BMP9 directly induces rapid GSK3-β phosphorylation in a Wnt-independent manner through class I PI3K-Akt axis in osteoblasts

BMP9 induces osteogenic differentiation through up-regulating LGR4 via the mTORC1/Stat3 pathway in mesenchymal stem cells

Bone defects and non-union are prevalent in clinical orthopedy, and the outcomes of current treatments are often suboptimal. Bone tissue engineering offers a promising approach to treating these conditions effectively. Bone morphogenetic protein 9 (BMP9) can commit mesenchymal stem cells to osteogenic lineage, and a knowledge of the underlying mechanisms may help advance the field of bone tissue engineering. Leucine-rich repeats containing G protein-coupled receptor 4 (LGR4), a member of G protein-coupled receptors, is essential for modulating bone development. This study is aimed at investigating the impact of LGR4 on BMP9-induced osteogenesis in mesenchymal stem cells as well as the underlying mechanisms. Bone marrow stromal cells from BMP9-knockout mice exhibited diminished LGR4 expression, and exogenous LGR4 clearly restored the impaired osteogenic potency of the bone marrow stromal cells. Furthermore, LGR4 expression was increased by BMP9 in C3H10T1/2 cells. LGR4 augmented the benefits of BMP9-induced osteogenic markers and bone formation, whereas LGR4 inhibition restricted these effects. Meanwhile, the BMP9-induced lipogenic markers were increased by LGR4 inhibition. The protein levels of Raptor and p-Stat3 were elevated by BMP9. Raptor knockdown or p-Stat3 suppression attenuated the osteoblastic markers and LGR4 expression brought on by BMP9. LGR4 significantly reversed the blocking effect of Raptor knockdown or p-Stat3 suppression on the BMP9-induced osteoblastic markers. Raptor interacts with p-Stat3, and p-Stat3 activates the LGR4 promoter activity. In conclusion, LGR4 boosts BMP9 osteoblastic potency in mesenchymal stem cells, and BMP9 may up-regulate LGR4 via the mTORC1/Stat3 signal activation.

17β-Estradiol (E2) Activates Matrix Mineralization through Genomic/Nongenomic Pathways in MC3T3-E1 Cells

Estrogen plays an important role in osteoporosis prevention. We herein report the possible novel signaling pathway of 17β-estradiol (E2) in the matrix mineralization of MC3T3-E1, an osteoblast-like cell line. In the culture media-containing stripped serum, in which small lipophilic molecules such as steroid hormones including E2 were depleted, matrix mineralization was significantly reduced. However, the E2 treatment induced this. The E2 effects were suppressed by ICI182,780, the estrogen receptor (ER)α, and the ERβ antagonist, as well as their mRNA knockdown, whereas Raloxifene, an inhibitor of estrogen-induced transcription, and G15, a G-protein-coupled estrogen receptor (GPER) 1 inhibitor, had little or no effect. Furthermore, the E2-activated matrix mineralization was disrupted by PMA, a PKC activator, and SB202190, a p38 MAPK inhibitor, but not by wortmannin, a PI3K inhibitor. Matrix mineralization was also induced by the culture media from the E2-stimulated cell culture. This effect was hindered by PMA or heat treatment, but not by SB202190. These results indicate that E2 activates the p38 MAPK pathway via ERs independently from actions in the nucleus. Such activation may cause the secretion of certain signaling molecule(s), which inhibit the PKC pathway. Our study provides a novel pathway of E2 action that could be a therapeutic target to activate matrix mineralization under various diseases, including osteoporosis.

Bone morphogenetic protein-9 downregulates StAR expression by inducing snail expression via SMAD1/5/8 signaling in human granulosa-lutein cells

