Radiobiologie des doses ablatives en radiothérapie stéréotaxique : mise au point des données récentes

Stereotactic radiotherapy is a radiation technique, which is becoming more and more available and applicable for physicians. A good efficacy and safety are observed in clinical practice. However, the radiobiology of ablative radiation is still under question. The radiobiological principles of the 5R have to be discussed. The roles of hypoxia and vascularization, more specifically, angiogenesis and vasculogenesis seem to be dominating.     

Endothelial progenitor cells for postnatal vasculogenesis

Bone marrow-derived endothelial progenitor cells (EPCs) are present in the systemic circulation, are augmented in response to certain cytokines and/or tissue ischemia, and are home to – as well as incorporate into – sites of neovascularization. On the basis of these aspects, EPCs have attractive potential therapeutic applications for cardiovascular ischemic diseases as a novel cell-based strategy, mainly via a vasculogenesis mechanism. This review provides an update of the biology of EPCs, as well as highlighting the potential use of these cells for therapeutic regeneration.     

G-CSF and HGF: combination of vasculogenesis and angiogenesis synergistically improves recovery in murine hind limb ischemia

Granulocyte colony-stimulating factor (G-CSF) is known to mobilize bone marrow stem cells into the peripheral circulation. This study was designed to investigate whether G-CSF by itself or in combination with hepatocyte growth factor (HGF) can promote vasculogenesis and angiogenesis in murine hind limb ischemia. Hind limb ischemia was induced in BALB/c nude or C57/BL6 mice that received bone marrow transplantation from green fluorescent protein (GFP)-transgenic mice. In the HGF group, hHGF expression plasmid was injected into the ischemic muscles. In the G-CSF group, G-CSF was administered subcutaneously for 10 days. The G-CSF+HGF group was concomitantly treated with G-CSF and HGF, and the control group received no treatment. All effects were confirmed at 4 weeks. The G-CSF+HGF group had a higher laser Doppler blood perfusion index, higher microvessel density, and a lower incidence of hind limb necrosis than the other groups. Confocal laser microscopy revealed that a number of GFP-positive cells infiltrated to the vasculature of the ischemic area. Some of the GFP positive cells were clearly co-immunostained with alpha-smooth muscle actin as well as von Willebrand factor. G-CSF-mobilized stem cells co-expressed CD49d and CD34, which would have promoted their adhesion to cells in the ischemic muscle that expressed HGF-induced vascular cell adhesion molecule-1. The combination of G-CSF and HGF had a significant synergistic effect, suggesting that the combination of mobilization of stem cells from bone marrow to peripheral circulation and their recruitment to the ischemic area might potentiate angiogenesis and vasculogenesis.     

Angiopoietin growth factors and Tie receptor tyrosine kinases in renal vascular development

Angiopoietin-1 (Ang-1) is a secreted growth factor which binds to and activates the Tie-2 receptor tyrosine kinase. The factor enhances endothelial cell survival and capillary morphogenesis, and also limits capillary permeability. Ang-2 binds the same receptor but fails to activate it: hence, it is a natural inhibitor of Ang-1. Ang-2 destabilises capillary integrity, facilitating sprouting when ambient vascular endothelial growth factor (VEGF) levels are high, but causing vessel regression when VEGF levels are low. Tie-1 is a Tie-2 homologue but its ligands are unknown. Angiopoietin and Tie genes are expressed in the mammalian metanephros, the precursor of the adult kidney, where they may play a role in endothelial precursor growth. Tie-1-expressing cells can be detected in the metanephros when it first forms and, based on transplantation experiments, these precursors contribute to the generation of glomerular capillaries. During glomerular maturation, podocyte-derived Ang-1 and mesangial-cell-derived Ang-2 may affect growth of nascent capillaries. After birth, vasa rectae acquire their mature configuration and Ang-2 expressed by descending limbs of loops of Henle would be well placed to affect the growth of this medullary microcirculation. Finally, preliminary data implicate angiopoietins in deregulated vessel growth in Wilms’ kidney tumours and in vascular remodelling after nephrotoxicity. Received: 13 July 2000 / Revised: 6 September 2000 / Accepted: 11 September 2000     

