Nrf2 establishes a glutathione-mediated gradient of UVB cytoprotection in the epidermis

Abstract

Ultraviolet (UV) B irradiation can severely damage the skin and even induce tumorigenesis. It exerts its effects by direct DNA modification and by formation of reactive oxygen species (ROS). We developed a strategy to genetically activate target gene expression of the transcription factor NF-E2-related factor 2 (Nrf2) in keratinocytes in vivo based on expression of a constitutively active Nrf2 mutant. Activation of Nrf2 target genes strongly reduced UVB cytotoxicity through enhancement of ROS detoxification. Remarkably, the protective effect was extended to neighboring cells. Using different combinations of genetically modified mice, we demonstrate that Nrf2 activates the production, recycling, and release of glutathione and cysteine by suprabasal keratinocytes, resulting in protection of basal cells in a paracrine, glutathione/cysteine-dependent manner. Most importantly, we found that endogenous Nrf2 controls selective protection of suprabasal keratinocytes from UVB-induced apoptosis through activation of cytoprotective genes. This finding explains the preferential UVB-induced apoptosis of basal cells, which is important for elimination of mutated stem cells as well as for preservation of skin integrity. Taken together, our results identify Nrf2 as a key regulator in the UV response of the skin.[Keywords: Apoptosis; Nrf2; UVB; reactive oxygen species; glutathione] Supplemental material is available at http://www.genesdev.org.

Autocrine and Paracrine Regulation of Keratinocyte Proliferation through a Novel Nrf2–IL-36γ Pathway

“…These are of major medical importance, because Nrf2 activation is considered a powerful strategy for protection of different tissues and organs from various insults and, in particular, for cancer prevention; however, evidence is emerging that activation of Nrf2 also has negative consequences. For example, genetic or pharmacological activation of Nrf2 in keratinocytes caused skin inflammation, hyperkeratosis, and sebaceous gland enlargement (4,5). Furthermore, various NRF2-activating compounds are skin sensitizers (22,23), and recent studies suggest that Nrf2 can promote atherosclerosis in mice (24).…”

“…This causes enhanced drug resistance, increased survival under stress conditions, and hyperproliferation of the tumor cells as a result of an increased abundance of multidrug-resistance proteins, ROSdetoxifying enzymes, and metabolic enzymes (2,3). Recent studies from our laboratory also demonstrated that chronic activation of Nrf2 in keratinocytes causes hyperkeratosis, epidermal thickening due to keratinocyte hyperproliferation, cutaneous inflammation, and sebocyte hyperplasia (4)(5)(6). Therefore, we searched for soluble mediators that are controlled by Nrf2 and may affect cell proliferation and/or inflammation.…”

“…To identify Nrf2 target genes encoding soluble mediators that may affect cell proliferation and/or inflammation, we analyzed microarray data obtained from skin of mice expressing low or high levels of caNrf2 in keratinocytes (designated K5cre-caNrf2 and K5cre-CMVcaNrf2 mice) (4,5). The Affymetrix expression profiling was performed at postnatal day 2.5 before the hyperproliferative and inflammatory phenotype had developed in these mice.…”

“…K5cre-caNrf2 mice, K5cre-CMVcaNrf2 mice, and Albcre-caNrf2 mice (C57BL/6/FVB F1 genetic background), as well as Nrf2ko mice (C57BL/6 genetic background) or mice expressing a dominant-negative Nrf2 mutant in keratinocytes (K14-dnNrf2 mice; FVB genetic background) were described previously (4,5,(7)(8)(9). Two thirds (partial) hepatectomy was performed as previously described (10).…”

Development and Homeostasis of the Skin Epidermis

“…Studies in human and mouse have shown that the proliferating basal cells of the IFE are more sensitive to UV irradiation compared with the more differentiated suprabasal cells (reviewed in Blanpain et al 2011). Upon UV irradiation the IFE basal cells exhibit sustained p53 accumulation and higher apoptosis rates, concomitant with an inverse gradient of Nrf2 expression, which controls the expression of oxidative stress regulators (Schafer et al 2010). Ex vivo studies of human epidermal SCs have shown that they are more resistant to ionizing radiation, possibly because of an autocrine/paracrine FGF2-mediated increase in DNA repair activity (Rachidi et al 2007;Harfouche et al 2010).…”