Abstract
Macrophages play an important role in inflammation and liver injury. In ALD, activated macrophages, including M1 (proinflammatory) and M2 (anti-inflammatory) macrophages, are present in the liver. As KLF4 has been described as a regulator of macrophage polarization, we investigated its role in ALD. Chronic alcohol feeding in C57Bl/6 mice led to increased expression of M1 (TNF-α, MCP1, and IL-1β) and M2 (Arg1, Mrc1, and IL-10) genes and the frequency of CD206+CD163+ M2 macrophages in the liver. KLF4 mRNA and protein levels were increased in the livers of EtFed compared with PF mice. In macrophages, in vivo and in vitro, EtOH increased KLF4 levels, transcriptional activity, and expression of M1 and M2 genes. KLF4 knockdown and overexpression experiments demonstrated alcohol-dependent and -independent functions of KLF4 in regulating M1 and M2 markers. KLF4 siRNA treatment, alone and in synergy with alcohol, increased the levels of M1 markers. In contrast, KLF4 overexpression increased the levels of M2 and decreased M1 markers, and this was enhanced further by alcohol. KLF4 was regulated by alcohol and its metabolites. KLF4 mRNA and activity were increased in the presence of 4-MP, an inhibitor of ADH, and CYP2E1. However, inhibition of acetaldehyde breakdown attenuated KLF4 induction and promoted M1 polarization. We conclude that KLF4 regulates M1 and M2 markers in ALD. EtOH promotes KLF4 and M2 phenotype, whereas acetaldehyde attenuates KLF4 and promotes M1 macrophage, which may explain the increased presence of M1 and M2 macrophage populations in ALD.