Inhibition of osteoclastogenesis by stem cell-derived extracellular matrix through modulation of intracellular reactive oxygen species

MSCs-Derived Decellularised Matrix: Cellular Responses and Regenerative Dentistry

The decellularised extracellular matrix (dECM) of in vitro cell culture is a naturally derived biomaterial formed by the removal of cellular components. The compositions of molecules in the extracellular matrix (ECM) differ depending on various factors, including the culture conditions. Cell-derived ECM provides a 3-dimensional structure that has a complex influence on cell signalling, which in turn affects cell survival and differentiation. This review describes the effects of dECM derived from mesenchymal stem cells (MSCs) on cell responses, including cell migration, cell proliferation, and cell differentiation in vitro. Published articles were searched in the PubMed databases in 2005 to 2022, with assigned keywords (MSCs and decellularisation and cell culture). The 41 articles were reviewed, with the following criteria. (1) ECM was produced exclusively from MSCs; (2) decellularisation processes were performed; and (3) the dECM production was discussed in terms of culture systems and specific supplementations that are suitable for creating the dECM biomaterials. The dECM derived from MSCs supports cell adhesion, enhances cell proliferation, and promotes cell differentiation. Importantly, dECM derived from dental MSCs shows promise in regenerative dentistry applications. Therefore, the literature strongly supports cell-based dECMs as a promising option for innovative tissue engineering approaches for regenerative medicine.

Decellularized extracellular matrix biomaterials for regenerative therapies: Advances, challenges and clinical prospects

Tissue engineering and regenerative medicine have shown potential in the repair and regeneration of tissues and organs via the use of engineered biomaterials and scaffolds. However, current constructs face limitations in replicating the intricate native microenvironment and achieving optimal regenerative capacity and functional recovery. To address these challenges, the utilization of decellularized tissues and cell-derived extracellular matrix (ECM) has emerged as a promising approach. These biocompatible and bioactive biomaterials can be engineered into porous scaffolds and grafts that mimic the structural and compositional aspects of the native tissue or organ microenvironment, both in vitro and in vivo. Bioactive dECM materials provide a unique tissue-specific microenvironment that can regulate and guide cellular processes, thereby enhancing regenerative therapies. In this review, we explore the emerging frontiers of decellularized tissue-derived and cell-derived biomaterials and bio-inks in the field of tissue engineering and regenerative medicine. We discuss the need for further improvements in decellularization methods and techniques to retain structural, biological, and physicochemical characteristics of the dECM products in a way to mimic native tissues and organs. This article underscores the potential of dECM biomaterials to stimulate in situ tissue repair through chemotactic effects for the development of growth factor and cell-free tissue engineering strategies. The article also identifies the challenges and opportunities in developing sterilization and preservation methods applicable for decellularized biomaterials and grafts and their translation into clinical products.

Extracellular derivatives for bone metabolism

BACKGROUND

Bone metabolism can maintain the normal homeostasis and function of bone tissue. Once the bone metabolism balance is broken, it will cause osteoporosis, osteoarthritis, bone defects, bone tumors, or other bone diseases. However, such orthopedic diseases still have many limitations in clinical treatment, such as drug restrictions, drug tolerance, drug side effects, and implant rejection.

AIM OF REVIEW

In complex bone therapy and bone regeneration, extracellular derivatives have become a promising research focus to solve the problems of bone metabolic diseases. These derivatives, which include components such as extracellular matrix, growth factors, and extracellular vesicles, have significant therapeutic potential. It has the advantages of good biocompatibility, low immune response, and dynamic demand for bone tissue. The purpose of this review is to provide a comprehensive perspective on extracellular derivatives for bone metabolism and elucidate the intrinsic properties and versatility of extracellular derivatives. Further discussion of them as innovative advanced orthopedic materials for improving the effectiveness of bone therapy and regeneration processes.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, we first listed the types and functions of three extracellular derivatives. Then, we discussed the effects of extracellular derivatives of different cell sources on bone metabolism. Subsequently, we collected applications of extracellular derivatives in the treatment of bone metabolic diseases and summarized the advantages and challenges of extracellular derivatives in clinical applications. Finally, we prospected the extracellular derivatives in novel orthopedic materials and clinical applications. We hope that the comprehensive understanding of extracellular derivatives in bone metabolism will provide new solutions to bone diseases.

The Preparation and Effects of Organic-Inorganic Antioxidative Biomaterials for Bone Repair

Reactive oxygen species (ROS) has great influence in many physiological or pathological processes in organisms. In the site of bone defects, the overproduced ROS significantly affects the dynamic balance process of bone regeneration. Many antioxidative organic and inorganic antioxidants showed good osteogenic ability, which has been widely used for bone repair. It is of great significance to summarize the antioxidative bone repair materials (ABRMs) to provide guidance for the future design and preparation of osteogenic materials with antioxidative function. Here, this review introduced the major research direction of ABRM at present in nanoscale, 2-dimensional coating, and 3-dimensional scaffolds. Moreover, the referring main active substances and antioxidative properties were classified, and the positive roles of antioxidative materials for bone repair have also been clearly summarized in signaling pathways, antioxidant enzymes, cellular responses and animal levels.

Photothermal extracellular matrix based nanocomposite films and their effect on the osteogenic differentiation of BMSCs

Mild thermal stimulation in vivo could induce osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). In this study, nano-functionalized photothermal extracellular matrix (ECM) nanocomposite films were obtained through adding graphene during cell culture, so that graphene could directly integrate with the ECM secreted by cells. Owing to the similarity of the ECM to the in vivo microenvironment and the apparent photothermal effect of graphene nanoflakes, heat could be generated and transferred at the material-cell interface in a biomimetic way. It was demonstrated that such nanocomposite films achieved an interface temperature rise with light illumination. This could be easily sensed by BMSCs through the ECM. According to alkaline phosphatase, osteogenic related gene expression, mineral deposition, and upregulated expression of heat shock protein (HSP70) and p-ERK, composite films with proper illumination significantly promoted the differentiation of BMSCs into osteoblasts. This work endeavors to study the thermal regulation of BMSC differentiation and provide a new perspective on biocompatible osteo-implant materials which can be remotely controlled.

