Tracking angiogenesis induced by skin wounding and contact hypersensitivity using a Vegfr2-luciferase transgenic mouse

The life cycle of a capillary: Mechanisms of angiogenesis and rarefaction in microvascular physiology and pathologies

Capillaries are the smallest blood vessels (<10 μm in diameter) in the body and their walls are lined by endothelial cells. These microvessels play a crucial role in nutrient and gas exchange between blood and tissues. Capillary endothelial cells also produce vasoactive molecules and initiate the electrical signals that underlie functional hyperemia and neurovascular coupling. Accordingly, capillary function and density are critical for all cell types to match blood flow to cellular activity. This begins with the process of angiogenesis, when new capillary blood vessels emerge from pre-existing vessels, and ends with rarefaction, the loss of these microvascular structures. This review explores the mechanisms behind these processes, emphasizing their roles in various microvascular diseases and their impact on surrounding cells in health and disease. We discuss recent work on the mechanisms controlling endothelial cell proliferation, migration, and tube formation that underlie angiogenesis under physiological and pathological conditions. The mechanisms underlying functional and anatomical rarefaction and the role of pericytes in this process are also discussed. Based on this work, a model is proposed in which the balance of angiogenic and rarefaction signaling pathways in a particular tissue match microvascular density to the metabolic demands of the surrounding cells. This negative feedback loop becomes disrupted during microvascular rarefaction: angiogenic mechanisms are blunted, reactive oxygen species accumulate, capillary function declines and eventually, capillaries disappear. This, we propose, forms the foundation of the reciprocal relationship between vascular density, blood flow, and metabolic needs and functionality of nearby cells.

Caffeine-reinforced Collagen as Localized Microenvironmental Trans-Browning Bio-Matrix for Soft Tissue Repair and Regeneration in Bariatric Condition

The wound exudates, hypoperfusion of the subcutaneous fat layer, and poor vasculature worsen wound management in obese subjects. In the current study, a multifunctional Caffeine-reinforced collagen biomaterial is developed that can simultaneously modulate lipid metabolism and angiogenesis in obese wound microenvironments for faster tissue regeneration. The biomaterial is fabricated specialized for obese conditions to initiate simultaneous lipolysis and angiogenesis locally in the hypoxic subcutaneous fat in wound margins of obese subjects. Caffeine-reinforced collagen biomatrix shows better structural integrity, thermal stability, bio-compatibility, and lesser proteolytic susceptibility. Caffeine-collagen biomaterial promote angiogenesis, fibroblast migration, and localized browning of white adipocytes to activate thermogenesis in the subcutaneous fat layer at the wound site. Full-thickness excision wound healing studies performed in obese C57BL6 mice shows faster wound closure within day 9 when compare to control mice. The Caffeine-reinforced collagen biomaterial remodeled the wound site locally by activating fibroblast to secrete collagen, activate endothelial cells to promote angiogenesis, and induce browning in white adipocytes in subcutaneous fat. The study opens a new direction in bariatric tissue regenerative medicine by locally modulating lipid metabolism, angiogenesis, and trans-browning at the injured site for faster complete restoration of the damaged tissue.

Effects of Hair Follicle Stem Cells Coupled With Polycaprolactone Scaffold on Cutaneous Wound Healing in Diabetic Male Rats

INTRODUCTION

Chronic wounds are debilitating complications of diabetes mellitus. The present study was conducted to investigate the effect of the hair follicle stem cells (HFSCs) by polycaprolactone scaffold on the healing of incisional cutaneous wounds on streptozotocin-induced diabetic male rats.

METHODS

The wound model was obtained by a biopsy punch of the skin of the animals' back. The animals were randomly divided into five groups as follows: (1) Sham (nondiabetic, not treated), (2) Control (diabetic, not treated), (3) Scaffold (diabetic, treated with polycaprolactone nanofiber scaffold), (4) HFSCs (diabetic, treated with HFSCs), and (5) Scaffold + HFSCs (diabetic, treated with combination of Scaffold and HFSCs). The wounds were photographed in the course of the treatment and their healing rate was assessed. The samples were collected from the wound sites 7, 14, and 28 d after their development. Angiogenesis was surveyed by examining messenger RNA expression and the protein synthesis levels of vascular endothelial growth factor receptor 2 (VEGFR2) and platelet/endothelial cell adhesion molecule-1/cluster of differentiation 31. The histological changes were investigated using hematoxylin and eosin and Masson's trichrome staining. Furthermore, the wound breaking strength was measured on the 28th day by tensiometry.

RESULTS

The application of the VEGFR2 as a substrate promotes the expression of CD31 in HFSCs and Scaffold + HFSCs groups compared to controls (P < 0.0001). HFSCs and scaffold also rescue the diabetes-induced dysfunction as assessed based on the parameters, such as viability, proliferation, colony formation, cellular adhesion, and chemotactic migration. HFSCs augment the levels of VEGFR2 and promote the restoration of the wound healing in diabetic groups. Furthermore, the maximum biomechanical stress significantly increased in the experimental diabetic groups (Scaffold: 1.38 ± 0.09, HFSCs: 2.13 ± 0.8, Scaffold + HFSCs: 2.38 ± 0.11) compared to the diabetes control group (1.16 ± 0.12). Using of HFSCs and scaffold on diabetic wounds leads to an accelerated wound closure, notably.

CONCLUSIONS

Thus, the current data showed that HFSCs and scaffold form excellent biomaterial in the treatment of diabetic wounds.

Immunoengineering strategies to enhance vascularization and tissue regeneration

Immune cells have emerged as powerful regulators of regenerative as well as pathological processes. The vast majority of regenerative immunoengineering efforts have focused on macrophages; however, growing evidence suggests that other cells of both the innate and adaptive immune system are as important for successful revascularization and tissue repair. Moreover, spatiotemporal regulation of immune cells and their signaling have a significant impact on the regeneration speed and the extent of functional recovery. In this review, we summarize the contribution of different types of immune cells to the healing process and discuss ways to manipulate and control immune cells in favor of vascularization and tissue regeneration. In addition to cell delivery and cell-free therapies using extracellular vesicles, we discuss in situ strategies and engineering approaches to attract specific types of immune cells and modulate their phenotypes. This field is making advances to uncover the extraordinary potential of immune cells and their secretome in the regulation of vascularization and tissue remodeling. Understanding the principles of immunoregulation will help us design advanced immunoengineering platforms to harness their power for tissue regeneration.

Pentoxifylline-induced protein expression change in RAW 264.7 cells as determined by immunoprecipitation-based high performance liquid chromatography

Although pentoxifylline (PTX) was identified as a competitive non-selective phosphodiesterase inhibitor, its pharmacological effect has not been clearly elucidated. The present study explored the effect of low dose 10 μg/mL PTX (therapeutic dose) compared to high dose 300 μg/mL PTX (experimental dose) in RAW 264.7 cells through immunoprecipitation-based high performance liquid chromatography (IP-HPLC), immunohistochemistry, and western blot. 10 μg/mL PTX increased the expression of proliferation (Ki-67, PCNA, cyclin D2, cdc25A), epigenetic modification (KDM4D, PCAF, HMGB1), protein translation (DOHH, DHPS, eIF5A1), RAS signaling (KRAS, pAKT1/2/3, PI3K), NFkB signaling (NFkB, GADD45, p38), protection (HSP70, SOD1, GSTO1/2), survival (pAKT1/2/3, SP1, sirtuin 6), neuromuscular differentiation (NSEγ, myosin-1a, desmin), osteoblastic differentiation (BMP2, RUNX2, osterix), acute inflammation (TNFα, IL-1, CXCR4), innate immunity (β-defensin 1, lactoferrin, TLR-3, -4), cell-mediated immunity (CD4, CD8, CD80), while decreased the expression of ER stress (eIF2α, eIF2AK3, ATF6α), fibrosis (FGF2, CTGF, collagen 3A1), and chronic inflammation (CD68, MMP-2, -3, COX2) versus the untreated controls. The activation of proliferation by 10 μg/mL PTX was also supported by the increase of cMyc-MAX heterodimer and β-catenin-TCF1 complex in double IP-HPLC. 10 μg/mL PTX enhanced FAS-mediated apoptosis but diminished p53-mediated apoptosis, and downregulated many angiogenesis proteins (angiogenin, VEGF-A, and FLT4), but upregulated HIF1α, VEGFR2, and CMG2 reactively. Whereas, 300 μg/mL PTX consistently decreased proliferation, epigenetic modification, RAS and NFkB signaling, neuromuscular and osteoblastic differentiation, but increased apoptosis, ER stress, and fibrosis compared to 10 μg/mL PTX. These data suggest PTX has different biological effect on RWA 264.7 cells depending on the concentration of 10 μg/mL and 300 μg/mL PTX. The low dose 10 μg/mL PTX enhanced RAS/NFkB signaling, proliferation, differentiation, and inflammation, particularly, it stimulated neuromuscular and osteoblastic differentiation, innate immunity, and cell-mediated immunity, but attenuated ER stress, fibrosis, angiogenesis, and chronic inflammation, while the high dose 300 μg/mL PTX was found to alleviate the 10 μg/mL PTX-induced biological effects, resulted in the suppression of RAS/NFkB signaling, proliferation, neuromuscular and osteoblastic differentiation, and inflammation.

