Mef2cb regulates late myocardial cell addition from a second heart field-like population of progenitors in zebrafish

Two populations of cells, termed the first and second heart field, drive heart growth during chick and mouse development. The zebrafish has become a powerful model for vertebrate heart development, partly due to the evolutionary conservation of developmental pathways in this process. Here we provide evidence that the zebrafish possesses a conserved homolog to the murine second heart field. We developed a photoconversion assay to observe and quantify the dynamic late addition of myocardial cells to the zebrafish arterial pole. We define an extra-cardiac region immediately posterior to the arterial pole, which we term the late ventricular region. The late ventricular region has cardiogenic properties, expressing myocardial markers such as vmhc and nkx2.5, but does not express a full complement of differentiated cardiomyocyte markers, lacking myl7 expression. We show that mef2cb, a zebrafish homolog of the mouse second heart field marker Mef2c, is expressed in the late ventricular region, and is necessary for late myocardial addition to the arterial pole. FGF signaling after heart cone formation is necessary for mef2cb expression, the establishment of the late ventricular region, and late myocardial addition to the arterial pole. Our study demonstrates that zebrafish heart growth shows more similarities to murine heart growth than previously thought. Further, as congenital heart disease is often associated with defects in second heart field development, the embryological and genetic advantages of the zebrafish model can be applied to study the vertebrate second heart field.     

Factors involved in capillary growth in the heart

Growth of capillaries in the heart occurs under physiological circumstances during endurance exercise training, exposure to high altitude and/or cold, and changes in cardiac metabolism or heart rate elicited by modification of thyroid hormone levels. Capillary growth in all these conditions can be linked with increased coronary blood flow, decreased heart rate, or both. This paper brings evidence that, although increased blood flow due to long-term administration of coronary vasodilators results in capillary growth, a long-term decrease in heart rate induced by electrical bradycardial pacing in rabbits and pigs, or by chronic administration of a bradycardic drug, alinidine, in rats, stimulates capillary growth with little or no change in coronary blood flow. Decreased heart rate results in increased capillary wall tension, increased end-diastolic volume and increased force of contraction, and thus stretch of the capillary wall. This could lead to release of various growth factors possibly stored in the capillary basement membrane. Correlation was found between capillary density (CD) and the levels of low molecular endothelial cell stimulating angiogenic factor (ESAF) both in rabbit and pig hearts with CD increased by pacing. There was no relation between expression of mRNA for basic fibroblast growth factor and CD in sham-operated and paced rabbit hearts. In contrast, mRNA for TGFß was increased in paced hearts, and the possible role of this factor in the regulation of capillary growth induced by bradycardia is discussed.     

Astrocytes enhance radical defence in capillary endothelial cells constituting the blood-brain barrier.

Astrocytes (AC) induce blood-brain barrier (BBB) properties in brain endothelial cells (EC). As antioxidative activity (AOA) is assumed to be a BBB characteristic, we tested whether AC improve AOA of EC. Monocultivated AC showed higher AOA [manganese superoxide dismutase (SOD), catalase (Cat), glutathione peroxidase (GPx)] than EC. Cocultivation elevated AOA in EC (MnSOD, CuZnSOD, Cat, GPx), and AC (MnSOD, CuZnSOD, GPx). Hypoxia increased radical-induced membrane lipid peroxidation in monocultivated, but not in cocultivated EC. Thus, EC/AC cocultivation intensifies AOA in both cell types, protects the EC, and therefore, the BBB against oxidative stress. The high AOA is regarded as an essential property of the BBB, which is induced by AC.     

Receptors for insulin-like growth factor-I (IGF-I) in myocardial capillary endothelium of the intact perfused heart

Isolated intact, beating hearts were perfused with HPLC-pure [125]-IGF-I (1 ng/ml) alone or [125]-IGF-I (1 ng/ml) plus varying concentrations of unlabeled IGF-I (10-3,000 ng/ml) or unlabeled insulin (1,000-100,000 ng/ml). After 1 min of perfusion with peptides, the hearts were rapidly fixed, sectioned and analyzed for radioautographic [125I] grain counts. Greater than 90% of [125I] grains were shown to represent intact [125I]-IGF. Maximal grain counts over capillaries occurred after perfusion with [125I]-IGF-I alone and decreased in a dose-dependent manner when unlabeled IGF-I was coperfused. Coperfusion of [125I]-IGF-I with unlabeled insulin also decreased 125I grains over capillaries but less potently than unlabeled IGF-I. EM radioautography demonstrated that [125I]-IGF-I grains were localized over capillary endothelial cells. Thus, specific IGF-I receptors are present in the capillary endothelium of the intact heart and have properties similar to IGF-I receptors in cultured capillary endothelial cells.     

