Resilient anatomy and local plasticity of naive and stress haematopoiesis

The bone marrow adjusts blood cell production to meet physiological demands in response to insults. The spatial organization of normal and stress responses are unknown owing to the lack of methods to visualize most steps of blood production. Here we develop strategies to image multipotent haematopoiesis, erythropoiesis and lymphopoiesis in mice. We combine these with imaging of myelopoiesis1 to define the anatomy of normal and stress haematopoiesis. In the steady state, across the skeleton, single stem cells and multipotent progenitors distribute through the marrow enriched near megakaryocytes. Lineage-committed progenitors are recruited to blood vessels, where they contribute to lineage-specific microanatomical structures composed of progenitors and immature cells, which function as the production sites for each major blood lineage. This overall anatomy is resilient to insults, as it was maintained after haemorrhage, systemic bacterial infection and granulocyte colony-stimulating factor (G-CSF) treatment, and during ageing. Production sites enable haematopoietic plasticity as they differentially and selectively modulate their numbers and output in response to insults. We found that stress responses are variable across the skeleton: the tibia and the sternum respond in opposite ways to G-CSF, and the skull does not increase erythropoiesis after haemorrhage. Our studies enable in situ analyses of haematopoiesis, define the anatomy of normal and stress responses, identify discrete microanatomical production sites that confer plasticity to haematopoiesis, and uncover unprecedented heterogeneity of stress responses across the skeleton.

Collection, processing and freezing of equine bone marrow cells

There is no consensus on aspects of equine bone marrow collection and processing. The study aimed to describe the collection of large volumes of bone marrow from horses of advanced age, with emphasis on bone marrow mononuclear cells (BMMCs) recovery and viability after cryopreservation. Fourteen horses, aged 3-24 years, were divided into three experiments. E1 studied the feasibility of collecting 200 mL from the sternums of horses of advanced age; E2 examined the number of cells obtained from the first and last syringe of each puncture; and E3 investigated the influence of heparin concentration on the prevention of cell aggregation, and cell viability after freezing in liquid nitrogen. Bone marrow aspirations were done with syringes pre-filled with Iscove's modified Dulbecco's medium and different concentrations of sodium heparin. BMMCs were counted, cell viability was determined, and samples were frozen. Bone marrow collection from the sternum is safe, even at large volumes and from horses of advanced age, and the number of cells recovered decreases with successive aspirations (p < 0.0001). Heparin concentration influenced cell aggregation, and recovered cells continued to be commercially viable after 150 days in frozen storage.

Apparent elastic modulus of ex vivo trabecular bovine bone increases with dynamic loading

Although it is widely known that bone tissue responds to mechanical stimuli, the underlying biological control is still not completely understood. The purpose of this study was to validate required methods necessary to maintain active osteocytes and minimize bone tissue injury in an ex vivo three-dimensional model that could mimic in vivo cellular function. The response of 22 bovine trabecular bone cores to uniaxial compressive load was investigated by using the ZETOS bone loading and bioreactor system while perfused with culture medium for 21 days. Two groups were formed, the "treatment" group (n = 12) was stimulated with a physiological compressive strain (4000 µε) in the form of a "jump" wave, while the "control" group (n = 10) was loaded only during three measurements for apparent elastic modulus on days 3, 10, and 21. At the end of the experiment, apoptosis and active osteocytes were quantified with histological analysis, and bone formation was identified by means of the calcium-binding dye, calcein. It was demonstrated that the treatment group increased the elastic modulus by 61%, whereas the control group increased by 28% (p<0.05). Of the total osteocytes observed at the end of 21 days, 1.7% (±0.3%) stained positive for apoptosis in the loaded group, whereas 2.7% (±0.4%) stained positive in the control group. Apoptosis in the center of the bone cores of both groups at the end of 21 days was similar to that observed in vivo. Therefore, the three-dimensional model used in this research permitted the investigation of physiological responses to mechanical loads on morphology adaptation of trabecular bone in a controlled defined load and chemical environment.

Prostaglandin E2 inhibits BMP signaling and delays chondrocyte maturation

While cyclooxygenases are important in endochondral bone formation during fracture healing, mechanisms involved in prostaglandin E2 (PGE2) regulation of chondrocyte maturation are incompletely understood. The present study was undertaken to determine if PGE2 effects on chondrocyte differentiation are related to modulation of the bone morphogenetic protein (BMP) signaling pathway. In primary murine sternal chondrocytes, PGE2 differentially regulated genes involved in differentiation. PGE2 induced type II collagen and MMP-13, had minimal effects on alkaline phosphatase, and inhibited the expression of the maturational marker, type X collagen. In BMP-2-treated cultures, PGE2 blocked the induction of type X collagen. All four EP receptors were expressed in chondrocytes and tended to be inhibited by BMP-2 treatment. RCJ3.1C5.18 chondrocytes transfected with the protein kinase A (PKA) responsive reporter, CRE-luciferase, showed luciferase induction following exposure to PGE2, consistent with activation of PKA signaling and the presence of the EP2 and EP4 receptors. Both PGE2 and the PKA agonist, dibutyryl cAMP, blocked the induction of the BMP-responsive reporter, 12XSBE, by BMP-2 in RCJ3.1C5.18 chondrocytes. In contrast, PGE2 increased the ability of TGF-beta to activate the TGF-beta-responsive reporter, 4XSBE. Finally, PGE2 down-regulated BMP-mediated phosphorylation of Smads 1, 5, and 8 in RCJ3.1C5.18 cells and in primary murine sternal chondrocytes. Altogether, the findings show that PGE2 regulates chondrocyte maturation in part by targeting BMP/Smad signaling and suggest an important role for PGE2 in endochondral bone formation.

Porous thermoresponsive-co-biodegradable hydrogels as tissue-engineering scaffolds for 3-dimensional in vitro culture of chondrocytes

A new porous, thermoresponsive, partially biodegradable, chemically crosslinked hydrogel system was developed, characterized, and tested as a cartilage tissue-engineering scaffold for in vitro chondrocyte culture over a 4-week period. The hydrogel system was composed of poly(N-isopropylacrylamide), poly(D,L-lactic acid), and dextran segments. Pores in the hydrogels were generated using a salt leaching technique. The hydrogels showed thermoresponsive properties, with a lower critical solution temperature at approximately 32 degrees C. They continuously swelled at physiological temperature in phosphate buffered saline (pH 7.4) for at least 1 month. Chondrocytes isolated from embryonic chick sterna were seeded into the hydrogel scaffolds at room temperature and cultured at 37 degrees C for 4 weeks. Real-time reverse-transcriptase polymerase chain reaction quantification was conducted every week to study messenger ribonucleic acid levels of 3 chondrocyte phenotypic markers: type II collagen, type X collagen, and Indian hedgehog. Results suggested that chondrocytes maintained their phenotype during the 4-week in vitro culture and could mimic in vivo development. Chondrocytes were non-enzymatically harvested from the hydrogel scaffold at the end of the fourth week by simply lowering the temperature from 37 degrees C to room temperature. The harvested chondrocytes kept a round morphology, confirming the maintenance of the chondrocyte phenotype in the hydrogel scaffolds.

Bone marrow aspiration: technique, grafts, and reports

This article describes a technique for obtaining adult stem cells from bone marrow aspirate. Case reports show how this procedure might replace the gold standard for bone grafts with the platinum standard of obtaining stem cells. The bone marrow aspirate and transplantation of adult stem cells within the resorbable) matrix and under the influence of soluble regulators have the potential for introducing the platinum standard for bone grafts. There are several advantages to using bone marrow aspirate. The technique is simple, a second surgical site is not needed, there is minimal postoperative morbidity, and adult stem cells populate the graft site with osteoblasts.

Irradiation has no effect on the incorporation of impacted morselized bone: a bone chamber study in goats

BACKGROUND

Gamma irradiation has been widely used for sterilization of bone allografts. However, gamma irradiation alters proteins. This is favorable when it reduces immunogenicity, but is undesirable when osteoinductive proteins are damaged. Although the effect of gamma irradiation on BMPs has been studied, the effect of irradiation on the process of incorporation of morselized bone chips remains unclear. We studied the effects of sterilization by gamma irradiation on the incorporation of impacted morselized allografts.

