Periostin induces proliferation of differentiated cardiomyocytes and promotes cardiac repair

Reawakening the Intrinsic Cardiac Regenerative Potential: Molecular Strategies to Boost Dedifferentiation and Proliferation of Endogenous Cardiomyocytes

Despite considerable efforts carried out to develop stem/progenitor cell-based technologies aiming at replacing and restoring the cardiac tissue following severe damages, thus far no strategies based on adult stem cell transplantation have been demonstrated to efficiently generate new cardiac muscle cells. Intriguingly, dedifferentiation, and proliferation of pre-existing cardiomyocytes and not stem cell differentiation represent the preponderant cellular mechanism by which lower vertebrates spontaneously regenerate the injured heart. Mammals can also regenerate their heart up to the early neonatal period, even in this case by activating the proliferation of endogenous cardiomyocytes. However, the mammalian cardiac regenerative potential is dramatically reduced soon after birth, when most cardiomyocytes exit from the cell cycle, undergo further maturation, and continue to grow in size. Although a slow rate of cardiomyocyte turnover has also been documented in adult mammals, both in mice and humans, this is not enough to sustain a robust regenerative process. Nevertheless, these remarkable findings opened the door to a branch of novel regenerative approaches aiming at reactivating the endogenous cardiac regenerative potential by triggering a partial dedifferentiation process and cell cycle re-entry in endogenous cardiomyocytes. Several adaptations from intrauterine to extrauterine life starting at birth and continuing in the immediate neonatal period concur to the loss of the mammalian cardiac regenerative ability. A wide range of systemic and microenvironmental factors or cell-intrinsic molecular players proved to regulate cardiomyocyte proliferation and their manipulation has been explored as a therapeutic strategy to boost cardiac function after injuries. We here review the scientific knowledge gained thus far in this novel and flourishing field of research, elucidating the key biological and molecular mechanisms whose modulation may represent a viable approach for regenerating the human damaged myocardium.

The Usefulness of Urinary Periostin, Cytokeratin-18, and Endoglin for Diagnosing Renal Fibrosis in Children with Congenital Obstructive Nephropathy

Congenital obstructive nephropathy (CON) leads to renal fibrosis and chronic kidney disease. The aim of the study was to investigate the predictive value of urinary endoglin, periostin, cytokeratin-18, and transforming growth factor-β1 (TGF-β1) for assessing the severity of renal fibrosis in 81 children with CON and 60 controls. Children were divided into three subgroups: severe, moderate scars, and borderline lesions based on 99mTc-ethylenedicysteine scintigraphy results. Periostin, periostin/Cr, and cytokeratin-18 levels were significantly higher in the study group compared to the controls. Children with severe scars had significantly higher urinary periostin/Cr levels than those with borderline lesions. In multivariate analysis, only periostin and cytokeratin-18 were independently related to the presence of severe and moderate scars, and periostin was independently related to borderline lesions. However, periostin did not differentiate advanced scars from borderline lesions. In ROC analysis, periostin and periostin/Cr demonstrated better diagnostic profiles for detection of advanced scars than TGF-β1 and cytokeratin-18 (AUC 0.849; 0.810 vs. 0.630; 0.611, respectively) and periostin for detecting borderline lesions than endoglin and periostin/Cr (AUC 0.777 vs. 0.661; 0.658, respectively). In conclusion, periostin seems to be a promising, non-invasive marker for assessing renal fibrosis in children with CON. CK-18 and TGF-β1 demonstrated low utility, and endoglin was not useful for diagnosing advanced scars.

TT-10-loaded nanoparticles promote cardiomyocyte proliferation and cardiac repair in a mouse model of myocardial infarction

The meager regenerative capacity of adult mammalian hearts appears to be driven by the proliferation of endogenous cardiomyocytes; thus, strategies targeting mechanisms of cardiomyocyte cell cycle regulation, such as the Hippo/Yes-associated protein (Hippo/Yap) pathway, could lead to the development of promising therapies for heart disease. The pharmacological product TT-10 increases cardiomyocyte proliferation by upregulating nuclear Yap levels. When intraperitoneal injections of TT-10 were administered to infarcted mouse hearts, the treatment promoted cardiomyocyte proliferation and was associated with declines in infarct size 1 week after administration, but cardiac function worsened at later time points. Here, we investigated whether encapsulating TT-10 into poly-lactic-co-glycolic acid nanoparticles (NPs) before administration could extend the duration of TT-10 delivery and improve the potency of TT-10 for myocardial repair. TT-10 was released from the TT-10–loaded NPs for up to 4 weeks in vitro, and intramyocardial injections of TT-10–delivered NPs stably improved cardiac function from week 1 to week 4 after administration to infarcted mouse hearts. TT-10–delivered NP treatment was also associated with significantly smaller infarcts at week 4, with increases in cardiomyocyte proliferation and nuclear Yap abundance and with declines in cardiomyocyte apoptosis. Thus, NP-mediated delivery appears to enhance both the potency and durability of TT-10 treatment for myocardial repair.

Identification of Novel and Potent Modulators Involved in Neonatal Cardiac Regeneration

Neonatal mammalian heart has been shown to possess the capacity to regenerate substantially after an injury. This remarkable regenerative capacity is lost in a week. This transition has been marked with cardiomyocyte cell cycle arrest and induction of fibrotic response similar to what occurs after myocardial infarction in adult hearts. Recent studies outlined the function of several cardiogenic factors that play a pivotal role in neonatal cardiac regeneration. However, underlying molecular mechanisms of neonatal cardiac regeneration and other cardiogenic factors remained elusive. Here, we investigated the involvement of novel putative cardiogenic factors in neonatal cardiac regeneration and cardiomyocyte cell cycle withdrawal. We have shown that Cbl, Dnmt3a, and Itch are significantly downregulated during neonatal cardiac regeneration process after cardiac injury in vivo. Intriguingly, several of studied factors are upregulated in non-regenerative period of 7-day-old mice after cardiac injury. Knockdown of Cbl, Dnmt3a and Itch in rat neonatal cardiomyocytes lead to the induction of cardiomyocyte proliferation. Cardiomyocyte proliferation accompanies upregulation of positive regulators of cardiomyocyte division and downregulation of CDKIs. Taken together, our findings suggest that Cbl, Dnmt3a, and Itch may be involved in the regulation of cardiomyocyte cell cycle withdrawal and may represent new targets for the induction of cardiac regeneration.

Exogenous extracellular matrix proteins decrease cardiac fibroblast activation in stiffening microenvironment through CAPG

Controlling fibrosis is an essential part of regenerating the post-ischemic heart. In the post-ischemic heart, fibroblasts differentiate to myofibroblasts that produce collagen-rich matrix to physically stabilize the infarct area. Infarct models in adult mice result in permanent scarring unlike newborn animals which fully regenerate. Decellularized extracellular matrix (dECM) hydrogels derived from early-aged hearts have been shown to be a transplantable therapy that preserves heart function and stimulates cardiomyocyte proliferation and vascularization. In this study, we investigate the anti-fibrotic effects of injectable dECM hydrogels in a cardiac explant model in the context of age-associated tissue compliance. Treatments with adult and fetal dECM hydrogels were tested for molecular effects on cardiac fibroblast activation and fibrosis. Altered sensitivity of fibroblasts to the mechanosignaling of the remodeling microenvironment was evaluated by manipulating the native extracellular matrix in explants and also with elastomeric substrates in the presence of dECM hydrogels. The injectable fetal dECM hydrogel treatment decreases fibroblast activation and contractility and lowers the stiffness-mediated increases in fibroblast activation observed in stiffened explants. The anti-fibrotic effect of dECM hydrogel is most observable at highest stiffness. Experiments with primary cells on elastomeric substrates with dECM treatment support this phenomenon. Transcriptome analysis indicated that dECM hydrogels affect cytoskeleton related signaling including Macrophage capping protein (CAPG) and Leupaxin (LPXN). CAPG was down-regulated by the fetal dECM hydrogel. LPXN expression was decreased by stiffening the explants; however, this effect was reversed by dECM hydrogel treatment. Pharmacological disruption of cytoskeleton polymerization lowered fibroblast activation and CAPG levels. Knocking down CAPG expression with siRNA inhibited fibroblast activation and collagen deposition. Collectively, fibroblast activation is dependent on cooperative action of extracellular molecular signals and mechanosignaling by cytoskeletal integrity.

