Molecular Biology of Small Heat Shock Proteins associated with Peripheral Neuropathies


Heat‐shock proteins (HSPs) are molecular chaperones that protect the cell from various types of stress. Although regulated by stress, some of these proteins are constitutively expressed and responsible for quality control and protein folding. Based on their molecular weight, the HSP family mainly consists of two groups: large and small HSPs. The large HSPs require adenosine triphosphate (ATP) for their functioning, whereas the small HSPs (HSPBs) are ATP independent. The latter bind improperly folded proteins and assist in the targeting process for refolding or degradation. These HSPBs are not only molecular chaperones but they are also involved in many essential cellular processes such as apoptosis, autophagy, splicing, cytoskeleton dynamics and neuronal survival. This review focusses on the small HSPs HSPB1, HSPB3 and HSPB8, as mutations in these proteins are causative for Charcot–Marie–Tooth (CMT) disease and distal hereditary motor neuropathies (dHMN). Moreover, this review discusses the functional consequences of these mutations and their role in the length‐dependent neurodegeneration typical of CMT diseases.

Key Concepts:

  • The molecular signature of the small HSPs is the conserved α‐crystallin domain.

  • Mutations in HSPB1, HSPB3 and HSPB8 are associated with dHMN and CMT subtypes.

  • Mutant HSPB1 causes instability of the cytoskeletal elements and therefore disorganisation of the neuronal cytoskeleton could underlie the peripheral neuropathies.

  • Mutant HSPB8 may induce pathomechanisms leading to CMT diseases through a loss of autophagy function, rather than a toxic gain of function.

  • The HSPB3 protein differs considerably from the other members regarding sequence similarity such as the poor conservation in the N‐terminal region and the very short C‐terminal domain.

  • It remains fragmentary how mutations in these small HSPs initiate a molecular cascade leading to progressive axonal degeneration.

Keywords: HSPB1; HSPB3; HSPB8; mutation; neurodegeneration; Charcot–Marie–Tooth disease; dHMN; apoptosis; autophagy

Figure 1.

Schematic presentation of the HSPB1, HSPB3 and HSPB8 proteins. This scheme shows the different protein domains of the small HSPs HSPB1, HSPB3 and HSPB8, and the arrows indicate the neuropathy‐associated mutations reported so far. The numbering refers to the amino acid residues delimiting the different protein domains. The HSPB1 protein is 205 amino acids long, has a monomeric mass of 27 kDa and contains both the amino‐terminal WDPF and the C‐terminal IXI/V motifs, which are well conserved among various HSPB members, and known to modulate the oligomerisation of the HSPB protein. The HSPB3 protein has a length of 150 amino acid residues and has a calculated monomeric mass of 17 kDa. Not much is known about this protein, nevertheless the almost complete absence of the C‐terminal extension is a striking feature. Both HSPB3 and HSPB8 do not have a WDPF or IXI/V motif. The HSPB8 protein contains 196 amino acids and has a monomeric mass of 22 kDa. The β‐sheets 4 and 8 are indicated as they form the hydrophic groove, which is essential for the formation of the HSPB8‐Bag3 complex. [P] , phosphorylation sites; ACD, α‐crystalline domain.

Figure 2.

The HSPB1 protein interferes with the cell death signalling pathways at various levels. In the extrinsic apoptosis pathway, HSPB1 prevents translocation of death domain‐associated protein G (Daxx) to the cytosol by interacting with it and thereby inhibiting the binding of Daxx to the Fas receptor and suppress Daxx‐dependent apoptosis. Upstream of the mitochondrial release of cytochrome c, HSPB1 can activate the protective protein kinase Akt directly or through the phosphatidylinositol 3‐kinase (PI3‐K). Subsequently, Akt can prevent cytochrome c release through suppression of Bax mitochondrial translocation. At the same time, HSPB1 can inactivate the pro‐death apoptosis‐signal regulated kinase 1 (Ask1)–c‐jun N‐terminal kinase (JNK) pathway. Downstream of the mitochondrial release of cytochrome c, HSPB1 can directly interact with cytochrome c and therefore diminish the activation of procaspase‐9, by inhibiting the proper formation of the apoptosome complex. But, it can also inhibit caspase‐3 activity by interacting with the procaspase‐3 molecule or by inhibiting the release of the mitochondria‐derived activator of caspases (Smac/Diablo).

