Critical Role of TLR4 Response in the Activation of Microglia Induced by Ethanol

Microglial cells are the primary immune effector cells in the brain and play a pivotal role in the neuroinflammatory processes associated with a variety of neurological and pathological disorders. Alcohol consumption induces brain damage, although the neuropathological processes are poorly understood. We previously suggested that ethanol promotes inflammatory processes in the brain, up-regulating inflammatory mediators and signaling pathways associated with IL-1RI/TLR4 receptors. In the present study we investigate whether ethanol induces microglia activation by stimulating TLR4 response and whether this response causes neuronal death and contributes to ethanol-induced neuroinflammatory damage. We demonstrate that ethanol activates microglía and stimulates NF-kappaB, MAPKs, and MyD88-independent (IFN regulatory factor-3, IFN-beta) pathways to trigger the production of inflammatory mediators, causing neuronal death. The inflammatory response induced by ethanol is completely abrogated in microglia of TLR4-deficient mice (TLR4(-/-)), thus supporting the role of these receptors in microglia activation and neuronal death. In accord with the in vitro findings, acute ethanol administration induces microglia activation (CD11b(+) cells) in cerebral cortex of TLR4(+/+) mice, but not in TLR4(-/-) mice. Taken together, our results not only provide the first evidence of the critical role of the TLR4 response in the ethanol-induced microglia activation, but also new insight into the basic mechanisms participating in ethanol-induced neuroinflammatory damage.