BMP2 induction of actin cytoskeleton reorganization and cell migration requires PI3-kinase and Cdc42 activity

Secreted exosomes induce filopodia formation

Filopodia are dynamic adhesive cytoskeletal structures that are critical for directional sensing, polarization, cell-cell adhesion, and migration of diverse cell types. Filopodia are also critical for neuronal synapse formation. While dynamic rearrangement of the actin cytoskeleton is known to be critical for filopodia biogenesis, little is known about the upstream extracellular signals. Here, we identify secreted exosomes as potent regulators of filopodia formation. Inhibition of exosome secretion inhibited the formation and stabilization of filopodia in both cancer cells and neurons and inhibited subsequent synapse formation by neurons. Rescue experiments with purified small and large extracellular vesicles (EVs) identified exosome-enriched small EVs (SEVs) as having potent filopodia-inducing activity. Proteomic analyses of cancer cell-derived SEVs identified the TGF-β family coreceptor endoglin as a key SEV-enriched cargo that regulates filopodia. Cancer cell endoglin levels also affected filopodia-dependent behaviors, including metastasis of cancer cells in chick embryos and 3D migration in collagen gels. As neurons do not express endoglin, we performed a second proteomics experiment to identify SEV cargoes regulated by endoglin that might promote filopodia in both cell types. We discovered a single SEV cargo that was altered in endoglin-KD cancer SEVs, the transmembrane protein Thrombospondin Type 1 Domain Containing 7A (THSD7A). We further found that both cancer cell and neuronal SEVs carry THSD7A and that add-back of purified THSD7A is sufficient to rescue filopodia defects of both endoglin-KD cancer cells and exosome-inhibited neurons. We also find that THSD7A induces filopodia formation through activation of the Rho GTPase, Cdc42. These findings suggest a new model for filopodia formation, triggered by exosomes carrying THSD7A.

Endothelial tip-cell position, filopodia formation and biomechanics require BMPR2 expression and signaling

Blood vessel formation relies on biochemical and mechanical signals, particularly during sprouting angiogenesis when endothelial tip cells (TCs) guide sprouting through filopodia formation. The contribution of BMP receptors in defining tip-cell characteristics is poorly understood. Our study combines genetic, biochemical, and molecular methods together with 3D traction force microscopy, which reveals an essential role of BMPR2 for actin-driven filopodia formation and mechanical properties of endothelial cells (ECs). Targeting of Bmpr2 reduced sprouting angiogenesis in zebrafish and BMPR2-deficient human ECs formed fewer filopodia, affecting cell migration and actomyosin localization. Spheroid assays revealed a reduced sprouting of BMPR2-deficient ECs in fibrin gels. Even more strikingly, in mosaic spheroids, BMPR2-deficient ECs failed to acquire tip-cell positions. Yet, 3D traction force microscopy revealed that these distinct cell behaviors of BMPR2-deficient tip cells cannot be explained by differences in force-induced matrix deformations, even though these cells adopted distinct cone-shaped morphologies. Notably, BMPR2 positively regulates local CDC42 activity at the plasma membrane to promote filopodia formation. Our findings reveal that BMPR2 functions as a nexus integrating biochemical and biomechanical processes crucial for TCs during angiogenesis.

Angiogenesis in bone tissue engineering via ceramic scaffolds: A review of concepts and recent advancements

Due to organ donor shortages, long transplant waitlists, and the complications/limitations associated with auto and allotransplantation, biomaterials and tissue-engineered models are gaining attention as feasible alternatives for replacing and reconstructing damaged organs and tissues. Among various tissue engineering applications, bone tissue engineering has become a promising strategy to replace or repair damaged bone. We aimed to provide an overview of bioactive ceramic scaffolds in bone tissue engineering, focusing on angiogenesis and the effect of different biofunctionalization strategies. Different routes to angiogenesis, including chemical induction through signaling molecules immobilized covalently or non-covalently, in situ secretion of angiogenic growth factors, and the degradation of inorganic scaffolds, are described. Physical induction mechanisms are also discussed, followed by a review of methods for fabricating bioactive ceramic scaffolds via microfabrication methods, such as photolithography and 3D printing. Finally, the strengths and weaknesses of the commonly used methodologies and future directions are discussed.

Vanillin Promotes Osteoblast Differentiation, Mineral Apposition, and Antioxidant Effects in Pre-Osteoblasts

Antioxidant vanillin (4-hydroxy-3-methoxybenzaldehyde) is used as a flavoring in foods, beverages, and pharmaceuticals. Vanillin possesses various biological effects, such as antioxidant, anti-inflammatory, antibacterial, and anticancer properties. This study aimed to investigate the biological activities of vanillin purified from Adenophora triphylla var. japonica Hara on bone-forming processes. Vanillin treatment induced mineralization as a marker for mature osteoblasts, after stimulating alkaline phosphatase (ALP) staining and activity. The bone-forming processes of vanillin are mainly mediated by the upregulation of the bone morphogenetic protein 2 (BMP2), phospho-Smad1/5/8, and runt-related transcription factor 2 (RUNX2) pathway during the differentiation of osteogenic cells. Moreover, vanillin promoted osteoblast-mediated bone-forming phenotypes by inducing migration and F-actin polymerization. Furthermore, we validated that vanillin-mediated bone-forming processes were attenuated by noggin and DKK1. Finally, we demonstrated that vanillin-mediated antioxidant effects prevent the death of osteoblasts during bone-forming processes. Overall, vanillin has bone-forming properties through the BMP2-mediated biological mechanism, indicating it as a bone-protective compound for bone health and bone diseases such as periodontitis and osteoporosis.

Activin A Limits VEGF-Induced Permeability via VE-PTP

The clinical success of neutralizing vascular endothelial growth factor (VEGF) has unequivocally identified VEGF as a driver of retinal edema that underlies a variety of blinding conditions. VEGF is not the only input that is received and integrated by the endothelium. For instance, the permeability of blood vessels is also regulated by the large and ubiquitously expressed transforming growth factor beta (TGF-β) family. In this project, we tested the hypothesis that members of the TGF-β family influence the VEGF-mediated control of the endothelial cell barrier. To this end, we compared the effect of bone morphogenetic protein-9 (BMP-9), TGF-β1, and activin A on the VEGF-driven permeability of primary human retinal endothelial cells. While BMP-9 and TGF-β1 had no effect on VEGF-induced permeability, activin A limited the extent to which VEGF relaxed the barrier. This activin A effect was associated with the reduced activation of VEGFR2 and its downstream effectors and an increased expression of vascular endothelial tyrosine phosphatase (VE-PTP). Attenuating the expression or activity of VE-PTP overcame the effect of activin A. Taken together, these observations indicate that the TGF-β superfamily governed VEGF-mediated responsiveness in a ligand-specific manner. Furthermore, activin A suppressed the responsiveness of cells to VEGF, and the underlying mechanism involved the VE-PTP-mediated dephosphorylation of VEGFR2.

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.

Material-driven fibronectin and vitronectin assembly enhances BMP-2 presentation and osteogenesis

Mesenchymal stem cell (MSC)-based tissue engineering strategies are of interest in the field of bone tissue regenerative medicine. MSCs are commonly investigated in combination with growth factors (GFs) and biomaterials to provide a regenerative environment for the cells. However, optimizing how biomaterials interact with MSCs and efficiently deliver GFs, remains a challenge. Here, via plasma polymerization, tissue culture plates are coated with a layer of poly (ethyl acrylate) (PEA), which is able to spontaneously permit fibronectin (FN) to form fibrillar nanonetworks. However, vitronectin (VN), another important extracellular matrix (ECM) protein forms multimeric globules on the polymer, thus not displaying functional groups to cells. Interestingly, when FN and VN are co-absorbed onto PEA surfaces, VN can be entrapped within the FN fibrillar nanonetwork in the monomeric form providing a heterogeneous, open ECM network. The combination of FN and VN promote MSC adhesion and leads to enhanced GF binding; here we demonstrate this with bone morphogenetic protein-2 (BMP2). Moreover, MSC differentiation into osteoblasts is enhanced, with elevated expression of osteopontin (OPN) and osteocalcin (OCN) quantified by immunostaining, and increased mineralization observed by von Kossa staining. Osteogenic intracellular signalling is also induced, with increased activity in the SMAD pathway. The study emphasizes the need of recapitulating the complexity of native ECM to achieve optimal cell-material interactions.

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Vitronectin can be incorporated within fibronectin fibril networks upon co-coating onto poly (ethyl acrylate) modified surfaces.

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Fibronectin and vitronectin networks promote mesenchymal stem cell adhesion and induce α5 integrin clustering.

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Fibronectin and vitronectin nanonetworks improve bone morphogenetic protein-2 presentation to mesenchymal stem cells and thus facilitates osteogenesis.

