Comparing human iPSC-cardiomyocytes versus HEK293T cells unveils disease-causing effects of Brugada mutation A735V of NaV1.5 sodium channels.

Loss-of-function mutations of the SCN5A gene encoding for the sodium channel α-subunit NaV1.5 result in the autosomal dominant hereditary disease Brugada Syndrome (BrS) with a high risk of sudden cardiac death in the adult. We here engineered human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the CRISPR/Cas9 introduced BrS-mutation p.A735V-NaV1.5 (g.2204C > T in exon 14 of SCN5A) as a novel model independent of patient´s genetic background. Recent studies raised concern regarding the use of hiPSC-CMs for studying adult-onset hereditary diseases due to cells' immature phenotype. To tackle this concern, long-term cultivation of hiPSC-CMs on a stiff matrix (27-42 days) was applied to promote maturation. Patch clamp recordings of A735V mutated hiPSC-CMs revealed a substantially reduced upstroke velocity and sodium current density, a prominent rightward shift of the steady state activation curve and decelerated recovery from inactivation as compared to isogenic hiPSC-CMs controls. These observations were substantiated by a comparative study on mutant A735V-NaV1.5 channels heterologously expressed in HEK293T cells. In contrast to mutated hiPSC-CMs, a leftward shift of sodium channel inactivation was not observed in HEK293T, emphasizing the importance of investigating mechanisms of BrS in independent systems. Overall, our approach supports hiPSC-CMs' relevance for investigating channelopathies in a dish.

Production of Cardiomyocytes from Human Pluripotent Stem Cells by Bioreactor Technologies.

Cardiomyocytes from human pluripotent stem cells (hPSCs) have the ability to advance specificity of in vitro assays for drug discovery and safety pharmacology. They may also provide a superior cell source for envisioned cell therapies to repair damaged hearts. All applications will require the production of cardiomyocytes (CMs) by robust upscalable bioprocesses via industry-compliant technologies. This paper describes a detailed procedure for producing hPSC-CMs in stirred tank bioreactors in 100 ml process scale. The strategy combines both hPSC expansion in suspension culture and, directly followed by, cardiogenic differentiation using small molecule-Wnt pathway modulators. We also provide a protocol describing how to plan and expand the pluripotent stem cells to enable parallel inoculation of 4× 150 ml parallel bioreactor differentiations, potentially producing more than 240 × 106 cardiomyocytes in 22 days.

Evaluating the Effect of Drug Compounds on Cardiac Spheroids Using the Cardiac Cell Outgrowth Assay.

The ideal cell culture model should mimic the cell physiology and the mechanical and the chemical cues that are present in specific tissues and organs, within a convenient high-throughput format. A possible key feature for such models is to recapture the cell polarity, the interactions between cells, and the interactions between the cells and the elastic extracellular matrix (ECM) by orienting the cells in a three-dimensional (3D) matrix. A common method to create 3D cell environments is to let the cells aggregate into spheroids with a diameter of around 200 µm. A major challenge for 3D cell cultures is to perform quick and easy imaging of the dense cell population, especially noninvasively. This protocol explains how to take advantage of the number of cells growing out from cell spheroids over time as a readout of the effect of a drug. The assay is compatible with standard imaging techniques and can be performed noninvasively using light microscopy or as a complement to other fluorescent imaging assays.

Femtosecond laser-based nanosurgery reveals the endogenous regeneration of single Z-discs including physiological consequences for cardiomyocytes.

A highly organized cytoskeleton architecture is the basis for continuous and controlled contraction in cardiomyocytes (CMs). Abnormalities in cytoskeletal elements, like the Z-disc, are linked to several diseases. It is challenging to reveal the mechanisms of CM failure, endogenous repair, or mechanical homeostasis on the scale of single cytoskeletal elements. Here, we used a femtosecond (fs) laser to ablate single Z-discs in human pluripotent stem cells (hPSC) -derived CMs (hPSC-CM) and neonatal rat CMs. We show, that CM viability was unaffected by the loss of a single Z-disc. Furthermore, more than 40% of neonatal rat and 68% of hPSC-CMs recovered the Z-disc loss within 24 h. Significant differences to control cells, after the Z-disc loss, in terms of cell perimeter, x- and y-expansion and calcium homeostasis were not found. Only 14 days in vitro old hPSC-CMs reacted with a significant decrease in cell area, x- and y-expansion 24 h past nanosurgery. This demonstrates that CMs can compensate the loss of a single Z-disc and recover a regular sarcomeric pattern during spontaneous contraction. It also highlights the significant potential of fs laser-based nanosurgery to physically micro manipulate CMs to investigate cytoskeletal functions and organization of single elements.

A Cardiac Cell Outgrowth Assay for Evaluating Drug Compounds Using a Cardiac Spheroid-on-a-Chip Device.

Three-dimensional (3D) models with cells arranged in clusters or spheroids have emerged as valuable tools to improve physiological relevance in drug screening. One of the challenges with cells cultured in 3D, especially for high-throughput applications, is to quickly and non-invasively assess the cellular state in vitro. In this article, we show that the number of cells growing out from human induced pluripotent stem cell (hiPSC)-derived cardiac spheroids can be quantified to serve as an indicator of a drug’s effect on spheroids captured in a microfluidic device. Combining this spheroid-on-a-chip with confocal high content imaging reveals easily accessible, quantitative outgrowth data. We found that effects on outgrowing cell numbers correlate to the concentrations of relevant pharmacological compounds and could thus serve as a practical readout to monitor drug effects. Here, we demonstrate the potential of this semi-high-throughput “cardiac cell outgrowth assay” with six compounds at three concentrations applied to spheroids for 48 h. The image-based readout complements end-point assays or may be used as a non-invasive assay for quality control during long-term culture.

Modulation of cardiomyocyte activity using pulsed laser irradiated gold nanoparticles.

Can photothermal gold nanoparticle mediated laser manipulation be applied to induce cardiac contraction? Based on our previous work, we present a novel concept of cell stimulation. A 532 nm picosecond laser was employed to heat gold nanoparticles on cardiomyocytes. This leads to calcium oscillations in the HL-1 cardiomyocyte cell line. As calcium is connected to the contractility, we aimed to alter the contraction rate of native and stem cell derived cardiomyocytes. A contraction rate increase was particularly observed in calcium containing buffer with neonatal rat cardiomyocytes. Consequently, the study provides conceptual ideas for a light based, nanoparticle mediated stimulation system.

Bulk cell density and Wnt/TGFbeta signalling regulate mesendodermal patterning of human pluripotent stem cells.

In vitro differentiation of human pluripotent stem cells (hPSCs) recapitulates early aspects of human embryogenesis, but the underlying processes are poorly understood and controlled. Here we show that modulating the bulk cell density (BCD: cell number per culture volume) deterministically alters anteroposterior patterning of primitive streak (PS)-like priming. The BCD in conjunction with the chemical WNT pathway activator CHIR99021 results in distinct paracrine microenvironments codifying hPSCs towards definitive endoderm, precardiac or presomitic mesoderm within the first 24 h of differentiation, respectively. Global gene expression and secretome analysis reveals that TGFß superfamily members, antagonist of Nodal signalling LEFTY1 and CER1, are paracrine determinants restricting PS progression. These data result in a tangible model disclosing how hPSC-released factors deflect CHIR99021-induced lineage commitment over time. By demonstrating a decisive, functional role of the BCD, we show its utility as a method to control lineage-specific differentiation. Furthermore, these findings have profound consequences for inter-experimental comparability, reproducibility, bioprocess optimization and scale-up.