(562.9) D4 dopamine receptors regulate Insulin sensitivity via activation of renal insulin receptors in mice

Poster Board Number: E183

Mingda Liu (Core Laboratory for Clinical Research, BenQ Medical Center, The Affiliated BenQ Hospital of Nanjing), Weiwan Wang (Core Laboratory for Clinical Research, BenQ Medical Center, The Affiliated BenQ Hospital of Nanjing), Mingzhuo Zhang (Core Laboratory for Clinical Research, BenQ Medical Center, The Affiliated BenQ Hospital of Nanjing), Zhiyun Ren (Core Laboratory for Clinical Research, BenQ Medical Center, The Affiliated BenQ Hospital of Nanjing), Quansheng Wang (Department of Endocrine,Nanjing BenQ Medical center,The Affiliated BenQ Hospital of Nanjing Medical University), Xiaoyan Wang (Core Laboratory for Clinical Research, BenQ Medical Center, The Affiliated BenQ Hospital of Nanjing)

Insulin resistance is a major concern in metabolic disorders related to diabetes. In order to explore the hypothesis that D4 dopamine receptor (D4R) increases insulin sensitivity through its activation of insulin receptor beta (IR-beta), we demonstrated the functional role of D4R in insulin resistance in aged mice. In C57Bl6J mice (male, 8 mos, D4R agonist (PD168077,1mg/kg) increased but D4R antagonist (L745870,1mg/kg) via osmotic mini-pump (1week) decreased insulin sensitivity; glucose tolerance was not altered . Drd4-/- mice ( 14 mos) had increased fasting blood glucose regardless of sex but their urines were negative for glucose and ketones, suggesting that the mice were pre-diabetic. Serum insulin levels were increased in male Drd4-/- mice but not altered in female Drd4-/- mice after an 8 hr fast indicating that those mice have insensitivity to endogenous insulin. Drd4-/- mice presented a blunted blood glucose lowering effect at 30, 45 min after insulin injection (0.75U/kg,I.P) suggesting that the mice also had insensitivity to exogenous insulin.The aged male and female Drd4-/- mice had similar body weights, fasting serum total and free cholesterols, triglycerides, to their age and sex -matched Drd4+/+ littermates, suggesting that the old Drd4-/- mice were not obese and had no dyslipidemia. Relative to Drd4+/+ littermates (100±7 %，n=6)， Drd4-/- mice had decreased IR-beta（19±4%, n=4）but normal protein expressions of IR-alpha, insulin degrading enzyme, insulin substrate 1, sodium glucose transporter 2 and glucose transporters in renal cortex homogenates, indicating that the decreased protein expression of IR-beta contributed to the insulin resistance in the aged Drd4-/- mice. Drd4-/- mice had decreased phosphorylated IR-beta at Tyr1631amp;1345, not Tyr972. Renal expression of insulin receptor beta was located in mouse renal glomeruli and tubules and co-localized with the apical membrane with NCC in the distal convoluted tubules in cortex and NKCC2 in the thick ascending limbs of loop of Henle in the outer medulla.D4R and IR-beta were co-immunoprecipitated in immortalized mouse renal distal convoluted tubule cells and the co-immunoprecipitation was increased by D4R agonist and not altered by D4R antagonist.

Our results suggest that D4R may play an important role in the insulin resistance via interactions with IR-beta in kidney.