FAK Promotes Osteoblast Progenitor Cell Proliferation and Differentiation by Enhancing Wnt Signaling

NELL2, a novel osteoinductive factor, regulates osteoblast differentiation and bone homeostasis through fibronectin 1/integrin-mediated FAK/AKT signaling

Neural EGFL-like 2 (NELL2) is a secreted protein known for its regulatory functions in the nervous and reproductive systems, yet its role in bone biology remains unexplored. In this study, we observed that NELL2 was diminished in the bone of aged and ovariectomized (OVX) mice, as well as in the serum of osteopenia and osteoporosis patients. In vitro loss-of-function and gain-of-function studies revealed that NELL2 facilitated osteoblast differentiation and impeded adipocyte differentiation from stromal progenitor cells. In vivo studies further demonstrated that the deletion of NELL2 in preosteoblasts resulted in decreased cancellous bone mass in mice. Mechanistically, NELL2 interacted with the FNI-type domain located at the C-terminus of Fibronectin 1 (Fn1). Moreover, we found that NELL2 activated the focal adhesion kinase (FAK)/AKT signaling pathway through Fn1/integrin β1 (ITGB1), leading to the promotion of osteogenesis and the inhibition of adipogenesis. Notably, administration of NELL2-AAV was found to ameliorate bone loss in OVX mice. These findings underscore the significant role of NELL2 in osteoblast differentiation and bone homeostasis, suggesting its potential as a therapeutic target for managing osteoporosis.

Nf2-FAK signaling axis is critical for cranial bone ossification and regeneration

Skeletal mesenchymal stem cells (MSCs) possess self-renewal capacities and play a leading role in the craniofacial system. However, their engagement in controlling cranial bone development and regeneration remains largely unidentified. Herein, we discovered the neurofibromin 2 (Nf2)-encoded regulator Merlin, demonstrating indispensableness in the craniofacial system. Mice lacking Nf2 in MSCs exhibit malformed cranial bones, diminished proliferation, increased apoptosis, and more severe osteogenesis impairment. Mechanically, we substantiate that Nf2 physically interacts with focal adhesion kinase (FAK) to preferentially mediate Erk1/2 and PI3K catalytic p110 subunit/Akt signaling. Meanwhile, Nf2-FAK disturbance in MSCs results in deficient migration, cytoskeletal organization and focal adhesion dynamics, and develops retarded regeneration of cranial bone defects. Collectively, our findings underscore an unrecognized scaffolding role for Nf2-FAK as upstream element in regulating PI3K/Akt and Erk1/2 action in osteoblasts, and illuminate its essentialness in coordinating cell migration, osteogenic lineage development, cranial bone ossification and regeneration.

CircFak promotes mechanical force-induced osteogenesis via FAK/AKT phosphorylation

OBJECTIVES

Orthodontic treatment is widely applied for addressing orofacial skeletal deformities, with the remodeling of the alveolar bone under mechanical force being the key factor. FAK is essential for cellular response to mechanical force. However, the function of circFak has never been reported. In this study, the microarrays showed that circFak may affect osteogenesis under mechanical force. We aimed to verify the effect of circFak in force-related bone remodeling and investigate the underlying mechanisms.

METHODS

Arraystar microarrays were used to identify differentially expressed circRNAs and microRNAs in response to mechanical stress. The subcellular distribution of circFak was analyzed via RT‒qPCR and FISH. ALP and ARS staining assays were performed to investigate the effects of circFak on osteogenesis. RNA sequencing, bioinformatics analysis, dual-luciferase reporter assays, and RNA immunoprecipitation were accomplished to discover the molecular mechanisms of circFak. AAV-sh-circFak mouse models with tooth movements were established. The role of circFak under mechanical force in vivo was assessed via immunofluorescence and micro-CT analyses.

RESULTS

CircFak expression was significantly upregulated under mechanical force. Osteogenic capacity of osteoblasts was positively correlated with the level of circFak. CircFak promoted mechanical force-induced osteogenesis through miR-425-5p/Ccn3 pathway, and further stimulated the phosphorylation of its parental sourced protein FAK. Our murine models showed that AAV-mediated circFak silencing suppressed osteogenesis.

CONCLUSION

CircFak could obviously promote osteogenesis under mechanical force and may possess ability to become a novel biomarker for prognosis of orthodontic treatments.

Selective Pyk2 inhibition enhances bone restoration through SCARA5-mediated bone marrow remodeling in ovariectomized mice

Understanding the intricate cellular interactions involved in bone restoration is crucial for developing effective strategies to promote bone healing and mitigate conditions such as osteoporosis and fractures. Here, we provide compelling evidence supporting the anabolic effects of a pharmacological Pyk2 inhibitor (Pyk2-Inh) in promoting bone restoration. In vitro, Pyk2 signaling inhibition markedly enhances alkaline phosphatase (ALP) activity, a hallmark of osteoblast differentiation, through activation of canonical Wnt/β-catenin signaling. Notably, analysis of human mesenchymal stem cells through RNA-seq revealed a novel candidate, SCARA5, identified through Pyk2-Inh treatment. We demonstrate that Scara5 plays a crucial role in suppressing the differentiation from stromal cells into adipocytes, and accelerates lineage commitment to osteoblasts, establishing Scara5 as a negative regulator of bone formation. Additionally, Pyk2 inhibition significantly impedes osteoclast differentiation and bone resorption. In a co-culture system comprising osteoblasts and osteoclasts, Pyk2-Inh effectively suppressed osteoclast differentiation, accompanied by a substantial increase in the transcriptional expression of Tnfrsf11b and Csf1 in osteoblasts, highlighting a dual regulatory role in osteoblast-osteoclast crosstalk. In an ovariectomized mouse model of osteoporosis, oral administration of Pyk2-Inh significantly increased bone mass by simultaneously reducing bone resorption, promoting bone formation and decreasing bone marrow fat. These results suggest Pyk2 as a potential therapeutic target for both adipogenesis and osteogenesis in bone marrow. Our findings underscore the importance of Pyk2 signaling inhibition as a key regulator of bone remodeling, offering promising prospects for the development of novel osteoporosis therapies.

Exploring the osteogenic potential of semisynthetic triterpenes from Combretum leprosum: An in vitro and in silico study

Combretum leprosum Mart. is a plant of the Combretaceae family, widely distributed in the Northeast region of Brazil, popularly used as an anti-inflammatory agent, and rich in triterpenes. This study evaluated in vitro and in silico potential osteogenic of two semisynthetic triterpenes (CL-P2 and CL-P2A) obtained from the pentacyclic triterpene 3β,6β,16β-trihydroxylup-20(29)-ene (CL-1) isolated from C. leprosum. Assays were carried out in cultured murine osteoblasts (OFCOL II), first investigating the possible toxicity of the compounds on these cells through viability assays (MTT). Cell proliferation and activation were investigated by immunohistochemical evaluation of Ki-67, bone alkaline phosphatase (ALP) activity, and mineralization test by Von Kossa. Molecular docking analysis was performed to predict the binding affinity of CL-P2 and CL-P2A to target proteins involved in the regulation of osteogenesis, including: bone morphogenetic protein 2 (BMP-2), proteins related to Wingless-related integration (WNT) pathway (Low-density lipoprotein receptor-related protein 6-LRP6 and sclerostin-SOST), and receptor activator of nuclear factor (NF)-kB-ligand (RANK-L). Next, Western Blot and immunofluorescence investigated BMP-2, WNT, RANK-L, and OPG protein expressions in cultured murine osteoblasts (OFCOL II). None of the CL-P2 and CL-P2A concentrations were toxic to osteoblasts. Increased cell proliferation, ALP activity, and bone mineralization were observed. Molecular docking assays demonstrated interactions with BMP-2, LRP6, SOST, and RANK-L/OPG. There was observed increased expression of BMP-2, WNT, and RANK-L/OPG proteins. These results suggest, for the first time, the osteogenic potential of CL-P2 and CL-P2A.

Regulation of intracellular cAMP levels in osteocytes by mechano-sensitive focal adhesion kinase via PDE8A

Osteocytes are the primary mechano-sensitive cell type in bone. Mechanical loading is sensed across the dendritic projections of osteocytes leading to transient reductions in focal adhesion kinase (FAK) activity. Knowledge regarding the signaling pathways downstream of FAK in osteocytes is incomplete. We performed tyrosine-focused phospho-proteomic profiling in osteocyte-like Ocy454 cells to identify FAK substrates. Gsα, parathyroid hormone receptor (PTH1R), and phosphodiesterase 8A (PDE8A), all proteins associated with cAMP signaling, were found as potential FAK targets based on their reduced tyrosine phosphorylation in both FAK- deficient or FAK inhibitor treated cells. Real time monitoring of intracellular cAMP levels revealed that FAK pharmacologic inhibition or gene deletion increased basal and GPCR ligand-stimulated cAMP levels and downstream phosphorylation of protein kinase A substrates. Mutating FAK phospho-acceptor sites in Gsα and PTH1R had no effect on PTH- or FAK inhibitor-stimulated cAMP levels. Since FAK inhibitor treatment augmented cAMP levels even in the presence of forskolin, we focused on potential FAK substrates downstream of cAMP generation. Indeed, PDE8A inhibition mimicked FAK inhibition at the level of increased cAMP, PKA activity, and expression of cAMP-regulated target genes. In vitro kinase assay showed that PDE8A is directly phosphorylated by FAK while immunoprecipitation assays revealed intracellular association between FAK and PDE8A. Thus, FAK inhibition in osteocytes acts synergistically with signals that activate adenylate cyclase to increase intracellular cAMP. Mechanically-regulated FAK can modulate intracellular cAMP levels via effects on PDE8A. These data suggest a novel signal transduction mechanism that mediates crosstalk between mechanical and cAMP-linked hormonal signaling in osteocytes.

