Insulin-like growth factor I stimulates proliferation and Fas-mediated apoptosis of human osteoblasts

Estrogens decrease osteoclast number by attenuating mitochondria oxidative phosphorylation and ATP production in early osteoclast precursors

Loss of estrogens at menopause is a major cause of osteoporosis and increased fracture risk. Estrogens protect against bone loss by decreasing osteoclast number through direct actions on cells of the myeloid lineage. Here, we investigated the molecular mechanism of this effect. We report that 17β-estradiol (E₂) decreased osteoclast number by promoting the apoptosis of early osteoclast progenitors, but not mature osteoclasts. This effect was abrogated in cells lacking Bak/Bax-two pro-apoptotic members of the Bcl-2 family of proteins required for mitochondrial apoptotic death. FasL has been previously implicated in the pro-apoptotic actions of E₂. However, we show herein that FasL-deficient mice lose bone mass following ovariectomy indistinguishably from FasL-intact controls, indicating that FasL is not a major contributor to the anti-osteoclastogenic actions of estrogens. Instead, using microarray analysis we have elucidated that ERα-mediated estrogen signaling in osteoclast progenitors decreases "oxidative phosphorylation" and the expression of mitochondria complex I genes. Additionally, E₂ decreased the activity of complex I and oxygen consumption rate. Similar to E₂, the complex I inhibitor Rotenone decreased osteoclastogenesis by promoting osteoclast progenitor apoptosis via Bak/Bax. These findings demonstrate that estrogens decrease osteoclast number by attenuating respiration, and thereby, promoting mitochondrial apoptotic death of early osteoclast progenitors.

An insulin-like growth factor homologue of Singapore grouper iridovirus modulates cell proliferation, apoptosis and enhances viral replication

Insulin-like growth factors (IGFs) play crucial roles in regulating cell differentiation, proliferation and apoptosis. In this study, a novel IGF homologue gene (IGF-like) encoded by Singapore grouper iridovirus (SGIV) ORF062R (termed SGIV–IGF), was cloned and characterized. The coding region of SGIV–IGF is 771 bp in length, with a variable number of tandem repeats (VNTR) locus at the 3′-end. We cloned one isoform of this novel gene, 582 bp in length, containing the predicted IGF domain and 3.6 copy numbers of the 27 bp repeat unit. SGIV–IGF was an early transcribed gene during viral infection, and SGIV–IGF was distributed predominantly in the cytoplasm with a diffused granular appearance. Intriguingly, overexpression of SGIV–IGF was able to promote the growth of grouper embryonic cells (GP cells) by promoting G1/S phase transition, which was at least partially dependent on its 3′-end VNTR locus. Furthermore, viral titre assay and real-time quantitative PCR (RT-qPCR) analysis proved that SGIV–IGF could promote SGIV replication in grouper cells. In addition, overexpression of SGIV–IGF mildly facilitated apoptosis in SGIV-infected non-host fathead minnow (FHM) cells. Together, our study demonstrated a novel functional gene of SGIV which may regulate viral replication and cellular processes through multiple mechanisms that appear to be cell type-dependent.

A Novel Role of IGF1 in Apo2L/TRAIL-Mediated Apoptosis of Ewing Tumor Cells

Insulin-like growth factor 1 (IGF1) reputedly opposes chemotoxicity in Ewing sarcoma family of tumor (ESFT) cells. However, the effect of IGF1 on apoptosis induced by apoptosis ligand 2 (Apo2L)/tumor necrosis factor (TNF-) related apoptosis-inducing ligand (TRAIL) remains to be established. We find that opposite to the partial survival effect of short-term IGF1 treatment, long-term IGF1 treatment amplified Apo2L/TRAIL-induced apoptosis in Apo2L/TRAIL-sensitive but not resistant ESFT cell lines. Remarkably, the specific IGF1 receptor (IGF1R) antibody α-IR3 was functionally equivalent to IGF1. Short-term IGF1 incubation of cells stimulated survival kinase AKT and increased X-linked inhibitor of apoptosis (XIAP) protein which was associated with Apo2L/TRAIL resistance. In contrast, long-term IGF1 incubation resulted in repression of XIAP protein through ceramide (Cer) formation derived from de novo synthesis which was associated with Apo2L/TRAIL sensitization. Addition of ceramide synthase (CerS) inhibitor fumonisin B1 during long-term IGF1 treatment reduced XIAP repression and Apo2L/TRAIL-induced apoptosis. Noteworthy, the resistance to conventional chemotherapeutic agents was maintained in cells following chronic IGF1 treatment. Overall, the results suggest that chronic IGF1 treatment renders ESFT cells susceptible to Apo2L/TRAIL-induced apoptosis and may have important implications for the biology as well as the clinical management of refractory ESFT.

Effects of Safflower Seed Oil in Osteoporosis Induced-Ovariectomized Rats

The effects of Korean Safflower (Carthamus tinctorius L) seed oil (SSO) on osteoporosis induced-ovariectomized rats were investigated. A total of 90 female Sprague-Dawley rats, 4-month-old, weighing 200–230 g were randomly assigned into 3 groups (30 animals/group). The animals in group I were sham operated and those of group II and III were ovariectomized (Ovx). After eight weeks, the animals of group I and II received solvent vehicle daily, whereas those of group III were administered SSO orally (1 ml/kg) daily for 30 days. The changes in the serum levels of insulin-like growth factor-I (IGF-I), IGF-II, insulin-like growth factor binding protein-3 (IGBP-3), estrogen, total alkaline phosphatase (TALP), bone-specific alkaline phosphatase (BALP), calcium and phosphorous in serum, and also the histomorphology of the proximal tibia metaphysis and femur/body weight (F/B) ratio were examined in all the groups at every 10 days interval. Thirty days later, IGF-I, IGF-II, IGBP-3 and BALP levels were significantly increased ( p < 0.05) in group III as compared to groups I and II. There were no significant differences in serum levels of estrogen, TALP and F/B ratio between groups II and III, but estrogen levels were higher in group I. These results suggest that the safflower seeds have possible roles in the improvement of osteoporosis induced-ovariectomized rats.

Development of POEMS syndrome after an initial manifestation of solitary plasmacytoma

A 44-year-old male was admitted for numbness in the left arm. CT showed a tumor impacting on the spinal cord with an adjacent thoracic vertebral osteosclerotic lesion. The histopathology of the tumor showed diffuse proliferation of atypical plasma cells with expressed vascular endothelial growth factor (VEGF), which is a known etiological factor in POEMS syndrome. Though serum VEGF (sVEGF) level was elevated, a diagnosis of solitary plasmacytoma with an osteosclerotic lesion was made as the patient presented no polyneuropathy, organomegaly, endocrinopathy, or skin changes. The patient experienced muscle weakness of the lower limbs and skin pigmentation/hemangioma one year after irradiation of the osteosclerotic lesion. Laboratory tests revealed hypothyroidism, hyperglycemia, serum monoclonal gammopathy, further elevation of sVEGF, and increased atypical bone marrow plasma cells. CT imaging showed splenomegaly, and a nerve conduction test revealed demyelinating motor peripheral neuropathy. The patient was therefore diagnosed with POEMS syndrome. Plasmacytoma is very rare as an initial manifestation of POEMS syndrome. Patients presenting with plasmacytoma with an osteosclerotic lesion should be carefully observed and evaluated for the expression of sVEGF and development of POEMS syndrome, as most bone plasmacytomas in POEMS syndrome patients are reported to be osteosclerotic. This is to our knowledge the first case of osteosclerotic plasmacytoma that progressed to POEMS syndrome, with an increase of sVEGF.

