Senescent impairment in synergistic cytokine pathways that provide rapid cardioprotection in the rat heart

Plasma polymerized nanoparticles are a safe platform for direct delivery of growth factor therapy to the injured heart

Introduction: Heart failure due to myocardial infarction is a progressive and debilitating condition, affecting millions worldwide. Novel treatment strategies are desperately needed to minimise cardiomyocyte damage after myocardial infarction and to promote repair and regeneration of the injured heart muscle. Plasma polymerized nanoparticles (PPN) are a new class of nanocarriers which allow for a facile, one-step functionalization with molecular cargo. Methods: Here, we conjugated platelet-derived growth factor AB (PDGF-AB) to PPN, engineering a stable nano-formulation, as demonstrated by optimal hydrodynamic parameters, including hydrodynamic size distribution, polydisperse index (PDI) and zeta potential, and further demonstrated safety and bioactivity in vitro and in vivo. We delivered PPN-PDGF-AB to human cardiac cells and directly to the injured rodent heart. Results: We found no evidence of cytotoxicity after delivery of PPN or PPN-PDGFAB to cardiomyocytes in vitro, as determined through viability and mitochondrial membrane potential assays. We then measured contractile amplitude of human stem cell derived cardiomyocytes and found no detrimental effect of PPN on cardiomyocyte contractility. We also confirmed that PDGF-AB remains functional when bound to PPN, with PDGF receptor alpha positive human coronary artery vascular smooth muscle cells and cardiac fibroblasts demonstrating migratory and phenotypic responses to PPN-PDGF-AB in the same manner as to unbound PDGF-AB. In our rodent model of PPN-PDGF-AB treatment after myocardial infarction, we found a modest improvement in cardiac function in PPN-PDGF-AB treated hearts compared to those treated with PPN, although this was not accompanied by changes in infarct scar size, scar composition, or border zone vessel density. Discussion: These results demonstrate safety and feasibility of the PPN platform for delivery of therapeutics directly to the myocardium. Future work will optimize PPN-PDGF-AB formulations for systemic delivery, including effective dosage and timing to enhance efficacy and bioavailability, and ultimately improve the therapeutic benefits of PDGF-AB in the treatment of heart failure cause by myocardial infarction.

Lin28b delays vasculature aging by reducing platelet-derived growth factor-beta resistance in senescent vascular smooth muscle cells

BACKGROUND AND AIMS

Platelet-derived growth factor-β (PDGFB) is an important mediator of vascular smooth muscle cell (VSMC) proliferation, and PDGFB resistance is observed in senescent VSMCs. Lin28b is a stemness regulator in the embryo; however, its role in vasculature aging and VSMC senescence is unknown. We aimed to investigate whether Lin28b could restore the VSMC response to PDGFB and delay vasculature aging.

METHODS

ApoE^-/- mice were fed a high-fat diet for different weeks to establish an aging model. PDGFB resistance was observed using EdU staining in vessel culture in vitro. Quantitative polymerase chain reaction and in situ hybridization were used to detect let-7 expression. Senescence was identified by Western blotting, senescence-associated beta-galactosidase activity or Sudan Black B staining, and VSMC function was determined using CCK-8, migration, and enzyme-linked immunosorbent assays.

RESULTS

Vessels from aged mice showed poor responses to PDGFB stimulation compared with those from young mice; similar results were found in senescent VSMCs. The expression levels of Lin28b and PDGF receptor-β were downregulated in aging vasculature and senescent VSMCs, whereas let-7 family levels increased with aging and VSMC passage growth. Transfection of VSMCs with let-7c induced PDGFB resistance and accelerated VSMC senescence, whereas blocking let-7c restored PDGFB reactions in VSMCs. Overexpression of Lin28b protein by lentivirus resulted in the restoration of PDGFB reactions and delayed VSMC senescence, which was blocked by a let-7c mimic.

CONCLUSIONS

This study reveals the role of Lin28b in delaying vasculature aging by decreasing senescent VSMC PDGFB resistance mediated by let-7.

Role of PDGF-A/B Ligands in Cardiac Repair After Myocardial Infarction

Platelet-derived growth factors (PDGFs) are powerful inducers of cellular mitosis, migration, angiogenesis, and matrix modulation that play pivotal roles in the development, homeostasis, and healing of cardiac tissues. PDGFs are key signaling molecules and important drug targets in the treatment of cardiovascular disease as multiple researchers have shown that delivery of recombinant PDGF ligands during or after myocardial infarction can reduce mortality and improve cardiac function in both rodents and porcine models. The mechanism involved cannot be easily elucidated due to the complexity of PDGF regulatory activities, crosstalk with other protein tyrosine kinase activators, and diversity of the pathological milieu. This review outlines the possible roles of PDGF ligands A and B in the healing of cardiac tissues including reduced cell death, improved vascularization, and improved extracellular matrix remodeling to improve cardiac architecture and function after acute myocardial injury. This review may highlight the use of recombinant PDGF-A and PDGF-B as a potential therapeutic modality in the treatment of cardiac injury.

