Age-related changes in effects of insulin-like growth factor I on human osteoblast-like cells

Melatonin effects on bone: Implications for use as a therapy for managing bone loss

Melatonin is the primary circadian output signal from the brain and is mainly synthesized in pinealocytes. The rhythm and secretion of melatonin are under the control of an endogenous oscillator located in the SCN or the master biological clock. Disruptions in circadian rhythms by shift work, aging, or light at night are associated with bone loss and increased fracture risk. Restoration of nocturnal melatonin peaks to normal levels or therapeutic levels through timed melatonin supplementation has been demonstrated to provide bone-protective actions in various models. Melatonin is a unique molecule with diverse molecular actions targeting melatonin receptors located on the plasma membrane or mitochondria or acting independently of receptors through its actions as an antioxidant or free radical scavenger to stimulate osteoblastogenesis, inhibit osteoclastogenesis, and improve bone density. Its additional actions on entraining circadian rhythms and improving quality of life in an aging population coupled with its safety profile make it an ideal therapeutic candidate for protecting against bone loss in susceptible populations. The intent of this review is to provide a focused discussion on bone loss and disorders of the bone as it relates to melatonin and conditions that modify melatonin levels with the hope that future therapies include those that include melatonin and correct those factors that modify melatonin levels like circadian disruption.

Biglycan Regulates MG63 Osteosarcoma Cell Growth Through a LPR6/β-Catenin/IGFR-IR Signaling Axis

Biglycan, a small leucine rich proteoglycan (SLRP), is an important participant in bone homeostasis and development as well as in bone pathology. In the present study biglycan was identified as a positive regulator of MG63 osteosarcoma cell growth (p ≤ 0.001). IGF-I was shown to increase biglycan expression (p ≤ 0.01), whereas biglycan-deficiency attenuated significantly both basal and IGF-I induced cell proliferation of MG63 cells (p ≤ 0.001; p ≤ 0.01, respectively). These effects were executed through the IGF-IR receptor whose activation was strongly attenuated (p ≤ 0.01) in biglycan-deficient MG63 cells. Biglycan, previously shown to regulate Wnt/β-catenin pathway, was demonstrated to induce a significant increase in β-catenin protein expression evident at cytoplasmic (p ≤ 0.01), membrane (p ≤ 0.01), and nucleus fractions in MG63 cells (p ≤ 0.05). As demonstrated by immunofluorescence, increase in β-catenin expression is attributed to co-localization of biglycan with the Wnt co-receptor low-density lipoprotein receptor-related protein 6 (LRP6) resulting in attenuated β-catenin degradation. Furthermore, applying anti-β-catenin and anti-pIGF-IR antibodies to MG-63 cells demonstrated a cytoplasmic and to the membrane interaction between these molecules that increased upon exogenous biglycan treatment. In parallel, the downregulation of biglycan significantly inhibited both basal and IGF-I-dependent ERK1/2 activation, (p ≤ 0.001). In summary, we report a novel mechanism where biglycan through a LRP6/β-catenin/IGF-IR signaling axis enhances osteosarcoma cell growth.

Decorin, a growth hormone-regulated protein in humans

CONTEXT

Growth hormone (GH) stimulates connective tissue and muscle growth, an effect that is potentiated by testosterone. Decorin, a myokine and a connective tissue protein, stimulates connective tissue accretion and muscle hypertrophy. Whether GH and testosterone regulate decorin in humans is not known.

OBJECTIVE

To determine whether decorin is stimulated by GH and testosterone.

DESIGN

Randomized, placebo-controlled, double-blind study.

PARTICIPANTS AND INTERVENTION

96 recreationally trained athletes (63 men, 33 women) received 8 weeks of treatment followed by a 6-week washout period. Men received placebo, GH (2 mg/day), testosterone (250 mg/week) or combination. Women received either placebo or GH (2 mg/day).

MAIN OUTCOME MEASURE

Serum decorin concentration.

RESULTS

GH treatment significantly increased mean serum decorin concentration by 12.7 ± 4.2%; P < 0.01. There was a gender difference in the decorin response to GH, with greater increase in men than in women (∆ 16.5 ± 5.3%; P < 0.05 compared to ∆ 9.4 ± 6.5%; P = 0.16). Testosterone did not significantly change serum decorin. Combined GH and testosterone treatment increased mean decorin concentration by 19.5 ± 3.7% (P < 0.05), a change not significantly different from GH alone.

CONCLUSION

GH significantly increases circulating decorin, an effect greater in men than in women. Decorin is not affected by testosterone. We conclude that GH positively regulates decorin in humans in a gender-dimorphic manner.

Melatonin dietary supplement as an anti-aging therapy for age-related bone loss

INTRODUCTION

Previous studies have shown that melatonin, an anti-oxidant molecule secreted from the pineal gland, is a positive regulator of bone mass. However, the potential effects of melatonin on bone mass have never been investigated in an old population. The aim of this study was to assess the effects of dietary melatonin supplementation on mass accrual and biomechanical properties of old rat femora.

METHODS

Twenty 22-month-old male Wistar rats were divided into two randomly assigned groups. The first group was treated for 10 weeks with melatonin, whereas the second group was untreated (control). Rat femurs were collected, and their phenotypes and biomechanical properties were investigated by micro-computed tomography, histomorphometry, and a three-point-bending test. Statistical analyses were performed by the Student two-tailed unpaired t-test. In all experiments, a value of p<0.05 was considered significant.

