Sclerostin binds to LRP5/6 and antagonizes canonical Wnt signaling

In vivo dynamics of hard tissue-forming cell origins: Insights from Cre/loxP-based cell lineage tracing studies

Bone tissue provides structural support for our bodies, with the inner bone marrow (BM) acting as a hematopoietic organ. Within the BM tissue, two types of stem cells play crucial roles: mesenchymal stem cells (MSCs) (or skeletal stem cells) and hematopoietic stem cells (HSCs). These stem cells are intricately connected, where BM-MSCs give rise to bone-forming osteoblasts and serve as essential components in the BM microenvironment for sustaining HSCs. Despite the mid-20th century proposal of BM-MSCs, their in vivo identification remained elusive owing to a lack of tools for analyzing stemness, specifically self-renewal and multipotency. To address this challenge, Cre/loxP-based cell lineage tracing analyses are being employed. This technology facilitated the in vivo labeling of specific cells, enabling the tracking of their lineage, determining their stemness, and providing a deeper understanding of the in vivo dynamics governing stem cell populations responsible for maintaining hard tissues. This review delves into cell lineage tracing studies conducted using commonly employed genetically modified mice expressing Cre under the influence of LepR, Gli1, and Axin2 genes. These studies focus on research fields spanning long bones and oral/maxillofacial hard tissues, offering insights into the in vivo dynamics of stem cell populations crucial for hard tissue homeostasis.

Relative Energy Deficiency in Sport (REDs): Endocrine Manifestations, Pathophysiology and Treatments

Research on lean, energy-deficient athletic and military cohorts has broadened the concept of the Female Athlete Triad into the Relative Energy Deficiency in Sport (REDs) syndrome. REDs represents a spectrum of abnormalities induced by low energy availability (LEA), which serves as the underlying cause of all symptoms described within the REDs concept, affecting exercising populations of either biological sex. Both short- and long-term LEA, in conjunction with other moderating factors, may produce a multitude of maladaptive changes that impair various physiological systems and adversely affect health, well-being, and sport performance. Consequently, the comprehensive definition of REDs encompasses a broad spectrum of physiological sequelae and adverse clinical outcomes related to LEA, such as neuroendocrine, bone, immune, and hematological effects, ultimately resulting in compromised health and performance. In this review, we discuss the pathophysiology of REDs and associated disorders. We briefly examine current treatment recommendations for REDs, primarily focusing on nonpharmacological, behavioral, and lifestyle modifications that target its underlying cause-energy deficit. We also discuss treatment approaches aimed at managing symptoms, such as menstrual dysfunction and bone stress injuries, and explore potential novel treatments that target the underlying physiology, emphasizing the roles of leptin and the activin-follistatin-inhibin axis, the roles of which remain to be fully elucidated, in the pathophysiology and management of REDs. In the near future, novel therapies leveraging our emerging understanding of molecules and physiological axes underlying energy availability or lack thereof may restore LEA-related abnormalities, thus preventing and/or treating REDs-related health complications, such as stress fractures, and improving performance.

Involvement of the Wnt/β-catenin signalling pathway in heterotopic ossification and ossification-related diseases

Heterotopic ossification (HO) is a pathological condition characterized by the formation of bone within soft tissues. The development of HO is a result of abnormal activation of the bone formation programs, where multiple signalling pathways, including Wnt/β-catenin, BMP and hedgehog signalling, are involved. The Wnt/β-catenin signalling pathway, a conserved pathway essential for various fundamental activities, has been found to play a significant role in pathological bone formation processes. It regulates angiogenesis, chondrocyte hypertrophy and osteoblast differentiation during the development of HO. More importantly, the crosstalk between Wnt signalling and other factors including BMP, Hedgehog signalling, YAP may contribute in a HO-favourable manner. Moreover, several miRNAs may also be involved in HO formation via the regulation of Wnt signalling. This review aims to summarize the role of Wnt/β-catenin signalling in the pathogenesis of HO, its interactions with related molecules, and potential preventive and therapeutic measures targeting Wnt/β-catenin signalling.

Unraveling the molecular and immunological landscape: Exploring signaling pathways in osteoporosis

Osteoporosis, characterized by compromised bone density and microarchitecture, represents a significant global health challenge, particularly in aging populations. This comprehensive review delves into the intricate signaling pathways implicated in the pathogenesis of osteoporosis, providing valuable insights into the pivotal role of signal transduction in maintaining bone homeostasis. The exploration encompasses cellular signaling pathways such as Wnt, Notch, JAK/STAT, NF-κB, and TGF-β, all of which play crucial roles in bone remodeling. The dysregulation of these pathways is a contributing factor to osteoporosis, necessitating a profound understanding of their complexities to unveil the molecular mechanisms underlying bone loss. The review highlights the pathological significance of disrupted signaling in osteoporosis, emphasizing how these deviations impact the functionality of osteoblasts and osteoclasts, ultimately resulting in heightened bone resorption and compromised bone formation. A nuanced analysis of the intricate crosstalk between these pathways is provided to underscore their relevance in the pathophysiology of osteoporosis. Furthermore, the study addresses some of the most crucial long non-coding RNAs (lncRNAs) associated with osteoporosis, adding an additional layer of academic depth to the exploration of immune system involvement in various types of osteoporosis. Finally, we propose that SKP1 can serve as a potential biomarker in osteoporosis.

Wnt/β-catenin pathway as a potential target for Parkinson's disease: a cohort study of romosozumab using routinely collected health data in Japan

Introduction

Romosozumab is a monoclonal antibody approved for osteoporosis which targets sclerostin, an endogenous inhibitor of Wnt/β-catenin pathway. Given the essential roles of the Wnt/β-catenin pathway in various tissues, we hypothesized romosozumab treatment may influence other conditions.

Methods

This cohort study included patients prescribed romosozumab or parathyroid receptor (PTHR) agonists after 1 January 2019, using a Japanese electronic medical record database. The outcomes of interest included autoimmune disease, interstitial pneumonia, cardiovascular outcome, Alzheimer's disease, Parkinson's disease (PD), serious infections, and malignancies. A stabilized inverse probability-weighted Cox proportional hazard model was used to estimate the hazard ratios. Age- and gender-based subgroup analyses were conducted. Exploratory outcomes based on three-digit International Classification of Diseases 10th Revision-based were also examined.

Results

In total, 2,673 patients treated with romosozumab and 5,980 treated with PTHR agonists were identified, respectively. While most outcomes of interest showed no association with romosozumab, the risk of PD decreased with romosozumab (hazard ratio [95% confidence interval], 0.37 [0.14-0.94]) compared with PTHR agonist. Regarding the cardiovascular outcome, no notable association was identified overall; however, gender-based subgroup analysis suggested that male sex may be a potential risk factor with romosozumab treatment. Only 16 of 903 exploratory outcomes were potentially influenced by romosozumab.

Conclusion

Romosozumab lowered the risk of PD development compared with PTHR agonist. The study also highlights the utility of routinely collected health data for drug repositioning. While further validation is warranted, the findings suggest that the Wnt-β-catenin pathway holds promise as a therapeutic target for PD.

Disparate effects of sclerostin deletion on alveolar bone and cellular cementum in mice

BACKGROUND

Cellular cementum (CC) includes cementocytes, cells suspected to regulate CC formation or resorption as osteocytes do in bone. Sclerostin (SOST) is a secreted negative regulator of Wnt/β-catenin signaling expressed by osteocytes and cementocytes. Osteocyte SOST expression reduces bone formation. We investigated the functional importance of SOST in CC compared with alveolar bone (AB) using a Sost knockout (Sost-/-) mouse model to better understand the role of cementocytes in CC.

METHODS

Mandibles and femurs of Sost-/- and wild-type (WT) mice were analyzed at 42 and 120 days postnatal (dpn). Maxillary first molars were bilaterally extracted at 42 dpn and both AB healing (maxillary molar sockets) and CC apposition (mandibular first molars) were examined at 21 days post-procedure. Analyses included micro-computed tomography, histology, and immunohistochemistry.

RESULTS

Femur cortical and trabecular bone and mandibular bone volumes were similarly increased in Sost-/- versus WT mice at 42 and/or 120 dpn. In contrast to previous reports, CC was not increased by Sost-/- at either age. We conducted challenge experiments on AB and CC to explore tissue-specific responses. Post-extraction AB healing was improved by Sost deletion. In contrast, experimentally-induced apposition in molars failed to stimulate increased CC formation in Sost-/- versus WT mice. Wnt pathway markers AXIN2 and DKK1, which were increased in Sost-/- versus WT AB osteocytes, were unchanged in cementocytes.

CONCLUSIONS

These data indicate CC is less responsive than AB to SOST deletion. Within the study limitations, these results do not support cementocytes as critical for directing increased CC formation.

