Abnormal ambient glucose levels inhibit proteoglycan core protein gene expression and reduce proteoglycan accumulation during chondrogenesis: possible mechanism for teratogenic effects of maternal diabetes

Optimization of culture media to enhance the growth of tissue engineered cartilage

Tissue engineering is a promising option for cartilage repair. However, several hurdles still need to be overcome to develop functional tissue constructs suitable for implantation. One of the most common challenges is the general low capacity of chondrocytes to synthesize cartilage-specific extracellular matrix (ECM). While different approaches have been explored to improve the biosynthetic response of chondrocytes, several studies have demonstrated that the nutritional environment (e.g., glucose concentration and media volume) can have a profound effect on ECM synthesis. Thus, the purpose of this study was to optimize the formulation of cell culture media to upregulate the accumulation of cartilaginous ECM constituents (i.e., proteoglycans and collagen) by chondrocytes in 3D culture. Using response surface methodology, four different media factors (basal media, media volume, glucose, and glutamine) were first screened to determine optimal media formulations. Constructs were then cultured under candidate optimal media formulations for 4 weeks and analyzed for their biochemical and structural properties. Interestingly, the maximal accumulation of proteoglycans and collagen appeared to be elicited by different media formulations. Most notably, proteoglycan accumulation was favored by high volume, low glucose-containing DMEM/F12 (1:1) media whereas collagen accumulation was favored by high volume, high glucose-containing F12 media. While high glutamine-containing media elicited increased DNA content, glutamine concentration had no apparent effect on ECM accumulation. Therefore, optimizing the nutritional environment during chondrocyte culture appears to be a promising, straight-forward approach to improve cartilaginous tissue formation. Future work will investigate the combined effects of the nutritional environment and external stimuli.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human

OBJECTIVE

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation.

DESIGN

SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1β-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes.

RESULTS

SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1β-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage.

CONCLUSIONS

SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.

Directing Chondrogenesis of Primary Chondrocytes by Exposure to Glucose Concentrations

Since articular cartilage is avascular, both nutrient supply and metabolic waste excretion depend on diffusion. However, the major cause of the progression of articular cartilage defect is the poor inherent regenerative capacity of chondrocytes which limits the process of cartilage tissue repair. Creation of nutrient gradients in in vitro cell culture, however, can provide a clue on zonal distributions of cells and glycosaminoglycan synthesis throughout the tissue engineered cartilage. We hypothesized that glucose gradient, in combination with growth factors, could induce differences in matrix distributions for articular cartilage regeneration. Chondrocytes were harvested from bovine cartilage and expanded in monolayers. First, either p0 or p2 chondrocytes were differentiated in serum-free chondrogenic medium containing different glucose concentrations supplemented with TGFβ3/dex or IGF-1under hypoxic or normoxic conditions for 7 days in monolayer. The results indicate that cellular metabolism, cell numbers and glycosaminoglycan (GAG) content increased with increase in glucose concentration in all conditions. Aggrecan (AGC) expression consistently increased with decreasing glucose concentration in both normoxic and hypoxic conditions. COL II and COL I expressions increased with increasing glucose concentration up to 5mmol/L. The expression of COMP increased with increasing glucose concentration under hypoxic conditions and interestingly showed an opposite trend under normoxic conditions. However, comparing the chondrogenic capacity of p0 and p2 cells in the different glucose concentrations did not show differences, but the potential of p2 cells was in general lower compared to p0. Hypoxia had stimulatory effects on matrix production compared to normoxia in both passages. Therefore, supplemented glucose concentration in monolayer could induce differences in matrix production, but the chondrogenic potential remained equal. Therefore, this information could be use to a create gradients through a tissue-engineered cartilage.

Echocardiographic findings of congenital cardiopathies among fetuses of diabetic pregnant women and their relationship with plasma fructosamine levels

OBJECTIVE

To study the occurrence of congenital cardiopathies at echocardiography (CCE) in fetuses whose mothers had preexisting diabetes mellitus (PGDM) and to study the potential of using fructosamine level as a late marker (beyond the first trimester) for CCE.

METHODS

A register study covering 91 pregnant women that underwent routine fetal echocardiography ordered due to PGDM. The first dosage of plasma fructosamine found in 65 medical records was analyzed during prenatal care (20.4 ± 8.0 weeks of gestation). The presence or absence of structural or functional CCE was associated with fructosamine levels by logistic regression. We assessed the effect modification odds ratio by maternal age and insulin usage.

