Comparison of the Ruthenium hexammine trichloride method to other methods of chemical fixation for preservation of avian physeal cartilage

HIF1α is a central regulator of collagen hydroxylation and secretion under hypoxia during bone development

Collagen production is fundamental for the ontogeny and the phylogeny of all multicellular organisms. It depends on hydroxylation of proline residues, a reaction that uses molecular oxygen as a substrate. This dependency is expected to limit collagen production to oxygenated cells. However, during embryogenesis, cells in different tissues that develop under low oxygen levels must produce this essential protein. In this study, using the growth plate of developing bones as a model system, we identify the transcription factor hypoxia-inducible factor 1 α (HIF1α) as a central component in a mechanism that underlies collagen hydroxylation and secretion by hypoxic cells. We show that Hif1a loss of function in growth plate chondrocytes arrests the secretion of extracellular matrix proteins, including collagen type II. Reduced collagen hydroxylation and endoplasmic reticulum stress induction in Hif1a-depleted cells suggests that HIF1α regulates collagen secretion by mediating its hydroxylation and consequently its folding. We demonstrate in vivo the ability of Hif1α to drive the transcription of collagen prolyl 4-hydroxylase, which catalyzes collagen hydroxylation. We also show that, concurrently, HIF1α maintains cellular levels of oxygen, most likely by controlling the expression of pyruvate dehydrogenase kinase 1, an inhibitor of the tricarboxylic acid cycle. Through this two-armed mechanism, HIF1α acts as a central regulator of collagen production that allows chondrocytes to maintain their function as professional secretory cells in the hypoxic growth plate. As hypoxic conditions occur also during pathological conditions such as cancer, our findings may promote the understanding not only of embryogenesis, but also of pathological processes.

Micromass culture of human anulus cells: morphology and extracellular matrix production

STUDY DESIGN

Micromass culture was assessed as a cell culture microenvironment for anulus cells from the human intervertebral disc.

OBJECTIVE

To determine whether the micromass culture technique might be useful for the culture of human anulus cells.

SUMMARY OF BACKGROUND DATA

Culture of cells in micromass has been traditionally used as a method to culture chondrocytes in a three-dimensional (3D) microenvironment with specialized chondrocyte media which allows expression of the chondrocytic phenotype. Recently it has also been used for disc cell 3D culture.

METHODS

Following approval of our human subjects Institutional Review Board, cells isolated from human anulus intervertebral disc tissue was cultured in micromass culture under control conditions or with addition of 5 ng/mL transforming growth factor-beta (TGF-beta). Cultures were grown for 7 days, and then analyzed for morphology with light microscopy, for extracellular matrix (ECM) production with transmission electron microscopy and quantitative measurement of total sulfated proteoglycan production. Immunohistochemistry was also performed to assess types I and II collagen, decorin, keratan sulfate, and chondroitin sulfate content of ECM.

RESULTS

Human anulus cells form multilayered colonies when cultured with minimal media and 20% fetal bovine serum in the micromass methodology. Stimulation of ECM production occurs when 5 ng/mL TGF-beta was added to the micromass media. TGF-beta also significantly increased the production of sulfated proteoglycans (P = 0.026). Under both control and TGF-beta-supplementation, the resulting micromass formed by anulus cells is not as compact as the micromass which results when stem cells cultured in chondrogenic media. Ultrastructural studies showed the presence of apoptotic cells and the presence of peroxisomes within cells. Immunohistochemical studies on production of type I collagen, decorin and keratan sulfate showed that there was localized production of these ECM components in focal regions; chondroitin sulfate and type II collagen, however, showed a more uniform overall production by cells within the micromass.

CONCLUSION

Human anulus cells were successfully cultured under micromass conditions in nonchondrogenic media and with TGF-beta supplementation which increased ECM production. The resulting anulus cell micromass, however, was not as rounded or compact as that which occurs with routine chondrocyte micromass or stem cells induced into chondrocyte differentiation. The presence of peroxisomes noted on ultrastructural studies may reflect cell stress or uneven distribution of nutrition within the micromass during the 7-day micromass culture period. Immunohistochemical studies showed nonuniform ECM gene expression and production within the micromass, suggesting variable gene expression patterns with this culture method.

