The cysteine-rich domain protein KCP is a suppressor of transforming growth factor beta/activin signaling in renal epithelia

Kielin/chordin-like protein deficiency aggravates pressure overload-induced cardiac dysfunction and remodeling via P53/P21/CCNB1 signaling in mice

Targeting cardiac remodeling is regarded as a key therapeutic strategy for heart failure. Kielin/chordin-like protein (KCP) is a secretory protein with 18 cysteine-rich domains and associated with kidney and liver fibrosis. However, the relationship between KCP and cardiac remodeling remains unclear. Here, we aimed to investigate the role of KCP in cardiac remodeling induced by pressure overload and explore its potential mechanisms. Left ventricular (LV) KCP expression was measured with real-time quantitative PCR, western blotting, and immunofluorescence staining in pressure overload-induced cardiac remodeling in mice. Cardiac function and remodeling were evaluated in wide-type (WT) mice and KCP knockout (KO) mice by echocardiography, which were further confirmed by histological analysis with hematoxylin and eosin and Masson staining. RNA sequence was performed with LV tissue from WT and KO mice to identify differentially expressed genes and related signaling pathways. Primary cardiac fibroblasts (CFs) were used to validate the regulatory role and potential mechanisms of KCP during fibrosis. KCP was down-regulated in the progression of cardiac remodeling induced by pressure overload, and was mainly expressed in fibroblasts. KCP deficiency significantly aggravated pressure overload-induced cardiac dysfunction and remodeling. RNA sequence revealed that the role of KCP deficiency in cardiac remodeling was associated with cell division, cell cycle, and P53 signaling pathway, while cyclin B1 (CCNB1) was the most significantly up-regulated gene. Further investigation in vivo and in vitro suggested that KCP deficiency promoted the proliferation of CFs via P53/P21/CCNB1 pathway. Taken together, these results suggested that KCP deficiency aggravates cardiac dysfunction and remodeling induced by pressure overload via P53/P21/CCNB1 signaling in mice.

Kielin/chordin-like protein deficiency causes cardiac aging in male mice

Previous studies have demonstrated that bone morphogenetic proteins (BMPs) play important roles in cardiovascular diseases, including atherosclerosis, artery calcification, myocardial remodeling, pulmonary arterial hypertension, and diabetic cardiomyopathy. Kielin/chordin-like protein (KCP) is a secreted protein that regulates the expression and function of BMPs. However, the role of KCP in cardiac aging remains unknown. In this study, we aimed to investigate the role of KCP in cardiac aging and its possible mechanisms. Echocardiogram showed that heart function was impaired in aged mice (24 months). In addition, analysis of heart structure showed that KCP knockout (KO) aggravated cardiac remodeling in aged mice. Moreover, KCP KO increased p-smad2/3 and TGF-β expression, while decreased BMP-2 expression in aged mice. Furthermore, KCP KO increased the expression of cardiac senescence-related proteins in aged mice. KCP KO aggravated the imbalance of oxidants and antioxidants and increased the expression of proinflammatory cytokines and cardiomyocyte apoptosis in aged mice. Our study demonstrated that KCP KO aggravated cardiac aging in mice by increasing the levels of oxidative stress, inflammation, and cardiomyocyte apoptosis. KEY MESSAGE: KCP KO aggravated aging-related cardiac dysfunction and remodeling in male mice. KCP KO aggravated cardiac aging by increasing the levels of oxidative stress, inflammation, and cardiomyocyte apoptosis.

Decoding anterior-posterior axis emergence among mouse, monkey, and human embryos

Anterior-posterior axis formation regulated by the distal visceral endoderm (DVE) and anterior visceral endoderm (AVE) is essential for peri-implantation embryogenesis. However, the principles of the origin and specialization of DVE and AVE remain elusive. Here, with single-cell transcriptome analysis and pseudotime prediction, we show that DVE and AVE independently originate from the specialized primary endoderm in mouse blastocysts. Along distinct developmental paths, these two lineages, respectively, undergo four representative states with stage-specific transcriptional patterns around implantation. Further comparative analysis shows that AVE, but not DVE, is detected in human and non-human primate embryos, defining differences in polarity formation across species. Moreover, stem cell-assembled human blastoids lack DVE or AVE precursors, implying that additional induction of stem cells with DVE/AVE potential could promote the current embryo-like models and their post-implantation growth. Our work provides insight into understanding of embryonic polarity formation and early mammalian development.

