From mouse to man: redefining the role of insulin-like growth factor-I in the acquisition of bone mass

Exposure to BPA and BPS during pregnancy disrupts the bone mineralization in the offspring

Exposure to plastic-derived estrogen-mimicking endocrine-disrupting bisphenols can have a long-lasting effect on bone health. However, gestational exposure to bisphenol A (BPA) and its analogue, bisphenol S (BPS), on offspring's bone mineralization is unclear. The effects of in-utero bisphenol exposure were examined on the offspring's bone parameters. BPA and BPS (0.0, 0.4 μg/kg bw) were administered to pregnant Wistar rats via oral gavage from gestational day 4-21. Maternal exposure to BPA and BPS increased bone mineral content and density in the offspring aged 30 and 90 days (P < 0.05). Plasma analysis revealed that alkaline phosphatase, and Gla-type osteocalcin were significantly elevated in the BPS-exposed offspring (P < 0.05). The expression of BMP1, BMP4, and their signaling mediators SMAD1 mRNAs were decreased in BPS-exposed osteoblast SaOS-2 cells (P < 0.05). The expression of extracellular matrix proteins such as ALPL, COL1A1, DMP1, and FN1 were downregulated (P < 0.05). Bisphenol co-incubation with noggin decreased TGF-β1 expression, indicating its involvement in bone mineralization. Altered mineralization could be due to dysregulated expression of bone morphogenetic proteins and signalling mediators in the osteoblast cells. Thus, bisphenol exposure during gestation altered growth and bone mineralization in the offspring, possibly by modulating the expression of Smad-dependent BMP/TGF-β1 signalling mediators.

The role of insulin-like growth factor-1 in bone remodeling: A review

Insulin-like growth factor (IGF)-1 is a polypeptide hormone with vital biological functions in bone cells. The abnormal expression of IGF-1 has a serious effect on bone growth, particularly bone remodeling. Evidence from animal models and human disease suggested that both IGF-1 deficiency and excess cause changes in bone remodeling equilibrium, resulting in profound alterations in bone mass and development. Here, we first introduced the functions and mechanisms of the members of IGFs in bone. Subsequently, the critical role of IGF-1 in the process of bone remodeling were emphasized from the aspects of bone resorption and bone formation respectively. This review explains the mechanism of IGF-1 in maintaining bone mass and bone homeostasis to a certain extent and provides a theoretical basis for further research.

Structural and Metabolic Changes in Bone

Simple Summary

Bone is an extremely metabolically active tissue that is regenerated and repaired over its lifetime by bone remodeling. Most bone diseases are caused by abnormal restructure processes that undermine bone structure and mechanical strength and trigger clinical symptoms, such as pain, deformity, fracture, and abnormalities of calcium and phosphate homoeostasis. The article examines the main aspects of bone development, anatomy, structure, and the mechanisms of cell and molecular regulation of bone remodeling.

Abstract

As an essential component of the skeleton, bone tissue provides solid support for the body and protects vital organs. Bone tissue is a reservoir of calcium, phosphate, and other ions that can be released or stored in a controlled manner to provide constant concentration in body fluids. Normally, bone development or osteogenesis occurs through two ossification processes (intra-articular and intra-chondral), but the first produces woven bone, which is quickly replaced by stronger lamellar bone. Contrary to commonly held misconceptions, bone is a relatively dynamic organ that undergoes significant turnover compared to other organs in the body. Bone metabolism is a dynamic process that involves simultaneous bone formation and resorption, controlled by numerous factors. Bone metabolism comprises the key actions. Skeletal mass, structure, and quality are accrued and maintained throughout life, and the anabolic and catabolic actions are mostly balanced due to the tight regulation of the activity of osteoblasts and osteoclasts. This activity is also provided by circulating hormones and cytokines. Bone tissue remodeling processes are regulated by various biologically active substances secreted by bone tissue cells, namely RANK, RANKL, MMP-1, MMP-9, or type 1 collagen. Bone-derived factors (BDF) influence bone function and metabolism, and pathophysiological conditions lead to bone dysfunction. This work aims to analyze and evaluate the current literature on various local and systemic factors or immune system interactions that can affect bone metabolism and its impairments.

Bone mass in newborns and its predictors

OBJECTIVE

Optimal bone mass (a function of foetal programming and adequate intrauterine bone mineral accrual) is essential for prevention of osteoporosis. The present study was planned with the objectives to describe newborn bone mass (NBBM) and study the associated factors.

DESIGN

Observational study Patients: Singleton pregnant women ≤16 weeks gestation.

MEASUREMENTS

Maternal factors and antenatal events: Dietary assessment (3 days-24-h diet recalls at ≤16 and 32-34 weeks), fetal femoral volume (FFV) assessment at 19 and 34 weeks, serum 25 hydroxyvitamin D (S.25OHD) and placental weight. Newborn anthropometric parameters, cord S.25OHD & IGF-1 level and NBBM by DXA (whole-body bone mineral content (BMC), bone mineral density (BMD) and bone area).

RESULTS

Total 224 subjects were studied: 198 full-term and 26 preterm. The mean BMC, BMD and bone area for term newborns was 46.5 g (95% confidence interval [CI]: 45.35-47.66), 0.209 g/cm² (95% CI: 0.206-0.212) and 221.6 cm² (95% CI: 218.52-224.62), respectively. The mean placental weight was 403.2 ± 75.01 g (n = 72) while FFV was 0.71 ± 0.28 ml (19 weeks; n = 59) and 4.4 ± 1.17 ml (34 weeks; n = 33). Factors significantly associated with NBBM -gestational age at delivery, gestational weight gain, FFV at 19 weeks, placental weight, third-trimester maternal serum albumin and newborn anthropometric parameters (univariable analysis) and newborn birth weight, placental weight and FFV at 19 weeks (multivariable analysis).

CONCLUSION

This study described NBBM among term newborns and birth weight, second-trimester FFV and placental weight were the associated factors.

Sexual Dimorphism and the Origins of Human Spinal Health

Recent observations indicate that the cross-sectional area (CSA) of vertebral bodies is on average 10% smaller in healthy newborn girls than in newborn boys, a striking difference that increases during infancy and puberty and is greatest by the time of sexual and skeletal maturity. The smaller CSA of female vertebrae is associated with greater spinal flexibility and could represent the human adaptation to fetal load in bipedal posture. Unfortunately, it also imparts a mechanical disadvantage that increases stress within the vertebrae for all physical activities. This review summarizes the potential endocrine, genetic, and environmental determinants of vertebral cross-sectional growth and current knowledge of the association between the small female vertebrae and greater risk for a broad array of spinal conditions across the lifespan.

Effects of reduced energy availability on bone metabolism in women and men

BACKGROUND

The short-term effects of low energy availability (EA) on bone metabolism in physically active women and men are currently unknown.

PURPOSE

We evaluated the effects of low EA on bone turnover markers (BTMs) in a cohort of women and a cohort of men, and compared effects between sexes.

METHODS

These studies were performed using a randomised, counterbalanced, crossover design. Eleven eumenorrheic women and eleven men completed two 5-day protocols of controlled (CON; 45kcal·kgLBM^-1·d^-1) and restricted (RES; 15kcal·kgLBM^-1·d^-1) EAs. Participants ran daily on a treadmill at 70% of their peak aerobic capacity (VO₂ peak) resulting in an exercise energy expenditure of 15kcal·kgLBM^-1·d^-1 and consumed diets providing 60 and 30kcal·kgLBM^-1·d^-1. Blood was analysed for BTMs [β-carboxyl-terminal cross-linked telopeptide of type I collagen (β-CTX) and amino-terminal propeptide of type 1 procollagen (P1NP)], markers of calcium metabolism [parathyroid hormone (PTH), albumin-adjusted calcium (ACa), magnesium (Mg) and phosphate (PO₄)] and regulatory hormones [sclerostin, insulin-like growth factor 1 (IGF-1), triiodothyronine (T₃), insulin, leptin, glucagon-like-peptide-2 (GLP-2)].

