| First Author | Chen M | Year | 2018 |
| Journal | J Mol Cell Cardiol | Volume | 123 |
| Pages | 185-197 | PubMed ID | 30261161 |
| Mgi Jnum | J:266854 | Mgi Id | MGI:6200444 |
| Doi | 10.1016/j.yjmcc.2018.09.008 | Citation | Chen M, et al. (2018) Phospholamban regulates nuclear Ca(2+) stores and inositol 1,4,5-trisphosphate mediated nuclear Ca(2+) cycling in cardiomyocytes. J Mol Cell Cardiol |
| abstractText | AIMS: Phospholamban (PLB) is the key regulator of the cardiac Ca(2+) pump (SERCA2a)-mediated sarcoplasmic reticulum Ca(2+) stores. We recently reported that PLB is highly concentrated in the nuclear envelope (NE) from where it can modulate perinuclear Ca(2+) handling of the cardiomyocytes (CMs). Since inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) mediates nuclear Ca(2+) release, we examined whether the nuclear pool of PLB regulates IP3-induced nuclear Ca(2+) handling. METHODS AND RESULTS: Fluo-4 based confocal Ca(2+) imaging was performed to measure Ca(2+) dynamics across both nucleus and cytosol in saponin-permeabilized CMs isolated from wild-type (WT) or PLB-knockout (PLB-KO) mice. At diastolic intracellular Ca(2+) ([Ca(2+)]i=100nM), the Fab fragment of the monoclonal PLB antibody (anti-PLB Fab) facilitated the formation and increased the length of spontaneous Ca(2+) waves (SCWs) originating from the nuclear region in CMs from WT but not from PLB-KO mice. We next examined nuclear Ca(2+) activities at basal condition and after sequential addition of IP3, anti-PLB Fab, and the IP3R inhibitor 2-aminoethoxydiphenyl borate (2-APB) at a series of [Ca(2+)]i. In WT mice, at 10nM [Ca(2+)]i where ryanodine receptor (RyR2) based spontaneous Ca(2+) sparks rarely occurred, IP3 increased fluorescence amplitude (F/F0) of overall nuclear region to 1.19+/-0.02. Subsequent addition of anti-PLB Fab significantly decreased F/F0 to 1.09+/-0.02. At 50nM [Ca(2+)]i, anti-PLB Fab not only decreased the overall nuclear F/F0 previously elevated by IP3, but also increased the amplitude and duration of spark-like nuclear Ca(2+) release events. These nuclear Ca(2+) releases were blocked by 2-APB. At 100nM [Ca(2+)]i, IP3 induced short SCWs originating from nucleus. Anti-PLB Fab transformed those short waves into long SCWs with propagation from the nucleus into the cytosol. In contrast, neither nuclear nor cytosolic Ca(2+) dynamics was affected by anti-PLB Fab in CMs from PLB-KO mice in all these conditions. Furthermore, in WT CMs pretreated with RyR2 blocker tetracaine, IP3 and anti-PLB Fab still increased the magnitude of nuclear Ca(2+) release but failed to regenerate SCWs. Finally, anti-PLB Fab increased low Ca(2+) affinity mag-fluo 4 fluorescence intensity in the lumen of NE of nuclei isolated from WT but not in PLB-KO mice. CONCLUSION: PLB regulates nuclear Ca(2+) handling. By increasing Ca(2+) uptake into lumen of the NE and perhaps other perinuclear membranes, the acute reversal of PLB inhibition decreases global Ca(2+) concentration at rest in the nucleoplasm, and increases Ca(2+) release into the nucleus, through mechanisms involving IP3R and RyR2 in the vicinity. |
