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Biomedical subjects

E Canalis

Publications and source records attributed to E Canalis.

At least 91 records · Page 5Linked to original sources
PubMed1995

Insulin-like growth factor (IGF) I and retinoic acid induce the synthesis of IGF-binding protein 5 in rat osteoblastic cells.

The insulin-like growth factor (IGF) regulatory system has a major impact on bone physiology. Among the modulators of IGFs, a family of structurally related proteins, the IGF-binding proteins (IGFBPs), have been shown to either potentiate or inhibit IGF actions on bone growth. However, the regulation of IGFBP expression in bone cells is not completely understood. In the present study, the expression of IGFBP-5 was analyzed in primary osteoblastic cells (Ob cells) isolated from 22-day-old fetal rat calvariae. Treatment of Ob cells with either IGF-I or all-trans-retinoic acid (RA) caused a time- and dose-dependent increase in IGFBP-5 messenger RNA (mRNA) levels, as determined by Northern blot analysis. Stimulation of IGFBP-5 mRNA was obtained at 100 nM IGF-I between 6 and 16 h (2- to 2.5-fold) and 100 nM RA between 16 and 24 h (3- to 4-fold). Concomitant treatment of Ob cells with IGF-I and RA revealed an additive effect and a 5- to 7-fold increase in IGFBP-5 mRNA levels after 16-24 h. The effect of IGF-I and RA and their combination on IGFBP-5 transcripts was similar in confluent and subconfluent cultures of Ob cells. IGF-I and RA did not change IGFBP-5 mRNA stability in Ob cells after transcription arrest with the RNA polymerase II inhibitor 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole. IGF-I and RA at 100 nM elevated the levels of IGFBP-5 heterogenous nuclear RNA, measured by reverse transcription-polymerase chain reaction. The effect was similar to that observed on mRNA levels. IGFBP-5 from rat Ob cells appeared as a single band of 31 kilodaltons in both the conditioned medium and the extracellular matrix as determined by Western immunoblots. IGF-I and RA, both at 100 nM, increased IGFBP-5 by 2- to 3-fold after 24 h. In conclusion, IGF-I and RA modify the synthesis and secretion of IGFBP-5 in rat Ob cells through pathways that may involve increased transcription and elongation and/or altered processing of heterogenous nuclear RNA. Our data suggest that IGFBP-5 may play a role in the osteoblastic-differentiated function regulated by IGF-I and RA.

Animals↗
PubMed1995

Basic fibroblast growth factor stimulates expression of interstitial collagenase and inhibitors of metalloproteinases in rat bone cells.

Basic fibroblast growth factor (bFGF) is a bone cell mitogen that affects osteoblastic function by suppressing type I collagen synthesis. The investigators in this study examined whether bFGF also regulates interstitial collagenase and tissue inhibitors of metalloproteinases (TIMPs) in osteoblast-enriched cells isolated from 22-day fetal rat calvariae. After exposure to 600 pM bFGF, interstitial collagenase messenger RNA (mRNA) levels, as determined by Northern hybridization analysis, increased after 2 h and were maximally stimulated to approximately 13-fold at 6 h. Exposure of osteoblast-enriched cells to 0.06-6 nM bFGF increased collagenase mRNA in a dose-dependent manner, and bFGF also increased immunoreactive collagenase measured in the culture medium by Western blot analysis. The protein synthesis inhibitor cycloheximide, as well as two inhibitors of protein kinase C, staurosporine and sangivamycin, prevented the bFGF induction of collagenase transcripts, whereas indomethacin, an inhibitor of prostaglandin synthesis, decreased the effect of bFGF on collagenase mRNA levels by about 50%. After exposure to 600 pM bFGF, levels of TIMP 1 and TIMP 3 mRNAs were also maximally stimulated to approximately 6-fold at 16 h and 4-fold at 6 h. bFGF did not modify TIMP 2 expression. In conclusion, bFGF may modulate degradation of collagenous bone matrix by inhibiting collagen as well as stimulating collagenase and TIMPs by osteoblasts.

Alkaloids↗
PubMed1995

Bone morphogenetic protein-2 inhibits the synthesis of insulin-like growth factor-binding protein-5 in bone cell cultures.

