Osteogenic Differentiation of MSC through Calcium Signaling Activation: Transcriptomics and Functional Analysis

Fibronectin/thermo-responsive polymer scaffold as a dynamic ex vivo niche for mesenchymal stem cells

In this paper, we created a dynamic adhesive environment (DAE) for adipose tissue-derived mesenchymal stem cells (ADMSCs) cultured on smart thermo-responsive substrates, i.e., poly (N-isopropyl acrylamide) (PNIPAM), via introducing periodic changes in the culture temperature. We further explored the particular role of adsorbed fibronectin (FN), an important cell adhesive protein that was recently attributed to the recruitment of stem cells in the niche. The engineered FN/PNIPAM DAE system significantly increased the symmetric renewal of ADMSCs, particularly between passages 7 and 9 (p7-p9), before it dropped down to the level of the control (FN-coated TC polystyrene). This decline in the growth curve was consistent with the increased number of senescent cells, the augmented average cell size and the suppressed FN matrix secretion at late passages (p10-p12), all of them characteristic for stem cells ageing, which equivocally tended to slow down at our DAE system. FN supported also the osteogenic response of ADMSCs (apart from the previous observations with plain PNIPAM substrata) indicated by the significant increase of alkaline phosphatase (ALP) activity at days 7 and 14. The minimal changes in the Ca deposition, however, suggest a restricted effect of DAE on the early osteogenic response of ADMSCs only. Thus, the engineering of niche-like DAE involving FN uncovers a new tissue engineering strategy for gaining larger amounts of functionally active stem cells for clinical application.

A Custom Ultra-Low-Cost 3D Bioprinter Supports Cell Growth and Differentiation

Advances in 3D bioprinting have allowed the use of stem cells along with biomaterials and growth factors toward novel tissue engineering approaches. However, the cost of these systems along with their consumables is currently extremely high, limiting their applicability. To address this, we converted a 3D printer into an open source 3D bioprinter and produced a customized bioink based on accessible alginate/gelatin precursors, leading to a cost-effective solution. The bioprinter's resolution, including line width, spreading ratio and extrusion uniformity measurements, along with the rheological properties of the bioinks were analyzed, revealing high bioprinting accuracy within the printability window. Following the bioprinting process, cell survival and proliferation were validated on HeLa Kyoto and HEK293T cell lines. In addition, we isolated and 3D bioprinted postnatal neural stem cell progenitors derived from the mouse subventricular zone as well as mesenchymal stem cells derived from mouse bone marrow. Our results suggest that our low-cost 3D bioprinter can support cell proliferation and differentiation of two different types of primary stem cell populations, indicating that it can be used as a reliable tool for developing efficient research models for stem cell research and tissue engineering.

Human Mesenchymal Stem Cell Derived Exosomes Enhance Cell-Free Bone Regeneration by Altering Their miRNAs Profiles

Implantation of stem cells for tissue regeneration faces significant challenges such as immune rejection and teratoma formation. Cell-free tissue regeneration thus has a potential to avoid these problems. Stem cell derived exosomes do not cause immune rejection or generate malignant tumors. Here, exosomes that can induce osteogenic differentiation of human mesenchymal stem cells (hMSCs) are identified and used to decorate 3D-printed titanium alloy scaffolds to achieve cell-free bone regeneration. Specifically, the exosomes secreted by hMSCs osteogenically pre-differentiated for different times are used to induce the osteogenesis of hMSCs. It is discovered that pre-differentiation for 10 and 15 days leads to the production of osteogenic exosomes. The purified exosomes are then loaded into the scaffolds. It is found that the cell-free exosome-coated scaffolds regenerate bone tissue as efficiently as hMSC-seeded exosome-free scaffolds within 12 weeks. RNA-sequencing suggests that the osteogenic exosomes induce the osteogenic differentiation by using their cargos, including upregulated osteogenic miRNAs (Hsa-miR-146a-5p, Hsa-miR-503-5p, Hsa-miR-483-3p, and Hsa-miR-129-5p) or downregulated anti-osteogenic miRNAs (Hsa-miR-32-5p, Hsa-miR-133a-3p, and Hsa-miR-204-5p), to activate the PI3K/Akt and MAPK signaling pathways. Consequently, identification of osteogenic exosomes secreted by pre-differentiated stem cells and the use of them to replace stem cells represent a novel cell-free bone regeneration strategy.

