Osteoblast apoptosis and bone turnover

The Emerging Role of the Mitochondrial Respiratory Chain in Skeletal Aging

Maintenance of mitochondrial homeostasis is crucial for ensuring healthy mitochondria and normal cellular function. This process is primarily responsible for regulating processes that include mitochondrial OXPHOS, which generates ATP, as well as mitochondrial oxidative stress, apoptosis, calcium homeostasis, and mitophagy. Bone mesenchymal stem cells express factors that aid in bone formation and vascular growth. Positive regulation of hematopoietic stem cells in the bone marrow affects the differentiation of osteoclasts. Furthermore, the metabolic regulation of cells that play fundamental roles in various regions of the bone, as well as interactions within the bone microenvironment, actively participates in regulating bone integrity and aging. The maintenance of cellular homeostasis is dependent on the regulation of intracellular organelles, thus understanding the impact of mitochondrial functional changes on overall bone metabolism is crucially important. Recent studies have revealed that mitochondrial homeostasis can lead to morphological and functional abnormalities in senescent cells, particularly in the context of bone diseases. Mitochondrial dysfunction in skeletal diseases results in abnormal metabolism of bone-associated cells and a secondary dysregulated microenvironment within bone tissue. This imbalance in the oxidative system and immune disruption in the bone microenvironment ultimately leads to bone dysplasia. In this review, we examine the latest developments in mitochondrial respiratory chain regulation and its impacts on maintenance of bone health. Specifically, we explored whether enhancing mitochondrial function can reduce the occurrence of bone cell deterioration and improve bone metabolism. These findings offer prospects for developing bone remodeling biology strategies to treat age-related degenerative diseases.

Targeting SAT1 prevents osteoporosis through promoting osteoclast apoptosis

Osteoporosis is a systemic bone disease characterized by decreased bone mass that is tightly regulated by the coordinated actions of osteoclasts and osteoblasts. Apoptosis as a precise programmed cell death involves a cascade of gene expression events which are mechanistically linked to the regulation of bone metabolism. Nevertheless, the critical biomolecules involved in regulating cell apoptosis in osteoporosis remain unknown. To gain a deeper insight into the relationship between apoptosis and osteoporosis, this study integrated the sequencing results of human samples and using a machine learning workflow to overcome the limitations of a single study. Among all immune cell populations, we assessed the apoptotic level and portrayed the distinct subtypes and lineage differentiation of monocytic cells in osteoporotic tissues. Osteoclasts expressed a higher level of Spermidine/spermine-N1-Acetyltransferase1 (SAT1) during osteoclastogenesis which prevented osteoclasts apoptosis and facilitate osteoporosis progression. In addition, Berenil, one potent SAT1 inhibitor, increased osteoclast apoptosis and reversed the bone loss in the femurs of a murine ovariectomy model. In summary, Berenil promotes osteoclast apoptosis, inhibits the bone resorption and improves the abnormal bone structure in vitro and in vivo models by targeting SAT1, demonstrating its potential as a precise therapeutic strategy for clinical osteoporosis treatment.

Aggregation of human osteoblasts unlocks self-reliant differentiation and constitutes a microenvironment for 3D-co-cultivation with other bone marrow cells

Skeletal bone function relies on both cells and cellular niches, which, when combined, provide guiding cues for the control of differentiation and remodeling processes. Here, we propose an in vitro 3D model based on human fetal osteoblasts, which eases the study of osteocyte commitment in vitro and thus provides a means to examine the influences of biomaterials, substances or cells on the regulation of these processes. Aggregates were formed from human fetal osteoblasts (hFOB1.19) and cultivated under proliferative, adipo- and osteoinductive conditions. When cultivated under osteoinductive conditions, the vitality of the aggregates was compromised, the expression levels of the mineralization-related gene DMP1 and the amount of calcification and matrix deposition were lower, and the growth of the spheroids stalled. However, within spheres under growth conditions without specific supplements, self-organization processes occur, which promote extracellular calcium deposition, and osteocyte-like cells develop. Long-term cultivated hFOB aggregates were free of necrotic areas. Moreover, hFOB aggregates cultivated under standard proliferative conditions supported the co-cultivation of human monocytes, microvascular endothelial cells and stromal cells. Overall, the model presented here comprises a self-organizing and easily accessible 3D osteoblast model for studying bone marrow formation and in vitro remodeling and thus provides a means to test druggable molecular pathways with the potential to promote life-long bone formation and remodeling.

Immunomodulatory nanomedicine for osteoporosis: Current practices and emerging prospects

Osteoporosis results from the disruption of the balance between bone resorption and bone formation. However, classical anti-osteoporosis drugs exhibit several limitations in clinical applications, such as multiple adverse reactions and poor therapeutic effects. Therefore, there is an urgent need for alternative treatment strategies. With the evolution of immunomodulatory nanomedicine, a variety of nanomaterials have been designed for anti-osteoporosis treatment, offering prospects of minimal adverse reactions, enhanced bone induction, and high osteogenic activity. This review initially provides a brief overview of the fundamental principles of bone reconstruction, current osteogenic clinical methods in osteoporosis treatment, and the significance of osteogenic-angiogenic coupling, laying the groundwork for understanding the pathophysiology and therapeutics of osteoporosis. Subsequently, the article emphasizes the relationship between bone immunity and osteogenesis-angiogenesis coupling and provides a detailed analysis of the application of immunomodulatory nanomedicines in the treatment of osteoporosis, including various types of nanomaterials and their integration with carrier biomaterials. Importantly, we discuss the potential of some emerging strategies in immunomodulatory nanomedicine for osteoporosis treatment. This review introduces the innovative applications of immunomodulatory nanomedicine in the treatment of osteoporosis, aiming to serve as a reference for the application of immunomodulatory nanomedicine strategies in osteoporosis treatment. STATEMENT OF SIGNIFICANCE: Osteoporosis, as one of the most prevalent skeletal disorders, poses a significant threat to public health. To date, conventional anti-osteoporosis strategies have been limited in efficacy and plagued with numerous side effects. Fortunately, with the advancement of research in osteoimmunology and nanomedicine, strategies integrating these two fields show great promise in combating osteoporosis. Nanomedicine with immunomodulatory properties exhibits enhanced efficiency, prolonged effectiveness, and increased safety. However, as of now, there exists no comprehensive review amalgamating immunomodulation with nanomedicine to delineate the progress of immunomodulatory nanomedicine in osteoporosis treatment, as well as the future direction of this strategy.

Biological processes and factors involved in soft and hard tissue healing

Wound healing is a complex and iterative process involving myriad cellular and biologic processes that are highly regulated to allow satisfactory repair and regeneration of damaged tissues. This review is intended to be an introductory chapter in a volume focusing on the use of platelet concentrates for tissue regeneration. In order to fully appreciate the clinical utility of these preparations, a sound understanding of the processes and factors involved in soft and hard tissue healing. This encompasses an appreciation of the cellular and biological mediators of both soft and hard tissues in general as well as specific consideration of the periodontal tissues. In light of good advances in this basic knowledge, there have been improvements in clinical strategies and therapeutic management of wound repair and regeneration. The use of platelet concentrates for tissue regeneration offers one such strategy and is based on the principles of cellular and biologic principles of wound repair discussed in this review.

Mechanical loading intensities affect the release of extracellular vesicles from mouse bone marrow-derived hematopoietic progenitor cells and change their osteoclast-modulating effect

Low-intensity loading maintains or increases bone mass, whereas lack of mechanical loading and high-intensity loading decreases bone mass, possibly via the release of extracellular vesicles by mechanosensitive bone cells. How different loading intensities alter the biological effect of these vesicles is not fully understood. Dynamic fluid shear stress at low intensity (0.7 ± 0.3 Pa, 5 Hz) or high intensity (2.9 ± 0.2 Pa, 1 Hz) was used on mouse hematopoietic progenitor cells for 2 min in the presence or absence of chemical compounds that inhibit release or biogenesis of extracellular vesicles. We used a Receptor activator of nuclear factor kappa-Β ligand-induced osteoclastogenesis assay to evaluate the biological effect of different fractions of extracellular vesicles obtained through centrifugation of medium from hematopoietic stem cells. Osteoclast formation was reduced by microvesicles (10 000× g) obtained after low-intensity loading and induced by exosomes (100 000× g) obtained after high-intensity loading. These osteoclast-modulating effects could be diminished or eliminated by depletion of extracellular vesicles from the conditioned medium, inhibition of general extracellular vesicle release, inhibition of microvesicle biogenesis (low intensity), inhibition of ESCRT-independent exosome biogenesis (high intensity), as well as by inhibition of dynamin-dependent vesicle uptake in osteoclast progenitor cells. Taken together, the intensity of mechanical loading affects the release of extracellular vesicles and change their osteoclast-modulating effect.

