The Epigenetic Regulation of Epidermal Stem Cells in Adult Skin Wound Healing

Project Summary The epidermis is a vital tissue that protects our bodies against infection and environmental insults. Upon wounding, epidermal basal cells undergo a transient transcriptional switch to increase proliferation and migrate into the wounded area to re-epithelize the epidermis. Regulation of this wound-activated transcriptional switch is unknown, but research has suggested that chromatin remodelers may be responsible. My analysis revealed that a key chromatin repressor, Polycomb repressive complex 1 (PRC1), occupies more than half of wound-related genes during homeostasis, suggesting a potential role of PRC1 as a regulator of the transient switch in epidermal basal cells upon wound induction. By generating and analyzing mice lacking PRC1 function in epidermal basal cells, I observed arrested wound repair as PRC1-null epidermal basal cells failed to migrate during the re- epithelialization stage of wound healing. Cell migration during wound repair is mediated by epithelial- mesenchymal plasticity (EMP), a biological process in which cells undergo molecular and functional changes to interconvert between an epithelial phenotype to a migratory mesenchymal phenotype. The regulation of EMP processes during wound healing is unknown. E-cadherin is an epithelial protein that is transcriptionally downregulated in migrating epidermal basal cells and a key marker of the EMP process. Interestingly, E-cadherin expression was retained in PRC1-null epidermal basal cells upon wound induction. Given these data, I hypothesize that PRC1 mediates the ability of epidermal basal cells to migrate by repressing E-cadherin and reprogramming the transcriptional landscape upon wound induction to undergo EMP processes. To test this hypothesis, in Aim 1, I will investigate the significance of E-cadherin repression in migrating epidermal basal cells by overexpressing E-cadherin in cultured primary epidermal basal cells and ex vivo wound explants. Additionally, I will perform CUT&Tag to investigate if E-cadherin is a direct target of PRC1 regulation, as well as use genetically engineered mice and shRNA technology to repress or ablate E-cadherin expression in PRC1- null mice and PRC1-null epidermal basal cell lines, respectively. In Aim 2, I will determine EMP genes that are most affected by the loss of PRC1 in epidermal basal cells during wound repair and examine the functionality of the identified genes for epidermal basal cell migration. I will also perform immunostaining to assess if PRC1- regulated EMP genes are misexpressed in samples of human chronic wounds. Altogether, these data will uncover a novel role for PRC1 regulation in reprogramming the transcriptional landscape needed for epidermal basal cell migration during wound healing, as well as define the role of PRC1 in controlling EMP during wound healing.