Normal gonadotropin production and fertility in gonadotrope-specific Bmpr1a knockout mice

Pituitary follicle-stimulating hormone (FSH) synthesis is regulated by transforming growth factorβsuperfamily ligands, most notably the activins and inhibins. Bone morphogenetic proteins (BMPs) also regulate FSHβ subunit (Fshb) expression in immortalized murine gonadotrope-like LβT2 cells and in primary murine or ovine primary pituitary cultures. BMP2 signals preferentially via the BMP type I receptor, BMPR1A, to stimulate murine Fshb transcription in vitro Here, we used a Cre-lox approach to assess BMPR1A's role in FSH synthesis in mice in vivo Gonadotrope-specific Bmpr1a knockout animals developed normally and had reproductive organ weights comparable with those of controls. Knockouts were fertile, with normal serum gonadotropins and pituitary gonadotropin subunit mRNA expression. Cre-mediated recombination of the floxed Bmpr1a allele was efficient and specific, as indicated by PCR analysis of diverse tissues and isolated gonadotrope cells. Furthermore, BMP2 stimulation of inhibitor of DNA binding 3 expression was impaired in gonadotropes isolated from Bmpr1a knockout mice, confirming the loss of functional receptor protein in these cells. Treatment of purified gonadotropes with small-molecule inhibitors of BMPR1A (and the related receptors BMPR1B and ACVR1) suppressed Fshb mRNA expression, suggesting that an autocrine BMP-like molecule might regulate FSH synthesis. However, deletion of Bmpr1a and Acvr1 in cultured pituitary cells did not alter Fshb expression, indicating that the inhibitors had off-target effects. In sum, BMPs or related ligands acting via BMPR1A or ACVR1 are unlikely to play direct physiological roles in FSH synthesis by murine gonadotrope cells.

Recombinant BMP4 and BMP7 downregulate pentraxin 3 in human granulosa cells

CONTEXT

Theca cell-derived bone morphogenetic protein 4 (BMP4) and BMP7 are important regulators of folliculogenesis and have been shown to inhibit luteinization. Pentraxin 3 (PTX3) plays a critical role in the assembly of the cumulus oophorus extracellular matrix, which is essential for cumulus expansion during ovulation and may be modulated by BMP4 and BMP7.

OBJECTIVE

The aim of this study was to investigate the effects of BMP4 and BMP7 on the expression of PTX3 in human granulosa cells and to examine their underlying molecular determinants.

DESIGN

An established immortalized human granulosa cell line (SVOG), a granulosa cell tumor cell line (KGN), and primary granulosa-lutein cells were used as study models. PTX3 expression and accumulation as well as Smad1/5/8 phosphorylation were examined after exposure to recombinant human BMP4 and BMP7. BMP type I receptor involvement was investigated with inhibitors (dorsomorphin and DMH-1 (4-[6-[4-(1-Methylethoxy)phenyl]pyrazolo[1,5-a]pyrimidin-3-yl]-quinoline)) and small interfering RNAs targeting activin receptor-like kinase (ALK)2, ALK3, and/or ALK6. Small interfering RNAs targeting Smad4 were used to verify the involvement of Smad signaling.

SETTING

The study was conducted at an academic research center.

MAIN OUTCOME MEASURES

Quantitative RT-PCR and Western blot were used to measure mRNA and protein levels, respectively. Levels of PTX3 and BMP4 were measured by ELISA.

RESULTS

Treatment with BMP4 and BMP7 significantly decreased PTX3 mRNA and protein production. These suppressive effects, along with the induction of Smad1/5/8 phosphorylation, were attenuated by cotreatment with 2 BMP type I receptor inhibitors (dorsomorphin and/or DMH-1). Combined knockdown (ALK3/ALK6 for BMP4 and ALK2/ALK3 for BMP7) reversed the effects of BMP4- and BMP7-induced Smad1/5/8 phosphorylation and PTX3 suppression. Furthermore, Smad4 knockdown reversed the suppressive effects of BMP4 and BMP7 on PTX3 expression. In follicular fluid, concentrations of PTX3 were negatively correlated with concentrations of BMP4.

CONCLUSION

BMP4 and BMP7 use differential subsets of BMP type I receptors to downregulate PTX3 expression via Smad-dependent signaling in human granulosa cells.

