A novel rationally designed chaperone that blocks amyloid beta neurotoxicity. Shailaja Emani^1,2, Swati Khare¹, Alfonso Martin-Pena¹, Yan Zhang¹, Pedro Fernandez-Funez¹, Diego Rincon-Limas¹. 1) Neurology, University of Florida, Gainesville, FL; 2) HHMI-UF Science for Life.

   Alzheimers disease (AD) is an incurable disorder characterized by memory loss, brain neurodegeneration, and an abundance of extracellular amyloid deposits composed of misfolded Amyloid-42 (A42) peptide. Since A42 oligomers are the neurotoxic agents driving AD pathology, targeting these toxic assemblies with chaperones that enhance protein folding capacity may have therapeutic effects. In this regard, the heat shock chaperone Hsp70 is a promising candidate due to its potent anti-misfolding activity. Unfortunately, this normally intracellular chaperone exists extracellularly at very low concentration and thus its activity has never been tested in this context. To address this, we engineered a new secreted version of Hsp70 (secHsp70) using dedicated software and capitalized on our fly model of AD-like pathology to test its protective activity (Casas-Tinto, HMG 2011). Strikingly, we found that secHsp70 exerts a robust protection against extracellular A42 deposition and toxicity in photoreceptor neurons. This dramatic effect requires the presence of Hsp70 in the extracellular space as neither overexpression of WT cytosolic Hsp70 nor the ER-bound chaperone BiP suppressed A42 toxicity. Remarkably, secHsp70 exerts its protection without the cochaperone Hsp40. We also confirmed the secretion of secHsp70 by looking at its distribution and confirming that it does not rescue the toxicity of Ataxin3-78Q, an intracellular amyloid implicated in Spinocerebellar ataxia type 3. Finally, secHsp70 does not affect total A42 levels, suggesting that its protection is mediated by regulating A42 misfolding, aggregation, and/or interaction with cellular targets. In summary, our new secHsp70 chaperone has an extraordinary ability to block A42 insults. Thus, enhancing protein-folding capacity in the extracellular space could represent a new therapeutic strategy for many serious extracellular amyloidoses such as AD, prion diseases, and type II diabetes.