Differential inhibition of Smad6 and Smad7 on bone morphogenetic protein- and activin-mediated growth arrest and apoptosis in B cells

Epiblast inducers capture mouse trophectoderm stem cells in vitro and pattern blastoids for implantation in utero

The embryo instructs the allocation of cell states to spatially regulate functions. In the blastocyst, patterning of trophoblast (TR) cells ensures successful implantation and placental development. Here, we defined an optimal set of molecules secreted by the epiblast (inducers) that captures in vitro stable, highly self-renewing mouse trophectoderm stem cells (TESCs) resembling the blastocyst stage. When exposed to suboptimal inducers, these stem cells fluctuate to form interconvertible subpopulations with reduced self-renewal and facilitated differentiation, resembling peri-implantation cells, known as TR stem cells (TSCs). TESCs have enhanced capacity to form blastoids that implant more efficiently in utero due to inducers maintaining not only local TR proliferation and self-renewal, but also WNT6/7B secretion that stimulates uterine decidualization. Overall, the epiblast maintains sustained growth and decidualization potential of abutting TR cells, while, as known, distancing imposed by the blastocyst cavity differentiates TR cells for uterus adhesion, thus patterning the essential functions of implantation.

Coordination of iron homeostasis by bone morphogenetic proteins: Current understanding and unanswered questions

Iron homeostasis is tightly regulated to balance the iron requirement for erythropoiesis and other vital cellular functions, while preventing cellular injury from iron excess. The liver hormone hepcidin is the master regulator of systemic iron balance by controlling the degradation and function of the sole known mammalian iron exporter ferroportin. Liver hepcidin expression is coordinately regulated by several signals that indicate the need for more or less iron, including plasma and tissue iron levels, inflammation, and erythropoietic drive. Most of these signals regulate hepcidin expression by modulating the activity of the bone morphogenetic protein (BMP)-SMAD pathway, which controls hepcidin transcription. Genetic disorders of iron overload and iron deficiency have identified several hepatocyte membrane proteins that play a critical role in mediating the BMP-SMAD and hepcidin regulatory response to iron. However, the precise molecular mechanisms by which serum and tissue iron levels are sensed to regulate BMP ligand production and promote the physical and/or functional interaction of these proteins to modulate SMAD signaling and hepcidin expression remain uncertain. This critical commentary will focus on the current understanding and key unanswered questions regarding how the liver senses iron levels to regulate BMP-SMAD signaling and thereby hepcidin expression to control systemic iron homeostasis.

Bone morphogenetic proteins: New insights into their roles and mechanisms in CNS development, pathology and repair

Bone morphogenetic proteins (BMPs) are a highly conserved and diverse family of proteins that play essential roles in various stages of development including the formation and patterning of the central nervous system (CNS). Bioavailability and function of BMPs are regulated by input from a plethora of transcription factors and signaling pathways. Intriguingly, recent literature has uncovered novel roles for BMPs in regulating homeostatic and pathological responses in the adult CNS. Basal levels of BMP ligands and receptors are widely expressed in the adult brain and spinal cord with differential expression patterns across CNS regions, cell types and subcellular locations. Recent evidence indicates that several BMP isoforms are transiently or chronically upregulated in the aged or pathological CNS. Genetic knockout and pharmacological studies have elucidated that BMPs regulate several aspects of CNS injury and repair including cell survival and differentiation, reactive astrogliosis and glial scar formation, axon regeneration, and myelin preservation and repair. Several BMP isoforms can be upregulated in the injured or diseased CNS simultaneously yet exert complementary or opposing effects on the endogenous cell responses after injury. Emerging studies also show that dysregulation of BMPs is associated with various CNS pathologies. Interestingly, modulation of BMPs can lead to beneficial or detrimental effects on CNS injury and repair mechanisms in a ligand, temporally or spatially specific manner, which reflect the complexity of BMP signaling. Given the significance of BMPs in neurodevelopment, a better understanding of their role in the context of injury may provide new therapeutic targets for the pathologic CNS. This review will provide a timely overview on the foundation and recent advancements in knowledge regarding the role and mechanisms of BMP signaling in the developing and adult CNS, and their implications in pathological responses and repair processes after injury or diseases.

Bone morphogenetic proteins mediate crosstalk between cancer cells and the tumour microenvironment at primary tumours and metastases (Review)

Bone morphogenetic proteins (BMP) are pluripotent molecules, co‑ordinating cellular functions from early embryonic and postnatal development to tissue repair, regeneration and homeostasis. They are also involved in tumourigenesis, disease progression and the metastasis of various solid tumours. Emerging evidence has indicated that BMPs are able to promote disease progression and metastasis by orchestrating communication between cancer cells and the surrounding microenvironment. The interactions occur between BMPs and epidermal growth factor receptor, hepatocyte growth factor, fibroblast growth factor, vascular endothelial growth factor and extracellular matrix components. Overall, these interactions co‑ordinate the cellular functions of tumour cells and other types of cell in the tumour to promote the growth of the primary tumour, local invasion, angiogenesis and metastasis, and the establishment and survival of cancer cells in the metastatic niche. Therefore, the present study aimed to provide an informative summary of the involvement of BMPs in the tumour microenvironment.

Trio, a novel high fecundity allele: I. Transcriptome analysis of granulosa cells from carriers and noncarriers of a major gene for bovine ovulation rate

A major gene for bovine ovulation rate has been mapped to a 1.2 Mb region of chromosome 10. Screening of coding regions of positional candidate genes within this region failed to reveal a causative polymorphism, leading to the hypothesis that the phenotype results from differences in candidate gene expression rather than alteration of gene structure. This study tested differences in expression of positional candidate genes in granulosa cells between carriers and noncarriers of the high fecundity allele, as well as characterizing differences in the transcriptomic profile between genotypes. Five carriers and five noncarriers, female descendants of "Trio," a carrier of the high fecundity allele were initially used in an RNA-seq analysis of gene expression. Four of ten samples were contaminated with theca cells, so that six samples were used in the final analysis (three of each genotype). Of 14 973 genes expressed, 143 were differentially expressed (false discovery rate P < 0.05) in carriers versus noncarriers. Among the positional candidate genes, SMAD6 was 6.6-fold overexpressed in the carriers compared to noncarriers (P < 5 × 10-5). This result was replicated in an independent group of 12 females (7 carriers and 5 noncarriers) using quantitative real-time PCR; SMAD6 was 9.3-fold overexpressed in carriers versus noncarriers (P = 1.17 × 10-6). Association of overexpression of SMAD6, an inhibitor of the BMP/SMAD signaling pathway, with high ovulation rate corresponds well with disabling mutations in ligands (BMP15 and GDF9) and a receptor (BMPR1B) of this pathway that cause increased ovulation rate in sheep.

Effect of canonical NF-κB signaling pathway on the differentiation of rat dental epithelial stem cells

BACKGROUND

Nuclear factor-κB (NF-κB), an important transcription factor, participates in many physiological and pathological processes such as growth, differentiation, organogenesis, apoptosis, inflammation, and immune response, including tooth development. However, it is still unknown whether NF-κB participates in the regulation of dental epithelial stem cells (DESCs) in postnatal rat incisors. Here, we investigated the specific differentiation regulatory mechanisms of the canonical NF-κB signaling pathway in DESCs and provided the mechanism of cross-talk involved in DESC differentiation.

