WNT signaling in bone homeostasis and disease: from human mutations to treatments. Nat Med. 2013;19:179-192. [PMID: 23389618 DOI: 10.1038/nm.3074]

Regulation of bone homeostasis by MERTK and TYRO3

The fine equilibrium of bone homeostasis is maintained by bone-forming osteoblasts and bone-resorbing osteoclasts. Here, we show that TAM receptors MERTK and TYRO3 exert reciprocal effects in osteoblast biology: Osteoblast-targeted deletion of MERTK promotes increased bone mass in healthy mice and mice with cancer-induced bone loss, whereas knockout of TYRO3 in osteoblasts shows the opposite phenotype. Functionally, the interaction of MERTK with its ligand PROS1 negatively regulates osteoblast differentiation via inducing the VAV2-RHOA-ROCK axis leading to increased cell contractility and motility while TYRO3 antagonizes this effect. Consequently, pharmacologic MERTK blockade by the small molecule inhibitor R992 increases osteoblast numbers and bone formation in mice. Furthermore, R992 counteracts cancer-induced bone loss, reduces bone metastasis and prolongs survival in preclinical models of multiple myeloma, breast- and lung cancer. In summary, MERTK and TYRO3 represent potent regulators of bone homeostasis with cell-type specific functions and MERTK blockade represents an osteoanabolic therapy with implications in cancer and beyond.

Home-based cardiac rehabilitation: A review of bibliometric studies and visual analysis of CiteSpace (2012-2021)

Home-based cardiac rehabilitation has been a major area in cardiac rehabilitation research for a long time. However, there are few systematic studies in this field using bibliometric analysis. We collected articles and reviews for home-based cardiac rehabilitation from the Web of Science Core Collection. Our objectives were to perform a bibliometric analysis and visualization study to determine hotspots and trends of home-based cardiac rehabilitation, identify collaboration and influence among authors, countries, institutions, and journals, and assess the knowledge base to develop clinical research in the future. This study will provide a valuable reference for researchers concerned with HBCR.

Molecular Features of the Mesenchymal and Osteoblastic Cells in Multiple Myeloma

Multiple myeloma (MM) is a monoclonal gammopathy characterized by biological heterogeneity and unregulated proliferation of plasma cells (PCs) in bone marrow (BM). MM is a multistep process based on genomic instability, epigenetic dysregulation and a tight cross-talk with the BM microenvironment that plays a pivotal role supporting the proliferation, survival, drug-resistance and homing of PCs. The BM microenvironment consists of a hematopoietic and a non-hematopoietic compartment, which cooperate to create a tumor environment. Among the non-hematopoietic component, mesenchymal stromal cells (MSCs) and osteoblasts (OBs) appear transcriptionally and functionally different in MM patients compared to healthy donors (HDs) and to patients with pre-malignant monoclonal gammopathies. Alterations of both MSCs and OBs underly the osteolytic lesions that characterize myeloma-associated bone disease. In this review, we will discuss the different characteristics of MSCs and OBs in MM patients, analyzing the transcriptome, the deregulated molecular pathways and the role performed by miRNAs and exosome in the pathophysiology of MM.

Wnt Signaling in the Development of Bone Metastasis

Wnt signaling occurs through evolutionarily conserved pathways that affect cellular proliferation and fate decisions during development and tissue maintenance. Alterations in these highly regulated pathways, however, play pivotal roles in various malignancies, promoting cancer initiation, growth and metastasis and the development of drug resistance. The ability of cancer cells to metastasize is the primary cause of cancer mortality. Bone is one of the most frequent sites of metastases that generally arise from breast, prostate, lung, melanoma or kidney cancer. Upon their arrival to the bone, cancer cells can enter a long-term dormancy period, from which they can be reactivated, but can rarely be cured. The activation of Wnt signaling during the bone metastasis process was found to enhance proliferation, induce the epithelial-to-mesenchymal transition, promote the modulation of the extracellular matrix, enhance angiogenesis and immune tolerance and metastasize and thrive in the bone. Due to the complexity of Wnt pathways and of the landscape of this mineralized tissue, Wnt function during metastatic progression within bone is not yet fully understood. Therefore, we believe that a better understanding of these pathways and their roles in the development of bone metastasis could improve our understanding of the disease and may constitute fertile ground for potential therapeutics.

Prrx1 marks stem cells for bone, white adipose tissue and dermis in adult mice

Specialized connective tissues, including bone and adipose tissues, control various physiological activities, including mineral and energy homeostasis. However, the identity of stem cells maintaining these tissues throughout adulthood remains elusive. By conducting genetic lineage tracing and cell depletion experiments in newly generated knock-in Cre/CreER^T2 lines, we show here that rare Prrx1-expressing cells act as stem cells for bone, white adipose tissue and dermis in adult mice, which are indispensable for the homeostasis and repair of these tissues. Single-cell profiling reveals the cycling and multipotent nature of Prrx1-expressing cells and the stemness of these cells is further validated by transplantation assays. Moreover, we identify the cell surface markers for Prrx1-expressing stem cells and show that the activities of these stem cells are regulated by Wnt signaling. These findings expand our knowledge of connective tissue homeostasis/regeneration and may help improve stem-cell-based therapies.

The fatty acid synthase inhibitor C75 differentially affects the adipogenic differentiation of multipotent cells and preadipocytes

Previously, we revealed the dual enhancing effect of netoglitazone, an agonist of the peroxisome proliferator-activated receptor γ, on adipogenesis and osteoblastogenesis, and reported that fatty acid synthase (FASN) knockdown selectively repressed its pro-adipogenic effect. Here, we examined if a FASN inhibitor, C75, could selectively repress the pro-adipogenic effect of netoglitazone. Surprisingly, C75 promoted the adipogenic differentiation of multipotent C3H10T1/2 cells but inhibited 3T3-L1 preadipocytes. By identifying glycogen synthase kinase-3β and intracellular cAMP levels as regulatory targets of C75, we ultimately found the differential expression of adenosine receptor 3 (AR3) and AR2a on these cells. Inhibition of AR3 on C3H10T1/2 and AR2a on 3T3-L1 inhibited the effects of C75 on the differentiation of these cells. Our findings imply that cell-type-specific AR expression might account for the differential adipogenic effects of C75.

Determinants of Low Bone Turnover in Type 2 Diabetes-the Role of PTH

Determinants of low bone turnover in type 2 diabetes (T2DM) are poorly understood. To investigate the relationship between markers of bone turnover, glycaemic control, disease duration and calciotropic hormones in T2DM we assessed baseline biochemical data from the DiabOS Study, a prospective multicenter observational cohort study. In a cross-sectional study-design data from 110 postmenopausal women and men aged 50-75 years diagnosed with T2DM for at least 3 years and 92 non-diabetic controls were evaluated. Biochemical markers of bone formation (N-terminal propeptide of type I procollagen [PINP]), bone-specific alkaline phosphatase [BAP]) and resorption (C-terminal cross-linking telopeptide of type I collagen [CTX]), measures of calcium homeostasis (intact parathormone [iPTH], 25-Hydroxyvitamin D, calcium, magnesium) and glycaemic control were assessed. After adjustment for age, gender and body mass index (BMI), patients with T2DM had lower serum levels of PINP (p < 0.001), CTX (p < 0.001), iPTH (p = 0.03) and magnesium (p < 0.001) compared to controls. Serum calcium, creatinine, 25-Hydroxyvitamin D and sclerostin did not differ between both groups. In multivariate linear regression analyses only serum iPTH remained an independent determinant of bone turnover markers in T2DM (PINP: p = 0.02; CTX: p < 0.001 and BAP: p < 0.01), whereas glycated haemoglobin (HbA1c), disease duration, age and BMI were not associated with bone turnover. In conclusion low bone turnover in T2DM is associated with low iPTH. The underlying mechanism remains to be elucidated.

Retinoic acid effects on in vitro palatal fusion and WNT signaling

Retinoic acid is the main active vitamin A derivate and a key regulator of embryonic development. Excess of retinoic acid can disturb palate development in mice leading to cleft palate. WNT signaling is one of the main pathways in palate development. We evaluated the effects of retinoic acid on palate fusion and WNT signaling in in vitro explant cultures. Unfused palates from E13.5 mouse embryos were cultured for 4 days with 0.5 μM, 2 μM or without retinoic acid. Apoptosis, proliferation, WNT signaling and bone formation were analyzed by histology and quantitative PCR. Retinoic acid treatment with 0.5 and 2.0 μM reduced palate fusion from 84% (SD 6.8%) in the controls to 56% (SD 26%) and 16% (SD 19%), respectively. Additionally, 2 μM retinoic acid treatment increased Axin2 expression. Retinoic acid also increased the proliferation marker Pcna as well as the number of Ki-67-positive cells in the palate epithelium. At the same time, the WNT inhibitors Dkk1, Dkk3, Wif1 and Sfrp1 were downregulated at least two-fold. Retinoic acid also down-regulated Alpl and Col1a2 gene expression. Alkaline phosphatase (ALP) activity was notably reduced in the osteogenic areas of the retinoic acid- treated palates. Our data suggest that retinoic acid impairs palate fusion and bone formation by upregulation of WNT signaling.