Non-Muscle MLCK Contributes to Endothelial Cell Hyper-Proliferation through the ERK Pathway as a Mechanism for Vascular Remodeling in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is characterized by endothelial dysfunction, uncontrolled proliferation and migration of pulmonary arterial endothelial cells leading to increased pulmonary vascular resistance resulting in great morbidity and poor survival. Bone morphogenetic protein receptor II (BMPR2) plays an important role in the pathogenesis of PAH as the most common genetic mutation. Non-muscle myosin light chain kinase (nmMLCK) is an essential component of the cellular cytoskeleton and recent studies have shown that increased nmMLCK activity regulates biological processes in various pulmonary diseases such as asthma and acute lung injury. In this study, we aimed to discover the role of nmMLCK in the proliferation and migration of pulmonary arterial endothelial cells (HPAECs) in the pathogenesis of PAH. We used two cellular models relevant to the pathobiology of PAH including BMPR2 silenced and vascular endothelial growth factor (VEGF) stimulated HPAECs. Both models demonstrated an increase in nmMLCK activity along with a robust increase in cellular proliferation, inflammation, and cellular migration. The upregulated nmMLCK activity was also associated with increased ERK expression pointing towards a potential integral cytoplasmic interaction. Mechanistically, we confirmed that when nmMLCK is inhibited by MLCK selective inhibitor (ML-7), proliferation and migration are attenuated. In conclusion, our results demonstrate that nmMLCK upregulation in association with increased ERK expression may contribute to the pathogenesis of PAHby stimulating cellular proliferation and migration.

Circ0007042 alleviates intervertebral disc degeneration by adsorbing miR-369 to upregulate BMP2 and activate the PI3K/AKt pathway

Background

To identify regulatory ncRNA molecules that can cause differential expression of CDH2 in intervertebral disc degeneration (IDD) and explore whether there are other ways to affect the progression of IDD.

Methods

A primary culture of human nucleus pulposus (NP) cells was established and identified by immunofluorescence. An in vitro IDD model was constructed by compressing human NP cells, and the MTT assay was used to measure cell viability. Changes in the ncRNA group were analysed by RNA-seq. The expression levels of hsa_circ_7042, CDH2, and miR-369-3p were detected by qPCR. Cell apoptosis, senescence, and extracellular matrix (ECM) metabolism were detected by flow cytometry, β-galactosidase staining, and Western blotting. hsa_circ_7042, miR-369-3p, and bone morphogenetic protein 2 (BMP2) were verified by luciferase and RNA immunoprecipitation (RIP) analyses. The PI3K/Akt pathway was validated by transfection of BMP2 siRNA. Furthermore, a mouse model of lumbar spine instability was constructed. circ_7042 adenovirus was packaged and injected into the intervertebral discs of mice, and the influence of circ_7042 overexpression on intervertebral disc degeneration was determined.

Results

Western blotting, qPCR, and flow cytometry analyses confirmed that overexpression of circ_7042 could downregulate miR-369-3p and upregulate the expression of CDH2 and BMP2 in IDD cell and animal models. Additionally, the levels of apoptotic and senescent cells decreased, and ECM degradation decreased. The PI3K/Akt pathway was significantly activated after circ_7042 was overexpressed. The injection of circ_7042-overexpressing adenovirus effectively reduced ECM degradation and the level of apoptosis in NP tissue.

Conclusions

circ_7042 could upregulate the expression of CDH2 and BMP2 by absorbing miR-369-3p, and the increased BMP2 activated the PI3K/Akt pathway, thus improving IDD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02895-7.

Discovery of a novel class of benzimidazoles as highly effective agonists of bone morphogenetic protein (BMP) receptor signaling

Increasing or restoring Bone Morphogenetic Protein receptor signaling is an effective therapy for conditions such as bone fracture and pulmonary arterial hypertension. However, direct use of recombinant BMPs has encountered significant obstacles. Moreover, synthetic, full agonists of BMP receptor signaling have yet to be identified. Here, we report the discovery of a novel class of indolyl-benzimidazoles, synthesized using a one-pot synthetic methodology, which appear to mimic the biochemical and functional activity of BMPs. The first-in-series compounds, SY-LB-35 and SY-LB-57, stimulated significant increases in cell number and cell viability in the C2C12 myoblast cell line. Cell cycle analysis revealed that these compounds induced a shift toward proliferative phases. SY-LB-35 and SY-LB-57 stimulated canonical Smad and non-canonical PI3K/Akt, ERK, p38 and JNK intracellular signaling pathways, similar to BMP2-stimulated responses. Importantly, increases in Smad phosphorylation and cell viability were dependent on type I BMP receptor activity. Thus, these compounds robustly activate intracellular signaling in a BMP receptor-dependent manner and may signify the first known, full agonists of BMP receptor signaling. Moreover, discovery of small molecule activators of BMP pathways, which can be efficiently formulated and targeted to diseased or damaged areas, could potentially substitute recombinant BMPs for treatment of BMP-related pathologies.

Bcar1/p130Cas is essential for ventricular development and neural crest cell remodelling of the cardiac outflow tract

AIMS

The adapter protein p130Cas, encoded by the Bcar1 gene, is a key regulator of cell movement, adhesion, and cell cycle control in diverse cell types. Bcar1 constitutive knockout mice are embryonic lethal by embryonic days (E) 11.5-12.5, but the role of Bcar1 in embryonic development remains unclear. Here, we investigated the role of Bcar1 specifically in cardiovascular development and defined the cellular and molecular mechanisms disrupted following targeted Bcar1 deletions.

METHODS AND RESULTS

We crossed Bcar1 floxed mice with Cre transgenic lines allowing for cell-specific knockout either in smooth muscle and early cardiac tissues (SM22-Cre), mature smooth muscle cells (smMHC-Cre), endothelial cells (Tie2-Cre), second heart field cells (Mef2c-Cre), or neural crest cells (NCC) (Pax3-Cre) and characterized these conditional knock outs using a combination of histological and molecular biology techniques. Conditional knockout of Bcar1 in SM22-expressing smooth muscle cells and cardiac tissues (Bcar1SM22KO) was embryonically lethal from E14.5-15.5 due to severe cardiovascular defects, including abnormal ventricular development and failure of outflow tract (OFT) septation leading to a single outflow vessel reminiscent of persistent truncus arteriosus. SM22-restricted loss of Bcar1 was associated with failure of OFT cushion cells to undergo differentiation to septal mesenchymal cells positive for SMC-specific α-actin, and disrupted expression of proteins and transcription factors involved in epithelial-to-mesenchymal transformation (EMT). Furthermore, knockout of Bcar1 specifically in NCC (Bcar1PAX3KO) recapitulated part of the OFT septation and aortic sac defects seen in the Bcar1SM22KO mutants, indicating a cell-specific requirement for Bcar1 in NCC essential for OFT septation. In contrast, conditional knockouts of Bcar1 in differentiated smooth muscle, endothelial cells, and second heart field cells survived to term and were phenotypically normal at birth and postnatally.

CONCLUSION

Our work reveals a cell-specific requirement for Bcar1 in NCC, early myogenic and cardiac cells, essential for OFT septation, myocardialization and EMT/cell cycle regulation and differentiation to myogenic lineages.

Immunomodulation and osseointegration activities of Na2TiO3 nanorods-arrayed coatings doped with different Sr content

To endow Ti-based orthopedic implants immunomodulatory capability and thus enhanced osseointegration, different amounts of Sr are doped in Na2TiO3 nanorods in the arrays with identical nanotopographic parameters (rod diameter, length and inter-rod spacing) by substitution of Na+ using hydrothermal treatment. The obtained arrays are denoted as STSr2, STSr4, and STSr7, where the arabic numbers indicate the incorporating amounts of Sr in Na2TiO3. The modulation effects of the Sr-doped nanorods arrays on macrophage polarization and osteogenetic functions of osteoblasts are investigated, together with the array without Sr (ST). Moreover, osseointegration of these arrays are also assayed in rat femoral condyles. Sr-doped nanorods arrays accelerate M1 (pro-inflammatory phenotype)-to-M2 (anti-inflammatory phenotype) transformation of the adhered macrophages, enhancing secretion of pro-osteogenetic cytokines and growth factors (TGF-β1 and BMP2), moreover, the Sr doped arrays directly enhance osteogenetic functions of osteoblasts. The enhancement of paracrine of M2 macrophages and osteogenetic function of osteoblasts is promoted with the increase of Sr incorporating amounts. Consequently, Sr doped arrays show significantly enhanced osseointegration in vivo compared to ST, and STSr7 exhibits the best performance. Our work sheds a new light on the design of surface chemical components and structures for orthopedic implants to enhance their osseointegration.

