Emerging therapeutic opportunities for skeletal restoration

Pathophysiology of bone remodelling cycle: Role of immune system and lipids

Osteoporosis is the most common skeletal disease worldwide, characterized by low bone mineral density, resulting in weaker bones, and an increased risk of fragility fractures. The maintenance of bone mass relies on the precise balance between bone synthesis and resorption. The close relationship between the immune and skeletal systems, called "osteoimmunology", was coined to identify these overlapping "scientific worlds", and its function resides in the evaluation of the mutual effects of the skeletal and immune systems at the molecular and cellular levels, in both physiological and pathological states. Lipids play an essential role in skeletal metabolism and bone health. Indeed, bone marrow and its skeletal components demand a dramatic amount of daily energy to control hematopoietic turnover, acquire and maintain bone mass, and actively being involved in whole-body metabolism. Statins, the main therapeutic agents in lowering plasma cholesterol levels, are able to promote osteoblastogenesis and inhibit osteoclastogenesis. This review is meant to provide an updated overview of the pathophysiology of bone remodelling cycle, focusing on the interplay between bone, immune system and lipids. Novel therapeutic strategies for the management of osteoporosis are also discussed.

Fragility Fracture: 10 Commandments

Background

Fragility fractures are a major health concern. It is a fracture that occurs from a low-impact event, such as a fall from standing height or less typically due to weakened bones. These fractures are most commonly associated with conditions like osteoporosis, where the bone density is reduced, making the bones more susceptible to get fractured. Fragility fractures often occur in older adults including post-menopausal women and commonly affect areas, such as the hip, spine, and wrist. These fractures reflect the underlying bone fragility, and following first fragility fracture, there is increased risk of getting further fractures. Apart from osteoporosis, the contributing factors have also to be considered like age, gender, nutritional deficiencies, physical activities, and medical conditions like chronic kidney disease. The other risk factors like smoking, and excessive alcohol consumption, and certain medications such as corticosteroids and anti-convulsants like sodium valproate, can overtime result into osteoporosis.

Methods

Fragility fractures basically revolve around the terminal management of osteoporosis and many issues have not been over emphasized. Hence, these 10 commandments have been crafted to focus on the areas which can help prevent fragility fractures or combat those cases who come with a history of fragility fractures.

Results

The ten commandments have crystallized into various headings, including fragility fracture-the risk factors & DEXA, subnormal turnover bone diseases, microbiota & microbiome, inflammaging including obesity, parathyroid, thyroid & testosterone, dilemmas in the management of osteoporosis in younger adults, vitamin D, calcium & albumin, pharmacologic treatment options, associated medications & alternative therapies, and monitoring. High and low turnover bone disease, dysbiosis in gut, and inflammaging are the highlights including therapy and monitoring.

Conclusion

Fragility fracture also known as osteoporotic fracture has significant morbidity and mortality. Management of osteoporosis has been emboldened with the existing basket of both anti-resorptive and anabolic drugs. Safety concerns on long-term use of these drugs are emerging. These ten commandments will help management strategies to concentrate on targeting therapy to persons most "at risk" of getting these fractures.

Critical roles of miR-21 in promotions angiogenesis: friend or foe?

MiRNAs are small RNA strands that are managed following transcription and are of substantial importance in blood vessel formation. It is essential to oversee the growth, differentiation, death, movement and construction of tubes by angiogenesis-affiliated cells. If miRNAs are not correctly regulated in regard to angiogenesis, it can deteriorate the health and lead to various illnesses, which include cancer, cardiovascular disorder, critical limb ischemia, Crohn's disease, ocular diseases, diabetic microvascular complications, and more. Consequently, it is vital to understand the crucial part that miRNAs play in the development of blood vessels, so we can develop reliable treatment plans for vascular diseases. This write-up will assess the critical role of miR-21/exosomal miR-21 in managing angiogenesis associated with bone growth, wound recovery, and other pathological conditions like tumor growth, ocular illnesses, diabetes, and other diseases connected to formation of blood vessels. Previous investigations have demonstrated that miR-21 is present at higher amounts in certain cancerous cells, and it influences a multitude of genes that moderate the increased creation of blood vessels. Furthermore, studies demonstrated that exosomal miR-21 has the capacity to interact with endothelial cells to foster tumor angiogenesis. For that reason, this review explains the critical importance of miR-21/exosomal miR-21 in managing both healthy and diseased states of angiogenesis.

Progranulin Protects Against Osteoporosis by Regulating Osteoclast and Osteoblast Balance via TNFR Pathway

Osteoporosis is a disease of bone metabolism caused by an imbalance between osteoclast-mediated bone destruction and osteoblast-mediated bone formation. Tumour necrosis factor α (TNFα) has been reported to promote osteoclast generation and inhibit osteoblast generation. Progranulin (PGRN), which has a strong anti-inflammatory effect, interacts with tumour necrosis factor receptor (TNFR). Serum and bone tissues from patients with or without osteoporosis were collected to analyse the relationship between PGRN content and bone metabolic markers. The role of TNFα and PGRN in osteoclast differentiation was explored by using RAW 264.7 cells and BMMs. MC3T3-E1 cells and BMSCs were used to observe the role of TNFα and PGRN in osteoblast differentiation. The PGRN content in the serum and bone tissues of osteoporosis patients was lower than that in the serum and bone tissues of nonosteoporosis patients. TNFα promoted osteoclast differentiation, while PGRN inhibited this effect by interacting with TNFR1. PGRN inhibited TNFα-mediated attenuation of osteoblast differentiation by interacting with TNFR1. Moreover, PGRN alone promoted osteoblast differentiation by interacting with TNFR2. Our findings reveal that PGRN can effectively inhibit TNFα-induced osteoporosis and has a certain osteogenic effect. This discovery might provide a potential target for osteoporosis treatment.

Key Interaction Changes Determine the Activation Process of Human Parathyroid Hormone Type 1 Receptor

The parathyroid hormone type 1 receptor (PTH1R) plays a crucial role in modulating various physiological functions and is considered an effective therapeutic target for osteoporosis. However, a lack of detailed molecular and energetic information about PTH1R limits our comprehensive understanding of its activation process. In this study, we performed computational simulations to explore key events in the activation process, such as conformational changes in PTH1R, Gs protein coupling, and the release of guanosine diphosphate (GDP). Our analysis identified kinetic information, including the rate-determining step, transition state, and energy barriers. Free-energy and structural analyses revealed that GDP could be released from the Gs protein when the binding cavity is partially open. Additionally, we predicted important residues, including potential pathogenic mutations, and verified their significance through site-directed mutations. These findings enhance our understanding of class B GPCR activation mechanisms. Furthermore, the methodology employed in this study can be applied to other biophysical systems.

Fam102a translocates Runx2 and Rbpjl to facilitate Osterix expression and bone formation

Bone remodeling maintains the robustness of the bone tissue by balancing bone resorption by osteoclasts and bone formation by osteoblasts. Although these cells together play a crucial role in bone remodeling, only a few reports are available on the common factors involved in the differentiation of the two types of cells. Here, we show family with sequence similarity 102 member A (Fam102a) as a bone-remodeling factor that positively regulates both osteoclast and osteoblast differentiation. Fam102a regulates osteoblast differentiation by controlling recombination signal binding protein for immunoglobulin κ J region-like (Rbpjl). The Fam102a-Rbpjl axis promotes the nuclear translocation of transcription factors and enhances the expression of Osterix, a transcription factor essential for osteoblast differentiation. The deletion of Fam102a or a functional mutation in Rbpjl leads to osteopenia accompanied by reduced osteoblastic bone formation. Thus, the Fam102a-Rbpjl axis plays an important role in osteoblasts and this finding provides insights into bone remodeling.

2'-Fucosyllactose ameliorates aging-related osteoporosis by restoring gut microbial and innate immune homeostasis

INTRODUCTION

Aging-related osteoporosis is considered as a serious public health concern for middle-aged and elderly people, with an intricated pathogenesis including the recently identified aging-induced immunological dysfunction and gut microbial disorder. The intervention based on dietary prebiotics is recommended to retain bone health and postpone the progression of osteoporosis.

