Identification of myeloid-derived growth factor as a mechanically-induced, growth-promoting angiocrine signal for human hepatocytes.

Recently, we have shown that after partial hepatectomy (PHx), an increased hepatic blood flow initiates liver growth in mice by vasodilation and mechanically-triggered release of angiocrine signals. Here, we use mass spectrometry to identify a mechanically-induced angiocrine signal in human hepatic endothelial cells, that is, myeloid-derived growth factor (MYDGF). We show that it induces proliferation and promotes survival of primary human hepatocytes derived from different donors in two-dimensional cell culture, via activation of mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3). MYDGF also enhances proliferation of human hepatocytes in three-dimensional organoids. In vivo, genetic deletion of MYDGF decreases hepatocyte proliferation in the regenerating mouse liver after PHx; conversely, adeno-associated viral delivery of MYDGF increases hepatocyte proliferation and MAPK signaling after PHx. We conclude that MYDGF represents a mechanically-induced angiocrine signal and that it triggers growth of, and provides protection to, primary mouse and human hepatocytes.

Hypoxia Attenuates Pressure Overload-Induced Heart Failure.

BACKGROUND: Alveolar hypoxia is protective in the context of cardiovascular and ischemic heart disease; however, the underlying mechanisms are incompletely understood. The present study sought to test the hypothesis that hypoxia is cardioprotective in left ventricular pressure overload (LVPO)-induced heart failure. We furthermore aimed to test that overlapping mechanisms promote cardiac recovery in heart failure patients following left ventricular assist device-mediated mechanical unloading and circulatory support. METHODS AND RESULTS: We established a novel murine model of combined chronic alveolar hypoxia and LVPO following transverse aortic constriction (HxTAC). The HxTAC model is resistant to cardiac hypertrophy and the development of heart failure. The cardioprotective mechanisms identified in our HxTAC model include increased activation of HIF (hypoxia-inducible factor)-1α-mediated angiogenesis, attenuated induction of genes associated with pathological remodeling, and preserved metabolic gene expression as identified by RNA sequencing. Furthermore, LVPO decreased Tbx5 and increased Hsd11b1 mRNA expression under normoxic conditions, which was attenuated under hypoxic conditions and may induce additional hypoxia-mediated cardioprotective effects. Analysis of samples from patients with advanced heart failure that demonstrated left ventricular assist device-mediated myocardial recovery revealed a similar expression pattern for TBX5 and HSD11B1 as observed in HxTAC hearts. CONCLUSIONS: Hypoxia attenuates LVPO-induced heart failure. Cardioprotective pathways identified in the HxTAC model might also contribute to cardiac recovery following left ventricular assist device support. These data highlight the potential of our novel HxTAC model to identify hypoxia-mediated cardioprotective mechanisms and therapeutic targets that attenuate LVPO-induced heart failure and mediate cardiac recovery following mechanical circulatory support.

Endothelial Cell GATA2 Modulates the Cardiomyocyte Stress Response through the Regulation of Two Long Non-Coding RNAs.

Capillary endothelial cells modulate myocardial growth and function during pathological stress, but it is unknown how and whether this contributes to the development of heart failure. We found that the endothelial cell transcription factor GATA2 is downregulated in human failing myocardium. Endothelial GATA2 knock-out (G2-EC-KO) mice develop heart failure and defective myocardial signal transduction during pressure overload, indicating that the GATA2 downregulation is maladaptive. Heart failure and perturbed signaling in G2-EC-KO mice could be induced by strong upregulation of two unknown, endothelial cell-derived long non-coding (lnc) RNAs (AK037972, AK038629, termed here GADLOR1 and 2). Mechanistically, the GADLOR1/2 lncRNAs transfer from endothelial cells to cardiomyocytes, where they block stress-induced signalling. Thereby, lncRNAs can contribute to disease as paracrine effectors of signal transduction and therefore might serve as therapeutic targets in the future.

