Noncanonical Wnt signaling through G protein-linked PKCdelta activation promotes bone formation

Wnt3a is an early regulator of the Wolffian duct directionality via the regulation of apicobasal cell polarity

The Wolffian duct is a pair of epithelial ductal structures along the body axis that induces nephron development by interaction with the metanephric mesenchyme. The interaction between the mesenchyme and the ureteric bud derived from the Wolffian duct is mediated by Wnt ligands, the loss of which results in kidney agenesis. Nonetheless, the early contribution of Wnt signaling to Wolffian duct formation remains unclear. We therefore examined these dynamics in knockout and transgenic mouse embryos. The Wnt signal reporter was active in the extending Wolffian duct, and Wnt3a-knockout embryos exhibited a fragmented and misdirectional Wolffian duct. Apicobasal polarity was disrupted under Wnt3a-deficiency. These findings suggest that Wnt3a plays an important role in Wolffian duct development by regulating apicobasal polarity.

KDM6B preferentially promotes bone formation over resorption to facilitate postnatal bone mass accrual through collagen triple helix repeat containing 1-mediated PKCδ/MAPKs signaling

Lysine demethylase 6B (KDM6B) plays a role in regulating osteoblast differentiation and fetal bone ossification. Nevertheless, its involvement in regulating postnatal bone homeostasis and bone mass accrual remains unclear. In this study, we generated mice lacking Kdm6b gene specifically in mesenchyme and osteoprogenitor cells using a conditional strategy. The adult mice of both mutant strains had decreased cancellous bone mass. The absence of Kdm6b in mesenchyme led to decreased numbers of osteoblasts and osteoclasts, increased marrow adipocytes, as well as repressed bone formation and resorption. Additionally, Kdm6b-deficient bone marrow stromal cells (BMSCs) displayed impaired osteogenic differentiation and exerted an inhibitory effect on osteoclastogenesis. RNA-seq combined with gene expression analysis uncovered downregulation of collagen triple helix repeat containing 1 (CTHRC1) and a lower RANKL/osteoprotegerin (OPG) ratio in BMSCs of the mutant mice. Further mechanistic explorations demonstrated that KDM6B epigenetically upregulated CTHRC1 expression by removing the repressive H3K27me3 mark from its promoter, thereby triggering PKCδ/MAPKs signaling to facilitate osteoblast differentiation. CTHRC1 was able to mitigate the dysregulated osteogenic and adipogenic differentiation induced by Kdm6b deficiency. This study provides evidence that KDM6B regulates postnatal bone homeostasis through balancing osteoblast and osteoclast differentiation. Given its predominant promotion of osteoblastic bone formation over osteoclastic bone resorption, KDM6B tends to promote postnatal bone mass accrual.

Ultrasound-Responsive Piezoelectric Membrane Promotes Osteoporotic Bone Regeneration via the "Two-Way Regulation" Bone Homeostasis Strategy

The repair of osteoporotic bone defects remains inadequately addressed, primarily due to a disruption in bone homeostasis, characterized by insufficient bone formation and excessive bone resorption. Current research either focuses on promoting bone formation or inhibiting bone resorption, however, the bone repair efficacy of these single-target therapeutic strategies is limited. Herein, a "two-way regulation" bone homeostasis strategy is proposed utilizing piezoelectric composite membranes (DAT/KS), capable of simultaneously regulating osteogenesis and osteoclastogenesis, with high piezoelectric performance, good biocompatibility, and excellent degradability, to promote bone regeneration under osteoporotic conditions. The DAT/KS membrane under ultrasound (US) treatment enables the controlled modulation of piezoelectric stimulation and the release of saikosaponin D (SSD), which promotes osteogenic differentiation while simultaneously inhibiting osteoclast differentiation and function, thereby effectively restoring bone homeostasis and enhancing osteoporotic bone repair. Mechanistic insights reveal the promotion of both canonical and non-canonical Wnt signaling in bone marrow mesenchymal stem cells (BMSCs), which determines their osteogenic differentiation fate, and the downregulation of the NF-κB signaling in bone marrow mononuclear macrophages (BMMs). This study presents optimized sono-piezoelectric biomaterials capable of bidirectionally regulating both osteogenic and osteoclastic differentiation, providing a new potential therapeutic approach for pathological bone injuries.

The potential key genes within focal adhesion that regulate mesenchymal stem cells osteogenesis or adipogenesis in microgravity related disuse osteoporosis: an integrated analysis

This study aimed to identify key genes related to focal adhesions (FA) and cells involved in osteoblast (OS) and adipocyte (AD) differentiation in osteoporosis. A mouse model of disuse osteoporosis was made by hindlimbs unloading (HLU)/Tail - suspension. Micro - CT and histological analysis were done, and differentially expressed genes (DEGs) from GSE100930 were analyzed. Soft clustering on GSE80614 OS/AD samples found FA - related candidate genes. protein-protein interaction (PPI) network and cytoHubba's Degree algorithm identified key FA - genes, validated by quantitative polymerase chain reaction (qPCR). Key OS/AD - associated cells were identified by single - cell analysis. The mouse model showed decreased bone density, microstructure damage, increased marrow adiposity, and altered gene expression. Key FA - related genes for osteogenesis (ITGB3, LAMC1, COL6A3, ITGA8, PDGFRB) and adipogenesis (ITGB3, ITGA4, LAMB1, ITGA8, LAMA4) were found and validated. Key cells (chondrocyte, adipocyte, and osteoblast progenitors) are involved in specific pathways, with osteoblast progenitors having stronger interactions. Pseudotime analysis implies differentiation from chondrocyte progenitors to adipocyte, then osteoblast progenitors. This study provides new insights for disuse osteoporosis research.

Signaling Pathways Driving MSC Osteogenesis: Mechanisms, Regulation, and Translational Applications

Mesenchymal stem cells (MSCs) are crucial for skeletal development, homeostasis, and repair, primarily through their differentiation into osteoblasts and other skeletal lineage cells. Key signaling pathways, including Wnt, TGF-β/BMP, PTH, Hedgehog, and IGF, act as critical regulators of MSC osteogenesis, playing pivotal roles in maintaining bone homeostasis and facilitating regeneration. These pathways interact in distinct ways at various stages of bone development, mineralization, and remodeling. This review provides an overview of the molecular mechanisms by which these pathways regulate MSC osteogenesis, their influence on bone tissue formation, and their implications in bone diseases and therapeutic strategies. Additionally, we explore the potential applications of these pathways in bone tissue engineering, with a particular focus on promoting the use of MSCs as seed cells for bone defect repair. Ultimately, this review aims to highlight potential avenues for advancing bone biology research, treating bone disorders, and enhancing regenerative medicine.

The Role of Protein Kinase C During the Differentiation of Stem and Precursor Cells into Tissue Cells

Protein kinase C (PKC) plays an essential role during many biological processes including development from early embryonic stages until the terminal differentiation of specialized cells. This review summarizes the current knowledge about the involvement of PKC in molecular processes during the differentiation of stem/precursor cells into tissue cells with a particular focus on osteogenic, adipogenic, chondrogenic and neuronal differentiation by using a comprehensive approach. Interestingly, studies examining the overall role of PKC, or one of its three isoform groups (classical, novel and atypical PKCs), often showed controversial results. A discrete observation of distinct isoforms demonstrated that the impact on differentiation differs highly between the isoforms, and that during a certain process, the influence of only some isoforms is crucial, while others are less important. In particular, PKCβ inhibits, and PKCδ strongly supports osteogenesis, whereas it is the other way around for adipogenesis. PKCε is another isoform that overwhelmingly supports adipogenic differentiation. In addition, PKCα plays an important role in chondrogenesis, while neuronal differentiation has been positively associated with numerous isoforms including classical, novel and atypical PKCs. In a cellular context, various upstream mediators, like the canonical and non-canonical Wnt pathways, endogenously control PKC activity and thus, their activity interferes with the influence of PKC on differentiation. Downstream of PKC, several proteins and pathways build the molecular bridge between the enzyme and the control of differentiation, of which only a few have been well characterized so far. In this context, PKC also cooperates with other kinases like Akt or protein kinase A (PKA). Furthermore, PKC is capable of directly phosphorylating transcription factors with pivotal function for a certain developmental process. Ultimately, profound knowledge about the role of distinct PKC isoforms and the involved signaling pathways during differentiation constitutes a promising tool to improve the use of stem cells in regenerative therapies by precisely manipulating the activity of PKC or downstream effectors.

