Heat shock activation of telomeric sequences in different tissues of Chironomus thummi

The authors present ultrastructural and immunohistochemical characteristics of an intracranial suprasellar tumor displaying features of cavernous angioma with islets of adipose tissue. Electron microscopy revealed thin-walled vessels separated by a loose collagenous stroma containing nests of mature adipocytes as well as fibroblasts, myofibroblasts, mast cells, and a few macrophages. Intracytoplasmic lipid droplets were also identified in scattered pericytes and smooth muscle cells of vascular walls and in the transitional cells resembling smooth muscle cells and adipocytes. Many adipose tissue cells were positive for S-100 protein with polyclonal antibodies. Other lipidized tumor cells were immunoreactive for some or all of the following: smooth muscle-specific actin, factor XIIIa, vimentin, and, occasionally, for desmin. Ultrastructure and immunohistochemistry indicate that in addition to typical adipocytes, lipidized cells of another nature contribute to the characteristic appearance of the adipose tissue component of angiolipoma.     

Angiogenesis in wound healing and tumor metastasis

Formation of new blood vessels is essential for several physiological and pathological events, e.g. embryogenesis, wound healing and tumor growth and metastasis. In order to increase the insight into the mechanisms of angiogenesis we have visualized the different components of the microvasculature in human wounds and tumors by immunohistochemistry on the light and electronmicroscopic level. For this purpose, antibodies recognizing distinct markers for human endothelial cells, pericytes and basal lamina were used on freshly frozen or paraformaldehyde-fixed tissue samples. In terms of efficacy, the PAL-E antigen is highly specific for blood vessel endothelium. Its sensitivity is less than other endothelial markers, such as von Willebrand factor and CD 31, as it is not expressed in arterioles. Within the context of the microvasculature alpha-smooth muscle actin and the HMW-MAA chondroitin sulphate proteoglycan are useful markers for pericytes. Type IV Collagen and Laminin can be visualized consistently in the microvascular basal lamina. During the formation of granulation tissue in wound healing a heterogeneity of the expression of endothelial and pericyte markers is found. In the least matured zone in granulation tissue of decubitus lesions and experimental skin wounds microvessels already contained both endothelial cells and pericytes, suggesting a role for both cell types in the early steps of angiogenesis. Regarding the tumor microvasculature, antibodies to von Willebrand factor often failed to stain capillaries, that did show expression of the other endothelial markers studied. Broad staining in pericytes was found for the HMW-MAA chondroitin sulphate proteoglycan. In contrast, these cells only locally expressed alpha-smooth muscle actin. Staining of the basal lamina components Type IV Collagen and Laminin within tumors was not restricted to the microvasculature. Therefore, antibodies recognizing endothelial markers, particularly PAL-E and BMA 120, are preferable as tools to visualize the tumor microvasculature. In accordance with the situation in granulation tissue of wound healing the broad presence of pericytes in the microvasculature of human tumor suggests an involvement of this cell type in tumor angiogenesis. Recent immunohistochemical studies on human tumor lesions indicated that a high number of microvessels adjacent to the tumor as a measure of tumor angiogenesis is an unfavorable prognostic factor in cutaneous melanoma, mammary carcinoma and non-small cell pulmonary carcinoma. This new application of immunohistochemistry represents a valuable, clinically relevant adjunct to the repertoire of the surgical pathologist.     

The effects of dexamethasone and 1,25-dihydroxyvitamin D3 on osteogenic differentiation of human marrow stromal cells in vitro

