Osteogenesis versus chondrogenesis by BMP-2 and BMP-7 in adipose stem cells

Genetic deletion of ITIH5 leads to increased development of adipose tissue in mice

BACKGROUND

Adipocytokines play a pivotal role in maintaining adipose tissue homeostasis by regulating cellular metabolism, proliferation, differentiation, and secretory activity. These soluble factors are relevant components for healthy adipose tissue, while their deficiency is closely associated with the development of obesity and related metabolic diseases, e.g., chronic inflammation. In human adipose tissue, inter-α-trypsin inhibitor heavy chain 5 (ITIH5) is expressed in proportion to the development of adipose tissue, i.e., the individual's BMI. Thus, ITIH5 has been proposed to be an inert marker of human obesity. However, when applied to adipose stem cells in vitro, recombinant (r)ITIH5 protein inhibited proliferation and adipogenesis, suggesting that ITIH5 negatively affects the development of fat mass. We now tested the role of ITIH5 in vivo and compared ITIH5+/+ wildtype with ITIH5-/- knockout mice.

RESULTS

Genetic deletion of ITIH5 significantly increased adipose tissue mass relative to animal bodyweight (p < 0.05). Next, we characterized adipose stem cells (ASCs) from both genotypes in vitro. ITIH5-/- cells exhibited increased proliferation and adipogenic differentiation (p < 0.001), which could explain the increase in adipose tissue in vivo. Furthermore, ASCs from ITIH5-/- animals were more responsive to stimulation with inflammatory mediators, i.e., these cells released greater amounts of IL-6 and MCP-1 (p < 0.001). Importantly, the application of the rITIH5 protein reversed the observed knockout effects in ASCs.

CONCLUSIONS

Our data suggest that ITIH5 potently regulates adipose tissue development and homeostasis by modulating ASC biology in mice. In addition, the effect of the rITIH5 protein underscores its potential as a therapeutic agent to correct the adipose tissue dysregulation often associated with obesity and metabolic disorders.

Angiopoietin-like growth factor-derived peptides as biological activators of adipose-derived mesenchymal stromal cells

Adipose-derived mesenchymal stromal cells (AD-MSCs) are an essential issue in modern medicine. Extensive preclinical and clinical studies have shown that mesenchymal stromal/stem cells, including AD-MSCs, have specific properties (ability to differentiate into other cells, recruitment to the site of injury) of particular importance in the regenerative process. Ongoing research aims to elucidate factors supporting AD-MSC culture and differentiation in vitro. Angiopoietin-like proteins (ANGPTLs), known for their pleiotropic effects in lipid and glucose metabolism, may play a significant role in this context. Regeneration is a complex and dynamic process controlled by many factors. ANGPTL6 (Angiopoietin-related growth factor, AGF), among many activities modulated the biological activity of stem cells. This study examined the influence of synthesized AGF-derived peptides, designated as AGF9 and AGF27, on AD-MSCs. AGF9 and AGF27 enhanced the viability and migration of AD-MSCs and acted as a chemotactic factor for these cells. AGF9 stimulated chondrogenesis and lipid synthesis during AD-MSCs differentiation, influenced AD-MSCs cytokine secretion and modulated transcriptome for such basic cell activities as migration, transport of molecules, and apoptosis. The ability of AGF9 to modulate the biological activity of AD-MSCs warrants the consideration of this peptide a noteworthy therapeutic agent that deserves further investigation for applications in regenerative medicine.

Aspirin Stimulates the Osteogenic Differentiation of Human Adipose Tissue-Derived Stem Cells In Vitro

This study investigates the impact of acetylsalicylic acid (ASA), also known as aspirin, on adipose tissue-derived stem cells (ASCs), aiming to elucidate its dose-dependent effects on morphology, viability, proliferation, and osteogenic differentiation. Isolated and characterized human ASCs were exposed to 0 µM, 100 µM, 200 µM, 400 µM, 800 µM, 1000 µM, 10,000 µM, and 16,000 µM of ASA in vitro. Cell morphology, viability, and proliferation were evaluated with fluorescent live/dead staining, alamarBlue viability reagent, and CyQUANT® cell proliferation assay, respectively. Osteogenic differentiation under stimulation with 400 µM or 1000 µM of ASA was assessed with alizarin red staining and qPCR of selected osteogenic differentiation markers (RUNX2, SPP1, ALPL, BGLAP) over a 3- and 21-day-period. ASA doses ≤ 1000 µM showed no significant impact on cell viability and proliferation. Live/dead staining revealed a visible reduction in viable cell confluency for ASA concentrations ≥ 1000 µM. Doses of 10,000 µM and 16,000 µM of ASA exhibited a strong cytotoxic and anti-proliferative effect in ASCs. Alizarin red staining revealed enhanced calcium accretion under the influence of ASA, which was macro- and microscopically visible and significant for 1000 µM of ASA (p = 0.0092) in quantification if compared to osteogenic differentiation without ASA addition over a 21-day-period. This enhancement correlated with a more pronounced upregulation of osteogenic markers under ASA exposure (ns). Our results indicate a stimulatory effect of 1000 µM of ASA on the osteogenic differentiation of ASCs. Further research is needed to elucidate the precise molecular mechanisms underlying this effect; however, this discovery suggests promising opportunities for enhancing bone tissue engineering with ASCs as cell source.

Scaffold-free bone-like 3D structure established through osteogenic differentiation from human gingiva-derived stem cells

Introduction & objectives

Stem cell therapy for regenerative medicine has been sincerely investigated, but not still popular although some clinical trials show hopeful results. This therapy is suggested to be a representative candidate such as bone defect due to the accident, iatrogenic resection oncological tumor, congenital disease, and severe periodontitis in oral region. Recently, the Bio-3D printer "Regenova®" has been introduced as an innovative three-dimensional culture system, equipped scaffold-free bio-assembling techniques without any biomaterials. Therefore, we expected a mount of bone defect could be repaired by the structure established from this Bio-3D printer using osteogenic potential stem cells.

Material & methods

The gingival tissue (1x1 mm) was removed from the distal part of the lower wisdom tooth of the patients who agreed our study. Human Gingival Mesenchymal Stem Cells (hGMSCs) were isolated from this tissue and cultured, since we confirmed the characteristics such as facile isolation and accelerated proliferation, further, strong potential of osteogenic-differentiation. Spheroids were formed using hGMSC in 96-well plates designed for low cell adhesion. The size of the spheroids was measured, and fluorescent immunostaining was employed to verify the expression of stem cell and apoptosis marker, and extracellular matrix. Following four weeks of bone differentiation, μCT imaging was performed. Calcification was confirmed by alizarin red and von Kossa staining. Fluorescent immunostaining was utilized to assess the expression of markers indicative of advanced bone differentiation.

Results

We have established and confirmed the spheroids (∼600 μm in diameter) constructed from human GMSCs (hGMSCs) still maintain stem cell potentials and osteogenic differentiation abilities from the results that CD73 and not CD34 were expressed as stem cell positive and negative marker, respectively. These spheroids were pilled up like cylindal shape to the "Kenzan" platform of Bio-3D printer and cultured for 7days. The cylindal structure originated from compound spheroids were tried to differentiate into bone four weeks with osteogenic induction medium. The calcification of bio-3D printed bone-like structures was confirmed by alizarin red and Von Kossa staining. In addition, μCT analysis revealed that the HU (Hounsfield Unit) of the calcified structures was almost identical to that of trabecular bone. Immunofluorescent staining detected osteocalcin expression, a late-stage bone differentiation marker.

Conclusion

For the first time, we have achieved the construction of a scaffold-free, bone-like luminal structure through the assembly of spheroids comprised of this hGMSCs. This success is sure to be close to the induction of clinical application against regenerative medicine especially for bone defect disease.