The importance of fusion protein activity in Ewing sarcoma and the cell intrinsic and extrinsic factors that regulate it: A review

Accumulating evidence shows that despite clonal origins tumors eventually become complex communities comprised of phenotypically distinct cell subpopulations. This heterogeneity arises from both tumor cell intrinsic programs and signals from spatially and temporally dynamic microenvironments. While pediatric cancers usually lack the mutational burden of adult cancers, they still exhibit high levels of cellular heterogeneity that are largely mediated by epigenetic mechanisms. Ewing sarcomas are aggressive bone and soft tissue malignancies with peak incidence in adolescence and the prognosis for patients with relapsed and metastatic disease is dismal. Ewing sarcomas are driven by a single pathognomonic fusion between a FET protein and an ETS family transcription factor, the most common of which is EWS::FLI1. Despite sharing a single driver mutation, Ewing sarcoma cells demonstrate a high degree of transcriptional heterogeneity both between and within tumors. Recent studies have identified differential fusion protein activity as a key source of this heterogeneity which leads to profoundly different cellular phenotypes. Paradoxically, increased invasive and metastatic potential is associated with lower EWS::FLI1 activity. Here, we review what is currently understood about EWS::FLI1 activity, the cell autonomous and tumor microenvironmental factors that regulate it, and the downstream consequences of these activity states on tumor progression. We specifically highlight how transcription factor regulation, signaling pathway modulation, and the extracellular matrix intersect to create a complex network of tumor cell phenotypes. We propose that elucidation of the mechanisms by which these essential elements interact will enable the development of novel therapeutic approaches that are designed to target this complexity and ultimately improve patient outcomes.

Induced inactivation of Wnt16 in young adult mice has no impact on osteoarthritis development

Osteoarthritis (OA) is a common disorder and a major cause of disability in the elderly population. WNT16 has been suggested to play important roles in joint formation, bone homeostasis and OA development, but the mechanism of action is not clear. Transgenic mice lacking Wnt16 expression (Wnt16-/-) have a more severe experimental OA than control mice. In addition, Wnt16-/- mice have a reduced cortical thickness and develop spontaneous fractures. Herein, we have used Cre-Wnt16flox/flox mice in which Wnt16 can be conditionally ablated at any age through tamoxifen-inducible Cre-mediated recombination. Wnt16 deletion was induced in 7-week-old mice to study if the Cre-Wnt16flox/flox mice have a more severe OA phenotype after destabilizing the medial meniscus (DMM surgery) than littermate controls with normal Wnt16 expression (Wnt16flox/flox). WNT16 deletion was confirmed in articular cartilage and cortical bone in Cre-Wnt16flox/flox mice, shown by immunohistochemistry and reduced cortical bone area compared to Wnt16flox/flox mice. After DMM surgery, there was no difference in OA severity in the articular cartilage in the knee joint between the Cre-Wnt16flox/flox and Wnt16flox/flox mice in neither female nor male mice. In addition, there was no difference in osteophyte size in the DMM-operated tibia between the genotypes. In conclusion, inactivation of Wnt16 in adult mice do not result in a more severe OA phenotype after DMM surgery. Thus, presence of WNT16 in adult mice does not have an impact on experimental OA development. Taken together, our results from Cre-Wnt16flox/flox mice and previous results from Wnt16-/- mice suggest that WNT16 is crucial during synovial joint establishment leading to limited joint degradation also later in life, after onset of OA. This may be important when developing new therapeutics for OA treatment.

Functionalized TiCu/TiCuN coating promotes osteoporotic fracture healing by upregulating the Wnt/β-catenin pathway

Osteoporosis results in decreased bone mass and insufficient osteogenic function. Existing titanium alloy implants have insufficient osteoinductivity and delayed/incomplete fracture union can occur when used to treat osteoporotic fractures. Copper ions have good osteogenic activity, but their dose-dependent cytotoxicity limits their clinical use for bone implants. In this study, titanium alloy implants functionalized with a TiCu/TiCuN coating by arc ion plating achieved a controlled release of copper ions in vitro for 28 days. The coated alloy was co-cultured with bone marrow mesenchymal stem cells and showed excellent biocompatibility and osteoinductivity in vitro. A further exploration of the underlying mechanism by quantitative real-time polymerase chain reaction and western blotting revealed that the enhancement effects are related to the upregulation of genes and proteins (such as axin2, β-catenin, GSK-3β, p-GSK-3β, LEF1 and TCF1/TCF7) involved in the Wnt/β-catenin pathway. In vivo experiments showed that the TiCu/TiCuN coating significantly promoted osteoporotic fracture healing in a rat femur fracture model, and has good in vivo biocompatibility based on various staining results. Our study confirmed that TiCu/TiCuN-coated Ti promotes osteoporotic fracture healing associated with the Wnt pathway. Because the coating effectively accelerates the healing of osteoporotic fractures and improves bone quality, it has significant clinical application prospects.

Influence of Long Non-Coding RNA in the Regulation of Cancer Stem Cell Signaling Pathways

Over the past two decades, cancer stem cells (CSCs) have emerged as an immensely studied and experimental topic, however a wide range of questions concerning the topic still remain unanswered; in particular, the mechanisms underlying the regulation of tumor stem cells and their characteristics. Understanding the cancer stem-cell signaling pathways may pave the way towards a better comprehension of these mechanisms. Signaling pathways such as WNT, STAT, Hedgehog, NOTCH, PI3K/AKT/mTOR, TGF-β, and NF-κB are responsible not only for modulating various features of CSCs but also their microenvironments. Recently, the prominent roles of various non-coding RNAs such as small non-coding RNAs (sncRNAs) and long non-coding RNAs (lncRNAs) in developing and enhancing the tumor phenotypes have been unfolded. This review attempts to shed light on understanding the influence of long non- coding RNAs in the modulation of various CSC-signaling pathways and its impact on the CSCs and tumor properties; highlighting the protagonistic and antagonistic roles of lncRNAs.

Long-acting PFI-2 small molecule release and multilayer scaffold design achieve extensive new formation of complex periodontal tissues with unprecedented fidelity

The faithful engineering of complex human tissues such as the bone/soft tissue/mineralized tissue interface in periodontal tissues requires innovative molecular cues in conjunction with tailored scaffolds. To address the loss of periodontal bone and connective tissues following periodontal disease, we have generated a polydopamine and collagen coated electrospun PLGA-PCL (PP) scaffold enriched with the small molecule mediator PFI-2 (PP-PFI-pDA-COL-PFI). In vitro 3D studies using PDL progenitors revealed that the PP-PFI-pDA-COL-PFI scaffold substantially enhanced Alizarin Red staining, increased Ca/P ratios 4-fold, and stimulated cell proliferation more than 12-fold compared to PP-controls, suggestive of its potential for mineralized tissue engineering. When applied in our experimental periodontitis model, the PP-PFI-pDA-COL-PFI scaffold resulted in a substantial 34% reduction in alveolar bone defect height, a 25% root-length gain in periodontal attachment, and the formation of highly ordered regenerated acellular cementum twice as thick as in controls. Explaining the mechanism of PFI-2 mineralized tissue regeneration in periodontal tissues, PFI-2 inhibited SETD7-mediated β-Catenin protein methylation and increased β-Catenin nuclear localization. Together, dual-level PFI-2 incorporation into a degradable, dopamine/collagen coated PLGA/PCL scaffold backbone resulted in the regeneration of the tripartite periodontal complex with unprecedented fidelity, including periodontal attachment and new formation of mineralized tissues in inflamed periodontal environments.

Phosphate promotes osteogenic differentiation through non-canonical Wnt signaling pathway in human mesenchymal stem cells

BACKGROUND

Phosphate is indispensable in osteogenesis and mineralization. However, mechanisms by which phosphate enhances osteogenic differentiation are not fully understood. In this study, we studied the effect of phosphate on osteogenic differentiation as well as signaling pathways induced by phosphate in the process.

METHOD

Induced human bone marrow-derived mesenchymal stem cells differentiation into osteoblasts by the change of media containing β-glycerophosphate (GP), 1 mM inorganic phosphate, or 3 mM inorganic phosphate (Pi). The differentiation of osteoblasts was verified by the expression of osteoblast differentiation markers and calcium deposition. RNA sequencing was performed to assess transcriptome in the early stage of osteogenic differentiation.

RESULTS

Osteogenic differentiation and mineralization were promoted in the 3 mM Pi group compared to those in the GP and 1 mM Pi groups on day 7 of culture. RNA sequencing revealed that the gene expressions involved in osteogenesis and the components in the Wnt signaling pathway was increased in 3 mM Pi group compared with those in the GP on day 7. Analysis with qPCR and Western blot suggested upregulation of components in the non-canonical Wnt signaling pathway, including WNT5b and phosphorylated-c-Jun in the 3 mM Pi group on day 7. WNT11 mRNA expression was increased in the 2 induction groups on day 7. Inhibition of WNT5b by siRNA experiment attenuated the components in non-canonical Wnt signaling expression, including WNT5b, WNT11 and ROR2 mRNA expression and phosphorylated-c-Jun protein expression. In addition, osteogenic differentiation and mineralization were partly decreased in 3 mM Pi group on day 7 by the inhibition of WNT5b.