Figure 3.

HSPB8 is involved in many different processes regulating the proteolytic degradation of unfolded proteins. The HSPB8 protein can stimulate the activity and affect the intracellular location of proteasomes and through this activate proteolytic degradation of certain proteins. More recently, HSPB8 was found to stimulate autophagy in a Bag3‐dependent manner. Although HSPB8 is thought to be responsible for recognising misfolded proteins, Bag3 interacts with HSPA and modulates the targeting of client protein. Through the interaction with Bag3, HSPB8 becomes part of a multiheteromeric complex formed by HSPB8, Bag3, HSPA and the chaperone‐associated ubiquitin ligase. The latter catalyses target proteins for ubiquitinylation and subsequent recruitment of the autophagic ubiquitin adaptor p62 leads to degradation of the misfolded proteins in autophagosomes, and thus autophagic removal. The HSPB8–Bag3 complex can also function independently of HSPA, as it was shown to lead to the phosphorylation of the α‐subunit of the translation initiator factor eIF2α, which results in the stimulation of autophagy (Carra, ). The HSPB8–Bag3‐mediated eIF2 phosphorylation was shown to be pancreatic endoplasmic reticulum kinase (PERK)‐ and phospholipase Cγ‐1‐independent, leaving the upstream player(s) responsible for eIF2α phosphorylation unknown. However, part of the effects may be through the activation of the General control non‐derepressible 2 kinase, and deletion of the PXXP domain of Bag3 affected the eIF2α phosphorylation, suggesting that the HspB8–Bag3 complex interacts through this domain with the unknown essential factor to modulate eIF2α phosphorylation.



Ackerley S, James PA, Kalli A et al. (2006) A mutation in the small heat‐shock protein HSPB1 leading to distal hereditary motor neuronopathy disrupts neurofilament assembly and the axonal transport of specific cellular cargoes. Human Molecular Genetics 15(2): 347–354.

Almeida‐Souza L, Asselbergh B, d'Ydewalle C et al. (2011a) Small heat shock protein HSPB1 mutants stabilize microtubules in Charcot–Marie–Tooth neuropathy. Journal of Neuroscience 31(43): 15320–15328.

Almeida‐Souza L, Goethals S, De Winter V et al. (2010) Increased monomerization of mutant HSPB1 leads to protein hyperactivity in Charcot–Marie–Tooth neuropathy. Journal of biological chemistry 285(17): 12778–12786.

Almeida‐Souza L, Timmerman V and Janssens S (2011b) Microtubule dynamics in the peripheral nervous system: a matter of balance. Bio Architecture 1(6): 267–270.

Arrigo AP (2007) The cellular “networking” of mammalian Hsp27 and its functions in the control of protein folding, redox state and apoptosis. Advances in Experimental Medicine and Biology 594: 14–26.

Asthana A, Raman B, Ramakrishna T et al. (2012) Structural aspects and chaperone activity of human HspB3: role of the “C‐Terminal Extension”. Cell Biochemistry and Biophysics 64: 61–72.

Baek SH, Min JN, Park EM et al. (2000) Role of small heat shock protein HSP25 in radioresistance and glutathione‐redox cycle. Journal of Cellular Physiology 183(1): 100–107.

Baranova EV, Weeks SD, Beelen S et al. (2011) Three‐dimensional structure of alpha‐crystallin domain dimers of human small heat shock proteins HSPB1 and HSPB6. Journal of Molecular Biology 411(1): 110–122.

Benndorf R, Sun XK, Gilmont RR et al. (2001) HSP22, a new member of the small heat shock protein superfamily, interacts with mimic of phosphorylated HSP27 ((3D)HSP27). Journal of Biological Chemistry 276(29): 26753–26761.

