ObjectivesWnt16 is implicated in bone fracture and bone mass accrual both in animals and humans. However, its functional roles and molecular mechanism in chondrocyte differentiation and osteoarthritis (OA) pathophysiology remain largely undefined. In this study, we analysed its mechanistic association and functional relationship in OA progression in chondrocyte lineage.MethodsThe role of Wnt16 during skeletal development was examined by Col2a1-Wnt16 transgenic mice and Wnt16fl/fl;Col2a1-Cre (Wnt16-cKO) mice. OA progression was assessed by micro-CT analysis and Osteoarthritis Research Society International score after anterior cruciate ligament transection (ACLT) surgery with Wnt16 manipulation by adenovirus intra-articular injection. The molecular mechanism was investigated in vitro using 3D chondrocyte pellet culture and biochemical analyses. Histological analysis was performed in mouse joints and human cartilage specimens.Results Wnt16 overexpression in chondrocytes in mice significantly inhibited chondrocyte hypertrophy during skeletal development. Wnt16 deficiency exaggerated OA progression, whereas intra-articular injection of Ad-Wnt16 markedly attenuated ACLT-induced OA. Cellular and molecular analyses showed that, instead of β-catenin and calcium pathways, Wnt16 activated the planar cell polarity (PCP) and JNK pathway by interacting mainly with AP2b1, and to a lesser extend Ror2 and CD146, and subsequently induced PTHrP expression through phosphor-Raptor mTORC1 pathway.ConclusionsOur findings indicate that Wnt16 activates PCP/JNK and crosstalks with mTORC1-PTHrP pathway to inhibit chondrocyte hypertrophy. Our preclinical study suggests that Wnt16 may be a potential therapeutic target for OA treatment.

Human induced pluripotent stem (iPS) cells have great potential in regenerative medicine, but this depends on the integrity of their genomes. iPS cells have been found to contain a large number of de novo genetic alterations due to DNA damage response during reprogramming. Thus, to maintain the genetic stability of iPS cells is an important goal in iPS cell technology. DNA damage response can trigger tumor suppressor p53 activation, which ensures genome integrity of reprogramming cells by inducing apoptosis and senescence. p53 isoform Δ133p53 is a p53 target gene and functions to not only antagonize p53 mediated apoptosis, but also promote DNA double-strand break (DSB) repair. Here we report that Δ133p53 is induced in reprogramming. Knockdown of Δ133p53 results 2-fold decrease in reprogramming efficiency, 4-fold increase in chromosomal aberrations, whereas overexpression of Δ133p53 with 4 Yamanaka factors showes 4-fold increase in reprogamming efficiency and 2-fold decrease in chromosomal aberrations, compared to those in iPS cells induced only with 4 Yamanaka factors. Overexpression of Δ133p53 can inhibit cell apoptosis and promote DNA DSB repair foci formation during reprogramming. Our finding demonstrates that the overexpression of Δ133p53 not only enhances reprogramming efficiency, but also results better genetic quality in iPS cells.

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Human embryonic stem cells (hESCs) are thought to be a promising resource for cell therapy, while it has to face the major problem of graft immunological rejection. Major histocompatibility complex (MHC) class I expressed on the cell surface is the major cause of graft rejection. Transporter associated with antigen presentation 1 (TAP1) and TAP-associated glycoprotein (TAPBP) play important roles in regulating MHC class I expression. In this study, we generated TAP1- and TAPBP-deficient hESC lines, respectively, using transcription activator-like effector nucleases technique. These cells showed deficient expression of MHC class I on the cell surface and reduced immunogenicity compared with wild types, but maintained normal pluripotency, karyotypes, and differentiation ability. Thus, our findings are instrumental in developing a universal cell resource with both pluripotency and hypo-immunogenicity for transplantation therapy in the future.

Wnt signaling, a highly conserved signaling pathway, plays important roles in endochondral ossification which is a key process for skeletal development and bone repair. Wnt16, as one of the nineteen Wnt ligands, is reported to repress osteoclastogenesis, prevent cortical bone fragility fractures and to be upregulated in osteoarthritis. But how Wnt16 mediates chondrocyte differentiation during endochondral ossification is still unclear. Here, we investigate the roles of Wnt16 specifically in chondrocytes during endochondral ossification. First, we generated Col2a1‐Wnt16 transgenic mice in which Wnt16 was overexpressed in chondrocytes under the control of Col2a1 promoter and enhancer. The transgenic mice showed a great reduction of tissue mineralization during embryonic development. We also genetically knocked out Wnt16 by generating Wnt16Loxp/Loxp;Col2a1‐Cre mutant mice to examine whether Wnt16 is required for skeletal development. The mutant mice showed no severe phenotype in early skeletal development. However, after 2‐month‐old, the mutant mice displayed a smaller body size and lower bone mass as compared to that of control littermates. In vitro, our studies showed that Wnt16 delays chondrocyte hypertrophy and subsequent maturation. Mechanistically, we found that Wnt16 mainly activates the planar cell polarity (PCP) pathway through activation of JNK in primary chondrocyte. After treated chondroprogenitor cell line ATDC5 with SP600125, a JNK specific inhibitor, Wnt16‐induced delay of chondrocyte hypertrophy is eliminated. In addition, our data suggest that Wnt16 mainly interacts with Ror2 or CD146, co‐receptors of PCP pathway, but not Vangl2 or Ryk. Collectively, our current study provides evidence that Wnt16 delays chondrocyte hypertrophy through PCP pathway partially by binding to Ror2 and CD146. Our findings deepen the understanding of chondrocyte differentiation during endochondral ossification.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.