Advanced BMP gene therapies for temporal and spatial control of bone regeneration

Spatial and temporal patterns of bone morphogenetic protein (BMP) signaling are crucial to the assembly of appropriately positioned and shaped bones of the face and head. This review advances the hypothesis that reconstitution of such patterns with cutting-edge gene therapies will transform the clinical management of craniofacial bone defects attributed to trauma, disease, or surgical resection. Gradients in BMP signaling within developing limbs and orofacial primordia regulate proliferation and differentiation of mesenchymal progenitors. Similarly, vascular and mesenchymal cells express BMPs in various places and at various times during normal fracture healing. In non-healing fractures of long bones, BMP signaling is severely attenuated. Devices that release recombinant BMPs promote healing of bone in spinal fusions and, in some cases, of open fractures, but cannot control the timing and localization of BMP release. Gene therapies with regulated expression systems may provide substantial improvements in efficacy and safety compared with protein-based therapies. Synthetic gene switches, activated by pharmacologics or light or hyperthermic stimuli, provide several avenues for the non-invasive regulation of the expression of BMP transgenes in both time and space. Through new gene therapy platforms such as these, active control over BMP signaling can be achieved to accelerate bone regeneration.

Grit blasting of medical stainless steel: implications on its corrosion behavior, ion release and biocompatibility

This study reports on the biocompatibility of 316 LVM steel blasted with small and rounded ZrO(2) particles or larger and angular shaped Al(2)O(3) particles. The effect of blasting on the in vitro corrosion behavior and the associated ion release is also considered. Surface of Al(2)O(3) blasted samples was rougher than that of ZrO(2) blasted samples, which was also manifested by a higher surface area. Compared to the polished alloy, blasted steels exhibited a lower corrosion resistance at the earlier stages of immersion, particularly when using Al(2)O(3) particles. With increasing immersion time, blasted samples experienced an improvement of the corrosion resistance, achieving impedance values typical of passive alloys. Blasting of the alloy led to an increase in Fe release and the leaching of Ni, Mn, Cr and Mo. On all surfaces, ion release is higher during the first 24 h exposure and tends to decrease during the subsequent exposure time. Despite the lower corrosion resistance and higher amount of ions released, blasted alloys exhibit a good biocompatibility, as demonstrated by culturing osteoblastic cells that attached and grew on the surfaces.

On the role of RhoA/ROCK signaling in contact guidance of bone-forming cells on anisotropic Ti6Al4V surfaces

Patterned surfaces direct cell spatial dynamics, yielding cells oriented along the surface geometry, in a process known as contact guidance. The Rho family of GTPases controls the assembly of focal adhesions and cytoskeleton dynamics, but its role in modulating bone-cell alignment on patterned surfaces remains unknown. This article describes the interactions of two human cell types involved in osseointegration, specifically mesenchymal stem cells and osteoblasts, with submicron- or nano-scale Ti6Al4V grooved surfaces generated by mechanical abrasion. The surface chemistry of the alloy was not affected by grinding, ensuring that the differences found in cellular responses were exclusively due to changes in topography. Patterned surfaces supported cell growth and stimulated mesenchymal stem cell viability. Anisotropic surfaces promoted cell orientation and elongation along the grates. Both cell types oriented on nanometric surfaces with grooves of 150 nm depth and 2 μm width. The number of aligned cells increased by approximately 30% on submicrometric grooves with sizes of about 1 μm depth and 10 μm width. Cells were treated with drugs that attenuate the activities of the GTPase RhoA and one of its downstream effectors, Rho-associated kinase (ROCK), and contact guidance of treated cells on the grooved surfaces was investigated. The data indicate that the RhoA/ROCK pathway is a key modulator of both mesenchymal stem cell and osteoblast orientation on nanometric surface features. RhoA and its effector participate in the alignment of mesenchymal stem cells on submicrometric grooves, but not of osteoblasts. These findings show that RhoA/ROCK signaling is involved in contact guidance of bone-related cells on metallic substrates, although to a varying extent depending on the specific cell type and the dimensions of the pattern.