Pathological Roles and Clinical Usefulness of Periostin in Type 2 Inflammation and Pulmonary Fibrosis

Periostin is known to be a useful biomarker for various diseases. In this article, we focus on allergic diseases and pulmonary fibrosis, for which we and others are now developing detection systems for periostin as a biomarker. Biomarker-based precision medicine in the management of type 2 inflammation and fibrotic diseases since heterogeneity is of utmost importance. Periostin expression is induced by type 2 cytokines (interleukin-4/-13) or transforming growth factor-β, and plays a vital role in the pathogenesis of allergic inflammation or interstitial lung disease, respectively, andits serum levels are correlated disease severity, prognosis and responsiveness to the treatment. We first summarise the importance of type 2 biomarker and then describe the pathological role of periostin in the development and progression of type 2 allergic inflammation and pulmonary fibrosis. In addition, then, we summarise the recent development of assay methods for periostin detection, and analyse the diseases in which periostin concentration is elevated in serum and local biological fluids and its usefulness as a biomarker. Furthermore, we describe recent findings of periostin as a biomarker in the use of biologics or anti-fibrotic therapy. Finally, we describe the factors that influence the change in periostin concentration under the healthy conditions.

Therapies to prevent post-infarction remodelling: From repair to regeneration

Myocardial infarction is the first cause of worldwide mortality, with an increasing incidence also reported in developing countries. Over the past decades, preclinical research and clinical trials continually tested the efficacy of cellular and acellular-based treatments. However, none of them resulted in a drug or device currently used in combination with either percutaneous coronary intervention or coronary artery bypass graft. Inflammatory, proliferation and remodelling phases follow the ischaemic event in the myocardial tissue. Only recently, single-cell sequencing analyses provided insights into the specific cell populations which determine the final fibrotic deposition in the affected region. In this review, ischaemia, inflammation, fibrosis, angiogenesis, cellular stress and fundamental cellular and molecular components are evaluated as therapeutic targets. Given the emerging evidence of biomaterial-based systems, the increasing use of injectable hydrogels/scaffolds and epicardial patches is reported both as acellular and cellularised/functionalised treatments. Since several variables influence the outcome of any experimented treatment, we return to the pathological basis with an unbiased view towards any specific process or cellular component. Thus, by evaluating the benefits and limitations of the approaches based on these targets, the reader can weigh the rationale of each of the strategies that reached the clinical trials stage. As recent studies focused on the relevance of the extracellular matrix in modulating ischaemic remodelling and enhancing myocardial regeneration, we aim to portray current trends in the field with this review. Finally, approaches towards feasible translational studies that are as yet unexplored are also suggested.

Posttranslational Modifications: Emerging Prospects for Cardiac Regeneration Therapy

Heart failure (HF) following ischemic heart disease (IHD) remains a hard nut to crack and a leading cause of death worldwide. Cardiac regeneration aims to promote cardiomyocyte (CM) proliferation by transitioning the cell cycle state of CMs from arrest to re-entry. Protein posttranslational modifications (PTMs) have recently attracted extensive attention in the field of cardiac regeneration due to their reversibility and effects on the stability, activity, and subcellular localization of target proteins. The balance of PTMs is disrupted when neonatal CMs withdraw from the cell cycle, resulting in significant dysfunction of downstream substrate protein localization, expression, and activity, ultimately limiting the maintenance of cardiac regeneration ability. In this review, we summarize recent research concerning the role of PTMs in cardiac regeneration, while focusing on phosphorylation, acetylation, ubiquitination, glycosylation, methylation, and neddylation, and the effects of these modifications on CM proliferation, which may provide potential targets for future treatments for IHD.

A Brief History in Cardiac Regeneration, and How the Extra Cellular Matrix May Turn the Tide

Tissue homeostasis is perturbed by stressful events, which can lead to organ dysfunction and failure. This is particularly true for the heart, where injury resulting from myocardial infarction or ischemic heart disease can result in a cascading event ultimately ending with the loss of functional myocardial tissue and heart failure. To help reverse this loss of healthy contractile tissue, researchers have spent decades in the hopes of characterizing a cell source capable of regenerating the injured heart. Unfortunately, these strategies have proven to be ineffective. With the goal of truly understanding cardiac regeneration, researchers have focused on the innate regenerative abilities of zebrafish and neonatal mammals. This has led to the realization that although cells play an important role in the repair of the diseased myocardium, inducing cardiac regeneration may instead lie in the composition of the extra cellular milieu, specifically the extra cellular matrix. In this review we will briefly summarize the current knowledge regarding cell sources used for cardiac regenerative approaches, since these have been extensively reviewed elsewhere. More importantly, by revisiting innate cardiac regeneration observed in zebrafish and neonatal mammals, we will stress the importance the extra cellular matrix has on reactivating this potential in the adult myocardium. Finally, we will address how we can harness the ability of the extra cellular matrix to guide cardiac repair thereby setting the stage of next generation regenerative strategies.

The Role of TGF-β Signaling in Cardiomyocyte Proliferation

PURPOSE OF REVIEW

The loss of contractile function after heart injury remains one of the major healthcare issues of our time. One strategy to deal with this problem would be to increase the number of cardiomyocytes to enhance cardiac function. In the last couple of years, reactivation of cardiomyocyte proliferation has repeatedly demonstrated to aid in functional recovery after cardiac injury.

RECENT FINDINGS

The Tgf-β superfamily plays key roles during development of the heart and populating the embryonic heart with cardiomyocytes. In this review, we discuss the role of Tgf-β signaling in regulating cardiomyocyte proliferation during development and in the setting of cardiac regeneration. Although various pathways to induce cardiomyocyte proliferation have been established, the extent to which cardiomyocyte proliferation requires or involves activation of the Tgf-β superfamily is not entirely clear. More research is needed to better understand cross-talk between pathways that regulate cardiomyocyte proliferation.

Toward the Goal of Human Heart Regeneration

Heart regeneration, a relatively new field of biology, is one of the most active and controversial areas of biomedical research. The potential impact of successful human heart regeneration therapeutics cannot be overstated, given the magnitude and prognosis of heart failure. However, the regenerative process is highly complex, and premature claims of successful heart regeneration have both fueled interest and created controversy. The field as a whole is now in the process of course correction, and a clearer picture is beginning to emerge. Despite the challenges, fundamental principles in developmental biology have provided a framework for hypothesis-driven approaches toward the ultimate goal of adult heart regeneration and repair. In this review, we discuss the current state of the field and outline the potential paths forward toward regenerating the human myocardium.

GLUT1 overexpression enhances glucose metabolism and promotes neonatal heart regeneration

The mammalian heart switches its main metabolic substrate from glucose to fatty acids shortly after birth. This metabolic switch coincides with the loss of regenerative capacity in the heart. However, it is unknown whether glucose metabolism regulates heart regeneration. Here, we report that glucose metabolism is a determinant of regenerative capacity in the neonatal mammalian heart. Cardiac-specific overexpression of Glut1, the embryonic form of constitutively active glucose transporter, resulted in an increase in glucose uptake and concomitant accumulation of glycogen storage in postnatal heart. Upon cryoinjury, Glut1 transgenic hearts showed higher regenerative capacity with less fibrosis than non-transgenic control hearts. Interestingly, flow cytometry analysis revealed two distinct populations of ventricular cardiomyocytes: Tnnt2-high and Tnnt2-low cardiomyocytes, the latter of which showed significantly higher mitotic activity in response to high intracellular glucose in Glut1 transgenic hearts. Metabolic profiling shows that Glut1-transgenic hearts have a significant increase in the glucose metabolites including nucleotides upon injury. Inhibition of the nucleotide biosynthesis abrogated the regenerative advantage of high intra-cardiomyocyte glucose level, suggesting that the glucose enhances the cardiomyocyte regeneration through the supply of nucleotides. Our data suggest that the increase in glucose metabolism promotes cardiac regeneration in neonatal mouse heart.

