Integrin binding angiopoietin-1 monomers reduce cardiac hypertrophy

Angiopoietin4 (ANGPT4) expression and potential mechanisms in carcinogenesis: current achievements and perspectives

Angiopoietin4(ANGPT4) which plays a significant role in endothelial cell proliferation, survival, angiogenesis and expansion in tumors and other pathological states is a significant regulator of tumor angiogenesis. ANGPT4 expression is enhanced in many cancer cells. For example, the overexpression of ANGPT4 promotes the formation, development and progress of lung adenocarcinoma, glioblastoma and ovarian cancer. Related studies show that ANGPT4 encourages the proliferation, survival and invasion of tumor cells, while promoting the expansion of the tumor vascular system and affecting the tumor immune microenvironment. ANGPT4 can also promote carcinogenesis by affecting the ERK1/2, PI3K/AKT and other signal pathways downstream of tyrosine kinase with immunoglobulin-like and EGF-like domains 2(TIE2) and TIE2. Therefore, ANGPT4 may be a potential and significant biomarker for predicting malignant tumor progression and adverse outcomes. In addition, inhibition of ANGPT4 may be a meaningful cancer treatment. This paper reviews the latest research results of ANGPT4 in preclinical research, and emphasizes its role in carcinogenesis. Additional research on the carcinogenic function of ANGPT4 could provide new insights into cancer biology and novel methods for cancer diagnosis and treatment.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

The Role of Fibrinolytic Regulators in Vascular Dysfunction of Systemic Sclerosis

Systemic sclerosis (SSc) is a connective tissue disease of autoimmune origin characterized by vascular dysfunction and extensive fibrosis of the skin and visceral organs. Vascular dysfunction is caused by endothelial cell (EC) apoptosis, defective angiogenesis, defective vasculogenesis, endothelial-to-mesenchymal transition (EndoMT), and coagulation abnormalities, and exacerbates the disease. Fibrinolytic regulators, such as plasminogen (Plg), plasmin, α2-antiplasmin (α2AP), tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) and its receptor (uPAR), plasminogen activator inhibitor 1 (PAI-1), and angiostatin, are considered to play an important role in the maintenance of endothelial homeostasis, and are associated with the endothelial dysfunction of SSc. This review considers the roles of fibrinolytic factors in vascular dysfunction of SSc.

Increased myocardial stiffness activates cardiac microvascular endothelial cell via VEGF paracrine signaling in cardiac hypertrophy

When the heart is subjected to an increased workload, mechanical stretch together with neurohumoral stimuli activate the "fetal gene program" and induce cardiac hypertrophy to optimize output. Due to a lack of effective methods/models to quantify and modulate cardiac mechanical properties, the connection between these properties and the development of cardiac hypertrophy remains largely unexplored. Here, we utilized an atomic force microscope (AFM) to directly measure the elastic modulus of the hypertrophic myocardium induced by pressure overload. Additionally, we investigated the effects of extracellular elasticity on angiogenesis, which provides blood and nutrition to support cardiomyocyte hypertrophic growth in this process. In response to pressure overload, the myocardium rapidly developed hypertrophy and correspondingly demonstrated a high elastic modulus property. This mechanical feature correlated with enhanced angiogenesis. Mechanistically, we found that a high elastic modulus promoted cultured cardiomyocytes to synthesize and paracrine vascular endothelial growth factor (VEGF) to activate cardiac microvascular endothelial cells. Further analysis showed that the increased elastic modulus enhanced the interaction between Talin1 and integrin β1 to activate the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/hypoxia-inducible factor 1α (Hif-1α) pathway, which contributed to VEGF production. Thus, our study revealed a critical role of the elastic modulus in regulating angiogenesis during the development of cardiac hypertrophy.

Cardioprotective Effects of QiShenYiQi Dripping Pills on Transverse Aortic Constriction-Induced Heart Failure in Mice

QiShenYiQi dripping pills (QSYQ), a traditional Chinese medicine, are commonly used to treat coronary heart disease, and QSYQ was recently approved as a complementary treatment for ischemic heart failure in China. However, only few studies reported on whether QSYQ exerts a protective effect on heart failure induced by pressure overload. In this study, we explored the role of QSYQ in a mouse model of heart failure induced by transverse aortic constriction (TAC). Twenty-eight C57BL/6J mice were divided into four groups: Sham + NS group, Sham + QSYQ group, TAC + NS group, and TAC + QSYQ group. QSYQ dissolved in normal saline (NS) was administered intragastrically (3.5 mg/100 g/day) in the Sham + QSYQ and TAC + QSYQ groups. In the Sham + NS and TAC + NS groups, NS was provided every day intragastrically. Eight weeks after TAC, echocardiography, and cardiac catheterization were performed to evaluate the cardiac function, and immunofluorescent staining with anti-actinin2 antibody was performed to determine the structure of the myocardial fibers. Moreover, TUNEL staining and Masson trichrome staining were employed to assess the effects of QSYQ on cardiac apoptosis and cardiac fibrosis. Western blots and real-time polymerase chain reaction (PCR) were used to measure the expression levels of vascular endothelial growth factor (VEGF) in the heart, and immunohistochemical staining with anti-CD31 antibody was performed to explore the role of QSYQ in cardiac angiogenesis. Results showed that TAC-induced cardiac dysfunction and disrupted structure of myocardial fibers significantly improved after QSYQ treatment. Moreover, QSYQ treatment also significantly improved cardiac apoptosis and cardiac fibrosis in TAC-induced heart failure, which was accompanied by an increase in VEGF expression levels and maintenance of microvessel density in the heart. In conclusion, QSYQ exerts a protective effect on TAC-induced heart failure, which could be attributed to enhanced cardiac angiogenesis, which is closely related to QSYQ. Thus, QSYQ may be a promising traditional Chinese medicine for the treatment of heart failure induced by pressure overload such as hypertension.

