Regulation of Notch signaling genes during BMP2-induced differentiation of osteoblast precursor cells

Osteobiologies for Spinal Fusion from Biological Mechanisms to Clinical Applications: A Narrative Review

Degenerative lumbar spinal disease (DLSD), including spondylolisthesis and spinal stenosis, is increasing due to the aging population. Along with the disease severity, lumbar interbody fusion (LIF) is a mainstay of surgical treatment through decompression, the restoration of intervertebral heights, and the stabilization of motion segments. Currently, pseudoarthrosis after LIF is an important and unsolved issue, which is closely related to osteobiologies. Of the many signaling pathways, the bone morphogenetic protein (BMP) signaling pathway contributes to osteoblast differentiation, which is generally regulated by SMAD proteins as common in the TGF-β superfamily. BMP-2 and -4 are also inter-connected with Wnt/β-catenin, Notch, and FGF signaling pathways. With the potent potential for osteoinduction in BMP-2 and -4, the combination of allogenous bone and recombinant human BMPs (rhBMPs) is currently an ideal fusion material, which has equalized or improved fusion rates compared to traditional materials. However, safety issues in the dosage of BMP remain, so overcoming current limitations will provide significant advancement in spine surgery. In the future, translational research and the application of clinical study will be important to overcome the current limitations of spinal surgery.

Insights into bone morphogenetic proteins in cardiovascular diseases

Bone morphogenetic proteins (BMPs) are secretory proteins belonging to the transforming growth factor-β (TGF-β) superfamily. These proteins play important roles in embryogenesis, bone morphogenesis, blood vessel remodeling and the development of various organs. In recent years, as research has progressed, BMPs have been found to be closely related to cardiovascular diseases, especially atherosclerosis, vascular calcification, cardiac remodeling, pulmonary arterial hypertension (PAH) and hereditary hemorrhagic telangiectasia (HHT). In this review, we summarized the potential roles and related mechanisms of the BMP family in the cardiovascular system and focused on atherosclerosis and PAH.

Epidrugs: novel epigenetic regulators that open a new window for targeting osteoblast differentiation

Efficient osteogenic differentiation of mesenchymal stem cells (MSCs) is a critical step in the treatment of bone defects and skeletal disorders, which present challenges for cell-based therapy and regenerative medicine. Thus, it is necessary to understand the regulatory agents involved in osteogenesis. Epigenetic mechanisms are considered to be the primary mediators that regulate gene expression during MSC differentiation. In recent years, epigenetic enzyme inhibitors have been used as epidrugs in cancer therapy. A number of studies mentioned the role of epigenetic inhibitors in the regulation of gene expression patterns related to osteogenic differentiation. This review attempts to provide an overview of the key regulatory agents of osteogenesis: transcription factors, signaling pathways, and, especially, epigenetic mechanisms. In addition, we propose to introduce epigenetic enzyme inhibitors (epidrugs) and their applications as future therapeutic approaches for bone defect regeneration.

Trim33 (Tif1γ) is not required for skeletal muscle development or regeneration but suppresses cholecystokinin expression

The expression of Trim33 (Tif1γ) increases in skeletal muscles during regeneration and decreases upon maturation. Although Trim33 is required for the normal development of other tissues, its role in skeletal muscle is unknown. The current study aimed to define the role of Trim33 in muscle development and regeneration. We generated mice with muscle-specific conditional knockout of Trim33 by combining floxed Trim33 and Cre recombinase under the Pax7 promoter. Muscle regeneration was induced by injuring mouse muscles with cardiotoxin. We studied the consequences of Trim33 knockdown on viability, body weight, skeletal muscle histology, muscle regeneration, and gene expression. We also studied the effect of Trim33 silencing in satellite cells and the C2C12 mouse muscle cell line. Although Trim33 knockdown mice weighed less than control mice, their skeletal muscles were histologically unremarkable and regenerated normally following injury. Unexpectedly, RNAseq analysis revealed dramatically increased expression of cholecystokinin (CCK) in regenerating muscle from Trim33 knockout mice, satellite cells from Trim33 knockout mice, and C2C12 cells treated with Trim33 siRNA. Trim33 knockdown had no demonstrable effect on muscle differentiation or regeneration. However, Trim33 knockdown induced CCK expression in muscle, suggesting that suppression of CCK expression requires Trim33.

The accelerated effect of recombinant human bone morphogenetic protein 2 delivered by β-tricalcium phosphate on tendon-to-bone repair process in rabbit models

BACKGROUND

Bone morphogenetic protein 2 (BMP-2) plays an important role in the tendon-to-bone repair process. However, there is no previous literature on acceleration of the tendon-to-bone repair process by BMP-2 delivered by β-tricalcium phosphate (β-TCP). The aim of this study was to investigate the accelerated effect of recombinant human BMP-2 (rhBMP-2) delivered by β-TCP on the tendon-to-bone repair process.

METHODS

The infraspinatus tendon of elderly female Japanese white rabbits was detached from its insertion site on the humerus. A bone tunnel (4.2 mm) was created at the original insertion site of the tendon, which was repaired using the McLaughlin procedure after filling in β-TCP (porosity 75%) without BMP-2 (control group) or with 10 µg rhBMP-2 (BMP group). The rabbits were sacrificed at the second, fourth, and eighth weeks after surgery for histologic analysis and biomechanical testing. We also evaluated the maturity of the tendon-to-bone junction using the tendon-to-bone maturity score.

RESULTS

Histologic analysis revealed no significant difference between the groups at 2 and 8 weeks but a more abundant organized fibrocartilage at the tendon-to-bone junction in the BMP group at 4 weeks. The tendon-to-bone maturity score improved sequentially. The interface of the BMP group at 4 weeks had significantly improved biomechanical properties than that of the control group.

CONCLUSION

The tendon-to-bone repair process was facilitated by the use of rhBMP-2 delivered by β-TCP at 4 weeks.

Mesenchymal Chondrosarcoma: a Review with Emphasis on its Fusion-Driven Biology

Mesenchymal chondrosarcoma is a rare but deadly form of chondrosarcoma that typically affects adolescents and young adults. While curative intent is possible for patients with localized disease, few options exist for patients in the unresectable/metastatic setting. Thus, it is imperative to understand the fusion-driven biology of this rare malignant neoplasm so as to lead to the future development of better therapeutics for this disease. This manuscript will briefly review the clinical and pathologic features of mesenchymal chondrosarcoma followed by an appraisal of existing data linked to the fusions, HEY1-NCOA2 and IRF2BP2-CDX1, and the associated downstream pathways.

Calcific Aortic Valve Disease: a Developmental Biology Perspective

PURPOSE OF REVIEW

This review aims to highlight the past and more current literature related to the multifaceted pathogenic programs that contribute to calcific aortic valve disease (CAVD) with a focus on the contribution of developmental programs.

RECENT FINDINGS

Calcification of the aortic valve is an active process characterized by calcific nodule formation on the aortic surface leading to a less supple and more stiffened cusp, thereby limiting movement and causing clinical stenosis. The mechanisms underlying these pathogenic changes are largely unknown, but emerging studies have suggested that signaling pathways common to valvulogenesis and bone development play significant roles and include Transforming Growth Factor-β (TGF-β), bone morphogenetic protein (BMP), Wnt, Notch, and Sox9. This comprehensive review of the literature highlights the complex nature of CAVD but concurrently identifies key regulators that can be targeted in the development of mechanistic-based therapies beyond surgical intervention to improve patient outcome.

