AIM: We investigated the molecular mechanisms of hyperglycaemia-induced insulin resistance and type 2 diabetes in rats receiving a continuous glucose infusion (GI). METHODS: Female Wistar rats were infused with either 2.8 mol/L glucose or saline (2 mL/h) for durations varying from 0 to 15 days. Blood samples were analysed daily to determine glucose and insulin dynamics. Subsets of animals were sacrificed and soleus muscles were extracted for determination of protein expression, subcellular location, and activities of insulin-signalling proteins. RESULTS: Rats accommodated this systemic glucose oversupply and developed insulin resistance on day 5 (normoglycaemia/hyperinsulinaemia) and type 2 diabetes on day 15 (hyperglycaemia/normoinsulinaemia). The effect of GI on protein kinase Czeta (PKCzeta) activity was independent of changes in phosphatidylinositol 3-kinase activity, and occurred in parallel with an increase in PDK1 activity. Activated PKCzeta was mainly located in the cytosol after 5 days of GI that was coincident with the translocation of GLUT4 to the plasma membrane, and normoglycaemia. After 15 days of GI, PKCzeta translocated from the cytosol to the plasma membrane with a concomitant decrease in PDK1 activity. This caused an increase in the association between PKCzeta and PKB and a decrease in PDK1-PKB reactions at the plasma membrane, leading to reduced PKB activity. The activity of PKCzeta per se was also compromised. The PKCzeta and PKB activity reduction and the blunted insulin-stimulated GLUT4 translocation eventually led to hyperglycaemia and diabetes. CONCLUSION: Translocation of PKCzeta may play a central role in the development of type 2 diabetes. Copyright (c) 2009 John Wiley & Sons, Ltd.
AIM: We investigated the molecular mechanisms of hyperglycaemia-induced insulin resistance and type 2 diabetes in rats receiving a continuous glucose infusion (GI). METHODS: Female Wistar rats were infused with either 2.8 mol/L glucose or saline (2 mL/h) for durations varying from 0 to 15 days. Blood samples were analysed daily to determine glucose and insulin dynamics. Subsets of animals were sacrificed and soleus muscles were extracted for determination of protein expression, subcellular location, and activities of insulin-signalling proteins. RESULTS:Rats accommodated this systemic glucose oversupply and developed insulin resistance on day 5 (normoglycaemia/hyperinsulinaemia) and type 2 diabetes on day 15 (hyperglycaemia/normoinsulinaemia). The effect of GI on protein kinase Czeta (PKCzeta) activity was independent of changes in phosphatidylinositol 3-kinase activity, and occurred in parallel with an increase in PDK1 activity. Activated PKCzeta was mainly located in the cytosol after 5 days of GI that was coincident with the translocation of GLUT4 to the plasma membrane, and normoglycaemia. After 15 days of GI, PKCzeta translocated from the cytosol to the plasma membrane with a concomitant decrease in PDK1 activity. This caused an increase in the association between PKCzeta and PKB and a decrease in PDK1-PKB reactions at the plasma membrane, leading to reduced PKB activity. The activity of PKCzeta per se was also compromised. The PKCzeta and PKB activity reduction and the blunted insulin-stimulated GLUT4 translocation eventually led to hyperglycaemia and diabetes. CONCLUSION: Translocation of PKCzeta may play a central role in the development of type 2 diabetes. Copyright (c) 2009 John Wiley & Sons, Ltd.