Abstract
The loss of nonregenerative, terminally differentiated cardiomyocytes (CMs) due to aging or diseases is generally considered irreversible. Human pluripotent stem cells (hPSCs) can self-renew while maintaining their pluripotency to differentiate into all cell types, including ventricular (V) cardiomyocytes (CMs), to provide a potential unlimited ex vivo source of CMs for heart disease modeling, drug/cardiotoxicity screening, and cell-based therapies. In the human heart, cytosolic Ca2+ signals are well characterized but the contribution of nuclear Ca2+ is essentially unexplored. The present study investigated nuclear Ca2+ signaling in hPSC-VCMs. Calcium transient or sparks in hPSC-VCMs were measured by line scanning using a spinning disc confocal microscope. We observed that nuclear Ca2+, which stems from unitary sparks due to the diffusion of cytosolic Ca2+ that are mediated by RyRs on the nuclear reticulum, is functional. Parvalbumin- (PV-) mediated Ca2+ buffering successfully manipulated Ca2+ transient and stimuli-induced apoptosis in hPSC-VCMs. We also investigated the effect of Ca2+ on gene transcription in hPSC-VCMs, and the involvement of nuclear factor of activated T-cell (NFAT) pathway was identified. The overexpression of Ca2+-sensitive, nuclear localized Ca2+/calmodulin-dependent protein kinase II δ B (CaMKIIδ B) induced cardiac hypertrophy through nuclear Ca2+/CaMKIIδB/HDAC4/MEF2 pathway. These findings provide insights into nuclear Ca2+ signal in hPSC-VCMs, which may lead to novel strategies for maturation as well as improved systems for disease modeling, drug discovery, and cell-based therapies.
Highlights
Human pluripotent stem cells can self-renew while harboring pluripotency to differentiate into various cell types including ventricular (V) cardiomyocytes
No autonomous nuclear Ca2+ transients or waves could be observed in human embryonic stem cells (hESCs)-VCMs during pacing, distinctive from neonatal rat cardiomyocytes [24]
When hESC-VCMs were pretreated with ryanodine to block RyRs and thereby inhibiting all cytosolic and nuclear CICR, LTCC activation by FPL caused a dramatic cytosolic and nuclear Ca2+ rise (Figure 1(b))
Summary
Human pluripotent stem cells (hPSCs) can self-renew while harboring pluripotency to differentiate into various cell types including ventricular (V) cardiomyocytes. Nuclear Ca2+ signaling is known to affect a range of cellular physiological processes [5] from cell proliferation [6], meiosis reinitiation [7], gene transcription [8, 9], cell protection [10] to cardiac hypertrophy and heart failure [11], this intriguing process has only recently been characterized in rat cardiomyocytes [5]and is poorly defined in hPSC-VCMs. Here, we sought to address the gap by comprehensively investigating both the global and local nuclear Ca2+ signals in hPSC-VCMs. We tested the hypothesis that nuclear Ca2+ signaling plays a pivotal role in human cardiac differentiation and maturation of hPSC-VCMs by studying in detail its structural and mechanistic bases in relation to those of the cytosolic Ca2+ pathway by drawing comparison between these cells and adult cardiomyocytes
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