While dysferlin and myoferlin are coexpressed in the human placenta, only dysferlin expression is responsive to trophoblast fusion in model systems

The proteomic landscape of trophoblasts unravels calcium-dependent syncytialization processes and beta-chorionic gonadotropin (ß-hCG) production

BACKGROUND

The syncytiotrophoblast (STB) layer of the placenta is formed by cell fusion of cytotrophoblasts, acts as a feto-maternal barrier, is required for the production of pregnancy hormones such as chorionic gonadotropin, estradiol and progesterone and is also responsible for feto-maternal mineral exchange such as calcium. Adequate mineral supply and placental hormone production are essential for the maintenance of pregnancy, and disturbances in trophoblast integrity are associated with pregnancy complications. Since knowledge about the identity and expression levels of proteins in trophoblast and syncytiotrophoblast cells is limited so far, we analyzed the proteomes of trophoblast-like and syncytiotrophoblast-like BeWo cells under different calcium conditions. The investigation of protein expression profiles in combination with hormone assays can provide a better understanding of calcium-dependent cellular processes in trophoblasts and syncytiotrophoblasts.

METHODS

Here, we combine human trophoblast model cell cultures, hormone assays, antibody-based detection methods and high-resolution mass spectrometry analyzes to assess changes in cellular processes during syncytialization.

RESULTS

We monitored the changes in protein expression profiles during forskolin induced syncytialization of trophoblast-like cells in an unbiased manner and show that the expression of numerous proteins is strongly altered. Among them are enzymes of the glucocorticoid and sex hormones synthesis pathways such as cytochrome P450 (CYP) 19A1, CYP11A1, adrenodoxin (FDX1), hydroxysteroid dehydrogenase (HSD) 11β2 and HSD17β1, whose expression is strongly induced by syncytialization. The production of beta human chorionic gonadotropin (ß-hCG), progesterone and estradiol increase during syncytialization, while the secretion and synthesis of ß-hCG and the expression of several protein syncytiotrophoblast markers show a clear calcium dependence.

CONCLUSION

The broad applicability of semi-quantitative proteome profiling of cytotrophoblast- and syncytiotrophoblast-like cells provides new insights into signaling processes that occur in cytotrophoblasts /syncytiotrophoblasts during pregnancy.

Ancestry dependent balancing selection of placental dysferlin at high-altitude

Introduction: The placenta mediates fetal growth by regulating gas and nutrient exchange between the mother and the fetus. The cell type in the placenta where this nutrient exchange occurs is called the syncytiotrophoblast, which is the barrier between the fetal and maternal blood. Residence at high-altitude is strongly associated with reduced 3rd trimester fetal growth and increased rates of complications such as preeclampsia. We asked whether altitude and/or ancestry-related placental gene expression contributes to differential fetal growth under high-altitude conditions, as native populations have greater fetal growth than migrants to high-altitude. Methods: We have previously shown that methylation differences largely accounted for altitude-associated differences in placental gene expression that favor improved fetal growth among high-altitude natives. We tested for differences in DNA methylation between Andean and European placental samples from Bolivia [La Paz (∼3,600 m) and Santa Cruz, Bolivia (∼400 m)]. One group of genes showing significant altitude-related differences are those involved in cell fusion and membrane repair in the syncytiotrophoblast. Dysferlin (DYSF) shows greater expression levels in high- vs. low-altitude placentas, regardless of ancestry. DYSF has a single nucleotide variant (rs10166384;G/A) located at a methylation site that can potentially stimulate or repress DYSF expression. Following up with individual DNA genotyping in an expanded sample size, we observed three classes of DNA methylation that corresponded to individual genotypes of rs10166384 (A/A < A/G < G/G). We tested whether these genotypes are under Darwinian selection pressure by sequencing a ∼2.5 kb fragment including the DYSF variants from 96 Bolivian samples and compared them to data from the 1000 genomes project. Results: We found that balancing selection (Tajima's D = 2.37) was acting on this fragment among Andeans regardless of altitude, and in Europeans at high-altitude (Tajima's D = 1.85). Discussion: This supports that balancing selection acting on dysferlin is capable of altering DNA methylation patterns based on environmental exposure to high-altitude hypoxia. This finding is analogous to balancing selection seen frequency-dependent selection, implying both alleles are advantageous in different ways depending on environmental circumstances. Preservation of the adenine (A) and guanine (G) alleles may therefore aid both Andeans and Europeans in an altitude dependent fashion.

