Targeted ablation of the 25-hydroxyvitamin D 1alpha -hydroxylase enzyme: evidence for skeletal, reproductive, and immune dysfunction.
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The active form of vitamin D, 1alpha,25-dihydroxyvitamin D [1alpha,25(OH)2D], is synthesized from its precursor 25 hydroxyvitamin D [25(OH)D] via the catalytic action of the 25(OH)D-1alpha-hydroxylase [1alpha(OH)ase] enzyme. Many roles in cell growth and differentiation have been attributed to 1,25(OH)2D, including a central role in calcium homeostasis and skeletal metabolism. To investigate the in vivo functions of 1,25(OH)2D and the molecular basis of its actions, we developed a mouse model deficient in 1alpha(OH)ase by targeted ablation of the hormone-binding and heme-binding domains of the 1alpha(OH)ase gene. After weaning, mice developed hypocalcemia, secondary hyperparathyroidism, retarded growth, and the skeletal abnormalities characteristic of rickets. These abnormalities are similar to those described in humans with the genetic disorder vitamin D dependent rickets type I [VDDR-I; also known as pseudovitamin D-deficiency rickets (PDDR)]. Altered non-collagenous matrix protein expression and reduced numbers of osteoclasts were also observed in bone. Female mutant mice were infertile and exhibited uterine hypoplasia and absent corpora lutea. Furthermore, histologically enlarged lymph nodes in the vicinity of the thyroid gland and a reduction in CD4- and CD8-positive peripheral T lymphocytes were observed. Alopecia, reported in vitamin D receptor (VDR)-deficient mice and in humans with VDDR-II, was not seen. The findings establish a critical role for the 1alpha(OH)ase enzyme in mineral and skeletal homeostasis as well as in female reproduction and also point to an important role in regulating immune function. (+info)
Osteoclast-like cells in an in vitro model of bone destruction by rheumatoid synovium.
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OBJECTIVE: Osteoclasts may be involved in the process of rheumatoid bone destruction. To test this hypothesis, we developed an in vitro model of bone destruction by osteoclast-like cells derived from cultured rheumatoid synovial tissue without using any inducers. METHODS: Synovial tissues were obtained from rheumatoid arthritis and osteoarthritis patients and tissue pieces of about 2 mm(3) that contained synovial lining were cultured. Multinucleated cells derived from cultured synovial tissues were studied cytochemically and morphologically for osteoclast-specific markers. RESULTS: Fibroblast-like and macrophage-like cells from the tissue pieces proliferated in the coexistence of lymphocytes. After 14 days of culture, multinucleated cells with tartrate-resistant acid phosphatase activity appeared. These cells expressed vacuolar H(+)-ATPase, the vitronectin receptor and cathepsin K. Although binding of (125)I-labelled salmon calcitonin was very low, the cells contained ringed structures of F-actin and showed strong bone-resorbing activity on ivory slices. Proliferation of macrophage-like cells and formation of multinucleated cells continued during 6 months of culture in the presence of fibroblast-like cells. The bone-resorbing activity of multinucleated cells derived from rheumatoid synovial tissue was much higher than that of cells from osteoarthritis synovial tissue, and was related to the disease activity of rheumatoid arthritis. CONCLUSION: Our culture system reproduced in vitro the process of bone destruction by rheumatoid synovium, including the proliferation and fusion of precursor cells, polarization, activation and bone tissue resorption. This system may provide a tool for understanding the mechanisms of bone destruction in rheumatoid arthritis and for the development of new therapies to prevent bone destruction. (+info)
Radiographic signs of bone destruction in the arthritic temporomandibular joint with special reference to markers of disease activity. A longitudinal study.
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OBJECTIVE: To investigate the progression of radiographic changes of the temporomandibular joint (TMJ) with reference to plasma levels of interleukin-1beta (IL-1beta), C-reactive protein (CRP) and disease duration. METHODS: Twenty-one patients with chronic inflammatory joint disease and TMJ involvement were included. Individualized tomography of the TMJ was performed twice with an interval of at least 12 months. Blood samples were analysed for IL-1beta and CRP. RESULTS: Significant progression of the overall grade of radiographic changes occurred during the observation period, whereas erosions showed great interindividual variability. Progression of TMJ bone loss was correlated to raised levels of CRP and, in patients with a diagnosis of rheumatoid arthritis, or with shorter duration, also to plasma IL-1beta. CONCLUSION: Progression of overall grade of radiographic changes in the TMJ occurs in patients with chronic inflammatory joint disease. Raised levels of serum CRP are associated with progression of TMJ bone loss. (+info)
The effects of intense exercise on the female reproductive system.
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Women have become increasingly physically active in recent decades. While exercise provides substantial health benefits, intensive exercise is also associated with a unique set of risks for the female athlete. Hypothalamic dysfunction associated with strenuous exercise, and the resulting disturbance of GnRH pulsatility, can result in delayed menarche and disruption of menstrual cyclicity. Specific mechanisms triggering reproductive dysfunction may vary across athletic disciplines. An energy drain incurred by women whose energy expenditure exceeds dietary energy intake appears to be the primary factor effecting GnRH suppression in athletes engaged in sports emphasizing leanness; nutritional restriction may be an important causal factor in the hypoestrogenism observed in these athletes. A distinct hormonal profile characterized by hyperandrogenism rather than hypoestrogenism is associated with athletes engaged in sports emphasizing strength over leanness. Complications associated with suppression of GnRH include infertility and compromised bone density. Failure to attain peak bone mass and bone loss predispose hypoestrogenic athletes to osteopenia and osteoporosis. Metabolic aberrations associated with nutritional insult may be the primary factors effecting low bone density in hypoestrogenic athletes, thus diagnosis should include careful screening for abnormal eating behavior. Increasing caloric intake to offset high energy demand may be sufficient to reverse menstrual dysfunction and stimulate bone accretion. Treatment with exogenous estrogen may help to curb further bone loss in the hypoestrogenic amenorrheic athlete, but may not be sufficient to stimulate bone growth. Treatment aimed at correcting metabolic abnormalities may in fact prove more effective than that aimed at correcting estrogen deficiencies. (+info)
Cellular and molecular interactions between immune system and bone.