Role of Adipose-Derived Mesenchymal Stem Cells in Bone Regeneration

Bone regeneration involves multiple factors such as tissue interactions, an inflammatory response, and vessel formation. In the event of diseases, old age, lifestyle, or trauma, bone regeneration can be impaired which could result in a prolonged healing duration or requiring an external intervention for repair. Currently, bone grafts hold the golden standard for bone regeneration. However, several limitations hinder its clinical applications, e.g., donor site morbidity, an insufficient tissue volume, and uncertain post-operative outcomes. Bone tissue engineering, involving stem cells seeded onto scaffolds, has thus been a promising treatment alternative for bone regeneration. Adipose-derived mesenchymal stem cells (AD-MSCs) are known to hold therapeutic value for the treatment of various clinical conditions and have displayed feasibility and significant effectiveness due to their ease of isolation, non-invasive, abundance in quantity, and osteogenic capacity. Notably, in vitro studies showed AD-MSCs holding a high proliferation capacity, multi-differentiation potential through the release of a variety of factors, and extracellular vesicles, allowing them to repair damaged tissues. In vivo and clinical studies showed AD-MSCs favoring better vascularization and the integration of the scaffolds, while the presence of scaffolds has enhanced the osteogenesis potential of AD-MSCs, thus yielding optimal bone formation outcomes. Effective bone regeneration requires the interplay of both AD-MSCs and scaffolds (material, pore size) to improve the osteogenic and vasculogenic capacity. This review presents the advances and applications of AD-MSCs for bone regeneration and bone tissue engineering, focusing on the in vitro, in vivo, and clinical studies involving AD-MSCs for bone tissue engineering.

Toward the Development of a Tissue Engineered Gradient Utilizing CRISPR-Guided Gene Modulation

Cellular, compositional, and mechanical gradients are found throughout biological tissues, especially in transition zones between tissue types. Yet, strategies to engineer such gradients have proven difficult due to the complex nature of these tissues. Current strategies for tissue engineering complex gradients often utilize stem cells; however, these multipotent cells require direction from environmental cues, which can be difficult to control both in vitro and in vivo. In this study, we utilize clustered regularly-interspaced short palindromic repeats (CRISPR)-guided gene modulation to direct the differentiation of multipotent adipose-derived stem cells (ASCs) to demonstrate the effectiveness of CRISPR-engineered cells in tissue engineering applications. Specifically, we screen CRISPR-interference (CRISPRi) constructs targeting the promotors of selected osteogenic inhibitors and demonstrate that ASC osteogenic differentiation and mineral deposition can be regulated with CRISPRi targeting of Noggin without the use of exogenous growth factors in tissue engineered constructs. As a proof of concept, we combine three technologies developed out of our laboratories to demonstrate the controlled deposition of these engineered cells in a gradient with CRISPR-activation multiplex-engineered aggrecan/collagen type-II-chondrogenic ASCs on a high density anisotropic type I collagen construct to create a cell and tissue gradient similar to the fibrocartilage-to-mineralized-fibrocartilage gradient in the enthesis. Our results display the promise of CRISPR-engineered ASCs to produce tissue gradients, similar to what is observed in native tissue.

ITIH5 inhibits proliferation, adipogenic differentiation, and secretion of inflammatory cytokines of human adipose stem cells-A new key in treating obesity?

Inter-α-trypsin inhibitor heavy chain 5 (ITIH5) is widely expressed in the human body, and it is detected to be particularly abundant in adipose tissue. ITIH5 expression is increased in people with obesity compared to lean persons and is decreased by diet-induced weight loss. This suggests that ITIH5 may be involved in the development of adiposity and clinical metabolic variables, although its exact function remains unknown. We measured the protein concentration of ITIH5 in adipose samples from patients undergoing abdominoplasty and tested for correlation with the subjects' BMI as well as inflammatory mediators. We stimulated human adipose stem cells (ASCs) with recombinant (r)ITIH5 protein and tested for an effect on proliferation, differentiation, and immunosuppressive properties when the cells were exposed to an artificial inflammatory environment. We found positive correlations between ITIH5 levels and the BMI (p < .001) as well as concentrations of inflammatory cytokines (TNF-α, IL-6, and MCP-1) in adipose tissue (p < .01). Application of the rITIH5 protein inhibited both proliferation (p < .001) and differentiation of ASCs. Especially, the development of mature adipocytes was reduced by over 50%. Moreover, rITIH5 decreased the release of IL-6 and MCP-1 when the cells were exposed to TNF-α and IL-1β (p < .001). Our data suggest that ITIH5 is an adipokine that is increasingly released during human adipose tissue development, acting as a regulator that inhibits proliferation and adipogenic differentiation of ASCs. ITIH5 thus presents itself as a positive regulator of adipose tissue homeostasis, possibly protecting against both hyperplasia and hypertrophy of adipose tissue and the associated chronic inflammation.

Long-Term Outcomes of Osteochondral Allograft with Osteogenic Protein-1 Augmentation: A Twelve-Year Follow-Up

Background

Osteochondral lesions (OCLs) can significantly impact functional status and activities of daily living. Weightbearing joints are disproportionately affected due to considerable biomechanical forces in these areas. Various biologic reconstructive procedures such as microfracture, osteochondral autograft transfer (OATS) or allograft transplantation (OCA), and matrix-induced autologous chondrocyte implantation (MACI) are utilized by surgeons to treat OCLs. The integration of osteochondral allografts can restore knee function and maintain the integrity of adjacent joint surfaces. Bone incorporation has been linked to successful outcomes following OCA. Pulse lavage and carbon dioxide have been used to remove marrow elements from the superficial, middle, and deep layers of the allograft; this has been combined with the use of various biologics such as bone marrow aspirate or whole blood to augment donor bone incorporation into the host bone. We present an innovative augmentation approach in OCA transplantation demonstrating excellent incorporation of an osteogenic protein-1 (OP-1) implant (Stryker, Kalamazoo, MI) to treat a large fresh osteoarticular allograft. Case Presentation. We present a 51-year-old male who received OCA augmented with an OP-1 implant (Stryker, Kalamazoo, MI) in 2011. Due to subsequent ACL reconstruction for two years and medial meniscal repair four years following OCA transplantation, we were able to arthroscopically evaluate graft status at short- and intermediate-term follow-ups. Positive findings were further verified with radiographic imaging and patient-reported outcome measures (PROMs).

Conclusion

OP-1 implants aided in the bone incorporation of a large osteochondral allograft, restoring a high functional level in a demanding sport.

Osteogenic induction of asiatic acid derivatives in human periodontal ligament stem cells

Asiatic acid (AA) and asiaticoside, pentacyclic triterpenoid compounds derived from Centella asiatica, are known for their biological effects in promoting type I collagen synthesis and inducing osteogenesis of stem cells. However, their applications in regenerative medicine are limited due to their low potency and poor aqueous solubility. This work aimed to evaluate the osteogenic induction activity of AA derivatives in human periodontal ligament stem cells (hPDLSCs) in vitro. Four compounds were synthesised, namely 501, 502, 503, and 506. AA was used as the control. The 502 exhibited low water solubility, while the 506 compound showed the highest. The cytotoxicity analysis demonstrated that 503 caused significant deterioration in cell viability, while other derivatives showed no harmful effect on hPDLSCs. The dimethyl aminopropyl amine derivative of AA, compound 506, demonstrated a relatively high potency in inducing osteogenic differentiation. An elevated mRNA expression of osteogenic-related genes, BMP2, WNT3A, ALP, OSX and IBSP was observed with 506. Additionally, the expression of BMP-2 protein was enhanced with increasing dose of 506, and the effect was pronounced when the Erk signalling molecule was inhibited. The 506 derivative was proposed for the promotion of osteogenic differentiation in hPDLSCs by upregulating BMP2 via the Erk signalling pathway. The 506 molecule showed promise in bone tissue regeneration.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Microtissues from mesenchymal stem cells and siRNA-loaded cross-linked gelatin microparticles for bone regeneration

The aim of this study was the evaluation of cross-linked gelatin microparticles (cGM) as substrates for osteogenic cell culture to assemble 3D microtissues and their use as delivery system for siRNA to cells in these assemblies.

