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

[Identification of the offspring of Vegfr2-luc transgenic mouse]

BACKGROUND AND OBJECTIVE

A transgenic mouse, Vegfr2-luc, in which a luciferase reporter (luc) is under control of the murine VEGFR2 promoter, can be used to track angiogenesis in vivo. The aim of this study is to identify the offspring of Vegfr2-luc transgenic mouse.

METHODS

Luc was detected with PCR in genomic DNA of the new-born mouse. Luc expression in the offspring of Vegfr2-luc transgenic mouse was monitored with IVIS in vivo imaging system during post-natal development. Wound-healing models of Vegfr2-luc transgenic mouse offspring were established and the expression of luc was monitored during the wound-healing process. Luc activity and VEGFR2 mRNA expression in different organs were detected with luc Assay System and Real-time PCR respectively.

RESULTS

PCR showed that 50% (56/112) of the offspring of Vegfr2-luc transgenic mouse carry luc. IVIS in vivo imaging results demonstrated that luc expression in Vegfr2-luc transgenic mouse dropped dramatically with age increase (P<0.001) and luc expression in the wound first increased and then decreased during the wound-healing process (P<0.001). Luc activity in female Vegfr2-luc transgenic mouse organs was positively correlated with VEGFR2 mRNA expression (r=0.948, P<0.001). Except testis, luc activity in male Vegfr2-luc transgenic mouse organs was also positively correlated with VEGFR2 mRNA expression (r=0.836, P<0.001).

CONCLUSION

The offspring of Vegfr2-luc transgenic mouse is applicable to tracking angiogenesis in vivo.

Bioluminescence imaging: progress and applications

Application of bioluminescence imaging has increased tremendously in the past decade and has significantly contributed to core conceptual advances in biomedical research. This technology provides valuable means for monitoring of different biological processes in immunology, oncology, virology and neuroscience. In this review, we discuss current trends in bioluminescence and its application in different fields with an emphasis on cancer research.

Pregnancy promotes melanoma metastasis through enhanced lymphangiogenesis

The relationships of pregnancy and melanoma have been debatable. Our aim was to assess the influence of gestation on the course of melanoma in a classic murine model of tumor progression and in women. B16 mouse melanoma cells were injected in nonpregnant or pregnant mice on day 5 of gestation. Animals were evaluated for tumor progression, metastases, and survival. Tumor sections were analyzed for lymphatic and blood vessel number and relative surface and expression of angiogenic growth factors. Finally, primary melanomas from pregnant and nonpregnant women, matched for age and tumor thickness, were also considered. Tumor growth, metastasis, and mortality were increased in B16-injected pregnant mice. Tumors displayed an increase in intratumoral lymphangiogenesis during gestation. This increased lymphatic angiogenesis was not observed in normal skin during gestation, showing its specificity to the tumor. An analysis of melanoma from pregnant and matched nonpregnant women showed a similar increase in lymphatic vessels. Tumors from pregnant mice had increased expression of vascular endothelial growth factor A at the RNA and protein levels. The increased vascular endothelial growth factor A production by melanoma cells could be reproduced in culture using pregnant mouse serum. In conclusion, pregnancy results in increased lymphangiogenesis and subsequent metastasis. Caution should be applied in the management of patients with advanced-stage melanoma during gestation.

Live in vivo imaging of Egr-1 promoter activity during neonatal development, liver regeneration and wound healing

BACKGROUND

The zinc finger transcription factor Egr-1 (Early growth response 1) is central to several growth factors and represents an important activator of target genes not only involved in physiological processes like embryogenesis and neonatal development, but also in a variety of pathophysiological processes, for example atherosclerosis or cancer. Current options to investigate its transcription and activation in vivo are end-point measurements that do not provide insights into dynamic changes in the living organism.

RESULTS

We developed a transgenic mouse (Egr-1-luc) in which the luciferase reporter gene is under the control of the murine Egr-1 promoter providing a versatile tool to study the time course of Egr-1 activation in vivo. In neonatal mice, bioluminescence imaging revealed a high Egr-1 promoter activity reaching basal levels three weeks after birth with activity at snout, ears and paws. Using a model of partial hepatectomy we could show that Egr-1 promoter activity and Egr-1 mRNA levels were increased in the regenerating liver. In a model of wound healing, we demonstrated that Egr-1 promoter activity was upregulated at the site of injury.

CONCLUSION

Taken together, we have developed a transgenic mouse model that allows real time in vivo imaging of the Egr-1 promoter activity. The ability to monitor and quantify Egr-1 activity in the living organism may facilitate a better understanding of Egr-1 function in vivo.

In vivo monitoring of fetoplacental Vegfr2 gene activity in a murine pregnancy model using a Vegfr2-luc reporter gene and bioluminescent imaging

BACKGROUND

Vascular endothelial growth factor receptor-2 (VEGFR2) plays a pivotal role in angiogenesis by eliciting vascular endothelial cell growth when bound to VEGF, a powerful pro-angiogenic ligand. While Vegf and Vegfr2 are expressed throughout gestation, the latter third of gestation in mice is characterized by a marked increase in fetoplacental angiogenesis. Thus, the objective of this study was to determine the feasibility of monitoring fetoplacental Vegfr2 gene activity non-invasively using a Vegfr2-luc reporter transgenic mouse and bioluminescent imaging.

METHODS

Imaging parameters were optimized using two wild-type (WT) females, bearing Vegfr2-luc fetuses. Then, seven WT females, bred to Vegfr2-luc males, were imaged from gestational day (GD) 12 to 18 to determine the usefulness of the Vegfr2-luc mouse as a model for studying fetoplacental Vegfr2 activity during pregnancy. Semi-quantitative RT-PCR of Vegfr2 was also performed on whole fetoplacental units during this time. Additionally, resultant neonates were imaged at postnatal day (PND) 7, 14 and 21 to monitor Vegfr2 activity during post-natal development.