Corrosion behaviour and biocompatibility of a novel Ni-free intermetallic coating growth on austenitic steel by hot dipping in an Al-12.6%Si alloy

Commercial 316 LVM austenitic stainless steel samples have been coated by immersion in a bath of molten Al-12.6%Si alloy for 120 s. The coating consists of the Al(12)(Fe,Cr)(3)Si(2) intermetallic. In vitro corrosion behaviour has been evaluated in the Ringer's solution by means of potentiodynamic curves and electrochemical impedance spectroscopy. The results reveal that the coated specimens exhibit lower susceptibility to localised corrosion with respect to the substrate. XPS analysis suggests that the ennoblement of the pitting potential is due to the formation of a chromium oxyhydroxide containing passive layer. The intermetallic coating shows a good biocompatibility, as demonstrated by culturing human mesenchymal stem cells isolated from bone marrow which attached, grew and differentiated to the osteoblastic lineage to a similar extent on coated and bare steels. In summary, this study proposes a method that generates Ni-free coatings of the stainless steel with useful properties for biomedical applications.

Identification of differentially expressed genes in trabecular bone from the iliac crest of osteoarthritic patients

OBJECTIVE

Osteoarthritis (OA) is clinically characterized by degeneration of the joints and has been traditionally considered a primary disorder of articular cartilage, with secondary changes in the subchondral bone. The increased bone mass and generalized changes in bone quality observed in osteoarthritic patients suggest that OA may be a primary systemic bone disorder with secondary articular cartilage damage. The iliac crest is a skeletal site distant from the affected joint, with a minimal load-bearing function. To provide evidence that OA is a systemic disorder, we searched for differentially expressed genes in the iliac crest bone of patients suffering from hip OA.

MATERIAL AND METHODS

Gene expression levels between bone samples collected at surgery from the iliac crest of patients undergoing total hip arthroplasty for primary OA and younger donors, who were undergoing spinal arthrodesis, were investigated by means of oligonucleotide microarrays. To verify data detected by microarrays technology, Real Time Reverse Transcription-Polymerase Chain Reaction (RT-PCR) assays were performed with specimens from osteoarthritic patients and donors, as well as from elderly donors who were undergoing arthroplasty for subcapital femoral neck fracture.

RESULTS

The microarray analysis surveyed 8327 genes and identified 83 whose expression levels differed at least 1.5-fold in the OA group (P<0.005). Comparisons between Real Time RT-PCR data from OA and the two donor groups indicated differential expression of genes involved in bone cell functions in the group of OA patients. The genes identified, including CCL2, FOS, PRSS11, DVL2, AKT1, CA2, BMP6, OMD, MMP2, TGFBR3, FLT1, BMP1 and TNFRS11B, have known roles in osteoblast or osteoclast activities.

CONCLUSIONS

The data from this study identify a set of genes, closely related to bone cell functions, in which differential regulation in osteoarthritic bone distant from the diseased subchondral bone might underlie the etiopathogenesis of OA as a generalized bone disease.

Calcium phosphate-based particles influence osteogenic maturation of human mesenchymal stem cells

Biphasic calcium phosphates (BCPs) consist of a mixture of hydroxyapatite and beta-tricalcium phosphate and are recommended as alternatives or additives to autogenous bone for orthopaedic and dental applications. There is clinical evidence showing particle release from bioceramics, which might impair the ability of human mesenchymal stem cells (hMSC) from bone marrow to proliferate or mature into a functional osteoblast phenotype. This study analyses the influence of BCP particles and their precursors, calcium-deficient apatite (CDA) particles, on in vitro hMSC behaviour. Both types of particles were efficiently internalized by hMSC. Cell viability, morphology and actin cytoskeleton reorganization were unaffected by exposure of hMSC to BCP or CDA particles. Direct exposure to BCP particles impaired hMSC osteogenic differentiation and bone matrix mineralization to a lesser extent than CDA, as assayed by evaluation of alkaline phosphatase activity, osteopontin secretion and mineralized nodule formation. The ability of bioceramic particles to affect osteogenic maturation through modification of soluble factors in media was assayed in an in vitro system that avoids direct cell-particle contact. Indirect exposure to CDA particles severely impaired hMSC osteogenic maturation owing to the uptake of Ca2+ from the culture media. Lower textural properties of BCP and the lack of calcium deficiency in its composition prevented Ca2+ uptake, allowing the development of a functional osteoblast phenotype.

