Hypoxia reduces endothelial Ang1-induced Tie2 activity in a Tie1-dependent manner

Cardiac programming in the placentally restricted sheep fetus in early gestation

Fetal growth restriction (FGR) occurs in 8% of human pregnancies, and the growth restricted newborn is at a greater risk of developing heart disease in later adult life. In sheep, experimental restriction of placental growth (PR) from conception results in FGR, a decrease in cardiomyocyte endowment and an upregulation of pathological hypertrophic signalling in the fetal heart in late gestation. However, there is no change in the expression of markers of cellular proliferation nor in the level of cardiomyocyte apoptosis in the heart of the PR fetus in late gestation. This suggests that FGR arises early in gestation and programs a decrease in cardiomyocyte endowment in early, rather than late, gestation. Here, control and PR fetal sheep were humanely killed at 55 days' gestation (term, 150 days). Fetal body and heart weight were lower in PR compared with control fetuses and there was evidence of sparing of fetal brain growth. While there was no change in the proportion of cardiomyocytes that were proliferating in the early gestation PR heart, there was an increase in measures of apoptosis, and markers of autophagy and pathological hypertrophy in the PR fetal heart. These changes in early gestation highlight that FGR is associated with evidence of early cell death and compensatory hypertrophic responses of cardiomyocytes in the fetal heart. The data suggest that early placental restriction results in a decrease in the pool of proliferative cardiomyocytes in early gestation, which would limit cardiomyocyte endowment in the heart of the PR fetus in late gestation. KEY POINTS: Placental restriction leading to fetal growth restriction (FGR) and chronic fetal hypoxaemia in sheep results in a decrease in cardiomyocyte endowment in late gestation. FGR did not change cardiomyocyte proliferation during early gestation but did result in increased apoptosis and markers of autophagy in the fetal heart, which may result in the decreased endowment of cardiomyocytes observed in late gestation. FGR in early gestation also results in increased hypoxia inducible factor signalling in the fetal heart, which in turn may result in the altered expression of epigenetic regulators, increased expression of insulin-like growth factor 2 and cardiomyocyte hypertrophy during late gestation and after birth.

Activation of CXCR7 alleviates cardiac insufficiency after myocardial infarction by promoting angiogenesis and reducing apoptosis

Angiogenesis is an important pathway for revascularization of ischemic tissues after acute myocardial infarction (AMI). It is unclear what role CXCR7 plays in angiogenesis in the ischemic area after AMI, although some researchers have shown that the activation of CXCR7 protectsthe heart under those conditions. Here, we hypothesize that the activation of CXCR7 promotes angiogenesis, reduces cell apoptosis and alleviates cardiac deficiency after AMI. C57BL/6 J mice were subjected to AMI and treated with TC14012 (10 mg/kg) for 24 days. HUVECs were cultured in a hypoxic (2% O₂) environment to generate a model of hypoxia. CXCR7 was knocked down in HUVECs by sh-CXCR7 transfection, and CXCR7 was activated by TC14012 (30 μM) treatment. The results showed that CXCR7 was downregulated in infarcted heart tissue and hypoxic HUVECs. The global activation of CXCR7 may alleviate the decrease in cardiac function indexes - (ejection fraction and fraction shortening), and reduce infarct size after AMI.. Moreover, CXCR7 activation has been shown to enhance the level of angiogenesis in ischemic heart tissue. In vitro, hypoxia-induced angiogenic functional loss and apoptosis are aggravated by CXCR7 knockdown in HUVECs. Both angiogenic impairment and cell apoptosis are rescued by CXCR7 activation. In conclusion, the present study indicates that activation of CXCR7 plays an important protective role for ischemic cells in hypoxic endothelial cells and AMI model mice by promoting angiogenesis and reducing apoptosis, which suggests that CXCR7 may be a potential therapeutic target to rescue the ischemic myocardium..

Angiopoietin 1 attenuates interleukin-6-induced endothelial cell permeability through SHP-1

The regulation of endothelial cell (EC) permeability is critical for the physiological homeostasis of blood vessels and tissues. The elevation of pro-inflammatory cytokines is highly associated with lesions, such as the increased vascular permeability of diabetic retinas. We have previously reported that interleukin-6 (IL-6) increases EC permeability through the downregulation of tight junction protein expression. Angiopoietin 1 (Ang1) has an anti-permeability function, but the effect of Ang1 on vascular permeability induced by inflammatory cytokines is unclear. In the present study, we investigated the effect of Ang1 on IL-6-induced EC permeability and its underlying molecular mechanisms. We demonstrated that Ang1 inhibited the IL-6-induced increase in EC permeability by inhibiting the reductions in the levels of tight junction protein ZO-1 and occludin, which was related to the decrease in vascular endothelial growth factor (VEGF) secretion through the inhibition of STAT3 activation by Ang1. Mechanistically, Ang1 induced the dissociation of the tyrosine phosphatase SHP-1 from the Tie2 receptor and increased the binding of SHP-1 to JAK1, JAK2, and STAT3, which are IL-6 downstream signaling proteins. We conclude that SHP-1 plays an important role in the Ang1-induced inhibition of JAK/STAT3 signaling. These results provide evidence for a potential beneficial role of Ang1 in suppressing the vascular permeability induced by the pro-inflammatory cytokine IL-6 in diabetic retinopathy.

