GLUTATHIONE-S-TRANSFERASE ISOENZYMES IN RAT-BRAIN NEURONS AND GLIA

The glutathione S-transferases (GSTs) constitute a family of cytosolic isoenzymes and a structurally unrelated microsomal enzyme that is inv olved in the detoxication of electrophilic xenobiotics. These enzymes also participate in the intracellular binding and transport of a broad range of lipophilic compounds including bilirubin, and hormones such as the glucocorticoids and thyroid hormones. The present investigation demonstrates that GSTs are present in neurons of the brainstem, foreb rain, and cerebellum. An isoenzyme-specific distribution of GSTs was f ound in cytoplasm, nuclei, and nucleoli. The regional and cellular dis tribution of cytosolic GSTs in the brain was studied by immunohistoche mistry, spectrophotometric enzyme assay, and reverse-phase HPLC. Polyc lonal antibody against microsomal GST was strongly reactive with Purki nje cells throughout the cerebellar cortex, and with neurons in the br ainstem and hippocampus. Nuclei of Purkinje cells and of neurons in th e brainstem, hippocampus, and cerebral cortex were immunopositive for alpha-class GST 1-1 (Y(a)Y(a)), whereas alpha-class GST 2-2 (Y(c)Y(c)) antibody was consistently immunoreactive with the nucleolus, but not with the nucleus or soma. All alpha-class GST antibodies studied were reactive, to various degrees, with astrocytes and choroid plexus; howe ver, ependymal cells of the subventricular zones were immunonegative. Alpha-class GST 8-8 (Y(k)Y(k)) immunoreactivity was specifically local ized to endothelial cells and/or astrocytic end feet associated with b lood vessels. Reverse-phase HPLC indicated that there were also substa ntial regional differences in the pattern of alpha-, mu-, and pi-class GST subunit expression. For example, the thalamus/hypothalamus had th e highest GST activity and greatest concentration of total GST protein and mu-class GST subunit 6 (Y(b3)), whereas the brainstem had the gre atest concentration of pi-class GST subunit (Y(p)). This regional vari ation in GST expression may be reflective of regional differences in c ell populations. In cerebellar cortex, the concentration of mu-class G ST subunit 4 (Y(b2)was greatest in the flocculus and lowest in the ver mis. This is of clinical interest because the pattern of expression of mu-class GST subunit 4 (Y(b2)) in the cerebellum coincides with the k nown regional susceptibility of this structure to degeneration after e xposure to toxic or metabolic insults. The vermis is most susceptible to these insults, whereas the lateral lobes and flocculus are most res istant. The nuclear localization of alpha-class GSTs in neurons, the c ytoplasmic localization of microsomal GST in neurons, and the associat ion between concentration of mu-class GST subunit 4 (Y(b2)) and resist ance of neurons to toxic events in the cerebellar cortex suggest that GSTs may confer protection against exogenous and/or endogenous neuroto xic metabolites.