Mechanisms of Cdc42-mediated rat MSC differentiation on micro/nano-textured topography

Response of preosteoblasts on micromachined Ti-6Al-4V surface to microstructure dimension

The cell incubation depends on the cultured surface, but various machining methods produce different surface topographies, but it has not been clear how it is related to the topographic feature until now. Hence, the machined Ti-6Al-4V surface is characterized for preosteoblasts incubation via different mechanical fabrication. The relationship between surface topography created by various machining methods and cell incubation behaviour was explored. The objective is to control the surface preosteoblasts growth in machining of biological titanium alloy. According to the cell growth kinetic, the cell incubation behaviour was first proposed and modelled in relation to microstructural dimension and culture duration. Then, the topological cultured microstructure surface was fabricated via mechanical fabrication. Finally, the cell initial adhesion and incubation behaviour on microstructured surface was investigated. It is shown that the surface undulation on machined microstructure is conducive to controlling the direction and distribution of cell incubation from cell growth kinetic model. The cell culture can be controlled on the peak with a small undulation, while it is concentred on the sidewall with a high aspect ratio. Increasing the aspect ratio extends cell growth, while low aspect ratio promotes initial cell adhesion and growth rate. Within the optimal cultured duration, the microstructured surface is more favourable for cell survival, and the cell growth keep positive beyond critical aspect ratio. As a result, the cell adhesion ability is topologically controlled to 5.4 times higher and the growth rate can be improved by 101.7% on milled microgrooved surface. It may be applied to the rapid production of biomedical Ti-6Al-4V implant.

CDC42-mediated Wnt signaling facilitates odontogenic differentiation of DPCs during tooth root elongation

BACKGROUND

CDC42 is a member of Rho GTPase family, acting as a molecular switch to regulate cytoskeleton organization and junction maturation of epithelium in organ development. Tooth root pattern is a highly complicated and dynamic process that dependens on interaction of epithelium and mesenchyme. However, there is a lack of understanding of the role of CDC42 during tooth root elongation.

METHODS

The dynamic expression of CDC42 was traced during tooth development through immunofluorescence staining. Then we constructed a model of lentivirus or inhibitor mediated Cdc42 knockdown in Herwig's epithelial root sheath (HERS) cells and dental papilla cells (DPCs), respectively. Long-term influence of CDC42 abnormality was assessed via renal capsule transplantation and in situ injection of alveolar socket.

RESULTS

CDC42 displayed a dynamic spatiotemporal pattern, with abundant expression in HERS cells and apical DPCs in developing root. Lentivirus-mediated Cdc42 knockdown in HERS cells didn't disrupt cell junctions as well as epithelium-mesenchyme transition. However, inhibition of CDC42 in DPCs undermined cell proliferation, migration and odontogenic differentiation. Wnt/β-catenin signaling as the downstream target of CDC42 modulated DPCs' odontogenic differentiation. The transplantation and in situ injection experiments verified that loss of CDC42 impeded root extension via inhibiting the proliferation and differentiation of DPCs.

CONCLUSIONS

We innovatively revealed that CDC42 was responsible for guiding root elongation in a mesenchyme-specific manner. Furthermore, CDC42-mediated canonical Wnt signaling regulated odontogenic differentiation of DPCs during root formation.

Wrinkled topography regulates osteogenesis via autophagy-mediated Wnt/β-catenin signaling pathway in MC3T3-E1 cells

OBJECTIVE

In this study, we aimed to evaluate the effects of different dimensional wrinkled in topography on the osteogenic differentiation of MC3T3-E1 cells and explored the underlying mechanisms.

DESIGN

Polydimethylsiloxane (PDMS) with a wrinkled topography was synthesized using an elastomer base and crosslinking while observing by atomic force microscopy. MC3T3-E1 proliferation was detected by Cell Counting Kit-8(CCK-8) assays and the cell morphology was determined by phalloidin staining. Osteogenetic genes expression levels were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. In addition, Autophagy-related genes expression levels were evaluated by immunostaining and western blotting in MC3T3-E1 in order to assess the induction of autophagy.

RESULTS

In this experiment, the 0.7 µm amplitude and 3 µm wavelength (W3) group increased the expression of osteogenic markers, whereas the 4.3 µm amplitude and 27 µm wavelength (W27) group showed inhibition. Both the cytoplasm and the nucleus of β-catenin, compared with those of the Flat, W3 increased, whereas W27 decreased. At the same time, the autophagy was consistent with the influence of the topography on osteogenic differentiation. Moreover, using CQ or RAPA significantly inhibited or promoted autophagy, as well as partially decreasing or increasing osteogenesis, respectively. Infecting siRNA-β-catenin decreased the expression of RUNX2 and OSX in MC3T3-E1 cells both treated with CQ and RAPA.

