Keap1 knockdown in melanocytes induces cell proliferation and survival via HO-1-associated β-catenin signaling

Effect of ultraviolet radiation on the Nrf2 signaling pathway in skin cells

PURPOSE

Excessive exposure of skin to solar radiation is associated with greatly increased production of reactive oxygen and nitrogen species (ROS, RNS) resulting in oxidative stress (OS), inflammation, immunosuppression, the production of matrix metalloproteinase, DNA damage and mutations. These events lead to increased incidence of various skin disorders including photoaing and both non-melanoma and melanoma skin cancers. The ultraviolet (UV) part of sunlight, in particular, is responsible for structural and cellular changes across the different layers of the skin. Among other effects, UV photons stimulate oxidative damage to biomolecules via the generation of unstable and highly reactive compounds. In response to oxidative damage, cytoprotective pathways are triggered. One of these is the pathway driven by the nuclear factor erythroid-2 related factor 2 (Nrf2). This transcription factor translocates to the nucleus and drives the expression of numerous genes, among them various detoxifying and antioxidant enzymes. Several studies concerning the effects of UV radiation on Nrf2 activation have been published, but different UV wavelengths, skin cells or tissues and incubation periods were used in the experiments that complicate the evaluation of UV radiation effects.

CONCLUSIONS

This review summarizes the effects of UVB (280-315 nm) and UVA (315-400 nm) radiation on the Nrf2 signaling pathway in dermal fibroblasts and epidermal keratinocytes and melanocytes. The effects of natural compounds (pure compounds or mixtures) on Nrf2 activation and level as well as on Nrf2-driven genes in UV irradiated human skin fibroblasts, keratinocytes and melanocytes are briefly mentioned as well.HighlightsUVB radiation is a rather poor activator of the Nrf2-driven pathway in fibroblastsUVA radiation stimulates Nrf2 activation in dermal fibroblastsEffects of UVA on the Nrf2 pathway in keratinocytes and melanocytes remain unclearLong-term Nrf2 activation in keratinocytes disturbs their normal differentiationPharmacological activation of Nrf2 in the skin needs to be performed carefully.

NRF2-dependent stress defense in tumor antioxidant control and immune evasion

The transcription factor NRF2 is known as the master regulator of the oxidative stress response. Tumor entities presenting oncogenic activation of NRF2, such as lung adenocarcinoma, are associated with drug resistance, and accumulating evidence demonstrates its involvement in immune evasion. In other cancer types, the KEAP1/NRF2 pathway is not commonly mutated, but NRF2 is activated by other means such as radiation, oncogenic activity, cytokines, or other pro-oxidant triggers characteristic of the tumor niche. The obvious effect of stress-activated NRF2 is the protection from oxidative or electrophilic damage and the adaptation of the tumor metabolism to changing conditions. However, data from melanoma also reveal a role of NRF2 in modulating differentiation and suppressing anti-tumor immunity. This review summarizes the function of NRF2 in this tumor entity and discusses the implications for current tumor therapies.

A Novel Kelch-Like-1 Is Involved in Antioxidant Response by Regulating Antioxidant Enzyme System in Penaeus vannamei

Heavy metals are typical cumulative pollutants that can enter and poison the human body through the food chain. However, the molecular mechanism of heavy metal-induced oxidative stress is unclear. In this study, we characterize PvKelch-like-1 from P. vannamei and explore its antioxidant roles in immune regulation of crustaceans. PvKelch-like-1 full length contains 2107 nucleotides, consists of a 5′ untranslated region (UTR) of 79 bp, a 3′ UTR of 180 bp, and a ORF of 1848 encoded 615 amino acids, which contain a BTB, BACK and Kelch motif, putative molecular mass and isoelectric point were 69 KDa and 6.54. PvKelch-like-1 mRNA was ubiquitously expressed in all detected tissue of P. vannamei, and mRNA expression levels were significantly up-regulated from 6 to 24 h after cadmium stress and reached the highest level (3.2-fold) at 12 h in the hepatopancreas. Subcellular localization analysis revealed that PvKelch-like-1 was localized in the nucleus. Silencing PvKelch-like-1 significantly increased reactive oxygen species (ROS) (1.61-fold) production and DNA damage (1.32-fold) in the shrimp hemolymph, and significantly decreased total hemocyte counts (THC) (0.64-fold) at 6 h in hemolymph. Additionally, the antioxidant genes PvCAT (0.43-fold), PvMnSOD (0.72-fold), PvGST (0.31-fold) and PvGPx (0.59-fold) at 6 h were decreased significantly in PvKelch-like-1 silenced shrimp after cadmium stress. Overexpression of PvKelch-like-1 has the opposite results in enzyme activity. The SOD (2.44-fold) and CAT (2.19-fold) activities were significantly increased after overexpressing PvKelch-like-1. These results suggest that PvKelch-like-1 plays a vital role in shrimp innate immune defense by positively regulating the expression of antioxidant enzyme genes to respond to cadmium stress.