Molecular signatures of differential responses to exercise trainings during rehabilitation

The loss and recovery of muscle mass and function following injury and during rehabilitation varies among individuals. While recent expression profiling studies have illustrated transcriptomic responses to muscle disuse and remodeling, how these changes contribute to the physiological responses are not clear. In this study, we quantified the effects of immobilization and subsequent rehabilitation training on muscle size and identified molecular pathways associated with muscle responsiveness in an orthopaedic patient cohort study. The injured leg of 16 individuals with ankle injury was immobilized for a minimum of 4 weeks, followed by a 6-week rehabilitation program. The maximal cross-sectional area (CSA) of the medial gastrocnemius muscle of the immobilized and control legs were determined by T1-weighted axial MRI images. Genome-wide mRNA profiling data were used to identify molecular signatures that distinguish the patients who responded to immobilization and rehabilitation and those who were considered minimal responders. RESULTS: Using 6% change as the threshold to define responsiveness, a greater degree of changes in muscle size was noted in high responders (−14.9 ± 3.6%) compared to low responders (0.1 ± 0.0%) during immobilization. In addition, a greater degree of changes in muscle size was observed in high responders (20.5 ± 3.2%) compared to low responders (2.5 ± 0.9%) at 6-week rehabilitation. Microarray analysis showed a higher number of genes differentially expressed in the responders compared to low responders in general; with more expression changes observed at the acute stage of rehabilitation in both groups. Pathways analysis revealed top molecular pathways differentially affected in the groups, including genes involved in mitochondrial function, protein turn over, integrin signaling and inflammation. This study confirmed the extent of muscle atrophy due to immobilization and recovery by exercise training is associated with distinct remodeling signature, which can potentially be used for evaluating and predicting clinical outcomes.

Constitutive Association of Tie1 and Tie2 with Endothelial Integrins is Functionally Modulated by Angiopoietin-1 and Fibronectin

Functional cross-talk between Tie2 and Integrin signaling pathways is essential to coordinate endothelial cell adhesion and migration in response to the extracellular matrix, yet the mechanisms behind this phenomenon are unclear. Here, we examine the possibility that receptor cross-talk is driven through uncharacterized Tie-integrin interactions on the endothelial surface. Using a live cell FRET-based proximity assay, we monitor Tie-integrin receptor recognition and demonstrate that both Tie1 and Tie2 readily associate with integrins α₅ß₁ and α_Vß₃ through their respective ectodomains. Although not required, Tie2-integrin association is significantly enhanced in the presence of the extracellular component and integrin ligand fibronectin. In vitro binding assays with purified components reveal that Tie-integrin recognition is direct, and further demonstrate that the receptor binding domain of the Tie2 ligand Ang-1, but not the receptor binding domain of Ang-2, can independently associate with α₅ß₁ or α_Vß₃. Finally, we reveal that cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang-1 and fibronectin, suggesting a molecular mechanism to sensitize Tie2 to extracellular matrix. We provide a mechanistic model highlighting the role of receptor localization and association in regulating distinct signaling cascades and in turn, the angiogenic switch.

Diabetic wound regeneration using peptide-modified hydrogels to target re-epithelialization

There is a clinical need for new, more effective treatments for chronic wounds in diabetic patients. Lack of epithelial cell migration is a hallmark of nonhealing wounds, and diabetes often involves endothelial dysfunction. Therefore, targeting re-epithelialization, which mainly involves keratinocytes, may improve therapeutic outcomes of current treatments. In this study, we present an integrin-binding prosurvival peptide derived from angiopoietin-1, QHREDGS (glutamine-histidine-arginine-glutamic acid-aspartic acid-glycine-serine), as a therapeutic candidate for diabetic wound treatments by demonstrating its efficacy in promoting the attachment, survival, and collective migration of human primary keratinocytes and the activation of protein kinase B Akt and MAPK_p42/44 The QHREDGS peptide, both as a soluble supplement and when immobilized in a substrate, protected keratinocytes against hydrogen peroxide stress in a dose-dependent manner. Collective migration of both normal and diabetic human keratinocytes was promoted on chitosan-collagen films with the immobilized QHREDGS peptide. The clinical relevance was demonstrated further by assessing the chitosan-collagen hydrogel with immobilized QHREDGS in full-thickness excisional wounds in a db/db diabetic mouse model; QHREDGS showed significantly accelerated and enhanced wound closure compared with a clinically approved collagen wound dressing, peptide-free hydrogel, or blank wound controls. The accelerated wound closure resulted primarily from faster re-epithelialization and increased formation of granulation tissue. There were no observable differences in blood vessel density or size within the wound; however, the total number of blood vessels was greater in the peptide-hydrogel-treated wounds. Together, these findings indicate that QHREDGS is a promising candidate for wound-healing interventions that enhance re-epithelialization and the formation of granulation tissue.

