Osteosarcopenic adiposity (OSA) phenotype and its connection with cardiometabolic disorders: Is there a cause-and-effect?

The objectives were to examine if there is a causal relationship between osteosarcopenic adiposity (OSA) syndrome (coexistence of osteopenia/osteoporosis, sarcopenia, and excess adiposity) and cardiometabolic disorders or if these disorders initiate the development of OSA and its worsening. The search was conducted in PubMed, Scopus, and Web of Science to include articles up to the end of 2023. Of n=539 articles retrieved, n=15 met the eligibility criteria. Only studies conducted in adults and with all three body composition compartments (bone, muscle/lean, adipose) measured were considered. The results revealed that several cardiometabolic disorders, namely, hypertension, dyslipidemia (elevated total and LDL-cholesterol, lower HDL-cholesterol), insulin resistance, hyperglycemia, lower serum vitamin D, and some inflammatory markers were accompanied by OSA. In most cases, the OSA phenotype was associated with worse outcomes than cases with healthy or less impaired body composition. Our initial questions about the reciprocal cause-and-effect relationships could be surmised with more certainty for the OSA and some cardiovascular risks (hypertension, dyslipidemia) and some metabolic abnormalities (several inflammatory markers). The results of this review underscore the importance of body composition in health and from a clinical perspective, all three body composition compartments should be measured by standardized technologies using regulated diagnostic criteria to identify OSA. Randomized trials and prospective studies in diverse groups of older and younger individuals are necessary to determine if the relationships between OSA and clinical endpoints are causal and reversible through intervention and to uncover the mechanisms.

Proteomic Insights into Osteoporosis: Unraveling Diagnostic Markers of and Therapeutic Targets for the Metabolic Bone Disease.

Osteoporosis (OP), a prevalent skeletal disorder characterized by compromised bone strength and increased susceptibility to fractures, poses a significant public health concern. This review aims to provide a comprehensive analysis of the current state of research in the field, focusing on the application of proteomic techniques to elucidate diagnostic markers and therapeutic targets for OP. The integration of cutting-edge proteomic technologies has enabled the identification and quantification of proteins associated with bone metabolism, leading to a deeper understanding of the molecular mechanisms underlying OP. In this review, we systematically examine recent advancements in proteomic studies related to OP, emphasizing the identification of potential biomarkers for OP diagnosis and the discovery of novel therapeutic targets. Additionally, we discuss the challenges and future directions in the field, highlighting the potential impact of proteomic research in transforming the landscape of OP diagnosis and treatment.

Sdc4 deletion perturbs intervertebral disc matrix homeostasis and promotes early osteopenia in the aging mouse spine.

Syndecan 4 (SDC4), a cell surface heparan sulfate proteoglycan, is known to regulate matrix catabolism by nucleus pulposus cells in an inflammatory milieu. However, the role of SDC4 in the aging spine has never been explored. Here we analyzed the spinal phenotype of Sdc4 global knockout (KO) mice as a function of age. Micro-computed tomography showed that Sdc4 deletion severely reduced vertebral trabecular and cortical bone mass, and biomechanical properties of vertebrae were significantly altered in Sdc4 KO mice. These changes in vertebral bone were likely due to elevated osteoclastic activity. The histological assessment showed subtle phenotypic changes in the intervertebral disc. Imaging-Fourier transform-infrared analyses showed a reduced relative ratio of mature collagen crosslinks in young adult nucleus pulposus (NP) and annulus fibrosus (AF) of KO compared to wildtype discs. Additionally, relative chondroitin sulfate levels increased in the NP compartment of the KO mice. Transcriptomic analysis of NP tissue using CompBio, an AI-based tool showed biological themes associated with prominent dysregulation of heparan sulfate GAG degradation, mitochondria metabolism, autophagy, endoplasmic reticulum (ER)-associated misfolded protein processes and ER to Golgi protein processing. Overall, this study highlights the important role of SDC4 in fine-tuning vertebral bone homeostasis and extracellular matrix homeostasis in the mouse intervertebral disc.

Chronic pancreatitis-associated metabolic bone diseases: epidemiology, mechanisms, and clinical advances.

