The mammalian brain and spinal cord do not regenerate after injury. It is believed that a predominance of inhibitory molecules, particularly in myelin, is responsible for this effect and that blocking these molecules would allow regeneration. Until recently a precise molecule(s) in myelin that could account for this inhibition had not been identified. Myelin associated glycoprotein (MAG), a glycoprotein specific to both CNS and PNS myelin, has been shown by the applicants to potently inhibit axonal outgrowth from all post-natal cerebellar and adult dorsal root ganglion (DRG) neurons but to promote outgrowth from newborn DRG neurons. In addition, MAG can account for a majority of the inhibitory properties of CNS myelin in vitro and has been shown to inhibit regeneration in vivo. Furthermore, a soluble form of MAG, MAG-Fc (the extracellular domain of MAG fused to the Fc portion of IgG) binds specifically to both cerebellar and DRG neurons via a sialo-glycoprotein and can inhibit axonal regeneration. Importantly, desialyation of neurons reverses inhibition, but because MAG mutated at its sialic acid recognition site, Arg118, still inhibits outgrowth when expressed by cells, implies there are two inter-dependent yet distinct epitopes on MAG; a sialic acid binding epitope and neurite inhibition epitope. The overall goals of this proposal are to characterize the interaction of MAG with its receptor and, using this information, test agents likely to block/disrupt the interaction and so prevent MAG's inhibition of spinal cord regeneration. First, using mutated forms of MAG and a panel of MAG monoclonal antibodies, the inhibition site will be precisely mapped. Second, MAG mutants and antibodies, identified in this way, will be tested for their ability to reverse the inhibition of wildtype MAG first in culture (MAG expressed by CHO cells) and then in vivo (by addition of the antibodies/mutated MAG to injured spinal cord). Also, in transgenic mice the effect of mis-expressing MAG in the PNS during normal regeneration will be assessed. Third, using MAG-Fc, MAG-binding proteins from neurons that are inhibited and that are promoted will be identified by molecular weight and compared. Antibodies will be raised to these proteins and tested for their ability to reverse the inhibition/promotion of neurite outgrowth. Accomplishment of these specific aims will advance our understanding of, not only inhibition of neurite outgrowth with a view to preventing such an inhibition after injury, but also of how the same molecule can, depending on the age and type of neuron, have opposite effects.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
3R01NS037060-02S2
Application #
6145943
Study Section
Neurology B Subcommittee 2 (NEUB)
Program Officer
Chiu, Arlene Y
Project Start
1997-12-04
Project End
2001-11-30
Budget Start
1998-12-01
Budget End
1999-11-30
Support Year
2
Fiscal Year
1999
Total Cost
Indirect Cost
Name
Hunter College
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
City
New York
State
NY
Country
United States
Zip Code
10065
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Siddiq, Mustafa M; Hannila, Sari S; Carmel, Jason B et al. (2015) Metallothionein-I/II Promotes Axonal Regeneration in the Central Nervous System. J Biol Chem 290:16343-56
Hannila, Sari S; Siddiq, Mustafa M; Carmel, Jason B et al. (2013) Secretory leukocyte protease inhibitor reverses inhibition by CNS myelin, promotes regeneration in the optic nerve, and suppresses expression of the transforming growth factor-? signaling protein Smad2. J Neurosci 33:5138-51
Perdigoto, Ana Luisa; Chaudhry, Nagarathnamma; Barnes, Gregory N et al. (2011) A novel role for PTEN in the inhibition of neurite outgrowth by myelin-associated glycoprotein in cortical neurons. Mol Cell Neurosci 46:235-44
Deng, Kangwen; He, Huifang; Qiu, Jin et al. (2009) Increased synthesis of spermidine as a result of upregulation of arginase I promotes axonal regeneration in culture and in vivo. J Neurosci 29:9545-52
Siddiq, Ambreena; Aminova, Leila R; Troy, Carol M et al. (2009) Selective inhibition of hypoxia-inducible factor (HIF) prolyl-hydroxylase 1 mediates neuroprotection against normoxic oxidative death via HIF- and CREB-independent pathways. J Neurosci 29:8828-38
Aminova, Leila R; Siddiq, Ambreena; Ratan, Rajiv R (2008) Antioxidants, HIF prolyl hydroxylase inhibitors or short interfering RNAs to BNIP3 or PUMA, can prevent prodeath effects of the transcriptional activator, HIF-1alpha, in a mouse hippocampal neuronal line. Antioxid Redox Signal 10:1989-98
Hannila, Sari S; Filbin, Marie T (2008) The role of cyclic AMP signaling in promoting axonal regeneration after spinal cord injury. Exp Neurol 209:321-32