Differential bioactivity of four BMP-family members as function of biomaterial stiffness

While a soft film itself is not able to induce cell spreading, BMP-2 presented via such soft film (so called "matrix-bound BMP-2") was previously shown to trigger cell spreading, migration and downstream BMP-2 signaling. Here, we used thin films of controlled stiffness presenting matrix-bound BMPs to study the effect of four BMP members (BMP-2, 4, 7, 9) on cell adhesion and differentiation of skeletal progenitors. We performed automated high-content screening of cellular responses, including cell number, cell spreading area, SMAD phosphorylation and alkaline phosphatase activity. We revealed that the cell response to bBMPs is BMP-type specific, and involved certain BMP receptors and beta chain integrins. In addition, this response is stiffness-dependent for several receptors. The basolateral presentation of the BMPs allowed us to discriminate the specificity of cellular response, especiallyd the role of type I and II BMP receptors and of β integrins in a BMP-type and stiffness-dependent manner. Notably, BMP-2 and BMP-4 were found to have distinct roles, while ALK5, previously known as a TGF-β receptor was revealed to be involved in the BMP-pathway.

Scaffold-Free Engineering of Human Cartilage Implants

OBJECTIVE

Despite new strategies in tissue engineering, cartilage repair remains a major challenge. Our aim is to treat patients with focal lesions of articular cartilage with autologous hyaline cartilage implants using a scaffold-free approach. In this article, we describe experiments to optimize production of scaffold-free cartilage discs.

DESIGN

Articular chondrocytes were expanded in vitro, seeded in transwell inserts and redifferentiated using established chondrogenic components. Experimental variables included testing 2 different expansion media, adding bone morphogenetic protein 2 (BMP2), insulin-like growth factor 1 (IGF1), growth/differentiation factor 5 (GDF5), or fibroblast growth factor 18 (FGF18) to the differentiation medium and allowing the disc to float freely in large wells. Cartilage discs were analyzed by weight and thickness, real-time RT-qPCR (reverse transcriptase qualitative polymerase chain reaction), fluorescence immunostaining, transmission electron microscopy, second harmonic generation imaging, and measurement of Young's modulus.

RESULTS

Addition of BMP2 to the chondrogenic differentiation medium (CDM) was essential for stable disc formation, while IGF1, GDF5, and FGF18 were redundant. Allowing discs to float freely in CDM on a moving platform increased disc thickness compared with discs kept continuously in transwell inserts. Discs cultured for 6 weeks reached a thickness of almost 2 mm and Young's modulus of >200 kPa. There was abundant type II collagen. Collagen fibrils were 25 nm thick, with a tendency to be organized perpendicular to the disc surface.

CONCLUSION

Scaffold-free engineering using BMP2 and providing free movement in CDM produced firm, elastic cartilage discs with abundant type II collagen. This approach may potentially be used in clinical trials.

Single Cell Center of Mass for the Analysis of BMP Receptor Heterodimers Distributions

At the plasma membrane, transmembrane receptors are at the interface between cells and their environment. They allow sensing and transduction of chemical and mechanical extracellular signals. The spatial distribution of receptors and the specific recruitment of receptor subunits to the cell membrane is crucial for the regulation of signaling and cell behavior. However, it is challenging to define what regulates such spatial patterns for receptor localization, as cell shapes are extremely diverse when cells are maintained in standard culture conditions. Bone morphogenetic protein receptors (BMPRs) are serine-threonine kinases, which build heteromeric complexes of BMPRI and II. These are especially interesting targets for receptor distribution studies, since the signaling pathways triggered by BMPR-complexes depends on their dimerization mode. They might exist as preformed complexes, or assemble upon binding of BMP, triggering cell signaling which leads to differentiation or migration. In this work we analyzed BMPR receptor distributions in single cells grown on micropatterns, which allow not only to control cell shape, but also the distribution of intracellular organelles and protein assemblies. We developed a script called ComRed (Center Of Mass Receptor Distribution), which uses center of mass calculations to analyze the shift and spread of receptor distributions according to the different cell shapes. ComRed was tested by simulating changes in experimental data showing that shift and spread of distributions can be reliably detected. Our ComRed-based analysis of BMPR-complexes indicates that receptor distribution depends on cell polarization. The absence of a coordinated internalization after addition of BMP suggests that a rapid and continual recycling of BMPRs might occur. Receptor complexes formation and localization in cells induced by BMP might yield insights into the local regulation of different signaling pathways.

Bone morphogenetic protein receptor 2 inhibition destabilizes microtubules promoting the activation of lysosomes and cell death of lung cancer cells

Background

Recent studies have shown that bone morphogenetic protein receptor 2 (BMPR2) regulates cell survival signaling events in cancer cells independent of the BMP type 1 receptor (BMPR1) or the Smad-1/5 transcription factor. Mutations in BMPR2 trafficking proteins leads to overactive BMP signaling, which leads to neurological diseases caused by BMPR2 stabilization of the microtubules. It is not known whether BMPR2 regulates the microtubules in cancer cells and what effect this has on cell survival. It is also not known whether alterations in BMPR2 trafficking effects activity and response to BMPR2 inhibitors.

Methods

We utilized BMPR2 siRNA and the BMP receptor inhibitors JL5 and Ym155, which decrease BMPR2 signaling and cause its mislocalization to the cytoplasm. Using the JL5 resistant MDA-MD-468 cell line and sensitive lung cancer cell lines, we examined the effects of BMPR2 inhibition on BMPR2 mislocalization to the cytoplasm, microtubule destabilization, lysosome activation and cell survival.

Results

We show that the inhibition of BMPR2 destabilizes the microtubules. Destabilization of the microtubules leads to the activation of the lysosomes. Activated lysosomes further decreases BMPR2 signaling by causing it to mislocalizated to the cytoplasm and/or lysosome for degradation. Inhibition of the lysosomes with chloroquine attenuates BMPR2 trafficking to the lysosome and cell death induced by BMPR2 inhibitors. Furthermore, in MDA-MD-468 cells that are resistant to JL5 induced cell death, BMPR2 was predominately located in the cytoplasm. BMPR2 failed to localize to the cytoplasm and/or lysosome following treatment with JL5 and did not destabilize the microtubules or activate the lysosomes.

Conclusions

These studies reveal that the inhibition of BMPR2 destabilizes the microtubules promoting cell death of cancer cells that involves the activation of the lysosomes. Resistance to small molecules targeting BMPR2 may occur if the BMPR2 is localized predominantly to the cytoplasm and/or fails to localize to the lysosome for degradation.

TGF-β signaling: A recap of SMAD-independent and SMAD-dependent pathways

Transforming growth factor-β (TGF-β) is a proinflammatory cytokine known to control a diverse array of pathological and physiological conditions during normal development and tumorigenesis. TGF-β-mediated physiological effects are heterogeneous and vary among different types of cells and environmental conditions. TGF-β serves as an antiproliferative agent and inhibits tumor development during primary stages of tumor progression; however, during the later stages, it encourages tumor development and mediates metastatic progression and chemoresistance. The fundamental elements of TGF-β signaling have been divulged more than a decade ago; however, the process by which the signals are relayed from cell surface to nucleus is very complex with additional layers added in tumor cell niches. Although the intricate understanding of TGF-β-mediated signaling pathways and their regulation are still evolving, we tried to make an attempt to summarize the TGF-β-mediated SMAD-dependent andSMAD-independent pathways. This manuscript emphasizes the functions of TGF-β as a metastatic promoter and tumor suppressor during the later and initial phases of tumor progression respectively.

A dynamic actin-dependent nucleoskeleton and cell identity

Actin is an essential regulator of cellular functions. In the eukaryotic cell nucleus, actin regulates chromatin as a bona fide component of chromatin remodelling complexes, it associates with nuclear RNA polymerases to regulate transcription and is involved in co-transcriptional assembly of nascent RNAs into ribonucleoprotein complexes. Actin dynamics are, therefore, emerging as a major regulatory factor affecting diverse cellular processes. Importantly, the involvement of actin dynamics in nuclear functions is redefining the concept of nucleoskeleton from a rigid scaffold to a dynamic entity that is likely linked to the three-dimensional organization of the nuclear genome. In this review, we discuss how nuclear actin, by regulating chromatin structure through phase separation may contribute to the architecture of the nuclear genome during cell differentiation and facilitate the expression of specific gene programs. We focus specifically on mitochondrial genes and how their dysregulation in the absence of actin raises important questions about the role of cytoskeletal proteins in regulating chromatin structure. The discovery of a novel pool of mitochondrial actin that serves as 'mitoskeleton' to facilitate organization of mtDNA supports a general role for actin in genome architecture and a possible function of distinct actin pools in the communication between nucleus and mitochondria.

