Investigating the function of RBC-TLR7 in Sepsis

/Abstract: Sepsis, the dysregulated host response to infection, is a leading cause of death in the United States and accounts for one-fifth of all deaths globally. A comprehensive mechanistic understanding of the host response during sepsis is imperative because the aberrant host response rather than the pathogen itself drives organ failure and mortality. One fundamental and critical knowledge gap is an understanding of how circulating red blood cells (RBCs) contribute to the abnormal immune response. This project aims to deepen our understanding of the host response in sepsis by focusing on the role of RBCs in regulating the inflammatory response to nucleic acids. This study investigates the hypothesis that RBCs, through the expression of Toll-Like Receptor 7 (TLR7), actively participate in immune responses during sepsis by regulating host derived RNA. Our preliminary data indicate that both human and murine RBCs express TLR7 and can bind single-stranded RNA through TLR7, that host derived RNA is increased on RBCs during sepsis, and that RBCs act as a trap for cell- free RNA, dampening the immune response. Based on these findings, we propose the following aims using human RBC samples from critically ill patients with sepsis, synthetic RNAs, and erythroid-specific genetically deficient mice. In specific aim 1, we will establish the subcellular localization of TLR7 in human RBCs and determine the RNA-sequestration capabilities of RBC-TLR7 during sepsis. RBC- TLR7 expression during sepsis will be compared with healthy subjects. Lastly, we will perform miRNA profiling and whole-genome sequencing of RNA associated with RBCs during sepsis. In aim 2, we will determine the role of RBC-TLR7 in delivering RNA to immune cells. In aim 3, we will employ novel erythroid tlr7 deficient mice to define the erythroid-specific functions of TLR7 in vivo using models of polymicrobial sepsis and reductionist models of TLR-induced inflammation. Knowledge derived from these studies will elucidate novel mechanisms of immune dysregulation in sepsis and serve as the foundation for studying RBC immune function, potentially bridging a significant gap in our current understanding of the host immune response. Project Number: 1R01HL177015-01 | Fiscal Year: 2025 | NIH Institute/Center: National Heart Lung and Blood Institute (NHLBI) | Principal Investigator: Nilam Mangalmurti | Institution: UNIVERSITY OF PENNSYLVANIA, PHILADELPHIA, PA | Award Amount: $392,660 | Activity Code: R01 | Study Section: Surgery, Anesthesiology and Trauma Study Section[SAT] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01HL17701501