The Mechanism of Monomethylfumarate (MMF) as an Anti-psoriatic Agent
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Abstract
Psoriasis is a chronic hyperproliferative inflammatory skin disorder whose primary etiology is not well understood. Keratinocytes play a pivotal role in the pathogenesis of psoriasis. The fumaric acid ester monomethylfuamarate (MMF) is the bioactive ingredient of the anti-psoriatic drug Fumaderm©, licensed in Germany since 1994. However, the exact mechanism of action of MMF is not yet well understood. Our data showed that MMF dose-dependently inhibited proliferation in primary murine and human keratinocytes and significantly increased the protein expression of the early marker of differentiation K10 and the activity of the late marker of differentiation transglutaminase enzyme. In addition, MMF inhibited mRNA expression of IL-6, TNFα and IL-1α and inhibited the protein expression of TNFα. Recently, the role of oxidative stress in psoriasis etiology has evolved and MMF has been shown to stimulate Nrf2 and mediate its nuclear translocation in other cell types. Therefore, we examined the effect of MMF on Nrf2 expression, localization and downstream effectors in keratinocytes. Nrf2 protein expression and nuclear translocation significantly increased following MMF treatment. Moreover, MMF significantly increased the mRNA expression of the Nrf2- downstream anti-oxidative enzymes, heme oxygense-1 and peroxiredoxin-6. MMF also decreased ROS generation in keratinocytes. Aquporin3 (AQP3) is a glycerol channel expressed in keratinocytes. Earlier studies from our group as well as others have shown that AQP3 plays a role in inducing early keratinocyte differentiation and that the activity of AQP3 correlates with its membranous localization. Therefore, we examined the effect of MMF on AQP3 expression and localization. MMF increased the mRNA and protein 3 expression of AQP3. In addition, MMF stimulated membranous translocation of AQP3 and increased glycerol uptake by keratinocytes. Eventually, we wanted to examine whether Nrf2 plays a role in the expression of AQP3. Our data showed that the Nrf2 stimulator sulforaphane (SFN) increased the expression of AQP3. Thus, our data suggest that MMF exerts its action through Nrf2 stimulation. Nrf2 stimulation helps to regain keratinocyte oxidative balance and may also play a role in inducing AQP3 expression and activity. This provides the molecular basis for the MMF-mediated improvement of keratinocyte differentiation and inhibition of keratinocyte proliferation.