Abstract 15050: UPR In Endoplasmic Reticulum vs. UPR In Mitochondria In Diabetic Myocardium: Which Is Responsible For Deficient Regulation Of Mitochondrial Permeability Transition Pores?
Background Unfolded protein response (UPR) in the endoplasmic reticulum (ER) has been suggested to be involved in myocardial dysfunction. However, UPR has been reported also for mitochondria, which cross-talk with ER. Here, we examined the relationships between ER UPR, mitochondrial UPR, and threshold for opening of the mitochondrial permeability transition pore (mPTP) in the diabetic myocardium.
Methods Markers of UPR and heat shock proteins (HSPs) in the myocardium were determined by immunoblotting in a model of type 2 diabetes (T2DM), Goto-Kakizaki rats (GK), and its non-diabetic control (Wistar). Separate groups of rats were treated with 4-phenylbutyric acid (4PBA), a chemical chaperone, for 1 week. Myocardial infarction was induced by 20-min coronary occlusion/2-hr reperfusion in vivo. As an index of threshold for mPTP opening, calcium retention capacity (CRC) in isolated mitochondria was determined.
Results GRP78 and GRP94, HSP70, and heat shock factors 1 and 2 in the cytosol were slightly increased in GK compared with those in Wistar, and CHOP level was significantly elevated by 180% in GK. Mitochondrial HSP60 level was higher by 75% in GK, but levels of GRP75 (mitochondrial HSP), putative regulatory subunits of mPTPs (adenine nucleotide translocase, inorganic phosphate carrier, VDAC1, cyclophilin D, hexokinase II) and mitochondrial GSK-3β were similar in GK and Wistar. CRC (μM/mg) tended to be lower before and after ischemia/reperfusion (I/R) in GK than in Wistar (460±18 vs. 478±23 before I/R and 255±23 vs. 336±37 after I/R). Activation of PI3K-Akt-GSK-3β signaling by erythropoietin (EPO) increased CRC after I/R in Wistar (450±31) but not in GK (271±25). Infarct size was limited by EPO in Wistar but not in GK. Treatment with 4PBA (40 mg/kg) did not significantly reduce CHOP but normalized HSP60 level in mitochondria and restored the protective effects of EPO both on CRC (371±25) and on infarct size (34.5±3.1% vs. 50.9±2.9%) in GK.
Conclusion Defect in mPTP regulation by PI3K-Akt-GSK-3β signaling is associated with up-regulation of both ER UPR markers and a mitochondrial matrix chaperone (HSP60) in GK. The results of 4PBA experiments support the notion that mitochondrial UPR is primarily responsible for dysregulation of mPTP in diabetic hearts.
- © 2011 by American Heart Association, Inc.