CONCLUSION

Pi promoted osteogenic differentiation through the up-regulation of the non-canonical Wnt signaling pathway, including WNT5b, WNT11, p-c-Jun/c-Jun, in the early stage of differentiation. These findings provide a new perspective into the association of Pi and the non-canonical Wnt signaling pathway during osteogenic differentiation.

Mechanically Robust Hydrogels Facilitating Bone Regeneration through Epigenetic Modulation

Development of artificial biomaterials by mimicking extracellular matrix of bone tissue is a promising strategy for bone regeneration. Hydrogel has emerged as a type of viable substitute, but its inhomogeneous networks and weak mechanics greatly impede clinical applications. Here, a dual crosslinked gelling system is developed with tunable architectures and mechanics to promote osteogenic capacity. Polyhedral oligomeric silsesquioxane (POSS) is designated as a rigid core surrounded by six disulfide-linked PEG shells and two 2-ureido-4[1H]-pyrimidinone (UPy) groups. Thiol-disulfide exchange is employed to fabricate chemical network because of the pH-responsive "on/off" function. While self-complementary UPy motif is capable of optimizing local microstructure to enhance mechanical properties. Taking the merits of biocompatibility and high-mechanics in periodontal ligament stem cells (PDLSCs) proliferation, attachment, and osteogenesis, hybrid hydrogel exhibits outstanding osteogenic potential both in vitro and in vivo. Importantly, it is the first time that a key epigenetic regulator of ten-eleven translocation 2 (Tet2) is discovered to significantly elevate the continuously active the WNT/β-catenin through Tet2/HDAC1/E-cadherin/β-catenin signaling cascade, thereby promoting PDLSCs osteogenesis. This work represents a general strategy to design the hydrogels with customized networks and biomimetic mechanics, and illustrates underlying osteogenic mechanisms that will extend the design rationales for high-functional biomaterials in tissue engineering.

High-density genotyping reveals candidate genomic regions for chicken body size in breeds of Asian origin

Body size is one of the main selection indices in chicken breeding. Although often investigated, knowledge of the underlying genetic mechanisms is incomplete. The aim of the current study was to identify genomic regions associated with body size differences between Asian Game and Asian Bantam type chickens. In this study, 94 and 107 chickens from 4 Asian Game and 5 Asian Bantam type breeds, respectively, were genotyped using the chicken 580K single nucleotide polymorphism (SNP) array. A genome-wide association study (GWAS) and principal component analyses (PCA) were performed to identify genomic regions associated with body size related-traits such as wing length, shank length, shank thickness, keel length, and body weight. Hierarchical clustering of genotype data showed a clear genetic difference between the investigated Asian Game and Asian Bantam chicken types. GWAS identified 16 genomic regions associated with wing length (2, FDR ≤ 0.018), shank thickness (6, FDR ≤ 0.008), keel length (5, FDR ≤ 0.023), and body weight (3, FDR ≤ 0.041). PCA showed that the first principal component (PC1) separated the 2 chicken types and significantly correlated with the measured body size related-traits (P ≤ 2.24e-40). SNPs contributing significantly to PC1 were subjected to a more detailed investigation. This analysis identified 11 regions potentially associated with differences in body size related-traits. A region on chromosome 4 (GGA4) (17.3-21.3 Mb) was detected in both analyses GWAS and PCA. This region harbors 60 genes. Among them are myotubularin 1 (MTM1) and secreted frizzled-related protein 2 (SFPR2) which can be considered as potential candidate genes for body size related-traits. Our results clearly show that the investigated Asian Game type chicken breeds are genetically different from the Asian Bantam breeds. A region on GGA4 between 17.3 and 21.3 Mb was identified which contributes to the phenotypic difference, though further validation of candidate genes is necessary.

Fibroblast growth factor 23 inhibits osteogenic differentiation and mineralization of chicken bone marrow mesenchymal stem cells

Fibroblast growth factor 23 (FGF23), a bone-derived hormone, is involved in the reabsorption of phosphate (P) and the production of vitamin D hormones in the kidney. However, whether and how FGF23 regulates chicken bone metabolism remains largely unknown. In the present study, we investigated the effect of FGF23 on osteogenic differentiation and mineralization of chicken bone marrow mesenchymal stem cells (BMSCs). First, we found that the transcription of FGF23 was inhibited by β-glycerophosphate sodium (GPS, 5 mM, 10 mM, 20 mM) and 10^-9 M 1, 25-dihydroxyvitamin D3 (1, 25(OH)₂D₃), but was stimulated by 10^-7 M 1, 25(OH)₂D₃ and parathyroid hormone (PTH, 10^-9 M, 10^-8 M, 10^-7 M). Second, overexpression of FGF23 by the FGF23 adenovirus (Adv-FGF23) suppressed the formation of mineralized nodules (P < 0.001) and alkaline phosphatase (ALP) activity (P < 0.05) in both differentiated and mineralized osteoblasts. Administration of FGF receptor 3 (FGFR3) inhibitor (50 nM) was sufficient to restore the FGF23-decreased ALP activity (P < 0.05), but not for the formation of mineralized nodules. In addition, the phosphorylation of ERK increased considerably with Adv-FGF23 overexpression (P < 0.05). Administration of an ERK-specific inhibitor (10 μM) could down-regulate the phosphorylation of ERK (P-ERK) (P < 0.05) and slightly restored the Adv-FGF23-reduction of ALP activity (P = 0.08). In summary, our data suggest that GPS, 1, 25(OH)₂D₃, and PTH could regulate FGF23 mRNA expression in vitro. FGF23 is a negative regulator of bone remodeling. FGF23 not only inhibits BMSCs osteogenesis through the FGFR3-ERK signaling pathway but also suppresses the mineralization of mature osteoblasts.

The Flavonol Quercitrin Hinders GSK3 Activity and Potentiates the Wnt/β-Catenin Signaling Pathway

The Wnt/β-catenin signaling pathway dictates cell proliferation and differentiation during embryonic development and tissue homeostasis. Its deregulation is associated with many pathological conditions, including neurodegenerative disease, frequently downregulated. The lack of efficient treatment for these diseases, including Alzheimer’s disease (AD), makes Wnt signaling an attractive target for therapies. Interestingly, novel Wnt signaling activating compounds are less frequently described than inhibitors, turning the quest for novel positive modulators even more appealing. In that sense, natural compounds are an outstanding source of potential drug leads. Here, we combine different experimental models, cell-based approaches, neuronal culture assays, and rodent behavior tests with Xenopus laevis phenotypic analysis to characterize quercitrin, a natural compound, as a novel Wnt signaling potentiator. We find that quercitrin potentiates the signaling in a concentration-dependent manner and increases the occurrence of the Xenopus secondary axis phenotype mediated by Xwnt8 injection. Using a GSK3 biosensor, we describe that quercitrin impairs GSK3 activity and increases phosphorylated GSK3β S9 levels. Treatment with XAV939, an inhibitor downstream of GSK3, impairs the quercitrin-mediated effect. Next, we show that quercitrin potentiates the Wnt3a-synaptogenic effect in hippocampal neurons in culture, which is blocked by XAV939. Quercitrin treatment also rescues the hippocampal synapse loss induced by intracerebroventricular injection of amyloid-β oligomers (AβO) in mice. Finally, quercitrin rescues AβO-mediated memory impairment, which is prevented by XAV939. Thus, our study uncovers a novel function for quercitrin as a Wnt/β-catenin signaling potentiator, describes its mechanism of action, and opens new avenues for AD treatments.

Optimized osteogenesis of biological hydroxyapatite-based bone grafting materials by ion doping and osteoimmunomodulation

BACKGROUND: Biological hydroxyapatite (BHA)-based bone grafting materials have been widely used for bone regeneration in implant surgery. Much effort has been made in the improvement of their osteogenic property as it remains unsatisfactory for clinical use. Osteoimmunomodulation plays a significant role in bone regeneration, which is highly related to active inorganic ions. Therefore, attempts have been made to obtain osteoimmunomodulatory BHA-based bone grafting materials with optimized osteogenic property by ion doping. OBJECTIVE: To summarize and discuss the active inorganic ions doped into BHA and their effects on BHA-based bone grafting materials. METHOD: A literature search was performed in databases including Google Scholar, Web of Science and PubMed, with the elementary keywords of “ion doped” and “biological hydroxyapatite”, as well as several supplementary keywords. All document types were included in this search. The searching period and language were not limited and kept updated to 2022. RESULTS: A total of 32 articles were finally included, of which 32 discussed the physiochemical properties of BHA-based biomaterials, while 12 investigated their biological features in vitro, and only three examined their biological performance in vivo. Various ions were doped into BHA, including fluoride, zinc, magnesium and lithium. Such ions improved the biological performance of BHA-based biomaterials, which was attributed to their osteoimmunomodulatory effect. CONCLUSION: The doping of active inorganic ions is a reliable strategy to endow BHA-based biomaterials with osteoimmunomodulatory property and promote bone regeneration. Further studies are still in need to explore more ions and their effects in the crosstalk between the skeletal and immune systems.