Negative regulators of TGF-β1 signaling in renal fibrosis; pathological mechanisms and novel therapeutic opportunities

Elevated expression of the multifunctional cytokine transforming growth factor β1 (TGF-β1) is causatively linked to kidney fibrosis progression initiated by diabetic, hypertensive, obstructive, ischemic and toxin-induced injury. Therapeutically relevant approaches to directly target the TGF-β1 pathway (e.g., neutralizing antibodies against TGF-β1), however, remain elusive in humans. TGF-β1 signaling is subjected to extensive negative control at the level of TGF-β1 receptor, SMAD2/3 activation, complex assembly and promoter engagement due to its critical role in tissue homeostasis and numerous pathologies. Progressive kidney injury is accompanied by the deregulation (loss or gain of expression) of several negative regulators of the TGF-β1 signaling cascade by mechanisms involving protein and mRNA stability or epigenetic silencing, further amplifying TGF-β1/SMAD3 signaling and fibrosis. Expression of bone morphogenetic proteins 6 and 7 (BMP6/7), SMAD7, Sloan-Kettering Institute proto-oncogene (Ski) and Ski-related novel gene (SnoN), phosphate tensin homolog on chromosome 10 (PTEN), protein phosphatase magnesium/manganese dependent 1A (PPM1A) and Klotho are dramatically decreased in various nephropathies in animals and humans albeit with different kinetics while the expression of Smurf1/2 E3 ligases are increased. Such deregulations frequently initiate maladaptive renal repair including renal epithelial cell dedifferentiation and growth arrest, fibrotic factor (connective tissue growth factor (CTGF/CCN2), plasminogen activator inhibitor type-1 (PAI-1), TGF-β1) synthesis/secretion, fibroproliferative responses and inflammation. This review addresses how loss of these negative regulators of TGF-β1 pathway exacerbates renal lesion formation and discusses the therapeutic value in restoring the expression of these molecules in ameliorating fibrosis, thus, presenting novel approaches to suppress TGF-β1 hyperactivation during chronic kidney disease (CKD) progression.

Effects of miR-101-3p on goat granulosa cells in vitro and ovarian development in vivo via STC1

Background

MiRNAs act as pivotal post-transcriptional gene mediators in the regulation of diverse biological processes, including proliferation, development and apoptosis. Our previous study has showed that miR-101-3p is differentially expressed in dairy goat ovaries compared single with multiple litters. The objective of this research was to explore the potential function and molecular mechanism of miR-101-3p via its target STC1 in goat ovarian growth and development.

Results

cDNA libraries were constructed using goat granulosa cells transfected with miR-101-3p mimics and negative control by RNA-sequencing. In total, 142 differentially expressed unigenes (DEGs) were detected between two libraries, including 78 down-regulated and 64 up-regulated genes. GO and KEGG enrichment analysis showed the potential impacts of DEGs on ovarian development. STC1 was singled out from DEGs for further research owing to it regulates reproductive-related processes. In vitro, bioinformatics analysis and 3′-UTR assays confirmed that STC1 was a target of miR-101-3p. ELISA was performed to detect the estrogen (E2) and progesterone (P4) levels. CCK8, EdU and flow cytometry assays were performed to detect the proliferation and apoptosis of granulosa cells. Results showed that miR-101-3p regulated STAR, CYP19A1, CYP11A1 and 3β-HSD steroid hormone synthesis-associated genes by STC1 depletion, thus promoted E2 and P4 secretions. MiR-101-3p also affected the key protein PI3K, PTEN, AKT and mTOR in PI3K-AKT pathway by STC1, thereby suppressing proliferation and promoting apoptosis of granulosa cells. In vivo, the distribution and expression levels of miR-101-3p in mouse ovaries were determined through fluorescence in situ hybridisation (FISH). Immunohistochemistry results showed that STC1 expression was suppressed in mouse ovaries in miR-101-3p-agonist and siRNA-STC1 groups. Small and stunted ovarian fragments, decreased numbers of follicles at diverse stages were observed using Hematoxylin-eosin (HE) staining, thereby showing unusual ovarian development after miR-101-3p overexpression or STC1 depletion. Inhibition of miR-101-3p manifested opposite results.

Conclusions

Taken together, our results demonstrated a regulatory mechanism of miR-101-3p via STC1 in goat granulosa cells, and offered the first in vivo example of miR-101-3p and STC1 functions required for ovarian development.

Conservation and divergence of protein pathways in the vertebrate heart

Heart disease is the leading cause of death in the western world. Attaining a mechanistic understanding of human heart development and homeostasis and the molecular basis of associated disease states relies on the use of animal models. Here, we present the cardiac proteomes of 4 model vertebrates with dual circulatory systems: the pig (Sus scrofa), the mouse (Mus musculus), and 2 frogs (Xenopus laevis and Xenopus tropicalis). Determination of which proteins and protein pathways are conserved and which have diverged within these species will aid in our ability to choose the appropriate models for determining protein function and to model human disease. We uncover mammalian- and amphibian-specific, as well as species-specific, enriched proteins and protein pathways. Among these, we find and validate an enrichment in cell-cycle-associated proteins within Xenopus laevis. To further investigate functional units within cardiac proteomes, we develop a computational approach to profile the abundance of protein complexes across species. Finally, we demonstrate the utility of these data sets for predicting appropriate model systems for studying given cardiac conditions by testing the role of Kielin/chordin-like protein (Kcp), a protein found as enriched in frog hearts compared to mammals. We establish that germ-line mutations in Kcp in Xenopus lead to valve defects and, ultimately, cardiac failure and death. Thus, integrating these findings with data on proteins responsible for cardiac disease should lead to the development of refined, species-specific models for protein function and disease states.

