Identification of miR-1246 as a new infection marker in human and canine macrophage-like cells infected by Leishmania infantum

In recent years, microRNAs (miRNAs) have emerged as key regulators of inflammation and immune responses. Leishmaniasis is a neglected infectious disease affecting humans and other mammals (mainly dogs), caused by protozoa belonging to the Leishmania genus. The parasite primarily infects the macrophages, establishing a niche permissive for its proliferation. Although several studies analyzed the host miRNome during infection with different Leishmania species, only a few reports investigated the miRNA dysregulation following infection with L. infantum. In this study, miRNA-seq was performed on human monocytic cells (U937, THP-1), and canine macrophage-like cells (DH82) infected by L. infantum for 24h or 48h, alongside culture media at 48h post-infection (for THP-1 and DH82 cells). Differential expression analysis identified miR-1246 as one of the most significantly upregulated miRNAs in infected U937,THP-1 cells, and THP-1 culture media. Although miR-1246 is not annotated in dog, its mature sequence shared 100% identity with a fragment of canine U2 spliceosomal RNA sequence which is identical to human RNU2. Interestingly, the miR-1246 qPCR human assay successfully detected miR-1246 in DH82 samples, revealing a significant upregulation in culture media of infected cells. To explore the potential functional impact of miR-1246, expression levels of three validated target genes involved in immune regulation (i.e., GSK3B, CD22, XK) were assessed in infected U937 and/or THP-1 cells. While GSK3B expression remained unchanged in both in vitro models, CD22 and XK were significantly downregulated in U937 cells. These preliminary findings suggest a potential role for miR-1246 in modulating host responses during L. infantum infection in a one health context, highlighting it as a candidate infection marker in both human and canine leishmaniasis.