title: Six-month partial suppression of Huntingtin is well tolerated in the adult rhesus striatum.
abstract: Huntington's disease is caused by expression of a mutant form of Huntingtin protein containing an expanded polyglutamine repeat. One possible treatment for Huntington's disease may be to reduce expression of mutant Huntingtin in the brain via RNA interference. Unless the therapeutic molecule is designed to be allele-specific, both wild-type and mutant protein will be suppressed by an RNA interference treatment. A key question is whether suppression of wild-type as well as mutant Huntingtin in targeted brain regions can be tolerated and result in a net benefit to patients with Huntington's disease. Whether Huntingtin performs essential functions in the adult brain is unclear. Here, we tested the hypothesis that the adult primate brain can tolerate moderately reduced levels of wild-type Huntingtin protein for an extended period of time. A serotype 2 adeno-associated viral vector encoding for a short hairpin RNA targeting rhesus huntingtin messenger RNA (active vector) was bilaterally injected into the striatum of four adult rhesus monkeys. Four additional animals received a comparable vector encoding a scrambled control short hairpin RNA (control vector). General health and motor behaviour were monitored for 6 months. Upon termination, brain tissues were sampled and assessed blindly for (i) huntingtin messenger RNA knockdown; (ii) Huntingtin protein expression; and (iii) neuropathological changes. Reduction in wild-type huntingtin messenger RNA levels averaging ∼30% was measured in the striatum of active vector recipients 6 months post-injection. A widespread reduction in Huntingtin protein levels was also observed by immunohistochemistry in these animals, with an average protein reduction of ∼45% relative to controls measured by western blot analysis in the putamen of active vector recipients. As with control vector recipients, no adverse effects were observed behaviourally, and no neurodegeneration was found on histological examination of active vector recipients. Our results suggest that long-term partial suppression of wild-type Huntingtin may be safe, and thus if a comparable level of suppression of mutant Huntingtin is beneficial, then partial suppression of both wild-type and mutant Huntingtin may result in a net benefit in patients with heterozygous Huntington's disease.
authors.affiliation: Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, 317 Whitney-Hendrickson (MRISC), Lexington, Kentucky 40536-0098, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Grondin
authors.forename: Michael D
authors.initials: MD
authors.lastname: Kaytor
authors.forename: Yi
authors.initials: Y
authors.lastname: Ai
authors.forename: Peter T
authors.initials: PT
authors.lastname: Nelson
authors.forename: Deepak R
authors.initials: DR
authors.lastname: Thakker
authors.forename: Jennifer
authors.initials: J
authors.lastname: Heisel
authors.forename: Marcy R
authors.initials: MR
authors.lastname: Weatherspoon
authors.forename: Janelle L
authors.initials: JL
authors.lastname: Blum
authors.forename: Eric N
authors.initials: EN
authors.lastname: Burright
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Zhang
authors.forename: William F
authors.initials: WF
authors.lastname: Kaemmerer
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D029681:Arabidopsis Proteins / Q000378:metabolism; D001835:Body Weight / Q000235:genetics; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002461:Cell Line, Transformed; D003094:Collagen / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000378:metabolism; D004435:Eating / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics; D005822:Genetic Vectors / Q000008:administration & dosage / Q000502:physiology; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006684:HLA-DR Antigens / Q000378:metabolism; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D019751:Intramolecular Transferases / Q000378:metabolism; D008253:Macaca mulatta; D008279:Magnetic Resonance Imaging; D009043:Motor Activity / Q000187:drug effects / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011597:Psychomotor Performance / Q000502:physiology; D034622:RNA Interference / Q000502:physiology*; D034741:RNA, Small Interfering / Q000008:administration & dosage; D014162:Transfection
chemical_list: D029681:Arabidopsis Proteins; C487851:C1QTNF5 protein, human; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D005904:Glial Fibrillary Acidic Protein; D006684:HLA-DR Antigens; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D003094:Collagen; D019751:Intramolecular Transferases; C568454:marneral synthase, Arabidopsis