Chronic pancreatitis (CP) is a progressive inflammatory disease with an increasing global prevalence. In recent years, a strong association between CP and metabolic bone diseases (MBDs), especially osteoporosis, has been identified, attracting significant attention in the research field. Epidemiological data suggest a rising trend in the incidence of MBDs among CP patients. Notably, recent studies have highlighted a profound interplay between CP and altered nutritional and immune profiles, offering insights into its linkage with MBDs. At the molecular level, CP introduces a series of biochemical disturbances that compromise bone homeostasis. One critical observation is the disrupted metabolism of vitamin D and vitamin K, both essential micronutrients for maintaining bone integrity, in CP patients. In this review, we provide physio-pathological perspectives on the development and mechanisms of CP-related MBDs. We also outline some of the latest therapeutic strategies for treating patients with CP-associated MBDs, including stem cell transplantation, monoclonal antibodies, and probiotic therapy. In summary, CP-associated MBDs represent a rising medical challenge, involving multiple tissues and organs, complex disease mechanisms, and diverse treatment approaches. More in-depth studies are required to understand the complex interplay between CP and MBDs to facilitate the development of more specific and effective therapeutic approaches.

Vasorin as an actor of bone turnover?

Bone diseases are increasing with aging populations and it is important to identify clues to develop innovative treatments. Vasn, which encodes vasorin (Vasn), a transmembrane protein involved in the pathophysiology of several organs, is expressed during the development in intramembranous and endochondral ossification zones. Here, we studied the impact of Vasn deletion on the osteoblast and osteoclast dialog through a cell Coculture model. In addition, we explored the bone phenotype of Vasn KO mice, either constitutive or tamoxifen-inducible, or with an osteoclast-specific deletion. First, we show that both osteoblasts and osteoclasts express Vasn. Second, we report that, in both KO mouse models but not in osteoclast-targeted KO mice, Vasn deficiency was associated with an osteopenic bone phenotype, due to an imbalance in favor of osteoclastic resorption. Finally, through the Coculture experiments, we identify a dysregulation of the Wnt/ß-catenin pathway together with an increase in RANKL release by osteoblasts, which led to an enhanced osteoclast activity. This study unravels a direct role of Vasn in bone turnover, introducing a new biomarker or potential therapeutic target for bone pathologies.

Wnt16 Increases Bone-to-Implant Contact in an Osteopenic Rat Model by Increasing Proliferation and Regulating the Differentiation of Bone Marrow Stromal Cells.

Osseointegration is a complex biological cascade that regulates bone regeneration after implant placement. Implants possessing complex multiscale surface topographies augment this regenerative process through the regulation of bone marrow stromal cells (MSCs) that are in contact with the implant surface. One pathway regulating osteoblastic differentiation is Wnt signaling, and upregulation of non-canonical Wnts increases differentiation of MSCs on these titanium substrates. Wnt16 is a non-canonical Wnt shown to regulate bone morphology in mouse models. This study evaluated the role of Wnt16 during surface-mediated osteoblastic differentiation of MSCs in vitro and osseointegration in vivo. MSCs were cultured on Ti substrates with different surface properties and non-canonical Wnt expression was determined. Subsequently, MSCs were cultured on Ti substrates +/-Wnt16 (100 ng/mL) and anti-Wnt16 antibodies (2 µg/mL). Wnt16 expression was increased in cells grown on microrough surfaces that were processed to be hydrophilic and have nanoscale roughness. However, treatment MSCs on these surfaces with exogenous rhWnt16b increased total DNA content and osteoprotegerin production, but reduced osteoblastic differentiation and production of local factors necessary for osteogenesis. Addition of anti-Wnt16 antibodies blocked the inhibitor effects of Wnt16. The response to Wnt16 was likely independent of other osteogenic pathways like Wnt11-Wnt5a signaling and semaphorin 3a signaling. We used an established rat model of cortical and trabecular femoral bone impairment following botox injections (2 injections of 8 units/leg each, starting and maintenance doses) to assess Wnt16 effects on whole bone morphology and implant osseointegration. Wnt16 injections did not alter whole bone morphology significantly (BV/TV, cortical thickness, restoration of trabecular bone) but were effective at increasing cortical bone-to-implant contact during impaired osseointegration in the botox model. The mechanical quality of the increased bone was not sufficient to rescue the deleterious effects of botox. Clinically, these results are important to understand the interaction of cortical and trabecular bone during implant integration. They suggest a role for Wnt16 in modulating bone remodeling by reducing osteoclastic activity. Targeted strategies to temporally regulate Wnt16 after implant placement could be used to improve osseointegration by increasing the net pool of osteoprogenitor cells.