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Functional interdependence between immune and bone systems is reflected in a number of regulatory molecules acting on the cells of both systems and common precursors for bone and immune cells. Therefore, the disturbances of the immune system may affect bone metabolism, and vice versa. This review addresses the roles of two major immune cell populations, T and B lymphocytes, in the regulation of bone metabolism. Experimental models and human diseases demonstrated that T lymphocytes may produce many bone cell regulatory cytokines, including two essential stimulators of osteoclastogenesis: receptor for activation of nuclear factor kappa b (NF-kappa B) (RANK) ligand (RANKL) and macrophage colony-stimulating factor. The effect of T lymphocytes on osteoclastogenesis may be both stimulatory and inhibitory, and depends on the activation stage and pattern of cytokine production. We showed that acute removal of T lymphocytes stimulated osteoclast differentiation in vitro and enhanced new cartilage and bone formation at non-osseous sites in vivo. B lymphocytes may be even more closely related to bone cells, as B lymphopoiesis requires an intimate contact with osteoblastic/stromal cells, and estrogens, powerful regulators of bone mass, are also involved in the differentiation of the B lymphocyte lineage. Also, B lymphocyte progenitors may give rise to functional osteoclasts. Both B and T lymphocytes may act through the RANKL/RANK/osteoprotegerin cytokine system, which has been independently discovered within immune and bone systems. These cytokines have crucial roles in the development and function of osteoclasts, dendritic cells, and T and B lymphocytes, as well as in the thymus and lymph node organogenesis. The cytokines produced by immune cells may affect bone cell function and vice versa, but the full complexity of these interactions awaits further investigation. (+info)
Renal imaging in 99m-Tc-polyphosphate bone scanning: focal increased renal uptake in metastic carcinoma of lung.
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A small group of patients with normal intravenous urograms showed focal increased renal uptake, usually unilateral, of 99m-Tc-polyphosphate. All had documented metastatic squamous cell carcinoma of the lung. The combination of focal increased renal 99m-Tc-polyphosphate uptake with normal intravenous urogram occurred in no other patients. (+info)
Growth hormone and gonadotropin-releasing hormone analog therapy in haploinsufficiency of SHOX.
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We report on GH (0.5 IU or 0.17 mg/kg/week) and GnRH analog (GnRHa, 60 microg/kg, every 4 weeks) therapy in SHOX haploinsufficiency. Case 1 was a 46,XY boy with microdeletion of the Y chromosomal pseudoautosomal region. At 7 years of age, he exhibited short stature (-3.9 SD) with a reduced growth rate (3.8 cm/year), short 4th metacarpals, and mild Madelung deformity. GH therapy resulted in a marked increase in height velocity (10.7 cm/year in the first year). Case 2 was a 46,XX girl with a heterozygous nonsense mutation of SHOX (C674T). At 6 years of age, she presented with short stature (-3.3 SD) with a low height velocity (4.0 cm/year). GH therapy caused a moderate increase in height velocity (6.6 cm/year in the first year and 6.0 cm/year in the second year) before puberty. Because of breast development, she received GnRHa from 9 8/12 years of age. At 10 10/12 years of age, she had mild shortening and borderline curvature of radius. Case 3 was a girl with a 46,X,der(X)t(X;2)(p22.3;p21) karyotype. She was treated with GH from 6 to 14 years of age, and also with GnRHa from 12 to 15 years of age. Her height remained around mean -4 SD, with no discernible alteration of height velocity. At 17 years of age, she had short stature (-4.1 SD), bilateral cubitus valgus, Madelung deformity, and full breast development. The results suggest that GH therapy may have variable statural effects in SHOX haploinsufficiency as in most disorders including Turner syndrome, and that GnRHa therapy after pubertal entry may be insufficient to prevent the development of skeletal lesions such as Madelung deformity. (+info)
Keratin particle-induced osteolysis: a mouse model of inflammatory bone remodeling related to cholesteatoma.
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We implanted keratin and poly(methyl methacrylate) (PMMA) particles to the surface of mouse calvariae to produce a quantitative, localized, inflammatory bone remodeling similar to that seen in cholesteatoma. Both types of particles resulted in increased osteoclast density compared with controls. Osteoclasts infiltrated from marrow and vascular spaces and were active at the periphery of these spaces leading to significant bone remodeling, as demonstrated by the incorporation of bone-labelling fluorophores. Osteoclasts were rarely found on the surface of the calvariae, and mineral apposition rate at the ventral surface was not altered in keratin-implanted animals compared with nonoperated controls. While not useful for the study of the root cause of cholesteatoma, this model will allow the study ofpathologic bone remodeling related to cholesteatoma in a genetically defined animal. (+info)