OBJECTIVES

As a well-defined prebiotic, 2'-fucosyllactose (2'-FL) has been thoroughly validated with positive effect on systemic health and was proposed in this study to unveil its intervention on aging-related osteoporosis, as well as the underlying mechanisms involving the gut microecology and innate immunity.

METHODS

The effects of dietary 2'-FL on osteoporosis phenotypes were identified by evaluating the severity of bone loss and microstructure damage in natural aging mice. The mechanisms relying on innate immune profile, intestinal barrier function, and gut microbial homeostasis, were analyzed to elucidate the signaling axis. The detailed molecular signaling was validated based on LPS-stimulated RAW 264.7 murine macrophages.

RESULTS

The results indicated that 12-week 2'-FL intervention retrieved bone loss and microstructure damage in natural aging mice. Also, 2'-FL alleviated aging-induced colonic inflammation, gut barrier dysfunction, and abnormal expression of intestinal tight-junction protein. The impact of 2'-FL treatment on the aging-induced gut microbial dysbiosis was validated by restoring gut microbiota diversity, recovering the abundance of Bifidobacterium, Prevotellaceae and Akkermansia, and inhibiting the growth of Stenotrophomonas. Flow cytometry analysis revealed changes in dendritic cell (DC) and macrophage subsets with age, and a decrease in M1-polarized macrophages was observed in 2'-FL-treated aged mice and RAW264.7 cells potentially through the interaction with toll-like receptor 4 (TLR4) to suppress NF-κB signaling and the secretion of proinflammatory factors.

CONCLUSION

These findings highlight the preventive effect of 2'-FL on aging-associated osteoporosis by regulating gut microbial homeostasis and innate immune responses.

Two-Year Outcomes of Daily and Twice-Weekly Teriparatide Treatment in Postmenopausal Women with Severe Osteoporosis: A Randomized Non-Blinded Prospective Study

BACKGROUND

The long-term effects of daily teriparatide (D-TPTD) and twice-weekly TPTD (W-TPTD) injections are compared among postmenopausal women with severe osteoporosis.

METHODS

A total of 102 patients were enrolled and randomly allocated into two groups for the administration of either D-TPTD or W-TPTD. Treatment efficacy was measured as the percentage change in bone mineral density (ΔBMD) from baseline in the lumbar spine, total hip, and femoral neck. The findings were compared between the two groups.

RESULTS

At 24 months after treatment, the persistence rates and medication possession ratios in the D-TPTD and W-TPTD groups were 68.6% and 56.9%, and 87.8% and 92.0%, respectively. The ΔBMD in the lumbar spine, total hip, and femoral neck were 15.6%±10.2%, 5.3%± 6.3%, and 5.5%±6.2%, respectively, in the D-TPTD group; and 9.5%±7.9%, 2.3%±6.2%, and 3.1%±7.4%, respectively, in the W-TPTD group following 24 months of treatment. The ΔBMD of the lumbar spine (p=0.008) at 24 months and total hip (p=0.024) at 18 months differed significantly between the two groups.

CONCLUSIONS

D-TPTD administration resulted in a significantly higher BMD in the lumbar spine and total hip, supporting this therapeutic regimen for postmenopausal women with severe osteoporosis.

Bone Targeting Nanoparticles for the Treatment of Osteoporosis

Osteoporosis (OP) affects millions of people worldwide, especially postmenopausal women and the elderly. Although current available anti-OP agents can show promise in slowing down bone resorption, most are not specifically delivered to the hard tissue, causing significant toxicity. A bone-targeted nanodrug delivery system can reduce side effects and precisely deliver drug candidates to the bone. This review focuses on the progress of bone-targeted nanoparticles in OP therapy. We enumerate the existing OP medications, types of bone-targeted nanoparticles and categorize pairs of the most common bone-targeting functional groups. Finally, we summarize the potential use of bone-targeted nanoparticles in OP treatment. Ongoing research into the development of targeted ligands and nanocarriers will continue to expand the possibilities of OP-targeted therapies into clinical application.

Alamandine attenuates ovariectomy-induced osteoporosis by promoting osteogenic differentiation via AMPK/eNOS axis

BACKGROUND

Alamandine is a newly characterized peptide of renin angiotensin system. Our study aims to investigate the osteo-preservative effects of alamandine, explore underlying mechanism and bring a potential preventive strategy for postmenopausal osteoporosis in the future.

METHODS

An ovariectomy (OVX)-induced rat osteoporosis model was established for in vivo experiments. Micro-computed tomography and three-point bending test were used to evaluate bone strength. Histological femur slices were processed for immunohistochemistry (IHC). Bone turnover markers and nitric oxide (NO) concentrations in serum were determined with enzyme-linked immunosorbent assay (ELISA). The mouse embryo osteoblast precursor (MC3T3-E1) cells were used for in vitro experiments. The cell viability was analysed with a Cell Counting Kit‑8. We performed Alizarin Red S staining and alkaline phosphatase (ALP) activity assay to observe the differentiation status of osteoblasts. Western blotting was adopted to detect the expression of osteogenesis related proteins and AMP-activated protein kinase/endothelial nitric oxide synthase (AMPK/eNOS) in osteoblasts. DAF-FM diacetate was used for semi-quantitation of intracellular NO.

RESULTS

In OVX rats, alamandine alleviated osteoporosis and maintained bone strength. The IHC showed alamandine increased osteocalcin and collagen type I α1 (COL1A1) expression. The ELISA revealed alamandine decreased bone turnover markers and restored NO level in serum. In MC3T3-E1 cells, alamandine promoted osteogenic differentiation. Western blotting demonstrated that alamandine upregulated the expression of osteopontin, Runt-related transcription factor 2 and COL1A1. The intracellular NO was also raised by alamandine. Additionally, the activation of AMPK/eNOS axis mediated the effects of alamandine on MC3T3-E1 cells and bone tissue. PD123319 and dorsomorphin could repress the regulating effect of alamandine on bone metabolism.

CONCLUSION

Alamandine attenuates ovariectomy-induced osteoporosis by promoting osteogenic differentiation via AMPK/eNOS axis.

The serine synthesis pathway drives osteoclast differentiation through epigenetic regulation of NFATc1 expression

Bone-resorbing osteoclasts are vital for postnatal bone health, as increased differentiation or activity results in skeletal pathologies such as osteoporosis. The metabolism of mature osteoclasts differs from their progenitor cells, but whether the observed metabolic changes are secondary to the altered cell state or actively drive the process of cell differentiation is unknown. Here, we show that transient activation of the serine synthesis pathway (SSP) is essential for osteoclastogenesis, as deletion of the rate-limiting enzyme phosphoglycerate dehydrogenase in osteoclast progenitors impairs their differentiation and results in increased bone mass. In addition, pharmacological phosphoglycerate dehydrogenase inhibition abrogated bone loss in a mouse model of postmenopausal osteoporosis by blocking bone resorption. Mechanistically, SSP-derived α-ketoglutarate is necessary for histone demethylases that remove repressive histone methylation marks at the nuclear factor of activated T cells, cytoplasmic 1 (Nfatc1) gene locus, thereby inducing NFATc1 expression and consequent osteoclast maturation. Taken together, this study reveals a metabolic-epigenetic coupling mechanism that directs osteoclast differentiation and suggests that the SSP can be therapeutically targeted to prevent osteoporotic bone loss.