Improving pulp revascularization outcomes with buccal fat autotransplantation

Several techniques have been introduced to improve the pulp revascularization outcomes. The use of the tissue graft can create more practical tissue regeneration, provide vascular supply, and enhance tissue healing. The aim of the present study was to investigate the histologic and molecular outcomes of pulp revascularization with buccal fat autotransplantation. Fifty-six open apex roots from four dogs aged 4-6 months were randomly allocated to five groups of endodontic regeneration models: Group 1 (negative control, n = 4); Group 2 (control and without intervention, n = 4); Group 3 (blood clot, n = 16); Group 4 (buccal fat autotransplantation, n = 16); and Group 5 (blood clot plus buccal fat autotransplantation, n = 16). After 3 months, the extracted dog teeth were analyzed by histological and immunohistochemical techniques. Furthermore, real-time quantitative polymerase chain reactions were implemented to assess the gene expression profiles of dentin sialophosphoprotein (DSPP), dentin matrix protein (DMP), collagen I (COL1), and alkaline phosphatase (ALP) on regenerated tissue in the root canals. There were no significant differences in the severity of inflammation and necrosis between intervention groups. Immunohistochemical analysis showed significant differences among the study groups in expression level of extracellular glycoproteins such as fibronectin, laminin, and tenascin C. Group 5 showed an increase in the expression of DMP1 and COL1 genes. The expression of DSPP gene increased significantly in Group 4. The expression of ALP gene increased significantly in Group 3. Using this procedure may open new fields of research for regenerative endodontic procedure in which tissue autotransplant, particularly adipose tissue, may improve the outcomes of pulp revascularization.

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

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

Semaphorin 3A-hypoxia inducible factor 1 subunit alpha co-overexpression enhances the osteogenic differentiation of induced pluripotent stem cells-derived mesenchymal stem cells in vitro

Background:

Mesenchymal stem or stromal cells (MSCs) derived from the induced pluripotent stem cells (iPSCs) have uniform biological activity, which makes the clinical application of MSCs in bone repair possible. Culturing the iPSC-MSCs onto osteoconductive materials is a promising tissue engineering-based strategy in bone regeneration. The aim of this work was to evaluate the effects of semaphorin 3A (Sema3A) and hypoxia inducible factor 1 subunit alpha (HIF1α) co-overexpression on the survival and osteogenic differentiation of iPSC-MSCs.

Methods:

Sema3A and HIF1α were linked together with the three (GGGGS; G, glycine; S, serine) peptide fragment, and their co-expression in iPSC-MSCs was mediated by a lentiviral vector. The fusion protein retained the immune reactivity for both Sema3A and HIF1α as determined with Western blotting. iPSC-MSCs were infected with overexpression lentivirus (oeLenti) as negative control, oeLenti-Sema3A, oeLenti-HIF1α or oeLenti-Sema3A-HIF1α lentiviruses.

Results:

Sema3A overexpression alone promoted the osteogenic differentiation of iPSC-MSCs (the activity and/or expression of osteoblast markers, such as alkaline phosphatase, osteopontin, and osteocalcin, were upregulated), and suppressed cell survival. The Sema3A-HIF1α fusion protein showed a comparable osteoconductive effect to that of Sema3A without reducing cell survival. We further seeded iPSC-MSCs modified by SemaA-HIF1α overexpression onto hydroxyapatite (HA) scaffolds, and evaluated their growth and differentiation on this three-dimensional material. Additional data indicated that, as compared to iPSC-MSCs cultured in ordinary two-dimensional dishes, cells cultured in HA scaffolds grew (blank vs. HA scaffolds: 0.83 vs. 1.39 for survival) and differentiated better (blank vs. HA scaffolds: 11.29 vs. 16.62 for alkaline phosphatase activity).

Conclusion:

Modifying iPSC-MSCs with pro-osteogenic (Sema3A) and pro-survival (HIF1α) factors may represent a promising strategy to optimize tissue engineering-based strategy in bone repair.

Calcium peroxide-mediated in situ formation of multifunctional hydrogels with enhanced mesenchymal stem cell behaviors and antibacterial properties

CaO₂ catalyzes the formation of in situ hydrogels with multifunctional properties through its decomposition into H₂O₂, O₂, and Ca²⁺ ions.

The role of CaO/SiO2 ratio and P2O5 content in gel-derived bioactive glass-polymer composites in the modulation of their bioactivity and osteoinductivity in human BMSCs

