ABSTRACT
Amyloid beta (Abeta) is a 40- to 42-residue peptide that is implicated in the pathogenesis of Alzheimer's Disease (AD). As a result of conformational changes, Abeta assembles into neurotoxic fibrils deposited as 'plaques' in the diseased brain. In AD brains, the small heat shock proteins (sHsps) alphaB-crystallin and Hsp27 occur at increased levels and colocalize with these plaques. In vitro, sHsps act as molecular chaperones that recognize unfolding peptides and prevent their aggregation. The presence of sHsps in AD brains may thus reflect an attempt to prevent amyloid fibril formation and toxicity. Here we report that alphaB-crystallin does indeed prevent in vitro fibril formation of Abeta(1-40). However, rather than protecting cultured neurons against Abeta(1-40) toxicity, alphaB-crystallin actually increases the toxic effect. This indicates that the interaction of alphaB-crystallin with conformationally altering Abeta(1-40) may keep the latter in a nonfibrillar, yet highly toxic form.
Subject(s)
Amyloid beta-Peptides/chemistry , Amyloid beta-Peptides/toxicity , Crystallins/pharmacology , Molecular Chaperones/pharmacology , Neurons/pathology , Peptide Fragments/chemistry , Peptide Fragments/toxicity , Plaque, Amyloid/drug effects , Alzheimer Disease/pathology , Amyloid beta-Peptides/metabolism , Animals , Animals, Newborn , Apoptosis/drug effects , Benzothiazoles , Cell Survival/drug effects , Cells, Cultured , Cerebral Cortex , Dose-Response Relationship, Drug , Hippocampus , Neurons/drug effects , Neurons/metabolism , Neurons/ultrastructure , Peptide Fragments/metabolism , Plaque, Amyloid/metabolism , Plaque, Amyloid/pathology , Plaque, Amyloid/ultrastructure , Protein Binding/drug effects , Protein Structure, Secondary/drug effects , Rats , ThiazolesABSTRACT
Homogenates of hatching gland explants were fractionated by means of different electrophoretic techniques, and the fractions analyzed for proteolytic activity and for their capacity to affect the envelope of the eggs. Agar gel electrophoresis resulted in two fractions that were able to digest the zona radiata interna, and a third fraction that caused a significant swelling of the egg envelope. All three fractions were proteolytically active. Agarose gel and polyacrylamide gel electrophoresis gave only two fractions that showed proteolytic activity and were capable of digesting the zona radiata interna. The presence of these two fractions may imply that hatching enzyme is stored as proenzyme in the hatching gland granules. Swelling of egg envelopes was also observed during envelope digestion by thermolysin, pronase, and 0.5-1.0 N NaOH. Moreover, breakdown by hatching enzyme and pepsin under suboptimal conditions showed a slight swelling of the envelope. These results demonstrate that substances capable of solubilizing the zona radiata interna may cause envelope swelling. The swelling of the envelopes probably represents an intermediate phase in the proteolysis of the zona radiata interna. The agar gel electrophoresis fraction of hatching gland homogenates that causes swelling may contain a physicochemically different form of hatching enzyme.