Repurpose dasatinib and quercetin: Targeting senescent cells ameliorates postmenopausal osteoporosis and rejuvenates bone regeneration

Clinical therapies developed for estrogen-deficiency-driven postmenopausal osteoporosis (PMO) and related diseases, such as bone degeneration, show multiple adverse effects nowadays. Targeting senescent cells (SnCs) and the consequent senescence-associated secretory phenotype (SASP) with a combination of dasatinib and quercetin (DQ) is a recently developed novel therapy for multiple age-related diseases. Herein, we found that estrogen deficiency induced-bone loss was attributed to a pro-inflammatory microenvironment with SASP secretions and accelerated SnC accumulation, especially senescent mesenchymal stem cells (MSCs) characterized by exhaustion and dysfunction in middle aged rats. Systematically targeting SnCs with DQ strikingly ameliorated PMO and restored MSC function. Local administration of DQ and bone morphogenetic protein 2 (BMP2) in combination promoted osteogenic differentiation of MSCs and rejuvenated osteoporotic bone regeneration. Our results repurposed DQ as an attractive therapy for treating PMO and related diseases.

Bone/cartilage organoid on-chip: Construction strategy and application

The necessity of disease models for bone/cartilage related disorders is well-recognized, but the barrier between ex-vivo cell culture, animal models and the real human body has been pending for decades. The organoid-on-a-chip technique showed opportunity to revolutionize basic research and drug screening for diseases like osteoporosis and arthritis. The bone/cartilage organoid on-chip (BCoC) system is a novel platform of multi-tissue which faithfully emulate the essential elements, biologic functions and pathophysiological response under real circumstances. In this review, we propose the concept of BCoC platform, summarize the basic modules and current efforts to orchestrate them on a single microfluidic system. Current disease models, unsolved problems and future challenging are also discussed, the aim should be a deeper understanding of diseases, and ultimate realization of generic ex-vivo tools for further therapeutic strategies of pathological conditions.

Identification of a binding site on soluble RANKL that can be targeted to inhibit soluble RANK-RANKL interactions and treat osteoporosis

One of the major challenges for discovering protein-protein interaction inhibitors is identifying selective and druggable binding sites at the protein surface. Here, we report an approach to identify a small molecular binding site to selectively inhibit the interaction of soluble RANKL and RANK for designing anti-osteoporosis drugs without undesirable immunosuppressive effects. Through molecular dynamic simulations, we discovered a binding site that allows a small molecule to selectively interrupt soluble RANKL-RANK interaction and without interfering with the membrane RANKL-RANK interaction. We describe a highly potent inhibitor, S3-15, and demonstrate its specificity to inhibit the soluble RANKL-RANK interaction with in vitro and in vivo studies. S3-15 exhibits anti-osteoporotic effects without causing immunosuppression. Through in silico and in vitro experiments we further confirm the binding model of S3-15 and soluble RANKL. This work might inspire structure-based drug discovery for targeting protein-protein interactions.

Skeletal Characteristics of Children and Adolescents with Turner Syndrome

Turner syndrome (TS) is a chromosomal disorder characterized by a short stature and gonadal dysgenesis, the latter of which requires estrogen replacement therapy (ERT) to induce and maintain secondary sexual characteristics. Insufficient ERT is associated with compromised skeletal health, including bone fragility, in adults with TS. In particular, estrogen insufficiency during adolescence is critical because the acquisition of a defective bone mass during this period results in impaired bone strength later in the life. In addition to bone mass, bone geometry is also a crucial factor influencing bone strength; therefore, a more detailed understanding of the skeletal characteristics of both bone mass and geometry during childhood and adolescence and their relationships with the estrogen status is needed to prevent compromised skeletal health during adulthood in TS. Although a delay in the initiation of ERT is associated with a lower bone mineral density during adulthood, limited information is currently available on the effects of ERT during adolescence on bone geometry. Herein, we summarize the current knowledge on skeletal characteristics in children and adolescents with TS and their relationships with estrogen sufficiency, and discuss the potential limitations of the current protocol for ERT during adolescence in order to achieve better skeletal health in adulthood.

Effects of Scoparone on differentiation, adhesion, migration, autophagy and mineralization through the osteogenic signalling pathways

Scoparone (SCOP), an active and efficient coumarin compound derived from Artemisia capillaris Thunb, has been used as a traditional Chinese herbal medicine. Herein, we investigated the effects of SCOP on the osteogenic processes using MC3T3‐E1 pre‐osteoblasts in in vitro cell systems. SCOP (C₁₁H₁₀O₄, > 99.17%) was purified and identified from A. capillaries. SCOP (0.1 to 100 μM concentrations) did not have cytotoxic effects in pre‐osteoblasts; however, it promoted alkaline phosphatase (ALP) staining and activity, and mineralized nodule formation under early and late osteogenic induction. SCOP elevated osteogenic signals through the bone morphogenetic protein 2 (BMP2)‐Smad1/5/8 pathway, leading to the increased expression of runt‐related transcription factor 2 (RUNX2) with its target protein, matrix metallopeptidase 13 (MMP13). SCOP also induced the non‐canonical BMP2‐MAPKs pathway, but not the Wnt3a‐β‐catenin pathway. Moreover, SCOP promoted autophagy, migration and adhesion under the osteogenic induction. Overall, the findings of this study demonstrated that SCOP has osteogenic effects associated with cell differentiation, adhesion, migration, autophagy and mineralization.

Osteoporosis and periodontal diseases - An update on their association and mechanistic links

Periodontitis and osteoporosis are prevalent inflammation-associated skeletal disorders that pose significant public health challenges to our aging population. Both periodontitis and osteoporosis are bone disorders closely associated with inflammation and aging. There has been consistent intrigue on whether a systemic skeletal disease such as osteoporosis will amplify the alveolar bone loss in periodontitis. A survey of the literature published in the past 25 years indicates that systemic low bone mineral density (BMD) is associated with alveolar bone loss, while recent evidence also suggests a correlation between clinical attachment loss and other parameters of periodontitis. Inflammation and its influence on bone remodeling play critical roles in the pathogenesis of both osteoporosis and periodontitis and could serve as the central mechanistic link between these disorders. Enhanced cytokine production and elevated inflammatory response exacerbate osteoclastic bone resorption while inhibiting osteoblastic bone formation, resulting in a net bone loss. With aging, accumulation of oxidative stress and cellular senescence drive the progression of osteoporosis and exacerbation of periodontitis. Vitamin D deficiency and smoking are shared risk factors and may mediate the connection between osteoporosis and periodontitis, through increasing oxidative stress and impairing host response to inflammation. With the connection between systemic and localized bone loss in mind, routine dental exams and intraoral radiographs may serve as a low-cost screening tool for low systemic BMD and increased fracture risk. Conversely, patients with fracture risk beyond the intervention threshold are at greater risk for developing severe periodontitis and undergo tooth loss. Various Food and Drug Administration-approved therapies for osteoporosis have shown promising results for treating periodontitis. Understanding the molecular mechanisms underlying their connection sheds light on potential therapeutic strategies that may facilitate co-management of systemic and localized bone loss.

Mechanisms involved in suppression of osteoclast supportive activity by transforming growth factor-β1 via the ubiquitin-proteasome system

Orthodontic treatment requires the regulation of bone remodeling in both compression and tension sides. Transforming growth factor-β1 (TGF-β1) is an important coupling factor for bone remodeling. However, the mechanism underlying the TGF-β1-mediated regulation of the osteoclast-supporting activity of osteoblasts and stromal cells remain unclear. The current study investigated the effect of TGF-β1 on receptor activator of nuclear factor kappa-B ligand (RANKL) expression in stromal cells induced by 1α,25(OH)2D3 (D3) and dexamethasone (Dex). TGF-β1 downregulated the expression of RANKL induced by D3 and Dex in mouse bone marrow stromal lineage, ST2 cells. Co-culture system revealed that TGF-β1 suppressed osteoclast differentiation from bone marrow cell induced by D3 and Dex-activated ST2 cells. The inhibitory effect of TGF-β1 on RANKL expression was recovered by inhibiting the interaction between TGF-β1 and the TGF-β type I/activin receptor or by downregulating of smad2/3 expression. Interestingly, TGF-β1 degraded the retinoid X receptor (RXR)-α protein which forms a complex with vitamin D receptor (VDR) and regulates transcriptional activity of RANKL without affecting nuclear translocation of VDR and phosphorylation of signal transducer and activator of transcription3 (STAT3). The degradation of RXR-α protein by TGF-β1 was recovered by a ubiquitin-proteasome inhibitor. We also observed that poly-ubiquitination of RXR-α protein was induced by TGF-β1 treatment. These results indicated that TGF-β1 downregulates RANKL expression and the osteoclast-supporting activity of osteoblasts/stromal cells induced by D3 and Dex through the degradation of the RXR-α protein mediated by ubiquitin-proteasome system.

