Circulating exomes induce tabular and glomerular alterations in sepsis-associated acute kidney injury

INTRODUCTION AND AIMS: The incidence of acute renal failure (ARF) has considerably increased over the last years. ARF is a frequent complications in critically ill patients admitted to intensive care units and it is associated to multiple organ failures and to a high rate of mortality. Sepsis and septic shock are the main causes of ARF in these compromised patients. The mechanisms of sepsis-induced tissue injury are related not only to the ischemic response to hypoperfusion, but also to a direct detrimental activity of circulating mediators. We have recently demonstrated that plasma derived from patients with sepsis-associated ARF induced functional alterations in tubular epithelial cells and glomerular podocytes in vitro. Exosomes are microparticles containing proteins and mRNAs released from different cell types and involved in cell-to-cell communication. Circulating platelet-derived exosomes from septic patients induced endothelial cell apoptosis and myocardial dysfunction. The aim of this study was to isolate and characterize exosomes present in plasma of patients with sepsis-related ARF and to evaluate their role in tubular and glomerular injury. METHODS: We enrolled in the study 10 patients with sepsis-accociated ARF. We collected exosomes from plasma of septic patients and by platelets of healthy donors activated by thrombin or LPS by serial ultracentrifugations. Exosomes were characterized by FACS analysis and for protein content. We then evaluated the mechanisms of exosome internalization and their effects ion tubular and glomerular cells (cytoxicity, apoptosis, cell polarity and permeability). RESULTS: The concentration of plasma exosomes was significantly higher in septic-ARF patients (19.25 mg/ml) than in healthy subjects (4.76 mg/ml). The enhancement of exosome production was due to the activation of leukocytes and platelets. Exosomes of septic patients express different integrins (alpha4, alpha6, beta-1, alphaVbeta3), CD44, HLA of class I and II, L-selectin and in particular Fas-Ligand and CD40-Ligand (CD154), molecules deeply involved in cell activation, inflammation and apoptosis. A similar pattern was found in exosomes derived from platelets activated by thrombin and LPS. Exosomes were internalized into tubular cells and podocytes inducing different biological activities. In particular, exosomes induced cytoxicity and apoptosis via caspase, Fas and CD40 pathway activation, altered cell polarity (trans-epithelial electrical resistance) and enhanced cell permeability. These results were not found after incubation of renal cells with exosomes derived from plasma of healthy subjects or produced by control cell types (fibroblasts). CONCLUSIONS: The results of this study show that exosomes circulating in plasma of septic patients or produced by activated platelets directly induce renal tubular and glomerular cell injury. Our data support the hypothesis of a crucial role of circulating exosomes in the pathogenesis of sepsis-associated ARF and underline the importance of the development of new therapeutic strategies aimed to their selective removal by blood purification techniques