Targeting Fas in osteoresorptive disorders

IMPORTANCE OF THE FIELD

Fas receptor is a mediator of the external apoptotic pathway in many cells and tissues. It is proposed that Fas receptor mediates osteoresorptive effects of estrogen deficiency and local/systemic inflammation.

AREAS COVERED IN THIS REVIEW

This review covers the past two decades of research on the expression and function of the Fas-Fas ligand system on bone cells, involvement in the pathogenesis of osteoresorption and potential therapeutic modulation.

WHAT THE READER WILL GAIN

We review the structure, biological function and intracellular signaling pathways of the Fas-Fas ligand system emphasizing the role of the non-apoptotic signaling pathways in bone cells, particularly osteoblast differentiation. We also present data on the in vitro expression and function of the Fas-Fas ligand system on osteoblast/osteoclast lineage cells, animal and human studies confirming its involvement in osteoresorptive disorders and potential therapeutic approaches to modulate its function.

TAKE HOME MESSAGE

Tissue specific therapeutic approaches need to be established to modify the Fas-Fas ligand system in osteoresorptive disorders as systemic targeting has many side effects. The most promising approach would be to target Fas signaling molecules coupled with osteoblast/osteoclast differentiation pathways, but a precise definition of these targets is still needed.

From estrogen-centric to aging and oxidative stress: a revised perspective of the pathogenesis of osteoporosis

Estrogen deficiency has been considered the seminal mechanism of osteoporosis in both women and men, but epidemiological evidence in humans and recent mechanistic studies in rodents indicate that aging and the associated increase in reactive oxygen species (ROS) are the proximal culprits. ROS greatly influence the generation and survival of osteoclasts, osteoblasts, and osteocytes. Moreover, oxidative defense by the FoxO transcription factors is indispensable for skeletal homeostasis at any age. Loss of estrogens or androgens decreases defense against oxidative stress in bone, and this accounts for the increased bone resorption associated with the acute loss of these hormones. ROS-activated FoxOs in early mesenchymal progenitors also divert ss-catenin away from Wnt signaling, leading to decreased osteoblastogenesis. This latter mechanism may be implicated in the pathogenesis of type 1 and 2 diabetes and ROS-mediated adverse effects of diabetes on bone formation. Attenuation of Wnt signaling by the activation of peroxisome proliferator-activated receptor gamma by ligands generated from lipid oxidation also contributes to the age-dependent decrease in bone formation, suggesting a mechanistic explanation for the link between atherosclerosis and osteoporosis. Additionally, increased glucocorticoid production and sensitivity with advancing age decrease skeletal hydration and thereby increase skeletal fragility by attenuating the volume of the bone vasculature and interstitial fluid. This emerging evidence provides a paradigm shift from the "estrogen-centric" account of the pathogenesis of involutional osteoporosis to one in which age-related mechanisms intrinsic to bone and oxidative stress are protagonists and age-related changes in other organs and tissues, such as ovaries, accentuate them.

The estrogen receptor-alpha in osteoclasts mediates the protective effects of estrogens on cancellous but not cortical bone

Estrogens attenuate osteoclastogenesis and stimulate osteoclast apoptosis, but the molecular mechanism and contribution of these effects to the overall antiosteoporotic efficacy of estrogens remain controversial. We selectively deleted the estrogen receptor (ER)alpha from the monocyte/macrophage cell lineage in mice (ERalpha(LysM)(-/-)) and found a 2-fold increase in osteoclast progenitors in the marrow and the number of osteoclasts in cancellous bone, along with a decrease in cancellous bone mass. After loss of estrogens these mice failed to exhibit the expected increase in osteoclast progenitors, the number of osteoclasts in bone, and further loss of cancellous bone. However, they lost cortical bone indistinguishably from their littermate controls. Mature osteoclasts from ERalpha(LysM)(-/-) were resistant to the proapoptotic effect of 17beta-estradiol. Nonetheless, the effects of estrogens on osteoclasts were unhindered in mice bearing an ERalpha knock-in mutation that prevented binding to DNA. Moreover, a polymeric form of estrogen that is not capable of stimulating the nuclear-initiated actions of ERalpha was as effective as 17beta-estradiol in inducing osteoclast apoptosis in cells with the wild-type ERalpha. We conclude that estrogens attenuate osteoclast generation and life span via cell autonomous effects mediated by DNA-binding-independent actions of ERalpha. Elimination of these effects is sufficient for loss of bone in the cancellous compartment in which complete perforation of trabeculae by osteoclastic resorption precludes subsequent refilling of the cavities by the bone-forming osteoblasts. However, additional effects of estrogens on osteoblasts, osteocytes, and perhaps other cell types are required for their protective effects on the cortical compartment, which constitutes 80% of the skeleton.

Pro- and anti-apoptotic roles for IGF-I in TNF-alpha-induced apoptosis: a MAP kinase mediated mechanism

OBJECTIVE

The concept of skeletal muscle homeostasis--often viewed as the net balance between two separate processes, namely protein degradation and protein synthesis--are not occurring independently of each other, but are finely co-ordinated by a web of intricate signalling networks.

MATERIALS AND METHODS

Using rodent muscle cell lines we have investigated TNF-alpha/IGF-I interactions, in an attempt to mimic and understand mechanisms underlying the wasting process.

RESULTS AND CONCLUSION

When myoblast cells are incubated with TNF-alpha (10 ng ml(- 1)) maximal damage ( approximately 21% +/- 0.7 myoblast death, p < 0.05) was induced. Co-incubation of TNF-alpha (10 ng ml(- 1)) with IGF-I resulted in cell survival ( approximately 50% reduction in myoblast death, p < 0.05), however, myotube formation was not evident. In contrast, a novel role of IGF-I has been identified whereby co-incubation of muscle cells with IGF-I (1.5 ng ml(- 1)) and a non-apoptotic dose of TNF-alpha (1.25 ng ml(- 1); sufficient to block differentiation) unexpectedly were shown not to rescue a block on differentiation but to facilitate significant myoblast death (p < 0.05). Interestingly, pre-administration of PD98059, a MAPK signal-blocking agent followed by co-incubation of 1.25 ng ml(- 1) TNF-alpha and 1.5 ng ml(- 1) IGF-I, reduced death to baseline levels (p < 0.05). We show for the first time that IGF-I can be apoptotic in the absence of TNF-alpha-induced cell death.