Here and there a trophoblast, a transcriptional evaluation of trophoblast cell models

A recent explosion of methods to produce human trophoblast and stem cells (hTSCs) is fuelling a renewed interest in this tissue. The trophoblast is critical to reproduction by facilitating implantation, maternal physiological adaptations to pregnancy and the growth of the fetus through transport of nutrients between the mother and fetus. More broadly, the trophoblast has phenotypic properties that make it of interest to other fields. Its angiogenic and invasive properties are similar to tumours and could identify novel drug targets, and its ability to regulate immunological tolerance of the allogenic fetus could lead to improvements in transplantations. Within this review, we integrate and assess transcriptomic data of cell-based models of hTSC alongside in vivo samples to identify the utility and applicability of these models. We also integrate single-cell RNA sequencing data sets of human blastoids, stem cells and embryos to identify how these models may recapitulate early trophoblast development.

RNA-Seq identifies genes whose proteins are upregulated during syncytia development in murine C2C12 myoblasts and human BeWo trophoblasts

The fusion of villous cytotrophoblasts into the multinucleated syncytiotrophoblast is critical for the essential functions of the mammalian placenta. Using RNA-Seq gene expression, quantitative protein expression, and siRNA knockdown we identified genes and their cognate proteins which are similarly upregulated in two cellular models of mammalian syncytia development (human BeWo cytotrophoblast to syncytiotrophoblast and murine C2C12 myoblast to myotube). These include DYSF, PDE4DIP, SPIRE2, NDRG1, PLEC, GPR146, HSPB8, DHCR7, and HDAC5. These findings provide avenues for further understanding of the mechanisms underlying mammalian placental syncytiotrophoblast development.

Functions of Vertebrate Ferlins

Ferlins are multiple-C2-domain proteins involved in Ca²⁺-triggered membrane dynamics within the secretory, endocytic and lysosomal pathways. In bony vertebrates there are six ferlin genes encoding, in humans, dysferlin, otoferlin, myoferlin, Fer1L5 and 6 and the long noncoding RNA Fer1L4. Mutations in DYSF (dysferlin) can cause a range of muscle diseases with various clinical manifestations collectively known as dysferlinopathies, including limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy. A mutation in MYOF (myoferlin) was linked to a muscular dystrophy accompanied by cardiomyopathy. Mutations in OTOF (otoferlin) can be the cause of nonsyndromic deafness DFNB9. Dysregulated expression of any human ferlin may be associated with development of cancer. This review provides a detailed description of functions of the vertebrate ferlins with a focus on muscle ferlins and discusses the mechanisms leading to disease development.

Myoferlin, a Membrane Protein with Emerging Oncogenic Roles

Myoferlin (MYOF), initially identified in muscle cells, is a member of the Ferlin family involved in membrane fusion, membrane repair, and membrane trafficking. Dysfunction of this protein is associated with muscular dysfunction. Recently, a growing body of studies have identified MYOF as an oncogenic protein. It is overexpressed in a variety of human cancers and promotes tumorigenesis, tumor cell motility, proliferation, migration, epithelial to mesenchymal transition, angiogenesis as well as metastasis. Clinically, MYOF overexpression is associated with poor outcome in various cancers. It can serve as a prognostic marker of human malignant disease. MYOF drives the progression of cancer in various processes, including surface receptor transportation, endocytosis, exocytosis, intercellular communication, fit mitochondrial structure maintenance and cell metabolism. Depletion of MYOF demonstrates significant antitumor effects both in vitro and in vivo, suggesting that targeting MYOF may produce promising clinical benefits in the treatment of malignant disease. In the present article, we reviewed the physiological function of MYOF as well as its role in cancer, thus providing a general understanding for further exploration of this protein.

