Expression of the components of the insulin-like growth factor axis across the growth-plate

A critical bioenergetic switch is regulated by IGF2 during murine cartilage development

Long bone growth requires the precise control of chondrocyte maturation from proliferation to hypertrophy during endochondral ossification, but the bioenergetic program that ensures normal cartilage development is still largely elusive. We show that chondrocytes have unique glucose metabolism signatures in these stages, and they undergo bioenergetic reprogramming from glycolysis to oxidative phosphorylation during maturation, accompanied by an upregulation of the pentose phosphate pathway. Inhibition of either oxidative phosphorylation or the pentose phosphate pathway in murine chondrocytes and bone organ cultures impaired hypertrophic differentiation, suggesting that the appropriate balance of these pathways is required for cartilage development. Insulin-like growth factor 2 (IGF2) deficiency resulted in a profound increase in oxidative phosphorylation in hypertrophic chondrocytes, suggesting that IGF2 is required to prevent overactive glucose metabolism and maintain a proper balance of metabolic pathways. Our results thus provide critical evidence of preference for a bioenergetic pathway in different stages of chondrocytes and highlight its importance as a fundamental mechanism in skeletal development.

Altered IGF-I activity and accelerated bone elongation in growth plates precede excess weight gain in a mouse model of juvenile obesity

Nearly one-third of children in the United States are overweight or obese by their preteens. Tall stature and accelerated bone elongation are characteristic features of childhood obesity, which cooccur with conditions such as limb bowing, slipped epiphyses, and fractures. Children with obesity paradoxically have normal circulating IGF-I, the major growth-stimulating hormone. Here, we describe and validate a mouse model of excess dietary fat to examine mechanisms of growth acceleration in obesity. We used in vivo multiphoton imaging and immunostaining to test the hypothesis that high-fat diet increases IGF-I activity and alters growth plate structure before the onset of obesity. We tracked bone and body growth in male and female C57BL/6 mice (n = 114) on high-fat (60% kcal fat) or control (10% kcal fat) diets from weaning (3 wk) to skeletal maturity (12 wk). Tibial and tail elongation rates increased after brief (1-2 wk) high-fat diet exposure without altering serum IGF-I. Femoral bone density and growth plate size were increased, but growth plates were disorganized in not-yet-obese high-fat diet mice. Multiphoton imaging revealed more IGF-I in the vasculature surrounding growth plates of high-fat diet mice and increased uptake when vascular levels peaked. High-fat diet growth plates had more activated IGF-I receptors and fewer inhibitory binding proteins, suggesting increased IGF-I bioavailability in growth plates. These results, which parallel pediatric growth patterns, highlight the fundamental role of diet in the earliest stages of developing obesity-related skeletal complications and validate the utility of the model for future studies aimed at determining mechanisms of diet-enhanced bone lengthening.NEW & NOTEWORTHY This paper validates a mouse model of linear growth acceleration in juvenile obesity. We demonstrate that high-fat diet induces rapid increases in bone elongation rate that precede excess weight gain and parallel pediatric growth. By imaging IGF-I delivery to growth plates in vivo, we reveal novel diet-induced changes in IGF-I uptake and activity. These results are important for understanding the sequelae of musculoskeletal complications that accompany advanced bone age and obesity in children.

Severe Obesity in Children and Adolescents: Metabolic Effects, Assessment, and Treatment

Childhood obesity has been increasing steadily in recent decades, and severe childhood obesity has emerged as a major public health problem both nationally and internationally. A current concern is that lockdown due to the coronavirus disease 2019 (COVID-19) pandemic could exacerbate the spread of childhood obesity and increase the gap in obesity risk. Recent research results indicate the aggravation of obesity after school closures. The consequences of severe childhood obesity are more devastating than those of mild to moderate obesity. Children with severe obesity are at greater risk than others for hypertension, type 2 diabetes, metabolic syndrome, non-alcoholic fatty liver disease, atherosclerosis, and adult obesity. Accurately assessing and diagnosing a child with severe obesity is the key to implementing successful therapy. A detailed and accurate patient history and physical examination are important to discriminate monogenic obesity and metabolic syndrome diagnoses from severe obesity without an underlying cause. Psychosocial factors, including eating behaviors, should be assessed to facilitate better weight management outcomes. Treatment options for severe pediatric obesity include lifestyle modification therapy, pharmacotherapy, and metabolic and bariatric surgery. However, lifestyle modification should be the priority. Although progress has been made, safe and effective treatment for severe pediatric obesity is still challenging. More efforts and innovations are needed to find a solution for the huge medical and emotional burden that these children and their families carry. Public health organizations also need to make efforts to encourage and normalize healthy eating habits and exercise to prevent severe obesity in childhood.

Management of severe pediatric obesity

Background: Pediatric obesity has increased over the decades, and in particular, severe pediatric obesity has become a serious public health problem. A concern has arisen that the COVID-19 pandemic may exacerbate the incidence of childhood obesity.Current Concepts: The consequences of severe pediatric obesity are more devastating than those of moderate obesity. Children with severe obesity are at a greater risk for hypertension, type 2 diabetes, metabolic syndrome, non-alcoholic fatty liver disease, atherosclerosis, and adult obesity. Correct assessment and diagnosis of a child with severe obesity is key to successful therapy. A thorough history and physical examination are important in identifying monogenic obesity or metabolic syndrome. Eating behaviors and psychosocial factors should be assessed to improve weight management outcomes. Treatment options for severe pediatric obesity include lifestyle modification, pharmacotherapy, and metabolic and bariatric surgery. Even though progress has been made with regard to the treatment of obesity, safe and effective treatment of severe pediatric obesity is challenging.Discussion and Conclusion: More efforts and innovations are needed to find a solution for the huge medical and emotional burden the children with severe obesity and their families are enduring.

Abnormal expression of Pappa2 gene may indirectly affect mouse hip development through the IGF signaling pathway

INTRODUCTION

Developmental dysplasia of the hip (DDH) is a major cause of disability in children, and the genetic mechanism of this disease remains unclear. In our previous study, we found that pregnancy-associated plasma protein-A2 (PAPP-A2) was associated with DDH significantly.

OBJECTIVES

The aim of this study was to investigate the insulin-like growth factor (IGF) expression and collagen synthesis as well as cartilage proliferation-related proteins in the case of abnormal expression of Pappa2 in mice to research the relationship between PAPP-A2 and the pathological changes of DDH.