Access routes, devices and guidance methods for intrapericardial delivery in cardiac conditions

Drug deposition into the intrapericardial space is favourable for achieving localised effects and targeted cardiac delivery owing to its proximity to the myocardium as well as facilitating optimised pharmacokinetic profiles and a reduction in systemic side effects. Access to the pericardium requires invasive procedures but the risks associated with this have been reduced with technological advances, such as combining transatrial and subxiphoid access with different guidance methods. A variety of introducer devices, ranging from needles to loop-catheters, have also been developed and validated in pre-clinical studies investigating intrapericardial delivery of therapeutic agents. Access techniques are generally well-tolerated, self-limiting and safe, although some rare complications associated with certain approaches have been reported. This review covers these access techniques and how they have been applied to the delivery of drugs, cells, and biologicals, demonstrating the potential of intrapericardial delivery for treatments in cardiac arrhythmia, vascular damage, and myocardial infarction.

Cardiac Fibroblasts and Myocardial Regeneration

The billions of cardiomyocytes lost to acute myocardial infarction (MI) cannot be replaced by the limited regenerative capacity of adult mammalian hearts, and despite decades of research, there are still no clinically effective therapies for remuscularizing and restoring damaged myocardial tissue. Although the majority of the cardiac mass is composed of cardiomyocytes, cardiac fibroblasts (CFs) are one type of most numerous cells in the heart and the primary drivers of fibrosis, which prevents ventricular rupture immediately after MI but the fibrotic scar expansion and LV dilatation can eventually lead to heart failure. However, embryonic CFs produce cytokines that can activate proliferation in cultured cardiomyocytes, and the structural proteins produced by CFs may regulate cardiomyocyte cell-cycle activity by modulating the stiffness of the extracellular matrix (ECM). CFs can also be used to generate induced-pluripotent stem cells and induced cardiac progenitor cells, both of which can differentiate into cardiomyocytes and vascular cells, but cardiomyocytes appear to be more readily differentiated from iPSCs that have been reprogrammed from CFs than from other cell types. Furthermore, the results from recent studies suggest that cultured CFs, as well as the CFs present in infarcted hearts, can be reprogrammed directly into cardiomyocytes. This finding is very exciting as should we be able to successfully increase the efficiency of this reprogramming, we could remuscularize the injured ventricle and restore the LV function without need the transplantation of cells or cell products. This review summarizes the role of CFs in the innate response to MI and how their phenotypic plasticity and involvement in ECM production might be manipulated to improve cardiac performance in injured hearts.

An exosomal-carried short periostin isoform induces cardiomyocyte proliferation

Although a small number of cardiomyocytes may reenter the cell cycle after injury, the adult mammalian heart is incapable of a robust cardiomyocyte proliferation. Periostin, a secreted extracellular matrix protein, has been implicated as a regulator of cardiomyocyte proliferation; however, this role remains controversial. Alternative splicing of the human periostin gene results in 6 isoforms lacking sequences between exons 17 and 21, in addition to full-length periostin. We previously showed that exosomes (Exo) secreted by human cardiac explant-derived progenitor cells (CPC) carried periostin. Here, we aimed to investigate their cell cycle activity.

Methods: CPC were derived as the cellular outgrowth of ex vivo cultured cardiac atrial explants. Exo were purified from CPC conditioned medium using size exclusion chromatography. Exosomal periostin was analyzed by Western blotting using a pair of antibodies (one raised against aa 537-836, and one raised against amino acids mapping at exon 17 of human periostin), by ELISA, and by cryo-EM with immune-gold labeling. Cell cycle activity was assessed in neonatal rat cardiomyocytes, in human induced pluripotent stem cell (iPS)-derived cardiomyocytes, and in adult rat cardiomyocytes after myocardial infarction. The role of periostin in cell cycle activity was investigated by transfecting donor CPC with a siRNA against this protein.

Results: Periostin expression in CPC-secreted exosomes was detected using the antibody raised against aa 537-836 of the human protein, but not with the exon 17-specific antibody, consistent with an isoform lacking exon 17. Periostin was visualized on vesicle surfaces by cryo-EM and immune-gold labeling. CPC-derived exosomes induced cell proliferation in neonatal rat cardiomyocytes both in vitro and in vivo, in human iPS-derived cardiomyocytes, and in adult rat cardiomyocytes after myocardial infarction. Exo promoted phosphorylation of focal adhesion kinase (FAK), actin polymerization, and nuclear translocation of Yes-associated protein (YAP) in cardiomyocytes. Knocking down of periostin or YAP, or blocking FAK phosphorylation with PF-573228 nullified Exo-induced proliferation. A truncated human periostin peptide (aa 22-669), but not recombinant human full-length periostin, mimicked the pro-proliferative activity of exosomes.

Conclusions: Our results show, for the first time, that CPC-secreted exosomes promote cardiomyocyte cell cycle-reentry via a short periostin isoform expressed on their surfaces, whereas recombinant full-length periostin does not. These findings highlight isoform-specific roles of periostin in cardiomyocyte proliferation.

Evolution of organoid technology: Lessons learnt in Co-Culture systems from developmental biology

In recent years, the development of 3D organoids has opened new avenues of investigation into development, physiology, and regenerative medicine. Organoid formation and the process of organogenesis share common developmental pathways; thus, our knowledge of developmental biology can help model the complexity of different organs to refine organoids into a more sophisticated platform. The developmental process is strongly dependent on complex networks and communication of cell-cell and cell-matrix interactions among different cell populations and their microenvironment, during embryogenesis. These interactions affect cell behaviors such as proliferation, survival, migration, and differentiation. Co-culture systems within the organoid technology were recently developed and provided the highly physiologically relevant systems. Supportive cells including various types of endothelial and stromal cells provide the proper microenvironment, facilitate organoid assembly, and improve vascularization and maturation of organoids. This review discusses the role of the co-culture systems in organoid generation, with a focus on how knowledge of developmental biology has directed and continues to shape the development of more evolved 3D co-culture system-derived organoids.

Functional regeneration and repair of tendons using biomimetic scaffolds loaded with recombinant periostin

Tendon injuries disrupt the balance between stability and mobility, causing compromised functions and disabilities. The regeneration of mature, functional tendons remains a clinical challenge. Here, we perform transcriptional profiling of tendon developmental processes to show that the extracellular matrix-associated protein periostin (Postn) contributes to the maintenance of tendon stem/progenitor cell (TSPC) functions and promotes tendon regeneration. We show that recombinant periostin (rPOSTN) promotes the proliferation and stemness of TSPCs, and maintains the tenogenic potentials of TSPCs in vitro. We also find that rPOSTN protects TSPCs against functional impairment during long-term passage in vitro. For in vivo tendon formation, we construct a biomimetic parallel-aligned collagen scaffold to facilitate TSPC tenogenesis. Using a rat full-cut Achilles tendon defect model, we demonstrate that scaffolds loaded with rPOSTN promote endogenous TSPC recruitment, tendon regeneration and repair with native-like hierarchically organized collagen fibers. Moreover, newly regenerated tendons show recovery of mechanical properties and locomotion functions.

The regeneration of functional tendons remains a clinical challenge. Here the authors develop a biomimetic scaffold loaded with recombinant periostin and demonstrate its functionality in promoting tendon stem/progenitor cell recruitment and tenogenic differentiation, and tendon regeneration in a rat full-cut Achilles tendon defect model.