RESULTS

Rats treated with melatonin had higher bone volume, bone trabecular number, trabecular thickness, and cortical thickness in comparison to the control group. Histomorphometric analyses confirmed the increase of bone volume in melatonin-treated rats. In agreement with these findings, melatonin-treated rats showed higher bone stiffness, flexural modulus, and ultimate load compared to controls.

CONCLUSION

These compelling results are the first evidence indicating that dietary melatonin supplementation is able to exert beneficial effects against age-related bone loss in old rats, improving the microstructure and biomechanical properties of aged bones.

Senescence-associated intrinsic mechanisms of osteoblast dysfunctions

Human aging is associated with bone loss leading to bone fragility and increased risk of fractures. The cellular and molecular causes of age-related bone loss are current intensive topic of investigation with the aim of identifying new approaches to abolish its negative effects on the skeleton. Age-related osteoblast dysfunction is the main cause of age-related bone loss in both men and women beyond the fifth decade and results from two groups of pathogenic mechanisms: extrinsic mechanisms that are mediated by age-related changes in bone microenvironment including changes in levels of hormones and growth factors, and intrinsic mechanisms caused by the osteoblast cellular senescence. The aim of this review is to provide a summary of the intrinsic senescence mechanisms affecting osteoblastic functions and how they can be targeted to abolish age-related osteoblastic dysfunction and bone loss associated with aging.

Oxidative stress inhibits insulin-like growth factor-I induction of chondrocyte proteoglycan synthesis through differential regulation of phosphatidylinositol 3-Kinase-Akt and MEK-ERK MAPK signaling pathways

The ability of insulin-like growth factor I (IGF-I) to stimulate cartilage matrix synthesis is reduced in aged and osteoarthritic cartilage. Aging and osteoarthritis are associated with an increase in reactive oxygen species, which we hypothesized would interfere with normal IGF-I signaling. We compared IGF-I signaling in normal and osteoarthritic human articular chondrocytes and investigated the effects of oxidative stress induced by tert-butylhydroperoxide (tBHP). In normal human chondrocytes, IGF-I initiated a strong and sustained phosphorylation of IRS-1 (Tyr-612) and Akt (Ser-473) and transient ERK phosphorylation. In contrast, in osteoarthritic chondrocytes, which possessed elevated basal IRS-1 (Ser-312) and ERK phosphorylation, IGF-I failed to stimulate IRS-1 (Tyr-612) or Akt phosphorylation. In normal human chondrocytes, tBHP triggered strong IRS-1 (Ser-312 and Ser-616) and ERK phosphorylation and inhibited IGF-I-induced IRS-1 (Tyr-612) and Akt phosphorylation. Lentivirus-mediated overexpression of constitutively active (CA) Akt significantly enhanced proteoglycan synthesis, whereas both dominant negative Akt and CA MEK inhibited proteoglycan synthesis. CA Akt also promoted type II collagen and Sox9 expression, whereas tBHP treatment and CA MEK inhibited aggrecan, collagen II, and Sox9 mRNA expression. In osteoarthritic chondrocytes, the antioxidants Mn(III) tetrakis(4-benzoic acid)porphyrin and N-acetylcysteine increased the ratio of Akt to ERK phosphorylation and promoted IGF-I-mediated proteoglycan synthesis. Chemical inhibition of ERK significantly enhanced IGF-I phosphorylation of Akt and alleviated tBHP inhibition of Akt phosphorylation. These results demonstrate opposing roles for phosphatidylinositol 3-kinase-Akt and MEK-ERK in cartilage matrix synthesis and suggest that elevated levels of reactive oxygen species cause chondrocyte IGF-I resistance by altering the balance of Akt to ERK activity.

Pre-eclampsia-associated alterations in decorin, biglycan and versican of the umbilical cord vein wall

OBJECTIVE

The role of proteoglycans in the rearrangement of the extracellular matrix of the umbilical cord vein wall in pre-eclampsia is not known. Decorin, biglycan and versican are the main proteoglycans of the umbilical cord vein wall. We decided to test whether the amounts of these proteoglycans alter in pre-eclampsia.

STUDY DESIGN

Study was performed on the umbilical cord veins taken from 10 newborns delivered by healthy mothers (control group) and from 10 newborns delivered by mothers with pre-eclampsia. Proteoglycans were extracted in dissociative conditions, purified by Q-Sepharose anion exchange chromatography and lyophilised. Decorin, biglycan and versican were analysed by SDS-PAGE followed by Western blotting before and after treatment with chondroitinase ABC. The amounts of decorin, biglycan and versican core proteins were assessed by ELISA method.

RESULTS

We found that both control and pre-eclamptic umbilical cord vein wall contained all the three proteoglycans. ELISA assay showed the amounts of the core proteins of decorin, biglycan and versican were distinctly higher in pre-eclamptic material in comparison to control vessel. Western blotting confirmed that the expression of all these proteoglycan core proteins increased in pre-eclampsia. They featured in the same electrophoretic mobility-45 and 47 kDa for decorin, 45 kDa for biglycan, and 300 and 320 kDa for versican.

CONCLUSION

The content of decorin, biglycan and versican in the umbilical cord vein wall is elevated in pre-eclampsia in comparison to the corresponding control vessel. These alterations may affect the mechanical properties of this vessel and disturb foetal blood circulation.

Aging impairs IGF-I receptor activation and induces skeletal resistance to IGF-I

IGF-I plays an important anabolic role in stimulating bone formation and maintaining bone mass. We show that the pro-proliferative, anti-apoptotic, and functional responses to IGF-I in bone and BMSCs decrease with aging. These changes are associated with impaired receptor activation and signal transduction through the MAPK and PI3K pathways.

