Hexokinase II-deficient mice -: Prenatal death of homozygotes without disturbances in glucose tolerance in heterozygotes

Type 2 diabetes is characterized by decreased rates of insulin-stimulated glucose uptake and utilization, reduced hexokinase II mRNA and enzyme production, and low basal levels of glucose 6-phosphate in insulin-sensitive skeletal muscle and adipose tissues. Hexokinase II is primarily expressed in muscle and adipose tissues where it catalyzes the phosphorylation of glucose to glucose 6-phosphate, a possible rate-limiting step for glucose disposal, To investigate the role of hexokinase II in insulin action and in glucose homeostasis as well as in mouse development, we generated a hexokinase II knock-out mouse. Mice homozygous for hexokinase II deficiency (HXII-/-) died at approximately 7.5 days post-fertilization, indicating that hexokinase II is vital for mouse embryogenesis after implantation and before organogenesis, HKII+/- mice were viable, fertile, and grew normally. Surprisingly, even though HKII+/- mice had significantly reduced (by 50%) hexokinase II mRNA and activity levels in skeletal muscle, heart, and adipose tissue, they did not exhibit impaired insulin action or glucose tolerance even when challenged with a high-fat diet.