LAUSR

The endoplasmic reticulum (ER) is responsible for protein synthesis and calcium storage. ER stress, reflected by protein unfolding and calcium handling abnormalities, has been studied as a pathogenetic factor in cardiovascular diseases. The aim of this study is to examine the effects of ER stress on mechanical and electrophysiological functions in the heart and explore the underlying molecular mechanisms. A total of 30 rats were randomly divided into control, ER stress induction (tunicamycin) and ER stress inhibition (4-phenylbutyric acid, 4-PBA) groups. ER stress induction led to significantly systolic and diastolic dysfunction as reflected by maximal increasing/decreasing rate of left intraventricular pressure (±dp/dt), LV peak systolic pressure, LV development pressure and LV end-diastolic pressure. Epicardial electrical mapping performed in vivo revealed reduced conduction velocity, increased conduction heterogeneity and spontaneous ventricular tachycardia. Masson's trichrome staining revealed marked fibrosis in the myocardial interstitium and sub-pericardium and thickened epicardium. Western blot analysis revealed increased pro-fibrotic factor TGF-β1, decreased mitochondrial biogenesis protein PGC-1a, decreased mitochondrial fusion protein MFN2. These changes were associated with decreased mitochondrial membrane potential (MMP) and connexin 43 translocation to mitochondria. These abnormalities can be partially prevented by the ER stress inhibitor 4-PBA. Our study shows that ER stress induction can produce cardiac electrical and mechanism dysfunction as well as structural remodeling. Mitochondrial function alterations are contributed by CX43 transposition to mitochondria. These abnormalities can be partially prevented by the ER stress inhibitor 4-PBA. National Natural Science Foundation of China (No. 81570298 to T.L.)