Role of Wnt11 during Osteogenic Differentiation of Human Mesenchymal Stem Cells on Microstructured Titanium Surfaces

Non-Canonical Wnt16 and microRNA-145 Mediate the Response of Human Bone Marrow Stromal Cells to Additively Manufactured Porous 3-Dimensional Biomimetic Titanium-Aluminum-Vanadium Constructs

Metal 3D printing is increasingly being used to manufacture titanium-aluminum-vanadium (Ti6Al4V) implants. In vitro studies using 2D substrates demonstrate that the osteoblastic differentiation of bone marrow stromal cells (MSCs) on Ti6Al4V surfaces, with a microscale/nanoscale surface topography that mimics an osteoclast resorption pit, involves non-canonical Wnt signaling; Wnt3a is downregulated and Wnt5a is upregulated, leading to the local production of BMP2 and semaphorin 3A (sema3A). In this study, it was examined whether the regulation of MSCs in a 3D environment occurs by a similar mechanism. Human MSCs from two different donors were cultured for 7, 14, or 21 days on porous (3D) or solid (2D) constructs fabricated by powder-bed laser fusion. mRNA and secretion of osteoblast markers, as well as factors that enhance peri-implant osteogenesis, were analyzed, with a primary focus on the Wnt family, sema3A, and microRNA-145 (miR-145) signaling pathways. MSCs exhibited greater production of osteocalcin, latent and active TGFβ1, sema3A, and Wnt16 on the 3D constructs compared to 2D, both of which had similar microscale/nanoscale surface modifications. Wnt3a was reduced on 2D constructs as a function of time; Wnt11 and Wnt5a remained elevated in the 3D and 2D cultures. To better understand the role of Wnt16, cultures were treated with rhWnt16; endogenous Wnt16 was blocked using an antibody. Wnt16 promoted proliferation and inhibited osteoblast differentiation, potentially by reducing production of BMP2 and BMP4. Wnt16 expression was reduced by exogenous Wnt16 in 3D cells. Addition of the anti-Wnt16 antibody to the cultures reversed the effects of exogenous Wnt16, indicating an autocrine mechanism. Wnt16 increased miR-145-5p, suggesting a potential feedback mechanism. The miR-145-5p mimic increased Wnt16 production and inhibited sema3A in a 3D porous substrate-specific manner. Wnt16 did not affect sema3A production, but it was reduced by miR-145-5p mimic on the 3D constructs and stimulated by miR-145-5p inhibitor. Media from 7-, 14-, and 21-day cultures of MSCs grown on 3D constructs inhibited osteoclast activity to a greater extent than media from the 2D cultures. The findings present a significant step towards understanding the complex molecular interplay that occurs in 3D Ti6Al4V constructs fabricated by additive manufacturing. In addition to enhancing osteogenesis, the 3D porous biomimetic structure inhibits osteoclast activities, indicating its role in modulating bone remodeling processes. Our data suggest that the pathway mediated by sema3A/Wnt16/miR145-5p was enhanced by the 3D surface and contributes to bone regeneration in the 3D implants. This comprehensive exploration contributes valuable insights to guide future strategies in implant design, customization, and ultimately aims at improving clinical outcomes and successful osseointegration.

Bone Marrow Stromal Cells Generate a Pro-Healing Inflammasome When Cultured on Titanium-Aluminum-Vanadium Surfaces with Microscale/Nanoscale Structural Features

The surface topography and chemistry of titanium-aluminum-vanadium (Ti6Al4V) implants play critical roles in the osteoblast differentiation of human bone marrow stromal cells (MSCs) and the creation of an osteogenic microenvironment. To assess the effects of a microscale/nanoscale (MN) topography, this study compared the effects of MN-modified, anodized, and smooth Ti6Al4V surfaces on MSC response, and for the first time, directly contrasted MN-induced osteoblast differentiation with culture on tissue culture polystyrene (TCPS) in osteogenic medium (OM). Surface characterization revealed distinct differences in microroughness, composition, and topography among the Ti6Al4V substrates. MSCs on MN surfaces exhibited enhanced osteoblastic differentiation, evidenced by increased expression of RUNX2, SP7, BGLAP, BMP2, and BMPR1A (fold increases: 3.2, 1.8, 1.4, 1.3, and 1.2). The MN surface also induced a pro-healing inflammasome with upregulation of anti-inflammatory mediators (170-200% increase) and downregulation of pro-inflammatory factors (40-82% reduction). Integrin expression shifted towards osteoblast-associated integrins on MN surfaces. RNA-seq analysis revealed distinct gene expression profiles between MSCs on MN surfaces and those in OM, with only 199 shared genes out of over 1000 differentially expressed genes. Pathway analysis showed that MN surfaces promoted bone formation, maturation, and remodeling through non-canonical Wnt signaling, while OM stimulated endochondral bone development and mineralization via canonical Wnt3a signaling. These findings highlight the importance of Ti6Al4V surface properties in directing MSC differentiation and indicate that MN-modified surfaces act via signaling pathways that differ from OM culture methods, more accurately mimicking peri-implant osteogenesis in vivo.

