Enzymatic outside-in cross-linking enables single-step microcapsule production for high-throughput three-dimensional cell microaggregate formation

Cell-laden hydrogel microcapsules enable the high-throughput production of cell aggregates, which are relevant for three-dimensional tissue engineering and drug screening applications. However, current microcapsule production strategies are limited by their throughput, multistep protocols, and limited amount of compatible biomaterials. We here present a single-step process for the controlled microfluidic production of single-core microcapsules using enzymatic outside-in cross-linking of tyramine-conjugated polymers. It was hypothesized that a physically, instead of the conventionally explored biochemically, controlled enzymatic cross-linking process would improve the reproducibility, operational window, and throughput of shell formation. Droplets were flown through a silicone delay line, which allowed for highly controlled diffusion of the enzymatic cross-linking initiator. The microcapsules' cross-linking density and shell thickness is strictly depended on the droplet's retention time in the delay line, which is predictably controlled by flow rate. The here presented hydrogel cross-linking method allows for facile and cytocompatible production of cell-laden microcapsules compatible with the formation and biorthogonal isolation of long-term viable cellular spheroids for tissue engineering and drug screening applications.

Dickkopf-related protein 1 and gremlin 1 show different response than frizzled-related protein in human synovial fluid following knee injury and in patients with osteoarthritis

OBJECTIVE

To explore the involvement of the wingless-type MMTV integration site (WNT) and bone morphogenetic protein (BMP) antagonists dickkopf-related protein 1 (DKK1), frizzled-related protein (FRZB) and gremlin 1 (GREM1) in knee injury and osteoarthritis (OA).

DESIGN

The antagonists were immunoassayed in synovial fluid from a cross-sectional cohort of nine knee healthy reference subjects, patients with recent (0-77 days, n = 158) or old (1-37 years, n = 50) knee injuries, and OA (n = 22). Cartilage (ARGS-aggrecan, cartilage oligomeric matrix protein and C2C type II collagen) and other biomarkers were assessed in synovial fluid in a subset of samples. Statistical analysis was by Kendall's tau (τ) correlation, Mann-Whitney U test, and linear regression analysis.

RESULTS

Compared to references, median concentration of GREM1 (but not DKK1 and FRZB) was elevated 1.5-fold immediately after injury, and FRZB was reduced 1000-folds in OA. All three antagonists decreased with increasing time after injury as well as with increasing age, but the temporal change after injury was less accentuated for FRZB (peaked 8-22 days after injury) compared to that of DKK1 and GREM1 (peaked immediately after injury). In the recent injury group, there was a correlation between GREM1 and DKK1 (τ = 0.172); FRZB concentrations correlated with concentrations of cartilage biomarkers (τ between 0.257 and 0.369), while DKK1 and GREM1 were inversely correlated (τ between -0.177 and -0.217) with these markers.

CONCLUSIONS

Our results indicate separate roles for the antagonists, where DKK1 and GREM1 had similarities in response to injury and in OA, with a different response for FRZB.

Trophic effects of adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells enhance cartilage generation by chondrocytes in co-culture

AIMS

Combining mesenchymal stem cells (MSCs) and chondrocytes has great potential for cell-based cartilage repair. However, there is much debate regarding the mechanisms behind this concept. We aimed to clarify the mechanisms that lead to chondrogenesis (chondrocyte driven MSC-differentiation versus MSC driven chondroinduction) and whether their effect was dependent on MSC-origin. Therefore, chondrogenesis of human adipose-tissue-derived MSCs (hAMSCs) and bone-marrow-derived MSCs (hBMSCs) combined with bovine articular chondrocytes (bACs) was compared.

METHODS

hAMSCs or hBMSCs were combined with bACs in alginate and cultured in vitro or implanted subcutaneously in mice. Cartilage formation was evaluated with biochemical, histological and biomechanical analyses. To further investigate the interactions between bACs and hMSCs, (1) co-culture, (2) pellet, (3) Transwell® and (4) conditioned media studies were conducted.

RESULTS

The presence of hMSCs-either hAMSCs or hBMSCs-increased chondrogenesis in culture; deposition of GAG was most evidently enhanced in hBMSC/bACs. This effect was similar when hMSCs and bAC were combined in pellet culture, in alginate culture or when conditioned media of hMSCs were used on bAC. Species-specific gene-expression analyses demonstrated that aggrecan was expressed by bACs only, indicating a predominantly trophic role for hMSCs. Collagen-10-gene expression of bACs was not affected by hBMSCs, but slightly enhanced by hAMSCs. After in-vivo implantation, hAMSC/bACs and hBMSC/bACs had similar cartilage matrix production, both appeared stable and did not calcify.

CONCLUSIONS

This study demonstrates that replacing 80% of bACs by either hAMSCs or hBMSCs does not influence cartilage matrix production or stability. The remaining chondrocytes produce more matrix due to trophic factors produced by hMSCs.

Arthroscopic airbrush assisted cell implantation for cartilage repair in the knee: a controlled laboratory and human cadaveric study

OBJECTIVE

The objective of this study was to investigate the feasibility of arthroscopic airbrush assisted cartilage repair.

METHODS

An airbrush device (Baxter) was used to spray both human expanded osteoarthritic chondrocytes and choncrocytes with their pericellular matrix (chondrons) at 1 × 10(6) cells/ml fibrin glue (Tissucol, Baxter) in vitro. Depth-dependent cell viability was assessed for both methods with confocal microscopy. Constructs were cultured for 21 days to assess matrix production. A controlled human cadaveric study (n = 8) was performed to test the feasibility of the procedure in which defects were filled with either arthroscopic airbrushing or needle extrusion. All knees were subjected to 60 min of continuous passive motion and scored on outline attachment and defect filling.

RESULTS

Spraying both chondrocytes and chondrons in fibrin glue resulted in a homogenous cell distribution throughout the scaffold. No difference in viability or matrix production between application methods was found nor between chondrons and chondrocytes. The cadaveric study revealed that airbrushing was highly feasible, and that defect filling through needle extrusion was more difficult to perform based on fibrin glue adhesion and gravity-induced seepage. Defect outline and coverage scores were consistently higher for extrusion, albeit not statistically significant.

CONCLUSION

Both chondrons and chondrocytes can be evenly distributed in a sprayed fibrin glue scaffold without affecting viability while supporting matrix production. The airbrush technology is feasible, easier to perform than needle extrusion and allows for reproducible arthroscopic filling of cartilage defects.

Differentiation capacity and maintenance of differentiated phenotypes of human mesenchymal stromal cells cultured on two distinct types of 3D polymeric scaffolds

This study shows that the classical validation of hMSC differentiation potential on 3D scaffolds might not be sufficient to ensure the maintenance of the cells functionality in the absence of differentiation inducing soluble factors.

Distinct Effect of TCF4 on the NFκB Pathway in Human Primary Chondrocytes and the C20/A4 Chondrocyte Cell Line

OBJECTIVE

Previous studies indicated a difference in crosstalk between canonical WNT pathway and nuclear factor-κB (NFκB) signaling in human and animal chondrocytes. To assess whether the differences found were dependent on cell types used, we tested the effect of WNT modulation on NFκB signaling in human primary articular chondrocytes in comparison with the immortalized human costal chondrocyte cell line C20/A4.

DESIGN

We used gene expression analysis to study the effect of WNT modulation on IL1β-induced matrix metalloproteinase (MMP) expression as well as on WNT and NFκB target gene expression. In addition, we tested the involvement of RelA and TCF4 on activation of the WNT and NFκB pathway by TCF/LEF and NFκB reporter experiments, respectively.

RESULTS

We found an inhibitory effect of both induction and inhibition of WNT signaling on IL1β-induced MMP mRNA expression in primary chondrocytes, whereas WNT modulation did not affect MMP expression in C20/A4 cells. Furthermore, TCF/LEF and NFκB reporter activation and WNT and NFκB target gene expression were regulated differentially by TCF4 and RelA in a cell type-dependent manner. Additionally, we found significantly higher mRNA and protein expression of TCF4 and RelA in C20/A4 cells in comparison with primary chondrocytes.

CONCLUSIONS

We conclude that WNT modulation of NFκB is, at least in part, cell type dependent and that the observed differences are likely because of impaired sensitivity of the NFκB pathway in C20/A4 cells to modulations in WNT signaling. This might be caused by higher basal levels of TCF4 and RelA in C20/A4 cells compared to primary chondrocytes.

Engineered micro-objects as scaffolding elements in cellular building blocks for bottom-up tissue engineering approaches

A material-based bottom-up approach is proposed towards an assembly of cells and engineered micro-objects at the macroscale. We show how shape, size and wettability of engineered micro-objects play an important role in the behavior of cells on these objects. This approach can, among other applications, be used as a tool to engineer complex 3D tissues of clinically relevant size.

