Disrupted Junctional Membrane Complexes and Hyperactive Ryanodine Receptors After Acute Junctophilin Knockdown in Mice
Background—Excitation-contraction coupling in striated muscle requires proper communication of plasmalemmal voltage-activated Ca2+ channels and Ca2+ release channels on sarcoplasmic reticulum within junctional membrane complexes. Although previous studies revealed a loss of junctional membrane complexes and embryonic lethality in germ-line junctophilin-2 (JPH2) knockout mice, it has remained unclear whether JPH2 plays an essential role in junctional membrane complex formation and the Ca2+-induced Ca2+ release process in the heart. Our recent work demonstrated loss-of-function mutations in JPH2 in patients with hypertrophic cardiomyopathy.
Methods and Results—To elucidate the role of JPH2 in the heart, we developed a novel approach to conditionally reduce JPH2 protein levels using RNA interference. Cardiac-specific JPH2 knockdown resulted in impaired cardiac contractility, which caused heart failure and increased mortality. JPH2 deficiency resulted in loss of excitation-contraction coupling gain, precipitated by a reduction in the number of junctional membrane complexes and increased variability in the plasmalemma–sarcoplasmic reticulum distance.
Conclusions—Loss of JPH2 had profound effects on Ca2+ release channel inactivation, suggesting a novel functional role for JPH2 in regulating intracellular Ca2+ release channels in cardiac myocytes. Thus, our novel approach of cardiac-specific short hairpin RNA–mediated knockdown of junctophilin-2 has uncovered a critical role for junctophilin in intracellular Ca2+ release in the heart.
- Received November 4, 2010.
- Accepted January 7, 2011.
- © 2011 American Heart Association, Inc.