Transcriptome analysis of cardiac endothelial cells after myocardial infarction reveals temporal changes and long-term deficits

Endothelial cells (ECs) have essential roles in cardiac tissue repair after myocardial infarction (MI). To establish stage-specific and long-term effects of the ischemic injury on cardiac ECs, we analyzed their transcriptome at landmark time points after MI in mice. We found that early EC response at Day 2 post-MI centered on metabolic changes, acquisition of proinflammatory phenotypes, initiation of the S phase of cell cycle, and activation of stress-response pathways, followed by progression to mitosis (M/G2 phase) and acquisition of proangiogenic and mesenchymal properties during scar formation at Day 7. In contrast, genes involved in vascular physiology and maintenance of vascular tone were suppressed. Importantly, ECs did not return to pre-injury phenotypes after repair has been completed but maintained inflammatory, fibrotic and thrombotic characteristics and lost circadian rhythmicity. We discovered that the highest induced transcript is the mammalian-specific Sh2d5 gene that promoted migration and invasion of ECs through Rac1 GTPase. Our results revealed a synchronized, temporal activation of disease phenotypes, metabolic pathways, and proliferation in quiescent ECs after MI, indicating that precisely-timed interventions are necessary to optimize cardiac tissue repair and improve outcomes. Furthermore, long-term effects of acute ischemic injury on ECs may contribute to vascular dysfunction and development of heart failure.

Pharmacological modulation of prostaglandin E2 (PGE2 ) EP receptors improves cardiomyocyte function under hyperglycemic conditions

Type 2 diabetes (T2D) affects >30 million Americans and nearly 70% of individuals with T2D will die from cardiovascular disease (CVD). Circulating levels of the inflammatory signaling lipid, prostaglandin E₂ (PGE₂ ), are elevated in the setting of obesity and T2D and are associated with decreased cardiac function. The EP3 and EP4 PGE₂ receptors have opposing actions in several tissues, including the heart: overexpression of EP3 in cardiomyocytes impairs function, while EP4 overexpression improves function. Here we performed complementary studies in vitro with isolated cardiomyocytes and in vivo using db/db mice, a model of T2D, to analyze the effects of EP3 inhibition or EP4 activation on cardiac function. Using echocardiography, we found that 2 weeks of systemic treatment of db/db mice with 20 mg/kg of EP3 antagonist, beginning at 6 weeks of age, improves ejection fraction and fractional shortening (with no effect on heart rate). We further show that either EP3 blockade or EP4 activation enhances contractility and calcium cycling in isolated mouse cardiomyocytes cultured in both normal and high glucose. Thus, peak [Ca²⁺ ]_I transient amplitude was increased, while time to peak [Ca²⁺ ]_I and [Ca²⁺ ]_I decay were decreased. These data suggest that modulation of EP3 and EP4 activity has beneficial effects on cardiomyocyte contractility and overall heart function.

Targeting 5-HT2B Receptor Signaling Prevents Border Zone Expansion and Improves Microstructural Remodeling After Myocardial Infarction

BACKGROUND

Myocardial infarction (MI) induces an intense injury response that ultimately generates a collagen-dominated scar. Although required to prevent ventricular rupture, the fibrotic process is often sustained in a manner detrimental to optimal recovery. Cardiac myofibroblasts are the cells tasked with depositing and remodeling collagen and are a prime target to limit the fibrotic process after MI. Serotonin 2B receptor (5-HT2B) signaling has been shown to be harmful in a variety of cardiopulmonary pathologies and could play an important role in mediating scar formation after MI.

METHODS

We used 2 pharmacological antagonists to explore the effect of 5-HT2B inhibition on outcomes after MI and characterized the histological and microstructural changes involved in tissue remodeling. Inducible 5-HT2B ablation driven by Tcf21MCM and PostnMCM was used to evaluate resident cardiac fibroblast- and myofibroblast-specific contributions of 5-HT2B, respectively. RNA sequencing was used to motivate subsequent in vitro analyses to explore cardiac fibroblast phenotype.

RESULTS

5-HT2B antagonism preserved cardiac structure and function by facilitating a less fibrotic scar, indicated by decreased scar thickness and decreased border zone area. 5-HT2B antagonism resulted in collagen fiber redistribution to thinner collagen fibers that were more anisotropic, enhancing left ventricular contractility, whereas fibrotic tissue stiffness was decreased, limiting the hypertrophic response of uninjured cardiomyocytes. Using a tamoxifen-inducible Cre, we ablated 5-HT2B from Tcf21-lineage resident cardiac fibroblasts and saw similar improvements to the pharmacological approach. Tamoxifen-inducible Cre-mediated ablation of 5-HT2B after onset of injury in Postn-lineage myofibroblasts also improved cardiac outcomes. RNA sequencing and subsequent in vitro analyses corroborate a decrease in fibroblast proliferation, migration, and remodeling capabilities through alterations in Dnajb4 expression and Src phosphorylation.

CONCLUSIONS

Together, our findings illustrate that 5-HT2B expression in either cardiac fibroblasts or activated myofibroblasts directly contributes to excessive scar formation, resulting in adverse remodeling and impaired cardiac function after MI.

Balanced Wnt/Dickkopf-1 signaling by mesenchymal vascular progenitor cells in the microvascular niche maintains distal lung structure and function

The well-described Wnt inhibitor Dickkopf-1 (DKK1) plays a role in angiogenesis as well as in regulation of growth factor signaling cascades in pulmonary remodeling associated with chronic lung diseases (CLDs) including emphysema and fibrosis. However, the specific mechanisms by which DKK1 influences mesenchymal vascular progenitor cells (MVPCs), microvascular endothelial cells (MVECs), and smooth muscle cells (SMCs) within the microvascular niche have not been elucidated. In this study, we show that knockdown of DKK1 in Abcg2pos lung mouse adult tissue resident MVPCs alters lung stiffness, parenchymal collagen deposition, microvessel muscularization and density as well as loss of tissue structure in response to hypoxia exposure. To complement the in vivo mouse modeling, we also identified cell- or disease-specific responses to DKK1, in primary lung chronic obstructive pulmonary disease (COPD) MVPCs, COPD MVECs, and SMCs, supporting a paradoxical disease-specific response of cells to well-characterized factors. Cell responses to DKK1 were dose dependent and correlated with varying expressions of the DKK1 receptor, CKAP4. These data demonstrate that DKK1 expression is necessary to maintain the microvascular niche whereas its effects are context specific. They also highlight DKK1 as a regulatory candidate to understand the role of Wnt and DKK1 signaling between cells of the microvascular niche during tissue homeostasis and during the development of chronic lung diseases.

The BDNF rs6265 Polymorphism is a Modifier of Cardiomyocyte Contractility and Dilated Cardiomyopathy

Brain-derived neurotrophic factor (BDNF) is a neuronal growth and survival factor that harbors cardioprotective qualities that may attenuate dilated cardiomyopathy. In ~30% of the population, BDNF has a common, nonsynonymous single nucleotide polymorphism rs6265 (Val66Met), which might be correlated with increased risk of cardiovascular events. We previously showed that BDNF correlates with better cardiac function in Duchenne muscular dystrophy (DMD) patients. However, the effect of the Val66Met polymorphism on cardiac function has not been determined. The goal of the current study was to determine the effects of rs6265 on BDNF biomarker suitability and DMD cardiac functions more generally. We assessed cardiovascular and skeletal muscle function in human DMD patients segregated by polymorphic allele. We also compared echocardiographic, electrophysiologic, and cardiomyocyte contractility in C57/BL-6 wild-type mice with rs6265 polymorphism and in mdx/mTR (mDMD) mouse model of DMD. In human DMD patients, plasma BDNF levels had a positive correlation with left ventricular function, opposite to that seen in rs6265 carriers. There was also a substantial decrease in skeletal muscle function in carriers compared to the Val homozygotes. Surprisingly, the opposite was true when cardiac function of DMD carriers and non-carriers were compared. On the other hand, Val66Met wild-type mice had only subtle functional differences at baseline but significantly decreased cardiomyocyte contractility. Our results indicate that the Val66Met polymorphism alters myocyte contractility, conferring worse skeletal muscle function but better cardiac function in DMD patients. Moreover, these results suggest a mechanism for the relative preservation of cardiac tissues compared to skeletal muscle in DMD patients and underscores the complexity of BDNF signaling in response to mechanical workload.

Cadherin-11 blockade reduces inflammation-driven fibrotic remodeling and improves outcomes after myocardial infarction

Over one million Americans experience myocardial infarction (MI) annually, and the resulting scar and subsequent cardiac fibrosis gives rise to heart failure. A specialized cell-cell adhesion protein, cadherin-11 (CDH11), contributes to inflammation and fibrosis in rheumatoid arthritis, pulmonary fibrosis, and aortic valve calcification but has not been studied in myocardium after MI. MI was induced by ligation of the left anterior descending artery in mice with either heterozygous or homozygous knockout of CDH11, wild-type mice receiving bone marrow transplants from Cdh11-deficient animals, and wild-type mice treated with a functional blocking antibody against CDH11 (SYN0012). Flow cytometry revealed significant CDH11 expression in noncardiomyocyte cells after MI. Animals given SYN0012 had improved cardiac function, as measured by echocardiogram, reduced tissue remodeling, and altered transcription of inflammatory and proangiogenic genes. Targeting CDH11 reduced bone marrow-derived myeloid cells and increased proangiogenic cells in the heart 3 days after MI. Cardiac fibroblast and macrophage interactions increased IL-6 secretion in vitro. Our findings suggest that CDH11-expressing cells contribute to inflammation-driven fibrotic remodeling after MI and that targeting CDH11 with a blocking antibody improves outcomes by altering recruitment of bone marrow-derived cells, limiting the macrophage-induced expression of IL-6 by fibroblasts and promoting vascularization.