Boelens WC, Van Boekel MA and De Jong WW (1998) HspB3, the most deviating of the six known human small heat shock proteins. Biochimica et Biophysica Acta 1388(2): 513–516.

Cairns J, Qin S, Philp R et al. (1994) Dephosphorylation of the small heat shock protein Hsp27 in vivo by protein phosphatase 2A. Journal of Biological Chemistry 269(12): 9176–9183.

Capponi S, Geroldi A, Fossa P et al. (2011) HSPB1 and HSPB8 in inherited neuropathies: study of an Italian cohort of dHMN and CMT2 patients. Journal of the Peripheral Nervous System 16(4): 287–294.

Carra S (2009) The stress‐inducible HspB8‐Bag3 complex induces the eIF2alpha kinase pathway: implications for protein quality control and viral factory degradation? Autophagy 5(3): 428–429.

Carra S, Boncoraglio A, Kanon B et al. (2010) Identification of the Drosophila ortholog of HSPB8: implication of HSPB8 loss of function in protein folding diseases. Journal of Biological Chemistry 285(48): 37811–37822.

Carra S, Seguin SJ and Landry J (2008) HspB8 and Bag3: a new chaperone complex targeting misfolded proteins to macroautophagy. Autophagy 4(2): 237–239.

Carra S, Sivilotti M, Chavez Zobel AT et al. (2005) HspB8, a small heat shock protein mutated in human neuromuscular disorders, has in vivo chaperone activity in cultured cells. Human Molecular Genetics 14(12): 1659–1669.

Chen S and Brown IR (2007) Neuronal expression of constitutive heat shock proteins: implications for neurodegenerative diseases. Cell Stress and Chaperones 12(1): 51–58.

Chen S, Owens GC, Makarenkova H et al. (2010) HDAC6 regulates mitochondrial transport in hippocampal neurons. PLoS One 5(5): e10848.

Crippa V, Sau D, Rusmini P et al. (2010) The small heat shock protein B8 (HspB8) promotes autophagic removal of misfolded proteins involved in amyotrophic lateral sclerosis (ALS). Human Molecular Genetics 19(17): 3440–3456.

den Engelsman J, Boros S, Dankers PY et al. (2009) The small heat‐shock proteins HSPB2 and HSPB3 form well‐defined heterooligomers in a unique 3 to 1 subunit ratio. Journal of Molecular Biology 393(5): 1022–1032.

Evgrafov OV, Mersiyanova IV, Irobi J et al. (2004) Mutant small heat‐shock protein 27 causes axonal Charcot–Marie–Tooth disease and distal hereditary motor neuropathy. Nature Genetics 36(6): 602–606.

Fontaine JM, Sun X, Hoppe AD et al. (2006) Abnormal small heat shock protein interactions involving neuropathy‐associated HSP22 (HSPB8) mutants. FASEB Journal 20(12): 2168–2170.

Fuchs M, Poirier DJ, Seguin SJ et al. (2010) Identification of the key structural motifs involved in HspB8/HspB6‐Bag3 interaction. Biochemical Journal 425(1): 245–255.

Gibert B, Eckel B, Fasquelle L et al. (2012) Knock down of heat shock protein 27 (HspB1) induces degradation of several putative client proteins. PLoS One 7(1): e29719.

Haslbeck M, Franzmann T, Weinfurtner D et al. (2005) Some like it hot: the structure and function of small heat‐shock proteins. Nature Structural and Moleular Biology 12(10): 842–846.

Houlden H, Laura M, Wavrant‐De Vrièze F et al. (2008) Mutations in the HSP27 (HSPB1) gene cause dominant, recessive, and sporadic distal HMN/CMT type 2. Neurology 71(21): 1660–1668.

Ikeda Y, Abe A, Ishida C et al. (2009) A clinical phenotype of distal hereditary motor neuronopathy type II with a novel HSPB1 mutation. Journal of the Neurological Sciences 277(1–2): 9–12.