Reduced osseointegration in disuse and denervation rat models results from impaired cellular responses to multiscale microstructured titanium surfaces

Immobilization-induced skeletal unloading results in muscle atrophy and rapid bone loss, thereby increasing the risk of falling and the need for implant therapy in patients with extended bed rest or neuromuscular injuries. Skeletal unloading causes bone loss by altering bone growth and resorption, suggesting that implant performance might be affected. To test this, we focused on early events in implant osseointegration. We used the rat sciatic neurectomy-induced disuse model under two different settings. In Study 1, 16 Sprague Dawley rats (SD) were separated into control, sham operated+cast immobilization, and sciatic neurectomy+casting groups; titanium implants with multiscale microtextured topography and hydrophilic chemistry (modSLA) were inserted in the distal femoral metaphysis. Neurectomy surgeries and casting were performed at the same surgical setting as implant placement; rats were euthanized 4 weeks post-implantation. In Study 2, we established the unloaded condition before implantation. A total of 12 SD rats were divided into control and sciatic+femoral neurectomy groups. A total of 24 days after sciatic and femoral neurectomy surgery, rats received implants. Study 2 rats were euthanized at 4 weeks post-implantation. MicroCT and histomorphometry showed that trabecular bone and osseointegration were reduced when disuse was established before implantation. Osteoblasts isolated from Study 1 sciatic neurectomy tibial bones exhibited impaired differentiation on modSLA culture disks, revealing a possible mechanism responsible for the decreased osseointegration observed in the Study 2 rats. This study addressed the importance of considering the mechanical unloading and muscle function history before implant insertion and suggests that implant performance was reduced due to poor cellular ability to regenerate.

Biomaterials Designed to Modulate Reactive Oxygen Species for Enhanced Bone Regeneration in Diabetic Conditions

Diabetes mellitus, characterized by enduring hyperglycemia, precipitates oxidative stress, engendering a spectrum of complications, notably increased bone vulnerability. The genesis of reactive oxygen species (ROS), a byproduct of oxygen metabolism, instigates oxidative detriment and impairs bone metabolism in diabetic conditions. This review delves into the mechanisms of ROS generation and its impact on bone homeostasis within the context of diabetes. Furthermore, the review summarizes the cutting-edge progress in the development of ROS-neutralizing biomaterials tailored for the amelioration of diabetic osteopathy. These biomaterials are engineered to modulate ROS dynamics, thereby mitigating inflammatory responses and facilitating bone repair. Additionally, the challenges and therapeutic prospects of ROS-targeted biomaterials in clinical application of diabetic bone disease treatment is addressed.

Wnt16 Increases Bone-to-Implant Contact in an Osteopenic Rat Model by Increasing Proliferation and Regulating the Differentiation of Bone Marrow Stromal Cells

Osseointegration is a complex biological cascade that regulates bone regeneration after implant placement. Implants possessing complex multiscale surface topographies augment this regenerative process through the regulation of bone marrow stromal cells (MSCs) that are in contact with the implant surface. One pathway regulating osteoblastic differentiation is Wnt signaling, and upregulation of non-canonical Wnts increases differentiation of MSCs on these titanium substrates. Wnt16 is a non-canonical Wnt shown to regulate bone morphology in mouse models. This study evaluated the role of Wnt16 during surface-mediated osteoblastic differentiation of MSCs in vitro and osseointegration in vivo. MSCs were cultured on Ti substrates with different surface properties and non-canonical Wnt expression was determined. Subsequently, MSCs were cultured on Ti substrates +/-Wnt16 (100 ng/mL) and anti-Wnt16 antibodies (2 μg/mL). Wnt16 expression was increased in cells grown on microrough surfaces that were processed to be hydrophilic and have nanoscale roughness. However, treatment MSCs on these surfaces with exogenous rhWnt16b increased total DNA content and osteoprotegerin production, but reduced osteoblastic differentiation and production of local factors necessary for osteogenesis. Addition of anti-Wnt16 antibodies blocked the inhibitor effects of Wnt16. The response to Wnt16 was likely independent of other osteogenic pathways like Wnt11-Wnt5a signaling and semaphorin 3a signaling. We used an established rat model of cortical and trabecular femoral bone impairment following botox injections (2 injections of 8 units/leg each, starting and maintenance doses) to assess Wnt16 effects on whole bone morphology and implant osseointegration. Wnt16 injections did not alter whole bone morphology significantly (BV/TV, cortical thickness, restoration of trabecular bone) but were effective at increasing cortical bone-to-implant contact during impaired osseointegration in the botox model. The mechanical quality of the increased bone was not sufficient to rescue the deleterious effects of botox. Clinically, these results are important to understand the interaction of cortical and trabecular bone during implant integration. They suggest a role for Wnt16 in modulating bone remodeling by reducing osteoclastic activity. Targeted strategies to temporally regulate Wnt16 after implant placement could be used to improve osseointegration by increasing the net pool of osteoprogenitor cells.

