Smad4 controls bone homeostasis through regulation of osteoblast/osteocyte viability

Comparison In Vitro Study on the Interface between Skin and Bone Cell Cultures and Microporous Titanium Samples Manufactured with 3D Printing Technology Versus Sintered Samples

Percutaneous implants osseointegrated into the residuum of a person with limb amputation need to provide mechanical stability and protection against infections. Although significant progress has been made in the biointegration of percutaneous implants, the problem of forming a reliable natural barrier at the level of the surface of the implant and the skin and bone tissues remains unresolved. The use of a microporous implant structure incorporated into the Skin and Bone Integrated Pylon (SBIP) should address the issue by allowing soft and bone tissues to grow directly into the implant structure itself, which, in turn, should form a reliable barrier to infections and support strong osseointegration. To evaluate biological interactions between dermal fibroblasts and MC3T3-E1 osteoblasts in vitro, small titanium discs (with varying pore sizes and volume fractions to achieve deep porosity) were fabricated via 3D printing and sintering. The cell viability MTT assay demonstrated low cytotoxicity for cells co-cultured in the pores of the 3D-printed and sintered Ti samples during the 14-day follow-up period. A subsequent Quantitative Real-Time Polymerase Chain Reaction (RT-PCR) analysis of the relative gene expression of biomarkers that are associated with cell adhesion (α2, α5, αV, and β1 integrins) and extracellular matrix components (fibronectin, vitronectin, type I collagen) demonstrated that micropore sizes ranging from 200 to 500 µm of the 3D printed and sintered Ti discs were favorable for dermal fibroblast adhesion. For example, for representative 3D-printed Ti sample S6 at 72 h the values were 4.71 ± 0.08 (α2 integrin), 4.96 ± 0.08 (α5 integrin), 4.71 ± 0.08 (αV integrin), and 1.87 ± 0.12 (β1 integrin). In contrast, Ti discs with pore sizes ranging from 400 to 800 µm demonstrated the best results (in terms of marker expression related to osteogenic differentiation, including osteopontin, osteonectin, osteocalcin, TGF-β1, and SMAD4) for MC3T3-E1 cells. For example, for the representative 3D sample S4 on day 14, the marker levels were 11.19 ± 0.77 (osteopontin), 7.15 ± 0.29 (osteonectin), and 6.08 ± 0.12 (osteocalcin), while for sintered samples the levels of markers constituted 5.85 ± 0.4 (osteopontin), 4.45 ± 0.36 (osteonectin), and 4.46 ± 0.3 (osteocalcin). In conclusion, the data obtained show the high biointegrative properties of porous titanium structures, while the ability to implement several pore options in one structure using 3D printing makes it possible to create personalized implants for the best one-time integration with both skin and bone tissues.

Unraveling the Link of Altered TGFβ Signaling with Scoliotic Vertebral Malformations in Osteogenesis Imperfecta: A Comprehensive Review

Osteogenesis Imperfecta (OI) is a genetic disorder caused by mutations in genes responsible for collagen synthesis or polypeptides involved in the formation of collagen fibers. Its predominant skeletal complication is scoliosis, impacting 25 to 80% of OI patients. Vertebral deformities of the scoliotic curves in OI include a variety of malformations such as codfish, wedged-shaped vertebrae or platyspondyly, craniocervical junction abnormalities, and lumbosacral spondylolysis and spondylolisthesis. Although the precise pathophysiology of these spinal deformities remains unclear, anomalies in bone metabolism have been implicated in the progression of scoliotic curves. Bone Mineral Density (BMD) measurements have demonstrated a significant reduction in the Z-score, indicating osteoporosis and a correlation with the advancement of scoliosis. Factors such as increased mechanical strains, joint hypermobility, lower leg length discrepancy, pelvic obliquity, spinal ligament hypermobility, or vertebrae microfractures may also contribute to the severity of scoliosis. Histological vertebral analysis has confirmed that changes in trabecular microarchitecture, associated with inadequate bone turnover, indicate generalized bone metabolic defects in OI. At the molecular level, the upregulation of Transforming Growth factor-β (TGFβ) signaling in OI can lead to disturbed bone turnover and changes in muscle mass and strength. Understanding the relationship between spinal clinical features and molecular pathways could unveil TGFβ -related molecular targets, paving the way for novel therapeutic approaches in OI.

