Distinct roles of β1 integrins during angiogenesis

Angiogenesis in the Outer Membrane of Chronic Subdural Hematomas through Thrombin-Cleaved Osteopontin and the Integrin α9 and Integrin β1 Signaling Pathways

BACKGROUND

A chronic subdural hematoma (CSDH) is considered to be an inflammatory and angiogenic disease. The CSDH outer membrane, which contains inflammatory cells, plays an important role in CSDH development. Osteopontin (OPN) is an extracellular matrix protein that is cleaved by thrombin, generating the N-terminal half of OPN, which is prominently involved in integrin signal transduction. We explored the expression of the N-terminal half of OPN in CSDH fluid and the expression of integrins α9 and β1 and the downstream components of the angiogenic signaling pathways in the outer membrane of CSDHs.

METHODS

Twenty samples of CSDH fluid and eight samples of CSDH outer membrane were collected from patients suffering from CSDHs. The concentrations of the N-terminal half of OPN in CSDH fluid samples were measured using ELISA kits. The expression levels of integrins α9 and β1, vinculin, talin-1, focal adhesion kinase (FAK), paxillin, α-actin, Src and β-actin were examined by Western blot analysis. The expression levels of integrins α9 and β1, FAK and paxillin were also examined by immunohistochemistry. We investigated whether CSDH fluid could activate FAK in cultured endothelial cells in vitro.

RESULTS

The concentration of the N-terminal half of OPN in CSDH fluid was significantly higher than that in the serum. Western blot analysis confirmed the presence of these molecules. In addition, integrins α9 and β1, FAK and paxillin were localized in the endothelial cells of vessels within the CSDH outer membrane. FAK was significantly phosphorylated immediately after treatment with CSDH fluid.

CONCLUSION

Our data suggest that the N-terminal half of OPN in CSDH fluid promotes neovascularization in endothelial cells through integrins α9 and β1. The N-terminal half of OPN, which is part of the extracellular matrix, plays a critical role in the promotion of CSDHs.

Single-Cell and Spatial Transcriptomics Decodes Wharton's Jelly-Derived Mesenchymal Stem Cells Heterogeneity and a Subpopulation with Wound Repair Signatures

The highly heterogeneous characteristics of Wharton's jelly mesenchymal stem cells (WJ-MSCs) may be responsible for the poor clinical outcomes and poor reproducibility of treatments based on WJ-MSCs. Exploration of WJ-MSC heterogeneity with multimodal single-cell technologies will aid in establishing accurate MSC subtyping and developing screening protocols for dominant functional subpopulations. Here, the characteristics of WJ-MSCs are systematically analyzed by single cell and spatial transcriptome sequencing. Single-cell transcriptomics analysis identifies four WJ-MSC subpopulations, namely proliferative_MSCs, niche-supporting_MSCs, metabolism-related_MSCs and biofunctional-type_MSCs. Furthermore, the transcriptome, cellular heterogeneity, and cell-state trajectories of these subpopulations are characterized. Intriguingly, the biofunctional-type MSCs (marked by S100A9, CD29, and CD142) selected in this study exhibit promising wound repair properties in vitro and in vivo. Finally, by integrating omics data, it has been found that the S100A9⁺ CD29⁺ CD142⁺ subpopulation is more enriched in the fetal segment of the umbilical cord, suggesting that this subpopulation deriving from the fetal segment may have potential for developing into an ideal therapeutic agent for wound healing. Overall, the presented study comprehensively maps the heterogeneity of WJ-MSCs and provides an essential resource for future development of WJ-MSC-based drugs.

Schwann cells-derived exosomes promote functional recovery after spinal cord injury by promoting angiogenesis

Exosomes are small vesicles that contain diverse miRNA, mRNA, and proteins that are secreted by multiple cells, and play a vital function in cell-cell communication. Numerous exosomes produced by cells have been demonstrated to be protective against spinal cord injury (SCI). This study aims to investigate the neuroprotective effect of Schwann cells-derived exosomes (SCs-Exos) on spinal cord injury. We found that SCs-Exos can be taken directly by brain-derived endothelial cells.3 (bEnd.3 cells) and promoted to proliferate, migrate, and form bEnd.3 tube. Additionally, our results showed that the pro-angiogenesis molecules, Integrin-β1, were highly expressed in SCs-Exos. Moreover, we used special shRNA technology to investigate the role of Integrin-β1 in mediating the effect of SCs-Exos-induced angiogenesis on bEnd.3 cells. We observed that the pro-angiogenic effect of SCs-Exos on bEnd.3 cells was suppressed by inhibiting the expression of integrin-β1 in SCs-Exos. In the SCI model, we found that SCs-Exos attenuated tissue damage and improved functional recovery after SCI. Using immunofluorescence staining, we observed that SCs-Exos treatment promoted angiogenesis in SCI, and integrin-β1 was required to promote angiogenesis. In conclusion, our results indicate that SCs-Exos promote angiogenesis by delivering integrin-β1 and may serve as a promising novel therapeutic agent for enhancing neurological functional recovery after SCI.

Palmitic acid inhibits prostate cancer cell proliferation and metastasis by suppressing the PI3K/Akt pathway

AIMS

Prostate cancer is one of the most frequent causes of cancer death in men worldwide, and novel drugs for prostate cancer therapies are still being developed. Palmitic acid is a common saturated long-chain fatty acid that is known to exhibit anti-inflammatory and metabolic regulatory effects and antitumor activities in several types of tumors. The present study aims to explore the antiproliferative and antimetastatic activities of palmitic acid on human prostate cancer cells and the underlying mechanism.