Meteorin-like promotes heart repair through endothelial KIT receptor tyrosine kinase.

Effective tissue repair after myocardial infarction entails a vigorous angiogenic response, guided by incompletely defined immune cell-endothelial cell interactions. We identify the monocyte- and macrophage-derived cytokine METRNL (meteorin-like) as a driver of postinfarction angiogenesis and high-affinity ligand for the stem cell factor receptor KIT (KIT receptor tyrosine kinase). METRNL mediated angiogenic effects in cultured human endothelial cells through KIT-dependent signaling pathways. In a mouse model of myocardial infarction, METRNL promoted infarct repair by selectively expanding the KIT-expressing endothelial cell population in the infarct border zone. Metrnl-deficient mice failed to mount this KIT-dependent angiogenic response and developed severe postinfarction heart failure. Our data establish METRNL as a KIT receptor ligand in the context of ischemic tissue repair.

Analysis of myocardial cellular gene expression during pressure overload reveals matrix based functional intercellular communication.

To identify cellular mechanisms responsible for pressure overload triggered heart failure, we isolated cardiomyocytes, endothelial cells, and fibroblasts as most abundant cell types from mouse hearts in the subacute and chronic stages after transverse aortic constriction (TAC) and performed RNA-sequencing. We detected highly cell-type specific transcriptional responses with characteristic time courses and active intercellular communication. Cardiomyocytes after TAC exerted an early and sustained upregulation of inflammatory and matrix genes and a concomitant suppression of metabolic and ion channel genes. Fibroblasts, in contrast, showed transient early upregulation of inflammatory and matrix genes and downregulation of angiogenesis genes, but sustained induction of cell cycle and ion channel genes during TAC. Endothelial cells transiently induced cell cycle and extracellular matrix genes early after TAC, but exerted a long-lasting upregulation of inflammatory genes. As we found that matrix production by multiple cell types triggers pathological cellular responses, it might serve as a future therapeutic target.

Skeletal muscle derived Musclin protects the heart during pathological overload.

Cachexia is associated with poor prognosis in chronic heart failure patients, but the underlying mechanisms of cachexia triggered disease progression remain poorly understood. Here, we investigate whether the dysregulation of myokine expression from wasting skeletal muscle exaggerates heart failure. RNA sequencing from wasting skeletal muscles of mice with heart failure reveals a reduced expression of Ostn, which encodes the secreted myokine Musclin, previously implicated in the enhancement of natriuretic peptide signaling. By generating skeletal muscle specific Ostn knock-out and overexpressing mice, we demonstrate that reduced skeletal muscle Musclin levels exaggerate, while its overexpression in muscle attenuates cardiac dysfunction and myocardial fibrosis during pressure overload. Mechanistically, Musclin enhances the abundance of C-type natriuretic peptide (CNP), thereby promoting cardiomyocyte contractility through protein kinase A and inhibiting fibroblast activation through protein kinase G signaling. Because we also find reduced OSTN expression in skeletal muscle of heart failure patients, augmentation of Musclin might serve as therapeutic strategy.

Myeloid-Derived Growth Factor Protects Against Pressure Overload-Induced Heart Failure by Preserving Sarco/Endoplasmic Reticulum Ca2+-ATPase Expression in Cardiomyocytes.

