Biomedical subjects

Lynda F Bonewald

Publications and source records attributed to Lynda F Bonewald.

16 recordsLinked to original sources

PubMed2007

Tissue strain amplification at the osteocyte lacuna: a microstructural finite element analysis.

A parametric finite element model of an osteocyte lacuna was developed to predict the microstructural response of the lacuna to imposed macroscopic strains. The model is composed of an osteocyte lacuna, a region of perilacunar tissue, canaliculi, and the surrounding bone tissue. A total of 45 different simulations were modeled with varying canalicular diameters, perilacunar tissue material moduli, and perilacunar tissue thicknesses. Maximum strain increased with a decrease in perilacunar tissue modulus and decreased with an increase in perilacunar tissue modulus, regardless of the thickness of the perilacunar region. An increase in the predicted maximum strain was observed with an increase in canalicular diameter from 0.362 to 0.421 microm. In response to the macroscopic application of strain, canalicular diameters increased 0.8% to over 1.0% depending on the perilacunar tissue modulus. Strain magnification factors of over 3 were predicted. However, varying the size of the perilacunar tissue region had no effect on the predicted perilacunar tissue strain. These results indicate that the application of average macroscopic strains similar to strain levels measured in vivo can result in significantly greater perilacunar tissue strains and canaliculi deformations. A decrease in the perilacunar tissue modulus amplifies the perilacunar tissue strain and canaliculi deformation while an increase in the local perilacunar tissue modulus attenuates this effect.

Adaptation, Physiological↗

PubMed2006

Loss of DMP1 causes rickets and osteomalacia and identifies a role for osteocytes in mineral metabolism.

The osteocyte, a terminally differentiated cell comprising 90%-95% of all bone cells, may have multiple functions, including acting as a mechanosensor in bone (re)modeling. Dentin matrix protein 1 (encoded by DMP1) is highly expressed in osteocytes and, when deleted in mice, results in a hypomineralized bone phenotype. We investigated the potential for this gene not only to direct skeletal mineralization but also to regulate phosphate (P(i)) homeostasis. Both Dmp1-null mice and individuals with a newly identified disorder, autosomal recessive hypophosphatemic rickets, manifest rickets and osteomalacia with isolated renal phosphate-wasting associated with elevated fibroblast growth factor 23 (FGF23) levels and normocalciuria. Mutational analyses showed that autosomal recessive hypophosphatemic rickets family carried a mutation affecting the DMP1 start codon, and a second family carried a 7-bp deletion disrupting the highly conserved DMP1 C terminus. Mechanistic studies using Dmp1-null mice demonstrated that absence of DMP1 results in defective osteocyte maturation and increased FGF23 expression, leading to pathological changes in bone mineralization. Our findings suggest a bone-renal axis that is central to guiding proper mineral metabolism.

Adult↗

PubMed2006

Erk pathways negatively regulate matrix mineralization.

Skeletal mineralization is an important step regulating the mechanical properties of the calcified tissues, but molecular events underlying mineralization still remain elusive. We examined the role of extracellular signal-regulated kinase (Erk) pathways in matrix mineralization of osteogenic cells both in vitro and in vivo. Matrix mineralization by preosteocytic MLO-A5 cells and osteoblastic MC3T3-E1 cells was increased by either PD98059 Mek inhibitor treatment or adenovirus vector-mediated dominant negative Ras (Ras(DN)) expression and was suppressed by Erk activation by platelet-derived growth factor (PDGF) treatment or constitutively active Mek1 (Mek(CA)) expression. Administration of adenovirus vectors carrying Ras(DN) gene onto the calvaria of 1-day-old mice increased the mineralization of the tissues, while that of the Mek(CA) adenovirus suppressed it. These results suggest that the Erk pathway is a negative regulator of the matrix mineralization both in vitro and in vivo.

Actins↗

PubMed2006

E11/gp38 selective expression in osteocytes: regulation by mechanical strain and role in dendrite elongation.