Litsea glutinosa extract promotes fracture healing and prevents bone loss via BMP2/SMAD1 signaling.

Estrogen deficiency is one of the main causes for postmenopausal osteoporosis. Current osteoporotic therapies are of high cost and associated with serious side effects. So there is an urgent need for cost-effective anti-osteoporotic agents. Anti-osteoporotic activity of Litsea glutinosa extract (LGE) is less explored. Moreover, its role in fracture healing and mechanism of action is still unknown. In the present study we explore the osteoprotective potential of LGE in osteoblast cells and fractured and ovariectomized (Ovx) mice models. Alkaline phosphatase (ALP), MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and mineralization assays revealed that LGE treatment increased osteoblast cell differentiation, viability and mineralization. LGE treatment at 0.01 µg increased the expression of BMP2, PSMAD, RUNX2 and type 1 col. LGE also mitigated RANKL-induced osteoclastogenesis. Next, drill hole injury Balb/C mice model was treated with LGE for 12 days. Micro-CT analysis and Calcein labeling at the fracture site showed that LGE (20 mg/kg) enhanced new bone formation and bone regeneration, also increased expression of BMP2/SMAD1 signaling genes at fracture site. Ovx mice were treated with LGE for 1 month. µCT analysis indicated that the treatment of LGE at 20 mg/kg dose prevented the alteration in bone microarchitecture and maintained bone mineral density and bone mineral content. Treatment also increased bone strength and restored the bone turnover markers. Furthermore, in bone samples, LGE increased osteogenesis by enhancing the expression of BMP2/SMAD1 signaling components and decreased osteoclast number and surface. We conclude that LGE promotes osteogenesis via modulating the BMP2/SMAD1 signaling pathway. The study advocates the therapeutic potential of LGE in osteoporosis treatment.

Icariin promotes bone marrow mesenchymal stem cells osteogenic differentiation via the mTOR/autophagy pathway to improve ketogenic diet-associated osteoporosis.

BACKGROUND: Icariin, a traditional Chinese medicine, has demonstrated anti-osteoporotic properties in ovariectomized mice. However, its effectiveness in preventing bone loss induced by ketogenic diet (KD), which mimics osteoporosis in human, remains unexplored. This study aims to investigate icariin's impact on KD-induced bone loss in mice. METHODS: Thirty mice were divided into: sham, KD, and KD + icariin groups. Post a 12-week intervention, evaluation including bone microstructures, serum concentrations of tartrate-resistant acid phosphatase (TRAP) and bone-specific alkaline phosphatase (ALP), and femoral tissue expression levels of osteocalcin (OCN) and TRAP. The expression levels of mammalian target of rapamycin (mTOR), ALP, peroxisome proliferator-activated receptor gamma (PPAR-γ), phosphorylated mTOR (p-mTOR), and the autophagy adaptor protein (p62) were also analyzed. Alizarin granule deposition and cellular ALP levels were measured following the induction of bone marrow mesenchymal stem cells (BMSCs) into osteogenesis. RESULTS: The study found that KD significantly impaired BMSCs' osteogenic differentiation, leading to bone loss. Icariin notably increased bone mass, stimulated osteogenesis, and reduced cancellous bone loss. In the KD + icariin group, measures such as bone tissue density (TMD), bone volume fraction (BV/TV), trabecular number (Tb.N), and trabecular thickness (Tb.Th) were significantly higher than in the KD group. Additionally, bone trabecular separation (Tb.Sp) was markedly lower in the KD + icariin group. Moreover, icariin increased OCN and ALP levels while suppressing PPAR-γ, TRAP, p62, and p-mTOR. In cellular studies, icariin encouraged osteogenic development in BMSCs under KD conditions. CONCLUSIONS: Icariin effectively counteracts bone thinning and improves bone microstructure. Its mechanism likely involves stimulating BMSCs osteogenic differentiation and inhibiting bone resorption, potentially through mTOR downregulation. These findings suggest icariin's potential as an alternative treatment for KD-induced bone loss.

Advancements in the pathogenesis of hepatic osteodystrophy and the potential therapeutic of mesenchymal stromal cells.

