Dkk2 has a role in terminal osteoblast differentiation and mineralized matrix formation

Wnt/β-catenin signaling components and mechanisms in bone formation, homeostasis, and disease

Wnts are secreted, lipid-modified proteins that bind to different receptors on the cell surface to activate canonical or non-canonical Wnt signaling pathways, which control various biological processes throughout embryonic development and adult life. Aberrant Wnt signaling pathway underlies a wide range of human disease pathogeneses. In this review, we provide an update of Wnt/β-catenin signaling components and mechanisms in bone formation, homeostasis, and diseases. The Wnt proteins, receptors, activators, inhibitors, and the crosstalk of Wnt signaling pathways with other signaling pathways are summarized and discussed. We mainly review Wnt signaling functions in bone formation, homeostasis, and related diseases, and summarize mouse models carrying genetic modifications of Wnt signaling components. Moreover, the therapeutic strategies for treating bone diseases by targeting Wnt signaling, including the extracellular molecules, cytosol components, and nuclear components of Wnt signaling are reviewed. In summary, this paper reviews our current understanding of the mechanisms by which Wnt signaling regulates bone formation, homeostasis, and the efforts targeting Wnt signaling for treating bone diseases. Finally, the paper evaluates the important questions in Wnt signaling to be further explored based on the progress of new biological analytical technologies.

Wnt/β-catenin signaling pathway as an important mediator in muscle and bone crosstalk: A systematic review

Background

The interaction between muscle and bone is shown to be clinically important but the underlying mechanisms are largely unknown. The canonical Wnt/β-catenin signaling pathway is reported to be involved in muscle-bone crosstalk, but its detailed function remains unclear. This systematic review aims to investigate and elucidate the role of the Wnt/β-catenin signaling pathways in muscle-bone crosstalk.

Methods

We conducted a literature search on the Web of Science, PubMed, EBSCO and Embase with keywords "Wnt*", "bone*" and "muscle*". A systematic review was completed according to the guideline of preferred reporting items of systematic reviews and meta-analyses (PRISMA). Data synthesis included species (human, animal or cell type used), treatments involved, outcome measures and key findings with respect to Wnts.

Results

Seventeen papers were published from 2007 to 2021 and were extracted from a total of 1529 search results in the databases of Web of Science (468 papers), PubMed (457 papers), EBSCO (371) and Embase (233). 12 Wnt family members were investigated in the papers, including Wnt1, Wnt2, Wnt2b, Wnt3a, Wnt4, Wnt5a, Wnt8a, Wnt8b, Wnt9a, Wnt10a, Wnt10b and Wnt16. Many studies showed that muscles were able to increase or decrease osteogenesis of bone, while bone increased myogenesis of muscle through Wnt/β-catenin signaling pathways. Wnt3a, Wnt4 and Wnt10b were shown to play important roles in the crosstalk between muscle and bone.

Conclusions

Wnt3a, Wnt4 and Wnt10b are found to play important mediatory roles in muscle-bone crosstalk. The role of Wnt4 was mostly found to regulate muscle from the bone side. Whilst the role of Wnt10b during muscle ageing was proposed, current evidence is insufficient to clarify the specific role of Wnt/β-catenin signaling in the interplay between sarcopenia and osteoporosis. More future studies are required to investigate the exact regulatory roles of Wnts in muscle-bone crosstalk in musculoskeletal disease models such as sarcopenia and osteoporosis.

Translational potential of this article

The systematic review provides an extensive overview to reveal the roles of Wnt/β-catenin signaling pathways in muscle-bone crosstalk. These results provide novel research directions to further understand the underlying mechanism of sarcopenia, osteoporosis, and their crosstalk, finally helping the future development of new therapeutic interventions.

A higher order PUF complex is central to regulation of C. elegans germline stem cells

PUF RNA-binding proteins are broadly conserved stem cell regulators. Nematode PUF proteins maintain germline stem cells (GSCs) and, with key partner proteins, repress differentiation mRNAs, including gld-1. Here we report that PUF protein FBF-2 and its partner LST-1 form a ternary complex that represses gld-1 via a pair of adjacent FBF-2 binding elements (FBEs) in its 3ÚTR. One LST-1 molecule links two FBF-2 molecules via motifs in the LST-1 intrinsically-disordered region; the gld-1 FBE pair includes a well-established 'canonical' FBE and a newly-identified noncanonical FBE. Remarkably, this FBE pair drives both full RNA repression in GSCs and full RNA activation upon differentiation. Discovery of the LST-1-FBF-2 ternary complex, the gld-1 adjacent FBEs, and their in vivo significance predicts an expanded regulatory repertoire of different assemblies of PUF-partner complexes in nematode germline stem cells. It also suggests analogous PUF controls may await discovery in other biological contexts and organisms.

WNT Signaling in Stem Cells: A Look into the Non-Canonical Pathway

Tissue homeostasis is crucial for multicellular organisms, wherein the loss of cells is compensated by generating new cells with the capacity for proliferation and differentiation. At the origin of these populations are the stem cells, which have the potential to give rise to cells with both capabilities, and persevere for a long time through the self-renewal and quiescence. Since the discovery of stem cells, an enormous effort has been focused on learning about their functions and the molecular regulation behind them. Wnt signaling is widely recognized as essential for normal and cancer stem cell. Moreover, β-catenin-dependent Wnt pathway, referred to as canonical, has gained attention, while β-catenin-independent Wnt pathways, known as non-canonical, have remained conspicuously less explored. However, recent evidence about non-canonical Wnt pathways in stem cells begins to lay the foundations of a conceivably vast field, and on which we aim to explain this in the present review. In this regard, we addressed the different aspects in which non-canonical Wnt pathways impact the properties of stem cells, both under normal conditions and also under disease, specifically in cancer.

The Role of Extracellular Vesicles in the Pathogenesis and Treatment of Rheumatoid Arthritis and Osteoarthritis

Cells can communicate with each other through extracellular vesicles (EVs), which are membrane-bound structures that transport proteins, lipids and nucleic acids. These structures have been found to mediate cellular differentiation and proliferation apoptosis, as well as inflammatory responses and senescence, among others. The cargo of these vesicles may include immunomodulatory molecules, which can then contribute to the pathogenesis of various diseases. By contrast, EVs secreted by mesenchymal stem cells (MSCs) have shown important immunosuppressive and regenerative properties. Moreover, EVs can be modified and used as drug carriers to precisely deliver therapeutic agents. In this review, we aim to summarize the current evidence on the roles of EVs in the progression and treatment of rheumatoid arthritis (RA) and osteoarthritis (OA), which are important and prevalent joint diseases with a significant global burden.

Bone Remodeling in Osteoarthritis-Biological and Radiological Aspects

Among available papers published on the given subject over the last century, various terms have been used as synonyms for one, now generally accepted-osteoarthritis, in some countries called "wear and tear" or "overload arthritis". The opsolent terms-hypertrophic arthritis, degenerative arthritis, arthritis deformans and osteoarthrosis-sought to highlight the dominant clinical signs of this ubiquitous, polymorph disease of the whole osteochondral unit, which by incidence and prevalence represents one of the leading chronic conditions that cause long-term pain and incapacity for work. Numerous in vitro and in vivo research resulted in broadened acknowledgments about osteoarthritis pathophysiology and pathology on both histological and cellular levels. However, the cause of osteoarthritis is still unknown and is currently the subject of a hypothesis. In this paper, we provide a review of recent findings on biological phenomena taking place in bone tissue during osteoarthritis to the extent useful for clinical practice. Choosing a proper radiological approach is a conditio sine qua non to the early diagnosis of this entity.

