Endothelial biomedicine: its status as an interdisciplinary field, its progress as a basic science, and its translational bench-to-bedside gap

Microfluidic bioprinting of tough hydrogel-based vascular conduits for functional blood vessels

Three-dimensional (3D) bioprinting of vascular tissues that are mechanically and functionally comparable to their native counterparts is an unmet challenge. Here, we developed a tough double-network hydrogel (bio)ink for microfluidic (bio)printing of mono- and dual-layered hollow conduits to recreate vein- and artery-like tissues, respectively. The tough hydrogel consisted of energy-dissipative ionically cross-linked alginate and elastic enzyme-cross-linked gelatin. The 3D bioprinted venous and arterial conduits exhibited key functionalities of respective vessels including relevant mechanical properties, perfusability, barrier performance, expressions of specific markers, and susceptibility to severe acute respiratory syndrome coronavirus 2 pseudo-viral infection. Notably, the arterial conduits revealed physiological vasoconstriction and vasodilatation responses. We further explored the feasibility of these conduits for vascular anastomosis. Together, our study presents biofabrication of mechanically and functionally relevant vascular conduits, showcasing their potentials as vascular models for disease studies in vitro and as grafts for vascular surgeries in vivo, possibly serving broad biomedical applications in the future.

Endothelial dysfunction: a unifying hypothesis for the burden of cardiovascular diseases in sub-Saharan Africa

It is well established that the leading causes of death and disability worldwide are cardiovascular diseases (CVD), chief among which is ischaemic heart disease. However, it is also recognised that ischaemic heart disease frequently coexists with other vascular conditions, such as cerebrovascular, renovascular and peripheral vascular disease, thus raising the notion of a common underlying pathobiology, albeit with differing manifestations, dictated by the implicated vascular bed.

The understanding that common metabolic and behavioural risk factors as well as social determinants and drivers are convergent in the development of CVD evokes the idea that the dysfunction of a common bio-molecular platform is central to the occurrence of these diseases. The state of endothelial activation, otherwise known as endothelial dysfunction, occurs when reactive oxygen signalling predominates due to an uncoupled state of endothelial nitric oxide synthase (eNOS). This can be a physiological response to stimulation of the innate immune system or a pathophysiological response triggered by cardiovascular disease risk factors.

The conventional wisdom is that the endothelium plays an important role in the initiation, progression and development of CVD and other non-communicable diseases. Consequently, the endothelium has remarkable relevance in clinical and public health practice as well as in health education, health promotion, and disease- and risk-factor prevention strategies. It also presents a plausible unifying hypothesis for the burden of CVD seen globally and in sub-Saharan Africa. Importantly, the heterogeneity in individual responses to metabolic, behavioural, and social drivers of CVD may stem from a complex interplay of these drivers with genomic, epigenetic and environmental factors that underpin eNOS uncoupling. Therefore, further biomedical research into the underlying genetic and other mechanisms of eNOS uncoupling may enlighten and shape strategies for addressing the burden of CVD in sub-Saharan Africa and other regions of the world.

T Lymphocyte-Endothelial Interactions: Emerging Understanding of Trafficking and Antigen-Specific Immunity

Antigen-specific immunity requires regulated trafficking of T cells in and out of diverse tissues in order to orchestrate lymphocyte development, immune surveillance, responses, and memory. The endothelium serves as a unique barrier, as well as a sentinel, between the blood and the tissues, and as such it plays an essential locally tuned role in regulating T cell migration and information exchange. While it is well established that chemoattractants and adhesion molecules are major determinants of T cell trafficking, emerging studies have now enumerated a large number of molecular players as well as a range of discrete cellular remodeling activities (e.g., transmigratory cups and invadosome-like protrusions) that participate in directed migration and pathfinding by T cells. In addition to providing trafficking cues, intimate cell-cell interaction between lymphocytes and endothelial cells provide instruction to T cells that influence their activation and differentiation states. Perhaps the most intriguing and underappreciated of these "sentinel" roles is the ability of the endothelium to act as a non-hematopoietic "semiprofessional" antigen-presenting cell. Close contacts between circulating T cells and antigen-presenting endothelium may play unique non-redundant roles in shaping adaptive immune responses within the periphery. A better understanding of the mechanisms directing T cell trafficking and the antigen-presenting role of the endothelium may not only increase our knowledge of the adaptive immune response but also empower the utility of emerging immunomodulatory therapeutics.

