Role of Wnt signaling and sclerostin in bone and as therapeutic targets in skeletal disorders

CRIP1 regulates osteogenic differentiation of bone marrow stromal cells and pre-osteoblasts via the Wnt signaling pathway

With the aging of the global demographic, the prevention and treatment of osteoporosis are becoming crucial issues. The gradual loss of self-renewal and osteogenic differentiation capabilities in bone marrow stromal cells (BMSCs) is one of the key factors contributing to osteoporosis. To explore the regulatory mechanisms of BMSCs differentiation, we collected bone marrow cells of femoral heads from patients undergoing total hip arthroplasty for single-cell RNA sequencing analysis. Single-cell RNA sequencing revealed significantly reduced CRIP1 (Cysteine-Rich Intestinal Protein 1) expression and osteogenic capacity in the BMSCs of osteoporosis patients compared to non-osteoporosis group. CRIP1 is a gene that encodes a member of the LIM/double zinc finger protein family, which is involved in the regulation of various cellular processes including cell growth, development, and differentiation. CRIP1 knockdown resulted in decreased alkaline phosphatase activity, mineralization and expression of osteogenic markers, indicating impaired osteogenic differentiation. Conversely, CRIP1 overexpression, both in vitro and in vivo, enhanced osteogenic differentiation and rescued bone mass reduction in ovariectomy-induced osteoporosis mice model. The study further established CRIP1's modulation of osteogenesis through the Wnt signaling pathway, suggesting that targeting CRIP1 could offer a novel approach for osteoporosis treatment by promoting bone formation and preventing bone loss.

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.

The oncogenic role and regulatory mechanism of ACAA2 in human ovarian cancer

Acetyl-CoAacyltransferase2 (ACAA2) is a key enzyme in the fatty acid oxidation pathway that catalyzes the final step of mitochondrial β oxidation, which plays an important role in fatty acid metabolism. The expression of ACAA2 is closely related to the occurrence and malignant progression of tumors. However, the function of ACAA2 in ovarian cancer is unclear. The expression level and prognostic value of ACAA2 were analyzed by databases. Gain and loss of function were carried out to explore the function of ACAA2 in ovarian cancer. RNA-seq and bioinformatics methods were applied to illustrate the regulatory mechanism of ACAA2. ACAA2 overexpression promoted the growth, proliferation, migration, and invasion of ovarian cancer, and ACAA2 knockdown inhibited the malignant progression of ovarian cancer as well as the ability of subcutaneous tumor formation in nude mice. At the same time, we found that OGT can induce glycosylation modification of ACAA2 and regulate the karyoplasmic distribution of ACAA2. OGT plays a vital role in ovarian cancer as a function of oncogenes. In addition, through RNA-seq sequencing, we found that ACAA2 regulates the expression of DIXDC1. ACAA2 regulated the malignant progression of ovarian cancer through the WNT/β-Catenin signaling pathway probably. ACAA2 is an oncogene in ovarian cancer and has the potential to be a target for ovarian cancer therapy.

Sclerostin inhibition in rare bone diseases: Molecular understanding and therapeutic perspectives

Sclerostin emerges as a novel target for bone anabolic therapy in bone diseases. Osteogenesis imperfecta (OI) and X-linked hypophosphatemia (XLH) are rare bone diseases in which therapeutic potential of sclerostin inhibition cannot be ignored. In OI, genetic/pharmacologic sclerostin inhibition promoted bone formation of mice, but responses varied by genotype and age. Serum sclerostin levels were higher in young OI-I patients, while lower in adult OI-I/III/IV. It's worth investigating whether therapeutic response of OI to sclerostin inhibition could be clinically predicted by genotype and age. In XLH, preclinical/clinical data suggested factors other than identified FGF23 contributing to XLH. Higher levels of circulating sclerostin were detected in XLH. Sclerostin inhibition promoted bone formation in Hyp mice, while restored phosphate homeostasis in age-/gender-dependent manner. The role of sclerostin in regulating phosphate metabolism deserves investigation. Sclerostin/FGF23 levels of XLH patients with/without response to FGF23-antibody warrants study to develop precise sclerostin/FGF23 inhibition strategy or synergistic/additive strategy. Notably, OI patients were associated with cardiovascular abnormalities, so were XLH patients receiving conventional therapy. Targeting sclerostin loop3 promoted bone formation without cardiovascular risks. Further, blockade of sclerostin loop3-LRP4 interaction while preserving sclerostin loop2-ApoER2 interaction could be a potential precise sclerostin inhibition strategy for OI and XLH with cardiovascular safety. The Translational Potential of this Article. Preclinical data on the molecular understanding of sclerostin inhibition in OI and therapeutic efficacy in mouse models of different genotypes, as well as clinical data on serum sclerostin levels in patients with different phenotypes of OI, were reviewed and discussed. Translationally, it would facilitate to develop clinical prediction strategies (e.g. based on genotype and age, not just phenotype) for OI patients responsive to sclerostin inhibition. Both preclinical and clinical data suggested sclerostin as another factor contributing to XLH, in addition to the identified FGF23. The molecular understanding and therapeutic effects of sclerostin inhibition on both promoting bone anabolism and improving phosphate homostasis in Hyp mice were reviewed and discussed. Translationaly, it would facilitate the development of precise sclerostin/FGF23 inhibition strategy or synergistic/additive strategy for the treatment of XLH. Cardiovascular risk could not be ruled out during sclerostin inhibition treatment, especially for OI and XLH patients with cardiovascular diseases history and cardiovascular abnormalities. Studies on the role of sclerostin in inhiting bone formation and protecting cardiovascular system were reviewed and discussed. Translationaly, blockade of sclerostin loop3-LRP4 interaction while preserving sclerostin loop2-ApoER2 interaction could be a potential precise sclerostin inhibition strategy for OI and XLH with cardiovascular safety.

Research progress in Alzheimer's disease and bone-brain axis

Alzheimer's disease (AD) is the most common type of cognitive impairment. AD is closely related to orthopedic diseases, such as osteoporosis and osteoarthritis, in terms of epidemiology and pathogenesis. Brain and bone tissues can regulate each other in different manners through bone-brain axis. This article reviews the research progress of the relationship between AD and orthopedic diseases, bone-brain axis mechanisms of AD, and AD therapy by targeting bone-brain axis, in order to deepen the understanding of bone-brain communication, promote early diagnosis and explore new therapy for AD patients.