MAIN METHODS

MTT and colony formation assays were utilized to determine the antiproliferative effect of palmitic acid. Cell metastasis was evaluated by wound healing, Transwell migration and invasion assay. The in vivo anticancer effect was assessed by a nude mouse xenograft model of prostate cancer. The involved molecular mechanisms were investigated by flow cytometry and Western blot analysis.

KEY FINDINGS

Palmitic acid significantly suppressed prostate cancer cell growth in vitro and in vivo. Treatment with palmitic acid induced G1 phase arrest, which was associated with downregulation of cyclin D1 and p-Rb and upregulation of p27. In addition, palmitic acid could inhibit prostate cancer cell metastasis, in which suppression of PKCζ and p-Integrinβ1 and an increase in E-cadherin expression might be involved. Furthermore, a mechanistic study indicated that palmitic acid inhibited the key molecules of the PI3K/Akt pathway to block prostate cancer proliferation and metastasis.

SIGNIFICANCE

Our findings suggested the antitumor potential of palmitic acid for prostate cancer by targeting the PI3K/Akt pathway.

Impact of chemically defined culture media formulations on extracellular vesicle production by amniotic epithelial cells

The therapeutic properties of cell derived extracellular vesicles (EVs) make them promising cell-free alternative to regenerative medicine. However, clinical translation of this technology relies on the ability to manufacture EVs in a scalable, reproducible, and cGMP-compliant manner. To generate EVs in sufficient quantity, a critical step is the selection and development of culture media, where differences in formulation may influence the EV manufacturing process. In this study, we used human amniotic epithelial cells (hAECs) as a model system to explore the effect of different formulations of chemically defined, commercially sourced media on EV production. Here, we determined that cell viability and proliferation rate are not reliable quality indicators for EV manufacturing. The levels of tetraspanins and epitope makers of EVs were significantly impacted by culture media formulations. Mass spectrometry-based proteomic profiling revealed proteome composition of hAEC-EVs and the influence of media formulations on composition of EV proteome. This study has revealed critical aspects including cell viability and proliferation rate, EV yield, and tetraspanins, surface epitopes and proteome composition of EVs influenced by media formulations, and further insight into standardised EV production culture media that should be considered in clinical-grade scalable EV manufacture for generation of therapeutic EVs.

Angiogenesis in the ischemic core: A potential treatment target?

The ischemic penumbra is both a concept in understanding the evolution of cerebral tissue injury outcome of focal ischemia and a potential therapeutic target for ischemic stroke. In this review, we examine the evidence that angiogenesis can contribute to beneficial outcomes following focal ischemia in model systems. Several studies have shown that, following cerebral ischemia, endothelial proliferation and subsequent angiogenesis can be detected beginning four days after cerebral ischemia in the border of the ischemic core, or in the ischemic periphery, in rodent and non-human primate models, although initial signals appear within hours of ischemia onset. Components of the neurovascular unit, its participation in new vessel formation, and the nature of the core and penumbra responses to experimental focal cerebral ischemia, are considered here. The potential co-localization of vascular remodeling and axonal outgrowth following focal cerebral ischemia based on the definition of tissue remodeling and the processes that follow ischemic stroke are also considered. The region of angiogenesis in the ischemic core and its surrounding tissue (ischemic periphery) may be a novel target for treatment. We summarize issues that are relevant to model studies of focal cerebral ischemia looking ahead to potential treatments.

Isolation and characterization of equine native MSC populations

Background

In contrast to humans in which mesenchymal stem/stromal cell (MSC) therapies are still largely in the clinical trial phase, MSCs have been used therapeutically in horses for over 15 years, thus constituting a valuable preclinical model for humans. In human tissues, MSCs have been shown to originate from perivascular cells, namely pericytes and adventitial cells, which are identified by the presence of the cell surface markers CD146 and CD34, respectively. In contrast, the origin of MSCs in equine tissues has not been established, preventing the isolation and culture of defined cell populations in that species. Moreover, a comparison between perivascular CD146⁺ and CD34⁺ cell populations has not been performed in any species.

Methods

Immunohistochemistry was used to identify adventitial cells (CD34⁺) and pericytes (CD146⁺) and to determine their localization in relation to MSCs in equine tissues. Isolation of CD34⁺ (CD34⁺/CD146^–/CD144^–/CD45^–) and CD146⁺ (CD146⁺/CD34^–/CD144^–/CD45^–) cell fractions from equine adipose tissue was achieved by fluorescence-activated cell sorting. The isolated cell fractions were cultured and analyzed for the expression of MSC markers, using qPCR and flow cytometry, and for the ability to undergo trilineage differentiation. Angiogenic properties were analyzed in vivo using a chorioallantoic membrane (CAM) assay.

Results

Both CD34⁺ and CD146⁺ cells displayed typical MSC features, namely growth in uncoated tissue culture dishes, clonal growth when seeded at low density, expression of typical MSC markers, and multipotency shown by the capacity for trilineage differentiation. Of note, CD146⁺ cells were distinctly angiogenic compared with CD34⁺ and non-sorted cells (conventional MSCs), demonstrated by the induction of blood vessels in a CAM assay, expression of elevated levels of VEGFA and ANGPT1, and association with vascular networks in cocultures with endothelial cells, indicating that CD146⁺ cells maintain a pericyte phenotype in culture.

Conclusion

This study reports for the first time the successful isolation and culture of CD146⁺ and CD34⁺ cell populations from equine tissues. Characterization of these cells evidenced their distinct properties and MSC-like phenotype, and identified CD146⁺ cells as distinctly angiogenic, which may provide a novel source for enhanced regenerative therapies.

