Abstract 2318: The Type 2 Diabetes Gene CDKAL1 Discovered by Genome-wide Association is Expressed in Beta Cells and Modulated by Glucose Concentration
In our genome wide association study on type 2 diabetes (T2D), a variant we had previously identified in TCF7L2 stood out as the most significant finding. In addition, a variant of the CDKAL1 gene was found to be associated with increased risk of T2D in a nearly recessive manner, with genotype odds ratio for the homozygous carrier 1.45 and 1.55 for individuals of European and Asian ancestry respectively. The function of the CDKAL1 gene product is unknown but it is similar to another protein, CDK5RAP1, an inhibitor of the CDK5/p35 complex in neuronal tissue. This complex is also expressed in pancreatic beta cells and, in the presence of its active form, insulin expression is decreased under glucotoxic conditions. This led to the suggestion that CDKAL1 may be an inhibitor of the CDK5/p35 complex in beta cells, similar to the role of CDK5RAP1 in neuronal tissue. Furthermore, we have shown that the risk variant of CDKAL1 is associated with reduced insulin secretion and this effect is mostly seen for the homozygote where a 24% reduction in insulin response is observed compared to the heterozygous carriers or non-carriers. This is in line with the nearly recessive mode of inheritance observed for this variant with respect to disease risk. The aim of this study was to gain further insight into the functional role of CDKAL1 using the rat pancreatic beta cell line INS-1. The rat pancreatic beta cell line INS-1 was cultured in the presence of variable glucose concentration, ranging from 2.5–30 mM, to evaluate whether CDKAL1 expression is regulated by glucose concentration. We demonstrated that the expression of CDKAL1 in rat INS-1 cells varied according to glucose concentration in the culture medium with reduced expression detected under glucotoxic conditions compared to normal glucose concentration. This indicates that CDKAL1 expression in pancreatic beta cells is sensitive to glucose concentration. It is possible that this response to glucose may be affected in individuals carrying the variant of CDKAL1 that is associated to T2D. This could explain the reduced insulin secretion observed for these individuals in response to an oral glucose tolerance test.