Luteolin Triggers Global Changes in the Microglial Transcriptome Leading to a Unique Anti-Inflammatory and Neuroprotective Phenotype

J Neuroinflammation. 2010 Jan 14;7:3. doi: 10.1186/1742-2094-7-3.

Abstract

Background: Luteolin, a plant derived flavonoid, exerts a variety of pharmacological activities and anti-oxidant properties associated with its capacity to scavenge oxygen and nitrogen species. Luteolin also shows potent anti-inflammatory activities by inhibiting nuclear factor kappa B (NFkB) signaling in immune cells. To better understand the immuno-modulatory effects of this important flavonoid, we performed a genome-wide expression analysis in pro-inflammatory challenged microglia treated with luteolin and conducted a phenotypic and functional characterization.

Methods: Resting and LPS-activated BV-2 microglia were treated with luteolin in various concentrations and mRNA levels of pro-inflammatory markers were determined. DNA microarray experiments and bioinformatic data mining were performed to capture global transcriptomic changes following luteolin stimulation of microglia. Extensive qRT-PCR analyses were carried out for an independent confirmation of newly identified luteolin-regulated transcripts. The activation state of luteolin-treated microglia was assessed by morphological characterization. Microglia-mediated neurotoxicity was assessed by quantifying secreted nitric oxide levels and apoptosis of 661W photoreceptors cultured in microglia-conditioned medium.

Results: Luteolin dose-dependently suppressed pro-inflammatory marker expression in LPS-activated microglia and triggered global changes in the microglial transcriptome with more than 50 differentially expressed transcripts. Pro-inflammatory and pro-apoptotic gene expression was effectively blocked by luteolin. In contrast, mRNA levels of genes related to anti-oxidant metabolism, phagocytic uptake, ramification, and chemotaxis were significantly induced. Luteolin treatment had a major effect on microglial morphology leading to ramification of formerly amoeboid cells associated with the formation of long filopodia. When co-incubated with luteolin, LPS-activated microglia showed strongly reduced NO secretion and significantly decreased neurotoxicity on 661W photoreceptor cultures.

Conclusions: Our findings confirm the inhibitory effects of luteolin on pro-inflammatory cytokine expression in microglia. Moreover, our transcriptomic data suggest that this flavonoid is a potent modulator of microglial activation and affects several signaling pathways leading to a unique phenotype with anti-inflammatory, anti-oxidative, and neuroprotective characteristics. With the identification of several novel luteolin-regulated genes, our findings provide a molecular basis to understand the versatile effects of luteolin on microglial homeostasis. The data also suggest that luteolin could be a promising candidate to develop immuno-modulatory and neuroprotective therapies for the treatment of neurodegenerative disorders.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Inflammatory Agents / pharmacology*
  • Apoptosis / drug effects
  • Caspases / metabolism
  • Cells, Cultured
  • Computational Biology / methods
  • Culture Media, Conditioned / pharmacology
  • Cytokines / genetics
  • Cytokines / metabolism*
  • Gene Expression Profiling / methods
  • Gene Expression Regulation / drug effects*
  • Lipopolysaccharides / pharmacology
  • Luteolin / pharmacology*
  • Mice
  • Mice, Inbred C57BL
  • Microglia / chemistry
  • Microglia / drug effects*
  • Neuroprotective Agents / pharmacology*
  • Nitric Oxide / metabolism
  • Oligonucleotide Array Sequence Analysis / methods
  • Signal Transduction / drug effects

Substances

  • Anti-Inflammatory Agents
  • Culture Media, Conditioned
  • Cytokines
  • Lipopolysaccharides
  • Neuroprotective Agents
  • Nitric Oxide
  • Caspases
  • Luteolin