The extracellular matrix protein Edil3 stimulates osteoblast differentiation through the integrin α5β1/ERK/Runx2 pathway

Characterization and preparation of food-derived peptides on improving osteoporosis: A review

Osteoporosis is a systemic bone disease characterized by reduced bone mass and deterioration of the microstructure of bone tissue, leading to an increased risk of fragility fractures and affecting human health worldwide. Food-derived peptides are widely used in functional foods due to their low toxicity, ease of digestion and absorption, and potential to improve osteoporosis. This review summarized and discussed methods of diagnosing osteoporosis, treatment approaches, specific peptides as alternatives to conventional drugs, and the laboratory preparation and identification methods of peptides. It was found that peptides interacting with RGD (arginine-glycine-aspartic acid)-binding active sites in integrin could alleviate osteoporosis, analyzed the interaction sites between these osteogenic peptides and integrin, and further discussed their effects on improving osteoporosis. These may provide new insights for rapid screening of osteogenic peptides, and provide a theoretical basis for their application in bone materials and functional foods.

HIV Modulates Osteoblast Differentiation via Upregulation of RANKL and Vitronectin

Bone loss is a prevalent characteristic among people with HIV (PWH). We focused on mesenchymal stem cells (MSCs) and osteoblasts, examining their susceptibility to different HIV strains (R5- and X4-tropic) and the subsequent effects on bone tissue homeostasis. Our findings suggest that MSCs and osteoblasts are susceptible to R5- and X4-tropic HIV but do not support productive HIV replication. HIV exposure during the osteoblast differentiation process revealed that the virus could not alter mineral and organic matrix deposition. However, the reduction in runt-related transcription factor 2 (RUNX2) transcription, the increase in the transcription of nuclear receptor activator ligand kappa B (RANKL), and the augmentation of vitronectin deposition strongly suggested that X4- and R5-HIV could affect bone homeostasis. This study highlights the HIV ability to alter MSCs' differentiation into osteoblasts, critical for maintaining bone and adipose tissue homeostasis and function.

Macromolecular crowding in human tenocyte and skin fibroblast cultures: A comparative analysis

Although human tenocytes and dermal fibroblasts have shown promise in tendon engineering, no tissue engineered medicine has been developed due to the prolonged ex vivo time required to develop an implantable device. Considering that macromolecular crowding has the potential to substantially accelerate the development of functional tissue facsimiles, herein we compared human tenocyte and dermal fibroblast behaviour under standard and macromolecular crowding conditions to inform future studies in tendon engineering. Basic cell function analysis made apparent the innocuousness of macromolecular crowding for both cell types. Gene expression analysis of the without macromolecular crowding groups revealed expression of tendon related molecules in human dermal fibroblasts and tenocytes. Protein electrophoresis and immunocytochemistry analyses showed significantly increased and similar deposition of collagen fibres by macromolecular crowding in the two cell types. Proteomics analysis demonstrated great similarities between human tenocyte and dermal fibroblast cultures, as well as the induction of haemostatic, anti-microbial and tissue-protective proteins by macromolecular crowding in both cell populations. Collectively, these data rationalise the use of either human dermal fibroblasts or tenocytes in combination with macromolecular crowding in tendon engineering.

Exoskeleton Partial-Coated Stem Cells for Infarcted Myocardium Restoring

The integration of abiotic materials with live cells has emerged as an exciting strategy for the control of cellular functions. Exoskeletons consisting ofmetal-organic frameworks are generated to produce partial-coated bone marrow stem cells (BMSCs) to overcome low cell survival leading to disappointing effects for cell-based cardiac therapy. Partially coated exoskeletons can promote the survival of suspended BMSCs by integrating the support of exoskeletons and unimpaired cellular properties. In addition, partial exoskeletons exhibit protective effects against detrimental environmental conditions, including reactive oxygen species, pH changes, and osmotic pressure. The partial-coated cells exhibit increased intercellular adhesion forces to aggregate and adhere, promoting cell survival and preventing cell escape during cell therapy. The exoskeletons interact with cell surface receptors integrin α5β1, leading to augmented biological functions with profitable gene expression alteration, such as Vegfa, Cxcl12, and Adm. The partial-coated BMSCs display enhanced cell retention in infarcted myocardium through non-invasive intravenous injections. The repair of myocardial infarction has been achieved with improved cardiac function, myocardial angiogenesis, proliferation, and inhibition of cell apoptosis. This discovery advances the elucidation of potential molecular and cellular mechanisms for cell-exoskeleton interactions and benefits the rational design and manufacture of next-generation nanobiohybrids.

