Novel BAC Mouse Model of Huntington's Disease with 225 CAG Repeats Exhibits an Early Widespread and Stable Degenerative Phenotype.

Wegrzynowicz M, Bichell TJ, Soares BD, Loth MK, McGlothan JS, Mori S, Alikhan FS, Hua K, Coughlin JM, Holt HK, Jetter CS, Pomper MG, Osmand AP, Guilarte TR, Bowman AB
J Huntingtons Dis. 2015 4 (1): 17-36

PMID: 26333255 · PMCID: PMC4657874

BACKGROUND - Unusually large CAG repeat expansions (>60) in exon one of Huntingtin (HTT) are invariably associated with a juvenile-onset form of Huntington's disease (HD), characterized by a more extensive and rapidly progressing neuropathology than the more prevalent adult-onset form. However, existing mouse models of HD that express the full-length Htt gene with CAG repeat lengths associated with juvenile HD (ranging between ~75 to ~150 repeats in published models) exhibit selective neurodegenerative phenotypes more consistent with adult-onset HD. Objective: To determine if a very large CAG repeat (>200) in full-length Htt elicits neurodegenerative phenotypes consistent with juvenile HD.

METHODS - Using a …bacterial artificial chromosome (BAC) system, we generated mice expressing full-length mouse Htt with ~225 CAG repeats under control of the mouse Htt promoter. Mice were characterized using behavioral, neuropathological, biochemical and brain imaging methods.

RESULTS - BAC-225Q mice exhibit phenotypes consistent with a subset of features seen in juvenile-onset HD: very early motor behavior abnormalities, reduced body weight, widespread and progressive increase in Htt aggregates, gliosis, and neurodegeneration. Early striatal pathology was observed, including reactive gliosis and loss of dopamine receptors, prior to detectable volume loss. HD-related blood markers of impaired energy metabolism and systemic inflammation were also increased. Aside from an age-dependent progression of diffuse nuclear aggregates at 6 months of age to abundant neuropil aggregates at 12 months of age, other pathological and motor phenotypes showed little to no progression.

CONCLUSIONS - The HD phenotypes present in animals 3 to 12 months of age make the BAC-225Q mice a unique and stable model of full-length mutant Htt associated phenotypes, including body weight loss, behavioral impairment and HD-like neurodegenerative phenotypes characteristic of juvenile-onset HD and/or late-stage adult-onset HD.

MeSH Terms (16)

Animals Atrophy Behavior, Animal Brain Chromosomes, Artificial, Bacterial Disease Models, Animal Disease Progression Huntington Disease Mice Mice, Inbred C57BL Mice, Transgenic Neurons Phenotype Promoter Regions, Genetic Serotonin Plasma Membrane Transport Proteins Trinucleotide Repeat Expansion

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