Moderate repulsive effects of E-unit-containing chondroitin sulfate (CSE) on behavior of retinal growth cones

Abstract

Chondroitin sulfate (CS), the carbohydrate chain of chondroitin sulfate proteoglycans, is involved in neuronal circuit formation during development. CS shows great structural diversity with combination of disaccharide units of different structure (A-, C-, D-, or E-unit). However, whether its structural diversity contributes to pathway formation remains unclear. We chemically coupled the reducing end of various types of CS to the amino group of phosphatidylethanolamine (lipid-derivatized CS, CS-PE) and established an in vitro time-lapse assay to observe the behaviors of growth cones of retinal ganglion cells from embryonic day 6 chick retina on exposure to beads coated with lipid-derivatized CS (CS-PE beads). Among CS-PEs with different content of the structural units, the beads coated with E-unit-containing CS-PE [E-unit: GlcAβ1-3GalNAc(4,6-O-disulfate)] (CSE-PE beads) significantly caused the growth cones to retract and to turn away from the beads, but the beads coated with CSA-, CSC- or CSD-PE beads did not. Importantly, not all the growth cones retracted equally from the CSE-PE beads, but they showed continuum of the repulsive behaviors; some behaved moderately and others remarkably. The growth cones distinguished different samples of CS: CSE and the others. Moreover, the continuum of the repulsive behaviors suggests that CS might be involved with the fine regulation of growth cones' behavior through its characteristic structure.