Increased Hemodynamic Load in Early Embryonic Stages Alters Myofibril and Mitochondrial Organization in the Myocardium

Experimental assessment of cardiovascular physiology in the chick embryo

High resolution assessment of cardiac functional parameters is crucial in translational animal research. The chick embryo is a historically well-used in vivo model for cardiovascular research due to its many practical advantages, and the conserved form and function of the chick and human cardiogenesis programs. This review aims to provide an overview of several different technical approaches for chick embryo cardiac assessment. Doppler echocardiography, optical coherence tomography, micromagnetic resonance imaging, microparticle image velocimetry, real-time pressure monitoring, and associated issues with the techniques will be discussed. Alongside this discussion, we also highlight recent advances in cardiac function measurements in chick embryos.

Automated large volume sample preparation for vEM

New developments in electron microscopy technology, improved efficiency of detectors, and artificial intelligence applications for data analysis over the past decade have increased the use of volume electron microscopy (vEM) in the life sciences field. Moreover, sample preparation methods are continuously being modified by investigators to improve final sample quality, increase electron density, combine imaging technologies, and minimize the introduction of artifacts into specimens under study. There are a variety of conventional bench protocols that a researcher can utilize, though most of these protocols require several days. In this work, we describe the utilization of an automated specimen processor, the mPrep™ ASP-2000™, to prepare samples for vEM that are compatible with focused ion beam scanning electron microscopy (FIB-SEM), serial block face scanning electron microscopy (SBF-SEM), and array tomography (AT). The protocols described here aimed for methods that are completed in a much shorter period of time while minimizing the exposure of the operator to hazardous and toxic chemicals and improving the reproducibility of the specimens' heavy metal staining, all without compromising the quality of the data acquired using backscattered electrons during SEM imaging. As a control, we have included a widely used sample bench protocol and have utilized it as a comparator for image quality analysis, both qualitatively and using image quality analysis metrics.

Congenital Heart Disease: An Immunological Perspective

Congenital heart disease (CHD) poses a significant global health and economic burden-despite advances in treating CHD reducing the mortality risk, globally CHD accounts for approximately 300,000 deaths yearly. Children with CHD experience both acute and chronic cardiac complications, and though treatment options have improved, some remain extremely invasive. A challenge in addressing these morbidity and mortality risks is that little is known regarding the cause of many CHDs and current evidence suggests a multifactorial etiology. Some studies implicate an immune contribution to CHD development; however, the role of the immune system is not well-understood. Defining the role of the immune and inflammatory responses in CHD therefore holds promise in elucidating mechanisms underlying these disorders and improving upon current diagnostic and treatment options. In this review, we address the current knowledge coinciding CHDs with immune and inflammatory associations, emphasizing conditions where this understanding would provide clinical benefit, and challenges in studying these mechanisms.

Fetal Blood Flow and Genetic Mutations in Conotruncal Congenital Heart Disease

In congenital heart disease, the presence of structural defects affects blood flow in the heart and circulation. However, because the fetal circulation bypasses the lungs, fetuses with cyanotic heart defects can survive in utero but need prompt intervention to survive after birth. Tetralogy of Fallot and persistent truncus arteriosus are two of the most significant conotruncal heart defects. In both defects, blood access to the lungs is restricted or non-existent, and babies with these critical conditions need intervention right after birth. While there are known genetic mutations that lead to these critical heart defects, early perturbations in blood flow can independently lead to critical heart defects. In this paper, we start by comparing the fetal circulation with the neonatal and adult circulation, and reviewing how altered fetal blood flow can be used as a diagnostic tool to plan interventions. We then look at known factors that lead to tetralogy of Fallot and persistent truncus arteriosus: namely early perturbations in blood flow and mutations within VEGF-related pathways. The interplay between physical and genetic factors means that any one alteration can cause significant disruptions during development and underscore our need to better understand the effects of both blood flow and flow-responsive genes.

Optogenetic cardiac pacing in cultured mouse embryos under imaging guidance

The mouse embryo is an established model for investigation of regulatory mechanisms controlling cardiac development and congenital heart defects in humans. Since cultured mouse embryos are very sensitive to any manipulations and environmental fluctuations, controlled alterations in mouse embryonic cardiac function are extremely challenging, which is a major hurdle in mammalian cardiac biomechanics research. This manuscript presents first optogenetic manipulation of cardiodynamics and hemodynamics in cultured mouse embryos. Optogenetic pacing was combined with 4D (3D + time) optical coherence tomography structural and Doppler imaging, demonstrating that embryonic hearts under optogenetic pacing can function efficiently and produce strong blood flows. This study demonstrates that the presented method is a powerful tool giving quick, consistent, reversible control over heart dynamics and blood flow under real time visualization, enabling various live cardiac biomechanics studies toward better understanding of normal cardiogenesis and congenital heart defects in humans.

Multiscale cardiac imaging spanning the whole heart and its internal cellular architecture in a small animal model

Cardiac pumping depends on the morphological structure of the heart, but also on its subcellular (ultrastructural) architecture, which enables cardiac contraction. In cases of congenital heart defects, localized ultrastructural disruptions that increase the risk of heart failure are only starting to be discovered. This is in part due to a lack of technologies that can image the three-dimensional (3D) heart structure, to assess malformations; and its ultrastructure, to assess organelle disruptions. We present here a multiscale, correlative imaging procedure that achieves high-resolution images of the whole heart, using 3D micro-computed tomography (micro-CT); and its ultrastructure, using 3D scanning electron microscopy (SEM). In a small animal model (chicken embryo), we achieved uniform fixation and staining of the whole heart, without losing ultrastructural preservation on the same sample, enabling correlative multiscale imaging. Our approach enables multiscale studies in models of congenital heart disease and beyond.

Validating the Paradigm That Biomechanical Forces Regulate Embryonic Cardiovascular Morphogenesis and Are Fundamental in the Etiology of Congenital Heart Disease

The goal of this review is to provide a broad overview of the biomechanical maturation and regulation of vertebrate cardiovascular (CV) morphogenesis and the evidence for mechanistic relationships between function and form relevant to the origins of congenital heart disease (CHD). The embryonic heart has been investigated for over a century, initially focusing on the chick embryo due to the opportunity to isolate and investigate myocardial electromechanical maturation, the ability to directly instrument and measure normal cardiac function, intervene to alter ventricular loading conditions, and then investigate changes in functional and structural maturation to deduce mechanism. The paradigm of "Develop and validate quantitative techniques, describe normal, perturb the system, describe abnormal, then deduce mechanisms" was taught to many young investigators by Dr. Edward B. Clark and then validated by a rapidly expanding number of teams dedicated to investigate CV morphogenesis, structure-function relationships, and pathogenic mechanisms of CHD. Pioneering studies using the chick embryo model rapidly expanded into a broad range of model systems, particularly the mouse and zebrafish, to investigate the interdependent genetic and biomechanical regulation of CV morphogenesis. Several central morphogenic themes have emerged. First, CV morphogenesis is inherently dependent upon the biomechanical forces that influence cell and tissue growth and remodeling. Second, embryonic CV systems dynamically adapt to changes in biomechanical loading conditions similar to mature systems. Third, biomechanical loading conditions dynamically impact and are regulated by genetic morphogenic systems. Fourth, advanced imaging techniques coupled with computational modeling provide novel insights to validate regulatory mechanisms. Finally, insights regarding the genetic and biomechanical regulation of CV morphogenesis and adaptation are relevant to current regenerative strategies for patients with CHD.

A workflow for visualizing human cancer biopsies using large-format electron microscopy

Recent developments in large format electron microscopy have enabled generation of images that provide detailed ultrastructural information on normal and diseased cells and tissues. Analyses of these images increase our understanding of cellular organization and interactions and disease-related changes therein. In this manuscript, we describe a workflow for two-dimensional (2D) and three-dimensional (3D) imaging, including both optical and scanning electron microscopy (SEM) methods, that allow pathologists and cancer biology researchers to identify areas of interest from human cancer biopsies. The protocols and mounting strategies described in this workflow are compatible with 2D large format EM mapping, 3D focused ion beam-SEM and serial block face-SEM. The flexibility to use diverse imaging technologies available at most academic institutions makes this workflow useful and applicable for most life science samples. Volumetric analysis of the biopsies studied here revealed morphological, organizational and ultrastructural aspects of the tumor cells and surrounding environment that cannot be revealed by conventional 2D EM imaging. Our results indicate that although 2D EM is still an important tool in many areas of diagnostic pathology, 3D images of ultrastructural relationships between both normal and cancerous cells, in combination with their extracellular matrix, enables cancer researchers and pathologists to better understand the progression of the disease and identify potential therapeutic targets.

Stem cell therapy of myocardial infarction: a promising opportunity in bioengineering

Myocardial infarction (MI) is a life-threatening disease resulting from irreversible death of cardiomyocytes (CMs) and weakening of the heart blood-pumping function. Stem cell-based therapies have been studied for MI treatment over the last two decades with promising outcome. In this review, we critically summarize the past work in this field to elucidate the advantages and disadvantages of treating MI using pluripotent stem cells (PSCs) including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), adult stem cells, and cardiac progenitor cells. The main advantage of the latter is their cytokine production capability to modulate immune responses and control the progression of healing. However, human adult stem cells have very limited (if not 'no') capacity to differentiate into functional CMs in vitro or in vivo. In contrast, PSCs can be differentiated into functional CMs although the protocols for the cardiac differentiation of PSCs are mainly for adherent cells under 2D culture. Derivation of PSC-CMs in 3D, allowing for large-scale production of CMs via modulation of the Wnt/β-catenin signal pathway with defined chemicals and medium, may be desired for clinical translation. Furthermore, the technology of purification and maturation of the PSC-CMs may need further improvements to eliminate teratoma formation after in vivo implantation of the PSC-CMs for treating MI. In addition, in vitro derived PSC-CMs may have mechanical and electrical mismatch with the patient's cardiac tissue, which causes arrhythmia. This supports the use of PSC-derived cells committed to cardiac lineage without beating for implantation to treat MI. In this case, the PSC derived cells may utilize the mechanical, electrical, and chemical cues in the heart to further differentiate into mature/functional CMs in situ. Another major challenge facing stem cell therapy of MI is the low retention/survival of stem cells or their derivatives (e.g., PSC-CMs) in the heart for MI treatment after injection in vivo. This may be resolved by using biomaterials to engineer stem cells for reduced immunogenicity, immobilization of the cells in the heart, and increased integration with the host cardiac tissue. Biomaterials have also been applied in the derivation of CMs in vitro to increase the efficiency and maturation of differentiation. Collectively, a lot has been learned from the past failure of simply injecting intact stem cells or their derivatives in vivo for treating MI, and bioengineering stem cells with biomaterials is expected to be a valuable strategy for advancing stem cell therapy towards its widespread application for treating MI in the clinic.

Second harmonic generation microscopy of early embryonic mouse hearts

The understanding of biomechanical regulation of early heart development in genetic mouse models can contribute to improved management of congenital cardiovascular defects and embryonic cardiac failures in humans. The extracellular matrix (ECM), and particularly fibrillar collagen, are central to heart biomechanics, regulating tissue strength, elasticity and contractility. Here, we explore second harmonic generation (SHG) microscopy for visualization of establishing cardiac fibers such as collagen in mouse embryos through the earliest stages of development. We detected significant increase in SHG positive fibrillar content and organization over the first 24 hours after initiation of contractions. SHG microscopy revealed regions of higher fibrillar organization in regions of higher contractility and reduced fibrillar content and organization in mouse Mlc2a model with cardiac contractility defect, suggesting regulatory role of mechanical load in production and organization of structural fibers from the earliest stages. Simultaneous volumetric SHG and two-photon excitation microscopy of vital fluorescent reporter EGFP in the heart was demonstrated. In summary, these data set SHG microscopy as a valuable non-bias imaging tool to investigate mouse embryonic cardiogenesis and biomechanics.

Reduced embryonic blood flow impacts extracellular matrix deposition in the maturing aorta

BACKGROUND

Perturbations to embryonic hemodynamics are known to adversely affect cardiovascular development. Vitelline vein ligation (VVL) is a model of reduced placental blood flow used to induce cardiac defects in early chick embryo development. The effect of these hemodynamic interventions on maturing elastic arteries is largely unknown. We hypothesize that hemodynamic changes impact maturation of the dorsal aorta (DA).

RESULTS

We examined the effects of VVL on hemodynamic properties well into the maturation process and the corresponding changes in aortic dimensions, wall composition, and gene expression. In chick embryos, we found that DA blood velocity was reduced immediately postsurgery at Hamburger-Hamilton (HH) stage 18 and later at HH36, but not in the interim. Throughout this period, DA diameter adapted to maintain a constant shear stress. At HH36, we found that VVL DAs showed a substantial decrease in elastin and a modest increase in collagen protein content. In VVL DAs, up-regulation of elastic fiber-related genes followed the down-regulation of flow-dependent genes. Together, these suggest the existence of a compensatory mechanism in response to shear-induced delays in maturation.

CONCLUSIONS

The DA's response to hemodynamic perturbations invokes coupled mechanisms for shear regulation and matrix maturation, potentially impacting the course of vascular development. Developmental Dynamics 247:914-923, 2018. © 2018 Wiley Periodicals, Inc.

WDR1-regulated actin dynamics is required for outflow tract and right ventricle development

Outflow tract (OFT) anomalies account for about 30% of human congenital heart defects detected at birth. The second heart field (SHF) progenitors contribute to OFT and right ventricle (RV) development, but the process largely remains unknown. WDR1 (WD-repeat domain 1) is a major co-factor of actin depolymerizing factor (ADF)/cofilin that actively disassembles ADF/cofilin-bound actin filaments. Its function in embryonic heart development has been unknown. Using Wdr1 floxed mice and Nkx2.5-Cre, we deleted Wdr1 in embryonic heart (Wdr1^F/F;Nkx2.5-Cre) and found that these mice exhibited embryonic lethality, and hypoplasia of OFT and RV. To investigate the role of WDR1 in OFT and RV development, we generated SHF progenitors-specific Wdr1 deletion mice (shfKO). shfKO mice began to die at embryonic day 11.5 (E11.5), and displayed decreased size of the proximal OFT and RV at E10.5. In shfKO embryos, neither the number of SHF cells deployment to OFT nor cell proliferation and the cell number were changed, whereas the cellular organization and myofibrillar assembly of cardiomyocytes were severely disrupted. In the proximal OFT and RV of both shfKO and Wdr1^F/F;Nkx2.5-Cre embryos, cardiomyocytes were dissociated from the outer compact myocardial layer and loosely and disorderly arranged into multilayered myocardium. Our results demonstrate that WDR1 is indispensable for normal OFT and RV development, and suggest that WDR1-mediated actin dynamics functions in controlling the size of OFT and RV, which might through regulating the spatial arrangement of cardiomyocytes.