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D Swolin-Eide and C Ohlsson

High levels of glucocorticoids are believed to alter bone remodeling by decreasing bone formation and increasing bone resorption. It has been suggested that different cytokines, like interleukin-6 (IL-6) and interleukin-1 (IL-1), are involved in bone resorption by activating immature osteoclasts, and some studies indicate that IL-6 promotes bone formation by a mitogenic effect on osteoblasts. The aim of the present investigation was to study whether cortisol regulates the expression of IL-6 and IL-1 beta in human osteoblast-like cells. A high dose of cortisol (10(-7)M) decreased, as expected, the C-terminal propeptide of type I collagen released into the culture medium. The IL-6 mRNA levels and IL-6 protein released into the culture medium were also decreased by cortisol in a dose-dependent manner. The maximum effect was seen at 1 microM cortisol (mRNA 23.1 +/- 7.9% of control culture; protein 28.2 +/- 8.3% of control culture). The decrease in IL-6 mRNA levels was apparent 4 h after the addition of cortisol and was still present 20 h later. The decrease in IL-6 protein released into the culture medium was seen 20 h later than the decrease in IL-6 mRNA levels. The production of IL-1 beta protein released into the culture medium was decreased in a dose-dependent manner after the addition of cortisol with a maximum effect at 1 microM. The effect of cortisol on IL-1 beta protein released into the culture medium was seen 16 h after the addition of cortisol. To summarize, cortisol decreases the expression of IL-6 as well as IL-1 beta in human osteoblast-like cells.

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D Swolin-Eide, A Nilsson, and C Ohlsson

It is well known that high levels of glucocorticoids cause osteoporosis and that physiologic levels of growth hormone (GH) are required for normal bone remodeling. It has been suggested that glucocorticoids regulate GH-responses via the regulation of GH-receptor expression. The aim of the present study was to investigate whether cortisol plays a role in the regulation of GH-receptor expression in cultured human osteoblasts. The effect of serum starvation and cortisol on GH-receptor expression was tested in human osteoblast (hOB)-like cells. Serum starvation for 24 h resulted in an increase in GH-receptor mRNA levels (90 +/- 1% over control culture). Cortisol increased GH-receptor mRNA levels in a dose-dependent manner with a maximal effect at 10(-6)M. The stimulating effect of cortisol on GH-receptor mRNA levels was time-dependent, reaching a peak 12 h after the addition of cortisol (126 +/- 29% over control culture) and remaining up to 12 h later. The increase in GH-receptor mRNA levels was accompanied by an increase in 125I-GH binding which reached a maximum at 24 h (196 +/- 87% over control culture). In conclusion, glucocorticoids increase GH-receptor expression in hOB-like cells. Further studies are needed to clarify whether glucocorticoid-induced regulation of the GH-receptor is important in human bone physiology.

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D Swolin, C Brantsing, G Matejka, and C Ohlsson

Abstract

Excess levels of glucocorticoids are known to cause osteoporosis. It is speculated that the effect of glucocorticoids could be mediated via regulation of IGF-I. The aims of the present study were to detect and quantify the expression of IGF-I and/or IGF-II mRNA transcripts in human osteoblast-like cells and to investigate whether glucocorticoids regulate the expression of IGF-I mRNA transcripts in human osteoblast-like cells.

Cultures of human osteoblast-like cells from trabecular bone were established. The IGF-IA and IGF-IB transcripts were detected in human osteoblast-like cells from seven out of nine patients while the IGF-II transcript was detected in human osteoblast-like cells from eight out of nine patients, as determined by RT-PCR assays. Human osteoblast-like cells, as well as human muscle tissue, expressed approximately 1/10 of the IGF-I mRNA levels found in liver, as determined by RNase protection solution hybridization assay. The IGF-I mRNA levels did not decrease with age in the human osteoblast-like cells and no difference was seen between males and females. However, cortisol (10−6 mol/l) decreased IGF-I mRNA levels.

In summary, the present study has shown that human osteoblast-like cells express IGF-I and IGF-II mRNA transcripts and that cortisol down-regulates the IGF-I mRNA levels, indicating that some of the inhibitory effect of glucocorticoids on bone formation in humans is mediated via a reduced autocrine/paracrine expression of IGF-I.