A novel lncRNA GM15416 regulates osteoblast apoptosis and differentiation through the c-Fos/Fas axis and mitigates osteoporosis

Osteoporosis (OP) is a common systemic bone disorder, and the programmed cell death of osteoblasts is closely linked to the development of osteoporosis. Previous studies have shown that c-fos can cause osteoblast apoptosis. Furthermore, it has been demonstrated that long non-coding RNA (lncRNA) plays a pervasive role in regulating the biology of osteoblasts. Nevertheless, the precise role and mechanism of long non-coding RNA (lncRNA) in relation to c-Fos at the transcriptional level in osteoblast cell death remain uncertain. Compared with normal osteoblasts, serum deprivation resulted in significant upregulation of the transcription factor c-Fos and apoptosis-related Fas proteins in osteoblasts. In addition, the expression of lncRNA GM15416 related to c-Fos was significantly increased. The results showed that overexpression of c-Fos leads to an increase in downstream Fas protein, which subsequently leads to osteoblast apoptosis and hinders osteogenesis. On the contrary, a decrease in lncRNA GM15416 expression leads to a decrease in c-Fos/Fas expression, which hinders osteoblast apoptosis and promotes osteogenesis. Our results suggest that lncRNA GM15416 exerts inhibitory effects on osteoblast apoptosis and acts as a preventive factor against osteoporosis. As a result, GM15416 emerges as an important lncRNA associated with osteoporosis and holds potential as a future therapeutic target.

Regulation of base excision repair during adipogenesis and osteogenesis of bone marrow-derived mesenchymal stem cells

Bone marrow-derived human mesenchymal stem cells (hMSCs) can differentiate into various lineages, such as chondrocytes, adipocytes, osteoblasts, and neuronal lineages. It has been shown that the high-efficiency DNA-repair capacity of hMSCs is decreased during their differentiation. However, the underlying its mechanism during adipogenesis and osteogenesis is unknown. Herein, we investigated how alkyl-damage repair is modulated during adipogenic and osteogenic differentiation, especially focusing on the base excision repair (BER) pathway. Response to an alkylation agent was assessed via quantification of the double-strand break (DSB) foci and activities of BER-related enzymes during differentiation in hMSCs. Adipocytes showed high resistance against methyl methanesulfonate (MMS)-induced alkyl damage, whereas osteoblasts were more sensitive than hMSCs. During the differentiation, activities, and protein levels of uracil-DNA glycosylase were found to be regulated. In addition, ligation-related proteins, such as X-ray repair cross-complementing protein 1 (XRCC1) and DNA polymerase β, were upregulated in adipocytes, whereas their levels and recruitment declined during osteogenesis. These modulations of BER enzyme activity during differentiation influenced DNA repair efficiency and the accumulation of DSBs as repair intermediates in the nucleus. Taken together, we suggest that BER enzymatic activity is regulated in adipogenic and osteogenic differentiation and these alterations in the BER pathway led to different responses to alkyl damage from those in hMSCs.

Aortic carboxypeptidase-like protein, a putative myokine, stimulates the differentiation and survival of bone-forming osteoblasts

A new target that stimulates bone formation is needed to overcome limitations of current anti-osteoporotic drugs. Myokines, factors secreted from muscles, may modulate it. In this study, we investigated the role of aortic carboxypeptidase-like protein (ACLP), which is highly expressed in skeletal muscles, on bone formation. MC3T3-E1 cells and/or calvaria osteoblasts were treated with recombinant N-terminal mouse ACLP containing a signal peptide [rmACLP (N)]. The expression and secretion of ACLP were higher in skeletal muscle and differentiated myotube than in other tissues and undifferentiated myoblasts, respectively. rmACLP (N) increased bone formation, ALP activity, and phosphorylated p38 mitogen-activated protein (MAP) kinase in osteoblasts; reversal was achieved by pre-treatment with a TGF-β receptor inhibitor. Under H2 O2 treatment, rmACLP (N) increased osteoblast survival, phosphorylated p38 MAP kinase, and the nuclear translocation of FoxO3a in osteoblasts. H2 O2 treatment caused rmACLP (N) to suppress its apoptotic, oxidative, and caspase-9 activities. rmACLP (N)-stimulated osteoblast survival was reversed by pre-treatment with a p38 inhibitor, a TGF-β-receptor II blocking antibody, and a FoxO3a shRNA. Conditioned media (CM) from muscle cells stimulated osteoblast survival under H2 O2 treatment, in contrast to CM from ACLP knockdown muscle cells. rmACLP (N) increased the expressions of FoxO3a target anti-oxidant genes such as Sod2, Trx2, and Prx5. In conclusion, ACLP stimulated the differentiation and survival of osteoblasts. This led to the stimulation of bone formation by the activation of p38 MAP kinase and/or FoxO3a via TGF-β receptors. These findings suggest a novel role for ACLP in bone metabolism as a putative myokine.

Smoking induces increased apoptosis in osteoblasts: changes in bone matrix organic components

Clinical studies demonstrate the impact of smoking on bone tissue fragility and higher incidence of fractures. However, it is not totally understood which physiological mechanisms could be involved in these events. Previously, we showed important changes in bone tissue components in experimental model of cigarette smoke (CS) exposure. CS exposure induces worsening in bone mineralization and a decrease in collagen type I deposition, leading to bone fragility. Considering that the majority of clinical studies described bone structural changes by radiographic images, in this study we performed analyses "in situ" using tissue samples from smokers, former smokers and non-smokers to better understand how the increase in inflammatory mediators induced by smoking exposure could interfere in bone cells activity leading bone structural changes. We observed increased levels of IL-1β, IL-6 and TNF-α in bone tissue homogenates with a concomitant increase in osteoblast apoptosis in smokers and former smokers compared with non-smokers. Histological changes in both smokers and former smokers were characterized by reduction in collagen type I. Only in smokers, it was observed decrease in trabecular area, suggesting increased bone resorption and increase in collagen type V. These results showed that osteoblasts apoptosis in association with increased bone resorption leads bone structural changes in smokers.

Transcriptome-wide association study identifies novel genes associated with bone mineral density and lean body mass in children

OBJECTIVE

To identify novel candidate genes whose expression is associated with bone mineral density (BMD) and body lean mass (LM) in children.

METHODS

A tissue-specific transcriptome-wide association study (TWAS) was conducted utilizing a large-scale genome-wide association study (GWAS) dataset associated with BMD and LM and involving 10,414 participants. The measurement of BMD and LM phenotypes was made based on total-body dual-energy X-ray absorptiometry (TB-DXA) scans. TWAS was conducted by using FUSION software. Reference panels for muscle skeleton (MS), peripheral blood (NBL) and whole blood (YBL) were used for TWAS analysis. Functional enrichment and protein-protein interaction (PPI) analyses of the genes identified by TWAS were performed by using the online tool Metascape ( http://metascape.org ).

RESULTS

For BMD, we identified 174 genes with P < 0.05, such as IKZF1 (P = 1.46 × 10^-9) and CHKB (P = 8.31 × 10^-7). For LM, we identified 208 genes with P < 0.05, such as COPS5 (P = 3.03 × 10^-12) and MRPS33 (P = 5.45 × 10^-10). Gene ontology (GO) enrichment analysis of the BMD-associated genes revealed 200 GO terms, such as protein catabolic process (Log P = -5.09) and steroid hormone-mediated signaling pathway (Log P = -3.13). GO enrichment analysis of the LM-associated genes detected 287 GO terms, such as the apoptotic signaling pathway (Log P = -8.08) and lipid storage (Log P = -3.55).

CONCLUSION

This study identified several candidate genes for BMD and LM in children, providing novel clues to the genetic mechanisms underlying the development of childhood BMD and LM.

Mitochondrial quality control and its role in osteoporosis

Mitochondria are important organelles that provide cellular energy and play a vital role in cell differentiation and apoptosis. Osteoporosis is a chronic metabolic bone disease mainly caused by an imbalance in osteoblast and osteoclast activity. Under physiological conditions, mitochondria regulate the balance between osteogenesis and osteoclast activity and maintain bone homeostasis. Under pathological conditions, mitochondrial dysfunction alters this balance; this disruption is important in the pathogenesis of osteoporosis. Because of the role of mitochondrial dysfunction in osteoporosis, mitochondrial function can be targeted therapeutically in osteoporosis-related diseases. This article reviews different aspects of the pathological mechanism of mitochondrial dysfunction in osteoporosis, including mitochondrial fusion and fission, mitochondrial biogenesis, and mitophagy, and highlights targeted therapy of mitochondria in osteoporosis (diabetes induced osteoporosis and postmenopausal osteoporosis) to provide novel targets and prevention strategies for the prevention and treatment of osteoporosis and other chronic bone diseases.

