Upregulation of miR-18a-5p contributes to epidermal necrolysis in severe drug eruptions

Background: Toxic epidermal necrolysis (TEN) is a severe drug-induced cutaneous reaction. Although one of the primary histologic features of TEN is keratinocyte apoptosis, its exact mechanism remains unknown. Objectives: We investigated the role of microRNAs (miRNAs) in the pathogenesis of severe drug eruptions and evaluated the possibility that miRNA can be a disease marker. Methods: miRNAs were extracted from tissues and sera of patients. PCR array analyses were performed to identify pathogenic miRNAs. The results were confirmed with quantitative real-time PCR, in situ hybridization, transient transfection of small interfering RNAs or miRNA mimics into cultured keratinocytes, flow cytometry, immunoblotting, luciferase assay, and immunohistochemistry. Results: PCR array analysis and real-time PCR using tissue miRNAs demonstrated that the miR-18a-5p level was increased in the skin of patients with TEN in vivo. Transfection of the miR-18a5p mimic into keratinocytes in vitro resulted in increased apoptotic cell numbers and caspase-9 activity, which were also increased in the skin of patients with TEN. The miR-18a-5p mimic also downregulated the expression of B-cell lymphoma/leukemia-2-like protein 10 (BCL2L10), an anti-intrinsic apoptotic molecule. A luciferase assay with the BCL2L10 39 untranslated region showed BCL2L10 is directly targeted by miR-18a-5p. The protein and mRNA expressions of BCL2L10 were decreased in the skin of patients with TEN. Transfection with BCL2L10 small interfering RNA induced keratinocyte apoptosis and caspase activity. Furthermore, serum miR-18a-5p levels tended to be increased in patients with TEN and were correlated with areas of skin erythema or erosion in patients with drug eruptions. Conclusions: Our results indicated that downregulated BCL2L10 caused by miR-18a-5p overexpression mediates intrinsic keratinocyte apoptosis in patients with TEN. Serum miR-18a-5p levels can be a useful disease marker for drug eruptions.