Identification of the role of bone morphogenetic protein (BMP) and transforming growth factor-β (TGF-β) signaling in the trajectory of serotonergic differentiation in a rapid assay in mouse embryonic stem cells in vitro

The mechanism by which extracellular molecules control serotonergic cell fate remains elusive. Recently, we showed that noggin, which inactivates bone morphogenetic proteins (BMPs), induces serotonergic differentiation of mouse embryonic (ES) and induced pluripotent stem cells with coordinated gene expression along the serotonergic lineage. Here, we created a rapid assay for serotonergic induction by generating knock-in ES cells expressing a naturally secreted Gaussia luciferase driven by the enhancer of Pet-1/Fev, a landmark of serotonergic differentiation. Using these cells, we performed candidate-based screening and identified BMP type I receptor kinase inhibitors LDN-193189 and DMH1 as activators of luciferase. LDN-193189 induced ES cells to express the genes encoding Pet-1, tryptophan hydroxylase 2, and the serotonin transporter, and increased serotonin release without altering dopamine release. In contrast, TGF-β receptor inhibitor SB-431542 selectively inhibited serotonergic differentiation, without changing overall neuronal differentiation. LDN-193189 inhibited expression of the BMP signaling target gene Id, and induced the TGF-β target gene Lefty, whereas the opposite effect was observed with SB-431542. This study thus provides a new tool to investigate serotonergic differentiation and suggests that inhibition of BMP type I receptors and concomitant activation of TGF-β receptor signaling are implicated in serotonergic differentiation. Candidate-based screening for serotonergic induction using a rapid assay in mouse embryonic stem cells revealed that the bone morphogenetic protein (BMP) type I receptor kinase inhibitors selectively induce serotonergic differentiation, whereas the TGF-β receptor inhibitor SB-431542 inhibits the differentiation. These results suggest that inhibition of BMP type I receptors and concomitant activation of transforming growth factor-β (TGF-β) receptor signaling are involved in the early trajectory of serotonergic differentiation.

Directional transport and active retention of Dpp/BMP create wing vein patterns in Drosophila

The bone morphogenetic protein (BMP) family ligand decapentaplegic (Dpp) plays critical roles in wing vein development during pupal stages in Drosophila. However, how the diffusible Dpp specifies elaborate wing vein patterns remains unknown. Here, we visualized Dpp distribution in the pupal wing and found that it tightly reflects the wing vein patterns. We show that Dpp is directionally transported from the longitudinal veins (LVs) into the posterior crossvein (PCV) primordial region by the extracellular BMP-binding proteins, short gastrulation (Sog) and crossveinless (Cv). Another BMP-type ligand, glass bottom boat (Gbb), also moves into the PCV region and is required for Dpp distribution, presumably as a Dpp-Gbb heterodimer. In contrast, we found that most of the Dpp is actively retained in the LVs by the BMP type I receptor thickveins (Tkv) and a positive feedback mechanism. We provide evidence that the directionality of Dpp transport is manifested by sog transcription that prepatterns the PCV position in a Dpp signal-independent manner. Taken together, our data suggest that spatial distribution of Dpp is tightly regulated at the extracellular level by combination of long-range facilitated transport toward the PCV and short-range signaling by active retention in the LVs, thereby allowing diffusible ligands to form elaborate wing vein patterns.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

Applications of small molecule BMP inhibitors in physiology and disease

Bone morphogenetic proteins (BMPs) provide critical signals for determining cell fate, specifying gastrulation, embryonic patterning, organogenesis, and the remodeling of diverse tissues. Recent work has suggested that in addition to coordinating pivotal events in development, BMPs may also regulate certain homeostatic physiological processes independently of effects on cell growth or differentiation. We recently described the identification of dorsomorphin, a small molecule inhibitor of BMP type I receptors which inhibits BMP signaling in preference to TGF-beta, Activin, and other ligands of the TGF-beta family. We describe a number of strategies using dorsomorphin and its derivatives as probes to assess the physiologic roles of BMP signaling. We also discuss several potential applications for small molecule BMP inhibitors, including stem cell manipulation, and the therapeutic modification of bone remodeling, heterotopic ossification, and iron homeostasis.

