Histone deacetylase inhibitor vorinostat (SAHA, MK0683) perturb miR-9-MCPIP1 axis to block IL-1-induced IL-6 expression in human OA chondrocytes

Aim of the Study: High levels of IL-6 are believed to contribute to osteoarthritis (OA) pathogenesis. The expression of IL-6 is regulated post-transcriptionally by the miR-9-MCPIP-1 axis in chondrocytes. Vorinostat (SAHA) inhibits the IL-6 expression in OA chondrocytes. We investigated whether SAHA suppresses the expression of IL-6 by perturbing the miR-9-MCPIP1 axis in OA chondrocytes under pathological conditions. Materials and Methods: OA chondrocytes were isolated by enzymatic digestion and treated with IL-1 in the absence or presence of SAHA. Genes and protein expression levels were determined by TaqMan assays and Western blotting, respectively. Secreted IL-6 was quantified by enzyme linked immunosorbent assay (ELISA). MCPIP1 promoter deletion mutants were generated by polymerase chain reaction (PCR). Promoter recruitment of transcription factors was determined by ChIP. Nuclear run-on was employed to measure the ongoing transcription. siRNA-mediated knockdown of the CEBP expression was employed for loss of function studies. Results: Expression of MCPIP1 was high in SAHA treated OA chondrocytes but expression of IL-6 mRNAs and secreted IL-6 were reduced by similar to 70%. SAHA suppressed the expression of miR-9 but enhanced the activity of the MCPIP1 promoter localized to a 156bp region which also harbors the binding site for CEBP. Treatment with SAHA enhanced the recruitment of CEBP to the MCPIP1 promoter. Ectopically expressed CEBP enhanced the promoter activity and the expression of MCPIP1 while siRNA-mediated knockdown of CEBP inhibited the expression of MCPIP1. Conclusions: Taken together our data indicate that SAHA-mediated suppression of the IL-6 expression is achieved through increased recruitment of CEBP to the MCPIP1 promoter and by relieving the miR-9-mediated inhibition of MCPIP1 expression in OA chondrocytes.