Platelet Reprogramming During Inflammation

Inflammation and sepsis are characterized by dysregulated host responses that span hemostatic, inflammatory, and immune continuums. Thrombosis is a common complication of sepsis, contributing to adverse outcomes including organ failure and death. The significance of these dysregulated host responses is demonstrated by studies suggesting half of all hospital deaths, including Veterans, may be attributed to sepsis. Sepsis also increases the long-term risk of cardiovascular disease and stroke, and causes substantial morbidity among Veteran patients. Established and emerging evidence supports the concept that dysregulated platelet responses mediate thrombotic events during inflammation, including sepsis. Nevertheless, the molecular mechanisms and functional consequences of dysregulated platelet functions during sepsis remain incompletely understood. Our proposal, entitled “Platelet Reprograming During Inflammation” will identify new pathways by which interferon alpha (IFN), which is systemically increased during sepsis, regulates the loading, trafficking, and secretion of cargo proteins in platelets and their parent cell, megakaryocytes (MKs). We have identified that the expression of interferon-induced transmembrane protein 3 (IFITM3) is robustly induced in platelets and MKs during inflammatory stress. Our preliminary data also suggest that increased IFITM3 in platelets regulates the secretion of cargo proteins to promote a thrombo-inflammatory milieu. In this proposal, we will perform complementary clinical, ex vivo, and in vivo studies to determine how IFITM3 governs cargo loading, trafficking, and secretion in platelets and MKs during inflammation. In specific aim 1, we will determine whether or not IFITM3 regulates cargo granule secretion during inflammation and identify proteins that IFITM3 interacts with. We will also examine the effects of a naturally-occurring, loss of function mutation in IFITM3 on secretion. In specific aim 2, we will use complementary pharmacologic and genetic toolsets to determine if IFITM3 regulates cargo loading and trafficking in platelet granules during inflammation. In specific aim 3, we will establish how IFITM3 participates in inflammatory and thrombotic host responses during sepsis. These studies are innovative as IFITM3 has not previously been identified as a regulator of cargo movement within platelets and MKs, or any other cell for that matter. Regulated cargo movement is critical for proper cell functions and disrupted cargo movement contributes to inflammation and thrombosis in many diseases. This work will therefore test an important functional hypothesis and elucidate completely new pathophysiologic mechanisms of thrombosis during inflammation and sepsis. This proposal will help us understand how interferons contribute to sepsis-associated thrombosis (a disease affecting thousands of Veterans each year), and may elucidate new therapeutic avenues to prevent these thrombotic complications. Discoveries made may also help us understand the basis for thrombosis that occurs in other thrombo-inflammatory diseases affecting Veterans (e.g., cancer, cardiovascular disease, others). Findings generated from our studies will also likely have relevance across other cell types, as IFITM3 is ubiquitously expressed and regulated cargo movement is critical for the function of most human cells.