Human embryonic stem cell-derived cardiovascular progenitor cells efficiently colonize in bFGF-tethered natural matrix to construct contracting humanized rat hearts.

Bioengineering of whole hearts using human embryonic stem cells (hESCs)-derived cardiovascular progenitor cells (CPCs) and natural matrices is a promising approach to overcome organ donor shortage threatening millions of patients awaiting for heart transplantation. Here, we developed a novel strategy for generation of heart constructs by repopulating engineered decellularized rat hearts using hESCs-derived CPCs. Careful expansion of CPCs in a scalable stirred-suspension bioreactor combined with step-wise seeding (60 million cells in 3 steps of 20 million per 1.5 h) onto decellularized hearts containing immobilized basic fibroblast growth factor (bFGF) resulted in improved retention of CPCs and differentiation to cardiomyocytes, smooth muscle cells and endothelial cells as evaluated by immunohistochemistry and qRT-PCR. We observed spontaneous and synchronous contractions of humanized hearts after 12 days of perfusion as well as advanced alignment of myofilaments. Our study provides a robust platform for generation of artificial human hearts and resolves major bottlenecks hindering further development of this technology.

The effects of polyunsaturated fatty acids and antioxidant vitamins on atrial oxidative stress, nitrotyrosine residues, and connexins following extracorporeal circulation in patients undergoing cardiac surgery.

Cardiac surgery with extracorporeal circulation is characterized by different degrees of myocardial ischemia/reperfusion, which is often associated with postoperative atrial fibrillation (POAF). We have previously shown that a novel preventive therapy based on the reinforcement of the antioxidant system using omega-3 fatty acids plus antioxidant vitamin supplementation applied to patients undergoing cardiac surgery reduces POAF occurrence. We hypothesized that oxidative stress and nitrosative stress are involved in the development of an arrhythmogenic substrate by their effect on connexins (Cx40, Cx43 and Cx45) abundance and distribution pattern. Therefore, we have assessed the effect of redox status on atrial tissue in patients undergoing cardiac surgery. Placebo/POAF and supplemented/POAF patients showed 276 and 170% higher reactive oxygen species (ROS) levels and 223 and 96% higher nitrotyrosine residues levels, respectively, compared to sinus rhythm (SR). In POAF tissue, antioxidant supplementation prevented Cx40 and Cx43 lateralization on cardiomyocyte sarcolemma, keeping them at the intercalated disks. POAF samples showed Cx40 heterogeneous distribution pattern, presenting tissue areas lacking this protein (49 and 55% lower levels in placebo/POAF and supplemented/POAF groups, respectively, compared to SR). Of note, Cx45 overexpression occurred in POAF, being 211 and 167% higher in placebo/POAF and supplemented/POAF groups, respectively, compared to SR. It is concluded that treatment with omega-3 fatty acids and antioxidant vitamins reduces oxidative and nitrosative stress and prevents Cx40/Cx43 lateralization in atrial tissue likely contributing to POAF prevention. However, it failed to fully prevent POAF occurrence because these compounds have no effects on the normalization of Cx40 down-regulation and Cx45 up-regulation, which may promote POAF.

BRAF activates PAX3 to control muscle precursor cell migration during forelimb muscle development.

Migration of skeletal muscle precursor cells is a key step during limb muscle development and depends on the activity of PAX3 and MET. Here, we demonstrate that BRAF serves a crucial function in formation of limb skeletal muscles during mouse embryogenesis downstream of MET and acts as a potent inducer of myoblast cell migration. We found that a fraction of BRAF accumulates in the nucleus after activation and endosomal transport to a perinuclear position. Mass spectrometry based screening for potential interaction partners revealed that BRAF interacts and phosphorylates PAX3. Mutation of BRAF dependent phosphorylation sites in PAX3 impaired the ability of PAX3 to promote migration of C2C12 myoblasts indicating that BRAF directly activates PAX3. Since PAX3 stimulates transcription of the Met gene we propose that MET signaling via BRAF fuels a positive feedback loop, which maintains high levels of PAX3 and MET activity required for limb muscle precursor cell migration.

ZBTB17 (MIZ1) Is Important for the Cardiac Stress Response and a Novel Candidate Gene for Cardiomyopathy and Heart Failure.

