HER2 signaling--induced microvessel dismantling

Isolated Fragments of Intact Microvessels: Tissue Vascularization, Modeling, and Therapeutics

The microvasculature is integral to nearly every tissue in the body, providing not only perfusion to and from the tissue, but also homing sites for immune cells, cellular niches for tissue dynamics, and cooperative interactions with other tissue elements. As a microtissue itself, the microvasculature is a composite of multiple cell types exquisitely organized into structures (individual vessel segments and extensive vessel networks) capable of considerable dynamics and plasticity. Consequently, it has been challenging to include a functional microvasculature in assembled or fabricated tissues. Isolated fragments of intact microvessels, which retain the cellular composition and structures of native microvessels, are proving effective in a variety of vascularization applications including tissue in vitro disease modeling, vascular biology, mechanistic discovery, and tissue prevascularization in regenerative therapeutics and grafting. In this review, we will discuss the importance of recapitulating native tissue biology and the successful vascularization applications of isolated microvessels.

Vascularized Tissue Organoids

Tissue organoids hold enormous potential as tools for a variety of applications, including disease modeling and drug screening. To effectively mimic the native tissue environment, it is critical to integrate a microvasculature with the parenchyma and stroma. In addition to providing a means to physiologically perfuse the organoids, the microvasculature also contributes to the cellular dynamics of the tissue model via the cells of the perivascular niche, thereby further modulating tissue function. In this review, we discuss current and developing strategies for vascularizing organoids, consider tissue-specific vascularization approaches, discuss the importance of perfusion, and provide perspectives on the state of the field.

The Evaluation of Neovessel Angiogenesis Behavior at Tissue Interfaces

Angiogenesis, the formation of new vessel elements from existing vessels, is important in homeostasis and tissue repair. Dysfunctional angiogenesis can contribute to numerous pathologies, including cancer, ischemia, and chronic wounds. In many instances, growing vessels must navigate along or across tissue-associated boundaries and interfaces tissue interfaces. To understand this dynamic, we developed a new model for studying angiogenesis at tissue interfaces utilizing intact microvessel fragments isolated from adipose tissue. Isolated microvessels retain their native structural and cellular complexity. When embedded in a 3D matrix, microvessels, sprout, grow, and connect to form a neovasculature. Here, we discuss and describe methodology for one application of our microvessel-based angiogenesis model, studying neovessel behavior at tissue interfaces.

Human Epidermal Growth Factor Receptor 2 Regulates Angiopoietin-2 Expression in Breast Cancer via AKT and Mitogen-Activated Protein Kinase Pathways

Abnormal activation of human epidermal growth factor receptor 2 (HER2; ErbB-2) in breast tumors results in increased metastasis and angiogenesis, as well as reduced survival. Here, we show that angiopoietin-2 (Ang-2) expression correlates with HER2 activity in human breast cancer cell lines. Inhibiting HER2 activity with anti-HER2 monoclonal antibody trastuzumab (Herceptin) or HER2 short interfering RNA in tumor cells down-regulates Ang-2 expression. Consistent with the important roles of AKT and mitogen-activated protein kinase in the HER2 signaling pathway, AKT and ERK mitogen-activated protein kinase (MAPK) kinase activity is necessary for Ang-2 up-regulation by HER2. Moreover, overexpression of HER2 protein up-regulates Ang-2 expression. Heregulin-beta1-induced Ang-2 up-regulation is abrogated when AKT and ERK kinase activity are blocked. Immunohistochemical analysis of HER2 and Ang-2 proteins in human breast carcinomas shows that Ang-2 expression in breast cancer correlates with HER2 expression. These studies provide evidence that the Ang-2 gene is regulated by HER2 activity in breast cancer, and propose an additional mechanism for HER2 contributing to tumor angiogenesis and metastasis.

Novel anti-inflammatory properties of the angiogenesis inhibitor vasostatin

Endothelial cells are critically involved in the pathogenesis of inflammation, which is characterized by vasopermeability, plasma leakage, leukocyte recruitment, and neovascularization. Therefore, inhibitors of endothelial cell function could reduce inflammation. In this study, we evaluated the effects of the angiogenesis inhibitor vasostatin on inflammations induced by contact hypersensitivity reactions in mouse ears. Vasostatin-treated mice revealed significantly reduced edema formation, resulting from lower plasma leakage and inhibition of inflammation-associated vascular remodeling. Intravital microscopy studies of inflamed ears showed a decrease in the fraction of rolling leukocytes in vasostatin-treated mice, and Lycopersicon esculentum lectin-perfused ears revealed fewer leukocytes adherent to the vessel wall. The inflammatory infiltrate from vasostatin-treated mice was characterized by fewer CD8+ T cells, neutrophils, and macrophages compared to the saline-treated animals. In a modified Miles assay, vasostatin inhibited vascular endothelial growth factor-A-induced permeability, and inflamed ear tissues from vasostatin-treated mice expressed significantly reduced levels of the vascular destabilizer angiopoietin-2. These results reveal a previously unrecognized anti-inflammatory property of the angiogenesis inhibitor vasostatin, and suggest that vasostatin is a potential candidate drug for the treatment of inflammation.