Characterization of M1 and M2 polarization of macrophages in vascularized human dermo-epidermal skin substitutes in vivo
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Aims and objectives
Vascularized bio-engineered human dermo-epidermal skin substitutes (vascDESS) hold promise for treating burn patients, including those with severe full-thickness wounds. We have previously shown that vascDESS promote wound healing by enhanced influx of macrophages and granulocytes. Immediately following transplantation, macrophages infiltrate the graft and differentiate into a pro-inflammatory (M1) or a pro-healing M2 phenotype. The aim of this study was to characterize the activation state of macrophages infiltrating skin transplants at distinct time points following transplantation.
Keratinocytes and the stromal vascular fraction (SVF) were derived from human skin or adipose tissue, respectively. Human SVF containing both endothelial and mesenchymal/stromal cells was used to generate vascularized dermal component in vitro, which was subsequently covered with human keratinocytes. Finally, vascDESS were transplanted on the back of immuno-incompetent rats, excised, and analyzed after 1 and 3 weeks using immunohistological techniques.
A panel of markers of macrophage M1 (nitric oxide synthase: iNOS) and M2 (CD206) subclass was used. All skin grafts were infiltrated by both M1 and M2 rat macrophages between 1–3 weeks post-transplantation. CD68 (PG-M1) was used as a pan-macrophage marker. The number of CD68+CD206+ M2-polarized macrophages was higher in 3-week transplants as compared to early-stage transplants (1 week). In contrast, the number of CD68+iNOS+ M1 cells was markedly decreased in later stages in vivo.
Macrophages exhibit a heterogeneous and temporally regulated polarization during skin wound healing. Our results suggest that the phenotype of macrophages changes during healing from a more pro-inflammatory (M1) profile in early stages after injury, to a less inflammatory, pro-healing (M2) phenotype in later phases in vivo.
KeywordsMacrophages Adipose stem cells Skin tissue engineering
This work was financially supported by the EU-FP6 project EuroSTEC (soft tissue engineering for congenital birth defects in children: contract: LSHB-CT-2006-037409), by the EU-FP7 project EuroSkinGraft (FP7/2007–2013: Grant Agreement nr 279024), by the EU-FP7 (MultiTERM, Grant Agreement nr 238551), and the Clinical Research Priority Programs (CRPP) of the Faculty of Medicine of the University of Zurich. We are particularly grateful to the Gaydoul Foundation and the sponsors of “DonaTissue” (Thérèse Meier and Robert Zingg) for their generous financial support and interest in our work.
Compliance with ethical standards
Conflict of interest
E. R. and M. M. are co-founding members and shareholders of “Cutiss AG”, a company to fund the further development of the tissue engineered skin substitutes. All other authors declare that they have no conflict of interest.
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