Serum Cytokine Profiles in Patients with Rheumatoid Arthritis Before and After Treatment with Methotrexate

Rheumatoid arthritis (RA) is an inflammatory autoimmune illness affecting around 1% of the population globally. Cytokines have a crucial role in the pathogenesis of RA. The objectives of the present study were to compare the serum cytokine profiles between methotrexate (MTX)-treated and MTX-naive RA patient groups, MTX-treated RA patient group and healthy controls, and MTX-naive RA patient group and healthy controls. Enzyme linked immunosorbent assay (ELISA) kits were used to quantify the serum concentrations of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-17, IL-6, interferon-gamma (IFN-γ), and IL-10 in 80 RA patients (48 MTX treated and 32 MTX naive) and 80 healthy controls. For all cytokine assays, absorbance was measured at 450 nm using a microplate reader (Bio-Rad). Independent sample t-test was used to compare the serum cytokine concentrations between the study groups using SPSS version 25. MTX-treated RA patient group had significantly reduced serum levels of TNF-α (36.13 ± 17.64 versus 45.82 ± 23.07, *P = 0.037), IL-17 (307.85 ± 151.74 versus 435.42 ± 241.19, **P = 0.006), and IFN-γ (414.93 ± 212.13 versus 527.15 ± 269.61, *P = 0.041) compared to MTX-naive RA patients. Both MTX-treated and MTX-naive RA patient groups had significantly high serum levels of TNF-α, IL-1β, IL-17, IL-6, IFN-γ, and IL-10 when compared to healthy controls (***P < 0.001). Downregulation of the serum concentrations of certain key cytokines, viz. TNF-α, IL-17, and IFN-γ, demonstrates the anti-inflammatory effect of MTX in RA patients.

Wnt7b: Is It an Important Factor in the Bone Formation Process after Calvarial Damage?

OBJECTIVE

Previous studies found that Wnt7b played a unique and indispensable role in the process of osteoblast differentiation and could accelerate the repair of bone loss. However, what is the role of Wnt7B in osteogenesis? Is it possible to increase the expression of Wnt7b to promote the repair of skull defects? This study intends to provide the basic data for the application of Wnt7b in the treatment of craniomaxillofacial bone repair.

METHODS

A calvarial defect mouse model that could induce Wnt7b overexpression was established. Three days after the operation, the mice in each group were intraperitoneally injected with tamoxifen (TAM) or oil eight times every other day. There were three groups. The TAMc group (R26^Wnt7b/Wnt7b) was injected with tamoxifen. The Oil group (3.2 kb Col1-Cre-ER^T2; R26^Wnt7b/Wnt7b) was injected with oil. The TAM group (3.2 kb Col1-Cre-ER^T2; R26^Wnt7b/Wnt7b) was injected with tamoxifen. Four weeks after the surgery, micro-CT scanning was utilized to observe new bone formation and compare the ability to form new bone around the defect area.

RESULTS

Four weeks after the operation, bone healing conditions were measured by using micro-CT scanning. The defect area of the TAM group was smaller than that of the other groups. Similarly, the bone volume fraction (BV/TV) significantly increased (p < 0.05), the trabecular number (Tb.N) increased, and the trabecular separation (Tb.Sp) decreased.

CONCLUSIONS

Wnt7b participates in the bone formation process after calvarial damage, indicating the important role of Wnt7b in osteogenesis.

Dikkopf-1 promotes matrix mineralization of osteoblasts by regulating Ca+-CAMK2A- CREB1 pathway

Dickkopf-1 (DKK1) is a secreted protein that acts as an antagonist of the canonical WNT/β-catenin pathway, which regulates osteoblast differentiation. However, the role of DKK1 on osteoblast differentiation has not yet been fully clarified. Here, we investigate the functional role of DKK1 on osteoblast differentiation. Primary osteoprogenitor cells were isolated from human spinal bone tissues. To examine the role of DKK1 in osteoblast differentiation, we manipulated the expression of DKK1, and the cells were differentiated into mature osteoblasts. DKK1 overexpression in osteoprogenitor cells promoted matrix mineralization of osteoblast differentiation but did not promote matrix maturation. DKK1 increased Ca⁺ influx and activation of the Ca⁺/calmodulin-dependent protein kinase II Alpha (CAMK2A)-cAMP response element-binding protein 1 (CREB1) and increased translocation of p-CREB1 into the nucleus. In contrast, stable DKK1 knockdown in human osteosarcoma cell line SaOS2 exhibited reduced nuclear translocation of p-CREB1 and matrix mineralization. Overall, we suggest that manipulating DKK1 regulates the matrix mineralization of osteoblasts by Ca⁺-CAMK2A-CREB1, and DKK1 is a crucial gene for bone mineralization of osteoblasts. [BMB Reports 2022; 55(12): 627-632].

Dikkopf-1 promotes matrix mineralization of osteoblasts by regulating Ca+-CAMK2A- CREB1 pathway

Dickkopf-1 (DKK1) is a secreted protein that acts as an antagonist of the canonical WNT/β-catenin pathway, which regulates osteoblast differentiation. However, the role of DKK1 on osteoblast differentiation has not yet been fully clarified. Here, we investigate the functional role of DKK1 on osteoblast differentiation. Primary osteoprogenitor cells were isolated from human spinal bone tissues. To examine the role of DKK1 in osteoblast differentiation, we manipulated the expression of DKK1, and the cells were differentiated into mature osteoblasts. DKK1 overexpression in osteoprogenitor cells promoted matrix mineralization of osteoblast differentiation but did not promote matrix maturation. DKK1 increased Ca+ influx and activation of the Ca+/calmodulin-dependent protein kinase II Alpha (CAMK2A)-cAMP response element-binding protein 1 (CREB1) and increased translocation of p-CREB1 into the nucleus. In contrast, stable DKK1 knockdown in human osteosarcoma cell line SaOS2 exhibited reduced nuclear translocation of p-CREB1 and matrix mineralization. Overall, we suggest that manipulating DKK1 regulates the matrix mineralization of osteoblasts by Ca+-CAMK2A-CREB1, and DKK1 is a crucial gene for bone mineralization of osteoblasts. [BMB Reports 2022; 55(12): 627-632].

MSX1 Drives Tooth Morphogenesis Through Controlling Wnt Signaling Activity

Tooth agenesis is a common structural birth defect in humans that results from failure of morphogenesis during early tooth development. The homeobox transcription factor Msx1 and the canonical Wnt signaling pathway are essential for "bud to cap" morphogenesis and are causal factors for tooth agenesis. Our recent study suggested that Msx1 regulates Wnt signaling during early tooth development by suppressing the expression of Dkk2 and Sfrp2 in the tooth bud mesenchyme, and it demonstrated partial rescue of Msx1-deficient molar teeth by a combination of DKK inhibition and genetic inactivation of SFRPs. In this study, we found that Sostdc1/Wise, another secreted Wnt antagonist, is involved in regulating the odontogenic pathway downstream of Msx1. Whereas Sostdc1 expression in the developing tooth germ was not increased in Msx1-/- embryos, genetic inactivation of Sostdc1 rescued maxillary molar, but not mandibular molar, morphogenesis in Msx1-/- mice with full penetrance. Since the Msx1-/-;Sostdc1-/- embryos exhibited ectopic Dkk2 expression in the developing dental mesenchyme, similar to Msx1-/- embryos, we generated and analyzed tooth development in Msx1-/-;Dkk2-/- double and Msx1-/-;Dkk2-/-;Sostdc1-/- triple mutant mice. The Msx1-/-;Dkk2-/- double mutants showed rescued maxillary molar morphogenesis at high penetrance, with a small percentage also exhibiting mandibular molars that transitioned to the cap stage. Furthermore, tooth development was rescued in the maxillary and mandibular molars, with full penetrance, in the Msx1-/-;Dkk2-/-;Sostdc1-/- mice. Together, these data reveal 1) that a key role of Msx1 in driving tooth development through the bud-to-cap transition is to control the expression of Dkk2 and 2) that modulation of Wnt signaling activity by Dkk2 and Sostdc1 plays a crucial role in the Msx1-dependent odontogenic pathway during early tooth morphogenesis.