RESULTS

In women, β-CTX AUC was significantly higher (P=0.03) and P1NP AUC was significantly lower (P=0.01) in RES compared to CON. In men, neither β-CTX (P=0.46) nor P1NP (P=0.12) AUCs were significantly different between CON and RES. There were no significant differences between sexes for any BTM AUCs (all P values>0.05). Insulin and leptin AUCs were significantly lower following RES in women only (for both P=0.01). There were no differences in any AUCs of regulatory hormones or markers of calcium metabolism between men and women following RES (all P values>0.05).

CONCLUSIONS

When comparing within groups, five days of low EA (15kcal·kgLBM^-1·d^-1) decreased bone formation and increased bone resorption in women, but not in men, and no sex specific differences were detected.

Physiological Bone Remodeling: Systemic Regulation and Growth Factor Involvement

Bone remodeling is essential for adult bone homeostasis. It comprises two phases: bone formation and resorption. The balance between the two phases is crucial for sustaining bone mass and systemic mineral homeostasis. This review highlights recent work on physiological bone remodeling and discusses our knowledge of how systemic and growth factors regulate this process.

Clec11a/osteolectin is an osteogenic growth factor that promotes the maintenance of the adult skeleton

Bone marrow stromal cells maintain the adult skeleton by forming osteoblasts throughout life that regenerate bone and repair fractures. We discovered that subsets of these stromal cells, osteoblasts, osteocytes, and hypertrophic chondrocytes secrete a C-type lectin domain protein, Clec11a, which promotes osteogenesis. Clec11a-deficient mice appeared developmentally normal and had normal hematopoiesis but reduced limb and vertebral bone. Clec11a-deficient mice exhibited accelerated bone loss during aging, reduced bone strength, and delayed fracture healing. Bone marrow stromal cells from Clec11a-deficient mice showed impaired osteogenic differentiation, but normal adipogenic and chondrogenic differentiation. Recombinant Clec11a promoted osteogenesis by stromal cells in culture and increased bone mass in osteoporotic mice in vivo. Recombinant human Clec11a promoted osteogenesis by human bone marrow stromal cells in culture and in vivo. Clec11a thus maintains the adult skeleton by promoting the differentiation of mesenchymal progenitors into mature osteoblasts. In light of this, we propose to call this factor Osteolectin.

DOI:http://dx.doi.org/10.7554/eLife.18782.001

Effects of Phlomis umbrosa Root on Longitudinal Bone Growth Rate in Adolescent Female Rats

This study aimed to investigate the effects of Phlomis umbrosa root on bone growth and growth mediators in rats. Female adolescent rats were administered P. umbrosa extract, recombinant human growth hormone or vehicle for 10 days. Tetracycline was injected intraperitoneally to produce a glowing fluorescence band on the newly formed bone on day 8, and 5-bromo-2'-deoxyuridine was injected to label proliferating chondrocytes on days 8-10. To assess possible endocrine or autocrine/paracrine mechanisms, we evaluated insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3) or bone morphogenetic protein-2 (BMP-2) in response to P. umbrosa administration in either growth plate or serum. Oral administration of P. umbrosa significantly increased longitudinal bone growth rate, height of hypertrophic zone and chondrocyte proliferation of the proximal tibial growth plate. P. umbrosa also increased serum IGFBP-3 levels and upregulated the expressions of IGF-1 and BMP-2 in growth plate. In conclusion, P. umbrosa increases longitudinal bone growth rate by stimulating proliferation and hypertrophy of chondrocyte with the increment of circulating IGFBP-3. Regarding the immunohistochemical study, the effect of P. umbrosa may also be attributable to upregulation of local IGF-1 and BMP-2 expressions in the growth plate, which can be considered as a GH dependent autocrine/paracrine pathway.

Relationship of insulin-like growth factor 1 and bone parameters in 7-15 years old apparently, healthy Indian children

OBJECTIVE

Growth hormone through insulin-like growth factor 1 (IGF-1) plays an important role in both bone growth and mineralization. This cross-sectional study was carried out to evaluate the relationship between serum IGF-1 concentrations and dual energy X-ray (DXA) measured whole body less head bone area (BA), lean body mass (LBM), and bone mineral content (BMC).

METHODS

One hundred and nineteen children (boys = 70, age = 7.3-15.6 years) were studied for their anthropometric parameters by standard methods and bone and body composition by DXA. Their fasting serum IGF-1 concentrations were assessed by enzyme-linked immunosorbent assay and Z-scores were calculated using available reference data. Bone and body composition parameter Z-scores were calculated using ethnic reference data.

RESULTS

Mean age of the boys and girls was similar (11.5 ± 1.8 years). The mean serum IGF-1concentrations and IGF-1 Z-scores were similar (P > 0.1) between boys and girls and were of the order of (302.3 ± 140.0 and - 1.4 ± 1.1, respectively). The LBM for age and BA for age Z-score was greater in children with IGF-1 Z-score > median than children with IGF-1 Z-score < median. The mean BMC for age Z-scores were 0.4 ± 0.9 and - 0.2 ± 0.8 in children with above and below the median of IGF-1 Z-score (P > 0.1).

CONCLUSION

Serum IGF-1 levels were more strongly associated with BA and LBM, suggesting that its effect on bone is greater with respect to periosteal bone acquisition and through its effect on muscle mass.

Pubertal timing, bone acquisition, and risk of fracture throughout life

Pubertal maturation plays a fundamental role in bone acquisition. In retrospective epidemiological surveys in pre- and postmenopausal women, relatively later menarcheal age was associated with low bone mineral mass and increased risk of osteoporotic fracture. This association was usually ascribed to shorter time exposure to estrogen from the onset of pubertal maturation to peak bone mass attainment. Recent prospective studies in healthy children and adolescents do not corroborate the limited estrogen exposure hypothesis. In prepubertal girls who will experience later menarche, a reduced bone mineral density was observed before the onset of pubertal maturation, with no further accumulated deficit until peak bone mass attainment. In young adulthood, later menarche is associated with impaired microstructural bone components and reduced mechanical resistance. This intrinsic bone deficit can explain the fact that later menarche increases fracture risk during childhood and adolescence. In healthy individuals, both pubertal timing and bone development share several similar characteristics including wide physiological variability and strong effect of heritable factors but moderate influence of environmental determinants such as nutrition and physical activity. Several conditions modify pubertal timing and bone acquisition, a certain number of them acting in concert on both traits. Taken together, these facts should prompt the search for common genetic regulators of pubertal timing and bone acquisition. It should also open epigenetic investigation avenues to pinpoint which environmental exposure in fetal and infancy life, such as vitamin D, calcium, and/or protein supplies, influences both pubertal timing and bone acquisition.

Evaluation of growth patterns and body composition in C57Bl/6J mice using dual energy X-ray absorptiometry

The normal growth pattern of female C57BL/6J mice, from 5 to 30 weeks of age, has been investigated in a longitudinal study. Weight, body surface area (BS), and body mass index (BMI) were evaluated in forty mice. Lean mass and fat mass, bone mineral content (BMC), and bone mineral density (BMD) were monitored by dual energy X-ray absorptiometry (DEXA). Weight and BS increased linearly (16.15 ± 0.64-27.64 ± 1.42 g; 51.13 ± 0.74-79.57 ± 2.15 cm(2), P < 0.01), more markedly from 5 to 9 weeks of age (P < 0.001). BMD showed a peak at 17 weeks (0.0548 ± 0.0011 g/cm(2) ∗ m, P < 0.01). Lean mass showed an evident gain at 9 (15.8 ± 0.8 g, P < 0.001) and 25 weeks (20.5 ± 0.3 g, P < 0.01), like fat mass from 13 to 17 weeks (2.0 ± 0.4-3.6 ± 0.7 g, P < 0.01). BMI and lean mass index (LMI) reached the highest value at 21 weeks (3.57 ± 0.02-0.284 ± 0.010 g/cm(2), resp.), like fat mass index (FMI) at 17 weeks (0.057 ± 0.009 g/cm(2)) (P < 0.01). BMI, weight, and BS showed a moderate positive correlation (0.45-0.85) with lean mass from 5 to 21 weeks. Mixed linear models provided a good prediction for lean mass, fat mass, and BMD. This study may represent a baseline reference for a future comparison of wild-type C57BL/6J mice with models of altered growth.

