Production of zebrafish cardiospheres and cardiac progenitor cells in vitro and three-dimensional culture of adult zebrafish cardiac tissue in scaffolds

Fish cell line: depositories, web resources and future applications

Cell lines are important bioresources to study the key biological processes in the areas like virology, pathology, immunology, toxicology, biotechnology, endocrinology and developmental biology. Cell lines developed from fish organs are utilized as a model in vitro system in disease surveillance programs, pharmacology, drug screening and resolving cases of metabolic abnormalities. During last decade, there were consistent efforts made globally to develop new fish cell lines from different organs like brain, eye muscles, fin, gill, heart, kidney, liver, skin, spleen, swim bladder, testes, vertebra etc. This increased use and development of cell lines necessitated the establishment of cell line depositories to store/preserve them and assure their availability to the researchers. These depositories are a source of authenticated and characterized cell lines with set protocols for material transfer agreements, maintenance and shipping as well as logistics enabling cellular research. Hence, it is important to cryopreserve and maintain cell lines in depositories and make them available to the research community. The present article reviews the current status of the fish cell lines available in different depositories across the world, along with the prominent role of cell lines in conservation of life on land or below water.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00601-2.

An Efficient and Reproducible Method for the Isolation and Culture of Primary Cardiomyocytes from Adult Zebrafish

Zebrafish is a popular animal model in regeneration studies due to their ability to regenerate the heart. Primary cardiomyocytes could be an alternative tool for studying the intrinsic mechanisms of cardiovascular disease in vitro. Thus, our objective is to develop an efficient protocol to isolate primary cardiomyocytes from zebrafish hearts. Low concentration of digestive enzyme (0.5 mg/mL collagenase type II) was utilized in our protocol to obtain single-cell suspension. The ventricles were fragmented, mechanically pipetted, and constantly shaken to ensure adequate contact between the tissues and the enzyme. Preplating the cell suspension onto culture plates for 2 h helped remove cardiac fibroblasts. The purity of isolated cells was validated by flow cytometry analysis of transgenic zebrafish with cardiomyocyte-specific expression of enhanced green fluorescent protein (EGFP) or endothelial cell-specific expression of mCherry. Quantitative real-time PCR analysis revealed a high level of the purity, with cardiac fibroblasts, endothelial cells, and epicardial cell markers scarcely detected in the purified cells. Altogether, this study established a reproducible protocol for isolating primary cardiomyocytes with high purity and activity from adult zebrafish hearts that can be cultured in vitro for up to 4 weeks. This protocol provides a valuable tool for studying the intrinsic mechanisms of cardiovascular disease in vitro using primary cardiomyocytes.

Live imaging of adult zebrafish cardiomyocyte proliferation ex vivo

Zebrafish are excellent at regenerating their heart by reinitiating proliferation in pre-existing cardiomyocytes. Studying how zebrafish achieve this holds great potential in developing new strategies to boost mammalian heart regeneration. Nevertheless, the lack of appropriate live-imaging tools for the adult zebrafish heart has limited detailed studies into the dynamics underlying cardiomyocyte proliferation. Here, we address this by developing a system in which cardiac slices of the injured zebrafish heart are cultured ex vivo for several days while retaining key regenerative characteristics, including cardiomyocyte proliferation. In addition, we show that the cardiac slice culture system is compatible with live timelapse imaging and allows manipulation of regenerating cardiomyocytes with drugs that normally would have toxic effects that prevent their use. Finally, we use the cardiac slices to demonstrate that adult cardiomyocytes with fully assembled sarcomeres can partially disassemble their sarcomeres in a calpain- and proteasome-dependent manner to progress through nuclear division and cytokinesis. In conclusion, we have developed a cardiac slice culture system, which allows imaging of native cardiomyocyte dynamics in real time to discover cellular mechanisms during heart regeneration.

Interactivity of biochemical and physical stimuli during epigenetic conditioning and cardiomyocytic differentiation of stem and progenitor cells derived from adult hearts

Mixed populations of cardiosphere-derived stem and progenitor cells containing proliferative and cardiomyogenically committed cells were obtained from adult rat hearts. The cells were cultured in either static 2D monolayers or dynamic 3D scaffold systems with fluid flow. Cardiomyocyte lineage commitment in terms of GATA4 and Nkx2.5 expression was significantly enhanced in the dynamic 3D cultures compared with static 2D conditions. Treatment of the cells with 5-azacytidine (5-aza) produced different responses in the two culture systems, as activity of this chemical epigenetic conditioning agent depended on the cell attachment and hydrodynamic conditions provided during culture. Cell growth was unaffected by 5-aza in the static 2D cultures but was significantly reduced under dynamic 3D conditions relative to untreated controls. Myogenic differentiation measured as Mef2c expression was markedly upregulated by 5-aza in the dynamic 3D cultures but downregulated in the static 2D cultures. The ability of the physical environment to modulate the cellular cardiomyogenic response to 5-aza underscores the interactivity of biochemical and physical stimuli applied for cell differentiation. Accordingly, observations about the efficacy of 5-aza as a cardiomyocyte induction agent may not be applicable across different culture systems. Overall, use of dynamic 3D rather than static 2D culture was more beneficial for cardio-specific myogenesis than 5-aza treatment, which generated a more ambiguous differentiation response.

