CNS Injury And Regrowth

Question 1

What is the difference between PNS and CNS regeneration?

Answer 1

PNS - has Schwann cells which are potent promoters of neurite outgrowth
CNS - central myelin is a potent inhibitor of axon outgrowth

Question 2

Why are Schwann cells important for nerve regeneration?

Answer 2

Produce growth promoting factors
Contain cell adhesion molecules in their basal laminae that promote axon outgrowth
Form endoneural tubes in which growth cones can act as feelers (not present in CNS)

Question 3

How do oligodendrocytes prevent regeneration?

Answer 3

Express molecules in the adult that block axon regrowth
White matter is selectively inhibitory for axonal growth

Question 4

What are the cell adhesion molecules found in Schwann cells?

Answer 4

Laminin
Fibronectin

Question 5

Name the myelin associated inhibitors

Answer 5

Nogo - Nogo-A NI-250
MAG - myelin associated glycoprotein
OMgp - oligodendrocyte myelin glycoprotein

Question 6

Where is Nogo found?

Answer 6

In the endoplasmic reticulum of the oligodendrocytes

Question 7

What are the 3 isoforms of Nogo?

Answer 7

Nogo-A (NI-250) - unique to oligodendria
Nogo-B (NI-35) - absent in myelin
Nogo-C - absent in myelin

Question 8

What are the two inhibitory domains of Nogo?

Answer 8

Amino Nogo (only in Nogo-A)
Nogo-66

Question 9

What is MAG?

Answer 9

Myelin associated glycoprotein
A type 1 transmembrane protein with an ectodomain composed of five Ig like domains

Question 10

Where is the amino-Nogo domain found?

Answer 10

Although it can be detected extracellularly a significant portion is thought to have a cytoplasmic orientation

Question 11

What is OMgp?

Answer 11

Oligodendrocyte myelin glycoprotein
A member of the leucine rich repeat proteins
Linked to cell surface by a GPI anchor

Question 12

What receptors are there for prototypic myelin inhibitors?

Answer 12

PirB
NgR1
NgR2

Question 13

What does PirB bind to?

Answer 13

MAG
Nogo-66
OMpg

Question 14

What does PirB do?

Answer 14

Signals neuronal growth cones to collapse and neurite outgrowth inhibition in vitro

Question 15

What does NgR1 bind to?

Answer 15

Nogo-66
MAG
OMgp

Question 16

What does NgR1 do?

Answer 16

Important for growth cone collapse responses toward acutely presented inhibitors
Form a tripartite receptor complex with Lingo-1 and the death domain containing TNFR superfamily members p75

Question 17

Describe NgR2

Answer 17

Selective receptor for MAG
Functionally redundant with NgR1

Question 18

What are CSPGs?

Answer 18

Chondroitin sulphate proteoglycans
A family of molecules with a protein core and negatively charged GAGs attached

Question 19

What are negatively charged GAGs?

Answer 19

Electrostatically repellent for growth cones

Question 20

What releases CSPGs?

Answer 20

Hypertrophic reactive phenotypic astrocytes found in the glial scar
Are re-expressed after injury in the brain or spinal cord

Question 21

What do CSPGs do?

Answer 21

Bind to many receptors
(LAR, PTP sigma, NGR)
Ultimately activating ROCK resulting in actin depolymerisation
Inhibition of axon growth

Question 22

What happens after injury?

Answer 22

CSGP expression is rapidly upregulated by reactive astrocytes
Forms an inhibition gradient
Highest concentration is at the centre of the lesion (diminishes towards the penumbra of the lesion)

Question 23

What are the secondary changes after CNS injury?

Answer 23

Astrocytes proliferation
Activation of microglia
Formation of a glial scar
Inflammation
Invasion by immune cells
Proliferation of oligodendrocyte precursor cells

Question 24

What is the impact of the secondary changes after CNS injury?

Answer 24

Render the environment inhospitable for regeneration

Question 25

Is environment the only factor affecting CNS nerves from regenerating?

Answer 25

Although a central axon can regenerate in a peripheral nerve, the rate of elongation is inferior to a peripheral axon navigating the same path This means there are intrinsic factors affecting CNS regeneration

Question 26

What are the intrinsic factors that also limit CNS regeneration?

Answer 26

Epigenetic changes lead to limited expression of regeneration associated genes (RAGs) upon injury Most CNS neurons lose growth associated protein 43 - they are retained in the PNS though High expression of proteins suppressing axonal growth in the CNS neurons (PTEN, SOCS3, EFA-6)

Question 27

What do neural grafts do?

Answer 27

Provide a source of depleted substances Stimulate neuron growth Promote survival of neurons Replace lost structure in brain and spinal cord

Question 28

What materials are needed for neural grafting?

Answer 28

Tissue from the foetal CNS Tissue from the PNS peripheral autonomic neurons Tissue from outside the nervous system Isolated, cultured, or genetically engineered cells

Question 29

What is the significance of the foetal CNS tissue?

Answer 29

Foetal tissue develops and integrates within a host organism following grafting Functional improvements seen in animals with neurological deficits Potential treatment for Parkinson’s

Question 30

What are concerns for using foetal CNS tissue?

Answer 30

Number of nerve cells needed - considering the brain size of the recipient Identification of the region of the foetal brain required for grafting is difficult

Question 31

Explain the example of using a peripheral nerve graft on the optic nerve

Answer 31

A section of peripheral nerve is attached to the cut end of the optic nerve and the other end is inserted into the superior colliculus Retinal ganglion axon regenerates and reinnervates the superior colliculus New functional synapses are formed (When photoreceptors are activated by light postsynaptic neurons in the colliculus respond) Administration of growth factors during nerve grafts can enhance regeneration

Question 32

What are the benefits of peripheral autonomic tissue?

Answer 32

Share common heritage with nervous tissue Synthesise neurotransmitters and other chemical substances that are similar to those in the CNS These neurons are easily accessible They exhibit great potential for regrowth

Question 33

Describe isolated and cultured cells needed for grafting

Answer 33

Most cells survive a limited time in primary culture Replicating a limited amount of time or not at all Some cells continue to replicate - could potentially survive indefinitely Sustained self propagating cells in culture are called continuous cell lines (CCLs)

Question 34

How can CCLs lend to neuronal grafting?

Answer 34

Experiments have shown that they can be successfully grafted into the CNS May attenuate functional problems produced by lesions in the CNS But! Uncontrolled growth could lead to tumour formation

Question 35

What are genetically engineered cells?

Answer 35

Cells designed to synthesise a specific chemical substance or to perform a specific function before being implanted into a recipient

Question 36

What cells can be genetically engineered for grafting?

Answer 36

Foetal CNS tissue cells The hosts cells Primary cell cultures CCLs

Question 37

Which two non neuronal cells can be genetically engineered for grafting?

Answer 37

Astrocytes Fibroblasts

Question 38

What are fibroblasts engineered for?

Answer 38

To synthesise the enzyme important for the production of the brain chemical L-dopa Which is a precursor of the brain chemical Dopamine

Question 39

Why are genetically engineered cells used during CNS grafting?

Answer 39

To enhance the survival and growth rates of neurons and improve CNS function

Question 40

List some clinical trials in place to improve CNS regeneration

Answer 40

Infusion of trophic factors into the injury site (Neurotrophins NGF, BDNF) Inhibition of RhoA by cethrin Insertion of conduits rich in matrix molecules Schwann cells grafting into the site of injury Administration of antibodies to the central inhibitory environmental factors to neutralise MAIs Transplantation of foetal neurons or neural stem cells into site of injury Immunosuppression