Bone Mesenchymal Stem Cell-Derived sEV-Encapsulated Thermosensitive Hydrogels Accelerate Osteogenesis and Angiogenesis by Release of Exosomal miR-21

Angiogenesis has been recognized to play an essential role in remodeling new bone (osteogenesis). Small extracellular vesicles (sEVs), the endogenously secreted nanovesicles by cells, exhibit great potential in the regeneration of bone defects and the realization of cell-free therapy. Chitosan, a natural polysaccharide, can form a thermosensitive injectable hydrogel through the addition of β-glycerophosphate. Herein, we developed injectable thermosensitive hydrogel-encapsulated sEVs derived from bone mesenchymal stem cells, which significantly prolonged delivery and release and synergistically enhanced bone regeneration. sEVs were isolated and characterized, and the physicochemical properties, release kinetics, and biocompatibility of the hydrogels were analyzed. In vitro experiments were performed to investigate osteogenic differentiation, cell proliferation and migration, and tube formation. Thereafter, sEVs were added to the chitosan/β-glycerophosphate hydrogel (sEV@CS/β-GP composite) to repair calvarial defects in rats. The results showed that sEV-loaded hydrogels were biocompatible, exhibiting excellent thermosensitive properties and enhancing bone regeneration. Furthermore, mechanistic studies revealed that exosomal miR-21 targeted SPRY2, thereby promoting angiogenesis. Our study provides new insights on the repair of bone defects with multifunctional controlled-sEV-release hydrogels, which shows great potential in the repair of tissues in the future.

The Role of Immune Microenvironment in Maxillofacial Bone Homeostasis

Maxillofacial bone defects are common medical problems caused by congenital defects, necrosis, trauma, tumor, inflammation, and fractures non-union. Maxillofacial bone defects often need bone graft, which has many difficulties, such as limited autogenous bone supply and donor site morbidity. Bone tissue engineering is a promising strategy to overcome the above-mentioned problems. Osteoimmunology is the inter-discipline that focuses on the relationship between the skeletal and immune systems. The immune microenvironment plays a crucial role in bone healing, tissue repair and regeneration in maxillofacial region. Recent studies have revealed the vital role of immune microenvironment and bone homeostasis. In this study, we analyzed the complex interaction between immune microenvironment and bone regeneration process in oral and maxillofacial region, which will be important to improve the clinical outcome of the bone injury treatment.

Paeonolide as a Novel Regulator of Core-Binding Factor Subunit Alpha-1 in Bone-Forming Cells

Paeonia suffruticosa has been extensively used as a traditional medicine with various beneficial effects; paeonolide (PALI) was isolated from its dried roots. This study aimed to investigate the novel effects and mechanisms of PALI in pre-osteoblasts. Here, cell viability was evaluated using an MTT assay. Early and late osteoblast differentiation was examined by analyzing the activity of alkaline phosphatase (ALP) and by staining it with Alizarin red S (ARS). Cell migration was assessed using wound healing and Boyden chamber assays. Western blot and immunofluorescence analyses were used to examine the intracellular signaling pathways and differentiation proteins. PALI (0.1, 1, 10, 30, and 100 μM) showed no cytotoxic or proliferative effects in pre-osteoblasts. In the absence of cytotoxicity, PALI (1, 10, and 30 μM) promoted wound healing and transmigration during osteoblast differentiation. ALP staining demonstrated that PALI (1, 10, and 30 μM) promoted early osteoblast differentiation in a dose-dependent manner, and ARS staining showed an enhanced mineralized nodule formation, a key indicator of late osteoblast differentiation. Additionally, low concentrations of PALI (1 and 10 μM) increased the bone morphogenetic protein (BMP)–Smad1/5/8 and Wnt–β-catenin pathways in osteoblast differentiation. Particularly, PALI (1 and 10 μM) increased the phosphorylation of ERK1/2 compared with BMP2 treatment, an FDA-approved drug for bone diseases. Furthermore, PALI-mediated early and late osteoblast differentiation was abolished in the presence of the ERK1/2 inhibitor U0126. PALI-induced RUNX2 (Cbfa1) expression and nuclear localization were also attenuated by blocking the ERK1/2 pathway during osteoblast differentiation. We suggest that PALI has biologically novel activities, such as enhanced osteoblast differentiation and bone mineralization mainly through the intracellular ERK1/2-RUNX2 signaling pathway, suggesting that PALI might have therapeutic action and aid the treatment and prevention of bone diseases, such as osteoporosis and periodontitis.

Ziyuglycoside I Upregulates RUNX2 through ERK1/2 in Promoting Osteoblast Differentiation and Bone Mineralization

Sanguisorba officinalis L. (Rosaceae) is a perennial herbaceous plant and its roots have been used as an important traditional medicine for over 2000 years. Ziyuglycoside I (Ziyu), an active compound isolated from the roots of S. officinalis L., has shown biological effects such as anti-oxidant, antiviral, and antiwrinkle activities. This study aimed to elucidate the underlying mechanisms of action of Ziyu on cytotoxicity, migration, and differentiation of pre-osteoblasts. Herein, at concentrations ranging from 1 to 100 [Formula: see text]M, Ziyu was not cytotoxic against pre-osteoblasts. Alkaline phosphatase activity assay and staining, and migration assay showed that Ziyu increased cell migration and promoted early osteoblast differentiation, followed by the enhancement of mineralized nodule formation in a dose-dependent manner, as indicated by Alizarin Red S staining. In addition, Ziyu increased the protein levels of runt-related transcription factor 2 (RUNX2) during osteoblast differentiation, whereas it did not affect the phosphorylation of Smad1/5/8 and GSK3b and expression of [Formula: see text]-catenin. Ziyu also activated ERK1/2 and mitogen-activated protein kinase during osteoblast differentiation, and ERK1/2 inhibitor attenuated Ziyu-mediated RUNX2 expression and nuclear accumulation. Furthermore, Ziyu-mediated early and late osteoblast differentiation was significantly suppressed by the inhibition of ERK1/2, which was accompanied by attenuation in the mRNA levels of osteoblast-related genes including bone sialoprotein, osteopontin, and osteocalcin. Taken together, the findings of this study provide evidence that Ziyu promotes cell migration, osteoblast differentiation, and bone mineralization and suggest a potential role for Ziyu in the treatment of bone diseases.

Limonoid Triterpene, Obacunone Increases Runt-Related Transcription Factor 2 to Promote Osteoblast Differentiation and Function

Root bark of Dictamnus dasycarpus Turcz. has been widely used as a traditional medicine and is a well-known anti-inflammatory agent. We isolated limonoid triterpene, obacunone (Obac) from the dried root bark of D. dasycarpus. Obac has been reported to exhibit varieties of biological activities including anti-inflammatory, anti-cancer, and anti-oxidant effects. This study aimed to investigate the beneficial effects and biological mechanisms of Obac in osteoblast differentiation and bone matrix mineralization. In the present study, Obac at concentrations ranging from 1 to 100 μM showed no proliferation effects in MC3T3-E1. The treatment of Obac (1 and 10 μM) increased wound healing and migration rates in a dose-dependent manner. Alkaline phosphatase (ALP) staining and activity showed that Obac (1 and 10 μM) enhanced early osteoblast differentiation in a dose-dependent manner. Obac also increased late osteoblast differentiation in a dose-dependent manner, as indicated by the mineralized nodule formation of ARS staining. The effects of Obac on osteoblast differentiation was validated by the levels of mRNAs encoding the bone differentiation markers, including Alp, bone sialoprotein (Bsp), osteopontin (Opn), and osteocalcin (Ocn). Obac increased the expression of bone morphogenetic protein (BMP), and the phosphorylation of smad1/5/8, and the expression of runt-related transcription factor 2 (RUNX2); Obac also inhibited GSK3β and upregulated the protein level of β-catenin in a dose-dependent manner during osteoblast differentiation. Obac-mediated osteoblast differentiation was attenuated by a BMP2 inhibitor, Noggin and a Wnt/β-catenin inhibitor, Dickkopf-1 (Dkk1) with the abolishment of RUNX2 expression and nuclear accumulation by Obac. Taken together, the findings of this study demonstrate that Obac has pharmacological and biological activates to promote osteoblast differentiation and bone mineralization through BMP2, β-catenin, and RUNX2 pathways, and suggest that Obac might be a therapeutic effect for the treatment and prevention of bone diseases such as osteoporosis and periodontitis.