PLAIN LANGUAGE SUMMARY

Sclerostin is a protein known to inhibit bone formation, and removing sclerostin leads to more bone formation. Cementum is the thin layer that covers the surface of the tooth's root. Previous studies suggest that inhibiting sclerostin can similarly increase the amount of cementum. We wanted to compare the response of cementum and bone when sclerostin is absent to understand similarities and differences between these two tissues. In this study, we removed the Sost gene (the gene which produces sclerostin) in mice. We found that mice without sclerostin have more bone in their legs and jaws. Moreover, mice without sclerostin also healed better after tooth removal compared with normal mice. Surprisingly, unlike previous studies, we found that the amount of cementum was not different in mice without sclerostin compared with normal mice. Additionally, we challenged the cementum by taking out the opposing tooth to cause the first mandibular molar to move up by building more cementum. Even with this challenge, we found no difference in the amount of cementum in mice lacking sclerostin compared with normal mice. Therefore, we conclude here that cementum is less sensitive to the absence of sclerostin compared with bone.

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.

Sclerostin and Wnt Signaling in Idiopathic Juvenile Osteoporosis Using High-Resolution Confocal Microscopy for Three-Dimensional Analyses

BACKGROUND

Idiopathic juvenile osteoporosis (IJO) is a rare condition characterized by low bone mass that can increase the risk of fractures in children. Treatment options for these patients are limited as the molecular mechanisms of disease initiation and progression are incompletely understood. Sclerostin inhibits canonical Wnt signaling, which is important for the bone formation activity of osteoblasts, and elevated sclerostin has been implicated in adult osteoporosis.

OBJECTIVE

To evaluate the role of sclerostin in IJO, high-resolution confocal microscopy analyses were performed on bone biopsies collected from 13 pediatric patients.

METHODS

Bone biopsies were stained with sclerostin, and β-catenin antibodies showed elevated expression across osteocytes and increased sclerostin-positive osteocytes in 8 of the 13 total IJO patients (62%).

RESULTS

Skeletal sclerostin was associated with static and dynamic histomorphometric parameters. Further, colocalization analyses showed that bone sclerostin colocalized with phosphorylated β-catenin, a hallmark of Wnt signaling that indicates Wnt inhibition. In contrast, sclerostin-positive osteocytes were not colocalized with an "active" unphosphorylated form of β-catenin.

CONCLUSIONS

These results support a model that altered levels of sclerostin and Wnt signaling activity occur in IJO patients.

Bone: A Neglected Endocrine Organ?

Bone has traditionally been viewed in the context of its structural contribution to the human body. Foremost providing necessary support for mobility, its roles in supporting calcium homeostasis and blood cell production are often afterthoughts. Recent research has further shed light on the ever-multifaceted role of bone and its importance not only for structure, but also as a complex endocrine organ producing hormones responsible for the autoregulation of bone metabolism. Osteocalcin is one of the most important substances produced in bone tissue. Osteocalcin in circulation increases insulin secretion and sensitivity, lowers blood glucose, and decreases visceral adipose tissue. In males, it has also been shown to enhance testosterone production by the testes. Neuropeptide Y is produced by various cell types including osteocytes and osteoblasts, and there is evidence suggesting that peripheral NPY is important for regulation of bone formation. Hormonal disorders are often associated with abnormal levels of bone turnover markers. These include commonly used bone formation markers (bone alkaline phosphatase, osteocalcin, and procollagen I N-propeptide) and commonly used resorption markers (serum C-telopeptides of type I collagen, urinary N-telopeptides of type I collagen, and tartrate-resistant acid phosphatase type 5b). Bone, however, is not exclusively comprised of osseous tissue. Bone marrow adipose tissue, an endocrine organ often compared to visceral adipose tissue, is found between trabecula in the bone cortex. It secretes a diverse range of hormones, lipid species, cytokines, and other factors to exert diverse local and systemic effects.

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.

Association of chronic liver disease with bone diseases and muscle weakness

The liver is a vital organ involved in nutrient metabolism, hormone regulation, immunity, cytokine production, and gut homeostasis. Impairment in liver function can result in malnutrition, chronic inflammation, decreased anabolic hormone levels, and dysbiosis. These conditions eventually cause an imbalance in osteoblast and osteoclast activities, resulting in bone loss. Osteoporosis is a frequent complication of chronic liver disease (CLD) that adversely affects quality of life and increases early mortality. Sarcopenia is another common complication of CLD characterized by progressive loss of skeletal muscle mass and function. Assessment criteria for sarcopenia specific to liver disease have been established, and sarcopenia has been reported to be associated with an increase in the risk of liver disease-related events and mortality in patients with CLD. Owing to their similar risk factors and underlying pathophysiological mechanisms, osteoporosis and sarcopenia often coexist (termed osteosarcopenia), progress in parallel, and further exacerbate the conditions mentioned above. Therefore, comprehensive management of these musculoskeletal disorders is imperative. This review summarizes the clinical implications and characteristics of osteoporosis, extending to sarcopenia and osteosarcopenia, in patients with CLD caused by different etiologies.

Roles of Sp7 in osteoblasts for the proliferation, differentiation, and osteocyte process formation

Background

Zinc finger-containing transcription factor Osterix/Specificity protein-7 (Sp7) is an essential transcription factor for osteoblast differentiation. However, its functions in differentiated osteoblasts remain unclear and the effects of osteoblast-specific Sp7 deletion on osteocytes have not been sufficiently studied.

Methods

Sp7 floxneo/floxneo mice, in which Sp7 expression was 30 % of that in wild-type mice because of disturbed splicing by neo gene insertion, and osteoblast-specific knockout (Sp7 fl/fl;Col1a1-Cre) mice using 2.3-kb Col1a1 enhanced green fluorescent protein (EGFP)-Cre were examined by micro-computed tomography (micro-CT), bone histomorphometry, serum markers, and histological analyses. The expression of osteoblast and osteocyte marker genes was examined by real-time reverse transcription (RT)-PCR analysis. Osteoblastogenesis, osteoclastogenesis, and regulation of the expression of collagen type I alpha 1 chain (Col1a1) were examined in primary osteoblasts.

Results

Femoral trabecular bone volume was higher in female Sp7 floxneo/floxneo and Sp7 fl/fl;Col1a1-Cre mice than in the respective controls, but not in males. Bromodeoxyuridine (BrdU)-positive osteoblastic cells were increased in male Sp7 fl/fl;Col1a1-Cre mice, and osteoblast number and the bone formation rate were increased in tibial trabecular bone in female Sp7 fl/fl;Col1a1-Cre mice, although osteoblast maturation was inhibited in female Sp7 fl/fl;Col1a1-Cre mice as shown by the increased expression of an immature osteoblast marker gene, secreted phosphoprotein 1 (Spp1), and reduced expression of a mature osteoblast marker gene, bone gamma-carboxyglutamate protein/bone gamma-carboxyglutamate protein 2 (Bglap/Bglap2). Furthermore, alkaline phosphatase activity was increased but mineralization was reduced in the culture of primary osteoblasts from Sp7 fl/fl;Col1a1-Cre mice. Therefore, the accumulated immature osteoblasts in Sp7 fl/fl;Col1a1-Cre mice was likely compensated for the inhibition of osteoblast maturation at different levels in males and females. Vertebral trabecular bone volume was lower in both male and female Sp7 fl/fl;Col1a1-Cre mice than in the controls and the osteoblast parameters and bone formation rate in females were lower in Sp7 fl/fl;Col1a1-Cre mice than in Sp7 fl/fl mice, suggesting differential regulatory mechanisms in long bones and vertebrae. The femoral cortical bone was thin and porous in Sp7 floxneo/floxneo and Sp7 fl/fl;Col1a1-Cre mice of both sexes, the number of canaliculi was reduced, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL)-positive lacunae and the osteoclasts were increased, whereas the bone formation rate was similar in Sp7 fl/fl;Col1a1-Cre and Sp7 fl/fl mice. The serum levels of total procollagen type 1 N-terminal propeptide (P1NP), a marker for bone formation, were similar, while those of tartrate-resistant acid phosphatase 5b (TRAP5b), a marker for bone resorption, were higher in Sp7 fl/fl;Col1a1-Cre mice. Osteoblasts were less cuboidal, the expression of Col1a1 and Col1a1-EGFP-Cre was lower in Sp7 fl/fl;Col1a1-Cre mice, and overexpression of Sp7 induced Col1a1 expression.

Conclusions

Our studies indicated that Sp7 inhibits the proliferation of immature osteoblasts, induces osteoblast maturation and Col1a1 expression, and is required for osteocytes to acquire a sufficient number of processes for their survival, which prevents cortical porosity.

The translational potential of this article

This study clarified the roles of Sp7 in differentiated osteoblasts in proliferarion, maturation, Col1a1 expression, and osteocyte process formation, which are required for targeting SP7 in the development of therapies for osteoporosis.

