Scutellarin Attenuates Pro-Inflammatory Foam Cell Formation and Facilitates M2 Polarization in Microglia during Copper Homeostasis Imbalance via the MAPK Signaling Pathway

Background: Clinical and experimental evidence indicates that copper has the ability to promote the progressive development of demyelinating diseases such as multiple sclerosis. Microglia-mediated neuroinflammation is believed to play a crucial role in this process. Scutellarin, a flavonoid compound, has anti-inflammatory, antioxidative, and neuroprotective effects.

Aim: We investigated the effect of scutellarin on copper-induced inflammatory foam cell formation in microglia.

Methods: We exposed BV2 murine microglial cells to copper, then collected the conditioned medium and co-cultured it with MO3.13 human glial cells to mimic myelin damage in vitro. The Cell Counting kit-8 assay, quantitative (polymerase chain reaction) PCR, enzyme-linked immunosorbent assay, Luxol fast blue staining, and western blotting were used to detect the cell phenotype. To investigate whether exposure of BV2 cells to copper can cause neurotoxicity and indirect damage to myelin cells, we determined whether BV2 cells promote inflammation through foam cell formation by oil red O staining and detection of malondialdehyde (MDA) content. Finally, we treated cells with scutellarin to investigate its therapeutic effects.

Results: Exposure to copper activated the pro-inflammatory phenotype of microglia, as assessed by measuring the transcription of M1/M2-related biomarkers. In addition, increased copper intake by microglia promoted intracellular lipid accumulation and oxidation, facilitating foam cell formation. Rescue experiments showed that copper chelator ammonium tetrathiomolybdate (ATTM) and the lipid oxidation inhibitor ferrostatin-1 (Fer-1) significantly inhibited copper-induced inflammation, reduced intracellular lipid accumulation and MDA levels, and decreased foam cell formation. Moreover, copper-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) in microglia led to a shift towards the M1 phenotype and foam cell transformation, which were effectively inhibited by ATTM, Fer-1, and the p38 MAPK Inhibitor SB203580. Lastly, after treatment with scutellarin, copper-induced foam microglia exhibited inhibited p38 MAPK phosphorylation, increased production of Neurotrophic Factors, decreased expression of inflammatory mediators, reduced lipid accumulation, and induced polarization towards the M2 phenotype.

Conclusions: Here, we demonstrated that copper can induce microglia to damage myelinating cells, with the key mechanism involving the phosphorylation of p38 MAPK. Scutellarin partially reversed the positive effects of copper on promoting microglial M1 polarization, lipid deposition, and lipid oxidation by mediating the p38 MAPK signaling pathway. Taken together, these results suggest that scutellarin may be a promising drug for the treatment of demyelinating diseases such as multiple sclerosis.

copper; foam cells; microglia; multiple sclerosis; scutellarin.