Holdase activity of secreted Hsp70 masks amyloid-β42 neurotoxicity in Drosophila

Abstract

Alzheimer’s disease (AD) is the most prevalent of a large group of related proteinopathies for which there is currently no cure. Here, we used Drosophila to explore a strategy to block Aβ42 neurotoxicity through engineering of the Heat shock protein 70 (Hsp70), a chaperone that has demonstrated neuroprotective activity against several intracellular amyloids. To target its protective activity against extracellular Aβ42, we added a signal peptide to Hsp70. This secreted form of Hsp70 (secHsp70) suppresses Aβ42 neurotoxicity in adult eyes, reduces cell death, protects the structural integrity of adult neurons, alleviates locomotor dysfunction, and extends lifespan. SecHsp70 binding to Aβ42 through its holdase domain is neuroprotective, but its ATPase activity is not required in the extracellular space. Thus, the holdase activity of secHsp70 masks Aβ42 neurotoxicity by promoting the accumulation of nontoxic aggregates. Combined with other approaches, this strategy may contribute to reduce the burden of AD and other extracellular proteinopathies.

Chaperones as Suppressors of Protein Misfolded Oligomer Toxicity

“…The pre-incubation of these aggregates with clusterin also reverted their ability to reduce the pharyngeal mobility in C. elegans nematodes (Beeg et al, 2016). In another study, Hsp70 was modified to be released in the extracellular space in order to address its protective activity against Aβ 42 in Drosophila melanogaster models (Fernandez-Funez et al, 2016). The secreted form, called secHsp70, suppressed Aβ 42 toxicity, as deduced by decreased eye degeneration, reduced neuronal death, structural integrity of adult neurons, suppression of locomotor neuron dysfunction, and lifespan extension.…”

“…The secreted form, called secHsp70, suppressed Aβ 42 toxicity, as deduced by decreased eye degeneration, reduced neuronal death, structural integrity of adult neurons, suppression of locomotor neuron dysfunction, and lifespan extension. An assay based on luciferase-derived luminescence showed that secHsp70 stabilizes Aβ 42 oligomeric species and masks their neurotoxic epitopes, thus promoting the accumulation of nontoxic aggregates (Fernandez-Funez et al, 2016). This activity was carried out in the absence of ATP, indicating therefore that secHsp70 exploits its holdase function to interact with the oligomers in the absence of detectable clustering (Fernandez-Funez et al, 2016).…”

“…An assay based on luciferase-derived luminescence showed that secHsp70 stabilizes Aβ 42 oligomeric species and masks their neurotoxic epitopes, thus promoting the accumulation of nontoxic aggregates (Fernandez-Funez et al, 2016). This activity was carried out in the absence of ATP, indicating therefore that secHsp70 exploits its holdase function to interact with the oligomers in the absence of detectable clustering (Fernandez-Funez et al, 2016). It is interesting to note that other Hsps that were found able to interact with aggregates, such as Hsp104 (Arimon et al, 2008; Castellano et al, 2015), Hsp70 (Mannini et al, 2012) and Ssa1p (Xu L. et al, 2013), exert the capacity to bind to the aggregates without consumption of ATP.…”

Designer protein disaggregases to counter neurodegenerative disease

“…Hsp70 variants with enhanced chaperone or disaggregase activity against specific model substrates have been uncovered [94–97], but whether these can be translated into neuroprotective agents in vivo is unknown. Engineering a secreted form of Hsp70 rescued a Drosophila model of AD, although in this case Hsp70 promoted clustering of Aβ42 into larger aggregates with reduced neurotoxicity [98•]. This clustering activity appears to be a general feature of molecular chaperones that must operate under ATP-limited conditions such as the extracellular space, and can be protective by minimizing exposure of reactive surfaces by confining them within the aggregate interior [43••,99].…”

Investigating Amyloid β toxicity in Drosophila melanogaste

“…Each ommatidium consists of eight photoreceptor neurons, which project axons that synapse in the optic ganglia of the brain [254]. The defined structure of the ommatidia can be disrupted by, for example, the expression of toxic proteins or genetic alterations, resulting in a rough eye phenotype easily detected by light microscopy or scanning electron microscopy [255]. A frequently used tool to study eye specific expression is the GMR-Gal4 driver.…”