Periyasamy, K.; Kingo, K.; Paneque, R. H.; Remm, A.; Pook, M.; Vaher, H.; Kingo, K.; Rebane, A.

miR-378a-3p has been reported to be upregulated in the lesional skin of patients with atopic dermatitis (AD); however, its function in AD remains unclear. Here, we demonstrate that miR-378a-3p expression is induced by IL-4 and live Staphylococcus aureus (S. aureus) in normal human epidermal keratinocytes (NHEKs) cultured in proliferative conditions or in a 3D epidermal culture model. Transcriptomic profiling and gene set enrichment analysis of miR-378a-3p-transfected NHEKs revealed positive enrichment of inflammatory response pathways alongside downregulation of genes associated with epidermal development. More specifically, miR-378a-3p enhanced expression of multiple NF-{kappa}B-dependent inflammatory mediators, accompanied by increased phosphorylation of p65, indicating activation of canonical NF-{kappa}B pathway. Notably, miR-378a-3p concomitantly reduced the expression of several NF-{kappa}B family members and upstream adaptor molecules, supporting a model in which miR-378a-3p promotes canonical NF-{kappa}B activity through coordinated modulation of multiple components within the NF-{kappa}B regulatory network. In NHEKs exposed to live S. aureus, miR-378a-3p significantly increased the secretion of IL-1{beta}, IL-1Ra, and IL-8, indicating that miR-378a-3p may amplify innate immune responses triggered by S. aureus colonization in AD. Collectively, these findings identify miR-378a-3p as a positive regulator of keratinocyte inflammatory responses that may contribute to AD exacerbation, particularly in the context of S. aureus colonization.