Expression of VEGF isoforms by epiphyseal chondrocytes during low-oxygen tension is HIF-1 alpha dependent

OBJECTIVE: To establish the role of hypoxia and HIF-1 alpha for VEGF expression of murine epiphyseal chondrocytes. To analyze the effect of hypoxia on VEGF isoform expression. MATERIALS AND METHODS: VEGF mRNA and VEGF isoform expression was investigated in epiphyses of murine newborns by in situ hybridization and real-time PCR. Further, epiphyseal chondrocytes were isolated from newborn mice with homozygous flanking of the HIF-1 alpha gene with lox-P sites. HIF-1 alpha was deleted by infection with adenovirus containing cre-recombinase. After chondrocytes reached confluency they were exposed to 0.5% or 20% oxygen, respectively. Total VEGF and VEGF isoform mRNA expression levels were measured by real-time PCR. Secreted VEGF protein was determined by ELISA. RESULTS: VEGF mRNA signals were detected in the hypertrophic zone and in the center of the proliferative zone of the murine epiphysis, which is considered to be hypoxic. Real-time PCR revealed that VEGF(120)is the dominant isoform in vivo. In cultured epiphyseal chondrocytes strongly increased VEGF gene expression levels were detected after exposure to hypoxia. Furthermore, secretion of VEGF protein was significantly enhanced under 0.5% oxygen. Remarkably, functional inactivation of HIF-1 alpha abolished the hypoxic increase of VEGF expression in chondrocytes completely. Furthermore, the soluble isoforms VEGF(120)and VEGF(164)are the most abundantly expressed splice variants in chondrocytes exposed to low oxygen levels. CONCLUSIONS: The data presented here clearly indicate that hypoxia is able to induce the synthesis of soluble VEGF isoforms by epiphyseal chondrocytes, most likely through stabilization of HIF-1 alpha. Thus it can be speculated that HIF-1 alpha is an essential prerequisite for hypoxic VEGF synthesis in the epiphysis, thereby contributing to the formation and invasion of blood vessels in long bone development.     

5/6肾切除大鼠低氧诱导因子1α和2α在肾内的表达和定位

目的 探讨慢性肾脏病（CKD）进程中低氧诱导因子（HIF）的肾内表达部位和动态表达变化。 方法 雄性SD大鼠行5/6肾切除后,分别于术后第1、2、4、6、8和12周处死大鼠。采集血、尿和肾组织标本,PAS染色观察残肾病理改变;连续切片免疫组化染色观察HIF-1α、HIF-2α在肾脏中的表达部位;Western印迹检测二者的蛋白表达变化;RT-PCR检测靶基因血管内皮生长因子（VEGF）、血红素加氧酶1（HO-1）的mRNA水平变化。 结果 （1）大鼠5/6肾切除后第1周出现了短暂的急性肾衰竭[Scr（122.8±22.1） μmol/L],之后Scr下降并进入稳定的慢性肾衰竭阶段[（66.0±3.7）～（66.4±8.4） μmol/L],第6周后Scr进行性升高,残肾皮质出现进行性间质纤维化病变。（2）在肾切除早期阶段（术后第1周末）,HIF-1α和HIF-2α表达即开始增加,其中HIF-1α仅在萎缩扩张的肾小管上皮细胞表达,HIF-2α则表达于血管内皮细胞、间质成纤维细胞和小动脉的平滑肌细胞;至第4和6周,两者表达到达峰值;此后,伴随Scr升高和病理损伤加重,两者表达逐渐下降。（3）HIF靶基因VEGF、HO-1的mRNA在第4和第6周时呈暂时性的高表达。 结论 CKD早期肾脏皮质HIF蛋白高表达和靶基因转录增加可能是对肾内缺氧的代偿性反应;CKD终末期HIF表达进行性减少,其在CKD进展中的作用值得进一步研究。     

Biological activity of adult cavernous malformations: a study of 56 patients

OBJECT: Cerebral cavernous malformations (CCMs) have previously been considered as congenital and biologically static malformations. On the other hand, the potential for growth and de novo generation of CCMs have also been reported. It is therefore important to study the proliferative and neoangiogenetic capacity of these lesions. METHODS: The authors studied the surgical specimens of 56 CCMs (23 deep and 33 superficial) obtained from adult patients. The proliferative activity of the endothelium and the neoangiogenetic capacity of these lesions were considered through immunohistochemical anaylsis of proliferating cell nuclear antigen (PCNA), MIB-1, Flk-1, vascular endothelial growth factor (VEGF), hypoxia-inducible factor (HIF)-1alpha, and endoglin antibodies. Positive immunostaining of endothelial cells occurred in 86% of patients for PCNA and in 38% of the cases for MIB 1. The expression of Flk-1 was observed in the endothelium of 71% of the cases, for VEGF in 41%, for HIF-1 alpha in 48.1%, and for endoglin in 63.6% of the cases. The correlation of immunohistochemical and clinical data indicated that VEGF was expressed in significantly less deep-seated lesions when compared with superficial CCMs. Neither the expression of the proliferative markers nor the expression of the angiogenetic antibodies correlated with patient age at surgery, sex, or the number of recent prior hemorrhagic episodes in the patients. CONCLUSIONS: The CCMs from adult patients are active lesions exhibiting endothelial proliferation and neoangiogenesis. According to the data in this study, neoangiogenesis is more prominent in superficial CCMs than in deep-seated CCMs and is not associated with recent prior hemorrhages.     