Disease Models & Mechanisms in the Age of Big Data

In the decade since Disease Models & Mechanisms was launched, the emergence of Big Data as the main foundation of biological information is having a profound effect on how we do research and it has provoked some interesting questions. Is Big Data exploration replacing hypothesis-driven basic research? And, to what extent is disease modeling in the laboratory still relevant to medical research? Recent examples of synergistic approaches utilizing animal modeling and electronic medical records mining show that combining efforts between disease models and clinical datasets can uncover not only disease etiologies, but also novel molecular and cellular mechanisms linked to gene function.

Summary: This Editorial reflects on how the emergence of Big Data has affected traditional disease modeling over the past decade, and on DMM's place in this changing landscape.

Bone morphogenetic protein signaling in inflammation

IMPACT STATEMENT

By compiling findings from recent studies, this review will garner novel insight on the dynamic and complex role of BMP signaling in diseases of inflammation, highlighting the specific roles played by both individual ligands and endogenous antagonists. Ultimately, this summary will help inform the high therapeutic value of targeting this pathway for modulating diseases of inflammation.

Abstract 114: A Role for Brain-derived Neurotrophic Factor in Duchenne Cardiomyopathy

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB) harbor cardioprotective qualities that may attenuate CM. In a small cohort of DMD patients we found that BDNF blood levels positively correlated with preserved ejection fraction (EF) and less fibrosis, and carriers of the common BDNF single nucleotide polymorphism rs6265 (Val66-Met) tended to exhibit earlier age of onset of fibrosis with subsequent progression to LV dysfunction, compared to non-carriers. We thus hypothesized that BDNF/TrkB signaling delays CM progression in DMD. To test this hypothesis, we administered the TrkB agonist 7,8-dihydroxyflavone (DHF) to mdx 4cv ; mTR KO mice in their drinking water for 26 weeks, beginning at 8 weeks of age. Based on echocardiography, DHF treatment preserved cardiac output compared to vehicle-treated controls. Conversely, mdx 4cv ; mTR KO mice injected intraperitoneally with the TrkB inhibitor (K252a) displayed bradycardia and PR interval prolongation, as measured by EKG, as well as acute (10-20 min) reduction in percent EF and fractional shortening, as measured by echocardiography. K252a also significantly reduced sarcomere shortening in isolated murine cardiomyocytes. BDNF might also contribute to cardiac repair. Using humanized BDNF polymorphic mice, which have the Val66-Met mutation, we found that post-myocardial infarction cardiac dysfunction was significantly exacerbated in Met/Met mice compared to Val/Val littermate controls. Finally, we evaluated the role of BDNF/TrkB in human cardiomyocytes differentiated from induced pluripotent cells obtained from DMD patients (DMD iPSC-CMs) and found that they highly express BDNF protein in lysates and supernatants. DMD iPSC-CMs also expressed a truncated version of TrkB that lacks the tyrosine kinase domain essential for canonical BDNF/TrkB signaling. Nonetheless, DMD iPSC-CMs responded to treatment with recombinant BDNF, including increased phosphorylation of GSK-3α, mTOR, AMPK, and MSK1/2. Considered together, our results indicate that BDNF plays a protective role in the dystrophic heart and might represent a novel therapeutic candidate for DMD cardiomyopathy.

TIME Trial: Effect of Timing of Stem Cell Delivery Following ST-Elevation Myocardial Infarction on the Recovery of Global and Regional Left Ventricular Function: Final 2-Year Analysis

RATIONALE

The TIME trial (Timing in Myocardial Infarction Evaluation) was the first cell therapy trial sufficiently powered to determine if timing of cell delivery after ST-segment-elevation myocardial infarction affects recovery of left ventricular (LV) function.

OBJECTIVE

To report the 2-year clinical and cardiac magnetic resonance imaging results and their modification by microvascular obstruction.

METHODS AND RESULTS

TIME was a randomized, double-blind, placebo-controlled trial comparing 150 million bone marrow mononuclear cells versus placebo in 120 patients with anterior ST-segment-elevation myocardial infarctions resulting in LV dysfunction. Primary end points included changes in global (LV ejection fraction) and regional (infarct and border zone) function. Secondary end points included changes in LV volumes, infarct size, and major adverse cardiac events. Here, we analyzed the continued trajectory of these measures out to 2 years and the influence of microvascular obstruction present at baseline on these long-term outcomes. At 2 years (n=85), LV ejection fraction was similar in the bone marrow mononuclear cells (48.7%) and placebo groups (51.6%) with no difference in regional LV function. Infarct size and LV mass decreased ≥30% in each group at 6 months and declined gradually to 2 years. LV volumes increased ≈10% at 6 months and remained stable to 2 years. Microvascular obstruction was present in 48 patients at baseline and was associated with significantly larger infarct size (56.5 versus 36.2 g), greater adverse LV remodeling, and marked reduction in LV ejection fraction recovery (0.2% versus 6.2%).

CONCLUSIONS

In one of the longest serial cardiac magnetic resonance imaging analyses of patients with large anterior ST-segment-elevation myocardial infarctions, bone marrow mononuclear cells administration did not improve recovery of LV function over 2 years. Microvascular obstruction was associated with reduced recovery of LV function, greater adverse LV remodeling, and more device implantations. The use of cardiac magnetic resonance imaging leads to greater dropout of patients over time because of device implantation in patients with more severe LV dysfunction resulting in overestimation of clinical stability of the cohort.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00684021.

Coordinated Proliferation and Differentiation of Human-Induced Pluripotent Stem Cell-Derived Cardiac Progenitor Cells Depend on Bone Morphogenetic Protein Signaling Regulation by GREMLIN 2

Heart development depends on coordinated proliferation and differentiation of cardiac progenitor cells (CPCs), but how the two processes are synchronized is not well understood. Here, we show that the secreted Bone Morphogenetic Protein (BMP) antagonist GREMLIN 2 (GREM2) is induced in CPCs shortly after cardiac mesoderm specification during differentiation of human pluripotent stem cells. GREM2 expression follows cardiac lineage differentiation independently of the differentiation method used, or the origin of the pluripotent stem cells, suggesting that GREM2 is linked to cardiogenesis. Addition of GREM2 protein strongly increases cardiomyocyte output compared to established procardiogenic differentiation methods. Our data show that inhibition of canonical BMP signaling by GREM2 is necessary to promote proliferation of CPCs. However, canonical BMP signaling inhibition alone is not sufficient to induce cardiac differentiation, which depends on subsequent JNK pathway activation specifically by GREM2. These findings may have broader implications in the design of approaches to orchestrate growth and differentiation of pluripotent stem cell-derived lineages that depend on precise regulation of BMP signaling.

Instructive Role of the Microenvironment in Preventing Renal Fibrosis

Accumulation of myofibroblasts is a hallmark of renal fibrosis. A significant proportion of myofibroblasts has been reported to originate via endothelial‐mesenchymal transition. We initially hypothesized that exposing myofibroblasts to the extract of endothelial progenitor cells (EPCs) could reverse this transition. Indeed, in vitro treatment of transforming growth factor‐β1 (TGF‐β1)‐activated fibroblasts with EPC extract prevented expression of α‐smooth muscle actin (α‐SMA); however, it did not enhance expression of endothelial markers. In two distinct models of renal fibrosis—unilateral ureteral obstruction and chronic phase of folic acid‐induced nephropathy—subcapsular injection of EPC extract to the kidney prevented and reversed accumulation of α‐SMA‐positive myofibroblasts and reduced fibrosis. Screening the composition of EPC extract for cytokines revealed that it is enriched in leukemia inhibitory factor (LIF) and vascular endothelial growth factor. Only LIF was capable of reducing fibroblast‐to‐myofibroblast transition of TGF‐β1‐activated fibroblasts. In vivo subcapsular administration of LIF reduced the number of myofibroblasts and improved the density of peritubular capillaries; however, it did not reduce the degree of fibrosis. A receptor‐independent ligand for the gp130/STAT3 pathway, hyper‐interleukin‐6 (hyper‐IL‐6), not only induced a robust downstream increase in pluripotency factors Nanog and c‐Myc but also exhibited a powerful antifibrotic effect. In conclusion, EPC extract prevented and reversed fibroblast‐to‐myofibroblast transition and renal fibrosis. The component of EPC extract, LIF, was capable of preventing development of the contractile phenotype of activated fibroblasts but did not eliminate TGF‐β1‐induced collagen synthesis in cultured fibroblasts and models of renal fibrosis, whereas a receptor‐independent gp130/STAT3 agonist, hyper‐IL‐6, prevented fibrosis. In summary, these studies, through the evolution from EPC extract to LIF and then to hyper‐IL‐6, demonstrate the instructive role of microenvironmental cues and may provide in the future a facile strategy to prevent and reverse renal fibrosis. Stem Cells Translational Medicine2017;6:992–1005

BMP Antagonist Gremlin 2 Limits Inflammation After Myocardial Infarction

RATIONALE

We have recently shown that the bone morphogenetic protein (BMP) antagonist Gremlin 2 (Grem2) is required for early cardiac development and cardiomyocyte differentiation. Our initial studies discovered that Grem2 is strongly induced in the adult heart after experimental myocardial infarction (MI). However, the function of Grem2 and BMP-signaling inhibitors after cardiac injury is currently unknown.

