The response of VEGF-stimulated endothelial cells to angiostatic molecules is substrate-dependent

Ex vivo HSC expansion challenges the paradigm of unidirectional human hematopoiesis

Understanding mechanisms that determine the behavior of human hematopoietic stem cells (HSCs) is essential for developing novel strategies to expand ex vivo the number of fully functional HSCs. In this review, we focus on the complex interplay between intrinsic mechanisms regulated by transcriptional and mitochondrial networks and extrinsic signals imposed by the bone marrow microenvironment, which in concert regulate the balance between HSC self‐renewal and differentiation. Such integrated signaling mechanisms that dictate the fate of HSCs in vivo must be recapitulated ex vivo to achieve successful expansion of clinically relevant HSCs. We also highlight some of the most recent ex vivo HSC expansion strategies that have currently entered clinical development. Finally, based on the evidence reviewed here and lessons learned from ex vivo HSC expansion, we raise some critical questions regarding HSC fate and the cellular plasticity of hematopoietic cells that challenge the unidirectional model of human hematopoiesis.

Increased Extracellular Matrix Protein Production in Chronic Diabetic Complications: Implications of Non-Coding RNAs

Management of chronic diabetic complications remains a major medical challenge worldwide. One of the characteristic features of all chronic diabetic complications is augmented production of extracellular matrix (ECM) proteins. Such ECM proteins are deposited in all tissues affected by chronic complications, ultimately causing organ damage and dysfunction. A contributing factor to this pathogenetic process is glucose-induced endothelial damage, which involves phenotypic transformation of endothelial cells (ECs). This phenotypic transition of ECs, from a quiescent state to an activated dysfunctional state, can be mediated through alterations in the synthesis of cellular proteins. In this review, we discussed the roles of non-coding RNAs, specifically microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), in such processes. We further outlined other epigenetic mechanisms regulating the biogenesis and/or function of non-coding RNAs. Overall, we believe that better understanding of such molecular processes may lead to the development of novel biomarkers and therapeutic strategies in the future.

Evaluation of Aqueous Endocan and Endostatin Levels in Patients With Pseudoexfoliation Syndrome

PURPOSE

The purpose of the present study was to evaluate the aqueous humor endocan and endostatin levels in patients with pseudoexfoliation (PEX) syndrome and to compare the results with healthy individuals.

MATERIALS AND METHODS

Twenty nine cataract patients with PEX syndrome (PEX group) and 32 cataract patients without PEX syndrome (control group) were enrolled in the study. Endocan and endostatin were measured in the aqueous humor of the PEX and control groups by enzyme-linked immunosorbent assay.

RESULTS

There was no difference between the PEX and control groups in terms of age (P=0.721) and sex (P=0.902). The aqueous levels of endocan in patients with PEX (26.39±5.80 pg/mL) was significantly higher than in the control group (11.42±2.44 pg/mL) (P=0.039). The aqueous levels of endostatin was 12.00±1.35 ng/mL in the PEX group and 14.22±3.31 ng/mL in the control group, however, the difference was not statistically significant (P=0.41).

CONCLUSIONS

The findings of the present study could suggest that the increased levels of aqueous endocan may be related to pathogenesis of PEX. However, levels of aqueous endostatin did not show any significant difference in PEX.

A fusion antitumor peptide regulates proliferation and apoptosis of endothelial cells

The present research has been carried out to elicit the mechanism of antiangiogenic activity of a fusion peptide P2. Peptide P2 was designed by the connection of a heptapeptide MMP inhibitor to ES-2, a fragment of Endostatin. In a previous study, P2 demonstrated strong antiangiogenic and antitumor effect, and the current work explains the antiangiogenic mechanism of P2 through endothelial cell proliferation and apoptosis. In our study, it was shown that P2 inhibited HUVECs proliferation at a low serum concentration and this effect might be achieved through arresting cell cycle by decreasing the expression level of Cyclin D1. In addition, P2 was found to induce apoptosis of HUVECs. Using Western blot, it was indicated that P2 induced the cleavage of Caspase-3, the hallmark protease of apoptosis. The activation and expression of the upstream regulator Caspase-9 can also be affected by P2 treatment. Furthermore, P2 reduced the protein level of antiangiogenic factors Bcl-xL and Bcl-2. These results revealed that P2 regulates endothelial cell apoptosis through intrinsic apoptotic pathway.

