http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Connexin 43 as a novel Ca2+ transport pathway in the nuclear envelope of human induced pluripotent stem cell derived cardiomyocytes
Nuclear envelope (NE) is a double lipid bilayer separating the nucleus from the cytosol. While cytoplasmic and sarcoplasmic reticulum (SR) Ca2+ signaling is extensively studied, the role of NE in cellular Ca2+ dynamics and the identity and regulation of nuclear Ca2+ transporters remain less explored. NE-associated Ca2+ activity was examined using a genetically engineered fluorescent Ca2+ probe targeting nuclear LaminB1 at the inner NE membrane in human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs). Confocal imaging of NE revealed larger and delayed but slower rise of Ca2+ in the nuclear lamina compared to ICa triggered cytosolic rise in Ca2+. Caffeine induced ∼4X larger Ca2+rise in NE lamina compared to ICa. To determine whether NE Ca2+ signaling depended on SR Ca2+ release, we measured the nuclear Ca2+signals of cells expressing genetically CICR-impaired RyR2 mutations (E3848A, Q3925E), where SR Ca2+ release was fully suppressed. In these CICR-deleted cells, although caffeine failed to activate robust NE Ca2+ transients, spontaneous beating persisted activating NE Ca2+ transients, suggesting Ca2+ signaling pathway remodeling and activation of an alternate Ca2+ pathway. Confocal imaging of hiPSCCMs infected with antibodies to Cx43 identified robust Cx43 expression in the NE, the inhibition of which by Gap19 protein blocked the rise of nuclear lamina Ca2+-transients. We conclude, that while SR Ca2+ release is essential in replenishing the NE Ca2+ content, RyR2 mutations that delete CICR induce remodeling of Ca2+signaling pathway that may include Cx43 to maintain Ca2+ fluxes critical for spontaneous beating and triggering of Ca2+transients.