Thermal oxidation enhances early interactions between human osteoblasts and alumina blasted Ti6Al4V alloy

Oxidation of Ti6Al4V at 500 degrees C for 1 h in air results in the formation of an outer ceramic layer that improves osteoblast behavior and decreases Ti and Al ion release. In this work, alumina blasted Ti6Al4V alloy has been thermally treated and its in vitro biocompatibility has been assessed. Roughness of the blasted alloy was not found significantly altered after heat treatment while chemical surface analysis indicated an increase in stable TiO(2) and Al(2)O(3) oxides. Cell attachment, spreading, cytoskeleton organization as well as cell proliferation, viability, and procollagen I peptide secretion of human primary osteoblasts, impaired on alumina blasted Ti6Al4V, were found to be greatly enhanced on the thermally oxidized blasted alloy. Other informative markers of the osteoblastic phenotype such as alkaline phosphatase, osteocalcin, osteoprotegerin, and mineralized nodule formation were evaluated and indicated that osteoblasts responded at the same extent on untreated and thermally treated blasted alloys. Taken together, our in vitro results indicate that thermal oxidation of alumina blasted Ti6Al4V may favor successful osseointegration by promoting early interactions of osteoblastic cells and the modified surface alloy.

Osteoblast response to plasma-spray porous Ti6Al4V coating on substrates of identical alloy

We have evaluated the in-vitro biocompatibility of Ti6Al4V alloy coated by plasma spraying with an identical alloy. These surfaces are widely used in cementless prosthetic components, although osteoblasts behavior on this treated alloy has not been evaluated to date. Cross sectional examination revealed a thick and rough coating of identical composition without sign of delamination. Within the coating, small discontinuities and nonconnected pores were observed. Osteoblast response was evaluated by assessing cell adhesion, proliferation, and differentiation of primary cultures of human osteoblastic cells. Compared to the polished alloy, osteoblast adhesion measured as cell attachment and actin network reorganization was delayed on the plasma-sprayed surface. Cell proliferation and viability were also impaired on the rough surface. Several informative markers of osteoblastic differentiation such as procollagen I peptide, alkaline phosphatase, osteocalcin, osteoprotegerin, and mineralized nodule formation were evaluated and indicated that the plasma-sprayed alloy favored a more differentiated phenotype than polished alloy. Taken together, our in vitro results indicate that successful osseointegration of plasma spraying of Ti6Al4V with an identical alloy is mediated by modulation of osteoblastic differentiation and mineralization.

Alumina particles influence the interactions of cocultured osteoblasts and macrophages

The purpose of the current study was to evaluate the effects of alumina particles on secretion of several cytokines involved in bone resorption in cocultures of macrophages and osteoblasts. To distinguish the contribution of each individual cell type, we have established a heterologous in vitro system that makes use of mouse J774 cells and primary cultured human osteoblasts. J744 cells decreased the production of TNF-alpha when they were cocultured with osteoblasts. Treatment of J744 cells with alumina particles increased TNF-alpha secretion, but the induction was lower when cells were cocultured with osteoblasts. Secretion of IL-6 by J744 cells was very low, and increased in the presence of osteoblasts. Alumina particles were only able to stimulate the release of IL-6 by J744 cells when cells were cocultured with osteoblasts. On the other hand, incubation of osteoblasts with alumina particles enhanced the release of IL-6 and GM-CSF. Coculturing osteoblasts with J744 cells induced them to release IL-6 and GM-CSF, and treatment with alumina further increased the secretion of both mediators by osteoblasts. According to these in vitro results, it seems rather plausible that alumina particles are able to initiate an inflammatory response in vivo.