RESULTS

Fetoplacental Vegfr2 gene activity was detected as light emissions beginning on GD 12 of gestation and increased throughout the imaging period (P < 0.05), and this paralleled the Vegfr2 mRNA data obtained from RT-PCR analysis. A decline in fetoplacental light emissions was associated with a poor pregnancy outcome in one pregnancy, indicating that this approach has potential use for studies monitoring pregnancy well being. Additionally, neonatal Vegfr2 activity was detected at PND 7, 14 and 21 but declined with time (P < 0.0001).

CONCLUSIONS

In utero fetoplacental Vegfr2 gene activity was monitored longitudinally in a quantitative manner using a luciferase reporter gene and bioluminescent imaging during the latter third of gestation. This study demonstrates the feasibility of using the Vegfr2-luc mouse to monitor late gestation fetoplacental angiogenic activity under normal and experimental conditions. Additionally, neonatal Vegfr2 gene activity was monitored for three weeks postpartum, allowing continuous monitoring of Vegfr2 activity during the latter third of gestation and postnatal development within the same animals.

Effects of VEGF loading on scaffold-confined vascularization

Adequate vascularization of tissue-engineered constructs remains a major challenge in bone grafting. In view of this, we loaded ß-tricalcium-phosphate (ß-TCP) and porous poly(L-lactide-co-glycolide) (PLGA) scaffolds via collagen coating with vascular endothelial growth factor (VEGF) and studied whether the VEGF loading improves scaffold angiogenesis and vascularization. Dorsal skinfold chambers were implanted into 48 balb/c mice, which were assigned to 6 groups (n = 8 each). Uncoated (controls), collagen-coated, and additionally VEGF-loaded PLGA and ß-TCP scaffolds were inserted into the chambers. Angiogenesis, neovascularization, and leukocyte-endothelial cell interaction were analyzed repeatedly during a 14-day observation period using intravital fluorescence microscopy. Furthermore, VEGF release from PLGA und ß-TCP scaffolds was studied by ELISA. Micromorphology was studied from histological specimens. Unloaded ß-TCP scaffolds showed an accelerated and increased angiogenic response when compared with unloaded PLGA scaffolds. In vitro, PLGA released significantly higher amounts of VEGF compared with ß-TCP at the first two days resulting in a rapid drop of the released amount at the following days up to day 7 where the VEGF release was negligible. Nonetheless, in vivo VEGF loading increased neovascularization, especially in ß-TCP scaffolds. This increased vascularization was associated with a temporary leukocytic response with pronounced leukocyte-endothelial cell interaction at days 3 and 6. Histology revealed adequate host tissue response and engraftment of both ß-TCP and PLGA scaffolds. Our study demonstrates that ß-TCP scaffolds offer more suitable conditions for vascularization than PLGA scaffolds, in particular if they are loaded with VEGF.

Bioluminescence imaging of angiogenesis in a murine orthotopic pancreatic cancer model

PURPOSE

Angiogenesis is essential for physiological processes as well as for carcinogenesis. New approaches to cancer therapy include targeting angiogenesis. One target is VEGF-A and its receptor VEGFR2. In this study, we sought to investigate pancreatic cancer angiogenesis in a genetically modified VEGFR2-luc-KI mouse.

PROCEDURES

Live in vivo bioluminescence imaging of angiogenesis was performed continuously until sacrifice in subcutaneous tumors as well as in orthotopically transplanted tumors. Tumor tissue was immunostained for CD-31 and VEGFR2.

RESULTS

Peritumoral angiogenesis measured by light emission was detected beginning at week 3 following subcutaneous injection. In the orthotopic model, light emission began at day 4, which likely corresponds to wound healing, and continued throughout the experimental period during tumor growth. Peritumoral CD-31 vessel- and VEGFR2-staining were positive.

CONCLUSIONS

The VEGFR2-luc-KI mouse is a valuable tool to demonstrate tumor angiogenesis and seems to be suitable to evaluate anti-angiogenic approaches in pancreatic cancer.

A phage-targeting strategy for the design of spatiotemporal drug delivery from grafted matrices

Background

The natural response to injury is dynamic and normally consists of complex temporal and spatial cellular changes in gene expression, which, when acting in synchrony, result in patent tissue repair and, in some instances, regeneration. However, current therapeutic regiments are static and most rely on matrices, gels and engineered skin tissue. Accordingly, there is a need to design next-generation grafting materials to enable biotherapeutic spatiotemporal targeting from clinically approved matrices. To this end, rather then focus on developing completely new grafting materials, we investigated whether phage display could be deployed onto clinically approved synthetic grafts to identify peptide motifs capable of linking pharmaceutical drugs with differential affinities and eventually, control drug delivery from matrices over both space and time.

Methods

To test this hypothesis, we biopanned combinatorial peptide libraries onto different formulations of a wound-healing matrix (Integra^®) and eluted the bound peptides with 1) high salt, 2) collagen and glycosaminoglycan or 3) low pH. After three to six rounds of biopanning, phage recovery and phage amplification of the bound particles, any phage that had acquired a capacity to bind the matrix was sequenced.

Results

In this first report, we identify distinct classes of matrix-binding peptides which elute differently from the screened matrix and demonstrate that they can be applied in a spatially relevant manner.

Conclusions

We suggest that further applications of these combinatorial techniques to wound-healing matrices may offer a new way to improve the performance of clinically approved matrices so as to introduce temporal and spatial control over drug delivery.

