Platelet-MLKL role in S100 Release with Age and Infection

Project Summary Advanced age is a single risk factor for developing serious complications from infections with respiratory viruses such as influenza, SARS-CoV-2 or RSV. These complications are reflected in thrombotic outcomes including microthrombosis, myocardial infarction and pulmonary embolism. The actual cause and mechanisms of these thrombotic outcomes remains elusive. Pathogen spreading and crossover of these viruses into the circulation is regulated by various mechanisms, some of which involve lytic programmed cell death pathways such as necroptosis executed by membrane channels formed by oligomerized phosho-Mixed Lineage Kinase Domain Like Pseudokinase (MLKL). Platelets express MLKL, have a plethora of immune-sensing viral receptors and are the major blood component responsible for thrombotic outcomes. We have shown that respiratory viral RNA can be found in circulating platelets from influenza patients and preliminary result support channel formation. In this proposal, we hypothesize that platelet-pMLKL channel formation, mediated by influenza, leads to cytoplasmic S100 content release and contributes to immunothrombosis with age. We propose to test this hypothesis with the following aims: 1. Determine the MLKL-specific platelet content release and whether platelets undergo necroptosis as a result of influenza and (or) age, and 2. Determine the contribution of age to MLKL-activation and immunothrombotic aggregates during infection. The proposed studies are central to elucidating mechanisms that may increase immunothrombotic risk and adverse cardiovascular outcomes beyond classical platelet activation, with advanced age, and provide a basis for novel and targeted treatments for prevention.