Significance of Small Heat Shock Proteins HSPB1 and HSPB5 in Aggregation and Degradation of Amyloid Proteins

Abstract

Molecular chaperones protect cells from the deleterious effects of protein misfolding and aggregation. Neurotoxicity of amyloid-beta (Ap) aggregates and its deposition in senile plaques are hallmarks of Alzheimer's disease (AD). We observed that the overall content of aB-crystallin, a small heat shock protein molecular chaperone, decreased in AD model mice in an age-dependent manner. We hypothesized that aB-crystallin protects cells against Ap toxicity. To test this, we crossed aB-crystallin/HspB2 deficient (CRYAB'A HSPB2'A) mice with AD model transgenic mice expressing mutant human amyloid precursor protein. Transgenic and non-transgenic mice in chaperone-sufficient or deficient backgrounds were examined for representative behavioral paradigms for locomotion and memory network functions - (i) spatial orientation and locomotion was monitored by open field test; (ii) sequential organization and associative learning was monitored by fear conditioning and (iii) evoked behavioral response was tested by hot plate method. Interestingly, aB-crystallin/HspB2 deficient transgenic mice were severely impaired in locomotion compared to each genetic model separately. Our results highlight a synergistic effect of combining chaperone deficiency in a transgenic mouse model for AD underscoring an important role for chaperones in protein misfolding diseases.