Enhanced engraftment of EPO-transduced human bone marrow stromal cells transplanted in a 3D matrix in non-conditioned NOD/SCID mice

Intravenous infusion of bone marrow stromal cells (BMSCs) has been proposed as a means to support hematopoiesis in bone marrow transplantation or as a vehicle for gene therapy. However, it seems that this route of injection leads to engraftment of a small proportion of BMSCs, possibly because they are unable to cross the endothelial barrier. We have transplanted human BMSCs, ex vivo expanded and transduced with a retrovirus encoding the human erythropoietin gene, either intravenously or subcutaneously with or without a tridimensional scaffold in non-conditioned NOD/SCID mice. Efficiency of engraftment was evaluated monitoring the hematocrit levels. Systemic infusion never significantly increased hematocrit levels, whereas subcutaneous transplantation of the same number of cells induced an important increase of the hematocrit (approximately 70%) for at least 2 months. A substantial increase in the length of the response was observed when cells were subcutaneously transplanted in a tridimensional scaffold. To determine whether the transient effect was due to cell loss or to reduction in expression, the cells implanted into a tridimensional scaffold were recovered, expanded in vitro, and re-implanted in a new group of mice. Again the hematocrit levels rose 2 weeks after transplantation ( approximately 70%). These results demonstrate that ex vivo expanded human BMSCs are not quantitatively transplantable by systemic infusion in non-conditioned recipients, whereas the local implantation into a tridimensional scaffold allows long-term engraftment and efficient expression of a foreign gene.

Extracellular fatty acid binding protein (ex-FABP) is a stress protein expressed during chondrocyte and myoblast differentiation

OBJECTIVE

We have isolated and characterized in our laboratory a lipocalin specifically binding unsaturated long chain fatty acids (Ex-FABP). In developing chicken embryo long bones, Ex-FABP first appears at the boundary of the cone of hypertrophic cartilage. 'In vitro' EX-FABP is highly expressed by differentiating hypertrophic chondrocytes. Ex-FABP is expressed also in the forming myotubes both 'in vivo' and 'in vitro'. In cultured chondrocytes, Ex-FABP expression is strongly induced by treatment with inflammatory agents such as the bacterial liposaccharide LPS or interleukin-6. The possible mechanism for this induction was investigated. Expression of Ex-FABP was studied in other stress conditions.

DESIGN

To investigate a possible mechanism for Ex-FABP induction by LPS or interleukin-6, we have cultured the cells in the presence of either hydrogen peroxide or the NO donor SNAP (S-nitrosil-acetil-D, L-penicillamine), two agents known to produce cellular stresses through the activation of specific signalling pathways. To investigate Ex-FABP expression in other stress conditions, chondrocytes were cultured for 3 days in the presence of alpha,alpha-dipyridyl, an agent inhibiting prolyl hydroxylase activity and collagen secretion. Supplement of this agent to the culture medium results in an impairment of collagen secretion and assembly and the consequent altered interaction of the cell with the surrounding extracellular matrix. In addition Ex-FABP expression was studied also in chondrocytes cultured in the absence of serum, a stress condition activating cell defence mechanisms.

RESULTS

We have excluded that induction of Ex-FABP expression by inflammatory agents is mediated by oxidative stress or NO production. Ex-FABP expression was induced also by changes in the hypertrophic chondrocyte microenvironment, considered either as extracellular matrix surrounding the cell in culture or as nature and concentration of growth factor in the culture medium.

CONCLUSIONS

No definitive data are so far available on the possible role of Ex-FABP when induced by cellular stresses. The capacity of the protein to specifically bind and transport unsaturated long chain fatty acids suggests that lipid metabolism and fatty acid utilization by the cells may be involved. Based on literature data the NRL/N-GAL (neu-related lipocalin/neutrophil gelatinase-associated lipocalin) protein was proposed as a possible mammal counterpart of the chick Ex-FABP. We have suggested that Ex-FABP and NRL/NGAL expression in forming bones and muscles is part of a 'physiological' acute phase response. Interestingly the expression of Ex-FABP and NRL/NGAL is also activated in osteoarthritic cartilage and in the case of NRL/N-GAL during neoplastic transformation of chondrogenic lineage cells.