The type I BMP receptors, Bmpr1a and Acvr1, activate multiple signaling pathways to regulate lens formation

BMPs play multiple roles in development and BMP signaling is essential for lens formation. However, the mechanisms by which BMP receptors function in vertebrate development are incompletely understood. To determine the downstream effectors of BMP signaling and their functions in the ectoderm that will form the lens, we deleted the genes encoding the type I BMP receptors, Bmpr1a and Acvr1, and the canonical transducers of BMP signaling, Smad4, Smad1 and Smad5. Bmpr1a and Acvr1 regulated cell survival and proliferation, respectively. Absence of both receptors interfered with the expression of proteins involved in normal lens development and prevented lens formation, demonstrating that BMPs induce lens formation by acting directly on the prospective lens ectoderm. Remarkably, the canonical Smad signaling pathway was not needed for most of these processes. Lens formation, placode cell proliferation, the expression of FoxE3, a lens-specific transcription factor, and the lens protein, alphaA-crystallin were regulated by BMP receptors in a Smad-independent manner. Placode cell survival was promoted by R-Smad signaling, but in a manner that did not involve Smad4. Of the responses tested, only maintaining a high level of Sox2 protein, a transcription factor expressed early in placode formation, required the canonical Smad pathway. A key function of Smad-independent BMP receptor signaling may be reorganization of actin cytoskeleton to drive lens invagination.

What is the true nature of the osteoblastic hematopoietic stem cell niche?

The recently revitalized interest in the regulation of hematopoietic stem cells (HSCs) by the bone marrow microenvironment has resulted in the identification of some important cell types that potentially form the HSC niche. The term 'osteoblast' has commonly been used to describe the endosteal elements of the HSC niche, but these cells are part of a larger family that functions in bone at different stages of differentiation. Given that there is much controversy as to what cell types have important roles in the HSC niche, this review offers an overview of the diverse osteoblastic cell types and discusses the current evidence regarding what roles they have in the HSC niche.

BMP signalling inhibits premature neural differentiation in the mouse embryo

The specification of a subset of epiblast cells to acquire a neural fate constitutes the first step in the generation of the nervous system. Little is known about the signals required for neural induction in the mouse. We have analysed the role of BMP signalling in this process. We demonstrate that prior to gastrulation, Bmp2/4 signalling via Bmpr1a maintains epiblast pluripotency and prevents precocious neural differentiation of this tissue, at least in part by maintaining Nodal signalling. We find that during gastrulation, BMPs of the 60A subgroup cooperate with Bmp2/4 to maintain pluripotency. The inhibition of neural fate by BMPs is independent of FGF signalling, as inhibition of FGF signalling between 5.5 and 7.5 days post-coitum does not block neural differentiation in the mouse embryo. Together, our results demonstrate that inhibition of BMP signalling has a central role during neural induction in mammals and suggest that FGFs do not act as neural inducers in the post-implantation mouse embryo.

Bone regeneration by regulated in vivo gene transfer using biocompatible polyplex nanomicelles

Gene therapy is a promising strategy for bone regenerative medicine. Although viral vectors have been intensively studied for delivery of osteogenic factors, the immune response inevitably inhibits bone formation. Thus, safe and efficient non-viral gene delivery systems are in high demand. Toward this end, we developed a polyplex nanomicelle system composed of poly(ethyleneglycol) (PEG)-block-catiomer (PEG-b-P[Asp-(DET)]) and plasmid DNA (pDNA). This system showed little cytotoxicity and excellent transfection efficiency to primary cells. By the transfection of constitutively active form of activin receptor-like kinase 6 (caALK6) and runt-related transcription factor 2 (Runx2), the osteogenic differentiation was induced on mouse calvarial cells to a greater extent than when poly(ethylenimine) (PEI) or FuGENE6 were used; this result was due to low cytotoxicity and a sustained gene expression profile. After incorporation into the calcium phosphate cement scaffold, the polyplex nanomicelles were successfully released from the scaffold and transfected surrounding cells. Finally, this system was applied to in vivo gene transfer for a bone defect model in a mouse skull bone. By delivering caALK6 and Runx2 genes from nanomicelles incorporated into the scaffold, substantial bone formation covering the entire lower surface of the implant was induced with no sign of inflammation at 4 weeks. These results demonstrate the first success in in vivo gene transfer with therapeutic potential using polyplex nanomicelles.

Identification of a potent combination of osteogenic genes for bone regeneration using embryonic stem (ES) cell‐based sensor

To identify potent bioactive factors for in vivo tissue regeneration by comprehensive screening remains a challenge for regenerative medicine. Here we report the development of an ES cell-based monitoring system for osteogenic differentiation, the identification of a potent combination of osteogenic genes using such a system, and an evaluation of its therapeutic potentials. ES cells were isolated from mice carrying a transgene expressing GFP driven by the 2.3 kb fragment of rat type I collagen alpha1 promoter. Using these cells engineered to fluoresce on osteogenic differentiation, we screened cDNA libraries and combinations of major osteogenesis-related genes. Among them, the combination of constitutively active activin receptor-like kinase 6 (caALK6) and runt-related transcription factor 2 (Runx2) was the minimal unit that induced fluorescence. The combination efficiently induced osteogenic differentiation in various cell types, including terminally differentiated nonosteogenic cells. The cooperative action of the combination occurred through protein stabilization of core binding factor beta (Cbfb), induction of Runx2-Cbfb complex formation, and its DNA binding. Furthermore, transplantation of a monolayer sheet of fibroblasts transduced with the combination achieved bone regeneration within 4 wk in mouse calvarial bone defects. Thus, we successfully identified the potent combination of genes for bone regeneration, which helped broaden cell sources.

