Association of a polymorphism of the transforming growth factor-beta1 gene with genetic susceptibility to osteoporosis in postmenopausal Japanese women

Absence of high-risk "s" allele associated with osteoporosis at the intronic SP1 binding-site of collagen Ialpha1 gene in Southern Chinese

The Sp1 polymorphism in the first intron of the collagen Ialpha1 gene was recently described to be associated with low bone mineral density (BMD) and increased fracture risk in Caucasian populations. The impact of this gene was assessed in a Southern Chinese population. One hundred and eighty-one women, aged 51.1+/-8.8 yr were evaluated for the Sp1 polymorphism. Twenty-two per cent of the women were classified as having osteoporosis on the basis of a T-score at the lumbar spine or the hip below -2.5 with or without a prevalent fracture. Genotype analysis was performed by PCR amplification and restriction enzyme digestion. Single-strand conformational polymorphism analysis (SSCP) was performed in 65 randomly selected samples to search for any polymorphic site in the PCR amplified region. The results showed that no restriction enzyme site could be identified in any of the 181 samples analyzed. Moreover, SSCP analysis revealed no polymorphism in the PCR amplified region of the first intron of the collagen Ialpha1 gene. In conclusion, the "s" allele, associated with low BMD and increased fracture risk in Caucasians, is non-existent or very rare in the Southern Chinese population. The absence of this "high risk" allele may in part account for the reduced fracture risk observed in the Chinese in comparison to Western populations.

The many faces of transforming growth factor-beta in pleural diseases

Transforming growth factor (TGF)-beta is responsible for critical regulatory functions in many physiologic and pathologic processes. Emerging evidence suggests that these roles also apply to a multitude of pleural diseases. Both mesothelial cells and infiltrating cells in the pleural space can produce TGFbeta, and elevated TGFbeta concentrations have been found in pleural effusions and in pleural tissues during disease processes. Recent animal studies have suggested that TGFbeta can induce significant pleurodesis and probably plays a central role in the pathogenesis of pleural fibrosis. Paradoxically, TGFbeta may also stimulate increased pleural fluid formation, in part by inducing the production of vascular endothelial growth factor. TGFbeta also participates in the regulation of pleural inflammation and cell proliferation. Further research into the roles of TGFbeta in the pathogenesis of various pleural diseases is needed and may lead to the development of novel treatment strategies.

Association between a polymorphism of the transforming growth factor-beta1 gene and genetic susceptibility to ossification of the posterior longitudinal ligament in Japanese patients

STUDY DESIGN

A study was conducted to determine the association between polymorphism of the transforming growth factor-beta1 (TGF-beta1) gene and ossification of the posterior longitudinal ligament (OPLL) prevalence.

OBJECTIVE

To examine whether the T869-->C polymorphism of the TGF-beta1 gene is associated with genetic susceptibility to OPLL in Japanese subjects.

SUMMARY OF BACKGROUND DATA

In the posterior longitudinal ligament, OPLL is associated with abnormal calcium metabolism. Several candidate genes are associated with the prevalence of OPLL. In the ossified matrix and chondrocytes of adjacent cartilaginous areas of OPLL, TGF-beta1 is overexpressed.

METHODS

The TGF-beta1 genotype was identified with an allele-specific polymerase chain reaction method in 319 Japanese subjects (46 subjects with OPLL and 273 control subjects).

RESULTS

There was a significant association between the T869-->C genotype and the prevalence of OPLL in the cervical spine. Multivariable logistic regression analysis, adjusted for gender, age, height, and body weight, showed that the frequency of the C allele was significantly higher in subjects with OPLL than in control subjects.

CONCLUSIONS

The T869-->C polymorphism of the TGF-beta1 gene is a genetic determinant of a predisposition to OPLL, with the C allele representing a risk factor for genetic susceptibility to OPLL in Japanese subjects. Therefore, TGF-beta1 genotyping may be useful in the prevention of OPLL.

