Insulin-like growth factor I accelerates proliferation and differentiation of cartilage progenitor cells in cultures of neonatal mandibular condyles

Stage-Dependent Activity and Pro-Chondrogenic Function of PI3K/AKT during Cartilage Neogenesis from Mesenchymal Stromal Cells

Differentiating mesenchymal stromal cells (MSCs) into articular chondrocytes (ACs) for application in clinical cartilage regeneration requires a profound understanding of signaling pathways regulating stem cell chondrogenesis and hypertrophic degeneration. Classifying endochondral signals into drivers of chondrogenic speed versus hypertrophy, we here focused on insulin/insulin-like growth factor 1 (IGF1)-induced phosphoinositide 3-kinase (PI3K)/AKT signaling. Aware of its proliferative function during early but not late MSC chondrogenesis, we aimed to unravel the late pro-chondrogenic versus pro-hypertrophic PI3K/AKT role. PI3K/AKT activity in human MSC and AC chondrogenic 3D cultures was assessed via Western blot detection of phosphorylated AKT. The effects of PI3K inhibition with LY294002 on chondrogenesis and hypertrophy were assessed via histology, qPCR, the quantification of proteoglycans, and alkaline phosphatase activity. Being repressed by ACs, PI3K/AKT activity transiently rose in differentiating MSCs independent of TGFβ or endogenous BMP/WNT activity and climaxed around day 21. PI3K/AKT inhibition from day 21 on equally reduced chondrocyte and hypertrophy markers. Proving important for TGFβ-induced SMAD2 phosphorylation and SOX9 accumulation, PI3K/AKT activity was here identified as a required stage-dependent driver of chondrogenic speed but not of hypertrophy. Thus, future attempts to improve MSC chondrogenesis will depend on the adequate stimulation and upregulation of PI3K/AKT activity to generate high-quality cartilage from human MSCs.

IGF-1 TMJ injections enhance mandibular growth and bone quality in juvenile rats

OBJECTIVES

Dentofacial orthopaedic treatment of mandibular hypoplasia has unpredictable skeletal outcomes. Although several biomodulators including insulin-like growth factor 1 (IGF-1) are known to contribute to chondrocyte proliferation, their efficacy in modulating mandibular growth has not been validated. The aim of this study was to determine the effect of locally delivered IGF-1 on mandibular growth and condylar bone quality/quantity in juvenile rats.

SETTING AND SAMPLE POPULATION

Institutional vivarium using twenty-four 35-day-old male Sprague-Dawley rats.

METHODS

PBS or 40 µg/kg (low-dose) IGF-1 or 80 µg/kg (high-dose) IGF-1 was injected bilaterally into the temporomandibular joints of the rats at weekly intervals for four weeks. Cephalometric and micro-computed tomography measurements were used to determine mandibular dimensions. Bone and tissue mineral density, volume fraction and mineral content were determined, and serum IGF-1 concentrations assayed.

RESULTS

Intra-articular administration of high-dose IGF-1 contributed to a significant 6%-12% increase in mandibular body and condylar length compared to control and low-dose IGF-1-treated animals. Additionally, IGF-1 treatment resulted in a significant decrease in the angulation of the lower incisors to mandibular plane. Condylar bone volume, bone volume fraction, mineral content and mineral density were significantly increased with high-dose IGF-1 relative to control and low-dose IGF-1 groups. Serum IGF-1 levels were similar between all groups confirming limited systemic exposure to the locally administered IGF-1.

CONCLUSION

Local administration of high-dose 80 µg/kg IGF-1 enhances mandibular growth and condylar bone quality and quantity in growing rats. The findings have implications for modulating mandibular growth and potentially enhancing condylar bone health and integrity.

Longitudinal evaluation of the association between Insulin-like growth factor-1, Bone specific alkaline phosphatase and changes in mandibular length

The aim of the current longitudinal study was to assess the levels of serum Bone-specific alkaline phosphatase (BALP) and serum Insulin like growth factor-1 (IGF-1) in different cervical vertebral maturation index (CVMI) stages and observe their association with the mandibular growth. Blood samples and lateral cephalograms of 63 subjects (age group of 11–17 years) were obtained at two time points, 12 months apart. On the basis of CVMI, all subjects were divided into six groups based on whether the subjects remained in same CVMI stage or transitioned to the next CVMI stage. Annual mandibular length was related with serum BALP and serum IGF-1 levels estimated using ELISA. Serum IGF-1 and BALP attained highest levels at CVMI stage 3 with peak BALP levels observed earlier than IGF-1. Although a positive correlation was determined between IGF-1 and BALP but BALP followed skeletal growth pattern more precisely. Overall IGF-1 and BALP were negatively correlated with mandibular length with notable growth in CVMI groups 3–3 (P < 0.01), 3-4 (P < 0.01), 4-4 (P < 0.001) and 5-5 (P < 0.001). In conclusion, BALP is a potential biomarker for skeletal growth assessment. However, the mandibular growth pattern was independent of changes in IGF-1 and BALP.

Systemic Complications of Acromegaly and the Impact of the Current Treatment Landscape: An Update

Acromegaly is a chronic systemic disease with many complications and is associated with increased mortality when not adequately treated. Substantial advances in acromegaly treatment, as well as in the treatment of many of its complications, mainly diabetes mellitus, heart failure, and arterial hypertension, were achieved in the last decades. These developments allowed change in both prevalence and severity of some acromegaly complications and furthermore resulted in a reduction of mortality. Currently, mortality seems to be similar to the general population in adequately treated patients with acromegaly. In this review, we update the knowledge in complications of acromegaly and detail the effects of different acromegaly treatment options on these complications. Incidence of mortality, its correlation with GH (cumulative exposure vs last value), and IGF-I levels and the shift in the main cause of mortality in patients with acromegaly are also addressed.

Osteocalcin and serum insulin-like growth factor-1 as biochemical skeletal maturity indicators

Background

With change in concepts of growth determination methods, there is a surge in the measurement of biomarkers for appraisal of growth status. Osteocalcin is a bone-specific protein and was observed to parallel the normal growth curve. Hence, the present study was intended to assess the levels of serum osteocalcin and serum insulin-like growth factor-1 (IGF-1) and compare them with cervical vertebral maturation index (CVMI) stages.