Previous work from our laboratory indicated that bone morphogenetic protein-2 (BMP-2) enhances the synthesis of insulin-like growth factor-I (IGF-I) and IGF-II by skeletal cells. The activity of IGF-I and -II is regulated by six known IGF-binding proteins (IGFBPs). Although most IGFBP's inhibit the actions of IGF on bone growth, IGFBP-5 is stimulatory, and its synthesis correlates with changes in osteoblast cell growth. We tested the effects of BMP-2 on IGFBP-5 expression in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). Treatment of Ob cells with BMP-2 caused a time- and dose-dependent decrease in IGFBP-5 messenger RNA (mRNA) levels, as determined by Northern blot analysis. The effect was maximal after 24 h of treatment and occurred at BMP-2 concentrations of 0.03-3.3 nM. Treatment with BMP-2 for 24 h also decreased IGFBP-5 polypeptide levels in the extracellular matrix, as determined by Western blot analysis. The effects of BMP-2 on IGFBP-5 transcripts were independent of cell division, as they were observed in the presence and absence of hydroxyurea (1 mM). IGFBP-5 transcripts were barely detectable in the presence of the protein synthesis inhibitor cycloheximide at 3.6 microM, and further suppressive effects of BMP-2 on IGFBP-5 mRNA could not be determined. BMP-2 did not modify the decay of IGFBP-5 mRNA in transcriptionally arrested Ob cells. In addition, BMP-2 inhibited IGFBP-5 heterogeneous nuclear RNA, determined by reverse transcription-polymerase chain reaction, after 2-6 h of treatment, suggesting an inhibition of IGFBP-5 transcription or processing. In conclusion, BMP-2 inhibits IGFBP-5 expression in Ob cells through pathways that are independent of its mitogenic activity and through mechanisms that may involve decreased transcription or altered RNA processing.

Animals↗
PubMed1994

Bone morphogenetic protein 2 increases insulin-like growth factor I and II transcripts and polypeptide levels in bone cell cultures.

Insulin-like growth factors (IGF) I and II are among the most prevalent growth factors secreted by bone cells and are presumed to act as autocrine regulators of bone formation. Certain growth factors, synthesized by skeletal cells and known to stimulate the replication but not the differentiated function of cells of the osteoblastic lineage, have been shown to inhibit skeletal IGF-I and II synthesis. We postulated that growth factors with limited mitogenic activity and with differentiation-inducing properties, such as bone morphogenetic protein (BMP) 2, have the opposite effect and enhance IGF-I and II synthesis. We tested the effects of BMP-2 on IGF-I and II mRNA expression and polypeptide concentrations in cultures of osteoblast-enriched (OB) cells from 22 day fetal rat calvariae. Steady-state IGF-I and II mRNA levels were determined by northern blot analysis, and IGF-I and II concentrations were determined in acidified and fractionated culture medium by a specific radioimmunoassay. After 24-48 h of treatment, BMP-2 at 3.3 nM increased IGF-I and II transcripts by up to twofold and polypeptide levels by up to fourfold. BMP-2 was a more potent stimulator of IGF-II synthesis, and it was active at doses as low as 0.03 nM for IGF-II mRNA and 0.3 nM for IGF-II protein, whereas a dose of 3.3 nM was required to observe the effect on IGF-I synthesis. The effects of BMP-2 on IGF-I and II transcripts and polypeptide levels were dependent on protein synthesis and decreased in the presence of cycloheximide at 3.6 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Cellular and clinical perspectives on skeletal insulin-like growth factor I.

Insulin-like growth factor (IGF) I, a polypeptide synthesized by skeletal cells, is presumed to act as an autocrine regulator of bone formation. IGF I stimulates bone replication of preosteoblastic cells and enhances the differentiated function of the osteoblast. The synthesis of skeletal IGF I is regulated by systemic hormones, most notably parathyroid hormone and glucocorticoids, as well as by locally produced factors, such as prostaglandins and other skeletal growth factors. Whereas hormones and growth factors regulate IGF I synthesis, the exact level of regulation has not been established and may involve both transcriptional and posttranscriptional mechanisms. The IGF I gene contains six exons, and both exon 1 and 2 contain transcription initiation sites. Extrahepatic tissues, including bone, express exon 1 transcripts, and regulation of the exon 1 promoter activity in osteoblasts is currently under study. It is apparent that the regulation of IGF I gene transcription as well as the regulation of mRNA stability is complex and tissue specific. It is possible that abnormalities in skeletal IGF I synthesis or activity play a role in the pathogenesis of bone disorders. In view of its important anabolic actions in bone, it is tempting to postulate the use of IGF I for the treatment of disorders characterized by decreased bone mass. An alternative could be the stimulation of the local production of IGF I in bone.