Effects of Triiodothyronine on Human Osteoblast-Like Cells: Novel Insights From a Global Transcriptome Analysis

Background: Thyroid hormones play a significant role in bone development and maintenance, with triiodothyronine (T3) particularly being an important modulator of osteoblast differentiation, proliferation, and maintenance. However, details of the biological processes (BPs) and molecular pathways affected by T3 in osteoblasts remain unclear.

Methods: To address this issue, primary cultures of human adipose-derived mesenchymal stem cells were subjected to our previously established osteoinduction protocol, and the resultant osteoblast-like cells were treated with 1 nm or 10 nm T3 for 72 h. RNA sequencing (RNA-Seq) was performed using the Illumina platform, and differentially expressed genes (DEGs) were identified from the raw data using Kallisto and DESeq2. Enrichment analysis of DEGs was performed against the Gene Ontology Consortium database for BP terms using the R package clusterProfiler and protein network analysis by STRING.

Results: Approximately 16,300 genes were analyzed by RNA-Seq, with 343 DEGs regulated in the 1 nm T3 group and 467 upregulated in the 10 nm T3 group. Several independent BP terms related to bone metabolism were significantly enriched, with a number of genes shared among them (FGFR2, WNT5A, WNT3, ROR2, VEGFA, FBLN1, S1PR1, PRKCZ, TGFB3, and OSR1 for 1nM T3; and FZD1, SMAD6, NOG, NEO1, and ENG for 10 nm T3). An osteoblast-related search in the literature regarding this set of genes suggests that both T3 doses are unfavorable for osteoblast development, mainly hindering BMP and canonical and non-canonical WNT signaling.

Conclusions: Therefore, this study provides new directions toward the elucidation of the mechanisms of T3 action on osteoblast metabolism, with potential future implications for the treatment of endocrine-related bone pathologies.

Cross-Talk between Wnt Signaling and Src Tyrosine Kinase

Src, a non-receptor tyrosine kinase, was first discovered as a prototype oncogene and has been shown to critical for cancer progression for a variety of tissues. Src activity is regulated by a number of post-translational modifications in response to various stimuli. Phosphorylations of Src Tyr419 (human; 416 in chicken) and Src Tyr530 (human; 527 in chicken) have been known to be critical for activation and inactivation of Src, respectively. Wnt signaling regulates a variety of cellular functions including for development and cell proliferation, and has a role in certain diseases such as cancer. Wnt signaling is carried out through two pathways: β-catenin-dependent canonical and β-catenin-independent non-canonical pathways as Wnt ligands bind to their receptors, Frizzled, LRP5/6, and ROR1/2. In addition, many signaling components including Axin, APC, Damm, Dishevelled, JNK kinase and Rho GTPases contribute to these canonical and non-canonical Wnt pathways. However, the communication between Wnt signaling and Src tyrosine kinase has not been well reviewed as Src regulates Wnt signaling through LRP6 tyrosine phosphorylation. GSK-3β phosphorylated by Wnt also regulates Src activity. As Wnt signaling and Src mutually regulate each other, it is noted that aberrant regulation of these components give rise to various diseases including typically cancer, and as such, merit a closer look.

Basal Cells in the Epidermis and Epidermal Differentiation

A definite identification of epidermal stem cells is not known and the mechanism of epidermal differentiation is not fully understood. Toward both of these quests, considerable information is available from the research on lineage tracing and clonal growth analysis in the basal layer of the epidermis, on the hair follicle and the interfollicular epidermal stem cells, and on Wnt signaling along with its role in the developmental patterning and cell differentiation. In this paper, literature on the aforementioned research has been collated and analyzed. In addition, models of the basal layer cellular composition and the epidermal differentiation have been presented. Graphical Abstract.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

The SFRP1 Inhibitor WAY-316606 Attenuates Osteoclastogenesis Through Dual Modulation of Canonical Wnt Signaling

Osteoporosis, a noteworthy age-related disease induced by imbalanced osteogenesis and osteoclastogenesis, is a serious economic burden on both individuals and society. Small molecule drugs with dual effects on both bone resorption and mineralization are pressingly needed. Secreted frizzled-related protein 1 (SFRP1), a well-known extracellular repressor of canonical Wnt signaling, has been reported to regulate osteogenesis. Global SFRP1 knockout mice show significantly elevated bone mass. Although osteoclasts (OCs) express and secrete SFRP1, the role of SFRP1 produced by OCs in osteoclastogenesis and osteoporosis remains unclear. In this work, the levels of SFRP1 were found to be increased in patients with osteoporosis compared with healthy controls. Pharmacological inhibition of SFRP1 by WAY-316606 (WAY)- attenuated osteoclastogenesis and bone resorption in vitro. The expressions of OC-specific genes were suppressed by the SFRP1 inhibitor, WAY. Mechanistically, both extracellular and intracellular SFRP1 could block activation of the canonical Wnt signaling pathway, and WAY reverse the silent status of canonical Wnt through dual effects, leading to osteoclastogenesis inhibition and osteogenesis promotion. Severe osteopenia was observed in the ovariectomized (OVX) mouse model, and WAY treatment effectively improved the OVX-induced osteoporosis. In summary, this work found that SFRP1 supports OC differentiation and function, which could be attenuated by WAY through dual modulation of canonical Wnt signaling, suggesting its therapeutic potential. © 2021 American Society for Bone and Mineral Research (ASBMR).

The TNF-NF-kB-DKK1 Axis Promoted Bone Formation in the Enthesis of Ankylosing Spondylitis

Objective

This study aimed to determine the serum Dickkopf 1 (DKK1) levels in ankylosing spondylitis (AS) patients and decipher the mechanism of tumor necrosis factor (TNF)-mediated DKK1 regulation in human AS enthesis cells.

Methods

The sera were obtained from 103 patients with AS and 30 healthy controls (HCs) The enthesis of facet joints were obtained from 4 AS patients and 5 controls The serum levels of DKK1 were measured using ELISA and compared between AS and HCs The impact of TNF on DKK1 expression in human primary spinal enthesis cells was evaluated using various molecular biology techniques and bone formation indicators.

Results

AS patients showed higher serum DKK1 levels than HCs after adjusting for age (9174 [6153∼1,3100] pg/mL vs 8262 [6703∼9278] pg/mL, p=0043) TNF treatment promoted bone formation and DKK1 expression in both control enthesis cells and those of AS This enhanced bone formation by TNF was pronounced in AS-enthesis than those of controls Mechanically, TNF induced NF-kB activation upregulates the DKK1 transcript level While, NF-kB inhibitor led to downregulate DKK1 expression in the enthesis Besides, DKK1 overexpression promoted bone formation in enthesis.

Conclusion

TNF induced DKK1 expression in the enthesis through NF-kB activation TNF-induced DKK1 expression may play a bone formation in the radiologic progression of ankylosing spondylitis.

An In Vitro and In Vivo Comparison of Osteogenic Differentiation of Human Mesenchymal Stromal/Stem Cells

The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.

Evaluate the effects of serum urate level on bone mineral density: a genome-wide gene-environment interaction analysis in UK Biobank cohort

INTRODUCTION

Serum urate is associated with BMD and may be a protective factor. However, the exact association and mechanism are still unclear. We performed a genome-wide gene-environmental interaction study (GWGEIS) to explore the interaction effects between gene and urate on BMD, using data from the UK Biobank cohort.

