Mechanisms underlying somatostatin receptor 2 down-regulation of vascular endothelial growth factor expression in response to hypoxia in mouse retinal explants.

Hypoxia is a trigger of VEGF expression, the primary cause of retinal pathologies characterized by neovascularization. During hypoxia, transcription factors such as STAT3 and HIF-1 promote the increase in VEGF expression. Octreotide, a somatostatin receptor 2 (sst(2) )-preferring agonist, reduces retinal VEGF expression and neovascularization. To investigate the intracellular pathways linking sst(2) activation to the inhibition of hypoxia-induced VEGF up-regulation, we used pharmacological approaches and siRNA in mouse retinal explants cultured in normoxia or hypoxia. In hypoxic explants in which STAT3 or HIF-1 was inhibited, we observed the existence of reciprocal interactions between STAT3 and HIF-1, which synergistically induced VEGF expression. Octreotide prevented hypoxia-induced activation of STAT3 and HIF-1, and the downstream increase in VEGF expression, as evaluated in hypoxic explants treated with pharmacological inhibitors of STAT3 or HIF-1 and in normoxic explants in which pharmacological activators of STAT3 or HIF-1 were used to mimic a hypoxia-like response. The effect of octreotide on STAT3 activation is in part indirect, through the blockade of VEGFR-2 phosphorylation. The effect of octreotide on STAT3, HIF-1, VEGFR-2, and VEGF required Src homology region 2 domain-containing phosphatase 1 (SHP-1). In hypoxic extracts, octreotide induced SHP-1 phosphorylation and activation, and inhibiting SHP-1 abolished the octreotide effect on STAT3, HIF-1, VEGFR-2, and VEGF. The central role of SHP-1 in the modulation of STAT3 and HIF-1 was confirmed in normoxic explants in which pharmacologically activated SHP-1 prevented the effect of STAT3 or HIF-1 activation. Immunohistochemical studies showed that under hypoxia sst(2) and VEGF are expressed by retinal vessels, thus indicating a possible direct effect of octreotide on VEGF-containing endothelial cells. These data clarify the mechanism by which octreotide prevents hypoxia-induced VEGF up-regulation and support the effectiveness of octreotide in treatment of oxygen-induced retinopathies. These results may have implications in designing therapies targeting STAT3 and/or HIF-1 aimed at preventing retinal neovascularization.

Mei S ，Cammalleri M ，Azara D ，Casini G ，Bagnoli P ，Dal Monte M ... -  《-》

Hypoxia effects on proangiogenic factors in human umbilical vein endothelial cells: functional role of the peptide somatostatin.

Dal Monte M ，Martini D ，Ristori C ，Azara D ，Armani C ，Balbarini A ，Bagnoli P ... -  《-》

Effects of somatostatin analogues on retinal angiogenesis in a mouse model of oxygen-induced retinopathy: involvement of the somatostatin receptor subtype 2.

Dal Monte M ，Ristori C ，Cammalleri M ，Bagnoli P ... -  《-》

Acetyl-11-keto-β-boswellic acid reduces retinal angiogenesis in a mouse model of oxygen-induced retinopathy.

Retinal diseases characterized by pathologic retinal angiogenesis are the leading causes of blindness worldwide. Although therapies directed toward vascular endothelial growth factor (VEGF) represent a significant step forward in the treatment of proliferative retinopathies, further improvements are needed. In the last few years, an intense research activity has focused around the use of herbal and traditional natural medicines as an alternative for slowing down the progression of proliferative retinopathies. In the present study, we investigated the antiangiogenic effects of acetyl-11-keto-β-boswellic acid (AKBA), one of the active principles derived from the plant Boswellia serrata, used in Ayurvedic systems of medicine. We studied the antiangiogenic properties of AKBA using the mouse model of oxygen-induced retinopathy (OIR), which mimics the neovascular response seen in human retinopathy of prematurity. We first evaluated the effects of subcutaneously administered AKBA on the expression/activity of proteins which are known to play a role in the OIR model. In the retina, AKBA increased expression and activity of Src homology region 2 domain-containing phosphatase 1 and reduced the phosphorylation of the transcription factor signal transducer and activator of transcription 3 (STAT3) as well as VEGF expression and VEGF receptor (VEGFR)-2 phosphorylation. Likely as a result of these effects, AKBA significantly reduced retinal neovascularization in OIR mice without affecting retinal cell survival and retinal function. Using retinal explants cultured in hypoxia and an activator of STAT3 phosphorylation, we showed that the AKBA-induced inhibition of VEGFR-2 phosphorylation is likely to be mediated by a mechanism depending on an SHP-1/STAT3/VEGF axis. In the OIR model, neovascularization results from the activation of retinal endothelial cells, therefore we evaluated whether AKBA affected the angiogenic response of human retinal microvascular endothelial cells (HRMECs). We observed that AKBA reduced proliferation, migration and tube formation in HRMECs stimulated with exogenous VEGF, while it reduced migration and tube formation in untreated HRMECs. Taken together, our results demonstrate the antiangiogenic effects of AKBA in a model of pathologic neovascularization, providing a rationale for further investigation of AKBA as a promising therapeutic agent to reduce the impact of proliferative retinopathies.

Lulli M ，Cammalleri M ，Fornaciari I ，Casini G ，Dal Monte M ... -  《-》

Expression, localization, and functional coupling of the somatostatin receptor subtype 2 in a mouse model of oxygen-induced retinopathy.

Dal Monte M ，Ristori C ，Videau C ，Loudes C ，Martini D ，Casini G ，Epelbaum J ，Bagnoli P ... -  《-》