Angiopoietins promote ovarian cancer progression by establishing a procancer microenvironment

Despite decades of research, the survival rate of ovarian cancer patients is largely unchanged. Current chemotherapeutic drugs are effective only transiently because patients with advanced disease eventually develop resistance. Thus, there is a pressing need for identifying novel therapeutic targets in ovarian cancer. Mounting evidence suggests that angiopoietins (Angpts) may play an essential role in cancer progression; however, the expression profiles and biological effects of Angpts on ovarian cancer remain largely unknown. Here, we show that, compared with their normal counterparts, expressions of Angpt1, Angpt2, and Angpt4 are increased in ovarian cancer cells and tissues and that human ovarian cancer cells also express the Angpt receptor Tie-2-receptor tyrosine kinase. We show that increased expression of Angpt1, Angpt2, or Angpt4 promotes intraperitoneal growth of ovarian cancers and shortens survival of the experimental mice. We further show, for the first time, that Angpts promote accumulation of cancer-associated fibroblasts and tumor angiogenesis in the ovarian cancer microenvironment, as well as enhance ovarian cancer cell proliferation and invasion in vivo. In addition, we establish a novel function of Angpts in promoting proliferation and invasion and inducing Tie-2 and extracellular signal-regulated kinase 1/2 activation in ovarian cancer-associated fibroblasts. Taken together, these data suggest that the Angpt-Tie-2 functional axis is an important player in ovarian cancer progression and an attractive target for ovarian cancer therapy.

Intravascular immunity as a key to systemic vasculitis: a work in progress, gaining momentum

Vascular inflammation contributes to the defence against invading microbes and to the repair of injured tissues. In most cases it resolves before becoming apparent. Vasculitis comprises heterogeneous clinical entities that are characterized by the persistence of vascular inflammation after it has served its homeostatic function. Most underlying mechanisms have so far remained elusive. Intravascular immunity refers to the surveillance of the vasculature by leucocytes that sense microbial or sterile threats to vessel integrity and initiate protective responses that entail most events that determine the clinical manifestations of vasculitis, such as end-organ ischaemia, neutrophil extracellular traps generation and thrombosis, leucocyte extravasation and degranulation. Understanding how the resolution of vascular inflammation goes awry in patients with systemic vasculitis will facilitate the identification of novel pharmacological targets and bring us a step closer in each patient to the selection of more effective and less toxic treatments.

Angiogenesis and cardiac hypertrophy: maintenance of cardiac function and causative roles in heart failure

Cardiac hypertrophy is an adaptive response to physiological and pathological overload. In response to the overload, individual cardiac myocytes become mechanically stretched and activate intracellular hypertrophic signaling pathways to re-use embryonic transcription factors and to increase the synthesis of various proteins, such as structural and contractile proteins. These hypertrophic responses increase oxygen demand and promote myocardial angiogenesis to dissolve the hypoxic situation and to maintain cardiac contractile function; thus, these responses suggest crosstalk between cardiac myocytes and microvasculature. However, sustained pathological overload induces maladaptation and cardiac remodeling, resulting in heart failure. In recent years, specific understanding has increased with regard to the molecular processes and cell-cell interactions that coordinate myocardial growth and angiogenesis. In this review, we summarize recent advances in understanding the regulatory mechanisms of coordinated myocardial growth and angiogenesis in the pathophysiology of cardiac hypertrophy and heart failure.

Angiopoietins in inflammation and their implication in the development of inflammatory bowel disease. A review

BACKGROUND

Angiopoietins are essential angiogenic mediators. Since inflammatory bowel disease (IBD) involves inflammation, ulceration and regeneration of the intestinal mucosa, the angiopoietin system has been proposed as a factor to maintain pathological angiogenesis during the development of the IBD.

AIM

To review the potential role of angiopoietins in the inflammation driven by angiogenesis during the course of the IBD.

METHODS

Publications were identified by PubMed searches using the following key words: angiopoietin; Tie-2 receptor; angiogenesis; inflammatory bowel disease and inflammation, in various combinations.

RESULTS

Angiopoietin-1 acts as a regulator of blood vessel maturation and has anti-inflammatory properties, whereas angiopoietin-2 marks the onset of angiogenesis and is required for normal formation of lymph vessels. Both angiopoietins make use of their angiogenic regulatory effects via the angiopoietin tyrosine-kinase receptor (Tie-2). While angiogenesis has been shown to promote and sustain many events of inflammation, the involvement of the angiopoietin system in IBD has been reported in few studies. It is not clear whether the angiopoietins' role in the development of intestinal inflammation is due to an imbalance in the levels of these proteins or this system exerts its pro-angiogenic properties through a different mechanism during the close-loop relationship between angiogenesis and inflammation.

CONCLUSIONS

Angiopoietins have key functions in the angiogenic process, and their abnormal activation might depend on their surrounding inflamed environment. The determination of these angiogenic factors in serum and tissue could be useful for monitoring IBD progression.

VE-PTP regulates VEGFR2 activity in stalk cells to establish endothelial cell polarity and lumen formation

Vascular endothelial growth factor (VEGF) guides the path of new vessel sprouts by inducing VEGF receptor-2 activity in the sprout tip. In the stalk cells of the sprout, VEGF receptor-2 activity is downregulated. Here, we show that VEGF receptor-2 in stalk cells is dephosphorylated by the endothelium-specific vascular endothelial-phosphotyrosine phosphatase (VE-PTP). VE-PTP acts on VEGF receptor-2 located in endothelial junctions indirectly, via the Angiopoietin-1 receptor Tie2. VE-PTP inactivation in mouse embryoid bodies leads to excess VEGF receptor-2 activity in stalk cells, increased tyrosine phosphorylation of VE-cadherin and loss of cell polarity and lumen formation. Vessels in ve-ptp^−/− teratomas also show increased VEGF receptor-2 activity and loss of endothelial polarization. Moreover, the zebrafish VE-PTP orthologue ptp-rb is essential for polarization and lumen formation in intersomitic vessels. We conclude that the role of Tie2 in maintenance of vascular quiescence involves VE-PTP-dependent dephosphorylation of VEGF receptor-2, and that VEGF receptor-2 activity regulates VE-cadherin tyrosine phosphorylation, endothelial cell polarity and lumen formation.