Increased cell seeding efficiency in bioplotted three-dimensional PEOT/PBT scaffolds

In regenerative medicine studies, cell seeding efficiency is not only optimized by changing the chemistry of the biomaterials used as cell culture substrates, but also by altering scaffold geometry, culture and seeding conditions. In this study, the importance of seeding parameters, such as initial cell number, seeding volume, seeding concentration and seeding condition is shown. Human mesenchymal stem cells (hMSCs) were seeded into cylindrically shaped 4 × 3 mm polymeric scaffolds, fabricated by fused deposition modelling. The initial cell number ranged from 5 × 10(4) to 8 × 10(5) cells, in volumes varying from 50 µl to 400 µl. To study the effect of seeding conditions, a dynamic system, by means of an agitation plate, was compared with static culture for both scaffolds placed in a well plate or in a confined agarose moulded well. Cell seeding efficiency decreased when seeded with high initial cell numbers, whereas 2 × 10(5) cells seemed to be an optimal initial cell number in the scaffolds used here. The influence of seeding volume was shown to be dependent on the initial cell number used. By optimizing seeding parameters for each specific culture system, a more efficient use of donor cells can be achieved. Copyright © 2013 John Wiley & Sons, Ltd.

Gene expression profiling of dedifferentiated human articular chondrocytes in monolayer culture

OBJECTIVE

When primary chondrocytes are cultured in monolayer, they undergo dedifferentiation during which they lose their phenotype and their capacity to form cartilage. Dedifferentiation is an obstacle for cell therapy for cartilage degeneration. In this study, we aimed to systemically evaluate the changes in gene expression during dedifferentiation of human articular chondrocytes to identify underlying mechanisms.

METHODS

RNA was isolated from monolayer-cultured primary human articular chondrocytes at serial passages. Gene expression was analyzed by microarray. Based on the microarray analysis, relevant genes and pathways were identified. Their functions in chondrocyte dedifferentiation were further investigated.

RESULTS

In vitro expanded human chondrocytes showed progressive changes in gene expression. Strikingly, an overall decrease in total gene expression was detected, which was both gradual and cumulative. DNA methylation was in part responsible for the expression downregulation of a number of genes. Genes involved in many pathways such as the extracellular-signal-regulated kinase (ERK) and Bone morphogenetic protein (BMP) pathways exhibited significant changes in expression. Inhibition of ERK pathway did not show dramatic effects in counteracting dedifferentiation process. BMP-2 was able to decelerate the dedifferentiation and reinforce the maintenance of chondrocyte phenotype in monolayer culture.

CONCLUSION

Our study not only improves our knowledge of the intricate signaling network regulating maintenance of chondrocyte phenotype, but also contributes to improved chondrocyte expansion and chondrogenic performance for cell therapy.

High throughput generated micro-aggregates of chondrocytes stimulate cartilage formation in vitro and in vivo

Cell-based cartilage repair strategies such as matrix-induced autologous chondrocyte implantation (MACI) could be improved by enhancing cell performance. We hypothesised that micro-aggregates of chondrocytes generated in high-throughput prior to implantation in a defect could stimulate cartilaginous matrix deposition and remodelling. To address this issue, we designed a micro-mould to enable controlled high-throughput formation of micro-aggregates. Morphology, stability, gene expression profiles and chondrogenic potential of micro-aggregates of human and bovine chondrocytes were evaluated and compared to single-cells cultured in micro-wells and in 3D after encapsulation in Dextran-Tyramine (Dex-TA) hydrogels in vitro and in vivo. We successfully formed micro-aggregates of human and bovine chondrocytes with highly controlled size, stability and viability within 24 hours. Micro-aggregates of 100 cells presented a superior balance in Collagen type I and Collagen type II gene expression over single cells and micro-aggregates of 50 and 200 cells. Matrix metalloproteinases 1, 9 and 13 mRNA levels were decreased in micro-aggregates compared to single-cells. Histological and biochemical analysis demonstrated enhanced matrix deposition in constructs seeded with micro-aggregates cultured in vitro and in vivo, compared to single-cell seeded constructs. Whole genome microarray analysis and single gene expression profiles using human chondrocytes confirmed increased expression of cartilage-related genes when chondrocytes were cultured in micro-aggregates. In conclusion, we succeeded in controlled high-throughput formation of micro-aggregates of chondrocytes. Compared to single cell-seeded constructs, seeding of constructs with micro-aggregates greatly improved neo-cartilage formation. Therefore, micro-aggregation prior to chondrocyte implantation in current MACI procedures, may effectively accelerate hyaline cartilage formation.

Inhibition of Gsk3β in cartilage induces osteoarthritic features through activation of the canonical Wnt signaling pathway

OBJECTIVE

In the past years, the canonical Wnt/β-catenin signaling pathway has emerged as a critical regulator of cartilage development and homeostasis. In this pathway, glycogen synthase kinase-3β (GSK3β) down-regulates transduction of the canonical Wnt signal by promoting degradation of β-catenin. In this study we wanted to further investigate the role of Gsk3β in cartilage maintenance.

DESIGN

Therefore, we have treated chondrocytes ex vivo and in vivo with GIN, a selective GSK3β inhibitor.

RESULTS

In E17.5 fetal mouse metatarsals, GIN treatment resulted in loss of expression of cartilage markers and decreased chondrocyte proliferation from day 1 onward. Late (3 days) effects of GIN included cartilage matrix degradation and increased apoptosis. Prolonged (7 days) GIN treatment resulted in resorption of the metatarsal. These changes were confirmed by microarray analysis showing a decrease in expression of typical chondrocyte markers and induction of expression of proteinases involved in cartilage matrix degradation. An intra-articular injection of GIN in rat knee joints induced nuclear accumulation of β-catenin in chondrocytes 72 h later. Three intra-articular GIN injections with a 2 days interval were associated with surface fibrillation, a decrease in glycosaminoglycan expression and chondrocyte hypocellularity 6 weeks later.

CONCLUSIONS

These results suggest that, by down-regulating β-catenin, Gsk3β preserves the chondrocytic phenotype, and is involved in maintenance of the cartilage extracellular matrix. Short term β-catenin up-regulation in cartilage secondary to Gsk3β inhibition may be sufficient to induce osteoarthritis-like features in vivo.

The severe short stature in two siblings with a heterozygous IGF1 mutation is not caused by a dominant negative effect of the putative truncated protein

OBJECTIVE

While in previous studies heterozygosity for an Insulin-Like Growth Factor 1 (IGF1) defect only modestly decreased height and head circumference, we recently reported on two siblings with severe short stature with a maternally transmitted heterozygous duplication of 4 nucleotides, resulting in a frame shift and a premature termination codon in the IGF1 gene. In this paper we describe the structural and functional characteristics of the putative truncated IGF-I protein.

DESIGN

Two children, their mother and maternal grandfather carried the mutation. In addition, two family members who were not affected were included in the study. Mutant (MT) IGF-I was synthesized in oxidized and reduced form using two methods. Neutral gel filtration studies were carried out with wild-type (WT) and synthetic MT IGF-I. Binding analysis of synthetic MT IGF-I to the IGF1R and insulin receptors were performed with EBNA-293 cells, stably transfected with the IGF-I receptor, and IM9 cells. L6 cells were used to examine the mitogenic potency and the potential antagonizing effect of synthetic MT IGF-I by [(3)H]-thymidine incorporation assays.

RESULTS

In the sera of both the carriers and non-carriers the proportion of (125)I-IGF-I that was associated with the 150 kDa complex was somewhat less (varying between ~37 and ~52%) than in normal pooled serum (~53-~63%) and, instead, slightly increased amounts of radioactivity were eluted in the 40-50 kDa fraction (consisting of binary IGF-IGFBP complexes) or remained unbound. Synthetic MT IGF-I did not bind to the IGF-I receptor, nor antagonize the growth-promoting effect of IGF-I. It did bind to IGFBPs, but was barely incorporated into 150 kDa complexes. Because in all cases WT IGF-I immunoreactivity was recovered in one peak, corresponding to the MW of WT IGF-I, i.e. ~7.6 kDa, an interaction of circulating truncated mutant peptide with WT IGF-I is very unlikely.

CONCLUSIONS

There is no evidence that the severe short stature associated with heterozygosity for this novel IGF1 mutation in children born from a mother with the same mutation is caused by a dominant negative effect of the truncated protein. We speculate that the growth failure is caused by a combination of partial IGF-I deficiency, placental IGF-I insufficiency, and other genetic factors.

