Fhl2 deteriorates the progression in IL-1β-induced chondrocyte-like ATDC5 cells through the inhibition of mTOR and NF-ĸB signaling pathways

Background: The role of nuclear translocation in the pathogenesis of osteoarthritis (OA)has received increased attention in recent years, and extensive research has shown that Fhl2 functions as a nuclear transmitter by interacting with other nuclear transcription factors.We aimed to determine the role of Fhl2 in the cell model of osteoarthritis. Methods: OA cartilage model was established by chondrocyte-like ATDC5 cells induced by 1% insulin-transferrin-selenium and then treated with interleukin-1β (IL-1β, 10ng/ml). Lentivirus transfection was employed to suppress the expression of Fhl2. Immunofluorescence and flow cytometry wereused to examine nuclear transcription and apoptosis, respectively. Western blotting was performed to analyze the expression of metabolism-related proteins, autophagy-related proteins, apoptosis-related proteins, NF-ĸB pathway-related proteins, and mTOR pathway-related proteins. Results: The elevated expression of Fhl2 occurred in both the cytoplasm and the nucleus. Knockdown of Fhl2 could inhibit IL-1β-induced phosphorylation of NF-ĸB and stabilize the extracellular matrix (ECM) by decreasing MMP-3 and MMP-13 expression, to suppress type 2 collagen degradation in chondrocyte-like ATDC5 cells. Meanwhile, the knockdown of Fhl2-activated autophagy in IL-1β-treated chondrocytes, characterized by an increased LC3-II/LC3-I ratio and Beclin-1. The downregulation of Fhl2 inhibited IL-1β-induced apoptosis by suppressing the expression of BAX and caspase-3, as well as enhancing BCL-2 protein levels. The mechanism may be related to the phosphorylation of AKT and the decreased expression of p-NF-ĸB. Conclusions: Fhl2 knockdown activated autophagy while suppressing inflammation, apoptosis, and ECM degradation. The mechanism behind these processes may be associated with the inhibition of mTOR and NF-ĸB signaling pathways.