LPS induces interleukin-6 and interleukin-8 but not tumor necrosis factor-alpha in human adipocytes

Adipose tissue-derived cytokines are presumably involved in obesity-associated pathologies including type 2 diabetes and atherosclerosis. Here we studied the lipopolysaccharide (LPS)-induced expression dynamics of tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6), IL-8 and IL-10 in human adipose tissue biopsies, in preadipocyte-derived adipocytes, and in mesenchymal stem cell (MSC)-derived adipocytes. TNFalpha, IL-6, IL-8 and IL-10 secretions by adipose tissue explants were increased 5.5-, 19.5-, 3.5- and 12.5-fold, respectively, by LPS (1 microg/mL) administration. Concordantly, IL-6 and IL-8 release was dose-dependently induced in MSC-derived adipocytes by LPS (<10 pg/mL). In contrast, TNFalpha and IL-10 remained undetectable even at the highest LPS dose (1 microg/mL) after 24h. In MSC- and preadipocyte-derived adipocytes, respectively, exposure to LPS evoked a weak and transient induction of TNFalpha mRNA whereas induction of IL-6 and IL-8 mRNA were pronounced and sustained for at least 24h. Basal glucose uptake, lipolysis and IL-6 mRNA were induced by exogenous TNFalpha (10 ng/mL) but not by IL-6 (10 ng/mL), IL-8 (100 ng/mL) and IL-10 (20 ng/mL). In this adipocyte model TNFalpha induces well known metabolic effects, but together with previous reports these data suggest that inflammation-induced TNFalpha may derive from non-adipocyte sources in adipose tissue, likely to be macrophages.