Son, Yura

The regulation of the cardiomyocyte cell cycle is central to understanding heart regeneration. In adult mammals, cardiomyocytes withdraw from the cell cycle, limiting their ability to proliferate and repair heart tissue after injury. This process is controlled by intrinsic genetic programs and extrinsic signals, which together restrict the regenerative response in mature hearts. Understanding the mechanisms that regulate cardiomyocyte cell cycle activity is therefore critical for advancing cardiac regenerative medicine. In this review, we provide a comparative and integrated overview of cardiomyocyte cell cycle regulation in lower vertebrates and mammals, and discuss the major intrinsic factors that govern this process, including cyclin/CDK pathways, transcription factors and co-activators, oxygen and metabolic regulation, and epigenetic mechanisms. We also review the influence of hormones and growth factors, as well as the supportive roles of nonmyocyte populations in heart regeneration. By integrating findings across species, developmental stages, and regulatory levels, these findings highlight the complex regulatory network controlling cardiomyocyte proliferation and provide insight into potential therapeutic strategies for stimulating cardiac repair in the adult mammalian heart.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) possess significant therapeutic potential for myocardial regeneration. However, clinical application remains constrained due to the immature phenotype of these cells, which impacts their engraftment as well as their electrical and mechanical integration post-transplantation into the injured heart. In particular, proper alignment of transplanted hiPSC-CMs is essential for synchronous contraction and efficient electromechanical coupling with native tissue. To address this critical clinical challenge, we engineered a tissue patch incorporating aligned electrospun nanofibers designed to enhance hiPSC-CM alignment and promote their structural maturation. Poly(caprolactone) (PCL) nanofibers were fabricated by electrospinning a 10% w/v solution in 1,1,1,3,3,3-hexafluoro-2-propanol at a flow rate of 0.5 mL/h. A voltage of 14 kV was applied to the spinneret and 3kV to the collector, positioned 13 cm away, with additional electrodes to induce fiber alignment. Scanning electron microscopy and ImageJ analysis confirmed fiber diameter and orientation. hiPSC-CMs (1 x 10 6 cells) were seeded onto fiber scaffolds with varied diameters (1.0, 1.5, and 2.0 μm) and densities (low: 20%, moderate: 30%, high: 40%). Among these, 1.5 ± 0.2 μm diameter fibers with a density of 40 ± 3% provided the most effective topographical cues for promoting cell elongation and alignment. Immunofluorescence staining demonstrated that hiPSC-CMs cultured on aligned fibers exhibited enhanced cytoskeletal organization along the fiber axis. Morphological assessment over time showed progressive alignment by day 3. Importantly, hiPSC-CMs cultured on aligned fibers demonstrated stronger and more synchronized contractile activity compared to those cultured on flat glass surfaces. Together, these findings suggest that our aligned nanofiber-based cardiac patch promotes the structural and functional maturation of hiPSC-CMs, highlighting their potential as an advanced platform for improving cardiac cell therapy outcomes.

Biomaterials like gold nanorod-embedded gelatin methacrylate (GelMA-GNR) hydrogels support the delivery of regenerative cells such as human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), enhancing EHT performance.

Heart disease continues to be the leading cause of death globally, even with the development and implementation of numerous pharmacological and surgical treatments. Transplanting cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) shows potential for repairing heart damage. However, tracking and quantifying these cells after transplantation in large animals remains challenging. This study aimed to develop a hiPSC line that overexpresses ferritin heavy chain (FHC) to enable tracking of transplanted hiPSC-CMs via magnetic resonance imaging (MRI). Using the CRISPR/dCas9 activation system, we increased FHC expression in hiPSCs and hiPSC-CMs. Both mRNA and protein levels of FHC were significantly elevated following transfection. Cell viability was unaffected by iron chloride concentrations between 0 μM and 2000 μM. hiPSCs and hiPSC-CMs overexpressing FHC (hiPSC-FHC OE and hiPSC-CM-FHC OE ) showed enhanced iron chloride uptake without changes in their electrophysiological properties compared to control hiPSC-CMs. Additionally, hiPSC-CM-FHCOE cells provided strong contrast and lower T 2 * values, indicating their effectiveness for cardiac MRI. When hiPSC-CM-FHCOE cells were injected into mouse hearts and imaged three days later, MRI revealed distinct signals from these cells with lower T 2 * values and rapid signal decay. Overall, endogenous FHC labeling in hiPSC-CMs could significantly improve the precision of cardiac MRI, marking a crucial advancement in assessing the success of hiPSC-CM transplantation in large animal models and enhancing cardiac regenerative therapies.