METHODS

A total of 4575 participants for femur total BMD, 4561 participants for L1-L4 BMD, and 237799 participants for heel BMD were included in the present study. Linear regression models were used to test for associations between urate and BMD (femur total BMD, L1-L4 BMD, heel BMD) by R software. GWGEIS was conducted by PLINK 2.0 using a generalize linear model, adjusted for age, sex, weight, smoking behavior, drinking behavior, physical activity and 10 principle components for population structure.

RESULTS

Results showed that urate was positively associated with femur total BMD, L1-L4 BMD and heel BMD and similar findings were observed in both the male and female subgroups. GWGEIS identified 261 genome-wide significant (P < 5.00 × 10^-8) SNP × urate interaction effects for femur total BMD (rs8192585 in NOTCH4, rs116080577 in PBX1, rs9409991 in COL5A1), 17 genome-wide significant SNP × urate interaction effects for heel BMD (rs145344540 in PDE11A and rs78485379 in DKK2), 17 suggestive genome-wide SNP × urate interaction effects (P < 1.00 × 10^-5) for L1-L4 BMD (rs10977015 in PTPRD). We also detected genome-wide significant and suggestive SNP × urate interaction effects for BMD in both the male and female subgroups.

CONCLUSIONS

This study reported several novel candidate genes, and strengthen the evidence of the interactive effects between gene and urate on the variations of BMD.

Multifunctional polyplex micelles for efficient microRNA delivery and accelerated osteogenesis

MicroRNAs (miRNAs) are emerging as a novel class of molecular targets and therapeutics to control gene expression for tissue repair and regeneration. However, a safe and effective transfection of miRNAs to cells has been a major barrier to their applications. In this work, a multifunctional polyplex micelle named PPP-RGI was developed as a non-viral gene vector for the efficient transfection of miR-218 (an osteogenic miRNA regulator) to bone marrow-derived mesenchymal stem cells (BMSCs) for accelerated osteogenic differentiation. PPP-RGI was designed and synthesized via conjugation of a multifunctional R₉-G₄-IKVAVW (RGI) peptide onto an amphiphilic poly(lactide-co-glycolide)-g-polyethylenimine-b-polyethylene glycol (PPP) copolymer. PPP-RGI self-assembled into polyplex micelles and strongly condensed miR-218 to prevent its RNase degradation. When the PPP-RGI/miR-218 complex was brought into contact with BMSCs, it exhibited high internalization efficiency and a fast escape from endo/lysosomes of the BMSCs. Subsequently, miR-218 released from the PPP-RGI/miR-218 complex regulated gene expressions and significantly enhanced the osteogenic differentiation of BMSCs. The multifunctional peptide conjugated nanocarrier serves as an effective miRNA delivery vector to promote osteogenesis.

Cell-fate decision of mesenchymal stem cells toward osteocyte differentiation is committed by spheroid culture

Osteocytes are mechanosensory commander cells to regulate bone remodeling throughout the lifespan. While the osteocytes are known as terminally differentiated cells derived from mesenchymal stem cells, the detailed mechanisms of osteocyte differentiation remain unclear. In this study, we fabricated 3D self-organized spheroids using human mesenchymal stem cells (MSCs). Under the osteogenesis induction medium, the spheroid culture model exerted the osteocyte-likeness within 2 days compared to a conventional 2D monolayer model. Moreover, we showed that an inhibition of actin polymerization in the spheroid further up-regulated the osteocyte gene expressions. Notably, we represented that the cell condensed condition acquired in the 3D spheroid culture model determined a differentiation fate of MSCs to osteocytes. Taken together, we suggest that our self-organized spheroid model can be utilized as a new in vitro model to represent the osteocyte and to recapitulate an in vitro ossification process.

Expression Profile of New Marker Genes Involved in Differentiation of Canine Adipose-Derived Stem Cells into Osteoblasts

Next-generation sequencing (RNAseq) analysis of gene expression changes during the long-term in vitro culture and osteogenic differentiation of ASCs remains to be important, as the analysis provides important clues toward employing stem cells as a therapeutic intervention. In this study, the cells were isolated from adipose tissue obtained during routine surgical procedures and subjected to 14-day in vitro culture and differentiation. The mRNA transcript levels were evaluated using the Illumina platform, resulting in the detection of 19,856 gene transcripts. The most differentially expressed genes (fold change >|2|, adjusted p value < 0.05), between day 1, day 14 and differentiated cell cultures were extracted and subjected to bioinformatical analysis based on the R programming language. The results of this study provide molecular insight into the processes that occur during long-term in vitro culture and osteogenic differentiation of ASCs, allowing the re-evaluation of the roles of some genes in MSC progression towards a range of lineages. The results improve the knowledge of the molecular mechanisms associated with long-term in vitro culture and differentiation of ASCs, as well as providing a point of reference for potential in vivo and clinical studies regarding these cells' application in regenerative medicine.

Pharmacological Wnt ligand inhibition overcomes key tumor-mediated resistance pathways to anti-PD-1 immunotherapy

While immune checkpoint blockade is associated with prolonged responses in multiple cancers, most patients still do not benefit from this therapeutic strategy. The Wnt-β-catenin pathway is associated with diminished T cell infiltration; however, activating mutations are rare, implicating a role for autocrine/paracrine Wnt ligand-driven signaling in immune evasion. In this study, we show that proximal mediators of the Wnt signaling pathway are associated with anti-PD-1 resistance, and pharmacologic inhibition of Wnt ligand signaling supports anti-PD-1 efficacy by reversing dendritic cell tolerization and the recruitment of granulocytic myeloid-derived suppressor cells in autochthonous tumor models. We further demonstrate that the inhibition of Wnt signaling promotes the development of a tumor microenvironment that is more conducive to favorable responses to checkpoint blockade in cancer patients. These findings support a rationale for Wnt ligand-focused treatment approaches in future immunotherapy clinical trials and suggest a strategy for selecting those tumors more responsive to Wnt inhibition.

Role of Dkk2 in the Muscle/bone Interaction of Androgen-Deficient Mice

Androgen deficiency is known to cause both osteoporosis and sarcopenia. Myokines, humoral factors secreted from the skeletal muscles, have recently been getting attention as the key factors related to the interactions between muscle and bone. Dickkopf (Dkk) 2 is known as an inhibitor of canonical Wnt/β-catenin signaling, and Wnt/β-catenin signaling is crucial for the maintenance of muscle and bone. The present study was therefore performed to investigate the roles of Dkk2 in the alterations of muscle and bone of androgen-deficient mice with orchidectomy (ORX). ORX significantly enhanced Dkk2 mRNA levels, but not other Dkks and secreted frizzled related proteins, in the soleus muscles of mice. Moreover, ORX enhanced serum Dkk2 levels, but not Dkk2 mRNA levels in the tibial bone tissues, the white adipose tissues and liver of mice. In simple regression analyses, serum Dkk2 levels were negatively related to trabecular bone mineral density at the tibias in mice employed in the experiments. In vitro experiments, testosterone suppressed Dkk2 mRNA levels in mouse muscle C2C12 cells. In conclusion, we showed that androgen deficiency enhances Dkk2 expression and secretion in the muscles of mice. Dkk2 might be involved in androgen deficiency-induced muscle wasting and osteopenia as a myokine linking muscle to bone.