Soft and Hard Tissue Integration around Percutaneous Bone-Anchored Titanium Prostheses: Toward Achieving Holistic Biointegration

A holistic biointegration of percutaneous bone-anchored metallic prostheses with both hard and soft tissues dictates their longevity in the human body. While titanium (Ti) has nearly solved osseointegration, soft tissue integration of percutaneous metallic prostheses is a perennial problem. Unlike the firm soft tissue sealing in biological percutaneous structures (fingernails and teeth), foreign body response of the skin to titanium (Ti) leads to inflammation, epidermal downgrowth and inferior peri-implant soft tissue sealing. This review discusses various implant surface treatments/texturing and coatings for osseointegration, soft tissue integration, and against bacterial attachment. While surface microroughness by SLA (sandblasting with large grit and acid etched) and porous calcium phosphate (CaP) coatings improve Ti osseointegration, smooth and textured titania nanopores, nanotubes, microgrooves, and biomolecular coatings encourage soft tissue attachment. However, the inferior peri-implant soft tissue sealing compared to natural teeth can lead to peri-implantitis. Toward this end, the application of smart multifunctional bioadhesives with strong adhesion to soft tissues, mechanical resilience, durability, antibacterial, and immunomodulatory properties for soft tissue attachment to metallic prostheses is proposed.

Wilforine inhibits rheumatoid arthritis pathology through the Wnt11/β-catenin signaling pathway axis

BACKGROUND

Wilforine (WFR) is a monomeric compound of the anti-RA plant Tripterygium wilfordii Hook. f. (TwHF). Whether WFR has anti-RA effect, its molecular mechanism has not been elucidated.

AIM OF THE STUDY

Our study aims to clarify how WFR inhibits fibroblast-like synovial cells (FLS) activation and improves RA through Wnt11 action on the Wnt11/β-catenin signaling pathway.

METHODS

The therapeutic effect of WFR on collagen-induced arthritis (CIA) rats was evaluated using methods such as rat arthritis score. The inhibitory effects and signaling pathways of WFR on the proliferation and inflammatory response of CIA FLS and RA FLS were studied using ELISA, CCK-8, RT-qPCR, Western blot, and immunofluorescence methods.

RESULTS

WFR could effectively alleviate the arthritis symptoms of CIA rats; reduce the levels of IL-6, IL-1β, and TNF-α in the peripheral blood of CIA rats; and inhibit the expression of MMP3 and fibronectin. The data showed that WFR has a significant inhibitory effect on FLS proliferation. Furthermore, WFR inhibited the activation of Wnt/β-catenin signaling pathway and decreased the expression of Wnt11, β-catenin, CCND1, GSK-3β, and c-Myc, while the effects of WFR were reversed after overexpression of Wnt11.

CONCLUSIONS

WFR improves RA by inhibiting the Wnt11/β-catenin signaling pathway, and Wnt11 is the direct target of WFR. This study provides a new molecular mechanism for WFR to improve RA and contributes to the clinical promotion of WFR.

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.

Topography-mediated immunomodulation in osseointegration; Ally or Enemy

Osteoimmunology is at full display during endosseous implant osseointegration. Bone formation, maintenance and resorption at the implant surface is a result of bidirectional and dynamic reciprocal communication between the bone and immune cells that extends beyond the well-defined osteoblast-osteoclast signaling. Implant surface topography informs adherent progenitor and immune cell function and their cross-talk to modulate the process of bone accrual. Integrating titanium surface engineering with the principles of immunology is utilized to harness the power of immune system to improve osseointegration in healthy and diseased microenvironments. This review summarizes current information regarding immune cell-titanium implant surface interactions and places these events in the context of surface-mediated immunomodulation and bone regeneration. A mechanistic approach is directed in demonstrating the central role of osteoimmunology in the process of osseointegration and exploring how regulation of immune cell function at the implant-bone interface may be used in future control of clinical therapies. The process of peri-implant bone loss is also informed by immunomodulation at the implant surface. How surface topography is exploited to prevent osteoclastogenesis is considered herein with respect to peri-implant inflammation, osteoclastic precursor-surface interactions, and the upstream/downstream effects of surface topography on immune and progenitor cell function.

