14-3-3 Proteins Negatively Regulate Microglial Activation via Inhibition of the NF-κB Pathway

Microglia, the resident immune cells of the central nervous system (CNS), are involved in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD), Dementia with Lewy Bodies (DLB), and Parkinson's disease (PD). 14-3-3 proteins act as molecular hubs to regulate protein-protein interactions, which are involved in numerous cellular functions, including cellular signaling, protein folding, and apoptosis. We previously revealed decreased 14-3-3 levels in the brains of human subjects with neurodegenerative diseases. In this study, we examined the role of 14-3-3 proteins in the microglial proinflammatory response to lipopolysaccharide (LPS). We found that LPS treatment induced 14-3-3 protein levels within 6 hours. With the use of BV02 and dimeric fourteen-three-three peptide inhibitor (difopein), a small molecule and peptide inhibitor of 14-3-3 protein-protein interactions, respectively, we found a dramatic increase in microglial activation markers in both immortalized BV-2 microglial cells and in primary mouse microglia. Both 14-3-3 inhibitors also increased LPS-induced microglial phagocytosis, lysosomal proteolysis, and cytokine release in primary microglia. In contrast, chemotaxis toward the cellular damage stimulus, adenosine triphosphate (ATP), was diminished with 14-3-3 inhibition. Inhibition of 14-3-3's hastened LPS-induced activation of the nuclear factor-kB (NF-κB) signaling pathway, as measured by its nuclear translocation. 14-3-3's reduced activation of the NF-κB pathway by binding and inhibiting the release of IκB kinase beta (IKKβ). Disruption of 14-3-3's binding to IKKβ with BV02 or difopein increased the downstream phosphorylation and degradation of the inhibitor of NF-κB alpha (IκBα). Collectively, our findings suggest 14-3-3 proteins play a critical role in the regulation of inflammatory responses in microglia and may serve as potential targets for immunotherapy of CNS diseases.