Rapid formation of 3D: Decellularized extracellular matrix spheroids for enhancing bone formation

Bone marrow mesenchymal stem cell sheet-derived spheroids (BMSCs spheroids) have been widely studied as native bioactive scaffolds. However, the abundant cells in BMSCs spheroids cause immunogenicity and make them difficult to store. This paper aimed to construct a new bioactive scaffold called 3D-decellularized extracellular matrix spheroids (ECM spheroids) via decellularization of BMSCs spheroids to enhance bone formation. Hematoxylin and eosin staining (HE), nuclear and cytoskeletal fluorescence, immunofluorescence (IF), and scanning electron microscopy (SEM) were utilized to detect the characteristics and components of ECM spheroids. Furthermore, the biological properties of migration, adhesion, and recellularization of cells in ECM spheroids were assessed in vitro, and bone formation was evaluated in rat calvarial defects. The results showed that both the nuclei and cytoskeleton in ECM spheroids were greatly altered and one of the major components of FN was intact. The migration, adhesion, and recellularization potential were improved in vitro. Meanwhile, ECM spheroids promoted osteogenesis in rat skull defects after 3 months (p < .01). In conclusion, ECM spheroids were successfully prepared and proven to promote cell migration, adhesion, and proliferation. Bone formation in vivo was also accelerated. We believe that ECM spheroids can be used as bioactive and biocompatible 3D scaffolds in the future.

Melatonin Prevents Cartilage Degradation in Early-Stage Osteoarthritis Through Activation of miR-146a/NRF2/HO-1 Axis

Reactive oxygen species (ROS) are implicated in induction of inflammatory response and cartilage degradation in osteoarthritis (OA). Melatonin has been shown to improve the chondrogenic differentiation and promote cartilage matrix synthesis in mesenchymal stem cells. However, the underlying mechanisms of melatonin-regulated antioxidant activity in OA cartilage are not known. The aim of this study was to explore the effect of melatonin on nuclear factor-erythroid 2-related factor 2 (NRF2), a key antioxidant transcription factor, and its target antioxidant genes in early-stage OA cartilage. Primary chondrocytes were isolated from rats with surgically induced OA. In vitro treatment of melatonin significantly increased cartilage matrix synthesis and upregulated antioxidant enzymes, mainly heme oxygenase 1 (HO-1), while decreasing matrix degradation enzymes and intracellular ROS. In vivo intraarticular injection of melatonin effectively ameliorated cartilage degeneration in an experimental rat OA model. Inhibition of melatonin membrane receptors by Luzindole or 4-P-PDOT reversed the beneficial effects of melatonin on cartilage matrix synthesis, implying that melatonin receptor-mediated pathway is involved in its anti-arthritic effects. Interestingly, melatonin showed no significant effect on the mRNA level of Nrf2 but significantly increased its protein level. Silencing of Nrf2 or HO-1 expression abolished the protective effects of melatonin, as shown by increased ROS levels and matrix degradation enzyme expression. Microarray assays revealed that miR-146a, a predicted target for Nrf2, was significantly upregulated in OA chondrocytes but was markedly reduced by melatonin treatment. Overexpression of miR-146a diminished the protective effects of melatonin by inhibiting NRF2 expression and aggravating OA-induced cartilage degradation. These findings demonstrate that melatonin supports the anabolic metabolism of cartilage matrix in OA chondrocytes by enhancing the protein levels of NRF2 via suppressing miR-146a. Melatonin-mediated activation of the NRF2/HO-1 axis prevents cartilage degeneration and represents a promising therapeutic target for treatment of early-stage OA. © 2022 American Society for Bone and Mineral Research (ASBMR).

Puerarin alleviates cadmium-induced oxidative damage to bone by reducing autophagy in rats

Autophagy is a regulatory mechanism involved in cadmium (Cd)-induced bone toxicity and is suppressed by various stimuli, including oxidative stress. Puerarin is an isoflavonoid compound isolated from Pueraria, a plant used in traditional Chinese medicine. The underlying mechanisms of action of puerarin remain unclear. The objective of this study was to explore the mitigating effects of puerarin on cadmium-induced oxidative damage in the bones of rats. Cadmium exposure increased oxidative damage in rat bones; this was markedly decreased by puerarin treatment, as demonstrated by changes in the activity of antioxidative enzymes. Cadmium-induced blockage of the expression of key bone regulatory proteins, autophagy-related markers, and signaling molecules was also alleviated by puerarin treatment. Additionally, cadmium reduced expression of the autophagic protein Rab7 and of late endosomal/lysosomal adaptor and MAPK and mTOR activator 1 (LAMTOR1); the decrease in these proteins was not restored by puerarin treatment. We speculate that puerarin relieves the inhibition of fusion of autophagosomes with lysosomes that is induced by cadmium; however, this specific effect of puerarin and downstream effects on bone regulatory mechanisms require further investigation. In conclusion, puerarin alleviates cadmium-induced oxidative damage in the bones of rats by attenuating autophagy, which is likely associated with the antioxidant activity of puerarin.

Bortezomib Rescues Ovariectomy-Induced Bone Loss via SMURF-Mediated Ubiquitination Pathway

A balance between bone formation by osteoblasts and bone resorption by osteoclasts is necessary to maintain bone health and homeostasis. As a cancer of plasma cells, multiple myeloma (MM) is accompanied with rapid bone loss and fragility fracture. Bortezomib has been used as a first-line for treating MM for decades. Recently, the potential protection of bortezomib on osteoporosis (OP) is reported; however, the specific mechanism involving bortezomib-mediated antiosteoporotic effect is undetermined. In the present study, we assessed the effects of in vitro bortezomib treatment on osteogenesis and osteoclastogenesis and the protective effect on bone loss in ovariectomized (OVX) mice. Our results indicated that bortezomib treatment increased osteogenic differentiation of MC3T3-E1 cells as evidenced by increased levels of matrix mineralization and osteoblast-specific markers. In bortezomib-treated bone marrow monocytes (BMMs), osteoclast differentiation was suppressed, substantiated by downregulated tartrate-resistant acid phosphatase- (TRAP-) positive multinucleated cells, areas of actin rings, pit formation, and osteoclast-specific genes. Mechanistically, bortezomib exerted a protective effect against OP through the Smad ubiquitination regulatory factor- (SMURF-) mediated ubiquitination pathway. Furthermore, in vivo intraperitoneal injection of bortezomib attenuated the bone microarchitecture in OVX mice. Accordingly, our findings corroborated that bortezomib might have future applications in the treatment of postmenopausal OP.

