N-cadherin adherens junctions mediate osteogenesis through PI3K signaling

Single-cell transcriptomic resolution of osteogenesis during craniofacial morphogenesis

Craniofacial morphogenesis depends on complex cell fate decisions during the differentiation of post-migratory cranial neural crest cells. Molecular mechanisms of cell differentiation of mesenchymal cells to developing bones, cartilage, teeth, tongue, and other craniofacial tissues are still poorly understood. We performed single-cell transcriptomic analysis of craniofacial mesenchymal cells derived from cranial NCCs in mouse embryo. Using FACS sorting of Wnt1-Cre2 progeny, we carefully mapped the cell heterogeneity in the craniofacial region during the initial stages of cartilage and bone formation. Transcriptomic data and in vivo validations identified molecular determinants of major cell populations involved in the development of lower and upper jaw, teeth, tongue, dermis, or periocular mesenchyme. Single-cell transcriptomic analysis of Meis2-deficient mice revealed critical gene expression differences, including increased osteogenic and cell adhesion markers. This leads to affected mesenchymal cell differentiation and increased ossification, resulting in impaired bone, cartilage, and tongue formation.

Analysis of metastasis‑related risk factors and clinical relevance in adult soft‑tissue sarcoma

Metastasis occurs in nearly 50% of cases of adult soft-tissue sarcoma (ASTS), leading to a dismal prognosis, with a 2-year survival rate of ~30%. Consequently, a prognostic model that incorporates metastatic characteristics may be instrumental in predicting survival time and in crafting optimal personalized therapeutic strategies for patients with ASTS. In the present study, a prognostic prediction model for ASTS was developed by examining genes that are differentially expressed between non-metastatic and metastatic patients in the Gene Expression Omnibus dataset. The prognostic model, which includes five featured genes [actin γ2 (ACTG2), apolipoprotein D, coatomer protein complex subunit γ2 imprinted transcript 1, collagen type VI α6 chain and osteomodulin], was further validated in patients with ASTS from the Cancer Genome Atlas dataset. Based on these five-gene signatures, patients were categorized into high- and low-risk groups. Functional and pathway analyses revealed disparities in stemness, extracellular matrix and cell adhesion-related pathways between the two risk groups, particularly noting the activation of the PI3K-Akt pathway in high-risk cases. Analysis of immune infiltration also revealed variations in immune microenvironment changes between the two risk groups. Immunohistochemical staining substantiated the prognostic significance of these gene signatures in a specific sarcoma subtype. Additionally, wound-healing and Transwell assays demonstrated that inhibition of ACTG2 by shRNAs curbed cell migration and invasion in a sarcoma HOS cell line, underscoring its role in sarcoma metastasis. In conclusion, the present study successfully developed and validated a metastasis-based prognosis prediction model. This model not only reliably forecasts the survival of patients with ASTS, but also may pave the way for further investigation into the processes underlying sarcoma metastasis, ultimately aiding in the design of tailored therapeutic regimens.

MetaLnc9 facilitates osteogenesis of human bone marrow mesenchymal stem cells by activating the AKT pathway

AIM OF THE STUDY

To investigate the role of MetaLnc9 in the osteogenesis of human bone marrow mesenchymal stem cells (hBMSCs).

MATERIALS AND METHODS

We used lentiviruses to knockdown or overexpress MetaLnc9 in hBMSCs. qRT-PCR was employed to determine the mRNA levels of osteogenic-related genes in transfected cells. ALP staining and activity assay, ARS staining and quantification were used to identify the degree of osteogenic differentiation. Ectopic bone formation was conducted to examine the osteogenesis of transfected cells in vivo. AKT pathway activator SC-79 and inhibitor LY294002 were used to validate the relationship between MetaLnc9 and AKT signaling pathway.

RESULTS

The expression of MetaLnc9 was significantly upregulated in the osteogenic differentiation of hBMSCs. MetaLnc9 knockdown inhibited the osteogenesis of hBMSCs, whereas overexpression of it promoted the osteogenic differentiation both in vitro and in vivo. Taking a deeper insight, we found that MetaLnc9 enhanced the osteogenic differentiation by activating AKT signaling. The inhibitor of AKT signaling LY294002 could reverse the positive effect on osteogenesis brought by MetaLnc9 overexpression, whereas the activator of AKT signaling SC-79 could reverse the negative effect caused by MetaLnc9 knockdown.

CONCLUSION

Our works uncovered a vital role of MetaLnc9 in osteogenesis via regulating the AKT signaling pathway. [Figure: see text].

Transcriptomic response of Mytilus coruscus mantle to acute sea water acidification and shell damage

Mytilus coruscus is an economically important marine calcifier living in the Yangtze River estuary sea area, where seasonal fluctuations in natural pH occur owing to freshwater input, resulting in a rapid reduction in seawater pH. In addition, Mytilus constantly suffers from shell fracture or injury in the natural environment, and the shell repair mechanisms in mussels have evolved to counteract shell injury. Therefore, we utilized shell-complete and shell-damaged Mytilus coruscus in this study and performed transcriptomic analysis of the mantle to investigate whether the expression of mantle-specific genes can be induced by acute seawater acidification and how the mantle responds to acute acidification during the shell repair process. We found that acute acidification induced more differentially expressed genes than shell damage in the mantle, and the biomineralization-related Gene Ontology terms and KEGG pathways were significantly enriched by these DEGs. Most DEGs were upregulated in enriched pathways, indicating the activation of biomineralization-related processes in the mussel mantle under acute acidification. The expression levels of some shell matrix proteins and antimicrobial peptides increased under acute acidification and/or shell damage, suggesting the molecular modulation of the mantle for the preparation and activation of the shell repairing and anti-infection under adverse environmental conditions. In addition, morphological and microstructural analyses were performed for the mantle edge and shell cross-section, and changes in the mantle secretory capacity and shell inner film system induced by the two stressors were observed. Our findings highlight the adaptation of M. coruscus in estuarine areas with dramatic fluctuations in pH and may prove instrumental in its ability to survive ocean acidification.

