MAPK-activated protein kinase 2 deficiency in microglia inhibits pro-inflammatory mediator release and resultant neurotoxicity - Relevance to neuroinflammation in a transgenic mouse model of Alzheimer disease

MAPK-activated protein kinase 2 (MAPKAP K2 or MK2) is one of several kinases directly regulated by p38 MAPK. A role for p38 MAPK in the pathology of Alzheimer disease (AD) has previously been suggested. Here, we provide evidence to suggest that MK2 also plays a role in neuroinflammatory and neurodegenerative pathology of relevance to AD. MK2 activation and expression were increased in lipopolysaccharide (LPS) + interferon gamma-stimulated microglial cells, implicating a role for MK2 in eliciting a pro-inflammatory response. Microglia cultured ex vivo from MK2-deficient (MK2(-/-)) mice demonstrated significant inhibition in release of tumor necrosis factor alpha, KC (mouse chemokine with highest sequence identity to human GROs and interleukin-8), and macrophage inflammatory protein 1 alpha on stimulation with LPS + interferon gamma or amyloid-beta peptide (1-42) compared with MK2(+/+) wild-type microglia. Consistent with an inhibition in pro- inflammatory mediator release, cortical neurons co-cultured with LPS + interferon gamma-stimulated or amyloid-beta peptide (1-42) stimulated MK2(+/+) microglia were protected from microglial-mediated neuronal cell toxicity. In a transgenic mouse model of AD in which amyloid precursor protein and presenilin-1 harboring familial AD mutations are over-expressed in specific regions of the brain, elevated activation and expression of MK2 correlated with beta-amyloid deposition, microglial activation, and up-regulation of tumor necrosis factor alpha, macrophage inflammatory protein 1 alpha, and KC gene expression in the same brain regions. Our data propose a role for MK2 in AD brain pathology, for which neuroinflammation involving cytokines and chemokines and overt neuronal loss have been documented.