GANGLIOSIDE AND NEUROTROPHIC GROWTH-FACTOR INTERACTIONS IN RETINAL NEURONAL AND GLIAL-CELLS

Ganglioside (GG) and neurotrophic growth factor (GF) interactions in r etinal neuronal and glial cells have been very little studied. Rat ret inas were mechanically separated into outer (photoreceptor or PR) and inner (other neurons, IR) halves by planar vibratome sectioning and re tinal Muller glial (RMG) cells were isolated and cultured according to previously published methods. The distribution on a percent molar bas is of individual GG was different between the two halves: PR were domi nated by GD3 (48% total GG) and contained only trace amounts (< 4%) of complex species (GT1b, GQ); IR was more typical of mature brain tissu e, exhibiting substantial amounts (similar to 25%) of more complex GG. The GG profile of RMG cells was also simple, dominated by GM3 (60%) a nd GD1a (20%). A single addition to the medium of 500 pM bFGF or EGF f or 48 hr to cultured RMG cells led to significant increases in total G G levels of 30-40%. Such treatments by both growth factors induced inc reases in GM3, whereas longer exposure (96 hr) of confluent RMG to the se factors additionally stimulated synthesis of more complex GG. Incub ations of RMG with [H-3]-glucosamine showed that GG synthesis was 2-fo ld stimulated by growth factors. We also tested the effect of GM3 on o ne of. the bFGF receptor transduction pathways, namely PI-3 kinase act ivation. To our knowledge these data constitute the first demonstratio n of neurotrophic factor stimulation of GG levels in cells of CNS in v itro. Such complex interactions may have particularly important conseq uences for neural physiopathology.