Effects of dexamethasone and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] were studied in cultures of adult human marrow stromal cells. In primary culture, dexamethasone (10(-8) M) increased the number of fibroblast colonies formed but decreased their average size. The number of colonies expressing alkaline phosphatase activity was increased, consistent with the enhancement of osteogenic differentiation by this glucocorticoid. In secondary culture, osteogenic differentiation was assessed by measurement of the steady-state levels of particular mRNAs that are characteristic of cells of the osteoblast lineage. The mRNAs for alpha 1(I)-procollagen, alkaline phosphatase, osteopontin and bone sialoprotein were expressed under all culture conditions used. In contrast, osteocalcin mRNA expression was detectable only in cultures treated with 1,25(OH)2D3 (10(-8) M). Addition of 1,25(OH)2D3 to control increased the expression of the mRNAs for alkaline phosphatase and osteopontin but had no significant effect on bone sialoprotein expression. The highest levels of expression of the mRNAs for alkaline phosphatase, bone sialoprotein and osteocalcin were observed in dexamethasone-treated cultures to which 1,25(OH)2D3 had been added. These results demonstrate that, as earlier found in other species, dexamethasone and 1,25(OH)2D3 promote the osteogenic differentiation of human marrow stromal cells as measured by expression of these osteogenic markers.     

Pericytes in the microvasculature

Pericytes, also known as Rouget cells or mural cells, are associated abluminally with all vascular capillaries and post-capillary venules. Differences in pericyte morphology and distribution among vascular beds suggest tissue-specific functions. Based on their location and their complement of muscle cytoskeletal proteins, pericytes have been proposed to play a role in the regulation of blood flow. In vitro studies demonstrating the contractile ability of pericytes support this concept. Pericytes have also been suggested to be oligopotential and have been reported to differentiate into adipocytes, osteoblasts and phagocytes. The mechanisms involved in vessel formation have yet to be elucidated but observations indicate that the primordial endothelium can recruit undifferentiated mesenchymal cells and direct their differentiation into pericytes in microvessels, and smooth muscle cells in large vessels. Communication between endothelial cells and pericytes, or their precursors, may take many forms. Soluble factors such as platelet-derived growth factor and transforming growth factors-beta are likely to be involved. In addition, physical contact mediated by cell adhesion molecules, integrins and gap junctions appear to contribute to the control of vascular growth and function. Development of culture methods has allowed some functions of pericytes to be directly examined. Co-culture of pericytes with endothelial cells leads to the activation of transforming growth factor-beta, which in turn influences the growth and differentiation of the vascular cells. Finally, the pericyte has been implicated in the development of a variety of pathologies including hypertension, multiple sclerosis, diabetic microangiopathy and tumor vascularization.     

Learning people''s names following severe closed-head injury

Endothelin-1 (ET-1) was first found as a vasoconstrictor protein excreted by vascular endothelial cells, but recently ET-1 has been considered to have widespread functions that include regulation of osteochondrogenic metabolism. We analyzed sections of head regions in ET-1 knockout mice that are known to have abnormalities in pharyngeal arch-derived tissues and found that there was severe hypoplasia in facial bones. The hypoplasia suggests that the matrix mineralization system of facial bones is disrupted in ET-1-/- homozygous mice. To elucidate whether osteogenic cells in facial bones are the targets for ET-1 and whether expression of bone matrix genes are modulated by ET-1, we examined gene expression of ET-1 receptors, ETA and ETB, and that of the bone matrix proteins, osteonectin (ON) and osteopontin (OP), both in the head regions of ET-1+/- heterozygous and ET-1-/- homozygous mice by means of in situ hybridization. Different patterns of expression between ETA and ETB mRNAs were observed in both groups. In 18.5 days post coitus fetuses, ETA mRNA was most strongly expressed in osteogenic cells along craniofacial bones, but ETB mRNA was most strongly expressed in trunks of trigeminal nerve. This finding suggests that ET-1 may modulate osteogenic cells through ETA receptor but not through ETB receptor. The expression patterns of ETA, OP, and ON mRNAs were distinct between the two groups. In the lower jaw of ET-1+/- heterozygous mice, the ETA, ON, and OP mRNA positive cells were scattered in the inner and outer regions of the thick bone matrix, but in ET-1-/- homozygous mice, cells containing those mRNAs were located close to each other at the surface of thin bone matrix. However, cellular expression of ON and OP mRNAs in osteogenic cells of ET-1-/- homozygous mice was not suppressed as compared with ET-1+/- heterozygous mice. We conclude that ET-1 may regulate proliferation and migration of osteogenic cells in the maxillofacial region, rather than modulating the expression level of ON and OP mRNAs.     