Stem cells immortalized by hTERT perform differently from those immortalized by SV40LT in proliferation, differentiation, and reconstruction of matrix microenvironment

Although matrix microenvironment has the potential to improve expanded stem cell proliferation and differentiation capacity, decellularized extracellular matrix (dECM) deposited by senescent cells does not contribute to the rejuvenation of adult stem cells, which has become a barrier to personalized stem cell therapy. Genetic modification is an effective strategy to protect cells from senescence but it carries the increased risk of malignant transformation and genetic instability. In this study, lentivirus carrying either human telomerase reverse transcriptase (hTERT) or simian virus 40 large T antigen (SV40LT) was used to transduce human infrapatellar fat pad-derived stem cells (IPFSCs). We found that virus transduction modified the proliferative, chondrogenic, and adipogenic abilities of IPFSCs. Interestingly, dECM deposited by immortalized cells significantly influenced replicative senescent IPFSCs in proliferation and differentiation preference, the effect of which is hinged on the approach of immortalization using either SV40LT or hTERT. Our findings indicate both dECM expansion and immortalization strategies can be used for replicative senescent adult stem cells' proliferation and lineage-specific differentiation, which benefits future stem cell-based tissue regeneration. This approach may also work for adult stem cells with premature senescence in elderly/aged patients, which needs further investigation. STATEMENT OF SIGNIFICANCE: Adult stem cells are a promising solution for autologous cell-based therapy. Unfortunately, cell senescence due to donor age and/or ex vivo expansion prevents clinical application. Recent progress with decellularized extracellular matrix provides a potential for the rejuvenation of senescent stem cells by improving their proliferation and differentiation capacities. Given the fact that the young matrix can provide a healthy and energetic microenvironment, in this study, two approaches using lentivirus transduction of hTERT and SV40LT were compared. The goal was to immortalize donor cells for deposition of decellularized extracellular matrix. The matrix was demonstrated to contribute diverging effects on the chondrogenic and adipogenic differentiation of expanded stem cells and exhibited proliferation benefits as well. These findings provide an invaluable asset for stem cell-based tissue regeneration.

Programmed core-shell electrospun nanofibers to sequentially regulate osteogenesis-osteoclastogenesis balance for promoting immediate implant osseointegration

The biology of immediate post-extraction implant osseointegration is mediated by a coordinated cascade of osteoblast-osteoclast interactions. The aim of this study was to develop a dual-delivery system that allowed sequential release of substance P (SP) to promote bone regeneration and alendronate (ALN) to reduce bone resorption, which will improve the implant osseointegration. We used coaxial electrospinning to fabricate the core-shell poly lactic-co-glycolic acid (PLGA)/gelatin nanofibers, which consists of SP in the shell and ALN in the core. This programmed delivery system was shown to release SP and ALN sequentially to match the spatio-temporal specificity of bone healing. The migration assay demonstrated that the SP-ALN dual-delivery system increased bone marrow mesenchymal stem cells (BMSCs) transmigration. Besides, the expression of osteogenic/osteoclastic markers, Alizarin Red staining, tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining and bone resorption experiment showed that the dual-delivery system can render a microenvironment favorable for osteogenic differentiation and adverse to osteoclastogenesis. Using a rat immediate implant model, we validated the promoted osteogenic property and osseointegration around the implants of SP-ALN dual-delivery system by micro-computed tomography (micro-CT) and histological analysis. These findings suggest that the dual-delivery system with time-controlled release of SP and ALN by core-shell nanofibers provides a promising strategy to facilitate immediate implant osseointegration through favorable osteogenesis. STATEMENT OF SIGNIFICANCE: Immediate implant placement is potentially challenged by the difficulties in achieving primary implant stability and early osteogenesis. Initial period of osteointegration is regulated by osteoblastic/osteoclastic cells resulting in a coordinated healing process. To have an efficient bone regeneration, the coaxial electrospinning was used to fabricate a programmed dual-delivery system. The SP released rapidly and favored for BMSCs migration and osteogenic differentiation, while the sustained release of ALN can reduce the bone resorption. The rat immediate implant model indicated that the SP-ALN dual-delivery system could present the promoted peri‑implant osteogenic property and osseointegration through modulating the osteogenesis-osteoclastogenesis balance. This work highlights the sequential dual delivery of SP and ALN has a promising potential of achieving enhanced osseointegration for immediate implant placement.

Inhibitory Effects of Combined Bone Morphogenetic Protein 2, Vascular Endothelial Growth Factor, and Basic Fibroblast Growth Factor on Osteoclast Differentiation and Activity

Bone morphogenetic protein 2 (BMP-2), vascular endothelial growth factor (VEGF), and basic fibroblast growth factors (bFGF) are important regulators of bone development and bone remodeling involving the coordination of osteoblast-mediated bone formation and osteoclast-mediated bone resorption. The synergistic promotions of these growth factors on osteogenesis in the appropriate combination have been confirmed by a lot of studies, but the effect of this combined application on osteoclastogenesis still remains ambiguous. On the basis of comparing the osteoclastic potentials under stimulation of BMP-2, VEGF, or bFGF alone, this study focused on their combined effects on the differentiation and activity of osteoclasts. Our results showed that osteoclastogenesis was enhanced to some extent under the stimulation of BMP-2, VEGF, or bFGF alone, and the potential of these three growth factors to stimulate osteoclastogenesis was VEGF > BMP-2 > bFGF. However, the treatment with the combination of BMP-2 (50 ng/mL), VEGF (1 ng/mL), and bFGF (10 ng/mL), the most suitable dose combination for osteogenesis optimized in our previous study, weakened osteoclast differentiation confirmed by smaller tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, lower TRAP activity, and lower expression of dendritic cell-specific transmembrane protein, an important molecule regulating osteoclast fusion. Moreover, BMP-2, VEGF, and bFGF in combination also moderately inhibited the bone-resorbing activity of mature osteoclasts by suppressing the expression of osteoclast-specific genes cathepsin K, and matrix metalloproteinase-9. The underlying molecular mechanisms involved the suppression of the receptor activator of nuclear factor-κB ligand-induced c-Fos levels and the activation of nuclear factor of activated T cells c1, two major transcription factors in osteoclast differentiation. Taken together, our study showed that the combination of BMP-2 (50 ng/mL), VEGF (1 ng/mL), and bFGF (10 ng/mL) promoted osteoblastogenesis but inhibited osteoclastogenesis. Thus, the simultaneous use of BMP-2 (50 ng/mL), VEGF (1 ng/mL), and bFGF (10 ng/mL) in an appropriate combination might improve efficacious bone regeneration in a clinical setting. Impact statement Few studies have addressed the combined effects of multiple growth factors on osteoclasts. This study demonstrated that the simultaneous use of bone morphogenetic protein 2 (BMP-2; 50 ng/mL), vascular endothelial growth factor (VEGF; 1 ng/mL), and basic fibroblast growth factors (bFGF; 10 ng/mL), the most suitable dose combination for osteogenesis optimized in our previous study, showed inhibitory effects on the differentiation and activity of osteoclasts. Our results suggest that the growth factor signaling pathways in osteoclasts may interact with each other. Furthermore, this study could provide new insights into the optimal application of BMP-2, VEGF, and bFGF for bone repair and regeneration.