Effect of different growth factors on the chondrogenic potential of human bone marrow stromal cells

OBJECTIVE

The aim of this study was to investigate the effects of different growth factors on the chondrogenic potential of human bone marrow stromal cells (BMSC).

DESIGN

Different growth factors which have been shown to sustain the osteogenic potential of BMSC during their 'in vitro' expansion were assayed for the maintenance of the chondrogenic potential. We compared the ability of BMSC to reconstitute cartilage in vitro with their ability to form bone on hydroxyapatite microporous particles in an ectopic bone formation assay.

RESULTS

Among the factors assayed, fibroblast growth factor 2 (FGF2) was the most effective in promoting growth of BMSC 'in vitro'. For all growth factors tested, we have found a complete overlap of the enhancement of chondrogenic and osteogenic potential. Any factor, either promoting or depressing bone formation, exerted the same effect on the chondrogenic potential of human BMSC. In particular, FGF2, either alone or in combination with other factors, strongly supported the formation of bone as well as of cartilage.

CONCLUSIONS

We conclude that FGF2 maintains human BMSC in an immature state allowing their 'in vitro' expansion. Expanded cells retain the chondro- osteogenic potential. Interestingly, the chondrogenic potential of BMSC 'in vitro' is directly related to their ability to form bone 'in vivo'. BMSC expanded 'ex vivo' are presently being proposed for cell therapy of bone defects. 'In vitro' chondrogenesis may be regarded as a rapid prediction assay to assess cell ability to form bone after 'in vivo' transplant.

Microenvironment and stem properties of bone marrow-derived mesenchymal cells

Adult stem cells are self-renewing, pluripotent, and able to repopulate the tissue in which they reside. Cells endowed with these properties have been isolated from several tissues and an increasing number of reports provide evidence of their ability, following transplantation, to engraft host tissues other than those of their origin. In this setting, interest in the well-documented capacity of bone marrow stromal cells to undergo multilineage differentiation is growing. Neural and cardiomyogenic lineages have recently been proposed as additional differentiative pathways of these cells. However, culture conditions and inductive molecules can alter the behavior of bone marrow stromal cells and the microenvironment is critical for proper in vivo delivery. The maintenance of their stem properties and the possibility of reprogramming their commitment is a field of primary interest given the potential use of these cells in regenerative medicine. We discuss here how the microenvironmental cues, and the growth factors that physiologically govern commitment and subsequent differentiation, influence the properties of bone marrow stromal cells and modulate their engraftment into host tissues.

High-dose chemotherapy shows a dose-dependent toxicity to bone marrow osteoprogenitors: a mechanism for post-bone marrow transplantation osteopenia

BACKGROUND

Osteoporosis is a sequela of hemopoietic cell transplantation with a complex multifactorial pathogenesis in which the relative role of chemotherapy and irradiation is not completely understood. Therefore, the authors investigated the toxicity of chemotherapy-only conditioning regimens on bone homeostasis and bone marrow osteoprogenitors, its dose dependency, and the mechanism of chemotherapy-induced osteopenia.

METHODS

Fifty-one patients with high-grade non-Hodgkin lymphoma or breast carcinoma who had been treated previously with high-dose + peripheral blood progenitor cell or conventional chemotherapy or who had not received any treatment (prechemotherapy) were enrolled. The authors measured the bone marrow colony-forming unit fibroblast (CFU-f) and long-term culture-initiating cell frequency, forearm bone mineral density, serum osteotropic hormones and metabolic markers of bone formation (plasma osteocalcin), and resorption (urinary collagen I C-crosslinks).