Intraspecies disparity in growth rate is associated with differences in expression of local growth plate regulators

Disparities in longitudinal growth within a species can be partly explained by endocrinological differences. We hypothesized that regulatory networks acting locally in the growth plate may also be important. We tested this hypothesis by evaluating the IGF/IGFBP expression, the vitamin D pathway, and the PTHrP-Indian hedgehog (IHH) feedback loop in rib growth plates from 10- and 21-wk-old small- (Miniature Poodles, MP) and large-breed dogs (Great Danes, GD) using immunohistochemistry and quantitative (q)PCR. The rib growth plates of GD were 1.7 times thicker compared with those of MP, with larger proliferative (in absolute terms) and larger hypertrophic (in absolute and relative terms) zones. IGF/IGFBP gene expression profiling of the growth plates revealed decreased gene expression of igfbp2, -4, and -6 and an unaltered expression of igf-I and igf-II and their respective receptors in GD vs. MP. Immunohistochemistry and qPCR findings showed that the vitamin D pathway was more active in GD than in MP. Staining for 1α- and 24-hydroxylase was more abundant and intense in GD and the gene expressions of 1α-hydroxylase and the vitamin D receptor-driven 24-hydroxylase were six- and eightfold higher in GD vs. MP, respectively. Consistent with the immunohistochemistry findings, the expression of mRNA for components of the parathyroid hormone-related peptide (PTHrP)-IHH loop was different in GD compared with MP, with there being a relative threefold downregulation of Pthrp and a tenfold upregulation of Ihh in GD vs MP. These differences suggest that the effects of IHH in the regulation of chondrocyte proliferation and hypertrophy, both independently of PTHrP, can become more dominant during rapid growth rates. In conclusion, our data suggest that, in addition to modest endocrine differences, more pronounced changes in the expression of locally acting regulatory networks, such as the IGF system, vitamin D pathway, and PTHrP-IHH feedback loop are important contributors to within-species disparities in growth rates.

Short stature associated with a novel heterozygous mutation in the insulin-like growth factor 1 gene

CONTEXT

Homozygous IGF1 deletions or mutations lead to severe short stature, deafness, microcephaly, and mental retardation. Heterozygosity for an IGF-I defect may modestly decrease height and head circumference.

OBJECTIVE

The objective of the study was to investigate the clinical features of heterozygous carriers of a novel mutation in the IGF1 gene in comparison with noncarriers in a short family and to establish the effect of human GH treatment.

SUBJECTS

Two children, their mother, and their maternal grandfather carried the mutation and were compared with two relatives who were noncarriers.

RESULTS

The two index cases had severe short stature (height sd score -4.1 and -4.6), microcephaly, and low IGF-I levels. Sequencing of IGF1 revealed a heterozygous duplication of four nucleotides, resulting in a frame shift and a premature termination codon. The mother and maternal grandfather had the same IGF1 mutation. Adult height (corrected for shrinking and secular trend) and head circumference sd score of carriers of the paternally transmitted mutation was -2.5 and -1.8, in comparison with -1.6 and 0.3 in noncarriers, respectively. After 2 yr of GH treatment, both index cases exhibited increased growth.

CONCLUSIONS

Heterozygosity for this novel IGF1 mutation in children born from a mother with the same mutation, presumably in combination with other genetic factors for short stature, leads to severe short stature, which can be successfully treated with GH.

Synthesis and characterization of hyaluronic acid-poly(ethylene glycol) hydrogels via Michael addition: An injectable biomaterial for cartilage repair

Injectable hydrogels based on hyaluronic acid (HA) and poly(ethylene glycol) (PEG) were designed as biodegradable matrices for cartilage tissue engineering. Solutions of HA conjugates containing thiol functional groups (HA-SH) and PEG vinylsulfone (PEG-VS) macromers were cross-linked via Michael addition to form a three-dimensional network under physiological conditions. Gelation times varied from 14min to less than 1min, depending on the molecular weights of HA-SH and PEG-VS, degree of substitution (DS) of HA-SH and total polymer concentration. When the polymer concentration was increased from 2% to 6% (w/v) in the presence of 100Uml(-1) hyaluronidase the degradation time increased from 3 to 15days. Hydrogels with a homogeneous distribution of cells were obtained when chondrocytes were mixed with the precursor solutions. Culturing cell-hydrogel constructs prepared from HA185k-SH with a DS of 28 and cross-linked with PEG5k-4VS for 3weeks in vitro revealed that the cells were viable and that cell division took place. Gel-cell matrices degraded in approximately 3weeks, as shown by a significant decrease in dry gel mass. At day 21 glycosaminoglycans and collagen type II were found to have accumulated in hydrogels. These results indicate that these injectable hydrogels have a high potential for cartilage tissue engineering.

Homozygous and heterozygous expression of a novel mutation of the acid-labile subunit

CONTEXT

Acid-labile subunit (ALS) deficiency due to homozygous inactivation of the ALS gene (IGFALS) is associated with moderate short stature, and in few cases pubertal delay. The clinical expression of heterozygosity is unknown.

OBJECTIVE

To investigate the clinical, laboratory, and radiological features of homozygous and heterozygous carriers of a novel mutation in the ALS gene in comparison with non-carriers.

SUBJECTS

Three short Kurdish brothers and their relatives.

RESULTS

The index cases presented with short stature, microcephaly, and low circulating IGF-I and IGF-binding protein-3 (IGFBP-3), and undetectable ALS levels. Two were known with a low bone mineral density and one of them had suffered from two fractures. We found a novel homozygous ALS gene mutation resulting in a premature stop codon (c.1490dupT, p.Leu497PhefsX40). The IGF-I, IGFBP-3, and ALS 150 kDa ternary complex was absent, and ALS proteins in serum were not detected with western blot. IGFPB-1 and IGFPB-2 were low and there was a mild insulin resistance. Five heterozygous carriers tended to have a lower height and head circumference than five non-carriers, and had low plasma ALS and IGFBP-3 levels. Bone mineral (apparent) density was low in two out of three homozygous carriers, and also in four out of nine relatives.

CONCLUSIONS

The clinical presentation of homozygous ALS mutations may, besides short stature, include microcephaly. Heterozygous carriers may have less statural and head growth, suggestive for a gene dosage effect.

Novel mutations in the parathyroid hormone (PTH)/PTH-related peptide receptor type 1 causing Blomstrand osteochondrodysplasia types I and II

CONTEXT

The PTH/PTHrP receptor type 1 (PTHR1) has a key role in endochondral ossification, which is emphasized by diseases resulting from mutations in the PTHR1 gene. Among these diseases is Blomstrand osteochondrodysplasia (BOCD).

OBJECTIVE

BOCD can be divided into two types, depending on the severity of the skeletal abnormalities. The molecular basis for this heterogenic presentation is unknown.

DESIGN AND PATIENTS

We performed mutation analysis in two families with type I and in three families with the less severe form of BOCD type II.

RESULTS

In one of the type I BOCD cases, a homozygous nonsense mutation (R104X) was found, resulting in a truncated PTHR1. In the second type I BOCD case, no mutation was found. A homozygous nucleotide change (intron M4+27C>T) was demonstrated in one of the type II BOCD cases creating a novel splice site. In dermal fibroblasts of the patient, this novel splice site was preferentially used, resulting in an aberrant transcript. The wild-type transcript remained, however, present, albeit at low levels. In the other two families with type II BOCD, a previously identified homozygous missense mutation (P132L) was found. Functional analysis demonstrated that the P132L mutant had low residual activity.

CONCLUSIONS

In combination with data presented in literature, we conclude that type I BOCD is caused by a complete inactivation of the PTHR1, whereas low levels of residual activity due to a near complete inactivation of the PTHR1 result in the relatively milder presentation of type II BOCD.

Human mesenchymal stem cells derived from bone marrow display a better chondrogenic differentiation compared with other sources

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiation into several mesodermal lineages. These cells have been isolated from various tissues, such as adult bone marrow, placenta, and fetal tissues. The comparative potential of these cells originating from different tissues to differentiate into the chondrogenic lineage is still not fully defined. The aim of our study was to investigate the chondrogenic potential of MSCs isolated from different sources. MSCs from fetal and adult tissues were phenotypically characterized and examined for their differentiation capacity, based on morphological criteria and expression of extracellular matrix components. Our results show that both fetal and adult MSCs have chondrogenic potential under appropriate conditions. The capacity of bone marrow-derived MSCs to differentiate into chondrocytes was reduced on passaging of cells. MSCs of bone marrow origin, either fetal or adult, exhibit a better chondrogenesis than fetal lung- and placenta-derived MSCs, as demonstrated by the appearance of typical morphological features of cartilage, the intensity of toluidine blue staining, and the expression of collagen type II, IX, and X after culture under chondrogenic conditions. As MSCs represent an attractive tool for cartilage tissue repair strategies, our data suggest that bone marrow should be considered the preferred MSC source for these therapeutic approaches.

