GK-NR4A1Interaction Regulate Glucose/Lipid Metabolism In Vivo

Normal glucose and lipid metabolism is critical for health, preliminary studies foundthat glycerol kinase (GK) protein interacts with nuclear orphan receptor NR4A1andrepresses its trans-activation. In vitro over expression of GK in liver could inhibit theregulation of NR4A1on glucose and lipid metabolism related genes, which suggestthat GK and NR4A1may regulate glucose and lipid metabolism in the liver throughprotein interaction. The in vivo biological roles of protein interaction of GK andNR4A1on liver glucose and lipid metabolism in mice were investigated and molecularmechanism was discussed.First, we study biological roles of NR4A1on liver glucose and lipid metabolismin vivo using NR4A1knockout mice. Mice were either fasted18hours or fed16weeks with high fat diet, then the glucose tolerance, pyruvate tolerance and insulintolerance were investigated, serum glucose and lipid, serum insulin and glucagon wereexamined, and expression of glucose and lipid metabolism related genes were analyzed.The results revealed that compared with NR4A1wide type mice, the gluconeogenesisability of long-term fasted NR4A1knockout mice was decreased and their fat andglycogen decomposed more quickly, weight loss faster(P <0.05). However, NR4A1knockout mice fed with high fat diet contained60%calories with obesity, and they hadhigher blood glucose, higher lipid index, fatty liver, and insulin resistance, whencompared with NR4A1wide type mice. The glucose metabolism gene of NR4A1knockout mice for example Eno3of G6Pase mRNA level reduced by62%,56%respectively compared with WT mice. In addition, the KO mice liver lipid metabolismgene such as Srebp-1c, Fas mRNA level increased by79%,40%compared to wildmice. This study indicated that NR4A1can regulate glucose and lipid metabolism, ifNR4A1knockout glucose and lipid metabolism of mice are disorder.In addition, we set out to identify the interaction between glycerol kinase GKprotein and nuclear orphan receptor NR4A1in vivo level, three models: NR4A1KO mice, STZ-I diabetic mice and db/db-II diabetic mice with endogenous NR4A1highexpression were used, GK protein expressed in mice liver by hydrodynamic deliveryinjecting GK-vector, we determined glucose tolerance,pyruvate tolerance and insulintolerance,serum glucose and lipid, gluconeogenesis, serum insulin and glucagon, andexpression of glucose and lipid metabolism genes. The result shows that GK overexpression in vivo inhibits the regulation of NR4A1to glucose and lipid metabolismand glucose and lipid metabolism related genes expression. By the same way, weidentified the influence of the interaction between GK kinase mutation and NR4A1onglucose and lipid metabolism. The results show that GK kinase mutation overexpression in vivo inhibits the regulation of NR4A1to glucose and lipidmetabolism,but GK kinase can regulation glucose and lipid metabolism in vivo alone.In conclusion, GK can not only suppress NR4A1regulation of glucose and lipidmetabolism genes indirectly, but also regulate glucose and lipid metabolism directly byits related kinase. Besides, their interaction can promote glycogenolysis, inhibitgluconeogenesis and feedback regulate the insulin. Therefore, their interaction plays akey role in maintaining a normal blood glucose and lipid.