ALK2/ALK3-BMPR2/ACVR2A Mediate BMP2-Induced Downregulation of Pentraxin 3 Expression in Human Granulosa-Lutein Cells

Bone morphogenetic protein 2 (BMP2) belongs to the transforming growth factor-β superfamily and plays a critical role in regulating ovarian follicle function. Currently, the role of BMP2 during cumulus expansion remains to be determined. The aim of this study was to investigate the effect of BMP2 on the regulation of pentraxin 3 (PTX3) expression (the major component of cumulus expansion) and the underlying mechanisms in human granulosa-lutein (hGL) cells. Both primary and immortalized hGL cells were used as research models. Our results showed that treatment with BMP2 significantly suppressed the basal and luteinizing hormone-induced upregulation of PTX3. In addition, BMP2 stimulated the phosphorylation of SMAD1/5/8, and this effect was abolished by the addition of BMP type I receptor inhibitors, dorsomorphin homolog 1, and dorsomorphin but not SB431542. Moreover, the knockdown of activin receptorlike kinase 2/3 or BMP receptor type II/activin receptor type IIB receptors completely reversed the BMP2-induced phosphorylation of SMAD1/5/8 and restored PTX3 expression. Similarly, the knockdown of SMAD4 completely reversed the suppressive effect of BMP2 on the expression of PTX3. These results improve our understanding of the molecular mechanisms of BMP2 signaling. Our findings suggest that BMP2 may be involved in the regulation of cumulus expansion during the periovulatory stage.

Notch pathway is active during osteogenic differentiation of human bone marrow mesenchymal stem cells induced by pulsed electromagnetic fields

Pulsed electromagnetic fields (PEMFs) have been used to treat bone diseases, particularly nonunion healing. Although it is known that PEMFs promote the osteogenic differentiation of human mesenchymal stem cells (hMSCs), to date PEMF molecular mechanisms remain not clearly elucidated. The Notch signalling is a highly conserved pathway that regulates cell fate decisions and skeletal development. The aim of this study was to investigate if the known PEMF-induced osteogenic effects may involve the modulation of the Notch pathway. To this purpose, during in vitro osteogenic differentiation of bone marrow hMSCs in the absence and in the presence of PEMFs, osteogenic markers (alkaline phosphatase activity, osteocalcin and matrix mineralization), the messenger ribonucleic acid expression of osteogenic transcription factors (Runx2, Dlx5, Osterix) as well as of Notch receptors (Notch1-4), their ligands (Jagged1, Dll1 and Dll4) and nuclear target genes (Hes1, Hes5, Hey1, Hey2) were investigated. PEMFs stimulated all osteogenic markers and increased the expression of Notch4, Dll4, Hey1, Hes1 and Hes5 in osteogenic medium compared to control. In the presence of DAPT and SAHM1, used as Notch pathway inhibitors, the expression of the osteogenic markers, including Runx2, Dlx5, Osterix, as well as Hes1 and Hes5 were significantly inhibited, both in unexposed and PEMF-exposed hMSCs. These results suggest that activation of Notch pathway is required for PEMFs-stimulated osteogenic differentiation. These new findings may be useful to improve autologous cell-based regeneration of bone defects in orthopaedics.

Notch signaling pathway promotes osteogenic differentiation of mesenchymal stem cells by enhancing BMP9/Smad signaling

Notch is an important pathway in that it regulates cell-to-cell signal transduction, which plays an essential role in skeletal remodeling. Bone morphogenetic protein (BMP)9 has been regarded as one of the most efficient BMPs by which to induce osteogenic differentiation in mesenchymal stem cells (MSCs). Understanding the interaction between Notch and BMP9 signaling is a critical issue for optimizing the application of MSCs and BMPs in bone tissue engineering. In the present study, we investigated the role of Notch signaling in the BMP9‑induced osteogenic differentiation of MSCs. Our data demonstrated that Notch signaling obviously enhanced BMP9‑induced osteogenic differentiation in MSCs in vitro and in vivo. Notch signaling augmented the activity of BMP9‑induced BMP/Smad signaling and increased the gene expression of essential osteogenic factors induced by BMP9 in MSCs, such as runt‑related transcription factor 2 (Runx2), type I collagen (Colla1) and inhibitor of differentiation (Id)1. We also found that Notch signaling promoted the expression of activin‑like kinase 2 (ALK2) induced by BMP9, and the inhibitory effect of dnALK2 on BMP9‑induced osteogenic differentiation was rescued by constitutive overexpression of Delta‑like 1 (DLL1). Notch signaling also exhibited an apparent effect on the proliferation of mouse embryo fibroblasts (MEFs) during BMP9‑induced osteogenic differentiation. These results indicate that Notch plays a significant role in mediating BMP9‑induced osteogenic differentiation in MSCs, which may be partly regulated by upregulation of the expression of ALK2.

Signaling Cross Talk between TGF-β/Smad and Other Signaling Pathways

Cytokines of the transforming growth factor β (TGF-β) family, including TGF-βs, bone morphogenic proteins (BMPs), activins, and Nodal, play crucial roles in embryonic development and adult tissue homeostasis by regulating cell proliferation, survival, and differentiation, as well as stem-cell self-renewal and lineage-specific differentiation. Smad proteins are critical downstream mediators of these signaling activities. In addition to regulating the transcription of direct target genes of TGF-β, BMP, activin, or Nodal, Smad proteins also participate in extensive cross talk with other signaling pathways, often in a cell-type- or developmental stage-specific manner. These combinatorial signals often produce context-, time-, and location-dependent biological outcomes that are critical for development. This review discusses recent progress in our understanding of the cross talk between Smad proteins and signaling pathways of Wnt, Notch, Hippo, Hedgehog (Hh), mitogen-activated protein (MAP), kinase, phosphoinositide 3-kinase (PI3K)-Akt, nuclear factor κB (NF-κB), and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

Signaling Cross Talk between TGF-β/Smad and Other Signaling Pathways

Cytokines of the transforming growth factor β (TGF-β) family, including TGF-βs, bone morphogenic proteins (BMPs), activins, and Nodal, play crucial roles in embryonic development and adult tissue homeostasis by regulating cell proliferation, survival, and differentiation, as well as stem-cell self-renewal and lineage-specific differentiation. Smad proteins are critical downstream mediators of these signaling activities. In addition to regulating the transcription of direct target genes of TGF-β, BMP, activin, or Nodal, Smad proteins also participate in extensive cross talk with other signaling pathways, often in a cell-type- or developmental stage-specific manner. These combinatorial signals often produce context-, time-, and location-dependent biological outcomes that are critical for development. This review discusses recent progress in our understanding of the cross talk between Smad proteins and signaling pathways of Wnt, Notch, Hippo, Hedgehog (Hh), mitogen-activated protein (MAP), kinase, phosphoinositide 3-kinase (PI3K)-Akt, nuclear factor κB (NF-κB), and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

TGF-β and BMP signaling in osteoblast, skeletal development, and bone formation, homeostasis and disease

Transforming growth factor-beta (TGF-β) and bone morphogenic protein (BMP) signaling has fundamental roles in both embryonic skeletal development and postnatal bone homeostasis. TGF-βs and BMPs, acting on a tetrameric receptor complex, transduce signals to both the canonical Smad-dependent signaling pathway (that is, TGF-β/BMP ligands, receptors, and Smads) and the non-canonical-Smad-independent signaling pathway (that is, p38 mitogen-activated protein kinase/p38 MAPK) to regulate mesenchymal stem cell differentiation during skeletal development, bone formation and bone homeostasis. Both the Smad and p38 MAPK signaling pathways converge at transcription factors, for example, Runx2 to promote osteoblast differentiation and chondrocyte differentiation from mesenchymal precursor cells. TGF-β and BMP signaling is controlled by multiple factors, including the ubiquitin–proteasome system, epigenetic factors, and microRNA. Dysregulated TGF-β and BMP signaling result in a number of bone disorders in humans. Knockout or mutation of TGF-β and BMP signaling-related genes in mice leads to bone abnormalities of varying severity, which enable a better understanding of TGF-β/BMP signaling in bone and the signaling networks underlying osteoblast differentiation and bone formation. There is also crosstalk between TGF-β/BMP signaling and several critical cytokines’ signaling pathways (for example, Wnt, Hedgehog, Notch, PTHrP, and FGF) to coordinate osteogenesis, skeletal development, and bone homeostasis. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in osteoblast differentiation, chondrocyte differentiation, skeletal development, cartilage formation, bone formation, bone homeostasis, and related human bone diseases caused by the disruption of TGF-β/BMP signaling.

