Huntingtin is required for ER-to-Golgi transport and for secretory vesicle fusion at the plasma membrane.
Bottom Line: Although the progression of Huntington's disease is linked to toxic accumulation of mutant huntingtin protein, loss of wild-type huntingtin function might also contribute to neuronal cell death, but its precise function is not well understood.Interestingly, heterozygous fibroblasts from a Huntington's disease patient with a 180Q expansion displayed no obvious defects in the early secretory pathway.Thus, our results highlight the requirement for wild-type huntingtin at distinct steps along the secretory pathway.
Affiliation: Cambridge Institute for Medical Research, University of Cambridge, Cambridge, CB2 0XY, UK.Show MeSH
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Mentions: Finally, we analysed the secretory pathway in human fibroblasts from a healthy control (GM23976A) and an individual with juvenile-onset HD [heterozygous for an expanded polyQ tract of 180Q (HTT+/180Q); GM09197B], and in primary MEFs isolated from wild-type mice (typically around E17/18) and homozygous Htt140Q/140Q KI mice. The human and mouse fibroblasts were transiently transfected with the GFP-hGH reporter construct and the amount of this reporter molecule in the Golgi area was analysed at 0, 15 and 30 minutes after AP21998 ligand addition. As shown in Fig. 4A, there was no significant difference in reporter movement from the ER to the Golgi in control compared with heterozygous HTT+/180Q patient fibroblasts. However, significantly less cargo accumulated in the Golgi 15 minutes after ligand addition in homozygote Htt140Q/140Q KI MEFs when compared with wild-type MEFs (Fig. 4B). Thus, efficient cargo transport in the early secretory pathway requires at least one copy of wild-type huntingtin, which cannot be replaced by the overexpression of mutant 140Q huntingtin in primary MEFs. At least in fibroblasts, the presence of one copy of mutant huntingtin with a 180Q tract does not seem to disrupt cargo transport in the secretory pathway.
Affiliation: Cambridge Institute for Medical Research, University of Cambridge, Cambridge, CB2 0XY, UK.