Irobi J, Holmgren A, De Winter V et al. (2012) Mutant HSPB8 causes protein aggregates and a reduced mitochondrial membrane potential in dermal fibroblasts from distal hereditary motor neuropathy patients. Neuromuscular Disorders 22(8): 699–711.

Irobi J, Van Impe K, Seeman P et al. (2004) Hot‐spot residue in small heat‐shock protein 22 causes distal motor neuropathy. Nature Genetics 36(6): 597–601.

Jaffer F, Murphy SM, Scoto M et al. (2012) BAG3 mutations: another cause of giant axonal neuropathy. Journal of the Peripheral Nervous System 17(2): 210–216.

James PA, Rankin J and Talbot K (2008) Asymmetrical late onset motor neuropathy associated with a novel mutation in the small heat shock protein HSPB1 (HSP27). Journal of Neurology, Neurosurgery and Psychiatry 79(4): 461–463.

Kappe G, Boelens WC and De Jong WW (2010) Why proteins without an alpha‐crystallin domain should not be included in the human small heat shock protein family HSPB. Cell Stress and Chaperones 15(4): 457–461.

Kazakov AS, Markov DI, Gusev NB et al. (2009) Thermally induced structural changes of intrinsically disordered small heat shock protein Hsp22. Biophysical Chemistry 145(2–3): 79–85.

Kijima K, Numakura C, Goto T et al. (2005) Small heat shock protein 27 mutation in a Japanese patient with distal hereditary motor neuropathy. Journal of Human Genetics 50(9): 473–476.

Kim MV, Kasakov AS, Seit‐Nebi AS et al. (2006) Structure and properties of K141E mutant of small heat shock protein HSP22 (HspB8, H11) that is expressed in human neuromuscular disorders. Archives of Biochemistry and Biophysics 454(1): 32–41.

Kim MV, Seit‐Nebi AS, Marston SB et al. (2004) Some properties of human small heat shock protein Hsp22 (H11 or HspB8). Biochemical and Biophysical Research Communications 315(4): 796–801.

Kolb SJ, Snyder PJ, Poi EJ et al. (2010) Mutant small heat shock protein B3 causes motor neuropathy: utility of a candidate gene approach. Neurology 74(6): 502–506.

Kostenko S, Moens U et al. (2009) Heat shock protein 27 phosphorylation: kinases, phosphatases, functions and pathology. Cellular and Molecular Life Sciences 66(20): 3289–3307.

Kwok AS, Phadwal K, Turner BJ et al. (2011) HspB8 mutation causing hereditary distal motor neuropathy impairs lysosomal delivery of autophagosomes. Journal of Neurochemistry 119(6): 1155–1161.

Langelier Y, Champoux L, Hamel M et al. (1998) The R1 subunit of herpes simplex virus ribonucleotide reductase is a good substrate for host cell protein kinases but is not itself a protein kinase. Journal of Biological Chemistry 273(3): 1435–1443.

Lanneau D, Wettstein G, Bonniaud P et al. (2010) Heat shock proteins: cell protection through protein triage. Scientific World Journal 10: 1543–1552.

Luigetti M, Fabrizi GM, Madia F et al. (2010) A novel HSPB1 mutation in an Italian patient with CMT2/dHMN phenotype. Journal of the Neurological Sciences 298(1–2): 114–117.

Mandich P, Grandis M, Varese A et al. (2010) Severe neuropathy after diphtheria‐tetanus‐pertussis vaccination in a child carrying a novel frame‐shift mutation in the small heat‐shock protein 27 gene. Journal of Child Neurology 25(1): 107–109.

Marin‐Vinader L, Shin C, Onnekink C et al. (2006) Hsp27 enhances recovery of splicing as well as rephosphorylation of SRp38 after heat shock. Molecular Biology of the Cell 17(2): 886–894.