Del1 Is a Growth Factor for Skeletal Progenitor Cells in the Fracture Callus

Failure to properly form bone or integrate surgical implants can lead to morbidity and additional surgical interventions in a significant proportion of orthopedic surgeries. While the role of skeletal stem cells (SSCs) in bone formation and repair is well-established, very little is known about the factors that regulate the downstream Bone, Cartilage, Stromal, Progenitors (BCSPs). BCSPs, as transit amplifying progenitor cells, undergo multiple mitotic divisions to expand the pool of lineage committed progenitors allowing stem cells to preserve their self-renewal and stemness. Del1 is a protein widely expressed in the skeletal system, but its deletion led to minimal phenotype changes in the uninjured mouse. In this paper, we demonstrate that Del1 is a key regulator of BCSP expansion following injury. In Del1 knockout mice, there is a significant reduction in the number of BCSPs which leads to a smaller callus and decreased bone formation compared with wildtype (WT) littermates. Del1 serves to promote BCSP proliferation and prevent apoptosis in vivo and in vitro. Moreover, exogenous Del1 promotes proliferation of aged human BCSPs. Our results highlight the potential of Del1 as a therapeutic target for improving bone formation and implant success. Del1 injections may improve the success of orthopedic surgeries and fracture healing by enhancing the proliferation and survival of BCSPs, which are crucial for generating new bone tissue during the process of bone formation and repair.

Targeting integrin α5β1 in urological tumors: opportunities and challenges

Urological tumors, such as prostate cancer, renal cell carcinoma, and bladder cancer, have shown a significant rise in prevalence in recent years and account for a significant proportion of malignant tumors. It has been established that metastasis to distant organs caused by urological tumors is the main cause of death, although the mechanisms underlying metastasis have not been fully elucidated. The fibronectin receptor integrin α5β1 reportedly plays an important role in distant metastasis and is closely related to tumor development. It is widely thought to be an important cancer mediator by interacting with different ligands, mediating tumor adhesion, invasion, and migration, and leading to immune escape. In this paper, we expound on the relationship and regulatory mechanisms of integrin α5β1 in these three cancers. In addition, the clinical applications of integrin α5β1 in these cancers, especially against treatment resistance, are discussed. Last but not least, the possibility of integrin α5β1 as a potential target for treatment is examined, with new ideas for future research being proposed.

The role of integrin family in bone metabolism and tumor bone metastasis

Integrins have been the research focus of cell-extracellular matrix adhesion (ECM) and cytokine receptor signal transduction. They are involved in the regulation of bone metabolism of bone precursor cells, mesenchymal stem cells (MSCs), osteoblasts (OBs), osteoclasts (OCs), and osteocytes. Recent studies expanded and updated the role of integrin in bone metabolism, and a large number of novel cytokines were found to activate bone metabolism pathways through interaction with integrin receptors. Integrins act as transducers that mediate the regulation of bone-related cells by mechanical stress, fluid shear stress (FSS), microgravity, hypergravity, extracellular pressure, and a variety of physical factors. Integrins mediate bone metastasis of breast, prostate, and lung cancer by promoting cancer cell adhesion, migration, and survival. Integrin-mediated targeted therapy showed promising prospects in bone metabolic diseases. This review emphasizes the latest research results of integrins in bone metabolism and bone metastasis and provides a vision for treatment strategies.