BACKGROUND: Mutations in sarcomeric and cytoskeletal proteins are a major cause of hereditary cardiomyopathies, but our knowledge remains incomplete as to how the genetic defects execute their effects. METHODS AND RESULTS: We used cysteine and glycine-rich protein 3, a known cardiomyopathy gene, in a yeast 2-hybrid screen and identified zinc-finger and BTB domain-containing protein 17 (ZBTB17) as a novel interacting partner. ZBTB17 is a transcription factor that contains the peak association signal (rs10927875) at the replicated 1p36 cardiomyopathy locus. ZBTB17 expression protected cardiac myocytes from apoptosis in vitro and in a mouse model with cardiac myocyte-specific deletion of Zbtb17, which develops cardiomyopathy and fibrosis after biomechanical stress. ZBTB17 also regulated cardiac myocyte hypertrophy in vitro and in vivo in a calcineurin-dependent manner. CONCLUSIONS: We revealed new functions for ZBTB17 in the heart, a transcription factor that may play a role as a novel cardiomyopathy gene.

Myocardial healing requires Reg3ß-dependent accumulation of macrophages in the ischemic heart.

Cardiac healing after myocardial ischemia depends on the recruitment and local expansion of myeloid cells, particularly macrophages. Here we identify Reg3ß as an essential regulator of macrophage trafficking to the damaged heart. Using mass spectrometry-based secretome analysis, we found that dedifferentiating cardiomyocytes release Reg3ß in response to the cytokine OSM, which signals through Jak1 and Stat3. Loss of Reg3ß led to a large decrease in the number of macrophages in the ischemic heart, accompanied by increased ventricular dilatation and insufficient removal of neutrophils. This defect in neutrophil removal in turn caused enhanced matrix degradation, delayed collagen deposition and increased susceptibility to cardiac rupture. Our data indicate that OSM, acting through distinct intracellular pathways, regulates both cardiomyocyte dedifferentiation and cardiomyocyte-dependent regulation of macrophage trafficking. Release of OSM from infiltrating neutrophils and macrophages initiates a positive feedback loop in which OSM-induced production of Reg3ß in cardiomyocytes attracts additional OSM-secreting macrophages. The activity of the feedback loop controls the degree of macrophage accumulation in the heart, which is instrumental in myocardial healing.

Phenotypical and ultrastructural features of Oct4-positive cells in the adult mouse lung.

Octamer binding trascription factor 4 (Oct4) is a transcription factor of POU family specifically expressed in embryonic stem cells (ESCs). A role for maintaining pluripotency and self-renewal of ESCs is assigned to Oct4 as a pluripotency marker. Oct4 can also be detected in adult stem cells such as bone marrow-derived mesenchymal stem cells. Several studies suggest a role for Oct4 in sustaining self-renewal capacity of adult stem cells. However, Oct4 gene ablation in adult stem cells revealed no abnormalities in tissue turnover or regenerative capacity. In the present study we have conspicuously found pulmonary Oct4-positive cells closely resembling the morphology of telocytes (TCs). These cells were found in the perivascular and peribronchial areas and their presence and location were confirmed by electron microscopy. Moreover, we have used Oct4-GFP transgenic mice which revealed a similar localization of the Oct4-GFP signal. We also found that Oct4 co-localized with several described TC markers such as vimentin, Sca-1, platelet-derived growth factor receptor-beta C-kit and VEGF. By flow cytometry analyses carried out with Oct4-GFP reporter mice, we described a population of EpCAM(neg) /CD45(neg) /Oct4-GFP(pos) that in culture displayed TC features. These results were supported by qRT-PCR with mRNA isolated from lungs by using laser capture microdissection. In addition, Oct4-positive cells were found to express Nanog and Klf4 mRNA. It is concluded for the first time that TCs in adult lung mouse tissue comprise Oct4-positive cells, which express pluripotency-related genes and represent therefore a population of adult stem cells which might contribute to lung regeneration.

Role of extracellular RNA in atherosclerotic plaque formation in mice.

