D005 Peripheral blood biomarkers at the single-cell resolution in Huntington's disease

<h3></h3> In the search of biomarkers in Huntinton’s disease (HD), RNA molecules can be screened using unbiased high-throughput approaches for the identification of cost-effective and sensitive indicators. However, past transcriptomics studies from peripheral blood of HD mutation carriers have produced inconsistent candidates, despite the expression of mHTT in blood cells. Altered gene expression patterns from relevant blood cell types may be masked in this highly heterogenous and ever changing body fluid. Single-cell gene profiling may provide insights regarding the best cellular sources for blood biomarkers. This study is a proof-of-concept about the use of single-cell transcriptomics in HD biomarker screening. From two pools of peripheral blood mononuclear cells (HD symptomatic patients and control donors balanced in gender and age), we conducted two independent single-cell RNA-seq assays according to Chromium 10xGenomics procedures. Bioinformatic analysis was performed to cluster single transcriptional profiles of good quality and to estimate the differentially expressed genes within each cluster. Despite similar behaviours between both technical replicates, we found substantial differencies in the number of cells and gene expression patterns (together with skewed representations of individual samples across cell clusters) that should be taken into account when interpretating the results. However, common alterations revealed interesting implications regarding the basal state of immune cells to be tested in a larger cohort. Technical replicates are advisable to consider, which may limit the application of this still expensive technology in biomarker screening, but single-cell transcriptomics remains a powerful approach for the formulation of unforeseen novel hypotheses. Work supported by grants CPII20/00025, PI19/00125, PI23/01858 (ISCIII, ESDF), CNS2022-136169 (MICIU, NextGenerationEU), 2021-0406, 2022-0338 (ISABIAL) and Fundación Navarro-Tripodi.