Apoptotic vesicles rescue impaired mesenchymal stem cells and their therapeutic capacity for osteoporosis by restoring miR-145a-5p deficiency

Apoptotic vesicles (apoVs) play a vital role in various pathological conditions; however, we have yet to fully understand their precise biological effects in rescuing impaired mesenchymal stem cells (MSCs) and regulating tissue homeostasis. Here, we proved that systemic infusion of bone marrow MSCs derived from wild-type (WT) mice effectively improved the osteopenia phenotype and hyperimmune state in ovariectomized (OVX) mice. Importantly, the WT MSCs rescued the impairment of OVX MSCs both in vivo and in vitro, whereas OVX MSCs did not show the same efficacy. Interestingly, treatment with apoVs derived from WT MSCs (WT apoVs) restored the impaired biological function of OVX MSCs and their ability to improve osteoporosis. This effect was not observed with OVX MSCs-derived apoVs (OVX apoVs) treatment. Mechanistically, the reduced miR-145a-5p expression hindered the osteogenic differentiation and immunomodulatory capacity of OVX MSCs by affecting the TGF-β/Smad 2/3-Wnt/β-catenin signaling axis, resulting in the development of osteoporosis. WT apoVs directly transferred miR-145a-5p to OVX MSCs, which were then reused to restore their impaired biological functions. Conversely, treatment with OVX apoVs did not produce significant effects due to their limited expression of miR-145a-5p. Overall, our findings unveil the remarkable potential of apoVs in rescuing the biological function and therapeutic capability of MSCs derived from individuals with diseases. This discovery offers a new avenue for exploring apoVs-based MSC engineering and expands the application scope of stem cell therapy, contributing to the maintenance of bone homeostasis through a previously unrecognized mechanism.

Influence of anti-sclerostin monoclonal antibody in the repair of post-extraction sockets of ovariectomized rats

OBJECTIVE

This study assessed the impact of an anti-sclerostin monoclonal antibody (Scl-Ab)-based osteoporosis drug on the post-extraction alveolar repair of ovariectomized rats.

DESIGN

Fifteen female rats were randomly distributed into three groups: CTR (healthy animals), OST (osteoporosis induced by ovariectomy), and OST+Scl-Ab (osteoporosis induction followed by Scl-Ab treatment). Ovariectomy or sham surgery was performed 30 days before baseline, and Scl-Ab or a vehicle was administered accordingly in the groups. After seven days, all rats underwent the first lower molar extraction and were euthanized 15 days later. Computed microtomography, histological analysis, and collagen content measurement were performed on post-extraction sockets and intact mandibular and maxillary bone areas.

RESULTS

Microtomographic analyses of the sockets and mandibles did not reveal significant differences between groups on bone morphometric parameters (p > 0.05), while maxillary bone analyses resulted in better maintenance of bone architecture in OST+Scl-Ab, compared to OST (p < 0.05). Descriptive histological analysis and polarization microscopy indicated better post-extraction socket repair characteristics and collagen content in OST+Scl-Ab compared to OST (p < 0.05).

CONCLUSIONS

Scl-Ab-based medication did not accelerate alveolar bone formation but exhibited better post-extraction repair characteristics, and collagen content compared to ovariectomized animals only.

A comprehensive review and advanced biomolecule-based therapies for osteoporosis

BACKGROUND

The prevalence of osteoporosis (OP) on a global scale is significantly elevated that causes life threatening issues. The potential of groundbreaking biomolecular therapeutics in the field of OP is highly encouraging. The administration of biomolecular agents has the potential to mitigate the process of bone demineralization while concurrently augmenting the regenerative capacity of bone tissue, thereby facilitating a personalized therapeutic approach. Biomolecules-based therapies showed promising results in term of bone mass protection and restoration in OP.

AIM OF REVIEW

We summarized the recent biomolecular therapies with notable progress in clinical, demonstrating the potential to transform illness management. These treatments frequently utilize different biomolecule based strategies. Biomolecular therapeutics has a targeted character, which results in heightened specificity and less off-target effects, ultimately leading to increased patient outcomes. These aspects have the capacity to greatly enhance the management of OP, thus resulting in a major enhancement in the quality of life encountered by individuals affected by this condition.

A practical approach for anabolic treatment of bone fragility with romosozumab

BACKGROUND

Romosozumab, a fully humanized anti-sclerostin-antibody, is a bone-builder stimulating osteoblasts and inhibiting osteoclast by activation of the canonical Wnt-beta catenin signaling. This unique mechanism of action has the potential to address unmet needs in osteoporosis management.

METHODS

The multifaceted practical clinical issues related to romosozumab are discussed, especially focusing on the rationale of employing a sclerostin inhibitor to target bone fragility as first line or second line treatment in post-menopausal osteoporosis and in males at increased risk of fractures.

RESULTS

Four randomized clinical trials with several post-hoc analyses and more than ten observational studies have consistently demonstrated that romosozumab is effective in rapidly increasing bone mineral density (BMD) and decreasing risk of vertebral, non-vertebral and hip fractures in post-menopausal women at very-high risk of fractures. In male osteoporosis, only data on BMD are available. Noteworthy, romosozumab was shown to be more effective and rapid than teriparatide in improving BMD, bone structure and strength at the hip, especially in women already treated with anti-resorptive drugs. Interestingly, even if romosozumab displays best results in treatment-naïve patients, its favourable effects on BMD were observed even in women previously treated with teriparatide or denosumab, although to a lesser extent.

CONCLUSIONS

Based on the available evidence, romosozumab could be proposed as ideal drug in several clinical settings, such as non-fractured post-menopausal women at very-high risk of fractures, patients with recent hip fracture, patients non responder to bisphosphonates and short-term denosumab therapy.

Plasma Sclerostin Levels in Rheumatoid Arthritis Women on TNF-α Inhibitor Therapy

Rheumatoid arthritis (RA) is associated with significant systemic and local bone loss. The aim of this study was to assess whether or not 15-month tumor necrosis factor α inhibitor (TNFαI) therapy in combination with methotrexate (MTX) affects circulating levels of sclerostin (SOST) in female RA patients. Plasma levels of SOST were measured using immunoassays kits. Baseline SOST levels showed no significant differences between RA patients and control participants. Postmenopausal women with RA tended to have higher sclerostin levels than premenopausal woman with RA. After 15 months of treatment with TNFαI, plasma levels of SOST were decreased. Before starting biological therapy, circulating levels of SOST significantly correlated with the patient's age (p < 0.05) and the marker of inflammation, such as ESR (p < 0.05). Multivariate regression analysis showed that age was the only significant predictor for baseline SOST levels in women with RA (β = 0.008, p = 0.028, R2 model = 0.293). Moreover, a positive correlation between SOST levels and the 28 joint disease activity score value based on the erythrocyte sedimentation rate (DAS28-ESR) was found at baseline (p < 0.05), as well as after 15 months of biological therapy (p < 0.05). Thus, plasma SOST levels may be helpful for monitoring the efficacy of TNFαI treatment in RA patients. According to our results, TNFαI, in combination with MTX, has a beneficial effect on bone turnover with a significant reduction in bone metabolism marker SOST.

