血管生成素及其受体、血管内皮生长因子与糖尿病肾脏微血管病变的关系

目的 探讨血管生成素(Ang)及其受体(Tie-2)和血管内皮生长因子(VEGF)在糖尿病肾脏中的表达变化规律，研究其与肾脏微血管结构变化的关系。 方法 将雄性成年SD大鼠分成糖尿病组和对照组，糖尿病组采用链脲佐菌素(STZ)腹腔注射造模。采用RT-PCR以及免疫组化技术，连续多时点观察肾脏Ang-1、Ang-2、Tie-2、VEGF以及血栓调节蛋白(TM-1) mRNA和蛋白表达变化规律，并分析其相关性。 结果 (1)糖尿病组Ang-1 mRNA于第4、8周时显著上调(吸光度A，83.58±10.23、88.59±6.97)， 第24周时低于对照组 (47.13±8.02比64.53±8.77，P < 0.05)。免疫组化显示Ang-1突出表达于肾小球，糖尿病组第4周后肾小球阳性染色明显强于对照组(A对数值，4周1.64±0.12比1.08±0.16，24周1.24±0.11比1.11±0.17)。(2) 糖尿病组Tie-2 mRNA在4~16周显著高于对照组(A，4周87.31±11.69比63.62±5.61，16周81.75±8.58比60.15±2.66)。免疫组化显示Tie-2突出表达于肾小球，糖尿病组各时点均显著高于对照组，高峰在4~8周。(3)糖尿病组仅在第16和20周时检测到明显的Ang-2 mRNA表达。免疫组化显示12周后仅在皮质区肾小管周围有Ang-2染色的微血管，而在第16周时最明显。(4) 糖尿病组2~20周时肾小球TM-1染色显著高于对照组(A对数值，2周0.99±0.15比0.68±0.17，20周1.03±0.17比0.74±0.13)， 第24周时低于对照组，但差异无统计学意义。(5)糖尿病组VEGF mRNA和蛋白表达均较对照组明显升高。(6) 糖尿病组Ang-1、Tie-2、VEGF和TM-1相互间均呈正相关，它们与尿蛋白、肾重/体重、肾小球体积、肾小球面积也均呈正相关。结论 (1)糖尿病肾脏存在VEGF、Ang及Tie-2表达的改变，早期Ang-1、Tie-2表达上调， 后期下调并伴Ang-2表达上调。(2)Ang、Tie及VEGF的改变与糖尿病肾脏新生血管生成有关，其Ang-1下调和VEGF、Ang-2上调起重要作用。(3)糖尿病肾脏中后期皮质区肾小管周围已有Ang-2染色的新生微血管生成。     

促血管生成素-1、2及Tie2在血管瘤及血管畸形中的表达及意义

目的探讨促血管生成素-1（Ang-1）、促血管生成素-2（Ang-2）及其受体Tie2在血管瘤和血管畸形组织中的表达及意义。方法应用免疫组织化学S—P方法，测定血管瘤、血管畸形的血管内皮细胞中Ang-1、Ang-2及Tie2的表达。结果Ang-2、Tie2的表达在增生期血管瘤最强；在退化期血管瘤中的表达次之；而在血管畸形中表达较弱，与小儿正常皮肤表达无显著性差异。而Ang-1的表达，各组差异无统计学意义。结论Ang-1、Ang-2及其受体Tie2在血管瘤的血管生成以及血管瘤的自然消退过程中可能起着重要的作用；Ang-1、Ang-2及其受体Tie2的表达可能与血管畸形的发病无明显关系。     

