Inhibition of TFG function causes hereditary axon degeneration by impairing endoplasmic reticulum structure

Proc Natl Acad Sci U S A. 2013 Mar 26;110(13):5091-6. doi: 10.1073/pnas.1217197110. Epub 2013 Mar 11.

Abstract

Hereditary spastic paraplegias are a clinically and genetically heterogeneous group of gait disorders. Their pathological hallmark is a length-dependent distal axonopathy of nerve fibers in the corticospinal tract. Involvement of other neurons can cause additional neurological symptoms, which define a diverse set of complex hereditary spastic paraplegias. We present two siblings who have the unusual combination of early-onset spastic paraplegia, optic atrophy, and neuropathy. Genome-wide SNP-typing, linkage analysis, and exome sequencing revealed a homozygous c.316C>T (p.R106C) variant in the Trk-fused gene (TFG) as the only plausible mutation. Biochemical characterization of the mutant protein demonstrated a defect in its ability to self-assemble into an oligomeric complex, which is critical for normal TFG function. In cell lines, TFG inhibition slows protein secretion from the endoplasmic reticulum (ER) and alters ER morphology, disrupting organization of peripheral ER tubules and causing collapse of the ER network onto the underlying microtubule cytoskeleton. The present study provides a unique link between altered ER architecture and neurodegeneration.

Publication types

  • Clinical Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Axons / metabolism*
  • Axons / pathology
  • Cell Line
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • Endoplasmic Reticulum / pathology
  • Exons / genetics
  • Female
  • Genetic Linkage
  • Genome-Wide Association Study
  • Humans
  • Male
  • Mice
  • Microtubules / genetics
  • Microtubules / metabolism
  • Microtubules / pathology
  • Mutation, Missense*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Pedigree
  • Polymorphism, Single Nucleotide*
  • Proteins / genetics
  • Proteins / metabolism*
  • Rats
  • Spastic Paraplegia, Hereditary / genetics
  • Spastic Paraplegia, Hereditary / metabolism*
  • Spastic Paraplegia, Hereditary / pathology
  • Xenopus
  • Zebrafish

Substances

  • Nerve Tissue Proteins
  • Proteins
  • TFG protein, human
  • Tfg protein, mouse