Wnt7b overexpression in osteoblasts stimulates bone formation and reduces obesity in mice on a high-fat diet

Previous studies have shown that Wnt7b potently stimulates bone formation by promoting osteoblast differentiation and activity. As high-fat feeding leads to obesity and systemic metabolic dysregulation, here we investigate the potential benefit of Wnt7b overexpression in osteoblasts on both bone and whole-body metabolism in mice fed with a high-fat diet (HFD). Wnt7b overexpression elicited massive overgrowth of trabecular and cortical bone but seemed to ameliorate body fat accumulation in mice with prolonged HFD feeding. In addition, Wnt7b overexpression modestly improved glucose tolerance in male mice on HFD. Collectively, the results indicate that targeted overexpression of Wnt7b in osteoblasts not only stimulates bone formation but also improves certain aspects of global metabolism in overnourished mice.

Metabolic reprogramming in skeletal cell differentiation

The human skeleton is a multifunctional organ made up of multiple cell types working in concert to maintain bone and mineral homeostasis and to perform critical mechanical and endocrine functions. From the beginning steps of chondrogenesis that prefigures most of the skeleton, to the rapid bone accrual during skeletal growth, followed by bone remodeling of the mature skeleton, cell differentiation is integral to skeletal health. While growth factors and nuclear proteins that influence skeletal cell differentiation have been extensively studied, the role of cellular metabolism is just beginning to be uncovered. Besides energy production, metabolic pathways have been shown to exert epigenetic regulation via key metabolites to influence cell fate in both cancerous and normal tissues. In this review, we will assess the role of growth factors and transcription factors in reprogramming cellular metabolism to meet the energetic and biosynthetic needs of chondrocytes, osteoblasts, or osteoclasts. We will also summarize the emerging evidence linking metabolic changes to epigenetic modifications during skeletal cell differentiation.

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.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

A founder variant expands the phenotype of WNT7B-related PDAC syndrome

Pulmonary hypoplasia, Diaphragmatic anomalies, Anophthalmia/microphthalmia, and Cardiac defects (PDAC) syndrome is a genetically heterogeneous multiple congenital malformation syndrome. Although pathogenic variants in RARB and STRA6 are established causes of PDAC, many PDAC cases remain unsolved at the molecular level. Recently, we proposed biallelic WNT7B variants as a novel etiology based on several families with typical features of PDAC syndrome albeit with variable expressivity. Here, we report three patients from two families that share a novel founder variant in WNT7B (c.739C > T; Arg247Trp). The phenotypic expression of this variant ranges from typical PDAC features to isolated genitourinary anomalies. Similar to previously reported PDAC-associated WNT7B variants, this variant was found to significantly impair WNT7B signaling activity further corroborating its proposed pathogenicity. This report adds further evidence to WNT7B-related PDAC and expands its variable expressivity.

Establishing stable and highly osteogenic hiPSC-derived MSCs for 3D-printed bone graft through microenvironment modulation by CHIR99021-treated osteocytes

Human induced pluripotent stem cell (hiPSC)-derived mesenchymal stem cells (iMSCs) are ideal candidates for the production of standardised and scalable bioengineered bone grafts. However, stable induction and osteogenic differentiation of iMSCs pose challenges in the industry. We developed a precise differentiation method to produce homogeneous and fully differentiated iMSCs. In this study, we established a standardised system to prepare iMSCs with increased osteogenic potential and improved bioactivity by introducing a CHIR99021 (C91)-treated osteogenic microenvironment (COOME). COOME enhances the osteogenic differentiation and mineralisation of iMSCs via canonical Wnt signalling. Global transcriptome analysis and co-culturing experiments indicated that COOME increased the pro-angiogenesis/neurogenesis activity of iMSCs. The superior osteogenic differentiation and mineralisation abilities of COOME-treated iMSCs were also confirmed in a Bio3D module generated using a polycaprolactone (PCL) and cell-integrated 3D printing (PCI3D) system, which is the closest model to in vivo research. This COOME-treated iMSCs differentiation system offers a new perspective for generating highly osteogenic, bioactive, and anatomically matched grafts for clinical applications.

Statement of significance

Although human induced pluripotent stem cell-derived MSCs (iMSCs) are ideal seed cells for synthetic bone implants, the challenges of stable induction and osteogenic differentiation hinder their clinical application. This study established a standardised system for the scalable preparation of iMSCs with improved osteogenic potential by combining our precise iMSC differentiation method with the CHIR99021 (C91)-treated osteocyte osteogenic microenvironment (COOME) through the activation of canonical Wnt signalling. Moreover, COOME upregulated the pro-angiogenic and pro-neurogenic capacities of iMSCs, which are crucial for the integration of implanted bone grafts. The superior osteogenic ability of COOME-treated iMSCs was confirmed in Bio3D modules generated using PCL and cell-integrated 3D printing systems, highlighting their functional potential in vivo. This study contributes to tissue engineering by providing insights into the functional differentiation of iMSCs for bone regeneration.

Osteoporosis: interferon-gamma-mediated bone remodeling in osteoimmunology

As the world population ages, osteoporosis, the most common disease of bone metabolism, affects more than 200 million people worldwide. The etiology is an imbalance in bone remodeling process resulting in more significant bone resorption than bone remodeling. With the advent of the osteoimmunology field, the immune system's role in skeletal pathologies is gradually being discovered. The cytokine interferon-gamma (IFN-γ), a member of the interferon family, is an important factor in the etiology and treatment of osteoporosis because it mediates bone remodeling. This review starts with bone remodeling process and includes the cellular and key signaling pathways of bone remodeling. The effects of IFN-γ on osteoblasts, osteoclasts, and bone mass are discussed separately, while the overall effects of IFN-γ on primary and secondary osteoporosis are summarized. The net effect of IFN-γ on bone appears to be highly dependent on the environment, dose, concentration, and stage of cellular differentiation. This review focuses on the mechanisms of bone remodeling and bone immunology, with a comprehensive discussion of the relationship between IFN-γ and osteoporosis. Finding the paradoxical balance of IFN-γ in bone immunology and exploring the potential of its clinical application provide new ideas for the clinical treatment of osteoporosis and drug development.

Toll-like receptor-2 induced inflammation causes local bone formation and activates canonical Wnt signaling

It is well established that inflammatory processes in the vicinity of bone often induce osteoclast formation and bone resorption. Effects of inflammatory processes on bone formation are less studied. Therefore, we investigated the effect of locally induced inflammation on bone formation. Toll-like receptor (TLR) 2 agonists LPS from Porphyromonas gingivalis and PAM2 were injected once subcutaneously above mouse calvarial bones. After five days, both agonists induced bone formation mainly at endocranial surfaces. The injection resulted in progressively increased calvarial thickness during 21 days. Excessive new bone formation was mainly observed separated from bone resorption cavities. Anti-RANKL did not affect the increase of bone formation. Inflammation caused increased bone formation rate due to increased mineralizing surfaces as assessed by dynamic histomorphometry. In areas close to new bone formation, an abundance of proliferating cells was observed as well as cells robustly stained for Runx2 and alkaline phosphatase. PAM2 increased the mRNA expression of Lrp5, Lrp6 and Wnt7b, and decreased the expression of Sost and Dkk1. In situ hybridization demonstrated decreased Sost mRNA expression in osteocytes present in old bone. An abundance of cells expressed Wnt7b in Runx2-positive osteoblasts and ß-catenin in areas with new bone formation. These data demonstrate that inflammation, not only induces osteoclastogenesis, but also locally activates canonical WNT signaling and stimulates new bone formation independent on bone resorption.