RESULTS

Both high-dose chemotherapy regimens caused a 50% reduction in CFU-f frequency, independently of gonadal function status, whereas conventional chemotherapy and prechemotherapy groups were unaffected. Bone mineral density was measured in 26 non-Hodgkin lymphoma patients and again only high-dose chemotherapy caused a 10% loss in cortical bone and 20% in trabecular bone. No endocrine abnormality was found except for the secondary amenorrhea uniformly induced in the high-dose chemotherapy group. In these patients, plasma osteocalcin unexpectedly failed to increase in response to the menopausal increase in bone resorption rate, showing a selective impairment of the osteoblast compartment to cope with increased functional demand.

CONCLUSIONS

Chemotherapy without irradiation shows a dose-dependent toxicity to bone marrow stromal osteoprogenitors and can cause osteopenia by direct damage of the osteoblastic compartment, as a mechanism distinct from and summable to hypogonadism.

Bone marrow stromal damage after chemo/radiotherapy: occurrence, consequences and possibilities of treatment

High dose chemotherapy (CT) followed by bone marrow transplant (BMT) is increasingly used for the treatment of both hematological and solid neoplasms, but an understanding of its late consequences on the marrow microenvironment is still only at its beginning. It is in fact known that marrow stroma is damaged by high-dose cytotoxic therapy and by radiation exposure. However little is known on the extent of this damage and on the self-repair ability of the stroma. The damage of the stromal microenvironment affects the long-term stem cell engraftment and the maintenance of hemopoietic functions. Furthermore, marrow stroma also represents a progenitor compartment for endosteal osteoblasts, and therefore its damage implies alterations of bone metabolism. Indeed, osteoporosis has recently been recognized as a consequence, of BMT, but only a few studies have been performed to establish the functional status of the stromal compartment after treatment with cytotoxic drugs with or without total body irradiation (TBI) and its role in post-BMT sequelae.

Unrelated donor marrow transplantation: an update of the experience of the Italian Bone Marrow Group (GITMO)

BACKGROUND AND OBJECTIVES

Unrelated donor bone marrow transplant (UD-BMT) has become an attractive alternative source of hematopoietic cells for patients lacking a matched sibling. The aim of this paper was to report on results of the 696 UD BMTs performed in 31 Italian institutions during the first 10 years of activity of the Italian Bone Marrow Donor Registry (IBMDR).

EVIDENCE AND INFORMATION SOURCES

In 1989 the Italian Bone Marrow Transplant Group (GITMO) established the IBMDR to facilitate donor search and marrow procurement for patients lacking an HLA identical sibling. By end of December 1999, 260,000 HLA-A, B typed volunteer donors had been cumulatively registered and 2,620 searches had been activated for Italian patients. At least one HLA-A, B, DRB1 matched donor was found for 54% of the patients and 696 UD BMTs were performed. In 50% of cases the donor was found in the IBMDR and in 50% in 15 other Registries. The average time from search activation to transplant was 6 months for disease other than CML. For CML it was 14 months. Actuarial 12-month transplant-related mortality (TRM) was 68% in patients grafted between 1979 and 1992 and 44% for patients grafted after 1993. Twenty-eight per cent of patients developed grade III or IV acute GvHD and 24% developed extensive chronic GvHD. The rate of disease free survival at three years was 57% for patients with 1st chronic phase CML, 37% for patients with 1st or 2nd CR ALL, 31% for AML or MDS patients 18 years of age and 54% for patients with inborn errors.

PERSPECTIVES

We conclude that the IBMDR has benefited a substantial number of patients lacking a matched sibling and has facilitated the recruitment of UDs into the international donor pool. The long time required for the search is the major obstacle to the success of this programme. This suggests that early transplant and a decrease in TRM could further improve these encouraging results.