The Impact of Non-alcohol Fatty Liver Disease on Bone Mineral Density is Mediated by Sclerostin by Mendelian Randomization Study

Non-alcoholic fatty liver disease (NAFLD) has been found to be associated with osteoporosis (OP) in observational studies. However, the precise causal relationship between NAFLD and OP remains unclear. Here, we used Mendelian randomization (MR) to explore the causal relationship. We selected NAFLD-related single-nucleotide polymorphisms from a genome-wide meta-analysis (8434 cases and 434,770 controls) as instrumental variants. We used inverse variance weighted analysis for the primary MR analysis. Furthermore, we used similar methodologies in parallel investigations of other chronic liver diseases (CLDs). We performed sensitivity analyses to ensure the reliability of the results. We observed a causality between NAFLD and forearm bone mineral density (FABMD) (beta-estimate [β]: - 0.212; p-value: 0.034). We also found that sclerostin can act as a mediator to influence the NAFLD and FABMD pathways to form a mediated MR network (mediated proportion = 8.8%). We also identified indications of causal relationships between other CLDs and OP. However, we were unable to establish any associated mediators. Notably, our analyses did not yield any evidence of pleiotropy. Our findings have implications in the development of preventive and interventional measures aimed at managing low bone mineral density in patients with NAFLD.

In vitro development and optimization of cell-laden injectable bioprinted gelatin methacryloyl (GelMA) microgels mineralized on the nanoscale

Bone defects may occur in different sizes and shapes due to trauma, infections, and cancer resection. Autografts are still considered the primary treatment choice for bone regeneration. However, they are hard to source and often create donor-site morbidity. Injectable microgels have attracted much attention in tissue engineering and regenerative medicine due to their ability to replace inert implants with a minimally invasive delivery. Here, we developed novel cell-laden bioprinted gelatin methacrylate (GelMA) injectable microgels, with controllable shapes and sizes that can be controllably mineralized on the nanoscale, while stimulating the response of cells embedded within the matrix. The injectable microgels were mineralized using a calcium and phosphate-rich medium that resulted in nanoscale crystalline hydroxyapatite deposition and increased stiffness within the crosslinked matrix of bioprinted GelMA microparticles. Next, we studied the effect of mineralization in osteocytes, a key bone homeostasis regulator. Viability stains showed that osteocytes were maintained at 98 % viability after mineralization with elevated expression of sclerostin in mineralized compared to non-mineralized microgels, showing that mineralization can effectively enhances osteocyte maturation. Based on our findings, bioprinted mineralized GelMA microgels appear to be an efficient material to approximate the bone microarchitecture and composition with desirable control of sample injectability and polymerization. These bone-like bioprinted mineralized biomaterials are exciting platforms for potential minimally invasive translational methods in bone regenerative therapies.

Research Progress on the Mechanism of the SFRP-Mediated Wnt Signalling Pathway Involved in Bone Metabolism in Osteoporosis

Osteoporosis (OP) is a metabolic bone disease linked to an elevated fracture risk, primarily stemming from disruptions in bone metabolism. Present clinical treatments for OP merely alleviate symptoms. Hence, there exists a pressing need to identify novel targets for the clinical treatment of OP. Research indicates that the Wnt signalling pathway is modulated by serum-secreted frizzled-related protein 5 (SFRP5), potentially serving as a pivotal regulator in bone metabolism disorders. Moreover, studies confirm elevated SFRP5 expression in OP, with SFRP5 overexpression leading to the downregulation of Wnt and β-catenin proteins in the Wnt signalling pathway, as well as the expression of osteogenesis-related marker molecules such as RUNX2, ALP, and OPN. Conversely, the opposite has been reported when SFRP5 is knocked out, suggesting that SFRP5 may be a key factor involved in the regulation of bone metabolism via the Wnt signalling axis. However, the molecular mechanisms underlying the action of SFRP5-induced OP have yet to be comprehensively elucidated. This review focusses on the molecular structure and function of SFRP5 and the potential molecular mechanisms of the SFRP5-mediated Wnt signalling pathway involved in bone metabolism in OP, providing reasonable evidence for the targeted therapy of SFRP5 for the prevention and treatment of OP.

Femoral neck width genetic risk score is a novel independent risk factor for hip fractures

Femoral neck width (FNW) derived from DXA scans may provide a useful adjunct to hip fracture prediction. Therefore, we investigated whether FNW is related to hip fracture risk independently of femoral neck bone mineral density (FN-BMD), using a genetic approach. FNW was derived from points automatically placed on the proximal femur using hip DXA scans from 38 150 individuals (mean age 63.8 yr, 48.0% males) in UK Biobank (UKB). Genome-wide association study (GWAS) identified 71 independent genome-wide significant FNW SNPs, comprising genes involved in cartilage differentiation, hedgehog, skeletal development, in contrast to SNPs identified by FN-BMD GWAS which primarily comprised runx1/Wnt signaling genes (MAGMA gene set analyses). FNW and FN-BMD SNPs were used to generate genetic instruments for multivariable Mendelian randomization. Greater genetically determined FNW increased risk of all hip fractures (odds ratio [OR] 1.53; 95% CI, 1.29-1.82 per SD increase) and femoral neck fractures (OR 1.58;1.30-1.92), but not trochanteric or forearm fractures. In contrast, greater genetically determined FN-BMD decreased fracture risk at all 4 sites. FNW and FN-BMD SNPs were also used to generate genetic risk scores (GRSs), which were examined in relation to incident hip fracture in UKB (excluding the FNW GWAS population; n = 338 742, 3222 cases) using a Cox proportional hazards model. FNW GRS was associated with increased risk of all incident hip fractures (HR 1.08;1.05-1.12) and femoral neck fractures (hazard ratio [HR] 1.10;1.06-1.15), but not trochanteric fractures, whereas FN-BMD GRS was associated with reduced risk of all hip fracture types. We conclude that the underlying biology regulating FNW and FN-BMD differs, and that DXA-derived FNW is causally related to hip fractures independently of FN-BMD, adding information beyond FN-BMD for hip fracture prediction. Hence, FNW derived from DXA analyses or a FNW GRS may contribute clinically useful information beyond FN-BMD for hip fracture prediction.

