Toll-like receptor 3 controls QT interval on the electrocardiogram by targeting the degradation of Kv4.2/4.3 channels in the endoplasmic reticulum.

TLRs have been proven to be essential mediators for the early innate immune response. Overactivation of TLR-mediated immune signaling promotes deterioration of cardiovascular diseases; however, the role of TLRs in the heart under physiologic conditions remains neglected. Here, we show that Tlr3 deficiency induced the endoplasmic reticulum (ER) retention of Kv4.2/4.3 proteins and consequent degradation via the ubiquitin-proteasome pathway. Knockout of Tlr3 resulted in a prolonged QT interval (the space between the start of the Q wave and the end of the T wave) in mice with no significant signs of inflammation and tissue abnormality in cardiac muscles. Prolongation of action potential duration resulted from the depression of transient outward potassium channel ( Ito ) currents in Tlr3-deficient ventricular myocytes mirrored the change in QT interval. Mechanistically, we found that Tlr3 was exclusively localized in the ER of cardiomyocytes where it interacted with Kv4.2/4.3 subunits of Ito channel. Thus, our data indicated that TLR3 directly regulates Ito channel protein dynamics to maintain cardiac repolarization, which may implicate a new molecular surveillance system for cardiac electrophysiological homeostasis.-Gao, X., Gao, S., Guan, Y., Huang, L., Huang, J., Lin, L., Liu, Y., Zhao, H., Huang, B., Yuan, T., Liu, Y., Liang, D., Zhang, Y., Ma, X., Li, L., Li, J., Zhou, D., Shi, D., Xu, L., Chen, Y.-H. Toll-like receptor 3 controls QT interval on the electrocardiogram by targeting the degradation of Kv4.2/4.3 channels in the endoplasmic reticulum.