title: Cryoinjury: a model of myocardial regeneration.
abstract: BACKGROUND
  Although traditionally adult cardiomyocytes are thought to be unable to divide, recent observations provide evidence for cardiomyocyte proliferation after myocardial injury. Myocardial cryoinjury has been shown to be followed by neovascularization. We hypothesize that, in addition to neovascularization, cardiomyocyte proliferation after myocardial cryoinjury contributes to regeneration.
  
  
  METHODS
  Cryolesions were applied to the left ventricle of mouse hearts. Inflammatory cell infiltration (F4/80, neutrophils), neovascularization (CD31), and cardiomyocyte proliferation (5-bromo-2-deoxyuridine, Ki-67, mitotic spindle) were determined at different time points (2-70 days) after cryoinjury.
  
  
  RESULTS
  Between Days 7 and 14 after injury, a 150- and 280-fold increase in number of proliferating cardiomyocytes was observed, as compared to controls. At the same time, numerous proliferating capillaries were found in between the proliferating cardiomyocytes. Presence of high numbers of macrophages in the cryolesion preceded and coincided with this proliferation. The area of cryolesion decreased significantly between Days 7 (23+/-5%) and 14 (8+/-2%) after cryoinjury. Moreover, regeneration of viable, nonhypertrophied myocardium was observed. After 14 days, cardiomyocyte proliferation decreased to numbers observed in controls, and concomitantly, the number of macrophages strongly decreased.
  
  
  CONCLUSIONS
  Our data show that adult cardiomyocytes proliferate in sufficiently high numbers to effectuate myocardial regeneration after left ventricular cryoinjury in mice.
authors.affiliation: Department of Pathology and Laboratory Medicine, University Medical Center Groningen, University of Groningen, Medical Biology Section, 9713 GZ, Groningen, The Netherlands. m.van.amerongen@med.rug.nl
authors.forename: Machteld J
authors.initials: MJ
authors.lastname: van Amerongen
authors.forename: Martin C
authors.initials: MC
authors.lastname: Harmsen
authors.forename: Arjen H
authors.initials: AH
authors.lastname: Petersen
authors.forename: Eliane R
authors.initials: ER
authors.lastname: Popa
authors.forename: Marja J A
authors.initials: MJ
authors.lastname: van Luyn
mesh_terms: D000818:Animals; D002196:Capillaries / Q000473:pathology; D049109:Cell Proliferation; D003080:Cold Temperature / Q000009:adverse effects*; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000473:pathology; D006335:Heart Injuries / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D006352:Heart Ventricles / Q000473:pathology; D008264:Macrophages / Q000473:pathology; D008297:Male; D008407:Mast Cells / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology*; D009206:Myocardium / Q000473:pathology*; D018919:Neovascularization, Physiologic; D009504:Neutrophils / Q000473:pathology; D012038:Regeneration; D013997:Time Factors