Ovarian steroidogenesis mediated by granulosa cells is pivotal in maintaining normal female reproductive function. The steroidogenic acute regulatory protein (StAR) regulates the rate-limiting step in steroidogenesis. Bone morphogenetic protein-9 (BMP-9), also known as growth differentiation factor-2 (GDF-2), is a member of the transforming growth factor-beta (TGF-β) superfamily. BMP-9 induces epithelial-mesenchymal transition (EMT) that contributes to cancer progression. However, the function of BMP-9 in the female reproductive system remains largely unknown. It has been recently shown that BMP-9 is expressed in human follicular fluid and can downregulate StAR expression in human ovarian granulosa cells. However, the underlying molecular mechanisms warrant investigation. Our results show that treatment of primary granulosa-lutein (hGL) cells with BMP-9 downregulates StAR expression. In addition, two EMT-related transcription factors, Snail and Slug, are upregulated by the treatment of BMP-9. Using pharmacological inhibitors and a siRNA-mediated knockdown approach, we show that BMP-9 upregulates Snail and Slug expression by activating SMAD1/5/8 signaling. We also examine the effects of BMP-9 on SMAD-independent signaling pathways, including ERK1/2, p38, JNK, AKT, and CREB. However, none of them is affected by the BMP-9. Moreover, we use gain- and loss-of-function approaches to reveal that only Snail, not Slug, is required for the BMP-9-induced downregulation of StAR expression in hGL cells. This study increases the understanding of the physiology function of BMP-9 in hGL cells and provides important insights into the regulation of StAR expression.

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.

The effect and mechanism of selenium supplementation on the proliferation capacity of bovine endometrial epithelial cells exposed to lipopolysaccharide in vitro under high cortisol background

Bovine endometritis severely inhibits uterine repair and causes considerable economic loss. Besides, parturition-induced high cortisol levels inhibit immune function, reduce cell proliferation, and further inhibit tissue repair. Selenium (Se) is an essential trace element for animals to maintain normal physiological function and has powerful antioxidant functions. This study investigated whether Se supplementation reduces endometrial damage and promotes tissue repair in cows with endometritis under stress and explored the underlying mechanism. Primary bovine endometrial epithelial cells were isolated and purified from healthy cows. The cells were treated with different combinations of lipopolysaccharide (LPS), cortisol, and various concentrations of Se. Data showed that LPS stimulation inhibited cell proliferation and increased cell apoptosis. High levels of cortisol further exacerbated these effects. Flow cytometry, scratch wound healing tests, and 5-ethynyl-2'-deoxyuridine (EdU) proliferation assays showed that Se supplementation promoted cell cycle progression, cell migration, and cell proliferation in the presence of LPS and cortisol. The quantitative PCR results showed that the expression of related growth factors was increased after Se supplementation. After administering various inhibitors, we further demonstrated that Se supplementation decreased the activity of glycogen synthetase kinase 3β (GSK-3β) through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway to reduce the degradation of β-catenin except the Wnt signal to promote cell proliferation. In conclusion, Se supplementation attenuated the cell damage induced by LPS at high cortisol levels and increased cell proliferation to promote uterine repair by elevating the mRNA expression of TGFB3 and VEGFA and activating the PI3K/AKT/GSK-3β/β-catenin signaling pathway.

Catalpol ameliorates dexamethasone-induced osteoporosis by promoting osteogenic differentiation of bone marrow mesenchymal stem cells via the activation of PKD1 promoter

OBJECTIVE

To investigate the effects of CA on glucocorticoid-induced osteoporosis (GIOP) and lucubrate the underlying mechanism of CA via the activation of polycystic kidney disease-1(PKD1) in bone marrow mesenchymal stem cells (BMSCs).

METHODS

In vivo, a GIOP model in mice treated with dexamethasone (Dex) was established. Biomechanical, micro-CT, immunofluorescence staining of OCN, ALP and PKD1 and others were severally determined. qRT-PCR and Western blot methods were adopted to elucidate the particular mechanisms of CA on GIOP. In addition, BMSCs cultured in vitro were also induced by Dex to verify the effects of CA. Finally, siRNA and luciferase activity assays were performed to confirm the mechanisms.

RESULTS

We found that CA could restore the destroyed bone microarchitecture and increase the bone mass in GIOP mice. CA could also upregulate PKD1 protein expression, reduce oxidative stress, and promote mRNA expression of bone formation-associated markers in GIOP mice. Furthermore, it was also observed that CA reduced oxidative stress and promoted osteogenic differentiation in Dex-induced BMSCs. Mechanically, CA could promote protein expression via increasing the activity of PKD1 promoter.

CONCLUSION

This study provides important evidences for CA in the further clinical treatment of GIOP, reveals the activation of PKD1 promoter as the underlying mechanism.