OBJECTIVE

To investigate the role of Grem2 during cardiac repair and assess its potential to improve ventricular function after injury.

METHODS AND RESULTS

Our data show that Grem2 is transiently induced after MI in peri-infarct area cardiomyocytes during the inflammatory phase of cardiac tissue repair. By engineering loss- (Grem2(-/-)) and gain- (TG(Grem2)) of-Grem2-function mice, we discovered that Grem2 controls the magnitude of the inflammatory response and limits infiltration of inflammatory cells in peri-infarct ventricular tissue, improving cardiac function. Excessive inflammation in Grem2(-/-) mice after MI was because of overactivation of canonical BMP signaling, as proven by the rescue of the inflammatory phenotype through administration of the canonical BMP inhibitor, DMH1. Furthermore, intraperitoneal administration of Grem2 protein in wild-type mice was sufficient to reduce inflammation after MI. Cellular analyses showed that BMP2 acts with TNFα to induce expression of proinflammatory proteins in endothelial cells and promote adhesion of leukocytes, whereas Grem2 specifically inhibits the BMP2 effect.

CONCLUSIONS

Our results indicate that Grem2 provides a molecular barrier that controls the magnitude and extent of inflammatory cell infiltration by suppressing canonical BMP signaling, thereby providing a novel mechanism for limiting the adverse effects of excessive inflammation after MI.

Integrated Genomic Analysis of Diverse Induced Pluripotent Stem Cells from the Progenitor Cell Biology Consortium

The rigorous characterization of distinct induced pluripotent stem cells (iPSC) derived from multiple reprogramming technologies, somatic sources, and donors is required to understand potential sources of variability and downstream potential. To achieve this goal, the Progenitor Cell Biology Consortium performed comprehensive experimental and genomic analyses of 58 iPSC from ten laboratories generated using a variety of reprogramming genes, vectors, and cells. Associated global molecular characterization studies identified functionally informative correlations in gene expression, DNA methylation, and/or copy-number variation among key developmental and oncogenic regulators as a result of donor, sex, line stability, reprogramming technology, and cell of origin. Furthermore, X-chromosome inactivation in PSC produced highly correlated differences in teratoma-lineage staining and regulator expression upon differentiation. All experimental results, and raw, processed, and metadata from these analyses, including powerful tools, are interactively accessible from a new online portal at https://www.synapse.org to serve as a reusable resource for the stem cell community.

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Comprehensive portal for diverse iPSC, protocols, metadata, and genomic assays

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Recurrent CNV occur during reprogramming, impact oncogenes and tumor suppressors

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DNA methylation is influenced by cell of origin in iPSC

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PSC X-chromosome inactivation impacts lineage differentiation outcomes

Differentiation of Atrial Cardiomyocytes from Pluripotent Stem Cells Using the BMP Antagonist Grem2

Protocols for generating populations of cardiomyocytes from pluripotent stem cells have been developed, but these generally yield cells of mixed phenotypes. Researchers interested in pursuing studies involving specific myocyte subtypes require a more directed differentiation approach. By treating mouse embryonic stem (ES) cells with Grem2, a secreted BMP antagonist that is necessary for atrial chamber formation in vivo, a large number of cardiac cells with an atrial phenotype can be generated. Use of the engineered Myh6-DSRed-Nuc pluripotent stem cell line allows for identification, selection, and purification of cardiomyocytes. In this protocol embryoid bodies are generated from Myh6-DSRed-Nuc cells using the hanging drop method and kept in suspension until differentiation day 4 (d4). At d4 cells are treated with Grem2 and plated onto gelatin coated plates. Between d8-d10 large contracting areas are observed in the cultures and continue to expand and mature through d14. Molecular, histological and electrophysiogical analyses indicate cells in Grem2-treated cells acquire atrial-like characteristics providing an in vitro model to study the biology of atrial cardiomyocytes and their response to various pharmacological agents.

Origin of Matrix-Producing Cells That Contribute to Aortic Fibrosis in Hypertension

Various hypertensive stimuli lead to exuberant adventitial collagen deposition in large arteries, exacerbating blood pressure elevation and end-organ damage. Collagen production is generally attributed to resident fibroblasts; however, other cells, including resident and bone marrow-derived stem cell antigen positive (Sca-1(+)) cells and endothelial and vascular smooth muscle cells, can produce collagen and contribute to vascular stiffening. Using flow cytometry and immunofluorescence, we found that adventitial Sca-1(+) progenitor cells begin to produce collagen and acquire a fibroblast-like phenotype in hypertension. We also found that bone marrow-derived cells represent more than half of the matrix-producing cells in hypertension, and that one-third of these are Sca-1(+). Cell sorting and lineage-tracing studies showed that cells of endothelial origin contribute to no more than one fourth of adventitial collagen I(+) cells, whereas those of vascular smooth muscle lineage do not contribute. Our findings indicate that Sca-1(+) progenitor cells and bone marrow-derived infiltrating fibrocytes are major sources of arterial fibrosis in hypertension. Endothelial to mesenchymal transition likely also contributes, albeit to a lesser extent and pre-existing resident fibroblasts represent a minority of aortic collagen-producing cells in hypertension. This study shows that vascular stiffening represents a complex process involving recruitment and transformation of multiple cells types that ultimately elaborate adventitial extracellular matrix.

Wnt10b Gain-of-Function Improves Cardiac Repair by Arteriole Formation and Attenuation of Fibrosis

RATIONALE

Myocardial infarction causes irreversible tissue damage, leading to heart failure. We recently discovered that canonical Wnt signaling and the Wnt10b ligand are strongly induced in mouse hearts after infarction. Wnt10b regulates cell fate in various organs, but its role in the heart is unknown.

OBJECTIVE

To investigate the effect of Wnt10b gain-of-function on cardiac repair mechanisms and to assess its potential to improve ventricular function after injury.

METHODS AND RESULTS

Histological and molecular analyses showed that Wnt10b is expressed in cardiomyocytes and localized in the intercalated discs of mouse and human hearts. After coronary artery ligation or cryoinjury in mice, Wnt10b is strongly and transiently induced in peri-infarct cardiomyocytes during granulation tissue formation. To determine the effect of Wnt10b on neovascularization and fibrosis, we generated a mouse line to increase endogenous Wnt10b levels in cardiomyocytes. We found that gain of Wnt10b function orchestrated a recovery phenotype characterized by robust neovascularization of the injury zone, less myofibroblasts, reduced scar size, and improved ventricular function compared with wild-type mice. Wnt10b stimulated expression of vascular endothelial growth factor receptor 2 in endothelial cells and angiopoietin-1 in vascular smooth muscle cells through nuclear factor-κB activation. These effects coordinated endothelial growth and smooth muscle cell recruitment, promoting robust formation of large, coronary-like blood vessels.

CONCLUSION

Wnt10b gain-of-function coordinates arterial formation and attenuates fibrosis in cardiac tissue after injury. Because generation of mature blood vessels is necessary for efficient perfusion, our findings could lead to novel strategies to optimize the inherent repair capacity of the heart and prevent the onset of heart failure.

Gremlin 2 promotes differentiation of embryonic stem cells to atrial fate by activation of the JNK signaling pathway

The bone morphogenetic protein antagonist Gremlin 2 (Grem2) is required for atrial differentiation and establishment of cardiac rhythm during embryonic development. A human Grem2 variant has been associated with familial atrial fibrillation, suggesting that abnormal Grem2 activity causes arrhythmias. However, it is not known how Grem2 integrates into signaling pathways to direct atrial cardiomyocyte differentiation. Here, we demonstrate that Grem2 expression is induced concurrently with the emergence of cardiovascular progenitor cells during differentiation of mouse embryonic stem cells (ESCs). Grem2 exposure enhances the cardiogenic potential of ESCs by 20-120-fold, preferentially inducing genes expressed in atrial myocytes such as Myl7, Nppa, and Sarcolipin. We show that Grem2 acts upstream to upregulate proatrial transcription factors CoupTFII and Hey1 and downregulate atrial fate repressors Irx4 and Hey2. The molecular phenotype of Grem2-induced atrial cardiomyocytes was further supported by induction of ion channels encoded by Kcnj3, Kcnj5, and Cacna1d genes and establishment of atrial-like action potentials shown by electrophysiological recordings. We show that promotion of atrial-like cardiomyocytes is specific to the Gremlin subfamily of BMP antagonists. Grem2 proatrial differentiation activity is conveyed by noncanonical BMP signaling through phosphorylation of JNK and can be reversed by specific JNK inhibitors, but not by dorsomorphin, an inhibitor of canonical BMP signaling. Taken together, our data provide novel mechanistic insights into atrial cardiomyocyte differentiation from pluripotent stem cells and will assist the development of future approaches to study and treat arrhythmias.