Vascular endothelial growth factor is implicated in blood vessel development. In zebrafish, Hayashi et al. find that blood vessel development is dependent on the suppression of vascular endothelial growth factor by the phosphatase VE-PTP, which is recruited by activation of the angiopoietin receptor Tie2.

The protective effect of Cold-inducible RNA-binding protein (CIRP) on testicular torsion/detorsion: an experimental study in mice

PURPOSE

To evaluate the expression of Cold-inducible RNA-binding protein (CIRP) in torsion/detorsion of the testes in different phases and demonstrate the protective effect of CIRP on testicular injury after torsion/detorsion (T/D) in an experimental mouse model.

METHODS

Twenty-four male BALB/c mice were divided randomly into 8 groups: normal control group (N), sham-operated group (S), torsion 2 h group (T2h), torsion/detorsion 12 h group (T/D12h), and T/D24h, T/D48h, T/D72h, and T/D96h groups. The testes were examined for the expression levels of CIRP. Another 32 male BALB/c mice were divided randomly in to 4 groups: normal control group (N), T/D group, T/D+pcDNA3.1 group, and T/D + pcDNA3.1-CIRP group. The plasmids were transfected into testes with in vivo-jetPEI. After 3 days, morphological changes, mean seminiferous tubule diameter (MSTD), and the number of the germ cell layers were observed. Superoxide dismutase (SOD) activity, the levels of malondialdehyde (MDA), and Bcl-2/Bax ratios were studied in the different groups.

RESULTS

Compared with the N and S groups, the expression of CIRP in the T2h group was down-regulated. In T/D groups, the levels of CIRP were reduced in a time dependent manner. Compared to T/D and T/D+pcDNA3.1 group, the MSTD, number of the germ cell layers, SOD activity, and Bcl-2/Bax ratio increased in T/D + pcDNA3.1-CIRP group, while the level of MDA decreased.

CONCLUSIONS

The results of our study have shown that down-regulated CIRP is involved in testicular injury after testicular torsion/detorsion. Up-regulation of the expression of CIRP may reduce the damage caused by torsion/detorsion, possibly by preventing germ cell oxidative stress and apoptosis.

Enhanced Angpt1/Tie2 signaling affects the differentiation and long-term repopulation ability of hematopoietic stem cells

Angiopoietin-1 (Angpt1) signaling via the Tie2 receptor regulates vascular and hematopoietic systems. To investigate the role of Angpt1-Tie2 signaling in hematopoiesis, we prepared conditionally inducible transgenic (Tg) mice expressing a genetically engineered Angpt1, cartridge oligomeric matrix protein (COMP)-Angpt1. The effects of COMP-Angpt1 overexpression in osteoblasts on hematopoiesis were then investigated by crossing COMP-Angpt1 Tg mice with Col1a1-Cre Tg mice. Interestingly, peripheral blood analyses showed that 4 week (wk)-old (but not 8 wk-old) Col1a1-Cre+/COMP-Angpt1+ mice had a lower percentage of circulating B cells and a higher percentage of myeloid cells than Col1a1-Cre-/COMP-Angpt1+ (control) mice. Although there were no significant differences in the immunophenotypic hematopoietic stem and progenitor cell (HSPC) populations between Col1a1-Cre+/COMP-Angpt1+ and control mice, lineage(-)Sca-1(+)c-Kit(+) (LSK) cells isolated from 8 wk-old Col1a1-Cre+/COMP-Angpt1+ mice showed better long-term bone marrow reconstitution ability. These data indicate that Angpt1-Tie2 signaling affects the differentiation capacity of hematopoietic lineages during development and increases the stem cell activity of HSCs.

Overexpression of angiopoietin-1 increases CD133+/c-kit+ cells and reduces myocardial apoptosis in db/db mouse infarcted hearts

Hematopoietic progenitor CD133(+)/c-kit(+) cells have been shown to be involved in myocardial healing following myocardial infarction (MI). Previously we demonstrated that angiopoietin-1(Ang-1) is beneficial in the repair of diabetic infarcted hearts. We now investigate whether Ang-1 affects CD133(+)/c-kit(+) cell recruitment to the infarcted myocardium thereby mediating cardiac repair in type II (db/db) diabetic mice. db/db mice were administered either adenovirus Ang-1 (Ad-Ang-1) or Ad-β-gal systemically immediately after ligation of the left anterior descending coronary artery (LAD). Overexpression of Ang-1 resulted in a significant increase in CXCR-4/SDF-1α expression and promoted CD133(+)/c-kit(+), CD133(+)/CXCR-4(+) and CD133(+)/SDF-1α(+) cell recruitment into ischemic hearts. Overexpression of Ang-1 led to significant increases in number of CD31(+) and smooth muscle-like cells and VEGF expression in bone marrow (BM). This was accompanied by significant decreases in cardiac apoptosis and fibrosis and an increase in myocardial capillary density. Ang-1 also upregulated Jagged-1, Notch3 and apelin expression followed by increases in arteriole formation in the infarcted myocardium. Furthermore, overexpression of Ang-1 resulted in a significant improvement of cardiac functional recovery after 14 days of ischemia. Our data strongly suggest that Ang-1 attenuates cardiac apoptosis and promotes cardiac repair by a mechanism involving in promoting CD133(+)/c-kit(+) cells and angiogenesis in diabetic db/db mouse infarcted hearts.