Journal of Endocrinology (1996) 149, 397–403

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NO Vidal, S Ekberg, S Enerback, A Lindahl, and C Ohlsson

The transcription factor C/EBP alpha, a member of the CCAAT/enhancer-binding protein family, is highly expressed in the liver and in adipose tissue. The aim of this study was to determine if C/EBP alpha is expressed in rat growth cartilage. The expression pattern of C/EBP alpha in monolayer-cultured growth plate chondrocytes was similar to that of C/EBP alpha during hepatocyte and preadipocyte differentiation. Immunohistochemistry with a polyclonal antibody for C/EBP alpha revealed that the C/EBP alpha protein is present in the perichondrial ring, in the germinal layer of the growth plate and on the surface of the articular cartilage. The growth hormone (GH) receptor has a similar distribution in the rat tibial growth plate, and hypophysectomised rats were used to investigate a possible connection between C/EBP alpha and GH. C/EBP alpha mRNA levels were decreased in rib cartilage after hypophysectomy. However, GH treatment did not counteract this effect, indicating that other pituitary hormones regulate the C/EBP alpha mRNA levels in growth plate cartilage. We thus demonstrate, for the first time, that C/EBP alpha is expressed in cartilage. The finding that C/EBP alpha, like the GH receptor, is predominantly expressed in stem cell areas of the rat growth plate indicates a possible functional role for C/EBP alpha during early chondrogenic differentiation.

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N Andersson, MK Lindberg, C Ohlsson, K Andersson, and B Ryberg

The recent development of different genetically modified mice with potentially interesting bone phenotypes has increased the demand for effective non-invasive methods to evaluate effects on bone of mice during growth and development, and for drug evaluation. In the present study, the skeleton was analyzed by repeated in vivo scans using dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Ovariectomized (ovx) mice treated with parathyroid hormone (PTH) were used as an animal model to evaluate these two techniques at different times after the onset of treatment. Female mice (6 weeks of age) were allocated randomly to four groups: (1) sham-operated+vehicle; (2) ovx+vehicle; (3) sham-operated+PTH(1-84) 150 microg/kg per day; (4) ovx+PTH. Six weeks after ovariectomy the drug treatment began and was continued for 8 weeks. The total body bone mineral content (BMC) and total body areal bone mineral density (BMD) were measured by DXA. Ovariectomy reduced total body BMC and total body areal BMD by 6.2+/-1.7% and 2.6+/-0.9% respectively. No effect of PTH on total body BMC was seen during the treatment period. The trabecular volumetric BMD was measured by pQCT. Ovariectomy reduced the trabecular volumetric BMD by 52+/-6.7%. The pQCT technique detected a clear effect on trabecular volumetric BMD after 2 weeks of PTH treatment (ovx 94+/-29% and sham-operated 46+/-10% more than vehicle-treated). The cortical bone was measured in a mid-diaphyseal pQCT scan of the tibia. Ovariectomy reduced the cortical BMC by 9+/-2%. PTH treatment for 8 weeks increased cortical BMC in ovx mice. In conclusion, the pQCT technique is more sensitive than the DXA technique in the detection of bone loss after ovariectomy and increased bone mass after PTH treatment in mice. Notably, the pQCT, but not the DXA, technique detected a dramatic effect as early as after 2 weeks of PTH treatment. Dynamic pQCT measurements will be useful for monitoring skeletal changes during growth and development, and for drug evaluation in mice.

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MC Slootweg, D Swolin, JC Netelenbos, OG Isaksson, and C Ohlsson

Postmenopausal bone loss is primarily due to estrogen deficiency. Recent clinical observation demonstrate that GH increases bone mass in GH deficient patients. The present study investigates whether estrogen regulates GH action and GH receptor expression in osteoblasts. 17 beta-estradiol or GH added to the culture medium as single substances did not influence rat osteosarcoma cell proliferation nor human osteoblast-like (hOB) cell proliferation. However, together they synergistically induced osteoblast proliferation (rat osteosarcoma cells 160.1 +/- 15.5% of control cells; human osteoblast-like cells 159.6 +/- 5.1% of control cells). 17 beta-estradiol stimulated 125I-GH binding and GH receptor (GHR) mRNA levels in rat osteosarcoma cells. The stimulatory effect of estradiol was time dependent, reaching a peak after 8 h of incubation with 17 beta-estradiol (binding 216.9 +/- 27.8% and mRNA 374.6 +/- 30.8% of control). The finding that estradiol stimulated 125I-GH binding was confirmed in human osteoblast-like cells. In these cells, 17 beta-estradiol (10(-12) M) increased 125I-GH binding to 203.8 +/- 3.6% of control levels. We conclude that estrogen stimulates GH activity as well as GH binding and GHR mRNA levels in osteoblasts. These findings indicate that estrogen potentiates the effect of GH at the receptor level.

