Fig. 3: Utx knockout promoted ECM synthesis and protected articular cartilage integrity.

Schematic drawing of the generation of chondrocyte-specific Utx knockout mice; exon 24 of Utx, containing the JmjC domain of the enzyme, was floxed and cleavage of these sites resulted in the transcription/translation of inactive Utx. Through mating Utx mice with Col2-Cre mice, its expression is further under control of the cartilage-specific collagen type II gene promoter (a). Confirmation of proper genotypes of UtxKO and WT mice; heterozygous UtxKO mice carried flox constructs corresponding to 430 and 249 bp, whereas homozygous UtxKO mice only expressed amplicons corresponding to 430 bp. Absence of a 100 bp PCR amplicon in WT mice, corresponding to the Cre construct, but presence in UtxKO mice (b). Appearance and hair color of UtxKO mice were similar to WT mice (c). mRNA expression (d) and protein abundance (e), respectively, confirming the absence of Utx and reduced H3K27me3 levels in UtxKO mice. Very faint Utx and H3K27me3 immunostaining in articular cartilage of KO mice (f); scale bar, 10 μm. Utx loss promoted Col2a1 and Acan expression (g). Safranin-O staining of articular cartilage (h; scale bar, 100 μm) and increased relative thickness of articular cartilage, uncalcified portion (i), calcified zone (j), and density of articular chondrocytes (k), respectively, in UtxKO mice. Articular cartilage degeneration and decreased OARSI scores (l) together with osteophyte formation (arrows) in 9-month-old mice (m). Data are expressed as mean ± standard errors calculated from five to six mice. *P < 0.05; **P < 0.001.