Critical role of endogenous thrombospondin-1 in preventing expansion of healing myocardial infarcts.
BACKGROUND
Matricellular proteins are extracellular matrix proteins that do not contribute directly to tissue integrity but are capable of modulating cell function. We hypothesized that the matricellular protein thrombospondin (TSP)-1, a potent inhibitor of angiogenesis and activator of transforming growth factor (TGF-beta), is induced in healing myocardial infarcts and plays a role in suppressing the postinfarction inflammatory response, inhibiting local angiogenesis, and limiting expansion of granulation tissue into the noninfarcted area.


RESULTS
We used a canine and a murine model of reperfused infarction. TSP-1 mRNA was induced in canine infarcts after 1 hour of ischemia and 3 to 7 days of reperfusion. TSP-1 protein showed a strikingly selective localization in the extracellular matrix, microvascular endothelium, and a subset of mononuclear cells of the infarct border zone after 5 to 28 days of reperfusion. Isolated canine venous endothelial cells showed low-level constitutive expression of TSP-1 mRNA, which was markedly induced by TGF-beta, and basic fibroblast growth factor. Murine infarcts also had marked TSP-1 deposition in the border zone. Infarcted TSP-1-/- mice exhibited sustained upregulation of the chemokines monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, and interferon-gamma-inducible protein-10/CXCL10 and the cytokines interleukin-1beta, interleukin-6, and TGF-beta, suggesting an enhanced and prolonged postinfarction inflammatory response. In addition, TSP-1-/- mice had markedly increased macrophage and myofibroblast density in infarcts and in remodeling noninfarcted myocardial areas neighboring the myocardial scar, suggesting expansion of granulation tissue formation into the noninfarcted territory. TSP-1-/- animals had more extensive postinfarction remodeling than wild-type mice, although infarct size was similar in both groups.


CONCLUSIONS
The infarct border zone may be capable of modulating the healing process through its unique extracellular matrix content. The selective endogenous expression of TSP-1 in the infarct border zone may serve as a "barrier," limiting expansion of granulation tissue and protecting the noninfarcted myocardium from fibrotic remodeling.
Frangogiannis
Nikolaos G
NG
Section of Cardiovascular Sciences, Methodist Hospital and DeBakey Heart Center, Baylor College of Medicine, Houston, Tex, USA. ngf@bcm.tmc.edu
Ren
Guofeng
G
Dewald
Oliver
O
Zymek
Pawel
P
Haudek
Sandra
S
Koerting
Anna
A
Winkelmann
Kim
K
Michael
Lloyd H
LH
Lawler
Jack
J
Entman
Mark L
ML
D000818:Animals; D018925:Chemokines / Q000235:genetics; D004195:Disease Models, Animal; D004285:Dogs; D004730:Endothelium, Vascular / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000502:physiology; D005786:Gene Expression Regulation; D007249:Inflammation; D051379:Mice; D018345:Mice, Knockout; D009203:Myocardial Infarction / Q000276:immunology* / Q000473:pathology*; D012333:RNA, Messenger / Q000032:analysis; D012038:Regeneration / Q000276:immunology; D015427:Reperfusion Injury; D019700:Thrombospondin 1 / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation
D018925:Chemokines; D016326:Extracellular Matrix Proteins; D012333:RNA, Messenger; D019700:Thrombospondin 1