Genome-Wide Gene-Set Analysis Identifies Molecular Mechanisms Associated with ALS

Amyotrophic lateral sclerosis (ALS) is a fatal late-onset motor neuron disease characterized by the loss of the upper and lower motor neurons. Our understanding of the molecular basis of ALS pathology remains elusive, complicating the development of efficient treatment. Gene-set analyses of genome-wide data have offered insight into the biological processes and pathways of complex diseases and can suggest new hypotheses regarding causal mechanisms. Our aim in this study was to identify and explore biological pathways and other gene sets having genomic association to ALS. Two cohorts of genomic data from the dbGaP repository were combined: (a) the largest available ALS individual-level genotype dataset (N = 12,319), and (b) a similarly sized control cohort (N = 13,210). Following comprehensive quality control pipelines, imputation and meta-analysis, we assembled a large European descent ALS-control cohort of 9244 ALS cases and 12,795 healthy controls represented by genetic variants of 19,242 genes. Multi-marker analysis of genomic annotation (MAGMA) gene-set analysis was applied to an extensive collection of 31,454 gene sets from the molecular signatures database (MSigDB). Statistically significant associations were observed for gene sets related to immune response, apoptosis, lipid metabolism, neuron differentiation, muscle cell function, synaptic plasticity and development. We also report novel interactions between gene sets, suggestive of mechanistic overlaps. A manual meta-categorization and enrichment mapping approach is used to explore the overlap of gene membership between significant gene sets, revealing a number of shared mechanisms.

Thiophanate-methyl induces notochord toxicity by activating the PI3K-mTOR pathway in zebrafish (Danio rerio) embryos

Thiophanate-methyl (TM), a typical pesticide widely used worldwide, was detected in rivers, soil, fruits, and vegetables. Thus, it is urgent to identify the potential harm of TM residual to non-target organisms and its molecular mechanisms. We used zebrafish (Danio rerio) in this study to evaluate TM toxicity. TM exposure induced developmental toxicity, including inhibited hatchability, reduced heart rates, restrained spontaneous locomotion, and decreased body length. Furthermore, we observed obvious toxicity in the notochord and detected increased expression levels of notochord-related genes (shha, col2a, and tbxta) by in situ hybridization in zebrafish larvae. In addition, calcein staining, alkaline phosphatase (ALP) activity analysis, and anatomic analysis indicated that TM induced notochord toxicity. We used rescue experiments to verify whether the PI3K-mTOR pathway involved in the notochord development was the cause of notochord abnormalities. Rapamycin and LY294002 (an inhibitor of PI3K) relieve notochord toxicity caused by TM, including morphological abnormalities. In summary, TM might induce notochord toxicity by activating the PI3K-mTOR pathway in zebrafish.

Interplay between integrins and cadherins to control bone differentiation upon BMP-2 stimulation

Introduction: Upon BMP-2 stimulation, the osteoblastic lineage commitment in C2C12 myoblasts is associated with a microenvironmental change that occurs over several days. How does BMP-2 operate a switch in adhesive machinery to adapt to the new microenvironment and to drive bone cell fate is not well understood. Here, we addressed this question for BMP-2 delivered either in solution or physically bound of a biomimetic film, to mimic its presentation to cells via the extracellular matrix (ECM). Methods: Biommetics films were prepared using a recently developed automated method that enable high content studies of cellular processes. Comparative gene expressions were done using RNA sequencing from the encyclopedia of the regulatory elements (ENCODE). Gene expressions of transcription factors, beta chain (1, 3, 5) integrins and cadherins (M, N, and Cad11) were studied using quantitative PCR. ECM proteins and adhesion receptor expressions were also quantified by Western blots and dot blots. Their spatial organization in and around cells was studied using immuno-stainings. The individual effect of each receptor on osteogenic transcription factors and alkaline phosphatase expression were studied using silencing RNA of each integrin and cadherin receptor. The organization of fibronectin was studied using immuno-staining and quantitative microscopic analysis. Results: Our findings highlight a switch of integrin and cadherin expression during muscle to bone transdifferentiation upon BMP-2 stimulation. This switch occurs no matter the presentation mode, for BMP-2 presented in solution or via the biomimetic film. While C2C12 muscle cells express M-cadherin and Laminin-specific integrins, the BMP-2-induced transdifferentiation into bone cells is associated with an increase in the expression of cadherin-11 and collagen-specific integrins. Biomimetic films presenting matrix-bound BMP-2 enable the revelation of specific roles of the adhesive receptors depending on the transcription factor. Discussion: While β3 integrin and cadherin-11 work in concert to control early pSMAD1,5,9 signaling, β1 integrin and Cadherin-11 control RunX2, ALP activity and fibronectin organization around the cells. In contrast, while β1 integrin is also important for osterix transcriptional activity, Cadherin-11 and β5 integrin act as negative osterix regulators. In addition, β5 integrin negatively regulates RunX2. Our results show that biomimetic films can be used to delinate the specific events associated with BMP-2-mediated muscle to bone transdifferentiation. Our study reveals how integrins and cadherins work together, while exerting distinct functions to drive osteogenic programming. Different sets of integrins and cadherins have complementary mechanical roles during the time window of this transdifferentiation.

Microfluidic Co-culture Platforms for Studying Osteocyte Regulation of Other Cell Types under Dynamic Mechanical Stimulation

PURPOSE OF REVIEW

Osteocytes are the most abundant cell type in bone. These unique cells act primarily as mechanosensors and play crucial roles in the functional adaptation of bone tissue. This review aims to summarize the recent microfluidic studies on mechanically stimulated osteocytes in regulating other cell types.

RECENT FINDINGS

Microfluidics is a powerful technology that has been widely employed in recent years. With the advantages of microfluidic platforms, researchers can mimic multicellular environments and integrate dynamic systems to study osteocyte regulation under mechanical stimulation. Microfluidic platforms have been developed to investigate mechanically stimulated osteocytes in the direct regulation of multiple cell types, including osteoclasts, osteoblasts, and cancer cells, and in the indirect regulation of cancer cells via endothelial cells. Overall, these microfluidic studies foster the development of treatment approaches targeting osteocytes under mechanical stimulation.

Single-cell RNA sequencing deconvolutes the in vivo heterogeneity of human bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are multipotent stromal cells that have a critical role in the maintenance of skeletal tissues such as bone, cartilage, and the fat in bone marrow. In addition to providing microenvironmental support for hematopoietic processes, BM-MSCs can differentiate into various mesodermal lineages including osteoblast/osteocyte, chondrocyte, and adipocyte that are crucial for bone metabolism. While BM-MSCs have high cell-to-cell heterogeneity in gene expression, the cell subtypes that contribute to this heterogeneity in vivo in humans have not been characterized. To investigate the transcriptional diversity of BM-MSCs, we applied single-cell RNA sequencing (scRNA-seq) on freshly isolated CD271+ BM-derived mononuclear cells (BM-MNCs) from two human subjects. We successfully identified LEPRhiCD45low BM-MSCs within the CD271+ BM-MNC population, and further codified the BM-MSCs into distinct subpopulations corresponding to the osteogenic, chondrogenic, and adipogenic differentiation trajectories, as well as terminal-stage quiescent cells. Biological functional annotations of the transcriptomes suggest that osteoblast precursors induce angiogenesis coupled with osteogenesis, and chondrocyte precursors have the potential to differentiate into myocytes. We also discovered transcripts for several clusters of differentiation (CD) markers that were either highly expressed (e.g., CD167b, CD91, CD130 and CD118) or absent (e.g., CD74, CD217, CD148 and CD68) in BM-MSCs, representing potential novel markers for human BM-MSC purification. This study is the first systematic in vivo dissection of human BM-MSCs cell subtypes at the single-cell resolution, revealing an insight into the extent of their cellular heterogeneity and roles in maintaining bone homeostasis.

