Kdm6b Regulates Cartilage Development And Homeostasis

Part Ⅰ:The role of Kdm6b in chondrocyte differentiation and maturationCartilage is an important connective tissue in human or vertebrates. From the perspective of developmental biology, chondrocytes are differentiated from condensed mesenchymal cells. The differentiation chondrocytes proliferate rapidly and secrete a lot of cartilage-specific extracellular matrix, including type Ⅱ collagen and chondroitin sulfate proteoglycan, and then form cartilage tissue. Cartilage functions as a template of endochondral bone. Currently, most research articles on chondrogenesis are focused on the regulation or interaction among signal pathways. Epigenetics is referred to as changes in gene expression caused by mechanisms other than changes in the underlying DNA sequences, such as DNA methylation, non-coding RNA regulation, histone modification, chromatin remodeling, and genomic imprinting. Now that, is epigenetics playing an important role in the chondrogenesis process?Our study firstly used in vitro chondrogenesis model of mesenchymal stem cells to screen many histone demethylases. It was found that Kdm6b (also named Jmjd3) was upregulated significantly during chondrogenesis, which indicated that Kdm6b may founction at this process. In order to verify the exact role of Kdm6b in chondrogenesis, we built a Kdm6b knock down mesenchymal stem cell. And then we conducted chondrogenic differentiation in vitro and found that the ability of chondrogenesis was weakened after knocking down Kdm6b. This revealed that Kdm6b was required in chondrocyte differentiation. Meanwhile, the in vivo Col2a1-CreERT2; Kdm6bf/f system pointed out that knocking down Kdm6b could inhibit chondrocyte proliferation and maturation at early developmental process.Part Ⅱ:The role of Kdm6b in chondrocyte phenotype maintenance and osteoarthritis progressOsteoarthritis (OA) is the most common joint disease among the elderly population, and is the main reason for chronic disability. The main symptoms of OA include articular cartilage degradation, synovial inflammation, subchondral bone sclerosis, degeneration of ligaments and meniscus, and hypertrophy of the joint capsule. Kdm6b (Jmjd3) is a H3K27me3 specific demethylase which could offset poly comb mediated transcriptional inhibition. Studies have reported that endochondral ossification process of Kdm6b-/- mouse was blocked. The knock-out mice has limb hypoplasia and lung dysfunction, so the mouse died shortly after birth. Therefore, research about the role of Kdm6b in OA process is blank.In this study, we firstly detected Kdm6b expression in normal and OA cartilage samples from human and mice. We found that the expression of Kdm6b was reduced significantly in OA cartilage compared with normal ones, suggesting that Kdm6b may involve in the occurrence and development of OA. In order to verify the role of Kdm6b in OA progression, we manufactured destabilization of the medial meniscus (DMM) to build the mice OA model, and then, we used Kdm6b shRNA lentiviral knee joint injection and Col2a1-CreERT2; Kdm6bf/f cartilage specific conditional knockout system to change Kdm6b expression of the joint cartilage. After surgery, histological examination of mouse knee cartilage found that OA progression was significantly serious in Kdm6b knockdown group compared with the control group.