Animals↗
PubMed1994

Mechanisms of glucocorticoid action in bone cells.

Glucocorticoids play an important role in the normal regulation of bone remodeling; however continued exposure of bone to glucocorticoid excess results in osteoporosis. In vivo, glucocorticoids stimulate bone resorption and decrease bone formation, and in vitro studies have shown that while glucocorticoids stimulate osteoblastic differentiation, they have important inhibitory actions on bone formation. Glucocorticoids have many effects on osteoblast gene expression, including down-regulation of type I collagen and osteocalcin, and up-regulation of interstitial collagenase. The synthesis and activity of osteoblast growth factors can be modulated by glucocorticoids as well. For example, insulin-like growth factor I (IGF-I) is an important stimulator of osteoblast function, and expression of IGF-I is decreased by glucocorticoids. The activity of IGF I can be modified by IGF binding proteins (IGFBPs), and their synthesis is also regulated by glucocorticoids. Thus, glucocorticoid action on osteoblasts can be direct, by activating or repressing osteoblast gene expression, or indirect by altering the expression or activity of osteoblast growth factors. Further investigation of the mechanisms by which glucocorticoids modulate gene expression in bone cells will contribute to our understanding of steroid hormone biology and will provide a basis for the design of effective treatments for glucocorticoid-induced osteoporosis.

Animals↗
PubMed1994

Complex pattern of insulin-like growth factor binding protein expression in primary rat osteoblast enriched cultures: regulation by prostaglandin E2, growth hormone, and the insulin-like growth factors.

Primary osteoblast-enriched (Ob) cultures from fetal rat bone synthesize insulin-like growth factor (IGF) I and IGF-II, which each enhance Ob function. While a number of agents modulate IGF-I production, IGF-II is constitutively expressed in this culture model. Independent of their expression, however, the activity of the IGFs can be modified by a small group of proteins termed IGF binding proteins (IGFBPs), but little is known about the regulation of individual IGFBPs that are synthesized by Ob cells. Northern blot analysis revealed that serum-deprived primary rat Ob cells express transcripts encoding IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-5, and IGFBP-6, but undetectable levels of IGFBP-1 transcripts. Western ligand blots of Ob culture medium probed with 125I-IGF-I or 125I-IGF-II showed predominant IGFBPs migrating at 30/32 kDa, with minor bands at 24 and 38-47 kDa. Western antibody analysis identified IGFBP-2 and IGFBP-5 within the 30/32 kDa complex, while gel mobility shift on SDS-PAGE following deglycosylation determined that IGFBP-3 comprised the 38-47 kDa complex. By Northern analysis, 6 h treatment with prostaglandin E2 (PGE2), growth hormone (hGH), IGF-I, or IGF-II revealed a complex pattern of regulatory effects on steady-state IGFBP transcript expression. PGE2 increased the transcript levels of IGFBP-3, IGFBP-4, and IGFBP-5, (approximately 22-, approximately 2- and approximately 4-fold respectively), but had no effect on IGFBP-2 or IGFBP-6 transcripts. hGH enhanced IGFBP-3 and IGFBP-5 transcripts (each approximately twofold). IGF-I and IGF-II had no effect on IGFBP-2 steady-state transcript levels but enhanced the level of IGFBP-5 transcripts (approximately fourfold). By Western ligand blot analysis, 24 h treatment with PGE2 elevated the 24 and 38-47 kDa IGFBPs and to a lesser extent the 30/32 kDa complex, hGH elevated the 38-47 kDa IGFBPs, and IGF-I and IGF-II each increased the 30/32 kDa IGFBP complex. Therefore, a comparison of results obtained from Northern, Western ligand, and Western antibody studies indicates that multiple IGFBPs are expressed by primary rat Ob cultures. While IGFBP-2 and IGFBP-6 synthesis in Ob cultures is relatively unaffected by short-term treatment with PGE2, hGH, or the IGFs, these agents modify IGFBP-3, IGFBP-4, and IGFBP-5 expression with individual patterns of effects. In addition, some changes in IGFBP polypeptide levels that are independent of alterations in transcript expression may result from the formation of complexes between IGFs and certain IGFBPs, which could serve to store IGFs for future utilization in the formation phase of bone remodeling.

