Nicotinamide mononucleotide mitigates neuroinflammation by enhancing GPX4-mediated ferroptosis defense in microglia
Numerous neurological diseases involve neuroinflammation, a process in which immune cells, particularly microglia, contribute to neuronal death. Ferroptosis, a recently identified form of regulated cell death, is implicated in various diseases characterized by neuronal injury. Nicotinamide mononucleotide (NMN), a potent NAD+ precursor supplement, has been found to inhibit neuroinflammation and ferroptosis. However, the mechanisms of NMN in both ferroptosis and neuroinflammation remains unclear. The present study aimed to investigate the impact of NMN on neuroinflammation and the susceptibility of microglia to ferroptosis. Ferroptosis markers in microglia exposed to lipopolysaccharide (LPS) were analyzed using CCK8, flow cytometry, ELISA, and RT-qPCR. The effects of NMN on LPS-induced ferroptosis in microglia were evaluated through flow cytometry, western blotting, and immunofluorescence staining. RT-qPCR analysis assessed the inflammatory cytokine production of microglia subjected to ferrostatin-1-regulated ferroptosis. RNA sequencing elucidated the underlying mechanisms of NMN-associated microglia ferroptosis under LPS induction. In BV2 microglia, an inhibitor of Glutathione Peroxidase 4(GPX4), RSL3, was employed to suppress GPX4 expression. Intracerebroventricular injection of LPS was performed to evaluate neuroinflammation and microglia activation in vivo. LPS treatment resulted in decreased cell viability, accompanied by upregulation of ferroptosis markers SLC7A11 and GPX4, and elevated levels of malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), and total iron in a dose-dependent manner. NMN effectively rescued LPS-induced ferroptosis and improved cell viability in microglia. Co-administration of NMN and ferrostatin-1 significantly reduced proinflammatory cytokine production in microglia following the introduction of LPS stimuli. Mechanistically, NMN facilitated glutathione (GSH) production, and promoted resistance to lipid peroxidation in a GPX4-dependent manner, repressing cytokine transcription and protecting cells from ferroptosis. RNA sequencing elucidated the underlying mechanism of NMN-associated microglia ferroptosis under LPS induction. Furthermore, simultaneous injection of NMN ameliorated LPS-induced ferroptosis and neuroinflammation in mouse brains. The data from the present study indicated that NMN enhances GPX4-mediated ferroptosis defense against LPS-induced ferroptosis in microglia by recruiting GSH, thereby inhibiting neuroinflammation. Therefore, therapeutic approaches targeting ferroptosis in diseases using NMN should consider both its anti-ferroptosis and anti-inflammatory effects to achieve optimal outcomes, presenting promising strategies for treating neuroinflammation-related diseases or disorders. Overall design: To unravel the molecular mechanism underlying NMN-mediated rescue of LPS-induced ferroptosis in BV2 cells, RNA sequencing was conducted to identify differentially expressed genes between the LPS and LPS + NMN groups