METHODS

In vivo animal experiments, the mice were directly injected with 50 µl of Cas9/PAPP-A2 sgRNA lentiviruses around the hip to downregulate the Pappa2 gene expression and injected with control lentiviruses on the other side, then to observe the expression and localization of related proteins. And in an in vitro experiment, mice fibroblasts and primary chondrocytes were cultured with insulin-like growth factor binding protein-5 (IGFBP-5) protein, PAPP-A2 protein and Cas9/PAPP-A2 sgRNA lentiviruses to detect of related proteins and mRNA expression.

RESULTS

Cartilage proliferation-related proteins demonstrated a significant decrease in the PAPP-A2 knockdown hips acetabulum and femoral head cartilage, meanwhile the IGF expression was also downregulated in the soft tissue around the acetabulum compared with the control hips. Furthermore, the role PAPP-A2 played in chondrocytes and fibroblasts was the same as in the in vivo experiments, downregulation of PAPP-A2 expression or upregulation of IGFBP-5 expression can reduce collagen synthesis and cartilage proliferation.

CONCLUSIONS

PAPP-A2 may be involved in the development of the mouse hip joint by interfering the fibrous and cartilaginous metabolism via IGF pathway-associated proteins pathway.

Expression of PAPP-A2 and IGF Pathway-Related Proteins in the Hip Joint of Normal Rat and Those with Developmental Dysplasia of the Hip

Developmental dysplasia of the hip (DDH) is one of the major causes of child disability and early osteoarthritis. Genetic factors play an important role, but which still remain unclear. Pregnancy-associated plasma protein-A2 (PAPP-A2), a special hydrolase of insulin-like growth factor binding protein-5 (IGFBP-5), has been confirmed to be associated with DDH by previous studies. The aim of this study was firstly, to investigate the expression of PAPP-A2 and insulin-like growth factor (IGF) pathway-related proteins in normal rat's hip joints; secondly, to compare the variations of those proteins between DDH model rats and normal ones. The DDH model was established by swaddling the rat's hind legs in hip adduction and extension position. The hip joints were collected for expression study of fetal rats, normal newborn rats, and DDH model rats. Positive expression of PAPP-A2 and IGF pathway-related proteins was observed in all the hip joints of growing-stage rats. Ultimately, IGF1 was downregulated; insulin-like growth factor 1 receptor (IGF1R) showed an opposite trend in DDH rats when compared with normal group. The PAPP-A2 and IGF pathway-associated proteins may also be involved in the development of the rat's hip joint, which bring the foundation for further revealing the pathogenic mechanism of DDH.

Prostacyclin regulates bone growth via the Epac/Rap1 pathway

Prostaglandins, particularly PGE2, are important to adult bone and joint health, but how prostaglandins act on growth plate cartilage to affect bone growth is unclear. We show that growth plate cartilage is distinct from articular cartilage with respect to cyclooxygenase (COX)-2 mRNA expression; although articular chondrocytes express very little COX-2, COX-2 expression is high in growth plate chondrocytes and is increased by IGF-I. In bovine primary growth plate chondrocytes, ATDC5 cells, and human metatarsal explants, inhibition of COX activity with nonsteroidal antiinflammatory drugs (NSAIDs) inhibits chondrocyte proliferation and ERK activation by IGF-I. This inhibition is reversed by prostaglandin E2 and prostacyclin (PGI2) but not by prostaglandin D2 or thromboxane B2. Inhibition of COX activity in young mice by ip injections of NSAIDs causes dwarfism. In growth plate chondrocytes, inhibition of proliferation and ERK activation by NSAIDs is reversed by forskolin, 8-bromoadenosine, 3',5'-cAMP and a prostacyclin analog, iloprost. The inhibition of proliferation and ERK activation by celecoxib is also reversed by 8CPT-2Me-cAMP, an activator of Epac, implicating the small G protein Rap1 in the pathway activated by iloprost. These results imply that prostacyclin is required for proper growth plate development and bone growth.

Current understanding on the molecular basis of chondrogenesis

Endochondral bone formation involves multiple steps, consisting of the condensation of undifferentiated mesenchymal cells, proliferation and hypertrophic differentiation of chondrocytes, and then mineralization. To date, various factors including transcription factors, soluble mediators, extracellular matrices (ECMs), and cell-cell and cell-matrix interactions have been identified to regulate this sequential, complex process. Moreover, recent studies have revealed that epigenetic and microRNA-mediated mechanisms also play roles in chondrogenesis. Defects in the regulators for the development of growth plate cartilage often cause skeletal dysplasias and growth failure. In this review article, I will describe the current understanding concerning the regulatory mechanisms underlying chondrogenesis.

Current understanding on the molecular basis of chondrogenesis

Endochondral bone formation involves multiple steps, consisting of the condensation of undifferentiated mesenchymal cells, proliferation and hypertrophic differentiation of chondrocytes, and then mineralization. To date, various factors including transcription factors, soluble mediators, extracellular matrices (ECMs), and cell-cell and cell-matrix interactions have been identified to regulate this sequential, complex process. Moreover, recent studies have revealed that epigenetic and microRNA-mediated mechanisms also play roles in chondrogenesis. Defects in the regulators for the development of growth plate cartilage often cause skeletal dysplasias and growth failure. In this review article, I will describe the current understanding concerning the regulatory mechanisms underlying chondrogenesis.

Molecular cloning, bioinformatics analysis and expression of insulin-like growth factor 2 from Tianzhu white yak, Bos grunniens

The IGF family is essential for normal embryonic and postnatal development and plays important roles in the immune system, myogenesis, bone metabolism and other physiological functions, which makes the study of its structure and biological characteristics important. Tianzhu white yak (Bos grunniens) domesticated under alpine hypoxia environments, is well adapted to survive and grow against severe hypoxia and cold temperatures for extended periods. In this study, a full coding sequence of the IGF2 gene of Tianzhu white yak was amplified by reverse transcription PCR and rapid-amplification of cDNA ends (RACE) for the first time. The cDNA sequence revealed an open reading frame of 450 nucleotides, encoding a protein with 179 amino acids. Its expression in different tissues was also studied by Real time PCR. Phylogenetic tree analysis indicated that yak IGF2 was similar to Bos taurus, and 3D structure showed high similarity with the human IGF2. The putative full CDS of yak IGF2 was amplified by PCR in five tissues, and cDNA sequence analysis showed high homology to bovine IGF2. Moreover the super secondary structure prediction showed a similar 3D structure with human IGF2. Its conservation in sequence and structure has facilitated research on IGF2 and its physiological function in yak.

