Copper overload worsens the inflammatory response of microglia to amyloid beta (Aβ) by impairing phagocytosis and promoting mitochondrial DNA-mediated NLRP3 inflammasome activation

Abstract

Microglia play a significant role in the development and progression of Alzheimer’s disease (AD). These brain-resident immune cells efficiently clear neurotoxic amyloid beta (Aβ) peptides; however, chronic activation may overwhelm their protective abilities, resulting in persistent neuroinflammation. The causes of aberrant microglial activation in AD remain elusive. Emerging evidence indicates that copper (Cu) accumulation, which can arise from prolonged exposure to various environmental sources, modifies the innate immune response in AD. Here, we sought to explore the mechanisms by which Cu overload regulates the microglial phenotype when exposed to Aβ. Our findings showed that exposure to sublethal doses of Cu led to the accumulation of this transition metal in the mitochondria. Elevated mitochondrial Cu (mtCu) levels were accompanied by reduced mitochondrial glutathione (mtGSH) and high oxidative stress, leading to Aβ-induced inflammasome activation through the release of oxidized mitochondrial DNA (ox-mtDNA). Moreover, increased intracellular Cu levels enhanced cholesterol biosynthesis and facilitated its transport to mitochondria. The combination of elevated cholesterol and mitochondrial oxidative stress hindered the ability of microglia to phagocytose Aβ effectively. As expected, conditioned medium from Cu-activated microglia reduced neuronal viability. The neurotoxicity caused by Cu-overloaded microglia was prevented by inhibiting inflammasome activation and restoring mtGSH levels. In conclusion, our study outlines a mechanistic pathway by which chronic exposure to environmental Cu may lead to neuroinflammation and Aβ accumulation in AD, underscoring the crucial role of mitochondrial oxidative stress. • Sub-toxic copper (Cu) exposure disrupts microglial function by promoting mitochondrial Cu buildup, reducing mitochondrial glutathione (mtGSH), and increasing oxidative stress. • Cu-induced mitochondrial oxidative stress activates the NLRP3 inflammasome via release of oxidized mitochondrial DNA (ox-mtDNA), amplifying Aβ-driven inflammatory response. • Cholesterol biosynthesis and mitochondrial transport are upregulated in microglia after Cu overload. • Altered cholesterol metabolism linked to high Cu levels downregulates ABCA7 expression levels, impairing microglial Aβ clearance and promoting neurotoxicity. • Restoring mtGSH and inhibiting inflammasome activation counteracts Cu-driven neurotoxicity, highlighting a potential therapeutic strategy for Alzheimer’s disease.

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