Cholecystokinin (CCK) is an incretin-like hormone that is also produced by pancreatic β-cells under conditions of stress and obesity. In the past, we have established a role for CCK in protection from β-cell apoptosis. However, the specific CCK receptor responsible for this protective effect was unknown. Both Cckar and Cckbr mRNA are expressed in mouse islet, although Cckbr expression is very low. Incubation of WT mouse pancreatic islets with CCK-8 (100nM) increases the transcript levels of Cckar but does not impact Cckbr expression. Conversely, 24-hour treatment with proinflammatory cytokine cocktail decreases CCKAR transcript levels but again does not modulate Cckbr expression. Therefore, we hypothesized that the CCKA receptor was the most likely mediator of CCK signaling in the β-cell. We used isolated islets from mice with germline knockout of CCK receptors to determine which receptor was required for the pro-survival effects of CCK on the β-cell. Using imaging flow cytometry of dissociated islet cells stained for annexin V and propidium iodide (PI) we find that islet cells from CCKBR knockout mice have a 19.3% (p<0.005) reduction in cytokine-mediated cell death when treated with CCK-8 (100 nM), similar to the protection seen in wild type islets. This protective effect is lost in the CCKAR and double knockout mouse islets. We also confirm this finding using insulin and TUNEL immunohistochemistry to specifically identify β-cell apoptosis. In CCKBR knockout mouse islets, CCK-8 (100 nM) reduces the % TUNEL positive β-cells from 12.98% to 4.39% (p<0.05) after cytokine exposure, similar to protection seen in WT mouse islets (10.47% to 4.48%). Again, CCK-8 does not protect β-cells from cytokine-induced apoptosis in CCKAR knockout or double CCKR null mouse islets. Taken together, CCKAR, but not CCKBR, is required for CCK-mediated protection of pancreatic β-cells from cytokine-induced stress.
H. Kim: None. S. Sacotte: None. R.A. Williams: None. A.H. de Souza: None. J. Han: None. J.T. Bartosiak: None. G.H. Yang: None. D.B. Davis: None.
National Institutes of Health