Activated Akt Is Associated with Hyperglycemia and Platelet Hyperactivity in a Mouse Model of Diabetes

Platelet hyperactivation has been reported in patients with both Type I and Type II diabetes mellitus and likely contributes to the increased prevalence of thrombotic complications in diabetic patients. However, the mechanisms leading to platelet hyperactivity in diabetes are not fully understood. Our previous studies showed that the Akt signaling pathway positively regulates platelet activity. Here, we evaluate the effect of hyperglycemia on Akt phosphorylation and platelet activation using a Type I diabetic mouse model. Hyperglycemia was induced by intraperitoneal injection of streptozotocin (STZ 50mg/kg for 5 days) in C57BL/6 mice. Blood glucose levels were elevated in 12 mice 4 weeks after STZ injection (mean ± SD: 410 ± 70 mg/ml) compared with 11 mice without STZ injection (212 ± 50 mg/ml). Platelets from hyperglycemic mice showed enhanced agonist-dependent aggregation (max % aggregation: 58% ± 10% in hyperglycemia versus 0% in normoglycemia at 0.6mM AYPGKF, n=3 each), fibrinogen binding (62.2% fibrinogen-bound cells ± 5.4% in hyperglycemic conditions versus 46.1% ± 16.3% in normoglycemia at 2mM AYPGKF) and P-selectin binding (42.1% cells with surface P-selectin ± 3.7% in hyperglycemic platelets, 25.3% ± 5.9% in normoglycemia at 2mM AYPGKF) compared with platelets from mice with normal glucose levels. The blood glucose levels were directly correlated with Alexafluor-fibrinogen binding (r=0.65, p=0.042) when platelets were stimulated with thrombin receptor agonist peptide AYPGKF (1.5mM), and also directly correlated with P-selectin surface exposure (r=0.95, p=0.003) after platelets were stimulated with 1.5mM AYPGKF. To determine whether the Akt pathway is involved in enhanced platelet activation in diabetes, we tested phosphorylation of Akt ser473 by immunoblotting. Akt phosphorylation of this residue was increased (35% ± 4%) in platelets from hyperglycemic mice compared with platelets from nondiabetic mice. In conclusion, platelets from hyperglycemic mice are more sensitive to PAR4 agonist-induced fibrinogen binding and P-selectin exposure compared with nondiabetic platelets. Enhanced activation of Akt in platelets under hyperglycemic conditions may play a role in platelet hyperactivation in diabetes.