Hyun Seok Hwang, PhD Florida State University

Role of Calcium in CPVT vs. LQTs

Korean Heart Rhythm Society Symposium November, 2015

Grant Support: NIH R01 HL71670, HL88635, Knollmann AHA Scientist Development Grant, Hwang

Vanderbilt University • Bjorn Knollmann • Sabine Huke • Dmytro Kryshtal • Kaylen Chuaquico Kor • Walter J Chazin • A. George

Acknowledgements

Florida State University Cardiac Arrhythmias Lab • Hyun Seok Hwang Univ. of Newcastle, Australia

• Derek Laver

Disclosures: None

University of California, Davis • Donald M Bers

University of Minnesota • Razvan L Cornea

• L-type Ca channel (Cav1.2) complex localized in t-tubular membrane

• RyR2 Ca release complex localized in junctional SR membrane

• Calmodulin (CaM) localized in cytosol binds to RyR2 and Cav1.2

• Ca binding to CaM on Cav1.2 inactivates Cav1.2 channels (Ca-dependent inactivation)

Dyad - Cardiac Ca release Unit

Excitation-Contraction Coupling in Myocytes

Knollmann, Nature, 2008

Mouse-CM

Calmodulin (CaM)

• CaM is an essential Ca signaling protein in a wide range of biological processes.

• CaM is highly conserved among different species with 148 amino acid residues.

• Humans have 3 CaM genes – CALM1, CALM2, CALM3 – encoding the identical amino acid sequence.

• CaM mutations are associated with genetic arrhythmia syndromes responsible for sudden cardiac death.

Crotti et al. Circulation. 2013;127:1009-1017

Calmodulin (CaM)

Calmodulin and Sudden Cardiac Death

Nyegaard et al., Mutations in calmodulin cause ventricular tachycardia and sudden cardiac death. Am J Hum Genet. 91:703–712, 2012

Crotti et al., Calmodulin mutations associated with recurrent cardiac arrest in infants.

Circulation.127:1009-1017, 2013

Autosomal dominant, clinical presentation consistent with Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)

Autosomal dominant, clinical presentation consistent with Long QT Syndrome (LQTS)

CaM mutations cause different arrhythmia phenotypes in humans

Catecholaminergic polymorphic ventricular tachycardia (CPVT) CALM1-N54I

CALM1-N98S

Nyegaard et al., Am J Hum Genet. 2012. 91, 703–712

Long QT syndrome (LQTS) CALM2-D96V

CALM1-D130G

CALM1-F142L

Crotti et al. Circulation. 2013;127:1009-1017)

CaM mutations cause different arrhythmia phenotypes in humans

• To determine the molecular mechanism responsible for CPVT caused by CaM mutations.

• To determine why CaM mutations cause divergent arrhythmia phenotypes in humans.

Hwang HS, et. al. 2014, Circ Res.

Differential effect of CaM mutations on C-lobe Ca binding

Differential effect of CaM mutations on Ca waves

Differential effect of CaM mutations on Ca waves

Effect of CaMKII inhibition on Ca waves

Effect of CPVT-CaMs on Ca sparks

50 nM free [Ca], 500uM EGTA

Regulation of single RyR2 channels by CPVT-CaMs

CPVT-CaMs exhibit a dominant activating effect on Ca waves

CPVT-CaMs exhibit a dominant activating effect on Ca waves

CPVT-CaMs bind with higher affinity to RyR2 channels in diastolic Ca conditions (Cardiac SR vesicles)

Flecainide reduced spontanous Ca waves in myocytes

LQTS-CaMs impair CaV1.2 current inactivation

Marsman et al. JACC. 2013

F90L CaM was identified in IVF, Sudden death at 5 years of age.

Differential effect of CaM mutations on C-lobe Ca binding

B

F90L CaM mutations on Ca waves

F90L CaM mutations on CaV1.2 current inactivation

• CPVT-CaMs are dominant activators of RyR2, whereas LQTS-CaMs have no effect on RyR2.

• LQTS-CaMs drastically impair CaV1.2 current inactivation, whereas CPVT-CaMs have little or no effect on CaV1.2.

• F90L CaM (IVF) mutation shares characteristics (a overlap syndrome) with both CPVT and LQTS CaMs.

Mechanisms of CPVT and LQTS caused by CaM mutations

F90L-CaM

Thank you,