[Immunohistochemical study of glutamine synthetase expression in normal human brain and intracranial tumors]

Specific expression in brain astrocytes, glutamine synthetase (GS) is considered to be an indicator of cell activity, owing to its functional significance. Glutamine, its enzymic reaction product, has been found to be a precursor of nucleic acid and purine, suggesting some sort of involvement in astrocyte differentiation and proliferation. So, we conducted immunohistochemical analysis of GS in normal autopsied brain and brain tumor tissue, using anti-GS antibody. In the normal brain, GS-immunoreactivity was marked in granular form in the cerebral cortex from the second layer to sixth layers, the cerebellar granular layer, and the astrocyte bodies and projections in the Purkinje layer, but its manifestation in the cerebral white matter was extremely poor. GS was not present at all in ventricular ependymal cells and choroid plexus epithelial cells. In the primary brain tumor, GS-immunoreactivity was seen only in the astrocytoma cells. An inverse correlation between histological malignancy and degree of GS expression was observed. Otherwise, GS was expressed only in the metastatic brain tumor cells and the craniopharyngioma epithelial cells. GS expression pattern in the normal brain reflected innate function through its pronounced presence in the astrocytes, where glutamic acid-transmitting synapse were abundant. This finding together with the histological malignancy-related expression of GS in the astrocytomas suggest that it could be not only a useful marker for pathologic tumor diagnosis but also useful for evaluating the functional cataplasia of tumor-composing cells or their potential of proliferation.