Redox signaling in cardiac renewal

Targeting the redox system for cardiovascular regeneration in aging

Cardiovascular aging presents a formidable challenge, as the aging process can lead to reduced cardiac function and heightened susceptibility to cardiovascular diseases. Consequently, there is an escalating, unmet medical need for innovative and effective cardiovascular regeneration strategies aimed at restoring and rejuvenating aging cardiovascular tissues. Altered redox homeostasis and the accumulation of oxidative damage play a pivotal role in detrimental changes to stem cell function and cellular senescence, hampering regenerative capacity in aged cardiovascular system. A mounting body of evidence underscores the significance of targeting redox machinery to restore stem cell self-renewal and enhance their differentiation potential into youthful cardiovascular lineages. Hence, the redox machinery holds promise as a target for optimizing cardiovascular regenerative therapies. In this context, we delve into the current understanding of redox homeostasis in regulating stem cell function and reprogramming processes that impact the regenerative potential of the cardiovascular system. Furthermore, we offer insights into the recent translational and clinical implications of redox-targeting compounds aimed at enhancing current regenerative therapies for aging cardiovascular tissues.

Unravelling the Interplay between Cardiac Metabolism and Heart Regeneration

Ischemic heart disease (IHD) is the leading cause of heart failure (HF) and is a significant cause of morbidity and mortality globally. An ischemic event induces cardiomyocyte death, and the ability for the adult heart to repair itself is challenged by the limited proliferative capacity of resident cardiomyocytes. Intriguingly, changes in metabolic substrate utilisation at birth coincide with the terminal differentiation and reduced proliferation of cardiomyocytes, which argues for a role of cardiac metabolism in heart regeneration. As such, strategies aimed at modulating this metabolism-proliferation axis could, in theory, promote heart regeneration in the setting of IHD. However, the lack of mechanistic understanding of these cellular processes has made it challenging to develop therapeutic modalities that can effectively promote regeneration. Here, we review the role of metabolic substrates and mitochondria in heart regeneration, and discuss potential targets aimed at promoting cardiomyocyte cell cycle re-entry. While advances in cardiovascular therapies have reduced IHD-related deaths, this has resulted in a substantial increase in HF cases. A comprehensive understanding of the interplay between cardiac metabolism and heart regeneration could facilitate the discovery of novel therapeutic targets to repair the damaged heart and reduce risk of HF in patients with IHD.

Redox-dependent Igfbp2 signaling controls Brca1 DNA damage response to govern neural stem cell fate

Neural stem cell (NSC) maintenance and functions are regulated by reactive oxygen species (ROS). However, the mechanisms by which ROS control NSC behavior remain unclear. Here we report that ROS-dependent Igfbp2 signaling controls DNA repair pathways which balance NSC self-renewal and lineage commitment. Ncf1 or Igfbp2 deficiency constrains NSCs to a self-renewing state and prevents neurosphere formation. Ncf1-dependent oxidation of Igfbp2 promotes neurogenesis by NSCs in vitro and in vivo while repressing Brca1 DNA damage response genes and inducing DNA double-strand breaks (DDSBs). By contrast, Ncf1^-/- and Igfbp2^-/- NSCs favor the formation of oligodendrocytes in vitro and in vivo. Notably, transient repression of Brca1 DNA repair pathway genes induces DDSBs and is sufficient to rescue the ability of Ncf1^-/- and Igfbp2^-/- NSCs to lineage-commit to form neurospheres and neurons. NSC lineage commitment is dependent on the oxidizable cysteine-43 residue of Igfbp2. Our study highlights the role of DNA damage/repair in orchestrating NSC fate decisions downstream of redox-regulated Igfbp2.

Cardiac Remodeling and Repair: Recent Approaches, Advancements, and Future Perspective

The limited ability of mammalian adult cardiomyocytes to proliferate following an injury to the heart, such as myocardial infarction, is a major factor that results in adverse fibrotic and myocardial remodeling that ultimately leads to heart failure. The continued high degree of heart failure-associated morbidity and lethality requires the special attention of researchers worldwide to develop efficient therapeutics for cardiac repair. Recently, various strategies and approaches have been developed and tested to extrinsically induce regeneration and restoration of the myocardium after cardiac injury have yielded encouraging results. Nevertheless, these interventions still lack adequate success to be used for clinical interventions. This review highlights and discusses both cell-based and cell-free therapeutic approaches as well as current advancements, major limitations, and future perspectives towards developing an efficient therapeutic method for cardiac repair.