In a 2D transwell cultivation system, we found that cGM are capable to accumulate calcium ions from the surrounding medium. Such a separation of cGM and SaOS-2 ​cells consequently led to a suppressed matrix mineral formation in the SaOS-2 culture on the well bottom of the transwell system. Thus, we decided to use cGM as component in 3D microtissues and get a close contact between calcium ion accumulating microparticles and cells to improve matrix mineralization.

Gelatin microparticles were cross-linked with a N,N-diethylethylenediamine-derivatized (DEED) maleic anhydride (MA) containing oligo (pentaerythritol diacrylate monostearate-co-N-isopropylacrylamide-co-MA) (oPNMA) and aggregated with SaOS-2 or human mesenchymal stem cells (hMSC) to microtissue spheroids. We systematically varied the content of cGM in microtissues and observed cell differentiation and tissue formation. Microtissues were characterized by gene expression, ALP activity and matrix mineralization. Mineralization was detectable in microtissues with SaOS-2 ​cells after 7 days and with hMSC after 24–28 days in osteogenic culture. When we transfected hMSC via cGM loaded with Lipofectamine complexed chordin siRNA, we found increased ALP activity and accelerated mineral formation in microtissues in presence of BMP-2. As a model for positive paracrine effects that indicate promising in vivo effects of these microtissues, we incubated pre-differentiated microtissues with freshly seeded hMSC monolayers and found improved mineral formation all over the well in the co-culture model. These findings may support the concept of microtissues from hMSC and siRNA-loaded cGM for bone regeneration.

γ-Tocotrienol induced the proliferation and differentiation of MC3T3-E1 cells through the stimulation of the Wnt/β-catenin signaling pathway

γ-Tocotrienol (γ-T3), an isoprenoid phytochemical, has shown the promotion of osteoblast proliferation and differentiation in our previous study. In this study, its underlying mechanism was investigated through regulating the Wnt/β-catenin signaling pathway in MC3T3-E1 cells. Comparative experiment results showed that γ-T3, not α-tocopherol (α-TOC) increased more significantly the viability and differentiation in MC3T3-E1 cells. After that, the cells were incubated with 10 mM LiCl, or 4 μM γ-T3 with or without 1 μM XAV-939. γ-T3 at 4 μM stimulated the Wnt/β-catenin signaling pathway by increasing the expression and nuclear accumulation of β-catenin, and the expressions of their downstream factors, such as cyclin-D1, c-Myc, BMP2 and BMP-4 in MC3T3-E1 cells. γ-T3 not only upregulated the viability, induced G0/G1 to the S phase, and promoted the expressions of PCNA (Proliferating Cell Nuclear Antigen) and Ki-67, but also increased ALP activity and the expressions of ON, OPN and OCN. Moreover, the effects of γ-T3 on the MC3T3-E1 cells resembled the actions of LiCl, an activator of the Wnt/β-catenin signaling pathway. Notably, all these effects of γ-T3 on the MC3T3-E1 cells were completely blocked by the Wnt/β-catenin signaling pathway inhibitor XAV-939. Our data demonstrated that γ-T3 can target β-catenin to enhance the Wnt/β-catenin signaling pathway, which led to increased expressions of the downstream cell proliferation and cell cycle-associated (cyclin D1 and c-myc), and cell differentiation-associated (BMP-2 and BMP-4) target genes, and ultimately promoted MC3T3-E1 cell proliferation and differentiation. Therefore, γ-T3 may be a potential agent to prevent and reverse osteoporosis due to its safety and powerful abilities of osteogenesis.

3D Printed Multiphasic Scaffolds for Osteochondral Repair: Challenges and Opportunities

Osteochondral (OC) defects are debilitating joint injuries characterized by the loss of full thickness articular cartilage along with the underlying calcified cartilage through to the subchondral bone. While current surgical treatments can provide some relief from pain, none can fully repair all the components of the OC unit and restore its native function. Engineering OC tissue is challenging due to the presence of the three distinct tissue regions. Recent advances in additive manufacturing provide unprecedented control over the internal microstructure of bioscaffolds, the patterning of growth factors and the encapsulation of potentially regenerative cells. These developments are ushering in a new paradigm of 'multiphasic' scaffold designs in which the optimal micro-environment for each tissue region is individually crafted. Although the adoption of these techniques provides new opportunities in OC research, it also introduces challenges, such as creating tissue interfaces, integrating multiple fabrication techniques and co-culturing different cells within the same construct. This review captures the considerations and capabilities in developing 3D printed OC scaffolds, including materials, fabrication techniques, mechanical function, biological components and design.

Bone marrow mesenchymal stem cells with low dose bone morphogenetic protein 2 enhances scaffold-based spinal fusion in a porcine model

High doses bone morphogenetic protein 2 (BMP-2) have resulted in a series of complications in spinal fusion. We previously established a polyelectrolyte complex (PEC) carrier system that reduces the therapeutic dose of BMP-2 in both rodent and porcine spinal fusion models. This study aimed to evaluate the safety and efficacy of the combination of bone marrow mesenchymal stem cells (BMSCs) and low dose BMP-2 delivered by PEC for bone regeneration in a porcine model of anterior lumbar interbody spinal fusion (ALIF) application. Six Yorkshire pigs underwent a tri-segmental (L2/L3; L3/L4; L4/L5) ALIF in four groups, namely: (a) BMSCs + 25 μg BMP-2/PEC (n = 9), (b) 25 μg BMP-2/PEC (n = 3), (c) BMSCs (n = 3), and (d) 50 μg BMP-2/absorbable collagen sponge (n = 3). Fusion outcomes were evaluated by radiography, biomechanical testing, and histological analysis after 12 weeks. Mean radiographic scores at 12 weeks were 2.7, 2.0, 1.0, and 1.0 for Groups 1 to 4, respectively. μ-CT scanning, biomechanical evaluation, and histological analysis demonstrated solid fusion and successful bone regeneration in Group 1. In contrast, Group 2 showed inferior quality and slow rate of fusion, and Groups 3 and 4 failed to fuse any of the interbody spaces. There was no obvious evidence of seroma formation, implant rejection, or any other complications in all groups. The results suggest that the combination of BMSCs and low dose BMP-2/PEC could further lower down the effective dose of the BMP-2 and be used as a bone graft substitute in the large animal ALIF model.