Ablation of Discoidin Domain Receptor 1 Provokes an Osteopenic Phenotype by Regulating Osteoblast/Osteocyte Autophagy and Apoptosis

Discoidin domain receptor 1 (DDR1) is a collagen receptor that belongs to the receptor tyrosine kinase family. We have previously shown that DDR1 plays a crucial role during bone development, resulting in dwarfism and a short stature in osteoblast-specific knockout mice (OKO mice). However, the detailed pathophysiological effects of DDR1 on bone development throughout adulthood have remained unclear. This study aims to identify how DDR1 regulates osteoblast and osteocyte functions in vivo and in vitro during bone development in adulthood. The metabolic changes in bone tissues were analyzed using Micro-CT and immunohistochemistry staining (IHC) in vivo; the role of DDR1 in regulating osteoblasts was examined in MC3T3-E1 cells in vitro. The Micro-CT analysis results demonstrated that OKO mice showed a 10% reduction in bone-related parameters from 10 to 14 weeks old and a significant reduction in cortical thickness and diameter compared with flox/flox control mice (FF) mice. These results indicated that DDR1 knockout in OKO mice exhibiting significant bone loss provokes an osteopenic phenotype. The IHC staining revealed a significant decrease in osteogenesis-related genes, including RUNX2, osteocalcin, and osterix. We noted that DDR1 knockout significantly induced osteoblast/osteocyte apoptosis and markedly decreased autophagy activity in vivo. Additionally, the results of the gain- and loss-of-function of the DDR1 assay in MC3T3-E1 cells indicated that DDR1 can regulate the osteoblast differentiation through activating autophagy by regulating the phosphorylation of the mechanistic target of rapamycin (p-mTOR), light chain 3 (LC3), and beclin-1. In conclusion, our study highlights that the ablation of DDR1 results in cancellous bone loss by regulating osteoblast/osteocyte autophagy. These results suggest that DDR1 can act as a potential therapeutic target for managing cancellous bone loss.

Omentin-1 promoted proliferation and ameliorated inflammation, apoptosis, and degeneration in human nucleus pulposus cells

PURPOSE

Intervertebral disc degeneration is an abnormal, cell-mediated process of tissue remodeling, recognized as the principal cause of low back pain affecting 80% of the population worldwide. Inflammatory cytokine, Interleukin-1beta (IL-1β) is involved in the intervertebral disc degeneration (IDD) process, and it is upregulated in degenerated discs. Omentin-1, also known as intelectin-1, is an adipokine with anti-inflammatory, anti-apoptosis, pro-proliferation, and proangiogenic properties in various types of cells. However, little is known about the effects of omentin-1 on human nucleus pulposus cells (HNPCs). This study aims to investigate the effects of omentin-1 on healthy HNPCs regarding proliferation and further investigate the effects of omentin-1 on IL-1β-induced inflammation, apoptosis, and degeneration in HNPCs.

METHODS

Genes and proteins of interest were measured by qRT-PCR, immunoblotting, and immunofluorescence to conduct related experiments. Cell viability (CCK-8), EdU, and mitochondrial membrane potential (JC-1), flow cytometry assays were used to assess proliferation and apoptosis, respectively.

RESULTS

Our study showed that omentin-1 promoted proliferation in normal HNPCs. Furthermore, omentin-1 expression was decreased in IL-1β-treated HNPCs. Omentin-1 protected against IL-1β-induced inflammation, apoptosis, and degeneration in HNPCs in vitro via the activation of the PI3K/Akt signaling pathway.

CONCLUSION

These findings may contribute to understanding the role of omentin-1 in HNPCs and may be a potential therapeutic candidate for intervertebral disc degeneration.

Local hormones and growth factors to enhance orthodontic tooth movement: A systematic review of animal studies

BACKGROUND

Prolonged treatment times are the main reason capable of affecting patient compliance with orthodontic treatment.

OBJECTIVES

A systematic review was made to determine whether the local administration of hormones and growth factors effectively enhances orthodontic tooth movement, and to identify possible adverse effects in animal studies.

MATERIALS AND METHODS

Five databases (PubMed, Scopus, EMBASE, Web of Science and Cochrane Library) were checked for experimental studies reporting one of the following outcomes: orthodontic tooth movement, histological outcomes and side effects. After data extraction, orthodontic tooth movement linked to adjunctive substances was analysed using forest plots. The risk of bias and the quality of evidence were determined with the SYRCLE tool and the GRADE tool, respectively.

RESULTS

Twenty-four studies were included in the systematic review. On a specific dose level, epidermal growth factor + liposomes, fibroblast growth factor and prostaglandin E₂  + Ca were supported by a moderate level of evidence and rated as highly effective in increasing tooth movement in animal models. Likewise, there was histological evidence of increased bone remodelling after the administration of these substances. Other compounds were supported by a low to very low level of evidence.

CONCLUSIONS

Hormones and growth factors may have a relevant impact upon orthodontic tooth movement rate. In specific formulations, prostaglandin E₂ , fibroblast growth factor and epidermal growth factor showed promising results.

Irisin recouples osteogenesis and osteoclastogenesis to protect wear-particle-induced osteolysis by suppressing oxidative stress and RANKL production

The disruption of bone homeostasis with the decrease in osteoblastic bone formation and facilitated osteoclastic bone resorption is the leading cause of periprosthetic osteolysis. Accumulative studies have indicated that irisin has the function of maintaining and rebalancing bone homeostasis. In this study, we explored the protective effect of irisin on wear-particle-induced osteolysis in mice. The results showed that irisin effectively inhibited titanium (Ti) particle-induced calvarial osteolysis, supported by a lower bone loss and existence of more collagen, compared with the ones stressed by Ti particles. Further analysis demonstrated that irisin not only rescued Ti-particle-impaired osteogenesis derived from bone mesenchymal stem cells (BMSCs) but also alleviated the increase in wear-particle-induced nuclear factor-κB ligand (RANKL) secreted by BMSCs-derived osteoblasts, which consequently restrained the activation of osteoclasts. Meanwhile, irisin inhibited osteoclastogenesis by the direct inactivation of reactive oxygen species (ROS) signaling. These results revealed that irisin functions to fight against osteolysis caused by wear particles through rebalancing the periprosthetic bone homeostasis microenvironment, which may provide a potential therapeutic strategy for the management of osteolysis and induced prosthetic loosening.

Bioinspired peptide adhesion on Ti implants alleviates wear particle-induced inflammation and improves interfacial osteogenesis

In the inflammatory peri-implant microenvironment, excessive polarization of macrophages to the proinflammatory M1 phenotype can trigger the secretion of inflammatory cytokines, which promote bone resorption and impede osteogenesis around implants. The direct consequence of this process is the failure of prosthetic implants due to aseptic loosening. To reverse the inflammatory microenvironment and prevent prosthesis loosening, a mussel adhesion-inspired surface strategy was used for bioengineering of titanium implants with integrin-binding ability. In our design, a mussel-inspired catecholic peptide with tetravalent 3,4-dihydroxy-l-phenylalanine (DOPA) and Arg-Gly-Asp (RGD) sequences was synthesized. The peptide can easily anchor to the surface of medical titanium materials through a mussel adhesive mechanism. We found that peptide-decorated titanium implants could effectively inhibit peri-implant inflammation in a wear particle model and could promote the polarization of macrophages to a pro-healing M2 phenotype by interfering with integrin-α₂β₁ and integrin-α_vβ₃. Moreover, the peptide coating increased the adherence of osteoblasts and promoted osteogenesis on titanium implants even under inflammatory conditions. This work suggested that this biomimetic catecholic integrin-binding peptide can provide facile tactics for surface bioengineering of medical prostheses with improved interfacial osteogenesis under inflammatory conditions, which might contribute greatly to the prevention of prosthesis loosening and the improvement of clinical outcomes.

Programmed cell death, redox imbalance, and cancer therapeutics

Cancer cells are disordered by nature and thus featured by higher internal redox level than healthy cells. Redox imbalance could trigger programmed cell death if exceeded a certain threshold, rendering therapeutic strategies relying on redox control a possible cancer management solution. Yet, various programmed cell death events have been consecutively discovered, complicating our understandings on their associations with redox imbalance and clinical implications especially therapeutic design. Thus, it is imperative to understand differences and similarities among programmed cell death events regarding their associations with redox imbalance for improved control over these events in malignant cells as well as appropriate design on therapeutic approaches relying on redox control. This review addresses these issues and concludes by bringing affront cold atmospheric plasma as an emerging redox controller with translational potential in clinics.

