The 'muscle-bone unit' during the pubertal growth spurt

Mechanostat theory postulates that developmental changes in bone strength are secondary to the increasing loads imposed by larger muscle forces. Therefore, the increase in muscle strength should precede the increase in bone strength. We tested this prediction using densitometric surrogate measures of muscle force (lean body mass, LBM) and bone strength (bone mineral content, BMC) in a study on 70 boys and 68 girls who were longitudinally examined during pubertal development. On the level of the total body, the peak in LBM accrual preceded the peak in BMC accretion by an average of 0.51 years in girls and by 0.36 years in boys. In the arms, the maximal increase in LBM was followed by arm peak BMC accrual after an interval of 0.71 years in girls and 0.63 years in boys. In the lower extremities, the maximal increase in LBM was followed by peak BMC accrual after an interval of 0.22 years in girls and 0.48 years in boys. A multiple regression model revealed that total body peak LBM velocity, but not peak height velocity and sex, was independently associated with total body peak BMC velocity (r(2) = 0.50; P < 0.001). Similarly, arm and leg peak LBM velocity, but not peak height velocity and sex, were independently associated with arm and leg peak BMC velocity, respectively (r(2) = 0.61 for arms, r(2) = 0.41 for legs; P < 0.001 in both cases). These results are compatible with the view that bone development is driven by muscle development, although the data do not exclude the hypothesis that the two processes are independently determined by genetic mechanisms. (C) 2004 Elsevier Inc. All rights reserved.

Relationship between bicarbonate retention and bone characteristics in broiler chickens

Determination of the bicarbonate retention factor (BRF) is an important step during development of the indicator amino acid oxidation technique for use in a new model. A series of 4-h oxidation experiments were performed to determine the BRF of broilers aged 7, 14, 21, 28, 35, and 42 d using 4 birds per age group. A priming dose of 1.2 mu Ci of (NaHCO3)-C-14, followed by eight half-hourly doses of 1 mu Ci of (NaHCO3)-C-14 were given orally to each of 4 birds per age. The percentage of 14 C dose expired by the bird at a steady state was measured. These birds, as well as 12 additional birds matched for age and BW, were killed, and femur bone mineral density was measured by quantitative computed tomography to determine the relationship between bone development and bicarbonate retention at each age. There was a correlation (r = 0.50; P < 0.05) between total cross-sectional femur bone mineral density and bicarbonate retention at each age. A prediction equation (Y = 6.95 x 10(-2) X - 3.51 x 10(5)X(2) + 27.58; P < 0.0001, R-2 = 0.79) where Y = bicarbonate retention and X = BW was generated to predict Y as a function of X. Bicarbonate retention values peaked at 28 d, during the stage of the most rapid bone deposition and the highest growth rate. A constant BRF was found from 1,900 to 2,700 g of BW of 35.15 +/- 1.095% (mean SEM). This retention factor will allow the accurate correction of oxidation of C-14-labeled substrates in broilers of different ages and BW in future indicator amino acid oxidation studies.

Sexual dimorphism of the femoral neck during the adolescent growth spurt: a structural analysis

Before puberty, there are only small sex differences in body shape and composition. During adolescence, sexual dimorphism in bone, lean, and fat mass increases, giving rise to the greater size and strength of the male skeleton. The question remains as to whether there are sex differences in bone strength or simply differences in anthropometric dimensions. To test this, we applied hip structural analysis (HSA) to derive strength and geometric indices of the femoral neck using bone densitometry scans (DXA) from a 6-year longitudinal study in Canadian children. Seventy boys and sixty-eight girls were assessed annually for 6 consecutive years. At the femoral neck, cross-sectional area (CSA, an index of axial strength), subperiosteal width (SPW), and section modulus (Z, an index of bending strength) were determined, and data were analyzed using a hierarchical (random effects) modeling approach. Biological age (BA) was defined as years from age at peak height velocity (PHV). When BA, stature, and total-body lean mass (TB lean) were controlled, boys had significantly higher Z than girls at all maturity levels (P < 0.05). Controlling height and TB lean for CSA demonstrated a significant independent sex by BA interaction effect (P < 0.05). That is, CSA was greater in boys before PHV but higher in girls after PHV The coefficients contributing the greatest proportion to the prediction of CSA, SPW, and Z were height and lean mass. Because the significant sex difference in Z was relatively small and close to the error of measurement, we questioned its biological significance. The sex difference in bending strength was therefore explained by anthropometric differences. In contrast to recent hypotheses, we conclude that the CSA-lean ratio does not imply altered mechanosensitivity in girls because bending dominates loading at the neck, and the Z-lean ratio remained similar between the sexes throughout adolescence. That is, despite the greater CSA in girls, the bone is strategically placed to resist bending; hence, the bones of girls and boys adapt to mechanical challenges in a similar way. (C) 2004 Elsevier Inc. All rights reserved.