A systematic dissection of human primary osteoblasts in vivo at single-cell resolution

Human osteoblasts are multifunctional bone cells, which play essential roles in bone formation, angiogenesis regulation, as well as maintenance of hematopoiesis. However, the categorization of primary osteoblast subtypes in vivo in humans has not yet been achieved. Here, we used single-cell RNA sequencing (scRNA-seq) to perform a systematic cellular taxonomy dissection of freshly isolated human osteoblasts from one 31-year-old male with osteoarthritis and osteopenia after hip replacement. Based on the gene expression patterns and cell lineage reconstruction, we identified three distinct cell clusters including preosteoblasts, mature osteoblasts, and an undetermined rare osteoblast subpopulation. This novel subtype was found to be the major source of the nuclear receptor subfamily 4 group A member 1 and 2 (NR4A1 and NR4A2) in primary osteoblasts, and the expression of NR4A1 was confirmed by immunofluorescence staining on mouse osteoblasts in vivo. Trajectory inference analysis suggested that the undetermined cluster, together with the preosteoblasts, are involved in the regulation of osteoblastogenesis and also give rise to mature osteoblasts. Investigation of the biological processes and signaling pathways enriched in each subpopulation revealed that in addition to bone formation, preosteoblasts and undetermined osteoblasts may also regulate both angiogenesis and hemopoiesis. Finally, we demonstrated that there are systematic differences between the transcriptional profiles of human and mouse osteoblasts, highlighting the necessity for studying bone physiological processes in humans rather than solely relying on mouse models. Our findings provide novel insights into the cellular heterogeneity and potential biological functions of human primary osteoblasts at the single-cell level.

Surface decoration of development-inspired synthetic N-cadherin motif via Ac-BP promotes osseointegration of metal implants

Research works on the synergistic effect of surface modified bioactive molecules and bone metal implants have been highlighted. N-cadherin is regarded as a key factor in directing cell-cell interactions during the mesenchymal condensation preceding the osteogenesis in the musculoskeletal system. In this study, the N-cadherin mimetic peptide (Cad) was biofunctionalized on the titanium metal surface via the acryloyl bisphosphonate (Ac-BP). To learn the synergistic effect of N-cadherin mimetic peptide, when tethered with titanium substrates, on promoting osteogenic differentiation of the seeded human mesenchymal stem cells (hMSCs) and the osseointegration at the bone-implant interfaces. Results show that the conjugation of N-cadherin mimetic peptide with Ac-BP promoted the osteogenic gene markers expression in the hMSCs. The biofunctionalized biomaterial surfaces promote the expression of the Wnt/β-catenin downstream axis in the attached hMSCs, and then enhance the in-situ bone formation and osseointegration at the bone-implant interfaces. We conclude that this N-cadherin mimetic peptide tethered on Ti surface promote osteogenic differentiation of hMSCs and osseointegration of biomaterial implants in vitro and in vivo. These findings demonstrate the importance of the development-inspired surface bioactivation of metal implants and shed light on the possible cellular mechanisms of the enhanced osseointegration.

Bio-functional strontium-containing photocrosslinked alginate hydrogels for promoting the osteogenic behaviors

In recent years, photocrosslinked alginate hydrogel has been widely studied in bone tissue engineering, owing to its numerous advantages. However, there are still some shortcomings like insufficient mechanical strength and lack of bone induction. To compensate for these deficiencies, in this work, a novel doped strontium (Sr) photocrosslinked methacrylated alginate (Sr-PMA) hydrogel was developed. Photocrosslinked alginate hydrogel fabricated via crosslinking methacrylate-modified alginate under ultraviolet (UV) light was placed into strontium solutions to prepare Sr-PMA gel by chelating reaction. The chemical structures, swelling behaviors, degradation profiles, elastic moduli, Sr²⁺ ion release and surface morphology of the Sr-PMA hydrogel were characterized, and we found that physical properties of the gels can be tailored by varying concentration of Sr²⁺ ions. And MC3T3-E1 cell viability, proliferation and mineralization outside the hydrogel were also investigated. Further research on cell survival, multiplication, osteogenic differentiation of the cells encapsulated in Sr-PMA hydrogels were explored. In vitro studies of biological properties revealed that incorporation of Sr²⁺ into photocrosslinked alginate gels significantly improved osteogenic differentiation capabilities and mineralization via stimulating expression of osteogenesis related genes and proteins of the cells compared to strontium-free photocrosslinked alginate gels. The research demonstrates that the innovative Sr-PMA hydrogels possessing adjustable physical performances, excellent biocompatibility and osteogenic differentiation capabilities could be potentially applied to bone tissue engineering and regenerative medicine. Meanwhile, it also provides a reference for the modification of biological properties of biomaterials.

Formation and Developmental Specification of the Odontogenic and Osteogenic Mesenchymes

Within the mandible, the odontogenic and osteogenic mesenchymes develop in a close proximity and form at about the same time. They both originate from the cranial neural crest. These two condensing ecto-mesenchymes are soon separated from each other by a very loose interstitial mesenchyme, whose cells do not express markers suggesting a neural crest origin. The two condensations give rise to mineralized tissues while the loose interstitial mesenchyme, remains as a soft tissue. This is crucial for proper anchorage of mammalian teeth. The situation in all three regions of the mesenchyme was compared with regard to cell heterogeneity. As the development progresses, the early phenotypic differences and the complexity in cell heterogeneity increases. The differences reported here and their evolution during development progressively specifies each of the three compartments. The aim of this review was to discuss the mechanisms underlying condensation in both the odontogenic and osteogenic compartments as well as the progressive differentiation of all three mesenchymes during development. Very early, they show physical and structural differences including cell density, shape and organization as well as the secretion of three distinct matrices, two of which will mineralize. Based on these data, this review highlights the consecutive differences in cell-cell and cell-matrix interactions, which support the cohesion as well as mechanosensing and mechanotransduction. These are involved in the conversion of mechanical energy into biochemical signals, cytoskeletal rearrangements cell differentiation, or collective cell behavior.