Hepatic osteodystrophy (HOD) is a metabolically associated bone disease mainly manifested as osteoporosis with the characteristic of bone loss induced by chronic liver disease (CLD). Due to its high incidence in CLD patients and increased risk of fracture, the research on HOD has received considerable interest. The specific pathogenesis of HOD has not been fully revealed. While it is widely believed that disturbance of hormone level, abnormal secretion of cytokines and damage of intestinal barrier caused by CLD might jointly affect the bone metabolic balance of bone formation and bone absorption. At present, the treatment of HOD is mainly to alleviate the bone loss by drug treatment, but the efficacy and safety are not satisfactory. Mesenchymal stromal cells (MSCs) are cells with multidirectional differentiation potential, cell transplantation therapy based on MSCs is an emerging therapeutic approach. This review mainly summarized the pathogenesis and treatment of HOD, reviewed the research progress of MSCs therapy and the combination of MSCs and scaffolds in the application of osteoporotic bone defects, and discussed the potential and limitations of MSCs therapy, providing theoretical basis for subsequent studies.

Water Extract of Desalted Salicornia europaea Inhibits RANKL-Induced Osteoclast Differentiation and Prevents Bone Loss in Ovariectomized Mice.

Osteoporosis, which is often associated with increased osteoclast activity due to menopause or aging, was the main focus of this study. We investigated the inhibitory effects of water extract of desalted Salicornia europaea L. (WSE) on osteoclast differentiation and bone loss in ovariectomized mice. Our findings revealed that WSE effectively inhibited RANKL-induced osteoclast differentiation, as demonstrated by TRAP staining, and also suppressed bone resorption and F-actin ring formation in a dose-dependent manner. The expression levels of genes related to osteoclast differentiation, including NFATc1, ACP5, Ctsk, and DCSTAMP, were downregulated by WSE. Oral administration of WSE improved bone density and structural parameters in ovariectomized mice. Dicaffeoylquinic acids (DCQAs) and saponins were detected in WSE, with 3,4-DCQA, 3,5-DCQA, and 4,5-DCQA being isolated and identified. All tested DCQAs, including the aforementioned types, inhibited osteoclast differentiation, bone resorption, and the expression of osteoclast-related genes. Furthermore, WSE and DCQAs reduced ROS production mediated by RANKL. These results indicate the potential of WSE and its components, DCQAs, as preventive or therapeutic agents against osteoporosis and related conditions.

Conjugated linoleic acid and glucosamine supplements may prevent bone loss in aging by regulating the RANKL/RANK/OPG pathway.

The skeleton is a living organ that undergoes constant changes, including bone formation and resorption. It is affected by various diseases, such as osteoporosis, osteopenia, and osteomalacia. Nowadays, several methods are applied to protect bone health, including the use of hormonal and non-hormonal medications and supplements. However, certain drugs like glucocorticoids, thiazolidinediones, heparin, anticonvulsants, chemotherapy, and proton pump inhibitors can endanger bone health and cause bone loss. New studies are exploring the use of supplements, such as conjugated linoleic acid (CLA) and glucosamine, with fewer side effects during treatment. Various mechanisms have been proposed for the effects of CLA and glucosamine on bone structure, both direct and indirect. One mechanism that deserves special attention is the regulatory effect of RANKL/RANK/OPG on bone turnover. The RANKL/RANK/OPG pathway is considered a motive for osteoclast maturation and bone resorption. The cytokine system, consisting of the receptor activator of the nuclear factor (NF)-kB ligand (RANKL), its receptor RANK, and its decoy receptor, osteoprotegerin (OPG), plays a vital role in bone turnover. Over the past few years, researchers have observed the impact of CLA and glucosamine on the RANKL/RANK/OPG mechanism of bone turnover. However, no comprehensive study has been published on these supplements and their mechanism. To address this gap in knowledge, we have critically reviewed their potential effects. This review aims to assist in developing efficient treatment strategies and focusing future studies on these supplements.

Water Extract of Angelica dahurica Inhibits Osteoclast Differentiation and Bone Loss.