Nanoparticle and Nanotopography-Induced Activation of the Wnt Pathway in Bone Regeneration

Background and Aims: Recent research has focused on developing nanoparticle and nanotopography-based technologies for bone regeneration. The Wingless-related integration site (Wnt) signaling pathway has been shown to play a vital role in this process, in particular in osteogenic differentiation and proliferation. The exact mechanisms by which nanoparticles and nanotopographies activate the Wnt signaling pathway, however, are not fully understood. This review aimed to elucidate the mechanisms by which nanoscale technologies activate the Wnt signaling pathway during bone regeneration. Methods: The terms "Wnt," "bone," and "nano*" were searched on PubMed and Ovid with no date limit. Only original research articles related to Wnt signaling and bone regeneration in the context of nanotopographies, nanoparticles, or scaffolds with nanotopographies/nanoparticles were reviewed. Results: The primary mechanism by which nanoparticles activated the Wnt pathway was by internalization through the endocytic pathway or diffusion through the cell membrane, leading to accumulation of nonphosphorylated β-catenin in the cytoplasm and subsequently downstream osteogenic signaling (e.g., upregulation of runt-related transcription factor 2 [RUNX2]). The specific size of the nanoparticles and the process of endocytosis itself has been shown to modulate the Wnt-β-catenin pathway. Nanotopographies were shown to directly activate frizzled receptors, initiating Wnt/β-catenin signaling. Additional studies showed nanotopographies to activate the Wnt/calcium (Wnt/Ca2+)-dependent and Wnt/planar cell polarity pathways through nuclear factor of activated T cells, and α5β1 integrin stimulation. Finally, scaffolds containing nanotopographies/nanoparticles were found to induce Wnt signaling through a combination of ion release (e.g., lithium, boron, lanthanum, and icariin), which inhibited glycogen synthase kinase 3 beta (GSK-3β) activity, and through similar mechanisms to the nanotopographies. Conclusion: This review concludes that nanoparticles and nanotopographies cause Wnt activation through several different mechanisms, specific to the size, shape, and structure of the nanoparticles or nanotopographies. Endocytosis-related mechanisms, integrin signaling and ion release were the major mechanisms identified across nanoparticles, nanotopographies, and scaffolds, respectively. Knowledge of these mechanisms will help develop more effective targeted nanoscale technologies for bone regeneration. Impact statement Nanoparticles and nanotopographies can activate the Wingless-related integration site (Wnt) signaling pathway, which is essential for bone regeneration. This review has identified that activation is due to endocytosis, integrin signaling and ion release, depending on the size, shape, and structure of the nanoparticles or nanotopographies. By identifying and further understanding these mechanisms, more effective nanoscale technologies that target the Wnt signaling pathway can be developed. These technologies can be used for the treatment of nonunion bone fractures, a major clinical challenge, with the potential to improve the quality of life of millions of patients around the world.

Inhibition of focal adhesion kinase 2 results in a macrophage polarization shift to M2 which attenuates local and systemic inflammation and reduces heterotopic ossification after polysystem extremity trauma

Introduction

Heterotopic ossification (HO) is a complex pathology often observed in combat injured casualties who have sustained severe, high energy polytraumatic extremity injuries. Once HO has developed, prophylactic therapies are limited outside of surgical excision. Tourniquet-induced ischemia injury (IR) exacerbates trauma-mediated musculoskeletal tissue injury, inflammation, osteogenic progenitor cell development and HO formation. Others have shown that focal adhesion kinase-2 (FAK2) plays a key role in regulating early inflammatory signaling events. Therefore, we hypothesized that targeting FAK2 prophylactically would mitigate extremity trauma induced IR inflammation and HO formation.

Methods

We tested whether the continuous infusion of a FAK2 inhibitor (Defactinib, PF-573228; 6.94 µg/kg/min for 14 days) can mitigate ectopic bone formation (HO) using an established blast-related extremity injury model involving femoral fracture, quadriceps crush injury, three hours of tourniquet-induced limb ischemia, and hindlimb amputation through the fracture site. Tissue inflammation, infiltrating cells, osteogenic progenitor cell content were assessed at POD-7. Micro-computed tomography imaging was used to quantify mature HO at POD-56.

Results

In comparison to vehicle control-treated rats, FAK2 administration resulted in no marked wound healing complications or weight loss. FAK2 treatment decreased HO by 43%. At POD-7, marked reductions in tissue proinflammatory gene expression and assayable osteogenic progenitor cells were measured, albeit no significant changes in expression patterns of angiogenic, chondrogenic and osteogenic genes. At the same timepoint, injured tissue from FAK-treated rats had fewer infiltrating cells. Additionally, gene expression analyses of tissue infiltrating cells resulted in a more measurable shift from an M1 inflammatory to an M2 anti-inflammatory macrophage phenotype in the FAK2 inhibitor-treated group.

Discussion

Our findings suggest that FAK2 inhibition may be a novel strategy to dampen trauma-induced inflammation and attenuate HO in patients at high risk as a consequence of severe musculoskeletal polytrauma.

Focal adhesion kinase (FAK): its structure, characteristics, and signaling in skeletal system

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase and distributes important regulatory functions in skeletal system. Mesenchymal stem cell (MSC) possesses significant migration and differentiation capacity, is an important source of distinctive bone cells production and a prominent bone development pathway. MSC has a wide range of applications in tissue bioengineering and regenerative medicine, and is frequently employed for hematopoietic support, immunological regulation, and defect repair, although current research is insufficient. FAK has been identified to cross-link with many other keys signaling pathways in bone biology and is considered as a fundamental "crossroad" on the signal transduction pathway and a "node" in the signal network to mediate MSC lineage development in skeletal system. In this review, we summarized the structure, characteristics, cellular signaling, and the interactions of FAK with other signaling pathways in the skeletal system. The discovery of FAK and its mediated molecules will lead to a new knowledge of bone development and bone construction as well as considerable potential for therapeutic use in the treatment of bone-related disorders such as osteoporosis, osteoarthritis, and osteosarcoma.

Assembling the Puzzle Pieces. Insights for in Vitro Bone Remodeling

As a highly dynamic organ, bone changes during throughout a person's life. This process is referred to as 'bone remodeling' and it involves two stages - a well-balanced osteoclastic bone resorption and an osteoblastic bone formation. Under normal physiological conditions bone remodeling is highly regulated that ensures tight coupling between bone formation and resorption, and its disruption results in a bone metabolic disorder, most commonly osteoporosis. Though osteoporosis is one of the most prevalent skeletal ailments that affect women and men aged over 40 of all races and ethnicities, currently there are few, if any safe and effective therapeutic interventions available. Developing state-of-the-art cellular systems for bone remodeling and osteoporosis can provide important insights into the cellular and molecular mechanisms involved in skeletal homeostasis and advise better therapies for patients. This review describes osteoblastogenesis and osteoclastogenesis as two vital processes for producing mature, active bone cells in the context of interactions between cells and the bone matrix. In addition, it considers current approaches in bone tissue engineering, pointing out cell sources, core factors and matrices used in scientific practice for modeling bone diseases and testing drugs. Finally, it focuses on the challenges that bone regenerative medicine is currently facing.

Matricellular Protein SMOC2 Potentiates BMP9-Induced Osteogenic Differentiation in Mesenchymal Stem Cells through the Enhancement of FAK/PI3K/AKT Signaling

Mesenchymal stem cells (MSCs) can self-renew and differentiate into multiple lineages, making MSC transplantation a promising option for bone regeneration. Both matricellular proteins and growth factors play an important role in regulating stem cell fate. In this study, we investigated the effects of matricellular protein SMOC2 (secreted modular calcium-binding protein 2) on bone morphogenetic protein 9 (BMP9) in mouse embryonic fibroblasts (MEFs) and revealed a possible molecular mechanism underlying this process. We found that SMOC2 was detectable in MEFs and that exogenous SMOC2 expression potentiated BMP9-induced osteogenic markers, matrix mineralization, and ectopic bone formation, whereas SMOC2 knockdown inhibited these effects. BMP9 increased the levels of p-FAK and p-AKT, which were either enhanced or reduced by SMOC2 and FAK silencing, respectively. BMP9-induced osteogenic markers were increased by SMOC2, and this increase was partially abolished by silencing FAK or LY290042. Furthermore, we found that general transcription factor 2I (GTF2I) was enriched at the promoter region of SMOC2 and that integrin β1 interacted with SMOC2 in BMP9-treated MEFs. Our findings demonstrate that SMOC2 can promote BMP9-induced osteogenic differentiation by enhancing the FAK/PI3K/AKT pathway, which may be triggered by facilitating the interaction between SMOC2 and integrin β1.