Avidin expression during chick chondrocyte and myoblast development in vitro and in vivo: regulation of cell proliferation

Avidin is a major [(35)S]methionine-labeled protein induced by bacterial lipopolysaccharide (LPS) and interleukin 6 (IL-6) in cultured chick embryo myoblasts and chondrocytes. It was identified by N-terminal sequencing of the protein purified from conditioned culture medium of LPS-stimulated myoblasts. In addition, avidin was secreted by unstimulated myoblasts and chondrocytes during in vitro differentiation; maximal expression being observed in differentiated myofibers and hypertrophic chondrocytes. In developing chick embryos, immunohistochemistry revealed avidin in skeletal muscles and growth plate hypertrophic cartilage. Avidin was secreted into culture as a biologically active tetramer. Exogenous avidin added to the medium of proliferating chondrocytes progressively inhibited cell proliferation, whereas addition of avidin to differentiating chondrocytes in suspension allowed full cell differentiation. No toxic effects for the cells were observed in both culture conditions. Western blots of samples from cytosolic extracts using alkaline-phosphatase-conjugated streptavidin showed three biotin-containing proteins. Acetyl-CoA carboxylase was identified by specific antibodies. Based on these data, we propose that avidin binds extracellular biotin and regulates cell proliferation by interfering with fatty acid biosynthesis during terminal cell differentiation and/or in response to inflammatory stimuli.

Developmental control of chondrogenesis and osteogenesis

During vertebrate embryogenesis, bones of the vertebral column, pelvis, and upper and lower limbs, are formed on an initial cartilaginous model. This process, called endochondral ossification, is characterized by a precise series of events such as aggregation and differentiation of mesenchymal cells, and proliferation, hypertrophy and death of chondrocytes. Bone formation initiates in the collar surrounding the hypertrophic cartilage core that is eventually invaded by blood vessels and replaced by bone tissue and bone marrow. Over the last years we have extensively investigated cellular and molecular events leading to cartilage and bone formation. This has been partially accomplished by using a cell culture model developed in our laboratory. In several cases observations have been confirmed or directly made in the developing embryonic bone of normal and genetically modified chick and mouse embryos. In this article we will review our work in this field.

Osteobiology, strain, and microgravity. Part II: studies at the tissue level

Loading microgravity, and/or defective mechanical strain-forces have important effects on bone cells and bone quality and quantity. The complex mechanisms induced by strain and microgravity on bone cells have been reviewed in Part I of this paper. In Part II, we have considered the data on the alterations induced by unloading and microgravity on the skeleton and the mechanisms that are involved at the tissue level in animals and humans.

Unrelated donor marrow transplantation: an update of the experience of the Italian Bone Marrow Transplant Group (GITMO)

Unrelated donor bone marrow transplant (UD-BMT) has become an attractive alternative source of hematopoietic cells for patients lacking a matched sibling. The aim of this paper was to report on results of the 696 UD BMTs performed in 31 Italian institutions during the first 10 years of activity of the Italian Bone Marrow Donor Registry (IBMDR). In 1989 the Italian Bone Marrow Transplant Group (GITMO) established the IBMDR to facilitate donor search and marrow procurement for patients lacking an HLA identical sibling. By end of December 1999, 260,000 HLA-A, B typed volunteer donors had been cumulatively registered and 2,620 searches had been activated for Italian patients. At least one HLA-A, B, DRB1 matched donor was found for 54% of the patients and 696 UD BMTs were performed. In 50% of cases the donor was found in the IBMDR and in 50% in 15 other Registries. The average time from search activation to transplant was 6 months for disease other than CML. For CML it was 14 months. Actuarial 12-month transplant-related mortality (TRM) was 68% in patients grafted between 1979 and 1992 and 44% for patients grafted after 1993. Twenty-eight per cent of patients developed grade III or IV acute GvHD and 24% developed extensive chronic GvHD. The rate of disease free survival at three years was 57% for patients with 1st chronic phase CML, 37% for patients with 1st or 2nd CR ALL, 31% for AML or MDS patients < or = 18 years of age and 54% for patients with inborn errors. We conclude that the IBMDR has benefited a substantial number of patients lacking a matched sibling and has facilitated the recruitment of UDs into the international donor pool. The long time required for the search is the major obstacle to the success of this programme. This suggests that early transplant and a decrease in TRM could further improve these encouraging results.

