Metabolomic Analysis of Plasma in Huntington’s Disease Transgenic Sheep (Ovis aries) Reveals Progressive Circadian Rhythm Dysregulation

Abstract

Background: Metabolic abnormalities have long been predicted in Huntington’s disease (HD) but remain poorly characterized. Chronobiological dysregulation has been described in HD and may include abnormalities in circadian-driven metabolism. Objective: Here we investigated metabolite profiles in the transgenic sheep model of HD (OVT73) at presymptomatic ages. Our goal was to understand changes to the metabolome as well as potential metabolite rhythm changes associated with HD. Methods: We used targeted liquid chromatography mass spectrometry (LC-MS) metabolomics to analyze metabolites in plasma samples taken from female HD transgenic and normal (control) sheep aged 5 and 7 years. Samples were taken hourly across a 27-h period. The resulting dataset was investigated by machine learning and chronobiological analysis. Results: The metabolic profiles of HD and control sheep were separable by machine learning at both ages. We found both absolute and rhythmic differences in metabolites in HD compared to control sheep at 5 years of age. An increase in both the number of disturbed metabolites and the magnitude of change of acrophase (the time at which the rhythms peak) was seen in samples from 7-year-old HD compared to control sheep. There were striking similarities between the dysregulated metabolites identified in HD sheep and human patients (notably of phosphatidylcholines, amino acids, urea, and threonine). Conclusion: This work provides the first integrated analysis of changes in metabolism and circadian rhythmicity of metabolites in a large animal model of presymptomatic HD.

Large animal models for Huntington’s disease research

“…Notably, samples from 7-year-old HD sheep exhibited an increased number of altered metabolites and a greater shift in the acrophase compared to control sheep. Furthermore, the dysregulated metabolites identified in HD sheep showed remarkable similarity to those found in human patients, particularly involving phosphatidylcholines, amino acids, urea, and threonine ( Morton, 2023 ; Spick et al, 2023 ).…”

“…These results reaffirm the suitability of HD sheep as a valuable large animal model for preclinical assessment of HD therapies and, importantly, for noninvasive evaluation of therapeutic efficacy ( Taghian et al, 2022 ). In a recent metabolomics study, Spick et al ( 2023 ) observed significant absolute and rhythmic differences in metabolites between HD sheep at 5 and 7 years of age compared to age-matched control sheep. Notably, samples from 7-year-old HD sheep exhibited an increased number of altered metabolites and a greater shift in the acrophase compared to control sheep.…”

Metabolomics: An Emerging “Omics” Platform for Systems Biology and Its Implications for Huntington Disease Research

“…These sheep have 73 full-length repeated CAG amplification units of human cDNA transgenes. However, they lack both clear behavioral changes and structural changes in the brain [54], with only subtle neuropathology [55] and few postmortem (PM) changes in the cerebellar and liver metabolism [56], indicating that the sheep, even at 5 years of age, are still in the pre-symptomatic stage of HD. An advantage of the HD sheep model is that it can be monitored long-term to document metabolic alterations in the course of development, which enables the progression of the disease to be monitored through metabolic alterations such as rate markers or disease progression [57].…”

“…In another previously conducted study investigating metabolite profiles using LC/MS in a transgenic sheep model of HD (OVT73) at pre-symptomatic ages, the circadian rhythmicity of metabolites (notably, phosphatidylcholines, amino acids, urea, and threonine) was found to be dysregulated in pre-symptomatic sheep. Alterations in the metabolomic profile could be used to differentiate the HD sheep from controls at 5 years of age [54].…”

Somatic CAG Repeat Stability in a Transgenic Sheep Model of Huntington’s Disease

“…OVT73 are a premanifest model expressing an 11,625 bp transgene consisting of full length human HTT cDNA with an exon 1 repeat (CAG)69(CAACAG)2, under the control of a minimal human HTT promoter (1.1 Kb genomic DNA immediately upstream of exon 1) [28]. The OVT73 model develops HTT positive aggregates, gene expression and metabolic changes in the brain but no discernible cell loss [28][29][30][31][32][33][34][35][36][37][38][39][40]. The transgene is integrated as multiple copies at a single locus in an intergenic region of ovine chromosome 10, with approximately 10 full length copies integrated head-to-tail, surrounded by several smaller transgene fragments that lack promoter sequence [30].…”