Toward improved myocardial maturity in an organ-on-chip platform with immature cardiac myocytes

Abstract

In vitro studies of cardiac physiology and drug response have traditionally been performed on individual isolated cardiomyocytes or isotropic monolayers of cells that may not mimic desired physiological traits of the laminar adult myocardium. Recent studies have reported a number of advances to Heart-on-a-Chip platforms for the fabrication of more sophisticated engineered myocardium, but cardiomyocyte immaturity remains a challenge. In the anisotropic musculature of the heart, interactions between cardiac myocytes, the extracellular matrix (ECM), and neighboring cells give rise to changes in cell shape and tissue architecture that have been implicated in both development and disease. We hypothesized that engineered myocardium fabricated from cardiac myocytes cultured in vitro could mimic the physiological characteristics and gene expression profile of adult heart muscle. To test this hypothesis, we fabricated engineered myocardium comprised of neonatal rat ventricular myocytes with laminar architectures reminiscent of that observed in the mature heart and compared their sarcomere organization, contractile performance characteristics, and cardiac gene expression profile to that of isolated adult rat ventricular muscle strips. We found that anisotropic engineered myocardium demonstrated a similar degree of global sarcomere alignment, contractile stress output, and inotropic concentration-response to the β-adrenergic agonist isoproterenol. Moreover, the anisotropic engineered myocardium exhibited comparable myofibril related gene expression to muscle strips isolated from adult rat ventricular tissue. These results suggest that tissue architecture serves an important developmental cue for building in vitro model systems of the myocardium that could potentially recapitulate the physiological characteristics of the adult heart. Impact statement With the recent focus on developing in vitro Organ-on-Chip platforms that recapitulate tissue and organ-level physiology using immature cells derived from stem cell sources, there is a strong need to assess the ability of these engineered tissues to adopt a mature phenotype. In the present study, we compared and contrasted engineered tissues fabricated from neonatal rat ventricular myocytes in a Heart-on-a-Chip platform to ventricular muscle strips isolated from adult rats. The results of this study support the notion that engineered tissues fabricated from immature cells have the potential to mimic mature tissues in an Organ-on-Chip platform.

Striated myocyte structural integrity: Automated analysis of sarcomeric z-discs

“…A major achievement of this work was automating z-line isolation, making analysis of zline architecture in single cells, engineered tissues, and tissue sections [35] possible without the need for experts to trace z-lines [32] or manually segment off-target staining [5,8,18,30,35]. Segmentation guided by local actin orientation eliminates pixels that correspond to off-target staining, where in manual segmentation it is only possible to eliminate large regions of offtarget staining.…”

Traction force microscopy of engineered cardiac tissues

“…This exquisitely-controlled, multi-scale dynamic is difficult to study in-vivo as one must compromise the organ structure to isolate individual cardiomyocytes. Alternatively, the spatial complexity of the heart musculature may be reconstructed in-vitro using cardiac microphysiological systems (MPS)[ 3 , 4 ]. In these platforms, we engineer muscle cells and tissues to recapitulate native-like structure and assess their contractile function using a variety of techniques.…”

Organ‐on‐chip models: Implications in drug discovery and clinical applications

“…Contractility, sarcomere structure, inotropic response to β‐adrenergic agonists, and gene expression were all measured to approximate the relative similarity to adult physiological phenotype. The global z‐line alignment and contractile force in this anisotropic cardiomyocyte microfabrication showed remarkably similar myofibrillar structure–function when compared to adult rat muscle strip isolates (Sheehy et al, ). Administration of the β‐adrenergic agonist isoproterenol to the anisotropic cardiomyocytes displayed similar inotropic responses when compared to a control group of in vitro cells and had an EC 50 value within the same order of magnitude as rat ventricular myocardium.…”