Mapping the structure and biological functions within mesenchymal bodies using microfluidics

Organoids that recapitulate the functional hallmarks of anatomic structures comprise cell populations able to self-organize cohesively in 3D. However, the rules underlying organoid formation in vitro remain poorly understood because a correlative analysis of individual cell fate and spatial organization has been challenging. Here, we use a novel microfluidics platform to investigate the mechanisms determining the formation of organoids by human mesenchymal stromal cells that recapitulate the early steps of condensation initiating bone repair in vivo. We find that heterogeneous mesenchymal stromal cells self-organize in 3D in a developmentally hierarchical manner. We demonstrate a link between structural organization and local regulation of specific molecular signaling pathways such as NF-κB and actin polymerization, which modulate osteo-endocrine functions. This study emphasizes the importance of resolving spatial heterogeneities within cellular aggregates to link organization and functional properties, enabling a better understanding of the mechanisms controlling organoid formation, relevant to organogenesis and tissue repair.

Human Umbilical Vein Endothelial Cells (HUVECs) Co-Culture with Osteogenic Cells: From Molecular Communication to Engineering Prevascularised Bone Grafts

The repair of bone defects caused by trauma, infection or tumor resection is a major clinical orthopedic challenge. The application of bone grafts in orthopedic procedures is associated with a problem of inadequate vascularization in the initial phase after implantation. Meanwhile, the survival of cells within the implanted graft and its integration with the host tissue is strongly dependent on nutrient and gaseous exchange, as well as waste product removal, which are effectuated by blood microcirculation. In the bone tissue, the vasculature also delivers the calcium and phosphate indispensable for the mineralization process. The critical role of vascularization for bone healing and function, led the researchers to the idea of generating a capillary-like network within the bone graft in vitro, which could allow increasing the cell survival and graft integration with a host tissue. New strategies for engineering pre-vascularized bone grafts, that apply the co-culture of endothelial and bone-forming cells, have recently gained interest. However, engineering of metabolically active graft, containing two types of cells requires deep understanding of the underlying mechanisms of interaction between these cells. The present review focuses on the best-characterized endothelial cells-human umbilical vein endothelial cells (HUVECs)-attempting to estimate whether the co-culture approach, using these cells, could bring us closer to development and possible clinical application of prevascularized bone grafts.

Immunophenotypic expression of UCP1 in hibernoma and other adipose/non adipose soft tissue tumours

BACKGROUND

Uncoupling protein 1 (UCP1) is a mitochondral protein transporter that uncouples electron transport from ATP production. UCP1 is highly expressed in brown adipose tissue (BAT), including hibernomas, but its expression in other adipose tumours is uncertain. UCP1 has also been found in other tissues (e.g. smooth muscle) but whether it is expressed in non-adipose benign and malignant soft tissue tumours is unknown.

METHODS

Immunohistochemical staining of normal (axillary) BAT and subcutaneous/abdominal white adipose tissue (WAT) as well as a wide range of benign and malignant primary soft tissue tumours (n = 171) was performed using a rabbit polyclonal antibody to UCP1. BAT and hibernomas were also stained by immunohistochemistry with monoclonal and polyclonal antibodies to adipose/non-adipose tumour markers in order to characterise the immunophenotype of BAT cells.

RESULTS

UCP1 was strongly expressed in the cytoplasm of brown fat cells in BAT and hibernomas, both of which also expressed aP2, S100, CD31, vimentin and calponin. UCP1 was not expressed in WAT or other adipose tumours with the exception a few tumour cells in pleomorphic liposarcoma. UCP1 was variably expressed by tumour cells in a few non-adipose sarcomas including leiomyosarcoma, rhabdomyosarcoma, alveolar soft part sarcoma, synovial sarcoma and clear cell sarcoma.

CONCLUSIONS

UCP1 is strongly expressed in BAT but not WAT and is found in all hibernomas and a few pleomorphic liposarcomas but not in other adipose tumours. UCP1 expression in a few non-adipose soft tissue sarcomas may possibly reflect origin of tumour cells from a common mesenchymal stem cell precursor and/or developmental pathway.

Effect of cell culture density on dental pulp-derived mesenchymal stem cells with reference to osteogenic differentiation

Dental pulp stem cells (DPSCs) are a good source for tissue regeneration, however, the number of DPSCs in the pulp tissue is limited. Cell propagation is essential for tissue engineering using DPSCs and the cell culture conditions may affect the properties of DPSCs. The purpose of this study was to analyze the effect of cell culture condition, especially dense culture condition, on the property and differentiation pathway of DPSCs. We cultured DPSCs under sparse (sDPSCs; 5 × 10³ cells/cm²) or dense (dDPSCs; 1 × 10⁵ cells/cm²) conditions for 4 days and compared their properties. The populations of CD73⁺ and CD105⁺ cells were significantly decreased in dDPSCs. Both groups showed multi-differentiation potential, but mineralized nodule formation was enhanced in dDPSCs. The phosphorylation of focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K) proteins was promoted in dDPSCs, and alkaline phosphatase (ALP) mRNA expression in dDPSCs was abolished in the presence of pan-PI3K and FAK inhibitors. dDPSCs implanted into mouse bone cavities induced more mineralized tissue formation than sDPSCs and control. These findings indicate that dense culture conditions modified the properties of DPSCs and gave rise to osteogenic-lineage commitment via integrin signaling and suggest that dense culture conditions favor the propagation of DPSCs to be used for mineralized tissue regeneration.

Novel Akt activator SC-79 is a potential treatment for alcohol-induced osteonecrosis of the femoral head

Alcohol is a leading risk factor for osteonecrosis of the femoral head (ONFH). We explored the molecular mechanisms underlying alcohol-induced ONFH and investigated the protective effect of the novel Akt activator SC-79 against this disease. We found that ethanol inhibited expression of the osteogenic genes RUNX2 and OCN, downregulated osteogenic differentiation, impaired the recruitment of Akt to the plasma membrane, and suppressed Akt phosphorylation at Ser473, thereby inhibiting the Akt/GSK3β/β-catenin signaling pathway in bone mesenchymal stem cells. To assess SC-79′s ability to counteract the inhibitory effect of ethanol on Akt-Ser73 phosphorylation, we performed micro-computerized tomography and immunofluorescent staining of osteopontin, osteocalcin and collagen type 1 in a rat model of alcohol-induced ONFH. We found that SC-79 injections inhibited alcohol-induced osteonecrosis. These results show that alcohol-induced ONFH is associated with suppression of p-Akt-Ser473 in the Akt/GSK3β/β-catenin signaling pathway in bone mesenchymal stem cells. We propose that SC-79 treatment to rescue Akt activation could be tested in the clinic as a potential therapeutic approach to preventing the development of alcohol-induced ONFH.

