Wnt7a Inhibits Cartilage Matrix Degradation in a Mouse In Vivo Osteoarthritis Model

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1 Wnt7a Inhibits Cartilage Matrix Degradation in a Mouse In Vivo Osteoarthritis Model Averi Leahy, Andrea Foote, Tomoya Uchimura, Li Zeng, PhD. Tufts University, Boston, MA, USA. Disclosures: A. Leahy: None. A. Foote: None. T. Uchimura: None. L. Zeng: None. Introduction: The Wnt signaling pathways, including both the canonical and non-canonical pathways, have been implicated in articular cartilage homeostasis and osteoarthritis (OA) pathogenesis. However, all of the current reports have no reached a consistent conclusion. For example, the overexpression of β-catenin, a downstream modulator of canonical Wnt signaling, and the loss of β-catenin both resulted in articular cartilage damage 1,2. Additionally, few studies have investigated if a specific Wnt protein can affect cartilage matrix levels during OA pathogenesis or progression in vivo. Wnt7a is one of the Wnt family members that is expressed in healthy articular cartilage 3, but has been studied little with respect to OA or its role in the response to inflammatory cytokines that are known to be upregulated in OA chondrocytes. Its potential effect on cartilage matrix in OA is unclear, as one study showed that Wnt7a decreased Collagen II production in rabbit chondrocytes, but that it also inhibited chondrocyte apoptosis 4, and no studies have been performed with human chondrocytes. The objective of this study is to investigate the effect of Wnt7a on cartilage matrix levels under in vivo OA conditions. Methods: 1) In vivo: Experimental OA was induced in 7 week old CD1 male mice by surgically severing the medial meniscotibial ligament, resulting in destabilization of the medial meniscus (DMM). Sham surgery was performed on the opposite knee of each mouse. Lentiviral Wnt7a or GFP (control) was intraarticular injected into both knees of the DMM mice on days 7 and 14 postsurgery. Mice were sacrificed at 5 or 7 weeks post-surgery for histological analysis. Safranin O images were blindly scored using the OARSI scoring system. 2) In vitro: Normal human articular chondrocytes (nhacs, Lonza) were redifferentiated for 3 weeks in alginate beads according to the Lonza protocol and then infected with lentivirus expressing Wnt7a or GFP (control). These cells were then treated with 5 ng/ml IL1β for 4 days. mrna expression levels of genes involved in cartilage matrix regulation were analyzed via RT-qPCR. Results: Intraarticular injection of Wnt7a lentivirus prevents cartilage matrix degradation in vivo. We evaluated the effect of Wnt7a on OA progression in the DMM in vivo mouse OA model. We found that Wnt7a injection into the mouse knee during OA development protected against cartilage matrix degradation 7 weeks post-surgery, as visualized through Safranin O staining (Fig. 1B). This observation was also quantified by blinded scoring of damage using the OARSI scoring system, which demonstrated that 7 weeks post-surgery, lenti-wnt7a injected knees resulted in a tibial plateau score that was significantly less than their GFP control counterparts (Fig. 1C). IHC confirmed that chondrocytes in the articular surface were infected with the lentivirus (data not shown). In both lenti-gfp and lenti-wnt7a injected knees, there was an induction of Collagen X as compared to knees with no surgery. However, at 7 weeks post-surgery there seems to be more cells present in the Wnt7a-treated DMM knees as compared to the GFP DMM knees (Fig. 1B). It is not clear yet whether Wnt7a affects cell proliferation or cell death in this setting. Wnt7a overexpression inhibits IL1β induction of MMP13 and Collagen X in primary human chondrocytes. To determine whether the effect as saw in the joint in vivo can be directly caused by Wnt7a infection in the chondrocytes rather than through other tissues in the joint, we evaluated the effect of Wnt7a overexpression on cartilage matrix gene expression and the IL1βinduced upregulation of OA related genes in human articular chondrocytes (nhacs). We found that while Wnt7a overexpression had no effect on the expression of the OA-associated genes MMP13 and Collagen X under control conditions, Wnt7a significantly reduced the IL1β induction of both MMP13 and Collagen X (Fig. 2). We also found that Wnt7a overexpression had no effect on Collagen II expression (data not shown), but that it did significantly reduce Aggrecan expression under control conditions. This difference did not persist after IL1β treatment, as IL1β downregulates Aggrecan expression to the same level in the Wnt7a and control groups (Fig. 2). Discussion: Current literature has demonstrated that the role of Wnt signaling in OA development and progression is not well understood and very complicated. It has been shown that multiple Wnt proteins can affect chondrocyte behavior in vitro, but few studies have examined what effect specific Wnt proteins have under OA conditions in vivo. Our results indicate that Wnt7a dramatically inhibits cartilage matrix degradation after surgically induced OA development in vivo. This demonstrates not only that a specific Wnt protein can have a strong effect on OA conditions in vivo, but also provides insight into new potential therapeutic strategies for OA treatment.

2 We have begun to investigate how Wnt7a is exerting these effects and will continue to explore this question, especially with respect to Wnt7a s effect on cell death. Another aspect we wish to examine is the signaling pathways through which Wnt7a is signaling in our model. DKK-1, an inhibitor of the Wnt canonical pathway, has also been shown to protect against cartilage matrix degradation in vivo 5, suggesting that Wnt canonical pathway activation may be actively involved in cartilage matrix degradation. As our data demonstrates that Wnt7a protects against cartilage matrix degradation, the opposite of what is expected for Wnt canonical pathway activation, this suggests that Wnt7a may be signaling through multiple Wnt pathways in this circumstance. Significance: This work resulted in identifying Wnt7a as a potential inhibitor of cartilage matrix degradation during OA development, providing a potentially new therapeutic strategy. Additionally, this has helped to demonstrate that a specific Wnt protein can have strong effects in vivo and further studies investigating how Wnt7a functions will provide us with a new understanding of the biology of cartilage under pathological conditions and how Wnt signaling is involved in OA. Acknowledgments: NIH and NSF References: 1. Zhu M et al. Journal of bone and mineral research Yuasa T et al. The American journal of pathology Yates KE et al. DNA and cell biology HwangSG et al. The journal of biological chemistry Oh H et al. Arthritis and rheumatism.

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