WNT signaling at the intersection between neurogenesis and brain tumorigenesis

Neurogenesis and tumorigenesis share signaling molecules/pathways involved in cell proliferation, differentiation, migration, and death. Self-renewal of neural stem cells is a tightly regulated process that secures the accuracy of cell division and eliminates cells that undergo mitotic errors. Abnormalities in the molecular mechanisms controlling this process can trigger aneuploidy and genome instability, leading to neoplastic transformation. Mutations that affect cell adhesion, polarity, or migration enhance the invasive potential and favor the progression of tumors. Here, we review recent evidence of the WNT pathway’s involvement in both neurogenesis and tumorigenesis and discuss the experimental progress on therapeutic opportunities targeting components of this pathway.

PTH1R translocation to primary cilia in mechanically-stimulated ostecytes prevents osteoclast formation via regulation of CXCL5 and IL-6 secretion

Osteocytes respond to mechanical forces controlling osteoblast and osteoclast function. Mechanical stimulation decreases osteocyte apoptosis and promotes bone formation. Primary cilia have been described as potential mechanosensors in bone cells. Certain osteogenic responses induced by fluid flow (FF) in vitro are decreased by primary cilia inhibition in MLO-Y4 osteocytes. The parathyroid hormone (PTH) receptor type 1 (PTH1R) modulates osteoblast, osteoclast, and osteocyte effects upon activation by PTH or PTH-related protein (PTHrP) in osteoblastic cells. Moreover, some actions of PTH1R seem to be triggered directly by mechanical stimulation. We hypothesize that PTH1R forms a signaling complex in the primary cilium that is essential for mechanotransduction in osteocytes and affects osteocyte-osteoclast communication. MLO-Y4 osteocytes were stimulated by FF or PTHrP (1-37). PTH1R and primary cilia signaling were abrogated using PTH1R or primary cilia specific siRNAs or inhibitors, respectively. Conditioned media obtained from mechanically- or PTHrP-stimulated MLO-Y4 cells inhibited the migration of preosteoclastic cells and osteoclast differentiation. Redistribution of PTH1R along the entire cilium was observed in mechanically stimulated MLO-Y4 osteocytic cells. Preincubation of MLO-Y4 cells with the Gli-1 antagonist, the adenylate cyclase inhibitor (SQ22536), or with the phospholipase C inhibitor (U73122), affected the migration of osteoclast precursors and osteoclastogenesis. Proteomic analysis and neutralizing experiments showed that FF and PTH1R activation control osteoclast function through the modulation of C-X-C Motif Chemokine Ligand 5 (CXCL5) and interleukin-6 (IL-6) secretion in osteocytes. These novel findings indicate that both primary cilium and PTH1R are necessary in osteocytes for proper communication with osteoclasts and show that mechanical stimulation inhibits osteoclast recruitment and differentiation through CXCL5, while PTH1R activation regulate these processes via IL-6.

Mesenchymal cell-derived Wnt1 signaling regulates subchondral bone remodeling but has no effects on the development of growth plate or articular cartilage in mice

Chondrocyte differentiation is a principal progress in endochondral ossification and in the formation of secondary ossification center (SOC) during the long bone development. We have previously reported that targeted deletion of Wnt1 in mesenchymal progenitors (Wnt1_Prrx^-/-) leads to spontaneous fractures and severe osteopenia in mouse long bones, suggesting that Wnt1 is a key regulator of bone metabolism. However, the effect of Wnt1 on the regulation of cartilage development and chondrocyte differentiation remained unknown. In this study, WNT1 protein expression was observed in lateral superficial cartilage and growth plate pre-hypertrophic chondrocytes in mice. Wnt1 mRNA expression was detected in epiphyseal cartilage from E16.5 to 3 month-old mice. Detailed histological analyses revealed that the average thickness and chondrocyte density of proximal tibial articular cartilage and growth plate were unchanged between Wnt1_Prrx^-/- and control mice. However, μCT analysis of tibial epiphyses showed that the subchondral bone mass was reduced in Wnt1_Prrx^-/- mice compared to control mice, as demonstrated by decreased bone volume, trabecular number, trabecular thickness, and increased trabecular separation in Wnt1_Prrx^-/- mice. Mechanistically, histomorphometric analyses showed that the reduced subchondral bone mass in Wnt1_Prrx^-/- mice was due to impaired bone formation and enhanced bone resorption. In vitro, exogenous Wnt1 inhibited chondrogenesis and chondrocyte hypertrophy in both cell autonomous and juxtacrine manners, while matrix mineralization and the expression of Mmp13, Mmp9 and Opn were induced in a juxtacrine manner. Taken together, mesenchymal cell-derived Wnt1 is an important regulator of subchondral bone remodeling, although it has no effect on the regulation of growth plate or articular cartilage.

Site-specific characteristics of bone and progenitor cells in control and ovariectomized rats

One-third of postmenopausal women experience at least one osteoporotic bone fracture in their lifetime that occurs spontaneously or from low-impact events. However, osteoporosis-associated jaw bone fractures are extremely rare. It was also observed that jaw bone marrow stem cells (BMSCs) have a higher capacity to form mineralized tissues than limb BMSCs. At present, the underlying causes and mechanisms of variations between jaw bone and limb bone during postmenopause are largely unknown. Thus, the objective of the current study was to examine the site-specific effects of estrogen deficiency using comprehensive analysis of bone quantity and quality, and its association with characterization of cellular components of bone. Nine rats (female, 6 months old) for each bilateral sham and ovariectomy (OVX) surgery were obtained and maintained for 2 months after surgery. A hemi-mandible and a femur from each rat were characterized for parameters of volume, mineral density, cortical and trabecular morphology, and static and dynamic mechanical analysis. Another set of 5 rats (female, 9 months old) was obtained for assays of BMSCs. Following cytometry to identify BMSCs, bioassays for proliferation, and osteogenic, adipogenic, chondrogenic differentiation, and cell mitochondrial stress tests were performed. In addition, mRNA expression of BMSCs was analyzed. OVX decreased bone quantity and quality (mineral content, morphology, and energy dissipation) of femur while those of mandible were not influenced. Cellular assays demonstrated that mandible BMSCs showed greater differentiation than femur BMSCs. Gene ontology pathway analysis indicated that the mandibular BMSCs showed most significant differential expression of genes in the regulatory pathways of osteoblast differentiation, SMAD signaling, cartilage development, and glucose transmembrane transporter activity. These findings suggested that active mandibular BMSCs maintain bone formation and mineralization by balancing the rapid bone resorption caused by estrogen deficiency. These characteristics likely help reduce the risk of osteoporotic fracture in postmenopausal jawbone.

Efficient lung-targeted delivery of risedronate sodium/vitamin D3 conjugated PAMAM-G5 dendrimers for managing osteoporosis: Pharmacodynamics, molecular pathways and metabolomics considerations

AIMS

This study aims at formulating combined delivery of Risedronate sodium (RIS) and Vitamin D3 (VITD3) for augmented therapeutic outcome against osteoporosis (OP) using deep lung targeted PAMAM-G5-NH2 dendrimers to minimize RIS gastrointestinal side effects and enhance both drugs bioavailability through absorption from the alveoli directly to the blood.

METHODS

RIS-PAMAM-G5-NH2, VITD3-PAMAM-G5-NH2, and RIS/VITD3-PAMAM-G5-NH2 were prepared and evaluated in vitro for particle size (PS), zeta potential (ZP), %loading efficiency (%LE), morphology and FTIR. The efficacy of the RIS/VITD3-PAMAM-G5-NH2 compared to oral RIS was evaluated in OP-induced rats by comparing serum calcium, phosphorus, and computed bone mineral density (BMD) pre- and post-treatment. Additionally, a comprehensive metabolomics and molecular pathways approach was applied to find serum potential biomarkers for diagnosis and to evaluate the efficacy of inhaled RIS/VITD3-PAMAM-G5-NH2.

KEY FINDINGS

RIS/VITD3-PAMAM-G5-NH2 was successfully prepared with a %LE of 92.4 ± 6.7 % (RIS) and 83.2 ± 4.4 % (VIT-D3) and a PS of 252.8 ± 34.1 adequate deep lung delivery. RIS/VITD3-PAMAM-G5-NH2 inhalation therapy was able to restore serum calcium, phosphorus, and BMD close to normal levels after 21 days of treatment in OP-induced rats. The WNT-signalling pathway and changes in the metabolite levels recovered to approximately normal levels upon treatment. Moreover, histone acetylation of the WNT-1 gene and miR-148a-3p interference proved to play a role in the regulation of the WNT-signalling pathway during OP progression and treatment.

SIGNIFICANCE

Pulmonary delivery of RIS/VITD3-PAMAM-G5-NH2 offers superior treatment for OP treatment compared to the oral route. Molecular and Metabolic pathways offer a key indicator of OP diagnosis and progression.

