TGF-β and microvessel homeostasis

Bioprinted vascular tissue: Assessing functions from cellular, tissue to organ levels

3D bioprinting technology is widely used to fabricate various tissue structures. However, the absence of vessels hampers the ability of bioprinted tissues to receive oxygen and nutrients as well as to remove wastes, leading to a significant reduction in their survival rate. Despite the advancements in bioinks and bioprinting technologies, bioprinted vascular structures continue to be unsuitable for transplantation compared to natural blood vessels. In addition, a complete assessment index system for evaluating the structure and function of bioprinted vessels in vitro has not yet been established. Therefore, in this review, we firstly highlight the significance of selecting suitable bioinks and bioprinting techniques as they two synergize with each other. Subsequently, focusing on both vascular-associated cells and vascular tissues, we provide a relatively thorough assessment of the functions of bioprinted vascular tissue based on the physiological functions that natural blood vessels possess. We end with a review of the applications of vascular models, such as vessel-on-a-chip, in simulating pathological processes and conducting drug screening at the organ level. We believe that the development of fully functional blood vessels will soon make great contributions to tissue engineering and regenerative medicine.

Research progress on drugs targeting the TGF-β signaling pathway in fibrotic diseases

Tissue fibrosis is a key factor leading to disability and death worldwide; however, thus far, there are no approved treatments for fibrosis. Transforming growth factor (TGF)-β is a major pro-fibrotic cytokine, which is expected to become a target in the treatment of fibrosis; however, since TGF-β has a wide range of biological functions involving a variety of biological processes in the body, a slight change in TGF-β may have a systematic effect. Indiscriminate inhibition of TGF-β can lead to adverse reactions, which can affect the efficacy of treatment. Therefore, it has become very important to explore how both the TGF-β signaling pathway is inhibited and the safe and efficient TGF-β small molecule inhibitors or neutralizing antibodies are designed in the treatment of fibrotic diseases. In this review, we mainly discuss the key role of the TGF-β signaling pathway in fibrotic diseases, as well as the development of fibrotic drugs in recent years, and explore potential targets in the treatment of fibrotic diseases in order to guide subsequent drug development.

Macrophages promote network formation and maturation of transplanted adipose tissue-derived microvascular fragments

Adipose tissue–derived microvascular fragments rapidly reassemble into microvascular networks within implanted scaffolds. Herein, we analyzed the contribution of macrophages to this process. C57BL/6 mice received clodronate (clo)-containing liposomes for macrophage depletion, whereas animals treated with phosphate-buffered-saline-containing liposomes served as controls. Microvascular fragments were isolated from clo- and phosphate-buffered-saline-treated donor mice and seeded onto collagen–glycosaminoglycan matrices, which were implanted into dorsal skinfold chambers of clo- and phosphate-buffered-saline-treated recipient mice. The implants’ vascularization and incorporation were analyzed by stereomicroscopy, intravital fluorescence microscopy, histology, and immunohistochemistry. Compared to controls, matrices within clo-treated animals exhibited a significantly reduced functional microvessel density. Moreover, they contained a lower fraction of microvessels with an α-smooth muscle actin (SMA)⁺ cell layer, indicating impaired vessel maturation. This was associated with a deteriorated implant incorporation. These findings demonstrate that macrophages not only promote the reassembly of microvascular fragments into microvascular networks, but also improve their maturation during this process.

S-endoglin expression is induced in hyperoxia and contributes to altered pulmonary angiogenesis in bronchopulmonary dysplasia development

Altered pulmonary angiogenesis contributes to disrupted alveolarization, which is the main characteristic of bronchopulmonary dysplasia (BPD). Transforming growth factor β (TGFβ) plays an important role during lung vascular development, and recent studies have demonstrated that endoglin is engaged in the modulation of TGFβ downstream signalling. Although there are two different isoforms of endoglin, L- and S-endoglin, little is known about the effect of S-endoglin in developing lungs. We analysed the expression of both L- and S-endoglin in the lung vasculature and its contribution to TGFβ-activin-like kinase (ALK)-Smad signalling with respect to BPD development. Hyperoxia impaired pulmonary angiogenesis accompanied by alveolar simplification in neonatal mouse lungs. S-endoglin, phosphorylated Smad2/3 and connective tissue growth factor levels were significantly increased in hyperoxia-exposed mice, while L-endoglin, phosphor-Smad1/5 and platelet-endothelial cell adhesion molecule-1 levels were significantly decreased. Hyperoxia suppressed the tubular growth of human pulmonary microvascular endothelial cells (ECs), and the selective inhibition of ALK5 signalling restored tubular growth. These results indicate that hyperoxia alters the balance in two isoforms of endoglin towards increased S-endoglin and that S-endoglin attenuates TGFβ-ALK1-Smad1/5 signalling but stimulates TGFβ-ALK5-Smad2/3 signalling in pulmonary ECs, which may lead to impaired pulmonary angiogenesis in developing lungs.