BMP-9 Improves the Osteogenic Differentiation Ability over BMP-2 through p53 Signaling In Vitro in Human Periosteum-Derived Cells

Bone morphogenetic proteins (BMPs) have tremendous therapeutic potential regarding the treatment of bone and musculoskeletal disorders due to their osteo-inductive ability. More than twenty BMPs have been identified in the human body with various functions, such as embryonic development, skeleton genesis, hematopoiesis, and neurogenesis. BMPs can induce the differentiation of MSCs into the osteoblast lineage and promote the proliferation of osteoblasts and chondrocytes. BMP signaling is also involved in tissue remodeling and regeneration processes to maintain homeostasis in adults. In particular, growth factors, such as BMP-2 and BMP-7, have already been approved and are being used as treatments, but it is unclear as to whether they are the most potent BMPs that induce bone formation. According to recent studies, BMP-9 is known to be the most potent inducer of the osteogenic differentiation of mesenchymal stem cells, both in vitro and in vivo. However, its exact role in the skeletal system is still unclear. In addition, research results suggest that the molecular mechanism of BMP-9-mediated bone formation is also different from the previously known BMP family, suggesting that research on signaling pathways related to BMP-9-mediated bone formation is actively being conducted. In this study, we performed a phosphorylation array to investigate the signaling mechanism of BMP-9 compared with BMP-2, another influential bone-forming growth factor, and we compared the downstream signaling system. We present a mechanism for the signal transduction of BMP-9, focusing on the previously known pathway and the p53 factor, which is relatively upregulated compared with BMP-2.

Early induction of Hes1 by bone morphogenetic protein 9 plays a regulatory role in osteoblastic differentiation of a mesenchymal stem cell line

Bone morphogenic protein 9 (BMP9) is one of the most potent inducers of osteogenic differentiation among the 14 BMP members, but its mechanism of action has not been fully demonstrated. Hes1 is a transcriptional regulator with basic helix-loop-helix (bHLH) domain and is a well-known Notch effector. In this study, we investigated the functional roles of early induction of Hes1 by BMP9 in a mouse mesenchymal stem cell line, ST2. Hes1 mRNA was transiently and periodically induced by BMP9 in ST2, which was inhibited by BMP signal inhibitors but not by Notch inhibitor. Interestingly, Hes1 knockdown in ST2 by siRNA increased the expression of osteogenic differentiation markers such as Sp7 and Ibsp and matrix mineralization in comparison with control siRNA transfected ST2. In contrast, forced expression of Hes1 by using the Tet-On system suppressed the expression of osteogenic markers and matrix mineralization by BMP9. We also found that the early induction of Hes1 by BMP9 suppressed the expression of Alk1, an essential receptor for BMP9. In conclusion, BMP9 rapidly induces the expression of Hes1 via the SMAD pathway in ST2 cells, which plays a negative regulatory role in osteogenic differentiation of mesenchymal stem cells induced by BMP9.

Identification of Maleimide-Fused Carbazoles as Novel Noncanonical Bone Morphogenetic Protein Synergizers

Morphogenic signaling pathways govern embryonic development and tissue homeostasis on the cellular level. Precise control of such signaling events paves the way for innovative therapeutic approaches in the field of regenerative medicine. In line with these notions, bone morphogenic protein (BMP) is a major osteogenic driver and pharmacological stimulation of BMP signaling holds supreme potential for diseases and defects of the skeleton. Efforts to identify small-molecule modalities that activate or potentiate the BMP pathway have primarily been focused on the canonical signaling cascade. Here, we describe the phenotypic identification and development of specific carbazolomaleimides 2 as novel noncanonical BMP synergizers with submicromolar osteogenic cellular potency. The devised chemical tools are characterized to specifically regulate Id gene expression in a SMAD-independent, yet highly BMP-dependent fashion. Mechanistic studies revealed that GSK3 inhibition and increased β-catenin levels are partly responsible for this activity. The utility of the new BMP synergizer profile was further exemplified by showing how the synergistic action of canonical and noncanonical BMP enhancers additively amplifies BMP-dependent osteogenic outputs. Carbazolomaleimide 2b serves as a new and unique pharmacological tool for the modulation and study of the BMP pathway.