Hypoxia-Inducible Factors Signaling in Osteogenesis and Skeletal Repair

Sufficient oxygen is required to maintain normal cellular and physiological function, such as a creature’s development, breeding, and homeostasis. Lately, some researchers have reported that both pathological hypoxia and environmental hypoxia might affect bone health. Adaptation to hypoxia is a pivotal cellular event in normal cell development and differentiation and in pathological settings such as ischemia. As central mediators of homeostasis, hypoxia-inducible transcription factors (HIFs) can allow cells to survive in a low-oxygen environment and are essential for the regulation of osteogenesis and skeletal repair. From this perspective, we summarized the role of HIF-1 and HIF-2 in signaling pathways implicated in bone development and skeletal repair and outlined the molecular mechanism of regulation of downstream growth factors and protein molecules such as VEGF, EPO, and so on. All of these present an opportunity for developing therapies for bone regeneration.

Dehydromiltirone inhibits osteoclast differentiation in RAW264.7 and bone marrow macrophages by modulating MAPK and NF-κB activity

Background: Osteoporosis is a type of systematic metabolic bone disease caused by the decrease in osteogenic activity or excessive resorption of bone with the relative enhancement of osteoclast function. As osteoporosis seriously affects the quality of patients’ life, effective drugs are needed to treat this disease. Based on the combination of network pharmacology and cellular studies, this study aimed to investigate the probable mechanism of Dehydromiltirone (DHT) in the treatment of osteoporosis.

Method: The targets of DHT in osteoporosis were searched using the PharmGKB, OMIM, and Genecard platforms. The PPI core targets, and the GO and KEGG enrichment analysis results were obtained using Cytoscape software, and the David and Metascape databases, respectively. The network pharmacology results were also verified via in vitro cellular experiments.

Results: Through network pharmacology and docking analysis, we found DHT was involved in peptide tyrosine phosphorylation, cell surface receptor tyrosine kinase signaling pathways, and MAPK signaling pathways. According to the molecular docking results, the binding of DHT to MAPK14 was more stable than other proteins, which suggests that DHT may affect osteoclast formation through the MAPK signaling pathway. Moreover, DHT was found to inhibit the expression of osteoclast-associated genes, including NFATc1, CTSK, c-Fos, Acp5, and MMP9; as well as the phosphorylation of P38, ERK, and JNK of the MAPK signaling pathway; and the degradation of IκB-α of NF-κB signaling pathway.

Conclusion: DHT exhibited an anti-osteoclastogenesis effect by reducing the expression of related genes, ultimately inhibiting bone resorption in vitro.

Pathology of Bone: Changes Associated With Different Classes of Compounds

During this presentation, a variety of class effects were reviewed by their differing effects on bone, including inhibition of endochondral ossification, inhibition of the growth hormone-insulin-like growth factor 1 axis, promotion of bone formation, inhibition of bone formation, abnormal bone formation, promotion of bone resorption, inhibition of bone resorption, and bone necrosis.

Cellular Senescence in Bone

Senescence is an irreversible cell-cycle arrest process induced by environmental, genetic, and epigenetic factors. An accumulation of senescent cells in bone results in age-related disorders, and one of the common problems is osteoporosis. Deciphering the basic mechanisms contributing to the chronic ailments of aging may uncover new avenues for targeted treatment. This review focuses on the mechanisms and the most relevant research advancements in skeletal cellular senescence. To identify new options for the treatment or prevention of age-related chronic diseases, researchers have targeted hallmarks of aging, including telomere attrition, genomic instability, cellular senescence, and epigenetic alterations. First, this chapter provides an overview of the fundamentals of bone tissue, the causes of skeletal involution, and the role of cellular senescence in bone and bone diseases such as osteoporosis. Next, this review will discuss the utilization of pharmacological interventions in aging tissues and, more specifically, highlight the role of senescent cells to identify the most effective and safe strategies.

Critical illness and bone metabolism: where are we now and what is next?

Critical illness refers to the clinical signs of severe, variable and life-threatening critical conditions, often accompanied by insufficiency or failure of one or more organs. Bone health of critically ill patients is severely affected during and after ICU admission. Therefore, clinical work should focus on ICU-related bone loss, and early development and implementation of related prevention and treatment strategies: optimized and personalized nutritional support (high-quality protein, trace elements and intestinal prebiotics) and appropriate physiotherapy and muscle training should be implemented as early as possible after ICU admission and discharge. At the same time, the drug regulates excessive metabolism and resists osteoporosis.

Tocotrienol as a Protecting Agent against Glucocorticoid-Induced Osteoporosis: A Mini Review of Potential Mechanisms

Glucocorticoid-induced osteogenic dysfunction is the main pathologyical mechanism underlying the development of glucocorticoid-induced osteoporosis. Glucocorticoids promote adipogenic differentiation and osteoblast apoptosis through various pathways. Various ongoing studies are exploring the potential of natural products in preventing glucocorticoid-induced osteoporosis. Preclinical studies have consistently shown the bone protective effects of tocotrienol through its antioxidant and anabolic effects. This review aims to summarise the potential mechanisms of tocotrienol in preventing glucocorticoid-induced osteoporosis based on existing in vivo and in vitro evidence. The current literature showed that tocotrienol prevents oxidative damage on osteoblasts exposed to high levels of glucocorticoids. Tocotrienol reduces lipid peroxidation and increases oxidative stress enzyme activities. The reduction in oxidative stress protects the osteoblasts and preserves the bone microstructure and biomechanical strength of glucocorticoid-treated animals. In other animal models, tocotrienol has been shown to activate the Wnt/β-catenin pathway and lower the RANKL/OPG ratio, which are the targets of glucocorticoids. In conclusion, tocotrienol enhances osteogenic differentiation and bone formation in glucocorticoid-treated osteoblasts while improving structural integrity in glucocorticoid-treated rats. This is achieved by preventing oxidative stress and osteoblast apoptosis. However, these preclinical results should be validated in a randomised controlled trial.

Salinomycin alleviates osteoarthritis progression via inhibiting Wnt/β-catenin signaling

Osteoarthritis (OA) is the most prevalent degenerative whole-joint disease characterized by cartilage degeneration, synovial hyperplasia, osteophyte formation, and subchondral bone sclerosis. Currently there are no disease-modifying treatments available for OA because its etiology and pathogenesis are largely unknown. Here we report that a natural carboxylic polyether ionophore that is used as an anti-tumor drug, salinomycin (SAL), may be a promising therapeutic drug for OA in the future. We found that SAL showed no cytotoxicity on mouse chondrocytes and displayed a protective effect against interleukin-1β (IL-1β), in cultured mouse chondrocytes and cartilage explants. Treatment with low SAL concentrations directly upregulated the anabolism factors collagen II and aggrecan, while it inhibited the catabolic factors matrix metalloproteinase-13 (MMP13) and metalloproteinase with thrombospondin motifs-5 (ADAMTS5) to protect against extracellular matrix (ECM) degradation, and also suppressed inflammatory responses in mouse chondrocytes. Furthermore, SAL reduced the severity of OA-associated changes and delayed cartilage destruction, subchondral bone sclerosis, and osteophyte formation in a destabilized medial meniscus (DMM) surgery-induced mouse OA model. Mechanistically, a low SAL concentration induced anabolism and inhibited catabolism in chondrocytes via inhibiting Lrp6 phosphorylation and Wnt/β-catenin signaling. Our results suggested that SAL may serve as a potential disease-modifying therapeutic against OA pathogenesis.

The effects of combined amplitude and high-frequency vibration on physically inactive osteopenic postmenopausal women

Purpose: To evaluate whole-body vibration (WBV) osteogenic potential in physically inactive postmenopausal women using high-frequency and combined amplitude stimuli.

Methods: Two-hundred fifty-five physically inactive postmenopausal women (55–75 years) with 10-year major osteoporotic fracture risk (3%–35%) participated in this 18-month study. For the first 12 months, the vibration group experienced progressive 20-min WBV sessions (up to 3 sessions/week) with rest periods (30–60 s) between exercises. Frequencies (30–50 Hz), with low (0.2–0.4 mm) and high (0.6–0.8 mm) amplitude stimuli were delivered via PowerPlate Pro5 platforms producing accelerations of (0.75–7.04 g). The last 6 months for the treatment group were a follow-up period similar to control. Serum bone remodelling markers [C-terminal crosslinked telopeptide of type-1 collagen (CTX), procollagen type-1 N-terminal propeptide (P1NP), bone alkaline phosphatase (BAP) and sclerostin] were measured at fasting. CTX and P1NP were determined by automated chemiluminescence immunoassay, bone alkaline phosphatase (BAP) by automated spectrophotometric immunoassay, and sclerostin by an enzyme-immunoassay. Bone mineral density (BMD) of the whole-body, proximal femur and lumbar vertebrae was measured by dual-energy X-ray absorptiometry (DXA). Bone microarchitecture of the distal non-dominant radius and tibia was measured by high-resolution peripheral quantitative computed tomography (HR-pQCT).