[Platelet-rich plasma alleviates myocardial ischemia-reperfusion injury in rats]

OBJECTIVE

To investigate the protective effect of platelet-rich plasma (PRP) against acute myocardial ischemiareperfusion (IR) injury and the possible mechanism.

OBJECTIVE

Aortic blood samples were collected from 10 SD rats to prepare PRP, in which the concentrations of platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-β1 (TGF-β1) were measured. Cell models of IR injury were established in primary cultures of neonatal SD rat cardiomyocytes by exposing the cells to 3 h of hypoxia. The cells were then reoxygenated and co-cultured with 1%, 5%, 10%, and 20% volume of PRP for 12 h, and the changes in cell viability was assessed. Immunofluorescence staining of the cardiomyocytes was performed, and the cellular expression of AMPK and its phosphorylation level were detected. The effects of PRP on the proliferation and migration of rat aortic endothelial cells (RAOECs) were examined. In a SD rat model of myocardial IR injury, 100 μL of PRP (n= 20) or normal saline (n=20) was injected at 4 sites around the ligation site immediately after cardiac reperfusion. One day after the injection, 6 rats were selected from each group for TTC staining of the myocardial tissues and measurement of troponin Ⅰ content. One week later, the cardiac function of the remaining rats was assessed by echocardiography, and HE staining of the myocardial tissues was performed. The effect of PRP treatment for 24 h on polarization of M1 and M2 macrophages was also examined by flow cytometry in RAW264.7 cells after hypoxic exposure for 3 h.

OBJECTIVE

The concentrations of PDGF-BB and TGF-β1 were significantly higher in PRP than in whole blood. Addition of 1% volume of PRP significantly reduced death of the cardiomyocytes following reoxygenation, and this effect was closely related with the activation of AMPK. Treatment with PRP obviously promoted the proliferation and migration of RAOECs. In rat models of acute myocardial IR injury, injections of PRP significantly reduced the infarct size and troponin Ⅰ concentration as compared with saline injection (P < 0.001). One week after PRP injection, the rats showed significantly improved cardiac function with a lowered level of inflammatory response in comparison with the rats with saline injection. In RAW264.7 cells with hypoxic exposure, treatment with PRP obviously decreased the number of M1 macrophages and increase the number of M2 macrophages.

OBJECTIVE

PRP can improve acute myocardial IR injury in rats by phosphorylating AMPK and regulating macrophage polarization, which produces a protective immunomodulatory effect on the ischemic myocardial tissues.

Growth factors in pulmonary arterial hypertension: Focus on preserving right ventricular function

Pulmonary arterial hypertension (PAH) is a rare and progressive disease, characterized by increased vascular resistance leading to right ventricle (RV) failure. The extent of right ventricular dysfunction crucially influences disease prognosis; however, currently no therapies have specific cardioprotective effects. Besides discussing the pathophysiology of right ventricular adaptation in PAH, this review focuses on the roles of growth factors (GFs) in disease pathomechanism. We also summarize the involvement of GFs in the preservation of cardiomyocyte function, to evaluate their potential as cardioprotective biomarkers and novel therapeutic targets in PAH.

Angiogenesis, Cancer, and Vascular Aging

Several lines of evidence have revealed that the angiogenic response to ischemic injury declines with age, which might account for the increased morbidity and mortality of cardiovascular disease (CVD) among the elderly. While impairment of angiogenesis with aging leads to delayed wound healing or exacerbation of atherosclerotic ischemic diseases, it also inhibits the progression of cancer. Age-related changes of angiogenesis have been considered to at least partly result from vascular aging or endothelial cell senescence. There is considerable evidence supporting the hypothesis that vascular cell senescence contributes to the pathogenesis of age-related CVD, suggesting that vascular aging could be an important therapeutic target. Since therapeutic angiogenesis is now regarded as a promising concept for patients with ischemic CVD, it has become even more important to understand the detailed molecular mechanisms underlying impairment of angiogenesis in older patients. To improve the usefulness of therapeutic angiogenesis, approaches are needed that can compensate for impaired angiogenic capacity in the elderly while not promoting the development or progression of malignancy. In this review, we briefly outline the mechanisms of angiogenesis and vascular aging, followed by a description of how vascular aging leads to impairment of angiogenesis. We also examine potential therapeutic approaches that could enhance angiogenesis and/or vascular function in the elderly, as well as discussing the possibility of anti-senescence therapy or reversal of endothelial cell senescence.

Platelet-derived Growth Factor-B Protects Rat Cardiac Allografts From Ischemia-reperfusion Injury

BACKGROUND

Microvascular dysfunction and cardiomyocyte injury are hallmarks of ischemia-reperfusion injury (IRI) after heart transplantation. Platelet-derived growth factors (PDGF) have an ambiguous role in this deleterious cascade. On one hand, PDGF may exert vascular stabilizing and antiapoptotic actions through endothelial-pericyte and endothelial-cardiomyocyte crosstalk in the heart; and on the other hand, PDGF signaling mediates neointimal formation and exacerbates chronic rejection in cardiac allografts. The balance between these potentially harmful and beneficial actions determines the final outcome of cardiac allografts.