El diálogo oculto entre el hueso y los tejidos a través del remodelado óseo

El hueso es mucho más que un reservorio de calcio y fósforo. Su disposición lacuno-canalicular ofrece una importante vía de intercambio con la circulación y actualmente, el esqueleto se considera un gran órgano endocrino, con acciones que van más allá del control del balance fosfocálcico mediado por el factor fibroblástico 23 (FGF23). Paralelamente al efecto modulador de las adipoquinas sobre el remodelado óseo, diversas proteínas óseas, como la osteocalcina y la esclerostina, ejercen cierta acción contra-reguladora sobre el metabolismo energético, posiblemente en un intento de asegurar los enormes requerimientos energéticos del remodelado. En esta interacción del hueso con otros tejidos, especialmente el adiposo, participa la señalización canónica Wnt/β-catenina y por ello la esclerostina, una proteína osteocítica que inhibe esta señalización, emerge como un potencial biomarcador. Es más, su participación en diversas patologías le posiciona como diana terapéutica, existiendo un anticuerpo anti-esclerostina, recientemente aprobado en nuestro país para el tratamiento de la osteoporosis. Esta revisión aborda el carácter endocrino del hueso, el papel de la osteocalcina y, especialmente, el papel regulador y modulador de la esclerostina sobre remodelado óseo y la homeóstasis energética a través de su interacción con la señalización canónica Wnt/β-catenina, así como su potencial utilidad como biomarcador.

The hidden cross talk between bone and tissues through bone turnover

Bone is more than a reservoir of calcium and phosphorus. Its lacuno-canalicular arrangement provides an important pathway for exchange with circulation and currently, the skeleton is considered a large endocrine organ with actions that go beyond the control of calcium-phosphorus balance mediated by fibroblastic growth factor 23 (FGF23). Parallel to the modulating effect of adipokines on bone turnover, certain bone proteins, such as osteocalcin and sclerostin, play a counter-regulatory role on energy metabolism, probably in an attempt to ensure its high energy requirement for bone turnover. In this crosstalk between bone and other tissues, especially with adipose tissue, canonical Wnt/β-catenin signaling is involved and therefore, sclerostin, an osteocyte derived protein that inhibits this signalling, emerges as a potential biomarker. Furthermore, its involvement in diverse pathologic conditions supports sclerostin as a therapeutic target, with an anti-sclerostin antibody recently approved in our country for the treatment of osteoporosis. This review addresses the endocrine nature of bone, the role of osteocalcin, and specially, the regulatory and modulatory role of sclerostin on bone turnover and energy homeostasis through its inhibitory effect on canonical Wnt/β-catenin signaling, as well as its potential utility as a biomarker.

Insights and implications of sexual dimorphism in osteoporosis

Osteoporosis, a metabolic bone disease characterized by low bone mineral density and deterioration of bone microarchitecture, has led to a high risk of fatal osteoporotic fractures worldwide. Accumulating evidence has revealed that sexual dimorphism is a notable feature of osteoporosis, with sex-specific differences in epidemiology and pathogenesis. Specifically, females are more susceptible than males to osteoporosis, while males are more prone to disability or death from the disease. To date, sex chromosome abnormalities and steroid hormones have been proven to contribute greatly to sexual dimorphism in osteoporosis by regulating the functions of bone cells. Understanding the sex-specific differences in osteoporosis and its related complications is essential for improving treatment strategies tailored to women and men. This literature review focuses on the mechanisms underlying sexual dimorphism in osteoporosis, mainly in a population of aging patients, chronic glucocorticoid administration, and diabetes. Moreover, we highlight the implications of sexual dimorphism for developing therapeutics and preventive strategies and screening approaches tailored to women and men. Additionally, the challenges in translating bench research to bedside treatments and future directions to overcome these obstacles will be discussed.

Bone metabolism and inflammatory biomarkers in radiographic and non-radiographic axial spondyloarthritis patients: a comprehensive evaluation

Introduction

Axial spondyloarthritis (axSpA) is a heterogeneous disease that can be represented by radiographic axSpA (r-axSpA) and non-radiographic axSpA (nr-axSpA). This study aimed to evaluate the relationship between the markers of inflammation and bone turnover in r-axSpA patients and nr-axSpA patients.

Methods

A cross-sectional study included 29 r-axSpA patients, 10 nr-axSpA patients, and 20 controls matched for age and sex. Plasma markers related to bone remodeling such as human procollagen type 1 N-terminal propeptide (P1NP), sclerostin, tartrate-resistant acid phosphatase 5b (TRACP5b), receptor activator of nuclear factor kappa B ligand (RANKL), and osteoprotegerin (OPG) were measured by an ELISA kit. A panel of 92 inflammatory molecules was analyzed by proximity extension assay.

Results

R-axSpA patients had decreased plasma levels of P1NP, a marker of bone formation, compared to controls. In addition, r-axSpA patients exhibited decreased plasma levels of sclerostin, an anti-anabolic bone hormone, which would not explain the co-existence of decreased plasma P1NP concentration; however, sclerostin levels could also be influenced by inflammatory processes. Plasma markers of osteoclast activity were similar in all groups. Regarding inflammation-related molecules, nr-axSpA patients showed increased levels of serum interleukin 13 (IL13) as compared with both r-axSpA patients and controls, which may participate in the prevention of inflammation. On the other hand, r-axSpA patients had higher levels of pro-inflammatory molecules compared to controls (i.e., IL6, Oncostatin M, and TNF receptor superfamily member 9). Correlation analysis showed that sclerostin was inversely associated with IL6 and Oncostatin M among others.

Conclusion

Altogether, different inflammatory profiles may play a role in the development of the skeletal features in axSpA patients particularly related to decreased bone formation. The relationship between sclerostin and inflammation and the protective actions of IL13 could be of relevance in the axSpA pathology, which is a topic for further investigation.

Mind the Gap: Unraveling the Intricate Dance Between Alzheimer's Disease and Related Dementias and Bone Health

PURPOSE OF REVIEW

This review examines the linked pathophysiology of Alzheimer's disease/related dementia (AD/ADRD) and bone disorders like osteoporosis. The emphasis is on "inflammaging"-a low-level inflammation common to both, and its implications in an aging population.

RECENT FINDINGS

Aging intensifies both ADRD and bone deterioration. Notably, ADRD patients have a heightened fracture risk, impacting morbidity and mortality, though it is uncertain if fractures worsen ADRD. Therapeutically, agents targeting inflammation pathways, especially Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) and TNF-α, appear beneficial for both conditions. Additionally, treatments like Sirtuin 1 (SIRT-1), known for anti-inflammatory and neuroprotective properties, are gaining attention. The interconnectedness of AD/ADRD and bone health necessitates a unified treatment approach. By addressing shared mechanisms, we can potentially transform therapeutic strategies, enriching our understanding and refining care in our aging society. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

SiJunZi decoction ameliorates bone quality and redox homeostasis and regulates advanced glycation end products/receptor for advanced glycation end products and WNT/β-catenin signaling pathways in diabetic mice

ETHNOPHARMACOLOGICAL RELEVANCE

SiJunZi decoction (SJZD), one of the traditional Chinese medicine formulas, has been clinically and traditionally used to improve glucose and lipid metabolism and promote bone remodeling.