Maternal Transient Receptor Potential Vanilloid 6 (Trpv6) Is Involved In Offspring Bone Development

Embryonic growth and bone development depend on placental Ca²⁺ transport across the feto-maternal barrier to supply minerals to the fetus. The individual factors and cellular mechanisms that regulate placental Ca²⁺ transfer, however, are only beginning to emerge. We find that the Ca²⁺ -selective transient receptor potential vanilloid 6 (TRPV6) channel is expressed in trophoblasts of the fetal labyrinth, in the yolk sac, and in the maternal part of the placenta. Lack of functional TRPV6 channels in the mother leads to a reduced Ca²⁺ content in both placenta and embryo. Ca²⁺ uptake in trophoblasts is impaired in the absence of Trpv6. Trpv6-deficient embryos are smaller, have a lower body weight, and shorter and less calcified femurs. The altered cortical bone microarchitecture persists in adulthood. We show that TRPV6's Ca²⁺ -conducting property causes this embryonic and bone phenotype. Our results show that TRPV6 is necessary for the Ca²⁺ uptake in trophoblasts and that TRPV6 deficiency in the placenta leads to reduced embryo growth, minor bone calcification, and impaired bone development. © 2019 American Society for Bone and Mineral Research.

Global analysis of protein expression in muscle tissues of dermatomyositis/polymyosisits patients demonstrated an association between dysferlin and human leucocyte antigen A

OBJECTIVES

DM and PM are characterized by myofibre damage with inflammatory cell infiltration due to the strong expressions of MHC class I HLA-A and monocyte chemoattractant protein-1 (MCP-1). Dysferlin (DYSF) is a transmembrane glycoprotein that anchors in the sarcolemma of myofibres. DYSF mutation is closely associated with inherited myopathies. This study aimed to determine the role of DYSF in the development of DM/PM.

METHODS

Mass spectrometry was performed in muscle tissues from DM/PM patients and controls. The DYSF levels in muscle tissue, peripheral blood cells and serum were detected by Western blotting, IF, flow cytometry or ELISA. Double IF and co-immunoprecipitation were used to investigate the relationship between DYSF and HLA-A.

RESULTS

Mass spectrometry and bioinformatics analysis findings suggested the dysregulated proteins in DM/PM patients participated in common biological processes and pathways, such as the generation of precursor metabolites and energy. DYSF was upregulated in the muscle tissue and serum of DM/PM patients. DYSF was mainly expressed in myofibres and co-localized with HLA-A and MCP-1. DYSF and HLA-A expressions were elevated in myocytes and endothelial cells after being stimulated by patient serum and IFN-β. However, no direct interactions were found between DYSF and HLA-A by co-immunoprecipitation.

CONCLUSION

Our study revealed the dysregulated proteins involved in common and specific biological processes in DM/PM patient samples. DYSF is upregulated and exhibits a potential role along with that of HLA-A and MCP-1 in inflammatory cell infiltration and muscle damage during the development of DM/PM.

FerA is a Membrane-Associating Four-Helix Bundle Domain in the Ferlin Family of Membrane-Fusion Proteins

Ferlin proteins participate in such diverse biological events as vesicle fusion in C. elegans, fusion of myoblast membranes to form myotubes, Ca²⁺-sensing during exocytosis in the hair cells of the inner ear, and Ca²⁺-dependent membrane repair in skeletal muscle cells. Ferlins are Ca²⁺-dependent, phospholipid-binding, multi-C2 domain-containing proteins with a single transmembrane helix that spans a vesicle membrane. The overall domain composition of the ferlins resembles the proteins involved in exocytosis; therefore, it is thought that they participate in membrane fusion at some level. But if ferlins do fuse membranes, then they are distinct from other known fusion proteins. Here we show that the central FerA domain from dysferlin, myoferlin, and otoferlin is a novel four-helix bundle fold with its own Ca²⁺-dependent phospholipid-binding activity. Small-angle X-ray scattering (SAXS), spectroscopic, and thermodynamic analysis of the dysferlin, myoferlin, and otoferlin FerA domains, in addition to clinically-defined dysferlin FerA mutations, suggests that the FerA domain interacts with the membrane and that this interaction is enhanced by the presence of Ca²⁺.

