title: The involvement of follistatin-like protein 1 in osteoarthritis by elevating NF-κB-mediated inflammatory cytokines and enhancing fibroblast like synoviocyte proliferation.
abstract: BACKGROUND
  Our previous work has revealed that expression of follistatin-like protein 1 (FSTL1) is elevated in the synovial tissues from osteoarthritis (OA) patients. The aim of this study was to elucidate the underlying molecular mechanisms by which FSTL1 plays a role in the pathogenesis of OA.
  
  
  METHODS
  Cultured fibroblast-like synoviocytes (FLSs) from synovial tissues of OA patients were stimulated with human recombinant FSTL1, and then the expression of inflammatory cytokines in FLS and their concentrations in the cell supernatants were measured by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Nuclear factor kappa B (NF-κB) activation was examined by western blot and chromatin immunoprecipitation (ChIP) assay at the p65 binding site. Finally, the proliferation of FLSs and the expression level of the proliferation-related tumor suppressors (p53 and p21) were determined by MTS assay kit and western blot in the presence or absence of FSTL1, respectively.
  
  
  RESULTS
  FSTL1 remarkably promoted expression levels of several inflammatory cytokines (tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6)) in vitro. Western blot analysis showed that FSTL1 activated the inflammatory-related NF-κB signaling pathway, as validated by ChIP assay detecting p65-binding level on the cytokine promoter region. Moreover, FSTL1 promoted the proliferation of OA FLS by downregulating the expression of p53 and p21. Interestingly, the concentration of synovial fluid IL-6 was remarkably elevated in OA patients, and was correlated with synovial fluid and serum FSTL1 levels.
  
  
  CONCLUSIONS
  These findings show that FSTL1 functions as an important proinflammatory factor in the pathogenesis of OA by activating the canonical NF-κB pathway and enhancing synoviocytes proliferation, suggesting that FSTL1 may be a promising target for the treatment of OA.
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. vivian.nisu@gmail.com.|Laboratory of Clinical Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. vivian.nisu@gmail.com.
authors.forename: Su
authors.initials: S
authors.lastname: Ni
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. miaokaisong@163.com.|Laboratory of Clinical Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. miaokaisong@163.com.
authors.forename: Kaisong
authors.initials: K
authors.lastname: Miao
authors.affiliation: Department of Neurology, Laboratory of Neurological Diseases, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. hippocampus2007@gmail.com.
authors.forename: Xianju
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. xunanwei1963@yahoo.com.cn.
authors.forename: Nanwei
authors.initials: N
authors.lastname: Xu
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. yuelpl@qq.com.|Laboratory of Clinical Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. yuelpl@qq.com.
authors.forename: Chenkai
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. 392849984@qq.com.
authors.forename: Ruixia
authors.initials: R
authors.lastname: Zhu
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. 275585025@qq.com.
authors.forename: Rongbin
authors.initials: R
authors.lastname: Sun
authors.affiliation: Department of Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. yujiwang@sohu.com.|Laboratory of Clinical Orthopedics, The Affiliated Hospital of Nanjing Medical University, Changzhou No.2 People's Hospital, 29 Xinglong Alley, Changzhou, 213003, China. yujiwang@sohu.com.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000368:Aged; D015153:Blotting, Western; D016022:Case-Control Studies; D049109:Cell Proliferation; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D018450:Disease Progression; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects; D038681:Follistatin / Q000494:pharmacology; D038702:Follistatin-Related Proteins / Q000378:metabolism*; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D016328:NF-kappa B / Q000378:metabolism*; D010003:Osteoarthritis / Q000097:blood* / Q000503:physiopathology; D060888:Real-Time Polymerase Chain Reaction; D012016:Reference Values; D013583:Synovial Membrane / Q000166:cytology
chemical_list: D016207:Cytokines; D038681:Follistatin; D038702:Follistatin-Related Proteins; D018836:Inflammation Mediators; D015850:Interleukin-6; D016328:NF-kappa B