AIM OF THE STUDY

To study the actions and mechanisms of SJZD on bone remodeling in a type 2 diabetes mouse model.

MATERIALS AND METHODS

Diabetic mice generated with a high-fat diet (HFD) and streptozotocin (STZ) were subjected to SJZD treatment for 8 weeks. Blood glucose and lipid profile, redox status and bone metabolism were determined by ELISA or biochemical assays. Bone quality was evaluated by micro-CT, three-point bending assay and Fourier transform infrared spectrum (FTIR). Bone histomorphometry alterations were evaluated by Hematoxylin-Eosin (H&E), tartrate resistant acid phosphatase (TRAP) staining and Safranin O-fast green staining. The expressions of superoxide dismutase 1 (SOD1), advanced glycation end products (AGEs), receptor for advanced glycosylation end products (RAGE), phosphorylated nuclear factor kappa-B (p-NF-κB), NF-κB, cathepsin K, semaphorin 3A (Sema3A), insulin-like growth factor 1 (IGF1), p-GSK-3β, (p)-β-catenin, Runt-related transcription factor 2 (Runx2) and Cyclin D1 in the femurs and/or tibias were examined by Western blot or immunohistochemical staining. The main constituents in the SJZD aqueous extract were characterized by a HPLC/MS.

RESULTS

SJZD intervention improved glucose and lipid metabolism and preserved bone quality in the diabetic mice, in particular glucose tolerance, lipid profile, bone microarchitecture, strength and material composition. SJZD administration to diabetic mice preserved redox homeostasis in serum and bone marrow, and prevented an increase in AGEs, RAGE, p-NF-κB/NF-κB, cathepsin K, p-GSK-3β, p-β-catenin expressions and a decrease in Sema3A, IGF1, β-catenin, Runx2 and Cyclin D1 expressions in tibias and/or femurs. Thirteen compounds were identified in SJZD aqueous extract, including astilbin, liquiritin apioside, ononin, ginsenoside Re, Rg1, Rb1, Rb2, Ro, Rb3, Rd, notoginsenoside R2, glycyrrhizic acid, and licoricesaponin B2.

CONCLUSIONS

SJZD ameliorates bone quality in diabetic mice possibly via maintaining redox homeostasis. The mechanism governing these alterations are possibly related to effects on the AGEs/RAGE and Wnt/β-catenin signaling pathways. SJZD may offer a novel source of drug candidates for the prevention and treatment of type 2 diabetes and osteoporosis.

Diabetic peripheral neuropathy: pathogenetic mechanisms and treatment

Diabetic peripheral neuropathy (DPN) refers to the development of peripheral nerve dysfunction in patients with diabetes when other causes are excluded. Diabetic distal symmetric polyneuropathy (DSPN) is the most representative form of DPN. As one of the most common complications of diabetes, its prevalence increases with the duration of diabetes. 10-15% of newly diagnosed T2DM patients have DSPN, and the prevalence can exceed 50% in patients with diabetes for more than 10 years. Bilateral limb pain, numbness, and paresthesia are the most common clinical manifestations in patients with DPN, and in severe cases, foot ulcers can occur, even leading to amputation. The etiology and pathogenesis of diabetic neuropathy are not yet completely clarified, but hyperglycemia, disorders of lipid metabolism, and abnormalities in insulin signaling pathways are currently considered to be the initiating factors for a range of pathophysiological changes in DPN. In the presence of abnormal metabolic factors, the normal structure and function of the entire peripheral nervous system are disrupted, including myelinated and unmyelinated nerve axons, perikaryon, neurovascular, and glial cells. In addition, abnormalities in the insulin signaling pathway will inhibit neural axon repair and promote apoptosis of damaged cells. Here, we will discuss recent advances in the study of DPN mechanisms, including oxidative stress pathways, mechanisms of microvascular damage, mechanisms of damage to insulin receptor signaling pathways, and other potential mechanisms associated with neuroinflammation, mitochondrial dysfunction, and cellular oxidative damage. Identifying the contributions from each pathway to neuropathy and the associations between them may help us to further explore more targeted screening and treatment interventions.

Exploring the Role of Wnt Ligands in Osteogenic Differentiation of Human Periodontal Ligament Stem Cells

OBJECTIVES

This study aimed to investigate the functions of 19 types of Wnt ligands during the process of osteogenic differentiation in human periodontal ligament stem cells (hPDLSCs), with particular attention to WNT3A and WNT4.

MATERIALS AND METHODS

The expression levels of 19 types of Wnt ligands were examined using real-time quantitative polymerase chain reaction (real-time qPCR) during hPDLSCs osteogenic differentiation at 7, 10, and 14 days. Knockdown of WNT3A and WNT4 expression was achieved using adenovirus vectors, and conditioned medium derived from WNT3A and WNT4 overexpression plasmids was employed to investigate their roles in hPDLSCs osteogenesis. Osteogenic-specific genes were analyzed using real-time qPCR. Alkaline phosphatase (ALP) and alizarin red S activities and staining were employed to assess hPDLSCs' osteogenic differentiation ability.

RESULTS

During hPDLSCs osteogenic differentiation, the expression of 19 types of Wnt ligands varied, with WNT3A and WNT4 showing significant upregulation. Inhibiting WNT3A and WNT4 expression hindered hPDLSCs' osteogenic capacity. Conditioned medium of WNT3A promoted early osteogenic differentiation, while WNT4 facilitated late osteogenesis slightly.

CONCLUSION

Wnt ligands, particularly WNT3A and WNT4, play an important role in hPDLSCs' osteogenic differentiation, highlighting their potential as promoters of osteogenesis.

CLINICAL RELEVANCE

Given the challenging nature of alveolar bone regeneration, therapeutic strategies that target WNT3A and WNT4 signaling pathways offer promising opportunities. Additionally, innovative gene therapy approaches aimed at regulating of WNT3A and WNT4 expression hold potential for improving alveolar bone regeneration outcomes.

The Emerging Role of Interleukin-(IL)-11/IL-11R in Bone Metabolism and Homeostasis: From Cytokine to Osteokine

Interleukin-(IL)-11 is a cytokine involved in hematopoiesis, cancer metastasis, and inflammation. IL-11 belongs to the IL-6 cytokine family, binding to the complex of receptors glycoprotein gp130 and the ligand-specific-receptor subunits (IL-11Rα or their soluble counterpart sIL-11R). IL-11/IL-11R signaling enhances osteoblast differentiation and bone formation and mitigates osteoclast-induced bone resorption and cancer bone metastasis. Recent studies have shown that systemic and osteoblast/osteocyte-specific IL-11 deficiency leads to reduced bone mass and formation, but also adiposity, glucose intolerance, and insulin resistance. In humans, mutations of IL-11 and the receptor IL-11RA genes are associated with height reduction, osteoarthritis, and craniosynostosis. In this review, we describe the emerging role of IL-11/IL-11R signaling in bone metabolism by targeting osteoblasts, osteoclasts, osteocytes, and bone mineralization. Furthermore, IL-11 promotes osteogenesis and suppresses adipogenesis, thereby influencing the fate of osteoblast/adipocyte differentiation derived from pluripotent mesenchymal stem cells. We have newly identified IL-11 as a bone-derived cytokine that regulates bone metabolism and the link between bone and other organs. Thus, IL-11 is vital in bone homeostasis and could be considered a potential therapeutic strategy.

