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.