BACKGROUND: Atherosclerosis and vascular remodeling after injury are driven by inflammation and mononuclear cell infiltration. Extracellular RNA (eRNA) has recently been implicated to become enriched at sites of tissue damage and to act as a proinflammatory mediator. Here, we addressed the role of eRNA in high-fat diet-induced atherosclerosis and neointima formation after injury in atherosclerosis-prone mice. METHODS AND RESULTS: The presence of eRNA was revealed in atherosclerotic lesions from high-fat diet-fed low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice in a time-progressive fashion. RNase activity in plasma increased within the first 2 weeks (44±9 versus 70±7 mU/mg protein; P=0.0012), followed by a decrease to levels below baseline after 4 weeks of high-fat diet (44±9 versus 12±2 mU/mg protein; P<0.0001). Exposure of bone marrow-derived macrophages to eRNA resulted in a concentration-dependent upregulation of the proinflammatory mediators tumor necrosis factor-α, arginase-2, interleukin-1ß, interleukin-6, and interferon-γ. In a model of accelerated atherosclerosis after arterial injury in apolipoprotein E-deficient (ApoE(-/-)) mice, treatment with RNase1 diminished the increased plasma level of eRNA evidenced after injury. Likewise, RNase1 administration reduced neointima formation in comparison with vehicle-treated ApoE(-/-) controls (25.0±6.2 versus 46.9±6.9×10(3) µm(2), P=0.0339) and was associated with a significant decrease in plaque macrophage content. Functionally, RNase1 treatment impaired monocyte arrest on activated smooth muscle cells under flow conditions in vitro and inhibited leukocyte recruitment to injured carotid arteries in vivo. CONCLUSIONS: Because eRNA is associated with atherosclerotic lesions and contributes to inflammation-dependent plaque progression in atherosclerosis-prone mice, its targeting with RNase1 may serve as a new treatment option against atherosclerosis.

Treatment with bone morphogenetic protein 2 limits infarct size after myocardial infarction in mice.

Various strategies have been devised to reduce the clinical consequences of myocardial infarction, including acute medical care, revascularization, stem cell transplantations, and more recently, prevention of cardiomyocyte cell death. Activation of embryonic signaling pathways is a particularly interesting option to complement these strategies and to improve the functional performance and survival rate of cardiomyocytes. Here, we have concentrated on bone morphogenetic protein 2 (BMP-2), which induces ectopic formation of beating cardiomyocytes during development in the mesoderm and protects neonatal cardiomyocytes from ischemia-reperfusion injury. In a mouse model of acute myocardial infarction, an i.v. injection of BMP-2 reduced infarct size in mice when given after left anterior descending artery ligation. Mice treated with BMP-2 are characterized by a reduced rate of apoptotic cardiomyocytes both in the border zone of the infarcts and in the remote myocardium. In vitro, BMP-2 increases the frequency of spontaneously beating neonatal cardiomyocytes and the contractile performance under electrical pacing at 2 Hz, preserves cellular adenosine triphosphate stores, and decreases the rate of apoptosis despite the increased workload. In addition, BMP-2 specifically induced phosphorylation of Smad1/5/8 proteins and protected adult cardiomyocytes from long-lasting hypoxia-induced cellular damage and oxidative stress without activation of the cardiodepressant transforming growth factor-ß pathway. Our data suggest that BMP-2 treatment may have considerable therapeutic potential in individuals with acute and chronic myocardial ischemia by improving the contractility of cardiomyocytes and preventing cardiomyocyte cell death.

Regression of cardiac hypertrophy by granulocyte colony-stimulating factor-stimulated interleukin-1ß synthesis.