Cardiac fibroblasts display endurance to ischemia, high ROS control and elevated respiration regulated by the JAK2/STAT pathway

Cardiovascular diseases are the leading cause of death globally and more than four out of five cases are due to ischemic events. Cardiac fibroblasts (CF) contribute to normal heart development and function, and produce the post-ischemic scar. Here, we characterize the biochemical and functional aspects related to CF endurance to ischemia-like conditions. Expression data mining showed that cultured human CF (HCF) express more BCL2 than pulmonary and dermal fibroblasts. In addition, gene set enrichment analysis showed overrepresentation of genes involved in the response to hypoxia and oxidative stress, respiration and Janus kinase (JAK)/Signal transducer and Activator of Transcription (STAT) signaling pathways in HCF. BCL2 sustained survival and proliferation of cultured rat CF, which also had higher respiration capacity and reactive oxygen species (ROS) production than pulmonary and dermal fibroblasts. This was associated with higher expression of the electron transport chain (ETC) and antioxidant enzymes. CF had high phosphorylation of JAK2 and its effectors STAT3 and STAT5, and their inhibition reduced viability and respiration, impaired ROS control and reduced the expression of BCL2, ETC complexes and antioxidant enzymes. Together, our results identify molecular and biochemical mechanisms conferring survival advantage to experimental ischemia in CF and show their control by the JAK2/STAT signaling pathway. The presented data point to potential targets for the regulation of cardiac fibrosis and also open the possibility of a general mechanism by which somatic cells required to acutely respond to ischemia are constitutively adapted to survive it.

Distinct fission signatures predict mitochondrial degradation or biogenesis

Mitochondrial fission is a highly regulated process that, when disrupted, can alter metabolism, proliferation and apoptosis^1-3. Dysregulation has been linked to neurodegeneration^3,4, cardiovascular disease³ and cancer⁵. Key components of the fission machinery include the endoplasmic reticulum⁶ and actin⁷, which initiate constriction before dynamin-related protein 1 (DRP1)⁸ binds to the outer mitochondrial membrane via adaptor proteins^9-11, to drive scission¹². In the mitochondrial life cycle, fission enables both biogenesis of new mitochondria and clearance of dysfunctional mitochondria through mitophagy^1,13. Current models of fission regulation cannot explain how those dual fates are decided. However, uncovering fate determinants is challenging, as fission is unpredictable, and mitochondrial morphology is heterogeneous, with ultrastructural features that are below the diffraction limit. Here, we used live-cell structured illumination microscopy to capture mitochondrial dynamics. By analysing hundreds of fissions in African green monkey Cos-7 cells and mouse cardiomyocytes, we discovered two functionally and mechanistically distinct types of fission. Division at the periphery enables damaged material to be shed into smaller mitochondria destined for mitophagy, whereas division at the midzone leads to the proliferation of mitochondria. Both types are mediated by DRP1, but endoplasmic reticulum- and actin-mediated pre-constriction and the adaptor MFF govern only midzone fission. Peripheral fission is preceded by lysosomal contact and is regulated by the mitochondrial outer membrane protein FIS1. These distinct molecular mechanisms explain how cells independently regulate fission, leading to distinct mitochondrial fates.

Research progress on myocardial regeneration: what is new?

The regeneration capacity of cardiomyocytes (CMs) is retained in neonatal mouse hearts but is limited in adult mouse hearts. Myocardial infarction (MI) in adult hearts usually leads to the loss of large amounts of cardiac tissue, and then accelerates the process of cardiac remodeling and heart failure. Therefore, it is necessary to explore the potential mechanisms of CM regeneration in the neonates and develop potential therapies aimed at promoting CM regeneration and cardiac repair in adults. Currently, studies indicate that a number of mechanisms are involved in neonatal endogenous myocardial regeneration, including cell cycle regulators, transcription factors, non-coding RNA, signaling pathways, acute inflammation, hypoxia, protein kinases, and others. Understanding the mechanisms of regeneration in neonatal CMs after MI provides theoretical support for the studies related to the promotion of heart repair after MI in adult mammals. However, several difficulties in the study of CM regeneration still need to be overcome. This article reviews the potential mechanisms of endogenous CM regeneration in neonatal mouse hearts and discusses possible therapeutic targets and future research directions.