Animals↗
PubMed1994

Differential effects of warfarin on mRNA levels of developmentally regulated vitamin K dependent proteins, osteocalcin, and matrix GLA protein in vitro.

The role of the vitamin K dependent proteins, osteocalcin which is bone specific and matrix Gla protein (MGP) found in many tissues, has been studied by inhibition of synthesis of their characteristic amino acid, gamma-carboxyglutamic acid (Gla) with the anticoagulant sodium warfarin. The effect of sodium warfarin on expression of these proteins, and other phenotypic markers of bone and cartilage during cellular differentiation and development of tissue extracellular matrix, was examined in several model systems. Parameters assayed include cell growth (reflected by histone gene expression) and collagen types I and II, osteopontin, alkaline phosphatase, and mineralization. Studies were carried out in calvarial bone organ cultures, normal diploid rat osteoblast and chondrocyte cultures, and rat osteosarcoma cell lines ROS 17/2.8 and 25/1. In normal diploid cells, warfarin consistently stimulated cell proliferation (twofold). In osteoblast cultures, MGP mRNA levels were generally increased (three to tenfold). Notably, MGP mRNA levels were not affected in chondrocyte cultures, either with chronic or acute warfarin treatments. Osteocalcin mRNA levels and synthesis were decreased up to 50% in ROS 17/2.8 cells and in chronically treated (1 and 5 micrograms/ml sodium warfarin) rat osteoblast cultures after 22 days. Early stages of osteoblast phenotype development from the proliferation period to initial tissue formation (nodules) appeared unaffected; while after day 14, further growth and mineralization of the nodule areas were significantly decreased in warfarin-treated cultures. In summary, warfarin has opposing effects on the expression of two vitamin K dependent proteins, MGP and osteocalcin, in osteoblast cultures and MGP is regulated differently between cartilage and bone as reflected by cellular mRNA levels. Additionally, warfarin effects expression of nonvitamin K dependent proteins which may reflect the influence of warfarin on endoplasmic reticulum associated enzymes.

Animals↗
PubMed1994

Platelet-derived growth factor enhances bone cell replication, but not differentiated function of osteoblasts.

Platelet-derived growth factor (PDGF), a polypeptide mitogen, is a dimer composed of PDGF-AA and -BB chains. In rats, PDGF-BB is the prevalent circulating form, whereas in bone, PDGF-AA is the isoform secreted by unstimulated normal bone cells. Although PDGF-BB increased DNA synthesis in fetal rat calvariae, the effects on collagen synthesis were small and inconsistent. To localize the cells in the cranial periosteum that were responding to PDGF isoforms AA and BB, we cultured 21-day-old fetal rat calvariae to assess the effects of human recombinant PDGF-AA and -BB on bone cell replication and matrix formation. Changes were assessed using histomorphometry and autoradiography and correlated with effects on collagen synthesis and [3H]thymidine incorporation, using biochemical assays. PDGF-AA and -BB at 0.03-3.3 nM (1-100 ng/ml) for 24-72 h increased DNA synthesis by 1.5- to 3-fold; PDGF-BB was more potent than PDGF-AA. Although PDGF increased cell replication in all cell zones, the effects of both PDGF-AA and -BB were preferentially greater in the periosteal fibroblast zone, in which, at 3.3 nM, the labeling index (LI) was increased by 3-fold with AA and by 5-fold with BB. Cell replication of the bone surface cell (osteoblast) layer was increased by 2-fold with AA and by 2.5-fold with BB, whereas replication in the intermediate osteoprogenitor zone increased by 50% with AA and by 2.5-fold with BB. The increase in cell replication was associated with a significant inhibition of bone matrix-forming surfaces, with PDGF-BB being more potent at equivalent doses than -AA after 24-72 h of continuous treatment. Continuous or intermittent exposure to PDGF-AA or PDGF-BB for 24-72 h stimulated neither the rate of collagen synthesis nor organized bone matrix formation in rat calvariae. In addition, PDGF-BB at 0.03-3.3 nM increased the number of osteoclasts and the percent eroded surface by 2- to 3-fold. Our studies show that PDGF-AA and -BB are mitogens affecting multiple bone cells, including those of the osteoblast and osteoclast lineage. Treatment with PDGF severely disrupted and inhibited bone matrix formation, and there was no evidence to show that cells incorporating [3H]thymidine differentiated into mature osteoblasts within the time frame of these experiments. In fetal rat calvaria, the most significant consequence of treatment with PDGF was the selective stimulation of fibroblast replication and function.