Characterization of Notch Signaling During Osteogenic Differentiation in Human Osteosarcoma Cell Line MG63

Osteogenic differentiation is a multi-step process controlled by a complex molecular framework. Notch is an evolutionarily conserved intercellular signaling pathway playing a prominent role in cell fate and differentiation, although the mechanisms by which this pathway regulates osteogenesis remain controversial. This study aimed to investigate, in vitro, the involvement of Notch pathway during all the developmental stages of osteogenic differentiation in human osteosarcoma cell line MG63. Cells were cultured in basal condition (control) and in osteoinductive medium (OM). Notch inhibitors were also added in OM to block Notch pathway. During osteogenic differentiation, early (alkaline phosphatase activity and collagen type I) and late osteogenic markers (osteocalcin levels and matrix mineralization), as well as the gene expression of the main osteogenic transcription factors (Runx2, Osterix, and Dlx5) increased. Time dependent changes in the expression of specific Notch receptors were identified in OM versus control with a significant reduction in the expression of Notch1 and Notch3 receptors in the early phase of differentiation, and an increase of Notch2 and Notch4 receptors in the late phase. Among Notch nuclear target genes, Hey1 expression was significantly higher in OM than control, while Hes5 expression decreased. Osteogenic markers were reduced and Hey1 was significantly inhibited by Notch inhibitors, suggesting a role for Notch through the canonical pathway. In conclusion, Notch pathway might be involved with a dual role in osteogenesis of MG63, through the activation of Notch2, Notch4, and Hey1, inducing osteoblast differentiation and the depression of Notch1, Notch3, and Hes5, maintaining an undifferentiated status. J. Cell. Physiol. 231: 2652-2663, 2016. © 2016 Wiley Periodicals, Inc.

Targeting BMP signalling in cardiovascular disease and anaemia

Bone morphogenetic proteins (BMPs) and their receptors, known to be essential regulators of embryonic patterning and organogenesis, are also critical for the regulation of cardiovascular structure and function. In addition to their contributions to syndromic disorders including heart and vascular development, BMP signalling is increasingly recognized for its influence on endocrine-like functions in postnatal cardiovascular and metabolic homeostasis. In this Review, we discuss several critical and novel aspects of BMP signalling in cardiovascular health and disease, which highlight the cell-specific and context-specific nature of BMP signalling. Based on advancing knowledge of the physiological roles and regulation of BMP signalling, we indicate opportunities for therapeutic intervention in a range of cardiovascular conditions including atherosclerosis and pulmonary arterial hypertension, as well as for anaemia of inflammation. Depending on the context and the repertoire of ligands and receptors involved in specific disease processes, the selective inhibition or enhancement of signalling via particular BMP ligands (such as in atherosclerosis and pulmonary arterial hypertension, respectively) might be beneficial. The development of selective small molecule antagonists of BMP receptors, and the identification of ligands selective for BMP receptor complexes expressed in the vasculature provide the most immediate opportunities for new therapies.

Evaluating Osteogenic Potential of Ligamentum Flavum Cells Cultivated in Photoresponsive Hydrogel that Incorporates Bone Morphogenetic Protein-2 for Spinal Fusion

Regenerative medicine is increasingly important in clinical practice. Ligamentum flava (LF) are typically removed during spine-related surgeries. LF may be a source of cells for spinal fusion that is conducted using tissue engineering techniques. In this investigation, LF cells of rabbits were isolated and then characterized by flow cytometry, morphological observation, and immunofluorescence staining. The LF cells were also cultivated in polyethylene (glycol) diacrylate (PEGDA) hydrogels that incorporated bone morphogenetic protein-2 (BMP-2) growth factor, to evaluate their proliferation and secretion of ECM and differentiation in vitro. The experimental results thus obtained that the proliferation, ECM secretion, and differentiation of the PEGDA-BMP-2 group exceeded those of the PEGDA group during the period of cultivation. The mineralization and histological staining results differed similarly. A nude mice model was utilized to prove that LF cells on hydrogels could undergo osteogenic differentiation in vivo. These experimental results also revealed that the PEGDA-BMP-2 group had better osteogenic effects than the PEGDA group following a 12 weeks after transplantation. According to all of these experimental results, LF cells are a source of cells for spinal fusion and PEGDA-BMP-2 hydrogel is a candidate biomaterial for spinal fusion by tissue engineering.

Bone morphogenetic protein 2 promotes primordial follicle formation in the ovary

Primordial follicles (PF) are formed when somatic cells differentiate into flattened pregranulosa cells, invaginate into the oocyte nests and encircle individual oocytes. We hypothesize that BMP2 regulates PF formation by promoting the transition of germ cells into oocytes and somatic cells into pregranulosa cells. E15 hamster ovaries were cultured for 8 days corresponding to postnatal day 8 (P8) in vivo, with or without BMP2, and the formation of PF was examined. BMP2 was expressed in the oocytes as well as ovarian somatic cells during development. BMP2 exposure for the first two days or the last two days or the entire 8 days of culture led to increase in PF formation suggesting that BMP2 affected both germ cell transition and somatic cell differentiation. Whereas an ALK2/3 inhibitor completely blocked BMP2-induced PF formation, an ALK2-specific inhibitor was partially effective, suggesting that BMP2 affected PF formation via both ALK2 and ALK3. BMP2 also reduced apoptosis in vitro. Further, more meiotic oocytes were present in BMP2 exposed ovaries. In summary, the results provide the first evidence that BMP2 regulates primordial follicle formation by promoting germ cell to oocyte transition and somatic cell to pre-granulosa cells formation and it acts via both ALK2 and ALK3.

Hairy/enhancer-of-split related with YRPW motif protein 1 promotes osteosarcoma metastasis via matrix metallopeptidase 9 expression

BACKGROUND

Activation of the Notch pathway has been reported in various types of cancers. However, the role of the hairy/enhancer-of-split related with YRPW motif protein 1 (HEY1) in osteosarcoma is unknown. We examined the function of HEY1 in osteosarcoma.

METHODS

Expression of HEY1 was studied in human osteosarcoma. The effects of HEY1 in osteosarcoma were evaluated in vitro and in a xenograft model. Moreover, we examined the function of matrix metallopeptidase 9 (MMP9) as a downstream effector of HEY1.

RESULTS

HEY1 was upregulated in human osteosarcoma. Knockdown of HEY1 inhibited the invasion of osteosarcoma cell lines. In contrast, the forced expression of HEY1 increased the invasion of mesenchymal stem cell. In addition, lung metastases were significantly inhibited by the knockdown of HEY1. We found that MMP9 was a downstream effector of HEY1 that promotes the invasion of osteosarcoma cells. Knockdown of HEY1 decreased the expression of MMP9. Addition of MMP9 rescued the invasion of osteosarcoma cells that had been rendered less invasive by knockdown of HEY1 expression.

CONCLUSIONS

Our findings suggested that HEY1 augmented the metastasis of osteosarcoma via upregulation of MMP9 expression. Therefore, inhibition of HEY1 may be a novel therapeutic strategy for preventing osteosarcoma metastasis.

