Cue integration and regeneration

Question 1

What is important for determining the polarity of a growth cones response?

Answer 1

levels of intracellular cyclic nucleotides

Question 2

what is db-cAMP?

Answer 2

a membrane permeable version of cAMP
was shown to be attractive

Question 3

how can you reverse an attractive response?

Answer 3

Kt5720 can be used to inhibit activity of cAMP-dependent protein kinase (PKA)
(cAMP signals through PKA)

Question 4

What receptors signal to increase cAMP?

Answer 4

Acetyl Choline, Netrin, BDNF, NGF, NT-3

Question 5

What receptors inhibit the increase in cAMP?

Answer 5

MAG, Nogo
(also integrin binding to laminin)

Question 6

What receptors signal to increase cGMP?

Answer 6

Sema3A, EphrinB

Question 7

netrin can be attractive or repulsive..

Answer 7

attractive w/ DCC
repulsive when DCC is accompanied by Unc5

Question 8

Describe the change in axon response of retinal ganglion cells:

Answer 8

Retinal ganglion cells grow towards the tectum
initially retinal ganglion cell axons are attracted by cells in the optic nerve head

contact with laminin in the optic nerve reverses response to netrin

Question 9

What 2 inhibitory mol are implicated in the failure of CNS regeneration?

Answer 9

Myelin associated glycoprotein (MAG)
Nogo
they affect cAMP levels by activating RhoA
(RhoA affects the RhoA/Rac balance)

Question 10

Axon regeneration in the PNS:

Answer 10

1. Injury to the peripheral nerve
2. Macrophage recruitment - clear up debris (esp myelin)
3. Activation of growth related genes
4. proliferating Schwann cells promote axon regen and regrowth

Question 11

Axon regeneration in the CNS:

Answer 11

1. Injury to the central nerve
2. Prolonged clearing of myelin debris
   (the CNS is an immunologically priveliged area = macrophages don’t get in easily)
3. Debris from myelin contains cAMP inhibitory factors e.g. MAG and Nogo
   - these interfere with axon extension
4. Astrocytes and glia from a glial scar - acts as a physical barrier

Question 12

What 2 things allow the CNS axon to regenerate?

Answer 12

1. if given the appropriate substrate
   (retinal ganglion cell axons regrow if they go through sciatic nerve)
2. If the right genes are activated
   (preconditioning lesion)

Question 13

What were the preconditioning lesion experiments?

Answer 13

injuries to the peripheral branch of the DRG can regrow
Injury to CNS cannot regrow
however….
a conditioning lesion to the peripheral branch of the DRG
= lesion a few days later of central branch can regenerate

Question 14

What ligands is the NogoR activated by?

Answer 14

MAG,OMgp, Nogo

Question 15

How has this inhibitory pathway been targeted to prevent its inhibition of regeneration?

Answer 15

• Db-cAMP to elevate cAMP
  increase in cAMP activates PKA which phosphorylates and inactivates RhoA

Question 16

What does the conditioning lesion lead to?

Answer 16

a large range of transcriptional changes
- of regeneration associated genes (RAGs)

Question 17

What is ROCK?

Answer 17

Rho- kinase
is downstream to RhoA
inhibition promotes regrowth through the DC lesion

Question 17

What are 2 inhibitors of ROCK?

Answer 17

• Y27632
• C3 transferase (use a cell permeable version)

Question 18

What effect does ibuprofen have on regrowth?

Answer 18

• enhances DRG growth on myelin and GSPG (component of glial scars)
• Inhibits RhoA activation in the spinal chord injury site
  enhanced recovery distal to lesion + enhanced motor recovery

Question 19

How does ibuprofen work?

Answer 19

acts by activating the TF PPARy
this upregulates phosphatase SHP-2
- inhibits RhoA GEF
= Suppresses RhoA activation!!!

Question 20

What gene involved in growth control was also implicated in regeneration?

Answer 20

PTEN

Question 21

What did KO of PTEN allow in the optic nerve after injury?

Answer 21

KO of PTEN =
enhanced neuronal survival
+
allows retinal ganglion cells axon regrowth in adult mice

= ALLOWS REGENERATION

Question 22

What does PTEN regulate?

Answer 22

The MTOR pathway

Question 23

What is the MTOR pathway involved in?

Answer 23

oxidative responses and is a key growth pathway
in normal development the mTOR pathway is progressively inhibited as development ceases

Question 24

What does functional recovery of a CNS axon need?

Answer 24

1. Neuron intrinsic growth capacity
2. Growth supportive substrate (growth factors e.g. FGF,EGF,NF)
3. Chemoattraction