Deletion of Runx2 in Articular Chondrocytes Decelerates the Progression of DMM-Induced Osteoarthritis in Adult Mice

Lifan Liao,Jianhong Gu,Lan Zhao,Yukio Yoneda,Shanxing Zhang,Baoli Wang,Meiqing Wang,Jun Li,Di Chen,Chun-Do Oh,Takeshi Takarada,Jian Huang

doi:10.1038/s41598-017-02490-w

Abstract

Runx2 may play an important role in development of osteoarthritis (OA). However, the specific role of Runx2 in articular chondrocyte function and in OA development in adult mice has not been fully defined. In this study, we performed the destabilization of the medial meniscus (DMM) surgery at 12-week-old mice to induce OA in adult Runx2Agc1CreER mice, in which Runx2 was specifically deleted in Aggrecan-expressing chondrocytes by administering tamoxifen at 8-weeks of age. Knee joint samples were collected 8- and 12-weeks post-surgery and analyzed through histology, histomorphometry and micro-computed tomography (μCT). Our results showed that severe OA-like defects were observed after DMM surgery in Cre-negative control mice, including articular cartilage degradation and subchondral sclerosis, while the defects were significantly ameliorated in Runx2Agc1CreER KO mice. Immunohistochemical (IHC) results showed significantly reduced expression of MMP13 in Runx2Agc1CreER KO mice compared to that in Cre-negative control mice. Results of quantitative reverse-transcription PCR (qRT-PCR) demonstrated that expression of the genes encoding for matrix degradation enzymes was significantly decreased in Runx2Agc1CreER KO mice. Thus, our findings suggest that inhibition of Runx2 in chondrocytes could at least partially rescue DMM-induced OA-like defects in adult mice.

Highlights

In our laboratory showed that deletion of Tgfbr[2] in chondrocytes up-regulates Runx[2] and accelerates OA progression[12]
We demonstrated, through mutation analysis and ChIP assays, that Runx[2] activates Mmp[13] expression by binding to the osteoblast-specific elemenet-2 (OSE2) site located in the proximal region of the human Mmp[13] promoter in chondrocytes[11]
Analysis of histologic frozen sections from 3-month-old mice using fluorescence microscopy showed that Agc1-CreER targeting cells are located in growth plate, articular cartilage and meniscus in Agc1-CreER; ROSAmT/membrane-targeted green fluorescent protein (mG) mice (Fig. 1a)

Summary

Introduction

In our laboratory showed that deletion of Tgfbr[2] in chondrocytes up-regulates Runx[2] and accelerates OA progression[12]. We determined if Runx[2] specific deletion in chondrocytes in adult mice has chondro-protective effect on DMM-induced OA development. Clinical investigation suggests that MMP13 may be associated with cartilage degradation during OA development[20] This clinical observation was further confirmed by the study with Mmp[13] KO mice. A recent study reported that the interaction of Runx[2] and Osterix, a downstream molecule of Runx[2], cooperatively induces Mmp[13] expression during chondrocyte differentiation[31]. We demonstrated, through mutation analysis and ChIP assays, that Runx[2] activates Mmp[13] expression by binding to the OSE2 site located in the proximal region of the human Mmp[13] promoter in chondrocytes[11]

Methods

Results

Conclusion