We obtained a range of PLGA-based composites containing sol-gel bioactive glasses (SBG) from the SiO₂-CaO and SiO₂-CaO-P₂O₅ systems. Eight SBGs with different CaO/SiO₂ ratios with and without P₂O₅ were incorporated at 50% w/w to PLGA matrix and structured into thin films suitable for cell culture. The SBG/PLGA composites were examined for their bioactivity in simulated body fluid (SBF), ion release profile in culture media with and without cells, and osteoinductivity in standard human bone marrow stromal cell (hBMSC) cultures without osteogenic growth factors. Our results indicate different surface activity of composites depending on the presence/absence of P₂O₅ in SBG composition. Furthermore, ion release profile to culture medium differed depending on the presence/absence of cells. Direct culture of hBMSC on the SiO₂-CaO/PLGA composite films resulted in elevated Runx-2 mRNA, opposite to low Runx-2 mRNA levels on SiO₂-CaO-P₂O₅/PLGA films. All studied composites increased Osx mRNA levels. Whereas some of SiO₂-CaO/PLGA composites did not elevate BMP-2 and -6 proteins in hBMSC cultures, high levels of these BMPs were present in all cultures on SiO₂-CaO-P₂O₅/PLGA composites. All composites induced BMP-related Tak1 signalling, whereas Smad1 signalling was restricted mostly to composites containing three-component SBGs. ALP activity of hBMSC and BMP-related luciferase activity of mouse BRITE cells differed depending on whether the cells were stimulated with culture medium conditioned with SBG/PLGA composites or the cells were directly cultured on the composite surfaces. Altogether, beyond bioactivity and osteoinductivity of SBG/PLGA composites, our studies show key differences in the biological response to both the bioactive material dissolution products and upon direct cell-material contacts.

Phosphate glass fibers facilitate proliferation and osteogenesis through Runx2 transcription in murine osteoblastic cells

Cell-material interactions and compatibility are important aspects of bioactive materials for bone tissue engineering. Phosphate glass fiber (PGF) is an attractive inorganic filler with fibrous structure and tunable composition, which has been widely investigated as a bioactive filler for bone repair applications. However, the interaction of osteoblasts with PGFs has not been widely investigated to elucidate the osteogenic mechanism of PGFs. In this study, different concentrations of short PGFs with interlaced oriented topography were cocultured with MC3T3-E1 cells for different periods, and the synergistic effects of fiber topography and ionic product of PGFs on osteoblast responses including cell adhesion, spreading, proliferation, and osteogenic differentiation were investigated. It was found that osteoblasts were more prone to adhere on PGFs through Vinculin protein, leading to enhanced cell proliferation with polygonal cell shape and spreading cellular actin filaments. In addition, osteoblasts incubated on PGF meshes showed enhanced alkaline phosphatase activity, extracellular matrix mineralization, and increased expression of osteogenesis-related marker genes, which could be attributed to the Wnt/β-catenin/Runx2 signaling pathway. This study elucidated the possible mechanism of PGF on triggering specific osteoblast behavior, which would be highly beneficial for designing PGF-based bone graft substitutes with excellent osteogenic functions.

Effect of Lactoferrin on the Expression Profiles of Long Non-coding RNA during Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

Lactoferrin (LF) has demonstrated stimulation of osteogenic differentiation of mesenchymal stem cells (MSCs). Long non-coding RNAs (lncRNAs) participate in regulating the osteogenic differentiation processes. However, the impact of LF on lncRNA expression in MSC osteogenic differentiation is poorly understood. Our aim was to investigate the effects of LF on lncRNAs expression profiles, during osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs), by RNA sequencing. A total number of 1331 putative lncRNAs were identified in rBMSCs during osteogenic differentiation in the study. LF influenced the expression of 120 lncRNAs (differentially expressed lncRNAs [DELs], Fold change > 1.5 or < −1.5; p < 0.05) in rBMSCs on day 14 of osteogenic differentiation, consisted of 60 upregulated and 60 down-regulated. Furthermore, the potential functions of DELs were of prediction by searching their target cis- and trans-regulated protein-coding genes. The bioinformatic analysis of DELs target gene revealed that LF led to the disfunction of transforming growth factor beta stimulus (TGF-β) and positive regulation of I-κappa B kinase/NF-κappa B signaling pathway, which may relate to osteogenic differentiation of rBMSCs. Our work is the first profiling of lncRNA in osteogenic differentiation of rBMSCs induced by LF, and provides valuable insights into the potential mechanisms for LF promoting osteogenic activity.

Effect of calcium glucoheptonate on proliferation and osteogenesis of osteoblast-like cells in vitro

Calcium is the key macromineral having a role in skeletal structure and function, muscle contraction, and neurotransmission. Bone remodeling is maintained through a constant balance between calcium resorption and deposition. Calcium deficiency is resolved through calcium supplementation, and among the supplements, water-soluble organic molecules attracted great pharmaceutical interest. Calcium glucoheptonate is a highly water-soluble organic calcium salt having clinical use; however, detailed investigations on its biological effects are limited. We assessed the effects of calcium glucoheptonate on cell viability and proliferation of osteoblast-like MG-63 cells. Calcium uptake and mineralization were evaluated using Alizarin red staining of osteoblast-like MG-63 cells treated with calcium glucoheptonate. Expression of osteogenic markers were monitored by western blotting, immunofluorescence, and qRT-PCR assays. Increased proliferation and calcium uptake were observed in the MG-63 cells treated with calcium glucoheptonate. The treatment also increased the expression of osteopontin and osteogenic genes such as collagen-1, secreted protein acidic and cysteine rich (SPARC), and osteocalcin. Calcium glucoheptonate treatment did not exert any cytotoxicity on colorectal and renal epithelial cells, indicating the safety of the treatment. This is the first report with evidence for its beneficial effect for pharmaceutical use in addressing calcium deficiency conditions.