Endothelium and haemostasis

The endothelium is a widely distributed organ system that plays an important role in health and disease. The endothelium is remarkably heterogeneous in structure and function. One vital function of the endothelium is to maintain blood in its fluid state, and to provide controlled haemostasis at sites of vascular injury. In keeping with the theme of endothelial cell heterogeneity, endothelial cells from different sites of the vascular employ different strategies to mediate local haemostatic balance. These differences are sufficient to explain why systemic imbalances of haemostatic components invariably lead to local thrombotic phenotypes. An important goal for the future is to identify diagnostic markers that reflect phenotypic changes at the level of individual vascular beds, and to develop therapies that target one or another site of the vasculature.

Endothelial cell heterogeneity

The endothelial lining of blood vessels shows remarkable heterogeneity in structure and function, in time and space, and in health and disease. An understanding of the molecular basis for phenotypic heterogeneity may provide important insights into vascular bed-specific therapies. First, we review the scope of endothelial heterogeneity and discuss its proximate and evolutionary mechanisms. Second, we apply these principles, together with their therapeutic implications, to a representative vascular bed in disease, namely, tumor endothelium.

Release of cellular tension signals self-restorative ventral lamellipodia to heal barrier micro-wounds

Endothelial and epithelial barrier disruptions are detected via local decrease in cellular tension, which are coupled to reactive oxygen species–dependent self-restorative actin remodeling dynamics.

Basic mechanisms by which cellular barriers sense and respond to integrity disruptions remain poorly understood. Despite its tenuous structure and constitutive exposure to disruptive strains, the vascular endothelium exhibits robust barrier function. We show that in response to micrometer-scale disruptions induced by transmigrating leukocytes, endothelial cells generate unique ventral lamellipodia that propagate via integrins toward and across these “micro-wounds” to close them. This novel actin remodeling activity progressively healed multiple micro-wounds in succession and changed direction during this process. Mechanical probe-induced micro-wounding of both endothelia and epithelia suggests that ventral lamellipodia formed as a response to force imbalance and specifically loss of isometric tension. Ventral lamellipodia were enriched in the Rac1 effectors cortactin, IQGAP, and p47Phox and exhibited localized production of hydrogen peroxide. Together with Apr2/3, these were functionally required for effective micro-wound healing. We propose that barrier disruptions are detected as local release of isometric tension/force unloading, which is directly coupled to reactive oxygen species–dependent self-restorative actin remodeling dynamics.

Dynamical systems approach to endothelial heterogeneity

Endothelial cells display remarkable phenotypic heterogeneity. An important goal is to elucidate the scope and mechanisms of endothelial heterogeneity and to use this information to develop vascular bed-specific therapies. We reexamine our current understanding of the molecular basis of endothelial heterogeneity. We introduce multistability as a new explanatory framework in vascular biology. We draw on the field of nonlinear dynamics to propose a dynamical systems framework for modeling multistability and its derivative properties, including robustness, memory, and plasticity. Our perspective allows for both a conceptual and quantitative description of system-level features of endothelial regulation.

Type 1 diabetes predisposes to enhanced gingival leukocyte margination and macromolecule extravasation in vivo

BACKGROUND AND OBJECTIVE

Diabetes predisposes to periodontal disease. However, the cellular and molecular mechanisms linking the two conditions are not clear. The impact of chronic hyperglycemia on leukocyte margination and macromolecule extravasation was determined in gingival vessels in vivo.

