Metatarsal Growth Research Articles

Stanniocalcin 1 Acts as a Paracrine Regulator of Growth Plate Chondrogenesis

During embryogenesis, the expression of mammalian stanniocalcin (STC1) in the appendicular skeleton suggests its involvement in the regulation of longitudinal bone growth. Such a role is further supported by the presence of dwarfism in mice overexpressing STC1. Yet, the STC 1 inhibitory effect on growth may be related to both postnatal metabolic abnormalities and prenatal defective bone formation. In our study, we used an organ culture system to evaluate the effects of STC on growth plate chondrogenesis, which is the primary determinant of longitudinal bone growth. Fetal rat metatarsal bones were cultured in the presence of recombinant human STC (rhSTC). After 3 days, rhSTC suppressed metatarsal growth, growth plate chondrocyte proliferation and hypertrophy/differentiation, and extracellular matrix synthesis. In addition, rhSTC increased the number of apoptotic chondrocytes in the growth plate. In cultured chondrocytes, rhSTC increased phosphate uptake, reduced chondrocyte proliferation and matrix synthesis, and induced apoptosis. All these effects were reversed by culturing chondrocytes with rhSTC and phosphonoformic acid, an inhibitor of phosphate transport. The rhSTC-mediated inhibition of metatarsal growth and growth plate chondrocyte proliferation and hypertrophy/differentiation was abolished by culturing metatarsals with rhSTC and phosphonoformic acid. Taken together, our findings indicate that STC1 inhibits longitudinal bone growth directly at the growth plate. Such growth inhibition, likely mediated by an increased chondrocyte phosphate uptake, results from suppressed chondrocyte proliferation, hypertrophy/differentiation, and matrix synthesis and by increased apoptosis. Last, the expression of both STC1 and its binding site in the growth plate would support an autocrine/paracrine role for this growth factor in the regulation of growth plate chondrogenesis.

Role of Cholesterol in the Regulation of Growth Plate Chondrogenesis and Longitudinal Bone Growth

Inborn errors of cholesterol synthesis are associated with multiple systemic abnormalities, including skeletal malformations. The regulatory role of cholesterol during embryogenesis appears to be mediated by Shh, a signaling molecule in which activity depends on molecular events involving cholesterol. Based on this evidence, we hypothesized that cholesterol, by modifying the activity of Ihh (another of the Hedgehog family proteins) in the growth plate, regulates longitudinal bone growth. To test this hypothesis, we treated rats with AY 9944, an inhibitor of the final reaction of cholesterol synthesis. After 3 weeks, AY 9944 reduced the cumulative growth, tibial growth, and the tibial growth plate height of the rats. To determine whether cholesterol deficiency affects bone growth directly at the growth plate, we then cultured fetal rat metatarsal bones in the presence of AY 9944. After 4 days, AY 9944 suppressed metatarsal growth and growth plate chondrocyte proliferation and hypertrophy. The inhibitory effect on chondrocyte hypertrophy was confirmed by the AY 9944-mediated decreased expression of collagen X. Lastly, AY 9944 decreased the expression of Ihh in the metatarsal growth plate. We conclude that reduced cholesterol synthesis in the growth plate, possibly by altering the normal activity of Ihh, results in suppressed longitudinal bone growth and growth plate chondrogenesis.

PROPOSAL FOR THE EFFECT OF CHONDROCYTE VOLUME ON THE MINERALIZATION RATE

Mineralization of the cartilage matrix in embryonic long bones and growth plates is preceded by hypertrophy of chondrocytes. We hypothesize that the swollen hypertrophic cells exert pressure on the matrix, and that this pressure plays a role in the cartilage mineralization process. For this study, we asked the following questions. First, does the ratio of cell volume to matrix volume (CV/MV) increase from the proliferation to the hypertrophic zone in embryonic long bones? Second, is there a correlation between cell-volume increase and the mineralization rate in embryonic and postnatal long bones? The CV/MV ratios in the proliferation and hypertrophic zones in embryonic mouse metatarsals at 17 days of gestational age were determined using morphometric analyses. Confocal laser scanning microscopy was used to determine chondrocyte volumes. Cell volumes in the proliferation and hypertrophic zones of embryonic mouse metatarsals at 17 days of gestational age were compared to the ones in the metatarsal growth plates of nine-day-old mice. The mineralization rate was determined using photographs at 24-hour intervals. The CV/MV increased significantly from the proliferation to the hypertrophic zone, from 1.30±0.15 (mean ± standard deviation) to 1.80±0.18. The relative increase in cell volume from the proliferation to the hypertrophic zone was 1.6 for embryonic cells, i.e. from 370±101 mm3 to 610±107 mm3, and 2.8 for postnatal cells, i.e. from 280±41 mm3 to 786±155 mm3(p<0.05). The mineralization rate was 295±47mm/24 hours and 382±149 mm/24 hours for embryonic and postnatal metatarsals, respectively (p<0.05). The finding that chondrocyte volume increase is accompanied by a higher mineralization rate supports the hypothesis that cell hypertrophy plays an important role during the mineralization process.