TGFβ1 Suppressed Matrix Mineralization of Osteoblasts Differentiation by Regulating SMURF1-C/EBPβ-DKK1 Axis

Transforming growth factor β1 (TGFβ1) is a major mediator in the modulation of osteoblast differentiation. However, the underlying molecular mechanism is still not fully understood. Here, we show that TGFβ1 has a dual stage-dependent role in osteoblast differentiation; TGFβ1 induced matrix maturation but inhibited matrix mineralization. We discovered the underlying mechanism of the TGFβ1 inhibitory role in mineralization using human osteoprogenitors. In particular, the matrix mineralization-related genes of osteoblasts such as osteocalcin (OCN), Dickkopf 1 (DKK1), and CCAAT/enhancer-binding protein beta (C/EBPβ) were dramatically suppressed by TGFβ1 treatment. The suppressive effects of TGFβ1 were reversed with anti-TGFβ1 treatment. Mechanically, TGFβ1 decreased protein levels of C/EBPβ without changing mRNA levels and reduced both mRNA and protein levels of DKK1. The degradation of the C/EBPβ protein by TGFβ1 was dependent on the ubiquitin–proteasome pathway. TGFβ1 degraded the C/EBPβ protein by inducing the expression of the E3 ubiquitin ligase Smad ubiquitin regulatory factor 1 (SMURF1) at the transcript level, thereby reducing the C/EBPβ-DKK1 regulatory mechanism. Collectively, our findings suggest that TGFβ1 suppressed the matrix mineralization of osteoblast differentiation by regulating the SMURF1-C/EBPβ-DKK1 axis.

The Interplay of WNT and PPARγ Signaling in Vascular Calcification

Vascular calcification (VC), the ectopic deposition of calcium phosphate crystals in the vessel wall, is one of the primary contributors to cardiovascular death. The pathology of VC is determined by vascular topography, pre-existing diseases, and our genetic heritage. VC evolves from inflammation, mediated by macrophages, and from the osteochondrogenic transition of vascular smooth muscle cells (VSMC) in the atherosclerotic plaque. This pathologic transition partly resembles endochondral ossification, involving the chronologically ordered activation of the β-catenin-independent and -dependent Wingless and Int-1 (WNT) pathways and the termination of peroxisome proliferator-activated receptor γ (PPARγ) signal transduction. Several atherosclerotic plaque studies confirmed the differential activity of PPARγ and the WNT signaling pathways in VC. Notably, the actively regulated β-catenin-dependent and -independent WNT signals increase the osteochondrogenic transformation of VSMC through the up-regulation of the osteochondrogenic transcription factors SRY-box transcription factor 9 (SOX9) and runt-related transcription factor 2 (RUNX2). In addition, we have reported studies showing that WNT signaling pathways may be antagonized by PPARγ activation via the expression of different families of WNT inhibitors and through its direct interaction with β-catenin. In this review, we summarize the existing knowledge on WNT and PPARγ signaling and their interplay during the osteochondrogenic differentiation of VSMC in VC. Finally, we discuss knowledge gaps on this interplay and its possible clinical impact.

Wnt16 signaling promotes osteoblast differentiation of periosteal derived cells in vitro and in vivo

Background

Periosteum plays critical roles in de novo bone formation and fracture repair. Wnt16 has been regarded as a key regulator in periosteum bone formation. However, the role of Wnt16 in periosteum derived cells (PDCs) osteogenic differentiation remains unclear. The study goal is to uncover whether and how Wnt16 acts on the osteogenesis of PDCs.

Methods

We detected the variation of Wnt16 mRNA expression in PDCs, which were isolated from mouse femur and identified by flow cytometry, cultured in osteogenic medium for 14 days, then knocked down and over-expressed Wnt16 in PDCs to analysis its effects in osteogenesis. Further, we seeded PDCs (Wnt16 over-expressed/vector) in β-tricalcium phosphate cubes, and transplanted this complex into a critical size calvarial defect. Lastly, we used immunofluorescence, Topflash and NFAT luciferase reporter assay to study the possible downstream signaling pathway of Wnt16.

Results

Wnt16 mRNA expression showed an increasing trend in PDCs under osteogenic induction for 14 days. Wnt16 shRNA reduced mRNA expression of Runx2, collage type I (Col-1) and osteocalcin (OCN) after 7 days of osteogenic induction, as well as alizarin red staining intensity after 21days. Wnt16 also increased the mRNA expression of Runx2 and OCN and the protein production of Runx2 and Col-1 after 2 days of osteogenic stimulation. In the orthotopic transplantation assay, more bone volume, trabecula number and less trabecula space were found in Wnt16 over-expressed group. Besides, in the newly formed tissue Brdu positive area was smaller and Col-1 was larger in Wnt16 over-expressed group compared to the control group. Finally, Wnt16 upregulated CTNNB1/β-catenin expression and its nuclear translocation in PDCs, also increased Topflash reporter luciferase activity. By contrast, Wnt16 failed to increase NFAT reporter luciferase activity.

Conclusion

Together, Wnt16 plays a positive role in regulating PDCs osteogenesis, and Wnt16 may have a potential use in improving bone regeneration.

Expression profiles of the Wnt/β-catenin signaling-related extracellular antagonists during proliferation and differentiation in human osteoblast-like cells

Bone formation is a dynamic process directed by osteoblast activity. The transition from the proliferation to differentiation stage during osteoblast maturation involves the downregulation of the Wnt/β-catenin signaling pathway, and extracellular antagonists are important for the regulation of Wnt signaling. However, the expression levels of Wnt antagonists in these stages of human osteoblast maturation have not been fully elucidated. Therefore, the aim of the present study was to investigate the expression levels of extracellular Wnt antagonists during proliferation and differentiation in osteoblast-like cell lines. The results demonstrated an overlap between the differential expression of secreted Frizzled-related protein (SFPR)2, SFRP3, SFRP4 and Dickkopf (DKK) 2 genes during the differentiation stage in the MG-63 and Saos-2 cells. Furthermore, high expression levels of DKK3 in MG-63 cells, Wnt inhibitory factor 1 (WIF1) in Saos-2 cells and DKK4 in hFOB 1.19 cells during the same stage (differentiation), were observed. The upregulated expression levels of Wnt antagonists were also correlated with the high expression of anxin 2 during the differentiation stage. These findings suggested that Wnt-related antagonists could modulate the Wnt/β-catenin signaling pathway. By contrast, DKK1 was the only gene that was found to be upregulated during the proliferation stage in hFOB 1.19 and Saos-2 cells. To the best of our knowledge, the present study provides, for the first time, the expression profile of Wnt antagonists during the proliferation stage and the initial phases of differentiation in osteoblast-like cell lines. The current results offer a basis to investigate potential targets for bone-related Wnt-signaling modulation in bone metabolism research.

Fgf and Wnt signaling interaction in the mesenchymal niche regulates the murine hair cycle clock

Tissue growth in the adult is an orchestrated process that often requires biological clocks to time stem cell and progenitor activity. Here, we employed the hair follicle, which cycles between growth and regression in a timely-restricted mode, to show that some components of the hair cycle clock reside within the mesenchymal niche of the hair follicle, the dermal papilla (DP), and both Fgf and Wnt signaling pathways interact within the DP to regulate the expression of these components that include Wnt agonists (Rspondins) and antagonists (Dkk2 and Notum). The levels of Wnt agonists and antagonists in the DP are progressively reduced and elevated during the growth phase, respectively. Consequently, Wnt signaling activity in the overlying epithelial progenitor cells decreases, resulting in the induction of the regression phase. Remarkably, DP properties allow Wnt activity in the DP to persist despite the Wnt-inhibiting milieu and consequently synchronize the induction and progression of the regression phase. This study provides insight into the importance of signaling crosstalk in coupling progenitors and their niche to regulate tissue growth.

The underlying mechanisms regulating the mouse hair cycle remain poorly understood. Here, the authors find that Fgf and Wnt signaling pathways interact in the mesenchymal niche of the hair follicle to regulate the molecular clock that dictates the duration of hair growth.