Interplay of vascular endothelial growth factor receptors in organ-specific vessel maintenance

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are quintessential for the development and maintenance of blood and lymphatic vessels. However, genetic interactions between the VEGFRs are poorly understood. VEGFR2 is the dominant receptor that is required for the growth and survival of the endothelium, whereas deletion of VEGFR1 or VEGFR3 was reported to induce vasculature overgrowth. Here we show that vascular regression induced by VEGFR2 deletion in postnatal and adult mice is aggravated by additional deletion of VEGFR1 or VEGFR3 in the intestine, kidney, and pancreas, but not in the liver or kidney glomeruli. In the adult mice, hepatic and intestinal vessels regressed within a few days after gene deletion, whereas vessels in skin and retina remained stable for at least four weeks. Our results show changes in endothelial transcriptomes and organ-specific vessel maintenance mechanisms that are dependent on VEGFR signaling pathways and reveal previously unknown functions of VEGFR1 and VEGFR3 in endothelial cells.

Differential action of pro-angiogenic and anti-angiogenic components of Danhong injection in ischemic vascular disease or tumor models

OBJECTIVE

We investigate the chemical basis and mechanism of angiogenesis regulation by a multicomponent Chinese medicine Danhong injection (DHI).

METHODS

DHI was fractionated and screened for angiogenesis activities by in vitro tube formation and migration assays. The composition of DHI components was determined by UPLC. The effects of the main active monomers on angiogenesis-related gene and protein expression in endothelial cells were determined by qPCR and Western blotting analyses. Mouse hind limb ischemia and tumor implant models were used to verify the angiogenesis effects in vivo by Laser Doppler and bioluminescent imaging, respectively.

RESULTS

Two distinct chemical components, one promoting (pro-angiogenic, PAC) and the other inhibiting (anti-angiogenic, AAC) angiogenesis, were identified in DHI. PAC enhanced angiogenesis and improved recovery of ischemic limb perfusion while AAC reduced Lewis lung carcinoma growth in vivo in VEGFR-2-Luc mice. Among the PAC or AAC monomers, caffeic acid and rosmarinic acid upregulated TSP1 expression and downregulated KDR and PECAM expression. Caffeic acid and rosmarinic acid significantly decreased while protocatechuic aldehyde increased CXCR4 expression, which are consistent with their differential effects on EC migration.

CONCLUSIONS

DHI is capable of bi-directional regulation of angiogenesis in disease-specific manner. The pro-angiogenesis activity of DHI promotes the repair of ischemic vascular injury, whereas the anti-angiogenesis activity inhibits tumor growth. The active pro- and anti-angiogenesis activities are composed of unique chemical combinations that differentially regulate angiogenesis-related gene networks.

Improved Immunotherapy Efficacy by Vascular Modulation

Several strategies have been developed to modulate the tumour vasculature for cancer therapy including anti-angiogenesis and vascular normalisation. Vasculature modulation results in changes to the tumour microenvironment including oxygenation and immune cell infiltration, therefore lending itself to combination with cancer therapy. The development of immunotherapies has led to significant improvements in cancer treatment. Particularly promising are immune checkpoint blockade and CAR T cell therapies, which use antibodies against negative regulators of T cell activation and T cells reprogrammed to better target tumour antigens, respectively. However, while immunotherapy is successful in some patients, including those with advanced or metastatic cancers, only a subset of patients respond. Therefore, better predictors of patient response and methods to overcome resistance warrant investigation. Poor, or periphery-limited, T cell infiltration in the tumour is associated with poor responses to immunotherapy. Given that (1) lymphocyte recruitment requires leucocyte-endothelial cell adhesion and (2) the vasculature controls tumour oxygenation and plays a pivotal role in T cell infiltration and activation, vessel targeting strategies including anti-angiogenesis and vascular normalisation in combination with immunotherapy are providing possible new strategies to enhance therapy. Here, we review the progress of vessel modulation in enhancing immunotherapy efficacy.

Effects of Strontium-Doped β-Tricalcium Scaffold on Longitudinal Nuclear Factor-Kappa Beta and Vascular Endothelial Growth Factor Receptor-2 Promoter Activities during Healing in a Murine Critical-Size Bone Defect Model

It was hypothesized that strontium (Sr)-doped β-tricalcium phosphate (TCP)-based scaffolds have a positive effect on the regeneration of large bone defects (LBD). Readouts in our mice models were nuclear factor-kappa beta (NF-κB) activity and vascular endothelial growth factor receptor-2 (VEGFR-2) promoter activity during the healing process. A 2-mm critical-size femoral fracture was performed in transgenic NF-κB- and VEGFR-2-luciferase reporter mice. The fracture was filled with a 3D-printed β-TCP scaffold with or without Sr. A bioluminescence in-vivo imaging system was used to sequentially investigate NF-κB and VEGFR-2 expression for two months. After sacrifice, soft and osseous tissue formation in the fracture sites was histologically examined. NF-κB activity increased in the β-TCP + Sr group in the latter stage (day 40–60). VEGFR-2 activity increased in the + Sr group from days 0–15 but decreased and showed significantly less activity than the β-TCP and non-scaffold groups from days 40–60. The new bone formation and soft tissue formation in the + Sr group were significantly higher than in the β-TCP group, whereas the percentage of osseous tissue formation in the β-TCP group was significantly higher than in the β-TCP + Sr group. We analyzed longitudinal VEGFR-2 promoter activity and NF-κB activity profiles, as respective agents of angiogenesis and inflammation, during LBD healing. The extended inflammation phase and eventually more rapid resorption of scaffold caused by the addition of strontium accelerates temporary bridging of the fracture gaps. This finding has the potential to inform an improved treatment strategy for patients who suffer from osteoporosis.

Untargeted Safety Pharmacology Screen of Blood-Activating and Stasis-Removing Patent Chinese Herbal Medicines Identified Nonherbal Ingredients as a Cause of Organ Damage in Experimental Models

Blood activation and stasis removal from circulation is a central principle for treatment of syndromes related to cerebral and cardiovascular diseases in Chinese herbal medicine. However, blood-activating and stasis-removing patent Chinese herbal medicine (BASR-pCHM) widely used with or without prescription in China and elsewhere are highly variable in composition and manufacture standard, making their safety assessment a challenging task. We proposed that an integrated evaluation of multiple toxicity parameters of BASR-pCHM would provide critical reference and guidelines for their safe clinical application. Examination of standardized extracts from 58 compound BASR-pCHM in vivo in VEGFR2-luc mice and in vitro in cardiac, renal, and hepatic cells identified Naoluotong capsule (NLTC) as a potent organ/cell damage inducer. Composition analysis revealed that NLTC was the one that contained nonherbal ingredients among the BASR-pCHM collection. In vivo and in vitro experiments confirmed that NLTC, as well as its chemical supplement tolperisone hydrochloride, caused organ and cell damage by reducing cell viability, mitochondrial mass/activity, while the NLTC herbal components did not. Taken together, our study showed that safety evaluation of patent herbal medicines already on market is still necessary and urgently needed. In addition, chemical/herbal interactions should be considered as an important contributor of potential toxicity when evaluating the safety of herbal medicine.

