Adenoviral delivery of LIM mineralization protein-1 induces new-bone formation in vitro and in vivo

BACKGROUND

The LIM mineralization protein-1 (LMP-1) gene encodes for an intracellular protein that induces the expression of several bone growth factors. The purpose of the present study was to determine the feasibility and the optimal dose of adenoviral delivery of the LMP-1 cDNA to promote spinal fusion.

METHODS

A replication-deficient human recombinant adenovirus was constructed with the LMP-1 cDNA driven by a cytomegalovirus promoter. In phase 1, an in vitro dose-response experiment was performed to determine the optimal adenovirus-LMP-1 (AdLMP-1) concentration and infection time. In phase 2, nine rabbits had a single-level posterolateral arthrodesis of the lumbar spine with implantation of a carrier matrix loaded with bone-marrow-derived buffy-coat cells that had been infected for ten minutes with adenovirus containing the cDNA for LMP-1 (AdLMP-1) or beta-galactosidase (AdBgal). In phase 3, posterolateral arthrodesis of the spine was performed with implantation of cells infected with AdLMP-1 (ten rabbits) or cells infected with an empty adenovirus that did not contain LMP-1 cDNA (ten rabbits) and the results were compared. In this phase, peripheral-blood-derived buffy-coat cells were used instead of bone-marrow-derived cells and a collagen-ceramic-composite sponge was used as the carrier.

RESULTS

In phase 1, the in vitro dose-response experiment showed that a multiplicity of infection of 0.25 plaque-forming units per cell was the most efficient dose. In phase 2, the implants that had received cells infected with AdLMP-1 induced a solid, continuous spinal fusion mass at five weeks. In contrast, the implants that had received cells infected with AdBgal or a lower dose of AdLMP-1 induced little or no bone formation. In phase 3, a solid spinal fusion was observed at four weeks in all ten rabbits that had received cells infected with AdLMP-1 and in none of the ten rabbits that had received cells infected with the empty adenovirus. Biomechanical and histological testing of the AdLMP-1-treated specimens revealed findings that were consistent with a high-quality spinal fusion.

CONCLUSIONS

Adenoviral delivery of LMP-1 cDNA promotes spinal fusion in immune-competent rabbits.

The effect of nicotine on gene expression during spine fusion

STUDY DESIGN

A rabbit model of posterolateral spine fusion was used to investigate the effect of nicotine on cytokine expression during spine fusion.

OBJECTIVES

To determine the effects of nicotine on the known gene expression pattern of bone morphogens and related proteins expressed during spine fusion.

SUMMARY OF BACKGROUND DATA

The mechanism by which nicotine increases the pseudarthrosis rate of spine fusion is unknown. Recently, a distinct temporal and spatial pattern of cytokine expression during bone formation has been described. The authors hypothesized that nicotine would alter this known pattern, thereby revealing the mechanism by which nicotine exerts its effect.

METHODS

Twenty-eight New Zealand White rabbits underwent posterolateral spine fusion with autogenous bone graft. Fourteen rabbits received systemic nicotine by a miniosmotic pump. Fusions were harvested at 0, 2, 5, and 7 days and 2, 3, and 4 weeks after arthrodesis. Specimens were divided into the outer zones adjacent to the transverse processes and the central zones between the transverse processes. Gene expression of type I and II collagen, bone morphogenic protein-2, -4, and -6 and basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) was then measured at each time point in each of the two zones.

RESULTS

Nicotine inhibited expression of all cytokines measured, mainly in the central zone. However, the previously described temporal and spatial patterns of expression were preserved.

CONCLUSIONS

Nicotine inhibits expression of a wide range of cytokines, including those associated with neovascularization and osteoblast differentiation. Therefore, the effects of nicotine appear to involve more than just local vasoconstriction.

Gene therapy for spine fusion

Spine fusion is a commonly performed yet often unsuccessful surgical procedure. As many as 40% of patients undergoing spine fusion may have a nonunion or failure to form a continuous bone bridge. This clinical challenge has focused much of the attention of osteoinductive bone growth factors toward spine applications. Clinical pilot and pivotal trials will show the feasibility of recombinant and purified bone growth factors to promote spine fusion in humans. Despite this, strategies of gene therapy for spine fusion and other bone healing applications are being pursued. This article reviews the state of the art of local gene therapy and highlights specific issues that must be addressed when pursuing a gene therapy program. Perhaps the most critical step in gene therapy for bone formation is choosing an appropriate osteoinductive gene. Such choices may be limited by differences in efficacy of the chosen gene and availability because of proprietary constraints. The choice of delivery vector is crucial and depends on the potency of the gene and the specific application intended. Establishing the effective dose, transduction time, and gene transfer method are important decisions. The choice of carrier material to form the scaffold for the new bone formation is paramount to successful bone formation. Finally, a strategy for in vitro and in vivo testing must be developed to maximize the chances of success in human trials.

Recombinant human bone morphogenetic protein-2 overcomes the inhibitory effect of ketorolac, a nonsteroidal anti-inflammatory drug (NSAID), on posterolateral lumbar intertransverse process spine fusion

STUDY DESIGN

An animal model of posterolateral intertransverse process spine fusion healing.

OBJECTIVE

To evaluate the effect of systemic ketorolac, alone and in combination with locally applied recombinant human bone morphogenetic protein-2, on spine fusion healing.

SUMMARY OF BACKGROUND DATA

The effect of nonsteroidal anti-inflammatory drugs on bone graft healing in animals remains controversial. However, most studies point to the inhibition of fracture repair, especially during the early healing period.

METHODS

Forty-nine adult New Zealand white rabbits underwent single-level lumbar fusion with autologous iliac bone graft. Two mini-osmotic pumps were implanted subcutaneously and filled with saline as a control or ketorolac. Rabbits were divided into three groups: 1) control (saline in pump); 2) nonsteroidal anti-inflammatory drug (ketorolac in pump); 3) nonsteroidal anti-inflammatory drug (ketorolac in pump) and bone morphogenetic protein (bone graft soaked in a 3.0 mg solution of recombinant human bone morphogenetic protein-2. All rabbits were killed after 6 weeks.

RESULTS

In the control group, 75% (12 in 16) of the surviving rabbits were judged to have solidly fused lumbar spines as compared with only 35% (6 in 17) of the animals that received ketorolacachieved fusion (P = 0.037). Of the animals that received ketorolac and recombinant bone morphogenetic protein-2, 100% (9 in 9) fused.

