Naturally Engineered Maturation of Cardiomyocytes

Abstract

Ischemic heart disease remains one of the most prominent causes of mortalities worldwide with heart transplantation being the gold-standard treatment option. However, due to the major limitations associated with heart transplants, such as an inadequate supply and heart rejection, there remains a significant clinical need for a viable cardiac regenerative therapy to restore native myocardial function. Over the course of the previous several decades, researchers have made prominent advances in the field of cardiac regeneration with the creation of in vitro human pluripotent stem cell-derived cardiomyocyte tissue engineered constructs. However, these engineered constructs exhibit a functionally immature, disorganized, fetal-like phenotype that is not equivalent physiologically to native adult cardiac tissue. Due to this major limitation, many recent studies have investigated approaches to improve pluripotent stem cell-derived cardiomyocyte maturation to close this large functionality gap between engineered and native cardiac tissue. This review integrates the natural developmental mechanisms of cardiomyocyte structural and functional maturation. The variety of ways researchers have attempted to improve cardiomyocyte maturation in vitro by mimicking natural development, known as natural engineering, is readily discussed. The main focus of this review involves the synergistic role of electrical and mechanical stimulation, extracellular matrix interactions, and non-cardiomyocyte interactions in facilitating cardiomyocyte maturation. Overall, even with these current natural engineering approaches, pluripotent stem cell-derived cardiomyocytes within three-dimensional engineered heart tissue still remain mostly within the early to late fetal stages of cardiomyocyte maturity. Therefore, although the end goal is to achieve adult phenotypic maturity, more emphasis must be placed on elucidating how the in vivo fetal microenvironment drives cardiomyocyte maturation. This information can then be utilized to develop natural engineering approaches that can emulate this fetal microenvironment and thus make prominent progress in pluripotent stem cell-derived maturity toward a more clinically relevant model for cardiac regeneration.

3D bioprinting for cardiovascular regeneration and pharmacology

“…To accelerate the maturation process, advanced bioengineering approaches focus on providing relevant environmental motifs via bioreactor or stimulation settings, including: biochemical, topographical, mechanical, and electrical signals [146–148]. Based on biological principles, these engineering designs attempt to recapitulate some of the crucial physiological events to improve the matrix reorganization during cardiovascular development.…”

“…Based on biological principles, these engineering designs attempt to recapitulate some of the crucial physiological events to improve the matrix reorganization during cardiovascular development. These relevant physio logical events and characteristics include anisotropic cell alignment, biochemical factors with spatiotemporal distribution, hydrodynamic forces associated with perfusion, rhythmical mechanical stretch, and pulsatile electrical stimulation [146,148,149] (Fig. 1).…”

“…Immature CMs are considered to be hypoxia resistant, and are able to develop without an apparent loss of function under anoxic conditions [15]. However, the maturation of CMs increases mechanical and electrical production, which may decrease resistance to hypoxia over time, and can lead to lower cell survival after implantation [148]. Due to the low solubility of oxygen in standard media, oxygen depletion becomes a serious problem in the micro-physiological systems that house 3D cardiac tissues, and may contribute to abnormal tissue function [12,80].…”

“…Strain can be employed by controlling the substrate properties of the constructs, such as the modulus and surface stiffness, or transferring external stimuli, such as compressive and tensile forces. Mechanical stretch is the most common method to generate contractile motion in vitro , which imitates the normal conditions of the heart contracting against the blood pressure [148,149]. Additionally, the passive tension is able to induce anisotropic alignment of the CMs along with the force direction, which improves mechano-transduction and facilitates electrical conduction [146].…”

“…Rhythmic beating of the heart (or synchronous contraction of CMs) is initiated by the pacemaker cells in the sinoatrial node, and is propagated by electrical signals over the whole heart [146,148,149,171,172]. The electrical signals mainly depend on the voltage-gated calcium channels of the cell membrane, and are converted into mechanical responses through an ECC process [146,148].…”