血管内皮生长因子和促血管生成素及其受体Tie2在肝细胞癌发生发展中的作用

目的探讨血管内皮生长因子(VEGF)和促血管生成素(Angiopietin)及其受体Tie2在启动肝细胞癌(HCC)血管生成中的调控机制及在HCC发生发展中的作用。方法新鲜HCC标本及癌旁肝组织38例,用实时定量逆转录-聚合酶链反应(RT-PCR)的方法检测Ang-1、Ang-2、Tie2和VEGF在各组织标本中的表达,以CD34标记新生血管内皮并计数微血管密度(MVD),分析上述因子在HCC组织和非癌肝组织中的表达差异、相互作用及其与MVD、临床病理特征之间的关系。结果Ang-1、Tie2在HCC和非癌肝组织中的表达差异无统计学意义(0．194 7±0．086 2比0．232 6±0．109 8,1．601 6±0．900 7比1．340 0±0．703 7,P均>0．05),而VEGF和Ang-2在HCC组织的表达高于非癌肝组织(1．038 0±0．572 0比0.832 3±0．182 4,0．621 3±0.417 6比0．442 9±0．330 1,P均<0．05);VEGF、Ang-2、Ang-2／1都与MVD和临床病理特征相关(P<0．01),但与组织分化程度无关(P>0．05)。结论Ang-2／1的失衡表达及其与VEGF和Tie2的共同作用是启动肝组织血管生成并诱发HCC发生、发展的重要因素;这种因素在HCC中的持续作用进一步促进了肿瘤血管生成和恶性生物学行为。     

血管内皮生长因子及其受体对糖尿病肾病大鼠微血管病变的作用

目的：探讨血管内皮生长因子（VEGF）及其受体（VEGFR2）在糖尿病肾病（DN）大鼠肾微血管病变发病中的作用。方法：将正常Wistar大鼠12只随机分为正常对照组、糖尿病肾病组。糖尿病肾病组用STZ诱导建立DN模型,大鼠自由进食、饮水。于第4周和第8周各组分别处死大鼠6只。测定血生化及24h尿蛋白定量,以正常肾小球为对照,采用特异性抗体和免疫组织化学方法,观察大鼠肾小球VEGF、VEGFR2、TM-1的分布及其强度变化,并结合肾脏病理进行分析。应用RT-PCR技术测定VEGF和VEGFR2mRNA的表达。结果：（1）糖尿病肾病组第4周,8周时,尿白蛋白排泄率,血糖,血脂升高,均高于正常对照组（P〈0.01）,肾组织光镜,出现早期糖尿病肾病典型的病理改变过程。（2）免疫组化显示糖尿病组4周、8周时肾脏VEGF、VEGFR2及TM-1表达均较正常对照组上调（P〈0.01）,VEGF与TM-1呈正相关（4周时r=0.947,P〈0.001;8周时r=0.923,P〈0.001）;RT-PCR检测结果显示糖尿病肾病组第8周时VEGF-mRNA和VEGFR2-mRNA表达均较正常对照组升高（P〈0.05）,第8周时VEGF-mRNA和VEGFR2-mRNA表达较第4周时增高（P〈0.05）。结论：糖尿病肾病大鼠肾小球VEGF、VEGFR2、TM-1表达增强,与糖尿病肾脏新生血管生成有关。     

血管内皮生长因子及其受体在单侧输尿管梗阻大鼠术侧肾脏的表达

血管内皮生长因子（VEGF）的主要作用是刺激血管内皮细胞的增殖与分化、抑制内皮细胞凋亡，主要通过两个受体Flk-1和Flt-1发挥作用。本研究旨在明确VEGF及其受体在单侧输尿管梗阻（UUO）大鼠术侧肾脏不同时间的表达变化情况，为进一步探讨其在UUO大鼠小管间质纤维化中的作用机制提供实验依据。     

nephrin、血管内皮生长因子及其受体表达与先兆子痫大鼠蛋白尿的关系

目的 研究nephrin、血管内皮生长因子（VEGF）及其受体（VEGFR）在先兆子痫大鼠肾组织的表达与蛋白尿的关系。 方法 采用一氧化氮合酶抑制剂（L-NAME）制备大鼠先兆子痫模型（n=8）,分别与正常雌性组（n=6）、正常妊娠组（n=8）、未孕L-NAME对照组（n=6）大鼠比较动脉收缩压（SBP）、尿蛋白量（24 h）。各组大鼠肾组织分别行光镜和电镜检查。Western印迹法、实时定量PCR检测nephrin在各组大鼠肾脏局部的表达;免疫荧光法检测各组大鼠肾小球内wilms肿瘤蛋白WT1的表达。Western印迹法检测VEGF及VEGFR（Flt-1、Flk-1）在各组大鼠肾脏局部的表达。 结果 先兆子痫模型组大鼠nephrin蛋白的表达（0.0726±0.0074）显著低于正常雌性组（0.3795±0.0509）、正常妊娠组（0.2361±0.0437）及未孕L-NAME对照组大鼠（0.7265±0.0503）（均P < 0.01）;而nephrin mRNA在各组大鼠间差异无统计学意义。各组大鼠足细胞数目差异无统计学意义。先兆子痫大鼠组VEGF的表达（1.5429±0.0898）显著高于正常雌性组（1.1870±0.1160）、正常妊娠组（1.3741±0.1165）、未孕L-NAME对照组大鼠（1.0155±0.0742）（均P < 0.01）;先兆子痫组大鼠VEGFR（Flt-1、Flk-1）的表达均显著高于其他各对照组大鼠（均P < 0.05）。 结论 先兆子痫大鼠中,nephrin蛋白水平表达明显降低,肾脏局部VEGF-VEGFR表达显著增强,可能参与了先兆子痫蛋白尿的生成,其具体机制有待进一步研究。     