Structural characterization and osteogenic differentiation-promoting activity of polysaccharide purified from Chroogomphus rutilus

Chroogomphus rutilus (CR) possesses anti-inflammatory, antioxidant, and hypoglycemic properties. However, studies are yet to evaluate the anti-osteoporotic activity of the fungi and its polysaccharides. Therefore, this study is aimed at characterizing and evaluating the anti-osteoporotic effects of a novel polysaccharide from CR. The neutral polysaccharide CRP2 extracted and purified from the fruiting body of CR had a molecular weight of 20.41 kDa. Monosaccharide composition analysis revealed that CRP2 is composed of galactose, glucose, fucose, and mannose. The backbone of CRP2 primarily consisted of →6)-α-D-Galp-(1 → residues, with specific site substitutions speculated at partial positions, such as O-CH3 substitution at H-3 position, or a branch site located at C-2, including α-L-Fucp-(1 → 6)-β-D-Glcp-(1 → and α-D-Manp-(1→. CRP2 treatment increased trabecular bone density, restored a network-shaped structure, and upregulated the expression of osteoblast differentiation markers, including runt-related transcription factor 2, osterix, osteocalcin, and osteopontin in the femoral tissue of mice with osteoporosis (OP). Additionally, CRP2 treatment suppressed the expression of tumor necrosis factor-α and interleukin-1β in the femoral tissue of mice with OP. Mechanistically, CRP2 exerted anti-OP effect by inhibiting inflammation and promoting osteogenesis through the transforming growth factor β-1/Smad pathway. Conclusively, these findings augment our understanding of the potential role of CRP2 in OP treatment.

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

Functional micro-RNA drugs acting as a fate manipulator in the regulation of osteoblastic death

Bone loss is prevalent in clinical pathological phenomena such as osteoporosis, which is characterized by decreased osteoblast function and number, increased osteoclast activity, and imbalanced bone homeostasis. However, current treatment strategies for bone diseases are limited. Regulated cell death (RCD) is a programmed cell death pattern activated by the expression of specific genes in response to environmental changes. Various studies have shown that RCD is closely associated with bone diseases, and manipulating the death fate of osteoblasts could contribute to effective bone treatment. Recently, microRNA-targeting therapy drugs have emerged as a potential solution because of their precise targeting, powerful curative effect, and limited side effects. Nevertheless, their clinical application is limited by their inherent instability, easy enzymatic degradation, and poor membrane penetrability. To address this challenge, a self-assembling tetrahedral DNA nanostructure (TDN)-based microRNA (Tmi) delivery system has been proposed. TDN features excellent biocompatibility, cell membrane penetrability, serum stability, and modification versatility, making it an ideal nucleic acid carrier for miRNA protection and intracellular transport. Once inside cells, Tmi can dissociate and release miRNAs to manipulate key molecules in the RCD signaling pathway, thereby regulating bone homeostasis and curing diseases caused by abnormal RCD activation. In this paper, we discuss the impact of the miRNA network on the initiation and termination of four critical RCD programs in bone tissues: apoptosis, autophagy, pyroptosis, and ferroptosis. Furthermore, we present the Tmi delivery system as a miRNA drug vector. This provides insight into the clinical translation of miRNA nucleic acid drugs and the application of miRNA drugs in bone diseases.

Fluchloralin induces developmental toxicity in heart, liver, and nervous system during early zebrafish embryogenesis

The zebrafish is a prominent vertebrate model popularly used for toxicity testing because of its rapid development and transparent embryos. Fluchloralin, a dinitroaniline herbicide used to control weeds, inhibits microtubule formation and cell division. The structurally homologous substances ethalfluralin and pendimethalin, which belong to the dinitroaniline family, were found to be genotoxic and to exert developmental toxicity via mitochondrial dysfunction in a zebrafish model. To date, developmental toxicity of fluchloralin in zebrafish has not been reported. In the present study, we identified morphological changes in developing zebrafish, including decreased survival rate and body length, and increased yolk sac edema. In dose-dependent response to fluchloralin exposure, inhibition of neurogenesis in the spinal cord and motor neuron defects were observed in transgenic zebrafish models (olig2:dsRed). Zebrafish exposed to fluchloralin also displayed organ dysfunction in the heart, liver, and pancreas in cmlc2:dsRed and lfabp:dsRed;elastase:GFP transgenic models. Fluchloralin increased cell death in the brain by promoting apoptosis, visualized via acridine orange staining, and by activating apoptosis signaling proteins, including cytochrome c1, zBax, and Bcl-XL. This study provides novel evidence supporting the necessity of controlling pollutants in aquatic environments.

Fluid shear stress-induced down-regulation of miR-146a-5p inhibits osteoblast apoptosis via targeting SMAD4

Fluid shear stress (FSS) plays an important role in osteoblast apoptosis. However, the role of miRNA in osteoblast apoptosis under FSS and possible molecular mechanisms remain unknown. Our aim of the study was to explore whether miR-146a-5p regulates osteoblast apoptosis under FSS and its molecular mechanisms. FSS could down-regulate the expression of miR-146a-5p in MC3T3-E1 cells. We confirm that up-regulation of miR-146a-5p promotes osteoblasts apoptosis and down-regulation of miR-146a-5p inhibits osteoblasts apoptosis. We further demonstrated that FSS inhibits osteoblast apoptosis by down-regulated miR-146a-5p. Dual-luciferase reporter assay validated that SMAD4 is a direct target gene of miR-146a-5p. In addition, mimic-146a-5p suppressed FSS-induced up-regulation of SMAD4 protein levels, which suggests that FSS elevated SMAD4 protein expression levels via regulation miR-146a-5p. Further investigations showed that SMAD4 could inhibit osteoblast apoptosis. We demonstrated that miR-146a-5p regulates osteoblast apoptosis via targeting SMAD4. Taken together, our present study showed that FSS-induced down-regulation miR-146a-5p inhibits osteoblast apoptosis via target SMAD4. These findings may provide novel mechanisms for FSS to inhibit osteoblast apoptosis, and also may provide a potential therapeutic target for osteoporosis.