缺氧诱导因子-1α及其相关基因在腹主动脉瘤中的表达及意义

目的研究缺氧诱导因子(HIF)-1α信号转导通路及其相关基因在腹主动脉瘤(AAA)中的表达,探讨AAA的发病机制。方法选取AAA标本22例,以5例腹主动脉(NA)标本作对照。采用Northern杂交、Western蛋白印迹及免疫组织化学方法检测HIF-1α的mRNA及蛋白产物表达,Western蛋白印迹或免疫组织化学方法检测血管内皮生长因子(VEGF)及半胱氨酸蛋白酶(caspase)-3的表达,免疫组织化学抗CD34染色法检测微血管密度(MVD)。结果 AAA组织中HIF-1α的mRNA及蛋白产物表达明显高于NA(P<0.01);caspase-3和VEGF表达亦明显增强(P<0.01),与HIF-1α表达呈显著正相关(r值分别为0.783和0.693,P<0.01)。HIF-1α表达主要分布在AAA中层血管平滑肌细胞及外膜处,与caspase-3和VEGF的分布部位基本一致。AAA中微血管密度明显增加(P<0.01))。结论HIF-1α在AAA疾病进展过程中可能发挥重要作用,其作用机制可能是通过调控VEGF或caspase-3的表达而实现的。     

Increased renal expression of vascular endothelial growth factor (VEGF) and its receptor VEGFR-2 in experimental diabetes.

It has been suggested that the cytokine vascular endothelial growth factor (VEGF) has an important role in the pathogenesis of diabetic retinopathy, but its role in nephropathy has not been clearly demonstrated. Assessment of VEGF, 125I-VEGF binding, and vascular endothelial growth factor receptor-2 (VEGFR-2) in the kidney was performed after 3 and 32 weeks of streptozotocin-induced diabetes. Gene expression of both VEGF and VEGFR-2 was assessed by Northern blot analysis and the localization of the ligand and receptor was examined by in situ hybridization. VEGF and VEGFR-2 protein were also evaluated by immunohistochemistry. Binding of the radioligand 125I-VEGF was evaluated by in vitro and in vivo autoradiography. Diabetes was associated with increased renal VEGF gene expression. VEGF mRNA and protein were localized to the visceral epithelial cells of the glomerulus and to distal tubules and collecting ducts in both diabetic and nondiabetic rats. Renal VEGFR-2 mRNA was increased after 3 weeks of diabetes but not in long-term diabetes. In situ hybridization and immunohistochemical studies revealed that glomerular endothelial cells were the major site of VEGFR-2 expression. In addition, VEGFR-2 gene expression was detected in cortical and renomedullary interstitial cells and on endothelial cells of peritubular capillaries. There was an increase in 125I-VEGF binding sites after 3 but not 32 weeks of diabetes. The major VEGF binding sites were in the glomeruli. 125I-VEGF binding was also observed in medullary rays and in the renal papillae. These studies indicate an early and persistent increase in renal VEGF gene expression in association with experimental diabetes. In addition, an early and transient increase in renal VEGF receptors was also observed in diabetic rats. These findings are consistent with a role for VEGF in mediating some of the changes observed in the diabetic kidney.     

Gene expression of prostanoid forming enzymes along the rat nephron

BACKGROUND: To obtain information about the general capability of nephron segments to elaborate prostanoids, we determined the gene expression of key enzymes for prostanoid formation. METHODS: For this goal mRNAs were assayed for cyclooxygenases-1 and -2 as well as for the synthases of prostaglandin D2 (PGD2), prostaglandin E2 (PGE2), prostacyclin (PGI2) and thromboxane A2 (TXA2) in microdissected rat nephron segments by RT-PCR. RESULTS: Cyclooxygenase-1 (COX-1) mRNA was strongly expressed in all segments of the collecting ducts and to a lesser extent in glomeruli. COX-2 mRNA was found in the cortical thick ascending limb of Henle, and weaker expression also was detected in glomeruli. The lipocalin-type PGD synthase mRNA displayed a broad expression pattern in the cortex and outer medulla, including proximal convoluted tubule, thick ascending limb of Henle, distal convoluted tubule, and cortical and outer medullary collecting duct. The hematopoietic PGD synthase mRNA was restricted to the outer medullary collecting duct, and the membrane-associated PGE-synthase mRNA was exclusively expressed in the whole collecting duct system. Prostacylin-synthase mRNA was found in the whole kidney, but not in any microdissected nephron segment analyzed in this study. TXA-synthase mRNA was expressed in glomeruli. CONCLUSION: Given that the existence of cyclooxygenase in combination with the different PG-synthases is a prerequisite for the formation of prostanoids, our data suggest that PGD2 is mainly formed in the thick ascending limb and in the collecting duct, while PGE2 appears to be mainly generated by the collecting ducts. Probably no formation of PGI2 occurs within the nephron. Whether TXA2 can be formed by nephron segments remains questionable.