Treatment of "stable" vitiligo by Timedsurgery and transplantation of cultured epidermal autografts

OBJECTIVE

To optimize melanocyte/keratinocyte co-cultivation and to evaluate the effectiveness of autologous cultured epidermal grafts in the surgical treatment of stable vitiligo.

DESIGN

After optimization of melanocyte/keratinocyte cultures, achromic lesions were disepithelialized by means of programmed diathermosurgery (Timedsurgery) and covered with autologous epidermal grafts prepared from secondary cultures. Melanocyte content was evaluated by dopa reaction. The percentage of repigmentation was calculated using a semiautomatic image analysis system.

SETTING

A biosafety level 3 cell culture facility and a dermatological department in a hospital.

PATIENTS

Thirty-two patients carrying different types of vitiligo were admitted to the study and treated with autologous cultured epidermal grafts. Inclusion criteria were (1) failure of at least 2 standard medical approaches; (2) no therapy for at least 12 months; (3) absence of progression of old lesions, absence of appearance of new lesions, and absence of Koebner phenomenon within the past 18 months; and (4) absence of autoimmune disorders.

RESULTS

One hundred five achromic lesions (a total of 6078.2 cm(2)) were treated. The average percentage of repigmentation, evaluated after 12 to 36 months of follow-up, was 77%. Independent of the type of vitiligo, average percentages of repigmentation of extremities and periorificial sites were 8% (31.8 cm(2) repigmented/420.5 cm(2) transplanted) and 35% (17.6 cm(2) repigmented/50.0 cm(2) transplanted), respectively. Percentages of repigmentation of all other body sites ranged from 88% to 96% (4329.7 cm(2) repigmented/4675.2 cm(2) transplanted). Color matching was good and scar formation was not observed.

CONCLUSION

Cultured epidermal grafts can be considered a real therapeutic surgical alternative for "stable" but not lip-tip vitiligo.

Ex-FABP: a fatty acid binding lipocalin developmentally regulated in chicken endochondral bone formation and myogenesis

Extracellular fatty acid binding protein (Ex-FABP) is a 21 kDa lipocalin specifically binding fatty acids, expressed during chicken embryo development in hypertrophic cartilage, in muscle fibers and in blood granulocytes. In chondrocyte and myoblast cultures Ex-FABP expression is increased by inflammatory agents and repressed by anti-inflammatory agents. In adult cartilage Ex-FABP is expressed only in pathological conditions such as in dyschondroplastic and osteoarthritic chickens. The possible mammalian counterpart is the Neu-related lipocalin (NRL), a lipocalin overexpressed in rat mammary cancer; NRL is homologous to the human neutrophil gelatinase associated lipocalin (NGAL) expressed in granulocytes and in epithelial cells in inflammation and malignancy and to the Sip24 (super-inducible protein 24), an acute phase lipocalin expressed in mouse after turpentine injection. Immunolocalization and in situ hybridization showed that NRL/NGAL is expressed in hypertrophic cartilage, in forming skeletal muscle fibers and in developing heart. In adult cartilage NRL/NGAL was expressed in articular cartilage from osteoarthritic patients and in chondrosarcoma. Moreover, NRL was induced in chondrocyte and myoblast cultures by an inflammatory agent. We propose that these lipocalins (Ex-FABP, NRL/NGAL, Sip24) represent stress proteins physiologically expressed in tissues where active remodeling is taking place during development and also present in tissues characterized by an acute phase response due to pathological conditions.

