Mutant HSPB8 causes motor neuron-specific neurite degeneration.
Missense mutations (K141N and K141E) in the alpha-crystallin domain of the small heat shock protein HSPB8 (HSP22) cause distal hereditary motor neuropathy (distal HMN) or Charcot-Marie-Tooth neuropathy type 2L (CMT2L). The mechanism through which mutant HSPB8 leads to a specific motor neuron disease phenotype is currently unknown. To address this question, we compared the effect of mutant HSPB8 in primary neuronal and glial cell cultures. In motor neurons, expression of both HSPB8 K141N and K141E mutations clearly resulted in neurite degeneration, as manifested by a reduction in number of neurites per cell, as well as in a reduction in average length of the neurites. Furthermore, expression of the K141E (and to a lesser extent, K141N) mutation also induced spheroids in the neurites. We did not detect any signs of apoptosis in motor neurons, showing that mutant HSPB8 resulted in neurite degeneration without inducing neuronal death. While overt in motor neurons, these phenotypes were only very mildly present in sensory neurons and completely absent in cortical neurons. Also glial cells did not show an altered phenotype upon expression of mutant HSPB8. These findings show that despite the ubiquitous presence of HSPB8, only motor neurons appear to be affected by the K141N and K141E mutations which explain the predominant motor neuron phenotype in distal HMN and CMT2L.
Peripheral Neuropathy, VIB Department of Molecular Genetics, University of Antwerp, Antwerp, Belgium.
Joy
J
Irobi
Leonardo
L
Almeida-Souza
Bob
B
Asselbergh
Vicky
V
De Winter
Sofie
S
Goethals
Ines
I
Dierick
Jyothsna
J
Krishnan
Jean-Pierre
JP
Timmermans
Wim
W
Robberecht
Peter
P
De Jonghe
Ludo
L
Van Den Bosch
Sophie
S
Janssens
Vincent
V
Timmerman
D019943:Amino Acid Substitution; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004249:DNA Damage; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D050886:HSP20 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins; D006801:Humans; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D018832:Molecular Chaperones; D009046:Motor Neurons / Q000378:metabolism* / Q000473:pathology; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D016501:Neurites / Q000378:metabolism* / Q000473:pathology; D009457:Neuroglia / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection
D016564:Amyloid beta-Protein Precursor; D050886:HSP20 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C490206:Hspb8 protein, mouse; D018832:Molecular Chaperones; D009124:Muscle Proteins; D049452:Green Fluorescent Proteins