Abstract: Sepsis is a life-threatening condition caused by an uncontrolled host response to infection and is a leading cause of death in intensive care units. Liver dysfunction contributes significantly to the morbidity and mortality associated with sepsis. Liver sinusoidal endothelial cells (LSECs) play a critical role in hepatic immune and metabolic functions, but their specific role in bacterial infection and sepsis remains poorly understood. Our study focused on HSPA12B, a member of the HSP70 family, shows distinct expression in liver sinusoidal endothelial cells (LSECs), being prominent in periportal LSECs and reduced in midzonal LSECs. Interestingly, mice lacking endothelial cell HSPA12B (eHSPA12B-/-) exhibit disrupted hepatic Kupffer zonation and impaired hepatic gluconeogenesis even under normal conditions. Furthermore, we induced sepsis in these mice and observed severe LSEC capillarization, along with increased bacterial load and lactate accumulation compared to WT septic mice. These findings highlight the importance of eHSPA12B in maintaining LSEC phenotype and as well as hepatic immune and metabolic function during sepsis. Further investigations revealed that eHSPA12B is necessary for GATA4 nuclear translocation in LSECs. Endothelial cell-specific GATA4 deficiency resulted in an abnormal LSEC phenotype, impaired Kupffer cell zonation, and dysfunction of hepatic gluconeogenesis. These data suggest a cooperative role of eGATA4 and HSPA12B in maintaining the specialized phenotype and function of LSECs. Patients with NASH/cirrhosis are more susceptible to bacterial infections and sepsis. Our study found decreased HSPA12B expression and impaired GATA4 transcriptional activity in LSECs of NASH/cirrhosis patients, suggesting their contribution to NASH/cirrhosis associated hepatic immune and metabolic dysfunction and increased susceptibility to bacterial infections. Based on our novel findings, we hypothesize that eHSPA12B serves as a novel co-transcriptional factor of GATA4 to maintain the unique phenotype and function of LSECs, and that functional LSECs play a crucial role in maintaining Kupffer cell zonation, enhancing bacterial clearance, and regulating hepatic gluconeogenesis during bacterial infections and sepsis. To critically evaluate this hypothesis, we propose the following aims. Aim 1. Investigate how HSPA12B and GATA4 cooperatively regulate LSEC phenotype and function during sepsis. Aim 2. Define the mechanisms by which LSECs regulate hepatic Kupffer cell zonation and bacterial clearance during sepsis. Aim3. Investigate the mechanisms by which LSECs regulate hepatic gluconeogenesis. Successful completion of these studies will provide novel insights into the novel role of LSEC in regulating hepatic immune and metabolic function. These findings could be an important foundation for the development of innovative therapeutic approaches to enhance hepatic hepatic immune and metabolic function, leading to improved outcomes in patien...