The role of Wnt signaling on Tooth Extraction Wound Healing: Narrative review

Compared to an incisional skin or mucosal wound, a tooth extraction wound results in far more soft tissue loss. A blood clot instantly fills the gap left by the extracted tooth. An embryonic type of bone forms during the healing of extraction wounds, and mature bone only later replaces it. Osteocytes in embryonic bone, also known as coarse fibrillar bone or immature bone, differ from those in adult bone in terms of number, size, and irregular arrangement. This immature bone is more radiolucent than mature bone due to the higher cell density and the smaller volume of calcified intercellular material. The Wnt gene family contains genes that encode secreted signaling proteins that have good promise for promoting bone regeneration. However, we still have a limited understanding the interplay of the molecular elements of the Wnt pathway in signal transduction, from ligand detection on the cell surface to transcription of target genes in the nucleus. We discuss the function of Wnt signaling molecules in this review, in tissue repair following tooth extraction and present recent results about these molecules. Conclusions: Wnt signaling activity helps to hasten bone regeneration while bone healing is slowed down by mutations in LRP5/6 or β-catenin.

Protein kinase C signaling "in" and "to" the nucleus: Master kinases in transcriptional regulation

PKC is a multifunctional family of Ser-Thr kinases widely implicated in the regulation of fundamental cellular functions, including proliferation, polarity, motility, and differentiation. Notwithstanding their primary cytoplasmic localization and stringent activation by cell surface receptors, PKC isozymes impel prominent nuclear signaling ultimately impacting gene expression. While transcriptional regulation may be wielded by nuclear PKCs, it most often relies on cytoplasmic phosphorylation events that result in nuclear shuttling of PKC downstream effectors, including transcription factors. As expected from the unique coupling of PKC isozymes to signaling effector pathways, glaring disparities in gene activation/repression are observed upon targeting individual PKC family members. Notably, specific PKCs control the expression and activation of transcription factors implicated in cell cycle/mitogenesis, epithelial-to-mesenchymal transition and immune function. Additionally, PKCs isozymes tightly regulate transcription factors involved in stepwise differentiation of pluripotent stem cells toward specific epithelial, mesenchymal, and hematopoietic cell lineages. Aberrant PKC expression and/or activation in pathological conditions, such as in cancer, leads to profound alterations in gene expression, leading to an extensive rewiring of transcriptional networks associated with mitogenesis, invasiveness, stemness, and tumor microenvironment dysregulation. In this review, we outline the current understanding of PKC signaling "in" and "to" the nucleus, with significant focus on established paradigms of PKC-mediated transcriptional control. Dissecting these complexities would allow the identification of relevant molecular targets implicated in a wide spectrum of diseases.

Muscle-bone crosstalk via endocrine signals and potential targets for osteosarcopenia-related fracture

BACKGROUND

Osteosarcopenia is a syndrome coexisting sarcopenia and osteopenia/osteoporosis, with a high fracture risk. Recently, skeletal muscle and bone have been recognized as endocrine organs capable of communication through secreting myokines and osteokines, respectively. With a deeper understanding of the muscle-bone crosstalk, these endocrine signals exhibit an important role in osteosarcopenia development and fracture healing.

METHODS

This review summarizes the role of myokines and osteokines in the development and treatment of osteosarcopenia and fracture, and discusses their potential for osteosarcopenia-related fracture treatment.

RESULTS

Several well-defined myokines (myostatin and irisin) and osteokines (RANKL and SOST) are found to not only regulate skeletal muscle and bone metabolism but also influence fracture healing processes. Systemic interventions targeting these biochemical signals has shown promising results in improving the mass and functions of skeletal muscle and bone, as well as accelerating fracture healing processes.

CONCLUSION

The regulation of muscle-bone crosstalk via biochemical signals presents a novel and promising strategy for treating osteosarcopenia and fracture by simultaneously enhancing bone and muscle anabolism. We propose that myostatin, irisin, RANKL, and SOST may serve as potential targets to treat fracture patients with osteosarcopenia.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Osteosarcopenia is an emerging geriatric syndrome where sarcopenia and osteoporosis coexist, with high fracture risk, delayed fracture healing, and increased mortality. However, no pharmacological agent is available to treat fracture patients with osteosarcopenia. This review summarizes the role of several myokines and osteokines in the development and treatment of osteosacropenia and fracture, as well as discusses their potential as intervention targets for osteosarcopenia-related fracture, which provides a novel and promising strategy for future osteosarcopenia-related fracture treatment.

SGMS2 in primary osteoporosis with facial nerve palsy

Pathogenic heterozygous variants in SGMS2 cause a rare monogenic form of osteoporosis known as calvarial doughnut lesions with bone fragility (CDL). The clinical presentations of SGMS2-related bone pathology range from childhood-onset osteoporosis with low bone mineral density and sclerotic doughnut-shaped lesions in the skull to a severe spondylometaphyseal dysplasia with neonatal fractures, long-bone deformities, and short stature. In addition, neurological manifestations occur in some patients. SGMS2 encodes sphingomyelin synthase 2 (SMS2), an enzyme involved in the production of sphingomyelin (SM). This review describes the biochemical structure of SM, SM metabolism, and their molecular actions in skeletal and neural tissue. We postulate how disrupted SM gradient can influence bone formation and how animal models may facilitate a better understanding of SGMS2-related osteoporosis.

Sustained release of a highly specific GSK3β inhibitor SB216763 in the PCL scaffold creates an osteogenic niche for osteogenesis, anti-adipogenesis, and potential angiogenesis

The safe and effective use of Wnt signaling is a hot topic in developing osteogenic drugs. SB216763 (S33) is a widely used highly specific GSK3β inhibitor. Here, we show that S33 initiates canonical Wnt signaling by inhibiting GSK3β activity in the bone marrow stromal cell line ST2 and increases osteoblast marker alkaline phosphatase activity, osteoblast marker gene expression including Alpl, Col1α1, and Runx2, promoting osteogenic differentiation and mineralization of ST2 cells. In addition, S33 suppressed the expression of adipogenic transcription factors Pparg and Cebpa in ST2 cells to suppress adipogenesis. ICRT-14, a specific transcriptional inhibitor of Wnt signaling, reversed the effects of S33 on the differentiation of ST2 cells. S33 also increased the expression of osteoclast cytokines RANKL and Opg but decreased the RANKL/Opg ratio and had the potential to inhibit osteoclast differentiation. In addition, we printed the PSCI3D (polycaprolactone, S33, cell-integrated 3D) scaffolds using a newly established integrated 3D printing system for hard materials and cells. S33 sustained release in the hydrogel of the scaffold with 25.4% release on day 1% and 81.7% release over 7 days. Cells in the scaffolds had good cell viability. The ratio of live/dead cells remained above 94% for 7 days, while the cells in the scaffolds proliferated linearly, and the proliferative activity of the PSCI3D scaffold group increased 1.4-fold and 1.7-fold on days 4 and 7, respectively. Similarly, in PSCI3D scaffolds, osteogenic differentiation of st2 cells was increased. The alkaline phosphatase activity increased 1.4- and 4.0-fold on days 7 and 14, respectively, and mineralization increased 1.7-fold at 21 days. In addition, PSCI3D conditioned medium promoted migration and tubulogenesis of HUVECs, and S33 upregulated the expression of Vegfa, a key factor in angiogenesis. In conclusion, our study suggests that S33 functions in osteogenesis, anti-adipogenesis, and potential inhibition of osteoclast differentiation. And the sustained release of S33 in PSCI3D scaffolds creates a safe osteogenic niche, which promotes cell proliferation, osteogenesis, and angiogenesis and has application prospects.

