1342-P: Reduction of Glucokinase and Glucokinase Regulatory Protein Expression by siRNA Is Associated with the Reduction of Lactate and Pyruvate Export from Canine Hepatocytes

Glucokinase (GCK) mediates hepatic glucose uptake during hyperglycemia and is crucial for the regulation of glucose-responsive glycolysis genes. Mutations in GCK are responsible for maturity-onset diabetes of the young, and glucokinase regulatory protein (GKRP) , the regulator of hepatic GCK, is also a diabetes susceptibility locus. Recently in in vivo experiments, we used hepatic lactate export as a surrogate for GCK activity, which was a measure of “glucose effectiveness.” We hypothesized that in vitro GCK and GKRP suppression in hepatocytes promotes a reduction in lactate and pyruvate export from the liver. We used cryopreserved canine hepatocytes and knocked down GCK and GKRP via lipid delivery of siRNA. A control group did not receive siRNA. We measured lactate dehydrogenase D (LDHD) and pyruvate kinase (PK) gene expression and lactate and pyruvate release into the medium 24 and 48 h after siRNA delivery. Selective blocking of GCK and GKRP did not change cell proliferation but reduced the expression of these genes by 90% and 85%, respectively (P<0.0vs. controls; n=4) . GCK and GKRP knockdown reduced LDHD by 71% and 74%, respectively (P<0.001) ; similarly, PK was reduced by 84% and 82%, respectively (P<0.001) . Lactate exported into the medium was reduced by 36% (P<0.001) and 26% (P<0.05) by GCK and GKRP siRNA, respectively, after 48 h of hepatocyte culture. However, pyruvate was reduced by 17% only after 48 h culture of GCK siRNA (P<0.05) . Thus, we showed that direct suppression of GCK and GKRP genes by siRNA in vitro affects glucose-responsive glycolysis genes, consequently reducing lactate export which can be used as a surrogate for reduced glucokinase activity in hepatocytes. The use of antisense oligonucleotides or CRISPR gene-editing methods in animals will be useful methods to study the glucose-lactate relationship in vivo and will evaluate the role of glucose effectiveness in the pathogenesis of type 2 diabetes.