Overexpression of Laminin 5γ2 Chain Correlates with Tumor Cell Proliferation, Invasion, and Poor Prognosis in Laryngeal Squamous Cell Carcinoma

Objective

Laryngeal squamous cell carcinoma (LSCC) is a common malignant tumor. Laminin 5γ2 chain (LAMC2) was reported to be associated with tumorigenesis. This study explored the role of LAMC2 on LSCC progression by regulating the integrinβ1/FAK/Src/AKT pathway.

Methods

The level of LAMC2 in 46 LSCC patients was detected by qRT-PCR and western blot. Then the relationship between LAMC2 expression and LSCC malignancy as well as prognosis was analyzed, and the effect of LAMC2 expression on LSCC patient survival was also analyzed using the Kaplan–Meier survival curves. Afterwards, the LSCC cells were transfected with LAMC2 overexpression and knockdown vectors, the effect of LAMC2 on LSCC cell viability, proliferation ability, cell cycle, cell migration, and invasion were detected by CCK-8, colony formation, flow cytometry, wound healing, and Transwell assays. The expression of EMT-related biomarkers and integrin β1/FAK/Src/AKT signaling-related proteins was detected by western blot. Moreover, the effect of LAMC2 on LSCC tumor growth was evaluated by in vivo xenograft experiments and western blot.

Results

LAMC2 was expressed at high level in LSCC tissues and associated with poor prognosis. LAMC2 overexpression increased TU177 cell viability, proliferation ability, promoted cell cycle, cell migration, and invasion capacity. The expression of N-cadherin, vimentin, and integrinβ1/FAK/Src/AKT related proteins was increased, while the expression of E-cadherin protein was decreased. When the LAMC2 knockdown in AMC-HN-8 cells had opposite effects. Furthermore, shLAMC2 decreased tumor volume and the expression of LAMC2, Ki-67 and integrinβ1, but increased the expression of E-cadherin in LSCC tumor-bearing mice.

Conclusion

The findings suggested that LAMC2 was overexpressed in LSCC and correlated with poor prognosis. LAMC2 knockdown inhibited LSCC progression by regulating the integrinβ1/FAK/Src/AKT signaling pathway. Therefore, LAMC2 could be a target for LSCC therapy.

Comprehensive ceRNA network for MACF1 regulates osteoblast proliferation

BACKGROUND

Previous studies have shown that microtubule actin crosslinking factor 1 (MACF1) can regulate osteoblast proliferation and differentiation through non-coding RNA (ncRNA) in bone-forming osteoblasts. However, the role of MACF1 in targeting the competing endogenous RNA (ceRNA) network to regulate osteoblast differentiation remains poorly understood. Here, we profiled messenger RNA (mRNA), microRNA (miRNA), and long ncRNA (lncRNA) expression in MACF1 knockdown MC3TC‑E1 pre‑osteoblast cells.

RESULTS

In total, 547 lncRNAs, 107 miRNAs, and 376 mRNAs were differentially expressed. Significantly altered lncRNAs, miRNAs, and mRNAs were primarily found on chromosome 2. A lncRNA-miRNA-mRNA network was constructed using a bioinformatics computational approach. The network indicated that mir-7063 and mir-7646 were the most potent ncRNA regulators and mef2c was the most potent target gene. Pathway enrichment analysis showed that the fluid shear stress and atherosclerosis, p53 signaling, and focal adhesion pathways were highly enriched and contributed to osteoblast proliferation. Importantly, the fluid shear stress and atherosclerosis pathway was co-regulated by lncRNAs and miRNAs. In this pathway, Dusp1 was regulated by AK079370, while Arhgef2 was regulated by mir-5101. Furthermore, Map3k5 was regulated by AK154638 and mir-466q simultaneously. AK003142 and mir-3082-5p as well as Ak141402 and mir-446 m-3p were identified as interacting pairs that regulate target genes.

CONCLUSION

This study revealed the global expression profile of ceRNAs involved in the differentiation of MC3TC‑E1 osteoblasts induced by MACF1 deletion. These results indicate that loss of MACF1 activates a comprehensive ceRNA network to regulate osteoblast proliferation.

ITGA5 Promotes Tumor Progression through the Activation of the FAK/AKT Signaling Pathway in Human Gastric Cancer

BACKGROUND

ITGA5 is an adhesion molecule that integrates the intracellular structures with the extracellular matrix to perform biological functions. However, ITGA5 is highly expressed in a variety of tumors and is involved in tumor progression by promoting cell proliferation and metastasis. Nevertheless, little research has been performed on its function in gastric cancer. Therefore, the aim of this study was to investigate the role of ITGA5 in gastric cancer, focusing on the mechanism regulating the proliferation, invasion and migration.

METHODS

The expression of ITGA5 in gastric cancer tissues was assessed by the use of molecular bioinformatics databases and high-throughput sequencing of gastric cancer tissues from patients. Western blot, qPCR, and immunohistochemistry were performed to detect the expression of ITGA5 in samples from gastric cancer patients and gastric cancer cell lines. Furthermore, the ITGA5 gene was silenced and overexpressed in gastric cancer cells, and the effect on proliferation, invasion, migration, and tumorigenic ability was assessed.

RESULTS

ITGA5 mRNA and protein expression were upregulated in gastric cancer cell lines and tissues from patients, and its expression was closely associated with tumor size, lymph node metastasis, and TNM stage. In vitro and in vivo experiments showed that ITGA5 silencing resulted in the inhibition of proliferation, invasion, migration, and graft growth of gastric cancer cells; conversely, the overexpression resulted in the promotion of these cell functions. Our results finally showed that the effect of ITGA5 on proliferation, invasion, and migration of gastric cancer cells was performed through the activation of the FAK/AKT pathway.

CONCLUSIONS

ITGA5 promotes proliferation, invasion, and migration of gastric cancer cells through the activation of FAK/AKT signaling pathway, suggesting that ITGA5 may be potentially considered as a new target in gastric cancer therapy.

Adipogenesis or osteogenesis: destiny decision made by mechanical properties of biomaterials

Regenerative medicine affords an effective approach for restoring defect-associated diseases, and biomaterials play a pivotal role as cell niches to support the cell behavior and decide the destiny of cell differentiation. Except for chemical inducers, mechanical properties such as stiffness, pore size and topography of biomaterials play a crucial role in the regulation of cell behaviors and functions. Stiffness may determine the adipogenesis or osteogenesis of mesenchymal stem cells (MSCs) via the translocation of yes-associated protein (YAP) and the transcriptional coactivator with a PDZ-binding motif (TAZ). External forces transmit through cytoskeleton reorientation to assist nuclear deformation and molecule transport, meanwhile, signal pathways including the Hippo, FAK/RhoA/ROCK, and Wnt/β-catenin have been evidenced to participate in the mechanotransduction. Different pore sizes not only tailor the scaffold stiffness but also conform to the requirements of cell migration and vessels in-growth. Topography guides cell geometry along with mobility and determines the cell fate ascribed to micro/nano-scale contact. Herein, we highlight the recent progress in exploring the regulation mechanism by the physical properties of biomaterials, which might lead to more innovative regenerative strategies for adipose or bone tissue repair.

Cratoxylumxanthone C, a natural xanthone, inhibits lung cancer proliferation and metastasis by regulating STAT3 and FAK signal pathways

To discover phytochemicals as lead compounds for cancer treatment, cratoxylumxanthone C, a natural xanthone, was obtained from Cratoxylum cochinchinense (Lour.) Bl., for which there have been no reports on the biological effects against cancer. Our study revealed that cratoxylumxanthone C had significant anti-tumor activity by inducing apoptosis, augmenting cellular reactive oxygen species (ROS), and arresting cell circle. The mechanistic examination showed the inhibition of A549 cell proliferation and metastasis by cratoxylumxanthone C was coupled with the signal transducer and activator of transcription 3 (STAT3) and focal adhesion kinase (FAK) signaling pathways. Furthermore, the zebrafish models confirmed its significant in vivo anti-tumor activity, in which cratoxylumxanthone C inhibited tumor proliferation and metastasis and suppressed the angiogenesis. Comprehensively, these cellular and zebrafish experiments implied that cratoxylumxanthone C may have the potential to become an anti-tumor agent for lung cancer, especially non-small cell lung cancer (NSCLC).

The molecular mechanism of baicalein repressing progression of gastric cancer mediating miR-7/FAK/AKT signaling pathway

BACKGROUND

Baicalein (BAI) has a significant anti-cancerous function in the treatment of gastric cancer (GC). Focal adhesion kinase (FAK) is a key regulatory molecule in integrin and growth factor receptor mediated signaling. MicroRNA-7 (miR-7), has been considered as a potential tumor suppressor in a variety of cancers. However, the possible mechanisms by which BAI inhibiting progression of gastric cancer mediating miR-7/FAK/AKT signaling pathway remain unclear.

PURPOSE

To investigate the molecular mechanism and effects of BAI inhibiting progression of gastric cancer mediating miR-7/FAK/AKT signaling pathway.