Opposing roles and potential antagonistic mechanism between TGF-β and BMP pathways: Implications for cancer progression

The transforming growth factor β (TGF-β) superfamily participates in tumour proliferation, apoptosis, differentiation, migration, invasion, immune evasion and extracellular matrix remodelling. Genetic deficiency in distinct components of TGF-β and BMP-induced signalling pathways or their excessive activation has been reported to regulate the development and progression of some cancers. As more in-depth studies about this superfamily have been conducted, more evidence suggests that the TGF-β and BMP pathways play an opposing role. The cross-talk of these 2 pathways has been widely studied in kidney disease and bone formation, and the opposing effects have also been observed in some cancers. However, the antagonistic mechanisms are still insufficiently investigated in cancer. In this review, we aim to display more evidences and possible mechanisms accounting for the antagonism between these 2 pathways, which might provide some clues for further study in cancer.

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Describe the basics of TGF-β and BMP signalling

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Summarize the potential mechanisms accounting for the antagonism between TGF-β and BMP pathways

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Provide some evidence about the antagonistic effects between pathways observed in some cancers

BMP Signalling at the Crossroad of Liver Fibrosis and Regeneration

Bone Morphogenetic Proteins (BMPs) belong to the Transforming Growth Factor-β (TGF-β) family. Initially identified due to their ability to induce bone formation, they are now known to have multiple functions in a variety of tissues, being critical not only during development for tissue morphogenesis and organogenesis but also during adult tissue homeostasis. This review focus on the liver as a target tissue for BMPs actions, devoting most efforts to summarize our knowledge on their recently recognized and/or emerging roles on regulation of the liver regenerative response to various insults, either acute or chronic and their effects on development and progression of liver fibrosis in different pathological conditions. In an attempt to provide the basis for guiding research efforts in this field both the more solid and more controversial areas of research were highlighted.

Clinical Relevance and Mechanisms of Antagonism Between the BMP and Activin/TGF-β Signaling Pathways

The transforming growth factor β (TGF-β) superfamily is a large group of signaling molecules that participate in embryogenesis, organogenesis, and tissue homeostasis. These molecules are present in all animal genomes. Dysfunction in the regulation or activity of this superfamily's components underlies numerous human diseases and developmental defects. There are 2 distinct arms downstream of the TGF-β superfamily ligands-the bone morphogenetic protein (BMP) and activin/TGF-β signaling pathways-and these 2 responses can oppose one another's effects, most notably in disease states. However, studies have commonly focused on a single arm of the TGF-β superfamily, and the antagonism between these pathways is unknown in most physiologic and pathologic contexts. In this review, the authors summarize the clinically relevant scenarios in which the BMP and activin/TGF-β pathways reportedly oppose one another and identify several molecular mechanisms proposed to mediate this interaction. Particular attention is paid to experimental findings that may be informative to human pathology to highlight potential therapeutic approaches for future investigation.

The kielin/chordin-like protein (KCP) attenuates high-fat diet-induced obesity and metabolic syndrome in mice

Obesity and its associated complications such as insulin resistance and non-alcoholic fatty liver disease are reaching epidemic proportions. In mice, the TGF-β superfamily is implicated in the regulation of white and brown adipose tissue differentiation. The kielin/chordin-like protein (KCP) is a secreted regulator of the TGF-β superfamily pathways that can inhibit both TGF-β and activin signals while enhancing bone morphogenetic protein (BMP) signaling. However, KCP's effects on metabolism and obesity have not been studied in animal models. Therefore, we examined the effects of KCP loss or gain of function in mice that were maintained on either a regular or a high-fat diet. KCP loss sensitized the mice to obesity and associated complications such as glucose intolerance and adipose tissue inflammation and fibrosis. In contrast, transgenic mice that expressed KCP in the kidney, liver, and adipose tissues were resistant to developing high-fat diet-induced obesity and had significantly reduced white adipose tissue. Moreover, KCP overexpression shifted the pattern of SMAD signaling in vivo, increasing the levels of phospho (P)-SMAD1 and decreasing P-SMAD3. Adipocytes in culture showed a cell-autonomous effect in response to added TGF-β1 or BMP7. Metabolic profiling indicated increased energy expenditure in KCP-overexpressing mice and reduced expenditure in the KCP mutants with no effect on food intake or activity. These findings demonstrate that shifting the TGF-β superfamily signaling with a secreted protein can alter the physiology and thermogenic properties of adipose tissue to reduce obesity even when mice are fed a high-fat diet.

Bone morphogenetic protein signaling in musculoskeletal cancer

PURPOSE

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-β (TGF-β) superfamily of proteins; they were initially named after their ability to induce ectopic bone formation. Published studies have proved BMPs' role in a variety of biological processes such as embryogenesis and patterning of body axes, and maintaining adult tissue homeostasis. Other studies have focused on BMPs properties, functions and possible involvement in skeletal diseases, including cancer.

METHODS

A literature search mainly paying attention to the role of BMPs in musculoskeletal tumors was performed in electronic databases.

RESULTS

This article discusses BMPs synthesis and signaling, and summarizes their prominent roles in the skeletal system for the differentiation of osteoblasts, osteocytes and chondrocytes.