The role of wnt signaling in diabetes-induced osteoporosis

Osteoporosis, a chronic complication of diabetes mellitus, is characterized by a reduction in bone mass, destruction of bone microarchitecture, decreased bone strength, and increased bone fragility. Because of its insidious onset, osteoporosis renders patients highly susceptible to pathological fractures, leading to increased disability and mortality rates. However, the specific pathogenesis of osteoporosis induced by chronic hyperglycemia has not yet been fully elucidated. But it is currently known that the disruption of Wnt signaling triggered by chronic hyperglycemia is involved in the pathogenesis of diabetic osteoporosis. There are two main types of Wnt signaling pathways, the canonical Wnt signaling pathway (β-catenin-dependent) and the non-canonical Wnt signaling pathway (non-β-catenin-dependent), both of which play an important role in regulating the balance between bone formation and bone resorption. Therefore, this review systematically describes the effects of abnormal Wnt pathway signaling on bone homeostasis under hyperglycemia, hoping to reveal the relationship between Wnt signaling and diabetic osteoporosis to further improve understanding of this disease.

Bi-allelic variants in WNT7B disrupt the development of multiple organs in humans

BACKGROUND

Pulmonary hypoplasia, Diaphragmatic anomalies, Anophthalmia/microphthalmia and Cardiac defects delineate the PDAC syndrome. We aim to identify the cause of PDAC syndrome in patients who do not carry pathogenic variants in RARB and STRA6, which have been previously associated with this disorder.

METHODS

We sequenced the exome of patients with unexplained PDAC syndrome and performed functional validation of candidate variants.

RESULTS

We identified bi-allelic variants in WNT7B in fetuses with PDAC syndrome from two unrelated families. In one family, the fetus was homozygous for the c.292C>T (p.(Arg98*)) variant whereas the fetuses from the other family were compound heterozygous for the variants c.225C>G (p.(Tyr75*)) and c.562G>A (p.(Gly188Ser)). Finally, a molecular autopsy by proxy in a consanguineous couple that lost two babies due to lung hypoplasia revealed that both parents carry the p.(Arg98*) variant. Using a WNT signalling canonical luciferase assay, we demonstrated that the identified variants are deleterious. In addition, we found that wnt7bb mutant zebrafish display a defect of the swimbladder, an air-filled organ that is a structural homolog of the mammalian lung, suggesting that the function of WNT7B has been conserved during evolution for the development of these structures.

CONCLUSION

Our findings indicate that defective WNT7B function underlies a form of lung hypoplasia that is associated with the PDAC syndrome, and provide evidence for involvement of the WNT-β-catenin pathway in human lung, tracheal, ocular, cardiac, and renal development.

A novel decellularized matrix of Wnt signaling-activated osteocytes accelerates the repair of critical-sized parietal bone defects with osteoclastogenesis, angiogenesis, and neurogenesis

Cell source is the key to decellularized matrix (DM) strategy. This study compared 3 cell types, osteocytes with/without dominant active Wnt/β-catenin signaling (daCO and WTO) and bone marrow stromal cells (BMSCs) for their DMs in bone repair. Decellularization removes all organelles and >95% DNA, and retained >74% collagen and >71% GAG, maintains the integrity of cell basement membrane with dense boundaries showing oval and honeycomb structure in osteocytic DM and smooth but irregular shape in the BMSC-DM. DM produced higher cell survival rate (90%) and higher proliferative activity. In vitro, daCO-DM induces more and longer stress fibers in BMSCs, conducive to cell adhesion, spreading, and osteogenic differentiation. 8-wk after implantation of the critical-sized parietal bone defect model, daCO-DM formed tight structures, composed of a large number of densely-arranged type-I collagen under polarized light microscope, which is similar to and integrated with host bone. BV/TV (>54%) was 1.5, 2.9, and 3.5 times of WTO-DM, BMSC-DM, and none-DM groups, and N.Ob/T.Ar (3.2 × 10²/mm²) was 1.7, 2.9, and 3.3 times. At 4-wk, daCO-DM induced osteoclastogenesis, 2.3 times higher than WTO-DM; but BMSC-DM or none-DM didn't. daCO-DM increased the expression of RANKL and MCSF, Vegfa and Angpt1, and Ngf in BMSCs, which contributes to osteoclastogenesis, angiogenesis, and neurogenesis, respectively. daCO-DM promoted H-type vessel formation and nerve markers β3-tubulin and NeuN expression. Conclusion: daCO-DM produces metabolic and neurovascularized organoid bone to accelerate the repair of bone defects. These features are expected to achieve the effect of autologous bone transplantation, suitable for transformation application.

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Decellularized matrix of osteocytes with dominant-active β-catenin (daCO-DM) promotes osteogenesis for regenerative repair.

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daCO-DM induces BMSCs to form stress fibers, conducive to cell adhesion, spreading, and differentiation towards osteoblasts.

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daCO-DM-induced osteoblasts have strong activity secreting dense and orderly-arranged type I collagen as host bone’s.

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daCO-DM induces BMSCs to express pre-osteoclastogenic cytokine RANKL and MCSF for osteoclastogenesis of marrow monocytes.

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daCO-DM enhances BMSCs to express angiogenic Vegfa and Angpt1, and neurogenic Ngf potentially for neurovascularization.

PPP3R1 Promotes MSCs Senescence by Inducing Plasma Membrane Depolarization and Increasing Ca2+ Influx

Aging of mesenchymal stem cells(MSCs) has been widely reported to be strongly associated with aging-related diseases, including osteoporosis (OP). In particular, the beneficial functions of mesenchymal stem cells decline with age, limiting their therapeutic efficacy in age-related bone loss diseases. Therefore, how to improve mesenchymal stem cell aging to treat age-related bone loss is the current research focus. However, the underlying mechanism remains unclear. In this study, protein phosphatase 3, regulatory subunit B, alpha isoform, calcineurin B, type I (PPP3R1) was found to accelerate the senescence of mesenchymal stem cells, resulting in reduced osteogenic differentiation and enhanced adipogenic differentiation in vitro. Mechanistically, PPP3R1 induces changes in membrane potential to promote cellular senescence by polarizing to depolarizing, increasing Ca²⁺ influx and activating downstream NFAT/ATF3/p53 signaling. In conclusion, the results identify a novel pathway of mesenchymal stem cell aging that may lead to novel therapeutic approaches for age-related bone loss.

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

Wnt signaling and its bone tissue-specific inhibitor sclerostin are key regulators of bone homeostasis. The therapeutic potential of anti-sclerostin antibodies (Scl-Abs), for bone mass recovery and fragility fracture prevention in low bone mass phenotypes, has been supported by animal studies. The Scl-Ab romosozumab is currently used for osteoporosis treatment.

INTRODUCTION

Wnt signaling is a key regulator of skeletal development and homeostasis; germinal mutations affecting genes encoding components, inhibitors, and enhancers of the Wnt pathways were shown to be responsible for the development of rare congenital metabolic bone disorders. Sclerostin is a bone tissue-specific inhibitor of the Wnt/β-catenin pathway, secreted by osteocytes, negatively regulating osteogenic differentiation and bone formation, and promoting osteoclastogenesis and bone resorption.

PURPOSE AND METHODS

Here, we reviewed current knowledge on the role of sclerostin and Wnt pathways in bone metabolism and skeletal disorders, and on the state of the art of therapy with sclerostin-neutralizing antibodies in low-bone-mass diseases.

