Molecular chaperone Hsp110 rescues a vesicle transport defect produced by an ALS-associated mutant SOD1 protein in squid axoplasm

Abstract

Mutant human Cu/Zn superoxide dismutase 1 (SOD1) is associated with motor neuron toxicity and death in an inherited form of amyotrophic lateral sclerosis (ALS; Lou Gehrig disease). One aspect of toxicity in motor neurons involves diminished fast axonal transport, observed both in transgenic mice and, more recently, in axoplasm isolated from squid giant axons. The latter effect appears to be directly mediated by misfolded SOD1, whose addition activates phosphorylation of p38 MAPK and phosphorylation of kinesin. Here, we observe that several different oligomeric states of a fusion protein, comprising ALS-associated human G85R SOD1 joined with yellow fluorescent protein (G85R SOD1YFP), which produces ALS in transgenic mice, inhibited anterograde transport when added to squid axoplasm. Inhibition was blocked both by an apoptosis signal-regulating kinase 1 (ASK1; MAPKKK) inhibitor and by a p38 inhibitor, indicating the transport defect is mediated through the MAPK cascade. In further incubations, we observed that addition of the mammalian molecular chaperone Hsc70, abundantly associated with G85R SOD1YFP in spinal cord of transgenic mice, exerted partial correction of the transport defect, associated with diminished phosphorylation of p38. Most striking, the addition of the molecular chaperone Hsp110, in a concentration substoichiometric to the mutant SOD1 protein, completely rescued both the transport defect and the phosphorylation of p38. Hsp110 has been demonstrated to act as a nucleotide exchange factor for Hsc70 and, more recently, to be able to cooperate with it to mediate protein disaggregation. We speculate that it can cooperate with endogenous squid Hsp(c)70 to mediate binding and/or disaggregation of mutant SOD1 protein, abrogating toxicity.

Axonal Transport: Cargo-Specific Mechanisms of Motility and Regulation

“…Recent work suggests that mitochondria are also aged in distal neurites (Ferree et al, 2013). This fact highlights the specific axonal requirement for distal quality control (Maday and Holzbaur, 2014) and for chaperones (Song et al, 2013; Terada et al, 2010) that maintain the integrity of the proteome in the distal axon.…”

Extended survival of misfolded G85R SOD1-linked ALS mice by transgenic expression of chaperone Hsp110

“…Addition of G85R SOD1YFP to squid axoplasm inhibits anterograde axonal vesicle transport, but purified human Hsp110 (HspA4L) prevents this effect even when added at substoichiometric amounts relative to the misfolded protein, suggesting that it cooperates with endogenous Hsc70 and DnaJ homologs to dissociate toxic oligomeric forms (21). In studies in Drosophila eye, transgenic expression of either Drosophila Hsp110 or human Hsp110 (HspA4L; APG1) was able to rescue toxicity from coexpressed polyQ-expanded proteins (22,23).…”

Targeting Assembly and Disassembly of Protein Aggregates

“…Expression of Hsp110, either alone or with Hsp70 and Hsp40 members, rescues in vivo neurotoxicity in Drosophila [292] and squid [293] models. Yeast Hsp104 synergizes with the mammalian chaperone machinery to provide amyloid-disaggregating capacity in vitro [291,294].…”