The Role of Nuclear Envelope Calcium Signaling in The Cellular Calcium Dynamics of hiPSC-derived Cardiomyocytes

Nuclear envelope (NE) is a bilayer membrane barrier separating the nucleus from the cytosol storing the Ca 2+ that may regulate gene transcription. Although, cytoplasmic and sarcoplasmic reticulum (SR) Ca 2+ signaling is well studied, the NE Ca 2+ signaling regulatory role in cellular Ca 2+ -dynamics and the nuclear Ca 2+ transporters remain unexplored. Here we investigated the Ca 2+ -activity of NE using genetically engineered fluorescent probes targeting nuclear lamin-B at the inner NE membrane in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Confocal measurements of NE showed rapid uptake of Ca 2+ that was activated by I CaL -triggered SR Ca 2+ release (CICR) but outlasted the cytosolic Ca 2+ transients. Application of caffeine caused a rapid cytosolic Ca 2+ rise followed by a delayed and slower but much larger NE Ca 2+ uptake. Longer duration caffeine applications, to empty the SR Ca 2+ content, induced a rise in NE Ca 2+ uptake followed by its decay. Lowering extracellular Na + in Ca 2+ -depleted SR, increased the baseline Ca 2+ concentrations of both SR and NE and reintroduction of control Na + decreased the NE calcium and enhanced the pacing rate of NE-transients. Spontaneously occurring NE Ca 2+ -transients were rapidly suppressed by blocking I CaL . Cx43 was expressed in the NE, and the inhibition of Cx43 by Gap19 blocked the rise of NE Ca 2+ . Similarly, using RyR2 mutant hiPSC-CM cell-lines (i.e.I4855M), where CICR was impaired, failed to increase NE Ca 2+ levels. We suggest that SR Ca 2+ content and the activation of CICR is essential in triggering SR Ca 2+ -release that replenishes NE Ca 2+ . Our results might provide a novel pathway for Cx43 mediated calcium influx into the nucleus regulating excitation-transcription coupling. This work was funded by National Institutes of Health 1R01HL153504 and the Jennifer Friedman Hillis Foundation. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.