Endothelial extracellular matrix: biosynthesis, remodeling, and functions during vascular morphogenesis and neovessel stabilization

Fentanyl stimulates tumor angiogenesis via activating multiple pro-angiogenic signaling pathways

Angiogenesis plays a vital role in tumor progression and metastasis. To better understand the role of anesthesia in tumor biology, we previously reported that bupivacaine displayed the inhibitory effects in endothelial cells. In this work, we demonstrated that fentanyl, an opioid medication commonly used in cancer patients, stimulated tumor angiogenesis. We found that fentanyl at nanomolar concentrations significantly stimulated capillary network formation of human lung tumor-associated endothelial cell (HLT-EC) in a similar manner as vascular endothelial growth factor (VEGF), and furthermore that the stimulatory effect of fentanyl was mainly involved in early stage of HLT-EC vascular structure assembly. Particularly, fentanyl significantly increased HLT-EC growth and migration. Fentanyl also protected HLT-EC from apoptosis induced by growth factor withdrawal. In contrast, the same concentrations of fentanyl did not affect human lung cancer cell growth and survival. Fentanyl stimulated migration of some but not all tested human lung cancer cells. Mechanism analysis suggested that fentanyl activates multiple pro-angiogenic signaling pathways, including VEGFR2/FAK/PI3K/Akt and small GTPases. Our work systematically demonstrates that fentanyl stimulates tumor angiogenesis via activating multiple pro-angiogenic signaling pathways. Our findings highlight the potential adverse effect of fentanyl in cancer patients.

Regulation of opticin on bioactivity of retinal vascular endothelial cells cultured in collagen

AIM

To investigate the effects of collagen and opticin on the bioactivity of human retinal vascular endothelial cells (hRVECs), and explore its regulations by integrins and RhoA/ROCK1 signal pathway.

METHODS

hRVECs were cultured in collagen and treated by opticin, and cell-based bioactivity assays of cell proliferation, migration, and adhesion were performed. The expression of integrin α2, integrin β1, RhoA and ROCK1 were examined with real-time PCR and Western blotting.

RESULTS

Collagen could promote cell viability of proliferation and migration (all P<0.05), and enhance the mRNA expression of integrin α2, integrin β1, RhoA and ROCK1 (all P<0.05). Opticin could inhibit proliferation and migration ability of hRVECs cultured in collagen, and reduce the mRNA expression of integrin α2, integrin β1, RhoA and ROCK1 (all P<0.05).

CONCLUSION

Collagen and opticin can affect bioactivity of hRVECs, which may be regulated by α2-, β1-integrins and RhoA/ROCK1 signal pathway.

Migration of endothelial cells and mesenchymal stem cells into hyaluronic acid hydrogels with different moduli under induction of pro-inflammatory macrophages

The design of hyaluronic acid (HA)-based and stimuli-responsive hydrogels to elicit highly controlled and tunable cell response and behaviors is a major field of interest in tissue engineering and regenerative medicine. The pH-responsive hydrogel can respond to pH variation during wound healing, which may in turn regulate the tissue regeneration process. In this study, a double-network hydrogel cross-linked with vinyl double bonds and Schiff base was prepared, whose properties were further adjusted by incubation in pH 7.4 and pH 5 buffers. The endothelial cells (ECs) migrated much deeper into the softer HA hydrogel pre-treated with pH 5 buffer than the stiffer hydrogel. By contrast, the mesenchymal stem cells (MSCs) migrated easily into the stiffer hydrogel. The ECs highly expressed RhoA and non-muscle myosin (NM) II genes in the softer hydrogel, which may facilitate amoeboid migration. Meanwhile, the MSCs were stiffer than the ECs, and highly expressed Rac1, RhoA, vinculin, NM II, hyaluronidase (HYAL) 2 and CD44 genes in the stiffer hydrogel, which facilitate mesenchymal migration. These results provide important clues for revealing the different migration strategies of the ECs and MSCs in HA hydrogels with different stiffness, and suggest that the mechanical properties and the network structure of hydrogels play an important role in regulating the three-dimensional migration process of these cells.

Development of a Dual Hydrogel Model System for Vascularization

Numerous hydrogel-based culture systems are used to create in vitro model for prevascularization. Hydrogels used to induce a microenvironment conducive to microvessel formation are typically soft and fast degradable, but often suffer from maintaining a lasting perfusable channel in vitro. Here, a dual hydrogel system that consists of photo-crosslinkable gelatin methacrylate (GelMA) and polyethylene glycol dimethacrylate (PEGDMA) is reported. GelMA hydrogels present soft and rapidly degradable properties and show microporous structures while PEGDMA is relatively stiff, almost nondegradable in vitro, and less porous. The dual hydrogel system is sequentially photo-crosslinked to construct an endothelial cell (EC)-lined perfusable PEGDMA channel and surrounding GelMA for endothelial vascular networks. Such dual hydrogel system exhibits seamless integration of the stiff PEGDMA channel and the surrounding soft GelMA, and facilitates rapid EC sprouting and extensive microvessel formation from a stable endothelium on the PEGDMA channel into the GelMA. Furthermore, diffusivity of biomolecules in the perfusable dual hydrogel system is affected by both the structural and physicochemical properties of the hydrogel system and the microvascular networks formed in the system. The establishment of the dual hydrogel system for vascularization holds great promise as an in vitro angiogenesis model and prevascularization strategy of large tissue constructs.

Alkaline phosphatase dual-binding sites for collagen dictate cell migration and microvessel assembly in vitro

Interactions between cell types, growth factors, and extracellular matrix components involved in angiogenesis are crucial for new vessel formation leading to tissue regeneration. This study investigated whether cocultures of fibroblasts and endothelial cells (ECs; from macro- or microvasculature) play a role in the formation of microvessel-like structures by ECs, as well as modulate fibroblast differentiation and growth factors production (vascular endothelial cell growth factor, basic fibroblast growth factor, active transforming growth factor-β1, and interleukin-8), which are important for vessel sprouting and maturation. Data obtained revealed that in vitro coculture systems of fibroblasts and human ECs stimulate collagen synthesis and growth factors production by fibroblasts that ultimately affect the formation and distribution of microvessel-like structures in cell cultures. In this study, areas with activated fibroblasts and high alkaline phosphatase (ALP) activity were also observed in cocultures. Molecular docking assays revealed that ALP has two binding positions for collagen, suggesting its impact in collagen proteins' aggregation, cell migration, and microvessel assembly. These findings indicate that bioinformatics and coculture systems are complementary tools for investigating the participation of proteins, like collagen and ALP in angiogenesis.

Pre-Seeding of Simple Electrospun Scaffolds with a Combination of Endothelial Cells and Fibroblasts Strongly Promotes Angiogenesis

BACKGROUND

Introduction of pro-angiogenic cells into tissue-engineered (TE) constructs (prevascularisation) is a promising approach to overcome delayed neovascularisation of such constructs post-implantation. Accordingly, in this study, we examined the contribution of human dermal microvascular endothelial cells (HDMECs) and human dermal fibroblasts (HDFs) alone and in combination on the formation of new blood vessels in ex-ovo chick chorioallantoic membrane (CAM) assay.

METHODS

Poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) and polycaprolactone (PCL) were first examined in terms of their physical, mechanical, and biological performances. The effect of gelatin coating and co-culture conditions on enhancing endothelial cell viability and growth was then investigated. Finally, the angiogenic potential of HDMECs and HDFs were assessed macroscopically and histologically after seeding on simple electrospun PHBV scaffolds either in isolation or in indirect co-culture using an ex-ovo CAM assay.

RESULTS

The results demonstrated that PHBV was slightly more favourable than PCL for HDMECs in terms of cell metabolic activity. The gelatin coating of PHBV scaffolds and co-culture of HDMECs with HDFs both showed a positive impact on HDMECs viability and growth. Both cell types induced angiogenesis over 7 days in the CAM assay either in isolation or in co-culture. The introduction of HDMECs to the scaffolds resulted in the production of more blood vessels in the area of implantation than the introduction of HDFs, but the co-culture of HDMECs and HDFs gave the most significant angiogenic activity.