METHODS AND RESULTS

We transplanted cardiac allografts from Dark Agouti rat and Balb mouse donors to fully major histocompatibility complex-mismatched Wistar Furth rat or C57 mouse recipients with a clinically relevant 2-hour cold ischemia and 1-hour warm ischemia. Ex vivo intracoronary delivery of adenovirus-mediated gene transfer of recombinant human PDGF-BB upregulated messenger RNA expression of anti-mesenchymal transition and survival factors BMP-7 and Bcl-2 and preserved capillary density in rat cardiac allografts at day 10. In mouse cardiac allografts PDGF receptor-β, but not -α intragraft messenger RNA levels were reduced and capillary protein localization was lost during IRI. The PDGF receptor tyrosine kinase inhibitor imatinib mesylate and a monoclonal antibody against PDGF receptor-α enhanced myocardial damage evidenced by serum cardiac troponin T release in the rat and mouse cardiac allografts 6 hours after reperfusion, respectively. Moreover, imatinib mesylate enhanced rat cardiac allograft vasculopathy, cardiac fibrosis, and late allograft loss at day 56.

CONCLUSIONS

Our results suggest that PDGF-B signaling may play a role in endothelial and cardiomyocyte recovery from IRI after heart transplantation.

Platelet-Derived Growth Factor in Heart Failure

Defective vascular and cardiomyocyte function are implicated in the development and progression of both heart failure with reduced and preserved ejection fraction. Any treatment option that augments these myocardial processes may therefore be of significant value. The platelet-derived growth factor (PDGF) family is involved in a wide range of growth processes and plays a key role in both regulating angiogenesis and mesenchymal cell development. Thus, PDGF may serve as a potent therapy for heart failure. While numerous animal studies have demonstrated beneficial cardiovascular effects of growth factor therapy, promising laboratory data has not yet translated to effective therapies. In this review, we outline the biological role of PDGF and summarize previous studies that have focused on the cardiovascular effects of normal PDGF signaling, administration of PDGF, and the effects of PDGF on stem cell therapy.

Platelet-Derived Growth Factor Receptor Alpha as a Marker of Mesenchymal Stem Cells in Development and Stem Cell Biology

Three decades on, the mesenchymal stem cells (MSCs) have been intensively researched on the bench top and used clinically. However, ambiguity still exists in regard to their anatomical locations, identities, functions, and extent of their differentiative abilities. One of the major impediments in the quest of the MSC research has been lack of appropriate in vivo markers. In recent years, this obstacle has been resolved to some degree as PDGFRα emerges as an important mesenchymal stem cell marker. Accumulating lines of evidence are showing that the PDGFRα (+) cells reside in the perivascular locations of many adult interstitium and fulfil the classic concepts of MSCs in vitro and in vivo. PDGFRα has long been recognised for its roles in the mesoderm formation and connective tissue development during the embryogenesis. Current review describes the lines of evidence regarding the role of PDGFRα in morphogenesis and differentiation and its implications for MSC biology.

Effects of aging on angiogenesis

Aging is a dominant risk factor for most forms of cardiovascular disease. Impaired angiogenesis and endothelial dysfunction likely contribute to the increased prevalence of both cardiovascular diseases and their adverse sequelae in the elderly. Angiogenesis is both an essential adaptive response to physiological stress and an endogenous repair mechanism after ischemic injury. In addition, induction of angiogenesis is a promising therapeutic approach for ischemic diseases. For these reasons, understanding the basis of age-related impairment of angiogenesis and endothelial function has important implications for understanding and managing cardiovascular disease. In this review, we discuss the molecular mechanisms that contribute to impaired angiogenesis in the elderly and potential therapeutic approaches to improving vascular function and angiogenesis in aging patients.

MicroRNA-9 is an activation-induced regulator of PDGFR-beta expression in cardiomyocytes

