BMP-3 is a novel inhibitor of both activin and BMP-4 signaling in Xenopus embryos

In Xenopus, the biological effects of BMP-3 oppose those of ventralizing BMPs, but the mechanism for this antagonism remains unclear. Here, we demonstrate that BMP-3 is a dorso-anteriorizing factor in Xenopus embryos that interferes with both activin and BMP signaling. BMP-3 acts by binding to ActRIIB, the common type II receptor for these proteins. Once BMP-3 binds to ActRIIB, it cannot be competed off by excess ligand making a receptor complex that is unable to activate R-Smads and transduce signal. Consistent with a model where BMP-3 interferes with activin and BMPs through a shared receptor, we show that overexpression of BMP-3 can only be rescued by co-injection of xActRIIB. Our results identify BMP-3 as a novel antagonist of both activin and BMPs and uncover how some of the diverse developmental processes that are regulated by both activin and BMP signaling can be modulated during embryogenesis.     

Identification of ligand-selective peptidic ActRIIB-antagonists using phage display technology

ActRIIB (activin receptor type-2B) is an activin receptor subtype constitutively expressed in the whole body, playing a role in cellular proliferation, differentiation, and metabolism. For its various physiological activities, ActRIIB interacts with activin and multiple other ligands including myostatin (MSTN), growth differentiation factor 11 (GDF11), and bone morphogenetic protein 9 (BMP9). Notably, the protein-protein interaction (PPI) between ActRIIB and MSTN negatively controls muscular development. Therefore, this PPI has been targeted for effective treatment of muscle degenerative diseases such as muscular dystrophy and sarcopenia. Here, we report the identification of ligand-selective peptidic ActRIIB-antagonists by phage display technology. Our peptides bound to the extracellular domain of ActRIIB, inhibited PPIs between ActRIIB expressed on the cell surface and its ligands, and subsequently suppressed activation of Smad that serves as the downstream signal of the ActRIIB pathway. Interestingly, these peptidic antagonists displayed different ligand selectivities; the AR2mini peptide inhibited multiple ligands (activin A, MSTN, GDF11, and BMP9), AR9 inhibited MSTN and GDF11, while AR8 selectively inhibited MSTN. This is the first report of artificial peptidic ActRIIB-antagonists possessing ligand-selectivity.     

Investigating the effect of peptide agonists on the chondrogenic differentiation of human mesenchymal stem cells using design of experiments

Human mesenchymal stem cells (MSCs) are attractive for use in cartilage tissue engineering. Cells are often seeded in a structural scaffold containing growth factors. Peptide mimics of full‐length growth factors are a promising alternative because they are less expensive and easier to manufacture. We investigated four short peptides for their effect on the chondrogenesis of human MSCs. The peptides were originally designed to mimic bone morphogenetic protein‐2 (BMP‐2), transforming growth factor‐beta 1 (TGF‐β1), and insulin, all of which have been shown to affect MSC chondrogenesis. Previous studies demonstrated that the peptides elicited bioactivity in other cell types, but the peptides have not been investigated for their effect on chondrogenesis in human MSCs. In a preliminary investigation, peptides were added to a pellet culture of human MSCs and assayed for their effect on glycosaminoglycan (GAG) production. These experiments determined peptide concentrations used in a full‐factorial experiment to investigate any interactions. The experiment revealed the BMP peptide as a robust stimulant for GAG production. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1550–1557, 2013     

BMP2, BMP4, and their receptors are expressed in the differentiating muscle tissues of mouse embryonic tongue

