Bioactive glasses promote rapid pre-osteoblastic cell migration in contrast to hydroxyapatite, while carbonated apatite shows migration inhibiting properties.

Different biomaterials have been clinically used as bone filling materials, although the mechanisms behind the biological effects are incompletely understood. To address this, we compared the effects of five different biomaterials: two bioactive glasses (45S5 and S53P4), hydroxyapatite (HAP), carbonated apatite (CAP), and alumina on the in vitro migration and viability of pre-osteoblastic cells. In addition, we studied the effects of biomaterials' calcium release on cell migration, viability and differentiation. We found differences between the materials as the bioactive glasses promoted rapid pre-osteoblastic cell migration. In contrast, CAP decreased cell migration, which was also associated with lower activity of migration related kinases. Bioactive glasses released significant amounts of calcium into the media, while CAP decreased the calcium concentration. The response of cells to calcium was mechanistically studied by blocking calcium sensing receptor (CaSR) and ATP-gated ion channel P2X7, but this had no effect on cell migration. Surprisingly, HAP and CAP initially decreased cell viability. In summary, bioactive glasses 45S5 and S53P4 had significant and long-lasting effects on the pre-osteoblastic cell migration, which could be related to the observed calcium dissolution. Additionally, bioactive glasses had no negative effects on cell viability, which was observed with HAP and CAP.

Biomaterial and implant induced ossification: in vitro and in vivo findings.

Material-induced ossification is suggested as a suitable approach to heal large bone defects. Fiber-reinforced composite-bioactive glasses (FRC-BGs) display properties that could enhance the ossification of calvarial defects. Here, we analyzed the healing processes of a FRC-BG implant in vivo from the perspective of material-induced ossification. Histological analysis of the implant, which was removed 5 months after insertion, showed the formation of viable, noninflammatory mesenchymal tissue with newly-formed mineralized woven bone, as well as nonmineralized connective tissue with capillaries and larger blood vessels. The presence of osteocytes was detected within the newly generated bone matrix. To expand our understanding on the osteogenic properties of FRC-BG, we cultured human adipose tissue-derived mesenchymal stromal cells (AD-MSCs) in the presence of two different BGs (45S5 and S53P4) and Al2 O3 control. AD-MSCs grew and proliferated on all the scaffolds tested, as well as secreted abundant extracellular matrix, when osteogenic differentiation was appropriately stimulated. 45S5 and S53P4 induced enhanced expression of COL2A1, COL10A1, COL5A1 collagen subunits, and pro-osteogenic genes BMP2 and BMP4. The concomitant downregulation of BMP3 was also detected. Our findings show that FRC-BG can support the vascularization of the implant and the formation of abundant connective tissue in vivo. Specifically, BG 45S5 and BG S53P4 are suited to evoke the osteogenic potential of host mesenchymal stromal cells. In conclusion, FRC-BG implant demonstrated material-induced ossification both in vitro and in vivo.

Dicer1 ablation in osterix positive bone forming cells affects cortical bone homeostasis.

The RNAse III enzyme Dicer plays a major role in the processing of microRNAs from large pre-miRNAs. Dicer1 processed microRNAs are known to play a comprehensive role in osteoblast differentiation, bone remodeling and skeletal disorders. Targeted deletion of Dicer1 in osteo-progenitor cells is deleterious to fetal survival whereas targeted deletion in mature osteoblasts leads to an increase in bone mass. To address the role of Dicer1 in post-natal skeletal homeostasis, we generated a pre-osteoblast specific Dicer1 knockout model employing Tamoxifen controllable Cre allele, enabling us, via tamoxifen administration, to time-controllably ablate Dicer1 gene expression in osterix expressing bone forming cells in post-natal mice. Inactivation of Dicer1 in osterix positive bone forming cells led to striking dysregulation of cortical bone formation in pre-pubertal as well as adult mice. Cortical bone thickness was found to be significantly decreased in the Cre+ femora of both young and adult mice. Further, biomechanical testing experiments showed increased ductility, reduced stiffness and altered load at upper yield among the Cre+ tibiae. Our results suggest that Dicer1 processed microRNAs might play an important role in the regulation of post-natal cortical bone formation.

Selective Calcium-Dependent Inhibition of ATP-Gated P2X3 Receptors by Bisphosphonate-Induced Endogenous ATP Analog ApppI.