Methods

The cross-sectional study was performed on 150 subjects (75 males and 75 females) in the age group of 8–20 years and segregated into six CVMI stages. Serum osteocalcin and IGF-1 were estimated by ELISA. Mann-Whitney U test was used to compare the mean ranks of serum osteocalcin and serum IGF-1 with different CVMI stages. Spearman correlation was performed to find association between serum osteocalcin and serum IGF-1 across six CVMI stages.

Results

Peak serum IGF-1 levels were obtained at CVMI stages 4 and 3 for males and females, respectively, with insignificant difference between stages 3 and 4 in females. Peak serum osteocalcin levels were found at stage 5 and 3 for males and females with insignificant difference from other stages except stages 5 and 6 in males. A statistically significant correlation was seen between serum IGF-1 and serum osteocalcin across six CVMI stages (P < 0.01).

Conclusions

Osteocalcin followed IGF-1 across all CVMI stages but showed insignificant interstage differences.

Gene Expression Profiling of Mouse Condylar Cartilage during Mastication by Means of Laser Microdissection and cDNA Array

Little is known about the mechanisms of mandibular condylar growth. In this study, gene expression in the mandibular condylar cartilage of young post-natal mice was monitored by means of a cDNA microarray, real-time PCR, and laser microdissection before and after the initiation of mastication (newborn, 7 days, 21 days, initiation of mastication, and 35 days). Insulin-like growth factor-1 (IGF-I), transforming-growth-factor-beta-2 (TGFbeta2), and aggrecan mRNAs were clearly expressed at 21 days, while the expression of osteopontin mRNAs was most clear at 35 days. Parathyroid-hormone-related protein (PTHrP), Indian-hedgehog (Ihh), and insulin-like growth factor-2 (IGF-2) mRNAs were clearly expressed during lactation (newborn and 7 days). Heat-shock-protein 84 (HSP-84) and heat-shock-protein 86 (HSP-86) were clearly expressed at 35 days. These results revealed that gene expression changed during mandibular condylar cartilage growth, and that, interestingly, these changes coincided with the initiation of mastication.

Evaluation of protein undernourishment on the condylar process of the Wistar rat mandible correlation with insulin receptor expression

The mandible condylar process cartilage (CP) of Wistar rats is a secondary cartilage and acts as a mandibular growth site. This phenomenon depends on adequate proteins intake and hormone actions, including insulin.

Signaling pathways in cartilage repair

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

Temporomandibular disorders: a review of etiology, clinical management, and tissue engineering strategies

Temporomandibular disorders (TMD) are a class of degenerative musculoskeletal conditions associated with morphologic and functional deformities that affect up to 25% of the population, but their etiology and progression are poorly understood and, as a result, treatment options are limited. In up to 70% of cases, TMD are accompanied by malpositioning of the temporomandibular joint (TMJ) disc, termed "internal derangement." Although the onset is not well characterized, correlations between internal derangement and osteoarthritic change have been identified. Because of the complex and unique nature of each TMD case, diagnosis requires patient-specific analysis accompanied by various diagnostic modalities. Likewise, treatment requires customized plans to address the specific characteristics of each patient's disease. In the mechanically demanding and biochemically active environment of the TMJ, therapeutic approaches that can restore joint functionality while responding to changes in the joint have become a necessity. One such approach, tissue engineering, which may be capable of integration and adaptation in the TMJ, carries significant potential for the development of repair and replacement tissues. The following review presents a synopsis of etiology, current treatment methods, and the future of tissue engineering for repairing and/or replacing diseased joint components, specifically the mandibular condyle and TMJ disc. An analysis of native tissue characterization to assist clinicians in identifying tissue engineering objectives and validation metrics for restoring healthy and functional structures of the TMJ is followed by a discussion of current trends in tissue engineering.

Altered mechano-chemical environment in hip articular cartilage: effect of obesity

The production of extracellular matrix (ECM) components of articular cartilage is regulated, among other factors, by an intercellular signaling mechanism mediated by the interaction of cell surface receptors (CSR) with insulin-like growth factor-1 (IGF-1). In ECM, the presence of binding proteins (IGFBP) hinders IGF-1 delivery to CSR. It has been reported that levels of IGF-1 and IGFBP in obese population are, respectively, lower and higher than those found in normal population. In this study, an experimental-numerical approach was adopted to quantify the effect of this metabolic alteration found in obese population on the homeostasis of femoral hip cartilage. A new computational model, based on the mechano-electrochemical mixture theory, was developed to describe competitive binding kinetics of IGF-1 with IGFBP and CSR, and associated glycosaminoglycan (GAG) biosynthesis. Moreover, a gait analysis was carried out on obese and normal subjects to experimentally characterize mechanical loads on hip cartilage during walking. This information was deployed into the model to account for effects of physiologically relevant tissue deformation on GAG production in ECM. Numerical simulations were performed to compare GAG biosynthesis in femoral hip cartilage of normal and obese subjects. Results indicated that the lower ratio of IGF-1 to IGFBP found in obese population reduces cartilage GAG concentration up to 18 % when compared to normal population. Moreover, moderate physical activity, such as walking, has a modest beneficial effect on GAG production. The findings of this study suggest that IGF-1/IGFBP metabolic unbalance should be accounted for when considering the association of obesity with hip osteoarthritis.