Augmented anti-angiogenesis activity of polysulfated heparin-endostatin and polyethylene glycol-endostatin in alkali burn-induced corneal ulcers in rabbits

Endostatin (ES) is an endogenous angiogenesis inhibitor that has the ability to inhibit tumor growth and metastasis. However, its clinical application is limited by a number of disadvantages, such as poor stability, short half-life and the requirement of high doses to maintain its efficacy. The chemical modification on ES may offer a solution to these disadvantages. The aim of the present study was to evaluate the effects of ES, polysulfated heparin-endostatin (PSH-ES) and polyethylene glycol-endostatin (PEG-ES) on the endothelial cell proliferation and angiogenesis associated with corneal neovascularization (CNV) and to determine their mechanisms of action. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) was used to study the effects of ES and its derivatives on endothelial cell proliferation in vitro, and rabbits were used to evaluate the effects of ES and its derivatives on CNV in vivo. In the evaluation of CNV, the expression of vascular endothelial growth factor in the cornea was measured via immunohistochemistry and microvessels were counted. ES and its derivatives significantly inhibited endothelial cell proliferation in vitro (P<0.05) and suppressed CNV in vivo. Among the compounds examined, ES most effectively inhibited endothelial cell proliferation in vitro (P<0.05); however, PSH-ES and PEG-ES most effectively inhibited CNV in vivo (P<0.05). These results indicate that PSH-ES and PEG-ES are candidate anti-angiogenesis drugs.

Fibronectin Interaction and Enhancement of Growth Factors: Importance for Wound Healing

Significance: This critical review focuses on interactions between cells, fibronectin (FN), and growth factors (GF). Recent Advances: Initially, the extracellular matrix (ECM) was thought to serve simply as a reservoir for GFs that would be released as soluble ligands during proteolytic degradation of ECM. This view was rather quickly extended by the observation that ECM could concentrate GFs to the pericellular matrix for more efficient presentation to cell surface receptors. However, recent reports support much more complex interactions among GFs and ECM molecules, particularly FN, and the way these interactions can fine-tune cell responses to the microenvironment. Critical Issues: Wounds that are unable to synthesize and sustain a functional ECM cannot optimally benefit from endogenous or exogenous GFs. Therefore, GF treatments have recently focused on utilizing ECM molecules as delivery vehicles. Thus, ECM can influence GF stability and activity, and GFs can modulate the ECM activity. Hence, both individually and together, ECM and GFs modulate cells that in turn control the type and level of GFs and ECM in the pericellular environment that ultimately results in new tissue generation. Although many ECM components are important for optimal tissue regeneration and wound healing, FN stands out as absolutely critical not only for wound healing and tissue regeneration but also for embryogenesis and morphogenesis. Future Directions: Understanding ECM/GF interactions will greatly facilitate our understanding of normal wound repair and regeneration, the failure of wounds to heal, and how the latter can be salvaged with proper ECM/GF combinations.

Tumor Microenvironment Remodeling by 4-Methylumbelliferone Boosts the Antitumor Effect of Combined Immunotherapy in Murine Colorectal Carcinoma

We have previously demonstrated that a low dose of cyclophosphamide (Cy) combined with gene therapy of interleukin-12 (AdIL-12) has a synergistic, although limited, antitumoral effect in mice with colorectal carcinoma. The main mechanism involved in the efficacy of Cy+AdIL-12 was the induction of a specific immune response mediated by cytotoxic T lymphocytes. Our current aims were to evaluate the effects of 4-methylumbelliferone (4Mu), a selective inhibitor of hyaluronan (HA) synthesis, on tumor microenvironment (TME) and to investigate how 4Mu affects the therapeutic efficacy of Cy+AdIL-12. The results showed that 4Mu significantly reduced the amount of tumoral HA leading to a significant decrease in tumor interstitial pressure (TIP). As a consequence, tumor perfusion was improved allowing an increased adenoviral transgene expression. In addition, treatment with 4Mu boosted the number of cytotoxic T lymphocytes that reach the tumor after adoptive transfer resulting in a potent inhibition of tumor growth. Importantly, we observed complete tumor regression in 75% of mice when 4Mu was administrated in combination with Cy+AdIL-12. The triple combination 4Mu+Cy+AdIL-12 also induced a shift toward antiangiogenic factors production in tumor milieu. Our results showed that TME remodeling is an interesting strategy to increase the efficacy of anticancer immunotherapies based on gene and/or cell therapy.

