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


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.
Institute of Vascular Medicine and Li Ka Shing Institute of Health Sciences, School of Biomedical Sciences, Chinese University of Hong Kong, Hong Kong, China.
Chi Yung
CY
Yuen
Siu Ling
SL
Wong
Chi Wai
CW
Lau
Suk-Ying
SY
Tsang
Aimin
A
Xu
Zhiming
Z
Zhu
Chi Fai
CF
Ng
Xiaoqiang
X
Yao
Siu Kai
SK
Kong
Hung Kay
HK
Lee
Yu
Y
Huang
D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D002450:Cell Communication / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000502:physiology; D003599:Cytoskeleton / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D058628:Myofibroblasts / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D015675:Osteocalcin / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000502:physiology*
C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D015675:Osteocalcin; D000804:Angiotensin II; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human