Explore the vast range of titles available.

Certain fish and amphibians retain a robust capacity for cardiac regeneration throughout life, but the same is not true of the adult mammalian heart. Whether the capacity for cardiac regeneration is absent in mammals or whether it exists and is switched off early after birth has been unclear. We found that the hearts of 1-day-old neonatal mice can regenerate after partial surgical resection, but this capacity is lost by 7 days of age. This regenerative response in 1-day-old mice was characterized by cardiomyocyte proliferation with minimal hypertrophy or fibrosis, thereby distinguishing it from repair processes. Genetic fate mapping indicated that the majority of cardiomyocytes within the regenerated tissue originated from preexisting cardiomyocytes. Echocardiography performed 2 months after surgery revealed that the regenerated ventricular apex had normal systolic function. Thus, for a brief period after birth, the mammalian heart appears to have the capacity to regenerate.

Cardiac regeneration Zebrafish are able to efficiently regenerate lost cardiac muscle, and is used as a model to understand why natural heart regeneration is blocked in mammals. Two groups reporting in the issue of Nature used genetic fate-mapping approaches to identify which population of cardiomyocytes contribute prominently to cardiac muscle regeneration after an injury approximating myocardial infarction. They show that cardiac muscle regenerates through activation and expansion of existing cardiomyocytes, and does not involve activation of a stem cell population. Zebrafish are able to replace lost heart muscle efficiently, and are used as a model to understand why natural heart regeneration — after a heart attack, for instance — is blocked in mammals. Here, and in an accompanying paper, genetic fate-mapping approaches reveal which cell population contributes prominently to cardiac muscle regeneration after an injury approximating myocardial infarction. The results show that cardiac muscle regenerates through activation and expansion of existing cardiomyocytes, without involving a stem-cell population. Although mammalian hearts show almost no ability to regenerate, there is a growing initiative to determine whether existing cardiomyocytes or progenitor cells can be coaxed into eliciting a regenerative response. In contrast to mammals, several non-mammalian vertebrate species are able to regenerate their hearts 1 , 2 , 3 , including the zebrafish 4 , 5 , which can fully regenerate its heart after amputation of up to 20% of the ventricle. To address directly the source of newly formed cardiomyocytes during zebrafish heart regeneration, we first established a genetic strategy to trace the lineage of cardiomyocytes in the adult fish, on the basis of the Cre/ lox system widely used in the mouse 6 . Here we use this system to show that regenerated heart muscle cells are derived from the proliferation of differentiated cardiomyocytes. Furthermore, we show that proliferating cardiomyocytes undergo limited dedifferentiation characterized by the disassembly of their sarcomeric structure, detachment from one another and the expression of regulators of cell-cycle progression. Specifically, we show that the gene product of polo-like kinase 1 ( plk1 ) is an essential component of cardiomyocyte proliferation during heart regeneration. Our data provide the first direct evidence for the source of proliferating cardiomyocytes during zebrafish heart regeneration and indicate that stem or progenitor cells are not significantly involved in this process.

Tortuous arteries and veins are commonly observed in humans and animals. While mild tortuosity is asymptomatic, severe tortuosity can lead to ischemic attack in distal organs. Clinical observations have linked tortuous arteries and veins with aging, atherosclerosis, hypertension, genetic defects and diabetes mellitus. However, the mechanisms of their formation and development are poorly understood. This review summarizes the current clinical and biomechanical studies on the initiation, development and treatment of tortuous blood vessels. We submit a new hypothesis that mechanical instability and remodeling could be mechanisms for the initiation and development of these tortuous vessels.

It has been difficult to establish whether we are limited to the heart muscle cells we are born with or if cardiomyocytes are generated also later in life. We have taken advantage of the integration of carbon-14, generated by nuclear bomb tests during the Cold War, into DNA to establish the age of cardiomyocytes in humans. We report that cardiomyocytes renew, with a gradual decrease from 1% turning over annually at the age of 25 to 0.45% at the age of 75. Fewer than 50% of cardiomyocytes are exchanged during a normal life span. The capacity to generate cardiomyocytes in the adult human heart suggests that it may be rational to work toward the development of therapeutic strategies aimed at stimulating this process in cardiac pathologies.