AbstractThe objective of the current study is to develop a new method for tracking transplanted human induced pluripotent stem cells‐derived cardiomyocytes (hiPSC‐CMs) using magnetic resonance imaging (MRI). The CRISPR/dCas9 activation system is employed to overexpress ferritin heavy chain (FHC) in hiPSC‐CMs. The mRNA and protein expression of FHC in hiPSC and hiPSC‐CMs significantly increased after transfection. Iron chloride does not affect the cell viability in a concentration range from 0 to 2000 µm. hiPSCs overexpressing FHC (hiPSC‐ FHCOE) and hiPSC‐CMs overexpressing FHC (hiPSC‐CM‐FHCOE) significantly enhanced cellular uptake of iron chloride but with no changes in electrophysiological properties compared to hiPSC‐CM‐Control. Furthermore, hiPSC‐CM‐FHCOE presented robust contrast and lower T2* values, signifying their potential as highly effective candidates for cardiac MRI. Next, hiPSC‐CM‐FHCOE is injected into mouse hearts and after 3 days of transplantation, MR images are obtained. hiPSC‐CM‐FHCOE cells exhibited clear signals in the hearts with lower T2* and rapid signal decay. Collectively, data from this proof‐of‐concept study demonstrated that endogenous labeling with FHC in hiPSC‐CMs can be a potent strategy for enhancing the accuracy of cardiac MRI. This technology represents a significant step forward in tracking the transplanted hiPSC‐CMs in the hearts of live animals.

Introduction: Transplantation of human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) emerges as a promising approach for the treatment of heart diseases. However, it is an unmet challenge to precisely localize the hiPSC-CMs upon transplantation and quantify the graft size in the live large animals. To address this issue, we established a new approach to track grafted CMs in large animals using magnetic resonance imaging detectable reporter molecules, which allows the assessment of graft size in live animals at different time points. Methods: We employed a CRISPR/Cas9 system as a virus-free approach to overexpress ferritin in hiPSCs. Results: hiPSC cells were transfected with ferritin heavy chain CRISPR activation plasmid for 24 hours. Before antibiotic selection, we established a kill curve to determine the appropriate antibiotic concentration. Based on the kill curve, we conducted antibiotic selection using puromycin for 7 days and isolated transfected colonies for further culture. Next, we treated various concentrations of iron chloride (0-100 μM) to the FHC transfected hiPSC for 4 hours to examine a proper concentration of iron loading for MRI detection. There was no significant difference in cell viability between 0 and 25 μM of iron chloride. In addition, we confirmed transfection efficiency with higher ferritin expression in transfected cells compared to controls (non-transfected wild-type hiPSC). Following, we plan to differentiate ferritin overexpressing hiPSC into cardiomyocytes, inject the cells into porcine hearts, and conduct magnetic resonance imaging to detect the engrafted transgenic cells in live animals. Conclusion: The ferritin-expressing hiPSC line has the potential to provide a reliable measurement of the graft size in large animals.

Heart failure secondary to myocardial injuries is a leading cause of death worldwide. Recently, a growing number of novel therapies have emerged for injured myocardium repairment. However, delivering therapeutic agents specifically to the injured heart remains a significant challenge. Nanoparticles are the most commonly used vehicles for targeted drug delivery. Various nanoparticles have been synthesized to deliver drugs and other therapeutic molecules to the injured heart via passive or active targeting approaches, and their targeting specificity and therapeutic efficacies have been investigated. Here, we summarized nanoparticle-based, cardiac-specific drug delivery systems, their potency for treating heart diseases, and the mechanisms underlying these cardiac-targeting strategies. We also discussed the clinical studies that have employed nanoparticle-based cardiac-specific drug delivery.