IGF-1 release kinetics from chitosan microparticles fabricated using environmentally benign conditions

The main objective of this study is to maximize growth factor encapsulation efficiency into microparticles. The novelty of this study is to maximize the encapsulated growth factors into microparticles by minimizing the use of organic solvents and using relatively low temperatures. The microparticles were fabricated using chitosan biopolymer as a base polymer and cross-linked with tripolyphosphate (TPP). Insulin like-growth factor-1 (IGF-1) was encapsulated into microparticles to study release kinetics and bioactivity. In order to authenticate the harms of using organic solvents like hexane and acetone during microparticle preparation, IGF-1 encapsulated microparticles prepared by the emulsification and coacervation methods were compared. The microparticles fabricated by emulsification method have shown a significant decrease (p<0.05) in IGF-1 encapsulation efficiency, and cumulative release during the two-week period. The biocompatibility of chitosan microparticles and the bioactivity of the released IGF-1 were determined in vitro by live/dead viability assay. The mineralization data observed with von Kossa assay, was supported by mRNA expression levels of osterix and runx2, which are transcription factors necessary for osteoblasts differentiation. Real time RT-PCR data showed an increased expression of runx2 and a decreased expression of osterix over time, indicating differentiating osteoblasts. Chitosan microparticles prepared in optimum environmental conditions are a promising controlled delivery system for cells to attach, proliferate, differentiate and mineralize, thereby acting as a suitable bone repairing material.

The interrelationship between bone and fat: from cellular see-saw to endocrine reciprocity

The number of mature osteoblasts and marrow adipocytes in bone is influenced by the differentiation of the common mesenchymal progenitor cell towards one phenotype and away from the other. Consequently, factors which promote adipogenesis not only lead to fatty marrow but also inhibit osteoblastogenesis, resulting in decreased osteoblast numbers, diminished bone formation and, potentially, inadequate bone mass and osteoporosis. In addition to osteoblast and bone adipocyte numbers being influenced by this skewing of progenitor cell differentiation towards one phenotype, mature osteoblasts and adipocytes secrete factors which may evoke changes in the cell fate and function of each other. This review examines the endogenous factors, such as PPAR-γ2, Wnt, IGF-1, GH, FGF-2, oestrogen, the GP130 signalling cytokines, vitamin D and glucocorticoids, which regulate the selection between osteoblastogenesis and adipogenesis and the interrelationship between fat and bone. The role of adipokines on bone, such as adiponectin and leptin, as well as adipose-derived oestrogen, is reviewed and the role of bone as an energy regulating endocrine organ is discussed.

Matrix IGF-1 maintains bone mass by activation of mTOR in mesenchymal stem cells

Insulin-like growth factor 1 (IGF-1), the most abundant growth factor in the bone matrix, maintains bone mass in adulthood. We now report that IGF-1 released from the bone matrix during bone remodeling stimulates osteoblastic differentiation of recruited mesenchymal stem cells (MSCs) by activation of mammalian target of rapamycin (mTOR), thus maintaining proper bone microarchitecture and mass. Mice with knockout of the IGF-1 receptor (Igf1r) in their pre-osteoblastic cells showed lower bone mass and mineral deposition rates than wild-type mice. Further, MSCs from Igf1rflox/flox mice with Igf1r deleted by a Cre adenovirus in vitro, although recruited to the bone surface after implantation, were unable to differentiate into osteoblasts. We also found that the concentrations of IGF-1 in the bone matrix and marrow of aged rats were lower than in those of young rats and directly correlated with the age-related decrease in bone mass. Likewise, in age-related osteoporosis in humans, we found that bone marrow IGF-1 concentrations were 40% lower in individuals with osteoporosis than in individuals without osteoporosis. Notably, injection of IGF-1 plus IGF binding protein 3 (IGFBP3), but not injection of IGF-1 alone, increased the concentration of IGF-1 in the bone matrix and stimulated new bone formation in aged rats. Together, these results provide mechanistic insight into how IGF-1 maintains adult bone mass, while also providing a further rationale for its therapeutic targeting to treat age-related osteoporosis.

Selective osteoblast overexpression of IGF-I in mice prevents low protein-induced deterioration of bone strength and material level properties

Protein deficiency is frequently observed in elderly osteoporotic patients. Undernutrition leads to decreased levels of IGF-I, an important factor in regulating bone homeostasis throughout life. IGF-I is produced in the liver and locally in the skeleton. We hypothesized that increasing IGF-I expression in the osteoblasts, the bone forming cells, would protect the skeleton from the negative effects of a low-protein diet. To test our hypothesis, we employed a mouse model in which IGF-I was overexpressed exclusively in osteoblasts and fed either a 15% (normal) or a 2.5% (low) protein isocaloric diet to the transgenic (TG) mice and their wild-type (WT) littermates for 8 weeks. Blood was collected for biochemical determinations and weight was monitored weekly. Bones were excised for microstructural analysis (μCT), as well as biomechanical and material level properties. Histomorphometric analysis was performed for bone formation parameters. A low protein diet decreased body weight, circulating IGF-I and osteocalcin levels regardless of genotype. Overexpression of IGF-I in the osteoblasts was, however, able to protect the negative effects of low protein diet on microstructure including tibia cortical thickness and volumetric density, and on bone strength. Overexpression of IGF-I in osteoblasts in these mice protected the vertebrae from the substantial negative effects of low protein on the material level properties as measured my nanoindentation. TG mice also had larger overall geometric properties than WT mice regardless of diet. This study provides evidence that while a low protein diet leads to decreased circulating IGF-I, altered microstructure and decreased bone strength, these negative effects can be prevented with IGF-I overexpression exclusively in bone cells.

Insulin-like growth factor-1 increases bone calcium accumulation only during rapid growth in female rats

Calcium retention varies with developmental state, which may be partially under the control of insulin-like growth factor 1 (IGF-1). IGF-1 levels can be manipulated through dietary and therapeutic interventions. We investigated the relationship between IGF-1 endogenous production and calcium utilization and bone accretion during growth as well as the effects of IGF-1 treatment on calcium utilization during rapid and slowed growth in intact female Sprague-Dawley rats. In 33 rats killed at 11 time points (n = 3 each) from age 4 to 24 wk, femoral and vertebral bone mass were paralleled by plasma IGF-1 up to 9 wk. Fractional calcium absorption was maximal at 9 wk, reduced by one-half at 12 wk, and there was no further change at 20 wk. From this study, we selected 2 stages of growth, rapid and slow, for a subsequent intervention study. A 4-wk intervention was initiated at 6 or 8 wk when rats (n = 15/group) received either continuous rhIGF-1/IGF binding protein 3 (IGFBP3) infusion (0.3 mg/d) or vehicle (control) by osmotic mini-pumps. In rapidly growing IGF-1/IGFBP3-treated rats compared to controls, but not in slowly growing treated compared to control rats, IGF-1 treatment increased (P < 0.05) calcium absorption (35 vs. 21%), bone calcium balance (0.55 vs. 0.3 mmol/d), and femoral calcium content (31 vs. 24% of dry weight). Exogenous IGF-1/IGFBP3 treatment increased calcium accretion during rapid growth, but rats past rapid growth were no longer as sensitive to this dose of IGF-1/IGFBP3. Thus, interventions designed to improve bone mass through increased IGF-1 will have the greatest impact during rapid growth.

Insulin-like growth factor (IGF)-I and IGF-II contribute differentially to the phenotype of pregnancy associated plasma protein-A knock-out mice

CONTEXT

Insulin-like growth factor (IGF) signaling is essential for achieving optimal body size during fetal development, peak bone mass during puberty, and maximal fecundity in the reproductive period. IGF-II is considered the main fetal IGF, whereas IGF-I is more important postnatally. Pregnancy-associated plasma protein-A (PAPP-A) enhances local IGF signaling through cleavage of inhibitory IGF binding proteins. Conversely, inhibition of PAPP-A results in reduced local IGF action. Thus, PAPP-A knock-out (KO) mice are born as proportional dwarfs due to the dysregulation of IGF-II signaling during early embryogenesis that impacts body size. Relaxation of IgfII imprinting through mutation of a reciprocally imprinted downstream gene, H19, which allowed transcription of IGF-II from the normally silent maternal allele, rescued the dwarf phenotype of PAPP-A KO mice.