大鼠缺血后肢骨骼肌血管内皮生长因子及其受体的表达

目的 研究大鼠缺血后肢侧枝代偿和血管内皮生长因子（VEGF）及其受体表达的动态变化。为外源性VEGF治疗下肢缺血性疾病提供理论依据。方法 切除SD大白鼠右后肢全长股动脉，随机分为9个时间组：造模后1、3d、1、2、3、4、6、8及12周，各组5只动物。分别于造模前后和观察期末检测双后肢大、小腿肌肉Fit-1、Flk-1蛋白及mRNA表达，各组观察期末实验动物后肢动脉DSA检查。结果 （1）缺血后3d，5只大鼠右后肢出现溃疡（11．11％）；2周后，4只大鼠后肢溃疡愈合，而1只趾端坏疽（2．22％）。（2）缺血后2周，患肢侧枝形成达到高峰，12周时仍可见侧支血管显影。（3）缺血早期（3周内），VEGF及其受体的表达均较健侧显著增强（P〈0．05）；缺血中期（3～8周）。VEGF和Flt-1表达迅速下降，Flk-1仍表达；缺血后期（8周后），VEGF及其受体的表达均低至极低水平，与对侧差异无统计学意义（P〉0．05）。结论（1）肢体缺血后自身的血管新生不能完全满足缺血组织的需要。（2）缺血早期外源性的VEGF补充是不必要的；缺血中期补充VEGF是适宜的；缺血后期在应用VEGF治疗的同时，也需要干预受体的表达。     

新生小鼠足细胞损伤对肾小球发育的影响

目的 探讨新生小鼠中足细胞损伤对肾小球发育的影响及其机制。 方法 于新生ICR小鼠出生后1 d注射嘌呤霉素(puromycin aminonucleoside，PA)，并以注射生理盐水作为对照。观察出生后第2、4、8、12、30、60、90天时肾重/体重、尿蛋白、血压及组织学的改变。应用免疫组化及定量RT-PCR方法测定肾皮质内肾母细胞瘤基因(WT-1)、CD31、血管内皮生长因子(VEGF)及其受体Flk-1、血管生成素(angiopoietin，Ang-1、Ang-2)及其受体Tie-1、Tie-2的表达水平。 结果 注射PA后，新生小鼠肾重、体重均明显低于对照组。出生后第2天(注射PA后1 d)时，肾小球足细胞出现足突广泛融合和微绒毛的脱落；第12天时，肾小球内CD31的表达明显下降，部分肾小球萎缩、发育不良，肾皮质浅层小球成熟指数明显下降；第30天时，原先发育不良的肾小球逐渐被吸收；第60天时，剩余肾小球出现系膜区的扩张和小球节段性硬化。PA鼠在第30天时出现蛋白尿；第60天时血压显著增高。定量RT-PCR显示，第2天时肾皮质Ang-1表达明显上调，Flk-1及Tie-2明显下降。 结论 PA可以在早期损伤的新生ICR小鼠足细胞，改变VEGF、血管生成素系统的表达，导致肾小球毛细血管袢发育不良及在后期产生蛋白尿、高血压和肾小球硬化。     