Pharmacological inhibition of VEGF-A has proven to be effective in inhibiting angiogenesis and vascular leak associated with cancers and various eye diseases. However, little information is currently available on the binding kinetics and relative biological activity of various VEGF inhibitors. Therefore, we have evaluated the binding kinetics of two anti-VEGF antibodies, ranibizumab and bevacizumab, and VEGF Trap (also known as aflibercept), a novel type of soluble decoy receptor, with substantially higher affinity than conventional soluble VEGF receptors. VEGF Trap bound to all isoforms of human VEGF-A tested with subpicomolar affinity. Ranibizumab and bevacizumab also bound human VEGF-A, but with markedly lower affinity. The association rate for VEGF Trap binding to VEGF-A was orders of magnitude faster than that measured for bevacizumab and ranibizumab. Similarly, in cell-based bioassays, VEGF Trap inhibited the activation of VEGFR1 and VEGFR2, as well as VEGF-A induced calcium mobilization and migration in human endothelial cells more potently than ranibizumab or bevacizumab. Only VEGF Trap bound human PlGF and VEGF-B, and inhibited VEGFR1 activation and HUVEC migration induced by PlGF. These data differentiate VEGF Trap from ranibizumab and bevacizumab in terms of its markedly higher affinity for VEGF-A, as well as its ability to bind VEGF-B and PlGF.

Purpose To provide clinicians with an evidence-based overview of all topics related to ultrasound vascular access. Methods An international evidence-based consensus provided definitions and recommendations. Medical literature on ultrasound vascular access was reviewed from January 1985 to October 2010. The GRADE and the GRADE-RAND methods were utilised to develop recommendations. Results The recommendations following the conference suggest the advantage of 2D vascular screening prior to cannulation and that real-time ultrasound needle guidance with an in-plane/long-axis technique optimises the probability of needle placement. Ultrasound guidance can be used not only for central venous cannulation but also in peripheral and arterial cannulation. Ultrasound can be used in order to check for immediate and life-threatening complications as well as the catheter’s tip position. Educational courses and training are required to achieve competence and minimal skills when cannulation is performed with ultrasound guidance. A recommendation to create an ultrasound curriculum on vascular access is proposed. This technique allows the reduction of infectious and mechanical complications. Conclusions These definitions and recommendations based on a critical evidence review and expert consensus are proposed to assist clinicians in ultrasound-guided vascular access and as a reference for future clinical research.

Cardiac regeneration Zebrafish are able to efficiently regenerate lost cardiac muscle, and is used as a model to understand why natural heart regeneration is blocked in mammals. Two groups reporting in the issue of Nature used genetic fate-mapping approaches to identify which population of cardiomyocytes contribute prominently to cardiac muscle regeneration after an injury approximating myocardial infarction. They show that cardiac muscle regenerates through activation and expansion of existing cardiomyocytes, and does not involve activation of a stem cell population. Zebrafish are able to replace lost heart muscle efficiently, and are used as a model to understand why natural heart regeneration — after a heart attack, for instance — is blocked in mammals. Here, and in an accompanying paper, genetic fate-mapping approaches reveal which cell population contributes prominently to cardiac muscle regeneration after an injury approximating myocardial infarction. The results show that cardiac muscle regenerates through activation and expansion of existing cardiomyocytes, without involving a stem-cell population. Recent studies indicate that mammals, including humans, maintain some capacity to renew cardiomyocytes throughout postnatal life 1 , 2 . Yet, there is little or no significant cardiac muscle regeneration after an injury such as acute myocardial infarction 3 . By contrast, zebrafish efficiently regenerate lost cardiac muscle, providing a model for understanding how natural heart regeneration may be blocked or enhanced 4 , 5 . In the absence of lineage-tracing technology applicable to adult zebrafish, the cellular origins of newly regenerated cardiac muscle have remained unclear. Using new genetic fate-mapping approaches, here we identify a population of cardiomyocytes that become activated after resection of the ventricular apex and contribute prominently to cardiac muscle regeneration. Through the use of a transgenic reporter strain, we found that cardiomyocytes throughout the subepicardial ventricular layer trigger expression of the embryonic cardiogenesis gene gata4 within a week of trauma, before expression localizes to proliferating cardiomyocytes surrounding and within the injury site. Cre-recombinase-based lineage-tracing of cells expressing gata4 before evident regeneration, or of cells expressing the contractile gene cmlc2 before injury, each labelled most cardiac muscle in the ensuing regenerate. By optical voltage mapping of surface myocardium in whole ventricles, we found that electrical conduction is re-established between existing and regenerated cardiomyocytes between 2 and 4 weeks post-injury. After injury and prolonged fibroblast growth factor receptor inhibition to arrest cardiac regeneration and enable scar formation, experimental release of the signalling block led to gata4 expression and morphological improvement of the injured ventricular wall without loss of scar tissue. Our results indicate that electrically coupled cardiac muscle regenerates after resection injury, primarily through activation and expansion of cardiomyocyte populations. These findings have implications for promoting regeneration of the injured human heart.