The development of the myocardium and endocardium in mouse embryos

Summary The formation of the single heart tube by hypothetical fusion of two separately developed heart tubes is re-investigated, because this intricate process is ambiguously and often incompletely described. To gain a better insight into this problem ten mouse embryos ranging from 7.5 to 8.5 days of development (presomite to 6 somites) were serially sectioned (1 m) and reconstructed graphically. Twenty mouse embryos of comparative ages, were studied by scanning electron microscopy. Two large embryonic mesodermal compartments, derived from the primitive streak, extend rostrally on either side of the embryonic axis, and meet in front of the buccopharyngeal membrane. In each compartment a coelomic cavity develops, splitting the mesoderm into a splanchnic and somatic layer. The splanchnic mesoderm differentiates into a layer of cuboidal splanchnic mesothelial cells (promyocardium) and a subjacent plexus of elongated endothelial cells (proendocardium). Before the 1-somite stage the left and right splanchnic mesoderm are separated in front of the buccopharyngeal membrane by a thickening of the yolk sac endoderm. The splanchnic mesoderm then fuses, forming a single horseshoe-shaped heart primordium consisting of a promyocardial layer and a subjacent vascular plexus. Until the 2-somite stage both coelomic cavities remain separated by a bilayer of squamous somatic mesothelial cells (mesocardium). The plexus of endothelial cells that forms the proendocardium, also seems to be the source of the lining of the vitelline veins, the pharyngeal arch arteries and the dorsal aortae. The relatively close adherence of endoderm to the medial part of the horseshoeshaped heart primordium, combined with a bilateral accumulation of cardiac jelly, is suggestive of a double heart tube. However, promyocardium and proendocardium are both translocated as one horseshoe-shaped layer, thus fusion of the left and right parts of the heart primordium does not occur.     

Lesion-targeted thrombopoietin potentiates vasculogenesis by enhancing motility and enlivenment of transplanted endothelial progenitor cells via activation of Akt/mTOR/p70S6kinase signaling pathway

Thrombopoietin (TPO), a physiological regulator of megakaryocyte and platelet development, is a multifunctional positive regulator in early hematopoiesis by hematopoietic stem cells. In this study, we investigated the effect of TPO on endothelial progenitor cells (EPCs) for therapeutic vasculogenesis in vitro and in vivo, and the intracellular signaling mechanism exerting the activity of EPCs. 7-day culture-expanded EPCs derived from human peripheral blood mononuclear cells were applied to each assay. Flow cytometry demonstrated the expression of c-Mpl, the receptor of TPO, in cultured EPCs. In vitro experiments revealed enhanced migration and survival of cultured EPCs by TPO. In vivo, TPO was intramuscularly administered into the foci of ischemic hindlimbs in athymic nude mice, immediately followed by intravenous injection of cultured EPCs, to assess the booster effect of TPO on vascular regeneration. At day 4 post-transplantation, transplanted EPCs were 1.7-fold higher in TPO-treated animals compared to control. At day 28, blood perfusion was recovered in the TPO-treated group, accompanied by an increase in microvascular density. The signaling transduction pathway underlying TPO-mediated activities of cultured EPCs was assessed by Western blotting. TPO induced sequential phosphorylations of Akt to p70S6kinase through mTOR. Inhibition of the PI3-kinase/Akt/mTOR/p70S6kinase signaling pathway negated the biological functions of cultured EPCs, either migration (by LY294002 for PI3-kinase and Rapamycin for mTOR) or survival and tubulogenesis (by Rapamycin). These findings provide evidence that TPO possesses booster potential for therapeutic vasculogenesis, by activating the PI3-kinase/Akt/mTOR/p70S6kinase pathway crucial to the biological activities of EPCs.     

