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Osteoarthritis is one of the leading causes of pain and disability in the aged population due to articular cartilage damage. This warrants investigation of signaling mechanisms that could protect cartilage from degeneration and degradation. Here we show in a murine model of experimental osteoarthritis that YAP activation by transgenic overexpression or by deletion of its upstream inhibitory kinases Mst1/2 preserves articular cartilage integrity, whereas deletion of YAP in chondrocytes promotes cartilage disruption. Our work shows that YAP is both necessary and sufficient for the maintenance of cartilage homeostasis in osteoarthritis. Mechanistically, inflammatory cytokines, such as TNFα or IL-1β, trigger YAP/TAZ degradation through TAK1-mediated phosphorylation. Furthermore, YAP directly interacts with TAK1 and attenuates NF-κB signaling by inhibiting substrate accessibility of TAK1. Our study establishes a reciprocal antagonism between Hippo-YAP/TAZ and NF-κB signaling in regulating the induction of matrix-degrading enzyme expression and cartilage degradation during osteoarthritis pathogenesis.

Hippo signaling controls organ size and tissue regeneration in many organs, but its roles in chondrocyte differentiation and bone repair remain elusive. Here, we demonstrate that Yap1, an effector of Hippo pathway inhibits skeletal development, postnatal growth, and bone repair. We show that Yap1 regulates chondrocyte differentiation at multiple steps in which it promotes early chondrocyte proliferation but inhibits subsequent chondrocyte maturation both in vitro and in vivo. Mechanistically, we find that Yap1 requires Teads binding for direct regulation of Sox6 expression to promote chondrocyte proliferation. In contrast, Yap1 inhibits chondrocyte maturation by suppression of Col10a1 expression through interaction with Runx2. In addition, Yap1 also governs the initiation of fracture repair by inhibition of cartilaginous callus tissue formation. Taken together, our work provides insights into the mechanism by which Yap1 regulates endochondral ossification, which may help the development of therapeutic treatment for bone regeneration.

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.

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Chemerin is an adipokine involved in obesity, inflammation, and innate immune system that is highly expressed in the liver. In the present study, we find that chemerin mRNA expression is decreased in the livers of rodents with nonalcoholic fatty liver disease as well as in HepG2 cells after lipid overloading. Moreover, we report that chemerin expression and secretion are induced in HepG2 cells and primary hepatocytes from wild-type mice, but not farnesoid X receptor (FXR)-/- mice, in response to the synthetic FXR ligand GW4064. Hepatic chemerin expression is decreased in FXR-/- mice but up-regulated by GW4064 administration in wild-type mice. Dual-luciferase reporter assay and chromatin immunoprecipitation analyses further identified a functional FXR response element located in the -258-bp /+121-bp region of the chemerin gene. These data demonstrate that chemerin, a novel target gene of FXR, is related to nonalcoholic steatohepatitis.

Objectives Podocyte injury is a prediction marker of diabetic nephropathy (DN), and AKT/mTOR pathway–mediated inhibition of autophagy is widely reported to contribute to podocyte damage. Recent study stated that sperm‐associated antigen 5 (SPAG5) activated AKT/mTOR signalling in bladder urothelial carcinoma, indicating SPAG5 might regulate autophagy and play a role in podocyte damage. Materials and methods Apoptosis and autophagy of human podocytes (HPCs) were detected by flow cytometry and immunofluorescence (IF). Gene level was assessed by Western blot and RT‐qPCR. Molecular interactions were determined by pulldown, RNA immunoprecipitation (RIP), co‐immunoprecipitation (co‐IP), chromatin immunoprecipitation (ChIP) and luciferase reporter assays. Results SPAG5 mRNA and protein levels were upregulated under high glucose treatment in HPCs. Silencing SPAG5 reversed the increase of apoptosis and decrease of autophagy in high glucose–treated HPCs. Later, we found a long non‐coding RNA (lncRNA) SPAG5 antisense RNA1 (SPAG5‐AS1) as a neighbour gene to SPAG5. Mechanistically, YY1 transcriptionally upregulated SPAG5‐AS1 and SPAG5 in high glucose–treated podocytes. SPAG5‐AS1 acted as a competitive endogenous RNA (ceRNA) to regulate miR‐769‐5p/YY1 axis and induce SPAG5. SPAG5‐AS1 interacted with ubiquitin‐specific peptidase 14 (USP14) and leads to de‐ubiquitination and stabilization of SPAG5 protein. Conclusions This study revealed that SPAG5‐AS1 inhibited autophagy and aggravated apoptosis of podocytes via SPAG5/AKT/mTOR pathway, indicating SPAG5‐AS1/SPAG5 as a potential target for the alleviation of podocyte injury and offering new thoughts for the treatments of DN.

Targeting immune checkpoints, such as PD‐L1 and its receptor PD‐1, has opened a new avenue for treating cancers. Understanding the regulatory mechanism of PD‐L1 and PD‐1 will improve the clinical response rate and efficacy of PD‐1/PD‐L1 blockade in cancer patients and the development of combinatorial strategies. VGLL4 inhibits YAP‐induced cell proliferation and tumorigenesis through competition with YAP for binding to TEADs. However, whether VGLL4 has a role in anti‐tumor immunity is largely unknown. Here, we found that disruption of Vgll4 results in potent T cell‐mediated tumor regression in murine syngeneic models. VGLL4 deficiency reduces PD‐L1 expression in tumor cells. VGLL4 interacts with IRF2BP2 and promotes its protein stability through inhibiting proteasome‐mediated protein degradation. Loss of IRF2BP2 results in persistent binding of IRF2, a transcriptional repressor, to PD‐L1 promoter. In addition, YAP inhibits IFNγ‐inducible PD‐L1 expression partially through suppressing the expression of VGLL4 and IRF1 by YAP target gene miR‐130a. Our study identifies VGLL4 as an important regulator of PD‐L1 expression and highlights a central role of VGLL4 and YAP in the regulation of tumor immunity.