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.