METHODS

Bone chambers with impacted allografts, rinsed impacted allografts, allografts that were rinsed and subsequently irradiated, and an empty control were implanted in proximal medial tibiae of goats. Incorporation was evaluated using histology and histomorphometry.

RESULTS

Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in unprocessed, rinsed, and both rinsed and irradiated bone grafts. After 12 weeks, no difference in bone and tissue ingrowth was found between the unprocessed, the rinsed, and the rinsed and subsequently irradiated allografts. The amount of unresorbed graft remnant was highest in the unprocessed bone grafts.

INTERPRETATION

We conclude that sterilization with gamma irradiation does not influence the incorporation of impacted rinsed bone allografts.

Robust Strategies for Automated AFM Force Curve Analysis—I. Non-adhesive Indentation of Soft, Inhomogeneous Materials

The atomic force microscope (AFM) has found wide applicability as a nanoindentation tool to measure local elastic properties of soft materials. An automated approach to the processing of AFM indentation data, namely, the extraction of Young’s modulus, is essential to realizing the high-throughput potential of the instrument as an elasticity probe for typical soft materials that exhibit inhomogeneity at microscopic scales. This paper focuses on Hertzian analysis techniques, which are applicable to linear elastic indentation. We compiled a series of synergistic strategies into an algorithm that overcomes many of the complications that have previously impeded efforts to automate the fitting of contact mechanics models to indentation data. AFM raster data sets containing up to 1024 individual force-displacement curves and macroscopic compression data were obtained from testing polyvinyl alcohol gels of known composition. Local elastic properties of tissue-engineered cartilage were also measured by the AFM. All AFM data sets were processed using customized software based on the algorithm, and the extracted values of Young’s modulus were compared to those obtained by macroscopic testing. Accuracy of the technique was verified by the good agreement between values of Young’s modulus obtained by AFM and by direct compression of the synthetic gels. Validation of robustness was achieved by successfully fitting the vastly different types of force curves generated from the indentation of tissue-engineered cartilage. For AFM indentation data that are amenable to Hertzian analysis, the method presented here minimizes subjectivity in preprocessing and allows for improved consistency and minimized user intervention. Automated, large-scale analysis of indentation data holds tremendous potential in bioengineering applications, such as high-resolution elasticity mapping of natural and artificial tissues.

Trypanosoma cruzi: experimental parasitism of bone and cartilage

Trypanosoma cruzi causes Chagas' disease, a systemic infection that affects cells of meso-, endo-, and ectodermic origin. However, as far as we know, the presence of T. cruzi stages in bone has not been reported previously, and it has scarcely been investigated in cartilage. We inoculated 7- and 20-day-old (8 and 15 g) NMRI albino mice i.p. with metacyclic trypomastigotes from Rhodnius prolixus used for xenodiagnosis of mice previously infected with mammalian, human, and triatomines isolates, characterized by randomly amplified polymorphic DNA as zymodeme 1 (equivalent to T. cruzi I). Tissular parasitism (quantified according to the number of pseudocysts/50 fields 400x) showed amastigotes, intermediate forms, or trypomastigotes in sternum chondroblasts, osteoblasts, macrophages, and fibroblasts; chondrocyte and osteocyte invasion was rare. All isolates parasitized bone marrow macrophages, with few amastigotes. We observed marked associated myotropism, with or without inflammatory infiltration; there were small numbers of intensely parasitized mononuclear cells in perichondrium and periosteum. We discuss the results in relation to the marked differences of the T. cruzi tropism toward the different types of sternum cells, and, additionally, we outline the possibility of transmitting parasitized bone marrow through transplants. The fact of finding parasite stages in sternum bone and cartilage may be considered important due to the studies on Chagas' disease paleoparasitology that are based on histological and molecular analysis.

[Relationship between DNA degradation and postmortem interval of corrupt corpse]

OBJECTIVE

To study the relationship between DNA degradation and postmortem interval of corrupt corpse.

METHODS

By determining the marrow DNA content with histochemical technique and image analysis.

RESULTS

The content of marrow DNA decreased gradually with prolongation of postmortem interval, and it evencould be detected till 14 days after death.

CONCLUSION

There was a linear relationship between the degradation rate of the nuclear DNA and postmortem interval.

Immortalized cell lines from mouse xiphisternum preserve chondrocyte phenotype

Chondrocytes are unique to cartilage and the study of these cells in vitro is important for advancing our understanding of the role of these cells in normal homeostasis and disease including osteoarthritis (OA). As there are limitations to the culture of primary chondrocytes, cell lines have been developed to overcome some of these obstacles. In this study, we developed a procedure to immortalize and characterize chondrocyte cell lines from mouse xiphisternum. The cells displayed a polygonal to fibroblastic morphology in monolayer culture. Gene expression studies using quantitative PCR showed that the cell lines responded to bone morphogenetic protein 2 (BMP-2) by increased expression of matrix molecules, aggrecan, and type II collagen together with transcriptional factor, Sox9. Stimulation by IL-1 results in the increased expression of catabolic effectors including MMP-13, nitric oxide synthase, ADAMTS4, and ADAMTS5. Cells cultured in alginate responded to BMP-2 by increased synthesis of proteoglycan (PG), a major matrix molecule of cartilage. IL-1 treatment of cells in alginate results in increased release of PG into the conditioned media. Further analysis of the media showed the presence of Aggrecanase-cleaved aggrecan fragments, a signature of matrix degradation. These results show that the xiphisternum chondrocyte cell lines preserve their chondrocyte phenotype cultured in either monolayer or 3-dimensional alginate bead culture systems. In summary, this study describes the establishment of chondrocyte cell lines from the mouse xiphisternum that may be useful as a surrogate model system to understand chondrocyte biology and to shed light on the underlying mechanism of pathogenesis in OA.

Nitric oxide-nitric oxide synthase regulates key maturational events during chondrocyte terminal differentiation

The goal of this investigation was to explore the mechanism by which NOS and NO serve to regulate events linked to chondrocyte terminal differentiation. NOS isoform expression and NO adducts in chick growth cartilage were detected by immunohistochemistry and Western blot analysis. All NOS isoforms were expressed in chick growth plate chondrocytes with the highest levels present in the hypertrophic region. The enzymes were active since nitrosocysteine and nitrotyrosine residues were detected in regions of the epiphysis with the highest levels of NOS expression. Maturing chick sternal chondrocytes evidenced an increase in NO release and a rise in NOS protein levels. When treated with NOS inhibitors, there was a decrease in the alkaline phosphatase activity of the hypertrophic cells. On the other hand, NO donors caused a small but significant elevation in alkaline phosphatase activity. Transient transfections of chondrocytes with an endothelial NOS isoform caused an increase in collagen type X promoter activity. Induction of both collagen type X expression and alkaline phosphatase activity was blocked by inhibitors of the cGMP pathway. These findings indicate that NO is generated by three NOS isoforms in terminally differentiated chondrocytes. The expression of NOS and the generation of NO enhanced maturation by upregulating alkaline phosphatase and collagen type X expression. Since expression of these two determinants was blocked by inhibitors of the cGMP pathway, it is concluded that NO metabolism is required for development of the mature chondrocyte phenotype.

In vitro comparison of equine cancellous bone graft donor sites and tibial periosteum as sources of viable osteoprogenitors

OBJECTIVE

To compare the osteogenic potential of cancellous bone of conventional graft sites with that of one nonconventional site (fourth coccygeal vertebra) and to investigate the tibial periosteum as a donor site with respect to osteogenic potential.

STUDY DESIGN

In vitro osteogenic cell culture system.

SAMPLE POPULATION

Eight adult horses.

METHODS

Cancellous bone or tibial periosteum was aseptically collected and cut into bone chips or periosteal strips of 1 to 2 mm(3) for primary explant cultures. After 2 weeks, primary tissue cultures that yielded a population of osteogenic cells were counted and subcultured at 1 x 10(5) cells/35-mm dish in osteogenic media. After 7 to 10 days, subcultures were stained with Von Kossa (VK) to assess mineralized bone nodule formation. VK-positive bone nodules were counted as osteoprogenitors and compared among 3 donor sites, which provided consistent primary osteogenic cells (tuber coxae, fourth coccygeal vertebra, periosteum) using ANOVA (P <.05).

