Primitive macrophages induce sarcomeric maturation and functional enhancement of developing human cardiac microtissues via efferocytic pathways.

Yolk sac macrophages are the first to seed the developing heart, however we have no understanding of their roles in human heart development and function due to a lack of accessible tissue. Here, we bridge this gap by differentiating human embryonic stem cells (hESCs) into primitive LYVE1+ macrophages (hESC-macrophages) that stably engraft within contractile cardiac microtissues composed of hESC-cardiomyocytes and fibroblasts. Engraftment induces a human fetal cardiac macrophage gene program enriched in efferocytic pathways. Functionally, hESC-macrophages trigger cardiomyocyte sarcomeric protein maturation, enhance contractile force and improve relaxation kinetics. Mechanistically, hESC-macrophages engage in phosphatidylserine dependent ingestion of apoptotic cardiomyocyte cargo, which reduces microtissue stress, leading hESC-cardiomyocytes to more closely resemble early human fetal ventricular cardiomyocytes, both transcriptionally and metabolically. Inhibiting hESC-macrophage efferocytosis impairs sarcomeric protein maturation and reduces cardiac microtissue function. Taken together, macrophage-engineered human cardiac microtissues represent a considerably improved model for human heart development, and reveal a major beneficial role for human primitive macrophages in enhancing early cardiac tissue function.

Primitive macrophages enable long-term vascularization of human heart-on-a-chip platforms.

The intricate anatomical structure and high cellular density of the myocardium complicate the bioengineering of perfusable vascular networks within cardiac tissues. In vivo neonatal studies highlight the key role of resident cardiac macrophages in post-injury regeneration and angiogenesis. Here, we integrate human pluripotent stem-cell-derived primitive yolk-sac-like macrophages within vascularized heart-on-chip platforms. Macrophage incorporation profoundly impacted the functionality and perfusability of microvascularized cardiac tissues up to 2 weeks of culture. Macrophages mitigated tissue cytotoxicity and the release of cell-free mitochondrial DNA (mtDNA), while upregulating the secretion of pro-angiogenic, matrix remodeling, and cardioprotective cytokines. Bulk RNA sequencing (RNA-seq) revealed an upregulation of cardiac maturation and angiogenesis genes. Further, single-nuclei RNA sequencing (snRNA-seq) and secretome data suggest that macrophages may prime stromal cells for vascular development by inducing insulin like growth factor binding protein 7 (IGFBP7) and hepatocyte growth factor (HGF) expression. Our results underscore the vital role of primitive macrophages in the long-term vascularization of cardiac tissues, offering insights for therapy and advancing heart-on-a-chip technologies.

Heart-on-a-Chip Model of Epicardial-Myocardial Interaction in Ischemia Reperfusion Injury.

Epicardial cells (EPIs) form the outer layer of the heart and play an important role in development and disease. Current heart-on-a-chip platforms still do not fully mimic the native cardiac environment due to the absence of relevant cell types, such as EPIs. Here, using the Biowire II platform, engineered cardiac tissues with an epicardial outer layer and inner myocardial structure are constructed, and an image analysis approach is developed to track the EPI cell migration in a beating myocardial environment. Functional properties of EPI cardiac tissues improve over two weeks in culture. In conditions mimicking ischemia reperfusion injury (IRI), the EPI cardiac tissues experience less cell death and a lower impact on functional properties. EPI cell coverage is significantly reduced and more diffuse under normoxic conditions compared to the post-IRI conditions. Upon IRI, migration of EPI cells into the cardiac tissue interior is observed, with contributions to alpha smooth muscle actin positive cell population. Altogether, a novel heart-on-a-chip model is designed to incorporate EPIs through a formation process that mimics cardiac development, and this work demonstrates that EPI cardiac tissues respond to injury differently than epicardium-free controls, highlighting the importance of including EPIs in heart-on-a-chip constructs that aim to accurately mimic the cardiac environment.

Noninvasive Quantification of Contractile Dynamics in Cardiac Cells, Spheroids, and Organs-on-a-Chip Using High-Frequency Ultrasound.

Cell-based models that mimic in vivo heart physiology are poised to make significant advances in cardiac disease modeling and drug discovery. In these systems, cardiomyocyte (CM) contractility is an important functional metric, but current measurement methods are inaccurate and low-throughput or require complex setups. To address this need, we developed a standalone noninvasive, label-free ultrasound technique operating at 40-200 MHz to measure the contractile kinetics of cardiac models, ranging from single adult CMs to 3D microtissue constructs in standard cell culture formats. The high temporal resolution of 1000 fps resolved the beat profile of single mouse CMs paced at up to 9 Hz, revealing limitations of lower speed optical based measurements to resolve beat kinetics or characterize aberrant beats. Coupling of ultrasound with traction force microscopy enabled the measurement of the CM longitudinal modulus and facile estimation of adult mouse CM contractile forces of 2.34 ± 1.40 µN, comparable to more complex measurement techniques. Similarly, the beat rate, rhythm, and drug responses of CM spheroid and microtissue models were measured, including in configurations without optical access. In conclusion, ultrasound can be used for the rapid characterization of CM contractile function in a wide range of commonly studied configurations ranging from single cells to 3D tissue constructs using standard well plates and custom microdevices, with applications in cardiac drug discovery and cardiotoxicity evaluation.

Modeling cardiac fibroblast heterogeneity from human pluripotent stem cell-derived epicardial cells.