METHODS

After adding the activator or inhibitor of the NF-κB signaling pathway, Western blot and quantitative real-time PCR were used to analyze the expressions of amelogenesis-related genes and proteins and canonical transforming growth factor-β (TGF-β) signaling. In addition, we used amelogenesis induction in vitro by adding the activator or inhibitor of the NF-κB signaling pathway to the amelogenesis-induction medium, respectively. Recombinant TGF-β was used to activate the TGF-β pathway, and SMAD7 siRNA was used to downregulate the expression of SMAD7 in DESCs.

RESULTS

We found that the expression of amelogenesis-related genes and proteins as well as TGF-β signaling were downregulated, while SMAD7 expression was increased in NF-κB-activated DESCs. In addition, NF-κB-inhibited DESCs exhibited opposite results compared with NF-κB-activated DESCs. Furthermore, the canonical NF-κB signaling pathway suppressed the canonical TGF-β-SMAD signaling by inducing SMAD7 expression involved in the regulation of DESC differentiation.

CONCLUSIONS

These results indicate that the canonical NF-κB signaling pathway participated in the regulation of DESC differentiation, which was through upregulating SMAD7 expression and further suppressing the canonical TGF-β-SMAD signaling pathway.

Sinapic acid-loaded chitosan nanoparticles in polycaprolactone electrospun fibers for bone regeneration in vitro and in vivo

Sinapic acid (SA) is a plant-derived phenolic compound known for its multiple biological properties, but its role in the promotion of bone formation is not yet well-studied. Moreover, the delivery of SA is hindered by its complex hydrophobic nature, limiting its bioavailability. In this study, we fabricated a drug delivery system using chitosan nanoparticles (nCS) loaded with SA at different concentrations. These were incorporated into polycaprolactone (PCL) fibers via an electrospinning method. nCS loaded with 50 μM SA in PCL fibers promoted osteoblast differentiation. Furthermore, SA treatment activated the osteogenesis signaling pathways in mouse mesenchymal stem cells. A critical-sized rat calvarial bone defect model system identified that the inclusion of SA into PCL/nCS fibers accelerated bone formation. Collectively, these data suggest that SA promoted osteoblast differentiation in vitro and bone formation in vivo, possibly by activating the TGF-β1/BMP/Smads/Runx2 signaling pathways, suggesting SA might have therapeutic benefits in bone regeneration.

MyD88 Regulates the Expression of SMAD4 and the Iron Regulatory Hormone Hepcidin

The myeloid differentiation primary response gene 88 (MyD88) is an adaptive protein that is essential for the induction of inflammatory cytokines through almost all the Toll-like receptors (TLRs). TLRs recognize molecular patterns present in microorganisms called pathogen-associated molecular patterns. Therefore, MyD88 plays an important role in innate immunity since its activation triggers the first line of defense against microorganisms. Herein, we describe the first reported role of MyD88 in an interconnection between innate immunity and the iron-sensing pathway (BMP/SMAD4). We found that direct interaction of MyD88 with SMAD4 protein activated hepcidin expression. The iron regulatory hormone hepcidin is indispensable for the intestinal regulation of iron absorption and iron recycling by macrophages. We show that MyD88 induces hepcidin expression in a manner dependent on the proximal BMP responsive element on the hepcidin gene (HAMP) promoter. We identified the Toll/interleukin-1 receptor (TIR) domain of MyD88 as the domain of interaction with SMAD4. Furthermore, we show that BMP6 stimulation, which activates SMAD6 expression, also induces MyD88 proteosomal degradation as a negative feedback mechanism to limit hepcidin induction. Finally, we report that the MyD88 gain-of-function L265P mutation, frequently encountered in B-cell lymphomas such as Waldenström’s macroglobulinemia, enhances hepcidin expression and iron accumulation in B cell lines. Our results reveal a new potential role for MyD88 in the SMAD signaling pathway and iron homeostasis regulation.

The Induction of Bone Formation: The Translation Enigma

A paradigmatic shift in the way of thinking is what bone tissue engineering science requires to decrypt the translation conundrum from animal models into human. The deductive work of Urist (1965), who discerned the principle of bone induction from the pioneering works of Senn, Huggins, Lacroix, Levander, and other bone regenerative scientists, provided the basis that has assisted future bone tissue regenerative scientists to extend the bone tissue engineering field and its potential uses for bone regenerative medicine in humans. However, major challenges remain that are preventing the formation of bone by induction clinically. Growing experimental evidence is indicating that bone inductive studies are non-translatable from animal models into a clinical environment. This is preventing bone tissue engineering from reaching the next phase in development. Countless studies are trying to discern how the formation of bone by induction functions mechanistically, so as to try and solve this enigmatic problem. However, are the correct questions being asked? Why do bone inductive animal studies not translate into humans? Why do bone induction principles not yield the same extent of bone formation as an autogenous bone graft? What are bone tissue engineering scientists missing? By critically re-assessing the past and present discoveries of the bone induction field, this review article attempts to re-discover the field of bone formation by induction, identifying some key features that may have been missed. These include a detailed library of all proteins in bones and their arrangement in the 3D superstructure of the bone together with some other important criteria not considered by tissue engineering scientists. The review therefore not only re-iterates possible avenues of research that need to be re-explored but also seeks to guide present and future scientists in how they assess their own research in light of experimental design and results. By addressing these issues bone formation by induction without autografts might finally become clinically viable.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

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.

Determination of dosage compensation and comparison of gene expression in a triploid hybrid fish

Background

Polyploidy and hybridization are both recognized as major forces in evolution. Most of our current knowledge about differences in gene regulation in polyploid hybrids comes from plant studies. The gene expression of diverged genomes and regulatory interactions are still unclear in lower vertebrates.

Results

We generated 229 million cleaned reads (42.23 Gbp) from triploid of maternal grass carp (Ctenopharyngodon idellus, Cyprininae, 2n = 48) × paternal blunt snout bream (Megalobrama amblycephala, Cultrinae, 2n = 48) and their diploid parents using next-generation sequencing. In total, 157,878 contigs were assembled and 15,444 genes were annotated. We examined gene expression level changes among the parents and their triploid offspring. The mechanisms of dosage compensation that reduced triploid expression levels to the diploid state were determined in triploid fish. In this situation, novel gene expression and gene silencing were observed. Then, we established a model to determine the extent and direction of expression level dominance (ELD) and homoeolog expression bias (HEB) based on the relative expression level among the parents and their triploid offspring.

Conclusions

Our results showed that the genome-wide ELD was biased toward maternal genome in triploid. Extensive alterations in homoeolog expression suggested a combination of regulatory and epigenetic interactions through the transcriptome network. Additionally, the expression patterns of growth genes provided insights into the relationship between the characteristics of growth and underlying mechanisms in triploids. Regulation patterns of triploid state suggest that various expression levels from the initial genomic merger have important roles in adaptation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3424-5) contains supplementary material, which is available to authorized users.

The expression of Smad signaling pathway in myocardium and potential therapeutic effects

Myocardial infarction (MI) is a life-threatening disease. The expression of Smad proteins in the ischemic myocardium changes significantly following myocardial infarction, suggesting a close relationship between Smad proteins and heart remodeling. Moreover, it is known that the expression of Smads is regulated by transforming growth factor-β (TGF-β) and bone morphogenetic proteins (BMP). Based on these findings, regulating the expression of Smad proteins by targeting TGF-β and BMP in the ischemic myocardium may be considered to be a possible therapeutic strategy for the treatment of myocardial infarction.