A Defined Combination of Four Active Principles From the Danhong Injection Is Necessary and Sufficient to Accelerate EPC-Mediated Vascular Repair and Local Angiogenesis

Many compounds in Chinese medicine formulae, including Danhong injection (DHI) formulae, are capable of stimulating angiogenesis and promoting vascular repair, but their chemical basis and action mechanisms remain poorly defined. The aim of this study is to determine the minimal native chemical composition of DHI for the pro-angiogenesis activity and to evaluate its contribution from local endothelial cells (ECs) and bone marrow-derived endothelial progenitor cells (EPCs). Our study demonstrated that the action of DHI in accelerating the recovery of hindlimb blood flow in a ischemic rat model was attributable to its local CXCR4-mediated pro-angiogenesis activity in mature endothelial cells, as well as to its ability to promote the proliferation, migration, adhesion, and angiogenesis of EPCs via integrated activation of SDF-1α/CXCR4, VEGF/KDR, and eNOS/MMP-9 signal pathways. Combination experiments narrowed down the angiogenic activity into a few components in DHI. Reconstitution experiment defined that a combination of tanshinol, protocatechuic aldehyde, salvianolic acid B, and salvianolic acid C in their native proportion was necessary and sufficient for DHI's angiogenic activity. Compared with the full DHI, the minimal reconstituted four active principles had the same effects in promoting tube formation in vitro, improving perfusion and recovery of ischemic limb, and enhancing angiogenesis in ischemic mice post-hindlimb ischemia in vivo.

Histopathological, immunohistochemical, and molecular studies for determination of wound age and vitality in rats

In forensic medicine, it is vital to verify with the best attainable accuracy once injuries occurred during vital or post-mortem conditions. An immunohistochemical study was carried out to examine the time-dependent expression of macrophage-specific gene CD68 (cluster of differentiation 68), alpha-smooth muscle actin (α-SMA), and vascular endothelial growth factor (VEGF) in different skin wound timings (0, 1, 3, 5, 7, and 14 days) in rats. Histopathological studies were performed to assess the wound age and vitality. Eighteen male albino Wister rats (weighing 170-200 g) were used for wound induction. Rats (n = 3) were euthanised at 0, 1, 3, 5, 7, and 14 days from the starting point of wound induction. Histopathological examination showed that the epidermal re-epithelialisation was completed 14 days after skin incision. The inflammatory phase was recorded during the first 3 days of healing and reached the maximum levels at 5 days, then declined after 7 days, and completely removed at 14 days. The beginning of the proliferative phase was dated to day 3 and the peak at days 5 and 7. The initiation of the granulation tissue formation and remodelling phase of the healing process was observed 5 days after wounding. By immunohistochemical staining, negative VEGF gene expressions at early stages (0-3 days) were observed, as well as neither CD68+ macrophages nor α-SMA+ myofibroblast cells were detected. By increasing the wound ages (5-7 days), granulation tissue and angiogenesis were observed, with the migration of macrophages and fibroblast, which expressed VEGF, CD68, and α-SMA positive reaction. Time-dependent expression of the above markers suggested that they would be useful indicators for the determination of wound age. Both VEGF and transforming growth factor-beta 1 (TGFb1) mRNA levels were determined in different skin wound ages. The transcription of TGFb1 and VEGF increased shortly after wounding, until post-wounding day 7. It then declined constantly, reaching minimal values on day 14.

Live imaging of collagen deposition during experimental hepatic schistosomiasis and recovery: a view on a dynamic process

Hepatic fibrosis is the central cause of chronic clinical pathology resulting from infection by the blood flukes Schistosoma japonicum or S. mansoni. Much has been elucidated regarding the molecular, cellular and immunological responses that correspond to the formation of the granulomatous response to trapped schistosome eggs. A central feature of this Th2 response is the deposition of collagen around the periphery of the granuloma. To date, traditional histology and transcriptional methods have been used to quantify the deposition of collagen and to monitor the formation of the hepatic granuloma during experimental animal models of schistosomiasis. We have investigated the dynamic nature of granuloma formation through the use of a transgenic mouse model (B6.Collagen 1(A) luciferase mice (B6.Coll 1A-luc⁺)). With this model and whole-animal bioluminescence imaging, we followed the deposition of collagen during an active schistosome infection with Chinese and Philippines geographical strains of S. japonicum and after clearance of the adult parasites by the drug praziquantel. Individual mice were re-imaged over the time course to provide robust real-time quantitation of the development of chronic fibrotic disease. This model provides an improved method to follow the course of hepatic schistosomiasis-induced hepatic pathology and effectively supports the current dogma of the formation of hepatic fibrosis, originally elucidated from static traditional histology. This study demonstrates the first use of the B6.Coll 1A-luc⁺ mouse to monitor the dynamics of disease development and the treatment of pathogen-induced infection with the underlying pathology of fibrosis.

Semaphorin 3E Inhibits House Dust Mite-Induced Angiogenesis in a Mouse Model of Allergic Asthma

Increased angiogenesis is a characteristic feature of remodeling in asthmatic airways and stems from the imbalance between pro-angiogenic and anti-angiogenic factors. Surprisingly, the factors regulating this process in allergic asthma are poorly defined. Previously, we showed an important role of semaphorins 3E (Sema3E) in growth factor-induced airway smooth muscle proliferation and migration in vitro, and in down-regulating airway inflammation, T helper 2/T helper 17 cytokine response, mucus cell hyperplasia, and airway hyperresponsiveness in vivo. However, the role of Sema3E in airway angiogenesis is not fully understood. Here, we investigated the role of Sema3E in airway angiogenesis using a house dust mite (HDM) murine model of allergic asthma. Intranasal treatment with recombinant Sema3E significantly reduced the expression of angiogenesis markers within the airways of HDM-challenged mice compared with untreated mice. HDM-induced expression of vascular endothelial growth factor (VEGF) and VEGF receptor 2 protein were diminished substantially on Sema3E treatment. Interestingly, Sema3E-treated mice showed an enhanced expression of the negative regulator of angiogenesis, soluble VEGF receptor 1, compared with the untreated mice. These events were reversed in Sema3E-deficient mice at baseline or on HDM challenge. Taken together, this study provides the first evidence that Sema3E modulates angiogenesis in allergic asthmatic airways via modulating pro- and anti-angiogenic factors.

Molecular Imaging of Therapeutic Effect of Mesenchymal Stem Cell-Derived Exosomes for Hindlimb Ischemia Treatment

Critical limb ischemia is a major cause of morbidity and mortality worldwide. Recently, many studies confirmed that MSC-derived exosomes (MSC-exosomes) had potential therapeutic effect to treat hindlimb ischemia through pro-angiogenesis. The therapeutic angiogenesis is a critical measurement to judge the beneficial effect of MSC-exosomes treatment. Formerly, the therapeutic effect of MSC-exosomes was usually evaluated through clinical assessment and histopathological examination. Here, we describe a strategy to evaluate the therapeutic effect of MSC-exosomes by monitoring the therapeutic angiogenesis with bioluminescent imaging in hindlimb ischemia mice models.

VEGF, FGF-2 and TGFβ expression in the normal and regenerating epidermis of geckos: implications for epidermal homeostasis and wound healing in reptiles

The skin is a bilayered organ that serves as a key barrier between an organism and its environment. In addition to protecting against microbial invasion, physical trauma and environmental damage, skin participates in maintaining homeostasis. Skin is also capable of spontaneous self-repair following injury. These functions are mediated by numerous pleiotrophic growth factors, including members of the vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and transforming growth factor β (TGFβ) families. Although growth factor expression has been well documented in mammals, particularly during wound healing, for groups such as reptiles less is known. Here, we investigate the spatio-temporal pattern of expression of multiple growth factors in normal skin and following a full-thickness cutaneous injury in the representative lizard Eublepharis macularius, the leopard gecko. Unlike mammals, leopard geckos can heal cutaneous wounds without scarring. We demonstrate that before, during and after injury, keratinocytes of the epidermis express a diverse panel of growth factor ligands and receptors, including: VEGF, VEGFR1, VEGFR2, and phosphorylated VEGFR2; FGF-2 and FGFR1; and phosphorylated SMAD2, TGFβ1, and activin βA. Unexpectedly, only the tyrosine kinase receptors VEGFR1 and FGFR1 were dynamically expressed, and only during the earliest phases of re-epithelization; otherwise all the proteins of interest were constitutively present. We propose that the ubiquitous pattern of growth factor expression by keratinocytes is associated with various roles during tissue homeostasis, including protection against ultraviolet photodamage and coordinated body-wide skin shedding.