Macrophage-Mediated Bone Formation in Scaffolds Modified With MSC-Derived Extracellular Matrix Is Dependent on the Migration Inhibitory Factor Signaling Pathway

The positive role of macrophages in the osteogenesis of mesenchymal stem cells (MSCs) has been a recent research focus. On the other hand, MSCs could carefully regulate the paracrine molecules derived from macrophages. Human umbilical cord mesenchymal stem cells (hucMSCs) can reduce the secretion of inflammatory factors from macrophages to improve injury healing. hucMSC-derived extracellular matrix (hucMSC-ECM) has the similar effect to hucMSCs, which could combat the inflammatory response of macrophages. Additionally, MSC-derived extracellular matrix also enhanced bone regeneration by inhibiting osteoclastic differentiation of monocyte/macrophage lineage. However, whether hucMSC-ECM could improve bone formation by guiding macrophage-induced osteogenic differentiation of MSCs is unknown. Here, we present decalcified bone scaffolds modified by hucMSC-derived extracellular matrix (DBM-ECM), which maintained multiple soluble cytokines from hucMSCs, including macrophage migration inhibitory factor (MIF). Compared with DBM, the DBM-ECM scaffolds induced bone formation in an improved heterotopic ossification model of severe combined immunodeficiency (SCID) mice in a macrophage-dependent manner. Macrophages cocultured with DBM-ECM expressed four osteoinductive cytokines (BMP2, FGF2, TGFβ3 and OSM), which were screened out by RNA sequencing and measured by qPCR and western blot. The conditioned medium from macrophages cocultured with DBM-ECM improved the osteogenic differentiation of hBMSCs. Furthermore, DBM-ECM activated CD74/CD44 (the typical MIF receptors) signal transduction in macrophages, including phosphorylation of P38 and dephosphorylation of c-jun. On the other side, the inhibitory effects of the DBM-ECM scaffolds with a deficient of MIF on osteogenesis in vitro and in vivo revealed that macrophage-mediated osteogenesis depended on MIF/CD74 signal transduction. The results of this study indicate that the coordinated crosstalk of macrophages and MSCs plays a key role on bone regeneration, with an emphasis on hucMSC-ECM constructing a macrophage-derived osteoinductive microenvironment.

Controlled release of dopamine coatings on titanium bidirectionally regulate osteoclastic and osteogenic response behaviors

Bone diseases, for example, osteoporosis, cause excessive differentiation of osteoclasts and decreased bone formation, resulting in imbalance of bone remodeling and poor osseointegration, which can be considered a relative contraindication for titanium implants. Dopamine (DA) might provide a solution to this problem by inhibiting osteoclasts and promoting osteoblasts at different concentrations. However, current commercial implants cannot load bone-active molecules, such as DA. Therefore, this study aimed to develop a surface modification method for implants to achieve a controlled release of DA and enhance the resistance of titanium implants to bone resorption and bone regeneration. DA-loaded alginate-arginine-glycine-aspartic acid (RGD) (AlgR) coatings on a vaterite-modified titanium surface were successfully assembled, which continuously and steadily released DA. In vitro studies have shown that materials showing good biocompatibility can not only inhibit receptor activator of nuclear factor-kappa B (NFκB) ligand (RANKL)-induced osteoclastogenesis but also enhance the adhesion and osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs). The optimal DA-loaded concentration of this bidirectional regulation is 100 μM. Interestingly, DA more effectively attenuated osteoclastogenesis when released in a sustained manner from titanium coatings than it did via traditional, free administration, and the alginate-RGD coating and DA clearly exhibited great synergy. This study provides a design of titanium implant surface modification to improve bone remodeling around implants.

The Role of Osteoclast Energy Metabolism in the Occurrence and Development of Osteoporosis

In recent decades, the mechanism underlying bone metabolic disorders based on energy metabolism has been heavily researched. Bone resorption by osteoclasts plays an important role in the occurrence and development of osteoporosis. However, the mechanism underlying the osteoclast energy metabolism disorder that interferes with bone homeostasis has not been determined. Bone resorption by osteoclasts is a process that consumes large amounts of adenosine triphosphate (ATP) produced by glycolysis and oxidative phosphorylation. In addition to glucose, fatty acids and amino acids can also be used as substrates to produce energy through oxidative phosphorylation. In this review, we summarize and analyze the energy-based phenotypic changes, epigenetic regulation, and coupling with systemic energy metabolism of osteoclasts during the development and progression of osteoporosis. At the same time, we propose a hypothesis, the compensatory recovery mechanism (involving the balance between osteoclast survival and functional activation), which may provide a new approach for the treatment of osteoporosis.

Extracellular Matrix: Emerging Roles and Potential Therapeutic Targets for Breast Cancer

Increasing evidence shows that the extracellular matrix (ECM) is an important regulator of breast cancer (BC). The ECM comprises of highly variable and dynamic components. Compared with normal breast tissue under homeostasis, the ECM undergoes many changes in composition and organization during BC progression. Induced ECM proteins, including fibrinogen, fibronectin, hyaluronic acid, and matricellular proteins, have been identified as important components of BC metastatic cells in recent years. These proteins play major roles in BC progression, invasion, and metastasis. Importantly, several specific ECM molecules, receptors, and remodeling enzymes are involved in promoting resistance to therapeutic intervention. Additional analysis of these ECM proteins and their downstream signaling pathways may reveal promising therapeutic targets against BC. These potential drug targets may be combined with new nanoparticle technologies. This review summarizes recent advances in functional nanoparticles that target the ECM to treat BC. Accurate nanomaterials may offer a new approach to BC treatment.

Effects of varying gelatin coating concentrations on RANKL induced osteoclastogenesis

Here, we assessed the effects of varying concentrations of gelatin coating on Receptor Activator of Nuclear Factor κ-B Ligand (RANKL)-induced RAW264.7 murine macrophage differentiation into osteoclast (OC) via osteoclastogenesis. The microstructures of coating surfaces with different concentrations of gelatin were examined by scanning electron microscopy and atomic force microscopy. Increased gelatin coating concentrations led to decreased gel rigidity but increased surface adhesion force attenuated OC differentiation and the decreased actin ring formation in RANKL-induced osteoclastogenesis. The decreased actin ring formation is associated with decreased lysosomal-associated membrane protein 1 (LAMP1) activity and bone resorption in the differentiated OCs with different gelatin coating concentrations as compared to the cells differentiated without gelatin coatings. In addition, increasing concentrations of gelatin coating attenuated the medium TGF-β1 protein levels and the expression levels of TGF-β and type-I (R1) and type-II (R2) TGF-β receptors in OCs, suggesting the gelatin-induced suppression of TGF-β signaling for the regulation of RNAKL-induced OC differentiation. Taken together, these findings showed that changes in gelatin coating concentrations, which were associated with altered gel thickness and substrate rigidity, might attenuate TGF-β signaling events to modulate OC differentiation and concomitant actin ring formation and bone matrix resorption in RANKL-induced osteoclastogenesis.