MATERIALS AND METHODS

Gingival intravital microscopy was employed to measure extravasation of fluorescein isothiocyanate (FITC)-dextran in diabetic Akita and healthy wild-type (WT) mice. Rhodamine 6G and FITC-LY6G were injected for nonspecific and polymorphonuclear-specific leukocyte labeling, respectively. Surface expression of leukocyte adhesion molecules was determined with flow cytometry and western blotting.

RESULTS

Vascular permeability was significantly increased in Akita gingival vessels compared with WT [permeability index (PI): WT, 0.75 ± 0.05; Akita, 1.1 ± 0.03: p < 0.05). Wild-type gingival vessels reached comparable permeability 2 h after intragingival injection of tumor necrosis factor α (TNFα), used here as positive control (PI, 1.17 ± 0.16). The number of rolling leukocytes was significantly elevated in diabetic gingiva (WT, 25 ± 3.7 cells/min; Akita, 42 ± 8.5 cells/min; p < 0.03). Similar rolling cell counts were obtained in WT after intragingival injection of TNFα (10 ng TNFα, 47 ± 1.3 cells/min; 100 ng TNFα, 57.5 ± 5.85 cells/min). The number of leukocytes firmly attached to the endothelium was similar in WT and Akita mice. Leukocyte cell-surface expression of P-selectin glycoprotein ligand-1 and CD11a was increased in Akita mice, while L-selectin remained unchanged when compared with WT. Moreover, P-selectin expression in Akita gingival tissues was elevated compared with that of WT.

CONCLUSION

Chronic hyperglycemia induces a proinflammatory state in the gingival microcirculation characterized by increased vascular permeability, and leukocyte and endothelial cell activation. Leukocyte-induced microvascular damage, in turn, may contribute to periodontal tissue damage in diabetes.

Blood Outgrowth Endothelial Cells as a Vehicle for Transgene Expression of Hepatocyte-Secreted Proteins viaSleeping Beauty

The therapeutic use of autologous cells with the capacity for extensive in vitro expansion and manipulation prior to host administration has been an area of significant investigation over the last decade. Blood outgrowth endothelial cells (BOECs) are derived from the circulation and exhibit proliferative growth, in vivo engraftment, and survival characteristics for long-term expression of endogenously secreted proteins, such as factor VIII (FVIII). The authors describe a modified method for the isolation, culture, and expansion of these cells that is readily accomplished using standard laboratory methods. Using a commercially available transfection reagent, approximately 30% of these primary cells can be routinely transfected with the nonviral Sleeping Beauty transposon for long-term, stable transgene expression. Moreover, the results indicate that these cells have the ability to secrete functionally active proteins that are synthesized endogenously by hepatocytes and require post-translational modification including alpha1-antitrypsin and clotting factors VII and IX. This, coupled with their notably long half-life of years, suggests that these cells may provide an appropriate vehicle for secretion of a variety of proteins produced by different cell types in vivo. Thus, BOECs have the potential to provide clinically relevant secreted proteins for diseases other than those of endothelial origin.

The EuroPhysiome, STEP and a roadmap for the virtual physiological human

Biomedical science and its allied disciplines are entering a new era in which computational methods and technologies are poised to play a prevalent role in supporting collaborative investigation of the human body. Within Europe, this has its focus in the virtual physiological human (VPH), which is an evolving entity that has emerged from the EuroPhysiome initiative and the strategy for the EuroPhysiome (STEP) consortium. The VPH is intended to be a solution to common infrastructure needs for physiome projects across the globe, providing a unifying architecture that facilitates integration and prediction, ultimately creating a framework capable of describing Homo sapiens in silico. The routine reliance of the biomedical industry, biomedical research and clinical practice on information technology (IT) highlights the importance of a tailor-made and robust IT infrastructure, but numerous challenges need to be addressed if the VPH is to become a mature technological reality. Appropriate investment will reap considerable rewards, since it is anticipated that the VPH will influence all sectors of society, with implications predominantly for improved healthcare, improved competitiveness in industry and greater understanding of (patho)physiological processes. This paper considers issues pertinent to the development of the VPH, highlighted by the work of the STEP consortium.