How does the pathophysiological context influence delivery of bone growth factors?

"Orthobiologics" represents an important category of therapeutics for the regeneration of bone defects caused by injuries or diseases, and bone growth factors are a particularly rapidly growing sub-category. Clinical application of bone growth factors has accelerated in the last two decades with the introduction of BMPs into clinical bone repair. Optimal use of growth factor-mediated treatments heavily relies on controlled delivery, which can substantially influence the local growth factor dose, release kinetics, and biological activity. The characteristics of the surrounding environment, or "context", during delivery can dictate growth factor loading efficiency, release and biological activity. This review discusses the influence of the surrounding environment on therapeutic delivery of bone growth factors. We specifically focus on pathophysiological components, including soluble components and cells, and how they can actively influence the therapeutic delivery and perhaps efficacy of bone growth factors.

Down-regulation of vascular endothelial growth factor and up-regulation of pigment epithelium derived factor make low molecular weight heparin-endostatin and polyethylene glycol-endostatin potential candidates for anti-angiogenesis drug

The aim was to study the effects and action mechanism of endostatin (ES), low molecular weight heparin-endostatin (LMWH-ES) and polyethylene glycol-endostatin (PEG-ES) on endothelial cell proliferation, choroidal neovascularization and zebrafish angiogenesis. Three-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazoliumbromide was used to study the effects of ES and its derivatives on endothelial cell proliferation in vitro. Choroidal neovascularization model was used to evaluate the effects of ES and its derivatives on choroidal neovascularization in vivo. Western blotting was employed to study the effects of ES and its derivatives on the expression of vascular endothelial growth factor (VEGF) and pigment epithelium derived factor (PEDF) in chorioid tissues. Zebrafish model was also used to study the anti-angiogenesis activities of ES and its derivatives. The results showed that ES and its derivatives could significantly inhibit endothelial cell proliferation in vitro (p<0.05), suppress choroidal neovascularization by down-regulating expression of VEGF and up-regulating expression of PEDF in chorioid tissues, and restrain angiogenesis in zebrafish. ES showed better activity in inhibiting endothelial cell proliferation in vitro (p<0.05), but LMWH-ES and PEG-ES showed higher activity in inhibiting choroidal neovascularization in vivo (p<0.05) and angiogenesis in zebrafish (p<0.05). These results indicate that LMWH-endostatin and PEG-endostatin are potential candidates for anti-angiogenesis drug.

Focal adhesion kinase inhibitors are potent anti-angiogenic agents

Focal adhesion kinase (FAK), a cytoplasmic tyrosine kinase and scaffold protein localized to focal adhesions, is uniquely positioned at the convergence point of integrin and receptor tyrosine kinase signal transduction pathways. FAK is overexpressed in many tumor cells, hence various inhibitors targeting its activity have been tested for anti-tumor activity. However, the direct effects of these pharmacologic agents on the endothelial cells of the vasculature have not been examined. Using primary human umbilical vein endothelial cells (HUVEC), we characterized the effects of two FAK inhibitors, PF-573,228 and FAK Inhibitor 14 on essential processes for angiogenesis, such as migration, proliferation, viability and endothelial cell tube formation. We observed that treatment with either FAK Inhibitor 14 or PF-573,228 resulted in reduced HUVEC viability, migration and tube formation in response to vascular endothelial growth factor (VEGF). Furthermore, we found that PF-573,228 had the added ability to induce apoptosis of endothelial cells within 36 h post-drug administration even in the continued presence of VEGF stimulation. FAK inhibitors also resulted in modification of the actin cytoskeleton within HUVEC, with observed increased stress fiber formation in the presence of drug. Given that endothelial cells were sensitive to FAK inhibitors at concentrations well below those reported to inhibit tumor cell migration, we confirmed their ability to inhibit endothelial-derived FAK autophosphorylation and FAK-mediated phosphorylation of recombinant paxillin at these doses. Taken together, our data indicate that small molecule inhibitors of FAK are potent anti-angiogenic agents and suggest their utility in combinatorial therapeutic approaches targeting tumor angiogenesis.

