Lipopolysaccharide increases the incidence of collagen-induced arthritis in mice through induction of protease HTRA-1 expression

Arthritis Rheum. 2013 Nov;65(11):2835-46. doi: 10.1002/art.38124.


Objective: The protease HTRA-1 is closely associated with rheumatoid arthritis (RA). The molecular mechanisms that control HTRA-1 expression are currently unknown. This study was undertaken to determine the regulatory role of Toll-like receptors (TLRs) on HTRA-1 expression in mice with collagen-induced arthritis (CIA) and in synovial cells from RA patients.

Methods: HTRA-1 messenger RNA and protein production in mouse fibroblasts, mouse macrophages, and freshly isolated RA patient synovial cells treated with TLR ligands were detected by real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Arthritis incidence and severity were determined using clinical scores and histopathologic analysis. Involvement of HTRA-1 in lipopolysaccharide (LPS)-increased arthritis incidence and severity in mice was determined using anti-HTRA-1 monoclonal antibody. The signal pathways involved in HTRA-1 expression were accessed by specific inhibitors, RNA interference, dual-luciferase reporter, and chromatin immunoprecipitation methods.

Results: LPS and tenascin-C, but not the other TLR ligands tested, strongly induced HTRA-1 expression. LPS significantly increased HTRA-1 expression in the joint tissue as well as arthritis incidence and severity in mice with CIA. Blocking HTRA-1 by antibody significantly decreased LPS-promoted CIA severity. Inhibiting NF-κB significantly decreased LPS-induced HTRA-1 expression in mouse and human cells. Dual-luciferase reporter assay and ChIP analysis showed that p65 directly binds to HTRA-1 promoter (amino acid 347).

Conclusion: Our findings indicate that TLR-4 activation increases HTRA-1 expression through the NF-κB pathway in fibroblasts and macrophages. HTRA-1 expression is involved in the enhancing effects of LPS on CIA. This study offers new insights into the regulation of HTRA-1 expression via LPS/TLR-4 and the role of HTRA-1 in RA pathogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arthritis, Experimental / genetics*
  • Arthritis, Experimental / immunology
  • Arthritis, Experimental / metabolism*
  • Disease Models, Animal
  • Fibroblasts / drug effects
  • Fibroblasts / physiology
  • Gene Expression Regulation, Enzymologic / drug effects
  • Gene Expression Regulation, Enzymologic / immunology
  • High-Temperature Requirement A Serine Peptidase 1
  • Humans
  • Incidence
  • Lipopolysaccharides / pharmacology*
  • Macrophages / drug effects
  • Macrophages / physiology
  • Mice
  • Mice, Inbred C57BL
  • NF-kappa B / metabolism
  • RNA, Messenger / metabolism
  • Serine Endopeptidases / genetics*
  • Serine Endopeptidases / metabolism*
  • Synovial Membrane / cytology
  • Synovial Membrane / physiology
  • Toll-Like Receptor 4 / metabolism


  • Lipopolysaccharides
  • NF-kappa B
  • RNA, Messenger
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • High-Temperature Requirement A Serine Peptidase 1
  • HtrA1 protein, mouse
  • Serine Endopeptidases