Angelica dahurica radix has a long history of traditional use in China and Korea for treating headaches, cold-damp pain and skin diseases. Despite various pharmacological studies on A. dahurica, its impact on bones remains unclear. Hence, this study investigated the inhibitory effect of A. dahurica's radix water extract (WEAD) on osteoclast differentiation. In vitro experiments showed that WEAD effectively suppresses osteoclast differentiation. Treatment of an osteoclast precursor with WEAD significantly suppressed the expression of nuclear factor of activated T-cells 1 (NFATc1), essential transcription factor for osteoclastogenesis, while increasing the expression of negative regulators, interferon regulatory factor 8 (Irf8) and v-maf musculoaponeurotic fibrosarcoma oncogene homolog B (MafB). Consistent with the in vitro findings, the oral administration of WEAD (100 and 300 mg/kg/day) to mice subjected to surgical ovariectomy for a duration of six weeks alleviated bone loss, while also mitigating weight gain and liver fat accumulation. In addition, we also identified phytochemicals present in WEAD, known to regulate osteoclastogenesis and/or bone loss. These results suggest the potential use of WEAD for treating various bone disorders caused by excessive bone resorption.

BMP6 participates in the pathogenesis of adolescent idiopathic scoliosis by regulating osteopenia.

Adolescent idiopathic scoliosis (AIS) is a complex disease characterized by three-dimensional structural deformities of the spine. Its pathogenesis is associated with osteopenia. Bone-marrow-derived mesenchymal stem cells (BMSCs) play an important role in bone metabolism. We detected 1919 differentially expressed mRNAs and 744 differentially expressed lncRNAs in BMSCs from seven patients with AIS and five patients without AIS via high-throughput sequencing. Multiple analyses identified bone morphogenetic protein-6 (BMP6) as a hub gene that regulates the abnormal osteogenic differentiation of BMSCs in AIS. BMP6 expression was found to be decreased in AIS and its knockdown in human BMSCs significantly altered the degree of osteogenic differentiation. Additionally, CAP1-217 has been shown to be a potential upstream regulatory molecule of BMP6. We showed that CAP1-217 knockdown downregulated the expression of BMP6 and the osteogenic differentiation of BMSCs. Simultaneously, knockout of BMP6 in zebrafish embryos significantly increased the deformity rate. The findings of this study suggest that BMP6 is a key gene that regulates the abnormal osteogenic differentiation of BMSCs in AIS via the CAP1-217/BMP6/RUNX2 axis.

Osteogenic Differentiation Potential of Mesenchymal Stem Cells Using Single Cell Multiomic Analysis.

Mesenchymal stem cells (MSC) are multipotent stem cells that can differentiate into multiple cell types, including osteoblasts, chondrocytes, and adipocytes. Osteoblast differentiation is reduced during osteoporosis development, resulting in reduced bone formation. Further, MSC isolated from different donors possess distinct osteogenic capacity. In this study, we used single-cell multiomic analysis to profile the transcriptome and epigenome of MSC from four healthy donors. Data were obtained from ~1300 to 1600 cells for each donor. These cells were clustered into four groups, indicating that MSC from different donors have distinct chromatin accessible regulatory elements for regulating gene expression. To investigate the mechanism by which MSC undergo osteogenic differentiation, we used the chromatin accessibility data from the single-cell multiome data to identify individual-specific enhancer-promoter pairs and evaluated the expression levels and activities of the transcriptional regulators. The MSC from four donors showed distinct differentiation potential into osteoblasts. MSC of donor 1 showed the largest average motif activities, indicating that MSC from donor 1 was most likely to differentiate into osteoblasts. The results of our validation experiments were consistent with the bioinformatics prediction. We also tested the enrichment of genome-wide association study (GWAS) signals of several musculoskeletal disease traits in the patient-specific chromatin accessible regions identified in the single-cell multiome data, including osteoporosis, osteopenia, and osteoarthritis. We found that osteoarthritis-associated variants were only enriched in the regions identified from donor 4. In contrast, osteoporosis and osteopenia variants were enriched in regions from donor 1 and least enriched in donor 4. Since osteoporosis and osteopenia are related to the density of bone cells, the enrichment of variants from these traits should be correlated with the osteogenic potential of MSC. In summary, this study provides large-scale data to link regulatory elements with their target genes to study the regulatory relationships during the differentiation of mesenchymal stem cells and provide a deeper insight into the gene regulatory mechanism.

Accelerated Bone Loss in Transgenic Mice Expressing Constitutively Active TGF-ß Receptor Type I.