Design principles and therapeutic applications of novel synthetic WNT signaling agonists

Wingless-related integration site or Wingless and Int-1 or Wingless-Int (WNT) signaling is crucial for embryonic development, and adult tissue homeostasis and regeneration, through its essential roles in cell fate, patterning, and stem cell regulation. The biophysical characteristics of WNT ligands have hindered efforts to interrogate ligand activity in vivo and prevented their development as therapeutics. Recent breakthroughs have enabled the generation of synthetic WNT signaling molecules that possess characteristics of natural ligands and potently activate the pathway, while also providing distinct advantages for therapeutic development and manufacturing. This review provides a detailed discussion of the protein engineering of these molecular platforms for WNT signaling agonism. We discuss the importance of WNT signaling in several organs and share insights from the initial application of these new classes of molecules in vitro and in vivo. These molecules offer a unique opportunity to enhance our understanding of how WNT signaling agonism promotes tissue repair, enabling targeted development of tailored therapeutics.

Multiscale and multidisciplinary analysis of aging processes in bone

The world population is increasingly aging, deeply affecting our society by challenging our healthcare systems and presenting an economic burden, thus turning the spotlight on aging-related diseases: exempli gratia, osteoporosis, a silent disease until you suddenly break a bone. The increase in bone fracture risk with age is generally associated with a loss of bone mass and an alteration in the skeletal architecture. However, such changes cannot fully explain increased fragility with age. To successfully tackle age-related bone diseases, it is paramount to comprehensively understand the fundamental mechanisms responsible for tissue degeneration. Aging mechanisms persist at multiple length scales within the complex hierarchical bone structure, raising the need for a multiscale and multidisciplinary approach to resolve them. This paper aims to provide an overarching analysis of aging processes in bone and to review the most prominent outcomes of bone aging. A systematic description of different length scales, highlighting the corresponding techniques adopted at each scale and motivating the need for combining diverse techniques, is provided to get a comprehensive description of the multi-physics phenomena involved.

Sclerostin modulates mineralization degree and stiffness profile in the fibrocartilaginous enthesis for mechanical tissue integrity

Fibrocartilaginous entheses consist of tendons, unmineralized and mineralized fibrocartilage, and subchondral bone, each exhibiting varying stiffness. Here we examined the functional role of sclerostin, expressed in mature mineralized fibrochondrocytes. Following rapid mineralization of unmineralized fibrocartilage and concurrent replacement of epiphyseal hyaline cartilage by bone, unmineralized fibrocartilage reexpanded after a decline in alkaline phosphatase activity at the mineralization front. Sclerostin was co-expressed with osteocalcin at the base of mineralized fibrocartilage adjacent to subchondral bone. In Scx-deficient mice with less mechanical loading due to defects of the Achilles tendon, sclerostin+ fibrochondrocyte count significantly decreased in the defective enthesis where chondrocyte maturation was markedly impaired in both fibrocartilage and hyaline cartilage. Loss of the Sost gene, encoding sclerostin, elevated mineral density in mineralized zones of fibrocartilaginous entheses. Atomic force microscopy analysis revealed increased fibrocartilage stiffness. These lines of evidence suggest that sclerostin in mature mineralized fibrochondrocytes acts as a modulator for mechanical tissue integrity of fibrocartilaginous entheses.

A Multifunctional Therapeutic Strategy Using P7C3 as A Countermeasure Against Bone Loss and Fragility in An Ovariectomized Rat Model of Postmenopausal Osteoporosis

By 2060, an estimated one in four Americans will be elderly. Consequently, the prevalence of osteoporosis and fragility fractures will also increase. Presently, no available intervention definitively prevents or manages osteoporosis. This study explores whether Pool 7 Compound 3 (P7C3) reduces progressive bone loss and fragility following the onset of ovariectomy (OVX)-induced osteoporosis. Results confirm OVX-induced weakened, osteoporotic bone together with a significant gain in adipogenic body weight. Treatment with P7C3 significantly reduced osteoclastic activity, bone marrow adiposity, whole-body weight gain, and preserved bone area, architecture, and mechanical strength. Analyses reveal significantly upregulated platelet derived growth factor-BB and leukemia inhibitory factor, with downregulation of interleukin-1 R6, and receptor activator of nuclear factor kappa-B (RANK). Together, proteomic data suggest the targeting of several key regulators of inflammation, bone, and adipose turnover, via transforming growth factor-beta/SMAD, and Wingless-related integration site/be-catenin signaling pathways. To the best of the knowledge, this is first evidence of an intervention that drives against bone loss via RANK. Metatranscriptomic analyses of the gut microbiota show P7C3 increased Porphyromonadaceae bacterium, Candidatus Melainabacteria, and Ruminococcaceae bacterium abundance, potentially contributing to the favorable inflammatory, and adipo-osteogenic metabolic regulation observed. The results reveal an undiscovered, and multifunctional therapeutic strategy to prevent the pathological progression of OVX-induced bone loss.

Sclerostin blockade inhibits bone resorption through PDGF receptor signaling in osteoblast lineage cells

While sclerostin-neutralizing antibodies (Scl-Abs) transiently stimulate bone formation by activating Wnt signaling in osteoblast lineage cells, they exert sustained inhibition of bone resorption, suggesting an alternate signaling pathway by which Scl-Abs control osteoclast activity. Since sclerostin can activate platelet-derived growth factor receptors (PDGFRs) in osteoblast lineage cells in vitro and PDGFR signaling in these cells induces bone resorption through M-CSF secretion, we hypothesized that the prolonged anticatabolic effect of Scl-Abs could result from PDGFR inhibition. We show here that inhibition of PDGFR signaling in osteoblast lineage cells is sufficient and necessary to mediate prolonged Scl-Ab effects on M-CSF secretion and osteoclast activity in mice. Indeed, sclerostin coactivates PDGFRs independently of Wnt/β-catenin signaling inhibition, by forming a ternary complex with LRP6 and PDGFRs in preosteoblasts. In turn, Scl-Ab prevents sclerostin-mediated coactivation of PDGFR signaling and consequent M-CSF upregulation in preosteoblast cultures, thereby inhibiting osteoclast activity in preosteoblast/osteoclast coculture assays. These results provide a potential mechanism explaining the dissociation between anabolic and antiresorptive effects of long-term Scl-Ab.

Alternated activation with relaxation of periosteum stimulates bone modeling and remodeling

Gradual elevation of the periosteum from the original bone surface, based on the principle of distraction osteogenesis, induces endogenous hard and soft tissue formation. This study aimed to assess the impact of alternating protocols of activation with relaxation (periosteal pumping) on bone modeling and remodeling. One hundred and sixty-two adult male Wistar rats were used in this study. Four test groups with different pumping protocols were created based on the relaxation applied. Two control groups underwent an activation period without relaxation or only a single activation. One group was sham-operated. Periosteal pumping without period of activation induced gene expression in bone and bone remodeling, and following activation period enhanced bone modeling. Four test groups and control group with activation period equaled the values of bone modeling at the end-consolidation period, showing significant downregulation of Sost in the bone and periosteum compared to that in the sham group (p < 0.001 and p < 0.001, respectively). When all test groups were pooled together, plate elevation from the bony surface increased bone remodeling on day 45 of the observation period (p = 0.003). Furthermore, bone modeling was significantly affected by plate elevation on days 17 and 45 (p = 0.047 and p = 0.005, respectively) and by pumping protocol on day 31 (p = 0.042). Periosteal pumping was beneficial for increasing bone repair when the periosteum remained in contact with the underlaying bony surface during the manipulation period. Following periosteal elevation, periosteal pumping accelerated bone formation from the bony surface by the modeling process.

Eldecalcitol Induces Minimodeling-Based Bone Formation and Inhibits Sclerostin Synthesis Preferentially in the Epiphyses Rather than the Metaphyses of the Long Bones in Rats

This study aimed to examine minimodeling-based bone formation between the epiphyses and metaphyses of the long bones of eldecalcitol (ELD)-administered ovariectomized rats. Sixteen-week-old female rats were divided into four groups: sham-operated rats receiving vehicle (Sham group), ovariectomized (OVX) rats receiving vehicle (Vehicle group), or ELDs (30 or 90 ng/kg BW, respectively; ELD30 and ELD90 groups). ELD administration increased bone volume and trabecular thickness, reducing the number of osteoclasts in both the epiphyses and metaphyses of OVX rats. The Sham and Vehicle groups exhibited mainly remodeling-based bone formation in both regions. The epiphyses of the ELD groups showed a significantly higher frequency of minimodeling-based bone formation than remodeling-based bone formation. In contrast, the metaphyses exhibited significantly more minimodeling-based bone formation in the ELD90 group compared with the ELD30 group. However, there was no significant difference between minimodeling-based bone formation and remodeling-based bone formation in the ELD90 group. While the minimodeling-induced new bone contained few sclerostin-immunoreactive osteocytes, the underlying pre-existing bone harbored many. The percentage of sclerostin-positive osteocytes was significantly reduced in the minimodeling-induced bone in the epiphyses but not in the metaphyses of the ELD groups. Thus, it seems likely that ELD could induce minimodeling-based bone formation in the epiphyses rather than in the metaphyses, and that ELD-driven minimodeling may be associated with the inhibition of sclerostin synthesis.

