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Acta neuropathologica 135(1), 131-148 (2018). doi:10.1007/s00401-017-1756-0, Published by Springer, Berlin ; Heidelberg

Mutations in the small heat shock protein HSPB1 (HSP27) are a cause of axonal Charcot–Marie–Tooth neuropathy (CMT2F) and distal hereditary motor neuropathy. To better understand the effect of mutations in HSPB1 on the neuronal cytoskeleton, we stably transduced neuronal cells with wild-type and mutant HSPB1 and investigated axonal transport of neurofilaments (NFs). We observed that mutant HSPB1 affected the binding of NFs to the anterograde motor protein kinesin, reducing anterograde transport of NFs. These deficits were associated with an increased phosphorylation of NFs and cyclin-dependent kinase Cdk5. As Cdk5 mediates NF phosphorylation, inhibition of Cdk5/p35 restored NF phosphorylation level, as well as NF binding to kinesin in mutant HSPB1 neuronal cells. Altogether, we demonstrate that HSPB1 mutations induce hyperphosphorylation of NFs through Cdk5 and reduce anterograde transport of NFs. Electronic supplementary material The online version of this article (doi:10.1007/s00401-013-1133-6) contains supplementary material, which is available to authorized users.

Missense mutations in the small heat shock protein HSPB8 cause distal hereditary motor neuropathy (dHMN) and axonal Charcot-Marie-Tooth disease (CMT2L). We previously demonstrated that, despite the ubiquitous expression of HSPB8, motor neurons appear to be predominantly affected by HSPB8 mutations. Here, we studied the effect of mutant HSPB8 in primary fibroblast cultures derived from dHMN patients’ skin biopsy. In early passage cultures, we observed in all patients’ fibroblasts HSPB8 protein aggregates that were not detected in control cells. After applying heat shock stress on the patients’ early passage cultured cells, the protein aggregates coalesced into larger formations, while in control cells a homogenous upregulation of HSPB8 protein expression was seen. We also found a reduction in the mitochondrial membrane potential in the early passage cultures. After three months in culture, the number of cells with aggregates had become indistinguishable from that in controls and the mitochondrial membrane potential had returned to normal. These results emphasize the possible drawbacks of using patients’ non-neuronal cells to study neuropathological disease mechanisms.

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

The intermediate filaments called neurofilaments (NFs) are the main cytoskeleton elements in neurons. They are mainly present in the adult axonal cytoskeleton, where they are extensively phosphorylated and their phosphorylation status is pivotal for their properties and functions. Specific phosphorylation of the C-terminal domains of the large NF subunits has been implicated in radial axonal growth, NF bundling, and NF axonal transport. Many kinases and phosphatases are involved in regulating the NF phosphorylation status, and this complex interplay is of growing interest as hyperphosphorylation of NFs is a hallmark of several neurodegenerative diseases. In this review, we focus on the in vivo relevance of C-tail phosphorylation of the large NF subunits and give an overview of the kinases and phosphatases involved in regulating the phosphorylation status of the NFs.

O2-5 The clinical spectrum of STXBP1 mutations in early onset epileptic encephalpathy: between Ohtahara-syndrome and West syndrome? B. Ceulemans1,2,3 *, S. Weckhuysen4,5,6, K. Verhaert1, L. Deprez7,8,9, A. Holmgren7,8,9, A. Janssen10, W. Van Paesschen11, A. Jordanova4,5,12, L. Lagae3,13, P. De Jonghe4,5,14. 1Child Neurology, University Hospital of Antwerp, Antwerp, Belgium; 2Child Neurology, University of Antwerp, Antwerp, Belgium; 3Child Neurology, Epilepsy Centre Pulderbos, Pulderbos, Belgium; 4Neurology, University of Antwerp, Antwerp, Belgium; 5Neurology, Department of Molecular Genetics, VIB, Antwerp, Belgium; 6Neurology, Epilepsy Centre Kempenhaeghe, Oosterhout, The Netherlands; 7Biochemistry, University of Antwerp, Antwerp, Belgium; 8Biochemistry, Department of Molecular Genetics, VIB, Antwerp, Belgium; 9Biochemistry, Institute Born-Bunge, Antwerp, Belgium; 10Child Neurology, University Hospital of Brussels, Brussels, Belgium; 11Neurology, University Hospital Gasthuisberg, KU Leuven, Leuven, Belgium; 12Neurology, Institute Born-Bunge, Antwerp, Belgium; 13Child Neurology, University Hospital Gasthuisberg, KU Leuven, Leuven, Belgium; 14Neurology, University Hospital of Antwerp, Antwerp, Belgium