OBJECTIVE

To determine the effect of increased IGF-II expression on postnatal phenotypes of PAPP-A KO mice.

DESIGN

Young adult wild-type (WT), PAPP-A KO, H19 mutant (ΔH19/WT) and ΔH19/PAPP-A KO mice were characterized for skeletal phenotype (peripheral quantitative computed tomography at the midshaft and distal metaphysis of the femur) and reproductive phenotype (time to first litter, time between litters, pups per litter).

RESULTS

Serum IGF-II levels were significantly increased in ΔH19/WT and ΔH19/PAPP-A KO mice compared to WT and PAPP-A KO mice; serum IGF-I levels were not affected by H19 mutation. PAPP-A KO mice had reductions in cortical thickness and in cortical and trabecular area, bone mineral content and bone mineral density compared to WT mice. There were no significant differences between PAPP-A KO and ΔH19/PAPP-A KO mice in any of the bone parameters. PAPP-A KO crossed with (×) PAPP-A KO had a longer time until first litter, normal time between subsequent litters, and significantly reduced number of pups per litter compared to WT×WT. ΔH19/PAPP-A KO×ΔH19/PAPP-A KO had an even longer time to first litter, but also longer time between litters. This phenotype was associated with female ΔH19/PAPP-A KO mice. Furthermore, these ΔH19/PAPP-A KO mouse mothers failed to care for their pups.

CONCLUSIONS

An increase in IGF-II expression did not rescue the skeletal and reproductive deficiencies associated with reduced local IGF-I signaling in PAPP-A KO mice. In addition, the data suggest a potential new role for genomic imprinting at the IgfII/H19 locus affecting maternal behavior.

Experimental assessment of nutrition and bone growth's velocity effects on Harris lines formation

Harris lines (HL) are radio-opaque transverse lines traditionally associated with stressors that halt or decelerate growth in humans. Harris lines' status as a stress marker is, however, questionable because their association to illness and deficient growth is low and they commonly form in the absence of stress during periods of accelerated growth. To assess Harris line's reliability as a stress marker, this study examined their association with nutritional status and bone growth velocity through an experimental study in rabbits. Forty-five New Zealand White rabbits were divided into: Control (normal laboratory conditions), Experimental-1 (moderately undernourished), and Experimental-2 (periodically fasted) groups during their growth. Variables analyzed included weight, forelimb length, humeral diaphyseal length, diaphyseal growth velocity, and number of Harris lines. Fewer lines were observed by the end of the study among Experimental-1 animals. More Harris lines formed during periods of rapid growth in the absence of nutritional stress. Accordingly, Harris lines are a poor marker of stress. Intrinsic limitations to paleopathological studies can be overcome, but even the most careful attentiveness to multiple stress markers and cultural context will go amiss if the markers used are unreliable.

Preterm infant massage therapy research: a review

In this paper, preterm infant massage therapy studies are reviewed. Massage therapy has led to weight gain in preterm infants when moderate pressure massage was provided. In studies on passive movement of the limbs, preterm infants also gained significantly more weight, and their bone density also increased. Research on ways of delivering the massage is also explored including using mothers versus therapists and the added effects of using oils. The use of mothers as therapists was effective in at least one study. The use of oils including coconut oil and safflower oil enhanced the average weight gain, and the transcutaneous absorption of oil also increased triglycerides. In addition, the use of synthetic oil increased vagal activity, which may indirectly contribute to weight gain. The weight gain was associated with shorter hospital stays and, thereby, significant hospital cost savings. Despite these benefits, preterm infant massage is only practiced in 38% of neonatal intensive care units. This may relate to the underlying mechanisms not being well understood. The increases noted in vagal activity, gastric motility, insulin and IGF-1 levels following moderate pressure massage are potential underlying mechanisms. However, those variables combined do not explain all of the variance in weight gain, highlighting the need for additional mechanism studies.

Growth hormone protects against ovariectomy-induced bone loss in states of low circulating insulin-like growth factor (IGF-1)

Early after estrogen loss in postmenopausal women and ovariectomy (OVX) of animals, accelerated endosteal bone resorption leads to marrow expansion of long bone shafts that reduce mechanical integrity. Both growth hormone (GH) and insulin-like growth factor (IGF-1) are potent regulators of bone remodeling processes. To investigate the role of the GH/IGF-1 axis with estrogen deficiency, we used the liver IGF-1-deficient (LID) mouse. Contrary to deficits in controls, OVX of LID mice resulted in maintenance of cortical bone mechanical integrity primarily owing to an enhanced periosteal expansion affect on cross-sectional structure (total area and cortical width). The serum balance in LID that favors GH over IGF-1 diminished the effects of ablated ovarian function on numbers of osteoclast precursors in the marrow and viability of osteocytes within the cortical matrix and led to less endosteal resorption in addition to greater periosteal bone formation. Interactions between estrogen and the GH/IGF-1 system as related to bone remodeling provide a pathway to minimize degeneration of bone tissue structure and osteoporotic fracture.

Rapid and robust response of biochemical markers of bone formation to teriparatide therapy

Teriparatide, a parathyroid hormone analogue, is a potent anabolic treatment for postmenopausal osteoporosis. Studies have shown that teriparatide induces large increases in biochemical markers of bone formation after 1 month of therapy followed by a delayed increase in bone resorption markers. The aims of this study were to (1) describe changes in bone turnover markers during 28 days of treatment with teriparatide; (2) identify the earliest time point by which most subjects showed a biochemical response to teriparatide; (3) identify potential biomarkers of positive bone response; (4) describe changes in bone turnover markers 4 weeks after stopping teriparatide. We recruited 15 osteopenic postmenopausal women, ages 55-69 (mean 62) years. All received 20 microg teriparatide subcutaneously for 28 days. Serum levels of the bone formation markers type I collagen N-terminal propeptide (PINP), type I collagen C-terminal propeptide (PICP), osteocalcin (OC), bone alkaline phosphatase (bone ALP), and the bone resorption markers crosslinked C-telopeptide of type I collagen (Sbeta-CTX), crosslinked N-telopeptide of type I collagen (S-NTX) and tartrate-resistant acid phosphatase type 5b (TRACP5b) were measured on 11 occasions: three times before dosing (baseline) and on days 3, 7, 10, 14, 19, 24 and 28 and at day 56 (i.e., 28 days after stopping teriparatide ). During the first 2 days of teriparatide treatment, PINP levels increased rapidly, by 8.2% (90% confidence interval (CI) 6.9%, 9.5%) and continued to increase until the end of treatment to 110.8%. PICP and OC showed a similar, but less pronounced, pattern. All three markers increased by at least 75% at day 28. A small, transient decrease in bone resorption markers occurred over the same period. Following cessation of treatment, concentrations of bone formation markers decreased to within 20% of baseline values by day 56. In conclusion, the bone formation markers PINP, PICP and OC show a rapid and robust increase in response to teriparatide, which is noticeable during the first week of therapy. PINP is the most responsive marker. These findings have important implications for monitoring patients treated with teriparatide and may also inform the design of studies of new anabolic agents for osteoporosis.

The EGFR network in bone biology and pathology

The resorption, formation and maintenance of bone are coordinated by the action of several hormones, growth factors and transcription factors. Recent experiments based on genetically modified mouse models, gene microarrays and pharmacological intervention indicate that the epidermal growth factor receptor (EGFR) system plays important roles in skeletal biology and pathology. This network, including a family of seven growth factors - the EGFR ligands - and the related tyrosine kinase receptors EGFR (ERBB1), ERBB2, ERBB3 and ERBB4, regulates aspects such as proliferation and differentiation of osteoblasts, chondrocytes and osteoclasts, parathyroid hormone-mediated bone formation and cancer metastases in bone. Here, we summarize and discuss the role of the EGFR and its ligands in skeletal biology and pathology.