CONCLUSIONS

Wrinkled topographies activated the autophagy-mediated Wnt/β-catenin signaling pathway and affected the osteogenic differentiation of MC3T3-E1 cells. The introduction of aligned topographies on biomaterial scaffolds could provide physical cues with which modulate MC3T3-E1 responses for bone engineering constructs.

Deterministic Single Cell Encapsulation in Asymmetric Microenvironments to Direct Cell Polarity

Various signals in tissue microenvironments are often unevenly distributed around cells. Cellular responses to asymmetric cell-matrix adhesion in a 3D space remain generally unclear and are to be studied at the single-cell resolution. Here, the authors developed a droplet-based microfluidic approach to manufacture a pure population of single cells in a microscale layer of compartmentalized 3D hydrogel matrices with a tunable spatial presentation of ligands at the subcellular level. Cells elongate with an asymmetric presentation of the integrin adhesion ligand Arg-Gly-Asp (RGD), while cells expand isotropically with a symmetric presentation of RGD. Membrane tension is higher on the side of single cells interacting with RGD than on the side without RGD. Finite element analysis shows that a non-uniform isotropic cell volume expansion model is sufficient to recapitulate the experimental results. At a longer timescale, asymmetric ligand presentation commits mesenchymal stem cells to the osteogenic lineage. Cdc42 is an essential mediator of cell polarization and lineage specification in response to asymmetric cell-matrix adhesion. This study highlights the utility of precisely controlling 3D ligand presentation around single cells to direct cell polarity for regenerative engineering and medicine.

Analysis of disordered abrasive scratches on titanium surfaces and their impact on nuclear translocation of yes-associated protein

The morphology of the metallic surface of an implant is important for its contact with bone tissue as it directly affects osteoblast functions, such as cell adhesion, proliferation, and differentiation. Firm contact between the implant and cells creates a barrier that prevents inflammation and bacterial infections. Therefore, optimizing surface morphology, such as surface roughness adjustments, is essential to improving the adhesion between the implant and cells for successful tissue regeneration. However, the manner in which the cells sense the surface roughness and morphology remains unclear. Previously, we analyzed cell adhesion behavior and observed that inhibited cell spreading can delay osteoblast functions. Therefore, assuming that the surface morphology can be sensed through cell spreading, we investigated the cell spreading area and yes-associated protein (YAP) localization in mouse osteoblasts (MC3T3-E1) on a titanium surface with disordered abrasive scratches. Surface roughness of 100-150 nm was obtained by polishing, which inhibited the cell spreading, indicating that YAP localization in the nucleus was lower than that on other surfaces. The obtained results indicate that the cells sense the surface environment based on their spreading area, which regulates cellular functions via the Hippo pathway.

Effect of microtopography on osseointegration of implantable biomaterials and its modification strategies

Orthopedic implants are widely used for the treatment of bone defects caused by injury, infection, tumor and congenital diseases. However, poor osseointegration and implant failures still occur frequently due to the lack of direct contact between the implant and the bone. In order to improve the biointegration of implants with the host bone, surface modification is of particular interest and requirement in the development of implant materials. Implant surfaces that mimic the inherent surface roughness and hydrophilicity of native bone have been shown to provide osteogenic cells with topographic cues to promote tissue regeneration and new bone formation. A growing number of studies have shown that cell attachment, proliferation and differentiation are sensitive to these implant surface microtopography. This review is to provide a summary of the latest science of surface modified bone implants, focusing on how surface microtopography modulates osteoblast differentiation in vitro and osseointegration in vivo, signaling pathways in the process and types of surface modifications. The aim is to systematically provide comprehensive reference information for better fabrication of orthopedic implants.