Within mineralized bone, osteocytes form dendritic processes that travel through canaliculi to make contact with other osteocytes and cells on the bone surface. This three-dimensional syncytium is thought to be necessary to maintain viability, cell-to-cell communication, and mechanosensation. E11/gp38 is the earliest osteocyte-selective protein to be expressed as the osteoblast differentiates into an osteoid cell or osteocyte, first appearing on the forming dendritic processes of these cells. Bone extracts contain large amounts of E11, but immunostaining only shows its presence in early osteocytes compared to more deeply embedded cells, suggesting epitope masking by mineral. Freshly isolated primary osteoblasts are negative for E11 expression but begin to express this protein in culture, and expression increases with time, suggesting differentiation into the osteocyte phenotype. Osteoblast-like cell lines 2T3 and Oct-1 also show increased expression of E11 with differentiation and mineralization. E11 is highly expressed in MLO-Y4 osteocyte-like cells compared to osteoblast cell lines and primary osteoblasts. Differentiated, mineralized 2T3 cells and MLO-Y4 cells subjected to fluid flow shear stress show an increase in mRNA for E11. MLO-Y4 cells show an increase in dendricity and elongation of dendrites in response to shear stress that is blocked by small interfering RNA specific to E11. In vivo, E11 expression is also increased by a mechanical load, not only in osteocytes near the bone surface but also in osteocytes more deeply embedded in bone. Maximal expression is observed not in regions of maximal strain but in a region of potential bone remodeling, suggesting that dendrite elongation may be occurring during this process. These data suggest that osteocytes may be able to extend their cellular processes after embedment in mineralized matrix and have implications for osteocytic modification of their microenvironment.

Animals↗

PubMed2005

Glucocorticoid-treated mice have localized changes in trabecular bone material properties and osteocyte lacunar size that are not observed in placebo-treated or estrogen-deficient mice.

UNLABELLED: This study compares changes in bone microstructure in 6-month-old male GC-treated and female ovariectomized mice to their respective controls. In addition to a reduction in trabecular bone volume, GC treatment reduced bone mineral and elastic modulus of bone adjacent to osteocytes that was not observed in control mice nor estrogen-deficient mice. These microstructural changes in combination with the macrostructural changes could amplify the bone fragility in this metabolic bone disease. INTRODUCTION: Patients with glucocorticoid (GC)-induced secondary osteoporosis tend to fracture at higher bone mineral densities than patients with postmenopausal osteoporosis. This suggests that GCs may alter bone material properties in addition to BMD and bone macrostructure. MATERIALS AND METHODS: Changes in trabecular bone structure, elastic modulus, and mineral to matrix ratio of the fifth lumbar vertebrae was assessed in prednisolone-treated mice and placebo-treated controls for comparison with estrogen-deficient mice and sham-operated controls. Compression testing of the third lumbar vertebrae was performed to assess whole bone strength. RESULTS: Significant reductions in trabecular bone volume and whole bone strength occurred in both prednisolone-treated and estrogen-deficient mice compared with controls after 21 days (p < 0.05). The average elastic modulus over the entire surface of each trabecula was similar in all the experimental groups. However, localized changes within the trabeculae in areas surrounding the osteocyte lacunae were observed only in the prednisolone-treated mice. The size of the osteocyte lacunae was increased, reduced elastic modulus around the lacunae was observed, and a "halo" of hypomineralized bone surrounding the lacunae was observed. This was associated with reduced (nearly 40%) mineral to matrix ratio determined by Raman microspectroscopy. These localized changes in elastic modulus and bone mineral to matrix ratio were not observed in the other three experimental groups. CONCLUSIONS: Based on these results, it seems that GCs may have direct effects on osteocytes, resulting in a modification of their microenvironment. These changes, including an enlargement of their lacunar space and the generation of a surrounding sphere of hypomineralized bone, seem to produce highly localized changes in bone material properties that may influence fracture risk.