BACKGROUND: Inflammation contributes to the pathogenesis of heart failure, but there is limited understanding of inflammation's potential benefits. Inflammatory cells secrete MYDGF (myeloid-derived growth factor) to promote tissue repair after acute myocardial infarction. We hypothesized that MYDGF has a role in cardiac adaptation to persistent pressure overload. METHODS: We defined the cellular sources and function of MYDGF in wild-type (WT), Mydgf-deficient (Mydgf-/-), and Mydgf bone marrow-chimeric or bone marrow-conditional transgenic mice with pressure overload-induced heart failure after transverse aortic constriction surgery. We measured MYDGF plasma concentrations by targeted liquid chromatography-mass spectrometry. We identified MYDGF signaling targets by phosphoproteomics and substrate-based kinase activity inference. We recorded Ca2+ transients and sarcomere contractions in isolated cardiomyocytes. Additionally, we explored the therapeutic potential of recombinant MYDGF. RESULTS: MYDGF protein abundance increased in the left ventricular myocardium and in blood plasma of pressure-overloaded mice. Patients with severe aortic stenosis also had elevated MYDGF plasma concentrations, which declined after transcatheter aortic valve implantation. Monocytes and macrophages emerged as the main MYDGF sources in the pressure-overloaded murine heart. While Mydgf-/- mice had no apparent phenotype at baseline, they developed more severe left ventricular hypertrophy and contractile dysfunction during pressure overload than WT mice. Conversely, conditional transgenic overexpression of MYDGF in bone marrow-derived inflammatory cells attenuated pressure overload-induced hypertrophy and dysfunction. Mechanistically, MYDGF inhibited G protein-coupled receptor agonist-induced hypertrophy and augmented SERCA2a (sarco/endoplasmic reticulum Ca2+-ATPase 2a) expression in cultured neonatal rat ventricular cardiomyocytes by enhancing PIM1 (Pim-1 proto-oncogene, serine/threonine kinase) expression and activity. Along this line, cardiomyocytes from pressure-overloaded Mydgf-/- mice displayed reduced PIM1 and SERCA2a expression, greater hypertrophy, and impaired Ca2+ cycling and sarcomere function compared with cardiomyocytes from pressure-overloaded WT mice. Transplanting Mydgf-/- mice with WT bone marrow cells augmented cardiac PIM1 and SERCA2a levels and ameliorated pressure overload-induced hypertrophy and dysfunction. Pressure-overloaded Mydgf-/- mice were similarly rescued by adenoviral Serca2a gene transfer. Treating pressure-overloaded WT mice subcutaneously with recombinant MYDGF enhanced SERCA2a expression, attenuated left ventricular hypertrophy and dysfunction, and improved survival. CONCLUSIONS: These findings establish a MYDGF-based adaptive crosstalk between inflammatory cells and cardiomyocytes that protects against pressure overload-induced heart failure.

Fibroblast GATA-4 and GATA-6 promote myocardial adaptation to pressure overload by enhancing cardiac angiogenesis.

Heart failure due to high blood pressure or ischemic injury remains a major problem for millions of patients worldwide. Despite enormous advances in deciphering the molecular mechanisms underlying heart failure progression, the cell-type specific adaptations and especially intercellular signaling remain poorly understood. Cardiac fibroblasts express high levels of cardiogenic transcription factors such as GATA-4 and GATA-6, but their role in fibroblasts during stress is not known. Here, we show that fibroblast GATA-4 and GATA-6 promote adaptive remodeling in pressure overload induced cardiac hypertrophy. Using a mouse model with specific single or double deletion of Gata4 and Gata6 in stress activated fibroblasts, we found a reduced myocardial capillarization in mice with Gata4/6 double deletion following pressure overload, while single deletion of Gata4 or Gata6 had no effect. Importantly, we confirmed the reduced angiogenic response using an in vitro co-culture system with Gata4/6 deleted cardiac fibroblasts and endothelial cells. A comprehensive RNA-sequencing analysis revealed an upregulation of anti-angiogenic genes upon Gata4/6 deletion in fibroblasts, and siRNA mediated downregulation of these genes restored endothelial cell growth. In conclusion, we identified a novel role for the cardiogenic transcription factors GATA-4 and GATA-6 in heart fibroblasts, where both proteins act in concert to promote myocardial capillarization and heart function by directing intercellular crosstalk.

Angiogenesis after acute myocardial infarction.