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

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

Akt/mTOR integrate energy metabolism with Wnt signal to influence wound epithelium growth in Gekko Japonicus

The formation of wound epithelium initiates regeneration of amputated tail in Gekko japonicus. Energy metabolism is indispensable for the growth of living creatures and typically influenced by temperature. In this study, we reveal that low temperature lowers energy metabolism level and inhibits the regeneration of amputated tails of Gekko japonicus. We further find that low temperature attenuates the activation of protein kinase B (Akt) and mammalian target of rapamycin (mTOR) in regenerated tissues upon injury signals, and the inhibition of Akt hinders proliferation of the wound epithelium. Additionally, wingless/integrated (Wnt) inhibition suppresses epithelium proliferation and formation by inhibiting Akt activation. Finally, low temperature elevates the activity of adenylate-activated kinase (AMPK) pathway and in turn attenuates wound epithelium formation. Meanwhile, either mTOR downregulation or AMPK upregulation is associated with worse wound epithelium formation. Summarily, low temperature restricts wound epithelium formation by influencing energy sensory pathways including Akt/mTOR and AMPK signaling, which is also modulated by injury induced Wnt signal. Our results provide a mechanism that incorporates the injury signals with metabolic pathway to facilitate regeneration.

Low temperature inhibits the regeneration of amputated tails of Gekko japonicus by influencing the energy sensory Akt/mTOR pathway, which is also modulated by injury-induced Wnt signal.

EGR1 Plays an Important Role in BMP9-Mediated Osteoblast Differentiation by Promoting SMAD1/5 Phosphorylation

Bone morphogenetic proteins (BMPs) are essential regulators of skeletal homeostasis, and BMP9 is the most potently osteogenic among them. Here, we found that BMP9 and BMP2 rapidly induced early growth response 1 (EGR1) protein expression in osteoblasts through MEK/ERK pathway-dependent transcriptional activation. Knockdown of EGR1 using siRNA significantly inhibited BMP9-induced matrix mineralization and osteogenic marker gene expression in osteoblasts. Knockdown of EGR1 significantly reduced SMAD1/5 phosphorylation and inhibited the expression of their transcriptional targets in osteoblasts stimulated by BMP9. In contrast, forced EGR1 overexpression in osteoblasts enhanced BMP9-mediated osteoblast differentiation and SMAD1/5 phosphorylation. An intracellular association between EGR1 and SMAD1/5 was identified using immunoprecipitation assays. These results indicated that EGR1 plays an important role in BMP9-stimulated osteoblast differentiation by enhancing SMAD1/5 phosphorylation.

HIF-1α plays an essential role in BMP9-mediated osteoblast differentiation through the induction of a glycolytic enzyme, PDK1

Bone homeostasis is regulated by bone morphogenic proteins (BMPs), among which BMP9 is one of the most osteogenic. Here, we have found that BMP9 rapidly increases the protein expression of hypoxia-inducible factor-1α (HIF-1α) in osteoblasts under normoxic conditions more efficiently than BMP2 or BMP4. A combination of BMP9 and hypoxia further increased HIF-1α protein expression. HIF-1α protein induction by BMP9 is not accompanied by messenger RNA (mRNA) increase and is inhibited by the activation of prolyl hydroxylase domain (PHD)-containing protein, indicating that BMP9 induces HIF-1α protein expression by inhibiting PHD-mediated protein degradation. BMP9-induced HIF-1α protein increase was abrogated by inhibitors of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT) kinase, indicating that it is mediated by PI3K-AKT signaling pathway. BMP9 increased mRNA expression of pyruvate dehydrogenase kinase 1 (PDK1), a glycolytic enzyme, and vascular endothelial growth factor-A (VEGF-A), an angiogenic factor, in osteoblasts. Notably, BMP9-induced mRNA expression of PDK1, but not that of VEGF-A, was significantly inhibited by small interference RNA-mediated knockdown of Hif-1α. BMP9-induced matrix mineralization and osteogenic marker gene expressions were significantly inhibited by chemical inhibition and gene knockdown of either Hif-1α or Pdk-1, respectively. Since increased glycolysis is an essential feature of differentiated osteoblasts, our findings indicate that HIF-1α expression is important in BMP9-mediated osteoblast differentiation through the induction of PDK1.

Bone morphogenetic protein 9 enhances osteogenic and angiogenic responses of human amniotic mesenchymal stem cells cocultured with umbilical vein endothelial cells through the PI3K/AKT/m-TOR signaling pathway

Background: Neovascularization plays an essential part in bone fracture and defect healing, constructing tissue engineered bone that targets bone regeneration. Bone morphogenetic protein 9 (BMP9) is a regular indicator that potentiates osteogenic and angiogenic differentiation of MSCs.

Objectives: To investigate the effects of BMP9 on osteogenesis and angiogenesis of human amniotic mesenchymal stem cells (hAMSCs) cocultured with human umbilical vein endothelial cells (HUVECs) and determine the possible underlying molecular mechanism.

