Altered duodenal N6-methyladenosine levels in common variable immunodeficiency associate with duodenal microbiota.

Introduction: Common variable immunodeficiency (CVID) is frequently complicated by duodenal inflammation, but the underlying molecular mechanisms remain poorly understood. While epigenetic alterations have been described in CVID, the epitranscriptome is largely unexplored. We therefore investigated whether RNA N6-methyladenosine (m6A) modifications in duodenal tissue are altered in CVID and whether such changes are associated with the local microbiota or m6A-related enzymes. Methods: m6A modification levels were analysed in snap-frozen duodenal biopsies from CVID patients with intraepithelial lymphocytosis and inflammation (CVID_IEL; n = 5), CVID patients with normal duodenal histology (CVID_N; n = 5) and controls with normal biopsies (n = 5) using m6A-RNA immunoprecipitation followed by microarray profiling and gene set enrichment analysis. Duodenal bacterial microbiota from the same anatomical region were characterised by 16S ribosomal RNA gene sequencing, and selected m6A-regulating enzymes were quantified in biopsies by targeted proteomics. Results: In total, 4,134 differentially methylated transcripts were identified, and unsupervised principal component analyses revealed partially overlapping, but clearly divergent m6A signatures for CVID_IEL, CVID_N and controls, with a gradient along the first principal component. Pathway analysis showed relative hypermethylation of mitochondria- and ribosome-related gene sets in both CVID subgroups versus controls, and hypomethylation of pathways linked to ubiquitination, proteasomal degradation, glycosylation and post-transcriptional gene silencing in CVID_IEL versus CVID_N. Sparse canonical correlation models demonstrated significant associations between specific duodenal bacterial genera and m6A-modified transcripts in CVID, but not in controls, whereas expression levels of the examined m6A-regulating enzymes did not differ between groups. Discussion: These findings suggest that duodenal inflammation in CVID may be associated with a distinct m6A epitranscriptomic signature that is linked to specific features of the mucosal microbiota, providing preliminary, hypothesis-generating evidence for a potential interaction between microbiota, epitranscriptomic regulation and local immune dysregulation in CVID.