β-Adrenergic receptor antagonists ameliorate myocyte T-tubule remodeling following myocardial infarction

beta-Adrenergic receptor (AR) blockers provide substantial clinical benefits, including improving overall survival and left ventricular (LV) function following myocardial infarction (MI), though the mechanisms remain incompletely defined. The transverse-tubule (T-tubule) system of ventricular myocytes is an important determinant of cardiac excitation-contraction function. T-tubule remodeling occurs early during LV failure. We hypothesized that beta-AR blockers prevent T-tubule remodeling and thereby provide therapeutic benefits. A murine model of MI was utilized to examine the effect of beta-AR blockers on T-tubule remodeling following LV MI. We applied the in situ imaging of T-tubule structure from Langendorff-perfused intact hearts with laser scanning confocal microscopy. We found that MI caused remarkable T-tubule remodeling near the infarction border zone and moderate LV remodeling remote from the MI. Metoprolol and carvedilol administered 6 d after MI for 4 wk each increased the T-tubule integrity at the remote and border zones. At the molecular level, both beta-AR blockers restored border and remote zone expression of junctophilin-2 (JP-2), which is involved in T-tubule organization and formation of the T-tubule/sarcoplasmic reticulum junctions. In contrast, beta-AR blockers had no significant effects on caveolin-3 expression. In summary, our data show that beta-AR antagonists can protect against T-tubule remodeling after MI, suggesting a novel therapeutic mechanism of action for this drug class. Preservation of JP-2 expression may contribute to the beneficial effects of metoprolol and carvedilol on T-tubule remodeling.-Chen, B., Li, Y., Jiang, S., Xie, Y.-P., Guo, A., Kutschke, W., Zimmerman, K., Weiss, R. M., Miller, F. J., Anderson, M. E., Song, L.-S. beta-Adrenergic receptor antagonists ameliorate myocyte T-tubule remodeling following myocardial infarction. FASEB J. 26, 2531-2537 (2012). www.fasebj.org