Results: The isolated hAMSCs expressed surface markers of MSCs. hAMSCs cocultured with HUVECs enhance osteogenic differentiation and upregulate the expression of angiogenic factors. BMP9 not only potentiates angiogenic signaling of hAMSCs cocultured with HUVECs also increases ectopic bone formation and subcutaneous vessel invasion. Mechanically, the coupling effect between osteogenesis and angiogenesis induced by BMP9 was activated by the BMP/Smad and PI3K/AKT/m-TOR signaling pathways.

Conclusions: BMP9-enhanced osteoblastic and angiogenic differentiation in cocultivation with hAMSCs and HUVECs in vitro and in vivo also provide a chance to harness the BMP9-regulated coordinated effect between osteogenic and angiogenic pathways through BMP/Smad and PI3K/AKT/m-TOR signalings.

Materials and Methods: The ALP and Alizarin Red S staining assay to determine the effects of osteoblastic differentiation. RT-qPCR and western blot was measured the expression of angiogenesis-related factors. Ectopic bone formation was established and retrieved bony masses were subjected to histochemical staining. The angiogenesis ability and vessel invasion were subsequently determined by immunofluorescence staining. Molecular mechanisms such as the BMP/Smad and PI3K/AKT/m-TOR signaling pathways were detected by ELISA and western blot analysis.

Enhanced bone formation of calvarial bone defects by low-intensity pulsed ultrasound and recombinant human bone morphogenetic protein-9: a preliminary experimental study in rats

OBJECTIVES

The aim of this study was to evaluate the combined effects of recombinant human bone morphogenetic protein - 9 (rhBMP-9) loaded onto absorbable collagen sponges (ACS) and low-intensity pulsed ultrasound (LIPUS) on bone formation in rat calvarial defects.

MATERIALS AND METHODS

Circular calvarial defects were surgically created in 18 Wistar rats, which were divided into LIPUS-applied (+) and LIPUS-non-applied (-) groups. The 36 defects in each group received ACS implantation (ACS group), ACS with rhBMP-9 (rhBMP-9/ACS group), or surgical control (control group), yielding the following six groups: ACS (+/-), rhBMP-9/ACS (+/-), and control (+/-). The LIPUS-applied groups received daily LIPUS exposure starting immediately after surgery. At 4 weeks, animals were sacrificed and their defects were investigated histologically and by microcomputed tomography.

RESULTS

Postoperative clinical healing was uneventful at all sites. More new bone was observed in the LIPUS-applied groups compared with the LIPUS-non-applied groups. Newly formed bone area (NBA)/total defect area (TA) in the ACS (+) group (46.49 ± 7.56%) was significantly greater than that observed in the ACS (-) (34.31 ± 5.68%) and control (-) (31.13 ± 6.74%) groups (p < 0.05). The rhBMP-9/ACS (+) group exhibited significantly greater bone volume, NBA, and NBA/TA than the rhBMP-9/ACS (-) group (2.46 ± 0.65 mm³ vs. 1.76 ± 0.44 mm³, 1.25 ± 0.31 mm² vs. 0.88 ± 0.22 mm², and 62.80 ± 11.87% vs. 42.66 ± 7.03%, respectively) (p < 0.05). Furthermore, the rhBMP-9/ ACS (+) group showed the highest level of bone formation among all groups.

CONCLUSION

Within their limits, it can be concluded that LIPUS had osteopromotive potential and enhanced rhBMP-9-induced bone formation in calvarial defects of rats.

CLINICAL RELEVANCE

The use of rhBMP-9 with LIPUS stimulation can be a potential bone regenerative therapy for craniofacial/peri-implant bone defects.

Osteoinductive function of fucoidan on periodontal ligament stem cells: Role of PI3K/Akt and Wnt/β-catenin signaling pathways

BACKGROUND/OBJECTIVES

Fucoidan has been focused as a multifunctional therapeutic uses including bone health supplements. However, the critical molecular mechanisms of fucoidan for bone therapeutic agents have not been fully understood. We investigated the osteoinductive effect of fucoidan on periodontal ligament stem cells (PDLSCs) and how this polymer encouraged PDLSC osteogenesis.

MATERIALS AND METHODS

Osteogenic induction of PDLSCs was processed by culturing cells with fucoidan treatment. Osteogenic differentiation of PDLSCs was verified by alkaline phosphatase (ALP) activity, matrix mineralization assay, intracellular calcium levels, and mRNA expression and protein levels of osteogenic markers.

