Origin of bone-forming cells in human osteosarcomas transplanted into nude mice--which cells produce bone, human or mouse?

Chick embryo xenograft model reveals a novel perineural niche for human adipose-derived stromal cells

Human adipose-derived stromal cells (hADSC) are a heterogeneous cell population that contains adult multipotent stem cells. Although it is well established that hADSC have skeletal potential in vivo in adult organisms, in vitro assays suggest further differentiation capacity, such as into glia. Thus, we propose that grafting hADSC into the embryo can provide them with a much more instructive microenvironment, allowing the human cells to adopt diverse fates or niches. Here, hADSC spheroids were grafted into either the presumptive presomitic mesoderm or the first branchial arch (BA1) regions of chick embryos. Cells were identified without previous manipulations via human-specific Alu probes, which allows efficient long-term tracing of heterogeneous primary cultures. When grafted into the trunk, in contrast to previous studies, hADSC were not found in chondrogenic or osteogenic territories up to E8. Surprisingly, 82.5% of the hADSC were associated with HNK1+ tissues, such as peripheral nerves. Human skin fibroblasts showed a smaller tropism for nerves. In line with other studies, hADSC also adopted perivascular locations. When grafted into the presumptive BA1, 74.6% of the cells were in the outflow tract, the final goal of cardiac neural crest cells, and were also associated with peripheral nerves. This is the first study showing that hADSC could adopt a perineural niche in vivo and were able to recognize cues for neural crest cell migration of the host. Therefore, we propose that xenografts of human cells into chick embryos can reveal novel behaviors of heterogeneous cell populations, such as response to migration cues.

The combined bone forming capacity of human periosteal derived cells and calcium phosphates

Current knowledge suggests that the periosteum, a fibrous tissue which covers the surface of all bones, contains a population of progenitor cells which mediate the repair of bone defects. In an effort to optimise the utilisation of this source of cells for bone engineering, herein we describe the rational selection of calcium phosphate (CaP) containing materials, based on biomaterial properties, and evaluation of their combined bone forming capacity. Five different commercially available orthopaedic 3D matrices composed of CaP particles in an open collagen network (NuOss™, CopiOs™, Bio-Oss(®), Collagraft™ and Vitoss(®)) were evaluated in vitro and in vivo with human periosteal derived cells (hPDCs). It was found that the cell-material combinations behaved quite differently in vivo, despite apparent in vitro similarities in gene expression profiles. Bone formation was highest within the NuOss™/hPDC implant at 13.03%, which also contained the highest incidence of bone marrow formation. The bone formed in this implant was chimeric with approximately 65% originating from implanted cells. Upon analysis of human specific gene expression, although it was found that predominantly osteogenic differentiation was observed within NuOss™/hPDC implants, a lesser induction of chondrogenic genes was also observed. The formation of a cartilage intermediate was confirmed by histology. Additionally the NuOss™/hPDC implant integrated into the mouse environment with apparent active scaffold resorption. This study demonstrates the importance of matching a cell support/biological matrix with a cell type and subsequently has outlined parameters which can be used for the rational selection of biomaterials for bone engineering.

A clinically relevant model of osteoinduction: a process requiring calcium phosphate and BMP/Wnt signalling

In this study, we investigated a clinically relevant model of in vivo ectopic bone formation utilizing human periosteum derived cells (HPDCs) seeded in a Collagraft™ carrier and explored the mechanisms by which this process is driven. Bone formation occurred after eight weeks when a minimum of one million HPDCs was loaded on Collagraft™ carriers and implanted subcutaneously in NMRI nu/nu mice. De novo bone matrix, mainly secreted by the HPDCs, was found juxta-proximal of the calcium phosphate (CaP) granules suggesting that CaP may have triggered the ‘osteoinductive program’. Indeed, removal of the CaP granules by ethylenediaminetetraacetic acid decalcification prior to cell seeding and implantation resulted in loss of bone formation. In addition, inhibition of endogenous bone morphogenetic protein and Wnt signalling by overexpression of the secreted antagonists Noggin and Frzb, respectively, also abrogated osteoinduction. Proliferation of the engrafted HPDCs was strongly reduced in the decalcified scaffolds or when seeded with adenovirus-Noggin/Frzb transduced HPDCs indicating that cell division of the engrafted HPDCs is required for the direct bone formation cascade. These data suggest that this model of bone formation is similar to that observed during physiological intramembranous bone development and may be of importance when investigating tissue engineering strategies.