Endothelial progenitor cells augment collateralization and hemodynamic rescue in a model of chronic cerebral ischemia

Surgical flow augmentation for treatment of cerebral hemodynamic impairment remains controversial. Here, we investigated the benefit of endothelial progenitor cell (EPC) treatment in a rat model of chronic cerebral hypoperfusion. At repeated time points after 3-vessel occlusion (3-VO), animals were treated with 1 × 10(6) DiI-labeled (a) ex vivo-expanded embryonic-EPC (e-EPC), (b) cyclic AMP-differentiated embryonic-endothelial progenitor-derived cells (e-EPDC as biologic control) or, (c) saline. The cerebrovascular reserve capacity (CVRC) was assessed immediately before and on days 7 and 21 after 3-VO. Structural effects were assessed by latex perfusion, immunohistochemistry, and intravital fluorescence video microscopy on day 21. Three-vessel occlusion resulted in a significant impairment of the CVRC with better functional recovery after treatment with e-EPC (16.4±8%) compared with e-EPDC (3.7±8%) or saline (6.4±9%) by day 21 (P<0.05), which was paralleled by a significant increase in the vessel diameters of the anterior Circle of Willis, a significantly higher number of leptomeningeal anastomoses and higher parenchymal capillary density in e-EPC-treated animals. Interestingly, despite in vivo interaction of e-EPC with the cerebral endothelium, e-EPC incorporation into the cerebral vasculature was not observed. Our results suggest that EPC may serve as a novel therapeutic agent in clinical trials for nonsurgical treatment of chronic cerebral hemodynamic impairment.

Endothelial cells contribute to generation of adult ventricular myocytes during cardiac homeostasis

Cardiac tissue undergoes renewal with low rates. Although resident stem cell populations have been identified to support cardiomyocyte turnover, the source of the cardiac stem cells and their niche remain elusive. Using Cre/Lox-based cell lineage tracing strategies, we discovered that labeling of endothelial cells in the adult heart yields progeny that have cardiac stem cell characteristics and express Gata4 and Sca1. Endothelial-derived cardiac progenitor cells were localized in the arterial coronary walls with quiescent and proliferative cells in the media and adventitia layers, respectively. Within the myocardium, we identified labeled cardiomyocytes organized in clusters of single-cell origin. Pulse-chase experiments showed that generation of individual clusters was rapid but confined to specific regions of the heart, primarily in the right anterior and left posterior ventricular walls and the junctions between the two ventricles. Our data demonstrate that endothelial cells are an intrinsic component of the cardiac renewal process.

SDF-1 fused to a fractalkine stalk and a GPI anchor enables functional neovascularization

The facilitated recruitment of vascular progenitor cells (VPCs) to ischemic areas might be a therapeutic target for neovascularization and repair. However, efficient and directed attraction of VPCs remains a major challenge in clinical application. To enhance VPC homing, we developed a fusion protein (S1FG), based on the biology of stroma-derived factor-1/CXCL12 and the mucin backbone taken from fractalkine/CXCL12. A GPI-anchor was included to link the fusion-protein to the cell surface. HUVECs transfected with S1FG were capable of increasing firm adhesion of CXCR4+-mononuclear cells (THP-1) under shear stress conditions in vitro. In an in vivo rabbit model of chronic hind limb ischemia, local S1FG application enhanced the recruitment of adoptively transferred embryonic EPCs (eEPCs) to the ischemic muscles 2.5-fold. S1FG combined with eEPC(low) (2 × 10(6)) yielded similar capillary growth as eEPC(high) (5 × 10(6)) alone. Compared to controls, collateral formation was increased in the S1FG eEPC(low) group, but not the eEPC(high) group without S1FG, whereas perfusion was found enhanced in both groups. In addition, S1FG also increased collateral formation and flow when combined with AMD3100 treatment, to increase circulating levels of endogenous VPC. These data demonstrate that the fusion protein S1FG is capable of enhancing the recruitment of exogenously applied or endogenously mobilized progenitor cells to sites of injury. Recombinant versions of S1FG applied via catheters in combination with progenitor cell mobilization may be useful in the treatment of chronic ischemic syndromes requiring improved perfusion.

Effect of the use and timing of bone marrow mononuclear cell delivery on left ventricular function after acute myocardial infarction: the TIME randomized trial

CONTEXT

While the delivery of cell therapy after ST-segment elevation myocardial infarction (STEMI) has been evaluated in previous clinical trials, the influence of the timing of cell delivery on the effect on left ventricular function has not been analyzed.

OBJECTIVES

To determine the effect of intracoronary autologous bone marrow mononuclear cell (BMC) delivery after STEMI on recovery of global and regional left ventricular function and whether timing of BMC delivery (3 days vs 7 days after reperfusion) influences this effect.

DESIGN, SETTING, AND PATIENTS

A randomized, 2 × 2 factorial, double-blind, placebo-controlled trial, Timing In Myocardial infarction Evaluation (TIME) enrolled 120 patients with left ventricular dysfunction (left ventricular ejection fraction [LVEF] ≤ 45%) after successful primary percutaneous coronary intervention (PCI) of anterior STEMI between July 17, 2008, and November 15, 2011, as part of the Cardiovascular Cell Therapy Research Network sponsored by the National Heart, Lung, and Blood Institute.

INTERVENTIONS

Intracoronary infusion of 150 × 106 BMCs or placebo (randomized 2:1) within 12 hours of aspiration and cell processing administered at day 3 or day 7 (randomized 1:1) after treatment with PCI.

MAIN OUTCOME MEASURES

The primary end points were change in global (LVEF) and regional (wall motion) left ventricular function in infarct and border zones at 6 months measured by cardiac magnetic resonance imaging and change in left ventricular function as affected by timing of treatment on day 3 vs day 7. The secondary end points included major adverse cardiovascular events as well as changes in left ventricular volumes and infarct size.

RESULTS

The mean (SD) patient age was 56.9 (10.9) years and 87.5% of participants were male. At 6 months, there was no significant increase in LVEF for the BMC group (45.2% [95% CI, 42.8% to 47.6%] to 48.3% [95% CI, 45.3% to 51.3%) vs the placebo group (44.5% [95% CI, 41.0% to 48.0%] to 47.8% [95% CI, 43.4% to 52.2%]) (P = .96). There was no significant treatment effect on regional left ventricular function observed in either infarct or border zones. There were no significant differences in change in global left ventricular function for patients treated at day 3 (−0.9% [95% CI, −6.6% to 4.9%], P = .76) or day 7 (1.1% [95% CI, −4.7% to 6.9%], P = .70). The timing of treatment had no significant effect on regional left ventricular function recovery. Major adverse events were rare among all treatment groups.

CONCLUSION

Among patients with STEMI treated with primary PCI, the administration of intracoronary BMCs at either 3 days or 7 days after the event had no significant effect on recovery of global or regional left ventricular function compared with placebo.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00684021.

Functional modeling in zebrafish demonstrates that the atrial-fibrillation-associated gene GREM2 regulates cardiac laterality, cardiomyocyte differentiation and atrial rhythm

Atrial fibrillation (AF) is the most common cardiac arrhythmia and carries a significant risk of stroke and heart failure. The molecular etiologies of AF are poorly understood, leaving patients with limited therapeutic options. AF has been recognized as an inherited disease in almost 30% of patient cases. However, few genetic loci have been identified and the mechanisms linking genetic variants to AF susceptibility remain unclear. By sequencing 193 probands with lone AF, we identified a Q76E variant within the coding sequence of the bone morphogenetic protein (BMP) antagonist gremlin-2 (GREM2) that increases its inhibitory activity. Functional modeling in zebrafish revealed that, through regulation of BMP signaling, GREM2 is required for cardiac laterality and atrial differentiation during embryonic development. GREM2 overactivity results in slower cardiac contraction rates in zebrafish, and induction of previously identified AF candidate genes encoding connexin-40, sarcolipin and atrial natriuretic peptide in differentiated mouse embryonic stem cells. By live heart imaging in zebrafish overexpressing wild-type or variant GREM2, we found abnormal contraction velocity specifically in atrial cardiomyocytes. These results implicate, for the first time, regulators of BMP signaling in human AF, providing mechanistic insights into the pathogenesis of the disease and identifying potential new therapeutic targets.

Effect of transendocardial delivery of autologous bone marrow mononuclear cells on functional capacity, left ventricular function, and perfusion in chronic heart failure: the FOCUS-CCTRN trial

CONTEXT

Previous studies using autologous bone marrow mononuclear cells (BMCs) in patients with ischemic cardiomyopathy have demonstrated safety and suggested efficacy.

OBJECTIVE

To determine if administration of BMCs through transendocardial injections improves myocardial perfusion, reduces left ventricular end-systolic volume (LVESV), or enhances maximal oxygen consumption in patients with coronary artery disease or LV dysfunction, and limiting heart failure or angina.

DESIGN, SETTING, AND PATIENTS

A phase 2 randomized double-blind, placebo-controlled trial of symptomatic patients (New York Heart Association classification II-III or Canadian Cardiovascular Society classification II-IV) with a left ventricular ejection fraction of 45% or less, a perfusion defect by single-photon emission tomography (SPECT), and coronary artery disease not amenable to revascularization who were receiving maximal medical therapy at 5 National Heart, Lung, and Blood Institute-sponsored Cardiovascular Cell Therapy Research Network (CCTRN) sites between April 29, 2009, and April 18, 2011.