To investigate the role of bone morphogenetic proteins (BMPs) in the differentiation process of skeletal muscle, we analyzed the in vivo expression of BMP2 and BMP4, of BMP receptors (BMPR) IA, IB, and II, and of activin receptors (ActR) IA, II, and IIB in mouse tongue muscle between embryonic day 11 (E11) and E17. The mRNA expression levels for BMP2 were 5-fold to 11-fold greater than those for BMP4 between E13 and E17 (P < 0.05-0.01). Expression of the BMP2, BMPRIB, ActRIA, ActRII, and ActRIIB proteins was first observed at E13. Expression of BMP2 and BMPRIB was detected in the whole area of the differentiating muscle tissues identified by immunostaining for fast myosin heavy chain (fMHC), but that of ActRIA, ActRII, and ActRIIB was detected only in the peripheral area of the differentiating muscle tissues. In the E15 tongue, all of the BMPs, BMPRs, and ActRs studied herein were expressed in the whole area of the differentiating muscle tissues identified by immunostaining for fMHC. These results suggest that BMPs play a role in the differentiation of tongue muscle tissues at E15 but have little or no effect at E13. This study was supported in part by grants-in-aid for funding scientific research (no. 16591871 to A.Y.) from the Bio-ventures and High-Technology Research Center of the Ministry of Education, Culture, Sports, Science, and Technology of Japan and by the Science Research Promotion Fund from the Promotion and Mutual Aid Corporation for Private Schools of Japan.     

A new FcεRI receptor‐mimetic peptide (PepE) that blocks IgE binding to its high affinity receptor and prevents mediator release from RBL 2H3 cells

We have recently reported on a class of IgE‐binding peptides designed based on the crystallographic structure of the high affinity FcεRI. Peptides contain receptor key residues located within the two distinct binding sites for IgE and selectively bind IgE with an affinity ranging between 6 and 60 µM . We have here designed and characterized a new molecule containing the receptor loops C′–E and B–C and an optimized linker for joining them made of a Lys side chain and a β‐Ala. This new peptide shows an increased affinity (around 30 times) compared to the parent loop C′–E + B–C previously described, while retaining the same two‐site mechanism of binding and the same selectivity. It also blocks the binding of IgE to the cell‐anchored receptor and efficiently prevents histamine release from mast cells. These properties make the peptide a useful scaffold for the development of new anti‐allergic drugs. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Bone morphogenetic protein 1 prodomain specifically binds and regulates signaling by bone morphogenetic proteins 2 and 4

Highly purified fractions of bone extracts capable of inducing ectopic bone formation have been reported to contain peptides corresponding to the mature active regions of the TGF-beta-like bone morphogenetic proteins (BMPs) 2-7, and to the prodomain region of the metalloproteinase BMP1. Co-purification of BMPs 2-7 with BMP1 prodomain sequences through the multiple biochemical steps used in these previous reports has suggested the possibility of interactions between the BMP1 prodomain and BMPs 2-7. Here we demonstrate that the BMP1 prodomain binds BMPs 2 and 4 with high specificity and with a KD of approximately 11 nM, in the physiological range. It is further demonstrated that the BMP1 prodomain is capable of modulating signaling by BMPs 2 and 4 in vitro and in vivo, and that endogenous BMP1 prodomain-BMP4 complexes exist in cell culture media and in tissues.     

LIM mineralization protein-1 potentiates bone morphogenetic protein responsiveness via a novel interaction with Smurf1 resulting in decreased ubiquitination of Smads

Development and repair of the skeletal system and other organs is highly dependent on precise regulation of bone morphogenetic proteins (BMPs), their receptors, and their intracellular signaling proteins known as Smads. The use of BMPs clinically to induce bone formation has been limited in part by the requirement of much higher doses of recombinant proteins in primates than were needed in cell culture or rodents. Therefore, control of cellular responsiveness to BMPs is now a critical area that is poorly understood. We determined that LMP-1, a LIM domain protein capable of inducing de novo bone formation, interacts with Smurf1 (Smad ubiquitin regulatory factor 1) and prevents ubiquitination of Smads. In the region of LMP responsible for bone formation, there is a motif that directly interacts with the Smurf1 WW2 domain and can effectively compete with Smad1 and Smad5 for binding. We have shown that small peptides containing this motif can mimic the ability to block Smurf1 from binding Smads. This novel interaction of LMP-1 with the WW2 domain of Smurf1 to block Smad binding results in increased cellular responsiveness to exogenous BMP and demonstrates a novel regulatory mechanism for the BMP signaling pathway.     

