OPN Deficiency Increases the Severity of Osteoarthritis Associated with Aberrant Chondrocyte Senescence and Apoptosis and Upregulates the Expression of Osteoarthritis-Associated Genes.

Jian Tian,Chao Su,Shi-Da Kuang,Chao Cheng,Shu-Guang Gao,Yu-Sheng Li,Yi-Lin Xiong,Xin Zhao

doi:10.1155/2020/3428587

Abstract

Objectives A recent work has reported that the elevated osteopontin (OPN) levels in the articular cartilage and synovial fluid are correlated with the progressive osteoarthritis (OA) joint damage, and OPN has a protective effect against OA by suppressing the expressions of OA-associated genes. The present study examined whether the OPN deficiency was susceptible to OA through the regulation of chondrocyte senescence and apoptosis and the expressions of OA-associated genes. Methods The mRNA levels of COL2A1 and OPN were compared between human OA chondrocytes and normal chondrocytes. The effects of OPN siRNA on the SA-β-Gal expressions and the percentage of apoptotic chondrocytes were examined by using SA-β-Gal staining and apoptosis assay, and the effects on the expressions of COL2A1 and OA-associated genes (COL10A1, IL-1β, TNF-ɑ, MMP-13, and ADAMTS5) were examined by western blot analysis and quantitative real-time RT-PCR. Furthermore, an in vivo OA model was established to examine the effects of OPN siRNA on the senescence and apoptosis of OA chondrocytes and the expressions of OA-associated genes. Results The mRNA levels of COL2A1 and OPN were decreased in knee OA chondrocytes in comparison with those in normal chondrocytes. The OPN deficiency enhanced the senescence and apoptosis of OA chondrocytes and increased the expressions of COL10A1, IL-1β, TNF-ɑ, MMP-13, and ADAMTS5 but decreased the expression of COL2A1. Meanwhile, OPN deficiency could result in severe, accelerated OA in vivo, which was also associated with enhanced senescence and apoptosis of chondrocytes and elevated expressions of OA-associated genes. Conclusions The findings of this study suggest that the OPN deficiency can result in accelerated OA, which is associated with enhanced senescence and apoptosis of OA chondrocytes and the upregulated expressions of OA-associated genes.

Highlights

As the most typical form of arthritis, osteoarthritis (OA) is characterized with the degradation of articular cartilage alongside alterations in other joint tissues
The knowledge about the effects of OPN deficiency on the senescence and apoptosis of OA chondrocytes in the pathogenesis of OA is still limited
To examine the effect of OPN in vivo, a loss of OPN function strategy was developed by injecting OPN small interfering RNA (siRNA) into the knee joints of rats in a DMM model. e prepared rat samples were compared with samples treated by nontargeting siRNA injection

Summary

Introduction

As the most typical form of arthritis, osteoarthritis (OA) is characterized with the degradation of articular cartilage alongside alterations in other joint tissues. E senescence and apoptosis of articular chondrocytes are found to be associated with the pathogenesis of OA [2, 3]. Our earlier studies demonstrated that the elevated SA-β-Gal was correlated with the progressive knee OA joint damage [4]. On such basis, the current study was performed for the purpose to further examine the upstream mediator(s) of senescence and apoptosis in cells of OA cartilages. Osteopontin (OPN), a multifunctional phosphoprotein comprising 300 amino acids, has a critical part in the progression of aging-associated and instability-induced spontaneous OA [5]. An increased expression of OPN and calcium deposits was found enhanced in the osteoarthritic cartilage, while the full-length OPN is mainly posttranslational modified with phosphorylation before it works. e phosphorylation status of OPN can inhibit the

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