Phosphate promotes osteogenic differentiation through non-canonical Wnt signaling pathway in human mesenchymal stem cells

BACKGROUND

Phosphate is indispensable in osteogenesis and mineralization. However, mechanisms by which phosphate enhances osteogenic differentiation are not fully understood. In this study, we studied the effect of phosphate on osteogenic differentiation as well as signaling pathways induced by phosphate in the process.

METHOD

Induced human bone marrow-derived mesenchymal stem cells differentiation into osteoblasts by the change of media containing β-glycerophosphate (GP), 1 mM inorganic phosphate, or 3 mM inorganic phosphate (Pi). The differentiation of osteoblasts was verified by the expression of osteoblast differentiation markers and calcium deposition. RNA sequencing was performed to assess transcriptome in the early stage of osteogenic differentiation.

RESULTS

Osteogenic differentiation and mineralization were promoted in the 3 mM Pi group compared to those in the GP and 1 mM Pi groups on day 7 of culture. RNA sequencing revealed that the gene expressions involved in osteogenesis and the components in the Wnt signaling pathway was increased in 3 mM Pi group compared with those in the GP on day 7. Analysis with qPCR and Western blot suggested upregulation of components in the non-canonical Wnt signaling pathway, including WNT5b and phosphorylated-c-Jun in the 3 mM Pi group on day 7. WNT11 mRNA expression was increased in the 2 induction groups on day 7. Inhibition of WNT5b by siRNA experiment attenuated the components in non-canonical Wnt signaling expression, including WNT5b, WNT11 and ROR2 mRNA expression and phosphorylated-c-Jun protein expression. In addition, osteogenic differentiation and mineralization were partly decreased in 3 mM Pi group on day 7 by the inhibition of WNT5b.

CONCLUSION

Pi promoted osteogenic differentiation through the up-regulation of the non-canonical Wnt signaling pathway, including WNT5b, WNT11, p-c-Jun/c-Jun, in the early stage of differentiation. These findings provide a new perspective into the association of Pi and the non-canonical Wnt signaling pathway during osteogenic differentiation.

The Biological Basis for Surface-dependent Regulation of Osteogenesis and Implant Osseointegration

Bone marrow stromal cells are regulated by the chemical and physical features of a biomaterial surface. When grown on titanium (Ti) and Ti alloy surfaces, such as titanium-aluminum-vanadium, with specific topographies that mimic the microscale, mesoscale, and nanoscale features of an osteoclast resorption pit, they undergo a rapid change in cell shape to assume a columnar morphology typical of a secretory osteoblast. These cells exhibit markers associated with an osteoblast phenotype, including osteocalcin and osteopontin, and they secrete factors associated with osteogenesis, including bone morphogenetic protein 2, vascular endothelial growth factor, and neurotrophic semaphorins. The pathway involves a shift in integrin expression from α5β1 to α2β1 and signaling by Wnt5a rather than Wnt3a. Conditioned media from these cultures can stimulate vasculogenesis by human endothelial cells and osteoblastic differentiation of marrow stromal cells not grown on the biomimetic substrate, suggesting that the surface could promote osteogenesis in vivo through similar mechanisms. In vivo studies using a variety of animal models confirm that implants with biomimetic surfaces result in improved osseointegration compared with Ti implants with smooth surfaces, as do meta-analyses comparing clinical performance of implant surface topographies.

Cell osteogenic bioactivity mediated precisely by varying scaled micro-pits on ordered micro/nano hierarchical structures of titanium

Hierarchical surface structures with micro–nano scale play a crucial role in regulation of cell proliferation and osteogenic differentiation. It has been proven that cells are extremely sensitive to the nanoscaled structure and show multifarious phenotypes. Though a vital function of microstructure on osseointegration has been confirmed, the cell performances response to different microscaled structure is needed to be further dissected and in depth understood. In this work, the ordered micro–nano hierarchical structures with varying micro-scaled pits were precisely fabricated on titanium successfully by the combination of electrochemical, chemical etching and anodization as well. In vitro systematical assessments indicated that the micro–nano multilevel structures on titanium exhibited excellent cells adhesion and spreading ability, as well as steerable proliferation and osteogenic differentiation behaviors. It is shown that smaller micro-pits and lower roughness of the hierarchical structures enabled faster cell propagation. Despite cell growth was delayed on micro–nano titanium with relatively larger cell-match-size micro-pits and roughness, osteogenic-specific genes were significantly elevated. Furthermore, the alkaline phosphatase activity, collagen secretion and extracellular matrix mineralization of MC3T3-E1 on multi-scaled titanium were suppressed by a large margin after adding IWP-2 (an inhibitor of Wnt/β-catenin signal pathway), indicating this pathway played a crucial part in cell osteogenic differentiation modulated by micro–nano structures.