Ephrin-B2/VEGF in angiogenesis control Ephrin-B ligands are well known as axon guidance molecules. Ephrin-B2 is also known to play a role in angiogenic remodelling. Two studies now show that signalling through ephrin-B2 controls vessel sprouting. Mechanistically, ephrin-B2 seems to function in part by regulating VEGFR internalization and signalling. The finding suggests that blocking ephrin-B2 signalling may be an alternative approach to blocking VEGFR function in angiogenesis. The protein ephrin-B2 is known to be upregulated during angiogenesis — the growth of new blood vessels — but its precise function has been unclear. Here it is shown that signalling through ephrin-B2 controls vessel sprouting. Mechanistically, ephrin-B2 seems to function in part by regulating the internalization of vascular endothelial growth factor receptors (VEGFRs). The results indicate that blocking ephrin-B2 signalling might be an alternative to blocking VEGFR function to disrupt angiogenesis in tumours. In development, tissue regeneration or certain diseases, angiogenic growth leads to the expansion of blood vessels and the lymphatic vasculature. This involves endothelial cell proliferation as well as angiogenic sprouting, in which a subset of cells, termed tip cells, acquires motile, invasive behaviour and extends filopodial protrusions 1 , 2 , 3 . Although it is already appreciated that angiogenesis is triggered by tissue-derived signals, such as vascular endothelial growth factor (VEGF) family growth factors, the resulting signalling processes in endothelial cells are only partly understood. Here we show with genetic experiments in mouse and zebrafish that ephrin-B2, a transmembrane ligand for Eph receptor tyrosine kinases, promotes sprouting behaviour and motility in the angiogenic endothelium. We link this pro-angiogenic function to a crucial role of ephrin-B2 in the VEGF signalling pathway, which we have studied in detail for VEGFR3, the receptor for VEGF-C. In the absence of ephrin-B2, the internalization of VEGFR3 in cultured cells and mutant mice is defective, which compromises downstream signal transduction by the small GTPase Rac1, Akt and the mitogen-activated protein kinase Erk. Our results show that full VEGFR3 signalling is coupled to receptor internalization. Ephrin-B2 is a key regulator of this process and thereby controls angiogenic and lymphangiogenic growth.

