Small heat shock protein αB-crystallin potentiates Aβ neurotoxicity by hetero-oligomeric stabilization.

Abstract

Amyloid plaque, a neuropathological hallmark of Alzheimer's disease (AD), is composed of neurotoxic amyloid-β (Aβ) peptides and other proteins, including the small heat shock protein αB-crystallin (also known as HSPB5). We investigated the cellular origin of αB-crystallin, its secretion properties and how it may affect formation of neurotoxic Aβ hetero-oligomers. Immunohistofluorescence, Confocal Microscopy, Immunogold electron microscopy, SDS-page and immunoblotting, electron paramagnetic resonance spectroscopy (EPR), quasi-elastic light scattering (QLS) spectroscopy, cell and organotypic slice culture, LDH and propidium iodide assays. Immunohistofluorescence analysis of human AD brain revealed that Aβ and αB-crystallin co-localize in extracellular dense core and diffuse plaques and in surrounding reactive astrocytes. Immunohistochemical and immunoblotting analyses showed that astrocytes secrete αB-crystallin in vitro via an exosomal pathway. Co-incubation of αB-crystallin and Aβ suppressed Aβ fibrillogenesis by sequestration in hetero-oligomeric complexes however, this resulted in αB-crystallin potentiated Aβ neurotoxicity in mouse primary neurons and organotypic rat hippocampus slice culture as revealed by LDH and Propidium Iodide assays. Moreover, αB-crystallin acutely potentiated Aβ-induced impairment of activity-dependent long-term potentiation (LTP) of rat Schaffer collateral-CA1 synaptic transmission. These results indicate that the small heat shock protein αB-crystallin is secreted by reactive astrocytes and potentiates Aβ neurotoxicity by stabilizing hetero-oligomers.