Fluid shear stress-induced down-regulation of miR-146a-5p inhibits osteoblast apoptosis via targeting SMAD4

Fluid shear stress (FSS) plays an important role in osteoblast apoptosis. However, the role of miRNA in osteoblast apoptosis under FSS and possible molecular mechanisms remain unknown. Our aim of the study was to explore whether miR-146a-5p regulates osteoblast apoptosis under FSS and its molecular mechanisms. FSS could down-regulate the expression of miR-146a-5p in MC3T3-E1 cells. We confirm that up-regulation of miR-146a-5p promotes osteoblasts apoptosis and down-regulation of miR-146a-5p inhibits osteoblasts apoptosis. We further demonstrated that FSS inhibits osteoblast apoptosis by down-regulated miR-146a-5p. Dual-luciferase reporter assay validated that SMAD4 is a direct target gene of miR-146a-5p. In addition, mimic-146a-5p suppressed FSS-induced up-regulation of SMAD4 protein levels, which suggests that FSS elevated SMAD4 protein expression levels via regulation miR-146a-5p. Further investigations showed that SMAD4 could inhibit osteoblast apoptosis. We demonstrated that miR-146a-5p regulates osteoblast apoptosis via targeting SMAD4. Taken together, our present study showed that FSS-induced down-regulation miR-146a-5p inhibits osteoblast apoptosis via target SMAD4. These findings may provide novel mechanisms for FSS to inhibit osteoblast apoptosis, and also may provide a potential therapeutic target for osteoporosis.

Gene Expression Profiles of Human Mesenchymal Stromal Cells Derived from Wharton’s Jelly and Amniotic Membrane before and after Osteo-Induction Using NanoString Platform

The use of perinatal mesenchymal stem cells (MSCs) in bone tissue regeneration and engineering to substitute bone marrow MSCs has drawn great interest due to their high yield, ease of procurement, multilineage differentiation potential and lack of ethical concerns. Although amniotic membrane (AM) and Wharton’s jelly (WJ)-derived MSCs have been widely shown to possess osteogenic differentiation potential, the intrinsic properties determining their osteogenic capacity remain unclear. Here, we compared gene expression profiles of AM- and WJ-MSCs at basal and osteogenic conditions by using the NanoString Stem Cell Panel containing regulatory genes associated with stemness, self-renewal, Wnt, Notch and Hedgehog signalling pathways. At basal condition, WJ-MSCs displayed higher expression in most genes regardless of their functional roles in self-renewal, adhesion, or differentiation signalling pathways. After osteo-induction, elevated expression of self-renewal genes ADAR and PAFAH1B1 was observed in AM-MSCs, while stemness genes MME and ALDH1A1 were upregulated in WJ-MSC. Both MSCs showed differences in genes associated with ligands, receptors and ubiquitin ligases of the Notch pathway. In addition, further evidence was demonstrated in some signalling molecules including CTBPs, protein kinases, phosphatases, RHOA, RAC1. Downstream targets HES1 and JUN especially showed higher expression in non-induced WJ-MSCs. Hedgehog genes initially expressed in both MSCs were downregulated in WJ-MSCs during osteogenesis. This study has provided insights into the intrinsic biological differences that may lead to their discrimination in therapeutic intervention.

YAP/TAZ in Bone and Cartilage Biology

YAP and TAZ were initially described as the main regulators of organ growth during development and more recently implicated in bone biology. YAP and TAZ are regulated by mechanical and cytoskeletal cues that lead to the control of cell fate in response to the cellular microenvironment. The mechanical component represents a major signal for bone tissue adaptation and remodelling, so YAP/TAZ contributes significantly in bone and cartilage homeostasis. Recently, mice and cellular models have been developed to investigate the precise roles of YAP/TAZ in bone and cartilage cells, and which appear to be crucial. This review provides an overview of YAP/TAZ regulation and function, notably providing new insights into the role of YAP/TAZ in bone biology.

SMAD4 contributes to chondrocyte and osteocyte development

Different cellular and molecular mechanisms contribute to chondrocyte and osteocyte development. Although vital roles of the mothers against decapentaplegic homolog 4 (also called 'SMAD4') have been discussed in different cancers and stem cell-related studies, there are a few reviews summarizing the roles of this protein in the skeletal development and bone homeostasis. In order to fill this gap, we discuss the critical roles of SMAD4 in the skeletal development. To this end, we review the different signalling pathways and also how SMAD4 defines stem cell features. We also elaborate how the epigenetic factors-ie DNA methylation, histone modifications and noncoding RNAs-make a contribution to the chondrocyte and osteocyte development. To better grasp the important roles of SMAD4 in the cartilage and bone development, we also review the genotype-phenotype correlation in animal models. This review helps us to understand the importance of the SMAD4 in the chondrocyte and bone development and the potential applications for therapeutic goals.

