Abstract
A cholecystokinin (CCK) system has been identified in white adipose tissue (WAT). Nevertheless, the endocrine actions of CCK on WAT remain unknown. Our goal was to investigate the role of CCK in regulating the production of adiponectin, an adipokine expressed in WAT, which is pivotal in preserving energy homeostasis. The effect of the bioactive CCK fragment CCK-8 on adiponectin production was studied both in vivo and in vitro. CCK-8 effects were characterized in rats treated with selective CCK1 and CCK2 receptor antagonists as well as in pre-adipocytes carrying the selective silencing of either CCK1 or CCK2 receptors. The influence of insulin on CCK-8 responses was also analysed. In WAT, CCK-8 increased plasma adiponectin levels and the expression of the adiponectin gene (Adipoq). In pre-adipocytes, CCK-8 up-regulated adiponectin production. CCK-8 effects were abolished by L-365,260, a selective CCK2 receptor antagonist. CCK2 receptor knockdown also abolished the effects of CCK-8 in pre-adipocytes. Moreover, in vitro CCK-8 effects were blocked by triciribine, a specific inhibitor of protein kinase B (Akt) and by the PPARγ antagonist T0070907. Silencing the expression of the insulin receptor inhibited CCK-8-induced Adipoq expression in pre-adipocytes. Furthermore, insulin potentiated the effect of CCK-8. CCK-8 stimulates adiponectin production in WAT by acting on CCK2 receptors, through a mechanism involving both Akt and PPARγ. Moreover, CCK-8 actions are only observed in the presence of insulin. Our results could have translational value in the design of new insulin-sensitizing therapies.
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