UVB exposure of a humanized skin model reveals unexpected dynamic of keratinocyte proliferation and Wnt inhibitor balancing

J Tissue Eng Regen Med. 2018 Feb;12(2):505-515. doi: 10.1002/term.2519. Epub 2017 Dec 10.


We developed human dermo-epidermal skin substitutes that are presently applied in phase I and II clinical trials. Here, we used these very same skin equivalents containing melanocytes, named MelSkin, as an experimental skin model. We investigated the effects of ultraviolet B (UVB) irradiation on the skin grafts transplanted on immune-compromised rats. The irradiation induces a strong wound healing response going along with massive proliferation of basal keratinocytes, basically quiescent under nonirradiated, homeostatic conditions. As a consequence of UVB irradiation, the initially clearly defined basal keratinocyte (mono)layer expands into about 3 layers of keratinocytes, all of which still express the basal keratinocyte marker keratin 15. In contrast, epidermal melanocytes remain quiescent under these circumstances. Moreover, the Wnt inhibitors Dickkopf 3 and Wif1 are downregulated upon UVB irradiation in basal keratinocytes, whereas melanocytes continue to express Wnt inhibitors. These findings suggest that there is (a) a suprabasal population, proliferating in the homeostatic state, hence maintaining the integrity of the epidermis, and (b) a basal, usually quiescent keratinocyte population that is induced to massively proliferate upon irradiation. Importantly, the finding that MelSkin responds in a physiological fashion to UVB is of paramount importance in light of the planned clinical application.

Keywords: DKK3; K15; UVB; WIF1; human pigmented skin substitute; keratinocytes; melanocytes; tissue engineering.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Adolescent
  • Animals
  • Cell Proliferation / radiation effects
  • Chemokines
  • Child
  • Child, Preschool
  • Epidermal Cells / radiation effects
  • Humans
  • Infant
  • Intercellular Signaling Peptides and Proteins / metabolism
  • Keratinocytes / cytology*
  • Keratinocytes / radiation effects*
  • Keratins / metabolism
  • Rats
  • Repressor Proteins / metabolism
  • Skin / cytology*
  • Skin, Artificial
  • Ultraviolet Rays*
  • Wnt Proteins / antagonists & inhibitors*
  • Wnt Proteins / metabolism
  • Wound Healing / radiation effects


  • Adaptor Proteins, Signal Transducing
  • Chemokines
  • DKK3 protein, human
  • Intercellular Signaling Peptides and Proteins
  • Repressor Proteins
  • WIF1 protein, human
  • Wnt Proteins
  • Keratins