INTRODUCTION

IGF-I is a potent anabolic agent having effects across diverse tissues and cell types. With aging, bone becomes resistant to the anabolic actions of IGF-I. To examine the effects of aging on bone responsiveness to IGF-I, we measured the pro-proliferative, anti-apoptotic, and functional responses of bone and bone marrow stromal cells (BMSCs) to IGF-I and evaluated IGF-I signal transduction in young, adult, and old mice.

MATERIALS AND METHODS

Male C57BL/6 mice 6 wk (young), 6 mo (adult), and 24 mo (old) were treated with IGF-I for 2 wk using osmotic minipumps, and osteoblast proliferation (BrdU labeling) in vivo, and osteoprogenitor number (BMSC culture and calcium nodule formation) were measured. Proliferation, apoptosis, and expression of key osteoblast factors (alkaline phosphatase, collagen, osteocalcin, RANKL, osteoprotegerin (OPG), macrophage-colony stimulating factor [M-CSF]) and IGF-I signaling elements and their activation in IGF-I-treated cells were studied using QRT-PCR and Western blot analysis. Data were analyzed using ANOVA.

RESULTS

Aging decreased the basal and IGF-I-stimulated number of BrdU-labeled osteoblasts and reduced the ability of IGF-I to stimulate osteoprogenitor formation (calcium nodule number) by 50%. The pro-proliferative and anti-apoptotic actions of IGF-I were blunted in cells from old animals. These changes were accompanied by age-related alterations in the ability of IGF-I to regulate alkaline phosphatase, collagen, osteocalcin, RANKL, OPG, and M-CSF expression. IGF-I binding was normal, but IGF-I receptor mRNA and protein expression was increased in aged animals by 2- and 10-fold, respectively. The age-related changes in proliferation, apoptosis, and function were accompanied by loss of IGF-I-induced signaling at the receptor level and at key regulatory sites along the MAPK (ERK1/2) and PI3K (AKT) pathways.

CONCLUSIONS

Our data show that aging is accompanied by loss of bone and BMSC/osteoblast responsiveness to IGF-I and that these changes are associated with resistance to IGF-I signaling that involve receptor activation and downstream signaling events.

The osteogenic potential of adipose-derived mesenchymal cells is maintained with aging

BACKGROUND

Adipose-derived mesenchymal cells are multipotent progenitor cells derived from the vascular-stromal compartment of adipose tissue. Although we have recently shown that these cells, from both juvenile and adult animals, are capable of forming bone in vivo, a detailed examination of the differences in the biology of these two populations (and in particular their ability to form bone) has not been performed.

METHODS

Adipose-derived mesenchymal cells were harvested from juvenile (6-day-old) and adult (60-day-old) mice. Differences in cellular attachment, proliferation, and proliferating cell nuclear antigen production were assessed. The ability of cells to undergo adipogenic differentiation was determined by Oil Red O staining. Early osteogenic differentiation was determined with alkaline phosphatase staining, and terminal differentiation with von Kossa staining as well as determination of extracellular matrix calcium content. All experiments were performed in triplicate.

RESULTS

Greater attachment, proliferation, and proliferating cell nuclear antigen production were seen in juvenile as compared with adult adipose-derived mesenchymal cells. The juvenile cells underwent significantly greater adipogenic differentiation than did adult cells (p < 0.001). Interestingly, the adult cells were capable of robust early and terminal osteogenic differentiation, with levels of all three osteo-genic assays being similar to those seen in juvenile cells. Differences were not statistically significant.

CONCLUSIONS

Although biologic differences exist between adipose-derived mesenchymal cells from juveniles and adults, the osteogenic capacity of these cells appears to be minimally affected by donor age. This suggests that these cells may be a particularly useful cellular resource in the design of cell-based therapies for skeletal regeneration in an aging population.

Bone metabolism in relation to alterations in systemic growth hormone

Growth hormone (GH) has a major role in the maintenance of bone mass in adults by regulating bone remodeling through a complex interaction of circulating GH, insulin-like growth factors (IGFs), IGF binding protein (IGFBPs), and locally produced IGFs and IGFBPs, acting in an autocrine and paracrine way. In vitro data has greatly increased our understanding of GH and IGFs effects and regulation in bone cells under controlled conditions, and especially the molecular pathways involved. However, the GH-and type I IGF-receptor are present in many tissues and various systemic factors may potentially regulate local expression of IGFs and IGFBPs in the intact organism. The use of genetically altered mice has changed this and had a major impact on defining the role of IGFs in skeletal homeostasis, and especially the role of systemic IGF-I in the development and maintenance of the adult skeleton. The focus of this review is to describe recent work on the effect of GH/IGF on remodeling in the adult skeleton emphasizing on data obtained in patient populations (i.e. acromegaly, GH deficiency, postmenopausal osteoporosis) and experimental models (i.e. animals with genetically altered expression of different GH and IGF family members) characterized by different systemic levels of these proteins. The role of IGF-I as a coupling agent between resorption and bone formation through effects on osteoprotegerin (OPG) and receptor activator of NFkappaB ligand (RANKL) are also discussed.