Pain is the most unbearable symptom accompanying primary bone cancers and bone metastases. Bone resorptive disorders are often associated with hypercalcemia, contributing to the pathologic process. Nitrogen-containing bisphosphonates (NBPs) are efficiently used to treat bone cancers and metastases. Apart from their toxic effect on cancer cells, NBPs also provide analgesia via poorly understood mechanisms. We previously showed that NBPs, by inhibiting the mevalonate pathway, induced formation of novel ATP analogs such as ApppI [1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) triphosphoric acid diester], which can potentially be involved in NBP analgesia. In this study, we used the patch-clamp technique to explore the action of ApppI on native ATP-gated P2X receptors in rat sensory neurons and rat and human P2X3, P2X2, and P2X7 receptors expressed in human embryonic kidney cells. We found that although ApppI has weak agonist activity, it is a potent inhibitor of P2X3 receptors operating in the nanomolar range. The inhibitory action of ApppI was completely blocked in hypercalcemia-like conditions and was stronger in human than in rat P2X3 receptors. In contrast, P2X2 and P2X7 receptors were insensitive to ApppI, suggesting a high selectivity of ApppI for the P2X3 receptor subtype. NBP, metabolite isopentenyl pyrophosphate, and endogenous AMP did not exert any inhibitory action, indicating that only intact ApppI has inhibitory activity. Ca2+-dependent inhibition was stronger in trigeminal neurons preferentially expressing desensitizing P2X3 subunits than in nodose ganglia neurons, which also express nondesensitizing P2X2 subunits. Altogether, we characterized previously unknown purinergic mechanisms of NBP-induced metabolites and suggest ApppI as the endogenous pain inhibitor contributing to cancer treatment with NBPs.

Fam3c modulates osteogenic differentiation by down-regulating Runx2.

Fam3c, a cytokine-like protein, is a member of the Fam3 family (family with sequence similarity 3) and has been implicated to play a crucial role in Epithelial-to- mesenchymal transition (EMT) and subsequent metastasis during cancer progression. A few independent genome-wide association studies on different population cohorts predicted the gene locus of Fam3c to be associated with bone mineral density and fractures. In this study, we examined the role of Fam3c during osteoblast differentiation. Fam3c was found to be expressed during osteogenic differentiation of both primary bone marrow stromal cells and MC3T3-E1 pre-osteoblasts. In differentiating osteoblasts, knockdown of Fam3c increased alkaline phosphatase expression and activity whereas overexpression of Fam3c reduced it. Furthermore, overexpression of Fam3c caused reduction of Runx2 expression at both mRNA and protein levels. Fam3c was localized in the cytoplasm and it was not secreted outside the cell during osteoblast differentiation and therefore, may function intracellularly. Furthermore, Fam3c and TGF-ß1 were found to regulate each other reciprocally. Our findings therefore suggest a functional role of Fam3c in the regulation of osteoblast differentiation.

Fam3c modulates osteogenic cell differentiation and affects bone volume and cortical bone mineral density.

Fam3c, a cytokine-like growth factor, has been suggested to have a role in epithelial-to-mesenchymal transition (EMT), tumor growth and metastasis. A single-nucleotide polymorphism affecting bone mineral density has been found in the first intron of the Fam3c gene in a study analyzing an Asian population cohort. Other independent studies on different population cohorts have found the fam3c locus to be associated with bone mineral density and fractures. In order to investigate the role of Fam3c in bone biology, we have generated a Fam3c knock-out (KO) mouse strain. The Fam3c KO mice were found to have normal appearance, behavior and fertility, but small changes in bone morphology and content were also observed. Micro-CT analysis of tibiae of the female mice revealed decreased number of trabeculae. In male mice the changes in the bone phenotype were smaller, but hematological changes were observed. Furthermore, there was a negative correlation between body weight and tibial trabecular and cortical bone volume in the male KO mice. There was a small increase in cortical bone mineral density, but in the lateral direction of tibiae the breaking strength was reduced. Fam3c KO bone marrow cells showed accelerated osteogenic differentiation and mineralization in vitro. The reduced number of bone trabeculae in Fam3c KO mice and the stimulated osteogenic differentiation indicate a role for Fam3c in osteoblast differentiation and bone homeostasis.

Uptake of free, calcium-bound and liposomal encapsulated nitrogen containing bisphosphonates by breast cancer cells.