Ultrastructure of inclusion bodies in annulus cells in the degenerating human intervertebral disc

The rough endoplasmic reticulum (rER) of the cell has an architectural editing function that checks whether protein structure and three-dimensional assembly have occurred properly prior to export of newly synthesized material out of the cell. If these have been faulty, the material is retained within the rER as an inclusion body. Inclusion bodies have been identified previously in chondrocytes and osteoblasts in chondrodysplasias and osteogenesis imperfecta. Inclusion bodies in intervertebral disc cells, however, have only recently been recognized. Our objectives were to use transmission electron microscopy to analyze more fully inclusion bodies in the annulus pulposus and to study the extracellular matrix (ECM) surrounding cells containing inclusion bodies. ECM frequently encapsulated cells with inclusion bodies, and commonly contained prominent banded aggregates of Type VI collagen. Inclusion body material had several morphologies, including relatively smooth, homogeneous material, or a rougher, less homogeneous feature. Such findings expand our knowledge of the fine structure of the human disc cell and ECM during disc degeneration, and indicate the potential utility of ultrastructural identification of discs with intracellular inclusion bodies as a screening method for molecular studies directed toward identification of defective gene products in degenerating discs.

Colony formation and matrix production by human anulus cells: modulation in three-dimensional culture

STUDY DESIGN

Human intervertebral disc cells from the anulus were tested in a study of colony formation and extracellular matrix (ECM) production during long-term three-dimensional culture with exposure to selected cytokines. Experimental studies were approved by the authors' Human Subjects Institutional Review Board.

OBJECTIVES

To quantitatively evaluate colony formation and qualitatively assess ECM production (using immunohistochemistry and in situ hybridization) in cells derived from Thompson Grades I to V discs and tested in culture with cytokines and nutrient supplementation.

SUMMARY OF THE BACKGROUND DATA

Human intervertebral disc cells offer special in vitro challenges because of the slow-growing nature of these cells and their need for specialized three-dimensional in vitro conditions, which permit the expression and production of proteoglycans and Type II collagen, two ECM products that are important for disc cell biology.

METHODS

Discs from 9 human subjects (2 control donors and 7 surgical patients, Thompson Grades I-V), mean age 35.8 years, were used to obtain anulus cells to be tested in three-dimensional agarose culture. Tests of specialized growth conditions included treatment with ITS (insulin-transferrin-sodium selenite supplement), insulin-like growth factor I (IGF-I), and transforming growth factor-beta1 (TGF-beta1). Cultures were evaluated after 14 to 36 days of culture for % colony formation and cell numbers/colony; immunocytochemistry, in situ hybridization, and quantitative histology were used to evaluate colony formation and ECM production.

RESULTS

: Data showed that compared with the average 17.5% colony formation observed in controls, ITS, TGF-beta1 and ITS with IGF-I significantly increased colony formation (28.4%, 30.4%, and 30.4%, respectively, P < or = 0.04). Even cells derived from Thompson Grade V disc showed responsiveness to cytokines and improved production of ECM in vitro.

CONCLUSIONS

: Findings indicated that cells derived from discs with advanced degeneration were still responsive to cytokines and could be modulated to produce Type II collagen and proteoglycans in three-dimensional culture by the addition of enriched media and selected cytokines. Such findings are important since they advance our understanding of how to modulate disc cell behavior in vitro, and may have application to potential future biologic therapies for disc degeneration.

Ultrastructure of the human intervertebral disc during aging and degeneration: comparison of surgical and control specimens

STUDY DESIGN

Human intervertebral disc tissue from the annulus was obtained in a prospective study investigating the ultrastructural features of disc cells and extracellular matrix. Experimental studies were approved by the authors' Human Subjects Institutional Review Board. Discs were obtained from surgical specimens and control donors.

OBJECTIVE

To compare the cellular and extracellular matrix characteristics of the annulus from control and surgical disc specimens using electron microscopy and specialized fixation that visualizes proteoglycans.

SUMMARY OF THE BACKGROUND DATA

The ultrastructural features of disc cells and the disc matrix have received little attention, as compared with the literature on age- and disease-related changes in bone and cartilage.

METHODS

Ultrastructural studies investigated disc tissue obtained from control and surgical disc specimens using transmission electron microscopy. Specialized fixation with ruthenium red was used to highlight matrix proteoglycans.