Development and transplantation of a mineralized matrix formed by osteoblasts in vitro for bone regeneration

The use of extracellular matrix materials as scaffolds for the repair and regeneration of tissues is receiving increased attention. The current study was undertaken to test whether extracellular matrix formed by osteoblasts in vitro could be used as a scaffold for osteoblast transplantation and induce new bone formation in critical size osseous defects in vivo. Human osteoblasts derived from alveolar bone were cultured in six-well plates until confluent and then in mineralization media for a further period of 3 weeks to form an osteoblast-mineralized matrix complex. Histologically, at this time point a tissue structure with a connective tissue-like morphology was formed. Type I collagen was the major extracellular component present and appeared to determine the matrix macrostructure. Other bone-related proteins such as alkaline phosphatase (ALP), bone morphogenetic protein (BMP)-2 and -4, bone sialoprotein (BSP), osteopontin (OPN), and osteocalcin (OCN) also accumulated in the matrix. The osteoblasts embedded in this matrix expressed mRNAs for these bone-related proteins very strongly. Nodules of calcification were detected in the matrix and there was a correlation between calcification and the distribution of BSP and OPN. When this matrix was transplanted into a critical size bone defect in skulls of inummodeficient mice (SCID), new bone formation occurred. Furthermore, the cells inside the matrix survived and proliferated in the recipient sites, and were traceable by the human-specific Alu gene sequence using in situ hybridization. It was found that bone-forming cells differentiated from both transplanted human osteoblasts and activated endogenous mesenchymal cells. This study indicates that a mineralized matrix, formed by human osteoblasts in vitro, can be used as a scaffold for osteoblast transplantation, which subsequently can induce new bone formation.

Risk factors for development of delirium among oncology patients

To determine the occurrence of delirium in oncology inpatients and to identify and evaluate admission characteristics associated with the development of delirium during inpatient admission, a prospective observational study was conducted of H 3 patients with a total of 145 admissions with histological diagnosis of cancer admitted to the oncology unit over a period of ten weeks. At the point of inpatient admission, all patients were assessed for the presence of potential risk factors for development of delirium. During the index admission patients were assessed daily for the presence of delirium using the Confusion Assessment Method. Delirium was confirmed by clinician assessment. Delirium developed in 26 of 145 admissions (18%) and 32 episodes of delirium were recorded with 6 patients having 2 episodes of delirium during the index admission. Delirium occurred on average 3.3 days into the admission. The average duration of an episode of delirium was 2.1 day. Four patients with delirium (15%) died. All other cases of delirium were reversed. Factors significantly associated with development of delirium on multivariate analysis were: advanced age, cognitive impairment, low albumin level, bone metastases, and the presence of hematological malignancy. Hospital inpatient admission was significantly longer in delirium group (mean: 8.8 days vs 4.5 days in nondelirium group, P