Microenvironment Influences on Human Umbilical Cord Mesenchymal Stem Cell-Based Bone Regeneration

The microenvironment, or niche, regulates stem cell fate and improves differentiation efficiency. Human umbilical cord mesenchymal stem cells (hUC-MSCs) are ideal cell source for bone tissue engineering. However, the role of the microenvironments in hUC-MSC-based bone regeneration is not yet fully understood. This study is aimed at investigating the effects of the in vitro culture microenvironment (hUC-MSCs, nano-hydroxyapatite/collagen/poly (L-lactide) (nHAC/PLA), osteogenic media (OMD), and recombinant human bone morphogenetic protein-7 (rhBMP-7)) and the in vivo transplanted microenvironment (ectopic and orthotopic) on bone regeneration ability of hUC-MSCs. The isolated hUC-MSCs showed self-renewal potential and MSCs' characteristics. In the in vitro two-dimensional culture microenvironment, OMD or OMD with rhBMP-7 significantly enhanced hUC-MSCs' osteocalcin immunofluorescence staining, alkaline phosphatase, and Alizarin red staining; OMD with rhBMP-7 exhibited the highest ALP secretion and mineralized matrix formation. In the in vitro three-dimensional culture microenvironment, nHAC/PLA supported hUC-MSCs' adhesion, proliferation, and differentiation; the microenvironment containing OMD or OMD and rhBMP-7 shortened cell proliferation progression and made osteogenic differentiation progression advance; rhBMP-7 significantly attenuated the inhibiting effect of OMD on hUC-MSCs' proliferation and significantly enhanced the promoting effect of OMD on gene expression and protein secretion of osteogenic differentiation markers, calcium and phosphorous concentration, and mineralized matrix formation. The in vitro three-dimensional culture microenvironment containing OMD and rhBMP-7 induced hUC-MSCs to form the most new bones in ectopic or orthotopic microenvironment as proved by microcomputed tomography and hematoxylin and eosin staining, but bone formation in orthotopic microenvironment was significantly higher than that in ectopic microenvironment. The results indicated that the combination of in vitro hUC-MSCs+nHAC/PLA+OMD+rhBMP-7 microenvironment and in vivo orthotopic microenvironment provided a more optimized niche for bone regeneration of hUC-MSCs. This study elucidates that hUC-MSCs and their local microenvironment, or niche, play an important role in hUC-MSC-based bone regeneration. The endogenously produced BMP may serve an important regulatory role in the process.

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Magnesium ions regulate mesenchymal stem cells population and osteogenic differentiation: A fuzzy agent-based modeling approach

Mesenchymal stem cells (MSCs) are proliferative and multipotent cells that play a key role in the bone regeneration process. Empirical data have repeatedly shown the bioregulatory importance of magnesium (Mg) ions in MSC growth and osteogenesis. In this study, we propose an agent-based model to predict the spatiotemporal dynamics of the MSC population and osteogenic differentiation in response to Mg2+ ions. A fuzzy-logic controller was designed to govern the decision-making process of cells by predicting four cellular processes of proliferation, differentiation, migration, and mortality in response to several important bioregulatory factors such as Mg2+ ions, pH, BMP2, and TGF-β1. The model was calibrated using the empirical data obtained from three sets of cell culture experiments. The model successfully reproduced the empirical observations regarding live cell count, viability, DNA content, and the differentiation-related markers of alkaline phosphate (ALP) and osteocalcin (OC). The simulation results, in agreement with the empirical data, showed that Mg2+ ions within 3-6 mM concentration have the highest stimulation effect on cell population growth. The model also correctly reproduced the stimulatory effect of Mg2+ ions on ALP and its inhibitory effect on OC as the early and late differentiation markers, respectively. Besides, the numerical simulation shed light on the innate cellular differences of the cells cultured in different experiments in terms of the proliferative capacity as well as sensitivity to Mg2+ ions. The proposed model can be adopted in the study of the osteogenesis around Mg-based implants where ions released due to degradation interact with local cells and regulate bone regeneration.

Bone morphogenetic protein 2-induced cellular chemotaxis drives tissue patterning during critical-sized bone defect healing: an in silico study

Critical-sized bone defects are critical healing conditions that, if left untreated, often lead to non-unions. To reduce the risk, critical-sized bone defects are often treated with recombinant human BMP-2. Although enhanced bone tissue formation is observed when BMP-2 is administered locally to the defect, spatial and temporal distribution of callus tissue often differs from that found during regular bone healing or in defects treated differently. How this altered tissue patterning due to BMP-2 treatment is linked to mechano-biological principles at the cellular scale remains largely unknown. In this study, the mechano-biological regulation of BMP-2-treated critical-sized bone defect healing was investigated using a multiphysics multiscale in silico approach. Finite element and agent-based modeling techniques were combined to simulate healing within a critical-sized bone defect (5 mm) in a rat femur. Computer model predictions were compared to in vivo microCT data outcome of bone tissue patterning at 2, 4, and 6 weeks postoperation. In vivo, BMP-2 treatment led to complete healing through periosteal bone bridging already after 2 weeks postoperation. Computer model simulations showed that the BMP-2 specific tissue patterning can be explained by the migration of mesenchymal stromal cells to regions with a specific concentration of BMP-2 (chemotaxis). This study shows how computational modeling can help us to further understand the mechanisms behind treatment effects on compromised healing conditions as well as to optimize future treatment strategies.

Progress in the use of mesenchymal stromal cells for osteoarthritis treatment

LITERATURE REVIEW OF MSCS IN THE TREATMENT OF OSTEOARTHRITIS IN THE PAST FIVE YEARS: Osteoarthritis (OA) is one of the most common chronic joint diseases, with prominent symptoms caused by many factors. However, current medical interventions for OA have resulted in poor clinical outcomes, demonstrating that there are huge unmet medical needs in this area. Cell therapy has opened new avenues of OA treatment. Different sources of mesenchymal stromal cells (MSCs) may have different phenotypes and cellular functions. Pre-clinical and clinical studies have demonstrated the feasibility, safety and efficacy of MSC therapy. Mitogen-activated protein kinase, Wnt and Notch signaling pathways are involved in the chondrogenesis of MSC-mediated treatments. MSCs may also exert effective immunoregulatory and paracrine effects to stimulate tissue repair. Therapy with extracellular vesicles containing cytokines, which are secreted by MSCs, might be a potential treatment for OA.

Adipose tissue-derived stem cells: a comparative review on isolation, culture, and differentiation methods

Adipose tissue-derived stem cells (ADSCs) are an available source of mesenchymal stem cells with the appropriate capacity to in vitro survive, propagate, and differentiate into cells from three lineages of ectoderm, mesoderm, and endoderm. The biological features of ADSCs depend on the donor physiology and health status, isolation procedure, culture conditions, and differentiation protocols used. Adipose tissue samples are provided by surgery and lipoaspiration-based methods and subjected to various mechanical and chemical digestion techniques to finally generate a heterogeneous mixture named stromal vascular fraction (SVF). ADSCs are purified through varied cell populations that exist within SVF and cultured under standard conditions to give rise to a highly rich resource of stem cells directly applied in the clinic or differentiated into a wide range of cells. The development and optimization of conventional isolation, expansion, and differentiation methods seem noteworthy to preserve the desirable biological functions of ADSCs in pre-clinical and clinical investigations.

3-D macro/microporous-nanofibrous bacterial cellulose scaffolds seeded with BMP-2 preconditioned mesenchymal stem cells exhibit remarkable potential for bone tissue engineering

Bone repair using BMP-2 is a promising therapeutic approach in clinical practices, however, high dosages required to be effective pose issues of cost and safety. The present study explores the potential of low dose BMP-2 treatment via tissue engineering approach, which amalgamates 3-D macro/microporous-nanofibrous bacterial cellulose (mNBC) scaffolds and low dose BMP-2 primed murine mesenchymal stem cells (C3H10T1/2 cells). Initial studies on cell-scaffold interaction using unprimed C3H10T1/2 cells confirmed that scaffolds provided a propitious environment for cell adhesion, growth, and infiltration, owing to its ECM-mimicking nano-micro-macro architecture. Osteogenic studies were conducted by preconditioning the cells with 50 ng/mL BMP-2 for 15 min, followed by culturing on mNBC scaffolds for up to three weeks. The results showed an early onset and significantly enhanced bone matrix secretion and maturation in the scaffolds seeded with BMP-2 primed cells compared to the unprimed ones. Moreover, mNBC scaffolds alone were able to facilitate the mineralization of cells to some extent. These findings suggest that, with the aid of 'osteoinduction' from low dose BMP-2 priming of stem cells and 'osteoconduction' from nano-macro/micro topography of mNBC scaffolds, a cost-effective bone tissue engineering strategy can be designed for quick and excellent in vivo osseointegration.