RESULTS

Sternal and tibial bone yielded viable osteogenic cells from 25% and 50% of horses, respectively, whereas yields from tuber coxae, coccygeal vertebra, and periosteum were 75%, 100%, and 100%, respectively. Tuber coxae and periosteum had significantly greater numbers of osteoprogenitors compared with fourth coccygeal vertebra.

CONCLUSIONS

Among the conventional donor sites, tuber coxae most consistently yielded viable osteogenic cells with an acceptable percentage of osteoprogenitors. Sternal and tibial sites were unreliable in providing osteogenic cells. Two new donor sites, the fourth coccygeal vertebra and tibial periosteum, were tissues with good osteogenic potential.

CLINICAL RELEVANCE

When a source of transplantable viable osteoprogenitor cells is desired, use of the tuber coxae as a conventional donor site is warranted. Use of tibial periosteum or fourth coccygeal vertebra as reliable sources of transplantable osteoprogenitors should be considered.

Gelatin sheet incorporating basic fibroblast growth factor enhances sternal healing after harvesting bilateral internal thoracic arteries

OBJECTIVE

We previously reported that a gelatin sheet incorporating basic fibroblast growth factor accelerated sternal healing after bilateral internal thoracic artery removal in normal and diabetic rats. The aim of this study was to evaluate the effects of this therapeutic modality on sternal healing in a large-animal model before performing a clinical trial.

METHODS

After median sternotomy and bilateral internal thoracic artery removal in a pedicled fashion, 14 beagle dogs received either a gelatin sheet incorporating basic fibroblast growth factor (100 mug per sheet) on the posterior table of the sternum (FGF group, n = 7) or did not receive a gelatin sheet (control, n = 7). We compared sternal healing 4 weeks after surgical intervention between the groups.

RESULTS

Scintigraphic images obtained by using technetium 99 methylene diphosphonate bone scanning were assessed visually, and the impulse rate was quantified 30 and 60 minutes after injection of technetium 99 methylene diphosphonate to evaluate the sternal perfusion. Sternal uptake was significantly increased in the FGF group (30 minutes: 221% +/- 30% vs 180% +/- 36%; 60 minutes: 267% +/- 26% vs 197% +/- 42%; P <.01). Apparent sternal dehiscence, as assessed radiographically, was observed only in the control animals. Histologically, complete healing of the sternum with marked angiogenesis was observed in the FGF group, whereas poor healing with limited angiogenesis was seen in the control animals. Both bone mineral content (134 +/- 49 vs 52 +/- 32 mg, P <.01) and bone mineral density (133 +/- 53 vs 66 +/- 32 mg/mm(2), P <.05) along the incision line of the sternum, as assessed by means of dual-energy x-ray absorptometry, were higher in the FGF group.

CONCLUSIONS

A gelatin sheet incorporating basic fibroblast growth factor enhances sternal perfusion and accelerates sternal bone healing in large animals.23

Control of skeletal patterning by ephrinB1-EphB interactions

We report that targeted inactivation of the Eph receptor ligand ephrinB1 in mouse caused perinatal lethality, edema, defective body wall closure, and skeletal abnormalities. In the thorax, sternocostal connections were arranged asymmetrically and sternebrae were fused, defects that were phenocopied in EphB2/EphB3 receptor mutants. In the wrist, loss of ephrinB1 led to abnormal cartilage segmentation and the formation of additional skeletal elements. We conclude that ephrinB1 and B class Eph receptors provide positional cues required for the normal morphogenesis of skeletal elements. Another malformation, preaxial polydactyly, was exclusively seen in heterozygous females in which expression of the X-linked ephrinB1 gene was mosaic, so that ectopic EphB-ephrinB1 interactions led to restricted cell movements and the bifurcation of digital rays. Our findings suggest that differential cell adhesion and sorting might be relevant for an unusual class of X-linked human genetic disorders, in which heterozygous females show more severe phenotypes than hemizygous males.

Retinoic acid stimulates chondrocyte differentiation and enhances bone morphogenetic protein effects through induction of Smad1 and Smad5

Whereas bone morphogenetic protein (BMP)-signaling events induce maturational characteristics in vitro, recent evidence suggests that the effects of other regulators might be mediated through BMP-signaling events. The present study examines the mechanism through which retinoic acid (RA) stimulates differentiation in chicken embryonic caudal sternal chondrocyte cultures. Both RA and BMP-2 induced expression of the chondrocyte maturational marker, colX, in chondrocyte cultures by 8 d. Though the RA effect was small, it synergistically enhanced the effect of BMP-2 on colX and phosphatase activity. Inhibition of either RA or BMP signaling, with selective inhibitors, interfered with the inductive effects of these agents but also inhibited the complementary pathway, demonstrating a codependence of RA and BMP signaling during chondrocyte maturation. BMP-2 did not enhance the effects of RA on an RA-responsive reporter construct, but RA enhanced basal activity and synergistically enhanced BMP-2 stimulation of the BMP-responsive chicken type X collagen reporter. A similar synergistic interaction between RA and BMP-2 was observed on colX expression. RA did not increase the expression of the type IA BMP receptor but did markedly up-regulate the expression of Smad1 and Smad5 proteins, important participants in the BMP pathway. Inhibition of RA signaling, with the selective inhibitor AGN 193109, blocked RA-mediated induction of the Smad proteins and chondrocyte differentiation. These findings demonstrate that RA induces the expression of BMP-signaling molecules and enhances BMP effects in chondrocytes.

The influence of pulsed low-intensity ultrasound on matrix production of chondrocytes at different stages of differentiation: an explant study

The proximal and distal parts of sterna of chick embryos represent cartilage undergoing endochondral ossification and hyaline cartilage, respectively. Cartilage explants from both regions were exposed for 20 min to pulsed low-intensity ultrasound (PLIUS) with an intensity of 30 mW. cm(-2) (spatial average-temporal average) at a frequency of 1.5 MHz, with a pulse burst frequency of 1 kHz and burst duration of 200 micros. Histological and immunohistochemical analysis was performed on days 1, 3, 5 and 7 after treatment. An anabolic effect of PLIUS on matrix production was shown by an increase of up to 10% to 20% in quantitative immunohistochemical staining for type II collagen and aggrecan in the two parts of the sternum. PLIUS also increased type X collagen staining by up to 10% in certain regions of the proximal part of the sternum. Staining for type X collagen was negative in the distal part of the sternum in both PLIUS and control groups. These results suggest that PLIUS may stimulate bone formation by increasing hypertrophy of chondrocytes directed to terminal differentiation. However, PLIUS did not induce hypertrophy in hyaline cartilage; moreover, increased matrix synthesis indicates a potential role in cartilage repair.

[The relationship between postmortem degradation of marrow DNA in bosom bone and late postmortem interval estimation]

OBJECTIVE

To study the relationship between degradation of marrow DNA and late postmortem interval (PMI).

METHODS

Marrow were left on natural condition for 0,1,3,5,7 day after death respectively, Marrow DNA were detected by using Feulgen staining and computerized image analysis.

RESULTS

The content of marrow DNA could be detected till 7 days after death yet.

CONCLUSION

The degradation of marrow DNA may be used on estimation the late PMI.

Changes in the expression of annexin A5 gene during in vitro chondrocyte differentiation: influence of cell attachment

Several lines of evidence indicate that annexin A5, a membrane-associated protein with calcium-channel activity, plays a key role in cartilage calcification during endochondral ossification. As a major constituent of cartilage matrix vesicles, which are released from microvilli of hypertrophic chondrocytes, it is involved in calcium uptake necessary for the initial stages of cartilage calcification. Little is known, however, concerning transcriptional regulation of the annexin A5 gene during chondrocyte differentiation. Here, we report on changes in annexin A5 expression by measuring mRNA and protein levels during in vitro differentiation of chick sternal chondrocytes to the hypertrophic phenotype. Terminal differentiation of mature sternal chondrocytes was achieved in the presence of sodium ascorbate in high-density cultures growing either in monolayer or over agarose as cell aggregates. Differentiation of chondrocytes to hypertrophic cells was followed by morphological analysis and by the onset of type X collagen expression. High expression levels of annexin A5 mRNA were detected in chondrocytes freshly isolated from the sterna by enzymatic digestion and subsequently in cells growing in monolayer, but annexin A5 gene transcription was rapidly downregulated when cells were grown in suspension as aggregates over agarose. However, protein levels did not decrease probably due to its low turnover rate. In suspension culture, annexin A5 mRNA reappeared after 3 weeks concomitantly with segregation of the aggregates into single cells and onset of chondrocyte hypertrophy. The downregulation of annexin A5 expression in cells growing as matrix-rich aggregates was reverted when extracellular matrix components were removed and cells were reseeded onto tissue culture plastic, suggesting that cell spreading, formation of focal contacts and stress fibers stimulated annexin A5 expression in proliferating as well as in hypertrophic chondrocytes.