Involvement of the mitochondrial nuclease EndoG in the regulation of cell proliferation through the control of reactive oxygen species

The apoptotic nuclease EndoG is involved in mitochondrial DNA replication. Previous results suggested that, in addition to regulate cardiomyocyte hypertrophy, EndoG could be involved in cell proliferation. Here, by using in vivo and cell culture models, we investigated the role of EndoG in cell proliferation. Genetic deletion of Endog both in vivo and in cultured cells or Endog silencing in vitro induced a defect in rodent and human cell proliferation with a tendency of cells to accumulate in the G₁ phase of cell cycle and increased reactive oxygen species (ROS) production. The defect in cell proliferation occurred with a decrease in the activity of the AKT/PKB-GSK-3β-Cyclin D axis and was reversed by addition of ROS scavengers. EndoG deficiency did not affect the expression of ROS detoxifying enzymes, nor the expression of the electron transport chain complexes and oxygen consumption rate. Addition of the micropeptide Humanin to EndoG-deficient cells restored AKT phosphorylation and proliferation without lowering ROS levels. Thus, our results show that EndoG is important for cell proliferation through the control of ROS and that Humanin can restore cell division in EndoG-deficient cells and counteracts the effects of ROS on AKT phosphorylation.

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Reduced expression of the mitochondrial nuclease EndoG induces ROS production.

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EndoG deficiency hampers cell proliferation through ROS-dependent signaling.

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Increased ROS in EndoG-deficient cells limits the Akt/Gsk3/cyclin axis activity.

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Humanin sustains proliferation despite high ROS levels induced by Endog deficiency.

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Romo-1 deficiency reduces cell proliferation independently of EndoG and ROS.

Hydrogen Sulfide Promotes Cardiomyocyte Proliferation and Heart Regeneration via ROS Scavenging

Neonatal mouse hearts can regenerate completely in 21 days after cardiac injury, providing an ideal model to exploring heart regenerative therapeutic targets. The oxidative damage by Reactive Oxygen Species (ROS) is one of the critical reasons for the cell cycle arrest of cardiomyocytes (CMs), which cause mouse hearts losing the capacity to regenerate in 7 days or shorter after birth. As an antioxidant, hydrogen sulfide (H₂S) plays a protective role in a variety of diseases by scavenging ROS produced during the pathological processes. In this study, we found that blocking H₂S synthesis by PAG (H₂S synthase inhibitor) suspended heart regeneration and CM proliferation with ROS deposition increase after cardiac injury (myocardial infarction or apex resection) in 2-day-old mice. NaHS (a H₂S donor) administration improved heart regeneration with CM proliferation and ROS elimination after myocardial infarction in 7-day-old mice. NaHS protected primary neonatal mouse CMs from H₂O₂-induced apoptosis and promoted CM proliferation via SOD2-dependent ROS scavenging. The oxidative DNA damage in CMs was reduced with the elimination of ROS by H₂S. Our results demonstrated for the first time that H₂S promotes heart regeneration and identified NaHS as a potent modulator for cardiac repair.

Oxidative CaMKII as a potential target for inflammatory disease (Review)

CaMKII is a calcium‑activated kinase, proved to be modulated by oxidation. Currently, the oxidative activation of CaMKII exists in several models of asthma, chronic rhinosinusitis with nasal polyps, cardiovascular disease, diabetes mellitus, acute ischemic stroke and cancer. Oxidized CaMKII (ox‑CaMKII) may be important in several of these diseases. The present review examines the mechanism underlying the oxidative activation of CaMKII and summarizes the current findings associated with the function of ox‑CaMKII in inflammatory diseases. Taken together, the findings of this review aim to improve current understanding of the function of ox‑CaMKII and provide novel insights for future research.

Enhanced Keap1-Nrf2 signaling protects the myocardium from isoproterenol-induced pathological remodeling in mice

Nuclear factor (erythroid-derived 2)-like 2 (NFE2L2/Nrf2) is an inducible transcription factor that is essential for maintenance of redox signaling in response to stress. This suggests that if Nrf2 expression response could be enhanced for a defined physiological pro-oxidant stress then it would be protective. This has important implications for the therapeutic manipulation of the Keap1/Nrf2 signaling pathway which is now gaining a lot of attention. We tested this hypothesis through the generation of Nrf2 transgene expression mouse model with and without isoproterenol-induced cardiac stress. Cardiac-specific mouse Nrf2 transgenic (mNrf2-TG) and non-transgenic (NTG) mice were subjected to isoproterenol (ISO) treatment and assessed for myocardial structure, function (echocardiography and electrocardiography), and glutathione redox state. Myocardial infarction and fibrosis along with increased inflammation leading to myocardial dysfunction was noted in NTG mice exposed to ISO, while mNrf2-TG hearts were resistant to the ISO insult. Preservation of myocardial structure and function in the mNrf2-TG mice was associated with the enhanced Nrf2 expression displayed in these hearts with an increased basal and post-treatment expression of redox modulatory genes and an overall enhanced antioxidant status. Of note, myocardium of ISO-treated TG mice displayed significantly increased stabilization of the KEAP1-NRF2 complex and enhanced release of NRF2 to the nucleus resulting in overall decreased pro-oxidant markers. Taken together, we suggest that a basal enhanced Nrf2 expression in mouse heart results in maintenance of redox homeostasis and counteracts ISO-induced oxidative stress, and suppresses pathological remodeling. These data suggest that an alternative therapeutic approach to enhance the efficacy of the Keap1-Nrf2 system is to stimulate basal expression of Nrf2.

