Differential responses of induced pluripotent stem cell-derived cardiomyocytes to anisotropic strain depends on disease status

Human pluripotent stem cell-derived cardiomyocytes align under cyclic strain when guided by cardiac fibroblasts

The myocardium is a mechanically active tissue typified by anisotropy of the resident cells [cardiomyocytes (CMs) and cardiac fibroblasts (cFBs)] and the extracellular matrix (ECM). Upon ischemic injury, the anisotropic tissue is replaced by disorganized scar tissue, resulting in loss of coordinated contraction. Efforts to re-establish tissue anisotropy in the injured myocardium are hampered by a lack of understanding of how CM and/or cFB structural organization is affected by the two major physical cues inherent in the myocardium: ECM organization and cyclic mechanical strain. Herein, we investigate the singular and combined effect of ECM (dis)organization and cyclic strain in a two-dimensional human in vitro co-culture model of the myocardial microenvironment. We show that (an)isotropic ECM protein patterning can guide the orientation of CMs and cFBs, both in mono- and co-culture. Subsequent application of uniaxial cyclic strain-mimicking the local anisotropic deformation of beating myocardium-causes no effect when applied parallel to the anisotropic ECM. However, when cultured on isotropic substrates, cFBs, but not CMs, orient away from the direction of cyclic uniaxial strain (strain avoidance). In contrast, CMs show strain avoidance via active remodeling of their sarcomeres only when co-cultured with at least 30% cFBs. Paracrine signaling or N-cadherin-mediated communication between CMs and cFBs was no contributing factor. Our findings suggest that the mechanoresponsive cFBs provide structural guidance for CM orientation and elongation. Our study, therefore, highlights a synergistic mechanobiological interplay between CMs and cFBs in shaping tissue organization, which is of relevance for regenerating functionally organized myocardium.

Scaffold-Mediated Developmental Effects on Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Are Preserved After External Support Removal

Human induced pluripotent stem (hiPS) cells have been used as a cell source for regenerative therapy and disease modeling. The purity of hiPS-cardiomyocytes (hiPS-CMs) has markedly improved with advancements in cell culture and differentiation protocols. However, the morphological features and molecular properties of the relatively immature cells are still unclear, which has hampered their clinical application. The aim of the present study was to investigate the extent to which topographic substrates actively influence hiPS-CMs. hiPS-CMs were seeded on randomized oriented fiber substrate (random), anisotropic aligned fiber substrate (align), and flat non-scaffold substrate (flat). After culturing for one week, the hiPS-CMs on the aligned patterns showed more mature-like properties, including elongated rod shape, shorter duration of action potential, accelerated conduction velocity, and elevated cardiac gene expression. Subsequently, to determine whether this development was irreversible or was altered after withdrawal of the structural support, the hiPS-CMs were harvested from the three different patterns and reseeded on the non-scaffold (flat) pattern. After culturing for one more week, the improvements in morphological and functional properties diminished, although hiPS-CMs pre-cultured on the aligned pattern retained the molecular features of development, which were even more significant as compared to that observed during the pre-culture stage. Our results suggested that the anisotropic fiber substrate can induce the formation of geometrical mimic-oriented heart tissue in a short time. Although the morphological and electrophysiological properties of hiPS-CMs obtained via facilitated maturation somehow rely on the existence of an exterior scaffold, the molecular developmental features were preserved even in the absence of the external support, which might persist throughout hiPS-CM development.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Drug-Induced Inotropic Effects in Early Drug Development. Part 2: Designing and Fabricating Microsystems for Assaying Cardiac Contractility With Physiological Relevance Using Human iPSC-Cardiomyocytes

