Zhang Q X, Magovern C J, Mack C A, Budenbender K T, Ko W, Rosengart T K
Department of Cardiothoracic Surgery, New York Hospital-Cornell University Medical College, New York 10021, USA.
J Surg Res. 1997 Feb 1;67(2):147-54. doi: 10.1006/jsre.1996.4983.
Omentum has been used clinically to promote wound healing and to stimulate the revascularization of ischemic tissues. The biologic mechanism responsible for these effects has, however, not yet been defined. A number of polypeptide growth factors that possess potent angiogenic properties have recently been identified, and we therefore sought to determine whether one of these growth factors might be responsible for the angiogenic properties of the omentum. The levels of vascular endothelial growth factor (VEGF) protein in a number of rat tissues and organs were analyzed by Western and enzyme immunoassay analysis. Because omentum was found to have the greatest VEGF concentrations of the tissues examined, antibody neutralization, transcription inhibition assays, and Northern blot analysis were performed under hypoxic and normoxic conditions on tissues extractions and primary tissue cultures of omentum to further characterize the functional significance of VEGF expression in these tissues. The omentum demonstrated the highest VEGF secretion rate as well as the highest concentration of VEGF protein of the various rat tissues and organs examined. Fractionation studies of the omentum furthermore demonstrated that omental adipocytes, rather than the stromal-vascular cells, were the primary source of VEGF protein. An endothelial cell mitogenic assay showed that a major portion of the mitogenic activity of heparin-binding proteins and conditioned media derived from omentum was abolished by VEGF antibody. Additional studies with the transcription inhibitor actinomycin-D furthermore demonstrated that the VEGF gene was continuously transcribed in the rat omental adipocytes. Incubation of the omental adipocytes under hypoxic conditions induced approximately a 1.7-fold increase in VEGF protein expression, which was abolished by actinomycin-D. Northern blot analysis demonstrated that hypoxia resulted in upregulation of the VEGF mRNA in the hypoxia-cultured omental adipocytes, suggesting that the augmentation of VEGF expression in omental adipocytes by hypoxia occurs at the transcriptional level. These data suggest that VEGF is the major angiogenic factor produced by omentum and possibly underlies the mechanism of omentum-induced angiogenesis. Augmented expression of VEGF by omental cells under hypoxic conditions may furthermore reflect the mechanism responsible for enhancing the angiogenic activity of omentum in the setting of ischemia.
大网膜已被临床用于促进伤口愈合和刺激缺血组织的血管再生。然而，导致这些作用的生物学机制尚未明确。最近已鉴定出多种具有强大血管生成特性的多肽生长因子，因此我们试图确定这些生长因子之一是否可能是大网膜血管生成特性的原因。通过蛋白质免疫印迹法和酶免疫分析，分析了多种大鼠组织和器官中血管内皮生长因子（VEGF）蛋白的水平。由于发现大网膜在所检测的组织中VEGF浓度最高，因此在缺氧和常氧条件下，对大网膜组织提取物和原代组织培养物进行了抗体中和、转录抑制试验和Northern印迹分析，以进一步确定VEGF在这些组织中表达的功能意义。在所检测的各种大鼠组织和器官中，大网膜显示出最高的VEGF分泌率以及最高的VEGF蛋白浓度。此外，对大网膜的分级研究表明，大网膜脂肪细胞而非基质血管细胞是VEGF蛋白的主要来源。内皮细胞有丝分裂试验表明，大网膜来源的肝素结合蛋白和条件培养基的大部分促有丝分裂活性被VEGF抗体消除。用转录抑制剂放线菌素-D进行的进一步研究表明，VEGF基因在大鼠大网膜脂肪细胞中持续转录。在缺氧条件下培养大网膜脂肪细胞，可使VEGF蛋白表达增加约1.7倍，这一增加被放线菌素-D消除。Northern印迹分析表明，缺氧导致缺氧培养的大网膜脂肪细胞中VEGF mRNA上调，提示缺氧在转录水平上增加大网膜脂肪细胞中VEGF的表达。这些数据表明，VEGF是大网膜产生的主要血管生成因子，可能是大网膜诱导血管生成机制的基础。在缺氧条件下，大网膜细胞中VEGF表达的增加可能进一步反映了在缺血情况下增强大网膜血管生成活性的机制。