Halofuginone inhibits radiotherapy-induced epithelial-mesenchymal transition in lung cancer

Radiotherapy is used to treat many different human tumors. Paradoxically, radiation can activate TGF-β1 signaling and induce the epithelial-mesenchymal transition (EMT), which is associated with enhanced tumor progression. This study investigated the inhibitory effects of halofuginone, a plant-derived alkaloid that has been shown to inhibit TGF-β1 signaling, on radiation-induced EMT and explored the underlying mechanisms using a Lewis lung carcinoma (LLC) xenograft model. The cells and animals were divided into five treatment groups: Normal Control (NC), Halofuginone alone (HF), Radiotherapy alone (RT), Radiotherapy combined with Halofuginone (RT+HF), and Radiotherapy combined with the TGF-β1 inhibitor SB431542 (RT+SB). Radiation induced EMT in lung cancer cells and xenografts, as evidenced by increased expression of the mesenchymal markers N-cadherin and Vimentin, and reduced expression of the epithelial markers E-cadherin and Cytokeratin. Further, radiotherapy treatment increased the migration and invasion of LLC cells. Halofuginone reversed the EMT induced by radiotherapy in vitro and in vivo, and inhibited the migration and invasion of LLC cells. In addition, TGF-β1/Smad signaling was activated by radiotherapy and the mRNA expression of Twist and Snail was elevated; this effect was reversed by halofuginone or the TGF-β1 inhibitor SB431542. Our results demonstrate that halofuginone inhibits radiation-induced EMT, and suggest that suppression of TGF-β1 signaling may be responsible for this effect.

Activins and Inhibins: Roles in Development, Physiology, and Disease

Since their original discovery as regulators of follicle-stimulating hormone (FSH) secretion and erythropoiesis, the TGF-β family members activin and inhibin have been shown to participate in a variety of biological processes, from the earliest stages of embryonic development to highly specialized functions in terminally differentiated cells and tissues. Herein, we present the history, structures, signaling mechanisms, regulation, and biological processes in which activins and inhibins participate, including several recently discovered biological activities and functional antagonists. The potential therapeutic relevance of these advances is also discussed.

TGF-β signaling is activated in patients with chronic HBV infection and repressed by SMAD7 overexpression after successful antiviral treatment

OBJECTIVES

Although animal studies demonstrated that Smad7 induction ameliorates TGF-β/SMAD-mediated fibrogenesis, its role in human hepatic diseases is rather obscure. Our study explored the activation status of TGF-β/activin pathway in patients with chronic liver diseases, and how it is affected by successful antiviral treatment in chronic HBV hepatitis (CHB).

METHODS

Thirty-seven CHB patients (19 with active disease, 14 completely remitted on long-term antiviral treatment and 4 with relapse after treatment withdrawal), 18 patients with chronic HCV hepatitis, 12 with non-alcoholic fatty liver disease (NAFLD), and 3 controls were enrolled in the study. Liver mRNA levels of CTGF, all TGF-β/activin isoforms, their receptors and intracellular mediators (SMADs) were evaluated using qRT-PCR and were correlated with the grade of liver inflammation and fibrosis staging. The expression and localization of pSMAD2 and pSMAD3 were assessed by immunohistochemistry.

RESULTS

TGF-β signalling is activated in CHB patients with active disease, while SMAD7 is up-regulated during the resolution of inflammation after successful treatment. SMAD7 overexpression was also observed in NAFLD patients exhibiting no or minimal fibrosis, despite the activation of TGF-β/activin signaling.

CONCLUSIONS

SMAD7 overexpression might represent a mechanism limiting TGF-β-mediated fibrogenesis in human hepatic diseases; therefore, SMAD7 induction likely represents a candidate for novel therapeutic approaches.

Bone morphogenetic proteins in tumour associated angiogenesis and implication in cancer therapies

Bone morphogenetic protein (BMP) belongs to transforming growth factor-β superfamily. To date, more than 20 BMPs have been identified in humans. BMPs play a critical role in embryonic and postnatal development, and also in maintaining homeostasis in different organs and tissues by regulating cell differentiation, proliferation, survival and motility. They play important roles in the development and progression of certain malignancies, including prostate cancer, breast cancer, lung cancer, etc. Recently, more evidence shows that BMPs are also involved in tumour associated angiogenesis. For example BMP can either directly regulate the functions of vascular endothelial cells or indirectly influence the angiogenesis via regulation of angiogenic factors, such as vascular endothelial growth factor (VEGF). Such crosstalk can also be reflected in the interaction with other angiogenic factors, like hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF). All these factors are involved in the orchestration of the angiogenic process during tumour development and progression. Review of the relevant studies will provide a comprehensive prospective on current understanding and shed light on the corresponding therapeutic opportunity.

Valproic acid suppresses collagen by selective regulation of Smads in conjunctival fibrosis

Overproduction of type I collagen is associated with a wide range of fibrotic diseases as well as surgical failure such as in glaucoma filtration surgery (GFS). Its modulation is therefore of clinical importance. Valproic acid (VPA) is known to reduce collagen in a variety of tissues with unclear mechanism of action. In this report, we demonstrate that VPA inhibited collagen production in both conjunctival fibroblasts and the mouse model of GFS. In fibroblasts, VPA decreased type I collagen expression which intensified with longer drug exposure and suppressed steady-state type I collagen promoter activity. Moreover, VPA decreased Smad2, Smad3 and Smad4 but increased Smad6 expression with a similar intensity-exposure profile. Reduction of Smad3 using small hairpin RNA and/or overexpression of Smad6 resulted in decreased collagen expression which was exacerbated when VPA was simultaneously present. Furthermore, fibrogenic TGF-β2 failed to induce collagen when VPA was present, as opposed to the myofibroblast markers, beta-actin, alpha-smooth muscle actin and tenascin-C, which were elevated by TGF-β2. VPA suppressed p3TP-Lux luciferase activity and selectively rescued Smad6 expression from suppression by TGF-β2. Notably, SMAD6 overexpression reduced the effectiveness of TGF-β2 in inducing collagen expression. In corroboration, VPA inhibited type I collagen but increased Smad6 expression in the late phase of wound healing in the mouse model of GFS. Taken together, our data indicate that VPA has the capacity to effectively suppress both steady-state and fibrogenic activation of type I collagen expression by modulating Smad expression. Hence, VPA is potentially applicable as an anti-fibrotic therapeutic by targeting collagen. Key message: • VPA modulates type I collagen expression via members of the Smad family. • VPA suppresses Smad2, Smad3 and Smad4 but upregulates Smad6. • Smad3 and Smad6 are involved in VPA regulation of steady-state collagen expression. • Smad6 is involved in VPA modulation of TGF-β-stimulated collagen expression. • VPA reduces collagen and upregulates Smad6 in the mouse model of glaucoma filtration surgery.

Arkadia enhances BMP signalling through ubiquitylation and degradation of Smad6

Arkadia, a positive regulator of Smad-dependent signalling via the transforming growth factor-β (TGF-β) family, is an E3 ubiquitin ligase that induces ubiquitylation and proteasome-dependent degradation of TGF-β suppressors such as Smad7, c-Ski and SnoN. In this study, we examined the effects of Arkadia on bone morphogenetic protein (BMP)-induced osteoblast differentiation. Knockdown of Arkadia reduced mineralization and expression of osteoblast differentiation markers. Furthermore, we showed that Smad6, a BMP-specific inhibitory Smad, is a target of Arkadia: wild-type (WT) Arkadia, but not the C937A (CA) mutant lacking E3 ubiquitin-ligase activity, induced ubiquitylation and proteasome-dependent degradation of Smad6. Accordingly, protein levels of Smad6, Smad7 and c-Ski were elevated in MEFs from Arkadia KO mice. Finally, expression of Arkadia attenuated blockade of BMP signalling by Smad6 in a transcriptional reporter assay. These results demonstrate that Smad6 is a novel target of Arkadia, and that Arkadia positively regulates BMP signalling via degradation of Smad6, Smad7 and c-Ski/SnoN.

