Deletion of CDKAL1 affects first-phase glucose stimulated insulin exocytosis

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A variant of the CDKAL1 gene was reported to be associated with type 2 diabetes. To determine the role of CDKAL1 in beta-cells, we studied insulin release profiles in CDKAL1 gene knockout (KO) mice. Total internal reflection fluorescence imaging of CDKAL1 KO beta-cells showed that the number of fusion events during first-phase insulin secretion was reduced with delayed and slow cytosolic Ca2+ increase. The responsiveness of KATP channels to glucose was blunted in KO cells. Although CDKAL1 is homologous to CDK5RAP1, there was no difference in CDK5 activity between WT and KO islets. Thus, CDKAL1 controls first-phase insulin exocytosis in beta-cells by facilitating KATP channel responsiveness and subsequent Ca2+ channels activity through pathways other than CDK5-mediated regulation. Defects in this process caused by decreased CDKAL1 expression levels may confer an increased risk of type 2 diabetes.