转化生长因子β1对大鼠原代肾小球系膜细胞血管内皮生长因子表达的影响

目的：探讨原代培养的大鼠肾小球系膜细胞血管内皮生长因子（vascular endothelial growth factor，VEGF）的表达及转化生长因子-β1（transforming growth factor-β1，TGF-β1）对其表达的影响。方法：采用RT-PCR和Westernblot方法检测大鼠原代培养的肾小球系膜细胞VEGF表达及不同浓度、不同时间的TGF-β1刺激对VEGF表达的作用。结果：原代培养的大鼠肾小球系膜细胞表达VEGF164、120mRNA，TGF-β1呈时间依赖性增加其表达，在12h表达最高，分别为刺激前3．17、2．925倍，有统计学差异（P〈0．001）。在剂量反应曲线上，2ng／ml TGF-β1刺激作用最强，VEGF164、120mRNA表达分别为未刺激组的2．82、2．45倍，有统计学差异（P〈0．001）。与VEGF mRNA表达一致，大鼠原代肾小球系膜细胞仅见VEGF164蛋白表达，2ng／ml TGF-β1呈时间依赖性的增加VEGF 164蛋白表达，24h达高峰，为刺激前的2．37倍。结论：促进肾小球系膜细胞VEGF表达可能是TGF-β1介导肾脏损害发生、发展的机制之一。     

血管生成素及其受体Tie2在大龄GK大鼠肾皮质中的表达及意义

目的：研究血管生成素（Angiopoietins）及其受体Tie2在大龄GK大鼠肾皮质中的表达及其意义。方法：自发性糖尿病动物（Goto—Kakizaki，GK）大鼠（GK组），在52周时取肾皮质进行病理切片，光镜检查；电镜观察超微结构改变；Re—alt—time RT—PCR和免疫组化法检测大鼠肾皮质血管生成素Ⅰ（Angiopoietin Ⅰ，Ang Ⅰ）、血管生成素Ⅱ（AngiopoietinⅡ，AngⅡ）、血管生成素受体Tie2和血管内皮生长因子（vascular endothelial growth factor，VEGF）mRNA和蛋白质的表达。并与链脲佐菌素（streptozocin，STZ）诱导的糖尿病大鼠（DM组）及正常SD大鼠（SD组）肾皮质进行比较。将Ang Ⅰ、AngⅡ、Tie2和VEGF与肾小球体积和肾小球细胞外基质（ECM）做相关性分析。结果：与SD组比较，GK组大鼠光镜下无病理改变；而DM组大鼠出现肾小球肥大和系膜基质增生；电镜下观察到GK组大鼠肾小球基底膜增厚。Real—time RT—PCR结果显示GK组肾皮质AngI、AngⅡ、Tie2、VEGFmRNA表达与SD对照组比较无统计学差异（P〉0．05）；而其AngⅡ和VEGF mRNA表达较DM组显著性减少（P〈0.05）。免疫组化半定量分析结果显示，GK组大鼠与SD组相比其肾皮质Ang Ⅰ表达显著性增高（P〈0．05），而AngⅡ、Tie2和VEGF的表达无统计学差异。AngⅡ、Tie2和VEGF与肾小球体积呈显著正相关，VEGF与肾小球ECM呈显著正相关。结论：大龄GK大鼠仅有轻微早期糖尿病肾脏改变，Ang Ⅰ表达增高可能是GK大鼠不易发生严重糖尿病肾损害的原因之一，AngⅡ和VEGF可能参与了糖尿病肾病的发病，其机制可能是通过促进血管增生和ECM增多。     

Roles of angiopoietins in kidney development and disease

Angiopoietins are a family of growth factors, the best studied being angiopoietin 1 (Ang-1), which binds to and tyrosine-phosphorylates endothelial Tie-2, causing enhanced survival and cell-cell stabilization. Ang-2 and Tie-1 downregulate Ang-1-induced Tie-2 signaling, and angiopoietin actions are further modified by vascular endothelial growth factor A and integrins. Metanephric capillaries express Tie genes, whereas metanephric mesenchyme, maturing tubules, and mature podocytes express Ang-1. Ang-1 null embryos begin to form blood vessels, but subsequent vascular remodeling fails, and analyses of chimeric wild-type/Tie null mutant embryos show that Tie genes are needed for renal endothelial survival. Ang-2 is transiently expressed in renal arterial smooth muscle and mesangial cells, and tubules around adult vasa rectae express Ang-2. Ang-2 null mice have increased pericytes around kidney cortical peritubular capillaries, perhaps an indirect consequence of upregulated Tie-2 signaling. Ang-1 therapies attenuate peritubular capillary loss in adult models of tubulointerstitial disease, although, in one study, this was accompanied by enhanced inflammation and fibrosis. Podocyte-directed Ang-2 transgenic overexpression causes glomerular endothelial apoptosis, downregulated nephrin expression, and increased albuminuria, and glomerular Ang-2 is upregulated in hyperglycemic and immune-mediated glomerulopathies. Thus, angiopoietins affect podocyte as well as glomerular endothelial biology, and imbalanced angiopoietin signaling contributes to glomerular pathobiology.     

