Oxidative stress contributes to inflammatory skin diseases, including psoriasis. Monomethylfumarate (MMF) is an antipsoriatic agent with a poorly understood mechanism of action. In other cell types MMF increases the expression of nuclear factor erythroid-derived 2-like 2 (Nrf2), a transcription factor that regulates cellular antioxidant responses, to reduce oxidative stress like that observed in inflammatory disorders such as multiple sclerosis. We tested the hypothesis that MMF enhances Nrf2 activity in keratinocytes, thereby improving their capacity to counteract environmental stresses. We used Western analysis, immunofluorescence, and real-time quantitative reverse-transcription polymerase chain reaction to examine the effect of MMF on the expression of Nrf2 and its targets. We also measured intracellular reactive oxygen species (ROS) levels following MMF treatment. Our data show that MMF increased total and nuclear Nrf2 levels in primary mouse keratinocytes and enhanced mRNA expression of several Nrf2-downstream effectors, including heme oxygenase-1 and peroxiredoxin-6. Moreover, MMF treatment attenuated the generation of ROS following hydrogen peroxide treatment. On the other hand, the expression and membranous localization of aquaporin-3 (AQP3), a glycerol channel implicated in keratinocyte differentiation, was stimulated by MMF, which also enhanced keratinocyte glycerol uptake. The Nrf2 activator sulforaphane also increased AQP3 levels, suggesting that AQP3 expression may be regulated by Nrf2. We show for the first time that MMF stimulates Nrf2 and AQP3 expression and function/activity in keratinocytes. This effect may account, in part, for the previously observed ability of MMF to inhibit proliferation and inflammatory mediator production and promote differentiation in keratinocytes and to treat psoriasis.
U.S. Government work not protected by U.S. copyright.