Activation of endogenous protein phosphatase 1 enhances the calcium sensitivity of the ryanodine receptor type 2 in murine ventricular cardiomyocytes.

Abstract

KEY POINTS:

Increased protein phosphatase 1 (PP-1) activity has been found in end stage human heart failure. Although PP-1 has been extensively studied, a detailed understanding of its role in the excitation-contraction coupling mechanism, in normal and diseased hearts, remains elusive. The present study investigates the functional effect of the PP-1 activity on local Ca2+ release events in ventricular cardiomyocytes, by using an activating peptide (PDP3) for the stimulation of the endogenous PP-1 protein. We report that acute de-phosphorylation may increase the sensitivity of RyR2 channels to Ca2+ in situ, and that the RyR2-serine2808 phosphorylation site may mediate such a process. Our approach unmasks the functional importance of PP-1 in the regulation of RyR2 activity, suggesting a potential role in the generation of a pathophysiological sarcoplasmic reticulum Ca2+ leak in the diseased heart.

ABSTRACT:

Changes in cardiac ryanodine receptor (RyR2) phosphorylation are considered to be important regulatory and disease related post-translational protein modifications. The extent of RyR2 phosphorylation is mainly determined by the balance of the activities of protein kinases and phosphatases, respectively. Increased protein phosphatase-1 (PP-1) activity has been observed in heart failure, although the regulatory role of this enzyme on intracellular Ca2+ handling remains poorly understood. To determine the physiological and pathophysiological significance of increased PP-1 activity, we investigated how the PP-1 catalytic subunit (PP-1c) alters Ca2+ sparks in permeabilized cardiomyocytes and we also applied a PP-1-disrupting peptide (PDP3) to specifically activate endogenous PP-1, including the one anchored on the RyR2 macromolecular complex. We compared wild-type and transgenic mice in which the usually highly phosphorylated site RyR2-S2808 has been ablated to investigate its involvement in RyR2 modulation (S2808A+/+ ). In wild-type myocytes, PP-1 increased Ca2+ spark frequency by two-fold, followed by depletion of the sarcoplasmic reticulum Ca2+ store. Similarly, PDP3 transiently increased spark frequency and decreased sarcoplasmic reticulum Ca2+ load. RyR2 Ca2+ sensitivity, which was assessed by Ca2+ spark recovery analysis, was increased in the presence of PDP3 compared to a negative control peptide. S2808A+/+ cardiomyocytes did not respond to both PP-1c and PDP3 treatment. Our results suggest an increased Ca2+ sensitivity of RyR2 upon de-phosphorylation by PP-1. Furthermore, we have confirmed the S2808 site as a target for PP-1 and as a potential link between RyR2s modulation and the cellular response.

• Authors: Duilio Michele Potenza, Radoslav Janicek, Miguel Fernandez-Tenorio, Ernst Niggli
• Journal: The Journal of physiology (J Physiol) Vol. 598 Issue 6 Pg. 1131-1150 (03 2020) ISSN: 1469-7793 [Electronic] England
• PMID: 31943206 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2020 The Authors. The Journal of Physiology © 2020 The Physiological Society.

Chemical References

• Ryanodine Receptor Calcium Release Channel
• Protein Phosphatase 1
• Calcium

Topics

• Animals
• Calcium (metabolism)
• Calcium Signaling
• Mice
• Mice, Transgenic
• Myocytes, Cardiac (metabolism)
• Phosphorylation
• Protein Phosphatase 1 (metabolism)
• Ryanodine Receptor Calcium Release Channel (metabolism)
• Sarcoplasmic Reticulum (metabolism)