RESULTS

Various in vivo studies on animal models of human low-bone-mass diseases showed that targeting sclerostin to recover bone mass, restore bone strength, and prevent fragility fracture was safe and effective in osteoporosis, osteogenesis imperfecta, and osteoporosis pseudoglioma. Currently, only treatment with romosozumab, a humanized monoclonal anti-sclerostin antibody, has been approved in human clinical practice for the treatment of osteoporosis, showing a valuable capability to increase BMD at various skeletal sites and reduce the occurrence of new vertebral, non-vertebral, and hip fragility fractures in treated male and female osteoporotic patients.

CONCLUSIONS

Preclinical studies demonstrated safety and efficacy of therapy with anti-sclerostin monoclonal antibodies in the preservation/restoration of bone mass and prevention of fragility fractures in low-bone-mass clinical phenotypes, other than osteoporosis, to be validated by clinical studies for their approved translation into prevalent clinical practice.

Deciphering postnatal limb development at single-cell resolution

The early postnatal limb developmental progression bridges embryonic and mature stages and mirrors the pathological remodeling of articular cartilage. However, compared with multitudinous research on embryonic limb development, the early postnatal stage seems relatively unnoticed. Here, a systematic work to portray the postnatal limb developmental landscape was carried out by characterization of 19,952 single cells from murine hindlimbs at 4 postnatal stages using single-cell RNA sequencing technique. By delineation of cell heterogeneity, the candidate progenitor sub-clusters marked by Cd34 and Ly6e were discovered in articular cartilage and enthesis, and three cellular developmental branches marked by Col10a1, Spp1, and Tnni2 were reflected in growth plate. The representative transcriptomes and developmental patterns were intensively explored, and the key regulation mechanisms as well as evolvement in osteoarthritis were discussed. Above all, these results expand horizons of postnatal limb developmental biology and reach the interconnections between limb development, remodeling, and regeneration.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effect of spheroid size on gene expression profiles of a mouse mesenchymal stem cell line in spheroid culture

BACKGROUND

Mesenchymal stem cell (MSC)-based therapies offer potential for bone repair. MSC spheroid cultures may harbor enhanced therapeutic potential over MSC monolayers through increased secretion of trophic factors. However, the impact of spheroid size on trophic factor expression is unclear.

OBJECTIVE

We investigated the effect of spheroid size on trophic factor-related gene expression.

METHODS

KUM10, a murine MSC line was used. RNA-seq was used to screen the transcriptional profiles of MSC monolayer and spheroid cultures. Differentially expressed genes identified in RNA-seq were evaluated by q-PCR in cultures of 5 × 104 (S group), 5 × 105 (M group), 5 × 106 (L group) cells/well.

RESULTS

Comparison of expression levels between KUM10 monolayer and spheroid cultures identified 2140 differentially expressed genes, of which 1047 were upregulated and 1093 were downregulated in KUM10 spheroids. Among these, 12 upregulated genes (Bmp2, Fgf9, Fgf18, Ngf, Pdgfa, Pdgfb, Tgfb1, Vegfa, Vegfc, Wnt4, Wnt5a, Wnt10a) were associated with secretory growth factors. Of these, expression of Fgf9, Fgf18, Vegfa and Vegfc was elevated in the L group, and Pdgfb and Tgfb1 was elevated in the S group.

CONCLUSIONS

Spheroid size may impact trophic factor expression. Our results will be useful for future studies assessing the utility of MSC spheroids for treating bone injury.

Runx2 regulates chromatin accessibility to direct the osteoblast program at neonatal stages

The transcriptional regulator Runx2 (runt-related transcription factor 2) has essential but distinct roles in osteoblasts and chondrocytes in skeletal development. However, Runx2-mediated regulatory mechanisms underlying the distinctive programming of osteoblasts and chondrocytes are not well understood. Here, we perform an integrative analysis to investigate Runx2-DNA binding and chromatin accessibility ex vivo using neonatal osteoblasts and chondrocytes. We find that Runx2 engages with cell-type-distinct chromatin-accessible regions, potentially interacting with different combinations of transcriptional regulators, forming cell-type-specific hotspots, and potentiating chromatin accessibility. Genetic analysis and direct cellular reprogramming studies suggest that Runx2 is essential for establishment of chromatin accessibility in osteoblasts. Functional enhancer studies identify an Sp7 distal enhancer driven by Runx2-dependent binding and osteoblast-specific chromatin accessibility, contributing to normal osteoblast differentiation. Our findings provide a framework for understanding the regulatory landscape encompassing Runx2-mediated and cell-type-distinct enhancer networks that underlie the specification of osteoblasts.

Hojo et al. investigate the gene-regulatory landscape underlying specification of skeletal cell types in neonatal mice. Runx2, an osteoblast determinant, engages with cell-type-distinct chromatin-accessible regions and is essential for establishment of chromatin accessibility in osteoblasts. The study provides insights into enhancer networks in skeletal development.

Canonical Wnt signaling works downstream of iron overload to prevent ferroptosis from damaging osteoblast differentiation

Excessive iron has emerged in a large population of patients suffering from degenerative or hematological diseases with a common outcome, osteoporosis. However, its underlying mechanism remains to be clarified in order to formulate effective prevention and intervention against the loss of bone-forming osteoblasts. We show herein that increased intracellular iron by ferric ammonium citrate (FAC) mimicking the so-called non-transferrin bound iron concentrations leads to ferroptosis and impaired osteoblast differentiation. FAC upregulates the expression of Trfr and DMT1 genes to increase iron uptake, accumulating intracellular labile ferrous iron for iron overload status. Then, the excessive ferrous iron generates reactive oxygen species (ROS) and lipid peroxidation products (LPO), causing ferroptosis with its typical mitochondrial morphological changes, such as shrinkaged and condensed membrane with diminution and loss of crista and outer membrane rupture. We further examined that ferroptosis is the main cause responsible for FAC-disrupted osteoblast differentiation, although apoptosis and senescence are concurrently induced as well. Mechanistically, we revealed that iron dose-dependently down-regulates the expression of Wnt target genes and inhibits the transcription of Wnt reporter TopFlash construct, so as to inhibit the canonical Wnt signaling. Wnt agonist, ferroptosis inhibitor, or antioxidant melatonin reverses iron-inhibited canonical Wnt signaling to restore osteoblast differentiation by reducing ROS and LPO production to prevent ferroptosis notably without reducing iron overload. This study proposes a working model against excessive iron-induced osteoporosis: iron chelator deferoxamine or the above three drugs prevent ferroptosis, restore traditional Wnt signaling to maintain osteoblast differentiation no matter whether iron overload is removed or not. Additionally, iron chelator should be used to a suitable extent because iron itself is necessary for osteogenic differentiation.

The role of the Wnt signalling pathway in the energy metabolism of bone remodelling

OBJECTIVES

Bone remodelling is necessary to repair old and impaired bone caused by aging and its effects. Injury in the process of bone remodelling generally leads to the development of various bone diseases. Energy metabolism plays crucial roles in bone cell formation and function, the disorder of which will disrupt the balance between bone formation and bone resorption.

MATERIALS AND METHODS

Here, we review the intrinsic interactions between bone remodelling and energy metabolism and the role of the Wnt signalling pathway.

RESULTS

We found a close interplay between metabolic pathways and bone homeostasis, demonstrating that bone plays an important role in the regulation of energy balance. We also discovered that Wnt signalling is associated with multiple biological processes regulating energy metabolism in bone cells.

CONCLUSIONS

Thus, targeted regulation of Wnt signalling and the recovery of the energy metabolism function of bone cells are key means for the treatment of metabolic bone diseases.

