title: Myocardial protection from ischemia/reperfusion injury by targeted deletion of matrix metalloproteinase-9.
abstract: OBJECTIVE
  Matrix metalloproteinase-9 (MMP-9) activity is up regulated in the heart subjected to ischemic insult. Whether increased MMP-9 activity contributes to acute myocardial injury after ischemia-reperfusion remains unknown. To investigate the role of MMP-9 in myocardial infarction, we utilized a MMP-9 knockout mouse.
  
  
  RESULTS
  Standard homologous recombination in embryonic stem cells was used to generate a mouse lacking MMP-9. The left anterior descending coronary artery was occluded for 30 min followed by 24 h reperfusion, and the ischemic and infarct sizes were determined. Targeted deletion of MMP-9 protected the heart from no-flow ischemia-reperfusion-induced myocardial injury. The myocardial infarct size was reduced by 17.5% in MMP-9 heterozygotes (+/-) (P<0.01) and 35.4% in MMP-9 knockout (-/-) mice (P<0.01) versus the wild-type (+/+) mice, respectively. Analysis of MMP activity in myocardial extracts by zymography demonstrated that ischemia-reperfusion-induced expression of proMMP-9 and active MMP-9 was reduced by 77.8% (P<0.01) and 69.1% (P<0.001), respectively, in (+/-) mice compared to (+/+) mice, and was absent in (-/-) animals. The expression of TIMP-1, an endogenous inhibitor of MMP-9, was elevated 4.7-fold (P<0.05) and 21.4-fold (P<0.05) in the (+/-) and (-/-) mice, respectively, compared to (+/+) mice. Immunohistochemical analysis revealed that neutrophils were the primary cellular source of MMP-9, and less neutrophils were detected in the ischemic region of the heart following ischemia-reperfusion in (-/-) mice compared to (+/+) mice. Measurement of myeloperoxidase activity, a marker enzyme of neutrophils, demonstrated a 44% reduction in neutrophils infiltrated into the ischemic myocardium in the (-/-) mice compared to the (+/+) mice (P<0.05).
  
  
  CONCLUSIONS
  These results suggest that MMP-9 plays an important role in ischemia-reperfusion-induced myocardial infarction and MMP-9 could be a target for prevention or treatment of acute ischemic myocardial injury.
authors.affiliation: Department of Cardiovascular Pharmacology, GlaxoSmithKline Pharmaceuticals, King of Prussia, PA 19046, USA. anne_romanic-1@gsk.com
authors.forename: Anne M
authors.initials: AM
authors.lastname: Romanic
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Harrison
authors.forename: Weike
authors.initials: W
authors.lastname: Bao
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Burns-Kurtis
authors.forename: Susan
authors.initials: S
authors.lastname: Pickering
authors.forename: Juanli
authors.initials: J
authors.lastname: Gu
authors.forename: Evelyn
authors.initials: E
authors.lastname: Grau
authors.forename: Joyce
authors.initials: J
authors.lastname: Mao
authors.forename: Ganesh M
authors.initials: GM
authors.lastname: Sathe
authors.forename: Eliot H
authors.initials: EH
authors.lastname: Ohlstein
authors.forename: Tian Li
authors.initials: TL
authors.lastname: Yue
mesh_terms: D000818:Animals; D017353:Gene Deletion; D007150:Immunohistochemistry / Q000379:methods; D020778:Matrix Metalloproteinase 2 / Q000032:analysis / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000032:analysis / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D015428:Myocardial Reperfusion Injury / Q000201:enzymology* / Q000235:genetics; D009206:Myocardium / Q000201:enzymology* / Q000276:immunology; D020556:Neutrophil Infiltration; D009504:Neutrophils / Q000201:enzymology; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000032:analysis / Q000378:metabolism; D020257:Ventricular Remodeling
chemical_list: D019715:Tissue Inhibitor of Metalloproteinase-1; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9