Targeted apoptosis of macrophages and osteoclasts in arthritic joints is effective against advanced inflammatory arthritis

Insufficient apoptosis of inflammatory macrophages and osteoclasts (OCs) in rheumatoid arthritis (RA) joints contributes toward the persistent progression of joint inflammation and destruction. Here, we deliver celastrol (CEL) to selectively induce apoptosis of OCs and macrophages in arthritic joints, with enzyme-responsive nanoparticles (termed PRNPs) composed of RGD modified nanoparticles (termed RNPs) covered with cleavable PEG chains. CEL-loaded PRNPs (CEL-PRNPs) dually target OCs and inflammatory macrophages derived from patients with RA via an RGD-αvβ3 integrin interaction after PEG cleavage by matrix metalloprotease 9, leading to increased apoptosis of these cells. In an adjuvant-induced arthritis rat model, PRNPs have an arthritic joint-specific distribution and CEL-PRNPs efficiently reduce the number of OCs and inflammatory macrophages within these joints. Additionally, rats with advanced arthritis go into inflammatory remission with bone erosion repair and negligible side effects after CEL-PRNPs treatment. These findings indicate potential for targeting chemotherapy-induced apoptosis in the treatment of advanced inflammatory arthritis.

Liraglutide Protects Nucleus Pulposus Cells Against High-Glucose Induced Apoptosis by Activating PI3K/Akt/ mTOR/Caspase-3 and PI3K/Akt/GSK3β/Caspase-3 Signaling Pathways

Background and Objective: Diabetes mellitus (DM) is reportedly a significant risk factor for intervertebral disc degeneration (IDD). Incretin system and particularly glucagon-like peptide 1 (GLP-1) because of its glucose-lowering effects has become an important target in therapeutic strategies of type 2 diabetes (T2D). Liraglutide is a GLP-1 receptor (GLP-1R) agonist with glucoregulatory and insulinotropic functions as well as regulatory functions on cell proliferation, differentiation, and apoptosis. However, little is known on the roles and signaling pathways of apoptosis protecting effects of liraglutide in IDD. This study aimed to investigate the potential protective effects of liraglutide against high glucose-induced apoptosis of nucleus pulposus cells (NPCs) and the possible involved signaling pathways.

Methods: The human NPCs were incubated with 100 nM liraglutide alone or in combination with LY294002 (PI3K inhibitor), rapamycin (mTOR inhibitor), and SB216763 (GSK3β inhibitor) in a high glucose culture for 48 h. The four groups were assessed further for apoptosis and genes expressions. The apoptotic effect was evaluated by flow cytometry and further confirmed by cell death detection enzyme-linked immunoassay plus (ELISAPLUS). The gene and protein expression levels were assessed by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting techniques. The results were comparatively assessed between the four groups.

Results: The results confirmed the presence of GLP-1R in the NPCs indicating that liraglutide inhibited the high glucose-induced apoptosis, which was blocked by silencing GLP-1R with siRNA. Moreover, liraglutide stimulated the phosphorylation of Akt, mTOR and GSK3β. Treatment with LY294002 significantly increased the apoptosis of NPCs and reduced the levels of their downstream substrates (p-AKT, p-mTOR, and p-GSK3β). Further assessments revealed that activation of mTOR and GSK3β was almost completely inhibited by rapamycin and SB216763, respectively, which significantly increased the caspase-3 levels.

Conclusion: Liraglutide could protect NPCs against high glucose-induced apoptosis by activating the PI3K/AKT/mTOR/caspase-3 and PI3K/AKT/GSK3β/caspase-3 signaling pathways.

New insights on the reparative cells in bone regeneration and repair

Bone possesses a remarkable repair capacity to regenerate completely without scar tissue formation. This unique characteristic, expressed during bone development, maintenance and injury (fracture) healing, is performed by the reparative cells including skeletal stem cells (SSCs) and their descendants. However, the identity and functional roles of SSCs remain controversial due to technological difficulties and the heterogeneity and plasticity of SSCs. Moreover, for many years, there has been a biased view that bone marrow is the main cell source for bone repair. Together, these limitations have greatly hampered our understanding of these important cell populations and their potential applications in the treatment of fractures and skeletal diseases. Here, we reanalyse and summarize current understanding of the reparative cells in bone regeneration and repair and outline recent progress in this area, with a particular emphasis on the temporal and spatial process of fracture healing, the sources of reparative cells, an updated definition of SSCs, and markers of skeletal stem/progenitor cells contributing to the repair of craniofacial and long bones, as well as the debate between SSCs and pericytes. Finally, we also discuss the existing problems, emerging novel technologies and future research directions in this field.

Intracellular Accumulation of Advanced Glycation End Products Induces Osteoblast Apoptosis Via Endoplasmic Reticulum Stress

Osteoporosis is an aging-associated disease that is attributed to excessive osteoblast apoptosis. It is known that the accumulation of advanced glycation end products (AGEs) in bone extracellular matrix deteriorates osteoblast functions. However, little is known about the interaction between intracellular AGE accumulation and the induction of osteoblast apoptosis. In this study, we investigated the effect of intracellular AGE accumulation on osteoblast apoptosis in vitro and in vivo. In vitro, murine osteoblastic MC3T3-E1 cells were treated with glycolaldehyde (GA), an AGE precursor. GA-induced intracellular AGE accumulation progressed in time- and dose-dependent manners, followed by apoptosis induction. Intracellular AGE formation also activated endoplasmic reticulum (ER) stress-related proteins (such as glucose-regulated protein 78, inositol-requiring protein-1α (IRE1α), and c-Jun N-terminal kinase) and induced apoptosis. In agreement, treatment with the ER stress inhibitor 4-phenylbutyric acid and knocking down IRE1α expression ameliorated osteoblast apoptosis. Furthermore, the ratio between AGE- and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive osteoblasts in human vertebral bodies was significantly higher in an elderly group than in a younger group. A positive linear correlation between the ratio of AGE-positive and TUNEL-positive osteoblasts (r = 0.72) was also observed. Collectively, these results indicate that AGEs accumulated in osteoblasts with age and that intracellular AGE accumulation induces apoptosis via ER stress. These findings offer new insight into the mechanisms of osteoblast apoptosis and age-related osteoporosis. © 2020 American Society for Bone and Mineral Research.

Combined Use of Recombinant Human BMP-7 and Osteogenic Media May Have No Ideal Synergistic Effect on Leporine Bone Regeneration of Human Umbilical Cord Mesenchymal Stem Cells Seeded on Nanohydroxyapatite/Collagen/Poly (l-Lactide)

Human umbilical cord mesenchymal stem cells (hUC-MSCs) are a promising alternative source of mesenchymal stem cells (MSCs) that are enormously attractive for clinical use. This study was designed to investigate the effect of recombinant human bone morphogenetic protein-7 (rhBMP-7) and/or osteogenic media (OMD) on bone regeneration of hUC-MSCs seeded on nanohydroxyapatite/collagen/poly(l-lactide) (nHAC/PLA) in a rabbit model. The characteristics of stem cells were analyzed by plastic adherence, cell phenotype, and multilineage differentiation potential. Cell proliferation was examined using cell counting kit-8 assay. Osteogenic differentiation was evaluated by quantitative Ca²⁺ concentration, PO₄^3- concentration, alkaline phosphatase (ALP) activity, osteocalcin (OCN) secretion, and mineralized matrix formation. Bone regeneration was investigated in jaw bone defect repair in rabbit by microcomputed tomography, fluorescent labeling, and hematoxylin and eosin staining. Except for initial stress response, OMD and OMD + rhBMP-7 inhibited the proliferation of hUC-MSCs seeded on nHAC/PLA; rhBMP-7 inhibited cell proliferation in the nonlogarithmic phase and attenuated the inhibitory effect of OMD on cell proliferation. The inhibitory effects of OMD, rhBMP-7, and OMD + rhBMP-7 on cell proliferation were ranked as OMD > OMD + rhBMP-7 > rhBMP-7. OMD, rhBMP-7, and OMD + rhBMP-7 promoted Ca²⁺ concentration, PO₄^3- concentration, ALP activity, OCN secretion, and mineralized matrix formation of hUC-MSCs seeded on nHAC/PLA. The promoting effects of OMD, rhBMP-7, and OMD+rhBMP-7 on Ca²⁺ concentration, PO₄^3- concentration, ALP activity, OCN secretion, and mineralized matrix formation were ranked as rhBMP-7 > OMD > OMD + rhBMP-7, OMD > OMD + rhBMP-7 > rhBMP-7, OMD > rhBMP-7 > OMD + rhBMP-7, rhBMP-7 > OMD + rhBMP-7 > OMD, and OMD > rhBMP-7 > OMD + rhBMP-7, respectively. In rabbit jaw bone defect repair, OMD, rhBMP-7, and OMD + rhBMP-7 enhanced bone regeneration of hUC-MSCs seeded on nHAC/PLA, but the largest bone mineral apposition rate and bone formation were presented in cultures with rhBMP-7. These findings suggested that the combined use of rhBMP-7 and OMD may have no ideal synergistic effect on bone regeneration of hUC-MSCs seeded on nHAC/PLA in rabbit jaw bone defect.