PURPOSE: We have examined the uptake routes by which breast cancer cells internalize different formulations of nitrogen containing bisphosphonates (N-BPs). METHODS: Cell viability was assessed with the tetrazolium colorimetric test (MTT assay) after treatment with different N-BP formulations in the presence or absence of inhibitors for different endocytosis mechanisms. Intracellular formation of isopentenyl pyrophosphate (IPP) and triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (ApppI), were quantified with mass spectrometry (ES-LTQ-MS) as surrogate markers for N-BP efficacy. Direct quantification intracellular [(14)C]-labeled zoledronic acid was done with liquid scintillation counting. RESULTS: The main uptake route for all the different formulations of nitrogen containing bisphosphonates was shown to be dynamin dependent endocytosis, which was significantly enhanced with calcium. This uptake mechanism was mostly caveolin and clathrin independent in MCF7 cells, but more clathrin dependent in T47D cells. Liposome encapsulation of the drug shifted the uptake mechanism to be more dependent on caveolin in both the cell lines. The cytotoxicity of N-BPs and the concentrations of formed intracellular ApppI and IPP were significantly increased by calcium chelation and liposome encapsulation, the latter being the most potent formulation. CONCLUSION: Nitrogen containing bisphosphonates require active endocytosis for cellular uptake and in the breast cancer cells the mechanism is uniformly dynamin dependent for all the formulations tested. This differs e.g. from the previous observations on macrophages, which mostly utilize macropinocytosis. Liposomal formulation was found to prolong the duration of the drug effect in cells.

Human breast cancer cells educate macrophages toward the M2 activation status.

INTRODUCTION: The immune system plays a major role in cancer progression. In solid tumors, 5-40 % of the tumor mass consists of tumor-associated macrophages (TAMs) and there is usually a correlation between the number of TAMs and poor prognosis, depending on the tumor type. TAMs usually resemble M2 macrophages. Unlike M1-macrophages which have pro-inflammatory and anti-cancer functions, M2-macrophages are immunosuppressive, contribute to the matrix-remodeling, and hence favor tumor growth. The role of TAMs is not fully understood in breast cancer progression. METHODS: Macrophage infiltration (CD68) and activation status (HLA-DRIIα, CD163) were evaluated in a large cohort of human primary breast tumors (562 tissue microarray samples), by immunohistochemistry and scored by automated image analysis algorithms. Survival between groups was compared using the Kaplan-Meier life-table method and a Cox multivariate proportional hazards model. Macrophage education by breast cancer cells was assessed by ex vivo differentiation of peripheral blood mononuclear cells (PBMCs) in the presence or absence of breast cancer cell conditioned media (MDA-MB231, MCF-7 or T47D cell lines) and M1 or M2 inducing cytokines (respectively IFN-γ, IL-4 and IL-10). Obtained macrophages were analyzed by flow cytometry (CD14, CD16, CD64, CD86, CD200R and CD163), ELISA (IL-6, IL-8, IL-10, monocyte colony stimulating factor M-CSF) and zymography (matrix metalloproteinase 9, MMP-9). RESULTS: Clinically, we found that high numbers of CD163(+) M2-macrophages were strongly associated with fast proliferation, poor differentiation, estrogen receptor negativity and histological ductal type (p<0.001) in the studied cohort of human primary breast tumors. We demonstrated ex vivo that breast cancer cell-secreted factors modulate macrophage differentiation toward the M2 phenotype. Furthermore, the more aggressive mesenchymal-like cell line MDA-MB231, which secretes high levels of M-CSF, skews macrophages toward the more immunosuppressive M2c subtype. CONCLUSIONS: This study demonstrates that human breast cancer cells influence macrophage differentiation and that TAM differentiation status correlates with recurrence free survival, thus further emphasizing that TAMs can similarly affect therapy efficacy and patient outcome.

Inactivation of estrogen receptor α in bone-forming cells induces bone loss in female mice.

The role of the estrogen receptor α (ERα) in bone-forming cells is incompletely understood at present. To examine the in vivo effects of ERα in these cells, we generated a mouse strain in which the ERα gene is inactivated in osteoblasts via osteocalcin promoter-regulated cyclic recombinase (Cre) activity (ERα(ΔOB/ΔOB)). This enabled micro-computed tomography- and histomorphometry-based analysis of ERα-mediated effects in bone-forming cells in mice, in which the systemic ERα-mediated effects are intact. In female ERα(ΔOB/ΔOB) mice, trabecular and cortical bone volumes were significantly reduced (31.5 and 11.4%, respectively) at 3.5 mo of age compared with control ERα(fl/fl) animals, and their response to ovariectomy was small compared with that of controls. In contrast with females, no differences could be detected in the bone phenotype of young males, whereas in 6-mo-old ERα(ΔOB/ΔOB) males, trabecular bone volume (Tb.BV) was decreased (27.5%). The ERα inactivation-related effects were compared with those of controls having a similar genetic background. Parental osteocalcin-Cre mice did not show Cre-related changes. Our results suggest that in female mice, Tb.BV and cortical bone volume are critically dependent on the ERα regulation of osteoblasts, whereas in male mice, osteoblastic ERα is not required for the regulation of bone formation during rapid skeletal growth, but it is involved in the maintenance of Tb.BV.

