L5 - Cue Intergration and Regeneration Strategies Flashcards by Jack Corston

What are able to turn growth cones in cultures

Analoges of cNMPs

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Why can cAMP not turn grow cones

What must be used instead, why?

Because it is unable to cross membranes

db-cAMP must be used - membrane soluble version

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How can the response to guidance cues be reversed?

By manipulating the concentrations of IC cyclic nucleotides

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How can the dependence on cAMP by netrin be seen

Inhibit activity of cAMP-dependent protein kinase A –> NETRIN ATTRACTION NOW BECOMES REPULSION

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What can be used to inhibit PK-A

KT5720

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The effect of cAMP was ____ or _____- this suggests that ….

All or nothing!

Suggests that cAMP acts as a switch determine the polarity of the netrin response

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In the context “determining the polarity of the netrin response” what does polarity mean

Whether the response is that of attraction or repulsion

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What is the crucial balance in terms of guidance cues

Balance between [cAMP]/[cGMP]

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How can responses to a specific cue be reversed …

According to the combination of receptors

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Give an examle of how response to a cue can be manipulated according to the combination of receptors present

Netrin is attractive if using DCC

But is repulsive if DCC is accompanied by the co-receptor Unc5

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How does MAG and NOGO work

By inhibiting cAMP

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Increase in cAMP and decrease in cGMP leads to

Attraction

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Decrease in cAMP and increase in cGMP can lead to

Repulsion

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Modulators such as laminin and glutamate

Increase the levels of cAMP

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Modulators such as NO

Can increase levels of cGMP

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Modulators such as NOGO and MAG

Inhibit cAMP (decrease levels of)

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In the initial stage of the journey to the tectum RGCs are _________ by ______ expressed by cells in the optic nerve head

Netrin Attracted

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However after cotnact with _________ the ONH ________ the repsonse to ________

This acts to…..

Laminin

Reverses repsonse to netrin

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Laminin receptors are members of the

Integrin family

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When the integrin family of receptors signal what is their effect

Supression of IC cAMP

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What are the two main inhibitory molecules of CNS myelin

MAG and NOGO

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How does MAG and NOGO contribute to decreasing cAMP

Activation of RhoA leads to an increase in cGMP and a decrease in cAMP

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CNS regeneration failure is due to

Failure to activate a growth promoting program in injured neurone
Presence of inhibitory factors in CNS myelin
Formation of Glial scar that acts as a physical barrier to grwth

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CNS axons can only regenerate if (2)

Given the appropriate substrate

Right genes activated

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If you cut a peripheral branch of DRG axons, then cut central branch of the SAME DRG axons what happens

Central as well as peripheral branch regeneration

In this experimental paradigm what was the cut to the peripheral branch called?

Conditioning lesion

What is MAG

Myelin associated glycoprotein

NOGO and MAG all feed into

RhoA

What is the effect of ibuprofen on RhoA

It inhibits RhoA

What is the effect of RhoA on ROCk and on nerve fibre growth

RhoA activates ROCK which then BLOCKS the growth of nerve fibres

Activation of the NOGO receptor changes with the ....

RhoA/Rac balance

What 3 substrates are their for the NgR

MAG OMgp Nogo-A

RhoGDI/RhoGEF leads to what effect in the Rac/RhoA balance

Increase RhoA and decrease Rac

Effect of Rho activation

Activation of ROCK then growth cone collapse

What is the effect of db-cAMP on RhoA - Rock

Activation of PK-A | Phosphorylation and INACTIVATION of RhoA

How to Rho GDIs work?

Prevent dissociation of GDP from RhoA thus dampen the ability of a cell to activate

Preconditioning peripheral lesion does what

Elevate cAMP levels

What is the effect of a db-cAMP inection into the DRG prior to the lesion

Can enhance regrowth

What is more effective: conditioning lesion or db-cAMP treatment

Conditioing lesion is more effect

What was the major effects of the conditioning lsion

Turning on of regeneration associated genes

Other effects of the conditioning lesion

Global increase in trafficking of numerous intracellular components into the injured branch that is not seen without CL or with cAMP

Conditioning lesion may affect

The overall polarity of the cell

What did Fournier et al test?

Regrowth in a different injury paradigm, involved the dorsal column lesion but monitoring the regrowth of the CST

What is C3 transferase

RhoA inhibitor

What is the effect of C3 transferase

Does affect regrwoth in cultured neurone but not in vivo

What when applied at the same time as the CL does promote regrowth throguh yhr DC lesion

Y27632 | Rock inhibitor

What is clethrin What is its function

A cell permable version of C3 transferase RhoA inhibitor

What is the affect of apllying clethrin

Works in animals - entering clinical trials

What is the effect of Ibuprofen on regeneration

Enhances DRG growth on myelin and CSPGs Inhibits RhoA activation in the injury site Enhanced recovery distal to spinal cord hemi-section (CST lesion)

What was the effect of ibuprofen on motr function How was this measured

Mildly enhances recovery of motor function Using the BBB score - a multi parameter measure of motor function

Do all NSAIDs enhance regeneration

Which NSAID enhances regeneration, which one doesnt

Ibuprofen does | Naproxen doesnt

The fact that other COX inhibitors dont work suggests what

That this is not the normal NSAID pathway that is involved

How then does ibuprofen work in this situation

Activation of the transcription factor PPARy which upregulates and phosphatase SHP-2 which inhibts a RhoA GEF to supress RhoA activation

What were the controversial reuslts of the Lee et al 2010

Triple mutant mice for NOGO MAG and OMgp failed to exhibit enhanced regeneration of either axonal tract after the spinal cord injury

What did Park et al deduce about signalling in growth and in regeneration

Pathways involved in regulating cell growth may also regulate the ability of axons to grow

What were the methods used by Park et al

Test a pool of mice carrying conditional knockouts for major GROWTH CONTROL GENES: Rb, P53, SMAD4, LKB1 and PTEN for their ability to regrow the optic nerve after injury

What were the reuslts of Park et al study

PTEN KNKCOUOT significantly enhanced neuronal survival and allowed the regrowth of retinal ganglion axons in adult mice

How does PTEN enchance neuronal survivial

Regulation of the mTOR pathway Axotomised axons downregulate p-s6 which is the mTOR branch of the pathway that is effected. Shown by the deletion of TSC-1 which allowed axons togrow

Deletion of what gene enhanced regrowth of axons in the spinal cord

pten

What is the issue with developing a drug to inhibit PTEN

Most drugs made activate it - as inactivated in many cancers (tumour supressor gene)