RESULTS

Thirty-four fetuses (52.3% of 65 fetuses) presented CCE. Twenty of them had functional CCE and 14 presented structural CCE. The mean maternal plasma fructosamine level was higher among pregnant women whose fetuses presented CCE than in those whose fetuses did not (2.86 ± 0.73 mmol/l, 2.22 ± 0.54 mmol/l, respectively, p < 0.0001). Crude OR for CCE and abnormal plasma fructosamine (>2.68 mmol/l) was 9.6 (2.8-33.7, 95% CI, p < 0.0001). Adjusted OR by maternal age and insulin usage was 10.9 (2.7-45.2, 95% CI p < 0.0001).

CONCLUSIONS

An abnormal plasma fructosamine level increases the chances of CCE occurring among referral pregnant women with PGDM.

The brown adipocyte differentiation pathway in birds: an evolutionary road not taken

Background

Thermogenic brown adipose tissue has never been described in birds or other non-mammalian vertebrates. Brown adipocytes in mammals are distinguished from the more common white fat adipocytes by having numerous small lipid droplets rather than a single large one, elevated numbers of mitochondria, and mitochondrial expression of the nuclear gene UCP1, the uncoupler of oxidative phosphorylation responsible for non-shivering thermogenesis.

Results

We have identified in vitro inductive conditions in which mesenchymal cells isolated from the embryonic chicken limb bud differentiate into avian brown adipocyte-like cells (ABALCs) with the morphological and many of the biochemical properties of terminally differentiated brown adipocytes. Avian, and as we show here, lizard species lack the gene for UCP1, although it is present in amphibian and fish species. While ABALCs are therefore not functional brown adipocytes, they are generated by a developmental pathway virtually identical to brown fat differentiation in mammals: both the common adipogenic transcription factor peroxisome proliferator-activated receptor-γ (PPARγ), and a coactivator of that factor specific to brown fat differentiation in mammals, PGC1α, are elevated in expression, as are mitochondrial volume and DNA. Furthermore, ABALCs induction resulted in strong transcription from a transfected mouse UCP1 promoter.

Conclusion

These findings strongly suggest that the brown fat differentiation pathway evolved in a common ancestor of birds and mammals and its thermogenicity was lost in the avian lineage, with the degradation of UCP1, after it separated from the mammalian lineage. Since this event occurred no later than the saurian ancestor of birds and lizards, an implication of this is that dinosaurs had neither UCP1 nor canonically thermogenic brown fat.

Influence of oxygen on the proliferation and metabolism of adipose derived adult stem cells

Articular cartilage is an avascular connective tissue that exhibits little intrinsic capacity for repair. Articular cartilage exists in a reduced oxygen ( approximately 5%) environment in vivo; therefore, oxygen tension may be an important factor that regulates the metabolism of chondrocyte progenitors. A number of recent studies have developed tissue engineering approaches for promoting cartilage repair using undifferentiated progenitor cells seeded on biomaterial scaffolds, but little is known about how oxygen might influence these engineered tissues. Human adipose-derived adult stem (hADAS) cells isolated from the stroma of subcutaneous fat were suspended in alginate beads and cultured in control or chondrogenic media in either low oxygen (5%) or atmospheric oxygen tension (20%) for up to 14 days. Under chondrogenic conditions, low oxygen tension significantly inhibited the proliferation of hADAS cells, but induced a two-fold increase in the rate of protein synthesis and a three-fold increase in total collagen synthesis. Low oxygen tension also increased glycosaminoglycan synthesis at certain timepoints. Immunohistochemical analysis showed significant production of cartilage-associated matrix molecules, including collagen type II and chondroitin-4-sulfate. These findings suggest oxygen tension may play an important role in regulating the proliferation and metabolism of hADAS cells as they undergo chondrogenesis, and the exogenous control of oxygen tension may provide a means of increasing the overall accumulation of matrix macromolecules in tissue-engineered cartilage.