Vascular disruption and the role of angiogenic proteins after spinal cord injury

Spinal cord injuries (SCI) can result in devastating paralysis, for which there is currently no robustly efficacious neuroprotective/neuroregenerative treatment. When the spinal cord is subjected to a traumatic injury, the local vasculature is disrupted and the blood–spinal cord barrier is compromised. Subsequent inflammation and ischemia may then contribute to further secondary damage, exacerbating neurological deficits. Therefore, understanding the vascular response to SCI and the molecular elements that regulate angiogenesis has considerable relevance from a therapeutic standpoint. In this paper, we review the nature of vascular damage after traumatic SCI and what is known about the role that angiogenic proteins—angiopoietin 1 (Ang1), angiopoietin 2 (Ang2) and angiogenin—may play in the subsequent response. To this, we add recent work that we have conducted in measuring these proteins in the cerebrospinal fluid (CSF) and serum after acute SCI in human patients. Intrathecal catheters were installed in 15 acute SCI patients within 48 h of injury. CSF and serum samples were collected over the following 3–5 days and analysed for Ang1, Ang2 and angiogenin protein levels using a standard ELISA technique. This represents the first description of the endogenous expression of these proteins in an acute human SCI setting.

Multiple roles of angiopoietins in atherogenesis

PURPOSE OF REVIEW

The roles of angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) during vascular development have been extensively investigated, as has been their role in controlling the responsiveness of the endothelium to exogenous cytokines. However, very little is known about the role of these vascular morphogenic molecules in the pathogenesis of atherosclerosis. Here, we summarize the recent research into angiopoietins in atherosclerosis.

RECENT FINDINGS

Angiopoietin-2 is a context-dependent agonist that protects against the development of arteriosclerosis in rat cardiac allograft. A recent study showed, contrary to expectations, that a single systemic administration of adenoviral Ang-2 to apoE mice, fed a Western diet, reduced atherosclerotic lesion size and LDL oxidation in a nitric oxide synthase dependent manner. In contrast, overexpression of Ang-1 fails to protect from rat cardiac allograft due to smooth muscle cell activation. The potential proatherogenic effect of Ang-1 is further supported by the induction of chemotaxis of monocytes by Ang-1 in a manner that is independent of Tie-2 and integrin binding. These studies highlight the need for extensive research to better understand the role of angiopoietins in the cardiovascular setting.

SUMMARY

Ang-2 inhibits atherosclerosis by limiting LDL oxidation via stimulation of nitric oxide production. In contrast, Ang-1 can promote monocyte and neutrophil migration. The angiopoietin-Tie-2 system provides an important new target for modulating vascular function.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Angiopoietin-1 promotes endothelial differentiation from embryonic stem cells and induced pluripotent stem cells

Angiopoietin-1 (Ang1) plays a crucial role in vascular and hematopoietic development, mainly through its cognate receptor Tie2. However, little is known about the precise role of Ang1 in embryonic stem cell (ESC) differentiation. In the present study, we used COMP-Ang1 (a soluble and potent variant of Ang1) to explore the effect of Ang1 on endothelial and hematopoietic differentiation of mouse ESCs in an OP9 coculture system and found that Ang1 promoted endothelial cell (EC) differentiation from Flk-1(+) mesodermal precursors. This effect mainly occurred through Tie2 signaling and was altered in the presence of soluble Tie2-Fc. We accounted for this Ang1-induced expansion of ECs as enhanced proliferation and survival. Ang1 also had an effect on CD41(+) cells, transient precursors that can differentiate into both endothelial and hematopoietic lineages. Intriguingly, Ang1 induced the preferential differentiation of CD41(+) cells toward ECs instead of hematopoietic cells. This EC expansion promoted by Ang1 was also recapitulated in induced pluripotent stem cells (iPSCs) and human ESCs. We successfully achieved in vivo neovascularization in mice by transplantation of ECs obtained from Ang1-stimulated ESCs. We conclude that Ang1/Tie2 signaling has a pivotal role in ESC-EC differentiation and that this effect can be exploited to expand EC populations.

Activated NHE1 is required to induce early cardiac hypertrophy in mice

The Na+/H+ exchanger isoform 1 (NHE1) has been implicated as being causal in cardiac hypertrophy and the protein level and activity are elevated in the diseased myocardium. However, it is unclear whether mere elevation of the protein is sufficient for cardiac pathology, or whether activation of the protein is required. In this study, we examined the comparative effects of elevation of wild type and activated NHE1. Two mouse transgenic models that expressed either a wild type NHE1 protein or an activated NHE1 protein were characterized. Expression of activated NHE1 caused significant increases in heart weight to body weight, apoptosis, cross-sectional area, interstitial fibrosis and decreased cardiac performance. Expression of wild type NHE1 caused a much milder pathology. When we examined 2 or 10-week-old mouse hearts, there was neither elevation of calcineurin levels nor increased phosphorylation of ERK or p38 in either NHE1 transgenic mouse line. Expression of activated NHE1 in intact mice caused an increased sensitivity to phenylephrine-induced hypertrophy. Our results show that expression of activated NHE1 promotes cardiac hypertrophy to a much greater degree than elevated levels of wild type NHE1 alone. In addition, expression of activated NHE1 promotes greater sensitivity to neurohormonal stimulation. The results suggest that activation of NHE1 is a key component that accentuates NHE1-induced myocardial pathology.

