Quantification of Huntington's Disease Related Markers in the R6/2 Mouse Model.

Estibaliz Etxeberria-Rekalde,Isabella Hable,Joerg Neddens,Stefanie Flunkert,Magdalena Daurer,Saioa Alzola-Aldamizetxebarria,Birgit Hutter-Paier

doi:10.3389/fnmol.2020.617229

Abstract

Huntington’s disease (HD) is caused by an expansion of CAG triplets in the huntingtin gene, leading to severe neuropathological changes that result in a devasting and lethal phenotype. Neurodegeneration in HD begins in the striatum and spreads to other brain regions such as cortex and hippocampus, causing motor and cognitive dysfunctions. To understand the signaling pathways involved in HD, animal models that mimic the human pathology are used. The R6/2 mouse as model of HD was already shown to present major neuropathological changes in the caudate putamen and other brain regions, but recently established biomarkers in HD patients were yet not analyzed in these mice. We therefore performed an in-depth analysis of R6/2 mice to establish new and highly translational readouts focusing on Ctip2 as biological marker for motor system-related neurons and translocator protein (TSPO) as a promising readout for early neuroinflammation. Our results validate already shown pathologies like mutant huntingtin aggregates, ubiquitination, and brain atrophy, but also provide evidence for decreased tyrosine hydroxylase and Ctip2 levels as indicators of a disturbed motor system, while vesicular acetyl choline transporter levels as marker for the cholinergic system barely change. Additionally, increased astrocytosis and activated microglia were observed by GFAP, Iba1 and TSPO labeling, illustrating, that TSPO is a more sensitive marker for early neuroinflammation compared to GFAP and Iba1. Our results thus demonstrate a high sensitivity and translational value of Ctip2 and TSPO as new marker for the preclinical evaluation of new compounds in the R6/2 mouse model of HD.

Highlights

Huntington’s disease (HD) is an autosomal-dominant inherited neurodegenerative disorder that typically starts in the fourth decade of life (Conneally, 1984) and affects about 5–10 per 100,000 individuals in the Western European population (Morrison et al, 1995; Rawlins et al, 2016)
Immunofluorescent signal was much lower at age 8 weeks, so the amount of mutated version of the huntingtin protein (mHTT) significantly increased with age in all three brain regions (230% in the cortex, 497% in the hippocampus, 2,250% in the caudate putamen; Figures 1A–C)
To evaluate motor-related pathologies, we used an antibody against COUPTF interacting protein 2 (Ctip2), while vesicular acetylcholine transporter (VAChT) was used as cholinergic neuron marker and tyrosine hydroxylase (TH) as marker for monoaminergic neurons and especially the dopaminergic system

Summary

Introduction

Huntington’s disease (HD) is an autosomal-dominant inherited neurodegenerative disorder that typically starts in the fourth decade of life (Conneally, 1984) and affects about 5–10 per 100,000 individuals in the Western European population (Morrison et al, 1995; Rawlins et al, 2016). R6/2 mice have a more severe phenotype and are characterized by progressive brain atrophy in the neostriatum and cerebral cortex, weight loss, motor dysfunction and neuronal accumulations of mHTT aggregates (Mangiarini et al, 1996; Carter et al, 1999; Stack et al, 2005). These mouse models are closely mimicking the human disease phenotype and are thought to be the most suitable model to mimic HD and evaluate new drugs against this devastating disease (Menalled et al, 2009). Both R6/2 sublines are available for HD research (Cowin et al, 2011)

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Conclusion