Transforming growth factor beta (TGF-ß) is a key factor mediating the intercellular crosstalk between the hematopoietic stem cells and their microenvironment. Here, we investigated the skeletal phenotype of transgenic mice expressing constitutively active TGF-ß receptor type I under the control of Mx1-Cre (Mx1;TßRICA mice). µCT analysis showed decreased cortical thickness, and cancellous bone volume in both femurs and mandibles. Histomorphometric analysis confirmed a decrease in cancellous bone volume due to increased osteoclast number and decreased osteoblast number. Primary osteoblasts showed decreased ALP and mineralization. Constitutive TßRI activation increased osteoclast differentiation. qPCR analysis showed that Tnfsf11/Tnfrsf11b ratio, Ctsk, Sufu, and Csf1 were increased whereas Runx2, Ptch1, and Ptch2 were decreased in Mx1;TßRICA femurs. Interestingly, Gli1, Wnt3a, Sp7, Alpl, Ptch1, Ptch2, and Shh mRNA expression were reduced whereas Tnfsf11/Tnfrsf11b ratio was increased in Mx1;TßRICA mandibles. Similarly, osteoclast-related genes were increased in Mx1;TßRICA osteoclasts whereas osteoblast-related genes were reduced in Mx1;TßRICA osteoblasts. Western blot analysis indicated that SMAD2 and SMAD3 phosphorylation was increased in Mx1;TßRICA osteoblasts, and SMAD3 phosphorylation was increased in Mx1;TßRICA osteoclasts. CTSK was increased while RUNX2 and PTCH1 was decreased in Mx1;TßRICA mice. Microindentation analysis indicated decreased hardness in Mx1;TßRICA mice. Our study indicated that Mx1;TßRICA mice were osteopenic by increasing osteoclast number and decreasing osteoblast number, possibly by suppressing Hedgehog signaling pathways.

Protaetia brevitarsis seulensis larvae ethanol extract inhibits RANKL-stimulated osteoclastogenesis and ameliorates bone loss in ovariectomized mice.

Modulation of osteoclast formation could be a therapeutic target for inhibiting pathological bone destruction. The receptor activator of nuclear factor (NF)-κB ligand (RANKL) is known to be an essential factor in osteoclast differentiation and activation inducers. However, whether Protaetia brevitarsis seulensis (P. brevitarsis) larvae-a traditional animal-derived medicine used in many Asian countries-can inhibit RANKL-induced osteoclast formation and prevent ovariectomy (OVX)-induced bone loss has not been evaluated. Here, we aimed to investigate the anti-osteoporotic effects of P. brevitarsis larvae ethanol extract (PBE) in RANKL-stimulated RAW264.7 cells and OVX mice. In vitro, PBE (0.1, 0.5, 1, and 2 mg/mL) decreased RANKL­induced tartrate-resistant acid phosphatase (TRAP) activity and expression of osteoclastogenesis-associated genes and proteins. Furthermore, PBE (0.1, 0.5, 1, and 2 mg/mL) significantly inhibited the phosphorylation of p38 and NF-κB. Female C3H/HeN mice were divided into five groups (n = 5 per group), namely, sham-operated, OVX, OVX+PBEL (100 mg/kg, oral gavage), OVX+PBEH (200 mg/kg, oral gavage), and OVX+estradiol (0.03 µg/day, subcutaneous injection). High doses of PBE significantly increased femoral bone mineral density (BMD) and bone volume/tissue volume (BV/TV), whereas femoral bone surface/bone volume (BS/BV) and osteoclastogenesis-associated protein expression decreased compared to those in the OVX group. Moreover, PBE (200 mg/kg) significantly increased estradiol and procollagen type I N-terminal propeptide and decreased N-terminal telopeptide of type I collagen and C-terminal telopeptide of type I collagen compared to those in the OVX group. Our results suggest that PBE can be an effective therapeutic candidate for preventing or treating postmenopausal osteoporosis.

Animal Experimental Models in Bone Metabolic Disease.

Bone is a highly specialized and dynamic tissue with several crucial functions, including support, movement support, protection of vital organs, and mineral storage [...].

Hedgehog signaling regulates bone homeostasis through orchestrating osteoclast differentiation and osteoclast-osteoblast coupling.

