Temporally resolved single-nucleus RNA-sequencing profiling of the cortex reveals mechanisms of neuronal vulnerability in Huntington’s disease

Feigenbutz, Dennis (2025): Temporally resolved single-nucleus RNA-sequencing profiling of the cortex reveals mechanisms of neuronal vulnerability in Huntington’s disease. Dissertation, LMU München: Fakultät für Biologie

Abstract

Huntington’s disease (HD) is a fatal neurodegenerative disease characterized by severe motor impairments. HD is caused by the expansion of CAG repeats in the Huntingtin (HTT) gene, resulting in the mutated HTT protein (mHTT) to form aggregates predominantly in the striatum and cortex of patients. Within these brain regions, neuronal populations exhibit varying degrees of cell loss, with cortical projection neurons (CPNs) in the motor cortex (MC) being particularly vulnerable, while locally projecting GABAergic interneurons are mostly spared. Despite extensive research, the underlying disease pathogenesis and molecular factors rendering certain populations more vulnerable remain elusive, with no effective treatments available. In this study, we utilized the transgenic R6/2 mouse model of HD to conduct a longitudinal single-nucleus RNA (snRNA-seq) study, investigating transcriptomic changes in the MC across three distinct time points from presymptomatic to disease onset to advanced disease stage. Our analysis uncovers several key mechanisms at play in R6/2 mice. We show that the vulnerable glutamatergic CPNs undergo a pronounced transcriptomic shift, while locally projecting GABAergic interneurons remain largely unaffected. Additionally, a subset of genes exhibits a bidirectional temporal expression pattern, characterized by early downregulation followed by late-stage upregulation, potentially contributing to disease onset. Furthermore, we demonstrate a decrease in marker gene expression across a multitude of cell populations in the MC of R6/2 mice. Moreover, our findings highlight two potentially disease-modifying molecular mechanisms. Firstly, we provide evidence for the occurrence of chronic endoplasmic reticulum (ER) stress and the subsequent upregulation of the unfolded protein response (UPR) in R6/2 mice. Interestingly, several receptors for autophagy of the ER (ER-phagy) are upregulated, suggesting a compensatory mechanism to alleviate ER stress. We demonstrate that ER-phagy is increased in cellular models of HD. Potentially, modification of ER-phagy might be utilized to prevent chronic ER stress in HD. Lastly, we identified a set of neuronal essential gene with increased expression in GABAergic interneurons, which might contribute to the enhanced resilience of interneurons to HD. Among these genes, the chaperone proSAAS emerged as an upregulated hub gene in R6/2 mice. Here, we demonstrate that proSAAS translocates to the nucleus in the presence of nuclear mHTT aggregates, suggesting an interplay between proSAAS and mHTT. Taken together, our temporally resolved analysis of single-nucleus transcriptomic changes in HD mouse cortex provides novel insights into the mechanisms of neuronal vulnerability, and points to new disease-relevant pathways that could be targeted for future therapeutic interventions.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Neuroscience, neurodegeneration, neuronal vulnerability, Huntingon's disease, motor cortex, single-cell RNAseq, single-nucleus RNAseq, ER stress, ER-phagy, proSAAS
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 4. Februar 2025
• 1. Bericht­erstatter:in: Klein, Rüdiger