Single-cell RNA sequencing of cerebrospinal fluid reveals the expansion of innate lymphoid cells with upregulated transposable elements in multiple sclerosis

<ns3:p>Background Multiple sclerosis (MS) is a chronic and often immune-mediated demyelinating disease with no definitive treatment. Transposable elements (TEs) are receiving increasing attention as potential contributors to neurodegenerative diseases. However, to the best of our knowledge, no studies have examined the possible association of TE expression and its potential role in MS pathogenesis at the single-cell level. Results In this study, we reanalyzed single-cell RNA sequencing data from human cerebrospinal fluid (CSF) samples. Our results revealed that TEs are overexpressed in a cluster of cells annotated as innate lymphoid cells (ILCs). Furthermore, enrichment analysis of the associated transcription factors (TFs) with highly upregulated TEs in ILCs revealed the relevance of these TFs to immune pathways and cis-regulatory regions in DNA. Conclusions We propose that upregulated TEs in ILCs are consistent with the plasticity of these cells, as TEs can insert themselves in coding or regulatory regions of immune-related genes and represent themselves as immune-related TF binding sites. We also hypothesize that ILCs with overexpressed TEs could present TE-derived antigens, potentially reactivating T cell-mediated immunity in the central nervous system (CNS) of MS patients. Therefore, this study indicates a possible mechanism involving TEs in ILC plasticity and their potential role in MS pathogenicity. Additionally, we suggest that repurposing nucleoside reverse transcriptase inhibitors (NRTIs) or developing new high-efficacy NRTIs could be a feasible approach to treating MS.</ns3:p>