Neuropathy-causing mutations in HSPB1 impair autophagy by disturbing the formation of SQSTM1/p62 bodies

Abstract

HSPB1 (heat shock protein family B [small] member 1) is a ubiquitously expressed molecular chaperone. Most mutations in HSPB1 cause axonal Charcot-Marie-Tooth neuropathy and/or distal hereditary motor neuropathy. In this study we show that mutations in HSPB1 lead to impairment of macroautophagic/ autophagic flux. In HSPB1 knockout cells, we demonstrate that HSPB1 is necessary for autophagosome formation, which was rescued upon re-expression of HSPB1. Employing a label-free LC-MS/MS analysis on the various HSPB1 variants (wild type and mutants), we identified autophagy-specific interactors. We reveal that the wild-type HSPB1 protein binds to the autophagy receptor SQSTM1/p62 and that the PB1 domain of SQSTM1 is essential for this interaction. Mutations in HSPB1 lead to a decrease in the formation of SQSTM1/p62 bodies, and subsequent impairment of phagophore formation, suggesting a regulatory role for HSPB1 in autophagy via interaction with SQSTM1. Remarkably, autophagy deficits could also be confirmed in patient-derived motor neurons thereby indicating that the impairment of autophagy might be one of the pathomechanisms by which mutations in HSPB1 lead to peripheral neuropathy.

Neuromuscular Diseases Due to Chaperone Mutations: A Review and Some New Results

“…HSPB1 mutants (p.R127W, p.S135F, and p.P182L) showed stronger interaction with SQSTM1 and impaired autophagic flux [367]. Decreased autophagic flux was also seen in motor neurons derived from patient iPSCs, supporting the relevance of this mechanism for the pathogenesis [367].…”

“…HSPB1 was shown to interact with SQSTM1/p62 and promote macroautophagy by driving the formation of SQSTM1 bodies and phagophores [367]. HSPB1 mutants (p.R127W, p.S135F, and p.P182L) showed stronger interaction with SQSTM1 and impaired autophagic flux [367]. Decreased autophagic flux was also seen in motor neurons derived from patient iPSCs, supporting the relevance of this mechanism for the pathogenesis [367].…”

“…Very recently, autophagy was added to the list of mechanisms potentially affected by HSPB1 mutations. HSPB1 was shown to interact with SQSTM1/p62 and promote macroautophagy by driving the formation of SQSTM1 bodies and phagophores [367]. HSPB1 mutants (p.R127W, p.S135F, and p.P182L) showed stronger interaction with SQSTM1 and impaired autophagic flux [367].…”

Small heat shock proteins in neurodegenerative diseases

“…Besides its canonical chaperone function, HSPB1 is involved in numerous cellular processes, such as apoptosis (Charette et al 2000;Qi et al 2014), cytoskeleton dynamics (Der Perng and Quinlan 2004;Almeida-Souza et al 2011;Clarke and Mearow 2013), translation (Cuesta et al 2000;Geuens et al 2017), and autophagy (Tang et al 2011;Matsumoto et al 2015). Haidar et al (2019) recently showed that different mutations in HSPB1 (R127W, S135F, and P182L) lead to an impairment of autophagy, a ubiquitous multi-step process which prevents the accumulation of misfolded proteins and damaged organelles in the cytoplasm. The autophagy receptor SQSTM1/p62 (sequestosome-1 or ubiquitin-binding protein p62) was identified as an interactor of wild-type and mutant HSPB1, the latter showing an increased binding affinity for this client.…”

Dysregulated interactions triggered by a neuropathy-causing mutation in the IPV motif of HSP27

“…The above experiments made use of protein samples that were recombinantly expressed and purified from E. coli. The oligomeric state of HSP27 and the P182L variant in human cells has also been reported to be altered, as overexpression of the P182L mutant to leads to increased formation of large insoluble HSP27-containing cytoplasmic aggregates (43)(44)(45). Typically, higher levels of mutant HSP27 expression resulted in higher percentages of aggregate-containing cells and vice versa, with the size of individual cellular aggregates strongly variable and extending to tens of microns (data not shown).…”