To investigate the expression profile of Annexin A1 (ANXA1) during the onset and progression of osteoarthritis (OA), and explore its pathogenic mechanism.

Primary human chondrocytes were induced with different concentrations of IL-1β to establish an osteoarthritis-like cell model. Cells were divided into control group (0 ng/mL), mild OA group (5 ng/mL) and severe OA group (10 ng/mL). Immunohistochemistry and immunofluorescence were used to verify the subcellular localization of ANXA1 in chondrocytes. Real-time quantitative polymerase chain reaction and Western blot were applied to detect the expression differences of ANXA1 at mRNA and protein levels, respectively. The changes of collagen typeⅡα1 chain (COL2A1) and matrix metalloproteinase 13 (MMP13) in OA-like chondrocytes were detected to confirm the successful establishment of the OA cell model.Furthermore, ANXA1 silencing group, ANXA1 overexpression group, empty vector control group and simple OA model group were set up in the OA-like cell model. CCK-8 assay and flow cytometry were performed to detect cell proliferation activity and apoptosis of OA-like chondrocytes after ANXA1 silencing or overexpression. Western blot was used to determine the expression of COL2A1 after ANXA1 knockdown. Western blot and co-immunoprecipitation (Co-IP) were utilized to explore the regulatory effect of ANXA1 on the MAPK signaling pathway. Analysis of variance was used to compare the measurement data among multiple groups, while t test was used to compare the measurement data between two groups.

In the OA-like chondrocyte model, the mRNA and protein expression levels of ANXA1 and MMP13 showed an upward trend with the increase of IL-1β concentration, with statistically significant differences (P < 0.05). The CCK-8 results showed that IL-1β inhibited chondrocyte proliferation activity, silencing the ANXA1 gene reversed this inhibitory effect, while overexpression of the ANXA1 gene further reduced chondrocyte proliferation activity. The flow cytometry results showed that compared with the control group, the total apoptosis rates in mild and severe OA groups were elevated from (20.3±1.80)% and (29.7±1.62)% to (32.1±1.96)% and (54.0±1.81)% after ANXA1 overexpression, with statistically significant differences (P < 0.05). In contrast, ANXA1 silencing decreased the total apoptosis rates to (15.4±1.33)% and (23.0±2.14)%. Moreover, ANXA1 overexpression markedly downregulated COL2A1 protein expression relative to the control group (P < 0.05), while ANXA1 knockdown exerted the opposite effect. Western blot and co-immunoprecipitation (Co-IP) assays confirmed that the expression of ANXA1 was positively correlated with the expressions of ERK1/2 and JNK.

The ANXA1 gene inhibits chondrocyte proliferation, and silencing the ANXA1 gene inhibits OA chondrocyte apoptosis. ANXA1 gene may promote chondrocyte apoptosis via the potential MAPK signaling pathway and is an important factor in the occurrence and development of OA.