Oxidative stress induced pyroptosis leads to osteogenic dysfunction of MG63 cells

Periodontitis is characterized by alveolar bone destruction and is one of the most common chronic oral diseases. Inflammatory cytokines released by pyroptosis, which can be triggered by oxidative stress, are critical in the development of periodontitis. This study aims to clarify whether oxidative stress causes osteoblast dysfunction by inducing pyroptosis in the process of periodontitis. We found that treatment with lipopolysaccharide (LPS) led to NLRP3 inflammasome-mediated pyroptosis of MG63 cells as well as decreased cell migration. Of note, LPS stimulation increased LDH release in a time- and dose-dependent manner. However, inhibition of reactive oxygen species with N-acetyl-L-cysteine attenuated oxidative stress-mediated pyroptosis and improved migration injury in osteoblasts treated with LPS. Further, inhibition of the NLRP3 inflammasome with MCC950 improved osteoblast migration and restored the expression of osteogenic differentiation-related proteins such as COL 1, RUNX 2 and ALP. In conclusion, oxidative stress caused by LPS induces pyroptosis in osteoblasts, leading to osteogenic dysfunction.

Cytokines and Bone: Osteoimmunology

Cytokines and hematopoietic growth factors have traditionally been thought of as regulators of the development and function of immune and blood cells. However, an ever-expanding number of these factors have been discovered to have major effects on bone cells and the development of the skeleton in health and disease (Table 1). In addition, several cytokines have been directly linked to the development of osteoporosis in both animal models and in patients. In order to understand the mechanisms regulating bone cells and how this may be dysregulated in disease states, it is necessary to appreciate the diverse effects that cytokines and inflammation have on osteoblasts, osteoclasts, and bone mass. This chapter provides a broad overview of this topic with extensive references so that, if desired, readers can access specific references to delve into individual topics in greater detail.

The Effects of Photobiomodulation on MC3T3-E1 Cells via 630 nm and 810 nm Light-Emitting Diode

BACKGROUND Photobiomodulation (PBM) has been explored as a promising therapeutic strategy to regulate bone cell growth; however, the effects of PBM on osteoblast cell lines remains poorly understood. In addition, as a light source of PBM, the light uniformity of light-emitting diode (LED) devices has not been given enough attention. MATERIAL AND METHODS Here, we sought to investigate the effects of PBM on MC3T3-E1 cells via 630 nm and 810 nm light from a newly designed LED with high uniformity of light. Cell proliferation, flow cytometric analysis, alkaline phosphatase (ALP) staining, ALP activity, Alizarin Red S staining, and quantitative real-time polymerase chain reaction (qRT-PCR) were carried out to assess treatment response. MC3T3-E1 cells were irradiated with LED devices (630±5 nm and 810±10 nm, continuous wave) for 200 seconds at a power density of 5 mW/cm² once daily. RESULTS Increases in cell proliferation and decreases in cell apoptosis were evident following irradiation. ALP staining intensity and activity were also significantly increased following irradiation. Level of mineralization was obviously enhanced in irradiated groups compared with non-irradiated controls. qRT-PCR also showed significant increases in mRNA expression of osteocalcin (OCN) and osteoprotegerin (OPG) in the irradiated groups. CONCLUSIONS Our results showed that LED PBM could promote the proliferation, ALP staining intensity and activity, level of mineralization, gene expression of OCN and OPG of MC3T3-E1 cells, with no significant difference between the 630 nm- and 810 nm-irradiated groups.

Enrichment of miR-126 enhances the effects of endothelial progenitor cell-derived microvesicles on modulating MC3T3-E1 cell function via Erk1/2-Bcl-2 signalling pathway

OBJECTIVE

To evaluate whether EPC-MVs could promote bone regeneration by directly regulating osteoblast through miR-126. The underlying mechanisms were also explored.

METHODS

EPCs were isolated from bone marrow mononuclear cells. EPC-MVs were collected from EPCs cultured medium. The lentivirus was used to induce miR-126 over-expression in EPCs and EPC-MVs. miR-126 expression was detected by qRT-PCR. The proliferation, migration, apoptosis and differentiation abilities of osteoblast cells MC3T3-E1 were analysed in the presence or absence of EPC-MVs or miR-126 overexpressed EPC-MVs (EPC-MVs-miR126). The proteins of Erk1/2 and Bcl-2 were analysed by western blot. Erk1/2 inhibitor was used for pathway exploration.

RESULTS

EPC-MVs reduced apoptosis and promoted proliferation and migration of MC3T3-E1 cells, which could be enhanced by miR-126 enrichment (p< 0.05). Neither EPC-MVs nor EPC-MVs-miR126 had an effect on MC3T3-E1 cell osteogenic differentiation (p> 0.05). EPC-MVs-miR126 had better effects than EPC-MVs on upregulating the expressions of p-Erk1/2 and Bcl-2, which were abolished by Erk1/2 inhibitor. ERK1/2-Bcl-2 activity plays a crucial role in the regulation of EPC-MVs/EPC-MVs-miR126 on the effect of MC3T3-E1 cells.

CONCLUSION

EPC-MVs promote proliferation and migration of MC3T3-E1 cell while reduced apoptosis via the miR-126/Erk1/2-Bcl-2 pathway. A combination of EPC-MVs and miR-126 might provide novel therapeutic targets for bone regeneration and fracture healing through regulating osteoblast.

Bidirectional regulation of osteogenic differentiation by the FOXO subfamily of Forkhead transcription factors in mammalian MSCs

Through loss‐ and gain‐of‐function experiments in knockout and transgenic mice, Forkhead box O (FOXO) family transcription factors have been demonstrated to play essential roles in many biological processes, including cellular proliferation, apoptosis and differentiation. Osteogenic differentiation from mesenchymal stem cells (MSCs) into osteoblasts is a well‐organized process that is carefully guided and characterized by various factors, such as runt‐related transcription factor 2 (Runx2), β‐catenin, osteocalcin (OCN), alkaline phosphatase (ALP) and activating transcription factor 4 (ATF4). Accumulating evidence suggests multiple interactions among FOXO members and the differentiation regulatory factors listed above, resulting in an enhancement or inhibition of osteogenesis in different stages of osteogenic differentiation. To systematically and integrally understand the role of FOXOs in osteogenic differentiation and explain the contrary phenomena observed in vitro and in vivo, we herein summarized FOXO‐interacting differentiation regulatory genes/factors and following alterations in differentiation. The underlying mechanism was further discussed on the basis of binding types, sites, phases and the consequent downstream transcriptional alterations of interactions among FOXOs and differentiation regulatory factors. Interestingly, a bidirectional effect of FOXOs on balancing osteogenic differentiation was discovered in MSCs. Moreover, FOXO factors are reported to be activated or suppressed by several context‐dependent signalling inputs during differentiation, and the underlying molecular basis may offer new drug development targets for treatments of bone formation defect diseases.

Fracture healing in a collagen-induced arthritis rat model: Radiology and histology evidence

This research was designed to investigate the fracture healing pattern in a rheumatoid arthritis (RA) rat model. A mid-shaft femur fracture (RA + F) model and normal fracture (NF) model as control were established. Micro-CT, H&E staining, TB staining, SO staining, tartrate-resistant acid phosphates, and immunohistochemistry test were performed. In the micro-CT images and H&E stains, fracture gaps were evident in the RA + F group 4 and 8 weeks after fracture. In detail, the bone mineral density, the ratio of bone volume to tissue volume, and trabecular thickness of the RA + F group were significantly lower than those of the NF group at all time points. Trabecular number value was significantly lower in the RA + F group 4 weeks after surgery in comparison with that of the NF group. Furthermore, the structure model index test result of the RA + F group was significantly higher than that of the NF group at all time points. TB staining and SO staining test results showed that the NF group had more cartilaginous callus in the earlier stage of bone healing process (4 weeks), and less cartilage callus formation in the later stage (8 weeks) in comparison with that of the RA + F group. Osteoclasts statistics score in the NF group were obviously lower than that of the RA + F group at all time points. MMP-3 and OPN protein levels of the fracture area in the RA + F group were significantly higher than those in the NF group. This study improves the understanding of the bone healing characteristics in patients with RA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2876-2885, 2018.