IGF-I and TGF-beta 1 incorporated in a poly(d,l-lactide) implant coating maintain their activity over long-term storage—cell culture studies on primary human osteoblast-like cells

Biodegradable coating of osteosynthetic materials with poly(D,L-lactide) (PDLLA) and incorporated growth factors has been used successfully as drug carrier to stimulate fracture healing in several rat and porcine models. A cold coating technique was used to incorporate growth factors without loss of activity during the coating process. The aim of this study was to investigate the activity of incorporated insulin like growth factor-I and transforming growth factor-beta 1 (TGF-beta1) after long-time storage (5 and 14 months at -20 degrees C). Primary human osteoblast-like cells (HOB) were cultured in a non-contact manner with titanium wires coated with PDLLA and IGF-I (33 microg) and TGF-beta1 (6 microg) for 0, 5, 10 and 15 days. Osteoblast culture without wires, with titanium wires or wires with the PDLLA coating served as control ( n=3 each time point and group). Cell vitality, cell proliferation and the production of procollagen 1 were measured. No differences in cell count and vitality were accessed in the two growth factor treated groups compared to the control groups at the same time point. Independently from the storage duration, the incorporated growth factors significantly stimulated the production of osteoblast specific type I collagen (CICP) compared to the controls. The results indicate, that the growth factors stimulated osteoblast to an enhanced collagen 1 production and that the coating method meets a major requirement for clinical use of growth factor-coated implants: biological activity of the incorporated growth factors for at least 14 months.

Local delivery of growth factors from coated titanium plates increases osteotomy healing in rats

Different methods for the stabilization of long bone fractures are used in clinic. Besides the development of further stabilization devices, the use of new materials, the modification of the surfaces, and the local application of stimulating factors for enhancement of healing are from great interest. Previous studies successfully used a biodegradable poly(d,l-lactide) coating as a local drug delivery system of growth factors from intramedullary (IM) implants to enhance fracture healing. In this study, we developed a new rat model (n = 60) for plate osteosynthesis and used a plate for stabilization and as a local drug delivery system for the growth factors IGF-I and TGF-beta1. A four-hole titanium plate was used for stabilization of a 0.6-mm osteotomy gap of the femur. The space between the inner holes was coated with 50 microg IGF-I and 10 microg TGF-beta1 incorporated in the poly(d,l-lactide) coating or with the coating alone. After 42 days, biomechanical tests and histomorphological analyses were performed to investigate osteotomy healing. Radiologically small differences were detectable between the groups. The biomechanical torsional testing revealed a significantly higher maximum load of the osteotomized femura after treatment with growth factors compared to the uncoated group. In the histomorphometric analyses measuring the callus composition, a significantly higher percentage of mineralized tissue in the osteotomy callus was assessed in the growth factor treated group compared to the uncoated. In conclusion, the local application of IGF-I and TGF-beta1 from a biodegradable coating enhances the osteotomy healing as shown in the biomechanical testing and the histomorphometry. Bioactive plates could be used in clinic for fracture stabilization and for local and controlled application of growth factors to stimulate bone healing.

Modulation of prostate cancer growth in bone microenvironments

Bone remains one of the major sites, and most lethal host organs, for prostate cancer metastasis. Prostate cell spread and establishment in bone depends on multiple reciprocal modifications of bone stromal and epithelial cancer cell behaviors. This review focuses on recent advances in the characterization of cell-cell and cell-matrix interplay, effects on cell growth, adhesion and invasion, and several therapeutic possibilities for co-targeting prostate cancer cells and bone stroma. We address the topic from three main perspectives: (1) the normal and aging bone stromal environment, (2) the "reactive" bone stromal environment, and (3) the cancerous prostate epithelial cells themselves. First, normal, and especially aging, bones provide uniquely rich and "fertile soil" for roaming cancer cells. The interactions between prostate cancer cells and insoluble extracellular matrices, soluble growth factors, and/or sex steroid hormones trigger bone remodeling, through increased osteoclastogenesis and furthur matrix metalloproteinase activity. Second, after cancer cell arrival and establishment in the bone, host stromal cells respond, becoming "reactive" in a process again involving extracellular matrix remodeling, together with growth factor and steroid receptor signaling this process ultimately enhances cancer cell migration, stromal transdifferentiation, and invasion of the cancer tissues by stromal, inflammatory, and immune-responsive cells. Third, prostate cancer cells also respond to supportive bone microenvironments, where soluble and matrix-associated molecules affect cancer cell growth and gene expression, especially altering cancer cell surface receptor and integrin-mediated cell signaling. We discuss both integrin cell-matrix and gap junctional cell-cell communication between cancer cells and their microenvironments during prostate cancer progression.

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.

IGF-I and TGF-beta 1 incorporated in a poly(D,L-lactide) implant coating stimulates osteoblast differentiation and collagen-1 production but reduces osteoblast proliferation in cell culture

Previous in vivo studies revealed a stimulating effect of locally applied IGF-I and TGF-beta1 released from poly(D,L-lactide)-coated titanium implants on rat and porcine fracture healing. The purpose of the present study was to evaluate the effect of IGF-I (5% w/w) and TGF-beta1 (1% w/w) and the carrier PDLLA on osteoblasts in cell culture to improve the understanding of these growth factors. The well-characterized human osteoblast cell line hFOB 1.19 was used in the study. The implants and cells were cocultured in a noncontact manner. The cells were incubated for 10 days in total, and the implants (n = 6 each group and time point) were added for 1 h, 12 h, 24 h, 2 d, 4 d, or 10 d. To analyze a possible effect of the growth factors or the coating, cell proliferation, metabolism, and differentiation were investigated. As an indicator for differentiation the production of collagen I was chosen. All experimental groups showed comparable cell vitality. No change in the pH of the medium was detectable between the analyzed groups. When the effect of the titanium implant and the PDLLA coating were compared with the control culture, no differences in proliferation, metabolic activity, and collagen I production were detectable. The osteoblasts treated with IGF-I and TGF-beta1 released from PDLLA revealed a significantly enhanced collagen I production with a decrease in proliferation and metabolic activity compared to the other groups. No significant differences in collagen I production were seen due to the incubation time points. None of the experimental groups evoked an immunological response on mouse macrophages. In conclusion, the PDLLA-carrier showed no negative effect on osteoblasts, whereas the incorporated growth factors stimulated osteoblast differentiation.