RESULTS

Fucoidan treatment showed higher osteogenic activity in the PDLSCs than the control groups. PDLSCs with fucoidan also presented increased levels of the phosphatidylinositol-3-kinase (PI3K) isoforms, p110α and p110γ compared to control cells. The phosphorylation of Akt, a PI3K downstream effector, was significantly increased at 90 min of fucoidan induction. Expression of β-catenin, a coactivator of canonical Wnt pathways, was increased in PDLSCs with fucoidan. β-catenin was found to link with PI3K activation during the fucoidan stimulation. When cells were blocked by PI3K inhibitor or β-catenin-specific siRNA, fucoidan-induced osteogenic activity of PDLSCs was significantly attenuated.

CONCLUSION

These findings suggest that the fucoidan stimulates osteogenic differentiation of PDLSCs via the PI3K/Akt and Wnt/β-catenin pathways.

LiCl induces apoptosis via CHOP/NOXA/Mcl-1 axis in human choroidal melanoma cells

Background

Choroidal melanoma is the most common primary intraocular malignancy that occurs in adults. Lithium Chloride Promotes Apoptosis in Human Leukemia NB4 Cells by Inhibiting Glycogen Synthase Kinase-3 Beta. In this study, we aimed to understand whether LiCl exerts anticancer effects on choroidal melanoma cells and elucidate the underlying molecular mechanisms.

Methods

Human choroidal melanoma cells were treated with LiCl, and cell survival was assessed with MTT assays. Cell reproductive viability was measured by plate colony formation assays. Cell apoptosis was evaluated using flow cytometry, and proteins were detected using western blotting. A human choroidal melanoma xenograft model was established to demonstrate the effect of LiCl on human choroidal melanoma in vivo.

Results

We found that LiCl inhibited cell survival and clonogenic potential and induced apoptosis in human choroidal melanoma cells. LiCl also reduced the proliferation of choroidal melanoma cells in vivo. Moreover, the upregulation of NOXA and downregulation of Mcl-1 were responsible for LiCl-induced apoptosis. Mcl-1 overexpression obviously impaired LiCl-induced apoptosis and cleavage of caspase8, caspase9, caspase3 and PARP. Moreover, the protein expression of endoplasmic reticulum stress markers, including IRE1α, Bip, p-eIF2α, ATF4 and CHOP, were upregulated following treatment with LiCl. When CHOP expression was knocked down and cells were treated with LiCl, the protein level of NOXA was partially increased, and Mcl-1 expression was increased, while the cleavage of caspase8, caspase9, caspase3 and PARP that was induced by the LiCl was reduced compared with the vehicle treated group. Prolonged ER stress results in the activation of the apoptotic pathway.

Conclusions

In summary, LiCl induced an endoplasmic reticulum stress response while activating intrinsic apoptosis. Furthermore, the CHOP/NOXA/Mcl-1 axis contributed to LiCl-induced apoptosis both in vitro and in vivo. The present study provides important mechanistic insight into potential cancer treatments involving LiCl and enhances the understanding of human choroidal melanoma.

Energy Metabolism During Osteogenic Differentiation: The Role of Akt

Osteogenic differentiation, the process by which bone marrow mesenchymal stem/stromal (a.k.a. skeletal stem) cells and osteoprogenitors form osteoblasts, is a critical event for bone formation during development, fracture repair, and tissue maintenance. Extra cellular and intracellular signaling pathways triggering osteogenic differentiation are relatively well known; however, the ensuing change in cell energy metabolism is less clearly defined. We and others have previously reported activation of mitochondria during osteogenic differentiation. To further elucidate the involved bioenergetic mechanisms and triggers, we tested the effect of osteogenic media containing ascorbate and β-glycerol phosphate, or various osteogenic hormones and growth factors on energy metabolism in long bone (ST2)- and calvarial bone (MC3T3-E1)-derived osteoprogenitors. We show that osteogenic media and differentiation factors, Wnt3a and BMP2, stimulate mitochondrial oxidative phosphorylation (OxPhos) with little effect on glycolysis. The activation of OxPhos occurs acutely, suggesting a metabolic signaling change rather than protein expression change. To this end, we found that the observed mitochondrial activation is Akt dependent. Akt is activated by osteogenic media, Wnt3a, and BMP2, leading to increased phosphorylation of various mitochondrial Akt targets, a phenomenon known to stimulate OxPhos. In sum, our data provide comprehensive analysis of cellular bioenergetics during osteoinduction in cells of two different origins (mesenchyme vs neural crest) and identify Wnt3a and BMP2 as physiological stimulators of mitochondrial respiration through Akt activation.