Divergence and convergence of TGF-beta/BMP signaling

The transforming growth factor-beta (TGF-beta) superfamily includes more than 30 members which have a broad array of biological activities. TGF-beta superfamily ligands bind to type II and type I serine/threonine kinase receptors and transduce signals via Smad proteins. Receptor-regulated Smads (R-Smads) can be classified into two subclasses, i.e. those activated by activin and TGF-beta signaling pathways (AR-Smads), and those activated by bone morphogenetic protein (BMP) pathways (BR-Smads). The numbers of type II and type I receptors and Smad proteins are limited. Thus, signaling of the TGF-beta superfamily converges at the receptor and Smad levels. In the intracellular signaling pathways, Smads interact with various partner proteins and thereby exhibit a wide variety of biological activities. Moreover, signaling by Smads is modulated by various other signaling pathways allowing TGF-beta superfamily ligands to elicit diverse effects on target cells. Perturbations of the TGF-beta/BMP signaling pathways result in various clinical disorders including cancers, vascular diseases, and bone disorders.

The influence of transforming growth factor-beta1 gene polymorphisms on the severity of gingival overgrowth associated with concomitant use of cyclosporin A and a calcium channel blocker

BACKGROUND

The purpose of this study was to determine whether the prevalence and severity of gingival overgrowth in renal transplant recipients concomitantly treated with cyclosporin and a calcium channel blocker was associated with functional polymorphisms within the signal sequence of the transforming growth factor-(TGF)beta1 gene.

METHODS

The extent and severity of gingival overgrowth for 164 renal transplant recipients immunosuppressed with cyclosporin A and concomitantly taking a calcium channel blocker since transplant were entered into the study (86 in Manchester, 78 in Belfast). Two biallelic polymorphisms of the TGF-beta1 gene were studied at position +869, codon 10 (leucine to proline substitution), and position +915, codon 25 (arginine to proline substitution).

RESULTS

Subjects who were homozygous for proline at codon 10 had significantly higher overgrowth scores than those who were heterozygous (P= 0.03) or homozygous for leucine (P= 0.01). Subjects who were heterozygous (arginine/proline) at codon 25 had a significantly higher (P= 0.04) gingival overgrowth score than those who were homozygous for arginine. Logistic regression analysis indicated that for codon 25 independent predictors of severe gingival overgrowth were the heterozygous arginine/proline genotype (P= 0.009) and whether the individual was young (P= 0.05).

CONCLUSIONS

Polymorphisms in the TGF-beta1 gene influence the expression of gingival overgrowth in renal transplant recipients concomitantly treated with cyclosporin and a calcium channel blocker. The polymorphism in the TGF-beta1 gene at codon 25 represented an independent genetic determinant of severe gingival overgrowth in the susceptible subjects studied.

The transforming growth factor-beta1 codon 10 gene polymorphism and accelerated graft vascular disease after clinical heart transplantation

BACKGROUND

The multifunctional cytokine transforming growth factor- (TGF) beta1 is thought to play a role in the pathogenesis of graft vascular disease (GVD). Polymorphisms at codon 10, (Leu10-->Pro) and codon 25 (Arg25-->Pro) in the signal sequence of the TGF-beta1 gene regulate the production and secretion of the protein. We investigated whether these polymorphisms are risk factors for the development of GVD after clinical heart transplantation.

METHOD

TGF-beta1 polymorphisms, Leu10-->Pro and Arg25-->Pro, were determined in DNA from heart transplant recipients (n=252) and their donors (n=213), using sequence-specific oligonucleotide probing. GVD was angiographically diagnosed 1 year after transplantation. In addition other potential risk factors including underlying disease, recipient and donor age, recipient and donor gender, number of acute rejections in the first year, cold ischemia time, and HLA mismatches were analyzed by univariate and multivariate logistic regression analysis.

RESULTS

Univariate analysis showed that the recipient TGF-beta1 polymorphism Leu10-->Pro, (P=0.056, chi2 test), underlying disease (P=0.01, chi2 test), number of acute rejections in the first-year (P=0.03, analysis of variance), and donor age (P<0.001, analysis of variance) were risk factors for the development of GVD. The TGF-beta1 Arg25-->Pro polymorphism was not a risk factor. Also in the multivariate analysis, the recipient TGF-beta1 codon 10 polymorphism was associated with GVD, with patients homozygous for Pro at greatest risk (odds ratio 7.7, P=0.03). Apart for the recipient TGF-beta1 Leu10-->Pro polymorphism, donor age appeared to be an independent risk factor for the development of GVD at 1 year. Patients with older donor hearts were at greater risk than patients receiving grafts from younger donors (odds ratio 1.1/year, P<0.001).