Hey bHLH transcription factors

Hey bHLH transcription factors are direct targets of canonical Notch signaling. The three mammalian Hey proteins are closely related to Hes proteins and they primarily repress target genes by either directly binding to core promoters or by inhibiting other transcriptional activators. Individual candidate gene approaches and systematic screens identified a number of Hey target genes, which often encode other transcription factors involved in various developmental processes. Here, we review data on interaction partners and target genes and conclude with a model for Hey target gene regulation. Furthermore, we discuss how expression of Hey proteins affects processes like cell fate decisions and differentiation, e.g., in cardiovascular, skeletal, and neural development or oncogenesis and how this relates to the observed developmental defects and phenotypes observed in various knockout mice.

Hesr2 knockout mice develop aortic valve disease with advancing age

OBJECTIVE

Acquired heart diseases, such as valve disease, are major causes of human morbidity and mortality. However, the pathological mechanisms underlying these diseases are largely unknown. Our aim is to identify the role of the hairy and enhancer of split-related (Hesr)-2 gene in the adult heart.

METHODS AND RESULTS

Echocardiography detected heart dysfunctions indicative of aortic valve anomalies, stenosis, and regurgitation, in ≈59% of >12-month-old Hesr2 knockout survivor mice. Morphological and histological analyses revealed thickened semilunar valves with increased fibrotic areas, indicating that sclerotic degeneration of valves is the main cause of aortic valve disease. The expression of osteogenic genes, such as osteopontin and sclerostin, were upregulated in the mutants, and the overexpression of sclerostin in endothelial cells resulted in thickened semilunar valves with increased fibrotic areas, similar to that seen in the Hesr2 knockout mice, suggesting that Hesr2 can regulate osteogenic gene expression in valves. Reduced left ventricular function, which may be caused by increased ventricular interstitial fibrosis, and enlarged myocardial cell size without ventricular wall thickening were found in both aortic valve stenosis/regurgitation-positive (33%) and aortic valve stenosis/regurgitation-negative (38%) subpopulations in 12-month-old survivor mice. Dilated left ventricular internal dimensions were specifically detected in the aortic valve stenosis/regurgitation-positive subpopulation, thus suggesting that the degeneration of cardiomyocytes is influenced by irregular hemodynamics.

CONCLUSIONS

These data revealed that survivor mice lacking the Hesr2 gene exhibit fibrosis in the aortic valve and ventricle in adulthood, thus suggesting that Hesr2 plays an important role in maintaining the homeostasis of the aortic valve and ventricle.

The transcriptional repressor activity of ASYMMETRIC LEAVES1 is inhibited by direct interaction with calmodulin in Arabidopsis

Calmodulin (CaM), a key Ca2+ sensor, regulates diverse cellular processes by modulating the activity of a variety of enzymes and proteins. However, little is known about the biological function of CaM in plant development. In this study, an ASYMMETRIC LEAVES1 (AS1) transcription factor was isolated as a CaM-binding protein. AS1 contains two putative CaM-binding domains (CaMBDs) at the N-terminus. Using domain mapping analysis, both predicted domains were identified as authentic Ca2+ -dependent CaMBDs. We identified three hydrophobic amino acid residues for CaM binding, Trp49 in CaMBDI, and Trp81 and Phe103 in CaMBDII. The interactions of AS1 with CaM were verified in yeast and plant cells. Based on electrophoretic mobility shift assays, CaM inhibited the DNA-binding activity of the AS1/AS2 complex to two cis-regulatory motifs in the KNAT1 promoter. Furthermore, CaM relieved the suppression of KNAT1 transcription by AS1 not only in transient expression assays of protoplasts but also by the overexpression of a CaM-binding negative form of AS1 in as1 mutant plant. Our study suggests that CaM, a calcium sensor, can be involved in the transcriptional control of meristem cell-specific genes by the inhibition of AS1 under the condition of higher levels of Ca2+ in plants.

Acetylcholine induces mesenchymal stem cell migration via Ca2+ /PKC/ERK1/2 signal pathway

Acetylcholine (ACh) plays an important role in neural and non-neural function, but its role in mesenchymal stem cell (MSC) migration remains to be determined. In the present study, we have found that ACh induces MSC migration via muscarinic acetylcholine receptors (mAChRs). Among several mAChRs, MSCs express mAChR subtype 1 (m1AChR). ACh induces MSC migration via interaction with mAChR1. MEK1/2 inhibitor PD98059 blocks ERK1/2 phosphorylation while partially inhibiting the ACh-induced MSC migration. InsP3Rs inhibitor 2-APB that inhibits MAPK/ERK phosphorylation completely blocks ACh-mediated MSC migration. Interestingly, intracellular Ca(2+) ATPase-specific inhibitor thapsigargin also completely blocks ACh-induced MSC migration through the depletion of intracellular Ca(2+) storage. PKCα or PKCβ inhibitor or their siRNAs only partially inhibit ACh-induced MSC migration, but PKC-ζ siRNA completely inhibits ACh-induced MSC migration via blocking ERK1/2 phosphorylation. These results indicate that ACh induces MSC migration via Ca(2+), PKC, and ERK1/2 signal pathways.

BMPs are mediators in tissue crosstalk of the regenerating musculoskeletal system

The musculoskeletal system is a tight network of many tissues. Coordinated interplay at a biochemical level between tissues is essential for development and repair. Traumatic injury usually affects several tissues and represents a large challenge in clinical settings. The current demand for potent growth factors in such applications thus accompanies the keen interest in molecular mechanisms and orchestration of tissue formation. Of special interest are multitasking growth factors that act as signals in a variety of cell types, both in a paracrine and in an autocrine manner, thereby inducing cell differentiation and coordinating not only tissue assembly at specific sites but also maturation and homeostasis. We concentrate here on bone morphogenetic proteins (BMPs), which are important crosstalk mediators known for their irreplaceable roles in vertebrate development. The molecular crosstalk during embryonic musculoskeletal tissue formation is recapitulated in adult repair. BMPs act at different levels from the initiation to maturation of newly formed tissue. Interestingly, this is influenced by the spatiotemporal expression of different BMPs, their receptors and co-factors at the site of repair. Thus, the regenerative potential of BMPs needs to be evaluated in the context of highly connected tissues such as muscle and bone and might indeed be different in more poorly connected tissues such as cartilage. This highlights the need for an understanding of BMP signaling across tissues in order to eventually improve BMP regenerative potential in clinical applications. In this review, the distinct members of the BMP family and their individual contribution to musculoskeletal tissue repair are summarized by focusing on their paracrine and autocrine functions.

TGF-β and BMP signaling in osteoblast differentiation and bone formation

Transforming growth factor-beta (TGF-β)/bone morphogenic protein (BMP) signaling is involved in a vast majority of cellular processes and is fundamentally important throughout life. TGF-β/BMPs have widely recognized roles in bone formation during mammalian development and exhibit versatile regulatory functions in the body. Signaling transduction by TGF-β/BMPs is specifically through both canonical Smad-dependent pathways (TGF-β/BMP ligands, receptors and Smads) and non-canonical Smad-independent signaling pathway (e.g. p38 mitogen-activated protein kinase pathway, MAPK). Following TGF-β/BMP induction, both the Smad and p38 MAPK pathways converge at the Runx2 gene to control mesenchymal precursor cell differentiation. The coordinated activity of Runx2 and TGF-β/BMP-activated Smads is critical for formation of the skeleton. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of TGF-β/BMP signaling in bone and in the signaling networks underlying osteoblast differentiation and bone formation. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in bone from studies of genetic mouse models and human diseases caused by the disruption of TGF-β/BMP signaling. This review also highlights the different modes of cross-talk between TGF-β/BMP signaling and the signaling pathways of MAPK, Wnt, Hedgehog, Notch, and FGF in osteoblast differentiation and bone formation.

