Differential expression of metallothioneins in human prion diseases.
We herein report an immunohistochemical and a Western blot analysis on metal/free radical chelating proteins, metallothioneins (MTs; MT-I/II and MT-III), in the brains of human prion disease patients with or without prion protein gene mutation and polymorphism. Irrespective of the isoforms of MTs, the immunoreaction was detected in the cytoplasm and processes of the astrocytes in the cerebral cortex and white matter in normal controls and prion disease brains. Although the immunoreactivities for MTs in Creutzfeldt-Jakob disease (CJD) brains varied from case to case, they were generally dependent upon the disease duration. In CJD patients with a relatively long disease course, the immunoreaction for both MT-I/II and MT-III in the astrocytes was significantly reduced, and this finding was not modified by the genotypes of the patients. On the other hand, in patients with Gerstmann-Sträussler-Scheinker syndrome, MT-I/II immunoreactivity in the astrocytes was exclusively reduced, while the immunoreaction for MT-III was relatively well preserved. Especially the astrocytes in the vicinities of the kuru plaques exhibited a weak or no immunoreaction even for MTs but a strong immunoreaction for glial fibrillary acidic protein. A quantitative Western blot analysis also revealed that MT-I/II protein accumulated in CJD brain with a short disease duration, whereas MT-III in CJD brain with a long disease duration was statistically significantly reduced in comparison to the normal brains. These findings suggest that the protein expression of MTs in the astrocytes is thus regulated differentially among human prion diseases and modified locally by such abnormal prion protein depositions as kuru plaques.