INTERVENTION

Bone marrow aspiration (isolation of BMCs using a standardized automated system performed locally) and transendocardial injection of 100 million BMCs or placebo (ratio of 2 for BMC group to 1 for placebo group).

MAIN OUTCOME MEASURES

Co-primary end points assessed at 6 months: changes in LVESV assessed by echocardiography, maximal oxygen consumption, and reversibility on SPECT. Phenotypic and functional analyses of the cell product were performed by the CCTRN biorepository core laboratory.

RESULTS

Of 153 patients who provided consent, a total of 92 (82 men; average age: 63 years) were randomized (n = 61 in BMC group and n = 31 in placebo group). Changes in LVESV index (-0.9 mL/m(2) [95% CI, -6.1 to 4.3]; P = .73), maximal oxygen consumption (1.0 [95% CI, -0.42 to 2.34]; P = .17), and reversible defect (-1.2 [95% CI, -12.50 to 10.12]; P = .84) were not statistically significant. There were no differences found in any of the secondary outcomes, including percent myocardial defect, total defect size, fixed defect size, regional wall motion, and clinical improvement.

CONCLUSION

Among patients with chronic ischemic heart failure, transendocardial injection of autologous BMCs compared with placebo did not improve LVESV, maximal oxygen consumption, or reversibility on SPECT.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00824005.

Discovering small molecules that promote cardiomyocyte generation by modulating Wnt signaling

We have developed a robust in vivo small-molecule screen that modulates heart size and cardiomyocyte generation in zebrafish. Three structurally related compounds (Cardionogen-1 to Cardionogen-3) identified from our screen enlarge the size of the developing heart via myocardial hyperplasia. Increased cardiomyocyte number in Cardionogen-treated embryos is due to expansion of cardiac progenitor cells. In zebrafish embryos and murine embryonic stem (ES) cells, Cardionogen treatment promotes cardiogenesis during and after gastrulation, whereas it inhibits heart formation before gastrulation. Cardionogen-induced effects can be antagonized by increasing Wnt/β-catenin signaling activity. We demonstrate that Cardionogen inhibits Wnt/β-catenin-dependent transcription in murine ES cells and zebrafish embryos. Cardionogen can rescue Wnt8-induced cardiomyocyte deficiency and heart-specific phenotypes during development. These findings demonstrate that in vivo small-molecule screens targeting heart size can reveal compounds with cardiomyogenic effects and identify underlying target pathways.

Tfap2a and Foxd3 regulate early steps in the development of the neural crest progenitor population

The neural crest is a stem cell-like population exclusive to vertebrates that gives rise to many different cell types including chondrocytes, neurons and melanocytes. Arising from the neural plate border at the intersection of Wnt and Bmp signaling pathways, the complexity of neural crest gene regulatory networks has made the earliest steps of induction difficult to elucidate. Here, we report that tfap2a and foxd3 participate in neural crest induction and are necessary and sufficient for this process to proceed. Double mutant tfap2a (mont blanc, mob) and foxd3 (mother superior, mos) mob;mos zebrafish embryos completely lack all neural crest-derived tissues. Moreover, tfap2a and foxd3 are expressed during gastrulation prior to neural crest induction in distinct, complementary, domains; tfap2a is expressed in the ventral non-neural ectoderm and foxd3 in the dorsal mesendoderm and ectoderm. We further show that Bmp signaling is expanded in mob;mos embryos while expression of dkk1, a Wnt signaling inhibitor, is increased and canonical Wnt targets are suppressed. These changes in Bmp and Wnt signaling result in specific perturbations of neural crest induction rather than general defects in neural plate border or dorso-ventral patterning. foxd3 overexpression, on the other hand, enhances the ability of tfap2a to ectopically induce neural crest around the neural plate, overriding the normal neural plate border limit of the early neural crest territory. Although loss of either Tfap2a or Foxd3 alters Bmp and Wnt signaling patterns, only their combined inactivation sufficiently alters these signaling gradients to abort neural crest induction. Collectively, our results indicate that tfap2a and foxd3, in addition to their respective roles in the differentiation of neural crest derivatives, also jointly maintain the balance of Bmp and Wnt signaling in order to delineate the neural crest induction domain.

Effect of intracoronary delivery of autologous bone marrow mononuclear cells 2 to 3 weeks following acute myocardial infarction on left ventricular function: the LateTIME randomized trial

CONTEXT

Clinical trial results suggest that intracoronary delivery of autologous bone marrow mononuclear cells (BMCs) may improve left ventricular (LV) function when administered within the first week following myocardial infarction (MI). However, because a substantial number of patients may not present for early cell delivery, the efficacy of autologous BMC delivery 2 to 3 weeks post-MI warrants investigation.

OBJECTIVE

To determine if intracoronary delivery of autologous BMCs improves global and regional LV function when delivered 2 to 3 weeks following first MI.

DESIGN, SETTING, AND PATIENTS

A randomized, double-blind, placebo-controlled trial (LateTIME) of the National Heart, Lung, and Blood Institute-sponsored Cardiovascular Cell Therapy Research Network of 87 patients with significant LV dysfunction (LV ejection fraction [LVEF] ≤45%) following successful primary percutaneous coronary intervention (PCI) between July 8, 2008, and February 28, 2011.

INTERVENTIONS

Intracoronary infusion of 150 × 10(6) autologous BMCs (total nucleated cells) or placebo (BMC:placebo, 2:1) was performed within 12 hours of bone marrow aspiration after local automated cell processing.

MAIN OUTCOME MEASURES

Changes in global (LVEF) and regional (wall motion) LV function in the infarct and border zone between baseline and 6 months, measured by cardiac magnetic resonance imaging. Secondary end points included changes in LV volumes and infarct size.

RESULTS

A total of 87 patients were randomized (mean [SD] age, 57 [11] years; 83% men). Harvesting, processing, and intracoronary delivery of BMCs in this setting was feasible. Change between baseline and 6 months in the BMC group vs placebo for mean LVEF (48.7% to 49.2% vs 45.3% to 48.8%; between-group mean difference, -3.00; 95% CI, -7.05 to 0.95), wall motion in the infarct zone (6.2 to 6.5 mm vs 4.9 to 5.9 mm; between-group mean difference, -0.70; 95% CI, -2.78 to 1.34), and wall motion in the border zone (16.0 to 16.6 mm vs 16.1 to 19.3 mm; between-group mean difference, -2.60; 95% CI, -6.03 to 0.77) were not statistically significant. No significant change in LV volumes and infarct volumes was observed; both groups decreased by a similar amount at 6 months vs baseline.

CONCLUSION

Among patients with MI and LV dysfunction following reperfusion with PCI, intracoronary infusion of autologous BMCs vs intracoronary placebo infusion, 2 to 3 weeks after PCI, did not improve global or regional function at 6 months.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00684060.

Role of guanylate binding protein-1 in vascular defects associated with chronic inflammatory diseases

Rheumatic autoimmune disorders are characterized by a sustained pro-inflammatory microenvironment associated with impaired function of endothelial progenitor cells (EPC) and concomitant vascular defects. Guanylate binding protein-1 (GBP-1) is a marker and intracellular regulator of the inhibition of proliferation, migration and invasion of endothelial cells induced by several pro-inflammatory cytokines. In addition, GBP-1 is actively secreted by endothelial cells. In this study, significantly increased levels of GBP-1 were detected in the sera of patients with chronic inflammatory disorders. Accordingly we investigated the function of GBP-1 in EPC. Interestingly, stable expression of GBP-1 in T17b EPC induced premature differentiation of these cells, as indicated by a robust up-regulation of both Flk-1 and von Willebrand factor expression. In addition, GBP-1 inhibited the proliferation and migration of EPC in vitro. We confirmed that GBP-1 inhibited vessel-directed migration of EPC at the tissue level using the rat arterio-venous loop model as a novel quantitative in vivo migration assay. Overall, our findings indicate that GBP-1 contributes to vascular dysfunction in chronic inflammatory diseases by inhibiting EPC angiogenic activity via the induction of premature EPC differentiation.

Continuous antagonism by Dkk1 counter activates canonical Wnt signaling and promotes cardiomyocyte differentiation of embryonic stem cells

Embryonic stem (ES) cells give rise to mesodermal progenitors that differentiate to hematopoietic and cardiovascular cells. The wnt signaling pathway plays multiple roles in cardiovascular development through a network of intracellular effectors. To monitor global changes in wnt signaling during ES cell differentiation, we generated independent ES cell lines carrying the luciferase gene under promoters that uniquely respond to specific wnt pathway branches. Our results show that successive, mutually exclusive waves of noncanonical and canonical wnt signaling precede mesoderm differentiation. Blocking the initial noncanonical JNK/AP-1 signaling with SP60125 aborts cardiovascular differentiation and promotes hematopoiesis, whereas interference with the subsequent peak of canonical wnt signaling using Dkk1 has the opposite effect. Dkk1 blockade triggers counter mechanisms that lead to delayed and extended activation of canonical wnt signaling and mesoderm differentiation that appear to favor the cardiomyocytic lineage at the expense of hematopoietic cells. The cardiomyocytic yield can be further enhanced by overexpression of Wnt11 leading to approximately 95-fold enrichment in contracting cells. Our results suggest that the initial noncanonical wnt signaling is necessary for subsequent activation of canonical signaling and that the latter operates under a regulatory loop which responds to suppression with hyperactivation of compensatory mechanisms. This model provides new insights on wnt signaling during ES cell differentiation and points to a method to induce cardiomyocytic differentiation without precise timing of wnt signaling manipulation. Taking into account the heterogeneity of pluripotent cells, these findings might present an advantage to enhance the cardiogenic potential of stem cells.

