Defining vaso-occlusion and approaches for its reversal

Abstract

Sickle Cell Anemia (SCA) is an inherited disease caused by the production of abnormal hemoglobin(Hb)S, whose deoxygenation-induced polymerization results in Red Blood Cell (RBC) sickling and numerous pathophysiological consequences. Sickle Cell Disease (SCD) affects approximately 300 000 newborns worldwide each year and is associated with acute and chronic complications, including frequent painful Vaso-Occlusive Episodes (VOE) that often require hospitalization. At this time, there exists no clinical approach for the treatment of VOE in SCD, other than pain management and rehydration. Vaso-Occlusive (VO) processes in SCD are the result of vascular inflammatory mechanisms that involve pancellular activation and the recruitment and adhesion of leukocytes and RBC to the endothelium of blood vessels, obstructing blood flow. Interactions between circulating platelets, neutrophils, and erythrocytes with the vascular endothelium, are thought to initiate the VO process, but the specific triggers in the initiation and propagation of vaso-occlusion are not well understood. In the clinical setting, VOE, are often seen to be prompted by infections (viral or bacterial), hemolysis, changes in temperature, physical exertion or other epigenetic factors. In mice models of SCD, VO-like processes can be triggered by a potent inflammatory stimuli (TNF cytokine or lipopolysaccharide [LPS] administration) and hypoxia-reperfusion. The aim of this study is to characterize whether different VO stimuli provoke similar or distinct mechanisms of cellular and inflammatory interactions in the vasculature. Having established whether mechanisms resulting in VO differ, or not, we aim to determine whether different pharmacological approaches may be necessary to revert different types of VO processes, once initiated. In vivo and ex vivo approaches will be used to determine whether different stimuli (TNF cytokine, LPS, recombinant PB1-F2 protein, hypoxia/reperfusion, hemolysis, dehydration, cold) trigger different types of activation and recruitment cellular and the predominant cell types involved. Intravital microscopy (conventional and confocal) will be used to study VO processes in vivo, while dynamic adhesion fluidic techniques will be used to study specific cellular and molecular interactions of blood cells treated ex vivo with varying stimuli. Based on these findings, we plan to identify whether drugs that modify the activation, function and interactions of different cell types (red cells, leukocyte, platelets, endothelium) may provide more efficient approaches to reversing SCD VO, depending on the inflammatory trigger. (AU)