Concentration-dependent effects of titanium and aluminium ions released from thermally oxidized Ti6Al4V alloy on human osteoblasts

Thermal oxidation treatments of Ti6Al4V, at 500 and 700 degrees C, for 1 h result in the formation of an outer "ceramic" layer of rutile, which enhances osteoblast response. In the present study, we have measured in vitro Ti and Al ion release from Ti64 alloy in the as-received state and after thermal oxidation treatments at 500 or 700 degrees C, to culture medium under standard cell-culture conditions. Concentrations of both Ti and Al released from both thermal oxidation treatments were lower than from polished alloy. Al was released from the treated or untreated surfaces in substantially lower extent than Ti. Titanium and aluminium ions affected primary human osteoblast proliferation, metabolic activity, and differentiation in a dose-dependent manner. Treatments with individual Ti or Al metal ions in similar concentration ranges than released from the surfaces did not alter osteoblast response, which also remained unaffected after treatments with combinations of Ti plus Al applied in the proportional relations than detected in ion-release experiments. We then selected higher concentrations of Ti that impaired osteoblast proliferation and differentiation, while the proportional lower concentrations of Al did not alter osteoblast behavior. In spite of its inert character, it was found that Al significantly enhanced the deleterious effect of Ti on osteoblast differentiation. Therefore, thermal oxidation treatments of Ti6Al4V alloy may improve the biocompatibility of the alloy by reducing both Ti and Al release, and thus attenuating ion-mediated interference with osteoblast differentiation.

Osteoblast response to thermally oxidized Ti6Al4V alloy

We have recently reported that thermal oxidation treatments of Ti6Al4V at 500 degrees and 700 degrees C for 1 h result in the formation of an outer "ceramic" layer of rutile that do not decrease the high in vitro corrosion resistance of the alloy. In the present work, surface roughness was measured and found marginally increased as a consequence of oxidation of the alloy at 700 degrees C, but not at 500 degrees C. We have evaluated the biocompatibility of the oxidized surfaces, by assessing cell adhesion, proliferation, and differentiation of primary cultures of human osteoblastic cells. Compared with polished alloy, both thermal treatments increased osteoblast adhesion measured as cell attachment, beta1 integrin and FAK-Y397 expression, as well as cytoskeletal reorganization. Compared with treatment at 500 degrees C, thermal oxidation at 700 degrees C enhanced cell adhesion. Treatment at 700 degrees C transiently impaired cell proliferation and viability, which were not altered in alloys oxidized at 500 degrees C. Several markers of osteoblastic differentiation such as procollagen I peptide, alkaline phosphatase, osteocalcin, and mineralized nodule formation were found either unaffected or differentially increased by alloys treated either at 500 degrees or 700 degrees C. In addition, thermal oxidation at 700 degrees C also increased osteoprotegerin secretion. Taken together, our results indicate that thermal oxidation treatments at 500 degrees or 700 degrees C for 1 h improve the in vitro biocompatibility of Ti6Al4V.

Heterologous expression of the transcriptional regulator escargot inhibits megakaryocytic endomitosis

Certain cell types escape the strict mechanisms imposed on the majority of somatic cells to ensure the faithful inheritance of parental DNA content. This is the case in many embryonic tissues and certain adult cells such as mammalian hepatocytes and megakaryocytes. Megakaryocytic endomitosis is characterized by repeated S phases followed by abortive mitoses, resulting in mononucleated polyploid cells. Several cell cycle regulators have been proposed to play an active role in megakaryocytic polyploidization; however, little is known about upstream factors that could control endomitosis. Here we show that ectopic expression of the transcriptional repressor escargot interferes with the establishment of megakaryocytic endomitosis. Phorbol ester-induced polyploidization was inhibited in stably transfected megakaryoblastic HEL cells constitutively expressing escargot. Analysis of the expression and activity of different cell cycle factors revealed that Escargot affects the G(1)/S transition by influencing Cdk2 activity and cyclin A transcription. Nuclear proteins that specifically bind the Escargot-binding element were detected in endomitotic and non-endomitotic megakaryoblastic cells, but down-regulation occurred only during differentiation of cells that become polyploid. As Escargot was originally implicated in ploidy maintenance of Drosophila embryonic and larval cells, our results suggest that polyploidization in megakaryocytes might respond to mechanisms conserved from early development to adult cells that need to escape normal control of the diploid state.