METHODS

Gastric cancer cell lines with FAK knockdown and overexpression were constructed by lentivirus transfection. After BAI treatment, the effects of FAK protein on proliferation, metastasis and angiogenesis of gastric cancer cells were detected by MTT, EdU, colony formation, wound healing, transwell and Matrigel tube formation assays. In vivo experiment was performed by xenograft model. Immunofluorescence and western blot assay were used to detect the effects of FAK protein on the expression levels of EMT markers and PI3K/AKT signaling pathway related proteins. qRT-PCR and luciferase reporter assay were used to clarify the targeting relationship between miR-7 and FAK.

RESULTS

BAI can regulate FAK to affect proliferation, metastasis and angiogenesis of gastric cancer cells through PI3K/AKT signaling pathway. qRT-PCR showed BAI can upregulated the expression of miR-7 and luciferase reporter assay showed the targeting relationship between miR-7 and FAK. Additionally, miR-7 mediates cell proliferation, metastasis and angiogenesis by directly targeting FAK 3'UTR to inhibit FAK expression.

CONCLUSION

BAI repressing progression of gastric cancer mediating miR-7/FAK/AKT signaling pathway.

Inhibition of focal adhesion turnover prevents osteoblastic differentiation through β‐catenin mediated transduction of pro‐osteogenic substrate

The mechanism by which substrate surface characteristics are transduced by osteoblastic cells and their progenitors is not fully known. Data from previous studies by our group suggest the involvement of β‐catenin in the mechanism by which substrate surface characteristics are transduced. This focal adhesion and β‐catenin mediated mechanism functions through the liberation of β‐catenin from focal adhesion complexes in response to pro‐osteogenic substrate (POS) characteristics. After liberation, β‐catenin translocates and facilitates upregulation of genes associated with osteogenesis. It is not known whether the observed correlation between focal adhesion turnover and β‐catenin translocation directly results from focal adhesion turnover. In this study we inhibited focal adhesion turnover using a focal adhesion kinase inhibitor PF‐573228. We found that inhibition of focal adhesion turnover resulted in an abrogation of the more rapid translocation and increased transcriptional activity of β‐catenin induced by POS. In addition, inhibition of focal adhesion turnover mitigated the increase in osteoblastic differentiation induced by a POS as measured by alkaline phosphatase enzymatic activity and osteogenic gene and protein expression. Together, these data, coupled with previous findings, suggest that the observed β‐catenin translocation is a result of focal adhesion turnover, providing evidence for a focal adhesion initiated, β‐catenin mediated mechanism of substrate surface signal transduction.

Low-Intensity Pulsed Ultrasound Alleviates Osteoarthritis Condition Through Focal Adhesion Kinase-Mediated Chondrocyte Proliferation and Differentiation

OBJECTIVE

Osteoarthritis (OA) is a prevalent chronic multifactorial degenerative disease characterized by joint tissue inflammation, osteophyte formation, subchondral bone sclerosis, and articular cartilage degradation. Low-intensity pulsed ultrasound (LIPUS), a noninvasive ultrasound technique, is widely used to attenuate diseases. The aim of this study was to investigate whether LIPUS can ameliorate OA, and to explore its underlying molecular mechanism.

DESIGN

The OA model was established in a C57BL/6 mouse by the anterior cruciate ligament transaction method. OA was assessed using arthritis scoring and weightbearing parameters. Chondrocyte proliferation was detected by a CCK-8 assay. The levels of interleukin-6 (IL-6), IL-8 and tumor necrosis factor-α (TNF-α) in synovial fluid of the mice were measured by enzyme-linked immunosorbent assay.

RESULTS

In OA mice, the arthritis score and weightbearing abilities were dramatically improved by LIPUS treatment. LIPUS also remarkably declined the levels of inflammatory cytokines IL-6, IL-8, and TNF-α in synovial fluid of OA mice. Moreover, LIPUS promoted chondrocyte proliferation and differentiation by activating focal adhesion kinase (FAK) signaling. Inhibition of FAK significantly blocked LIPUS-mediated cell proliferation and differentiation in vitro, as well as inflammation condition in OA mice.

CONCLUSION

LIPUS alleviates OA through promoting chondrocytes proliferation and differentiation by activating FAK, which could act as an intervening target for OA treatment.

High-mobility group AT-Hook 1 mediates the role of nuclear factor I/X in osteogenic differentiation through activating canonical Wnt signaling

It was previously reported that the loss of the transcription factor nuclear factor I/X (NFIX) gene in mice impaired endochondral ossification and mineralization in bone. However, the cellular and molecular basis for the defect remains unexplored. In this study, we investigated if and how NFIX regulates osteoblast differentiation. Nfix mRNA was induced during osteogenic and adipogenic differentiation of progenitor cells. Loss-of-function and gain-of-function studies revealed that NFIX induced osteoblast differentiation and impaired adipocyte formation from progenitor cells. RNA-seq and promoter analysis revealed that NFIX transcriptionally stimulated the expression of high-mobility group AT-Hook 1 (HMGA1). We then demonstrated that HMGA1 stimulated osteogenic differentiation of progenitor cells at the expense of adipogenic differentiation. The effect of Nfix siRNA on the differentiation of progenitor cells could be attenuated when HMGA1 was simultaneously overexpressed. Further investigations revealed the stimulatory effect of NFIX and HMGA1 on canonical wingless-type MMTV integration site family (Wnt) signaling. HMGA1 transcriptionally activates the expression of low-density lipoprotein receptor-related protein 5. Finally, in vivo transfection of Nfix siRNA to the marrow of mice reduced osteoblasts and increased fat accumulation in the marrow, and inactivated HMGA1/β-catenin signaling in bone marrow mesenchymal stem cells. This study suggests that HMGA1 plays a role in osteoblast commitment and mediates the function of NFIX through transcriptionally activating canonical Wnt signaling.

Bioinspired peptide adhesion on Ti implants alleviates wear particle-induced inflammation and improves interfacial osteogenesis

In the inflammatory peri-implant microenvironment, excessive polarization of macrophages to the proinflammatory M1 phenotype can trigger the secretion of inflammatory cytokines, which promote bone resorption and impede osteogenesis around implants. The direct consequence of this process is the failure of prosthetic implants due to aseptic loosening. To reverse the inflammatory microenvironment and prevent prosthesis loosening, a mussel adhesion-inspired surface strategy was used for bioengineering of titanium implants with integrin-binding ability. In our design, a mussel-inspired catecholic peptide with tetravalent 3,4-dihydroxy-l-phenylalanine (DOPA) and Arg-Gly-Asp (RGD) sequences was synthesized. The peptide can easily anchor to the surface of medical titanium materials through a mussel adhesive mechanism. We found that peptide-decorated titanium implants could effectively inhibit peri-implant inflammation in a wear particle model and could promote the polarization of macrophages to a pro-healing M2 phenotype by interfering with integrin-α₂β₁ and integrin-α_vβ₃. Moreover, the peptide coating increased the adherence of osteoblasts and promoted osteogenesis on titanium implants even under inflammatory conditions. This work suggested that this biomimetic catecholic integrin-binding peptide can provide facile tactics for surface bioengineering of medical prostheses with improved interfacial osteogenesis under inflammatory conditions, which might contribute greatly to the prevention of prosthesis loosening and the improvement of clinical outcomes.

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

With increasing life expectations, more and more patients suffer from fractures either induced by intensive sports or other bone-related diseases. The balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption is the basis for maintaining bone health. Osterix (Osx) has long been known to be an essential transcription factor for the osteoblast differentiation and bone mineralization. Emerging evidence suggests that Osx not only plays an important role in intramembranous bone formation, but also affects endochondral ossification by participating in the terminal cartilage differentiation. Given its essentiality in skeletal development and bone formation, Osx has become a new research hotspot in recent years. In this review, we focus on the progress of Osx's function and its regulation in osteoblast differentiation and bone mass. And the potential role of Osx in developing new therapeutic strategies for osteolytic diseases was discussed.

The Crosstalk between FAK and Wnt Signaling Pathways in Cancer and Its Therapeutic Implication

Focal adhesion kinase (FAK) and Wnt signaling pathways are important contributors to tumorigenesis in several cancers. While most results come from studies investigating these pathways individually, there is increasing evidence of a functional crosstalk between both signaling pathways during development and tumor progression. A number of FAK-Wnt interactions are described, suggesting an intricate, context-specific, and cell type-dependent relationship. During development for instance, FAK acts mainly upstream of Wnt signaling; and although in intestinal homeostasis and mucosal regeneration Wnt seems to function upstream of FAK signaling, FAK activates the Wnt/β-catenin signaling pathway during APC-driven intestinal tumorigenesis. In breast, lung, and pancreatic cancers, FAK is reported to modulate the Wnt signaling pathway, while in prostate cancer, FAK is downstream of Wnt. In malignant mesothelioma, FAK and Wnt show an antagonistic relationship: Inhibiting FAK signaling activates the Wnt pathway and vice versa. As the identification of effective Wnt inhibitors to translate in the clinical setting remains an outstanding challenge, further understanding of the functional interaction between Wnt and FAK could reveal new therapeutic opportunities and approaches greatly needed in clinical oncology. In this review, we summarize some of the most relevant interactions between FAK and Wnt in different cancers, address the current landscape of Wnt- and FAK-targeted therapies in different clinical trials, and discuss the rationale for targeting the FAK-Wnt crosstalk, along with the possible translational implications.