Anti-sclerostin antibody therapy prevents post-ischemic osteonecrosis bone collapse via interleukin-6 association

Osteonecrosis of the femoral head (ONFH) is a debilitating condition characterized by subchondral bone necrosis, which frequently culminates in joint destruction. Although total hip arthroplasty is conventionally practiced to remediate ONFH, for patients under the age of 60, the outcomes can be suboptimal. Chronic inflammation, particularly that mediated by interleukin-6 (IL-6), has been conjectured to be a potential mechanism underlying the etiology of ONFH. This study aimed at exploring the interplay between IL-6, the canonical Wnt signaling pathway, and ONFH to provide insights for potential therapeutic interventions. Human ONFH specimens depicted an elevation in β-catenin expression in the transitional layer, while IL-6 levels were pronounced in the same region. Subsequently, mouse models of ischemic osteonecrosis were treated with an anti-sclerostin antibody to assess its effects on bone metabolism and cellular processes. Histological analysis revealed that the administration of anti-sclerostin antibodies effectuated early recovery from bone necrosis, reduced empty lacunae, and suppressed IL-6 expression. The treatment evidently initiated the activation of the Wnt/β-catenin signaling pathway, presenting a potential mechanism associated with IL-6-mediated inflammation. Furthermore, the antibody upregulated osteoblast formation, downregulated osteoclast formation, and increased bone volume. Micro-CT imaging demonstrated increased bone volume, prevented epiphyseal deformity, and improved compression strength. Therefore, this study yields significant findings, indicating the potency of anti-sclerostin antibodies in effectively modulating the Wnt/β-catenin pathway, associating with IL-6 expression, and preventing post-ONFH bone collapse. Additionally, this preclinical investigation in mouse models offers an avenue for prospective research on potential therapeutic interventions against human ONFH.

Osteocyte-mediated mechanical response controls osteoblast differentiation and function

Low bone mass is a pervasive global health concern, with implications for osteoporosis, frailty, disability, and mortality. Lifestyle factors, including sedentary habits, metabolic dysfunction, and an aging population, contribute to the escalating prevalence of osteopenia and osteoporosis. The application of mechanical load to bone through physical activity and exercise prevents bone loss, while sufficient mechanical load stimulates new bone mass acquisition. Osteocytes, cells embedded within the bone, receive mechanical signals and translate these mechanical cues into biological signals, termed mechano-transduction. Mechano-transduction signals regulate other bone resident cells, such as osteoblasts and osteoclasts, to orchestrate changes in bone mass. This review explores the mechanisms through which osteocyte-mediated response to mechanical loading regulates osteoblast differentiation and bone formation. An overview of bone cell biology and the impact of mechanical load will be provided, with emphasis on the mechanical cues, mechano-transduction pathways, and factors that direct progenitor cells toward the osteoblast lineage. While there are a wide range of clinically available treatments for osteoporosis, the majority act through manipulation of the osteoclast and may have significant disadvantages. Despite the central role of osteoblasts to the deposition of new bone, few therapies directly target osteoblasts for the preservation of bone mass. Improved understanding of the mechanisms leading to osteoblastogenesis may reveal novel targets for translational investigation.

Osteocyte-derived sclerostin impairs cognitive function during ageing and Alzheimer's disease progression

Ageing increases susceptibility to neurodegenerative disorders, such as Alzheimer's disease (AD). Serum levels of sclerostin, an osteocyte-derived Wnt-β-catenin signalling antagonist, increase with age and inhibit osteoblastogenesis. As Wnt-β-catenin signalling acts as a protective mechanism for memory, we hypothesize that osteocyte-derived sclerostin can impact cognitive function under pathological conditions. Here we show that osteocyte-derived sclerostin can cross the blood-brain barrier of old mice, where it can dysregulate Wnt-β-catenin signalling. Gain-of-function and loss-of-function experiments show that abnormally elevated osteocyte-derived sclerostin impairs synaptic plasticity and memory in old mice of both sexes. Mechanistically, sclerostin increases amyloid β (Aβ) production through β-catenin-β-secretase 1 (BACE1) signalling, indicating a functional role for sclerostin in AD. Accordingly, high sclerostin levels in patients with AD of both sexes are associated with severe cognitive impairment, which is in line with the acceleration of Αβ production in an AD mouse model with bone-specific overexpression of sclerostin. Thus, we demonstrate osteocyte-derived sclerostin-mediated bone-brain crosstalk, which could serve as a target for developing therapeutic interventions against AD.

The multi-faceted nature of age-associated osteoporosis

Age-associated osteoporosis (AAOP) poses a significant health burden, characterized by increased fracture risk due to declining bone mass and strength. Effective prevention and early treatment strategies are crucial to mitigate the disease burden and the associated healthcare costs. Current therapeutic approaches effectively target the individual contributing factors to AAOP. Nonetheless, the management of AAOP is complicated by the multitude of variables that affect its development. Main intrinsic and extrinsic factors contributing to AAOP risk are reviewed here, including mechanical unloading, nutrient deficiency, hormonal disbalance, disrupted metabolism, cognitive decline, inflammation and circadian disruption. Furthermore, it is discussed how these can be targeted for prevention and treatment. Although valuable as individual targets for intervention, the interconnectedness of these risk factors result in a unique etiology for every patient. Acknowledgement of the multifaceted nature of AAOP will enable the development of more effective and sustainable management strategies, based on a holistic, patient-centered approach.

Bridging the Gap in Understanding Bone Metastasis: A Multifaceted Perspective

The treatment of patients with advanced cancer poses clinical problems due to the complications that arise as the disease progresses. Bone metastases are a common problem that cancer patients may face, and currently, there are no effective drugs to treat these individuals. Prostate, breast, and lung cancers often spread to the bone, causing significant and disabling health conditions. The bone is a highly active and dynamic tissue and is considered a favorable environment for the growth of cancer. The role of osteoblasts and osteoclasts in the process of bone remodeling and the way in which their interactions change during the progression of metastasis is critical to understanding the pathophysiology of this disease. These interactions create a self-perpetuating loop that stimulates the growth of metastatic cells in the bone. The metabolic reprogramming of both cancer cells and cells in the bone microenvironment has serious implications for the development and progression of metastasis. Insight into the process of bone remodeling and the systemic elements that regulate this process, as well as the cellular changes that occur during the progression of bone metastases, is critical to the discovery of a cure for this disease. It is crucial to explore different therapeutic options that focus specifically on malignancy in the bone microenvironment in order to effectively treat this disease. This review will focus on the bone remodeling process and the effects of metabolic disorders as well as systemic factors like hormones and cytokines on the development of bone metastases. We will also examine the various therapeutic alternatives available today and the upcoming advances in novel treatments.

Wnt Signaling in Atherosclerosis: Mechanisms to Therapeutic Implications

Atherosclerosis is a vascular disease in which inflammation plays a pivotal role. Receptor-mediated signaling pathways regulate vascular inflammation and the pathophysiology of atherosclerosis. Emerging evidence has revealed the role of the Wnt pathway in atherosclerosis progression. The Wnt pathway influences almost all stages of atherosclerosis progression, including endothelial dysfunction, monocyte infiltration, smooth muscle cell proliferation and migration, and plaque formation. Targeting the Wnt pathway to treat atherosclerosis represents a promising therapeutic approach that remains understudied. Blocking Wnt signaling utilizing small molecule inhibitors, recombinant proteins, and/or neutralizing antibodies ameliorates atherosclerosis in preclinical models. The Wnt pathway can be potentially manipulated through targeting Wnt ligands, receptors, co-receptors, and downstream signaling molecules. However, there are challenges associated with developing a real world therapeutic compound that targets the Wnt pathway. This review focuses on the role of Wnt signaling in atherosclerosis development, and the rationale for targeting this pathway for the treatment of atherosclerosis.

Protein profiling in systemic sclerosis patients with different pulmonary complications using proteomic antibody microarray

BACKGROUND

Pulmonary arterial hypertension (PAH) and interstitial lung disease (ILD) are leading causes of systemic sclerosis (SSc)-related death. In this study, we aimed to identify biomarkers for detecting SSc pulmonary complications that are mild and in the early stages to improve the prognosis.

METHODS

We screened for serum biomarkers using a proteomic antibody microarray that simultaneously assessed 1000 proteins. Differentially expressed proteins were further verified using ELISA. Finally, we performed a correlation analysis using clinical data.

