HIF-2 Inhibition Supresses Inflammatory Responses and Osteoclastic Differentiation in Human Periodontal Ligament Cells

Recent reports suggest that hypoxia inducible factor-2 (HIF-2) is a key regulator of osteoarthritis cartilage destruction. However, the precise role of HIF-2 in the inflammatory response and osteoclast differentiation remains unclear. The purpose of this study was to investigate the effect of HIF-2 on inflammatory cytokines, extracellular matrix (ECM) destruction enzymes, and osteoclastic differentiation in nicotine and lipopolysaccharide (LPS)-stimulated human periodontal ligament cells (PDLCs). HIF-2 was upregulated in chronically inflamed PDLCs of periodontitis patients, and in nicotine- and LPS-exposed PDLC in dose- and time-dependent manners. HIF-2 inhibitor and HIF-2 siRNA attenuated the nicotine- and LPS- induced production of NO and PGE(2), upregulation of iNOS, COX-2, pro-inflammatory cytokines (IL-1, TNF-, IL-1, IL-6, IL-8, IL-10, IL-11, and IL-17), and matrix metalloproteinases (MMPs; MMP-1, -8, -13, -2 and -9), and reversed the effect on TIMPs (TIMP-1 and -2) in PDLCs. The conditioned medium produced by nicotine and LPS-treated PDLCs increased the number of TRAP-stained osteoclasts, TRAP activity and osteoclast-specific genes, which has been blocked by HIF-2 inhibition and silencing. HIF-2 inhibitor and HIF-2 siRNA inhibited the effects of nicotine and LPS on the activation of Akt, JAK2 and STAT3, ERK and JNK MAPK, nuclear factor-B, c-Jun, and c-Fos. Taken together, this study is the first to demonstrate that HIF-2 inhibition exhibits anti-inflammatory activity through the inhibition of inflammatory cytokines and impairment of ECM destruction, as well as blocking of osteoclastic differentiation in a nicotine- and periodontopathogen-stimulated PDLCs model. Thus, HIF-2 inhibition may be a novel molecular target for therapeutic approaches in periodontitis. J. Cell. Biochem. 116: 1241-1255, 2015. (c) 2015 Wiley Periodicals, Inc.