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Krüppel-like factor 4 is a transcriptional regulator of M1/M2 macrophage polarization in alcoholic liver disease
Banishree Saha1, Shashi Bala1, Nooshin Hosseini1
1University of Massachusetts Medical School, Worcester, Massachusetts, USA.
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.
Insights
Kruppel-like factor 4 (KLF4) influences macrophage polarization in alcoholic liver disease (ALD). Alcohol promotes KLF4 and M2 macrophages, while acetaldehyde promotes M1 macrophages, explaining mixed M1/M2 populations in ALD.
Area of Science:
- Immunology
- Hepatology
- Molecular Biology
Background:
- Macrophages, including proinflammatory M1 and anti-inflammatory M2 types, are key players in liver injury associated with alcoholic liver disease (ALD).
- Kruppel-like factor 4 (KLF4) is known to regulate macrophage polarization, but its specific role in ALD remains unclear.
Purpose of the Study:
- To investigate the role of KLF4 in macrophage polarization within the context of alcoholic liver disease.
- To elucidate how alcohol and its metabolites influence KLF4 expression and macrophage phenotypes in the liver.
Main Methods:
- Chronic alcohol feeding in C57Bl/6 mice to induce ALD.
- Analysis of M1 and M2 macrophage gene expression and frequency.
- Assessment of KLF4 mRNA and protein levels.
- In vitro and in vivo experiments involving KLF4 knockdown and overexpression.
- Investigation of alcohol metabolites' effects on KLF4 activity.
Main Results:
- Alcohol feeding increased both M1 and M2 macrophage markers and KLF4 expression in mouse livers.
- Ethanol exposure increased KLF4 levels and M1/M2 gene expression in macrophages.
- KLF4 knockdown exacerbated M1 markers, while KLF4 overexpression promoted M2 markers, with alcohol potentiating these effects.
- Alcohol metabolism influenced KLF4 activity; inhibiting alcohol dehydrogenase (ADH) and CYP2E1 increased KLF4, whereas inhibiting acetaldehyde breakdown attenuated KLF4 and favored M1 polarization.
Conclusions:
- KLF4 plays a critical role in regulating M1 and M2 macrophage polarization in alcoholic liver disease.
- Ethanol promotes KLF4 and an M2 macrophage phenotype, whereas acetaldehyde inhibits KLF4 and promotes an M1 phenotype.
- These opposing effects of alcohol and acetaldehyde on KLF4 and macrophage polarization may explain the coexistence of M1 and M2 macrophages observed in ALD.