Interaction of NK Cells, Trophoblast, and Endothelial Cells during Angiogenesis

We studied changes in angiogenesis during contact interaction of natural killer cells and endothelial cells in the presence of secretory products of trophoblast cells activated by various cytokines. Activated trophoblast regulates angiogenesis by producing soluble factors that affect endothelial cells either directly or indirectly through activation of proangiogenic activity of natural killer cells. A stimulating effect of the trophoblast supernatants activated by IL-1β and an inhibitory effect of trophoblast supernatants activated by IL-6 and TGFβ for the formation of tube-like structures by endothelial cells were revealed. During contact culturing, natural killer cells increased the length of tube-like structures formed by endothelial cells. The trophoblast activated by IL-1β affects angiogenesis both directly through the production of proangiogenic factors and indirectly through activation of the proangiogenic potential of natural killer cells. Trophoblast activated by IFNγ affects angiogenesis only by stimulating the proangiogenic potential of natural killer cells. Under conditions of contact interaction of natural killer cells and endothelial cells, soluble factors of trophoblast activated by IL-6 or TGFβ attenuated the angiogenesis-stimulating effect of natural killer cells.

The Controversial Role of TGF-β in Neovascular Age-Related Macular Degeneration Pathogenesis

The multifunctional transforming growth factors-beta (TGF-βs) have been extensively studied regarding their role in the pathogenesis of neovascular age-related macular degeneration (nAMD), a major cause of severe visual loss in the elderly in developed countries. Despite this, their effect remains somewhat controversial. Indeed, both pro- and antiangiogenic activities have been suggested for TGF-β signaling in the development and progression of nAMD, and opposite therapies have been proposed targeting the inhibition or activation of the TGF-β pathway. The present article summarizes the current literature linking TGF-β and nAMD, and reviews experimental data supporting both pro- and antiangiogenic hypotheses, taking into account the limitations of the experimental approaches.

Regulating VEGF signaling in platelet concentrates via specific VEGF sequestering

Platelets contain an abundance of growth factors that mimic the composition of the wound healing milieu, and platelet-derived VEGF in particular can negatively influence wound healing if unregulated. Here, we sought to capture and regulate the activity of VEGF factor from human platelets using poly(ethylene glycol) microspheres. In this communication, we demonstrate that platelet freeze/thaw produced significantly higher levels of Vascular Endothelial Growth Factor (VEGF) than either calcium chloride treatment, protease activated receptor 1 activating peptide (PAR1AP) treatment, or thrombin treatment. PEG microspheres containing a VEGF-binding peptide (VBP), derived from VEGFR2, sequestered VEGF from platelet concentrate, prepared via freeze/thaw, and reduced the bioactivity of platelet concentrate in HUVEC culture, which suggests that VBP microspheres sequestered and reduced the activity of VEGF from patient-derived platelets. Here, we demonstrate the ability of VEGF sequestering microspheres to regulate the activity of VEGF derived from a growth factor-rich autologous human blood product.

Effect of Monocyte-Like THP-1 Cells on the Formation of Vascular Tubes by EA.Hy926s Endothelial Cells in the Presence of Cytokines

The interaction of endothelial cells with cells of the microenvironment, including monocytes/ macrophages, and extracellular matrix during angiogenesis is controlled by cytokines. The stimulating effect bFGF, IL-8, and VEGF on the formation of capillary-like structures by endothelial cells was demonstrated in both monoculture and in co-culture with THP-1 cells; in the latter case, the effects of bFGF and VEGF were more pronounced. IL-8 reduced branching of vascular tubes in co-culture in comparison with monoculture of endothelial cells. Placental growth factor PlGF had no effect of tube formation by endothelial cells in monoculture, but in co-culture with THP-1 cells this cytokine in high concentrations exhibited proangiogenic activity. TGFb inhibited the formation of vascular tubes by endothelial cells and its antiangiogenic potential was more pronounced in co-culture with THP-1 cells.