Biomimetic Bilayer Scaffold as an Incubator to Induce Sequential Chondrogenesis and Osteogenesis of Adipose Derived Stem Cells for Construction of Osteochondral Tissue

Toward osteochondral tissue construction, the present study introduced a bilayer scaffold to induce sequential chondrogenesis and osteogenesis of stem cells in vitro. Two scaffolds that are both based on poly(l-glutamic acid) (PLGA) and chitosan (CS) were combined to form the bilayer scaffold. The cartilage region was the covalently cross-linked PLGA/CS hydrogel with a tubular pore structure, possessing a swollen network to prevent cellular adhesion, while inducing spontaneous cellular aggregate formation. The bone region was the electrostatically cross-linked PLGA-grafted nano hydroxyapatite (nHA-g-PLGA)/CS scaffold, which supported cellular adhesion and spreading. Human adipose derived stem cells (hASCs) were seeded into the cartilage region and observed to aggregate, formimg multicellular spheroids, which subsequently fused to rod-like aggregates with a larger size. At the same time, hASCs in aggregates crossed the interface and entered the bone region, presenting adhesion and spreading. With the induction of bone morphogenetic protein 2 (BMP-2) and insulin-like growth factor 1 (IGF-1) during the first 14 days and BMP-2 alone during the last 14 days, hASCs aggregates in the cartilage region underwent chondrogenesis, expressing an abundant cartilage matrix including glycosaminoglycans (GAGs) and type II collagen (COL II) at 28 days. The chondrogenic induced hASCs migrated in the bone region turned to osteogenesis at 28 days, which was associated with their large spreading area and the switch of the induce factor. Thus, the present bilayer scaffold induced the different distribution of hASCs, resulting in subsequent chondrogenesis and osteogenesis, realizing osteochondral tissue construction in vitro.

A bioengineering approach to Schlemm's canal-like stem cell differentiation for in vitro glaucoma drug screening

Human Schlemm's canal (HSC) cells are critical for understanding outflow physiology and glaucoma etiology. However, primary donor cells frequently used in research are difficult to isolate. HSC cells exhibit both vascular and lymphatic markers. Human adipose-derived stem cells (ADSCs) represent a potential source of HSC due to their capacity to differentiate into both vascular and lymphatic endothelial cells, via VEGF-A and VEGF-C. Shear stress plays a critical role in maintaining HSC integrity, function, and PROX1 expression. Additionally, the human trabecular meshwork (HTM) microenvironment could provide cues for HSC-like differentiation. We hypothesize that subjecting ADSCs to VEGF-A or VEGF-C, shear stress, and co-culture with HTM cells could provide biological, mechanical, and cellular cues necessary for HSC-like differentiation. To test this hypothesis, effects of VEGF-A, VEGF-C, and shear stress on ADSC differentiation were examined and compared to primary HSC cells in terms of cell morphology, and HSC marker expression using qPCR, immunoblotting, and immunocytochemistry analysis. Furthermore, the effect of co-culture with HTM cells on porous scaffolds on ADSC differentiation was studied. Treatment with VEGF-C under shear stress is effective in differentiating ADSCs into PROX1-expressing HSC-like cells. Co-culture with HTM cells on porous scaffolds leads to HTM/ADSC-derived HSC-like constructs that regulate through-flow and respond as expected to dexamethasone. STATEMENT OF SIGNIFICANCE: We successfully generated human Schlemm's canal (HSC) like cells from adipocyte-derived stem cells induced by biochemical and biomechanical cues as well as bioengineered human trabecular meshwork (HTM) on micropatterned, porous SU8 scaffolds. These stem cell-derived HSC-like cells co-cultured with HTM cells on SU8 scaffolds can regulate through-flow, and in particular, are responsive to steroid treatment as expected. These findings show that ADSC-derived HSC-like cells have the potential to recreate the ocular outflow pathway for in vitro glaucoma drug screening. To the best of our knowledge, it is the very first time to demonstrate derivation of Schlemm's canal-like cells from stem cells. It provides an important alternative source to primary Schlemm's canal cells that are very difficult to be isolated and cultured from human donors.

Three dimensional (3D) printed polylactic acid with nano-hydroxyapatite doped with europium(III) ions (nHAp/PLLA@Eu3+) composite for osteochondral defect regeneration and theranostics

In the current research previously developed composites composed from poly (l-lactide) (PLLA) and nano-hydroxyapatite (10 wt% nHAp/PLLA) were functionalized with different concentrations of europium (III) (Eu³⁺). The aim of this study was to determine whether Eu³⁺ ions doped within the 10 wt% nHAp/PLLA scaffolds will improve the bioactivity of composites. Therefore, first set of experiments was designed to evaluate the effect of Eu³⁺ ions on morphology, viability, proliferation and metabolism of progenitor cells isolated from adipose tissue (hASC). Three different concentration were tested i.e. 1 mol%, 3 mol% and 5%mol. We identified the 10 wt% nHAp/PLLA@3 mol% Eu³⁺ scaffolds as the most cytocompatible. Further, we investigated the influence of the composites doped with 3 mol% Eu³⁺ ions on differentiation of hASC toward bone and cartilage forming cells. Our results showed that 10 wt% nHAp/PLLA@3 mol% Eu³⁺ scaffolds promotes osteogenesis and chondrogenesis of hASCs what was associated with improved synthesis and secretion of extracellular matrix proteins specific for bone and articular cartilage tissue. We also proved that obtained biomaterials have bio-imaging function and their integration with bone can be monitored using micro computed tomography (μCT).

Effect of Hydroxyapatite Nanorods on the Fate of Human Adipose-Derived Stem Cells Assessed In Situ at the Single Cell Level with a High-Throughput, Real-Time Microfluidic Chip

The fate of stem cells at the single cell level with limited communication with other cells is still unknown due to the lack of an efficient tool for highly accurate molecular detection. Moreover, the conditional sensitivity of biological experiments requires a sufficient number of parallel experiments to support a conclusion. In this work, a microfluidic single cell chip is designed for use with a protein chip to investigate the effect of hydroxyapatite (HAp) on the osteogenic differentiation of human adipose-derived stem cells (hADSCs) in situ at the single cell level. By successfully detecting secretory proteins in situ, it is found that the HAp nanorods enhance osteogenic differentiation at the single cell level. In the chip, the single cell seeding approach confirms the osteogenic differentiation of the hADSCs, which endocytoses HAp, by reducing the influence of the factors secreted by neighboring differentiating cells. Most importantly, more than 7000 microchambers provide a sufficient number of parallel experiments for statistical analysis, which ensure a high level of repeatability of the HAp nanorod-induced osteogenic differentiation. The microfluidic chip comprising single cell culture microchambers with in situ detection capability is a promising tool for research on cell behavior or cell fate at the single cell level.

Exendin‑4 promotes osteogenic differentiation of adipose‑derived stem cells and facilitates bone repair

Inflammation-related bone defects pose a heavy burden on patients and orthopedic surgeons. Although stem-cell-based bone repair has developed rapidly, it is of great significance to characterize bio-active molecules that facilitate bone regeneration. It is reported that a glucagon-like peptide 1 receptor agonist, exendin-4, promoted bone regeneration mediated by the transplantation of adipose-derived stem cells in a metaphyseal defect mouse model of femur injury. However, the underlying mechanism is unclear. Bone imaging, immunohistochemistry real-time PCR and western blot analysis were used in the present study, and the results revealed that exendin-4 increased the transcription of the osteogenic differentiation-related genes and induced osteogenic differentiation in situ. Furthermore, the present data obtained from sorted adipose-derived stem cells revealed that exendin-4 promoted osteogenic differentiation and inhibited adipogenic differentiation in vitro. These findings indicated that exendin-4 facilitates osteogenic differentiation of transplanted adipose-derived stem cells for bone repair and illuminated clinical prospects of both adipose-derived stem cells and exendin-4 in stem-cell-based bone defect repair.