Cartilage tissue engineering of nasal septal chondrocyte-macroaggregates in human demineralized bone matrix

Tissue Engineering is an important method for generating cartilage tissue with isolated autologous cells and the support of biomaterials. In contrast to various gel-like biomaterials, human demineralized bone matrix (DBM) guarantees some biomechanical stability for an application in biomechanically loaded regions. The present study combined for the first time the method of seeding chondrocyte-macroaggregates in DBM for the purpose of cartilage tissue engineering. After isolating human nasal chondrocytes and creating a three-dimensional macroaggregate arrangement, the DBM was cultivated in vitro with the macroaggregates. The interaction of the cells within the DBM was analyzed with respect to cell differentiation and the inhibitory effects of chondrocyte proliferation. In contrast to chondrocyte-macroaggregates in the cell-DBM constructs, morphologically modified cells expressing type I collagen dominated. The redifferentiation of chondrocytes, characterized by the expression of type II collagen, was only found in low amounts in the cell-DBM constructs. Furthermore, caspase 3, a marker for apoptosis, was detected in the chondrocyte-DBM constructs. In another experimental setting, the vitality of chondrocytes as related to culture time and the amount of DBM was analyzed with the BrdU assay. Higher amounts of DBM tended to result in significantly higher proliferation rates of the cells within the first 48 h. After 96 h, the vitality decreased in a dose-dependent fashion. In conclusion, this study provides the proof of concept of chondrocyte-macroaggregates with DBM as an interesting method for the tissue engineering of cartilage. The as-yet insufficient redifferentiation of the chondrocytes and the sporadic initiation of apoptosis will require further investigations.

GLUT4 in murine bone growth: from uptake and translocation to proliferation and differentiation

Skeletal growth, taking place in the cartilaginous growth plates of long bones, consumes high levels of glucose for both metabolic and anabolic purposes. We previously showed that Glut4 is present in growing bone and is decreased in diabetes. In the present study, we examined the hypothesis that in bone, GLUT4 gene expression and function are regulated via the IGF-I receptor (IGF-IR) and that Glut4 plays an important role in bone growth. Insulin and IGF-I actions on skeletal growth and glucose uptake were determined using mandibular condyle (MC) organ cultures and MC-derived primary cell cultures (MCDC). Chondrogenesis was determined by following proliferation and differentiation activities using immunohistochemical (IHC) analysis of proliferating cell nuclear antigen and type II collagen expression, respectively. Overall condylar growth was assessed morphometrically. GLUT4 mRNA and protein levels were determined using in situ hybridization and IHC, respectively. Glut4 translocation to the cell membrane was assessed using confocal microscopy analysis of GFP-Glut4 fusion-transfected cells and immunogold and electron microscopy on MC sections; glucose uptake was assayed by 2-deoxyglucose (2-DOG) uptake. Both IGF-I and insulin-stimulated glucose uptake in MCDC, with IGF-I being tenfold more potent than insulin. Blockage of IGF-IR abrogated both IGF-I- and insulin-induced chondrogenesis and glucose metabolism. IGF-I, but not insulin, induced Glut4 translocation to the plasma membrane. Additionally, insulin induced both GLUT4 and IGF-IR gene expression and improved condylar growth in insulin receptor knockout mice-derived MC. Moreover, silencing of GLUT4 gene in MCDC culture abolished both IGF-I-induced glucose uptake and chondrocytic proliferation and differentiation. In growing bone, the IGF-IR pathway stimulates Glut4 translocation and enhances glucose uptake. Moreover, intact Glut4 cellular levels and translocation machinery are essential for early skeletal growth.

Effect of serum and growth factors on chondrogenic differentiation of synovium-derived stromal cells

We used fetal bovine serum (FBS) and different growth factors to investigate their potential for inducing chondrogenic differentiation of synovium-derived stromal cells. Human synovium was harvested from patients suffering from osteoarthritis and expanded in monolayer. To evaluate the effect of serum and growth factors on chondrogenic differentiation, 10 ng/mL of transforming growth factor-beta1 (TGF-beta1), 100 ng/mL of bone morphogenic protein-2 (BMP-2), 100 ng/mL of insulin-like growth factor-1, 20 ng/mL of basic fibroblast growth factor (bFGF), and 10% FBS were added to the chemically defined chondrogenic medium singly or in combination during pellet culture for 21 days. The cell size and weight, glycosaminoglycan content, histology, and cartilage matrix-associated genes expression were analyzed. TGF-beta1 alone and TGF-beta1 + BMP-2 induced chondrogenic differentiation of synovium-derived stromal cells and synthesized cartilage-like matrix confirmed by histological analysis and immunohistochemistry. FBS, BMP-2, insulin-like growth factor-1, and bFGF as a single factor or other combinations except for TGF-beta1 + BMP-2 hardly induced chondrogenesis. Chondrogenic differentiation appeared to be inhibited when bFGF or the serum was added to the chondrogenic medium during pellet culture. The results of this study demonstrate the negative or positive role of serum and growth factors on chondrogenic differentiation of synovium-derived stromal cells.

The contribution of the synovium, synovial derived inflammatory cytokines and neuropeptides to the pathogenesis of osteoarthritis

Osteoarthritis (OA) is one of the most common and disabling chronic joint disorders affecting horses, dogs and humans. Synovial inflammation or synovitis is a frequently observed phenomenon in osteoarthritic joints and contributes to the pathogenesis of OA through formation of various catabolic and pro-inflammatory mediators altering the balance of cartilage matrix degradation and repair. Catabolic mediators produced by the inflamed synovium include pro-inflammatory cytokines, nitric oxide, prostaglandin E(2) and several neuropeptides, which further contribute to the pathogenesis of OA by increasing cartilage degradation. Recent studies suggest that substance P, corticotropin-releasing factor, urocortin and vasoactive intestinal peptide may also be involved in OA development, but the precise role of these neuropeptides in the pathogenesis of OA is not known. Since increased production of matrix metalloproteinases by the synovium is stimulated by pro-inflammatory cytokines, future anti-inflammatory therapies should focus on the synovium as a means of controlling subsequent inflammatory damage.

Interplay of mechanical loading and growth factors in the mandibular condyle

The mandibular condyle is an important growth site in the developing mandible. The growth of the condyle is known to be highly adaptable to functional factors. This property is exploited in orthodontics for the treatment of class II malocclusions and mandibular asymmetries. However, there is an ongoing debate on the efficacy of functional appliances. The comparison of experimental studies is complicated by the lack of detailed analyses of the load distribution within the condyle. In spite of this, there is a large body of evidence showing that mechanical manipulation of the condyle induces metabolic changes, and changes in the expression of growth factors and other signalling molecules. This review aims to give an overview of the role of growth factors in the condyle with special emphasis on their responsiveness to mechanical perturbation.