T-cadherin is critical for adiponectin-mediated cardioprotection in mice

The circulating, adipocyte-secreted hormone adiponectin (APN) exerts protective effects on the heart under stress conditions. The receptors binding APN to cardiac tissue, however, have remained elusive. Here, we report that the glycosyl phosphatidylinositol–anchored cell surface glycoprotein T-cadherin (encoded by Cdh13) protects against cardiac stress through its association with APN in mice. We observed extensive colocalization of T-cadherin and APN on cardiomyocytes in vivo. In T-cadherin-deficient mice, APN failed to associate with cardiac tissue, and its levels dramatically increased in the circulation. Pressure overload stress resulted in exacerbated cardiac hypertrophy in T-cadherin-null mice and paralleled corresponding defects in mice lacking APN. During ischemia-reperfusion injury, the absence of T-cadherin increased infarct size similar to that in APN-null mice. Myocardial AMPK is a major downstream protective signaling target of APN. In both cardiac hypertrophy and ischemia-reperfusion models, T-cadherin was necessary for APN-dependent AMPK phosphorylation. In APN-null mice, recombinant adenovirus-expressed APN reduced exaggerated hypertrophy and infarct size and restored AMPK phosphorylation as previously reported. In contrast, rescue was ineffective in mice lacking T-cadherin in addition to APN. These data suggest that T-cadherin protects from stress-induced pathological cardiac remodeling by binding APN and activating its cardioprotective functions.

Photocrosslinkable chitosan modified with angiopoietin-1 peptide, QHREDGS, promotes survival of neonatal rat heart cells

Myocardial infarction (MI) results in the death of cardiomyocytes (CM), which causes scar formation and pathological remodeling of the heart. The delivery of healthy myocytes or bone marrow cells reduces pathological remodeling after MI, however, current cell injection methods have low cell survival rates and high cell loss. The main objective of this work was to develop a novel hydrogel that can promote survival of CMs. Photocrosslinkable azidobenzoic acid modified chitosan (Az-chitosan) was conjugated with the angiopoietin-1-derived peptide, QHREDGS. This novel peptide is thought to mediate attachment and survival responses of CM to angiopoietin-1 via integrin binding. Thin layers of Az-chitosan, Az-chitosan-QHREDGS, and Az-chitosan-DGQESHR (scrambled peptide control) were spin coated on glass slides and photocrosslinked with application of UV light (365 nm). Neonatal rat heart cells cultured up to 5 days, demonstrated significantly higher attachment and viability on Az-chitosan-QHREDGS compared to cells on other hydrogel controls. Surfaces were also stained for the CM-specific marker troponin I, demonstrating significantly higher percentage of CMs on Az-chitosan-QHREDGS compared to Az-chitosan. The cells cultivated on Az-chitosan-QHREDGS demonstrated significantly lower levels of caspase 3/7 activation after taxol treatment in comparison to cells cultivated on the control hydrogels, glass substrate, or Az-chitosan linked to RGD, an established integrin binding peptide that did not protect against apoptosis. Thus, Az-chitosan-QHREDGS supports attachment and survival of neonatal rat heart cells.

Angiopoietin-4 promotes glioblastoma progression by enhancing tumor cell viability and angiogenesis

Glioblastoma multiforme (GBM) is a highly invasive and vascularized aggressive brain tumor. Less than 10% of GBM patients survive >5 years after diagnosis. Angiogenesis plays an important role in GBM growth, and antiangiogenesis-based therapies have shown clinical efficacy for GBM patients. Unfortunately, therapeutic resistance often develops in these patients, suggesting that GBM cells are capable of switching their dependency on one proangiogenic signaling pathway to an alternative one. Therefore, it is important to identify novel angiogenic factors that play essential roles in tumor angiogenesis and GBM progression. Angiopoietins (Ang-1, Ang-2, and Ang-4) are the ligands of the Tie-2 receptor tyrosine kinase (RTK). The roles of Ang-1 and Ang-2 in tumor angiogenesis have been established. However, little is known about how Ang-4 affects tumor angiogenesis and GBM progression and the mechanism underlying its effects. In our current study, we establish that Ang-4 is upregulated in human GBM tissues and cells. We show that, like endothelial cells, human GBM cells express Tie-2 RTK. We first establish that Ang-4 promotes in vivo growth of human GBM cells by promoting tumor angiogenesis and directly activating extracellular signal-regulated kinase 1/2 (Erk1/2) in GBM cells. Our results establish the novel effects of Ang-4 on tumor angiogenesis and GBM progression and suggest that this pro-GBM effect of Ang-4 is mediated by promoting tumor angiogenesis and activating Erk1/2 kinase in GBM cells. Together, our results suggest that the Ang-4-Tie-2 functional axis is an attractive therapeutic target for GBM.