Transforming growth factor-β(1) represses bone morphogenetic protein-mediated Smad signaling in pulmonary artery smooth muscle cells via Smad3

Previous studies of pulmonary arterial hypertension (PAH) have implicated excessive transforming growth factor (TGF)-β1 signaling and reduced bone morphogenetic protein (BMP) signaling in the disease pathogenesis. Reduced BMP signaling in pulmonary artery smooth muscle cells (PASMCs) from patients with heritable PAH is a consequence of germline mutations in the BMP type II receptor (BMPR-II). We sought to establish whether the TGF-β1 and BMP4 pathways interact in PASMCs, and if this is altered in cells with BMPR-II mutations. Control PASMCs or from patients with PAH harboring BMPR-II mutations were treated with BMP4, TGF-β1, or cotreated with both ligands. Signaling was assessed by examination of Smad phosphorylation, luciferase reporters, and the transcription of BMP4 or TGF-β1-responsive genes. TGF-β1 attenuated BMP4-mediated inhibitors of differentiation 1/2 induction and abolished the response in BMPR-II mutant PASMCs, whereas BMP4 did not alter TGF-β1-mediated transcription. Activin-like kinase 5 inhibition blocked this effect, whereas cycloheximide or pharmacological inhibitors of TGF-β-activated kinase 1, extracellular signal-regulated kinase 1/2, or p38 mitogen-activated protein kinase were ineffective. BMP4 and TGF-β1 cotreatment did not alter the activation or nuclear translocation of their respective Smad signaling proteins. Small interfering RNA for Smad3, but not Smad2, Smad6, or Smad7, reversed the inhibition by TGF-β1. In addition, TGF-β-activated kinase 1 inhibition blocked Smad3 phosphorylation, implying that C-terminal Smad3 phosphorylation is not required for the inhibition of BMP4 signaling by TGF-β1. TGF-β1 reduces BMP4 signaling in PASMCs, a response that is exacerbated on the background of reduced BMP responsiveness due to BMPR-II mutations. These data provide a rationale for therapeutic inhibition of TGF-β1 signaling in PAH.

Regulation of TGF-β family signalling by ubiquitination and deubiquitination

Members of the transforming growth factor-β (TGF-β) family, including TGF-βs, activin and bone morphogenetic proteins (BMPs), are multifunctional proteins that regulate a wide variety of cellular responses, such as proliferation, differentiation, migration and apoptosis. TGF-β family signalling is mainly mediated by membranous serine/threonine kinase receptors and intracellular Smad proteins. This signalling is tightly regulated by various post-translational modifications including ubiquitination. Several E3 ubiquitin ligases play a crucial role in the recognition and ubiquitin-dependent degradation of TGF-β family receptors, Smad proteins and their interacted proteins to regulate positively and negatively TGF-β family signalling. In contrast, non-degradative ubiquitin modifications also regulate TGF-β family signalling. Recently, in addition to protein ubiquitination, deubiquitination by deubiquitinating enzymes has been reported to control TGF-β family signalling pathways. Interestingly, more recent studies suggest that TGF-β signalling is not only regulated via ubiquitination and/or deubiquitination, but also it relies on ubiquitination for its effect on other pathways. Thus, ubiquitin modifications play key roles in TGF-β family signal transduction and cross-talk between TGF-β family signalling and other signalling pathways. Here, we review the current understandings of the positive and negative regulatory mechanisms by ubiquitin modifications that control TGF-β family signalling.

Regulation of fetal gene expression in heart failure

During the processes leading to adverse cardiac remodeling and heart failure, cardiomyocytes react to neurohumoral stimuli and biomechanical stress by activating pathways that induce pathological hypertrophy. The gene expression patterns and molecular changes observed during cardiac hypertrophic remodeling bare resemblance to those observed during fetal cardiac development. The re-activation of fetal genes in the adult failing heart is a complex biological process that involves transcriptional, posttranscriptional and epigenetic regulation of the cardiac genome. In this review, the mechanistic actions of transcription factors, microRNAs and chromatin remodeling processes in regulating fetal gene expression in heart failure are discussed.

Smad7 regulates terminal maturation of chondrocytes in the growth plate

Members of the bone morphogenetic protein (BMP) superfamily, including transforming growth factor-betas (TGFβ), regulate multiple aspects of chondrogenesis. Smad7 is an intracellular inhibitor of BMP and TGFβ signaling. Studies in which Smad7 was overexpressed in chondrocytes demonstrated that Smad7 can impact chondrogenesis by inhibiting BMP signaling. However, whether Smad7 is actually required for endochondral ossification in vivo is unclear. Moreover, whether Smad7 regulates TGFβ in addition to BMP signaling in developing cartilage is unknown. In this study, we found that Smad7 is required for both axial and appendicular skeletal development. Loss of Smad7 led to impairment of the cell cycle in chondrocytes and to defects in terminal maturation. This phenotype was attributed to upregulation of both BMP and TGFβ signaling in Smad7 mutant growth plates. Moreover, Smad7-/- mice develop hypocellular cores in the medial growth plates, associated with elevated HIF1α levels, cell death, and intracellular retention of types II and X collagen. Thus, Smad7 may be required to mediate cell stress responses in the growth plate during development.

SMAD7 antagonizes key TGFβ superfamily signaling in mouse granulosa cells in vitro

Transforming growth factor β (TGFβ) superfamily signaling is essential for female reproduction. Dysregulation of the TGFβ signaling pathway can cause reproductive diseases. SMA and MAD (mothers against decapentaplegic) (SMAD) proteins are downstream signaling transducers of the TGFβ superfamily. SMAD7 is an inhibitory SMAD that regulates TGFβ signalingin vitro. However, the function of SMAD7 in the ovary remains poorly defined. To determine the signaling preference and potential role of SMAD7 in the ovary, we herein examined the expression, regulation, and function of SMAD7 in mouse granulosa cells. We showed that SMAD7 was expressed in granulosa cells and subject to regulation by intraovarian growth factors from the TGFβ superfamily. TGFB1 (TGFβ1), bone morphogenetic protein 4, and oocyte-derived growth differentiation factor 9 (GDF9) were capable of inducingSmad7expression, suggesting a modulatory role of SMAD7 in a negative feedback loop. Using a small interfering RNA approach, we further demonstrated that SMAD7 was a negative regulator of TGFB1. Moreover, we revealed a link between SMAD7 and GDF9-mediated oocyte paracrine signaling, an essential component of oocyte–granulosa cell communication and folliculogenesis. Collectively, our results suggest that SMAD7 may function during follicular development via preferentially antagonizing and/or fine-tuning essential TGFβ superfamily signaling, which is involved in the regulation of oocyte–somatic cell interaction and granulosa cell function.

