Research: NOGO Receptor and CRMP-2

Petratos et al. S. Limiting multiple sclerosis related axonopathy by blocking Nogo receptor and CRMP-2 phosphorylation. Brain April [Epub ahead of Print]


Multiple sclerosis involves demyelination and axonal degeneration of the central nervous system. The molecular mechanisms of axonal degeneration are relatively unexplored in both multiple sclerosis and its mouse model, experimental autoimmune encephalomyelitis. We previously reported that targeting the axonal growth inhibitor, Nogo-A, may protect against neurodegeneration in experimental autoimmune encephalomyelitis; however, the mechanism by which this occurs is unclear.












We now show that the collapsin response mediator protein 2 (CRMP-2), an important tubulin-associated protein that regulates axonal (nerve) growth, is phosphorylated (gains a phosphorous molecule that is a activation signal) and hence inhibited during the progression of experimental autoimmune encephalomyelitis in degenerating axons.

The phosphorylated form of CRMP-2 (pCRMP-2) is localized to spinal cord neurons and axons in chronic-active multiple sclerosis lesions. Specifically, pCRMP-2 is implicated to be Nogo-66 receptor 1 (NgR1)-dependent, since myelin oligodendrocyte glycoprotein (MOG)35–55-induced NgR1 knock-out (ngr1−/−) mice display a reduced experimental autoimmune encephalomyelitis disease progression, without a deregulation of ngr1−/−MOG35–55-reactive lymphocytes and monocytes.

The limitation of axonal degeneration/loss in experimental autoimmune encephalomyelitis-induced ngr1−/− mice is associated with lower levels of pCRMP-2 in the spinal cord and optic nerve during experimental autoimmune encephalomyelitis.

Furthermore, transduction of retinal ganglion cells (nerve cells in the eye) with an gene therapy viral vector of CRMP-2 (inhibitor of phosphorylated NOGO receptor) , limits optic nerve axonal degeneration occurring at peak stage of experimental autoimmune encephalomyelitis. Therapeutic administration of the anti-Nogo(623–640) antibody (inhibitor of NOGO receptor) during the course of experimental autoimmune encephalomyelitis, associated with an improved clinical outcome, is demonstrated to abrogate the protein levels of pThr555CRMP-2 in the spinal cord and improve pathological outcome.

We conclude that phosphorylation of CRMP-2 may be downstream (occurs after) of NgR1 activation and play a role in axonal degeneration in experimental autoimmune encephalomyelitis and multiple sclerosis. Blockade of Nogo-A/NgR1 interaction may serve as a viable therapeutic target in multiple sclerosis.


Reticulon-4, also known as Neurite outgrowth inhibitor or Nogo, has been identified as an inhibitor of neurite outgrowth specific to the central nervous system.  The product of this gene is a potent neurite outgrowth inhibitor that may also help block the regeneration of the central nervous system  There are three isoforms: Nogo A, B and C. Nogo-A has two known inhibitory domains including amino-Nogo, at the N-terminus and Nogo-66, which makes up the molecules extracellular (outside of the cell) loop. Both amino-Nogo and Nogo-66 are involved in inhibitory responses, where amino-Nogo is a strong inhibitor of neurite outgrowth, and Nogo-66 is involved in growth cone destruction. It has been suggested that blocking Nogo-A during neuronal damage will help to protect or restore the damaged neurons.
 


The study reports there are changes in the level of CRMP-2 during stages of nerve damage. They then show that that mice that lack CRMP-2 accumulate less neurodegeneration

Importantly they show that inhibitors of phosphorylation of CRMP-2 (blocks activation of a negative signal) can be associated with protection of nerves from damage. So if this approach could be translated to MS, then you may have a molecule to slow nerve damage. This is great however...

The data as presented and the stuff published earlier makes me wonder if NOGO-deficient mice in past studies and the CRMP-2 knockout in this study was somehow have an effect that is influencing the immune response, rather than having anything to do directly with nerve damage, was it a fluke result?


It was shown that compared to mean score of 1.9 (paralysis score. 0= good 3-4= bad) in the normal mice verses 1.0 in the knockout, but only 6 of 16 got disease so the score in the animals that got disease 16 divided by 6 = 2.3. So the mice either get disease or they don't whereas the way the data is presented it suggests that animals get less disease. However the histology presented in the paper did not support this and showed no disease. As such no infiltrates, loss of myelin and lack of nerve loss was reported, which it should not have done if it was representative of the data presented as some level of disease must be associated with some histological changes.  If the agent was just stopping nerve damage it would not of stopped the immune attack occuring.

The study just concerned itself with nerve damage and did not look for overt influences on the immune response, which could have accounted for the observed results had they looked for this properly. Notably the studies with antibody inhibition smack of an direct effect on the immune response rather than the effect being due to neurodegeneration as may also be the case for treatment with anti-LINGO-1. in earlier animal studies.

Nevertheless this offers future potential, although one would be concerned that antibodies will not get in the brain and so would not be active there. This is interesting but it is at a very early stage so do not get your hopes up to high, yet.
 

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