Animals↗

PubMed2005

Osteocyte lacunae tissue strain in cortical bone.

Current theories suggest that bone modeling and remodeling are controlled at the cellular level through signals mediated by osteocytes. However, the specific signals to which bone cells respond are still unknown. Two primary theories are: (1) osteocytes are stimulated via the mechanical deformation of the perilacunar bone matrix and (2) osteocytes are stimulated via fluid flow generated shear stresses acting on osteocyte cell processes within canaliculi. Recently, much focus has been placed on fluid flow theories since in vitro experiments have shown that bone cells are more responsive to analytically estimated levels of fluid shear stress than to direct mechanical stretching using macroscopic strain levels measured on bone in vivo. However, due to the complex microstructural organization of bone, local perilacunar bone tissue strains potentially acting on osteocytes cannot be reliably estimated from macroscopic bone strain measurements. Thus, the objective of this study was to quantify local perilacunar bone matrix strains due to macroscopically applied bone strains similar in magnitude to those that occur in vivo. Using a digital image correlation strain measurement technique, experimentally measured bone matrix strains around osteocyte lacunae resulting from macroscopic strains of approximately 2000 microstrain are significantly greater than macroscopic strain on average and can reach peak levels of over 30,000 microstrain locally. Average strain concentration factors ranged from 1.1 to 3.8, which is consistent with analytical and numerical estimates. This information should lead to a better understanding of how bone cells are affected by whole bone functional loading.

Animals↗

PubMed2005

Mechanical strain opens connexin 43 hemichannels in osteocytes: a novel mechanism for the release of prostaglandin.

Mechanosensing bone osteocytes express large amounts of connexin (Cx)43, the component of gap junctions; yet, gap junctions are only active at the small tips of their dendritic processes, suggesting another function for Cx43. Both primary osteocytes and the osteocyte-like MLO-Y4 cells respond to fluid flow shear stress by releasing intracellular prostaglandin E2 (PGE2). Cells plated at lower densities release more PGE2 than cells plated at higher densities. This response was significantly reduced by antisense to Cx43 and by the gap junction and hemichannel inhibitors 18 beta-glycyrrhetinic acid and carbenoxolone, even in cells without physical contact, suggesting the involvement of Cx43-hemichannels. Inhibitors of other channels, such as the purinergic receptor P2X7 and the prostaglandin transporter PGT, had no effect on PGE2 release. Cell surface biotinylation analysis showed that surface expression of Cx43 was increased by shear stress. Together, these results suggest fluid flow shear stress induces the translocation of Cx43 to the membrane surface and that unapposed hemichannels formed by Cx43 serve as a novel portal for the release of PGE2 in response to mechanical strain.

Animals↗

PubMed2005

Dentin matrix protein 1 gene cis-regulation: use in osteocytes to characterize local responses to mechanical loading in vitro and in vivo.

Dentin matrix protein 1 (DMP1) is highly expressed in osteocytes and is mechanically responsive. To study osteocyte-specific and mechanically regulated DMP1 gene expression, the transcriptional activity of three cis-regulatory regions was first examined in an osteoblast differentiation model in vitro using a green fluorescent protein (GFP) reporter. Expression of the -9624 to +1996 bp (10 kb) and -7892 to +4439 bp (8 kb) DMP1 cis-regulatory regions dramatically increased in areas of mineralized matrix, in dendritic, osteocyte-like cells. Mineralizing cultures expressing the 8-kb construct show dramatic GFP increases in response to loading in cells with a dendritic morphology. Transgenic mice expressing the 8-kb DMP1-GFP and -2433 to +4439 bp (2.5 kb) DMP1-LacZ were generated. Osteocyte-specific expression was found with the 8 kb but not with the 2.5 kb in postnatal animals. However, the 2.5 kb could support expression in rapidly forming osteoblasts and pre-osteocytes in the embryo. Primary calvarial osteoblast cultures demonstrated that the 2.5 kb supports weak expression in a subset of osteoblasts and pre-osteocytes, but not in mature osteocytes. However, the 8 kb supports robust expression in primary bone marrow cultures. Therefore the region -7892 to -2433 bp, termed a 5.5-kb "Osteocyte Enhancer Module," appears to be required for osteocyte specificity. Ulnae of mice with the 8-kb DMP1-GFP were subjected to mechanical loading where GFP expression increased selectively and locally in osteocytes, distal to the mid-shaft and near the surface of the bone. Thus, the 8-kb region of the DMP1 gene is a target for mechanotransduction in osteocytes, and its cis-regulatory activity may be correlated to local strain in bone.