MicroRNAs in pulmonary arterial remodeling

Pulmonary arterial remodeling is a presently irreversible pathologic hallmark of pulmonary arterial hypertension (PAH). This complex disease involves pathogenic dysregulation of all cell types within the small pulmonary arteries contributing to vascular remodeling leading to intimal lesions, resulting in elevated pulmonary vascular resistance and right heart dysfunction. Mutations within the bone morphogenetic protein receptor 2 gene, leading to dysregulated proliferation of pulmonary artery smooth muscle cells, have been identified as being responsible for heritable PAH. Indeed, the disease is characterized by excessive cellular proliferation and resistance to apoptosis of smooth muscle and endothelial cells. Significant gene dysregulation at the transcriptional and signaling level has been identified. MicroRNAs are small non-coding RNA molecules that negatively regulate gene expression and have the ability to target numerous genes, therefore potentially controlling a host of gene regulatory and signaling pathways. The major role of miRNAs in pulmonary arterial remodeling is still relatively unknown although research data is emerging apace. Modulation of miRNAs represents a possible therapeutic target for altering the remodeling phenotype in the pulmonary vasculature. This review will focus on the role of miRNAs in regulating smooth muscle and endothelial cell phenotypes and their influence on pulmonary remodeling in the setting of PAH.

Spatio-temporal distribution of Smads and role of Smads/TGF-β/BMP-4 in the regulation of mouse bladder organogenesis

Although Shh, TGF-β and BMP-4 regulate radial patterning of the bladder mesenchyme and smooth muscle differentiation, it is not known what transcription factors, local environmental cues or signaling cascades mediate bladder smooth muscle differentiation. We investigated the expression patterns of signaling mediated by Smad2 and Smad3 in the mouse embryonic bladder from E12.5 to E16.5 by using qRT-PCR, in situ hybridization and antibodies specifically recognizing individual Smad proteins. The role of Smad2 and Smad3 during smooth muscle formation was examined by disrupting the Smad2/3 signaling pathway using TβR1 inhibitor SB-431542 in organ culture system. qRT-PCR results showed that R-Smads, Co-Smad and I-Smads were all expressed during bladder development. RNA ISH for BMP-4 and immunostaining of TGF-β1 showed that BMP-4 and TGF-β1 were expressed in the transitional epithelium, lamina propia and muscularis mucosa. Smad1, Smad5 and Smad8 were first expressed in the bladder epithelium and continued to be expressed in the transitional epithelium, muscularis mesenchyme and lamina propia as the bladder developed. Smad2, Smad3 and Smad4 were first detected in the bladder epithelium and subsequently were expressed in the muscularis mesenchyme and lamina propia. Smad6 and Smad7 showed overlapping expression with R-Smads, which are critical for bladder development. In bladder explants (E12.5 to E16.5) culture, Smad2 and Smad3 were found localized within the nuclei, suggesting critical transcriptional regulatory effects during bladder development. E12.5 to E16.5 bladders were cultured with and without TβR1 inhibitor SB-431542 and assessed by qRT-PCR and immunofluorescence. After three days in culture in SB-431542, α-SMA, Smad2 and Smad3 expressions were significantly decreased compared with controls, however, with no significant changes in the expression of smooth muscle myosin heavy chain (SM-Myh. Based on the Smad expression patterns, we suggest that individual or combinations of Smads may be necessary during mouse bladder organogenesis and may be critical mediators for bladder smooth muscle differentiation.

Rare allelic forms of PRDM9 associated with childhood leukemogenesis

One of the most rapidly evolving genes in humans, PRDM9, is a key determinant of the distribution of meiotic recombination events. Mutations in this meiotic-specific gene have previously been associated with male infertility in humans and recent studies suggest that PRDM9 may be involved in pathological genomic rearrangements. In studying genomes from families with children affected by B-cell precursor acute lymphoblastic leukemia (B-ALL), we characterized meiotic recombination patterns within a family with two siblings having hyperdiploid childhood B-ALL and observed unusual localization of maternal recombination events. The mother of the family carries a rare PRDM9 allele, potentially explaining the unusual patterns found. From exomes sequenced in 44 additional parents of children affected with B-ALL, we discovered a substantial and significant excess of rare allelic forms of PRDM9. The rare PRDM9 alleles are transmitted to the affected children in half the cases; nonetheless there remains a significant excess of rare alleles among patients relative to controls. We successfully replicated this latter observation in an independent cohort of 50 children with B-ALL, where we found an excess of rare PRDM9 alleles in aneuploid and infant B-ALL patients. PRDM9 variability in humans is thought to influence genomic instability, and these data support a potential role for PRDM9 variation in risk of acquiring aneuploidies or genomic rearrangements associated with childhood leukemogenesis.

Ski inhibits TGF-β/phospho-Smad3 signaling and accelerates hypertrophic differentiation in chondrocytes

Since transforming growing factor-β (TGF-β)/Smad signaling inhibits chondrocyte maturation, endogenous negative regulators of TGF-β signaling are likely also important regulators of the chondrocyte differentiation process. One such negative regulator, Ski, is an oncoprotein that is known to inhibit TGF-β/Smad3 signaling via its interaction with phospho-Smad3 and recruitment of histone deacetylases (HDACs) to the DNA binding complex. Based on this, we hypothesized that Ski inhibits TGF-β signaling and accelerates maturation in chondrocytes via recruitment of HDACs to transcriptional complexes containing Smads. We tested this hypothesis in chick upper sternal chondrocytes (USCs), where gain and loss of Ski expression experiments were performed. Over-expression of Ski not only reversed the inhibitory effect of TGF-β on the expression of hypertrophic marker genes such as type X collagen (colX) and osteocalcin, it induced these genes basally as well. Conversely, knockdown of Ski by RNA interference led to a reduction of colX and osteocalcin expression under basal conditions. Furthermore, Ski blocked TGF-β induction of cyclinD1 and caused a basal up-regulation of Runx2, consistent with the observed acceleration of hypertrophy. Regarding mechanism, not only does Ski associate with phospho-Smad2 and 3, but its association with phospho-Smad3 is required for recruitment of HDAC4 and 5. Implicating this recruitment of HDACs in the phenotypic effects of Ski in chondrocytes, the HDAC inhibitor SAHA reversed the up-regulation of colX and osteocalcin in Ski over-expressing cells. These results suggest that inhibition of TGF-β signaling by Ski, which involves its association with phospho-Smad3 and recruitment of HDAC4 and 5, leads to accelerated chondrocyte differentiation.

CCN6 modulates BMP signaling via the Smad-independent TAK1/p38 pathway, acting to suppress metastasis of breast cancer

CCN6 (WISP3) is an extracellular matrix protein that exerts tumor suppressive functions in breast cancer, where its decreased expression is a feature of advanced disease. However, neither its role nor mechanism of action in breast cancer metastasis has been established. Bone morphogenetic proteins (BMPs), which constitute ligands of the TGF-β superfamily, are multifunctional cytokines that induce epithelial-mesenchymal transition, cell invasion, and metastasis. In this study, we identify a CCN6-BMP4-TAK1 kinase signaling pathway that controls the ability of the p38 MAP kinase to regulate acinar morphogenesis and invasion of breast cells. ShRNA-mediated attenuation of CCN6 in human mammary epithelial cells led to BMP4 upregulation as a major response to exposure to the TGF-β superfamily. CCN6 attenuation also induced BMP4-mediated activation of the Smad-independent TAK1 and p38 kinases. Conversely, ectopic expression of CCN6 in breast cancer cells antagonized BMP4-mediated TAK1/p38 activation and invasive capacity, both by binding BMP4 protein as well as decreasing BMP4 protein levels. Effects on BMP4 and p38 were confirmed in vivo where they correlated with decreased metastasis. In clinical specimens, we found that CCN6 expression was inversely associated with BMP4 and phospho-p38 levels in 69% of invasive breast carcinomas examined, consistent with the functional results. Together our findings identify a novel modifier pathway through which CCN6 acts to limit breast cancer invasion and metastasis.

