Platelet Metabolism in Diabetes Mellitus

Project Summary/Abstract Heart disease and stroke are the No. 1 and 5 causes of deaths in the US. Type 1 Diabetes mellitus (T1DM) significantly increases the risk for heart attack and stroke. Intense glycemic control has been reported to reduce major cardiovascular events by >30%, suggesting that hyperglycemia is a major contributor to T1DM-associated risk elevation for heart attack and stroke. However, how T1DM and hyperglycemia exacerbates such risk is unclear. Platelets are vascular first-responders that activate for hemostasis upon blood vessel damage; whereas pathogenic platelet activation leads to spurious thrombosis and acute vascular obstruction. T1DM and hyperglycemia lead to platelet hyperactivity and increased propensity to form thrombi. This proposals aim to understand how hyperglycemia causes platelet hyperactivity and thrombosis in T1DM, and to develop new therapeutic strategies to reduce T1DM-associated risk for heart attack and stroke. Utilizing an integrated toolkit including state-of-the-art Stable Isotope Resolved Metabolomics (SIRM), we demonstrated critical role of altered platelet metabolism in thrombin-induced platelet activation. Specifically, thrombin stimulation altered metabolism centered around glycogenesis and glycogenolysis, pentose phosphate pathway (PPP), and fructose 1,6- bisphosphate (F1,6BP – a key glycolysis and gluconeogenesis intermediate), namely, “the glycogen-PPP- F1,6BP axis”, modulating energy, redox and calcium homeostasis in platelets and leading to their activation. Literature and our compelling preliminary data further revealed that hyperglycemia induced glycogen storage/mobilization that increase ATP production, PPP inhibition, reactive oxygen species, and intracellular calcium, all of which are consistent with increased propensity for platelets to activate. Therefore, our overarching hypothesis is that hyperglycemia changes the glycogen-PPP-F1,6BP axis in platelets to drive platelet hyperactivity thus thrombotic risk in T1DM. In Aim 1, we will delineate these hyperglycemia- induced changes in the glycogen-PPP-F1,6BP axis in both human and mouse platelets in vitro. In Aims 2 and 3, we will determine how modulation of this axis by pharmacological and genetic means suppresses hyperglycemia- induced hyperactivity in both human and mouse platelets in vitro (Aim 2) and reduces hyperglycemia- exacerbated thrombosis and stroke in a streptozotocin (STZ) T1DM mouse model (Aim 3). We are in a unique position to address our hypothesis with recognized expertise in metabolism and metabolomics (Qingjun Wang PhD and Matthew Gentry PhD), platelet biology (Sidney Whiteheart PhD), T1DM (Lisa Tannock MD), and stroke (Jill Roberts PhD and Justin Fraser MD), as well as strong partnership with the University of Kentucky Metabolomics, Redox Metabolism, and Rodent Surgery Cores. In the short term, we will have presented a novel mechanism for metabolic dysregulation of platelets to mediate hyperglycemia-induced platelet hyperactivity and aggravated thrombosis and stroke in T1DM and have identified new therapeutic targets for mitigating T1DM- and hyperglycemia-exacerbated major cardiovascular events. In the long term, these mechanistic insights and new targets may lead to new therapeutic strategies to reduce T1DM morbidity and mortality.