cell Replacement Therapy)

Question 1

Neurogenesis

Answer 1

Development: more neurons than needed in human brain are produced by CNS

Sculpting process of brain: ~ half cells undergo apoptosis

Survived neurons -> integrate into circuitry and given survival cues

Question 2

Regions where neurogenesis persists

Answer 2

Dentate gyrus of hippocampus

Subventricular zone (SVZ)

Question 3

How does adult neurogenesis occur in olfactory bull

What can this process do in the future

Answer 3

Dentate gyrus & SVZ [neuroblasts]-> Proliferation -> initiate Differentiation + migrate down rostral migratory stream -> olfactory bulb [mature neurons] -> replacing neurons constantly lost

Mechanism of neurogenesis that can be enhanced for therapy

Question 4

List markers of neurogenesis
- proliferation
- migratory neuroblasts
- mature neuron

Answer 4

Ki67
PCNA
BrdU incorporation

PSA-NCAM
DCX

NeuN
MAP2

Question 5

Explain endogenous neural repair

Answer 5

Stressful stimuli -> increase proliferation -> migration & differentiation -> may divert cells to affected region to replace lost neurons

Question 6

Huntington’s disease and endogenous neural repair

1. Normal huntingtin protein
2. Mutant huntingtin protein
3. Evidence of neural repair

Answer 6

1. Many functions -> regulate cell signal & transcription, involved in BDNF production
2. Protein aggregate formation -> BDNF production affected -> neuron death in many cerebral cortex parts especially medium spiny neurons (striatum) [massive loss of striatum]
3. Elevated neurogenesis in SVZ adjacent to lateral ventricles [HD - huge SVZ]

Question 7

Stroke and endogenous neural repair
1. Necrotic core & ischaemia penumbra
2. Cerebral ischemia & neural repair evidence

Answer 7

1. Necrotic core -> little chance of saving , penumbra -> saved if treated rapidly, undergo more neural repair
2. Cerebral ischemia -> increase neurogenesis [new neurons located in penumbra]

Question 8

Why does increased neurogenesis not mean that repair can occur

Answer 8

1. Repair rate is slow
2. Lack of migration/differentiation of neuroblasts to correct neuronal type lost in disease
3. Survival of differentiated neurons

Question 9

List and explain diseases that deteriorate neurogenesis

Answer 9

1. Alzheimer’s disease (AD)
   - reduced hippocampal neurogenesis in dentate gyrus
   - hippocampal and cholinergic neurons of basal forebrain lost
2. Parkinson’s disease (PD)
   - dopaminergic (DA) neurons loss [substantia nigra pars compacta] -> reduce DA synapses [striatum]
   - SVZ & hippocampal neurogenesis reduced

Question 10

PD circuit (slide 830)

Answer 10

1. DA neurons (SNC to putamen) die
2. Reduce dopamine in putamen / striatum
3. Putamen: D1 neuron lower activity , D2 neuron higher activity
4. D2 stimulates a neuron which inhibits another neuron less so that neuron is overexcited
5. Overexcited neuron stimulates an inhibitory neuron
6. Inhibits neuron in thalamus -> lower activity of neuron in sensorimotor cortex -> lower activity to rest of neurons

Question 11

Classical therapies of PD (reduce symptoms)

Answer 11

1. Dopamine replacement therapy : levodopa + dopa decarboxylase = dopamine
2. Surgical interventions: deep brain stimulate, stereotactic surgeries

Question 12

What are some new lines of cell replacement therapies? (FEMXI)

What is their purpose?

Answer 12

Fetal brain cell transplantation
Embryonic stem cell therapy
Mesenchymal stem cell therapy
Xenotransplantation
Induced pluripotent stemm cell therapy

Reduce symptoms, slow down or reverse neurodegeneration

Question 13

Fetal brain cell transplantation
- method
- results
- PD application

Answer 13

• taken from aborted fetuses developing brains. DA cells isolated from ventral mesencephalon and transplanted into PD patients striatum
• transplanted neurons : integrated well & formed connections, supplied DA to striata’s neurons. Significant improvement in UPDRS scores, motor symptoms
• patients no need L-dopa for an extended time

Question 14

Pros and cons of fetal brain cell transplantation

Answer 14

Pros:
- already primed to become brain cells
- integrate well into local circuitry and survive
- les likely form tumors

Cons:
- tissue availability
- immune rejection
- ethical issues
- progress no stop

Question 15

Embryonic stem cells
- method
- results
- PD application

Answer 15

• cells harvested & expanded, further differentiated or transplanted into brain
• hESCs differentiated into DA neurons, integrated into striatum and secreted DA
• reduce some PD symptoms

Question 16

Pro and cons of embryonic stem cells

Answer 16

Pros:
- obtain quite easily
- differentiate into certain cell lineages

Cons:
- immune rejection (Heterologous transplant)
- higher tumour formation risk
- ethical issues

Question 17

Mesenchymal stem cell therapy
- define
- pros
- cons

Answer 17

Adult stem cells from bone marrow/skin/umbilical cord

Pros: autologous, adult, readily available

Cons: MSCs - not neuroectodermal lineage, benefits: maybe tropic factor release not neural

Question 18

Xenotransplantation in PD

Answer 18

Pig cells intro humans,
Benefits: trophic factor release origin

Question 19

Induced pluripotent stem cell technology
-method
-results
- PD application

Answer 19

• any adult cell induced with 4 transcription factors : turn back to pluripotent stem cell.
• can be autologous but trials done are heterologous. Not commercially available.
• dopamine higher. Patients say everyday life improved

Question 20

Pros and cons of induced pluripotent stem cells

Answer 20

Pros:
- create stem cells from differentiated adult human cells
- potentially turn into any body cell
- Lots of knowledge transferred/ translated from ESC technology
- readily available
- very little ethical issues

Cons:
- genetic manipulations required. (Potentially cancerous, trying to work around it)
- very young technology, lots to figure out

Question 21

Gene therapy (neural repair)

Answer 21

Process fo inserting genes into cell to treat a disease by therapeutic proteins expression or aberrant protein correction