Analysis of BMP4 and BMP7 signaling in breast cancer cells unveils time-dependent transcription patterns and highlights a common synexpression group of genes

Background

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily of growth factors. They are known for their roles in regulation of osteogenesis and developmental processes and, in recent years, evidence has accumulated of their crucial functions in tumor biology. BMP4 and BMP7, in particular, have been implicated in breast cancer. However, little is known about BMP target genes in the context of tumor. We explored the effects of BMP4 and BMP7 treatment on global gene transcription in seven breast cancer cell lines during a 6-point time series, using a whole-genome oligo microarray. Data analysis included hierarchical clustering of differentially expressed genes, gene ontology enrichment analyses and model based clustering of temporal data.

Results

Both ligands had a strong effect on gene expression, although the response to BMP4 treatment was more pronounced. The cellular functions most strongly affected by BMP signaling were regulation of transcription and development. The observed transcriptional response, as well as its functional outcome, followed a temporal sequence, with regulation of gene expression and signal transduction leading to changes in metabolism and cell proliferation. Hierarchical clustering revealed distinct differences in the response of individual cell lines to BMPs, but also highlighted a synexpression group of genes for both ligands. Interestingly, the majority of the genes within these synexpression groups were shared by the two ligands, probably representing the core molecular responses common to BMP4 and BMP7 signaling pathways.

Conclusions

All in all, we show that BMP signaling has a remarkable effect on gene transcription in breast cancer cells and that the functions affected follow a logical temporal pattern. Our results also uncover components of the common cellular transcriptional response to BMP4 and BMP7. Most importantly, this study provides a list of potential novel BMP target genes relevant in breast cancer.

Enhancement of rotator cuff tendon-bone healing with injectable periosteum progenitor cells-BMP-2 hydrogel in vivo

PURPOSE

The fixation and incorporation of ruptured rotator cuff tendon to bone is a major concern in rotator cuff repair surgery. Rotator cuff repair usually fails at the tendon-bone interface, especially in case of large or massive tears. To enhance tendon-bone healing, an injectable hydrogel made with periosteal progenitor cells(PPCs) and poly (ethylene glycol) diacrylate (PEGDA) tethered with bone morphogenic protein-2(BMP-2) was developed to encourage extracellular matrix synthesis for tendon-to-bone healing in rotator cuff repair.

METHODS

The infraspinatus tendon was cut from the greater tuberosity and repaired through a transosseous tunnel with the injectable progenitor cell-BMP-2 hydrogel applied between the tendon-bone interface. The injectable hydrogel was prepared from 10% poly (ethylene glycol) diacrylate (PEGDA) containing 0.05% of the photoinitiator. BMP-2 tethered with poly(ethylene glycol) (PEG) was blended to the hydrogel. Rabbit periosteal progenitor cells (PPCs) isolated from periosteum were mixed with hydrogel and injected on the tendon-bone interface. Ultraviolet radiation (365 nm) was applied for 60 s to photopolymerize the injection and solidify the hydrogel. The rabbits were killed at 4 and 8 weeks. The morphological characteristics of the healing tendon-to-bone interface were evaluated by histological and immunohistochemical methods. The biomechanical test was done to determine healing attachment strength.

RESULTS

At both the 4- and 8-week killing, histological analysis of the tendon-bone interface showed an increasing fibrocartilage and bone layer formed in the tendon-bone interface in PEGDA group. At 4 weeks, fibrocartilage-like tissue was observed in a focal area. At 8 weeks, further matrix deposition occurred with fibrocartilage formation in the tendon-bone junction, and bone formation appeared near host bone. Immunohistochemistry revealed the presence of aggrecan and type II collagen. Biomechanical testing revealed a higher maximum pull-out load at all time points with a statistically significant difference at 4 and 8 weeks postoperatively.

CONCLUSION

PEGDA hydrogel was approved as an adequate matrix for the encapsulation of cells and signal factor, and as an effective local delivery method to the tendon-bone interface through injection and photopolymerization. The PPCs-BMP2-hydrogel provides a powerful inductive ability between the tendon and the bone and enhances tendon-bone healing through the neoformation of fibrocartilage.

Time series gene expression profiling and temporal regulatory pathway analysis of BMP6 induced osteoblast differentiation and mineralization

Background

BMP6 mediated osteoblast differentiation plays a key role in skeletal development and bone disease. Unfortunately, the signaling pathways regulated by BMP6 are largely uncharacterized due to both a lack of data and the complexity of the response.

Results

To better characterize the signaling pathways responsive to BMP6, we conducted a time series microarray study to track BMP6 induced osteoblast differentiation and mineralization. These temporal data were analyzed using a customized gene set analysis approach to identify temporally coherent sets of genes that act downstream of BMP6. Our analysis identified BMP6 regulation of previously reported pathways, such as the TGF-beta pathway. We also identified previously unknown connections between BMP6 and pathways such as Notch signaling and the MYB and BAF57 regulatory modules. In addition, we identify a super-network of pathways that are sequentially activated following BMP6 induction.

Conclusion

In this work, we carried out a microarray-based temporal regulatory pathway analysis of BMP6 induced osteoblast differentiation and mineralization using GAGE method. This novel temporal analysis is more informative and powerful than the classical static pathway analysis in that: (1) it captures the interconnections between signaling pathways or functional modules and demonstrates the even higher level organization of molecular biological systems; (2) it describes the temporal perturbation patterns of each pathway or module and their dynamic roles in osteoblast differentiation. The same set of experimental and computational strategies employed in our work could be useful for studying other complex biological processes.

Prospectively isolated CD133/CD24-positive ependymal cells from the adult spinal cord and lateral ventricle wall differ in their long-term in vitro self-renewal and in vivo gene expression

In contrast to ependymal cells located above the subventricular zone (SVZ) of the adult lateral ventricle wall (LVW), adult spinal cord (SC) ependymal cells possess certain neural stem cell characteristics. The molecular basis of this difference is unknown. In this study, antibodies against multiple cell surface markers were applied to isolate pure populations of SC and LVW ependymal cells, which allowed a direct comparison of their in vitro behavior and in vivo gene expression profile. Isolated CD133(+)/CD24(+)/CD45(-)/CD34(-) ependymal cells from the SC displayed in vitro self-renewal and differentiation capacity, whereas those from the LVW did not. SC ependymal cells showed a higher expression of several genes involved in cell division, cell cycle regulation, and chromosome stability, which is consistent with a long-term self-renewal capacity, and shared certain transcripts with neural stem cells of the embryonic forebrain. They also expressed several retinoic acid (RA)-regulated genes and responded to RA exposure. LVW ependymal cells showed higher transcript levels of many genes regulated by transforming growth factor-β family members. Among them were Dlx2, Id2, Hey1, which together with Foxg1 could explain their potential to turn into neuroblasts under certain environmental conditions.

Functional nicotinic and muscarinic receptors on mesenchymal stem cells

Mesenchymal stem cells (MSCs) are under the control of a large number of signaling systems. In this study, the presence and functionality of the acetylcholine (ACh) signaling system in MSCs was examined. We detected the expression of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and the presence of ACh in MSCs. MSCs also expressed the nicotinic acetylcholine receptor subunits alpha 3, alpha 5, alpha 7, and the muscarinic acetylcholine receptor 2 (M2-receptor). The M2-receptor and the nicotinic alpha 7 receptor subunits were expressed on distinct subpopulations of cells, indicating differential regulation of cholinergic signaling between MSCs. Stimulation of MSCs with the nicotinic receptor agonist nicotine and the muscarinic receptor agonist muscarine induced immediate and transient increases in intracellular Ca(2+) concentration. Furthermore, muscarine had an inhibiting effect on the production of the intracellular signaling molecule cyclic adenosine 3',5'-monophosphate (cAMP). The AChE inhibitor chlorpyrifos, which is widely used as an agricultural insecticide, had similar effects on intracellular Ca(2+) and cAMP in MSCs. Nicotine, muscarine, and chlorpyrifos induced the phosphorylation of extracellular signal-regulated kinases 1 and 2. This study demonstrates that several components of a cholinergic signaling system are present and functional in MSCs. Environmental compounds such as nicotine and agricultural insecticides can interfere with this system and may affect cellular processes in the MSC.

