A Novel Function for 15-Lipoxygenases in Cholesterol Homeostasis and CCL17 Production in Human Macrophages

Front Immunol. 2018 Aug 24;9:1906. doi: 10.3389/fimmu.2018.01906. eCollection 2018.

Abstract

Arachidonate 15-lipoxygenase (ALOX15) and arachidonate 15-lipoxygenase, type B (ALOX15B) catalyze the dioxygenation of polyunsaturated fatty acids and are upregulated in human alternatively activated macrophages (AAMs) induced by Th2 cytokine interleukin-4 (IL-4) and/or interleukin-13. Known primarily for roles in bioactive lipid mediator synthesis, 15-lipoxygenases (15-LOXs) have been implicated in various macrophage functions including efferocytosis and ferroptosis. Using a combination of inhibitors and siRNAs to suppress 15-LOX isoforms, we studied the role of 15-LOXs in cellular cholesterol homeostasis and immune function in naïve and AAMs. Silencing or inhibiting the 15-LOX isoforms impaired sterol regulatory element binding protein (SREBP)-2 signaling by inhibiting SREBP-2 processing into mature transcription factor and reduced SREBP-2 binding to sterol regulatory elements and subsequent target gene expression. Silencing ALOX15B reduced cellular cholesterol and the cholesterol intermediates desmosterol, lanosterol, 24,25-dihydrolanosterol, and lathosterol as well as oxysterols in IL-4-stimulated macrophages. In addition, attenuating both 15-LOX isoforms did not generally affect IL-4 gene expression but rather uniquely impacted IL-4-induced CCL17 production in an SREBP-2-dependent manner resulting in reduced T cell migration to macrophage conditioned media. In conclusion, we identified a novel role for ALOX15B, and to a lesser extent ALOX15, in cholesterol homeostasis and CCL17 production in human macrophages.

Keywords: arachidonate 15-lipoxygenase; chemokine; cholesterol; interleukin-4; lipoxygenase; macrophage; sterol regulatory element binding protein-2; type B.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arachidonate 15-Lipoxygenase / genetics
  • Arachidonate 15-Lipoxygenase / metabolism*
  • Cell Movement / genetics
  • Chemokine CCL17 / biosynthesis*
  • Cholesterol / metabolism*
  • Cytokines / genetics
  • Cytokines / metabolism
  • Gene Expression
  • Homeostasis*
  • Humans
  • Lipid Metabolism
  • Macrophages / immunology*
  • Macrophages / metabolism*
  • Protein Binding
  • RNA, Small Interfering / genetics
  • Serum Response Element
  • Sterol Regulatory Element Binding Protein 2 / metabolism

Substances

  • Chemokine CCL17
  • Cytokines
  • RNA, Small Interfering
  • SREBF2 protein, human
  • Sterol Regulatory Element Binding Protein 2
  • Cholesterol
  • Arachidonate 15-Lipoxygenase