Animals↗
PubMed1994

Regulation of interstitial collagenase expression and collagen degradation by retinoic acid in bone cells.

In osteoblasts, retinoic acid (RA) modulates the synthesis of various proteins, including collagen. However, little is known about the effects of RA on the regulation of interstitial collagenase synthesis and collagen degradation. After treatment of primary osteoblast-enriched (Ob) cells from fetal rat calvariae with 100 nM all-trans-RA (tRA), collagenase mRNA levels, as determined by Northern blotting, did not change after 2 h, increased by 13- to 18-fold after 6 h, and remained elevated until 48 h. Exposure of Ob cells to 10 nM to 1 microM tRA, 13-cis-RA, and 9-cis-RA induced collagenase mRNA in a dose-dependent manner. Collagenase mRNA induction by RA was blocked by cycloheximide. RA increased the stability of collagenase mRNA in Ob cells, suggesting posttranscriptional regulation. Exposure of Ob cells to RA induced immunoreactive procollagenase in medium, as determined by enzyme-linked immunosorbent assay and Western blotting. RA action on collagen degradation was examined in [3H]proline-pulsed intact calvariae chased with and without tRA for 72 h. The release of [3H]hydroxyproline into culture medium was increased by 64% in the presence of 10 nM to 1 microM tRA. In conclusion, RA increases collagenase synthesis and collagen degradation in bone and is likely to play an important role in bone remodeling.

Animals↗
PubMed1994

Platelet-derived growth factor-AA and -BB (PDGF-AA and -BB) enhance the synthesis of PDGF-AA in bone cell cultures.

Platelet-derived growth factor (PDGF), an agent with important mitogenic effects for bone cells, exists in three isoforms, PDGF-AA, -BB, and -AB. PDGF-AB and -BB are the prevalent circulating isoforms, whereas normal unstimulated cells of the osteoblast lineage synthesize primarily PDGF-AA. We examined the effects of PDGF-BB on PDGF-A mRNA expression and PDGF-AA polypeptide concentrations in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). In a selected number of experiments we compared the effects of PDGF-BB with those of PDGF-AA on PDGF-A mRNA levels. Steady state PDGF-A mRNA levels were determined by Northern blot analysis, and PDGF-AA concentrations were determined in acidified and fractionated culture medium by a specific RIA for PDGF-A chains. Treatment of Ob cells with PDGF-AA or -BB at 0.3-3.3 nM caused a dose-dependent increase in steady state PDGF-A mRNA, an effect that was initially observed after 2 h. Treatment with PDGF-BB at 1-3.3 nM for 24 h increased PDGF-AA polypeptide concentrations by 2- to 5-fold. The effects of PDGF on PDGF-A mRNA and polypeptide levels were prevented by the protein synthesis inhibitor cycloheximide at 3.6 microM. Phorbol 12-myristate 13-acetate at 1 microM increased PDGF-A mRNA after 2-6 h and PDGF-AA polypeptide levels after 24 h by 2-fold. However, the protein kinase-C inhibitor staurosporine at 50 nM did not modify basal PDGF-A mRNA levels and did not prevent the stimulatory effect of PDGF-AA or -BB on PDGF-A mRNA or PDGF-AA polypeptide levels. In conclusion, PDGF-BB and -AA increase skeletal PDGF-A synthesis, an effect that reveals autoinduction of PDGF in bone cells.

Alkaloids↗
PubMed1994

Regulation of insulin-like growth factor-II synthesis in bone cell cultures by skeletal growth factors.