CONCLUSION

Our findings showed that the in vitro prevascularisation of TE constructs with HDMECs and HDFs alone or in co-culture promotes angiogenesis in implantable TE constructs.

Lidocaine inhibits vascular endothelial growth factor-A-induced angiogenesis

PURPOSE

Angiogenesis is closely related to the pathophysiology of diseases such as cancer or ischemia. Here, we investigated the effect of lidocaine at clinically effective blood concentrations on vascular endothelial growth factor A (VEGF-A)-induced angiogenesis. In addition, we aimed to clarify the mechanisms by which lidocaine could inhibit angiogenesis.

METHODS

Angiogenesis was analyzed using commercially available in vitro assay kits in human umbilical vein endothelial cells (HUVECs)/normal human dermal fibroblast co-culture systems. The effects of lidocaine on cytotoxicity, VEGF-induced cell migration, and VEGF-induced cell proliferation were examined in HUVECs using lactate dehydrogenase cytotoxic, Boyden chamber, and WST-8 assays, respectively. The VEGF signaling pathway via VEGF receptor 2 (VEGFR-2) was analyzed by western blotting.

RESULTS

Lidocaine elicited a significant dose-dependent, angiogenesis-inhibitory effect at a concentration range of 1-10 μg/ml. At this concentration range, cell death was not observed. Lidocaine, at a concentration of 10 μg/ml, significantly inhibited cell proliferation but not cell migration, induced by VEGF-A in HUVECs. Furthermore, lidocaine, in a dose-dependent manner, significantly inhibited the VEGF-A-induced phosphorylation of VEGFR-2 at 3 and 10 μg/ml.

CONCLUSION

We demonstrated that lidocaine has an anti-angiogenesis effect on clinically effective blood concentrations without causing cell death. This finding could represent a new avenue for future research into anesthesia, cancer-related analgesia, and revascularization therapy.

Alamandine attenuates angiotensin II-induced vascular fibrosis via inhibiting p38 MAPK pathway

Alamandine attenuates hypertension and cardiac remodeling in spontaneously hypertensive rats (SHRs). We examined whether alamandine attenuates vascular remodeling in mice, and regulates angiotensin II (Ang II)-induced fibrosis in rat vascular smooth muscle cells (VSMCs). Alamandine attenuated hypertension in mice induced by Ang II. Ang II increased the fibrosis of thoracic aorta in mice, which was attenuated by alamandine treatment. Increased levels of collagen I, transforming growth factor-β (TGF-β), and connective tissue growth factor (CTGF) levels in thoracic aortas after Ang II treatment in mice were inhibited by alamandine. Ang II-stimulated collagen I, TGF-β, and CTGF level increases were inhibited by alamandine in rat VSMCs. This could be reversed by Mas-related G protein-coupled receptor, member D (MrgD) antagonist D-Pro⁷-Ang-(1-7) but not Mas receptor antagonist A779. MrgD expression was increased in the thoracic aortas of mice or VSMCs treatment with Ang II. Ang II increased p-p38 and cAMP levels in rat VSMCs, and alamandine blocked Ang II-induced these increases. Cyclic adenosine monophosphate (cAMP) reversed the inhibitory effects of alamandine on the Ang II-induced increases in collagen I, TGF-β, and CTGF levels. These results demonstrate alamandine attenuates vascular fibrosis by stimulating MrgD expression and decreases arterial fibrosis by blocking p-p38 expression. Alamandine/MrgD axis is a potential target for the treatment of vascular remodeling.

Cathepsin K Deficiency Impaired Ischemia-Induced Neovascularization in Aged Mice

Background

Aging is a major risk factor for cardiovascular disease. Cysteine protease cathepsin K (CatK) has been implicated in the process of angiogenesis, but the exact roles of individual CatK in vessel formation during aging are poorly understood.

Methods and Results

To study the putative role of CatK in ischemia-induced angiogenesis, we applied a hindlimb ischemia model to aged wild-type (CatK^+/+) and CatK-deficient (CatK^−/−) mice. A serial laser Doppler blood-flow analysis revealed that the recovery of the ischemic/normal blood-flow ratio in the aged CatK^−/−mice was impaired throughout the follow-up period. On postoperative day 14, CatK deficiency had also impaired capillary formation. CatK deficiency reduced the levels of cleaved Notch1, phospho-Akt, and/or vascular endothelial growth factor (VEGF) proteins in the ischemic muscles and bone marrow-derived c-Kit⁺ cells. A flow cytometry analysis revealed that CatK deficiency reduced the numbers of endothelial progenitor cell (EPC)-like CD31⁺/c-Kit⁺ cells in the peripheral blood as well as the ischemic vasculature. In vitro experiments, CatK^−/− impaired bone-derived c-Kit⁺ cellular functions (migration, invasion, proliferation, and tubulogenesis) in aged mice. Our findings demonstrated that aging impaired the ischemia-induced angiogenesis associated with the reductions of the production and mobilization of CD31⁺/c-Kit⁺ cells in mice.

Conclusions

These findings established that the impairment of ischemia-induced neovascularization in aged CatK^−/− mice is due, at least in part, to the reduction of EPC mobilization and the homing of the cells into vasculature that is associated with the impairment of Notch1 signaling activation at advanced ages.

Evolutionarily conserved sequence motif analysis guides development of chemically defined hydrogels for therapeutic vascularization

Biologically active ligands (e.g., RGDS from fibronectin) play critical roles in the development of chemically defined biomaterials. However, recent decades have shown only limited progress in discovering novel extracellular matrix-protein-derived ligands for translational applications. Through motif analysis of evolutionarily conserved RGD-containing regions in laminin (LM) and peptide-functionalized hydrogel microarray screening, we identified a peptide (a1) that showed superior supports for endothelial cell (EC) functions. Mechanistic studies attributed the results to the capacity of a1 engaging both LM- and Fn-binding integrins. RNA sequencing of ECs in a1-functionalized hydrogels showed ~60% similarities with Matrigel in "vasculature development" gene ontology terms. Vasculogenesis assays revealed the capacity of a1-formulated hydrogels to improve EC network formation. Injectable alginates functionalized with a1 and MMPQK (a vascular endothelial growth factor-mimetic peptide with a matrix metalloproteinase-degradable linker) increased blood perfusion and functional recovery over decellularized extracellular matrix and (RGDS + MMPQK)-functionalized hydrogels in an ischemic hindlimb model, illustrating the power of this approach.

Laminin-511 and α6 integrins regulate the expression of CXCR4 to promote endothelial morphogenesis

During angiogenesis, endothelial cells engage components of the extracellular matrix through integrin-mediated adhesion. Endothelial expression of laminin-411 and laminin-511 is known to promote vessel stability. However, little is known about the contribution of these laminins to endothelial morphogenesis. We used two organotypic cell culture angiogenesis assays, in conjunction with RNAi approaches, to demonstrate that depletion of either the α4 chain of laminin-411 (LAMA4) or the α5 chain of laminin-511 (LAMA5) from endothelial cells inhibits sprouting and tube formation. Depletion of α6 (ITGA6) integrins resulted in similar phenotypes. Gene expression analysis indicated that loss of either laminin-511 or α6 integrins inhibited the expression of CXCR4, a gene previously associated with angiogenic endothelial cells. Pharmacological or RNAi-dependent inhibition of CXCR4 suppressed endothelial sprouting and morphogenesis. Importantly, expression of recombinant CXCR4 rescued endothelial morphogenesis when α6 integrin expression was inhibited. Additionally, the depletion of α6 integrins from established tubes resulted in the loss of tube integrity and laminin-511. Taken together, our results indicate that α6 integrins and laminin-511 can promote endothelial morphogenesis by regulating the expression of CXCR4 and suggest that the α6-dependent deposition of laminin-511 protects the integrity of established endothelial tubes.

