title: Proteinase inhibitor 9 is reduced in human atherosclerotic lesion development.
abstract: BACKGROUND
  Granzyme B, a proapoptotic serine protease, is abundant in advanced, unstable atherosclerotic plaques, and it is suggested to contribute to plaque instability by inducing vascular smooth muscle cells apoptosis and by degrading plaque extracellular matrix. Proteinase inhibitor 9, the only known endogenous inhibitor of granzyme B in humans, confers protection against granzyme-B-induced apoptosis. However, the role of proteinase inhibitor 9 in atherosclerotic lesion development has yet to be determined. We hypothesized that atherosclerotic lesions have lower proteinase inhibitor 9 expression levels that will increase their susceptibility to granzyme-B-induced apoptosis.
  
  
  METHODS
  Serial sections of human coronary arteries exhibiting different stages of lesion development were assessed by immunohistochemistry for proteinase inhibitor 9, α-smooth muscle cells actin, granzyme B, CD8, and active caspase-3. Frozen samples were analyzed by Western blot to evaluate total proteinase inhibitor 9 levels.
  
  
  RESULTS
  Vascular smooth muscle cells express less proteinase inhibitor 9 as disease severity increases, and a significant difference in proteinase inhibitor 9 expression is observed between medial and intimal smooth muscle cells. High granzyme B levels colocalize with CD8+ cells and foam cells in the shoulder region and necrotic core area of advanced lesions. In advanced lesions, increased expression of activated caspase-3 in intimal SMC was associated with reduced proteinase inhibitor 9 expression in the presence of granzyme B.
  
  
  CONCLUSIONS
  Reduced proteinase inhibitor 9 expression in human vascular smooth muscle cells is associated with atherosclerotic disease progression and is inversely related to the extent of apoptosis within the intima. Reduced proteinase inhibitor 9 expression may contribute to increased smooth muscle cell susceptibility to granzyme-B-induced apoptosis within the plaque.
authors.affiliation: Providence Heart+Lung Institute, The James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research, University of British Columbia,Vancouver, Canada V6Z 1Y6.
authors.forename: Alon
authors.initials: A
authors.lastname: Hendel
authors.forename: Dawn
authors.initials: D
authors.lastname: Cooper
authors.forename: Thomas
authors.initials: T
authors.lastname: Abraham
authors.forename: Hongyan
authors.initials: H
authors.lastname: Zhao
authors.forename: Michael F
authors.initials: MF
authors.lastname: Allard
authors.forename: David J
authors.initials: DJ
authors.lastname: Granville
mesh_terms: D000199:Actins / Q000378:metabolism; D017209:Apoptosis; D050197:Atherosclerosis / Q000378:metabolism / Q000473:pathology*; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D016827:CD8 Antigens / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D003331:Coronary Vessels / Q000378:metabolism / Q000473:pathology*; D018450:Disease Progression; D053804:Granzymes / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000473:pathology*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000473:pathology*; D015843:Serpins / Q000378:metabolism*; D017539:Tunica Intima / Q000378:metabolism / Q000473:pathology; D017540:Tunica Media / Q000378:metabolism / Q000473:pathology
chemical_list: C541116:ACTA2 protein, human; D000199:Actins; D015415:Biomarkers; D016827:CD8 Antigens; C102316:SERPINB9 protein, human; D015843:Serpins; D053804:Granzymes; D053148:Caspase 3