From iPSC towards cardiac tissue-a road under construction

Abstract

The possibility to generate induced pluripotent stem cells (iPSC) opens the way to generate virtually all cell types of our human body. In combination with modern gene editing techniques like CRISPR/CAS, a new set of powerful tools becomes available for life science. Scientific fields like genotype and cell type-specific pharmacology, disease modeling, stem cell biology, and developmental biology have been dramatically fostered and their faces have been changed. However, as golden as the age of iPSC-derived cells and their manipulation has started, the shine begins to tarnish. Researchers face more and more practical problems intrinsic to the system. These problems are related to the specific culturing conditions which are not yet sufficient to mimic the natural environment of native stem cells differentiating towards adult cells. However, researchers work hard to uncover these factors. Here, we review a common standard approach to generate iPSCs and transduce these to iPSC cardiomyocytes. Further, we review recent achievements and discuss their current limitations and future perspectives. We are on track, but the road is still under construction.

Keywords: Cardiac differentiation; Induced pluripotent stem cell; Long QT syndrome; Myocyte physiology; Signaling pathway.

Fig. 1

Smad-signaling pathways. Smad 2/3 in cooperation with Smad 4 evoke the expression of pluripotency genes such as NANOG, while the presence of Smad 1/5/8 blocks the expression of pluripotency genes when Smad 4 is present

Fig. 2

Stem cell line SFS.1 used for cardiac differentiation in optimal conditions. Left: SFS.1 at day 1 after replating. The cell layer is already dense and the cell morphology is vital. Right: SFS.1 at day 4 after replating. Cells reached confluency and individual cell bodies cannot be distinguished. Cells are ready for the start of the differentiation

Fig. 3

Activation of WNT signaling by CHIR is crucial for differentiation. Left: Wnt binding to β Catenin is blocked by GSK3, suppressing the Wnt pathway and inhibiting gene transcription. Right: The Wnt activator CHIR acts as a GSK3 inhibitor leading to Wnt/β Catenin interaction with subsequent gene transcription

Fig. 4

Principle of cardiac differentiation. Most important is activation of the Wnt and BMP pathway from hour 0–24 and the Wnt inhibition from 48 to 96 h after initiation of differentiation

Fig. 5

Differentiated cardiac tissue on day 8 of trans-differentiation. Morphological changes from stem cell to cardiac like cell. Autonomously active beating muscular tissue expressing cardiac markers and producing action potentials

Fig. 6

Mechanisms to drive stem cells into a specific lineage are well compared to an electrical circuit diagram. Growth factor stimuli applied in cascade can be compared to control dials in an electrical circuit. Switching specific dials shifts the driving force for differentiation from one line to the other. Resistive dials are better suited to describe the biological processes rather than simple on/off switches. The increase in resistance in one electrical path increases currents in the alternative path and thereby determine which light emitting diode (LED) will glow. Here, blue represents cardiac cells (cardiac lineage), other mesodermal cells (other mesodermal lineage) are indicated by pink, and neurogenic cells (neuronal lineage) are indicated by green