ABSTRACT
Netrin is a neuronal guidance molecule implicated in the development of spinal commissural neurons and cortical neurons. The attractive function of netrin requires the receptor, Deleted in Colorectal Cancer (DCC), while the receptor Unc5h is involved in the repulsive action of netrin during embryonic development. Although the expression of netrin and its receptor has been demonstrated in the adult nervous system, the function of netrin in adult neurons has not yet been elucidated. Here, we show that netrin treatment inhibited neurite outgrowth of adult dorsal root ganglion (DRG) neurons in explant and dissociated cultures. In addition, unc5h1-3 mRNAs, but not the dcc mRNA, are abundantly expressed in the adult DRG. An in situ hybridization study demonstrated that unc5h mRNAs were expressed in DRG neurons. This finding indicates that netrin/Unc5h signaling may play a role in the neurite outgrowth of adult DRG neurons and that netrin may be involved in the regulation of peripheral nerve regeneration.
Subject(s)
Animals , Male , Rats , Axons/drug effects , Cells, Cultured , Ganglia, Spinal/cytology , Gene Expression/drug effects , In Situ Hybridization , Nerve Growth Factors/pharmacology , Nerve Regeneration/drug effects , Neurites/drug effects , Neurons/drug effects , RNA, Messenger/genetics , Rats, Sprague-Dawley , Receptors, Cell Surface/genetics , Reverse Transcriptase Polymerase Chain Reaction , Time Factors , Tissue Culture Techniques , Tumor Suppressor Proteins/pharmacologyABSTRACT
Ganglioside (GG) and neurotrophic growth factor (GF) interactions in retinal neuronal and glial cells have been very little studied. Rat retinas were mechanically separated into outer (photoreceptor or PR) and inner (other neurons, IR) halves by planar vibratome sectioning and retinal Müller glial (RMG) cells were isolated and cultured according to previously published methods. The distribution on a percent molar basis of individual GG was different between the two halves: PR were dominated by GD3 (48% total GG) and contained only trace amounts (< 4%) of complex species (GT1b, GQ); IR was more typical of mature brain tissue, exhibiting substantial amounts (approximately 25%) of more complex GG. The GG profile of RMG cells was also simple, dominated by GM3 (60%) and GD1a (20%). A single addition to the medium of 500 pM bFGF or EGF for 48 hr to cultured RMG cells led to significant increases in total GG levels of 30-40%. Such treatments by both growth factors induced increases in GM3, whereas longer exposure (96 hr) of confluent RMG to these factors additionally stimulated synthesis of more complex GG. Incubations of RMG with [3H]-glucosamine showed that GG synthesis was 2-fold stimulated by growth factors. We also tested the effect of GM3 on one of the bFGF receptor transduction pathways, namely PI-3 kinase activation. To our knowledge these data constitute the first demonstration of neurotrophic factor stimulation of GG levels in cells of CNS in vitro. Such complex interactions may have particularly important consequences for neural physiopathology.
Subject(s)
Animals , Cells, Cultured , Epidermal Growth Factor/pharmacology , Fibroblast Growth Factor 2/pharmacology , Gangliosides/metabolism , Lipid Metabolism , Nerve Growth Factors/pharmacology , Neuroglia/drug effects , Neurons/drug effects , Rats , Retina/cytologyABSTRACT
La década pasada ha declarado una verdadera explosión en el número de estudios sobre los factores de crecimiento polipeptídicos a la propiedad de estos compuestos de promover la proliferación y/o diferenciación de diferentes tipos de células. Hay fuertes evidencias que plantean que durante el desarrollo o después de una lesión, las neuronas del sistema nervioso central o periférico requieren de agentes tróficos para sobrevivir y crecer. El objetivo de este trabajo es resumir algunos estudios fundamentales del factor de crecimiemto nervioso; tales como su papel vital y acción sobre las células diana, como mensajero trófico, mecanismo de acción y algunas de las tendencias actuales relacionadas con el uso del factor de crecimiento nervioso en los estudios de regeneración del sistema nervioso central