Ubiquitous overexpression of Hey1 transcription factor leads to osteopenia and chondrocyte hypertrophy in bone

The transcription factor Hey1, a known Notch target gene of the HES family, has recently been described as a target gene of bone morphogenetic protein-2 (BMP-2) during osteoblastic differentiation in vitro. As the role of Hey1 in skeletal physiology is unknown, we analyzed bones of mice ubiquitously lacking or overexpressing Hey1. This strategy enabled us to evaluate whether Hey1 modulation in the whole organism could serve as a drug or antibody target for therapy of diseases associated with bone loss. Hey1 deficiency resulted in modest osteopenia in vivo and increased number and activity of osteoclasts generated ex vivo. Hey1 overexpression resulted in distinct progressive osteopenia and inhibition of osteoblasts ex vivo, an effect apparently dominant to a mild inhibition of osteoclasts. In both Hey1 deficient and overexpressing mice, males were less affected than females and skeleton was not affected during development. Bone histomorphometry did not reveal major changes in animals at 20 weeks, suggesting that modulation had occurred before. Adult Hey1 transgenics also displayed increased type X collagen expression and an enlarged hypertrophic zone in the growth plate. Taken together, our data suggest that ubiquitous in vivo Hey1 regulation affects osteoblasts, osteoclasts and chondrocytes. Due to the complex role of Hey1 in bone, inhibition of Hey1 does not appear to be a straightforward therapeutic strategy to increase the bone mass.

Expression pattern and clinical prognostic relevance of bone morphogenetic protein-2 in human gliomas

OBJECTIVE

Bone morphogenetic protein-2 (BMP-2) is normally expressed in the embryo promoting the development of several organs. Aberrant expression of BMP-2 occurs in various tumors. However, a correlation between BMP-2 expression in human gliomas and patients' prognosis has not been reported. To address this question, this study was to investigate the BMP-2 expression pattern in human gliomas and to evaluate its prognostic relevance.

METHODS

We analyzed the expression of the BMP-2 antigen in a series of 98 gliomas of various grade and histology by immunohistochemistry on paraffin-embedded sections. Then, the correlation of BMP-2 expression pattern with clinical-pathological features of patients and its prognostic relevance were determined.

RESULTS

Immunohistochemical analysis with anti-BMP-2 antibody revealed dense and spotty staining in the tumor cells and its expression levels became significantly higher as the gliomas' grade advanced (P < 0.001). The median survival of patients with intensively positive BMP-2 expression was significantly shorter than that with negative expression (318 vs. 1197 days, P < 0.0001). The Kaplan-Meier survival curves showed that the BMP-2 expression was not only a significant predictor of survival in high-grade gliomas (grade IV, P = 0.02), but also in lower-grade gliomas (grades II and III, P < 0.001).

CONCLUSIONS

These results indicate that BMP-2 is a highly sensitive marker for gliomas prognosis and suggest that the expression level of BMP-2 may be a potent tool for the clinical prognosis of gliomas patients.

Graft healing in anterior cruciate ligament reconstruction

Successful anterior cruciate ligament reconstruction with a tendon graft necessitates solid healing of the tendon graft in the bone tunnel. Improvement of graft healing to bone is crucial for facilitating an early and aggressive rehabilitation and ensuring rapid return to pre-injury levels activity. Tendon graft healing in a bone tunnel requires bone ingrowth into the tendon. Indirect Sharpey fiber formation and direct fibrocartilage fixation confer different anchorage strength and interface properties at the tendon-bone interface. For enhancing tendon graft-to-bone healing, we introduce a strategy that includes the use of periosteum, hydrogel supplemented with periosteal progenitor cells and bone morphogenetic protein-2, and a periosteal progenitor cell sheet. Future studies include the use of cytokines, gene therapy, stem cells, platelet-rich plasma, and mechanical stress for tendon-to-bone healing. These strategies are currently under investigation, and will be applied in the clinical setting in the near future.

Specific expression of BMP2/4 ortholog in biomineralizing tissues of corals and action on mouse BMP receptor

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor beta superfamily, and have been identified by their ability to induce bone formation in vertebrates. The biomineral-forming process, called biomineralization, is a widespread process, present in all kingdoms of living organisms and among which stony corals are one of the major groups of calcifying animals. Here, we report the presence of a BMP2/4 ortholog in eight species of adult corals. The synthesis of such a protein by the calcifying epithelium of corals suggests that coral BMP2/4 plays a role in skeletogenesis, making BMP the first common protein involved in biomineralization among Eumetazoans. In addition we show that recombinant coral BMP2/4 is able to inhibit human BMP2-induced osteoblastic differentiation in mesenchymal C2C12 cells. We suggest that this inhibition results from a competition between coral BMP2/4 and human BMP2, indicating conservation of binding affinity of BMP and its receptor during evolution from corals to vertebrates. Further studies are needed to understand interactions between coral BMP2/4 and its receptors, and, thus, the action of BMP2/4 in adult corals.

Direct response to Notch activation: signaling crosstalk and incoherent logic

Notch is the receptor in one of a small group of conserved signaling pathways that are essential at multiple stages in development. Although the mechanism of transduction impinges directly on the nucleus to regulate transcription through the CSL [CBF-1/Su(H)/LAG-1] [corrected] DNA binding protein, there are few known direct target genes. Thus, relatively little is known about the immediate cellular consequences of Notch activation. We therefore set out to determine the genome-wide response to Notch activation by analyzing the changes in messenger RNA (mRNA) expression and the sites of CSL occupancy within 30 minutes of activating Notch in Drosophila cells. Through combining these data, we identify high-confidence direct targets of Notch that are implicated in the maintenance of adult muscle progenitors in vivo. These targets are enriched in cell morphogenesis genes and in components of other cell signaling pathways, especially the epidermal growth factor receptor (EGFR) pathway. Also evident are examples of incoherent network logic, where Notch stimulates the expression of both a gene and the repressor of that gene, which may result in a transient window of competence after Notch activation. Furthermore, because targets comprise both positive and negative regulators, cells become poised for both outcomes, suggesting one mechanism through which Notch activation can lead to opposite effects in different contexts.

Notch signaling in chondrogenesis

The different stages of cartilage development are well described but no transcription factor capable of specifically inducing differentiation to articular cartilage has been identified and little is known about the molecular mechanisms regulating cartilage development. Notch signaling is an evolutionarily conserved pathway taking part in many developmental and cell type specification processes. It has been demonstrated that markers for Notch signaling are differentially expressed during cartilage development and there is evidence for their functional role during this process. Notch signaling has further been implicated in osteoarthritis and Notch1 has been suggested as a marker for chondrogenic progenitor cells. This review summarizes the current knowledge on the role of the Notch signaling pathway in cartilage development and osteoarthritis.

Photoencapsulation of bone morphogenetic protein-2 and periosteal progenitor cells improve tendon graft healing in a bone tunnel

BACKGROUND

Tissue-engineered solutions for promoting the tendon graft incorporation within the bone tunnel appear to be promising.

HYPOTHESIS

To determine the feasibility that conjugation of hyaluronic acid-tethered bone morphogenetic protein-2 can be used to stimulate periosteal progenitor cells direct fibrocartilagenous attachment and new bone formation in an extra-articular tendon-bone healing model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 42 mature New Zealand White rabbits were used. The long digitorum extensor tendon was transplanted into a bone tunnel of the proximal tibia. The tendon was pulled through a drill hole in the proximal tibia and attached to the medial aspect of the tibia. Photopolymerizable hydrogel based on poly (ethylene glycol) diacrylate with hyaluronic acid-tethered bone morphogenetic protein-2 was injected and photogelated in a bone tunnel. Histological and biomechanical examination of the tendon-bone interface was evaluated at postoperative weeks 3 and 6.

