HEPARAN-SULFATE PROTEOGLYCAN IN DIFFUSE PLAQUES OF HIPPOCAMPUS BUT NOT OF CEREBELLUM IN ALZHEIMERS-DISEASE BRAIN

Previous studies have shown the basement membrane form of heparan sulf ate proteoglycan (HSPG) known as perlecan, co-localized to beta-amyloi d protein (A beta)-containing amyloid deposits in brains of patients w ith Alzheimer's disease (AD) and Down's syndrome. Although HSPG was lo calized to diffuse A beta plaques in hippocampus, amygdala, and neocor tex, it is not known whether they are present in diffuse A beta plaque s in cerebellum. In the present study, Alcian blue staining and immuno cytochemical techniques were used to determine whether highly sulfated glycosaminoglycans (GAGs) and/or HSPG (perlecan) were also persent in diffuse AP plaques of cerebellum. Tissues from cases of AD were exami ned for the co-localization of highly sulfated GAGs, HSPGs, and AP in diffuse plaques in cerebellum in comparison with hippocampus. Consecut ive serial sections of AD brain tissue were stained or immunostained w ith 1) the modified Bielschowsky stain; 2) a polyclonal antibody direc ted against synthetic A beta(1-40); 3) Congo red; 4) Alcian blue (pH 5 .7) with varying concentrations of magnesium chloride for identificati on of sulfated and highly sulfated GAGs; and 5) polyclonal and monoclo nal antibodies recognizing either the core protein or a specific GAG e pitope on perlecan. All cases (7 of 7) of AD contained diffuse A beta plaques in the cerebellum as identified by positive Bielschowsky stain ing and A beta immunoreactivity. None of the cases demonstrated positi ve Alcian blue staining (at 0.3 and 0.7 mol/L MgCl2), HSPG, or HS GAG immunoreactivity in the same diffuse cerebellar plaques on adjacent se rial sections. However, Alcian blue staining, HSPG, and/or HS GAG immu noreactivity were observed in blood vessel walls, choroid plexus, and within Purkinje cells, suggesting that the techniques used were reliab le and specific. In cerebellum, all plaques containing amyloid cores t hat were Congo red-positive were also positive for highly sulfated GAG s (by Alcian blue staining at 0.7 mol/L MgCl2) and HSPG (both core pro tein an GAG chain) immunoreactivity. Even though HSPG immunoreactivity was not present in cerebellar diffuse plaques, all cases (4 of 4) exa mined demonstrated HSPG (both core protein and GAG chain) immunoreacti vity in diffuse A beta plaques in hippocampus. Therefore, by Alcian bl ue staining and immunocytochemical methods, highly sulfated GAGs and H SPGs are not present in A beta diffuse plaques in cerebellum. Since pr evious studies indicate that the cerebellum contains relatively few am yloid-containing plaques in comparison with diffuse plaques, these stu dies suggest that HSPG may be an essential component needed for amyloi d formation and/or persistence in brain as observed in cortical areas. The presence of HSPG in diffuse plaques in hippocampus but not in cer ebellum may explain why amyloid-containing plaques in hippocampus may be selectively formed or persist in comparison with cerebellum. Furthe rmore, the lack of a neuritic response in cerebellar diffuse plaques m ay also be due to the lack of HSPGs, which have been shown to play a r ole in potentiating neurite outgrowth.