70 research outputs found
Structural Immaturity of Human iPSC-Derived Cardiomyocytes: In Silico Investigation of Effects on Function and Disease Modeling
Background: Human induced pluripotent stem cell-derived cardiomyocytes
(hiPSC-CMs) have emerged as a promising experimental tool for translational
heart research and drug development. However, their usability as a human adult
cardiomyocyte model is limited by their functional immaturity. Our aim is to analyse
quantitatively those characteristics and how they differ from adult CMs.
Methods and Results: We have developed a novel in silico model with all essential
functional electrophysiology and calcium handling features of hiPSC-CMs. Importantly,
the virtual cell recapitulates the immature intracellular ion dynamics that are characteristic
for hiPSC-CMs, as quantified based our in vitro imaging data. The strong âcalcium clockâ
is a source for a dual function of excitation-contraction coupling in hiPSC-CMs: action
potential and calcium transient morphology vary substantially depending on the activation
sequence of underlying ionic currents and fluxes that is altered in spontaneous vs.
paced mode. Furthermore, parallel simulations with hiPSC-CM and adult cardiomyocyte
models demonstrate the central differences. Results indicate that hiPSC-CMs translate
poorly the disease specific phenotypes of Brugada syndrome, long QT Syndrome
and catecholaminergic polymorphic ventricular tachycardia, showing less robustness
and greater tendency for arrhythmic events than adult CMs. Based on a comparative
sensitivity analysis, hiPSC-CMs share some features with adult CMs, but are still
functionally closer to prenatal CMs than adult CMs. A database analysis of 3000
hiPSC-CM model variants suggests that hiPSC-CMs recapitulate poorly fundamental
physiological properties of adult CMs. Single modifications do not appear to solve this
problem, which is mostly contributed by the immaturity of intracellular calcium handling.
Conclusion: Our data indicates that translation of findings from hiPSC-CMs to human
disease should be made with great caution. Furthermore, we established a mathematical
platform that can be used to improve the translation from hiPSC-CMs to human, and
to quantitatively evaluate hiPSC-CMs development toward more general and valuable
model for human cardiac diseases
Mechanical load induced by glass microspheres releases angiogenic factors from neonatal rat ventricular myocytes cultures and causes arrhythmias
In the present study, we tested the hypothesis that similar to other mechanical loads, notably cyclic stretch (simulating pre-load), glass microspheres simulating afterload will stimulate the secretion of angiogenic factors. Hence, we employed glass microspheres (average diameter 15.7 microm, average mass 5.2 ng) as a new method for imposing mechanical load on neonatal rat ventricular myocytes (NRVM) in culture. The collagen-coated microspheres were spread over the cultures at an estimated density of 3000 microspheres/mm2, they adhered strongly to the myocytes, and acted as small weights carried by the cells during their contraction. NRVM were exposed to either glass microspheres or to cyclic stretch, and several key angiogenic factors were measured by RT-PCR. The major findings were: (1) In contrast to other mechanical loads, such as cyclic stretch, microspheres (at 24 hrs) did not cause hypertrophy. (2) Further, in contrast to cyclic stretch, glass microspheres did not affect Cx43 expression, or the conduction velocity measured by means of the Micro-Electrode-Array system. (3) At 24 hrs, glass microspheres caused arrhythmias, probably resulting from early afterdepolarizations. (4) Glass microspheres caused the release of angiogenic factors as indicated by an increase in mRNA levels of vascular endothelial growth factor (80%), angiopoietin-2 (60%), transforming growth factor-beta (40%) and basic fibroblast growth factor (15%); these effects were comparable to those of cyclic stretch. (5) As compared with control cultures, conditioned media from cultures exposed to microspheres increased endothelial cell migration by 15% (P<0.05) and endothelial cell tube formation by 120% (P<0.05), both common assays for angiogenesis. In conclusion, based on these findings we propose that loading cardiomyocytes with glass microspheres may serve as a new in vitro model for investigating the role of mechanical forces in angiogenesis and arrhythmias
Cardiac Fibroblast-Induced Pluripotent Stem Cell-Derived Exosomes as a Potential Therapeutic Mean for Heart Failure
The limited regenerative capacity of the injured myocardium leads to remodeling and often heart failure. Novel therapeutic approaches are essential. Induced pluripotent stem cells (iPSC) differentiated into cardiomyocytes are a potential future therapeutics. We hypothesized that organ-specific reprogramed fibroblasts may serve an advantageous source for future cardiomyocytes. Moreover, exosomes secreted from those cells may have a beneficial effect on cardiac differentiation and/or function. We compared RNA from different sources of human iPSC using chip gene expression. Protein expression was evaluated as well as exosome micro-RNA levels and their impact on embryoid bodies (EBs) differentiation. Statistical analysis identified 51 genes that were altered (p †0.05), and confirmed in the protein level, cardiac fibroblasts-iPSCs (CF-iPSCs) vs. dermal fibroblasts-iPSCs (DF-iPSCs). Several miRs were altered especially miR22, a key regulator of cardiac hypertrophy and remodeling. Lower expression of miR22 in CF-iPSCs vs. DF-iPSCs was observed. EBs treated with these exosomes exhibited more beating EBs p = 0.05. vs. control. We identify CF-iPSC and its exosomes as a potential source for cardiac recovery induction. The decrease in miR22 level points out that our CF-iPSC-exosomes are naïve of congestive heart cell memory, making them a potential biological source for future therapy for the injured heart
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