Modulation of tolerance by mutant heat shock transcription factors

It ought to be possible to recruit normal cellular defenses to mitigate ischemia/reperfusion damage and to reduce toxicity of chemotherapeutic drugs. Stress-preconditioned cells acquire a tolerant state characterized by increased resistance to such insults. This state is widely believed to be mediated, partially, by heat shock proteins (Hsps). Indirect evidence suggests that stress-induced Hsp expression is controlled by heat shock transcription factor 1 (Hsf1), which factor may therefore represent a preferred target for therapeutic modulation of tolerance. In support, positively acting (Hsf1(+)) and negatively acting (Hsf1(-)) mutants of Hsf1 were identified. Inhibition of endogenous Hsf1 activity by Hsf1(-) prevents stress-induced Hsp synthesis and development of tolerance. Hsf1(+) drastically enhances expression of major Hsps in the absence of stress and induces tolerance against heat, simulated ischemia and toxicity by cyclophosphamide. Where compared, tolerance induced was slightly better than that produced by heat preconditioning. Thus, development of the tolerant state is dependent on increased levels of the cohort of Hsps induced by stress preconditioning, and Hsf1 can induce accumulation of a typical set of Hsps, which proteins are alone capable of providing tolerance at a similar level as heat preconditioning. These findings make Hsf1 a preferred target for pharmacological intervention to deliberately induce tolerance.

Transcriptional activation of heat shock factor HSF1 probed by phosphopeptide analysis of factor 32P-labeled in vivo

Mapping of tryptic phosphopeptides of heat shock factor 1 (HSF1) from non-stressed or moderately heat-stressed HeLa cells, labeled in vivo by [32P]orthophosphate, revealed four major phosphopeptides A to D. Heat stress drastically increased phosphopeptide signals. To identify target peptides and amino acids and to correlate phosphorylation and transactivation function, phosphopeptide maps were produced of LexA-human HSF1 chimeras and mutant derivatives thereof, and transactivation activities of original and mutant chimeras were compared. LexA-HSF1 chimeras were previously shown to be regulated identically to HSF1, except that they transactivate promoters with LexA-binding sites instead of hsp promoters. The patterns of phosphopeptides of LexA-HSF1 and endogenous HSF1 were similar. Analysis of single residue substitutions suggested that phosphopeptide C is peptide VKEEPPSPPQSPR (297-309) phosphorylated on Ser-307 but not Ser-303. Substitution of Ser-307 but not Ser-303 caused deregulation of factor activity. Mapping of several constitutively active chimeras associated unphosphorylated peptide C with the transcriptionally active HSF1 conformation, suggesting that dephosphorylation of this peptide (at Ser-307) may either be an integral step in the activation process or serve to maintain the active conformation of HSF1. Exploiting this correlation, indirect evidence was obtained that activation domains of HSF1 interact with the distantly located regulatory domain to maintain the factor in an inactive state.

Differential modulation of the expression of the intermediate filament proteins vimentin and nuclear lamins A and C by differentiation inducers in human myeloid leukemia (U-937, HL-60) cells

Earlier reports seemed to indicate that the cytoplasmic intermediate filament protein vimentin and the nuclear intermediate-type filament proteins A and C lamins are expressed in a coordinate manner in human myeloid cells. We have comparatively studied the expression of the vimentin and the A/C lamin genes at the RNA and protein levels in human U-937 promonocytic and HL-60 promyelocytic cells treated with differentiation inducers. 12-O-Tetradecanoyl phorbol-13-acetate and cytosine arabinoside produced a coordinate and stable stimulation of both vimentin and A/C lamin expression in U-937 cells. A stable increase in vimentin expression was also produced by sodium butyrate and by dibutyryl cyclic AMP in U-937 cells and by dimethyl sulfoxide in HL-60 cells. In contrast, these agents produced only a transient increase in A/C lamin expression (maximum mRNA levels at 6-24 h), which later returned to expression levels similar to or even lower than those in untreated cells. Retinoic acid greatly inhibited vimentin expression in HL-60 cells, but it had little effect on A/C lamin expression. Taken together, the present results suggest that there are important differences in the mechanisms which regulate the expression of the vimentin and nuclear lamin genes, as well as in their implication in the differentiation of human myeloid cells.