Anti-Inflammatory Effects of Dimethyl Fumarate in Microglia via an Autophagy Dependent Pathway

Abstract

Dimethyl fumarate (DMF), which has been approved by the Food and Drug Administration for the treatment of relapsing-remitting multiple sclerosis, is considered to exert anti-inflammatory and antioxidant effects. Microglia maintain homeostasis in the central nervous system and play a key role in neuroinflammation, while autophagy controls numerous fundamental biological processes, including pathogen removal, cytokine production, and clearance of toxic aggregates. However, the role of DMF in autophagy induction and the relationship of this effect with its anti-inflammatory functions in microglia are not well known. In the present study, we investigated whether DMF inhibited neuroinflammation and induced autophagy in microglia. First, we confirmed the anti-neuroinflammatory effect of DMF in mice with streptozotocin-induced diabetic neuropathy. Next, we used in vitro models including microglial cell lines and primary microglial cells to examine the anti-inflammatory and neuroprotective effects of DMF. We found that DMF significantly inhibited nitric oxide and proinflammatory cytokine production in lipopolysaccharide-stimulated microglia and induced the switch of microglia to the M2 state. In addition, DMF treatment increased the expression levels of autophagy markers including microtubule-associated protein light chain 3 (LC3) and autophagy-related protein 7 (ATG7) and the formation of LC3 puncta in microglia. The anti-inflammatory effect of DMF in microglia was significantly reduced by pretreatment with autophagy inhibitors. These data suggest that DMF leads to the induction of autophagy in microglia and that its anti-inflammatory effects are partially mediated through an autophagy-dependent pathway.

Fluoxetine Potentiates Phagocytosis and Autophagy in Microglia

“…Treatment with autophagy-inducing drugs led to a robust recovery rate and decline in clinical symptoms in rodent models of neurodegenerative diseases (Rusmini et al, 2019). Our recently published article also showed autophagy induction by DMF, reduced neuroinflammation by the inhibition of the M1 phenotype, and an increase in the M2 phenotype of microglia (Lee et al, 2021). Fluoxetine treatment exhibits autophagy induction in lymphoma (Cloonan and Williams, 2011) and adipose-derived stem cells (Sun et al, 2015).…”

“…Autophagy is known to be involved in the regulation of microglial function (Lee et al, 2021). Therefore, we examined whether fluoxetine induces autophagy in microglia.…”

“…We found that LC3-II accumulation (LC3-II/loading control β-actin) was increased by fluoxetine treatment in both cells with or without LPS treatment (Figures 3A, B). DMF, an autophagy inducer, was used as a positive control (Lee et al, 2021). To determine whether fluoxetine increases the autophagy flux, we perturbed it by treatment with its inhibitor CQ.…”

The Modulatory Effects of DMF on Microglia in Aged Mice Are Sex-Specific

“…For instance, it attenuates LPS-induced changes in microglial cell lines [ 19 , 20 ] and primary microglia [ 29 ], but our unpublished data indicate that neither sex-related or DMF-associated change were observed on ECAR in cultured microglia (data not shown). In addition to the effects on LPS-induced changes in vitro, DMF also suppresses microglial activation in the hippocampus induced by a peripheral LPS challenge in mice [ 29 ] and decreased microglial activation in the spinal cord [ 19 ] and hippocampus [ 30 ] of streptozotocin-treated animals. These latter changes were described in young mice and no sex-related differences were reported.…”

“…However, DMF exerts multiple other effects including inhibition of NFκB, perhaps secondary to Nrf2 activation [ 17 ] while it also inhibits glycolysis as a result of succination and inactivation of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) [ 18 ]. Less is known about the effect of DMF in microglia, although it attenuates LPS-induced inflammatory cytokine production in rat [ 19 ] and mouse [ 20 ] microglial cell lines.…”