Angiopoietin 1 and vascular endothelial growth factor modulate human glomerular endothelial cell barrier properties

Normal glomerular filtration depends on the combined properties of the three layers of glomerular capillary wall: glomerular endothelial cells (GEnC), basement membrane, and podocytes. Podocytes produce endothelial factors, including angiopoietin 1 (ang1), and vascular endothelial growth factor (VEGF), whereas GEnC express their respective receptors Tie2 and VEGFR2 in vivo. As ang1 acts to maintain the endothelium in other vascular beds, regulating some actions of VEGF, these observations suggest a mechanism whereby podocytes may direct the unique properties of the glomerular endothelium. This interaction was investigated by studies on the barrier properties of human GEnC in vitro. GEnC were examined for expression of endothelium-specific markers by immunofluorescence and Western blotting and for typical responses to TNF-alpha by a cell-based immunoassay. Expression of angiopoietin and VEGF receptors was examined similarly. Barrier properties of GEnC monolayers cultured on porous supports were investigated by measurement of transendothelial electrical resistance (TEER) and passage of labeled albumin. Responses to a cAMP analogue and thrombin were examined before those to ang1 and VEGF. Results confirmed the endothelial origin of GEnC and their expression of Tie2 and VEGFR2. GEnC formed monolayers with a mean TEER of 30 to 40 Omega/cm(2). The cAMP analogue and thrombin increased and decreased TEER by 34.4 and 14.8 Omega/cm(2), respectively, with corresponding effects on protein passage. Ang1 increased TEER by 11.4 Omega/cm(2) and reduced protein passage by 45.2%, whereas VEGF reduced TEER by 12.5 Omega/cm(2) but had no effect on protein passage. Both ang1 and VEGF modulate GEnC barrier properties, consistent with potential in vivo roles; ang1 stabilizing the endothelium and resisting angiogenesis while VEGF induces the high permeability to water, characteristic of the glomerular endothelium.     

Expression of the Vascular Endothelial Growth Factor and Angiopoietins in Mucoepidermoid Carcinoma of Salivary Gland

Disrupted coordination of angiogenesis regulating signals, among them the vascular endothelial growth factor (VEGF) and angiopoietins (Angs), has been associated with abnormal angiogenesis and tumor progression. While VEGF induces endothelial cell proliferation, thereby initiating vessel formation, Angs are subsequently required for mural cell attachment, thus influencing remodeling and maturation of this vasculature. In addition to tumor cell, endothelial and mural cells, as well as myofibroblasts may also contribute to the secretion of these factors. In this study, we have analyzed by immunohistochemistry the expression of VEGF, Ang-1, Ang-2 and the Angs receptor Tie2 in both the stroma and tumor cells of mucoepidermoid carcinoma (MEC) of salivary gland. We have demonstrated that when myofibroblasts were detected adjacent to the cancer cells, they were frequently associated with intense positive staining for Ang-1 and Ang-2, and no reactivity to VEGF and Tie2. These myofibroblast-rich Ang-1 and Ang-2-stained areas were more commonly found in high-grade MEC cases than in low-grade ones. As for the malignant cells, they frequently expressed all proteins studied, but Ang-2 and VEGF were detected at higher levels compared to Ang-1 and Tie2. Our results indicate that the MEC environment favors cooperative activity between Angs and VEGF in modulating vascular growth and tumor aggressiveness.     