Noggin blocks invasive growth of murine B16-F1 melanoma cells in the optic cup of the chick embryo

Melanoma cells originate from the neural crest and are characterized by high migratory potential and invasive growth. After transplantation into the neural tube of the chick embryo, melanoma cells spontaneously emigrate along the neural crest pathways without tumor formation or malignant growth. This emigration depends on the constitutive over-expression of bone morphogenetic protein-2 (BMP-2) and can be ablated by the BMP-antagonist noggin. When transplanted into the embryonic optic cup, melanoma cells invade the host tissue and form malignant tumors. Here, we asked if the invasive growth of melanoma cells in the optic cup could be influenced by BMP-2 or noggin. Mouse B16-F1 cells were grown as aggregates, treated with BMP-2 or noggin during aggregation and transplanted into the optic cup of 3-day chick embryos. After 3 days of subsequent incubation, embryos were evaluated for melanoma cell invasiveness. Immunohistochemical examination revealed that untreated and BMP-2-treated melanoma cells had grown malignantly into the host tissue. However, noggin pretreatment of the aggregates had blocked melanoma cell invasiveness and tumor formation. We conclude that invasive growth of melanoma cells in vivo is BMP-dependent and can be ablated by noggin, thus rendering noggin a promising agent for the treatment of BMP-over-expressing melanoma.

Assessment of bone formation capacity using in vivo transplantation assays: procedure and tissue analysis

In vivo assessment of bone formation (osteogenesis) potential by isolated cells is an important method for analysis of cells and factors control ling bone formation. Currently, cell implantation mixed with hydroxyapa-tite/tricalcium phosphate in an open system (subcutaneous implantation) in immunodeficient mice is the standard method for in vivo assessment of bone formation capacity of a particular cell type. The method is easy to perform and provides reproducible results. Assessment of the donor origin of tissue formation is possible, especially in the case of human-to-mouse transplanta tion, by employing human specific antibodies or in situ hybridization using human specific Alu-repeat probes. Recently, several methods have been developed to quantitate the newly formed bone using histomorphometric methods or using non-invasive imaging methods. This chapter describes the use of in vivo transplantation methods in testing bone formationpotential of human mesenchymal stem cells.

Human esophageal cancer endothelial cells increase tumor growth by incorporating with mouse endothelium

Current in vivo investigations of tumor angiogenesis mainly rely on the results obtained from engrafted models in mice. In the present study, we attempt to assess the potential of human tumor endothelium to form neovasculature in different engrafted tumor models. The tumor endothelial cells were isolated from human esophageal squamous cell carcinoma, and then identified by anti-VEGFR1/2 immunoreactions and tube formation assay. Esophageal and lung cancer cells were subcutaneously inoculated into nude mice with human esophageal cancer endothelial cells (HECECs), respectively. The human umbilical vein endothelial cells (HUVECs) were also co-inoculated into mice with esophageal cancer cells as a control. The engrafted tumor growth was significantly promoted by co-inoculation of HECECs in comparison with injection of esophageal tumor cells alone. Immunohistochemistry of anti-CD31 and anti-huCD31 was performed to detect the micro-vessels in the engrafted tumors which revealed that the HECECs formed humanized micro-vessels and significantly increased the micro-vessel density in engrafted tumors comparing with the tumors without HECECs. However, HUVEC cells could not enhance the esophageal tumor growth and the growth of lung tumors could not be increased by HECECs, either. Few humanized blood vessels were found in these two groups of xenografts. These results suggest that the specific interaction between HECECs and esophageal tumor cells contributes to the neovasculature construction and esophageal tumor growth in xenografts.

