In Vivo Therapeutic Success of MicroRNA‐155 Antagomir in a Mouse Model of Lupus Alveolar Hemorrhage

Objective Diffuse alveolar hemorrhage (DAH) is a rare but life‐threatening complication of systemic lupus erythematosus (SLE). Pristane‐treated B6 mice develop severe DAH within 2 weeks of treatment. MicroRNA‐155 (miR‐155) is a pleiotropic microRNA that plays a crucial role in the regulation of immune responses. Recent studies have revealed a pathogenic role of miR‐155 in various autoimmune disorders. The purpose of this study was to examine the role of miR‐155 in the development of DAH in pristane‐induced lupus using miR‐155–knockout (miR‐155 −/− ) mice and miR‐155 antagomir to silence miR‐155. Methods DAH was induced by an intraperitoneal injection of 0.5 ml of pristane. MicroRNA‐155 antagomir was administered intravenously to silence miR‐155 expression. Lung tissues were collected for RNA extraction and were embedded in paraffin for sectioning. Gene expression profiling data were analyzed using Ingenuity Pathway Analysis. Real‐time quantitative polymerase chain reaction analysis was used for single‐gene validation. Luciferase reporter assay and argonaute 2 immunoprecipitation were performed for target validation. Results MicroRNA‐155 expression was significantly increased during the development of DAH. Disease progression was reduced in miR‐155 −/− mice as well as by in vivo silencing of miR‐155 using a miR‐155 antagomir. MicroRNA‐155 silencing dampened pristane‐induced ectopic activation of multiple inflammatory pathways and reduced the expression of proinflammatory cytokines. Several negative regulators of NF‐κB signaling were inhibited by pristane and were reactivated in miR‐155 −/− mice. In particular, the antiinflammatory factor peroxisome proliferator–activated receptor α was identified as a direct target of miR‐155. Conclusion MicroRNA‐155 promotes pristane‐induced lung inflammation. It contributes to ectopic activation of NF‐κB signaling pathways by targeting multiple negative regulators. MicroRNA‐155 antagomir may be a promising therapeutic strategy for treating acute lung inflammation in lupus.