Similarities in the phenotypic expression of pericytes and bone cells

Bovine brain microvessel pericytes, bone cells, and fibroblasts were grown in tissue culture in 3%, 21%, or 60% oxygen for 7 weeks. Alkaline phosphatase activity was highest in bone cells and pericytes grown in 3% oxygen, with the activity higher in the former than the latter. Alkaline phosphatase activity was very low in fibroblasts at every oxygen concentration. Osteocalcin concentration was higher in bone cells than in pericytes, was not detected in fibroblasts, and in bone cells and pericytes the concentration was highest in 21% oxygen. Other bovine brain microvessel pericytes were grown in 3% or 21% oxygen for 3 to 24 days in the presence or absence of bone morphogenetic protein 2 and in the presence or absence of parathyroid hormone. At Day 3 of culture, alkaline phosphatase activity was highest in 21% oxygen in the presence of bone morphogenetic protein 2. By Day 17 of culture, alkaline phosphatase activity was highest in 3% oxygen whether bone morphogenetic protein was present or not. Cyclic adenosine monophosphate production in pericytes in response to parathyroid hormone stimulation was very modest when compared with that of bone cells, and this response was not found to be significantly altered by bone morphogenetic protein 2, duration of culture, or the oxygen concentration during incubation. These findings show that the microvessel pericyte is capable of exhibiting several oxygen dependent, phenotypic characteristics ascribed to osteoblasts.     

Differential expression of bone and cartilage related genes in fibrodysplasia ossificans progressiva, myositis ossificans traumatica, and osteogenic sarcoma

Fibrodysplasia ossificans progressiva, myositis ossificans traumatica, and osteogenic sarcoma are representative genetic, traumatic, and neoplastic disorders of osteogenesis, respectively. However, the pathology, pathophysiology, and natural history of the disorders differ substantially. Gene expression related to bone induction was studied in these disorders. Primary cell lines established from lesional tissues derived from each of these disorders expressed different patterns of protooncogenes, bone morphogenetic protein genes, and bone phenotype specific genes. The osteogenic sarcoma cell line expressed the entire repertoire bone morphogenetic proteins 1 to 7, c-fos and c-jun messenger ribonucleic acids. Myositis ossificans traumatica cells expressed phenotype markers similar to those of the osteogenic sarcoma cells, and expressed bone morphogenetic proteins 1, 4, and 6 and c-fos messenger ribonucleic acids, but not c-jun messenger ribonucleic acid. Fibrodysplasia ossificans progressiva early lesional cells demonstrated specific over-expression of bone morphogenetic protein 4 messenger ribonucleic acid. Differential expression of genes related to osteogenesis have important implications for understanding the earliest molecular events in normal and dysregulated osteogenesis in humans.     

Regulatory role of osteogenic growth polypeptides in bone formation and hemopoiesis

Osteogenic growth polypeptides such as the osteogenic growth peptide (OGP), fragments of the parathyroid hormone (PTH), and insulin-like growth factors (IGF) regulate bone cell activity in vitro and may affect in vivo osteoblastic functions in an autocrine, paracrine, or endocrine manner. Several growth polypeptides capable of regulating osteogenesis circulate in the blood in an inactive form, complexed to parent molecules or binding proteins. During postablation bone marrow regeneration these factors may be activated, released from the blood clot, and together with locally produced polypeptides mediate the initial intramedullary/systemic osteogenic phase of this process. Then osteogenic growth polypeptides expressed by osteoblasts and other stromal cells have the potential to promote the second phase of regeneration that consists of osteoclastogenesis, resorption of the transient intramedullary bone, and hemopoiesis. This is probably an indirect effect inasmuch as these polypeptides can regulate the stromal cell expression of hemopoietic factors such as macrophage colony stimulating factor (M-CSF), granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 6 (IL-6), and the stem cell factor (SCF). The postablation marrow regeneration model is suitable for studying the expression and activity of osteogenic growth polypeptides and already has been used to assess the effect of aging on these parameters. Clinically, the osteogenic growth polypeptides and marrow regeneration have a potential role in osteoporosis therapy, implant and corrective bone surgery, and bone marrow transplantation.     

