Pathomechanisms of mutant proteins in Charcot-Marie-Tooth disease.
We review the putative functions and malfunctions of proteins encoded by genes mutated in Charcot-Marie-Tooth disease (CMT; inherited motor and sensory neuropathies) in normal and affected peripheral nerves. Some proteins implicated in demyelinating CMT, peripheral myelin protein 22, protein zero (P0), and connexin32 (Cx32/GJB1) are crucial components of myelin. Periaxin is involved in connecting myelin to the surrounding basal lamina. Early growth response 2 (EGR2) and Sox10 are transcriptional regulators of myelin genes. Mutations in the small integral membrane protein of lysosome/late endosome, the myotubularin-related protein 2 (MTMR2), and MTMR13/set-binding factor 2 are involved in vesicle and membrane transport and the regulation of protein degradation. Pathomechanisms related to alterations of these processes are a widespread phenomenon in demyelinating neuropathies because mutations of myelin components may also affect protein biosynthesis, transport, and/or degradation. Related disease mechanisms are also involved in axonal neuropathies although there is considerably more functional heterogeneity. Some mutations, most notably in P0, GJB1, ganglioside-induced differentiation-associated protein 1 (GDAP1), neurofilament light chain (NF-L), and dynamin 2 (DNM2), can result in demyelinating or axonal neuropathies introducing additional complexity in the pathogenesis. Often, this relates to the intimate connection between Schwann cells and neurons/axons leading to axonal damage even if the mutation-caused defect is Schwann-cell-autonomous. This mechanism is likely for P0 and Cx32 mutations and provides the basis for the unifying hypothesis that also demyelinating neuropathies develop into functional axonopathies. In GDAP1 and DNM2 mutants, both Schwann cells and axons/neurons might be directly affected. NF-L mutants have a primary neuronal defect but also cause demyelination. The major challenge ahead lies in determining the individual contributions by neurons and Schwann cells to the pathology over time and to delineate the detailed molecular functions of the proteins associated with CMT in health and disease.
Niemann
Axel
A
Institute of Cell Biology, Department of Biology, Swiss Federal Institute of Technology, ETH-Hönggerberg, CH-8093 Zürich, Switzerland.
Berger
Philipp
P
Suter
Ueli
U
D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002607:Charcot-Marie-Tooth Disease / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D003711:Demyelinating Diseases / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D034285:Dynamin II / Q000235:genetics / Q000378:metabolism; D051767:Early Growth Response Protein 2 / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology; D020558:GTP Phosphohydrolases; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D016547:Kinesins / Q000235:genetics / Q000378:metabolism; D034904:Lamin Type A / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D018993:Myelin P0 Protein / Q000235:genetics / Q000378:metabolism; D009185:Myelin Proteins / Q000235:genetics / Q000378:metabolism; D018991:Myelin Proteolipid Protein / Q000235:genetics / Q000378:metabolism; D009186:Myelin Sheath / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D016900:Neurofilament Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D055757:SOXE Transcription Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins; D000097002:Gap Junction beta-1 Protein; D000099259:N-myc Downstream-Regulated Gene 1 Protein
D018797:Cell Cycle Proteins; D017630:Connexins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D034285:Dynamin II; D051767:Early Growth Response Protein 2; D020558:GTP Phosphohydrolases; D006360:Heat-Shock Proteins; D006609:High Mobility Group Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016547:Kinesins; D034904:Lamin Type A; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D018993:Myelin P0 Protein; D009185:Myelin Proteins; D018991:Myelin Proteolipid Protein; D009419:Nerve Tissue Proteins; D016900:Neurofilament Proteins; D009687:Nuclear Proteins; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011506:Proteins; D055757:SOXE Transcription Factors; D014157:Transcription Factors; D020691:rab GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins; D000097002:Gap Junction beta-1 Protein; D000099259:N-myc Downstream-Regulated Gene 1 Protein; C497326:EGR2 protein, human; C416508:GAN protein, human; C118663:GDAP protein; C118738:LITAF protein, human; C494847:LMNA protein, human; C073687:PMP22 protein, human; C488620:SH3TC2 protein, human; C527923:SOX10 protein, human; C086745:periaxin; C408986:MTMR2 protein, human; C475072:SBF2 protein, human; C470018:MFN2 protein, human