Harnessing chaperone-mediated autophagy for the selective degradation of mutant huntingtin protein

Abstract

Huntington's Disease (HD) is a dominantly inherited pathology caused by the accumulation of mutant huntingtin protein (HTT) containing an expanded polyglutamine (polyQ) tract. As the polyglutamine binding peptide 1 (QBP1) is known to bind an expanded polyQ tract but not the polyQ motif found in normal HTT, we selectively targeted mutant HTT for degradation by expressing a fusion molecule comprising two copies of QBP1 and copies of two different heat shock cognate protein 70 (HSC70)-binding motifs in cellular and mouse models of HD. Chaperone-mediated autophagy contributed to the specific degradation of mutant HTT in cultured cells expressing the construct. Intrastriatal delivery of a virus expressing the fusion molecule ameliorated the disease phenotype in the R6/2 mouse model of HD. Similar adaptor molecules comprising HSC70-binding motifs fused to an appropriate structure-specific binding agent(s) may have therapeutic potential for treating diseases caused by misfolded proteins other than those with expanded polyQ tracts.

Chaperone-mediated autophagy: roles in disease and aging

“…Genetic manipulation to enhance CMA has proved useful in mitigating mutant α-synuclein-induced neurodegeneration in mouse models of PD [62]. Similarly, experimental upregulation of CMA also attenuates the toxicity associated with HD in brain slice cultures [18] and interventions that enhance targeting of the HD toxic protein to CMA have also succeeded in slowing down neurodegeneration in HD mouse models [85]. Interestingly, rather than targeting the pathogenic proteins that induce CMA blockage in each of these diseases, the promising results from attempting to slow down the decline of CMA with age by preserving normal levels of the CMA receptor until late in life, support that restoration of CMA in old organisms could be of value to prevent a myriad of age-related diseases.…”

Spontaneous self-assembly of pathogenic huntingtin exon 1 protein into amyloid structures

“…The peptide activates CMA by stimulating the association of mHTT with the chaperone machinery. Enhanced clearance of mHTT fragments through treatment with this construct was observed in cell models as well as transgenic mice [33]. A similar strategy was applied to promote the degradation of polyQ aggregates through macroautophagy.…”

“…Selective catabolism in CMA is conferred by the presence of a KFERQ-like targeting motif in polyQ proteins, by which molecular chaperones recognize the hydrophobic surfaces of the misfolded substrates and transfer them to the lysosomal membrane protein LAMP-2A. They are then taken up into lysosomes, where they are degraded by lysosomal enzymes [33]. A synthetic fusion-peptide consisting of an Hsc70-binding motif and two polyQ-binding sequences can promote the degradation of mHTT through CMA [33].…”

“…They are then taken up into lysosomes, where they are degraded by lysosomal enzymes [33]. A synthetic fusion-peptide consisting of an Hsc70-binding motif and two polyQ-binding sequences can promote the degradation of mHTT through CMA [33]. The peptide activates CMA by stimulating the association of mHTT with the chaperone machinery.…”

Molecular chaperones and neuronal proteostasis

“…BiP (HSPA5) AD/ Aβ Bound APP and reduced Aβ secretion [72]; reduced polyQ aggregation and toxicity in cells [73]; reduced α-synuclein toxicity in rat [74] and toxicity in cells and mice [79], ATPase mutant reduced large polyQ aggregates but no effect on toxicity [80], reduced axonal transport defect in polyQ fly [81]; binds α-synuclein and reduced toxicity of fibrils [82] [83]; binding to mutant SOD1 [84].…”