Double child burial from sunghir (Russia): Pathology and inferences for upper paleolithic funerary practices

The double child burial from Sunghir (Russia) is a spectacular Mid Upper Palaeolithic funerary example dated to about 24,000 BP. A boy (Sunghir 2) and a girl (Sunghir 3), about 12-13 and 9-10 years old, respectively, were buried at the same time, head to head, covered by red ocher and ornamented with extraordinarily rich grave goods. Examination of the two skeletons reveals that the Sunghir 3 femora are short and exhibit marked antero-posterior bowing. The two femora do not show any asymmetry in the degree of shortening and bowing. Bowing affects the whole diaphysis and shows a regularly incurved profile, with the highest point at midshaft. Pathology is confined to the femora, and no other part of this well-preserved specimen shows abnormality. The isolated nature of the Sunghir 3 anomalies points to cases reported in the medical literature under the label of "congenital bowing of long bones" (CBLB). These are a group of rare conditions exhibiting localized, sometimes bilateral, bowing and shortening which are nonspecific and may result from different causes, including abnormalities of the primary cartilaginous anlage (i.e., the aggregation of cells representing the first trace of an organ). Localized ossification disturbances, possibly linked to a diabetic maternal condition, might explain the shortening and the coincidence of maximum midshaft curvature with the position of the primary ossification center, as well as the lack of involvement of other skeletal parts. This scenario, rather than other possibilities (early bilateral midshaft fracture, acute plastic bowing deformities, or faulty fetal posture), provides the most likely explanation for the Sunghir 3 femoral deformities. The intriguing combination of a pathological condition apparent since birth with a spectacular burial of unusually positioned young individuals of different sexes recalls significant aspects of the triple burial from the contemporary site of Dolní Vestonice (Moravia), evoking a patterned relationship between physical abnormality and extraordinary Upper Paleolithic funerary behavior.

Ectodermal FGFs induce perinodular inhibition of limb chondrogenesis in vitro and in vivo via FGF receptor 2

The formation of cartilage elements in the developing vertebrate limb, where they serve as primordia for the appendicular skeleton, is preceded by the appearance of discrete cellular condensations. Control of the size and spacing of these condensations is a key aspect of skeletal pattern formation. Limb bud cell cultures grown in the absence of ectoderm formed continuous sheet-like masses of cartilage. With the inclusion of ectoderm, these cultures produced one or more cartilage nodules surrounded by zones of noncartilaginous mesenchyme. Ectodermal fibroblast growth factors (FGF2 and FGF8), but not a mesodermal FGF (FGF7), substituted for ectoderm in inhibiting chondrogenic gene expression, with some combinations of the two ectodermal factors leading to well-spaced cartilage nodules of relatively uniform size. Treatment of cultures with SU5402, an inhibitor FGF receptor tyrosine kinase activity, rendered FGFs ineffective in inducing perinodular inhibition. Inhibition of production of FGF receptor 2 (FGFR2) by transfection of wing and leg cell cultures with antisense oligodeoxynucleotides blocked appearance of ectoderm- or FGF-induced zones of perinodular inhibition of chondrogenesis and, when introduced into the limb buds of developing embryos, led to shorter, thicker, and fused cartilage elements. Because FGFR2 is expressed mainly at sites of precartilage condensation during limb development in vivo and in vitro, these results suggest that activation of FGFR2 by FGFs during development elicits a lateral inhibitor of chondrogenesis that limits the expansion of developing skeletal elements.

Immunocytochemical demonstration of glucose transporters in epiphyseal growth plate chondrocytes of young rats in correlation with autoradiographic distribution of 2-deoxyglucose in chondrocytes of mice

The epiphyseal growth plate, where chondrocytes proliferate and differentiate, is the major site for longitudinal bone growth, matrix synthesis and mineralization. Glucose is an important energy source for the metabolism and growth of chondrocytes. The family of facilitative glucose transporters (GLUTs) mediates glucose transport across the plasma membrane in mammalian cells. We used immunocytochemical methods with anti-GLUT antibodies to investigate the localization of GLUTs in chondrocytes of the epiphyseal growth plate in 3 age groups of rats (3, 7, and 28 days after birth). Intense immunoreactivity of GLUT isoforms 1-5 was detected in chondrocytes of 3-day and 7-day old rats, and all GLUTs were localized in the maturation zone of the hypertrophic zone. On postnatal day 28, chondrocytes in the maturation zone showed intense GLUT1, 4 and 5 immunoreactivity, and weak GLUT2 and 3 immunoreactivity. In addition to chondrocytes in the maturation zone, those in the degenerative zone and in the zone of provisional calcification showed strong GLUT4 and 5 immunoreactivity. Autoradiography of bone sections from 4-week old mice injected with 14C-2-deoxyglucose showed high silver grain density within matrix tissue in the reserve and proliferative zones but not around chondrocytes. However, in the hypertrophic zone, silver grain density was high in matrix and chondrocytes. These data indicate that chondrocytes in the hypertrophic zones use glucose as energy source. High levels of GLUT4 expression imply that glucose use in chondrocytes is regulated by insulin. Expression of GLUT5 in chondrocytes suggests that fructose is also used as an energy source.