Essential functions of Alk3 during AV cushion morphogenesis in mouse embryonic hearts

Accumulated evidence has suggested that BMP pathways play critical roles during mammalian cardiogenesis and impairment of BMP signaling may contribute to human congenital heart diseases (CHDs), which are the leading cause of infant morbidity and mortality. Alk3 encodes a BMP specific type I receptor expressed in mouse embryonic hearts. To reveal functions of Alk3 during atrioventricular (AV) cushion morphogenesis and to overcome the early lethality of Alk3(-/-) embryos, we applied a Cre/loxp approach to specifically inactivate Alk3 in the endothelium/endocardium. Our studies showed that endocardial depletion of Alk3 severely impairs epithelium-mesenchymal-transformation (EMT) in the atrioventricular canal (AVC) region; the number of mesenchymal cells formed in Tie1-Cre;Alk3(loxp/loxp) embryos was reduced to only approximately 20% of the normal level from both in vivo section studies and in vitro explant assays. We showed, for the first time, that in addition to its functions on mesenchyme formation, Alk3 is also required for the normal growth/survival of AV cushion mesenchymal cells. Functions of Alk3 are accomplished through regulating expression/activation/subcellular localization of multiple downstream genes including Smads and cell-cycle regulators. Taken together, our study supports the notion that Alk3-mediated BMP signaling in AV endocardial/mesenchymal cells plays a central role during cushion morphogenesis.

Potential involvement of BMP receptor type IB activation in a synergistic effect of chondrogenic promotion between rhTGFbeta3 and rhGDF5 or rhBMP7 in human mesenchymal stem cells

Chondrogenic promotion by rhGDF5 with or without rhTGFbeta3 was studied in pellet culture of human mesenchymal stem cells (HMSCs). A synergy between rhGDF5 and rhTGFbeta3 was observed in promoting chondrogenesis. rhBMP2, rhBMP6, rhBMP7 and rhTGFbeta1 were further tested and showed the same effect. To explore the mechanism, the expression of TGFbetatype I and II receptors, ALK5, ALK2, ALK3, ALK6, TGFbetaRII, BMPRII, ActRII was studied. ALK6 showed increase by the rhTGFbeta1 or rhTGFbeta3 treatment. ALK6 protein expression also showed increase by rhTGFbeta3. rhTGFbeta1/rhTGFbeta3 induced ALK6 up-regulation was inhibited by SD-208, a TGFbeta type I receptor inhibitor. Chondrogenesis by rhTGFbetal/rhTGFbeta3 or the combination between rhTGFbetal/rhTGFbeta3 and rhGDF5 also was diminished by SD-208. SMAD1/5/8 phosphorylation in nascent human mesenchymal stem cells (HMSCs) was stimulated weakly by rhGDF5 but strongly by rhBMP7. The rhGDF5 stimulated SMAD1/5/8 phosphorylation was enhanced by rhTGFbetal/rhTGFbeta3 but inhibited by SD-208. The rhBMP7 stimulated SMAD1/5/8 phosphorylation did not show influence by rhTGFbeta3 and SD-208. Our results indicated the potential involvement of ALK6 activation by rhTGFbetas in the synergy between rhTGFbetas and rhBMPs.

BMP signaling in the epiblast is required for proper recruitment of the prospective paraxial mesoderm and development of the somites

Bmpr1a encodes the BMP type IA receptor for bone morphogenetic proteins (BMPs), including 2 and 4. Here, we use mosaic inactivation of Bmpr1a in the epiblast of the mouse embryo (Bmpr-MORE embryos) to assess functions of this gene in mesoderm development. Unlike Bmpr1a-null embryos, which fail to gastrulate, Bmpr-MORE embryos initiate gastrulation, but the recruitment of prospective paraxial mesoderm cells to the primitive streak is delayed. This delay causes a more proximal distribution of cells with paraxial mesoderm character within the primitive streak, resulting in a lateral expansion of somitic mesoderm to form multiple columns. Inhibition of FGF signaling restores the normal timing of recruitment of prospective paraxial mesoderm and partially rescues the development of somites. This suggests that BMP and FGF signaling function antagonistically during paraxial mesoderm development.

