Microencapsulating stem cells in injectable microbeads can enhance delivery and localization, but their ability to act as growth factor production sources is still unknown. To address this concern, growth factor mRNA levels and production from alginate microbeads with encapsulated human adipose stem cells (ASC microbeads) cultured in both growth and chondrogenic media (GM and CM) were measured over a two week period. Human ASCs in microbeads were either commercially purchased (Lonza) or isolated from six human donors and compared to human ASCs on tissue culture polystyrene (TCPS). The effects of crosslinking and alginate compositions on growth factor mRNA levels and production were also determined. Secretion profiles of IGF-I, TGF-β3 and VEGF-A from commercial human ASC microbeads were linear and at a significantly higher rate than TCPS cultures over two weeks. For human ASCs derived from different donors, microencapsulation increased pthlh and both IGF-I and TGF-β3 secretion. CM decreased fgf2 and VEGF-A secretion from ASC microbeads derived from the same donor population. Crosslinking microbeads in BaCl2 instead of CaCl2 did not eliminate microencapsulation’s beneficial effects, but did decrease IGF-I production. Increasing the guluronate content of the alginate microbead increased IGF-I retention. Decreasing alginate molecular weight eliminated the effects microencapsulation had on increasing IGF-I secretion. This study demonstrated that microencapsulation can enhance chondrogenic growth factor production and that chondrogenic medium treatment can decrease angiogenic growth factor production from ASCs, making these cells a potential source for paracrine factors that can stimulate cartilage regeneration.
Microencapsulation; Adipose stem cells; Alginate; Growth factor delivery; Cartilage
Craniosynostosis is the premature fusion of cranial sutures, which can result in progressive cranial deformations, increased intracranial pressure, and restricted brain growth. Most cases of craniosynostosis require surgical reconstruction of the cranial vault with the goal of increasing the intracranial volume and correcting the craniofacial deformities. However, patients often experience rapid post-operative bone re-growth, known as re-synostosis, which necessitates additional surgical intervention. Bone morphogenic protein (BMP) inhibitors have tremendous potential to treat re-synostosis, but the realization of a clinically viable inhibitor-based therapeutic requires the development of a delivery vehicle that can localize the release to the site of administration. Here, we present an in situ rapidly crosslinking injectable hydrogel that has the properties necessary to encapsulate co-administered proteins and demonstrate that the delivery of rmGremlin1 via our hydrogel system delays bone re-growth in a weanling mouse model of re-synostosis. Our hydrogel is composed of two mutually reactive poly(ethylene glycol) macromolecules, which when mixed crosslink via a bio-orthogonal Cu free click reaction. Hydrogels containing Gremlin caused a dose-dependent inhibition of bone regrowth. In addition to craniofacial applications, our injectable click hydrogel has the potential to provide customizable protein, small molecule, and cell delivery to any site accessible via needle or catheter.
Bone ingrowth; Hydrogel; BMP (bone morphogenetic protein); Craniosynostosis; Re-synostosis
Additive manufacturing by laser sintering is able to produce high resolution metal constructs for orthopaedic and dental implants. In this study, we used a human trabecular bone template to design and manufacture Ti-6Al-4V constructs with varying porosity via laser sintering. Characterization of constructs revealed interconnected porosities ranging from 15–70% with compressive moduli of 2063–2954 MPa. These constructs with macro porosity were further surface-treated to create a desirable multi-scale micro-/nano-roughness, which has been shown to enhance the osseointegration process. Osteoblasts (MG63 cells) exhibited high viability when grown on the constructs. Proliferation (DNA) and alkaline phosphatase specific activity (ALP), an early differentiation marker, decreased as porosity increased, while osteocalcin (OCN), a late differentiation marker, as well as osteoprotegerin (OPG), vascular endothelial growth factor (VEGF) and bone morphogenetic proteins 2 and 4 (BMP2, BMP4) increased with increasing porosity. 3D constructs with the highest porosity and surface modification supported the greatest osteoblast differentiation and local factor production. These results indicate that additively manufactured 3D porous constructs mimicking human trabecular bone and produced with additional surface treatment can be customized for increased osteoblast response. Increased factors for osteoblast maturation and differentiation on high porosity constructs suggest the enhanced performance of these surfaces for increasing osseointegration in vivo.
