NADPH is rate limiting in beta-cell ER stress response

Alex Bennett (1), Huntley Chang (1), Jonathan Rocheleau (1)

(1) Institute of Biomaterials and Biomedical Engineering, University of Toronto

Endoplasmic reticulum (ER) stress is triggered by protein misfolding and the inability to accommodate protein refolding. ER stress has been implicated in numerous diseases including Alzheimer’s, Parkinson’s and Type 2 Diabetes (T2D). If ER stress is not remediated by proper protein refolding, then the cell will trigger apoptosis. A new homoFRET ER stress sensor, Apollo-IRE1, has been developed to investigate the beta-cells ER stress response. By utilizing the inherent up regulation of IRE1 during ER stress, Apollo-IRE1 can monitor ER stress by dimerizing when misfolded proteins bind to it. In the same Apollo sensor suite, Apollo-NADPH was created to monitor NADPH levels in different cellular compartments. Apollo-IRE1 and Apollo-NAPDH have been used in tandem to track fluctuating NADPH levels during ER stress in INS1e beta-cells. The results show that cytoplasmic NADPH is depleted during ER stress, suggesting NADPH may be rate limiting in the beta-cell ER stress response. Increased NADPH levels during ER stress then would be a potential therapeutic technique to increase beta-cell function in T2D patients.