Fig. 3

SPI1 and PERK are involved in mechanical stress-induced chondrocyte senescence. a Genome-editing strategy for generating inducible SPI1 knockout alleles. Col2a1-Cre-ERT2 mice carry the tamoxifen-responsive Cre recombinase transgene downstream of the Col2a1 promoter. SPI1^fl/fl mice contain two loxP sites flanking SPI1 exons 5 and 6. Intraperitoneal injection of tamoxifen in the adult mouse induces the nuclear translocation of the ubiquitously expressed Cre–ERT2 fusion protein, resulting in the excision of the genomic fragment located between the loxP sites to generate SPI1 null alleles. b Safranin O/fast green staining was used to assess cartilage destruction and OARSI scores in the articular cartilage of SPI1-CKO mice. Scale bar: 200 μm. c Analysis of BMD and knee joint bone histomorphometric parameters using micro-CT data in SPI1 CKO mice. Original magnification ×50. d IHC of SPI1, PERK, p16^INK4A, p21, Col2a1 and MMP13 expression in cartilage tissues of SPI1-CKO mice. Scale bar: 50 μm. The sample size is n = 4. Experiments were independently repeated three times. The data were expressed as mean ± SD. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.000 1 versus the Control group. ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, ^####P < 0.000 1 versus the SPI1-CKO group. ⁺P < 0.05, ⁺⁺P < 0.01 versus the 13.5 N group. ns indicates not significant. One-way ANOVA