Extensive early motor and non-motor behavioral deficits are followed by striatal neuronal loss in knock-in Huntington's disease mice

Abstract

Huntington’s disease is a neurodegenerative disorder, caused by an elongation of CAG repeats in the huntingtin gene. Mice with an insertion of an expanded polyglutamine repeat in the mouse huntingtin gene (knock-in mice) most closely model the disease because the mutation is expressed in the proper genomic and protein context. However, few knock-in mouse lines have been extensively characterized and available data suggest marked differences in the extent and time course of their behavioral and pathological phenotype. We have previously described behavioral anomalies in the open field as early as 1 month of age, followed by the appearance at 2 months of progressive huntingtin neuropathology, in a mouse carrying a portion of human exon 1 with approximately 140 CAG repeats inserted into the mouse huntingtin gene. Here we extend these observations by showing that early behavioral anomalies exist in a wide range of motor (climbing, vertical pole, rotarod, and running wheel performance) and non-motor functions (fear conditioning and anxiety) starting at 1–4 months of age, and are followed by progressive gliosis and decrease in DARPP32 (12 months) and a loss of striatal neurons at 2 years. At this age, mice also present striking spontaneous behavioral deficits in their home cage. The data show that this line of knock-in mice reproduces canonical characteristics of Huntington’s disease, preceded by deficits which may correspond to the protracted pre-manifest phase of the disease in humans. Accordingly, they provide a useful model to elucidate early mechanisms of pathophysiology and the progression to overt neurodegeneration.

Proteomic Analysis of Wild-type and Mutant Huntingtin-associated Proteins in Mouse Brains Identifies Unique Interactions and Involvement in Protein Synthesis

“…Non-FLAG-tagged 140Q mice (the FLAG-140Q mice were derived from the same targeting vector) are reported to develop gait abnormalities, tremors, and other behavioral phenotypes. Furthermore, these mice form nuclear and neuropil Htt aggregates after two months in a pattern similar to what is observed in human HD patient tissue (29,30). Both wild-type and mutant FLAG-Htt mice have no apparent behavioral or histological differences from their untagged counterparts, develop normally, and produce fertile offspring.…”

“…5 One-monthold 140Q/ϩ mice displayed behaviors suggestive of hyper-excitability, which subsequently decreased with age (rearing and exploratory behaviors) (30). These altered behaviors preceded any overt pathology: lack of significant Htt nuclear accumulation, aggregation, cell loss, or reduced levels of the striatal marker protein DARPP-32 (29,30). This suggests that even at this early age, the mutant Htt allele exerts an effect on normal brain function that could contribute to the more dramatic later stage outcomes.…”

“…To discriminate heterozygous Hdh3ϫFLAG140Q/ϩ from homozygous Hdh3ϫFLAG140Q/ 3ϫFLAG140Q mice, the following oligonucleotides were used; 140for (5Ј-CTGCACCGACCGTGAGTCC-3Ј) and 140rev (5Ј-GAAGGCACTGGAGTCGTGAC-3Ј) oligonucleotides flank a 100-bp intron 1 deletion that is present in the Hdh3ϫ FLAG140Q allele (this deletion is identical to the deletion present in the Hdh140Q allele lacking an epitope tag; Ref. 29) and will generate a 150-bp PCR product, whereas the wild-type Hdh allele lacking the intron 1 deletion generates a 235-bp product.…”

The Knockout of Secretin in Cerebellar Purkinje Cells Impairs Mouse Motor Coordination and Motor Learning

“…Subsequently, the vertical climbing test provided evidence for impairments in fine motor coordination (Brooks and Dunnett, 2009) because of SCT knockout, as a majority of the knockout mice climbed slowly, stayed still, or even fell off the wire. Profound impairments in vertical climbing have been reported in mice with reduced neurite formation (Mocholi et al, 2011) and in knock-in Huntington's disease transgenic mice (Hickey et al, 2008). Moreover, rotarod motor latencies for Sct À / À , Sctr À / À , and Pur-Sct À / À mice increased slightly after repeated trials (Figures 3c and d), illustrating motor learning deficits.…”

Dysregulation of dopamine receptor D2 as a sensitive measure for Huntington disease pathology in model mice

“…Many mouse models for HD show a corresponding loss of Drd2 expression early in the progression of neuronal pathology (3,10,11). Because mouse models of HD do not lose neurons in great numbers until very late in disease progression (12,13), this reduction is likely on a cell-by-cell level.…”