The Wnt/β-catenin signaling pathway inhibits osteoporosis by regulating the expression of TERT: an in vivo and in vitro study

Our study was performed to investigate whether the Wingless and int-1 (Wnt) signaling pathway promotes osteogenic differentiation and inhibits apoptosis in bone marrow mesenchymal stem cells (BMSCs) by regulating telomerase reverse transcriptase (TERT) expression. An in vivo model of osteoporosis (OP) in C57BL/6J mice by bilateral ovariectomy (OVX) and an in vitro model of H2O2-induced BMSCs were established separately. Western blotting was used to detect the expression of the pathway-related proteins TERT, β-catenin, and phosphorylated-glycogen synthase kinase-3beta (p-GSK3β)/GSK3β, the osteogenic-related markers osteopontin (OPN), bone morphogenetic protein 2 (BMP2), and runt-related transcription factor 2 (Runx2), and the apoptosis-related indicators B-cell lymphoma-2 (Bcl-2) and BAX. Osteoblastic phenotypes were also evaluated by alkaline phosphatase (ALP) staining and serum ALP activity assays. Osteogenic differentiation phenotypes in mice were verified by H&E staining, micro-CT, and parameter analysis of the femur. Western blotting results showed that the expression of the pathway-related proteins TERT, β-catenin, p-GSK3β/GSK3β was reduced in OVX mice and H2O2-induced BMSCs, accompanied by downregulated protein expression of osteogenic-related markers and antiapoptotic indicators and upregulated protein expression of apoptotic proteins compared to those in the control group. Mechanistic studies showed that the activation of Wnt signaling pathway in BMSCs promoted β-catenin translocation to the nucleus, as verified by immunofluorescence and facilitated colocalization between β-catenin and TERT, as verified by double-labeling immunofluorescence, thereby promoting osteogenic differentiation and reducing apoptosis. In summary, our experiments confirmed that the GSK3β/β-catenin/TERT pathway could regulate the osteogenic differentiation and apoptosis of BMSCs and that TERT might be a promising target for the future treatment of osteoporosis.

Gingival crevicular fluid periodontal ligament-associated protein-1, sclerostin, and tumor necrosis factor-alpha levels in periodontitis

BACKGROUND

In periodontitis, the equilibrium between bone formation and resorption skews in favor of bone loss. Periodontal ligament-associated protein-1 (PLAP-1) and sclerostin play a significant role in the suppression of bone formation. Tumor necrosis factor-alpha (TNF-α) is a central proinflammatory cytokine related to periodontal bone loss. This study aims to assess gingival crevicular fluid (GCF) PLAP-1, sclerostin, and TNF-α levels in individuals with periodontal disease.

METHODS

Seventy-one individuals diagnosed with generalized stage III grade C periodontitis (n = 23), gingivitis (n = 24), and periodontal health (n = 24) were included in the study. Full-mouth clinical periodontal measurements were performed. PLAP-1, sclerostin, and TNF-α total amounts in GCF were quantified by ELISA. Nonparametric methods were used for the data analyses.

RESULTS

Periodontitis group exhibited significantly higher GCF PLAP-1, sclerostin and TNF-α levels compared with gingivitis and periodontally healthy groups (p < 0.05). GCF PLAP-1 and TNF-α levels of gingivitis group were higher than healthy controls (p < 0.05) whereas GCF sclerostin levels were similar in two groups (p > 0.05). Significant positive correlations were found between GCF PLAP-1, sclerostin and TNF-α levels and all clinical parameters (p < 0.01).

CONCLUSIONS

To our knowledge, this is the first study showing GCF PLAP-1 levels in periodontal health and disease. Increased GCF PLAP-1 and sclerostin levels and their correlations with TNF-α in periodontitis imply that those molecules might be involved in the pathogenesis of periodontal disease. Further studies in larger mixed cohorts are needed to enlighten the possible role of PLAP-1 and sclerostin in periodontal bone loss.

LRP5, Bone Mass Polymorphisms and Skeletal Disorders

The formation and maintenance of the gross structure and microarchitecture of the human skeleton require the concerted functioning of a plethora of morphogenic signaling processes. Through recent discoveries in the field of genetics, numerous genotypic variants have been implicated in pathologic skeletal phenotypes and disorders arising from the disturbance of one or more of these processes. For example, total loss-of-function variants of LRP5 were found to be the cause of osteoporosis-pseudoglioma syndrome (OPPG). LRP5 encodes for the low-density lipoprotein receptor-related protein 5, a co-receptor in the canonical WNT-β-catenin signaling pathway and a crucial protein involved in the formation and maintenance of homeostasis of the human skeleton. Beyond OPPG, other partial loss-of-function variants of LRP5 have been found to be associated with other low bone mass phenotypes and disorders, while LRP5 gain-of-function variants have been implicated in high bone mass phenotypes. This review introduces the roles that LRP5 plays in skeletal morphogenesis and discusses some of the structural consequences that result from abnormalities in LRP5. A greater understanding of how the LRP5 receptor functions in bone and other body tissues could provide insights into a variety of pathologies and their potential treatments, from osteoporosis and a variety of skeletal abnormalities to congenital disorders that can lead to lifelong disabilities.

Common miRNAs of Osteoporosis and Fibromyalgia: A Review

A significant clinical association between osteoporosis (OP) and fibromyalgia (FM) has been shown in the literature. Given the need for specific biomarkers to improve OP and FM management, common miRNAs might provide promising tracks for future prevention and treatment. The aim of this review is to identify miRNAs described in OP and FM, and dysregulated in the same direction in both pathologies. The PubMed database was searched until June 2023, with a clear mention of OP, FM, and miRNA expression. Clinical trials, case-control, and cross-sectional studies were included. Gray literature was not searched. Out of the 184 miRNAs found in our research, 23 are shared by OP and FM: 7 common miRNAs are dysregulated in the same direction for both pathologies (3 up-, 4 downregulated). The majority of these common miRNAs are involved in the Wnt pathway and the cholinergic system and a possible link has been highlighted. Further studies are needed to explore this relationship. Moreover, the harmonization of technical methods is necessary to confirm miRNAs shared between OP and FM.