Horse species symposium: a novel approach to monitoring pathogen progression during uterine and placental infection in the mare using bioluminescence imaging technology and lux-modified bacteria

Uterine and placental infections are the leading cause of abortion, stillbirth, and preterm delivery in the mare. Whereas uterine and placental infections in women have been studied extensively, a comprehensive examination of the pathogenic processes leading to this unsatisfactory pregnancy outcome in the mare has yet to be completed. Most information in the literature relating to late-term pregnancy loss in mares is based on retrospective studies of clinical cases submitted for necropsy. Here we report the development and application of a novel approach, whereby transgenically modified bacteria transformed with lux genes of Xenorhabdus luminescens or Photorhabdus luminescens origin and biophotonic imaging are utilized to better understand pathogen-induced preterm birth in late-term pregnant mares. This technology uses highly sensitive bioluminescence imaging camera systems to localize and monitor pathogen progression during tissue invasion by measuring the bioluminescent signatures emitted by the lux-modified pathogens. This method has an important advantage in that it allows for the potential tracking of pathogens in vivo in real time and over time, which was hitherto impossible. Although the application of this technology in domestic animals is in its infancy, investigators were successful in identifying the fetal lungs, sinuses, nares, urinary, and gastrointestinal systems as primary tissues for pathogen invasion after experimental infection of pregnant mares with lux-modified Escherichia coli. It is important that pathogens were not detected in other vital organs, such as the liver, brain, and cardiac system. Such precision in localizing sites of pathogen invasion provides potential application for this novel approach in the development of more targeted therapeutic interventions for pathogen-related diseases in the equine and other domestic species.

Optical advances in skeletal imaging applied to bone metastases

Optical Imaging has evolved into one of the standard molecular imaging modalities used in pre-clinical cancer research. Bone research however, strongly depends on other imaging modalities such as SPECT, PET, x-ray and μCT. Each imaging modality has its own specific strengths and weaknesses concerning spatial resolution, sensitivity and the possibility to quantify the signal. An increasing number of bone specific optical imaging models and probes have been developed over the past years. This review gives an overview of optical imaging modalities, models and probes that can be used to study skeletal complications of cancer in small laboratory animals.

Perioperative conditions affect long-term hypertrophic scar formation

Corticosteroids are widely used as treatment for excessive scarring by intralesional injection with variable success rates. It is conceivable that systemically administered corticosteroids affect a wider range of inflammatory processes that influence wound healing and may be more successful in preventing hypertrophic scar formation. To study this presumption, we have used a standardized model of presternal scars caused by cardiothoracic surgery through a median sternotomy incision. During cardiac surgery with cardiopulmonary bypass, 1 mg/kg dexamethasone was administered preoperatively, and 0.5 mg/kg 8 hours postoperatively. The presternal scars were evaluated prospectively 2, 4, 6, 12, and 52 weeks postoperatively at standardized measuring points. The height and width of the scars were measured 12 and 52 weeks postoperatively using both a slide caliper and a 7.5-MHz ultrasound probe. Cardiopulmonary bypass was used in 31 of the 43 participants. Eleven patients (35%) in the dexamethasone group developed clinical hypertrophic scars compared with 4 patients (33%) in the control group. These differences were not statistically significant. However, cranial scars became significantly wider in the dexamethasone group compared with the control group (P = 0.04). Twelve weeks postoperatively scars were significantly higher in the dexamethasone group, both cranial (P = 0.05) and caudal (P = 0.03). The differences in scar width and height were mainly present in patients that developed hypertrophic scars. The present results suggest that administration of high-dose perioperative dexamethasone does not prevent hypertrophic scar formation. Its use together with the cardiopulmonary bypass, however, did affect scar dimensions negatively up to 52 weeks after surgery. These findings contribute to the concept of the involvement of perioperative immunologic responses in the etiology of hypertrophic scar formation.

Differential effects of VEGFR-1 and VEGFR-2 inhibition on tumor metastases based on host organ environment

Tumors induce new blood vessel growth primarily from host organ microvascular endothelial cells (EC), and microvasculature differs significantly between the lung and liver. Vascular endothelial growth factor (VEGF or VEGF-A) promotion of tumor angiogenesis is thought to be mediated primarily by VEGF receptor-2 (VEGFR-2). In this study, VEGFR-2 antibody (DC101) inhibited growth of RenCa renal cell carcinoma lung metastases by 26%, whereas VEGFR-1 antibody (MF-1) had no effect. However, VEGFR-2 neutralization had no effect on RenCa liver metastases, whereas VEGFR-1 neutralization decreased RenCa liver metastases by 31%. For CT26 colon carcinoma liver metastases, inhibition of both VEGFR-1 and VEGFR-2 was required to induce growth delay. VEGFR-1 or VEGFR-2 inhibition decreased tumor burden not by preventing the establishment of micrometastases but rather by preventing vascularization and growth of micrometastases by 55% and 43%, respectively. VEGF induced greater phosphorylation of VEGFR-2 in lung ECs and of VEGFR-1 in liver ECs. EC proliferation, migration, and capillary tube formation in vitro were suppressed more by VEGFR-2 inhibition for lung EC and more by VEGFR-1 inhibition for liver EC. Collectively, our results indicate that liver metastases are more reliant on VEGFR-1 than lung metastases to mediate angiogenesis due to differential activity of VEGFRs on liver EC versus lung EC. Thus, therapies inhibiting specific VEGFRs should consider the targeted sites of metastatic disease.

'In vivo' optical approaches to angiogenesis imaging

In recent years, molecular imaging gained significant importance in biomedical research. Optical imaging developed into a modality which enables the visualization and quantification of all kinds of cellular processes and cancerous cell growth in small animals. Novel gene reporter mice and cell lines and the development of targeted and cleavable fluorescent "smart" probes form a powerful imaging toolbox. The development of systems collecting tomographic bioluminescence and fluorescence data enabled even more spatial accuracy and more quantitative measurements. Here we describe various bioluminescent and fluorescent gene reporter models and probes that can be used to specifically image and quantify neovascularization or the angiogenic process itself.

