Adipokine expression and secretion by canine adipocytes: stimulation of inflammatory adipokine production by LPS and TNFα

Abstract

Adiposity and obesity are increasing in dogs. We have examined here the endocrine function of canine adipose tissue and the regulation of production of inflammation-related adipokines by dog adipocytes. Adiponectin, leptin, IL-6, MCP-1 and TNFalpha genes were expressed in the main adipose depots of dogs, but there were no major depot differences in mRNA levels. Each adipokine was expressed in canine adipocytes differentiated in culture and secreted into the medium (leptin undetected). IL-6, MCP-1 and TNFalpha were also expressed and secreted by preadipocytes; adiponectin and leptin were only expressed after adipocyte differentiation. The inflammatory mediators LPS and TNFalpha had major stimulatory effects on the expression and secretion of IL-6, MCP-1 and TNFalpha; there was a >5,000-fold increase in IL-6 mRNA level with LPS. IL-6 release into the medium was increased >50-fold over 24 h with LPS and TNFalpha, while MCP-1 release was increased 23- and 40-fold by TNFalpha and LPS, respectively. However, there was no effect, or small reductions, in adiponectin and leptin mRNA levels with the inflammatory mediators. Dexamethasone-stimulated leptin gene expression, had no effect on adiponectin expression, but decreased the expression and secretion of IL-6 and MCP-1. The PPARgamma agonist rosiglitazone stimulated both adiponectin and leptin expression and inhibited the expression of IL-6, MCP-1 and TNFalpha; MCP-1 secretion was reduced. These results demonstrate that canine adipocytes express and secrete key adipokines and show that adipocytes of this species are highly responsive to inflammatory mediators with the induction of major increases in the production of inflammation-related adipokines.