Estrogen and the selective estrogen receptor modulator (SERM) protection against cell death in estrogen receptor alpha and beta expressing U2OS cells

In the current work, we compared the ability of 17beta-estradiol (E2) and the selective estrogen receptor modulators (SERMs), tamoxifen (Tam), raloxifene (Ral) and ospemifene (Osp) to promote the survival of osteoblast-derived cells against etoposide-induced apoptosis. In order to compare the roles of the two estrogen receptor (ER) isotypes, we created a U2OS human osteosarcoma cell line stably expressing either ERalpha (ERalpha) or ERbeta (ERbeta). Transfection with either of the ERs was able to render the U2OS cells sensitive to E2. We show that E2 opposed etoposide-induced apoptosis and that the effect was mediated via both ER isotypes. The ER isotype selective agonists propyl-pyrazole-triol (PPT) and diarylpropionitrile (DPN) had the same effect in U2OS/ERalpha and U2OS/ERbeta cells, respectively. Osp also opposed apoptosis at least in U2OS/ERalpha cells. Tam and Ral were not able to protect against etoposide-induced cell death. In order to evaluate the protective effects of E2 and Osp upon etoposide challenge, we studied the expression of two E2-regulated, osteoblast-produced cytokines, IL-6 and OPG in E2 and SERM-treated U2OS/ERalpha and U2OS/ERbeta cells. Etoposide strongly increased expression of IL-6 and decreased that of OPG. E2 opposed IL-6 increase only in U2OS/ERalpha cells and OPG decrease primarily in ERbeta cells. Osp opposed the effect of etoposide on OPG primarily in U2OS/ERbeta cells but interestingly, it had little effect on IL-6 expression. E2, PPT, DNP and Osp also inhibited etoposide-induced death and cytokine changes in SAOS-2 osteosarcoma cells expressing endogenous ERalpha and ERbeta. Collectively, our results suggest that the osteoblast protective anti-apoptotic effects of E2 are mediated by both ERalpha and ERbeta but those of Osp primarily by ERalpha. In addition, E2 and Osp opposed the etoposide-induced increase of IL-6 and decrease of OPG which changes would increase osteoclastic activity. These anti-resorptive effects of E2 and Osp upon etoposide challenge differed from each other and they seemed to be differentially mediated in ERalpha and ERbeta expressing osteoblast-derived U2OS cells.

Adrenomedullin is anti-apoptotic in osteoblasts through CGRP1 receptors and MEK-ERK pathway

Adrenomedullin (ADM) has been shown to mediate multifunctional responses in cell culture and animal system such as regulation of growth and apoptosis. ADM stimulates the proliferation of osteoblasts in vitro and promotes bone growth in vivo. The ability of ADM to influence osteoblastic cell number through inhibition of apoptosis has not yet been studied. To address this question we have investigated its effect on the apoptosis of serum-deprived osteoblastic cells using mouse MC3T3-E1 cells which express both ADM and ADM receptors. Treatment with ADM significantly blunted apoptosis, evaluated by caspase-3 activity, DNA fragmentation quantification and annexin V-FITC labeling. This effect was abolished by the subtype-1 CGRP receptor antagonist, CGRP(8-37). Both ADM and its specific receptor antagonist, the (22-52) ADM fragment exhibited a similar anti-apoptotic effect. Thus, our data suggest that ADM exerts anti-apoptotic effects through CGRP1 receptors. This was substantiated by a similar protective effect of CGRP on MC3T3-E1 cells apoptosis. Accordingly, neutralization of endogenous ADM by a specific antibody enhanced apoptosis. Finally, the selective inhibitor of MAPK kinase (MEK), PD98059, abolished the apoptosis protective effect of ADM and prevented ADM activation of ERK1/2. These data show that ADM acts as a survival factor in osteoblastic cells via a CGRP1 receptor-MEK-ERK pathway, which provides further understanding on the physiological function of ADM in osteoblasts.

Temporal analysis of E2 transcriptional induction of PTP and MKP and downregulation of IGF-I pathway key components in the mouse uterus

17beta-Estradiol (E2) is well known to be associated with uterine cancer, endometriosis, and leiomyomas. Although insulin-like growth factor I (IGF-I) has been identified as a mediator of the uterotrophic effect of E2 in several studies, this mechanism is still not well understood. In the present study, identification of the genes modulated by a physiological dose of E2, in the uterus, has been done in ovariectomized mice using Affymetrix microarrays. The E2-induced genomic profile shows that multiple genes belonging to the IGF-I pathway are affected after exposure to E2. Two phases of regulation could be identified. First, from 0 to 6 h, the expression of genes involved in the cell cycle, growth factors, protein tyrosine phosphatases, and MAPK phosphatases is quickly upregulated by E2, while IGF-I receptor and several genes of the MAPK and phosphatidylinositol 3-kinase pathways are downregulated. Later, i.e., from 6 to 24 h, transporters and peptidases/proteases are stimulated, whereas defense-related genes are differentially regulated by E2. Finally, cytoarchitectural genes are modulated later. The present data show that a physiological dose of E2 induces, within 24 h, a series of transcriptional events that promote the uterotrophic effect. Among these, the E2-mediated activation of the IGF-I pathway seems to play a pivotal role in the uterotrophic effect. Furthermore, the protein tyrosine phosphatases and MAPK phosphatases are likely to modulate the estrogenic uterotrophic action by targeting, at different steps, the IGF-I pathway.

Insulin-like growth factor-I receptor correlates with connexin 26 and Bcl-xL expression in human colorectal cancer

Insulin-like growth factor (IGF) and its receptor (IGF-IR) play an important role in mitogenesis, apoptosis, growth, and proliferation of several types of cancers. Overexpression of IGF-IR in colorectal cancer is associated with increase of cancer cell proliferation and migration as well as inhibition of apoptosis. In our previous reports we demonstrated correlations between IGF-IR and apoptosis. Moreover, we observed relationships between connexin26 (Cx26) expression and apoptotic markers in human colorectal cancer. Recently, it has been shown that expression of connexins and gap junction (GJ) functions are also regulated by growth factors, including IGF-I. Therefore, in this study we have focused on the relationships between IGF-IR and Cx26 as well as Bcl-xL expression. A total number of 115 cases of colorectal cancer were examined by immunohistochemistry, using the avidin-biotin-peroxidase method. Associations among the above proteins were assessed in the entire group of colorectal cancer patients and its subgroups, depending on lymph node involvement (N0 and N1), histological grade (G2 and G3), extent of tumor growth (pT1+pT2 and pT3+pT4), histopathologic type (adenocarcinoma and mucinous carcinoma), sex, age (<or=60 and>60), and tumor site (colon and rectum). The expression of IGF-IR, Cx26, and Bcl-xL was noted in 47%, 56.5%, and 75.6% of the tumors, respectively. In the entire group of patients we found a positive correlation between IGF-IR and Cx26 (P<0.0001, r=0.374) as well as between IGF-IR and Bcl-xL (P<0.0001, r=0.344). Our results may suggest that the insulin-like growth system is involved in regulation of apoptosis and probably connexin expression in colorectal cancer cells.

