Mechanism-Based Cardiac Regeneration Strategies in Mammals

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.

Hydrogels for Cardiac Restorative Support: Relevance of Gelation Mechanisms for Prospective Clinical Use

PURPOSE OF REVIEW

Cardiac tissue regenerative strategies have gained much traction over the years, in particular those utilizing hydrogels. With our review, and with special focus on supporting post-myocardial infarcted tissue, we aim to provide insights in determining crucial design considerations of a hydrogel and the implications these could have for future clinical use.

RECENT FINDINGS

To date, two hydrogel delivery strategies are being explored, cardiac injection or patch, to treat myocardial infarction. Recent advances have demonstrated that the mechanism by which a hydrogel is gelated (i.e., physically or chemically cross-linked) not only impacts the biocompatibility, mechanical properties, and chemical structure, but also the route of delivery of the hydrogel and thus its effect on cardiac repair. With regard to cardiac regeneration, various hydrogels have been developed with the ability to function as a delivery system for therapeutic strategies (e.g., drug and stem cells treatments), as well as a scaffold to guide cardiac tissue regeneration following myocardial infarction. However, these developments remain within the experimental and pre-clinical realm and have yet to transition towards the clinical setting.

Fluoroscopy Guided Minimally Invasive Swine Model of Myocardial Infarction by Left Coronary Artery Occlusion for Regenerative Cardiology

BACKGROUND

Despite the recent advancements in the cardiac regenerative technologies, the lack of an ideal translationally relevant experimental model simulating the clinical setting of acute myocardial infarction (MI) hurdles the success of cardiac regenerative strategies.

METHODS

We developed a modified minimally invasive acute MI model in Yucatan miniswine by catheter-driven controlled occlusion of LCX branches for regenerative cardiology. Using a balloon catheter in three pigs, the angiography guided occlusion of LCX for 10-15 minutes resulted in MI induction which was confirmed by the pathological ECG changes compared to the baseline control.

RESULTS

Ejection fraction was considerably decreased post-procedure compared to the baseline. Importantly, the highly sensitive MI biomarker Troponin I was significantly increased in post-MI and follow-up groups along with LDH and CCK than the baseline control. The postmortem infarct zone tissue displayed the classical features of MI including ECM disorganization, hypertrophy, inflammation, and angiogenesis confirming the MI at the tissue level.

CONCLUSIONS

The present model possesses the advantage of minimal mortality, simulating the pathological features of clinical MI and the suitability for injectable regenerative therapies suggesting the translational significance in regenerative cardiology.

Remuscularization with triiodothyronine and β1-blocker therapy reverses post-ischemic left ventricular dysfunction and adverse remodeling

Renewal of the myocardium by preexisting cardiomyocytes is a powerful strategy for restoring the architecture and function of hearts injured by myocardial infarction. To advance this strategy, we show that combining two clinically approved drugs, but neither alone, muscularizes the heart through cardiomyocyte proliferation. Specifically, in adult murine cardiomyocytes, metoprolol, a cardioselective β1-adrenergic receptor blocker, when given with triiodothyronine (T3, a thyroid hormone) accentuates the ability of T3 to stimulate ERK1/2 phosphorylation and proliferative signaling by inhibiting expression of the nuclear phospho-ERK1/2-specific phosphatase, dual-specificity phosphatase-5. While short-duration metoprolol plus T3 therapy generates new heart muscle in healthy mice, in mice with myocardial infarction-induced left ventricular dysfunction and pathological remodeling, it remuscularizes the heart, restores contractile function and reverses chamber dilatation; outcomes that are enduring. If the beneficial effects of metoprolol plus T3 are replicated in humans, this therapeutic strategy has the potential to definitively address ischemic heart failure.