Regulatory mechanisms for the development of growth plate cartilage

In vertebrates, most of the skeleton is formed through endochondral ossification. Endochondral bone formation is a complex process involving the mesenchymal condensation of undifferentiated cells, the proliferation of chondrocytes and their differentiation into hypertrophic chondrocytes, and mineralization. This process is tightly regulated by various factors including transcription factors, soluble mediators, extracellular matrices, and cell-cell and cell-matrix interactions. Defects of these factors often lead to skeletal dysplasias and short stature. Moreover, there is growing evidence that epigenetic and microRNA-mediated mechanisms also play critical roles in chondrogenesis. This review provides an overview of our current understanding of the regulators for the development of growth plate cartilage and their molecular mechanisms of action. A knowledge of the regulatory mechanisms underlying the proliferation and differentiation of chondrocytes will provide insights into future therapeutic options for skeletal disorders.

Fibroblast growth factor 23 and Klotho are present in the growth plate

INTRODUCTION

Regulation of phosphate homeostasis is essential for mineralization and enchondral ossification. Fibroblast growth factor 23 (FGF23) and its obligatory co-receptor Klotho (KL) play a key role in this process by influencing both renal phosphate reabsorption and vitamin D metabolism. In disease, excessive action of FGF23 leads to hypophosphatemic rickets, while its deficiency causes tumoral calcinosis. Although osteocytes and osteoblasts are widely seen as the primary source of FGF23 under physiological conditions, the origin of systemic FGF23 remains controversial. In this study, we investigated the expression of FGF23 and KL in porcine growth plate cartilage, adjacent tissues, and parenchymal tissues.

MATERIALS AND METHODS

Tissue samples were obtained from 4- to 6-week-old piglets. mRNA expression was quantified by real-time PCR and normalized to 18S rRNA. Immunohistochemical staining was performed for FGF23, KL, collagen type X, and FGF receptor 1. Growth plate chondrocyte subpopulations were acquired by collagenase digestion of growth plate explants and subsequent density gradient centrifugation.

RESULTS

We could detect both FGF23 and KL mRNA and protein in growth plate chondrocytes. FGF23 expression was mainly found in hypertrophic and resting chondrocytes. Furthermore, significant expression of both genes was observed in bone, liver, and spleen.

CONCLUSION

These data challenge previous expression analyses, in particular theories of bone as the exclusive source of FGF23. Moreover, significant expression of FGF23 and KL within the growth plate and adjacent tissues imply a potential local role of FGF23 in chondrocyte differentiation and tissue mineralization.

Fibroblast growth factor receptor 3 effects on proliferation and telomerase activity in sheep growth plate chondrocytes

BACKGROUND

Fibroblast growth factor receptor 3 (FGFR3) inhibits growth-plate chondrocyte proliferation and limits bone elongation. Gain-of-function FGFR3 mutations cause dwarfism, reduced telomerase activity and shorter telomeres in growth plate chondroyctes suggesting that FGFR3 reduces proliferative capacity, inhibits telomerase, and enhances senescence. Thyroid hormone (T3) plays a role in cellular maturation of growth plate chondrocytes and a known target of T3 is FGFR3. The present study addressed whether reduced FGFR3 expression enhanced telomerase activity, mRNA expression of telomerase reverse transcriptase (TERT) and RNA component of telomerase (TR), and chondrocyte proliferation, and whether the stimulation of FGFR3 by T3 evoked the opposite response.

RESULTS

Sheep growth-plate proliferative zone chondrocytes were cultured and transfected with siRNA to reduce FGFR3 expression; FGFR3 siRNA reduced chondrocyte FGFR3 mRNA and protein resulting in greater proliferation and increased TERT mRNA expression and telomerase activity (p < 0.05). Chondrocytes treated with T3 significantly enhanced FGFR3 mRNA and protein expression and reduced telomerase activity (p < 0.05); TERT and TR were not significantly reduced. The action of T3 at the growth plate may be partially mediated through the FGFR3 pathway.

CONCLUSIONS

The results suggest that FGFR3 inhibits chondrocyte proliferation by down-regulating TERT expression and reducing telomerase activity indicating an important role for telomerase in sustaining chondrocyte proliferative capacity during bone elongation.

Regulation of placental calcium transport and offspring bone health

Osteoporosis causes considerable morbidity and mortality in later life, and the risk of the disease is strongly determined by peak bone mass, which is achieved in early adulthood. Poor intrauterine and early childhood growth are associated with reduced peak bone mass, and increased risk of osteoporotic fracture in older age. In this review we describe the regulatory aspects of intrauterine bone development, and then summarize the evidence relating early growth to later fracture risk. Physiological systems include vitamin D, parathyroid hormone, leptin, GH/IGF-1; finally the potential role of epigenetic processes in the underlying mechanisms will be explored. Thus factors such as maternal lifestyle, diet, body build, physical activity, and vitamin D status in pregnancy all appear to influence offspring bone mineral accrual. These data demonstrate a likely interaction between environmental factors and gene expression, a phenomenon ubiquitous in the natural world (developmental plasticity), as the potential key process. Intervention studies are now required to test the hypotheses generated by these epidemiological and physiological findings, to inform potential novel public health interventions aimed at improving childhood bone health and reducing the burden of osteoporotic fracture in future generations.

Maternal diet, behaviour and offspring skeletal health

Osteoporotic fracture has a major impact upon health, both in terms of acute and long term disability and economic cost. Peak bone mass, achieved in early adulthood, is a major determinant of osteoporosis risk in later life. Poor early growth predicts reduced bone mass, and so risk of fracture in later life. Maternal lifestyle, body build and 25(OH) vitamin D status predict offspring bone mass. Recent work has suggested epigenetic mechanisms as key to these observations. This review will explore the role of the early environment in determining later osteoporotic fracture risk.

Cartilage engineering from mesenchymal stem cells

Mesenchymal progenitor cells known as multipotent mesenchymal stromal cells or mesenchymal stem cells (MSC) have been isolated from various tissues. Since they are able to differentiate along the mesenchymal lineages of cartilage and bone, they are regarded as promising sources for the treatment of skeletal defects. Tissue regeneration in the adult organism and in vitro engineering of tissues is hypothesized to follow the principles of embryogenesis. The embryonic development of the skeleton has been studied extensively with respect to the regulatory mechanisms governing morphogenesis, differentiation, and tissue formation. Various concepts have been designed for engineering tissues in vitro based on these developmental principles, most of them involving regulatory molecules such as growth factors or cytokines known to be the key regulators in developmental processes. Growth factors most commonly used for in vitro cultivation of cartilage tissue belong to the fibroblast growth factor (FGF) family, the transforming growth factor-beta (TGF-β) super-family, and the insulin-like growth factor (IGF) family. In this chapter, in vivo actions of members of these growth factors described in the literature are compared with in vitro concepts of cartilage engineering making use of these growth factors.