A variable degree of intrauterine and postnatal growth retardation in a family with a missense mutation in the insulin-like growth factor I receptor

CONTEXT

The type 1 IGF-I receptor (IGF1R) mediates the biological functions of IGF-I. Binding of IGF-I to the IGF1R results in autophosphorylation of the intracellular beta-subunit and activation of intracellular signaling.

OBJECTIVE

The objective of this study was to evaluate the functional characteristics of a novel IGF1R mutation and describe the phenotypic features of two patients with this mutation.

DESIGN

The study was performed in a university hospital.

PATIENTS

We describe a 35-yr-old female with mild intrauterine growth failure, progressive postnatal growth retardation, severe failure to thrive, and microcephaly. Her daughter was born with severe intrauterine growth retardation and also showed postnatal failure to thrive and microcephaly.

RESULTS

We found a heterozygous G3148-->A nucleotide substitution in the IGF1R gene, changing a negatively charged glutamic acid at position 1050 into a positively charged lysine residue (E1050K). E1050 is a conserved residue in the intracellular kinase domain. Dermal fibroblasts of the mother showed normal binding of iodinated IGF-I, but autophosphorylation and activation of downstream signaling cascades upon challenging with IGF-I was markedly reduced. Consequently, the maximal [(3)H]thymidine incorporation upon challenge with a dose range of IGF-I was reduced compared with a panel of control cells (3.65 +/- 1.79-fold vs. 6.75 +/- 4.7-fold stimulation; P < 0.01). These data suggest that the mutation results in the inactivation of one copy of the IGF1R gene.

CONCLUSIONS

These two patients support the key role for IGF-I in intrauterine and postnatal growth. The different phenotypes of these and earlier described patients may be associated with variability in IGF-I signaling. The degree of intrauterine growth retardation may be partially determined by the presence or absence of maternal IGF-I resistance.

Normalization of serum calcium by cinacalcet in a patient with hypercalcaemia due to a de novo inactivating mutation of the calcium-sensing receptor

Familial benign hypocalciuric hypercalcaemia (FHH) results from a heterozygous inactivating mutation of the calcium-sensing receptor (CaR) and is characterized by hypercalcaemia, hypocalciuria and inappropriately normal plasma levels of parathyroid hormone. In a minority of patients, a loss of function mutation of the CaR results in severe hypercalcaemia associated with complications for which no effective surgical or medical treatment is available. We investigated the effects of the calcimimetic agent cinacalcet, an allosteric modulator of the CaR, in a 26-year-old man presenting with hypercalcaemia due to a de novo inactivating mutation of the CaR. Complicating features were recurrent psychosis and progressive severe osteoporosis. A single dose of either 30 or 60 mg of cinacalcet resulted in a 63-88% decline in plasma parathyroid hormone levels within 2 h of administration of the agent, reverting to baseline levels after 12 h. Normalization of serum calcium was more gradual but sustained for up to 12 months of treatment with a maintenance twice-daily oral dose of 60+30 mg cinacalcet. In addition to its beneficial effects in primary and secondary hyperparathyroidism, cinacalcet may open new therapeutic avenues in the management of a subset of patients with severe hypercalcaemia due to inactivating mutations of the CaR.

Lithium as adjuvant to radioiodine therapy in differentiated thyroid carcinoma: clinical and in vitro studies

OBJECTIVE

Lithium has been reported to increase radioactive iodine (RaI) doses in benign thyroid disease and in differentiated thyroid carcinoma (DTC). It is not known whether lithium influences the outcome of RaI therapy in DTC. We therefore studied the clinical effects of RaI without and with lithium carbonate in patients with proven metastatic DTC. Controversy also exists on the mechanism by which lithium increases RaI dose in DTC. We performed an in vitro study specifically aimed at examining the effects of lithium on the sodium iodide symporter (NIS).

DESIGN

In a clinical study, 12 patients were selected with metastases of DTC who had received previous RaI therapy without lithium (control) that had not influenced tumour progression, despite RaI accumulation in metastases. The patients received 1200 mg lithium carbonate/day followed by 6000 MBq RaI. Outcome parameters were RaI uptake, serum thyroglobulin (Tg) levels and radiological dimensions of metastases compared between RaI with lithium and control. In an in vitro study, iodide uptake was studied in the benign rat thyroid cell line FRTL-5, in the polarized non-thyroid MDCK cell line, stably transfected with human sodium iodide symporter (hNIS) to study the effects of lithium on NIS in a non-thyroid background, and the human follicular thyroid carcinoma cell line FTC133-hNIS to study lithium effects in a background of DTC. Lithium chloride (LiCl) was added in concentrations up to 2 mM for 0-48 h. Both steady-state iodide uptake (30 min) and initial rate (2 min) were studied using a specific activity of 100 mCi/mmol I, the latter experiment to determine lithium effects on substrate dependency. Iodide efflux studies were performed as well.

RESULTS

Despite an increased uptake of RaI in seven patients, no beneficial effect of RaI with lithium was observed on the clinical course as assessed by serum Tg measurements and radiographically. In the in vitro studies, no effects of LiCl on iodide uptake or efflux were observed.

CONCLUSIONS

The addition of lithium to RaI did not have any beneficial effects on the clinical course in 12 patients with metastatic DTC. No beneficial effects of lithium on iodide uptake were observed in vitro. Therefore, the clinical value of lithium in DTC remains subject to debate.

A bioluminescence assay for thyrotropin receptor antibodies predicts serum thyroid hormone levels in patients with de novo Graves' disease

BACKGROUND

TSH receptor antibodies (TBII) in Graves' disease (GD) may be TSH receptor stimulating (TSAb) and blocking (TBAb) antibodies. In commercially available assays however, only total TBII titres can be measured, without discriminating between TSAb and TBAb.

OBJECTIVE

To design a TBII bioassay to detect of TSAb and to correlate TSAb activity with severity of hyperthyroidism in de novo GD patients.

PATIENTS

Thirty-five patients with de novo GD and 27 controls.

METHODS

The JP-26-26 cell line, which constitutively expresses the TSH receptor (TSHR), was stably transfected with a cyclic adenosine monophosphate responsive element--luciferase construct. The clone B1 exhibited a near linear increase in luminescence from 0.2 mU/l to 50 mU/l bovine TSH and was used as a TBII bioassay. TBII, free T4 and TSH were measured in the sera of all patients and controls.

RESULTS

In the sera of 35 GD patients, TBII titres did not correlate with serum free T4 concentrations. In contrast, a strong and highly significant correlation was found between TSHR stimulating activity (luminescence) as measured with the TBII bioassay and serum free T4 levels (R = 0.80, P < 0.001). Interestingly, the luminescence/TBII ratio had a wide range at low TBII titres, whereas high TBII titres were associated with a low degree of TSHR activation. The TBII bioassay also detected TBAb in GD patients who spontaneously developed hypothyroidism.

CONCLUSIONS

The B1-TBII-bioassay as developed in our laboratory has a high sensitivity for the detection of TSAb in GD and predicts the severity of hyperthyroidism in untreated GD patients. In addition, we found that high TBII titres are associated with weak TSHR activation.

Homozygous and heterozygous expression of a novel insulin-like growth factor-I mutation

IGF-I is a key factor in intrauterine development and postnatal growth and metabolism. The secretion of IGF-I in utero is not dependent on GH, whereas in childhood and adult life, IGF-I secretion seems to be mainly controlled by GH, as revealed from studies on patients with GHRH receptor and GH receptor mutations. In a 55-yr-old male, the first child of consanguineous parents, presenting with severe intrauterine and postnatal growth retardation, microcephaly, and sensorineural deafness, we found a homozygous G to A nucleotide substitution in the IGF-I gene changing valine 44 into methione. The inactivating nature of the mutation was proven by functional analysis demonstrating a 90-fold reduced affinity of recombinantly produced for the IGF-I receptor. Additional investigations revealed osteoporosis, a partial gonadal dysfunction, and a relatively well-preserved cardiac function. Nine of the 24 relatives studied carried the mutation. They had a significantly lower birth weight, final height, and head circumference than noncarriers. In conclusion, the phenotype of our patient consists of severe intrauterine growth retardation, deafness, and mental retardation, reflecting the GH-independent secretion of IGF-I in utero. The postnatal growth pattern, similar to growth of untreated GH-deficient or GH-insensitive children, is in agreement with the hypothesis that IGF-I secretion in childhood is mainly GH dependent. Remarkably, IGF-I deficiency is relatively well tolerated during the subsequent four decades of adulthood. IGF-I haploinsufficiency results in subtle inhibition of intrauterine and postnatal growth.