CONCLUSION

Recipient TGF-beta1 Leu10-->Pro polymorphism and higher donor age are independent risk factors for the development of GVD after clinical heart transplantation.

Sequence variation in the transforming growth factor-beta1 (TGFB1) gene and multiple sclerosis susceptibility

Genome screenings in multiple sclerosis (MS) have identified multiple susceptibility regions supporting a polygenic model for this disease. Evidence for linkage was consistently observed at ch.19q13 suggesting the presence of an MS gene(s) in this region. Several interesting candidate genes are encoded within this region, including transforming growth factor-beta 1 (TGFB1) and interleukin-11 (IL11). Both are multifunctional cytokines with significant and well-characterized immunomodulatory properties. We performed a comprehensive evaluation of common polymorphisms within the TGFB1 and IL11 loci and three closely flanking microsatellite markers (D19S421, CEA, D19S908) in 161 stringently ascertained and clinically characterized MS multiplex families using tests of both linkage (lod score, sib-pair analysis) and association (pedigree disequilibrium test or PDT). Patients and families were stratified by HLA-DR2 status to search for two-locus interactions. Suggestive evidence for linkage and association to CEA (lod score = 1.25, theta = 0.20, p = 0.015, respectively), located 0.4 cM from TGFB1, was observed in DR2 positive families only. Distinct clinical phenotypes were also examined and an association between a TGFB1 haplotype and a mild disease course was present (p = 0.008), raising the possibility that TGFB1 or a nearby locus may influence disease expression.

Relationship between cytokine levels and coronary artery disease in women

Inflammation is thought to have a role in the pathogenesis of atherosclerotic coronary artery disease (CAD), and the measurement of markers of inflammation has been suggested to improve the identification of individuals at risk for this disease. The incidence of CAD in women is not accounted for by conventional risk factors, and the association of CAD and the antiinflammatory cytokine transforming growth factor beta1 (TGF-beta1) in this population is unknown. Associations among TGF-beta1, the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha), and CAD severity in inner city women were examined. Fifty-three women requiring angiography (mean age, 60.7 years) were stratified as having on of the following conditions: 0 vessel disease (VD) (n = 20), 1 (VD) (n = 10), 2 VD (n = 9), or 3 VD (n = 14). Fasting serum cytokine levels were determined by enzyme-linked immunosorbent assay. Serum TGF-beta1 was lower in patients with extensive disease (2 and 3 VD versus 0 and 1 VD). The lowest TGF-beta1 levels (<30 ng/mL) were in the 2 and 3 VD groups. In contrast, in the 0 and 1 VD groups, TGF-beta1 was above 41 ng/mL. Serum TGF-beta1 correctly classified the severity of CAD in 62.3% of patients, with a predictive threshold of 58 ng/mL by discriminant function analysis. TGF-beta1 may be a determinant of clinical events and outcome in CAD in women.

Determination of cytokine regulatory haplotypes by induced heteroduplex analysis of DNA

Multiple single nucleotide polymorphisms (SNP) in the promoter region of the human interleukin-10 (IL-10) gene and in the signal/leader sequence of the human transforming growth factor beta 1 (TGF-beta1) gene, have been associated with susceptibility, severity and clinical outcome for a number of diseases. One common explanation for this, is that different haplotypes of these SNPs regulate the expression of the respective cytokines. Therefore, accurate determination of haplotypes by physical linkage analysis represents an important tool in investigating the pathogenesis of such diseases. Here, we demonstrate that the use of induced heteroduplex generators (IHGs) may be used to identify haplotypes within target sequences in the IL-10 and TGF-beta1 genes. Four haplotypes were observed within the IL-10 promoter region, consisting of -1082, -851, -819 and -592 SNPs. For the TGF-beta1 signal/leader sequence, we observed three haplotypes of the T869C (Leu10Pro) and G915C (Arg25Pro) SNPs. In both cases, all combinations of these haplotypes could be resolved unequivocally with a single IHG reagent.