Acute myocardial infarction (MI) inflicts massive injury to the coronary microcirculation leading to vascular disintegration and capillary rarefication in the infarct region. Tissue repair after MI involves a robust angiogenic response that commences in the infarct border zone and extends into the necrotic infarct core. Technological advances in several areas have provided novel mechanistic understanding of postinfarction angiogenesis and how it may be targeted to improve heart function after MI. Cell lineage tracing studies indicate that new capillary structures arise by sprouting angiogenesis from pre-existing endothelial cells (ECs) in the infarct border zone with no meaningful contribution from non-EC sources. Single-cell RNA sequencing shows that ECs in infarcted hearts may be grouped into clusters with distinct gene expression signatures, likely reflecting functionally distinct cell populations. EC-specific multicolour lineage tracing reveals that EC subsets clonally expand after MI. Expanding EC clones may arise from tissue-resident ECs with stem cell characteristics that have been identified in multiple organs including the heart. Tissue repair after MI involves interactions among multiple cell types which occur, to a large extent, through secreted proteins and their cognate receptors. While we are only beginning to understand the full complexity of this intercellular communication, macrophage and fibroblast populations have emerged as major drivers of the angiogenic response after MI. Animal data support the view that the endogenous angiogenic response after MI can be boosted to reduce scarring and adverse left ventricular remodelling. The improved mechanistic understanding of infarct angiogenesis therefore creates multiple therapeutic opportunities. During preclinical development, all proangiogenic strategies should be tested in animal models that replicate both cardiovascular risk factor(s) and the pharmacotherapy typically prescribed to patients with acute MI. Considering that the majority of patients nowadays do well after MI, clinical translation will require careful selection of patients in need of proangiogenic therapies.

Crystal structure and receptor-interacting residues of MYDGF - a protein mediating ischemic tissue repair.

Myeloid-derived growth factor (MYDGF) is a paracrine-acting protein that is produced by bone marrow-derived monocytes and macrophages to protect and repair the heart after myocardial infarction (MI). This effect can be used for the development of protein-based therapies for ischemic tissue repair, also beyond the sole application in heart tissue. Here, we report the X-ray structure of MYDGF and identify its functionally relevant receptor binding epitope. MYDGF consists of a 10-stranded ß-sandwich with a folding topology showing no similarities to other cytokines or growth factors. By characterizing the epitope of a neutralizing antibody and utilizing functional assays to study the activity of surface patch-mutations, we were able to localize the receptor interaction interface to a region around two surface tyrosine residues 71 and 73 and an adjacent prominent loop structure of residues 97-101. These findings enable structure-guided protein engineering to develop modified MYDGF variants with potentially improved properties for clinical use.

Heparan Sulfate-Editing Extracellular Sulfatases Enhance VEGF Bioavailability for Ischemic Heart Repair.

RATIONALE: Mechanistic insight into the inflammatory response after acute myocardial infarction may inform new molecularly targeted treatment strategies to prevent chronic heart failure. OBJECTIVE: We identified the sulfatase SULF2 in an in silico secretome analysis in bone marrow cells from patients with acute myocardial infarction and detected increased sulfatase activity in myocardial autopsy samples. SULF2 (Sulf2 in mice) and its isoform SULF1 (Sulf1) act as endosulfatases removing 6-O-sulfate groups from heparan sulfate (HS) in the extracellular space, thus eliminating docking sites for HS-binding proteins. We hypothesized that the Sulfs have a role in tissue repair after myocardial infarction. METHODS AND RESULTS: Both Sulfs were dynamically upregulated after coronary artery ligation in mice, attaining peak expression and activity levels during the first week after injury. Sulf2 was expressed by monocytes and macrophages, Sulf1 by endothelial cells and fibroblasts. Infarct border zone capillarization was impaired, scar size increased, and cardiac dysfunction more pronounced in mice with a genetic deletion of either Sulf1 or Sulf2. Studies in bone marrow-chimeric Sulf-deficient mice and Sulf-deficient cardiac endothelial cells established that inflammatory cell-derived Sulf2 and endothelial cell-autonomous Sulf1 promote angiogenesis. Mechanistically, both Sulfs reduced HS sulfation in the infarcted myocardium, thereby diminishing Vegfa (vascular endothelial growth factor A) interaction with HS. Along this line, both Sulfs rendered infarcted mouse heart explants responsive to the angiogenic effects of HS-binding Vegfa164 but did not modulate the angiogenic effects of non-HS-binding Vegfa120. Treating wild-type mice systemically with the small molecule HS-antagonist surfen (bis-2-methyl-4-amino-quinolyl-6-carbamide, 1 mg/kg/day) for 7 days after myocardial infarction released Vegfa from HS, enhanced infarct border-zone capillarization, and exerted sustained beneficial effects on cardiac function and survival. CONCLUSIONS: These findings establish HS-editing Sulfs as critical inducers of postinfarction angiogenesis and identify HS sulfation as a therapeutic target for ischemic tissue repair.