Targeted nanomedicines for the treatment of bone disease and regeneration

Targeted delivery by either passive or active targeting of therapeutics to the bone is an attractive treatment for various bone related diseases such as osteoporosis, osteosarcoma, multiple myeloma, and metastatic bone tumors. Engineering novel drug delivery carriers can increase therapeutic efficacy and minimize the risk of side effects. Developmnet of nanocarrier delivery systems is an interesting field of ongoing studies with opportunities to provide more effective therapies. In addition, preclinical nanomedicine research can open new opportunities for preclinical bone-targeted drug delivery; nevertheless, further research is needed to progress these therapies towards clinical applications. In the present review, the latest advancements in targeting moieties and nanocarrier drug delivery systems for the treatment of bone diseases are summarized. We also review the regeneration capability and effective delivery of nanomedicines for orthopedic applications.

Effects of PIN on Osteoblast Differentiation and Matrix Mineralization through Runt-Related Transcription Factor

Styrax Japonica Sieb. et Zucc. has been used as traditional medicine in inflammatory diseases, and isolated compounds have shown pharmacological activities. Pinoresinol glucoside (PIN) belonging to lignins was isolated from the stem bark of S. Japonica. This study aimed to investigate the biological function and mechanisms of PIN on cell migration, osteoblast differentiation, and matrix mineralization. Herein, we investigated the effects of PIN in MC3T3-E1 pre-osteoblasts, which are widely used for studying osteoblast behavior in in vitro cell systems. At concentrations ranging from 0.1 to 100 μM, PIN had no cell toxicity in pre-osteoblasts. Pre-osteoblasts induced osteoblast differentiation, and the treatment of PIN (10 and 30 μM) promoted the cell migration rate in a dose-dependent manner. At concentrations of 10 and 30 μM, PIN elevated early osteoblast differentiation in a dose-dependent manner, as indicated by increases in alkaline phosphatase (ALP) staining and activity. Subsequently, PIN also increased the formation of mineralized nodules in a dose-dependent manner, as indicated by alizarin red S (ARS) staining, demonstrating positive effects of PIN on late osteoblast differentiation. In addition, PIN induced the mRNA level of BMP2, ALP, and osteocalcin (OCN). PIN also upregulated the protein level of BMP2 and increased canonical BMP2 signaling molecules, the phosphorylation of Smad1/5/8, and the protein level of Runt-related transcription factor 2 (RUNX2). Furthermore, PIN activated non-canonical BMP2 signaling molecules, activated MAP kinases, and increased β-catenin signaling. The findings of this study indicate that PIN has biological roles in osteoblast differentiation and matrix mineralization, and suggest that PIN might have anabolic effects in bone diseases such as osteoporosis and periodontitis.

Shikonin promotes osteogenesis and suppresses osteoclastogenesis in vitro

Shikonin, as a traditional Chinese herbal medicine with a role of anti-cancer, anti-inflammatory, anti-bacterial and other effects. However, there are few studies on the effect of shikonin on osteoporosis. Therefore, the purpose of this study aims to investigate the role and mechanism of shikonin on differentiation of BMSCs and BMMs into osteoblasts and osteoclasts formation. In our study, we treated the cells with different concentrations of shikonin, and then illuminated its effect on oteogenesis and osteoclast differentiation by ALP/alizarin red staining, ALP activity, qRT-PCR, immunofluorescence, Western blot, and TRAP staining. The result showed that shikonin may promote BMSCs differentiate into osteoblasts through the Wnt/β-catenin signaling pathway. At the same time, it may also inhibit the formation of osteoclasts mediated by RANK/RANKL/OPG pathway in vitro. Our research explains excellently the mechanism of shikonin alleviating osteoporosis in vitro, which maybe contributing to the exploration of a new way to prevent osteoporosis.

Finite element analysis of human skull bone adaptation to mechanical loading

Bones self-optimize their mechanical behavior in response to mechanical stimulus. The objective of this research was to develop an integrated bone remodeling and stress binning algorithms into a finite element environment to elucidate the evolution of the bone properties as a function of loading. The bone remodeling algorithm was used to calculate the change in the density and elastic modulus based on the strain energy stimulus. The stress-binning procedure seeks to assign the properties to each element based on the levels of stress from the previous cycle, eliminating pseudo-lazy-zoning and stress dilation effects. The developed algorithms were used to analyze the response skull to loading associated with orthodontic devices. Specifically, a load was applied between the roots of the canine teeth and the first premolars while constraining the foramen magnum. Full-field contours of the displacement, strain, and strain energy were extracted after each remodeling cycle at nine commonly cephalometric landmarks. The results indicate that the overall mechanical response and the associated properties reached a steady-state behavior after nearly 50 cycles of applying the algorithm, where different zones within the skull exhibited unique evolution based on the locations from the loading and boundary sites. When approaching this steady-state condition, it was found that the upper incisor displacement is reduced by 72%, and the density is reduced by almost 7.5%. The finite element approach can be used in defining the treatment process by dynamically changing the loads. Future research will focus on integrating the time-dependent behavior of the bone.

7-HYB, a Phenolic Compound Isolated from Myristica fragrans Houtt Increases Cell Migration, Osteoblast Differentiation, and Mineralization through BMP2 and β-catenin Signaling

The seeds (nutmegs) of Myristica fragrans Houtt have been used as popular spices and traditional medicine to treat a variety of diseases. A phenolic compound, ((7S)-8′-(benzo[3′,4′]dioxol-1′-yl)-7-hydroxypropyl)benzene-2,4-diol (7-HYB) was isolated from the seeds of M. fragrans. This study aimed to investigate the anabolic effects of 7-HYB in osteogenesis and bone mineralization. In the present study, 7-HYB promotes the early and late differentiation of MC3T3-E1 preosteoblasts. 7-HYB also elevated cell migration rate during differentiation of the preosteoblasts with the increased phosphorylation of mitogen-activated protein kinases (MAPKs) including ERK1/2, p38, and JNK. In addition, 7-HYB induced the protein level of BMP2, the phosphorylation of Smad1/5/8, and the expression of RUNX2. 7-HYB also inhibited GSK3β and subsequently increased the level of β-catenin. However, in bone marrow macrophages (BMMs), 7-HYB has no biological effects in cell viability, TRAP-positive multinuclear osteoclasts, and gene expression (c-Fos and NF-ATc1) in receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis. Our findings suggest that 7-HYB plays an important role in osteoblast differentiation through the BMP2 and β-catenin signaling pathway. It also indicates that 7-HYB might have a therapeutic effect for the treatment of bone diseases such as osteoporosis and periodontitis.