Mutations in the NSD1 gene in patients with Sotos syndrome associate with endocrine and paracrine alterations in the IGF system

OBJECTIVE

To investigate the effect of nuclear receptor Su-var, 3-9, enhancer of zeste, trithorax (SET) domain-containing protein 1 (NSD1) gene alteration in patients with Sotos syndrome on plasma IGFs and IGF-binding proteins (IGFBPs), as well as on the IGF/IGFBP system activity at the tissue level.

DESIGN

Twenty-nine patients suspected of Sotos syndrome were divided into two groups: patients with heterozygous deletions or mutations in the NSD1 gene (NSD1(+/-)) (n=11) and subjects without (NSD1(+/+)) (n=18). Plasma samples (n=29) and skin fibroblasts (n=23) were obtained. The results of both groups were compared and related to reference values.

METHODS

IGF-I, IGF-II, IGFBP-2, IGFBP-3, IGFBP-4 and IGFBP-6 levels were determined by RIAs. The mitogenic response of fibroblasts to IGFs was investigated by [methyl-(3)H]thymidine incorporation. IGFBP-3 levels in the culture media were measured by RIA. IGFBP-3 mRNA expression was determined by real time RT-PCR.

RESULTS

NSD1(+/-) patients showed significantly altered levels of IGF-I (mean-1.2 SDS), IGF-II (-1.2), IGFBP-3 (-1.7), IGFBP-4 (-0.4), IGFBP-2 (+0.8) and IGFBP-6 (+1.5). The NSD1(+/+) patients did not differ from the reference, with the exception of the mean IGFBP-3 level (-1.3). Basal proliferation and mitogenic response to IGFs was diminished in NSD1(+/-) fibroblasts compared with NSD1(+/+) (basal, P=0.02; IGF-I, P<0.001; IGF-II, P=0.02). Compared with control fibroblasts, only the mitogenic response was diminished (basal, P=0.07; IGF-I, P=0.04; IGF-II, P=0.04). A trend of higher IGFBP-3 secretion after IGF-I stimulation (P=0.09) and 3.5-5 times higher mRNA expression of IGFBP-3 in basal conditions was found in NSD1(+/-) fibroblasts in comparison to controls.

CONCLUSIONS

NSD1(+/-) patients show endocrine and paracrine changes in the IGF system. These changes may contribute to the abnormal growth pattern.

Familial Paget's disease in The Netherlands: occurrence, identification of new mutations in the sequestosome 1 gene, and their clinical associations

OBJECTIVE

To estimate the occurrence of familial Paget's disease of bone in The Netherlands, to examine the prevalence of mutations of the sequestosome 1 gene (SQSTM1) in identified families, and to assess potential genotype-phenotype associations.

METHODS

We performed a case-control study of patients with Paget's disease and a mutation analysis of the SQSTM1 gene of index patients with familial disease and of the relatives of those with a mutation. Serum alkaline phosphatase (AP) activity was assessed, and bone scintigraphy was performed.

RESULTS

Five percent of patients had at least 1 first-degree relative with the disease, compared with 0.5% of the controls (relative risk 10; 95% confidence interval 1.3-75.6). In 38.9% of patients with familial disease, heterozygous mutations in the SQSTM1 gene were identified. These were the previously described P392L mutation, which was present in 22.2% of patients, and 3 new mutations, S399P, G425R, M404T, 9 of which were present in 3 different families. All mutations were located in the ubiquitin-associated domain of the gene. There was a relationship between serum AP activity, as a marker of the disease, and the presence or absence of the G425R and P392L mutations, the subject's age, and the presence of Paget's disease.

CONCLUSION

Our data provide further evidence of a causal role of SQSTM1 gene mutations in the pathogenesis of Paget's disease and allow the design of a strategy based on measurements of serum AP activity and age for investigating asymptomatic relatives of patients with familial Paget's disease of bone.

Plasma insulin-like growth factors (IGFs), IGF-Binding proteins (IGFBPs), acid-labile subunit (ALS) and IGFBP-3 proteolysis in individuals with clinical characteristics of Sotos syndrome

OBJECTIVE

Sotos syndrome is an overgrowth syndrome of poorly understood aetiology. We investigated whether this syndrome is related to alterations in plasma insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs), acid-labile subunit (ALS) and serum IGFBP-3 proteolysis.

DESIGN

Based on clinical criteria, 32 patients with clinical characteristics of Sotos syndrome (median age 8.4 years, range 1.8-48.4) were categorised into three groups: typical (n = 10, group 1), dubious (n = 12, group 2) and atypical (n = 10, group 3). Blood samples were obtained from 29 patients.

MEASUREMENTS

Plasma IGF-I, IGF-II, E-II (pro-IGF-II and E-domain fragments), IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-6 and ALS were measured by specific radioimmunoassays (RIAs). Except for E-II immunoreactivity, the concentrations were compared with those of age references, and expressed as standard deviation scores (SDS). IGFBP-3 proteolysis was assessed by incubation of serum with [125I]-IGFBP-3, followed by gel electrophoresis and was then compared with that in normal serum and third trimester pregnancy serum.

RESULTS

Patients in group 1 showed significantly reduced plasma levels of IGF-II (median -0.9 SDS; p = 0.01), IGFBP-4 (-0.5 SDS; p = 0.02) and IGFBP-3 (-1.0 SDS; p = 0.01). Mean IGFBP-3 proteolysis was higher than in normal standard serum (61% vs 37%; p < 0.01) but lower than in third trimester pregnancy serum (94%; p < 0.01). Plasma IGF-I showed a tendency towards low values (median -0.9 SDS; p = 0.09), IGFBP-6 and ALS a tendency towards elevated levels (median values +0.8 SDS; p = 0.07 and +2.3 SDS; p = 0.09), and IGFBP-2 was normal. The mean value of E-II immunoreactivity was 8.7 nmol/l, similar to that in pooled normal plasma (8.6 nmol/l). Plasma and serum parameters in groups 2 and 3 were similar to reference values with the exception of plasma IGFBP-3 (in groups 2 and 3 median < or = -1.1 SDS; p < or = 0.02) and ALS (in group 3 median +1.3 SDS; p < 0.01).

CONCLUSIONS

Patients with typical Sotos syndrome show low plasma IGF-II, IGFBP-3, IGFBP-4, and increased proteolysis of IGFBP-3 in serum. The extent to which these findings are associated with the pathophysiology of Sotos syndrome remains uncertain.

Expression of estrogen receptors and enzymes involved in sex steroid metabolism in the rat tibia during sexual maturation

Estrogens are essential for bone mass accrual but their role before sexual maturation has remained elusive. Using in situ hybridization and immunohistochemistry, we investigated the expression of both estrogen receptor (ER) alpha and beta mRNA and protein as well as several mRNAs coding for enzymes involved in sex steroid metabolism (aromatase, type I and II 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD), steroid sulfatase (STS) and type I 5 alpha-reductase) on sections of tibial metaphyses before (1- and 4-week-old), during (7-week-old) and after (16-week-old) sexual maturation in female and male rats. ER alpha and ER beta mRNA and protein were detected in metaphyseal bone in lining cells, osteoblasts, osteoclasts and some osteocytes with no apparent differences in expression during development or between the sexes. In contrast, aromatase, type I and II 17 beta-HSD and type I 5 alpha-reductase mRNAs were first detected in osteoblasts, osteoclasts and occasionally in osteocytes from sexual maturation (7-week-old rat) and onwards. Only STS was present before sexual maturation. To study the significance of ER alpha and beta expression in bone before sexual maturation when circulating sex steroid levels are low, 26-day-old female and male rats underwent gonadectomy or 17 beta-estradiol (E(2)) supplementation (0.5 mg/21 days) during 3 weeks. Following gonadectomy, trabecular bone volume (TBV) was lower in males (P=0.03) and there was a trend towards reduction in females (P=0.057). E(2) supplementation increased tibial TBV compared with controls in both genders as assessed by Masson-Goldner staining. These data suggest that the presence of ERs in bone cells before sex maturation might be of significance for bone mass accrual. Furthermore, based on the mRNA expression of the crucial enzymes aromatase and type I 17 beta-HSD, we suggest that bone cells in the tibial metaphysis acquire the intrinsic capacity to metabolize sex steroids from sexual maturation onwards. This process may contribute to the beneficial effects of estrogen on bone mass accrual, possibly by intracrinology.

