title: Full-length huntingtin levels modulate body weight by influencing insulin-like growth factor 1 expression.
abstract: Levels of full-length huntingtin (FL htt) influence organ and body weight, independent of polyglutamine length. The growth hormone-insulin like growth factor-1 (GH-IGF-1) axis is well established as a regulator of organ growth and body weight. In this study, we investigate the involvement of the IGF-1 pathway in mediating the effect of htt on body weight. IGF-1 expression was examined in transgenic mouse lines expressing different levels of FL wild-type (WT) htt (YAC18 mice), FL mutant htt (YAC128 and BACHD mice) and truncated mutant htt (shortstop mice). We demonstrate that htt influences body weight by modulating the IGF-1 pathway. Plasma IGF-1 levels correlate with body weight and htt levels in the transgenic YAC mice expressing human htt. The effect of htt on IGF-1 expression is independent of CAG size. No effect on body weight is observed in transgenic YAC mice expressing a truncated N-terminal htt fragment (shortstop), indicating that FL htt is required for the modulation of IGF-1 expression. Treatment with 17beta-estradiol (17beta-ED) lowers the levels of circulating IGF-1 in mammals. Treatment of YAC128 with 17beta-ED, but not placebo, reduces plasma IGF-1 levels and decreases the body weight of YAC128 animals to WT levels. Furthermore, given the ubiquitous expression of IGF-1 within the central nervous system, we also examined the impact of FL htt levels on IGF-1 expression in different regions of the brain, including the striatum, cerebellum of YAC18, YAC128 and littermate WT mice. We demonstrate that the levels of FL htt influence IGF-1 expression in striatal tissues. Our data identify a novel function for FL htt in influencing IGF-1 expression.
authors.affiliation: Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, and Child and Family Research Institute, Vancouver, BC, Canada V5Z 4H4.
authors.forename: Mahmoud A
authors.initials: MA
authors.lastname: Pouladi
authors.forename: Yuanyun
authors.initials: Y
authors.lastname: Xie
authors.forename: Niels Henning
authors.initials: NH
authors.lastname: Skotte
authors.forename: Dagmar E
authors.initials: DE
authors.lastname: Ehrnhoefer
authors.forename: Rona K
authors.initials: RK
authors.lastname: Graham
authors.forename: Jeong Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Nagat
authors.initials: N
authors.lastname: Bissada
authors.forename: X William
authors.initials: XW
authors.lastname: Yang
authors.forename: Paolo
authors.initials: P
authors.lastname: Paganetti
authors.forename: Robert M
authors.initials: RM
authors.lastname: Friedlander
authors.forename: Blair R
authors.initials: BR
authors.lastname: Leavitt
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hayden
mesh_terms: D000818:Animals; D001835:Body Weight; D001921:Brain / Q000378:metabolism; D004195:Disease Models, Animal; D015870:Gene Expression; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D007334:Insulin-Like Growth Factor I