Characterization of human fetal osteoblasts by microarray analysis following stimulation with 58S bioactive gel-glass ionic dissolution products

Bioactive glasses dissolve upon immersion in culture medium, releasing their constitutive ions in solution. There is evidence suggesting that these ionic dissolution products influence osteoblast-specific processes. Here, we investigated the effect of 58S sol-gel-derived bioactive glass (60 mol % SiO2, 36 mol % CaO, 4 mol % P2O5) dissolution products on primary osteoblasts derived from human fetal long bone explant cultures (hFOBs). We used U133A human genome GeneChip oligonucleotide arrays to examine 22,283 transcripts and variants, which represent over 18,000 well-substantiated human genes. Hybridization of samples (biotinylated cRNA) derived from monolayer cultures of hFOBs on the arrays revealed that 10,571 transcripts were expressed by these cells, with high confidence. These included transcripts representing osteoblast-related genes coding for growth factors and their associated molecules or receptors, protein components of the extracellular matrix (ECM), enzymes involved in degradation of the ECM, transcription factors, and other important osteoblast-associated markers. A 24-h treatment with a single dosage of ionic products of sol-gel 58S dissolution induced the differential expression of a number of genes, including IL-6 signal transducer/gp130, ISGF-3/STAT1, HIF-1 responsive RTP801, ERK1 p44 MAPK (MAPK3), MAPKAPK2, IGF-I and IGFBP-5. The over 2-fold up-regulation of gp130 and MAPK3 and down-regulation of IGF-I were confirmed by real-time RT-PCR analysis. These data suggest that 58S ionic dissolution products possibly mediate the bioactive effect of 58S through components of the IGF system and MAPK signaling pathways.

Insulin-like growth factor-1 treatment prevents anti-Fas antibody-induced apoptosis in endplate chondrocytes

STUDY DESIGN

In vitro investigation of vertebral endplate chondrocyte apoptosis.

OBJECTIVES

To determine whether Fas antibody caused apoptosis in endplate chondrocytes, and whether insulin-like growth factor-1 (IGF-1) inhibited this effect. Integrin-alpha1 and focal adhesion kinase (FAK) expression in conjunction with apoptosis was also investigated.

SUMMARY OF BACKGROUND DATA

Binding of Fas antibody to Fas mimics Fas-FasL ligation, which causes apoptosis. IGF-1 has been shown to have anti-apoptotic effects.

MATERIALS AND METHODS

Rat cervical endplate chondrocytes were cultured and treated with Fas antibody, with or without IGF-1. Cellular morphology was examined by microscopy. Apoptotic changes were evaluated by transmission electron microscopy, TUNEL staining, and immunostaining. Apoptosis-induced changes in the expression of integrin-alpha1 chain and FAK were also investigated.

RESULTS

Endplate chondrocytes were able to be cultured; a chondrocytic phenotype was maintained. Fas antibody induced apoptosis in endplate chondrocytes; this was confirmed by TUNEL staining. Bcl-2 expression was decreased by Fas antibody, while Bax expression increased. Integrin-alpha1 and FAK expression was decreased by Fas antibody. IGF-1 treatment inhibited these Fas antibody-induced changes.

CONCLUSIONS

Fas antibody induces apoptosis and decreases Integrin-alpha1 and FAK expression in cultured endplate chondrocytes; IGF-1 is protective against these changes.

Membrane rafts segregate pro- from anti-apoptotic insulin-like growth factor-I receptor signaling in colon carcinoma cells stimulated by members of the tumor necrosis factor superfamily

In the tumor microenvironment, autocrine/paracrine loops of insulin-like growth factors (IGFs) contribute to cancer cell survival. However, we report here that IGF-I can send contradictory signals that interfere with cell death induced by different ligands of the tumor necrosis factor (TNF) superfamily. IGF-I protected human colon carcinoma cells from TNF-alpha-induced apoptosis, but it enhanced the apoptotic response to anti-Fas antibody and TNF-related apoptosis inducing ligand stimulation. This proapoptotic effect of IGF-I, observed in several but not all tested colon cancer cell lines, was mediated via the phosphatidylinositol 3'-kinase (PI3K)/Akt pathway. Furthermore, IGF-I receptors (IGF-IR) were located in and out of membrane lipid rafts and were tyrosine autophosphorylated in response to IGF-I. However, disruption of rafts by acute cholesterol depletion shifted IGF-IR to non-raft domains, abolished the IGF-I-mediated proapoptotic effect, and inhibited the IGF-I-dependent IRS-1 and Akt recruitment into and phosphorylation/activation within lipid rafts. Replenishing cell membranes with cholesterol reversed these effects. Activation of extracellular-regulated kinase-1/2 and p38 mitogen-activated protein kinase, which convey the IGF-I anti-apoptotic effect, occurred independently of lipid rafts. Thus, we propose that segregation of IGF-IR in and out of lipid rafts may dynamically regulate the pro- and anti-apoptotic effects of IGF-I on apoptosis induced by TNF superfamily members.

Syndecan-2 overexpression induces osteosarcoma cell apoptosis: Implication of syndecan-2 cytoplasmic domain and JNK signaling

Syndecans are cell surface heparan sulfate proteoglycans that serve as co-receptors and modulate the actions of a number of extracellular ligands. Syndecans thereby regulate cell adhesion, proliferation, and differentiation. Studies in cancer cells suggest that syndecans may also modulate cell viability. We previously showed that syndecan-2 controls the growth of normal human osteoblastic cells. In this study, we examined the role of syndecan-2 in osteosarcoma cell proliferation and apoptosis. To this goal, MG63 osteosarcoma cells which express low syndecan-2 levels were transfected to overexpress full-length syndecan-2 or truncated syndecan-2 lacking its cytoplasmic domain. Determination of cell growth by cell counting and 3H-thymidine incorporation showed that truncated syndecan-2 inhibited MG63 cell proliferation. Flow cytometry analysis of DNA content and colony forming test revealed that syndecan-2, but not truncated syndecan-2, induced MG63 cell death. We show that characteristic features of apoptosis such as caspase activation, PARP cleavage, cytochrome c release, increased Bax expression, and DNA fragmentation were associated with syndecan-2-induced cell death. We further show that expression of full-length or truncated syndecan-2 induced differential activation of MAPK phosphorylation in MG63 cells. Notably, syndecan-2 but not truncated syndecan-2 overexpression increased JNK phosphorylation. Moreover, SP600125, a specific inhibitor of JNK, suppressed Bax expression induced by syndecan-2 overexpression, indicating that JNK activation mediates syndecan-2-induced apoptosis. The results show that syndecan-2 induces osteoblastic cell apoptosis through the JNK/Bax apoptotic pathway and that the cytoplasmic domain of syndecan-2 is required for this action. This supports a role for syndecan-2 in the regulation of osteosarcoma cell fate and identifies one signaling pathway by which syndecan-2 induces apoptosis in osteosarcoma cells.

