Mechanisms of cardiomyocyte dysfunction in pediatric septic shock

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PROJECT SUMMARY / ABSTRACT Title: Mechanisms of cardiomyocyte dysfunction in pediatric septic shock Despite decades of research in pediatric sepsis, mortality remains at approximately 25% for children with septic shock. Sepsis-associated myocardial dysfunction (SAMD) is common in children and has an association with mortality that is not simply a reflection of the severity of illness. As no disease-modifying therapies exist for SAMD, there is a critical need to understand the biologic basis of cardiomyocyte dysfunction in sepsis. Furthermore, there is a need for novel human modeling with patient-derived materials given the failure to translate molecular discoveries in murine models of sepsis to improvements in human organ injury. Our objectives are to establish human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) as a model for cardiomyocyte dysfunction in pediatric sepsis and to examine the roles of host genetic background and serum factors in the pathogenesis of SAMD. We have built upon our large, established biobank of serum from children with sepsis to study the cardiomyocyte response to septic serum banked from children who did and who did not have SAMD. We have found that the contractility of hiPSC-CMs is depressed by serum banked from children with SAMD but not by control septic serum from children without SAMD. This depressant effect was reversible after removal of the serum, suggesting this was not reflective of cell death. Furthermore, we identified a significant association of interleukin-8 (IL-8) with SAMD in children with septic shock and found that recombinant human IL-8 depresses hiPSC-CM contractility. Our proposal will address three important questions as specific aims: First, we will determine whether hiPSC-CMs and cardiomyocytes derived from the same children share common functional and transcriptional patterns of responses when exposed to banked septic serum. We will provide a comprehensive comparison of hiPSC-CMs to ex vivo cardiomyocytes by isolating cardiomyocytes from discarded surgical tissue from children undergoing cardiac surgery and by generating hiPSC-CMs from these same patients. Second, we will determine the degree to which host genetic background contributes to cardiomyocyte dysfunction in SAMD. We will develop hiPSC- CMs from pediatric patients with and without SAMD to determine responses to septic serum to identify patterns of functional and transcriptional responses associated with susceptibility to SAMD. Third, we will dissect the role of IL-8 signaling in cardiomyocyte dysfunction in sepsis. We will employ a combination of IL-8 modulation in serum and IL-8 receptor (CXCR1 and CXCR2) knockouts in hiPSC-CMs, providing evidence for IL-8 blockade as a potential therapeutic target in SAMD. This career development proposal will build on my background in translational research in myocardial dysfunction to gain new expertise in cardiomyocyte functional analysis, hiPSC generation and differentiation, and next-generation RNA sequencing technology to facilitate my transition to independence as a physician-scientist focused on elucidating and targeting mechanisms of pediatric SAMD.