CONCLUSIONS

The results of this study confirm the detrimental effect of a commonly used nonsteroidal anti-inflammatory drug on spinal fusion during the immediate postoperation period in a established rabbit model of posterolateral lumbar spine fusion. The addition of recombinant bone morphogenetic protein-2 to the autograft bone was able to compensate for the inhibitory effect of ketorolac on bone formation. On the basis of these data, caution is urged in the routine use of nonsteroidal anti-inflammatory drugs for postoperation analgesia in patients undergoing spine arthrodesis.

Molecular biology and spinal disorders. A survey for the clinician

Over the past 10 years, advances in molecular biology techniques have extended the potential for understanding spinal disorders from the microscopic (histologic) level down to the molecular level of gene expression within individual cells. These advances are initiating new avenues of research and, ultimately, novel clinical treatments. The intent of this update is to provide the spine clinician with a basic understanding of molecular biology, the type of information that may be learned from its application, and the potential for gene therapy in spine disorders.

New formulations of demineralized bone matrix as a more effective graft alternative in experimental posterolateral lumbar spine arthrodesis

STUDY DESIGN

A rabbit model of posterolateral intertransverse process spine arthrodesis was used.

OBJECTIVE

To determine the efficacy of two new formulations of demineralized bone matrix.

SUMMARY OF BACKGROUND DATA

The flowable gel form of Grafton (Osteotech, Eatontown, NJ) demineralized bone matrix has been shown to have osteoinductive properties in various models and currently is used clinically as bone graft material in posterolateral lumbar spine arthrodesis. Two new formulations of Grafton, one made of flexible sheets (Flex) and the other made in a malleable consistency (Putty), have improved handling characteristics compared with the gel form.

METHODS

In this study, 108 New Zealand white rabbits underwent bilateral posterolateral intertransverse spine arthrodesis at L5-L6 using autogenous iliac crest bone graft alone (control), one of the new forms of demineralized bone matrix (DBM; made from rabbit bone) alone or in combination with autogenous iliac crest bone. Rabbits were killed 6 weeks after surgery. The lumbar spines were excised, and fusion success or failure was determined by manual palpation and radiography. Specimens also were processed for undecalcified histologic analysis.

RESULTS

Manual palpation of the harvested lumbar spines revealed that the fusion rates of the Flex-DBM/Auto group (9/9, 100%) and Putty-DBM/Auto group (10/10, 100%) were superior (P < 0.01) to those of the Auto/control group (3/9, 33%). As a stand-alone graft substitute, Flex-DBM performed superiorly with a fusion rate of 11/11 (100%) compared with that of Putty-DBM (10/12, 83%) and Gel-DBM (7/12, 58%). The devitalized version of Flex-DBM had a fusion rate of 4/11 (36%), which was comparable with the devitalized Putty-DBM rate of 4/12 (33%). Both were superior (P < 0.05) to the devitalized Gel-DBM rate of 0/12 (0%). More mature fusions with greater amounts of trabecular bone were present radiographically and histologically in rabbits that received all forms of demineralized bone matrix than in those in which autograft was used.

CONCLUSIONS

The new flexible sheet and malleable putty forms of demineralized bone matrix were effective as graft extender and graft enhancer in a model of posterolateral lumbar spine fusion. These newer formulations of Grafton appear to have a greater capacity to form bone than the gel form or autogenous bone graft alone in this model.

The use of coralline hydroxyapatite with bone marrow, autogenous bone graft, or osteoinductive bone protein extract for posterolateral lumbar spine fusion

STUDY DESIGN

A posterolateral lumbar arthrodesis animal model using coralline hydroxyapatite as a bone graft substitute.

OBJECTIVE

To determine the effectiveness of coralline hydroxyapatite as a bone graft substitute for lumbar spine fusion when used with bone marrow, autogenous bone graft, or an osteoinductive bone protein extract.

SUMMARY OF BACKGROUND DATA

Coralline hydroxyapatite is commonly used as a bone graft substitute in metaphysial defects but its use in a more challenging healing environment such as the posterolateral spine remains controversial. There are no published animal studies in which the use of coralline hydroxyapatite has been evaluated in a posterolateral lumbar arthrodesis model.

METHODS

Single-level posterolateral lumbar arthrodesis was performed at L5-L6 in 48 adult New Zealand White rabbits. Rabbits were assigned to one of three groups based on the graft material they received: 3.0 mL coralline hydroxyapatite 1.5 mL plus bone marrow; 1.5 mL coralline hydroxyapatite plus 1.5 mL autogenous iliac crest bone; and, 3.0 mL coralline hydroxyapatite plus 500 micrograms bovine-derived osteoinductive bone protein extract on each side. Rabbits were killed after 2, 5, or 10 weeks, and the spines were excised and evaluated by manual palpation, radiographs, tensile biomechanical testing, and nondecalcified histology.

RESULTS

Fusions were assessed by manual palpation at 5 weeks for comparisons among the three groups of graft materials. The coralline hydroxyapatite used with bone marrow produced no solid fusions (0/14). When combined with an equal amount of autogenous iliac crest bone, coralline hydroxyapatite resulted in solid fusion in 50% (7/14) of the rabbits (P < 0.05). When combined with the osteoinductive growth factor extract, the coralline hydroxyapatite resulted in solid fusion in 100% (11/11) of the rabbits (P < 0.05). The fusion masses in the growth factor group were significantly stronger (1.8 +/- 0.2 vs. 1.3 +/- 0.1; P = 0.02) and stiffer (1.5 +/- 0.2 vs. 1.2 +/- 0.1, P = 0.04) based on tensile testing to failure when normalized to the adjacent unfused level.

CONCLUSION

These data indicate that coralline hydroxyapatite with bone marrow was not an acceptable bone graft substitute for posterolateral spine fusion. When combined with autogenous iliac crest bone graft-coralline hydroxyapatite served as a graft extender yielding results comparable to those obtained with autograft alone. Coralline hydroxyapatite served as an excellent carrier for the bovine osteoinductive bone protein extract yielding superior results to those obtained with autograft or bone marrow.

