Differentially expressed microRNAs, including a large microRNA cluster on chromosome 24, are associated with equine sarcoid and squamous cell carcinoma.

The aim of this study was to investigate microRNA (miRNA) differential expression in the two most common equine skin tumours, equine sarcoid (ES) and squamous cell carcinoma (SCC), and its potential influence on the tumour microenvironment at post-transcriptional level. We investigated miRNA fingerprints in four subgroups: mild (ESM) and aggressive (ESA) ES and ocular SCC (oSCC) and genital SCC (gSCC). Three tumours and three control samples were included in each of the four subgroups. Following next generation sequencing, miRNA differential expression analysis using DESeq2 was carried out. Pathways associated with the human mature homologues of identified dysregulated miRNAs were predicted using DIANA- miRPath v3.0. When comparing tumour vs control tissue, 57 miRNAs in ESM, six in ESA, 47 in oSCC and zero in gSCC were found to be differentially expressed and may thus serve as potential diagnostic tissue biomarkers. Whereas, ES lesions in general were associated with downregulation of the miR-200 family, which may trigger epithelial-mesenchymal transition, ESM lesions were associated with upregulation of the proposed tumour-suppressive miRNA cluster on equine chromosome 24. In contrast, the oSCC tumours showed downregulation of this cluster as well as downregulation of the miR-34 family, which may favour oSCC tumour cell metabolism. To further validate the proposed diagnostic miRNA fingerprints and their suggested biological effects, further miRNA studies need to be carried out in larger study cohorts.