RESUMEN
Subplate neurons of mammalian neocortex undergo pronounced cell death postnatally, long after they have matured and become incorporated into functional cortical circuits. They express the p75 neurotrophin receptor (p75NTR), which is known to signal cell death in some types of neurons via the activation of sphingomyelinase and the concomitant increase in the sphingolipid ceramide. To evaluate the role of p75NTR in subplate neurons, they were immunopurified and cultured in vitro. Contrary to its known function as a death receptor, ligand binding to p75NTR promotes subplate neuron survival. Moreover, p75NTR-dependent survival is blocked by inhibition of ceramide synthesis and rescued by addition of its precursor sphingomyelin. Inhibition of Trk signaling does not block survival, nor is Trk signaling alone sufficient to promote survival. Thus, ligand-dependent p75NTR regulation of the ceramide pathway mediates survival in certain neurons and may represent an important target for neuroprotective drugs in degenerative diseases involving p75NTR-expressing neurons, such as Alzheimer's disease.
Asunto(s)
Supervivencia Celular/fisiología , Neuronas/metabolismo , Receptores de Factor de Crecimiento Nervioso/metabolismo , Transducción de Señal/fisiología , Animales , Anticuerpos/farmacología , Factor Neurotrófico Derivado del Encéfalo/farmacología , Bromodesoxiuridina , Separación Celular , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Relación Dosis-Respuesta a Droga , Técnicas de Inmunoadsorción , Hibridación in Situ , Neocórtex , Neuronas/citología , Neuronas/efectos de los fármacos , Ratas , Ratas Long-Evans , Proteínas Tirosina Quinasas Receptoras/metabolismo , Receptor de Factor de Crecimiento Nervioso , Receptores de Factor de Crecimiento Nervioso/antagonistas & inhibidores , Transducción de Señal/efectos de los fármacos , Esfingolípidos/metabolismoRESUMEN
Thrombospondins are a family of extracellular matrix proteins expressed throughout the developing nervous system that promote neurite outgrowth in vitro and help mediate the migration of granule cells across the molecular layer in explants of neonatal cerebellum. The receptors mediating these interactions have not previously been identified. In this study, monoclonal antibodies raised to the integrin alpha 3 beta 1 heterodimer are shown to inhibit neurite outgrowth by rat sympathetic neurons on thrombospondin-1. Alpha 3 beta 1 is found to be expressed on the cell body, neurites, and growth cones of sympathetic neurons in vitro and on sympathetic axons passing through the thrombospondin-rich outer sheath of the superior cervical ganglion in vivo, consistent with its role in mediating axon outgrowth. A receptor-ligand binding assay is used to demonstrate the direct binding of immunopurified alpha 3 beta 1 to thrombospondin-1. These results demonstrate a direct interaction between the integrin alpha 3 beta 1 and thrombospondin-1, which mediates neurite outgrowth in vitro and is likely to mediate the same interactions in vivo.