Chondroitin sulfate proteoglycans in demyelinated lesions impair remyelination

Failure of remyelination is a critical impediment to recovery in multiple sclerosis (MS). Chondroitin sulfate proteoglycans (CSPGs) have been reported to accumulate in MS lesions, and we thus examined the functional roles of CSPGs on oligodendrocyte precursor cells (OPCs), oligodendrocytes, and remyelination.

We evaluated the expression of CSPGs in lysolecithin-injected mouse spinal cord, an animal model of demyelination and spontaneous remyelination. The functional impact of CSPGs on OPCs and remyelination was investigated using cultured adult murine and human OPCs and by treating demyelinated mice with xyloside to reduce the CSPG deposition that occurred following injury.

Early and robust upregulation of CSPGs following lysolecithin-induced demyelination was cleared during remyelination. In culture, CSPGs anchored onto the substratum reduced the adhesion of mouse and human OPCs and their subsequent morphological differentiation into process-bearing oligodendrocytes. Soluble CSPGs added to already adherent OPCs reduced the development of processes, whereas the acquisition of mature myelin proteins was unimpeded. Stripe assays of alternating CSPG and control substrata confirmed the nonpermissive nature of CSPGs for OPC adhesion and morphological differentiation. Enzymatic degradation of CSPGs with chondroitinase ABC was sufficient to overcome CSPG-dependent inhibition of human oligodendrocytes. Finally, in vivo xyloside treatment to reduce CSPG synthesis in lysolecithin-demyelinated mice increased numbers of OPCs and oligodendrocytes in lesions, and culminated in improved remyelination.

These results identify CSPGs as a nonpermissive substrate for OPCs and oligodendrocytes, and as a prominent impediment to remyelination. The data suggest the requirement for the neutralization of CSPGs for repair after demyelination.