LMP-1, a LIM-domain protein, mediates BMP-6 effects on bone formation

Glucocorticoids can promote osteoblast differentiation from fetal calvarial cells and bone marrow stromal cells. We recently reported that glucocorticoid specifically induced bone morphogenetic protein-6 (BMP-6), a glycoprotein signaling molecule that is a multifunctional regulator of vertebrate development. In the present study, we used fetal rat secondary calvarial cultures to determine genes induced during early osteoblast differentiation as initiated by glucocorticoid treatment. Glucocorticoid, and subsequently BMP-6, was found to induce a novel rat intracellular protein, LIM mineralization protein-1 (LMP-1), that in turn resulted in synthesis of one or more soluble factors that could induce de novo bone formation. Blocking expression of LMP-1 using antisense oligonucleotide prevented osteoblast differentiation in vitro. Overexpression of LMP-1 using a mammalian expression vector was sufficient to initiate de novo bone nodule formation in vitro and in sc implants in vivo. These data demonstrate that LMP-1 is an essential positive regulator of the osteoblast differentiation program as well as an important intermediate step in the BMP-6 signaling pathway.

Lumbar spine fusion by local gene therapy with a cDNA encoding a novel osteoinductive protein (LMP-1)

STUDY DESIGN

A posterior arthrodesis animal model using local expression of a newly discovered osteoinductive protein delivered in bone marrow cells.

OBJECTIVE

To introduce the concept of local gene therapy and determine its feasibility for achieving lumbar spine fusion using a gene for a novel osteoinductive protein: LIM Mineralization Protein-1 (LMP-1).

SUMMARY OF BACKGROUND DATA

Extensive work is currently underway to improve the healing success and morbidity associated with the gold standard bone-grafting material of autogenous iliac crest. As a result, alternative osteoinductive proteins and new delivery methods warrant investigation. The authors' laboratory recently identified a novel gene that had osteoinductive capacity in vitro and is therefore a candidate for a new in vivo osteoinductive agent.

METHODS

Single-level posterior lumbar and thoracic arthrodesis was attempted in 14 athymic rats. The graft material, which consisted of a devitalized bone matrix (no osteoinductive activity) soaked with 0.75 to 1.5 million bone marrow cells, was inserted with the dorsal spine exposed. In each rat, one site received marrow cells transfected with the cDNA encoding a novel osteoinductive protein. At the other site for a control, the marrow cells were transfected with the reverse copy of the cDNA that did not express any protein. Transfection of marrow cells for 2 hours was accomplished using the mammalian expression vector pCMV2. Rats were killed after 4 weeks, and the spines were evaluated by manual palpation, radiographs, and nondecalcified histology.

RESULTS

In the pivotal experiment, successful spine fusion was obtained in 9/9 (100%) of the sites receiving marrow cells transfected with the active LMP-1 cDNA and in 0/9 (0%) of the sites receiving marrow cells transfected with the reverse (inactive) LMP-1 cDNA. Radiographs and histology confirmed the manual palpation results, demonstrating controlled new bone formation in the carrier and marrow transfected with the active LMP-1 cDNA and essentially no bone induction in the sites treated with marrow cells that did not express the protein.

CONCLUSIONS

These data confirm that local delivery of the novel LMP-1 cDNA using bone marrow cells is feasible in vivo. Furthermore, these results demonstrate that posterior thoracic or lumbar spine fusion can be achieved in rats by local delivery of the LMP-1 cDNA.

The Marshall R. Urist Young Investigator Award. Gene expression during autograft lumbar spine fusion and the effect of bone morphogenetic protein 2

A prospective animal study of posterolateral lumbar spine arthrodesis was performed to determine the temporal and spatial pattern of gene expression and to determine the effect of recombinant human bone morphogenetic protein 2 on the gene expression pattern of a healing spine fusion mass. In Group 1, 20 adult New Zealand rabbits underwent L4-L5 posterolateral intertransverse process arthrodesis using autograft alone. Two rabbits were euthanized at each of the following points: 0, 2, and 4 days, and 1, 2, 3, 4, 5, 6, and 10 weeks after surgery. The same surgical technique was used for 16 rabbits in Group II, except that the autograft first was soaked in a solution of recombinant human bone morphogenetic protein 2 before implantation. Ribonucleic acid was extracted from different regions of the fusion mass at each point and analyzed for expression of bone and cartilage related genes using reverse transcription polymerase chain reaction. A reproducible temporal sequence and spatial pattern of gene expression was found in healing spine fusions. In the central portion of the fusion mass a temporal lag in gene expression was observed that parallels the lag in healing within the central zone previously observed in histologic studies. Treatment of bone graft with recombinant human bone morphogenetic protein 2 resulted in an increase in the early expression of bone morphogenetic protein 6 which was associated with expression of higher levels of Type I collagen, osteocalcin, and other bone related genes. These findings suggest that central nonunion may be associated with delayed expression of osteoblast related genes in the central region of the forming fusion mass. The growth factor, recombinant human bone morphogenetic protein 2, increased the level of bone related gene expression throughout the fusion mass, eliminated the delay in healing within the central zone, and may decrease the likelihood of a nonunion.

Glucocorticoid-induced differentiation of fetal rat calvarial osteoblasts is mediated by bone morphogenetic protein-6

Glucocorticoids (GCs) at physiological concentrations promote osteoblast differentiation from fetal calvarial cells, calvarial organ cultures, and bone marrow stromal cells; however, the cellular pathways involved are not known. Bone morphogenetic proteins (BMPs) are recognized as important mediators of osteoblast differentiation. Specific roles for individual BMPs during postembryonic membranous bone formation have yet to be determined. We recently reported that GC potentiated the osteoblast differentiation effects of BMP-2 and BMP-4, but not of BMP-6, which, by itself, was the most potent of the three. In the present study, we used fetal rat secondary calvarial cultures to study the role of BMP-6 during early osteoblast differentiation. Treatment with the GC triamcinolone (10(-9) M) resulted in a 5- to 8-fold increase in BMP-6 steady-state messenger RNA levels, peaking at 12 h. In contrast, BMPs -2, -4, -5, -7, and transforming growth factor (TGF)-beta1 messenger RNA levels increased by less than 2-fold, after GC treatment, compared with untreated control cultures at 24 h. BMP-6 protein secretion increased 6- to 7-fold by 12 h and 12-fold (from 7.5 to 90 ng/ml) by 24 h, as measured by quantitative Western analysis. Treatment of cells with oligodeoxynucleotides antisense to BMP-6 diminished secretion of BMP-6 protein and significantly inhibited the GC-induced differentiation, as determined by a 10-fold decrease in the number of mineralized bone nodules, compared with controls that were treated with sense oligonucleotides or no oligonucleotides (ANOVA, P < 0.05). The antisense oligonucleotide inhibition of differentiation was rescued by treatment with exogenous recombinant human BMP-6. We conclude that GC-induced differentiation of osteoblasts from the pluripotent precursors is mediated, in part, by BMP-6. These results suggest that BMP-6 has an important and unique role during early osteoblast differentiation.

