Chondroitin sulfate proteoglycans in astrocyte-Schwann cell cocultures limit neurite extension and crossing of cellular boundaries

Abstract

Axon regeneration in the injured spinal cord was restricted at the interface between Schwann cell graft and the host astrocytes. Chondroitin sulfate proteoglycans (CSPG) are implicated in the axon-restrictive property of the interface [1] . Astrocytes and Schwann cells were cocultured to mimic the in vivo situation. In the cocultures, we found that: (1) cocultures stained live with the CS56 showed pericellular immunopositivity on Schwann cells; (2) PGs recovered from conditioned medium were digested with chondroitinase and the disaccharide products showed dominance of Di4S over Di6S as assayed with fluorophore-assisted carbohydrate electrophoresis (FACE); (3) RT-PCR for chondroitin 6- sulfotransferase (C6ST) and chondroitin 4-sulfotransferase (C4ST) mRNAs showed dominance of C4ST over C6ST; (4) FACE analysis of the pericellular matrix recovered from the cocultures indicated hyaluronan and non-sulfated chondroitin. Taken together, this suggests that CSPGs enriched in 4-sulfated chondroitins were secreted into the medium, but hyaluronan and non-sulfated chondroitins were immobilized at the cell surface. Next, we seeded cortical neurons (E18 rats) on the astrocyte-Schwann cell coculture and studied the consequent neurite growth pattern. We found that: (1) neurons extended neurites along Schwann cell processes, contrasting the multidirectional growth on astrocytes; (2) neurites growing on astrocytes hardly changed course to grow on Schwann cells. Chondroitinase ABC treatment to remove pericellular CS and hyaluronan components indicated neurite growth that could cross from astrocytes to Schwann cells; (3) the average neurite length along Schwann cells was longer in Chondroitinase ABC treated group than in the non-treated group. The results suggest that immobilized non-sulfated chondroitins and hyaluronan contribute to limiting neurite extension and crossing from astrocyte to Schwann cells when Schwann cells meet astrocytes. Reference 1 Chau CH, Shum DK, Li H, et al: FASEB J 2004; 18: 194–196.