High-Throughput Screening Platform in Postnatal Heart Cells and Chemical Probe Toolbox to Assess Cardiomyocyte Proliferation

Cell cycle visualization tools to study cardiomyocyte proliferation in real-time

Cardiomyocytes in the adult human heart are quiescent and those lost following heart injury are not replaced by proliferating survivors. Considerable effort has been made to understand the mechanisms underlying cardiomyocyte cell cycle exit and re-entry, with view to discovering therapeutics that could stimulate cardiomyocyte proliferation and heart regeneration. The advent of large compound libraries and robotic liquid handling platforms has enabled the screening of thousands of conditions in a single experiment but success of these screens depends on the appropriateness and quality of the model used. Quantification of (human) cardiomyocyte proliferation in high throughput has remained problematic because conventional antibody-based staining is costly, technically challenging and does not discriminate between cardiomyocyte division and failure in karyokinesis or cytokinesis. Live cell imaging has provided alternatives that facilitate high-throughput screening but these have other limitations. Here, we (i) review the cell cycle features of cardiomyocytes, (ii) discuss various cell cycle fluorescent reporter systems, and (iii) speculate on what could improve their predictive value in the context of cardiomyocyte proliferation. Finally, we consider how these new methods can be used in combination with state-of-the-art three-dimensional human cardiac organoid platforms to identify pro-proliferative signalling pathways that could stimulate regeneration of the human heart.

Drug Discovery for Adult Cardiomyocyte Regeneration: Opportunities and Challenges

Significance: Cardiovascular disease is a major contributor to human mortality and morbidity. The cardiac tissue undergoes fibrotic healing after injury because of the limited regenerative capacity of adult mammalian cardiomyocyte (CM). Extensive research has been performed to identify therapeutic targets for CM regeneration, as the success of promoting adult human CM regeneration to repair the injured heart is considered the Holy Grail in the field. Recent Advances: To date, more than 30 target genes have been shown to regulate adult mammalian CM proliferation. More than 20 targets have been validated in adult mouse myocardial infarction (MI) model in a therapeutic setting. In this review, the translational efficacy readouts from 17 selected pharmaceutical targets are summarized, among which the Hippo-yes-associated protein (Yap) pathway is the most extensively investigated and fits the criteria for a promising target for pro-CM-regeneration therapy development. Critical Issues and Future Directions: As the pro-CM-regeneration potential of current drug treatment for cardiovascular patients is limited, to help identify and fill the gap between basic research and drug discovery in this specific field, details regarding target identification, validation in mouse MI models, high-throughput screening assay development, and preclinical in vivo efficacy model optimization are discussed. Finally, suggestions and recommendations are also provided to help establish a common guideline for in vivo translational studies for drug discovery focusing on CM regeneration. Antioxid. Redox Signal. 39, 1070-1087.

Regulatory Mechanisms That Guide the Fetal to Postnatal Transition of Cardiomyocytes

Heart disease remains a global leading cause of death and disability, necessitating a comprehensive understanding of the heart's development, repair, and dysfunction. This review surveys recent discoveries that explore the developmental transition of proliferative fetal cardiomyocytes into hypertrophic postnatal cardiomyocytes, a process yet to be well-defined. This transition is key to the heart's growth and has promising therapeutic potential, particularly for congenital or acquired heart damage, such as myocardial infarctions. Although significant progress has been made, much work is needed to unravel the complex interplay of signaling pathways that regulate cardiomyocyte proliferation and hypertrophy. This review provides a detailed perspective for future research directions aimed at the potential therapeutic harnessing of the perinatal heart transitions.

Phenotypic screen identifies FOXO inhibitor to counteract maturation and promote expansion of human iPS cell-derived cardiomyocytes

Achieving pharmacological control over cardiomyocyte proliferation represents a prime goal in therapeutic cardiovascular research. Here, we identify a novel chemical tool compound for the expansion of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. The forkhead box O (FOXO) inhibitor AS1842856 was identified as a significant hit from an unbiased proliferation screen in early, immature hiPSC- cardiomyocytes (eCMs). The mitogenic effects of AS1842856 turned out to be robust, dose-dependent, sustained, and reversible. eCM numbers increased >30-fold as induced by AS1842856 over three passages. Phenotypically as well as by marker gene expression, the compound interestingly appeared to counteract cellular maturation both in immature hiPSC-CMs as well as in more advanced ones. Thus, FOXO inhibitor AS1842856 presents a novel proliferation inducer for the chemically defined, xeno-free expansion of hiPSC-derived CMs, while its de-differentiation effect might as well bear potential in regenerative medicine.