Expression of IGF-binding protein-1 phosphoisoforms in fasted rat skin and its role in regulation of collagen biosynthesis

Insulin-like growth factor-I (IGF-I) is an important stimulator of collagen and glycosaminoglycan (GAG) biosynthesis in tissues. IGF-I activity is modulated by a family of IGF-binding proteins (IGFBPs) with different IGF-I binding affinities. At least IGFBP-1 and IGFBP-2 are known as inhibitors of IGF functions. Some IGFBPs (IGFBP-1, IGFBP-3 and IGFBP-5) may undergo phosphorylation that dramatically increase their affinity for IGF. During fasting of animals there is a significant decrease of the collagen and GAG content of the skin, accompanied by a reduction of plasma IGF-I levels. However, in previous studies we showed that in the skin of fasted rats IGF-I as well as IGFBP-1 and IGFBP-2 expressions were not different, compared to control rat skin, although collagen content was significantly decreased. In the present study we show that fasted rat skin contains similar amounts of IGF-I, IGFBP-3 and IGFBP-1, although extract from fasted rat skin induced inhibition of collagen biosynthesis in cultured fibroblasts, compared to control rat skin extract. Western immunoblot analysis of control and fasted rat skin extracts, using anti-phosphoserine antibodies for immunoprecipitated IGFBP-1 and IGFBP-3, revealed that both proteins are present in phosphorylated form. Although no differences were found in the expression of phosphorylated IGFBP-3 between control and fasted rat skins, that of phosphorylated IGFBP-1 in fasted rat skin extract was higher than in control one. We suggest that there is an increased level of IGFBP-1 phosphoisoform in fasted rat skin, associated with increased affinity for IGF-I. The increase of phosphorylated IGFBP-1 in fasted rat skin tissue may augment IGF-I binding affinity for IGF and decrease its bioavailability for receptor interaction. This mechanism may prevent IGF-I dependent stimulation of fibroblasts to produce extracellular matrix components. The specific expression of IGFBPs and their phosphoisoforms in tissues may play an important role in regulation of IGF-I action during physiologic and pathologic responses.

Mammographic density is related to stroma and stromal proteoglycan expression

BACKGROUND

Mammographic density and certain histological changes in breast tissues are both risk factors for breast cancer. However, the relationship between these factors remains uncertain. Previous studies have focused on the histology of the epithelial changes, even though breast stroma is the major tissue compartment by volume. We have previously identified lumican and decorin as abundant small leucine-rich proteoglycans in breast stroma that show altered expression after breast tumorigenesis. In this study we have examined breast biopsies for a relationship between mammographic density and stromal alterations.

METHODS

We reviewed mammograms from women aged 50-69 years who had enrolled in a provincial mammography screening program and had undergone an excision biopsy for an abnormality that was subsequently diagnosed as benign or pre-invasive breast disease. The overall mammographic density was classified into density categories. All biopsy tissue sections were reviewed and tissue blocks from excision margins distant from the diagnostic lesion were selected. Histological composition was assessed in sections stained with haematoxylin and eosin, and the expression of lumican and decorin was assessed by immunohistochemistry; both were quantified by semi-quantitative scoring.

RESULTS

Tissue sections corresponding to regions of high in comparison with low mammographic density showed no significant difference in the density of ductal and lobular units but showed significantly higher collagen density and extent of fibrosis. Similarly, the expression of lumican and decorin was significantly increased.

CONCLUSION

Alteration in stromal composition is correlated with increased mammographic density. Although epithelial changes define the eventual pathway for breast cancer development, mammographic density might correspond more directly to alterations in stromal composition.

Human abdominal aortic aneurysm is characterized by decreased versican concentration and specific downregulation of versican isoform V(0)

Abdominal aortic aneurysm (AAA) is a common disease of human aorta with increased incidence. It is a complication to atherosclerosis and it is closely associated with alterations in extracellular macromolecules. In this study, the levels of mRNA for versican--the major extracellular arterial proteoglycan (PG)--present in AAA and normal aortas were evaluated by reverse-transcriptase polymerase chain reaction. The concentration of versican was also examined in corresponding tissue samples. Versican was almost completely extracted with 4 M guanidine hydrochloride in the presence of Triton X-100, isolated by chromatography on DEAE-Sephacel and characterized using treatment with specific chondro-/dermato-lyases and agarose gel electrophoresis. Versican localization in tissue as well as the variation and distribution of smooth muscle cells (SMCs) and macrophages were also investigated immunohistochemically. The mRNAs coding for versican isoforms V(0) and V(1) were identified in both tissues, whereas V(2) was absent. The expression of V(0) was decreased 40% in aneurysmal vessel wall, whereas that for V(1) remained constant. This change was simultaneous with a significant decrease in versican concentration by 89%. In normal aortas, most versican was seen in the intima, whereas in AAA, this layer is characterized by advanced atherosclerotic lesion, rich in lipids and macrophages but poor in versican. The decreased transcription and the still lower amount of versican in the AAA may correlate to (i) a decrease in density of SMCs, these cells being the major source of versican in aorta, and (ii) the presence of macrophages, which may induce versican degradation and modulate versican synthesis. It is proposed that the decreased synthesis and increased degradation of versican, particularly of isoform V(0), and the resulting low concentration in the intima are crucial factors contributing to the altered viscoelastic and compressive properties and thereby to the deformity and dilatation of aorta.