FAK Promotes Early Osteoprogenitor Cell Proliferation by Enhancing mTORC1 Signaling

Focal adhesion kinase (FAK) has important functions in bone homeostasis but its role in early osteoprogenitor cells is unknown. We show herein that mice lacking FAK in Dermo1-expressing cells exhibited low bone mass and decreased osteoblast number. Mechanistically, FAK-deficient early osteoprogenitor cells had decreased proliferation and significantly reduced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, a central regulator of cell growth and proliferation. Furthermore, our data showed that the pharmacological inhibition of FAK kinase-dependent function alone was sufficient to decrease the proliferation and compromise the mineralization of early osteoprogenitor cells. In contrast to the Fak deletion in early osteoprogenitor cells, FAK loss in Col3.6 Cre-targeted osteoblasts did not cause bone loss, and Fak deletion in osteoblasts did not affect proliferation, differentiation, and mTORC1 signaling but increased the level of active proline-rich tyrosine kinase 2 (PYK2), which belongs to the same non-receptor tyrosine kinase family as FAK. Importantly, mTORC1 signaling in bone marrow stromal cells (BMSCs) was reduced if FAK kinase was inhibited at the early osteogenic differentiation stage. In contrast, mTORC1 signaling in BMSCs was not affected if FAK kinase was inhibited at a later osteogenic differentiation stage, in which, however, the concomitant inhibition of both FAK kinase and PYK2 kinase reduced mTORC1 signaling. In summary, our data suggest that FAK promotes early osteoprogenitor cell proliferation by enhancing mTORC1 signaling via its kinase-dependent function and the loss of FAK in osteoblasts can be compensated by the upregulated active PYK2. © 2020 American Society for Bone and Mineral Research.

Protocadherins at the Crossroad of Signaling Pathways

Protocadherins (Pcdhs) are cell adhesion molecules that belong to the cadherin superfamily, and are subdivided into clustered (cPcdhs) and non-clustered Pcdhs (ncPcdhs) in vertebrates. In this review, we summarize their discovery, expression mechanisms, and roles in neuronal development and cancer, thereby highlighting the context-dependent nature of their actions. We furthermore provide an extensive overview of current structural knowledge, and its implications concerning extracellular interactions between cPcdhs, ncPcdhs, and classical cadherins. Next, we survey the known molecular action mechanisms of Pcdhs, emphasizing the regulatory functions of proteolytic processing and domain shedding. In addition, we outline the importance of Pcdh intracellular domains in the regulation of downstream signaling cascades, and we describe putative Pcdh interactions with intracellular molecules including components of the WAVE complex, the Wnt pathway, and apoptotic cascades. Our overview combines molecular interaction data from different contexts, such as neural development and cancer. This comprehensive approach reveals potential common Pcdh signaling hubs, and points out future directions for research. Functional studies of such key factors within the context of neural development might yield innovative insights into the molecular etiology of Pcdh-related neurodevelopmental disorders.

Molecular mechanosensors in osteocytes

Osteocytes, the most abundant and long-lived cells in bone, are the master regulators of bone remodeling. In addition to their functions in endocrine regulation and calcium and phosphate metabolism, osteocytes are the major responsive cells in force adaptation due to mechanical stimulation. Mechanically induced bone formation and adaptation, disuse-induced bone loss and skeletal fragility are mediated by osteocytes, which sense local mechanical cues and respond to these cues in both direct and indirect ways. The mechanotransduction process in osteocytes is a complex but exquisite regulatory process between cells and their environment, between neighboring cells, and between different functional mechanosensors in individual cells. Over the past two decades, great efforts have focused on finding various mechanosensors in osteocytes that transmit extracellular mechanical signals into osteocytes and regulate responsive gene expression. The osteocyte cytoskeleton, dendritic processes, Integrin-based focal adhesions, connexin-based intercellular junctions, primary cilium, ion channels, and extracellular matrix are the major mechanosensors in osteocytes reported so far with evidence from both in vitro and in vitro studies. This review aims to give a systematic introduction to osteocyte mechanobiology, provide details of osteocyte mechanosensors, and discuss the roles of osteocyte mechanosensitive signaling pathways in the regulation of bone homeostasis.

BMP9 is a potential therapeutic agent for use in oral and maxillofacial bone tissue engineering

Oral and maxillofacial surgery is often challenging due to defective bone healing owing to the microbial environment of the oral cavity, the additional involvement of teeth and esthetic concerns. Insufficient bone volume as a consequence of aging and some oral and maxillofacial surgical procedures, such as tumor resection of the jaw, may further impact facial esthetics and cause the failure of certain procedures, such as oral and maxillofacial implantation. Bone morphogenetic protein (BMP) 9 (BMP9) is one of the most effective BMPs to induce the osteogenic differentiation of different stem cells. A large cross-talk network that includes the BMP9, Wnt/β, Hedgehog, EGF, TGF-β and Notch signaling pathways finely regulates osteogenesis induced by BMP9. Epigenetic control during BMP9-induced osteogenesis is mainly dependent on histone deacetylases (HDACs), microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), which adds another layer of complexity. As a result, all these factors work together to orchestrate the molecular and cellular events underlying BMP9-related tissue engineering. In this review, we summarize our current understanding of the SMAD-dependent and SMAD-independent BMP9 pathways, with a particular focus on cross-talk and cross-regulation between BMP9 and other major signaling pathways in BMP9-induced osteogenesis. Furthermore, recently discovered epigenetic regulation of BMP9 pathways and the molecular and cellular basis of the application of BMP9 in tissue engineering in current oral and maxillofacial surgery and other orthopedic-related clinical settings are also discussed.

A novel Sprouty4-ERK1/2-Wnt/β-catenin regulatory loop in marrow stromal progenitor cells controls osteogenic and adipogenic differentiation

BACKGROUND

Sprouty (SPRY) proteins play critical roles in controlling cell proliferation, differentiation, and survival by inhibiting receptor tyrosine kinase (RTK)-mediated extracellular signal-regulated kinase (ERK) signaling. Recent studies have demonstrated that SPRY4 negatively regulates angiogenesis and tumor growth. However, whether SPRY4 regulates osteogenic and/or adipogenic differentiation of mesenchymal stem cells remains to be explored.

RESULTS

In this study, we investigated the expression pattern of Spry4 and found that its expression was regulated during the differentiation of mouse marrow stromal progenitor cells and increased in the metaphysis of ovariectomized mice. In vitro loss-of-function and gain-of-function studies demonstrated that SPRY4 inhibited osteogenic differentiation and stimulated adipogenic differentiation of progenitor cells. In vivo experiments showed that silencing of Spry4 in the marrow of C57BL/6 mice blocked fat accumulation and promoted osteoblast differentiation in ovariectomized mice. Mechanistic investigations revealed the inhibitory effect of SPRY4 on canonical wingless-type MMTV integration site (Wnt) signaling and ERK pathway. ERK1/2 was shown to interact with low-density lipoprotein receptor-related protein 6 (LRP6) and activate the canonical Wnt signaling pathway. Inactivation of Wnt signaling attenuated the inhibition of adipogenic differentiation and stimulation of osteogenic differentiation by Spry4 small interfering RNA (siRNA). Finally, promoter study revealed that β-catenin transcriptionally inhibited the expression of Spry4.

CONCLUSIONS

Our study for the first time suggests that a novel SPRY4-ERK1/2-Wnt/β-catenin regulatory loop exists in marrow stromal progenitor cells and plays a key role in cell fate determination. It also highlights the potential of SPRY4 as a novel therapeutic target for the treatment of metabolic bone disorders such as osteoporosis.

A Peptide Construct Mediates Focal Adhesion Pathway Through the Activation of Integrin Receptor

BACKGROUND

The integrin family receptors stimulate the cellular proliferation and migration through the focal adhesion pathway by the activation of PTK2, VASP and TSP1 proteins. The purpose of this study was to investigate the integrin-ligated motifs through the activation of focal adhesion pathway.

METHODS

A chimeric peptide was predicted from the integrin-mediated ligands by bioinformatics tools. The VSMCs were treated with the chimeric peptide and simvastatin. The PTK2, VASP and TSP1 protein and gene expression levels were measured by RT-qPCR and Western Blotting techniques, respectively. AutoDock Tools were used for the docking technique.

RESULTS

The PTK2, VASP and TSP1 protein expression levels increased significantly in the VSMCs treated with chimeric peptide in conversely with the effects of simvastatin. The docking results suggested two motifs in the chimeric peptide.

CONCLUSION

In conclusion, the chimeric peptide activated the focal adhesion pathway. The motifs 1 and 2 may be directly involved in the transduction of signal by integrin family receptors.

