Motivational, proteostatic and transcriptional deficits precede synapse loss, gliosis and neurodegeneration in the B6.HttQ111/+ model of Huntington’s disease

Abstract

We investigated the appearance and progression of disease-relevant signs in the B6.HttQ111/+ mouse, a genetically precise model of the mutation that causes Huntington’s disease (HD). We find that B6.HttQ111/+ mice are healthy, show no overt signs of central or peripheral inflammation, and no gross motor impairment as late as 12 months of age. Behaviorally, we find that 4–9 month old B6.HttQ111/+ mice have normal activity levels and show no clear signs of anxiety or depression, but do show clear signs of reduced motivation. The neuronal density, neuronal size, synaptic density and number of glia is normal in B6.HttQ111/+ striatum, the most vulnerable brain region in HD, up to 12 months of age. Despite this preservation of the synaptic and cellular composition of the striatum, we observe clear progressive, striatal-specific transcriptional dysregulation and accumulation of neuronal intranuclear inclusions (NIIs). Simulation studies suggest these molecular endpoints are sufficiently robust for future preclinical studies, and that B6.HttQ111/+ mice are a useful tool for modeling disease-modifying or neuroprotective strategies for disease processes before the onset of overt phenotypes.

Peripheral huntingtin silencing does not ameliorate central signs of disease in the B6.HttQ111/+ mouse model of Huntington’s disease

“…Consistent with previous observations [16,26], we did not observe changes in body weight in Htt Q111/+ mice relative to wild-types ( P min = 0.27, p = 0.92). Therefore, we solely focused on the treatment effects by pooling weight observations from both the Htt Q111/+ and Htt +/+ mice.…”

“…In order to restrict our analysis to neurons, we created a mask for our images by selecting only cells immunoreactive for Rbfox3 (also known as NeuN), a pan-neuronal marker protein [28]. Consistent with previous investigations [16], we observe accumulation of p62-immunoreactive NII’s in striatal neurons from Htt Q111/+ mice (22.5 ± 0.14% of Htt Q111/+ striatal neurons have NIIs (0.5–5 μm 2 size cutoff) compared to 0 ± 0.3% of Htt +/+ neurons, Fig 3). Peripheral treatment of Htt Q111/+ mice with Htt ASO does not impact this phenotype (effect of treatment: F (2,24) = 1.6, p = 0.2, Fig 3).…”

“…In each case, transcript levels were reduced in the striatum of Htt Q111/+ mice relative to Htt +/+ mice using both RNASeq ( Drd1a : F (1,29) = 103.78, FDR = 1.66 x 10 −12 , Pde10a : F (1,29) = 168.06, FDR = 5.94 x 10 −15 ) and QRT-PCR detection methods ( Drd1a : F (1,53) = 67.97, p = 4.57 x 10 −11 , Pde10a : F (1,53) = 44.47, p = 1.54 x 10 −8 ). To ensure neither our QRT-PCR or RNAseq methods preferentially detected only downregulated genes, we quantified HD-relevant transcripts previously reported as upregulated in the striatum of Htt Q111/+ mice [16]. For instance, we successfully replicated increased steady state levels of Islr2 and N4bp2 in 10-month Htt Q111/+ mice (Fig 5) using both RNAseq ( Islr2 : F (1,29) = 42.84, FDR = 3.45 x 10 −8 and N4bp2 : F (1,29) = 10.96, FDR = 1.67 x 10 −3 ) and QRT-PCR ( Islr2 : F (1,52) = 10.65, p = 1.95 x 10 −3 and N4bp2 : F (1,53) = 7.68, p = 7.68 x 10 −3 ).…”

“…QRT-PCR was conducted and analyzed as described [16] using the following taqman probes purchased from Life Technologies: Drd1a: Mm02620146\_s1, N4bp2: Mm01208882\_m1, Islr2: Mm00623260\_s1, Pde10a: Mm00449329\_m1, and β-actin: Mm02619580_g1. All transcripts were normalized to β-actin.…”

Early Detection of Apathetic Phenotypes in Huntington’s Disease Knock-in Mice Using Open Source Tools

“…Htt Q111/ + mice, a knock-in mouse model of the HD mutation 23 . Using commercially available tools we, and others, have previously observed motivational phenotypes in this model that precede motor or cognitive changes 24 – 27 . Using the open-source ROBucket, we confirm specific deficits in progressive, but not fixed, ratio tasks in B6.…”