Fibronectin rescues aberrant phenotype of endothelial cells lacking either CCM1, CCM2 or CCM3

Loss-of-function variants in CCM1/KRIT1, CCM2, and CCM3/PDCD10 are associated with autosomal dominant cerebral cavernous malformations (CCMs). CRISPR/Cas9-mediated CCM3 inactivation in human endothelial cells (ECs) has been shown to induce profound defects in cell-cell interaction as well as actin cytoskeleton organization. We here show that CCM3 inactivation impairs fibronectin expression and consequently leads to reduced fibers in the extracellular matrix. Despite the complexity and high molecular weight of fibronectin fibrils, our in vitro model allowed us to reveal that fibronectin supplementation restored aberrant spheroid formation as well as altered EC morphology, and suppressed actin stress fiber formation. Yet, fibronectin replacement neither enhanced the stability of tube-like structures nor inhibited the survival advantage of CCM3^-/- ECs. Importantly, CRISPR/Cas9-mediated introduction of biallelic loss-of-function variants into either CCM1 or CCM2 demonstrated that the impaired production of a functional fibronectin matrix is a common feature of CCM1-, CCM2-, and CCM3-deficient ECs.

Age-related morphology and function of human arterial endothelial cells

Endothelialization of cardiovascular implants is regarded as a promising strategy for long-term compatibility. While umbilical vein endothelial cells are typically applied in research, human arterial endothelial cells (HAEC) from elderly donors would be the obvious source for autologous cellularization strategies.In our approach, HAEC from 16 donors of varying age (16-63 years) were divided into two groups (<30 years and >30 years) and analyzed regarding morphology, viability, proliferation, function and senescence status.No age-related differences were found regarding morphology, viability, density, prostacyclin and nitrite secretion or collagen and laminin production. However, the metabolic activity was slightly decreased (p = 0.0374) and the membrane integrity marginally impaired (p = 0.0404) in cells from older donors. Two out of three senescence assays detected more senescence markers in cells from older donors.According to the assays applied here, HAEC from young and elderly donors up to the age of 63 years could be judged equally suitable for autologous cellularization strategies. However, this finding should be regarded with caution due to the extremely large variability between individual donors. Further studies comprising a larger sample size are necessary to investigate this issue more thoroughly.

Sevoflurane inhibits growth factor-induced angiogenesis through suppressing Rac1/paxillin/FAK and Ras/Akt/mTOR

Aim: We investigated the direct effects of sevoflurane on angiogenesis and a variety of tumor cells. Materials & methods: The antiangiogenic activity of sevoflurane was determined using angiogenesis and biochemical assays. Results: Sevoflurane at low doses inhibits capillary network formation. Sevoflurane inhibited VEGF- and bFGF-stimulated migration, adhesion and growth in endothelial cells and induced apoptosis. Sevoflurane only at high doses inhibited growth and migration of tumor cells, suggesting differential effects of sevoflurane between endothelial and tumor cells. Mechanistically, sevoflurane decreased growth factors-induced Ras and Rac1 activation, and suppressed Ras and Rac1 signaling. Conclusion: We demonstrate the antiangiogenic effects of sevoflurane and provide preclinical evidence into the potential mechanisms by which sevoflurane may negatively affect cancer growth and metastasis.

Extracellular Matrix Analysis of Human Renal Arteries in Both Quiescent and Active Vascular State

In vascular tissue engineering strategies, the addition of vascular-specific extracellular matrix (ECM) components may better mimic the in vivo microenvironment and potentially enhance cell-matrix interactions and subsequent tissue growth. For this purpose, the exact composition of the human vascular ECM first needs to be fully characterized. Most research has focused on characterizing ECM components in mature vascular tissue; however, the developing fetal ECM matches the active environment required in vascular tissue engineering more closely. Consequently, we characterized the ECM protein composition of active (fetal) and quiescent (mature) renal arteries using a proteome analysis of decellularized tissue. The obtained human fetal renal artery ECM proteome dataset contains higher levels of 15 ECM proteins versus the mature renal artery ECM proteome, whereas 16 ECM proteins showed higher levels in the mature tissue compared to fetal. Elastic ECM proteins EMILIN1 and FBN1 are significantly enriched in fetal renal arteries and are mainly produced by cells of mesenchymal origin. We functionally tested the role of EMILIN1 and FBN1 by anchoring the ECM secreted by vascular smooth muscle cells (SMCs) to glass coverslips. This ECM layer was depleted from either EMILIN1 or FBN1 by using siRNA targeting of the SMCs. Cultured endothelial cells (ECs) on this modified ECM layer showed alterations on the transcriptome level of multiple pathways, especially the Rho GTPase controlled pathways. However, no significant alterations in adhesion, migration or proliferation were observed when ECs were cultured on EMILIN1- or FNB1-deficient ECM. To conclude, the proteome analysis identified unique ECM proteins involved in the embryonic development of renal arteries. Alterations in transcriptome levels of ECs cultured on EMILIN1- or FBN1-deficient ECM showed that these candidate proteins could affect the endothelial (regenerative) response.

Key Regulatory miRNAs and their Interplay with Mechanosensing and Mechanotransduction Signaling Pathways in Breast Cancer Progression

According to the WHO, breast cancer is the most common cancer in women worldwide. Identification of underlying mechanisms in breast cancer progression is the main concerns of researches. The mechanical forces within the tumor microenvironment, in addition to biochemical stimuli such as different growth factors and cytokines, activate signaling cascades, resulting in various changes in cancer cell physiology. Cancer cell proliferation, invasiveness, migration, and, even, resistance to cancer therapeutic agents are changed due to activation of mechanotransduction signaling. The mechanotransduction signaling is frequently dysregulated in breast cancer, indicating its important role in cancer cell features. So far, a variety of experimental investigations have been conducted to determine the main regulators of the mechanotransduction signaling. Currently, the role of miRNAs has been well-defined in the cancer process through advances in molecular-based approaches. miRNAs are small groups of RNAs (∼22 nucleotides) that contribute to various biological events in cells. The central role of miRNAs in the regulation of various mediators involved in the mechanotransduction signaling has been well clarified over the last decade. Unbalanced expression of miRNAs is associated with different pathologic conditions. Overexpression and downregulation of certain miRNAs were found to be along with dysregulation of mechanotransduction signaling effectors. This study aimed to critically review the role of miRNAs in the regulation of mediators involved in the mechanosensing pathways and clarify how the cross-talk between miRNAs and their targets affect the cell behavior and physiology of breast cancer cells.

UV irradiation of Type I collagen gels changed the morphology of the interconnected brain capillary endothelial cells on them

We cultured mouse brain capillary endothelial cell line bEnd.3 on the UV-irradiated Type I collagen gel. Morphology of bEnd.3 cells on the Type I collagen gel was drastically changed if the gel was crosslinked by UV irradiation. The interconnecting network of bEnd.3 cells which have cord-like morphology on the soft collagen gels was converted to the monolayer of the flat cells, tightly-bound each other covering the gel surface, in a confluent state. The collagen gels were mechanically stiffened by UV irradiation for 15 min with UV light at 254 nm showing approximately two times higher value of Young's modulus E (1.51 ± 0.58 kPa) than the control gel (3.17 ± 1.17 kPa). AFM images of the collagen fibrils were not severely changed after irradiation. Collagen subunit proteins were crosslinked and degraded simultaneously under UV irradiation proved by results of SDS-PAGE and separation by centrifugation. Expression of Integrin gene was measured by quantitative real-time PCR. Expression of the integrin α2 gene, tight junction protein 1 gene, and claudin 5 gene were down-regulated in cells on the UV irradiated collagen gel in comparison with the unirradiated one while expression of the integrin β1 gene and Integrin α1 gene did not significantly change. Thick actin filaments were more clearly observed in the cells on the UV-irradiated collagen gel than the unirradiated one by fluorescent microscopy. We conclude that UV irradiation made the collagen gel stiffened and changed the physiological state of bEnd.3 cells including their adhesion, extension, and proliferation.