Direct electrical stimulation enhances osteogenesis by inducing Bmp2 and Spp1 expressions from macrophages and preosteoblasts

The capability of electrical stimulation (ES) in promoting bone regeneration has already been addressed in clinical studies. However, its mechanism is still being investigated and discussed. This study aims to investigate the responses of macrophages (J774A.1) and preosteoblasts (MC3T3-E1) to ES and the faradic by-products from ES. It is found that pH of the culture media was not significantly changed, whereas the average hydrogen peroxide concentration was increased by 3.6 and 5.4 µM after 1 and 2 hr of ES, respectively. The upregulation of Bmp2 and Spp1 messenger RNAs was observed after 3 days of stimulation, which is consistent among two cell types. It is also found that Spp1 expression of macrophages was partially enhanced by faradic by-products. Osteogenic differentiation of preosteoblasts was not observed during the early stage of ES as the level of Runx2 expression remains unchanged. However, cell proliferation was impaired by the excessive current density from the electrodes, and also faradic by-products in the case of macrophages. This study shows that macrophages could respond to ES and potentially contribute to the bone formation alongside preosteoblasts. The upregulation of Bmp2 and Spp1 expressions induced by ES could be one of the mechanisms behind the electrically stimulated osteogenesis.

MiR-137 knockdown promotes the osteogenic differentiation of human adipose-derived stem cells via the LSD1/BMP2/SMAD4 signaling network

MicroRNAs are a group of endogenous regulators that participate in several cellular physiological processes. However, the role of miR-137 in the osteogenic differentiation of human adipose-derived stem cells (hASCs) has not been reported. This study verified a general downward trend in miR-137 expression during the osteogenic differentiation of hASCs. MiR-137 knockdown promoted the osteogenesis of hASCs in vitro and in vivo. Mechanistically, inhibition of miR-137 activated the bone morphogenetic protein 2 (BMP2)-mothers against the decapentaplegic homolog 4 (SMAD4) pathway, whereas repressed lysine-specific histone demethylase 1 (LSD1), which was confirmed as a negative regulator of osteogenesis in our previous studies. Furthermore, LSD1 knockdown enhanced the expression of BMP2 and SMAD4, suggesting the coordination of LSD1 in the osteogenic regulation of miR-137. This study indicated that miR-137 negatively regulated the osteogenic differentiation of hASCs via the LSD1/BMP2/SMAD4 signaling network, revealing a new potential therapeutic target of hASC-based bone tissue engineering.

Metformin Augments Anti-Inflammatory and Chondroprotective Properties of Mesenchymal Stem Cells in Experimental Osteoarthritis

Mesenchymal stem cells (MSCs) can protect against cartilage breakdown in osteoarthritis (OA) via their immunomodulatory capacities. However, the optimization strategy for using MSCs remains challenging. This study's objective was to identify the in vivo effects of metformin-stimulated adipose tissue-derived human MSCs (Ad-hMSCs) in OA. An animal model of OA was established by intra-articular injection of monosodium iodoacetate into rats. OA rats were divided into a control group and two therapy groups (treated with Ad-hMSCs or metformin-stimulated Ad-hMSCs). Limb nociception was assessed by measuring the paw withdrawal latency and threshold. Our data show that metformin increased IL-10 and IDO expression in Ad-hMSCs and decreased high-mobility group box 1 protein, IL-1β, and IL-6 expression. Metformin increased the migration capacity of Ad-hMSCs with upregulation of chemokine expression. In cocultures, metformin-stimulated Ad-hMSCs inhibited the mRNA expression of RUNX2, COL X, VEGF, MMP1, MMP3, and MMP13 in IL-1β-stimulated OA chondrocytes and increased the expression of TIMP1 and TIMP3. The antinociceptive activity and chondroprotective effects were greater in OA rats treated with metformin-stimulated Ad-hMSCs than in those treated with unstimulated Ad-hMSCs. TGF-β expression in subchondral bone of OA joints was attenuated more in OA rats treated with metformin-stimulated Ad-hMSCs. Our findings suggest that metformin offers a promising option for the clinical application of Ad-hMSCs as a cell therapy for OA.

Epigallocatechin-3-gallate enhances the osteoblastogenic differentiation of human adipose-derived stem cells

Purpose

The aim of this study is to investigate the effects of epigallocatechin-3-gallate (EGCG), a major polyphenol extracted from green tea, on the osteoblastogenic differentiation of human adipose-derived stem cells (hASCs).

Patients and methods

hASCs were acquired from human adipose tissue. With informed consent, subcutaneous adipose tissue samples were harvested from periorbital fat pad resections from ten healthy female adults who underwent double eyelid surgery. hASCs were cultured in osteogenic medium with or without EGCG (1 μM, 5 μM, or 10 μM) for 14 days. We evaluated the effects of EGCG by quantifying cell growth, ALP activity (an early osteoblastogenic differentiation marker), BSP, OCN (a late osteoblastogenic differentiation marker), and extracellular matrix mineralization. We also performed Western blots to measure osteoblastogenesis-related proteins such as Runx2 and adipoblastogenesis-related transcription factors, such as STAT3, C/EBP-α, and PPAR-γ.

Results

EGCG at 5 μM resulted in significantly higher cell proliferation and ALP activity than did the control on days 3, 7, and 14. On day 7, 5 μM EGCG significantly enhanced BSP expression. On day 14, EGCG at all concentrations promoted OCN expression. In addition, EGCG at 5 μM resulted in the highest level of extracellular matrix mineralization. On day 3, the expression levels of Runx2 were significantly higher in the 5 μM EGCG group than in the other groups, whereas later, on days 7 and 14, Runx2 expression levels in the EGCG group were significantly lower than those of the control group. EGCG at all three concentrations was associated with significantly lower levels of phosphorylated STAT3, C/EBP-α, and PPAR-γ.

Conclusion

EGCG at 5 μM significantly enhanced the osteoblastogenic differentiation of hASCs.

Growth factor sustained delivery from poly-lactic-co-glycolic acid microcarriers and its mass transfer modeling by finite element in a dynamic and static three-dimensional environment bioengineered with stem cells

