Metabolic disruption identified in the Huntington’s disease transgenic sheep model

Huntington’s disease (HD) is a dominantly inherited, progressive neurodegenerative disorder caused by a CAG repeat expansion within exon 1 of HTT, encoding huntingtin. There are no therapies that can delay the progression of this devastating disease. One feature of HD that may play a critical role in its pathogenesis is metabolic disruption. Consequently, we undertook a comparative study of metabolites in our transgenic sheep model of HD (OVT73). This model does not display overt symptoms of HD but has circadian rhythm alterations and molecular changes characteristic of the early phase disease. Quantitative metabolite profiles were generated from the motor cortex, hippocampus, cerebellum and liver tissue of 5 year old transgenic sheep and matched controls by gas chromatography-mass spectrometry. Differentially abundant metabolites were evident in the cerebellum and liver. There was striking tissue-specificity, with predominantly amino acids affected in the transgenic cerebellum and fatty acids in the transgenic liver, which together may indicate a hyper-metabolic state. Furthermore, there were more strong pair-wise correlations of metabolite abundance in transgenic than in wild-type cerebellum and liver, suggesting altered metabolic constraints. Together these differences indicate a metabolic disruption in the sheep model of HD and could provide insight into the presymptomatic human disease

Effect of <i>PIGR</i> genotype on IgA yield and <i>PIGR</i> expression.

<p>Phenotypic effects (± SEM) of the six possible <i>PIGR</i> genotypes (I/I, II/II, III/III, I/II, I/III, II/III – I: blue; II: green; III: red; cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g004" target="_blank">Fig. 4</a>) on IgA yield of the 8^th colostrum (<b>A</b>) and <i>PIGR</i> expression in liver (<b>B</b>). In general the phenotypic mean of the heterozygotes is intermediate between the corresponding alternate homozygotes, supporting additivity.</p

Effects of hidden haplotype states.

<p>Bivariate effects (Y-axis: <i>PIGR</i> expression in liver; X-axis: IgA yield of 8^th colostrum) of the 20 Hidden Haplotype States at the most likely position of the 8^th colostrum IgA yield QTL (4,533,875). Hidden Haplotype States are labelled according to their <i>PIGR</i> haplotype (I: blue; II: green; III: red; cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g004" target="_blank">Fig. 4</a>).</p

Chromosome 16 eQTL for <i>PIGR</i> mRNA expression.

<p>(<b>A</b>) Location scores (LRT = likelihood ratio test) obtained when scanning bovine chromosome 16 for QTL influencing <i>PIGR</i> transcript levels (black line) in liver using a mixed-model based approach that simultaneously extracts linkage and LD information. The red curve corresponds to the location scores obtained for <i>PIGR</i> mRNA expression level (liver) when adding the effect of <i>PIGR</i> haplotype (I, II and III; cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g004" target="_blank">Fig. 4</a>) in the model. The gray line corresponds to the location score obtained for IgA yield of the 8^th colostrum (cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g001" target="_blank">Fig. 1A</a>). (<b>B</b>) Effect (± SEM) of the haplotypes of the six F1 sires on <i>PIGR</i> expression level in liver. The haplotypes are labeled according to their corresponding <i>PIGR</i> genotype (I: blue; II: green; III: red; cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g004" target="_blank">Fig. 4</a>).</p

A triad of highly divergent polymeric immunoglobulin receptor (PIGR) haplotypes with major effect on IgA concentration in bovine milk.

The aim of this study was to determine a genetic basis for IgA concentration in milk of Bos taurus. We used a Holstein-Friesian x Jersey F2 crossbred pedigree to undertake a genome-wide search for QTL influencing IgA concentration and yield in colostrum and milk. We identified a single genome-wide significant QTL on chromosome 16, maximising at 4.8 Mbp. The polymeric immunoglobulin receptor gene (PIGR) was within the confidence interval of the QTL. In addition, mRNA expression analysis revealed a liver PIGR expression QTL mapping to the same locus as the IgA quantitative trait locus. Sequencing and subsequent genotyping of the PIGR gene revealed three divergent haplotypes that explained the variance of both the IgA QTL and the PIGR expression QTL. Genetic selection based on these markers will facilitate the production of bovine herds producing milk with higher concentrations of IgA

Sequence comparison of <i>PIGR</i> haplotypes.

<p>(<b>A</b>) Variant positions at which the corresponding pair of <i>PIGR</i> haplotypes <b><i>D</i></b>iffer (upper line; “D”), or are the <b><i>S</i></b>ame (lower line; “S”). The positions of the <i>PIGR</i> exons are marked by the transparent gray boxes. (B) Schematic representation of the three major <i>PIGR</i> haplotypes with indication of the positions at which they differ or not. Within the body of the <i>PIGR</i> gene, haplotype I is appears as a recombinant between haplotype II and III, which differ on average every 109 nucleotides. Upstream of the gene, the three haplotypes differ on average every ∼200 nculeotides.</p

Chromosome 16 QTL for colostrum and milk IgA content.

<p>(<b>A</b>) Location scores (LRT = likelihood ratio test) obtained when scanning bovine chromosome 16 for QTL influencing IgA concentration (dotted lines) and yield (continuous line) in colostrum collected at the 2^nd milking (“2^nd colostrum”; light gray), colostrum collected at the 8^th milking (“8^th colostrum”; dark gray) and mid-lactation milk (black) using a mixed-model based approach that simultaneously extracts linkage and LD information. The red curve corresponds to the location scores obtained for IgA yield of 8^th colostrum (giving the strongest signal in single QTL analysis) when adding the effect of <i>PIGR</i> haplotype (I, II and III; cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g004" target="_blank">Fig. 4</a>) in the model. (<b>B</b>) Effect (± SEM) of the haplotypes of the six F1 sires on IgA yield of the 8^th colostrum (mg/milking). The haplotypes are labeled according to their corresponding <i>PIGR</i> genotype (I: blue; II: green; III: red; cfr. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057219#pone-0057219-g004" target="_blank">Fig. 4</a>).</p