Animals↗

PubMed2004

Dmp1-deficient mice display severe defects in cartilage formation responsible for a chondrodysplasia-like phenotype.

Understanding the molecular mechanisms by which cartilage formation is regulated is essential toward understanding the physiology of both embryonic bone development and postnatal bone growth. Although much is known about growth factor signaling in cartilage formation, the regulatory role of noncollagenous matrix proteins in this process are still largely unknown. In the present studies, we present evidence for a critical role of DMP1 (dentin matrix protein 1) in postnatal chondrogenesis. The Dmp1 gene was originally identified from a rat incisor cDNA library and has been shown to play an important role in late stage dentinogenesis. Whereas no apparent abnormalities were observed in prenatal bone development, Dmp1-deficient (Dmp1(-/-)) mice unexpectedly develop a severe defect in cartilage formation during postnatal chondrogenesis. Vertebrae and long bones in Dmp1-deficient (Dmp1(-/-)) mice are shorter and wider with delayed and malformed secondary ossification centers and an irregular and highly expanded growth plate, results of both a highly expanded proliferation and a highly expanded hypertrophic zone creating a phenotype resembling dwarfism with chondrodysplasia. This phenotype appears to be due to increased cell proliferation in the proliferating zone and reduced apoptosis in the hypertrophic zone. In addition, blood vessel invasion is impaired in the epiphyses of Dmp1(-/-) mice. These findings show that DMP1 is essential for normal postnatal chondrogenesis and subsequent osteogenesis.

Animals↗

PubMed2003

Effects of mechanical strain on the function of Gap junctions in osteocytes are mediated through the prostaglandin EP2 receptor.

Osteocytes embedded in the matrix of bone are thought to be mechanosensory cells that translate mechanical strain into biochemical signals that regulate bone modeling and remodeling. We have shown previously that fluid flow shear stress dramatically induces prostaglandin release and COX-2 mRNA expression in osteocyte-like MLO-Y4 cells, and that prostaglandin E2 (PGE2) released by these cells functions in an autocrine manner to regulate gap junction function and connexin 43 (Cx43) expression. Here we show that fluid flow regulates gap junctions through the PGE2 receptor EP2 activation of cAMP-dependent protein kinase A (PKA) signaling. The expression of the EP2 receptor, but not the subtypes EP1,EP3, and EP4, increased in response to fluid flow. Application of PGE2 or conditioned medium from fluid flow-treated cells to non-stressed MLO-Y4 cells increased expression of the EP2 receptor. The EP2 receptor antagonist, AH6809, suppressed the stimulatory effects of PGE2 and fluid flow-conditioned medium on the expression of the EP2 receptor, on Cx43 protein expression, and on gap junction-mediated intercellular coupling. In contrast, the EP2 receptor agonist butaprost, not the E1/E3 receptor agonist sulprostone, stimulated the expression of Cx43 and gap junction function. Fluid flow conditioned medium and PGE2 stimulated cAMP production and PKA activity suggesting that PGE2 released by mechanically stimulated cells is responsible for the activation of cAMP and PKA. The adenylate cyclase activators, forskolin and 8-bromo-cAMP, enhanced intercellular connectivity, the number of functional gap junctions, and Cx43 protein expression, whereas the PKA inhibitor, H89, inhibited the stimulatory effect of PGE2 on gap junctions. These studies suggest that the EP2 receptor mediates the effects of autocrine PGE2 on the osteocyte gap junction in response to fluid flow-induced shear stress. These data support the hypothesis that the EP2 receptor, cAMP, and PKA are critical components of the signaling cascade between mechanical strain and gap junction-mediated communication between osteocytes.