Annexin-A5 promotes membrane resealing in human trophoblasts

Annexin-A5 (AnxA5) is the smallest member of the annexins, a group of soluble proteins that bind to membranes containing negatively-charged phospholipids, principally phosphatidylserine, in a Ca(2+)-dependent manner. AnxA5 presents unique properties of binding and self-assembling on membrane surfaces, forming highly ordered two-dimensional (2D) arrays. We showed previously that AnxA5 plays a central role in the machinery of cell membrane repair of murine perivascular cells, promoting the resealing of membrane damages via the formation of 2D protein arrays at membrane disrupted sites and preventing the extension of membrane ruptures. As the placenta is one of the richest source of AnxA5 in humans, we investigated whether AnxA5 was involved in membrane repair in this organ. We addressed this question at the level of human trophoblasts, either mononucleated cytotrophoblasts or multinucleated syncytiotrophoblasts, in choriocarcinoma cells and primary trophoblasts. Using established procedure of laser irradiation and fluorescence microscopy, we observed that both human cytotrophoblasts and syncytiotrophoblasts repair efficiently a μm²-size disruption. Compared to wild-type cells, AnxA5-deficient trophoblasts exhibit severe defect of membrane repair. Through specifically binding to the disrupted site as early as a few seconds after membrane wounding, AnxA5 promotes membrane resealing of injured human trophoblasts. In addition, we observed that a large membrane area containing the disrupted site was released in the extracellular milieu. We propose mechanisms ensuring membrane resealing and subsequent lesion removal in human trophoblasts. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Cell fusion mediates dramatic alterations in the actin cytoskeleton, focal adhesions, and E-cadherin in trophoblastic cells

The syncytiotrophoblast of the human placenta is a unique epithelia structure with millions of nuclei sharing a common cytoplasm. The syncytiotrophoblast forms by cell-cell fusion of cytotrophoblasts (CTB), the mononuclear precursor cells. The trophoblastic BeWo cell line has been used as a surrogate for CTB since they can be induced to fuse, and subsequently display numerous syncytiotrophoblast differentiation markers following syncytial formation. In this study, we have focused on alterations in the cell-adhesion molecule E-cadherin, actin cytoskeleton, and focal adhesions following BeWo cell fusion, since these entities may be interrelated. There was a dramatic reorganization of the distribution of E-cadherin as well as a reduction in the amount of E-cadherin following cell fusion. Reorganization of the actin cytoskeleton was also observed, which was associated with a change in the globular actin (G-actin)/filamentous actin (F-actin) ratio. Concomitantly, the morphology of focal adhesions was altered, but this occurred without a corresponding change in the levels of focal adhesion marker proteins. Thus, extensive remodeling of the actin cytoskeleton and focal adhesions accompanies cell fusion and differentiation and appears related to alterations in E-cadherin in trophoblastic cells.

Dysferlin is essential for endocytosis in the sea star oocyte

Dysferlin is a calcium-binding transmembrane protein involved in membrane fusion and membrane repair. In humans, mutations in the dysferlin gene are associated with muscular dystrophy. In this study, we isolated plasma membrane-enriched fractions from full-grown immature oocytes of the sea star, and identified dysferlin by mass spectrometry analysis. The full-length dysferlin sequence is highly conserved between human and the sea star. We learned that in the sea star Patiria miniata, dysferlin RNA and protein are expressed from oogenesis to gastrulation. Interestingly, the protein is highly enriched in the plasma membrane of oocytes. Injection of a morpholino against dysferlin leads to a decrease of endocytosis in oocytes, and to a developmental arrest during gastrulation. These results suggest that dysferlin is critical for normal endocytosis during oogenesis and for embryogenesis in the sea star and that this animal may be a useful model for studying the relationship of dysferlin structure as it relates to its function.

Trophoblast cell fusion and differentiation are mediated by both the protein kinase C and a pathways