Heterogeneity of Intestinal Tissue Eosinophils: Potential Considerations for Next-Generation Eosinophil-Targeting Strategies

Eosinophils are implicated in the pathophysiology of a spectrum of eosinophil-associated diseases, including gastrointestinal eosinophilic diseases (EGIDs). Biologics that target the IL-5 pathway and are intended to ablate eosinophils have proved beneficial in severe eosinophilic asthma and may offer promise in treating some endotypes of EGIDs. However, destructive effector functions of eosinophils are only one side of the coin; eosinophils also play important roles in immune and tissue homeostasis. A growing body of data suggest tissue eosinophils represent a plastic and heterogeneous population of functional sub-phenotypes, shaped by environmental (systemic and local) pressures, which may differentially impact disease outcomes. This may be particularly relevant to the GI tract, wherein the highest density of eosinophils reside in the steady state, resident immune cells are exposed to an especially broad range of external and internal environmental pressures, and greater eosinophil longevity may uniquely enrich for co-expression of eosinophil sub-phenotypes. Here we review the growing evidence for functional sub-phenotypes of intestinal tissue eosinophils, with emphasis on the multifactorial pressures that shape and diversify eosinophil identity and potential targets to inform next-generation eosinophil-targeting strategies designed to restrain inflammatory eosinophil functions while sustaining homeostatic roles.

Engineering Extracellular Matrix Proteins to Enhance Cardiac Regeneration After Myocardial Infarction

Engineering microenvironments for accelerated myocardial repair is a challenging goal. Cell therapy has evolved over a few decades to engraft therapeutic cells to replenish lost cardiomyocytes in the left ventricle. However, compelling evidence supports that tailoring specific signals to endogenous cells rather than the direct integration of therapeutic cells could be an attractive strategy for better clinical outcomes. Of many possible routes to instruct endogenous cells, we reviewed recent cases that extracellular matrix (ECM) proteins contribute to enhanced cardiomyocyte proliferation from neonates to adults. In addition, the presence of ECM proteins exerts biophysical regulation in tissue, leading to the control of microenvironments and adaptation for enhanced cardiomyocyte proliferation. Finally, we also summarized recent clinical trials exclusively using ECM proteins, further supporting the notion that engineering ECM proteins would be a critical strategy to enhance myocardial repair without taking any risks or complications of applying therapeutic cardiac cells.

Cardiac Regeneration: New Insights Into the Frontier of Ischemic Heart Failure Therapy

Ischemic heart disease is the leading cause of morbidity and mortality in the world. While pharmacological and surgical interventions developed in the late twentieth century drastically improved patient outcomes, mortality rates over the last two decades have begun to plateau. Following ischemic injury, pathological remodeling leads to cardiomyocyte loss and fibrosis leading to impaired heart function. Cardiomyocyte turnover rate in the adult heart is limited, and no clinical therapies currently exist to regenerate cardiomyocytes lost following ischemic injury. In this review, we summarize the progress of therapeutic strategies including revascularization and cell-based interventions to regenerate the heart: transiently inducing cardiomyocyte proliferation and direct reprogramming of fibroblasts into cardiomyocytes. Moreover, we highlight recent mechanistic insights governing these strategies to promote heart regeneration and identify current challenges in translating these approaches to human patients.

Ccn2a is an injury-induced matricellular factor that promotes cardiac regeneration in zebrafish

The ability of zebrafish to heal their heart after injury makes them an attractive model for investigating the mechanisms governing the regenerative process. In this study, we show that the gene cellular communication network factor 2a (ccn2a), previously known as ctgfa, is induced in endocardial cells in the injured tissue and regulates CM proliferation and repopulation of the damaged tissue. We find that, whereas in wild-type animals, CMs track along the newly formed blood vessels that revascularize the injured tissue, in ccn2a mutants CM proliferation and repopulation are disrupted, despite apparently unaffected revascularization. In addition, we find that ccn2a overexpression enhances CM proliferation and improves the resolution of transient collagen deposition. Through loss- and gain-of-function as well as pharmacological approaches, we provide evidence that Ccn2a is necessary for and promotes heart regeneration by enhancing the expression of pro-regenerative extracellular matrix genes, and by inhibiting the chemokine receptor gene cxcr3.1 through a mechanism involving Tgfβ/pSmad3 signaling. Thus, Ccn2a positively modulates the innate regenerative response of the adult zebrafish heart.

Bearing My Heart: The Role of Extracellular Matrix on Cardiac Development, Homeostasis, and Injury Response

The extracellular matrix (ECM) is an essential component of the heart that imparts fundamental cellular processes during organ development and homeostasis. Most cardiovascular diseases involve severe remodeling of the ECM, culminating in the formation of fibrotic tissue that is deleterious to organ function. Treatment schemes effective at managing fibrosis and promoting physiological ECM repair are not yet in reach. Of note, the composition of the cardiac ECM changes significantly in a short period after birth, concurrent with the loss of the regenerative capacity of the heart. This highlights the importance of understanding ECM composition and function headed for the development of more efficient therapies. In this review, we explore the impact of ECM alterations, throughout heart ontogeny and disease, on cardiac cells and debate available approaches to deeper insights on cell–ECM interactions, toward the design of new regenerative therapies.

Defining human mesenchymal and epithelial heterogeneity in response to oral inflammatory disease

Human oral soft tissues provide the first barrier of defence against chronic inflammatory disease and hold a remarkable scarless wounding phenotype. Tissue homeostasis requires coordinated actions of epithelial, mesenchymal, and immune cells. However, the extent of heterogeneity within the human oral mucosa and how tissue cell types are affected during the course of disease progression is unknown. Using single-cell transcriptome profiling we reveal a striking remodelling of the epithelial and mesenchymal niches with a decrease in functional populations that are linked to the aetiology of the disease. Analysis of ligand–receptor interaction pairs identify potential intercellular hubs driving the inflammatory component of the disease. Our work establishes a reference map of the human oral mucosa in health and disease, and a framework for the development of new therapeutic strategies.

Extracellular Matrix in Ischemic Heart Disease, Part 4/4: JACC Focus Seminar

Myocardial ischemia and infarction, both in the acute and chronic phases, are associated with cardiomyocyte loss and dramatic changes in the cardiac extracellular matrix (ECM). It has long been appreciated that these changes in the cardiac ECM result in altered mechanical properties of ischemic or infarcted myocardial segments. However, a growing body of evidence now clearly demonstrates that these alterations of the ECM not only affect the structural properties of the ischemic and post-infarct heart, but they also play a crucial and sometimes direct role in mediating a range of biological pathways, including the orchestration of inflammatory and reparative processes, as well as the pathogenesis of adverse remodeling. This final part of a 4-part JACC Focus Seminar reviews the evidence on the role of the ECM in relation to the ischemic and infarcted heart, as well as its contribution to cardiac dysfunction and adverse clinical outcomes.

Proximity to injury, but neither number of nuclei nor ploidy define pathological adaptation and plasticity in cardiomyocytes

The adult mammalian heart consists of mononuclear and binuclear cardiomyocytes (CMs) with various ploidies. However, it remains unclear whether a variation in ploidy or number of nuclei is associated with distinct functions and injury responses in CMs, including regeneration. Therefore, we investigated transcriptomes and cellular as well as nuclear features of mononucleated and binucleated CMs in adult mouse hearts with and without injury. To be able to identify the role of ploidy we analyzed control and failing human ventricular CMs because human CMs show a larger and disease-sensitive degree of polyploidization. Using transgenic Myh6-H2BmCh to identify mononucleated and binucleated mouse CMs, we found that cellular volume and RNA content were similar in both. On average nuclei of mononuclear CMs showed a 2-fold higher ploidy, as compared to binuclear CMs indicating that most mononuclear CMs are tetraploid. After myocardial infarction mononucleated and binucleated CMs in the border zone of the lesion responded with hypertrophy and corresponding changes in gene expression, as well as a low level of induction of cell cycle gene expression. Human CMs allowed us to study a wide range of polyploidy spanning from 2n to 16n. Notably, basal as well as pathological gene expression signatures and programs in failing CMs proved to be independent of ploidy. In summary, gene expression profiles were induced in proximity to injury, but independent of number of nuclei or ploidy levels in CMs.