osteoblast differentiation; laser sintering; surface roughness; material properties; custom implants; additive manufacturing
Wnt5a and 1α,25(OH)2D3 are important regulators of endochondral ossification. In osteoblasts and growth plate chondrocytes, 1α,25(OH)2D3 initiates rapid effects via its membrane-associated receptor protein disulfide isomerase A3 (Pdia3) in caveolae, activating phospholipase A2 (PLA2)-activating protein (PLAA), calcium/calmodulin-dependent protein kinase II (CaMKII), and PLA2, resulting in protein kinase C (PKC) activation. Wnt5a initiates its calcium-dependent effects via intracellular calcium release, activating PKC and CaMKII. We investigated the requirement for components of the Pdia3 receptor complex in Wnt5a calcium-dependent signaling. We determined that Wnt5a signals through a CaMKII/PLA2/PGE2/PKC cascade. Silencing or blocking Pdia3, PLAA, or vitamin D receptor (VDR), and inhibition of calmodulin (CaM), CaMKII, or PLA2 inhibited Wnt5a-induced PKC activity. Wnt5a activated PKC in Caveolin-1-silenced cells, but methyl-beta-cyclodextrin reduced its stimulatory effect. 1α,25(OH)2D3 reduced stimulatory effects of Wnt5a on PKC in a dose-dependent manner. In contrast, Wnt5a had a biphasic effect on 1α,25(OH)2D3-stimulated PKC activation; 50ng/ml Wnt5a caused a 2-fold increase in 1α,25(OH)2D3-stimulated PKC but higher Wnt5a concentrations reduced 1α,25(OH)2D3-stimulated PKC activation. Western blots showed that Wnt receptors Frizzled2 (FZD2) and Frizzled5 (FZD5), and receptor tyrosine kinase-like orphan receptor 2 (ROR2) were localized to caveolae. Blocking ROR2, but not FZD2 or FZD5, abolished the stimulatory effects of 1α,25(OH)2D3 on PKC and CaMKII. 1α,25(OH)2D3 membrane receptor complex components (Pdia3, PLAA, Caveolin-1, CaM) interacted with Wnt5a receptors/co-receptors (ROR2, FZD2, FZD5) in immunoprecipitation studies, interactions that changed with either 1α,25(OH)2D3 or Wnt5a treatment. This study demonstrates that 1α,25(OH)2D3 and Wnt5a mediate their effects via similar receptor components and suggests that these pathways may interact.
1,25-Dihydroxy vitamin D3; 1α,25(OH)2D3; Wnt5a; Pdia3; PLAA; PKC; MC3T3-E1 osteoblast-like cells; Costochondral cartilage growth zone chondrocytes
17β-estradiol can promote the growth and development of several estrogen receptor (ER)-negative breast cancers. The effects are rapid and non-genomic, suggesting a membrane-associated ER is involved. ERα36 has been shown to mediate rapid, nongenomic, membrane-associated effects of 17β-estradiol in several cancer cell lines, including triple negative HCC38 breast cancer cells. Moreover, the effect is anti-apoptotic. The aim of this study was to determine if ERα36 mediates this anti-apoptotic effect, and to elucidate the mechanism involved. Taxol was used to induce apoptosis in HCC38 cells, and the effect of 17β-estradiol pre-treatment was determined. Antibodies to ERα36, signal pathway inhibitors, ERα36 deletion mutants, and ERα36-silencing were used prior to these treatments to determine the role of ERα36 in these effects and to determine which signaling molecules were involved. We found that the anti-apoptotic effect of 17β-estradiol in HCC38 breast cancer cells is in fact mediated by membrane-associated ERα36. We also showed that this signaling occurs through a pathway that requires PLD, LPA, and PI3K; Gαs and calcium signaling may also be involved. In addition, dynamic palmitoylation is required for the membrane-associated effect of 17β-estradiol. Exon 9 of ERα36, a unique exon to ERα36 not found in other identified splice variants of ERα with previously unknown function, is necessary for these effects. This study provides a working model for a mechanism by which estradiol promotes anti-apoptosis through membrane-associated ERα36, suggesting that ERα36 may be a potential membrane target for drug design against breast cancer, particularly triple negative breast cancer.
estrogen; breast cancer; taxol; estrogen receptor-alpha 36; plasma membrane; anti-apoptosis
Recent studies of new surface modifications that superimpose well-defined nanostructures on microrough implants, thereby mimicking the hierarchical complexity of native bone, report synergistically enhanced osteoblast maturation and local factor production at the protein level compared to growth on surfaces that are smooth, nanorough, or microrough. Whether the complex micro/nanorough surfaces enhance the osteogenic response by triggering similar patterns of integrin receptors and their associated signaling pathways as with well-established microrough surfaces, is not well understood. Human osteoblasts (hOBs) were cultured until confluent for gene expression studies on tissue culture polystyrene (TCPS) or on titanium alloy (Ti6Al4V) disks with different surface topographies: smooth, nanorough, microrough, and micro/nanorough surfaces. mRNA expression of osteogenesis-related markers such as osteocalcin (BGLAP) and bone sialoprotein (BSP), bone morphogenetic protein 2 (BMP2), BMP4, noggin (NOG) and gremlin 1 (GREM1) were all higher on microrough and micro/nanorough surfaces, with few differences between them, compared to smooth and nanorough groups. Interestingly, expression of integrins α1 and β2, which interact primarily with collagens and laminin and have been commonly associated with osteoblast differentiation on microrough Ti and Ti6Al4V, were expressed at lower levels on micro/nanorough surfaces compared to microrough ones. Conversely, the av subunit, which binds ligands such as vitronectin, osteopontin, and bone sialoprotein among others, had higher expression on micro/nanorough surfaces concomitantly with regulation of the β3 mRNA levels on nanomodified surfaces. These results suggest that the maturation of osteoblasts on micro/nanorough surfaces may be occurring through different integrin engagement than those established for microrough-only surfaces.