Molecular heterogeneity of tumor endothelium

Tumors depend on a vascular supply for their growth. Tumor blood vessels, which are derived from normal tissue vasculature, display a markedly abnormal phenotype. Tumor endothelial properties are highly varied in space and time. An important goal is to delineate the range of phenotypes in tumor endothelium and to identify tumor endothelial-specific molecular signatures. This information should lead to a more complete understanding of the mechanisms of tumor growth, the discovery of new therapeutic targets, and the development of biomarkers for diagnosis and surveillance. The goals of this review are to outline recent advances in dissecting tumor endothelial-cell-specific gene expression, to address mechanisms of phenotypic heterogeneity in tumor vascular beds, and to discuss the therapeutic implications of these findings.

[Endothelial progenitor cells: new biomarkers and potential therapy in intensive care]

One of the most important breakthroughs in the field of vascular biology in the last decade was the discovery of endothelial progenitor cells (EPCs). These angiogenic cells dwell in bone marrow, and may be found in the general circulation spontaneously or in response to various stimuli such as ischemia, growth factor, pro-inflammatory cytokines, and drugs such as statins. There is growing evidence that EPCs can differentiate into mature endothelial cells and facilitate endothelial repair and angiogenesis in vivo. In recent years, consistent publications have shown that EPCs provide both diagnostic and prognostic information with respect to cardiovascular diseases, acute lung injury, and sepsis. Activation of EPCs from the bone marrow or injection of these cells may be used as a therapeutic option for the treatment of ischemic cardiovascular diseases.

Oxygen reduces accumulation of type IV collagen in endothelial cell subcellular matrix via oxidative stress

Anchorage-dependent cells in culture attach initially to proteins adsorbed to the culture substrate from the medium, and produce and deposit a subcellular matrix during the course of the cultivation. The aim of this study was to determine whether the concentration of O(2) in the culture atmosphere affects the accumulation of type IV collagen and laminin under human endothelial-cell monolayers. Enzyme-linked immunoassays on decellularized polystyrene substrates showed less type IV collagen, but not less laminin, under cells incubated in the standard atmosphere (5% CO(2) in air, i.e., approximately 20% O(2)) compared to an atmosphere of 5% O(2) and 5% CO(2) in N(2). Type IV collagen accumulation was inhibited via oxidative stress, because the inhibitory effect of 20% O(2) was antagonized by antioxidant ascorbic acid, and mimicked by prooxidant pyrogallol and exogenous H(2)O(2). Measurements of endogenous H(2)O(2) accumulation demonstrated that endothelial cells partially adapt to the high O(2) concentration. These results may have implications in endothelium modeling in vitro and in engineering of endothelial cell sheets and endothelialized vascular grafts.

Endothelium and cardiopulmonary resuscitation

The endothelium is a viable target for injury, repair and cellular modulation. Because of its vast extension and active metabolic status of producing mediators for vasomotor tone, coagulation, and inflammation, it is a key target for therapy during ischemia/reperfusion injury. Cardiopulmonary resuscitation is a model of whole-body ischemia/reperfusion injury. It has become apparent that the endothelium participates in a host of responses elicited by ischemia/reperfusion. This review examines the role of the endothelium during and after ischemia/reperfusion and the participation by its mediators and evidence for endothelial involvement during and after cardiopulmonary resuscitation. The strategic location of the endothelium makes it an excellent signal transduction mechanism for a host of disease processes. In addition to biochemical stimuli, mechanical stimulation of the endothelium elicits production of several mediators, including endothelium-derived nitric oxide, prostaglandins, and antithrombotics and anticoagulants. Whole-body, periodic acceleration is a novel method of stimulating the endothelium via pulsatile shear stress. Periodic acceleration has been shown to be an effective experimental method of cardiopulmonary resuscitation, with evidence of postresuscitation cardioprotective effects. This review indicates that understanding endothelial modulation during and after ischemia/reperfusion will significantly improve therapeutic choices.