Inflammatory intracellular pathways activated by electronegative LDL in monocytes

Biochim Biophys Acta. 2016 Sep;1861(9 Pt A):963-969. doi: 10.1016/j.bbalip.2016.05.010. Epub 2016 May 25.

Abstract

Aims: Electronegative LDL (LDL(-)) is a plasma LDL subfraction that induces cytokine release in monocytes through toll-like receptor 4 (TLR4) activation. However, the intracellular pathways induced by LDL(-) downstream TLR4 activation are unknown. We aimed to identify the pathways activated by LDL(-) leading to cytokine release in monocytes.

Methods and results: We determined LDL(-)-induced activation of several intracellular kinases in protein extracts from monocytes using a multikinase ELISA array. LDL(-) induced higher p38 mitogen-activated protein kinase (MAPK) phosphorylation than native LDL. This was corroborated by a specific cell-based assay and it was dependent on TLR4 and phosphoinositide 3-kinase (PI3k)/Akt pathway. P38 MAPK activation was involved in cytokine release promoted by LDL(-). A specific ELISA showed that LDL(-) activated cAMP response-element binding (CREB) in a p38 MAPK dependent manner. P38 MAPK was also involved in the nuclear factor kappa-B (NF-kB) and activating protein-1 (AP-1) activation by LDL(-). We found that NF-kB, AP-1 and CREB inhibitors decreased LDL(-)-induced cytokine release, mainly on MCP1, IL6 and IL10 release, respectively.

Conclusions: LDL(-) promotes p38 MAPK phosphorylation through TLR4 and PI3k/Akt pathways. Phosphorylation of p38 MAPK is involved in NF-kB, AP-1 and CREB activation, leading to LDL(-)-induced cytokine release in monocytes.

Keywords: Cell signaling; Cytokines; Electronegative LDL; MAP kinases; Toll-like receptor (TLR); Transcription factors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cyclic AMP / metabolism
  • Cyclic AMP Response Element-Binding Protein / biosynthesis
  • Cyclic AMP Response Element-Binding Protein / genetics
  • Cytokines / biosynthesis
  • Cytokines / genetics
  • Elafin / genetics
  • Humans
  • Lipoproteins, LDL / biosynthesis
  • Lipoproteins, LDL / blood*
  • Monocytes / metabolism*
  • NF-kappa B / biosynthesis
  • NF-kappa B / genetics
  • Phosphorylation
  • Proto-Oncogene Proteins c-akt / genetics
  • Signal Transduction
  • Toll-Like Receptor 4 / genetics*
  • Transcription Factor AP-1 / biosynthesis
  • Transcription Factor AP-1 / genetics
  • p38 Mitogen-Activated Protein Kinases / biosynthesis
  • p38 Mitogen-Activated Protein Kinases / genetics*

Substances

  • CREB1 protein, human
  • Cyclic AMP Response Element-Binding Protein
  • Cytokines
  • Elafin
  • Lipoproteins, LDL
  • NF-kappa B
  • PI3 protein, human
  • TLR4 protein, human
  • Toll-Like Receptor 4
  • Transcription Factor AP-1
  • oxidized low density lipoprotein
  • Cyclic AMP
  • Proto-Oncogene Proteins c-akt
  • p38 Mitogen-Activated Protein Kinases