Induction of apoptosis in chondrocytes by tumor necrosis factor-alpha

Tumor necrosis factor alpha (TNF-alpha) induces apoptosis in a number of cell types and plays an essential role in bone remodeling, both stimulating the proliferation of osteoblasts and activating osteoclasts. During endochondral ossification, apoptosis of chondrocytes occurs concurrently with new bone formation and the resorption and replacement of mineralized cartilage with woven bone. In the present study, the role of TNF-alpha in promoting chondrocyte apoptosis was examined. Chondrocyte cell populations, enriched in either hypertrophic or non-hypertrophic cells, were isolated from the cephalic and caudal portions of 17-day chick embryo sterna, respectively, and treated in vitro with 0.1-10 nM recombinant human TNF-alpha. As a positive control, apoptosis was also induced by Fas receptor antibody binding. Dye exclusion assays of the live/dead ratios of cells showed that TNF-alpha caused a dose-dependent 1.5- and 2.0-fold increase in the number of dead cells in both hypertrophic and non-hypertrophic chondrocytes. Induction of apoptosis was independently assayed by measurement of interleukin-1beta-converting enzyme (ICE) activity, and analyzed by a semi-quantitative determination of DNA fragmentation. When compared to untreated cells, these analyses also showed dose-dependent increases in TNF-alpha induced apoptosis in both chondrocyte populations, with increases in the levels of ICE activity for all doses of TNF-alpha (from approximately 5 to approximately 20 fold). Osteoblasts, however, were not affected by treatment with TNF-alpha or by Fas antibody/protein G induction. Immunostaining of chondrocytes for Fas receptor and caspase-2 protein expression showed that most of the chondrocytes expressed these two markers of apoptosis after treatment with TNF-alpha. Although cell killing and ICE induction were higher in the more hypertrophic cells, TNF-alpha induced apoptosis in both hypertrophic and non-hypertrophic chondrocyte populations. These results demonstrate that apoptosis may be induced in both hypertrophic and non-hypertrophic chondrocytes through both Fas and TNF-alpha receptor mediated signaling, and suggest that chondrocytes are more sensitive to apoptotic effects of TNF-alpha within the skeletal lineage than are osteoblasts.

Basic fibroblast growth factor may improve devascularized sternal healing

BACKGROUND

We have shown that a gelatin sheet incorporating basic fibroblast growth factor enhanced bone regeneration of the devascularized sternum. The purpose of this study was to determine if topical use of the gelatin sheet accelerated normal sternal regeneration and bone remodeling.

METHODS

Thirty Wistar rats had median sternotomy and were divided into 3 groups: 10 had the bilateral internal thoracic arteries removed and basic fibroblast growth factor sheet applied on the sternum (group A), 10 had just the bilateral internal thoracic arteries removed (group B), and 10 had intact bilateral internal thoracic arteries (group C).

RESULTS

Four weeks later the peristernal blood flow significantly increased and marked angiogenesis was seen around the sternum in group A. Histologically, the sternum was almost completely healed only in group A. In group A the bone mineral content was highest, but the bone mineral density was similar to that in other groups. The osteoclast index in group A was highest at the border zone of bone formation and remained high in regenerated bone.

CONCLUSIONS

The basic fibroblast growth factor sheet offset sternal ischemia and accelerated normal sternal bone regeneration and remodeling, not only by callus formation but also by callus resorption.

Utilization of bone morphogenetic protein receptors during chondrocyte maturation

Cartilage from the upper, cephalic portion of embryonic chick sternums undergoes hypertrophy, while the lower, caudal portion of the sternum remains as cartilage. Bone morphogenetic proteins (BMPs) induce type X collagen (colX) in cultured upper but not lower sternal chondrocytes (LSCs). We have examined the utilization of BMP receptors (BMPRs) by upper sternal chondrocytes (USCs) and LSCs both by analyzing receptor expression and by overexpressing mutant BMPRs. Reverse-transcription polymerase chain reaction (RT-PCR) analyses indicate that both upper and lower chondrocytes produce messenger RNA (mRNA) for all three receptors: BMPR type IA (BMPR-IA), BMPR type IB (BMPR-IB), and BMPR type II (BMPR-II). Infection of USC with retroviral vectors expressing constitutively active (CA) BMPRs showed that CA-BMPR-IB, like exogenous BMP-4, induced both colX mRNA and elevated alkaline phosphatase (AP), while CA-BMPR-IA was markedly less potent. However, expression of activated receptors in LSC cultures resulted in only minimal induction of hypertrophic markers. Consistent with the results seen for CA receptors, dominant negative (DN) BMPR-IB blocked BMP-induced hypertrophy in USCs more effectively than DN-BMPR-IA. These results imply that the major BMPR required for BMP induction of chondrocyte hypertrophy is BMPR-IB, and that difference between permanent and prehypertrophic chondrocytes is not caused by absence of receptors required for BMP signaling.

Response of engineered cartilage tissue to biochemical agents as studied by proton magnetic resonance microscopy

OBJECTIVE

To test the hypothesis that magnetic resonance imaging (MRI) results correlate with the biochemical composition of cartilage matrix and can therefore be used to evaluate natural tissue development and the effects of biologic interventions.

METHODS

Chondrocytes harvested from day-16 chick embryo sterna were inoculated into an MRI-compatible hollow-fiber bioreactor. The tissue that formed over a period of 2-4 weeks was studied biochemically, histologically, and with MRI. Besides natural development, the response of the tissue to administration of retinoic acid, interleukin-1beta (IL-1beta), and daily dosing with ascorbic acid was studied.

RESULTS

Tissue wet and dry weight, glycosaminoglycan (GAG) content, and collagen content all increased with development time, while tissue hydration decreased. The administration of retinoic acid resulted in a significant reduction in tissue wet weight, proteoglycan content, and cell number and an increase in hydration as compared with controls. Daily dosing with ascorbic acid increased tissue collagen content significantly compared with controls, while the administration of IL-1beta resulted in increased proteoglycan content. The water proton longitudinal and transverse relaxation rates correlated well with GAG and collagen concentrations of the matrix as well as with tissue hydration. In contrast, the magnetization transfer value for the tissue correlated only with total collagen. Finally, the self-diffusion coefficient of water correlated with tissue hydration.

CONCLUSION

Parameters derived from MR images obtained noninvasively can be used to quantitatively assess the composition of cartilage tissue generated in a bioreactor. We conclude that MRI is a promising modality for the assessment of certain biochemical properties of cartilage in a wide variety of settings.

Retinoid signaling is required for chondrocyte maturation and endochondral bone formation during limb skeletogenesis

Retinoids have long been known to influence skeletogenesis but the specific roles played by these effectors and their nuclear receptors remain unclear. Thus, it is not known whether endogenous retinoids are present in developing skeletal elements, whether expression of the retinoic acid receptor (RAR) genes alpha, beta, and gamma changes during chondrocyte maturation, or how interference with retinoid signaling affects skeletogenesis. We found that immature chondrocytes present in stage 27 (Day 5.5) chick embryo humerus exhibited low and diffuse expression of RARalpha and gamma, while RARbeta expression was strong in perichondrium. Emergence of hypertrophic chondrocytes in Day 8-10 embryo limbs was accompanied by a marked and selective up-regulation of RARgamma gene expression. The RARgamma-rich type X collagen-expressing hypertrophic chondrocytes lay below metaphyseal prehypertrophic chondrocytes expressing Indian hedgehog (Ihh) and were followed by mineralizing chondrocytes undergoing endochondral ossification. Bioassays revealed that cartilaginous elements in Day 5.5, 8.5, and 10 chick embryo limbs all contained endogenous retinoids; strikingly, the perichondrial tissues surrounding the cartilages contained very large amounts of retinoids. Implantation of beads filled with retinoid antagonist Ro 41-5253 or AGN 193109 near the humeral anlagens in stage 21 (Day 3.5) or stage 27 chick embryos severely affected humerus development. In comparison to their normal counterparts, antagonist-treated humeri in Day 8.5-10 chick embryos were significantly shorter and abnormally bent; their diaphyseal chondrocytes had remained prehypertrophic Ihh-expressing cells, did not express RARgamma, and were not undergoing endochondral ossification. Interestingly, formation of an intramembranous bony collar around the diaphysis was not affected by antagonist treatment. Using chondrocyte cultures, we found that the antagonists effectively interfered with the ability of all-trans-retinoic acid to induce terminal cell maturation. The results provide clear evidence that retinoid-dependent and RAR-mediated mechanisms are required for completion of the chondrocyte maturation process and endochondral ossification in the developing limb. These mechanisms may be positively influenced by cooperative interactions between the chondrocytes and their retinoid-rich perichondrial tissues.