Strontium-loaded titanium implant with rough surface modulates osseointegration by changing sfrp4 in canonical and noncanonical Wnt signaling pathways

A rough morphology and strontium can activate the Wnt pathway to regulate bone mesenchymal stem cells (rBMSCs) osteogenic differentiation, but the mechanism remains unclear. We constructed smooth Ti (ST) surfaces, rough Ti (RT) surfaces subjected to hydrofluoric acid etching, strontium-loaded smooth Ti (ST-Sr) surfaces subjected to magnetron sputtering, and rough strontium-loaded Ti (RT-Sr) surfaces. We systematically studied the in vitro osteogenic differentiation of rBMSCs on these four surfaces by alkaline phosphatase measurement, Alizarin Red staining and PCR. We also investigated whether crosstalk of the canonical and noncanonical Wnt signaling pathways regulated by sfrp4, which is an inhibitor of canonical and noncanonical Wnt, is the underlying mechanism via PCR on rBMSCs in different stages of osteogenic differentiation. We confirmed the effect of sfrp4 through an in vivo sfrp4-siRNA test. The in vitro osteogenic differentiation of rBMSCs decreased in the order RT-Sr, RT, ST-Sr, and ST. Regarding the mechanism, rough morphology and strontium both enhanced the canonical Wnt pathway to promote osseointegration. Additionally, rough morphology can inhibit sfrp4 to activate the noncanonical Wnt pathway, and then, the activated noncanonical Wnt pathway can suppress the canonical Wnt pathway at the early stage of osteogenic differentiation. Strontium continuously enhanced sfrp4 to inhibit the canonical Wnt pathway instead of activating the noncanonical Wnt pathway. Interestingly, the effect of rough morphology on sfrp4 changed from inhibition to enhancement, and the enhancing effect of strontium on sfrp4 was gradually attenuated. The results of the in vivo sfrp4-siRNA test showed that osseointegration decreased in the order RT-Sr, RT-Sr-siRNA, and ST. Our results suggest that the lack of sfrp4 could suppress osseointegration, indicating that sfrp4 acts as a crucial regulatory molecule for the canonical and noncanonical Wnt pathways during the response of rBMSCs to rough morphology and strontium.

Effect of Controlled Microtopography on Osteogenic Differentiation of Mesenchymal Stem Cells

Various kinds of controlled microtopographies can promote osteogenic differentiation of mesenchymal stem cells (MSCs), such as microgrooves, micropillars, and micropits. However, the optimal shape, size, and mechanism remain unclear. In this review, we summarize the relationship between the parameters of different microtopographies and the behavior of MSCs. Then, we try to reveal the potential mechanism between them. The results showed that the microgrooves with a width of 4–60 μm and ridge width <10 μm, micropillars with parameters less than 10 μm, and square micropits had the full potential to promote osteogenic differentiation of MSCs, while the micromorphology of the same size could induce larger focal adhesions (FAs), well-organized cytoskeleton, and superior cell areas. Therefore, such events are possibly mediated by microtopography-induced mechanotransduction pathways.

Beta1-integrin/Hedgehog-Gli1 signaling pathway fuels the diameter-dependent osteoblast differentiation on different TiO2 nanotubes: The optimal-diameter nanotubes for osteoblast differentiation

Micro/nanotextured topographies (MNTs) can modulate cell-biomaterial interactions mostly by their controllable geometrics. Among them, TiO₂ nanotubes, regarded as having a highly controllable nanoscale geometry, have been extensively investigated and applied and significantly affect diameter-dependent cell biological behaviors. In this study, we used five typical MNTs decorated with TiO₂ nanotubes with diameters of 30, 50, 70, 100 and 120 nm to explore the optimal nanotube diameter for improving the biofunctional properties and to more deeply understand the underlying mechanisms by which these MNTs affect osteogenic differentiation by revealing the effect of beta1-integrin/Hedgehog-Gli1 signaling on this process. The MNTs affected MG63 osteoblast-like cell spreading, osteogenic gene expression (BMP-2, Runx2 and ALP), mineralization and ALP activity in a diameter-dependent pattern, and the optimal TiO₂ nanotube diameter of 70 nm provided the best microenvironment for osteogenic differentiation as well as beta1-integrin/Hedgehog-Gli1 signaling activation. This enhanced osteogenic differentiation by the optimal-diameter TiO₂ nanotubes of 70 nm was attenuated via suppression of the beta1-integrin/ Hedgehog-Gli1 signaling, which indicated a significant role of this pathway in mediating the diameter-dependent osteogenic differentiation promotional effect of MNTs with different TiO₂ nanotube diameters. These results might provide deeper insights into the signal transduction mechanisms by which different nanoscale geometries influence cellular functions for biomaterial modification and biofunctionalization.

mTORC2 regulates hierarchical micro/nano topography-induced osteogenic differentiation via promoting cell adhesion and cytoskeletal polymerization