Mutations in the gene encoding the latency-associated peptide of TGF-beta 1 cause Camurati-Engelmann disease

Camurati-Engelmann disease (CED; MIM 131300), or progressive diaphyseal dysplasia, is a rare, sclerosing bone dysplasia inherited in an autosomal dominant manner. Recently, the gene causing CED has been assigned to the chromosomal region 19q13 (refs 1-3). Because this region contains the gene encoding transforming growth factor-beta 1 (TGFB1), an important mediator of bone remodelling, we evaluated TGFB1 as a candidate gene for causing CED.

Osteoporosis in beta-thalassaemia major patients: analysis of the genetic background

Regular blood transfusions from infancy until adulthood in beta-thalassaemia major patients have substituted severe bone deformities with less marked skeletal lesions as osteoporosis. Osteoporosis is characterized by low bone mass and disruption of bone architecture, resulting in reduced bone strength and increased risk of fractures. Genetic factors have an important role in determining bone mineral density (BMD). We have investigated the possible association between BMD and two polymorphisms in 135 beta-thalassaemic patients: (i) a substitution G-->Tau in a regulatory region of the COLIA1 gene encoding for the major protein of bone (type 1 collagen), and (ii) a one-base deletion in intron 4 (713-8del C) of transforming growth factor beta 1 (TGF-beta1) gene. We have found a remarkable incidence (90%) of osteopenia and osteoporosis among regularly transfused patients. Bone mass was lower in men than in women (P = 0.0023), with a more prevalent osteopenia/osteoporosis of the spine in men than in women (P = 0. 001). The sample was stratified on the basis of BMD expressed as Z-score, i.e. normal, osteopenic and osteoporotic patients, and genotype frequencies of each group were evaluated. TGF-beta1 polymorphism failed to demonstrate a statistical difference in BMD groups. However, subjects with heterozygous or homozygous polymorphism of the COLIA1 gene showed a lower BMD than subjects without the sequence variation (P = 0.012). The differences among genotypes were still present when the BMD was analysed as adjusted Z-score and when men and women were analysed separately (P = 0.022 and 0.004 respectively), with men more severely affected. Analysis of COLIA1 polymorphism could help to identify those thalassaemic patients at risk of osteoporosis and fractures.

A polymorphism in the promoter region of the gene for interleukin-6 is associated with susceptibility to type 1 diabetes mellitus

Type 1 diabetes mellitus is an autoimmune disease characterized by the destruction of the insulin-producing islet beta cells. It is likely that several genetic and environmental factors contribute to this process. There is increasing evidence showing that polymorphisms in cytokine genes may play an important role in modifying the immune response. Interleukin-6 (IL-6) is a cytokine that has been implicated in a number of immune-mediated diseases. Further, there is a polymorphism at position -174 (G(-174)C) of the promoter region of the IL-6 gene that may alter the expression of the gene. In this study, the G(-174)C polymorphism was investigated in 257 Caucasoid patients with type 1 diabetes, 53 two-parent-proband trios, and 120 normal, healthy controls. DNA was amplified using amplimers that flank the G(-174)C site, and the products were digested with the restriction endonuclease NlaIII to detect the G or the C allele. The homozygous G,G(-174) genotype was increased in the patients compared with the normal controls (50.6% vs. 33.3%, p < 0.002), with a decrease in the C,C genotype in the patients compared with the controls (12.5% vs. 24.2%, respectively, p < 0.004). In the 53 trios studied, the G allele was transmitted in 29 of 53 informative meioses. There was no association with age at onset of diabetes or the presence of diabetic complications. In conclusion, these results suggest that the IL-6 gene may contribute to the genetic susceptibility to type 1 diabetes.