Age-related changes of lymphocyte subsets in normal bone marrow biopsies

There is a paucity of information in the literature concerning the age-related changes of the lymphocyte subsets in bone marrow (BM), and the available reports disagree about the characteristics of the population studied and the methods for obtaining, handling, and analyzing the samples. The purpose of the present study was to determine the distribution of lymphoid subsets in the BM from infants, children, and adults by analyzing fragments of sternum obtained during cardiovascular surgery. The samples were studied by flow cytometry employing the whole blood lysis method and excluding from the analysis the contamination of the lymphoid window by erythroid precursors. We observed that in the first 4 years of life the B subset represented more than 65% of all cells in the lymphoid window, most of them (80%) exhibiting the immature phenotype CD19+CD100+. Conversely, the T subset was composed of mature CD4+ or CD8+ cells, with the CD4/CD8 ratio being less than 1 in all age groups. With age there was a progressive decrease in the percentage of B cells and an increase of T cells, reaching similar proportions in the BM from adults (33.6% and 34.8%, respectively). Furthermore, the percentage of CD10+ cells in the B subset decreased independently, whereas the CD20 expression increased. The percentage of NK cells did not change with age.

Laminin chain expression by chick chondrocytes and mouse cartilaginous tissues in vivo and in vitro

We have observed that laminins are expressed in the chondrocytes of chick embryo sternum, mouse limb bud, and adult mouse knee joint by the methods of in situ hybridization, immunohistochemistry, Western blotting, and immunoprecipitation. From in situ hybridization using similar sized RNA probes for different mouse laminin chains, mRNAs for the alpha 1, alpha 2, beta 1, beta 2, and gamma 1 chains were expressed in the chondrocytes of chick embryo sternum, mouse limb bud, and the articular cartilage cap and epiphyseal growth plate of adult mouse knee joint. Through the use of chain-specific antibodies, staining for laminins was observed in the cytoplasm of chondrocytes from chick embryo sternum, mouse limb bud, and adult mouse knee joint. Western blot analysis confirmed the presence of laminin chains in the cells and sternal tissues. Cultured chick embryonic sternal chondrocytes expressed laminin mRNAs in the proliferating stage (2-3 days of culture) but the level increased in the aggregated cells during the maturation stage (5-7 days of culture). Comparable data were also obtained after immunostaining the cells. Thus, laminins are expressed in significant amounts by chondrocytes and may have an important role in cartilage development.

Articular chondrocytes produce factors that inhibit maturation of sternal chondrocytes in serum-free agarose cultures: a TGF-beta independent process

Under normal conditions, articular chondrocytes persist throughout postnatal life, whereas "transient" chondrocytes, which constitute the bulk of prenatal and early postnatal cartilaginous skeleton, undergo maturation, hypertrophy, and replacement by bone cells. The mechanisms regulating the markedly different behavior and fate of articular and transient chondrocytes are largely unclear. In the present study, we asked whether articular chondrocytes possess dominant antimaturation properties which may subtend their ability to persist throughout life. Adult chicken articular chondrocytes and transient maturing chondrocytes from the core region of day 17, chick embryo cephalic sternum were cultured or cocultured in serum-free agarose conditions. When the sternal cells were grown by themselves, they quickly developed into hypertrophic type X collagen-synthesizing cells; however, when they were cocultured with as few as 10% articular chondrocytes or fed with articular chondrocyte-conditioned medium, their maturation was markedly impaired, as revealed by a sharp drop in type X collagen synthesis. A similar, albeit less potent, antimaturation activity characterized resting and proliferating immature chondrocytes isolated from other regions of embryonic sternum. Transforming growth factor-beta 2 (TGF-beta 2) was previously suggested to be an inhibitor of chondrocyte maturation. We found, however, that treatment with a neutralizing antiserum to TGF-beta did not counteract the inhibition of maturation in cocultures of articular and maturing core sternal chondrocytes. Indeed, articular chondrocytes produced and accumulated relatively low levels of TGF-beta in their culture medium, about 15 ng/ml/48 h, of which over 90% was latent; surprisingly, maturing sternal core chondrocytes accumulated over 10-fold more TGF-beta in the medium, about 150 ng/ml/48 h, of which over 20% was endogenously active. These results indicate that articular chondrocytes do possess dominant antimaturation properties which appear to be TGF-beta independent. The TGF-beta s may thus have a more prominent role in the terminal phases of chondrocyte maturation, as indicated by their abundance and greater activity in hypertrophic chondrocytes.

Apoptosis of terminally differentiated chondrocytes in culture

During the process of endochondral ossification chondrocytes progress through stages of terminal differentiation culminating in apoptotic death. We have developed a serum-free suspension culture that allows terminal differentiation and facilitates the investigation of factors affecting chondrocyte apoptosis. We have found that chondrocytes not committed to terminal differentiation, i.e., those from the caudal region of chick embryo sterna, a region that remains cartilaginous for some months after the chick hatches, maintained high viability in serum-free suspension culture. A strong dependence of viability on culture density and sensitivity to induction of apoptosis with the protein kinase inhibitor, staurosporine, was consistent with the proposal that these chondrocytes, like nearly all cells, require intercellular communication for survival. Chondrocytes that were committed to terminal differentiation, i.e., those from the cephalic region of chick embryo sterna, a region that is replaced by bone before the chick hatches, expressed the hypertrophic phenotype but maintained their viability in culture for only approximately 6 days. Subsequent cell death was very consistent between cultures and shown to occur by an apoptotic process by analysis of DNA fragmentation and cell morphology. Short-term viability of hypertrophic chondrocytes was independent of culture density and relatively resistant to treatment with staurosporine. Induction of the hypertrophic phenotype in immature chondrocytes committed them to cell death and prevention of expression of the hypertrophic phenotype prevented cell death. We conclude that commitment of chondrocytes to terminal differentiation is associated with a commitment to apoptosis and apoptosis of hypertrophic chondrocytes in growth cartilage does not require initiation by external signals.

Structural and functional analysis of the chick chondroitin sulfate proteoglycan (aggrecan) promoter and enhancer region

Aggrecan is a large chondroitin sulfate proteoglycan, the expression of which is both tissue-specific and developmentally regulated. Here we report the cloning and sequencing of the 1.8-kilobase genomic 5' flanking sequence of the chick aggrecan gene and provide a functional and structural characterization of its promoter and enhancer region. Sequence analysis reveals potential Sp1, AP2, and NF-I related sites, as well as several putative transcription factor binding sites, including the cartilage-associated silencers CIIS1 and CIIS2. A number of these transcription factor binding motifs are embedded in a sequence flanked by prominent inverted repeats. Although lacking a classic TATA box, there are two instances in the 1.8-kb genomic fragment of TATA-like TCTAA sequences, as have been defined previously in other promoter regions. Primer extension and S1 protection analyses reveal three major transcription start sites, also located between the inverted repeats. Transient transfections of chick sternal chondrocytes and fibroblasts with reporter plasmids bearing progressively reduced portions of the aggrecan promoter region allowed mapping of chondrocyte-specific transcription enhancer and silencer elements that are consistent with the sequence analysis. These findings suggest the importance of this regulatory region in the tissue-specific expression of the chick aggrecan gene.