RESULTS

Histological analysis showed an interface fibrocartilage and new bone formed by photoencapsulation of bone morphogenetic protein-2 and periosteal progenitor cells at 6 weeks. Biomechanical testing revealed higher maximum pullout strength and stiffness in experimental groups with a statistically significant difference at 3 and 6 weeks after tendon transplantation.

CONCLUSION

The healing tendon-bone interface undergoes a gradual remodeling process; it appears that photoencapsulation of bone morphogenetic protein-2 and periosteal progenitor cells possesses a powerful inductive ability between the tendon and the bone to incorporate the healing in a rabbit model.

CLINICAL RELEVANCE

Novel technologies, such as those described in this study, including photopolymerization and tissue engineering, may provide minimally invasive therapeutic procedures via arthroscopy to enhance biological healing after reconstruction of the anterior cruciate ligament.

Bone morphogenetic protein (BMP) type II receptor is required for BMP-mediated growth arrest and differentiation in pulmonary artery smooth muscle cells

Bone morphogenetic protein (BMP) signals regulate the growth and differentiation of diverse lineages. The association of mutations in the BMP type II receptor (BMPRII) with idiopathic pulmonary arterial hypertension suggests an important role of this receptor in vascular remodeling. Pulmonary artery smooth muscle cells lacking BMPRII can transduce BMP signals using ActRIIa (Activin type II receptor). We investigated whether or not BMP signaling via the two receptors leads to differential effects on vascular smooth muscle cells. BMP4, but not BMP7, inhibited platelet-derived growth factor-activated proliferation in wild-type pulmonary artery smooth muscle cells, whereas neither ligand inhibited the growth of BMPRII-deficient cells. Adenoviral gene transfer of BMPRII enabled BMP4, as well as BMP7, to inhibit proliferation in BMPRII-deficient cells. BMP-mediated growth inhibition was also reconstituted by the BMPRII short isoform, lacking the C-terminal domain present in the long form. BMP4, but not BMP7, induced the expression of osteoblast markers in wild-type cells, whereas neither ligand induced these markers in BMPRII-deficient cells. Overexpression of short or long forms of BMPRII in BMPRII-deficient cells enabled BMP4 and BMP7 to induce osteogenic differentiation. Although signaling via BMPRII or ActRIIa transiently activated SMAD1/5/8, only BMPRII signaling led to persistent SMAD1/5/8 activation and sustained increases in Id1 mRNA and protein expression. Pharmacologic blockade of BMP type I receptor function within 24 h after BMP stimulation abrogated differentiation. These data suggest that sustained BMP pathway activation, such as that mediated by BMPRII, is necessary for growth and differentiation control in vascular smooth muscle.

Transforming growth factor-beta (TGF- 1) down-regulates Notch3 in fibroblasts to promote smooth muscle gene expression

Select signaling pathways have emerged as key players in regulating smooth muscle gene expression during myofibroblast and smooth muscle differentiation, an event that is important for wound healing and vascular remodeling. These include the transforming growth factor-beta (TGF-beta1) signaling cascade, which has been assigned multiple roles in these cells, and the Notch pathway. Notch family members have been implicated in governing cell fate in a variety of cells; however, the mechanisms are not well understood. We sought to explore how these prominent signaling mediators regulate differentiation, and in particular, how they might converge to control the transcription of smooth muscle genes. Using TGF-beta1 to induce the differentiation of 10T1/2 fibroblasts, we investigated the specific function of Notch3. Overexpression of activated Notch3 caused repression of TGF-beta1-induced smooth muscle-specific genes, whereas knockdown of Notch3 by small interfering RNA did not convincingly alter their expression. Surprisingly, the addition of TGF-beta1 caused a significant decrease in Notch3 RNA and protein and a reciprocal increase in Hes1 gene transcription. The repression of Notch3 was mediated by SMAD activity and p38 mitogen-activated protein (MAP) kinase, whereas analysis of the Hes1 promoter revealed direct activation by Smad2 but not Smad3. Furthermore, the Hes1 repressor protein augmented Smad3 transactivation of the SM22alpha promoter. These results offer a novel mechanism by which TGF-beta1 promotes the expression of smooth muscle differentiation genes through the inhibition of Notch3 and activation of Hes1.

Biochemical markers in preclinical models of osteoporosis

Although several treatments for osteoporosis exist, further understanding of the mode of action of current treatments, as well as development of novel treatments, are of interest. Thus, preclinical models of osteoporosis are very useful, as they provide the possibility for gaining knowledge about the cellular mechanisms underlying the disease and for studying pharmaceutical prevention or intervention of the disease in simple and strictly controlled systems. In this review, we present a comprehensive collection of studies using biochemical markers of bone turnover for investigation of preclinical models of osteoporosis. These range from pure and simple in vitro systems, such as osteoclast cultures, to ex vivo models, such as cultures of embryonic murine tibiae and, finally, to in vivo models, such as ovariectomy and orchidectomy of rats. We discuss the relevance of the markers in the individual models, and compare their responses to those observed using 'golden standard' methods.

Heterobifunctional poly(ethylene glycol)-tethered bone morphogenetic protein-2-stimulated bone marrow mesenchymal stromal cell differentiation and osteogenesis

We describe a biomimetic mode of insoluble signaling stimulation to provide target delivery of bone morphogenetic protein-2 (BMP-2), with the aim of prolonging the retention of BMP-2 use in bone tissue engineering and to enable its localized release in response to cellular activity. In our novel localization process, we used heterobifunctional acrylate-N-hydroxysuccinimide poly(ethylene glycol) (PEG) as a spacer to tether BMP-2 onto a poly(lactide-co-glycolide) scaffold. Use of PEG-tethered BMP-2 was feasible because BMP-2 retained its activity after covalent conjugation. The PEG-tethered BMP-2 conjugate sustained stimulation and retained its mitogenic activity, notably affecting pluripotent stem cell proliferation and differentiation. We seeded the scaffolds with bone marrow-derived mesenchymal stromal cells as progenitor cells to evaluate their morphology and phenotypic expression. We also created bilateral, full-thickness cranial defects in rabbits to investigate the osteogenic effect of cultured mesenchymal stromal cells on bone regeneration in vivo. Histomorphometry and histology demonstrated that the PEG-tethered BMP-2 conjugate enhanced de novo bone formation after surgery. Our work revealed the potential for biomimetic surface engineering by entrapping signaling growth factor to stimulate osteogenesis. Our technique may provide a new platform for bone-engineered stem cell therapies.

BMP-2 promotes differentiation of osteoblasts and chondroblasts in Runx2-deficient cell lines

To investigate the molecular mechanism underlying the differentiation of osteoblasts and chondroblasts, we established a clonal cell lines, RD-C6, from Runx2-deficient mouse embryos. RD-C6 cells expressed almost undetectable levels of phenotypes related to osteoblast and chondroblast differentiation at basal culture condition, whereas treatment with recombinant human bone morphogenetic protein-2 (rhBMP-2) or transduction of BMP-2 by adenovirus effectively induced this cell line to express mRNA related to the differentiation of osteoblasts and chondroblasts including alkaline phosphatase, osteocalcin, and osterix. Transduction of Runx2 also induced the expression of these mRNA in RD-C6 cells. BMP-2 transduction increased expression levels of mRNA for Msx2 and Dlx5, but Runx2 transduction induced no significant increases in expression levels of these mRNA. Microarray analysis using RD-C6 cells with or without rhBMP-2 treatment demonstrated that BMP-2 upregulated 66 genes including 13 transcription-related molecules such as Id1, Id2, Id4, Hey1, Smad6, Smad7, and Msx2. To confirm bone and cartilage formation ability of RD-C6 cells, we transplanted RD-C6 cells into the peritoneal cavity of athymic mice using diffusion chambers with rhBMP-2. RD-C6 cells generated unmineralized cartilage but not bone. These results indicate that BMP-2 induces Runx2-deficient cells to express markers related to osteoblast and chondroblast differentiation using a Runx2-independent pathway, but it failed to induce these cells to differentiate into bone-forming osteoblasts and mature chondrocytes.