Disordered metabolism in mice lacking irisin

Irisin is a product of fibronectin type III domain-containing protein (Fndc5) and is involved in the regulation of adipokine secretion and the differentiation of osteoblasts and osteoclasts. In this study, we aimed to determine whether irisin lacking affects glucose/lipid and bone metabolism. We knocked out the Fndc5 gene to generate irisin-lacking mice. Remarkable, irisin lacking was related to poor 'browning response', with a bigger size of the intraperitoneal white adipose cell and decreased a number of brown adipose cells in brown adipose of interscapular tissue. The irisin lacking mice had hyperlipidemia and insulin resistance, reduced HDL-cholesterol level, increased LDL-cholesterol level, and decreased insulin sensitivity. The lacking of irisin was associated with reduced bone strength and bone mass in mice. The increased number of osteoclasts and higher expression of RANKL indicated increased bone resorption in irisin lacking mice. The level of IL-6 and TNF-α also increased in irisin lacking mice. The results showed that irisin lacking was related to decreased 'browning response', glucose/lipid metabolic derangement, and reduced bone mass with increased bone resorption. Further studies are needed to confirm these initial observations and explore the mechanisms underlying the effects of irisin on glucose/lipid and bone metabolism.

Zebrafish as a model to study autophagy and its role in skeletal development and disease

In the last twenty years, research using zebrafish as a model organism has increased immensely. With the many advantages that zebrafish offer such as high fecundity, optical transparency, ex vivo development, and genetic tractability, they are well suited to studying developmental processes and the effect of genetic mutations. More recently, zebrafish models have been used to study autophagy. This important protein degradation pathway is needed for cell and tissue homeostasis in a variety of contexts. Correspondingly, its dysregulation has been implicated in multiple diseases including skeletal disorders. In this review, we explore how zebrafish are being used to study autophagy in the context of skeletal development and disease, and the ways these areas are intersecting to help identify potential therapeutic targets for skeletal disorders.

AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS/AMERICAN COLLEGE OF ENDOCRINOLOGY CLINICAL PRACTICE GUIDELINES FOR THE DIAGNOSIS AND TREATMENT OF POSTMENOPAUSAL OSTEOPOROSIS-2020 UPDATE

Objective: The development of these guidelines is sponsored by the American Association of Clinical Endocrinologists (AACE) Board of Directors and American College of Endocrinology (ACE) Board of Trustees and adheres with published AACE protocols for the standardized production of clinical practice guidelines (CPGs). Methods: Recommendations are based on diligent reviews of the clinical evidence with transparent incorporation of subjective factors, according to established AACE/ACE guidelines for guidelines protocols. Results: The Executive Summary of this 2020 updated guideline contains 52 recommendations: 21 Grade A (40%), 24 Grade B (46%), 7 Grade C (14%), and no Grade D (0%). These detailed, evidence-based recommendations allow for nuance-based clinical decision-making that addresses multiple aspects of real-world care of patients. The evidence base presented in the subsequent Appendix provides relevant supporting information for the Executive Summary recommendations. This update contains 368 citations: 123 (33.5%) evidence level (EL) 1 (highest), 132 (36%) EL 2 (intermediate), 20 (5.5%) EL 3 (weak), and 93 (25%) EL 4 (lowest). New or updated topics in this CPG include: clarification of the diagnosis of osteoporosis, stratification of the patient according to high-risk and very-high-risk features, a new dual-action therapy option, and transitions from therapeutic options. Conclusion: This guideline is a practical tool for endocrinologists, physicians in general, regulatory bodies, health-related organizations, and interested laypersons regarding the diagnosis, evaluation, and treatment of post-menopausal osteoporosis. Abbreviations: 25(OH)D = 25-hydroxyvitamin D; AACE = American Association of Clinical Endocrinologists; ACE = American College of Endocrinology; AFF = atypical femoral fracture; ASBMR = American Society for Bone and Mineral Research; BEL = best evidence level; BMD = bone mineral density; BTM = bone turnover marker; CI = confidence interval; CPG = clinical practice guideline; CTX = C-terminal telopeptide type-I collagen; DXA = dual-energy X-ray absorptiometry; EL = evidence level; FDA = U.S. Food and Drug Administration; FRAX® = Fracture Risk Assessment Tool; GI = gastrointestinal; HORIZON = Health Outcomes and Reduced Incidence with Zoledronic acid ONce yearly Pivotal Fracture Trial (zoledronic acid and zoledronate are equivalent terms); ISCD = International Society for Clinical Densitometry; IU = international units; IV = intravenous; LSC = least significant change; NOF = National Osteoporosis Foundation; ONJ = osteonecrosis of the jaw; PINP = serum amino-terminal propeptide of type-I collagen; PTH = parathyroid hormone; R = recommendation; ROI = region of interest; RR = relative risk; SD = standard deviation; TBS = trabecular bone score; VFA = vertebral fracture assessment; WHO = World Health Organization.

Allosteric interactions in the parathyroid hormone GPCR-arrestin complex formation

Peptide ligands of class B G-protein-coupled receptors act via a two-step binding process, but the essential mechanisms that link their extracellular binding to intracellular receptor-arrestin interactions are not fully understood. Using NMR, crosslinking coupled to mass spectrometry, signaling experiments and computational approaches on the parathyroid hormone (PTH) type 1 receptor (PTHR), we show that initial binding of the PTH C-terminal part constrains the conformation of the flexible PTH N-terminal signaling epitope before a second binding event occurs. A 'hot-spot' PTH residue, His9, that inserts into the PTHR transmembrane domain at this second step allosterically engages receptor-arrestin coupling. A conformational change in PTHR intracellular loop 3 permits favorable interactions with β-arrestin's finger loop. These results unveil structural determinants for PTHR-arrestin complex formation and reveal that the two-step binding mechanism proceeds via cooperative fluctuations between ligand and receptor, which extend to other class B G-protein-coupled receptors.

Unique anabolic action of stem cell gene therapy overexpressing PDGFB-DSS6 fusion protein in OVX osteoporosis mouse model

In the present study we sought to improve the efficacy and safety of our Sca1+ PDGFB stem cell gene therapy for osteoporosis in ovariectomized (OVX) mouse model. This therapy is administered by marrow transplantation. We established the promise of this approach by previously showing that this therapy in normal mice increase bone density, increased endosteal cortical and trabecular bone formation, caused de novo trabecular bone formation, increased cortical thickness and improve bone strength. In the current study we produced a fusion gene, PDGFB-DSS6. We reasoned that the DSS6, calcium binding protein would trap the PDGFB at the bone surface and thereby limit the amount of PDGFB required to produce an optimal bone formation response, i.e. efficacy with a lower engraftment. The result shows that indeed with a very low level of engraftment we achieved a large increase in bone formation in the OVX model of bone loss. Serum analysis for biochemical marker of new bone formation showed an approximate 75% increase in alkaline phosphatase levels in Sca1+PDGFB-DSS6 group as compared to other groups. Quantitative analysis of bone by microCT showed a massive increase in trabecular bone density and trabecular connectivity of the femur in the metaphysis in Sca1+ PDGFB-DSS6 group. The increased cortical porosity produced by OVX was replaced by the Sca1+ PDGFB-DSS6 therapy but not by the positive control Sca1+ PDGFB. Additionally, an increase in the femur bone strength was also observed specifically in Sca1+ PDGFB-DSS6 as compared to other treatment groups, emphasizing the functional significance of the observed anabolic action is on bone formation. In future work we will focus on nontoxic preconditioning of our marrow transplantation procedure and also on transcriptional control of therapeutic gene expression to avoid excess bone formation.

In silico experiments of bone remodeling explore metabolic diseases and their drug treatment

Bone structure and function are maintained by well-regulated bone metabolism and remodeling. Although the underlying molecular and cellular mechanisms are now being understood, physiological and pathological states of bone are still difficult to predict due to the complexity of intercellular signaling. We have now developed a novel in silico experimental platform, V-Bone, to integratively explore bone remodeling by linking complex microscopic molecular/cellular interactions to macroscopic tissue/organ adaptations. Mechano-biochemical couplings modeled in V-Bone relate bone adaptation to mechanical loading and reproduce metabolic bone diseases such as osteoporosis and osteopetrosis. V-Bone also enables in silico perturbation on a specific signaling molecule to observe bone metabolic dynamics over time. We also demonstrate that this platform provides a powerful way to predict in silico therapeutic effects of drugs against metabolic bone diseases. We anticipate that these in silico experiments will substantially accelerate research into bone metabolism and remodeling.

