Laquinimod rescues striatal, cortical and white matter pathology and results in modest behavioural improvements in the YAC128 model of Huntington disease

Abstract

Increasing evidence supports a role for abnormal immune activation and inflammatory responses in Huntington disease (HD). In this study, we evaluated the therapeutic potential of laquinimod (1 and 10 mg/kg), a novel immunomodulatory agent shown to be protective in a number of neuroinflammatory conditions, in the YAC128 mouse model of HD. Treatment with laquinimod for 6 months rescued atrophy in the striatum, in certain cortical regions, and in the corpus callosum of YAC128 HD mice. Diffusion tensor imaging showed that white matter microstructural abnormalities in the posterior corpus callosum were improved following treatment with low dose (1 mg/kg) laquinimod, and were paralleled by reduced levels of interleukin-6 in the periphery of YAC128 HD mice. Functionally, treatment with laquinimod (1 and 10 mg/kg) led to modest improvements in motor function and in depressive-like behaviour. Taken together, these results suggest that laquinimod may improve some features of pathology in HD, and provides support for the role of immune activation in the pathogenesis of HD.

Figure 1. Laquinimod rescues striatal, cortical, and corpus callosum atrophy in YAC128 HD mice.

Striatal and cortical atrophy was assessed by structural MRI in the caudate-putamen, and five different areas of the cortex (A). Vehicle-treated YAC128 mice presented striatal atrophy compared with vehicle-treated WT mice as measured by structural MRI (B) and stereological assessment (H). Treatment with the highest dose of laquinimod (10 mg/kg) rescued striatal atrophy in YAC128 mice (A,H). Vehicle-treated YAC128 mice displayed cortical atrophy in the piriform (C) cingulate (E) and retrosplenial (F) areas of the cortex as measured by structural MRI. Treatment with laquinimod rescued cortical atrophy in the piriform (C) cingulate (E) and restrosplenial (F) areas of the cortex in YAC128 HD mice. Laquinimod-treated (10 mg/kg) YAC128 mice increased significantly the volume of the cingulate (E) and somatosensory (G) cortical regions compared with vehicle-treated YAC128 mice. Also, vehicle-treated YAC128 HD mice presented atrophy in the corpus callosum (CC) compared with vehicle-treated WT mice as measured by stereological assessment (I). Both doses of Laquinimod rescued CC atrophy in YAC128 mice (I). (B) Values shown as percentage of total brain volume ± SEM; n = 9 WT-vehicle, n = 6 YAC128-vehicle, n = 8 YAC128-laquinimod (1 mg/kg), n = 8, YAC128-laquinimod (10 mg/kg); *p < 0.05, ***p < 0.001, paired two-tailed Student’s t-test. CPu – caudate-putamen. (C,D,F) Values shown as mean ± SEM; n = 9 WT-vehicle, n = 7 YAC128-vehicle, n = 6–8 YAC128-laquinimod (1 mg/kg), n = 8, YAC128-laquinimod (10 mg/kg); *p < 0.05, **p < 0.01, ***p < 0.001 by one-way ANOVA with Tukey’s post hoc analysis. (E,G) Values shown as mean ± SEM; n = 9 WT-vehicle, n = 7 YAC128-vehicle, n = 6–8 YAC128-laquinimod (1 mg/kg), n = 8, YAC128-laquinimod (10 mg/kg); *p < 0.05 by paired two-tailed Student’s t-test. (H,I) Values shown as mean ± SEM; n = 9–10 WT-vehicle, n = 15–16 YAC128-vehicle, n = 18–19 YAC128-laquinimod (1 mg/kg), n = 20–21 YAC128-laquinimod (10 mg/kg); *p < 0.05, **p < 0.01 by paired two-tailed Student’s t-test. LAQ – laquinimod. CC – Corpus Callosum.

Figure 2. Laquinimod improves white matter microstructures in YAC128 HD mice.