Programmatic change: lung disease research in the era of induced pluripotency

Human lung research has made remarkable progress over the last century largely through the use of animal models of disease. The challenge for the future is to translate these findings into human disease and bring about meaningful disease modification or even cure. The ability to generate transformative therapies in the future will require human tissue, currently scarce under the best of circumstances. Unfortunately, patient-derived somatic cells are often poorly characterized and have a limited life span in culture. Moreover, these cells are frequently obtained from patients with end-stage disease exposed to multiple drug therapies, leaving researchers with questions about whether their findings recapitulate disease-initiating processes or are simply the result of pharmacological intervention or subsequent host responses. The goal of studying early disease in multiple cell and tissue types has driven interest in the use of induced pluripotent stem cells (iPSCs) to model lung disease. These cells provide an alternative model for relevant lung research and hold promise in particular for studying the initiation of disease processes in genetic conditions such as heritable pulmonary arterial hypertension as well as other lung diseases. In this Perspective, we focus on potential iPSC use in pulmonary vascular disease research as a model for iPSC use in many types of advanced lung disease.

The feelgood mutation in zebrafish dysregulates COPII-dependent secretion of select extracellular matrix proteins in skeletal morphogenesis

Craniofacial and skeletal dysmorphologies account for the majority of birth defects. A number of the disease phenotypes have been attributed to abnormal synthesis, maintenance and composition of extracellular matrix (ECM), yet the molecular and cellular mechanisms causing these ECM defects remain poorly understood. The zebrafish feelgood mutant manifests a severely malformed head skeleton and shortened body length due to defects in the maturation stage of chondrocyte development. In vivo analyses reveal a backlog of type II and type IV collagens in rough endoplasmic reticulum (ER) similar to those found in coat protein II complex (COPII)-deficient cells. The feelgood mutation hinders collagen deposition in the ECM, but trafficking of small cargos and other large ECM proteins such as laminin to the extracellular space is unaffected. We demonstrate that the zebrafish feelgood mutation causes a single amino acid substitution within the DNA-binding domain of transcription factor Creb3l2. We show that Creb3l2 selectively regulates the expression of genes encoding distinct COPII proteins (sec23a, sec23b and sec24d) but find no evidence for its regulation of sec24c expression. Moreover, we did not detect activation of ER stress response genes despite intracellular accumulation of collagen and prominent skeletal defects. Promoter trans-activation assays show that the Creb3l2 feelgood variant is a hypomorphic allele that retains approximately 50% of its transcriptional activity. Transgenic rescue experiments of the feelgood phenotype restore craniofacial development, illustrating that a precise level of Creb3l2 transcriptional activity is essential for skeletogenesis. Our results indicate that Creb3l2 modulates the availability of COPII machinery in a tissue- and cargo-specific manner. These findings could lead to a better understanding of the etiology of human craniofacial and skeletal birth defects as well as adult-onset diseases that are linked to dysregulated ECM deposition, such as arthritis, fibrosis or osteoporosis.

Nfatc1 coordinates valve endocardial cell lineage development required for heart valve formation

RATIONALE

Formation of heart valves requires early endocardial to mesenchymal transformation (EMT) to generate valve mesenchyme and subsequent endocardial cell proliferation to elongate valve leaflets. Nfatc1 (nuclear factor of activated T cells, cytoplasmic 1) is highly expressed in valve endocardial cells and is required for normal valve formation, but its role in the fate of valve endocardial cells during valve development is unknown.

OBJECTIVE

Our aim was to investigate the function of Nfatc1 in cell-fate decision making by valve endocardial cells during EMT and early valve elongation.

METHODS AND RESULTS

Nfatc1 transcription enhancer was used to generate a novel valve endocardial cell-specific Cre mouse line for fate-mapping analyses of valve endocardial cells. The results demonstrate that a subpopulation of valve endocardial cells marked by the Nfatc1 enhancer do not undergo EMT. Instead, these cells remain within the endocardium as a proliferative population to support valve leaflet extension. In contrast, loss of Nfatc1 function leads to enhanced EMT and decreased proliferation of valve endocardium and mesenchyme. The results of blastocyst complementation assays show that Nfatc1 inhibits EMT in a cell-autonomous manner. We further reveal by gene expression studies that Nfatc1 suppresses transcription of Snail1 and Snail2, the key transcriptional factors for initiation of EMT.

CONCLUSIONS

These results show that Nfatc1 regulates the cell-fate decision making of valve endocardial cells during valve development and coordinates EMT and valve elongation by allocating endocardial cells to the 2 morphological events essential for valve development.

Experimental myocardial infarction triggers canonical Wnt signaling and endothelial-to-mesenchymal transition

Despite available therapies, myocardial infarction (MI) remains a leading cause of death worldwide. Better understanding of the molecular and cellular mechanisms that regulate cardiac repair should help to improve the clinical outcome of MI patients. Using the reporter mouse line TOPGAL, we show that canonical (β-catenin-dependent) Wnt signaling is induced 4 days after experimental MI in subepicardial endothelial cells and perivascular smooth muscle actin (SMA)-positive (SMA⁺) cells. At 1 week after ischemic injury, a large number of canonical-Wnt-positive cells accumulated in the infarct area during granulation tissue formation. Coincidently with canonical Wnt activation, endothelial-to-mesenchymal transition (EndMT) was also triggered after MI. Using cell lineage tracing, we show that a significant portion of the canonical-Wnt-marked SMA⁺ mesenchymal cells is derived from endothelial cells. Canonical Wnt signaling induces mesenchymal characteristics in cultured endothelial cells, suggesting a direct role in EndMT. In conclusion, our study demonstrates that canonical Wnt activation and EndMT are molecular and cellular responses to MI and that canonical Wnt signaling activity is a characteristic property of EndMT-derived mesenchymal cells that take part in cardiac tissue repair after MI. These findings could lead to new strategies to improve the course of cardiac repair by temporal and cell-type-specific manipulation of canonical Wnt signaling.

Neuregulin-1β regulation of embryonic endothelial progenitor cell survival

Endothelial progenitor cells (EPCs) are mobilized into the vascular space and home to damaged tissues, where they promote repair in part through a process of angiogenesis. Neuregulins (NRGs) are ligands in the epidermal growth factor family that signal through type I receptor tyrosine kinases in the erbB family (erbB2, erbB3, and erbB4) and regulate endothelial cell biology, promoting angiogenesis. Stimuli such as ischemia and exercise that promote EPC mobilization also induce cleavage and release of transmembrane NRG from cardiac microvascular endothelial cells (CMECs). We hypothesized that NRG/erbB signaling may regulate EPC biology. Using an embryonic (e)EPC cell line that homes to and repairs injured myocardium, we were able to detect erbB2 and erbB3 transcripts. Identical receptor expression was found in EPCs isolated from rat bone marrow and human whole blood. NRG treatment of eEPCs induces phosphorylation of kinases including Akt, GSK-3β, and Erk1/2 and the nuclear accumulation and transcriptional activation of β-catenin. NRG does not induce eEPC proliferation or migration but does protect eEPCs against serum deprivation-induced apoptosis. These results suggest a role for tissue-derived NRG in the regulation of EPC survival.

Thymosin beta4: a key factor for protective effects of eEPCs in acute and chronic ischemia

Acute myocardial infarction is still one of the leading causes of death in the industrial nations. Even after successful revascularization, myocardial ischemia results in a loss of cardiomyocytes and scar formation. Embryonic EPCs (eEPCs), retroinfused into the ischemic region of the pig heart, provided rapid paracrine benefit to acute and chronic ischemia in a PI-3K/Akt-dependent manner. In a model of acute myocardial ischemia, infarct size and loss of regional myocardial function decreased after eEPC application, unless cell pre-treatment with thymosin beta4 shRNA was performed. Thymosin beta4 peptide retroinfusion mimicked the eEPC-derived improvement of infarct size and myocardial function. In chronic ischemia (rabbit model), eEPCs retroinfused into the ischemic hindlimb enhanced capillary density, collateral growth, and perfusion. Therapeutic neovascularization was absent when thymosin beta4 shRNA was introduced into eEPCs before application. In conclusion, eEPCs are capable of acute and chronic ischemia protection in a thymosin beta4 dependent manner.