Endothelial stem and progenitor cells (stem cells): (2017 Grover Conference Series)

The capacity of existing blood vessels to give rise to new blood vessels via endothelial cell sprouting is called angiogenesis and is a well-studied biologic process. In contrast, little is known about the mechanisms for endothelial cell replacement or regeneration within established blood vessels. Since clear definitions exist for identifying cells with stem and progenitor cell properties in many tissues and organs of the body, several groups have begun to accumulate evidence that endothelial stem and progenitor cells exist within the endothelial intima of existing blood vessels. This paper will review stem and progenitor cell definitions and highlight several recent papers purporting to have identified resident vascular endothelial stem and progenitor cells.

A macroporous heparin-releasing silk fibroin scaffold improves islet transplantation outcome by promoting islet revascularisation and survival

Islet transplantation is considered the most promising therapeutic option with the potential to cure diabetes. However, efficacy of current clinical islet transplantation is limited by long-term graft dysfunction and attrition. We have investigated the therapeutic potential of a silk fibroin macroporous (SF) scaffold for syngeneic islet transplantation in diabetic mice. The SF scaffold was prepared via lyophilisation, which enables incorporation of active compounds including cytokines, peptide and growth factors without compromising their biological activity. For the present study, a heparin-releasing SF scaffold (H-SF) in order to evaluate the versatility of the SF scaffold for biological functionalisation. Islets were then co-transplanted with H-SF or SF scaffolds in the epididymal fat pad of diabetic mice. Mice from both H-SF and SF groups achieved 100% euglycaemia, which was maintained for 1year. More importantly, the H-SF-islets co-transplantation led to more rapid reversal of hyperglycaemia, complete normalisation of glucose responsiveness and lower long-term blood glucose levels. This superior transplantation outcome is attributable to H-SF-facilitated islet revascularisation and cell proliferation since significant increase of islet endocrine and endothelial cells proliferation was shown in grafts retrieved from H-SF-islets co-transplanted mice. Better intra-islet vascular reformation was also evident, accompanied by VEGF upregulation. In addition, when H-SF was co-transplanted with islets extracted from vegfr2-luc transgenic mice in vivo, sustained elevation of bioluminescent signal that corresponds to vegfr2 expression was collected, implicating a role of heparin-dependent activation of endogenous VEGF/VEGFR2 pathway in promoting islet revascularisation and proliferation. In summary, the SF scaffolds provide an open platform as scaffold development for islet transplantation. Furthermore, given the pro-angiogenic, pro-survival and minimal post-transplantation inflammatory reactions of H-SF, our data also support the feasibility of clinical implementation of H-SF to improve islet transplantation outcome.

STATEMENT OF SIGNIFICANCE

1) The silk fibroin scaffold presented in the present study provides an open platform for scaffold development in islet transplantation, with heparinisation as an example. 2) Both heparin and silk fibroin have been used clinically. The excellent in vivo therapeutic outcome reported here may therefore be clinically relevant and provide valuable insights for bench to bed translation. 3) Compared to conventional clinical islet transplantation, during which islets are injected via the hepatic portal vein, the physical/mechanical properties of silk fibroin scaffolds create a more accessible transplantation site (i.e., within fat pad), which significantly reduces discomfort. 4) Islet implantation into the fat pad also avoids an instant blood mediated inflammatory response, which occurs upon contact of islet with recipient's blood during intraportal injection, and prolongs survival and function of implanted islets.

Safer topical treatment for inflammation using 5α-tetrahydrocorticosterone in mouse models

Use of topical glucocorticoid for inflammatory skin conditions is limited by systemic and local side-effects. This investigation addressed the hypothesis that topical 5α-tetrahydrocorticosterone (5αTHB, a corticosterone metabolite) inhibits dermal inflammation without affecting processes responsible for skin thinning and impaired wound healing. The topical anti-inflammatory properties of 5αTHB were compared with those of corticosterone in C57Bl/6 male mice with irritant dermatitis induced by croton oil, whereas its effects on angiogenesis, inflammation, and collagen deposition were investigated by subcutaneous sponge implantation. 5αTHB decreased dermal swelling and total cell infiltration associated with dermatitis similarly to corticosterone after 24 h, although at a five fold higher dose, but in contrast did not have any effects after 6 h. Pre-treatment with the glucocorticoid receptor antagonist RU486 attenuated the effect of corticosterone on swelling at 24 h, but not that of 5αTHB. After 24 h 5αTHB reduced myeloperoxidase activity (representative of neutrophil infiltration) to a greater extent than corticosterone. At equipotent anti-inflammatory doses 5αTHB suppressed angiogenesis to a limited extent, unlike corticosterone which substantially decreased angiogenesis compared to vehicle. Furthermore, 5αTHB reduced only endothelial cell recruitment in sponges whereas corticosterone also inhibited smooth muscle cell recruitment and decreased transcripts of angiogenic and inflammatory genes. Strikingly, corticosterone, but not 5αTHB, reduced collagen deposition. However, both 5αTHB and corticosterone attenuated macrophage infiltration into sponges. In conclusion, 5αTHB displays the profile of a safer topical anti-inflammatory compound. With limited effects on angiogenesis and extracellular matrix, it is less likely to impair wound healing or cause skin thinning.

Functional Definition of Progenitors Versus Mature Endothelial Cells Reveals Key SoxF-Dependent Differentiation Process

BACKGROUND

During adult life, blood vessel formation is thought to occur via angiogenic processes involving branching from existing vessels. An alternate proposal suggests that neovessels form from endothelial progenitors able to assemble the intimal layers. We here aimed to define vessel-resident endothelial progenitors in vivo in a variety of tissues in physiological and pathological situations such as normal aorta, lungs, and wound healing, tumors, and placenta, as well.

METHODS

Based on protein expression levels of common endothelial markers using flow cytometry, 3 subpopulations of endothelial cells could be identified among VE-Cadherin+ and CD45- cells.

RESULTS

Lineage tracing by using Cdh5cre^ERt2/Rosa-YFP reporter strategy demonstrated that the CD31-/loVEGFR2lo/intracellular endothelial population was indeed an endovascular progenitor (EVP) of an intermediate CD31intVEGFR2lo/intracellular transit amplifying (TA) and a definitive differentiated (D) CD31hiVEGFR2hi/extracellular population. EVP cells arose from vascular-resident beds that could not be transferred by bone marrow transplantation. Furthermore, EVP displayed progenitor-like status with a high proportion of cells in a quiescent cell cycle phase as assessed in wounds, tumors, and aorta. Only EVP cells and not TA and D cells had self-renewal capacity as demonstrated by colony-forming capacity in limiting dilution and by transplantation in Matrigel plugs in recipient mice. RNA sequencing revealed prominent gene expression differences between EVP and D cells. In particular, EVP cells highly expressed genes related to progenitor function including Sox9, Il33, Egfr, and Pdfgrα. Conversely, D cells highly expressed genes related to differentiated endothelium including Ets1&2, Gata2, Cd31, Vwf, and Notch. The RNA sequencing also pointed to an essential role of the Sox18 transcription factor. The role of SOX18 in the differentiation process was validated by using lineage-tracing experiments based on Sox18Cre^ERt2/Rosa-YFP mice. Besides, in the absence of functional SOX18/SOXF, EVP progenitors were still present, but TA and D populations were significantly reduced.

CONCLUSIONS

Our findings support an entirely novel endothelial hierarchy, from EVP to TA to D, as defined by self-renewal, differentiation, and molecular profiling of an endothelial progenitor. This paradigm shift in our understanding of vascular-resident endothelial progenitors in tissue regeneration opens new avenues for better understanding of cardiovascular biology.

Markers of Response to Antiangiogenic Therapies in Colorectal Cancer: Where Are We Now and What Should Be Next?