The platelet derived growth factor receptor (PDGFR) is an important target for novel anti-cancer therapeutics, but agents targeting PDGFR have been associated with cardiotoxicity. Cardiomyocyte PDGFR-β signaling in pressure-overloaded hearts induces compensatory angiogenesis via a paracrine-signaling cascade. Tight regulation of receptor tyrosine kinases in response to ligand stimulation is a critical part of any such cascade. The objective of the present study was to characterize the early and late regulation of PDGFR-β following ligand stimulation and define a potential role for microRNAs (miRNAs) predicted to interact with the 3'UTR of PDGFR-β in feedback regulation. Using two in-vitro model systems (U87 glioblastoma cells and neonatal cardiomyocytes), we observed that in response to stimulation with PDGF-BB, levels of PDGFR-β declined beginning at one hour, persisting for 48 h. PDGFR-β mRNA levels declined beginning at 6h after receptor activation. Early, but not late activation-induced receptor downregulation was proteasome dependent. Levels of miRNA-9 (miR-9) were significantly increased in U87 cells and cardiomyocytes beginning 6h after addition of ligand. In response to pressure overload, miR-9 levels were significantly reduced in the hearts of cardiac-specific PDGFR-β knockout mice. Luciferase reporter assays demonstrate that miR-9 directly interacts with its predicted seed in the 3'UTR of PDGFR-β. Increasing miR-9 levels reduces levels of PDGFR-β, resulting in a reduction in the paracrine angiogenic capacity of cardiomyocytes, consistent with the established function of cardiomyocyte PDGFR-β. Importantly, increase of anti-miR-9 in cardiomyocytes attenuates ligand-induced PDGFR-β downregulation. In conclusion, we have identified miR-9 as an activation-induced regulator of PDGFR-β expression in cardiomyocytes that is part of a negative feedback loop which serves to modulate PDGFR-β expression upon ligand-stimulation through direct interaction with the 3'UTR of PDFGR-β. This article is part of a Special Issue entitled 'Possible Editorial'.

The role of inflammatory and fibrogenic pathways in heart failure associated with aging

Heart failure is strongly associated with aging. Elderly patients with heart failure often have preserved systolic function exhibiting left ventricular hypertrophy accompanied by a decline in diastolic function. Experimental studies have demonstrated that age-related cardiac fibrosis plays an important role in the pathogenesis of diastolic heart failure in senescent hearts. Reactive oxygen species and angiotensin II are critically involved in fibrotic remodeling of the aging ventricle; their fibrogenic actions may be mediated, at least in part, through transforming growth factor (TGF)-beta. The increased prevalence of heart failure in the elderly is also due to impaired responses of the senescent heart to cardiac injury. Aging is associated with suppressed inflammation, delayed phagocytosis of dead cardiomyocytes, and markedly diminished collagen deposition following myocardial infarction, due to a blunted response of fibroblasts to fibrogenic growth factors. Thus, in addition to a baseline activation of fibrogenic pathways, senescent hearts exhibit an impaired reparative reserve due to decreased responses of mesenchymal cells to stimulatory signals. Impaired scar formation in senescent hearts is associated with accentuated dilative remodeling and worse systolic dysfunction. Understanding the pathogenesis of interstitial fibrosis in the aging heart and dissecting the mechanisms responsible for age-associated healing defects following cardiac injury are critical in order to design new strategies for prevention of adverse remodeling and heart failure in elderly patients.

Therapeutic potential of stem cells in elderly patients with cardiovascular disease

The success of treatment for acute myocardial infarction and chronic myocardial ischemia has improved general medical care in Europe, resulting in an increasing population of patients with chronic and congestive heart failure. By applying currently available therapeutic options the quality of life and lifespan of these patients have both increased. However, amongst patients -- predominantly the elderly -- who remain symptomatic despite intensive medical treatment, autologous bone marrow-derived mononuclear cells may trigger attempts to repopulate lost tissues directly as a novel therapeutic option. In this concised paper the current understanding of stem cell therapy and early clinical experiences are discussed and related to the application of stem cells in elderly patients with myocardial ischemia.

The immune system and cardiac repair

Myocardial infarction is the most common cause of cardiac injury and results in acute loss of a large number of myocardial cells. Because the heart has negligible regenerative capacity, cardiomyocyte death triggers a reparative response that ultimately results in formation of a scar and is associated with dilative remodeling of the ventricle. Cardiac injury activates innate immune mechanisms initiating an inflammatory reaction. Toll-like receptor-mediated pathways, the complement cascade and reactive oxygen generation induce nuclear factor (NF)-kappaB activation and upregulate chemokine and cytokine synthesis in the infarcted heart. Chemokines stimulate the chemotactic recruitment of inflammatory leukocytes into the infarct, while cytokines promote adhesive interactions between leukocytes and endothelial cells, resulting in transmigration of inflammatory cells into the site of injury. Monocyte subsets play distinct roles in phagocytosis of dead cardiomyocytes and in granulation tissue formation through the release of growth factors. Clearance of dead cells and matrix debris may be essential for resolution of inflammation and transition into the reparative phase. Transforming growth factor (TGF)-beta plays a crucial role in cardiac repair by suppressing inflammation while promoting myofibroblast phenotypic modulation and extracellular matrix deposition. Myofibroblast proliferation and angiogenesis result in formation of highly vascularized granulation tissue. As the healing infarct matures, fibroblasts become apoptotic and a collagen-based matrix is formed, while many infarct neovessels acquire a muscular coat and uncoated vessels regress. Timely resolution of the inflammatory infiltrate and spatial containment of the inflammatory and reparative response into the infarcted area are essential for optimal infarct healing. Targeting inflammatory pathways following infarction may reduce cardiomyocyte injury and attenuate adverse remodeling. In addition, understanding the role of the immune system in cardiac repair is necessary in order to design optimal strategies for cardiac regeneration.

