A sulfated carbohydrate epitope inhibits axon regeneration after injury

Abstract

Chondroitin sulfate proteoglycans (CSPGs) represent a major barrier to regenerating axons in the central nervous system (CNS), but the structural diversity of their polysaccharides has hampered efforts to dissect the structure-activity relationships underlying their physiological activity. By taking advantage of our ability to chemically synthesize specific oligosaccharides, we demonstrate that a sugar epitope on CSPGs, chondroitin sulfate-E (CS-E), potently inhibits axon growth. Removal of the CS-E motif significantly attenuates the inhibitory activity of CSPGs on axon growth. Furthermore, CS-E functions as a protein recognition element to engage receptors including the transmembrane protein tyrosine phosphatase PTPσ, thereby triggering downstream pathways that inhibit axon growth. Finally, masking the CS-E motif using a CS-Especific antibody reversed the inhibitory activity of CSPGs and stimulated axon regeneration in vivo. These results demonstrate that a specific sugar epitope within chondroitin sulfate polysaccharides can direct important physiological processes and provide new therapeutic strategies to regenerate axons after CNS injury.

Creation of an injectable in situ gelling native extracellular matrix for nucleus pulposus tissue engineering

“…An optimized decellularization process for nucleus pulposus needs to balance the removal of cells with the maintenance of sGAGs. The sGAGs are essential in maintaining the osmotic pressure of the nucleus pulposus [8], and they have the potential to play a role in driving cell phenotype [45][46][47]50,58] and preventing innervation [59][60][61][62]. The gentle decellularization protocol used in our laboratory for nerve [39,43,63] and lung tissue [38] was adapted for use in the nucleus pulposus by shortening the duration of wash cycles substantially.…”

Predicting glycosaminoglycan surface protein interactions and implications for studying axonal growth

“…Unlike heparin, no structural information is available for chondroitin sulfate motifs CS-D and CS-E, despite increasing evidence of their biological importance (6,8,11). This is because of the difficulty in obtaining CS oligosaccharides that are purely one type (e.g., CS-E) for use in structural studies.…”

“…1). Recent studies have shown that the biological activity of GAGs is often dependent on their sulfation sequence, with specific, highly sulfated sequences directing interactions with growth factors and other signaling proteins (5)(6)(7)(8). Despite the importance of GAG-protein interactions, there is remarkably little structural information about these complexes.…”

“…CS and its associated proteoglycans are the principal inhibitory components of the glial scar, which forms after neuronal damage and acts as a barrier to axon regeneration (12)(13)(14). Blocking the interactions of CS using chondroitinase ABC or an antibody specific for the CS-E motif can promote axon regeneration, sprouting, and functional recovery following injury in vivo (8,15). Intriguingly, RPTPσ engagement by CS and HS can exert opposing effects on neuronal growth, with CS inhibiting and HS promoting axon growth (10).…”

“…GAGs play critical roles in neuronal growth and axon regeneration after spinal cord and other CNS injuries through their ability to engage transmembrane proteins such as the receptor protein tyrosine phosphatases protein tyrosine phosphatase σ RPTPσ and LAR and Nogo receptors (NgRs) NgR1 and NgR3 (8)(9)(10)(11). CS and its associated proteoglycans are the principal inhibitory components of the glial scar, which forms after neuronal damage and acts as a barrier to axon regeneration (12)(13)(14).…”