Both inflammatory and classical lipolytic pathways are involved in lipopolysaccharide-induced lipolysis in human adipocytes

Innate Immun. 2012 Feb;18(1):25-34. doi: 10.1177/1753425910386632. Epub 2010 Nov 18.

Abstract

High fat diet-induced endotoxaemia triggers low-grade inflammation and lipid release from adipose tissue. This study aims to unravel the cellular mechanisms leading to the lipopolysaccharide (LPS) effects in human adipocytes. Subcutaneous pre-adipocytes surgically isolated from patients were differentiated into mature adipocytes in vitro. Lipolysis was assessed by measurement of glycerol release and mRNA expression of pro-inflammatory cytokines were evaluated by real-time PCR. Treatment with LPS for 24 h induced a dose-dependent increase in interleukin (IL)-6 and IL-8 mRNA expression. At 1 µg/ml LPS, IL-6 and IL-8 were induced to 19.5 ± 1.8-fold and 662.7 ± 91.5-fold (P < 0.01 vs basal), respectively. From 100 ng/ml to 1 µg/ml, LPS-induced lipolysis increased to a plateau of 3.1-fold above basal level (P < 0.001 vs basal). Co-treatment with inhibitors of inhibitory kappa B kinase kinase beta (IKKβ) or NF-κB inhibited LPS-induced glycerol release. Co-treatment with the protein kinase A (PKA) inhibitor H-89, the lipase inhibitor orlistat or the hormone-sensitive lipase (HSL) inhibitor CAY10499 abolished the lipolytic effects of LPS. Co-treatment with the MAPK inhibitor, U0126 also reduced LPS-induced glycerol release. Inhibition of lipolysis by orlistat or CAY10499 reduced LPS-induced IL-6 and IL-8 mRNA expression. Induction of lipolysis by the synthetic catecholamine isoproterenol or the phosphodiesterase type III inhibitor milrinone did not alter basal IL-6 and IL-8 mRNA expression after 24 treatments whereas these compounds enhanced LPS-induced IL-6 and IL-8 mRNA expression. Both the inflammatory IKKβ/NF-κB pathway and the lipolytic PKA/HSL pathways mediate LPS-induced lipolysis. In turn, LPS-induced lipolysis reinforces the expression of pro-inflammatory cytokines and, thereby, triggers its own lipolytic activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipocytes / drug effects
  • Adipocytes / immunology*
  • Adipocytes / pathology
  • Cell Differentiation
  • Cells, Cultured
  • Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors
  • Enzyme Inhibitors / pharmacology
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / immunology
  • Glycerol / metabolism
  • Humans
  • I-kappa B Kinase / antagonists & inhibitors
  • Inflammation Mediators / metabolism*
  • Interleukin-6 / genetics
  • Interleukin-6 / immunology
  • Interleukin-6 / metabolism*
  • Interleukin-8 / genetics
  • Interleukin-8 / immunology
  • Interleukin-8 / metabolism*
  • Isoproterenol / pharmacology
  • Lipolysis / drug effects
  • Lipolysis / immunology*
  • Lipopolysaccharides / immunology*

Substances

  • Enzyme Inhibitors
  • Inflammation Mediators
  • Interleukin-6
  • Interleukin-8
  • Lipopolysaccharides
  • I-kappa B Kinase
  • Cyclic AMP-Dependent Protein Kinases
  • Isoproterenol
  • Glycerol