Heparanse-syndecan-3 interaction in neurons of the adult spinal cord

Abstract

Heparan sulfate proteoglycans (HSPGs) are found in the extracellular matrix, on the cell surface and even in intracellular organelles of mammalian neural tissue. The HS moiety can be cleaved endoglycosidically at limited sites by heparanase to yield HS fragments. Most studies of heparanase expression have been related to tissue invasion by tumor cells and inflammatory cells, our study has however been focused on heparanase expression in the normal adult spinal cord. RT-PCR revealed the expression of heparanase mRNA in the spinal cord. In situ hybridization with DIG-labeled anti-sense riboprobe located heparanase mRNA in cells of the spinal cord. Intensely stained signals were found in motor neurons (ventral gray column), interneurons (substantia gelatinosa) and tract cells (dorsal gray column). In the white matter, signals were found mainly in glial cell bodies, such as astrocytes. These results were further confirmed immunocytochemically in combination with in situ hybridization. To find interaction of heparanase with HSPG in spinal cord, we explored spinal cord sections with double immunofluorscence for colocalization of heparanase and syndecan-3. Syndecan-3 was found in neuronal cell bodies of the gray matter, similar to heparanase in cellular distribution. In the white matter, although axon tract were syndecan-3-positivity, there was no detectable heparanase immunoreactivity. No syndecan-3 expression was observable in astrocytes. These observations suggest functional significance of interaction of heparanase and syndecan-3 in the neurons within the normal adult spinal cord.