Mesenchymal stem cell-derived extracellular matrix (mECM): a bioactive and versatile scaffold for musculoskeletal tissue engineering

Mesenchymal stem cell-derived extracellular matrix (mECM) has received increased attention in the fields of tissue engineering and scaffold-assisted regeneration. mECM exhibits many unique characteristics, such as robust bioactivity, biocompatibility, ease of use, and the potential for autologous tissue engineering. As the use of mECM has increased in musculoskeletal tissue engineering, it should be noted that mECM generated from current methods has inherited insufficiencies, such as low mechanical properties and lack of internal architecture. In this review, we first summarize the development and use of mECM as a scaffold for musculoskeletal tissue regeneration and highlight our current progress on moving this technology toward clinical application. Then we review recent methods to improve the properties of mECM that will overcome current weaknesses. Lastly, we propose future studies that will pave the road for mECM application in regenerating tissues in humans.

Therapeutic Potential of Reactive Oxygen Species: State of the Art and Recent Advances

In the last decade, several studies have proven that when at low concentration reactive oxygen species (ROS) show an adaptive beneficial effect and posited the idea that they can be utilized as inexpensive and convenient inducers of tissue regeneration. On the other hand, the recent discovery that cancer cells are more sensitive to oxidative damage paved the way for their use in the selective killing of tumor cells, and sensors to monitor ROS production during cancer treatment are under extensive investigation. Nevertheless, although ROS-activated signaling pathways are well established, less is known about the mechanisms underlying the switch from an anabolic to a cytotoxic response. Furthermore, a high variability in biological response is observed between different modalities of administration, cell types, donor ages, eventual concomitant diseases, and external microenvironment. On the other hand, available preclinical studies are scarce, whereas the quest for the most suitable systems for in vivo delivery is still elusive. Furthermore, new strategies to control the temporal pattern of ROS release need to be developed, if considering their tumorigenic potential. This review initially discusses ROS mechanisms of action and their potential application in stem cell biology, tissue engineering, and cancer therapy. It then outlines the state of art of ROS-based drugs and identifies challenges faced in translating ROS research into clinical practice.

The role of cystatin C as a proteasome inhibitor in multiple myeloma

Objectives: Bone destruction and renal impairment are two frequent complications of multiple myeloma (MM). Cystatin C, an extracellular cysteine proteinase inhibitor, is encoded by the housekeeping gene CST3 and associated with human tumors. The role of cystatin C in multiple myeloma has been revealed recently. The purpose of this study was to explore the role of cystatin C as a proteasome inhibitor in multiple myeloma. Methods : A comprehensive literature review was conducted through Pubmed to summarize the published evidence on cystatin C in multiple myeloma. English literature sources since 1999 were searched, using the terms cystatin C, multiple myeloma. Results: cystatin C is a sensitive indicator for the diagnosis of myeloma nephropathy and has a dual role in myeloma bone disease. Also, cystatin C reflects tumor burden and is strongly associated with prognosis in patients with multiple myeloma. Conclusion: Cystatin C have great diagnostic and prognostic value in multiple myeloma. It can provide a new treatment direction for MM by designing and searching for antagonists of cystatin C or cysteine protease agonists using cystatin C as a therapeutic target.

Puerarin alleviates osteoporosis in the ovariectomy-induced mice by suppressing osteoclastogenesis via inhibition of TRAF6/ROS-dependent MAPK/NF-κB signaling pathways

In this study, we investigated the mechanisms by which puerarin alleviates osteoclast-related loss of bone mass in ovariectomy (OVX)-induced osteoporosis model mice. Puerarin-treated OVX mice exhibited higher bone density, fewer tartrate-resistant acid phosphatase (TRAcP)-positive osteoclasts, and levels of lower reactive oxygen species (ROS) within bone tissues than vehicle-treated OVX mice. Puerarin suppressed in vitro osteoclast differentiation, hydroxyapatite resorption activity, and expression of osteoclastogenesis-related genes, such as NFATc1, MMP9, CTSK, Acp5 and c-Fos, in RANKL-induced bone marrow macrophages (BMMs) and RAW264.7 cells. It also reduced intracellular ROS levels by suppressing expression of TRAF6 and NADPH oxidase 1 (NOX1) and increasing expression of antioxidant enzymes such as heme oxygenase-1 (HO-1). Puerarin inhibited TRAF6/ROS-dependent activation of the MAPK and NF-κB signaling pathways in RANKL-induced RAW264.7 cells, and these effects were partially reversed by HO-1 silencing or TRAF6 overexpression. These findings suggest puerarin alleviates loss of bone mass in the OVX-model mice by suppressing osteoclastogenesis via inhibition of the TRAF6/ROS-dependent MAPK/NF-κB signaling pathway.

Human Umbilical Cord Mesenchymal Stem Cell-induced Osterix, Bone Morphogenetic Protein-2, and Tartrate-resistant Acid Phosphatase Expression in Osteoporotic Mandibular Bone

OBJECTIVES

 The aim of this study was to prove that human umbilical cord mesenchymal stem cell (hUCMSC) therapy conducted according to the mandibular osteoporotic model will increase Osterix (Osx) and bone morphogenetic protein-2 (BMP-2) expression, while reducing tartrate-resistant acid phosphatase (TRAP) expression. PKH26 labeling proves that mandibular bone regeneration is produced by hUCMSCs induction.

MATERIALS AND METHODS

 This study incorporated a true posttest only control group design. Twenty-five female Wistar rats were randomly divided into five groups consisting of the sham surgery (N) group, osteoporotic groups injected with gelatin for 4 weeks (G4) and 8 weeks (G8), and osteoporotic groups injected with hUCMSC-gelatin for 4weeks (SC4) and 8 weeks (SC8). All subjects were provided for BMP-2, Osx, and TRAP on immunohistochemistry examination and PKH-26 labeling.

STATISTICAL ANALYSIS

 All data were analyzed using ANOVA and Tukey HSD tests with p < 0.05 being considered as statistically significant.

RESULTS

 Compared with other groups, the highest level of BMP-2 and Osx occurred in the sham surgery (N) and osteoporotic groups injected with hUCMSCs-gelatin (SC), while the lowest level of TRAP was found in SC4. During 4- and 8-week observation periods, the PKH 26 appeared green (fluorescent).

CONCLUSIONS

 hUCMSC demonstrates high-osteogenic activity and increased osteoporotic mandibular bone regeneration, as shown by increased expression of Osx and BMP-2 and decreased TRAP expression. From the labeling, PKH-26 proved that viable hUCMSCs in gelatin solvent can be present in the mandibular bone and be capable of promoting osteogenic differentiation and increasing mineralization and bone formation in the osteoporotic mandibular bone.