Immunomodulatory Role of the Extracellular Matrix Within the Liver Disease Microenvironment

Chronic liver disease when accompanied by underlying fibrosis, is characterized by an accumulation of extracellular matrix (ECM) proteins and chronic inflammation. Although traditionally considered as a passive and largely architectural structure, the ECM is now being recognized as a source of potent damage-associated molecular pattern (DAMP)s with immune-active peptides and domains. In parallel, the ECM anchors a range of cytokines, chemokines and growth factors, all of which are capable of modulating immune responses. A growing body of evidence shows that ECM proteins themselves are capable of modulating immunity either directly via ligation with immune cell receptors including integrins and TLRs, or indirectly through release of immunoactive molecules such as cytokines which are stored within the ECM structure. Notably, ECM deposition and remodeling during injury and fibrosis can result in release or formation of ECM-DAMPs within the tissue, which can promote local inflammatory immune response and chemotactic immune cell recruitment and inflammation. It is well described that the ECM and immune response are interlinked and mutually participate in driving fibrosis, although their precise interactions in the context of chronic liver disease are poorly understood. This review aims to describe the known pro-/anti-inflammatory and fibrogenic properties of ECM proteins and DAMPs, with particular reference to the immunomodulatory properties of the ECM in the context of chronic liver disease. Finally, we discuss the importance of developing novel biotechnological platforms based on decellularized ECM-scaffolds, which provide opportunities to directly explore liver ECM-immune cell interactions in greater detail.

Cardiomyocyte Induction and Regeneration for Myocardial Infarction Treatment: Cell Sources and Administration Strategies

Occlusion of coronary artery and subsequent damage or death of myocardium can lead to myocardial infarction (MI) and even heart failure-one of the leading causes of deaths world wide. Notably, myocardium has extremely limited regeneration potential due to the loss or death of cardiomyocytes (i.e., the cells of which the myocardium is comprised) upon MI. A variety of stem cells and stem cell-derived cardiovascular cells, in situ cardiac fibroblasts and endogenous proliferative epicardium, have been exploited to provide renewable cellular sources to treat injured myocardium. Also, different strategies, including direct injection of cell suspensions, bioactive molecules, or cell-incorporated biomaterials, and implantation of artificial cardiac scaffolds (e.g., cell sheets and cardiac patches), have been developed to deliver renewable cells and/or bioactive molecules to the MI site for the myocardium regeneration. This article briefly surveys cell sources and delivery strategies, along with biomaterials and their processing techniques, developed for MI treatment. Key issues and challenges, as well as recommendations for future research, are also discussed.

Microenvironment stiffness requires decellularized cardiac extracellular matrix to promote heart regeneration in the neonatal mouse heart

The transient period of regeneration potential in the postnatal heart suggests molecular changes with maturation influence the cardiac response to damage. We have previously demonstrated that injury and exercise can stimulate cardiomyocyte proliferation in the adult heart suggesting a sensitivity to exogenous signals. Here, we consider whether exogenous fetal ECM and mechanically unloading interstitial matrix can drive regeneration after myocardial infarction (MI) surgery in low-regenerative hearts of day5 mice. Compared to controls, exogenous fetal ECM increases cardiac function and lowers fibrosis at 3 weeks post-injury and this effect can be augmented by softening heart tissue. In vitro experiments support a mechano-sensitivity to exogenous ECM signaling. We tested potential mechanisms and observed that fetal ECM increases nuclear YAP localization which could be enhanced by pharmacological stabilization of the cytoskeleton. Blocking YAP expression lowered fetal ECM effects though not completely. Lastly we observed mechanically unloading heart interstitial matrix increased agrin expression, an extracellular node in the YAP signaling pathway. Collectively, these data support a combined effect of exogenous factors and mechanical activity in altering agrin expression, cytoskeletal remodeling, and YAP signaling in driving cardiomyocyte cell cycle activity and regeneration in postnatal non-regenerative mice. STATEMENT OF SIGNIFICANCE: With the purpose of developing regenerative strategies, we investigate the influence of the local niche on the cardiac injury response. We conclude tissue stiffness, as anticipated in aging or disease, impairs regenerative therapeutics. Most novel, mechanical unloading facilitates enhanced cardiac regeneration only after cells are pushed into a permissive state by fetal biomolecules. Specifically, mechanical unloading appears to increase extracellular agrin expression that amplifies fetal-stimulation of nuclear YAP signaling which correlates with observed increases of cell cycle activity in cardiomyocytes. The results further suggest the cytoskeleton is critical to this interaction between mechanical unloading and independently actived YAP signaling. Using animal models, tissue explants, and cells, this work indicates that local mechanical stimuli can augment proliferating-permissive cardiomyocytes in the natural cardiac niche.

PIM1 Promotes Survival of Cardiomyocytes by Upregulating c-Kit Protein Expression

Enhancing cardiomyocyte survival is crucial to blunt deterioration of myocardial structure and function following pathological damage. PIM1 (Proviral Insertion site in Murine leukemia virus (PIM) kinase 1) is a cardioprotective serine threonine kinase that promotes cardiomyocyte survival and antagonizes senescence through multiple concurrent molecular signaling cascades. In hematopoietic stem cells, PIM1 interacts with the receptor tyrosine kinase c-Kit upstream of the ERK (Extracellular signal-Regulated Kinase) and Akt signaling pathways involved in cell proliferation and survival. The relationship between PIM1 and c-Kit activity has not been explored in the myocardial context. This study delineates the interaction between PIM1 and c-Kit leading to enhanced protection of cardiomyocytes from stress. Elevated c-Kit expression is induced in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1. Co-immunoprecipitation and proximity ligation assay reveal protein–protein interaction between PIM1 and c-Kit. Following treatment with Stem Cell Factor, PIM1-overexpressing cardiomyocytes display elevated ERK activity consistent with c-Kit receptor activation. Functionally, elevated c-Kit expression confers enhanced protection against oxidative stress in vitro. This study identifies the mechanistic relationship between PIM1 and c-Kit in cardiomyocytes, demonstrating another facet of cardioprotection regulated by PIM1 kinase.

Doevendans P, Schiffelers RM, Lei Z, Sluijter JP. Cellular and Molecular Mechanism of Cardiac Regeneration: A Comparison of Newts, Zebrafish, and Mammals

Cardiovascular disease is the leading cause of death worldwide. Current palliative treatments can slow the progression of heart failure, but ultimately, the only curative treatment for end-stage heart failure is heart transplantation, which is only available for a minority of patients due to lack of donors' hearts. Explorative research has shown the replacement of the damaged and lost myocardium by inducing cardiac regeneration from preexisting myocardial cells. Lower vertebrates, such as the newt and zebrafish, can regenerate lost myocardium through cardiomyocyte proliferation. The preexisting adult cardiomyocytes replace the lost cells through subsequent dedifferentiation, proliferation, migration, and re-differentiation. Similarly, neonatal mice show complete cardiac regeneration post-injury; however, this regenerative capacity is remarkably diminished one week after birth. In contrast, the adult mammalian heart presents a fibrotic rather than a regenerative response and only shows signs of partial pathological cardiomyocyte dedifferentiation after injury. In this review, we explore the cellular and molecular responses to myocardial insults in different adult species to give insights for future interventional directions by which one can promote or activate cardiac regeneration in mammals.

Effects of Lipids and Lipoproteins on Mesenchymal Stem Cells Used in Cardiac Tissue Regeneration

Mesenchymal stem cells (MSCs) have two characteristics of interest for this paper: the ability to self-renew, and the potential for multiple-lineage differentiation into various cells. MSCs have been used in cardiac tissue regeneration for over a decade. Adult cardiac tissue regeneration ability is quite low; it cannot repair itself after injury, as the heart cells are replaced by fibroblasts and lose function. It is therefore important to search for a feasible way to repair and restore heart function through stem cell therapy. Stem cells can differentiate and provide a source of progenitor cells for cardiomyocytes, endothelial cells, and supporting cells. Studies have shown that the concentrations of blood lipids and lipoproteins affect cardiovascular diseases, such as atherosclerosis, hypertension, and obesity. Furthermore, the MSC lipid profiles, such as the triglyceride and cholesterol content, have been revealed by lipidomics, as well as their correlation with MSC differentiation. Abnormal blood lipids can cause serious damage to internal organs, especially heart tissue. In the past decade, the accumulated literature has indicated that lipids/lipoproteins affect stem cell behavior and biological functions, including their multiple lineage capability, and in turn affect the outcome of regenerative medicine. This review will focus on the effect of lipids/lipoproteins on MSC cardiac regenerative medicine, as well as the effect of lipid-lowering drugs in promoting cardiomyogenesis-associated MSC differentiation.