Missense mutations in IHH impair Indian Hedgehog signaling in C3H10T1/2 cells: Implications for brachydactyly type A1, and new targets for Hedgehog signaling

Heterozygous missense mutations in IHH result in Brachydactyly type A1 (BDA1; OMIM 112500), a condition characterized by the shortening of digits due to hypoplasia/aplasia of the middle phalanx. Indian Hedgehog signaling regulates the proliferation and differentiation of chondrocytes and is essential for endochondral bone formation. Analyses of activated IHH signaling in C3H10T1/2 cells showed that three BDA1-associated mutations (p.E95K, p.D100E and p.E131K) severely impaired the induction of targets such as Ptch1 and Gli1. However, this was not a complete loss of function, suggesting that these mutations may affect the interaction with the receptor PTCH1 or its partners, with an impact on the induction potency. From comparative microarray expression analyses and quantitative real-time PCR, we identified three additional targets, Sostdc1, Penk1 and Igfbp5, which were also severely affected. Penk1 and Igfbp5 were confirmed to be regulated by GLI1, while the induction of Sostdc1 by IHH is independent of GLI1. SOSTDC1 is a BMP antagonist, and altered BMP signaling is known to affect digit formation. The role of Penk1 and Igfbp5 in skeletogenesis is not known. However, we have shown that both Penk1 and Igfbp5 are expressed in the interzone region of the developing joint of mouse digits, providing another link for a role for IHH signaling in the formation of the distal digits.

Gli2 and p53 cooperate to regulate IGFBP-3- mediated chondrocyte apoptosis in the progression from benign to malignant cartilage tumors

Clinical evidence suggests that benign cartilage lesions can progress to malignant chondrosarcoma, but the molecular events in this progression are unknown. Mice that develop benign cartilage lesions due to overexpression of Gli2 in chondrocytes developed lesions similar to chondrosarcomas when they were also deficient in p53. Gli2 overexpression and p53 deficiency had opposing effects on chondrocyte differentiation, but had additive effects negatively regulating apoptosis. Regulation of Igfbp3 expression and insulin-like growth factor (IGF) signaling by Gli and p53 integrated their effect on apoptosis. Treatment of human chondrosarcomas or fetal mouse limb explants with IGFBP3 or by blocking IGF increased the apoptosis rate, and mice expressing Gli2 developed substantially fewer tumors when they were also deficient for Igf2. IGF signaling-meditated apoptosis regulates the progression to malignant chondrosarcoma.

Vitamin D and growth hormone regulate growth hormone/insulin-like growth factor (GH-IGF) axis gene expression in human fetal epiphyseal chondrocytes

OBJECTIVE

Cell proliferation and gene expression regulation were studied in human fetal epiphyseal chondrocytes to ascertain the involvement of GH-IGF axis components in human fetal growth regulation by 1,25-dihydroxyvitamin D(3) (VitD) and growth hormone (GH).

DESIGN

Chondrocytes from primary cultures were plated in serum-free medium for 48 h and incubated for a further 48 h with VitD (10(-11) to 10(-6)M) and/or IGF-I (100 ng/ml) and/or GH (500 ng/ml). We analyzed (3)H-thymidine incorporation into DNA and IGF-I, IGFBP-3, GHR, SOX9, COL2A1, aggrecan and COMP gene expression by real-time quantitative PCR.

RESULTS

VitD dose-dependently and significantly inhibited (3)H-thymidine incorporation whereas GH had no effect on proliferation and, when combined with VitD, the same inhibition was observed as with VitD alone. IGF-I (100 ng/ml) significantly stimulated proliferation and opposed inhibition by VitD. VitD dose-dependently stimulated IGF-I (11.1+/-19.8 at VitD10(-6)M), IGFBP-3 (2.6+/-0.9), GHR (3.8+/-2.8) and COMP (1.5+/-0.6) expression whereas it inhibited SOX9 (0.7+/-0.2), COL2A1 (0.6+/-0.3) and aggrecan (0.6+/-0.2) expression and had no significant effect on IGF-II. IGF-I stimulated IGF-I, IGFBP-3, SOX9, COL2A1 and aggrecan expression and opposed COL2A1 and aggrecan gene expression inhibition by VitD. GH alone had no effect on gene expression whereas, in the presence of VitD, significantly-increased IGF-I expression stimulation was observed above values obtained with VitD alone (17.5+/-7.4).

CONCLUSIONS

Our results suggest that VitD regulation of fetal growth cartilage could have consisted of parallel enhancing of cell differentiation and conditioning to a phenotype more sensitive to regulation by other hormones such as GH as shown by increased GHR and IGF-I expression, but not by IGF-II expression which was not regulated.

IGF-I and not IGF-II expression is regulated by glucocorticoids in human fetal epiphyseal chondrocytes

OBJECTIVE

To elucidate the involvement of IGF axis components and the potential effects of glucocorticoids (GCs) in human fetal growth regulation.

DESIGN

We studied the regulation by dexamethasone (Dx) and IGF-I of proliferation and IGF axis components and matrix protein gene expression in human fetal epiphyseal chondrocytes.

RESULTS

High Dx concentration (10(-7)-10(-6)M) inhibited (3)H-thymidine incorporation, mifepristone (MF) 10(-6)M limited inhibition by Dx, and IGF-I (100 ng/ml) significantly stimulated proliferation and completely opposed inhibition by Dx. Dx dose-dependently (10(-9)-10(-6)M) inhibited IGF-I, IGFBP3 and SOX9 gene expression and expression of GHR, COL2A1 and aggrecan from 10(-7)M to 10(-6)M whereas it stimulated IGF-IR expression. By contrast, Dx had no significant effect on IGF-II expression. IGF-I stimulated IGF-I, IGFBP3, SOX9, COL2A1 and aggrecan expression whereas it inhibited IGF-IR expression. IGF-I could oppose COL2A1 and aggrecan gene expression inhibition by Dx.

CONCLUSIONS

We demonstrated for the first time by real-time quantitative PCR that human fetal epiphyseal chondrocytes expressed IGF axis components, such as IGF-I, IGF-II, IGFBP3, IGF-IR and GHR and SOX9, COL2A1 and aggrecan, and that their expression was regulated by Dx and IGF-I. Among IGFs, IGF-I and not IGF-II expression was demonstrated to be down-regulated by GCs whereas IGF-I expression was up-regulated by itself.