Despite advances in the treatment of colorectal cancer (CRC), it remains the second most common cause of cancer-related death in the Western world. Angiogenesis is a complex process that involves the formation of new blood vessels from preexisting vessels. It is essential for promoting cancer survival, growth, and dissemination. The inhibition of angiogenesis has been shown to prevent tumor progression experimentally, and several chemotherapeutic targets of tumor angiogenesis have been identified. These include anti-vascular endothelial growth factor (VEGF) treatments, such as bevacizumab (a VEGF-specific binding antibody) and anti-VEGF receptor tyrosine kinase inhibitors, although antiangiogenic therapy has been shown to be effective in the treatment of several cancers, including CRC. However, it is also associated with its own side effects and financial costs. Therefore, the identification of biomarkers that are able to identify patients who are more likely to benefit from antiangiogenic treatment is very important. This article intends to be a concise summary of the potential biomarkers that can predict or prognosticate the benefit of antiangiogenic treatments in CRC, and also what we can expect in the near future.

IGF-1 C Domain-Modified Hydrogel Enhances Cell Therapy for AKI

Low cell retention and engraftment after transplantation limit the successful application of stem cell therapy for AKI. Engineered microenvironments consisting of a hydrogel matrix and growth factors have been increasingly successful in controlling stem cell fate by mimicking native stem cell niche components. Here, we synthesized a bioactive hydrogel by immobilizing the C domain peptide of IGF-1 (IGF-1C) on chitosan, and we hypothesized that this hydrogel could provide a favorable niche for adipose-derived mesenchymal stem cells (ADSCs) and thereby enhance cell survival in an AKI model. In vitro studies demonstrated that compared with no hydrogel or chitosan hydrogel only, the chitosan-IGF-1C hydrogel increased cell viability through paracrine effects. In vivo, cotransplantation of the chitosan-IGF-1C hydrogel and ADSCs in ischemic kidneys ameliorated renal function, likely by the observed promotion of stem cell survival and angiogenesis, as visualized by bioluminescence imaging and attenuation of fibrosis. In conclusion, IGF-1C immobilized on a chitosan hydrogel provides an artificial microenvironment for ADSCs and may be a promising therapeutic approach for AKI.

VEGF released from a fibrin biomatrix increases VEGFR-2 expression and improves early outcome after ischaemia-reperfusion injury

Skeletal ischaemia-reperfusion (I-R) injury may influence patient outcome after severe vascular trauma or clamping of major vessels. The aim of this study was to observe whether locally applied vascular endothelial growth factor (VEGF) in fibrin could induce the expression of VEGF-receptor-2 (VEGFR-2) and improve the outcome after I-R injury. Transgenic mice expressing VEGFR-2 promoter-controlled luciferase were used for the assessment of VEGFR-2 expression. Ischaemia was induced for 2 h by a tension-controlled tourniquet to the hind limb, followed by 24 h of reperfusion. The animals were locally injected subcutaneously with fibrin sealant containing 20 or 200 ng VEGF; control animals received no treatment or fibrin sealant application. In vivo VEGFR-2 expression was quantified upon administration of luciferin at several observation times. For oedema and inflammation quantification, wet:dry ratio measurements and a myeloperoxidase assay of the muscle tissue were performed. Laser Doppler imaging showed that ischaemia was present and that the blood flow had returned to baseline levels after 24 h of reperfusion. VEGFR-2 expression levels in the fibrin + 200 ng VEGF were significantly higher than in all other groups. Granulocyte infiltration was reduced in both treatment groups, as well as reduced oedema formation. These results showed that VEGF released from fibrin had a positive effect on early I-R outcome in a mouse model, possibly via VEGFR-2. Copyright © 2016 John Wiley & Sons, Ltd.

VEGFR-2 Expression in Glioblastoma Multiforme Depends on Inflammatory Tumor Microenvironment

Glioblastoma multiforme (GBM) is one of the most angiogenic tumors. However, antiangiogenic therapy has not shown significant clinical efficacy. The aim of our study was to evaluate the impact of inflammatory tumor microenvironment on the expression of vascular endothelial growth factor receptor 2 (VEGFR-2). Surgically excised primary GBM tissues were histologically examined for overall extent of inflammation (score 1-3). After immunohistochemistry, the tissue expression of ICAM-1 (optical density), the number of VEGFR-2 positive (VEGFR-2+) blood vessels (per microscopic field), and the endothelial staining intensity of VEGFR-2 (score 0-3) were determined. In GBM, the extent of inflammation was 1.9 ± 0.7 (group mean ± SD). Mean optical density of inflammatory mediator ICAM-1 was 57.0 ± 27.1 (pixel values). The number of VEGFR-2+ blood vessels and endothelial VEGFR-2 staining intensity were 6.2 ± 2.4 and 1.2 ± 0.8, respectively. A positive association was found between endothelial VEGFR-2 staining intensity and the extent of inflammation (p = 0.005). Moreover, VEGFR-2 staining intensity correlated with the expression level of ICAM-1 (p = 0.026). The expression of VEGFR-2, one of the main targets of antiangiogenic therapy, depends on GBM microenvironment. Higher endothelial VEGFR-2 levels were seen in the presence of more pronounced inflammation. Target dependence on inflammatory tumor microenvironment has to be taken into consideration when treatment approaches that block VEGFR-2 signaling are designed.

Overexpression of miRNA-497 inhibits tumor angiogenesis by targeting VEGFR2

Recent studies reported miR-497 exhibited inhibitory effects in various cancers. However, whether miR-497 is involved in inhibiting angiogenesis, which is critical for tumor growth and metastasis, is still unknown. The purpose of this study was to investigate the potential role of miR-497 in tumor angiogenesis. In this work, cell proliferation and apoptosis analyses were conducted to explore the potential function of miR-497 in HUVECs by using MTT and TUNEL assays. Western blotting (WB) was employed to validate the downstream targets of miR-497. Furthermore, in order to disclose the role of miR-497 on angiogenesis, VEGFR2-luc transgenic mice were treated with miR-497 mimic and applied to monitor tumor angiogenesis and growth by in vivo bioluminescent imaging (BLI). The results demonstrated that overexpression of miR-497 showed inhibitory effects on VEGFR2 activation and downstream Raf/MEK/ERK signal pathways in vitro and in vivo. Moreover, overexpression of miR-497 effectively induced HUVECs apoptosis by targeting VEGFR2 and downstream PI3K/AKT signaling pathway. Furthermore, miR-497 exhibited anti-angiogenesis and anti-tumor effects in the VEGFR2-luc breast tumor model proven by BLI, WB and immunohistochemistry analysis. In summary, miR-497 inhibits tumor angiogenesis and growth via targeting VEGFR2, indicating miR-497 can be explored as a potential drug candidate for cancer therapy.

Nitric oxide releasing hydrogel enhances the therapeutic efficacy of mesenchymal stem cells for myocardial infarction

Stem cell therapy has been proved to be an effective approach to ameliorate the heart remodeling post myocardial infarction (MI). However, poor cell engraftment and survival in ischemic myocardium limits the successful use of cellular therapy for treating MI. Here, we sought to transplant adipose derived-mesenchymal stem cells (AD-MSCs) with a hydrogel (NapFF-NO), naphthalene covalently conjugated a short peptide, FFGGG, and β-galactose caged nitric oxide (NO) donor, which can release NO molecule in response to β-galactosidase. AD-MSCs, either from transgenic mice that constitutively express GFP and firefly luciferase (Fluc), or express Fluc under the control of VEGFR2 promoter, were co-transplanted with NapFF-NO hydrogel into murine MI models. Improved cell survival and enhanced cardiac function were confirmed by bioluminescence imaging (BLI) and echocardiogram respectively. Moreover, increasing VEGFR2-luc expression was also tracked in real-time in vivo, indicating NapFF-NO hydrogel stimulated VEGF secretion of AD-MSCs. To investigate the therapeutic mechanism of NapFF-NO hydrogel, cell migration assay, paracrine action of AD-MSCs, and histology analysis were carried out. Our results revealed that condition medium from AD-MSCs cultured with NapFF-NO hydrogel could promote endothelial cell migration. Additionally, AD-MSCs showed significant improvement secretion of angiogenic factors VEGF and SDF-1α in the presence of NapFF-NO hydrogel. Finally, postmortem analysis confirmed that transplanted AD-MSCs with NapFF-NO hydrogel could ameliorate heart function by promoting angiogenesis and attenuating ventricular remodeling. In conclusion, NapFF-NO hydrogel can obviously improve therapeutic efficacy of AD-MSCs for MI by increasing cell engraftment and angiogenic paracrine action.

microRNA-200b as a Switch for Inducible Adult Angiogenesis

SIGNIFICANCE

Angiogenesis is the process by which new blood vessels develop from a pre-existing vascular system. It is required for physiological processes such as developmental biology and wound healing. Angiogenesis also plays a crucial role in pathological conditions such as tumor progression. The underlying importance of angiogenesis necessitates a highly regulated process.