AIMS: Aortic stenosis causes cardiac hypertrophy and fibrosis, which often persists despite pressure unloading after aortic valve replacement. The persistence of myocardial fibrosis in particular leads to impaired cardiac function and increased mortality. We investigated whether granulocyte colony-stimulating factor (G-CSF) beneficially influences cardiac remodelling after pressure unloading. METHODS AND RESULTS: Left ventricular hypertrophy was induced by transverse aortic constriction in C57bl6 mice followed by debanding after 8 weeks. This model closely mimics aortic stenosis and subsequent aortic valve replacement. After debanding, mice were treated with either G-CSF or saline injection. Granulocyte colony-stimulating factor treatment significantly improved systolic (ejection fraction 70.48 ± 1.17 vs. 58.41 ± 1.56%, P < 0.001) and diastolic (E/E' 26.0 ± 1.0 vs. 32.6 ± 0.8, P < 0.05) function. Furthermore, cardiac fibrosis was significantly reduced in G-CSF-treated mice (collagen-I area fraction 7.96 ± 0.47 vs. 11.64 ± 1.22%, P < 0.05; collagen-III area fraction 10.73 ± 0.99 vs. 18.46 ± 0.71%, P < 0.001). Direct effects of G-CSF on cardiac fibroblasts or a relevant transdifferentiation of mobilized bone marrow cells could be excluded. However, a considerable infiltration of neutrophils was observed in G-CSF-treated mice. This sterile inflammation was accompanied by a selective release of interleukin-1 ß (IL-1ß) in the absence of other proinflammatory cytokines. In vitro experiments confirmed an increased expression of IL-1ß in neutrophils after G-CSF treatment. Interleukin-1ß directly induced the expression of the gelatinases matrix metalloproteinase-2 (MMP-2) and MMP-9 in cardiac fibroblasts thereby providing the regression of cardiac fibrosis. CONCLUSION: Granulocyte colony-stimulating factor treatment improves the cardiac function and leads to the regression of myocardial fibrosis after pressure unloading. These findings reveal a previously unknown mechanism of fibrosis regression. Granulocyte colony-stimulating factor might be a potential pharmacological treatment approach for patients suffering from congestive heart failure after aortic valve replacement, although further basic research and clinical trials are required in order to prove beneficial effects of G-CSF in the human organism.

Platelet-derived growth factor receptor-ß-positive telocytes in skeletal muscle interstitium.

Telocytes (TCs) represent a new cell type recently described in mammalian skeletal muscle interstitium as well as in other organs. These have a specific morphology and phenotype, both in situ and in vitro. Telocytes are cells with long and slender cell prolongations, in contact with other interstitial cells, nerve fibres, blood capillaries and resident stem cells in niches. Our aim was to investigate the potential contribution of TCs to micro-vascular networks by immunofluorescent labelling of specific angiogenic growth factors and receptors. We found that in human skeletal muscle TCs were constantly located around intermediate and small blood vessels and endomysial capillaries. Epi-fluorescence and laser confocal microscopy showed that TCs express c-kit, platelet-derived growth factor receptor (PDGFR)-ß and VEGF, both in situ and in vitro. Telocytes were constantly located in the perivascular or pericapillary space, as confirmed by double staining of c-kit/CD31, PDGFR-ß/CD31 and PDGFR-ß/α-smooth muscle actin, respectively. Electron microscopy (EM) differentiated between pericytes and other cell types. Laminin labelling showed that TCs are not enclosed or surrounded by a basal lamina in contrast to mural cells. In conclusion, a) PDGFR-ß could be used as a marker for TCs and b) TCs are presumably a transitional population in the complex process of mural cell recruitment during angiogenesis and vascular remodelling.

Inducible NOS inhibition reverses tobacco-smoke-induced emphysema and pulmonary hypertension in mice.

Chronic obstructive pulmonary disease (COPD) is one of the most common causes of death worldwide. We report in an emphysema model of mice chronically exposed to tobacco smoke that pulmonary vascular dysfunction, vascular remodeling, and pulmonary hypertension (PH) precede development of alveolar destruction. We provide evidence for a causative role of inducible nitric oxide synthase (iNOS) and peroxynitrite in this context. Mice lacking iNOS were protected against emphysema and PH. Treatment of wild-type mice with the iNOS inhibitor N(6)-(1-iminoethyl)-L-lysine (L-NIL) prevented structural and functional alterations of both the lung vasculature and alveoli and also reversed established disease. In chimeric mice lacking iNOS in bone marrow (BM)-derived cells, PH was dependent on iNOS from BM-derived cells, whereas emphysema development was dependent on iNOS from non-BM-derived cells. Similar regulatory and structural alterations as seen in mouse lungs were found in lung tissue from humans with end-stage COPD.

Telethonin deficiency is associated with maladaptation to biomechanical stress in the mammalian heart.