Insulin-like growth factor I regulates apoptosis in condylar cartilage

Endogenous insulin-like growth factor-I (IGF-I) is known to affect the growth and development of condylar cartilage. However, the critical effect of IGF-I on cell survival is still unknown. We hypothesized that endogenous IGF-I could regulate the survival of cells of the mandibular condylar cartilage. Mandibular condyles dissected from 12-day-old rats were cultured for 1, 3, and 5 days in medium containing antisense oligodeoxynucleotide (AS-ODN) for IGF-I. Real-time RT-PCR analysis showed that the levels of IGF-I and IGF binding protein (IGFBP)3 mRNAs in the AS-ODN group were significantly decreased. After 3 days' culture, the number of necrotic cells was observed in the undifferentiated mesenchymal cell layer. These cells were TUNEL-positive and confirmed to be apoptotic by electron microscopic observation. Immunoblotting revealed that expression of cleaved caspase3 was increased with AS-ODN. These results may suggest that the cells in the undifferentiated mesenchymal cell layer of the mandibular condyle require IGF-I for survival.

Insulin-like growth factor I releasing silk fibroin scaffolds induce chondrogenic differentiation of human mesenchymal stem cells

Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implants, providing a biologically active template for tissue (re)-generation. The goal of this study is to evaluate the feasibility of controlled insulin-like growth factor I (IGF-I) releasing silk fibroin (SF) scaffolds in the context of cartilage repair. The impact of manufacturing parameters (pH, methanol treatment and drug load) was correlated with IGF-I release kinetics using ELISA and potency tests. Methanol treatment induced water insolubility of SF scaffolds, allowed the control of bioactive IGF-I delivery and did not affect IGF-I potency. The cumulative drug release correlated linearly with the IGF-I load. To evaluate the chondrogenic potential of the scaffolds, hMSC were seeded on unloaded and IGF-I loaded scaffolds in TGF-beta supplemented medium. Chondrogenic differentiation of hMSC was observed on IGF-I loaded scaffolds, starting after 2 weeks and more strongly after 3 weeks, whereas no chondrogenic responses were observed on unloaded control scaffolds. IGF-I loaded porous SF scaffolds have the potential to provide chondrogenic stimuli to hMSC. Evidence for in vivo cartilage (re)generation must be demonstrated by future, pre-clinical proof of concept studies.

A longitudinal study of craniofacial growth in idiopathic short stature and growth hormone-deficient boys treated with growth hormone

The aim of this prospective, longitudinal, controlled study is to describe the long-term safety and efficacy of growth hormone (GH) administration on craniofacial morphology in boys with short stature. Forty-six boys, who started GH treatment at the Department of Paediatrics Göteborg Paediatric Growth Research Centre, were consecutively included in the study. Twenty-five boys were classified as growth hormone-deficient (GHD) and 21 as idiopathic short stature (ISS). The patients were injected with 33 (n=31) or 67 (n=15) microg GH/kg body weight/day. The mean age at the start of treatment was 11.8 years [standard deviation (SD) 1.7]. To assess craniofacial growth, standard lateral cephalometric radiographs were obtained at the start of GH treatment, annually during 4 years, and at the end of GH treatment or when growth was less than 1 cm/year. The mean follow-up period was 6.4 years (SD 1.4). Growth changes were compared with boys from a semi-longitudinal reference group of 130 healthy subjects, 7-21 years of age. t-tests for independent and paired samples and multiple regression analysis were applied. Age- and gender-specific standard deviation scores for the cephalometric variables were calculated. Repeated measures analysis of variance was used to identify significant covariates over time, such as low/high GH dose and GHD/ISS and orthodontic treatment. During the study period, eight (out of 40) boys were treated with fixed orthodontic appliances, three with functional appliances (activators), and three with other appliances (plates and lingual arches). During GH treatment period, an overall enhancement in growth of the facial skeleton was observed in boys with short stature. The changes induced by GH yielded a more prognathic growth pattern, a more anterior position of the jaws in relation to the cranial base, and increased anterior rotation of the mandible. The mandibular corpus length and anterior face height of the GH-treated boys were greater at the end of the study compared with the boys in the reference group. No differences in growth response were noted either between the GHD and ISS boys or between those treated with either 33 (low dose) or 67 (high dose) microg GH/kg body weight/day. The only change that remained significantly correlated with orthodontic treatment was the alteration in mandibular ramus height, showing a larger change in the boys who had not undergone orthodontic therapy. The findings of this study demonstrate that GH treatment has a favourable influence on the craniofacial growth pattern of boys with short stature without acromegalic features.

Enamel matrix derivative stimulates chondrogenic differentiation of ATDC5 cells

BACKGROUND AND OBJECTIVES

Although enamel matrix derivative can promote chondrogenic differentiation of pluripotent mesenchymal precursor cells, the molecular mechanism that underlies this phenomenon is unclear. The purpose of this study was to determine the effect of enamel matrix derivative on chondrogenic differentiation. ATDC5 cells, which undergo a reproducible multistep chondrogenic differentiation, were cultured with or without enamel matrix derivative for up to 35 d.

METHODS AND RESULTS

Cell proliferation and alkaline phosphatase activity increased markedly in cells cultured in the presence of enamel matrix derivative, compared with cells cultured in its absence. Deposition of Alcian blue-positive cartilage matrix and Alizarin red-positive mineralized nodules also increased significantly upon treatment with enamel matrix derivative. Expression of mRNAs encoding cartilage extracellular matrix proteins (type II collagen, type X collagen and aggrecan) and chondrogenic-related transcription factors (Sox9, Zfp60 and AJ18) were measured using the real-time polymerase chain reaction. Type II collagen, type X collagen and aggrecan mRNA expression increased markedly with enamel matrix derivative treatment. Transcription of Sox9, an important transcription factor that mediates chondrogenic differentiation, also increased with enamel matrix derivative treatment. The KRAB/C2H2 zinc-finger transcription factors, Zfp60 and AJ18, were transiently expressed in the prehypertrophic stage, and their expression increased with enamel matrix derivative treatment. In a western blot analysis with anti-insulin-like growth factor-I and anti-bone morphogenetic protein-6 immunoglobulin, bands corresponding to approximately 14, approximately 18 and approximately 60 kDa were found in enamel matrix derivative.