NF kappaB activation in embryonic endothelial progenitor cells enhances neovascularization via PSGL-1 mediated recruitment: novel role for LL37

Embryonal endothelial progenitor cells (eEPCs) are capable of inducing therapeutic angiogenesis in a chronic hind limb model. However, the proportion of eEPCs recruited to the ischemic tissue appears to be a limiting step for the induction of cell-based therapeutic neovascularization. In the present study, we primed eEPCs with the human cathelicidin LL37 (hCAP-18) ex vivo to selectively enhance the eEPC-dependent gain of perfusion in vivo and elucidated the mechanism of action of LL37 on eEPCs. Seven days after femoral artery excision, 5 x 10(6) eEPCs (wt, wild type; p65t, transiently p65 transient; p65s, stable p65-transfected; LL37-eEPCs, LL37 peptide preincubated) were retroinfused into the anterior tibial vein. Recruitment of diI-labeled eEPCs in the ischemic gastrocnemic muscle was investigated 2 days later, whereas collateral growth and perfusion score (obtained by fluorescent microspheres) were assessed at day 7 and day 35 and are given as percentage of day 7 level. Capillary/muscle fiber ratio in the ischemic lower limb was obtained at day 35. Embryonic EPC recruitment in vitro and in vivo was found elevated after LL37 and p65t pretreatment, but not in p65s-eEPCs displaying increased IkappaBalpha or after LL37 in IkappaB-DN overexpressing eEPCs. Using LL37- and p65t-eEPCs, collateral growth (181 +/- 10% and 165 +/- 8%, respectively) surpassed that of wt-eEPCs (135 +/- 7%), increasing perfusion ratio (208 +/- 20% and 210 +/- 17% vs. 142 +/- 12% in wt-eEPCs, respectively), whereas p65s-eEPCs exerted no additive effect (collateral growth 130 +/- 8%; perfusion ratio 155 +/- 15%). Moreover, p65t-eEPC-induced neovascularization was abrogated by blocking antibodies against E-selectin and P-selectin glycoprotein ligand-1 (PSGL-1). We conclude that NF kappaB activation by LL37 or transient p65-transfection increases functionally relevant eEPC recruitment to ischemic muscle tissue via induction of PSGL-1 and E-selectin.

Endothelial progenitors encapsulated in bioartificial niches are insulated from systemic cytotoxicity and are angiogenesis competent

Intrinsic stem cells (SC) participate in tissue remodeling and regeneration in various diseases and following toxic insults. Failure of tissue regeneration is in part attributed to lack of SC protection from toxic stress of noxious stimuli, thus prompting intense research efforts to develop strategies for SC protection and functional preservation for in vivo delivery. One strategy is creation of artificial SC niches in an attempt to mimic the requirements of endogenous SC niches by generating scaffolds with properties of extracellular matrix. Here, we investigated the use of hyaluronic acid (HA) hydrogels as an artificial SC niche and examined regenerative capabilities of encapsulated embryonic endothelial progenitor cells (eEPC) in three different in vivo models. Hydrogel-encapsulated eEPC demonstrated improved resistance to toxic insult (adriamycin) in vitro, thus prompting in vivo studies. Implantation of HA hydrogels containing eEPC to mice with adriamycin nephropathy or renal ischemia resulted in eEPC mobilization to injured kidneys (and to a lesser extent to the spleen) and improvement of renal function, which was equal or superior to adoptively transferred EPC by intravenous infusion. In mice with hindlimb ischemia, EPC encapsulated in HA hydrogels dramatically accelerated the recovery of collateral circulation with the efficacy superior to intravenous infusion of EPC. In conclusion, HA hydrogels protect eEPC against adriamycin cytotoxicity and implantation of eEPC encapsulated in HA hydrogels supports renal regeneration in ischemic and cytotoxic (adriamycin) nephropathy and neovascularization of ischemic hindlimb, thus establishing their functional competence and superior capabilities to deliver stem cells stored in and released from this bioartificial niche.

Adriamycin nephropathy: a failure of endothelial progenitor cell-induced repair

Adriamycin-associated nephropathy (AAN) remains poorly understood. We hypothesized that adriamycin affects endothelial progenitor cells (EPCs), leading to impaired regeneration. We analyzed renal hematopoietic stem cells (HSCs) and EPCs in mice with AAN and examined the potential contribution of adoptive transfer of intact EPCs to the repair processes. FACS analyses revealed that populations of HSCs and EPCs were scarcely represented in control kidneys and did not change numerically in kidneys obtained from mice with AAN. The observed defect in engraftment was attributable to the decreased viability and increased senescence of EPCs. Adoptive transfer of intact EPCs improved proteinuria and renal function, with a threefold decrease in mortality. Infusion of EPCs to adriamycin-treated mice reduced plasma levels of interleukin-1alpha and -beta and granulocyte-colony stimulating factor as well as increased the level of vascular endothelial growth factor with concomitant improvement of vascular density and reduction of apoptosis. An additional mechanism of tissue repair is proposed based on tunneling nanotube formation between EPCs and endothelial cells exposed to adriamycin, leading to the multiple rounds of exchange between EPCs and mature cells. In conclusion, AAN is associated with development of EPC incompetence; adoptive transfer of intact EPCs blunts morphological and functional manifestations of AAN; and the proposed mechanisms of repair by EPCs include direct incorporation into blood vessels, paracrine signaling, and tunneling nanotube renewal of mitochondrial pool in endothelial cells.

LateTIME: a phase-II, randomized, double-blinded, placebo-controlled, pilot trial evaluating the safety and effect of administration of bone marrow mononuclear cells 2 to 3 weeks after acute myocardial infarction

A realistic goal for cardiac cell therapy may be to attenuate left ventricular remodeling following acute myocardial infarction to prevent the development of congestive heart failure. Initial clinical trials of cell therapy have delivered cells 1 to 7 days after acute myocardial infarction. However, many patients at risk of developing congestive heart failure may not be ready for cell delivery at that time-point because of clinical instability or hospitalization at facilities without access to cell therapy. Experience with cell delivery 2 to 3 weeks after acute myocardial infarction has not to date been explored in a clinical trial. The objective of the LateTIME study is to evaluate by cardiac magnetic resonance the effect on global and regional left ventricular function, between baseline and 6 months, of a single intracoronary infusion of 150 × 106 autologous bone marrow mononuclear cells (compared with placebo) when that infusion is administered 2 to 3 weeks after moderate-to-large acute myocardial infarction. The 5 clinical sites of the Cardiovascular Cell Therapy Research Network (CCTRN) will enroll a total of 87 eligible patients in a 2:1 bone marrow mononuclear cells-to-placebo patient ratio; these 87 will have undergone successful percutaneous coronary intervention of a major coronary artery and have left ventricular ejection fractions ≤0.45 by echocardiography. When the results become available, this study should provide insight into the clinical feasibility and appropriate timing of autologous cell therapy in high-risk patients after acute myocardial infarction and percutaneous coronary intervention.

Stem cell therapy: pieces of the puzzle

Acute ischemic injury and chronic cardiomyopathies can cause irreversible loss of cardiac tissue leading to heart failure. Cellular therapy offers a new paradigm for treatment of heart disease. Stem cell therapies in animal models show that transplantation of various cell preparations improves ventricular function after injury. The first clinical trials in patients produced some encouraging results, despite limited evidence for the long-term survival of transplanted cells. Ongoing research at the bench and the bedside aims to compare sources of donor cells, test methods of cell delivery, improve myocardial homing, bolster cell survival, and promote cardiomyocyte differentiation. This article reviews progress toward these goals.

T17b murine embryonal endothelial progenitor cells can be induced towards both proliferation and differentiation in a fibrin matrix

Endothelial progenitor cells (EPC) may enhance blood vessel formation in a variety of clinical settings such as ischaemia and tumour angiogenesis as well as in tissue-engineered matrices. In the present study, we cultured a murine endothelial progenitor cell line, T17b, in vitro in cell culture as well as in an FDA-approved fibrin matrix and investigated cell proliferation, differentiation and secretion patterns of the angiogenic growth factor VEGF under hypoxia and differentiation. We show that T17b EPC remain viable for at least 8 days in the fibrin matrix where they proliferate and form clusters including lumen-like structures. Proliferation in fibrin clots overlayed with basal medium (BM) was confirmed morphologically and immunohistochemically by positive Ki67 staining, indicating mitotic activity. Significant cell proliferation and Ki-67 expression were absent when cells were incubated with dibutyryl-cAMP and retinoic acid (RA). Incubation with dibutyryl-cAMP and RA stimulated the expression of the EPC differentiation markers von Willebrand Factor (vWF) and VEGF receptor 2 (VEGFR-2), indicating successful differentiation in the fibrin clot. EPC differentiation induced by dibutyryl-cAMP and RA was confirmed in 2-D chamber slide cultures by positive vWF immunostaining, which was absent in BM controls. EPC chamber slides also displayed positive vWF staining when exposed to hypoxia under BM conditions, indicating EPC activation and differentiation could also be induced by hypoxia. Taken together, T17b EPC secrete increased levels of VEGF when submitted to either hypoxia or differentiation and can be differentiated into mature endothelial cells not only in cell and matrigel cultures but also in a fibrin matrix that is FDA approved for clinical application.

The FunGenES database: a genomics resource for mouse embryonic stem cell differentiation

Embryonic stem (ES) cells have high self-renewal capacity and the potential to differentiate into a large variety of cell types. To investigate gene networks operating in pluripotent ES cells and their derivatives, the “Functional Genomics in Embryonic Stem Cells” consortium (FunGenES) has analyzed the transcriptome of mouse ES cells in eleven diverse settings representing sixty-seven experimental conditions. To better illustrate gene expression profiles in mouse ES cells, we have organized the results in an interactive database with a number of features and tools. Specifically, we have generated clusters of transcripts that behave the same way under the entire spectrum of the sixty-seven experimental conditions; we have assembled genes in groups according to their time of expression during successive days of ES cell differentiation; we have included expression profiles of specific gene classes such as transcription regulatory factors and Expressed Sequence Tags; transcripts have been arranged in “Expression Waves” and juxtaposed to genes with opposite or complementary expression patterns; we have designed search engines to display the expression profile of any transcript during ES cell differentiation; gene expression data have been organized in animated graphs of KEGG signaling and metabolic pathways; and finally, we have incorporated advanced functional annotations for individual genes or gene clusters of interest and links to microarray and genomic resources. The FunGenES database provides a comprehensive resource for studies into the biology of ES cells.

