Foxn1 expression in keratinocytes is stimulated by hypoxia: further evidence of its role in skin wound healing

Abstract

Recent studies have shown that the transcription factor Foxn1, which is expressed in keratinocytes, is involved in the skin wound healing process, yet how Foxn1 functions remains largely unknown. Our latest data indicate that Foxn1 drives skin healing via engagement in re-epithelization and the epithelial-mesenchymal transition (EMT) process. In the present study, 2D-DIGE proteomic profiling analysis of in vitro cultured keratinocytes transfected with adenoviral vector carrying Foxn1-GFP or GFP alone (control) revealed forty proteins with differential abundance between the compared groups. Among the proteins with Foxn1-dependent expression, several enable adaptation to hypoxia. Subsequent experiments revealed that hypoxic conditions (1% O2) stimulate endogenous and exogenous (transfected Ad-Foxn1) Foxn1 expression in cultured keratinocytes. A proteomics analysis also identified proteins that can act as a factors controlling the balance between cell proliferation, differentiation and apoptosis in response to Foxn1. We also showed that in C57BL/6 keratinocytes, the stimulation of Foxn1 by hypoxia is accompanied by increases in Mmp-9 expression. These data corroborate the detected co-localization of Foxn1 and Mmp-9 expression in vivo in post-wounding skin samples of Foxn1::Egfp transgenic mice. Together, our data indicate that Foxn1 orchestrates cellular changes in keratinocytes in both physiological (self-renewal) and pathological (skin wound healing) contexts.

Impairment of the Hif-1α regulatory pathway in Foxn1-deficient (Foxn1−/−) mice affects the skin wound healing process

“…Mori, Itoi, Tsukamoto, & Amagai, 2010). In the skin, where Foxn1 is expressed in the epidermis and in hair follicles, it participates in hair follicle development, promotes keratinocyte differentiation and participates in the pigmentation process (Kur-Piotrowska et al, 2018;Lee, Prowse, & Brissette, 1999;Li et al, 2007;Weiner et al, 2007). Loss-of-function mutations in the Foxn1 gene has pleiotropic effects, similar in humans and mice and result in a lack of hair and the absence of the thymus and T cells (Brissette, Li, Kamimura, Lee, & Dotto, 1996;Frank et al, 1999;Nehls, Pfeifer, Schorpp, Hedrich, & Boehm, 1994;Pignata et al, 1996).…”

“…Under hypoxic conditions, Hif-1α is protected from degradation due to depletion of PHDs and Fih-1 via proteasomal degradation and enhancement of the Hif-1α protein levels by thioredoxin (Trx-1) (Karlenius & Tonissen, 2010;Kur-Piotrowska et al, 2018;Zhou, Damdimopoulos, Spyrou, & Brune, 2007). Then, Hif-1α translocates to the nucleus, undergoes dimerization with Hif-1β and activates the transcription of downstream genes, e.g., vascular endothelial growth factor (VEGF), platelet-derived growth factor B-chain (PDGF-B) and heat shock protein (HSP-90) (L. Chen, Gajendrareddy, & DiPietro, 2012;Lokmic et al, 2012).…”

“…Recently, using next-generation high-throughput DNA sequencing, we performed detailed analyses of differentially expressed genes in the skins of Foxn1 -/and Foxn1 +/+ (wild type) mice and found significant differences in the expression of genes associated with hypoxia (Kur-Piotrowska et al, 2018). Furthermore, the in vitro experiments showed that under low-oxygen conditions, Foxn1 expression is induced in primary cultures of keratinocytes (Kur-Piotrowska et al, 2018).…”

Wnt signaling and the transcription factor Foxn1 contribute to cutaneous wound repair in mice

“…Communication between the epidermis and underlying dermis is necessary for tissue homeostasis and involves the secretion of multiple factors 16 . We previously showed that the profiles of synthesized transcripts (e.g., Wnt10a, Wnt11, and β-catenin) and proteins that may be implicated in the molecular cross-layer dialogue differ between Foxn1deficient (nude) and Foxn1-active (wild-type control) mice 17,18 . Foxn1 transcription factor deficiency corresponds with the unique ability of mammalian skin to regenerate when injury occurs [19][20][21] .…”

MAP4 regulates Tctex‐1 and promotes the migration of epidermal cells in hypoxia

“…The re‐epithelialization process includes three stages of epidermal cell proliferation, migration and differentiation in which the migration of epidermal cells is the key step of re‐epithelialization on the wound surface . After acute wound formation, due to the disorder of the local blood circulation, the oxygen supply is reduced; meanwhile, the metabolism of the wound cells is active and proliferation increases, which leads to an increase in oxygen consumption, which results in the formation of an acute hypoxic microenvironment . Related studies have shown that acute hypoxia of the wound promotes wound healing by promoting the proliferation and migration of epidermal cells, fibroblasts and vascular endothelial cells, but the specific molecular mechanism is unclear.…”