Contractility of the myocardium engines the pumping function of the heart and is enabled by the collective contractile activity of its muscle cells: cardiomyocytes. The effects of drugs on the contractility of human cardiomyocytes in vitro can provide mechanistic insight that can support the prediction of clinical cardiac drug effects early in drug development. Cardiomyocytes differentiated from human-induced pluripotent stem cells have high potential for overcoming the current limitations of contractility assays because they attach easily to extracellular materials and last long in culture, while having human- and patient-specific properties. Under these conditions, contractility measurements can be non-destructive and minimally invasive, which allow assaying sub-chronic effects of drugs. For this purpose, the function of cardiomyocytes in vitro must reflect physiological settings, which is not observed in cultured cardiomyocytes derived from induced pluripotent stem cells because of the fetal-like properties of their contractile machinery. Primary cardiomyocytes or tissues of human origin fully represent physiological cellular properties, but are not easily available, do not last long in culture, and do not attach easily to force sensors or mechanical actuators. Microengineered cellular systems with a more mature contractile function have been developed in the last 5 years to overcome this limitation of stem cell-derived cardiomyocytes, while simultaneously measuring contractile endpoints with integrated force sensors/actuators and image-based techniques. Known effects of engineered microenvironments on the maturity of cardiomyocyte contractility have also been discovered in the development of these systems. Based on these discoveries, we review here design criteria of microengineered platforms of cardiomyocytes derived from pluripotent stem cells for measuring contractility with higher physiological relevance. These criteria involve the use of electromechanical, chemical and morphological cues, co-culture of different cell types, and three-dimensional cellular microenvironments. We further discuss the use and the current challenges for developing and improving these novel technologies for predicting clinical effects of drugs based on contractility measurements with cardiomyocytes differentiated from induced pluripotent stem cells. Future research should establish contexts of use in drug development for novel contractility assays with stem cell-derived cardiomyocytes.

Engineering hiPSC cardiomyocyte in vitro model systems for functional and structural assessment

The study of human cardiomyopathies and the development and testing of new therapies has long been limited by the availability of appropriate in vitro model systems. Cardiomyocytes are highly specialized cells whose internal structure and contractile function are sensitive to the local microenvironment and the combination of mechanical and biochemical cues they receive. The complementary technologies of human induced pluripotent stem cell (hiPSC) derived cardiomyocytes (CMs) and microphysiological systems (MPS) allow for precise control of the genetics and microenvironment of human cells in in vitro contexts. These combined systems also enable quantitative measurement of mechanical function and intracellular organization. This review describes relevant factors in the myocardium microenvironment that affect CM structure and mechanical function and demonstrates the application of several engineered microphysiological systems for studying development, disease, and drug discovery.

A magnetics-based approach for fine-tuning afterload in engineered heart tissues

Afterload plays important roles during heart development and disease progression, however, studying these effects in a laboratory setting is challenging. Current techniques lack the ability to precisely and reversibly alter afterload over time. Here, we describe a magnetics-based approach for achieving this control and present results from experiments in which this device was employed to sequentially increase afterload applied to rat engineered heart tissues (rEHTs) over a 7-day period. The contractile properties of rEHTs grown on control posts marginally increased over the observation period. The average post deflection, fractional shortening, and twitch velocities measured for afterload-affected tissues initially followed this same trend, but fell below control tissue values at high magnitudes of afterload. However, the average force, force production rate, and force relaxation rate for these rEHTs were consistently up to 3-fold higher than in control tissues. Transcript levels of hypertrophic or fibrotic markers and cell size remained unaffected by afterload, suggesting that the increased force output was not accompanied by pathological remodeling. Accordingly, the increased force output was fully reversed to control levels during a stepwise decrease in afterload over 4 hours. Afterload application did not affect systolic or diastolic tissue lengths, indicating that the afterload system was likely not a source of changes in preload strain. In summary, the afterload system developed herein is capable of fine-tuning EHT afterload while simultaneously allowing optical force measurements. Using this system, we found that small daily alterations in afterload can enhance the contractile properties of rEHTs, while larger increases can have temporary undesirable effects. Overall, these findings demonstrate the significant role that afterload plays in cardiac force regulation. Future studies with this system may allow for novel insights into the mechanisms that underlie afterload-induced adaptations in cardiac force development.

