Phenylbutyric Acid Rescues Endoplasmic Reticulum Stress-Induced Suppression of APP Proteolysis and Prevents Apoptosis in Neuronal Cells
Figure 9
Amyloid biogenesis (Aβ40 and Aβ42) is unaffected by the PBA mediated stimulation in AICD production.
The NAG cells were treated with titrated values of PBA (0, 0.5, 1.5, and 5 mM). A two-part assay measured γ-secretase dependent AICD production (A and B) and secreted amyloid biogenesis (C and D) from the same samples. The Gal4-reporter assays were performed with the cell lysate, while the media was assayed for species specific amyloid concentrations. PBA stimulated γ-secretase mediated proteolysis approximately ten-fold (A and B) in parallel assays to the ELISA measures for Aβ40 (C) and Aβ42 (D). Each concentration step in the PBA titration induced a statistically significant increase in Gal4-reporter activity ([PBA] shift: 0 to 0.5 mM, p<0.0003; 0.5 mM to 1.5 mM, p<0.0002; 1.5 mM to 5 mM, p<0.0001; analysis performed with the values in (A)). In contrast, there was no statistically significant change in either Aβ40 or Aβ42 levels. Aβ40 levels increased slightly from 142 picograms/ml to 188 picograms/ml, with a p-value of 0.09. In contrast, Aβ42 levels decreased from 35.6 picograms/ml to 22.7 picograms/ml, with a p-value of 0.06. In total, Aβ40 levels increased by 32.3 percent and Aβ42 levels decreased 36.05 percent—neither change reaching statistical significance. Each assay was performed in triplicate. The standard curves for Aβ40 and Aβ42 were linear in the tested concentration range with R2>0.96. Consequently, PBA stimulation of APP proteolysis occurs in a non-amyloidogenic manner.