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Abstract: TH-PO804

Complement Activation Causes Major Metabolic and Energetic Changes on Endothelial Cells

Session Information

Category: Genetic Diseases of the Kidneys

  • 1002 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Riedl Khursigara, Magdalena, The Hospital for Sick Children, Toronto, Ontario, Canada
  • Bruno, Valentina, Santobono-Pausilipon Children's Hospital, Naples, Italy
  • Licht, Christoph, The Hospital for Sick Children, Toronto, Ontario, Canada
  • Ortiz, Carolina, The Hospital for Sick Children, Toronto, Ontario, Canada
Background

Complement dysregulation and formation of the membrane attack complex (MAC, C5b-9) on vascular endothelial cells (ECs) cause EC injury and can lead to thrombotic microangiopathy (TMA). Effects of chronic complement exposure on cellular level are not well established. Here, we especially focused on metabolic and energetic changes as previous data indicated that C5b-9 formation on the surfaces of ECs did not result in cellular necrosis or apoptosis.

Methods

Human blood outgrowth endothelial cells (BOECs) derived from healthy donors were sensitized with an anti-CD59 antibody. Complement activation was initiated by adding normal human serum. Microscopy, luminescence, flow cytometry and western blot were used to measure intracellular calcium, ATP, mitochondrial membrane potential as well as autophagy pathways, respectively.

Results

BOECs exposed to complement showed cell surface C5b-9 deposition followed by an abrupt rise in intracellular Ca2+ that was sustained over 6 hours. Under complement stress, cell motility was impaired, which resulted in defective wound healing. We suggested a defect in endothelial cell energy homeostasis as likely cause for the observed functional defects. Indeed, complement activation caused a sustained drop in intracellular ATP levels and mitochondrial membrane potential. These effects were reversible following discontinuation of complement stress (i.e., removal of serum or blockage of complement activation via C5-depleted or heat inactivated serum), indicating that ECs were still viable. Thus we hypothesized that ECs are able to switch on a survival machinery. In keeping with this we found upregulation of autophagy, as indicated by the degradation of the markers LC3 and p62.

Conclusion

In summary, chronic complement activation leads to an EC energy deficit. BOECs activate a survival machinery to sustain complement attack, including the re-sealing of the plasma membrane and the activation of autophagy. All cellular effects were reversible, implying a window of opportunity for treatment initiation and recovery of endothelial cell function.