Imbalance of bone homeostasis induces bone degenerative diseases such as osteoporosis. Hedgehog (Hh) signaling plays critical roles in regulating the development of limb and joint. However, its unique role in bone homeostasis remained largely unknown. Here, we found that canonical Hh signaling pathway was gradually augmented during osteoclast differentiation. Genetic inactivation of Hh signaling in osteoclasts, using Ctsk-Cre;Smof/f conditional knockout mice, disrupted both osteoclast formation and subsequent osteoclast-osteoblast coupling. Concordantly, either Hh signaling inhibitors or Smo/Gli2 knockdown stunted in vitro osteoclast formation. Mechanistically, Hh signaling positively regulated osteoclast differentiation via transactivation of Traf6 and stabilization of TRAF6 protein. Then, we identified connective tissue growth factor (CTGF) as an Hh-regulatory bone formation-stimulating factor derived from osteoclasts, whose loss played a causative role in osteopenia seen in CKO mice. In line with this, recombinant CTGF exerted mitigating effects against ovariectomy induced bone loss, supporting a potential extension of local rCTGF treatment to osteoporotic diseases. Collectively, our findings firstly demonstrate that Hh signaling, which dictates osteoclast differentiation and osteoclast-osteoblast coupling by regulating TRAF6 and CTGF, is crucial for maintaining bone homeostasis, shedding mechanistic and therapeutic insights into the realm of osteoporosis.

Exercise maintains bone homeostasis by promoting osteogenesis through STAT3.

Bone exhibits changes in density, strength, and microarchitecture in relation to mechanical loading mediated by exercise. Appropriate exercise maintains bone homeostasis, while the absence of exercise leads to disuse bone loss. However, the acting mechanism of mechanotransduction in bone remains unclear. We performed the running-wheel exercise and tail suspension model to study the effects of exercise on bone metabolism, and found that osteoblastic Signal transducer and activator of transcription 3 (STAT3) activity was closely related to exercise-induced bone mass and metabolism changes. With the Flexcell tension-loading system in vitro, mechanical force promoted STAT3 activity, which was accompanied by increased osteoblastic differentiation of the bone marrow mesenchymal stem cells (BMSCs). In contrast, the inhibition of STAT3 phosphorylation blocked force-induced osteoblastic differentiation. Furthermore, pharmacological inactivation of STAT3 impaired the increase in exercise-induced bone mass and osteogenesis. With an inducible conditional deletion mouse model, we found that the osteoblast lineage-specific Stat3 deletion could also block force-induced osteoblastic differentiation in vitro and impair exercise-promoted bone mass and osteogenesis in vivo. This confirmed the crucial role of osteoblastic STAT3 in exercise-mediated bone metabolism. Finally, colivelin, a STAT3 agonist, promoted osteoblastic differentiation in vitro and partly rescued exercise loss-induced disuse bone loss by improving osteogenesis in the tail suspension model. Taken together, our study revealed the essential role of STAT3 in maintaining exercise-mediated bone homeostasis. In addition, STAT3 might act as a potential target for osteoporosis caused by exercise loss.

Pro-Osteogenic and Anti-Inflammatory Synergistic Effect of Orthosilicic Acid, Vitamin K2, Curcumin, Polydatin and Quercetin Combination in Young and Senescent Bone Marrow-Derived Mesenchymal Stromal Cells.

During aging, bone marrow mesenchymal stromal cells (MSCs)-the precursors of osteoblasts-undergo cellular senescence, losing their osteogenic potential and acquiring a pro-inflammatory secretory phenotype. These dysfunctions cause bone loss and lead to osteoporosis. Prevention and intervention at an early stage of bone loss are important, and naturally active compounds could represent a valid help in addition to diet. Here, we tested the hypothesis that the combination of two pro-osteogenic factors, namely orthosilicic acid (OA) and vitamin K2 (VK2), and three other anti-inflammatory compounds, namely curcumin (CUR), polydatin (PD) and quercetin (QCT)-that mirror the nutraceutical BlastiMin Complex® (Mivell, Italy)-would be effective in promoting MSC osteogenesis, even of replicative senescent cells (sMSCs), and inhibiting their pro-inflammatory phenotype in vitro. Results showed that when used at non-cytotoxic doses, (i) the association of OA and VK2 promoted MSC differentiation into osteoblasts, even when cultured without other pro-differentiating factors; and (ii) CUR, PD and QCT exerted an anti-inflammatory effect on sMSCs, and also synergized with OA and VK2 in promoting the expression of the pivotal osteogenic marker ALP in these cells. Overall, these data suggest a potential role of using a combination of all of these natural compounds as a supplement to prevent or control the progression of age-related osteoporosis.