Metformin Inhibits Microglial Activation-Mediated Cuproptosis by Modulating the TLR4/Myd88/NF-κB Signaling Pathway in Parkinson’s Disease

This study investigated the role of metformin (Met) in regulating cuproptosis and its neuroprotective mechanisms in Parkinson's disease (PD) using a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated murine model and a 1-methyl-4-phenylpyridinium (MPP⁺)-treated BV2 cell model. Met significantly relieved motor deficits induced by MPTP and prevented DA neuronal loss in the substantia nigra (SN) compacta. In addition, Met reversed MPTP-induced changes in tyrosine hydroxylase (TH) expression and α-synuclein accumulation in the SN while protecting against MPP⁺-induced morphological damage in BV2 cells. Notably, the neuroprotective effects of Met were partially reversed by elesclomol (ELC), a known cuproptosis inducer. Met treatment also decreased the copper ion concentration and expression level of cuproptosis-associated proteins, including ferredoxin 1 (FDX1), the solute carrier family 31 member 1 (SLC31A1), and heat shock protein 70 (HSP70), in the PD murine/cell models, suggesting that Met exerts neuroprotective effects by inhibiting cuproptosis. Lipopolysaccharide (LPS), a microglial activation agonist, significantly increased the copper ion concentration and reversed the decrease in the expression levels of FDX1, SLC31A1, and HSP70 in the PD models, whereas Met deteriorated the effects of LPS, suggesting that Met inhibits cuproptosis through restraining microglial activation in PD. Meanwhile, Met decreased the protein expression of TLR4, MyD88, and p-NF-κB p65 associated with the TLR4/Myd88/NF-κB signaling pathway. LPS (a TLR4/Myd88/NF-κB activator) reversed the Met-induced decrease in these signaling molecules, suggesting that Met's effect on microglial activation is TLR4/MyD88/NF-κB dependent. This study demonstrated that Met inhibits microglial activation-mediated cuproptosis by modulating the TLR4/Myd88/NF-κB signal pathway in PD murine/cell models, thus exerting neuroprotective effects. These findings therefore suggest that Met may serve as a promising therapeutic agent for preventing DA neuron degeneration in PD.