The Interplay between Integrins and Immune Cells as a Regulator in Cancer Immunology

Integrins are a group of heterodimers consisting of α and β subunits that mediate a variety of physiological activities of immune cells, including cell migration, adhesion, proliferation, survival, and immunotolerance. Multiple types of integrins act differently on the same immune cells, while the same integrin may exert various effects on different immune cells. In the development of cancer, integrins are involved in the regulation of cancer cell proliferation, invasion, migration, and angiogenesis; conversely, integrins promote immune cell aggregation to mediate the elimination of tumors. The important roles of integrins in cancer progression have provided valuable clues for the diagnosis and targeted treatment of cancer. Furthermore, many integrin inhibitors have been investigated in clinical trials to explore effective regimens and reduce side effects. Due to the complexity of the mechanism of integrin-mediated cancer progression, challenges remain in the research and development of cancer immunotherapies (CITs). This review enumerates the effects of integrins on four types of immune cells and the potential mechanisms involved in the progression of cancer, which will provide ideas for more optimal CIT in the future.

Genome-wide analysis for nanofiber induced global gene expression profile: A study in MC3T3-E1 cells by RNA-Seq

Nanofibers are one of the attractive biomaterials that can provide unique environments to direct cell behaviors. However, how nanofiber structure affects the global gene expression of laden cells remains unclear. Herein, high-throughput mRNA sequencing (RNA-seq) is applied to analyze the transcriptome of the MC3T3-E1 cells (a model osteoblast cell line) cultured on electrospun nanofibers. The cell-adhesive poly(L-lactide) nanofibers and membranes are developed by the mussel-inspired coating of gelatin-dopamine conjugate under H₂O₂-mediated oxidation. The MC3T3-E1 cells cultured on nanofibers exhibit elongated morphology and increased proliferation compared with those on membranes. The differences in global gene expression profiles are determined by RNA-seq, in which 905 differentially expressed genes (DEGs) are identified. Significantly, the DEGs related to cytoskeleton, promotion of cell cycle progression, cell adhesion, and cell proliferation, are higher expressed in the cells on nanofibers, while the DEGs involved in cell-cycle arrest and osteoblast mineralization are up-regulated in the cells on membranes. This study elucidates the roles of nanofiber structure in affecting gene expression of laden cells at the whole transcriptome level, and it will lay the foundation for understanding nanofiber-guided cell behaviors.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Genome Wide Scan to Identify Potential Genomic Regions Associated With Milk Protein and Minerals in Vrindavani Cattle

In this study, genome-wide association study (GWAS) was conducted for identifying significantly associated genomic regions/SNPs with milk protein and minerals in the 96 taurine-indicine crossbred (Vrindavani) cows using 50K SNP Chip. After quality control, a total of 41,427 SNPs were retained and were further analyzed using a single-SNP additive linear model. Lactation stage, parity, test day milk yield and proportion of exotic inheritance were included as fixed effects in GWAS model. Across all traits, 13 genome-wide significant (p < 1.20 x 10⁻⁰⁶) and 49 suggestive significant (p < 2.41 x 10⁻⁰⁵) SNPs were identified which were located on 18 different autosomes. The strongest association for protein percentage, calcium (Ca), phosphorus (P), copper (Cu), zinc (Zn), and iron (Fe) were found on BTA 18, 7, 2, 3, 14, and 2, respectively. No significant SNP was detected for manganese (Mn). Several significant SNPs identified were within or close proximity to CDH13, BHLHE40, EDIL3, HAPLN1, INHBB, USP24, ZFAT, and IKZF2 gene, respectively. Enrichment analysis of the identified candidate genes elucidated biological processes, cellular components, and molecular functions involved in metal ion binding, ion transportation, transmembrane protein, and signaling pathways. This study provided a groundwork to characterize the molecular mechanism for the phenotypic variation in milk protein percentage and minerals in crossbred cattle. Further work is required on a larger sample size with fine mapping of identified QTL to validate potential candidate regions.

Clonal osteoblastic cell lines with CRISPR/Cas9-mediated ablation of Pit1 or Pit2 show enhanced mineralization despite reduced osteogenic gene expression