RECENT ADVANCES

Recent works have demonstrated that the process of angiogenesis is regulated by small noncoding RNA molecules called microRNAs (miRs). These miRs, collectively referred to as angiomiRs, have been reported to have a profound effect on the process of angiogenesis by acting as either pro-angiogenic or anti-angiogenic regulators.

CRITICAL ISSUES

In this review, we will discuss the role of miR-200b as a regulator of angiogenesis. Once the process of angiogenesis is complete, anti-angiogenic miR-200b has been reported to provide necessary braking. Downregulation of miR-200b has been reported across various tumor types, as deregulated angiogenesis is necessary for tumor development. Transient downregulation of miR-200b in wounds drives wound angiogenesis.

FUTURE DIRECTIONS

New insights and understanding of the molecular mechanism of regulation of angiogenesis by miR-200b has opened new avenues of possible therapeutic interventions to treat angiogenesis-related patho-physiological conditions. Antioxid. Redox Signal. 22, 1257-1272.

The use of a whole animal biophotonic model as a screen for the angiogenic potential of estrogenic compounds

BACKGROUND

Vascular endothelial growth factor (VEGF) is essential for normal vascular growth and development during wound repair. VEGF is estrogen responsive and capable of regulating its own receptor, vascular endothelial growth factor receptor-2 (VEGFR-2). Several agricultural pesticides (e.g., methoxychlor) have estrogenic potential that can initiate inappropriate physiological responses in estrogenic-sensitive tissues following exposure in vivo. Thus, the current study was designed to determine whether the VEGFR-2-Luciferase (Luc) reporter transgenic mouse is a useful model for evaluating estrogenic tendencies of methoxychlor by monitoring wound healing via VEGFR-2-mediated gene expression using bioluminescence and real-time imaging technology.

RESULTS

VEGFR-2-Luc gene activity peaked by d 7 (P<0.001) in all groups but was not different (P>0.05) between control and estrogen/methoxychlor exposed mice.

CONCLUSIONS

Changes in VEGFR-2-Luc gene activity associated with the dermal wound healing process were able to be measured via photonic emission. The increase in vasculature recruitment and formation is paralleled by the increase of VEGFR-2-Luc activity with a peak on day 7. However, estrogen/methoxychlor did not significantly alter wound healing mediated VEGFR-2-Luc gene expression patterns compared to controls. This suggests that the VEGFR-2-Luc transgenic mouse wound model tested in this study may not be optimal for use as a screen for the angiogenic potential of estrogenic compounds.

Imaging aspects of the tumor stroma with therapeutic implications

Cancer cells rely on extensive support from the stroma in order to survive, proliferate and invade. The tumor stroma is thus an important potential target for anti-cancer therapy. Typical changes in the stroma include a shift from the quiescence promoting-antiangiogenic extracellular matrix to a provisional matrix that promotes invasion and angiogenesis. These changes in the extracellular matrix are induced by changes in the secretion of extracellular matrix proteins and glucose amino glycans, extravasation of plasma proteins from hyperpermeable vessels and release of matrix modifying enzymes resulting in cleavage and cross-linking of matrix macromolecules. These in turn alter the rigidity of the matrix and the exposure and release of cytokines. Changes in matrix rigidity and vessel permeability affect drug delivery and mediate resistance to cytotoxic therapy. These stroma changes are brought about not only by the cancer cells, but also through the action of many cell types that are recruited by tumors including immune cells, fibroblasts and endothelial cells. Within the tumor, these normal host cells are activated resulting in loss of inhibitory and induction of cancer promoting activities. Key to the development of stroma-targeted therapies, selective biomarkers were developed for specific imaging of key aspects of the tumor stroma.

In vivo monitoring of angiogenesis inhibition via down-regulation of mir-21 in a VEGFR2-luc murine breast cancer model using bioluminescent imaging

MicroRNA-21 (miR-21) is overexpressed in a wide range of cancers and involved in tumor proliferation and metastasis. However, the potential function of miR-21 in regulating tumor angiogenesis has been little disclosed. In this study, we treated the cultured 4T1 murine breast cancer cells and human umbilical vein endothelial cells (HUVECs) with miR-21 mimic, antagomir-21 or negative control (scramble), which were subjected to MTT, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), quantitative Reverse Transcriptase PCR (qRT-PCR) and immunoblotting analysis. In addition, 4T1 cells were implanted beneath the right breast fat pad of the VEGFR2-luc transgenic mice, which were randomly divided into three groups and received saline, antagomir-21 or scramble treatment once respectively after tumor model establishment. Bioluminescent imaging was used to monitor tumor growth and angiogenesis in vivo at 0d, 3d, 5d, 7d, 10d, and 14d after treatment. Mice were killed at the end of study and tumor tissues were collected for use. The results showed that knockdown of miR-21 by antagomir-21 decreased cell proliferation and induced apoptosis via targeting PTEN both in 4T1 cells and HUVECs. We also found the anti-angiogenesis and anti-tumor effects of antagomir-21 in the VEGFR2-luc transgenic mouse model using bioluminescent imaging. Moreover, the Western blotting data revealed that antagomir-21 inhibited tumor angiogenesis through suppressing HIF-1α/VEGF/VEGFR2-associated signaling pathway. In conclusion, the results from current study demonstrate that antagomir-21 can effectively suppress tumor growth and angiogenesis in VEGFR2-luc mouse breast tumor model and bioluminescent imaging can be used as a tool for noninvasively and continuously monitoring tumor angiogenesis in vivo.

Current understanding of molecular and cellular mechanisms in fibroplasia and angiogenesis during acute wound healing

Cutaneous wound healing ultimately functions to facilitate barrier restoration following injury-induced loss of skin integrity. It is an evolutionarily conserved, multi-cellular, multi-molecular process involving co-ordinated inter-play between complex signalling networks. Cellular proliferation is recognised as the third stage of this sequence. Within this phase, fibroplasia and angiogenesis are co-dependent processes which must be successfully completed in order to form an evolving extracellular matrix and granulation tissue. The resultant structures guide cellular infiltration, differentiation and secretory profile within the wound environment and consequently have major influence on the success or failure of wound healing. This review integrates in vitro, animal and human in vivo studies, to provide up to date descriptions of molecular and cellular interactions involved in fibroplasia and angiogenesis. Significant molecular networks include adhesion molecules, proteinases, cytokines and chemokines as well as a plethora of growth factors. These signals are produced by, and affect behaviour of, cells including fibroblasts, fibrocytes, keratinocytes, endothelial cells and inflammatory cells resulting in significant cellular phenotypic and functional plasticity, as well as controlling composition and remodelling of structural proteins including collagen and fibronectin. The interdependent relationship between angiogenesis and fibroplasia relies on dynamic reciprocity between cellular components, matrix proteins and bioactive molecules. Unbalanced regulation of any one component can have significant consequences resulting in delayed healing, chronic wounds or abnormal scar formation. Greater understanding of angiogenic and fibroplastic mechanisms underlying chronic wound pathogenesis has identified novel therapeutic targets and enabled development of improved treatment strategies including topical growth factors and skin substitutes.