Tissue chambers--a useful model for in vivo studies of cytokine production in the pig

An in vivo tissue chamber model was developed to enable studies of local cytokine production and cellular events during inflammatory and immune reactions in the pig. Tissue chambers made of sialistic rubber tubing were surgically implanted in the subcutaneous tissue- and samples of tissue chamber fluid (TCF) and inflammatory cells were collected by aspiration with a syringe. To evaluate the model for local cytokine production, two cytokine inducers, polyribinosinic-polyribocytidylic acid (poly I:C) and fixed Aujeszky's disease virus infected PK15 cells (ADV-PK15), were injected into the tissue chambers and samples of TCF were collected 0, 4, 8, 12, 24 and 48 h post injection. Poly I:C injections induced local production of interferon-alpha (IFN-alpha) as well as tumor necrosis factor (TNF) in the TCF but kinetic differences in the production of the cytokines were noted. Poly I:C also induced an increase in cell numbers in the TCF, mainly due to increased neutrophil numbers. Injections of ADV-PK15 induced local IFN-alpha production in the TCF as long as the pigs were serologically negative to ADV. Immunofluorescence and in situ hybridization techniques could be applied for characterization of TCF cells. Moreover, cells recovered from the tissue chambers were viable and could be used in functional in vitro tests. Taken together, this tissue chamber model could prove very useful in in vivo studies of inflammatory/immune responses and cytokine production in the pig.     

Human cord blood cells as targets for gene transfer: potential use in genetic therapies of severe combined immunodeficiency disease

Human cord blood (CB) contains large numbers of both committed and primitive hematopoietic progenitor cells and has been shown to have the capacity to reconstitute the lympho-hematopoietic system in transplant protocols. To investigate the potential usefulness of CB stem and progenitor cell populations to deliver new genetic material into the blood and immune systems, we have transduced these cells using retroviral technology and compared the efficiency of gene transfer into CB cells with normal adult human bone marrow cells using a variety of infection protocols. Using two retroviral vectors which differ significantly in both recombinant viral titers and vector design, low density CB or adult bone marrow (ABM) cells were infected, and committed progenitor and more primitive hematopoietic cells were analyzed for gene expression by G418 drug resistance (G418r) of neophosphotransferase and protein analysis for murine adenosine deaminase (mADA). Standard methylcellulose progenitor assays were used to quantitate transduction efficiency of committed progenitor cells, and the long term culture-initiating cell (LTC-IC) assay was used to quantitate transduction efficiency of more primitive cells. Our results indicate that CB cells were more efficiently transduced via retroviral-mediated gene transfer as compared with ABM-derived cells. In addition, stable expression of the introduced gene sequences, including the ADA cDNA, was demonstrated in the progeny of infected LTC-ICs after 5 wk in long-term marrow cultures. Expression of the introduced ADA cDNA was higher than the endogenous human ADA gene in the LTC-IC-derived colonies examined. These studies demonstrate that CB progenitor and stem cells can be efficiently infected using retroviral vectors and suggest that CB cells may provide a suitable target population in gene transfer protocols for some genetic diseases.     