Bioluminescent imaging: a critical tool in pre-clinical oncology research

Bioluminescent imaging (BLI) is a non-invasive imaging modality widely used in the field of pre-clinical oncology research. Imaging of small animal tumour models using BLI involves the generation of light by luciferase-expressing cells in the animal following administration of substrate. This light may be imaged using an external detector. The technique allows a variety of tumour-associated properties to be visualized dynamically in living models. The increasing use of BLI as a small-animal imaging modality has led to advances in the development of xenogeneic, orthotopic, and genetically engineered animal models expressing luciferase genes. This review aims to provide insight into the principles of BLI and its applications in cancer research. Many studies to assess tumour growth and development, as well as efficacy of candidate therapeutics, have been performed using BLI. More recently, advances have also been made using bioluminescent imaging in studies of protein-protein interactions, genetic screening, cell-cycle regulators, and spontaneous cancer development. Such novel studies highlight the versatility and potential of bioluminescent imaging in future oncological research.

Subconjunctival bevacizumab as an adjunct to trabeculectomy in eyes with refractory glaucoma: a case series

This prospective observational case series study included 6 eyes of 6 consecutive glaucomatous patients. Each patient underwent trabeculectomy with mitomycin C, and received a 1.25 mg of subconjunctival bevacizumab injection at completion of the trabeculectomy. Study eyes included two with neovascular glaucoma, three with uveitic glaucoma, and one with secondary glaucoma following vitrectomy. All eyes had undergone failed glaucoma laser/surgical treatment or an intraocular surgical procedure. Intraocular pressure (IOP) at the following postoperative visits: preoperative, 1 week, 1 month, 2 months, 3 months, and 6 months, was measured. We also evaluated postoperative bleb findings and complications. IOP measured at each visit was 37.5±14.4 mmHg, 6.2±3.4 mmHg, 8.3±7.2 mmHg, 12.0±4.4 mmHg, 10.8±3.1 mmHg, and 12.2±3.3 mmHg, respectively, for each visit. All eyes had functioning blebs with normal IOP at postoperative 6 months with no additional IOP-lowering medication.

Angiogenesis, vascular endothelial growth factor and its receptors in human surgical wounds

BACKGROUND

Angiogenesis plays an essential role in tissue repair. Vascular endothelial growth factor (VEGF) mediates angiogenesis through receptor kinases VEGF-R1 and VEGF-R2, and co-receptors, neuropilins Np1 and Np2. This study examined the spatial and temporal expression of these factors in relation to angiogenesis in surgical wounds.

METHODS

Scar biopsies were obtained from patients between 3 days and 2 years after surgery. Normal skin control biopsies were taken during surgery. Microvessel density (MVD) was quantified using a Chalkley grid. VEGF, VEGF-R1, VEGF-R2, Np1 and Np2 endothelial expression was determined by immunohistochemistry, and correlated with MVD and scar age.

RESULTS

Cumulative MVD was significantly greater in scars than controls (P = 0.011), and was related to scar age (P = 0.007). Expression of VEGF, VEGF-R2, Np1 and Np2 was increased significantly in all scars and correlated with MVD. In contrast, scar VEGF-R1 expression was decreased, and correlated with increased VEGF and VEGF-R2.

CONCLUSION

Levels of VEGF, VEGF-R2, Np1 and Np2 are increased, whereas VEGF-R1 expression is decreased in angiogenesis, suggesting a role for VEGF-receptor complexes in early wound healing. This altered protein expression and increased presence of vessels is prolonged, suggesting that structural remodelling continues for at least 2 years after surgery.

Real-time analysis of the kinetics of angiogenesis and vascular permeability in an animal model of wound healing

The use of engineered tissue for the treatment of a variety of acute to chronic wounds has become a clinical standard, and a better understanding of the cellular mechanisms of re-vascularization and barrier integrity could enhance clinical outcomes. Here, we focus on the characterization of the re-vascularization of acellular grafts such as Integra in an animal model to better understand the physiological properties of blood vessels growing in the collagen-glycosaminoglycan matrix vs. wound margins. While Integra has been extensively studied in pre-clinical models, the re-modeling mechanisms of the capillary bed under these matrices are not well understood. Therefore, our first objective was to quantify the kinetics of re-vascularization. The second objective was to assess changes in vascular permeability (VP) of the wound bed compared to normal adjacent skin. The third objective was to establish a non-invasive and quantitative assay for the measurement of VP to facilitate the rapid and reproducible characterization of vascular integrity. Using an excisional wound model in mice, we characterize the appearance, growth, and maturation of blood vessels in an Integra graft over 28 days after surgery. Initial appearance of blood vessels in the graft was observed at 7 days, with angiogenesis peaking between 7 and 14 days. The onset of VP coincided with the increase in re-vascularization of the wound bed and there was a sustained elevation of VP that declined to baseline by 28 days. We propose a non-invasive strategy to assess VP of the wound capillary bed will facilitate a better understanding of the cell and molecular basis of angiogenesis in wound healing.

Following up tumour angiogenesis: from the basic laboratory to the clinic

Preceded by three decades of intense basic research on tumour angiogenesis, we are assisting to the translation of anti-antiangiogenic therapies as medical oncologists are increasingly using pioneering anti-angiogenic drugs in combination with standard treatments. While basic knowledge in the field of angiogenesis is reaching maturity and our level of understanding of the complex process of vessel development and growth in health and disease has been enriched at the molecular and cellular levels, the translation of this knowledge to the clinic is still in its infancy. Identifying the most suitable drugs, and the optimal dosage and schedule, as well as monitoring patients' responses to anti-angiogenic therapy, remain challenging issues that currently limit the benefit of this new therapeutic approach in cancer. This review will focus on a comprehensive description of the experimental assays in which angiogenesis research has been founded and how the different assays complement and provide relevant information for the task of characterising the angiogenic properties of diverse tumours, giving us a variety of tools to follow up tumour angiogenesis in research models. Following up tumour angiogenesis in patients and their response to antiangiogenic therapy is a more challenging task that will benefit in the near future from the use of non-invasive imaging methods as well as molecular and cellular biomarkers of angiogenesis suitable for clinical oncology. As both the design of the anti-angiogenic therapies and monitoring of the response are improved in the coming years to properly tailor them to the angiogenic profile of every patient, we hope to achieve increasing response and benefit of including antiangiogenic drugs as standard in cancer therapy.