Antioxidant effects of hyaluronan and its alpha-methyl-prednisolone derivative in chondrocyte and cartilage cultures

OBJECTIVE

To compare hyaluronan and its alpha-methyl prednisolone derivative (HYC-141) with respect to their potential to directly cause tissue damage and to protect tissues from attack by reactive oxygen species.

METHODS

Cartilage samples and chondrocytes were isolated from 15-day chick embryos and were exposed to enzyme-based and activated inflammatory cell-free radical generating systems in the presence of varying concentrations of alpha-methyl prednisolone, hyaluronan, and HYC-141. Tissue and cell vitality was measured by determining the incorporation of radioactive sulphate into newly synthesized glycosaminoglycans.

RESULTS

Only alpha-methyl prednisolone caused a significant decrease in biosynthetic activity. All the tested substances were capable, to some extent, of protecting tissues and cells from damage by reactive oxygen species; HYC-141 demonstrated the greatest protective effect.

CONCLUSION

These data suggest that HYC-141 may possess certain advantages over the individual component molecules in the local treatment of arthropathies.

Identification and characterization of up-regulated genes during chondrocyte hypertrophy

Chondrocyte hypertrophy involves de novo acquisition and/or increased expression of certain gene products including, among others, type X collagen, alkaline phosphatase, and matrix metalloproteinases. To analyze further the genetic program associated with chondrocyte hypertrophy, we have employed a modification of the polymerase chain reaction-mediated subtractive hybridization method of Wang and Brown (Wang and Brown [1991] Proc. Natl. Acad. Sci 88:11505). Cultures of hypertrophic tibial chondrocytes and nonhypertrophic sternal cells were used for poly A+ RNA isolation. Among 50 individual cDNA fragments isolated for up-regulated hypertrophic genes, 18 were tentatively identified by their similarities to entries in the GenBank database, whereas the other 32 showed no significant similarity. The identified genes included translational and transcriptional regulatory factors, ribosomal proteins, the enzymes transglutaminase and glycogen phosphorylase, type X collagen (highly specific for hypertrophic cartilage matrix), gelsolin, and the carbohydrate-binding protein galectin. Two of these, transglutaminase and galectin, were cloned and were further characterized. The chondrocyte transglutaminase revealed previously in hypertrophic cartilage by immunochemical methods appears to be the chicken equivalent of mammalian factor XIIIa (showing 75% overall protein similarity). The chicken chondrocyte galectin is a variant of mammalian galectin-3. Galectins are known to bind to components found in hypertrophic cartilage, and factor XIIIa is known to crosslink some of the same components, possibly modifying them for calcification and/or removal.

Increased cell diameter precedes chondrocyte terminal differentiation, whereas cell-matrix attachment complex proteins appear constant

BACKGROUND

Chondrocytes in specific areas of chick sterna have different developmental fates. Cephalic chondrocytes become hypertrophic and secrete type X collagen into the extracellular matrix, whereas middle and caudal chondrocytes remain cartilagenous throughout development, continuing to secrete collagen types II, IX, and XI. In this report, we ask if the cell size and cytoarchitecture of chondrocytes differ in cephalic, middle, and caudal portions of whole sterna prior to and during hypertrophy. In addition, what is the distribution of integrin subunits and actin associate proteins in differentiating chondrocytes?

METHODS

Phalloidin was used to stain filamentous actin, and immunohistochemistry was used to localize the distribution of collagen molecules, integrin receptor subunits, and actin-associated proteins.

RESULTS

Chondrocytes stained for filamentous actin demonstrated that on day 14 cephalic chondrocytes had a significantly larger diameter than middle and caudal chondrocytes. Day 17 chondrocytes in nonhypertrophic cephalic and middle regions of sterna were significantly smaller than hypertrophic chondrocytes and significantly larger than caudal chondrocytes. In contrast to day 14 chondrocytes, day 17 chondrocytes in the hypertrophic region demonstrated similar diameters at all cartilagenous depths. The beta 1 integrin subunit appeared punctate and associated with cell membranes, allowing nonpolarized interactions with extracellular matrix molecules. The distribution of alpha integrin subunits was similar to the beta 1 integrin subunit, although alpha integrin subunits also appeared cytoplasmic. Actin-associated proteins, vinculin, and alpha-actinin, were associated with F-actin, but vinculin was more specifically localized to the ends of the actin filaments. Focal adhesion kinase was diffusely distributed throughout the cytoplasm but also demonstrated areas of colocalization with vinculin. Zyxin and paxillin demonstrated a punctate distribution, although paxillin was slightly more diffuse. Using immunohistochemical detection, no difference in integrin subunit or actin associated protein distribution could be determined between chondrocytes and hypertrophic chondrocytes.

CONCLUSIONS

The increased chondrocyte diameter observed in cephalic regions of sterna on day 14 suggests that intracellular changes may precede the specific hypertrophic marker, type X collagen, by several days. In addition, the presence of integrin subunits, which are known to interact with collagen and cytoskeletal proteins, suggests that communication may exist between chondrocytes and their extracellular matrix via these receptor molecules.

Differential regulation of COL2A1 expression in developing and mature chondrocytes

To investigate the regulation of type II collagen gene expression in cells undergoing chondrogenic differentiation, we have employed a 5-kbp genomic fragment of the human type II collagen gene which contains 1.8kbp of upstream sequences, the transcription start site, the first exon and 3 kbp of intronic sequences, fused to either lac Z or chloramphenicol acetyl transferase-reporter gene. Transient expression studies revealed a parallel increase in transgene activity and endogenous type II collagen mRNA levels during the onset of the cartilage differentiation of limb mesenchymal cells in high-density micromass cultures. At later periods in culture, however, the transgene activity declines, although steady-state levels of type II collagen mRNA are reported to continue to increase (Kosher et al.: J. Cell. Biol. 102: 1151-1156, 1986; Kravis and Upholt. Dev. Biol. 108: 164-172, 1985). In addition, the activity of the transgene is seven-fold higher at the onset of chondrogenic differentiation in micromass cultures that in well differentiated sternal chondrocytes, although similar levels of type II collagen transcripts are found in these cells. Furthermore, deletions of intronic segments resulted in greater drop in activity of the constructs in differentiating chondrocytes in micromass cultures than in mature sternal chondrocytes. The expression of the construct in transgenic mice is higher at the onset of chondrogenic differentiation and in newly differentiated chondrocytes than in more mature differentiated chondrocytes. Based on these observations, it appears that the mechanisms involved in the regulation of the type II collagen gene at the onset of chondrocyte differentiation are different from those resulting in the maintenance of its expression in fully differentiated chondrocytes.

Chondrocyte apoptosis in endochondral ossification of chick sterna

In the process of endochondral ossification, chondrocytes progress through a series of maturational changes, including division and hypertrophy, that culminate in chondrocyte loss and cartilage resorption. From an investigation of morphology, DNA fragmentation and collagen synthesis in the developing chick sterna we have characterized chondrocytes death in this process. Light microscopy of resorbing sterna demonstrated chondrocyte condensation at the interface with the invading vasculature and electron microscopy demonstrated a range of chondrocyte morphologies, including retraction from the pericellular matrix, cytoplasmic and nuclear condensation, and vesiculation suggestive of sequential changes characteristic of apoptosis. Isolation and end-labeling of DNA from chick primary ossification centers demonstrated fragmentation to nucleosome sized units, only in primary ossification centers exhibiting active resorption, and in situ detection of DNA fragmentation showed a restriction to chondrocytes at the interface with invading blood. We conclude that terminal differentiation of chondrocytes results in death by an apoptotic process prior to resorption of the tissue and invasion by blood vessels. The extent of DNA fragmentation correlated closely with the proportion of cells displaying a condensed phenotype in contralateral primary ossification centers and peaked at an early stage of resorption, suggesting that chondrocyte apoptosis may be an initiating event in tissue resorption and vascular invasion. Comparison of DNA fragmentation with expression of the hypertrophic chondrocyte phenotype, as indicated by type X collagen synthesis, suggested that DNA fragmentation was a late event in the process of chondrocyte hypertrophy and probably corresponded with chondrocyte condensation

Endochondral resorption of chick sterna in culture

Endochondral resorption is most clearly recognized at the metaphyseal interface of the growth plate with the adjacent vasculature; however, apparently identical processes of endochondral resorption are seen in sites of primary and secondary ossification of the cartilaginous anlage of bones and in ossifying fracture callus. Recent evidence of the expression of the hypertrophic phenotype in osteoarthrotic articular cartilage suggests that endochondral resorption also may be a factor in the loss of articular cartilage in this condition. To investigate the mechanism of endochondral resorption, a model culture system was developed and characterized. The two primary centers of ossification with surrounding cartilage were dissected from embryonic chick sterna prior to (18-day-old embryos) or after (20-day-old embryos) the initiation of resorption. They were cultured either in plastic culture dishes or on chorioallantoic membranes, and resorption was detected by analysis of the loss of types II and X collagen and by histological characterization. Only sterna showing active resorption in vivo were resorbed when cultured on chorioallantoic membrane. The histological appearance of the resorption site and the specificity of resorption to the primary ossification center, seen from both the analysis of loss of collagen and histological observation, suggested that the resorption of sterna cultured on chorioallantoic membrane was similar to that observed in vivo. These studies further indicated that both vascular cells and viable chondrocytes were required for resorption. Susceptibility to resorption could be induced in resistant primary ossification centers by prior culture in the absence of vascular cells, and it is suggested that it results from the accumulation of resorption-susceptible cells and matrix as a result of continued chondrocyte development.

