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Hypoxia decreases sclerostin expression and increases Wnt signaling in osteoblasts

Damian C Genetos1, Chrisoula A Toupadakis, Leah F Raheja

  • 1Department of Surgical and Radiological Sciences, School of Veterinary Medicine, UC Davis, Davis, California 95616, USA. dgenetos@ucdavis.edu

Journal of Cellular Biochemistry
|March 26, 2010
PubMed

Insights

Cellular hypoxia decreases sclerostin expression by inhibiting Wnt/Lrp5 signaling. This finding offers new insights into bone development and sclerosing bone dysplasias, impacting bone mineral density.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Bone Biology

Background:

  • Sclerostin mutations cause sclerosing bone dysplasias by reducing Wnt/Lrp5 signaling antagonism.
  • VHL tumor suppressor deletion in osteoblasts increases bone mass via HIF-alpha stabilization.
  • The role of cellular oxygen levels on sclerostin and Wnt signaling requires further investigation.

Purpose of the Study:

  • To investigate the impact of cellular hypoxia on sclerostin expression and canonical Wnt signaling.
  • To elucidate the molecular mechanisms linking oxygen levels to sclerostin regulation.

Main Methods:

  • Osteoblasts and osteocytes were cultured under hypoxic conditions (1% oxygen).
  • Sclerostin transcript and protein levels were measured.
  • Beta-catenin expression, nuclear localization, and gene reporter activity were assessed.
  • Expression of BMP antagonists (gremlin, noggin) and Smad phosphorylation were analyzed.
  • MEF2 and VEGF signaling pathways were modulated and analyzed.

Main Results:

  • Hypoxia significantly decreased sclerostin transcript and protein levels in osteoblasts and osteocytes.
  • Hypoxia and DFO (hypoxia mimetic) increased beta-catenin expression and nuclear localization.
  • Hypoxia increased BMP antagonists (gremlin, noggin) and decreased Smad-1/5/8 phosphorylation.
  • MEF2 reporter activity decreased under hypoxia, suggesting a role in sclerostin regulation.
  • VEGF signaling modulation did not affect Sost transcription under normoxia or hypoxia.

Conclusions:

  • Cellular hypoxia inhibits sclerostin expression.
  • This inhibition is mediated through enhanced antagonism of BMP signaling, independently of VEGF.
  • Findings suggest a novel regulatory mechanism for sclerostin by oxygen levels, impacting Wnt signaling pathways.

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