Application of the extremum stack to neurological MRI

The decrease in bone volume associated with osteoporosis and age-related osteopenia is accompanied by increased marrow adipose tissue formation. Reversal of this process may provide a novel therapeutic approach for osteopenic disorders. We have shown that cells cultured from human trabecular bone are not only osteogenic, but are able also to undergo adipocyte differentiation under defined culture conditions. Osteoblast differentiation was induced by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and adipocyte differentiation by dexamethasone (dex) plus 3-isobutyl-1-methylxanthine (IBMX) treatment. Adipogenesis was characterized by lineage-specific enzyme and gene activities, alpha-glycerophosphate-3-dehydrogenase activity, fatty acid binding protein, aP2 and lipoprotein lipase expression. Osteoblastogenesis was assessed by osteoblast characteristic 1,25(OH)2D3 induction of alkaline phosphatase activity and osteoblast-specific 1,25(OH)2D3-induced osteocalcin synthesis and release. We provide evidence for a common pluripotent mesenchymal stem cell that is able either to undergo adipogenesis or osteoblastogenesis, using clonal cell lines derived from human trabecular bone cell cultures. Adipogenesis can be induced also by long chain fatty acids and the thiazolidinedione troglitazone. Dex plus IBMX-induced adipogenesis can be inhibited by interleukin-1beta, tumor necrosis factor-alpha, and transforming growth factor-beta. Interestingly, and in contrast to extramedullary adipocyte differentiation as shown by mouse 3T3L-1 and a human liposarcoma SW872 cell line, trabecular bone adipogenesis was unaffected by insulin. Also, the formation of fully differentiated adipocytes from trabecular bone cells after troglitazone treatment and long chain fatty acids was dependent on increased expression of the nuclear hormone receptor peroxisome proliferator-activated receptor gamma2 caused by dex plus IBMX. Specific inhibition of marrow adipogenesis and promotion of osteoblastogenesis of a common precursor cell may provide a novel therapeutic approach to the treatment of osteopenic disorders.     

Coexpression of hepatocyte growth factor and receptor (Met) in human breast carcinoma

Expression of hepatocyte growth factor (HGF) and HGF receptor (HGFR, product of the met proto-oncogene) mRNA were examined by nonisotopic in situ hybridization in a spectrum of benign and malignant human breast tissues. mRNA for both HGFR and HGF was detected in benign ductal epithelium. Epithelial expression of HGF mRNA was particularly intense in regions of ductal epithelial hyperplasia. Positive expression of HGF (but not HGFR) mRNA was also found in adipocytes, endothelial cells, and to varying degrees in stromal fibroblasts. In 12 of 12 cases of ductal carcinoma in situ and infiltrating ductal carcinoma, carcinoma cells showed a heterogeneous pattern of expression for both HGFR and HGF mRNA. In infiltrating ductal carcinomas, intense expression of HGFR mRNA was not restricted to ductular structures but as also seen in non-duct-forming carcinoma cells. The same zones of the tumors (most commonly at the advancing margins) that expressed strongly HGFR mRNA often were also strongly positive for HGF mRNA, suggesting a possible autocrine effect. The expression pattern of HGFR protein in 25 cases including the same series of tissues used for in situ hybridization analysis was similar to that of HGFR mRNA, as determined by an immunoperoxidase technique. The finding that HGFR is expressed by both benign and malignant epithelium, and its not restricted to duct-forming structures, suggests that, although the potential for HGF/HGFR binding is maintained in malignancy, the response to ligand binding at the level of the receptor or the cellular response to receptor activation may change at some point during progression.     

Growth and differentiation of human bone marrow osteoprogenitors on novel calcium phosphate cements

Materials that augment bone cell proliferation and osteogenic activity have important therapeutic implications for bone regeneration and for use in skeletal reconstruction and joint replacement. We have studied the growth and interactions of human bone marrow cells on a variety of new cement composites in vitro. These cement materials are composed of calcium-deficient hydroxyapatites, carbonated apatite and amorphous calcium phosphate. Cell proliferation was significantly reduced and cell differentiation increased in the presence of these cements compared with cells cultured on tissue culture plastic. Alkaline phosphatase, one of the markers of the osteoblast phenotype, was dramatically stimulated by 3 of the 4 cements examined between day 4 and day 10, above levels observed following culture of human osteoblasts on plastic alone. Photomicroscopic examination demonstrated growth and close integration of bone marrow cells and 3 of the composites. Longer term marrow cultures (15 day) on the cements confirmed the stimulation of cell differentiation over proliferation. From these studies, enhanced osteoblastic differentiation was observed on a 70% carbonated apatite, which has a composition similar to bone mineral, whereas, cell toxicity was observed on cells grown on amorphous calcium phosphate. This in vitro culture system demonstrates the use of human bone marrow cells for the potential evaluation of new biomaterials and the development of a novel carbonated apatite that may be of potential use in orthopaedic implants.     