Poly-lactic-co-glycolic acid (PLGA) microcarriers (0.8 ± 0.2 μm) have been fabricated with a load of 20 μg/g_PLGA by an emulsion-based-proprietary technology to sustained deliver human bone morphogenetic protein 2 (hBMP2), a growth factor largely used for osteogenic induction. hBMP2 release profile, measured in vitro, showed a moderate "burst" release of 20% of the load in first 3 days, followed by a sustained release of 3% of the load along the following 21 days. PLGA microbeads loaded with fluorescent marker (8 mg/g_PLGA ) and hydroxyapatite (30 mg/g_PLGA ) were also fabricated and successfully dispersed within three-dimensional (3D) alginate scaffold (Ca-alginate 2% wt/wt) in a range between 50 and 200 mg/cm³ ; the presence of microcarriers within the scaffold induced a variation of its stiffness between 0.03 and 0.06 MPa; whereas the scaffold surface area was monitored always in the range of 190-200 m² /g. Uniform microcarriers dispersion was obtained up to 200 mg/cm³ ; higher loading values in the 3D scaffold produced large aggregates. The release data and the surface area were, then, used to simulate by finite element modeling the hBMP2 mass transfer within the 3D hydrogel bioengineered with stem cells, in dynamic and static cultivations. The simulation was developed with COMSOL Multiphysics® giving a good representation of hBMP2 mass balances along microbeads (bulk eroded) and on cell surface (cell binding). hBMP2 degradation rate was also taken into account in the simulations. hBMP2 concentration of 20 ng/cm³ was set as a target because it has been described as the minimum effective value for stem cells stimulation versus the osteogenic phenotype. The sensitivity analysis suggested the best microbeads/cells ratio in the 3D microenvironment, along 21 days of cultivations in both static and dynamic cultivation (perfusion) conditions. The simulated formulation was so assembled experimentally using human mesenchymal stem cells and an improved scaffold stiffness up to 0.09 MPa (n = 3; p ≤ 0.01) was monitored after 21 days of cultivation; moreover a uniform extracellular matrix deposition within the 3D system was detected by Von Kossa staining, especially in dynamic conditions. The results indicated that the described tool can be useful for the design of 3D bioengineered microarchitecture by quantitative understanding.

A comparison of human mesenchymal stem cell osteogenesis in poly(ethylene glycol) hydrogels as a function of MMP-sensitive crosslinker and crosslink density in chemically defined medium

This study investigated osteogenesis of human mesenchymal stem cells encapsulated in matrix-metalloproteinase (MMP)-sensitive poly(ethylene glycol) (PEG) hydrogels in chemically defined medium (10 ng/ml bone morphogenic factor-2). Thiol-norbornene photoclick hydrogels were formed with CRGDS and crosslinkers of PEG dithiol (nondegradable), CVPLS-LYSGC (P1) or CRGRIGF-LRTDC (P2; dash indicates cleavage site) at two crosslink densities. Exogenous MMP-2 degraded P1 and P2 hydrogels similarly. MMP-14 degraded P1 hydrogels more rapidly than P2 hydrogels. Cell spreading was greatest in P1 low crosslinked hydrogels and to a lesser degree in P2 low crosslinked hydrogels, but not evident in nondegradable and high crosslinked MMP-sensitive hydrogels. Early osteogenesis (Alkaline phosphatase [ALP] activity) was accelerated in hydrogels that facilitated cell spreading. Contrarily, late osteogenesis (mineralization) was independent of cell spreading. Mineralized matrix was present in P1 hydrogels, but only present in P2 high crosslinked hydrogels and not yet present in nondegradable hydrogels. Overall, the low crosslinked P1 hydrogels exhibited an accelerated early and late osteogenesis with the highest ALP activity (Day 7), greatest calcium content (Day 14), and greatest collagen content (Day 28), concomitant with increased compressive modulus over time. Collectively, this study demonstrates that in chemically defined medium, hydrogel degradability is critical to accelerating early osteogenesis, but other factors are important in late osteogenesis.

3D Printing-Encompassing the Facets of Dentistry

This narrative review presents an overview on the currently available 3D printing technologies and their utilization in experimental, clinical and educational facets, from the perspective of different specialties of dentistry, including oral and maxillofacial surgery, orthodontics, endodontics, prosthodontics, and periodontics. It covers research and innovation, treatment modalities, education and training, employing the rapidly developing 3D printing process. Research-oriented advancement in 3D printing in dentistry is witnessed by the rising number of publications on this topic. Visualization of treatment outcomes makes it a promising clinical tool. Educational programs utilizing 3D-printed models stimulate training of dental skills in students and trainees. 3D printing has enormous potential to ameliorate oral health care in research, clinical treatment, and education in dentistry.

Enhanced biocompatibility and improved osteogenesis of coralline hydroxyapatite modified by bone morphogenetic protein 2 incorporated into a biomimetic coating

OBJECTIVES

(1) To determine whether the biocompatibility of coralline hydroxyapatite (CHA) granules could be improved by using an octacalcium phosphate (OCP) coating layer, and/or functionalized with bone morphogenetic protein 2 (BMP-2), and (2) to investigate if BMP-2 incorporated into this coating is able to enhance its osteoinductive efficiency, in comparison to its surface-adsorbed delivery mode.

METHODS

CHA granules (0.25 g per sample) bearing a coating-incorporated depot of BMP-2 (20 μg/sample) together with the controls (CHA bearing an adsorbed depot of BMP-2; CHA granules with an OCP coating without BMP-2; pure CHA granules) were implanted subcutaneously in rats (n = 6 animals per group). Five weeks later, the implants were retrieved for histomorphometric analysis to quantify the volume of newly generated bone, bone marrow, fibrous tissue and foreign body giant cells (FBGCs). The osteoinductive efficiency of BMP-2 and the rates of CHA degradation were also determined.

RESULTS

The group with an OCP coating-incorporated depot of BMP-2 showed the highest volume and quality or bone, and the highest osteoinductive efficacy. OCP coating was able to reduce inflammatory responses (improve biocompatibility), and also simple adsorption of BMP-2 to CHA achieved this.

CONCLUSIONS

The biocompatibility of CHA granules (reduction of inflammation) was significantly improved by coating with a layer of OCP. Pure surface adsorption of BMP-2 to CHA also reduced inflammation. Incorporation of BMP-2 into the OCP coatings was associated with the highest volume and quality of bone, and the highest biocompatibility degree of the CHA granules.

CLINICAL SIGNIFICANCE

Higher osteoinductivity and improved biocompatibility of CHA can be obtained when a layer of BMP-2 functionalized OCP is deposited on the surfaces of CHA granules.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Enhanced bone morphogenic property of parylene-C

The ability to induce osteointegration was introduced to a parylene-C surface via the simple and intuitive process of protein adsorption mediated by hydrophobic interactions. In this way, bone morphogenetic protein (BMP)-2, fibronectin, and platelet-rich plasma (PRP) could be immobilized on parylene-C surfaces. This approach alleviates concerns related to the use of potentially harmful substances in parylene-C modification processes. The adsorbed protein molecules were quantitatively characterized with respect to adsorption efficacy and binding affinity, and the important biological activities of the proteins were also examined using both early and late markers of osteogenetic activity, including alkaline phosphatase expression, calcium mineralization and marker gene expression. Additionally, the adsorbed PRP exhibited potential as a substitute for expensive recombinant growth factors by effectively inducing comparable osteogenetic activity. In addition to the excellent biocompatibility of parylene-C and its ability to coat a wide variety of substrate materials, the modification of parylene-C via protein adsorption provides unlimited possibilities for installing specific biological functions, expanding the potential applications of this material to include various biointerface platforms.

Emerging Strategies for Stem Cell Lineage Commitment in Tissue Engineering and Regenerative Medicine

Stem cells have transformed the fields of tissue engineering and regenerative medicine, and their potential to further advance these fields cannot be overstated. The stem cell niche is a dynamic microenvironment that determines cell fate during development and tissue repair following an injury. Classically, stem cells were studied in isolation of their microenvironment; however, contemporary research has produced a myriad of evidence that shows the importance of multiple aspects of the stem cell niche in regulating their processes. In the context of tissue engineering and regenerative medicine studies, the niche is an artificial environment provided by culture conditions. In vitro culture conditions may involve coculturing with other cell types, developing specific biomaterials, and applying relevant forces to promote the desired lineage commitment. Considerable advance has been made over the past few years toward directed stem cell differentiation; however, the unspecific differentiation of stem cells yielding a mixed population of cells has been a challenge. In this review, we provide a systematic review of the emerging strategies used for lineage commitment within the context of tissue engineering and regenerative medicine. These strategies include scaffold pore-size and pore-shape gradients, stress relaxation, sonic and electromagnetic effects, and magnetic forces. Finally, we provide insights and perspectives into future directions focusing on signaling pathways activated during lineage commitment using external stimuli.