Bone; integrin gene expression; metallic implants; nanostructures; osseointegration; surface properties
The use of spinal implants for spine fusion has been steadily increasing to avoid the risks of complications and donor site morbidity involved when using autologous bone. A variety of fusion cages are clinically available, with different shapes and chemical compositions. However, detailed information about their surface properties and the effects of such properties on osteogenesis is lacking in the literature. Here we evaluate the role of surface properties for spinal implant applications, covering some of the key biological processes that occur around an implant and focusing on the role of surface properties, specifically surface structure, on osseointegration, drawing examples from other implantology fields when required. Our findings revealed that surface properties such as micro-roughness and nanostructures can directly affect early cell behavior and long-term osseointegration. Micro-roughness has been well established in the literature to have a beneficial effect on osseointegration of implants. In the case of the role of nanostructures, the number of reports is increasing and most studies reveal a positive effect from the nanostructures alone and a synergistic effect when combined with micro-rough surfaces. Still, long-term clinical results are necessary to establish the full implications of surface nanomodifications.
(4 to 6) spine fusion; spinal implants; osseointegration; titanium; bone; nano structures; surface roughness; microrough
This study assessed contributions of micron-scale topography on clinically relevant titanium (Ti) to differentiation of osteoprogenitor cells and osteoblasts; the interaction of this effect with 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3); and if the effects are sex-dependent. Male and female rat bone marrow cells (BMCs) were cultured on acid-etched (A, Ra = 0.87 μm), grit-blasted (GB, Ra = 3.90 μm), or grit-blasted/acid-etched (SLA, Ra = 3.22 μm) Ti. BMCs were sensitive to surface topography and underwent osteoblast differentiation. This was greatest on SLA; acid etching and grit blasting contributed additively. Primary osteoblasts were also sensitive to SLA, with less effect from individual structural components, demonstrated by enhanced local factor production. Sex-dependent responses of BMCs to topography varied with parameter whereas male and female osteoblasts responded similarly to surface treatment. 1α,25(OH)2D3 enhanced cell responses on all surfaces similarly. Effects were sex-dependent and male cells grown on a complex microstructured surface were much more sensitive than female cells. These results indicate that effects of the complex SLA topography are greater than acid etching or grit blasting alone on multipotent BMCs and committed osteoblasts and that individual parameters are sex-specific. The effect of 1α,25(OH)2D3 was sex dependent. The results also suggest that levels of 1α,25(OH)2D3 in the patient may be important in osseointegration.
An in vitro study examining factors produced by human mesenchymal stem cells on spine implant materials. Mesenchymal stem cells undergo differentiation to osteoblasts and secrete anti-inflammatory factors on micro-/nano-textured Ti alloy surfaces. Mesenchymal stem cells fail to differentiate on PEEK and produce high levels of proinflammatory factors.
An in vitro study examining factors produced by human mesenchymal stem cells on spine implant materials.
The aim of this study was to examine whether the inflammatory microenvironment generated by cells on titanium-aluminum-vanadium (Ti-alloy, TiAlV) surfaces is affected by surface microtexture and whether it differs from that generated on poly-ether-ether-ketone (PEEK).
Summary of Background Data.
Histologically, implants fabricated from PEEK have a fibrous connective tissue surface interface whereas Ti-alloy implants demonstrate close approximation with surrounding bone. Ti-alloy surfaces with complex micron/submicron scale roughness promote osteoblastic differentiation and foster a specific cellular environment that favors bone formation whereas PEEK favors fibrous tissue formation.
Human mesenchymal stem cells were cultured on tissue culture polystyrene, PEEK, smooth TiAlV, or macro-/micro-/nano-textured rough TiAlV (mmnTiAlV) disks. Osteoblastic differentiation and secreted inflammatory interleukins were assessed after 7 days. Fold changes in mRNAs for inflammation, necrosis, DNA damage, or apoptosis with respect to tissue culture polystyrene were measured by low-density polymerase chain reaction array. Data were analyzed by analysis of variance, followed by Bonferroni's correction of Student's t-test.