Quantitative proteomics reveals the effect of Yigu decoction (YGD) on protein expression in bone tissue

Background

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone mass, destruction of the bone tissue microstructure, increased bone brittleness and an increased risk of fracture. OP has a high incidence rate and long disease course and is associated with serious complications. Yigu decoction (YGD) is a compound prescription in traditional Chinese medicine that is used to treat OP. However, its mechanism in OP is not clear. This study used a tandem mass tag (TMT)quantitative proteomics method to explore the potential bone-protective mechanism of YGD in an osteoporotic rat model.

Materials and methods

A rat model of OP was established by ovariectomy. Eighteen 12-week-old specific-pathogen-free female Wistar rats weighing 220 ± 10 g were selected. The eighteen rats were randomly divided into 3 groups (n = 6 in each group): the normal, model and YGD groups. The right femurs from each group were subjected to quantitative biological analysis. TMT quantitative proteomics was used to analyze the proteins extracted from the bone tissue of rats in the model and YGD groups, and the differentially expressed proteins after intervention with YGD were identified as biologically relevant proteins of interest. Functional annotation correlation analysis was also performed to explore the biological function and mechanism of YGD.

Result

Compared with the model group, the YGD group showed significant upregulation of 26 proteins (FC > 1.2, P < 0.05) and significant downregulation of 39 proteins (FC < 0.833, P < 0.05). Four important targets involved in OP and 5 important signaling pathways involved in bone metabolism were identified.

Conclusions

YGD can significantly increase the bone mineral density (BMD) of osteoporotic rats and may play a therapeutic role by regulating target proteins involved in multiple signaling pathways. Therefore, these results improve the understanding of the OP mechanism and provide an experimental basis for the clinical application of YGD in OP treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-021-09330-0.

Shaping the bone through iron and iron-related proteins

Well-controlled iron levels are indispensable for health. Iron deficiency is the most common cause of anemia, whereas iron overload, either hereditary or secondary due to disorders of ineffective erythropoiesis, causes widespread organ failure. Bone is particularly sensitive to fluctuations in systemic iron levels as both iron deficiency and overload are associated with low bone mineral density and fragility. Recent studies have shown that not only iron itself, but also iron-regulatory proteins that are mutated in hereditary hemochromatosis can control bone mass. This review will summarize the current knowledge on the effects of iron on bone homeostasis and bone cell activities, and on the role of proteins that regulate iron homeostasis, i.e. hemochromatosis proteins and proteins of the bone morphogenetic protein pathway, on bone remodeling. As disorders of iron homeostasis are closely linked to bone fragility, deeper insights into common regulatory mechanisms may provide new opportunities to concurrently treat disorders affecting iron homeostasis and bone.

mRNA-miRNA-lncRNA Regulatory Network in Nonalcoholic Fatty Liver Disease

AIM

we aimed to construct a bioinformatics-based co-regulatory network of mRNAs and non coding RNAs (ncRNAs), which is implicated in the pathogenesis of non-alcoholic fatty liver disease (NAFLD), followed by its validation in a NAFLD animal model.

MATERIALS AND METHODS

The mRNAs-miRNAs-lncRNAs regulatory network involved in NAFLD was retrieved and constructed utilizing bioinformatics tools. Then, we validated this network using an NAFLD animal model, high sucrose and high fat diet (HSHF)-fed rats. Finally, the expression level of the network players was assessed in the liver tissues using reverse transcriptase real-time polymerase chain reaction.

RESULTS

in-silico constructed network revealed six mRNAs (YAP1, FOXA2, AMOTL2, TEAD2, SMAD4 and NF2), two miRNAs (miR-650 and miR-1205), and two lncRNAs (RPARP-AS1 and SRD5A3-AS1) that play important roles as a co-regulatory network in NAFLD pathogenesis. Moreover, the expression level of these constructed network-players was significantly different between NAFLD and normal control. Conclusion and future perspectives: this study provides new insight into the molecular mechanism of NAFLD pathogenesis and valuable clues for the potential use of the constructed RNA network in effective diagnostic or management strategies of NAFLD.