Tissue Engineering and Biomaterial Strategies to Elicit Endogenous Neuronal Replacement in the Brain

Neurogenesis in the postnatal mammalian brain is known to occur in the dentate gyrus of the hippocampus and the subventricular zone. These neurogenic niches serve as endogenous sources of neural precursor cells that could potentially replace neurons that have been lost or damaged throughout the brain. As an example, manipulation of the subventricular zone to augment neurogenesis has become a popular strategy for attempting to replace neurons that have been lost due to acute brain injury or neurodegenerative disease. In this review article, we describe current experimental strategies to enhance the regenerative potential of endogenous neural precursor cell sources by enhancing cell proliferation in neurogenic regions and/or redirecting migration, including pharmacological, biomaterial, and tissue engineering strategies. In particular, we discuss a novel replacement strategy based on exogenously biofabricated "living scaffolds" that could enhance and redirect endogenous neuroblast migration from the subventricular zone to specified regions throughout the brain. This approach utilizes the first implantable, biomimetic tissue-engineered rostral migratory stream, thereby leveraging the brain's natural mechanism for sustained neuronal replacement by replicating the structure and function of the native rostral migratory stream. Across all these strategies, we discuss several challenges that need to be overcome to successfully harness endogenous neural precursor cells to promote nervous system repair and functional restoration. With further development, the diverse and innovative tissue engineering and biomaterial strategies explored in this review have the potential to facilitate functional neuronal replacement to mitigate neurological and psychiatric symptoms caused by injury, developmental disorders, or neurodegenerative disease.

EOFAZ inhibits endothelial‑to‑mesenchymal transition through downregulation of KLF4

Essential oil from Alpinia zerumbet rhizome (EOFAZ), which is termed Yan shanjiang in China, is extensively used as an herbal medicine in the Guizhou area and has been shown to protect against the damaging effects of cardiovascular injury in vitro and in vivo. In the present study, it was hypothesized that the protective effects of EOFAZ on transforming growth factor (TGF)-β1-induced endothelial-to-mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs) were mediated by inhibition of Krüppel-like factor 4 (KLF4). Cell motility was assessed using wound healing and Transwell assays. The expression of endothelial markers and mesenchymal markers were determined by reverse transcription-quantitative PCR, immunofluorescence staining and western blotting, and additionally, phosphorylated NF-κB p65 expression was determined by western blotting. Furthermore, the involvement of KLF4 in EndMT was determined using RNA interference to knockdown the expression of KLF4. TGF-β1 treatment significantly promoted EndMT, as evidenced by downregu-lation of vascular endothelial-cadherin and upregulation of α-smooth muscle actin in HUVECs, and by enhancing cell migration. Small interfering RNA-mediated knockdown of KLF4 reversed TGF-β1-induced EndMT. Additionally, treatment with EOFAZ inhibited TGF-β1-induced EndMT in a dose-dependent manner. These results suggest that TGF-β1 may induce EndMT through upregulation of KLF4, and this may be reversed by EOFAZ. Therefore, EOFAZ was shown to inhibit TGF-β1-induced EndMT through regulation of KLF4.

Biofabrication Strategies and Engineered In Vitro Systems for Vascular Mechanobiology

The vascular system is integral for maintaining organ-specific functions and homeostasis. Dysregulation in vascular architecture and function can lead to various chronic or acute disorders. Investigation of the role of the vascular system in health and disease has been accelerated through the development of tissue-engineered constructs and microphysiological on-chip platforms. These in vitro systems permit studies of biochemical regulation of vascular networks and parenchymal tissue and provide mechanistic insights into the biophysical and hemodynamic forces acting in organ-specific niches. Detailed understanding of these forces and the mechanotransductory pathways involved is necessary to develop preventative and therapeutic strategies targeting the vascular system. This review describes vascular structure and function, the role of hemodynamic forces in maintaining vascular homeostasis, and measurement approaches for cell and tissue level mechanical properties influencing vascular phenomena. State-of-the-art techniques for fabricating in vitro microvascular systems, with varying degrees of biological and engineering complexity, are summarized. Finally, the role of vascular mechanobiology in organ-specific niches and pathophysiological states, and efforts to recapitulate these events using in vitro microphysiological systems, are explored. It is hoped that this review will help readers appreciate the important, but understudied, role of vascular-parenchymal mechanotransduction in health and disease toward developing mechanotherapeutics for treatment strategies.

Advanced gelatin-based vascularization bioinks for extrusion-based bioprinting of vascularized bone equivalents

Bone tissue is highly vascularized. The crosstalk of vascular and osteogenic cells is not only responsible for the formation of the strongly divergent tissue types but also for their physiological maintenance and repair. Extrusion-based bioprinting presents a promising fabrication method for bone replacement. It allows for the production of large-volume constructs, which can be tailored to individual tissue defect geometries. In this study, we used the all-gelatin-based toolbox of methacryl-modified gelatin (GM), non-modified gelatin (G) and acetylated GM (GMA) to tailor both the properties of the bioink towards improved printability, and the properties of the crosslinked hydrogel towards enhanced support of vascular network formation by simple blending. The vasculogenic behavior of human dermal microvascular endothelial cells (HDMECs) and human adipose-derived stem cells (ASCs) was evaluated in the different hydrogel formulations for 14 days. Co-culture constructs including a vascular component and an osteogenic component (i.e. a bone bioink based on GM, hydroxyapatite and ASCs) were fabricated via extrusion-based bioprinting. Bioprinted co-culture constructs exhibited functional tissue-specific cells whose interplay positively affected the formation and maintenance of vascular-like structures. The setup further enabled the deposition of bone matrix associated proteins like collagen type I, fibronectin and alkaline phosphatase within the 30-day culture.

Downregulation of lysyl oxidase in venous malformations: Association with vascular destabilization and sclerotherapy

Venous malformations (VM) are localized defects in vascular morphogenesis manifested by dilated venous channels with reduced perivascular cell coverage. As a vital enzyme for extracellular matrix (ECM) deposition, lysyl oxidase (LOX) plays important roles in vascular development and diseases. However, the expression and significance of LOX are unknown in VM. Herein, 22 VM specimens and eight samples of normal skin tissues were evaluated immunohistochemically for the expression of LOX, α-smooth muscle cell actin (α-SMA) and transforming growth factor-β (TGF-β). In vitro studies on human umbilical vein endothelial cells (HUVEC) were employed for determining potential mechanisms. Our results showed that LOX expression was significantly reduced in VM compared with normal skin tissues, in parallel with attenuated perivascular α-SMA⁺ cell coverage and TGF-β downregulation in VM. Further correlation analysis indicated that LOX expression was positively correlated with perivascular α-SMA⁺ cell coverage and TGF-β expression in VM. Moreover, marked elevation of LOX, TGF-β and α-SMA was observed in bleomycin-treated VM samples. Furthermore, our in vitro data demonstrated that both recombinant TGF-β and bleomycin induced obvious increase of LOX expression and activity and a concomitant increase in ECM components in HUVEC, which could be reversed by LOX inhibition. To our best knowledge, this study revealed for the first time the downregulation of LOX in VM and its correlation with vascular destabilization and TGF-β-induced endothelial ECM deposition. Moreover, our results highlighted that LOX may be implicated in the sclerotherapy of VM and holds promise as a therapeutic target.