Surface topography acts as an irreplaceable role in the long‐term success of intraosseous implants. In this study, we prepared the hierarchical micro/nano topography using selective laser melting combined with alkali heat treatment (SLM‐AHT) and explored the underlying mechanism of SLM‐AHT surface‐elicited osteogenesis. Our results show that cells cultured on SLM‐AHT surface possess the largest number of mature FAs and exhibit a cytoskeleton reorganization compared with control groups. SLM‐AHT surface could also significantly upregulate the expression of the cell adhesion‐related molecule p‐FAK, the osteogenic differentiation‐related molecules RUNX2 and OCN as well as the mTORC2 signalling pathway key molecule Rictor. Notably, after the knocked‐down of Rictor, there were no longer significant differences in the gene expression levels of the cell adhesion‐related molecules and osteogenic differentiation‐related molecules among the three titanium surfaces, and the cells on SLM‐AHT surface failed to trigger cytoskeleton reorganization. In conclusion, the results suggest that mTORC2 can regulate the hierarchical micro/nano topography‐mediated osteogenesis via cell adhesion and cytoskeletal reorganization.

Micro/nano-textured hierarchical titanium topography promotes exosome biogenesis and secretion to improve osseointegration

Background

Micro/nano-textured hierarchical titanium topography is more bioactive and biomimetic than smooth, micro-textured or nano-textured titanium topographies. Bone marrow mesenchymal stem cells (BMSCs) and exosomes derived from BMSCs play important roles in the osseointegration of titanium implants, but the effects and mechanisms of titanium topography on BMSCs-derived exosome secretion are still unclear. This study determined whether the secretion behavior of exosomes derived from BMSCs is differently affected by different titanium topographies both in vitro and in vivo.

Results

We found that both micro/nanonet-textured hierarchical titanium topography and micro/nanotube-textured hierarchical titanium topography showed favorable roughness and hydrophilicity. These two micro/nano-textured hierarchical titanium topographies enhanced the spreading areas of BMSCs on the titanium surface with stronger promotion of BMSCs proliferation in vitro. Compared to micro-textured titanium topography, micro/nano-textured hierarchical titanium topography significantly enhanced osseointegration in vivo and promoted BMSCs to synthesize and transport exosomes and then release these exosomes into the extracellular environment both in vitro and in vivo. Moreover, micro/nanonet-textured hierarchical titanium topography promoted exosome secretion by upregulating RAB27B and SMPD3 gene expression and micro/nanotube-textured hierarchical titanium topography promoted exosome secretion due to the strongest enhancement in cell proliferation.

Conclusions

These findings provide evidence that micro/nano-textured hierarchical titanium topography promotes exosome biogenesis and extracellular secretion for enhanced osseointegration. Our findings also highlight that the optimized titanium topography can increase exosome secretion from BMSCs, which may promote osseointegration of titanium implants.

Molecular Mechanisms of Topography Sensing by Osteoblasts: An Update

Bone is a specialized tissue formed by different cell types and a multiscale, complex mineralized matrix. The architecture and the surface chemistry of this microenvironment can be factors of considerable influence on cell biology, and can affect cell proliferation, commitment to differentiation, gene expression, matrix production and/or composition. It has been shown that osteoblasts encounter natural motifs in vivo, with various topographies (shapes, sizes, organization), and that cell cultures on flat surfaces do not reflect the total potential of the tissue. Therefore, studies investigating the role of topographies on cell behavior are important in order to better understand the interaction between cells and surfaces, to improve osseointegration processes in vivo between tissues and biomaterials, and to find a better topographic surface to enhance bone repair. In this review, we evaluate the main available data about surface topographies, techniques for topographies’ production, mechanical signal transduction from surfaces to cells and the impact of cell–surface interactions on osteoblasts or preosteoblasts’ behavior.

MiR-181d-5p regulates implant surface roughness-induced osteogenic differentiation of bone marrow stem cells