Integrated Transcriptome and Network Analysis Reveals Spatiotemporal Dynamics of Calvarial Suturogenesis

Craniofacial abnormalities often involve sutures, the growth centers of the skull. To characterize the organization and processes governing their development, we profile the murine frontal suture, a model for sutural growth and fusion, at the tissue- and single-cell level on embryonic days (E)16.5 and E18.5. For the wild-type suture, bulk RNA sequencing (RNA-seq) analysis identifies mesenchyme-, osteogenic front-, and stage-enriched genes and biological processes, as well as alternative splicing events modifying the extracellular matrix. Single-cell RNA-seq analysis distinguishes multiple subpopulations, of which five define a mesenchyme-osteoblast differentiation trajectory and show variation along the anteroposterior axis. Similar analyses of in vivo mouse models of impaired frontal suturogenesis in Saethre-Chotzen and Apert syndromes, Twist1+/- and Fgfr2+/S252W, demonstrate distinct transcriptional changes involving angiogenesis and ribogenesis, respectively. Co-expression network analysis reveals gene expression modules from which we validate key driver genes regulating osteoblast differentiation. Our study provides a global approach to gain insights into suturogenesis.

The Emerging Role of Exosomal Non-coding RNAs in Musculoskeletal Diseases

Exosomes are phospholipid bilayer-enclosed membrane vesicles derived and constitutively secreted by various metabolically active cells. They are capable of mediating hetero- and homotypic intercellular communication by transferring multiple cargos from donor cells to recipient cells. Nowadays, non-coding RNAs (ncRNAs) have emerged as novel potential biomarkers or disease-targeting agents in a variety of diseases. However, the lack of effective delivery systems may impair their clinical application. Recently, accumulating evidence demonstrated that ncRNAs could be efficiently delivered to recipient cells using exosomes as a carrier, and therefore can exert a critical role in musculoskeletal diseases including osteoarthritis, rheumatoid arthritis, osteoporosis, muscular dystrophies, osteosarcoma and other diseases. Herein, we present an extensive review of biogenesis, physiological relevance and clinical implication of exosome-derived ncRNAs in musculoskeletal diseases.

Wnt7b-induced Sox11 functions enhance self-renewal and osteogenic commitment of bone marrow mesenchymal stem cells

As a profoundly anabolic regulator of bone, Wnt7b is well acknowledged to enhance osteoblast activities. Here, we report that bone marrow mesenchymal stem cells (BMSCs) are another important population responding to Wnt7b. In this study, we systematically investigated the in vivo role of Wnt7b in BMSCs using transgenic mice, high-throughput RNA-seq, immunohistochemistry, RT-qPCR, and in situ hybridization. These methods led us to uncover that Sox11 is induced via Wnt7b in BMSCs. Colony formation assay, flow cytometry, EdU incorporation labeling, RT-qPCR, and Western blot were conducted to detect the self-renewal capacity of BMSCs. Alkaline phosphatase staining, alizarin red staining, and ex vivo BMSCs transplantation were utilized to detect the osteogenic ability of BMSCs. ChIP-qPCR, shRNAs, and immunofluorescence staining were utilized to investigate the underlying mechanisms. Consequently, bone-derived Wnt7b was found to decrease in osteoporosis and elevate in bone fracture healing. During bone fracture healing, Wnt7b was particularly expressed in the mesenchymal cells residing within healing frontiers. RNA-seq data of Wnt7b-overexpressed bones uncovered the significant upregulation of Sox11. Histological results further unveiled that Sox11 is specifically increased in BMSCs. Wnt7b-induced Sox11 was demonstrated to reinforce both self-renewal and osteogenic differentiation of BMSCs. Mechanistically, Wnt7b activates the Ca²⁺ -dependent Nfatc1 signaling to directly induce Sox11 transcription, which in turn activates the transcriptions of both proliferation-related transcription factors (Ccnb1 and Sox2) and osteogenesis-related factors (Runx2, Sp7) in BMSCs. It is intriguing that this Wnt7b-Sox11 signaling in BMSCs is β-Catenin-independent. Overall, this study provides brand new insights of Wnt7b in bone formation, namely, Wnt7b can enhance both self-renewal and osteogenic differentiation of BMSCs via inducing Sox11. These findings present a new crosstalk between Wnt and Sox signaling in BMSCs.

Rational design of peptides for identification of linear epitopes and generation of neutralizing monoclonal antibodies against DKK2 for cancer therapy

Dickkopf-related protein 2 (DKK2)is a member of the Dickkopf family in Wnt signaling pathway. Recently, we found that antibodies against DKK2 could activate natural killer (NK) and CD8+ T cells in tumors and inhibit tumor growth. In this paper, we report the rational design of peptides for identification of linear epitopes and generation of neutralizing monoclonal anti-DKK2 antibodies. To break the immune tolerance, we designed and chemically synthesized six peptides corresponding to different regions of DKK2 as immunogens and found five of them could generate mouse polyclonal antibodies that can bind to the active recombinant human DKK2 protein. Neutralizing mouse monoclonal antibodies (5F8 and 1A10) against human DKK2 were successfully developed by immunizing the mice with two different peptides (³⁴KLNSIKSSL⁴² and ²⁴⁰KVWKDATYS²⁴⁸) conjugated to Keyhole limpet hemocyanin (KLH). The monoclonal antibodies not only abolish DKK2’s suppression of Wnt signaling in vitro but also inhibits tumor growth in vivo. Currently, those two mAbs are undergoing humanization as immunotherapy candidates and may offer a new drug for treatment of human cancers.

Roles of Dkk2 in the Linkage from Muscle to Bone during Mechanical Unloading in Mice

Mechanical unloading simultaneously induces muscle and bone loss, but its mechanisms are not fully understood. The interactions between skeletal muscle and bone have been recently noted. Although canonical wingless-related integration site (Wnt)/β-catenin signaling is crucial for bone metabolism, its roles in the muscle and bone interactions have remained unknown. Here, we performed comprehensive DNA microarray analyses to clarify humoral factors linking muscle to bone in response to mechanical unloading and hypergravity with 3 g in mice. We identified Dickkopf (Dkk) 2, a Wnt/β-catenin signaling inhibitor, as a gene whose expression was increased by hindlimb unloading (HU) and reduced by hypergravity in the soleus muscle of mice. HU significantly elevated serum Dkk2 levels and Dkk2 mRNA levels in the soleus muscle of mice whereas hypergravity significantly decreased those Dkk2 levels. In the simple regression analyses, serum Dkk2 levels were negatively and positively related to trabecular bone mineral density and mRNA levels of receptor activator of nuclear factor-kappa B ligand (RANKL) in the tibia of mice, respectively. Moreover, shear stress significantly suppressed Dkk2 mRNA levels in C2C12 cells, and cyclooxygenase inhibitors significantly antagonized the effects of shear stress on Dkk2 expression. On the other hand, Dkk2 suppressed the mRNA levels of osteogenic genes, alkaline phosphatase activity and mineralization, and it increased RANKL mRNA levels in mouse osteoblasts. In conclusion, we showed that muscle and serum Dkk2 levels are positively and negatively regulated during mechanical unloading and hypergravity in mice, respectively. An increase in Dkk2 expression in the skeletal muscle might contribute to disuse- and microgravity-induced bone and muscle loss.