Smad6 is essential to limit BMP signaling during cartilage development

Bone morphogenetic protein (BMP) signaling pathways regulate multiple aspects of endochondral bone formation. The importance of extracellular antagonists as regulators of BMP signaling has been defined. In vitro studies reveal that the intracellular regulators, inhibitory Smads 6 and 7, can regulate BMP-mediated effects on chondrocytes. Although in vivo studies in which inhibitory Smads were overexpressed in cartilage have shown that inhibitory Smads have the potential to limit BMP signaling in vivo, the physiological relevance of inhibitory Smad activity in skeletal tissues is unknown. In this study, we have determined the role of Smad6 in endochondral bone formation. Loss of Smad6 in mice leads to defects in both axial and appendicular skeletal development. Specifically, Smad6-/- mice exhibit a posterior transformation of the seventh cervical vertebra, bilateral ossification centers in lumbar vertebrae, and bifid sternebrae due to incomplete sternal band fusion. Histological analysis of appendicular bones revealed delayed onset of hypertrophic differentiation and mineralization at midgestation in Smad6-/- mice. By late gestation, however, an expanded hypertrophic zone, associated with an increased pool of proliferating cells undergoing hypertrophy, was evident in Smad6 mutant growth plates. The mutant phenotype is attributed, at least in part, to increased BMP responsiveness in Smad6-deficient chondrocytes. Overall, our results show that Smad6 is required to limit BMP signaling during endochondral bone formation.

Inhibitory machinery for the TGF-β family signaling pathway

Transforming growth factor-β (TGF-β) family signaling regulates cell growth and differentiation of many different cell types and is widely involved in the regulation of homeostasis during both embryogenesis and adult life. Therefore, aberrant TGF-β family signal transduction is linked to congenital disorders, tumorigenicity, and fibrosis, which can be life-threatening. A specific receptor-ligand complex initiates transduction of TGF-β family signaling to the nucleus via intracellular signal molecules, mainly Smads, whereby a number of bioactivities such as wound healing, immunomodulation, apoptosis, and angiogenesis are controlled. To avoid an excess of TGF-β family signaling in cells, the duration and intensity of the TGF-β family signal appear to be subject to elaborate regulation. In this paper, we describe recent advances in the understanding of how TGF-β family signals are perturbed and terminated to maintain homeostasis in cells.

IL-13 induces connective tissue growth factor in rat hepatic stellate cells via TGF-β-independent Smad signaling

Connective tissue growth factor (CTGF) plays a central role in stimulating extracellular matrix deposition in the liver, and hence is considered a critical mediator of TGF-β-dependent fibrogenesis. Hepatic stellate cells (HSCs) are known as the major source of CTGF in damaged liver. However, previous studies revealed that IL-13, rather than TGF-β, represents the predominant inducer of CTGF expression in HSCs. We now dissected IL-13 downstream signaling that modulates CTGF expression in HSCs. IL-13 induces a time- and dosage-dependent increase of CTGF in a TGF-β-independent manner. This process requires participation of different Smad proteins and their upstream receptor kinases (activin receptor-like kinases). Smad1 and Smad2 were identified as the key mediators of IL-13-dependent CTGF expression. Furthermore, IL-13 induces Stat6 phosphorylation in HSCs, but Stat6 was not involved in CTGF induction. Instead, the Erk1/2-MAPK pathway was found to be responsible for IL-13-induced early Smad phosphorylation and CTGF synthesis. We demonstrate that IL-13 induces CTGF expression in HSCs by activating TGF-β-independent activin receptor-like kinase/Smad signaling via the Erk-MAPK pathway rather than via its canonical JAK/Stat6 pathway. These results provide an improved new insight into the molecular mechanisms of profibrotic IL-13 activities in the liver.

Emerging roles for the transforming growth factor-{beta} superfamily in regulating adiposity and energy expenditure

Members of the TGF-β superfamily regulate many aspects of development, including adipogenesis. Studies in cells and animal models have characterized the effects of superfamily signaling on adipocyte development, adiposity, and energy expenditure. Although bone morphogenetic protein (BMP) 4 is generally considered a protein that promotes the differentiation of white adipocytes, BMP7 has emerged as a selective regulator of brown adipogenesis. Conversely, TGF-β and activin A inhibit adipocyte development, a process augmented in TGF-β-treated cells by Smads 6 and 7, negative regulators of canonical TGF-β signaling. Other superfamily members have mixed effects on adipogenesis depending on cell culture conditions, the timing of expression, and the cell type, and many of these effects occur by altering the expression or activities of proteins that control the adipogenic cascade, including members of the CCAAT/enhancer binding protein family and peroxisome proliferator-activated receptor-γ. BMP7, growth differentiation factor (GDF) 8, and GDF3 are versatile in their mechanisms of action, and altering their normal expression characteristics has significant effects on adiposity in vivo. In addition to their roles in adipogenesis, activins and BMP7 regulate energy expenditure by affecting the expression of genes that contribute to mitochondrial biogenesis and function. GDF8 signals through its own receptors during adipogenesis while antagonizing BMP7, an example of a ligand from one major branch of the superfamily regulating the other. With such intricate relationships that ultimately affect adiposity, TGF-β superfamily signaling holds considerable promise as a target for treating human obesity and its comorbidities.

Role of p38 MAPK pathway in BMP4-mediated Smad-dependent premature senescence in lung cancer cells

BMP4 (bone morphogenetic protein 4) is a multifunctional cytokine known to exert its biological effects through a variety of signalling pathways. The diverse function of BMP4 appears to be due to multiple pathways activated by BMP4 itself. Our previous studies have demonstrated that BMP4 is able to drive lung cancer cells into a process of premature senescence; however, the signalling pathways, as well their interplays and roles associated with this process, are not well understood. To address these questions, in the present study we investigated the signalling and molecular mechanisms underlying the BMP4-induced senescence, and our data demonstrated that p38 MAPK (mitogen-activated protein kinase) and Smad pathways were necessary for this process. Meanwhile, the ERK1/2 (extracellular-signal-regulated kinase 1/2) pathway, which is required for senescence, was not activated by BMP4 in the lung cancer cell line NCI-H460. We also showed that the BMP4-responsive R-Smads (receptor-regulated Smads), i.e. Smad1 and Smad5, were necessary for the up-regulation of p16(INK)⁴(a) and p21(WAF)¹(/cip)¹ and for the induction of premature senescence. Furthermore, we found that activation of the p38 MAPK pathway by BMP4 was essential for the full activation of transcription potential of Smad1/5. Overall, the results of the present study implicate a complex co-operation between p38 MAPK and Smad pathways in BMP4-mediated premature senescence.