Glycyrrhizin protects human melanocytes from H2O2‑induced oxidative damage via the Nrf2‑dependent induction of HO‑1

Oxidative stress serves a critical role in melanocyte death and is considered to be a major cause of vitiligo. The nuclear factor E2-related factor 2 (Nrf2) signaling pathway has an important role in the antioxidative stress mechanisms of melanocytes. Glycyrrhizin (GR) is a derivative of herbal medicines used to treat hepatitis and allergic disease due to its antiviral and anti-allergy effects. GR also activates Nrf2 and induces the expression of heme oxygenase (HO)-1 in macrophages. Whether GR can protect human melanocytes from oxidative stress remains unknown. The present study investigated the potential protective effects of GR against oxidative stress in human melanocytes and the mechanisms involved. Following exposure to 0.5 mM hydrogen peroxide (H₂O₂), human primary melanocytes were treated with 1 mM GR. Cell viability was determined using a Cell Counting Kit-8 assay, and apoptosis was evaluated by flow cytometry. GR treatment significantly improved cell viability, reduced the apoptotic rate of melanocytes and reduced the level of reactive oxygen species in human melanocytes. Furthermore, GR induced the nuclear translocation of Nrf2 and induced the expression of HO-1 in melanocytes. The knockdown of Nrf2 by small interfering RNA or the inhibition of HO-1 by ZnPP reversed the protective effect of GR on melanocytes against H₂O₂-induced cytotoxicity and apoptosis. These data demonstrate that GR protects human melanocytes from H₂O₂-induced oxidative damage via the Nrf2-dependent induction of HO-1, providing evidence for the application of GR in the treatment of vitiligo.

Positive Effects against UV-A Induced Damage and Oxidative Stress on an In Vitro Cell Model Using a Hyaluronic Acid Based Formulation Containing Amino Acids, Vitamins, and Minerals

Ultraviolet (UV) radiations are responsible for skin photoaging inducing alteration of the molecular and cellular pathways resulting in dryness and reduction of skin elasticity. In this study, we investigated, in vitro, the antiaging and antioxidant effects of hyaluronan formulations based hydrogel. Skinkò E, an intradermic formulation composed of hyaluronic acid (HA), minerals, amino acids, and vitamins, was compared with the sole HA of the same size. For this purpose, HaCaT cells were subjected to UV-A radiations and H₂O₂ exposure and then treated with growth medium (CTR) combined with M-HA or Skinkò E to evaluate their protective ability against stressful conditions. Cells reparation was evaluated using a scratch in vitro model and Time-Lapse Video Microscopy. A significant protective effect for Skinkò E was shown with respect to M-HA. In addition, Skinkò E increased cell reparation. Therefore, NF-kB, SOD-2, and HO-1 were significantly reduced at the transcriptional and protein level. Interestingly, γ-H2AX and protein damage assay confirmed the protection by hyaluronans tested against oxidative stress. G6pdΔ ES cell line, highly susceptible to oxidative stress, was used as a further cellular model to assess the antioxidant effect of Skinkò E. Western blotting analyses showed that the treatment with this new formulation exerts marked antioxidant action in cells exposed to UV-A and H₂O₂. Thus, the protective and reparative properties of Skinkò E make it an interesting tool to treat skin aging.