Renal failure after clinical heart transplantation is associated with the TGF-beta 1 codon 10 gene polymorphism

BACKGROUND

To determine whether genetic factors are involved in the development of renal dysfunction due to cyclosporine nephrotoxicity, we analyzed 2 polymorphisms in the signal sequence of the transforming growth factor (TGF)-beta 1 gene; codon 10 (Leu(10) --> Pro) and codon 25 (Arg(25) --> Pro).

METHOD

Using sequence specific oligonucleotide probing, we analyzed both TGF-beta1 gene polymorphisms in cardiac allograft recipients (n = 168) who survived at least 1 year with minimal follow-up of 7 years. Patients received cyclosporine and steroids as maintenance immunosuppressive therapy. Renal dysfunction was defined as a serum creatinine > or = 250 micromol/liter.

RESULTS

Renal dysfunction was observed in 2% (3/168) of the patients at 1 year, in 7% (11/160) at 3 years, in 12% (18/152) at 5 years, and in 20% (26/131) at 7 years post-transplantation. The genotypic distributions for TGF-beta1 codon 10 were 7% Pro/Pro, 61% Pro/Leu, and 32% Leu/Leu, and for codon 25 these percentages were 1% Pro/Pro, 12% Pro/Arg, and 87% Arg/Arg. We found an association between the TGF-beta 1 genotype encoding proline at codon 10 and renal dysfunction. At 7 years post-transplantation, 26% (23/89) of the patients with the heterozygous Pro/Leu or homozygous Pro/Pro genotype had renal dysfunction vs only 7% (3/42) of the patients with the homozygous Leu/Leu genotype (p = 0.017). For the TGF-beta1 codon 25 genotypes, we found no association between TGF-beta 1 genotypes and renal dysfunction.

CONCLUSION

Our data support the hypothesis that TGF-beta 1 is involved in the process leading to renal insufficiency in cyclosporine-treated cardiac allograft recipients. In these patients the presence of TGF-beta 1 Pro(10) might be a risk factor.

Association of a Leu(10)-->Pro polymorphism of the transforming growth factor-beta1 with genetic susceptibility to osteoporosis and spinal osteoarthritis

Osteoporosis and osteoarthritis each exhibit a strong genetic component. Although polymorphisms of a variety of genes have been associated with bone mineral density and genetic susceptibility to osteoporosis or to osteoarthritis, the genes responsible for these conditions have not been definitively identified. We have shown that a T(869)-->C polymorphism of the transforming growth factor-beta1 (TGF-beta1) gene, which results in a Leu-->Pro substitution at amino acid 10, is associated with bone mineral density in Japanese adolescents and postmenopausal women, with genetic susceptibility to osteoporosis or spinal osteoarthritis, and with the outcome of treatment for osteoporosis with active vitamin D. I here review our recent studies, which have provided insight into the function of TGF-beta1 as well as into the role of genetic factors in the development of osteoporosis and osteoarthritis.

B lymphocytes inhibit human osteoclastogenesis by secretion of TGFbeta

The role of B lymphocytes in osteoclast (OC) formation is controversial, because both stimulatory and inhibitory effects of B-lineage cells on osteoclastogenesis and life span have been reported. In this study, we have investigated the effects of mature B cells on human osteoclastogenesis using cultures of peripheral blood stem cells (PBSC), a system that generates functional OCs in the absence of stromal cells. We report that B cells inhibit the formation of OCs and shorten the life span of mature OCs by secreting transforming growth factor beta (TGFbeta), a factor that induces apoptosis in these cells. The antiosteoclastogenic effects of B cells are abolished by addition of anti-TGFbeta antibody to osteoclast cultures and mimicked by treatment of B cell-deprived PBSC cultures with recombinant TGFbeta, thus confirming TGFbeta as the B cell produced antiosteoclastogenic activity. Thus, the ability of B cells to downregulate osteoclastogenesis by secretion of the apoptotic cytokine TGFbeta provides new insights into the ability of immune cells to regulate OC formation under basal and inflammatory conditions.