Evidence that autocrine signaling through Bmpr1a regulates the proliferation, survival and morphogenetic behavior of distal lung epithelial cells

Lung development requires reciprocal epithelial/mesenchymal interactions, mediated by signaling factors such as Bmps made in both cell populations. To address the role of Bmp signaling in the epithelium, we have exploited the fact that Bmp receptor type Ia (Alk3) is expressed in the epithelium during branching morphogenesis. Deletion of Bmpr1a in the epithelium with an Sftpc-cre transgene leads to dramatic defects in lung development. There is reduced epithelial proliferation, extensive apoptosis, changes in cell morphology and extrusion of cells into the lumen. By E18.5, there are fewer Type II cells than normal, and the lung contains large fluid-filled spaces. If cell death is prevented by making embryos homozygous null for the proapoptotic gene, Bax, the epithelial cells that are rescued can apparently differentiate, but normal morphogenesis is not restored. To determine whether Bmps made by the epithelium can function in an autocrine manner, mesenchyme-free endoderm was cultured in Matrigel with Fgfs. Under these conditions, the mutant epithelium fails to undergo secondary budding. Abnormal development was also seen when Bmp4 was specifically deleted in the epithelium using the Sftpc-cre transgene. Our results support a model in which Bmp signaling primarily regulates the proliferation, survival and morphogenetic behavior of distal lung epithelial cells.

Mutual regulation of follicle-stimulating hormone signaling and bone morphogenetic protein system in human granulosa cells

Bone morphogenetic proteins (BMPs) play critical roles in folliculogenesis by modulating the actions of follicle-stimulating hormone (FSH) in the ovary. However, the effects of FSH on the BMP system remain unknown. Here, we have investigated the effects of FSH on BMP signaling using the human granulosa-like tumor cell line KGN. KGN cells express BMP type I and type II receptors and the BMP signaling molecules SMADs. FSH administration upregulated BMP type IA (BMPR1A) and IB (BMPR1B) receptors, activin type II receptor (ACVR2), and BMP type II receptor (BMPR2). FSH also augmented SMAD1 and SMAD5 expression, and conversely, FSH suppressed the expression of the inhibitory SMADs, SMAD6 and SMAD7. Bioassays revealed that FSH enhances BMP-induced SMAD1/5/8 phosphorylation and cellular DNA synthesis induced by BMP6 and BMP7. Since overexpression of BMPR1A and BMPR1B, but not SMADs, significantly enhanced the BMP responses, these type I receptors were revealed to be limiting factors for BMP signaling in KGN cells. BMPs significantly suppressed progesterone synthesis induced by forskolin and dibutyryl-cAMP (BtcAMP) but had no effect on estradiol induced by the same factors. KGN cAMP levels induced by forskolin were not altered by BMPs, suggesting that BMPs regulate steroidogenesis at a level downstream of cAMP synthesis in KGN cells. In this regard, BMPs specifically reduced the STAR transcription, whereas the levels of CYP11A, HSD3B2, and CYP19 stimulated by forskolin as well as BtcAMP were not altered. Collectively, the two major factors, FSH-cAMP pathway and BMP system, are reciprocally and functionally linked. Given that BMPs downregulate FSH receptors in KGN cells, this interaction may contribute to fine-tuning of the mutual sensitivity toward BMP ligands and FSH.

Bone morphogenetic protein signaling modulates myocardin transactivation of cardiac genes

Bone morphogenetic proteins (BMPs) play important roles in cardiovascular development. However, how BMP-signaling pathways regulate cardiac gene expression is less clear. We have previously identified myocardin as a cardiac and smooth muscle-specific transcriptional cofactor for serum response factor (SRF). Myocardin potently activates target gene expression by tethering with SRF bound to SRF-responsive elements, the CArG box. Here, we show that Smad1, an effector of the BMP-signaling pathway, synergistically activates myocardin-dependent cardiac gene expression. Interestingly, the CArG box is necessary and sufficient to mediate such synergy, whereas no obvious Smad-binding element appears to be involved. Consistent with their functional interaction, we find that myocardin and Smad1 proteins interact directly. Furthermore, myocardin protein levels were dramatically increased by BMP-2 treatment in cardiomyocytes. These findings suggest myocardin participates in a BMP signaling-dependent cardiac gene transcriptional program.