Insulin-like growth factor-binding protein-5 inhibits osteoblast differentiation and skeletal growth by blocking insulin-like growth factor actions

Signaling through the IGF-I receptor by locally synthesized IGF-I or IGF-II is critical for normal skeletal development and for bone remodeling and repair throughout the lifespan. In most tissues, IGF actions are modulated by IGF-binding proteins (IGFBPs). IGFBP-5 is the most abundant IGFBP in bone, and previous studies have suggested that it may either enhance or inhibit osteoblast differentiation in culture and may facilitate or block bone growth in vivo. To resolve these contradictory observations and discern the mechanisms of action of IGFBP-5 in bone, we studied its effects in differentiating osteoblasts and in primary bone cultures. Purified wild-type (WT) mouse IGFBP-5 or a recombinant adenovirus expressing IGFBP-5WT each prevented osteogenic differentiation induced by the cytokine bone morphogenetic protein (BMP)-2 at its earliest stages without interfering with BMP-mediated signaling, whereas an analog with reduced IGF binding (N domain mutant) was ineffective. When added at later phases of bone cell maturation, IGFBP-5WT but not IGFBP-5N blocked mineralization, prevented longitudinal growth of mouse metatarsal bones in short-term primary culture, and inhibited their endochondral ossification. Because an IGF-I variant (R3IGF-I) with diminished affinity for IGFBPs promoted full osteogenic differentiation in the presence of IGFBP-5WT, our results show that IGFBP-5 interferes with IGF action in osteoblasts and provides a framework for discerning mechanisms of collaboration between signal transduction pathways activated by BMPs and IGFs in bone.

Insulin-like growth factor-I and fibroblast growth factor, but not growth hormone, affect growth plate chondrocyte proliferation

Of the many factors that regulate linear growth, IGF-I has a central role in epiphyseal chondrocyte development. Whether IGF-I is solely of systemic or also of local origin is uncertain, as is how other growth factors interact with IGF-I at the growth plate. We studied the proliferative effects of IGF-I on juvenile bovine epiphyseal chondrocytes fractionated by density gradient centrifugation. Cell density correlated with size, glycogen content, and gene expression patterns. There was a gradient of response to IGF-I, with the greatest proliferative response in high-density cells corresponding to the reserve zone, as measured by [3H]thymidine uptake. Low-density (hypertrophic zone) cells proliferated only when exposed to IGF-I and basic fibroblast growth factor (FGF). The gradient of IGF-I response correlated with [125I]IGF-I binding as determined by Scatchard analysis: IGF-I receptor number was 10-fold greater in reserve zone cells than in hypertrophic cells. When exposed to basic FGF for 24 hours, IGF-I binding in hypertrophic cells increased 3-fold. In contrast, no specific binding of GH was demonstrated in juvenile bovine chondrocytes. GH produced neither signal transducer and activator of transcription phosphorylation, increased proliferation, nor increased IGF-I mRNA levels in any chondrocyte fraction. IGF-I mRNA levels were extremely low at 800-1100 copies/microg 18S RNA in bovine chondrocytes. These results suggest that the major regulator of chondrocyte proliferation is systemic IGF-I; FGFs may influence the actions of IGF-I at the growth plate by altering its receptor number in chondrocytes.

Age- and site-specific decline in insulin-like growth factor-I receptor expression is correlated with differential growth plate activity in the mouse hindlimb

The proximal and distal growth plates of the principal long bones do not contribute equally to longitudinal growth. Most forelimb elongation occurs at the shoulder and wrist, while most hindlimb growth occurs at the knee. This study examined whether insulin-like growth factor-I (IGF-I), a potent growth regulator, could underlie this variation via differential receptor expression. The spatiotemporal distribution of the IGF-I receptor (IGF-IR) was mapped in hindlimb growth plates (overall and within regional zones) from immature mice using immunohistochemistry. Growth activity was assessed by size/morphology of the growth plate and proliferating cell nuclear antigen (PCNA) expression. Both IGF-IR and PCNA staining declined considerably with age in the proximal femur and distal tibia (hip and ankle), but expression remained high in the more active distal femur and proximal tibia (knee) throughout growth. Growth plate size decreased with age in all sites, but the absolute and relative decline in IGF-IR in the hips and ankles of older mice indicated a site-specific loss of IGF-I sensitivity in these less active regions. These results suggest that regulation of the IGF-IR may at least partially mediate differential long bone growth, thereby providing a local mechanism for altering skeletal proportions absent modification of systemic hormone levels.

Insulin-like growth factor binding protein-5 in osteogenesis: facilitator or inhibitor?

The insulin-like growth factors (IGFs) play a central role in controlling somatic growth in mammals and exert anabolic effects on most tissues, including bone. IGF action is mediated by the IGF-I receptor and additionally is regulated by six high-affinity IGF binding proteins (IGFBP-1 through IGFBP-6), of which IGFBP-4 and IGFBP-5 are most abundant in bone. The focus of this brief review is on the role of IGFBP-5 in bone biology. IGFBP-5 has been implicated as a pro-osteogenic factor in several studies but conversely has been shown to act as an inhibitor of bone formation, primarily by interfering with IGF actions on osteoblasts. These potentially contradictory effects of IGFBP-5 in bone are further complicated by observations indicating that IGFBP-5 additionally may function in an IGF-independent way, and may have been accentuated by differences in both experimental design and methodology among published studies. Suggestions are made for a more systematic approach to help discern the true roles of IGFBP-5 in bone physiology.

Effects of insulin-like growth factor binding proteins in bone -- a matter of cell and site

The actions of the insulin-like growth factor (IGF)-system are controlled by six IGF-binding proteins (IGFBPs). The IGFBPs are thought to affect local effects of IGF-I and IGF-II due to higher affinity if compared to IGF-I receptors and due to cell-type specific IGFBP expression patterns. It was found in IGFBP knockout models that the IGFBP family is functionally redundant. Thus, functional analysis of potential effects of IGFBPs is dependent on descriptive studies and models of IGFBP overexposure in vitro and in vivo. In the literature, the role of the IGFBPs for bone growth is highly controversial and, to date, no systematic look has been taken at IGFBPs resolving functional aspects of IGFBPs at levels of cell types and specific locations within bones. Since IGFBPs are thought to represent local modulators of the IGF actions and also exert IGF-independent effects, this approach is particularly reasonable on a physiological level. By sorting the huge number of in part controversial results on IGFBP effects in bone present in the literature for distinct cell types and bone sites it is possible to generate a focused, more specific and a less controversial picture of IGFBP functions in bone.