Cells on PEEK upregulated mRNAs for chemokine ligand-2, interleukin (IL) 1β, IL6, IL8, and tumor necrosis factor. Cells grown on the mmnTiAlV had an 8-fold reduction in mRNAs for toll-like receptor-4. Cells grown on mmnTiAlV had reduced levels of proinflammatory interleukins. Cells on PEEK had higher mRNAs for factors strongly associated with cell death/apoptosis, whereas cells on mmnTiAlV exhibited reduced cytokine factor levels. All results were significant (P < 0.05).
These results suggest that fibrous tissue around PEEK implants may be due to several factors: reduced osteoblastic differentiation of progenitor cells and production of an inflammatory environment that favors cell death via apoptosis and necrosis. Ti alloy surfaces with complex macro/micro/nanoscale roughness promote osteoblastic differentiation and foster a specific cellular environment that favors bone formation.
Level of Evidence: N/A
mesenchymal stem cells; PEEK; Ti6Al4V; interbody spine cage; inflammatory mediators; implant surface; osteogenesis; fibrosis; mRNA array
Despite progress in bone tissue engineering, the healing of critically sized diaphyseal defects remains a clinical challenge. A stem cell-based approach is an attractive alternative to current treatment techniques. The objective of this study was to examine the ability of adult stem cells to enhance bone formation when co-delivered with the osteoinductive factor bone morphogenetic protein-2 (BMP-2) in a biologically functionalized hydrogel. First, adipose and bone marrow-derived mesenchymal stem cells (ADSCs and BMMSCs) were screened for their potential to form bone when delivered in an RGD functionalized alginate hydrogel using a subcutaneous implant model. BMMSCs co-delivered with BMP-2 produced significantly more mineralized tissue compared with either ADSCs co-delivered with BMP-2 or acellular hydrogels containing BMP-2. Next, the ability of BMMSCs to heal a critically sized diaphyseal defect with a nonhealing dose of BMP-2 was tested using the alginate hydrogel as an injectable cell carrier. The effect of timing of therapeutic delivery on bone regeneration was also tested in the diaphyseal model. A 7 day delayed injection of the hydrogel into the defect site resulted in less mineralized tissue formation than immediate delivery of the hydrogel. By 12 weeks, BMMSC-loaded hydrogels produced significantly more bone than acellular constructs regardless of immediate or delayed treatment. For immediate delivery, bridging of defects treated with BMMSC-loaded hydrogels occurred at a rate of 75% compared with a 33% bridging rate for acellular-treated defects. No bridging was observed in any of the delayed delivery samples for any of the groups. Therefore, for this cell-based bone tissue engineering approach, immediate delivery of constructs leads to an overall enhanced healing response compared with delayed delivery techniques. Further, these studies demonstrate that co-delivery of adult stem cells, specifically BMMSCs, with BMP-2 enhances bone regeneration in a critically sized femoral segmental defect compared with acellular hydrogels containing BMP-2.
Recent endeavors to use stem cells as trophic factor production sources have the potential to translate into viable therapies for damaged or diseased musculoskeletal tissues. Adipose stem cells (ASCs) can be differentiated into chondrocytes using the chondrogenic medium (CM), but it is unknown if this approach can optimize ASC growth factor secretion for cartilage regeneration by increasing the chondrogenic factor production, while decreasing angiogenic and hypertrophic factor production. The objective of this study was to determine the effects the CM and its components have on growth factor production from ASCs to promote cartilage regeneration. ASCs isolated from male Sprague-Dawley rats and cultured in monolayer or alginate microbeads were treated with either the growth medium (GM) or the CM for 5 days. In subsequent studies, ASC monolayers were treated with either the GM supplemented with different combinations of 50 μg/mL ascorbic acid-2-phosphate (AA2P), 100 nM dexamethasone (Dex), 10 ng/mL transforming growth factor (TGF)-β1, and 100 ng/mL bone morphogenetic protein (BMP)-6 or with the CM excluding different combinations of AA2P, Dex, TGF-β1, and BMP-6. mRNA levels and growth factor production were quantified at 8 and 24 h after the last media change, respectively. The CM increased chondrogenic factor secretion (TGF-β2, TGF-β3, and insulin-like growth factor [IGF]-I) and decreased angiogenic factor production (the vascular endothelial growth factor [VEGF]-A, the fibroblast growth factor [FGF]-2). Microencapsulation in the GM increased production of the chondrogenic (IGF-I, TGF-β2) and angiogenic (VEGF-A) factors. AA2P increased secretion of chondrogenic factors (IGF-I, TGF-β2), and decreased angiogenic factor (VEGF-A) secretion, in addition to decreasing mRNA levels for factors associated with chondrocyte hypertrophy (FGF-18). Dex increased mRNA levels for hypertrophic factors (BMP-2, FGF-18) and decreased angiogenic factor secretion (VEGF-A). TGF-β1 increased angiogenic factor production (FGF-2, VEGF-A) and decreased chondrogenic factor mRNA levels (IGF-I, PTHrP). BMP-6 increased hypertrophic mRNA levels (FGF-18) and chondrogenic factor production (TGF-β2). When ASC microbeads preconditioned with the CM were implanted in a focal cartilage defect and immobilized within an RGD-conjugated hydrogel, tissue infiltration from the edges of the defect and perichondrium was observed. These results show that differentiation media components have distinct effects on ASC's production of angiogenic, chondrogenic, and hypertrophic factors and that AA2P may be the most beneficial CM component for preconditioning ASCs to stimulate cartilage regeneration.