Aging-related defects are associated with adverse cardiac remodeling in a mouse model of reperfused myocardial infarction

OBJECTIVES

The purpose of this study was to study aging-associated alterations in the inflammatory and reparative response after myocardial infarction (MI) and their involvement in adverse post-infarction remodeling of the senescent heart.

BACKGROUND

Advanced age is a predictor of death and ventricular dilation in patients with MI; however, the cellular mechanisms responsible for increased remodeling of the infarcted senescent heart remain poorly understood.

METHODS

Histomorphometric, molecular, and echocardiographic end points were compared between young and senescent mice undergoing reperfused infarction protocols. The response of young and senescent mouse cardiac fibroblasts to transforming growth factor (TGF)-beta stimulation was examined.

RESULTS

Senescence was associated with decreased and delayed neutrophil and macrophage infiltration, markedly reduced cytokine and chemokine expression in the infarcted myocardium, and impaired phagocytosis of dead cardiomyocytes. Reduced inflammation in senescent mouse infarcts was followed by decreased myofibroblast density and markedly diminished collagen deposition in the scar. The healing defects in senescent animals were associated with enhanced dilative and hypertrophic remodeling and worse systolic dysfunction. Fibroblasts isolated from senescent mouse hearts showed a blunted response to TGF-beta1.

CONCLUSIONS

Although young mice exhibit a robust post-infarction inflammatory response and form dense collagenous scars, senescent mice show suppressed inflammation, delayed granulation tissue formation, and markedly reduced collagen deposition. These defects might contribute to adverse remodeling. These observations suggest that caution is necessary when attempting to therapeutically target the post-infarction inflammatory response in patients with reperfused MI. The injurious potential of inflammatory mediators might have been overstated, owing to extrapolation of experimental findings from young animals to older human patients.

Stem Cells and the Regeneration of the Aging Cardiovascular System

It is well established that cardiovascular repair mechanisms become progressively impaired with age and that advanced age is itself a significant risk factor for cardiovascular disease. Although therapeutic developments have improved the prognosis for those with cardiovascular disease, mortality rates have nevertheless remained virtually unchanged in the last twenty years. Clearly, there is a need for alternative strategies for the treatment of cardiovascular disease. In recent years, the idea that the heart is capable of regeneration has raised the possibility that cell-based therapies may provide such an alternative to conventional treatments. Cells that have the potential to generate cardiomyocytes and vascular cells have been identified in both the adult heart and peripheral tissues, and in vivo experiments suggest that these cardiovascular stem cells and cardiovascular progenitor cells, including endothelial progenitor cells, are capable of replacing damaged myocardium and vascular tissues. Despite these findings, the endogenous actions of cardiovascular stem cells and cardiovascular progenitor cells appear to be insufficient to protect against cardiovascular disease in older individuals. Because recent evidence suggests that cardiovascular stem cells and cardiovascular progenitor cells are subject to age-associated changes that impair their function, these changes may contribute to the dysregulation of endogenous cardiovascular repair mechanisms in the aging heart and vasculature. Here we present the evidence for the impact of aging on cardiovascular stem cell/cardiovascular progenitor cell function and its potential importance in the increased severity of cardiovascular pathophysiology observed in the geriatric population.

Coordinate release of angiogenic growth factors after acute myocardial infarction: evidence of a two-wave production

BACKGROUND

Previous studies have shown that angiopoietic growth factors, including vascular endothelial growth factor (VEGF), angiopoietin-2 (Ang-2), hepatocyte growth factor (HGF) and transforming growth factor (TGF)-beta1 are released after acute myocardial infarction (AMI). It was suggested that the release of these factors, triggered by ischemia, may be related to a reparative neoangiogenetic process.

METHODS

Plasma VEGF, Ang-2, HGF and TGF-beta levels were measured on admission (baseline) and at various times during the acute (0-48 h) and the subacute (48-240 h) phase in 44 patients with AMI.

RESULTS

In the present study, we have explored in detail the kinetics of release of these growth factors after AMI with the precise aim of evaluating the existence of a double wave of release of these factors: (i) a first wave in the acute and (ii) a second one in the subacute period. The results of these analyses provided evidence for an early (peak at 24-28 h) and late (peak at approximately 170 h) increase of VEGF, Ang-2 and TGF-beta.

CONCLUSIONS

According to these data, we suggest that two waves of release of angiogenic factors occur after AMI. The early release makes part of an acute phase response, whereas the late release may underlie the induction of angiogenetic mechanisms involved in tissue reparation.

Local Controlled Intramyocardial Delivery of Platelet-Derived Growth Factor Improves Postinfarction Ventricular Function Without Pulmonary Toxicity

Background— Local delivery methods can target therapies to specific tissues and potentially avoid toxicity to other organs. Platelet-derived growth factor can protect the myocardium, but it also plays an important role in promoting pulmonary hypertension. It is not known whether local myocardial delivery of platelet-derived growth factor during myocardial infarction (MI) can lead to sustained cardiac benefit without causing pulmonary hypertension.

