Smooth muscle cells deficient in osteopontin have enhanced susceptibility to calcification in vitro.
OBJECTIVE
Vascular calcification is an actively regulated process, correlating with cardiovascular morbidity and mortality especially in patients with diabetes and chronic renal diseases. Osteopontin (OPN) is abundantly expressed in human calcified arteries and inhibits vascular calcification in vitro and in vivo. How OPN functions in vascular calcification, however, is less clear.


METHODS
Smooth muscle cells (SMCs) were isolated from aortas of OPN knock-out (OPN-/-) and wild type (OPN+/+) mice.


RESULTS
OPN-/- SMCs were identical to OPN+/+ SMCs in morphology and stained positively for SM lineage proteins, desmin, smooth muscle alpha-actin and SM22alpha. No spontaneous calcification was observed in OPN-/- SMCs under normal culture conditions or in medium containing 1%, 3%, or 5% fetal bovine serum. However, when cultured in medium containing elevated concentrations of inorganic phosphate, an inducer of vascular calcification, a significantly higher calcification was observed in OPN-/- SMCs compared to OPN+/+ SMCs that, in response to elevated phosphate, synthesized and secreted OPN into the culture. Finally, retroviral transduction of mouse OPN cDNA into OPN-/- SMCs rescued the calcification phenotype of the cells.


CONCLUSIONS
These results are the first to demonstrate an inhibitory role of endogenously produced OPN on SMC calcification, suggesting a novel feedback mechanism where OPN produced locally by the SMCs may serve as an important inducible inhibitor of vascular calcification.
Speer
Mei Y
MY
Bioengineering Department, Box 351720 University of Washington, Seattle, WA 98195, USA.
Chien
Yung-Ching
YC
Quan
Mary
M
Yang
Hsueh-Ying
HY
Vali
Hojatollah
H
McKee
Marc D
MD
Giachelli
Cecilia M
CM
D000818:Animals; D001011:Aorta; D002114:Calcinosis / Q000209:etiology* / Q000378:metabolism; D018929:Cell Culture Techniques; D018076:DNA, Complementary / Q000008:administration & dosage; D004198:Disease Susceptibility; D005822:Genetic Vectors / Q000008:administration & dosage; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D053495:Osteopontin; D010710:Phosphates / Q000494:pharmacology; D012190:Retroviridae / Q000235:genetics; D012795:Sialoglycoproteins / Q000172:deficiency* / Q000235:genetics; D014161:Transduction, Genetic / Q000379:methods
D018076:DNA, Complementary; D010710:Phosphates; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D053495:Osteopontin