Total flavonoids of rhizoma drynariae ameliorates bone formation and mineralization in BMP-Smad signaling pathway induced large tibial defect rats

Osteogenesis and angiogenesis acts as an essential role in repairing large tibial defects (LTDs). Total flavonoids of rhizoma drynariae (TFRD), a traditional Chinese medicinal herb, is reported to show anabolic effects on fracture healing. However, whether TFRD could improve the bone formation and angiogenesis in LTDs remains unknown. The purpose of this study was to evaluate the effect of TFRD on bone formation and angiogenesis in LTDs in distraction osteogenesis (DO). Using a previously established fracture model, LTD rats was established with circular external fixator (CEF). All rats then randomly divided into TFRD low dosage group (with DO), TFRD medium dosage group (with DO), TFRD high dosage group (with DO), model group (with DO) and blank group (without DO). Twelve weeks after treatment, according to X-ray and Micro-CT, TFRD groups (especially in medium dosage group) can significantly promote the formation of a large number of epiphyses and improve new bone mineralization compared with model group, and the results of HE and Masson staining and in vitro ALP level of BMSC also demonstrated the formation of bone matrix and mineralization in the TFRD groups. Also, angiographic imaging suggested that total flavonoids of TFRD was able to promote angiogenesis in the defect area. Consistently, TFRD significantly increased the levels of BMP-2, SMAD1, SMAD4, RUNX-2, OSX and VEGF in LTD rats based on ELISA and Real-Time PCR. In addition, we found that ALP activity of TFRD medium dosage group reached a peak after 10 days of induction through BMSC cell culture in vitro experiment. TFRD promoted bone formation in LTD through activation of BMP-Smad signaling pathway, which provides a promising new strategy for repairing bone defects in DO surgeries.

Polydopamine coating with static magnetic field promotes the osteogenic differentiation of human bone-derived mesenchymal stem cells on three-dimensional printed porous titanium scaffolds by upregulation of the BMP-Smads signaling pathway

Bone regeneration has always been a hot topic for orthopedic surgeons. The role of polydopamine coating in promoting bone regeneration has attracted much attention. Static magnetic field (SMF) is considered an effective and noninvasive treatment for enhancing bone regeneration. However, the effect of polydopamine combined with SMF on bone regeneration on scaffolds is not clear. The aim of this study was to investigate the effects and potential mechanism of polydopamine coating combined with SMF on bone regeneration in three-dimensional printed scaffolds. The polydopamine coating (pTi group) was applied onto porous Ti6Al4V scaffolds (Ti group). Surface characterization was performed by scanning electron microscopy. The 100 mT SMF environment (pTi-SMF group) was established to enhance osteogenic differentiation of human bone-derived mesenchymal stem cells (hBMSCs) on polydopamine coating scaffolds. The cell viability and proliferation were significantly enhanced in the SMF environment (pTi-SMF vs. Ti: P=0.005). Improved morphology (pTi-SMF vs. pTi: P=0.024, pTi-SMF vs. Ti: P=0.001) and adhesion (Ti: x̅±s=1.585±0.324; pTi: x̅±s=2.164±0.314; pTi-SMF: x̅±s=4.634±0.247, P<0.001) of hBMSCs were observed in the pTi-SMF group. The high expression of osteogenesis-related RNA and protein (ALP: Ti, x̅±s=1.249±0.218; pTi, x̅±s=2.503±0.209; pTi-SMF, x̅±s=2.810±0.246. OCN: Ti, x̅±s=1.483±0.304; pTi, x̅±s=3.636±0.322; pTi-SMF, x̅±s=4.641±0.278. Runx2: Ti, x̅±s=1.372±0.227; pTi, x̅±s=3.054±0.229; pTi-SMF, x̅±s=3.914±0.253) was found in the pTi-SMF group (pTi-SMF vs. Ti: P<0.001). Proteomics was applied to explore the osteogenic mechanism of polydopamine coating combined with SMF. A total of 147 different proteins were identified between the pTi-SMF and Ti group. The osteogenic effect might be associated with the BMP-Smads signaling pathway (pTi-SMF vs. Ti: BMPR1A, P=0.001; BMPR2, P<0.001; Smad4, P=0.001; Smad1/5/8, P=0.008). In conclusion, the osteogenic differentiation of hBMSCs on polydopamine coating scaffolds could be enhanced by SMF stimulation by upregulation of the BMP-Smads signaling pathway.

Tankyrase inhibitor XAV-939 enhances osteoblastogenesis and mineralization of human skeletal (mesenchymal) stem cells

