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Ultraviolet (UV) irradiation causes cellular oxidative stress. Under redox imbalance, Keap1-dependent Nrf2 degradation is minimal. In this study, we examined the role of Ca 2+ in Nrf2 homeostasis after UVB irradiation using human dermal fibroblasts. UVB irradiation stimulates 12-lipoxygenase and the product 12-hydroxyeicosatetraenoic acid then activates TRPV1 increasing the cell's cytosolic Ca 2+ concentration. UVB irradiation induced reactive oxygen species generation and apoptosis are inhibited in the absence of Ca 2+ or in the presence of either a 12-lipoxygenase inhibitor or a TRPV1 inhibitor during and after UVB irradiation. Thus, the Ca 2+ increase via TRPV1 is a critical factor in UVB irradiation induced oxidative stress. UVB irradiation induces a Ca 2+ dependent Nrf2 degradation and thus activation of TRPV1 with 12-hydroxyeicosatetraenoic acid also decreasing Nrf2 levels. UVB irradiation induced Nrf2 degradation is inhibited by co-treatment of cells with W-7, cyclosporin A, SB-216763 or MG-132, which are inhibitors of calmodulin, calcineurin, GSK3β and the proteasome, respectively. Furthermore, UVB irradiation in parallel induces GSK3β dephosphorylation in a Ca 2+ dependent manner. Co-immunoprecipitation showed that UVB irradiation induces an increase in Nrf2 phosphorylation, an increase in the binding of β-TrCP and Nrf2, and an increase in Nrf2 ubiquitination; these effects are all Ca 2+ dependent. These findings suggest that UVB irradiation induced GSK3β activation in a Ca 2+ dependent manner, which then stimulates the phosphorylation and ubiquitination of Nrf2 via β-TrCP. Indeed, silencing of β-TrCP was found to inhibit UVB irradiation-induced oxidative stress, Nrf2 degradation and apoptosis, while it had no effect on the Ca 2+ increase. Taken together, our results suggest that a Ca 2+ influx via TRPV1 is responsible for UVB irradiation-induced Nrf2 degradation and that modulation of the Ca 2+ -calmodulin-calcineurin-GSK3β-Nrf2-β-TrCP-Cullin-1 pathway may explain Ca 2+ dependent Nrf2 degradation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Increased matrix metalloproteinase 1 (MMP-1) expression is a feature of photo-aged skin. We investigated the effects of baicalein and sulphoraphane on ultraviolet B (UVB) irradiation-induced MMP-1 expression and apoptosis using human dermal fibroblasts. UVB irradiation not only increased MMP-1 expression, but also caused apoptosis. Both baicalein and sulphoraphane protected cells from UVB irradiation-induced apoptosis, but only baicalein inhibited MMP-1 expression. UVB irradiation activated 12-lipoxygenase, and its product, 12-hydroxyeicosatetraenoic acid, activated TRPV1 channels. The resulting UVB irradiation-induced Ca 2+ increase was blocked by the 12-lipoxygenase inhibitor baicalein and the TRPV1 blocker capsazepine, but not by the Nrf2 inducer sulphoraphane. UVB irradiation also increased ROS generation and decreased Nrf2 protein levels. UVB irradiation-induced MMP-1 expression was blocked by the Ca 2+ chelator BAPTA, by capsazepine and by TRPV1 silencing. However, induction was unaffected by the antioxidant N-acetylcysteine. ERK phosphorylation and JNK phosphorylation were induced by UVB irradiation, but only ERK phosphorylation was Ca 2+ sensitive. Increased MMP-1 expression was blocked by PD98059, but not by SP600125. Thus, increased MMP-1 expression is mediated by increased cytosolic Ca 2+ and ERK phosphorylation. UVB irradiation-induced ROS generation is also Ca 2+ sensitive, and UVB irradiation-induced apoptosis is caused by increased ROS. Thus, baicalein, by blocking the UVB irradiation-induced cytosolic Ca 2+ increase, protects cells from UVB irradiation-induced MMP-1 expression and apoptosis. In contrast, sulphoraphane, by decreasing cellular ROS, protects cells from only UVB-induced apoptosis. Thus, targeting 12-lipoxygenase may provide a therapeutic approach to improving the health of photo-aged human skin., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)