Angiopoietins, abdominal aortic aneurysm and atherosclerosis

Abdominal aortic aneurysm (AAA) and atherosclerosis are common causes of mortality and morbidity in an aging population. Angiogenesis is believed to contribute to the development and progression of these diseases. Angiopoietins (angpts) are known to be important regulators of angiogenesis. Angpts can also influence inflammation and have been shown to possess both pro-atherosclerotic and atheroprotective effects. This review explores the potential roles that the angpts play in the development and progression of AAA and atherosclerosis.

Clinical and genetic correlates of circulating angiopoietin-2 and soluble Tie-2 in the community

BACKGROUND

Experimental studies suggest that endothelial growth factors play an important role in angiogenesis and vascular remodeling. The clinical and genetic correlates of circulating angiopoietin-2 (Ang-2) and its soluble receptor/regulator Tie-2 (sTie-2) have not been determined in a community-based sample.

METHODS AND RESULTS

Serum Ang-2 and sTie-2 were assayed in 3778 third-generation cohort participants of the Framingham Heart Study (mean age, 40+/-9 years; 53% women). Clinical correlates and heritability of both biomarkers were assessed using generalized estimating equations and variance-component analyses. Ang-2 levels were higher and sTie-2 levels were lower in women than in men. Ang-2 was positively related to age, smoking, systolic blood pressure, hypertension treatment, and diabetes (P<0.05 for all) but was inversely associated with total cholesterol and diastolic blood pressure (P<0.0001 for both), and sTie-2 was positively associated with body mass index, diabetes, and triglycerides but was inversely related to age, alcohol consumption, and glomerular filtration rate (P<0.05 for all). Both Ang-2 and sTie-2 were higher in participants with metabolic syndrome (P<0.005), with stronger associations of Ang-2 with blood pressure traits and of sTie-2 with obesity-dyslipidemia components. Heritability estimates for Ang-2 and sTie-2 were 27% and 56%, respectively (P<0.0001). A region on chromosome 9 was significantly linked to circulating sTie-2 levels (logarithm of the odds score, 8.31).

CONCLUSION

Circulating levels of Ang-2 and sTie-2 are heritable traits associated with cardiovascular disease risk factors, including the metabolic syndrome. These observations are consistent with the notion that angiogenesis and vascular remodeling are determined in part by genetic influences and associated with metabolic risk factors.

Angiopoietin-1 reduces H(2)O(2)-induced increases in reactive oxygen species and oxidative damage to skin cells

UV light-based damage to skin cells can cause photoaging and skin cancer. A major cause of UV light-induced damage to skin is increased free radicals, such as superoxides. Increased superoxides can cause oxidative and nitrative damage to cell components. Thus, agents that counteract these damages may have therapeutic value. Herein, we show that angiopoietin-1 (ang1) prevented and blocked H(2)O(2)-induced increases in superoxides in human spontaneously immortalized keratinocyte line, HaCaT, and primary melanocytes (HeMn). Ang1 prevented H(2)O(2)-induced increases in damage to DNA (8-hydroxy-2'-deoxyguanosine) and proteins (nitrotyrosinylation). Ang1 promoted skin cell metabolism/viability, adhesion, and akt and MAPK(p42/44) activations. Using multi-gene transcriptional profiling, we found that skin cells express integrin subunits {(beta(1), beta(4-6), beta(8), alpha(v), alpha(2), alpha(3), alpha(6) (HaCaT)), (beta(1), beta(3), beta(5), beta(8), alpha(v), alpha(3) (HeMn))} and lack tie2 receptor mRNA. Integrin antibodies (alpha(v), beta(1)) disrupted skin cell adhesion to ang1 and ang1-induced decreases in superoxides. Our findings show that ang1 blocks free radical damage to skin cells and may be clinically useful to prevent and/or reduce photoaging and skin cancer.

The role of the Angiopoietins in vascular morphogenesis

The Angiopoietin/Tie system acts as a vascular specific ligand/receptor system to control endothelial cell survival and vascular maturation. The Angiopoietin family includes four ligands (Angiopoietin-1, Angiopoietin-2 and Angiopoietin-3/4) and two corresponding tyrosine kinase receptors (Tie1 and Tie2). Ang-1 and Ang-2 are specific ligands of Tie2 binding the receptor with similar affinity. Tie2 activation promotes vessel assembly and maturation by mediating survival signals for endothelial cells and regulating the recruitment of mural cells. Ang-1 acts in a paracrine agonistic manner inducing Tie2 phosphorylation and subsequent vessel stabilization. In contrast, Ang-2 is produced by endothelial cells and acts as an autocrine antagonist of Ang-1-mediated Tie2 activation. Ang-2 thereby primes the vascular endothelium to exogenous cytokines and induces vascular destabilization at higher concentrations. Ang-2 is strongly expressed in the vasculature of many tumors and it has been suggested that Ang-2 may act synergistically with other cytokines such as vascular endothelial growth factor to promote tumor-associated angiogenesis and tumor progression. The better mechanistic understanding of the Ang/Tie system is gradually paving the way toward the rationale exploitation of this vascular signaling system as a therapeutic target for neoplastic and non-neoplastic diseases.