Differential effects and glucocorticoid potentiation of bone morphogenetic protein action during rat osteoblast differentiation in vitro

Bone morphogenetic proteins (BMPs) induce cartilage and bone differentiation in vivo and promote osteoblast differentiation from calvarial and marrow stromal cell preparations. Functional differences between BMP-2, -4, and -6 are not well understood. Recent investigations find that these three closely related osteoinductive proteins may exert different effects in primary rat calvarial cell cultures, suggesting the possibility of unique functions in vivo. In this study, we use a fetal rat secondary calvarial cell culture system to examine the differential effects of BMP-2, -4, and -6 on early osteoblast differentiation. These cells do not spontaneously differentiate into osteoblasts, as do cells in primary calvarial cultures, but rather require exposure to a differentiation initiator such as glucocorticoid or BMP. We determined that BMP-6 is a 2- to 2.5-fold more potent inducer of osteoblast differentiation than BMP-2 or -4. BMP-6 induced the formation of more and larger bone nodules as well as increased osteocalcin secretion. The effects of all three of these BMPs were potentiated up to 10-fold by cotreatment or pretreatment with the glucocorticoid triamcinolone (Trm). The Trm effects were synergistic with those of BMP-2 or -4, suggesting that this glucocorticoid may increase the cell responsiveness to these BMPs. Finally, BMP-6 did not require either cotreatment or pretreatment with Trm to achieve greater amounts of osteoblast differentiation than seen with BMP-2 or BMP-4 treatment, suggesting that BMP-6 may act at an earlier stage of cell differentiation.

1,25(OH)2D3 and cAMP synergistically induce complement 5a receptor messenger RNA

Complement 5a receptor (C5aR) mediates both acute and chronic participation of monocytes in the immune response. In the human U937 monoblast, C5aR is maximally expressed 4 days after treatment with 1,25(OH)2D3 (or cycloheximide) and prostaglandin E2 combined. The authors asked whether these agents altered expression of C5aR messenger RNA (mRNA). Unstimulated U937 cells expressed neither C5aR mRNA nor C5a binding. Complement 5aR mRNA rose 3 hours after prostaglandin E2 application and fell to basal levels by 12 hours. This early rise in C5aR mRNA did not cause an acute rise in C5a binding, which gradually increased between 1 and 4 days. Neither 1,25(OH)2D3 nor cycloheximide induced expression of C5aR mRNA in the absence of prostaglandin E2 but did enhance prostaglandin E2-stimulated C5aR mRNA expression and C5a binding. The authors observed a late increase in C5aR mRNA at day 3 in treated cells. Inhibition of this late rise in mRNA with 5,6-dichlorobenzimidazole riboside attenuated C5a binding by 65%, indicating its importance in the generation of C5a binding sites. The expression of functional C5aR is, therefore, a complex process involving regulation at transcriptional and posttranscriptional levels.

Formation of osteoclast-like cells is suppressed by low frequency, low intensity electric fields

With use of a solenoid to generate uniform time-varying electric fields, the effect of extremely low frequency electric fields on osteoclast-like cell formation stimulated by 1,25(OH)2D3 was studied in primary murine marrow culture. Recruitment of osteoclast-like cells was assessed by counting multinuclear, tartrate-resistant acid phosphatase positive cells on day 8 of culture. A solenoid was used to impose uniform time-varying electric fields on cells; sham exposures were performed with an identical solenoid with a null net electric field. During the experiments, both solenoids heated interiorly to approximately 1.5 degrees C above ambient incubator temperature. As a result of the heating, cultures in the sham solenoid formed more osteoclast-like cells than those on the incubator shelf (132 +/- 12%). For this reason, cells exposed to the sham solenoid were used for comparison with cultures exposed to the active coil. Marrow cells were plated at 1.4 x 10(6)/cm2 in square chamber dishes and exposed to 60 Hz electric fields at 9.6 muV/cm from days 1 to 8. Field exposure inhibited osteoclast-like cell recruitment by 17 +/- 3% as compared with sham exposure (p < 0.0001). Several variables, including initial cell plating density, addition of prostaglandin E2 to enhance osteoclast-like cell recruitment, and field parameters, were also assessed. In this secondary series, extremely low frequency fields inhibited osteoclast-like cell formation by 24 +/- 4% (p < 0.0001), with their inhibitory effect consistent throughout all variations in protocol. These experiments demonstrate that extremely low intensity, low frequency sinusoidal electric fields suppress the formation of osteoclast-like cells in marrow culture. The in vitro results support in vivo findings that demonstrate that electric fields inhibit the onset of osteopenia and the progression of osteonecrosis; this suggests that extremely low frequency fields may inhibit osteoclast recruitment in vivo.

Nursing ethics committees--where are they?

When establishing Nursing Ethics Committees (NECs), statewide nursing organizations play an important role in developing and disseminating resources. The Connecticut Nurses Association Ethics and Human Rights Committee surveyed 85 healthcare facilities to identify active NECs. Representatives facilitated other committees by providing guidelines and assistance to those agencies developing NECs--the ultimate goal.

