Although it is well accepted that bone architecture adapts to withstand the loads placed on it, the manner in which this occurs in the immature growing skeleton is not fully understood. To investigate the possible mechanisms, we have compared morphometric differences between tibiae from chickens with fast and those with slow growth potential and also distinguished between the effects of genetic potential and growth rate on their impact on bone quality. Two different fast-growing (ad lib modern) strains, one additionally feed-restricted and one slow-growing (control) strain of chicken, were compared at 15 and 42 days of age. The ad lib modern strains had similar final body weights and were approximately twice the weight of the control and restricted-fed birds. Tibiae from the control and restricted birds had a higher ash content and lower porosity than the ad lib modern strain at 42 days. The porosity was a result of rapid primary osteon formation at the periosteal surface and incomplete infilling of the resultant canal by osteoblasts. When adjusted to average body weight of contemporaries, bones from the control strain and the restricted-fed modern birds were stiffer and at least as strong as those from the fast growing ad lib-fed birds. In conclusion, rapid bone deposition at the periosteal surface was associated with decreased mineralization, increased cortical porosity, and altered biomechanical properties. Our results also indicate that growth rate, and not genetic potential, of the fast growing birds was responsible for the rapid periosteal bone deposition.
Early osteoarthritis (OA) is poorly understood, but abnormal chondrocyte morphology might be important. We studied IL-1β and pericellular collagen type VI in morphologically normal and abnormal chondrocytes. In situ chondrocytes within explants from nondegenerate (grade 0/1) areas of human tibial plateaus (n = 21) were fluorescently labeled and visualized [2-photon laser scanning microscopy (2PLSM)]. Normal chondrocytes exhibited a “smooth” membrane surface, whereas abnormal cells were defined as demonstrating ≥1 cytoplasmic process. Abnormal chondrocytes were further classified by number and average length of cytoplasmic processes/cell. IL-1β or collagen type VI associated with single chondrocytes were visualized by fluorescence immuno-histochemistry and confocal laser scanning microscopy (CLSM). Fluorescence was quantified as the number of positive voxels (i.e., 3D pixels with fluorescence above baseline)/cell. IL-1β-associated fluorescence increased between normal and all abnormal cells in the superficial (99.7 ± 29.8 [11 (72)] vs. 784 ± 382 [15 (132)]; p = 0.04, positive voxels/cell) and deep zones (66.5 ± 29.4 [9 (64)] vs. 795 ± 224 [9 (56)]; p = 0.006). There was a correlation (r2 = 0.988) between the number of processes/cell (0–5) and IL-1β, and an increase particularly with short processes (≤5 µm; p = 0.022). Collagen type VI coverage and thickness decreased (p < 0.001 and p = 0.005, respectively) with development of processes. Abnormal chondrocytes in macroscopically nondegenerate cartilage demonstrated a marked increase in IL-1β and loss of pericellular type VI collagen, changes that could lead to cartilage degeneration. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1507–1514, 2010
SUMMARYPhotosynthesis and resistance to rust infection were studied in upper, uninfected leaves of broad bean, Vicia faba L., where the lower two leaves were infected with rust, Uromyces viciae-fabae (Pers.) Shroet. Following inoculation of the lower leaves, rates of net photosynthesis were significantiy increased in the upper, uninfected, fully-developed leaves and the young developing leaves, compared to controls. In contrast, photosynthesis was substantially reduced in the lower, rusted leaves. When '*CO,, was fed to the upper, uninfected leaves of rusted plants, there was a considerable increase in labeJIed assimilate in those leaves, compared to controls. In addition, there was substantial movement of labelled assimilate into lower, rusted leaves, into young, developing leaves and into roots. On the other hand, there was a substantial reduction in labelled assimilates moving into shoot apices.Upper, uninfected leaves of rusted beans exhibited Increased resistance to rust infection. Thus, the percentage leaf area covered with rust and the number of pustules per cm^ were reduced in these leaves compared to controls. This resistance to rust infection was greatest when the upper leaves were challenged 1 d after inoculation of the lower leaves with rust and decreased with increasing time after inoculation of the lower leaves. Young, developing leaves on rusted beans also exhibited increased resistance to rust infection. When photosynthesis in the upper leaves was reduced to near control values or well below control values by shading, resistance to rust infection in those leaves was also reduced, although not in proportion to the reduction in photosynthesis. It is suggested tbat the increased photosynthesis in upper, uninfected bean leaves probably facilitates maximum expression of resistance to infection in those leaves.
Bone strength is, in part, dependent on a mechanical input that regulates the (re)modelling of skeletal elements to an appropriate size and architecture to resist fracture during habitual use. The rate of longitudinal bone growth in juveniles can also affect fracture incidence in adulthood, suggesting an influence of growth rate on later bone quality. We have compared the effects of fast and slow growth on bone strength and architecture in the tibiotarsi of embryonic and juvenile birds. The loading-related biochemical responses (intracellular G6PD activity and NO release) to mechanical load were also determined. Further, we have analysed the proliferation and differentiation characteristics of primary tibiotarsal osteoblasts from fast and slow-growing strains. We found that bones from chicks with divergent growth rates display equal resistance to applied loads, but weight-correction revealed that the bones from juvenile fast growth birds are weaker, with reduced stiffness and lower resistance to fracture. Primary osteoblasts from slow-growing juvenile birds proliferated more rapidly and had lower alkaline phosphatase activity. Bones from fast-growing embryonic chicks display rapid radial expansion and incomplete osteonal infilling but, importantly, lack mechanical responsiveness. These findings are further evidence that the ability to respond to mechanical inputs is crucial to adapt skeletal architecture to generate a functionally appropriate bone structure and that fast embryonic and juvenile growth rates may predispose bone to particular architectures with increased fragility in the adult.
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