Deletion of p16 prevents estrogen deficiency-induced osteoporosis by inhibiting oxidative stress and osteocyte senescence

To investigate whether p16 deletion can prevent osteoporosis caused by estrogen deficiency, we first confirmed that p16 protein expression levels were significantly up-regulated in bony tissue of ovariectomized (OVX) wild-type mice. Eight-week-old wild-type and p16^-/- mice were then sham-operated or bilateral OVX. After 12 weeks, the bone phenotypes of all models were analyzed by radiography, micro-computed tomography, histology, immunohistochemistry, and molecular biology. The results showed that p16 deficiency could rescue OVX-induced osteoporosis by significantly increased bone mineral density, trabecular bone volume, total collagen positive area, osteoblast number, type I collagen positive area, fibroblast colony-forming unit (CFU-f) and alkaline phosphatase-positive CFU-f with up-regulation of the mRNA expression levels of Alp, Runx2, type I collagen and osteocalcin, and significantly reduced osteoclast surface and the ratio of RANKL/OPG mRNA expression level. Furthermore, we also demonstrated that p16 deletion inhibited OVX-induced oxidative stress and bone cell senescence, such as a significant decrease in reactive oxygen species levels, up-regulation of superoxide dismutase 1 and 2 protein expression levels, and reduction of the percentage of β-galactosidase-positive osteocytes and p21 protein expression levels in bony tissue. Our results indicate that p16 deletion can prevent estrogen deficiency-induced osteoporosis by inhibiting oxidative stress, osteocyte senescence and osteoclastic bone resorption, stimulating osteogenesis and osteoblastic bone formation. Therefore, this study provides new insights into the potential of p16 as a novel therapeutic target for estrogen deficiency-induced osteoporosis.

RANKL biology: bone metabolism, the immune system, and beyond

Receptor activator of NF-κB (RANK) ligand (RANKL) induces the differentiation of monocyte/macrophage-lineage cells into the bone-resorbing cells called osteoclasts. Because abnormalities in RANKL, its signaling receptor RANK, or decoy receptor osteoprotegerin (OPG) lead to bone diseases such as osteopetrosis, the RANKL/RANK/OPG system is essential for bone resorption. RANKL was first discovered as a T cell-derived activator of dendritic cells (DCs) and has many functions in the immune system, including organogenesis, cellular development. The essentiality of RANKL in the bone and the immune systems lies at the root of the field of "osteoimmunology." Furthermore, this cytokine functions beyond the domains of bone metabolism and the immune system, e.g., mammary gland and hair follicle formation, body temperature regulation, muscle metabolism, and tumor development. In this review, we will summarize the current understanding of the functions of the RANKL/RANK/OPG system in biological processes.

TGFβ1 Regulates Human RANKL-Induced Osteoclastogenesis via Suppression of NFATc1 Expression

Osteoclasts are multinucleated giant cells responsible for bone resorption. Various mediators involved in osteoclast differentiation have been investigated as possible therapeutic targets for osteoporosis and rheumatoid arthritis (RA). Although transforming growth factor beta1 (TGFβ1) has been described as one such multifunctional cytokine essential for bone remodeling, its effect on osteoclastogenesis remains controversial. Therefore, we sought to examine the effect of TGFβ1 on osteoclast generation induced by receptor activator of nuclear factor (NF)-κB ligand (RANKL) in humans. Peripheral blood monocytes, isolated using magnetic bead sorting, were cultured with macrophage-colony stimulating factor (M-CSF) or RANKL with or without TGFβ1. Tartrate-resistant acid phosphatase (TRAP) staining, as well as bone resorption assays, revealed that TGFβ1 suppressed RANKL-mediated human osteoclast development. Real-time reverse transcription PCR and Western blotting revealed that TGFβ1 reduced the gene and protein expression of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), the master regulator of osteoclast differentiation, respectively. Luciferase assays indicated that TGFβ1 inhibited the NF-κB p65-stimulated promoter activity of NFATc1. Immunofluorescence analysis demonstrated that TGFβ1 abrogated RANKL-induced nuclear translocation of p65. Thus, TGFβ1 regulates human RANKL-induced osteoclastogenesis via downregulation of NFATc1 by blocking nuclear translocation of NF-κB, suggesting that TGFβ1 may be a potential therapeutic target for RA.

Targeting heme-oxidized soluble guanylate cyclase to promote osteoblast function

The enzyme soluble guanylate cyclase (sGC) plays an essential part in the nitric oxide (NO) signaling pathway by binding to the prosthetic heme group; thereby catalyzing the synthesis of cyclic guanosine monophosphate (cGMP)-dependent protein kinases. Impaired NO-sGC-cGMP signaling could lead to osteoblast apoptosis by mechanisms involving the oxidative-stress-induced shift of the redox state of the reduced heme to oxidized sGC, leading to diminished heme binding to the enzyme and rendering the sGC unresponsive to NO. Targeting oxidized sGC to enhance cGMP production could restore proliferation and differentiation of osteoblasts into osteocytes. Here, the potential role of sGC activators of an oxidized or heme-free sGC as a target for promoting osteoblast function is reviewed and strategies for delivering drugs to bone are identified.

A soluble bone morphogenetic protein type 1A receptor fusion protein treatment prevents glucocorticoid-Induced bone loss in mice

Glucocorticoid-induced osteoporosis (GIOP) is a frequent complication of systemic glucocorticoid (GC) therapy, is the most common form of secondary osteoporosis, and is associated with skeletal fragility and increased fracture risk. A soluble form of BMP receptor type 1A fusion protein (mBMPR1A-mFc) acts as an antagonist to endogenous BMPR1A and could increase bone mass in both ovariectomized and ovary-intact mice, but its effects in GIOP mice remained unclear. The aim of this study was to evaluate the effects of mBMPR1A-mFc on the skeleton in experimental models of GIOP. mBMPR1A-mFc treatment could increase the bone mineral density (BMD), trabecular bone volume, thickness, and number, and cortical thickness, and reduce the structure model index and trabecular separation in GIOP mice. mBMPR1A-mFc treatment could also prevent bone loss and enhance biomechanical strength in GIOP mice by promoting osteoblastic bone formation and inhibiting osteoclastic bone resorption. Mechanistic studies revealed that mBMPR1A-mFc treatment increased murine osteoblastogenesis by activating the Wnt/β-catenin signaling pathway while decreasing osteoclastogenesis by inhibiting the RANK/RANKL/osteoprotegerin (OPG) signaling pathway. These findings demonstrate that mBMPR1A-mFc treatment in GIOP mice improves bone mass, microarchitecture, and strength by enhancing osteoblastic bone formation and inhibiting osteoclastic bone resorption in GIOP mice and offers a promising novel alternative for the treatment of GIOP.

Cooperative impact of thiazolidinedione and fatty acid synthase on human osteogenesis

Previous, we found that the small molecules capable of inhibiting the expression and the pro-adipogenic activity of ZNF521 might improve the osteogenic performance of aging human bone marrow MSCs (bmMSCs), and that fatty acid synthase (FASN) was a critical effector of ZNF521's pro-adipogenic activity. Here, by characterizing the netoglitazone (MCC-555), one of the thiazolidinediones known as adipogenic enhancers, as an inhibitor of ZNF521 expression, we found that MCC-555 indeed also harbored pro-osteoblastic effect. Investigation revealed that MCC-555 might function as a GSK3β inhibitor to promote osteoblastogenesis and bone formation. Importantly, combination of MCC-555 with FASN knockdown, but not with GW9662 (a PPARγ2 antagonist), blocked the pro-adipogenic but retained the pro-osteoblastic effect of MCC-555. Using a 3-dimentional culture system, we showed that MCC-555 facilitated the FASN-knockdown of aging human bmMSCs to form cell clusters in scaffolds, and to promote osteoblastic differentiation and biomineralization in cell clusters. These data indicated that MCC-555 promoted bmMSCs to produce bone-like tissues. Our data narrate a thiazolidinedione-based novel strategy to improve the osteogenic performance of aging bmMSCs to support the application of autologous aging bmMSCs in cell therapy and in producing bone-like tissues for repairing bone injury in the elderly.

