Sarcoplasmic reticulum Ca2+ -induced Ca2+ release regulates class IIa HDAC localization in mouse embryonic cardiomyocytes

Abstract

In embryonic cardiomyocytes, sarcoplasmic reticulum (SR)-derived Ca²⁺ release is required to induce Ca²⁺ oscillations for contraction and to control cardiac development through Ca²⁺ -activated pathways. Here, our aim was to study how SR Ca²⁺ release regulates cytosolic and nuclear Ca²⁺ distribution and the subsequent effects on the Ca²⁺ -dependent localization of class IIa histone deacetylases (HDAC) and cardiac-specific gene expression in embryonic cardiomyocytes. Confocal microscopy was used to study changes in Ca²⁺ -distribution and localization of immunolabeled HDAC4 and HDAC5 upon changes in SR Ca²⁺ release in mouse embryonic cardiomyocytes. Dynamics of translocation were also observed with a confocal microscope, using HDAC5-green fluorescent protein transfected myocytes. Expression of class IIa HDACs in differentiating myocytes and changes in cardiac-specific gene expression were studied using real-time quantitative PCR. Inhibition of SR Ca²⁺ release caused a significant decrease in intranuclear Ca²⁺ concentration, a rapid nuclear import of HDAC5 and subnuclear redistribution of HDAC4. Endogenous localization of HDAC5 and HDAC4 was mostly cytosolic and at the nuclear periphery, respectively. Downregulated expression of cardiac-specific genes was also observed upon SR Ca²⁺ release inhibition. Electrical stimulation of sarcolemmal Ca²⁺ influx was not sufficient to rescue either the HDAC localization or the gene expression changes. SR Ca²⁺ release controls subcellular Ca²⁺ distribution and regulates localization of HDAC4 and HDAC5 in embryonic cardiomyocytes. Changes in SR Ca²⁺ release also caused changes in expression of the developmental phase-specific genes, which may be due to the changes in HDAC-localization.

Keywords: Calcium; cardiomyocyte differentiation; gene expression; histone deacetylase; sarcoplasmic reticulum.