CONCLUSIONS

The review emphasizes on the role of BMP signaling in the initiation and progression of musculoskeletal cancer.

The kielin/chordin-like protein KCP attenuates nonalcoholic fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and is increasing with the rising rate of obesity in the developed world. Signaling pathways known to influence the rate of lipid deposition in liver, known as hepatic steatosis, include the transforming growth factor (TGF) superfamily, which function through the SMAD second messengers. The kielin/chordin-like protein (KCP) is a large secreted protein that can enhance bone morphogenetic protein signaling while suppressing TGF-β signaling in cells and in genetically modified mice. In this report, we show that aging KCP mutant (Kcp-/-) mice are increasingly susceptible to developing hepatic steatosis and liver fibrosis. When young mice are put on a high-fat diet, Kcp-/- mice are also more susceptible to developing liver pathology, compared with their wild-type littermates. Furthermore, mice that express a Pepck-KCP transgene (KcpTg) in the liver are resistant to developing liver pathology even when fed a high-fat diet. Analyses of liver tissues reveal a significant reduction of P-Smad3, consistent with a role for KCP in suppressing TGF-β signaling. Transcriptome analyses show that livers from Kcp-/- mice fed a normal diet are more like wild-type livers from mice fed a high-fat diet. However, the KCP transgene can suppress many of the changes in liver gene expression that are due to a high-fat diet. These data demonstrate that shifting the TGF-β signaling paradigm with the secreted regulatory protein KCP can significantly alter the liver pathology in aging mice and in diet-induced NAFLD.

Agonists and Antagonists of TGF-β Family Ligands

The discovery of the transforming growth factor β (TGF-β) family ligands and the realization that their bioactivities need to be tightly controlled temporally and spatially led to intensive research that has identified a multitude of extracellular modulators of TGF-β family ligands, uncovered their functions in developmental and pathophysiological processes, defined the mechanisms of their activities, and explored potential modulator-based therapeutic applications in treating human diseases. These studies revealed a diverse repertoire of extracellular and membrane-associated molecules that are capable of modulating TGF-β family signals via control of ligand availability, processing, ligand-receptor interaction, and receptor activation. These molecules include not only soluble ligand-binding proteins that were conventionally considered as agonists and antagonists of TGF-β family of growth factors, but also extracellular matrix (ECM) proteins and proteoglycans that can serve as "sink" and control storage and release of both the TGF-β family ligands and their regulators. This extensive network of soluble and ECM modulators helps to ensure dynamic and cell-specific control of TGF-β family signals. This article reviews our knowledge of extracellular modulation of TGF-β growth factors by diverse proteins and their molecular mechanisms to regulate TGF-β family signaling.

Host-Associated Genomic Features of the Novel Uncultured Intracellular Pathogen Ca. Ichthyocystis Revealed by Direct Sequencing of Epitheliocysts

Advances in single-cell and mini-metagenome sequencing have enabled important investigations into uncultured bacteria. In this study, we applied the mini-metagenome sequencing method to assemble genome drafts of the uncultured causative agents of epitheliocystis, an emerging infectious disease in the Mediterranean aquaculture species gilthead seabream. We sequenced multiple cyst samples and constructed 11 genome drafts from a novel beta-proteobacterial lineage, Candidatus Ichthyocystis. The draft genomes demonstrate features typical of pathogenic bacteria with an obligate intracellular lifestyle: a reduced genome of up to 2.6 Mb, reduced G + C content, and reduced metabolic capacity. Reconstruction of metabolic pathways reveals that Ca Ichthyocystis genomes lack all amino acid synthesis pathways, compelling them to scavenge from the fish host. All genomes encode type II, III, and IV secretion systems, a large repertoire of predicted effectors, and a type IV pilus. These are all considered to be virulence factors, required for adherence, invasion, and host manipulation. However, no evidence of lipopolysaccharide synthesis could be found. Beyond the core functions shared within the genus, alignments showed distinction into different species, characterized by alternative large gene families. These comprise up to a third of each genome, appear to have arisen through duplication and diversification, encode many effector proteins, and are seemingly critical for virulence. Thus, Ca Ichthyocystis represents a novel obligatory intracellular pathogenic beta-proteobacterial lineage. The methods used: mini-metagenome analysis and manual annotation, have generated important insights into the lifestyle and evolution of the novel, uncultured pathogens, elucidating many putative virulence factors including an unprecedented array of novel gene families.

Bone morphogenetic proteins and their antagonists: current and emerging clinical uses

Bone morphogenetic proteins (BMPs) are members of the TGFβ superfamily of secreted cysteine knot proteins that includes TGFβ1, nodal, activins and inhibins. BMPs were first discovered by Urist in the 1960s when he showed that implantation of demineralized bone into intramuscular tissue of rabbits induced bone and cartilage formation. Since this seminal discovery, BMPs have also been shown to play key roles in several other biological processes, including limb, kidney, skin, hair and neuronal development, as well as maintaining vascular homeostasis. The multifunctional effects of BMPs make them attractive targets for the treatment of several pathologies, including bone disorders, kidney and lung fibrosis, and cancer. This review will summarize current knowledge on the BMP signalling pathway and critically evaluate the potential of recombinant BMPs as pharmacological agents for the treatment of bone repair and tissue fibrosis in patients.