Constructing moderate surface roughness is a widely used, non-toxic, cost-effective, and outcome-predictable approach to accelerate implant osteointegration in clinical settings. MicroRNAs (miRNAs) play vital regulatory roles in the osteogenic differentiation of bone marrow stem cells (BMSCs). However, their specific contribution to the influence of surface roughness on osteoblastic behavior remains unknown. Therefore, applying the smooth titanium surface as a control, a typical titanium surface with moderate roughness was prepared here to reveal the mechanism through which surface roughness regulates cell osteogenic behavior by altering miRNA expression. First, the morphology and roughness of two surfaces were characterized, and the enhanced osteogenic differentiation of BMSCs on rough surfaces was verified. Then, twenty-nine differentially expressed miRNAs in BMSCs cultured on different surfaces were selected via miRNA chip and corresponding functional prediction. After verifying the expression of these miRNAs using quantitative real-time polymerase chain reaction, four were considered eligible candidates. Among these, only miR-181d-5p significantly affected RUNX2 gene expression based on overexpression and knockdown experiments. From the osteogenesis-related gene and protein expression, as well as alkaline phosphatase and alizarin red experiments, we further confirmed that the downregulation of miR-181d-5p promoted osteogenic differentiation of BMSCs, and vice versa. In addition, rescue assays showed that the knockdown of miR-181d-5p improved the inferior osteogenesis observed on smooth surfaces, whereas the overexpression of miR-181d-5p suppressed the superior osteogenesis observed on rough surfaces. These results indicate that the moderate surface roughness of the implant stimulates the osteogenic differentiation of BMSCs by remarkably downregulating miR-181d-5p. These findings provide helpful information and a theoretical basis for the development of advanced implant materials for fast osteointegration.

New perspectives on the roles of nanoscale surface topography in modulating intracellular signaling

The physical properties of biomaterials, such as elasticity, stiffness, and surface nanotopography, are mechanical cues that regulate a broad spectrum of cell behaviors, including migration, differentiation, proliferation, and reprogramming. Among them, nanoscale surface topography, i.e. nanotopography, defines the nanoscale shape and spatial arrangement of surface elements, which directly interact with the cell membranes and stimulate changes in the cell signaling pathways. In biological systems, the effects of nanotopography are often entangled with those of other mechanical and biochemical factors. Precise engineering of 2D nanopatterns and 3D nanostructures with well-defined features has provided a powerful means to study the cellular responses to specific topographic features. In this Review, we discuss efforts in the last three years to understand how nanotopography affects membrane receptor activation, curvature-induced cell signaling, and stem cell differentiation.

Nature-inspired topographies on hydroxyapatite surfaces regulate stem cells behaviour

Surface topography is one of the key factors in regulating interactions between materials and cells. While topographies presented to cells in vivo are non-symmetrical and in complex shapes, current fabrication techniques are limited to replicate these complex geometries. In this study, we developed a microcasting technique and successfully produced imprinted hydroxyapatite (HAp) surfaces with nature-inspired (honeycomb, pillars, and isolated islands) topographies. The in vitro biological performance of the developed non-symmetrical topographies was evaluated using adipose-derived stem cells (ADSCs). We demonstrated that ADSCs cultured on all HAp surfaces, except honeycomb patterns, presented well-defined stress fibers and expressed focal adhesion protein (paxillin) molecules. Isolated islands topographies significantly promoted osteogenic differentiation of ADSCs with increased alkaline phosphatase activity and upregulation of key osteogenic markers, compared to the other topographies and the control unmodified (flat) HAp surface. In contrast, honeycomb topographies hampered the ability of the ADSCs to proliferate and differentiate to the osteogenic lineage. This work presents a facile technique to imprint nature-derived topographies on the surface of bioceramics which opens up opportunities for the development of bioresponsive interfaces in tissue engineering and regenerative medicine.

Novel Bionic Topography with MiR-21 Coating for Improving Bone-Implant Integration through Regulating Cell Adhesion and Angiogenesis

Implant loosening is still the major form of the failure of artificial joints. Herein, inspired by the operculum of the river snail, we prepared a novel bionic micro/nanoscale topography on a titanium surface. This bionic topography promoted early cell adhesion through up-regulating the expression of ITG α5β1 and thus accelerated the following cell spreading, proliferation, and differentiation. Moreover, a miR-21 coating, which promoted the angiogenic differentiation of MSCs, was fabricated on the bionic topography. Benefiting from both bionic micro/nanoscale topography and miR-21, blood vessel growth and bone formation and mineralization around the implant, as well as bone-implant bonding strength, were significantly improved. Collectively, the present study highlights the combination of the bionic micro/nanoscale topography and miR-21 on promoting cell adhesion and angiogenic differentiation and improving in vivo angiogenesis and bone-implant osseointegration. This work provides a new train of thought propelling the development of implants for potential application in the orthopedics field.