Expression of the insulin-like growth factor-I receptor and proapoptotic Bax and Bak proteins in human colorectal cancer

Insulin-like growth factor-I (IGF-I) and IGF-I receptor (IGF-IR), despite their well-known roles in cell survival and proliferation, can also weakly enhance apoptosis. To study the relationships between the IGF-IR and Bax as well as Bak, 144 cases of colorectal cancer were examined by immunohistochemistry, using the avidin-biotin-peroxidase method. The results were correlated with selected clinicopathological features of colorectal cancer and with the expression of IGF-IR, Bax, and Bak in normal colon mucosa. In Bax-, Bak-, or IGF-IR-positive cancers, the adjacent colorectal mucosa revealed positive immunostaining for these proteins. In the majority of Bax-, Bak-, or IGF-IR-negative tumors, we observed no staining for these proteins in adjacent mucosa. The strong immunostaining for IGF-IR, Bax, and Bak was noted in 50.8, 55.5, and 49.3% of tumors, respectively. We observed positive correlations between IGF-IR and Bax (P < 0.002, r = 0.302), between IGF-IR and Bak (P < 0.0001, r = 0.407), and between Bax and Bak (P < 0.0001, r = 0.474). No relationship was noted between IGF-IR expression and tumor grade, stage, or lymph node status. We found negative associations between Bax, Bak, and tumor grade (P < 0.01 and P < 0.003, respectively), but no relationships between Bax and Bak and tumor stage or between Bax and Bak and lymph node status. Our results demonstrate that, in addition to overexpressed IGF-IR, there are relationships between IGF-IR and proapoptotic proteins in colorectal carcinomas that could contribute to increased cell turnover and the progression of colorectal cancer.

Age-related femoral bone loss in men: evidence for hyperparathyroidism and insulin-like growth factor-1 deficiency

BACKGROUND

We sought to determine the extent to which the age-related decline of femoral neck (FN) bone mineral density (BMD) might be explained by the age-related change of body composition and biological parameters and the mechanisms by which these factors might influence FN BMD in men.

METHODS

The relationships between FN BMD and anthropometric, hormonal, and biochemical parameters and bone turnover markers were studied in 82 men aged 25-86 years.

RESULTS

Age was associated with a decline of FN BMD and osteocalcin (OC), bone alkaline phosphatase (bALP), and urinary C-telopeptide (p <.05). The significant relationship between FN BMD and OC (p <.01) did not remain after adjustment for age. With use of multiple linear regression and adjusting for all significant variables associated with FN BMD in univariate analysis (p <.01) (age, weight, lean and fat mass, height, and levels of dehydroepiandrosterone sulfate, insulin-like growth factor [IGF-1], testosterone, and parathyroid hormone [PTH]), age accounted for 29.5% of FN BMD variance. When age was excluded from the model, PTH accounted for 19.5% and IGF-1 for 10% of the FN BMD variance. Bone turnover markers were significantly intercorrelated, and levels of IGF-1 were positively associated with those of bALP and OC (p <.05).

CONCLUSIONS

These results show that age is a strong predictor of FN BMD in men, resulting in a decline of bone remodeling, especially of bone formation. The results also show that, after taking into account anthropometric and other biological factors possibly involved in bone aging, the major part of the effect of age on bone is explained by the age-related increase of PTH and decrease of IGF-1 in men, suggesting that all measures taken to limit these age-related changes may be effective in the prevention of the age-related decline of FN BMD in men.

Effect of tensile force on the expression of IGF-I and IGF-I receptor in the organ-cultured rat cranial suture

Insulin-like growth factors (IGFs) play an important role in the regulation of bone metabolism. In this study, we investigated changes in the expression of IGF-I and IGF-I receptor and cell proliferation when a continuous tensile force was applied to the cranial suture of cultured rat calvaria. The parietal bones with the midsagittal suture were removed from male Wistar rats (19-days old), cultured for 24h, and divided into two groups. In the experimental group, tensile force (3 x 10(-3)N) was applied by helical springs to the midsagittal suture, whereas helical springs with no tension (0 N) were set in the control group. The tensile force significantly increased the expression of both IGF-I mRNA and protein (P < 0.05). By using in situ hybridisation, we also confirmed that IGF-I and IGF-I receptor mRNAs were localized in osteoblast-like and fibroblastic cells subjected to the tensile force. Also, this force stimulated the proliferation of osteoblast-like and fibroblastic cells in calvaria, without affecting their alkaline phosphatase activity. These results indicate that a tensile force applied to a cranial suture can cause an increase in the production of IGF-I and IGF-I receptors in osteoblast-like and fibroblastic cells, and this increase in IGF-I may cause the proliferation of the cells in an autocrine or paracrine manner.

Vitamin D inhibits Fas ligand-induced apoptosis in human osteoblasts by regulating components of both the mitochondrial and Fas-related pathways

Apoptosis plays an important role in the regulation of bone turnover. Previously, we showed that 1,25(OH)2D3, the active form of vitamin D, may increase osteoblast survival by inhibiting apoptosis induced by serum deprivation. Human osteoblasts express the Fas receptor on their surface and its interaction with Fas ligand has been closely associated with human osteoblast apoptosis. To investigate the mechanism of 1,25(OH)2D3 inhibition of apoptosis in osteoblasts isolated from human calvaria, cells were exposed to Fas antibody. Visualization of apoptotic cells using annexin V revealed a significant decrease in apoptosis at 48 h in the presence of 1,25(OH)2D3 (14 +/- 4%, P < 0.04) compared with non-treated cells (52 +/- 4%). Furthermore, flow cytometric analysis of TUNEL-labeled osteoblasts showed a significant decrease in apoptotic cells in 1,25(OH)2D3-treated cultures (12 +/- 2%) at 48 h compared with non-treated cultures (44 +/- 3%, P < 0.04). Additionally, cells treated with 1,25(OH)2D3 survived longer as found by MTS analysis. To further explore the mechanism of 1,25(OH)2D3-mediated inhibition of apoptosis, we examined the changes in activation of death domain proteins, cleavage of caspases and mitochondrial regulators of apoptosis by Western blot analysis. A significant inhibition of caspase-8 cleavage and activity in 1,25(OH)2D3-treated cells was observed in conjunction with a decrease in the expression of the proapoptotic protein Bax with a significant increase in the expression of antiapoptotic protein Bcl-2. Furthermore, the levels of p21Cip1/WAF1, which inhibits the cleavage of caspase-8, was found to be highly induced in 1,25(OH)2D3-treated cells. In summary, these results demonstrate that the anti-apoptotic effect of 1,25(OH)2D3 in human osteoblasts after the activation of Fas-ligand is mediated by the regulation of components of both the mitochondrial and Fas-related pathways.

