The coagulopathy and vasculopathy of sepsis remain common disabling and life-threatening complications of infection that are increasing in incidence as human populations escalate with the prevalence and virulence of infectious organisms. Lack of sufficient knowledge of the pathophysiology of sepsis is represented by the paucity and ineffectiveness of current treatments. We have recently made discoveries that reveal a novel interaction between the host and pathogen in pneumococcal sepsis during which host glycoproteins in the blood and vasculature undergo a post-translational remodeling that alters their homeostasis and function. This remodeling results in asialoglycoproteins deficient in sialic acid linkages that are then selectively recognized by the endocytic Ashwell-Morell receptor (AMR). Asialoglycoproteins are formed by neuraminidases that hydrolyze sialic acid linkages or by a deficiency of one or more sialyltransferases. Asialoglycoprotein modulation by the AMR results in a profound mitigation of coagulopathy, vasculopathy, and mortality in pneumococcal sepsis. The present application represents an expanded investigation of the role of glycoprotein remodeling in the pathogenesis of coagulopathy and endothelial dysfunction during sepsis. The project takes continued advantage of a unique synergistic and productive interdisciplinary integration of glycobiology, molecular and cell biology with microbiology, immunology and infectious disease modeling that has to date produced unexpected and paradigm changing observations -- ones that carry strong translational implications for novel therapeutics. Glycoprotein remodeling will be modulated genetically in the mouse by targeting the biochemical pathways responsible for biologically important modifications involving terminal sialylation (host sialyltransferases ST3Gal-I and ST3Gal-IV) and by modulating the rapid and powerful asialoglycoprotein clearance function of the hepatic AMR - as we have recently published. From the microbiology perspective, we will expand our studies beyond our published work on Streptococcus pneumoniae (SPN) to include two other major human pathogens associated with invasive bloodstream infections and sepsis, Staphylococcus aureus (SA) and group A Streptococcus (GAS). Additional mechanistic insight will be provided through analysis of virulence factors express by these bacteria that provoke pathogenic coagulation and microvascular dysfunction (coagulases, M protein), including the use of isogenic bacterial mutants. Human tissue culture studies will explore the effects of glycoprotein remodeling on interactions between bacterial sepsis pathogens, coagulation proteins, neutrophils and endothelium. In vivo live infection models with wild-type and genetically engineered mice will guide therapeutic manipulation of glycoprotein remodeling, to identify tools to improve coagulation parameters, endothelial function, bacterial clearance and clinical outcomes in sepsis.
Sepsis is a major cause of human suffering and death, afflicting a million or more people in the U.S. each year. Death as an outcome averages 30%, underscoring our incomplete knowledge of pathogen-host interactions and the absence of more effective therapeutics. This proposal seeks to transform our understanding and treatment of sepsis by research focused on a newly discovered mechanism of pathogen-host interaction and a related possible new treatment that targets the coagulopathy and vasculopathy of this deadly syndrome.
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