Matsushima‐Nishiwaki R, Takai S, Adachi S et al. (2008) Phosphorylated heat shock protein 27 represses growth of hepatocellular carcinoma via inhibition of extracellular signal‐regulated kinase. Journal of Biological Chemistry 283(27): 18852–18860.

Mymrikov EV, Seit‐Nebi AS and Gusev NB (2011) Large potentials of small heat shock proteins. Physiological Reviews 91(4): 1123–1159.

Preville X, Salvemini F, Giraud S et al. (1999) Mammalian small stress proteins protect against oxidative stress through their ability to increase glucose‐6‐phosphate dehydrogenase activity and by maintaining optimal cellular detoxifying machinery. Experimental Cell Research 247(1): 61–78.

Qiu H, Lizano P, Laure L et al. (2011) H11 kinase/heat shock protein 22 deletion impairs both nuclear and mitochondrial functions of STAT3 and accelerates the transition into heart failure on cardiac overload. Circulation 124(4): 406–415.

Rossor AM, Davidson GL, Blake J et al. (2012) A novel p.Glu175X premature stop mutation in the C‐terminal end of HSP27 is a cause of CMT2. Journal of the Peripheral Nervous System 17(2): 201–205.

Schepers H, Geugien M, van der Toorn M et al. (2005) HSP27 protects AML cells against VP‐16‐induced apoptosis through modulation of p38 and c‐Jun. Experimental Hematology 33(6): 660–670.

Shemetov AA, Seit‐Nebi AS and Gusev NB (2008) Structure, properties, and functions of the human small heat‐shock protein HSP22 (HspB8, H11, E2IG1): a critical review. Journal of Neuroscience Research 86(2): 264–269.

Smith CC, Yu YX, Kulka M et al. (2000) A novel human gene similar to the protein kinase (PK) coding domain of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) codes for a serine‐threonine PK and is expressed in melanoma cells. Journal of Biological Chemistry 275(33): 25690–25699.

Srivastava AK, Renusch SR, Naiman NE et al. (2012) Mutant HSPB1 overexpression in neurons is sufficient to cause age‐related motor neuronopathy in mice. Neurobiology of Disease 47(2): 163–173.

Takayama S and Reed JC (2001) Molecular chaperone targeting and regulation by BAG family proteins. Nature Cell Biology 3(10): E237–E241.

Tang BS, Zhao GH, Luo W et al. (2005) Small heat‐shock protein 22 mutated in autosomal dominant Charcot–Marie–Tooth disease type 2L. Human Genetics 116(3): 222–224.

de Thonel A, Le Mouel A, Mezger V et al. (2012) Transcriptional regulation of small HSP‐HSF1 and beyond. The International Journal of Biochemistry & Cell Biology 44: 1593–1612.

Wettstein G, Bellaye PS, Micheau O et al. (2012) Small heat shock proteins and the cytoskeleton: an essential interplay for cell integrity? International Journal of Biochemistry and Cell Biology 44: 1680–1686.

d'Ydewalle C, Krishnan J, Chiheb DM et al. (2011) HDAC6 inhibitors reverse axonal loss in a mouse model of mutant HSPB1‐induced Charcot–Marie–Tooth disease. Nature Medicine 17(8): 968–974.

Zhai J, Lin H, Julien JP et al. (2007) Disruption of neurofilament network with aggregation of light neurofilament protein: a common pathway leading to motor neuron degeneration due to Charcot–Marie–Tooth disease‐linked mutations in NFL and HSPB1. Human Molecular Genetics 16(24): 3103–3116.

Zheng C, Lin Z, Zhao ZJ et al. (2006) MAPK‐activated protein kinase‐2 (MK2)‐mediated formation and phosphorylation‐regulated dissociation of the signal complex consisting of p38, MK2, Akt, and Hsp27. Journal of Biological Chemistry 281(48): 37215–37226.

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Holmgren, Anne, Bouhy, Delphine, and Timmerman, Vincent(Nov 2012) Molecular Biology of Small Heat Shock Proteins associated with Peripheral Neuropathies. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0024294]