Statins in prevention and treatment of ischemic stroke

Based on the published data, including the results of large-scale, randomized, placebo-controlled trials, the article presents current strategies for the use of statins in primary and secondary prevention of ischemic stroke. Special attention is paid to the efficacy and advanced applications of statins in acute stroke. Based on the gross data, recommendations for the use of statins in prevention and treatment of ischemic stroke are presented.     

Insulin and IGF-1 manifest differential effects in a clonal capillary endothelial cell line.

125I-insulin (10 fmoles) binding plus internalization (BI) to a clonal capillary endothelial (CE) cell line reached to a steady state after 20 min. Acid-washed fraction accounted for nearly half of the total specifically-bound hormone. Dissociation constants (Kd) for insulin-surface receptor in acid-extractable fraction were 0.04 nM (high affinity) and 4.7 nM (low affinity) with a total number of 210,000 high affinity receptors per cell. When 125I-labeled IGF-1 (15 fmoles) was incubated similarly, BI reached only a quasi-equilibrium by 6 min and continued to increase thereafter. 2-Deoxyglucose transport in these cells was stimulated by insulin whereas IGF-1 inhibited its entry.     

A retrospective clonal analysis of the myocardium reveals two phases of clonal growth in the developing mouse heart

Key molecules which regulate the formation of the heart have been identified; however, the mechanism of cardiac morphogenesis remains poorly understood at the cellular level. We have adopted a genetic approach, which permits retrospective clonal analysis of myocardial cells in the mouse embryo, based on the targeting of an nlaacZ reporter to the alpha-cardiac actin gene. A rare intragenic recombination event leads to a clone of beta-galactosidase-positive myocardial cells. Analysis of clones at different developmental stages demonstrates that myocardial cells and their precursors follow a proliferative mode of growth, rather than a stem cell mode, with an initial dispersive phase, followed by coherent cell growth. Clusters of cells are dispersed along the venous-arterial axis of the heart tube. Coherent growth is oriented locally, with a main axis, which corresponds to the elongation of the cluster, and rows of cells, which form secondary axes. The angle between the primary and secondary axes varies, indicating independent events of growth orientation. At later stages, as the ventricular wall thickens, wedge shaped clusters traverse the wall and contain rows of cells at a progressive angle to each other. The cellular organisation of the myocardium appears to prefigure myofibre architecture. We discuss how the characteristics of myocardial cell growth, which we describe, underlie the formation of the heart tube and its subsequent regionalised expansion.     

EEG and clinical psychophysiological study of functional changes in the chronically ischemic brain upon an increase in cholinergic activity

Electrophysiological and neuropsychological parameters of improvement of the functional state of the brain were studied in patients with mild vascular dementia upon an increase in the activity of cholinergic systems (as a result of treatment with Reminyl). The functional state of the brain was significantly improved as evidenced by a decrease in the EEG spectral power in slow-wave bands and its increase in the band of the γ rhythm, which is involved in cognitive processes in humans. Psychometric tests indicated a significant improvement in cognitive functions.     

The clonal origin of myocardial cells in different regions of the embryonic mouse heart

When and how cells form and pattern the myocardium is a central issue for heart morphogenesis. Many genes are differentially expressed and function in subsets of myocardial cells. However, the lineage relationships between these cells remain poorly understood. To examine this, we have adopted a retrospective approach in the mouse embryo, based on the use of the laacZ reporter gene, targeted to the alpha-cardiac actin locus. This clonal analysis demonstrates the existence of two lineages that segregate early from a common precursor. The primitive left ventricle and the presumptive outflow tract are derived exclusively from a single lineage. Unexpectedly, all other regions of the heart, including the primitive atria, are colonized by both lineages. These results are not consistent with the prespecification of the cardiac tube as a segmented structure. They are discussed in the context of different heart fields and of the evolution of the heart.     