A rapid and ultrasensitive method for measurement of DNA, calcium and protein content, and alkaline phosphatase activity of chondrocyte cultures

Most investigators are cognizant of the problems inherent in counting cells embedded in a complex and abundant extracellular matrix. To overcome these obstacles, we developed a new method of isolating nucleic acids from chondrocytes which facilitates measurement of cell number by DNA analysis. Chondrocytes were isolated from chick embryo sterna and grown continuously without subculturing for 2-3 weeks in monolayer. The cells were treated with triton X-100 and the nucleic acid content of the extract was determined by measuring DNA fluorescence in the presence of Hoechst dye 33258. To minimize background fluorescence due to the triton, we precipitated the DNA with alcohol and then solubilized the nucleic acids in EDTA. This simple procedure removed the detergent and substantially increased the sensitivity of the method. Thus, we could measure with high precision and high recovery, the DNA content of cultures of 10,000-50,000 cells. In a single well containing 0.5-1.0 million cells, sufficient material remained for subsequent measurements of alkaline phosphatase activity and protein and calcium content. As the mineral present in the triton-treated samples was soluble in EDTA, we experienced no problems in measuring the calcium content of the culture. In addition, as triton X-100 is a nonionic detergent, we were able to measure cell and matrix proteins; moreover, the presence of the triton maintained the catalytic state of alkaline phosphatase. We conclude that this procedure provides a simple and rapid approach to measuring major indicators of chondrocyte maturation and function.

Autocrine or paracrine transforming growth factor-beta modulates the phenotype of chick embryo sternal chondrocytes in serum-free agarose culture

Sternal chondrocytes of 17-day-old chick embryos in serum-free agarose culture secrete transforming growth factor-beta. Media conditioned by such cells prevent serum-induced chondrocyte hypertrophy and cause a phenotypic modulation in serum-free culture which is similar to that observed for chondrocytes in monolayer culture. The modulated cells lose the round shape of differentiated chondrocytes and increasingly with time resemble tendon fibroblasts embedded into agarose. In addition, they produce less matrix macromolecules which include collagen I rather than cartilage collagens II, IX, X, and XI. All of these effects are abolished upon addition to the conditioned media of a monoclonal antibody against recombinant human transforming growth factor-beta 2. The same factor caused effects closely similar to those elicited by conditioned media. Therefore, the phenotypic modulation in adhesion-dependent cultures of chondrocytes in vitro does not directly result from cell-matrix interactions but can be produced also in suspension culture under the direction of appropriate diffusible stimuli that include transforming growth factor-beta. In addition, the results support the concept of transforming growth factor-beta as a multifunctional cytokine acting differently on cells of the same developmental origin depending on their stage of differentiation.

Comparison of intraosseous and intravenous delivery of hypertonic saline/dextran in anesthetized, euvolemic pigs

STUDY OBJECTIVES

With renewed interest in intraosseous (IO) infusion, the present study examined if sternal IO infusion provided vascular entry of 7.5% NaCl/6% dextran-70 (HSD) as efficiently as IV infusion. DESIGN, SETTING, TYPE OF PARTICIPANTS, INTERVENTIONS: Twelve anesthetized pigs were catheterized for measurement of cardiovascular parameters. Six pigs were given a 4-mL/kg IO infusion of HSD under pressure over two to six minutes; each pig was paired with another that had been given HSD IV over the same time course. Rapid arterial blood sampling was used to evaluate vascular entry of NaCl and dextran with monitoring continued for two hours after infusion.

MEASUREMENTS AND MAIN RESULTS

Complete vascular entry of infused sodium and dextran was generally complete within one minute after infusion in all experiments. Increases in mean arterial pressure, cardiac output, and other cardiovascular parameters were indistinguishable between IO and IV infusions. Plasma volume expansion was about 20% above baseline in both groups of pigs. Histologic examination showed minimum pathology to the sternum and no significant pulmonary complications.

CONCLUSION

1O vascular delivery of HSD is a viable alternative in emergency scenarios in which vascular access is compromised.

Domains of type X collagen: alteration of cartilage matrix by fibril association and proteoglycan accumulation

During endochondral bone formation, hypertrophic cartilage is replaced by bone or by a marrow cavity. The matrix of hypertrophic cartilage contains at least one tissue-specific component, type X collagen. Structurally type X collagen contains both a collagenous domain and a COOH-terminal non-collagenous one. However, the function(s) of this molecule have remained largely speculative. To examine the behavior and functions of type X collagen within hypertrophic cartilage, we (Chen, Q., E. Gibney, J. M. Fitch, C. Linsenmayer, T. M. Schmid, and T. F. Linsenmayer. 1990. Proc. Natl. Acad. Sci. USA. 87:8046-8050) recently devised an in vitro system in which exogenous type X collagen rapidly (15 min to several hours) moves into non-hypertrophic cartilage. There the molecule becomes associated with preexisting cartilage collagen fibrils. In the present investigation, we find that the isolated collagenous domain of type X collagen is sufficient for its association with fibrils. Furthermore, when non-hypertrophic cartilage is incubated for a longer time (overnight) with "intact" type X collagen, the molecule is found both in the matrix and inside of the chondrocytes. The properties of the matrix of such type X collagen-infiltrated cartilage become altered. Such changes include: (a) antigenic masking of type X collagen by proteoglycans; (b) loss of the permissiveness for further infiltration by type X collagen; and (c) enhanced accumulation of proteoglycans. Some of these changes are dependent on the presence of the COOH-terminal non-collagenous domain of the molecule. In fact, the isolated collagenous domain of type X collagen appears to exert an opposite effect on proteoglycan accumulation, producing a net decrease in their accumulation, particularly of the light form(s) of proteoglycans. Certain of these matrix alterations are similar to ones that have been observed to occur in vivo. This suggests that within hypertrophic cartilage type X collagen has regulatory as well as structural functions, and that these functions are achieved specifically by its two different domains.

Proteoglycan and collagen synthesis are correlated with actin organization in dedifferentiating chondrocytes

The dedifferentiation of chondrocytes in culture is classically associated with a transition from a rounded to a spread morphology. However, the loss of chondroitin sulfate proteoglycan (CSPG) and type II collagen gene expression (markers of the differentiated chondrocyte) does not occur for all polygonal or fibroblast-like cells at the same stage of culture. Furthermore, it has been demonstrated that retinoic acid-dedifferentiated chondrocytes can reexpress type II collagen if treated by the microfilament disruptive drug dihydrocytochalasin B, without a return to the spherical shape. In the present study, we have investigated by fluorescent double-staining whether the synthesis of both CSPG and type II collagen by dedifferentiating chick chondrocytes in low density cultures is dependent on a type of actin organization. We report that the synthesis of CSPG and type II collagen synthesis is coincident with the presence of a faint microfibrillar actin architecture but is absent in chondrocytes showing well defined actin cables. This correlation was observed independently of the shapes exhibited by the cells. Moreover, type I collagen (marker of the dedifferentiated chondrocyte) is synthesized mainly in cells showing large actin cables. This study, performed in the absence of drugs, suggests that actin organization, rather than changes in cell shape, is involved in modulating the chondrogenic phenotype in vitro.