Factors that affect bone mineral accrual in the adolescent growth spurt

The development of bone mass during the growing years is an important determinant for risk of osteoporosis in later life. Adequate dietary intake during the growth period may be critical in reaching bone growth potential. The Saskatchewan Bone Mineral Accrual Study (BMAS) is a longitudinal study of bone growth in Caucasian children. We have calculated the times of maximal peak bone mineral content (BMC) velocity to be 14.0 +/- 1.0 y in boys and 12.5 +/- 0.9 y in girls; bone growth is maximal similar to6 mo after peak height velocity. In the 2 y of peak skeletal growth, adolescents accumulate over 25% of adult bone. BMAS data may provide biological data on calcium requirements through application of calcium accrual values to factorial calculations of requirement. As well, our data are beginning to reveal how dietary patterns may influence attainment of bone mass during the adolescent growth spurt. Replacing milk intake by soft drinks appears to be detrimental to bone gain by girls, but not boys. Fruit and vegetable intake, providing alkalinity to bones and/or acting as a marker of a healthy diet, appears to influence BMC in adolescent girls, but not boys. The reason why these dietary factors appear to be more influential in girls than in boys may be that BMAS girls are consuming less than their requirement for calcium, while boys are above their threshold. Specific dietary and nutrient recommendations for adolescents are needed in order to ensure optimal bone growth and consolidation during this important life stage.

Osteopontin and related SIBLING glycoprotein genes are expressed by sertoli cells during mouse testis development

Matrix proteins play important roles in tissue morphogenesis. We have studied the expression of genes encoding the related SIBLING glycoproteins osteopontin (OPN), bone sialoprotein (BSP), and dentin matrix protein (DMP) during the development of male and female gonads during mouse embryogenesis. Opn mRNA was expressed specifically by Sertoli cells of the developing testis cords, in the mesonephric tubules of both sexes, and, transiently, in the Mullerian ducts of both sexes, as determined by whole-mount and section in situ hybridization. OPN protein was detected in the cytoplasm of Sertoli cells and luminal cells of the mesonephric tubules, with small amounts associated with the plasma membrane of germ cells. We found no defects in developing testes of Opn-/- mice using a range of cell type-specific markers, suggesting that other SIBLING proteins may function in testis development. Dmp and Bsp mRNA was also expressed in the developing testis cords, supporting the view that all three SIBLING proteins may contribute to testis differentiation. (c) 2005 Wiley-Liss, Inc.

Role of growth hormone receptor signaling in osteogenesis from murine bone marrow progenitor cells

Growth hormone (GH) regulates many of the factors responsible for controlling the development of bone marrow progenitor cells (BMPCs). The aim of this study was to elucidate the role of GH in osteogenic differentiation of BMPCs using GH receptor null mice (GHRKO). BMPCs from GHRKO and their wild-type (WT) littermates were quantified by flow cytometry and their osteogenic differentiation in vitro was determined by cell morphology, real-time RT-PCR, and biochemical analyses. We found that freshly harvested GHRKO marrow contains 3% CD34 (hernatopoietic lineage), 43.5% CD45 (monocyte/macrophage lineage), and 2.5% CD106 positive (CFU-F/BMPC) cells compared to 11.2%, 45%, and 3.4% positive cells for (WT) marrow cells, respectively. When cultured for 14 days under conditions suitable for CFU-F expansion, GHRKO marrow cells lost CD34 positivity, and were markedly reduced for CD45, but 3- to 4-fold higher for CD106. While WT marrow cells also lost CD34 expression, they maintained CD45 and increased CD106 levels by 16-fold. When BMPCs from GHRKO mice were cultured under osteogenic conditions, they failed to elongate, in contrast to WT cells. Furthermore, GHRKO cultures expressed less alkaline phosphatase, contained less mineralized calcium, and displayed lower osteocalcin expression than WT cells. However, GHRKO cells displayed similar or higher expression of cbfa-1, collagen 1, and osteopontin mRNA compared to WT. In conclusion, we show that GH has an effect on the proportions of hematopoietic and mesenchymal progenitor cells in the bone marrow, and that GH is essential for both the induction and later progression of osteogenesis. (c) 2005 Elsevier Inc. All rights reserved.