Infusion of angiotensin II reduces loss of glomerular capillary area in the early phase of anti-Thy-1.1 nephritis possibly via regulating angiogenesis-associated factors

BACKGROUND: Although angiotensin II (Ang II) is involved in the progression of renal diseases, infusion of Ang II was reported to surprisingly ameliorate the early phase of anti-Thy-1.1 nephritis. Considering the known proangiogenic effect of Ang II and that angiogenic glomerular capillary repair is required for the recovery of damaged glomeruli in rat anti-Thy-1.1 nephritis, we hypothesized that Ang II infusion starting prior to the initiation of nephritis may induce the expression of angiogenic growth factors such as vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), resulting in the increased glomerular capillary area in the early phase. METHODS: Ang II was infused (170 ng/min) in rats, and 5 days later, nephritis was induced by the administration of monoclonal 1-22-3 antibodies. Ang II type 1 or type 2 receptor antagonist (AT(1)R or AT(2)R, respectively) (losartan or PD123319, respectively) was coadministered. RESULTS: Ang II infusion affected on neither the deposition of Ig nor mesangiolysis in the initial phase, and resulted in the aggravation of creatinine clearance at day 14 and 35 after initiating anti-Thy-1.1 nephritis. Histologic alterations were ameliorated accompanied by reduced loss in rat endothelial cell antigen (RECA)-1(+) endothelial area in Ang II-infused nephritic rats on day 6 and 14 as compared to control nephritic group, and nephritic alterations were mostly resolved on day 35 in both groups. At the early stage (day 6), glomerular expression of VEGF and receptors flk-1 and flt-1 as well as Ang-1, and receptor Tie2 were increased, and glomerular monocyte infiltration and the expression of angiopoietin-2 (Ang-2), a natural antagonist of Ang-1, were reduced. Both Ang II receptors were involved in the regulation of angiogenic factors and receptors. CONCLUSION: These results demonstrate that infusion of exogenous Ang II starting prior to the induction of nephritis activates VEGF and Ang-1 signaling regulated via both Ang II receptors, potentially leading to the accelerated recovery of injured glomerular endothelial cells in the early phase of anti-Thy-1.1 nephritis. Increased expression of VEGF and Ang-1 on podocytes further suggests the crucial association of endothelial cells and podocytes in maintaining proper glomerular capillary structures.     

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     

Vascular endothelial growth factor induces nephrogenesis and vasculogenesis.

The expression of vascular endothelial growth factor (VEGF) and its receptors Flt-1 and Flk-1 in the rat kidney was examined during ontogeny using Northern blot analysis and immunocytochemistry. In prevascular embryonic kidneys (embryonic day 14 [E14]), immunoreactive Flt-1 and Flk-1 were observed in isolated angioblasts, whereas VEGF was not detected. Angioblasts aligned forming cords before morphologically differentiating into endothelial cells. In late fetal kidneys (E19), immunoreactive VEGF was detected in glomerular epithelial and tubular cells, whereas Flt-1 and Flk-1 were expressed in contiguous endothelial cells. To determine whether VEGF induces endothelial cell differentiation and vascular development in the kidney, the effect of recombinant human VEGF (5 ng/ml) was examined on rat metanephric organ culture, a model known to recapitulate nephrogenesis in the absence of vessels. After 6 d in culture in serum-free, defined media, metanephric kidney growth and morphology were assessed. DNA content was higher in VEGF-treated explants (1.9 +/- 0.17 microg/kidney, n = 9) than in paired control explants (1.4 +/- 0.10 microg/kidney, n = 9) (P < 0.05). VEGF induced proliferation of tubular epithelial cells, as indicated by an increased number of tubules and tubular proliferating cell nuclear antigen-containing cells. VEGF induced upregulation of Flk-1 and Flt-1 expression, as assessed by Western blot analysis. Developing endothelial cells were identified and localized using immunocytochemistry and electron microscopy. Flt-1, Flk-1, and angiotensin-converting enzyme-containing cells were detected in VEGF-treated explants, whereas control explants were negative. These studies confirmed previous reports indicating that the expression of VEGF and its receptors is temporally and spatially associated with kidney vascularization and identified angioblasts expressing Flt-1 and Flk-1 in prevascular embryonic kidneys. The data indicate that VEGF expression is downregulated in standard culture conditions and that VEGF stimulates growth of embryonic kidney explants by expanding both endothelium and epithelium, resulting in vasculogenesis and enhanced tubulogenesis. These data suggest that VEGF plays a critical role in renal development by promoting endothelial cell differentiation, capillary formation, and proliferation of tubular epithelia.