Osteoporosis in adults with cerebral palsy

Life expectancy for the 400 000 adults with cerebral palsy (CP) in the USA is increasing. Although there is a perception of increased fractured rate in the adult with CP, it has not been well studied. Low bone mineral density is found in more than 50% of adults with a variety of disabilities, including CP. Dual-energy X-ray absorptiometry scanning is commonly used to assess bone mineral density, but is limited by positioning and other artifacts in adults with CP. Novel scanning regions of interest, such as the distal femur, are not yet standardized in adults. Nutritional assessment and physical activity, the basis of most fracture prevention programs, are difficult to do in the adult with CP. A better understanding of the 'muscle-bone unit' physiology and its exploitation may lead to better treatment modifications. Clinical research trials with bisphosphonates (e.g. pamidronate), estrogen, selective estrogen receptor modulators, parathyroid hormone analogs, and growth hormone need to be targeted to the adult with CP. Longitudinal studies of fracture risk factors, genetic research in bone and neuromuscular biology, and the development of treatment surrogates for physical activity are additional areas of needed expertise. This could be facilitated by an adult CP registry and the centralization of clinical research efforts.

Relationship among insulinlike growth factor I concentrations, bone mineral density, and biochemical markers of bone turnover in postmenopausal women: a population-based study

OBJECTIVE

: To assess the association among serum insulinlike growth factor I (IGF-I) concentrations, bone mineral density (BMD), and biochemical markers of bone turnover in a large group of postmenopausal women from the general population.

DESIGN

: As an extension of a larger epidemiological study, the Iranian Multicentral Osteoporosis Study, a total of 406 healthy postmenopausal women (age, 59.0 +/- 7.6 years) were randomly selected from 13 clusters in Bushehr Port. IGF-I, serum CrossLaps, degradation products of C-terminal telopeptides of type I collagen, and osteocalcin were measured by highly specific enzyme-linked immunosorbent assay. BMD was determined for the lumbar spine (L2-4) and proximal femur using dual-energy x-ray absorptiometry.

RESULTS

: The mean (+/- SD) serum IGF-I concentration for all postmenopausal women was 183.35 +/- 65.60 ng/mL. In age-adjusted analyses, there was no correlation between IGF-I and BMD at the lumbar spine and femoral neck. Compared with women in the lowest quartile of IGF-I, women in the highest quartile had a significantly greater means of osteocalcin (P = 0.04) and alkaline phosphatase (P = 0.01). Analysis by quartiles of IGF-I did not reveal an association with serum CrossLaps.

CONCLUSIONS

: Circulating IGF-I is associated with biochemical markers of bone formation, but there is no relationship among IGF-I, degradation products of C-terminal telopeptides of type I collagen, and BMD in postmenopausal women. Clearly more work will be needed before serum IGF-I can be used in clinical practice as a risk predictor for postmenopause-associated loss of bone mass.

Determination of mineral content in methanolic safflower (Carthamus tinctorius L.) seed extract and its effect on osteoblast markers

Safflower (Carthamus tinctorius L.) seeds are used as a folk medicine to enhance bone formation or to prevent osteoporosis in Korea. Therefore, the methanolic extract of safflower seeds (MESS) containing high mineral content, such as calcium (Ca), potassium (K) and phosphorous (P), was evaluated for the role on osteoblast (Ob) markers of Sprague-Dawley rats. In serum of 3 to 11 weeks (wks) old rats, both osteocalcin (OC) content and bone-specific alkaline phosphatase (B-ALP) activity increased to their maximum levels in 4–7 wks. Hence, 3 wks old rats were selected for 8 wks oral treatment of MESS, resulted in the significant increase of Ob markers in serum such as OC content (4–8 wks), B-ALP activity (1–2 wks) and insulin-like growth factor I (IGF-I) level (1 wk), and the growth parameter such as the length of femur (2–8 wks) and tibia (4 wks). On the basis of Pearson’s correlation coefficient, there were a moderate correlation between OC and B-ALP at 8 wks, a low correlation between OC and IGF-I at 1, 4 and 8 wks, a moderate correlation between OC and femur length at 1, 2 and 8 wks, and a moderate correlations between OC and tibia length at 1 and 8 wks of MESS-treated groups. The result reveals that the changes of OC correlated at low to moderate level with the changes of B-ALP activity, IGF-I content and femur and tibia length in the MESS-treatment period. On the other hand, there were a strong correlation between IGF-I and femur length at 2 wks and moderate correlation between IGF-I and tibia length at 1, 2 and 8 wks of MESS-treated groups. Therefore, the effect of MESS on bone formation likely appears to be mediated by IGF-I at the early stage of treatment.

Controlled release of insulin-like growth factor-1 and bone marrow stromal cell function of bone-like mineral layer-coated poly(lactic-co-glycolic acid) scaffolds

Controlled release of growth factors or drugs provides great therapeutic advantages for bone defects which do not heal with normal therapeutic treatments. We have accelerated the deposition of bone-like mineral (BLM) on the surface of three-dimensional (3D) poly(lactic-co-glycolic acid) (PLGA) porous scaffolds to 36-48 h by modifying the biomimetic process parameters and applying surface treatments onto PLGA scaffolds. We used simulated body fluid containing insulin-like growth factor-1 (IGF-1; 1 microg/ml) to mineralize the PLGA scaffolds for 48 h. IGF-1 was co-precipitated with mineral on the surface of the PLGA scaffolds. IGF-1-incorporated mineralized scaffolds demonstrated slow controlled release over a 30 day period when they were incubated in phosphate-buffered saline (PBS) at 37 degrees C. Bone marrow stromal cell (BMSC) function on three different types of scaffolds, such as control (non-mineralized) scaffolds, mineralized scaffolds, and IGF-1-incorporated mineralized scaffolds was also investigated. BMSC attachment and proliferation was enhanced for IGF-1-incorporated mineralized scaffolds compared with controls during the culture period. BMSC differentiation was not changed during the culture period among the three groups of scaffolds, as assessed by alkaline phosphatase activity and osteocalcin assay. According to findings from this study, BLM has great potential to be used as a carrier for biological molecules for localized release applications as well as bone tissue-engineering applications.

Growth-related changes in prehistoric Jomon and modern Japanese mandibles with emphasis on cortical bone distribution

Cortical bone distribution of the anthropoid mandibular symphysis has been addressed in relation to mechanical stress generated by mastication. To examine whether or not bone mass and distribution patterns of the human mandibular symphysis could be interpreted as an example of functional adaptation, we compared the skeletal growth series of two populations, prehistoric Jomon, considered to represent a "robust" mandibular morphology associated with a presumed heavier masticatory load, and modern Japanese. Results showed that the adult Jomon symphysis possessed significantly greater bone mass and thicker cortical bone compared to the modern Japanese condition. However, the second moments of area did not differ significantly between the two, indicating comparable rigidity against bending. Furthermore, the Jomon mandibles of the infant to juvenile stages exhibited most of the adult characteristics, in both bone mass/distribution of the symphysis and in mandibular corpus/ramus morphologies. The present study also demonstrated the presence of a growth pattern of symphyseal cortical thickness, common to both the Jomon and the modern Japanese series. In both populations, subsequent to deciduous molar occlusion, cortical bone tends to be thickest at the inferolingual symphysis, at the location where the highest tensile stresses presumably occur during mastication. These findings suggest that the "robust" characteristics of the Jomon mandible are initially manifested early in development, and that the effect of mechanical stimulus to bone mass formation in the human symphysis is largely confined to a regulatory role during growth modeling.