Adenylyl Cyclases↗

PubMed2003

CD40 ligand blocks apoptosis induced by tumor necrosis factor alpha, glucocorticoids, and etoposide in osteoblasts and the osteocyte-like cell line murine long bone osteocyte-Y4.

During characterization of the osteocyte-like murine long bone osteocyte-Y4 (MLO-Y4) cell line, comparison was made with antigen-presenting cells of the immune system known as dendritic cells. It was observed that the MLO-Y4 osteocyte-like cells express CD40 antigen and MHC class I antigen, but they are negative for a series of other dendritic cells markers (DEC-205, CD11b, CD11c, CD86, and MHC class II) and immune cell markers [CD45, CD3, CD4, B220, Gr-1, and CD40 ligand (CD40L)]. RT-PCR results showed expression of CD40 mRNA and lack of CD40L mRNA expression. Like MLO-Y4 osteocyte cells, both primary osteoblasts and the osteoblast-like cell lines MC3T3, OCT-1, and 2T3 were shown to express CD40 antigen by fluorescence-activated cell sorting. Because CD40L has been shown to function as an antiapoptotic factor in dendritic cells, it was reasoned that this molecule may have a similar function in bone cells. In three different assays for apoptosis, including trypan blue exclusion, changes in nuclear morphology, and fluorescence-activated cell sorting staining for annexin V/propidium iodide, CD40L significantly inhibited apoptosis of MLO-Y4 cells induced by dexamethasone, TNF alpha, or etoposide. CD40L also inhibited dexamethasone and TNF alpha-induced apoptosis in the osteoblast cell lines, OCT1 and MC3T3-E1. These data support the hypothesis that CD40L preserves viability of osteoblasts and osteocytes against a wide variety of apoptotic factors independent of signaling or transcriptional mechanisms. Because osteocyte cell death appears to result in bone loss, these studies have important implications for the treatment of bone loss due to glucocorticoid excess and/or to osteoporosis in general.

Animals↗

PubMed2003

Mechanical loading stimulates dentin matrix protein 1 (DMP1) expression in osteocytes in vivo.

Dentin matrix protein 1 (DMP1) was originally postulated to be dentin specific. Further analysis showed that DMP1 is also expressed in mature cartilage and bone. In bone tissue, DMP1 is expressed predominantly in late osteoblasts and osteocytes. DMP1 belongs to the SIBLING (Small Integrin Binding Ligand N-linked Glycoprotein) family of cellular matrix proteins that also includes osteopontin, bone sialoprotein, dentin sialophosphoprotein, and others. In this study, we examined the effect of mechanical loading on expression of DMP1 mRNA and DMP1 protein in alveolar bone in the mouse tooth movement model by in situ hybridization and immunocytochemistry. The expression of DMP1 mRNA was determined quantitatively in mechanically loaded and control sites of dento-alveolar tissue at several time points from 6 h to 7 days after loading. The tooth movement model allows simultaneous evaluation of bone resorption and bone formation sites. Expression of DMP1 mRNA in osteocytes increased 2-fold as early as 6 h after treatment in both the bone formation and bone resorption sites. After 4 days, DMP1 expression in osteocytes increased to a maximum of 3.7-fold in the bone formation sites and 3.5-fold in the resorption sites. Osteoblasts responded in the opposite manner and showed a transient 45% decrease of DMP1 mRNA in bone formation sites and a constant decrease of DMP1 mRNA during the entire course of treatment in the bone resorption sites, with a peak inhibition of 67% at day 2. By immunocytochemistry using a C-terminal region peptide antibody to DMP1, we found that there was a transient decrease in immunoreactivity at 3 days after treatment on both the formation side and the resorption side compared with the matched contralateral control tissue. However by 7 days of loading, there was a dramatic increase in DMP1 protein immunoreactivity on both the formation side and the resorption side. These results represent changes in epitope availability using this antibody or true changes in protein levels. The observations imply that the DMP1 protein is undergoing dynamic changes in either synthesis or other protein/matrix interaction after mechanical loading of alveolar bone. The findings indicate that DMP1 is involved in the responses of osteocytes and osteoblasts to mechanical loading of bone. These results support the hypothesis that osteocytes alter their matrix microenvironment in response to mechanical loading.