脐血内皮祖细胞梗塞心肌移植参与血管再生

目的 观察犬脐血内皮祖细胞(EPCs)参与梗死心肌血管再生.方法 从妊娠犬脐血提取EPCs,免疫组化鉴定,建立成年杂种犬冠状动脉梗死模型,将1,1-二(十八烷基)-3,3,3′, 3′-四甲基吲哚羰花青高氯酸盐(Dil)标记的EPCs移植入梗死区域,1、4、8周后于冠脉灌注Ⅰ型荆豆凝集素(UEA-1)标记EPCs,处死动物.取心肌标本HE染色确认梗死模型,并在荧光显微镜下观察Dil和UEA-1标记确认EPCs参与梗死心肌血管再生.结果 EPCs呈"铺路石"样外观,细胞标记白细胞分化抗原31阳性(CD31 ),血管性假血友病因子阳性(vWF ),胎肝激酶1阳性(FLK-1 ),白细胞分化抗原34阳性(CD34 );心肌梗死区可见有大量的瘢痕组织、成纤维细胞以及小血管再生;实验组梗死心肌区域标本内小血管上见Dil和UEA-1标记阳性细胞,对照组仅见UEA-1标记细胞.结论 犬脐血EPCs梗死心肌移植可参与血管再生.     

Molecular identity of arteries,veins, and lymphatics

Background

Arteries, veins, and lymphatic vessels are distinguished by structural differences that correspond to their different functions. Each of these vessels is also defined by specific molecular markers that persist throughout adult life; these markers are some of the molecular determinants that control the differentiation of embryonic undifferentiated cells into arteries, veins, or lymphatics.

Vasculogenesis in early human placental villi: an ultrastructural study

In this study we examined the chorionic villi of 5 normal human placentas at 12–14 weeks of gestation ultrastructurally with regard to differentiation of the vascular components. The aim of the present report is to discuss the factors influencing vasculogenesis (in situ formation of blood vessels) at the ultrastructural level.

Our observations have led us to think that the cytotrophoblast influences vasculogenesis in human chorionic villi. Mesenchymal-preendothelial cell groups were always found in very close association with the cytotrophoblast at the periphery of the villi, forming blood vessels. The cytotrophoblast probably attracts mesenchymal cells towards the margin of the villi by secreting vascular endothelial growth factor (VEGF). Once cells attach to the trophoblastic basement membrane they begin to differentiate into endothelial cells. This close structural relation between two cell types (cytotrophoblast and mesenchymal cells) may not be the only mechanism controlling vasculogenesis, but it seems to be one of the factors influencing the differentiation of mesenchymal cells into the endothelial cells of blood vessels in early human chorionic villi.     

The effects of lithium on vascular development in the chick area vasculosa

The effects of lithium on vascular development were examined using the chick embryo area vasculosa in shell-less culture as an experimental model. Embryos were explanted after 48 h in ovo and LiCl (50, 100, 150 and 200 μg in 10 μl water) was applied to the centre of the blastodisc. Controls were untreated or given equimolar amounts of NaCl. At 24 h and 48 h after treatment, untreated and NaCl controls were identical, having well developed extraembryonic vessels. At doses of 100 μg and greater, LiCl significantly inhibited normal vascular development and expansion of the area vasculosa in the majority of explants. In many specimens blood islands continued to form but their assembly into primitive vessels was prevented, indicating that lithium affects the mechanism regulating the assembly of vascular endothelium. At the same time the embryos were alive but retarded in development compared with controls. When LiCl (150 μg) was applied to cultures explanted after 72 h in ovo (when the primary vascular network had already formed through vasculogenesis) no adverse effects were seen. This suggests that lithium affects vasculogenesis but not angiogenesis. Treatment with myo-inositol completely reversed the effects of lithium in a time dependent manner indicating that the phosphatidylinositol second messenger cycle may be involved in the cellular events of vasculogenesis. Finally the results of this study show that the yolk sac vasculature is particularly vulnerable to lithium and the consequent effects of this interference on embryonic development are discussed.