A single up-stream element confers responsiveness to 1,25-dihydroxyvitamin D3 and tumor necrosis factor-alpha in the rat osteocalcin gene

Tumor necrosis factor-alpha (TNF alpha) is one of several autocrine/paracrine factors known to exert potent inhibitory effects on bone. We have shown that TNF alpha inhibition of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-stimulated synthesis of the bone-specific protein osteocalcin (OC) occurs by decreasing steady state levels of OC mRNA, suggesting a pretranslational mechanism. In many genes, TNF alpha action is mediated by the transcription factor NF kappa B. Analysis of OC 5'-flanking DNA revealed a sequence structurally homologous to the previously described NF kappa B-binding site and, thus, a potential TNF alpha response element. Deletion analysis was performed to identify the sequences mediating the response to TNF alpha in osteoblastic ROS 17/2.8 cells by transient transfection with reporter constructs containing rat OC 5'-flanking DNA [chloramphenicol acetyltransferase (CAT)] that retained or deleted homologous NF kappa B sites or a previously defined 1,25-(OH)2D3 response element (VDRE). Transfection with all reporter constructs resulted in low basal CAT activity, measured 72 h after transfection. 1,25-(OH)2D3 stimulated CAT activity 2.8- to 4.5-fold in cells transfected with constructs that included the VDRE. TNF alpha inhibited 1,25-(OH)2D3-stimulated, but not basal, CAT activity. Deletion analysis localized the effect of TNF alpha to a sequence between -522 and -306 relative to the OC transcription start site, an area that included the VDRE but deleted a homologous NF kappa B element. Transfection of cells with a heterologous reporter containing one copy of the OC VDRE inserted in correct orientation or two copies in inverse orientation was sufficient to confer a response to TNF alpha. Gel mobility shift analysis of DNA-nuclear protein interaction revealed that 1,25-(OH)2D3 stimulated an increase in binding of nuclear proteins to an OC 32P-VDRE probe. Preincubation of nuclear extract with specific monoclonal antibodies confirmed that the proteins binding the VDRE included the vitamin D receptor and retinoid-X receptor. TNF alpha treatment of cells inhibited the 1,25-(OH)2D3-stimulated increase in nuclear protein binding to the VDRE. These results suggest 1) the VDRE is sufficient to confer a response to the inhibitory effect of TNF alpha on 1,25-(OH)2D3-stimulated rat OC gene transcription; 2) the action of TNF alpha does not require homologous NF kappa B response elements; and 3) the mechanism of TNF alpha inhibition of 1,25-(OH)2D3-stimulated OC gene expression includes modulation of binding of the vitamin D receptor/retinoid-X receptor heterodimer to the VDRE.

Increased expression of tissue plasminogen activator messenger ribonucleic acid is an immediate response to parathyroid hormone in neonatal rat osteoblasts

Osteoblasts have been reported to produce tissue-type (t) plasminogen activator (PA), which may be involved in the initiation of bone resorption via plasmin-metalloproteinase degradation of adjacent extracellular matrix. To investigate this cAMP-activated gene, we characterized the PTH regulation of tPA messenger RNA (mRNA) in neonatal rat osteoblast cultures before and after differentiation in vitro. RNA was purified from cultures at confluence or after treatment with glucocorticoid for 1 week and BGJ/ascorbic acid/beta-glycerophosphate for a second week. Northern blots of total or poly(A)+ RNA were hybridized simultaneously with an oligonucleotide or complementary RNA probe for rat tPA and an oligomeric DNA probe for cyclophilin (CYP), an abundant control gene. Differentiation was monitored by expression of rat osteocalcin mRNA and protein. Both bovine PTH1-34 and forskolin caused an increase in tPA/CYP ratio in the presence of phosphodiesterase inhibitor (IBMX) and cycloheximide (CHX). The effect was maximal (16- to 21-fold increase in tPA mRNA and 6- to 8-fold increase in tPA/CYP ratio) with 25 nM hormone for 6 h and was half-maximally stimulated by 0.75-2.5 nM PTH. The tPA response to PTH was present in first passage osteoblast cultures at confluence and after 1 to 2 weeks of glucocorticoid treatment. Exposure of the differentiated cultures of 1,25-dihydroxyvitamin D (10 nM) for 2 days markedly stimulated osteocalcin mRNA while having no effect on tPA. In Northern blots of poly(A)+ RNA from cultures not treated with CHX, IBMX and PTH (2.5 h) independently stimulated tPA mRNA with no significant effect on CYP mRNA levels. The tPA/CYP ratio increased in five consecutive experiments and the effect of IBMX and PTH were additive. These data indicate that PTH acts via cAMP to stimulate tPA expression by a mechanism that is independent of protein synthesis. The enhancement of PTH action by CHX is compatible with feedback inhibition of tPA transcription by a hormone-activated repressor (which has been proposed to occur in granulosa cells) but effects of CHX on tPA mRNA stability may also occur. Expression of tPA mRNA before and after differentiation may indicate that the enzyme has more than one function.

Rat osteoblasts and ROS 17/2.8 cells contain a similar protein tyrosine phosphatase

Tyrosine phosphorylation plays a central role in intracellular signaling by many hormones and growth factors. Termination of the signal is thought to involve dephosphorylation of target proteins by phosphotyrosine phosphatases (PTPase). Soluble protein PTPases from neonatal rat osteoblasts (ROBs) and rat osteosarcoma (ROS 17/2.8) cells were chromatographically distinguished and characterized using 32P-labelled glutamate/tyrosine co-polymer as substrate. Two activities from both cell types were chromatographically separable. The dominant PTPase activity in the presence of 60-125 mM salt (E1), was eluted from phosphocellulose by 180-280 mM NaCl, bound weakly to a strong anion exchange column (QAE-trisacryl), had an apparent Km for [32P]glutamate/tyrosine copolymer of 52 micrograms/ml, was enhanced (5-10-fold, ROS; 1.5-3-fold, ROB) by assay in 125 mM NaCl, had no significant alkaline, acid, or serine phosphatase activity and had an M(r) of 53,000. A second activity (E2) was not retained by phosphocellulose but eluted from QAE-trisacryl in a single peak at 90-130 mM NaCl. It had an apparent Km for [32P]glutamate/tyrosine copolymer of 30 micrograms/ml (ROS) and its activity was not enhanced by NaCl in the assay. Activity E1 from both cells was 50% inhibited by 0.05 microM Na3VO4, 20 microM ZnCl2, or 5-10 microM CoCl2, but not by 1 mM NaF; activity E2 had a similar inhibition profile, but was more sensitive to ZnCl2 (IC50, 5 microM). Co2+ is a relatively non-toxic metal which may be a useful tool for investigating the role of phosphotyrosine in osteoblast proliferation and function. The similarity between the E1 activity from ROS cells and ROBs suggests that ROS cells may be useful in studying PTPase regulation by hormones, but molecular approaches will be required to establish the identity of PTPases in ROBs and ROS cells.