Shed syndecan-2 inhibits angiogenesis

Angiogenesis is essential for the development of a normal vasculature, tissue repair and reproduction, and also has roles in the progression of diseases such as cancer and rheumatoid arthritis. The heparan sulphate proteoglycan syndecan-2 is expressed on mesenchymal cells in the vasculature and, like the other members of its family, can be shed from the cell surface resulting in the release of its extracellular core protein. The purpose of this study was to establish whether shed syndecan-2 affects angiogenesis. We demonstrate that shed syndecan-2 regulates angiogenesis by inhibiting endothelial cell migration in human and rodent models and, as a result, reduces tumour growth. Furthermore, our findings show that these effects are mediated by the protein tyrosine phosphatase receptor CD148 (also known as PTPRJ) and this interaction corresponds with a decrease in active β1 integrin. Collectively, these data demonstrate an unexplored pathway for the regulation of new blood vessel formation and identify syndecan-2 as a therapeutic target in pathologies characterised by angiogenesis.

Proteins involved in focal adhesion signaling pathways are differentially regulated in experimental branch retinal vein occlusion

Branch retinal vein occlusion (BRVO) is a common retinal vascular disease, but global protein changes following the condition remain largely unelucidated. To bring new insights into pathological processes and identify potential therapeutic targets, large-scale retinal protein changes following BRVO were studied by combining a porcine model of experimental BRVO with proteomic analysis by label-free liquid chromatography mass spectrometry. Among a total set of 1974 proteins, 52 significantly upregulated proteins and 10 significantly downregulated proteins were identified in retinas with BRVO after 15 days. Significantly upregulated proteins were involved in signaling pathways of focal adhesion via integrin and blood coagulation. Proteins involved in focal adhesion signaling included collagen α-2 chain, laminin subunit β-2, laminin subunit γ-1, lipocalin-7, nidogen-2, osteopontin, integrin-β, α-actinin-1, isoform 2 of α-actinin-1, talin-2 and filamin C. The identified proteins indicate that BRVO was associated with extracellular matrix remodeling processes. The present study identified focal adhesion signaling and ECM remodeling as important biological mechanisms to evaluate in the search for signaling pathways that promote neovascularisation and macular edema following BRVO.

Brain endothelial cell specific integrins and ischemic stroke

Ischemic stroke, a devastating event caused by the blockage of a blood vessel(s) supplying the brain, continues to affect thousands of people in the USA every year. While no true advances in stroke therapy have arisen to further improve patient outcomes since the introduction of the blood clot buster tissue plasminogen activator and mechanical clot removal, fewer people are dying from the immediate stroke insult. Instead, patients often suffer significant morbidity due to post-recanalization secondary damage. Central to this damage is the breakdown of the blood-brain barrier, which, in addition to contributing to edema and inflammation, triggers an upregulation in angiogenic growth factors in the brain's attempt to salvage and repair itself. Recent studies have begun to improve our understanding of the post-stroke angiogenic response of brain endothelial cells in the ischemic penumbra, which has long been held to be an important site for medical intervention. These studies suggest that endothelial cell integrin matrix receptors play an important and therapeutically significant role in moderating cellular responses to ischemic brain injury.

A conserved C-terminal sequence of high-risk cutaneous beta-human papillomavirus E6 proteins alters localization and signalling of β1-integrin to promote cell migration

Beta-human papillomaviruses (β-HPV) infect cutaneous epithelia, and accumulating evidence suggests that the virus may act as a co-factor with UV-induced DNA damage in the development and progression of non-melanoma skin cancer, although the molecular mechanisms involved are poorly understood. The E6 protein of cutaneous β-HPV types encodes functions consistent with a role in tumorigenesis, and E6 expression can result in papilloma formation in transgenic animals. The E6 proteins of high-risk α-HPV types, which are associated with the development of anogenital cancers, have a conserved 4 aa motif at their extreme C terminus that binds to specific PDZ domain-containing proteins to promote cell invasion. Likewise, the high-risk β-HPVs HPV5 and HPV8 E6 proteins also share a conserved C-terminal motif, but this is markedly different from that of α-HPV types, implying functional differences. Using binding and functional studies, we have shown that β-HPV E6 proteins target β1-integrin using this C-terminal motif. E6 expression reduced membrane localization of β1-integrin, but increased overall levels of β1-integrin protein and its downstream effector focal adhesion kinase in human keratinocytes. Altered β1-integrin localization due to E6 expression was associated with actin cytoskeleton rearrangement and increased cell migration that was abolished by point mutations in the C-terminal motif of E6. We concluded that modulation of β1-integrin signalling by E6 proteins may contribute towards the pathogenicity of these β-HPV types.

Regulation of Tumor Angiogenesis and Choroidal Neovascularization by Endogenous Angioinhibitors

Angiogenesis is the process of neovascularization from parent blood vessels, which is a prerequisite for many physiological and pathological conditions and is regulated by a balance between endogenous angioinhibitors and angioactivators or angiogenic factors. Imbalance between angioinhibitors and angioactivators is associated with neovascularization capacity during progression of tumor development and Choroidal Neovascularization (CNV). Normalization of pathological angiogenesis is considered as an alternative strategy to prevent the tumor growth in cancer progression or retinal damage in CNV. Various angioinhibitors are being identified and evaluated for their pathological angiogenesis regulation, of which endogenous angioinhibitors are one class derived either from extra cellular matrix or from non-extra cellular matrix of human origin. Endogenous angioinhibitors are gaining much significance as they interact with proliferating endothelial cells by binding to distinct integrins and non-integrin receptors, regulating different intracellular signaling mechanisms leading to inhibition of choroidal neovascularization and tumor growth. This review will focus on endogenous angioinhibitors and their receptor(s) mediated angioinhibitory signaling, which are of major concern in angiogenesis and their clinical and pharmaceutical implications.