Insulin-like growth factor-II (IGF-II) is a growth factor secreted by bone cells and presumed to act as an autocrine regulator of bone formation. Although hormones and growth factors regulate the synthesis of skeletal IGF-I, hormones do not seem to modify the synthesis of skeletal IGF-II. We postulated that skeletal IGF-II is regulated by growth factors, and we tested the effects of basic fibroblast growth factor (bFGF), transforming growth factor-beta 1 (TGF beta 1), and platelet-derived growth factor-BB (PDGF-BB) on IGF-II messenger RNA (mRNA) expression and polypeptide concentrations in cultures of osteoblast-enriched (Ob) cells from 22-day-old fetal rat calvariae. Steady state IGF-II mRNA levels were determined by Northern blot analysis, and IGF-II concentrations were determined in acidified and fractionated culture medium by a specific RIA. Treatment of Ob cells with bFGF, TGF beta 1, and PDGF-BB decreased IGF-II mRNA levels after 24-48 h. A continuous 48-h treatment with bFGF at 0.6-6 nM, TGF beta 1 at 0.04-1.2 nM, and PDGF-BB at 0.3-3.3 nM caused a dose-dependent decrease in steady state IGF-II mRNA. The effects of bFGF, TGF beta 1, and PDGF-BB on IGF-II mRNA were dependent on protein synthesis and decreased in the presence of cycloheximide at 3.6 microM, but were independent of cell division, because they were observed in the presence and absence of 1 mM hydroxyurea. Treatment with bFGF, TGF beta 1, and PDGF-BB for 24 h did not cause a change in IGF-II polypeptide levels. PDGF-BB at 3.3 nM and TGF beta 1 at 0.04-0.4 nM for 48 h decreased IGF-II polypeptide levels by about 50%, although bFGF had no effect. In conclusion, bFGF, TGF beta 1, and PDGF decrease skeletal IGF-II transcript levels, and this effect may contribute to their actions on selected aspects of Ob cell function.

Animals↗
PubMed1993

Systemic and local factors and the maintenance of bone quality.

Bone formation, an essential process for the maintenance of bone mass and strength, depends on changes in osteoblast number or function. Bone formation is modified by systemic hormones such as parathyroid hormone, growth hormone, insulin and steroids, and by local factors that act in an antocrine or paracrine fashion on the osteoblast. Skeletal cells synthesize platelet-derived growth factors and fibroblast growth factors, agents which affect osteoblast cell replication. In addition, skeletal cells synthesize insulin-like growth factors and transforming growth factors beta, agents which also affect the differentiated function of the osteoblast. Systemic and local factors that modify bone formation are likely critical in the maintenance of normal bone.

Bone Development↗
PubMed1993

Growth factors regulate the synthesis of insulin-like growth factor-I in bone cell cultures.

Insulin-like growth factor-I (IGF-I), a prevalent growth factor secreted by bone cells, has important effects on bone remodeling. Hormones are known to regulate the synthesis of skeletal IGF-I, but there is limited information about the actions of growth factors on IGF-I synthesis. We tested the effects of basic fibroblast growth factor (bFGF), transforming growth factor-beta 1 (TGF beta 1), and platelet-derived growth factors (PDGF) AA and BB on IGF-I mRNA expression and polypeptide concentrations in cultures of osteoblast-enriched (Ob) cells from 22-day-old fetal rat calvariae. Steady state IGF-I mRNA levels were determined by Northern blot analysis, and IGF-I concentrations were determined in acidified and fractionated culture medium by a specific RIA. Treatment of Ob cells with bFGF at 0.06-6 nM, TGF beta 1 at 0.04-4 nM, and PDGF BB at 0.3-3.3 nM caused a dose-dependent decrease in steady state IGF-I mRNA. A smaller effect was observed with PDGF AA. The effect was initially observed after 6-8 h of treatment and was maximal after 16 h. Treatment with bFGF at 0.6-6 nM, TGF beta 1 at 0.4-4 nM, and PDGF BB at 0.3-3.3 nM for 24 h decreased IGF-I polypeptide concentrations by 40-80%. The effects of bFGF, TGF beta 1, and PDGF BB and AA on IGF-I mRNA were independent of protein synthesis and cell division, as they were observed in the presence and absence of cycloheximide at 3.6 microM or hydroxyurea at 1 mM. Similarly, their inhibitory actions on immunoreactive IGF-I were not prevented by hydroxyurea. In conclusion, bFGF, TGF beta 1, PDGF BB, and, to a lesser extent, PDGF AA decrease skeletal IGF-I synthesis by reducing IGF-I transcript levels, and this effect may contribute to their actions on selected aspects of Ob cell function.