RATIONALE: Telethonin (also known as titin-cap or t-cap) is a 19-kDa Z-disk protein with a unique ß-sheet structure, hypothesized to assemble in a palindromic way with the N-terminal portion of titin and to constitute a signalosome participating in the process of cardiomechanosensing. In addition, a variety of telethonin mutations are associated with the development of several different diseases; however, little is known about the underlying molecular mechanisms and telethonin's in vivo function. OBJECTIVE: Here we aim to investigate the role of telethonin in vivo and to identify molecular mechanisms underlying disease as a result of its mutation. METHODS AND RESULTS: By using a variety of different genetically altered animal models and biophysical experiments we show that contrary to previous views, telethonin is not an indispensable component of the titin-anchoring system, nor is deletion of the gene or cardiac specific overexpression associated with a spontaneous cardiac phenotype. Rather, additional titin-anchorage sites, such as actin-titin cross-links via α-actinin, are sufficient to maintain Z-disk stability despite the loss of telethonin. We demonstrate that a main novel function of telethonin is to modulate the turnover of the proapoptotic tumor suppressor p53 after biomechanical stress in the nuclear compartment, thus linking telethonin, a protein well known to be present at the Z-disk, directly to apoptosis ("mechanoptosis"). In addition, loss of telethonin mRNA and nuclear accumulation of this protein is associated with human heart failure, an effect that may contribute to enhanced rates of apoptosis found in these hearts. CONCLUSIONS: Telethonin knockout mice do not reveal defective heart development or heart function under basal conditions, but develop heart failure following biomechanical stress, owing at least in part to apoptosis of cardiomyocytes, an effect that may also play a role in human heart failure.

Tissue-engineered cardiac constructs for cardiac repair.

Several recent basic research studies have described surgical methods for cardiac repair using tissue cardiomyoplasty. This review summarizes recent advances in cardiac repair using bioengineered tissue from the viewpoint of the cardiac surgeon. We conclude that the results of many basic and preclinical studies indicate that bioengineered tissue can be adapted to conventional surgical techniques. However, no clinical studies have yet proved bioengineered tissue is effective as a treatment for human heart failure. Today's cardiac surgeons can look forward to the advent of new techniques to benefit patients who respond poorly to existing treatment for heart failure.

Assessment of human MAPCs for stem cell transplantation and cardiac regeneration after myocardial infarction in SCID mice.

OBJECTIVE: Clinical studies suggest that transplantation of total bone marrow (BM) after myocardial infarction (MI) is feasible and potentially effective. However, focusing on a defined BM-derived stem cell type may enable a more specific and optimized treatment. Multilineage differentiation potential makes BM-derived multipotent adult progenitor cells (MAPCs) a promising stem cell pool for regenerative purposes. We analyzed the cardioregenerative potential of human MAPCs in a murine model of myocardial infarction. MATERIALS AND METHODS: Human MAPCs were selected by negative depletion of CD45(+)/glycophorin(+) BM cells and plated on fibronectin-coated dishes. In vitro, stem cells were analyzed by reverse transcription polymerase chain reaction. In vivo, we transplanted human MAPCs (5 × 10(5)) by intramyocardial injection after MI in severe combined immunodeficient (SCID) beige mice. Six and 30 days after the surgical procedure, pressure-volume relationships were investigated in vivo. Heart tissues were analyzed immunohistochemically. RESULTS: Reverse transcription polymerase chain reaction experiments on early human MAPC passages evidenced an expression of Oct-4, a stem cell marker indicating pluripotency. In later passages, cardiac markers (Nkx2.5, GATA4, MLC-2v, MLC-2a, ANP, cTnT, cTnI,) and smooth muscle cell markers (SMA, SM22α) were expressed. Transplantation of human MAPCs into the ischemic border zone after MI resulted in an improved cardiac function at day 6 (ejection fraction, 26% vs 20%) and day 30 (ejection fraction, 30% vs 23%). Confirmation of human MAPC marker vimentin in immunohistochemistry demonstrated that human MAPC integrated in the peri-infarct region. The proliferation marker Ki67 was absent in immunohistochemistry and teratoma formation was not found, indicating no tumorous potential of transplanted human MAPCs in the tumor-sensitive SCID model. CONCLUSIONS: Transplantation of human MAPCs after MI ameliorates myocardial function, which may be explained by trophic effects of human MAPCs. Lack of evidence of tumorous potential in the tumor-sensitive SCID model indicates that human MAPCs may deliver an effective and safe stem cell pool for potential treatment of ischemic heart disease.