Energy metabolism: A newly emerging target of BMP signaling in bone homeostasis

Energy metabolism is the process of generating energy (i.e. ATP) from nutrients. This process is indispensable for cell homeostasis maintenance and responses to varying conditions. Cells require energy for growth and maintenance and have evolved to have multiple pathways to produce energy. Both genetic and functional studies have demonstrated that energy metabolism, such as glucose, fatty acid, and amino acid metabolism, plays important roles in the formation and function of bone cells including osteoblasts, osteocytes, and osteoclasts. Dysregulation of energy metabolism in bone cells consequently disturbs the balance between bone formation and bone resorption. Metabolic diseases have also been reported to affect bone homeostasis. Bone morphogenic protein (BMP) signaling plays critical roles in regulating the formation and function of bone cells, thus affecting bone development and homeostasis. Mutations of BMP signaling-related genes in mice have been reported to show abnormalities in energy metabolism in many tissues, including bone. In addition, BMP signaling correlates with critical signaling pathways such as mTOR, HIF, Wnt, and self-degradative process autophagy to coordinate energy metabolism and bone homeostasis. These findings will provide a newly emerging target of BMP signaling and potential therapeutic strategies and the improved management of bone diseases. This review summarizes the recent advances in our understanding of (1) energy metabolism in regulating the formation and function of bone cells, (2) function of BMP signaling in whole body energy metabolism, and (3) mechanistic interaction of BMP signaling with other signaling pathways and biological processes critical for energy metabolism and bone homeostasis.

Topical sodium alendronate combined or not with photodynamic therapy as an adjunct to scaling and root planing: Histochemical and immunohistochemical study in rats

OBJECTIVE

The purpose of this study was to evaluate influence of topical sodium alendronate (ALN), photodynamic therapy (aPDT), or a combination thereof as adjuvant to scaling and root planing (SRP) in the treatment of experimental periodontitis in rats.

BACKGROUND

Therapeutic protocols to control periodontitis progression that aim to equalize bacterial action and load with tissue immune response are well addressed in current scientific research.

METHODS

Experimental periodontitis was induced in 96 rats with a ligature around the mandibular left first molar. After 7 days, ligature was removed and animals were treated according to the following experimental groups (n = 8): control-SRP plus saline solution; ALN-SRP plus ALN; aPDT-SRP plus methylene blue irrigation, followed by low-level laser therapy (LLLT); and ALN/aPDT-SRP plus ALN and methylene blue irrigation followed by LLLT. The animals were euthanized at 7, 15, and 30 days after treatments. Collagen maturation (picrosirius red staining) and immunohistochemical analyses (TRAP, RANKL and osteoprotegerin [OPG]) were performed. Data were submitted to statistical analysis (P < .05).

RESULTS

At 7 days, group ALN presented a significantly higher number of TRAP-positive cells and percentage of immature collagen fibers than group ALN/aPDT, while group ALN/aPDT presented a significantly higher percentage of mature collagen fibers than group ALN. At 30 days, group ALN presented significantly lower percentage of immature collagen fibers and higher percentage of mature collagen fibers than control.

CONCLUSION

It can be concluded that topical use of ALN coadjutant to SRP, alone or combined with aPDT, enhanced collagen maturation and reduced osteoclastogenesis during the healing of experimental periodontitis.

Alendronate loaded graphene oxide functionalized collagen sponge for the dual effects of osteogenesis and anti-osteoclastogenesis in osteoporotic rats

Graphene Oxide (GO)-related hydrogels have been extensively studied in hard tissue repair, because GO can not only enhance the mechanical properties of polymers but also promote osteogenic differentiation of mesenchymal stem cells. However, simple GO-related hydrogels are not ideal for the repair of osteoporotic bone defects as the overactive osteoclasts in osteoporosis. Alendronate (Aln) is known to inhibit osteoclasts and may bind to GO through covalent connection. Therefore, delivering Aln in GO-related hydrogels may be effective to repair osteoporotic bone defects. Here, we developed a control-released system which is constructed by collagen (Col)-GO sponges loaded with Aln (Col-GO-Aln) for osteoporotic bone defect repair. In vitro, Col-GO-Aln sponges prolonged the release period of Aln, and the sponge containing 0.05% (w/v) GO released Aln faster than sponge with 0.2% GO. Furthermore, tartrate-resistant acid phosphatase (TRAP) and F-actin staining demonstrated that Col-GO-Aln sponges effectively inhibited osteoclastogenesis of monocyte-macrophages. In vivo, micro-CT scan showed that the volume of newborn bone in defect site by 0.05% GO sponge was nearly three times larger than that of other groups. Moreover, the CT and histological examinations of rat femur proved that Col-GO-Aln sponges decreased the number of osteoclasts and suppressed the systemic bone loss in osteoporotic rats. These findings reveal that the application of GO as carriers of anti-osteoporosis drugs is a viable treatment for osteoporosis. The results also underscore the potential of GO-related hydrogels with Aln-releasing capacity for bone regeneration in osteoporosis.

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Alendronate-loading graphene oxide modified collagen sponge (Col-GO-Aln) exhibit a sustained drug delivery.

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Col-GO-Aln sponge showed active anti-osteoclastogenesis and osteogenesis ability in vitro and in situ repair.

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Col-GO-Aln sponge achieved a potential systemic resistance to bone loss in osteoporotic rats.

Improved Immunoregulation of Ultra-Low-Dose Silver Nanoparticle-Loaded TiO2 Nanotubes via M2 Macrophage Polarization by Regulating GLUT1 and Autophagy

Introduction

The bone regeneration of endosseous implanted biomaterials is often impaired by the host immune response, especially macrophage-related inflammation which plays an important role in the bone healing process. Thus, it is a promising strategy to design an osteo-immunomodulatory biomaterial to take advantage of the macrophage-related immune response and improve the osseointegration performance of the implant.

Methods

In this study, we developed an antibacterial silver nanoparticle-loaded TiO₂ nanotubes (Ag@TiO₂-NTs) using an electrochemical anodization method to make the surface modification and investigated the influences of Ag@TiO₂-NTs on the macrophage polarization, osteo-immune microenvironment as well as its potential molecular mechanisms in vitro and in vivo.