RESULTS

Cellular and extracellular matrix fine structure was assessed in disc specimens from 29 control donors (newborns to 79-year-olds) and surgical disc specimens from 49 patients (16- to 77-year-olds). Control and surgical tissue showed similar ultrastructural features. Unusual matrix surrounding and encircling single cells or clusters of cells was common (48% of control and 63% of surgical specimens) and often contained fibrous long-spacing collagen (41.3% of control and 36.7% of surgical specimens). Ruthenium red greatly aided visualization of proteoglycans pooled in lacunar spaces. Variable cross-sectional diameters of collagen fibrils was present in 34% of control and 59% of surgical specimens. Regions with sparse interterritorial matrix were common. Cell morphology showed both cells with apoptotic nuclei and synthetically active cells that appeared healthy.

CONCLUSIONS

Control and surgical specimens of the annulus showed similar ultrastructural features. Heterogeneity of collagen fibril diameter is an important observation because it is believed that fibril size relates to biomechanical disc function. Fibrous long-spacing collagen may reflect extracellular matrix remodeling or the presence of previous fibril depolymerization followed by repolymerization and reassociation with proteoglycans. Synthetic activity of disc cells is reflected in active rough endoplasmic reticulum, Golgi, and pools of proteoglycans in lacunar spaces and unusual extracellular matrix components that encircle cells and cell clusters. Such components may influence biomechanical quality. Departures from normal extracellular matrix organization of the aging or degenerating disc undoubtedly contribute to decreased biomechanical function of the annulus because they disrupt the normal annulus architecture. This study underscores the need for a fuller understanding of the dynamic relation between disc cells and the surrounding extracellular matrix, which they continually produce and remodel.

Observations on morphologic changes in the aging and degenerating human disc: secondary collagen alterations

BACKGROUND

In the annulus, collagen fibers that make up the lamellae have a wavy, planar crimped pattern. This crimping plays a role in disc biomechanical function by allowing collagen fibers to stretch during compression. The relationship between morphologic changes in the aging/degenerating disc and collagen crimping have not been explored.

METHODS

Ultrastructural studies were performed on annulus tissue from 29 control (normal) donors (aged newborn to 79 years) and surgical specimens from 49 patients (aged 16 to 77 years). Light microscopy and specialized image analysis to visualize crimping was performed on additional control and surgical specimens. Human intervertebral disc tissue from the annulus was obtained in a prospective morphologic study of the annulus. Studies were approved by the authors' Human Subjects Institutional Review Board.

RESULTS

Three types of morphologic changes were found to alter the crimping morphology of collagen: 1) encircling layers of unusual matrix disrupted the lamellar collagen architecture; 2) collagen fibers were reduced in amount, and 3) collagen was absent in regions with focal matrix loss.

CONCLUSIONS

Although proteoglycan loss is well recognized as playing a role in the decreased shock absorber function of the aging/degenerating disc, collagen changes have received little attention. This study suggests that important stretch responses of collagen made possible by collagen crimping may be markedly altered by morphologic changes during aging/degeneration and may contribute to the early tissue changes involved in annular tears.

New aspects of endochondral ossification in the chick: chondrocyte apoptosis, bone formation by former chondrocytes, and acid phosphatase activity in the endochondral bone matrix

A detailed histological study of the growth plates from 9- to 20-day-old embryonic chick long bones was carried out with the aim of clarifying the long-debated question of the fate of the hypertrophic chondrocytes. Since resorption in chick bones does not occur synchronously across the plate as it does in mammals, specialized regions develop and the fate of the chondrocyte depends on its location within the growth plate. Where resorption took place, as at the sites of primary vascular invasion or at the main cartilage/marrow interface, chondrocytes underwent apoptosis before the lacunae were opened. In addition, spontaneous apoptosis of chondrocytes occurred at apparently random sites throughout all stages of chondrocyte differentiation. In older chick bones, a thick layer of endochondral bone matrix covered the cartilage edge. This consisted of type I collagen and the typical noncollagenous bone proteins but, in addition, contained tartrate-resistant acid phosphatase in the mineralized matrix. Where such matrix temporarily protected the subjacent cartilage from resorption, chondrocytes differentiated to bone-forming cells and deposited bone matrix inside their lacunae. At sites of first endochondral bone formation, some chondrocytes underwent an asymmetric cell division resulting in one daughter cell which underwent apoptosis, while the other cell remained viable and re-entered the cell cycle. This provided further support for the notion that chondrocytes as well as marrow stromal cells give rise to endochondral osteoblasts.