TIP30 counteracts cardiac hypertrophy and failure by inhibiting translational elongation.

Pathological cardiac overload induces myocardial protein synthesis and hypertrophy, which predisposes to heart failure. To inhibit hypertrophy therapeutically, the identification of negative regulators of cardiomyocyte protein synthesis is needed. Here, we identified the tumor suppressor protein TIP30 as novel inhibitor of cardiac hypertrophy and dysfunction. Reduced TIP30 levels in mice entailed exaggerated cardiac growth during experimental pressure overload, which was associated with cardiomyocyte cellular hypertrophy, increased myocardial protein synthesis, reduced capillary density, and left ventricular dysfunction. Pharmacological inhibition of protein synthesis improved these defects. Our results are relevant for human disease, since we found diminished cardiac TIP30 levels in samples from patients suffering from end-stage heart failure or hypertrophic cardiomyopathy. Importantly, therapeutic overexpression of TIP30 in mouse hearts inhibited cardiac hypertrophy and improved left ventricular function during pressure overload and in cardiomyopathic mdx mice. Mechanistically, we identified a previously unknown anti-hypertrophic mechanism, whereby TIP30 binds the eukaryotic elongation factor 1A (eEF1A) to prevent the interaction with its essential co-factor eEF1B2 and translational elongation. Therefore, TIP30 could be a therapeutic target to counteract cardiac hypertrophy.

C-X-C Motif Chemokine Receptor 4 Blockade Promotes Tissue Repair After Myocardial Infarction by Enhancing Regulatory T Cell Mobilization and Immune-Regulatory Function.

BACKGROUND: Acute myocardial infarction (MI) elicits an inflammatory response that drives tissue repair and adverse cardiac remodeling. Inflammatory cell trafficking after MI is controlled by C-X-C motif chemokine ligand 12 (CXCL12) and its receptor, C-X-C motif chemokine receptor 4 (CXCR4). CXCR4 antagonists mobilize inflammatory cells and promote infarct repair, but the cellular mechanisms are unclear. METHODS: We investigated the therapeutic potential and mode of action of the peptidic macrocycle CXCR4 antagonist POL5551 in mice with reperfused MI. We applied cell depletion and adoptive transfer strategies using lymphocyte-deficient Rag1 knockout mice; DEREG mice, which express a diphtheria toxin receptor-enhanced green fluorescent protein fusion protein under the control of the promoter/enhancer region of the regulatory T (Treg) cell-restricted Foxp3 transcription factor; and dendritic cell-depleted CD11c-Cre iDTR mice. Translational potential was explored in a porcine model of reperfused MI using serial contrast-enhanced magnetic resonance imaging. RESULTS: Intraperitoneal POL5551 injections in wild-type mice (8 mg/kg at 2, 4, 6, and 8 days) enhanced angiogenesis in the infarct border zone, reduced scar size, and attenuated left ventricular remodeling and contractile dysfunction at 28 days. Treatment effects were absent in splenectomized wild-type mice, Rag1 knockout mice, and Treg cell-depleted DEREG mice. Conversely, treatment effects could be transferred into infarcted splenectomized wild-type mice by transplanting splenic Treg cells from POL5551-treated infarcted DEREG mice. Instructive cues provided by infarct-primed dendritic cells were required for POL5551 treatment effects. POL5551 injections mobilized Treg cells into the peripheral blood, followed by enhanced Treg cell accumulation in the infarcted region. Neutrophils, monocytes, and lymphocytes displayed similar mobilization kinetics, but their cardiac recruitment was not affected. POL5551, however, attenuated inflammatory gene expression in monocytes and macrophages in the infarcted region via Treg cells. Intravenous infusion of the clinical-stage POL5551 analogue POL6326 (3 mg/kg at 4, 6, 8, and 10 days) decreased infarct volume and improved left ventricular ejection fraction in pigs. CONCLUSIONS: These data confirm CXCR4 blockade as a promising treatment strategy after MI. We identify dendritic cell-primed splenic Treg cells as the central arbiters of these therapeutic effects and thereby delineate a pharmacological strategy to promote infarct repair by augmenting Treg cell function in vivo.