The role of antimiR-26a-5p/biphasic calcium phosphate in repairing rat femoral defects

Although miRNAs have been implicated in the osteogenic differentiation of stem cells, their role in bone repair and reconstruction in tissue‑engineered bone grafts remains unclear. We previously reported that microRNA (miR)‑26a‑5p inhibited the osteogenic differentiation of adipose‑derived mesenchymal stem cells (ADSCs), and that antimiR‑26a‑5p exerted the opposite effect. In the present study, the role of miR‑26a‑5p‑ and antimiR‑26a‑5p‑modified ADSCs combined with biphasic calcium phosphate (BCP) scaffolds was evaluated in a rat femur defect model. The aim of the present study was to improve the understanding of the role of miR‑26a‑5p in bone regeneration in vivo, as well as to provide a new method to optimize the osteogenic ability of BCPs. ADSCs were infected with Lv‑miR‑26a‑5p, Lv‑miR‑NC, Lv‑antimiR‑26a‑5p or Lv‑antimiR‑NC respectively, and then combined with BCP scaffolds to repair rat femoral defects. Using X‑rays, micro‑computed tomography and histology at 2, 4, and 8 weeks postoperatively, the quantity and rate of bone regeneration were analyzed, revealing that they were the highest in animals treated with antimiR‑26a‑5p and the lowest in the miR‑26a‑5p treatment group. The expression levels of osteocalcin, collagen I, Runt‑related transcription factor 2, Wnt family member 5A and calmodulin‑dependent protein kinase II proteins were positively correlated with the bone formation rate. Taken together, the present results demonstrated that miR‑26a‑5p inhibited bone formation while antimiR‑26a‑5p accelerated bone formation via the Wnt/Ca2+ signaling pathway. Therefore, antimiR‑26a‑5p‑modified ADSCs combined with BCP scaffolds may be used to construct an effective tissue‑engineering bone graft for bone repair and reconstruction.

Rapid fabrication of vascularized and innervated cell-laden bone models with biomimetic intrafibrillar collagen mineralization

Bone tissue, by definition, is an organic–inorganic nanocomposite, where metabolically active cells are embedded within a matrix that is heavily calcified on the nanoscale. Currently, there are no strategies that replicate these definitive characteristics of bone tissue. Here we describe a biomimetic approach where a supersaturated calcium and phosphate medium is used in combination with a non-collagenous protein analog to direct the deposition of nanoscale apatite, both in the intra- and extrafibrillar spaces of collagen embedded with osteoprogenitor, vascular, and neural cells. This process enables engineering of bone models replicating the key hallmarks of the bone cellular and extracellular microenvironment, including its protein-guided biomineralization, nanostructure, vasculature, innervation, inherent osteoinductive properties (without exogenous supplements), and cell-homing effects on bone-targeting diseases, such as prostate cancer. Ultimately, this approach enables fabrication of bone-like tissue models with high levels of biomimicry that may have broad implications for disease modeling, drug discovery, and regenerative engineering.

Bone tissue is a complex organic-inorganic nanocomposite and strategies that replicate the characteristics of bone tissue are scarce. Here the authors demonstrate the deposition of nanoscale apatite in collagen embedded with mesenchymal, vascular and nerve cells, using a protein-guided biomineralization approach.

Self-mineralizing Ca-enriched methacrylated gellan gum beads for bone tissue engineering

In this study, methacrylated gellan-gum (GG-MA) heteropolysaccharide is proposed as a hydrogel for drug delivery and bone tissue engineering applications. Calcium-enriched beads obtained from the crosslinking of 1% (w/v) GG-MA solutions with 0.1 MCaCl₂ were investigated, considering their intrinsic capacity to promote self-mineralization by ion binding and deposition. Indeed, when immersed in a physiological environment, the Ca-enriched beads promoted the development of a bone-like apatite layer, as confirmed by EDS and XRD chemical analysis. Additionally, the mild production process is compatible with drugs incorporation and release. After encapsulation, Dextran with different molecular weights as well as Dexamethasone 21-phosphate were efficiently released to the surrounding environment. The engineered system was also evaluated considering its biocompatibility, by means of qualitative determination of total complement activation, macrophage proliferation, cytokine release and in vitro cell culture. These experiments showed that the developed hydrogels may not stimulate a disproportionate pro-inflammatory reaction once transplanted. At last, when implanted subcutaneously in CD1 male mice up to 8 weeks, the beads were completely calcified, and no inflammatory reaction was observed. Summing up, these results show that calcium-enriched GG-MA hydrogel beads hold great potential as news tools for bone tissue regeneration and local drug delivery applications. STATEMENT OF SIGNIFICANCE: This work describes a low-cost and straightforward strategy to prepare bioactive methacrylated gellan gum (GG-MA) hydrogels, which can be used as drug delivery systems. GG-MA is a highly anionic polymer, that can be crosslinked with divalent ions, as calcium. Taking advantage of this feature, it was possible to prepare Ca-enriched GG-MA hydrogel beads. These beads display a bioactive behavior, since they promote apatite deposition when placed in physiological conditions. Studies on the immune response suggest that the developed beads do not trigger severe immune responses. Importantly, the mild processing method render these beads compliant with drug delivery strategies, paving the way for the application of dual-functional materials on bone tissue engineering.