Gene-metabolite networks associated with impediment of bone fracture repair in spaceflight

Adverse effects of spaceflight on musculoskeletal health increase the risk of bone injury and impairment of fracture healing. Its yet elusive molecular comprehension warrants immediate attention, since space travel is becoming more frequent. Here we examined the effects of spaceflight on bone fracture healing using a 2 mm femoral segmental bone defect (SBD) model. Forty, 9-week-old, male C57BL/6J mice were randomized into 4 groups: 1) Sham surgery on Ground (G-Sham); 2) Sham surgery housed in Spaceflight (FLT-Sham); 3) SBD surgery on Ground (G-Surgery); and 4) SBD surgery housed in Spaceflight (FLT-Surgery). Surgery procedures occurred 4 days prior to launch; post-launch, the spaceflight mice were house in the rodent habitats on the International Space Station (ISS) for approximately 4 weeks before euthanasia. Mice remaining on the Earth were subjected to identical housing and experimental conditions. The right femur from half of the spaceflight and ground groups was investigated by micro-computed tomography (µCT). In the remaining mice, the callus regions from surgery groups and corresponding femoral segments in sham mice were probed by global transcriptomic and metabolomic assays. µCT confirmed escalated bone loss in FLT-Sham compared to G-Sham mice. Comparing to their respective on-ground counterparts, the morbidity gene-network signal was inhibited in sham spaceflight mice but activated in the spaceflight callus. µCT analyses of spaceflight callus revealed increased trabecular spacing and decreased trabecular connectivity. Activated apoptotic signals in spaceflight callus were synchronized with inhibited cell migration signals that potentially hindered the wound site to recruit growth factors. A major pro-apoptotic and anti-migration gene network, namely the RANK-NFκB axis, emerged as the central node in spaceflight callus. Concluding, spaceflight suppressed a unique biomolecular mechanism in callus tissue to facilitate a failed regeneration, which merits a customized intervention strategy.

Surface Co-presentation of BMP-2 and integrin selective ligands at the nanoscale favors α5β1 integrin-mediated adhesion

Here we present the use of surface nanopatterning of covalently immobilized BMP-2 and integrin selective ligands to determine the specificity of their interactions in regulating cell adhesion and focal adhesion assembly. Gold nanoparticle arrays carrying single BMP-2 dimers are prepared by block-copolymer micellar nanolithography and azide-functionalized integrin ligands (cyclic-RGD peptides or α₅β₁ integrin peptidomimetics) are immobilized on the surrounding polyethylene glycol alkyne by click chemistry. Compared to BMP-2 added to the media, surface immobilized BMP-2 (iBMP-2) favors the spatial segregation of adhesion clusters and enhances focal adhesion (FA) size in cells adhering to α₅β₁ integrin selective ligands. Moreover, iBMP-2 copresented with α₅β₁ integrin ligands induces the recruitment of α_vβ₃ integrins in FAs. When copresented with RGD, iBMP-2 induces the assembly of a higher number of FAs, which are not affected by α₅β₁ integrin blocking. Our dual-functionalized platforms offer the possibility to study the crosstalk between integrins and BMP receptors, and more in general they could be used to address the spatial regulation of growth factors and adhesion receptors crosstalk on biomimetic surfaces.

Hydrothermally grown TiO2-nanorods on surface mechanical attrition treated Ti: Improved corrosion fatigue and osteogenesis

Current bioactive modifications of Ti-based materials for promoting osteogenesis often decrease corrosion fatigue strength (σ_cf) of the resultant implants, thereby shortening their service lifespan. To solve this issue and accelerate the osteogenesis process, in the present study, a TiO₂ nanorods (TNR)-arrayed coating was hydrothermally grown on optimal surface mechanical attrition treated (SMATed) titanium (S-Ti). The microstructure, bond integrity, residual stress distribution, and corrosion fatigue of TNR-coated S-Ti (TNR/S-Ti) and the response of macrophages and bone marrow-derived mesenchymal stem cells (BMSCs) to TNR/S-Ti were investigated and compared with those of mechanically polished Ti (P-Ti), S-Ti, and TNR-coated P-Ti (TNR/P-Ti). S-Ti showed a nanograined layer and an underlying grain-deformed region with residual compressive stress, which was sustained even when it was hydrothermally coated with TNR. TNR on S-Ti showed nanotopography, composition, and bond strength almost identical to those of P-Ti. While TNR/P-Ti showed a considerable decrease in σ_cf compared to P-Ti, TNR/S-Ti exhibited an improved σ_cf which was even higher than that of P-Ti. Biologically, TNR/S-Ti enhanced adhesion, differentiation, and mineralization of BMSCs, and it also promoted adhesion and M1-to-M2 transition of macrophages as compared to S-Ti and P-Ti. With rapid phenotype switch of macrophages, the level of proinflammatory cytokines decreased, while anti-inflammatory cytokines were upregulated. In co-culture conditions, the migration, differentiation, and mineralization of BMSCs were enhanced by increased level of secretion factors of macrophages on TNR/S-Ti. The modified structure accelerated bone apposition in rabbit femur and is expected to induce a favorable immune microenvironment to facilitate osseointegration earlier; it can also simultaneously improve corrosion fatigue resistance of Ti-based implants and thereby enhance their service life.

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Soft Hydrogels for Balancing Cell Proliferation and Differentiation

Hydrogels have been widely explored for the delivery of cells in a variety of regenerative medicine applications due to their ability to mimic both the biochemical and physical cues of cell microniches. For bone regeneration, in particular, stiff hydrogels mimicking osteoid stiffness have been utilized due to the fact that stiff substrates favor stem cell osteogenic differentiation. Unlike cell adhesion in two dimensions, three-dimensional hydrogels offer mechanical stimulation but limit the cell spreading and growth due to the dense matrix network. Therefore, we designed degradable, soft hydrogels (∼0.5 kPa) mimicking the soft bone marrow stiffness, with incorporated matrix metalloproteinase (MMP)-cleavable sites and RGD-based adhesive sites, to enhance the spreading and proliferation of the encapsulated cells, which are commonly inhibited in nondegradable and/or stiff implants. When the hydrogels were cultured on rigid surfaces to mirror the microenvironment of bone defects in vivo, the cells were shown to migrate toward the interface and differentiate down the osteogenic lineage, enhanced by the codelivery of bone morphogenetic protein-2 (BMP-2). Furthermore, this soft hydrogel might find applications in therapeutic interventions since it is easily injectable and cost-efficient. Taken together, we have designed a new system to balance cell growth and differentiation for improving hydrogel-based bone regenerative medicine strategies.

BMP-2 Signaling and Mechanotransduction Synergize to Drive Osteogenic Differentiation via YAP/TAZ

Growth factors and mechanical cues synergistically affect cellular functions, triggering a variety of signaling pathways. The molecular levels of such cooperative interactions are not fully understood. Due to its role in osteogenesis, the growth factor bone morphogenetic protein 2 (BMP-2) is of tremendous interest for bone regenerative medicine, osteoporosis therapeutics, and beyond. Here, contribution of BMP-2 signaling and extracellular mechanical cues to the osteogenic commitment of C2C12 cells is investigated. It is revealed that these two distinct pathways are integrated at the transcriptional level to provide multifactorial control of cell differentiation. The activation of osteogenic genes requires the cooperation of BMP-2 pathway-associated Smad1/5/8 heteromeric complexes and mechanosensitive YAP/TAZ translocation. It is further demonstrated that the Smad complexes remain bound onto and active on target genes, even after BMP-2 removal, suggesting that they act as a "molecular memory unit." Thus, synergistic stimulation with BMP-2 and mechanical cues drives osteogenic differentiation in a programmable fashion.

Food for Bone: Evidence for a Role for Delta-Tocotrienol in the Physiological Control of Osteoblast Migration

Bone remodeling and repair require osteogenic cells to reach the sites that need to be rebuilt, indicating that stimulation of osteoblast migration could be a promising osteoanabolic strategy. We showed that purified δ-tocotrienol (δ-TT, 10 μg/mL), isolated from commercial palm oil (Elaeis guineensis) fraction, stimulates the migration of both MC3T3-E1 osteoblast-like cells and primary human bone marrow mesenchymal stem cells (BMSC) as detected by wound healing assay or Boyden chamber assay respectively. The ability of δ-TT to promote MC3T3-E1 cells migration is dependent on Akt phosphorylation detected by Western blotting and involves Wnt/β-catenin signalling pathway activation. In fact, δ-TT increased β-catenin transcriptional activity, measured using a Nano luciferase assay and pretreatment with procaine (2 µM), an inhibitor of the Wnt/β-catenin signalling pathway, reducing the wound healing activity of δ-TT on MC3T3-E1 cells. Moreover, δ-TT treatment increased the expression of β-catenin specific target genes, such as Osteocalcin and Bone Morphogenetic Protein-2, involved in osteoblast differentiation and migration, and increased alkaline phosphatase and collagen content, osteoblast differentiation markers. The ability of δ-TT to enhance the recruitment of BMSC, and to promote MC3T3-E1 differentiation and migratory behavior, indicates that δ-TT could be considered a promising natural anabolic compound.