RESULTS

We identified 125 differentially expressed proteins, of which calcitonin, sclerostin (SOST), CD40, and fibronectin were selected for further verification. Serum calcitonin and SOST levels were significantly elevated in all SSc pulmonary complication subgroups, whereas serum calcitonin levels were higher in the SSc with PAH subgroup than in the SSc without PAH and ILD subgroup. Serum SOST levels were possibly associated with the presence of ILD and positively related to the presence of cardiac and gastrointestinal involvement. Serum CD40 and calcitonin levels appeared to be positively related to the presence of renal involvement, and serum calcitonin was also positively related to the presence of gastrointestinal involvement.

CONCLUSIONS

This study indicated that serum calcitonin and SOST levels may be promising biomarkers for SSc-related PAH and ILD, respectively. Further research is needed to verify this result and understand the underlying mechanisms.

Profiles of Wnt pathway gene expression during tooth morphogenesis

Mouse and human genetic studies indicate key roles of the Wnt10a ligand in odontogenesis. Previous studies have identified effectors and regulators of the Wnt signaling pathway actively expressed during key stages of tooth morphogenesis. However, limitations in multiplexing and spatial resolution hindered a more comprehensive analysis of these signaling molecules. Here, profiling of transcriptomes using fluorescent multiplex in situ hybridization and single-cell RNA-sequencing (scRNA-seq) provide robust insight into the synchronized expression patterns of Wnt10a, Dkk1, and Sost simultaneously during tooth development. First, we identified Wnt10a transcripts restricted to the epithelium at the stage of tooth bud morphogenesis, contrasting that of Sost and Dkk1 localization to the dental mesenchyme. By embryonic day 15.5 (E15.5), a marked shift of Wnt10a expression from dental epithelium to mesenchyme was noted, while Sost and Dkk1 expression remained enriched in the mesenchyme. By postnatal day 0 (P0), co-localization patterns of Wnt10a, Dkk1, and Sost were observed in both terminally differentiating and secreting odontoblasts of molars and incisors. Interestingly, Wnt10a exhibited robust expression in fully differentiated ameloblasts at the developing cusp tip of both molars and incisors, an observation not previously noted in prior studies. At P7 and 14, after the mineralization of dentin and enamel, Wnt10a expression was limited to odontoblasts. Meanwhile, Wnt modulators showed reduced or absent signals in molars. In contrast, strong signals persisted in ameloblasts (for Wnt10a) and odontoblasts (for Wnt10a, Sost, and Dkk1) towards the proximal end of incisors, near the cervical loop. Our scRNA-seq analysis used CellChat to further contextualize Wnt pathway-mediated communication between cells by examining ligand-receptor interactions among different clusters. The co-localization pattern of Wnt10a, Dkk1, and Sost in both terminally differentiating and secreting odontoblasts of molars and incisors potentially signifies the crucial ligand-modulator interaction along the gradient of cytodifferentiation starting from each cusp tip towards the apical region. These data provide cell type-specific insight into the role of Wnt ligands and mediators during epithelial-mesenchymal interactions in odontogenesis.

Canonical and noncanonical Wnt signaling: Multilayered mediators, signaling mechanisms and major signaling crosstalk

Wnt signaling plays a major role in regulating cell proliferation and differentiation. The Wnt ligands are a family of 19 secreted glycoproteins that mediate their signaling effects via binding to Frizzled receptors and LRP5/6 coreceptors and transducing the signal either through β-catenin in the canonical pathway or through a series of other proteins in the noncanonical pathway. Many of the individual components of both canonical and noncanonical Wnt signaling have additional functions throughout the body, establishing the complex interplay between Wnt signaling and other signaling pathways. This crosstalk between Wnt signaling and other pathways gives Wnt signaling a vital role in many cellular and organ processes. Dysregulation of this system has been implicated in many diseases affecting a wide array of organ systems, including cancer and embryological defects, and can even cause embryonic lethality. The complexity of this system and its interacting proteins have made Wnt signaling a target for many therapeutic treatments. However, both stimulatory and inhibitory treatments come with potential risks that need to be addressed. This review synthesized much of the current knowledge on the Wnt signaling pathway, beginning with the history of Wnt signaling. It thoroughly described the different variants of Wnt signaling, including canonical, noncanonical Wnt/PCP, and the noncanonical Wnt/Ca2+ pathway. Further description involved each of its components and their involvement in other cellular processes. Finally, this review explained the various other pathways and processes that crosstalk with Wnt signaling.

The effect of light compressive and tensile mechanical forces on SOST and POSTN expressions in human periodontal ligament cells: an in vitro study

Periodontal ligament (PDL) cells play an important role in mechanosensing and secretion of signaling molecules during bone remodeling. However, the regulatory mechanism is unknown. The aim of the present study is to investigate the expression pattern of periostin and sclerostin in response to orthodontic forces in periodontal ligament cells in vitro. PDL cells were isolated from extracted teeth and treated with compressive forces of 25 gr/cm2 or equiaxial tension forces at frequency 1 Hz for 0, 24, 48, and 72 h. qRT-PCR was applied to evaluate the gene expressions. The secretion of sclerostin and periostin was assessed using ELISA. DAPI staining was used to evaluate apoptosis. The expression of sclerostin elevated significantly at protein and gene levels under compression forces after 24 h, while the application of tensile forces induced the expression of periostin and its upstream regulator RUNX2 (p < 0.05). Gene expression up-regulation was significant for POSTN and RUNX2 after 48 and 72 h tensile forces. Also, the gene expression of sclerostin reduced in a time-dependent manner after application of tensile force. The compression forces enhanced apoptosis to 7.5 ± 3.5% and induced gene expression of apoptotic markers of CASP9, and BCL2 within 72 h of exposure. Periostin and sclerostin play an important role in orthodontic loads and their expressions are affected oppositely by compressive and tensile forces that might be suggested as a biomarker for assessment of bone remodeling during orthodontic treatment.

Targeting WNT signalling pathways as new therapeutic strategies for osteoarthritis

Osteoarthritis (OA) is a highly prevalent chronic joint disease and the leading cause of disability. Currently, no drugs are available to control joint damage or ease the associated pain. The wingless-type (WNT) signalling pathway is vital in OA progression. Excessive activation of the WNT signalling pathway is pertinent to OA progression and severity. Therefore, agonists and antagonists of the WNT pathway are considered potential drug candidates for OA treatment. For example, SM04690, a novel small molecule inhibitor of WNT signalling, has demonstrated its potential in a recent phase III clinical trial as a disease-modifying osteoarthritis drug (DMOAD). Therefore, targeting the WNT signalling pathway may be a distinctive approach to developing particular agents helpful in treating OA. This review aims to update the most recent progress in OA drug development by targeting the WNT pathway. In this, we introduce WNT pathways and their crosstalk with other signalling pathways in OA development and highlight the role of the WNT signalling pathway as a key regulator in OA development. Several articles have reviewed the Wnt pathway from different aspects. This candid review provides an introduction to WNT pathways and their crosstalk with other signalling pathways in OA development, highlighting the role of the WNT signalling pathway as a key regulator in OA development with the latest research. Particularly, we emphasise the state-of-the-art in targeting the WNT pathway as a promising therapeutic approach for OA and challenges in their development and the nanocarrier-based delivery of WNT modulators for treating OA.

Loss of Nmp4 enhances bone gain from sclerostin antibody administration

Severe osteoporosis is often treated with one of three Food and Drug Administration (FDA)-approved osteoanabolics. These drugs act by (1) parathyroid hormone (PTH) receptor stimulation using analogues to PTH (teriparatide) or PTH-related peptide (abaloparatide) or by (2) monoclonal antibody neutralization of sclerostin, an innate Wnt inhibitor (Scl-mAb, romosozumab-aqqg). The efficacies of both strategies wane over time. The transcription factor Nmp4 (Nuclear Matrix Protein 4) is expressed in all tissues yet mice lacking this gene are healthy and exhibit enhanced PTH-induced bone formation. Conditional deletion of Nmp4 in mesenchymal stem progenitor cells (MSPCs) phenocopies the elevated response to PTH in global Nmp4-/- mice. However, targeted deletion in later osteoblast stages does not replicate this response. In this study we queried whether loss of Nmp4 improves Scl-mAb potency. Experimental cohorts included global Nmp4-/- and Nmp4+/+ littermates and three conditional knockout models. Nmp4-floxed (Nmp4fl/fl) mice were crossed with mice harboring one of three Cre-drivers (i) Prx1Cre+ targeting MSPCs, (ii) BglapCre+ (mature osteocalcin-expressing osteoblasts), and (iii) Dmp1Cre+ (osteocytes). Female mice were treated with Scl-mAb or 0.9 % saline vehicle for 4 or 7 weeks from 10 weeks of age. Skeletal response was assessed using micro-computed tomography, dual-energy X-ray absorptiometry, bone histomorphometry, and serum analysis. Global Nmp4-/- mice exhibited enhanced Scl-mAb-induced increases in trabecular bone in the femur and spine and a heightened increase in whole body areal bone mineral density compared to global Nmp4+/+ controls. This improved Scl-mAb potency was primarily driven by enhanced increases in bone formation. Nmp4fl/fl;PrxCre+ mice showed an exaggerated Scl-mAb-induced increase in femoral bone but not in the spine since Prrx1 is not expressed in vertebra. The Nmp4fl/fl;BglapCre+ and Nmp4fl/fl;Dmp1Cre+ mice did not exhibit an improved Scl-mAb response. We conclude that Nmp4 expression in MSPCs interferes with the bone anabolic response to anti-sclerostin therapy.

