Fig 2: METTL3/IGF2BP2 axis regulates STAT1 stability and expression. (A–B) RIP assay for binding of IGF2BP2 and STAT1 in patients with OA and rat models. n = 5. (C) RIP assay for binding of IGF2BP2 and STAT1 in IL-1β-treated rat chondrocytes. n = 3. (D) STAT1 stability detected via RT-qPCR in IL-1β-treated rat chondrocytes transfected with NC or shIGF2BP2 through actinomycin D assay. n = 3. (E-F) The mRNA and protein levels of STAT1 and ADAMTS12 in IL-1β-treated rat chondrocytes transfected with OE-NC, OE-METTL3, OE-METTL3 + NC, or OE-METTL3 + shIGF2BP2 by RT-qPCR and western blot. n = 3. (G) TUNEL staining of rat chondrocyte. n = 3 (H) Apoptosis of rat chondrocyte detected by flow cytometry. n = 3. *P < 0.05; **, P < 0.01; ***, P < 0.001

Fig 3: METTL3 regulates STAT1 expression. (A) MeRIP-qPCR assay for m6A methylation level of STAT1 in cartilage tissues of normal cases or patients with OA. n = 5. (B–D) METTL3 levels in cartilage tissues of normal or patients with OA by IHC, RT-qRCR, and western blot assays. n = 5. (E) MeRIP-qPCR assay for m6A methylation level of STAT1 in cartilage tissues in sham or OA rat model groups. n = 5. (F–H) METTL3 levels in cartilage tissues in sham or OA rat model groups by IHC, RT-qRCR, and western blot. n = 5. (I) MeRIP-qPCR assay for m6A methylation level of STAT1 in rat chondrocytes transfected with NC or shMETTL3 before IL-1β stimulation. n = 3. (J–K) The mRNA and protein expression levels of STAT1 in rat chondrocytes by qPCR and western blot assays. n = 3. *P < 0.05; **, P < 0.01; ***, P < 0.001

Fig 4: STAT1 regulates ADAMTS12 transcription. Tissues of patients with OA and cartilage tissues of controls. (A) HE, PAS, and safranin O-fast green of human cartilage tissues. n = 5 (B) IHC analysis for STAT1 and ADAMTS12 levels in human cartilage tissues. n = 5 (C and D) The binding of STAT1 on ADAMTS12 promoter in human cartilage tissues by ChIP-qPCR and EMSA analyses. n = 5 (E) Luciferase reporter assay for binding of STAT1 on ADAMTS12 promoter in 293T cells. n = 3. *P < 0.05; **, P < 0.01

Fig 5: STAT1 regulates ADAMTS12 transcription. Rat chondrocytes were transfected with NC or shSTAT1, followed by IL-1β incubation. Cells were grouped as control, IL-1β, NC + IL-1β, or shSTAT1 + IL-1β. (A) ChIP-qPCR analysis for binding of STAT1 on ADAMTS12 promoter in rat chondrocytes stimulated with or without IL-1β. n = 3 (B) The binding of STAT1 on ADAMTS12 promoter in rat chondrocytes through EMSA assay. n = 3 (C-D) RT-qPCR and western blot assays for STAT1 and ADAMTS12 levels in rat chondrocytes. n = 3 (E) TUNEL staining of rat chondrocyte. n = 3 (F) Apoptosis of rat chondrocyte detected by flow cytometry. n = 3. *P < 0.05; **, P < 0.01