Activin A receptor type 1-mediated BMP signaling regulates RANKL-induced osteoclastogenesis via canonical SMAD-signaling pathway

Bone morphogenetic proteins (BMPs) are important mediators of osteoclast differentiation. Although accumulating evidence has implicated BMPs in osteoblastogenesis, the mechanisms by which BMPs regulate osteoclastogenesis remain unclear. Activin A receptor type 1 (ACVR1) is a BMP type 1 receptor essential for skeletal development. Here, we observed that BMP-7, which preferentially binds to ACVR1, promotes osteoclast differentiation, suggesting ACVR1 is involved in osteoclastogenesis. To investigate this further, we isolated osteoclasts from either Acvr1-floxed mice or mice with constitutively-activated Acvr1 (caAcvr1) carrying tamoxifen-inducible Cre driven by a ubiquitin promotor and induced Cre activity in culture. Osteoclasts from the Acvr1-floxed mice had reduced osteoclast numbers and demineralization activity, whereas those from the caAcvr1-mutant mice formed large osteoclasts and demineralized pits, suggesting that BMP signaling through ACVR1 regulates osteoclast fusion and activity. It is reported that BMP-2 binds to BMPR1A, another BMP type 1 receptor, whereas BMP-7 binds to ACVR1 to activate SMAD1/5/9 signaling. Here, Bmpr1a-disrupted osteoclasts displayed reduced phospho-SMAD1/5/9 (pSMAD1/5/9) levels when induced by BMP-2, whereas no impacts on pSMAD1/5/9 were observed when induced by BMP-7. In contract, Acvr1-disrupted osteoclasts displayed reduced pSMAD1/5/9 levels when induced either by BMP-2 or BMP-7, suggesting that ACVR1 is the major receptor for transducing BMP-7 signals in osteoclasts. Indeed, LDN-193189 and LDN-212854, which specifically block SMAD1/5/9 phosphorylation, inhibited osteoclastogenesis of caAcvr1-mutant cells. Moreover, increased BMP signaling promoted nuclear translocation of nuclear factor-activated T-cells 1 (NFATc1), which was inhibited by LDN treatments. Taken together, ACVR1-mediated BMP-SMAD signaling activates NFATc1, a regulatory protein crucial for receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis.

Early Steps of Mammary Stem Cell Transformation by Exogenous Signals; Effects of Bisphenol Endocrine Disrupting Chemicals and Bone Morphogenetic Proteins

Estrogens are major regulators of the mammary gland development, notably during puberty, via estrogen receptor (ER) activation, leading to the proliferation and differentiation of mammary cells. In addition to estrogens, the bone morphogenetic proteins (BMPs) family is involved in breast stem cell/progenitor commitment. However, these two pathways that synergistically contribute to the biology of the normal mammary gland have also been described to initiate and/or promote breast cancer development. In addition to intrinsic events, lifestyle habits and exposure to environmental cues are key risk factors for cancer in general, and especially for breast cancer. In the latter case, bisphenol A (BPA), an estrogen-mimetic compound, is a critical pollutant both in terms of the quantities released in our environment and of its known and speculated effects on mammary gland biology. In this review, we summarize the current knowledge on the actions of BMPs and estrogens in both normal mammary gland development and breast cancer initiation, dissemination, and resistance to treatment, focusing on the dysregulations of these processes by BPA but also by other bisphenols, including BPS and BPF, initially considered as safer alternatives to BPA.

Formulation, Colloidal Characterization, and In Vitro Biological Effect of BMP-2 Loaded PLGA Nanoparticles for Bone Regeneration

Nanoparticles (NPs) based on the polymer poly (lactide-co-glycolide) acid (PLGA) have been widely studied in developing delivery systems for drugs and therapeutic biomolecules, due to the biocompatible and biodegradable properties of the PLGA. In this work, a synthesis method for bone morphogenetic protein (BMP-2)-loaded PLGA NPs was developed and optimized, in order to carry out and control the release of BMP-2, based on the double-emulsion (water/oil/water, W/O/W) solvent evaporation technique. The polymeric surfactant Pluronic F68 was used in the synthesis procedure, as it is known to have an effect on the reduction of the size of the NPs, the enhancement of their stability, and the protection of the encapsulated biomolecule. Spherical solid polymeric NPs were synthesized, showing a reproducible multimodal size distribution, with diameters between 100 and 500 nm. This size range appears to allow the protein to act on the cell surface and at the cytoplasm level. The effect of carrying BMP-2 co-adsorbed with bovine serum albumin on the NP surface was analyzed. The colloidal properties of these systems (morphology by SEM, hydrodynamic size, electrophoretic mobility, temporal stability, protein encapsulation, and short-term release profile) were studied. The effect of both BMP2-loaded NPs on the proliferation, migration, and osteogenic differentiation of mesenchymal stromal cells from human alveolar bone (ABSC) was also analyzed in vitro.

Chemotropic signaling by BMP7 requires selective interaction at a key residue in ActRIIA

BMP7 evokes acute chemotropic PI3K-dependent responses, such as growth cone collapse and monocyte chemotaxis, as well as classical Smad-dependent gene transcription. That these divergent responses can be activated in the same cell raises the question of how the BMP-dependent signaling apparatus is manipulated to produce chemotropic and transcriptional signals. RNA interference and site-directed mutagenesis were used to explore functional and structural BMP receptor requirements for BMP7-evoked chemotropic activity. We show that specific type II BMP receptor subunits, ActRIIA and BMPR2, are required for BMP7-induced growth cone collapse in developing spinal neurons and for chemotaxis of monocytes. Reintroduction of wild-type ActRIIA into monocytic cells lacking endogenous ActRIIA restores BMP7-evoked chemotaxis, whereas expression of an ActRIIA K76A receptor variant fails to rescue. BMP7-evoked Smad-dependent signaling is unaffected by either ActRIIA knockdown or expression of the ActRIIA K76A variant. In contrast, BMP7-evoked PI3K-dependent signaling is significantly disturbed in the presence of ActRIIA K76A. These results support a model for selective engagement of chemotropic BMPs with type II BMP receptors, through specific residues, that results in strict regulation of PI3K-dependent signal transduction.

This article has an associated First Person interview with the first author of the paper.

Summary: Chemotropic BMPs, typified by BMP7, mediate selective receptor recruitment and transduction of PI3K-dependent intracellular signals through interaction with a key residue in the ActRIIA type II BMP receptor.

Recombinant human BMP-2 accelerates the migration of bone marrow mesenchymal stem cells via the CDC42/PAK1/LIMK1 pathway in vitro and in vivo

Biomaterials are widely used for bone regeneration and fracture repair. The migration of bone marrow mesenchymal stem cells (BMSCs) into bone defect sites or material implantation sites, and their differentiation into osteoblasts, is central to the fracture healing process, and the directional migration of BMSCs depends on cytokines or chemokines at the defect site. BMP-2 can stimulate the migration of a variety of cells, but it remains unclear whether BMSC migration can be induced. To provide evidence for BMP-2-induced BMSC migration, we tested the cytoskeletal changes and migration ability of BMSCs after treatment with recombinant human BMP-2 (rhBMP-2). We also explored the recruitment of BMSCs from the circulatory system using a collagen sponge incorporating rhBMP-2 that was implanted in vivo. Furthermore, to understand the mechanism underlying this migration, we investigated the effect of rhBMP-2 on migration-related signal pathways. Here, we found that, rhBMP-2 treatment significantly increased the migration of BMSCs in vitro via activation of the CDC42/PAK1/LIMK1 pathway, and that this migration could be blocked by silencing CDC42. In vivo, collagen sponge material loaded with rhBMP-2 could recruit BMSCs injected into the circulatory system. Moreover, inhibition using the small interfering RNA for CDC42 led to a significant decrease in the number of BMSCs within the material. In conclusion, our data prove that rhBMP-2 can accelerate BMSC migration via the CDC42/PAK1/LIMK1 pathway both in vivo and in vitro, and therefore provides a foundation for further understanding and application of rhBMP-2-incorporated materials by enhancing BMSC recruitment.

Specificity, versatility, and control of TGF-β family signaling

Encoded in mammalian cells by 33 genes, the transforming growth factor-β (TGF-β) family of secreted, homodimeric and heterodimeric proteins controls the differentiation of most, if not all, cell lineages and many aspects of cell and tissue physiology in multicellular eukaryotes. Deregulation of TGF-β family signaling leads to developmental anomalies and disease, whereas enhanced TGF-β signaling contributes to cancer and fibrosis. Here, we review the fundamentals of the signaling mechanisms that are initiated upon TGF-β ligand binding to its cell surface receptors and the dependence of the signaling responses on input from and cooperation with other signaling pathways. We discuss how cells exquisitely control the functional presentation and activation of heteromeric receptor complexes of transmembrane, dual-specificity kinases and, thus, define their context-dependent responsiveness to ligands. We also introduce the mechanisms through which proteins called Smads act as intracellular effectors of ligand-induced gene expression responses and show that the specificity and impressive versatility of Smad signaling depend on cross-talk from other pathways. Last, we discuss how non-Smad signaling mechanisms, initiated by distinct ligand-activated receptor complexes, complement Smad signaling and thus contribute to cellular responses.