A molecular switch for eNOS The enzyme eNOS (endothelial nitric oxide synthase) is vital for regulating vascular function as it can produce both the vasodilator nitric oxide and the vasoconstrictor superoxide. Jay Zweier and colleagues show that a modification associated with oxidant stress, S-glutathionylation, switches the enzyme from forming nitric oxide to forming superoxide. In hypertensive vessels, S-glutathionylation of eNOS is increased, and this is associated with impaired endothelium-dependent vasodilation. Oxidant stress occurs in many diseases including heart attack, stroke, diabetes and cancer. This work suggests that agents that reset this redox switch, thereby restoring normal nitric oxide synthase function, may have therapeutic potential. The enzyme eNOS is crucial for regulating vascular function as it can produce both the vasodilator nitric oxide and the vasoconstrictor superoxide. Here it is shown that a modification associated with oxidant stress, S-glutathionylation, switches the enzyme from forming nitric oxide to forming superoxide. In hypertensive vessels, S-glutathionylation of eNOS is increased and this is associated with impaired endothelium-dependent vasodilation. Endothelial nitric oxide synthase (eNOS) is critical in the regulation of vascular function, and can generate both nitric oxide (NO) and superoxide (O 2 • − ), which are key mediators of cellular signalling. In the presence of Ca 2+ /calmodulin, eNOS produces NO, endothelial-derived relaxing factor, from l -arginine ( l -Arg) by means of electron transfer from NADPH through a flavin containing reductase domain to oxygen bound at the haem of an oxygenase domain, which also contains binding sites for tetrahydrobiopterin (BH 4 ) and l -Arg 1 , 2 , 3 . In the absence of BH 4 , NO synthesis is abrogated and instead O 2 • − is generated 4 , 5 , 6 , 7 . While NOS dysfunction occurs in diseases with redox stress, BH 4 repletion only partly restores NOS activity and NOS-dependent vasodilation 7 . This suggests that there is an as yet unidentified redox-regulated mechanism controlling NOS function. Protein thiols can undergo S-glutathionylation, a reversible protein modification involved in cellular signalling and adaptation 8 , 9 . Under oxidative stress, S-glutathionylation occurs through thiol–disulphide exchange with oxidized glutathione or reaction of oxidant-induced protein thiyl radicals with reduced glutathione 10 , 11 . Cysteine residues are critical for the maintenance of eNOS function 12 , 13 ; we therefore speculated that oxidative stress could alter eNOS activity through S-glutathionylation. Here we show that S-glutathionylation of eNOS reversibly decreases NOS activity with an increase in O 2 • − generation primarily from the reductase, in which two highly conserved cysteine residues are identified as sites of S-glutathionylation and found to be critical for redox-regulation of eNOS function. We show that eNOS S-glutathionylation in endothelial cells, with loss of NO and gain of O 2 • − generation, is associated with impaired endothelium-dependent vasodilation. In hypertensive vessels, eNOS S-glutathionylation is increased with impaired endothelium-dependent vasodilation that is restored by thiol-specific reducing agents, which reverse this S-glutathionylation. Thus, S-glutathionylation of eNOS is a pivotal switch providing redox regulation of cellular signalling, endothelial function and vascular tone.

This study presents a new model for the regulation of nitric oxide signalling in endothelial cells; the oxidation state of endothelial haemoglobin α, controlled by cytochrome B5 reductase 3, regulates nitric oxide bioactivity and diffusion towards its vascular smooth muscle targets. Nitric oxide signalling in blood vessels This manuscript provides evidence for a new model of the regulation of nitric oxide signalling in myoendothelial gap junctions. The oxidation state of endothelial haemoglobin α, controlled by cytochrome b5 reductase 3, regulates nitric oxide bioavailability and diffusion towards its vascular smooth muscle targets by promoting either the formation of vasodilator S -nitrosothiols or the scavenging of nitric oxide. This endothelial regulation of nitric oxide modulates the effects of agents involved in the control of vascular tone, such as α-adrenergic agonists or substances that evoke endothelium-dependent relaxations. Models of unregulated nitric oxide (NO) diffusion do not consistently account for the biochemistry of NO synthase (NOS)-dependent signalling in many cell systems 1 , 2 , 3 . For example, endothelial NOS controls blood pressure, blood flow and oxygen delivery through its effect on vascular smooth muscle tone 4 , but the regulation of these processes is not adequately explained by simple NO diffusion from endothelium to smooth muscle 3 , 5 . Here we report a new model for the regulation of NO signalling by demonstrating that haemoglobin (Hb) α (encoded by the HBA1 and HBA2 genes in humans) is expressed in human and mouse arterial endothelial cells and enriched at the myoendothelial junction, where it regulates the effects of NO on vascular reactivity. Notably, this function is unique to Hb α and is abrogated by its genetic depletion. Mechanistically, endothelial Hb α haem iron in the Fe 3+ state permits NO signalling, and this signalling is shut off when Hb α is reduced to the Fe 2+ state by endothelial cytochrome b5 reductase 3 (CYB5R3, also known as diaphorase 1) 6 . Genetic and pharmacological inhibition of CYB5R3 increases NO bioactivity in small arteries. These data reveal a new mechanism by which the regulation of the intracellular Hb α oxidation state controls NOS signalling in non-erythroid cells. This model may be relevant to haem-containing globins in a broad range of NOS-containing somatic cells 7 , 8 , 9 , 10 , 11 , 12 , 13 .