Cardiac fibroblasts play an essential role in the development of the heart and are implicated in disease progression in the context of fibrosis and regeneration. Here, we establish a simple organoid culture platform using human pluripotent stem cell-derived epicardial cells and ventricular cardiomyocytes to study the development, maturation, and heterogeneity of cardiac fibroblasts under normal conditions and following treatment with pathological stimuli. We demonstrate that this system models the early interactions between epicardial cells and cardiomyocytes to generate a population of fibroblasts that recapitulates many aspects of fibroblast behavior in vivo, including changes associated with maturation and in response to pathological stimuli associated with cardiac injury. Using single cell transcriptomics, we show that the hPSC-derived organoid fibroblast population displays a high degree of heterogeneity that approximates the heterogeneity of populations in both the normal and diseased human heart. Additionally, we identify a unique subpopulation of fibroblasts possessing reparative features previously characterized in the hearts of model organisms. Taken together, our system recapitulates many aspects of human cardiac fibroblast specification, development, and maturation, providing a platform to investigate the role of these cells in human cardiovascular development and disease.

Modeling human multi-lineage heart field development with pluripotent stem cells.

The cardiomyocyte (CM) subtypes in the mammalian heart derive from distinct lineages known as the first heart field (FHF), the anterior second heart field (aSHF), and the posterior second heart field (pSHF) lineages that are specified during gastrulation. We modeled human heart field development from human pluripotent stem cells (hPSCs) by using single-cell RNA-sequencing to delineate lineage specification and progression. Analyses of hPSC-derived and mouse mesoderm transcriptomes enabled the identification of distinct human FHF, aSHF, and pSHF mesoderm subpopulations. Through staged manipulation of signaling pathways identified from transcriptomics, we generated myocyte populations that display molecular characteristics of key CM subtypes. The developmental trajectory of the human cardiac lineages recapitulated that of the mouse, demonstrating conserved cardiovascular programs. These findings establish a comprehensive landscape of human embryonic cardiogenesis that provides access to a broad spectrum of cardiomyocytes for modeling congenital heart diseases and chamber-specific cardiomyopathies as well as for developing new therapies to treat them.

Generation of mature compact ventricular cardiomyocytes from human pluripotent stem cells.

Compact cardiomyocytes that make up the ventricular wall of the adult heart represent an important therapeutic target population for modeling and treating cardiovascular diseases. Here, we established a differentiation strategy that promotes the specification, proliferation and maturation of compact ventricular cardiomyocytes from human pluripotent stem cells (hPSCs). The cardiomyocytes generated under these conditions display the ability to use fatty acids as an energy source, a high mitochondrial mass, well-defined sarcomere structures and enhanced contraction force. These ventricular cells undergo metabolic changes indicative of those associated with heart failure when challenged in vitro with pathological stimuli and were found to generate grafts consisting of more mature cells than those derived from immature cardiomyocytes following transplantation into infarcted rat hearts. hPSC-derived atrial cardiomyocytes also responded to the maturation cues identified in this study, indicating that the approach is broadly applicable to different subtypes of the heart. Collectively, these findings highlight the power of recapitulating key aspects of embryonic and postnatal development for generating therapeutically relevant cell types from hPSCs.

Functional arrays of human pluripotent stem cell-derived cardiac microtissues.

To accelerate the cardiac drug discovery pipeline, we set out to develop a platform that would be capable of quantifying tissue-level functions such as contractile force and be amenable to standard multiwell-plate manipulations. We report a 96-well-based array of 3D human pluripotent stem cell (hPSC)-derived cardiac microtissues - termed Cardiac MicroRings (CaMiRi) - in custom 3D-print-molded multiwell plates capable of contractile force measurement. Within each well, two elastomeric microcantilevers are situated above a circumferential ramp. The wells are seeded with cell-laden collagen, which, in response to the gradual slope of the circumferential ramp, self-organizes around tip-gated microcantilevers to form contracting CaMiRi. The contractile force exerted by the CaMiRi is measured and calculated using the deflection of the cantilevers. Platform responses were robust and comparable across wells, and we used it to determine an optimal tissue formulation. We validated the contractile force response of CaMiRi using selected cardiotropic compounds with known effects. Additionally, we developed automated protocols for CaMiRi seeding, image acquisition, and analysis to enable the measurement of contractile force with increased throughput. The unique tissue fabrication properties of the platform, and the consequent effects on tissue function, were demonstrated upon adding hPSC-derived epicardial cells to the system. This platform represents an open-source contractile force screening system useful for drug screening and tissue engineering applications.

Anomalous origins of the coronary arteries: current knowledge and future perspectives.

PURPOSE OF REVIEW: The purpose of this review is to survey the contemporary literature surrounding congenital anomalies of origin of the coronary arteries and to identify remaining gaps in knowledge. RECENT FINDINGS: In recent years, lineage tracing analyses and mechanistic studies in model organisms have enhanced our understanding of the normal embryologic development of the coronary arteries, and how disruption of this intricate process can lead to congenital coronary anomalies. The true incidence of these anomalies remains unknown. Although a majority of cases are believed to be clinically silent, clinical presentation varies widely, from asymptomatic to sudden cardiac death. Cardiac computed tomography angiography and/or magnetic resonance angiography are the mainstay diagnostic modalities. Management of anomalous coronary arteries depends on the morphology and clinical presentation. Surgery is the gold-standard treatment for anomalous left coronary artery arising from the pulmonary artery and anomalous aortic origin of a coronary artery with intramural or interarterial course. SUMMARY: Several large multicenter initiatives are currently underway and should help address some of the numerous knowledge gaps surrounding the evaluation and management of anomalous coronary arteries.