The protective effect of PFTα on alcohol-induced osteonecrosis of the femoral head

Epidemiologic studies have shown alcohol plays a pivotal role in the development of osteonecrosis of the femoral head (ONFH). The aim of this study was to explore the underlying mechanism of alcohol-induced ONFH and the protective effect of pifithrin-α (PFTα). In vitro, we found ethanol treatment significantly activated p53, suppressed Wnt/β-catenin signaling and inhibited osteogenic-related proteins. Furthermore, by separating the cytoplasmic and nuclear proteins, we found ethanol inhibited osteogenesis by impairing the accumulation of β-catenin in both the cytoplasm and nucleus in human bone mesenchymal stem cells (hBMSCs), which resulted from activating glycogen synthase kinase-3β (GSK-3β). Therefore, PFTα, a p53 inhibitor, was introduced in this study to block the ethanol-triggered activation of p53 in hBMSCs and alcohol-induced ONFH in a rat model. In vivo, we established alcohol-induced ONFH in rats and investigated the protective effect of PFTα. Hematoxylin & eosin (H&E) staining combined with TdT-mediated dUTP nick end labeling (TUNEL), cleaved caspase-3 immunohistochemical staining, and micro-CT images revealed substantial ONFH in the alcohol-administered rats, whereas significantly less osteonecrosis developed in the rats injected with PFTα. Osteogenic-related proteins, including osteocalcin, osteopontin and collagen I, were significantly decreased in the alcohol-administered rats, whereas these results were reversed in the PFTα-injected rats. Fluorochrome labeling similarly showed that alcohol significantly reduced the osteogenic activity in the rat femoral head, which was blocked by the injection of PFTα. In conclusion, PFTα had an antagonistic effect against the effects of ethanol on hBMSCs and could be a clinical strategy to prevent the development of alcohol-induced ONFH.

The role of adhesion junctions in the biomechanical behaviour and osteogenic differentiation of 3D mesenchymal stem cell spheroids

Osteogenesis of mesenchymal stem cells (MSC) can be regulated by the mechanical environment. MSCs grown in 3D spheroids (mesenspheres) have preserved multi-lineage potential, improved differentiation efficiency, and exhibit enhanced osteogenic gene expression and matrix composition in comparison to MSCs grown in 2D culture. Within 3D mesenspheres, mechanical cues are primarily in the form of cell-cell contraction, mediated by adhesion junctions, and as such adhesion junctions are likely to play an important role in the osteogenic differentiation of mesenspheres. However the precise role of N- and OB-cadherin on the biomechanical behaviour of mesenspheres remains unknown. Here we have mechanically tested mesenspheres cultured in suspension using parallel plate compression to assess the influence of N-cadherin and OB-cadherin adhesion junctions on the viscoelastic properties of the mesenspheres during osteogenesis. Our results demonstrate that N-cadherin and OB-cadherin have different effects on mesensphere viscoelastic behaviour and osteogenesis. When OB-cadherin was silenced, the viscosity, initial and long term Young's moduli and actin stress fibre formation of the mesenspheres increased in comparison to N-cadherin silenced mesenspheres and mesenspheres treated with a scrambled siRNA (Scram) at day 2. Additionally, the increased viscoelastic material properties correlate with evidence of calcification at an earlier time point (day 7) of OB-cadherin silenced mesenspheres but not Scram. Interestingly, both N-cadherin and OB-cadherin silenced mesenspheres had higher BSP2 expression than Scram at day 14. Taken together, these results indicate that N-cadherin and OB-cadherin both influence mesensphere biomechanics and osteogenesis, but play different roles.

Research Advancements in Porcine Derived Mesenchymal Stem Cells

In the present era of stem cell biology, various animals such as Mouse, Bovine, Rabbit and Porcine have been tested for the efficiency of their mesenchymal stem cells (MSCs) before their actual use for stem cell based application in humans. Among them pigs have many similarities to humans in the form of organ size, physiology and their functioning, therefore they have been considered as a valuable model system for in vitro studies and preclinical assessments. Easy assessability, few ethical issues, successful MSC isolation from different origins like bone marrow, skin, umbilical cord blood, Wharton’s jelly, endometrium, amniotic fluid and peripheral blood make porcine a good model for stem cell therapy. Porcine derived MSCs (pMSCs) have shown greater in vitro differentiation and transdifferention potential towards mesenchymal lineages and specialized lineages such as cardiomyocytes, neurons, hepatocytes and pancreatic beta cells. Immunomodulatory and low immunogenic profiles as shown by autologous and heterologous MSCs proves them safe and appropriate models for xenotransplantation purposes. Furthermore, tissue engineered stem cell constructs can be of immense importance in relation to various osteochondral defects which are difficult to treat otherwise. Using pMSCs successful treatment of various disorders like Parkinson’s disease, cardiac ischemia, hepatic failure, has been reported by many studies. Here, in this review we highlight current research findings in the area of porcine mesenchymal stem cells dealing with their isolation methods, differentiation ability, transplantation applications and their therapeutic potential towards various diseases.

Lack of SIRPα phosphorylation and concomitantly reduced SHP-2-PI3K-Akt2 signaling decrease osteoblast differentiation

Normal differentiation of bone forming osteoblasts is a prerequisite for maintenance of skeletal health and is dependent on intricate cellular signaling pathways, including the essential transcription factor Runx2. The cell surface glycoprotein CD47 and its receptor signal regulatory protein alpha (SIRPα) have both been suggested to regulate bone cell differentiation. Here we investigated osteoblastic differentiation of bone marrow stromal cells from SIRPα mutant mice lacking the cytoplasmic signaling domain of SIRPα. An impaired osteoblastogenesis in SIRPα-mutant cell cultures was demonstrated by lower alkaline phosphatase activity and less mineral formation compared to wild-type cultures. This reduced osteoblastic differentiation potential in SIRPα-mutant stromal cells was associated with a significantly reduced expression of Runx2, osterix, osteocalcin, and alkaline phosphatase mRNA, as well as a reduced phosphorylation of SHP-2 and Akt2, as compared with that in wild-type stromal cells. Addition of a PI3K-inhibitor to wild-type stromal cells could mimic the impaired osteoblastogenesis seen in SIRPα-mutant cells. In conclusion, our data suggest that SIRPα signaling through SHP-2-PI3K-Akt2 strongly influences osteoblast differentiation from bone marrow stromal cells.

