Cellular localization of heparanase in the normal versus injured spinal cord of adult rats

Abstract

We reported that soluble heparan sulfates (HS) upregulated regeneration of transected nerves (Eur. J. Neurosci. (1999) 11:1914-1926). This suggests that mobile HS glycoforms are important for axonal growth in normal physiological process and tissue repair after injury. So far heparanase is the only known mammalian enzyme that cleaves the HS moiety to yield biologically relevant HS fragments. We asked if this enzyme is upregulated in injured neural tissues and if so, whether or not this expression is in phase with tissue repair and axonal regrowth. Reverse transcriptase/polymerase chain reaction (RT-PCR) and in situ hybridization for the heparanase transcript revealed expression in neurons and white matter glia of the normal, intact spinal cord (J. Comp. Neurol. (2006) 494:345-357). This was confirmed by immunohistochemistry showing cytoplasmic localization of the heparanase protein. Double immunofluorescence for heparanase and cell markers revealed colocalization of the proteins in cell bodies of neurons and oligodendrocytes. In contrast, only subpopulations of astrocytes and NG2-expressing glia in the white matter expressed heparanase in the intact cord. In the injured cord, heparanase mRNA indicated initial decrease in the expression both about and distal to the lesion and subsequent increase to levels in excess of that in the normal cord. While the initial decrease was caused by cell death, the subsequent increase was attributable to reactive astrocytes and macrophages recruited to the environment of the lesion. Cultures of astrocytes further evidenced upregulation of heparanase expression with TGF-β1 treatment. These provide preliminary evidence in support of heparanase function not only in normal tissue turnover in the intact spinal cord, but also in neural tissue repair in the injured spinal cord.