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Isoproterenol induces oxidative/inflammatory stresses and leading to myocardial remodeling.

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Cardiac specific expression of Nrf2 augments Keap1-Nrf2 association, thereby timely responds to isoproterenol-induced stress.

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Augmented levels of Keap1-Nrf2 signaling is crucial to combat isoproterenol toxicity in the heart.

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Enhanced Nrf2-dependent antioxidant defense suppresses oxidative stress and prevents pathological cardiac remodeling.

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A controlled activation of global antioxidant signaling is vital for myocardial protection in stress conditions.

Targeting Oxidative Stress Using Nanoparticles as a Theranostic Strategy for Cardiovascular Diseases

SIGNIFICANCE

Nanomedicine is an application of nanotechnology that provides solutions to unmet medical challenges. The unique features of nanoparticles, such as their small size, modifiable components, and diverse functionality, make them attractive and suitable materials for novel diagnostic, therapeutic, or theranostic applications. Cardiovascular diseases (CVDs) are the major cause of noncommunicable illness in both developing and developed countries. Nanomedicine offers novel theranostic options for the treatment of CVDs. Recent Advances: Many innovative nanoparticles to target reactive oxygen species (ROS) have been developed. In this article, we review the characteristics of nanoparticles that are responsive to ROS, their limitations, and their potential clinical uses. Significant advances made in diagnosis of atherosclerosis and treatment of acute coronary syndrome using nanoparticles are discussed.

CRITICAL ISSUES

Although there is a tremendous potential for the nanoparticle applications in medicine, their safety should be considered while using in humans. We discuss the challenges that may be encountered with some of the innovative nanoparticles used in CVDs.

FUTURE DIRECTIONS

The unique properties of nanoparticles offer novel diagnostic tool and potential therapeutic strategies. However, nanomedicine is still in its infancy, and further in-depth studies are needed before wide clinical application is achieved.

Targeting the Cardiomyocyte Cell Cycle for Heart Regeneration

Adult mammalian cardiomyocytes (CMs) exhibit limited proliferative capacity, as cell cycle activity leads to an increase in DNA content, but mitosis and cytokinesis are infrequent. This makes the heart highly inefficient in replacing with neoformed cardiomyocytes lost contractile cells as occurs in diseases such as myocardial infarction and dilated cardiomyopathy. Regenerative therapies based on the implant of stem cells of diverse origin do not warrant engraftment and electromechanical connection of the new cells with the resident ones, a fundamental condition to restore the physiology of the cardiac syncytium. Consequently, there is a growing interest in identifying factors playing relevant roles in the regulation of the CM cell cycle to be targeted in order to induce the resident cardiomyocytes to divide into daughter cells and thus achieve myocardial regeneration with preservation of physiologic syncytial performance.

Redox-dependent BMI1 activity drives in vivo adult cardiac progenitor cell differentiation

Accumulation of reactive oxygen species (ROS) is associated with several cardiovascular pathologies and with cell cycle exit by neonanatal cardiomyocytes, a key limiting factor in the regenerative capacity of the adult mammalian heart. The polycomb complex component BMI1 is linked to adult progenitors and is an important partner in DNA repair and redox regulation. We found that high BMI1 expression is associated with an adult Sca1⁺ cardiac progenitor sub-population with low ROS levels. In homeostasis, BMI1 repressed cell fate genes, including a cardiogenic differentiation program. Oxidative damage nonetheless modified BMI1 activity in vivo by derepressing canonical target genes in favor of their antioxidant and anticlastogenic functions. This redox-mediated mechanism is not restricted to damage situations, however, and we report ROS-associated differentiation of cardiac progenitors in steady state. These findings demonstrate how redox status influences the cardiac progenitor response, and identify redox-mediated BMI1 regulation with implications in maintenance of cellular identity in vivo.