Effect of adenosine monophosphate-activated protein kinase-p53-Krüppel-like factor 2a pathway in hyperglycemia-induced cardiac remodeling in adult zebrafish

Aims/Introduction

Diabetic cardiomyopathy is a type of myocardial disease. It causes left ventricular hypertrophy, followed by diastolic and systolic dysfunction, eventually leading to congestive heart failure. However, the underlying mechanism still requires further elucidation.

Materials and Methods

A high‐glucose zebrafish model was constructed by administering streptozocin intraperitoneally to enhance the development of cardiomyopathy and then treated with adenosine monophosphate‐activated protein kinase (AMPK) activator. Cardiac structure and function, and protein and gene expression were then analyzed. Cardiomyocytes (CMs) culture in vitro using lentivirus were used for detection of AMPK, p53 and Krüppel‐like factor 2a (klf2a) gene expression.

Results

In the hyperglycemia group, electrocardiogram findings showed arrhythmia, echocardiography results showed heart enlargement and dysfunction, and many differences, such as increased apoptosis and myocardial fiber loss, were observed. The phospho‐AMPK and klf2a expression were downregulated, and p53 expression was upregulated. Activation of phospho‐AMPK reduced p53 and increased klf2a expression, alleviated apoptosis in CMs and improved cardiac function in the hyperglycemic zebrafish. In vitro knockdown system of AMPK, p53 and klf2a using lentivirus illustrated an increased p53 expression and decreased klf2a expression in CMs by inhibiting AMPK. Repression of p53 and upregulation of klf2a expression were observed, but no changes in the expression of AMPK and its phosphorylated type.

Conclusions

In the model of streptozocin‐induced hyperglycemia zebrafish, the reduction of phosphorylated AMPK increased p53, which led to KLF2a decrease to facilitate apoptosis of CMs, inducing the cardiac remodeling and cardiac dysfunction. These results can be reversed by AMPK activator, which means the AMPK–p53–klf2a pathway might be a potential target for diabetic cardiomyopathy intervention.

Spontaneously contracting cell aggregates derived from grass carp heart as a promising tool in in vitro heart research

Regarding challenges in isolation and maintenance of cultured heart cells, introduction of new in vitro heart model that is stable and exhibits long-term spontaneously contracting cell aggregates (SCCs), whose electrophysiological properties are comparable to the human heart, is required. This research aimed to establish cardiac primary cells and to evaluate the effects of culture conditions. Also the effect of fish age on beating SCC and cardiac cell morphology were studied. Twelve healthy grass carps (Ctenopharyngodon idella) were divided into four groups based on their age. Non-enzymatic explant culture was used and heart explants were incubated at 21-31 °C for 60 days. After proliferation of the cardiac primary cells, changes in their morphology and their beatings were recorded. The results showed that the explants derived from different age of grass carp fish are fully viable and proliferative with formation of SCC for a long period of time. By increasing the number of adhered cells, the cardiac primary cells became more flat and elongated. Increasing the medium temperature and fetal bovine serum concentration in culture medium led to decline and enhancement in beat frequencies of heart cell aggregates, respectively. Also, grass carp heart explant had high potential in regeneration (especially in young fish) and thus high feasibility to generate stable long-term cultures. In general, it seems that explant culture of heart from grass carp can be considered as a promising tool in heart research area.

A Cardiac Cell Outgrowth Assay for Evaluating Drug Compounds Using a Cardiac Spheroid-on-a-Chip Device

Three-dimensional (3D) models with cells arranged in clusters or spheroids have emerged as valuable tools to improve physiological relevance in drug screening. One of the challenges with cells cultured in 3D, especially for high-throughput applications, is to quickly and non-invasively assess the cellular state in vitro. In this article, we show that the number of cells growing out from human induced pluripotent stem cell (hiPSC)-derived cardiac spheroids can be quantified to serve as an indicator of a drug’s effect on spheroids captured in a microfluidic device. Combining this spheroid-on-a-chip with confocal high content imaging reveals easily accessible, quantitative outgrowth data. We found that effects on outgrowing cell numbers correlate to the concentrations of relevant pharmacological compounds and could thus serve as a practical readout to monitor drug effects. Here, we demonstrate the potential of this semi-high-throughput “cardiac cell outgrowth assay” with six compounds at three concentrations applied to spheroids for 48 h. The image-based readout complements end-point assays or may be used as a non-invasive assay for quality control during long-term culture.