Inhibition of CaMKII does not attenuate cardiac hypertrophy in mice with dysfunctional ryanodine receptor.

Asima Chakraborty,Tai-Qin Huang,Naohiro Yamaguchi,Gerhard Meissner,Angela C Gomez,Mark E Anderson,Daniel A Pasek,Edward J Lesnefsky

doi:10.1371/journal.pone.0104338

Abstract

In cardiac muscle, the release of calcium ions from the sarcoplasmic reticulum through ryanodine receptor ion channels (RyR2s) leads to muscle contraction. RyR2 is negatively regulated by calmodulin (CaM) and by phosphorylation of Ca2+/CaM-dependent protein kinase II (CaMKII). Substitution of three amino acid residues in the CaM binding domain of RyR2 (RyR2-W3587A/L3591D/F3603A, RyR2ADA) impairs inhibition of RyR2 by CaM and results in cardiac hypertrophy and early death of mice carrying the RyR2ADA mutation. To test the cellular function of CaMKII in cardiac hypertrophy, mutant mice were crossed with mice expressing the CaMKII inhibitory AC3-I peptide or the control AC3-C peptide in the myocardium. Inhibition of CaMKII by AC3-I modestly reduced CaMKII-dependent phosphorylation of RyR2 at Ser-2815 and markedly reduced CaMKII-dependent phosphorylation of SERCA2a regulatory subunit phospholamban at Thr-17. However the average life span and heart-to-body weight ratio of Ryr2ADA/ADA mice expressing the inhibitory peptide were not altered compared to control mice. In Ryr2ADA/ADA homozygous mice, AC3-I did not alter cardiac morphology, enhance cardiac function, improve sarcoplasmic reticulum Ca2+ handling, or suppress the expression of genes implicated in cardiac remodeling. The results suggest that CaMKII was not required for the rapid development of cardiac hypertrophy in Ryr2ADA/ADA mice.

Highlights

In cardiac muscle, excitation-contraction coupling in response to an action potential initiates an influx of Ca2+ ions via dihydropyridine-sensitive L-type Ca2+ channels (Cav1.2)
The present study shows that calmodulin-dependent protein kinase II (CaMKII) inhibitory peptide autocamtide 3 inhibitory peptide (AC3-I) reduced phosphorylation of PLN at Thr-17 in Ryr2+/+ and Ryr2ADA/ADA mice without significantly altering life span, cardiac morphology and performance, or markers of cardiac hypertrophy relative to mice expressing the control peptide
Expression of the AC3-I inhibitory peptide did not suppress an increase in left ventricular weight-to-body weight ratio of Ryr2ADA/ADA mice compared with mutant mice expressing the AC3-C control peptide (Table 1)

Summary

Introduction

Excitation-contraction coupling in response to an action potential initiates an influx of Ca2+ ions via dihydropyridine-sensitive L-type Ca2+ channels (Cav1.2). This triggers the massive release of Ca2+ from an intracellular Ca2+-. Sequestration of released Ca2+ back into the SR by an ATP-dependent Ca2+ pump (SERCA2a) leads to muscle relaxation. Ca2+/calmodulin-dependent protein kinase II (CaMKII) regulates the cellular entry of activator Ca2+ through Cav1.2 and thereby SR Ca2+ release via RyR2 [1,2,3,4]. Phosphorylation of SERCA2a regulatory protein phospholamban (PLN) at Ser-16 by protein kinase A and Thr-17 by CaMKII enhances SR Ca2+

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