EFFECTS OF ALL-TRANS RETINOIC ACID AND RETINOIDS ON ANGIOGENESIS

天然类维甲酸全反式维甲酸（ATRA）通过维甲酸受体（RAR）调节多种重要的细胞功能。ATRA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，ATRA也被认为对动脉粥样硬化性血管疾病有益。然而，它对血管生成的影响仍然存在争议。因此，我们利用人脐静脉内皮细胞(HUVEC)/正常人真皮成纤维细胞（NHDF）共培养，研究了ATRA对体外血管生成的影响，即毛细血管样管的形成。ATRA和RAR激动剂Am80显著诱导毛细血管样管形成。与RAR拮抗剂LE540/LE135共孵育可抑制atra诱导的小管形成。ATRA诱导HUVEC增殖，但不诱导其迁移。与血管内皮生长因子（VEGF）中和抗体或与VEGF受体(VEGFR)-2 （KDR）中和抗体共孵育可完全消除atra诱导的管形成，但与VEGFR-1 （Flt-1）中和抗体共孵育不能完全消除。ATRA和Am80诱导的NHDF中VEGF基因启动子受到ATRA的刺激，RAR过表达增强了VEGF基因启动子的表达。ATRA还能诱导HUVEC中VDGFR-2/KDR mRNA的表达。此外，ATRA在共培养中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VEGF信号，部分通过诱导HGF和Ang-2的产生，通过RAR诱导血管生成。因此，类维生素a可能是治疗血管生成对抗缺血性血管疾病的潜在候选者。

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.