Biomimetic hydrogels with VEGF induce angiogenic processes in both hUVEC and hMEC

Angiogenesis is the process by which new blood vessels arise from the pre-existing vasculature. Human endothelial cells are known to be involved in three key cellular processes during angiogenesis: increased cell proliferation, degradation of the extracellular matrix during cell migration, and the survival of apoptosis. The above processes depend upon the presence of growth factors, such as vascular endothelial growth factor isoform 165 (VEGF(165)) that is released from the extracellular matrix as it is being degraded or secreted from activated endothelial cells. Thus, the goal of the current study is to develop a system with a backbone of polyethylene glycol (PEG) and grafted angiogenic signals to compare the initial angiogenic response of human umbilical vein endothelial cells (hUVEC) or human microvascular endothelial cells (hMEC). Adhesion ligands (PEG-RGDS) for cell attachment and PEG-modified VEGF(165) (PEG-VEGF(165)) are grafted into the hydrogels to encourage the angiogenic response. Our data suggest that our biomimetic system is equally effective in stimulating proliferation, migration, and survival of apoptosis in hMEC as compared to the response to hUVEC.

Molecular mediators of angiogenesis

Angiogenesis, or the formation of new blood vessels from the preexisting vasculature, is a key component in numerous physiologic and pathologic responses and has broad impact in many medical and surgical specialties. In this review, we discuss the key cellular steps that lead to the neovascularization of tissues and highlight the main molecular mechanisms and mediators in this process. We include discussions on proteolytic enzymes, cell-matrix interactions, and pertinent cell signaling pathways and end with a survey of the mechanisms that lead to the stabilization and maturation of neovasculatures.

VEGF induces expression of Bcl-2 and multiple signaling factors in microvascular endothelial cells in a prostate cancer model

PURPOSE

We have previously demonstrated that prostate tumors that highly express Bcl-2 are not only more tumorigenic, but also more angiogenic than low Bcl-2 expressing tumors. Observed increased rates of angiogenesis are likely due to the secretion of multiple factors from the tumor cells.

EXPERIMENTAL DESIGN

Human endothelial cells were subjected to exogenous VEGF or conditioned media from PC-3 cells and assayed by several in vitro systems to better characterize the effects of tumor microenvironment on endothelial cells.

RESULTS

VEGF stimulation increased Bcl-2 expression in human microvascular endothelial cells (HMVECs), at least partially through stabilization of Bcl-2 mRNA transcripts, and protected these cells from apoptosis. These effects were mimicked by treatment of HMVECs with conditioned media from cultured PC-3 prostate tumor cells manipulated to overexpress Bcl-2. Through the use of kinase inhibitors and molecular profiling, several distinct pathways were implicated in the regulation of Bcl-2 in HMVECs, including those involving PI3K/AKT, PKC, mTOR, STAT-1, and IL-8, factors associated with tumor survival and growth.

CONCLUSIONS

This study identifies molecular elements of a link between Bcl-2 expression in distinct cell types within a tumor and reaffirms that strategies designed to target Bcl-2 are desirable as they might enhance treatment response through dual effects.

Bcl-2 mediated modulation of vascularization in prostate cancer xenografts

PURPOSE

We previously demonstrated that Bcl-2 overexpression enhances the radiation resistance of PC-3 human prostate cancer cells and xenografts by inhibiting apoptosis, increasing proliferation, and promoting angiogenesis. To further elucidate the relationship between Bcl-2 expression and the angiogenic potential of PC-3-Bcl-2 cells, tumorigenicity, angiogenesis, and lymphangiogenesis were evaluated and compared in a Bcl-2 overexpressing clone in vitro and in vivo.

EXPERIMENTAL DESIGN

Human prostate cancer cells over expressing Bcl-2 were studied in vitro and in vivo to determine the angiogenic and lymphangiogenic properties of these cells.