Proposal for the Effect of Chondrocyte Volume on the Mineralization Rate

Mineralization of the cartilage matrix in embryonic long bones and growth plates is preceded by hypertrophy of chondrocytes. We hypothesize that the swollen hypertrophic cells exert pressure on the matrix, and that this pressure plays a role in the cartilage mineralization process. For this study, we asked the following questions. First, does the ratio of cell volume to matrix volume (CV/MV) increase from the proliferation to the hypertrophic zone in embryonic long bones? Second, is there a correlation between cell-volume increase and the mineralization rate in embryonic and postnatal long bones? The CV/MV ratios in the proliferation and hypertrophic zones in embryonic mouse metatarsals at 17 days of gestational age were determined using morphometric analyses. Confocal laser scanning microscopy was used to determine chondrocyte volumes. Cell volumes in the proliferation and hypertrophic zones of embryonic mouse metatarsals at 17 days of gestational age were compared to the ones in the metatarsal growth plates of nine-day-old mice. The mineralization rate was determined using photographs at 24-hour intervals. The CV/MV increased significantly from the proliferation to the hypertrophic zone, from 1.30±0.15 (mean ± standard deviation) to 1.80±0.18. The relative increase in cell volume from the proliferation to the hypertrophic zone was 1.6 for embryonic cells, i.e. from 370±101 mm3 to 610±107 mm3, and 2.8 for postnatal cells, i.e. from 280±41 mm3 to 786±155 mm3(p<0.05). The mineralization rate was 295±47mm/24 hours and 382±149 mm/24 hours for embryonic and postnatal metatarsals, respectively (p<0.05). The finding that chondrocyte volume increase is accompanied by a higher mineralization rate supports the hypothesis that cell hypertrophy plays an important role during the mineralization process.

Metatarsal growth during the second trimester: a predictor of gestational age?

Metatarsal growth was studied in 780 human fetal metatarsal bones, crown-rump length ranging from 120 to 260 mm and gestational age ranging from 14 to 23 wk postconception. Total length, diaphyseal length and diameter were measured and statistical analysis performed. Means and standard deviations for each measurement were calculated at 1 wk intervals. These data were correlated with crown-rump length and gestational age and an equation was constructed in an attempt to predict gestational age.

Growth of the human metatarsal bones in the fetal period (13-24 weeks postconception): a quantitative study.

We studied metatarsal growth in 600 metatarsal bones (60 pairs of feet) taken from 60 human fetuses (35 males and 25 females) ranging in age from 13 to 24 weeks postconception. The data obtained for the total length (TL) and for the ossified metatarsal length (OML) were correlated to fetal crown-rump length (C-R). The ossified metatarsal length presented a growth rate greater than the total length growth rate. There was no statistical difference between either the right and left metatarsals or males and females in total length and ossified metatarsal length growth during the period studied. We believe that metatarsal growth curves could be used to monitor fetal foot growth.

Cell proliferation within the growth plate of long bones assessed by bromodeoxyuridine uptake and its relationship to glucose 6-phosphate dehydrogenase activity

Bromodeoxyuridine (BrdUrd) was incorporated into the DNA of proliferating chondrocytes of the tibiae and metatarsal growth plate of rats of differing ages. Immunodetection of the incorporated BrdUrd was achieved using a monoclonal antibody to BrdUrd and indirect immunofluorescence procedures. The labelling index within the growth plate was found to decrease with advancing age in the tibia and metatarsal. Glucose 6-phosphate dehydrogenase (G6PD) activity appeared to be related to chondrocyte proliferation as a significant correlation was observed between G6PD activity and the labelling index of the tibial chondrocytes. The results of this study indicate that G6PD activity is a possible marker for cartilage growth and also that the BrdUrd technique has several advantages over the conventional autoradiographic methods for the assessment of cell replication.

Selected skeletal morphology and pathology of moose from the Kenai Peninsula, Alaska, and Isle Royale, Michigan

Age-specific parameters of growth and incidence of skeletal pathology were determined for moose populations at Kenai, Alaska, and Isle Royale, Michigan, primarily from skeletal remains of wolf-killed animals. Growth patterns, determined from the metatarsus, were similar for the two populations, with cessation of growth after the third summer. Kenai moose were consistently larger than Isle Royale moose after the first summer, with an average asymptote for metatarsal growth 3% greater. Size of Isle Royale calves was inversely correlated with winter severity prior to birth. The incidence of debilitating arthritis and periodontal disease increased with age, with a similar age of onset among female moose from both populations. Coxofemoral arthritis (degenerative joint disease) occurred more often among old (&gt; 10 years) female moose from Isle Royale than from Kenai, probably contributing to a generally shorter life span. Periodontal disease occurred at a similar rate in both populations, despite a far greater rate of incisiform tooth wear in Kenai moose. The study furnished base-line data for a determination of trends in population quality and physical condition.

Radiology and histopathology of lameness in young cattle with secondary copper deficiency

The radiographical and histological lesions found in a natural outbreak of lameness in cattle, suffering form copper deficiency associated with high dietary molybdenum and sulphate, are described. Consistent lesions in the distal metacarpal or metatarsal growth plates were characterized radiographically by a widening of the physis with marked irregularity and fragmentation of the metaphysis. Microscopically, focal widenings of the growth plate consisted of tongues of uncalcified cartilage with delayed or impaired provisional calcification in the presence of active osteoblasts. It was concluded that molybdenum-induced copper deficiency in cattle is possibly not the same syndrome as primary copper deficiency of dogs, pigs and sheep, which is characterized by decreased osteoblast activity and osteoporosis.