Kruppel-like factor 9 may regulate the inflammatory injury of chondrocytes by affecting NF-κB signaling.

BACKGROUND

Kruppel-like factor 9 (KLF9) is involved in the development of osteoarthritis (OA), which is a chronic joint disorder. However, the pathogenesis of OA remains unclear. This study aimed to investigate the relationship between KLF9 and the pathogenesis of OA.

METHODS

KLF9 expression in the Gene Expression Omnibus database was analyzed, and the most significantly upregulated and downregulated genes were visualized using a volcano map. Analyses were performed using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes to determine the most significantly changed genes. Interleukin-1 beta (IL-1β) was applied to CHON-001 cells and human synovial cells (HSyCs) to establish an OA in vitro cell model. Real-time quantitative polymerase chain reaction (RT-qPCR) and western blot analysis were conducted to evaluate the expressions of KLF9 and cell death genes. Enzyme-linked immunosorbent assay (ELISA) was conducted to examine IL-1β, interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α). IL-1β induced CHON-001 cells; HSyCs were transfected with KLF9 overexpression (OE); and ELISA was conducted to examine IL-1β, IL-6, and TNF-α. An inhibitor of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) was used, and its effects on CHON-001 cells and HSyC were examined.

RESULTS

KLF9 was one of the most significantly downregulated genes during OA development. KLF9 was downregulated in IL-1β-treated CHON-001 cells and HSyCs. IL-1β induced the significant upregulation of IL-1β, IL-6, and TNF-α and increased cell death in CHON-001 cells and HSyCs. KLF9 OE partially mitigated the effects of IL-1β and markedly attenuated the IL-1β-induced upregulation of TNF-α and IL-6. IL-1β treatment significantly upregulated B-cell lymphoma 2-associated X protein (Bax) and Caspase-3 and downregulated B-cell lymphoma 2 (Bcl-2) on both messenger ribonucleic acid and protein levels, and KLF9 OE mitigated the effects of IL-1β. IL-1β decreased the levels of type II collagen and aggrecan, whereas KLF9 OE increased the levels of type II collagen and aggrecan. An NF-κB inhibitor could partially abrogate the KLF9-induced effects on Bax, Caspase-3, and Bcl-2. The NF-κB inhibitor also reversed the KLF9 OE-induced increase in the levels of type II collagen and aggrecan.

CONCLUSIONS

KLF9 mitigated the IL-1β-induced inflammatory condition via the NF-κB pathway.