Tankyrase is part of poly (ADP-ribose) polymerase superfamily required for numerous cellular and molecular processes. Tankyrase inhibition negatively regulates Wnt pathway. Thus, Tankyrase inhibitors have been extensively investigated for the treatment of clinical conditions associated with activated Wnt signaling such as cancer and fibrotic diseases. Moreover, Tankyrase inhibition has been recently reported to upregulate osteogenesis through the accumulation of SH3 domain-binding protein 2, an adaptor protein required for bone metabolism. In this study, we investigated the effect of Tankyrase inhibition in osteoblast differentiation of human skeletal (mesenchymal) stem cells (hMSCs). A Tankyrase inhibitor, XAV-939, identified during a functional library screening of small molecules. Alkaline phosphatase activity and Alizarin red staining were employed as markers for osteoblastic differentiation and in vitro mineralized matrix formation, respectively. Global gene expression profiling was performed using the Agilent microarray platform. XAV-939, a Tankyrase inhibitor, enhanced osteoblast differentiation of hBMSCs as evidenced by increased ALP activity, in vitro mineralized matrix formation, and upregulation of osteoblast-related gene expression. Global gene expression profiling of XAV-939-treated cells identified 847 upregulated and 614 downregulated mRNA transcripts, compared to vehicle-treated control cells. It also points towards possible changes in multiple signaling pathways, including TGFβ, insulin signaling, focal adhesion, estrogen metabolism, oxidative stress, RANK-RANKL (receptor activator of nuclear factor κB ligand) signaling, Vitamin D synthesis, IL6, and cytokines and inflammatory responses. Further bioinformatic analysis, employing Ingenuity Pathway Analysis identified significant enrichment in XAV-939-treated cells of functional categories and networks involved in TNF, NFκB, and STAT signaling. We identified a Tankyrase inhibitor (XAV-939) as a powerful enhancer of osteoblastic differentiation of hBMSC that may be useful as a therapeutic option for treating conditions associated with low bone formation.

The Role of Tantalum Nanoparticles in Bone Regeneration Involves the BMP2/Smad4/Runx2 Signaling Pathway

Background

In recent years, nanomaterials have been increasingly developed and applied in the field of bone tissue engineering. However, there are few studies on the induction of bone regeneration by tantalum nanoparticles (Ta NPs) and no reports on the effects of Ta NPs on the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and the underlying mechanisms. The main purpose of this study was to investigate the effects of Ta NPs on bone regeneration and BMSC osteogenic differentiation and the underlying mechanisms.

Materials and Methods

The effects of Ta NPs on bone regeneration were evaluated in an animal experiment, and the effects of Ta NPs on osteogenic differentiation of BMSCs and the underlying mechanisms were evaluated in cell experiments. In the animal experiment, hematoxylin-eosin (HE) staining and hard-tissue section analysis showed that Ta NPs promoted bone regeneration, and immunohistochemistry revealed elevated expression of BMP2 and Smad4 in cells cultured with Ta NPs.

Results

The results of the cell experiments showed that Ta NPs promoted BMSC proliferation, alkaline phosphatase (ALP) activity, BMP2 secretion and extracellular matrix (ECM) mineralization, and the expression of related osteogenic genes and proteins (especially BMP2, Smad4 and Runx2) was upregulated under culture with Ta NPs. Smad4 expression, ALP activity, ECM mineralization, and osteogenesis-related gene and protein expression decreased after inhibiting Smad4.

Conclusion

These data suggest that Ta NPs have an osteogenic effect and induce bone regeneration by activating the BMP2/Smad4/Runx2 signaling pathway, which in turn causes BMSCs to undergo osteogenic differentiation. This study provides insight into the molecular mechanisms underlying the effects of Ta NPs in bone regeneration.

Osterix regulates corticalization for longitudinal bone growth via integrin β3 expression

Corticalization, coalescence of trabecular bone into the metaphyseal cortex, is important for the longitudinal growth of long bones. However, little is known about the molecular mechanisms controlling corticalization. To understand the molecular mechanisms underlying corticalization, we analyzed osteoblast-specific Osterix-knockout mice (Col-OMT). In control mice, corticalization was initiated after 7 postnatal days, and the number of osteoblasts in the peripheral spongiosa was increased compared to the number in the central spongiosa. In contrast, in Col-OMT mice, corticalization was delayed, and the number of osteoblasts in peripheral zones was unchanged compared to the central zone. Furthermore, femoral length was decreased in Col-OMT mice at 1 month. Because Col-OMT mice exhibited impaired matrix coalescence and osteoblast migration, we evaluated integrin signaling in Col-OMT mice. Osterix bound to the Itgb3 promoter and increased transcription of the Itgb3 gene in osteoblast cells. Interestingly, the inner and outer cortical bones were separated in Itgb3-null mice at postnatal day 7. In Itgb3-null mice, the number of osteoblasts in peripheral zones was not changed, and the femoral length was decreased. Taken together, these results indicate that Osterix regulates corticalization for longitudinal bone growth via the control of integrin β3 expression in osteoblasts. Our findings imply that the ability to control osteoblast function during corticalization may help in the treatment of short stature.

Reduction of protein phosphatase 2A Cα promotes in vivo bone formation and adipocyte differentiation

Serine/threonine protein phosphatase 2A (PP2A) regulates diverse physiological processes such as cell cycle, growth, apoptosis, and signal transduction. Previously, we demonstrated that silencing of the α-isoform of PP2A catalytic subunit (PP2A Cα) in osteoblasts accelerated osteoblast differentiation, whereas its overexpression suppressed differentiation. In this study, we examined the role of PP2A Cα in in vivo bone formation by generating transgenic mice (PP2A-Tg), in which the dominant negative form of PP2A Cα was specifically expressed in osteoblasts. PP2A-Tg mice exhibited an increase in body weight, cortical bone mineral density, and cortical bone thickness. Interestingly, they also displayed higher amounts of adipose tissue in the bone marrow of tibiae. The co-culture study showed that PP2A Cα-knockdown osteoblasts stimulated adipocyte differentiation from undifferentiated mesenchymal cells via upregulation of the adipocyte marker genes, such as peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer binding protein α (C/EBPα). These results indicated that the reduction of PP2A Cα levels in osteoblasts promoted bone formation in vivo. Additionally, PP2A Cα in osteoblasts was also potentially involved in controlling adipocyte differentiation through a paracrine mechanism.