Role of advanced glycation end products in mobility and considerations in possible dietary and nutritional intervention strategies

Advanced glycation end products (AGEs), a group of compounds that are formed by non-enzymatic reactions between carbonyl groups of reducing sugars and free amino groups of proteins, lipids or nucleic acids, can be obtained exogenously from diet or formed endogenously within the body. AGEs accumulate intracellularly and extracellularly in all tissues and body fluids and can cross-link with other proteins and thus affect their normal functions. Furthermore, AGEs can interact with specific cell surface receptors and hence alter cell intracellular signaling, gene expression, the production of reactive oxygen species and the activation of several inflammatory pathways. High levels of AGEs in diet as well as in tissues and the circulation are pathogenic to a wide range of diseases. With respect to mobility, AGEs accumulate in bones, joints and skeletal muscles, playing important roles in the development of osteoporosis, osteoarthritis, and sarcopenia with aging. This report covered the related pathological mechanisms and the potential pharmaceutical and dietary intervention strategies in reducing systemic AGEs. More prospective studies are needed to determine whether elevated serum AGEs and/or skin autofluorescence predict a decline in measures of mobility. In addition, human intervention studies are required to investigate the beneficial effects of exogenous AGEs inhibitors on mobility outcomes.

Bone remodeling: A tissue-level process emerging from cell-level molecular algorithms

The human skeleton undergoes constant remodeling throughout the lifetime. Processes occurring on microscopic and molecular scales degrade bone and replace it with new, fully functional tissue. Multiple bone remodeling events occur simultaneously, continuously and independently throughout the body, so that the entire skeleton is completely renewed about every ten years.Bone remodeling is performed by groups of cells called Bone Multicellular Units (BMU). BMUs consist of different cell types, some specialized in the resorption of old bone, others encharged with producing new bone to replace the former. These processes are tightly regulated so that the amount of new bone produced is in perfect equilibrium with that of old bone removed, thus maintaining bone microscopic structure.To date, many regulatory molecules involved in bone remodeling have been identified, but the precise mechanism of BMU operation remains to be fully elucidated. Given the complexity of the signaling pathways already known, one may question whether such complexity is an inherent requirement of the process or whether some subset of the multiple constituents could fulfill the essential role, leaving functional redundancy to serve an alternative safety role. We propose in this work a minimal model of BMU function that involves a limited number of signals able to account for fully functional BMU operation. Our main assumptions were i) at any given time, any cell within a BMU can select only one among a limited choice of decisions, i.e. divide, die, migrate or differentiate, ii) this decision is irreversibly determined by depletion of an appropriate internal inhibitor and iii) the dynamics of any such inhibitor are coupled to that of specific external mediators, such as hormones, cytokines, growth factors. It was thus shown that efficient BMU operation manifests as an emergent process, which results from the individual and collective decisions taken by cells within the BMU unit in the absence of any external planning.

Safflower (Carthamus tinctorius L.) polysaccharide attenuates cellular apoptosis in steroid-induced avascular necrosis of femoral head by targeting caspase-3-dependent signaling pathway

The present study aimed to investigate the effects of a purified polysaccharide (SPS) from the safflower in a cellular model of steroid-associated necrosis of the femoral head (SANFH), which was established in primary murine osteoblasts suffering dexamethasone pretreatment. After treatment with SPS (25, 50 and 100 μg/ml), the degree of necrosis induced by dexamethasone was significantly reduced in osteoblasts as evidenced by an increase of cell viability and a decrease of apoptosis in osteoblasts. Furthermore, pretreatment with SPS (25, 50 and 100 μg/ml) significantly attenuated the activation of caspase-3 and cleavage of PARP relative to the model control cells. The addition of caspase-3 inhibitor (Z-DEVD-FMK) in dexamethasone-treated osteoblasts resulted in the inefficiency of SPS for inhibiting cellular apoptosis. Dose-dependent increases in alkaline phosphatase (ALP) activity, collagen synthesis and mineralization were also observed in SPS-treated osteoblasts at 72 h. The present study demonstrates that SPS may alleviate dexamethasone associated osteonecrosis by inhibiting caspsae-3-mediated apoptosis and may provide an alternative treatment for SANFH.

Liraglutide Inhibits the Apoptosis of MC3T3-E1 Cells Induced by Serum Deprivation through cAMP/PKA/β-Catenin and PI3K/AKT/GSK3β Signaling Pathways

In recent years, the interest towards the relationship between incretins and bone has been increasing. Previous studies have suggested that glucagon-like peptide-1 (GLP-1) and its receptor agonists exert beneficial anabolic influence on skeletal metabolism, such as promoting proliferation and differentiation of osteoblasts via entero-osseous-axis. However, little is known regarding the effects of GLP-1 on osteoblast apoptosis and the underlying mechanisms involved. Thus, in the present study, we investigated the effects of liraglutide, a glucagon-like peptide-1 receptor agonist, on apoptosis of murine MC3T3-E1 osteoblastic cells. We confirmed the presence of GLP-1 receptor (GLP-1R) in MC3T3-E1 cells. Our data demonstrated that liraglutide inhibited the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation, as detected by Annexin V/PI and Hoechst 33258 staining and ELISA assays. Moreover, liraglutide upregulated Bcl-2 expression and downregulated Bax expression and caspase-3 activity at intermediate concentration (100 nM) for maximum effect. Further study suggested that liraglutide stimulated the phosphorylation of AKT and enhanced cAMP level, along with decreased phosphorylation of GSK3β, increased β-catenin phosphorylation at Ser675 site and upregulated nuclear β-catenin content and transcriptional activity. Pretreatment of cells with the PI3K inhibitor LY294002, PKA inhibitor H89, and siRNAs GLP-1R, β-catenin abrogated the liraglutide-induced activation of cAMP, AKT, β-catenin, respectively. In conclusion, these findings illustrate that activation of GLP-1 receptor by liraglutide inhibits the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation through cAMP/PKA/β-catenin and PI3K/Akt/GSK3β signaling pathways.

Activation of Pro-apoptotic Caspases in Non-apoptotic Cells During Odontogenesis and Related Osteogenesis

Caspases are well known proteases in the context of inflammation and apoptosis. Recently, novel roles of pro-apoptotic caspases have been reported, including findings related to the development of hard tissues. To further investigate these emerging functions of pro-apoptotic caspases, the in vivo localisation of key pro-apoptotic caspases (-3,-6,-7,-8, and -9) was assessed, concentrating on the development of two neighbouring hard tissues, cells participating in odontogenesis (represented by the first mouse molar) and intramembranous osteogenesis (mandibular/alveolar bone). The expression of the different caspases within the developing tissues was correlated with the apoptotic status of the cells, to produce a picture of whether different caspases have potentially distinct, or overlapping non-apoptotic functions. The in vivo investigation was additionally supported by examination of caspases in an osteoblast-like cell line in vitro. Caspases-3,-7, and -9 were activated in apoptotic cells of the primary enamel knot of the first molar; however, caspase-7 and -8 activation was also associated with the non-apoptotic enamel epithelium at the same stage and later with differentiating/differentiated odontoblasts and ameloblasts. In the adjacent bone, active caspases-7 and -8 were present abundantly in the prenatal period, while the appearance of caspases-3,-6, and -9 was marginal. Perinatally, caspases-3 and -7 were evident in some osteoclasts and osteoblastic cells, and caspase-8 was abundant mostly in osteoclasts. In addition, postnatal activation of caspases-7 and -8 was retained in osteocytes. The results provide a comprehensive temporo-spatial pattern of pro-apoptotic caspase activation, and demonstrate both unique and overlapping activation in non-apoptotic cells during development of the molar tooth and mandibular/alveolar bone. The importance of caspases in osteogenic pathways is highlighted by caspase inhibition in osteoblast-like cells, which led to a significant decrease in osteocalcin expression, supporting a role in hard tissue cell differentiation.

Oxygen-distribution within 3-D collagen I hydrogels for bone tissue engineering

Tissue engineering (TE) approaches typically envisage the structural and functional reconstitution of previously damaged tissue in situ. An adequate three-dimensional environment is therefore of fundamental importance for the designated cells associated to the scaffold material. The sufficient supply with nutrients and oxygen in vitro and in vivo mark thereby critical challenges of TE. In this study, we intended to analyse the level of locally dissolved oxygen within 3-D cell-loaded collagen I gels in vitro. For the analysis of the oxygen levels in situ, we employed an optical fibre-based micro sensor setup, as well as a camera supported non-invasive optical sensor foil based technique. These complementary analytical tools enable the identification, localization, and temporal follow-up investigation of specified regions of interest within TE constructs. Human adipose-derived mesenchymal stem cells (hAdMSCs) cultured in collagen I gels under normoxic conditions were analysed periodically and kinetically up to 70 days - thereby revealing dynamic changes of the level of dissolved oxygen inside the gel constructs. Dependent on the applied cell concentration, the in vitro oxygen concentration (cO₂) within the gels reached physiological ranges (7-9%) after 21 days, or 35 days of culture. The minimal cO₂ was measured after 35 days in vitro, featuring an oxygen level of 4.8 ± 1.3%. Upon prolonged culture, a plateau-like status of the cO₂ around 8-9% established, indicating a change in the physiological activity of the cells under investigation. The expression patterns of BCL2, CASP3 and MCM5 revealed significant differences among the proliferative and apoptotic stages of the cell-loaded samples at the investigated time points of 7 and 70 days in culture. In summary, these data show the temporary dynamic nature of the oxygen distribution in cell-loaded gel constructs. The applied technique is an ideal tool for the evaluation of multiple parameters affecting the oxygen distribution in vitro. We conclude that it takes 5 weeks for establishing an equilibrium of cO₂. Levels reached in a 3-D gel construct are comparable with physiological oxygenation ranges in bone-associated tissues.