Systemic and local regulation of the growth plate

The growth plate is the final target organ for longitudinal growth and results from chondrocyte proliferation and differentiation. During the first year of life, longitudinal growth rates are high, followed by a decade of modest longitudinal growth. The age at onset of puberty and the growth rate during the pubertal growth spurt (which occurs under the influence of estrogens and GH) contribute to sex difference in final height between boys and girls. At the end of puberty, growth plates fuse, thereby ceasing longitudinal growth. It has been recognized that receptors for many hormones such as estrogen, GH, and glucocorticoids are present in or on growth plate chondrocytes, suggesting that these hormones may influence processes in the growth plate directly. Moreover, many growth factors, i.e., IGF-I, Indian hedgehog, PTHrP, fibroblast growth factors, bone morphogenetic proteins, and vascular endothelial growth factor, are now considered as crucial regulators of chondrocyte proliferation and differentiation. In this review, we present an update on the present perception of growth plate function and the regulation of chondrocyte proliferation and differentiation by systemic and local regulators of which most are now related to human growth disorders.

Effect of x-irradiation on growth and the expression of parathyroid hormone-related peptide and Indian hedgehog in the tibial growth plate of the rat

AIM

To study the effect of irradiation on the longitudinal growth and the expression of parathyroid hormone-related peptide (PTHrP) and Indian hedgehog (IHh) in tibial growth plates of rats.

METHODS

At 3 weeks of age, 30 male rats received a single fraction of irradiation (8 Gy) to their right hind limb, and small groups of animals were sacrificed 1, 2, 3, 5, 7, 10, 15, and 26 weeks after irradiation. Weight and length of both irradiated and nonirradiated tibiae were measured, and sections of the tibiae were stained with HE. PTHrP and IHh were visualized using immunohistochemical techniques.

RESULTS

Radiation resulted in persistent growth delay of the irradiated tibiae, with a difference in length of more than 10% between the irradiated and the nonirradiated tibiae 15 weeks or more after irradiation. The growth plate architecture was disturbed, and the expression of both PTHrP and IHh was decreased in the irradiated tibiae.

CONCLUSION

As PTHrP and IHh are key regulators of both the pace and the synchronization of the differentiation of growth plate chondrocytes, the reduced expression of PTHrP and IHh may contribute to the changes found after irradiation.

Differentiation of murine preosteoblastic KS483 cells depends on autocrine bone morphogenetic protein signaling during all phases of osteoblast formation

In this study, we examine the role of bone morphogenetic protein (BMP) signaling during differentiation of the murine preosteoblastic KS483 cell line, which formed alkaline phosphatase (ALP)-positive and mineralized nodules during a 3 week culture period. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) demonstrated the presence of various BMPs (BMP-2, -3, -4, -6, -7, and -8A and -8B), BMP type I and II receptors (ALK2, ALK3, ALK4, BMPR-II, and ActR-IIA and -IIB), BMP antagonists (DAN, gremlin, chordin, cerberus, noggin, and tsg), and Smads 1-8. mRNA expression of these genes did not change during differentiation, except for BMP-3, BMP-8a, and noggin. BMP-3 increased gradually, particularly in the matrix formation phase; BMP-8a was induced from the onset of matrix maturation and mineralization, in parallel to the expression of osteocalcin; and noggin tended to decline during the mineralization phase. Treatment of KS483 cells with the BMP antagonists noggin or soluble truncated BMPR-IA, either continuously or during distinct periods of osteoblast differentiation; that is, matrix formation or matrix maturation and mineralization phase, decreased ALP-positive and mineralized nodule area independent of the phase of osteoblast differentiation. Notably, the antagonists inhibited mineralization of already existing nodules. Similarly, BMP-4 stimulated differentiation not only at the beginning of the culture period, but also at late stages of differentiation. These data indicate that autocrine BMP signaling is involved in KS483 osteoblastic differentiation not only during the early phase of differentiation, but also during matrix maturation and mineralization. The different expression patterns of components of BMP signaling in the KS483 cells suggest distinct functions of individual BMPs during osteoblast differentiation. In summary, our data suggest that BMP activity is required not only for initiation of osteoblast differentiation and further development of early osteoblasts, but is also involved in late-stage osteoblast differentiation and matrix mineralization.

Evidence for genomic and nongenomic actions of estrogen in growth plate regulation in female and male rats at the onset of sexual maturation

Recently, both estrogen receptor (ER) alpha and beta were detected in growth plate chondrocytes of rats before sexual maturation, implying a role for estrogen at this stage. In this study, therefore, we investigated the effects of ovariectomy (OVX) or estrogen supplementation on parameters of longitudinal growth in 26-day-old rats, which were sexually immature at the start of the experiment. OVX caused an increase in body weight gain, tibial length and growth plate width due to an increased proliferating zone. This increase correlated with an increase in cell number, with a decrease in cell diameter and with increased proliferating cell nuclear antigen (PCNA) immunostaining compared with sham. Interestingly, the increase in proliferation was not caused by an increase in insulin-like growth factor-I (IGF-I) mRNA expression in the growth plate as assessed by real-time PCR. In contrast to OVX, 17beta-estradiol (E(2)) supplementation (0.5 mg/21 days) of 26-day-old female rats caused a strong decrease in body weight gain, tibial length and growth plate width. The latter was explained by a reduction of the proliferating zone width, which correlated with a reduced number of PCNA-positive cells (not significant) and by a reduction of the hypertrophic zone width. In male rats supplemented with E(2), similar effects were observed compared with the females. ERalpha and beta immunostaining was found predominantly in late proliferating and early hypertrophic chondrocytes. OVX did not affect ER expression but E(2) supplementation strongly decreased immunostaining for both ERalpha and beta in both sexes. Besides E(2), desoxyestrone (DE), an activator of nongenomic estrogen-like signaling (ANGEL) and 2-methoxyestradiol (2-MeO-E(2)), a tissue-selective naturally occurring metabolite of E(2), were administered to female and male rats of the same age. Compared with E(2), these compounds had less pronounced, though significant, effects on some parameters of longitudinal growth in both sexes, especially on growth plate characteristics. In conclusion, E(2) may exert effects on longitudinal growth before and at the onset of sexual maturation, despite very low endogenous serum levels at these stages. There may be a role for nongenomic signaling in body weight gain, tibial length and growth plate width but genomic signaling prevails.

Sex steroid metabolism in the tibial growth plate of the rat

To assess whether growth plate-specific production of sex steroids is possible, we have surveyed the presence of several key-enzymes involved in androgen and estrogen metabolism in the tibial growth plate of female and male rats during development. Using in situ hybridization, mRNAs of aromatase p450, type I and II 17beta-hydroxysteroid dehydrogenase (HSD), steroid sulfatase (STS), and 5alpha-reductase were detected in proliferating and hypertrophic chondrocytes of the growth plate. The former three were strongly up-regulated around sexual maturation (7 wk), whereas the latter two were expressed at a relatively constant level during development. These data were supported by measuring aromatase, type I 17beta-HSD, and STS enzyme activities in chondrocytes collected from tibial growth plates at 1 and 7 wk of age. Of the enzymes studied, there were minor differences between the sexes in aromatase and 5alpha-reductase expression only. In conclusion, our findings clearly indicate the presence of various enzymes involved in sex steroid metabolism in the tibial growth plate, especially in sexually maturing rats, a timepoint at which sex steroids have major effects on longitudinal growth. Our data suggest that intracrinology in the rat growth plate can occur and may be a major source of local sex steroid delivery.

Gender differences in expression of androgen receptor in tibial growth plate and metaphyseal bone of the rat

In this study, we investigate the expression of the androgen receptor (AR) in the tibial growth plate and metaphyseal bone of male and female rats at the mRNA and protein level. Using in situ hybridization and immunohistochemistry, AR mRNA and protein were demonstrated in proliferating and early hypertrophic chondrocytes in the growth plate of 1-, 4-, and 7-week-old male and female rats. Immunostaining for AR was observed both in the nucleus and the cytoplasm. After sexual maturation at 12 and 16 weeks of age, AR expression decreased in both genders and was confined to a small rim of prehypertrophic chondrocytes. In female rats of 40 weeks of age, this expression pattern was still visible. In most age groups there was a tendency toward an increased AR mRNA expression in male vs. female rats except in the 7-week-old animals. At the protein level, sexually maturing 7-week-old male rats demonstrated a higher staining intensity compared to their female counterparts. At this stage, AR staining in the males was mainly confined to the nucleus, whereas in females staining was predominantly found in the cytoplasm. In the tibial metaphysis, AR mRNA was detected in lining cells, osteoblasts, osteocytes, and osteoclasts at all stages of development. At the protein level, a similar expression pattern was observed, except for an absence of immunostaining in the lining cells. The staining was both nuclear and cytoplasmic. In most age groups, mRNA and protein signals were higher in males compared with females. We have demonstrated the presence of AR mRNA and protein in the tibial growth plate and the underlying metaphyseal bone during development of the rat. In male rats, the presence of higher messenger and protein staining intensities, as well as preferential nuclear staining during sexual maturation, suggests that direct actions of androgens in chondrocytes and in bone forming cells may be involved in establishing the gender differences in the skeleton.

