Increased caspase-2, calpain activations and decreased mitochondrial complex II activity in cells expressing exogenous huntingtin exon 1 containing CAG repeat in the pathogenic range

Cell Mol Neurobiol. 2007 Dec;27(8):1127-45. doi: 10.1007/s10571-007-9220-7. Epub 2007 Sep 28.


(1) Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by the expansion of polymorphic CAG repeats beyond 36 at exon 1 of huntingtin gene (htt). To study cellular effects by expressing N-terminal domain of Huntingtin (Htt) in specific cell lines, we expressed exon 1 of htt that codes for 40 glutamines (40Q) and 16Q in Neuro2A and HeLa cells. (2) Aggregates and various apoptotic markers were detected at various time points after transfection. In addition, we checked the alterations of expressions of few apoptotic genes by RT-PCR. (3) Cells expressing exon 1 of htt coding 40Q at a stretch exhibited nuclear and cytoplasmic aggregates, increased caspase-1, caspase-2, caspase-8, caspase-9/6, and calpain activations, release of cytochrome c and AIF from mitochondria in a time-dependent manner. Truncation of Bid was increased, while the activity of mitochondrial complex II was decreased in such cells. These changes were significantly higher in cells expressing N-terminal Htt with 40Q than that obtained in cells expressing N-terminal Htt with 16Q. Expressions of caspase-1, caspase-2, caspase-3, caspase-7, and caspase-8 were increased while expression of Bcl-2 was decreased in cells expressing mutated Htt-exon 1. (4) Results presented in this communication showed that expression of mutated Htt-exon 1 could mimic the cellular phenotypes observed in Huntington's disease and this cell model can be used for screening the agents that would interfere with the apoptotic pathway and aggregate formation.

MeSH terms

  • Animals
  • Apoptosis / genetics
  • Apoptosis Inducing Factor / metabolism
  • Calpain / metabolism*
  • Caspase 2 / metabolism*
  • Cell Survival / genetics
  • Cells, Cultured
  • Cytochromes c / metabolism
  • DNA Fragmentation
  • Electron Transport Complex II / metabolism*
  • Enzyme Activation
  • Exons / genetics
  • Green Fluorescent Proteins / genetics
  • HeLa Cells
  • Humans
  • Huntingtin Protein
  • Huntington Disease / genetics*
  • Mice
  • Mitochondria / metabolism
  • Nerve Tissue Proteins / genetics*
  • Nuclear Proteins / genetics*
  • Recombinant Fusion Proteins / genetics
  • Transfection
  • Trinucleotide Repeats / genetics*


  • Apoptosis Inducing Factor
  • HTT protein, human
  • Huntingtin Protein
  • Nerve Tissue Proteins
  • Nuclear Proteins
  • Recombinant Fusion Proteins
  • respiratory complex II
  • Green Fluorescent Proteins
  • Cytochromes c
  • Electron Transport Complex II
  • Calpain
  • Caspase 2