Human aortic valve calcification is associated with an osteoblast phenotype.
BACKGROUND
Calcific aortic stenosis is the third most common cardiovascular disease in the United States. We hypothesized that the mechanism for aortic valve calcification is similar to skeletal bone formation and that this process is mediated by an osteoblast-like phenotype.


RESULTS
To test this hypothesis, we examined calcified human aortic valves replaced at surgery (n=22) and normal human valves (n=20) removed at time of cardiac transplantation. Contact microradiography and micro-computerized tomography were used to assess the 2-dimensional and 3-dimensional extent of mineralization. Mineralization borders were identified with von Kossa and Goldner's stains. Electron microscopy and energy-dispersive spectroscopy were performed for identification of bone ultrastructure and CaPO4 composition. To analyze for the osteoblast and bone markers, reverse transcriptase-polymerase chain reaction was performed on calcified versus normal human valves for osteopontin, bone sialoprotein, osteocalcin, alkaline phosphatase, and the osteoblast-specific transcription factor Cbfa1. Microradiography and micro-computerized tomography confirmed the presence of calcification in the valve. Special stains for hydroxyapatite and CaPO4 were positive in calcification margins. Electron microscopy identified mineralization, whereas energy-dispersive spectroscopy confirmed the presence of elemental CaPO4. Reverse transcriptase-polymerase chain reaction revealed increased mRNA levels of osteopontin, bone sialoprotein, osteocalcin, and Cbfa1 in the calcified valves. There was no change in alkaline phosphatase mRNA level but an increase in the protein expression in the diseased valves.


CONCLUSIONS
These findings support the concept that aortic valve calcification is not a random degenerative process but an active regulated process associated with an osteoblast-like phenotype.
Rajamannan
Nalini M
NM
Division of Cardiology, Northwestern University Feinberg School of Medicine, Northwestern University, 201 East Huron St, Galter Suite 10-240, Chicago, Ill 60611, USA. n.rajamannan@northwestern.edu
Subramaniam
Malayannan
M
Rickard
David
D
Stock
Stuart R
SR
Donovan
Janis
J
Springett
Margaret
M
Orszulak
Thomas
T
Fullerton
David A
DA
Tajik
A J
AJ
Bonow
Robert O
RO
Spelsberg
Thomas
T
D001021:Aortic Valve / Q000648:ultrastructure; D001024:Aortic Valve Stenosis / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology*; D015415:Biomarkers / Q000032:analysis; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000473:pathology / Q000648:ultrastructure; D002114:Calcinosis / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008852:Microradiography; D010006:Osteoblasts / Q000378:metabolism; D010012:Osteogenesis; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013057:Spectrum Analysis; D014057:Tomography, X-Ray Computed
D015415:Biomarkers