Methods and Results— We performed a randomized and blinded experiment of 127 rats that survived experimental MI or sham surgery. We delivered platelet-derived growth factor (PDGF)-BB with self-assembling peptide nanofibers (NFs) to provide controlled release within the myocardium. There were 6 groups with n≥20 in each group: sham, sham+NF, sham+NF/PDGF, MI, MI+NF, and MI+NF/PDGF. Serial echocardiography from 1 day to 3 months showed significant improvement of ventricular fractional shortening, end-systolic dimension, and end-diastolic dimension with local PDGF delivery ( P <0.05 for MI+NF/PDGF versus MI or MI+NF). Catheterization at 4 months revealed improved ventricular function in the controlled delivery group (left ventricular end-diastolic pressure, cardiac index, +dP/dt, −dP/dt, and time constant of exponential decay all P <0.05 for MI+NF/P versus MI or MI+NF). Infarcted myocardial volume was reduced by NF/PDGF therapy (34.0±13.3% in MI, 28.9±12.9% in MI+NF, and 12.0±5.8% in MI+NF/PDGF; P <0.001). There was no evidence of pulmonary toxicity from the therapy, with no differences in right ventricular end-systolic pressure, right ventricular dP/dt, bromodeoxyuridine staining, or pulmonary artery medial wall thickness.

Conclusions— Intramyocardial delivery of PDGF by self-assembling peptide NFs leads to long-term improvement in cardiac performance after experimental infarction without apparent pulmonary toxicity. Local myocardial protection may allow prevention of heart failure without systemic toxicity.

Aging impairs the beneficial effect of granulocyte colony-stimulating factor and stem cell factor on post-myocardial infarction remodeling

Granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) are potential new therapies to ameliorate post-myocardial infarction (post-MI) remodeling, as they enhance endogenous cardiac repair mechanisms and decrease cardiomyocyte apoptosis. Because both of these pathways undergo alterations with increasing age, we hypothesized that therapeutic efficacy of G-CSF and SCF is impaired in old versus young adult rats. MI was induced in 6- and 20-month-old rats by permanent ligation of the left coronary artery. In young animals, G-CSF/SCF therapy stabilized and reversed a decline in cardiac function, attenuated left ventricular dilation, decreased infarct size, and reduced cardiomyocyte hypertrophy. Remarkably, these effects on cardiac structure and function were absent in aged rodents. This could not be attributed to ineffective mobilization of bone marrow cells or decreased quantity of c-Kit(+) cells within the myocardium with aging. However, whereas the G-CSF/SCF cocktail reduced cardiac myocyte apoptosis in old as well as in young hearts, the degree of reduction was substantially less with age and the rate of cardiomyocyte apoptosis in old animals remained high despite cytokine treatment. These findings demonstrate that G-CSF/SCF lacks therapeutic efficacy in old animals by failing to offset periinfarct apoptosis and therefore raise important concerns regarding the efficacy of novel cytokine therapies in elderly individuals at greatest risk for adverse consequences of MI.

Vascular tenascin‐C regulates cardiac endothelial phenotype and neovascularization

Microenvironmental cues mediate postnatal neovascularization via modulation of endothelial cell and bone marrow-derived endothelial progenitor cell (EPC) activity. Numerous signals regulate the activity of both of these cell types in response to vascular injury, which suggests that parallel mechanisms regulate angiogenesis in the vascular beds of both the heart and bone marrow. To identify mediators of such shared pathways, in vivo bone marrow/cardiac phage display biopanning was performed and led to the identification of tenascin-C as a candidate protein. Functionally, tenascin-C inhibits cardiac endothelial cell spreading and enhances migration in response to angiogenic growth factors. Analysis of human coronary thrombi revealed tenascin-C protein expression colocalized with the endothelial cell/EPC marker Tie-2 in intrathrombi vascular channels. Immunostains in the rodent heart demonstrated that tenascin-C also colocalizes with EPCs homing to sites of cardiac angiogenic induction. To determine the importance of tenascin-C in cardiac neovascularization, we used an established cardiac transplantation model and showed that unlike wild-type mice, tenascin-C-/- mice fail to vascularize cardiac allografts. This demonstrates for the first time that tenascin-C is essential for postnatal cardiac angiogenic function. Together, our data highlight the role of tenascin-C as a microenvironmental regulator of cardiac endothelial/EPC activity.