Hypoxia-induced myocardial regeneration

The underlying cause of systolic heart failure is the inability of the adult mammalian heart to regenerate damaged myocardium. In contrast, some vertebrate species and immature mammals are capable of full cardiac regeneration following multiple types of injury through cardiomyocyte proliferation. Little is known about what distinguishes proliferative cardiomyocytes from terminally differentiated, nonproliferative cardiomyocytes. Recently, several reports have suggested that oxygen metabolism and oxidative stress play a pivotal role in regulating the proliferative capacity of mammalian cardiomyocytes. Moreover, reducing oxygen metabolism in the adult mammalian heart can induce cardiomyocyte cell cycle reentry through blunting oxidative damage, which is sufficient for functional improvement following myocardial infarction. Here we concisely summarize recent findings that highlight the role of oxygen metabolism and oxidative stress in cardiomyocyte cell cycle regulation, and discuss future therapeutic approaches targeting oxidative metabolism to induce cardiac regeneration.

Cardiomyocyte proliferation in zebrafish and mammals: lessons for human disease

Cardiomyocytes proliferate profusely during early development and for a brief period after birth in mammals. Within a month after birth, this proliferative capability is dramatically reduced in mammals unlike lower vertebrates where it persists into adult life. The zebrafish, for example, retains the ability to regenerate the apex of the heart following resection by a mechanism predominantly driven by cardiomyocyte proliferation. Differences in proliferative capacity of cardiomyocytes in adulthood between mammals and lower vertebrates are closely liked to ontogenetic or phylogenetic factors. Elucidation of these factors has the potential to provide enormous benefits if they lead to the development of therapeutic strategies that facilitate cardiomyocyte proliferation. In this review, we highlight the differences between Mammalian and Zebrafish cardiomyocytes, which could explain at least in part the different proliferative capacities in these two species. We discuss the advantages of the zebrafish as a model of cardiomyocyte proliferation, particularly at the embryonic stage. We also identify a number of key molecular pathways with potential to reveal key steps in switching cardiomyocytes from a quiescent to a proliferative phenotype.

Functional Effect of Pim1 Depends upon Intracellular Localization in Human Cardiac Progenitor Cells

Human cardiac progenitor cells (hCPC) improve heart function after autologous transfer in heart failure patients. Regenerative potential of hCPCs is severely limited with age, requiring genetic modification to enhance therapeutic potential. A legacy of work from our laboratory with Pim1 kinase reveals effects on proliferation, survival, metabolism, and rejuvenation of hCPCs in vitro and in vivo. We demonstrate that subcellular targeting of Pim1 bolsters the distinct cardioprotective effects of this kinase in hCPCs to increase proliferation and survival, and antagonize cellular senescence. Adult hCPCs isolated from patients undergoing left ventricular assist device implantation were engineered to overexpress Pim1 throughout the cell (PimWT) or targeted to either mitochondrial (Mito-Pim1) or nuclear (Nuc-Pim1) compartments. Nuc-Pim1 enhances stem cell youthfulness associated with decreased senescence-associated β-galactosidase activity, preserved telomere length, reduced expression of p16 and p53, and up-regulation of nucleostemin relative to PimWT hCPCs. Alternately, Mito-Pim1 enhances survival by increasing expression of Bcl-2 and Bcl-XL and decreasing cell death after H2O2 treatment, thereby preserving mitochondrial integrity superior to PimWT. Mito-Pim1 increases the proliferation rate by up-regulation of cell cycle modulators Cyclin D, CDK4, and phospho-Rb. Optimal stem cell traits such as proliferation, survival, and increased youthful properties of aged hCPCs are enhanced after targeted Pim1 localization to mitochondrial or nuclear compartments. Targeted Pim1 overexpression in hCPCs allows for selection of the desired phenotypic properties to overcome patient variability and improve specific stem cell characteristics.

Selenoproteins and cardiovascular stress

Dietary selenium (Se) is an essential micronutrient that exerts its biological effects through its incorporation into selenoproteins. This family of proteins contains several antioxidant enzymes such as the glutathione peroxidases, redox-regulating enzymes such as thioredoxin reductases, a methionine sulfoxide reductase, and others. In this review, we summarise the current understanding of the roles these selenoproteins play in protecting the cardiovascular system from different types of stress including ischaemia-reperfusion, homocysteine dysregulation, myocardial hypertrophy, doxirubicin toxicity, Keshan disease, and others.