Molecular structure, expression, and functional role of Clec11a in skeletal biology and cancers

C-type lectin domain family 11 member A (Clec11a), also known as stem cell growth factor (SCGF), C-type lectin superfamily member 3 (CLECSF3), or osteolectin was initially identified as a growth factor for hematopoietic progenitor cells. The human Clec11a gene encodes a polypeptide of 323 amino acids with characteristics of a secreted glycoprotein encompassing two integrin-binding motifs, RGD (Arg-Gly-Asp) and LDT (Leu-Asp-Thr), a putative leucine zipper domain, and a functional C-type lectin domain. It regulates hematopoietic differentiation and homeostasis and exhibits a protective effect against severe malarial anemia and lipotoxicity. Furthermore, Clec11a promotes the differentiation of mesenchymal progenitors into mature osteoblasts in vitro and plays an important role in the maintenance of adult skeleton age-related bone loss and fracture repair. Receptor ligand binding results in activation of downstream signaling cascades including glycogen synthase kinase 3 (GSK3), β-catenin, and Wnt, resulting in the expression of osteoblast-related gene transcripts including Alp, Runx2, Lef1, and Axin2. In addition, Clec11a is also associated with the development of several cancers, including leukemia, multiple myeloma, and gastrointestinal tract tumors. To date, however, the mechanisms governing transcription regulation of the Clec11a gene are not known and remain to be uncovered. Understanding the function and mechanism of action of Clec11a will pave the way for the development of Clec11a as a novel therapeutic target for conditions such as cancer, anemia, and skeletal diseases.

Changed cellular functions and aberrantly expressed miRNAs and circRNAs in bone marrow stem cells in osteonecrosis of the femoral head

The present study aimed to detect the correlations between altered cellular functions in bone marrow stem cells (BMSCs) and osteonecrosis of the femoral head (ONFH). By profiling the aberrant expression of miRNAs and circRNAs in BMSCs isolated from ONFH patients, the present study aimed to further explore the potential regulatory mechanisms of action of circRNAs in ONFH using integrated bioinfor-matics analysis. BMSCs were isolated from seven ONFH patients and seven controls. Cellular functions, including proliferation, apoptosis and differentiation, were compared. miRNA and circRNA sequencing were conducted using RNA samples of three ONFH patients and three controls to identify differentially expressed circRNAs and miRNAs. The expression of hsa_circ_0000219, hsa_circ_0004588 and hsa_circ_0005936 were validated by qPCR. Target miRNAs were also predicted and validated by qPCR and circRNA-miRNA co-expression networks were constructed. BMSCs of ONFH patients displayed decreased proliferation and increased apoptosis during in vitro culturing. In addition, reduced osteogenesis and enhanced adipogenesis were found in the ONFH group. A total of 129 miRNAs and 231 circRNAs were detected to be differentially expressed. The expression levels of hsa_circ_0000219, hsa_circ_0004588 and hsa_circ_0005936 were significantly decreased in BMSCs of ONFH patients. A number of target miRNAs related to cell proliferation, apoptosis and differentiation were predicted for hsa_circ_0000219 and hsa_circ_0005936. The expression levels of miR-144-3p and miR-1270 were found to be elevated in ONFH patients, which was consistent with miRNA sequencing data and competitive endogenous RNA hypothesis. Time-dependent expression patterns of hsa_circ_0000219, hsa_circ_0004588, hsa_circ_0005936, miR-144-3p and miR-1270 were also validated during osteogenic and adipogenic differentiation in BMSCs. The results of the present study substantiated the involvement of BMSCs in ONFH development. hsa_circ_0000219 and hsa_circ_0005936 may regulate the progression of ONFH by mediating the proliferation and differentiation of BMSCs by sponging miRNAs.

Inhibition of MSTN signal pathway may participate in LIPUS preventing bone loss in ovariectomized rats

INTRODUCTION

Menopause can lead to osteoporosis, which is characterized by destruction of bone microstructure, poor mechanical properties, and prone to fracture. LIPUS can effectively promote bone formation and fracture healing. MSTN is a transforming growth factor-β family member that acts as a negative regulator of skeletal muscle growth. A MSTN deficiency also has a positive effect on bone formation. However, whether LIPUS could inhibit bone loss and promote healing of bone injury of menopause through the inhibition of the MSTN signaling pathway has not been previously investigated. We herein investigated the effects of LIPUS on bone architecture, mechanical properties, the healing of bone defects, and its potential molecular mechanisms in ovariectomized rats.

MATERIALS AND METHODS

The rats were randomly divided into three groups: sham ovariectomized group (Sham), ovariectomized model group (OVX), ovariectomized model with LIPUS therapy group (OVX + LIPUS). The OVX + LIPUS rats were treated with LIPUS (1.5 MHz, 30 mW/cm²) on the femur for 20 min/day that lasted for 19 days.

RESULTS

LIPUS effectively improved the bone microstructure, increased mechanical properties and promoted the healing of bone defects in ovariectomized rats. Moreover, LIPUS effectively decreased the MSTN content in serum and quadriceps muscle in ovariectomized rats, and inhibited the expression of MSTN downstream signaling molecules and activated the Wnt signaling pathway in the femur.

CONCLUSIONS

The present study shows that LIPUS improved osteoporosis and promoted bone defect healing in the ovariectomized rats may through the inhibition of the MSTN signal pathway.

FAK mediates BMP9-induced osteogenic differentiation via Wnt and MAPK signaling pathway in synovial mesenchymal stem cells

Objective: Focal adhesion kinase (FAK) has critical functions in proliferation and differentiation of many cell types, however, the role of FAK on BMP9-induced osteogenic differentiation in SMSCs has not been characted. The purpose of current study is to explore the mechanism of FAK on the BMP9-induced osteogenesis of SMSCs in vitro and in vivo. Methods: The optimal dose of BMP9 was determined by incubation in different BMP9 concentrations, then cells were transfected with siRNA-induced FAK knockdown in BMP9-induced osteogenesis. Cell proliferation, migration, the osteogenic capacity, and the underlying mechanism were further detected in vitro. Imaging and pathological examination were conducted to observe the bone formation in vivo. Results: Our findings suggested that BMP9 could obviously promote FAK phosphorylation in osteogenic conditions. In contrast, FAK knockdown significantly decreased the cell proliferation, migration, the osteogenic capacity of SMSCs. To be specific, FAK knockdown could markedly inhibit the Wnt and MAPK signal pathway of SMSCs induced by BMP9. Besides, FAK knockdown could also effectively inhibit BMP-9-induced bone formation in vivo. Conclusion: FAK plays a pivotal role in promoting BMP9-induced osteogenesis of SMSCs, which is probably via activating Wnt and MAPK pathway.

Autophagy Regulates Craniofacial Bone Acquisition

Increasing evidence has demonstrated the important role of autophagy in skeletal homeostasis; however, the role of autophagy in craniofacial bone development and acquisition is largely unknown. In this study, we investigated the effect of autophagy suppression on craniofacial bone acquisition by deleting Fip200 or Atg5, two essential autophagy genes, using Osterix-Cre (Osx-Cre). We found that the Osx-Cre transgene mildly decreased the bone mass of parietal bone but not frontal bone, and did not affect cranial base bone mass in adult mice. In the cranial vault, Fip200 or Atg5 deletion similarly decreased 50% bone mass of neural crest-derived frontal bone; Atg5 deletion decreased 50% and Fip200 deletion decreased 30% bone mass of mesoderm-derived parietal bone. In the cranial base, Fip200 or Atg5 deletion similarly decreased 30% bone mass of neural crest-derived presphenoid bone; Atg5 deletion decreased 30% and Fip200 deletion decreased 16% bone mass of mesoderm-derive basioccipital bone. Lastly, we used doxycycline treatment to inhibit the Osx-Cre expression until 2 months of age and showed that postnatal Fip200 deletion led to cranial vault bone mass decrease in association with a small increase in both bone volume/tissue volume and tissue mineral density. Altogether, this study demonstrated the important role of autophagy in craniofacial bone acquisition during development and postnatal growth.

Focal adhesion kinase promotes BMP2-induced osteogenic differentiation of human urinary stem cells via AMPK and Wnt signaling pathways

Human urine-derived stem cells (hUSCs) serve as favorable candidates for bone transplants due to their efficient proliferative and multipotent differentiation abilities, as well as the capacity to secrete a variety of vasoactive agents to facilitate tissue engineering. The present study aimed to explore the role of focal adhesion kinase (FAK) in bone morphogenetic protein 2 (BMP2)-induced osteogenic differentiation of hUSCs and to investigate the underlying mechanism. The degree of osteogenic differentiation and the correlated signals, following BMP2 overexpression and siRNA-mediated silencing of FAK, were determined in vitro. Moreover, hUSCs induced bone formation in a rat model with cranial defects, in vivo. Our findings revealed that alkaline phosphatase production, calcium deposits, osteocalcin and osteopontin expression, and bone formation were upregulated in vitro and in vivo following BMP2-induced osteogenic differentiation, and AMPK and Wnt signaling pathway activation by FAK could effectively regulate BMP2-enhanced osteogenic differentiation of hUSCs. Taken together, these findings indicated that FAK could mediate BMP2-enhanced osteogenic differentiation of hUSCs through activating adenosine 5'-monophosphate-activated protein kinase and Wnt signaling pathways.