MiR-221-inhibited adipose tissue-derived mesenchymal stem cells bioengineered in a nano-hydroxy apatite scaffold

The repair of skeletal defects is the main goal of bone tissue engineering. Recent literature highlighted various regulatory roles of microRNAs in stem cell fate determination. In addition, the role of porous hydroxyapatite/polycaprolacton (nHA/PCL) as a bioactive scaffold which enhances adipose tissue-derived mesenchymal stem cells (AT-MSCs) growth and osteogenic differentiation has been proved. The aim of the present study was to investigate the synergistic potential of both down-regulating miR-221 and nHA/PCL scaffold seeding in osteogenic potential of AT-MSCs. After isolation and characterization of AT-MSCs, the transfection of anti-miR-221 was performed into the cells using lipofectamine 2000 and the transfected cells were seeded into a synthesized nHA/PCL scaffold. The DAPI staining confirmed the presence of AT-MSCs on nHA/PCL scaffold. Quantitative expression of osteoblast marker genes, Runx2, and osteocalcin of the transfected cells in the scaffold were evaluated. Interestingly, significant upregulation of transcribed Runx2 and osteocalcin genes (P < 0.01) were observed in miR-221-inhibited nHA/PCL seeded cells. Also, alkaline phosphatase activity (ALP) was significantly higher (P < 0.01) in miR-221-inhibited AT-MSCs seeded on nHA/PCL than those seeded on nHA/PCL or transfected with anti-miR-221, individually. The results of this combination suggest a valuable method for enhancing osteogenesis in AT-MSCs. This method could be applicable for gene-cell therapy of bone defects.

Glycosylation of Dentin Matrix Protein 1 is critical for osteogenesis

Proteoglycans play important roles in regulating osteogenesis. Dentin matrix protein 1 (DMP1) is a highly expressed bone extracellular matrix protein that regulates both bone development and phosphate metabolism. After glycosylation, an N-terminal fragment of DMP1 protein was identified as a new proteoglycan (DMP1-PG) in bone matrix. In vitro investigations showed that Ser⁸⁹ is the key glycosylation site in mouse DMP1. However, the specific role of DMP1 glycosylation is still not understood. In this study, a mutant DMP1 mouse model was developed in which the glycosylation site S⁸⁹ was substituted with G⁸⁹ (S89G-DMP1). The glycosylation level of DMP1 was down-regulated in the bone matrix of S89G-DMP1 mice. Compared with wild type mice, the long bones of S89G-DMP1 mice showed developmental changes, including the speed of bone remodeling and mineralization, the morphology and activities of osteocytes, and activities of both osteoblasts and osteoclasts. These findings indicate that glycosylation of DMP1 is a key posttranslational modification process during development and that DMP1-PG functions as an indispensable proteoglycan in osteogenesis.

Recruitment of β-catenin to N-cadherin is necessary for smooth muscle contraction

β-Catenin is a key component that connects transmembrane cadherin with the actin cytoskeleton at the cell-cell interface. However, the role of the β-catenin/cadherin interaction in smooth muscle has not been well characterized. Here stimulation with acetylcholine promoted the recruitment of β-catenin to N-cadherin in smooth muscle cells/tissues. Knockdown of β-catenin by lentivirus-mediated shRNA attenuated smooth muscle contraction. Nevertheless, myosin light chain phosphorylation at Ser-19 and actin polymerization in response to contractile activation were not reduced by β-catenin knockdown. In addition, the expression of the β-catenin armadillo domain disrupted the recruitment of β-catenin to N-cadherin. Force development, but not myosin light chain phosphorylation and actin polymerization, was reduced by the expression of the β-catenin armadillo domain. Furthermore, actin polymerization and microtubules have been implicated in intracellular trafficking. In this study, the treatment with the inhibitor latrunculin A diminished the interaction of β-catenin with N-cadherin in smooth muscle. In contrast, the exposure of smooth muscle to the microtubule depolymerizer nocodazole did not affect the protein-protein interaction. Together, these findings suggest that smooth muscle contraction is mediated by the recruitment of β-catenin to N-cadherin, which may facilitate intercellular mechanotransduction. The association of β-catenin with N-cadherin is regulated by actin polymerization during contractile activation.

Integrin and cadherin signaling in bone: role and potential therapeutic targets

Cell-cell and cell-matrix interactions mediated by cell adhesion molecules are important mechanisms controlling cell fate and function. Here, we review recent advances in the implication of the cell adhesion molecules integrins and cadherins in the control of osteoblastogenesis and bone formation. We discuss emerging evidence indicating that signaling pathways mediated by integrins and cadherins and their crosstalk with the Wnt/β-catenin signaling pathway regulate osteogenic differentiation and mechanotransduction. We also offer a comprehensive view of the mechanisms by which some integrins and cadherins control the differentiation of cells of the osteoblast lineage in bone marrow niches. Understanding how specific integrins or cadherins may promote osteogenic cell differentiation, bone formation, and repair may lead to novel therapeutic strategies.

MiR-378 overexpression attenuates high glucose-suppressed osteogenic differentiation through targeting CASP3 and activating PI3K/Akt signaling pathway

Hyperglycemia is one of the possible causes for osteoporosis and bone fracture in diabetes mellitus. Here we modeled diabetes-induced osteoporosis in vitro using preosteoblastic cell line MC3T3-E1 and a diabetic mice model for in vivo studies. We found that in addition to reducing osteoblast viability and differentiation (mineralization), culture in elevated glucose down regulated microRNA-378 (miR-378) expression but ectopic miR-378 expression reversed the effects of high glucose. We identified caspase-3 (CASP3) as a target of miR-378 and showed that miR-378 repressed CASP3 mRNA and protein expression under high glucose condition. We further showed that both miR-378 expression and CASP3 silencing independently restored alkaline phosphatase (ALP) activity and the expression of osteoblastic differentiation markers Runt-related transcription factor 2 (Runx2), osteorix (Osx), collagen I (Col I), osteocalcin (OCN), and osteonectin (ON). We also found that under high glucose conditions miR-378 activated the PI3K/Akt signaling pathway and down regulated pro-apoptotic CytC, Apaf-1 and Bax proteins via the PI3K/Akt pathway. Collectively, these results suggest that miR-378 overexpression attenuates high glucose-suppressed osteogenic differentiation through targeting CASP3 and activating the PI3K/Akt pathway.

Difference in apical and basal growth of the frontal bone primordium in Foxc1ch/ch mice

The frontal and parietal bones form the major part of the calvarium and their primordia appear at the basolateral region of the head and grow apically. A spontaneous loss of Foxc1 function mutant mouse, congenital hydrocephalus (Foxc1(ch/ch)), results in congenital hydrocephalus accompanied by defects in the apical part of the skull vault. We found that during the initiation stage of apical growth of the frontal bone primordium in the Foxc1(ch/ch) mouse, the Runx2 expression domain extended only to the basal side and bone sialoprotein (Bsp) and N-cadherin expression domains appeared only in the basal region. Fluorescent dye (DiI) labeling of the frontal primordium by ex-utero surgery confirmed that apical extension of the frontal bone primordium of the mouse was severely retarded, while extension to the basal side underneath the brain was largely unaffected. Consistent with this observation, decreased cell proliferation activity was seen at the apical tip but not the basal tip of the frontal bone primordium as determined by double detection of Runx2 transcripts and BrdU incorporation. Furthermore, expression of the osteogenic-related genes Bmp4 and-7 was observed only in the basal part of the meninges during the initiation period of primordium growth. These results suggest that a loss of Foxc1 function affects skull bone formation of the apical region and that Bmp expression in the meninges might influence the growth of the calvarial bone primordium.