Multiple actions of extracellular Pi on the skeletal cells are likely to be partly mediated by type III sodium/phosphate (Na⁺/Pi) cotransporters Pit1 and Pit2, although the details are not fully understood. In the current study, to determine the roles of Pit1 and Pit2 in osteoblasts, we generated Pit1-knockout (KO) and Pit2-KO osteoblastic cells by applying CRISPR/Cas9 genome editing to an osteoblastic cell line MC3T3-E1 subclone 4. The extracellular Pi level was increased in the Pit1-KO and Pit2-KO clones due to the reduced Pi uptake. Interestingly, in vitro mineralization was accelerated in the Pit1-KO and Pit2-KO clones, although the induction of the expression of osteogenic marker genes was suppressed. In the cells before mineralization, extracellular levels of pyrophosphate (PPi) and adenosine triphosphate (ATP) were increased in the Pit1-KO and Pit2-KO clones, which might be attributable to the reduced expression and activity of tissue-nonspecific alkaline phosphatase (TNSALP). A 24-h treatment with high Pi reduced the expression and activity of TNSALP, suggesting that the suppression of TNSALP in the Pit1-KO and Pit2-KO clones was caused by the increased availability of extracellular Pi. Lentiviral gene transfer of Pit1 and Pit2 restored the changes observed in Pit1-KO and Pit2-KO clones, respectively. The expressions of P2Y2 and P2X7 which encode receptors for extracellular ATP were altered in the Pit1-KO and Pit2-KO clones, suggesting an influence on purinergic signaling. In mineralized cells after long-term culture, intracellular levels of PPi and ATP were higher in the Pit1-KO and Pit2-KO clones. Taken together, ablation of Pit1 or Pit2 in this osteoblastic cell model led to accelerated mineralization, suppressed TNSALP and altered the levels of extracellular and intracellular PPi and ATP, which might be partly mediated by changes in the availability of extracellular Pi.

Staphylococcus aureus internalization impairs osteoblastic activity and early differentiation process

Staphylococcus aureus is the most frequent aetiology of bone and joint infections (BJI) and can cause relapsing and chronic infections. One of the main factors involved in the chronicization of staphylococcal BJIs is the internalization of S. aureus into osteoblasts, the bone-forming cells. Previous studies have shown that S. aureus triggers an impairment of osteoblasts function that could contribute to bone loss. However, these studies focused mainly on the extracellular effects of S. aureus. Our study aimed at understanding the intracellular effects of S. aureus on the early osteoblast differentiation process. In our in vitro model of osteoblast lineage infection, we first observed that internalized S. aureus 8325-4 (a reference lab strain) significantly impacted RUNX2 and COL1A1 expression compared to its non-internalized counterpart 8325-4^∆fnbAB (with deletion of fnbA and fnbB). Then, in a murine model of osteomyelitis, we reported no significant effect for S. aureus 8325-4 and 8325-4^∆fnbAB on bone parameters at 7 days post-infection whereas S. aureus 8325-4 significantly decreased trabecular bone thickness at 14 days post-infection compared to 8325-4^∆fnbAB. When challenged with two clinical isogenic strains isolated from initial and relapse phase of the same BJI, significant impairments of bone parameters were observed for both initial and relapse strain, without differences between the two strains. Finally, in our in vitro osteoblast infection model, both clinical strains impacted alkaline phosphatase activity whereas the expression of bone differentiation genes was significantly decreased only after infection with the relapse strain. Globally, we highlighted that S. aureus internalization into osteoblasts is responsible for an impairment of the early differentiation in vitro and that S. aureus impaired bone parameters in vivo in a strain-dependent manner.

Effects of Erythromycin on Osteoclasts and Bone Resorption via DEL-1 Induction in Mice

Macrolides are used to treat various infectious diseases, including periodontitis. Furthermore, macrolides are known to have immunomodulatory effects; however, the underlying mechanism of their action remains unclear. DEL-1 has emerged as an important factor in homeostatic immunity and osteoclastogenesis. Specifically, DEL-1 is downregulated in periodontitis tissues. Therefore, in the present study, we investigated whether the osteoclastogenesis inhibitory effects of erythromycin (ERM) are mediated through upregulation of DEL-1 expression. We used a ligature-induced periodontitis model in C57BL/6Ncrl wild-type or DEL-1-deficient mice and in vitro cell-based mechanistic studies to investigate how ERM inhibits alveolar bone resorption. As a result of measuring alveolar bone resorption and gene expression in the tooth ligation model, ERM treatment reduced bone loss by increasing DEL-1 expression and decreasing the expression of osteoclast-related factors in wild-type mice. In DEL-1-deficient mice, ERM failed to suppress bone loss and gene expression of osteoclast-related factors. In addition, ERM treatment downregulated osteoclast differentiation and calcium resorption in in vitro experiments with mouse bone marrow-derived macrophages. In conclusion, ERM promotes the induction of DEL-1 in periodontal tissue, which may regulate osteoclastogenesis and decrease inflammatory bone resorption. These findings suggest that ERM may exert immunomodulatory effects in a DEL-1-dependent manner.