Compressive Stimulation Enhances Ovarian Cancer Proliferation, Invasion, Chemoresistance, and Mechanotransduction via CDC42 in a 3D Bioreactor

This report investigates the role of compressive stress on ovarian cancer in a 3D custom built bioreactor. Cells within the ovarian tumor microenvironment experience a range of compressive stimuli that contribute to mechanotransduction. As the ovarian tumor expands, cells are exposed to chronic load from hydrostatic pressure, displacement of surrounding cells, and growth induced stress. External dynamic stimuli have been correlated with an increase in metastasis, cancer stem cell marker expression, chemoresistance, and proliferation in a variety of cancers. However, how these compressive stimuli contribute to ovarian cancer progression is not fully understood. In this report, high grade serous ovarian cancer cell lines were encapsulated within an ECM mimicking hydrogel comprising of agarose and collagen type I, and stimulated with confined cyclic or static compressive stresses for 24 and 72 h. Compression stimulation resulted in a significant increase in proliferation, invasive morphology, and chemoresistance. Additionally, CDC42 was upregulated in compression stimulated conditions, and was necessary to drive increased proliferation and chemoresistance. Inhibition of CDC42 lead to significant decrease in proliferation, survival, and increased chemosensitivity. In summary, the dynamic in vitro 3D platform developed in this report, is ideal for understanding the influence of compressive stimuli, and can be widely applicable to any epithelial cancers. This work reinforces the critical need to consider compressive stimulation in basic cancer biology and therapeutic developments.

Microarray analysis reveals that lncRNA PWRN1-209 promotes human bone marrow mesenchymal stem cell osteogenic differentiation on microtopography titanium surface in vitro

Sandblasted, large-grit, and acid-etched (SLA) titanium (Ti) with microtopography is currently one of the most widely used implant materials to accelerate osseointegration. Numerous long noncoding RNAs (lncRNAs) have been involved in bone remodeling, with their role in osseointegration, and the underlying mechanisms remain largely unclear. Here, microarrays of human bone marrow mesenchymal stem cells (hBMSCs) were used to identify differentially expressed lncRNAs during early cell differentiation stages (0-7 days) on SLA Ti and polished Ti surfaces. The function of lncRNAs in the osteogenic differentiation of hBMSCs was identified by RNA silencing and overexpression assays. RT-PCR and Western blot were used to detect RNA and protein expression. Alkaline phosphatase (ALP) protein activity was tested by ALP staining. Altogether, 4112 differentially expressed lncRNAs were identified from day 0 to day 7 on SLA Ti with a novel lncRNA, Prader-willi region non-coding RNA 1-209 (PWRN1-209) upregulated. We then proved that PWRN1-209 promoted osteogenic differentiation in hBMSCs by genetic tools. The upregulation of PWRN1-209 was further confirmed to be related to the surface topography of Ti by comparing SLA Ti and polished Ti. Interestingly, this trend seems to have a certain correlation with the mRNA expression level of integrins (α2, αV, β1, β2) and the phosphorylation of focal adhesion kinase (FAK). Taken together, the lncRNA PWRN1-209 was upregulated by the SLA microtopography Ti surface, which may regulate osteogenic differentiation of hBMSCs through integrin-FAK-ALP signaling. Our results provide new insights into the relationship between surface topography and osseointergration.

The Role of Tantalum Nanoparticles in Bone Regeneration Involves the BMP2/Smad4/Runx2 Signaling Pathway

Background

In recent years, nanomaterials have been increasingly developed and applied in the field of bone tissue engineering. However, there are few studies on the induction of bone regeneration by tantalum nanoparticles (Ta NPs) and no reports on the effects of Ta NPs on the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and the underlying mechanisms. The main purpose of this study was to investigate the effects of Ta NPs on bone regeneration and BMSC osteogenic differentiation and the underlying mechanisms.

Materials and Methods

The effects of Ta NPs on bone regeneration were evaluated in an animal experiment, and the effects of Ta NPs on osteogenic differentiation of BMSCs and the underlying mechanisms were evaluated in cell experiments. In the animal experiment, hematoxylin-eosin (HE) staining and hard-tissue section analysis showed that Ta NPs promoted bone regeneration, and immunohistochemistry revealed elevated expression of BMP2 and Smad4 in cells cultured with Ta NPs.

Results

The results of the cell experiments showed that Ta NPs promoted BMSC proliferation, alkaline phosphatase (ALP) activity, BMP2 secretion and extracellular matrix (ECM) mineralization, and the expression of related osteogenic genes and proteins (especially BMP2, Smad4 and Runx2) was upregulated under culture with Ta NPs. Smad4 expression, ALP activity, ECM mineralization, and osteogenesis-related gene and protein expression decreased after inhibiting Smad4.

