Platelet-monocyte interactions drive… (F31HL188849) – Project Grant to University Of Pittsburgh - Of…

Abstract: Traumatic injury is a leading global cause of morbidity and mortality. Improvements in trauma and critical care have increased the number of patients who survive the initial acute phase of injury (e.g., hemorrhage). As a result, more patients survive to experience the downstream sequelae of a dysfunctional immune response. The immune system is normally activated after injury to sterilize the wound bed and prepare for tissue healing and regeneration. After severe trauma, however, a massive efflux of damage-associated molecular patterns (damps) occurs as they are released from tissue damaged from injury and ischemia caused by vasoconstriction and severe blood loss. This massive damp release activates a hyperactive innate immune response and dampens the adaptive immune response. Between 40 and 60% of trauma patients experience organ failure, poor wound healing, long-term disability, and increased susceptibility to recurrent infections because of this dysfunction. There are currently no available therapies designed to attenuate or correct this immune response in patients. Platelets are also activated in response to injury and are largely recognized as important players in bleeding cessation. Recently, platelets have been acknowledged as important immune mediators, but their role in a dysfunctional immune response after trauma is inadequately characterized. Platelets express the receptor p- selectin upon activation, which is recognized by the constitutively expressed p-selectin glycoprotein ligand 1 (PSGL1) on leukocytes. Others have shown that platelets use this interaction to preferentially interact with monocytes to form monocyte-platelet aggregates (mpas). Direct interaction with platelets drives monocytes to mature into pro- or anti-inflammatory subtypes depending on the inflammatory milieu in which the interaction occurs. While mpas have been documented after traumatic injury, the specific mechanisms and consequences of their interactions in this setting remain unclear. This project hypothesizes that platelets interact with monocytes after severe injury to drive monocytes toward pro-inflammatory behavior that is associated with poor outcomes in patients and that exacerbates endothelial injury. In aim 1A of this project, the incidence of mpas and monocyte subtypes will be quantified in trauma patients and related to relevant clinical outcomes, such as mortality and incidence of organ failure. In aim 1B of this project, platelets will be traumatically activated in vitro and combined with monocytes. Monocyte surface receptor expression and cytokine secretion will be quantified to ascertain how traumatically altered platelets drive changes in monocyte behavior through direct interaction. Lastly, in aim 2, MPA secretomes will be incubated with endothelial cells to assess the effects of released soluble mediators on endothelial cell activation, injury, and barrier function. Successful completion of this project will identify novel mechanisms of platelet-driven immune dysfunction after injury, biomarkers for immune dysfunction after injury, and therapeutic targets to attenuate a dysfunctional post- trauma immune response.

Platelet-monocyte interactions drive thromboinflammation after severe traumatic injury

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