Involvement of N-cadherin/β-catenin interaction in the micro/nanotopography induced indirect mechanotransduction

Topographical modification at micro- and nanoscale is widely applied to enhance the tissue integration properties of biomaterials, but the underlying molecular mechanism is poorly understood. The biomaterial topography modulates cell functions via mechanotransduction of direct and indirect. We propose that N-cadherin may play a role in the topographically induced indirect mechanotransduction by regulating the β-catenin signaling. For confirmation, the cell functions, N-cadherin expression and β-catenin signaling activation of osteoblasts on titanium (Ti) surfaces with micro- or/and nanotopography are systemically compared with naive and N-cadherin down-regulating MC3T3-E1 cells. We find that the N-cadherin expression is reversely related to the intracellular β-catenin signaling and the N-cadherin/β-catenin signaling is modulated differentially by the micro- and nanotopography. The nanotopography significantly up-regulates the N-cadherin expression leading to lower β-catenin signaling activity and consequently depressed differentiation, whereas the microtopography down-regulates the N-cadherin expression resulting in enhanced β-catenin signaling and thus osteoblast differentiation. Artificial down-regulation of the N-cadherin expression can significantly up-regulate the β-catenin signaling and consequently enhance the osteoblast differentiation on all the Ti surfaces. The study for the first time clarifies the involvement of the N-cadherin/β-catenin interaction in the micro/nanotopography induced indirect mechanotransduction and provides a potentially new approach for biomaterial modification and biofunctionalization by down-regulating the cell N-cadherin expression to achieve improved clinical performance.

Down-regulation of Sox11 is required for efficient osteogenic differentiation of adipose-derived stem cells

Adipose-derived stem cells represent a type of mesenchymal stem cells with the attendant capacity to self-renew and differentiate into multiple cell lineages. We have performed a microarray-based gene expression profiling of osteogenic differentiation and found that the transcription factor Sox11 is down-regulated during the process. Functional assays demonstrate that down-regulation of Sox11 is required for an efficient differentiation. Furthermore, results from forced expression of constitutively-active and dominant-negative derivatives of Sox11 indicate that Sox11 functions as a transcriptional activator in inhibiting osteogenesis. Sox11 thus represents a novel regulator of osteogenesis whose expression and activity can be potentially manipulated for controlled differentiation.

Cadherin-mediated cell-cell adhesion and signaling in the skeleton

Direct cell-to-cell interactions via cell adhesion molecules, in particular cadherins, are critical for morphogenesis, tissue architecture, and cell sorting and differentiation. Partially overlapping, yet distinct roles of N-cadherin (cadherin-2) and cadherin-11 in the skeletal system have emerged from mouse genetics and in vitro studies. Both cadherins are important for precursor commitment to the osteogenic lineage, and genetic ablation of Cdh2 and Cdh11 results in skeletal growth defects and impaired bone formation. While Cdh11 defines the osteogenic lineage, persistence of Cdh2 in osteoblasts in vivo actually inhibits their terminal differentiation and impairs bone formation. The action of cadherins involves both cell-cell adhesion and interference with intracellular signaling, and in particular the Wnt/β-catenin pathway. Both cadherin-2 and cadherin-11 bind to β-catenin, thus modulating its cytoplasmic pools and transcriptional activity. Recent data demonstrate that cadherin-2 also interferes with Lrp5/6 signaling by sequestering these receptors in inactive pools via axin binding. These data extend the biologic action of cadherins in bone forming cells, and provide novel mechanisms for development of therapeutic strategies aimed at enhancing bone formation.

EB1 levels are elevated in ascorbic Acid (AA)-stimulated osteoblasts and mediate cell-cell adhesion-induced osteoblast differentiation

Osteoblasts are differentiated mesenchymal cells that function as the major bone-producing cells of the body. Differentiation cues including ascorbic acid (AA) stimulation provoke intracellular changes in osteoblasts leading to the synthesis of the organic portion of the bone, which includes collagen type I α1, proteoglycans, and matrix proteins, such as osteocalcin. During our microarray analysis of AA-stimulated osteoblasts, we observed a significant up-regulation of the microtubule (MT) plus-end binding protein, EB1, compared with undifferentiated osteoblasts. EB1 knockdown significantly impaired AA-induced osteoblast differentiation, as detected by reduced expression of osteoblast differentiation marker genes. Intracellular examination of AA-stimulated osteoblasts treated with EB1 siRNA revealed a reduction in MT stability with a concomitant loss of β-catenin distribution at the cell cortex and within the nucleus. Diminished β-catenin levels in EB1 siRNA-treated osteoblasts paralleled an increase in phospho-β-catenin and active glycogen synthase kinase 3β, a kinase known to target β-catenin to the proteasome. EB1 siRNA treatment also reduced the expression of the β-catenin gene targets, cyclin D1 and Runx2. Live immunofluorescent imaging of differentiated osteoblasts revealed a cortical association of EB1-mcherry with β-catenin-GFP. Immunoprecipitation analysis confirmed an interaction between EB1 and β-catenin. We also determined that cell-cell contacts and cortically associated EB1/β-catenin interactions are necessary for osteoblast differentiation. Finally, using functional blocking antibodies, we identified E-cadherin as a major contributor to the cell-cell contact-induced osteoblast differentiation.

Osteoimmunology: the study of the relationship between the immune system and bone tissue

Bone tissue is a highly regulated structure, which plays an essential role in various physiological functions. Through autocrine and paracrine mechanisms, bone tissue is involved in hematopoiesis, influencing the fate of hematopoietic stem cells. There are a number of molecules shared by bone cells and immune system cells indicating that there are multiple connections between the immune system and bone tissue. In order to pool all the knowledge concerning both systems, a new discipline known under the term «osteoimmunology» has been developed. Their progress in recent years has been exponential and allowed us to connect and increase our knowledge in areas not seemingly related such as rheumatoid erosion, postmenopausal osteoporosis, bone metastases or periodontal disease. In this review, we have tried to summarize the most important advances that have occurred in the last decade, especially in those areas of interest related to rheumatology.

