Investigating the non-cell autonomous role of glial chaperones in Alzheimer's disease

Astrocytes are vital in the onset and progression of Alzheimer's disease (AD). Accumulation of reactive astrocytes, together with tau phosphorylation, correlates very strongly with cognitive decline. Molecular chaperones are essential for maintaining protein homeostasis. One family of chaperones are the small heat shock proteins (sHSPs), which include HSPB1 and CRYAB. Expression of these sHSPs seems to be restricted to glial cells, and levels are found to increase in those astrocytes found in AD brains. The role that sHSP play in astrocytes in AD is still not known. Emerging evidence suggests vital interplay between different cell types during neurodegenerative diseases. We therefore aim to investigate the non-cell autonomous role of astrocytic sHSPs in AD. We are using primary mouse neurons and organotypic brain slice cultures in conjunction with the recombinant adeno-associated viral system (rAAV). These systems will allow us to replicate the tau pathology found in AD, investigate neuron-astrocyte interactions and determine whether either can be altered by overexpression of our sHSPs. Using immunofluorescence, confocal microscopy and western blotting we are characterising expression and localization of sHSPs in post-mortem human AD brain tissue and brain slice cultures. Our data shows that HSPB1 is specifically expressed in astrocytes in both human brain tissue and slice cultures. Interestingly, HSPB1 levels in the human brain increase in GFAP-positive astrocytes surrounding amyloid plaques. When organotypic brain slices are treated with cytokines or Aβ oligomers, reactive astrocytes are induced and levels of HSPB1 and CRYAB are also increased, similar to what we observe in human AD brain. Our results in human AD brain highlight the importance of astrocytic HSPB1 in AD, and we provide evidence to suggest not only that organotypic brain slices are a good model to replicate and study the function of sHSPs in AD, but that HSPB1 and CRYAB play an important role in the response to AD-relevant pathology. Using rAAVs, we aim to manipulate astrocytic sHSPs levels in organotypic brain slices to investigate whether astrocytic sHSPs could modulate neuronal health and tau pathology in a non-cell autonomous manner. [Abstract copyright: © 2021 the Alzheimer's Association.]