Regulation of Ca2+ signaling by acute hypoxia and acidosis in cardiomyocytes derived from human induced pluripotent stem cells

Abstract

Aims:The effects of acute (100s) hypoxia and/or acidosis on Ca 2+ signaling parameters of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are explored here for the first time.Methods and Results: 1) hiPSC-CMs express two cell populations: rapidly-inactivating I Ca myocytes (τ i <40ms, in 4-5 day cultures) and slowly-inactivating I Ca (τ i ≥ 40ms, in 6-8 day cultures). 2) Hypoxia suppressed I Ca by 10-20% in rapidly-and 40-55% in slowly-inactivating I Ca cells. 3) Isoproterenol enhanced I Ca in hiPSC-CMs, but either enhanced or did not alter the hypoxic suppression. 4) Hypoxia had no differential suppressive effects in the two cell-types when Ba 2+ was the charge carrier through the calcium channels, implicating Ca 2+ -dependent inactivation in O 2 sensing. 5) Acidosis suppressed I Ca by ~35% and ~25% in rapidly and slowly inactivating I Ca cells, respectively. 6) Hypoxia and acidosis suppressive effects on Ca-transients depended on whether global or RyR2-microdomain were measured: with acidosis suppression was ~25% in global and ~37% in RyR2 Ca 2+ -microdomains in either cell type, whereas with hypoxia suppression was ~20% and ~25% respectively in global and RyR2-microdomaine in rapidly and ~35% and ~45% respectively in global and RyR2-microdomaine in slowly-inactivating cells. Conclusions:Variability in I Ca inactivation kinetics rather than cellular ancestry seems to underlie the action potential morphology differences generally attributed to mixed atrial and ventricular cell populations in hiPSC-CMs cultures. The differential hypoxic regulation of Ca 2+signaling in the two-cell types arises from differential Ca 2+ -dependent inactivation of the Ca 2+channel caused by proximity of Ca 2+ -release stores to the Ca 2+ channels.

Beyond Family: Modeling Non-hereditary Heart Diseases With Human Pluripotent Stem Cell-Derived Cardiomyocytes

“…Nevertheless, unprimed hPSC-CMs (no maturation protocol applied) still represent a valid reductionist model in dissecting molecular mechanisms within human and cardiac cell backgrounds. For instance, a recent study successfully identified direct inactivation mechanisms of human voltagesensitive L-type calcium channels by molecular O 2 and acidosis (Fernandez-Morales et al, 2019), complementing our findings in murine models (Martewicz et al, 2012). Simultaneously, the authors clearly show how studying more complex functional features requires careful evaluation of cardiac structural maturation, with whole-cell ion dynamics changing following substrate interaction, which our group showed to be mediated by mechanotransduction signaling (Martewicz et al, 2017).…”

Role of mitochondrial Ca2+ homeostasis in cardiac muscles

“…Finally, it is worth mentioning that mitochondria may serve as a significant dynamic buffer of [Ca 2+ ] c under physiological conditions on a beat-to-beat basis in other types of cardiomyocytes such as neonatal cardiomyocytes [14], although the MCU complex is not likely to be involved in cytosolic Ca 2+ handling in adult ventricular myocytes. Since neonatal cardiomyocytes, adult atrial myocytes, and cardiomyocytes derived from human induced pluripotent stem cells have fewer T-tubules and smaller gain of Ca 2+ -induced Ca 2+ release compared to adult ventricular myocytes, the MCU complex and/or NCLX may have a larger contribution to cytosolic Ca 2+ handling [14,28,125,126]. Indeed, using genetically engineered mitochondria-targeted Ca 2+ biosensors, several groups clearly showed that spontaneous beating promotes beat-tobeat mitochondrial Ca 2+ uptake in neonatal cardiomyocytes [14,28].…”

Human induced pluripotent stem cell-based platform for modeling cardiac ischemia

“…Furthermore, changes in the functionality and electrophysiology have been observed, including decrease in hiPSC-CM beating frequency 11 , 12 , 15 , 16 , 24 , contractility, calcium overload and arrhythmias 14 . In these models, hypoxic conditions have been induced to the hiPSC-CMs by multiple methods, such as by using hypoxic gas 8 – 10 , 13 – 15 , 24 , 25 or causing oxidative stress via peroxide treatment 16 . In addition, cell culture media composition has been modified to better recapitulate the ischemic conditions in several studies.…”

“…In addition, cell culture media composition has been modified to better recapitulate the ischemic conditions in several studies. The modifications include removal of glucose 23 or serum 11 , or both 8 – 10 , 13 , 14 , 22 , as well as acidosis to better mimic the physiological ischemic event 8 – 10 , 13 , 22 .…”