Alcohol-induced macrophage apoptosis modulates the intrahepatic inflammatory phenotype and limits liver inflammation

The transcription factor FOXO3 serves as an alcohol protection factor but the mechanisms are unknown. We previously demonstrated that ethanol causes selective phosphorylation of FOXO3 that enhances its ability to induce... [ view full abstract ]

The transcription factor FOXO3 serves as an alcohol protection factor but the mechanisms are unknown. We previously demonstrated that ethanol causes selective phosphorylation of FOXO3 that enhances its ability to induce apoptosis. In this study we aimed to determine if FOXO3-dependent macrophage apoptosis plays a role in this hepatic protection. Acute alcohol gavage and chronic alcohol feeding caused rapid hepatic macrophage apoptosis. In both whole body and myeloid specific Foxo3^-/- mice, ethanol failed to cause macrophage apoptosis. In Foxo3-/- mice as compared to wild-type mice, alcohol produced an increase in pro-inflammatory Ly6C⁺ macrophage content of the liver, increased proinflammatory cytokines TNFα, IL6 and IL-1β, and a decrease in the anti-inflammatory cytokine IL4. After 10 days of alcohol, a single dose of LPS produced greater inflammatory cytokine expression, serum cytokine levels, inflammasome activity and liver injury in the Foxo3^-/- mice. Restoring an early macrophage apoptosis burst in Foxo3^-/- mice with a pulse of IV GdCl₃ on day 2 after ethanol exposure was able to correct this hyper-inflammatory phenotype at day 10. At this time, although macrophage numbers had returned to normal, there was a decrease in Ly6C⁺ population and diminished inflammatory cytokine production. The anti-inflammatory effect of FOXO3-dependent macrophage apoptosis was due to its ability to alter subsequent differentiation of infiltrating macrophages and not due to selective apoptosis of the pro-inflammatory macrophages themselves. In conclusion, FOXO3-dependent hepatic macrophage apoptosis is a normal mechanism that limits the development of an inflammatory response to ethanol by modulating the evolution of intrahepatic macrophage pool.