Figure 4. Physiologically relevant levels of oxidative stress inactivate the proteasome in ARPE-19 cells.

Panel A: ARPE-19 cells were exposed to a continuously generated H₂O₂ for 4 hours. Panel B: The ARPE-19 cells were exposed to blue light alone, accumulated A2E alone, or accumulated A2E and exposed to blue light as indicated in Fig. 1. The cells were harvested and proteasome activities were determined using fluorogenic peptides as substrates, Panel C. ARPE-19 cells were exposed to a continuously generated H₂O₂ for 4 and 8 hours, respectively. Cell viability was determined with MTS assay using the kits from Promega. The proteasome activity and viability of the cells that were not treated with H₂O₂ were arbitrarily defied as 100% and the rest were expressed as a relative activities normalized with controls.