cAMP promotion of osteoclast-like cell development from mouse bone marrow cells requires a permissive action of 1,25-(OH)2D3

Recruitment of osteoclasts from monocytic precursors is modulated by local signals. We previously showed that monoblastic differentiation in U937 cells is stimulated by 1,25-(OH)2D3 and cAMP in series. We investigate here the combined effects of these agents to stimulate differentiation of osteoclast-like cells from mouse marrow. Cells from mouse marrow were harvested and cultured in alpha-MEM with 10% fetal bovine serum. The appearance of tartrate-resistant acid phosphatase-containing multinuclear cells was measured after 8 days in culture by cytochemical staining. Continuous exposure of cultures to 10 nM 1,25-(OH)2D3 positively stimulated development of these cells after 8 days (101 +/- 3 cells per well, n = 74). No osteoclast-like cells were found when 1,25-(OH)2D3 was added for the first 4 days followed by 4 days more with no treatment. PGE2 (1 microM) as a single agent added during the last 4 days of culture was not able to recruit osteoclast-like cells. However, cultures exposed to 1,25-(OH)2D3 during the first 4 days and 1 microM PGE2 during the second 4 days developed osteoclast-like cells at 8 days [66 +/- 8% of the formation seen with 1,25-(OH)2D3 alone, p less than 0.05]. Dibutyryl cAMP (1 microM to 3 mM) was also not effective used as a single agent, but was able to stimulate formation of TRAP-positive multinuclear cells when 1,25-(OH)2D3 preceded its addition to culture medium. cAMP analogs therefore mimicked the effect of 1 microM PGE2, but these experiments do not allow us to assign the PGE2 action entirely to activation of cAMP second messenger.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of complement 5a receptor expression in U937 cells by phorbol ester

Receptors for the anaphylactic portion of complement, C5a, are not initially expressed in the monoblastic U937 cell line, but appear as the cell is induced to differentiate by the synergistic actions of 1,25(OH)2D and cyclic adenosine monophosphate (cAMP). Phorbol myristate acetate (PMA), which activates the protein kinase C pathway (PKC), does not cause C5a receptor (C5aR) expression when used as a single agent. The induction of C5aR by the synergistic actions of 1,25(OH)2D and cAMP, however, can be augmented as much as 180% by the addition of PMA. C5aR arising in cells exposed to 1,25(OH)2D and 8,4-chlorophenylthio-cAMP have an affinity constant of about 0.4 nM as assessed by cold competition analysis. We show here that when phorbol augmentation of receptor number occurs, the affinity constant is increased by 3.6-fold. In an effort to ascertain whether the change in C5aR Kd involved a PKC-dependent event we examined whether 5-60 min exposure of C5aR-positive cells to PMA would change C5aR Kd. Acutely, PMA caused a downregulation of receptor binding with decreases in apparent receptor number out of proportion to changes in Kd. One hundred nanomolar PMA, which effects nearly complete translocation of PKC to the membrane, consistently caused a 70-90% decrease in C5a surface binding. This downregulation was proportional to PMA dose and exposure time. Micromolar concentrations of the microtubule depolymerizing agents colchicine and vinblastine caused a less drastic downregulation, about 50% of the maximal phorbol effect. Our data suggest that activation of the PKC system might acutely limit the macrophage's ability to respond to C5a; chronically, phorbols upregulate receptor expression, most likely through positive effects on C5aR gene expression.

1,25-dihydroxyvitamin D reduces parathyroid hormone receptor number in ROS 17/2.8 cells and prevents the glucocorticoid-induced increase in these receptors: relationship to adenylate cyclase activation

We have previously shown that 1,25-dihydroxyvitamin D [1,25-(OH)2D3] and glucocorticoid modulate adenylate cyclase activation by PTH in osteoblast-like cells. Here we examine whether steroid effects on PTH receptor density explain the modulation of PTH action. Receptor assays were performed on late logarithmicphase monolayers of ROS 17/2.8 cells using human PTH-like peptide (hPLP) as radioligand. Kd and receptor density were computed from competition of tracer amounts of [125I-Tyr36] hPLP-(1-36) with unlabeled hPLP-(1-36) (0.1-30 nM). Steroid treatment had little or no effect on affinity for ligand. Pretreating cells with 10 nM 1,25-(OH)2D3 for 48 h decreased PTH receptor number to 17% of control values. Treating cells with 10 nM of the glucocorticoid triamcinolone acetonide (TRM) increased receptor number 10-fold, but simultaneous treatment with 1,25-(OH)2D3 (10 nM) completely prevented this receptor increase. Steroid effects required 13-18 h of treatment. Dose-response relationships for steroid modulation, determined from binding at 0.17 nM radioligand, indicated an EC50 of 0.3 nM for glucocorticoid augmentation of PTH receptor number and 0.02 nM for 1,25-(OH)2D3 reduction of receptor number in the presence of absence of the maximum TRM effect. The initial rate of cAMP production by receptor-saturating concentrations of PTH was 11,500 molecules per receptor per minute in untreated cells, comparable to reported turnover numbers for mammalian adenylate cyclase. Control experiments were validated measuring cAMP in intact cells as an indicator of adenylate cyclase activity. Cyclic AMP production was reduced 63% by 1,25-(OH)2D3 (10 nM) treatment. Glucocorticoid (10 nM) enhanced cAMP production twofold but reduced cAMP generation per receptor by 80%.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor necrosis factor-alpha inhibits 1,25-dihydroxyvitamin D3-stimulated bone Gla protein synthesis in rat osteosarcoma cells (ROS 17/2.8) by a pretranslational mechanism