Utility of human bone marrow obtained incidental to orthopedic surgery for hematopoietic clonal assays

We describe the establishment of a convenient method of acquiring human bone marrow cells for use in microcapillary clonal assays. Femoral epiphyseal and diaphyseal bone fragments and femoral canal reamings were collected incidental to total hip replacement surgery and cultured for human granulocyte-macrophage colony-forming units, erythroid burst-forming units and erythroid colony-forming units. This readily available source of normal human marrow provides an abundant quantity of hematopoietic progenitors of documented normalcy.

Comparative morphological and biochemical analysis of hypertrophic, non-hypertrophic and 1,25(OH)2D3 treated non-hypertrophic chondrocytes

A comparative study of Type X collagen expression, chondrocyte morphology, and the expression of two genes controlling chondrocyte morphology (beta-actin and fibronectin) was carried out on chondrocytes derived from a tissue that remains as permanent hyaline cartilage in vivo (embryonic chicken caudal sterna), from a tissue that undergoes endochondral replacement (embryonic chicken ventral vertebrae) and caudal sternal chondrocytes treated with 1,25(OH)2D3. Under identical in vitro growth conditions and times, sternal chondrocytes grew as rounded non-adherent cells, and vertebral chondrocytes grew as adherent polygonal cells. Upon treatment with 10(-8) M 1,25(OH)2D3 over a twelve day period the sternal chondrocytes showed complete adherence and took on an identical appearance as the vertebral chondrocytes. Cellular adherence of both vertebral and 1,25(OH)2D3 treated sternal chondrocytes was associated with 10 X increased beta-actin, fibronectin and their corresponding mRNA's. Changes in connective tissue expression were observed with altered cellular morphology. Total collagen synthesis was 35-50% lower in both hormone treated and vertebral chondrocytes. Type II collagen was the major collagen type produced by all chondrocyte cultures; however, in both vertebral and 1,25(OH)2D3 treated sternal chondrocytes, a 60 kD collagenous protein was identified. This short chain collagen was determined to be Type X collagen based on its molecular weight and its CNBr peptide maps. Analysis of Type X mRNA levels using a 33 base pair anti sense oligonucleotide sequence to Type X, demonstrated that vertebral cells showed six to seven times more mRNA than sternal chondrocytes. However, the low mRNA levels of type X mRNA in sternal chondrocytes were increased two to three times by 1,25(OH)2D3 treatment. These studies demonstrate that the steroid hormone 1,25(OH)2 vitamin D3 induced morphological, biochemical and molecular changes indicative of chondrocyte maturation from a hyaline to a more hypertrophic phenotype.

A comparison of the morphological, histochemical and biochemical features of embryonic chick sternal chondrocytes in vivo with chondrocytes cultured in three-dimensional collagen gels

Disaggregated chondrocytes from embryonic chick whole sterna proliferate in three-dimensional collagen gels forming mixtures of cartilage nodules (chondroids) and columns of cells. A typical matrix elaborated by the cells is composed of collagen type II and chondroitin and keratan sulphate proteoglycans. The cells of the chondroids are small and uniform whilst those in the columns are larger (hypertrophic) and have a vacuolated cytoplasm. Disaggregated cells from the caudal portion of the sternum (which in vivo contains small uniform cells and does not calcify) tend to form chondroids in culture whilst cells from the cephalic portion (which in vivo contains large hypertrophic cells and whose matrix calcifies) tend to form columns of hypertrophic cells. Only the cultures containing hypertrophic cells synthesise collagen type X and only the hypertrophic cells contain alkaline phosphatase. Collagen type X and alkaline phosphatase may therefore be coregulators of the calcification of hypertrophic cartilage matrix.

Bone lining cells and hematopoiesis: an electron microscopic study of canine bone marrow

Hematopoietic bone marrow in the dog is enclosed by a nearly complete and rather complex layer of endosteum, consisting of a diverse group of cells collectively called bone lining cells (BLC). Cell types comprising BLC include osteoblasts and osteoclasts, and other cell types, among which are elongated, flat cells with a spindle-shaped nucleus, and small cytoplasmic vesicles. The composition and thickness of the layer of BLC varies along the perimeter of the marrow. The layer may be simple or stratified. Occasionally a zone of tightly packed regularly arranged collagenous fibers lies between the bone lining cells and bone. Hematopoiesis, particularly neutrophilic, often occurs in the bone marrow next to the BLC. Cytoplasmic processes of BLC occasionally extend into the hematopoietic spaces and stromal cells in the hematopoietic compartment may extend processes to the layer of BLC. Occasionally cells of the BLC are similar in appearance to stromal cells within the marrow. Our observations together with the experimental findings of others (that fibroblastic stromal cells contribute to the hematopoietic inductive microenvironment, that hematopoietic stem cells are concentrated subosteally, that cells responsible for regeneration of the marrow stroma are derived from the endosteal layer, and that high concentrations of hematopoietic colony-stimulating factors are produced there) indicate that the hematopoietic capacities of bone marrow may be regulated by BLC.

Acquisition and clonal growth of human sternal bone marrow obtained incidental to open-heart surgery

The establishment of a convenient method of acquiring ample human bone marrow and the successful growth of hematopoietic precursor cells in standard methylcellulose assay is described. Human sternal marrow curettings were obtained at open-heart surgery. Growth of colonies derived from CFU-gm, BFU-e, and CFU-e was successful. Comparison of the CFU-gm colony production between this and prior studies indicates a consistent mean and range of growth. These results document this to be an efficient source of normal human marrow.

The effect of ascorbate on embryonic chick sternal chondrocytes cultured in agarose

Primary cultures of embryonic chick sternal chondrocytes were embedded in a three-dimensional matrix of 1% solid agarose which was overlaid with nutrient media. The chondrocytes divided and formed nests of spherically shaped cells which were surrounded by an extensive extracellular matrix containing high molecular weight proteoglycans. Using light and electron microscopy, condensation of proteoglycan was observed pericellularly, often forming septa between cells of a nest, and as part of the outer boundary of the cell nest. No cross-striated collagen fibers were observed in the extracellular matrix although proteoglycan appeared to decorate a network of fine strands. Upon the addition of ascorbate to the nutrient media high molecular weight proteoglycans were synthesized, but there was a marked decrease in the synthesis of proteoglycans after a 10 day exposure to ascorbate. Morphologically, the decrease in proteoglycan synthesis was manifested in the discontinuous arrangement of the pericellular matrix as well as the diffuse form of the cell-nest boundary. Both of these structures were clearly defined in control cultures and were enriched in proteoglycan as demonstrated by ruthenium red staining. This study demonstrates that embryonic chondrocytes remain differentiated when cultured in solid agarose for a period of up to 15 days. They continue to synthesize their tissue specific macromolecules and are phenotypically stable when exposed to ascorbate for extended periods of time.

Selective hypoplasia of pelvic bone marrow

6 patients with thrombocytopenia and anaemia had fatty marrow replacement at the site of an iliac crest. 52Fe scans showed marked abnormalities of bone marrow distribution. Particularly, the uptake of radioiron into the pelvis was almost absent. The sternal marrow was cellular. Studies of the bone marrow which included cytology, histology and electron microscopy failed to reveal why the pelvic marrow was aplastic. Occasional vascular lesions could not seen in the iliac crest bone marrow sections. The cellular morphology showed slight maturation abnormalities. Ferrokinetics were consistent with erythroid marrow hypoplasia. The pelvic and sternal marrow cellularity in patients with pancytopenia may not be representative of the cellularity of the whole marrow, and the pelvic marrow especially may be prone to aplasia.

Distribution of granulopoietic activity in the human skeleton, studied by colony growth in agar diffusion chambers

The colony forming ability of bone marrow cells from 110 haematologically normal patients was investigated by their growth in semi-solid agar in intraperitoneal diffusion chambers. Marrow aspirated from the sternum showed a consistently higher colony yield than that from the iliac crest. Study of site variation in the individual was possible in donors for bone marrow transplantation. In each of four cases, sternal marrow produced more colonies than any other site. Examination of smears made from the aspirated samples suggested that the difference in yield was not due to varying dilution by peripheral blood on aspiration from different sites. It is concluded, therefore, that the incidence of colony precursor cells is not uniform throughout the active marrow.