Myelin-associated glycoprotein modulates apoptosis of motoneurons during early postnatal development via NgR/p75(NTR) receptor-mediated activation of RhoA signaling pathways.
Myelin-associated glycoprotein (MAG) is a minor constituent of nervous system myelin, selectively expressed on the periaxonal myelin wrap. By engaging multiple axonal receptors, including Nogo-receptors (NgRs), MAG exerts a nurturing and protective effect the axons it ensheaths. Pharmacological activation of NgRs has a modulatory role on p75(NTR)-dependent postnatal apoptosis of motoneurons (MNs). However, it is not clear whether this reflects a physiological role of NgRs in MN development. NgRs are part of a multimeric receptor complex, which includes p75(NTR), Lingo-1 and gangliosides. Upon ligand binding, this multimeric complex activates RhoA/ROCK signaling in a p75(NTR)-dependent manner. The aim of this study was to analyze a possible modulatory role of MAG on MN apoptosis during postnatal development. A time course study showed that Mag-null mice suffer a loss of MNs during the first postnatal week. Also, these mice exhibited increased susceptibility in an animal model of p75(NTR)-dependent MN apoptosis induced by nerve-crush injury, which was prevented by treatment with a soluble form of MAG (MAG-Fc). The protective role of MAG was confirmed in in vitro models of p75(NTR)-dependent MN apoptosis using the MN1 cell line and primary cultures. Lentiviral expression of shRNA sequences targeting NgRs on these cells abolished protection by MAG-Fc. Analysis of RhoA activity using a FRET-based RhoA biosensor showed that MAG-Fc activates RhoA. Pharmacological inhibition of p75(NTR)/RhoA/ROCK pathway, or overexpression of a p75(NTR) mutant unable to activate RhoA, completely blocked MAG-Fc protection against apoptosis. The role of RhoA/ROCK signaling was further confirmed in the nerve-crush model, where pretreatment with ROCK inhibitor Y-27632 blocked the pro-survival effect of MAG-Fc. These findings identify a new protective role of MAG as a modulator of apoptosis of MNs during postnatal development by a mechanism involving the p75(NTR)/RhoA/ROCK signaling pathway. Also, our results highlight the relevance of the nurture/protective effects of myelin on neurons.
Laboratorio de Neurobiología, Instituto de Investigación Médica Mercedes y Martin Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Córdoba, Argentina.
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Palandri
Laboratorio de Neurobiología, Instituto de Investigación Médica Mercedes y Martin Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Córdoba, Argentina.
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Salvador
Laboratorio de Neurobiología, Instituto de Investigación Médica Mercedes y Martin Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Córdoba, Argentina.
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Wojnacki
Laboratorio de Neurobiología, Instituto de Investigación Médica Mercedes y Martin Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Córdoba, Argentina.
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Vivinetto
Department of Pharmacology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.|Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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Schnaar
Laboratorio de Neurobiología, Instituto de Investigación Médica Mercedes y Martin Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Córdoba, Argentina.|Facultad de Psicología, Universidad Nacional de Córdoba, Córdoba, Argentina.
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Lopez
D000818:Animals; D017209:Apoptosis; D058851:GPI-Linked Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D009046:Motor Neurons / Q000378:metabolism*; D009185:Myelin Proteins / Q000235:genetics* / Q000378:metabolism*; D018992:Myelin-Associated Glycoprotein / Q000378:metabolism; D000070816:Nogo Receptor 1; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D058851:GPI-Linked Proteins; D009185:Myelin Proteins; D018992:Myelin-Associated Glycoprotein; D000070816:Nogo Receptor 1; C486580:RTN4R protein, human; D011956:Receptors, Cell Surface; D020742:rhoA GTP-Binding Protein