Proliferation kinetics and differentiation potential of ex vivo expanded human bone marrow stromal cells: Implications for their use in cell therapy

Bone marrow stromal cells (BMSC) are an attractive target for novel strategies in the gene/cell therapy of hematologic and skeletal pathologies, involving BMSC in vitro expansion/transfection and reinfusion. We investigated the effects of in vitro expansion on BMSC pluripotentiality, proliferative ability, and bone-forming efficiency in vivo. BMSC from three marrow donors were cultured to determine their growth kinetics. At each passage, their differentiation potential was verified by culture in inductive media and staining with alizarin red, alcian blue, or Sudan black, and by immunostaining for osteocalcin or collagen II. First passage cells were compared to fresh marrow for their bone-forming efficiency in vivo. Stromal cell clones were isolated from five donors and characterized for their multidifferentiation ability. The lifespan and differentiation kinetics of five of these clones were determined. After the first passage, BMSC had a markedly diminish proliferation rate and gradually lost their multiple differentiation potential. Their bone-forming efficiency in vivo was reduced by about 36 times at first confluence as compared to fresh bone marrow. Experiments on the clones yielded comparable results. Culture expansion causes BMSC to gradually lose their early progenitor properties. Both the duration and the conditions of culture could be crucial to successful clinical use of these cells and must be considered when designing novel therapeutic strategies involving stromal mesenchymal progenitor manipulation and reinfusion.

cDNA cloning, characterization and chromosome mapping of the gene encoding human cartilage associated protein (CRTAP)

We have recently isolated and characterized cDNA clones coding for a novel developmentally regulated avian and mouse embryo protein, CASP for Cartilage Associated Protein. Here we describe the isolation and characterization of the gene coding for the human CASP. The comparison of the putative human and mouse protein sequences with the chick sequence revealed an overall high identity (89% and 51%, respectively). Homology search with known DNA and protein sequences showed that CASPs are related to two mammalian nuclear proteins. Here we demonstrate definitively that CASPs are distinct from these nuclear proteins. However, sequence comparison analyses suggest that all of these proteins belong to a new family. In all human tissues examined two CASP mRNA species were detected, whereas a single mRNA and three mRNAs were found in chick and mouse, respectively. The human CASP gene (CRTAP) was assigned to chromosome 3p22 by fluorescence in situ hybridization.

Clonal mesenchymal progenitors from human bone marrow differentiate in vitro according to a hierarchical model

Bone marrow stromal cells can give rise to several mesenchymal lineages. The existence of a common stem/progenitor cell, the mesenchymal stem cell, has been proposed, but which developmental stages follow this mesenchymal multipotent progenitor is not known. Based on experimental evidence, a model of mesenchymal stem cell differentiation has been proposed in which individual lineages branch directly from the same progenitor. We have verified this model by using clonal cultures of bone marrow derived stromal fibroblasts. We have analyzed the ability of 185 non-immortalized human bone marrow stromal cell clones to differentiate into the three main lineages: osteo-, chondro- and adipogenic. All clones but one differentiated into the osteogenic lineage. About one third of the clones differentiated into all three lineages analyzed. Most clones (60-80%) displayed an osteo-chondrogenic potential. We have never observed clones with a differentiation potential limited to the osteo-adipo- or to the chondro-adipogenic phenotype, nor pure chondrogenic and adipogenic clones. How long the differentiation potential of a number of clones was maintained was assessed throughout their life span. Clones progressively lost their adipogenic and chondrogenic differentiation potential at increasing cell doublings. Our data suggest a possible model of predetermined bone marrow stromal cells differentiation where the tripotent cells can be considered as early mesenchymal progenitors that display a sequential loss of lineage potentials, generating osteochondrogenic progenitors which, in turn, give rise to osteogenic precursors.