Altered Expression of Bone Morphogenetic Protein Accessory Proteins in Murine and Human Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a chronic, progressive fibrotic disease with a poor prognosis. The balance between transforming growth factor β1 and bone morphogenetic protein (BMP) signaling plays an important role in tissue homeostasis, and alterations can result in pulmonary fibrosis. We hypothesized that multiple BMP accessory proteins may be responsible for maintaining this balance in the lung. Using the bleomycin mouse model for fibrosis, we examined an array of BMP accessory proteins for changes in mRNA expression. We report significant increases in mRNA expression of gremlin 1, noggin, follistatin, and follistatin-like 1 (Fstl1), and significant decreases in mRNA expression of chordin, kielin/chordin-like protein, nephroblastoma overexpressed gene, and BMP and activin membrane-bound inhibitor (BAMBI). Protein expression studies demonstrated increased levels of noggin, BAMBI, and FSTL1 in the lungs of bleomycin-treated mice and in the lungs of idiopathic pulmonary fibrosis patients. Furthermore, we demonstrated that transforming growth factor β stimulation resulted in increased expression of noggin, BAMBI, and FSTL1 in human small airway epithelial cells. These results provide the first evidence that multiple BMP accessory proteins are altered in fibrosis and may play a role in promoting fibrotic injury.

The Bone Morphogenetic Proteins and Their Antagonists

The bone morphogenetic proteins (BMPs) and the growth and differentiation factors comprise a single family of some 20 homologous, dimeric cytokines which share the cystine-knot domain typical of the TGF-β superfamily. They control the differentiation and activity of a range of cell types, including many outside bone and cartilage. They serve as developmental morphogens, but are also important in chronic pathologies, including tissue fibrosis and cancer. One mechanism for enabling tight spatiotemporal control of their activities is through a number of antagonist proteins, including Noggin, Follistatin, Chordin, Twisted gastrulation (TSG), and the seven members of the Cerberus and Dan family. These antagonists are secreted proteins that bind selectively to particular BMPs with high affinity, thereby blocking receptor engagement and signaling. Most of these antagonists also possess a TGF-β cystine-knot domain. Here, we discuss current knowledge and understanding of the structures and activities of the BMPs and their antagonists, with a particular focus on the latter proteins. Recent advances in structural biology of BMP antagonists have begun the process of elucidating the molecular basis of their activity, displaying a surprising variety between the modes of action of these closely related proteins. We also discuss the interactions of the antagonists with the glycosaminoglycan heparan sulfate, which is found ubiquitously on cell surfaces and in the extracellular matrix.

A unique tool to selectively detect the chondrogenic IIB form of human type II procollagen protein

Type II collagen, the major fibrillar collagen of cartilage, is synthesized as precursor forms (procollagens) containing N- and C-terminal propeptides. Three splice variants are thought to be translated to produce procollagen II isoforms (IIA/D and IIB) which differ in their amino propeptide parts. The IIA and IID are transient embryonic isoforms that include an additional cysteine-rich domain encoded by exon 2. The IIA and IID transcripts are co-expressed during chondrogenesis then decline and the IIB isoform is the only one expressed and synthesized in fully differentiated chondrocytes. Additionally, procollagens IIA/D can be re-expressed by dedifferentiating chondrocytes and in osteoarthritic cartilage. Therefore, it is an important point to determine which isoform(s) is (are) synthesized in vivo in normal and pathological situations and in vitro, to fully assess the phenotype of cells producing type II collagen protein. Antibodies directed against the cysteine-rich extra domain found in procollagens IIA and IID are already available but antibodies detecting only the chondrogenic IIB form of type II procollagen were missing so far. A synthetic peptide encompassing the junction between exon 1 and exon 3 of the human sequence was used as immunogen to produce rabbit polyclonal antibodies to procollagen IIB. After affinity purification on immobilized peptide their absence of crossreaction with procollagens IIA/D and with the fibrillar procollagens I, III and V was demonstrated by Western blotting. These antibodies were used to reveal at the protein level that the treatment of dedifferentiated human chondrocytes by bone morphogenic protein (BMP)-2 induces the synthesis of the IIB (chondrocytic) isoform of procollagen II. In addition, immunohistochemical staining of bovine cartilage demonstrates the potential of these antibodies in the analysis of the differential spatiotemporal distribution of N-propeptides of procollagens IIA/D and IIB during normal development and in pathological situations.