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T Ahmad, C Ohlsson, M Saaf, CG Ostenson, and A Kreicbergs

We characterized appendicular and axial bones in rats with type-2 diabetes in five female Goto-Kakizaki (GK) rats, a strain developed from the Wistar rat showing spontaneous type-2 diabetes, and five age- and sex-matched non-diabetic Wistar rats. The humerus, tibia, metatarsals and vertebral bodies were analysed by peripheral quantitative computerized tomography (pQCT). In diabetic rats, the height of the vertebral bodies and length of the humerus were decreased while the length of the metatarsals was increased. A decreased cross-sectional area was found in the vertebral end-plate region and the tibial metaphysis. Notably, the diaphysis in all long bones showed expansion of periosteal and endosteal circumference. In tibia this resulted in increased cortical thickness, whereas in humerus and metatarsal it was unchanged. Areal moment of inertia was increased in all diaphyses suggesting greater bending strength. The most conspicuous finding in diabetic rats pertained to trabecular osteopenia. Thus, trabecular bone mineral density was significantly reduced in all bones examined, by 33-53%. Our pQCT study of axial and appendicular bones suggests that the typical feature of diabetic osteopathy in the GK rat is loss of trabecular bone and expansion of the diaphysis. The loss of metaphyseal trabecular bone if also present in diabetic patients may prove to underlie the susceptibility to periarticular fracture and Charcot arthropathy. The findings suggest that the risk of fracture in diabetes varies according to the specific sub-regions of a bone. The approach described may prove to be useful in the early detection of osteopathy in diabetic patients who may be amenable to preventive treatment.

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MC Erlandsson, CA Jonsson, MK Lindberg, C Ohlsson, and H Carlsten

Raloxifene is a selective estrogen receptor modulator approved for the prevention of osteoporosis in postmenopausal women. It is selective by having estrogen-agonistic effects on bone, vessels and blood lipids while it is antagonistic on mammary and uterine tissue. Our aim was to study the agonistic and antagonistic properties of the raloxifene analogue LY117018 (LY) on uterus, bone, B lymphopoiesis and B cell function. Oophorectomized and sham-operated animals were treated with s.c. injections of equipotent anti-osteoporotic doses of 17beta-estradiol (E2) (0.1 mg/kg) or LY (3 mg/kg) or vehicle as controls. Effects on bone mineral density (BMD) were studied using peripheral quantitative computed tomography, uterine weight was examined, B lymphopoiesis was examined using flow cytometry and B cell function in bone marrow and spleen was studied by the use of an ELISPOT assay. E2 and LY had similar effects on BMD and bone marrow B lymphopoiesis, while LY had a clear antagonistic effect on endogenous estrogen in uterine tissue and no stimulating effect on the frequency of Ig-producing B cells in sham-operated animals. Our results are discussed in the context of estrogen receptor biology, relations between the immune system and bone metabolism and also with respect to the estrogen-mediated effects on rheumatic diseases.

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NO Vidal, H Brandstrom, KB Jonsson, and C Ohlsson

Osteoprotegerin (OPG) is a recently cloned member of the tumour necrosis factor receptor family. It has been suggested that this secreted glycoprotein acts as an inhibitor of osteoclastic differentiation. Expression of OPG has previously been demonstrated in a number of tissues. However, it is still unclear whether or not OPG is expressed by human osteoblasts. We have used the RNase protection assay to demonstrate the OPG transcript in primary cultured human osteoblast-like cells, human marrow stroma cells and osteosarcoma cell lines. Furthermore, we have studied the effect of glucocorticoids on OPG mRNA levels in these cells. We demonstrate that glucocorticoids decrease the OPG transcript in a dose- and time-dependent manner. The time-course study reveals that hydrocortisone (10(-6) M) decreases OPG mRNA levels within 2 h. This decrease is transient, reaching control levels again after 24 h. Our findings demonstrate that human osteoblasts express the mRNA corresponding to OPG, an inhibitor of osteoclast differentiation. The finding that OPG mRNA levels are decreased by glucocorticoids indicates that a reduced production of OPG from osteoblasts and/or marrow stroma cells could, in part, explain glucocorticoid-induced bone resorption.

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JM Kindblom, O Nilsson, T Hurme, C Ohlsson, and L Savendahl

Indian Hedgehog (Ihh) has been reported to control the rate of cartilage differentiation during skeletal morphogenesis in rodents through a negative feedback loop involving parathyroid hormone related protein (PTHrP). The role of Ihh and PTHrP in the regulation of human epiphyseal chondrocytes is unknown. The aim of the current study was to examine the expression and localization of Ihh and PTHrP in the human growth plate at various pubertal stages. Growth plate biopsies were obtained from patients subjected to epiphyseal surgery and the expression of Ihh and PTHrP was detected by immunohistochemistry. We show that Ihh and PTHrP are expressed mainly in early hypertrophic chondrocytes in the human growth plate. The levels of expression of Ihh and PTHrP are higher in early stages of puberty than later. Our results suggest that Ihh and PTHrP are present in the human growth plate and that Ihh and PTHrP may be involved in the regulation of pubertal growth in humans.