Zinc Deficiency Promoted Fibrosis via ROS and TIMP/MMPs in the Myocardium of Mice

Zinc (Zn) is an important trace element in the body that has antioxidant effects. It has been proven that Zn deficiency can cause oxidative stress. The purpose of the present study was to clarify the effect and mechanism of Zn deficiency on myocardial fibrosis. Mice were fed with different Zn levels dietary for 9 weeks: Zn-normal group (ZnN, 34 mg Zn/kg), Zn-deficient group (ZnD, 2 mg Zn/kg), and Zn-adequate group (ZnA, 100 mg Zn/kg). We found that the Zn-deficient diet reduced the Zn concentration in myocardial tissue. Moreover, the TUNEL results demonstrated that cardiomyocytes in the ZnD group died in large numbers. Furthermore, ROS levels were significantly increased, and metallothionein (MT) expression levels decreased in the ZnD group. The results of Sirius Red staining indicated an increase in collagen in the ZnD group. Moreover, the ELISA results showed that collagen I, III, and IV and fibronectin (FN) were increased. In addition, the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) was detected by RT-qPCR. The results showed that the expression of TIMP-1 in the ZnD group was increased, while MMPs were decreased. Immunohistochemical results showed an increase in the content of α-smooth muscle actin (α-SMA), while H&E staining showed an increase in interstitial width and a decrease in the number of cardiac cells. All data suggest that Zn deficiency enhances the oxidative stress response of myocardial tissue and eventually triggers myocardial fibrosis.

Modulation of Mammalian Cardiomyocyte Cytokinesis by the Extracellular Matrix

RATIONALE

After birth, cycling mammalian CMs (cardiomyocytes) progressively lose the ability to undergo cytokinesis and hence they become binucleated, which leads to cell cycle exit and loss of regenerative capacity. During late embryonic and early postnatal heart growth, CM development is accompanied by an expansion of the cardiac fibroblast (cFb) population and compositional changes in the ECM (extracellular matrix). Whether and how these changes influence cardiomyocyte cytokinesis is currently unknown.

OBJECTIVE

To elucidate the role of postnatal cFbs and the ECM in cardiomyocyte cytokinesis and identify ECM proteins that promote cardiomyocyte cytokinesis.

METHODS AND RESULTS

Using primary rat cardiomyocyte cultures, we found that a proportion of postnatal, but not embryonic, cycling cardiomyocytes fail to progress through cytokinesis and subsequently binucleate, consistent with published reports of in vitro and in vivo observations. Direct coculture with postnatal cFbs increased cardiomyocyte binucleation, which could be inhibited by RGD peptide treatment. In contrast, cFb-conditioned medium or transwell coculture did not significantly increase cardiomyocyte binucleation, suggesting that cFbs inhibit cardiomyocyte cytokinesis through ECM modulation rather than by secreting diffusible factors. Furthermore, we found that both embryonic and postnatal CMs binucleate at a significantly higher rate when cultured on postnatal cFb-derived ECM compared with embryonic cFb-derived ECM. These cytokinetic defects correlate with cardiomyocyte inefficiency in mitotic rounding, a process which is key to successful cytokinesis. To identify ECM proteins that modulate cardiomyocyte cytokinesis, we compared the composition of embryonic and postnatal cFb-derived ECM by mass spectrometry followed by functional assessment. We found that 2 embryonically enriched ECM proteins, SLIT2 and NPNT (nephronectin), promote cytokinesis of postnatal CMs in vitro and in vivo.

CONCLUSIONS

We identified the postnatal cardiac ECM as a nonpermissive environment for cardiomyocyte cytokinesis and uncovered novel functions for the embryonic ECM proteins SLIT2 and NPNT (nephronectin) in promoting postnatal cardiomyocyte cytokinesis. Graphic Abstract: A graphic abstract is available for this article.

Site-Specific N-Glycoproteomic Analysis Reveals Upregulated Sialylation and Core Fucosylation during Transient Regeneration Loss in Neonatal Mouse Hearts

Myocardial infarction (MI) is one of the leading causes of deaths worldwide. Because of the incapability of regeneration, the cardiomyocyte loss with MI is replaced by fibrotic scar tissue, which eventually leads to heart failure. Reconstructing regeneration of an adult human heart has been recognized as a promising strategy for cardiac therapeutics. A neonatal mouse heart, which possesses transient regenerative capacity at the first week after birth, represents an ideal model to investigate processes associated with cardiac regeneration. In this work, an integrated glycoproteomic and proteomic analysis was performed to investigate the differences in glycoprotein abundances and site-specific glycosylation between postneonatal day 1 (P1) and day 7 (P7) of mouse hearts. By large-scale profiling and quantifying more than 2900 intact N-glycopeptides in neonatal mouse hearts, we identified 227 altered N-glycopeptides between P1 and P7 hearts. By extracting protein changes from the global proteome data, the normalized glycosylation changes for site-specific glycans were obtained, which showed heterogeneity on glycosites and glycoproteins. Systematic analysis of the glycosylation changes demonstrated an overall upregulation of sialylation and core fucosylation in P7 mice. Notably, the upregulated sialylation was a comprehensive result of increased sialylated glycans with Neu5Gc, with both Neu5Gc and core fucose, and decreased sialylated glycans with Neu5Ac. The upregulated core fucosylation resulted from the increase of glycans containing both core fucose and Neu5Gc but not glycans containing sole core fucose. These data provide a valuable resource for future functional and mechanism studies on heart regeneration and discovery of novel therapeutic targets. All mass spectrometry proteomic data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD017139.

Role of Mononuclear Cardiomyocytes in Cardiac Turnover and Regeneration

Purpose of Review

The typical remodeling process after cardiac injury is scarring and compensatory hypertrophy. The limited regeneration potential of the adult heart is thought to be due to the post-mitotic status of postnatal cardiomyocytes, which are mostly binucleated and/or polyploid. Nevertheless, there is evidence for cardiomyocyte turnover in the adult heart. The purpose of this review is to describe the recent findings regarding the proliferative potential of mononuclear cardiomyocytes and to evaluate their function in cardiac turnover and disease.

Recent Findings

There is overwhelming evidence from carbon-dating in humans and multi-isotope imaging mass spectrometry in mice that there is a very low but detectable level of turnover of cardiomyocytes in the heart. The source of this renewal is not clear, but recent evidence points to a population of mononuclear, diploid cardiomyocytes that are still capable of authentic cell division. Controversy arises when their role in cardiac repair is considered, as some studies claim that they contribute to repair by cell division while other studies do not find evidence for hyperplasia but hypertrophy. Stimulation of the mononuclear cardiomyocyte population has been proposed as a therapeutic strategy in cardiac disease.

Summary

The studies reviewed here agree on the existence of a low annual cardiomyocyte turnover rate which can be attributed to the proliferation of mononuclear cardiomyocytes. Potential roles of mononucleated cardiomyocytes in cardiac repair after injury are discussed.

Serum periostin levels in acute rheumatic fever: is it useful as a new biomarker?

