Foxn1 and Mmp‐9 expression in intact skin and during excisional wound repair in young, adult, and old C57Bl/6 mice

Abstract

The transcription factor Foxn1 is essential for skin development. Our previous studies performed on young C57BL/6J mice model showed that Foxn1 acts as regulator of the skin wound healing process. The present study extended our initial research regarding the expression and potential role of Foxn1 in the intact and wounded skin as a function of animal age and stage of the wound healing process. We analyzed Foxn1 and Mmp-9 expression in the intact and postinjured skin of young, adult, and old C57BL/6J and transgenic Foxn1::Egfp mice. The similar levels of epidermal Foxn1 mRNA expression were detected in young and adult C57BL/6J mice and higher levels in old animals. Postinjured skin tissues displayed a gradual decrease of Foxn1 mRNA expression at Days 1, 5, and 7 after injury. Foxn1-eGFP positive cells were abundant at wound margin and in re-epithelialized epidermis at postwounded Days 1, 5, and 7 and colocalized with E-cadherin and Mmp-9. Postwounded skin at Days 14-36 displayed Foxn1-eGFP cells in the epidermis and in the dermal part of the skin (papillary dermis). A subset of Foxn1-eGFP positive cells in the papillary dermis expressed the myofibroblast marker αSMA. Flow cytometric analysis of cells isolated from postwounded (Day 7) skin tissues showed a significant increase in the percentage of Foxn1-eGFP positive cells with phenotype of double positivity for E-cadherin/N-cadherin (epithelial/mesenchymal markers). Collectively, these data identify the transcription factor Foxn1 as a potential key epidermal regulator modifying both epidermal and dermal healing processes after cutaneous wounding.

The Transcription Factor FOXN1 Regulates Skin Adipogenesis and Affects Susceptibility to Diet-Induced Obesity

“…Furthermore, the large differences in body mass gain between young FOXN1 þ/þ mice and young FOXN1 eGFP/þ mice and the less prominent differences in old mice may reflect the age-related downregulation of FOXN1 expression. The decrease in FOXN1 expression was detected in old (21 months of age) mice; we did not observe this phenomenon in our previous experiments employing 16-to 18-month-old mice (Kopcewicz et al, 2017). This observation is consistent with research on the thymus that showed a decrease in FOXN1 expression with age and concomitant age-related thymic involution (Chen et al, 2009;Ortman et al, 2002).…”

“…Collectively, our previous and present data suggest that the transcription factor FOXN1 acts as a pro-scarring factor in the skin wound healing process. We observed scarless skin healing in FOXN1-deficient mice (Gawronska-Kozak et al, 2006), participation of FOXN1 in re-epithelialization and epithelial to mesenchymal transition during skin wound healing, (Gawronska-Kozak et al, 2016;Kopcewicz et al, 2017) and its stimulatory role in skin adipogenesis (present data). A decrease in FOXN1 expression with age coincided with scarless skin healing observed in older individuals (Ashcroft et al, 2002), which additionally underlines the role of FOXN1 in mouse and possible human skin wound healing processes.…”

“…For this study, we utilized transgenic mice in which an eGFP transgene is driven by Foxn1 regulatory sequences (Terszowski et al, 2006). Thus, the presence of eGFP reflects FOXN1 expression in the thymus (Terszowski et al, 2006) and skin (Gawronska-Kozak et al, 2016;Kopcewicz et al, 2017). FOXN1 eGFP/þ mice did not show any obvious phenotypic differences compared with their littermates at birth.…”

“…The transcription factor FOXN1 plays a regulatory role in maintaining homeostasis in the skin but also contributes to skin wound healing through its role in re-epithelialization and epithelial to mesenchymal transition (Gawronska-Kozak et al, 2016;Kopcewicz et al, 2017). Taking advantage of eGFP protein expression as a substitute for FOXN1, we analyzed the re-epithelialization process in post-wound skin tissues from FOXN1 eGFP/þ mice in relation to age and diet (Figure 2d and e).…”

“…The wound model was generated according to a previously described procedure (Gawronska-Kozak et al, 2016;Kopcewicz et al, 2017). Briefly, four excisional skin wounds with a diameter of 4 mm each were made on the back of the mice.…”