Non-malignant migration of B16 mouse melanoma cells in the neural crest and invasive growth in the eye cup of the chick embryo

Melanocytes originate from the neural crest. In a previous study, we observed that human SK-Mel 28 human melanoma cells resumed neural crest cell migration after transplantation into the chick embryo neural tube. Here, we used transgenic mouse B16-F1 melanoma cells transfected with green fluorescent protein-vasodilator-stimulated phosphoprotein construct to extend these observations. After the injection of a cell suspension into the trunk neural tube of E2 chick embryos, the migration of melanoma cells was followed by live fluorescence microscopy. Within 12 h, the melanoma cells formed clusters in the neural tube at the levels of the intersegmental clefts between somites. After 24 h, a segmental pattern of emigration was visible. Emigrated melanoma cells were identified in serial paraffin sections by immunohistochemistry with ab732 as a marker for melanoma cells and by in-situ hybridization of mouse-specific repetitive genomic sequence mL1. After 24 h, melanoma cells were found along the medial neural crest pathway and in the sympathetic trunk ganglia and, after 48 h, also in the lateral melanocytic pathway. During migration along the neural crest pathways, mouse melanoma cells underwent apoptosis, which was assessed by anti-caspase 3 and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling staining. To prove the ablation of malignant behavior after back-transplantation into the original embryonic neural crest environment, we injected the same cell suspension into the eye cup of the E3 embryo. In this location, invasive melanomas formed.

BMP-2-dependent integration of adult mouse subventricular stem cells into the neural crest of chick and quail embryos

Central nervous system (CNS) stem cells isolated from the subventricular zone (SVZ) show a remarkable differentiation potential into neural derivatives. Surprisingly adult SVZ cells can also be induced in vitro to differentiate into neural crest cell fates. This fate switch is dependent on the combination of fibroblast growth factor 2 (FGF2) and bone morphogenetic proteins (BMPs). Here we transplanted adult SVZ stem cells from GFP mice as neurospheres into the trunk neural tube of chick and quail embryos. Only neurospheres pre-exposed to BMP-2 and FGF2 formed close contacts with the dorsal neuroepithelium corresponding to the neural crest area. GFP-positive cells emigrated from the neurosphere and were identified in the roof plate, the dorsal neuroepithelium and among emigrating neural crest cells adjacent to the neural tube. Neurospheres not treated with BMP-2 did not integrate into the neuroepithelium. Our data demonstrate that adult CNS stem cells can be efficiently prepared in vitro for integration into the embryonic neural crest. BMP-2 treatment conveys the necessary morphogenetic capabilities to adult stem cells for future clinical transplantation strategies.

MR imaging findings of an unusual case of myositis ossificans presenting as a progressive mass with features of fluid-fluid level

We present a case of myositis ossificans involving the upper arm in which features of fluid-fluid level became apparent on magnetic resonance imaging (MRI). Serial MR images obtained over a 6-month period exhibited progressive appearances in the absence of dense mineralization in the early and mid phases, which simulate neoplastic conditions. Twenty-four weeks following the biopsy, MR images revealed that the mass had decreased in size with the disappearance of most of the features of fluid-fluid level. To the best of our knowledge, no example of myositis ossificans accompanied by features of fluid-fluid level, which was closely monitored by MRI, exists in the literature. These features of image examination should be evaluated cautiously to avoid unnecessary surgical intervention, especially in instances where lesions exhibit expansive appearance. This case provided beneficial information regarding the sequence of changes in terms of MR appearance of myositis ossificans.