Nuclear factor I transcription factors regulate IGF binding protein 5 gene transcription in human osteoblasts

Insulin-like growth factor binding protein 5 (IGFBP5) is expressed in many cell types including osteoblasts and modulates IGF activities. IGFBP5 may affect osteoblasts and bone formation, in part by mechanisms independent of binding IGFs. The highly conserved IGFBP5 proximal promoter within 100 nucleotides of the start of transcription contains functional cis regulatory elements for C/EBP, Myb and AP-2. We report evidence for a functional Nuclear Factor I (NFI) cis element that mediates activation or repression of IGFBP5 transcription by the NFI gene family. All four NFI genes were expressed in human osteoblast cultures and osteosarcoma cell lines. Co-transfection with human IGFBP5 promoter luciferase reporter and murine Nfi expression vectors showed that Nfib was the most active in stimulating transcription. Nfix was less active and Nfia and Nfic were inhibitory. Knockdown of NFIB and NFIC expression using siRNA decreased and increased IGFBP5 expression, respectively. Analysis of IGFBP5 promoter deletion and mutation reporter constructs identified a functional NFI cis element. All four NFI proteins bound the NFI site in electrophoretic mobility shift experiments and NFIB bound in chromatin immunoprecipitation assays. Results suggest that NFI proteins are important regulators of IGFBP5 expression in human osteoblasts and thus in modulating IGFBP5 functions in bone.

Delayed pubertal development by hypothalamic suppression causes an increase in periosteal modeling but a reduction in bone strength in growing female rats

The timing of the pubertal growth is a critical event in skeletal development. A delay in the onset of puberty has been correlated with increased stress fracture incidence in young women and as a result, suboptimal skeletal development may affect long-term bone strength. Gonadotropin releasing hormone antagonist (GnRH-a) injections were used to delay the onset of puberty in growing female rats. 23-day-old female rats were injected with a GnRH-antagonist at 2 dosage levels (n=15/group). The Low Dose group (1.25 mg/kg/dose) received daily injections for 27 days (sacrifice 49 days). The High Dose group received (5.0 mg/kg/dose) only 5 days per week over a 26 day period (sacrifice 48 days). Calcein injections measured bone formation activity on the periosteal and endocortical surfaces. Standard histomorphometric and biomechanical analyses were performed on the femora and ash content was measured on the tibiae of all animals. Serum estradiol and insulin-like growth factor (IGF)-1 levels were assayed. Significant delays in pubertal development occurred in the two GnRH-a groups as evidenced by delayed vaginal openings, decreased uterine and ovarian weights and suppressed estradiol levels compared to control. Femoral lengths were significantly shorter in the experimental groups and serum IGF-1 levels were higher than control. Bone strength and stiffness were significantly lower in the GnRH-a groups. Cortical bone area was decreased and total area was not different between groups. There was a significant decrease in % Ct.Ar/T.Ar. The decreased bone strength may have resulted from a decrease in the amount and distribution of bone, however, stress and Young's modulus were also decreased. There was a different response between endocortical formation indices and periosteal formation indices to the GnRH-a protocol. Endocortical bone formation rates decreased and there was an increase in periosteal labeled surface. A dose response between bone strength and GnRH-a dosage was found. The data suggest that hypothalamic suppression during pubertal development resulted in decreased bone strength which may result in fracture development.

Impact of pregnancy-associated plasma protein-a deletion on the adult murine skeleton

INTRODUCTION

The metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A) functions to enhance local insulin-like growth factor (IGF)-I bioavailability through cleavage of inhibitory IGF binding proteins. Because IGF-I is an important regulator of skeletal growth and remodeling and PAPP-A is highly expressed by osteoblastic cells, we hypothesized that, in the absence of PAPP-A, bone physiology would be compromised because of a blunting of local IGF-I action even in the presence of normal circulating IGF-I levels.

MATERIALS AND METHODS

pQCT, muCT, histomorphometry, and mechanical strength testing were performed on bones from PAPP-A knockout (KO) mice and wildtype (WT) littermates at 2-12 mo of age. IGF-I levels and bone formation and resorption markers were determined in sera from these animals.

RESULTS

Volumetric BMD in PAPP-A KO mice measured by pQCT at the femoral midshaft, which is primarily cortical bone, was 10% less than WT at 2 mo. This difference was maintained at 4, 6, and 12 mo. Cortical thickness at this site was similarly decreased. On the other hand, trabecular bone at the distal femur (pQCT) and in the tibia (muCT) showed age-progressive decreases in bone volume fraction in PAPP-A KO compared with WT mice. Tibial muCT indicated a 46% relative decrease in trabecular bone volume/total volume (BV/TV) and a 28% relative decrease in trabecular thickness in PAPP-A KO compared with WT mice at 6 mo. These trabecular deficiencies in PAPP-A KO mice corresponded to a weakening of the bone. Serum markers and bone histomorphometry indicated that the primary impact of PAPP-A is on skeletal remodeling resulting in a state of low-turnover osteopenia in adult PAPP-A KO mice. Circulating IGF-I levels were not altered in PAPP-A KO mice.

CONCLUSIONS

PAPP-A is a bone growth regulatory factor in vivo and, in its absence, mice show skeletal insufficiency in mass, density, architecture, and strength. The data suggest a primary role for PAPP-A in modulating local IGF bioavailability for trabecular bone remodeling.

Relationships between insulin-like growth factor-I (IGF-I) and OPG, RANKL, bone mineral density in healthy Chinese women

Serum IGF-I level was negatively correlated with OPG and OPG/RANKL ratio, but positively correlated with RANKL. Serum OPG level in the highest quintile of IGF-I was significantly lower than that in the lowest. We conclude that the effect of IGF-I on bone remodeling may be mediated by the OPG/RANKL system.

INTRODUCTION

Insulin-like growth factor I (IGF-I) is an important factor in coupling bone remodeling, activating both formation and resorption. Compared with the many studies on the role of IGF-I in bone formation, the information regarding its effects on bone resorption is limited and conflicting. The balance of the two peptides produced by osteoblasts, osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand (RANKL), is critical for the bone resorption process. Our study was designed to analyze the relationships of serum concentrations of IGF-I with OPG, RANKL, OPG/RANKL ratio as well as BMDs in healthy Chinese women.

METHODS

BMDs at lumbar spine and proximal femur in 504 pre- and postmenopausal women were measured by DXA. Serum levels of IGF-I, OPG and RANKL were also measured. Pearson's correlation and partial correlation analysis, ANOVA, covariance analysis and stepwise multiple regression analysis were used as appropriate.

RESULTS

Age was negatively correlated with serum levels of IGF-I (r = -0.702, p < 0.001). IGF-I was negatively correlated with OPG and OPG/RANKL ratio, but positively correlated with RANKL. The relationship between IGF-I and BMDs disappeared after adjustment for age. In postmenopausal women, IGF-I was lower in women with osteoporosis than in those with normal BMD (p = 0.056), but no differences were found among OPG, RANKL and OPG/RANKL ratio. Serum levels of OPG in the highest quintile of IGF-I were significantly lower than those in the lowest quintile of IGF-I, while no difference was found in RANKL. In the multiple regression analysis model, serum levels of IGF-I were the main determinants of the bone mass in Chinese women.

CONCLUSIONS

In conclusion, the relationship between decreasing IGF-I and BMDs in healthy Chinese women influenced by age, whereas the effect of IGF-I on bone remodeling (bone resorption) may be mediated by the OPG/RANKL system.

Spinal bone mineral density, IGF-1 and IGFBP-3 in children with cerebral palsy

BACKGROUND/AIMS

Childhood cerebral palsy (CP) is associated with osteopenia and the GH-IGF axis plays an important role in bone metabolism. We studied the relationship between spinal bone mineral density (BMD) and serum IGF-1 and IGFBP-3 in children with CP.

METHODS

Cross-sectional study of 30 children (9 F and 21 M, ages 4.5-15) with CP. Subjects underwent dual-energy x-ray absorptiometry scans (spinal BMD), blood tests (IGF-1, IGFBP-3, Ca, P, PTH, vitamin D, osteocalcin) and urine tests (N-telopeptide).