Results: Femoral neck (p = 0.520) and spine BMD (p = 0.444) failed to improve after 12 months of WBV. Bone macro and microstructural parameters were not impacted by WBV, as well as estimated failure load at the distal radius (p = 0.354) and tibia (p = 0.813). As expected, most DXA and HR-pQCT parameters displayed age-related degradation in this postmenopausal population. BAP and CTX increased over time in both groups, with CTX more marginally elevated in the vibration group when comparing baseline changes to month-12 (480.80 pmol/L; p = 0.039) and month-18 (492.78 pmol/L; p = 0.075). However, no differences were found when comparing group concentrations only at month-12 (506.35 pmol/L; p = 0.415) and month-18 (518.33 pmol/L; p = 0.480), indicating differences below the threshold of clinical significance. Overall, HR-pQCT, DXA bone parameters and bone turnover markers remained unaffected.

Conclusion: Combined amplitude and high-frequency training for one year had no ameliorating effect on DXA and HR-pQCT bone parameters in physically inactive postmenopausal women. Serum analysis did not display any significant improvement in formation and resorption markers and also failed to alter sclerostin concentrations between groups.

Zebrafish mutants reveal unexpected role of Lrp5 in osteoclast regulation

Low-density Lipoprotein Receptor-related Protein 5 (LRP5) functions as a co-receptor for Wnt ligands, controlling expression of genes involved in osteogenesis. In humans, loss-of-function mutations in LRP5 cause Osteoporosis-Pseudoglioma syndrome, a low bone mass disorder, while gain-of-function missense mutations have been observed in individuals with high bone mass. Zebrafish (Danio rerio) is a popular model for human disease research, as genetic determinants that control bone formation are generally conserved between zebrafish and mammals. We generated lrp5- knock-out zebrafish to study its role in skeletogenesis and homeostasis. Loss of lrp5 in zebrafish leads to craniofacial deformities and low bone mineral density (total body and head) at adult ages. To understand the mechanism and consequences of the observed phenotypes, we performed transcriptome analysis of the cranium of adult lrp5 mutants and siblings. Enrichment analysis revealed upregulation of genes significantly associated with hydrolase activity: mmp9, mmp13a, acp5a. acp5a encodes Tartrate-resistant acid phosphatase (TRAP) which is commonly used as an osteoclast marker, while Matrix metalloprotease 9, Mmp9, is known to be secreted by osteoclasts and stimulate bone resorption. These genes point to changes in osteoclast differentiation regulated by lrp5. To analyze these changes functionally, we assessed osteoclast dynamics in mutants and observed increased TRAP staining, significantly larger resorption areas, and developmental skeletal dysmorphologies in the mutant, suggesting higher resorptive activity in the absence of Lrp5 signaling. Our findings support a conserved role of Lrp5 in maintaining bone mineral density and revealed unexpected insights into the function of Lrp5 in bone homeostasis through moderation of osteoclast function.

Experimental study on the effects of simvastatin in reversing the femoral metaphyseal defects induced by sodium valproate in normal and ovariectomized rats

Introduction

Long-term treatment with antiepileptic drugs may cause secondary osteoporosis. The present study investigated the influence of simvastatin (SIM) in reversing the effects of valproate on bone defect healing in normal and ovariectomized (OVX) rats.

Methods

Bone defects in femora were established in seven experimental groups of rats: control (vehicle), sodium valproate (SVP; 300 mg/kg/d), SVP plus SIM (25 mg/kg/d), sham control (sham), OVX, OVX SVP and OVX SVP plus SIM. All rats were euthanized at 8 weeks after bone defect creation.

Results

Micro-CT, biomechanical and histological evaluations demonstrated lower bone strength and delayed bone healing in the SVP therapy group compared with the SVP plus SIM therapy group. Biochemical and immunohistochemical results showed that osteocalcin (OCN), collagen I (Col I) and procollagen type I N-terminal propeptide (P1NP) levels decreased, tartrate-resistant acid phosphatase type 5 precursor (TRACP-5b) expression increased, and Dickkopf-1 (DKK-1) and receptor activator of nuclear factor-κ B ligand (RANKL) expression were upregulated in the SVP therapy rats compared with the SVP plus SIM therapy group. Bone loss was exacerbated by OVX, but the effect of SIM in ameliorating bone loss was also more marked in the OVX rats.

Conclusions

This study indicated lower bone strength and delayed healing of bone defects in rats given SVP therapy, especially the OVX SVP treatment group. In contrast, treatment with SIM was effective in enhancing bone strength and promoting bone defect repair and showed significant influence on promoting osteogenesis and inhibiting osteoclastogenesis.

Rheumatoid arthritis and osteoimmunology: The adverse impact of a deregulated immune system on bone metabolism

The term osteoimmunology describes an interdisciplinary research field that links the investigation of osteology (bone cells) with immunology. The crosstalk between innate and adaptive immune cells and cells involved in bone remodeling, mainly bone-resorbing osteoclasts and bone-forming osteoblasts, becomes particularly obvious in the inflammatory autoimmune disease rheumatoid arthritis (RA). Besides striking inflammation of the joints, RA causes bone loss, leading to joint damage and disabilities as well as generalized osteoporosis. Mechanistically, RA-associated immune cells (macrophages, T cells, B cells etc.) produce high levels of pro-inflammatory cytokines, receptor activator of nuclear factor κB ligand (RANKL) and autoantibodies that promote bone degradation and at the same time counteract new bone formation. Today, antirheumatic therapy effectively ceases joint inflammation and arrests bone erosion. However, the repair of established bone lesions still presents a challenging task and requires improved treatment options. In this review, we outline the knowledge gained over the past years about the immunopathogenesis of RA and the impact of a dysregulated immune system on bone metabolism.

Early-Onset Osteoporosis: Rare Monogenic Forms Elucidate the Complexity of Disease Pathogenesis Beyond Type I Collagen

Early-onset osteoporosis (EOOP), characterized by low bone mineral density (BMD) and fractures, affects children, premenopausal women and men aged <50 years. EOOP may be secondary to a chronic illness, long-term medication, nutritional deficiencies, etc. If no such cause is identified, EOOP is regarded primary and may then be related to rare variants in genes playing a pivotal role in bone homeostasis. If the cause remains unknown, EOOP is considered idiopathic. The scope of this review is to guide through clinical and genetic diagnostics of EOOP, summarize the present knowledge on rare monogenic forms of EOOP, and describe how analysis of bone biopsy samples can lead to a better understanding of the disease pathogenesis. The diagnostic pathway of EOOP is often complicated and extensive assessments may be needed to reliably exclude secondary causes. Due to the genetic heterogeneity and overlapping features in the various genetic forms of EOOP and other bone fragility disorders, the genetic diagnosis usually requires the use of next-generation sequencing to investigate several genes simultaneously. Recent discoveries have elucidated the complexity of disease pathogenesis both regarding genetic architecture and bone tissue-level pathology. Two rare monogenic forms of EOOP are due to defects in genes partaking in the canonical WNT pathway: LRP5 and WNT1. Variants in the genes encoding plastin-3 (PLS3) and sphingomyelin synthase 2 (SGMS2) have also been found in children and young adults with skeletal fragility. The molecular mechanisms leading from gene defects to clinical manifestations are often not fully understood. Detailed analysis of patient-derived transiliac bone biopsies gives valuable information to understand disease pathogenesis, distinguishes EOOP from other bone fragility disorders, and guides in patient management, but is not widely available in clinical settings. Despite the great advances in this field, EOOP remains an insufficiently explored entity and further research is needed to optimize diagnostic and therapeutic approaches. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Nanosilicate-Reinforced Silk Fibroin Hydrogel for Endogenous Regeneration of Both Cartilage and Subchondral Bone

Osteochondral defects are characterized by injuries to both cartilage and subchondral bone, which is a result of trauma, inflammation, or inappropriate loading. Due to the unique biological properties of subchondral bone and cartilage, developing a tissue engineering scaffold that can promote dual-lineage regeneration of cartilage and bone simultaneously remains a great challenge. In this study, a microporous nanosilicate-reinforced enzymatically crosslinked silk fibroin (SF) hydrogel is fabricated by introducing montmorillonite (MMT) nanoparticles via intercalation chemistry. In vitro studies show that SF-MMT nanocomposite hydrogel has improved mechanical properties and hydrophilicity, as well as the bioactivities to promote the osteogenic differentiation of bone marrow mesenchymal stem cells and maintain chondrocyte phenotype compared with SF hydrogel. Global proteomic analysis verifies the dual-lineage bioactivities of SF-MMT nanocomposite hydrogel, which are probably regulated by multiple signaling pathways. Furthermore, it is observed that the biophysical interaction of cells and SF-MMT nanocomposite hydrogel is partially mediated by clathrin-mediated endocytosis and its downstream processes. In vivo, the SF-MMT nanocomposite hydrogel effectively promotes osteochondral regeneration as evidenced by macroscopic, micro-CT, and histological evaluation. In conclusion, a functionalized SF-MMT nanocomposite hydrogel is developed with dual-lineage bioactivity for osteochondral regeneration, indicating its potential in osteochondral tissue engineering.

