Expression analysis of a cholecystokinin system in human and rat white adipose tissue

Aim: Cholecystokinin (CCK) participates in the storage of dietary triglycerides in white adipose tissue (WAT). Our goal was to characterize, both in subcutaneous (Sc-WAT) and visceral WAT (Vis-WAT), the functional expression of the two known CCK receptors, CCK-1 (CCK-1R) and CCK-2 (CCK-2R), as well as of CCK. Main methods: Gene and protein expression was assessed in different cell types of rat and human WAT by means of RT-PCR and western-blot, respectively. The functionality of CCK-Rs was tested by quantifying protein kinase B (Akt) phosphorylation after treatment of pre-adipocytes with the bioactive fragment of CCK, CCK-8. The CCK receptor subtype involved in Akt phosphorylation was investigated by using selective CCK-1R (SR-27,897) and CCK-2R antagonists (L-365,260). Key findings: In rats, CCK-1R (Cckar) and CCK-2R (Cckbr) gene expression was detected in the two types of WAT analyzed as well as in isolated adipocytes, mesenchymal stem cells and pre-adipocytes. CCK-1R and CCK-2R proteins were identified in adipocytes and, to a minor extent, in pre-adipocytes. In addition, CCK-2R were detected in subcutaneous mesenchymal stem cells. Gene expression of the CCK precursor preproCCK as well as CCK immunoreactivity were also found in Sc-WAT and Vis-WAT. In human WAT, CCK gene expression as well as CCK-2Rs and CCK were also identified. CCK-8 evoked Akt phosphorylation in rat pre-adipocytes, and this effect was antagonized by SR-27,897 and L-365,260. Significance: Our data show that both human and rat WAT express a complete CCK system, and suggest that CCK may have an autocrine/paracrine role in regulating adipose tissue biology.