RESULTS

Increased Bcl-2 expression enhanced the tumorigenicity of prostate cancer xenografts. It also enhanced the expression and secretion of key angiogenic and lymphangiogenic factors that stimulated the synthesis of CD31-positive blood vessels and LYVE-1 positive lymphatics. Specifically, the increased angiogenic and lymphangiogenic potential correlated with increased serum levels of basic fibroblast growth factor (bFGF), interleukin 8 (CXCL8), and matrix metalloproteinase (MMP 9). In vitro analysis demonstrated that Bcl-2 expressing tumor cells secreted bFGF and vascular endothelial growth factor (VEGF) into culture supernatants. Microarray analysis of Bcl-2 expressing PC-3 cells demonstrated increased transcription of genes involved in metabolism, such as interleukins, growth factors, tumor necrosis factors (TNF) family members, and peptidases.

CONCLUSIONS

Together, these results demonstrate that Bcl-2 can regulate tumoral angiogenesis and lymphangiogenesis and suggest that therapy targeted at Bcl-2 expression, angiogenesis, and lymphangiogenesis may synergistically modulate tumor growth and confirm that Bcl-2 is a pivotal target for cancer therapy.

Attenuation of retinal endothelial cell migration and capillary morphogenesis in the absence of bcl-2

Apoptosis plays a critical role during development and in the maintenance of the vascular system. B-cell leukemia lymphoma 2 (bcl-2) protects endothelial cells (EC) from apoptosis in response to a variety of stimuli. Previous work from this laboratory demonstrated attenuation of postnatal retinal vascular development and retinal neovascularization during oxygen-induced ischemic retinopathy in bcl-2-deficient (bcl-2-/-) mice. To gain further insight into the function of bcl-2 in the endothelium, we isolated retinal EC from bcl-2+/+ and bcl-2-/- mice. Retinal EC lacking bcl-2 demonstrated reduced cell migration, tenascin-C expression, and adhesion to vitronectin and fibronectin. The bcl-2-/- retinal EC also failed to undergo capillary morphogenesis in Matrigel. In addition, using an ex vivo angiogenesis assay, we observed reduced sprouting from aortic rings grown in culture from bcl-2-/- mice compared with bcl-2+/+ mice. Furthermore, reexpression of bcl-2 was sufficient to restore migration and capillary morphogenesis defects observed in bcl-2-/- retinal EC. Mechanistically, bcl-2-/- cells expressed significantly less endothelial nitric oxide synthase, an important downstream effecter of proangiogenic signaling. This may be attributed to increased oxidative stress in the absence of bcl-2. In fact, incubation of retinal EC or aortic rings from bcl-2-/- mice with the antioxidant N-acetylcysteine rescued their capillary morphogenesis and sprouting defects. Thus, bcl-2-mediated cellular functions play important roles not only in survival but also in proangiogenic phenotype of EC with a significant impact on vascular development and angiogenesis.

Voltage-dependent anion channel 1 is involved in endostatin-induced endothelial cell apoptosis

Endostatin (ES) was reported to stimulate apoptosis in endothelial cells, but the exact mechanism remains controversial. In the present study, we elucidate the mechanism of ES-induced endothelial cell apoptosis. Our results indicate that ES induces cytochrome c release and caspase-9 activation in human microvascular endothelial cells (HMECs) at the concentration of 1 microM for 24 h, which initiates the apoptosis process. Further, ATP production, mitochondrial membrane potential, and tubule formation assays showed that ES promotes the mitochondrial permeability transition pore (mPTP) opening via voltage-dependent anion channel 1 (VDAC1), a major component of mitochondrial outer membrane. Knocking down VDAC1 by small interfering RNA attenuates ES-induced apoptosis, while overexpression of VDAC1 enhances the sensitivity of endothelial cells to ES. Moreover, we reveal that ES induces the reduction of hexokinase 2 (HK2), which, in turn, promotes VDAC1 phosphorylation and accumulation. Data from two-dimensional electrophoresis, immunoprecipitation, mPTP opening, and caspase-3 activation assays indicate that two serine residues of VDAC1, Ser-12 and Ser-103, can modulate VDAC1 protein level and thus the sensitivity to apoptosis stimuli. On the basis of these findings, we conclude that VDAC1 plays a vital role in modulating ES-induced endothelial cell apoptosis.