Deletion of Smad4 reduces hepatic inflammation and fibrogenesis during nonalcoholic steatohepatitis progression

OBJECTIVE

To explore the effects of mothers against decapentaplegic homolog family member 4 (Smad4) deletion on inflammation and fibrogenesis in nonalcoholic steatohepatitis (NASH).

METHODS

Biopsied liver samples from NASH patients and normal liver tissue samples from patients who had received liver resection for trauma were collected. Smad4^Co/Co and wild-type (WT) mice were used to construct the NASH model using a high-fat diet (HFD) or methionine- and choline-deficient diet (MCD). HE staining and TUNEL assay were used to observe the pathological changes and cell apoptosis, respectively. Quantitative real-time polymerase chain reaction was used to detect the expression of inflammatory, fibrogenesis and apoptosis-related genes, and immunohistochemistry to determine the protein expression of SMAD4, MCP-1 and α-SMA.

RESULTS

SMAD4 protein expression significantly increased in NASH patients than in the control group. Compared with WT mice, HFD- and MCD-fed Smad4^Co/Co mice showed decreased hepatic steatosis, inflammation, liver cell apoptosis and nonalcoholic fatty liver activity score, reduced plasma glucose, triglyceride, free fatty acids, alanine aminotransferase and aspartate aminotransferase levels but increased adiponectin. Moreover, Smad4^Co/Co decreased the expression of inflammatory markers (TNF-α, MCP-1, IFN-γ), fibrogenetic markers (COL1A1, α-SMA and TGF-β1), lipogenic (Srebp1c, Fas and Acc) and proapoptotic genes (Bax and caspase-3), but increased the expression of β-oxidation (Ppar-α, Cpt1 and Aco) and antiapoptotic genes (Bcl-2).

CONCLUSION

Smad4 deletion may inhibit lipogenesis, stimulate β-oxidation, improve lipid metabolism and liver function, alleviate inflammation and fibrosis, and reduce cell apoptosis in NASH.

Liraglutide exerts a bone-protective effect in ovariectomized rats with streptozotocin-induced diabetes by inhibiting osteoclastogenesis

Liraglutide, a glucagon-like peptide-1 receptor agonist, is an anti-diabetic medicine associated with a reduced risk of fracture in diabetic patients. In the present study, rats with streptozotocin (STZ)-induced diabetes and/or bilateral ovariectomy (OVX) were treated with liraglutide for eight weeks. Liraglutide treatment increased insulin secretion and managed blood glucose levels in the rats following STZ-induced diabetes. In addition, STZ- and OVX-induced reduction of femoral bone mineral density and destruction of bone microarchitecture were alleviated by liraglutide. STZ decreased, whereas OVX increased, serum osteocalcin (OC) level (a bone formation marker) and osteoblast counts in the trabecular bone. OVX, however not STZ, markedly increased the level of serum c-terminal telopeptide of type 1 collagen (CTX-1, a bone resorption marker) and osteoclast counts in the trabecular area. Liraglutide treatment significantly increased serum OC levels in all three osteoporotic models, however had minimal effects on osteoblast counts. Furthermore, liraglutide significantly decreased serum CTX-1 level and osteoclast numbers in OVX and STZ+OVX rats. Furthermore, the present study examined the mRNA expression and serum concentrations of osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL), and liraglutide significantly decreased the RANKL/OPG ratio compared with the untreated rats, indicating that osteoclastogenesis was inhibited by liraglutide. In summary, the results suggested that liraglutide ameliorates STZ+OVX-induced bone deterioration in the rat model, primarily through the inhibition of osteoclastogenesis. These preliminary findings propose a potentially beneficial effect of liraglutide on the bone health of postmenopausal diabetic patients.

Glucagon-like peptide 2 decreases osteoclasts by stimulating apoptosis dependent on nitric oxide synthase

OBJECTIVES

Glucagon-like peptide 2 (GLP2) is involved in the regulation of energy absorption and metabolism. Despite the importance of the GLP2 signalling mechanisms on osteoclast, little has been studied on how GLP2 works during osteoclastogenesis.

MATERIALS AND METHODS

RAW264.7 cells were infected with rLV-Green-GLP2. The induction of osteoclasts was performed by RANKL. TRAP were detected by RT-PCR, Western blotting and staining. Total nitric oxide and total NOS activity were measured. Cells apoptosis was detected by Hoest33258 and Annix V staining. Animal test, chromatin immunoprecipitation (CHIP), co-immunoprecipitation(IP) and luciferase reporter assay were also performed.