FGF-, BMP- and Shh-mediated signalling pathways in the regulation of cranial suture morphogenesis and calvarial bone development

The development of calvarial bones is tightly co-ordinated with the growth of the brain and needs harmonious interactions between different tissues within the calvarial sutures. Premature fusion of cranial sutures, known as craniosynostosis, presumably involves disturbance of these interactions. Mutations in the homeobox gene Msx2 as well as the FGF receptors cause human craniosynostosis syndromes. Our histological analysis of mouse calvarial development demonstrated morphological differences in the sagittal suture between embryonic and postnatal stages. In vitro culture of mouse calvaria showed that embryonic, but not postnatal, dura mater regulated suture patency. We next analysed by in situ hybridisation the expression of several genes, which are known to act in conserved signalling pathways, in the sagittal suture during embryonic (E15-E18) and postnatal stages (P1-P6). Msx1 and Msx2 were expressed in the sutural mesenchyme and the dura mater. FGFR2(BEK), as well as Bmp2 and Bmp4, were intensely expressed in the osteogenic fronts and Bmp4 also in the mesenchyme of the sagittal suture and in the dura mater. Fgf9 was expressed throughout the calvarial mesenchyme, the dura mater, the developing bones and the overlying skin, but Fgf4 was not detected in these tissues. Interestingly, Shh and Ptc started to be expressed in patched pattern along the osteogenic fronts at the end of embryonic development and, at this time, the expression of Bmp4 and sequentially those of Msx2 and Bmp2 were reduced, and they also acquired patched expression patterns. The expression of Msx2 in the dura mater disappeared after birth. FGF and BMP signalling pathways were further examined in vitro, in E15 mouse calvarial explants. Interestingly, beads soaked in FGF4 accelerated sutural closure when placed on the osteogenic fronts, but had no such effect when placed on the mid-sutural mesenchyme. BMP4 beads caused an increase in tissue volume both when placed on the osteogenic fronts and on the mid-sutural area, but did not effect suture closure. BMP4 induced the expression of both Msx1 and Msx2 genes in sutural tissue, while FGF4 induced only Msx1. We suggest that the local application of FGF on the osteogenic fronts accelerating suture closure in vitro, mimics the pathogenesis of human craniosynostosis syndromes in which mutations in the FGF receptor genes apparently cause constitutive activation of the receptors. Taken together, our data suggest that conserved signalling pathways regulate tissue interactions during suture morphogenesis and intramembranous bone formation of the calvaria and that morphogenesis of mouse sagittal suture is controlled by different molecular mechanisms during the embryonic and postnatal stages. Signals from the dura mater may regulate the maintenance of sutural patency prenatally, whereas signals in the osteogenic fronts dominate after birth.     

Traumatic myositis ossificans. Posttraumatic non-neoplastic heterotopic ossification

Myositis ossificans traumatica (MOT) is a nonneoplastic, heterotopic ossification of soft tissues i.e. skeletal muscle, tendons, aponeuroses and fascia. It is often encountered in young male athletes participating in contact sports as a result of a single or repeated contusion. MOT tends to be solitary, localized and well circumscribed with a self-limited growth potential that may culminate in regression. The pathogenesis of MOT is still enigmatic. Recent animal experiments have led to a theory that mesenchymal connective tissue cells, undergo metaplasia induced by trauma and probably osteogenic proteins, to fibroblasts and osteoblasts. These cells deposit and structure osteoid centripetally in the lesion. As the lesion matures, cancellous bone develops into mature, lamellar bone in the periphery of the lesion. In its earlier stages MOT is easily cytologically and radiologically confused with osteogenic sarcoma. The management of MOT is largely conservative and the principles are of considerable value to physicians and physiotherapists engaged in the treatment of sports injuries. This article reviews the various forms of myositis ossificans as well as the pathology, diagnosis and treatment options.     

