Biomimetic Cardiac Tissue Models for In Vitro Arrhythmia Studies.

Cardiac arrhythmias are a major cause of cardiovascular mortality worldwide. Many arrhythmias are caused by reentry, a phenomenon where excitation waves circulate in the heart. Optical mapping techniques have revealed the role of reentry in arrhythmia initiation and fibrillation transition, but the underlying biophysical mechanisms are still difficult to investigate in intact hearts. Tissue engineering models of cardiac tissue can mimic the structure and function of native cardiac tissue and enable interactive observation of reentry formation and wave propagation. This review will present various approaches to constructing cardiac tissue models for reentry studies, using the authors' work as examples. The review will highlight the evolution of tissue engineering designs based on different substrates, cell types, and structural parameters. A new approach using polymer materials and cellular reprogramming to create biomimetic cardiac tissues will be introduced. The review will also show how computational modeling of cardiac tissue can complement experimental data and how such models can be applied in the biomimetics of cardiac tissue.

Novel Molecular Vehicle-Based Approach for Cardiac Cell Transplantation Leads to Rapid Electromechanical Graft-Host Coupling.

Myocardial remodeling is an inevitable risk factor for cardiac arrhythmias and can potentially be corrected with cell therapy. Although the generation of cardiac cells ex vivo is possible, specific approaches to cell replacement therapy remain unclear. On the one hand, adhesive myocyte cells must be viable and conjugated with the electromechanical syncytium of the recipient tissue, which is unattainable without an external scaffold substrate. On the other hand, the outer scaffold may hinder cell delivery, for example, making intramyocardial injection difficult. To resolve this contradiction, we developed molecular vehicles that combine a wrapped (rather than outer) polymer scaffold that is enveloped by the cell and provides excitability restoration (lost when cells were harvested) before engraftment. It also provides a coating with human fibronectin, which initiates the process of graft adhesion into the recipient tissue and can carry fluorescent markers for the external control of the non-invasive cell position. In this work, we used a type of scaffold that allowed us to use the advantages of a scaffold-free cell suspension for cell delivery. Fragmented nanofibers (0.85 µm ± 0.18 µm in diameter) with fluorescent labels were used, with solitary cells seeded on them. Cell implantation experiments were performed in vivo. The proposed molecular vehicles made it possible to establish rapid (30 min) electromechanical contact between excitable grafts and the recipient heart. Excitable grafts were visualized with optical mapping on a rat heart with Langendorff perfusion at a 0.72 ± 0.32 Hz heart rate. Thus, the pre-restored grafts' excitability (with the help of a wrapped polymer scaffold) allowed rapid electromechanical coupling with the recipient tissue. This information could provide a basis for the reduction of engraftment arrhythmias in the first days after cell therapy.

Polymer Kernels as Compact Carriers for Suspended Cardiomyocytes.

Induced pluripotent stem cells (iPSCs) constitute a potential source of patient-specific human cardiomyocytes for a cardiac cell replacement therapy via intramyocardial injections, providing a major benefit over other cell sources in terms of immune rejection. However, intramyocardial injection of the cardiomyocytes has substantial challenges related to cell survival and electrophysiological coupling with recipient tissue. Current methods of manipulating cell suspensions do not allow one to control the processes of adhesion of injected cells to the tissue and electrophysiological coupling with surrounding cells. In this article, we documented the possibility of influencing these processes using polymer kernels: biocompatible fiber fragments of subcellular size that can be adsorbed to a cell, thereby creating the minimum necessary adhesion foci to shape the cell and provide support for the organization of the cytoskeleton and the contractile apparatus prior to adhesion to the recipient tissue. Using optical excitation markers, the restoration of the excitability of cardiomyocytes in suspension upon adsorption of polymer kernels was shown. It increased the likelihood of the formation of a stable electrophysiological coupling in vitro. The obtained results may be considered as a proof of concept that the stochastic engraftment process of injected suspension cells can be controlled by smart biomaterials.

The Oligomeric Form of the Escherichia coli Dps Protein Depends on the Availability of Iron Ions.

The Dps protein of Escherichia coli, which combines ferroxidase activity and the ability to bind DNA, is effectively used by bacteria to protect their genomes from damage. Both activities depend on the integrity of this multi-subunit protein, which has an inner cavity for iron oxides; however, the diversity of its oligomeric forms has only been studied fragmentarily. Here, we show that iron ions stabilize the dodecameric form of Dps. This was found by electrophoretic fractionation and size exclusion chromatography, which revealed several oligomers in highly purified protein samples and demonstrated their conversion to dodecamers in the presence of 1 mM Mohr's salt. The transmission electron microscopy data contradicted the assumption that the stabilizing effect is given by the optimal core size formed in the inner cavity of Dps. The charge state of iron ions was evaluated using Mössbauer spectroscopy, which showed the presence of Fe3O4, rather than the expected Fe2O3, in the sample. Assuming that Fe2+ can form additional inter-subunit contacts, we modeled the interaction of FeO and Fe2O3 with Dps, but the binding sites with putative functionality were predicted only for Fe2O3. The question of how the dodecameric form can be stabilized by ferric oxides is discussed.

Regularities in the E. coli promoters composition in connection with the DNA strands interaction and promoter activity.

The energy of interaction between DNA strands in promoters is of great functional importance. Visualization of the energy of DNA strands distribution in promoter sequences was achieved. The separation of promoters in groups by their energetic properties enables evaluation of the dependence of promoter strength on the energetic properties. The analysis of groups (clusters) of promoters distributed by the energy of DNA strands interaction in -55, -35, -10 and +6 sequences indicates their connection with the transcriptional activity.

Dependence of the E. coli promoter strength and physical parameters upon the nucleotide sequence.

The energy of interaction between complementary nucleotides in promoter sequences of E. coli was calculated and visualized. The graphic method for presentation of energy properties of promoter sequences was elaborated on. Data obtained indicated that energy distribution through the length of promoter sequence results in picture with minima at -35, -8 and +7 regions corresponding to areas with elevated AT (adenine-thymine) content. The most important difference from the random sequences area is related to -8. Four promoter groups and their energy properties were revealed. The promoters with minimal and maximal energy of interaction between complementary nucleotides have low strengths, the strongest promoters correspond to promoter clusters characterized by intermediate energy values.