Glycogen metabolism in the brain and heart in ischemic myocardial necrosis and stress

It is established that the emotional stress preceding the acute development of ischemic necrosis of the myocardium is the most important condition of the glycogen metabolism disturbance in the central nervous and cardiovascular systems. The most considerable changes in the glycogen metabolism are detected in the heart.     

Peroxide modification of low density lipoproteins in ischemic heart disease

It is shown that the LDL peroxide lipid products level is 1.6-4 times higher in patients with the ischemic heart diseases (IHD) than in normal subjects. At the same time the LDL uptake by macrophages was identical in case of normal subjects and of IHD patients. It is suggested that the LDL premodification in the blood flow in the IHD patients promotes the further modification of LDL particles after their penetration into the vessel wall.     

Moderate abiotic stresses increase rhizome growth and outgrowth of axillary buds in Alstroemeria cultured in vitro

Alstroemeria is multiplied in vitro by forced outgrowth of lateral rhizomes from rhizome explants. The multiplication rate is very low because of strong apical dominance and poor rhizome growth. We report here that moderate abiotic stresses stimulate both rhizome growth and outgrowth of lateral rhizomes, and accordingly increase multiplication. Rhizome explants were exposed to heat by a hot-water treatment (HWT) or by a hot-air treatment. Both increased rhizome growth when applied for 1 or 2?h in the range of 30?C40?°C. The maximal enhancement was 75?%. Other abiotic stresses were also examined. Cold (0?°C) and partial anaerobiosis increased rhizome growth significantly. The increases brought about by drought and salinity were not statistically significant. Because underground storage tissues like rhizomes are adaptations to survive climatic stresses, we presume that the increased sink-strength of rhizomes induced by moderate stress is related to stress adaptation. Moderate heat stress (38?°C HWT, 1?h) also resulted in protection of Alstroemeria plantlets from severe heat stress (45?°C HWT, 1?C2?h) a few hours after the moderate stress. All abiotic stresses also increased the outgrowth of lateral rhizomes.     

Enhancement of colony-stimulating-factor--dependent clonal growth of murine macrophage progenitors and their phagocytic activity by retinoic acid

The effect of retinoic acid (RA) on the colony-stimulating-factor-dependent clonal growth of myeloid progenitors was assessed in semisolid agar cultures of mouse bone marrow cells using L-cell-conditioned medium that gave rise to macrophage colonies, granulocyte colonies, and mixed macrophage-granulocyte colonies and clusters. RA was found to enhance the overall formation of myeloid colonies (about 50%) and clusters in 7-day cultures. The increase was due to an enhanced formation of macrophage colonies (70-250%) and clusters which reached a maximal value at about 3 microM RA. In 4-day cultures, the effect of RA on macrophage colony formation was biphasic with a maximal enhancement at 10 nM. RA suppressed granulocyte-colony formation in 4-day cultures. RA increased the phagocytic activity of bone-marrow-derived macrophages at all stages of differentiation and/or maturation in culture. The Fc-receptor-mediated erythrophagocytosis as well as the phagocytosis of heat-killed yeast cells (HK-yeast) and starch particles increased by RA treatment in a dose-dependent manner, reaching an increase of 100-200% of the activity expressed in the absence of RA. Peritoneal exudate macrophages likewise exhibited an increased phagocytic response to a variety of particles, at both physiological and pharmacological concentrations of RA. Expression of an RA-mediated increase in phagocytic activity required a prolonged incubation with RA (greater than 19 hr). The data suggest that RA may be of physiological relevance in the regulation of proliferation and function of hemopoietic cells. Therapeutic doses of RA may potentiate macrophage proliferation and function, elements that are crucial at all phases of the various defense mechanisms that the organism possesses.     

Density-dependent growth responses in two clonal herbs: regulation of shoot density

