Protection by dietary restriction in the YAC128 mouse model of Huntington's disease: Relation to genes regulating histone acetylation and HTT

Abstract

Huntington's disease (HD) is a fatal neurodegenerative disease characterized by metabolic, cognitive, and motor deficits. HD is caused by an expanded CAG repeat in the first exon of the HTT gene, resulting in an expanded polyglutamine section. Dietary restriction (DR) increases lifespan and ameliorates age-related pathologies, including in a model of HD, but the mechanisms mediating these protective effects are unknown. We report metabolic and behavioral effects of DR in the full-length YAC128 HD mouse model, and associated transcriptional changes in hypothalamus and striatum. DR corrected many effects of the transgene including increased body weight, decreased blood glucose, and impaired motor function. These changes were associated with reduced striatal human (but not mouse) HTT expression, as well as alteration in gene expression regulating histone acetylation modifications, particularly Hdac2. Other mRNAs related to Huntington's pathology in striatal tissue showed significant modulation by the transgene, dietary restriction or both. These results establish a protective role of DR in a transgenic model that contains the complete human HTT gene and for the first time suggest a role for DR in lowering HTT level, which correlates with severity of symptoms.

Keywords: Creb-binding protein; Dietary restriction; HDAC; HTT; Huntington's disease; NF-κB; YAC128.

Figure 1. Dietary restriction prevents metabolic YAC128 phenotypes

(A) Body weights of WT and HD mice under ad lib conditions or dietary restriction (started at ~4 months and continued to ~8 months of age). Values are mean ±SEM (N=12–21 per group). HD Ad lib vs. WT ad lib by Bonferroni post-tests revealed significant differences; *, p<.05. **, p<.01. ***, p<.001. (B, C) Tail blood glucose and insulin measured at 3 months of diet (after overnight feeding). Data are mean ±SEM (n=12–21). *, p<.05 transgene effect; #, p<.05, ###, p<.001 diet effect by 2Way ANOVA. (D) Glucose levels (mg/dl) measured after glucose IP injection. Values are mean ±SEM (N=7–11 per group). Main effect of diet by 2-Way ANOVA was detected, p<.01. (E) Daily blood glucose difference (measurements taken at ZT21-ZT9 in ~8 month old mice). Data are means ± SEM (N=12–21). §§, p<.01; §§§, p<.001 Bonferroni post-test. (2-column fitting image)

Figure 2. Dietary restriction prevents motor YAC128 phenotypes

(A–B) Time spent on rotarod before falling of WT and HD mice under ad lib conditions or dietary restriction. Values are mean ±SEM (n=12–21 per group). **, p<.01 2-Way ANOVA transgene effect. §, p<.01 Bonferroni post test. (C) Average activity measured in 5-minute bins of a 1-hour period. (B) Average activity bins measured in 5-minute intervals for 60 minutes. Values are means ± SEM (n=12–16 per group). **, p<.01 by 1Way ANOVA followed by Dunnett’s post hoc. (2-column fitting image)

Figure 3. Dietary restriction results in hypothalamic reprogramming towards fatty acid metabolism and away from glucose

Quantitative real-time PCR data for murine (A) Cbp, (B) Pomc, (C) Agrp, (D) Npy, (E) Gsk3b, (F) Pdk3, (G) Pdk1, (H) Crot, (I) Crat, (J) Acox3, and (K) Acox1. Data is expressed in fold changes compared to Ad lib WT. Data are means ±SEM (n=6–11). *, p<0.05 2-Way ANOVA transgene effect. #, p<0.05; ##, p<.01; ###, p<.001 2-Way ANOVA diet effect. §, p<0.05 using Bonferroni’s post test. (2-column fitting image)

Figure 4. Dietary restriction is associated with histone modification transcripts in the striatum

Expression of HD related genes in the striatum after 4 months of dietary restriction in YAC128 mice and WT controls. Quantitative real-time PCR data for murine (A) Cbp,(B) Hdac1, and (C) Hdac2. Data is expressed in fold changes compared to ad lib WT. Data are means ±SEM (n=7–9). **, p<0.01; ***, p<.001 2-Way ANOVA transgene effect. #, p<0.05 2-Way ANOVA diet effect. §, p<0.05 using Bonferroni’s post test. (single column fitting image)

Figure 5. Many striatal genes that modulate calcium signaling were regulated by mutant HTT and unaffected by dietary restriction

Expression of HD related genes in the striatum after 4 months of dietary restriction in the YAC128 mouse and WT controls. White bars indicate ad libitum, black bars indicate dietary restricted animals. Quantitative real-time PCR data for murine genes (A) Atp2b2, (B) Calb1, (C) Cd44, (D) Cnr1, (E) Dctn1, (F) Elmo1, (G) Grb2, (H) Grm5, (I) Homer1, (J) Itpr1, (K) Map3k10, (L) Ncor1, (M) Ngef, (N) Ppp3ca, (O) Rest, (P) Rph3a, (Q) Sgk1, and (R) Slc25a4. Data is expressed in fold changes compared to ad lib WT. Data are means ±SEM (n=7–9). *, p<0.05; **, p<.01; ***, p<.001 2-Way ANOVA transgene effect. (2-column fitting image)

Figure 6. Dietary restriction regulates striatal genes involved in transcriptional regulation

Expression of HD related genes in the striatum after 4 months of dietary restriction in the Yac128 mouse and WT controls. White bars indicate ad libitum, black bars indicate dietary restricted animals. Quantitative real-time PCR data for murine genes (A) Bbox1, (B) Cltc, (C) Eef1a2, (D) Gabrd, (E) Gjb6, (F) Hip1, (G) Pgk1, (H) Prpf40a, (I) Sod1, (J) Sp1, (K) Sympk, (L) Tbp, (M) Trp53, and (N)Tubb5. Data is expressed in fold changes compared to ad lib WT. Data are means ±SEM (n=7–9). #, p<0.05; ##, p<.01; ###, p<.001 2-Way ANOVA diet effect. (2-column fitting image)

Figure 7. Mutant HTT blocks effects of dietary restriction on mRNA levels

Expression of HD related genes in the striatum after 4 months of dietary restriction in the Yac128 mouse and WT controls. White bars indicate ad libitum, black bars indicate dietary restricted animals. Quantitative real-time PCR data for murine genes (A) Apoe, (B) Ppp1r1b, (C) Gja1, (D) Gpx1, (E) Kcnab1, (F) Ntrk2, (G) Plod2, and (H) Rgs4. Data is expressed in fold changes compared to ad lib WT. Data are means ±SEM (n=7–9). Interactions between diet and transgene were detected in these genes by 2-Way ANOVA. *, p< 0.05; **, p<.01; ***, p<.001 2-Way ANOVA transgene effect. #, p<0.05; ##, p<.01 2-Way ANOVA diet effect. §, p<.05 Bonferroni post-test. (Single column fitting image)

Figure 8. DR specifically reduces Human HTT in the Striatum

Expression of HD related genes after 4 months of dietary restriction in the Yac128 mouse and WT controls. Quantitative real-time PCR data for striatal (A) HTT (Human), (B) Htt (Mouse), (C) Nfkb1, and hypothalamic (D) HTT (Human). Data are means ±SEM (n=7–9). **, P<.01 Student’s t-test. ###, P< 0.05 2-Way ANOVA diet effect. (Single column fitting image)