Tumor necrosis factor-alpha (TNF alpha), a 17,000 mol wt protein, mediates a variety of immunological and inflammatory events. TNF alpha is a potent inhibitor of bone collagen synthesis and stimulator of osteoclastic bone resorption, the net effect of which is to cause bone loss. We have previously reported that TNF alpha inhibits the synthesis of collagen by osteoblastic cells in culture out of proportion to effects on total protein synthesis, suggesting that inhibition of bone formation by TNF alpha may be due to selective inhibition of matrix protein synthesis. To further test this hypothesis and to evaluate the mechanism of TNF alpha action, we studied the effect of TNF alpha on synthesis of the osteoblast-specific bone Gla protein (BGP) by ROS 17/2.8 cells, which have the osteoblast phenotype. Cells were cultured with 10 nM 1,25-dihydroxyvitamin D3 to stimulate BGP secretion, followed by the addition of TNF alpha (1-100 ng/ml) in 1,25-dihydroxyvitamin D3-containing medium. TNF alpha (10 ng/ml) inhibited BGP secretion to 42 +/- 5%, 19 +/- 10%, and 15 +/- 3% of control values after 24, 48, and 72 h of treatment. After 48 h, inhibition of BGP secretion was observed with 2 ng/ml TNF alpha and was maximum with 100 ng/ml. To determine the effect of TNF alpha on total protein synthesis, cells were pulse labeled with [14C]leucine during the last 4 h of TNF alpha treatment, and incorporation of radioactivity into trichloroacetic acid-precipitable protein in cell layer and medium was determined. The TNF alpha inhibition of BGP secretion was independent of changes in [14C]leucine incorporation, suggesting that TNF alpha did not have a general inhibitory effect on total protein synthesis. Cell number was not affected by TNF alpha. Northern analysis of steady state BGP mRNA revealed a dose-dependent decrease in the BGP/cyclophilin mRNA hybridization signal intensity after 24 h of treatment. The maximum inhibitory effect was 41 +/- 5% of the control value with 100 ng/ml TNF alpha. The effect of TNF alpha on steady state BGP mRNA levels was not prevented by treatment of cells with cycloheximide, suggesting that TNF-induced new protein synthesis was not required for TNF alpha action. These results suggest that the mechanism of TNF alpha inhibition of BGP synthesis includes a pretranslational site and support the hypothesis that TNF alpha inhibits bone formation by a selective inhibition of matrix protein production.

Prostaglandin E2 induction of monoblastic differentiation utilizes both cAMP and non-cAMP dependent signalling systems

U937 cells can be induced to express receptor for complement 5a (C5aR) by sequential 2 day treatments of cells with dihydroxyvitamin D-3 (1,25(OH)2D3) followed by prostaglandin E2. We asked whether the action of prostaglandin E2 to cause maximal C5aR expression required only activation of the cAMP-dependent protein kinase (PKA). Prostaglandin E2 dose dependently activated PKA in control and 1,25(OH)2D3 treated cells; by 4 h the PKA did not respond to further prostaglandin E2 challenge. We hypothesized that prostaglandin E2 actions transduced via PKA should be complete by 4 h; i.e., C5aR induction should be equivalent in cells treated with prostaglandin E2 for 4 h and for 2 days. All cells were treated for the first 2 days with 1,25(OH)2D3 and the second 2 days with prostaglandin E2 or cAMP analogs. C5aR number was measured after 4 days total culture. 4 h pulse treatments with agents were given at the end of the 1,25(OH)2D3 treatment. Cells exposed to a 4 h pulse of prostaglandin E2 had only 68.2 +/- 4.4% the amount of C5aR seen in cells continuously exposed to prostaglandin E2. Continuous culture with a cAMP analog pair (50 microM each of 8-thiomethyl-cAMP + N6-benzoyl-cAMP), which caused a 41.7% +/- 10.8% increase PKA activation above basal, resulted in only 51% +/- 16% of the C5aR numbers seen in cells cultured for 2 days with prostaglandin E2, where PKA remained at basal activity. We therefore concluded that C5aR expression caused by prostaglandin E2 could not be ascribed entirely to duration or degree of activation of cAMP-dependent signalling pathways. We investigated the possibility that the calcium sensitive protein kinase C was involved. Cytoplasmic protein kinase C was increased 154% +/- 14% above control in cells treated with sequential 2 days treatments of 1,25(OH)2D3 and prostaglandin E2. A 147% +/- 2% increase in membrane associated protein kinase C was also seen 10 min after phorbol myristate acetate stimulation in the above treatment group. Finally, phorbol myristate acetate augmented the C5aR induction caused by cAMP analog. We propose that the mechanism of prostaglandin E2 synergism with 1,25(OH)2D3 in causing C5aR induction in U937 cells includes signal transduction not only by the cAMP cascade, but also via protein kinase C modulated pathways.

Interferon-gamma inhibits 1,25-dihydroxyvitamin D3-stimulated synthesis of bone GLA protein in rat osteosarcoma cells by a pretranslational mechanism

Interferon-gamma (IFN) is produced by lymphocytes in areas of inflammation and connective tissue destruction. IFN inhibits collagen and DNA synthesis in cultured rat long bones and osteoblastic ROS 17/2.8 cells, suggesting that the periarticular loss of bone that occurs in inflammatory joint diseases may be due to IFN inhibition of bone formation. Since serum levels of bone gla protein (BGP) have been correlated with the bone formation rate, we studied the effect of IFN on production of this osteoblast-specific protein and steady state BGP messenger RNA (mRNA) levels in ROS 17/2.8 cells. RIA of BGP was done using an antibody raised against rat BGP peptide. BGP synthesis was stimulated with 10(-8) M 1,25-dihydroxyvitamin D3 24 h before and continuously after addition of recombinant rat IFN. IFN (100 U/ml) inhibited BGP secretion 52%, 78%, and 70% in the first, second, and third 24 h periods after IFN treatment, compared to control cells cultured with 1,25-dihydroxyvitamin D3 alone. The ED50 for IFN inhibition of BGP production was 3.3 U/ml (0.29 nM). Pulse labeling with [14C]leucine or [3H]proline during the last 4 h of culture revealed that IFN (3-100 U/ml) did not inhibit total protein secretion into the medium. The percent inhibition of BGP production by IFN was independent of media serum concentration or cell density. IFN (100 U/ml) decreased the steady state level of BGP mRNA as measured by Northern analysis using an oligomeric probe for rat BGP. The decrease in hybridization signal for BGP mRNA was detectable by 1 h after IFN exposure and continued to decline at 6 and 24 h. Treatment with cycloheximide (5 micrograms/ml) blocked the inhibitory effect of IFN on steady state levels of BGP mRNA. These results suggest that IFN may inhibit bone formation by selective inhibition of osteoblast matrix protein production. The mechanism of IFN inhibition of BGP production is, at least in part, pretranslational.