Conclusion

These data suggest that Ta NPs have an osteogenic effect and induce bone regeneration by activating the BMP2/Smad4/Runx2 signaling pathway, which in turn causes BMSCs to undergo osteogenic differentiation. This study provides insight into the molecular mechanisms underlying the effects of Ta NPs in bone regeneration.

Nanotopography on titanium promotes osteogenesis via autophagy-mediated signaling between YAP and β-catenin

Nanostructured titanium implants are recognized for inducing osteogenesis, but the cell signal transductions related to topography are not fully understood. Implant topography is associated with the functionality of osteogenic transcription factors directed by β-catenin in the nucleus, and autophagic flux in the cytoplasm; YAP (Yes-associated protein) is implicated in the destruction of β-catenin in the cytoplasm and is susceptible to autophagic flux. This study investigated whether surface topography of the titanium implant modulates autophagy-lysosome degradation of cytoplasmic YAP. Titanium surfaces were modified with smooth, micro, or nanotopographies. Compared with the smooth and micro surfaces, nanotopography was associated with higher β-catenin nuclear translocation, osteogenic differentiation, and autophagy, and less cytoplasmic YAP. Blockade of the autophagy-lysosome pathway resulted in YAP retention in MC3T3-E1 cells. Cytoplasmic YAP restricted β-catenin nuclear translocation. In the nano surface group, β-catenin accumulation in the nucleus and expression of osteogenesis genes was improved. However, in the absence of cell-cell (confluent) contact, manipulation of YAP and β-catenin localization associated with topography-induced autophagy was lost. In summary, the osteogenesis observed in response to titanium implants with nanotopography involves a signaling link between YAP and β-catenin. STATEMENT OF SIGNIFICANCE: Titanium with rough topographical surfaces is extensively applied in orthopedic and dental clinics. However, the cellular response to topographies that promotes osteogenesis and underlying mechanisms are not fully understood. In this study, we modified titanium surfaces to produce smooth, micro, or nano topographies. Experiments indicated that the nanotopography induced a stronger autophagic response, leading to degraded cytoplasmic YAP. With the lower levels of YAP, β-catenin transported and accumulated in the nucleus to activate TCF/LEF transcription factors, resulting in stronger osteogenesis. Additionally, cell-cell contact was essential in the autophagy-mediated signaling link between YAP and β-catenin. Consequently, our investigation revealed a novel signal transduction in nanotopography-regulated osteogenesis, and supports the modification of biomaterial surfaces to maximize osseointegration.

AMOT130/YAP pathway in topography-induced BMSC osteoblastic differentiation

Micro/nano-topography (MNT) is an important variable affecting osseointegration of bone biomaterials, but the underlying mechanisms are not fully understood. We probed the role of a AMOT130/YAP pathway in osteoblastic differentiation of bone marrow mesenchymal stems cultured on titanium (Ti) carrying MNTs. Ti surfaces with two well-defined MNTs (TiO2 nanotubes of different diameters and wall thicknesses) were prepared by anodization. Rat BMSCs were cultured on flat Ti and Ti surfaces carrying MNTs, and cell behaviors (i.e., morphology, F-actin development, osteoblastic differentiation, YAP localization) were studied. Ti surfaces carrying MNTs increased F-actin formation, osteoblastic gene expression, and protein AMOT130 production in BMSCs (all vs. flat Ti), and the surface carrying larger nantubes was more effective, confirming osteoblastic differentiation induced by MNTs. Elevation of the AMOT130 level (by inhibiting its degradation) increased the osteoblastic gene expression, F-actin formation, and nuclear localization of YAP. These show that, AMOT130/YAP is an important pathway mediating the translation of MNT signals to BMSC osteoblastic commitment, likely via the cascade: AMOT130 promotion of F-actin formation, increased YAP nuclear import, and activation of osteoblastic gene expression.

