From skeleton to cytoskeleton: osteocalcin transforms vascular fibroblasts to myofibroblasts via angiotensin II and Toll-like receptor 4

Circ Res. 2012 Jul 20;111(3):e55-66. doi: 10.1161/CIRCRESAHA.112.271361. Epub 2012 Jun 7.


Rationale: The expression of osteocalcin is augmented in human atherosclerotic lesions. How osteocalcin triggers vascular pathogenesis and remodeling is unclear.

Objective: To investigate whether osteocalcin promotes transformation of adventitial fibroblast to myofibroblasts and the molecular mechanism involved.

Methods and results: Immunohistochemistry indicated that osteocalcin was expressed in the neointima of renal arteries from diabetic patients. Western blotting and wound-healing assay showed that osteocalcin induced fibroblast transformation and migration, which were attenuated by blockers of the renin-angiotensin system and protein kinase Cδ (PKCδ), toll-like receptor 4 (TLR4) neutralizing antibody, and antagonist and inhibitors of free radical production and cyclooxygenase-2. Small interfering RNA silencing of TLR4 and PKCδ abolished fibroblast transformation. Angiotensin II level in the conditioned medium from the osteocalcin-treated fibroblasts was found elevated using enzyme immunoassay. Culturing of fibroblasts in conditioned medium collected from differentiated osteoblasts promoted fibroblast transformation. The expression of fibronectin, TLR4, and cyclooxygenase-2 is augmented in human mesenteric arteries after 5-day in vitro exposure to osteocalcin.

Conclusions: Osteocalcin transforms adventitial fibroblasts to myofibroblasts through stimulating angiotensin II release and subsequent activation of PKCδ/TLR4/reactive oxygen species/cyclooxygenase-2 signaling cascade. This study reveals that the skeletal hormone osteocalcin cross-talks with vascular system and contributes to vascular remodeling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiotensin II / metabolism*
  • Animals
  • Bone and Bones / cytology
  • Bone and Bones / metabolism
  • Bone and Bones / physiology
  • Cell Communication / physiology
  • Cell Differentiation / physiology
  • Cells, Cultured
  • Cyclooxygenase 2 / physiology
  • Cytoskeleton / enzymology
  • Cytoskeleton / metabolism*
  • Cytoskeleton / physiology
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / enzymology
  • Endothelium, Vascular / metabolism
  • Fibroblasts / cytology
  • Fibroblasts / enzymology
  • Fibroblasts / metabolism*
  • Humans
  • Myofibroblasts / cytology
  • Myofibroblasts / enzymology
  • Myofibroblasts / metabolism*
  • Osteocalcin / physiology*
  • Rats
  • Signal Transduction / physiology
  • Toll-Like Receptor 4 / physiology*


  • TLR4 protein, human
  • Toll-Like Receptor 4
  • Osteocalcin
  • Angiotensin II
  • Cyclooxygenase 2
  • PTGS2 protein, human