Poster abstracts

Poster number 92 submitted by Liz Stone

Charcot-Marie-Tooth disease type 2E mutant neurofilament subunit proteins assemble into neurofilaments

Elizabeth Stone (Neuroscience Graduate Program), Atsuko Uchida (Department of Neuroscience, The Ohio State University), Anthony Brown (Department of Neuroscience, The Ohio State University)

Abstract:
Charcot-Marie-Tooth (CMT) is a slow, progressive peripheral neurodegenerative disease inherited with autosomal dominance. The CMT subtype “2E” defines the disease as an axonopathy arising from mutations in the gene that encodes for the low molecular weight neurofilament subunit protein (NFL). NFL is one of five subunits that comprise neurofilaments, which are neuron-specific cytoskeletal polymers that fulfill a structural role in axons. Some previous studies in cell culture have shown that the mutant proteins make amorphous aggregates rather than distinct polymers and have therefore concluded that pathology is caused by a dominant negative effect of the mutant proteins on neurofilament assembly. However, electron micrographs of patient nerve biopsies depict swollen axons full of neurofilament polymers. In order to reconcile these apparently conflicting observations, we have reexamined the polymerization capability of CMT2E mutant NFL protein. We have done this by co-expressing CMT2E mutant NFL with wild type neurofilament protein subunits in neurons and in a cell line that lacks endogenous intermediate filament proteins, and then visualizing the proteins by fluorescent microscopy. We found that several of the CMT2E NFL mutant proteins co-assemble freely into filaments with one other wild type subunit, and that others could also co-assemble if additional subunits were also present. These data highlight the importance of subunit composition in evaluating the assembly of neurofilament proteins, and they question the prevailing notion that neurofilament assembly is defective in CMT2E disease. We propose that CMT2E disease is caused not by defects in neurofilament assembly, but rather by other mechanisms such as changes in their transport or interactions.

We would like to acknowledge the following funding sources: NIH R01 NS038526 and NIH P30 NS045758.

Keywords: neurodegeneration, neurofilament, assembly