Connective Tissue Growth Factor and Insulin-Like Growth Factor 2 Show Upregulation in Early Growth Plate Radiorecovery Response following Irradiation

INTRODUCTION

The growth plate response following radiotherapy is poorly understood. In particular, little is known about the changes in growth plate growth factors and cytokines following irradiation. The hypothesis was that a limited number of growth factors and cytokines play a role in growth plate proliferative and hypertrophic chondrocyte radio-recovery.

METHODS

The right limbs of 6 rats were irradiated (17.5 Gy), leaving the left limbs as controls. Limbs were harvested 1 (n = 3) and 2 (n = 3) weeks later. Microarrays were constructed from chondrocytes obtained by laser microdissection from the proliferative zone (PZ) and the hypertrophic zone (HZ) of normal and irradiated tibia growth plates. Real-time PCR was used to confirm the expression of parathyroid hormone receptor 1 (Pthr1), connective tissue growth factor (CTGF), insulin-like growth factor I receptor (IGF1R), insulin-like growth factor II (IGF2), interleukin 17beta (IL17b) and chemokine ligand 12 (CXCL12).

RESULTS AND CONCLUSIONS

IGF2 is upregulated in the PZ and CTGF is upregulated in both the PZ and HZ 1 week after irradiation, prior to the histomorphometric appearance of growth plate recovery in this immature animal radiation model, supporting their role in stimulating early return of the growth plate. By 2 weeks after irradiation, a number of growth factors and cytokines, including CTGF and Pthr1 in both zones, CXCL12 and its receptor in the PZ, and IL17b and bone morphogenetic protein 2 in the HZ, show upregulation, suggesting a possible later role in radiorecovery. The effects of irradiation on Pthr1, CTGF, IGF2 and CXCL12 in PZ and Pthr1, CTGF, IL17b and IGF1R in the HZ determined by microarray and real-time RT-PCR was highly correlated (r = 0.797, p < 0.05 in the PZ and r = 0.875, p < 0.01 in the HZ, respectively).

Postnatal growth and bone mass in mice with IGF-I haploinsufficiency

We examined the influence of IGF-I haploinsufficiency on growth, bone mass and osteoblast differentiation in Igf1 heterozygous knockout (HET) mice. Cohorts of male and female wild type (WT) and HET mice in the outbred CD-1 background were analyzed at 1, 2, 4, 8, 12, 15 and 18 months of age for body weight, serum IGF-I and bone morphometry. Compared to WT mice, HET mice had 20-30% lower serum IGF-I levels in both genders and in all age groups. Female HET mice showed significant reductions in body weight (10-20%), femur length (4-6%) and femoral bone mineral density (BMD) (7-12%) before 15 months of age. Male HET mice showed significant differences in all parameters at 2 months and thereafter. At 8 and 12 months, WT mice also showed a significant gender effect: despite their lower body weight, female mice had higher femoral BMD and femur length compared to males. Microcomputed tomography showed a significant reduction in cortical bone area (7-20%) and periosteal circumference (5-13%) with no consistent pattern of change in trabecular bone measurements in 2- and 8-month old HET mice in both genders. HET primary osteoblast cultures showed a 40% reduction in IGF-I protein expression and a 50% decrease in IGF-I mRNA expression. Cell growth and proliferation were decreased in HET cultures. Thus, IGF-I haploinsufficiency in outbred male and female mice resulted in reduced body weight, femur length and areal BMD at most ages. Serum IGF-I levels showed a high level of positive correlation with body weight and skeletal morphometry. These studies show that IGF-I is a determinant of bone size and mass in postnatal life. We speculate that impaired osteoblast proliferation may contribute to the skeletal phenotype of mice with IGF-I haploinsufficiency.

Elevated IGFBP-1 cause high bone turnover in growth-restricted monochorionic twins with discordant birth weight

OBJECTIVE

To test the hypothesis that low birth weight twins have a higher risk of osteoportotic fracture in later life, we investigated the association between fetal IGF axis and type-1 collagen markers of bone turnover in monochorionic (MC) twins with or without discordant birth weight of >or=20%.

METHODS

Maternal and cord bloods were collected from gestational age matched MC twins of discordant (n = 16) and concordant birth weights (n = 16). The samples were assayed for cross linked carboxyl terminal telopeptide (ICTP, a marker of bone resorption) and pro-peptide (PICP, a marker of bone formation) of type I collagen, IGF-1, and IGFBP-1 by radio-immunoassay.

RESULTS

The growth-restricted twins (IUGR) of discordant group had higher fetal IGFBP-1 and ICTP (P < 0.001) levels, while PICP (P < 0.001) was lower than the co-twins with normal weight (AGA). In contrast, cord blood levels of IGF-1, IGFBP-1, ICTP, and PICP in concordant twin pairs were comparable to AGA twins. The concordant and AGA twins had a positive correlation between ICTP and PICP levels (y = 23x - 711; r = 0.84; P < 0.001; n = 48) but no such association was found in IUGR twins. Instead, IGFBP-1 levels in IUGR twins had a negative association with PICP (r = 0.81; P < 0.001; n = 16) and a positive correlation with ICTP (r- = 0.51; P < 0.05; n = 16). No such association was found in concordant and AGA twins.

CONCLUSION

These data suggest that growth-restricted twins had high bone turnover, due to elevated IGFBP-1. This association seems to be independent of maternal and genetic factors.

Where tendons and ligaments meet bone: attachment sites ('entheses') in relation to exercise and/or mechanical load

Entheses (insertion sites, osteotendinous junctions, osteoligamentous junctions) are sites of stress concentration at the region where tendons and ligaments attach to bone. Consequently, they are commonly subject to overuse injuries (enthesopathies) that are well documented in a number of sports. In this review, we focus on the structure-function correlations of entheses on both the hard and the soft tissue sides of the junction. Particular attention is paid to mechanical factors that influence form and function and thus to exploring the relationship between entheses and exercise. The molecular parameters indicative of adaptation to mechanical stress are evaluated, and the basis on which entheses are classified is explained. The application of the 'enthesis organ' concept (a collection of tissues adjacent to the enthesis itself, which jointly serve the common function of stress dissipation) to understanding enthesopathies is considered and novel roles of adipose tissue at entheses are reviewed. A distinction is made between different locations of fat at entheses, and possible functions include space-filling and proprioception. The basic anchorage role of entheses is considered in detail and comparisons are explored between entheses and other biological 'anchorage' sites. The ability of entheses for self-repair is emphasized and a range of enthesopathies common in sport are reviewed (e.g. tennis elbow, golfer's elbow, jumper's knee, plantar fasciitis and Achilles insertional tendinopathies). Attention is drawn to the degenerative, rather than inflammatory, nature of most enthesopathies in sport. The biomechanical factors contributing to the development of enthesopathies are reviewed and the importance of considering the muscle-tendon-bone unit as a whole is recognized. Bony spur formation is assessed in relation to other changes at entheses which parallel those in osteoarthritic synovial joints.

