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Chronic alcohol-induced microRNA-155 contributes to neuroinflammation in a TLR4-dependent manner in mice
Dora Lippai1, Shashi Bala, Timea Csak
1Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
Introduction:
Alcohol-induced neuroinflammation is mediated by pro-inflammatory cytokines and chemokines including tumor necrosis factor-α (TNFα), monocyte chemotactic protein-1 (MCP1) and interleukin-1-beta (IL-1β). Toll-like receptor-4 (TLR4) pathway induced nuclear factor-κB (NF-κB) activation is involved in the pathogenesis of alcohol-induced neuroinflammation. Inflammation is a highly regulated process. Recent studies suggest that microRNAs (miRNAs) play crucial role in fine tuning gene expression and miR-155 is a major regulator of inflammation in immune cells after TLR stimulation.
Aim:
To evaluate the role of miR-155 in the pathogenesis of alcohol-induced neuroinflammation.
Methods:
Wild type (WT), miR-155- and TLR4-knockout (KO) mice received 5% ethanol-containing or isocaloric control diet for 5 weeks. Microglia markers were measured by q-RTPCR; inflammasome activation was measured by enzyme activity; TNFα, MCP1, IL-1β mRNA and protein were measured by q-RTPCR and ELISA; phospho-p65 protein and NF-κB were measured by Western-blotting and EMSA; miRNAs were measured by q-PCR in the cerebellum. MiR-155 was measured in immortalized and primary mouse microglia after lipopolysaccharide and ethanol stimulation.
Results:
Chronic ethanol feeding up-regulated miR-155 and miR-132 expression in mouse cerebellum. Deficiency in miR-155 protected mice from alcohol-induced increase in inflammatory cytokines; TNFα, MCP1 protein and TNFα, MCP1, pro-IL-1β and pro-caspase-1 mRNA levels were reduced in miR-155 KO alcohol-fed mice. NF-κB was activated in WT but not in miR-155 KO alcohol-fed mice. However increases in cerebellar caspase-1 activity and IL-1β levels were similar in alcohol-fed miR-155-KO and WT mice. Alcohol-fed TLR4-KO mice were protected from the induction of miR-155. NF-κB activation measured by phosphorylation of p65 and neuroinflammation were reduced in alcohol-fed TLR4-KO compared to control mice. TLR4 stimulation with lipopolysaccharide in primary or immortalized mouse microglia resulted in increased miR-155.
Conclusion:
Chronic alcohol induces miR-155 in the cerebellum in a TLR4-dependent manner. Alcohol-induced miR-155 regulates TNFα and MCP1 expression but not caspase-dependent IL-1β increase in neuroinflammation.
Insights
Chronic alcohol consumption increases miR-155, a key regulator of inflammation, in the brain. This microRNA influences alcohol-induced neuroinflammation by affecting specific inflammatory markers.
Area of Science:
- Neuroscience
- Immunology
- Molecular Biology
Background:
- Alcohol-induced neuroinflammation involves pro-inflammatory cytokines like TNFα, MCP1, and IL-1β.
- The Toll-like receptor-4 (TLR4) pathway and subsequent NF-κB activation are implicated in alcohol-related neuroinflammation.
- MicroRNAs (miRNAs), such as miR-155, are emerging as critical regulators of inflammatory gene expression.
Purpose of the Study:
- To investigate the specific role of miR-155 in the development of alcohol-induced neuroinflammation.
- To elucidate the relationship between alcohol, TLR4 signaling, NF-κB activation, and miR-155 expression in the cerebellum.
Main Methods:
- Utilized wild-type, miR-155 knockout, and TLR4 knockout mice fed an ethanol-containing or control diet for five weeks.
- Assessed inflammatory markers (TNFα, MCP1, IL-1β), NF-κB activation (p-p65, EMSA), and miRNA expression (q-PCR) in cerebellar tissue.
- Examined miR-155 expression in microglia stimulated with lipopolysaccharide and ethanol.
Main Results:
- Chronic ethanol consumption upregulated miR-155 and miR-132 in the mouse cerebellum.
- miR-155 deficiency protected against alcohol-induced increases in TNFα and MCP1, and reduced NF-κB activation.
- While miR-155 influenced TNFα and MCP1, it did not affect caspase-dependent IL-1β levels.
- Ethanol-induced miR-155 upregulation was dependent on TLR4 signaling, as TLR4 knockout mice showed reduced neuroinflammation.
Conclusions:
- Chronic alcohol intake induces cerebellar miR-155 expression through a TLR4-dependent mechanism.
- miR-155 plays a significant role in regulating alcohol-induced TNFα and MCP1 expression in neuroinflammation.
- The study highlights miR-155 as a potential therapeutic target in alcohol-related brain damage, while noting its limited role in caspase-dependent IL-1β regulation.