Background: Acute rheumatic fever (ARF) continues to be a public health problem in low- and middle-income countries. Because there is no specific laboratory test for the exact diagnosis of ARF, the diagnosis is made by the modified Jones criteria. Periostin is an extracellular matrix protein which has been shown to be expressed during remodelling, mechanical stress and tissue repair. There are no data on the relationship between periostin and ARF.Aim: To evaluate serum periostin levels in patients with ARF and investigate its usefulness as a biomarker for diagnosing and monitoring the efficacy of treatment.Methods: Serum periostin levels were estimated in 31 patients with ARF and compared with a control group of 25 healthy patients. The control group comprised patients referred to the outpatient clinic for further evaluation of cardiac murmur, palpitations or chest pain. Patients who were diagnosed with any other cardiac or systemic illness after detailed systemic and cardiac examination were excluded.Results: The mean (SD) age at diagnosis was 12.1 (3.3) years in the patient group, 48.4% of whom were male. There were no significant differences in age or gender between patients and controls. All the study patients had various degrees of carditis, 58.1% had arthritis and 9.6% had Sydenham chorea. Mean (SD) serum periostin levels in patients with ARF on admission [58.4 (13.9) ng/mL] were significantly higher than in the control group [35.1 (10.7) ng/mL, p < 0.01] and were also significantly decreased in the patient group after treatment [35.1 (13.1) ng/mL, p < 0.01]. There was no significant difference in serum periostin levels regarding the severity of carditis in the patient group while patients with any severity of carditis had significantly higher periostin levels than the controls (p < 0.01). Periostin levels were significantly correlated with ESR and CRP values before treatment, but this correlation was detected for only ESR after treatment. For the initial diagnosis of ARF, a serum periostin level of 53.45 ng/mL was found to be the cut-off point with 80.6% sensitivity and 100% specificity.Conclusion: There was a significant increase in serum periostin levels in patients with ARF and a reduction after adequate treatment which was independent of the severity of carditis. Periostin may be a biomarker which acts as an acute phase reactant in ARF.

Extracellular matrix-based biomaterials for cardiac regeneration and repair

The spectrum of ischemic heart diseases, encompassing acute myocardial infarction to heart failure, represents the leading cause of death worldwide. Although extensive progress in cardiovascular diagnoses and therapy has been made, the prevalence of the disease continues to increase. Cardiac regeneration has a promising perspective for the therapy of heart failure. Recently, extracellular matrix (ECM) has been shown to play an important role in cardiac regeneration and repair after cardiac injury. There is also evidence that the ECM could be directly used as a drug to promote cardiomyocyte proliferation and cardiac regeneration. Increasing evidence supports that applying ECM biomaterials to maintain heart function recovery is an important approach to apply the concept of cardiac regenerative medicine to clinical practice in the future. Here, we will introduce the essential role of cardiac ECM in cardiac regeneration and summarize the approaches of delivering ECM biomaterials to promote cardiac repair in this review.

Pkm2 Regulates Cardiomyocyte Cell Cycle and Promotes Cardiac Regeneration

BACKGROUND

The adult mammalian heart has limited regenerative capacity, mostly attributable to postnatal cardiomyocyte cell cycle arrest. In the last 2 decades, numerous studies have explored cardiomyocyte cell cycle regulatory mechanisms to enhance myocardial regeneration after myocardial infarction. Pkm2 (Pyruvate kinase muscle isoenzyme 2) is an isoenzyme of the glycolytic enzyme pyruvate kinase. The role of Pkm2 in cardiomyocyte proliferation, heart development, and cardiac regeneration is unknown.

METHODS

We investigated the effect of Pkm2 in cardiomyocytes through models of loss (cardiomyocyte-specific Pkm2 deletion during cardiac development) or gain using cardiomyocyte-specific Pkm2 modified mRNA to evaluate Pkm2 function and regenerative affects after acute or chronic myocardial infarction in mice.

RESULTS

Here, we identify Pkm2 as an important regulator of the cardiomyocyte cell cycle. We show that Pkm2 is expressed in cardiomyocytes during development and immediately after birth but not during adulthood. Loss of function studies show that cardiomyocyte-specific Pkm2 deletion during cardiac development resulted in significantly reduced cardiomyocyte cell cycle, cardiomyocyte numbers, and myocardial size. In addition, using cardiomyocyte-specific Pkm2 modified RNA, our novel cardiomyocyte-targeted strategy, after acute or chronic myocardial infarction, resulted in increased cardiomyocyte cell division, enhanced cardiac function, and improved long-term survival. We mechanistically show that Pkm2 regulates the cardiomyocyte cell cycle and reduces oxidative stress damage through anabolic pathways and β-catenin.

CONCLUSIONS

We demonstrate that Pkm2 is an important intrinsic regulator of the cardiomyocyte cell cycle and oxidative stress, and highlight its therapeutic potential using cardiomyocyte-specific Pkm2 modified RNA as a gene delivery platform.

Epicardial transplantation of atrial appendage micrograft patch salvages myocardium after infarction

BACKGROUND

Ischemic heart disease remains the leading cause of mortality and morbidity worldwide despite improved possibilities in medical care. Alongside interventional therapies, such as coronary artery bypass grafting, adjuvant tissue-engineered and cell-based treatments can provide regenerative improvement. Unfortunately, most of these advanced approaches require multiple lengthy and costly preparation stages without delivering significant clinical benefits.

METHODS

We evaluated the effect of epicardially delivered minute pieces of atrial appendage tissue material, defined as atrial appendage micrografts (AAMs), in a mouse myocardial infarction model. An extracellular matrix patch was used to cover and fix the AAMs onto the surface of the infarcted heart.

RESULTS

The matrix-covered AAMs salvaged the heart from the infarction-induced loss of functional myocardium and attenuated scarring. Site-selective proteomics of injured ischemic and uninjured distal myocardium from AAMs-treated and -untreated tissue sections revealed increased expression of several cardiac regeneration-associated proteins (i.e., periostin, transglutaminases, and glutathione peroxidases) and activation of pathways responsible for angiogenesis and cardiogenesis in relation to AAMs therapy.

CONCLUSIONS

Epicardial delivery of AAMs encased in an extracellular matrix patch scaffold salvages functional cardiac tissue from ischemic injury and restricts fibrosis after myocardial infarction. Our results support the use of AAMs as tissue-based therapy adjuvants for salvaging the ischemic myocardium.

Regulation of Myocardial Extracellular Matrix Dynamic Changes in Myocardial Infarction and Postinfarct Remodeling

The article represents literature review dedicated to molecular and cellular mechanisms underlying clinical manifestations and outcomes of acute myocardial infarction. Extracellular matrix adaptive changes are described in detail as one of the most important factors contributing to healing of damaged myocardium and post-infarction cardiac remodeling. Extracellular matrix is reviewed as dynamic constantly remodeling structure that plays a pivotal role in myocardial repair. The role of matrix metalloproteinases and their tissue inhibitors in fragmentation and degradation of extracellular matrix as well as in myocardium healing is discussed. This review provides current information about fibroblasts activity, the role of growth factors, particularly transforming growth factor β and cardiotrophin-1, colony-stimulating factors, adipokines and gastrointestinal hormones, various matricellular proteins. In conclusion considering the fact that dynamic transformation of extracellular matrix after myocardial ischemic damage plays a pivotal role in myocardial infarction outcomes and prognosis, we suggest a high importance of further investigation of mechanisms underlying extracellular matrix remodeling and cell-matrix interactions in cardiovascular diseases.

Mending a broken heart: current strategies and limitations of cell-based therapy

The versatility of pluripotent stem cells, attributable to their unlimited self-renewal capacity and plasticity, has sparked a considerable interest for potential application in regenerative medicine. Over the past decade, the concept of replenishing the lost cardiomyocytes, the crux of the matter in ischemic heart disease, with pluripotent stem cell-derived cardiomyocytes (PSC-CM) has been validated with promising pre-clinical results. Nevertheless, clinical translation was hemmed in by limitations such as immature cardiac properties, long-term engraftment, graft-associated arrhythmias, immunogenicity, and risk of tumorigenicity. The continuous progress of stem cell-based cardiac therapy, incorporated with tissue engineering strategies and delivery of cardio-protective exosomes, provides an optimistic outlook on the development of curative treatment for heart failure. This review provides an overview and current status of stem cell-based therapy for heart regeneration, with particular focus on the use of PSC-CM. In addition, we also highlight the associated challenges in clinical application and discuss the potential strategies in developing successful cardiac-regenerative therapy.