Recombinant human BMP-2 accelerates the migration of bone marrow mesenchymal stem cells via the CDC42/PAK1/LIMK1 pathway in vitro and in vivo

Biomaterials are widely used for bone regeneration and fracture repair. The migration of bone marrow mesenchymal stem cells (BMSCs) into bone defect sites or material implantation sites, and their differentiation into osteoblasts, is central to the fracture healing process, and the directional migration of BMSCs depends on cytokines or chemokines at the defect site. BMP-2 can stimulate the migration of a variety of cells, but it remains unclear whether BMSC migration can be induced. To provide evidence for BMP-2-induced BMSC migration, we tested the cytoskeletal changes and migration ability of BMSCs after treatment with recombinant human BMP-2 (rhBMP-2). We also explored the recruitment of BMSCs from the circulatory system using a collagen sponge incorporating rhBMP-2 that was implanted in vivo. Furthermore, to understand the mechanism underlying this migration, we investigated the effect of rhBMP-2 on migration-related signal pathways. Here, we found that, rhBMP-2 treatment significantly increased the migration of BMSCs in vitro via activation of the CDC42/PAK1/LIMK1 pathway, and that this migration could be blocked by silencing CDC42. In vivo, collagen sponge material loaded with rhBMP-2 could recruit BMSCs injected into the circulatory system. Moreover, inhibition using the small interfering RNA for CDC42 led to a significant decrease in the number of BMSCs within the material. In conclusion, our data prove that rhBMP-2 can accelerate BMSC migration via the CDC42/PAK1/LIMK1 pathway both in vivo and in vitro, and therefore provides a foundation for further understanding and application of rhBMP-2-incorporated materials by enhancing BMSC recruitment.

Genome-wide DNA-methylation profiles in human bone marrow mesenchymal stem cells on titanium surfaces

The characteristics of titanium (Ti) have been shown to influence dental implant fixation. Treatment of surfaces using the sandblasted, large-grit, acid-etched (SLA) method is widely used to provide effective osseointegration. However, the DNA methylation-associated mechanism by which SLA surface treatment affects osseointegration of human bone marrow mesenchymal stem cells (hBMSCs) remains elusive. Genome-wide methylation profiling of hBMSCs on SLA-treated and machined smooth Ti was performed using Illumina Infinium Methylation EPIC BeadChip at day 7 of osteogenic induction. In total, 2,846 CpG sites were differentially methylated in the SLA group compared with the machined group. Of these sites, 1,651 (covering 1,066 genes) were significantly hypermethylated and 1,195 (covering 775 genes) were significantly hypomethylated. Thirty significant enrichment pathways were observed, with Wnt signaling being the most significant. mRNA expression was identified by microarray and combined with DNA-methylation profiles. Thirty-seven genes displayed negative association between mRNA expression and DNA-methylation level, with the osteogenesis-related genes insulin-like growth factor 2 (IGF2) and carboxypeptidase X, M14 Family Member 2 (CPXM2) showing significant up-regulation and down-regulation, respectively. In summary, our results demonstrate differences between SLA-treated and machined surfaces in their effects on genome-wide DNA methylation and enrichment of osteogenic pathways in hBMSCs. We provide novel insights into genes and pathways affected by SLA treatment in hBMSCs at the molecular level.

The relationship between substrate topography and stem cell differentiation in the musculoskeletal system

It is well known that biomaterial topography can exert a profound influence on various cellular functions such as migration, polarization, and adhesion. With the development and refinement of manufacturing technology, much research has recently been focused on substrate topography-induced cell differentiation, particularly in the field of tissue engineering. Even without biological and chemical stimuli, the differentiation of stem cells can also be initiated by various biomaterials with different topographic features. However, the underlying mechanisms of this biological phenomenon remain elusive. During the past few decades, many researchers have demonstrated that cells can sense the topography of materials through the assembly and polymerization of membrane proteins. Following the activation of RHO, TGF-b or FAK signaling pathways, cells can be induced into various differentiation states. But these signaling pathways often coincide with canonical mechanical transduction pathways, and no firm conclusion has been reached among researchers in this field on topography-specific signaling pathways. On the other hand, some substrate topographies are reported to have the ability to inhibit differentiation and maintain the 'stemness' of stem cells. In this review, we will summarize the role of topography in musculoskeletal system regeneration and explore possible topography-related signaling pathways involved in cell differentiation.

Role of ILK/p38 pathway in mediating the enhanced osteogenic differentiation of bone marrow mesenchymal stem cells on amorphous carbon coating

Amorphous carbon (a-C) film is a promising candidate for metallic implant surface coatings to improve corrosion resistance and osteogenesis in vivo.

Amorphous polyphosphate, a smart bioinspired nano-/bio-material for bone and cartilage regeneration: towards a new paradigm in tissue engineering

Physiological amorphous polyphosphate nano/micro-particles, injectable and implantable, attract and stimulate MSCs into implants for tissue regeneration.