WNT11, a new gene associated with early onset osteoporosis, is required for osteoblastogenesis

Monogenic early onset osteoporosis (EOOP) is a rare disease defined by low bone mineral density (BMD) that results in increased risk of fracture in children and young adults. Although several causative genes have been identified, some of the EOOP causation remains unresolved. Whole-exome sequencing revealed a de novo heterozygous loss-of-function mutation in Wnt family member 11 (WNT11) (NM_004626.2:c.677_678dup p.Leu227Glyfs*22) in a 4-year-old boy with low BMD and fractures. We identified two heterozygous WNT11 missense variants (NM_004626.2:c.217G > A p.Ala73Thr) and (NM_004626.2:c.865G > A p.Val289Met) in a 51-year-old woman and in a 61-year-old woman, respectively, both with bone fragility. U2OS cells with heterozygous WNT11 mutation (NM_004626.2:c.690_721delfs*40) generated by CRISPR-Cas9 showed reduced cell proliferation (30%) and osteoblast differentiation (80%) as compared with wild-type U2OS cells. The expression of genes in the Wnt canonical and non-canonical pathways was inhibited in these mutant cells, but recombinant WNT11 treatment rescued the expression of Wnt pathway target genes. Furthermore, the expression of RSPO2, a WNT11 target involved in bone cell differentiation, and its receptor leucine-rich repeat containing G protein-coupled receptor 5 (LGR5), was decreased in WNT11 mutant cells. Treatment with WNT5A and WNT11 recombinant proteins reversed LGR5 expression, but Wnt family member 3A (WNT3A) recombinant protein treatment had no effect on LGR5 expression in mutant cells. Moreover, treatment with recombinant RSPO2 but not WNT11 or WNT3A activated the canonical pathway in mutant cells. In conclusion, we have identified WNT11 as a new gene responsible for EOOP, with loss-of-function variant inhibiting bone formation via Wnt canonical and non-canonical pathways. WNT11 may activate Wnt signaling by inducing the RSPO2-LGR5 complex via the non-canonical Wnt pathway.

Signaling network regulating osteogenesis in mesenchymal stem cells

Osteogenesis is an important developmental event that results in bone formation. Bone forming cells or osteoblasts develop from mesenchymal stem cells (MSCs) through a highly controlled process regulated by several signaling pathways. The osteogenic lineage commitment of MSCs is controlled by cell-cell interactions, paracrine factors, mechanical signals, hormones, and cytokines present in their niche, which activate a plethora of signaling molecules belonging to bone morphogenetic proteins, Wnt, Hedgehog, and Notch signaling. These signaling pathways individually as well as in coordination with other signaling molecules, regulate the osteogenic lineage commitment of MSCs by activating several osteo-lineage specific transcription factors. Here, we discuss the key signaling pathways that regulate osteogenic differentiation of MSCs and the cross-talk between them during osteogenic differentiation. We also discuss how these signaling pathways can be modified for therapy for bone repair and regeneration.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

Interleukin 15 participates in Jagged1-induced mineralization in human dental pulp cells

OBJECTIVES

Crosstalk between Notch and other cell signaling molecules has been implicated to regulate the osteogenic differentiation. Understanding the interaction between Notch and IL15 is essential to reveal molecular mechanism. Thus, the objective of the present study was to investigate whether IL15 participates in the Notch signaling-induced mineral deposition in human dental pulp cells (hDPs).

METHODS

hDPs were explanted from dental pulp tissues. To activate Notch signaling, the cells were seeded on Jagged1-immobilized surfaces. The mRNA expression was evaluated using real-time polymerase chain reaction. hDPs were treated with 5-50 ng/mL IL15. Cell viability and proliferation were determined using an MTT assay. Mineral deposition was examined using alizarin red s and Von Kossa staining. In some experiments, the cells were pretreated with a JAK inhibitor prior to stimulation.

RESULTS

Jagged1 induced IL15 and IL15RA expression in hDPs. IL15 treatment significantly increased mineral deposition at 14 d and upregulated ALP, OCN, OSX, ANKH, and ENPP1 mRNA expression. IL15-induced mineralization was attenuated by JAK inhibitor pretreatment. Further, JAK inhibitor pretreatment inhibited the effect of Jagged1 on hDP mineral deposition.

CONCLUSION

IL15 promoted the osteogenic differentiation in hDPs. Moreover, IL15 participated in the Jagged1-induced mineralization in hDPs.