Growth factor delivery from self-assembling nanofibers to facilitate islet transplantation

Recent advances in nanotechnology and molecular self-assembly may provide novel solutions to current cell transplantation deficiencies. Heparin-binding peptide amphiphiles (HBPAs) self-assemble from aqueous media into nanofibers that bind growth factors through interactions with the bioactive polymer heparin. In this report, we demonstrate that delivery of vascular endothelial growth factor and fibroblast growth factor-2 from HBPA scaffolds significantly increases blood vessel density in the mouse omentum over control scaffolds without growth factors (P<0.0005) and significantly enhances islet engraftment. Diabetic recipients transplanted with 250 isologous islets and HBPA scaffolds containing vascular endothelial growth factor/fibroblast growth factor-2 achieved normoglycemia at a higher rate (78%) than control animals receiving identical scaffolds without growth factors (30%; P<0.05) or growth factors alone (20%). These data indicate that the enhanced engraftment can be attributed to specific growth factor effects that were made possible by the delivery mechanism of HBPA nanostructures.

Functional imaging of interleukin 1 beta expression in inflammatory process using bioluminescence imaging in transgenic mice

Background

Interleukin 1 beta (IL-1β) plays an important role in a number of chronic and acute inflammatory diseases. To understand the role of IL-1β in disease processes and develop an in vivo screening system for anti-inflammatory drugs, a transgenic mouse line was generated which incorporated the transgene firefly luciferase gene driven by a 4.5-kb fragment of the human IL-1β gene promoter. Luciferase gene expression was monitored in live mice under anesthesia using bioluminescence imaging in a number of inflammatory disease models.

Results

In a LPS-induced sepsis model, dramatic increase in luciferase activity was observed in the mice. This transgene induction was time dependent and correlated with an increase of endogenous IL-1β mRNA and pro-IL-1β protein levels in the mice. In a zymosan-induced arthritis model and an oxazolone-induced skin hypersensitivity reaction model, luciferase expression was locally induced in the zymosan injected knee joint and in the ear with oxazolone application, respectively. Dexamethasone suppressed the expression of luciferase gene both in the acute sepsis model and in the acute arthritis model.

Conclusion

Our data suggest that the transgenic mice model could be used to study transcriptional regulation of the IL-1β gene expression in the inflammatory process and evaluation the effect of anti-inflammatory drug in vivo.

Regulation of scar formation by vascular endothelial growth factor

Vascular endothelial growth factor (VEGF-A) is known for its effects on endothelial cells and as a positive mediator of angiogenesis. VEGF is thought to promote repair of cutaneous wounds due to its proangiogenic properties, but its ability to regulate other aspects of wound repair, such as the generation of scar tissue, has not been studied well. We examined the role of VEGF in scar tissue production using models of scarless and fibrotic repair. Scarless fetal wounds had lower levels of VEGF and were less vascular than fibrotic fetal wounds, and the scarless phenotype could be converted to a scar-forming phenotype by adding exogenous VEGF. Similarly, neutralization of VEGF reduced vascularity and decreased scar formation in adult wounds. These results show that VEGF levels have a strong influence on scar tissue formation. Our data suggest that VEGF may not simply function as a mediator of wound angiogenesis, but instead may play a more diverse role in the wound repair process.

Dexamethasone treatment of post-MI rats attenuates sympathetic innervation of the infarct region

Sympathetic fiber innervation of the damaged region following injury represents a conserved event of wound healing. The present study tested the hypothesis that impaired scar healing in post-myocardial infarction (post-MI) rats was associated with a reduction of sympathetic fibers innervating the infarct region. In 1-wk post-MI rats, neurofilament-M-immunoreactive fibers (1,116 ± 250 μm2/mm2) were detected innervating the infarct region and observed in close proximity to a modest number of endothelial nitric oxide synthase-immunoreactive scar-residing vessels. Dexamethasone (Dex) treatment (6 days) of post-MI rats led to a significant reduction of scar weight (Dex + MI 38 ± 4 mg vs. MI 63 ± 2 mg) and a disproportionate nonsignificant decrease of scar surface area (Dex + MI 0.54 ± 0.06 cm2vs. MI 0.68 ± 0.06 cm2). In Dex-treated post-MI rats, the density of neurofilament-M-immunoreactive fibers (125 ± 47 μm2/mm2) innervating the infarct region was significantly reduced and associated with a decreased expression of nerve growth factor (NGF) mRNA (Dex + MI 0.80 ± 0.07 vs. MI 1.11 ± 0.08; P < 0.05 vs. MI). Previous studies have demonstrated that scar myofibroblasts synthesize NGF and may represent a cellular target of Dex. The exposure of 1st passage scar myofibroblasts to Dex led to a dose-dependent suppression of [3H]thymidine uptake and a concomitant attenuation of NGF mRNA expression (untreated 3.47 ± 0.35 vs. Dex treated 2.28 ± 0.40; P < 0.05 vs. untreated). Thus the present study has demonstrated that impaired scar healing in Dex-treated post-MI rats was associated with a reduction of neurofilament-M-immunoreactive fibers innervating the infarct region. The attenuation of scar myofibroblast proliferation and NGF mRNA expression may represent underlying mechanisms contributing to the diminished neural response in the infarct region of Dex-treated post-MI rats.