Enhancement of bone formation in the setting of repeated tissue deformation

The purpose of this study was to investigate whether the osteoinductive recombinant human bone morphogenetic protein 2, combined with a collagen carrier, could enhance bone formation when exposed to controlled amounts of tissue deformation. Chambers that allow for the multiple harvestings of tissue specimen were used. The devices were implanted in the tibial metaphyses of skeletally mature New Zealand White rabbits. A tissue ingrowth canal in each device either was left empty or filled with a collagen carrier with or without 0.6 microgram of recombinant human bone morphogenetic protein 2. The tissue ingrowth canal was deformed cyclically during a period of 2 minutes daily, according to a previously described deformation protocol. The tissue that developed in the chambers was harvested every 3 weeks. Undecalcified histologic sections of each tissue sample were stained with trichrome and von Kossa stains and subjected to histomorphometric analysis. It was found that deformation decreased the area occupied by bone trabeculae in the empty chambers and carrier controls. The amount of bone formed in the chambers treated with bone morphogenetic protein 2 was significantly greater than that in the chambers subjected to micromotion and left empty or implanted with the collagen carrier. The amount of bone in chambers with motion and bone morphogenetic protein 2 was equal to that in chambers left empty and not subjected to micromotion. Qualitative histologic analysis of the bone formed with bone morphogenetic protein 2 revealed normal bone trabeculae. These findings indicate that bone morphogenetic protein 2 may be useful in augmenting bone formation in conditions that otherwise would favor the formation of fibrous tissue.     

Misrepresentation of publications by applicants for radiology fellowships: is it a problem?

In light of the recently described experimental technique of in vivo bone reconstitution with biotechnologic methods (from bone marrow stromal cells) and the prefabrication flap procedures, the possibility to obtain autologous bone growth in a myocutaneous flap, thus creating a composite osteomyocutaneous preformed flap, is postulated. Human bone marrow stromal cells were delivered into the latissimus dorsi of athymic mice by a porous hydroxyapatite ceramic model. Eight weeks after the implantation, histologic examination revealed the presence of spongious bone tissue. A simple myocutaneous flap was thus transformed into a composite osteomyocutaneous flap. This flap is called the biotechnologic prefabricated flap, because it was the result of ex vivo expanded osteogenic precursor cells and in vivo bone tissue neoformation. The shape of the bone flap was exactly the same as the shape of the ceramic model used. A possible clinical application may be the correction of skeletal defects. The advantages of this procedure are simple surgical execution, the possibility of preshaping the graft to the exact characteristics of the defect, and the availability of autogenous donor tissue without donor site morbidity.     

Membrane-type-1 matrix metalloproteinase is abundantly expressed in fibroblasts and osteoclasts at the bone-implant interface of aseptically loosened joint arthroplasties in situ

OBJECTIVE: To investigate the distribution pattern of membrane-type-1 matrix metalloproteinase (MT1-MMP) within the synovial-like interface membranes of failed prosthetic joints. METHODS: Interface tissue around loose arthroplasties containing both fibrous membrane and attached bone was obtained from 6 patients at revision surgery. In situ hybridization with digoxigenin labeled RNA probes was applied to investigate MT1-MMP expression in paraffin sections of the samples. In addition, double labeling using immunohistochemistry was performed to characterize MT1-MMP producing cells. RESULTS: Apart from being present in fibroblasts, MT1-MMP was also found expressed in osteoclasts at sites of bone resorption. Our results revealed no expression of MT1-MMP at parts of the membrane that originally had been located next to the prosthesis. In contrast, abundant staining for MT1-MMP was observed at sites attached to bone. MT1-MMP mRNA expression was more intense at those sites of bone resorption covered by a thicker interface membrane. CONCLUSION: These results indicate a role for MT1-MMP not only in matrix degradation by fibroblasts but also in osteoclast mediated bone resorption. Given the ability of MT1-MMP to activate MMP2 and MMP13, they suggest also that osteoclasts might contribute to matrix degradation by activating these MMP. This could be of potential interest not only for other conditions in which bone resorption by fibroproliferative tissue plays a role, but also to design novel strategies to prevent loosening of prosthetic joints.