A gene therapeutic approach to inhibit calcium and integrin binding protein 1 ameliorates maladaptive remodelling in pressure overload.

Aims: Chronic heart failure is becoming increasingly prevalent and is still associated with a high mortality rate. Myocardial hypertrophy and fibrosis drive cardiac remodelling and heart failure, but they are not sufficiently inhibited by current treatment strategies. Furthermore, despite increasing knowledge on cardiomyocyte intracellular signalling proteins inducing pathological hypertrophy, therapeutic approaches to target these molecules are currently unavailable. In this study, we aimed to establish and test a therapeutic tool to counteract the 22 kDa calcium and integrin binding protein (CIB) 1, which we have previously identified as nodal regulator of pathological cardiac hypertrophy and as activator of the maladaptive calcineurin/NFAT axis. Methods and results: Among three different sequences, we selected a shRNA construct (shCIB1) to specifically down-regulate CIB1 by 50% upon adenoviral overexpression in neonatal rat cardiomyocytes (NRCM), and upon overexpression by an adeno-associated-virus (AAV) 9 vector in mouse hearts. Overexpression of shCIB1 in NRCM markedly reduced cellular growth, improved contractility of bioartificial cardiac tissue and reduced calcineurin/NFAT activation in response to hypertrophic stimulation. In mice, administration of AAV-shCIB1 strongly ameliorated eccentric cardiac hypertrophy and cardiac dysfunction during 2 weeks of pressure overload by transverse aortic constriction (TAC). Ultrastructural and molecular analyses revealed markedly reduced myocardial fibrosis, inhibition of hypertrophy associated gene expression and calcineurin/NFAT as well as ERK MAP kinase activation after TAC in AAV-shCIB1 vs. AAV-shControl treated mice. During long-term exposure to pressure overload for 10 weeks, AAV-shCIB1 treatment maintained its anti-hypertrophic and anti-fibrotic effects, but cardiac function was no longer improved vs. AAV-shControl treatment, most likely resulting from a reduction in myocardial angiogenesis upon downregulation of CIB1. Conclusions: Inhibition of CIB1 by a shRNA-mediated gene therapy potently inhibits pathological cardiac hypertrophy and fibrosis during pressure overload. While cardiac function is initially improved by shCIB1, this cannot be kept up during persisting overload.

Anti-androgenic therapy with finasteride improves cardiac function, attenuates remodeling and reverts pathologic gene-expression after myocardial infarction in mice.