Peptide drugs accelerate BMP‐2‐induced calvarial bone regeneration and stimulate osteoblast differentiation through mTORC1 signaling

Both W9 and OP3‐4 were known to bind the receptor activator of NF‐κB ligand (RANKL), inhibiting osteoclastogenesis. Recently, both peptides were shown to stimulate osteoblast differentiation; however, the mechanism underlying the activity of these peptides remains to be clarified. A primary osteoblast culture showed that rapamycin, an mTORC1 inhibitor, which was recently demonstrated to be an important serine/threonine kinase for bone formation, inhibited the peptide‐induced alkaline phosphatase activity. Furthermore, both peptides promoted the phosphorylation of Akt and S6K1, an upstream molecule of mTORC1 and the effector molecule of mTORC1, respectively. In the in vivo calvarial defect model, W9 and OP3‐4 accelerated BMP‐2‐induced bone formation to a similar extent, which was confirmed by histomorphometric analyses using fluorescence images of undecalcified sections. Our data suggest that these RANKL‐binding peptides could stimulate the mTORC1 activity, which might play a role in the acceleration of BMP‐2‐induced bone regeneration by the RANKL‐binding peptides.     

Cell responses to bone morphogenetic proteins and peptides derived from them: Biomedical applications and limitations

The bone morphogenetic proteins (BMPs) are cytokines of the transforming growth factor beta family. Some BMPs such as BMP-2 and BMP-7 play a major role in the development of the skeleton and the maintenance of homeostasis during bone remodelling. To date, only BMP-2 and BMP-7 have been approved by the Food and Drug Administration for specific orthopaedic applications. However, due to BMP cost, peptides derived from their knuckle epitope with osteogenic properties have been developed. BMPs are involved in many other biological events, including embryogenesis, angiogenesis and cancer. BMPs therefore have great biomedical potential as osteogenic factors and as anti-cancer agents. This review focuses on the use of BMPs and their derived peptides in biomedical delivery systems and gene therapy.     

Uncoupling the BMP receptor antagonist function from the WNT agonist function of R-spondin 2 using the inhibitory peptide dendrimer RWd

Signaling by bone morphogenetic proteins (BMPs) plays pivotal roles in embryogenesis, adult tissue homeostasis, and disease. Recent studies revealed that the well-established WNT agonist R-spondin 2 (RSPO2) is also a BMP receptor (BMP receptor type 1A) antagonist, with roles in early Xenopus embryogenesis and human acute myeloid leukemia (AML). To uncouple the BMP antagonist function from the WNT agonist function and to promote development of AML therapeutics, here we identified a 10-mer peptide (RW) derived from the thrombospondin 1 domain of RSPO2, which specifically prevents binding between RSPO2 and BMP receptor type 1A without altering WNT signaling. We also show that a corresponding RW dendrimer (RW^d) exhibiting improved half-life relieves inhibition of BMP receptor signaling by RSPO2 in human AML cells, reduces cell growth, and induces differentiation. Moreover, microinjection of RW^d in Xenopus embryos ventralizes the dorsoventral embryonic patterning by upregulating BMP signaling without affecting WNT signaling. Our study corroborates the function of RSPO2 as a BMP receptor antagonist and provides a proof of concept for pharmacologically uncoupling BMP antagonist from WNT agonist functions of RSPO2 using the inhibitor peptide RW^d with enhanced target selectivity and limited side effects.     

Comparison of marmoset and human FSH using synthetic peptides of the β‐subunit L2 loop region and anti‐peptide antibodies

Follicle stimulating hormone (FSH) is a glycoprotein hormone required for female and male gametogenesis in vertebrates. Common marmoset (Callithrix jacchus) is a New World primate monkey, used as animal model in biomedical research. Observations like, requirement of extremely high dose of human FSH in marmosets for superovulation compared to other primates and generation of antibodies in marmoset against human FSH after repeated superovulation cycles, point towards the possibility that FSH–FSH receptor (FSHR) interaction in marmosets might be different than in the humans. In this study we attempted to understand some of these structural differences using FSH peptides and anti‐peptide antibody approach. Based on sequence alignment, in silico modeling and docking studies, L2 loop of FSH β‐subunit (L2β) was found to be different between marmoset and human. Hence, peptides corresponding to region 32–50 of marmoset and human L2β loop were synthesized, purified and characterized. The peptides displayed dissimilarity in terms of molecular mass, predicted isoelectric point, predicted charge and in the ability to inhibit hormone–receptor interaction. Polyclonal antibodies generated against both the peptides were found to exhibit specific binding for the corresponding peptide and parent FSH in ELISA and Western blotting respectively and exhibited negligible reactivity to cross‐species peptide and FSH in ELISA. The anti‐peptide antibody against marmoset FSH was also able to detect native FSH in marmoset plasma samples and pituitary sections. In summary, the L2β loop of marmoset and human FSH has distinct receptor interaction ability and immunoreactivity indicating possibility of subtle conformational and biochemical differences between the two regions which may affect the FSH–FSHR interaction in these two primates. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Structural and functional characterization of peptides derived from the carboxy‐terminal region of a defensin from the tick Ornithodoros savignyi