Stiffness of Nanoparticulate Mineralized Collagen Scaffolds Triggers Osteogenesis via Mechanotransduction and Canonical Wnt Signaling

The ability of the extracellular matrix (ECM) to instruct progenitor cell differentiation has generated excitement for the development of materials-based regenerative solutions. Described a nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) material capable of inducing in vivo skull regeneration without exogenous growth factors or ex vivo progenitor cell-priming is described previously. Here, the contribution of titrating stiffness to osteogenicity is evaluated by comparing noncrosslinked (NX-MC) and crosslinked (MC) forms of MC-GAG. While both materials are osteogenic, MC demonstrates an increased expression of osteogenic markers and mineralization compared to NX-MC. Both materials are capable of autogenously activating the canonical BMPR signaling pathway with phosphorylation of Smad1/5. However, unlike NX-MC, human mesenchymal stem cells cultured on MC demonstrate significant elevations in the major mechanotransduction mediators YAP and TAZ expression, coincident with β-catenin activation in the canonical Wnt signaling pathway. Inhibition of YAP/TAZ activation reduces osteogenic expression, mineralization, and β-catenin activation in MC, with less of an effect on NX-MC. YAP/TAZ inhibition also results in a reciprocal increase in Smad1/5 phosphorylation and BMP2 expression. The results indicate that increasing MC-GAG stiffness induces osteogenic differentiation via the mechanotransduction mediators YAP/TAZ and the canonical Wnt signaling pathway, whereas the canonical BMPR signaling pathway is activated independent of stiffness.

ROS Dependent Wnt/β-Catenin Pathway and Its Regulation on Defined Micro-Pillars-A Combined In Vitro and In Silico Study

The physico-chemical surface design of implants influences the surrounding cells. Osteoblasts on sharp-edged micro-topographies revealed an impaired cell phenotype, function and Ca2+ mobilization. The influence of edges and ridges on the Wnt/β-catenin pathway in combination with the cells' stress response has not been clear. Therefore, MG-63 osteoblasts were studied on defined titanium-coated micro-pillars (5 × 5 × 5 µm) in vitro and in silico. MG-63s on micro-pillars indicated an activated state of the Wnt/β-catenin pathway. The β-catenin protein accumulated in the cytosol and translocated into the nucleus. Gene profiling indicated an antagonism mechanism of the transcriptional activity of β-catenin due to an increased expression of inhibitors like ICAT (inhibitor of β-catenin and transcription factor-4). Cells on pillars produced a significant reactive oxygen species (ROS) amount after 1 and 24 h. In silico analyses provided a detailed view on how transcriptional activity of Wnt signaling is coordinated in response to the oxidative stress induced by the micro-topography. Based on a coordinated expression of regulatory elements of the Wnt/β-catenin pathway, MG-63s are able to cope with an increased accumulation of β-catenin on micro-pillars and suppress an unintended target gene expression. Further, β-catenin may be diverted into other signaling pathways to support defense mechanisms against ROS.

TiO2 Nanotubes Alleviate Diabetes-Induced Osteogenetic Inhibition

Background

Patients with diabetes mellitus (DM) have a higher failure rate of dental implant treatments. However, whether titanium (Ti) implants with TiO₂ nanotubes (TNT) surface can retain their biocompatibility and osteogenetic ability under DM conditions has not been investigated; in addition, their behavior in DM conditions is not well characterized.

Materials and Methods

Pure Ti discs were surface treated into the polishing (mechanically polished, MP), sandblasted and acid-etched (SLA), and TNT groups. Scanning electron microscopy was used to examine the surface morphology. The cell adhesion and proliferation ability on different modified Ti surfaces at various glucose concentrations (5.5, 11, 16.5, and 22 mM) was detected by the CCK-8 assay. The osteogenetic ability on different modified Ti surfaces under high-glucose conditions was evaluated by alkaline phosphatase (ALP), osteopontin (OPN) immunofluorescence, Western blot, and Alizarin Red staining in vitro. Detection of cell apoptosis and intracellular reactive oxygen species (ROS) was undertaken both before and after N-acetylcysteine (NAC) treatment to assess the oxidative stress associated with different modified Ti surfaces under high-glucose conditions. An in vivo study was conducted in DM rats with different modified Ti femoral implants. The osteogenetic ability of different modified Ti implants in DM rats was assessed using a micro-CT scan.

Results

High-glucose conditions inhibited cell adhesion, proliferation, and osteogenetic ability of different modified Ti surfaces. High-glucose conditions induced higher apoptosis rate and intracellular ROS level on different modified Ti surfaces; these effects were alleviated by NAC. Compared with the SLA surface, the TNT surface alleviated the osteogenetic inhibition induced by high-glucose states by reversing the overproduction of ROS in vitro. In the in vivo experiment, micro-CT scan analysis further confirmed the best osteogenetic ability of TNT surface in rats with DM.