Growth factor-mediated reversal of senescent dysfunction of ischemia-induced cardioprotection

Based on the role of tumor necrosis factor-α (TNF-α) in ischemic preconditioning (IPC) and the age-associated loss of both TNF-α-induced platelet-derived growth factor-AB (PDGF-AB)-mediated cardioprotection and IPC-mediated cardioprotection, we hypothesized that targeting of PDGF-AB-based pathways would restore cardioprotection by IPC in the aging heart. To study this, IPC was induced in 4- and 24-mo-old F344 rats. Sections of young hearts isolated 1 day post-IPC revealed increased TNF-α compared with controls. In old rats, TNF-α was higher at baseline than IPC young rats and was not significantly altered after IPC. Treatment of old rats with PDGF-AB with vascular endothelial growth factor and angiopoietin-2 (a combination termed PVA), but not PDGF-AB alone, at the time of IPC decreased TNF-α. In addition, when compared with young hearts, IPC induced greater apoptosis in the old hearts, which was decreased with PVA treatment but was markedly increased with PDGF-AB. To test the significance of these findings, additional rats underwent permanent coronary ligation 1 day post-IPC. IPC was cardioprotective in young rats [14 days postmyocardial infarction (MI), fractional shortening 29 ± 6% vs. control MI 17 ± 4%, P < 0.05; Masson’s trichrome stain MI size: 13 ± 2% vs. control MI 17 ± 4% left ventricular area (LVA); P < 0.05]. In old rats, however, IPC reduced the post-MI 14-day survival (33% vs. controls 67%; P < 0.05). Treatment of IPC-aging rats with PVA, but not PDGF-AB-alone, reversed IPC-induced mortality (PVA-IPC-MI survival, 88%; PDGF-AB-IPC-MI, 14%) and reduced myocardial injury (fractional shortening: PVA-IPC, 31 ± 1% vs. control MI, 21 ± 6%, P < 0.05; MI size: PVA-IPC, 12 ± 2% vs. control MI, 18 ± 3% LVA, P < 0.05) and thus demonstrated that PDGF-AB-based pathways can reverse the senescent impairment in IPC-mediated cardioprotection.

Endothelial-cardiomyocyte interactions in cardiac development and repair

Communication between endothelial cells and cardiomyocytes regulates not only early cardiac development but also adult cardiomyocyte function, including the contractile state. In the normal mammalian myocardium, each cardiomyocyte is surrounded by an intricate network of capillaries and is next to endothelial cells. Cardiomyocytes depend on endothelial cells not only for oxygenated blood supply but also for local protective signals that promote cardiomyocyte organization and survival. While endothelial cells direct cardiomyocytes, cardiomyocytes reciprocally secrete factors that impact endothelial cell function. Understanding how endothelial cells communicate with cardiomyocytes will be critical for cardiac regeneration, in which the ultimate goal is not simply to improve systolic function transiently but to establish new myocardium that is both structurally and functionally normal in the long term.

Harnessing Hormonal Signaling for Cardioprotection

Cardiovascular disease is the leading cause of death in women in the Western world and is predominant among the elderly. A large body of evidence suggests that hormonal signaling plays a critical role in the regulation of cardioprotective mechanisms, as premenopausal women are at significantly lower risk of heart disease compared with men, but the risk greatly increases with the onset of menopause. This association indicates that estrogen may protect the heart from cardiovascular disease. Whereas a number of analyses of the effects of hormone replacement therapy (HRT) on postmenopausal women supported the idea that estrogen is a cardioprotective factor, the findings of the more recent Women's Health Initiative (WHI) study suggested that HRT may actually increase the risk of cardiovascular events. These conflicting reports have left both patients and clinicians reluctant to continue using current HRT regimes. The WHI findings do not, however, negate the epidemiological link between menopause and increased cardiovascular risk. Hence, the identification of the specific actions of estrogen that promote cardioprotective pathways without enhancing deleterious vascular mechanisms may provide novel estrogen-based alternatives to current HRT strategies. In this Review, we outline the known actions of estrogen on the cardiovascular system, focusing on cardioprotective mechanisms that may be targeted for the development of new therapeutic approaches.

Controlled delivery of PDGF-BB for myocardial protection using injectable self-assembling peptide nanofibers

Endothelial cells can protect cardiomyocytes from injury, but the mechanism of this protection is incompletely described. Here we demonstrate that protection of cardiomyocytes by endothelial cells occurs through PDGF-BB signaling. PDGF-BB induced cardiomyocyte Akt phosphorylation in a time- and dose-dependent manner and prevented apoptosis via PI3K/Akt signaling. Using injectable self-assembling peptide nanofibers, which bound PDGF-BB in vitro, sustained delivery of PDGF-BB to the myocardium at the injected sites for 14 days was achieved. A blinded and randomized study in 96 rats showed that injecting nanofibers with PDGF-BB, but not nanofibers or PDGF-BB alone, decreased cardiomyocyte death and preserved systolic function after myocardial infarction. A separate blinded and randomized study in 52 rats showed that PDGF-BB delivered with nanofibers decreased infarct size after ischemia/reperfusion. PDGF-BB with nanofibers induced PDGFR-beta and Akt phosphorylation in cardiomyocytes in vivo. These data demonstrate that endothelial cells protect cardiomyocytes via PDGF-BB signaling and that this in vitro finding can be translated into an effective in vivo method of protecting myocardium after infarction. Furthermore, this study shows that injectable nanofibers allow precise and sustained delivery of proteins to the myocardium with potential therapeutic benefits.