Glucose regulation of the IGF response system in chondrocytes: induction of an IGF-I-resistant state

Nonresponsiveness to the growth-stimulatory actions of insulin-like growth factor (IGF)-I in chondrocytes has been reported in a number of disease states associated with impaired glucose metabolism. Primary rabbit chondrocytes were investigated for changes in their IGF response system [type-I IGF receptor and IGF-binding protein (IGFBP) expression] and in their ability to mount a synthetic response to IGF-I [as 35S-labeled proteoglycan ([35S]PG) production] in media containing varying ambient glucose concentrations. Whereas basal [35S]PG synthetic rate was unaffected by glucose concentration, synthetic responsiveness to IGF-I was lost in media containing <5 mmol/l glucose or in media containing a "diabetic" glucose concentration (25 mmol/l). IGFBP expression, as measured by Northern analysis of mRNA levels and Western ligand blotting of secreted protein levels, was not significantly altered in the different glucose media, nor were there any differences in the cell surface localization of IGFBPs as assessed by affinity cross-linking with 125I-labeled IGF-I, suggesting that IGFBPs do not induce the IGF-I resistance. The nonresponsiveness to IGF-I in reduced glucose occurred with 25-50% reductions in steady-state levels of IGF type-I receptor mRNA and protein. A significant correlation between IGF receptor mRNA level and synthetic response to IGF-I was observed between 0 and 10 mmol/l glucose concentrations, suggesting that the loss of responsiveness in reduced glucose is manifested at the level of transcription and/or receptor mRNA stability. In contrast, nonresponsiveness to IGF-I in chondrocytes in diabetic glucose concentrations occurred without changes in receptor mRNA and protein levels, suggesting that IGF-I resistance was due to post-ligand-binding receptor defects. It is proposed that IGF-I resistance in chondrocytes subjected to inappropriate glucose levels may constitute an important pathogenic mechanism in degenerative cartilage disorders.

Changes in proteoglycans of intervertebral disc in diabetic patients. A possible cause of increased back pain

STUDY DESIGN

Characterization of the analytic profile of proteoglycans in the intervertebral discs at L4-L5 of nondiabetic (n = 5) and diabetic (n = 5) age-matched subjects. The discs used were discarded material from operations.

OBJECTIVES

To clarify the reason for the higher risk of disc prolapse in diabetic patients.

SUMMARY OF BACKGROUND DATA

The pathogenesis of diabetes results from a combination of neurologic dysfunctions and a yet undefined metabolic failure, which leads to an abnormal proteoglycan profile.

METHODS

The following methods were used to determine the proteoglycan profile: the measurement of 35S-sulfate uptake per gram wet tissue into sulfated glycosaminoglycan using fresh tissue explants; extraction of proteoglycans by 4 M guanidinium chloride containing protease inhibitors, with further purification by ultracentrifugation on cesium chloride buoyant density gradient under dissociative conditions; total uronic acid and protein contents in the various gradient fractions; assessing the length of sugar side chains of isolated 35Sulfate-glycosaminoglycan molecules by separation of the glycosaminoglycan molecules on a Sepharose 6B-CL column; and paper chromatography of the final digest products of glycosaminoglycan molecules obtained by chondroitinase ABC, a glycosaminoglycan-degrading enzyme.

RESULTS

The findings show that discs from normal nondiabetic subjects have 15 times the rate of 35Sulfate incorporation into glycosaminoglycan molecules than do discs of diabetic patients. The proteoglycans of diabetic patients are banded at a lower buoyant density, indicating a lowered glycosylation rate and a lower number of sugar side chains per core protein. In discs of diabetic patients, there is a slight increase in the chain length of chondroitin sulfate. Further analysis of the glycosaminoglycan chains showed a decreased amount of keratan sulfate, compared with that in nondiabetic subjects. However, the total uronic acid content of the disc tissues and the ratio of uronic acid to protein of each fraction were unchanged in diabetic patients versus that in control subjects.

CONCLUSIONS

Discs in patients with diabetes have proteoglycans with lower buoyant density and substantially undersulfated glycosaminoglycan, which with the specific neurologic damage in these patients, might lead to increased susceptibility to disc prolapse.