The role of extracellular matrix in vascular branching morphogenesis

Angiogenesis requires the development of a hierarchically branched network of vessels, which undergoes radial expansion and anastomosis to form a close circuit. Branching is achieved by coordinated behavior of endothelial cells that organize into leading “tip” cells and trailing “stalk” cells. Such organization is under control of the Dll4-Notch signaling pathway, which sets a hierarchy in receptiveness of cells to VEGF-A. Recent studies have shed light on a control of the Notch pathway by basement membrane proteins and integrin signaling, disclosing that extracellular matrix exerts active control on vascular branching morphogenesis. We will survey in the present review how extracellular matrix is a multifaceted substrate, which behind a classical structural role hides a powerful conductor function to shape the branching pattern of vessels.

Integrins and p53 pathways in glioblastoma resistance to temozolomide

Glioblastoma is the most common malignant primary brain tumor. Surgical resection, postoperative radiotherapy plus concomitant and adjuvant chemotherapy with temozolomide (TMZ) is the standard of care for newly diagnosed glioblastoma. In the past decade, efforts have been made to decipher genomic and core pathway alterations to identify clinically relevant glioblastoma subtypes. Based on these studies and more academic explorations, new potential therapeutic targets were found and several targeting agents were developed. Such molecules should hopefully overcome the resistance of glioblastoma to the current therapy. One of the hallmarks of glioblastoma subtypes was the enrichment of extracellular matrix/invasion-related genes. Integrins, which are cell adhesion molecules important in glioma cell migration/invasion and angiogenesis were one of those genes. Integrins seem to be pertinent therapeutic targets and antagonists recently reached the clinic. Although the p53 pathway appears often altered in glioblastoma, conflicting results can be found in the literature about the clinically relevant impact of the p53 status in the resistance to TMZ. Here, we will summarize the current knowledge on (1) integrin expression, (2) p53 status, and (3) relationship between integrins and p53 to discuss their potential impact on the resistance of glioblastoma to temozolomide.

VEGF-induced endothelial cell migration requires urokinase receptor (uPAR)-dependent integrin redistribution

AIMS

Vascular endothelial growth factor (VEGF)-initiated angiogenesis requires coordinated proteolytic degradation of extracellular matrix provided by the urokinase plasminogen activator/urokinase receptor (uPA/uPAR) system and regulation of cell migration provided by integrin-matrix interaction. In this study, we investigated the mechanisms underlying the uPAR-dependent modulation of VEGF-induced endothelial migration.

METHODS AND RESULTS

We used flow cytometry to quantify integrins at the cell surface. Stimulation of human and murine endothelial cells with VEGF resulted in internalization of α5β1-integrins. Micropatterning and immunocytochemistry revealed co-clustering of uPAR and α5β1-integrins and retrieval via clathrin-coated vesicles. It was also contingent on receptors of the low-density lipoprotein receptor (LDL-R) family. VEGF-induced integrin redistribution was inhibited by elimination of uPAR from the endothelial cell surface or by inhibitory peptides that block the uPAR-integrin interaction. Under these conditions, the migratory response of endothelial cells upon VEGF stimulation was impaired both in vitro and in vivo.

CONCLUSIONS

The observations indicate that uPAR is an essential component of the network through which VEGF controls endothelial cell migration. uPAR is a bottleneck through which the VEGF-induced signal must be funnelled for both focused proteolytic activity at the leading edge and for redistribution of integrins.

Fibronectin induces endothelial cell migration through β1 integrin and Src-dependent phosphorylation of fibroblast growth factor receptor-1 at tyrosines 653/654 and 766

The extracellular matrix microenvironment regulates cell phenotype and function. One mechanism by which this is achieved is the transactivation of receptor tyrosine kinases by specific matrix molecules. Here, we demonstrate that the provisional matrix protein, fibronectin (FN), activates fibroblast growth factor (FGF) receptor-1 (FGFR1) independent of FGF ligand in liver endothelial cells. FN activation of FGFR1 requires β1 integrin, as evidenced by neutralizing antibody and siRNA-based studies. Complementary genetic and pharmacologic approaches identify that the non-receptor tyrosine kinase Src is required for FN transactivation of FGFR1. Whereas FGF ligand-induced phosphorylation of FGFR1 preferentially activates ERK, FN-induced phosphorylation of FGFR1 preferentially activates AKT, indicating differential downstream signaling of FGFR1 in response to alternate stimuli. Mutation analysis of known tyrosine residues of FGFR1 reveals that tyrosine 653/654 and 766 residues are required for FN-FGFR1 activation of AKT and chemotaxis. Thus, our study mechanistically dissects a new signaling pathway by which FN achieves endothelial cell chemotaxis, demonstrates how differential phosphorylation profiles of FGFR1 can achieve alternate downstream signals, and, more broadly, highlights the diversity of mechanisms by which the extracellular matrix microenvironment regulates cell behavior through transactivation of receptor tyrosine kinases.