Microenvironmental regulation of biomacromolecular therapies

There is currently great interest in molecular therapies to treat various diseases, and this has prompted extensive efforts to achieve target-specific and controlled delivery of bioactive macromolecules (for example, proteins, antibodies, DNA and small interfering RNA) through the design of smart drug carriers. By contrast, the influence of the microenvironment in which the target cell resides and the effect it might have on the success of biomacromolecular therapies has been under-appreciated. The extracellular matrix (ECM) component of the cellular niche may be particularly important, as many diseases and injury disrupt the normal ECM architecture, the cell adhesion to ECM, and the subsequent cellular activities. This Review will discuss the importance of the ECM and the ECM-cell interactions on the cell response to bioactive macromolecules, and suggest how this information could lead to new criteria for the design of novel drug delivery systems.

Identification of novel short peptides derived from the alpha 4, alpha 5, and alpha 6 fibrils of type IV collagen with anti-angiogenic properties

Angiogenesis, or neovascularization, is tightly controlled by positive and negative regulators, many of which reside in the extracellular matrix. We have now identified eight novel 19- to 20-residue peptides derived from the alpha4, alpha5, and alpha6 fibrils of type IV collagen, which we have designated tetrastatins, pentastatins, and hexastatins, respectively. We have shown that these endogenous peptides suppress the proliferation and migration of HUVECs in vitro. By performing clustering analyses of the sequences using sequence similarity criteria and of the experimental results using a hierarchical algorithm, we report that the clusters identified by the experimental results coincide with the sequence-based clusters, indicating a tight relationship between peptide sequence and anti-angiogenic potency. These peptides may have potential as anti-angiogenic therapeutic agents.

Modulation of response to tumor therapies by the extracellular matrix

The composition of the extracellular matrix in tumors is vastly different from that found in the normal tissue counterparts. As the extracellular matrix can signal to cells via integrin binding and activation, which is known to modulate cell proliferation, survival and migration, it may influence the response of both tumor and endothelial cells to anticancer therapies. Certain tumor-associated extracellular matrix proteins have been shown to confer resistance to chemotherapeutic drugs, radiation and anti-angiogenic factors. The current literature regarding this phenomenon and the potential therapeutic modalities to overcome extracellular matrix-induced resistance will be discussed.

The inhibitory effects of endostatin on endothelial cells are modulated by extracellular matrix

We investigated the ability of extracellular matrix (ECM) proteins to modulate the response of endothelial cells to both promoters and inhibitors of angiogenesis. Using human dermal microvascular endothelial cells (HDMEC), we found that cells demonstrated different adhesive properties and proliferative responses to the growth factor VEGF depending upon which ECM protein with which they were in contact, with fibronectin having the most impact on VEGF-induced HDMEC proliferation and survival. More importantly, we observed that ECM could modulate the ability of the angiogenic inhibitor endostatin to prevent endothelial cell proliferation, survival and migration. We observed that growth on vitronectin or fibronectin impaired the ability of endostatin to inhibit VEGF-induced HDMEC proliferation to the greatest extent as determined by BrdU incorporation. We found that, following growth on collagen I or collagen IV, endostatin only inhibited VEGF-induced HDMEC proliferation at the highest dose tested (2500 ng/ml). In a similar manner, we observed that growth on ECM proteins modulated the ability of endostatin to induce endothelial cell apoptosis, with growth on collagen I, fibronectin and collagen IV impairing endostatin-induced apoptosis. Interestingly, endostatin inhibited VEGF-induced HDMEC migration following culture on collagen I, collagen IV and laminin, while migration was not inhibited by endostatin following HDMEC culture on other matrices including vitronectin, fibronectin and tenascin-C. These results suggest that different matrix proteins may affect different mechanisms of endostatin inhibition of angiogenesis. Taken together, our results suggest that the ECM may have a profound impact on the ability of angiostatic molecules such as endostatin to inhibit angiogenesis and thus may have impact on the clinical efficacy of such inhibitors.