CONCLUSION

Our study provides clear evidence that enamel matrix derivative promotes chondrogenic differentiation of ATDC5 cells.

Primary and secondary cartilages of the neonatal rat: the femoral head and the mandibular condyle

Primary and secondary cartilages differ in embryonic origin and in histological organization, and are generally considered to have a different mode of growth. However, few studies have directly compared the two types of cartilage of the same animal at the same age. Therefore, we analysed several histological and biochemical differences between secondary cartilage of the mandibular condyle and primary cartilage of the femoral head of 4-d-old rats. We evaluated the tissue organization, the level of DNA and glycosaminoglycan (GAG) synthesis, and the GAG and collagen content. The expression of collagen types I, II and III and of receptors for insulin-like growth factor (IGF)-I, fibroblast growth factor (FGF), and transforming growth factor (TGF)-beta were investigated by immunohistochemistry. The ex vivo DNA and GAG synthesis as well as the GAG content of femoral heads were much higher than that of mandibular condyles. Mandibular condyles expressed both collagen types I and II, while femoral heads expressed only type II collagen. In the mandibular condyles, receptors for IGF-I, FGF, and TGF-beta were observed mainly in the superficial layers, whereas they were found throughout the entire femoral head. In conclusion, major differences were found between both types of cartilage, which might be related to their specific functional demands.

Growth stimulation of mandibular condyles and femoral heads of newborn rats by IGF-I

Primary and secondary cartilage differ in embryonic origin and are generally considered to have a different mode of growth. However, few experimental studies exist that directly compare the two types of cartilage and their growth regulation. The regulation of cartilage growth is a complex mechanism involving growth factors like insulin-like growth factor-I (IGF-I). The purpose of this study was to compare the growth of mandibular condyles of 4-day-old rats with that of femoral heads in vitro and to analyze the effects of IGF-I. Explants were cultured for up to 2 weeks with 0, 5, and 25 ng/ml IGF-1. Both, 5 and 25 ng/ml IGF-I significantly stimulated growth of the mandibular condyles while only 25 ng/ml IGF-I stimulated growth of the femoral heads. IGF-I increased glycosaminoglycan synthesis of both condylar and femoral cartilage. However, only the DNA synthesis of the mandibular condyles was significantly increased by IGF-I while that of the femoral heads was not affected. It is concluded that IGF-I stimulates growth of both secondary condylar cartilage and primary femoral cartilage. The mandibular condyle appears to be more sensitive to IGF-I than the femoral head, which may partly be due to the different developmental stage.

Propulsive appliance stimulates the synthesis of insulin-like growth factors I and II in the mandibular condylar cartilage of young rats

Functional orthopedic appliances correct dental malocclusion partially by exerting indirect mechanical stimulus on the condylar cartilage, modulating growth and the adaptation of orofacial structures. However, the exact nature of the biological responses to this therapy is not well understood. Insulin-like growth factors I and II (IGF-I and IGF-II) are important local factors during growth and differentiation of several tissues, including cartilage. The aim of this study was to verify the mRNA and protein expression of IGF-I and IGF-II in the condylar cartilage of young male Wistar rats that used a mandibular propulsive appliance for 3, 5, 7, 9, 11, 13 or 15 days. For this purpose, sagittal sections of decalcified and paraffin-embedded condyles were submitted to immunohistochemistry and in situ hybridization. IGF-I and IGF-II expression increased with developmental age in the control and treated rats. After 9 days of treatment the positivity for both peptides in the animals that wore the propulsive appliance increased even more, expressively different from the age-matched controls. The expression patterns of both IGFs were similar, although IGF-I labelling was stronger. Furthermore, the enhanced expression of both peptides was in parallel with the proliferating cell nuclear antigen (PCNA) positivity, a proliferation cell marker. The modulation of IGF-I and IGF-II expression in the condylar cartilage in response to the propulsive appliance suggests that both peptides are involved in the mandibular adaptation during this therapy.

Growth velocity during the first postnatal week of life is linked to a spurt of IGF-I effect

There is adequate evidence that growth during the perinatal period is linked to the risk of several adult onset diseases, and recent findings indicate that the insulin-like growth factor (IGF) system is involved in prenatal growth, as reflected in birthweight. However, whether major components of the IGF system are involved in the immediate post-natal growth has not been studied. Maternal questionnaires were completed, and laboratory measurements of several variables, including IGF-I, IGF-II and IGF-binding protein-3 (IGFBP-3), were made for a total of 331 apparently healthy full-term newborns, from whom routine blood samples were taken during the first 5 days of their life. Birthweight and weight at the time of bleeding were among the recorded variables, and the difference divided by the age in days of the newborn was considered as reflecting immediate postnatal growth velocity. Immediate postnatal growth velocity was strongly positively associated with IGF-I. The squared adjusted correlation coefficient was 0.29 when IGF-I was incorporated in the model predicting postnatal growth velocity but was only 0.08 when IGF-I was excluded. In contrast, IGF-II and IGFBP-3 had no effect on postnatal growth velocity. It thus appears that IGF-I underlies growth during the immediate postnatal period. To the extent that perinatal growth may affect adult onset diseases, the findings of this study suggest that the action of IGF-I during the immediate postnatal period may represent a process of major importance.

Expression of parathyroid hormone-related peptide and insulin-like growth factor I during rat fracture healing

Parathyroid hormone-related peptide (PTHrP) and insulin-like growth factor I (IGF-I) are both involved in the regulation of bone and cartilage metabolisms and their interaction has been reported in osteoblasts. To investigate the interaction of PTHrP and IGF-I during fracture healing, the expression of mRNA for PTHrP and IGF-I, and receptors for PTH/PTHrP and IGF were examined during rat femoral fracture healing using an in situ hybridization method and an immunohistochemistry method, respectively. During intramembranous ossification, PTHrP mRNA, IGF-I mRNA and IGF receptors were detected in preosteoblasts, differentiated osteoblasts and osteocytes in the newly formed trabecular bone. PTH/PTHrP receptors were markedly detected in osteoblasts and osteocytes, but only barely so in preosteoblasts. During cartilaginous callus formation, PTHrP mRNA was expressed by mesenchymal cells and proliferating chondrocytes. PTH/PTHrP receptors were detected in proliferating chondrocytes and early hypertrophic chondrocytes. IGF-I mRNA and IGF receptor were co-expressed by mesenchymal cells, proliferating chondrocytes, and early hypertrophic chondrocytes. At the endochondral ossification front, osteoblasts were positive for PTHrP and IGF-I mRNA as well as their receptors. These results suggest that IGF-I is involved in cell proliferation or differentiation in mesenchymal cells, periosteal cells, osteoblasts and chondrocytes in an autocrine and/or paracrine fashion. Furthermore, PTHrP may be involved in primary callus formation presumably co-operating with IGF-I in osteoblasts and osteocytes, and by regulating chondrocyte differentiation in endochondral ossification.