Autologous bone marrow stromal cells loaded onto porous hydroxyapatite ceramic accelerate bone repair in critical-size defects of sheep long bones

The ability of marrow-derived osteoprogenitor cells to promote repair of critical-size tibial gaps upon autologous transplantation on a hydroxyapatite ceramic (HAC) carrier was tested in a sheep model. Conditions for in vitro expansion of sheep bone marrow stromal cells (BMSC) were established and the osteogenic potential of the expanded cells was validated. Ectopic implantation of sheep BMSC in immunocompromised mice led to extensive bone formation. When used to repair tibial gaps in sheep, cell-loaded implants (n = 2) conducted a far more extensive bone formation than did cell-free HAC cylinders (n = 2) over a 2-month period. In cell-loaded implants, bone formation was found to occur both within the internal macropore space and around the HAC cylinder while in control cell-free implants, bone formation was limited mostly to the outer surface and was not observed in most of the inner pores. As tested in an indentation assay, the stiffness of the complex HAC-bone material was found to be higher in cell-loaded implants compared to controls. Our pilot study on a limited number of large-sized animals suggests that the use of autologous BMSC in conjunction with HAC-based carriers results in faster bone repair compared to HAC alone. Potentially this combination could be used clinically in the treatment of extensive long bone defects.

Expression of NRL/NGAL (neu-related lipocalin/neutrophil gelatinase-associated lipocalin) during mammalian embryonic development and in inflammation

The neu-related lipocalin (NRL) is a protein overexpressed in rat mammary cancer induced by activated neu (HER-2/c-erbB2). This protein belongs to the family of the lipocalins or low molecular weight proteins able to bind and transport small hydrophobic molecules. The NRL homologue in mouse is SIP24, an acute phase protein induced in the animal by turpentine injection; the human homologous protein is NGAL expressed in granulocytes and epithelial cells in pathological conditions, such as inflammation and malignancy. We have investigated NRL expression in developing rat embryos. By immunolocalization we have shown localization of the protein in the hypertrophic region of growth plate cartilage. NRL was particularly enriched in prehypertrophic chondrocytes. In addition, we observed localization of the protein in forming skeletal muscle fibres and in the myocardium of developing heart. In agreement with the immunolocalization data, by in situ hybridization we have demonstrated the presence of the specific mRNA in the same tissues. At an early stage of differentiation, cultured rat embryo-derived chondrocytes did not express NRL; nevertheless expression of the protein was induced in these cells by treatment with an inflammatory agent, such as LPS. By Western blot analysis with specific antibodies we showed protein synthesis by cultured myoblasts also in the absence of LPS treatment, but only when forming myotubes were observed in culture. Stimulation of myoblast cultures with LPS resulted in an enhancement of the NRL expression in well formed myotubes. Our data suggest a role of NRL in cartilage and muscle differentiation. NRL expression was induced by inflammatory agents. We wish to propose that the expression of NRL in hypertrophic chondrocytes and forming myotubes is part of a "physiological" acute phase response occurring during cartilage and muscle development. In this manuscript we also report that NRL is not detectable by immunolocalization in adult cartilage (both articular and tracheal) from normal subjects. On the contrary articular cartilage from osteoarthritic patients was highly positive for the presence of NRL/NGAL. Interestingly the expression of this protein is also activated during neoplastic transformation of chondrogenic lineage cells.

Extracellular fatty acid binding protein (Ex-FABP) modulation by inflammatory agents: "physiological" acute phase response in endochondral bone formation

Ex-FABP, extracellular fatty acid binding protein, is a 21 kDa lipocalin expressed in hypertrophic cartilage, muscle and heart during chick embryo development and in granulocytes. Ex-FABP synthesis was increased in chondrocyte and myoblast cultures by inflammatory agents (LPS; IL6) and repressed by antiinflammatory agents. Expression of Ex-FABP and specific gelatinases is paralleled in hypertrophic cartilage; LPS specifically induced high molecular weight gelatinase ( > 200 kDa). LPS-treated hypertrophic chondrocytes showed increased chemotactic activity for endothelial cells paralleled by increased expression of transferrin. A high amount of Ex-FABP was expressed in adult pathological cartilage both in dyschondroplastic and osteoarthritic chickens. Controls were negative. Ex-FABP could represent a stress protein physiologically expressed in tissues where active remodelling is taking place during development and in tissues characterized by an acute phase response due to pathological conditions. We also suggest that during endochondral bone formation other responses characteristic of a local inflammatory status, such as gelatinase production and angiogenic factor secretion, are "physiologically" activated.