Molecular Mechanisms of Isolated Polycystic Liver Diseases

Polycystic liver disease (PLD) is a rare autosomal dominant disorder including two genetically and clinically distinct forms: autosomal dominant polycystic kidney disease (ADPKD) and isolated polycystic liver disease (PCLD). The main manifestation of ADPKD is kidney cysts, while PCLD has predominantly liver presentations with mild or absent kidney cysts. Over the past decade, PRKCSH, SEC63, ALG8, and LRP5 have been candidate genes of PCLD. Recently, more candidate genes such as GANAB, SEC61B, and ALR9 were also reported in PCLD patients. This review focused on all candidate genes of PCLD, including the newly established novel candidate genes. In addition, we also discussed some other genes which might also contribute to the disease.

The Osteocyte Stimulated by Wnt Agonist SKL2001 Is a Safe Osteogenic Niche Improving Bioactivities in a Polycaprolactone and Cell Integrated 3D Module

Finding and constructing an osteogenic microenvironment similar to natural bone tissue has always been a frontier topic in orthopedics. We found that osteocytes are targeting cells controlling bone anabolism produced by PTH (JBMR 2017, PMID: 27704638), and osteocytes with activated Wnt signaling orchestrate bone formation and resorption (PNAS 2015, PMID: 25605937). However, methods for taking advantage of the leading role of osteocytes in bone regeneration remain unexplored. Herein, we found that the osteocytes with SKL2001-activated Wnt signaling could be an osteogenic microenvironment (SOOME) which upregulates the expression of bone transcription factor Runx2 and Bglap and promotes the differentiation of bone marrow stromal cell ST2 into osteoblasts. Interestingly, 60 μM SKL2001 treatment of osteocytic MLO-Y4 for 24 h maintained Wnt signaling activation for three days after removal, which was sufficient to induce osteoblast differentiation. Triptonide, a Wnt inhibitor, could eliminate this differentiation. Moreover, on day 5, the Wnt signaling naturally decreased to the level of the control group, indicating that this method of Wnt-signaling induction is safe to use. We quickly verified in vivo function of SOOME to a good proximation in 3D bioprinted modules composed of reciprocally printed polycaprolactone bundles (for support) and cell bundles (for bioactivity). In the cell bundles, SOOME stably supported the growth and development of ST2 cells, the 7-day survival rate was as high as 91.6%, and proliferation ability increased linearly. Similarly, SOOME greatly promoted ST2 differentiation and mineralization for 28 days. In addition, SOOME upregulated the expression of angiopoietin 1, promoted endothelial cell migration and angiogenesis, and increased node number and total length of tubes and branches. Finally, we found that the function of SOOME could be realized through the paracrine pathway. This study reveals that osteocytes with Wnt signaling activated by SKL2001 are a safe osteogenic microenvironment. Both SOOME itself and its cell-free culture supernatant can improve bioactivity for osteoblast differentiation, with composite scaffolds especially bearing application value.

Ca2+-independent phospholipase A2β-derived PGE2 contributes to osteogenesis

Bone modeling can be modulated by lipid signals such as arachidonic acid (AA) and its cyclooxygenase 2 (COX2) metabolite, prostaglandin E₂ (PGE₂), which are recognized mediators of optimal bone formation. Hydrolysis of AA from membrane glycerophospholipids is catalyzed by phospholipases A₂ (PLA₂s). We reported that mice deficient in the Ca²⁺- independent PLA₂beta (iPLA₂β), encoded by Pla2g6, exhibit a low bone phenotype, but the cause for this remains to be identified. Here, we examined the mechanistic and molecular roles of iPLA₂β in bone formation using bone marrow stromal cells and calvarial osteoblasts from WT and iPLA₂β-deficient mice, and the MC3T3-E1 osteoblast precursor cell line. Our data reveal that transcription of osteogenic factors (Bmp2, Alpl, and Runx2) and osteogenesis are decreased with iPLA₂β-deficiency. These outcomes are corroborated and recapitulated in WT cells treated with a selective inhibitor of iPLA₂ β (10 μM S-BEL), and rescued in iPLA₂β-deficient cells by additions of 10 μM PGE₂. Further, under osteogenic conditions we find that PGE₂ production is through iPLA₂β activity and that this leads to induction of Runx2 and iPLA₂β transcription. These findings reveal a strong link between osteogenesis and iPLA₂β-derived lipids and raise the intriguing possibility that iPLA₂β-derived PGE₂ participates in osteogenesis and in the regulation of Runx2 and also iPLA₂β.

The Wnt Signaling Pathway in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious kidney-related complication of both type 1 and type 2 diabetes mellitus (T1DM, T2DM) and the second major cause of end-stage kidney disease. DN can lead to hypertension, edema, and proteinuria. In some cases, DN can even progress to kidney failure, a life-threatening condition. The precise etiology and pathogenesis of DN remain unknown, although multiple factors are believed to be involved. The main pathological manifestations of DN include mesangial expansion, thickening of the glomerular basement membrane, and podocyte injury. Eventually, these pathological manifestations will lead to glomerulosclerosis, thus affecting renal function. There is an urgent need to develop new strategies for the prevention and treatment of DN. Existing evidence shows that the Wnt signaling cascade plays a key role in regulating the development of DN. Previous studies focused on the role of the Wnt canonical signaling pathway in DN. Subsequently, accumulated evidence on the mechanism of the Wnt non-canonical signaling indicated that Wnt/Ca²⁺ and Wnt/PCP also have essential roles in the progression of DN. In this review, we summarize the specific mechanisms of Wnt signaling in the occurrence and development of DN in podocyte injury, mesangial cell injury, and renal fibrosis. Also, to elucidate the significance of the Wnt canonical pathway in the process of DN, we uncovered evidence supporting that both Wnt/PCP and Wnt/Ca²⁺ signaling are critical for DN development.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

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

A Highly Selective GSK-3β Inhibitor CHIR99021 Promotes Osteogenesis by Activating Canonical and Autophagy-Mediated Wnt Signaling

The discovery and application of small molecules is one of the practical strategies of safe osteogenic drugs. The small molecule CHIR99021 (C91) is a highly specific, safe, and most effective GSK-3β Inhibitor. This study found that it efficiently activates the canonical Wnt signaling of bone marrow stromal cell ST2 and promotes osteoblast differentiation and mineralization. C91 increases the production and biochemical activity of osteoblast marker alkaline phosphatase, the expression of osteoblast marker genes Alpl, Bglap, Runx2, and Sp7, and the formation of bone nodules. Triptonide is a transcription inhibitor of Wnt target gene, which diminishes C91-induced osteoblast differentiation in a dose-dependent manner. Meanwhile, C91 also induces autophagy through autophagosome formation and conversion of autophagy biomarker LC-3I into LC-3II. Autophagy inhibitor 3MA partially reduces C91-induced osteoblast differentiation and mineralization; autophagy inducer Rapamycin increases the expression of β-catenin to promote osteogenic differentiation, but cannot alleviate the inhibition of Triptonide on C91-induced osteogenic differentiation, indicating the crosstalk of canonical Wnt signaling and autophagy regulates C91-induced osteoblast differentiation. Furthermore, in order to simulate the in vivo detection of C91 in osteogenesis process, we made a C91 slow-release hydrogel with our newly established polycaprolactone and cell-integrated 3D printing system (PCCI3D module). The sustained release C91 promotes the differentiation and mineralization of ST2 cells. C91 can also enhance the proliferative activity of ST2 cells. The release rate of C91 from hydrogel gradually decreases within 7 days. During this period, the C91 is released by 83.0% and the cell viability maintained at 96.4%. Therefore, the small molecule Wnt agonist C91 promotes osteogenesis through caonical and autophagy-mediated Wnt signaling pathway with an option for translational application.

