PROJECT SUMMARY Obesity is a serious health concern in the United States, affecting 41.9% of the population and resulting in an estimated annual medical cost of nearly $179 billion. Notably, obesity increases the risk of cardiovascular diseases due to inflammation and thrombotic events. Individuals with obesity often exhibit hyper-reactive platelets and reduced sensitivity to anti-platelet therapy, yet the mechanisms driving these altered platelet phenotypes remain poorly understood, representing a significant knowledge gap in platelet biology. Our preliminary data reveal that platelets from obese mice exhibit an altered lipidome that corresponds with enhanced reactivity. Further, we previously demonstrated that platelet-generating cells, megakaryocytes (MKs), can effectively incorporate fatty acids into their membrane, both in vivo and in vitro. However, it is unknown if and how this uptake directly translates into alterations in platelet membrane composition in disease. As such, our central hypothesis is that the hyper-reactive platelet phenotype observed in obesity arises from the increased incorporation of dietary saturated fatty acids (SFAs) into platelet membranes, leading to a higher membrane lipid saturation that in turn enhances receptor accumulation within lipid rafts, ultimately augmenting platelet reactivity. To test this hypothesis, Aim 1 will unravel how fatty acid uptake influences platelet membrane composition. Through in vitro experiments and in vivo studies utilizing high-fat diets with varying SFA concentrations, I aim to determine whether platelets acquire fatty acids from both MKs and the plasma. Aim 2 will test the influence of dietary SFAs on platelet reactivity and thrombus formation. By conducting in vivo studies with escalating SFA content in diets, I will establish a direct link between dietary factors and altered platelet phenotypes. Aim 3 will investigate whether dietary SFA-induced platelet hyper-reactivity is caused by changes in lipid raft content and subsequent receptor signaling. My investigations will include characterizing lipid raft density and receptor content, as well as analyzing the effects on downstream signaling both in vitro and in vivo. Overall, this proposal aims to uncover the precise mechanisms by which dietary SFAs are integrated into platelet membranes and how this integration influences platelet function. The main aims of this proposal are the identification of new avenues for pharmacological interventions targeting lipid receptors in platelets or of novel dietary modifications for obese individuals, ultimately contributing to a better management of obesity-related cardiovascular complications.