The role of actively released fibrin-conjugated VEGF for VEGF receptor 2 gene activation and the enhancement of angiogenesis

A major challenge for therapeutic delivery of angiogenic agents such as vascular endothelial growth factor (VEGF) is to achieve sustained, low dose signaling leading to durable neovessel formation. To this end, we recently created a variant of VEGF(121), TG-VEGF(121) that directly binds to fibrin and gets released locally in proteolysis-triggered manner. Here we combined noninvasive biophotonic monitoring of VEGF receptor 2 gene activation in transgenic VEGFR2-luc mice and histomorphometry to compare endothelial activation and long-term neovascularization by actively released TG-VEGF(121)versus passively released, diffusible wild-type VEGF(121) in subcutaneous fibrin implants. Monitoring in real-time over 3 weeks of luciferase signal driven by the VEGFR2 promoter revealed endothelial activation in skin exposed to wild-type VEGF(121), but no detectable elevation over fibrin alone by TG-VEGF(121). Histology at 3 weeks, however, demonstrated that TG-VEGF(121) promoted vessel growth significantly more effectively and reliably than wild-type VEGF(121). The majority of vessels surviving to 3 weeks contained stabilizing smooth muscle cells. Yet, by 6 weeks, no extra vessels induced by exogenous VEGF were left. In conclusion, release of fibrin-conjugated variant TG-VEGF(121) elicited lower VEGFR2-luc activation than wild-type VEGF(121) yet significantly more vascularization. In the absence of true physiological demand, even stabilized vessels are ultimately regressed.

Inflammation and ischemia-induced lung angiogenesis

A role for inflammation in modulating the extent of angiogenesis has been shown for a number of organs. The present study was undertaken to evaluate the importance of leukocyte subpopulations for systemic angiogenesis of the lung after left pulmonary artery ligation (LPAL) in a mouse model of chronic pulmonary thromboembolism. Since we (24) previously showed that depletion of neutrophils did not alter the angiogenic outcome, we focused on the effects of dexamethasone pretreatment (general anti-inflammatory) and gadolinium chloride treatment (macrophage inactivator) and studied Rag-1(-/-) mice (T/B lymphocyte deficient). We measured inflammatory cells in bronchoalveolar lavage fluid and lung homogenate macrophage inflammatory protein-2 (MIP-2) and IL-6 protein levels within 24 h after LPAL and systemic blood flow to the lung 14 days after LPAL with labeled microspheres as a measure of angiogenesis. Blood flow to the left lung was significantly reduced after dexamethasone treatment compared with untreated control LPAL mice (66% decrease; P < 0.05) and significantly increased in T/B lymphocyte-deficient mice (88% increase; P < 0.05). Adoptive transfer of splenocytes (T/B lymphocytes) significantly reversed the degree of angiogenesis observed in the Rag-1(-/-) mice back to the level of control LPAL. Average number of lavaged macrophages for each group significantly correlated with average blood flow in the study groups (r(2) = 0.9181; P = 0.01 different from 0). Despite differences in angiogenesis, left lung homogenate MIP-2 and IL-6 did not differ among study groups. We conclude that inflammatory cells modulate the degree of angiogenesis in this lung model where lymphocytes appear to limit the degree of neovascularization, whereas monocytes/macrophages likely promote angiogenesis.

Advances in optical imaging and novel model systems for cancer metastasis research

Research into the genetic and physiological interactions of tumours with their host environment requires in vivo assays to address molecular expression patterns and function. In recent years much of this work has been performed using bioluminescent and fluorescent imaging techniques that allow real-time and non-invasive imaging of gene expression and (tumour) tissue development. Luminescence imaging has until now been more or less the only tool that allows the imaging of intra-osseous breast cancer cells and indeed this technique has been pioneered in our laboratory. Here we summarise some recent innovations and developments using cancer cells and some of the first imaging models of multimodal dual luminescence and luminescence combined with fluorescence of intra-osseous tumours. We further engineered our models to incorporate a specific insertion site in the genome and will discuss some of the possible applications. These include the insertion of signalling pathway-specific reporters and studying the fate of multiple injected populations in a single mouse. We conclude that recent improvements in luminescence- and fluorescence-detection platforms now clearly allow multimodal imaging which will greatly enhance our ability to assess gene function and for the first time to visualise multiple gene- and cellular interactions in real time and in vivo.

Whole-body optical imaging in animal models to assess cancer development and progression

Different optical-based imaging models were used to investigate tumor progression and metastasis with particular emphasis on metastasis to bone and bone marrow. We describe how optical imaging can be used to follow important processes in tumor development and treatment response, including angiogenesis, apoptosis, and proteolysis. Finally, we discuss the translation of one optical imaging modality, near-IR fluorescence, from animal validation studies to applications in the clinic related to cancer management.

In Vivo Imaging of Farnesoid X Receptor Activity Reveals the Ileum as the Primary Bile Acid Signaling Tissue

We generated and characterized a firefly luciferase reporter mouse for the nuclear receptor farnesoid X receptor (FXR). This FXR reporter mouse has basal luciferase expression in the terminal ileum, an organ with well-characterized FXRalpha signaling. In vivo luciferase activity reflected the diurnal activity pattern of the mouse, and is regulated by both natural (bile acids, chenodeoxycholic acid) and synthetic (GW4064) FXRalpha ligands. Moreover, in vivo and in vitro analysis showed luciferase activity after GW4064 administration in the liver, kidney, and adrenal gland, indicating that FXRalpha signaling is functional in these tissues. Hepatic luciferase activity was robustly induced in cholestatic mice, showing that FXRalpha signaling pathways are activated in this disease. In conclusion, we have developed an FXR reporter mouse that is useful to monitor FXRalpha signaling in vivo in health and disease. The use of this animal could facilitate the development of new therapeutic compounds that target FXRalpha in a tissue-specific manner.