FSH stimulated bovine granulosa cell steroidogenesis involves both canonical and noncanonical WNT signaling

Gonadotrophins play key roles in follicular development; however, the underlying molecular mechanisms are not fully understood. Follicle stimulating hormone (FSH) regulation of aromatase and subsequent estradiol (E₂) production relies on β-catenin, a key effector of WNT signaling. We previously demonstrated that treatment with the canonical WNT inhibitor, IWR-1, reduced FSH induced bovine granulosa cell E₂ production in vitro. Here we demonstrated that intrafollicular injection in vivo with IWR-1 alters steroidogenesis and triggers a significant decrease in estrogen to progesterone ratio in the IWR-1 treated follicles compared to diluent injected control follicles. We next examined markers of canonical and noncanonical WNT signaling in dominant and subordinate follicles collected at different stages of follicular development and showed that protein for both CTNNB1 (canonical pathway) and phosphorylated (p)-LEF1 (noncanonical pathway) was significantly elevated in dominant compared to subordinate follicles at the early dominance stage of development. Therefore, we hypothesized that canonical and/or noncanonical WNT ligands modulate FSH stimulated E₂ production. Hence, we examined the effects of specific WNT ligands on FSH stimulated E₂ production in the absence of endogenous WNT production in vitro. Universal WNT signaling inhibitor, LGK-974 was able to inhibit FSH stimulation of E₂ and reduce the abundance of proteins linked to canonical and noncanonical WNT pathway activation. Supplementation with the canonical ligand WNT2b did not affect the inhibitory effects of LGK-974 on FSH stimulated E₂ production but rescued the LGK-974 mediated inhibition of CTNNB1 (canonical pathway) but not p-LEF1, p-JNK or p-P38 abundance (noncanonical pathway) abundance. In contrast, WNT5a treatment rescued FSH stimulated estradiol production and indices of activation of both the canonical (CTNNB1) and noncanonical (p-LEF1, p-JNK and p-P38) WNT signaling pathways in LGK-974 treated granulosa cells. Taken together, these results suggest that both canonical and noncanonical WNT pathways activation is linked to FSH stimulation of E₂ production by bovine granulosa cells.

Wnt7b Inhibits Osteoclastogenesis via AKT Activation and Glucose Metabolic Rewiring

The imbalance between bone formation and bone resorption causes osteoporosis, which leads to severe bone fractures. It is known that increases in osteoclast numbers and activities are the main reasons for increasing bone resorption. Although extensive studies have investigated the regulation of osteoclastogenesis of bone marrow macrophages (BMMs), new pharmacological avenues still need to be unveiled for clinical purpose. Wnt ligands have been widely demonstrated as stimulators of bone formation; however, the inhibitory effect of the Wnt pathway in osteoclastogenesis is largely unknown. Here, we demonstrate that Wnt7b, a potent Wnt ligand that enhances bone formation and increases bone mass, also abolishes osteoclastogenesis in vitro. Importantly, enforced expression of Wnt in bone marrow macrophage lineage cells significantly disrupts osteoclast formation and activity, which leads to a dramatic increase in bone mass. Mechanistically, Wnt7b impacts the glucose metabolic process and AKT activation during osteoclastogenesis. Thus, we demonstrate that Wnt7b diminishes osteoclast formation, which will be beneficial for osteoporosis therapy in the future.

Roles of Non-Canonical Wnt Signalling Pathways in Bone Biology

The Wnt signalling pathway is one of the central signalling pathways in bone development, homeostasis and regulation of bone mineral density. It consists of numerous Wnt ligands, receptors and co-receptors, which ensure tight spatiotemporal regulation of Wnt signalling pathway activity and thus tight regulation of bone tissue homeostasis. This enables maintenance of optimal mineral density, tissue healing and adaptation to changes in bone loading. While the role of the canonical/β-catenin Wnt signalling pathway in bone homeostasis is relatively well researched, Wnt ligands can also activate several non-canonical, β-catenin independent signalling pathways with important effects on bone tissue. In this review, we will provide a thorough overview of the current knowledge on different non-canonical Wnt signalling pathways involved in bone biology, focusing especially on the pathways that affect bone cell differentiation, maturation and function, processes involved in bone tissue structure regulation. We will describe the role of the two most known non-canonical pathways (Wnt/planar cell polarity pathways and Wnt/Ca2+ pathway), as well as other signalling pathways with a strong role in bone biology that communicate with the Wnt signalling pathway through non-canonical Wnt signalling. Our goal is to bring additional attention to these still not well researched but important pathways in the regulation of bone biology in the hope of prompting additional research in the area of non-canonical Wnt signalling pathways.

WNT7B overexpression rescues bone loss caused by glucocorticoids in mice

Glucocorticoids, widely prescribed for anti-inflammatory and immunosuppressive purposes, are the most common secondary cause for osteoporosis and related fractures. Current anti-resorptive and anabolic therapies are insufficient for treating glucocorticoid-induced osteoporosis due to contraindications or concerns of side effects. Glucocorticoids have been shown to disrupt Wnt signaling in osteoblast-lineage cells, but the efficacy for Wnt proteins to restore bone mass after glucocorticoid therapy has not been examined. Here by using two mouse genetic models wherein WNT7B expression is temporally activated by either tamoxifen or doxycycline in osteoblast-lineage cells, we show that WNT7B recovers bone mass following glucocorticoid-induced bone loss, thanks to increased osteoblast number and function. However, WNT7B overexpression in bone either before or after glucocorticoid treatments does not ameliorate the abnormal accumulation of body fat. The study demonstrates a potent bone anabolic function for WNT7B in countering glucocorticoid-induced bone loss.

PKCδ deficiency inhibits fetal development and is associated with heart elastic fiber hyperplasia and lung inflammation in adult PKCδ knockout mice

Protein kinase C-delta (PKCδ) has a caspase-3 recognition sequence in its structure, suggesting its involvement in apoptosis. In addition, PKCδ was recently reported to function as an anti-cancer factor. The generation of a PKCδ knockout mouse model indicated that PKCδ plays a role in B cell homeostasis. However, the Pkcrd gene, which is regulated through complex transcription, produces multiple proteins via alternative splicing. Since gene mutations can result in the loss of function of molecular species required for each tissue, in the present study, conditional PKCδ knockout mice lacking PKCδI, II, IV, V, VI, and VII were generated to enable tissue-specific deletion of PKCδ using a suitable Cre mouse. We generated PKCδ-null mice that lacked whole-body expression of PKCδ. PKCδ+/- parental mice gave birth to only 3.4% PKCδ-/- offsprings that deviated significantly from the expected Mendelian ratio (χ2(2) = 101.7, P < 0.001). Examination of mice on embryonic day 11.5 (E11.5) showed the proportion of PKCδ-/- mice implanted in the uterus in accordance with Mendelian rules; however, approximately 70% of the fetuses did not survive at E11.5. PKCδ-/- mice that survived until adulthood showed enlarged spleens, with some having cardiac and pulmonary abnormalities. Our findings suggest that the lack of PKCδ may have harmful effects on fetal development, and heart and lung functions after birth. Furthermore, our study provides a reference for future studies on PKCδ deficient mice that would elucidate the effects of the multiple protein variants in mice and decipher the roles of PKCδ in various diseases.

