MicroRNA-146a alleviates chronic skin inflammation in atopic dermatitis through suppression of innate immune responses in keratinocytes

Background Chronic skin inflammation in atopic dermatitis (AD) is associated with elevated expression of proinflammatory genes and activation of innate immune responses in keratinocytes. microRNAs (miRNAs) are short, single-stranded RNA molecules that silence genes via the degradation of target mRNAs or inhibition of translation. Objective The aim of this study was to investigate the role of miR-146a in skin inflammation in AD. Methods RNA and protein expression was analyzed using miRNA and mRNA arrays, RT-quantitative PCR, Western blotting, and immunonohistochemistry. Transfection of miR-146a precursors and inhibitors into human primary keratinocytes, luciferase assays, and MC903-dependent mouse model of AD were used to study miR-146a function. Results We show that miR-146a expression is increased in keratinocytes and chronic lesional skin of patients with AD. miR-146a inhibited the expression of numerous proinflammatory factors, including IFN-γ–inducible and AD-associated genes CCL5, CCL8 , and ubiquitin D ( UBD ) in human primary keratinocytes stimulated with IFN-γ, TNF-α, or IL-1β. In a mouse model of AD, miR-146a–deficient mice developed stronger inflammation characterized by increased accumulation of infiltrating cells in the dermis, elevated expression of IFN-γ, CCL5, CCL8, and UBD in the skin, and IFN-γ, IL-1β, and UBD in draining lymph nodes. Both tissue culture and in vivo experiments in mice demonstrated that miR-146a–mediated suppression in allergic skin inflammation partially occurs through direct targeting of upstream nuclear factor kappa B signal transducers caspase recruitment domain-containing protein 10 and IL-1 receptor–associated kinase 1. In addition, human CCL5 was determined as a novel, direct target of miR-146a. Conclusion Our data demonstrate that miR-146a controls nuclear factor kappa B–dependent inflammatory responses in keratinocytes and chronic skin inflammation in AD.