Determinants of stem cell lineage differentiation toward chondrogenesis versus adipogenesis

Adult stem cells, also termed as somatic stem cells, are undifferentiated cells, detected among differentiated cells in a tissue or an organ. Adult stem cells can differentiate toward lineage specific cell types of the tissue or organ in which they reside. They also have the ability to differentiate into mature cells of mesenchymal tissues, such as cartilage, fat and bone. Despite the fact that the balance has been comprehensively scrutinized between adipogenesis and osteogenesis and between chondrogenesis and osteogenesis, few reviews discuss the relationship between chondrogenesis and adipogenesis. In this review, the developmental and transcriptional crosstalk of chondrogenic and adipogenic lineages are briefly explored, followed by elucidation of signaling pathways and external factors guiding lineage determination between chondrogenic and adipogenic differentiation. An in-depth understanding of overlap and discrepancy between these two mesenchymal tissues in lineage differentiation would benefit regeneration of high-quality cartilage tissues and adipose tissues for clinical applications.

Engineering a multifunctional 3D-printed PLA-collagen-minocycline-nanoHydroxyapatite scaffold with combined antimicrobial and osteogenic effects for bone regeneration

3D-printing and additive manufacturing can be powerful techniques to design customized structures and produce synthetic bone grafts with multifunctional effects suitable for bone repair. In our work we aimed the development of novel multifunctionalized 3D printed poly(lactic acid) (PLA) scaffolds with bioinspired surface coatings able to reduce bacterial biofilm formation while favoring human bone marrow-derived mesenchymal stem cells (hMSCs) activity. For that purpose, 3D printing was used to prepare PLA scaffolds that were further multifunctionalized with collagen (Col), minocycline (MH) and bioinspired citrate- hydroxyapatite nanoparticles (cHA). PLA-Col-MH-cHA scaffolds provide a closer structural support approximation to native bone architecture with uniform macroporous, adequate wettability and an excellent compressive strength. The addition of MH resulted in an adequate antibiotic release profile that by being compatible with local drug delivery therapy was translated into antibacterial activities against Staphylococcus aureus, a main pathogen associated to bone-related infections. Subsequently, the hMSCs response to these scaffolds revealed that the incorporation of cHA significantly stimulated the adhesion, proliferation and osteogenesis-related gene expression (RUNX2, OCN and OPN) of hMSCs. Furthermore, the association of a bioinspired material (cHA) with the antibiotic MH resulted in a combined effect of an enhanced osteogenic activity. These findings, together with the antibiofilm activity depicted strengthen the appropriateness of this 3D-printed PLA-Col-MH-cHA scaffold for future use in bone repair. By targeting bone repair while mitigating the typical infections associated to bone implants, our 3D scaffolds deliver an integrated strategy with the combined effects further envisaging an increase in the success rate of bone-implanted devices.

Calcium mimics the chemotactic effect of conditioned media and is an effective inducer of bone regeneration

Background

After bone resorption, ions and degraded organic components are co-released into the extracellular space. Ions and growth factors, although different in their biological nature, induce a common and coordinated chemotactic effect. Conditioned media has been used successfully in bone regeneration by promoting endogenous cell recruitment. Likewise, calcium alone act as a paracrine chemotactic signal, inducing the host’s undifferentiated progenitor cell infiltration into the implanted biomaterials. The aim of the present study was to compare the chemotactic effect of calcium and conditioned media in primary calvarial cells.

Methods

The chemotactic cell response was evaluated in vitro using an agarose spot and a wound healing assay. In addition, we used a calvarial bone explant model ex-vivo. The healing potential was also tested through an in vivo model, a critical-size calvarial bone defect in mice. For the in vivo experiment, cell-free calcium-containing or conditioned media-containing scaffolds were implanted, and MSC’s seeded scaffolds were used as positive control. After seven weeks post-implantation, samples were retrieved, and bone regeneration was evaluated by μCT and histological analysis. Osteogenic gene expression was evaluated by qPCR.

