title: The fibroblast expression of RANKL in CoCrMo-particle-induced osteolysis is mediated by ER stress and XBP1s.
abstract: Particle-induced osteolysis is a major cause of aseptic loosening, which is the most common reason for total hip arthroplasty (THA) failure and revision surgery. Although existing studies suggest that synovial fibroblasts present in the interfacial membrane are important targets of wear particles during bone resorption, the interaction mechanisms between the particles and fibroblasts remains elusive. In the present study, we investigated the effect of ER stress induced by CoCrMo particles (CoPs) in fibroblasts, calvarial resorption animal models and aseptic loosening clinical samples and its role in the stimulation of the RANKL expression. Our study further demonstrated that CoPs could induce significant ER stress in fibroblasts. Blocking ER stress with a specific inhibitor dramatically reduced the particle-induced expression of RANKL in vitro and in vivo. Furthermore, in fibroblasts, downregulation of the expression of XBP1s, a signaling molecule of ER stress, significantly reduced the expression of RANKL induced by wear particles. Moreover, inhibition of ER stress or XBP1s both ameliorated the CoPs-induced osteolysis in animal models. Collectively, these results suggested that in particle-induced osteolysis, CoPs could stimulate fibroblasts to secret RANKL through ER stress and the signaling molecule XBP1s. Therefore, downregulating ER stress or the signaling molecule XBP1s of fibroblasts represents a potential therapeutic approach for treating particle-induced peri-implant osteolysis.
  
  
  CONCLUSIONS
  For the first time, our study demonstrated that ER stress mediated the induction of RANKL expression by CoPs in fibroblasts and promoted particle-induced osteolysis. Furthermore, the upregulation of RANKL by CoPs in fibroblasts was mediated by the ER stress signaling molecule XBP1s. Both blocking ER stress and inhibiting the protein XBP1s by specific inhibitors resulted in downregulation of the expression of RANKL and amelioration of osteolysis induced by the implanted particles. Collectively, these findings suggest a possible mechanism underlying the RANKL expression induced by wear particles in fibroblasts, and downregulating ER stress and the XBP1s expression of fibroblasts represents a potential therapeutic approach for treating aseptic loosening.
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Zhenheng
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Gan
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Naicheng
authors.initials: N
authors.lastname: Liu
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Zhou
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Tongguo
authors.initials: T
authors.lastname: Shi
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Zhenzhen
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Nirong
authors.initials: N
authors.lastname: Bao
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Guo
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China.
authors.forename: Jiangning
authors.initials: J
authors.lastname: Chen
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China; Jiangsu Provincial Laboratory for Nano-Technology, Nanjing University, Nanjing 210093, China. Electronic address: jfzhang@nju.edu.cn.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China. Electronic address: leidong@nju.edu.cn.
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.affiliation: Jinling Hospital, Department of Orthopaedics, School of Medicine and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, 210093, China. Electronic address: zhaojianning.0207@163.com.
authors.forename: Jianning
authors.initials: J
authors.lastname: Zhao
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D059865:Endoplasmic Reticulum Stress; D005260:Female; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008297:Male; D051379:Mice; D010014:Osteolysis / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D053245:RANK Ligand / Q000096:biosynthesis*; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000378:metabolism*; D014800:Vitallium / Q000009:adverse effects*; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D053245:RANK Ligand; D000071701:Regulatory Factor X Transcription Factors; C505688:TNFSF11 protein, human; C505689:Tnfsf11 protein, mouse; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; D014800:Vitallium
keywords: Aseptic loosening; ER stress; Fibroblasts; Wear particles; XBP1s