Maltol Mitigates Thioacetamide-induced Liver Fibrosis through TGF-β1-mediated Activation of PI3K/Akt Signaling Pathway

Our previous study has confirmed that maltol can attenuate alcohol-induced acute hepatic damage and prevent oxidative stress in mice. Therefore, maltol might have the capacity to improve thioacetamide (TAA)-induced liver fibrosis. The purpose of this work was to explore the antifibrotic efficacy and underlying mechanisms of maltol for TAA-treated mice. Progressive liver fibrosis was established with a dose-escalating protocol in which the mice received TAA intraperitoneal three times a week for a total duration of 9 weeks. The injection doses of TAA were 50 mg/kg for the first week, 100 mg/kg for the second and third weeks, and 150 mg/kg for the rest of the injections. Maltol with doses of 50 and 100 mg/kg was given by gavage after 4 weeks of intraperitoneal injection of TAA, respectively, once daily for 5 weeks. Results indicated that TAA intraperitoneal injection significantly increased serum activities of alanine aminotransferase (ALT) (52.93 ± 13.21 U/L vs 10.22 ± 3.36 U/L) and aspartate aminotransferase (AST) (67.58 ± 25.84 U/L vs 39.34 ± 3.89 U/L); these elevations were significantly diminished by pretreatment with maltol. Additionally, maltol ameliorated TAA-induced oxidative stress with attenuation in MDA ( p < 0.05 or p < 0.01) content; evident elevation in the GSH levels, GSH/GSSG ratio ( p < 0.05 or p < 0.01), and superoxide dismutase (SOD) ( p < 0.01); and restored liver histology accompanied by a decrease of α-smooth muscle actin (α-SMA) expression. Furthermore, maltol significantly suppressed the transforming growth factor-β1 (TGF-β1) expression and the PI3K/Akt pathway. This study suggested that maltol alleviated experimental liver fibrosis by suppressing the activation of HSCs and inducing apoptosis of activated HSCs through TGF-β1-mediated PI3K/Akt signaling pathway. These findings further clearly suggested that maltol is a potent therapeutic candidate for the alleviation of liver fibrosis.

BMP-2 induces human mononuclear cell chemotaxis and adhesion and modulates monocyte-to-macrophage differentiation

Type 2 diabetes mellitus (T2DM) is a cardiovascular risk factor which leads to atherosclerosis, an inflammatory disease characterized by the infiltration of mononuclear cells in the vessel. Bone morphogenetic protein (BMP)‐2 is a cytokine which has been recently shown to be elevated in atherosclerosis and T2DM and to contribute to vascular inflammation. However, the role of BMP‐2 in the regulation of mononuclear cell function remains to be established. Herein, we demonstrate that BMP‐2 induced human monocyte chemotaxis via phosphoinositide 3 kinase and mitogen‐activated protein kinases. Inhibition of endogenous BMP‐2 signalling, by Noggin or a BMP receptor inhibitor, interfered with monocyte migration. Although BMP‐2 expression was increased in monocytes from T2DM patients, it could still stimulate their migration. Furthermore, BMP‐2 interfered with their differentiation into M2 macrophages. Finally, BMP‐2 both induced the adhesion of monocytes to fibronectin and endothelial cells (ECs), and promoted the adhesive properties of ECs, by increasing expression of adhesion and pro‐inflammatory molecules. Our data demonstrate that BMP‐2 could exert its pro‐inflammatory effects by inducing monocyte migration and adhesiveness to ECs and by interfering with the monocyte differentiation into M2 macrophages. Our findings provide novel insights into the mechanisms by which BMP‐2 may contribute to the development of atherosclerosis.

1α,25(OH)2D3-glycosides from Solanum glaucophyllum leaves extract induce myoblasts differentiation through p38 MAPK and AKT activation

We have previously shown that Solanum glaucophyllum leaf extract (SGE) increases VDR protein levels and promotes myoblast differentiation. Here, we investigated whether p38 MAPK and AKT are involved in SGE actions. Cell-cycle studies showed that SGE prompted a peak of S-phase followed by an arrest in the G0/G1-phase through p38 MAPK. Time course studies showed that p38 MAPK and AKT phosphorylation were statistically increased by SGE (10 nM) or synthetic 1α,25(OH)₂D₃ (1 nM) treatment. Furthermore, p38 MAPK and AKT inhibitors, SB203580 and LY294002 respectively, suppressed myoblasts fusion induced by SGE or synthetic 1α,25(OH)₂D₃ We have also studied differentiation genes by qRT-PCR. myoD1 mRNA increased significantly by SGE (24-72 h) or 1α,25(OH)₂D₃ (24 h) treatment. mRNA expression of myogenin also increased upon SGE or 1α,25(OH)₂D₃ treatment. Finally, MHC2b mRNA expression, a late differentiation marker, was increased significantly by both compounds at 72 h compared to control. Taken together, these results suggest that SGE, as synthetic 1α,25(OH)₂D₃, promotes myotube formation through p38 MAPK and AKT activation.

Relevant biological processes for tissue development with stem cells and their mechanistic modeling: A review

A potential alternative for tissue transplants is tissue engineering, in which the interaction of cells and biomaterials can be optimized. Tissue development in vitro depends on the complex interaction of several biological processes such as extracellular matrix synthesis, vascularization and cell proliferation, adhesion, migration, death, and differentiation. The complexity of an individual phenomenon or of the combination of these processes can be studied with phenomenological modeling techniques. This work reviews the main biological phenomena in tissue development and their mathematical modeling, focusing on mesenchymal stem cell growth in three-dimensional scaffolds.

Identification of novel microRNA inhibiting actin cytoskeletal rearrangement thereby suppressing osteoblast differentiation

We report the role of miR-1187 in regulation of osteoblast functions. Over-expression of miR-1187 inhibited osteoblast differentiation. Target prediction analysis tools and experimental validation by luciferase 3' UTR reporter assay identified BMPR-II and ArhGEF-9 as direct targets of miR-1187. ArhGEF-9 activates Cdc42 which has a major role in actin reorganization. BMP-2 also induces actin polymerization. Role of miR-1187 in actin reorganization was determined by western blotting, immunofluorescence, and in vivo gene silencing studies. Reduced protein levels of BMPR-II, activated Cdc42, and downstream signaling molecules were observed in miR-1187-transfected osteoblasts. miR-1187 over-expression resulted in decreased actin polymerization. Additionally, P-cofilin, which does not bind F-actin, was decreased in miR-1187-transfected cells. These results were corroborated by administration of BMPR-II exogenously in miR-1187-transfected osteoblasts. Silencing of miR-1187 in neonatal mice mitigated all the inhibitory effects of miR-1187 on actin cytoskeletal rearrangement. Importantly, in vivo treatment of miR-1187 inhibitor to ovariectomized BALB/c mice led to significant improvement in trabecular bone microarchitecture. Overall, miR-1187 functions as a negative regulator of osteogenesis by repressing BMPR-II and ArhGEF-9 expression thus suppressing non-Smad BMP2/Cdc42 signaling pathway and inhibiting actin reorganization. miR-1187 functions as a negative regulator of osteogenesis by repressing BMPR-II expression, which in turn, suppresses non-Smad BMP2/Cdc42 signaling pathway, thus inhibiting actin cytoskeletal rearrangement. Silencing of miR-1187 significantly improves trabecular bone microarchitecture. As miR-1187 exerts a negative regulatory role in osteoblasts function, hence, we propose that therapeutic approaches targeting miR-1187 could be useful in enhancing the bone formation and treatment of pathological conditions of bone loss.

Bone Morphogenetic Proteins in Vascular Homeostasis and Disease

It is well established that control of vascular morphogenesis and homeostasis is regulated by vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), Delta-like 4 (Dll4), angiopoietin, and ephrin signaling. It has become clear that signaling by bone morphogenetic proteins (BMPs), which have a long history of studies in bone and early heart development, are also essential for regulating vascular function. Indeed, mutations that cause deregulated BMP signaling are linked to two human vascular diseases, hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension. These observations are corroborated by data obtained with vascular cells in cell culture and in mouse models. BMPs are required for normal endothelial cell differentiation and for venous/arterial and lymphatic specification. In adult life, BMP signaling orchestrates neo-angiogenesis as well as vascular inflammation, remodeling, and calcification responses to shear and oxidative stress. This review emphasizes the pivotal role of BMPs in the vascular system, based on studies of mouse models and human vascular disorders.