Results

We found that chemotactic cell migration in response to either calcium or conditioned media was equivalent in vitro and ex vivo. Accordingly, μCT analysis showed that bone regeneration induced by the MSC’s seeded scaffolds was similar to that obtained with cell-free calcium or conditioned media-containing scaffolds. Pre-treatment with SB202190, a highly selective p38 inhibitor, abrogated the chemotactic effect induced by conditioned media. In contrast, p38 activity was not essential for the calcium-induced chemotaxis. Moreover, BAPTA-AM treatment, a cytosolic calcium chelator, decreased the chemotactic effect and the expression of key osteogenic genes induced by calcium or conditioned media.

Conclusion

We show that calcium ions alone not only mimic the conditioned media chemotactic effect, but also induce an osteogenic effect similar to that produced by transplanted MSC’s in vivo. Furthermore, the chemotactic effect induced by conditioned media is calcium and p38 dependent. The rise in cytosolic calcium might integrate the different signaling pathways triggered by conditioned media and extracellular Ca²⁺. This calcium-driven in situ bone regeneration is a promising and convenient alternative to promote endogenous cell recruitment into the injured bone site. This pre-clinical cell-free and growth factor-free approach might avoid the disadvantages of the ex vivo cell manipulation.

Angiogenesis-promoted bone repair with silicate-shelled hydrogel fiber scaffolds

The silicate-shelled alginate hydrogel fiber scaffold is highly effective for promoting ion-induced angiogenesis and bone bioactivity, ultimately useful for the repair and regeneration of hard tissues.

The Role of Physical Stimuli on Calcium Channels in Chondrogenic Differentiation of Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSC) are becoming increasingly popular in tissue engineering. They are the most frequently used stem cell source for clinical applications due to their high potential to differentiate into several lineages. Cartilage is known for its low capacity for self-maintenance and currently there are no efficient methods to improve cartilage repair. Chondrogenic differentiation of hMSC isolated from different tissues is widely employed due to a high clinical demand for the improvement of cartilage regeneration. Calcium channels that are regulated by physical stimuli seem to play a pivotal role in chondrogenic differentiation of MSCs. These channels increase intracellular calcium concentration, which leads to the initiation of the relevant cellular processes that are required for differentiation. This review will focus on the impact of different physical stimuli, including electrical, electromagnetic/magnetic and mechanical on various calcium channels and calcium signaling mechanisms during chondrogenic differentiation of hMSC.

Surface functionalization of halloysite nanotubes with supermagnetic iron oxide, chitosan and 2-D calcium-phosphate nanoflakes for synergistic osteoconduction enhancement of human adipose tissue-derived mesenchymal stem cells

Halloysite nanotubes (HNTs) are known to be the highly emerging materials in nano-medicinal applications. However, comprehensive exploitation of HNTs for the regenerative medicinal applications is still necessary to be done. Therefore, towards enhancing the osteogenic potential of human adipose tissue-derived mesenchymal stem cells (hADMSCs), this study synthesized a novel and multifunctional nanoscaffold of chitosan (CTs) functionalized supermagnetic halloysite nanotubes (M-HNTs) decorated with the calcium phosphate 2-D nanoflakes (CaP) (termed as; M-HNTs-CTs-CaP). Stepwise modified nanoscaffolds were characterized by FE-SEM, FE-SEM-EDS, FE-HR-TEM, XPS, FT-IR and VSM analyses. The hADMSCs osteogenic potential was confirmed by calcification (Alizarin Red S staining), phosphate quantification and immunocytochemistry. Nanoscaffolds; CaP, M-HNTs-CaP and M-HNTs-CTs-CaP were significantly enhanced and up-regulated osteogenic potential compared to the HNTs, M-HNTs, M-HNTs-CTs. Among the nanoscaffolds studied, M-HNTs-CTs-CaP exhibited highest osteogenesis, due to the enhanced CaP distribution on M-HNTs-CTs surface, and synergistic osteoconduction contributed from Fe₃O₄, chitosan and CaP. Moreover, immunocytochemistry analysis and morphologically observation showed well differentiated osteoblast on the M-HNTs-CTs-CaP surface. Therefore, M-HNTs-CTs-CaP found to have a strong osteogenic potential of hADMSCs, and might be serve as highly applicable, next generation nanoscaffold for bone tissue engineering application.