Animals↗
PubMed1993

Effects of prostaglandin E2 on bone formation in cultured fetal rat calvariae: role of insulin-like growth factor-I.

Prostaglandin E2 (PGE2) can stimulate collagen synthesis in bone at low concentrations or in the presence of cortisol. Moreover, cortisol inhibits and PGE2 stimulates the production of insulin-like growth factor (IGF-I) in cultured osteoblastic cells. Therefore, we examined the role of IGF-I in the response to PGE2. In 96-h fetal rat calvarial organ cultures, PGE2 increased, and cortisol and indomethacin decreased the medium IGF-I concentration, suggesting that both exogenous and endogenous PGs regulate IGF-I production. In the presence of cortisol, the stimulatory effects of PGE2 on medium IGF-I and incorporation of [3H] proline into collagenase-digestible protein were highly correlated (r = 0.95). When exogenous IGF-I (30 nM) was added, the stimulatory effect of PGE2 was abrogated in the absence, but not the presence, of cortisol. When we added IGF-binding proteins, which blocked the effects of IGF-I and IGF-II, collagenase-digestible protein labeling was decreased in control and cortisol-treated cultures, whereas the stimulatory effect of PGE2 was reduced, but not abrogated. We conclude that endogenous IGFs play a role in maintaining bone formation in cultured fetal rat calvariae and may mediate in part the anabolic response to PGE2. However, the PGE2 response probably involves additional IGF-independent pathways.

Animals↗
PubMed1993

Skeletal growth factors.

Growth factors are polypeptides with important actions on the replication and differentiated function of cells. Skeletal cells synthesize a variety of growth factors, which are believed to act in an autocrine or paracrine fashion. These growth factors include platelet-derived growth factor, fibroblast growth factor 1 and 2, insulin-like growth factor I and II, transforming growth factors beta 1, 2, and 3, and selected bone morphogenetic proteins. Skeletal cells also synthesize specific binding proteins for selected growth factors. In addition, bone marrow cells synthesize a variety of cytokines known to have important actions in bone remodeling. Fibroblast growth factors and platelet-derived growth factors are, for the most part, mitogenic for skeletal cells, whereas insulin-like growth factors and transforming growth factor beta enhance the differentiated function of the osteoblast. Growth factors also modify osteoclast recruitment and function and as such, bone resorption. Skeletal growth factors can be regulated at the level of synthesis, activation, binding proteins, and receptor binding, and, as a result, their activity can be modified by exogenous agents.

Animals↗
PubMed1992

Effects of deflazacort on aspects of bone formation in cultures of intact calvariae and osteoblast-enriched cells.

Deflazacort, a synthetic glucocorticoid reported to have bone-sparing properties in vivo, and cortisol were compared for their effects on bone formation in vitro. Deflazacort and cortisol were studied for their effects on DNA and collagen synthesis in cultures of intact fetal rat calvariae and of osteoblast-enriched (Ob) cells from 21- to 22-day-old fetal rat parietal bone. Both steroids were also examined for their effects on skeletal insulin-like growth factor (IGF) I production, which is decreased by cortisol and appears relevant to its mode of action. After 24 h of culture, deflazacort and cortisol had limited effects on the parameters studied, although cortisol at 100 nM decreased [3H]proline incorporation into collagen in intact calvariae. In contrast, after 72 h deflazacort and cortisol at 1-100 nM inhibited the incorporation of [3H]thymidine into DNA and at 100 nM decreased the incorporation of [3H]proline into collagen and noncollagen protein in intact calvariae. Deflazacort and cortisol at 10-1000 nM decreased calvarial collagen degradation to a similar extent. Both steroids had a similar activity, and at 100 nM for 72 h they decreased IGF-I production by calvariae; however, cortisol at 10 nM was somewhat more effective than deflazacort in decreasing IGF-I levels. Deflazacort and cortisol had analogous effects in Ob cell cultures. After 24 h of treatment, deflazacort at 100-1000 nM and cortisol at 10-1000 nM decreased the labeling of DNA, and both steroids at 100-1000 nM caused a similar decrease in [3H]proline incorporation into collagen in Ob cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