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Monomethyl Fumarate Modulates Iron Metabolism and Mitochondrial Function in Microglia with Implications for Multiple
Justus Dann1, Katharina Klöster1, Ulas Ceylan1
1Department of Neurology, Ruhr-University Bochum, St. Josef-Hospital, Gudrunstr. 56, 44791, Bochum, Germany.
Abstract:
Fumaric acid esters have proven to be effective medications in relapsing-remitting multiple sclerosis with neuroprotective effects. In this study, we investigated the impact of fumaric acid esters on primary murine microglia in vitro compared to DMSO vehicle control. Monomethyl fumarate (MMF) increased MTT reduction in a dose-dependent manner, whereas dimethyl fumarate (DMF) exhibited a biphasic response with low concentrations enhancing MTT reduction and higher concentrations inducing toxicity. Notably, complementary analyses of cell number and cell death did not reveal differences between MMF-treated and control conditions, indicating that the increased MTT reduction reflects enhanced cellular metabolic activity rather than increased viability. Consistent with this interpretation, MMF-treated cells exhibited higher basal and maximal oxygen consumption, spare respiratory capacity, and ATP production in the Seahorse XF Cell Mito Stress Test. Proteomic analysis did not indicate an upregulation of mitochondrial respiratory chain proteins, but instead suggested a qualitative shift in mitochondrial homeostasis, including increased expression of mitophagy-associated proteins. MMF-treated Nrf2-deficient microglia showed a blunted increase in MTT reduction, suggesting an involvement of Nrf2 in mediating MMF-induced metabolic effects. Additionally, MMF modulated the microglial iron metabolism and reduced the uptake of non-transferrin-bound iron and altered the gene expression of iron transport proteins, promoting a shift toward the uptake of less toxic, transferrin-bound iron. MMF mitigated iron-induced toxicity and was associated with upregulation of the ferroptosis suppressor protein, indicating a protective response to iron overload. Together, these findings suggest that MMF enhances microglial metabolic activity and mitochondrial function while reducing iron-mediated toxicity, thereby contributing to its neuroprotective effects.
Insights
Monomethyl fumarate (MMF) enhances microglial metabolic activity and mitochondrial function, potentially contributing to its neuroprotective effects in multiple sclerosis. It also modulates iron metabolism, reducing toxicity.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Fumaric acid esters are effective in relapsing-remitting multiple sclerosis.
- They exhibit neuroprotective effects.
- The impact on microglia, key immune cells in the central nervous system, requires further elucidation.
Purpose of the Study:
- To investigate the effects of fumaric acid esters, specifically monomethyl fumarate (MMF) and dimethyl fumarate (DMF), on primary murine microglia in vitro.
- To understand the mechanisms underlying MMF's impact on microglial metabolic activity, mitochondrial function, and iron metabolism.
Main Methods:
- Primary murine microglia were treated with MMF and DMF.
- Cell viability and metabolic activity were assessed using MTT assays.
- Mitochondrial function was analyzed using the Seahorse XF Cell Mito Stress Test.
- Proteomic analysis was performed.
- Nrf2-deficient microglia were used to investigate Nrf2's role.
- Microglial iron metabolism, including iron uptake and gene expression of iron transport proteins, was examined.
Main Results:
- MMF increased MTT reduction dose-dependently, indicating enhanced metabolic activity.
- DMF showed a biphasic response, with toxicity at higher concentrations.
- MMF-treated microglia exhibited increased oxygen consumption, ATP production, and spare respiratory capacity.
- Proteomic analysis suggested a shift in mitochondrial homeostasis and increased mitophagy.
- MMF's metabolic effects were partially dependent on Nrf2.
- MMF modulated iron metabolism, reducing non-transferrin-bound iron uptake and promoting transferrin-bound iron uptake.
- MMF mitigated iron-induced toxicity and upregulated ferroptosis suppressor protein.
Conclusions:
- MMF enhances microglial metabolic and mitochondrial function.
- MMF modulates microglial iron metabolism, conferring protection against iron overload.
- These effects likely contribute to the neuroprotective properties of MMF in multiple sclerosis.