Cardiac repair and regeneration: the Rubik's cube of cell therapy for heart disease

Acute ischemic injury and chronic cardiomyopathies damage healthy heart tissue. Dead cells are gradually replaced by a fibrotic scar, which disrupts the normal electromechanical continuum of the ventricular muscle and compromises its pumping capacity. Recent studies in animal models of ischemic cardiomyopathy suggest that transplantation of various stem cell preparations can improve heart recovery after injury. The first clinical trials in patients produced some encouraging results, showing modest benefits. Most of the positive effects are probably because of a favorable paracrine influence of stem cells on the disease microenvironment. Stem cell therapy attenuates inflammation, reduces apoptosis of surrounding cells, induces angiogenesis, and lessens the extent of fibrosis. However, little new heart tissue is formed. The current challenge is to find ways to improve the engraftment, long-term survival and appropriate differentiation of transplanted stem cells within the cardiovascular tissue. Hence, there has been a surge of interest in pluripotent stem cells with robust cardiogenic potential, as well as in the inherent repair and regenerative mechanisms of the heart. Recent discoveries on the biology of adult stem cells could have relevance for cardiac regeneration. Here, we discuss current developments in the field of cardiac repair and regeneration, and present our ideas about the future of stem cell therapy.

Rafs constitute a nodal point in the regulation of embryonic endothelial progenitor cell growth and differentiation

Mouse embryonic endothelial progenitor cells (eEPCs) acquire a mature phenotype after treatment with cyclic adenosine monophosphate (cAMP), suggesting an involvement of Raf serine/threonine kinases in the differentiation process. To test this idea, we investigated the role of B-Raf and C-Raf in proliferation and differentiation of eEPCs by expressing fusion proteins consisting of the kinase domains from Raf molecules and the hormone binding site of the estrogen receptor (ER), or its variant, the tamoxifen receptor. Our findings show that both B- and C-Raf kinase domains, when lacking adjacent regulatory parts, are equally effective in inducing eEPC differentiation. In contrast, the C-Raf kinase domain is a more potent stimulator of eEPC proliferation than B-Raf. In a complimentary approach, we used siRNA silencing to knockdown endogenously expressed B-Raf and C-Raf in eEPCs. In this experimental setting, we found that eEPCs lacking B-Raf failed to differentiate, whereas loss-of C-Raf function primarily slowed cell growth without impairing cAMP-induced differentiation. These findings were further corroborated in B-Raf null eEPCs, isolated from the corresponding knockout embryos, which failed to differentiate in vitro. Thus, gain- and loss-of-function experiments point to distinct roles of B-Raf and C-Raf in regulating growth and differentiation of endothelial progenitor cells, which may harbour therapeutic implications.

Egr-1 regulates expression of the glial scar component phosphacan in astrocytes after experimental stroke

Ischemic brain injury causes tissue damage and neuronal death. The deficits can often be permanent because adult neurons fail to regenerate. One barrier to neuronal regeneration is the formation of the glial scar, a repair mechanism that is otherwise necessary to seal off necrotic areas. The process of gliosis has been well described, but the mechanisms regulating the robust production of scar components after injury remain poorly understood. Here we show that the early growth response 1 transcriptional factor (Egr-1, also called Krox24, Zif268, and NGFI-A) is expressed in astrocytes in the ventricular wall, corpus callosum, and striatum of normal mouse brain. After experimental stroke caused by permanent occlusion of the middle cerebral artery, Egr-1 was expressed long term in reactive astrocytes that accumulate around the injury site. Gain- and loss-of-function studies in primary astrocytes indicated that Egr-1 regulates the transcription of chondroitin sulfate proteoglycans genes, the main extracellular matrix proteins of the glial scar. Egr-1 bound to a site within the phosphacan promoter and transactivated its expression. Egr-1-deficient mice accumulated lower levels of phosphacan RNA and protein than wild-type mice after stroke, but there were no measurable differences in neurite outgrowth toward the infarct area between the two groups. Our findings suggest that Egr-1 is an important component of the transcriptional network regulating genes involved in gliosis after ischemic injury.

B-Raf-mediated signaling pathway regulates T cell development

The activities of the Raf kinase family proteins control extracellular signal-regulated kinase (ERK) activation in many aspects of cellular responses. However, the relative contributions of individual isozymes to cellular functions including T cell responses are still unclear. In addition to Raf-1, another Raf family kinase, B-Raf, is expressed in murine thymocytes and peripheral T cells, and its activation was induced by TCR stimulation. Here, we investigated the function of B-Raf in development of T cells by generating chimeric mice in which a T cell-compromised host was reconstituted with fetal liver-derived cells from embryonic lethal B-Raf-deficient mice. Although B-Raf was dispensable for normal T cell lineage differentiation at the CD4(-)CD8(-) double-negative stage, thymocytes in the chimeric mice derived from B-Raf(-/-) cells exhibited a drastic arrest of differentiation at the CD4(+)CD8(+) double-positive stage, suggesting that B-Raf is crucial for T cell development, especially for the transition to CD4(+) and CD8(+) single-positive thymocytes. Regarding intracellular signaling, we found that activation of ERK following TCR stimulation was impaired in the thymocytes from the chimeric mice. In conclusion, we present first evidence for the important role of B-Raf-mediated signaling in T cell development.

Thymosin beta4 is an essential paracrine factor of embryonic endothelial progenitor cell-mediated cardioprotection

BACKGROUND

Prolonged myocardial ischemia results in cardiomyocyte loss despite successful revascularization. We have reported that retrograde application of embryonic endothelial progenitor cells (eEPCs) provides rapid paracrine protection against ischemia-reperfusion injury. Here, we investigated the role of thymosin beta4 (Tbeta4) as a mediator of eEPC-mediated cardioprotection.

METHODS AND RESULTS

In vitro, neonatal rat cardiomyocytes were subjected to hypoxia-reoxygenation in the absence or presence of eEPCs with or without Tbeta4 short hairpin RNA (shRNA) transfection. In vivo, pigs (n=9 per group) underwent percutaneous left anterior descending artery occlusion for 60 minutes on day 1. After 55 minutes of ischemia, control eEPCs (5x10(6) cells) or cells transfected with Tbeta4 shRNA when indicated or 15 mg Tbeta4 alone were retroinfused into the anterior interventricular vein. Segmental endocardial shortening in the infarct zone at 150-bpm atrial pacing, infarct size (triphenyl tetrazolium chloride viability and methylene blue exclusion), and inflammatory cell influx (myeloperoxidase activity) were determined 24 hours later. Survival of neonatal rat cardiomyocytes increased from 32+/-4% to 90+/-2% after eEPC application, an effect sensitive to shRNA transfection compared with Tbeta4 (45+/-7%). In vivo, infarct size decreased with eEPC application (38+/-4% versus 54+/-4% of area at risk; P<0.01), an effect abolished by Tbeta4 shRNA (62+/-3%). Segmental subendocardial shortening improved after eEPC treatment (22+/-3% versus -3+/-4% of control area) unless Tbeta4 shRNA was transfected (-6+/-4%). Retroinfusion of Tbeta4 mimicked eEPC application (infarct size, 37+/-3%; segmental endocardial shortening, 34+/-7%). Myeloperoxidase activity (3323+/-388 U/mg in controls) was decreased by eEPCs (1996+/-546 U/mg) or Tbeta4 alone (1455+/-197 U/mg) but not Tbeta4 shRNA-treated eEPCs (5449+/-829 U/mg).

CONCLUSIONS

Our findings show that short-term cardioprotection derived by regional application of eEPCs can be attributed, at least in part, to Tbeta4.

Proteins of the secretory pathway govern virus productivity during lytic gammaherpesvirus infection

Background: Diseases caused by gammaherpesviruses continue to be a challenge for human health and antiviral treatment. Most of the commonly used antiviral drugs are directed against viral gene products. However, the emergence of drug-resistant mutations ma limit the effectiveness of these drugs. Since viruses require a host cell to propagate, the search for host cell targets is an interestin alternative. Methods: In this study, we infected three different cell types (fibroblasts, endothelial precursor cells and macrophages with a murine gammaherpesvirus and analysed the host cell response for changes either common to all or unique to a particular cell type using oligonucleotide microarrays. Results: The analysis revealed a number of genes whose transcription was significantly up- or down-regulated in either one or two of the cell types tested. After infection, only two genes, Lman1 (also known as ERGIC53) an synaptobrevin-like 1 (sybl1) were significantly up-regulated in all three cell types, suggestive for a general role for the virus life cycl independent of the cell type. Both proteins have been implicated in cellular exocytosis and transport of glycoproteins through the secre tory pathway. To test the significance of the observed up-regulation, the functionality of these proteins was modulated, and the effect on virus replication was monitored. Inhibition of either Lman1 or sybl1 resulted in a significant reduction in virus production. Conclusions: This suggests that proteins of the secretory pathway which appear to be rate limiting for virus production may represent new targets for intervention.