Review on the protective activity of osthole against the pathogenesis of osteoporosis

Osteoporosis (OP), characterized by continuous bone loss and increased fracture risk, has posed a challenge to patients and society. Long-term administration of current pharmacological agents may cause severe side effects. Traditional medicines, acting as alternative agents, show promise in treating OP. Osthole, a natural coumarin derivative separated from Cnidium monnieri (L.) Cusson and Angelica pubescens Maxim. f., exhibits protective effects against the pathological development of OP. Osthole increases osteoblast-related bone formation and decreases osteoclast-related bone resorption, suppressing OP-related fragility fracture. In addition, the metabolites of osthole may exhibit pharmacological effectiveness against OP development. Mechanically, osthole promotes osteogenic differentiation by activating the Wnt/β-catenin and BMP-2/Smad1/5/8 signaling pathways and suppresses RANKL-induced osteoclastogenesis and osteoclast activity. Thus, osthole may become a promising agent to protect against OP development. However, more studies should be performed due to, at least in part, the uncertainty of drug targets. Further pharmacological investigation of osthole in OP treatment might lead to the development of potential drug candidates.

Alzheimer's disease and its associated risk of bone fractures: a narrative review

Background

Alzheimer's disease (AD) is a neurodegenerative disorder that is the major cause of dementia in the aged population. Recent researches indicate that patients with AD have a significantly increased fracture risk, but the pathological mechanisms are still unclear.

Objective

We systematically reviewed studies regarding bone fracture risk in AD to uncover links between the pathologies of osteoporosis and AD.

Methods

We searched the literature using the databases of PubMed, Web of Science, Embase and Cochrane Library. Studies were included if they evaluated bone fracture risk in AD patients and if they explored the pathogenesis and prevention of bone fractures in these patients.

Results

AD patients had a significantly higher risk of bone fractures than age-matched controls. Multiple factors contributed to the increased risk of bone fractures in AD patients, including the direct effects of amyloid pathology on bone cells, abnormal brain-bone interconnection, Wnt/β-catenin signalling deficits, reduced activity, high risk of falls and frailty, and chronic immune activity. Exercise, prevention of falls and fortified nutrition were beneficial for reducing the fracture risk in AD patients. However, the efficacy of anti-osteoporotic agents in preventing bone fractures should be further evaluated in AD patients as corresponding clinical studies are very scarce.

Conclusion

Alzheimer's disease patients have increased bone fracture risk and decreased bone mineral density owing to multiple factors. Assessment of anti-osteoporotic agents' efficacy in preventing bone fractures of AD patients is urgently needed.

Targeting signaling pathways in osteosarcoma: Mechanisms and clinical studies

Osteosarcoma (OS) is a highly prevalent bone malignancy among adolescents, accounting for 40% of all primary malignant bone tumors. Neoadjuvant chemotherapy combined with limb-preserving surgery has effectively reduced patient disability and mortality, but pulmonary metastases and OS cells' resistance to chemotherapeutic agents are pressing challenges in the clinical management of OS. There has been an urgent need to identify new biomarkers for OS to develop specific targeted therapies. Recently, the continued advancements in genomic analysis have contributed to the identification of clinically significant molecular biomarkers for diagnosing OS, acting as therapeutic targets, and predicting prognosis. Additionally, the contemporary molecular classifications have revealed that the signaling pathways, including Wnt/β-catenin, PI3K/AKT/mTOR, JAK/STAT3, Hippo, Notch, PD-1/PD-L1, MAPK, and NF-κB, have an integral role in OS onset, progression, metastasis, and treatment response. These molecular classifications and biological markers have created new avenues for more accurate OS diagnosis and relevant treatment. We herein present a review of the recent findings for the modulatory role of signaling pathways as possible biological markers and treatment targets for OS. This review also discusses current OS therapeutic approaches, including signaling pathway-based therapies developed over the past decade. Additionally, the review covers the signaling targets involved in the curative effects of traditional Chinese medicines in the context of expression regulation of relevant genes and proteins through the signaling pathways to inhibit OS cell growth. These findings are expected to provide directions for integrating genomic, molecular, and clinical profiles to enhance OS diagnosis and treatment.

Dietary intervention reprograms bone marrow cellular signaling in obese mice

Objectives

The current study aimed to investigate the pathogenesis of obesity-induced impaired bone mass accrual and the impact of dietary intervention on bone density in the mouse model of obesity.

Methods

Mice were fed with chow diet (CD) for 10 months, high-fat-diet (HFD) for 10 months, or HFD for 6 months then transferred to chow diet for 4 months (HFDt).

Results

Weight loss and decreased intrahepatic lipid accumulation were observed in mice following dietary intervention. Additionally, HFD feeding induced bone mass accrual, while diet intervention restrained trabecular bone density. These changes were further reflected by increased osteogenesis and decreased adipogenesis in HFDt mice compared to HFD mice. Furthermore, HFD feeding decreased the activity of the Wingless-related integration site (Wnt)-β-Catenin signaling pathway, while the Wnt signaling was augmented by diet intervention in the HFDt group.

Conclusions

Our findings suggest that a HFD inhibits bone formation and that dietary intervention reverses this inhibition. Furthermore, the dietary intervention was able to compensate for the suppressed increase in bone mass to a level comparable to that in the CD group. Our study suggests that targeting the Wnt signaling pathway may be a potential approach to treat obesity-induced impaired bone mass accrual.

PCDH7 as the key gene related to the co-occurrence of sarcopenia and osteoporosis

Sarcopenia and osteoporosis, two degenerative diseases in older patients, have become severe health problems in aging societies. Muscles and bones, the most important components of the motor system, are derived from mesodermal and ectodermal mesenchymal stem cells. The adjacent anatomical relationship between them provides the basic conditions for mechanical and chemical signals, which may contribute to the co-occurrence of sarcopenia and osteoporosis. Identifying the potential common crosstalk genes between them may provide new insights for preventing and treating their development. In this study, DEG analysis, WGCNA, and machine learning algorithms were used to identify the key crosstalk genes of sarcopenia and osteoporosis; this was then validated using independent datasets and clinical samples. Finally, four crosstalk genes (ARHGEF10, PCDH7, CST6, and ROBO3) were identified, and mRNA expression and protein levels of PCDH7 in clinical samples from patients with sarcopenia, with osteoporosis, and with both sarcopenia and osteoporosis were found to be significantly higher than those from patients without sarcopenia or osteoporosis. PCDH7 seems to be a key gene related to the development of both sarcopenia and osteoporosis.