Exposure of KS483 cells to estrogen enhances osteogenesis and inhibits adipogenesis

Osteoblasts and adipocytes arise from a common progenitor cell in bone marrow. Whether estrogen directly regulates the progenitor cells differentiating into osteoblasts or adipocytes remains unknown. Using a mouse clonal cell line KS483 cultured in charcoal-stripped fetal bovine serum (FBS), we showed that 17beta-estradiol (E2) stimulates the differentiation of progenitor cells into osteoblasts and concurrently inhibits adipocyte formation in an estrogen receptor (ER)-dependent way. E2 increased alkaline phosphate (ALP) activity and nodule formation and stimulated messenger RNA (mRNA) expression of core-binding factor alpha-1 (Cbfa1), parathyroid hormone/parathyroid hormone-related protein receptors (PTH/PTHrP-Rs), and osteocalcin. In contrast, E2 decreased adipocyte numbers and down-regulated mRNA expression of peroxisome proliferator-activated receptor-gamma (PPARgamma)2, adipocyte protein 2 (aP2), and lipoprotein lipase (LPL). Furthermore, the reciprocal control of osteoblast and adipocyte differentiation by E2 was observed also in the presence of the adipogenic mixture of isobutylmethylxanthine, dexamethasone, and insulin. Immunohistochemical staining showed that ERalpha and ERbeta were present in osteoblasts and adipocytes. A new mouse splice variant ERbeta2 was identified, which differed in two amino acid residues from the rat isoform. E2 down-regulated mRNA expression of ERalpha, ERbeta1, and ERbeta2. The effects of E2 are not restricted to the KS483 cell line because similar results were obtained in mouse bone marrow cell cultures. Our results indicate that estrogen, in addition to stimulation of osteogenesis, inhibits adipogenesis, which might explain the clinical observations that estrogen-deficiency leads to an increase in adipocytes.

Expression of estrogen receptor alpha and beta in the epiphyseal plate of the rat

In this study we examine the spatial and temporal expression of estrogen receptor (ER) alpha and beta mRNA and protein in the tibial growth plate of the rat after birth, as well as the hormonal regulation of their expression. Using in situ hybridization and immunohistochemistry, we demonstrated ER alpha and ER beta mRNA and protein in tibial growth plates from 1 to 40 weeks after birth. ER alpha and beta mRNA and protein were localized in late proliferating and early hypertrophic chondrocytes during early life (1 and 4 weeks of age), whereas the immunohistochemistry also showed staining for ER alpha and beta in the resting cells. A similar expression pattern was observed during sexual maturation (7 weeks of age) except that ER beta mRNA was also detected in early proliferating chondrocytes. After sexual maturation (from 12 up to 40 weeks of age) ER alpha and beta mRNA and protein expression was confined to late proliferating and early hypertrophic chondrocytes. Apart from a relatively higher ER alpha mRNA expression in males after sexual maturation, we did not detect differences in expression of ERs between genders. Expression of ER beta mRNA in epiphyseal plates was increased in growth-retarded hypophysectomized rats compared with controls. Administration of growth hormone (GH) did not reverse the increased ER expression to normal. These data suggest that ER alpha and beta are coexpressed in growth plates of the rat after birth and that the level of expression of ERs in these tissues is hormonally regulated. Furthermore, our data indicate that the absence of growth-plate closure in the rat cannot be explained by disappearance of ER alpha expression during sexual maturation per se.

Expression of the human sodium/iodide symporter (hNIS) in xenotransplanted human thyroid carcinoma

The uptake of iodide in thyroid epithelial cells is mediated by the sodium/iodide symporter (NIS). The uptake of iodide is of vital importance for thyroid physiology and is a prerequisite for radioiodine therapy in thyroid cancer. Loss of iodide uptake due to diminished expression of the human NIS (hNIS) is frequently observed in metastasized thyroid cancer. So far, no animal model for the study of radioiodine therapy in thyroid cancer has been available. Strategies to restore iodide uptake in thyroid cancer include the exploration of hNIS gene transfer into hNIS defective thyroid cancer. We have performed a stable transfection of hNIS into the hNIS defective follicular thyroid carcinoma cell line FTC133. Stably transfected colonies exhibited high uptake of Na125I, which could be blocked completely with sodium perchlorate. hNIS transfected FTC133 and non-transfected cell lines injected subcutaneously in nude mice formed tumors after 6 weeks. Iodide uptake in the hNIS transfected tumor was much higher than in non-transfected tumor, but a rapid release of radioactivity from the hNIS transfected tumor was observed. Further studies are necessary to investigate the role of hNIS in relation to other thyroid specific proteins in iodide metabolism in thyroid cancer.

Urokinase-receptor/integrin complexes are functionally involved in adhesion and progression of human breast cancer in vivo

Interactions between specific cell-surface molecules, which include the urokinase receptor (uPAR) and integrins, are crucial to processes of tumor invasion and metastasis. Here we demonstrate that uPAR and beta1-integrins may cluster at distinct sites at the cell surface of metastatic MDA-MB-231 breast cancer cells and form functional complexes. Attachment assays performed in the presence of a synthetic peptide (p25), which interferes with the formation of uPAR-integrin complexes, reveal that uPAR is able to regulate the adhesive function of integrins in breast cancer cells. On dissociation of the uPAR-integrin complexes by p25, tumor cell attachment to the extracellular matrix was either decreased (vitronectin) or increased (fibronectin). Moreover, the tumor cells display remarkable morphological changes when cultured on fibronectin in the continuous presence of p25, leading to increased cell spreading and attachment. In marked contrast to control conditions, increased cellular adhesion to fibronectin after p25 treatment was entirely beta1-integrin-mediated. The role of uPAR-integrin complexes in tumor progression was studied in an in vivo bone xenograft model. Stably transfected MDA-MB-231 cells that overexpress p25 showed a significant reduction in tumor progression in bone (P < or = 0.0001 versus mock-control). In line with these observations, continuous administration of p25 (25 microg/mouse/day, osmotic minipumps) for 28 days resulted in significantly reduced tumor progression of MDA-MB-231 cells in bone (P < or = 0.005) when compared to scrambled control peptide. In conclusion, our data demonstrate that uPAR can act as an adhesion receptor in breast cancer and is capable of regulating integrin function. Our findings strongly suggest that adhesive and proteolytic events are tightly associated in metastatic breast cancer cells and that functional integrin-uPAR complexes are involved in tumor progression in vivo.

Recombinant human extracellular matrix protein 1 inhibits alkaline phosphatase activity and mineralization of mouse embryonic metatarsals in vitro

Two mRNAs are transcribed from the extracellular matrix protein 1 gene (Ecm1): Ecm1a and an alternatively spliced Ecm1b. We studied Ecm1 mRNA expression and localization during endochondral bone formation and investigated the effect of recombinant human (rh) Ecm1a protein on organ cultures of embryonic mouse metatarsals. Of the two transcripts, Ecm1a mRNA was predominantly expressed in fetal metacarpals from day 16 to 19 after gestation. Ecm1 expression was not found in 16- and 17-day-old metatarsals of which the perichondrium was removed. In situ hybridization and immunohistochemistry demonstrated Ecm1 expression in the connective tissues surrounding the developing bones, but not in the cartilage. Biological effects of rhEcm1a protein on fetal metatarsal cultures were biphasic: at low concentrations, Ecm1a stimulated alkaline phosphatase activity and had no effect on mineralization, whereas at higher concentrations, Ecm1a dose dependently inhibited alkaline phosphatase activity and mineralization. These results suggest that Ecm1a acts as a novel negative regulator of endochondral bone formation.

The estrogen receptor in the growth plate: implications for pubertal growth

It is well established that estrogen is essential for statural growth during puberty, but until recently it was generally accepted that the role of estrogen was negligible during puberty in boys. Clinical findings in three male patients, one with an inactivating mutation in the estrogen receptor and two with P-450 aromatase deficiency, have, however, advanced our knowledge of the role of estrogen in the male. It has become apparent that estrogen (1) initiates the pubertal growth spurt, (2) causes growth plate fusion at the end of puberty, and (3) augments accrual of bone during puberty. Two estrogen receptors (alpha and beta) mediate the actions of estrogen, and the presence of both has been demonstrated in the growth plate. The mechanism by which estrogen acts locally on the growth plate, however, remains largely unknown. With the recent development of knockout models for both estrogen receptors, attempts are being made to unravel the local actions of estrogen in order to characterize further their roles in the regulation of longitudinal growth.