CD45+ Cells Present Within Mesenchymal Stem Cell Populations Affect Network Formation of Blood-Derived Endothelial Outgrowth Cells

Mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) represent promising cell sources for angiogenic therapies. There are, however, conflicting reports regarding the ability of MSCs to support network formation of endothelial cells. The goal of this study was to assess the ability of human bone marrow-derived MSCs to support network formation of endothelial outgrowth cells (EOCs) derived from umbilical cord blood EPCs. We hypothesized that upon in vitro coculture, MSCs and EOCs promote a microenvironment conducive for EOC network formation without the addition of angiogenic growth supplements. EOC networks formed by coculture with MSCs underwent regression and cell loss by day 10 with a near 4-fold and 2-fold reduction in branch points and mean segment length, respectively, in comparison with networks formed by coculture vascular smooth muscle cell (SMC) cocultures. EOC network regression in MSC cocultures was not caused by lack of vascular endothelial growth factor (VEGF)-A or changes in TGF-β1 or Ang-2 supernatant concentrations in comparison with SMC cocultures. Removal of CD45+ cells from MSCs improved EOC network formation through a 2-fold increase in total segment length and number of branch points in comparison to unsorted MSCs by day 6. These improvements, however, were not sustained by day 10. CD45 expression in MSC cocultures correlated with EOC network regression with a 5-fold increase between day 6 and day 10 of culture. The addition of supplemental growth factors VEGF, fibroblastic growth factor-2, EGF, hydrocortisone, insulin growth factor-1, ascorbic acid, and heparin to MSC cocultures promoted stable EOC network formation over 2 weeks in vitro, without affecting CD45 expression, as evidenced by a lack of significant differences in total segment length (p=0.96). These findings demonstrate the ability of MSCs to support EOC network formation correlates with removal of CD45+ cells and improves upon the addition of soluble growth factors.

Design of growth factor sequestering biomaterials

Growth factors (GFs) are major regulatory proteins that can govern cell fate, migration, and organization. Numerous aspects of the cell milieu can modulate cell responses to GFs, and GF regulation is often achieved by the native extracellular matrix (ECM). For example, the ECM can sequester GFs and thereby control GF bioavailability. In addition, GFs can exert distinct effects depending on whether they are sequestered in solution, at two-dimensional interfaces, or within three-dimensional matrices. Understanding how the context of GF sequestering impacts cell function in the native ECM can instruct the design of soluble or insoluble GF sequestering moieties, which can then be used in a variety of bioengineering applications. This Feature Article provides an overview of the natural mechanisms of GF sequestering in the cell milieu, and reviews the recent bioengineering approaches that have sequestered GFs to modulate cell function. Results to date demonstrate that the cell response to GF sequestering depends on the affinity of the sequestering interaction, the spatial proximity of sequestering in relation to cells, the source of the GF (supplemented or endogenous), and the phase of the sequestering moiety (soluble or insoluble). We highlight the importance of context for the future design of biomaterials that can leverage endogenous molecules in the cell milieu and mitigate the need for supplemented factors.

Retrospective analysis of the frequency of centrofacial telangiectasia in systemic sclerosis patients treated with bosentan or ilomedin

Background

Bosentan is a dual endothelin receptor antagonist initially introduced for the treatment of pulmonary arterial hypertension and recently approved for the treatment of digital ulcers in patients with systemic sclerosis (SSc). Our clinical observations indicate that bosentan therapy may be associated with an increased frequency of centrofacial telangiectasia (TAE). Here, we sought to analyze the frequency of TAE in patients with SSc who were treated with either bosentan or the prostacyclin analog iloprost.

Methods

We conducted a retrospective analysis in 27 patients with SSc undergoing therapy with either bosentan (n = 11) or iloprost (n = 16). Standardized photodocumentations of all patients (n = 27) were obtained at a time point ten months after therapy initiation and analyzed. A subgroup of patients (bosentan: n = 6; iloprost: n = 6) was additionally photodocumented prior to therapy initiation, enabling an intraindividual analysis over the course of therapy.