Tcf21 regulates the specification and maturation of proepicardial cells

The epicardium is a mesothelial cell layer essential for vertebrate heart development and pertinent for cardiac repair post-injury in the adult. The epicardium initially forms from a dynamic precursor structure, the proepicardial organ, from which cells migrate onto the heart surface. During the initial stage of epicardial development crucial epicardial-derived cell lineages are thought to be determined. Here, we define an essential requirement for transcription factor Tcf21 during early stages of epicardial development in Xenopus, and show that depletion of Tcf21 results in a disruption in proepicardial cell specification and failure to form a mature epithelial epicardium. Using a mass spectrometry-based approach we defined Tcf21 interactions and established its association with proteins that function as transcriptional co-repressors. Furthermore, using an in vivo systems-based approach, we identified a panel of previously unreported proepicardial precursor genes that are persistently expressed in the epicardial layer upon Tcf21 depletion, thereby confirming a primary role for Tcf21 in the correct determination of the proepicardial lineage. Collectively, these studies lead us to propose that Tcf21 functions as a transcriptional repressor to regulate proepicardial cell specification and the correct formation of a mature epithelial epicardium.

Kielin/chordin-like protein attenuates both acute and chronic renal injury

The secreted kielin/chordin-like (KCP) protein, one of a family of cysteine-rich proteins, suppresses TGF-β signaling by sequestering the ligand from its receptor, but it enhances bone morphogenetic protein (BMP) signaling by promoting ligand-receptor interactions. Given the critical roles for TGF-β and BMP proteins in enhancing or suppressing renal interstitial fibrosis, respectively, we examined whether secreted KCP could attenuate renal fibrosis in mouse models of chronic and acute disease. Transgenic mice that express KCP in adult kidneys showed significantly less expression of collagen IV, α-smooth muscle actin, and other markers of disease progression in the unilateral ureteral obstruction model of renal interstitial fibrosis. In the folic acid nephrotoxicity model of acute tubular necrosis, mice expressing KCP survived high doses of folic acid that were lethal for wild-type mice. With a lower dose of folic acid, mice expressing KCP exhibited improved renal recovery compared with wild-type mice. Thus, these data suggest that extracellular regulation of the TGF-β/BMP signaling axis by KCP, and by extension possibly other cysteine-rich domain proteins, can attenuate both acute and chronic renal injury.

miR-181a promotes osteoblastic differentiation through repression of TGF-β signaling molecules

Osteoblastic differentiation is controlled by complex interplay of several signaling pathways and associated key transcription factors, as well as by microRNAs (miRNAs). In our current study, we found miR-181a to be highly upregulated during BMP induced osteoblastic differentiation of C2C12 and MC3T3 cells. Overexpression of miR-181a led to upregulation of key markers of osteoblastic differentiation as well as enhanced ALP levels and Alizarin red staining, indicating the importance of this miRNA for osteoblastic differentiation. Further, we show that miR-181 isoforms (181a, 181b, 181c) are expressed during different stages of mouse calvarial and tibial development, implying their role in both endochondral and intramembranous ossification. We found several direct and indirect targets of miR-181a to be downregulated by global mRNA expression profiling. Our results demonstrate that miR-181a promotes osteoblastic differentiation via repression of TGF-β signaling molecules by targeting the negative regulator of osteoblastic differentiation Tgfbi (Tgf-beta induced) and TβR-I/Alk5 (TGF-β type I receptor). Furthermore, our findings suggest that Rgs4 and Gata6 are direct targets of miR-181a. Taken together, we provide evidence for a crucial functional link between a specific miRNA, miR-181a and osteoblastic differentiation.

Activation of Wnt11 by transforming growth factor-β drives mesenchymal gene expression through non-canonical Wnt protein signaling in renal epithelial cells

Transforming growth factor β1 (TGF-β) promotes renal interstitial fibrosis in vivo and the expression of mesenchymal genes in vitro; however, most of its direct targets in epithelial cells are still elusive. In a screen for genes directly activated by TGF-β, we found that components of the Wnt signaling pathway, especially Wnt11, were targets of activation by TGF-β and Smad3 in primary renal epithelial cells. In gain and loss of function experiments, Wnt11 mediated the actions of TGF-β through enhanced activation of mesenchymal marker genes, such as Zeb1, Snail1, Pai1, and αSMA, without affecting Smad3 phosphorylation. Inhibition of Wnt11 by receptor knockdown or treatment with Wnt inhibitors limited the effects of TGF-β on gene expression. We found no evidence that Wnt11 activated the canonical Wnt signaling pathway in renal epithelial cells; rather, the function of Wnt11 was mediated by the c-Jun N-terminal kinase (JNK) pathway. Consistent with the in vitro results, all the TGF-β, Wnt11, and JNK targets were activated in a unilateral ureteral obstruction (UUO) model of renal fibrosis in vivo. Our findings demonstrated cooperativity among the TGF-β, Wnt11, and JNK signaling pathways and suggest new targets for anti-fibrotic therapy in renal tissue.