RESULTS

We indicate that GLP2 is associated with osteoporosis-related factors in aged rats, including BALP, TRAP, IL6, TNFα, Nitric Oxide (NO), iNOS, calcitonin and occludin. Moreover, GLP2 is demonstrated to result in negative action during proliferation of tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts. Furthermore, GLP2 decreases osteoclasts induced from monocyte/macrophage cells RAW264.7 as well as the serum TRAP activity in aged rats. Mechanistic investigations reveal GLP2 enhances the expression of iNOS through stimulating the activity of TGFβ-Smad2/3 signalling in osteoclasts. In particular, inhibition of TGFβ fully abrogates this function of GLP2 in osteoclasts. Strikingly, overexpression of GLP2 significantly increases the product of nitric oxide via iNOS which promotes apoptosis of osteoclasts by decreasing bcl2 or increasing caspase3. Thereby, the ability of GLP2 to regulate apoptosis depends on TGFβ-Smad2/3-iNOS-NO signalling pathway since total NOS inhibitor L-NMMA specifically inhibits the actions by GLP2.

CONCLUSIONS

GLP2 induces apoptosis via TGFβ-Smad2/3 signalling, which contributes to the inhibition of the proliferation of osteoclasts and which may provide potential therapeutic targets for the treatment of osteoporosis.

Sumoylation of SMAD 4 ameliorates the oxidative stress-induced apoptosis in osteoblasts

Oxidative stress-induced mitochondrial function and cell apoptosis to osteoblasts, plays a critical role in the pathophysiology of osteoporosis. However, mechanisms underlying such process remain not yet clear. We aims in this study to investigate a possible role of SMAD (the mothers against decapentaplegic homolog 4 (SMAD4) in the oxidative stress-induced apoptosis, in homo sapiens osteoblast hFOB1.19 cells. Results demonstrated that the treatment with more than 100μM H₂O₂ significantly downregulated the cellular viability, whereas markedly induced apoptosis in hFOB1.19 cells. The SMAD4 was markedly reduced in both mRNA and protein levels in the H₂O₂ -treated hFOB1.19 cells, along with the reduction of Small ubiquitin-related modifier 1 (SUMO 1) and SUMO 2/3. The immunoprecipitation assay confirmed indicated the interaction between SUMO 1 (or SUMO 2/3) and SMAD4. Moreover, the SMAD4 overexpression markedly ameliorated the H₂O₂-resulted viability reduction and apoptosis induction in hFOB1.19 cells. Interestingly, such amelioration was blocked by the knockdown of SUMO 2/3. Taken together, we conclued that SMAD4 inhibits the H₂O₂-induced apoptosis in osteoblast hFOB1.19 cells; such inhibition might depend on the SUMOylation by SUMO 2/3. It implies a promising role of SMAD4 in oxidative stress-promoted damage to osteoblasts.

Three-dimensional system enabling the maintenance and directed differentiation of pluripotent stem cells under defined conditions

The development of in vitro models for the maintenance and differentiation of pluripotent stem cells (PSCs) is an active area of stem cell research. The strategies used so far are based mainly on two-dimensional (2D) cultures, in which cellular phenotypes are regulated by soluble factors. We show that a 3D culture system with atelocollagen porous scaffolds can significantly improve the outcome of the current platforms intended for the maintenance and lineage specification of mouse PSCs (mPSCs). Unlike 2D conditions, the 3D conditions maintained the undifferentiated state of mouse embryonic stem cells (mESCs) without exogenous stimulation and also supported endoderm, mesoderm, and ectoderm differentiation of mESCs under serum-free conditions. Moreover, 3D mPSC-derived mesodermal cells showed accelerated osteogenic differentiation, giving rise to functional osteoblast-osteocyte populations within calcified structures. The present strategy offers a 3D platform suitable for the formation of organoids that mimic in vivo organs containing various cell types, and it may be adaptable to the generation of ectoderm-, mesoderm-, and endoderm-derived tissues when combined with appropriate differentiation treatments.

Differential Impacts of Alternative Splicing Networks on Apoptosis

Apoptosis functions as a common mechanism to eliminate unnecessary or damaged cells during cell renewal and tissue development in multicellular organisms. More than 200 proteins constitute complex networks involved in apoptotic regulation. Imbalanced expressions of apoptosis-related factors frequently lead to malignant diseases. The biological functions of several apoptotic factors are manipulated through alternative splicing mechanisms which expand gene diversity by generating discrete variants from one messenger RNA precursor. It is widely observed that alternatively-spliced variants encoded from apoptosis-related genes exhibit differential effects on apoptotic regulation. Alternative splicing events are meticulously regulated by the interplay between trans-splicing factors and cis-responsive elements surrounding the regulated exons. The major focus of this review is to highlight recent studies that illustrate the influences of alternative splicing networks on apoptotic regulation which participates in diverse cellular processes and diseases.