IL1RN promotes osteoblastic differentiation via interacting with ITGB3 in osteoporosis

The occurrence and progress of osteoporosis (OP) are partially caused by impaired osteoblast differentiation. Interleukin-I receptor antagonist (IL1RN) is an immune modulatory molecule that commonly functions by means of competing the binding site of IL-1R with IL-1. Although it was recently reported that IL1RN is involved in osteoblast differentiation, the role of IL1RN in osteogenesis remains unclear. In this work, we first investigated the expression pattern of IL1RN in ovariectomy mice and in vitro osteogenic induction of MC3T3-E1 and C3H10T1/2 cells. To verify the exact role of IL1RN in osteoblast differentiation, we established IL1RN-downregulated/upregulated cell lines. The results indicated that IL1RN was constantly expressed in MC3T3-E1 and C3H10T1/2 cells. Interestingly, an increase of IL1RN expression in osteoblasts occurred when osteoblasts were cultured in osteogenic medium (OM). As expected, silencing of IL1RN attenuated the osteogenic effect of OM, while IL1RN overexpression increased the osteogenic staining and promoted the expression of osteogenic markers, including alkaline phosphatase, osterix, and osteocalcin. In addition to evaluating the function of IL1RN in osteoblasts, we also investigated the molecular mechanism of the role of IL1RN in osteoblasts. We found that IL1RN interacts with integrin β3 to activate β-catenin signaling, which finally regulates osteoblast differentiation. Taken together, this study provides the framework that IL1RN, as a novel regulator of osteogenesis, may be a potential therapeutic target for the treatment of OP.

The Roles of Integrin α5β1 in Human Cancer

Cell adhesion to the extracellular matrix has important roles in tissue integrity and human health. Integrins are heterodimeric cell surface receptors that are composed by two non-covalently linked alpha and beta subunits that mainly participate in the interaction of cell-cell adhesion and cell-extracellular matrix and regulate cell motility, adhesion, differentiation, migration, proliferation, etc. In mammals, there have been eighteen α subunits and 8 β subunits and so far 24 distinct types of αβ integrin heterodimers have been identified in humans. Integrin α5β1, also known as the fibronectin receptor, is a heterodimer with α5 and β1 subunits and has emerged as an essential mediator in many human carcinomas. Integrin α5β1 alteration is closely linked to the progression of several types of human cancers, including cell proliferation, angiogenesis, tumor metastasis, and cancerogenesis. In this review, we will introduce the functions of integrin α5β1 in cancer progression and also explore its regulatory mechanisms. Additionally, the potential clinical applications as a target for cancer imaging and therapy are discussed. Collectively, the information reviewed here may increase the understanding of integrin α5β1 as a potential therapeutic target for cancer.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

The secreted protein DEL-1 activates a β3 integrin-FAK-ERK1/2-RUNX2 pathway and promotes osteogenic differentiation and bone regeneration

