Progression of aortic valve stenosis: TGF-beta1 is present in calcified aortic valve cusps and promotes aortic valve interstitial cell calcification via apoptosis.
BACKGROUND
Aortic valve stenosis characteristically progresses due to cuspal calcification, often necessitating valve replacement surgery. The present study investigated the hypothesis that TGF-beta1, a cytokine that causes calcification of vascular smooth muscle cells in culture, initiates apoptosis of valvular interstitial cells as a mechanistic event in cuspal calcification.


METHODS
Noncalcified and calcified human aortic valve cusps were obtained at autopsy or at the time of cardiac surgery. The distributions within cusps of TGF-beta1, latent-TGF-beta1-associated peptide, and TGF-beta receptors were studied using immunohistochemistry. The effects of TGF-beta1 on mechanistic events contributing to aortic valve calcification were also investigated using sheep aortic valve interstitial cell (SAVIC) cultures.


RESULTS
Immunohistochemistry studies revealed that calcific aortic stenosis cusps characteristically contained within the extracellular matrix qualitatively higher levels of TGF-beta1 than noncalcified cusps. Noncalcified normal valves demonstrated only focal intracellular TGF-beta1. Addition of TGF-beta1 to SAVIC cultures led to a cascade of events, including: cellular migration, aggregation, formation of apoptotic-alkaline phosphatase enriched nodules, and calcification of these nodules. The time course of these events in the SAVIC culture system was rapid with nodule formation with apoptosis by 72 hours, and calcification after 7 days. Furthermore, ZVAD-FMK, an antiapoptosis agent (caspase inhibitor), significantly inhibited calcification and apoptosis induced by TGF-beta1, but had no effect on nodule formation. However, cytochalasin D, an actin-depolymerizing agent, inhibited nodule formation, but not calcification.


CONCLUSIONS
TGF-beta1 is characteristically present within calcific aortic stenosis cusps, and mediates the calcification of aortic valve interstitial cells in culture through mechanisms involving apoptosis.
Jian
Bo
B
Cardiology Research Laboratory, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104-4318, USA.
Narula
Navneet
N
Li
Quan-yi
QY
Mohler
Emile R
ER
Levy
Robert J
RJ
D000368:Aged; D000369:Aged, 80 and over; D000469:Alkaline Phosphatase / Q000378:metabolism; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D001021:Aortic Valve / Q000737:chemistry; D001024:Aortic Valve Stenosis / Q000473:pathology / Q000503:physiopathology*; D017209:Apoptosis / Q000502:physiology; D002114:Calcinosis / Q000503:physiopathology*; D061945:Caspase Inhibitors; D002478:Cells, Cultured; D018450:Disease Progression; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D012756:Sheep; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000502:physiology*; D053773:Transforming Growth Factor beta1
D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D000469:Alkaline Phosphatase