Alternative method for diagnosis of two polymorphisms in the human transforming growth factor-beta1 by PCR-mediated double site-directed mutagenesis

Cytokine transforming growth factor-beta1 plays an important role in physiological processes during ontogenesis, cell differentiation, immune responses, carcinogenesis, inflammation, wound healing, fibroproduction, progression of renal insufficiency and arteriosclerotic lesion development. Its biological function is influenced through the two signal peptide polymorphisms. We describe a new, economical, easy and fast alternative method which allows detection of both polymorphisms from one PCR product with subsequent restriction analysis with two different restriction enzymes. This method could facilitate further research on the role of this cytokine in human disease.

Possible involvement of the p57(Kip2) gene in bone metabolism

We previously uncovered that growth stimulation of rat primary osteoblasts by transforming growth factor-beta1 (TGF-beta1) resulted in a dramatic decrease in p57(Kip2), a member of cyclin-dependent kinase (CDK) inhibitors, through the proteasomal degradation pathway (Urano et al., J. Biol. Chem. 274, 12197-12200, 1999). Here we demonstrated that the amount of p57 protein increases markedly, when rat calvarial primary osteoblasts treated with 1,25-dihydroxyvitamin D3 transit from proliferation toward differentiation. Next, we have analyzed the association of four amino acids deletion polymorphism of p57 and bone mineral density (BMD). The p57 genotype was determined in 154 postmenopausal Japanese women. When we separated the subjects into two groups, one having one or two copies of deletion polymorphism and the other without the deletion, the former subjects had higher BMD (Z score of total body, 0.67 +/- 0.93 vs 0. 23 +/- 0.90, mean +/- standard deviation; P = 0.021). Taken together, these findings suggest that the p57 regulated in the osteoblast proliferation and differentiation may play a role in determination of bone mineral density and pathogenesis of osteoporosis.

Association of transforming growth factor beta1 genotype with therapeutic response to active vitamin D for postmenopausal osteoporosis

Transforming growth factor beta (TGF-beta) is an important regulator of bone metabolism, its effects being intertwined with those of estrogen and vitamin D. A T-->C polymorphism in exon 1 of the TGF-beta1 gene, which results in the substitution of proline for leucine, is associated with bone mineral density (BMD). However, it is not known whether this polymorphism affects the response to treatment with active vitamin D or to hormone replacement therapy (HRT) in individuals with osteoporosis. Changes in BMD at the lumbar spine (L2-L4 BMD) were compared among TGF-beta1 genotypes in 363 postmenopausal Japanese women who were divided into three groups: an untreated, control group (n = 130), an active vitamin D treatment group (n = 117), and an HRT group (n = 116). TGF-beta1 genotype was determined with an allele-specific polymerase chain reaction assay. In the control group, the rate of bone loss decreased according to the rank order of genotypes TT (homozygous for the T allele) > TC (heterozygous) > CC (homozygous for the C allele), with a significant difference detected between the CC and TT genotypes. The positive response of L2-L4 BMD to HRT increased according to the rank order of genotypes TT < TC < CC, although the differences among genotypes were not statistically significant. Individuals with the CC genotype responded to active vitamin D treatment with an annual increase in L2-L4 BMD of 1.6%, whereas those with the TT or TC genotypes similarly treated lost bone to a similar extent as did untreated subjects of the corresponding genotype. These results suggest that TGF-beta1 genotype is associated with both the rate of bone loss and the response to active vitamin D treatment.

Identification of human TGF-beta1 signal (leader) sequence polymorphisms by PCR-RFLP

Links between disease susceptibility and genetically determined variation in human cytokine expression have recently been described. This has led to a demand for simple methods of identifying cytokine gene polymorphisms of potential clinical relevance. Here, we describe a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for identifying two human transforming growth factor beta1 (TGF-beta1) signal (leader) sequence polymorphisms, T869C (Leu10Pro) and G915C (Arg25Pro). This permits simple and robust identification of TGF-beta1 leader sequence genotypes and demonstrates the physical linkage in cis between T869C (Leu10Pro) and G915C (Arg25Pro). The method does not require previously genotyped standards. The efficacy of enzyme digestion is internally controlled by the presence of conserved restriction sites.