Establishment of a bipotent cell line CL-1 which differentiates into chondrocytes and adipocytes from adult mouse

OBJECTIVE

Establishment of a clonal bipotent chondroprogenitor cell line from adult mouse to provide a new tool for the elucidation of chondrogenesis in adult animal.

DESIGN

A clonal cell line CL-1 was established from tibia of adult mouse. Differentiation of CL-1 was characterized in monolayer culture. Effects of growth factors (TGF-beta(1), IGF-I, bFGF) and hormones (all trans retinoic acid, 1 alpha.25(OH)(2)D(3), PTH (1-34)) on the growth and differentiation of CL-1 were examined. Bipotency of CL-1 in vivo was examined by transplantation into SCID mice.

RESULTS

CL-1 formed alcian blue (pH1.0) positive nodules spontaneously. The nodules were mineralized in the presence of ascorbic acid and beta-glycerophosphate. CL-1 differentiated also into oil red O positive adipocytes spontaneously. CL-1 cells expressed specific genes of chondrocytes (collagen type II, X, aggrecan) and adipocytes (PPAR-gamma(2), aP(2)). Hyaline cartilage and adipose tissue formation was observed also in subcutaneously transplanted CL-1 cells into SCID mice. These data demonstrate that CL-1 has bipotency either in vitro or in vivo. TGF-beta(1)suppressed growth of CL-1 and induced dominant chondrogenesis accompanied with marked suppression of adipogenesis in 10% FCS. IGF-I stimulated both growth (in 3% FCS) and differentiation of CL-1 into both lineages (in 10% FCS). 1 alpha.25(OH)(2)D(3)and all trans retinoic acid acted as negative regulators on proliferation and differentiation of CL-1 in 10% FCS.

CONCLUSIONS

CL-1 will be a useful tool for the understanding of chondrogenesis in adult animal. Furthermore, CL-1 can be also a powerful tool for screening of the chondrogenic agent.

IGF-I does not affect the proliferation or early osteogenic differentiation of human marrow stromal cells

The ability of insulin-like growth factor-I (IGF-I) to regulate the proliferation and differentiation of primitive osteogenic precursors (CFU-F) has been investigated in cultures of bone marrow stromal cells (BMSC) derived from a large cohort of adult human donors. Treatment with IGF-I (0.1-20 ng/mL, days 0-28) had no consistent effect on the number or size of colonies that formed or the proportion of colonies that expressed the developmental marker alkaline phosphatase (AP). At the end of primary culture, similar numbers of cells were harvested from the control and IGF-I-treated groups and there was no detectable difference in the expression of AP (activity or percentage of positive cells) or the developmental marker STRO-1. This was found to be the case whether IGF-I was added alone or in combination with 10 nM dexamethasone (Dx), a known inducer of osteogenic differentiation in this cell culture system. In contrast, cells derived from the same cohort of donors responded to treatment with fibroblast growth factor-2 (FGF-2) with an increase in the number and size of the colonies that formed, in proliferation and in the number of cells recovered in STRO-1(+)/AP(+) (osteoprogenitor) fraction. Further analysis revealed that the majority of BMSC expressed the alpha and beta subunits of the type 1 receptor for IGF-I (IGF-IR), in the expected 1:1 ratio. Treatment with Dx did not affect the expression of these receptor subunits (percentage of positive cells or number of sites per cell) but did increase the proportion of cells present in the IGF-I(+)/AP(+) fraction. The results of this investigation suggest that the beneficial effects of IGF-I on the skeleton are not mediated primarily via an effect on osteoprogenitor fraction and are thus consistent with the hypothesis that the effects of IGF-I are differentiation dependent and restricted largely to the more mature cells of the osteoblast lineage.

Bone growth stimulators. New tools for treating bone loss and mending fractures

In the new millennium, humans will be traveling to Mars and eventually beyond with skeletons that respond to microgravity by self-destructing. Meanwhile in Earth's aging populations growing numbers of men and many more women are suffering from crippling bone loss. During the first decade after menopause all women suffer an accelerating loss of bone, which in some of them is severe enough to result in "spontaneous" crushing of vertebrae and fracturing of hips by ordinary body movements. This is osteoporosis, which all too often requires prolonged and expensive care, the physical and mental stress of which may even kill the patient. Osteoporosis in postmenopausal women is caused by the loss of estrogen. The slower development of osteoporosis in aging men is also due at least in part to a loss of the estrogen made in ever smaller amounts in bone cells from the declining level of circulating testosterone and is needed for bone maintenance as it is in women. The loss of estrogen increases the generation, longevity, and activity of bone-resorbing osteoclasts. The destructive osteoclast surge can be blocked by estrogens and selective estrogen receptor modulators (SERMs) as well as antiosteoclast agents such as bisphosphonates and calcitonin. But these agents stimulate only a limited amount of bone growth as the unaffected osteoblasts fill in the holes that were dug by the now suppressed osteoclasts. They do not stimulate osteoblasts to make bone--they are antiresorptives not bone anabolic agents. (However, certain estrogen analogs and bisphosphates may stimulate bone growth to some extent by lengthening osteoblast working lives.) To grow new bone and restore bone strength lost in space and on Earth we must know what controls bone growth and destruction. Here we discuss the newest bone controllers and how they might operate. These include leptin from adipocytes and osteoblasts and the statins that are widely used to reduce blood cholesterol and cardiovascular damage. But the main focus of this article is necessarily the currently most promising of the anabolic agents, the potent parathyroid hormone (PTH) and certain of its 31- to 38-aminoacid fragments, which are either in or about to be in clinical trial or in the case of Lilly's Forteo [hPTH-(1-34)] tentatively approved by the Food and Drug Administration for treating osteoporosis and mending fractures.