A common MLP (muscle LIM protein) variant is associated with cardiomyopathy.

RATIONALE: We previously discovered the human 10T-->C (Trp4Arg) missense mutation in exon 2 of the muscle LIM protein (MLP, CSRP3) gene. OBJECTIVE: We sought to study the effects of this single-nucleotide polymorphism in the in vivo situation. METHODS AND RESULTS: We now report the generation and detailed analysis of the corresponding Mlp(W4R/+) and Mlp(W4R/W4R) knock-in animals, which develop an age- and gene dosage-dependent hypertrophic cardiomyopathy and heart failure phenotype, characterized by almost complete loss of contractile reserve under catecholamine induced stress. In addition, evidence for skeletal muscle pathology, which might have implications for human mutation carriers, was observed. Importantly, we found significantly reduced MLP mRNA and MLP protein expression levels in hearts of heterozygous and homozygous W4R-MLP knock-in animals. We also detected a weaker in vitro interaction of telethonin with W4R-MLP than with wild-type MLP. These alterations may contribute to an increased nuclear localization of W4R-MLP, which was observed by immunohistochemistry. CONCLUSIONS: Given the well-known high frequency of this mutation in Caucasians of up to 1%, our data suggest that (W4R-MLP) might contribute significantly to human cardiovascular disease.

Soluble adenylyl cyclase controls mitochondria-dependent apoptosis in coronary endothelial cells.

The cAMP signaling pathway plays an essential role in modulating the apoptotic response to various stress stimuli. Until now, it was attributed exclusively to the activity of the G-protein-responsive transmembrane adenylyl cyclase. In addition to transmembrane AC, mammalian cells possess a second source of cAMP, the ubiquitously expressed soluble adenylyl cyclase (sAC). However, the role of this cyclase in apoptosis was unknown. A mitochondrial localization of this cyclase has recently been demonstrated, which led us to the hypothesis that sAC may play a role in apoptosis through modulation of mitochondria-dependent apoptosis. To prove this hypothesis, apoptosis was induced by simulated in vitro ischemia or by acidosis, which is an important component of ischemia. Suppression of sAC activity with the selective inhibitor KH7 or sAC knockdown by small interfering RNA transfection abolished endothelial apoptosis. Furthermore, pharmacological inhibition or knockdown of protein kinase A, an important cAMP target, demonstrated a significant anti-apoptotic effect. Analysis of the underlying mechanisms revealed (i) the translocation of sAC to mitochondria under acidic stress and (ii) activation of the mitochondrial pathway of apoptosis, i.e. cytochrome c release and caspase-9 cleavage. sAC inhibition or knockdown abolished the activation of the mitochondrial pathway of apoptosis. Analysis of mitochondrial co-localization of Bcl-2 family proteins demonstrated sAC- and protein kinase A-dependent translocation of Bax to mitochondria. Taken together, these results suggest the important role of sAC in modulating the mitochondria-dependent pathway of apoptosis in endothelial cells.

Acidic preconditioning protects endothelial cells against apoptosis through p38- and Akt-dependent Bcl-xL overexpression.

To analyze the underlying cellular mechanisms of adaptation to ischemia-induced apoptosis through short acidic pretreatment, i.e. acidic preconditioning (APC), Wistar rat coronary endothelial cells (EC) were exposed for 40 min to acidosis (pH 6.4) followed by a 14 h recovery period (pH 7.4) and finally treated for 2 h with simulated in vitro ischemia (glucose-free anoxia at pH 6.4). APC led to a transient activation of p38 and Akt kinases, but not of JNK and ERK1/2 kinases, which was accompanied by significant reduction of the apoptotic cell number, caspase-12/-3 cleavage and Bcl-xL overexpression. These effects of APC were completely abolished by prevention of Akt- or p38-phosphorylation during APC. Furthermore, knock-down of Bcl-xL by siRNA-transfection also abolished the anti-apoptotic effect of APC. Therefore, APC leads to protection of EC against ischemic apoptosis by activation of Akt and p38 followed by overexpression of Bcl-xL, which is a key anti-apoptotic mechanism of APC.