Tick defensins may serve as templates for the development of multifunctional peptides. The purpose of this study was to evaluate shorter peptides derived from tick defensin isoform 2 (OsDef2) in terms of their antibacterial, antioxidant, and cytotoxic activities. We compared the structural and functional properties of a synthetic peptide derived from the carboxy‐terminal of the parent peptide (Os) to that of an analogue in which the three cysteine residues were omitted (Os–C). Here, we report that both peptides were bactericidal (MBC values ranging from 0.94–15 µg/ml) to both Gram‐positive and Gram‐negative bacteria, whereas the parent peptide only exhibited Gram‐positive antibacterial activity. The Os peptide was found to be two‐fold more active than Os–C against three of the four tested bacteria but equally active against Staphylococcus aureus. Os showed rapid killing kinetics against both Escherichia coli and Bacillus subtilis, whereas Os–C took longer, suggesting different modes of action. Scanning electron microscopy showed that in contrast to melittin for which blebbing of bacterial surfaces was observed, cells exposed to either peptide appeared flattened and empty. Circular dichroism data indicated that in a membrane‐mimicking environment, the cysteine‐containing peptide has a higher α‐helical content. Both peptides were found to be non‐toxic to mammalian cells. Moreover, the peptides displayed potent antioxidant activity and were 12 times more active than melittin. Multifunctional peptides hold potential for a wide range of clinical applications and further investigation into their mode of antibacterial and antioxidant properties is therefore warranted. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Bone morphogenic protein 2 directly enhances differentiation of murine osteoclast precursors

Previous studies found that bone morphogenic proteins (BMPs) support osteoclast formation, but it is not clear whether this is a direct effect on osteoclasts or mediated indirectly through osteoblasts. We have shown that a mouse deficient for the BMP antagonist Twisted gastrulation suggested a direct positive role for BMPs on osteoclastogenesis. In this report, we further determine the significance of BMP signaling on osteoclast formation in vitro. We find that BMP2 synergizes with suboptimal levels of receptor activator of NF‐κB ligand (RANKL) to enhance in vitro differentiation of osteoclast‐like cells. The enhancement by BMP2 is not a result of changes in the rate of proliferation or survival of the bone marrow‐derived cultures, but is accompanied by an increase in expression of genes involved in osteoclast differentiation and fusion. Treatment with BMP2 did not significantly alter expression of RANKL or OPG in our osteoclast cultures, suggesting that the enhancement of osteoclastogenesis is not mediated indirectly through osteoblasts or stromal cells. Consistent with this, we detected phosphorylated SMAD1,5,8 (p‐SMAD) in the nuclei of mononuclear and multinucleated cells in osteoclast cultures. Levels of p‐SMAD, BMP2, and BMP receptors increased during differentiation. RNAi suppression of Type II BMP receptor inhibited RANKL‐stimulated formation of multinuclear TRAP‐positive cells. The BMP antagonist noggin inhibited RANKL‐mediated osteoclast differentiation when added prior to day 3, while addition of noggin on day 3 or later failed to inhibit their differentiation. Taken together, these data indicate that osteoclasts express BMP2 and BMP receptors, and that autocrine BMP signaling directly promotes the differentiation of osteoclasts‐like cells. J. Cell. Biochem. 109: 672–682, 2010. © 2009 Wiley‐Liss, Inc.     

