STRESS PROTEIN COLOCALIZATION TO AUTOFLUORESCENT ASTROCYTIC INCLUSIONS IN-SITU AND IN CYSTEAMINE-TREATED GLIAL CULTURES

In the aging brain, a unique subpopulation of limbic and periventricul ar astrocytes accumulates red autofluorescent, peroxidase-positive cyt oplasmic inclusions distinct from lipofuscin. Cysteamine (CSH) exposur e rapidly induces identical inclusions in cultured, immature astroglia . CSH induces a cellular stress response prior to astrocyte granulatio n. To determine whether stress proteins are actual constituents of the autofluorescent granules, 12-week-old rat brain sections and CSH-trea ted astroglial cultures were immunostained with various anti-stress pr otein antibodies and evaluated by laser scanning confocal microscopy. We observed intense co-localization of heat shock protein (HSP) 27 and ubiquitin (Ub) to the autofluorescent astrocyte granules in situ and in CSH-treated glial cultures. In both preparations, glucose regulated protein (GRP) 94 consistently exhibited partial co-localization to th e granule periphery and adjacent cytoplasm. In contrast, HSP72 co-loca lization to these inclusions was only occasionally seen and the granul es appeared entirely devoid of HSP90 and alphaB-crystallin. Acute expo sure of cultured astroglia to CSH induced intense cytoplasmic Ub stain ing, suggesting that activation of the Ub pathway may be an early even t in the biogenesis of these astrocytic granules. Taken together, our results support the notion that the autofluorescent astrocyte inclusio ns are stress or heat shock granules which progressively accumulate in the aging periventricular brain. Moreover, CSH greatly accelerates th e appearance of this senescent astrocyte phenotype in primary culture.