Circulating tumor cells in patients with solid malignancy treated by high-intensity focused ultrasound

The theoretical possibility that exposure of a solid malignancy to high-intensity focused ultrasound (US), or HIFU, could lead to an increased rate of metastasis still remains. Using reverse transcriptase polymerase chain reaction (RT-PCR), the potential risk of hematogenous dissemination was assessed in HIFU-treated patients with solid malignancy. RT-PCR can demonstrate the presence or absence of specific RNA fragments. On the day before HIFU ablation, 5-mL peripheral blood samples were collected, and again 5 to 7 days after HIFU, from 26 enrolled patients (hepatocellular carcinoma, HCC: 10; osteosarcoma: 16). Total RNA was isolated and RT-PCR was performed to analyze the mRNA expression of (alpha-fetoprotein (AFP) and bone-specific alkaline phosphatase (BALP) genes. Positive AFP mRNA expression was preoperatively detected in 8 of 10 patients with HCC. In the postoperative specimens, positive expression was also detected in 8 of 10 patients. In 2 patients, circulating tumor cells were found preoperatively, but not postoperatively. Conversely, 2 patients with no circulating tumor cells preoperatively were found to have circulating tumor cells after HIFU. Of 16 osteosarcoma patients, 12 patients had circulating tumor cells and 4 had none. After HIFU treatment, 2 of the 12 patients had converted from presence to absence of circulating cells and the remaining 4 patients remained negative. It is concluded that patients undergoing complete HIFU ablation may demonstrate conversion from presence to absence of circulating tumor-specific marker mRNA, and that HIFU would not enhance the potential risk of metastasis in patients with malignant diseases.

Identification of human cells in brain xenografts and in neural co-cultures of rat by in situ hybridisation with Alu probe

Transplantation of human cells into animal models of neurodegenerative disorders is an important scientific application to analyse the survival and developmental capacity of grafted human cells under in vivo conditions. It is critical, therefore, to have a reliable method to distinguish between human and animal cells. In the present study, we describe a combined in situ hybridisation and immunocytochemistry method for the identification of human cells in cultured rat brain cells and xenografts. The specific Alu probe we utilised, which corresponds to the consensus sequence of human Alu repeats was evaluated by southern blot hybridisation of zoo blot and by in situ hybridisation of primary and neoplastic cells from man, rat, mouse, and hamster. This method allows a definite identification of human cells in neural xenografts and, in combination with additional in situ techniques, a further detection of grafted cells.

A PCR-ELISA assay for the detection of disseminated osteosarcoma cells in a mouse metastatic model

Circulating tumor cells in the blood play a central role in the metastatic process. There have been no reports describing the relationship between lung metastasis and circulating osteosarcoma cells. We developed a system with a polymerase chain reaction assay based on an enzyme-linked immunosorbent assay (PCR-ELISA) to detect circulating osteosarcoma cells in a mouse metastatic model. Osf2/Cbfa1, hereafter called Osf2, a member of the runt family of transcription factors, was used as a target gene. One splicing variant of Osf2 mRNA was identified and its expression was restricted to the bones and osteosarcomas. The amount of the splicing variant of Osf2 mRNA was significantly higher in the blood of mice with metastasis than in the blood of the control group. The PCR-ELISA using Osf2 mRNA is a potential method to detect circulating osteosarcoma cells in peripheral blood.

Molecular markers predictive of the capacity of expanded human articular chondrocytes to form stable cartilage in vivo

OBJECTIVE

To establish a model and associated molecular markers for monitoring the capacity of in vitro-expanded chondrocytes to generate stable cartilage in vivo.