Revisiting the Advances in Isolation, Characterization and Secretome of Adipose-Derived Stromal/Stem Cells

Adipose-derived stromal/stem cells (ASCs) seems to be a promising regenerative therapeutic agent due to the minimally invasive approach of their harvest and multi-lineage differentiation potential. The harvested adipose tissues are further digested to extract stromal vascular fraction (SVF), which is cultured, and the anchorage-dependent cells are isolated in order to characterize their stemness, surface markers, and multi-differentiation potential. The differentiation potential of ASCs is directed through manipulating culture medium composition with an introduction of growth factors to obtain the desired cell type. ASCs have been widely studied for its regenerative therapeutic solution to neurologic, skin, wound, muscle, bone, and other disorders. These therapeutic outcomes of ASCs are achieved possibly via autocrine and paracrine effects of their secretome comprising of cytokines, extracellular proteins and RNAs. Therefore, secretome-derivatives might offer huge advantages over cells through their synthesis and storage for long-term use. When considering the therapeutic significance and future prospects of ASCs, this review summarizes the recent developments made in harvesting, isolation, and characterization. Furthermore, this article also provides a deeper insight into secretome of ASCs mediating regenerative efficacy.

RhBMP-2 and concomitant rapid material degradation synergistically promote bone repair and regeneration with collagen-hydroxyapatite nanocomposites

The effective treatment of bone defects is still a great challenge in clinical practice. Synthetic bone-grafting substitutes of composition and structure analogous to bone as well as incorporated with growth factors are considered to be a promising solution. In this study, a collagen-hydroxyapatite (CHA) nanocomposite scaffold was developed by collagen self-assembly with simultaneous HA synthesis. The physicochemical properties such as morphology, inorganic phase, thermal decomposition, specific surface area and pore size distribution were characterized. The osteogenicity of CHA in the absence or presence of recombinant human bone morphogenetic protein-2 (rhBMP-2) was assessed both by cell culturing and animal implantation experiments. The gene expression results showed that the osteogenic differentiation capacity of rat bone mesenchymal stem cells (rBMSCs) has been enhanced both by CHA and rhBMP-2. The efficient bone regeneration of femoral defects in rabbits was achieved with CHA and CHA pre-absorbed rhBMP-2 (CHA/B), confirmed by micro-computed tomography measurements, histological observation and immunohistochemical analyses. The CHA nanocomposite was completely degraded within 8 weeks and replaced by new bone. It was found that rhBMP-2 not only accelerated and enhanced bone formation, but also expedited the degradation of CHA. It is believed that the rhBMP-2 and concomitant rapid material degradation synergistically promote bone repair and regeneration with CHA. The biodegradation behavior of CHA in the presence of rhBMP-2 can be further investigated to gain an in-depth understanding of the complex interplays among biomaterials, growth factors and their target cells. The relevant knowledge will facilitate the search for a reasonable, safe and efficient methodology for the introduction of growth factors to biomaterials so as to achieve satisfactory tissue regeneration.

Polylactic Acid Nanopillar Array-Driven Osteogenic Differentiation of Human Adipose-Derived Stem Cells Determined by Pillar Diameter

Numerous studies have determined that physical cues, especially the nanotopography of materials, play key roles in directing stem cell differentiation. However, most research on nanoarrays for stem cell fate regulation is based on nonbiodegradable materials, such as silicon wafers, TiO₂, and poly(methyl methacrylate), which are rarely used as tissue engineering biomaterials. In this study, we prepared biodegradable polylactic acid (PLA) nanopillar arrays with different diameters but the same center-to-center distance using a series of anodic aluminum oxide nanowell arrays as templates. Human adipose-derived stem cells (hADSCs) were selected to investigate the effect of the diameter of PLA nanopillar arrays on stem cell differentiation. By culturing hADSCs without the assistance of any growth factors or osteogenic-induced media, the differentiation tendencies of hADSCs on the nanopillar arrays were assessed at the gene and protein levels. The assessment results suggested that the osteogenic differentiation of hADSCs can be driven by nanopillar arrays, especially by nanopillar arrays with a diameter of 200 nm. Moreover, an in vivo animal model of the samples demonstrated that PLA film with the 200 nm pillar array exhibits an improved ectopic osteogenic ability compared with the planar PLA film after 4 weeks of ectopic implantation. This study has provided a new variable to investigate in the interaction between stem cells and nanoarray structures, which will guide the bone regeneration clinical research field. This work paves the way for the utility of degradable biopolymer nanoarrays with specific geometrical and mechanical signals in biomedical applications, such as patches and strips for spine fusion, bone crack repair, and restoration of tooth enamel.

Identification of satellite cells from anole lizard skeletal muscle and demonstration of expanded musculoskeletal potential

The lizards are evolutionarily the closest vertebrates to humans that demonstrate the ability to regenerate entire appendages containing cartilage, muscle, skin, and nervous tissue. We previously isolated PAX7-positive cells from muscle of the green anole lizard, Anolis carolinensis, that can differentiate into multinucleated myotubes and express the muscle structural protein, myosin heavy chain. Studying gene expression in these satellite/progenitor cell populations from A. carolinensis can provide insight into the mechanisms regulating tissue regeneration. We generated a transcriptome from proliferating lizard myoprogenitor cells and compared them to transcriptomes from the mouse and human tissues from the ENCODE project using XGSA, a statistical method for cross-species gene set analysis. These analyses determined that the lizard progenitor cell transcriptome was most similar to mammalian satellite cells. Further examination of specific GO categories of genes demonstrated that among genes with the highest level of expression in lizard satellite cells were an increased number of genetic regulators of chondrogenesis, as compared to mouse satellite cells. In micromass culture, lizard PAX7-positive cells formed Alcian blue and collagen 2a1 positive nodules, without the addition of exogenous morphogens, unlike their mouse counterparts. Subsequent quantitative RT-PCR confirmed up-regulation of expression of chondrogenic regulatory genes in lizard cells, including bmp2, sox9, runx2, and cartilage specific structural genes, aggrecan and collagen 2a1. Taken together, these data suggest that tail regeneration in lizards involves significant alterations in gene regulation with expanded musculoskeletal potency.

Honing Cell and Tissue Culture Conditions for Bone and Cartilage Tissue Engineering

An avenue of tremendous interest and need in health care encompasses the regeneration of bone and cartilage. Over the years, numerous tissue engineering strategies have contributed substantial progress toward the realization of clinically relevant therapies. Cell and tissue culture protocols, however, show many variations that make experimental results among different publications challenging to compare. This collection surveys prevalent cell sources, soluble factors, culture medium formulations, environmental factors, and genetic modification approaches in the literature. The intent of consolidating this information is to provide a starting resource for scientists considering how to optimize the parameters for cell differentiation and tissue culture procedures within the context of bone and cartilage tissue engineering.

Adipose stem cells for bone tissue repair

Adipose-derived stem/stromal cells (ASCs), together with adipocytes, vascular endothelial cells, and vascular smooth muscle cells, are contained in fat tissue. ASCs, like the human bone marrow stromal/stem cells (BMSCs), can differentiate into several lineages (adipose cells, fibroblast, chondrocytes, osteoblasts, neuronal cells, endothelial cells, myocytes, and cardiomyocytes). They have also been shown to be immunoprivileged, and genetically stable in long-term cultures. Nevertheless, unlike the BMSCs, ASCs can be easily harvested in large amounts with minimal invasive procedures. The combination of these properties suggests that these cells may be a useful tool in tissue engineering and regenerative medicine.