Rapid, fluorometric DNA determination for chick limb-bud mesenchymal-cell microcultures

Micromass cultures of chick and mouse limb-bud mesenchymal cells are commonly used for in vitro studies of cellular differentiation. Previously, adaptation of these cultures to 96-well plates facilitated analyses of various aspects of cellular behavior and the effects of different media components in these cultures. These adjustments allowed development of a serum-free medium for chick limb-bud mesenchymal cells and substantially decreased costs associated with media and reagents. Here we report a further development for this model system; a Hoechst 33342-based in situ DNA assay that provides reliable data much more quickly and with considerably less effort than had been feasible in the past. Because it allows quantitation of products of cellular differentiation and DNA in the same cultures, the number of cultures needed to provide the same data is essentially halved and the accuracy of normalized values for quantitative estimates of markers of differentiation is improved. Studies of the effects of retinoic acid on chick limb-bud mesenchymal cells were performed to document the usefulness of this method.

Increased mitogenic response to heparin-binding epidermal growth factor-like growth factor in vascular smooth muscle cells of diabetic rats

We investigated the mitogenic effects of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in vascular smooth muscle cells (SMCs) obtained from rats with streptozotocin (STZ)-induced diabetes and evaluated the role of heparan sulfate proteoglycan (HSPG) in inducing these effects. HB-EGF significantly increased DNA synthesis in the SMCs of diabetic rats (STZ-SMCs) compared with control rats (control SMCs). However, the mitogenic effects of EGF, which shares EGF receptors with HB-EGF, and basic fibroblast growth factor, another heparin-binding growth factor, were similar in STZ-SMCs and control SMCs. The mitogenic response to HB-EGF in SMCs of insulin-treated diabetic rats was similar to the response in control SMCs. HB-EGF-induced autophosphorylation of EGF receptors was increased in STZ-SMCs compared with control SMCs, although the number of EGF receptors in STZ-SMCs was 40% of that in controls. This increased mitogenic response to HB-EGF in STZ-SMCs was completely inhibited by treatment with heparitinase, chlorate, and a synthetic peptide corresponding to the heparin-binding domain of HB-EGF. Compared with heparan sulfate isolated from control SMCs, heparan sulfate isolated from STZ-SMCs was of smaller molecular size and caused a greater mitogenic effect of HB-EGF. These findings suggest that the mitogenic response to HB-EGF is increased in SMCs of diabetic rats. Changes in cell-associated heparan sulfate in STZ-SMCs may be related to the increased mitogenic response to HB-EGF.

Crystallization and preliminary X-ray diffraction studies of the cartilage link protein from bovine trachea

Cartilage extracellular matrix link protein, having molecular mass of approximately 40 kDa, is a metalloprotein that binds divalent cations and is only soluble in low ionic strength solutions. The link protein was purified from bovine trachea and has been crystallized by a vapor diffusion method using PEG 3350 as precipitant. The crystal symmetry is P1, and the unit cell dimensions are a = 43.55, b = 53.11, c = 60.10 A, alpha = 90.44, beta = 106.21, gamma = 101.51 degrees. The VM of 1.8 A3/Da is consistent with the presence of two molecules of the link protein in the asymmetric unit. The crystals diffract X-rays from a synchrotron source to 1.7 A resolution.

Stage- and region-dependent responses of chick wing-bud mesenchymal cells to retinoic acid in serum-free microcultures

Retinoic acid (RA) has been shown to affect skeletal patterning in vivo in both developing and regenerating limbs. Regional differences in RA concentrations alone cannot account for the region-specific cell behaviors involved in limb-skeletal morphogenesis. The present study explores a role for regional differences in signal interpretation in RA's effects along the anteroposterior and proximodistal axes of stage 21-22 and 23-24 chick wing-buds. Mesenchymal cells isolated from specific limb regions were grown in chemically defined medium and exposed to 5 or 50 ng/ml of RA for 4 days in high-density microtiter cultures. Previous studies showed that RA's effects on chondrogenesis and growth in such cultures differed depending on the position along the limb's proximodistal axis from which the cells were isolated. The present study is the first to show that such differences in RA-responsiveness also exist along the limb's anteroposterior axis, especially in the distal subridge mesenchyme. The region-dependent relationships between RA's effects on growth and chondrogenesis suggest that RA affects these two behaviors through different mechanisms. The regional differences in the responsiveness of these cells to exogenous RA are discussed with respect to their correspondence to the in vivo patterns of expression of RA-binding proteins, RA-receptors, and other patterning-related genes.