Epithelial-like transport of mineral distinguishes bone formation from other connective tissues

We review unique properties of bone formation including current understanding of mechanisms of bone mineral transport. We focus on formation only; mechanism of bone degradation is a separate topic not considered. Bone matrix is compared to other connective tissues composed mainly of the same proteins, but without the specialized mechanism for continuous transport and deposition of mineral. Indeed other connective tissues add mechanisms to prevent mineral formation. We start with the epithelial-like surfaces that mediate transport of phosphate to be incorporated into hydroxyapatite in bone, or in its ancestral tissue, the tooth. These include several phosphate producing or phosphate transport-related proteins with special expression in large quantities in bone, particularly in the bone-surface osteoblasts. In all connective tissues including bone, the proteins that constitute the protein matrix are mainly type I collagen and γ-carboxylate-containing small proteins in similar molar quantities to collagen. Specialized proteins that regulate connective tissue structure and formation are surprisingly similar in mineralized and non-mineralized tissues. While serum calcium and phosphate are adequate to precipitate mineral, specialized mechanisms normally prevent mineral formation except in bone, where continuous transport and deposition of mineral occurs.

The Roles of WNT Signaling Pathways in Skin Development and Mechanical-Stretch-Induced Skin Regeneration

The WNT signaling pathway plays a critical role in a variety of biological processes, including development, adult tissue homeostasis maintenance, and stem cell regulation. Variations in skin conditions can influence the expression of the WNT signaling pathway. In light of the above, a deeper understanding of the specific mechanisms of the WNT signaling pathway in different physiological and pathological states of the skin holds the potential to significantly advance clinical treatments of skin-related diseases. In this review, we present a comprehensive analysis of the molecular and cellular mechanisms of the WNT signaling pathway in skin development, wound healing, and mechanical stretching. Our review sheds new light on the crucial role of the WNT signaling pathway in the regulation of skin physiology and pathology.

Glycogen synthase kinase 3 inhibition enhances mineral nodule formation by cementoblasts in vitro

This study aimed to investigate whether GSK-3 inhibition (CHIR99021) effectively promoted mineralization by cementoblasts (OCCM-30). OCCM-30 cells were used and treated with different concentrations of CHIR99021 (2.5, 5, and 10 mM). Experiments included proliferation and viability, cellular metabolic activity, gene expression, and mineral nodule formation by Xylene Orange at the experimental time points. In general, CHIR99021 did not significantly affect OCCM-30 viability and cell metabolism (MTT assay) (p > 0.05), but increased OCCM-30 proliferation at 2.5 mM on days 2 and 4 (p < 0.05). Data analysis further showed that inhibition of GSK-3 resulted in increased transcript levels of Axin2 in OCCM-30 cells starting as early as 4 h, and regulated the expression of key bone markers including alkaline phosphatase (Alp), runt-related transcription factor 2 (Runx-2), osteocalcin (Ocn), and osterix (Osx). In addition, CHIR99021 led to an enhanced mineral nodule formation in vitro under both osteogenic and non-osteogenic conditions as early as 5 days after treatment. Altogether, the results of the current study suggest that inhibition of GSK-3 has the potential to promote cementoblast differentiation leading to increased mineral deposition in vitro.

Peak Bone Mass Formation: Modern View of the Problem

Peak bone mass is the amount of bone tissue that is formed when a stable skeletal state is achieved at a young age. To date, there are no established peak bone mass standards nor clear data on the age at which peak bone mass occurs. At the same time, the level of peak bone mass at a young age is an important predictor of the onset of primary osteoporosis. The purpose of this review is to analyze the results of studies of levels of peak bone mass in general, the age of its onset, as well as factors influencing its formation. Factors such as hormonal levels, body composition, physical activity, nutrition, heredity, smoking, lifestyle, prenatal predictors, intestinal microbiota, and vitamin and micronutrient status were considered, and a comprehensive scheme of the influence of these factors on the level of peak bone mass was created. Determining the standards and timing of the formation of peak bone mass, and the factors affecting it, will help in the development of measures to prevent its shortage and the consequent prevention of osteoporosis and concomitant diseases.

Buds of new bone formation within the Femoral Head of Hip Fracture Patients Coincide with Zones of Low Osteocyte Sclerostin

Romosozumab treatment reduces the rate of hip fractures and increases hip bone density, increasing bone formation by inhibiting sclerostin protein. We studied the normal pattern of bone formation and osteocyte expression in the human proximal femur because it is relevant to both antisclerostin treatment effects and fracture. Having visualized and quantified buds of new bone formation in trabeculae, we hypothesized that they would coincide with areas of (a) higher mechanical stress and (b) low sclerostin expression by osteocytes. In patients with hip fracture, we visualized each bud of active modeling-based formation (forming minimodeling structure [FMiS]) in trabecular cores taken from different parts of the femoral head. Trabecular bone structure was also measured with high-resolution imaging. More buds of new bone formation (by volume) were present in the higher stress superomedial zone (FMiS density, N.FMiS/T.Ar) than lower stress superolateral (p < 0.05), and inferomedial (p < 0.001) regions. There were fewer sclerostin expressing osteocytes close to or within FMiS. FMiS density correlated with greater amount, thickness, number, and connectivity of trabeculae (bone volume BV/TV, r = 0.65, p < 0.0001; bone surface BS/TV, r = 0.47, p < 0.01; trabecular thickness Tb.Th, r = 0.55, p < 0.001; trabecular number Tb.N, r = 0.47, p < 0.01; and connectivity density Conn.D, r = 0.40, p < 0.05) and lower trabecular separation (Tb.Sp, r = -0.56, p < 0.001). These results demonstrate modeling-based bone formation in femoral trabeculae from patients with hip fracture as a potential therapeutic target to enhance bone structure. © 2023 American Society for Bone and Mineral Research (ASBMR).

All the might of the osteocyte: emerging roles in chronic kidney disease

Osteocytes are the most abundant type of bone cell and play crucial roles in bone health. Osteocytes sense mechanical stress and orchestrate osteoblasts and osteoclasts to maintain bone density and strength. Beyond this, osteocytes have also emerged as key regulators of organ crosstalk, and they function as endocrine organs via their roles in secreting factors that mediate signaling within their neighboring bone cells and in distant tissues. As such, osteocyte dysfunction has been associated with the bone abnormalities seen across a spectrum of chronic kidney disease. Specifically, dysregulated osteocyte morphology and signaling have been observed in the earliest stages of chronic kidney disease and have been suggested to contribute to kidney disease progression. More important, US Food and Drug Administration-approved inhibitors of osteocytic secreted proteins, such as fibroblast growth factor 23 and sclerostin, have been used to treat bone diseases. The present mini review highlights new research that links dysfunctional osteocytes to the pathogenesis of chronic kidney disease mineral and bone disorder.

Serum levels of sclerostin in prediabetes and its correlation with bone mineral density

Background

Diabetes is a major burden globally, more commonly so in developing countries, as its complications are detected relatively late due to underdeveloped healthcare systems. These complications, when detected, are more or less irreversible, thereby leading to increased morbidity and mortality. Among these, complications related to bones (mainly osteoporosis) start fairly early (even in the prediabetes stage) but are less emphasized, nonetheless are major contributors to morbidity in diabetics due to increased fracture risk. One of the novel bone markers recently discovered is sclerostin, which helps in the assessment of the effect of hyperglycemia on bone homeostasis. Bone mineral density (BMD) by DXA scan is a good tool to assess the status of bone health but requires modern expensive radiological equipment. In this study, we wanted to see the correlation of serum levels of sclerostin to BMD so that by a simple serum investigation, early detection of poor bone quality in treatment-naive prediabetics can be done.

Objective

The aim of the study was to measure serum levels of sclerostin in prediabetics, compare them with normoglycemic controls, and find the correlation of serum levels of sclerostin with BMD.

Methods

50 prediabetic patients and 50 age, sex, blood pressure, and BMI-matched controls were recruited in the study. In both the groups, serum levels of fasting blood glucose and postprandial glucose, glycated hemoglobin (HbA1c), Vitamin D, fasting insulin, and serum sclerostin levels were measured in both groups using ELISA. The obtained values were compared between the two groups. Bone mineral density is measured by DXA scan in cases and a correlation between BMD and serum levels of sclerostin was observed.