Expression of insulin-like growth factor system constituents in differentiating rat osteoblastic cell populations

The synthetic glucocorticoid dexamethasone (Dex) and insulin-like growth factor-I and -II (IGF-I and -II) stimulate osteoprogenitor proliferation and differentiation in bone cell populations isolated from adult rat vertebrae. Since glucocorticoids have been shown to regulate gene expression of IGFs and IGF binding proteins (IGFBPs) in several experimental models, we investigated whether Dex-stimulated osteoprogenitor proliferation and differentiation was associated with changes in mRNA levels of the IGF system components (i.e., IGF-I and -II, the type 1 and 2 IGF receptor, the insulin receptor and six IGFBPs). Osteoprogenitor-containing bone cell populations were isolated from the outgrowth of vertebral explant cultures of 3-month-old female rats and cultured for 20 days. Total RNA was extracted at day 8, 14, and 20, and mRNA levels of the IGF system constituents were compared between differentiating (Dex-treated) and non-differentiating (control) cultures. Northern hybridization data from 8- and 20-day cultures showed that mRNA levels of IGF-I were markedly lower in Dex-treated cultures than in control cultures at day 8 and 20. At day 20, mRNA levels of IGFBP-3 were also lower in Dex-treated cultures. Signals of IGFBP-5 mRNA were undetectable. To increase the sensitivity of our detection methods and therefore evaluate mRNA levels of all the components of the IGF system, we performed reverse transcription-polymerase chain reaction (RT-PCR) analysis of RNA extracted at day 8, 14, and 20 of culture. In agreement with the Northern data, IGF-I mRNA levels in Dex-treated cultures were lower than in control cultures at all three time points, and IGFBP-3 levels were lower in Dex-treated cultures at day 20 of culture. However, at day 8 and 14, IGFBP-3 mRNA levels were higher in Dex-treated cultures than in controls. Levels of the 2 IGF receptor mRNA and the insulin receptor mRNA were lower in Dex-treated cultures. Dex-treated cultures also had decreased levels of IGFBP-1 mRNA but increased levels of IGFBP-2 mRNA at all three time points. IGFBP-4 levels were lower at day 14 in Dex-treated cultures than in controls but higher at day 20. IGF-II and IGFBP-5 mRNA levels in control and Dex-treated cultures were similar. Signals for IGFBP-6 were undetectable. Our findings show that glucocorticoid-induced osteoprogenitor proliferation and differentiation in adult rat bone cell populations are associated with significant changes in the mRNA levels of virtually all components of the IGF system. Some of these changes are dependent on the stages of development (e.g., regulation of IGFBP-3 and -4) and some remain similar trends at all stages (e.g., regulation of IGF-I and the three receptors).

Mechanisms balancing skeletal matrix synthesis and degradation

Bone is regulated by evolutionarily conserved signals that balance continuous differentiation of bone matrix-producing cells against apoptosis and matrix removal. This is continued from embryogenesis, where the skeleton differentiates as a solid mass and is shaped into separate bones by cell death and proteolysis. The two major tissues of the skeleton are avascular cartilage, with an extracellular matrix based on type II collagen and hydrophilic proteoglycans, and bone, a stronger and lighter material based on oriented type I collagen and hydroxyapatite. Both differentiate from the same mesenchymal stem cells. This differentiation is regulated by a family of related signals centred on bone morphogenic proteins. Fibroblast growth factors, Indian hedgehog and parathyroid hormone-related protein are important in determining the type of matrix and the relation of skeletal and non-skeletal structures. Removal of mineralized matrix involves apoptosis of matrix cells and differentiation of acid-secreting cells (osteoclasts) from macrophage precursors. Key regulators of matrix removal are signals in the tumour-necrosis-factor family. Osteoclasts dissolve bone by isolating a region of the matrix and secreting HCl and proteinases at that site. Successive cycles of removal and replacement allow growth, repair and remodelling. The signals for bone turnover are predominantly cell-membrane-associated, allowing very specific spatial regulation. In addition to its support function, bone is a reservoir of Ca2+, PO3-(4) and OH-. Secondary modulation of mineral secretion and bone degradation are mediated by humoral signals, including parathyroid hormone and vitamin D, as well as the cytokines that also regulate the underlying cell differentiation.

Effects of triiodothyronine on the insulin-like growth factor system in primary human osteoblastic cells in vitro

Thyroid hormone plays a major role in the regulation of bone metabolism but the mechanism by which this is accomplished is not clear. Interactions of thyroid hormone with the growth hormone/insulin-like growth factors (IGFs) axis suggest an alternate pathway of action for triiodothyronine (T(3)) on bone formation, besides direct effects. The present study investigates the influence of T(3) on IGF-1, IGF-2, IGF-1 receptor (IGF-1R), and IGF binding protein (IGFBP) transcripts, and on IGF-1 action in human osteoblastic cells (hOB) under serum-free culture conditions. No influence of T(3) on IGF-1, IGF-2, IGFBP-3, or IGFBP-4 mRNA levels in hOB was observed. However, T(3) at concentrations of 10(-8) mol/L and 10(-7) mol/L increased IGF-1R mRNA levels in a dose-dependent manner (p < 0.01) and enhanced IGFBP-5 mRNA levels at a concentration of 10(-7) mol/L (p < 0.05), as assessed by reverse transcriptase-polymerase chain reaction. Correspondingly, Scatchard analysis of [(125)I]-IGF-1 binding revealed that T(3) at 10(-7) mol/L increased the number of IGF-1 binding sites in hOB, with small changes in receptor affinity. In addition, a synergistic effect of T(3) and IGF-1 on hOB proliferation was found (p < 0.05). We conclude that IGF-1R and IGFBP-5 are thyroid hormone target genes in human osteoblasts, whereas IGF-1 mRNA expression itself appears not to be regulated by T(3) in hOB. However, T(3) stimulates IGF-1R mRNA expression as well as IGF-1 binding and IGF-1 induced cell proliferation in osteoblasts, thus suggesting thyroid hormone may potentiate the effect of IGF-1 at the receptor level. This may contribute to the positive effects of thyroid hormone on bone formation, which, in addition, may be modulated by increased IGFBP-5 expression.

Insulin-like growth factors (IGF-I and IGF-II) inhibit C2 skeletal myoblast differentiation and enhance TNF alpha-induced apoptosis

IGF-I and IGF-II are thought to be unique in their ability to promote muscle cell differentiation. Murine C2 myoblasts differentiate when placed into low serum media (LSM), accompanied by increased IGF-II and IGF binding protein-5 (IGFBP-5) production. Addition of 20 ng/ml TNF alpha on transfer into LSM blocked differentiation, IGF-II and IGFBP-5 secretion and induced apoptosis. We, therefore, wished to assess whether IGFs could protect against the effects of TNF alpha. Neither inhibition of differentiation or induction of apoptosis was rescued by co-incubation with IGF-I or IGF-II. A lower dose of TNF alpha (1 ng/ml) while not inducing apoptosis still inhibited myoblast differentiation by 56% +/- 12, (P < 0.001), indicating that induction of apoptosis is not the sole mechanism by which TNF alpha inhibits myoblast differentiation. Addition of IGF-I or IGF-II alone reduced differentiation by 49% +/- 15 and 33% +/- 20, respectively, (P < 0.001), although neither induced apoptosis. For muscle cells to differentiate, they must arrest in G0. We established that addition of IGF-I, IGF-II or TNF alpha to the myoblasts promoted proliferation. The myoblasts could not exit the cell cycle as efficiently as controls and differentiation was thus reduced. Unexpectedly, co-incubation of IGF-I or IGF-II with 1 ng/ml TNF alpha enhanced the inhibition of differentiation and induced apoptosis. In the absence of apoptosis we show an association between IGF-induced inhibition of differentiation and increased IGFBP-5 secretion. These results indicate that the effects of the IGFs on muscle may depend on the cytokine environment. In the absence of TNF alpha, the IGFs delay differentiation and promote myoblast proliferation whereas in the presence of TNF alpha the IGFs induce apoptosis.