Genome-Wide Analysis Reveals Human-Mediated Introgression from Western Pigs to Indigenous Chinese Breeds

Genetic variations introduced via introgression from Western to Chinese pigs have contributed to the performance of Chinese breeds in traits such as growth rate and feed conversion efficiency. However, little is known about the underlying genomic changes that occurred during introgression and the types of traits affected by introgression. To address these questions, 525 animals were characterized using an SNP array to detect genomic regions that had been introgressed from European to indigenous Chinese breeds. The functions of genes located in introgressed regions were also investigated. Our data show that five out of six indigenous Chinese breeds show evidence of introgression from Western pigs, and eight introgressed genome regions are shared by five of the Chinese breeds. A region located on chr13: 12.8-13.1 M was affected by both introgression and artificial selection, and this region contains the glucose absorption related gene, OXSM, and the sensory related gene, NGLY. The results provide a foundation for understanding introgression from Western to indigenous Chinese pigs.

MiR-128 promotes osteogenic differentiation of bone marrow mesenchymal stem cells in rat by targeting DKK2

Bone loss caused by inflammatory disease, such as peri-implantitis, poses a great challenge to clinicians for restoration. Emerging evidence indicates that microRNAs (miRNAs) are indispensable regulators of bone growth, development, and formation. In the present study, we found that microRNA-128 (miR-128) was differentially up-regulated during the osteogenic differentiation of rat bone marrow stem cells (rBMSCs). Overexpression of miR-128 promoted osteogenic differentiation of rBMSCs by up-regulating alkaline phosphatase (ALP), matrix mineralization, mRNA, and protein levels of osteogenic makers (e.g. RUNX2, BMP-2, and COLIA1), whereas inhibition of miR-128 suppressed osteoblastic differentiation in vitro. Mechanistically, miR-128 directly and functionally targeted Dickkopf2 (DKK2), which is a Wnt signaling pathway antagonist, and enhanced Wnt/β-catenin signaling activity. Furthermore, the positive effect of miR-128 on osteogenic differentiation was apparently abrogated by DKK2 overexpression. Collectively, these results indicate that miR-128 promotes osteogenic differentiation of rBMSCs by targeting DKK2, which may provide a promising approach to the treatment of peri-implantitis.

Pro-inflammatory Cytokines: Cellular and Molecular Drug Targets for Glucocorticoid-induced-osteoporosis via Osteocyte

Glucocorticoids are widely used to treat varieties of allergic and autoimmune diseases, however, long-term application results in glucocorticoid-induced osteoporosis (GIOP). Inflammatory cytokines: tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) play important regulatory roles in bone metabolism, but their roles in GIOP remain largely unknown. Osteocytes can modulate the formation and function of both osteoblasts and osteoclasts, directly via gap junctions, or indirectly by transferring molecule signaling. Apoptotic osteocytes release RANKL, HMGB1 and pro-inflammatory cytokines to stimulate osteoclastogenesis. Moreover, osteocytes can secrete FGF23 to regulate bone metabolism. Exposure to high levels of GCs can drive osteocyte apoptosis and influence gap junctions, leading to bone loss. GCs treatment is regarded to produce more FGF23 to inhibit bone mineralization. GCs also disrupt the vascular to decrease osteocyte feasibility and mineral appositional rate, resulting in a decline in bone strength. Apoptotic bodies from osteocytes induced by GCs treatment can enhance production of TNF-α and IL-6. On the other hand, TNF-α and IL-6 show synergistic effects by altering osteocytes signaling towards osteoclasts and osteoblasts. In addition, TNF-α can induce osteocyte apoptosis and attribute to a worsened bone quality in GCs. IL-6 and osteocytes may interact with each other. Therefore, we hypothesize that GCs regulate osteocyteogenesis through TNF-α and IL-6, which are highly expressed around osteocyte undergoing apoptosis. In the present review, we summarized the roles of osteocytes in regulating osteoblasts and osteoclasts. Furthermore, the mechanism of GCs altered relationship between osteocytes and osteoblasts/osteoclasts. In addition, we discussed the roles of TNF-α and IL-6 in GIOP by modulating osteocytes. Lastly, we discussed the possibility of using pro-inflammatory signaling pathway as therapeutic targets to develop drugs for GIOP.

DKK1 Induced by 1,25D3 Is Required for the Mineralization of Osteoblasts

1α,25-dihydroxyvitamin D3 (1,25D3), the most popular drug for osteoporosis treatment, drives osteoblast differentiation and bone mineralization. Wnt/β-catenin signaling is involved in commitment and differentiation of osteoblasts, but the role of the Dickkopf-related protein 1 (DKK1), a Wnt antagonist, in osteoblasts remains unknown. Here, we demonstrate the molecular mechanism of DKK1 induction by 1,25D3 and its physiological role during osteoblast differentiation. 1,25D3 markedly promoted the expression of both CCAAT/enhancer binding protein beta (C/EBPβ) and DKK1 at day 7 during osteoblast differentiation. Interestingly, mRNA and protein levels of C/EBPβ and DKK1 in osteoblasts were elevated by 1,25D3. We also found that C/EBPβ, in response to 1,25D3, directly binds to the human DKK1 promoter. Knockdown of C/EBPβ downregulated the expression of DKK1 in osteoblasts, which was partially reversed by 1,25D3. In contrast, overexpression of C/EBPβ upregulated DKK1 expression in osteoblasts, which was enhanced by 1,25D3. Furthermore, 1,25D3 treatment in osteoblasts stimulated secretion of DKK1 protein within the endoplasmic reticulum to extracellular. Intriguingly, blocking DKK1 attenuated calcified nodule formation in mineralized osteoblasts, but not ALP activity or collagen synthesis. Taken together, these observations suggest that 1,25D3 promotes the mineralization of osteoblasts through activation of DKK1 followed by an increase of C/EBPβ.

Dickkopf 2-Expressing Adenovirus Increases the Survival of Random-Pattern Flaps and Promotes Vasculogenesis in a Rat Model

BACKGROUND

Dickkopf 2 (DKK2) has important roles in vertebrate development; it inhibits Wnt signaling-related processes, such as axial patterning, limb development, somitogenesis, and eye formation. However, DKK2 also acts as a Wnt signaling agonist. Dickkopf 2, induced during endothelial cell morphogenesis, promotes angiogenesis in cultured human endothelial cells. In this study, we explored the effect of DKK2-expressing adenovirus on random-pattern flaps using a rodent model.

METHODS

A DKK2-expressing (dE1-RGD/DKK2) adenovirus was generated and 20 Sprague-Dawley rats were randomly divided into 2 groups: a DKK2 group and a control group. Each group was intradermally injected with 1 × 10 plaque-forming units of DKK2-expressing adenovirus (DKK2 group) or control virus (control group) 48 hours before and immediately before surgery. Then, random-pattern dorsal cutaneous flaps of 3 × 9 cm were elevated. Flap survival rates and cutaneous blood flow were measured over time, and immunohistochemical staining was performed 10 days after surgery to detect CD31 and vascular endothelial growth factor (VEGF).

RESULTS

Immunofluorescence staining confirmed the expression of DKK2 in the DKK2 group. The flap survival rate was higher in the DKK2 group (80.0 ± 4.49%) than in the control group (57.5 ± 4.21%; P < 0.05). Blood flow to the most distal compartment was higher in the DKK2 group than the control group during the early postoperative period. Although vascular density was greater in the DKK2 group, there was no difference in the VEGF concentration between groups.

CONCLUSIONS

The findings of the present study suggest that the DKK2-expressing adenovirus increases the survival of the random-pattern cutaneous flap independently of VEGF. The administration of the DKK2-expressing adenovirus into elevated skin flaps increased the number of capillaries and blood flow, thereby improving skin flap survival.