A novel insulin-like growth factor (IGF)-independent role for IGF binding protein-3 in mesenchymal chondroprogenitor cell apoptosis

Chondrogenesis results from the condensation of mesenchymal chondroprogenitor cells (MCC) that proliferate and differentiate into chondrocytes. We have previously shown that IGF binding protein (IGFBP)-3 has an IGF-independent antiproliferative effect in MCC. The current study evaluates the IGF-independent apoptotic effect of IGFBP-3 on MCC to modulate chondrocyte differentiation. We employed the RCJ3.1C5.18 chondrogenic cell line, which in culture progresses from MCC to differentiated chondrocytes; cells do not express IGFs or IGFBP-3. We also used IGFBP-3 mutants with decreased (I56 substituted to G56; L80 and L81 to G80G81) or abolished binding for IGFs (I56, L80, and L81 to G56G80G81). MCC transfected with IGFBP-3 detached, changed their phenotype, and underwent apoptosis. A maximal IGFBP-3 apoptotic effect was observed 24 h after transfection (463 +/- 73% of controls; P < 0.001). Remarkably, IGFBP-3 mutants had similar effects, demonstrating that the IGFBP-3 apoptotic action was clearly IGF independent. In addition, treatment with IGFBP-3 in serum-free conditions resulted in a significant increase of apoptosis (173 +/- 23% of controls; P < 0.05). Moreover, this apoptotic effect was selective for MCC, resulting in a selective reduction of chondrocytic nodules and a significant decrease in type II collagen expression and proteoglycan synthesis. In summary, we have identified a novel IGF-independent role for IGFBP-3 in the modulation of chondrocyte differentiation.

Combined effects of insulin-like growth factor-1 and transforming growth factor-beta1 on periosteal mesenchymal cells during chondrogenesis in vitro

OBJECTIVE

Periosteum contains undifferentiated mesenchymal stem cells that have both chondrogenic and osteogenic potential, and has been used to repair articular cartilage defects. During this process, the role of growth factors that stimulate the periosteal mesenchymal cells toward chondrogenesis to regenerate articular cartilage and maintain its phenotype is not yet fully understood. In this study, we examined the effects of insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta1 (TGF-beta1), alone and in combination, on periosteal chondrogenesis using an in vitro organ culture model.

METHODS

Periosteal explants from the medial proximal tibia of 2-month-old rabbits were cultured in agarose under serum free conditions for up to 6 weeks. After culture the explants were weighed, assayed for cartilage production via Safranin O staining and histomorphometry, assessed for proliferation via proliferative cell nuclear antigen (PCNA) immunostaining, and assessed for type II collagen mRNA expression via in situ hybridization.

RESULTS

IGF-1 significantly increased chondrogenesis in a dose-dependent manner when administered continuously throughout the culture period. Continuous IGF-1, in combination with TGF-beta1 for the first 2 days, further enhanced overall total cartilage growth. Immunohistochemistry for PCNA revealed that combining IGF-1 with TGF-beta1 gave the strongest proliferative stimulus early during chondrogenesis. In situ hybridization for type II collagen showed that continuous IGF-1 maintained type II collagen mRNA expression throughout the cambium layer from 2 to 6 weeks.

CONCLUSION

The results of this study demonstrate that IGF-1 and TGF-beta1 can act in combination to regulate proliferation and differentiation of periosteal mesenchymal cells during chondrogenesis.

Regulation of cell proliferation in rat mandibular condylar cartilage in explant culture by insulin-like growth factor-1 and fibroblast growth factor-2

Insulin-like growth factor-1 (IGF-1) and fibroblast growth factor-2 (FGF-2) regulate the proliferation and differentiation of growth-plate chondrocytes, but surprisingly little is known of the mechanisms underlying growth regulation in secondary cartilages such as the mandibular condylar. The aims here were to investigate whether IGF-1 and FGF-2 receptors are present in mandibular condylar cartilage in vivo from 28-day-old male Sprague-Dawley rats (by immunohistochemistry), how proliferation in that cartilage responds to increasing concentrations of exogenous IGF-1 or FGF-2 in explant culture (by [3H]thymidine incorporation), and whether the expression of these growth factors and their receptors in the cartilage changes during the transition to puberty (quantitative reverse transcriptase-polymerase chain reaction). Immunoreactivity for receptors (R) for IGF-1 and FGF-2 (IGF-1R, FGFR1, and FGFR3) was most pronounced in chondroblasts and hypertrophic chondrocytes, while FGFR2 immunoreactivity was strongest in the articular and prechondroblastic zones. The proliferative response elicited by exogenous IGF-1 was considerably greater than that induced by FGF-2, although the threshold concentration for a significant response was lower for FGF-2. In the transition from prepuberty (31 days) to the beginning of late puberty (42 days), a pronounced trend of increasing IGF-1 and decreasing FGF-2 gene expression was evident. Of the receptors, only FGFR2 and FGFR3 expression increased. These data provide evidence that proliferation in the mandibular condylar cartilage might be regulated in part by IGF-1 and FGF-2, and that expression of these genes changes considerably at puberty. The data also suggest that mechanisms governing proliferation in mandibular condylar cartilage might have as much in common with those regulating cranial sutures as those regulating growth-plate.

