title: Disrupted junctional membrane complexes and hyperactive ryanodine receptors after acute junctophilin knockdown in mice.
abstract: 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 Ca(2+)-induced Ca(2+) release process in the heart. Our recent work demonstrated loss-of-function mutations in JPH2 in patients with hypertrophic cardiomyopathy.
  
  
  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.
authors.affiliation: Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, BCM335, Houston, TX 77030, USA.
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: van Oort
authors.forename: Alejandro
authors.initials: A
authors.lastname: Garbino
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Sayali S
authors.initials: SS
authors.lastname: Dixit
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Landstrom
authors.forename: Namit
authors.initials: N
authors.lastname: Gaur
authors.forename: Angela C
authors.initials: AC
authors.lastname: De Almeida
authors.forename: Darlene G
authors.initials: DG
authors.lastname: Skapura
authors.forename: Yoram
authors.initials: Y
authors.lastname: Rudy
authors.forename: Alan R
authors.initials: AR
authors.lastname: Burns
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
authors.forename: Xander H T
authors.initials: XH
authors.lastname: Wehrens
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D055785:Gene Knockdown Techniques / Q000379:methods; D006333:Heart Failure / Q000235:genetics / Q000401:mortality / Q000473:pathology; D007365:Intercellular Junctions / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000172:deficiency* / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D015220:Calcium Channels; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D019837:Ryanodine Receptor Calcium Release Channel; C412507:junctophilin