Lung tumor cells inhibit bone mineralization and osteoblast activity

Patients with non-small cell lung cancer (NSLC) often develop skeletal complications and fractures. To understand mechanisms of bone loss, we developed a murine model of non-metastatic NSLC. Decreased bone mineral density, trabecular thickness and mineralization, without an increase in bone resorption, were observed in vivo in mice injected with Lewis lung adenocarcinoma (LLC1) cells in the absence of tumor cell metastases. A decrease in trabecular bone mineral density was observed in mice injected with cell-free LLC1 CM. Plasma osteoblast biomarkers and PTH-related peptide (PTHrP) were reduced, and parathyroid hormone (PTH), 1,25-dihydroxyvitamin D, calcium and phosphate concentrations were normal in tumor-bearing mice. LLC1 cell conditioned medium (CM) inhibited alkaline phosphatase activity, osteoblast mineralization, and expression of Alpl and Ocn/Bglap mRNA in MC3T3 osteoblast cultures, whereas non-CM or CM from NIH/3T3 fibroblasts did not induce similar changes. LLC1 CM reduced Wnt3a-stimulated Tcf/Lef reporter plasmid activity and Wnt5A, Tcf1 and Lef1 mRNA expression in MC3T3 cells. Although concentrations of the Wnt inhibitor, DKK2, were increased in LLC1 CM compared to non-CM, depletion of DKK2 from LLC1 CM did not completely restore Wnt3a activity in MC3T3 cultures, and recombinant DKK2 failed to inhibit osteoblast mineralization. The data indicate that in a model of lung adenocarcinoma without bone metastases, tumor cells elaborate a secreted factor(s) that reduces bone mass, bone formation and osteoblast Wnt signaling without increases in bone resorption or calcium-regulating hormone concentrations. The factor(s) mediating this inhibition of osteoblast mineralization require further characterization.

Osteocyte Death and Bone Overgrowth in Mice Lacking Fibroblast Growth Factor Receptors 1 and 2 in Mature Osteoblasts and Osteocytes

Fibroblast growth factor (FGF) signaling pathways have well-established roles in skeletal development, with essential functions in both chondrogenesis and osteogenesis. In mice, previous conditional knockout studies suggested distinct roles for FGF receptor 1 (FGFR1) signaling at different stages of osteogenesis and a role for FGFR2 in osteoblast maturation. However, the potential for redundancy among FGFRs and the mechanisms and consequences of stage-specific osteoblast lineage regulation were not addressed. Here, we conditionally inactivate Fgfr1 and Fgfr2 in mature osteoblasts with an Osteocalcin (OC)-Cre or Dentin matrix protein 1 (Dmp1)-CreER driver. We find that young mice lacking both receptors or only FGFR1 are phenotypically normal. However, between 6 and 12 weeks of age, OC-Cre Fgfr1/Fgfr2 double- and Fgfr1 single-conditional knockout mice develop a high bone mass phenotype with increased periosteal apposition, increased and disorganized endocortical bone with increased porosity, and biomechanical properties that reflect increased bone mass but impaired material properties. Histopathological and gene expression analyses show that this phenotype is preceded by a striking loss of osteocytes and accompanied by activation of the Wnt/β-catenin signaling pathway. These data identify a role for FGFR1 signaling in mature osteoblasts/osteocytes that is directly or indirectly required for osteocyte survival and regulation of bone mass during postnatal bone growth. © 2019 American Society for Bone and Mineral Research.

Low Serum Levels of DKK2 Predict Incident Low-Impact Fracture in Older Women

There are currently no robust noninvasive markers of fragility fractures. Secreted frizzled related protein‐1 (sFRP‐1), dickkopf‐related protein 1 (DKK1) and DKK2, and sclerostin (SOST) inhibit Wnt signaling and interfere with osteoblast‐mediated bone formation. We evaluated associations of serum levels of sFRP‐1, DKK1, DKK2, and SOST with incident low‐impact fracture and BMD in 828 women aged ≥65 years from EpiDoC, a longitudinal population‐based cohort. A structured questionnaire during a baseline clinical appointment assessed prevalent fragility fractures and clinical risk factors (CRFs) for fracture. Blood was collected to measure serum levels of bone turnover markers and Wnt regulators. Lumbar spine and hip BMD were determined by DXA scanning. Follow‐up assessment was performed through a phone interview; incident fragility fracture was defined by any new self‐reported low‐impact fracture. Multivariate Cox proportional hazard models were used to analyze fracture risk adjusted for CRFs and BMD. During a mean follow‐up of 2.3 ± 1.0 years, 62 low‐impact fractures were sustained in 58 women. A low serum DKK2 level (per 1 SD decrease) was associated with a 1.5‐fold increase in fracture risk independently of BMD and CRFs. Women in the two lowest DKK2 quartiles had a fracture incidence rate of 32 per 1000 person‐years, whereas women in the two highest quartiles had 14 fragility fractures per 1000 person‐years. A high serum sFRP1 level was associated with a 1.6‐fold increase in fracture risk adjusted for CRFs, but not independently of BMD. Serum levels of SOST (r = 0.191; p = 0.0025) and DKK1(r = −0.1725; p = 0.011) were correlated with hip BMD, but not with incident fragility fracture. These results indicate that serum DKK2 and sFRP1 may predict low‐impact fracture. The low number of incident fractures recorded is a limitation and serum levels of Wnt regulators should be further studied in other populations as potential noninvasive markers of fragility fractures. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Serum sclerostin level and its relation to subclinical atherosclerosis in subjects with type 2 diabetes

BACKGROUND

Sclerostin, a Wnt-signalling inhibitor, is an established negative regulator of bone formation. However, data regarding its potential importance in vascular disease are less clear. Common carotid artery media thickness (CIMT) assessment and plaque identification using ultrasound imaging are well-recognized tools for identifying and monitoring atherosclerosis. The aim of the present study is to examine the relationship between serum sclerostin and subclinical atherosclerosis (as evidenced by CIMT).

METHODS

This cross-sectional study included 50 subjects with T2DM and 20 subjects as a control group. Multivariable linear regression models were used to assess the association of sclerostin with subclinical atherosclerosis.

RESULTS

Serum sclerostin levels in T2DM patients were significantly higher compared to the control group (167.16 ± 63.60 versus 85.98 ± 23.74 pg/ml, P < 0.0001). A concentration of ≥162.5 pg/ml showed a sensitivity of 90% and a specificity of 86.67% to detect an increased risk of subclinical atherosclerosis. Univariate analysis revealed a significant positive correlation between serum sclerostin and CIMT (r = 0.635, P < 0.001). Sclerostin concentrations remained independently associated with CIMT (β = 63.188 [6.919-119.456], P = 0.017) after adjusting for age and gender.

CONCLUSION

Our data suggest a positive correlation between serum sclerostin level and subclinical atherosclerosis in subjects with type 2 diabetes mellitus.

Neutralizing monoclonal antibody against Dickkopf2 impairs lung cancer progression via activating NK cells

Adenomatous polyposis coli (APC) and KRAS proto-oncogene (KRAS) mutations frequently co-occur in non-small cell lung cancer. Inactivating APC mutations in colorectal carcinoma has been well characterized, leading to the approaches targeting on dysregulated APC pathway. However, it remains undetermined whether such approaches are also applicable to non-small cell lung cancer patients harboring similar mutations of APC. Dickkopf-related protein 2 (DKK2) is a Wnt antagonist. Our previous study has proved that anti-DKK2 antibody 5F8 suppressed the growth of colorectal carcinoma with APC mutations, illustrating a new target agent of APC-mutated tumors. This study aimed to investigate the potential of applying anti-DKK2 antibody to non-small cell lung cancer with APC mutations. We found significant upregulation of Dkk2 expression in APC-mutated lung cancers. Administration of DKK2 antibody inhibited cancer growth via modulating tumor immune microenvironment in lung cancer mouse models. Our study provided strong evidence supporting APC mutations-directed applications of anti-DKK2 targeted therapy in a wide range of cancer types, including lung cancer.