The Matrix Revolution: Matricellular Proteins and Restructuring of the Cancer Microenvironment

The extracellular matrix (ECM) surrounding cells is indispensable for regulating their behavior. The dynamics of ECM signaling are tightly controlled throughout growth and development. During tissue remodeling, matricellular proteins (MCP) are secreted into the ECM. These factors do not serve classical structural roles, but rather regulate matrix proteins and cell-matrix interactions to influence normal cellular functions. In the tumor microenvironment, it is becoming increasingly clear that aberrantly expressed MCPs can support multiple hallmarks of carcinogenesis by interacting with various cellular components that are coupled to an array of downstream signals. Moreover, MCPs also reorganize the biomechanical properties of the ECM to accommodate metastasis and tumor colonization. This realization is stimulating new research on MCPs as reliable and accessible biomarkers in cancer, as well as effective and selective therapeutic targets.

STAT3 for Cardiac Regenerative Medicine: Involvement in Stem Cell Biology, Pathophysiology, and Bioengineering

Heart disease is the most common cause of death in developed countries, but the medical treatments for heart failure remain limited. In this context, the development of cardiac regeneration therapy for severe heart failure is important. Owing to their unique characteristics, including multiple differentiation and infinitive self-renewal, pluripotent stem cells can be considered as a novel source for regenerative medicine. Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) signaling plays critical roles in the induction, maintenance, and differentiation of pluripotent stem cells. In the heart, JAK/STAT3 signaling has diverse cellular functions, including myocardial differentiation, cell cycle re-entry of matured myocyte after injury, and anti-apoptosis in pathological conditions. Therefore, regulating STAT3 activity has great potential as a strategy of cardiac regeneration therapy. In this review, we summarize the current understanding of STAT3, focusing on stem cell biology and pathophysiology, as they contribute to cardiac regeneration therapy. We also introduce a recently reported therapeutic strategy for myocardial regeneration that uses engineered artificial receptors that trigger endogenous STAT3 signal activation.

Direct Comparison of Mononucleated and Binucleated Cardiomyocytes Reveals Molecular Mechanisms Underlying Distinct Proliferative Competencies

The mammalian heart is incapable of regenerating a sufficient number of cardiomyocytes to ameliorate the loss of contractile muscle after acute myocardial injury. Several reports have demonstrated that mononucleated cardiomyocytes are more responsive than are binucleated cardiomyocytes to pro-proliferative stimuli. We have developed a strategy to isolate and characterize highly enriched populations of mononucleated and binucleated cardiomyocytes at various times of development. Our results suggest that an E2f/Rb transcriptional network is central to the divergence of these two populations and that remnants of the differences acquired during the neonatal period remain in adult cardiomyocytes. Moreover, inducing binucleation by genetically blocking the ability of cardiomyocytes to complete cytokinesis leads to a reduction in E2f target gene expression, directly linking the E2f pathway with nucleation. These data identify key molecular differences between mononucleated and binucleated mammalian cardiomyocytes that can be used to leverage cardiomyocyte proliferation for promoting injury repair in the heart.

Respiratory chain signalling is essential for adaptive remodelling following cardiac ischaemia

Cardiac ischaemia-reperfusion (I/R) injury has been attributed to stress signals arising from an impaired mitochondrial electron transport chain (ETC), which include redox imbalance, metabolic stalling and excessive production of reactive oxygen species (ROS). The alternative oxidase (AOX) is a respiratory enzyme, absent in mammals, that accepts electrons from a reduced quinone pool to reduce oxygen to water, thereby restoring electron flux when impaired and, in the process, blunting ROS production. Hence, AOX represents a natural rescue mechanism from respiratory stress. This study aimed to determine how respiratory restoration through xenotopically expressed AOX affects the re-perfused post-ischaemic mouse heart. As expected, AOX supports ETC function and attenuates the ROS load in post-anoxic heart mitochondria. However, post-ischaemic cardiac remodelling over 3 and 9 weeks was not improved. AOX blunted transcript levels of factors known to be up-regulated upon I/R such as the atrial natriuretic peptide (Anp) whilst expression of pro-fibrotic and pro-apoptotic transcripts were increased. Ex vivo analysis revealed contractile failure at nine but not 3 weeks after ischaemia whilst label-free quantitative proteomics identified an increase in proteins promoting adverse extracellular matrix remodelling. Together, this indicates an essential role for ETC-derived signals during cardiac adaptive remodelling and identified ROS as a possible effector.

Polyploidy in Cardiomyocytes: Roadblock to Heart Regeneration?

The hallmark of most cardiac diseases is the progressive loss of cardiomyocytes. In the perinatal period, cardiomyocytes still proliferate, and the heart shows the capacity to regenerate upon injury. In the adult heart, however, the actual rate of cardiomyocyte renewal is too low to efficiently counteract substantial cell loss caused by cardiac injury. In mammals, cardiac growth by cell number expansion changes to growth by cardiomyocyte enlargement soon after birth, coinciding with a period in which most cardiomyocytes increase their DNA content by multinucleation and nuclear polyploidization. Although cardiomyocyte hypertrophy is often associated with these processes, whether polyploidy is a prerequisite or a consequence of hypertrophic growth is unclear. Both the benefits of cardiomyocyte enlargement over proliferative growth of the heart and the physiological role of polyploidy in cardiomyocytes are enigmatic. Interestingly, hearts in animal species with substantial cardiac regenerative capacity dominantly comprise diploid cardiomyocytes, raising the hypothesis that cardiomyocyte polyploidy poses a barrier for cardiomyocyte proliferation and subsequent heart regeneration. On the contrary, there is also evidence for self-duplication of multinucleated myocytes, suggesting a more complex picture of polyploidy in heart regeneration. Polyploidy is not restricted to the heart but also occurs in other cell types in the body. In this review, we explore the biological relevance of polyploidy in different species and tissues to acquire insight into its specific role in cardiomyocytes. Furthermore, we speculate about the physiological role of polyploidy in cardiomyocytes and how this might relate to renewal and regeneration.

Periostin plays a critical role in the cell cycle in lung fibroblasts

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a devastating disease with a median survival of only three to 5 years. Fibroblast proliferation is a hallmark of IPF as is secretion of extracellular matrix proteins from fibroblasts. However, it is still uncertain how IPF fibroblasts acquire the ability to progressively proliferate. Periostin is a matricellular protein highly expressed in the lung tissues of IPF patients, playing a critical role in the pathogenesis of pulmonary fibrosis. However, it remains undetermined whether periostin affects lung fibroblast proliferation.

METHODS

In this study, we first aimed at identifying periostin-dependently expressed genes in lung fibroblasts using DNA microarrays. We then examined whether expression of cyclins and CDKs controlling cell cycle progression occur in a periostin-dependent manner. We next examined whether downregulation of cell proliferation-promoting genes by knockdown of periostin or integrin, a periostin receptor, using siRNA, is reflected in the cell proliferation of lung fibroblasts. We then looked at whether lung fibroblasts derived from IPF patients also require periostin for maximum proliferation. We finally investigated whether CP4715, a potent inhibitor against integrin α_Vβ₃ (a periostin receptor), which we have recently found blocks TGF-β signaling, followed by reduced BLM-induced pulmonary fibrosis in mice, can block proliferation of lung fibroblasts derived from IPF patients.

RESULTS

Many cell-cycle-related genes are involved in the upregulated or downregulated genes by periostin knockdown. We confirmed that in lung fibroblasts, periostin silencing downregulates expression of several cell-cycle-related molecules, including the cyclin, CDK, and, E2F families, as well as transcription factors such as B-MYB and FOXM1. Periostin or integrin silencing slowed proliferation of lung fibroblasts and periostin silencing increased the distribution of the G0/G1 phase, whereas the distribution of the G2/M phase was decreased. Lung fibroblasts derived from IPF patients also required periostin for maximum proliferation. Moreover, CP4715 downregulated proliferation along with expression of cell-cycle-related genes in IPF lung fibroblasts as well as in normal lung fibroblasts.

CONCLUSIONS

Periostin plays a critical role in the proliferation of lung fibroblasts and the present results provide us a solid basis for considering inhibitors of the periostin/integrin α_Vβ₃ interaction for the treatment of IPF patients.