Conclusion

TNT surface modification alleviates osteogenetic inhibition induced by DM. It may provide a more favorable Ti implant surface for patients with DM.

Regulation of mesenchymal stem cell differentiation on microstructured titanium surfaces by semaphorin 3A

Peri-implant bone formation depends on the ability of mesenchymal stem cells (MSCs) to colonize implant surfaces and differentiate into osteoblasts, but the precise mechanisms controlling this process remain unclear. In vitro, MSCs undergo osteoblastic differentiation on microstructured titanium (Ti) surfaces in the absence of exogenous media supplements and produce factors that promote osteogenesis while regulating osteoclast activity, including semaphorins. The goal of this study was to evaluate the role of semaphorin 3A (Sema3A) on surface-mediated osteoblastic differentiation and determine the hierarchy of this signaling cascade. Human MSCs were cultured on 15 mm grade 2 smooth (pretreatment, PT), hydrophobic-microrough (sand blasted/acid etched, SLA), hydrophilic-microrough Ti (mSLA) (Institut Straumann AG, Basel, Switzerland), or tissue culture polystyrene (TCPS). Expression of SEMA3A family proteins increased after 7 days of culture, and the increased expression in response to microstructured Ti was dependent on recognition of the surface by integrin α2β1. Exogenous Sema3A increased differentiation whereas differentiation was decreased in cells treated with a Sema3A antibody. Furthermore, Sema3A influenced the production of osteoprotegerin and osteopontin suggesting it as an important local regulator of bone remodeling. Inhibition of Wnt3A and Wnt5A revealed that activation of Sema3A occurs downstream of Wnt5A and may facilitate the translocation of β-catenin bypassing the canonical Wnt3A initiating signal associated with osteoblastic differentiation. Furthermore, chemical inhibition of calmodulin (CaM), Ca²⁺/calmodulin-dependent protein kinase (CaMKII), phospholipase A₂ (PLA2), protein kinase C (PKC), and BMP receptors suggest that Sema3A could serve as a feedback mechanism for both Wnt5A and BMP2. Here, we show novel roles for Sema3A family proteins in the surface-dependent modulation of MSCs as well as important interactions with pathways known to be associated with osteoblastic differentiation. Moreover, their effects on bone remodeling markers have significant implications for peri-implant bone remodeling and downstream modulation of osteoclastic activity. These results suggest that Sema3A aids in peri-implant bone formation through regulation on multiple stages of osseointegration, making it a potential target to promote osseointegration in patients with compromised bone remodeling.

Frizzled 6 disruption suppresses osteoblast differentiation induced by nanotopography through the canonical Wnt signaling pathway

This study aimed to investigate if wingless-related integration site (Wnt) signaling participates in the high osteogenic potential of titanium with nanotopography (Ti-Nano). We showed that among the several components of the Wnt signaling pathway, Frizzled 6 (Fzd6) was the transcript most intensely modulated by nanotopography compared with the untreated Ti surface (Ti-Machined). Then, we investigated whether and how Fzd6 participates in the regulation of osteoblast differentiation caused by nanotopography. The Fzd6 silencing with CRISPR-Cas9 transfection in MC3T3-E1 cells induced a more pronounced inhibition of osteoblast differentiation of cells cultured on nanotopography than those cultured on Ti-Machined. The analysis of the expression of calcium-calmodulin-dependent protein kinase II and β-catenin demonstrated that Fzd6 disruption inhibited the osteoblast differentiation induced by Ti-Nano by preventing the activation of Wnt/β-catenin but not that of Wnt/Ca²⁺ signaling, which is usually triggered by the receptor Fzd6. These findings elucidate the biological function of Fzd6 as a receptor that triggers Wnt/β-catenin signaling and the cellular mechanisms modulated by nanotopography during osteoblast differentiation.

Titanium implant surface properties enhance osseointegration in ovariectomy induced osteoporotic rats without pharmacologic intervention

OBJECTIVES

This study determined whether implant surfaces that promote osseointegration in normal rats can promote osseointegration in osteoporotic rats without pharmacologic intervention.