Lung Microvascular Niche, Repair, and Engineering

Biomaterials have been used for a long time in the field of medicine. Since the success of "tissue engineering" pioneered by Langer and Vacanti in 1993, tissue engineering studies have advanced from simple tissue generation to whole organ generation with three-dimensional reconstruction. Decellularized scaffolds have been widely used in the field of reconstructive surgery because the tissues used to generate decellularized scaffolds can be easily harvested from animals or humans. When a patient's own cells can be seeded onto decellularized biomaterials, theoretically this will create immunocompatible organs generated from allo- or xeno-organs. The most important aspect of lung tissue engineering is that the delicate three-dimensional structure of the organ is maintained during the tissue engineering process. Therefore, organ decellularization has special advantages for lung tissue engineering where it is essential to maintain the extremely thin basement membrane in the alveoli. Since 2010, there have been many methodological developments in the decellularization and recellularization of lung scaffolds, which includes improvements in the decellularization protocols and the selection and preparation of seeding cells. However, early transplanted engineered lungs terminated in organ failure in a short period. Immature vasculature reconstruction is considered to be the main cause of engineered organ failure. Immature vasculature causes thrombus formation in the engineered lung. Successful reconstruction of a mature vasculature network would be a major breakthrough in achieving success in lung engineering. In order to regenerate the mature vasculature network, we need to remodel the vascular niche, especially the microvasculature, in the organ scaffold. This review highlights the reconstruction of the vascular niche in a decellularized lung scaffold. Because the vascular niche consists of endothelial cells (ECs), pericytes, extracellular matrix (ECM), and the epithelial-endothelial interface, all of which might affect the vascular tight junction (TJ), we discuss ECM composition and reconstruction, the contribution of ECs and perivascular cells, the air-blood barrier (ABB) function, and the effects of physiological factors during the lung microvasculature repair and engineering process. The goal of the present review is to confirm the possibility of success in lung microvascular engineering in whole organ engineering and explore the future direction of the current methodology.

Variable Responses to Corneal Grafts: Insights from Immunology and Systems Biology

Corneal grafts interact with their hosts via complex immunobiological processes that sometimes lead to graft failure. Prediction of graft failure is often a tedious task due to the genetic and nongenetic heterogeneity of patients. As in other areas of medicine, a reliable prediction method would impact therapeutic decision-making in corneal transplantation. Valuable insights into the clinically observed heterogeneity of host responses to corneal grafts have emerged from multidisciplinary approaches, including genomics analyses, mechanical studies, immunobiology, and theoretical modeling. Here, we review the emerging concepts, tools, and new biomarkers that may allow for the prediction of graft survival.

Models for Monocytic Cells in the Tumor Microenvironment

Monocytes (Mos) are immune cells that critically regulate cancer, enabling tumor growth and modulating metastasis. Mos can give rise to tumor-associated macrophages (TAMs) and Mo-derived dendritic cells (moDCs), all of which shape the tumor microenvironment (TME). Thus, understanding their roles in the TME is key for improved immunotherapy. Concurrently, various biological and mechanical factors including changes in local cytokines, extracellular matrix production, and metabolic changes in the TME affect the roles of monocytic cells. As such, relevant TME models are critical to achieve meaningful insight on the precise functions, mechanisms, and effects of monocytic cells. Notably, murine models have yielded significant insight into human Mo biology. However, many of these results have yet to be confirmed in humans, reinforcing the need for improved in vitro human TME models for the development of cancer interventions. Thus, this chapter (1) summarizes current insight on the tumor biology of Mos, TAMs, and moDCs, (2) highlights key therapeutic applications relevant to these cells, and (3) discusses various TME models to study their TME-related activity. We conclude with a perspective on the future research trajectory of this topic.

Microglial responses after phagocytosis: Escherichia coli bioparticles, but not cell debris or amyloid beta, induce matrix metalloproteinase-9 secretion in cultured rat primary microglial cells

Upon infection or brain damage, microglia are activated to play roles in immune responses, including phagocytosis and soluble factor release. However, little is known whether the event of phagocytosis could be a trigger for releasing soluble factors from microglia. In this study, we tested if microglia secrete a neurovascular mediator matrix metalloproteinase-9 (MMP-9) after phagocytosis in vitro. Primary microglial cultures were prepared from neonatal rat brains. Cultured microglia phagocytosed Escherichia coli bioparticles within 2 hr after incubation and started to secrete MMP-9 at around 12 hr after the phagocytosis. A TLR4 inhibitor TAK242 suppressed the E. coli-bioparticle-induced MMP-9 secretion. However, TAK242 did not change the engulfment of E. coli bioparticles in microglial cultures. Because lipopolysaccharides (LPS), the major component of the outer membrane of E. coli, also induced MMP-9 secretion in a dose-response manner and because the response was inhibited by TAK242 treatment, we assumed that the LPS-TLR4 pathway, which was activated by adhering to the substance, but not through the engulfing process of phagocytosis, would play a role in releasing MMP-9 from microglia after E. coli bioparticle treatment. To support the finding that the engulfing step would not be a critical trigger for MMP-9 secretion after the event of phagocytosis in microglia, we confirmed that cell debris and amyloid beta were both captured into microglia via phagocytosis, but neither of them induced MMP-9 secretion from microglia. Taken together, these data demonstrate that microglial response in MMP-9 secretion after phagocytosis differs depending on the types of particles/substances that microglia encountered.

Immobilized RGD concentration and proteolytic degradation synergistically enhance vascular sprouting within hydrogel scaffolds of varying modulus

Insufficient vascularization limits the volume and complexity of engineered tissue. The formation of new blood vessels (neovascularization) is regulated by a complex interplay of cellular interactions with biochemical and biophysical signals provided by the extracellular matrix (ECM) necessitating the development of biomaterial approaches that enable systematic modulation in matrix properties. To address this need poly(ethylene) glycol-based hydrogel scaffolds were engineered with a range of decoupled and combined variations in integrin-binding peptide (RGD) ligand concentration, elastic modulus and proteolytic degradation rate using free-radical polymerization chemistry. The modularity of this system enabled a full factorial experimental design to simultaneously investigate the individual and interaction effects of these matrix cues on vascular sprout formation in 3 D culture. Enhancements in scaffold proteolytic degradation rate promoted significant increases in vascular sprout length and junction number while increases in modulus significantly and negatively impacted vascular sprouting. We also observed that individual variations in immobilized RGD concentration did not significantly impact 3 D vascular sprouting. Our findings revealed a previously unidentified and optimized combination whereby increases in both immobilized RGD concentration and proteolytic degradation rate resulted in significant and synergistic enhancements in 3 D vascular spouting. The above-mentioned findings would have been challenging to uncover using one-factor-at-time experimental analyses.

Vascularization in tissue engineering: fundamentals and state-of-art

Vascularization is among the top challenges that impede the clinical application of engineered tissues. This challenge has spurred tremendous research endeavor, defined as vascular tissue engineering (VTE) in this article, to establish a pre-existing vascular network inside the tissue engineered graft prior to implantation. Ideally, the engineered vasculature can be integrated into the host vasculature via anastomosis to supply nutrient to all cells instantaneously after surgery. Moreover, sufficient vascularization is of great significance in regenerative medicine from many other perspectives. Due to the critical role of vascularization in successful tissue engineering, we aim to provide an up-to-date overview of the fundamentals and VTE strategies in this article, including angiogenic cells, biomaterial/bio-scaffold design and bio-fabrication approaches, along with the reported utility of vascularized tissue complex in regenerative medicine. We will also share our opinion on the future perspective of this field.

Differential HDAC6 Activity Modulates Ciliogenesis and Subsequent Mechanosensing of Endothelial Cells Derived from Pluripotent Stem Cells

The role of primary cilia in mechanosensation is essential in endothelial cell (EC) shear responsiveness. Here, we find that venous, capillary, and progenitor ECs respond to shear stress in vitro in a cilia-dependent manner. We then demonstrate that primary cilia assembly in human induced pluripotent stem cell (hiPSC)-derived ECs varies between different cell lines with marginal influence of differentiation protocol. hiPSC-derived ECs lacking cilia do not align to shear stress, lack stress fiber assembly, have uncoordinated migration during wound closure in vitro, and have aberrant calcium influx upon shear exposure. Transcriptional analysis reveals variation in regulatory genes involved in ciliogenesis among different hiPSC-derived ECs. Moreover, inhibition of histone deacetylase 6 (HDAC6) activity in hiPSC-ECs lacking cilia rescues cilia formation and restores mechanical sensing. Taken together, these results show the importance of primary cilia in hiPSC-EC mechano-responsiveness and its modulation through HDAC6 activity varies among hiPSC-ECs.