Trichostatin a prevents TGF-beta1-induced apoptosis by inhibiting ERK activation in human renal tubular epithelial cells

Histone deacetylase (HDAC) inhibitors have recently been reported to have possible reno-protective effects in the last few years. In this study, we found that tricostatin A (TSA), an HDAC inhibitor, prevented transforming growth factor beta1 (TGF-beta1)-induced apoptosis in cultured human renal proximal tubular epithelial cells (RPTECs). TGF-beta1-induced apoptosis via the activation of both caspase-8 and caspase-9 but did not activate the Fas receptor and did not alter Bcl-2 or Bax protein expression. TSA prevented TGF-beta1-induced apoptosis and the activation of caspase-8 and caspase-9 in RPTECs but did not inhibit the TGF-beta1-induced phosphorylation of Smad3 and p38 mitogen-activated protein kinase (MAPK). However, TSA inhibited the TGF-beta1-induced phosphorylation of extracellular signal regulated kinase (ERK), and the MAPK/ERK kinase inhibitor U0126, which specifically inhibits ERK, also prevented TGF-beta1-induced apoptosis. Our results show, for the first time, that TSA inhibits TGF-beta1-induced ERK activation and overrides pro-apoptotic signals like Smad3 and p38 in human RPTECs.

The extracellular regulation of bone morphogenetic protein signaling

In many cases, the level, positioning and timing of signaling through the bone morphogenetic protein (BMP) pathway are regulated by molecules that bind BMP ligands in the extracellular space. Whereas many BMP-binding proteins inhibit signaling by sequestering BMPs from their receptors, other BMP-binding proteins cause remarkably context-specific gains or losses in signaling. Here, we review recent findings and hypotheses on the complex mechanisms that lead to these effects, with data from developing systems, biochemical analyses and mathematical modeling.

A critical role for sFRP proteins in maintaining caudal neural tube closure in mice via inhibition of BMP signaling

Both the BMP and Wnt pathways have been implicated in directing aspects of dorsal neural tube closure and cell fate specification. However, the mechanisms that control the diverse responses to these signals are poorly understood. In this study, we provide genetic and functional evidence that the secreted sFRP1 and sFRP2 proteins, which have been primarily implicated as negative regulators of Wnt signaling, can also antagonize BMP signaling in the caudal neural tube and that this function is critical to maintain proper neural tube closure and dorsal cell fate segregation. Our studies thus reveal a novel role for specific sFRP proteins in balancing the response of cells to two critical extracellular signaling pathways.

Hyaluronan promotes the chondrocyte response to BMP-7

OBJECTIVE

Chondrocytes exhibit specific responses to bone morphogenetic proteins (BMPs) and transforming growth factor-betas (TGF-betas). The bioactivity of these growth factors is regulated by numerous mediators. In our previous study, Smad1 was found to interact with the cytoplasmic domain of the hyaluronan receptor CD44. The purpose of this study was to determine the ability of hyaluronan in the pericellular matrix to modulate the chondrocyte responses to BMP-7 or TGF-beta1.

EXPERIMENTAL DESIGN

Nuclear translocation of Smad1, Smad2 and Smad4 was studied in bovine articular chondrocytes in response to BMP-7 and TGF-beta1. The effects of matrix disruption by hyaluronidase treatment and the initiation of matrix repair by the addition of hyaluronan on the nuclear translocation of Smad proteins, Smad1 phosphorylation and luciferase expression by a CD44 reporter construct in response to BMP-7 were also studied.

RESULTS

The disruption of the hyaluronan-dependent pericellular matrix of chondrocytes resulted in diminished nuclear translocation of endogenous Smad1 and Smad4 in response to BMP-7; however, the nuclear translocation of Smad2 and Smad4 in these matrix-depleted chondrocytes in response to TGF-beta1 was not diminished. Incubation of the matrix-depleted chondrocytes with exogenous hyaluronan restored Smad1 and Smad4 nuclear translocation and increased pCD44(499)-Luc luciferase expression in response to BMP-7. Both exogenous hyaluronan and matrix re-growth enhanced by hyaluronan synthase-2 (HAS2) transfection restored Smad1 phosphorylation.

CONCLUSIONS

Disruption of hyaluronan-CD44 interactions has little effect on the TGF-beta responses; however, re-establishing CD44-hyaluronan ligation promotes a robust cellular response to BMP-7 by articular chondrocytes. Thus, changes in cell-hyaluronan interactions may serve as a mechanism to modulate cellular responsiveness to BMP-7.

BMP modulators regulate the function of BMP during body patterning and disease progression

Bone morphogenetic proteins (BMPs) are phylogenetically conserved signaling molecules that belong to the transforming growth factor (TGF)-beta superfamily and are involved in the cascades of body patterning and morphogenesis. The activities of BMPs are precisely regulated at various stages, and extracellulary, mainly regulated by certain classes of molecules termed as BMP antagonists and pro-BMP factors. BMP antagonists inhibit BMP function by prohibiting them from binding their cognate receptors, whereas pro-BMP factors stimulate BMP function. In this review, the functions of these BMP regulators will be discussed. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.