Genetic insight into the putative causal proteins and druggable targets of osteoporosis: a large-scale proteome-wide mendelian randomization study

Background: Osteoporosis is a major causative factor of the global burden of disease and disability, characterized by low bone mineral density (BMD) and high risks of fracture. We aimed to identify putative causal proteins and druggable targets of osteoporosis. Methods: This study utilized the largest GWAS summary statistics on plasma proteins and estimated heel BMD (eBMD) to identify causal proteins of osteoporosis by mendelian randomization (MR) analysis. Different GWAS datasets were used to validate the results. Multiple sensitivity analyses were conducted to evaluate the robustness of primary MR findings. We have also performed an enrichment analysis for the identified causal proteins and evaluated their druggability. Results: After Bonferroni correction, 67 proteins were identified to be causally associated with estimated BMD (eBMD) (p < 4 × 10^-5). We further replicated 38 of the 67 proteins to be associated with total body BMD, lumbar spine BMD, femoral neck BMD as well as fractures, such as RSPO3, IDUA, SMOC2, and LRP4. The findings were supported by sensitivity analyses. Enrichment analysis identified multiple Gene Ontology items, including collagen-containing extracellular matrix (GO:0062023, p = 1.6 × 10^-10), collagen binding (GO:0005518, p = 8.6 × 10^-5), and extracellular matrix structural constituent (GO:0005201, p = 2.7 × 10^-5). Conclusion: The study identified novel putative causal proteins for osteoporosis which may serve as potential early screening biomarkers and druggable targets. Furthermore, the role of plasma proteins involved in collagen binding and extracellular matrix in the development of osteoporosis was highlighted. Further studies are warranted to validate our findings and investigate the underlying mechanism.

Mature primary human osteocytes in mini organotypic cultures secrete FGF23 and PTH1-34-regulated sclerostin

Introduction

For decades, functional primary human osteocyte cultures have been crucially needed for understanding their role in bone anabolic processes and in endocrine phosphate regulation via the bone-kidney axis. Mature osteocyte proteins (sclerostin, DMP1, Phex and FGF23) play a key role in various systemic diseases and are targeted by successful bone anabolic drugs (anti-sclerostin antibody and teriparatide (PTH1-34)). However, cell lines available to study osteocytes produce very little sclerostin and low levels of mature osteocyte markers. We have developed a primary human 3D organotypic culture system that replicates the formation of mature osteocytes in bone.

Methods

Primary human osteoblasts were seeded in a fibrinogen / thrombin gel around 3D-printed hanging posts. Following contraction of the gel around the posts, cells were cultured in osteogenic media and conditioned media was collected for analysis of secreted markers of osteocyte formation.

Results

The organoids were viable for at least 6 months, allowing co-culture with different cell types and testing of bone anabolic drugs. Bulk RNAseq data displayed the developing marker trajectory of ossification and human primary osteocyte formation in vitro over an initial 8- week period. Vitamin D3 supplementation increased mineralization and sclerostin secretion, while hypoxia and PTH1-34 modulated sclerostin. Our culture system also secreted FGF23, enabling the future development of a bone-kidney-parathyroid-vascular multi-organoid or organ-on-a-chip system to study disease processes and drug effects using purely human cells.

Discussion

This 3D organotypic culture system provides a stable, long-lived, and regulated population of mature human primary osteocytes for a variety of research applications.

Laser-Modified Ti Surface Improves Paracrine Osteogenesis by Modulating the Expression of DKK1 in Osteoblasts

Titanium surface modifications are widely used to modulate cellular behavior by recognition of topographical cues. However, how those modifications affect the expression of mediators that will influence neighboring cells is still elusive. This study aimed to evaluate the effects of conditioned media from osteoblasts cultured on laser-modified titanium surfaces on the differentiation of bone marrow cells in a paracrine manner and to analyze the expression of Wnt pathway inhibitors. Mice calvarial osteoblasts were seeded on polished (P) and Yb:YAG laser-irradiated (L) Ti surfaces. Osteoblast culture media were collected and filtered on alternate days to stimulate mice BMCs. Resazurin assay was performed every other day for 20 days to check BMC viability and proliferation. After 7 and 14 days of BMCs maintained with osteoblasts P and L-conditioned media, alkaline phosphatase activity, Alizarin Red staining, and RT-qPCR were performed. ELISA of conditioned media was conducted to investigate the expression of Wnt inhibitors Dickkopf-1 (DKK1) and Sclerostin (SOST). BMCs showed increased mineralized nodule formation and alkaline phosphatase activity. The L-conditioned media enhanced the BMC mRNA expression of bone-related markers Bglap, Alpl, and Sp7. L-conditioned media decreased the expression of DKK1 compared with P-conditioned media. The contact of osteoblasts with Yb:YAG laser-modified Ti surfaces induces the regulation of the expression of mediators that affect the osteoblastic differentiation of neighboring cells. DKK1 is among these regulated mediators.

Ubiquitin-specific peptidases: Players in bone metabolism

Osteoporosis is an ageing-related disease, that has become a major public health problem and its pathogenesis has not yet been fully elucidated. Substantial evidence suggests a strong link between overall age-related disease progression and epigenetic modifications throughout the life cycle. As an important epigenetic modification, ubiquitination is extensively involved in various physiological processes, and its role in bone metabolism has attracted increasing attention. Ubiquitination can be reversed by deubiquitinases, which counteract protein ubiquitination degradation. As the largest and most structurally diverse cysteinase family of deubiquitinating enzymes, ubiquitin-specific proteases (USPs), comprising the largest and most structurally diverse cysteine kinase family of deubiquitinating enzymes, have been found to be important players in maintaining the balance between bone formation and resorption. The aim of this review is to explore recent findings highlighting the regulatory functions of USPs in bone metabolism and provide insight into the molecular mechanisms governing their actions during bone loss. An in-deep understanding of USPs-mediated regulation of bone formation and bone resorption will provide a scientific rationale for the discovery and development of novel USP-targeted therapeutic strategies for osteoporosis.

Role of Sostdc1 in skeletal biology and cancer

Sclerostin domain-containing protein-1 (Sostdc1) is a member of the sclerostin family and encodes a secreted 28–32 kDa protein with a cystine knot-like domain and two N-linked glycosylation sites. Sostdc1 functions as an antagonist to bone morphogenetic protein (BMP), mediating BMP signaling. It also interacts with LRP6, mediating LRP6 and Wnt signaling, thus regulating cellular proliferation, differentiation, and programmed cell death. Sostdc1 plays various roles in the skin, intestines, brain, lungs, kidneys, and vasculature. Deletion of Sostdc1 gene in mice resulted in supernumerary teeth and improved the loss of renal function in Alport syndrome. In the skeletal system, Sostdc1 is essential for bone metabolism, bone density maintenance, and fracture healing. Recently, Sostdc1 has been found to be closely related to the development and progression of multiple cancer types, including breast, renal, gastric, and thyroid cancers. This article summarises the role of Sostdc1 in skeletal biology and related cancers to provide a theoretical basis for the treatment of related diseases.