Mice expressing reduced levels of hepatic glucose-6-phosphatase-α activity do not develop age-related insulin resistance or obesity

Glycogen storage disease type-Ia (GSD-Ia) is caused by a lack of glucose-6-phosphatase-alpha (G6Pase-alpha or G6PC) activity. We have shown that gene therapy mediated by a recombinant adeno-associated virus (rAAV) vector expressing human G6Pase-alpha normalizes blood glucose homeostasis in the global G6pc knockout (G6pc(-/-)) mice for 70-90 weeks. The treated G6pc(-/-) mice expressing 3-63% of normal hepatic G6Pase-alpha activity (AAV mice) produce endogenous hepatic glucose levels 61-68% of wildtype littermates, have a leaner phenotype and exhibit fasting blood insulin levels more typical of young adult mice. We now show that unlike wild-type mice, the lean AAV mice have increased caloric intake and do not develop age-related obesity or insulin resistance. Pathway analysis shows that signaling by hepatic carbohydrate response element binding protein that improves glucose tolerance and insulin signaling is activated in AAV mice. In addition, several longevity factors in the calorie restriction pathway, including the NADH shuttle systems, NAD(+) concentrations and the AMP-activated protein kinase/sirtuin 1/peroxisome proliferator-activated receptor-gamma coactivator 1 alpha pathway are upregulated in the livers of AAV mice. The finding that partial restoration of hepatic G6Pase-alpha activity in GSD-Ia mice not only attenuates the phenotype of hepatic G6Pase-alpha deficiency but also prevents the development of age-related obesity and insulin resistance seen in wild-type mice may suggest relevance of the G6Pase-alpha enzyme to obesity and diabetes.