Results

The results showed that Ag@TiO₂-NTs with controlled releasing of ultra-low-dose Ag⁺ ions had the excellent ability to induce the macrophage polarization towards the M2 phenotype and create a suitable osteo-immune microenvironment in vitro, via inhibiting PI3K/Akt, suppressing the downstream effector GLUT1, and activating autophagy. Moreover, Ag@TiO₂-NTs surface could improve bone formation, suppress inflammation, and promote osteo-immune microenvironment compared to the TiO₂-NTs and polished Ti surfaces in vivo. These findings suggested that Ag@TiO₂-NTs with controlled releasing of ultra-low-dose Ag⁺ ions could not only inhibit the inflammation process but also promote the bone healing by inducing healing-associated M2 polarization.

Discussion

Using this surface modification strategy to modulate the macrophage-related immune response, rather than prevent the host response, maybe a promising strategy for implant surgeries in the future.

Melatonin restores the osteoporosis-impaired osteogenic potential of bone marrow mesenchymal stem cells by preserving SIRT1-mediated intracellular antioxidant properties

Postmenopausal osteoporosis (OP) is one of the most common bone diseases that affects millions of aging women. Reduced osteogenesis and increased oxidative stress have been implicated in bone marrow mesenchymal stem cells (BMMSCs) derived from OP patients. Melatonin has shown positive effects on osteoblast differentiation and bone formation; however, it was unknown whether melatonin could restore OP-impaired osteogenic potential of BMMSCs and what the underlying mechanisms entailed. The objective of this study is to investigate (1) whether melatonin can restore the impaired osteogenic potential of OP BMMSCs by preserving their antioxidant functions, and if so, (2) whether intravenous administration of melatonin can prevent OP-induced bone loss in ovariectomized (OVX) rats. Ovariectomies were performed in female rats and BMMSCs were isolated from the osteoporotic rats 3 months later. In vitro treatment with melatonin successfully improved the osteogenic differentiation of OP BMMSCs, as evidenced by increased levels of matrix mineralization and osteoblast-specific genes. In melatonin-treated OP BMMSCs, intracellular oxidative stress was significantly attenuated, while levels of intracellular antioxidant enzymes were noticeably up-regulated - particularly superoxide dismutase 2 (SOD2) and glutathione peroxidase 1 (GPX1). Silent information regulator type 1 (SIRT1) was involved in the melatonin-mediated recovery of osteogenesis and antioxidant functions. Meanwhile, in vivo injections of melatonin via the tail vein successfully ameliorated the bone micro-architecture in ovariectomized rat femurs. Further experiments confirmed that BMMSCs derived from melatonin-treated OVX rats exerted well-preserved antioxidant properties and osteogenic potential. Our findings demonstrate that the administration of melatonin is a promising strategy for treating patients with postmenopausal OP by preserving the antioxidant properties and osteogenic potential of their BMMSCs.

Synovium stem cell-derived matrix enhances anti-inflammatory properties of rabbit articular chondrocytes via the SIRT1 pathway

Autologous chondrocyte implantation (ACI) is a promising approach to repair cartilage defects; however, the cartilage trauma-induced inflammatory environment compromises its clinical outcomes. Cell-derived decellularized extracellular matrix (DECM) has been used as a culture substrate for mesenchymal stem cells (MSCs) to improve the cell proliferation and lineage-specific differentiation. In this study, DECM deposited by synovium-derived MSCs was used as an in vitro expansion system for rabbit articular chondrocytes and the response of DECM-expanded chondrocytes to pro-inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) was evaluated. Compared with those grown on tissue culture polystyrene (TCPS), the proliferation rate was significantly improved in DECM-expanded chondrocytes. TCPS- and DECM-expanded chondrocytes were isolated and induced to redifferentiation in a high-density pellet culture. DECM-expanded chondrocytes exerted a stronger resistance to 1 ng/mL of IL-1β than TCPS-expanded cells, but the production of cartilage matrix in both groups was inhibited by 5 ng/mL of IL-1β. When exposed to 1 or 5 ng/mL of TNF-α, DECM-expanded chondrocytes showed higher levels of cartilage matrix synthesis than TCPS-expanded cells. In addition, the gene expression of IL-1β- or TNF-α-induced matrix degrading enzymes (MMP3, MMP9, MMP13, and ADAMTS5) was significantly lower in DECM-expanded chondrocytes than TCPS-expanded cells. Furthermore, we found that SIRT1 inhibition by nicotinamide completely counteracted the protective effect of DECM on chondrocytes in the presence of IL-1β or TNF-α, indicating that the SIRT1 signaling pathway was involved in the DECM-mediated enhancement of anti-inflammatory properties of chondrocytes. Taken together, this work suggests that stem cell-derived DECM is a superior culture substrate for in vitro chondrocyte expansion by improving proliferation and enhancing the anti-inflammatory properties of chondrocytes. DECM-expanded chondrocytes with enhanced anti-inflammatory properties hold great potential in clinically ACI-based cartilage repair.

Nrf2 activation in osteoblasts suppresses osteoclastogenesis via inhibiting IL-6 expression

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ALA/SFC induced the activation of Nrf2 in osteoblasts.

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IL-6 and RANKL expression in osteoblasts was increased by LPS, but decreased by Nrf2 activation.

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LPS-mediated RANKL augmentation was dependent on IL-6 induction.

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Nrf2 activation in osteoblasts suppresses indirectly osteoclastogenesis via inhibiting the expression of IL-6.

Bone destructive diseases such as periodontitis and rheumatoid arthritis are caused by excessive activation of osteoclasts. Osteoclastogenesis is regulated by Receptor activator of nuclear factor kappa-β ligand (RANKL) produced by osteoclastogenesis supporting cells such as osteoblast and osteocyte. Previously, we reported that NF-E2-related factor-2 (Nrf2) activation in osteoclast precursors inhibited osteoclastogenesis and bone destruction via induction of anti-oxidation and thereby attenuated intracellular ROS signaling. However, it still remains unknown whether Nrf2 activation in cells other than osteoclasts give any negative influence on supporting property for osteoclastogenesis. Here we discovered that Nrf2 activation in osteoblasts suppresses indirectly osteoclastogenesis via inhibiting the expression of interleukin-6 (IL-6) which promotes osteoclastogenesis. In this study, 5-aminolevulinic acid hydrochloride (ALA) and sodium ferrous citrate (SFC) was used as the Nrf2 activator. in vitro experiments, using osteoblast cell line, MC3T3-E1, revealed that the expression of IL-6 was increased by LPS stimulation, but decreased after ALA/SFC treatment in mRNA and protein levels. Furthermore, RANKL expression was augmented by LPS, which was blocked by ALA/SFC treatment. Neutralizing antibody against IL-6 confirmed that LPS-mediated RANKL augmentation was dependent on IL-6 induction. in vivo experiments with LPS-mediated bone destruction in mice, confirmed that augmented IL-6 expression in osteoblasts by immunochemical analysis. ALA/SFC treatment attenuated LPS-mediated IL-6 upregulation. These results suggest that Nrf2 activation in osteoblasts suppress IL-6 and inflammatory bone destruction. The Nrf2 activator acts not only on osteoclasts but also on osteoblasts, in other word, Nrf2 activation indirectly suppresses osteoclastogenesis. In conclusion, the Nrf2 activator exhibits dual inhibitory effects via direct action on osteoclast and indirect action on osteoclast supporting cells.