Animals↗

PubMed2002

Proteolysis of latent transforming growth factor-beta (TGF-beta )-binding protein-1 by osteoclasts. A cellular mechanism for release of TGF-beta from bone matrix.

The binding of growth factors to the extracellular matrix (ECM) may be a key pathway for regulation of their activity. We have shown that a major mechanism for storage of transforming growth factor-beta (TGF-beta) in bone ECM is via its association with latent TGF-beta-binding protein-1 (LTBP1). Although proteolytic cleavage of LTBP1 has been reported, it remains unclear whether this represents a physiological mechanism for release of matrix-bound TGF-beta. Here we examined the role of LTBP1 in cell-mediated release of TGF-beta from bone ECM. We first characterized the soluble and ECM-bound forms of latent TGF-beta produced by primary osteoblasts. Next, we examined release of ECM-bound TGF-beta by bone resorbing cells. Isolated avian osteoclasts and rabbit bone marrow-derived osteoclasts released bone matrix-bound TGF-beta via LTBP1 cleavage. 1,25-Dihydroxyvitamin D3 enhanced LTBP1 cleavage, resulting in release of 90% of the ECM-bound LTBP1. In contrast, osteoblasts failed to cleave LTBP1 or release TGF-beta from bone ECM. Cleavage of LTBP1 by avian osteoclasts was inhibited by serine protease and metalloproteinase (MMP) inhibitors. Studies using purified proteases showed that plasmin, elastase, MMP2, and MMP9 were able to cleave LTBP1 to produce 125-165-kDa fragments. These studies identify LTBP1 as a novel substrate for MMPs and provide the first demonstration that LTBP1 proteolysis may be a physiological mechanism for release of TGF-beta from ECM-bound stores, potentially the first step in the pathway by which matrix-bound TGF-beta is rendered active.

Animals↗

PubMed2002

Evidence for distinct membrane receptors for 1 alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) in osteoblasts.

1 alpha,25-(OH)(2)D(3) exerts its effects on chondrocytes and enterocytes via nuclear receptors (1,25-nVDR) and a separate membrane receptor (1,25-mVDR) that activates protein kinase C (PKC). 24R,25-(OH)(2)D(3) also stimulates PKC in chondrocytes, but through other membrane mechanisms. This study examined the hypothesis that osteoblasts possess distinct membrane receptors for 1 alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) that are involved in the activation of PKC and that receptor expression varies as a function of cell maturation state. 1 alpha,25-(OH)(2)D(3) stimulated PKC in well differentiated (UMR-106, MC-3T3-E1) and moderately differentiated (ROS 17/2.8) osteoblast-like cells, and in cultures of fetal rat calvarial (FRC) cells and 2T3 cells treated with rhBMP-2 to promote differentiation. 24R,25-(OH)(2)D(3) stimulated PKC in FRC and 2T3 cultures that had not been treated to induce differentiation, and in ROS 17/2.8 cells. MG63 cells, a relatively undifferentiated osteoblast-like cell line, had no response to either metabolite. Ab99, a polyclonal antibody generated to the chick enterocyte 1,25-mVDR, but not a specific antibody to the 1,25-nVDR, inhibited response to 1 alpha,25-(OH)(2)D(3). 1 alpha,25-(OH)(2)D(3) exhibited specific binding to plasma membrane preparations from cells demonstrating a PKC response to this metabolite that is typical of positive cooperativity. Western blots of these membrane proteins reacted with Ab99, and the Ab99-positive protein had an Mr of 64 kDa. There was no cross-reaction with antibodies to the C- or N-terminus of annexin II. The effect of 24,25-(OH)(2)D(3) on PKC was stereospecific; 24S,25-(OH)(2)D(3) had no effect. These results demonstrate that response to 1 alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) depends on osteoblast maturation state and suggest that specific and distinct membrane receptors are involved.