RESULTS

Spinal BMD was decreased in children with CP (average Z-score -2.14 +/- 1.08) compared to age- and gender-matched norms. IGF-1 and IGFBP-3 were also decreased compared to age-matched norms (average IGF-1 Z-score -0.74 +/- 1.2, average IGFBP-3 Z-score -0.68 +/- 1.2). All other blood and urine tests, including measures of calcium and vitamin D status, were normal. In 25 CP children with osteopenia (Z-score >-1), there was a trend towards correlation between spinal BMD Z-score and serum IGF-1 SDS score (r = 0.328, p = 0.09). IGFBP-3 Z-scores were available in 24 of these patients and had a statistically significant correlation with spinal BMD Z-score (r = 0.386, p = 0.05).

CONCLUSION

Osteopenia is common in children withCP and may be associated with lower IGF-1 and IGFBP-3 levels.

IGF-I receptor is required for the anabolic actions of parathyroid hormone on bone

We showed that the IGF-IR-null mutation in mature osteoblasts leads to less bone and decreased periosteal bone formation and impaired the stimulatory effects of PTH on osteoprogenitor cell proliferation and differentiation.

INTRODUCTION

This study was carried out to examine the role of IGF-I signaling in mediating the actions of PTH on bone.

MATERIALS AND METHODS

Three-month-old mice with an osteoblast-specific IGF-I receptor null mutation (IGF-IR OBKO) and their normal littermates were treated with vehicle or PTH (80 microg/kg body weight/d for 2 wk). Structural measurements of the proximal and midshaft of the tibia were made by microCT. Trabecular and cortical bone formation was measured by bone histomorphometry. Bone marrow stromal cells (BMSCs) were obtained to assess the effects of PTH on osteoprogenitor number and differentiation.

RESULTS

The fat-free weight of bone normalized to body weight (FFW/BW), bone volume (BV/TV), and cortical thickness (C.Th) in both proximal tibia and shaft were all less in the IGF-IR OBKO mice compared with controls. PTH decreased FFW/BW of the proximal tibia more substantially in controls than in IGF-IR OBKO mice. The increase in C.Th after PTH in the proximal tibia was comparable in both control and IGF-IR OBKO mice. Although trabecular and periosteal bone formation was markedly lower in the IGF-IR OBKO mice than in the control mice, endosteal bone formation was comparable in control and IGF-IR OBKO mice. PTH stimulated endosteal bone formation only in the control animals. Compared with BMSCs from control mice, BMSCs from IGF-IR OBKO mice showed equal alkaline phosphatase (ALP)(+) colonies on day 14, but fewer mineralized nodules on day 28. Administration of PTH increased the number of ALP(+) colonies and mineralized nodules on days 14 and 28 in BMSCs from control mice, but not in BMSCs from IGF-IR OBKO mice.

CONCLUSIONS

Our results indicate that the IGF-IR null mutation in mature osteoblasts leads to less bone and decreased bone formation, in part because of the requirement for the IGF-IR in mature osteoblasts to enable PTH to stimulate osteoprogenitor cell proliferation and differentiation.

Roles of epidermal growth factor family in the regulation of postnatal somatic growth

Ligands of the epidermal growth factor receptor (EGF-R), known to be important for supporting tissue development particularly in the gut and brain, have also been implicated in regulating postnatal somatic growth. Although optimal levels of both milk-borne and endogenous EGF-R ligands are important for supporting postnatal somatic growth through regulating gastrointestinal growth and maturation, supraphysiological levels of EGF-R ligands can cause retarded and disproportionate growth and alter body composition because they can increase growth of epithelial tissues but decrease masses of muscle, fat, and bone. Apart from their indirect roles in influencing growth, possibly via regulating levels of IGF-I and IGF binding proteins, EGF-R ligands can regulate bone growth and modeling directly because they can enhance proliferation but suppress maturation of growth plate chondrocytes (for building a calcified cartilage scaffold for bone deposition), stimulate proliferation but inhibit differentiation of osteoblasts (for depositing bone matrix), and promote formation and function of osteoclasts (for resorption of calcified cartilage or bone). In addition, EGF-like ligands, particularly amphiregulin, can be strongly regulated by PTH, an important regulatory factor in bone modeling and remodeling. Finally, EGF-R ligands can regulate bone homeostasis by regulating a pool of progenitor cells in the bone marrow through promoting proliferation but suppressing differentiation of bone marrow mesenchymal stem cells.

Influences of diabetes (db/db), obese (ob/ob) and dystrophic (dy/dy) genotype mutations on hind limb bone maturation: a morphometric, radiological and cytochemical indices analysis

The influences of single-gene missense mutations expressing diabetes (db/db), obese (ob/ob) or dystrophia (dy/dy) dysregulated metabolic syndromes on hind limb bone maturation and cytodevelopment in C57BL/KsJ mice were evaluated by radiological, macro- and cytomorphometric analysis of the resulting variances in os coxae, femur and tibia osteodevelopment indices relative to control parameters between 8 and 16 weeks of age. Associated with obesity and hyperglycaemic/hyperinsulinaemic states, both db/db and ob/ob mutants demonstrated significant suppression of hind limb maturation (length) and cytodensity indices relative to control growth parameters. By contrast, skeletal growth suppression induced by dy/dy mutation expression was associated with lean body mass and normoglycaemic/hypoinsulinaemic systemic endometabolic indices. In both db/db and ob/ob mutation syndromes, osteovascular, -interstitial and -cytolipidaemia were prominent cytochemical aberrations of the osteopaenic states relative to the dyslipidaemia/fibrodysplasia characteristic of dy/dy osteomaturation. Between 8 and 16 weeks of age, both ob/ob and db/db groups demonstrated extensive cortical interstitial (laminal) osteolipidaemia and suppressed cytodensities compared to control indices. These data demonstrate that the abnormal hyperglycaemic/hyperinsulinaemic endometabolic states associated with the expression of db/db and ob/ob genomutations promote extensive lipidaemia-induced osteopaenia, compromising hind limb osteomaturation and cytodensity indices, as compared to the hyperfibritic osteopaenia characteristic of dy/dy mutation syndromes. Recognized therapeutic modulation of the hypercytolipidaemic component of diabetes-obesity syndromes may prove to be effective towards amelioration of the deleterious influences of these expressed hyperglycaemic, dysregulated lipometabolic conditions on osteomaturation and cytodevelopment.

Growth hormone therapy improves bone mineral density in children with cerebral palsy: a preliminary pilot study

CONTEXT

Cerebral palsy is associated with osteopenia, increased fracture risk, short stature, and decreased muscle mass, whereas GH therapy is associated with increased bone mineral density (BMD) and linear growth and improvement in body composition.

OBJECTIVE

We conducted a pilot study to evaluate the effect of 18 months of GH therapy on spinal BMD, linear growth, biochemical markers, and functional measures in children with cerebral palsy.

DESIGN AND SETTING

The study was a randomized control trial, conducted from 2002-2005 at the University of California, Los Angeles, Orthopedic Hospital's Center for Cerebral Palsy.

PATIENTS

Patients included 12 males with cerebral palsy, ages 4.5-15.4 yr.

INTERVENTION

We compared 18 months of GH (50 microg daily) vs. no treatment.

PRIMARY OUTCOME MEASURES

Spinal BMD (dual-energy x-ray absorptiometry scan), height, growth factors, and bone markers were assessed.

RESULTS

Ten subjects (five in each group) completed the study. Pre- and post-average height z-scores were -1.47 +/- 0.23 and 0.8 +/- 0.2 (GH-treated group) vs. -1.35 +/- 1.26 and -1.36 +/- 1.27 (control group) (Delta SD score, 0.67 vs. -0.01; P = 0.01). Average change in spinal BMD z-score (Delta SD score corrected for height) was 1.169 +/- 0.614 vs. 0.24 +/- 0.25 in the treated and control groups, respectively (P = 0.03). Osteocalcin, IGF-I, and IGF-binding protein 3 levels increased during GH therapy. There was no change in quality of life scores as measured by the Pediatric Orthopedic Disability Inventory.

CONCLUSIONS

This small pilot study suggests that 18 months of GH therapy is associated with statistically significant improvement in spinal BMD and linear growth.