Regulator of G Protein Signaling Protein 12 (Rgs12) Controls Mouse Osteoblast Differentiation via Calcium Channel/Oscillation and Gαi-ERK Signaling

Bone homeostasis intimately relies on the balance between osteoblasts (OBs) and osteoclasts (OCs). Our previous studies have revealed that regulator of G protein signaling protein 12 (Rgs12), the largest protein in the Rgs super family, is essential for osteoclastogenesis from hematopoietic cells and OC precursors. However, how Rgs12 regulates OB differentiation and function is still unknown. To understand that, we generated an OB-targeted Rgs12 conditional knockout (CKO) mice model by crossing Rgs12fl/fl mice with Osterix (Osx)-Cre transgenic mice. We found that Rgs12 was highly expressed in both OB precursor cells (OPCs) and OBs of wild-type (WT) mice, and gradually increased during OB differentiation, whereas Rgs12-CKO mice (OsxCre/+ ; Rgs12fl/fl ) exhibited a dramatic decrease in both trabecular and cortical bone mass, with reduced numbers of OBs and increased apoptotic cell population. Loss of Rgs12 in OPCs in vitro significantly inhibited OB differentiation and the expression of OB marker genes, resulting in suppression of OB maturation and mineralization. Further mechanism study showed that deletion of Rgs12 in OPCs significantly inhibited guanosine triphosphatase (GTPase) activity and cyclic adenosine monophosphate (cAMP) level, and impaired Calcium (Ca2+ ) oscillations via restraints of major Ca2+ entry sources (extracellular Ca2+ influx and intracellular Ca2+ release from endoplasmic reticulum), partially contributed by the blockage of L-type Ca2+ channel mediated Ca2+ influx. Downstream mediator extracellular signal-related protein kinase (ERK) was found inactive in OBs of OsxCre/+ ; Rgs12fl/fl mice and in OPCs after Rgs12 deletion, whereas application of pertussis toxin (PTX) or overexpression of Rgs12 could rescue the defective OB differentiation via restoration of ERK phosphorylation. Our findings reveal that Rgs12 is an important regulator during osteogenesis and highlight Rgs12 as a potential therapeutic target for bone disorders. © 2018 American Society for Bone and Mineral Research.

Pyrroloquinoline Quinone Prevents Estrogen Deficiency-Induced Osteoporosis by Inhibiting Oxidative Stress and Osteocyte Senescence

Accumulating studies have shown that oxidative stress increases with aging, which is related to the pathophysiology of postmenopausal osteoporosis. Pyrroloquinoline quinone (PQQ) is a natural anti-oxidant with anti-oxidative and anti-aging effects. However, it is unclear whether PQQ has a protective role against estrogen deficiency-induced osteoporosis. Here, we evaluated the efficacy of PQQ on bone mineral density, bone microarchitecture, bone turnover and biomechanical strength in ovariectomy (OVX)-induced osteoporosis mouse model. Although dietary PQQ supplement did not affect serum E2 levels and uterine weight in OVX mice, it could prevent OVX-induced bone loss and improve bone strength by inhibiting oxidative stress, osteocyte senescence and senescence-associated secretory phenotype (SASP), subsequently promoting osteoblastic bone formation and inhibiting osteoclastic bone resorption, which was comparable to treatment with exogenous estrogen. The results from our study provide experimental evidence for the clinical use of PQQ to prevent estrogen deficiency-induced osteoporosis.

Identification of an Epigenetic Signature of Osteoporosis in Blood DNA of Postmenopausal Women

Osteoporosis is one of the most common age-related progressive bone diseases in elderly people. Approximately one in three women and one in five men are predisposed to developing osteoporosis. In postmenopausal women, a reduction in BMD leads to an increased risk of fractures. In the current study, we delineated the DNA methylation signatures in whole blood samples of postmenopausal osteoporotic women. We obtained whole blood DNA from 22 normal women and 22 postmenopausal osteoporotic women (51 to 89 years old) from the Canadian Multicenter Osteoporosis Study (CaMos) cohort. These DNA samples were subjected to Illumina Infinium human methylation 450 K analysis. Illumina 450K raw data were analyzed by Genome Studio software. Analysis of the female participants with early and advanced osteoporosis resulted in the generation of a list of 1233 differentially methylated CpG sites when compared with age-matched normal women. T test, ANOVA, and post hoc statistical analyses were performed, and 77 significantly differentially methylated CpG sites were identified. From the 13 most significant genes, ZNF267, ABLIM2, RHOJ, CDKL5, and PDCD1 were selected for their potential role in bone biology. A weighted polygenic DNA methylation score of these genes predicted osteoporosis at an early stage with high sensitivity and specificity and correlated with measures of bone density. Pyrosequencing analysis of these genes was performed to validate the results obtained from Illumina 450 K methylation analysis. The current study provides proof of principal for the role of DNA methylation in osteoporosis. Using whole blood DNA methylation analysis, women at risk of developing osteoporosis can be identified before a diagnosis of osteoporosis is made using BMD as a screening method. Early diagnosis will help to select patients who might benefit from early therapeutic intervention. © 2018 American Society for Bone and Mineral Research.

Dickkopf-1: Current knowledge and related diseases

Dickkopf-1(DKK-1) has been identified as a secretory protein that can inhibit the Wnt signaling transduction pathway. It is well known that the Wnt signaling pathway plays an important role in embryogenesis, organogenesis and homeostasis. This signaling cascade is essential for many normal physiological processes such as cellular proliferation, tissue regeneration, embryonic development and many other systemic and local effects, and it can be regulated at different levels. Therefore, defects in the pathway may lead to some complicated effects. In addition, it has been demonstrated that defects in this pathway are closely linked to some diseases including cancer, rheumatism, bone disease, diabetes, and Alzheimer disease. Since DKK-1 is an antagonist of the Wnt pathway, it may be related to these diseases; in fact, many studies have identified this fact. This review will summarize the current knowledge of DKK-1 and DKK-1-mediated regulation of Wnt signaling in the development of these related diseases.

25 S-Adamantyl-23-yne-26,27-dinor-1α,25-dihydroxyvitamin D3: Synthesis, Tissue Selective Biological Activities, and X-ray Crystal Structural Analysis of Its Vitamin D Receptor Complex

Both 25 R- and 25 S-25-adamantyl-23-yne-26,27-dinor-1α,25-dihydroxyvitamin D₃ (4a and 4b) were stereoselectively synthesized by a Pd(0)-catalyzed ring closure and Suzuki-Miyaura coupling between enol-triflate 7 and alkenyl-boronic ester 8. The 25 S isomer (4b) showed high vitamin D receptor (VDR) affinity (50% of that of the natural hormone 1α,25-dihydroxyvitamin D₃, 1) and transactivation potency (kidney HEK293, 90%). In endogenous gene expression, it showed high cell-type selectivity for kidney cells (HEK293, CYP24A1 160% of 1), bone cells (MG63, osteocalcin 64%), and monocytes (U937, CAMP 96%) over intestine (SW480, CYP24A1 8%) and skin (HaCaT, CYP24A1 7%) cells. The X-ray crystal structural analysis of 4b in complex with rat VDR-ligand binding domain (LBD) showed the highest Cα positional shift from the 1/VDR-LBD complex at helix 11. Helix 11 of the 4b and 1 VDR-LBD complexes also showed significant differences in surface properties. These results suggest that 4b should be examined further as another candidate for a mild preventive osteoporosis agent.