Osteogenic Potential of Caspases Related to Endochondral Ossification

Caspases have functions particularly in apoptosis and inflammation. Increasing evidence indicates novel roles of these proteases in cell differentiation, including those involved in osteogenesis. This investigation provides a complex screening of osteogenic markers affected by pan caspase inhibition in micromass cultures derived from mouse forelimbs. PCR Array analysis showed significant alterations in expression of 49 osteogenic genes after 7 days of inhibition. The largest change was a decrease in CD36 expression, which was confirmed at organ level by caspase inhibition in cultured mouse ulnae followed by CD36 immunohistochemical analysis. So far, available data point to osteogenic potential of pro-apoptotic caspases. Therefore, the expression of pro-apoptotic caspases (-3, -6, -7, -8, -9) within the growth plate of mouse forelimbs at the stage where the individual zones are clearly apparent was studied. Caspase-9 was reported in the growth plate for the first time as well as caspase-6 and -7 in the resting zone, caspase-7 in the proliferation, and caspase-6 and -8 in the ossification zone. For all caspases, there was a gradient increase in activation toward the ossification zone. The distribution of staining varied significantly from that of apoptotic cells, and thus, the results further support non-apoptotic participation of caspases in osteogenesis.

Evaluation of the anti-osteoporotic effect of Ginkgo biloba L. in Wistar rats with glucocorticoid-induced-osteoporosis by bone densitometry using dual-energy x-ray absorptiometry (DEXA) and mechanical testing

Evaluate the effect of the extract of Ginkgo biloba in the bone alkaline phosphatase, bone mineral density, in the mechanical properties of the tibia in rats with glucocorticoid-induced-osteoporosis. After osteoporosis induction, the rats were divided into five groups: Osteoporosis; EGb1 (28 mg/Kg); EGb2 (56 mg/Kg); alendronate (0.2 mg/animal) and control. The animals were treated during 20 and 30 days. The control group was compared with the osteoporosis's (Student's t-test), while the other were analyzed by ANOVA test followed by Tukey/Dunnett'T3 (p<0.05). In the osteoporosis group the bone alkaline phosphatase, bone mineral density, the bone stiffness, the maximum load and the resilience were reduced. The bone alkaline phosphatase values increased in the EGb1 and EGb2 groups (30 days). In addition, in the EGb2 and alendronate groups (20 and 30 days) the bone mineral density increased. The extract of Ginkgo biloba restored bone alkaline phosphatase and bone mineral density using dual-energy x-ray absorptiometry.

Diabetes and Bone Disease

The World Health Organization estimates that diabetes mellitus occurs in more than 415 million people; this number could double by the year 2040. Epidemiologic data have shown that the skeletal system may be a target of diabetes-mediated damage, leading to the development of diabetes-induced osteoporosis. T1D and T2D have been associated with an increased risk of fracture. Bone mineral density and fracture risk prediction tools developed for the general population capture some of the risk associated with diabetes. Recent adaptations to these tools have improved their efficacy in patients with diabetes.

The Cooperative Effect of Genistein and Protein Hydrolysates on the Proliferation and Survival of Osteoblastic Cells (hFOB 1.19)

Chum salmon skin gelatin, de-isoflavoned soy protein, and casein were hydrolyzed at two degrees of hydrolysis. Genistein, the prepared hydrolysates, and genistein-hydrolysate combinations were assessed for their proliferative and anti-apoptotic effects on human osteoblasts (hFOB 1.19) to clarify potential cooperative effects between genistein and these hydrolysates in these two activities. Genistein at 2.5 μg/L demonstrated the highest proliferative activity, while the higher dose of genistein inhibited cell growth. All hydrolysates promoted osteoblast proliferation by increasing cell viability to 102.9%–131.1%. Regarding etoposide- or NaF-induced osteoblast apoptosis, these hydrolysates at 0.05 g/L showed both preventive and therapeutic effects against apoptosis. In the mode of apoptotic prevention, the hydrolysates decreased apoptotic cells from 32.9% to 15.2%–23.7% (etoposide treatment) or from 23.6% to 14.3%–19.6% (NaF treatment). In the mode of apoptotic rescue, the hydrolysates lessened the extent of apoptotic cells from 15.9% to 13.0%–15.3% (etoposide treatment) or from 13.3% to 10.9%–12.7% (NaF treatment). Gelatin hydrolysates showed the highest activities among all hydrolysates in all cases. All investigated combinations (especially the genistein-gelatin hydrolysate combination) had stronger proliferation, apoptotic prevention, and rescue than genistein itself or their counterpart hydrolysates alone, suggesting that genistein cooperated with these hydrolysates, rendering greater activities in osteoblast proliferation and anti-apoptosis.

Quiescent Bone Lining Cells Are a Major Source of Osteoblasts During Adulthood

The in vivo origin of bone-producing osteoblasts is not fully defined. Skeletal stem cells, a population of mesenchymal stem cells resident in the bone marrow compartment, are thought to act as osteoprogenitors during growth and adulthood. Quiescent bone lining cells (BLCs) have been suggested as a population capable of activation into mature osteoblasts. These cells were defined by location and their morphology and studies addressing their significance have been hampered by their inaccessibility, and lack of markers that would allow for their identification and tracing. Using lineage tracing models, we have observed labeled osteoblasts at time points extending beyond the reported lifespan for this cell type, suggesting continuous reactivation of BLCs. BLCs also make a major contribution to bone formation after osteoblast ablation, which includes the ability to proliferate. In contrast, mesenchymal progenitors labeled by Gremlin1 or alpha smooth muscle actin do not contribute to bone formation in this setting. BLC activation is inhibited by glucocorticoids, which represent a well-established cause of osteoporosis. BLCs express cell surface markers characteristic of mesenchymal stem/progenitors that are largely absent in osteoblasts including Sca1 and Leptin Receptor. BLCs also show different gene expression profiles to osteoblasts, including elevated expression of Mmp13, and osteoclast regulators RANKL and macrophage colony stimulating factor, and retain osteogenic potential upon transplantation. Our findings provide evidence that bone lining cells represent a major source of osteoblasts during adulthood. Stem Cells 2016;34:2930-2942.

Porcine placenta hydrolysates enhance osteoblast differentiation through their antioxidant activity and effects on ER stress

BACKGROUND

Osteoporosis is a disease characterized by decreased bone strength, decreased bone mass, and bone deterioration. Oxidative damage is an important contributor to functional changes in the development of osteoporosis. Here we found that porcine placenta hydrolysates (PPHs) protect MC3T3-E1 osteoblastic cells against hydrogen peroxide (H2O2)-induced oxidative damage.

METHODS

In vitro cell viability was determined using trypan blue dye exclusion. ER stress and apoptosis were evaluated using immunoblotting and a commercially available caspase kit. ALP, osteocalcin, Runx2, and osterix expression levels were evaluated by RT-PCR using isolated RNA. ROS, NADPH oxidase, and SOD activity levels were also measured.

RESULTS

We investigated the mechanisms underlying PPH-mediated inhibition of H2O2-induced ER stress and ROS production. PPHs also regulated osteoblast differentiation via the upregulation of alkaline phosphatase (ALP) expression in MC3T3-E1 osteoblastic cells. Also, treatment with PPHs enhanced the transcription of osteocalcin, Runx2, and osterix. These effects were all associated with the antioxidant actions of PPHs. Moreover, PPHs reversed the decrease in SOD activity, decreased ROS release, and inhibited NADPH oxidase activity in H2O2-treated MC3T3-E1 osteoblastic cells.

CONCLUSIONS

PPHs protect cells against H2O2-induced cell damage when ER stress is involved. In addition, PPHs enhance osteoblast differentiation. This enhancement likely explains the regulatory effect of PPHs on bone metabolism disturbances, i.e. PPHs control ER stress and the related ROS production in osteoblasts.