Differential regulation of angiogenesis in the developing mouse brain in response to exogenous activation of the hypoxia-inducible transcription factor system

Angiogenesis due to hypoxic-ischemic (HI) injury represents a crucial compensatory mechanism of the developing brain that is mainly regulated by hypoxia-inducible transcription factors (HIF). Pharmacological stimulation of HIF is suggested as a neuroprotective option, however, studies of its effects on vascular development are limited. We analyzed the influence of the prolyl-4-hydroxylase inhibitor (PHI), FG-4497, and erythropoietin (rhEPO) on post-hypoxic angiogenesis (angiogenic growth factors, vessel structures) in the developing mouse brain (P7) assessed after a regeneration period of 72 h. Exposure to systemic hypoxia (8% O₂, 6 h) was followed by treatment (i.p.) with rhEPO (2500/5000 IU/kg) at 0, 24 and 48 h or FG-4497 (60/100 mg/kg) compared to controls. In response to FG-4497 treatment cortical and hippocampal vessel area and branching were significantly increased compared to controls. This was associated with elevated ANGPT-2 as well as decreased ANGPT-1 and TIE-2 mRNA levels. In response to rhEPO, mildly increased angiogenesis was associated with elevated ANGPT-2 but also TIE-2 mRNA levels in comparison to controls. In conclusion, present data demonstrate a differential regulation of the angiopoietin/TIE-2 system in response to PHI and rhEPO in the post-hypoxic developing brain pointing to potential functional consequences for vascular regeneration and vessel development.

Receptor tyrosine kinase gene expression profiles of Ewing sarcomas reveal ROR1 as a potential therapeutic target in metastatic disease

Receptor tyrosine kinases (RTKs) have provided molecular targets for the development of novel, prognosis-improving agents in many cancers; however, resistances to these therapies occur. On the cellular level, one resistance mechanism is attributed to functional RTK redundancies and compensatory cross-signaling, leading to perception of RTKs as signaling and target networks. To provide a basis for better exploitation of this network in Ewing sarcoma, we generated comprehensive qPCR gene expression profiles of RTKs in Ewing sarcoma cell lines and 21 untreated primary tumors. Key findings confirm broad-spectrum RTK expressions with potential for signaling redundancy. Profile analyses with regard to patient risk-group further revealed several individual RTKs of interest. Among them, VEGFR3 and TIE1 showed high-level expressions and also were suggestive of poor prognosis in localized tumors; underscoring the relevance of angiogenic signaling pathways and tumor-stroma interactions in Ewing sarcoma. Of note, compared to localized disease, tumors derived from metastatic disease were marked by global high-level RTK expressions. Nine individual RTKs were significantly over-expressed, suggesting contributions to molecular mechanisms of metastasis. Of these, ROR1 is being pursued as therapeutic target in leukemias and carcinomas, but un-characterized in sarcomas. We demonstrate expression of ROR1 and its putative ligand Wnt5a in Ewing sarcomas, and of an active ROR1 protein variant in cell lines. ROR1 silencing impaired cell migration in vitro. Therefore, ROR1 calls for further evaluation as a therapeutic target in metastatic Ewing sarcoma; and described as a pseudo-kinase with several isoforms, underlines these additional complexities arising in our understanding of RTK signaling networks.

Effect of aging and cardiovascular risk factors on receptor Tie1 expression in human erectile tissue

INTRODUCTION

Erectile dysfunction is highly prevalent in patients with advanced age or cardiovascular disease risk factors (CVDRFs). These conditions interfere on expression of vascular growth factors and respective receptors causing disturbance in endothelial function.

AIM

This study aims to assess the effect of aging and CVDRF on the expression of tyrosine kinase with immunoglobulin-like and EGF-like domains (Tie) 1 in human corpus cavernosum (CC).

METHODS

CC fragments obtained from programmed surgeries or organ donors were divided into three groups: young, healthy aged, and aged with CVDRF. Angiopoietin (Ang) 1, Ang2, Tie1, and Tie2 mRNA and protein levels were assessed by real-time polymerase chain reaction and Western blotting, respectively. Dual-immunolabeling of Tie1 with specific markers of endothelium and smooth muscle and Ang1 and Ang2 was performed.

MAIN OUTCOME MEASURES

To characterize the expression of Tie1 in human CC and elucidate its potential inhibitory effect in Ang-Tie2 system.

RESULTS

Analysis of mRNAs demonstrated a decrease in Tie1 expression in CVDRF individuals compared with aged or young healthy individuals. No variation for Tie2, Ang1, or Ang2 expression was observed among the studied groups. In all analyzed CC fragments, a 125 kDa band, Tie1, was detected. This protein presented a significant age-related decrease, specially in individuals with CVDRF. Immunofluorescence study revealed Tie1 expression in the endothelium of samples of all experimental groups.

CONCLUSIONS

Employing different methodological approaches, we show for the first time that Tie1 is expressed in human CC endothelium, and its level of expression diminishes in aged individuals, particularly those with CVDRF. This finding reinforces the view that delivery of Ang1 to the CC of erectile dysfunction affected CVDRF patients is able to activate a beneficial Tie2 response.