Surface micro and nanostructural modifications of dental and orthopaedic implants have shown promising in vitro, in vivo, and clinical results. Surface wettability has also been suggested to play an important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically-relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remains unclear. In the current study, surface wettability analyses (optical sessile drop analysis, ESEM analysis, and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells (MSCs) cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors, exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment.
commercially pure grade 2 titanium implants; osseointegration; bone; nanostructures; mesenchymal stem cell differentiation; dynamic contact angle
Microtextured implant surfaces increase osteoblast differentiation in vitro and enhance bone-to-implant contact in vivo and clinically. These implants may be used in combination with recombinant human bone morphogenetic protein 2 (rhBMP-2) to enhance peri-implant bone formation. However, the effect of surface modifications alone or in combination with rhBMP-2 on osteoblast-produced inflammatory microenvironment is unknown. MG63 cells were cultured on tissue culture polystyrene or titanium substrates: smooth pretreated (PT, Ra=0.2μm), sandblasted/acid-etched (SLA, Ra=3.2μm), or hydrophilic-SLA (modSLA). Expression and protein production of pro-inflammatory interleukins (IL1b, IL6, IL8, IL17) and anti-inflammatory interleukins (IL10) were measured in cells with or without rhBMP-2. To determine which BMP signaling pathways were involved, cultures were incubated with BMP pathway inhibitors to blocking Smad (dorsomorphin), TAB/TAK1 ((5Z)-7-oxozeaenol), or PKA (H-8) signaling. Culture on rough SLA and modSLA surfaces decreased pro-inflammatory interleukins and increased anti-inflammatory IL10. This effect was negated in cells treated with rhBMP-2, which caused an increase in pro-inflammatory interleukins and a decrease in anti-inflammatory interleukins through TAB/TAK signaling. The results suggest that surface microtexture modulates the inflammatory process during osseointegration, an effect that may enhance healing. However, rhBMP-2 in combination with microtextured titanium implants can influence the effect of cells on these surfaces, and may adversely affect cells involved in osseointegration.
Microstructure; Inflammation; BMP (bone morphogenetic protein); Titanium
Craniosynostosis is the premature fusion of the cranial sutures early in development. If left untreated, craniosynostosis can lead to complications resulting from cranial deformities or increased intracranial pressure. The standard treatment involves calvarial reconstruction, which in many cases undergoes rapid re-synostosis. This requires additional surgical intervention that is associated with a high incidence of life threatening complications. To better understand this rapid healing, a pediatric mouse model of re-synostosis was developed and characterized. Defects (1.5 mm by 2.5 mm) over the posterior frontal suture were created surgically in weanling (21 days post-natal) and adolescent (50 days post-natal) C57Bl/6J mice. In addition, defects were created in the frontal bone lateral to the posterior frontal suture. The regeneration of bone in the defect was assessed using advanced image processing algorithms on micro-computed tomography scans. The genes associated with defect healing were assessed by real-time PCR of mRNA isolated from the tissue present in the defect. The results showed that the weanling mouse healed in a biphasic process with bone bridging the defect by post-operative (post-op) day 3 followed by an increase in the bone volume on day 14. In adolescent mice, there was a delay in bone bridging across the defect, and no subsequent increase in bone volume. No bridging of the defect by 14 days post-op was seen in identically sized defects placed lateral to the suture in both a weanling and adolescent animals. This study demonstrates that bone regeneration in the cranium is both age and location dependent. Rapid and robust bone regeneration only occurred when the defect was created over the posterior frontal suture in immature weanling mice.
