Abstract
Molecular mechanisms underlying Ca(2+) regulation by perinuclear endoplasmic/sarcoplasmic reticulum (ER/SR) cisternae in cardiomyocytes remain obscure. To investigate the mechanisms of changes in cardiac calsequestrin (CSQ2) trafficking on perinuclear Ca(2+) signaling, we manipulated the subcellular distribution of CSQ2 by overexpression of CSQ2-DsRed, which specifically accumulates in the perinuclear rough ER. Adult ventricular myocytes were infected with adenoviruses expressing CSQ2-DsRed, CSQ2-WT, or empty vector. We found that perinuclear enriched CSQ2-DsRed, but not normally distributed CSQ2-WT, enhanced nuclear Ca(2+) transients more potently than cytosolic Ca(2+) transients. Overexpression of CSQ2-DsRed produced more actively propagating Ca(2+) waves from perinuclear regions than did CSQ2-WT. Activities of the SR/ER Ca(2+)-ATPase and ryanodine receptor type 2, but not inositol 1,4,5-trisphosphate receptor type 2, were required for the generation of these perinuclear initiated Ca(2+) waves. In addition, CSQ2-DsRed was more potent than CSQ2-WT in inducing cellular hypertrophy in cultured neonatal cardiomyocytes. Our data demonstrate for the first time that CSQ2 retention in the rough ER/perinuclear region promotes perinuclear Ca(2+) signaling and predisposes to ryanodine receptor type 2-mediated Ca(2+) waves from CSQ2-enriched perinuclear compartments and myocyte hypotrophy. These findings provide new insights into the mechanism of CSQ2 in Ca(2+) homeostasis, suggesting that rough ER-localized Ca(2+) stores can operate independently in raising levels of cytosolic/nucleoplasmic Ca(2+) as a source of Ca(2+) for Ca(2+)-dependent signaling in health and disease.
Highlights
Calsequestrin is a high-capacity Ca2ϩ-binding protein that stores Ca2ϩ within the sarcoplasmic reticulum
Confocal immunofluorescence showed that CSQ2-WT was overexpressed with brighter CSQ2 fluorescence and normally distributed throughout the junctional sarcoplasmic reticulum (SR), whereas exogenously expressed CSQ2-DsRed localized to the perinuclear region of cardiomyocytes in both rats (Fig. 2, A–F) and mice
Confocal duo-imaging of RyR2 immunofluorescence and CSQ2-DsRed fluorescence in Ad-CSQ2-DsRed-infected myocytes showed that RyR2 was present in perinuclear SR puncta that co-localized with CSQ2-DsRed (Fig. 2, G–L)
Summary
Calsequestrin is a high-capacity Ca2ϩ-binding protein that stores Ca2ϩ within the sarcoplasmic reticulum. Our data demonstrate for the first time that CSQ2 retention in the rough ER/perinuclear region promotes perinuclear Ca2؉ signaling and predisposes to ryanodine receptor type 2-mediated Ca2؉ waves from CSQ2enriched perinuclear compartments and myocyte hypotrophy. These findings provide new insights into the mechanism of CSQ2 in Ca2؉ homeostasis, suggesting that rough ER-localized Ca2؉ stores can operate independently in raising levels of cytosolic/nucleoplasmic Ca2؉ as a source of Ca2؉ for Ca2؉-dependent signaling in health and disease. Our data show that enrichment of CSQ2 in the perinuclear cisternae was sufficient to enhance nuclear Ca2ϩ transients, promoting Ca2ϩ-dependent transcription and myocyte hypertrophy, and led to the shift of spontaneous arrhythmogenic Ca2ϩ waves emanating from the perinuclear region instead of the junctional SR
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
