Inhibition of Proteoglycan Synthesis Influences Regeneration of Goldfish Retinal Axons on Polylysine and Laminin

Previous studies have shown that goldfish retinal axons regenerating in vivo transport increased radioactivity in the glycosaminoglycan (GAG) components of proteoglycans (PGs). During this enhanced transport, the ratio of chondroitin sulfate (CS) to heparan sulfate (HS) was 60/40. In the present investigation, PG synthesis was inhibited during in vitro axon growth from regenerating goldfish retinal explants. Explants growing on either poly- l-lysine (PLYS) or poly- l-lysine + laminin (PLYS + LN) incorporated 35SO 4 into proteoglycan-bound CS and HS in an approximate 2/1 ratio. Addition of 4-methylumbelliferyl β- d-xyloside (β-xyloside) to the culture medium reduced the sulfate radioactivity in proteoglycan-bound CS and HS by 89 and 71%, respectively, on PLYS and by 89 and 72% on PLYS + LN. Morphological evaluation of explants revealed that β-xyloside treatment reduced both the number of retinal axons per explant and their growth rate on PLYS; on PLYS + LN this treatment reduced the number of axons, but had no effect on growth rate. This study suggests that retinal ganglion cell PGs containing CS and/or HS GAG chains are required for both the initiation and the maintenance of axonal outgrowth on artificial polycationic substrata such as PLYS, but only for the initiation of outgrowth on laminin.