Role of ADTRP (Androgen-Dependent Tissue Factor Pathway Inhibitor Regulating Protein) in Vascular Development and Function

Background

The physiological function of ADTRP (androgen‐dependent tissue factor pathway inhibitor regulating protein) is unknown. We previously identified ADTRP as coregulating with and supporting the anticoagulant activity of tissue factor pathway inhibitor in endothelial cells in vitro. Here, we studied the role of ADTRP in vivo, specifically related to vascular development, stability, and function.

Methods and Results

Genetic inhibition of Adtrp produced vascular malformations in the low‐pressure vasculature of zebrafish embryos and newborn mice: dilation/tortuosity, perivascular inflammation, extravascular proteolysis, increased permeability, and microhemorrhages, which produced partially penetrant lethality. Vascular leakiness correlated with decreased endothelial cell junction components VE‐cadherin and claudin‐5. Changes in hemostasis in young adults comprised modest decrease of tissue factor pathway inhibitor antigen and activity and increased tail bleeding time and volume. Cell‐based reporter assays revealed that ADTRP negatively regulates canonical Wnt signaling, affecting membrane events downstream of low‐density lipoprotein receptor‐related protein 6 (LRP6) and upstream of glycogen synthase kinase 3 beta. ADTRP deficiency increased aberrant/ectopic Wnt/β‐catenin signaling in vivo in newborn mice and zebrafish embryos, and upregulated matrix metallopeptidase (MMP)‐9 in endothelial cells and mast cells (MCs). Vascular lesions in newborn Adtrp^−/− pups displayed accumulation of MCs, decreased extracellular matrix content, and deficient perivascular cell coverage. Wnt‐pathway inhibition reversed the increased mmp9 in zebrafish embryos, demonstrating that mmp9 expression induced by Adtrp deficiency was downstream of canonical Wnt signaling.

Conclusions

Our studies demonstrate that ADTRP plays a major role in vascular development and function, most likely through expression in endothelial cells and/or perivascular cells of Wnt‐regulated genes that control vascular stability and integrity.

Prolargin and matrix metalloproteinase-2 in heart failure after heart transplantation and their association with haemodynamics

Aims

Remodelling of the extracellular matrix (ECM) is a key mechanism involved in the development and progression of heart failure (HF) but also functional in associated pulmonary hypertension (PH). Our aim was to identify plasma ECM proteins associated to end‐stage HF and secondary PH in relation to haemodynamics, before and after heart transplantation (HT).

Methods and results

Twenty ECM plasma proteins were analysed with proximity extension assay in 20 controls and 26 HF patients pre‐HT and 1 year post‐HT. Right heart catherization haemodynamics were assessed in the patients during the preoperative evaluation and at the 1 year follow‐up post‐HT. Plasma levels of prolargin and matrix metalloproteinase‐2 (MMP‐2) were elevated (P < 0.0001) in HF patients compared with controls and decreased (P < 0.0001) post‐HT towards controls' levels. The decrease in prolargin post‐HT correlated with improved mean right atrial pressure (r_s = 0.63; P = 0.00091), stroke volume index (r_s = −0.73; P < 0.0001), cardiac index (r_s = −0.64; P = 0.00057), left ventricular stroke work index (r_s = −0.49; P = 0.015), and N‐terminal pro brain natriuretic peptide (r_s = 0.7; P < 0.0001). The decrease in MMP‐2 post‐HT correlated with improved mean pulmonary artery pressure (r_s = 0.58; P = 0.0025), mean right atrial pressure (r_s = 0.56; P = 0.0046), pulmonary artery wedge pressure (r_s = 0.48; P = 0.016), and N‐terminal pro brain natriuretic peptide (r_s = 0.56; P = 0.0029).

Conclusions

The normalization pattern in HF patients of plasma prolargin and MMP‐2 post‐HT towards controls' levels and their associations with improved haemodynamics indicate that prolargin and MMP‐2 may reflect, in part, the aberrant ECM remodelling involved in the pathophysiology of HF and associated PH. Their potential clinical use as biomarkers or targets for future therapy in HF and related PH remains to be investigated.

Extracellular matrix, regional heterogeneity of the aorta, and aortic aneurysm

Aortic aneurysm is an asymptomatic disease with dire outcomes if undiagnosed. Aortic aneurysm rupture is a significant cause of death worldwide. To date, surgical repair or endovascular repair (EVAR) is the only effective treatment for aortic aneurysm, as no pharmacological treatment has been found effective. Aortic aneurysm, a focal dilation of the aorta, can be formed in the thoracic (TAA) or the abdominal (AAA) region; however, our understanding as to what determines the site of aneurysm formation remains quite limited. The extracellular matrix (ECM) is the noncellular component of the aortic wall, that in addition to providing structural support, regulates bioavailability of an array of growth factors and cytokines, thereby influencing cell function and behavior that ultimately determine physiological or pathological remodeling of the aortic wall. Here, we provide an overview of the ECM proteins that have been reported to be involved in aortic aneurysm formation in humans or animal models, and the experimental models for TAA and AAA and the link to ECM manipulations. We also provide a comparative analysis, where data available, between TAA and AAA, and how aberrant ECM proteolysis versus disrupted synthesis may determine the site of aneurysm formation.

A review of aneurysm formation, swelling in blood vessel, in the aorta, examines distinctions between two forms of the condition and the role of proteins in the extracellular matrix which surrounds cells of the arterial wall. Rupture of aneurysms in the aorta, the body’s main artery, is a major cause of death. Researchers led by Zamaneh Kassiri at the University of Alberta, Edmonton, Canada, emphasize that aneurysms in the thoracic and abdominal regions of the aorta are distinct conditions with crucial differences in their causes. Disrupted production and assembly of the extracellular matrix and its proteins may underlie thoracic aneurysm formation. Factors triggering the degradation of extracellular matrix proteins may be more significant in abdominal aneurysms. Understanding the differing molecular mechanisms involved could help address the current lack of effective drug treatments for these dangerous conditions.

Tight Junctions in Cell Proliferation

Tight junction (TJ) proteins form a continuous intercellular network creating a barrier with selective regulation of water, ion, and solutes across endothelial, epithelial, and glial tissues. TJ proteins include the claudin family that confers barrier properties, members of the MARVEL family that contribute to barrier regulation, and JAM molecules, which regulate junction organization and diapedesis. In addition, the membrane-associated proteins such as MAGUK family members, i.e., zonula occludens, form the scaffold linking the transmembrane proteins to both cell signaling molecules and the cytoskeleton. Most studies of TJ have focused on the contribution to cell-cell adhesion and tissue barrier properties. However, recent studies reveal that, similar to adherens junction proteins, TJ proteins contribute to the control of cell proliferation. In this review, we will summarize and discuss the specific role of TJ proteins in the control of epithelial and endothelial cell proliferation. In some cases, the TJ proteins act as a reservoir of critical cell cycle modulators, by binding and regulating their nuclear access, while in other cases, junctional proteins are located at cellular organelles, regulating transcription and proliferation. Collectively, these studies reveal that TJ proteins contribute to the control of cell proliferation and differentiation required for forming and maintaining a tissue barrier.

