Endochondral bone growth, bone calcium accretion, and bone mineral density: how are they related?
ABSTRACT Endochondral bone growth in young growing mammals or adult mammals with persistent growth plates progresses from proliferation, maturation and hypertrophy of growth plate chondrocytes to mineralization of cartilaginous matrix to form an osseous tissue. This complex process is tightly regulated by a number of factors with different impacts, such as genetics, endocrine/paracrine factors [e.g., PTHrP, 1,25(OH)(2)D(3), IGF-1, FGFs, and prolactin], and nutritional status (e.g., dietary calcium and vitamin D). Despite a strong link between growth plate function and elongation of the long bone, little is known whether endochondral bone growth indeed determines bone calcium accretion, bone mineral density (BMD), and/or peak bone mass. Since the process ends with cartilaginous matrix calcification, an increase in endochondral bone growth typically leads to more calcium accretion in the primary spongiosa and thus higher BMD. However, in lactating rats with enhanced trabecular bone resorption, bone elongation is inversely correlated with BMD. Although BMD can be increased by factors that enhance endochondral bone growth, the endochondral bone growth itself is unlikely to be an important determinant of peak bone mass since it is strongly determined by genetics. Therefore, endochondral bone growth and bone elongation are associated with calcium accretion only in a particular subregion of the long bone, but do not necessarily predict BMD and peak bone mass.
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ABSTRACT: A correlation between obesity and bone metabolism is strongly assumed because adipocytes and osteoblasts originate from the same precursor cells and their differentiation is conversely regulated by the same factors. It is controversially discussed if obesity protects bone or leads to loss of bone mass. Thus, the aim of the present study was to investigate the influence of diet-induced mild obesity (11% increased body weight compared to control) on bone microstructure in mice. Four-week-old male C57BL/6J mice received a high-fat diet (HFD, 60% kcal from fat) and were analyzed by means of dual X-ray absorptiometry, histological methods, real-time RT-PCR, and transmission electron microscopy in comparison to control animals (10% kcal from fat). The cancellous bone mass, collagen 1α1 expression, amount of osteoid, and cohesion of cells via cell-to-cell contacts decreased in HFD mice whereas the bone mineral density and the amount of osteoblasts and osteoclasts were not modified. The amount of apoptotic osteocytes was increased in HFD mice in comparison to controls. We conclude that moderately increased body weight does not protect bone architecture from age-dependent degeneration. By contrast, bone microstructure is negatively affected and reduced maintenance of cell-cell contacts may be one of the underlying mechanisms.International Journal of Endocrinology 02/2014; 2014:318924. DOI:10.1155/2014/318924 · 1.52 Impact Factor
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ABSTRACT: In lactating rats, the endochondral bone growth is markedly enhanced, leading to the lengthening of long bone. This lactation-induced bone elongation could be abolished by a dopaminergic D2 receptor agonist bromocriptine, but how bromocriptine altered the expression of major chondroregulatory proteins in the growth plate cartilage was elusive. Here, we performed a quantitative immunohistochemical analysis to determine the expression of various peptides and transcription factors known to control the growth plate chondrocyte proliferation and differentiation [i.e., parathyroid hormone-related protein (PTHrP), PTHrP receptor, Indian hedgehog (Ihh), and runt-related transcription factor 2 (Runx2)], in bromocriptine-treated lactating rats. The results showed that bromocriptine markedly increased Ihh expression in hypertrophic chondrocytes during early and mid-lactation, while the expression of PTHrP receptor, but not its ligand PTHrP, was upregulated in the proliferative and hypertrophic zones during mid and late lactation. In contrast, the expression of Runx2, an important transcription factor for chondrocyte differentiation, was suppressed in the hypertrophic chondrocytes of bromocriptine-treated rats. In conclusion, bromocriptine increased Ihh and PTHrP receptor expressions and decreased Runx2 expression, which might, in turn, enhance chondrocyte proliferation and delay chondrocyte hypertrophy, thereby slowing down endochondral bone growth. This finding could explain how bromocriptine compromised the lactation-induced bone elongation.Molecular and Cellular Biochemistry 06/2013; DOI:10.1007/s11010-013-1702-y · 2.39 Impact Factor
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ABSTRACT: We studied the effect of metal mixture (MM), comprising of As, Cd and Pb, in developing female rat skeleton from gestation day-5 until postnatal day-60 (P-60). MM resulted in synergistic inhibition in viability and differentiation of osteoblasts in vitro, likely induced by reactive oxygen species. MM, administered at their most frequently occurring concentrations present in the ground-water of India, i.e. As: 0.38ppm, Pb: 0.22 ppm and Cd: 0.098 ppm or 10× of the ratio to developing rats exhibited a synergistic decrease in ex vivo mineralization of bone marrow stromal (osteoprogenitor) cells. MM group showed a dose-dependent attenuation in weight and axial lengths, and shortening of tibias at P-60. Furthermore, the growth plate was shortened, which was associated with shorter proliferative- and hypertrophic zones, decreased parathyroid hormone-related protein and Indian hedgehog expression in the chondrocytes, reduced primary- and secondary spongiosa, and hypomineralized osteoids - a major characteristic of osteomalacia. In addition, compared to the control, MM treated rats were clearly osteopenic based on BMD, micro-architecture, biomechanical strength, and particularly the biochemical profile, that suggested high turnover bone loss. Finally, in comparison to the control, the fracture healing ability of MM group was delayed and accompanied by inferior quality of the healed bone. Together, these data demonstrated that the mixture of As, Cd and Pb induced synergistic toxicity to developing skeleton thereby diminishing modeling-directed bone accrual, inducing osteopenia and dampening fracture healing.Toxicological Sciences 04/2013; 134(1). DOI:10.1093/toxsci/kft093 · 4.48 Impact Factor