Effect of maturation on the osteogenic response of cultured stromal bone marrow cells to basic fibroblast growth factor

Formation of bone-like tissue in culture by stromal bone marrow cells (SBMC) derived from young growing rats is dependent on dexamethasone (Dex) (Cell Tissue Res 254:317; 1988) and is significantly enhanced by basic fibroblast growth factor (bFGF) (J Bone Miner Res 8:919; 1993). The aim of this study was to examine the effect of maturation on the osteogenic potential and the response to Dex and bFGF of SBMC by using cultures derived from young growing (6 weeks old) and adult (9 months old) rats. SBMC cultures were grown in the presence of Dex (10(-8) or 10(-7) mol/L) at both P(0) and P(1) and either in the presence or absence of bFGF. The effect of Dex and bFGF on mineralized bone-like tissue (MBT) formation was assessed at P(1). The highest levels of mineralized tissue formation in P(1) subcultures in the absence of bFGF were obtained when cultures derived from young rats (6 weeks old) were treated with Dex 10(-7) and 10(-8) mol/L at P(0) and P(1), respectively, and when cultures derived from adult rats were exposed to Dex 10(-8) mol/L both at P(0) and P(1). Under these optimal Dex concentrations, the amount of MBT formed by adult rat-derived cultures was 15-fold lower than that of young rat-derived ones. The addition of bFGF to P(0) cultures or to P(1) cultures grown under optimal Dex conditions enhanced MBT formation in P(1) cultures derived from both young and adult rats, but this effect was considerably more pronounced in the adult rat-derived cultures. The maximal levels of MBT formation were produced by cultures derived from adult rats treated with bFGF at both P(0) and P(1), whereas in cultures derived from young rats, the addition of bFGF at P(0) was not necessary for maximal MBT production. This stimulating effect of bFGF on MBT formation by adult rat-derived cultures was accompanied by a 2.2-, 1.8-, and 4.3-fold increase in proliferation, alkaline phosphatase activity, and Ca(2+) deposition rate, respectively. bFGF increased the level of glucocorticoid receptor by approximately 2. 3-fold in Dex-treated cultures derived from young animals. These results indicate that maturation is associated with a decrease in the proportion of osteoprogenitor cells in the stromal bone marrow and in their capacity to express the osteogenic phenotype. They further point to the significant role of bFGF in stimulating proliferation and osteogenic expression of stromal bone marrow osteoprogenitors derived from adult rats.

Stimulation of collagen biosynthesis by the umbilical cord serum of newborns delivered by mothers with EPH-gestosis (preeclampsia)

Edema, proteinuria, hypertension (EPH)-gestosis, known also as preeclampsia, is the most common, pregnancy-associated pathological syndrome. It is accompanied by a significant increase in collagen content in the umbilical cord arteries and premature replacement of hyaluronic acid by sulfated glycosaminoglycans both in these arteries and in Wharton's jelly. This remodelling of the umbilical cord tissues is accompanied by a distinct increase in insulin-like growth factor-I (IGF-I) concentration in the umbilical cord serum. Such a serum introduced into the culture medium of fibroblasts growing in vitro strongly stimulated the incorporation of radioactive proline into collagen (hydroxyproline-containing and collagenase-sensitive protein). Biosynthesis of noncollagenous proteins was not stimulated. Since IGF-I is known as a stimulator of collagen and sulfated glycosaminoglycan biosynthesis, the high concentration of this growth factor in the umbilical cord plasma may be an agent responsible for preeclampsia-associated remodelling of the umbilical cord, which results in dysfunction in fetal circulation.

Preeclampsia is associated with alterations in insulin-like growth factor (IGF)-1 and IGF-binding proteins in Wharton's jelly of the umbilical cord

Wharton's jelly is abundant in extracellular matrix, which is known as a storage site to concentrate and stabilise growth factors in the vicinity of cells. It was previously found that Wharton's jelly contains significant amounts of insulin-like growth factor (IGF)-1 and IGF-binding proteins (BPs). IGF-1 is a stimulator of biosynthetics of collagen and sulphated glycosaminoglycans. Preeclampsia (edema, proteinuria, hypertension (EPH)-gestosis) is accompanied by an accumulation of sulphated glycosaminoglycans in Wharton's jelly. IGF-1 and BPs may play an important role in such a remodelling of this tissue. It was decided to evaluate the alterations in amounts of IGF-1 and BPs in Wharton's jelly of newborns delivered by mothers with preeclampsia. Studies were performed on Wharton's jelly of 10 controls and 10 newborns delivered by mothers with preeclampsia (edema, proteinuria > 500 mg/l, arterial pressure: systolic > 140 mm Hg, diastolic > 90 mmHg). Radioimmunological techniques were employed to determine IGF-1 and IGF-BPs (BP-1 and BP-3). It was found that preeclampsia is associated with a decrease in IGF-1 and IGF-BP-1 in Wharton's jelly. A slight increase in IGF-BP-3 was found. Ligand blotting demonstrated that BP-3 (not BP-1) is a main component of Wharton's jelly, which binds IGF-1. Heparin drastically inhibited the binding of IGF-1 by BP-3. It is known from our previous studies that preeclampsia is associated with an increase in the amount of sulphated glycosaminoglycans (heparin, heparan sulphate, dermatan sulphate) in Wharton's jelly. This may be a factor, which prevents the binding of IGF-1 by BPs and facilitates the binding of IGF-1 to cells, stimulating them to produce sulphated glycosaminoglycans in Wharton's jelly.

