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Orphan nuclear receptor NR4A2 induces synoviocyte proliferation, invasion, and matrix metalloproteinase 13

Kimberlee S Mix1, Kevin McMahon, Jason P McMorrow

  • 1Loyola University New Orleans, Department of Biological Sciences, New Orleans, Louisiana 70118, USA. kix@loyno.edu

Arthritis and Rheumatism
|January 26, 2012
PubMed
Abstract

Insights

The nuclear receptor 4A (NR4A) family, particularly NR4A2, drives synoviocyte proliferation and invasion in inflammatory arthritis by mediating TNFα signaling. Targeting NR4A2 may offer a new therapeutic strategy for arthritis.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Rheumatology

Background:

  • Inflammatory arthritis involves synovial tissue hyperplasia and cartilage destruction.
  • Orphan nuclear receptors, including the NR4A family, play roles in cellular processes relevant to arthritis.
  • Understanding the specific functions of NR4A in synoviocytes is crucial for developing targeted therapies.

Purpose of the Study:

  • To investigate the role of the nuclear receptor 4A (NR4A) family in synoviocyte transformation, hyperplasia, and the regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in inflammatory arthritis models.
  • To elucidate the signaling pathways involving NR4A, specifically NR4A2, in response to TNFα in synovial cells.

Main Methods:

  • Quantitative reverse transcription-polymerase chain reaction (RT-PCR) to measure NR4A mRNA levels in synovial tissue and primary synoviocytes.
  • In vitro studies involving stable overexpression or shRNA-mediated depletion of NR4A2 in synoviocytes to assess proliferation, survival, migration, invasion, and MMP/TIMP expression.
  • Reporter assays to determine NR4A2's direct transcriptional activity on the MMP-13 promoter.

Main Results:

  • NR4A2 expression was elevated in synovial tissues and RA synoviocytes, and rapidly induced by TNFα.
  • Overexpression of NR4A2 enhanced synoviocyte proliferation, survival, anchorage-independent growth, migration, and invasion.
  • NR4A2 synergistically induced MMP-13 expression with TNFα, directly transactivated the MMP-13 promoter, and antagonized TIMP-2 expression. Depletion of NR4A reduced these effects.

Conclusions:

  • NR4A2 acts as a downstream mediator of TNFα signaling in synovial tissue.
  • NR4A2-driven transcriptional activity contributes to the hyperplastic and invasive synoviocyte phenotype, leading to cartilage destruction.
  • NR4A2 represents a potential therapeutic target for inflammatory arthritis.

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