Craniosynostosis; Cranial defect; Micro-CT; Endochondral ossification; Re-synostosis
Large doses of bone morphogenetic protein 2 (BMP2) are used clinically to induce bone formation in challenging bone defects. However, complications after treatment include swelling, ectopic bone formation, and adjacent bone resorption. While BMP2 can be effective, it is important to characterize the mechanism of the deleterious effects to optimize its use. The aim of this study was to determine the effect of BMP2 on apoptosis in osteoblast lineage cells and to determine the role of the BMP inhibitor Noggin in this process. Human mesenchymal stem cells (MSCs), immature osteoblast-like MG63 cells, and mature normal human osteoblasts (NHOst) were treated with BMP2. A model system of increased endogenous BMP signaling was created by silencing Noggin (shNOG-MG63). Finally, the BMP pathway regulating apoptosis in NHOst was examined using BMP signaling inhibitors (5Z-7-oxozeaenol, dorsomorphin, H-8). Apoptosis was characterized by caspase-3, BAX/BCL2, p53, and DNA fragmentation. BMP2 induced apoptosis in a cell-type dependent manner. While the effect was minor in MSCs, MG63 cells had modest increases and NHOst cells had robust increases apoptosis after BMP2 treatment. Apoptosis was significantly higher in shNOG-MG63 than MG63 cells. 5Z-7-oxozeaenol and dorsomorphin eliminated the BMP2-induced increase in DNA fragmentation in NHOst, suggesting roles for TAB/TAK1 and Smad signaling. These results indicate that the apoptotic effect of BMP2 is dependent on cell maturation state, inducing apoptosis in committed osteoblasts through Smad and TAB/TAK1 signaling, and is regulated by Noggin. Dose and delivery must be optimized in therapeutic applications of BMP2 to minimize complications.
Human osteoblasts; BMP (bone morphogenetic protein); Apoptosis; Noggin silencing; Human mesenchymal stem cells
Surface structural modifications at the micrometer and nanometer scales have driven improved success rates of dental and orthopaedic implants by mimicking the hierarchical structure of bone. However, how initial osteoblast-lineage cells populating an implant surface respond to different hierarchical surface topographical cues remains to be elucidated, with bone marrow mesenchymal stem cells (MSCs) or immature osteoblasts as possible initial colonizers. Here we show that in the absence of any exogenous soluble factors, osteoblastic maturation of primary human osteoblasts (HOBs) but not osteoblastic differentiation of MSCs is strongly influenced by nanostructures superimposed onto a microrough Ti6Al4V (TiAlV) alloy. The sensitivity of osteoblasts to both surface microroughness and nanostructures led to a synergistic effect on maturation and local factor production. Osteoblastic differentiation of MSCs was sensitive to TiAlV surface microroughness with respect to production of differentiation markers, but no further enhancement was found when cultured on micro/nanostructured surfaces. Superposition of nanostructures to microroughened surfaces affected final MSC numbers and enhanced production of vascular endothelial growth factor (VEGF) but the magnitude of the response was lower than for HOB cultures. Our results suggest that the differentiation state of osteoblast-lineage cells determines the recognition of surface nanostructures and subsequent cell response, which has implications for clinical evaluation of new implant surface nanomodifications.
(4 to 6) metallic implants; osteointegration; titanium aluminum vanadium alloy; bone; nanostructures; osteoblast differentiation
The surface properties of materials contribute to host cellular response and play a significant role in determining the overall success or failure of an implanted biomaterial. Rough titanium (Ti) surface microtopography and high surface free energy have been shown to enhance osteoblast maturation in vitro and increase bone formation in vivo. While the surface properties of Ti are known to affect osteoblast response, host bone quality also plays a significant role in determining successful osseointegration. One factor affecting host bone quality is patient age. We examined both in vitro and in vivo whether response to Ti surface features was affected by animal age. Calvarial osteoblasts isolated from 1-, 3-, and 11-month-old rats all displayed a reduction in cell number and increases in alkaline phosphatase specific activity and osteocalcin in response to increasing Ti surface microtopography and surface energy. Further, osteoblasts from the three ages examined displayed increased production of osteocalcin and local factors osteoprotegerin, VEGF-A, and active TGF-β1 in response to increasing Ti surface roughness and surface energy. Latent TGF-β1 only increased in cultures of osteoblasts from 1- and 3-month-old rats. Treatment with the systemic osteotropic hormone 1α,25(OH)2D3 further enhanced the response of osteoblasts to Ti surface features for all three age groups. However, osteoblasts derived from 11-month-old animals had a reduced response to 1α,25(OH)2D3 as compared to osteoblasts derived from 1-or 3-month-old animals. These results were confirmed in vivo. Ti implants placed in the femoral intramedullary canal of old (9-month) mice yielded lower bone-to-implant contract and neovascularization in response to Ti surface roughness and energy compared to younger (2-month) mice. These results show that rodent osteoblast maturation in vitro as well as new bone formation in vivo is reduced with age. Whether comparable age differences exist in humans needs to be determined.
