RESUMEN
Following spinal cord injury (SCI), semaphorin 3A (Sema3A) prevents axonal regeneration through binding to the neuropilin-1 (NRP-1)/PlexinA4 receptor complex. Here, we show that galectin-1 (Gal-1), an endogenous glycan-binding protein, selectively bound to the NRP-1/PlexinA4 receptor complex in injured neurons through a glycan-dependent mechanism, interrupts the Sema3A pathway and contributes to axonal regeneration and locomotor recovery after SCI. Although both Gal-1 and its monomeric variant contribute to de-activation of microglia, only high concentrations of wild-type Gal-1 (which co-exists in a monomer-dimer equilibrium) bind to the NRP-1/PlexinA4 receptor complex and promote axonal regeneration. Our results show that Gal-1, mainly in its dimeric form, promotes functional recovery of spinal lesions by interfering with inhibitory signals triggered by Sema3A binding to NRP-1/PlexinA4 complex, supporting the use of this lectin for the treatment of SCI patients.
Asunto(s)
Galectina 1/metabolismo , Neuropilina-1/metabolismo , Regeneración , Traumatismos de la Médula Espinal/metabolismo , Animales , Axones/metabolismo , Axones/patología , Galectina 1/genética , Humanos , Lectinas/metabolismo , Lectinas/uso terapéutico , Ratones Noqueados , Polisacáridos/metabolismo , Semaforina-3A/genética , Semaforina-3A/metabolismo , Médula Espinal/crecimiento & desarrollo , Médula Espinal/metabolismo , Traumatismos de la Médula Espinal/patología , Traumatismos de la Médula Espinal/terapiaRESUMEN
Chondroitin sulfate (CS) carrying proteoglycans (PGs) are widely expressed in the nervous system, and there is increasing evidence that they regulate developmental mechanisms like neurite outgrowth, axonal guidance and neuronal migration. Moreover, they can also act indirectly by organizing and/or modulating growth factors and guidance molecules. We found that chondroitin-4-sulfate is coexpressed with semaphorin 3A (Sema 3A) in the striatal mantle zone (SMZ), a nontarget region of neuropilin (Nrp)-1-expressing cortical interneurons flanking their migratory route in the subpallium. Using in vitro assays, we showed that CS PGs exert a repulsive effect on cortical interneurons, independently of Sema 3A, due to the CS side chains. We further showed that extracellular Sema 3A binds to CS. Disrupting Sema 3A-Nrp-1 signaling led migrating medial ganglionic eminence neurons to inappropriately invade the SMZ and even more so after removal of the CS side chains. Moreover, we found that soluble Sema 3A enhances the CS-induced repulsion in vitro. We concluded that CS acts as a repellent for cortical interneurons and that, in addition, CS restricts secreted Sema 3A within SMZ. Thus, both molecules act in concert to repel cortical interneurons from the SMZ during tangential migration toward the cerebral cortex.
Asunto(s)
Movimiento Celular/fisiología , Corteza Cerebral/citología , Sulfatos de Condroitina/metabolismo , Cuerpo Estriado/metabolismo , Interneuronas/fisiología , Semaforina-3A/metabolismo , Animales , Movimiento Celular/efectos de los fármacos , Condroitina ABC Liasa/farmacología , Proteoglicanos Tipo Condroitín Sulfato/genética , Proteoglicanos Tipo Condroitín Sulfato/metabolismo , Embrión de Mamíferos , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas Fluorescentes Verdes/genética , Interneuronas/efectos de los fármacos , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Microscopía Confocal/métodos , Neuropilina-1/metabolismo , Técnicas de Cultivo de Órganos , Semaforina-3A/genéticaRESUMEN
By analyzing the mechanisms that govern dopaminergic axon pathfinding from the midbrain to the striatum in embryonic rat brains, we identified neuroepithelial regions that exert chemotropic effects on mesencephalic dopaminergic axons. Explants from the pretectum and the striatum showed an attractive effect, whereas those from the midhindbrain boundary, the dorsal thalamus, and the ventral thalamus had no effect. Expression of semaphorin (Sema) 3C and Sema3F in the pretectum and of Sema3A in the striatum suggested a role for these axon guidance molecules in dopaminergic axon pathfinding. When expressed in HEK293 cell aggregates, Sema3C had an attractive effect and enhanced axon growth, Sema3A enhanced axon growth, and Sema3F had a repulsive effect on dopaminergic axons. Antineuropilin-1 and antineuropilin-2 antibodies reduced attraction by the pretectum, whereas attraction by the striatum was not affected by the presence of antineuropilin-1 antibodies. Moreover, neuropilin-1- and neuropilin-2-soluble Fc chimeras reduced the attraction by the pretectum. These results suggest that semaphorins may help to establish the dopaminergic projection from the midbrain to the striatum during embryonic development.