Acheron regulates vascular endothelial proliferation and angiogenesis together with Id1 during wound healing

RNA binding protein acheron has proved to be either the mediator of integrin-extracellular matrix interactions or the regulatory factor that participates in vertebrate development, cell differentiation and cell death. We report the role of acheron in vascular endothelial proliferation, angiogenesis and wound healing post-trauma. Co-immunoprecipitation showed that Acheron forms a ternary complex with β1 integrin and Id1 in human umbilical vein endothelial cells following stimulation with serious trauma serum. Acheron, vascular endothelial growth factor (VEGF), and β1 integrin mRNA expression was apparently inhibited, and capillary density and wound healing rate also were reduced in Id1-deficient mice trauma model. Acheron together with Id1 significantly induces VEGF, not CD105 level inhibition by serious trauma serum for 24 h. In conclusion, we have demonstrated that acheron may be an effective mediator of promoting endothelial proliferation, angiogenesis and wound healing probably by regulating VEGF together with Id1.

β1-integrins signaling and mammary tumor progression in transgenic mouse models: implications for human breast cancer

Consistent with their essential role in cell adhesion to the extracellular matrix, integrins and their associated signaling pathways have been shown to be involved in cell proliferation, migration, invasion and survival, processes required in both tumorigenesis and metastasis. β1-integrins represent the predominantly expressed integrins in mammary epithelial cells and have been proven crucial for mammary gland development and differentiation. Here we provide an overview of the studies that have used transgenic mouse models of mammary tumorigenesis to establish β1-integrin as a critical mediator of breast cancer progression and thereby as a potential therapeutic target for the development of new anticancer strategies.

alpha(5)beta(1) Integrin Ligand PHSRN Induces Invasion and alpha(5) mRNA in Endothelial Cells to Stimulate Angiogenesis

Angiogenesis requires endothelial cell invasion and is crucial for wound healing and for tumor growth and metastasis. Invasion of native collagen is mediated by the alpha(5)beta(1) integrin fibronectin receptor. Thus, alpha(5)beta(1) up-regulation on the surfaces of endothelial cells may induce endothelial cell invasion to stimulate angiogenesis. We report that the interaction of alpha(5)beta(1) with its PHSRN peptide ligand induces human microvascular endothelial cell invasion and that PHSRN-induced endothelial cell invasion is regulated by alpha(4)beta(1) integrin and requires matrix metalloproteinase 1 (MMP-1). Moreover, our results show that exposure to PHSRN causes rapid, specific up-regulation of surface levels of alpha(5)beta(1) integrin and significantly increases alpha(5) integrin mRNA in microvascular endothelial cells. Consistent with these results, alpha(5) small interfering RNA abrogates PHSRN-induced surface alpha(5) and MMP-1 up-regulation, as well as blocking invasion induction. We also observed dose-dependent, PHSRN-induced alpha(5)beta(1) integrin up-regulation on endothelial cells in vivo in Matrigel plugs. We further report that the PHSCN peptide, an alpha(5)beta(1)-targeted invasion inhibitor, blocks PHSRN-induced invasion, alpha(5)beta(1) up-regulation, alpha(5) mRNA induction, and MMP-1 secretion in microvascular endothelial cells and that systemic PHSCN administration prevents PHSRN-induced alpha(5)beta(1) up-regulation and angiogenesis in Matrigel plugs. These results demonstrate a critical role for alpha(5)beta(1) integrin and MMP-1 in mediating the endothelial cell invasion and angiogenesis and suggest that PHSRN-induced alpha(5) transcription and alpha(5)beta(1) up-regulation may form an important feed-forward mechanism for stimulating angiogenesis.

Diverse functions for the semaphorin receptor PlexinD1 in development and disease

Plexins are a family of single-pass transmembrane proteins that serve as cell surface receptors for Semaphorins during the embryonic development of animals. Semaphorin-Plexin signaling is critical for many cellular aspects of organogenesis, including cell migration, proliferation and survival. Until recently, little was known about the function of PlexinD1, the sole member of the vertebrate-specific PlexinD (PlxnD1) subfamily. Here we review novel findings about PlxnD1's roles in the development of the cardiovascular, nervous and immune systems and salivary gland branching morphogenesis and discuss new insights concerning the molecular mechanisms of PlxnD1 activity.

Lipocalin-7 is a matricellular regulator of angiogenesis

BACKGROUND

Matricellular proteins are extracellular regulators of cellular adhesion, signaling and performing a variety of physiological behaviors such as proliferation, migration and differentiation. Within vascular microenvironments, matricellular proteins exert both positive and negative regulatory cues to vascular endothelium. The relative balance of these matricellular cues is believed to be critical for vascular homeostasis, angiogenesis activation or angiogenesis resolution. However, our knowledge of matricellular proteins within vascular microenvironments and the mechanisms by which these proteins impact vascular function remain largely undefined. The matricellular protein lipocalin-7 (LCN7) is found throughout vascular microenvironments, and circumstantial evidence suggests that LCN7 may be an important regulator of angiogenesis. Therefore, we hypothesized that LCN7 may be an important regulator of vascular function.

METHODOLOGY AND PRINCIPAL FINDINGS

To test this hypothesis, we examined the effect of LCN7 overexpression, recombinant protein and gene knockdown in a series of in vitro and in vivo models of angiogenesis. We found that overexpression of LCN7 in MB114 and SVEC murine endothelial cell lines or administration of highly purified recombinant LCN7 protein increased endothelial cell invasion. Similarly, LCN7 increased angiogenic sprouting from quiescent endothelial cell monolayers and ex vivo aortic rings. Moreover, LCN7 increased endothelial cell sensitivity to TGF-β but did not affect sensitivity to other pro-angiogenic growth factors including bFGF and VEGF. Finally, morpholino based knockdown of LCN7 in zebrafish embryos specifically inhibited angiogenic sprouting but did not affect vasculogenesis within injected embryos.

CONCLUSIONS AND SIGNIFICANCE

No functional analysis has previously been performed to elucidate the function of LCN7 in vascular or other cellular processes. Collectively, our results show for the first time that LCN7 is an important pro-angiogenic matricellular protein of vascular microenvironments.