Hyperstimulation of CaSR in human MSCs by biomimetic apatite inhibits endochondral ossification via temporal down-regulation of PTH1R

In adult bone injuries, periosteum-derived mesenchymal stem/stromal cells (MSCs) form bone via endochondral ossification (EO), whereas those from bone marrow (BM)/endosteum form bone primarily through intramembranous ossification (IMO). We hypothesized that this phenomenon is influenced by the proximity of MSCs residing in the BM to the trabecular bone microenvironment. Herein, we investigated the impact of the bone mineral phase on human BM-derived MSCs' choice of ossification pathway, using a biomimetic bone-like hydroxyapatite (BBHAp) interface. BBHAp induced hyperstimulation of extracellular calcium-sensing receptor (CaSR) and temporal down-regulation of parathyroid hormone 1 receptor (PTH1R), leading to inhibition of chondrogenic differentiation of MSCs even in the presence of chondroinductive factors, such as transforming growth factor-β1 (TGF-β1). Interestingly rescuing PTH1R expression using human PTH fragment (1-34) partially restored chondrogenesis in the BBHAp environment. In vivo studies in an ectopic site revealed that the BBHAp interface inhibits EO and strictly promotes IMO. Furthermore, CaSR knockdown (CaSR KD) disrupted the bone-forming potential of MSCs irrespective of the absence or presence of the BBHAp interface. Our findings confirm the expression of CaSR in human BM-derived MSCs and unravel a prominent role for the interplay between CaSR and PTH1R in regulating MSC fate and the choice of pathway for bone formation.

Osteogenic differentiation of mouse bone marrow stromal cells on fibroin microcarriers

We investigated the proliferation and osteogenic differentiation of mesenchymal stem cells cultured on fibroin microcarriers. Effective cell proliferation on the surface of the microcarriers, determined by the large surface area, and the contribution of microcarrier mineralization to the stimulation of the osteogenic differentiation of mesenchymal stem cells was revealed.

Microenvironmental factors that regulate mesenchymal stem cells: lessons learned from the study of heterotopic ossification

Bone marrow contains a non-hematopoietic, clonogenic, multipotent population of stromal cells that are later called mesenchymal stem cells (MSC). Similar cells that share many common features with MSC are also found in other organs, which are thought to contribute both to normal tissue regeneration and to pathological processes such as heterotopic ossification (HO), the formation of ectopic bone in soft tissue. Understanding the microenvironmental factors that regulate MSC in vivo is essential both for understanding the biology of the stem cells and for effective translational applications of MSC. Unfortunately, this important aspect has been largely underappreciated. This review tries to raise the attention and highlight this critical issue by updating the relevant literature along with discussions of the key issues in the area.

Bioinspired Collagen Scaffolds in Cranial Bone Regeneration: From Bedside to Bench

Calvarial defects are common reconstructive dilemmas secondary to a variety of etiologies including traumatic brain injury, cerebrovascular disease, oncologic resection, and congenital anomalies. Reconstruction of the calvarium is generally undertaken for the purposes of cerebral protection, contour restoration for psychosocial well-being, and normalization of neurological dysfunction frequently found in patients with massive cranial defects. Current methods for reconstruction using autologous grafts, allogeneic grafts, or alloplastic materials have significant drawbacks that are unique to each material. The combination of wide medical relevance and the need for a better clinical solution render defects of the cranial skeleton an ideal target for development of regenerative strategies focused on calvarial bone. With the improved understanding of the instructive properties of tissue-specific extracellular matrices and the advent of precise nanoscale modulation in materials science, strategies in regenerative medicine have shifted in paradigm. Previously considered to be simple carriers of stem cells and growth factors, increasing evidence exists for differential materials directing lineage specific differentiation of progenitor cells and tissue regeneration. In this work, we review the clinical challenges for calvarial reconstruction, the anatomy and physiology of bone, and extracellular matrix-inspired, collagen-based materials that have been tested for in vivo cranial defect healing.

miR-139-5p Represses BMSC Osteogenesis via Targeting Wnt/β-Catenin Signaling Pathway

Osteogenesis of mesenchymal stem cells (MSCs) has played a necessary role in the repair of bone. According to some reports, microRNAs participate in different physiological activity of the cells, including cell differentiation. This study investigated the function that miR-139-5p plays in the osteogenic differentiation of human bone marrow MSCs (hBMSCs). In addition to miR-139-5p, the effects of alkaline phosphatase (ALP), a membrane-bound metalloenzyme that is considered an early osteogenic differentiation marker, have also been investigated. Calcium-rich deposit (mineralization) is also a typical osteogenic differentiation marker that could be visualized by alizarin red S (ARS) staining. Inhibiting miR-139-5p notably promotes the hBMSC osteoblast differentiation, which, however, will be reduced by overexpressed miR-139-5p. This result has been made based on the alternations of ALP activity, ARS staining, as well as expression of osteogenic genes, including runt-related gene-2 (Runx2), collagen I (Col-1), and osteocalcin (OCN). miR-139-5p exerts its role in BMSC osteogenesis most probably through the Wnt/β-catenin pathway, by direct targeting CTNNB1 and frizzled 4 (FZD4), essential factors of Wnt/β-catenin pathway. In conclusion, according to the present study, inhibiting miR-139-5p could be a promising strategy in hBMSC osteogenesis.