Synthesis,characterization, and biological activity of poly(arginine)‐derived cancer‐targeting peptides in HepG2 liver cancer cells

The solid‐phase synthesis, structural characterization, and biological evaluation of a small library of cancer‐targeting peptides have been determined in HepG2 hepatoblastoma cells. These peptides are based on the highly specific Pep42 motif, which has been shown to target the glucose‐regulated protein 78 receptors overexpressed and exclusively localized on the cell surface of tumors. In this study, Pep42 was designed to contain varying lengths (3–12) of poly(arginine) sequences to assess their influence on peptide structure and biology. Peptides were effectively synthesized by 9‐fluorenylmethoxycarbonyl‐based solid‐phase peptide synthesis, in which the use of a poly(ethylene glycol) resin provided good yields (14–46%) and crude purities >95% as analyzed by liquid chromatography–mass spectrometry. Peptide structure and biophysical properties were investigated using circular dichroism spectroscopy. Interestingly, peptides displayed secondary structures that were contingent on solvent and length of the poly(arginine) sequences. Peptides exhibited helical and turn conformations, while retaining significant thermal stability. Structure–activity relationship studies conducted by flow cytometry and confocal microscopy revealed that the poly(arginine) derived Pep42 sequences maintained glucose‐regulated protein 78 binding on HepG2 cells while exhibiting cell translocation activity that was contingent on the length of the poly(arginine) strand. In single dose (0.15 mM) and dose‐response (0–1.5 mM) cell viability assays, peptides were found to be nontoxic in human HepG2 liver cancer cells, illustrating their potential as safe cancer‐targeting delivery agents. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Adiponectin increases BMP‐2 expression in osteoblasts via AdipoR receptor signaling pathway

Adiponectin is a protein hormone secreted predominantly by differentiated adipocytes and involved in energy homeostasis. Bone morphogenetic protein (BMP) plays important roles in osteoblastic differentiation and bone formation. However, the effects of adiponectin on BMPs expression in cultured osteoblasts are largely unknown. Here we found that adiponectin increased mRNA expression of BMP‐2 but not other BMPs in cultured osteoblastic cells. Stimulation of osteoblasts with adiponectin also increased protein levels of BMP‐2 by Western blot and ELISA assay. Adiponectin‐mediated BMP‐2 expression was attenuated by 5′‐AMP‐activated protein kinase (AMPK) small interference RNA and AMPK inhibitor (araA and compound C). Activations of p38 and NF‐κB pathways after adiponectin treatment were demonstrated, and adiponectin‐induced expression of BMP‐2 was inhibited by the specific inhibitor and mutant of p38 and NF‐κB cascades. Taken together, our results provide evidence that adiponectin enhances BMP‐2 expression in osteoblastic cells, and AdipoR1 receptor, AMPK, p38 and NF‐κB signaling pathways may be involved in increasing BMP‐2 expression by adiponectin. J. Cell. Physiol. 224: 475–483, 2010. © 2010 Wiley‐Liss, Inc.     

The bone morphogenetic protein family and osteogenesis.

The BMPs (bone morphogenetic proteins) are a group of related proteins originally identified by their presence in bone-inductive extracts of demineralized bone. By molecular cloning, at least six related members of this family have been identified and are called BMP-2 through BMP-7. These molecules are part of the TGF-beta superfamily, based on primary amino acid sequence homology, including the absolute conservation of seven cysteine residues between the TGF-betas and the BMPs. The BMPs can be divided into subgroups with BMP-2 and BMP-4 being 92% identical, and BMP-5, BMP-6, and BMP-7 being an average of about 90% identical. To examine the individual activities of these molecules, we are producing each BMP in a mammalian expression system. In this system, each BMP is synthesized as a precursor peptide, which is glycosylated, processed to the mature peptide, and secreted as a homodimer. These reagents have been used to demonstrate that single molecules, such as BMP-2, are capable of inducing the formation of new cartilage and bone when implanted ectopically in a rodent assay system. Whether each of the BMPs possesses the same inductive activities in an animal is the subject of ongoing research. Based on the chondrogenic and osteogenic abilities of the BMPs in the adult animal, the expression of the mRNAs for the BMPs has been examined in the development of the embryonic skeleton by in situ hybridization. These studies demonstrate that the BMP mRNAs are spatially and temporally expressed appropriately for the proteins involved in the induction and development of cartilage and bone in the embryonic limb bud.(ABSTRACT TRUNCATED AT 250 WORDS)