ATP and UTP stimulate bone morphogenetic protein-2,-4 and -5 gene expression and mineralization by rat primary osteoblasts involving PI3K/AKT pathway

The modulation of purinergic receptors plays an important role in the regulation of bone formation by the osteoblast. On the other hand, bone morphogenetic proteins (BMPs), members of the transforming growth factor-β superfamily, regulate the differentiation of osteoprogenitor bone cells and stimulate bone formation. In this study, we investigate the effects of several nucleotides on osteoblast differentiation and function, and their relation with the gene expression of osteogenic proteins BMP-2, BMP-4 and BMP-5 as well as of differentiation markers alkaline phosphatase (ALP) and bone sialoprotein (BSP). Our results indicate that 100μM ATP, ATPγS and UTP, but not ADP, ADPβS or UDP, promote ALP activity in rat primary osteoblasts, showing a peak about day 7 of the treatment. ATP, ATPγS and UTP also increase the mRNA levels of ALP, BMP-2, BMP-4, BMP-5 and BSP. Both the ALP activity and ALP and BMP-4 mRNA increments induced by ATP and UTP are inhibited by Ly294002, a PI3K inhibitor, suggesting the involvement of PI3K/AKT signaling pathway in purinergic modulation of osteoblast differentiation. Furthermore, bone mineralization enhance 1 and 1.5 fold after culturing osteoblasts in the presence of 100μM ATP or UTP, respectively, but not of ADP or UDP for 22 days. This information suggests that P2Y2 receptors (responsive to ATP, ATPγS and UTP) enhance osteoblast differentiation involving PI3K/AKT signaling pathway activation and gene expression induction of ALP, BMP-2, BMP-4, BMP-5 and BSP. Our findings state a novel molecular mechanism that involves specific gene expression activation of osteoblast function by the purinoreceptors, which would be of help in setting up new pharmacological strategies for the intervention in bone loss pathologies.

Cadherins and Wnt signalling: a functional link controlling bone formation

Cadherins are calcium-dependent cell adhesion molecules that have a major role in morphogenesis and tissue formation. In bone, cadherins control osteoblast differentiation by mediating cell-cell adhesion and signals that promote phenotypic osteoblast gene expression. Furthermore, cadherins can interact with Wnt signalling to modulate osteoblastogenesis. One mechanism involves the interaction of N-cadherin with β-catenin at the cell membrane, resulting in β-catenin sequestration, reduction of the cytosolic β-catenin pool and inhibition of Wnt signalling. In addition to modulating the β-catenin pool, N-cadherin can regulate osteoblasts by interacting with the Wnt coreceptors LRP5 or LRP6. We showed that the functional interaction between N-cadherin and LRP5/6 in osteoblasts promotes β-catenin degradation and reduces canonical Wnt signalling. This crosstalk between N-cadherin and Wnt signalling has a negative impact on osteoblast proliferation, differentiation and survival, independently of cell-cell adhesion, which results in decreased bone formation and delayed bone accrual in mice. The identification of this crosstalk between N-cadherin and Wnt signalling may have therapeutic implications, as a disruption of the N-cadherin-LRP5/6 interaction using a competitor peptide can increase Wnt/β-catenin signalling without affecting cell-cell adhesion, and this effect results in increased osteoblastogenesis and bone tissue formation in vivo. In this review, we summarize our current knowledge of the key crosstalks between cadherins and Wnt signalling that impact osteoblast function, bone formation and bone mass, and the possible therapeutic implications of such interactions for promoting osteoblastogenesis, bone formation and bone mass.

N-cadherin regulates osteogenesis and migration of bone marrow-derived mesenchymal stem cells

N-cadherin, a calcium-dependent cellular adhesive protein, plays important roles during embryonic development and bone formation. The potential of mesenchymal stem cells (MSCs) in osteoblast differentiation and homing to the sites of injury make it a promising cell resource for tissue engineering. However, the role of N-cadherin in MSCs osteoblast differentiation and migration remains still obscure. In the present study, our results showed that prolonged N-cadherin overexpression inhibited osteogenic differentiation of MSCs through negatively regulating β-catenin and ERK1/2 signaling pathways. The mRNA expression levels of osteogenesis-related genes (Osteopontin, Osteocalcin, runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and bone morphogenetic protein 2) were significantly inhibited by N-cadherin, as well as the ALP activity and calcium deposit as stained by Alizarin Red S. While, silencing N-cadherin using shRNA reversed this effect. Furthermore, ectopic bone formation conducted in nude mice verified that N-cadherin significantly inhibited ectopic bone formation of MSCs in vivo. In addition, we also found that the N-cadherin overexpression could promote the migration potential of MSCs. These findings reveal that N-cadherin inhibits osteogenesis but promotes migration of MSCs. The underlying mechanism of N-cadherin inhibiting osteogenesis may through suppressing β-catenin and ERK1/2 signaling pathways.

Signaling pathways affecting skeletal health

Skeletal health is dependent on the balance between bone resorption and formation during bone remodeling. Multiple signaling pathways play essential roles in the maintenance of skeletal integrity by positively or negatively regulating bone cells. During the last years, significant advances have been made in our understanding of the essential signaling pathways that regulate bone cell commitment, differentiation and survival. New signaling anabolic pathways triggered by parathyroid hormone, local growth factors, Wnt signaling, and calcium sensing receptor have been identified. Novel signals induced by interactions between bone cells-matrix (integrins), osteoblasts/osteocytes (cadherins, connexins), and osteoblasts/osteoclast (ephrins, Wnt-RhoA, semaphorins) have been discovered. Recent studies revealed the key pathways (MAPK, PI3K/Akt) that critically control bone cells and skeletal mass. This review summarizes the most recent knowledge on the major signaling pathways that control bone cells, and their potential impact on the development of therapeutic strategies to improve human bone health.

Down-regulation of miRNA-221 triggers osteogenic differentiation in human stem cells

Despite interesting in silico evidence, the specific role of mir-221 in osteogenesis has not been studied. We evaluated the osteogenic induction of transient-transfected anti-mir-221 in human unrestricted somatic stem cells and human mesenchymal stem cells both transcriptionally and translationally. In transfected unrestricted somatic stem cells, transcriptions of some osteogenic markers were twice that of the control and translations of osteopontin and osteocalcin were increased from 9 to 39 % and from 0 to 21 %, respectively. Up-regulation of transcribed osteogenic markers in transfected mesenchymal stem cells were 50 times greater than controls while no significant change in translations were observed. Prior to these analyses, the authenticity of stem cells, their osteogenic differentiation and transfection efficiency were verified. Transient modulation of mir-221 therefore suggests a mechanism for rapid induction of osteogenesis as a useful strategy for cell-based therapy.