Post-hatching growth and development of the pectoral and pelvic limbs in the black noddy, Anous minutus

The black tern (Anous minutus) uses a semi-precocial growth strategy. Terrestrial locomotor capacity occurs soon after hatching, but pectoral limb development is delayed and flight is not possible until about post-hatching day 50. A growth series (hatchlings to fledglings) was used to explore how limb musculoskeletal development varied with body mass. In the pelvic limb, bone lengths scaled isometrically or with negative allometry. Gastrocnemius muscle mass and the failure load and stiffness of the tibiotarsus scaled isometrically. In the pectoral limb, pectoralis and supracoracoideus muscle masses increased with strong positive allometry that was mirrored by increases in wing bone strength and stiffness. Bending strength (σult) and modulus (E) remained fairly constant throughout development to fledging for all limb bones. The moment of inertia (I) scaled with negative allometry for the tibiotarsus and with strong positive allometry in the wing bones. Differences in σult and E of the tibiotarsus between pre-fledged chicks and adults was due, primarily, to increases in bone density rather than increases in the moment of inertia of the skeletal elements, whereas σult of wing bones was a function of increases in both bone density and I. Early development of functional pelvic limbs in tree-nesting birds is relatively unusual, and presumably reflects a familial trait that does not appear to compromise breeding success in this species.

Knockdown of zebrafish crim1 results in a bent tail phenotype with defects in somite and vascular development

The Crim1 gene encodes a transmembrane protein containing six cysteine-rich repeats similar to those found in the BMP antagonist, chordin (chd). To investigate its physiological role, zebrafish crim1 was cloned and shown to be both maternally and zygotically expressed during zebrafish development in sites including the vasculature, intermediate cell mass. notochord, and otic vesicle. Bent or hooked tails with U-shaped somites were observed in 85% of morphants from 12 hpf. This was accompanied by a loss of muscle pioneer cells. While morpholino knockdown of crim1 showed some evidence of ventralisation, including expansion of the intermediate cell mass (ICM), reduction in head size bent tails and disruption to the somites and notochord, this did not mimic the classically ventralised phenotype, as assessed by the pattern of expression of the dorsal markers chordin, otx2 and the ventral markers eve1, pax2.1, tall and gata1 between 75% epiboly and six-somites. From 24 hpf, morphants displayed an expansion of the ventral mesoderm-derived ICM, as evidenced by expansion of tall. Imo2 and crim1 itself. Analysis of the crim1 morphant phenotype in Tg(fli:EGFP) fish showed a clear reduction in the endothelial cells forming the intersegmental vessels and a loss of the dorsal longitudinal anastomotic vessel (DLAV). Hence, the primary role of zebrafish crim1 is likely to be the regulation of somitic and vascular development. (c) 2006 Elsevier Ireland Ltd. All rights reserved.

The JNK are important for development and survival of macrophages

We report in, this study that activation of the JNK by the growth factor, CSF-1 is critical for macrophage development, proliferation, and survival. Inhibition of JNK with two distinct classes of inhibitors, the pharmacological agent SP600125, or the peptide D-JNKI1 resulted in cell cycle inhibition with an arrest at the G(2)/M transition and subsequent apoptosis. JNK inhibition resulted in decreased expression of CSF-1R (c-fins) and Bcl-x(L) mRNA in mature macrophages and repressed CSF-1-dependent differentiation of bone marrow cells to macrophages. Macrophage sensitivity to JNK inhibitors may be linked to phosphorylation of the PU.1 transcription factor. Inhibition of JNK disrupted PUA binding to an element in the c-fins gene promoter and decreased promoter activity. Promoter activity could be restored by overexpression of PUA. A comparison of expression profiles of macrophages with 22 other tissue types showed that genes that signal JNK activation downstream of tyrosine kinase receptors, such as focal adhesion kinase, Nck-interacting kinase, and Rac1 and scaffold proteins are highly expressed in macrophages relative to other tissues. This pattern of expression may underlie the novel role of JNK in macrophages.

What does the animal model teach us about the effects of physical activity on growing bone?

Experiments to design physical activity programs that optimize their osteogenic potential are difficult to accomplish in humans. The aim of this article is to review the contributions that animal studies have made to knowledge of the loading conditions that are osteogenic to the skeleton during growth, as well as to consider to what extent animal studies fail to provide valid models of physical activity and skeletal maturation. Controlled loading studies demonstrate that static loads are ineffective, and that bone formation is threshold driven and dependent on strain rate, amplitude, and duration of loading. Only a few loading cycles per session are required, and distributed bouts are more osteogenic than sessions of long duration. Finally, animal models fail to inform us of the most appropriate ways to account for the variations in biological maturation that occur in our studies of children and adolescents, requiring the use of techniques for studying human growth and development.