Comparison of anti-apoptotic signalling by the insulin receptor and IGF-I receptor in preadipocytes and adipocytes

We compared the effectiveness of insulin receptor (IR) and type I insulin-like growth factor (IGF) receptor (IGFR) cytoplasmic domains in mediating anti-apoptotic effects in 3T3-L1 preadipocytes and adipocytes. We used TrkC/IR and TrkC/IGFR chimeras, stably expressed in these cells and stimulated with neurotrophin-3 (NT-3), so as to avoid interference from endogenous receptors. After 24-h serum deprivation, 10% of preadipocytes and 2% of adipocytes appeared apoptotic as determined by fluorescence-activated cell sorter (FACS) analysis of cells stained with propidium iodide (PI) and Annexin V. When NT-3 was added, the two chimeras inhibited apoptosis to the same extent by 80% in preadipocytes and 50% in adipocytes. Mutation of juxtamembrane tyrosines (IR Y960F, IGFR Y950F) abrogated these anti-apoptotic effects. Qualitatively similar results were obtained by determination of viable rather than apoptotic cells. We conclude that IR and IGFR have equal potential to inhibit apoptosis in cell backgrounds, which are normally responsive to either IGF-I or insulin.

Effect of vitamin K2 on osteoblast apoptosis: vitamin K2 inhibits apoptotic cell death of human osteoblasts induced by Fas, proteasome inhibitor, etoposide, and staurosporine

Vitamin K2 is used for the treatment of osteoporosis, but the precise mode of action is still not clear. We investigated the effects of vitamin K2 on apoptosis of human osteoblasts. Human osteoblastic cell line MG63 cells and human primary osteoblast-like cells obtained from bone fragments in corrective surgery were used as human osteoblasts. Cells were cultured with or without various concentrations of vitamin K2 and tumor necrosis factor-alpha (TNF-alpha). We then determined the proliferative response, expression of Fas and Bcl-2-related proteins, and Fas-mediated apoptosis of these cells induced by anti-Fas immunoglobulin M (IgM). In addition, the effect of vitamin K2 in osteoblast apoptosis induced by Z-Leu-Leu-Leu-aldehyde (LLL-CHO), etoposide, or staurosporine was also examined. Human osteoblasts did not show spontaneous apoptosis in culture, even in the presence of vitamin K2 or TNF-alpha. Furthermore, proliferation of the cells was not influenced by vitamin K2 or TNF-alpha. Fas was functionally expressed on human osteoblasts, and the treatment with TNF-alpha significantly enhanced both Fas expression and Fas-mediated apoptosis of osteoblasts. The addition of vitamin K2 to the culture resulted in a dose-dependent inhibition of functional Fas expression on osteoblasts, in the presence or absence of TNF-alpha. Treatment of human osteoblasts with vitamin K2 clearly suppressed Bax expression of the cells, although the expression of Bcl-2 was not influenced by vitamin K2. Fas ligand (FasL) cDNA transformants were cytotoxic against osteoblasts, and the cytotoxicity was increased when osteoblasts were treated with TNF-alpha. The addition of vitamin K2 to osteoblasts significantly decreased the cytotoxic effects of FasL cDNA transformants. Furthermore, apoptosis of human osteoblasts induced by LLL-CHO, etoposide, or staurosporine was also clearly suppressed in vitamin K2-treated osteoblasts. Our results suggest that vitamin K2 inhibits apoptotic cell death of osteoblasts and maintains the number of osteoblasts. These actions may explain the therapeutic efficacy of vitamin K2 in osteoporosis.

Differential effects of the insulin-like growth factor I receptor on radiosensitivity and spontaneous necrosis formation of human glioblastoma cells grown in multicellular spheroids

The purpose of this study is to investigate how the insulin-like growth factor I receptor (IGF-IR) affects cellular radiosensitivity when cells are cultured under different growth conditions. For this, A7(R) and A7(puro) cells were established from human glioblastoma GB A7 cells. The former were derived from the parent cells by stable cotransfection with plasmids carrying human IGF-IR cDNA and a puromycin resistance gene and the latter had the marker gene alone. The cells were either grown exponentially in monolayer cultures or grown in multicellular spheroids as an in vitro model for solid tumors. Spheroids were formed in the two different methods, liquid-overlay (LOC) and spinner (SPC) cultures. Although the growth rate of both cell lines in monolayer was exactly the same, the growth rate of A7(R) spheroids formed in LOC was higher than that of A7(puro) spheroids. A central necrosis region was histologically observed in A7(puro) spheroids, but the corresponding region in A7(R) spheroids was almost completely filled with intact cells in both LOC and SPC spheroids. Both cell lines showed the same radiosensitivity in monolayer cultures in terms of cell viability and clonogenic cell survival. When the spheroids formed in LOC were X-irradiated, the radiosensitivity of A7(R) and A7(puro) cells assayed for cellular clonogenicity was also the same. However, in the spheroids formed in SPC, A7(R) cells were significantly more radiosensitive than A7(puro) cells. The results indicate that overexpression of the IGF-IR could induce radiosensitization of human tumor cells in spheroids while inhibiting spontaneous necrosis formation. This may open a possibility to explore the novel function of the IGF-IR.

Growth hormone prevents human monocytic cells from Fas-mediated apoptosis by up-regulating Bcl-2 expression

Apoptosis and particularly Fas-mediated apoptosis has been proposed to play a key role in controlling monocyte homeostasis. We and others have documented the regulatory function of human growth hormone (hGH) on monocytic cells, which prompted us to investigate the role of hGH on their response to Fas antigen cross-linking. Using human promonocytic U937 cells constitutively producing hGH upon gene transfer and human primary monocytes cultured in the presence of recombinant hGH, we demonstrated that hGH diminished Fas-mediated cell death by enhancing the expression of the antiapoptotic oncoprotein Bcl-2 as well as the level of bcl-2alpha mRNA. In parallel, we established that overexpression of Bcl-2 through gene transfer into normal U937 cells also diminished Fas-induced apoptosis. Further, as a result of Bcl-2 overexpression, we found that hGH greatly depressed Fas-induced activation of the cysteine protease caspase-3 (CPP32), which in turn affected the cleavage of poly(ADP-ribose) polymerase. Altogether, these data provide evidence that hGH mediates its protective effect through a Bcl-2-dependent pathway, clearly a crucial step in enhanced survival of monocytic cells exposed to Fas-induced death.