Mouse proximal tubular epithelial cell studies. A: Increased intensity of cathepsin D and Lamp1 (lysosomal membrane marker) immunofluorescent staining is seen with 100 μg/mL and 200 μg/mL AGE-BSA compared with 5 mmol/L glucose, 25 mmol/L glucose, 100 μg/mL ctr-BSA, and 200 μg/mL ctr-BSA. Magnification ×40. B: Cathepsin D enzyme activity (measured in RFU) is increased with exposure to AGE-BSA compared with ctr-BSA. C and E: In the setting of 100 μg/mL AGE-BSA exposure, IL-1 and KIM-1 concentrations are significantly elevated in the media of MCT transfected with cathepsin D small interfering RNA (CatD-siRNA) compared with cells transfected with control small interfering RNA (ctr-siRNA). IL-1 was additionally significantly elevated with CatD-siRNA compared with ctr-siRNA in the setting of 100 μg/mL ctr-BSA exposure. D: The concentration of IL-6 is increased in the media of cells (AGE-BSA-MCT) transfected with CatD-siRNA vs. ctr-siRNA, though this difference does not meet statistical significance. Concentrations of 5.5 mmol/L glucose, 100 μg/mL AGE-BSA, and 100 μg/mL ctr-BSA were used unless otherwise indicated. **P < 0.01; ***P < 0.001; ****P < 0.0001.