Pluripotent and multipotent stem cells adopt an osteoblastic phenotype when cultured in environments that enhance their osteogenic potential. Embryonic stem cells differentiated as embryoid bodies (EBs) in osteogenic medium containing β-glycerophosphate exhibit increased expression of bone markers, indicating that cells are osteoblastic. Interestingly, 1α,25-dihydroxyvitaminD3 (1,25D) enhances the osteogenic phenotype not just in EBs but also in multipotent adult mesenchymal stem cells (MSCs). 1,25D acts on osteoblasts via classical vitamin D receptors (VDR) and via a membrane 1,25D-binding protein [protein disulfide isomerase family A, member 3 (PDIA3)], which activates protein kinase C -signaling. The aims of this study were to determine whether these receptors are regulated during osteogenic differentiation of stem cells and if stem cells and differentiated progeny are responsive to 1,25D. mRNA and protein levels for VDR, PDIA3, and osteoblast-associated proteins were measured in undifferentiated cells and in cells treated with osteogenic medium. Mouse EBs expressed both VDR and PDIA3, but VDR increased as cells underwent osteogenic differentiation. Human MSCs expressed Pdia3 at constant levels throughout differentiation, but VDR increased in cells treated with osteogenic medium. These results suggest that both 1,25D signaling mechanisms are important, with PDIA3 playing a greater role during early events and VDR playing a greater role in later stages of differentiation. Understanding these coordinated events provide a powerful tool to control pluripotent and multipotent stem cell differentiation through induction medium.
Ideal outcomes in the field of tissue engineering and regenerative medicine involve biomaterials that can enhance cell differentiation and production of local factors for natural tissue regeneration without the use of systemic drugs. Biomaterials typically used in tissue engineering applications include polymeric scaffolds that mimic the 3-D structural environment of the native tissue, but these are often functionalized with proteins or small peptides to improve their biological performance. For bone applications, titanium (Ti) implants, or more appropriately the titania (TiO2) passive oxide layer formed on their surface, have been shown to enhance osteoblast differentiation in vitro and to promote osseointegration in vivo. In this study we evaluated the effect on osteoblast differentiation of pure TiO2 nano-fiber meshes with different surface micro-roughness and nano-fiber diameters, prepared by the electrospinning method. MG63 cells were seeded on TiO2 meshes, and cell number, differentiation markers and local factor production were analyzed. The results showed that cells grew throughout the entire surfaces and with similar morphology in all groups. Cell number was sensitive to surface micro-roughness, whereas cell differentiation and local factor production was regulated by both surface roughness and nano-fiber diameter. These results indicate that scaffold structural cues alone can be used to drive cell differentiation and create an osteogenic environment without the use of exogenous factors.
nano structures; electrospinning; scaffold; titanium implant; tissue engineering; bone
The surface wettability of biomaterials determines the biological cascade of events at the biomaterial/host interface. Wettability is modulated by surface characteristics, such as surface chemistry and surface topography. However, the design of current implant surfaces focuses mainly on specific micro- and nanotopographical features and is still far from predicting the concomitant wetting behavior. There is an increasing interest in understanding the wetting mechanisms of implant surfaces and the role of wettability on the biological response at the implant/bone or implant/soft tissue interface. Fundamental knowledge related to the influence of surface roughness (i.e., a quantification of surface topography) on titanium and titanium alloy surface wettability, and the different associated wetting regimes, can improve our understanding of the role of wettability of rough implant surfaces on the biological outcome. Such an approach has been applied to biomaterial surfaces only in a limited way. Focusing on titanium dental and orthopaedic implants, the present study reviews the current knowledge on the wettability of biomaterial surfaces, encompassing basic and applied aspects that include measurement techniques, thermodynamic aspects of wetting, and models predicting topographical and roughness effects on the wetting behavior.
Wettability; hydrophilicity; surface energy; contact angle hysteresis; roughness induced wetting; protein adsorption; titanium implant
Dental and orthopaedic implants have been under continuous advancement to improve their interactions with bone and ensure a successful outcome for patients. Surface characteristics such as surface topography and surface chemistry can serve as design tools to enhance the biological response around the implant, with in vitro, in vivo and clinical studies confirming their effects. However, the comprehensive design of implants to promote early and long-term osseointegration requires a better understanding of the role of surface wettability and the mechanisms by which it affects the surrounding biological environment. This review provides a general overview of the available information about the contact angle values of experimental and of marketed implant surfaces, some of the techniques used to modify surface wettability of implants, and results from in vitro and clinical studies. We aim to expand the current understanding on the role of wettability of metallic implants at their interface with blood and the biological milieu, as well as with bacteria, and hard and soft tissues.