ADAM10 releases a soluble form of the GPNMB/Osteoactivin extracellular domain with angiogenic properties

Background

Glycoprotein non-metastatic melanoma protein B (GPNMB)/Osteoactivin (OA) is a transmembrane protein expressed in approximately 40–75% of breast cancers. GPNMB/OA promotes the migration, invasion and metastasis of breast cancer cells; it is commonly expressed in basal/triple-negative breast tumors and is associated with shorter recurrence-free and overall survival times in patients with breast cancer. Thus, GPNMB/OA represents an attractive target for therapeutic intervention in breast cancer; however, little is known about the functions of GPNMB/OA within the primary tumor microenvironment.

Methodology/Principal Findings

We have employed mouse and human breast cancer cells to investigate the effects of GPNMB/OA on tumor growth and angiogenesis. GPNMB/OA-expressing tumors display elevated endothelial recruitment and reduced apoptosis when compared to vector control-derived tumors. Primary human breast cancers characterized by high vascular density also display elevated levels of GPNMB/OA when compared to those with low vascular density. Using immunoblot and ELISA assays, we demonstrate the GPNMB/OA ectodomain is shed from the surface of breast cancer cells. Transient siRNA-mediated knockdown studies of known sheddases identified ADAM10 as the protease responsible for GPNMB/OA processing. Finally, we demonstrate that the shed extracellular domain (ECD) of GPNMB/OA can promote endothelial migration in vitro.

Conclusions/Significance

GPNMB/OA expression promotes tumor growth, which is associated with enhanced endothelial recruitment. We identify ADAM10 as a sheddase capable of releasing the GPNMB/OA ectodomain from the surface of breast cancer cells, which induces endothelial cell migration. Thus, ectodomain shedding may serve as a novel mechanism by which GPNMB/OA promotes angiogenesis in breast cancer.

Temporal effect of functional blocking of beta1 integrin on cell adhesion strength under serum depletion

Cell adhesion is generally concomitant to the formation of focal adhesion. Although it is well-known that focal adhesion plays an important role in the functional regulations of anchorage dependent cells, previous experimental studies have not provided quantitative description of the relation between focal adhesion and biophysical responses of cells. Furthermore, there is lack of knowledge on the importance of the beta1 integrin subunit to the dynamic responses of cells during initial cell seeding. In this study, we attempt to bridge the quantitative connection between focal adhesion density and cell-substrate interactions and evaluate the influence on functional blocking of beta1 integrin on adhesion strength. Total internal reflection fluorescence microscopy (TIRFM), fluorescence microscopy, and phase contrast microscopy was employed to study the time-dependent evolvement of vinculin pattern, distribution of actin filament, and morphological change, respectively, during 4 h of culture for porcine esophageal fibroblasts (non-blocked and beta1-blocked) on a fibronectin-coated surface. Micropipet aspiration technique was used to study the change of mechanotransduction through the determination of adhesion force and strength. It is shown in our experimental results that spread area, adhesion force, and adhesion strength increases over time on the two types of cells. Throughout the culture period, the two key mechanotransduction parameters of non-blocked cells is higher than those of beta1-blocked cells. Interestingly, adhesion strength initially ascends, then begins to diminish at a critical time point, and finally resumes increasing linearly against the increase of focal adhesion density. This variation as mentioned above can be explained by peeling and fracture models based on the dissimilar vinculin pattern of cells after being cultured for different time periods. Moreover, the averaged focal adhesion strength and non-focal adhesion strength of beta1-blocked cells are significantly less than those of non-blocked of cells. The weaker adhesion strength on beta(1)-blocked cells is directly caused by lower focal and non-focal adhesion strength, as well as by smaller focal adhesion density.

In vitro assays for endothelial cell functions related to angiogenesis: proliferation, motility, tubular differentiation, and proteolysis

This chapter covers the breakdown of the process of angiogenesis into simple assays to measure discrete endothelial cell functions. The techniques described are suitable for studying stimulators or inhibitors of angiogenesis and determining which aspect of the process is modulated. The procedures outlined are robust and straightforward but cannot cover the complexity of the angiogenic process as a whole, incorporating as it does myriad positive and negative signals, three-dimensional interactions with host tissues and many accessory cells, including fibroblasts, macrophages, pericytes, and platelets. The extent to which in vitro assays predict responses in vivo (e.g., wound healing, tumor angiogenesis, or surrogate techniques such as Matrigel plugs, sponge implants, corneal assays, etc.) remains to be determined.

Peritubular capillaries are rarefied in congenital nephrotic syndrome of the Finnish type

Congenital nephrotic syndrome of the Finnish type (NPHS1) is associated with the rapid development of glomerular and tubulointerstitial fibrosis. Here we measured morphologic and molecular changes in the peritubular capillaries of the kidney in patients with NPHS1. Immunohistochemical analysis for the endothelial cell marker CD31 showed marked narrowing and a moderate but significant reduction in peritubular capillary density, especially in areas of increased collagen I and alpha-smooth muscle actin content. No evidence of endothelial-mesenchymal transformation was found. There was increased expression (up to 43-fold) of hypoxia inducible factor-1alpha suggesting tubulointerstitial hypoxia. Double-labeling for CD31 and vimentin showed small foci of peritubular capillary loss and tubular cell damage. While the amount of intercellular adhesion molecule-1 was upregulated in endothelial cells, other adhesion molecules were only modestly expressed. Vascular endothelial growth factor expression was reduced by up to half and decreased endothelial progenitor cell marker CD34 expression indicated lack of vascular repair. Our results suggest that hypoxia in the tubulointerstitium caused by hypoperfusion of glomerular and tubulointerstitial capillaries and rarefaction of the latter may be important for the rapid progression of fibrosis in the kidneys of patients with NPHS1.