Calcium-containing scaffolds induce bone regeneration by regulating mesenchymal stem cell differentiation and migration

Background

Osteoinduction and subsequent bone formation rely on efficient mesenchymal stem cell (MSC) recruitment. It is also known that migration is induced by gradients of growth factors and cytokines. Degradation of Ca²⁺-containing biomaterials mimics the bone remodeling compartment producing a localized calcium-rich osteoinductive microenvironment. The aim of our study was to determine the effect of calcium sulfate (CaSO₄) on MSC migration. In addition, to evaluate the influence of CaSO₄ on MSC differentiation and the potential molecular mechanisms involved.

Methods

A circular calvarial bone defect (5 mm diameter) was created in the parietal bone of 35 Balb-C mice. We prepared and implanted a cell-free agarose/gelatin scaffold alone or in combination with different CaSO₄ concentrations into the bone defects. After 7 weeks, we determined the new bone regenerated by micro-CT and histological analysis. In vitro, we evaluated the CaSO₄ effects on MSC migration by both wound healing and agarose spot assays. Osteoblastic gene expression after BMP-2 and CaSO₄ treatment was also evaluated by qPCR.

Results

CaSO₄ increased MSC migration and bone formation in a concentration-dependent manner. Micro-CT analysis showed that the addition of CaSO₄ significantly enhanced bone regeneration compared to the scaffold alone. The histological evaluation confirmed an increased number of endogenous cells recruited into the cell-free CaSO₄-containing scaffolds. Furthermore, MSC migration in vitro and active AKT levels were attenuated when CaSO₄ and BMP-2 were in combination. Addition of LY294002 and Wortmannin abrogated the CaSO₄ effects on MSC migration.

Conclusions

Specific CaSO₄ concentrations induce bone regeneration of calvarial defects in part by acting on the host’s undifferentiated MSCs and promoting their migration. Progenitor cell recruitment is followed by a gradual increment in osteoblast gene expression. Moreover, CaSO₄ regulates BMP-2-induced MSC migration by differentially activating the PI3K/AKT pathway. Altogether, these results suggest that CaSO₄ scaffolds could have potential applications for bone regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0713-0) contains supplementary material, which is available to authorized users.

Integrin-Linked Kinase Regulates Bone Formation by Controlling Cytoskeletal Organization and Modulating BMP and Wnt Signaling in Osteoprogenitors

Cell-matrix interactions constitute a fundamental aspect of skeletal cell biology and play essential roles in bone homeostasis. These interactions are primarily mediated by transmembrane integrin receptors, which mediate cell adhesion and transduce signals from the extracellular matrix to intracellular responses via various downstream effectors, including integrin-linked kinase (ILK). ILK functions as adaptor protein at focal adhesion sites, linking integrins to the actin cytoskeleton, and has been reported to act as a kinase phosphorylating signaling molecules such as GSK-3β and Akt. Thereby, ILK plays important roles in cellular attachment, motility, proliferation and survival. To assess the in vivo role of ILK signaling in osteoprogenitors and the osteoblast lineage cells descending thereof, we generated conditional knockout mice using the Osx-Cre:GFP driver strain. Mice lacking functional ILK in osterix-expressing cells and their derivatives showed no apparent developmental or growth phenotype, but by 5 weeks of age they displayed a significantly reduced trabecular bone mass, which persisted into adulthood in male mice. Histomorphometry and serum analysis indicated no alterations in osteoclast formation and activity, but provided evidence that osteoblast function was impaired, resulting in reduced bone mineralization and increased accumulation of unmineralized osteoid. In vitro analyses further substantiated that absence of ILK in osteogenic cells was associated with compromised collagen matrix production and mineralization. Mechanistically, we found evidence for both impaired cytoskeletal functioning and reduced signal transduction in osteoblasts lacking ILK. Indeed, loss of ILK in primary osteogenic cells impaired F-actin organization, cellular adhesion, spreading, and migration, indicative of defective coupling of cell-matrix interactions to the cytoskeleton. In addition, BMP/Smad and Wnt/β-catenin signaling was reduced in the absence of ILK. Taken together, these data demonstrate the importance of integrin-mediated cell-matrix interactions and ILK signaling in osteoprogenitors in the control of osteoblast functioning during juvenile bone mass acquisition and adult bone remodeling and homeostasis. © 2017 American Society for Bone and Mineral Research.

Actin cytoskeleton mediates BMP2-Smad signaling via calponin 1 in preosteoblast under simulated microgravity

Microgravity influences the activity of osteoblast, induces actin microfilament disruption and leads to bone loss during spaceflight. Mechanical stress such as gravity, regulates cell function, response and differentiation through dynamic cytoskeleton changes, but the mechanotransduction mechanism remains to be fully elucidated. Previous, we demonstrated actin microfilament mediated osteoblast Cbfa1 responsiveness to BMP2 under simulated microgravity (SMG). Here, we explored a potential molecular and its detailed mechanism of actin cytoskeleton functioning on BMP2-Smad signaling in MC3T3-E1 under SMG. Results showed that the actin microfilament-disrupting agent, cytochalasin B (CB), reduced BMP2-induced activation, translocation of Smad1/5/8 and Runx2 expression. SMG also inhibited BMP2-Smad signaling, which was rescued by actin cytoskeleton stabilizing agent, Jasplakinolide (JAS). Furthermore, we found that siRNA mediated knockdown of calponin 1 (CNN1), an actin binding protein, markedly promoted BMP2-Smad signaling and abolished both inhibition of CB, SMG on BMP2-Smad signaling and the rescue action of JAS. Overexpression of CNN1 inhibited the p-Smad induced by BMP2. Bidirectional Co-IP experiments demonstrated CNN1 could interacted with Smad or p-Smad protein. Furthermore, CB or SMG decreased the phosphorylated CNN1 and increased its interaction with Smad or p-Smad. Combined with the phosphorylation of CNN1 inhibites its actin binding activity, these results indicate that actin cytoskeleton depolymerization inhibites BMP2 signaling via blocking of Smad by dephosphorylated CNN1 in osteoblast cells. Thus, we provide new important insights into the mechanism of mechanotransduction under SMG condition, which probably contribute to bone formation decrease induced by SMG.

Non-Smad Signaling Pathways of the TGF-β Family

Transforming growth factor β (TGF-β) and structurally related factors use several intracellular signaling pathways in addition to Smad signaling to regulate a wide array of cellular functions. These non-Smad signaling pathways are activated directly by ligand-occupied receptors to reinforce, attenuate, or otherwise modulate downstream cellular responses. This review summarizes the current knowledge of the mechanisms by which non-Smad signaling pathways are directly activated in response to ligand binding, how activation of these pathways impinges on Smads and non-Smad targets, and how final cellular responses are affected in response to these noncanonical signaling modes.

Signal mingle: Micropatterns of BMP-2 and fibronectin on soft biopolymeric films regulate myoblast shape and SMAD signaling

In vivo, bone morphogenetic protein 2 (BMP-2) exists both in solution and bound to the extracellular matrix (ECM). While these two modes of presentation are known to influence cell behavior distinctly, their role in the niche microenvironment and their functional relevance in the genesis of a biological response has sparsely been investigated at a cellular level. Here we used the natural affinity of BMP-2 for fibronectin (FN) to engineer cell-sized micropatterns of BMP-2. This technique allowed the simultaneous control of the spatial presentation of fibronectin-bound BMP-2 and cell spreading. These micropatterns induced a specific actin and adhesion organization around the nucleus, and triggered the phosphorylation and nuclear translocation of SMAD1/5/8 in C2C12 myoblasts and mesenchymal stem cells, an early indicator of their osteoblastic trans-differentiation. We found that cell spreading itself potentiated a BMP-2-dependent phosphorylation of SMAD1/5/8. Finally, we demonstrated that FN/BMP-2-mediated early SMAD signaling depended on LIM kinase 2 and ROCK, rather than myosin II activation. Altogether, our results show that FN/BMP-2 micropatterns are a useful tool to study the mechanisms underlying BMP-2-mediated mechanotransduction. More broadly, our approach could be adapted to other combinations of ECM proteins and growth factors, opening an exciting avenue to recreate tissue-specific niches in vitro.