Bone morphogenetic protein 9 (BMP9) directly induces Notch effector molecule Hes1 through the SMAD signaling pathway in osteoblasts

Bone morphogenetic protein (BMP) 9 is one of the most osteogenic BMPs, but its mechanism of action has not been fully elucidated. Hes1, a transcriptional regulator with a basic helix-loop-helix domain, is a well-known effector of Notch signaling. Here, we find that BMP9 induces periodic increases of Hes1 mRNA and protein expression in osteoblasts, presumably through an autocrine negative feedback mechanism. BMP9-mediated Hes1 induction is significantly inhibited by an ALK inhibitor and overexpression of Smad7, an inhibitory Smad. Luciferase and ChIP assays revealed that two Smad-binding sites in the 5' upstream region of the mouse Hes1 gene are essential for transcriptional activation by BMP9. Thus, our data indicate that BMP9 induces Hes1 expression in osteoblasts via the Smad signaling pathway.

SNP-adjacent super enhancer network mediates enhanced osteogenic differentiation of MSCs in ankylosing spondylitis

Ankylosing spondylitis (AS) is a rheumatic disease with pathological osteogenesis that causes bony ankylosis and even deformity over time. Mesenchymal stem cells (MSCs) are multipotent stem cells that are the main source of osteoblasts. We previously demonstrated that enhanced osteogenic differentiation of MSCs from AS patients (ASMSCs) is related to pathological osteogenesis in AS. However, the more concrete mechanism needs further exploration. Super enhancers (SEs) are dense clusters of stitched enhancers that control cell identity determination and disease development. Single-nucleotide polymorphisms (SNPs) regulate the formation and interaction of SEs and denote genes accounting for AS susceptibility. Via integrative analysis of multiomic data, including histone 3 lysine 27 acetylation (H3K27ac), chromatin immunoprecipitation sequencing (ChIP-seq), SNPs and RNA sequencing (RNA-seq) data, we discovered a transcription network mediated by AS SNP-adjacent SEs (SASEs) in ASMSCs and identified key genes, such as Toll-like receptor 4 (TLR4), interleukin 18 receptor 1 (IL18R1), insulin-like growth factor binding protein 4 (IGFBP4), transportin 1 (TNPO1) and proprotein convertase subtilisin/kexin type 5 (PCSK5), which are pivotal in osteogenesis and AS pathogenesis. The SASE-regulated network modulates the enhanced osteogenic differentiation of ASMSCs by synergistically activating the PI3K-Akt, NF-kappaB and Hippo signaling pathways. Our results emphasize the crucial role of the SASE-regulated network in pathological osteogenesis in AS, and the preferential inhibition of ASMSC osteogenic differentiation by JQ1 indicates that SEs may be attractive targets in future treatment for new bone formation in AS.

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

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

Schnurri-3 regulates BMP9-induced osteogenic differentiation and angiogenesis of human amniotic mesenchymal stem cells through Runx2 and VEGF

Human amniotic mesenchymal stem cells (hAMSCs) are multiple potent progenitor cells (MPCs) that can differentiate into different lineages (osteogenic, chondrogenic, and adipogenic cells) and have a favorable capacity for angiogenesis. Schnurri-3 (Shn3) is a large zinc finger protein related to Drosophila Shn, which is a critical mediator of postnatal bone formation. Bone morphogenetic protein 9 (BMP9), one of the most potent osteogenic BMPs, can strongly upregulate various osteogenesis- and angiogenesis-related factors in MSCs. It remains unclear how Shn3 is involved in BMP9-induced osteogenic differentiation coupled with angiogenesis in hAMSCs. In this investigation, we conducted a comprehensive study to identify the effect of Shn3 on BMP9-induced osteogenic differentiation and angiogenesis in hAMSCs and analyze the responsible signaling pathway. The results from in vitro and in vivo experimentation show that Shn3 notably inhibits BMP9-induced early and late osteogenic differentiation of hAMSCs, expression of osteogenesis-related factors, and subcutaneous ectopic bone formation from hAMSCs in nude mice. Shn3 also inhibited BMP9-induced angiogenic differentiation, expression of angiogenesis-related factors, and subcutaneous vascular invasion in mice. Mechanistically, we found that Shn3 prominently inhibited the expression of BMP9 and activation of the BMP/Smad and BMP/MAPK signaling pathways. In addition, we further found activity on runt-related transcription factor 2 (Runx2), vascular endothelial growth factor (VEGF), and the target genes shared by BMP and Shn3 signaling pathways. Silencing Shn3 could dramatically enhance the expression of Runx2, which directly regulates the downstream target VEGF to couple osteogenic differentiation with angiogenesis. To summarize, our findings suggested that Shn3 significantly inhibited the BMP9-induced osteogenic differentiation and angiogenesis in hAMSCs. The effect of Shn3 was primarily seen through inhibition of the BMP/Smad signaling pathway and depressed expression of Runx2, which directly regulates VEGF, which couples BMP9-induced osteogenic differentiation with angiogenesis.