Inactivation of the androgen receptor in bone-forming cells leads to trabecular bone loss in adult female mice.

Removal of the androgen receptor (AR) from bone-forming cells has been shown to reduce trabecular bone volume in male mice. In female mice, the role of AR in the regulation of bone homeostasis has been poorly understood. We generated a mouse strain in which the AR is completely inactivated only in mineralizing osteoblasts and osteocytes by breeding mice carrying osteocalcin promoter-regulated Cre-recombinase with mice possessing loxP recombination sites flanking exon 2 of the AR gene (AR(ΔOB/ΔOB) mice). In female AR(ΔOB/ΔOB) mice, the trabecular bone volume was reduced owing to a smaller number of trabeculae at 6 months of age compared with the control AR(fl/fl) animals. In male AR(ΔOB/ΔOB) mice, an increase in trabecular bone separation could already be detected at 3.5 months of age, and at 6 months, the trabecular bone volume was significantly reduced compared with that of male AR(fl/fl) mice. No AR-dependent changes were observed in the cortical bone of either sex. On the basis of micro-computed tomography and histomorphometry, we conclude that in male mice, the AR is involved in the regulation of osteoclast number by osteoblasts, whereas in female mice, the lack of the AR in the bone-forming cells leads to a decreased number of trabeculae upon aging.

Phenotypic characterization of transgenic mice harboring Nf1+/- or Nf1-/- osteoclasts in otherwise Nf1+/+ background.

Skeletal abnormalities in neurofibromatosis type 1 syndrome (NF1) are observed in ∼50% of patients. Here, we describe the phenotype of Nf1(Ocl) mouse model with Nf1-deficient osteoclasts. Nf1Ocl mice with Nf1+/- or Nf1-/- osteoclasts in otherwise Nf1+/+ background were successfully generated by mating parental Nf1flox/flox and TRAP-Cre mice. Contrary to our original hypothesis, osteoporotic or fragile bone phenotype was not observed. The µCT analysis revealed that tibial bone marrow cavity, trabecular tissue volume, and the perimeter of cortical bone were smaller in Nf1 Ocl-/- mice compared to Nf1 Ocl+/+ control mice. Nf1 Ocl-/- mice also a displayed narrowed growth plate in the proximal tibia. In vitro analysis showed increased bone resorption capacity and cytoskeletal changes including irregular cell shape and abnormal actin ring formation in Nf1-/- osteoclasts. Surprisingly, the size of spleen in Nf1 Ocl-/- mice was two times larger than in controls and histomorphometric analysis showed splenic megakaryocytosis. In summary, Nf1Ocl mouse model presented with a mild but specific bone phenotype. This study shows that NF1-deficiency in osteoclasts may have a role in the development of NF1-related skeletal abnormalities, but Nf1-deficiency in osteoclasts in Nf1+/+ background is not sufficient to induce skeletal abnormalities analogous to those observed in patients with NF1.

Receptor tyrosine kinase inhibition causes simultaneous bone loss and excess bone formation within growing bone in rats.

During postnatal skeletal growth, adaptation to mechanical loading leads to cellular activities at the growth plate. It has recently become evident that bone forming and bone resorbing cells are affected by the receptor tyrosine kinase (RTK) inhibitor imatinib mesylate (STI571, Gleevec®). Imatinib targets PDGF, ABL-related gene, c-Abl, c-Kit and c-Fms receptors, many of which have multiple functions in the bone microenvironment. We therefore studied the effects of imatinib in growing bone. Young rats were exposed to imatinib (150mg/kg on postnatal days 5-7, or 100mg/kg on postnatal days 5-13), and the effects of RTK inhibition on bone physiology were studied after 8 and 70days (3-day treatment), or after 14days (9-day treatment). X-ray imaging, computer tomography, histomorphometry, RNA analysis and immunohistochemistry were used to evaluate bone modeling and remodeling in vivo. Imatinib treatment eliminated osteoclasts from the metaphyseal osteochondral junction at 8 and 14days. This led to a resorption arrest at the growth plate, but also increased bone apposition by osteoblasts, thus resulting in local osteopetrosis at the osteochondral junction. The impaired bone remodelation observed on day 8 remained significant until adulthood. Within the same bone, increased osteoclast activity, leading to bone loss, was observed at distal bone trabeculae on days 8 and 14. Peripheral quantitative computer tomography (pQCT) and micro-CT analysis confirmed that, at the osteochondral junction, imatinib shifted the balance from bone resorption towards bone formation, thereby altering bone modeling. At distal trabecular bone, in turn, the balance was turned towards bone resorption, leading to bone loss.

