Cardiac resynchronization sensitizes the sarcomere to calcium by reactivating GSK-3β
Jonathan A. Kirk, … , Jennifer Van Eyk, David A. Kass
Jonathan A. Kirk, … , Jennifer Van Eyk, David A. Kass
Published December 2, 2013
Citation Information: J Clin Invest. 2014;124(1):129-139. https://doi.org/10.1172/JCI69253.
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Research Article Cardiology

Cardiac resynchronization sensitizes the sarcomere to calcium by reactivating GSK-3β

Abstract

Cardiac resynchronization therapy (CRT), the application of biventricular stimulation to correct discoordinate contraction, is the only heart failure treatment that enhances acute and chronic systolic function, increases cardiac work, and reduces mortality. Resting myocyte function also increases after CRT despite only modest improvement in calcium transients, suggesting that CRT may enhance myofilament calcium responsiveness. To test this hypothesis, we examined adult dogs subjected to tachypacing-induced heart failure for 6 weeks, concurrent with ventricular dyssynchrony (HFdys) or CRT. Myofilament force-calcium relationships were measured in skinned trabeculae and/or myocytes. Compared with control, maximal calcium-activated force and calcium sensitivity declined globally in HFdys; however, CRT restored both. Phosphatase PP1 induced calcium desensitization in control and CRT-treated cells, while HFdys cells were unaffected, implying that CRT enhances myofilament phosphorylation. Proteomics revealed phosphorylation sites on Z-disk and M-band proteins, which were predicted to be targets of glycogen synthase kinase-3β (GSK-3β). We found that GSK-3β was deactivated in HFdys and reactivated by CRT. Mass spectrometry of myofilament proteins from HFdys animals incubated with GSK-3β confirmed GSK-3β–dependent phosphorylation at many of the same sites observed with CRT. GSK-3β restored calcium sensitivity in HFdys, but did not affect control or CRT cells. These data indicate that CRT improves calcium responsiveness of myofilaments following HFdys through GSK-3β reactivation, identifying a therapeutic approach to enhancing contractile function.

Authors

Jonathan A. Kirk, Ronald J. Holewinski, Viola Kooij, Giulio Agnetti, Richard S. Tunin, Namthip Witayavanitkul, Pieter P. de Tombe, Wei Dong Gao, Jennifer Van Eyk, David A. Kass

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Figure 6

Increased phosphorylation at GSK-3β sites in CRT mediated the calcium-sensitizing effect.

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Increased phosphorylation at GSK-3β sites in CRT mediated the calcium-se...
(A) Schematic of the cardiac sarcomere showing Z-disk (green), titin (gray) thick filament (blue), M-line (black), and thin filament (red). The proteins (and sites) that were identified as increased with CRT are shown, with their best-known localization. Asterisks indicate matches with GSK-3β consensus sequence. (B) Representative force-calcium relationships in controls (top), HFdys (middle), and CRT (bottom) before (solid lines) and after GSK-3β treatment (dashed lines). (C) There was a calcium-sensitizing effect of GSK-3β in HFdys (n = 8), bringing it to the same level as controls and CRT. GSK-3β had no effect on controls (n = 5) or CRT myocytes (n = 8). *P < 0.05 vs. control baseline value.