Changes in mediators of pro-cell growth, senescence, and inflammation during murine gestation

PROBLEM

Senescence of the fetal membranes and senescence-associated inflammation have been associated with parturition at term and pre-term in both mice and humans. Using a pregnant mouse model, we determined changes in multiple molecular signalers contributing to senescence and inflammation associated with parturition.

METHOD OF STUDY

Fetal membranes were collected from timed-pregnant CD-1 mice on gestation days (E) 13, 15, 17, 18, and 19. Immunohistochemistry (IHC) localized pro-cell growth factors glycogen synthase kinase 3β (GSK3β) and β-catenin. Gestational age-associated changes in pro-cell growth vs senescence mediators (p38 mitogen-activated protein kinase [p38MAPK]), prooxidants (heme oxygenase-1 [HO-1], peroxisome proliferator-activated receptor γ [PPARγ]), and pro- and anti-inflammatory cytokines (IL-6, IL-8, IL-10, and IL-1β) were determined by Western blots and Luminex assays.

RESULTS

Fetal membrane expressions of phosphorylated forms of GSK3β (inactivation) and p38MAPK (activation) increased, while β-catenin expression decreased, as gestation progressed. Antioxidant HO-1 expression decreased while PPARγ increased toward term gestation. IL-6 and IL-8 concentrations were highest on E19 (day of delivery), while IL-10 and IL-1β concentrations were highest on E15.

CONCLUSION

Mouse fetal membranes showed a progressive senescence marker increase coincided with downregulation of cell growth factors. Development of senescence is associated with inflammation. Senescence-associated changes are natural and physiologic and indicative of fetal membranes' readiness for parturition.

TGFβ1 induces bone formation from BMP9-activated Bone Mesenchymal Stem Cells, with possible involvement of non-canonical pathways

Reconstruction of bone defects is one of the most substantial and difficult clinical challenges in orthopedics. Transforming growth factor beta 1 (TGFβ1) might play an important role in stimulating osteogenic differentiation of bone morphogenetic protein 9 (BMP9)-induced C3H10T1/2 mesenchymal stem cells. In our current study, we examined the potential synergy between TGFβ1 and BMP9 in promoting the osteogenesis of C3H10T1/2 cells, and whether such effects could contribute to bone formation in vivo. Our experiment data indicated that TGFβ1 could increase the expression of osteogenic markers and the formation of mineralized calcium nodules in, while suppressing the proliferation of, BMP9-induced C3H10T1/2 cells. Furthermore, mice intramuscularly injected with BMP9/TGFβ1-transduced C3H10T1/2 cells into the gastrocnemius muscle on their tibiae developed ectopic bone masses with more mature osteoid structures, compared to those grafted with cells expressing BMP9/RFP. Subsequent mechanistic studies found that TGFβ1-induced enhancement of osteogenesis in BMP9-overexpressing C3H10T1/2 cells was accompanied by augmented expression of heat shock protein 47 (HSP47), a collagen-specific molecular chaperone essential for collagen biosynthesis, and can be attenuated by pirfenidone, a known anti-fibrotic inhibitor. Interestingly, protein microarray analysis suggested that TGFβ1/BMP9-dependent osteogenesis of C3H10T1/2 cells seemed to involve several non-canonical signaling pathways such as Janus kinase-signal transducer and activator of transcription, phosphoinositide-3-kinase-protein kinase B, and mitogen-activated protein kinase. These results provided further evidence that TGFβ1 could promote bone formation from BMP9-induced C3H10T1/2 cells and shed important light on the underlying molecular mechanisms.