RESUMO
Inhibitory molecules associated with myelin and the glial scar limit axon regeneration in the adult central nervous system (CNS), but the underlying signaling mechanisms of regeneration inhibition are not fully understood. Here, we show that suppressing the kinase function of the epidermal growth factor receptor (EGFR) blocks the activities of both myelin inhibitors and chondroitin sulfate proteoglycans in inhibiting neurite outgrowth. In addition, regeneration inhibitors trigger the phosphorylation of EGFR in a calcium-dependent manner. Local administration of EGFR inhibitors promotes significant regeneration of injured optic nerve fibers, pointing to a promising therapeutic avenue for enhancing axon regeneration after CNS injury.
Assuntos
Axônios/fisiologia , Proteoglicanas de Sulfatos de Condroitina/metabolismo , Receptores ErbB/antagonistas & inibidores , Receptores ErbB/metabolismo , Proteínas da Mielina/metabolismo , Regeneração Nervosa , Animais , Axônios/efeitos dos fármacos , Cálcio/metabolismo , Células Cultivadas , Inibidores Enzimáticos/farmacologia , Cloridrato de Erlotinib , Proteínas Ligadas por GPI , Humanos , Camundongos , Proteínas da Mielina/farmacologia , Compressão Nervosa , Regeneração Nervosa/efeitos dos fármacos , Neuritos/efeitos dos fármacos , Neuritos/fisiologia , Proteínas Nogo , Receptor Nogo 1 , Nervo Óptico/efeitos dos fármacos , Nervo Óptico/fisiologia , Traumatismos do Nervo Óptico/tratamento farmacológico , Fosforilação , Quinazolinas/farmacologia , Receptores de Superfície Celular/metabolismo , Células Ganglionares da Retina/efeitos dos fármacos , Células Ganglionares da Retina/fisiologia , Transdução de Sinais/efeitos dos fármacos , Tirfostinas/farmacologiaRESUMO
In inhibiting neurite outgrowth, several myelin components, including the extracellular domain of Nogo-A (Nogo-66), oligodendrocyte myelin glycoprotein (OMgp) and myelin-associated glycoprotein (MAG), exert their effects through the same Nogo receptor (NgR). The glycosyl phosphatidylinositol (GPI)-anchored nature of NgR indicates the requirement for additional transmembrane protein(s) to transduce the inhibitory signals into the interior of responding neurons. Here, we demonstrate that p75, a transmembrane protein known to be a receptor for the neurotrophin family of growth factors, specifically interacts with NgR. p75 is required for NgR-mediated signalling, as neurons from p75 knockout mice are no longer responsive to myelin and to each of the known NgR ligands. Blocking the p75-NgR interaction also reduces the activities of these inhibitors. Moreover, a truncated p75 protein lacking the intracellular domain, when overexpressed in primary neurons, attenuates the same set of inhibitory activities, suggesting that p75 is a signal transducer of the NgR-p75 receptor complex. Thus, interfering with p75 and its downstream signalling pathways may allow lesioned axons to overcome most of the inhibitory activities associated with central nervous system myelin.
Assuntos
Proteínas da Mielina/metabolismo , Glicoproteína Associada a Mielina/metabolismo , Receptores de Superfície Celular/metabolismo , Receptores de Fator de Crescimento Neural/metabolismo , Animais , Fator Neurotrófico Derivado do Encéfalo/farmacologia , Linhagem Celular , Células Cultivadas , Embrião de Galinha , Cricetinae , Proteínas Ligadas por GPI , Gânglios Espinais/citologia , Humanos , Camundongos , Camundongos Knockout , Proteínas da Mielina/química , Proteínas da Mielina/genética , Glicoproteína Mielina-Oligodendrócito , Fator de Crescimento Neural/farmacologia , Neuritos/efeitos dos fármacos , Neuritos/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Proteínas Nogo , Receptor Nogo 1 , Testes de Precipitina , Ligação Proteica , Estrutura Terciária de Proteína , Ratos , Receptor de Fator de Crescimento Neural , Receptores de Superfície Celular/química , Receptores de Superfície Celular/genética , Receptores de Fator de Crescimento Neural/química , Receptores de Fator de Crescimento Neural/genética , Transdução de Sinais/efeitos dos fármacosRESUMO
The inhibitory activity associated with myelin is a major obstacle for successful axon regeneration in the adult mammalian central nervous system (CNS). In addition to myelin-associated glycoprotein (MAG) and Nogo-A, available evidence suggests the existence of additional inhibitors in CNS myelin. We show here that a glycosylphosphatidylinositol (GPI)-anchored CNS myelin protein, oligodendrocyte-myelin glycoprotein (OMgp), is a potent inhibitor of neurite outgrowth in cultured neurons. Like Nogo-A, OMgp contributes significantly to the inhibitory activity associated with CNS myelin. To further elucidate the mechanisms that mediate this inhibitory activity of OMgp, we screened an expression library and identified the Nogo receptor (NgR) as a high-affinity OMgp-binding protein. Cleavage of NgR and other GPI-linked proteins from the cell surface renders axons of dorsal root ganglia insensitive to OMgp. Introduction of exogenous NgR confers OMgp responsiveness to otherwise insensitive neurons. Thus, OMgp is an important inhibitor of neurite outgrowth that acts through NgR and its associated receptor complex. Interfering with the OMgp/NgR pathway may allow lesioned axons to regenerate after injury in vivo.