Leptin acts as a growth factor on the chondrocytes of skeletal growth centers

Childhood obesity frequently is associated with an increase in height velocity and acceleration of epiphyseal growth plate maturation despite low levels of serum growth hormone (GH). In addition, obesity is associated with higher circulating levels of leptin, a 16-kDa protein that is secreted from the adipocytes. In this study, we evaluated the direct effect of leptin on the chondrocyte population of the skeletal growth centers in the mouse mandibular condyle, a model of endochondral ossification. We found that chondrocytes in the growth centers contain specific binding sites for leptin. Leptin, at a concentration of 0.5-1.0 microg/ml, stimulated in a dose-dependent manner the width of the chondroprogenitor zone (up to 64%), whereas higher concentrations had an inhibitory effect. Leptin induction of both proliferation and differentiation activities in the mandibular condyle was confirmed by our findings of an increase in bromodeoxyuridine (BrdU) incorporation into DNA and in (acidic) Alcian blue (AB) staining of the cartilaginous matrix. Leptin also increased the abundance of the insulin-like growth factor (IGF) I receptor and IGF-I receptor messenger RNA (mRNA) within the chondrocytes and the progenitor cell population. Our results indicate that leptin acts as a skeletal growth factor with a direct peripheral effect on skeletal growth centers. Some of its effects on the growing bone may be mediated by the IGF system via regulation of IGF-I receptor expression. We speculate that the high circulating levels of leptin in obese children might contribute to their growth.

Chondrogenesis in cartilage repair is induced by members of the transforming growth factor-beta superfamily

The authors recently reported on the principle of an intrinsic repair strategy for partial-thickness articular cartilage defects, which is based on the introduction of a biocompatible and biodegradable matrix loaded with a free chemotactic and mitogenic agent (transforming growth factor-beta 1, at low concentration) and a liposome-encapsulated chondrogenic factor (transforming growth factor-beta 1 at high concentration). In the current study, the potential of other members of the transforming growth factor-beta superfamily (transforming growth factor-beta 2, transforming growth factor-beta 3, bone morphogenetic protein-2 and bone morphogenetic protein-13), and of insulinlike growth factor-1, epidermal growth factor, transforming growth factor-alpha, and Tenascin-C, to induce chondrogenesis within the authors' adult miniature pig articular cartilage defect model, was evaluated. The degree of chondrogenic tissue differentiation was assessed 6 weeks after surgery, on a semiquantitative basis, histologic assessment of cell morphologic features, and intercellular matrix staining being used as the relevant criteria. All selected members of the transforming growth factor-beta superfamily were efficacious in inducing chondrogenic tissue transformation, whereas the other signaling substances tested were not. When encapsulated at high activity levels, bone morphogenetic proteins were less prone than transforming growth factor-beta 1, transforming growth factor-beta 2, and transforming growth factor-beta 3 to evoke undesired side effects as a result of incidental leakage into the joint cavities and subsynovial connective tissue spaces, and therefore they are potentially more suitable candidates for use in human patients.

Effects of mechanical stimulation on gene expression of articular chondrocytes in polylayer culture

Mechanical loads are constantly being applied to articular cartilage. However, comparatively few studies have investigated the effects of mechanical stress on the gene expression of chondrocytes. Hence, the objective of the present study was to clarify the effects of mechanical stress on cultured chondrocytes. Articular chondrocytes of rabbits were isolated and placed in minimun essential medium eagle a modification containing 10% fetal bovine serum. The chondrocytes were cultured in polylayer in polypropylene tubes. After 48 hours, centrifugal stress (2.7 MJ) was applied once every 24 hours for 28 consecutive days. The mRNA expression of insulin-like growth factor-I (IGF-I) and cartilage-specific genes (type II collagen and aggrecan) in chondrocytes, cell count, wet tissue mass and protein content were subsequently measured. The results showed that the mRNA expression of the IGF-I gene for the stress groups was significantly greater than that of the control group from days 3 to 5 of incubation, as was the mRNA expression of the type II collagen gene from days 7 to 14 of incubation. However, there were no significant differences in the mRNA expression of the aggrecan gene between the control and stress groups. The cell count for the stress groups was significantly higher from days 7 to 28 of incubation, and the wet tissue mass and protein content were significantly higher from days 14 to 28 of incubation. These findings suggest that one of the mechanisms by which mechanical stress increases the number of cultured chondrocytes and the volume of extracellular matrix is to increase IGF-I expression at the early stage of incubation.

Effect of metabolic acidosis on the growth hormone/IGF-I endocrine axis in skeletal growth centers

BACKGROUND

Chronic metabolic acidosis (CMA) adversely affects bone metabolism and skeletal growth. Given the cardinal role played by the local growth hormone (GH)/insulin-like growth factor-I (IGF-I) in promoting cell proliferation and differentiation in growth plates, we tested the effect of CMA on the GH/IGF-I axis in a skeletal growth center.

METHODS

We employed an in vitro organ culture system using the murine mandibular condyle as a model for endochondral active growth center. Condyles from six-day-old ICR mice were cultured in BGJb medium of either neutral pH (pH approximately 7.4) or acidic pH (pH approximately 7.15). After 24, 48, 72, and 96 hours of culture, the condyles were washed, fixed in formaldehyde, and processed for paraffin embedding. We assessed histologic markers of the growth center. In addition, the protein level and mRNA expression for the different components of the GH/IGF-I axis were evaluated by immunohistochemistry and in situ hybridization, respectively. Finally, we evaluated the effect of acidosis on the biological functions mediated by GH and IGF-I (namely, proliferation and differentiation of cartilage cells in the active growth center).

RESULTS

Following three to four days in acidic conditions, there was a marked reduction in the size of young chondrocytic population, suggesting a defect in the process of endochondral differentiation. Immunohistochemistry and in situ hybridization analyses revealed a marked reduction in the expression of the IGF-I receptor, as well as in the GH receptor. These changes were already evident after 48 hours of incubation in acidic conditions. At 48 hours of acidosis, there was also a marked reduction in the expression of IGF-I both under basal conditions (nonstimulated) and following stimulation with GH. The expression of IGF binding protein 2 (IGFBP-2) and IGFBP-4, which serve as negative modulators of IGF-I, was enhanced in CMA. IGF-I markedly stimulated chondrocytic proliferation (assessed by BrdU incorporation into DNA) and differentiation (assessed as cartilage specific proteoglycan expression). These responses were markedly attenuated in acidic conditions.