surface energy; hydrophilicity; contact angle; titanium implant roughness; surface conditioning; osteoblast; keratinocyte differentiation; bone to implant contact; osseointegration
Peri-implant bone formation depends on the ability of mesenchymal cells to colonize the implant surface and differentiate into osteoblasts. Human mesenchymal stem cells (HMSCs) undergo osteoblastic differentiation on microstructured titanium (Ti) surfaces in the absence of exogenous factors, but the mechanisms are unknown. Wnt proteins are associated with an osteoblast phenotype, but how Wnt signaling regulates HMSC differentiation on microstructured Ti surfaces is not known. HMSCs were cultured on tissue culture polystyrene or Ti (PT [Sa=0.33μm, θ=96°], SLA [Sa=2.5μm, θ=132°], modSLA [hydrophilic-SLA]). Expression of calcium-dependent Wnt ligand WNT5A increased and canonical Wnt pathway ligands decreased on microstructured Ti in a time-dependent manner. Treatment of HMSCs with canonical ligand Wnt3a preserved the mesenchymal phenotype on smooth surfaces. Treatment with Wnt5a increased osteoblastic differentiation. Expression of integrins ITGA1, ITGA2, and ITGAV increased over time and correlated with increased WNT5A expression. Treatment of HMSCs with Wnt5a, but not Wnt3a, increased integrin expression. Regulation of integrin expression due to surface roughness and energy was ablated in WNT5A-knockdown HMSCs. This indicates that surface properties regulate stem cell fate and induce osteoblast differentiation via the Wnt calcium-dependent pathway. Wnt5a enhances osteogenesis through a positive feedback with integrins and local factor regulation, particularly though BMP signaling.
Cell signaling; Surface roughness; Titanium; Stem cell; Growth factors
Height is the result of many growth and development processes. Most of the genes associated with height are known to play a role in skeletal development. Single-nucleotide polymorphisms in the SPAG17 gene have been associated with human height. However, it is not clear how this gene influences linear growth. Here we show that a targeted mutation in Spag17 leads to skeletal malformations. Hind limb length in mutants was significantly shorter than in wild-type mice. Studies revealed differences in maturation of femur and tibia suggesting alterations in limb patterning. Morphometric studies showed increased bone formation evidenced by increased trabecular bone area and the ratio of bone area to total area, leading to reductions in the ratio of marrow area/total area in the femur. Micro-CTs and von Kossa staining demonstrated increased mineral in the femur. Moreover, osteocalcin and osterix were more highly expressed in mutant mice than in wild-type mice femurs. These data suggest that femur bone shortening may be due to premature ossification. On the other hand, tibias appear to be shorter due to a delay in cartilage and bone development. Morphometric studies showed reduction in growth plate and bone formation. These defects did not affect bone mineralization, although the volume of primary bone and levels of osteocalcin and osterix were higher. Other skeletal malformations were observed including fused sternebrae, reduced mineralization in the skull, medial and metacarpal phalanges. Primary cilia from chondrocytes, osteoblasts, and embryonic fibroblasts (MEFs) isolated from knockout mice were shorter and fewer cells had primary cilia in comparison to cells from wild-type mice. In addition, Spag17 knockdown in wild-type MEFs by Spag17 siRNA duplex reproduced the shorter primary cilia phenotype. Our findings disclosed unexpected functions for Spag17 in the regulation of skeletal growth and mineralization, perhaps because of its role in primary cilia of chondrocytes and osteoblasts.
The progressive loss of endogenous regenerative capacity that accompanies mammalian aging has been attributed at least in part to alterations in the extracellular matrix (ECM) composition of adult tissues. Thus, creation of a more regenerative microenvironment, analogous to embryonic morphogenesis, may be achieved via pluripotent embryonic stem cell (ESC) differentiation and derivation of devitalized materials as an alternative to decellularized adult tissues, such as demineralized bone matrix (DBM). Transplantation of devitalized ESC materials represents a novel approach to promote functional tissue regeneration and reduce the inherent batch-to-batch variability of allograft-derived materials. In this study, the osteoinductivity of embryoid body-derived material (EBM) was compared to DBM in a standard in vivo ectopic osteoinduction assay in nude mice. EBM derived from EBs differentiated for 10 days with osteogenic media (+β-glycerophosphate) exhibited similar osteoinductivity to active DBM (osteoinduction score = 2.50 ± 0.27 vs. 2.75 ± 0.16) based on histological scoring, and exceeded inactive DBM (1.13 ± 0.13, p < 0.005). Moreover, EBM stimulated formation of new bone, ossicles, and marrow spaces, similar to active DBM. The potent osteoinductivity of EBM demonstrates that morphogenic factors expressed by ESCs undergoing osteogenic differentiation yield a novel devitalized material capable of stimulating de novo bone formation in vivo.