RNAi Screening in Primary Human Hepatocytes of Genes Implicated in Genome-Wide Association Studies for Roles in Type 2 Diabetes Identifies Roles for CAMK1D and CDKAL1, among Others, in Hepatic Glucose Regulation

Abstract

Genome-wide association (GWA) studies have described a large number of new candidate genes that contribute to of Type 2 Diabetes (T2D). In some cases, small clusters of genes are implicated, rather than a single gene, and in all cases, the genetic contribution is not defined through the effects on a specific organ, such as the pancreas or liver. There is a significant need to develop and use human cell-based models to examine the effects these genes may have on glucose regulation. We describe the development of a primary human hepatocyte model that adjusts glucose disposition according to hormonal signals. This model was used to determine whether candidate genes identified in GWA studies regulate hepatic glucose disposition through siRNAs corresponding to the list of identified genes. We find that several genes affect the storage of glucose as glycogen (glycolytic response) and/or affect the utilization of pyruvate, the critical step in gluconeogenesis. Of the genes that affect both of these processes, CAMK1D, TSPAN8 and KIF11 affect the localization of a mediator of both gluconeogenesis and glycolysis regulation, CRTC2, to the nucleus in response to glucagon. In addition, the gene CDKAL1 was observed to affect glycogen storage, and molecular experiments using mutant forms of CDK5, a putative target of CDKAL1, in HepG2 cells show that this is mediated by coordinate regulation of CDK5 and PKA on MEK, which ultimately regulates the phosphorylation of ribosomal protein S6, a critical step in the insulin signaling pathway.

Maternal Obesity in Pregnancy Developmentally Programs Adipose Tissue Inflammation in Young, Lean Male Mice Offspring

“…This process may be an attempt by the adipose tissue to try and restrict lipid accumulation and, thus, restoring functionality in the tissue. CAMK1D is currently not well characterized in terms of biological function, however, as well as being involved in inflammatory signaling, evidence from the liver suggests that it is important for glucose metabolism (38). The impact of increased of CAMK1D and IL-33 expression on adipocytes warrants further investigation.…”

Genome-wide investigation of schizophrenia associated plasma Ndel1 enzyme activity

“…CAMk1D has been reported to be associated in GWAS meta-analysis studies with type II Diabetes (Zeggini et al, 2008) and was later shown to reduce glucose response , possibly due to an effect on the localization of a mediator of both gluconeogenesis and glycolysis (Haney et al, 2013). This raises the question about the effect of metabolic process in Ndel1 measures and whether they converge to impact on SCZ pathophysiology or whether Ndel1 would be only a biomarker of these processes.…”

Contribution of independent and pleiotropic genetic effects in the metabolic syndrome in a hypertensive rat

“…Camk1d is member of the calcium/calmodulin-dependent protein kinase 1 gene family that plays role in granulocyte respiratory burst, phagocytosis, adhesion and migration [ 35 ]. It is also known to activate CREB-mediated transcriptional activation [ 36 ] and may play a role in regulating hepatocyte glycolysis and gluconeogenesis independent of insulin signaling [ 37 ]. Of important relevance to this project, variants in Camk1d have replicated association with Type II diabetes [ 24 – 26 ] and a recent study also found association of this gene to hypertension [ 38 ].…”