Glucocorticoid and 1,25-dihydroxyvitamin D modulate the degree of adenosine 3',5'-monophosphate-dependent protein kinase isoenzyme I and II activation by parathyroid hormone in rat osteosarcoma cells

Glucocorticoid increases and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] decreases PTH activation of adenylate cyclase and cAMP-dependent protein kinase in rat osteosarcoma cells (ROS 17/2.8). Since selective cAMP-dependent protein kinase isoenzyme activation may account for specific physiological hormonal responses, we investigated steroid effects on activation of isoenzymes I and II in response to PTH using a new ion exchange separation procedure. Pretreatment of cells for 2 days with the glucocorticoid triamcinolone acetonide (TRM) or 1,25-(OH)2D3 altered the degree of cAMP-dependent protein kinase isoenzyme activation by PTH in accordance with their modulation of intracellular cAMP accumulation, but did not alter the amount of each isoenzyme present or the order in which isoenzymes I and II were activated. In all treatment groups isoenzyme I was preferentially activated by low doses of PTH, while high concentrations activated both isoenzymes, as predicted by the relative affinities of each isoenzyme for cAMP. Glucocorticoid reduced the concentration of bovine PTH-(1-34) required for maximal activation of isoenzyme I from 1 to 0.05 ng/ml and that required for activation of isoenzyme II from 10 to 1 ng/ml. This effect was abolished by simultaneous treatment of cells with 1,25-(OH)2D3. At doses of PTH that caused partial activation (0.05-0.1 ng/ml for isoenzyme I; 1 ng/ml for isoenzyme II), 1,25-(OH)2D3 treatment attenuated this activation. In all groups both isoenzymes were fully activated by 100 ng/ml PTH. Control experiments demonstrated that isoenzyme activation is not a result of cell disruption over the range of PTH doses that regulation by steroid hormone was observed. These results extend our studies on modulation of the cAMP pathway by steroid hormones and make it feasible to correlate selective isoenzyme activation with specific responses to PTH.

Glucocorticoids and 1,25-dihydroxyvitamin D3 regulate parathyroid hormone stimulation of adenosine 3',5'-monophosphate-dependent protein kinase in rat osteosarcoma cells

Glucocorticoids increase and 1,25-dihydoxyvitamin D3 [1,25-(OH)2D3] decreases the activity of PTH-responsive adenylate cyclase, altering intracellular cAMP in a rat osteoblast-like cell line (ROS 17/2.8). This study was undertaken to measure the subsequent activation of the cAMP-dependent protein kinase (PKA). Pretreatment of ROS cells for 2 days with the glucocorticoid triamcinolone acetonide (TRM), shifted the dose-response curve for PKA activation by PTH upward compared to the control value. Basal PKA activity was enhanced 50% by TRM, and the PTH concentration required for maximal activation of PKA decreased from 1.0 to 0.05 ng/ml. At the lowest effective PTH concentration (0.05 ng/ml) the mean PKA activity ratio increased to 0.73 in TRM-treated cells compared with 0.45 in untreated cells. Pretreatment with 1,25-(OH)2D3 had opposite effects, shifting the dose-response curve for PKA activation by PTH downward and to the right, decreasing the basal activity ratio from 0.26 to 0.16, and increasing the PTH concentration required for maximal activation to 10 ng/ml. 1,25-(OH)2D3-treated cells stimulated with 0.5-1 ng/ml PTH consistently had lower PKA activity ratios than untreated cells. Simultaneous treatment with 1,25-(OH)2D3 reversed the effect of TRM. There were no differences in total PKA activity (2.57 +/- 0.09 pmol 32P/min.micrograms protein) between treatment groups, suggesting that TRM and 1,25-(OH)2D3 do not alter the cellular PKA concentration. In control experiments exogenous PKA was added to sonication buffer of PTH-stimulated cells to verify that the TRM and 1,25-(OH)2D3 shifts in PKA activation at low PTH doses occur before sonication. cAMP-dependent protein kinase activation was also studied by measuring the progressive occupation of regulatory subunit-binding sites by hormonally stimulated endogenous cAMP. [3H] cAMP binding was expressed as the percent change in bound [3H]cAMP per microgram protein compared to that in unstimulated cells not steroid treated. [3H]cAMP binding to all cytosol fractions decreased as PTH increased over the concentration range predicted by our PKA activation experiments. TRM treatment shifted the curve for [3H]cAMP binding to regulatory subunit downward and to the left, and 1,25-(OH)2D3 treatment shifted it upward and to the right. In cells treated with both TRM and 1,25-(OH)2D3, the curve was similar to control curve. Sonicating unstimulated cells in buffer containing comparable concentrations of added cAMP did not alter [3H]cAMP binding. These and the previous controls suggest that changes in PKA activation at low doses of PKA reflect cellular events occurring before cell disruption.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of cholinergic and adrenergic agonists on phosphorylation of a 165,000-dalton myofibrillar protein in intact cardiac muscle

The purpose of this investigation was to examine the effects of beta-adrenergic and muscarinic cholinergic agonists on protein phosphorylation in intact frog atrium. beta-Adrenergic agonists increase and muscarinic agonists decrease 32P incorporation into a 165,000-dalton (165K) protein within less than 1 min. The concentrations of isoproterenol that produce increases in 32P incorporation into the 165K protein and in systolic tension are similar. Further, the changes in 32P incorporation and tension produced by isoproterenol occur with similar time courses. Carbamylcholine decreases tension somewhat more quickly and at lower concentrations than it decreases 32P incorporation, however. Isoproterenol-stimulated 32P incorporation is thought to be mediated by cAMP-dependent protein kinase because bath application of dibutyryl cAMP, cholera toxin, or phosphodiesterase inhibitors increase 32P incorporation into the 165K protein in intact atria. When heart homogenates are incubated in the presence of [gamma-32P]ATP, cAMP stimulates the incorporation of 32P into the 165K protein. cGMP is much less effective. We suggest that carbamylcholine decreases 32P incorporation into the 165K protein by a mechanism independent of cAMP levels because carbamylcholine inhibits the stimulation of 32P incorporation into the 165K band produced by 8-bromo cAMP in intact cells. Phosphorylation of the 165K protein occurs in cardiac muscle but not in other tissues. We hypothesize that the 165K protein is C-protein, because the 165K- and C-proteins have similar solubilities and are associated with the myofibril. Further, antibodies produced against the 165K protein bind to C-protein purified from rabbit heart and also bind to the same region of the myofibril where C-protein is found.