Roles of Endothelial Cell Heat Shock Protein A12B and β-glucan, a reagent for trained Immunity in the Regulation of Inflammation in Sepsis

Sepsis is dysregulated host immune response to infection causing life-threatening organ dysfunction. Endothelial cell dysfunction and uncontrolled inflammatory responses are two contributors for sepsis-induced mortality. The crosstalk between endothelial and immune cells plays a critical role in the pathophysiology of sepsis. Therefore, understanding the mechanism of interaction between endothelial and immune cells will provide novel information to develop therapeutic strategies for sepsis. Pathogen associated moleculear patterns (PAMPs) and/or damage associated molecular patterns (DAMPs) produced during sepsis, activate endothelial cells to increase the expression of adhesion molecules, attracting immune cell infiltration into the tissues. Uncontrolled inflammatory responses during the early phase of sepsis contribute to organ failure and lethality. Over 100 clinical trials, targeting inflammatory responses in sepsis, have failed in the past three decades. Thereby, developing novel therapeutic strategies for sepsis are urgent. Heat shock protein A12B (HSPA12B), as one member of HSP70 family, predominately expressed in the endothelial cells, plays important roles in many pathophysiological processes. Currently, we observed endothelial cell specific HSPA12B deficiency (HSPA12B-/-) exacerbates mortality in sepsis induced by cecal ligation puncture (CLP). HSPA12B-/- septic mice exhibits increased expressions of adhesion molecule and infiltrated macrophages in the myocardium and activated macrophages in the peritoneal cavity. In vitro studies show that HSPA12B could be secreted from endothelial cells via exosome. HSPA12B carried by exosomes can be uptaken by macrophages to downregulate macrophage NF-kB activation and pro-inflammatory cytokine production. Trained immunity, induced by β-glucan, causes immune memory in innate immune cells, with an altered response towards another challenge. We have found that mice received β-glucan seven days before CLP sepsis exhibit attenuated mortality with decreased pro-inflammatory responses. We found that β-glucan significantly increased the levels of HSPA12B in endothelial cells and endothelial exosomes. β-glucan induced endothelial exosomes markedly suppress macrophage NF-kB activation and pro-inflammatory responses. The current data suggests that HSPA12B plays a novel role in the regulation of immune and inflammatory responses and that HSPA12B could be an important mediator for the crosstalk between endothelial cells and macrophages during sepsis. β-glucan regulates endothelial cell functions and immune/inflammatory responses, thus improving survival outcome in CLP sepsis