Natural and synthetic regulators of embryonic stem cell cardiogenesis

Abstract

Debilitating cardiomyocyte loss underlies the progression to heart failure. Although there have been significant advances in treatment, current therapies are intended to improve or preserve heart function rather than regenerate lost myocardium. A major hurdle in implementing a cell-based regenerative therapy is the inefficient differentiation of cardiomyocytes from either endogenous or exogenous stem cell sources. Moreover, cardiomyocytes that develop in human embryonic stem cell (hESC) or human-induced pluripotent stem cell (hIPSC) cultures are comparatively immature, even after prolonged culture, and differences in their calcium handling, ion channel, and force generation properties relative to adult cardiomyocytes raise concerns of improper integration and function after transplantation. Thus, the discovery of natural and novel small molecule synthetic regulators of differentiation and maturation would accelerate the development of stem-cell-based myocardial therapies. Here, we document recent advances in defining natural signaling pathways that direct the multistep cardiomyogenic differentiation program and the development of small molecules that might be used to enhance differentiation as well as the potential characteristics of lead candidates for pharmaceutical stimulation of endogenous myocardial replacement.

Fig. 1

Schematic overview of the sequential steps and the reported growth factors required for obtaining cardiomyocytes from ESCs. Beating cardiomyocytes can be obtained as soon as 8 days after the initiation of differentiation, going through crucial stages such as mesoderm induction, patterning of mesoderm toward the more anterior fate, specification to cardiac mesoderm, and, finally, maturation to beating cardiomyocytes. From the embryo, we know that each step is controlled by specific growth factors and some of these have been successfully applied on mouse embryonic stem cells (mESC) in specific time windows as indicated in green (pathway activation) or red (pathway inhibition) bars. Blue bars represent the ability of these factors to replicate a certain cell population. SB: SB-431542, a specific Nodal signaling inhibitor [18]

Fig. 2

Schematic comparison between HTSs and HCSs of cell-based assays using fluorescent proteins. Cells carrying a fluorescent reporter are plated after which small molecules are added at a time point of interest. Hits will be identified by the expression of GFP, which can be quantified by using plate readers (HTS) or automated imagers (HCS). Plate readers quantify the GFP signal over the entire well, whereas, with automatic imaging, GFP is quantified by masking the GFP-specific areas alone. The dynamic range of the GFP signal can be about 10-fold greater in HCSs than in HTSs [4]