MATERIALS AND METHODS

Virgin female 8-month-old CD Sprague Dawley rats (N = 25) were ovariectomized. At 6 weeks, microstructured/non-nanostructured/hydrophobic, microstructured/nanostructured/hydrophobic, or microstructured/nanostructured/hydrophilic Ti implants (Ø2.5 × 3.5 mm; Institut Straumann AG, Basel, Switzerland) were placed in the distal metaphysis of each femur. At 28 days, bone quality and implant osseointegration were assessed using microCT, histomorphometrics, and removal torque values (RTVs). Calvarial osteoblasts were isolated and cultured for 7 days on Ø15 mm Ti disks processed to exhibit similar surface characteristics as the implants used for the in vivo studies. The phenotype was assessed by measuring the production of osteocalcin, osteoprotegerin, osteopontin, BMP2, VEGF, and RANKL.

RESULTS

Microstructured/nanostructured/hydrophilic implants promoted increased bone-to-implant contact and RTVs in vivo and increased osteoblastic marker production in vitro compared to microstructured/non-nanostructured/hydrophobic and microstructured/nanostructured/hydrophobic implants, suggesting that osseointegration occurs in osteoporotic animals, and implant surface properties improve its rate.

CONCLUSIONS

Although all modified implants were able to osseointegrate in rats with OVX-induced osteoporosis without pharmacologic intervention, the degree of osseointegration was greater around microstructured/nanostructured/hydrophilic implant surfaces. These results suggest that when appropriate microstructure is present, hydrophilicity has a greater influence on Ti implant osseointegration compared to nanostructures. Moreover, modified implant surfaces can exert their control over the altered bone turnover observed in osteoporotic patients to stimulate functional osseointegration. These results provide critical insight for developing implants with improved osseointegration in patients with metabolic disorders of bone remodeling.

Accumulation of kynurenine elevates oxidative stress and alters microRNA profile in human bone marrow stromal cells

Kynurenine, a metabolite of tryptophan breakdown, has been shown to increase with age, and plays a vital role in a number of age-related pathophysiological changes, including bone loss. Accumulation of kynurenine in bone marrow stromal cells (BMSCs) has been associated with a decrease in cell proliferation and differentiation, though the exact mechanism by which kynurenine mediates these changes is poorly understood. MiRNAs have been shown to regulate BMSC function, and accumulation of kynurenine may alter the miRNA expression profile of BMSCs. The aim of this study was to identify differentially expressed miRNAs in human BMSCs in response to treatment with kynurenine, and correlate miRNAs function in BMSCs biology through bioinformatics analysis. Human BMSCs were cultured and treated with and without kynurenine, and subsequent miRNA isolation was performed. MiRNA array was performed to identify differentially expressed miRNA. Microarray analysis identified 50 up-regulated, and 36 down-regulated miRNAs in kynurenine-treated BMSC cultures. Differentially expressed miRNA included miR-1281, miR-330-3p, let-7f-5p, and miR-493-5p, which are important for BMSC proliferation and differentiation. KEGG analysis found up-regulated miRNA targeting glutathione metabolism, a pathway critical for removing oxidative species. Our data support that the kynurenine dependent degenerative effect is partially due to changes in the miRNA profile of BMSCs.

Role of offset and gradient architectures of 3-D melt electrowritten scaffold on differentiation and mineralization of osteoblasts

BACKGROUND

Cell-scaffold based therapies have the potential to offer an efficient osseous regenerative treatment and PCL has been commonly used as a scaffold, however its effectiveness is limited by poor cellular retention properties. This may be improved through a porous scaffold structure with efficient pore arrangement to increase cell entrapment. To facilitate this, melt electrowriting (MEW) has been developed as a technique able to fabricate cell-supporting scaffolds with precise micro pore sizes via predictable fibre deposition. The effect of the scaffold's architecture on cellular gene expression however has not been fully elucidated.

METHODS

The design and fabrication of three different uniform pore structures (250, 500 and 750 μm), as well as two offset scaffolds with different layout of fibres (30 and 50%) and one complex scaffold with three gradient pore sizes of 250-500 - 750 μm, was performed by using MEW. Calcium phosphate modification was applied to enhance the PCL scaffold hydrophilicity and bone inductivity prior to seeding with osteoblasts which were then maintained in culture for up to 30 days. Over this time, osteoblast cell morphology, matrix mineralisation, osteogenic gene expression and collagen production were assessed.

RESULTS

The in vitro findings revealed that the gradient scaffold significantly increased alkaline phosphatase activity in the attached osteoblasts while matrix mineralization was higher in the 50% offset scaffolds. The expression of osteocalcin and osteopontin genes were also upregulated compared to other osteogenic genes following 30 days culture, particularly in offset and gradient scaffold structures. Immunostaining showed significant expression of osteocalcin in offset and gradient scaffold structures.

CONCLUSIONS

This study demonstrated that the heterogenous pore sizes in gradient and fibre offset PCL scaffolds prepared using MEW significantly improved the osteogenic potential of osteoblasts and hence may provide superior outcomes in bone regeneration applications.