Purpose: Arrhythmia is often found a complication of diabetes, which takes major responsibility of malignant ventricular arrhythmias and even sudden cardiac death (SCD) in patients with diabetic cardiomyopathy (DbCM). In our previous study, rats model of DbCM was established and verified by occurrence of diabetes and impaired cardiac function. Increased incidence of ventricular arrhythmia was observed in these rats, which was accompanied by intensified endoplasmic reticulum stress (ERS) in cardiac tissue. ERS was suggested related with calcium homeostasis, whose fluctuation may further induce arrhythmia by initiating cellular electrophysiological changes. Though previous results indicated ERS might play a role in ventricular arrhythmia in DbCM, much further investigations are still need to explore the mechanisms. This current study was aimed to preliminarily reveal the possible molecular regulators in this process.
Methods: DbCM rat model was induced by intraperitoneal injection of streptozotocin and testified by cardiac function determination. Occurrence of ventricular arrhythmia was observed after rats received 4-PBA administration. After isolated from hearts of neonatal rats, myocytes were treated by siRNA to knockdown the expressions of three transducers of ERS, namely protein kinase RNA-like ER kinase (PERK), inositol- requiring enzyme-1 (IRE1) and activating transcription factor-6 (ATF6) respectively. Myocytes were then treated by high- glucose incubation, and cytoplasmic calcium uptake and release were evaluated by Fura2-AM staining under a fluorescence microscope. Enzymatic activity of calcineurin and unclear translocation of nuclear factor of activated T cells c1 (NFATc1) were also examined in myocytes.
Results: 1. After treated by 4-PBA, an ERS specific inhibitor, the occurrence of ventricular arrhythmia was decreased significantly in DbCM rats. 2. 4-PBA treatment decreased both cytoplasmic calcium uptake and ER calcium release in high- glucose incubated myocytes. 3. PERK knockdown stabilized calcium dynamics rather than IRE-1 or ATF-6 knockdown in high- glucose incubated myocytes. 4. Both calcineurin activity and NFATc1 tanslocation were increased by inhibited by PERK knockdown myocytes in high- glucose incubated myocytes.
Conclusions: 1. ERS induces ventricular arrhythmia in DbCM, probably via affecting calcium dynamics in myocytes; 2. PERK/calcinerin/NFAT signaling pathway may act an important role in introducing fluctuation of calcium homeostasis in DbCM.