METHODS

Adult human articular chondrocytes (AHAC) were prepared by collagenase digestion of samples obtained postmortem and were expanded in monolayer. Upon passaging, aliquots of chondrocyte suspensions were either injected intramuscularly into nude mice, cultured in agarose, or used for gene expression analysis. Cartilage formation in vivo was documented by histology, histochemistry, immunofluorescence for type II collagen, and proteoglycan analysis by 35S-sulfate incorporation and molecular sieve chromatography of the radiolabeled macromolecules. In situ hybridization for species-specific genomic repeats was used to discriminate human-derived from mouse-derived cells. Gene expression dynamics were analyzed by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

Intramuscular injection of freshly isolated AHAC into nude mice resulted in stable cartilage implants that were resistant to mineralization, vascular invasion, and replacement by bone. In vitro expansion of AHAC resulted in the loss of in vivo cartilage formation. This capacity was positively associated with the expression of fibroblast growth factor receptor 3, bone morphogenetic protein 2, and alpha1(II) collagen (COL2A1), and its loss was marked by the up-regulation of activin receptor-like kinase 1 messenger RNA. Anchorage-independent growth and the reexpression of COL2A1 in agarose culture were insufficient to predict cartilage formation in vivo.

CONCLUSION

AHAC have a finite capacity to form stable cartilage in vivo; this capacity is lost throughout passaging and can be monitored using a nude mouse model and associated molecular markers. This cartilage-forming ability in vivo may be pivotal for successful cell-based joint surface defect repair protocols.

Expression of metalloproteinase-13 (Collagenase-3) is induced during fracture healing in mice

In fracture healing, a large amount of cartilage is formed, then rapidly replaced by osseous tissue. This process requires the transition of extracellular matrix component from type II to type I collagen. We investigated the expression of matrix metalloproteinase-13 (MMP-13), which has a high potential to cleave type II as well as type I collagen, during fracture repair in mouse ribs. In situ hybridization demonstrated that MMP-13 mRNA was present throughout the healing process. It was detected in the cells of the periosteum at day 1. As fracture callus grew, strong MMP-13 mRNA signals were detected in cells of the cartilaginous callus. In the reparative and remodeling phases, both hypertrophic chondrocytes and immature osteoblastic cells in the fracture callus expressed MMP-13 mRNA strongly. These cells were located adjacent to tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts at the sites of cartilage/bone transition. In osteoclasts, MMP-13 expression was not detected. The level of MMP-13 mRNA peaked at day 14 postfracture by northern blotting. Immunohistochemical staining showed that MMP-13 was detected primarily in hypertrophic chondrocytes. These results indicate that MMP-13 is induced during fracture healing. The site- and cell-specific expression of MMP-13 and its enzymatic property suggest that MMP-13 initiates the degradation of cartilage matrix, resulting in resorption and remodeling of the callus. In conclusion, MMP-13 plays an important role in the healing process of fractured bone in mice.

Origin of histiocyte-like cells and multinucleated giant cells in malignant fibrous histiocytoma: neoplastic or reactive?

The origin of histiocyte-like cells in malignant fibrous histiocytoma (MFH) remains controversial. To determine whether histiocyte-like cells and multinucleated giant cells show reactive or neoplastic proliferation, we transplanted human storiform-pleomorphic MFH to nude mice and investigated the origin of histiocyte-like cells using the DNA in situ hybridization (ISH) system. In addition, we analyzed the mRNA expression of mouse c-fms and human colony stimulating factor-1 (CSF-1); immunohistochemical expression of markers detectable in cells of monocyte/macrophage lineage. The DNA ISH revealed neoplastic proliferation of fibroblastic cells and bizarre multinucleated giant cells of human origin. Monocyte/macrophage lineage cells were seen in parental tumors, whereas they did not participate in neoplastic proliferation in transplanted tumors. The parental tumors expressed human CSF-1 mRNA and the histiocyte-like cells in transplanted tumors expressed 'mouse' c-fms mRNA. These results suggest that MFH induce infiltration of monocyte/macrophage and CSF-1 is one of the mediators involved in this phenomenon, because the human CSF-1 can act as a ligand to the mouse c-fms. Histiocyte-like cells in MFH should be considered as a reactive monocyte/macrophage lineage rather than as an element of neoplasm.