Retinoic acid abrogates LPS-induced inflammatory response via negative regulation of NF-kappa B/miR-21 signaling

Immunopharmacol Immunotoxicol. 2021 Jun;43(3):299-308. doi: 10.1080/08923973.2021.1902348. Epub 2021 Mar 24.

Abstract

Context: Macrophages are essential components of the immune system, with significant roles in inflammation modulation. They can be activated into pro-inflammatory M1 or anti-inflammatory M2 phenotypes, depending on their micro-environment. Molecular factors that modulate macrophage polarization are hot targets for therapeutic strategies to counter chronic inflammatory pathological conditions.

Objective: The current study aimed to elucidate the molecular mechanisms by which Retinoic acid (RA), a potent immunomodulator, suppresses LPS-induced inflammatory response in macrophages.

Materials and methods: RAW 264.7 macrophages were treated with RA and/or LPS, and analyzed for inflammatory genes and miR-21 by PCR. The roles of miR-21 and NF-ĸB signaling pathway were also assessed by knock-down experiments, immunofluorescence, and ChIP assays.

Results: Pretreatment with RA quenched the LPS-induced inflammatory responses, including phagocytosis, ROS generation, and NO production. RA shifted the polarization away from the M1 state by negative regulation of IKKα/β, p65, and miR-21. RA hindered the phosphorylation of IKKα/β, translocation of p65 into the nucleus, and the subsequent upregulation of miR-21. Knock-in and knock-down experiments showed that miR-21 is central for the polarization shift toward the pro-inflammatory M1 state.

Conclusion: miR-21 is involved in the LPS-induced pro-inflammatory profile of macrophages and that RA negatively regulates the inflammatory response by targeting NF-ĸB/miR-21 signaling. Our data exposes RA's potential as a pharmacological agent to manipulate miR-21 and counteract hyper-inflammatory response.

Keywords: Macrophage polarization; NF-ĸB; miR-21; pro-inflammation; retinoic acid.

Publication types

  • Video-Audio Media

MeSH terms

  • Animals
  • Inflammation / chemically induced
  • Inflammation / metabolism
  • Lipopolysaccharides / toxicity*
  • Macrophages / metabolism*
  • Mice
  • MicroRNAs / metabolism*
  • NF-kappa B / metabolism*
  • RAW 264.7 Cells
  • Signal Transduction / drug effects*
  • Tretinoin / pharmacology*

Substances

  • Lipopolysaccharides
  • MIRN21 microRNA, mouse
  • MicroRNAs
  • NF-kappa B
  • Tretinoin