Safranin O reduces loss of glycosaminoglycans from bovine articular cartilage during histological specimen preparation

The ability of Safranin O, added to fixation and decalcification solutions, to prevent the escape of glycosaminoglycans (GAGs) from small cartilage tissue blocks during histological processing of cartilage has been studied. GAGs in the fixatives and decalcifying solutions used and those remaining in the 1 mm3 cubes of cartilage were assayed biochemically. The quantity of GAGs remaining in the cartilage cubes were determined from Safranin O-stained sections using videomicroscopy or microspectrophotometry. A quantity (10.6%) of GAGs were lost during a conventional 4% buffered formaldehyde fixation (48 h) and a subsequent decalcification in 10% EDTA (12 days) at 4 degrees C. Roughly one-quarter of the total GAG loss occurred during the 48 h fixation, and three-quarters during the 12 days of decalcification. Inclusion of 4% formaldehyde in the decalcification fluid decreased the loss of GAGs to 6.2%. The presence of 0.5% Safranin O in the fixative reduced this loss to 3.4%. When 0.5% Safranin O was included in the fixative and 4% formaldehyde in the decalcification solution, Safranin O staining of the histological sections increased on average by 13.5%. After fixation in the presence of 0.5% Safranin O, there was no difference in the staining intensities when decalcification was carried out in the presence of either Safranin O or formaldehyde, or both. It took 24 h for Safranin O to penetrate into the deep zone of articular cartilage, warranting a fixation period of at least this long. In conclusion, the addition of Safranin O to the fixative and either Safranin O or formaldehyde in the following decalcification fluid, markedly reduces the loss of GAGs from small articular cartilage explants during histological processing. However, for immunohistochemical studies, Safranin O cannot be included in the processing solutions, because it may interfere.

Hyaluronan contributes to the enlargement of hypertrophic lacunae in the growth plate

Histochemical staining of the epiphysial growth plate revealed that free hyaluronan (i.e. available to the staining probe) was restricted to the zone of hypertrophy, where it was located in the pericellular space between the chondrocytes and the edge of the lacunae. Furthermore, the amount of hyaluronan staining was directly proportional to the size of the lacunae. Autoradiographic analysis of growth plates cultured with isotopically labeled glucosamine indicated that at least a portion of this hyaluronan was newly synthesized by the hypertrophic chondrocytes. Since hyaluronan can adsorb large amounts of water, it is possible that it exerted a hydrostatic pressure on the surrounding territorial matrix and thereby caused the expansion of hypertrophic lacunae. To assess this possibility, segments of the growth plate were placed in organ culture under different conditions. Under normal culture conditions, a band of hyaluronan staining migrated across the segments coinciding with the enlargement of lacunae in these regions, and the segments, as a whole, increased in size. In contrast, when the segments were cultured in the presence of hyaluronidase, which degraded the pericellular hyaluronan, the lacunae did not undergo enlargement and the overall size of the segments did not increase. These results suggest that the production of hyaluronan contributes to the enlargement of hypertrophic lacunae which is important for determining both the body's stature and proportions.

Ultrastructural changes of chondrocytes of growth plates of young broiler chickens predisposed to tibial dyschondroplasia

Growth plates from the proximal tibiotarsal bones of growing broiler chickens from lines exhibiting high and low incidences of tibial dyschondroplasia (TD) were compared for ultrastructural differences. Samples of growth plates were collected from five chickens of each line at 2, 7, 14, and 21 d of age. Each sample was prepared for ultrastructural evaluation after initial fixation in 2.5% glutaraldehyde and secondary fixation in 1% osmium tetroxide, each containing .7% ruthenium hexamine trichloride. No gross TD lesions were observed. The ultrastructure of growth plates of birds at 2, 7, and 14 d of age was similar between the groups. However, at 21 d of age, chondrocytes in the prehypertrophic zone of the high incidence group contained large lipid inclusions and vesiculated and disarranged stacks of rough endoplasmic reticulum with greatly dilated cisternae. Apoptotic and necrotic chondrocytes were present in the hypertrophic zone. Nuclei of apoptotic chondrocytes contained crescentic caps of condensed chromatin. The cytoplasm contained short segments of dilated granular endoplasmic reticulum, lipid droplets, and vacuoles. Necrotic chondrocytes appeared as amorphous masses with pyknotic and karyorrhectic nuclei. These changes were not observed in chondrocytes of the low TD incidence group and have not been previously reported in nonthickened growth plate cartilage.