CK1α/RUNX2 Axis in the Bone Marrow Microenvironment: A Novel Therapeutic Target in Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is an incurable disease for which novel therapeutic approaches targeting the malignant cells and the associated bone disease are urgently needed. CK1α is a protein kinase that plays a crucial role in the signaling network that sustains plasma cell (PC) survival and bone disease. This protein regulates Wnt/β-catenin signaling, which is fundamental for both MM cell survival and mesenchymal stromal cell (MSC) osteogenic differentiation. In this study, we investigated its involvement in MM–MSC cross-talk. We found that, by lowering CK1α expression levels in co-cultures of MM and MSC cells, expression of RUNX2—the master regulator of osteogenic differentiation—was regulated differently in the two cell types. Our data suggest the possibility of using a specific CK1α inhibitor as part of a novel therapeutic approach to selectively kill malignant PCs and overcome the blocking of osteogenic differentiation induced by MM cells in MSCs.

Abstract

Multiple myeloma (MM) is a malignant plasma cell (PC) neoplasm, which also displays pathological bone involvement. Clonal expansion of MM cells in the bone marrow causes a perturbation of bone homeostasis that culminates in MM-associated bone disease (MMABD). We previously demonstrated that the S/T kinase CK1α sustains MM cell survival through the activation of AKT and β-catenin signaling. CK1α is a negative regulator of the Wnt/β-catenin cascade, the activation of which promotes osteogenesis by directly stimulating the expression of RUNX2, the master gene regulator of osteoblastogenesis. In this study, we investigated the role of CK1α in the osteoblastogenic potential of mesenchymal stromal cells (MSCs) and its involvement in MM–MSC cross-talk. We found that CK1α silencing in in vitro co-cultures of MMs and MSCs modulated RUNX2 expression differently in PCs and in MSCs, mainly through the regulation of Wnt/β-catenin signaling. Our findings suggest that the CK1α/RUNX2 axis could be a potential therapeutic target for constraining malignant PC expansion and supporting the osteoblastic transcriptional program of MSCs, with potential for ameliorating MMABD. Moreover, considering that Lenalidomide treatment leads to MM cell death through Ikaros, Aiolos and CK1α proteasomal degradation, we examined its effects on the osteoblastogenic potential of MSC compartments.

P16INK4A-More Than a Senescence Marker

Aging is a biological feature that is characterized by gradual degeneration of function in cells, tissues, organs, or an intact organism due to the accumulation of environmental factors and stresses with time. Several factors have been attributed to aging such as oxidative stress and augmented production or exposure to reactive oxygen species, inflammatory cytokines production, telomere shortening, DNA damage, and, importantly, the deposit of senescent cells. These are irreversibly mitotically inactive, yet metabolically active cells. The reason underlying their senescence lies within the extrinsic and the intrinsic arms. The extrinsic arm is mainly characterized by the expression and the secretory profile known as the senescence-associated secretory phenotype (SASP). The intrinsic arm results from the impact of several genes meant to regulate the cell cycle, such as tumor suppressor genes. P16INK4A is a tumor suppressor and cell cycle regulator that has been linked to aging and senescence. Extensive research has revealed that p16 expression is significantly increased in senescent cells, as well as during natural aging or age-related pathologies. Based on this fact, p16 is considered as a specific biomarker for detecting senescent cells and aging. Other studies have found that p16 is not only a senescence marker, but also a protein with many functions outside of senescence and aging. In this paper, we discuss and shed light on several studies that show the different functions of p16 and provide insights in its role in several biological processes besides senescence and aging.

Bioinspired Laminated Bioceramics with High Toughness for Bone Tissue Engineering

For the research of biomaterials in bone tissue engineering, it is still a challenge to fabricate bioceramics that overcome brittleness while maintaining the great biological performance. Here, inspired by the toughness of natural materials with hierarchical laminated structure, we presented a directional assembly-sintering approach to fabricate laminated MXene/calcium silicate-based (L-M/CS) bioceramics. Benefiting from the orderly laminated structure, the L-M/CS bioceramics exhibited significantly enhanced toughness (2.23 MPa·m^1/2) and high flexural strength (145 MPa), which were close to the mechanical properties of cortical bone. Furthermore, the L-M/CS bioceramics possessed more suitable degradability than traditional CaSiO₃ bioceramics due to the newly formed CaTiSiO₅ after sintering. Moreover, the L-M/CS bioceramics showed good biocompatibility and could stimulate the expression of osteogenesis-related genes. The mechanism of promoting osteogenic differentiation had been shown to be related to the Wnt signaling pathway. This work not only fabricated calcium silicate-based bioceramics with excellent mechanical and biological properties for bone tissue engineering but also provided a strategy for the combination of bionics and bioceramics.

People living with HIV have low trabecular bone mineral density, high bone marrow adiposity, and poor trabecular bone microarchitecture at the proximal femur

People living with HIV (PLWH) have increased risk of osteoporosis and fractures. We assessed the proximal femur of PLWH and age-matched seronegative controls using quantitative computed tomography and magnetic resonance imaging. Results suggest that the trabecular compartment is compromised at fracture-prone regions in the proximal femur of PLWH.

INTRODUCTION

People living with HIV (PLWH) have increased risk of osteoporosis and fractures. However, studies assessing the main determinants of bone strength in the proximal femur exclude this vulnerable population. We assessed the proximal femur of 40 PLWH and 26 age-matched seronegative controls using quantitative computed tomography and magnetic resonance imaging.

METHODS

We examined cortical volumetric bone mineral density (Ct.vBMD), trabecular vBMD (Tb.vBMD), cortical thickness (Ct.Th), bone marrow adiposity (BMA), and trabecular number, separation, and bone volume fraction. Parametric comparisons between the two groups were made for the femoral head, femoral neck, trochanter, and total hip using linear regression adjusting for several covariates, including metrics of body composition. In addition, we investigated the associations of BMA with Tb.vBMD and trabecular microarchitecture with Spearman's rank partial correlations.

RESULTS

PLWH had lower Tb.vBMD and deteriorated trabecular microarchitecture in the femoral neck, trochanter and total hip, and elevated BMA in the femoral head, femoral neck, and total hip. Ct.vBMD and Ct.Th were not significantly different between the two groups. BMA was significantly associated with lower Tb.vBMD and deteriorated trabecular microarchitecture in both groups albeit at different femoral regions.

CONCLUSIONS

Our findings suggest that the trabecular, and not the cortical, compartment is compromised in the proximal femur of PLWH. The observed impairments in fracture-prone regions in PLWH indicate lower femoral strength and suggest higher fracture risk. The inverse associations of BMA with trabecular bone density and microarchitecture quality agree with findings at other anatomic sites and in other populations, suggesting that excess BMA possibly due to a switch from the osteoblast to the adipocyte lineage may be implicated in the pathogenesis of bone fragility at the femur in PLWH.

Activation of canonical Wnt signaling accelerates intramembranous bone regeneration in male mice

Canonical Wnt signaling plays an important role in skeletal development, homeostasis, and both endochondral and intramembranous repair. While studies have demonstrated that the inhibition of Wnt signaling impairs intramembranous bone regeneration, how its activation affects intramembranous bone regeneration has been underexplored. Therefore, we sought to determine the effects of activation of canonical Wnt signaling on intramembranous bone regeneration by using the well-established marrow ablation model. We hypothesized that mice with a mutation in the Wnt ligand coreceptor gene Lrp5 would have accelerated intramembranous bone regeneration. Male and female wild-type and Lrp5-mutant mice underwent unilateral femoral bone marrow ablation surgery in the right femur at 4 weeks of age. Both the left intact and right operated femurs were assessed at Days 3, 5, 7, 10, and 14. The intact femur of Lrp5 mutant mice of both sexes had higher bone mass than wild-type littermates, although to a greater degree in males than females. Overall, the regenerated bone volume in Lrp5 mutant male mice was 1.8-fold higher than that of littermate controls, whereas no changes were observed between female Lrp5 mutant and littermate control mice. In addition, the rate of intramembranous bone regeneration (from Day 3 to Day 7) was higher in Lrp5 mutant male mice compared to their same-sex littermate controls with no difference in the females. Thus, activation of canonical Wnt signaling increases bone mass in intact bones of both sexes, but accelerates intramembranous bone regeneration following an injury challenge only in male mice.

Effects of diabetes on osteocytes

PURPOSE OF REVIEW

Better understanding of the mechanisms underlying skeletal dysfunction in the context of diabetes is needed to guide the development of therapeutic interventions to reduce the burden of diabetic fractures. Osteocytes, the 'master regulators' of bone remodeling, have emerged as key culprits in the pathogenesis of diabetes-related skeletal fragility.

RECENT FINDINGS

Both type 1 diabetes and type 2 diabetes cause chronic hyperglycemia that, over time, reduces bone quality and bone formation. In addition to acting as mechanosensors, osteocytes are important regulators of osteoblast and osteoclast activities; however, diabetes leads to osteocyte dysfunction. Indeed, diabetes causes the accumulation of advanced glycation end-products and senescent cells that can affect osteocyte viability and functions via increased receptor for advanced glycation endproducts (RAGE) signaling or the production of a pro-inflammatory senescence-associated secretory phenotype. These changes may increase osteocyte-derived sclerostin production and decrease the ability of osteocytes to sense mechanical stimuli thereby contributing to poor bone quality in humans with diabetes.

