June 2023
Volume 64, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2023
Oxidative stress tips the balance in favor of anaphylatoxin C5a receptor signaling triggering excessive mitochondrial fission instead of fusion in RPE cells.
Author Affiliations & Notes
  • Baerbel Rohrer
    Ophthalmology, Medical University of South Carolina, Charleston, South Carolina, United States
    Division of Research, Ralph H. Johnson VA Medical Center, Charleston, South Carolina, United States
  • Masaaki Ishii
    Ophthalmology, Medical University of South Carolina, Charleston, South Carolina, United States
  • Footnotes
    Commercial Relationships   Baerbel Rohrer Kriya TX, Iveric, Character Bio, Code C (Consultant/Contractor), MitoChem, Code O (Owner), Q32 Bio, Xequel Bio, Kriya TX, MitoChemiya , Code P (Patent); Masaaki Ishii None
  • Footnotes
    Support  This work was supported by the National Institutes of Health (EY030072), the Department of Veterans Affairs (IK6BX004858), and The SC SmartState Endowment.
Investigative Ophthalmology & Visual Science June 2023, Vol.64, 4453. doi:
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    • Get Citation

      Baerbel Rohrer, Masaaki Ishii; Oxidative stress tips the balance in favor of anaphylatoxin C5a receptor signaling triggering excessive mitochondrial fission instead of fusion in RPE cells.. Invest. Ophthalmol. Vis. Sci. 2023;64(8):4453.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Complement component C5 fragment C5a is an anaphylatoxin involved in promoting cellular responses important in immune response and host defense. Its receptor (C5a receptor, C5aR) is distributed on the plasma membrane; however, intracellular localization in immune cells has been reported. We have previously shown that C5a stimulation in ARPE-19 cells resulted in increases in free cytosolic Ca2+, which was driven by ryanodine-receptor-dependent activation of L-type channels in addition to maxi-K and TRP channels. C5aR signals through Gα units and activates PI3 kinase and Akt; and inhibitors to both reduced the C5a-evoked Ca2+ rises. Phospho-Akt is known to activate GSK-3β, which, via modulation of mitochondrial fission/fusion proteins, leads to mitochondrial fusion. Finally, oxidative stress increases intracellular reactive oxygen species (ROS), and ROS activate complement signaling.

Methods : Mitochondrial dynamics in ARPE-19 cells is analyzed using high resolution live-cell imaging, protein levels are followed up by Western blotting.

Results : C5a treatment induced mitochondrial fusion, independent of intracellular ROS. C5aR activation resulted in GSK-3β phosphorylation, increased mitochondrial fusion proteins Mitofusin-1, -2 and OPA1, and enhanced OPA1 cleavage required for mitochondrial fusion. Interestingly, C5aR activation increased mitochondrial-ER contacts. While oxidative stress increased mitochondrial fission, C5a-receptor activation mediated fusion sensitizes mitochondrial network to exogenous ROS, resulting in excessive fission, followed by increased cell death.

Conclusions : Our findings combine three observations in AMD, complement activation, oxidative stress and mitochondrial dysfunction, results which will have important implications in our understanding on the balance of complement signaling in controlling cellular health and dysfunction.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

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