Angiopoietin 2 is a partial agonist/antagonist of Tie2 signaling in the endothelium

Angiopoietin 2 (Ang2) was originally shown to be a competitive antagonist for Ang1 of the receptor tyrosine kinase Tie2 in endothelial cells (ECs). Since then, reports have conflicted on whether Ang2 is an agonist or antagonist of Tie2. Here we show that Ang2 functions as an agonist when Ang1 is absent but as a dose-dependent antagonist when Ang1 is present. Exogenous Ang2 activates Tie2 and the promigratory, prosurvival PI3K/Akt pathway in ECs but with less potency and lower affinity than exogenous Ang1. ECs produce Ang2 but not Ang1. This endogenous Ang2 maintains Tie2, phosphatidylinositol 3-kinase, and Akt activities, and it promotes EC survival, migration, and tube formation. However, when ECs are stimulated with Ang1 and Ang2, Ang2 dose-dependently inhibits Ang1-induced Tie2 phosphorylation, Akt activation, and EC survival. We conclude that Ang2 is both an agonist and an antagonist of Tie2. Although Ang2 is a weaker agonist than Ang1, endogenous Ang2 maintains a level of Tie2 activation that is critical to a spectrum of EC functions. These findings may reconcile disparate reports of Ang2's effect on Tie2, impact our understanding of endogenous receptor tyrosine kinase signal transduction mechanisms, and affect how Ang2 and Tie2 are targeted under conditions such as sepsis and cancer.

Estrogen stimulates the human endometrium to express a factor(s) that promotes vascular smooth muscle cell migration as an early step in microvessel remodeling

Vascular smooth muscle cell (VSMC) migration is a pivotal early step in blood vessel remodeling; however, very little is known about the regulation of this process in the human endometrium during the menstrual cycle. In this study, explants of human endometrium were incubated with estradiol and/or progesterone and the conditioned medium (CM) applied to cultures of VSMC to test the hypothesis that estrogen and progesterone stimulate endometrial cells to secrete a factor(s) that promotes VSMC migration. Endometrial explants were composed of highly organized glands and stroma. VSMC migration (cells migrated in 21 h/mm(2) fibronectin-coated semipermeable membrane) in the presence of CM from human endometrial explants obtained in the proliferative phase of the menstrual cycle and incubated for 24 h with estradiol was approximately threefold greater (P < 0.001) than with medium alone and greater (P < 0.05) than with CM from explants treated with estradiol plus progesterone or progesterone. It is concluded, therefore, that estrogen stimulates endometrial secretion of a factor(s) that promotes VSMC migration as an early step in vessel remodeling within the endometrium.

Integrin and growth factor receptor alliance in angiogenesis

A sequence of events in vascular and stromal cells maintained in a highly coordinated manner regulates angiogenesis and tissue remodeling. These processes are mediated by the ability of cells to respond to environmental cues and activate surface integrins. Physiological and pathological processes in vascular biology are dependent on the specificity of important signaling mechanisms that are activated through the association between growth factors, their receptors, integrins, and their specific extracellular matrix ligands. A large body of evidence from in vitro and in vivo models demonstrates the importance of coordination of signals from the extracellular environment that activates specific tyrosine kinase receptors and integrins in order to regulate angiogenic processes in vivo. In addition to complex formation between growth factor receptors and integrins, growth factors and cytokines also directly interact with integrins, depending upon their concentration levels in the environment, and differentially regulate integrin-related processes. Recent studies from a number of laboratories including ours have provided important novel insights into the involvement of many signaling events that improve our existing knowledge on the cross-talk between growth factor receptors and integrins in the regulation of angiogenesis. In this review, our focus will be on updating the recent developments in the field of integrin-growth factor receptor associations and their implications in the vascular processes.

Ang-1 gene therapy inhibits hypoxia-inducible factor-1alpha (HIF-1alpha)-prolyl-4-hydroxylase-2, stabilizes HIF-1alpha expression, and normalizes immature vasculature in db/db mice

OBJECTIVE

Diabetic impaired angiogenesis is associated with impairment of hypoxia-inducible factor-1alpha (HIF-1alpha) as well as vasculature maturation. We investigated the potential roles and intracellular mechanisms of angiopoietin-1 (Ang-1) gene therapy on myocardial HIF-1alpha stabilization and vascular maturation in db/db mice.

RESEARCH DESIGN AND METHODS

db/db mice were systemically administrated adenovirus Ang-1 (Ad-CMV-Ang-1). Myocardial HIF-1alpha, vascular endothelial growth factor (VEGF), hemeoxygenase-1 (HO-1), endothelial nitric oxide synthase (eNOS), Akt, and HIF-1alpha-prolyl-4-hydroxylase-2 (PHD)2 expression were measured. Vasculature maturation, capillary and arteriole densities, and cardiac interstitial fibrosis were analyzed in the border zone of infarcted myocardium.

RESULTS

Systemic administration of Ad-CMV-Ang-1 results in overexpression of Ang-1 in db/db mice hearts. Ang-1 gene therapy causes a significant increase in Akt and eNOS expression and HIF-1alpha stabilization. This is accompanied by a significant upregulation of VEGF and HO-1 expression. Intriguingly, Ang-1 gene therapy also leads to a significant inhibition of PHD2 expression. Smooth muscle recruitment and smooth muscle coverage in the neovessels of the border zone of infarcted myocardium are severely impaired in db/db mice compared with wild-type mice. Ang-1 gene therapy rescues these abnormalities, which leads to a dramatic increase in capillary and arteriole densities and a significant reduction of cardiac hypertrophy and interstitial fibrosis at 14 days after ischemia. Taken together, our data show that Ang-1 increases myocardial vascular maturation and angiogenesis together with suppression of PHD2 and the upregulation of HIF-1alpha signaling.

CONCLUSIONS

Normalization of immature vasculature by Ang-1 gene therapy may represent a novel therapeutic strategy for treatment of the diabetes-associated impairment of myocardial angiogenesis.