Constitutive epidermal growth factor receptor (EGFR) overactivation mitigates synovitis and ectopic cartilage formation in joint after loading. (A) Representative H&E-stained sections of WT and HBEGF OverCol2 mouse synovium at 2 weeks, 1 month, and 3 months after 6 or 9 N loading. Scale bars, 100 μm. (B) Synovitis score was quantified (n = 6/group). (C) Representative safranin-O/Fast green-stained sections of WT and HBEGF OverCol2 mouse joints at 3 months post 9 N loading. An arrow points to the heterotopic ossification area in synovium tissue. F, femur; S, synovium; T, tibia. Scale bars, 100 μm. (D) At 2 weeks, 1 month, and 3 months after 6 N loading, joint allodynia (50% PWT) was measured by von Frey assay. Value at Day 0 was obtained before loading. PWT, paw withdrawal threshold. (n = 5/group). P values indicate significant difference of 50% PWT between WT 6 N and HBEGF OverCol2 6 N. The comparisons were conducted by two-way ANOVA with Tukey–Kramer multiple comparison test.