SUMMARY

Osteocyte dysfunction exists at the nexus of diabetic skeletal disease. Therefore, interventions targeting the RAGE signaling pathway, senescent cells, and those that inhibit sclerostin or mechanically stimulate osteocytes may alleviate the deleterious effects of diabetes on osteocytes and bone quality.

Regulation of sclerostin by the SIRT1 stabilization pathway in osteocytes

Osteocytes play a critical role in bone remodeling through the secretion of paracrine factors regulating the differentiation and activity of osteoblasts and osteoclasts. Sclerostin is a key osteocyte-derived factor that suppresses bone formation and promotes bone resorption, therefore regulators of sclerostin secretion are a likely source of new therapeutic strategies for treatment of skeletal disorders. Here, we demonstrate that protein kinase CK2 (casein kinase 2) controls sclerostin expression in osteocytes via the deubiquitinase ubiquitin-specific peptidase 4 (USP4)-mediated stabilization of Sirtuin1 (SIRT1). Deletion of CK2 regulatory subunit, Csnk2b, in osteocytes (Csnk2bDmp1) results in low bone mass due to elevated levels of sclerostin. This phenotype in Csnk2bDmp1 mice was partly reversed when sclerostin expression was downregulated by a single intravenous injection with bone-targeting adeno-associated virus 9 (AAV9) carrying an artificial-microRNA that targets Sost. Mechanistically, CK2-induced phosphorylation of USP4 is important for stabilization of SIRT1 by suppressing ubiquitin-dependent proteasomal degradation. Upregulated expression of SIRT1 inhibits sclerostin transcription in osteocytes. Collectively, the CK2-USP4-SIRT1 pathway is crucial for the regulation of sclerostin expression in osteocytes to maintain bone homeostasis.

Wnt Inhibitors and Bone Mineral Density in Patients with Graves' Disease Treated with Antithyroid Drugs: A Preliminary Prospective Study

This study aimed to investigate the association of Wnt inhibitors with thyroid hormones, bone turnover markers, and bone mineral density (BMD) in patients with newly diagnosed Graves’ disease (GD) at the beginning of the antithyroid treatment and after a follow-up period of one year. The study included 37 patients with newly diagnosed GD who were treated with antithyroid drugs (ATD). At baseline and after one year, thyroid hormones and thyroid-stimulating hormone (TSH), serum concentrations of sclerostin, and Dickkopf-1 (DKK1) were measured by an enzyme-linked immunosorbent assay (ELISA). In addition, BMD was measured by dual-energy X-ray absorptiometry (DXA), and markers of bone turnover including osteocalcin (OC), beta-cross laps (β-CTX), and deoxypyridinoline (DPD) were determined. After one year of ATD therapy sclerostin levels were significantly decreased (p < 0.001), whereas DKK1 levels were significantly increased (p = 0.01). In addition, BMD of the lumbar spine, total hip, and femoral neck was significantly improved (p < 0.001), accompanied by an increase in OC, β-CTX, and DPD concentrations (p < 0.001). At baseline, sclerostin levels were positively associated with free triiodothyronine (FT3). Following ATD therapy, a positive correlation was observed between FT3 and DKK1 (p = 0.003), whereas a negative correlation was found between TSH and DKK1 (p = 0.04). Correlation analysis demonstrated no association of the sclerostin and DKK1 with other bone remodeling biomarkers OC, β-CTX, or DPD. Also, no significant correlation between sclerostin or DKK1 and T-score or BMD of the lumbar spine, hip, and femoral neck was observed at both time points. Conclusion: Observed differences in sclerostin and DKK1 serum following GD treatment indicate involvement of Wnt inhibitors in the etiopathogenesis of bone loss associated with hyperthyroidism. Furthermore, both sclerostin and DKK1 are involved in the reversal of changes in bone metabolism following ATD therapy, thus presenting potentially valuable bone remodeling markers worth further investigation.

The Low-density Lipoprotein Receptor-related Protein 6 Pathway in the Treatment of Intestinal Barrier Dysfunction Induced by Hypoxia and Intestinal Microbiota through the Wnt/β-catenin Pathway

Our study is to explore the key molecular of Low-density lipoprotein receptor-related protein 6 (LRP6) and the related Wnt/β-catenin pathway regulated by LRP6 during the intestinal barrier dysfunction. Colorectal protein profile analysis showed that LRP6 expression was decreased in dextran sulfate sodium (DSS)-induced colitis mice, and mice received fecal bacteria transplantation from stroke patients. Mice with intestinal hypoxia and intestinal epithelial cells cultured in hypoxia showed decreased expression of LRP6. Overexpression of LPR6 or its N-terminus rescued the Wnt/β-catenin signaling pathway which was inhibited by hypoxia and endoplasmic reticulum stress. In mice overexpressing of LRP6, the expression of β-catenin and DKK1 increased, Bcl2 decreased, and Bax increased. Mice with LRP6 knockout showed an opposite trend, and the expression of Claudin2, Occludin and ZO-1 decreased. Two drugs, curcumin and auranofin could alleviate intestinal barrier damage in DSS-induced colitis mice by targeting LRP-6. Therefore, gut microbiota dysbiosis and hypoxia can inhibit the LRP6 and Wnt/β-catenin pathway, and drugs targeting LRP6 can protect the intestinal barrier.

Knowledge Domains and Emerging Trends of Osteoblasts-Osteoclasts in Bone Disease From 2002 to 2021: A Bibliometrics Analysis and Visualization Study

Background

Osteoblasts-Osteoclasts has been a major area in bone disease research for a long time. However, there are few systematic studies in this field using bibliometric analysis. We aimed to perform a bibliometric analysis and visualization study to determine hotspots and trends of osteoblasts-osteoclasts in bone diseases, identify collaboration and influence among authors, countries, institutions, and journals, and assess the knowledge base to develop basic and clinical research in the future.

Methods

We collected articles and reviews for osteoblasts-osteoclasts in bone diseases from the Web of Science Core Collection. In addition, we utilized scientometrics software (CiteSpace5.8 and VOSviewer1.6.18) for visual analysis of countries/regions, institutions, authors, references, and keywords in the field.

Results

In total, 16,832 authors from 579 institutions in 73 countries/regions have published 3,490 papers in 928 academic journals. The literature in this field is rapidly increasing, with Bone publishing the most articles, whereas Journal of Bone and Mineral Research had the most co-cited journals. These two journals mainly focused on molecular biology and the clinical medicine domain. The countries with the highest number of publications were the US and China, and the University of Arkansas for Medical Sciences was the most active institution. Regarding authors, Stavros C. Manolagas published the most articles, and Hiroshi Takayanagi had the most co-cited papers. Research in this field mainly includes molecular expression and regulatory mechanisms, differentiation, osteoprotection, inflammation, and tumors. The latest research hotspots are oxidative stress, mutation, osteocyte formation and absorption, bone metabolism, tumor therapy, and in-depth mechanisms.

Conclusion

We identified the research hotspots and development process of osteoblasts-osteoclasts in bone disease using bibliometric and visual methods. Osteoblasts-osteoclasts have attracted increasing attention in bone disease. This study will provide a valuable reference for researchers concerned with osteoblasts-osteoclasts in bone diseases.

Associations of Bone Mineral Density with RANKL and Osteoprotegerin in Arab Postmenopausal Women: A Cross-Sectional Study

Background and objective: There is limited information as to the association of several key bone markers with bone mineral density (BMD) in understudied ethnic groups. This study investigated the relationship between circulating levels of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-Β ligand (RANKL) with BMD in Arab postmenopausal women. Materials and methods: In this cross-sectional study, a total of 617 Saudi postmenopausal women from the Osteoporosis Registry of the Chair for Biomarkers of Chronic Diseases were included. Anthropometric data, BMD, and biochemical data were retrieved from the registry. Participants were stratified into three groups based on T-score; n = 169 with osteoporosis, n = 282 with osteopenia, and n = 166 normal. Analysis of bone markers including RANKL, OPG, osteocalcin, and N-terminal telopeptide (NTx) was completed using commercially available bioassays. Results: The results suggested that OPG was significantly and positively correlated with age in the osteoporosis group (r = 0.29, p < 0.05), while it was inversely correlated with BMD femoral neck left (r = −0.56, p < 0.001) and BMD femoral neck right (r = −0.37, p < 0.05) in the same group. Moreover, RANKL showed a significant inverse correlation with NTx in the osteopenia group (r = −0.37, p < 0.05). Furthermore, the RANKL/OPG ratio had a positive and significant correlation with BMI (r = 0.34, p < 0.05), BMD femoral neck left (r = 0.36, p < 0.05) and BMD femoral neck right (r = 0.35, p < 0.05) in the osteopenia group. By contrast, it showed a significant inverse correlation with waist to hip ratio in the osteoporosis group (r = −0.38, p < 0.05). Multiple regression analysis showed that OPG contributes to BMD variations in the osteopenia group (p = 0.03). Conclusions: In conclusion, changes in circulating levels of RANKL and OPG might be a protective mechanism contrary to the increased bone loss in postmenopausal women.