The BMP-binding protein Crossveinless 2 is a short-range, concentration-dependent, biphasic modulator of BMP signaling in Drosophila

In Drosophila, the secreted BMP-binding protein Short gastrulation (Sog) inhibits signaling by sequestering BMPs from receptors, but enhances signaling by transporting BMPs through tissues. We show that Crossveinless 2 (Cv-2) is also a secreted BMP-binding protein that enhances or inhibits BMP signaling. Unlike Sog, however, Cv-2 does not promote signaling by transporting BMPs. Rather, Cv-2 binds cell surfaces and heparan sulfate proteoglygans and acts over a short range. Cv-2 binds the type I BMP receptor Thickveins (Tkv), and we demonstrate how the exchange of BMPs between Cv-2 and receptor can produce the observed biphasic response to Cv-2 concentration, where low levels promote and high levels inhibit signaling. Importantly, we show also how the concentration or type of BMP present can determine whether Cv-2 promotes or inhibits signaling. We also find that Cv-2 expression is controlled by BMP signaling, and these combined properties enable Cv-2 to exquisitely tune BMP signaling.

Highly conserved non-coding sequences and the 18q critical region for short stature: a common mechanism of disease?

Background

Isolated growth hormone deficiency (IGHD) and multiple pituitary hormone deficiency (MPHD) are heterogeneous disorders with several different etiologies and they are responsible for most cases of short stature. Mutations in different genes have been identified but still many patients did not present mutations in any of the known genes. Chromosomal rearrangements may also be involved in short stature and, among others, deletions of 18q23 defined a critical region for the disorder. No gene was yet identified.

Methodology/Principal Findings

We now report a balanced translocation X;18 in a patient presenting a breakpoint in 18q23 that was surprisingly mapped about 500 Kb distal from the short stature critical region. It separated from the flanking SALL3 gene a region enriched in highly conserved non-coding elements (HCNE) that appeared to be regulatory sequences, active as enhancers or silencers during embryonic development.

Conclusion

We propose that, during pituitary development, the 18q rearrangement may alter expression of 18q genes or of X chromosome genes that are translocated next to the HCNEs. Alteration of expression of developmentally regulated genes by translocation of HCNEs may represent a common mechanism for disorders associated to isolated chromosomal rearrangements.

Gremlin-mediated decrease in bone morphogenetic protein signaling promotes pulmonary fibrosis

RATIONALE

Members of the transforming growth factor (TGF)-beta superfamily, including TGF-betas and bone morphogenetic proteins (BMPs), are essential for the maintenance of tissue homeostasis and regeneration after injury. We have observed that the BMP antagonist, gremlin, is highly up-regulated in idiopathic pulmonary fibrosis (IPF).

OBJECTIVES

To investigate the role of gremlin in the regulation of BMP signaling in pulmonary fibrosis.

METHODS

Progressive asbestos-induced fibrosis in the mouse was used as a model of human IPF. TGF-beta and BMP expression and signaling activities were measured from murine and human fibrotic lungs. The mechanism of gremlin induction was analyzed in cultured lung epithelial cells. In addition, the possible therapeutic role of gremlin inhibition was tested by administration of BMP-7 to mice after asbestos exposure.

MEASUREMENTS AND MAIN RESULTS

Gremlin mRNA levels were up-regulated in the asbestos-exposed mouse lungs, which is in agreement with the human IPF biopsy data. Down-regulation of BMP signaling was demonstrated by reduced levels of Smad1/5/8 and enhanced Smad2 phosphorylation in asbestos-treated lungs. Accordingly, analyses of cultured human bronchial epithelial cells indicated that asbestos-induced gremlin expression could be prevented by inhibitors of the TGF-beta receptor and also by inhibitors of the mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase pathways. BMP-7 treatment significantly reduced hydroxyproline contents in the asbestos-treated mice.

CONCLUSIONS

The TGF-beta and BMP signaling balance is important for lung regenerative events and is significantly perturbed in pulmonary fibrosis. Rescue of BMP signaling activity may represent a potential beneficial strategy for treating human pulmonary fibrosis.

von Willebrand Factor Type C Domain-containing Proteins Regulate Bone Morphogenetic Protein Signaling through Different Recognition Mechanisms

Bone morphogenetic protein (BMP) function is regulated in the extracellular space by many modulator proteins, including those containing a von Willebrand factor type C (VWC) domain. The function of the VWC domain-containing proteins in development and diseases has been extensively studied. The structural basis, however, for the mechanism by which BMP is regulated by these proteins is still poorly understood. By analyzing chordin, CHL2 (chordin-like 2), and CV2 (crossveinless 2) as well as their individual VWC domains, we show that the VWC domain is a versatile binding module that in its multiple forms and environments can expose a variety of binding specificities. Three of four, two of three, and one of five VWCs from chordin, CHL2, and CV2, respectively, can bind BMPs. Using an array of BMP-2 mutant proteins, it can be demonstrated that the binding-competent VWC domains all use a specific subset of BMP-2 binding determinants that overlap with the binding site for the type II receptors (knuckle epitope) or for the type I receptors (wrist epitope). This explains the competition between modulator proteins and receptors for BMP binding and therefore the inhibition of BMP signaling. A subset of VWC domains from CHL2 binds to the Tsg (twisted gastrulation) protein similar to chordin. A stable ternary complex consisting of BMP-2, CHL2, and Tsg can be formed, thus making CHL2 a more efficient BMP-2 inhibitor. The VWCs of CV2, however, do not interact with Tsg. The present results show that chordin, CHL2, and CV2 regulate BMP-2 signaling by different recognition mechanisms.