Efficient homing of multipotent adult mesenchymal stem cells depends on FROUNT-mediated clustering of CCR2.

Circulating stem cells of different origin have been demonstrated to improve repair of various organs both after systemic and local application, although the mechanisms that cause these effects are still not fully understood. We have used a combination of DNA microarray analysis and in vitro migration assays to screen for molecules that mediate homing of long-term renewing adult bone marrow-derived multipotent mesenchymal stem cells (BM-MASCs). We show that the cytokine receptor CCR2 is necessary for organ-specific homing of bone marrow-derived MASCs to the heart in a transgenic mouse model and into hearts damaged by ischemia/reperfusion. Homing and migration of stem cells was dependent on the intracellular adaptor molecule FROUNT, which interacts with CCR2. FROUNT was required for polarization of MASCs, resulting in clustering of CCR2 and reorganization of the cytoskeleton. Recruited MASCs summoned by the CCR2 ligand MCP-1/CCL2 expressed SDF1, which might trap additional bone marrow-derived circulating cells to contribute to the complex process of homing and retention of circulating stem and progenitor cells to remodel diseased organs.

Sirt7 increases stress resistance of cardiomyocytes and prevents apoptosis and inflammatory cardiomyopathy in mice.

Sirt7 is a member of the mammalian sirtuin family consisting of 7 genes, Sirt1 to Sirt7, which all share a homology to the founding family member, the yeast Sir2 gene. Most sirtuins are supposed to act as histone/protein deacetylases, which use oxidized NAD in a sirtuin-specific, 2-step deacetylation reaction. To begin to decipher the biological role of Sirt7, we inactivated the Sirt7 gene in mice. Sirt7-deficient animals undergo a reduction in mean and maximum lifespans and develop heart hypertrophy and inflammatory cardiomyopathy. Sirt7 mutant hearts are also characterized by an extensive fibrosis, which leads to a 3-fold increase in collagen III accumulation. We found that Sirt7 interacts with p53 and efficiently deacetylates p53 in vitro, which corresponds to hyperacetylation of p53 in vivo and an increased rate of apoptosis in the myocardium of mutant mice. Sirt7-deficient primary cardiomyocytes show a approximately 200% increase in basal apoptosis and a significantly diminished resistance to oxidative and genotoxic stress suggesting a critical role of Sirt7 in the regulation of stress responses and cell death in the heart. We propose that enhanced activation of p53 by lack of Sirt7-mediated deacetylation contributes to the heart phenotype of Sirt7 mutant mice.

Extracellular RNA mediates endothelial-cell permeability via vascular endothelial growth factor.

Cell injury leads to exposure of intracellular material and is associated with increased permeability of vessels in the vicinity of the damage. Here, we demonstrate that natural extracellular RNA as well as artificial RNA (poly-I:C), or single-stranded RNA but not DNA, significantly increased the permeability across brain microvascular endothelial cells in vitro and in vivo. RNA-induced hyperpermeability of tight monolayers of endothelial cells correlated with disintegration of tight junctions and was mediated through vascular endothelial growth factor (VEGF), reminiscent of heparin's activities. Antisense oligonucleotides against VEGF-receptor 2 (VEGF-R2) prevented the permeability-inducing activity of extracellular RNA and heparin completely. Hence, these polyanionic substances can lead to mobilization/stabilization of VEGF with the subsequent activation of VEGF-R2. In accordance with these functional data, strong binding of VEGF as well as other growth factors to RNA was demonstrable. In in vivo rat models of FeCl(3)-induced sinus sagittal is superior thrombosis and stroke/brain edema, pretreatment of animals with RNase (but not DNase) resulted in a significant reduction of vessel occlusion, infarct volume, and prevention of brain edema formation. Together, these results identify extracellular RNA as a novel natural permeability factor, upstream of VEGF, whereas counteracting RNase treatment may serve as new vessel-protective modality.