The pericyte microenvironment during vascular development

Vascular pericytes provide critical contributions to the formation and integrity of the blood vessel wall within the microcirculation. Pericytes maintain vascular stability and homeostasis by promoting endothelial cell junctions and depositing extracellular matrix (ECM) components within the vascular basement membrane, among other vital functions. As their importance in sustaining microvessel health within various tissues and organs continues to emerge, so does their role in a number of pathological conditions including cancer, diabetic retinopathy, and neurological disorders. Here, we review vascular pericyte contributions to the development and remodeling of the microcirculation, with a focus on the local microenvironment during these processes. We discuss observations of their earliest involvement in vascular development and essential cues for their recruitment to the remodeling endothelium. Pericyte involvement in the angiogenic sprouting context is also considered with specific attention to crosstalk with endothelial cells such as through signaling regulation and ECM deposition. We also address specific aspects of the collective cell migration and dynamic interactions between pericytes and endothelial cells during angiogenic sprouting. Lastly, we discuss pericyte contributions to mechanisms underlying the transition from active vessel remodeling to the maturation and quiescence phase of vascular development.

Generation of complex human organoid models including vascular networks by incorporation of mesodermal progenitor cells

Organoids derived from human pluripotent stem cells are interesting models to study mechanisms of morphogenesis and promising platforms for disease modeling and drug screening. However, they mostly remain incomplete as they lack stroma, tissue resident immune cells and in particular vasculature, which create important niches during development and disease. We propose, that the directed incorporation of mesodermal progenitor cells (MPCs) into organoids will overcome the aforementioned limitations. In order to demonstrate the feasibility of the method, we generated complex human tumor as well as neural organoids. We show that the formed blood vessels display a hierarchic organization and mural cells are assembled into the vessel wall. Moreover, we demonstrate a typical blood vessel ultrastructure including endothelial cell-cell junctions, a basement membrane as well as luminal caveolae and microvesicles. We observe a high plasticity in the endothelial network, which expands, while the organoids grow and is responsive to anti-angiogenic compounds and pro-angiogenic conditions such as hypoxia. We show that vessels within tumor organoids connect to host vessels following transplantation. Remarkably, MPCs also deliver Iba1⁺ cells that infiltrate the neural tissue in a microglia-like manner.

Acellular polycaprolactone scaffolds laden with fibroblast/endothelial cell-derived extracellular matrix for bone regeneration

Inconsistencies in graft osteoconduction and osteoinduction present a clinical challenge in regeneration of large bone defects. Deposition of decellularized extracellular matrix (dECM) on tissue engineered scaffolds offers an alternative approach that can enhance these properties by mimicking bone's molecular complexity and direct infiltrating cells to repair damaged bone. However, dECMs derived from homogenous cell populations do not adequately simulate the heterogeneous and vascularized microenvironment of the bone. In this study, successive culture and decellularization of fibroblasts and endothelial cells (ECs) grown on polycaprolactone microfibers was used to develop a bioactive scaffold with heterogeneous dECM mimicking endothelial basement membrane. These scaffolds had greater amount of protein and minimally increased nucleic acid content than scaffolds with homogenous culture dECM. Coomassie Blue and antibody staining revealed extensive tube formation by ECs on fibroblast dECM. Fibroblast/endothelial dECM significantly enhanced osteoblast attachment, alkaline phosphatase activity, and osteocalcin- and osteopontin-positive extracellular mineral deposits. We demonstrated that the osteoconduction of dECMs can be tailored with the appropriate combination of cells to accelerate osteoblast mineral secretion. The overall concept can be expanded to generate increasingly more complex tissue constructs for regeneration of bone defects and other vascularized tissues.

A Virus-Derived Immune Modulating Serpin Accelerates Wound Closure with Improved Collagen Remodeling

Numerous treatments have been developed to promote wound healing based on current understandings of the healing process. Hemorrhaging, clotting, and associated inflammation regulate early wound healing. We investigated treatment with a virus-derived immune modulating serine protease inhibitor (SERPIN), Serp-1, which inhibits thrombolytic proteases and inflammation, in a mouse excisional wound model. Saline or recombinant Serp-1 were applied directly to wounds as single doses of 1 μg or 2 µg or as two 1 µg boluses. A chitosan-collagen hydrogel was also tested for Serp-1 delivery. Wound size was measured daily for 15 days and scarring assessed by Masson’s trichrome, Herovici’s staining, and immune cell dynamics and angiogenesis by immunohistochemistry. Serp-1 treatment significantly accelerated wound healing, but was blocked by urokinase-type plasminogen activator (uPAR) antibody. Repeated dosing at a lower concentration was more effective than single high-dose serpin. A single application of Serp-1-loaded chitosan-collagen hydrogel was as effective as repeated aqueous Serp-1 dosing. Serp-1 treatment of wounds increased arginase-1-expressing M2-polarized macrophage counts and periwound angiogenesis in the wound bed. Collagen staining also demonstrated that Serp-1 improves collagen maturation and organization at the wound site. Serp-1 has potential as a safe and effective immune modulating treatment that targets thrombolytic proteases, accelerating healing and reducing scar in deep cutaneous wounds.

Quantifying the effects of engineered nanomaterials on endothelial cell architecture and vascular barrier integrity using a cell pair model

Engineered nanomaterials (ENMs) are increasingly used in consumer products due to their unique physicochemical properties, but the specific hazards they pose to the structural and functional integrity of endothelial barriers remain elusive. When assessing the effects of ENMs on vascular barrier function, endothelial cell monolayers are commonly used as in vitro models. Monolayer models, however, do not offer a granular understanding of how the structure-function relationships between endothelial cells and tissues are disrupted due to ENM exposure. To address this issue, we developed a micropatterned endothelial cell pair model to quantitatively evaluate the effects of 10 ENMs (8 metal/metal oxides and 2 organic ENMs) on multiple cellular parameters and determine how these parameters correlate to changes in vascular barrier function. This minimalistic approach showed concerted changes in endothelial cell morphology, intercellular junction formation, and cytoskeletal organization due to ENM exposure, which were then quantified and compared to unexposed pairs using a "similarity scoring" method. Using the cell pair model, this study revealed dose-dependent changes in actin organization and adherens junction formation following exposure to representative ENMs (Ag, TiO2 and cellulose nanocrystals), which exhibited trends that correlate with changes in tissue permeability measured using an endothelial monolayer assay. Together, these results demonstrate that we can quantitatively evaluate changes in endothelial architecture emergent from nucleo-cytoskeletal network remodeling using micropatterned cell pairs. The endothelial pair model therefore presents potential applicability as a standardized assay for systematically screening ENMs and other test agents for their cellular-level structural effects on vascular barriers.

Emerging roles of ECM remodeling processes in cancer

Extracellular matrix (ECM) plays a central and dynamic role in the creation of tumor microenvironment. Herein we discuss the emerging biophysical and biochemical aspects of ECM buildup and proteolysis in cancer niche formation. Dysregulated ECM remodeling by cancer cells facilitate irreversible proteolysis and crosslinking, which in turn influence cell signaling, micro environmental cues, angiogenesis and tissue biomechanics. Further, we introduce the emerging roles of cancer microbiome in aberrant tumor ECM remodeling and membrane bound nano-sized vesicles called exosomes in creation of distant pre-metastatic niches. A detailed molecular and biophysical understanding of the ECM morphologies and its components such as key enzymes, structural and signaling molecules are critical in identifying the next generation of therapeutic and diagnostic targets in cancer.

Colloidal Gels for Guiding Endothelial Cell Organization via Microstructural Morphology

One of the fundamental challenges in vascular morphogenesis is to understand how the microstructural morphology of a 3D matrix can provide the spatial cues to organize the endothelial cells (ECs) into specific vascular structures. Colloidal gels can provide well-controlled distinct morphological matrices because these gels are formed by the aggregation of particles. By altering the aggregation mode, the spatial organization of the particles can be controlled to yield different microstructural morphology. To demonstrate this, colloidal aggregates and gels were developed by electrostatic interaction-mediated aggregation of cationic polyurethane (PU) colloidal particles by using low molecular weight electrolyte and polyelectrolyte to develop microstructurally different colloidal gels without altering their bulk elasticity. Compact dense colloidal aggregates with constricted voids were developed via electrolyte-mediated aggregation, whereas stranded branched networks with interconnected voids were formed via polyelectrolyte-mediated bridging interactions. Results show that the microstructure of aggregated colloids and gels can regulate EC organizations. Within endothelial matrices, ECs track the microstructure of particulate phase to interconnect with stranded colloidal network but cluster around compact colloidal aggregate. Similarly, in colloidal gels, ECs formed capillary-like structures by interconnecting along the stranded networks with enhanced cell-matrix interactions and increased cell extension but aggregated within the constricted voids of compact dense gel with enhanced cell-cell interaction. Both morphometric analysis and expression of EC markers corroborated the cell organizations in these gels. Using these colloidal gels, we demonstrated the role of 3D microstructural morphology as an important regulator for spatial guidance of ECs and simultaneously established the significance of colloidal gels as 3D matrix to regulate cellular morphogenesis.

