Nrf2-mediated fibroblast reprogramming drives cellular senescence by targeting the matrisome

Nrf2 is a key regulator of the antioxidant defense system, and pharmacological Nrf2 activation is a promising strategy for cancer prevention and promotion of tissue repair. Here we show, however, that activation of Nrf2 in fibroblasts induces cellular senescence. Using a combination of transcriptomics, matrix proteomics, chromatin immunoprecipitation and bioinformatics we demonstrate that fibroblasts with activated Nrf2 deposit a senescence-promoting matrix, with plasminogen activator inhibitor-1 being a key inducer of the senescence program. In vivo, activation of Nrf2 in fibroblasts promoted re-epithelialization of skin wounds, but also skin tumorigenesis. The pro-tumorigenic activity is of general relevance, since Nrf2 activation in skin fibroblasts induced the expression of genes characteristic for cancer-associated fibroblasts from different mouse and human tumors. Therefore, activated Nrf2 qualifies as a marker of the cancer-associated fibroblast phenotype. These data highlight the bright and the dark sides of Nrf2 and the need for time-controlled activation of this transcription factor

The Role of Regulatory T Cells and T Cell Cytokines in Skin Wound Repair: Tregs in wound healing

Successful wound healing in skin depends on the interplay of a multitude of different cell types, including immune cells, fibroblasts and keratinocytes, which are responding to signals from chemokines, cytokines and growth factors. Activin A is a growth and differentiation factor that is strongly induced at the wound site rapidly after injury and promotes reepithelialization and granulation tissue formation to achieve wound closure and restore tissue integrity. Our laboratory previously showed that overexpression of activin under control of the keratin 14 promoter in the basal layer of the epidermis in mice leads to accelerated wound closure, but at the same time predisposes to an enhanced fibrotic response at later stages of repair. Since modulation of regulatory T cells (Tregs) has been implicated in pro-fibrotic effects associated with tissue repair/remodeling, we investigated if these cells mediate at least in part the pro-healing effects of activin. Therefore, we depleted Tregs in mice that overexpress activin and also in control mice and evaluated the consequences on the wound healing process. Consistent with previous studies, activin accelerated reepithelialization and granulation tissue formation. However, both processes were strongly impaired in the absence of Tregs, independent of the activin transgene. These results demonstrate that Tregs promote wound healing in normal mice and contribute to the healing- promoting effect of activin. To determine the effect of Treg depletion on other immune cells, we established a protocol that allows efficient and reproducible isolation of different cell types from skin and wounds for further flow cytometry analysis. Using this protocol we demonstrated that Treg-depleted wounds show Summary 7 increased infiltration by αβ T cells, both CD4+ and CD4- cells. Since a large fraction of these cells expressed T-bet, but another group expressed GATA-3, these αβ T cells constitute a mixed Th1/Th2-prone population that is responsible for major changes in the cytokine profile of these wounds. While the pro-inflammatory cytokines IL-6 and TNF were detected at elevated levels in wounds compared to non-injured skin in all groups of mice, levels of IL-4 were significantly increased in wounds of Treg-depleted mice. Since overexpression of IL-4 was previously shown to inhibit wound healing, these findings provide a likely explanation for the wound healing defect in Treg depleted mice. We also investigated the importance of cytokine signaling on wound healing in mice deficient for IL-4Rα, IL-22, IFNγ, IL-17A or both IFNγ and IL-17A in comparison to wild-type mice and found that wound closure was improved by a lack in IL-4Rα or IL-22, but strongly impaired in the absence of IL-17A. While the molecular and cellular mechanisms of these alterations remain to be determined, these findings unravel important activities of T cell cytokines in the wound healing response