Results

Serum sclerostin was significantly higher in the cases [18.22 (19.42) ng/ml] compared to the control group [11.08 (4.73) ng/ml] with a P value of 0.013. The mean of BMD in prediabetes is 1.06 g/cm2, T score is - 1.02, and Z score is - 0.59. There was a significant negative correlation between serum sclerostin levels and BMD in prediabetes (r = -0.404, P < 0.001).

Conclusion

Serum levels of sclerostin are increased in prediabetes and correlate well with low BMD in prediabetes, and can therefore be used for early recognition of osteoporosis and fractures in diabetes.

A pilot study: effect of irisin on trabecular bone in a streptozotocin-induced animal model of type 1 diabetic osteopathy utilizing a micro-CT

Background

Osteoporosis is a significant co-morbidity of type 1 diabetes mellitus (DM1) leading to increased fracture risk. Exercise-induced hormone 'irisin' in low dosage has been shown to have a beneficial effect on bone metabolism by increasing osteoblast differentiation and reducing osteoclast maturation, and inhibiting apoptosis and inflammation. We investigated the role of irisin in treating diabetic osteopathy by observing its effect on trabecular bone.

Methods

DM1 was induced by intraperitoneal injection of streptozotocin 60 mg/kg body weight. Irisin in low dosage (5 µg twice a week for 6 weeks I/P) was injected into half of the control and 4-week diabetic male Wistar rats. Animals were sacrificed six months after induction of diabetes. The trabecular bone in the femoral head and neck was analyzed using a micro-CT technique. Bone turnover markers were measured using ELISA, Western blot, and RT-PCR techniques.

Results

It was found that DM1 deteriorates the trabecular bone microstructure by increasing trabecular separation (Tb-Sp) and decreasing trabecular thickness (Tb-Th), bone volume fraction (BV/TV), and bone mineral density (BMD). Irisin treatment positively affects bone quality by increasing trabecular number p < 0.05 and improves the BMD, Tb-Sp, and BV/TV by 21-28%. The deterioration in bone microarchitecture is mainly attributed to decreased bone formation observed as low osteocalcin and high sclerostin levels in diabetic bone samples p < 0.001. The irisin treatment significantly suppressed the serum and bone sclerostin levels p < 0.001, increased the serum CTX1 levels p < 0.05, and also showed non-significant improvement in osteocalcin levels.

Conclusions

This is the first pilot study to our knowledge that shows that a low dose of irisin marginally improves the trabecular bone in DM1 and is an effective peptide in reducing sclerostin levels.

Lowering of Circulating Sclerostin May Increase Risk of Atherosclerosis and Its Risk Factors: Evidence From a Genome-Wide Association Meta-Analysis Followed by Mendelian Randomization

OBJECTIVE

In this study, we aimed to establish the causal effects of lowering sclerostin, target of the antiosteoporosis drug romosozumab, on atherosclerosis and its risk factors.

METHODS

A genome-wide association study meta-analysis was performed of circulating sclerostin levels in 33,961 European individuals. Mendelian randomization (MR) was used to predict the causal effects of sclerostin lowering on 15 atherosclerosis-related diseases and risk factors.

RESULTS

We found that 18 conditionally independent variants were associated with circulating sclerostin. Of these, 1 cis signal in SOST and 3 trans signals in B4GALNT3, RIN3, and SERPINA1 regions showed directionally opposite signals for sclerostin levels and estimated bone mineral density. Variants with these 4 regions were selected as genetic instruments. MR using 5 correlated cis-SNPs suggested that lower sclerostin increased the risk of type 2 diabetes mellitus (DM) (odds ratio [OR] 1.32 [95% confidence interval (95% CI) 1.03-1.69]) and myocardial infarction (MI) (OR 1.35 [95% CI 1.01-1.79]); sclerostin lowering was also suggested to increase the extent of coronary artery calcification (CAC) (β = 0.24 [95% CI 0.02-0.45]). MR using both cis and trans instruments suggested that lower sclerostin increased hypertension risk (OR 1.09 [95% CI 1.04-1.15]), but otherwise had attenuated effects.

CONCLUSION

This study provides genetic evidence to suggest that lower levels of sclerostin may increase the risk of hypertension, type 2 DM, MI, and the extent of CAC. Taken together, these findings underscore the requirement for strategies to mitigate potential adverse effects of romosozumab treatment on atherosclerosis and its related risk factors.

The Role of Sclerostin in Rheumatic Diseases: A Review

Systemic connective tissue disorders constitute a heterogenous group of autoimmune diseases with the potential to affect a range of organs. Rheumatoid arthritis (RA) is a chronic, progressive, autoimmune inflammatory disease affecting the joints. Systemic lupus erythematosus (SLE) may manifest with multiple system involvement as a result of inflammatory response to autoantibodies. Spondyloarthropathies (SpAs) such as ankylosing spondylitis (AS) or psoriatic arthritis (PsA) are diseases characterised by the inflammation of spinal joints, paraspinal tissues, peripheral joints and enthesitis as well as inflammatory changes in many other systems and organs. Physiologically, sclerostin helps to maintain balance in bone tissue metabolism through the Wnt/β-catenin pathway, which represents a major intracellular signalling pathway. This review article aims to present the current knowledge on the role of sclerostin in the Wnt/β-catenin pathway and its correlation with clinical data from RA, SLE, AS and PsA patients.

Sclerostin, Osteocytes, and Wnt Signaling in Pediatric Renal Osteodystrophy

The pathophysiology of chronic kidney disease-mineral and bone disorder (CKD-MBD) is not well understood. Specific factors secreted by osteocytes are elevated in the serum of adults and pediatric patients with CKD-MBD, including FGF-23 and sclerostin, a known inhibitor of the Wnt signaling pathway. The molecular mechanisms that promote bone disease during the progression of CKD are incompletely understood. In this study, we performed a cross-sectional analysis of 87 pediatric patients with pre-dialysis CKD and post-dialysis (CKD 5D). We assessed the associations between serum and bone sclerostin levels and biomarkers of bone turnover and bone histomorphometry. We report that serum sclerostin levels were elevated in both early and late CKD. Higher circulating and bone sclerostin levels were associated with histomorphometric parameters of bone turnover and mineralization. Immunofluorescence analyses of bone biopsies evaluated osteocyte staining of antibodies towards the canonical Wnt target, β-catenin, in the phosphorylated (inhibited) or unphosphorylated (active) forms. Bone sclerostin was found to be colocalized with phosphorylated β-catenin, which suggests that Wnt signaling was inhibited. In patients with low serum sclerostin levels, increased unphosphorylated "active" β-catenin staining was observed in osteocytes. These data provide new mechanistic insight into the pathogenesis of CKD-MBD and suggest that sclerostin may offer a potential biomarker or therapeutic target in pediatric renal osteodystrophy.

The role of cells and signal pathways in subchondral bone in osteoarthritis

Osteoarthritis (OA) is mainly caused by ageing, strain, trauma, and congenital joint abnormalities, resulting in articular cartilage degeneration. During the pathogenesis of OA, the changes in subchondral bone (SB) are not only secondary manifestations of OA, but also an active part of the disease, and are closely associated with the severity of OA. In different stages of OA, there were microstructural changes in SB. Osteocytes, osteoblasts, and osteoclasts in SB are important in the pathogenesis of OA. The signal transduction mechanism in SB is necessary to maintain the balance of a stable phenotype, extracellular matrix (ECM) synthesis, and bone remodelling between articular cartilage and SB. An imbalance in signal transduction can lead to reduced cartilage quality and SB thickening, which leads to the progression of OA. By understanding changes in SB in OA, researchers are exploring drugs that can regulate these changes, which will help to provide new ideas for the treatment of OA.

A Novel Long Noncoding RNA in Osteocytes Regulates Bone Formation through the Wnt/β-Catenin Signaling Pathway

The vast majority of transcribed RNAs are noncoding RNAs. Among noncoding RNAs, long noncoding RNAs (lncRNAs), which contain hundreds to thousands of bases, have received attention in many fields. The vast majority of the constituent cells in bone tissue are osteocytes, but their regulatory mechanisms are incompletely understood. Considering the wide range of potential contributions of lncRNAs to physiological processes and pathological conditions, we hypothesized that lncRNAs in osteocytes, which have not been reported, could be involved in bone metabolism. Here, we first isolated osteocytes from femurs of mice with osteocyte-specific GFP expression. Then, through RNA-sequencing, we identified osteocyte-specific lncRNAs and focused on a novel lncRNA, 9530026P05Rik (lncRNA953Rik), which strongly suppressed osteogenic differentiation. In the IDG-SW3 osteocyte line with lncRNA953Rik overexpression, the expression of Osterix and its downstream genes was reduced. RNA pull-down and subsequent LC-MS/MS analysis revealed that lncRNA953Rik bound the nuclear protein CCAR2. We demonstrated that CCAR2 promoted Wnt/β-catenin signaling and that lncRNA953Rik inhibited this pathway. lncRNA953Rik sequestered CCAR2 from HDAC1, leading to deacetylation of H3K27 in the Osterix promoter and consequent transcriptional downregulation of Osterix. This research is the first to clarify the role of a lncRNA in osteocytes. Our findings can pave the way for novel therapeutic options targeting lncRNAs in osteocytes to treat bone metabolic diseases such as osteoporosis.

