Endocannabinoids regulate adipokine production and the immune balance of omental adipose tissue in human obesity

Abstract

(1) To investigate whether modulation of the cannabinoid type 1 receptor (CB1R) directly regulates the production of adiponectin (ApN) and other adipokines in omental adipose tissue (OAT) of obese subjects, (2) to establish in which cellular fraction of OAT the effects of CB1R blockade take place and (3) to unravel the underlying mechanisms. OAT was obtained from 30 obese subjects (body mass index: 40.6±1.3 kg m(-2)) undergoing abdominal surgery. Primary cultures of explants or of freshly isolated adipocytes or stromal-vascular cells (SVCs) were used. In OAT explants, the CB1R blocker Rimonabant upregulated ApN gene expression. mRNA abundance of omentin that exhibits insulin-sensitizing properties was upregulated as well. Conversely, mRNA levels of two pro-inflammatory cytokines, macrophage inflammatory protein (MIP)-1β and interleukin (IL)-7 were downregulated. We next examined where these effects took place within OAT. CB1R expression was similar in both cellular fractions. In isolated mature adipocytes, blockade of CB1R reproduced the increase of ApN mRNA and the decrease of IL-7 mRNA, while inducing a rise of ApN secretion into the medium. In isolated SVC, gene expression of omentin, which is restricted to this fraction, was augmented, while that of MIP-1β was diminished. Finally, we deciphered the mechanisms leading to ApN regulation by the endocannabinoid system (ES). We first established that ApN regulation was actually mediated by the CB1R: ApN gene expression was upregulated by Rimonabant and downregulated by the CB1R agonist arachidonyl-2-chloroethylamide (ACEA). Upregulation of ApN by Rimonabant was unaltered by inhibiting cAMP production. However, downregulation of ApN by ACEA was fully reversed by an inhibitor of p38 mitogen-activated protein kinase (p38MAPK) and ACEA increased p38MAPK phosphorylation. Blockade of CB1R attenuates the inflammatory state in both cellular fractions of OAT either by increasing ApN and omentin production or by decreasing mRNAs of MIP-1β and IL-7. ApN regulation by the ES partly involves p38MAPK.