Inhibition of gamma-secretases alters both proliferation and differentiation of mesenchymal stem cells

INTRODUCTION

Human mesenchymal stem cell (hMSC) proliferation and development is regulated by many signalling pathways. gamma-Secretases play an important role in Notch signalling as well as other processes that are involved in developmental decisions, but their role in hMSC proliferation and cell fate decisions has not been explored.

OBJECTIVE

To investigate the role of gamma-secretases in hMSC proliferation and differentiation.

MATERIALS AND METHODS

Using the gamma-secretase inhibitor N-[N-(3,5-Difluorophenacetyl-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), we investigated their role in hMSC growth and differentiation to chondrogenic, osteogenic and adipogenic fates.

RESULTS

We found that inhibiting gamma-secretases reduced the rate of hMSC proliferation, and altered hMSC differentiation in vitro. Addition of DAPT had an inhibitory effect on chondrogenesis resulting in impaired cartilage matrix production and altered chondrocyte morphology. DAPT treated chrodrocytic pellets had reduced levels of Hes1 and Hey1 suggesting that these effects are mediated via Notch signalling. Addition of the DAPT inhibitor to osteogenic cultures did not alter the appearance of bone markers, however, adipogenesis occurred in these cultures in a DAPT concentration-dependent manner. DAPT did not enhance adipogenesis in the presence of a potent adipogenic cocktail, but had an adipogenic effect when combined with dexamethasone only.

CONCLUSION

We conclude that gamma-secretases play an important role in both hMSC proliferation and differentiation.

MicroRNA-1 facilitates skeletal myogenic differentiation without affecting osteoblastic and adipogenic differentiation

MicroRNAs (miRNAs) are small non-coding RNAs emerging as important post-transcriptional gene regulators. In this study, we examined the role of miR-1, an miRNA specifically expressed in cardiac and skeletal muscle tissue, on the myogenic, osteoblastic, and adipogenic differentiation of C2C12 cells. Upon induction of myogenic differentiation, miR-1 was robustly expressed. Retrovirus-mediated overexpression of miR-1 markedly enhanced expression of muscle creatine kinase, sarcomeric myosin, and alpha-actinin, while the effects on myogenin and MyoD expression were modest. Formation of myotubes was significantly augmented in miR-1-overexpressing cells, indicating miR-1 expression enhanced not only myogenic differentiation but also maturation into myotubes. In contrast, osteoblastic and adipogenic differentiation was not affected by forced expression of miR-1. Thus, the muscle-specific miRNA, miR-1, plays important roles in controlling myogenic differentiation and maturation in lineage-committed cells, rather than functioning in fate determination.

Targeted delivery system for juxtacrine signaling growth factor based on rhBMP-2-mediated carrier-protein conjugation

We propose a model of artificial juxtacrine signaling for the controlled release of recombinant human bone morphogenetic protein-2 (rhBMP-2) suitable for guided bone regeneration. A porous three-dimensional scaffold of poly-(lactide-co-glycolide) was fabricated by means of gel molding and particulate leaching. Collagen immobilization onto the scaffold surface was produced by performing photo-induced graft polymerization of acrylic acid, and rhBMP-2 was tethered to the collagenous surface by covalent conjugation. On pharmacokinetic analysis, in vitro enzyme-linked immunosorbent and alkaline phosphatase assays revealed sustained, slow release of rhBMP-2 over 28 days, with a cumulative release of one third of the initial load diffusing out of the scaffold. Conjugation of rhBMP-2 inhibited the free lateral diffusion and internalization of the activated complex of rhBMP-2 and the bone morphogenetic protein receptor. Osteoprogenitor cells were used as bone precursors to determine the expression of biosignaling growth factor in regulating cell proliferation and differentiation. To identify the phenotype of cells seeded on the rhBMP-2-conjugated scaffold, cellular activity was evaluated with scanning electron microscopy and with viability, histological, and immunohistochemical testing. The rhBMP-2-conjugated scaffold prolonged stimulation of intracellular signal proteins in cells. Enhancement of cell growth and differentiation was considered a consequence of juxtacrine signaling transduction. Animal studies of rhBMP-2-containing filling implants showed evidence of resorption and de novo bone formation. The present study revealed the potential of biomimetic constructs with co-immobilized adhesion and growth factors to induce osteoinduction and osteogenesis. Such constructs may be useful as synthetic bone-graft materials in orthopaedic tissue engineering.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Expression of bone morphogenetic proteins in human lung carcinomas

BACKGROUND

The bone morphogenetic proteins (BMP) are phytogenetically conserved proteins, which are essential for embryonic development. Bone morphogenetic protein-2 (BMP-2) was recently shown to be expressed in a small sample of lung carcinomas. Studies have suggested that BMP-2 may enhance tumor growth. The present study examined which BMP family members are expressed in non-small cell lung carcinomas (NSCLC). Furthermore, the frequency of BMP-2 overexpression and the types of lung carcinomas expressing BMP-2 were determined.

METHODS

Tissue samples were obtained from the operating room and frozen in liquid nitrogen. Samples included metastatic NSCLC, benign lung tumors, adenocarcinoma, squamous cell carcinoma, bronchioloalveolar, and neuroendocrine carcinomas. Paired normal lung tissues served as the controls. The BMP-2, BMP-4, BMP-6, BMP-7, and growth differentiation factor 5 (GDF-5) expressions were examined by Western blot analysis.

RESULTS

The BMP-4, BMP-6, BMP-7, and GDF-5 were infrequently expressed in NSCLC. The BMP-2 was expressed in 41 of 42 NSCLC with minimal expression in normal lung tissue; BMP-2 was expressed 17 fold higher than that of normal lung tissue. The BMP-2 was over-expressed in all subtypes of NSCLC, including neuroendocrine carcinomas. The BMP-2 expression was similar between squamous cell carcinomas and adenocarcinomas; however, bronchioloalveolar carcinomas tended to have a lower level of expression. The BMP-2 was not significantly expressed in benign lung tumors.

CONCLUSIONS

Bone morphogenetic protein-2 is the predominant family member expressed in NSCLC. The BMP-2 is overexpressed in the majority of human lung carcinomas independent of cell type.

The Effects of Anticholinergic Insecticides on Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are located primarily in the bone marrow and are characterized by their capacity to differentiate into mesenchymal lineages such as bone, fat, and cartilage in response to appropriate signals. Several signaling mechanisms act to control MSC survival, proliferation, and differentiation, and failure or disruption of these signaling pathways can lead to degenerative disease or neoplasia. Organophosphate (OP) and carbamate pesticides, which are used in large amounts in agriculture to control insects, are designed to disrupt acetylcholine signaling by inhibiting the enzyme acetylcholinesterase (AChE). Effects of OP and carbamate pesticides on the human central nervous system have been well documented. However, AChE is broadly distributed, and the effects of anticholinergic insecticides on nonnervous tissue have received little attention. In the present study we found that human MSCs express AChE, which makes these cells potential targets for AChE inhibiting agents. We therefore examined the effects of an OP pesticide, chlorpyrifos, and a carbamate, carbofuran, on MSC characteristics. It was found that micromolar concentrations of these anticholinergic insecticides had no effect on MSC survival or proliferation but limited MSC differentiation capacity by inhibiting osteogenic differentiation. These results demonstrate that exposure to micromolar concentrations of OP and carbamate pesticides may affect tissue turnover and pathophysiology by interfering with MSC regulation.