Differential expression of IGF system components in proliferating vs. differentiating growth plate chondrocytes: the functional role of IGFBP-5

The growth plate is an important target tissue for insulin-like growth factors (IGFs), but little is known about the regulation of the IGF system during the developmental sequence of chondrocytes. We therefore examined the expression profile of IGF system components in proliferating vs. differentiating growth plate chondrocytes by use of two cell culture models of the growth cartilage. In rat growth plate chondrocytes in primary culture, IGF-I expression increased twofold during the process of differentiation. IGF-binding protein-3 (IGFBP-3) expression showed a biphasic pattern of with a twofold increase at the onset of differentiation and a downregulation in late differentiating chondrocytes to 25% of baseline levels; the expression patterns of IGFBP-2, -4 and -6 were not dependent on the developmental stage. In IGF- and IGFBP-3-deficient RCJ3.1C5.18 (RCJ) mesenchymal chondrogenic cells, IGFBP-2 and -6 synthesis declined by 50% during differentiation. IGFBP-5 expression was markedly upregulated during the process of differentiation in both cell culture models. Although IGFBP-5 overexpression did not have an IGF-independent effect on RCJ cell differentiation, it promoted IGF-I-enhanced differentiation of these cells. A potential mechanism for this effect is the specific increase of Akt phosphorylation in IGFBP-5-overexpressing cells in the presence of IGF-I, indicating an increased activity of the phosphatidylinositol (PI) 3-kinase pathway. These data suggest that the developmental stage of the chondrocyte is an important determinant of IGF and IGFBP expression and imply a functional role for IGFBP-5 for upregulating IGF action during chondrocyte differentiation in vivo.

Growth factor regulation of human growth plate chondrocyte proliferation in vitro

Linear growth occurs as the result of growth plate chondrocytes undergoing proliferative and hypertrophic phases. Paracrine feedback loops that regulate the entry of chondrocytes into the hypertrophic phase have been shown and similar pathways likely exist for the proliferative phase. Human long-bone growth plate chondrocytes were cultured in vitro. The proliferative effects of a variety of factors were determined by [3H]thymidine uptake and the gene expression profile of these cells was determined by DNA microarray analysis. Serum, insulin-like growth factor (IGF)-I and -II, transforming growth factor-beta (TGF-beta, fibroblast growth factor (FGF)-1, -2, and -18, and platelet-derived growth factor (PDGF)-BB were potent stimulators of proliferation. FGF-10, testosterone, and bone morphogenetic proteins (BMP)-2, -4, and -6 inhibited proliferation. Microarray analysis showed that the genes for multiple members of the IGF-I, TGF-beta, FGF, and BMP pathways were expressed, suggesting the presence of autocrine/paracrine pathways that regulate the proliferative phase of growth plate-mediated growth.

Insulin-like growth factor-I augments chondrocyte hypertrophy and reverses glucocorticoid-mediated growth retardation in fetal mice metatarsal cultures

The study aims were to improve our understanding of the mechanisms of glucocorticoid-induced growth retardation at the growth plate and determine whether IGF-I could ameliorate the effects. Fetal mouse metatarsals were cultured for up to 10 d with dexamethasone (Dex; 10(-6) m) and/or IGF-I and GH (both at 100 ng/ml). Both continuous and alternate-day Dex treatment inhibited bone growth to a similar degree, whereas IGF-I alone or together with Dex caused an increase in bone growth. GH had no effects. These observations may be explained at the cellular level; cell proliferation within the growing bone was decreased by Dex and increased by IGF-I and these effects were more marked in the cells of the perichondrium than those in the growth plate. However, the most prominent observation was noted in the hypertrophic zone where all treatments containing IGF-I significantly increased (3-fold) the length of this zone, whereas Dex alone had no significant effect. In conclusion, Dex impaired longitudinal growth by inhibiting chondrocyte proliferation, whereas IGF-I stimulated chondrocyte hypertrophy and reversed the growth-inhibitory Dex effects. However, the IGF-I-mediated improvement in growth was at the expense of altering the balance between proliferating and hypertrophic chondrocytes within the metatarsal.

Umbilical venous IGF-1 concentration, neonatal bone mass, and body composition

IGF-1 is a key growth factor during fetal life. Using DXA, we found that the concentration of IGF-1 in umbilical cord serum is strongly related to neonatal whole body bone mineral content, lean mass, and fat mass. However IGF-1 did not explain the relationships of maternal smoking, fat mass, and physical activity with neonatal bone mass. The study supports a direct role for circulating IGF-1 in growth of the fetal skeleton.

INTRODUCTION

Evidence is accumulating that the risk of osteoporosis in later life may be determined in part by environmental influences during intrauterine and early postnatal life. We previously reported that maternal birthweight, smoking, fat stores, and physical activity during pregnancy predict neonatal bone mass. While the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis is an important determinant of postnatal skeletal growth, there are few data relating the concentration of growth factors in umbilical cord blood to bone mineral content (BMC) and other indices of body composition in the newborn infant.

MATERIALS AND METHODS

We conducted a population-based study in a cohort of full-term, newborn infants whose mothers were characterized for lifestyle, body composition, and nutrition through their normal pregnancies. In a sample of 119 infants from the cohort, we related cord serum IGF-1 and insulin-like growth factor binding protein (IGFBP)-3 concentrations to neonatal body composition measured by DXA and evaluated the extent to which this cytokine mediates the previously reported effects of maternal diet and lifestyle on neonatal bone mass.

RESULTS

There were strong positive associations between cord serum IGF-1 concentration and whole body BMC (r = 0.38, p < 0.001), whole body lean mass (r = 0.40, p < 0.001), and whole body fat mass (r = 0.50, p < 0.001) after adjusting for gestational age and sex. There was no association between cord serum IGF-1 and BMC adjusted for bone size. Neither cord serum IGF-1 nor IGFBP-3 explained the relationships that we previously reported between maternal influences and neonatal bone mass.

CONCLUSIONS

Cord serum IGF-1 is more closely related to the size of the neonatal skeleton than to its degree of mineralization. Documented maternal determinants of neonatal bone mass seem to mediate their effects independently of variations in cord serum IGF-1 in healthy pregnancies.

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.