Damage and recovery of the bone growth mechanism in young rats following 5-fluorouracil acute chemotherapy

Chemotherapy-induced bone growth arrest and osteoporosis are significant problems in paediatric cancer patients, and yet how chemotherapy affects bone growth remains unclear. This study characterised development and resolution of damage caused by acute chemotherapy with antimetabolite 5-fluorouracil (5-FU) in young rats in the growth plate cartilage and metaphyseal bone, two important tissues responsible for bone lengthening. In metaphysis, 5-FU induced apoptosis among osteoblasts and preosteoblasts on days 1-2. In growth plate, chondrocyte apoptosis appeared on days 5-10. Interestingly, Bax was induced prior to apoptosis and Bcl-2 was upregulated during recovery. 5-FU also suppressed cell proliferation on days 1-2. While proliferation returned to normal by day 3 in metaphysis, it recovered partially on day 3, overshot on days 5-7 and normalised by day 10 in growth plate. Histologically, growth plate heights decreased by days 4-5 and returned normal by day 10. In metaphysis, primary spongiosa height was also reduced, mirroring changes in growth plate thickness. In metaphyseal secondary spongiosa, a reduced bone volume was observed on days 7-10 as there were fewer but more separated trabeculae. Starting from day 4, expression of some cartilage/bone matrix proteins and growth factors (TGF-beta1 and IGF-I) was increased. By day 14, cellular activity, histological structure and gene expression had returned normal in both tissues. Therefore, 5-FU chemotherapy affects bone growth directly by inducing apoptosis and inhibiting proliferation at growth plate cartilage and metaphyseal bone; after the acute damage, bone growth mechanism can recover, which is associated with upregulated expression of matrix proteins and growth factors.

Postnatally elevated levels of insulin-like growth factor (IGF)-II fail to rescue the dwarfism of IGF-I-deficient mice except kidney weight

This study tested whether elevated levels of IGF-II in the postnatal period can rescue the dwarfism in IGF-I-deficient mice. Heterozygous Igf1 mutant mice [I(+/-) II(wt)] were crossed with heterozygous Igf1 mutant, phosphoenolpyruvate carboxykinase promoter IGF-II transgenic mice [I(+/-) II(tg)], and [I(+/+) II(wt)], [I(+/+) II(tg)], [I(-/-) II(wt)], and [I(-/-) II(tg)] offspring were investigated. IGF-II levels were 11- and 6-fold higher in male and female [I(-/-) II(tg)] vs. [I(-/-) II(wt)] animals. Western ligand blot analysis revealed markedly reduced activities of 30- and 32-kDa IGF binding proteins (IGFBPs) (most likely IGFBP-1 and IGFBP-2) and the 39- to 43-kDa IGFBP-3 double band in serum from IGF-I-deficient mice. These binding proteins were partially restored by overexpression of IGF-II. Analysis of weight data from the early postnatal period until d 60 showed that, in the absence of IGF-I, elevated levels of IGF-II have no effect on body weight gain. A detailed analysis of body proportions, bone parameters, and organ weights of 60-d-old mice also failed to show effects of IGF-II with one important exception: in Igf1 mutant and also Igf1 intact male mice, IGF-II overexpression significantly increased absolute (+32.4 and +28.6%; P < 0.01) and relative kidney weights (+29.0 and +22.4%; P < 0.001). These changes in kidney weight were associated with reduced phosphorylation of p38 MAPK. In summary, our genetic model shows that substantial amounts of IGF-II in the circulation do not rescue the postnatal growth deficit of IGF-I-deficient mice but increase absolute and relative kidney weights of normal and IGF-I-deficient male mice, suggesting a gender-specific role of IGF-II for kidney growth.

Role of IGF-I signaling in regulating osteoclastogenesis

We showed that IGF-I deficiency impaired osteoclastogenesis directly and/or indirectly by altering the interaction between stromal/osteoblastic cells and osteoclast precursors, reducing RANKL and M-CSF production. These changes lead to impaired bone resorption, resulting in high BV/TV in IGF-I null mice.

INTRODUCTION

Although IGF-I has been clearly identified as an important growth factor in regulating osteoblast function, information regarding its role in osteoclastogenesis is limited. Our study was designed to analyze the role of IGF-I in modulating osteoclastogenesis using IGF-I knockout mice (IGF-I(-/-)).

MATERIALS AND METHODS

Trabecular bone volume (BV/TV), osteoclast number, and morphology of IGF-I(-/-) or wildtype mice (IGF-I(+/+)) were evaluated in vivo by histological analysis. Osteoclast precursors from these mice were cultured in the presence of RANKL and macrophage-colony stimulating factor (M-CSF) or co-cultured with stromal/osteoblastic cells from either genotype. Osteoclast formation was assessed by measuring the number of multinucleated TRACP+ cells and pit formation. The mRNA levels of osteoclast regulation markers were determined by quantitative RT-PCR.

RESULTS

In vivo, IGF-I(-/-) mice have higher BV/TV and fewer (76% of IGF-I(+/+)) and smaller osteoclasts with fewer nuclei. In vitro, in the presence of RANKL and M-CSF, osteoclast number (55% of IGF-I(+/+)) and resorptive area (30% of IGF-I(+/+)) in osteoclast precursor cultures from IGF-I(-/-) mice were significantly fewer and smaller than that from the IGF-I(+/+) mice. IGF-I (10 ng/ml) increased the size, number (2.6-fold), and function (resorptive area, 2.7-fold) of osteoclasts in cultures from IGF-I(+/+) mice, with weaker stimulation in cultures from IGF-I(-/-) mice. In co-cultures of IGF-I(-/-) osteoblasts with IGF-I(+/+) osteoclast precursors, or IGF-I(+/+) osteoblasts with IGF-I(-/-) osteoclast precursors, the number of osteoclasts formed was only 11% and 48%, respectively, of that from co-cultures of IGF-I(+/+) osteoblasts and IGF-I(+/+) osteoclast precursors. In the long bones from IGF-I(-/-) mice, mRNA levels of RANKL, RANK, M-CSF, and c-fms were 55%, 33%, 60%, and 35% of that from IGF-I(+/+) mice, respectively.

CONCLUSIONS

Our results indicate that IGF-I regulates osteoclastogenesis by promoting their differentiation. IGF-I is required for maintaining the normal interaction between the osteoblast and osteoclast to support osteoclastogenesis through its regulation of RANKL and RANK expression.

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.

Teriparatide increases bone formation in modeling and remodeling osteons and enhances IGF-II immunoreactivity in postmenopausal women with osteoporosis

Transiliac bone biopsies were obtained from 55 women treated with teriparatide or placebo for 12-24 months. We report direct evidence that modeling bone formation at quiescent surfaces was present only in teriparatide-treated patients and bone formation at remodeling sites was higher with teriparatide than placebo.

INTRODUCTION

Recombinant teriparatide [human PTH(1-34)], a bone formation agent for the treatment of osteoporosis when given once daily subcutaneously, increases biochemical markers of bone turnover and activation frequency in histomorphometry studies.

MATERIALS AND METHODS

We studied the mechanisms underlying this bone-forming action of teriparatide at the basic multicellular unit by the appearance of cement lines, a method used to directly classify surfaces as modeling or remodeling osteons, and by the immunolocalization of IGF-I and IGF-II. Transiliac bone biopsies were obtained from 55 postmenopausal women treated with teriparatide 20 or 40 microg or placebo for 12-24 months (median, 19.8 months) in the Fracture Prevention Trial.

RESULTS

A dose-dependent relationship was observed in modeling and mixed remodeling/modeling trabecular hemiosteons. Trabecular and endosteal hemiosteon mean wall thicknesses were significantly higher in both teriparatide groups than in placebo. There was a dose-dependent relationship in IGF-II immunoreactive staining at all bone envelopes studied. The greater local IGF-II presence after treatment with teriparatide may play a key role in stimulating bone formation.

CONCLUSIONS

Direct evidence is presented that 12-24 months of teriparatide treatment induced modeling bone formation at quiescent surfaces and resulted in greater bone formation at remodeling sites, relative to placebo.