The integrin-binding secreted protein developmental endothelial locus-1 (DEL-1) is involved in the regulation of both the initiation and resolution of inflammation in different diseases, including periodontitis, an oral disorder characterized by inflammatory bone loss. Here, using a mouse model of bone regeneration and in vitro cell-based mechanistic studies, we investigated whether and how DEL-1 can promote alveolar bone regeneration during resolution of experimental periodontitis. Compared with WT mice, mice lacking DEL-1 or expressing a DEL-1 variant with an Asp-to-Glu substitution in the RGD motif ("RGE point mutant"), which does not interact with RGD-dependent integrins, exhibited defective bone regeneration. Local administration of DEL-1 or of its N-terminal segment containing the integrin-binding RGD motif, but not of the RGE point mutant, reversed the defective bone regeneration in the DEL-1-deficient mice. Moreover, DEL-1 (but not the RGE point mutant) promoted osteogenic differentiation of MC3T3-E1 osteoprogenitor cells or of primary calvarial osteoblastic cells in a β3 integrin-dependent manner. The ability of DEL-1 to promote in vitro osteogenesis, indicated by induction of osteogenic genes such as the master transcription factor Runt-related transcription factor-2 (Runx2) and by mineralized nodule formation, depended on its capacity to induce the phosphorylation of focal adhesion kinase (FAK) and of extracellular signal-regulated kinase 1/2 (ERK1/2). We conclude that DEL-1 can activate a β3 integrin-FAK-ERK1/2-RUNX2 pathway in osteoprogenitors and promote new bone formation in mice. These findings suggest that DEL-1 may be therapeutically exploited to restore bone lost due to periodontitis and perhaps other osteolytic conditions.

Revealing hidden information in osteoblast's mechanotransduction through analysis of time patterns of critical events

BACKGROUND

Mechanotransduction in bone cells plays a pivotal role in osteoblast differentiation and bone remodelling. Mechanotransduction provides the link between modulation of the extracellular matrix by mechanical load and intracellular activity. By controlling the balance between the intracellular and extracellular domains, mechanotransduction determines the optimum functionality of skeletal dynamics. Failure of this relationship was suggested to contribute to bone-related diseases such as osteoporosis.

RESULTS

A hybrid mechanical and agent-based model (Mech-ABM), simulating mechanotransduction in a single osteoblast under external mechanical perturbations, was utilised to simulate and examine modulation of the activation dynamics of molecules within mechanotransduction on the cellular response to mechanical stimulation. The number of molecules and their fluctuations have been analysed in terms of recurrences of critical events. A numerical approach has been developed to invert subordination processes and to extract the direction processes from the molecular signals in order to derive the distribution of recurring events. These predict that there are large fluctuations enclosing information hidden in the noise which is beyond the dynamic variations of molecular baselines. Moreover, studying the system under different mechanical load regimes and altered dynamics of feedback loops, illustrate that the waiting time distributions of each molecule are a signature of the system's state.

CONCLUSIONS

The behaviours of the molecular waiting times change with the changing of mechanical load regimes and altered dynamics of feedback loops, presenting the same variation of patterns for similar interacting molecules and identifying specific alterations for key molecules in mechanotransduction. This methodology could be used to provide a new tool to identify potent molecular candidates to modulate mechanotransduction, hence accelerate drug discovery towards therapeutic targets for bone mass upregulation.

Biomechanical stress regulates mammalian tooth replacement via the integrin β1-RUNX2-Wnt pathway

Renewal of integumentary organs occurs cyclically throughout an organism's lifetime, but the mechanism that initiates each cycle remains largely unknown. In a miniature pig model of tooth development that resembles tooth development in humans, the permanent tooth did not begin transitioning from the resting to the initiation stage until the deciduous tooth began to erupt. This eruption released the accumulated mechanical stress inside the mandible. Mechanical stress prevented permanent tooth development by regulating expression and activity of the integrin β1-ERK1-RUNX2 axis in the surrounding mesenchyme. We observed similar molecular expression patterns in human tooth germs. Importantly, the release of biomechanical stress induced downregulation of RUNX2-wingless/integrated (Wnt) signaling in the mesenchyme between the deciduous and permanent tooth and upregulation of Wnt signaling in the epithelium of the permanent tooth, triggering initiation of its development. Consequently, our findings identified biomechanical stress-associated Wnt modulation as a critical initiator of organ renewal, possibly shedding light on the mechanisms of integumentary organ regeneration.