Substrate Stiffness, Cell Anisotropy, and Cell-Cell Contact Contribute to Enhanced Structural and Calcium Handling Properties of Human Embryonic Stem Cell-Derived Cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) can be utilized to understand the mechanisms underlying the development and progression of heart disease, as well as to develop better interventions and treatments for this disease. However, these cells are structurally and functionally immature, which undermines some of their adequacy in modeling adult heart tissue. Previous studies with immature cardiomyocytes have shown that altering substrate stiffness, cell anisotropy, and/or cell-cell contact can enhance the contractile and structural maturation of hPSC-CMs. In this study, the structural and calcium handling properties of human embryonic stem cell-derived cardiomyocytes (hESC-CMs) were enhanced by exposure to a downselected combination of these three maturation stimuli. First, hESC-CMs were seeded onto substrates composed of two commercial formulations of polydimethylsiloxane (PDMS), Sylgard 184 and Sylgard 527, whose stiffness ranged from 5 kPa to 101 kPa. Upon analyzing the morphological and calcium transient properties of these cells, it was concluded that a 21 kPa substrate yielded cells with the highest degree of maturation. Next, these PDMS substrates were microcontact-printed with laminin to force the cultured cells into rod-shaped geometries using line patterns that were 12, 18, or 24 μm in width. We found that cells on the 18 and 24 μm pattern widths had structural and functional properties that were superior to those on the 12 μm pattern. The hESC-CMs were then seeded onto these line-stamped surfaces at a density of 500 000 cells per 25-mm-diameter substrate, to enable the formation of cell-cell contacts at their distal ends. We discovered that this combination of culture conditions resulted in cells that were more structurally and functionally mature than those that were only exposed to one or two stimuli. Our results suggest that downselecting a combination of mechanobiological stimuli could prove to be an effective means of maturing hPSC-CMs in vitro.

Unchain My Heart: Integrins at the Basis of iPSC Cardiomyocyte Differentiation

The cellular response to the extracellular matrix (ECM) microenvironment mediated by integrin adhesion is of fundamental importance, in both developmental and pathological processes. In particular, mechanotransduction is of growing importance in groundbreaking cellular models such as induced pluripotent stem cells (iPSC), since this process may strongly influence cell fate and, thus, augment the precision of differentiation into specific cell types, e.g., cardiomyocytes. The decryption of the cellular machinery starting from ECM sensing to iPSC differentiation calls for new in vitro methods. Conveniently, engineered biomaterials activating controlled integrin-mediated responses through chemical, physical, and geometrical designs are key to resolving this issue and could foster clinical translation of optimized iPSC-based technology. This review introduces the main integrin-dependent mechanisms and signalling pathways involved in mechanotransduction. Special consideration is given to the integrin-iPSC linkage signalling chain in the cardiovascular field, focusing on biomaterial-based in vitro models to evaluate the relevance of this process in iPSC differentiation into cardiomyocytes.

Mechanical activation of noncoding-RNA-mediated regulation of disease-associated phenotypes in human cardiomyocytes

How common polymorphisms in noncoding genome regions can regulate cellular function remains largely unknown. Here we show that cardiac fibrosis, mimicked using a hydrogel with controllable stiffness, affects the regulation of the phenotypes of human cardiomyocytes by a portion of the long noncoding RNA ANRIL, the gene of which is located in the disease-associated 9p21 locus. In a physiological environment, cultured cardiomyocytes derived from induced pluripotent stem cells obtained from patients who are homozygous for cardiovascular-risk alleles (R/R cardiomyocytes) or from healthy individuals who are homozygous for nonrisk alleles contracted synchronously, independently of genotype. After hydrogel stiffening to mimic fibrosis, only the R/R cardiomyocytes exhibited asynchronous contractions. These effects were associated with increased expression of the short ANRIL isoform in R/R cardiomyocytes, which induced a c-Jun N-terminal kinase (JNK) phosphorylation-based mechanism that impaired gap junctions (particularly, loss of connexin-43 expression) following stiffening. Deletion of the risk locus or treatment with a JNK antagonist was sufficient to maintain gap junctions and prevent asynchronous contraction of cardiomyocytes. Our findings suggest that mechanical changes in the microenvironment of cardiomyocytes can activate the regulation of their function by noncoding loci.

