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Related Experiment Video

Updated: Jan 10, 2026

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Disruption of Proteoglycan 4 (PRG4)-CD44 Signaling Modulates Chronic Synovitis in Conditionally Inactivated Mice.

Khaled Elsaid1, Ling Zhang2, Thomas Zhao3

  • 1Chapman University.

Research Square
|November 24, 2025
PubMed
Summary
This summary is machine-generated.

Proteoglycan-4 (PRG4) loss leads to synovitis in osteoarthritis (OA) by activating xanthine oxidase (XO) and hypoxia inducible factor alpha (HIF-1α). CD44 deficiency abrogates this, suggesting CD44 as a therapeutic target for OA-related inflammation.

Keywords:
CD44HIF-1aOsteoarthritisProteoglycan-4SynovitisXanthine Oxidase

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Area of Science:

  • Biochemistry
  • Immunology
  • Molecular Biology

Background:

  • Proteoglycan-4 (PRG4) is a glycoprotein that inhibits synovial macrophage (SM) activation via xanthine oxidase (XO) and hypoxia inducible factor alpha (HIF-1α) suppression.
  • PRG4's role in maintaining synovial homeostasis and its signaling dysfunction in osteoarthritis (OA) are not fully understood.
  • It is hypothesized that CD44 mediates synovitis due to PRG4 loss and that PRG4 signaling dysfunction correlates with high-grade synovitis in OA.

Purpose of the Study:

  • To evaluate the contribution of the PRG4-CD44 interaction to synovial homeostasis.
  • To investigate PRG4 signaling dysfunction in synovial tissues from patients with osteoarthritis (OA).
  • To determine if CD44 mediates synovitis in the context of PRG4 loss.

Main Methods:

  • Utilized transgenic mice (Prg4 knockout) crossed with CD44-deficient mice to study PRG4-CD44 interactions.
  • Analyzed xanthine oxidase (XO) and hypoxia inducible factor alpha (HIF-1α) expression via immunostaining and ELISA.
  • Assessed synovial macrophage (SM) activation and glycolytic activity using proton efflux rate (PER) assays.
  • Examined synovial tissues from OA patients, classifying them by Krenn's synovitis score and performing immunohistochemistry (IHC) for PRG4, CD44, XO, and HIF-1α.

Main Results:

  • CD44 deficiency reduced XO and HIF-1α expression and attenuated synovial pathology following PRG4 inactivation.
  • Synovial macrophages from CD44-deficient, PRG4-inactivated mice showed significantly lower activation and HIF-1α levels.
  • High-grade synovitis tissues exhibited decreased PRG4 and increased CD44, XO, and HIF-1α expression compared to low-grade and normal tissues.
  • Febuxostat treatment reduced CD14+ cell activation in synovial tissues.

Conclusions:

  • CD44 loss effectively abrogated the chronic synovitis observed after PRG4 loss.
  • PRG4 signaling dysfunction, characterized by reduced PRG4 and elevated CD44, XO, and HIF-1α, is associated with high-grade synovitis in OA.
  • Targeting downstream events of PRG4 loss, potentially involving CD44, presents a therapeutic strategy for OA synovitis.