STIMULATION OF ENDOGENOUS GANGLIOSIDE METABOLISM BY NEUROTROPHIC GROWTH-FACTORS IN CULTURED RETINAL MULLER GLIA

Neurotrophic factors such as basic fibroblast and epidermal factor (bF GF and EGF respectively) are known to influence many differentiative p rocesses, but their effects on an important group of glycosylated sign alling molecules involved in neural differentiation, the gangliosides, are unknown. To study this possibility, we analyzed the effects of ex ogenously added bFGF and EGF upon the amount and type of endogenous ga ngliosides extracted from purified cultures of retinal Muller glial ce lls. A single addition of 500 pM bFGF or EGF for 48 h to such cultures led to significant increases in total ganglioside levels of 30-40%. A nalysis of the distribution of specific ganglioside species within con trol and growth factor treated cells revealed that, the precursor form GM3 formed 50-00% of the total ganglioside pool in all cases, the rem ainder being composed principally of GD1a (20%) with no detectable tri -sialogangliosides. Growth factor treatment for 48 h led to increases mainly in GM3, whereas longer exposure (96 h) of confluent glial cultu res to growth factors additionally stimulated synthesis of GT1b. Furth ermore, growth factor-induced ganglioside increases were dose-dependen t, reaching maximal stimulation at 500 pM for bFGF. Incorporation of r adiolabelled [H-3]-glucosamine into glial cultures showed that ganglio side synthesis was stimulated a-fold by the growth factors. To our kno wledge these data constitute the first demonstration of neurotrophic f actor stimulation of ganglioside levels in cells of central nervous sy stem origin. Such complex interactions between peptide growth factors and gangliosides, if occurring in vivo, could have important consequen ces for retinal cell behaviour. (C) 1996 Wiley-Liss, Inc.