Simultaneous targeting of tumor antigens and the tumor vasculature using T lymphocyte transfer synergize to induce regression of established tumors in mice

Most systemic cancer therapies target tumor cells directly, although there is increasing interest in targeting the tumor stroma that can comprise a substantial portion of the tumor mass. We report here a synergy between two T-cell therapies, one directed against the stromal tumor vasculature and the other directed against antigens expressed on the tumor cell. Simultaneous transfer of genetically engineered syngeneic T cells expressing a chimeric antigen receptor targeting the VEGF receptor-2 (VEGFR2; KDR) that is overexpressed on tumor vasculature and T-cells specific for the tumor antigens gp100 (PMEL), TRP-1 (TYRP1), or TRP-2 (DCT) synergistically eradicated established B16 melanoma tumors in mice and dramatically increased the tumor-free survival of mice compared with treatment with either cell type alone or T cells coexpressing these two targeting molecules. Host lymphodepletion before cell transfer was required to mediate the antitumor effect. The synergistic antitumor response was accompanied by a significant increase in the infiltration and expansion and/or persistence of the adoptively transferred tumor antigen-specific T cells in the tumor microenvironment and thus enhanced their antitumor potency. The data presented here emphasize the possible beneficial effects of combining antiangiogenic with tumor-specific immunotherapeutic approaches for the treatment of patients with cancer.

G13 controls angiogenesis through regulation of VEGFR-2 expression

At sites of angiogenesis, the expression of the key angiogenesis regulator vascular endothelial growth factor (VEGF) and its main receptor, VEGF receptor 2 (VEGFR-2), are strongly upregulated. Whereas the processes controlling VEGF expression are well described, the mechanisms underlying VEGFR-2 upregulation have remained unclear. We found that endothelial VEGFR-2 expression is strongly reduced in the absence of the G protein G13, resulting in an impaired responsiveness to VEGF-A, a phenotype that can be rescued by normalization of VEGFR-2 levels. G13-mediated VEGFR-2 expression involved activation of the small GTPase RhoA and transcription factor NF-κB, the latter acting via a specific binding site at position -84 of the VEGFR-2 promoter. Mice with endothelial cell-specific loss of G13 showed reduced VEGFR-2 expression at sites of angiogenesis and attenuated VEGF effects, resulting in impaired retinal angiogenesis and tumor vascularization. Taken together, we identified G-protein-mediated signaling via G13 as a critical regulator of VEGFR-2 expression during angiogenesis.

Illuminating cancer systems with genetically engineered mouse models and coupled luciferase reporters in vivo

Bioluminescent imaging (BLI) is a powerful noninvasive tool that has dramatically accelerated the in vivo interrogation of cancer systems and longitudinal analysis of mouse models of cancer over the past decade. Various luciferase enzymes have been genetically engineered into mouse models (GEMM) of cancer, which permit investigation of cellular and molecular events associated with oncogenic transcription, posttranslational processing, protein-protein interactions, transformation, and oncogene addiction in live cells and animals. Luciferase-coupled GEMMs ultimately serve as a noninvasive, repetitive, longitudinal, and physiologic means by which cancer systems and therapeutic responses can be investigated accurately within the autochthonous context of a living animal.

Non-invasive imaging for studying anti-angiogenic therapy effects

Noninvasive imaging plays an emerging role in preclinical and clinical cancer research and has high potential to improve clinical translation of new drugs. This article summarises and discusses tools and methods to image tumour angiogenesis and monitor anti-angiogenic therapy effects. In this context, micro-computed tomography (µCT) is recommended to visualise and quantify the micro-architecture of functional tumour vessels. Contrast-enhanced ultrasound (US) and magnetic resonance imaging (MRI) are favourable tools to assess functional vascular parameters, such as perfusion and relative blood volume. These functional parameters have been shown to indicate anti-angiogenic therapy response at an early stage, before changes in tumour size appear. For tumour characterisation, the imaging of the molecular characteristics of tumour blood vessels, such as receptor expression, might have an even higher diagnostic potential and has been shown to be highly suitable for therapy monitoring as well. In this context, US using targeted microbubbles is currently evaluated in clinical trials as an important tool for the molecular characterisation of the angiogenic endothelium. Other modalities, being preferably used for molecular imaging of vessels and their surrounding stroma, are photoacoustic imaging (PAI), near-infrared fluorescence optical imaging (OI), MRI, positron emission tomography (PET) and single photon emission computed tomography (SPECT). The latter two are particularly useful if very high sensitivity is needed, and/or if the molecular target is difficult to access. Carefully considering the pros and cons of different imaging modalities in a multimodal imaging setup enables a comprehensive longitudinal assessment of the (micro)morphology, function and molecular regulation of tumour vessels.

Bioluminescence imaging: a shining future for cardiac regeneration

Advances in bioanalytical techniques have become crucial for both basic research and medical practice. One example, bioluminescence imaging (BLI), is based on the application of natural reactants with light-emitting capabilities (photoproteins and luciferases) isolated from a widespread group of organisms. The main challenges in cardiac regeneration remain unresolved, but a vast number of studies have harnessed BLI with the discovery of aequorin and green fluorescent proteins. First described in the luminous hydromedusan Aequorea victoria in the early 1960s, bioluminescent proteins have greatly contributed to the design and initiation of ongoing cell-based clinical trials on cardiovascular diseases. In conjunction with advances in reporter gene technology, BLI provides valuable information about the location and functional status of regenerative cells implanted into numerous animal models of disease. The purpose of this review was to present the great potential of BLI, among other existing imaging modalities, to refine effectiveness and underlying mechanisms of cardiac cell therapy. We recount the first discovery of natural primary compounds with light-emitting capabilities, and follow their applications to bioanalysis. We also illustrate insights and perspectives on BLI to illuminate current efforts in cardiac regeneration, where the future is bright.

Tumor vessel-injuring ability improves antitumor effect of cytotoxic T lymphocytes in adoptive immunotherapy

Angiogenesis is required for normal physiologic processes, but it is also involved in tumor growth, progression and metastasis. Here, we report the development of an immune-based antiangiogenic strategy based on the generation of T lymphocytes that possess killing specificity for cells expressing vascular endothelial growth factor receptor 2 (VEGFR2). To target VEGFR2-expressing cells, we engineered cytotoxic T lymphocyte (CTL) expressing chimeric T-cell receptors (cTCR-CTL) comprised of a single-chain variable fragment (scFv) against VEGFR2 linked to an intracellular signaling sequence derived from the CD3ζ chain of the TCR and CD28 by retroviral gene transduction methods. The cTCR-CTL exhibited efficient killing specificity against VEGFR2 and a tumor-targeting function in vitro and in vivo. Reflecting such abilities, we confirmed that the cTCR-CTL strongly inhibited the growth of a variety of syngeneic tumors after adoptive transfer into tumor-bearing mice without consequent damage to normal tissue. In addition, CTL expressing both cTCR and tumor-specific TCR induced complete tumor regression due to enhanced tumor infiltration by the CTL and long-term antigen-specific function. These findings provide evidence that the tumor vessel-injuring ability improved the antitumor effect of CTLs in adoptive immunotherapy for a broad range of cancers by inducing immune-mediated destruction of the tumor neovasculature.

Generation of a new bioluminescent model for visualisation of mammary tumour development in transgenic mice

BACKGROUND

Numerous transgenic models have been generated to study breast cancer. However, despite many advantages, traditional transgenic models for breast cancer are also burdened with difficulties in early detection and longitudinal observation of transgene-induced tumours, which in most cases are randomly located and occur at various time points. Methods such as palpation followed by mechanical measurement of the tumours are of limited value in transgenic models. There is a crucial need for making these previously generated models suitable for modern methods of tumour visualisation and monitoring, e.g. by bioluminescence-based techniques. This approach was successfully used in the current study.

RESULTS

A new mouse strain (MMTV-Luc2 mice) expressing Luc2 luciferase primarily in mammary tissue in females, with low-level background expression in internal organs, was generated and bred to homozygosity. After these mice were intercrossed with MMTV-PyVT mice, all double transgenic females developed mammary tumours by the age of 10 weeks, the localisation and progression of which could be effectively monitored using the luminescence-based in vivo imaging. Luminescence-based readout allowed for early visualisation of the locally overgrown mammary tissue and for longitudinal evaluation of local progression of the tumours. When sampled ex vivo at the age of 10 weeks, all tumours derived from MMTV-Luc2PyVT females displayed robust bioluminescent signal.

CONCLUSIONS

We have created a novel transgenic strain for visualisation and longitudinal monitoring of mammary tumour development in transgenic mice as an addition and/or a new and more advanced alternative to manual methods. Generation of this mouse strain is vital for making many of the existing mammary tumour transgenic models applicable for in vivo imaging techniques.

