The Chondroitin Sulfate Proteoglycans Neurocan and Phosphacan Are Expressed by Reactive Astrocytes in the Chronic CNS Glial Scar

TLDR

Chondroitin sulfate proteoglycans expressed by reactive astrocytes are thought to contribute to the axon‑growth‑inhibitory environment of injured CNS, yet the specific inhibitory CS‑PGs present in reactive gliosis remain incompletely characterized. The study aims to determine which CS‑PGs are expressed by reactive astrocytes in the chronic glial scar following cortical injury. Immunohistochemistry, combined immunohistochemistry–in situ hybridization, immunoblotting, and RT‑PCR were employed to assess CS‑PG expression in an in vivo model of reactive gliosis. Neurocan and phosphacan are expressed by reactive astrocytes in the chronic glial scar, with neurocan up‑regulated (including neonatal isoform) and phosphacan down‑regulated, whereas brevican and versican are absent; these CS‑PGs’ known neurite‑inhibitory activity implies they may hinder axonal regeneration after CNS injury.

Abstract

Chondroitin sulfate proteoglycans (CS-PGs) expressed by reactive astrocytes may contribute to the axon growth-inhibitory environment of the injured CNS. The specific potentially inhibitory CS-PGs present in areas of reactive gliosis, however, have yet to be thoroughly examined. In this study, we used immunohistochemistry, combined immunohistochemistry– in situ hybridization, immunoblot analysis, and reverse transcription-PCR to examine the expression of specific CS-PGs by reactive astrocytes in an in vivo model of reactive gliosis: that is, the glial scar, after cortical injury. Neurocan and phosphacan can be localized to reactive astrocytes 30 d after CNS injury, whereas brevican and versican are not expressed in the chronic glial scar. Neurocan is also expressed by astrocytes in primary cell culture. Relative to the amount present in cultured astrocytes or uninjured cortex, neurocan expression increases significantly in the glial scar resulting from cortical injury, including the re-expression of the neonatal isoform of neurocan. In contrast, phosphacan protein levels are decreased in the glial scar compared with the uninjured brain. Because these CS-PGs are capable of inhibiting neurite outgrowth in vitro , our data suggest that phosphacan and neurocan in areas of reactive gliosis may contribute to axonal regenerative failure after CNS injury.