Maladaptive cardiac remodeling after myocardial infarction (MI) is increasingly contributing to the prevalence of chronic heart failure. Women show less severe remodeling, a reduced mortality and a better systolic function after MI compared to men. Although sex hormones are being made responsible for these differences, it remains currently unknown how this could be translated into therapeutic strategies. Because we had recently demonstrated that inhibition of the conversion of testosterone to its highly active metabolite dihydrotestosterone (DHT) by finasteride effectively reduces cardiac hypertrophy and improves heart function during pressure overload, we asked here whether this strategy could be applied to post-MI remodeling. We found increased abundance of DHT and increased expression of androgen responsive genes in the mouse myocardium after experimental MI. Treatment of mice with finasteride for 21 days (starting 7 days after surgery), reduced myocardial DHT levels and markedly attenuated cardiac dysfunction as well as hypertrophic remodeling after MI. Histological and molecular analyses showed reduced MI triggered interstitial fibrosis, reduced cardiomyocyte hypertrophy and increased capillary density in the myocardium of finasteride treated mice. Mechanistically, this was associated with decreased activation of myocardial growth-signaling pathways, a comprehensive normalization of pathological myocardial gene-expression as revealed by RNA deep-sequencing and with direct effects of finasteride on cardiac fibroblasts and endothelial cells. In conclusion, we demonstrated a beneficial role of anti-androgenic treatment with finasteride in post-MI remodeling of mice. As finasteride is already approved for the treatment of benign prostate disease, it could potentially be evaluated as therapeutic strategy for heart failure after MI.

EMC10 (Endoplasmic Reticulum Membrane Protein Complex Subunit 10) Is a Bone Marrow-Derived Angiogenic Growth Factor Promoting Tissue Repair After Myocardial Infarction.

BACKGROUND: Clinical trials of bone marrow cell-based therapies after acute myocardial infarction (MI) have produced mostly neutral results. Treatment with specific bone marrow cell-derived secreted proteins may provide an alternative biological approach to improving tissue repair and heart function after MI. We recently performed a bioinformatic secretome analysis in bone marrow cells from patients with acute MI and discovered a poorly characterized secreted protein, EMC10 (endoplasmic reticulum membrane protein complex subunit 10), showing activity in an angiogenic screen. METHODS: We investigated the angiogenic potential of EMC10 and its mouse homolog (Emc10) in cultured endothelial cells and infarcted heart explants. We defined the cellular sources and function of Emc10 after MI using wild-type, Emc10-deficient, and Emc10 bone marrow-chimeric mice subjected to transient coronary artery ligation. Furthermore, we explored the therapeutic potential of recombinant Emc10 delivered by osmotic minipumps after MI in heart failure-prone FVB/N mice. RESULTS: Emc10 signaled through small GTPases, p21-activated kinase, and the p38 mitogen-activated protein kinase (MAPK)-MAPK-activated protein kinase 2 (MK2) pathway to promote actin polymerization and endothelial cell migration. Confirming the importance of these signaling events in the context of acute MI, Emc10 stimulated endothelial cell outgrowth from infarcted mouse heart explants via p38 MAPK-MK2. Emc10 protein abundance was increased in the infarcted region of the left ventricle and in the circulation of wild-type mice after MI. Emc10 expression was also increased in left ventricular tissue samples from patients with acute MI. Bone marrow-derived monocytes and macrophages were the predominant sources of Emc10 in the infarcted murine heart. Emc10 KO mice showed no cardiovascular phenotype at baseline. After MI, however, capillarization of the infarct border zone was impaired in KO mice, and the animals developed larger infarct scars and more pronounced left ventricular remodeling compared with wild-type mice. Transplanting KO mice with wild-type bone marrow cells rescued the angiogenic defect and ameliorated left ventricular remodeling. Treating FVB/N mice with recombinant Emc10 enhanced infarct border-zone capillarization and exerted a sustained beneficial effect on left ventricular remodeling. CONCLUSIONS: We have identified Emc10 as a previously unknown angiogenic growth factor that is produced by bone marrow-derived monocytes and macrophages as part of an endogenous adaptive response that can be enhanced therapeutically to repair the heart after MI.