Pre-eclampsia-induced alterations in IGF-I of human umbilical cord

BACKGROUND

Extracellular matrix (ECM)-components serve as a storage site to concentrate and stabilise growth factors in the vicinity of cells. Human umbilical cord (UC) tissues contain significant amounts of IGF-I and IGF-binding proteins (BPs). IGF-I is known as a stimulator of collagen and sulphated glycosaminoglycans (GAGs) biosynthesis. Pre-eclampsia, the most common pregnancy associated syndrome, is accompanied by an accumulation of collagen and sulphated glycosaminoglycans in the UC. One may expect that IGF-I and BPs play an important role in such a remodelling of the UC tissue. For this reason it was decided to evaluate the alterations in amounts of IGF-I and BPs in UC serum and in the UC arterial wall of newborns delivered by mothers with pre-eclampsia.

MATERIALS AND METHODS

Studies were performed on the UCs of 12 control and 12 investigated newborns, delivered by mothers with pre-eclampsia (edema, proteinuria > 500 mg l-1, arterial pressure: systolic > 140 mmHg, diastolic > 100 mmHg). Radioimmunological techniques were employed to determine IGF-I and IGF-BPs (BP-1 and BP-3).

RESULTS

It was found that pre-eclampsia is associated with an increase of IGF-I concentration in the UC serum and with simultaneous decrease of its content in the umbilical cord artery (UCA). The decrease of IGF-I content in the UCA wall was accompanied by an increase of BP-3 and BP-1 in this tissue. The increase in BPs content in the UCA wall was not associated with an enhancement of IGF binding by extracts from the homogenates of arterial wall. Heparin drastically decreased the binding of IGF-I by BP-3.

CONCLUSIONS

Pre-eclampsia is associated with an increase of IGF-I-concentration in the umbilical cord blood and an elevation of BPs contents in the UCA wall. Despite a high concentration of binding proteins, IGF-I is not accumulated in this tissue. High amounts of sulphated GAGs in the UCA wall may be a factor that prevents the binding of IGF-I by BPs. Free IGF-I can easily bind to cell receptors and stimulate the cells to produce collagen and sulphated GAGs in the arterial wall.

An accumulation of IGF-I and IGF-binding proteins in human umbilical cord

It is known that extracellular matrix components (ECM) may serve as a storage site to concentrate and stabilize growth factors in the vicinity of cells. IGF-I is expressed in most fetal tissues and it is involved in anabolic effects on protein and sulphated glycosaminoglycans biosynthesis, cell proliferation and differentiation. We demonstrated that human umbilical cord (UC) tissues contain large amounts of IGF-I and IGF-I-binding proteins (BP-3 and BP-1). Particularly Wharton's jelly appears to be an abundant reservoir of IGF-I and BPs. Relatively low amount of cells and large amounts of collagen and glycosaminoglycans in UC tissues (especially in Wharton's jelly) suggest that IGF-I may play a major role in stimulation of these cells to produce ECM components. The specific BPs in these tissues may be important modulators of IGF-I action during fetal development.

Insulin-Like growth factor I: implications in aging

According to the somatomedin model, growth hormone (GH)-dependent hepatic synthesis is responsible for maintaining circulating insulin-like growth factor (IGF)-I levels. On the other hand, the local autocrine/paracrine IGF-I expression in peripheral tissue is generally GH-independent and reflects the effects of various and tissue-specific trophic hormones. Circulating IGF-I levels undergo important age-related variations increasing at puberty and decreasing, thereafter, to low levels in the elderly. Low IGF-I levels in the elderly mainly reflect impaired somatotroph secretion but the decline in gonadal sex steroid levels, some protein and micronutrients malnutrition as well as age-dependent variations in IGF-binding proteins may also play a role in the age-related decrease in IGF-I activity. This, in turn, partially accounts for age-related changes in bones, muscles, cardiovascular system, central nervous system and the immune system. However, it is currently unclear whether treatment with exogenous IGF-I can retard or reverse age-related changes in body structure and function.

Age-related inhibitory activity of rat bone marrow supernatant on osteoblast proliferation

Because histomorphometric indices of bone formation (osteoblastic index, tetracyclin-labeled perimeter) are deeply depressed in aged rats, while in vitro proliferation of trabecular bone cells was found increased, we hypothesized that a signal to proliferate, correctly induced by increased strains on scarce bone, could be opposed in vivo by an inhibitor present in the bone marrow extracellular medium. Thus, we tested the effect of bone marrow extracellular fluid (BM supernatant) of rat femoral diaphysis on cultures of primary osteoblasts and osteoblastic cell lines and found that it inhibited bone cell proliferation. In a group of 69 female rats aged 4, 12, and 15/21 months, there was a stepwise increase in the inhibitory activity of the BM supernatant. The double reciprocal plots relating inhibition power of the medium to BM supernatant dilution suggest that we deal with a simple system and that the kinetics of the phenomenon are the same in older and younger animals. Moreover, proliferation inhibition by BM supernatant and trabecular bone surface measured by histomorphometry in the distal femoral metaphysis were inversely correlated. Because the extracellular fluid of bone marrow is also the medium surrounding the osteoblasts and their precursor cells, our results suggest that the bone marrow negatively regulates osteogenic cells and that this inhibition could contribute to the inability of older animals to supply osteoblasts to bone in proportion to the demand. Preliminary biochemical characterization of the inhibitor suggests it to be a protein of 30-40 kDa with an isoelectric point (pI) of about 6.5.

