EFFECTS OF ALL-TRANS RETINOIC ACID AND RETINOIDS ON ANGIOGENESIS

天然全反式维甲酸(ATRA)通过维甲酸受体(RAR)调节多种重要的细胞功能。全反式维甲酸已被用于治疗各种恶性肿瘤，包括急性早幼粒细胞白血病。最近，全反式维甲酸也被认为对动脉粥样硬化性血管疾病有好处。然而，它对血管生成的影响仍然存在争议。因此，我们采用人脐静脉内皮细胞(HUVEC)/正常人真皮成纤维细胞(NHDF)共培养的方法，通过毛细血管样管的形成来检测ATRA对体外血管生成的影响。ATRA和RAR激动剂AM80均能显著诱导毛细血管样管形成。与RAR拮抗剂LE540/LE135共同孵育可抑制ATRA诱导的小管形成。ATRA也能诱导HUVEC增殖，但不能诱导其迁移。与血管内皮生长因子中和抗体或血管内皮生长因子受体-2(VEGFR-2，KDR)中和抗体共同孵育，可完全消除ATRA诱导的小管形成，但不能与VEGFR-1(Flt-1)中和抗体共同孵育。ATRA可激活ATRA和Am80诱导的NHDF中的血管内皮生长因子基因启动子，RAR过表达可增强ATRA和Am80诱导的血管内皮生长因子基因启动子表达。ATRA还可诱导HUVEC VDGFR-2/KDR基因的表达。此外，ATRA还能诱导肝细胞生长因子(HGF)和血管生成素-2(Ang-2)的分泌。综上所述，ATRA可能主要通过刺激HUVEC增殖和增强内源性血管内皮生长因子信号通路，部分通过诱导HGF和Ang-2的产生，通过RAR诱导血管生成。因此，维甲酸可能是治疗缺血性血管疾病血管生成的潜在候选者。

A natural retinoid all-trans retinoic acid (ATRA) regulates a variety of important cellular functions via retinoic acid receptor (RAR). ATRA has therapeutically been utilized against various malignancies including acute promyelocytic leukemia. Recently, ATRA has also been recognized to be beneficial against atherosclerotic vascular disorders. However, its effects on angiogenesis remain controversial. We therefore examined ATRA effects on in vitro angiogenesis in terms of capillary-like tube formation using human umbilical vein endothelial cells (HUVEC)/normal human dermal fibroblasts (NHDF) co-culture. ATRA as well as RAR agonist Am80 significantly induced capillary-like tube formation. The ATRA-induced tube formation was inhibited by co-incubation with RAR antagonist LE540/LE135. HUVEC proliferation, but not its migration, was also induced by ATRA. The ATRA-induced tube formation was completely abolished by co-incubation with vascular endothelial growth factor (VEGF) neutralizing antibody or with VEGF receptor (VEGFR)-2 (KDR) neutralizing antibody, but not with VEGFR-1 (Flt-1) neutralizing antibody. ATRA and Am80 induced VEGF gene promoter in NHDF was stimulated by ATRA, which was augmented by RAR overexpression. ATRA also induced VDGFR-2/KDR mRNA expression in HUVEC. Moreover, ATRA induced secretion of hepatocyte growth factor (HGF) as well as angiopoietin-2 (Ang-2) in the co-culture. Taken together, ATRA may have induced angiogenesis via RAR mainly by stimulation of HUVEC proliferation and enhancement of endogenous VEGF signaling, and in part by induction of HGF and Ang-2 production. Retinoids may therefore be potential candiadates for therapeutic angiogenesis against ischemic vascular disorders.