Dexamethasone-induced cytotoxicity in human osteoblasts is associated with circular RNA HIPK3 downregulation

Dexamethasone (DEX) exerts potent cytotoxicity against cultured human osteoblasts. The current study examined the role of the circular RNA HIPK3 (circHIPK3) in the mechanism of cell death. We found that circHIPK3 expression was downregulated in DEX-treated human osteoblasts and circHIPK3 levels decreased in human necrotic femoral head tissues. In OB-6 osteoblastic cells and primary human osteoblasts ectopic overexpression of circHIPK3 potently suppressed DEX-induced apoptosis and programmed necrosis. Conversely, knockdown of circHIPK3by targeted siRNAs enhanced DEX-induced cytotoxicity in human osteoblasts. We further observed that microRNA-124 (miR-124), a key miRNA sponged by circHIPK3, accumulated following DEX treatment in OB-6 cells and primary osteoblasts. Confirming the role of miR-124 in DEX-induced cytotoxicity, miR-124 inhibitor attenuated cell death in human osteoblasts. Conversely, forced overexpression of miR-124 mimicked DEX-induced actions and induced cytotoxicity in human osteoblasts. We conclude that DEX-induced cytotoxicity in human osteoblasts is associated with circHIPK3 downregulation.