Kruppel-Like Factor 2 Suppression by High Glucose as a Possible Mechanism of Diabetic Vasculopathy

BACKGROUND AND OBJECTIVES: Endothelial dysfunction is widely observed in diabetes mellitus, resulting in diabetic vascular complications. Kruppel-like factor 2 (KLF2) is implicated as being a key molecule that maintains endothelial function. We evaluated the expression of KLF2 in endothelial cells cultured in high glucose and investigated its functional implication in a diabetic animal model. SUBJECTS AND METHODS: Human umbilical vein endothelial cells (HUVECs) were cultured in physiologically high glucose (35 mM) condition. The Otsuka Long Evans Tokushima Fatty (OLETF) strain of rat was used as an excellent model of obese type II diabetes, and their lean littermates are Long Evans Tokushima Otsuka (LETO) rats. RESULTS: In HUVECs cultured in physiologically high glucose condition, FOXO1 was activated whereas KLF2 and endothelial nitric oxide synthase (eNOS) expression was near completely abolished, which was completely reversed by FOXO1 small interfering ribonucleic acid. In the vessels harvested from the OLETF rats, the animal model of type II diabetes, KLF2 and eNOS expression were found depleted. When vascular remodeling was induced in the left common carotid artery by reduction of blood flow with partial ligation of the distal branches, greater neointimal hypertrophy was observed in OLETF rats compared with the control LETO rats. CONCLUSION: KLF2 suppression in endothelial cells by high glucose is a possible mechanism of diabetic endothelial dysfunction. The strategy of replenishing KLF2 may be effective for preventing diabetic vascular dysfunction.

Angiopoietin-1 Protects Endothelial Cells From Hypoxia-Induced Apoptosis via Inhibition of Phosphatase and Tensin Homologue Deleted From Chromosome Ten

BACKGROUND AND OBJECTIVES: Angiopoietin-1 (Ang1) is a regulator of blood vessel growth and maturation, and prevents radiation-induced or serum deprivation-induced apoptosis. Phosphatase and tensin homologue deleted from chromosome ten (PTEN), a well-known tumor suppressor, regulates cell cycle arrest and apoptosis. Hypoxia induces apoptosis by increasing the expression of PTEN. We hypothesized that Ang1 may regulate PTEN expression and, thus, reduce endothelial apoptosis under hypoxia in vitro and in vivo. Materials and METHODS: In vitro, human umbilical vein endothelial cells (HUVECs) were treated with Ang1, and signaling pathways were investigated. In vivo, eight-week-old C57BL/6 mice were used for a hind limb ischemia model. Ang1 or normal saline was intramusculary injected. Blood flow was evaluated by a laser Doppler perfusion analyzer and tissue histology. RESULTS: The expression of PTEN was markedly upregulated in HUVECs after hypoxic stimulation, whereas Ang1 suppressed PTEN expression. Tie2-Fc, a soluble form of Tie2 (sTie2) that blocks Ang1, reversed the Ang1 effect on PTEN reduction under hypoxia. Ang1 inhibited the nuclear translocation of nuclear transcription factor-kB (NF-kB), a binding factor for the PTEN promoter and Foxo1. Hypoxia-induced p27 expression and apoptosis were also suppressed by Ang1. In the mouse hind limb ischemia model, we observed a high capillary density, numerous proliferating cells and diminished cell death in skeletal muscle tissue in the Ang1 injected group. CONCLUSION: Ang1 enhanced endothelial cell survival by reducing apoptosis via PTEN down-regulation in HUVECs under hypoxia. Local injection of Ang1 significantly reduced apoptotic cells in vivo, and prevented limb loss for ischemic hind limb mice. Thus, Ang1 may be an effective therapeutic for protection from ischemic-endothelial cell injury.