Investigating bone morphogenetic protein (BMP) signaling in a newly established human cell line expressing BMP receptor type II

Bone morphogenetic proteins (BMPs), members of the transforming growth factor β cytokine superfamily, elicit various biological effects in different tissues. BMP receptor type II (BMPRII) contains a unique carboxyl-terminal region that interacts with multiple signaling molecules. However, expression of endogenous BMPRII is low in various mammalian cell lines, which hampers the analysis of BMP signaling. Therefore, we established a human cell line expressing BMPRII tagged with a Flag epitope (BMPRII-Flag) using the tetracycline-controlled Flp-In T-REx gene expression system. The BMPRII-Flag gene was introduced into the Flp-In T-REx 293 (FT293) cell line, a derivative of human 293 embryonic kidney fibroblasts. Then we analyzed the expression of key BMP target genes, inhibitors of DNA binding (Id) family members (Id1, Id2, and Id3) and the inhibitory Smads Smad6 and Smad7, in parental FT293 cells and an established cell line, FT293-BMPRII, by quantitative real-time PCR. Tetracycline treatment significantly increased the expression of BMPRII-Flag mRNA and protein in FT293-BMPRII cells, but induced no significant changes in expression of Id1, Id2, Id3, Smad6, or Smad7 mRNA. In contrast, treatment with a BMPRII ligand BMP2 induced the expression of Id1, Id2, Id3, and Smad6 in parental FT293 cells and FT293-BMPRII cells. Tetracycline-induced BMPRII-Flag expression significantly enhanced the induction of Id1, Id3, and Smad6 mRNA expression in FT293-BMPRII cells treated with BMP2. These findings provide evidence that although BMPRII has no obvious effect on the expression of representative BMP target genes, it differentially modulates the responsiveness of target genes to BMP2.

Splitting placodes: effects of bone morphogenetic protein and Activin on the patterning and identity of mouse incisors

The single large rodent incisor in each jaw quadrant is evolutionarily derived from a mammalian ancestor with many small incisors. The embryonic placode giving rise to the mouse incisor is considerably larger than the molar placode, and the question remains whether this large incisor placode is a developmental requisite to make a thick incisor. Here we used in vitro culture system to experiment with the molecular mechanism regulating tooth placode development and how mice have thick incisors. We found that large placodes are prone to disintegration and formation of two to three small incisor placodes. The balance between one large or multiple small placodes was altered through the regulation of bone morphogenetic protein (BMP) and Activin signaling. Exogenous Noggin, which inhibits BMP signaling, or exogenous Activin cause the development of two to three incisors. These incisors were more slender than normal incisors. Additionally, two inhibitor molecules, Sostdc1 and Follistatin, which regulate the effects of BMPs and Activin and have opposite expression patterns, are likely to be involved in the incisor placode regulation in vivo. Furthermore, inhibition of BMPs by recombinant Noggin has been previously suggested to cause a change in the tooth identity from the incisor to the molar. This evidence has been used to support a homeobox code in determining tooth identity. Our work provides an alternative interpretation, where the inhibition of BMP signaling can lead to splitting of the large incisor placode and the formation of partly separate incisors, thereby acquiring molar-like morphology without a change in tooth identity.

Trigenic neural crest-restricted Smad7 over-expression results in congenital craniofacial and cardiovascular defects

Smad7 is a negative regulator of TGFbeta superfamily signaling. Using a three-component triple transgenic system, expression of the inhibitory Smad7 was induced via doxycycline within the NCC lineages at pre- and post-migratory stages. Consistent with its role in negatively regulating both TGFbeta and BMP signaling in vitro, induction of Smad7 within the NCC significantly suppressed phosphorylation levels of both Smad1/5/8 and Smad2/3 in vivo, resulting in subsequent loss of NCC-derived craniofacial, pharyngeal and cardiac OFT cushion cells. At the cellular level, increased cell death was observed in pharyngeal arches. However, cell proliferation and NCC-derived smooth muscle differentiation were unaltered. NCC lineage mapping demonstrated that cardiac NCC emigration and initial migration were not affected, but subsequent colonization of the OFT was significantly reduced. Induction of Smad7 in post-migratory NCC resulted in interventricular septal chamber septation defects, suggesting that TGFbeta superfamily signaling is also essential for cardiac NCC at post-migratory stages to govern normal cardiac development. Taken together, the data illustrate that tightly regulated TGFbeta superfamily signaling plays an essential role during craniofacial and cardiac NCC colonization and cell survival in vivo.

Nodal signaling regulates the bone morphogenic protein pluripotency pathway in mouse embryonic stem cells

Members of the transforming growth factor-beta superfamily play essential roles in both the pluripotency and differentiation of embryonic stem (ES) cells. Although bone morphogenic proteins (BMPs) maintain pluripotency of undifferentiated mouse ES cells, the role of autocrine Nodal signaling is less clear. Pharmacological, molecular, and genetic methods were used to further understand the roles and potential interactions of these pathways. Treatment of undifferentiated ES cells with SB431542, a pharmacological inhibitor of Smad2 signaling, resulted in a rapid reduction of phosphorylated Smad2 and altered the expression of several putative downstream targets. Unexpectedly, inhibition of the Nodal signaling pathway resulted in enhanced BMP signaling, as assessed by Smad1/5 phosphorylation. SB431542-treated cells also demonstrated significant induction of the Id genes, which are known direct targets of BMP signaling and important factors in ES cell pluripotency. Inhibition of BMP signaling decreased the SB431542-mediated phosphorylation of Smad1/5 and induction of Id genes, suggesting that BMP signaling is necessary for some Smad2-mediated activity. Because Smad7, a known inhibitory factor to both Nodal and BMP signaling, was down-regulated following inhibition of Nodal-Smad2 signaling, the contribution of Smad7 to the cross-talk between the transforming growth factor-beta pathways in ES cells was examined. Biochemical manipulation of Smad7 expression, through shRNA knockdown or inducible gene expression, significantly reduced the SB431542-mediated phosphorylation of Smad1/5 and induction of the Id genes. We conclude that autocrine Nodal signaling in undifferentiated mouse ES cells modulates the vital pluripotency pathway of BMP signaling.

Overexpression of Smad6 exacerbates pancreatic fibrosis in murine caerulein-induced chronic pancreatic injuries

OBJECTIVES

We examined the effect of the overexpression of Smad6 on pancreatic fibrosis after chronic pancreatic injury.

METHODS

Chronic pancreatic injury was induced in transgenic mice overexpressing Smad6 (Tg mice) in acini and wild-type (Wt) mice by 3 episodes of acute pancreatitis per week for 1 to 4 consecutive weeks. Acute pancreatitis was elicited by 6 intraperitoneal injections of caerulein (Cn) at 50 microg/kg of body weight at hourly intervals. Pancreatic fibrosis was evaluated by histological examination and hydroxyproline content before and 1, 2, 3, and 4 weeks of repetitive episodes of Cn-induced acute pancreatitis. We further determined transforming growth factor beta1 (TGF-beta1) messenger RNA expression and trypsin activity in the pancreas.

RESULTS

After repetitive episodes of acute pancreatitis, pancreatic fibrosis in Tg mice was significantly severer than that in Wt mice at all time points (weeks 1-4). The expression of TGF-beta1 messenger RNA and the activity of trypsin in the pancreas in the Tg mice were significantly high compared with those in the Wt mice at all corresponding time points after repetitive episodes of acute pancreatitis.

CONCLUSIONS

These results demonstrated that overexpression of Smad6 in acini enhanced the development of pancreatic fibrosis after chronic pancreatic injury.