Analysis of white matter microstructural changes by diffusion tension imaging (DTI) revealed a regionally dependent decrease of FA values in vehicle/laquinimod-treated YAC128 mice compared with vehicle-treated WT mice (A,B) (red-yellow indicates higher FA values in vehicle-treated WT mice; blue-light blue indicates lower FA values). Treatment with the lowest dose of laquinimod (1 mg/kg) increased FA values in the posterior CC (B middle panel) but not in the anterior CC or cingulum (B right and left panel, respectively). No effects on FA values were observed using high dose laquinimod (10 mg/kg) (B). Parallel (Dp) and radial (Dr) diffusivity were also investigated but no differences were observed between vehicle- or laquinimod-treated YAC128 HD mice compared to vehicle-treated WT mice (C,D). (B–D) Values shown as mean ± SEM; n = 8 WT-vehicle, n = 7 YAC128-vehicle, n = 8 YAC128-laquinimod (1 mg/kg), n = 8, YAC128-laquinimod (10 mg/kg); *p < 0.05, **p < 0.01 by one-way ANOVA with Tukey’s post hoc analysis; CC – Corpus Callosum. LAQ – laquinimod.

Figure 3. Effect of laquinimod on interleukin-6 levels in serum of YAC128 HD mice.

Vehicle-treated YAC128 HD mice presented increased serum levels of interleukin-6 (IL-6) compared with vehicle-treated WT mice. Low dose laquinimod (1 mg/kg) reduced the levels of serum IL-6 in YAC128 HD mice, whereas no effect was observed with high dose laquinimod (10 mg/kg). Values shown as mean ± SEM; n = 8 WT-vehicle, n = 16 YAC128-vehicle, n = 15 YAC128-laquinimod (1 mg/kg), n = 18 YAC128-laquinimod (10 mg/kg); *p < 0.05 and n.s. = not significant (compared with vehicle-treated WT) by paired Student’s t-test. LAQ – laquinimod.

Figure 4. Laquinimod improves motor function and depressive behaviour in YAC128 HD mice.

Vehicle-treated YAC128 HD mice displayed motor deficits in the climbing test (A). Low dose laquinimod partially restored performance in the climbing test in YAC128 HD mice by decreasing latency to climb at 4 and 8 months of age (A, upper panel) and increasing time spent climbing at 4 months of age (A, lower panel). High dose laquinimod improved latency to climb at 8 months of age (A, upper panel). In addition, vehicle-treated YAC128 HD mice displayed motor deficits in the accelerating rotarod test (B). Both doses of Laquinimod improved motor function in YAC128 HD mice at 6 months of age, which were maintained at 8 months with low dose laquinimod treatment (B). Also, vehicle-treated YAC128 HD mice exhibited increased immobility in the forced swim test of depression, which was reduced in laquinimod-treated YAC128 HD mice (C). Laquinimod treatment had no effect on weight gain in YAC128 HD mice (D). (A) Values shown as mean ± SEM; n = 10–11 WT-vehicle, n = 12–16 YAC128-vehicle, n = 19 YAC128-laquinimod (1 mg/kg), n = 19–22 YAC128-laquinimod (10 mg/kg); *p < 0.05, **p < 0.01, ****p < 0.0001 (compared with vehicle-treated WT) and ^#p < 0.05, ^##p < 0.01 (compared to vehicle-treated YAC128) by one-way ANOVA with LSD post hoc analysis. LAQ – laquinimod. (B) Values shown as percentage of baseline ± SEM.; n = 10–12 WT-vehicle, n = 16 YAC128-vehicle, n = 19 YAC128-laquinimod (1 mg/kg), n = 21–22 YAC128-laquinimod (10 mg/kg); *p < 0.05, **p < 0.01 (compared with vehicle-treated WT) by one-way ANOVA with Tukey’s post hoc analysis. (C) Values shown as mean ± SEM; n = 9 WT-vehicle, n = 17 YAC128-vehicle, n = 19 YAC128-laquinimod (1 mg/kg), n = 22 YAC128-laquinimod (10 mg/kg); *p < 0.05 (compared with vehicle-treated WT) by paired Student’s t-test. (D) Values shown as mean ± SEM; n = 12 WT-vehicle, n = 15 YAC128-vehicle, n = 19 YAC128-laquinimod (1 mg/kg), n = 22 YAC128-laquinimod (10 mg/kg); *p < 0.05, **p < 0.01, ***p < 0.001 by one-way ANOVA with Tukey’s post hoc analysis. LAQ – laquinimod.