The march of pluripotent stem cells in cardiovascular regenerative medicine

Cardiovascular disease (CVD) continues to be the leading cause of global morbidity and mortality. Heart failure remains a major contributor to this mortality. Despite major therapeutic advances over the past decades, a better understanding of molecular and cellular mechanisms of CVD as well as improved therapeutic strategies for the management or treatment of heart failure are increasingly needed. Loss of myocardium is a major driver of heart failure. An attractive approach that appears to provide promising results in reducing cardiac degeneration is stem cell therapy (SCT). In this review, we describe different types of stem cells, including embryonic and adult stem cells, and we provide a detailed discussion of the properties of induced pluripotent stem cells (iPSCs). We also present and critically discuss the key methods used for converting somatic cells to pluripotent cells and iPSCs to cardiomyocytes (CMs), along with their advantages and limitations. Integrating and non-integrating reprogramming methods as well as characterization of iPSCs and iPSC-derived CMs are discussed. Furthermore, we critically present various methods of differentiating iPSCs to CMs. The value of iPSC-CMs in regenerative medicine as well as myocardial disease modeling and cardiac regeneration are emphasized.

Genome Editing and Induced Pluripotent Stem Cell Technologies for Personalized Study of Cardiovascular Diseases

PURPOSE OF REVIEW

The goal of this review is to highlight the potential of induced pluripotent stem cell (iPSC)-based modeling as a tool for studying human cardiovascular diseases. We present some of the current cardiovascular disease models utilizing genome editing and patient-derived iPSCs.

RECENT FINDINGS

The incorporation of genome-editing and iPSC technologies provides an innovative research platform, providing novel insight into human cardiovascular disease at molecular, cellular, and functional level. In addition, genome editing in diseased iPSC lines holds potential for personalized regenerative therapies. The study of human cardiovascular disease has been revolutionized by cellular reprogramming and genome editing discoveries. These exceptional technologies provide an opportunity to generate human cell cardiovascular disease models and enable therapeutic strategy development in a dish. We anticipate these technologies to improve our understanding of cardiovascular disease pathophysiology leading to optimal treatment for heart diseases in the future.

Nanotopographic Influence on the In Vitro Behavior of Induced Pluripotent Stem Cells

While the influence of nanotopography on stem cell behavior has been extensively investigated on adult stem cells, far fewer studies have investigated the interaction of induced pluripotent stem cells (iPSCs) with various nanotopographical patterns. The purpose of this study was to identify nanopatterns that can influence the stemness and proliferation, as well as the adhesive properties in iPSCs, and thereby explore the feasibility of applying these nano-features for regenerative medicine. Three kinds of nanopatterns were fabricated from polydimethylsiloxane membranes, irregular patterned membrane (IPM), groove patterned membrane (GPM), and postpatterned membrane (PPM), in addition to flat patterned membrane (FPM) which did not have any nanotopographic features and was used as the control pattern. On the surfaces of GPM or PPM, iPSCs showed tendency for aggregation and did not spread out well at passage 1. However, with continued passaging (P6, P10), the tendency to form aggregates was greatly reduced. While iPSCs cultured on GPM and PPM had low population doubling time values compared with FPM and IPM at P1, the differences disappeared in later passages. The expression of the cell proliferation marker Ki67 in iPSCs gradually decreased with continued passaging in cells cultured on FPM and IPM, but not in those cultured on GPM and PPM. The expression of Oct3/4 and Nanog, marker of stemness, was significantly higher on GPM and PPM than on FPM at P6 and P10. At P5, numerous filopodia were demonstrated in the peripheral attachments of iPSC colonies on FPM and IPM, while GPM and PPM generally had globular appearance. The expression of the focal adhesion (FA) molecules α-actinin, vinculin, phalloidin, or FA kinase was significantly greater on GPM and PPM than on FPM and IPM at P6 or P10. In conclusion, continued passaging on regular nanopatterns, including groove- and post-forms, was effective in maintaining an undifferentiated state and proliferation of iPSCs and also in increasing the expression of FA molecules.