Epigallocatechin-3-Gallate Modulates Postoperative Pain by Regulating Biochemical and Molecular Pathways

Treating postoperative (PO) pain is a clinical challenge. Inadequate PO pain management can lead to worse outcomes, for example chronic post-surgical pain. Therefore, acquiring new information on the PO pain mechanism would increase the therapeutic options available. In this paper, we evaluated the role of a natural substance, epigallocatechin-3-gallate (EGCG), on pain and neuroinflammation induced by a surgical procedure in an animal model of PO pain. We performed an incision of the hind paw and EGCG was administered for five days. Mechanical allodynia, thermal hyperalgesia, and motor dysfunction were assessed 24 h, and three and five days after surgery. At the same time points, animals were sacrificed, and sera and lumbar spinal cord tissues were harvested for molecular analysis. EGCG administration significantly alleviated hyperalgesia and allodynia, and reduced motor disfunction. From the molecular point of view, EGCG reduced the activation of the WNT pathway, reducing WNT3a, cysteine-rich domain frizzled (FZ)1 and FZ8 expressions, and both cytosolic and nuclear β-catenin expression, and the noncanonical β-catenin–independent signaling pathways, reducing the activation of the NMDA receptor subtype NR2B (pNR2B), pPKC and cAMP response element-binding protein (pCREB) expressions at all time points. Additionally, EGCG reduced spinal astrocytes and microglia activation, cytokines overexpression and nuclear factor kappa-light-chain-enhancer of activated B cells (NFkB) pathway, downregulating inducible nitric oxide synthase (iNOS) activation, cyclooxygenase 2 (COX-2) expression, and prostaglandin E2 (PGE2) levels. Thus, EGCG administration managing the WNT/β-catenin signaling pathways modulates PO pain related neurochemical and inflammatory alterations.

RhoA/Rock activation represents a new mechanism for inactivating Wnt/β-catenin signaling in the aging-associated bone loss

The Wnt/β-catenin signaling pathway appears to be particularly important for bone homeostasis, whereas nuclear accumulation of β-catenin requires the activation of Rac1, a member of the Rho small GTPase family. The aim of the present study was to investigate the role of RhoA/Rho kinase (Rock)-mediated Wnt/β-catenin signaling in the regulation of aging-associated bone loss. We find that Lrp5/6-dependent and Lrp5/6-independent RhoA/Rock activation by Wnt3a activates Jak1/2 to directly phosphorylate Gsk3β at Tyr216, resulting in Gsk3β activation and subsequent β-catenin destabilization. In line with these molecular events, RhoA loss- or gain-of-function in mouse embryonic limb bud ectoderms interacts genetically with Dkk1 gain-of-function to rescue the severe limb truncation phenotypes or to phenocopy the deletion of β-catenin, respectively. Likewise, RhoA loss-of-function in pre-osteoblasts robustly increases bone formation while gain-of-function decreases it. Importantly, high RhoA/Rock activity closely correlates with Jak and Gsk3β activities but inversely correlates with β-catenin signaling activity in bone marrow mesenchymal stromal cells from elderly male humans and mice, whereas systemic inhibition of Rock therefore activates the β-catenin signaling to antagonize aging-associated bone loss. Taken together, these results identify RhoA/Rock-dependent Gsk3β activation and subsequent β-catenin destabilization as a hitherto uncharacterized mechanism controlling limb outgrowth and bone homeostasis.

Wnt signaling contributes to withdrawal symptoms from opioid receptor activation induced by morphine exposure or chronic inflammation

Preventing and treating opioid dependence and withdrawal is a major clinical challenge, and the underlying mechanisms of opioid dependence and withdrawal remain elusive. We hypothesized that prolonged morphine exposure or chronic inflammation-induced μ-opioid receptor activity serves as a severe stress that elicits neuronal alterations and recapitulates events during development. Here, we report that Wnt signaling, which is important in developmental processes of the nervous system, plays a critical role in withdrawal symptoms from opioid receptor activation in mice. Repeated exposures of morphine or peripheral inflammation produced by intraplantar injection of complete Freund's adjuvant significantly increase the expression of Wnt5b in the primary sensory neurons in dorsal root ganglion (DRG). Accumulated Wnt5b in DRG neurons quickly transmits to the spinal cord dorsal horn (DH) after naloxone treatment. In the DH, Wnt5b, acts through the atypical Wnt-Ryk receptor and alternative Wnt-YAP/TAZ signaling pathways, contributing to the naloxone-precipitated opioid withdrawal-like behavioral symptoms and hyperalgesia. Inhibition of Wnt synthesis and blockage of Wnt signaling pathways greatly suppress the behavioral and neurochemical alterations after naloxone-precipitated withdrawal. These findings reveal a critical mechanism underlying naloxone-precipitated opioid withdrawal, suggesting that targeting Wnt5b synthesis in DRG neurons and Wnt signaling in DH may be an effective approach for prevention and treatment of opioid withdrawal syndromes, as well as the transition from acute to chronic pain.

Biphasic regulation of glutamine consumption by WNT during osteoblast differentiation

Osteoblasts are the principal bone-forming cells. As such, osteoblasts have enhanced demand for amino acids to sustain high rates of matrix synthesis associated with bone formation. The precise systems utilized by osteoblasts to meet these synthetic demands are not well understood. WNT signaling is known to rapidly stimulate glutamine uptake during osteoblast differentiation. Using a cell biology approach, we identified two amino acid transporters, γ(+)-LAT1 and ASCT2 (encoded by Slc7a7 and Slc1a5, respectively), as the primary transporters of glutamine in response to WNT. ASCT2 mediates the majority of glutamine uptake, whereas γ(+)-LAT1 mediates the rapid increase in glutamine uptake in response to WNT. Mechanistically, WNT signals through the canonical β-catenin (CTNNB1)-dependent pathway to rapidly induce Slc7a7 expression. Conversely, Slc1a5 expression is regulated by the transcription factor ATF4 downstream of the mTORC1 pathway. Targeting either Slc1a5 or Slc7a7 using shRNA reduced WNT-induced glutamine uptake and prevented osteoblast differentiation. Collectively, these data highlight the critical nature of glutamine transport for WNT-induced osteoblast differentiation.This article has an associated First Person interview with the joint first authors of the paper.

Adipsin promotes bone marrow adiposity by priming mesenchymal stem cells

Background

Marrow adipose tissue (MAT) has been shown to be vital for regulating metabolism and maintaining skeletal homeostasis in the bone marrow (BM) niche. As a reflection of BM remodeling, MAT is highly responsive to nutrient fluctuations, hormonal changes, and metabolic disturbances such as obesity and diabetes mellitus. Expansion of MAT has also been strongly associated with bone loss in mice and humans. However, the regulation of BM plasticity remains poorly understood, as does the mechanism that links changes in marrow adiposity with bone remodeling.

Methods

We studied deletion of Adipsin, and its downstream effector, C3, in C57BL/6 mice as well as the bone-protected PPARγ constitutive deacetylation 2KR mice to assess BM plasticity. The mice were challenged with thiazolidinedione treatment, calorie restriction, or aging to induce bone loss and MAT expansion. Analysis of bone mineral density and marrow adiposity was performed using a μCT scanner and by RNA analysis to assess adipocyte and osteoblast markers. For in vitro studies, primary bone marrow stromal cells were isolated and subjected to osteoblastogenic or adipogenic differentiation or chemical treatment followed by morphological and molecular analyses. Clinical data was obtained from samples of a previous clinical trial of fasting and high-calorie diet in healthy human volunteers.

Results

We show that Adipsin is the most upregulated adipokine during MAT expansion in mice and humans in a PPARγ acetylation-dependent manner. Genetic ablation of Adipsin in mice specifically inhibited MAT expansion but not peripheral adipose depots, and improved bone mass during calorie restriction, thiazolidinedione treatment, and aging. These effects were mediated through its downstream effector, complement component C3, to prime common progenitor cells toward adipogenesis rather than osteoblastogenesis through inhibiting Wnt/β-catenin signaling.

Conclusions

Adipsin promotes new adipocyte formation and affects skeletal remodeling in the BM niche. Our study reveals a novel mechanism whereby the BM sustains its own plasticity through paracrine and endocrine actions of a unique adipokine.

Funding

This work was supported by the National Institutes of Health T32DK007328 (NA), F31DK124926 (NA), R01DK121140 (JCL), R01AR068970 (BZ), R01AR071463 (BZ), R01DK112943 (LQ), R24DK092759 (CJR), and P01HL087123 (LQ).