BK ablation attenuates osteoblast bone formation via integrin pathway

Impaired bone formation is one of the major causes of low bone mass and skeletal fragility that occurs in osteoporosis. However, the mechanisms underlying the defects in bone formation are not well understood. Here, we report that big conductance calcium-activated potassium channels (BKs) are required for bone formation and osteoblast function both in vivo and in vitro. By 15 weeks of age, BK knockout (BKO) mice exhibited a decline in bone mineral density and trabecular bone volume of the tibiae and lumbar vertebrae, which were associated with impaired bone formation and osteoblast activity. Mechanistically, BK ablation in bone and bone marrow mesenchymal stem cells (BMSCs) of BKO mice inhibited integrin signaling. Furthermore, the binding of α subunit of BK with integrin β1 protein in osteoblasts was confirmed, and FAK-ERK1/2 signaling was proved to be involved by genetic modification of KCNMA1 (which encodes the α subunit of BK) in ROS17/2.8 osteoblast cells. These findings indicated that BK regulates bone formation by promoting osteoblast differentiation via integrin pathway, which provided novel insight into ion transporter crosstalk with the extracellular matrix in osteoblast regulation and revealed a new potential strategy for intervention in correcting bone formation defects.

Regional difference in microRNA regulation in the skull vault

BACKGROUND

The murine calvaria has several membrane bones with different tissue origins (e.g., neural crest-derived frontal bone vs. mesoderm-derived parietal bone). Neural crest-derived frontal bone exhibits superior osteogenic activities and bone regeneration. MicroRNA (miRNA) has been emerged as a crucial regulator during organogenesis and is involved in a range of developmental processes. However, the underlying roles of miRNA regulation in frontal bone and parietal bone is unknown.

RESULTS

Total of 83 significantly expressed known miRNAs were identified in frontal bones versus parietal bones. The significantly enriched gene ontology and KEGG pathway that were predicted by the enrichment miRNAs were involved in several biological processes (cell differentiation, cell adhesion, and transcription), and multiple osteogenic pathways (e.g., focal adhesion, MAPK, VEGF, Wnt, and insulin signaling pathway. Focal adhesion and insulin signaling pathway were selected for target verification and functional analysis, and several genes were predicted to be targets genes by the differentially expressed miRNAs, and these targets genes were tested with significant expressions.

CONCLUSIONS

Our results revealed a novel pattern of miRNAs in murine calvaria with dual tissue origins, and explorations of these miRNAs will be valuable for the translational studies to enhance osteogenic potential and bone regeneration in the clinic.

Delta Like-1 Gene Mutation: A Novel Cause of Congenital Vertebral Malformation

Skeletal development throughout the embryonic and postnatal phases is a dynamic process, based on bone remodeling and the balance between the activities of osteoclasts and osteoblasts modulating skeletal homeostasis. The Notch signaling pathway is a regulator of several developmental processes, and plays a crucial role in the development of the human skeleton by regulating the proliferation and differentiation of skeletal cells. The Delta Like-1 (DLL1) gene plays an important role in Notch signaling. We propose that an identified alteration in DLL1 protein may affect the downstream signaling. In this article, we present for the first time two siblings with a mutation in the DLL1 gene, presenting with congenital vertebral malformation. Using variable in silico prediction tools, it was predicted that the variant was responsible for the development of disease. Quantitative reverse-transcription polymerase chain reaction (PCR) for the Notch signaling pathway, using samples obtained from patients, showed a significant alteration in the expression of various related genes. Specifically, the expression of neurogenic locus notch homolog protein 1, SNW domain-containing protein 1, disintegrin, and metalloproteinase domain-containing proteins 10 and 17, was upregulated. In contrast, the expression of HEY1, HEY2, adenosine deaminase (ADA), and mastermind-like-1 (MAML-1) was downregulated. Furthermore, in a phosphokinase array, four kinases were significantly changed in patients, namely, p27, JANK1/2/3, mitogen- and stress-activated protein kinases 1 and 2, and focal adhesion kinase. Our results suggest an implication of a DLL1 defect related to the Notch signaling pathway, at least in part, in the morphologic abnormality observed in these patients. A limitation of our study was the low number of patients and samples. Further studies in this area are warranted to decipher the link between a DLL1 defect and skeletal abnormality.

High concentration magnesium inhibits extracellular matrix calcification and protects articular cartilage via Erk/autophagy pathway

The significant cytopathological changes of osteoarthritis are chondrocyte hypertrophy, proteoglycan loss, extracellular matrix (ECM) calcification, and terminally, the replacement of cartilage by bone. Meanwhile, magnesium ion (Mg²⁺ ), as the second most abundant divalent cation in the human body, has been proved to inhibit the ECM calcification of hBMSCs (human bone marrow stromal cells), hVSMCs (Human vascular smooth muscle cells), and TDSCs (tendon-derived stem cells) in vitro studies. The ATDC5 cell line, which holds chondrocyte characteristics, was used in this study as an in vitro subject. We found that Mg²⁺ can efficiently suppress the ECM calcification and downregulate both hypertrophy and matrix metalloproteinase-related genes. Meanwhile, Mg²⁺ inhibits the formation of autophagy by inhibiting Erk phosphorylation signaling and lowers the expression of LC3, and eventually effectively reduces the formation of ECM calcification in vitro. In this study, we also used destabilization of the medial meniscus (DMM)-induced osteoarthritis (OA) animal model to further confirm the protective effect of Mg²⁺ on articular cartilage. Compared with the control group (saline-injected), continuous intra-articular magnesium chloride (MgCl₂ ) injection can significantly alleviate the severity of cartilage calcification in OA animal model. Immunofluorescence staining also revealed that saline-injected DMM group had a higher positive rate of LC3 expression in cartilage chondrocytes, compared with MgCl₂ -injected DMM group. In general, Mg²⁺ can significantly downregulate the hypertrophic gene Runx2, MMP13, and Col10α1, upregulate the chondrogenic genes Sox9 and Col1α1, inhibit the Erk phosphorylation signaling, reduce the expression of autophagy protein LC3, and effectively inhibit the ECM calcification of ATDC5. In vivo study also proved that intra-articular injection of Mg²⁺ protected knee cartilage by inhibiting the autophagy formation.

Integrin alpha11 is an Osteolectin receptor and is required for the maintenance of adult skeletal bone mass

We previously discovered a new osteogenic growth factor that is required to maintain adult skeletal bone mass, Osteolectin/Clec11a. Osteolectin acts on Leptin Receptor⁺ (LepR⁺) skeletal stem cells and other osteogenic progenitors in bone marrow to promote their differentiation into osteoblasts. Here we identify a receptor for Osteolectin, integrin α11, which is expressed by LepR⁺ cells and osteoblasts. α11β1 integrin binds Osteolectin with nanomolar affinity and is required for the osteogenic response to Osteolectin. Deletion of Itga11 (which encodes α11) from mouse and human bone marrow stromal cells impaired osteogenic differentiation and blocked their response to Osteolectin. Like Osteolectin deficient mice, Lepr-cre; Itga11^fl/fl mice appeared grossly normal but exhibited reduced osteogenesis and accelerated bone loss during adulthood. Osteolectin binding to α11β1 promoted Wnt pathway activation, which was necessary for the osteogenic response to Osteolectin. This reveals a new mechanism for maintenance of adult bone mass: Wnt pathway activation by Osteolectin/α11β1 signaling.

Throughout our lives, our bones undergo constant remodeling. Cells called osteoclasts break down old bone and cells called osteoblasts lay down new. Normally, the two cell types work in balance but if the rate of breakdown outpaces new bone formation the skeleton can become weak. This weakness leads to a condition called osteoporosis, in which people suffer from fragile bones. Osteoporosis is hard to reverse, in part because our ability to encourage new bone to form is limited.

In 2016, researchers discovered a protein called osteolectin, which promotes new bone formation during adulthood by helping skeletal stem cells transform into bone cells. But so far, it has been unclear how osteolectin achieves this. To investigate this further, Shen et al. – including some researchers involved in the 2016 study – marked osteolectin with a molecular tag and tested what it bound on the surface of mouse and human bone marrow cells.

The experiments revealed that osteolectin binds to a specific receptor protein called α11 integrin, which can only be found on skeletal stem cells and the osteoblasts they give rise to. Once osteolectin binds to the receptor, it activates a signaling pathway that induces the stem cells to develop into osteoblasts. Mice that lacked either osteolectin or α11 integrin produced less bone and lost bone tissue faster as adults.

Osteolectin could potentially be useful in the treatment of osteoporosis or broken bones. Since only skeletal stem cells and osteoblasts cells produce α11 integrin, osteolectin would specifically target these cells without affecting cells that do not form bones. A next step will be to assess how well osteolectin compares to existing treatments for fragile bones.