CT-based handling and analysis of preclinical multimodality imaging data of bone metastases

The pathogenesis of bone metastases is a complex and multifaceted process. Often multiple imaging modalities are needed to follow both the structural and functional changes over time during metastatic bone disease. Researchers face extended data sets of one experiment acquired with multiple modalities at multiple points in time. This review gives an overview of an integrated approach for handling these kinds of complex data. It focuses on the analysis of whole-body micro-computerized tomography and optical data handling. We show how researchers can generate side-by-side visualizations of scans taken with one imaging modality at multiple time points and with multiple modalities at one point. Moreover, we highlight methods for normalized volumes of interest selection and quantification of bone volume and thickness.

Down-regulation of microRNA-26a promotes mouse hepatocyte proliferation during liver regeneration

Background

Inadequate liver regeneration (LR) is still an unsolved problem in major liver resection and small-for-size syndrome post-living donor liver transplantation. A number of microRNAs have been shown to play important roles in cell proliferation. Herein, we investigated the role of miR-26a as a pivotal regulator of hepatocyte proliferation in LR.

Methodology/Principal Findings

Adult male C57BL/6J mice, undergoing 70% partial hepatectomy (PH), were treated with Ad5-anti-miR-26a-LUC or Ad5-miR-26a-LUC or Ad5-LUC vector via portal vein. The animals were subjected to in vivo bioluminescence imaging. Serum and liver samples were collected to test liver function, calculate liver-to-body weight ratio (LBWR), document hepatocyte proliferation (Ki-67 staining), and investigate potential targeted gene expression of miR-26a by quantitative real-time PCR and Western blot. The miR-26a level declined during LR after 70% PH. Down-regulation of miR-26a by anti-miR-26a expression led to enhanced proliferation of hepatocytes, and both LBWR and hepatocyte proliferation (Ki-67⁺ cells %) showed an increased tendency, while liver damage, indicated by aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total bilirubin (T-Bil), was reduced. Furthermore, CCND2 and CCNE2, as possible targeted genes of miR-26a, were up-regulated. In addition, miR-26a over-expression showed converse results.

Conclusions/Significance

MiR-26a plays crucial role in regulating the proliferative phase of LR, probably by repressing expressions of cell cycle proteins CCND2 and CCNE2. The current study reveals a novel miRNA-mediated regulation pattern during the proliferative phase of LR.

In vivo imaging of lymphatic vessels in development, wound healing, inflammation, and tumor metastasis

Lymphatic vessel growth or lymphangiogenesis occurs during embryonic development and wound healing and plays an important role in tumor metastasis and inflammatory diseases. However, the possibility of noninvasive detection and quantification of lymphangiogenesis has been lacking. Here, we present the Vegfr3(EGFPLuc) mouse model, where an EGFP-luciferase fusion protein, expressed under the endogenous transcriptional control of the Vegfr3 gene, allows the monitoring of physiological and pathological lymphangiogenesis in vivo. We show tracking of lymphatic vessel development during embryogenesis as well as lymphangiogenesis induced by specific growth factors, during wound healing and in contact hypersensitivity (CHS)--induced inflammation where we also monitor down-regulation of lymphangiogenesis by the glucocorticoid dexamethasone. Importantly, the Vegfr3-reporter allowed us to tracking tumor-induced lymphangiogenesis at the tumor periphery and in lymph nodes in association with the metastatic process. This is the first reporter mouse model for luminescence imaging of lymphangiogenesis. It should provide an important tool for studying the involvement of lymphangiogenesis in pathological processes.

Preclinical imaging of the cellular and molecular events in the multistep process of bone metastasis

Bone metastasis is a complex process that ultimately leads to devastating metastatic bone disease. It is therefore of key interest to unravel the mechanisms underlying the multistep process of skeletal metastasis and cancer-induced bone disease, and to develop better treatment and management of patients with this devastating disease. Fortunately, novel technologies are rapidly emerging that allow real-time imaging of molecules, pathogenic processes, drug delivery and drug response in preclinical in vivo models. The outcome of these experimental studies will facilitate clinical cancer research by improving the detection of cancer cell invasion, metastasis and therapy response.

Dietary L-arginine supplementation during gestation in mice enhances reproductive performance and Vegfr2 transcription activity in the fetoplacental unit

Regarded as one of the most versatile amino acids, arginine serves as a precursor for many molecules and has been reported to improve the reproductive performance of rats and pigs. To this end, we sought to determine if dietary L-arginine alters fetoplacental vascular endothelial growth factor receptor-2 (Vegfr2) transcription activity. Eighteen wild-type FVB/N female mice were bred to homozygous FVB/N-Tg(Vegfr2-luc)-Xen male mice. Bred female mice received 1 of 2 experimental diets: one supplemented with 2.00% (wt:wt) L-arginine (+Arg) or 1 supplemented with 4.10% (wt:wt) alanine (+Ala) to serve as an isonitrogenous control for +Arg. In addition, 6 mice were fed a nonsupplemented control (Con) diet to normalize bioluminescent imaging data. All data were analyzed using ANOVA followed by Fisher's least significant difference. Total feed intake did not differ between groups; however, mice in the +Arg group consumed more arginine (P < 0.05). Arginine supplementation increased weight gain during the latter one-third of gestation (d 12- 18), total litter size, number of pups born alive, number of placental attachment sites, litter birth weight, and litter weight of pups born alive but decreased the individual birth weights (P < 0.05). During d 12-18, arginine supplementation increased (P < 0.05) the mean total Vegfr2 transcription activity and Vegfr2 transcription activity corrected for fetoplacental mass. Moreover, mice in the +Arg group had an earlier rise in Vegfr2 transcription activity. In conclusion, our results demonstrate that the beneficial effect of dietary L-arginine supplementation on mammalian reproduction is associated with enhanced Vegfr2 transcription activity in fetoplacental tissues.

Local delivery of interleukin-12 using T cells targeting VEGF receptor-2 eradicates multiple vascularized tumors in mice

PURPOSE

We investigated the feasibility of delivering the proinflammatory cytokine interleukin (IL)-12 into tumor using T cells genetically engineered to express a chimeric antigen receptor (CAR) against the VEGF receptor-2 (VEGFR-2).

EXPERIMENTAL DESIGN

Two different strains of mice bearing five different established subcutaneous tumors were treated with syngeneic T cells cotransduced with an anti-VEGFR-2 CAR and a constitutively expressed single-chain murine IL-12 or an inducible IL-12 gene after host lymphodepletion. Tumor regression, survival of mice, and persistence of the transferred cells were evaluated.

RESULTS

Adoptive transfer of syngeneic T cells cotransduced with an anti-VEGFR-2 CAR and a constitutively expressing single-chain IL-12 resulted in the regression of five different established tumors of different histologies without the need for IL-2 administration. T cells transduced with either anti-VEGFR-2 CAR or single-chain IL-12 alone did not alter the tumor growth indicating that both of them had to be expressed in the same cell to mediate tumor regression. Anti-VEGFR-2 CAR and IL-12-cotransduced T cells infiltrated the tumors, expanded, and persisted for prolonged periods. The antitumor effect did not require the presence of host T and B cells but was dependent on host IL-12R-expressing cells. The anti-VEGFR-2 CAR changed the immunosuppressive tumor environment by altering/reducing both the systemic and the intratumoral CD11b(+)Gr1(+) myeloid suppressor cell subsets that expressed VEGFR-2.

CONCLUSIONS

These results suggest that targeted delivery of IL-12 into the tumor environment with T cells redirected against VEGFR-2 is a promising approach for treating patients with a variety of solid tumor types.

Preclinical models that illuminate the bone metastasis cascade

In this chapter currently available preclinical models of tumor progression and bone metastasis, including genetically engineered mice that develop primary and metastatic carcinomas and transplantable animal models, will be described. Understanding the multistep process of incurable bone metastasis is pivotal to the development of new therapeutic strategies. Novel technologies for imaging molecules or pathologic processes in cancers and their surrounding stroma have emerged rapidly and have greatly facilitated cancer research, in particular the cellular behavior of osteotropic tumors and their response to new and existing therapeutic agents. Optical imaging, in particular, has become an important tool in preclinical bone metastasis models, clinical trials and medical practice. Advances in experimental and clinical imaging will-in the long run-result in significant improvements in diagnosis, tumor localization, enhanced drug delivery and treatment.