Hydrogel vehicles for sequential delivery of protein drugs to promote vascular regeneration

In recent years, as the mechanisms of vasculogenesis and angiogenesis have been uncovered, the functions of various pro-angiogenic growth factors (GFs) and cytokines have been identified. Therefore, therapeutic angiogenesis, by delivery of GFs, has been sought as a treatment for many vascular diseases. However, direct injection of these protein drugs has proven to have limited clinical success due to their short half-lives and systemic off-target effects. To overcome this, hydrogel carriers have been developed to conjugate single or multiple GFs with controllable, sustained, and localized delivery. However, these attempts have failed to account for the temporal complexity of natural angiogenic pathways, resulting in limited therapeutic effects. Recently, the emerging ideas of optimal sequential delivery of multiple GFs have been suggested to better mimic the biological processes and to enhance therapeutic angiogenesis. Incorporating sequential release into drug delivery platforms will likely promote the formation of neovasculature and generate vast therapeutic potential.

Engineering the vasculature for islet transplantation

The microvasculature in the pancreatic islet is highly specialized for glucose sensing and insulin secretion. Although pancreatic islet transplantation is a potentially life-changing treatment for patients with insulin-dependent diabetes, a lack of blood perfusion reduces viability and function of newly transplanted tissues. Functional vasculature around an implant is not only necessary for the supply of oxygen and nutrients but also required for rapid insulin release kinetics and removal of metabolic waste. Inadequate vascularization is particularly a challenge in islet encapsulation. Selectively permeable membranes increase the barrier to diffusion and often elicit a foreign body reaction including a fibrotic capsule that is not well vascularized. Therefore, approaches that aid in the rapid formation of a mature and robust vasculature in close proximity to the transplanted cells are crucial for successful islet transplantation or other cellular therapies. In this paper, we review various strategies to engineer vasculature for islet transplantation. We consider properties of materials (both synthetic and naturally derived), prevascularization, local release of proangiogenic factors, and co-transplantation of vascular cells that have all been harnessed to increase vasculature. We then discuss the various other challenges in engineering mature, long-term functional and clinically viable vasculature as well as some emerging technologies developed to address them. The benefits of physiological glucose control for patients and the healthcare system demand vigorous pursuit of solutions to cell transplant challenges. STATEMENT OF SIGNIFICANCE: Insulin-dependent diabetes affects more than 1.25 million people in the United States alone. Pancreatic islets secrete insulin and other endocrine hormones that control glucose to normal levels. During preparation for transplantation, the specialized islet blood vessel supply is lost. Furthermore, in the case of cell encapsulation, cells are protected within a device, further limiting delivery of nutrients and absorption of hormones. To overcome these issues, this review considers methods to rapidly vascularize sites and implants through material properties, pre-vascularization, delivery of growth factors, or co-transplantation of vessel supporting cells. Other challenges and emerging technologies are also discussed. Proper vascular growth is a significant component of successful islet transplantation, a treatment that can provide life-changing benefits to patients.

Single-cell transcriptome analyses reveal novel targets modulating cardiac neovascularization by resident endothelial cells following myocardial infarction

AIMS

A better understanding of the pathways that regulate regeneration of the coronary vasculature is of fundamental importance for the advancement of strategies to treat patients with heart disease. Here, we aimed to investigate the origin and clonal dynamics of endothelial cells (ECs) associated with neovascularization in the adult mouse heart following myocardial infarction (MI). Furthermore, we sought to define murine cardiac endothelial heterogeneity and to characterize the transcriptional profiles of pro-angiogenic resident ECs in the adult mouse heart, at single-cell resolution.

METHODS AND RESULTS

An EC-specific multispectral lineage-tracing mouse (Pdgfb-iCreERT2-R26R-Brainbow2.1) was used to demonstrate that structural integrity of adult cardiac endothelium following MI was maintained through clonal proliferation by resident ECs in the infarct border region, without significant contributions from bone marrow cells or endothelial-to-mesenchymal transition. Ten transcriptionally discrete heterogeneous EC states, as well as the pathways through which each endothelial state is likely to enhance neovasculogenesis and tissue regeneration following ischaemic injury were defined. Plasmalemma vesicle-associated protein (Plvap) was selected for further study, which showed an endothelial-specific and increased expression in both the ischaemic mouse and human heart, and played a direct role in regulating human endothelial proliferation in vitro.

CONCLUSION

We present a single-cell gene expression atlas of cardiac specific resident ECs, and the transcriptional hierarchy underpinning endogenous vascular repair following MI. These data provide a rich resource that could assist in the development of new therapeutic interventions to augment endogenous myocardial perfusion and enhance regeneration in the injured heart.

Human Ocular Angiogenesis-Inspired Vascular Models on an Injection-Molded Microfluidic Chip

Angiogenic sprouting, which is the growth of new blood vessels from pre-existing vessels, is orchestrated by cues from the cellular microenvironment, such as spatially controlled gradients of angiogenic factors. However, current in vitro models are less scalable for in-depth studies of angiogenesis. In this study, a plastic-based microfluidic chip is developed to reconstruct in vitro 3D vascular networks. The main disadvantages of the preexisting system are identified, namely, the low productivity and difficulty of experiments, and a breakthrough is suggested while minimizing disadvantages. The selection of plastic materials contributes to the productivity and usability of in vitro devices. By adopting this material, this chip offers simple fluid patterning, facilitating the construction of a cell-culture microenvironment. Compared with previous systems, the chip, which can form both inward and outwardly radial vascular sprouting, demonstrates the growth of functional, morphologically integral microvessels. The developed angiogenic model yields dose-dependent results for antiangiogenic drug screening. This model may contribute significantly not only to vascular studies under normal and pathological conditions, but also to fundamental research on the ocular neovascularization. Furthermore, it can be applied as a tool for more practical, extended preclinical research, providing an alternative to animal experiments.

Balance of interstitial flow magnitude and vascular endothelial growth factor concentration modulates three-dimensional microvascular network formation

Hemodynamic and biochemical factors play important roles in critical steps of angiogenesis. In particular, interstitial flow has attracted attention as an important hemodynamic factor controlling the angiogenic process. Here, we applied a wide range of interstitial flow magnitudes to an in vitro three-dimensional (3D) angiogenesis model in a microfluidic device. This study aimed to investigate the effect of interstitial flow magnitude in combination with the vascular endothelial growth factor (VEGF) concentration on 3D microvascular network formation. Human umbilical vein endothelial cells (HUVECs) were cultured in a series of interstitial flow generated by 2, 8, and 25 mmH₂O. Our findings indicated that interstitial flow significantly enhanced vascular sprout formation, network extension, and the development of branching networks in a magnitude-dependent manner. Furthermore, we demonstrated that the proangiogenic effect of interstitial flow application could not be substituted by the increased VEGF concentration. In addition, we found that HUVECs near vascular sprouts significantly elongated in >8 mmH₂O conditions, while activation of Src was detected even in 2 mmH₂O conditions. Our results suggest that the balance between the interstitial flow magnitude and the VEGF concentration plays an important role in the regulation of 3D microvascular network formation in vitro.