Autologous bone marrow stromal cells loaded onto porous hydroxyapatite ceramic accelerate bone repair in critical-size defects of sheep long bones

The ability of marrow-derived osteoprogenitor cells to promote repair of critical-size tibial gaps upon autologous transplantation on a hydroxyapatite ceramic (HAC) carrier was tested in a sheep model. Conditions for in vitro expansion of sheep bone marrow stromal cells (BMSC) were established and the osteogenic potential of the expanded cells was validated. Ectopic implantation of sheep BMSC in immunocompromised mice led to extensive bone formation. When used to repair tibial gaps in sheep, cell-loaded implants (n = 2) conducted a far more extensive bone formation than did cell-free HAC cylinders (n = 2) over a 2-month period. In cell-loaded implants, bone formation was found to occur both within the internal macropore space and around the HAC cylinder while in control cell-free implants, bone formation was limited mostly to the outer surface and was not observed in most of the inner pores. As tested in an indentation assay, the stiffness of the complex HAC-bone material was found to be higher in cell-loaded implants compared to controls. Our pilot study on a limited number of large-sized animals suggests that the use of autologous BMSC in conjunction with HAC-based carriers results in faster bone repair compared to HAC alone. Potentially this combination could be used clinically in the treatment of extensive long bone defects.

Vascular endothelial growth factor (VEGF) in cartilage neovascularization and chondrocyte differentiation: auto-paracrine role during endochondral bone formation

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) induces endothelial cell migration and proliferation in culture and is strongly angiogenic in vivo. VEGF synthesis has been shown to occur in both normal and transformed cells. The receptors for the factor have been shown to be localized mainly in endothelial cells, however, the presence of VEGF synthesis and the VEGF receptor in cells other than endothelial cells has been demonstrated. Neoangiogenesis in cartilage growth plate plays a fundamental role in endochondral ossification. We have shown that, in an avian in vitro system for chondrocyte differentiation, VEGF was produced and localized in cell clusters totally resembling in vivo cartilage. The factor was synthesized by hypertrophic chondrocytes and was released into their conditioned medium, which is highly chemotactic for endothelial cells. Antibodies against VEGF inhibited endothelial cell migration induced by chondrocyte conditioned media. Similarly, endothelial cell migration was inhibited also by antibodies directed against the VEGF receptor 2/Flk1 (VEGFR2). In avian and mammalian embryo long bones, immediately before vascular invasion, VEGF was distinctly localized in growth plate hypertrophic chondrocytes. In contrast, VEGF was not observed in quiescent and proliferating chondrocytes earlier in development. VEGF receptor 2 colocalized with the factor both in hypertrophic cartilage in vivo and hypertrophic cartilage engineered in vitro, suggesting an autocrine loop in chondrocytes at the time of their maturation to hypertrophic cells and of cartilage erosion. Regardless of cell exposure to exogenous VEGF, VEGFR-2 phosphorylation was recognized in cultured hypertrophic chondrocytes, supporting the idea of an autocrine functional activation of signal transduction in this non-endothelial cell type as a consequence of the endogenous VEGF production. In summary we propose that VEGF is actively responsible for hypertrophic cartilage neovascularization through a paracrine release by chondrocytes, with invading endothelial cells as a target. Furthermore, VEGF receptor localization and signal transduction in chondrocytes strongly support the hypothesis of a VEGF autocrine activity also in morphogenesis and differentiation of a mesoderm derived cell.