24,25-Dihydroxyvitamin D 3↗

PubMed2002

Nitric oxide and prostaglandin E2 production in response to ultra-high molecular weight polyethylene particles depends on osteoblast maturation state.

BACKGROUND: Recent studies have shown that osteoblast-like cells respond directly to ultra-high molecular weight polyethylene particles in culture, suggesting that they may be involved in aseptic loosening of endoprostheses. We tested the hypothesis that the state of cell maturation plays a role in the response of osteogenic cells to ultra-high molecular weight polyethylene particles. METHODS: MG63 cells (immature osteoblast-like cells), OCT-1 cells (mature secretory osteoblast-like cells), and MLO-Y4 cells (osteocyte-like cells) were treated for twenty-four hours with commercial ultra-high molecular weight polyethylene particles with an average diameter of 1 mm. The effect of particle treatment on cell proliferation was assessed by measuring the number of cells, whereas the effects on differentiation and local factor production were assessed by measuring the production of osteocalcin, prostaglandin E2, and nitric oxide. The effect of particles on apoptosis was also evaluated. RESULTS: The addition of ultra-high molecular weight polyethylene particles increased the number of MG63 cells, did not affect the number of OCT-1 cells, and led to a decrease in the number of MLO-Y4 cells. The observed changes in cell number were not due to programmed cell death, as no more than 3% of the cells in cultures treated with the highest concentration of particles were undergoing apoptosis. Osteocalcin production was not affected by the addition of particles. Prostaglandin E2 production was increased in all three types of cultures, but the effect was greatest in OCT-1 cell cultures, as was the absolute amount of prostaglandin E2 produced. Nitric oxide production was unaffected in MG63 cell cultures, but it was stimulated in OCT-1 and MLO-Y4 cell cultures. CONCLUSIONS: The results of the present study support the hypothesis that osteoblast cell maturation state plays an important role in the response to ultra-high molecular weight polyethylene particles and that the terminally differentiated osteocyte may be involved in the bone response to wear debris in vivo.

Alprostadil↗

PubMedDate not supplied

Measurement of microstructural strain in cortical bone.

It is well known that mechanical factors affect bone remodeling such that increased mechanical demand results in net bone formation, whereas decreased demand results in net bone resorption. Current theories suggest that bone modeling and remodeling is controlled at the cellular level through signals mediated by osteocytes. The objective of this study was to investigate how macroscopically applied bone strains similar in magnitude to those that occur in vivo are manifest at the microscopic level in the bone matrix. Using a digital image correlation strain measurement technique, experimentally determined bone matrix strains around osteocyte lacuna resulting from macroscopic strains of approximately 2,000 microstrain (0.2%) reach levels of over 30,000 microstrain (3%) over fifteen times greater than the applied macroscopic strain. Strain patterns were highly heterogeneous and in some locations similar to observed microdamage around osteocyte lacuna indicating the resulting strains may represent the precursors to microdamage. This information may lead to a better understanding of how bone cells are affected by whole bone functional loading.

Animals↗