NOX2 inhibition enables retention of the circadian clock in BV2 microglia and primary macrophages

Abstract

IntroductionSustained neuroinflammation is a major contributor to the progression of neurodegenerative diseases such as Alzheimer’s (AD) and Parkinson’s (PD) diseases. Neuroinflammation, like other cellular processes, is affected by the circadian clock. Microglia, the resident immune cells in the brain, act as major contributors to neuroinflammation and are under the influence of the circadian clock. Microglial responses such as activation, recruitment, and cytokine expression are rhythmic in their response to various stimuli. While the link between circadian rhythms and neuroinflammation is clear, significant gaps remain in our understanding of this complex relationship. To gain a greater understanding of this relationship, the interaction between the microglial circadian clock and the enzyme NADPH Oxidase Isoform 2 (NOX2) was studied; NOX2 is essential for the production of reactive oxygen species (ROS) in oxidative stress, an integral characteristic of neuroinflammation.MethodsBV2 microglia were examined over circadian time, demonstrating oscillations of the clock genes Per2 and Bmal1 and the NOX2 subunits gp91phox and p47phox.ResultsThe BV2 microglial clock exerted significant control over NOX2 expression and inhibition of NOX2 enabled the microglia to retain a functional circadian clock while reducing levels of ROS and inflammatory cytokines. These trends were mirrored in mouse bone marrow-derived primary macrophages.ConclusionsNOX2 plays a crucial role in the interaction between the circadian clock and the activation of microglia/macrophages into their pro-inflammatory state, which has important implications in the control of neuroinflammation.

New insight on microglia activation in neurodegenerative diseases and therapeutics

“…The BV2 microglial biological clock substantially inhibits the expression of the enzyme NADPH Oxidase Isoform 2 (NOX2), which maintains a functional biological clock. NOX2 also reduces ROS and inflammatory cytokine levels and activates microglia into a pro-inflammatory state (Muthukumarasamy et al, 2023). The circadian biological clock protein Rev-erbα deficiency leads to spontaneous microglia activation, increased microglia NF-κB signaling, and neuronal injury (Griffin et al, 2019).…”

Ionizing radiation altered the expression profiles and intracellular distribution of the circadian gene per1 in mouse brain neuronal cells

“…As the central circadian clock, the SCN receives light information through the retinohypothalamic tract embedded in the optic nerve, and the SCN transmits circadian information to peripheral clocks through the sympathetic and parasympathetic nervous systems [3,13] . Therefore, brain nerve cells are ideal experimental subjects for research on circadian rhythm [14][15][16][17] .…”