1,25(OH)2D3 regulates the proangiogenic activity of pericyte through VDR-mediated modulation of VEGF production and signaling of VEGF and PDGF receptors

We have previously demonstrated that the active form of vitamin D (calcitriol; 1,25(OH)₂D₃) is a potent inhibitor of retinal neovascularization. However, the underlying molecular and cellular mechanisms involved remained poorly understood. Perivascular supporting cells including pericytes (PC) play important roles during angiogenesis, vascular maturation, and stabilization of blood vessels. How 1,25(OH)₂D₃ affects retinal PC proliferation and migration, and whether these effects are mediated through vitamin D receptor (VDR), are unknown. Here, we determined the impact of 1,25(OH)₂D₃ on retinal PC prepared from wild‐type (Vdr+/+) and VDR‐deficient (Vdr−/−) mice. Retinal PC expressed significantly higher VDR levels compared to retinal endothelial cells (EC). Unlike retinal EC, 1,25(OH)₂D₃ significantly decreased PC proliferation and migration and resulted in a G₀/G₁ cell cycle arrest. Although 1,25(OH)₂D₃ did not inhibit the proliferation of Vdr−/− PC, it did inhibit their migration. PC adhesion to various extracellular matrix (ECM) proteins and ECM production were also affected by incubation of PC with 1,25(OH)₂D₃. Vdr−/− PC were more adherent compared with Vdr+/+ cells. Mechanistically, incubation of Vdr+/+ PC with 1,25(OH)₂D₃ resulted in an increased expression of vascular endothelial growth factor (VEGF) and attenuation of signaling through VEGF‐R2 and platelet‐derived growth factor receptor‐beta. Incubation with soluble VEGF‐R1 (sFlt‐1) partially reversed the effect of VEGF on Vdr+/+ PC. In addition, incubation of Vdr+/+ PC with VEGF or inhibition of VEGF‐R2 increased VDR expression. Together, these results suggest an important role for retinal PC as a target for vitamin D and VDR action for attenuation of angiogenesis.

Tumor derived EDIL3 modulates the expansion and osteoclastogenesis of myeloid derived suppressor cells in murine breast cancer model

Epidermal growth factor-like repeats and discoidin I like domain 3 (EDIL3) is an integrin ligand which is implicated in bone metabolism and bone marrow myelopoiesis. Recently, myeloid derived suppressor cells (MDSCs) as osteoclast progenitor have been demonstrated in several kinds of cancers including breast cancer. In this paper we explored the association between tumor derived EDIL3 and MDSCs in a murine breast cancer model. Knockdown of EDIL3 in MDA-MB-231 breast cancer cells inhibited the expansion of tumor induced MDSCs in bone marrow. However, generation of bone marrow derived MDSCs in vitro was not affected by recombinant EDIL3. Osteoclastogenesis of MDSCs was dose-dependently inhibited by recombinant EDIL3 in vitro via binding to Mac-1 but not LFA-1. Moreover, in accordance with previous studies, our data showed that tumor derived EDIL3 was involved in tumor associated bone loss. The convoluted effects of EDIL3 on MDSCs compose a potential mechanism hired by tumor cells for perpetration approximately.

Isolation and Characterization of Peptides from Mytilus edulis with Osteogenic Activity in Mouse MC3T3-E1 Preosteoblast Cells

Seafood provides a range of health benefits because of its high protein levels. In this study, a novel peptide, YPRKDETGAERT, was identified from NHA-2 of Mytilus edulis by capillary-electrophoresis electrospray ionization-quadrupole-time of flight (CESI-Q-TOF). Peptide YPRKDETGAERT showed the highest affinity among all the peptides, with -CDOCKER energy values of 204.482 kcal/mol on one integrin (PDB: 3VI4 ) and 210.16 kcal/mol on another integrin (PDB: 1L5G ). The secondary mass spectrogram at the m/ z of peptide YPRKDETGAERT was 1422.53 Da, which was determined by CESI-Q-TOF. Peptide YPRKDETGAERT induced an increase of 28.27 ± 3.66% in mouse-MC3T3-E1-preosteoblast-cell growth. The alkaline-phosphatase activity of peptide YPRKDETGAERT was 2.79 ± 0.07 mU, which was an increase of 21.25% compared with that of the control. These results provide theoretical and practical insights for the preparation and application of osteogenic peptides in the functional-foods industry.

Regulation of Skeletal Homeostasis

Landmark advances in skeletal biology have arisen mainly from the identification of disease-causing mutations and the advent of rapid and selective gene-targeting technologies to phenocopy human disease in mice. Here, we discuss work on newly identified mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, and crosstalk between bone and vital organs as these relate to the therapeutic targeting of the skeleton.