Results

After ten months of therapy patients with SSc receiving bosentan showed a significantly (P = 0.0028) higher frequency of centrofacial TAE (41.6 ± 27.8) as compared to patients with SSc receiving iloprost (14.3 ± 13.1). Detailed subgroup analysis revealed that the frequency of TAE in the bosentan group (n = 6 patients) increased markedly and significantly (P = 0.027) by 44.4 after ten months of therapy (TAE at therapy initiation: 10.8 ± 5.1; TAE after ten months of therapy: 55.2 ± 29.8), whereas an only minor increase of 1.9 was observed in the iloprost group (n = 6 patients; TAE at therapy initiation: 18.3 ± 14.5; TAE after ten months of therapy: 20.2 ± 15.5), yet without reaching statistical significance (P = 0.420).

Conclusions

The use of bosentan may be associated with an increased frequency of TAE in patients with SSc. Patients should be informed about this potential adverse effect prior to therapy. Treatment options may include camouflage or laser therapy.

The role of shear-induced transforming growth factor-β signaling in the endothelium

OBJECTIVE

Vascular endothelial cells (ECs) are continuously exposed to blood flow that contributes to the maintenance of vessel structure and function; however, the effect of hemodynamic forces on transforming growth factor-β (TGF-β) signaling in the endothelium is poorly described. We examined the potential role of TGF-β signaling in mediating the protective effects of shear stress on ECs.

APPROACH AND RESULTS

Human umbilical vein ECs (HUVECs) exposed to shear stress were compared with cells grown under static conditions. Signaling through the TGF-β receptor ALK5 was inhibited with SB525334. Cells were examined for morphological changes and harvested for analysis by real-time polymerase chain reaction, Western blot analysis, apoptosis, proliferation, and immunocytochemistry. Shear stress resulted in ALK5-dependent alignment of HUVECs as well as attenuation of apoptosis and proliferation compared with static controls. Shear stress led to an ALK5-dependent increase in TGF-β3 and Krüppel-like factor 2, phosphorylation of endothelial NO synthase, and NO release. Addition of the NO donor S-nitroso-N-acetylpenicillamine rescued the cells from apoptosis attributable to ALK5 inhibition under shear stress. Knockdown of TGF-β3, but not TGF-β1, disrupted the HUVEC monolayer and prevented the induction of Krüppel-like factor 2 by shear.

CONCLUSIONS

Shear stress of HUVECs induces TGF-β3 signaling and subsequent activation of Krüppel-like factor 2 and NO, and represents a novel role for TGF-β3 in the maintenance of HUVEC homeostasis in a hemodynamic environment.

Endothelium-dependent epithelial-mesenchymal transition of tumor cells: exclusive roles of transforming growth factor β1 and β2

BACKGROUND

Induction of epithelial-mesenchymal transition (EMT) is essential for the metastasis of tumor cells and maintaining their stemness. This study aimed to examine whether endothelial cells, which are most closely located to tumor cells in vivo, play a role in inducing EMT in tumor cells or not.

METHODS

Concentrated culture medium of bovine aortic endothelial cells (BAECs) was applied to tumor cell lines (A549 and PANC-1) and epithelial cell line (NMuMg). Cadherin conversion, expressions of α-smooth muscle actin and ZO-1, actin fiber formation and cell migration were examined as hallmarks of the induction of EMT in these cell lines. Transforming growth factor β (TGFβ) antibodies were used to neutralize TGFβ1, TGFβ2 and TGFβ3. Expression and release of TGFβ proteins in BAECs as well as in porcine and human endothelial cells were assessed by Western blotting and ELISA, respectively.

RESULTS

Conditioned medium of BAEC induced EMT in the examined cell lines. All endothelial cells from various species and locations expressed TGFβ1 and TGFβ2 proteins and much lower level of TGFβ3 protein. Conditioned medium from these endothelial cells contained TGFβ1 and TGFβ2, but TGFβ3 could not be detected. Neutralizing antibody against each of TGFβ1 or TGFβ2 did not reverse endothelium-dependent EMT, but simultaneous neutralization of both TGFβ1 and TGFβ2 completely abolished it.

CONCLUSIONS

Endothelial cells may play a role in the induction and maintenance of EMT in tumor cells by constitutively releasing TGFβ1 and TGFβ2.

GENERAL SIGNIFICANCE

The present results provide a novel strategy of the inhibition of tumor metastasis by targeting vascular endothelium.