Integrin alpha V polymorphisms and haplotypes in a Korean population are associated with susceptibility to chronic hepatitis and hepatocellular carcinoma

BACKGROUND/AIMS

Integrins are cell surface receptors for extracellular matrix (ECM) proteins that initiate signalling pathways that modulate proliferation, survival, invasion or metastasis. Consequently, integrins are potential targets for the treatment of cancer. In this study, we investigated whether single nucleotide polymorphisms (SNPs) in integrin alpha(V) (ITGAV) in a Korean population were associated with chronic hepatitis B virus (HBV) infection and HBV-infected hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

Thirteen ITGAV SNPs in 111 cases of chronic HBV infection, 86 cases of HBV-infected HCC and 107 cases of acute self-limited HBV infection were genotyped using Illumina's Sentrix array matrix (SAM) chip.

RESULTS

The ITGAV intron SNPs rs9333289 and rs11685758, the 3'-untranslated region SNP rs1839123 and haplotype 3 (T-T-A) were associated with enhanced susceptibility to HBV-infected HCC (OR=1.75-2.42; P=0.02-0.05), while the intron SNP rs2290083 was associated with both chronic infection and HBV-infected HCC (OR=1.73-2.01; P=0.01-0.04). In addition, both rs2290083 and ht1 (C-C-G) were associated with the age at which chronic infection occurred, as determined by Cox relative hazard analysis (RH=1.39-1.62, P=0.04-0.01)

CONCLUSION

ITGAV SNPs and haplotypes may be genetic factors that increase the susceptibility of Koreans to chronic HBV infection and HBV-infected HCC.

Therapeutic potential of novel modulators of neovascularization

Neovacularization is an important biological process whereby new blood vessels develop in both health and disease. During development, blood vessels are formed from mesodermal cells in a process called vasculogenesis. The vascular network then expands by the sprouting of new vessel networks from pre-established vessels in a process known as angiogenesis. However, in adult life, undesirable neovascularization is associated with tumor development and a growing list of 'angiogenesis-dependent' diseases, including cardiovascular complications. Furthermore, diseases characterized by ischemia-induced tissue damage cause a neovascularization response to facilitate tissue repair. Recent research has identified novel molecular and cellular mediators of neovascularization that, in adult life, recapitulate angiogenic processes observed during embryonic development. The discovery of vascular progenitor cells and new molecules that display selective functions in modulating endothelial cell fate, migration and patterning, vessel morphogenesis and the amplification of angiogenic signaling by regulating the master signal VEGF, opens the door to new clinical strategies that target angiogenesis-dependent diseases or that can promote therapeutic neovascularization.

Beta1 integrin expression on endothelial cells is required for angiogenesis but not for vasculogenesis

Integrins are a family of cell adhesion receptors that are involved in cell-matrix and cell-cell communications. They facilitate cell proliferation, migration, and survival. Using the Cre-Lox system, we deleted beta1 integrin on Tie2-positive (Tie2-cre beta1 Int (fl/fl)) vascular endothelial cells. Deletion of beta1 integrin on vascular endothelial cells results in embryonic lethality. Blood vessel defects are encountered in the Tie2-Cre beta1 Int (fl/fl) embryos at embryonic age (E9.5), and embryos die before reaching E10.5. The embryos exhibit growth retardation and both histological evaluation and PECAM-1 staining of E9.5 embryos revealed defects in angiogenic sprouting and vascular branching morphogenesis. Large and medium-size vessel formation is not affected in these embryos. Angiogenic defects were observed in several regions of the embryo and yolk sacs. These results indicate that beta1 integrin expression on vascular endothelial cells is crucial for embryonic angiogenesis but dispensable for vasculogenesis.

Extracellular matrix regulation of drug resistance in small-cell lung cancer

PURPOSE

Lung cancer is the leading cause of cancer deaths in the developed world. Small cell lung cancer (SCLC) has the worst prognosis due to the emergence of resistance to chemotherapy. This article will review recent work that has defined mechanisms of chemo-resistance focusing on the role of integrins.

RESULTS

SCLC is surrounded by an extensive stroma of extracellular matrix (ECM) and high levels of expression correlate with poor prognosis. ECM protects SCLC cells against chemotherapy-induced cell death by activating beta1 integrins leading to activation of phosphoinositide-3-OH kinase (PI3-kinase), which prevents etoposide-induced caspase-3 activation and subsequent apoptosis. Engagement of ECM prevents etoposide and radiation induced G2/M cell cycle arrest in SCLC cells by blocking the up-regulation of p21Cip1/WAF1 and p27Kip1 and the down-regulation of cyclins E, A and B. These effects are abrogated by pharmacological and genetic inhibition of PI3-kinase signalling.

CONCLUSIONS

Thus, ECM via beta1 integrin-mediated PI3-kinase activation allows SCLC cells to survive treatment induced cell cycle arrest and apoptosis with persistent DNA damage, providing a model to account for the emergence of acquired drug resistance. Novel therapeutic strategies may therefore be directed at inhibiting integrin-mediated cell survival signals improving response rates and cure in this devastating cancer.