Bilateral femoral hypoplasia and maternal diabetes mellitus: case report and review of the literature

The case of a 21-week fetus with bilateral femoral hypoplasia and bowing related to maternal diabetes mellitus is reported. The femoral middiaphysis (site of hypoplasia and bowing) showed intramembranous ossification instead of the normal endochondral ossification, thus pointing to a transient inhibition of chondrogenesis of the mesenchymal femoral model as the causative mechanism. This finding is correlated with the recent experimental advances in the field of limb development in vertebrates.

Stage- and region-dependent chondrogenesis and growth of chick wing-bud mesenchyme in serum-containing and defined tissue culture media

During development, limb-bud mesenchymal cells carry out complex spatiotemporal-patterns of growth and differentiation. Tissue and organ culture facilitate analysis of environmental influences on these cell behaviors, allowing their partial dissection into exogenous and endogenous components. Two factors that complicate such in vitro analyses are the heterogeneity of the cultured cells and imprecise knowledge of culture medium composition. Limb mesenchyme comprises a heterogenous cell population with important regional differences in cell type. Dividing the limb into subregions helps limit the cellular heterogeneity and using chemically defined, serum-free medium alloys concerns about medium composition. In the present study, mesenchyme from different regions along the anteroposterior and proximodistal axes of stage 21-22 and stage 23-24 chick wing buds was grown in high-density microtiter cultures in chemically defined and in serum-containing medium. Four-day cultures of the various regions were compared in terms of culture morphology and the accumulation of Alcian blue-positive cartilage matrix and DNA. The results demonstrate stage- and region-dependent differences in the in vitro growth, differentiation, and responsiveness of these cells. For example, mesenchyme from the distal anterior region of the wing bud exhibited lower intrinsic chondrogenic capacity and greater responsiveness to serum than other regions. Patterns of in vitro chondrogenesis also suggest that, at the stages examined, distal wing-bud mesenchyme may be less homogeneous than has been believed. A case is made for the suitability of serum-free medium for future in vitro studies of chick limb-bud mesenchyme. The results are considered in relation to the process of limb development and regional expression of pattern-related genes.

The role of the visceral yolk sac in hyperglycemia-induced embryopathies in mouse embryos in vitro

The adverse developmental effects of hyperglycemia to rodent embryos have been shown using whole embryo culture. Although, a mechanism by which hyperglycemia-induced effects occur is unknown, recent work has focused on the visceral yolk sac as a potential target tissue. Therefore, we have evaluated the developmental effects of hyperglycemia in early head fold stage mouse embryos in vitro and assessed the histiotrophic function of the visceral yolk sac. As has been previously shown in rodents, hyperglycemia produced neural tube closure defects in a concentration dependent manner at 33, 50, and 67 mM glucose using a 44 h exposure period. However, exposure times between 6 and 12 h were sufficient to alter embryonic development when the glucose concentration was 50 or 67 mM. In contrast, early somite stage embryos (4-6 somite stage) appear to be less sensitive to dysmorphogenesis and a 48 h exposure to 67 mM glucose but not 33 or 50 mM also produced neural tube defects. Hyperglycemia (67 mM) did not alter the uptake of 35S-methionine and 35S-cysteine-labeled hemoglobin (35S-Hb) in the visceral yolk sac (VYS) in early headfold staged embryos. However, the accumulation of 35S in the embryo was reduced by 16-18% at glucose concentrations of 50 or 67 mM during the last 12 h of a 44 h exposure period. No effect on VYS uptake or embryonic accumulation of 35S-labeled products was observed at shorter exposure periods (12-24 and 24-36 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of cartilage proteoglycan (aggrecan) core protein and link protein gene expression during human skeletal development

The distribution of cartilage proteoglycan core protein (aggrecan) and cartilage proteoglycan link protein was investigated by in situ hybridization during different stages of human skeletal development. Aggrecan and link protein expression were confined to chondrocytes of the developing skeleton and other cartilaginous structures. Distribution and intensity of the signal was identical with aggrecan as compared to link protein probes. Parallel to the calcification of cartilaginous matrix, chondrocytes of this area lost the expression of aggrecan and link protein specific mRNA and stayed negative throughout the following stages of skeletal development. Highest expression was found in the lower proliferative and upper hypertrophic zone whereas the resting zone showed less expression. Aggrecan gene expression was additionally investigated in iliac crest biopsies of 3 patients with pseudoachondroplasia and compared to age-matched controls. Distribution and intensity of staining revealed no abnormalities. Thus, the phenotypic changes during chondrocyte maturation are accompanied by distinct changes in aggrecan and link protein gene expression. This pattern was maintained in the growth plate of patients with pseudoachondroplasia.