Three isolation techniques for primary culture of human osteoblast-like cells: a comparison

The culture of osteoblast-like cells of human origin has become an important experimental model in bone biology. We report here a comparison and evaluation of three of the most widely used systems available today: bone marrow stroma cell cultures (BMSC), human osteoblast explant cultures (hOB) and osteoblast explant cultures from collagenase-treated bone (hOBcol). Cultures from 16 bone specimens obtained from various donors were established and their expression of the osteoblast phenotype were then compared in secondary cultures by use of biochemical markers. BMSC had the highest basal and 1,25-dihydroxyvitaminD3 (1,25(OH)2D3)-induced alkaline phosphatase activities in all cell isolations, with levels approximately twice those in explant cultures. Basal osteocalcin secretion was low-to-undetectable in all cell cultures but was detected in 1,25(OH)2D3-stimulated cultures. BMSC produced half of the amount of osteocalcin synthesized in explant cultures. The BMSC cultures also synthesized the lowest amounts of type I collagen, whereas collagen type III synthesis did not differ significantly among the various cultures. When secondary cultures were treated with 100 nM dexamethasone in the presence of ascorbic acid (50 microg/mL) and beta-glycerophosphate (10 mM), cultures deposited calcium mineral into the cell layer within 2-4 weeks. PTH-induced cAMP formation was detected in only 5 of 15 isolations and no consistent isolation-dependent response pattern was seen. We conclude that BMSC cultures differ significantly from explant cultures obtained from the same bone specimen. However, all cultures represent cells which can differentiate further and induce mineralization of the extracellular matrix in response to osteoinductive drugs.

Serum Insulin-like Growth Factors and Insulin-like Growth Factor-binding Proteins: Clinical Implications

The last decade has been characterized by a major investigative thrust into the physiology of two unique but ubiquitous peptides, insulin-like growth factor (IGF)-I and IGF-II. The regulatory systems that control the tissue bioactivity of the IGFs have been delineated, and subcellular signaling mechanisms have been clarified. Clearly, both tissue and circulating growth factor concentrations are important in defining the relationship between IGF-I and cell activity. Bone, liver, and circulatory IGF-I have received the most attention by investigators, in part because of the ease of measurement and the interaction with disease states such as osteoporosis. More recently, attention has focused on the role IGF-I plays in neoplastic transformation and growth. Two large prospective observational studies have demonstrated greater risk for prostate and breast cancer associated with high circulating concentrations of IGF-I. Animal models and in vitro studies confirm that there is a close, albeit complex, interaction between IGF-I signaling and bone turnover. This report will focus on: (a) IGF physiology, including IGF ligands, binding proteins, and proteases; (b) the relationship between IGF-I and bone mass in respect to risk for osteoporosis; (c) the heritable regulation of the IGF-I phenotype; and (d) the association between serum IGF-I and cancer risk. The IGFs remain a major area for basic and clinical investigations; future studies may define both diagnostic and therapeutic roles for these peptides or their related proteins in several disease states.

Thrombospondin is sequentially expressed and then de-expressed during early pregnancy in the rat uterus

The expression of thrombospondin on Day 1, Day 3 and Day 6 of pregnancy has been examined in the rat, using light microscopic immunoperoxidase and electron immunogold techniques. The glycoprotein was expressed in the apical, lateral and basal uterine epithelium on Days 1 and 3 but was then de-expressed at the time of implantation on Day 6. We propose that these data suggest a role for thrombospondin in remodellig the uterine epithelium during the plasma membrane transformation, but that it does not play a part in attachment and implantation.

Recombinant human bone morphogenetic protein-2 stimulates osteoblast differentiation and suppresses matrix metalloproteinase-1 production in human bone cells isolated from mandibulae

Bone morphogenetic protein (BMP), a member of the transforming growth factor superfamily, is one of the most potent growth factors that stimulate osteoblast differentiation and bone formation. We investigated the effects of recombinant human BMP-2 (rhBMP-2) on osteoblast differentiation and matrix metalloproteinase-1 (MMP-1) production in human bone cells (HBC) isolated from mandibulae of 3 adult patients. rhBMP-2 at concentrations over 50 ng/ml significantly stimulated alkaline phosphatase activity and parathyroid hormone (PTH)-dependent 3', 5'-cyclic adenosine monophosphate accumulation, which are early markers of osteoblast differentiation, in HBCs. rhBMP-2 (500 ng/ml) also enhanced the level of PTH/PTH related-peptide receptor mRNA expression in HBCs. Although neither HBCs untreated nor treated with rhBMP-2 produced measurable amounts of osteocalcin, which is a marker of more mature osteoblasts, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] induced ostocalcin mRNA expression and its protein synthesis in these cells. rhBMP-2 inhibited 1,25(OH)2D3-induced osteocalcin synthesis in HBCs at both the mRNA and protein level. rhBMP-2 also significantly suppressed MMP-1 production and MMP-1 mRNA expression at concentrations over 500 ng/ml. These results suggest that rhBMP-2 exerts anabolic effects on human osteoblastic cells derived from mandibulae by stimulation of osteoblast differentiation and down-regulation of MMP-1 synthesis.