Regulation by glucocorticoids of cell differentiation and insulin-like growth factor binding protein production in cultured fetal rat nasal chondrocytes

Glucocorticoids (GCs) modulate insulin-like growth factor action in cartilage through mechanisms that are complex and insufficiently defined, especially in the context of cranio-facial growth. Because the family of IGF-binding proteins (IGFBP-1 to -6) is important in the regulation of IGF availability and bioactivity, we examined the effect of GCs on chondrocyte differentiation in correlation with IGFBP production in cultured fetal rat chondrocytes isolated from nasal septum cartilage of fetal rat. Dexamethasone (DEX) effects were tested before and at the onset of extracellular matrix maturation. DEX induced a dose-dependent increase in the size of cartilage nodule formed, (45)Ca incorporation into extracellular matrix, alkaline phosphatase activity, and sulfatation of glycosaminoglycans, maximal effects being obtained with a 10-mM DEX concentration. The IGFBPs produced by cultured chondrocytes were characterized in culture medium which had been conditioned for 24 h under serum-free conditions by these cells. Western ligand blotting with a mixture of [(125)I]IGF-I and -II revealed bands of 20, 24, 29, a 31-32 kDa doublet and a 39-41 kDa triplet which were differently regulated by DEX. Immunoblotting showed that following DEX exposure, IGFBP-3 and -6 were up-regulated whereas IGFBP-2, -5, and the 24 kDa band were down-regulated. The effect of DEX on both differentiation and IGFBP production showed a same dependence, and developed when extracellular matrix maturation had been just induced. The results obtained in this chondrocyte culture system show that production of IGFBPs is modulated by DEX at physiological concentrations thus regulating IGF availability and action, a control which could promote the primordial role of the rat nasal septum in craniofacial growth.

Distribution of insulin-like growth factor-I mRNA in the mandibular condyle and rib cartilage of the rat during growth

This study makes a molecular biological comparison of primary and secondary cartilage at an early phase of postnatal development. The distribution of insulin-like growth factor-I (IGF-I) mRNA expression in the mandibular condyle and rib cartilage of 1-28-day-old rats was examined after in situ hybridisation using an oligo probe cocktail for IGF-I mRNA. In the condyle, expression was localised to a narrow strip under the articular layer where the cells are undifferentiated. Essentially, no differences were found in IGF-I synthesis within three samples from the same age group or between different age groups. In rib cartilage, IGF-I mRNA was localised within the germinative, proliferative and early hypertrophic cell layers in 1-28-day-old rats. Again, there were no differences in expression among animals of the same age or as a function of age. This pattern of IGF-I mRNA expression indicates that IGF-I synthesis during growth of the mandibular condylar cartilage is different from that of costal cartilage. The findings shed light on the problem of overgrowth often associated with the use of costochondral grafts to replace defective mandibular condyles.

Interactions between GH, IGF-I, glucocorticoids, and thyroid hormones during skeletal growth

Linear growth occurs during development and the childhood years until epiphyseal fusion occurs. This process results from endochondral ossification in the growth plates of long bones and is regulated by systemic hormones and paracrine or autocrine factors. The major regulators of developmental and childhood growth are GH, IGF-I, glucocorticoids, and thyroid hormone. Sex steroids are responsible for the pubertal growth spurt and epiphyseal fusion. This review will consider interactions between GH, IGF-I, glucocorticoids, and thyroid hormone during linear growth. It is well known from physiologic and clinical studies that these hormones interact at the level of the hypothalamus and pituitary. Interacting effects on peripheral tissues such as liver are also well understood, but we concentrate here on the epiphyseal growth plate as an important and newly appreciated target organ for convergent hormone action.

Real-time RT-PCR quantification of insulin-like growth factor (IGF)-1, IGF-1 receptor, IGF-2, IGF-2 receptor, insulin receptor, growth hormone receptor, IGF-binding proteins 1, 2 and 3 in the bovine species

Reverse transcription (RT) followed by polymerase chain reaction (PCR) is the technique of choice for analysing mRNA in extremely low abundance. Real-time RT-PCR using SYBR Green I detection combines the ease and necessary exactness to be able to produce reliable as well as rapid results. To obtain highly accurate and reliable results in a real-time RT-PCR a highly defined calibration curve is needed. We designed and developed nine different calibration curves, based on recombinant DNA plasmid standards and established them on a constant real-time PCR platform for the following factors: growth hormone receptor (GHR), insulin-like growth factor (IGF)-1, IGF-1 receptor (IGF-1R), IGF-2, IGF-2 receptor (IGF-2R), insulin receptor (INSR), and IGF-binding proteins (IGF-BP) 1, 2 and 3. Developed assays were applied in the LightCycler system on bovine ileum and liver total RNA and showed high specificity and sensitivity of quantification. All assays had a detection limit of under 35 recombinant DNA molecules present in the capillary. The SYBR Green I determination resulted in a reliable and accurate quantification with high test linearity (Pearson correlation coefficient r > 0.99) over seven orders of magnitude from <10(2) to >10(8) recombinant DNA start molecules and an assay variation of maximal 5.3%. Applicability of the method was shown by analysing mRNA levels in newborn calves: mRNA concentrations per gram tissue of mRNAs of IGF-1, IGF-1R, IGF-2, IGF-2R, GHR, INSR, and IGF-BP1, 2 and 3 were all different between in liver and ileum and the traits all exhibited individual differences.

Recombinant species-specific growth hormone increases hard callus formation in distraction osteogenesis

The effect of growth hormone (GH) on secondary fracture healing and callus formation has been demonstrated in several previously investigated animal models. The aim of this study was to investigate and quantify the effects of GH on bone regenerates in a distraction osteogenesis model. In 20 mature female Yucatan micropigs, the tibia and fibula were osteotomized, stabilized with an external fixator, and distracted at 2 mm/day for 10 days after a 4 day latency period. The regenerates were allowed to consolidate for 10 days. Micropigs in the study group (ten animals) received a daily injection of 100 microg per kilogram body weight of recombinant porcine growth hormone (r-pGH). Micropigs in the control group (ten animals) received sodium chloride as placebo. After killing on day 25, a quantitative histomorphometrical analysis of the formed callus and the adjacent cortical bone was performed and the results of polychrome in vivo labeling were assessed. The regenerates of the r-pGH-treated animals showed a significantly larger callus area but no change in callus structure. We found islands of cartilage tissue in the regenerates of both groups; the calli from the control group exhibited a higher fraction of cartilage compared with the r-pGH group, but this was not significant. Quantification of the fluorescent in vivo labeling revealed that the distraction gap in GH-treated group showed significant ossification even during distraction. These results demonstrate that growth hormone can accelerate the maturation of the regenerate in distraction osteogenesis without changing the callus microstructure. This may prove to be a useful clinical tool for shortening the healing time in limb lengthening and bone segment transport.