Inhibitor of differentiation (Id) genes are expressed in the steroidogenic cells of the ovine ovary and are differentially regulated by members of the transforming growth factor-beta family

Inhibitor of differentiation (Id) proteins act during embryogenesis and development to repress gene transcription required for lineage commitment, while promoting cell growth. Growth factors belonging to the TGFbeta superfamily of signaling molecules, notably the bone morphogenetic proteins (BMPs) and activin, can regulate Id expression in these tissues. Id expression and function in adult physiology is less well determined, and we hypothesized a role for Id proteins in the adult mammalian ovary. Immunohistochemistry for Id1, Id2, Id3, and Id4 in the sheep ovary revealed consistent expression in granulosa and thecal cells of ovarian follicles throughout development. In atretic follicles, Id proteins were selectively down-regulated in thecal cells (P < 0.0001). Additionally, Id1 was universally up-regulated in the cumulus cells adjacent to the oocyte. Immunohistochemistry for phospho (p)-smad 1/5/8 signaling components (stimulated by BMPs) showed a punctate pattern of expression whereas p-smad 2/3 (stimulated by activin) was ubiquitously expressed in follicles. Neither pathway, however, displayed differential staining in line with Id1 cumulus-specific expression, suggesting a more complex relationship between Id1 expression and TGFbeta signaling in these cells. Nevertheless, in vitro, stimulation of ovine granulosa cells with BMP6 or activin A led to a respective increase and decrease in Id1 (P < 0.0001), Id2 (P < 0.0001), Id3 (P < 0.0001), and Id4 (P < 0.05) transcripts, and Id1 gene expression was further manipulated by the oocyte-secreted factors BMP15 and growth differentiation factor 9 (P < 0.001). These data confirm that TGFbeta signaling can regulate Id gene expression in the sheep ovarian follicle and suggest a functional role for the Id family in the mammalian ovary.

Analysis of activin/TGFB-signaling modulators within the normal and dysfunctional adult human testis reveals evidence of altered signaling capacity in a subset of seminomas

Activin is a pleiotropic growth factor belonging to the transforming growth factor-beta (TGFB) superfamily of signaling molecules. Regulated activin signaling is known to influence several steps in rodent male gamete differentiation. TGFB ligand isoforms, TGFB1-B3, also influence germ cell survival in the rodent testis at the onset of spermatogenesis and around the time of puberty. Given the importance of regulated activin and TGFB signaling in testis development and function, we sought to investigate the cellular production sites of activin/TGFB-signaling modulators in normal and dysfunctional adult human testes samples. Signaling transducers phosphorylated SMAD2/3, and signaling modulators SMAD6, MAN-1, inhibin alpha (INHA), and beta-glycan were detected in Bouins fixed, paraffin-embedded adult human testis sections using immunohistochemistry. Additional samples examined were from testicular cancer patients and from normal men subjected to gonadotropin suppression with androgen-based contraceptives. Our findings identify distinct differences between normal and gonadotropin-deprived human testis in the expression and cellular localization of activin/TGFB-signaling modulators. The presence of a nuclear phosphorylated SMAD2/3 signal in all analyzed seminoma specimens indicated active activin/TGFB signaling. Moreover, a subset of seminoma specimens exhibited selective enhanced expression of beta-glycan (4 out of 28 seminoma tumors), INHA (6 out of 28), and MAN-1 (6 out of 28), highlighting potential functional differences between individual tumors in their capacity to regulate activin/TGFB signaling. Within the heterogenous nonseminomas, expression of signaling modulators was variable and reflected the degree of somatic differentiation. Thus, synthesis of activin and TGFB-signaling modulators may be affected by spermatogenic disruption and altered hormone levels in the testis.

Growth differentiation factor 9 enhances activin a-induced inhibin B production in human granulosa cells

Activin A or growth differentiation factor 9 (GDF9) alone can increase beta(B)-mRNA level in human granulosa-lutein cells from women undergoing in vitro fertilization, but their potential interactions and related cell signaling pathways involved are unknown. We therefore compared inhibin subunit and inhibin levels and activation of activin receptors (ACVRs) and Smad signaling pathway in these human granulosa-lutein cells with and without GDF9 and/or activin A treatment. Inhibin subunit (alpha, beta(A), beta(B)), ACVR, and Smad2/3/4/7 mRNA levels, inhibin A and B production, and Smad phosphorylation were assessed by real-time RT-PCR, ELISA, and immunoblotting, respectively. Data were analyzed by ANOVA followed by Tukey's test. Activin A (1-50 ng/ml) or GDF9 (1-200 ng/ml) alone had only little stimulatory effects on alpha- and beta(A)-mRNA levels. In contrast, GDF9 could stimulate beta(B)-subunit levels but to a lesser degree than the dose- and time-dependent effects of activin A. Compared with untreated cells, GDF9 pretreatment for 24 h significantly enhanced activin A-induced beta(B)-mRNA levels, inhibin B secretion, and Smad2/3 phosphorylation (effects attenuated by bone morphogenetic protein receptor 2 extracellular domain, a GDF9 antagonist); and induced ACVR2B/1B and Smad2/3 but reduced Smad7 (an inhibitory Smad) mRNA levels. We report here for the first time that GDF9 enhances cell response to activin A by modulating key components of the activin signaling pathway in regulating inhibin subunits and hence inhibin B production in human granulosa-lutein cells.

BMP4-Smad signaling pathway mediates adriamycin-induced premature senescence in lung cancer cells

Cell senescence, an irreversible cell cycle arrest, reflects a safeguard program that limits the capacity of uncontrolled cell proliferation. Treatment of tumor cells with certain chemotherapeutic agents activates premature senescence to decrease the tumorigenecity. Here we show that sublethal concentrations of adriamycin could induce premature senescence in lung cancer cells. Adriamycin treatment resulted in the up-regulation of BMP4, which is underexpressed in NSCLC (non-small cell lung cancers). Moreover, the BMP4-Smad pathway played a key role in mediating adriamycin-induced senescence. Overexpression of BMP4 was able to induce premature senescence in lung cancer cells and this process required the participation of cyclin/cyclin-dependent kinase (cdk) inhibitors p16(INK4a) and p21(WAF1/cip1). We also show that increases of p16(INK4a) and p21(WAF1/cip1) expression in response to BMP4 were mediated by the Smad signaling pathway. Furthermore, our data revealed that p300 was recruited to P16(INK4a) and P21(WAF1/cip1) promoters by Smad1/5/8 to induce the hyperacetylation of histones H3 and H4 at the promoters. The present study provides useful clues to the evaluation of the potentiality of BMP4 as a responsive molecular target for cancer chemotherapy.

Skeletal overexpression of connective tissue growth factor impairs bone formation and causes osteopenia

Connective tissue growth factor (CTGF), a member of the CCN family of proteins, is expressed in skeletal cells, and the ctgf null mutation leads to neonatal lethality due to defects in skeletal development. To define the function of CTGF in the postnatal skeleton, we created transgenic mice overexpressing CTGF under the control of the human osteocalcin promoter. CTGF transgenic female and male mice exhibited a significant decrease in bone mineral density, compared with wild-type littermate controls. Bone histomorphometry revealed that CTGF overexpression caused decreased trabecular bone volume due to impaired osteoblastic activity because mineral apposition and bone formation rates were decreased. Osteoblast and osteoclast number and bone resorption were not altered. Calvarial osteoblasts and stromal cells from CTGF transgenics displayed decreased alkaline phosphatase and osteocalcin mRNA levels and reduced bone morphogenetic protein (BMP) signaling mothers against decapentaplegic, Wnt/beta-catenin, and IGF-I/Akt signaling. In conclusion, CTGF overexpression in vivo causes osteopenia, secondary to decreased bone formation, possibly by antagonizing BMP, Wnt, and IGF-I signaling and activity.