BDNF-mediated enhancement of inflammation and injury in the aging heart

Aging is associated with shifts in autocrine and paracrine pathways in the cardiac vasculature that may contribute to the risk of cardiovascular disease in older persons. To elucidate the molecular basis of these changes in vivo, phage-display biopanning of 3- and 18-mo-old mouse hearts was performed that identified peptide epitopes with homology to brain-derived neurotrophic factor (BDNF) in old but not young phage pools. Quantification of cardiac phage binding by titration and immunostaining after injection with BDNF-like phage identified a twofold increased density of the BDNF receptor, truncated Trk B, in the aging hearts. Studies focused on the receptor ligand using a rat model of transient myocardial ischemia revealed increases in cardiac BDNF associated with local mononuclear infiltrates in 24- but not 4-mo-old rats. To investigate these changes, both 4- and 24-mo-old rat hearts were treated with intramyocardial injections of BDNF (or PBS control), demonstrating significant inflammatory increases with activated macrophage (ED1+) in BDNF-treated aging hearts compared with aging controls and similarly treated young hearts. Additional studies with permanent coronary occlusion following intramyocardial growth factor pretreatment revealed that BDNF significantly increased the extent of myocardial injury in older rat hearts (BDNF 35 +/- 10% vs. PBS 16.2 +/- 7.9% left ventricular injury; P < 0.05) without affecting younger hearts (BDNF 15 +/- 5.1% vs. PBS 14.5 +/- 6.0% left ventricular injury). Overall, these studies suggest that age-associated changes in BDNF-Trk B pathways may predispose the aging heart to increased injury after acute myocardial infarction and potentially contribute to the enhanced severity of cardiovascular disease in older individuals.

Synergistic targeting with bone marrow-derived cells and PDGF improves diabetic vascular function

Diabetes mellitus is associated with an increased risk of vascular disease, with significant alterations in systemic endothelial progenitor cells (EPCs) and peripheral vascular function. To identify the contribution of the different vascular compartments in the diabetic impairment of vascularization, we employed streptozotocin- and control-treated 3-mo-old C57Bl/6 mice in an isogeneic pinnal cardiac allograft model, revealing a significant delay in vascularization of wild-type cardiac tissue transplanted into diabetic mice. To investigate the basis of this impairment, the function of diabetic bone marrow cells was tested by transplantation of bone marrow cells isolated from diabetic and control mice into intact, unirradiated 18-mo-old C57Bl/6 mice, which have impaired function of both EPCs and peripheral endothelial cells. Importantly, cells derived from control, but not diabetic, bone marrow integrated into transplanted cardiac allografts. To assess the contribution of diabetic changes in the local vasculature, diabetic mice were treated with pinnal injections of platelet-derived growth factor (PDGF)-AB, which promotes cardiac angiogenesis in wild-type mice. However, whereas PDGF-AB enhanced allograft function in control mice, the activity of the cardiac transplants in the PDGF-AB-treated diabetic mice was significantly decreased. To decipher the potential interactions between systemic bone marrow-derived cells and local vascular pathways, diabetic mice were transplanted with wild-type bone marrow cells with or without PDGF-AB pinnal pretreatment, resulting in improved allograft function and donor cell recruitment only in the combination treatment arm. Overall, these studies show that the diabetic impairment in cardiac angiogenesis can be reversed by targeting the synergism between local trophic pathways and systemic cell function.

Phage display identification of age-associated TNFα-mediated cardiac oxidative induction

Age-associated alterations in the actions of tumor necrosis factor-α (TNFα) in the heart with impaired cardioprotective pathways and enhanced apoptotic induction may contribute to the increased severity of cardiovascular pathology in older persons. To identify the molecular events mediating these changes in the microvasculature of the aging rodent heart, the biochemical properties of in vivo phage-display cyclic peptide cardiac biopanning were studied. Analysis of individual amino acid positions revealed that the center of the peptide motif (amino acid position 4) had a significantly higher frequency of aromatic amino acid side chains in phage homing to the old hearts compared with young controls (18 mo old, 11% vs. 3 mo old, 3%, P < 0.05). This subset of phage motifs revealed an age-associated homology with oxidoreductase enzymes (homology: 18 mo, 7/7; 3 mo, 0/2), suggesting the substrates and/or binding sites of these enzymes are increased in the aging hearts. Immunostaining for the oxidoreductase substrate 4-hydroxy-2-nonenal (HNE), a cardiotoxic lipid peroxidation product, demonstrated a twofold higher density of HNE(+) cells in PBS-treated hearts of old mice (18 mo) compared with young controls (3 mo) (18 mo, 3.2 ± 2.8 vs. 3 mo, 1.0 ± 0.9 cells/HPF, P < 0.05). Moreover, intracardiac injection of TNFα resulted in a significantly greater increase in HNE staining in the old hearts (18 mo, 16.9 ± 13.8 vs. 3 mo, 9.1 ± 6.0 cells/HPF, P < 0.05). Overall, these studies demonstrate that aging-associated alterations in TNFα-mediated pathways with induction of reactive oxidative species and changes in vascular surface binding sites may contribute mechanistically to the increased cardiovascular pathology of the aging heart.