Three-dimensional printed polycaprolactone-based scaffolds provide an advantageous environment for osteogenic differentiation of human adipose-derived stem cells

The capacity of bone grafts to repair critical size defects can be greatly enhanced by the delivery of mesenchymal stem cells (MSCs). Adipose tissue is considered the most effective source of MSCs (ADSCs); however, the efficiency of bone regeneration using undifferentiated ADSCs is low. Therefore, this study proposes scaffolds based on polycaprolactone (PCL), which is widely considered a suitable MSC delivery system, were used as a three-dimensional (3D) culture environment promoting osteogenic differentiation of ADSCs. PCL scaffolds enriched with 5% tricalcium phosphate (TCP) were used. Human ADSCs were cultured in osteogenic medium both on the scaffolds and in 2D culture. Cell viability and osteogenic differentiation were tested at various time points for 42 days. The expression of RUNX2, collagen I, alkaline phosphatase, osteonectin and osteocalcin, measured by real-time polymerase chain reaction was significantly upregulated in 3D culture. Production of osteocalcin, a specific marker of terminally differentiated osteoblasts, was significantly higher in 3D cultures than in 2D cultures, as confirmed by western blot and immunostaining, and accompanied by earlier and enhanced mineralization. Subcutaneous implantation into immunodeficient mice was used for in vivo observations. Immunohistological and micro-computed tomography analysis revealed ADSC survival and activity toward extracellular production after 4 and 12 weeks, although heterotopic osteogenesis was not confirmed - probably resulting from insufficient availability of Ca/P ions. Additionally, TCP did not contribute to the upregulation of differentiation on the scaffolds in culture, and we postulate that the 3D architecture is a critical factor and provides a useful environment for prior-to-implantation osteogenic differentiation of ADSCs. Copyright © 2016 John Wiley & Sons, Ltd.

RALA complexed α-TCP nanoparticle delivery to mesenchymal stem cells induces bone formation in tissue engineered constructs in vitro and in vivo

A range of bone regeneration strategies, from growth factor delivery and/or mesenchymal stem cell (MSC) transplantation to endochondral tissue engineering, have been developed in recent years. Despite their tremendous promise, the clinical translation and future use of many of these strategies is being hampered by concerns such as off target effects associated with growth factor delivery. Therefore the overall objective of this study was to investigate the influence of alpha-tricalcium phosphate (α-TCP) nanoparticle delivery into MSCs using an amphipathic cell penetrating peptide RALA, on osteogenesis in vitro and both intramembranous and endochondral bone formation in vivo. RALA complexed α-TCP nanoparticle delivery to MSCs resulted in an increased expression of bone morphogenetic protein-2 (BMP-2) and an upregulation in a number of key osteogenic genes. When α-TCP stimulated MSCs were encapsulated into alginate hydrogels, enhanced mineralization of the engineered construct was observed over a 28 day culture period. Furthermore, the in vivo bone forming potential of RALA complexed α-TCP nanoparticle delivery to MSCs was found to be comparable to growth factor delivery. Recognizing the potential and limitations associated with endochondral bone tissue engineering strategies, we then sought to explore how α-TCP nanoparticle delivery to MSCs influences early mineralization of engineered cartilage templates in vitro and their subsequent ossification in vivo. Despite accelerating mineralization of engineered cartilage templates in vitro, RALA complexed α-TCP nanoparticle delivery did not enhance endochondral bone formation in vivo. Therefore the potential of RALA complexed α-TCP nanoparticle delivery appears to be as an alternative to growth factor delivery as a single stage strategy for promoting bone generation.

Calcium phosphate-phosphorylated adenosine hybrid microspheres for anti-osteosarcoma drug delivery and osteogenic differentiation

Biocompatibility, biodegradability and bioactivity are significantly important in practical applications of various biomaterials for bone tissue engineering. Herein, we develop a functional inorganic-organic hybrid system of calcium phosphate-phosphorylated adenosine (CPPA). Both calcium phosphate and phosphorylated adenosine molecules in CPPA are fundamental components in mammalians and play important roles in biological metabolism. In this work, we report our three leading research qualities: (1) CPPA hybrid microspheres with hollow and porous structure are synthesized by a facile one-step microwave-assisted solvothermal method; (2) CPPA hybrid microspheres show high doxorubicin loading capacity and pH-responsive drug release properties, and demonstrate positive therapeutic effects on six osteosarcoma cell lines in vitro and a mouse model of 143B osteosarcoma subcutaneous tumor in vivo; (3) CPPA hybrid microspheres are favorable to promote osteogenic differentiation of human bone mesenchymal stem cells (hBMSCs) by activating the AMPK pathway, with satisfactory evidences from cellular alkaline phosphatase staining, alizarin red staining, real time PCR and western analysis. The as-prepared CPPA hybrid microspheres are promising in anti-osteosarcoma and bone regeneration, which simultaneously display excellent properties on drug delivery and osteogenic differentiation of hBMSCs.