Removal of cell surface heparan sulfate increases TACE activity and cleavage of ErbB4 receptor.

BACKGROUND: Nuclear localization of proteolytically formed intracellular fragment of ErbB4 receptor tyrosine kinase has been shown to promote cell survival, and nuclear localization of ErbB4 receptor has been described in human breast cancer. Tumor necrosis factor alpha converting enzyme (TACE) initiates the proteolytic cascade leading to ErbB4 intracellular domain formation. Interactions between matrix metalloproteases and heparan sulfate have been described, but the effect of cell surface heparan sulfate on TACE activity has not been previously described. RESULTS: As indicated by immunodetection of increased ErbB4 intracellular domain formation and direct enzyme activity analysis, TACE activity was substantially amplified by enzymatic removal of cell surface heparan sulfate but not chondroitin sulfate. CONCLUSION: In this communication, we suggest a novel role for cell surface heparan sulfate. Removal of cell surface heparan sulfate led to increased formation of ErbB4 intracellular domain. As ErbB4 intracellular domain has previously been shown to promote cell survival this finding may indicate a novel mechanism how HS degradation active in tumor tissue may favor cell survival.

Proteolytic cleavage and phosphorylation of a tumor-associated ErbB4 isoform promote ligand-independent survival and cancer cell growth.

The ErbB1 and ErbB2 receptors are oncogenes with therapeutic significance in human cancer, whereas the transforming potential of the related ErbB4 receptor has remained controversial. Here, we have addressed whether four alternatively spliced ErbB4 isoforms differ in regulating cellular responses relevant for tumor growth. We show that the two tumor necrosis factor-alpha converting enzyme (TACE)-cleavable ErbB4 isoforms (the juxtamembrane [JM]-a isoforms) were overexpressed in a subset of primary human breast cancers together with TACE. The overexpression of the JM-a cytoplasmic (CYT)-2 ErbB4 isoform promoted ErbB4 phosphorylation, survival of interleukin-3-dependent cells, and proliferation of breast cancer cells even in the absence of ligand stimulation, whereas activation of the other three ErbB4 isoforms required ligand stimulation. Ligand-independent cellular responses to ErbB4 JM-a CYT-2 overexpression were regulated by both tyrosine kinase activity and a two-step proteolytic generation of an intracellular receptor fragment involving first a TACE-like proteinase, followed by gamma-secretase activity. These data suggest a novel transforming mechanism for the ErbB4 receptor in human breast cancer that is 1) specific for a single receptor isoform and 2) depends on proteinase cleavage and kinase activity but not ligand activation of the receptor.

Angiopoietin-regulated recruitment of vascular smooth muscle cells by endothelial-derived heparin binding EGF-like growth factor.

Recruitment of vascular smooth muscle cells (SMC) by endothelial cells (EC) is essential for angiogenesis. Endothelial-derived heparin binding EGF-like growth factor (HB-EGF) was shown to mediate this process by signaling via ErbB1 and ErbB2 receptors in SMCs. 1) Analysis of ErbB-ligands demonstrated that primary ECs expressed only HB-EGF and neuregulin-1. 2) Primary SMCs expressed ErbB1 and ErbB2, but not ErbB3 or ErbB4. 3) Consistent with their known receptor specificities, recombinant HB-EGF, but not neuregulin-1, stimulated tyrosine phosphorylation of ErbB1 and ErbB2 and migration in SMCs. 4) Neutralization of HB-EGF or inhibition of ErbB1 or ErbB2 blocked 70-90% of the potential of ECs to stimulate SMC migration. Moreover, 5) angiopoietin-1, an EC effector with a role in recruitment of SMC-like cells to vascular structures in vivo, enhanced EC-stimulated SMC migration by a mechanism involving up-regulation of endothelial HB-EGF. Finally, 6) immunohistochemical analysis of developing human tissues demonstrated that HB-EGF was expressed in vivo in ECs associated with SMCs or pericytes but not in ECs of the hyaloid vessels not associated with SMCs. These results suggest an important role for HB-EGF and ErbB receptors in the recruitment of SMCs by ECs and elaborate on the mechanism by which angiopoietins exert their vascular effects.