A series of N-terminal epitope tagged Hdh knock-in alleles expressing normal and mutant huntingtin: their application to understanding the effect of increasing the length of normal Huntingtin's polyglutamine stretch on CAG140 mouse model pathogenesis

Mol Brain. 2012 Aug 14;5:28. doi: 10.1186/1756-6606-5-28.

Abstract

Background: Huntington's disease (HD) is an autosomal dominant neurodegenerative disease that is caused by the expansion of a polyglutamine (polyQ) stretch within Huntingtin (htt), the protein product of the HD gene. Although studies in vitro have suggested that the mutant htt can act in a potentially dominant negative fashion by sequestering wild-type htt into insoluble protein aggregates, the role of the length of the normal htt polyQ stretch, and the adjacent proline-rich region (PRR) in modulating HD mouse model pathogenesis is currently unknown.

Results: We describe the generation and characterization of a series of knock-in HD mouse models that express versions of the mouse HD gene (Hdh) encoding N-terminal hemaglutinin (HA) or 3xFlag epitope tagged full-length htt with different polyQ lengths (HA7Q-, 3xFlag7Q-, 3xFlag20Q-, and 3xFlag140Q-htt) and substitution of the adjacent mouse PRR with the human PRR (3xFlag20Q- and 3xFlag140Q-htt). Using co-immunoprecipitation and immunohistochemistry analyses, we detect no significant interaction between soluble full-length normal 7Q- htt and mutant (140Q) htt, but we do observe N-terminal fragments of epitope-tagged normal htt in mutant htt aggregates. When the sequences encoding normal mouse htt's polyQ stretch and PRR are replaced with non-pathogenic human sequence in mice also expressing 140Q-htt, aggregation foci within the striatum, and the mean size of htt inclusions are increased, along with an increase in striatal lipofuscin and gliosis.

Conclusion: In mice, soluble full-length normal and mutant htt are predominantly monomeric. In heterozygous knock-in HD mouse models, substituting the normal mouse polyQ and PRR with normal human sequence can exacerbate some neuropathological phenotypes.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Alleles*
  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Brain / metabolism
  • Brain / pathology
  • Chi-Square Distribution
  • Crosses, Genetic
  • Disease Models, Animal
  • Epitopes / chemistry*
  • Exons / genetics
  • Female
  • Gliosis / metabolism
  • Gliosis / pathology
  • Hemizygote
  • Heterozygote
  • Humans
  • Huntingtin Protein
  • Huntington Disease / metabolism*
  • Huntington Disease / pathology
  • Lipofuscin / metabolism
  • Male
  • Mice
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism*
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Nuclear Proteins / chemistry*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Peptides / chemistry*
  • Protein Binding
  • Trinucleotide Repeat Expansion / genetics

Substances

  • Epitopes
  • HTT protein, human
  • Htt protein, mouse
  • Huntingtin Protein
  • Lipofuscin
  • Mutant Proteins
  • Nerve Tissue Proteins
  • Nuclear Proteins
  • Peptides
  • polyglutamine