title: In vivo visualization of the origination of skin graft vasculature in a wild-type/GFP crossover model.
abstract: BACKGROUND
  Skin substitutes are increasingly produced in tissue engineering, but still the understanding of the physiological skin revascularization process is lacking. To study in vivo conditions we recently introduced a mouse model, in which we already characterized the angiogenic changes within the wound bed and the skin graft. The aim of this study was to identify the origination of the vasculature during skin graft revascularization in vivo and to track vessel development over time.
  
  
  METHODS
  We created a crossover wild-type/GFP skin transplantation model, in which each animal carried the graft from the other strain. The preparation of the modified dorsal skin fold chamber including cross-over skin grafting was performed in male C57BL/6J wild-type mice (n=5) and C57BL/6-Tg(ACTB-EGFP)1O sb/J mice (n=5). Intravital microscopy in 12 areas of wild-type and GFP skin grafts was performed daily over a time period of 10 days.
  
  
  RESULTS
  Graft reperfusion started after 48-72 h. After reperfusion GFP-positive structures from the wound bed were visible in the graft capillaries with the highest density in the center of the graft. Overall, we observed a replacement of existing graft capillaries with vessels from the wound bed in 68% of the vessels. Of note, vessel replacement occurred in almost 100% of graft vessels in the periphery. Additionally, vessels within the graft showed a temporary angiogenic response between days 3-8, which originated predominantly from the autochthonous graft vasculature, but also contained already grown-in vessels from the wound bed.
  
  
  CONCLUSIONS
  These in vivo data indicate an early in-growth of angiogenic bed vessels into the existing vascular channels of the graft and subsequent centripetal replacement. Additionally we observed a temporary angiogenic response of the autochthonous capillaries of the skin graft with contribution from bed vessels. These findings further support the theory that sprouting angiogenesis from the wound bed in combination with the replacement of existing graft vessels are the key factors in skin graft taking. Thus, manufacturing of skin substitutes should be aimed at providing pre-formed vascular channels within the construct to improve vascularization.
authors.affiliation: Division of Plastic and Reconstructive Surgery, Department of Surgery, University Hospital Zurich, Rämistrasse 100, 8091 Zürich, Switzerland.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Calcagni
authors.forename: Martina K
authors.initials: MK
authors.lastname: Althaus
authors.forename: Alicia D
authors.initials: AD
authors.lastname: Knapik
authors.forename: Niels
authors.initials: N
authors.lastname: Hegland
authors.forename: Claudio
authors.initials: C
authors.lastname: Contaldo
authors.forename: Pietro
authors.initials: P
authors.lastname: Giovanoli
authors.forename: Nicole
authors.initials: N
authors.lastname: Lindenblatt
mesh_terms: D000818:Animals; D002196:Capillaries / Q000378:metabolism / Q000502:physiology*; D006085:Graft Survival; D049452:Green Fluorescent Proteins / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D023421:Models, Animal; D018919:Neovascularization, Physiologic; D012039:Regional Blood Flow; D012867:Skin / Q000098:blood supply*; D016038:Skin Transplantation; D013997:Time Factors; D014945:Wound Healing
chemical_list: C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins