Calcium signaling regulates ventricular hypertrophy during development independent of contraction or blood flow

A bioelectrical phase transition patterns the first vertebrate heartbeats

A regular heartbeat is essential to vertebrate life. In the mature heart, this function is driven by an anatomically localized pacemaker. By contrast, pacemaking capability is broadly distributed in the early embryonic heart1-3, raising the question of how tissue-scale activity is first established and then maintained during embryonic development. The initial transition of the heart from silent to beating has never been characterized at the timescale of individual electrical events, and the structure in space and time of the early heartbeats remains poorly understood. Using all-optical electrophysiology, we captured the very first heartbeat of a zebrafish and analysed the development of cardiac excitability and conduction around this singular event. The first few beats appeared suddenly, had irregular interbeat intervals, propagated coherently across the primordial heart and emanated from loci that varied between animals and over time. The bioelectrical dynamics were well described by a noisy saddle-node on invariant circle bifurcation with action potential upstroke driven by CaV1.2. Our work shows how gradual and largely asynchronous development of single-cell bioelectrical properties produces a stereotyped and robust tissue-scale transition from quiescence to coordinated beating.

Can Blebbistatin block the hypertrophy status in the zebrafish exvivo cardiac model?

Ex-vivo simple models are powered tools to study cardiac hypertrophy. It is possible to control the activation of critical genes and thus test the effects of drug therapies before the in vivo tests. A zebrafish cardiac hypertrophy developed by 500 μM phenylephrine (PE) treatment in ex vivo culture has been demonstrated to activate the essential expression of the embryonal genes. These genes are the same as those described in several previous pieces of research on hypertrophic pathology in humans. The efficacy of the chemical drug Blebbistatin (BL) on hypertrophy induced ex vivo cultured hearts is studied in this research. BL can inhibit the myosins and the calcium wave in counteracting the hypertrophy status caused by PE. Samples treated with PE, BL and PE simultaneously, or pre/post-treatment with BL, have been analysed for the embryonal gene activation concerning the hypertrophy status. The qRTPCR has shown an inhibitory effect of BL treatments on the microRNAs downregulation with the consequent low expression of essential embryonal genes. In particular, BL seems to be effective in blocking the hyperplasia of the epicardium but less effective in myocardium hypertrophy. The model can make it possible to obtain knowledge on the transduction pathways activated by BL and investigate the potential use of this drug in treating cardiac hypertrophy in humans.

A Meta-Analysis of Bioelectric Data in Cancer, Embryogenesis, and Regeneration

Developmental bioelectricity is the study of the endogenous role of bioelectrical signaling in all cell types. Resting potentials and other aspects of ionic cell physiology are known to be important regulatory parameters in embryogenesis, regeneration, and cancer. However, relevant quantitative measurement and genetic phenotyping data are distributed throughout wide-ranging literature, hampering experimental design and hypothesis generation. Here, we analyze published studies on bioelectrics and transcriptomic and genomic/phenotypic databases to provide a novel synthesis of what is known in three important aspects of bioelectrics research. First, we provide a comprehensive list of channelopathies-ion channel and pump gene mutations-in a range of important model systems with developmental patterning phenotypes, illustrating the breadth of channel types, tissues, and phyla (including man) in which bioelectric signaling is a critical endogenous aspect of embryogenesis. Second, we perform a novel bioinformatic analysis of transcriptomic data during regeneration in diverse taxa that reveals an electrogenic protein to be the one common factor specifically expressed in regeneration blastemas across Kingdoms. Finally, we analyze data on distinct V_mem signatures in normal and cancer cells, revealing a specific bioelectrical signature corresponding to some types of malignancies. These analyses shed light on fundamental questions in developmental bioelectricity and suggest new avenues for research in this exciting field.

Sodium dehydroacetate induces cardiovascular toxicity associated with Ca2+ imbalance in zebrafish

The environmental effects of additives have attracted increasing attention. Sodium dehydroacetate (DHA-S), as an approved preservative, is widely added in processed foods, cosmetics and personal care products. However, DHA-S has been recently reported to induce hemorrhage and coagulation aberration in rats. Yet little is known about the ecotoxicological effect and underlying mechanisms of DHA-S. Here, we utilized the advantage of zebrafish model to evaluate such effects. DHA-S induced cerebral hemorrhage, mandibular dysplasia and pericardial edema in zebrafish after 24 h exposure (48-72 hpf) at 50 mg/L. We also observed the defective heart looping and apoptosis in DHA-S-treated zebrafish through o-dianisidine and acridine orange staining. Meanwhile, DHA-S induced the deficiency of Ca²⁺ and vitamin D3 in zebrafish. We further demonstrated that DHA-S stimulated Ca²⁺ influx resulting in Ca²⁺-dependent mitochondrial damage in cardiomyocytes. Additionally, DHA-S inhibited glucose uptake and repressed the biosynthesis of amino acids. Finally, we identified that sodium bicarbonate could rescue zebrafish from DHA-S induced cardiovascular toxicity. Altogether, our results suggest that DHA-S is a potential risk for cardiovascular system.

Prospective therapeutic potential of Tanshinone IIA: An updated overview

In the past decades, the branch of complementary and alternative medicine based therapeutics has gained considerable attention worldwide. Pharmacological efficacy of various traditional medicinal plants, their products and/or product derivatives have been explored on an increasing scale. Tanshinone IIA (Tan IIA) is a pharmacologically active lipophilic component of Salvia miltiorrhiza extract. Tan IIA shares a history of high repute in Traditional Chinese Medicine. Reckoning with these, the present review collates the pharmacological properties of Tan IIA with a special emphasis on its therapeutic potential against diverse diseases including cardiovascular diseases, cerebrovascular diseases, cancer, diabetes, obesity and neurogenerative diseases. Further, possible applications of various therapeutic preparations of Tan IIA were discussed with special emphasis on nano-based drug delivery formulations. Considering the tremendous advancement in the field of nanomedicine and the therapeutic potential of Tan IIA, the convergence of these two aspects can be foreseen with great promise in clinical application.

Biventricular Conversion in the Borderline Hypoplastic Heart

PURPOSE OF REVIEW

The development of biventricular repair and conversion pathways for patients with borderline hypoplastic heart disease represents an area of recent inquiry and innovation. This review summarizes emerging techniques and novel treatment algorithms for borderline hypoplastic heart disease with a focus on surgical advances within the last 10 years.

RECENT FINDINGS

Many patients with borderline hypoplastic heart disease are amenable to primary biventricular repair, or biventricular conversion following single-ventricle palliation coupled with ventricular rehabilitation strategies. New insights into the potential for growth and recovery of borderline ventricles have been uncovered. However, questions remain regarding optimal patient selection and the long-term outcomes of select patient groups treated with single-ventricle palliation versus biventricular repair/conversion or transplantation. Efforts to direct a greater proportion of borderline hypoplastic heart patients towards a biventricular circulation are accelerating and represent important avenues for progress and future research in the field of congenital heart disease.

Using Zebrafish to Analyze the Genetic and Environmental Etiologies of Congenital Heart Defects

Congenital heart defects (CHDs) are among the most common human birth defects. However, the etiology of a large proportion of CHDs remains undefined. Studies identifying the molecular and cellular mechanisms that underlie cardiac development have been critical to elucidating the origin of CHDs. Building upon this knowledge to understand the pathogenesis of CHDs requires examining how genetic or environmental stress changes normal cardiac development. Due to strong molecular conservation to humans and unique technical advantages, studies using zebrafish have elucidated both fundamental principles of cardiac development and have been used to create cardiac disease models. In this chapter we examine the unique toolset available to zebrafish researchers and how those tools are used to interrogate the genetic and environmental contributions to CHDs.

The CaMKII phosphorylation site Thr1604 in the CaV1.2 channel is involved in pathological myocardial hypertrophy in rats

Residue Thr1604 in the Ca_V1.2 channel is a Ca²⁺/calmodulin dependent protein kinase II (CaMKII) phosphorylation site, and its phosphorylation status maintains the basic activity of the channel. However, the role of Ca_V1.2 phosphorylation at Thr1604 in myocardial hypertrophy is incompletely understood. Isoproterenol (ISO) was used to induce cardiomyocyte hypertrophy, and autocamtide-2-related inhibitory peptide (AIP) was added as a treatment. Rats in a myocardial hypertrophy development model were subcutaneously injected with ISO for two or three weeks. The heart and left ventricle weights, each of which were normalized to the body weight and cross-sectional area of the myocardial cells, were used to describe the degree of hypertrophy. Protein expression levels were detected by western blotting. CaMKII-induced Ca_V1.2 (Thr1604) phosphorylation (p-Ca_V1.2) was assayed by coimmunoprecipitation. The results showed that CaMKII, HDAC, MEF2 C, and atrial natriuretic peptide (ANP) expression was increased in the ISO group and downregulated by AIP treatment in vitro. There was no difference in the expression of these proteins between the ISO 2-week group and the ISO 3-week group in vivo. Ca_V1.2 channel expression did not change, but p-Ca_V1.2 expression was increased after ISO stimulation and decreased by AIP. In the rat model, p-Ca_V1.2 levels and CaMKII activity were much higher in the ISO 3-week group than in the ISO 2-week group. CaMKII-induced Ca_V1.2 channel phosphorylation at residue Thr1604 may be one of the key features of myocardial hypertrophy and disease development.Abbreviations: CaMKII: Ca2+/calmodulin dependent protein kinase II; p-CaMKII: autophosphorylated Ca2+/calmodulin dependent protein kinase II; CaM: calmodulin; AIP: autocamtide-2-related inhibitory peptide; ECC: excitation-contraction coupling; ISO: isoproterenol; BW: body weight; HW: heart weight; LVW: left ventricle weight; HDAC: histone deacetylase; p-HDAC: phosphorylated histone deacetylase; MEF2C: myocyte-specific enhancer factor 2C; ANP: atrial natriuretic peptide; PKC: protein kinase C

Investigation of human iPSC-derived cardiac myocyte functional maturation by single cell traction force microscopy

Recent advances have made it possible to readily derive cardiac myocytes from human induced pluripotent stem cells (hiPSC-CMs). HiPSC-CMs represent a valuable new experimental model for studying human cardiac muscle physiology and disease. Many laboratories have devoted substantial effort to examining the functional properties of isolated hiPSC-CMs, but to date, force production has not been adequately characterized. Here, we utilized traction force microscopy (TFM) with micro-patterning cell printing to investigate the maximum force production of isolated single hiPSC-CMs under varied culture and assay conditions. We examined the role of length of differentiation in culture and the effects of varied extracellular calcium concentration in the culture media on the maturation of hiPSC-CMs. Results show that hiPSC-CMs developing in culture for two weeks produced significantly less force than cells cultured from one to three months, with hiPSC-CMs cultured for three months resembling the cell morphology and function of neonatal rat ventricular myocytes in terms of size, dimensions, and force production. Furthermore, hiPSC-CMs cultured long term in conditions of physiologic calcium concentrations were larger and produced more force than hiPSC-CMs cultured in standard media with sub-physiological calcium. We also examined relationships between cell morphology, substrate stiffness and force production. Results showed a significant relationship between cell area and force. Implementing directed modifications of substrate stiffness, by varying stiffness from embryonic-like to adult myocardium-like, hiPSC-CMs produced maximal forces on substrates with a lower modulus and significantly less force when assayed on increasingly stiff adult myocardium-like substrates. Calculated strain energy measurements paralleled these findings. Collectively, these findings further establish single cell TFM as a valuable approach to illuminate the quantitative physiological maturation of force in hiPSC-CMs.

Effect of PMA-induced protein kinase C activation on development and apoptosis in early zebrafish embryos

Protein kinase C (PKC) isoforms have been implicated in several key steps during early development, but the consequences of xenobiotic-induced PKC activation during early embryogenesis are still unknown. In this study, zebrafish embryos were exposed to a range of phorbol 12-myristate 13-acetate (PMA) concentrations (0-200μg/L) at different time points after fertilization. Results showed that 200μgPMA/L caused development of yolk bags, cardiac edema, slow blood flow, pulsating blood flow, slow pulse, elongated heart, lack of tail fins, curved tail, and coagulation. PMA exposure decreased survival rate of the embryos starting within the first 24h and becoming more pronounced after prolonged exposure (96h). PMA increased the number of apoptotic cells in the brain region as demonstrated by acridine orange staining and caused up-regulation of caspase 9 (casp9) and p53 up-regulated modulator of apoptosis (puma) mRNA in whole embryos. PMA caused oxidative stress in the embryos as demonstrated by decreased mRNA expression of catalase and superoxide dismutase 2. Inhibition of Pkc with GF109203X improved overall survival rate, reduced apoptosis in the brain and decreased expression of casp9 and puma in the PMA-exposed embryos. However, Pkc inhibition neither prevented development of deformities nor reversed oxidative stress in the PMA-exposed embryos. These data suggest that direct over-activation of Pkc during early embryogenesis of zebrafish is associated with apoptosis and decreased survival rate of the embryos.

Calcium handling precedes cardiac differentiation to initiate the first heartbeat

The mammalian heartbeat is thought to begin just prior to the linear heart tube stage of development. How the initial contractions are established and the downstream consequences of the earliest contractile function on cardiac differentiation and morphogenesis have not been described. Using high-resolution live imaging of mouse embryos, we observed randomly distributed spontaneous asynchronous Ca²⁺-oscillations (SACOs) in the forming cardiac crescent (stage E7.75) prior to overt beating. Nascent contraction initiated at around E8.0 and was associated with sarcomeric assembly and rapid Ca²⁺ transients, underpinned by sequential expression of the Na⁺-Ca²⁺ exchanger (NCX1) and L-type Ca²⁺ channel (LTCC). Pharmacological inhibition of NCX1 and LTCC revealed rapid development of Ca²⁺ handling in the early heart and an essential early role for NCX1 in establishing SACOs through to the initiation of beating. NCX1 blockade impacted on CaMKII signalling to down-regulate cardiac gene expression, leading to impaired differentiation and failed crescent maturation.

DOI:http://dx.doi.org/10.7554/eLife.17113.001

The heart is the first organ to form and to begin working in an embryo during pregnancy. It must begin pumping early to supply oxygen and nutrients to the developing embryo. Coordinated contractions of specialised muscle cells in the heart, called cardiomyocytes, generate the force needed to pump blood. The flow of calcium ions into and out of the cardiomyocytes triggers these heartbeats. In addition to triggering heart contractions, calcium ions also act as a messenger that drives changes in which genes are active in the cardiomyocytes and how these cells behave.

Scientists commonly think of the first heartbeat as occurring after a tube-like structure forms in the embryo that will eventually develop into the heart. However, it is not yet clear how the first heartbeat starts or how the initial heartbeats affect further heart development.

Tyser, Miranda et al. now show that the first heartbeat actually occurs much earlier in embryonic development than widely appreciated. In the experiments, videos of live mouse embryos showed that prior to the first heartbeat the flow of calcium ions between different cardiomyocytes is not synchronised. However, as the heart grows these calcium flows become coordinated leading to the first heartbeat. The heartbeats also become faster as the heart grows. Using drugs to block the movement of calcium ions, Tyser, Miranda et al. also show that a protein called NCX1 is required to trigger the calcium flows prior to the first heartbeat. Moreover, the experiments revealed that these early heartbeats help drive the growth of cardiomyocytes and shape the developing heart.

Together, the experiments show that the first heartbeats are essential for normal heart development. Future studies are needed to determine what controls the speed of the first heartbeats, and what organises the calcium flows that trigger the first heartbeat. Such studies may help scientists better understand birth defects of the heart, and may suggest strategies to rebuild hearts that have been damaged by a heart attack or other injury.

DOI:http://dx.doi.org/10.7554/eLife.17113.002