Porous Se@SiO2 nanocomposite promotes migration and osteogenic differentiation of rat bone marrow mesenchymal stem cell to accelerate bone fracture healing in a rat model

Background: Delay or failure of bone union is a significant clinical challenge all over the world, and it has been reported that bone marrow mesenchymal stem cells (BMSCs) offer a promising approach to accelerate bone fracture healing. Se can modulate the proliferation and differentiation of BMSCs. Se-treatment enhances the osteoblastic differentiation of BMSCs and inhibiting the differentiation and formation of mature osteoclasts. The purpose of this study was to assess the effects of porous Se@SiO₂ nanocomposite on bone regeneration and the underlying biological mechanisms.

Methods: We oxidized Se^2- to develop Se quantum dots, then we used the Se quantum dots to form a solid Se@SiO₂ nanocomposite which was then coated with polyvinylpyrrolidone (PVP) and etched in hot water to synthesize porous Se@SiO₂ nanocomposite. We used XRD pattern to assess the phase structure of the solid Se@SiO₂ nanocomposite. The morphology of porous Se@SiO₂ nanocomposite were evaluated by scanning electron microscope (SEM) and the biocompatibility of porous Se@SiO₂ nanocomposite were investigated by cell counting kit-8 (CCK-8) assays. Then, a release assay was also performed. We used a Transwell assay to determine cell mobility in response to the porous Se@SiO₂ nanocomposite. For in vitro experiments, BMSCs were divided into four groups to detect reactive oxygen species (ROS) generation, cell apoptosis, alkaline phosphatase activity, calcium deposition, gene activation and protein expression. For in vivo experiments, femur fracture model of rats was constructed to assess the osteogenic effects of porous Se@SiO₂ nanocomposite.

Results: In vitro, intervention with porous Se@SiO₂ nanocomposite can promote migration and osteogenic differentiation of BMSCs, and protect BMSCs against H₂O₂-induced inhibition of osteogenic differentiation. In vivo, we demonstrated that the porous Se@SiO₂ nanocomposite accelerated bone fracture healing using a rat femur fracture model.

Conclusion: Porous Se@SiO₂ nanocomposite promotes migration and osteogenesis differentiation of rat BMSCs and accelerates bone fracture healing, and porous Se@SiO₂ nanocomposite may provide clinic benefit for bone tissue engineering.

Nanoparticulate mineralized collagen glycosaminoglycan materials directly and indirectly inhibit osteoclastogenesis and osteoclast activation

The ability of the extracellular matrix (ECM) to direct cell fate has generated the potential for developing a materials-only strategy for tissue regeneration. Previously, we described a nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) material that efficiently induced osteogenic differentiation of human mesenchymal stem cells (hMSCs) and calvarial bone healing without exogenous growth factors or progenitor cell expansion. In this work, we evaluated the interactions between MC-GAG and primary human osteoclasts (hOCs). In the absence of hMSCs, mineralized Col-GAG materials directly inhibited hOC viability, proliferation, and resorption in contrast to nonmineralized Col-GAG, which demonstrated a modest inhibition of resorptive activity only. Cocultures containing differentiating hMSCs with hOCs demonstrated increased hOC-mediated resorption only on Col-GAG while MC-GAG cocultures continued to inhibit resorption. Unlike Col-GAG, hMSCs on MC-GAG expressed increased amounts of osteoprotegerin (OPG) protein, the major endogenous osteoclast inhibitor. Interestingly, OPG expression was found to be antagonized by small mothers against decapentaplegic1/5 (Smad1/5) phosphorylation, an obligate pathway for osteogenic differentiation of hMSCs on MC-GAG, and potentiated by extracellular signal-regulated kinase (ERK1/2) phosphorylation. Collectively, these results suggested that the MC-GAG material both directly inhibited the osteoclast viability, proliferation, and resorptive activity as well as induced hMSCs to secrete osteoprotegerin, an antiosteoclastogenic factor, via a signalling pathway distinct from osteogenic differentiation.

A prospect of cell immortalization combined with matrix microenvironmental optimization strategy for tissue engineering and regeneration

Cellular senescence is a major hurdle for primary cell-based tissue engineering and regenerative medicine. Telomere erosion, oxidative stress, the expression of oncogenes and the loss of tumor suppressor genes all may account for the cellular senescence process with the involvement of various signaling pathways. To establish immortalized cell lines for research and clinical use, strategies have been applied including internal genomic or external matrix microenvironment modification. Considering the potential risks of malignant transformation and tumorigenesis of genetic manipulation, environmental modification methods, especially the decellularized cell-deposited extracellular matrix (dECM)-based preconditioning strategy, appear to be promising for tissue engineering-aimed cell immortalization. Due to few review articles focusing on this topic, this review provides a summary of cell senescence and immortalization and discusses advantages and limitations of tissue engineering and regeneration with the use of immortalized cells as well as a potential rejuvenation strategy through combination with the dECM approach.

Upregulation of SIRT1 by Kartogenin Enhances Antioxidant Functions and Promotes Osteogenesis in Human Mesenchymal Stem Cells

Osteoarthritis is a chronic degenerative joint disease involving both articular cartilage and subchondral bone. Kartogenin (KGN) was recently identified to improve in vivo cartilage repair; however, its effect on bone formation is unknown. The aim of this study was to investigate the effect of KGN on antioxidant properties and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs). Human BM-MSCs were treated with KGN at concentrations ranging from 10-8 M to 10-6 M. Our results indicated that KGN improved cell proliferation and attenuated intracellular reactive oxygen species. The levels of antioxidant enzymes and osteogenic differentiation of BM-MSCs were enhanced by KGN in a dose-dependent manner. Furthermore, KGN-treated BM-MSCs showed upregulation of silent information regulator type 1 (SIRT1) and increased phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK), indicating that KGN activated the AMPK-SIRT1 signaling pathway in BM-MSCs. Inhibition of SIRT1 by nicotinamide reversed the antioxidant effect of KGN on BM-MSCs and suppressed osteogenic differentiation. In conclusion, our results demonstrated that KGN improved intracellular antioxidant properties and promoted osteogenic differentiation of BM-MSCs by activating the AMPK-SIRT1 signaling pathway. Thus, KGN may have the potential for not only articular cartilage repair but also the clinical application of MSCs in bone tissue engineering.