Porcine placenta hydrolysates regulate calcium disturbance in MC3T3-E1 osteoblastic cells

BACKGROUND

In bone metabolism, Ca(2+) disturbance and oxidative damage are the main biochemical factors related to pathology. Osteoblasts are bone-forming cells that also control bone endocrinology. Endocrine hormones and proteins are matured, folded, and secreted in the endoplasmic reticulum (ER). ER stress has emerged as a new pathological mechanism to explain bone disturbance. Here we studied the role of porcine placenta hydrolysates (PPHs) in the regulation of ER stress.

METHODS

Cell viability was determined in vitro using trypan blue dye exclusion. ER stress and apoptosis were evaluated using immunoblotting and a caspase kit. The fluorescent Ca(2+)-binding dye Fura-2/AM was used to measure changes in intracellular Ca(2+) ([Ca(2+)]i). ROS levels, NADPH oxidase activity, and superoxide dismutase (SOD) activity were also measured.

RESULTS

PPHs protected MC3T3-E1 osteoblastic cells against thapsigargin (Tg)-induced ER stress. Moreover, PPHs regulated caspase-12 and -3 activities, thereby protecting against cell death, and also regulated Tg-induced Ca(2+) release. The Ca(2+) chelator BAPT/AM also regulated caspase-12 and -3 activities and prevented Ca(2) stress-induced cell death. In the presence of PPHs or BAPTA/AM, Ca(2+)-related ROS were also regulated, as demonstrated by alterations in NADPH oxidase and SOD activity.

CONCLUSIONS

PPHs appear to regulate bone metabolism disturbance by controlling Ca(2+) concentrations, and thus ER stress and ROS, in osteoblasts cultured in vitro.

Self-assembling bisphosphonates into nanofibers to enhance their inhibitory capacity on bone resorption

Osteoporosis (OP) is an important aging-related disease and the effective prevention/treatment of this disease remains challenging. Considering the acidic microenvironment of bone resorption lacunae, herein, we rationally designed two pamidronate (Pami)-derivative and alendronate (Alen)-derivative hydrogelators and which self-assemble into nanofibers to form supramolecular hydrogels under acidic conditions. Cell viability assay, osteoclastogenesis, osteoclastic gene expression, and in vitro bone resorption results indicated that both and have better inhibitory effects on osteoclastic formation and bone resorption than Pami and Alen, respectively. We anticipate that our new drugs and could "smartly" self-assemble and locally concentrate the drugs at bone resorption lacunae in vivo and subsequently prevent/treat osteoporosis more efficiently.

Arg972 insulin receptor substrate-1 enhances tumor necrosis factor-α-induced apoptosis in osteoblasts

The presence of Arg972 insulin receptor substrate-1 (IRS-1) is associated with impaired insulin/IRS-1 signaling to activate phosphatidylinositol-3 kinase (PI3K). Tumor necrosis factor-α (TNF-α), an inflammatory cytokine with a central role in the pathogenesis of rheumatoid arthritis (RA), induces apoptosis in osteoblasts, which are the principal cell type responsible for bone loss in RA. In our previous study, an association between Arg972 IRS-1 and a high risk and severity of RA was identified. In the present study, the effects of Arg972 IRS-1 and IRS-1 on TNF-α-induced apoptosis in human osteoblasts were examined. Normal and RA osteoblasts were stably transfected with Arg972 IRS-1 and IRS-1. In addition, cells were stably transduced with IRS-1-shRNA to knock down IRS1. Following stimulation with 10 nM insulin for 30 min, the stable overexpression of Arg972 IRS-1 and knock down of IRS-1 significantly decreased IRS-1-associated PI3K activity and Akt activation/phosphorylation at serine 473 (ser473) and enhanced TNF-α-induced apoptosis in normal and in RA osteoblasts. By contrast, the stable overexpression of IRS-1 significantly increased the levels of IRS-1-associated PI3K activity and Akt phosphorylation (ser473) and inhibited TNF-α-induced apoptosis, which was eliminated by pretreatment with 50 µn BJM120, a selective PI3K inhibitor, for 30 min. In conclusion, the present study provided the first evidence, to the best of our knowledge, that insulin stimulation of Arg972 IRS-1 and IRS-1 enhanced and inhibited TNF-α-induced apoptosis, respectively in normal and RA osteoblasts by a PI3K‑dependent mechanism. These findings suggest that insulin/IRS-1 signaling is important in the pathogenesis of RA.

MicroRNA-1 participates in nitric oxide-induced apoptotic insults to MC3T3-E1 cells by targeting heat-shock protein-70

Our previous studies showed that nitric oxide (NO) could induce osteoblast apoptosis. MicroRNA-1 (miR-1), a skeletal- and cardiac muscle-specific small non-coding RNA, contributes to the regulation of multiple cell activities. In this study, we evaluated the roles of miR-1 in NO-induced insults to osteoblasts and the possible mechanisms. Exposure of mouse MC3T3-E1 cells to sodium nitroprusside (SNP) increased amounts of cellular NO and intracellular reactive oxygen species. Sequentially, SNP decreased cell survival but induced caspase-3 activation, DNA fragmentation, and cell apoptosis. In parallel, treatment with SNP induced miR-1 expression in a time-dependent manner. Application of miR-1 antisense inhibitors to osteoblasts caused significant inhibition of SNP-induced miR-1 expression. Knocking down miR-1 concurrently attenuated SNP-induced alterations in cell morphology and survival. Consecutively, SNP time-dependently inhibited heat-shock protein (HSP)-70 messenger (m)RNA and protein expressions. A bioinformatic search predicted the existence of miR-1-specific binding elements in the 3'-untranslational region of HSP-70 mRNA. Downregulation of miR-1 expression simultaneously lessened SNP-induced inhibition of HSP-70 mRNA and protein expressions. Consequently, SNP-induced modifications in the mitochondrial membrane potential, caspase-3 activation, DNA fragmentation, and apoptotic insults were significantly alleviated by miR-1 antisense inhibitors. Therefore, this study showed that miR-1 participates in NO-induced apoptotic insults through targeting HSP-70 gene expression.

Muscle-bone and fat-bone interactions in regulating bone mass: do PTH and PTHrP play any role?

Metabolic bone disease occurs when there is a net loss in bone density. Osteoporosis, the most common metabolic bone disease, is a devastating problem and an increasingly major public health issue. A substantial body of evidence in the elderly population indicates that a relationship exists between the components of body weight and various measures of bone/mass, density, and function. Both muscle and fat contribute to the body's total weight and the intimate associations of muscle, fat, and bone are known. But the close functional interactions between muscle and bone or fat and bone are largely unidentified and have drawn much attention in recent years. Each of these tissues not only responds to afferent signals from traditional hormone systems and the central nervous systems but also secretes factors with important endocrine functions. Studies suggest that during growth, development, and aging, the relationship of muscle and fat with the skeleton possibly governs bone homeostasis and turnover. A better understanding of the endocrine function and the cellular and molecular mechanisms and pathways linking muscle or adipose tissues with bone anabolism and catabolism is a new avenue for novel pathways for anabolic drug discovery. These in turn will likely lead to more rational therapy toward increasingly prevalent disorders like osteoporosis. In this review, some of the recent works on the interaction of bone with muscle and fat are highlighted, and in so doing the role of parathyroid hormone (PTH), and PTH-related peptide (PTHrP) is surveyed.

17β-Estradiol inhibits ER stress-induced apoptosis through promotion of TFII-I-dependent Grp78 induction in osteoblasts

Although many studies have suggested that estrogen prevents postmenopausal bone loss partially due to its anti-apoptosis effects in osteoblasts, the underlying mechanism has not been fully elucidated. In the present study, we found that 17β-estradiol (17β-E₂), one of the primary estrogens, inhibited endoplasmic reticulum (ER) stress-induced apoptosis in MC3T3-E1 cells and primary osteoblasts. Interestingly, 17β-E₂-promoted Grp78 induction, but not CHOP induction in response to ER stress. We further confirmed that Grp78-specific siRNA reversed the inhibition of 17β-E₂ on ER stress-induced apoptosis by activating caspase-12 and caspase-3. Moreover, we found that 17β-E₂ markedly increased the phosphorylated TFII-I levels and nuclear localization of TFII-I in ER stress conditions. 17β-E₂ stimulated Grp78 promoter activity in a dose-dependent manner in the presence of TFII-I and enhanced the binding of TFII-I to the Grp78 promoter. In addition, 17β-E₂ notably increased phosphorylated ERK1/2 levels and Ras kinase activity in MC3T3-E1 cells. The ERK1/2 activity-specific inhibitor U0126 remarkably blocked 17β-E₂-induced TFII-I phosphorylation and Grp78 expression in response to ER stress. Together, 17β-E₂ protected MC3T3-E1 cells against ER stress-induced apoptosis by promoting Ras-ERK1/2-TFII-I signaling pathway-dependent Grp78 induction.