Reestablishment of in vitro and in vivo iodide uptake by transfection of the human sodium iodide symporter (hNIS) in a hNIS defective human thyroid carcinoma cell line

Uptake of iodide is a prerequisite for radioiodine therapy in thyroid cancer. However, loss of iodide uptake is frequently observed in metastasized thyroid cancer, which may be explained by diminished expression of the human sodium iodide symporter (hNIS). Strategies to restore iodide uptake in thyroid cancer include the exploration of hNIS gene transfer into hNIS defective thyroid cancer. In this study, we report the stable transfection of a hNIS expression vector into the hNIS defective follicular thyroid carcinoma cell line FTC133. Stablely transfected colonies exhibited high uptake of Na125I, which could be blocked completely with sodiumperchlorate. hNIS mRNA expression corresponded with iodide uptake in semiquantitative polymerase chain reaction. Iodide uptake was maximal after 60 minutes, whereas iodide efflux was complete after 120 minutes. hNIS transfected FTC133 and control cell lines injected subcutaneously in nude mice formed tumors after 6 weeks. Iodide uptake in the hNIS transfected tumor was much higher than in the nontransfected tumor, which corresponded with hNIS mRNA expression in tumors.

The monoclonal antibodies 18d7/91f2 recognize a receptor regulatory protein on mouse bone marrow stromal cells

Two monoclonal antibodies 18D7 and 91F2 were developed by immunizing rats with the mouse bone marrow-derived osteogenic cell line MN7. Hybridomas secreting rat antibodies against MN7 cell surface markers were selected by flow cytometry analysis. Both the monoclonal antibody 18D7 and the monoclonal antibody 91F2 are directed against the same cell surface antigen present on MN7 cells. Here, we report on the immunopurification of the 18D7/91F2 antigen and its identification as the prostaglandin F2 alpha receptor regulatory protein (FPRP). FPRP is expressed as a single messenger RNA (mRNA) of approximately 6 kilobases (kb) in MN7 cells and is differentially expressed in developing osteogenic cultures of bone marrow cells of the mouse. However, addition of the monoclonal antibodies 18D7 and 91F2 to these cultures did not inhibit bone formation in vitro. Both monoclonal antibodies reacted with mouse stromal cell lines established from bone marrow, thymus, spleen, and mandibular condyles. Immunohistochemical analysis of mature tibia of mice using the monoclonal antibody 18D7 revealed the presence of a distinct population of bone marrow cells close to trabecular and endosteal bone surfaces. In the central bone marrow, hardly any positive cells were found. In 17-day-old fetal mouse radius 18D7 immunoreactivity was restricted to cells in the periosteum in close vicinity to the bone collar. Mature osteoblasts, osteoclasts, osteocytes, growth plate chondrocytes, and mature macrophages were all negative. Taken together, these results suggest that FPRP plays a role in the osteogenic differentiation process.

Expression of Indian hedgehog, parathyroid hormone-related protein, and their receptors in the postnatal growth plate of the rat: evidence for a locally acting growth restraining feedback loop after birth

A locally acting growth restraining feedback loop has been identified in the murine embryonic growth plate in which the level of parathyroid hormone-related peptide (PTHrP) expression regulates the pace of chondrocyte differentiation. To date, it is largely unknown whether this feedback loop also regulates the pace of chondrocyte differentiation in the growth plate after birth. We therefore characterized the spatio-temporal expression of Indian hedgehog (IHH), PTHrP, and their receptors in the postnatal growth plate from female and male rats of 1, 4, 7, and 12 weeks of age. These stages are representative for early life and puberty in rats. Using semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) on growth plate tissue, IHH and components of its receptor complex, patched (PTC) and smoothened (SMO), PTHrP and the type I PTH/PTHrP receptor messenger RNA (mRNA) were shown at all ages studied irrespective of gender. Using in situ hybridization, IHH, PTHrP, and PTH/PTHrP receptor mRNA were detected in prehypertrophic and hypertrophic chondrocytes in both sexes during development. In addition, especially in the younger age groups, faint expression of PTH/PTHrP receptor mRNA also was shown in stem cells and proliferative chondrocytes. Immunohistochemistry confirmed the observations made with in situ hybridization, by showing the presence of IHH, PTC, PTHrP, and PTH/PTHrP receptor protein in prehypertrophic and hypertrophic chondrocytes. In addition, staining for hedgehog, PTC, and PTHrP also was observed in growth plate stem cells. No differences in staining patterns were observed between the sexes. Furthermore, no mRNA or protein expression of the mentioned factors was detected in the perichondrium. Our data suggest that in contrast to the proposed feedback loop in the early embryonic growth plate, which requires the presence of the perichondrium, a feedback loop in the postnatal growth plate can be confined to the growth plate itself. In fact, two loops might exist: (1) a loop confined to the transition zone and early hypertrophic chondrocytes, which might in part be autocrine and (2) a loop involving the growth plate stem cells.

Expression of vascular endothelial growth factors and their receptors during osteoblast differentiation

Endochondral bone formation is regulated by systemically and locally acting growth factors. A role for vascular endothelial growth factor (VEGF) in this process has recently been proposed, because inactivation of VEGF inhibits endochondral bone formation via inhibition of angiogenesis. Despite the known effect of VEGF as specific endothelial growth factor, its effects on osteoblast differentiation have not been studied. We, therefore, examined the expression of VEGF-A, -B, -C, and -D and their receptors in a model of osteoblast differentiation using the mouse preosteoblast-like cell line KS483. Early in differentiation, KS483 cells express low levels VEGF-A, -B, and -D messenger RNA, whereas during mineralization, KS483 cells express high levels. In addition, expression of the VEGF receptors, VEGFR1, VEGFR2, and VEGF165R/neuropilin, coincided with expression of their ligands, being maximally expressed during mineralization. VEGF-A production during osteoblast differentiation was stimulated by insulin-like growth factor I that enhances osteoblast differentiation and was inhibited by PTH-related peptide that inhibits osteoblast differentiation. Furthermore, continuous treatment of KS483 cells with recombinant human VEGF-A stimulated nodule formation. Although treatment of KS483 cells with soluble FLT1, an agent that blocks binding of VEGF-A and -B to VEGFR1, did not inhibit nodule formation, this observation does not exclude involvement of VEGFR2 in the regulation of osteoblast differentiation. As it is known that VEGF-A, -C, and -D can act through activation of VEGFR2, other isoforms might compensate for VEGF-A loss. The expression pattern of VEGFs and their receptors shown here suggests that VEGFs play an important role in the regulation of bone remodeling by attracting endothelial cells and osteoclasts and by stimulating osteoblast differentiation.

Differentiation-dependent alternative splicing and expression of the extracellular matrix protein 1 gene in human keratinocytes

The human extracellular matrix protein 1 (Ecm1) gene is located at chromosome band 1q21 close to the epidermal differentiation complex and is transcribed in two discrete mRNAs: a full length Ecm1a and a shorter, alternatively spliced, Ecm1b transcript, the expression of which is restricted to tonsils and skin. The chromosomal localization and the Ecm1b expression in skin prompted us to investigate the role of Ecm1 in keratinocyte differentiation. In this study, we provide evidence for the existence of a relationship between keratinocyte differentiation and expression of the Ecm1b transcript. Cultures of subconfluent undifferentiated normal human keratinocytes express only Ecm1a. Upon reaching confluence, the cells start to differentiate, as measured by keratin K10 mRNA expression. Concomitantly Ecm1b mRNA expression is induced, although expression of Ecm1a mRNA remains unchanged. In addition, treatment of undifferentiated normal human keratinocyte cells with 12-O-tetradecanoyl-phorbol-13-acetate strongly induces the expression of Ecm1b mRNA. Expression of Ecm1b can also be induced by coculturing normal human keratinocytes with lethally irradiated feeder cells and by a diffusible factor secreted by stromal cells. In adult human skin, Ecm1a mRNA is expressed throughout the epidermis with the strongest expression in the basal and first suprabasal cell layers, whereas expression of Ecm1b mRNA is predominantly found in spinous and granular cell layers. Immunohistochemically, Ecm1a expression is almost completely restricted to the basal cell layer, whereas Ecm1b is detected in the suprabasal layers. These results are strongly suggestive of a role for Ecm1b in terminal keratinocyte differentiation, which is also supported by the localization of the Ecm1 gene at 1q21. Refinement of its genomic localization, however, placed Ecm1 centromeric of the epidermal differentiation complex.