A function blocking anti-mouse integrin alpha5beta1 antibody inhibits angiogenesis and impedes tumor growth in vivo

BACKGROUND

Integrins are important adhesion molecules that regulate tumor and endothelial cell survival, proliferation and migration. The integrin alpha5beta1 has been shown to play a critical role during angiogenesis. An inhibitor of this integrin, volociximab (M200), inhibits endothelial cell growth and movement in vitro, independent of the growth factor milieu, and inhibits tumor growth in vivo in the rabbit VX2 carcinoma model. Although volociximab has already been tested in open label, pilot phase II clinical trials in melanoma, pancreatic and renal cell cancer, evaluation of the mechanism of action of volociximab has been limited because this antibody does not cross-react with murine alpha5beta1, precluding its use in standard mouse xenograft models.

METHODS

We generated a panel of rat-anti-mouse alpha5beta1 antibodies, with the intent of identifying an antibody that recapitulated the properties of volociximab. Hybridoma clones were screened for analogous function to volociximab, including specificity for alpha5beta1 heterodimer and blocking of integrin binding to fibronectin. A subset of antibodies that met these criteria were further characterized for their capacities to bind to mouse endothelial cells, inhibit cell migration and block angiogenesis in vitro. One antibody that encompassed all of these attributes, 339.1, was selected from this panel and tested in xenograft models.

RESULTS

A panel of antibodies was characterized for specificity and potency. The affinity of antibody 339.1 for mouse integrin alpha5beta1 was determined to be 0.59 nM, as measured by BIAcore. This antibody does not significantly cross-react with human integrin, however 339.1 inhibits murine endothelial cell migration and tube formation and elicits cell death in these cells (EC50 = 5.3 nM). In multiple xenograft models, 339.1 inhibited the growth of established tumors by 40-60% (p < 0.05) and this inhibition correlates with a concomitant decrease in vessel density.

CONCLUSION

The results herein demonstrate that 339.1, like volociximab, exhibits potent anti-alpha5beta1 activity and confirms that inhibition of integrin alpha5beta1 impedes angiogenesis and slows tumor growth in vivo.

Enhancement of neuroplasticity through upregulation of β1-integrin in human umbilical cord-derived stromal cell implanted stroke model

Neuroplasticity subsequent to functional angiogenesis is an important goal for cell-based therapy of ischemic neural tissues. At present, the cellular and molecular mechanisms involved are still not well understood. In this study, we isolated mesenchymal stem cells (MSCs) from Wharton's jelly (WJ) to obtain clonally expanded human umbilical cord-derived mesenchymal stem cells (HUCMSCs) with multilineage differentiation potential. Experimental rats receiving intracerebral HUCMSC transplantation showed significantly improved neurological function compared to vehicle-treated control rats. Cortical neuronal activity, as evaluated by proton MR spectroscopy (1H-MRS), also increased considerably in the transplantation group. Transplanted HUCMSCs migrated towards the ischemic boundary zone and differentiated into glial, neuronal, doublecortin+, CXCR4+, and vascular endothelial cells to enhance neuroplasticity in the ischemic brain. In addition, HUCMSC transplantation promoted the formation of new vessels to increase local cortical blood flow in the ischemic hemisphere. Modulation by stem cell-derived macrophage/microglial interactions, and increased beta1-integrin expression, might enhance this angiogenic architecture within the ischemic brain. Inhibition of beta1-integrin expression blocked local angiogenesis and reduced recovery from neurological deficit. In addition, significantly increased modulation of neurotrophic factor expression was also found in the HUCMSC transplantation group. In summary, regulation of beta1-integrin expression plays a critical role in the plasticity of the ischemic brain after the implantation of HUCMSCs.

Cell-matrix adhesion in vascular development

Vascular development requires correct interactions among endothelial cells, pericytes and surrounding cells. These interactions involve many cell adhesion interactions, including cell-matrix interactions both with basement membranes and with surrounding extracellular matrices. Investigations of the contributions of these various interactions in vascular development and angiogenesis have been rather uneven and incomplete over the past 10-15 years. There has been considerable concentration on a few receptors, matrix proteins and proteolytic fragments with the goal of finding means to control angiogenesis. Many other potential contributors have received much less attention. Even for those molecules that have been subject to intensive investigation, our knowledge is incomplete. This review will survey the spectrum of extracellular matrix (ECM) proteins and cell-matrix adhesion receptors (particularly integrins) that are likely to contribute to angiogenesis and discuss what is known and not known about the roles of each of them.

Adrenocortical zonation factor 1 is a novel matricellular protein promoting integrin-mediated adhesion of adrenocortical and vascular smooth muscle cells

Expression of a previously cloned secretory protein named adrenocortical zonation factor 1 (AZ-1, also called Tin-ag-RP or lipocalin 7) is tightly linked with the zonal differentiation of adrenocortical cells. It is also present in vascular smooth muscle (VSM), although its function has remained unknown. In this study, the location of AZ-1 was specified to the basal laminae along adrenocortical sinusoidal capillaries and surrounding VSM cells in the arterial system, consistent with the fact that AZ-1 was extractable under denaturing conditions as a 52 kDa polypeptide. Purified recombinant AZ-1 exhibited abilities to bind to fibronectins via the first type III repeat (anastellin) and to collagens with affinities in submicromolar ranges. AZ-1 immobilized on substratum or bound to collagens or anastellin promoted adhesion and spreading of adrenocortical cells. Although VSM cells spread on AZ-1 slowly, AZ-1 bound to anastellin facilitated the spreading. The adhesion activity of AZ-1 was mediated by a subset of integrins, including alpha(1)beta(1), alpha(2)beta(1), and alpha(5)beta(1), in a cell type-specific manner. Collectively with the putative role of AZ-1 in the adrenocortical zonation, we propose that AZ-1 potentially regulates functions of adrenocortical and VSM cells by modulating cell-matrix interactions.