Tsc1 Regulates the Balance Between Osteoblast and Adipocyte Differentiation Through Autophagy/Notch1/β-Catenin Cascade

A reduction in trabecular bone mass is often associated with an increase in marrow fat in osteoporotic bones. The molecular mechanisms underlying this inverse correlation are incompletely understood. Here, we report that mice lacking tuberous sclerosis 1 (Tsc1) in Osterix-expressing cells had a significant decrease in trabecular bone mass characterized by decreased osteoblastogenesis, increased osteoclastogenesis, and increased bone marrow adiposity in vivo. In vitro study showed that Tsc1-deficient bone marrow stromal cells (BMSCs) had decreased proliferation, decreased osteogenic differentiation, and increased adipogenic differentiation in association with the downregulation of Wnt/β-catenin signaling. Mechanistically, TSC1 deficiency led to autophagy suppression and consequent Notch1 protein increase, which mediated the GSK3β-independent β-catenin degradation. Together, our results indicate that Tsc1 controls the balance between osteoblast and adipocyte differentiation of BMSCs. © 2018 American Society for Bone and Mineral Research.

Forced expression of mouse progerin attenuates the osteoblast differentiation interrupting β-catenin signal pathway in vitro

Nuclear protein, lamin A, which is a component of inner membrane on nucleoplasm, plays a role in nuclear formation and cell differentiation. The expression of mutated lamin A, termed progerin, causes a rare genetic aging disorder, Hutchinson-Gilford progeria syndrome, which shows abnormal bone formation with the decrease in a number of osteoblasts and osteocytes. However, exact molecular mechanism how progerin exerts depressive effects on osteogenesis has not been fully understood. Here, we created mouse lamin A dC50 cDNA encoding progerin that lacks 50 amino acid residues at C-terminus, transfected it in mouse preosteoblast-like MC3T3-E1 cells, and examined the changes in osteoblast phenotype. When lamin A dC50-expressed cells were cultured with differentiation-inductive medium, alkaline phosphatase (ALP) activity and mRNA levels of major osteoblast markers, type I collagen (Col1), bone sialoprotein (BSP), dentine matrix protein 1 (DMP1), and Runx2 were significantly decreased, and no mineralized nodules were detected as seen in control cells expressing empty vector. In the culture with mineralization-inductive medium, mRNA levels of BSP, osteocalcin, DMP1, Runx2, and osterix were strongly decreased parallel with loss of mineralization in lamin A dC50-expressed cells, while mineralized nodules appear at 21 days in control cells. Furthermore, lamin A dC50 expression was depressed nuclear localization of β-catenin with the decrease of GSK-3β phosphorylation level. These results suggest that lamin A dC50 depresses osteoblast differentiation in both early and late stages, and it negatively regulates β-catenin activity interacting with GSK-3β in cytoplasm.

Gene expression analysis of human adipose tissue-derived stem cells during the initial steps of in vitro osteogenesis

Mesenchymal stem cells (MSCs) have been widely studied with regard to their potential use in cell therapy protocols and regenerative medicine. However, a better comprehension about the factors and molecular mechanisms driving cell differentiation is now mandatory to improve our chance to manipulate MSC behavior and to benefit future applications. In this work, we aimed to study gene regulatory networks at an early step of osteogenic differentiation. Therefore, we analyzed both the total mRNA and the mRNA fraction associated with polysomes on human adipose tissue-derived stem cells (hASCs) at 24 h of osteogenesis induction. The RNA-seq results evidenced that hASC fate is not compromised with osteogenesis at this time and that 21 days of continuous cell culture stimuli are necessary for full osteogenic differentiation of hASCs. Furthermore, early stages of osteogenesis induction involved gene regulation that was linked to the management of cell behavior in culture, such as the control of cell adhesion and proliferation. In conclusion, although discrete initial gene regulation related to osteogenesis occur, the first 24 h of induction is not sufficient to trigger and drive in vitro osteogenic differentiation of hASCs.

Long noncoding RNA MEG3 suppresses liver cancer cells growth through inhibiting β-catenin by activating PKM2 and inactivating PTEN

Maternally expressed gene 3 (MEG3) encodes an lncRNA which is suggested to function as a tumor suppressor and has been showed to involve in a variety of cancers. Herein, our findings demonstrate that MEG3 inhibits the malignant progression of liver cancer cells in vitro and in vivo. Mechanistically, MEG3 promotes the expression and maturition of miR122 which targets PKM2. Therefore, MEG3 decreases the expression and nuclear location of PKM2 dependent on miR122. Furthermore, MEG3 also inhibits CyclinD1 and C-Myc via PKM2 in liver cancer cells. On the other hand, MEG3 promotes β-catenin degradation through ubiquitin-proteasome system dependent on PTEN. Strikingly, MEG3 inhibits β-catenin activity through PKM2 reduction and PTEN increase. Significantly, we also found that excessive β-catenin abrogated the effect of MEG3 in liver cancer. In conclusion, our study for the first time demonstrates that MEG3 acts as a tumor suppressor by negatively regulating the activity of the PKM2 and β-catenin signaling pathway in hepatocarcinogenesis and could provide potential therapeutic targets for the treatment of liver cancer.

LARG GEF and ARHGAP18 orchestrate RhoA activity to control mesenchymal stem cell lineage

The quantity and quality of bone depends on osteoblastic differentiation of mesenchymal stem cells (MSCs), where adipogenic commitment depletes the available pool for osteogenesis. Cell architecture influences lineage decisions, where interfering with cytoskeletal structure promotes adipogenesis. Mechanical strain suppresses MSC adipogenesis partially through RhoA driven enhancement of cytoskeletal structure. To understand the basis of force-driven RhoA activation, we considered critical GEFs (activators) and GAPs (inactivators) on bone marrow MSC lineage fate. Knockdown of LARG accelerated adipogenesis and repressed basal RhoA activity. Importantly, mechanical activation of RhoA was almost entirely inhibited following LARG depletion, and the ability of strain to inhibit adipogenesis was impaired. Knockdown of ARHGAP18 increased basal RhoA activity and actin stress fiber formation, but did not enhance mechanical strain activation of RhoA. ARHGAP18 null MSCs exhibited suppressed adipogenesis assessed by Oil-Red-O staining and Western blot of adipogenic markers. Furthermore, ARHGAP18 knockdown enhanced osteogenic commitment, confirmed by alkaline phosphatase staining and qPCR of Sp7, Alpl, and Bglap genes. This suggests that ARHGAP18 conveys tonic inhibition of MSC cytoskeletal assembly, returning RhoA to an "off state" and affecting cell lineage in the static state. In contrast, LARG is recruited during dynamic mechanical strain, and is necessary for mechanical suppression of adipogenesis. In summary, mechanical activation of RhoA in mesenchymal progenitors is dependent on LARG, while ARHGAP18 limits RhoA delineated cytoskeletal structure in static cultures. Thus, on and off GTP exchangers work through RhoA to influence MSC fate and responses to static and dynamic physical factors in the microenvironment.

The Expanding Life and Functions of Osteogenic Cells: From Simple Bone-Making Cells to Multifunctional Cells and Beyond

During the last three decades, important progress in bone cell biology and in human and mouse genetics led to major advances in our understanding of the life and functions of cells of the osteoblast lineage. Previously unrecognized sources of osteogenic cells have been identified. Novel cellular and molecular mechanisms controlling osteoblast differentiation and senescence have been determined. New mechanisms of communications between osteogenic cells, osteocytes, osteoclasts, and chondrocytes, as well as novel links between osteogenic cells and blood vessels have been identified. Additionally, cells of the osteoblast lineage were shown to be important components of the hematopoietic niche and to be implicated in hematologic dysfunctions and malignancy. Lastly, unexpected interactions were found between osteogenic cells and several soft tissues, including the central nervous system, gut, muscle, fat, and testis through the release of paracrine factors, making osteogenic cells multifunctional regulatory cells, in addition to their bone-making function. These discoveries considerably enlarged our vision of the life and functions of osteogenic cells, which may lead to the development of novel therapeutics with immediate applications in bone disorders. © 2017 American Society for Bone and Mineral Research.

GLP2 Promotes Directed Differentiation from Osteosarcoma Cells to Osteoblasts and Inhibits Growth of Osteosarcoma Cells

Glucagon-like peptide 2 (GLP2) is a proglucagon-derived peptide that is involved in the regulation of energy absorption and exerts beneficial effects on glucose metabolism. However, the exact mechanisms underlying the GLP2 during osteogenic differentiation has not been illustrated. Herein, we indicated that GLP2 was demonstrated to result in positive action during the osteogenic differentiation of human osteosarcoma cells. Our findings demonstrate that GLP2 inhibis the growth of osteosarcoma cells in vivo and in vitro. Mechanistic investigations reveal GLP2 inhibits the expression and activity of nuclear factor κB (NF-κB), triggering the decrease of c-Myc, PKM2, and CyclinD1 in osteosarcoma cells. In particular, rescued NF-κB abrogates the functions of GLP2 in osteosarcoma cells. Strikingly, GLP2 overexpression significantly increased the expression of osteogenesis-associated genes (e.g., Ocn and PICP) dependent on c-Fos-BMP signaling, which promotes directed differentiation from osteosarcoma cells to osteoblasts with higher alkaline phosphatase activity. Taken together, our results suggested that GLP2 could be a valuable drug to promote directed differentiation from osteosarcoma cells to osteoblasts, which may provide potential therapeutic targets for the treatment of osteosarcoma.