The role of sclerostin in lipid and glucose metabolism disorders

Lipid and glucose metabolism are critical for human activities, and their disorders can cause diabetes and obesity, two prevalent metabolic diseases. Studies suggest that the bone involved in lipid and glucose metabolism is emerging as an endocrine organ that regulates systemic metabolism through bone-derived molecules. Sclerostin, a protein mainly produced by osteocytes, has been therapeutically targeted by antibodies for treating osteoporosis owing to its ability to inhibit bone formation. Moreover, recent evidence indicates that sclerostin plays a role in lipid and glucose metabolism disorders. Although the effects of sclerostin on bone have been extensively examined and reviewed, its effects on systemic metabolism have not yet been well summarized. In this paper, we provide a systemic review of the effects of sclerostin on lipid and glucose metabolism based on in vitro and in vivo evidence, summarize the research progress on sclerostin, and prospect its potential manipulation for obesity and diabetes treatment.

Sclerostin small-molecule inhibitors promote osteogenesis by activating canonical Wnt and BMP pathways

Background

The clinical healing environment after a posterior spinal arthrodesis surgery is one of the most clinically challenging bone-healing environments across all orthopedic interventions due to the absence of a contained space and the need to form de novo bone. Our group has previously reported that sclerostin in expressed locally at high levels throughout a developing spinal fusion. However, the role of sclerostin in controlling bone fusion remains to be established.

Methods

We computationally identified two FDA-approved drugs, as well as a single novel small-molecule drug, for their ability to disrupt the interaction between sclerostin and its receptor, LRP5/6. The drugs were tested in several in vitro biochemical assays using murine MC3T3 and MSCs, assessing their ability to (1) enhance canonical Wnt signaling, (2) promote the accumulation of the active (non-phosphorylated) form of β-catenin, and (3) enhance the intensity and signaling duration of BMP signaling. These drugs were then tested subcutaneously in rats as standalone osteoinductive agents on plain collagen sponges. Finally, the top drug candidates (called VA1 and C07) were tested in a rabbit posterolateral spine fusion model for their ability to achieve a successful fusion at 6 wk.

Results

We show that by controlling GSK3b phosphorylation our three small-molecule inhibitors (SMIs) simultaneously enhance canonical Wnt signaling and potentiate canonical BMP signaling intensity and duration. We also demonstrate that the SMIs produce dose-dependent ectopic mineralization in vivo in rats as well as significantly increase posterolateral spine fusion rates in rabbits in vivo, both as standalone osteogenic drugs and in combination with autologous iliac crest bone graft.

Conclusions

Few if any osteogenic small molecules possess the osteoinductive potency of BMP itself - that is, the ability to form de novo ectopic bone as a standalone agent. Herein, we describe two such SMIs that have this unique ability and were shown to induce de novo bone in a stringent in vivo environment. These SMIs may have the potential to be used in novel, cost-effective bone graft substitutes for either achieving spinal fusion or in the healing of critical-sized fracture defects.

Funding

This work was supported by a Veteran Affairs Career Development Award (IK2-BX003845).

Meta-analysis of the effects of denosumab and romosozumab on bone mineral density and turnover markers in patients with osteoporosis

Purpose

To assess the alterations in bone mineral density and bone turnover marker concentrations following the administration of denosumab and romosozumab therapies in patients with osteoporosis.

Methods

PubMed was searched for studies published until January 28, 2023, that investigated the clinical efficacy and bone turnover marker changes of denosumab and romosozumab in the treatment of osteoporosis, with a minimum follow-up of 3 months in each study. Studies were screened, and data on changes in bone mineral density (BMD), P1NP, and TRACP-5b levels after treatment were extracted and included in the analysis.

Results

Six studies were analyzed. At 3 months after treatment, the romosozumab group showed greater changes in lumbar BMD and bone turnover markers. BMD of total hip and femoral neck was relatively delayed. Beginning at 6 to 12 months, romosozumab showed greater changes in bone mineral density and markers of bone turnover.

Conclusion

Both romosozumab and denosumab have antiosteoporotic effects, with greater effects on BMD and bone turnover markers observed within 12 months of romosozumab treatment.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero, identifier CRD42023395034.

Regulation of the Osteocyte Secretome with Aging and Disease

As the most numerous and long-lived of all bone cells, osteocytes have essential functions in regulating skeletal health. Through the lacunar-canalicular system, secreted proteins from osteocytes can reach cells throughout the bone. Furthermore, the intimate connectivity between the lacunar-canalicular system and the bone vasculature allows for the transport of osteocyte-secreted factors into the circulation to reach the entire body. Local and endocrine osteocyte signaling regulates physiological processes such as bone remodeling, bone mechanoadaptation, and mineral homeostasis. However, these processes are disrupted by impaired osteocyte function induced by aging and disease. Dysfunctional osteocyte signaling is now associated with the pathogenesis of many disorders, including chronic kidney disease, cancer, diabetes mellitus, and periodontitis. In this review, we focus on the targeting of bone and extraskeletal tissues by the osteocyte secretome. In particular, we highlight the secreted osteocyte proteins, which are known to be dysregulated during aging and disease, and their roles during disease progression. We also discuss how therapeutic or genetic targeting of osteocyte-secreted proteins can improve both skeletal and systemic health.

Fgfr1 deficiency in osteocytes leads to increased bone mass by enhancing Wnt/β-catenin signaling

Osteoporosis (OP) is the most common skeletal disease in middle-aged and elderly people. A comprehensive understanding of the pathogenesis of osteoporosis is important. Fibroblast growth factor receptor 1 (FGFR1) is an important molecule for skeletal development and bone remodeling. Osteocytes are the most numerous cells in bone and play critical roles in bone homeostasis, however the effect of FGFR1 on osteocytes is still unclear. To clarify the direct effects of FGFR1 on osteocytes, we conditionally deleted Fgfr1 in osteocytes with Dentin matrix protein 1 (Dmp1)-Cre. We found that mice lacking Fgfr1 in osteocytes (Fgfr1^f/f;Dmp-cre, MUT) showed increased trabecular bone mass at 2 and 6 months of age, which resulted from enhanced bone formation and decreased bone resorption. Furthermore, the cortical bone was thicker in WT mice than that in MUT mice at 2 and 6 months of age. Histological analysis showed that MUT mice had a decreased number of osteocytes but an increased number of osteocyte dendrites. We further found that mice lacking Fgfr1 in osteocytes showed enhanced activation of β-catenin signaling. The expression of sclerostin, an inhibitor of Wnt/β-catenin signaling, was obviously decreased in MUT mice. Furthermore, we found that FGFR1 can inhibit the expression of β-catenin and decrease the activity of β-catenin signaling. In brief, our study showed that FGFR1 in osteocytes can regulate bone mass by regulating Wnt/β-catenin signaling, providing genetic evidence that FGFR1 plays essential roles in osteocytes during bone remodeling and suggesting that FGFR1 is a potential therapeutic target for the prevention of bone loss.

Assessment of sclerostin levels in the gingival crevicular fluid of patients with periodontitis: A clinico-biochemical crosssectional study

Background

Sclerostin, a glycoprotein, plays a key role in regulating bone mass. In this study, sclerostin levels in the gingival crevicular fluid (GCF) were assessed in patients with Stage III Grade C generalized periodontitis (SIII-GC) and Stage III Grade B generalized periodontitis (SIII-GB).

Methods

This cross-sectional study included 30 participants divided equally into three groups: group I (gingival health), group II (SIII-GC), and group III (SIII-GB). Clinical periodontal parameters like plaque index (PI), gingival bleeding index (GBI), probing pocket depth (PD), and clinical attachment level (CAL) were recorded. A sandwich ELISA was used to determine the sclerostin levels in GCF samples. One-way ANOVA and post hoc Tukey tests were used to analyze the clinical parameters and GCF sclerostin levels. The association between GCF sclerostin levels and periodontal parameters was assessed using Pearson's correlation coefficient (r).

Results

Patients in groups II and III had much higher sclerostin levels in their GCF than in group I (P≤0.05). In contrast, no significant difference in sclerostin levels was observed between the two diseased conditions (P=0.841). Concerning periodontal parameters, a statistically significant difference was observed between the three groups. There was a positive correlation between the periodontal clinical parameters and the expression levels of sclerostin in GCF (P≤0.05).

Conclusion

Increased expression of sclerostin in GCF in patients with periodontitis indicated that it could be considered a reliable biomarker of periodontal disease activity.