Noninvasive indirect imaging of vascular endothelial growth factor gene expression using bioluminescence imaging in living transgenic mice

Vascular endothelial growth factor (VEGF) plays a critical role in the early activation of stromal tissues during wound healing and tumor growth. We report the use of a two-step transcriptional amplification (TSTA) approach to augment the transcriptional activity of the relatively weak VEGF promoter (pVEGF) using firefly luciferase (fl) reporter gene and bioluminescence imaging (BLI). In cell culture, we demonstrate that TSTA-based fl gene expression can be significantly enhanced over the direct one-step system. Using a transgenic mouse model (pVEGF-TSTA-fl), we demonstrate the induction of VEGF gene expression using a wound-healing model and a subcutaneous mammary tumor model. In skin-wounding experiments, pVEGF-induced fl expression in the wound lesion is detected on days 4 and 5 and peaks on days 15-22. Furthermore, the bioluminescence signal shows good correlation with the endogenous VEGF protein levels in the wound tissue (r2 = 0.70). In the mammary tumor model, fl expression is detected on day 3, peaks at day 17, and declines thereafter. These results support the use of noninvasive BLI for the longitudinal monitoring of VEGF induction during wound healing and tumor progression, and this mouse model should find use in various applications in which it is important to noninvasively study VEGF gene expression.

Maternal neoangiogenesis during pregnancy partly derives from fetal endothelial progenitor cells

Fetal progenitor cells enter the maternal circulation during pregnancy and can persist for decades. We aimed to determine the role of these cells in tissue inflammation during pregnancy. WT female mice were mated to males transgenic for the EGFP (ubiquitous) or the luciferase gene controlled by the VEGF receptor 2 (VEGFR2; V-Luc) promoter. A contact hypersensitivity reaction was triggered during such pregnancies. Fetal cells were tracked by using real-time quantitative amplification of the transgene (real-time PCR), Y chromosome in situ hybridization (FISH), immunofluorescence or in vivo bioluminescence imaging. Real-time PCR disclosed fetal cells in the inflamed areas in all tested mice (17/17) with higher frequency and numbers in the inflamed compared with the control areas (P = 0.01). Double labeling demonstrated CD31+ EGFP+ fetal cells organized as blood vessels. In WT pregnant mice bearing V-Luc fetuses, a specific luciferase activity signal could be detected at the hypersensitivity site only, demonstrating the elective presence of VEGFR2-expressing fetal cells. In conclusion, using various techniques, we found the presence of fetal endothelial cells lining blood vessels in maternal sites of inflammation. These results imply that fetal endothelial progenitor cells are acquired by the mother and participate in maternal angiogenesis during pregnancy.

Molecular mechanisms of VEGF-A action during tissue repair

Vascular endothelial growth factor-A (VEGF-A) is a crucial mediator of vascular hyperpermeability, angiogenesis, and inflammation, processes intimately involved in tissue repair. Although much emphasis has been placed on understanding the synthesis and stability of VEGF-A mRNA, relatively little attention has been given to the study of the stability and processing of VEGF-A proteins themselves. In recent years, several studies indicated that VEGF-A protein activity is highly controlled through interaction with angiogenic or non-angiogenic mediators. We analyzed mechanisms that might control extracellular VEGF-A processing during wound repair. First, our studies provide evidence that VEGF-A protein is a target of proteases present in the microenvironment of human chronic non-healing wounds. Serine proteases, in particular plasmin cleave VEGF165 and digested VEGF fragments, showed decreased mitogenic activity. Inactivation of the plasmin cleavage site Arg110/Ala111 preserved the structural integrity and increased the angiogenic potency of VEGF165 when tested in an impaired healing mouse model. Secondly, we identified significantly increased levels of the potent VEGF-A inhibitor, the soluble form of the VEGF receptor VEGFR-1 (sVEGFR-1) in non-healing wounds when compared to healing wounds. Wound closure in healing and non-healing wounds correlated significantly with a decline in sVEGFR-1 levels. These observations support the concept that VEGF-A and VEGF-A receptors are important mediators in tissue repair. Further, our data provide mechanisms how VEGF-A-mediated interactions are disturbed during impaired healing.

Real-time monitoring of stress erythropoiesis in vivo using Gata1 and beta-globin LCR luciferase transgenic mice

Erythroid progenitors have the potential to proliferate rapidly in response to environmental stimuli. This process is referred to as stress erythropoiesis, with erythropoietin (EPO) playing central roles in its promotion. In this study, we wanted to elucidate the molecular mechanisms governing the regulation of stress erythropoiesis and the maintenance of red-cell homeostasis. This was achieved by our development of a noninvasive real-time monitoring system for erythropoiesis using transgenic mouse lines expressing luciferase under the control of the mouse Gata1 hematopoietic regulatory domain (G1-HRD-luc) or human beta-globin locus control region (Hbb-LCR-luc). Optical bioluminescence images revealed that the luciferase was specifically expressed in spleen and bone marrow and was induced rapidly in response to anemia and hypoxia stimuli. The G1-HRD-luc activity tracked the emergence and disappearance of proerythroblast-stage progenitors, whereas the Hbb-LCR-luc activity tracked erythroblasts and later stage erythroid cells. Increased plasma EPO concentration preceded an increase in G1-HRD-luc, supporting our contention that EPO acts as the key upstream signal in stress erythropoiesis. Hence, we conclude that G1-HRD-luc and Hbb-LCR-luc reporters are differentially activated during stress erythropoiesis and that the transgenic mouse lines used serve as an important means for understanding the homeostatic regulation of erythropoiesis.