3D bioprinting of GelMA scaffolds triggers mineral deposition by primary human osteoblasts

Due to its relatively low level of antigenicity and high durability, titanium has successfully been used as the major material for biological implants. However, because the typical interface between titanium and tissue precludes adequate transmission of load into the surrounding bone, over time, load-bearing implants tend to loosen and revision surgeries are required. Osseointegration of titanium implants requires presentation of both biological and mechanical cues that promote attachment of and trigger mineral deposition by osteoblasts. While many factors contribute to differentiation, the relative importance of the various cues is unclear. To substantially improve osseointegration of titanium implants, we generated a gelatin methacryloyl (GelMA) scaffold, using an extrusion-based 3D bioprinter, which can be directly printed on and grafted to the titanium implant surface. We demonstrate that this scaffold is able to trigger mineral deposition of both MG63 osteoblasts and primary normal human osteoblasts in the absence of any exogenous osteogenic factors. Films of the same formulation failed to promote mineral deposition suggesting that the three dimensional scaffold was able to tip the balance in favor of differentiation despite other potentially unfavorable differentiation cues of the material. We further show that these GelMA lattices can be directly grafted to titanium alloy and are secure in vitro over a period of seven weeks. When grafted within a groove system, the GelMA hydrogel is protected from shearing forces in a marrow implantation model. This prepares the way for osteogenic coatings to be directly manufactured on the implant surface and packaged for surgery.

Class I PI-3-Kinase Signaling Is Critical for Bone Formation Through Regulation of SMAD1 Activity in Osteoblasts

Bone formation and homeostasis is carried out by osteoblasts, whose differentiation and activity are regulated by osteogenic signaling networks. A central mediator of these inputs is the lipid kinase phosphatidylinositol 3-kinase (PI3K). However, at present, there are no data on the specific role of distinct class IA PI3K isoforms in bone biology. Here, we performed osteoblast-specific deletion in mice to show that both p110α and p110β isoforms are required for survival and differentiation and function of osteoblasts and thereby control bone formation and postnatal homeostasis. Impaired osteogenesis arises from increased GSK3 activity and a depletion of SMAD1 protein levels in PI3K-deficient osteoblasts. Accordingly, pharmacological inhibition of GSK3 activity or ectopic expression of SMAD1 or SMAD5 normalizes bone morphogenetic protein (BMP) transduction and osteoblast differentiation. Together, these results identify the PI3K-GSK3-SMAD1 axis as a central node integrating multiple signaling networks that govern bone formation and homeostasis. © 2016 American Society for Bone and Mineral Research.

p38 MAPK Signaling in Osteoblast Differentiation

The skeleton is a highly dynamic tissue whose structure relies on the balance between bone deposition and resorption. This equilibrium, which depends on osteoblast and osteoclast functions, is controlled by multiple factors that can be modulated post-translationally. Some of the modulators are Mitogen-activated kinases (MAPKs), whose role has been studied in vivo and in vitro. p38-MAPK modifies the transactivation ability of some key transcription factors in chondrocytes, osteoblasts and osteoclasts, which affects their differentiation and function. Several commercially available inhibitors have helped to determine p38 action on these processes. Although it is frequently mentioned in the literature, this chemical approach is not always as accurate as it should be. Conditional knockouts are a useful genetic tool that could unravel the role of p38 in shaping the skeleton. In this review, we will summarize the state of the art on p38 activity during osteoblast differentiation and function, and emphasize the triggers of this MAPK.

β3 integrin-mediated spreading induced by matrix-bound BMP-2 controls Smad signaling in a stiffness-independent manner

Matrix-bound BMP-2 is sufficient to induce β3 integrin–dependent, Cdc42/Src/FAK/ILK-mediated cell spreading by overriding the stiffness response through actin and adhesion site dynamics, showing BMP receptors and integrins work together to control signaling and tensional homeostasis, thereby coupling cell adhesion and fate commitment.

Understanding how cells integrate multiple signaling pathways to achieve specific cell differentiation is a challenging question in cell biology. We have explored the physiological presentation of BMP-2 by using a biomaterial that harbors tunable mechanical properties to promote localized BMP-2 signaling. We show that matrix-bound BMP-2 is sufficient to induce β3 integrin–dependent C2C12 cell spreading by overriding the soft signal of the biomaterial and impacting actin organization and adhesion site dynamics. In turn, αvβ3 integrin is required to mediate BMP-2–induced Smad signaling through a Cdc42–Src–FAK–ILK pathway. β3 integrin regulates a multistep process to control first BMP-2 receptor activity and second the inhibitory role of GSK3 on Smad signaling. Overall, our results show that BMP receptors and β3 integrin work together to control Smad signaling and tensional homeostasis, thereby coupling cell adhesion and fate commitment, two fundamental aspects of developmental biology and regenerative medicine.

BMP2 rescues deficient cell migration in Tgfbr3(-/-) epicardial cells and requires Src kinase

During embryogenesis, the epicardium undergoes proliferation, migration, and differentiation into several cardiac cell types which contribute to the coronary vessels. The type III transforming growth factor-β receptor (TGFβR3) is required for epicardial cell invasion and development of coronary vasculature in vivo. Bone Morphogenic Protein-2 (BMP2) is a driver of epicardial cell migration. Utilizing a primary epicardial cell line derived from Tgfbr3(+/+) and Tgfbr3(-/-) mouse embryos, we show that Tgfbr3(-/-) epicardial cells are deficient in BMP2 mRNA expression. Tgfbr3(-/-) epicardial cells are deficient in 2-dimensional migration relative to Tgfbr3(+/+) cells; BMP2 induces cellular migration to Tgfbr3(+/+) levels without affecting proliferation. We further demonstrate that Src kinase activity is required for BMP2 driven Tgfbr3(-/-) migration. BMP2 also requires Src for filamentous actin polymerization in Tgfbr3(-/-) epicardial cells. Taken together, our data identifies a novel pathway in epicardial cell migration required for development of the coronary vessels.

Tuning cellular responses to BMP-2 with material surfaces

Bone morphogenetic protein 2 (BMP-2) has been known for decades as a strong osteoinductive factor and for clinical applications is combined solely with collagen as carrier material. The growing concerns regarding side effects and the importance of BMP-2 in several developmental and physiological processes have raised the need to improve the design of materials by controlling BMP-2 presentation. Inspired by the natural cell environment, new material surfaces have been engineered and tailored to provide both physical and chemical cues that regulate BMP-2 activity. Here we describe surfaces designed to present BMP-2 to cells in a spatially and temporally controlled manner. This is achieved by trapping BMP-2 using physicochemical interactions, either covalently grafted or combined with other extracellular matrix components. In the near future, we anticipate that material science and biology will integrate and further develop tools for in vitro studies and potentially bring some of them toward in vivo applications.

Apical constriction and epithelial invagination are regulated by BMP activity

Epithelial invagination is a morphological process in which flat cell sheets transform into three-dimensional structures through bending of the tissue. It is accompanied by apical constriction, in which the apical cell surface is reduced in relation to the basal cell surface. Although much is known about the intra-cellular molecular machinery driving apical constriction and epithelial invagination, information of how extra-cellular signals affect these processes remains insufficient. In this study we have established several in vivo assays of placodal invagination to explore whether the external signal BMP regulates processes connected to epithelial invagination. By inhibiting BMP activity in prospective cranial placodes, we provide evidence that BMP signals are required for RhoA and F-actin rearrangements, apical constriction, cell elongation and epithelial invagination. The failure of placode invagination after BMP inhibition appears to be a direct consequence of disrupted apical accumulation of RhoA and F-actin, rather than changes in cell death or proliferation. In addition, our results show that epithelial invagination and acquisition of placode-specific identities are two distinct and separable developmental processes. In summary, our results provide evidence that BMP signals promote epithelial invagination by acting upstream of the intracellular molecular machinery that drives apical constriction and cell elongation.

Summary: We describe a novel role for BMP activity in promoting a direct and cell type-independent mechanism for apical constriction, cell elongation and epithelial invagination, separate from acquisition of placode-specific identities.

The lymphocyte secretome from young adults enhances skeletal muscle proliferation and migration, but effects are attenuated in the secretome of older adults

Older people experience skeletal muscle wasting, in part due to impaired proliferative capacity of quiescent skeletal muscle satellite cells which can be reversed by exposure to young blood. To investigate the role of immune cells in muscle regeneration, we isolated lymphocytes from whole blood of young and older healthy volunteers and cultured them with, or without, anti-CD3/CD28 activators to induce release of cytokines, interleukins, and growth factors into the media. The secreted proteins were collected to prepare a conditioned media, which was subsequently used to culture C2C12 myoblasts. The conditioned media from the activated young lymphocytes increased the rate of proliferation of myoblasts by around threefold (P < 0.005) and caused an approximate fourfold (P < 0.005) increase in migration compared with nonactivated lymphocyte control media. These responses were characterized by minimal myotube formation (2%), low fusion index (5%), low myosin heavy chain content, and substantial migration. In contrast, myoblasts treated with conditioned media from activated old lymphocytes exhibited a high degree of differentiation, and multi-nucleated myotube formation that was comparable to control conditions, thus showing no effect on proliferation or migration of myoblasts. These results indicate that secreted proteins from lymphocytes of young people enhance the muscle cell proliferation and migration, whereas secreted proteins from lymphocytes of older people may contribute to the attenuated skeletal muscle satellite cell proliferation and migration.