Summary It has been shown in clonal perennial herbs that shoot natality decreases, and shoot mortality increases, in stands of increasing density. In a two-year garden experiment, we have tested Hutchings' (1979) hypothesis that these responses are the result of physiological integration, i.e. the exchange of resources and growth substances between shoots of a single clone. Dense monocultures of two rhizomatous graminoids, Brachypodium pinnatum and Carex flacca, were created that differed more than 10-fold in the density of clones (genets), but that had similar densities of shoots. A more effective shoot density control was expected in stands with the smaller clone densities (larger clones) due to more extensive clonal connections. Shoot turnover was evaluated by counting living and dead shoots at different times. In the summer of the second year, when shoot densities and stand structure were similar between treatments, shoot natality (the number of shoots born per plot) and shoot mortality (the number of shoots that died per plot) were usually unrelated to clone density in either species. If there was a significant treatment effect, it could be attributed to (small) differences in shoot density. Over the whole range of shoot densities, natality was negatively density-dependent. The number of shoots that died in a given growth period was proportional to the number of shoots present, suggesting that mortality rates were density independent. In Carex, however, there were some indications that mortality rate increased with increasing density. Our study confirms that clonal herbaceous species can effectively prevent an overproduction of shoots, but in contrast to Hutchings' (1979) propositions, we found no evidence that physiological integration may be the responsible mechanism. An alternative explanation for the observed patterns is proposed.     

mu-Opiate receptor activation and increase in heart resistance to ischemic and reperfusion injury

Stimulation of mu-opioid receptors was found to contribute to prevention of myocardial contractile dysfunction and ventricular arrhythmias in ischemia and reperfusion of the rat isolated heart. Endogenous agonists of the mu-opioid receptors were not involved in tonic regulation of the heart resistance against reperfusion disturbances of the rhythm and contractility. On the other hand, mu-opioid receptors are important for development of postischemic contracture.     

Control of intracellular pH and growth by fibronectin in capillary endothelial cells

The aim of this work was to analyze the mechanism by which fibronectin (FN) regulates capillary endothelial cell proliferation. Endothelial cell growth can be controlled in chemically-defined medium by varying the density of FN coated on the substratum (Ingber, D. E., and J. Folkman. J. Cell Biol. 1989. 109:317-330). In this system, DNA synthetic rates are stimulated by FN in direct proportion to its effect on cell extension (projected cell areas) both in the presence and absence of saturating amounts of basic FGF. To investigate direct growth signaling by FN, we carried out microfluorometric measurements of intracellular pH (pHi), a cytoplasmic signal that is commonly influenced by soluble mitogens. pHi increased 0.18 pH units as FN coating densities were raised and cells progressed from round to spread. Intracellular alkalinization induced by attachment to FN was rapid and followed the time course of cell spreading. When measured in the presence and absence of FGF, the effects of FN and FGF on pHi were found to be independent and additive. Furthermore, DNA synthesis correlated with pHi for all combinations of FGF and FN. Ethylisopropylamiloride, a specific inhibitor of the plasma membrane Na+/H+ antiporter, completely suppressed the effects of FN on both pHi and DNA synthesis. However, cytoplasmic pH per se did not appear to be a critical determinant of growth since DNA synthesis was not significantly inhibited when pHi was lowered over the physiological range by varying the pH of the medium. We conclude that FN and FGF exert their growth-modulating effects in part through activation of the Na+/H+ exchanger, although they appear to trigger this system via separate pathways.     

模拟源株密度对蝴蝶花生长和克隆繁殖的影响

通过不同蝴蝶花(Iris japonica)起始源株密度的控制实验, 探讨源株对克隆植物蝴蝶花克隆繁殖、生长和生物量分配的影响。结果表明: 1)克隆数量特征: 1个起始源株处理(O)蝴蝶花新分株数显著高于2个起始源株(T)及4个起始源株处理(F), 而新分株死亡率显著低于后二者; 随着起始源株数增加(竞争增强), 一级与二级子株数显著降低。随着源株竞争增强, 克隆细根茎与根的长度、表面积、体积与根(茎)长密度逐渐降低。2)叶片特征: 随着源株竞争增强, 母株重度枯萎与总枯萎叶片数显著增加, 子株中度枯萎、重度枯萎与总枯萎叶片数显著增加; 源株竞争增强, 源株叶面积、源株与子株叶片数显著降低, 而源株叶面积比(leaf area ratio, LAR)显著增加。3)生物量及分配: 随着源株竞争增强, 细根茎、粗根茎、克隆繁殖、地上部分、地下部分及总生物量显著降低, 细根茎与地下部分分配降低, 母株粗根茎分配与地上部分分配显著增加。总的看来, 随着蝴蝶花源株竞争增强, 植株叶片生长状况受到更大的影响, 植株生长受限, 克隆繁殖减弱, 而其通过增加LAR, 提高叶片效率与增加母株粗根茎分配, 降低生长强度与消耗, 储备资源, 以待来年的生长与繁殖。