Bioluminescent imaging: Emerging technology for non-invasive imaging of bone tissue engineering

Bone tissue engineering is a multidisciplinary research area in which new strategies are developed to treat patients with large bone defects as occurring during e.g. hip revisions, upon trauma or in spinal fusions. In vivo evaluation of bone formation in animal models is highly relevant for graft evaluation but is time-consuming, invasive and difficult to quantify. As a consequence, most in vivo studies ignore the dynamic nature of bone regeneration and the molecular processes underlying it. In vivo bioluminescent imaging (BLI) is a relatively young research field with great potential that may overcome these problems. BLI encompasses non-invasive imaging of luciferase gene activity using cooled charge coupled device cameras in luciferase transgenic animals or in grafted, luciferase transgenic cells. The imaging procedure is technically simple and quantifiable. Because luciferase expression can be put under the control of tissue-specific regulatory elements, BLI allows non-invasive imaging of processes highly relevant to bone tissue engineering like differentiation, apoptosis, vasculogenesis and inflammation. In this review, we describe the basic principle of BLI and discuss transgenic animals and constructs currently available for application in bone tissue engineering. Furthermore, we reflect on technical developments that will make BLI even more promising for future application in bone tissue engineering research.

Photonic Monitoring in Real Time of Vascular Endothelial Growth Factor Receptor 2 Gene Expression under Relaxin-Induced Conditions in a Novel Murine Wound Model

Relaxin is known to promote vascular endothelial growth factor (VEGF) expression in reproductive tissue, and successful wound healing depends on good vascularization of wound sites, a process that relaxin may facilitate. Thus, the objective of this study was to evaluate the efficacy of relaxin on the development of vascular tissue at wound sites in a novel VEGF receptor 2-luc (VEGFR2-luc) transgenic mouse wound model by monitoring the rate of VEGFR2-luc-mediated gene expression using bioluminescence and real-time imaging. To this end, 12 FVB/N VEGFR2-luc transgenic male mice were assigned to treatments (six per group): saline alone or relaxin (1 g/6 h/14 days) administered intraperitoneally (i.p.). On day 0, a set of full-thickness wounds (6-mm punch) were generated under anesthesia on the dorsal aspect of each mouse. Photonic emissions were recorded (5-min collection of photons) from wound sites 10 min after the administration of luciferin (150 mg/kg i.p.) on day 0 and on days 1, 2, 4, 7, 9, 11, and 14 postwounding to quantify luciferase activity using an IVIS 100 biophotonic imaging system. Animals were sacrificed (three per group) on day 7 or 14, and wound tissue specimens were recovered for molecular and histologic analyses. Although photonic emission from wound sites increased (P < .001) over time with peak values obtained by day 7, no significant (P > .05) effect of relaxin treatment on VEGFR2-luc gene expression was noted at wound sites. Whereas measuring relaxin's effect on angiogenesis indirectly via the VEGFR2 model was not successful, photonic imaging provides an exciting new tool using alternative models (i.e., VEGF-luc mouse) to study relaxin-induced gene expression in normal (i.e., wound healing) or tumorigenic tissues in real time.

Novel Function for Vascular Endothelial Growth Factor Receptor-1 on Epidermal Keratinocytes

Vascular endothelial growth factor (VEGF-A), a potent stimulus for angiogenesis, is up-regulated in the skin after wounding. Although studies have shown that VEGF is important for wound repair, it is unclear whether this is based solely on its ability to promote angiogenesis or if VEGF can also promote healing by acting directly on non-endothelial cell types. By immunohistochemistry and reverse transcriptase-polymerase chain reaction, expression of VEGF receptor-1 (VEGFR-1), but not VEGFR-2, was detected in murine keratinocytes during wound repair and in normal human epidermal keratinocytes (NHEKs). The presence of VEGF receptors on NHEKs was verified by binding studies with 125I-VEGF. In vitro, VEGF stimulated the proliferation of NHEKs, an effect that could be blocked by treatment with neutralizing VEGFR-1 antibodies. A role for VEGFR-1 in keratinocytes was also shown in vivo because treatment of excisional wounds with neutralizing VEGFR-1 antibodies delayed re-epithelialization. Treatment with anti-VEGFR-1 antibodies also reduced the number of proliferating keratinocytes at the leading edge of the wound, suggesting that VEGF sends a proliferative signal to these cells. Together, these data describe a novel role for VEGFR-1 in keratinocytes and suggest that VEGF may play several roles in cutaneous wound repair.

Transient inflammatory response induced by apoptotic cells is an important mediator of melanoma cell engraftment and growth

Two murine melanoma cell lines, Tm1 and Tm5, were derived from a nontumorigenic lineage of pigmented murine melanocytes, melan-a. Both Tm1 and Tm5 are invariably tumorigenic in syngeneic mice when inoculated s.c. in doses higher than 10(4) cells; 10(3) or fewer cells rarely give rise to tumors. We demonstrate that subtumorigenic inocula of Tm1 or Tm5 cells (10(3)) as well as of a known murine melanoma cell line (B16F10) develop as vigorously growing tumor grafts only when coinoculated with apoptotic, but not necrotic cells. The presence of apoptotic cells correlates with a transient inflammatory infiltrate, composed mainly of neutrophils and macrophages. Kinin B1 receptor-deficient mice, which have impaired transmigration of neutrophils to inflamed tissues, had significant growth inhibition of subtumorigenic doses of melanoma cells coinjected with apoptotic cells. Using the same model, tumor take in athymic mice was similar to that seen in wild-type mice, suggesting that a T cell-dependent inflammatory response is not necessary to promote the survival and growth of subtumorigenic doses of melanoma cells. Taken together, our results describe how tumor engraftment and growth can be profoundly affected by microenvironmental alterations in response to the presence of apoptotic cells. Disrupting the delicate balance between apoptotic cells and leukocyte infiltration may provide potentially important insights for understanding and interfering with tumor cell viability during treatment with either gamma-radiation or apoptosis-inducing drugs.