Update on the epidemiology of osteoporosis

Osteoporosis is a major public health problem that affects the entire aging population. This report provides an update on the epidemiology of osteoporosis and its associated fractures. Published studies from 1997 to the present are highlighted. The current US prevalence estimates for osteoporosis, trends in fracture incidence rates, and latest reports on the morbidity, mortality, and costs attributable to osteoporotic fractures are discussed. Recent advances in our understanding of risk factors associated with osteoporosis and related fractures are reviewed. Special attention is paid to the rapid progress being made in the field of genetics, the growing importance of nutrition, and the new questions being raised as to the influence of hormonal factors on bone mineral density and fracture risk. New studies linking osteoporosis to several other important diseases in women including breast cancer, osteoarthritis, and stroke are also reviewed.

Regulation of osteogenesis by fetuin

Osteoporosis is a common problem of aging and results from a failure of homeostatic mechanisms to regulate osteogenesis and mineralization. Bovine and human forms of fetuin glycoprotein bind to the transforming growth factor (TGF)-beta/BMP (bone morphogenic protein) cytokines and block their osteogenic activity in cell culture assays (Demetriou, M., Binkert, C., Sukhu, B., Tenenbaum, H. C., and Dennis, J. W. (1996) J. Biol. Chem. 271, 12755-12761). Fetuin is a prominent serum glycoprotein and a major noncollagenous component of mineralized bone in mammals. In this study, we show that recombinant fetuin and native serum protein have similar potency as inhibitors of osteogenesis in dexamethasone-treated rat bone marrow cell cultures (dex-RBMC). Recombinant bovine fetuin also bound to TGF-beta1 and BMP-2 in vitro with kinetics similar to native fetuin. Although TGF-beta1 is required for osteogenesis in dex-RBMC, the cytokine also inhibited osteogenesis at concentrations >/=10 pM. Titration of fetuin or anti-TGF-beta1 antibodies into the bone marrow cultures in the presence of 10 pM TGF-beta1 restored osteogenesis, whereas titrations of the same reagents into cultures with 0.3 pM added TGF-beta1 were inhibitory, confirming the biphasic nature of the TGF-beta1 response. Suppression of osteogenesis by both TGF-beta1 and the antagonist proteins required their presence within the first 6 days of culture, well before mineralization at 10-12 days. Northern analysis showed that both fetuin and high dose TGF-beta1 suppressed expression of the bone-associated transcripts alkaline phosphatase, osteopontin, collagen type I, and bone sialoprotein. The suppression of osteogenesis by fetuin and by high dose TGF-beta1 was accompanied by the differentiation of an alternate cell lineage with adipocyte characteristics. In summary, the biphasic osteogenic response to TGF-beta1 suggests that overlapping gradients of TGF-beta/BMP cytokines and fetuin regulate osteogenesis in remodeling bone.

Transforming growth factor beta (TGF-beta) levels in the conditioned media of human bone cells: relationship to donor age, bone volume, and concentration of TGF-beta in human bone matrix in vivo

Transforming growth factor-beta (TGF-beta) is thought to play an important role in human bone remodeling. In the present study, we examined constitutive differences in TGF-beta levels in primary bone cell cultures from the iliac crest of 112 women, aged 28-79 years. TGF-beta1 was the major TGF-beta isoform in the conditioned media, as determined by neutralizing TGF-beta activity with specific antibodies against TGF-beta1-3 in the mink lung cell bioassay, and by enzyme-linked immunoassay (ELISA). TGF-beta1 levels in the conditioned media did not change with donor age. There was a lack of association between TGF-beta levels in vitro and the concentration of matrix-associated TGF-beta in vivo. TGF-beta1 levels failed to be associated with the local trabecular bone volume in the complete study population (r = +0.15, p = 0.16, n = 89). A significant association between TGF-beta1 levels and bone volume was present in premenopausal women (r = +0.39, p = 0.02, n = 33), but was largely accounted for by the two samples with the highest TGF-beta concentrations. In conclusion, our data suggest that TGF-beta1 is the major TGF-beta isoform produced by human bone cells in vitro, and that the constitutive secretion of TGF-beta by bone cells does not change with age. Whether constitutive differences in TGF-beta secretion may be a determinant of human bone mass remains to be clarified in further studies.