CONCLUSION

CMA exerts an anti-anabolic effect in bone growth centers, which is partly related to a state of resistance to GH and IGF-I, created by CMA. This phenomenon may underlie the disturbance in longitudinal bone growth in CMA (that is, renal tubular acidosis) and may contribute to renal osteodystrophy in patients suffering from chronic renal failure.

Parathyroid hormone-(1-34) enhances aggrecan synthesis via an insulin-like growth factor-I pathway

During endochondral bone formation, the growth plate chondrocytes proliferate, become hypertrophic, lose the cartilage phenotype, undergo mineralization, and provide a scaffold upon which subsequent longitudinal bone growth occurs. Parathyroid hormone (PTH), a calcium-regulating hormone, and parathyroid hormone-related peptide (PTHrP), which shares several properties with PTH, have profound effects on skeletal growth and new bone formation. In order to define further the mechanism by which PTH/PTHrP promotes the cartilage phenotype, chondrocytes isolated from the rib cages of developing rat embryos were evaluated for the biosynthesis of aggrecan. Cells treated with PTH-(1-34) for a 4-h period followed by a 20-h recovery period showed a significant increase in cartilage proteoglycan (aggrecan) synthesis in a dose-dependent manner. Only N-terminally intact PTH and PTHrP were effective in stimulating aggrecan synthesis. Addition of a neutralizing antibody to insulin-like growth factor-I (IGF-I) during PTH treatment resulted in the inhibition of PTH-stimulated aggrecan synthesis, whereas the addition of a neutralizing antibody to insulin-like growth factor-binding protein-2 (IGFBP-2) resulted in an increase in synthesis in both the control and PTH-treated cells. In addition, PTH treatment resulted in an increase in the mRNA for aggrecan, a reduction in IGFBP-3 mRNA, and no discernible changes in IGF-I mRNA levels, which was complemented by quantitative changes in IGFBP-3 and free IGF-I levels. The reciprocal relationship in the expression of aggrecan and IGFBP was further confirmed in chondrocytes from various gestational stages during normal development. Collectively, our results indicate that the effect of PTH may be mediated at least in part through the regulation of the IGF/IGFBP axis, by a decrease in the level of IGFBP-3, and an increase in free IGF-I levels. It is likely that the local increase in IGF-I may lead to an increase in cartilage type proteoglycan synthesis and maintenance of the cartilage phenotype. The consequence of the prolonged maintenance may be to halt mineralization while a new scaffolding is created.

Testosterone stimulates insulin-like growth factor-I and insulin-like growth factor-I-receptor gene expression in the mandibular condyle--a model of endochondral ossification

Puberty is associated with an increase in the plasma concentration of sex steroids, GH, and insulin-like growth factor-I (IGF-I). Gonadal steroid hormones are important for the normal pubertal growth spurt and skeletal growth. The mechanism by which gonadal steroids induce skeletal growth is still not fully understood. To better understand the direct effect sex steroids have on bone growth, we studied an isolated organ culture system of the mandibular condyle, derived from 3.5-5.5-week-old male and female mice. We found that testosterone 10(-6) M, but not estradiol, stimulated thymidine incorporation into the DNA of male-derived condyle. Three days of testosterone treatment doubled the condyle size and increased the chondroprogenitor zone, while maintaining the normal gradient of the developing chondrocytes. Immunohistochemistry and in situ hybridization techniques showed that testosterone stimulated IGF-I and IGF-I-R and their messenger RNAs (mRNAs) mainly in the mature chondrocyte layer. Immunoneutralization of IGF-I in the testosterone-treated condyle caused the disappearance of the chondroblast and young chondrocyte layers, though the progenitor cell layer remained almost unaffected. Overtreatment with testosterone (dose or duration) accelerated condylar ossification. In the presence of testosterone 10(-5) M (high dose), calcification "climbs" up to the chondroprogenitor zone, and most of the condylar chondrocytes are replaced by bone tissue. Similar changes occurred after 7 days of testosterone treatment (long duration) with 10(-6) M. In conclusion, testosterone stimulates growth and local production of IGF-I and IGF-I-R in chondrocyte cell layers of an isolated organ culture of mice mandibular condyle. Part of the effect testosterone has on condylar growth is mediated by IGF-I.

The insulin-sensitive glucose transporter (GLUT4) is involved in early bone growth in control and diabetic mice, but is regulated through the insulin-like growth factor I receptor

Children with uncontrolled type I (insulin-dependent) diabetes mellitus are characterized by a slow growth rate, which improves upon adequate therapy. While skeletal growth is an energy-consuming process involving high glucose utilization, the role of glucose transporters (GLUT) and their regulation in the bone formation process are not yet fully understood. Thus, we studied both in vivo and in vitro early endochondral bone formation in control and streptozotocin-induced young diabetic mice. Using in situ hybridization and immunohistochemistry techniques, we demonstrated the novel existence of the insulin-sensitive glucose transporter (GLUT4), as well as GLUT1, in juvenile-derived murine mandibular condyles and in the humeral growth plate-two models for endochondral bone formation. Insulin-like growth factor (IGF) I receptors (IGF-I-R), but not insulin receptors (IR), were shown to have cellular distribution similar to GLUT4, being more abundant in mature chondrocytes. Further, in the skeletal growth centers of streptozotocin-induced diabetic mice, GLUT4, IGF-I, and IGF-I and insulin receptor levels, but not GLUT1 were markedly reduced. The decrease in GLUT4 and in IGF-I and insulin receptors was associated with severe histological changes in the mandibular condyles and humeral growth plate. Insulin therapy restored IR levels to normalcy, whereas IGF-I-R and GLUT4 levels were only partially recovered. Thus, GLUT4 and IGF-I-R have a potential role in early bone growth in mice. Further, during early bone growth GLUT4 may be regulated through the IGF-I receptor rather than via the insulin receptor. We propose that skeletal growth retardation in type I diabetes may be associated with reduced expression of the GLUT4 and IGF-I receptor in the bone growth center.