The syncytiotrophoblast of the human placenta is an epithelial barrier that interacts with maternal blood and is a key for the transfer of nutrients and other solutes to the developing fetus. The syncytiotrophoblast is a true syncytium and fusion of progenitor cytotrophoblasts is the cardinal event leading to the formation of this layer. BeWo cells are often used as a surrogate for cytotrophoblasts, since they can be induced to fuse, and then express certain differentiation markers associated with trophoblast syncytialization. Dysferlin, a syncytiotrophoblast membrane repair protein, is up-regulated in BeWo cells induced to fuse by treatment with forskolin; this fusion is thought to occur through cAMP/protein kinase A-dependent mechanisms. We hypothesized that dysferlin may also be up-regulated in response to fusion through other pathways. Here, we show that BeWo cells can also be induced to fuse by treatment with an activator of protein kinase C, and that this fusion is accompanied by increased expression of dysferlin. Moreover, a dramatic synergistic increase in dysferlin expression is observed when both the protein kinase A and protein kinase C pathways are activated in BeWo cells. This synergy in fusion is also accompanied by dramatic increases in mRNA for the placental fusion proteins syncytin 1, syncytin 2, as well as dysferlin. Dysferlin, however, was shown to be dispensable for stimulus-induced BeWo cell syncytialization, since dysferlin knockdown lines fused to the same extent as control cells. The classical trophoblast differentiation marker human chorionic gonadotropin was also monitored and changes in the expression closely parallel that of dysferlin in all of the experimental conditions employed. Thus different biochemical markers of trophoblast fusion behave in concert supporting the hypothesis that activation of both protein kinase C and A pathways lead to trophoblastic differentiation.

Characterization Analysis of Schistosoma japonicum Plasma Membrane Repair Relative Gene Myoferlin

Myoferlin is a member of the ferlin family of proteins, which are involved in plasma membrane repair, and has been identified as one of the tegument proteins of Schistosoma japonicum. The tegument proteins are potential candidates for vaccines and new drug targets. In this study, myoferlin of S. japonicum (SjMF) was cloned, expressed and characterized, the potential of SjMF recombinant protein (rSjMF) as a vaccine candidate was evaluated, and the effect of praziquantel on SjMF was detected by Real-time PCR. Immunofluorescence showed that this protein was mainly distributed on the surface of worms at different stages. Sequence analysis revealed that the SjMF open reading frame was conserved at all stages of the S. japonicum life cycle. And SjMF transcription was upregulated in 42-day-old worms, and was significantly higher in female worms. Western blotting revealed that rSjMF showed strong immunogenicity. The cytokine profile and IgG isotype analysis demonstrated that rSjMF plus ISA206 immunization induced a mixed T helper (Th)1/Th2 response. Purified rSjMF emulsified with ISA206 adjuvant significantly reduced worm burden from 21.8% to 23.21% and liver egg number from42.58% to 28.35%. Besides, SjMF transcription was downregulated when worms were exposed to low-dose praziquantel (PZQ) and upregulated when PZQ was degraded, accompanied by recovery of damaged tegument. When worms were exposed to high-dose PZQ, SjMF transcription was downregulated all the time and the damaged tegument did not recover. These findings indicated that SjMF is a potential vaccine against S. japonicum and provides the basis for further investigations into the biological function of SjMF.

Dramatic alterations in the protein biosynthetic machinery accompany trophoblast fusion

This report represents a summary of a seminar presentation at Nippon Medical School on September 24, 2012. It is a synopsis of some of our research on trophoblast fusion.

Expression of myoferlin in human and murine carcinoma tumors: role in membrane repair, cell proliferation, and tumorigenesis

Cancer cells are often characterized by high proliferation rates, a consequence of increased mitotic signaling coupled with unchecked cellular growth. We recently demonstrated that vascular endothelial cells unexpectedly express ferlins, a family of muscle-specific proteins capable of regulating the fusion of lipid patches to the plasma membrane, and that these highly regulated membrane fusion events are essential to endothelial cell proliferation and homeostasis. Here, we show that human and mouse breast cancer cell lines also express myoferlin at various levels, and that the processes of transformation, epithelial-mesenchymal transition, and metastasis do not appear to have any effect on myoferlin expression in vitro. In vivo, we observed that solid mouse and human carcinoma tissues also express high levels of myoferlin protein. Loss-of-function studies performed in mice revealed that myoferlin gene knockdown can attenuate cancer cell proliferation in vitro and decrease tumor burden, and that accelerated tumor cell growth appears to rely on intact myoferlin-dependent membrane repair and signaling under exponential growth conditions. To our knowledge, these data provide the first evidence of myoferlin expression in solid human and mouse tumors. We have thus identified a novel membrane repair process that likely helps sustain the high growth rates characteristic of tumors, and we suggest that interfering with normal myoferlin expression and/or membrane repair and remodeling may provide therapeutically relevant antiproliferative effects.

Correlative fluorescence and transmission electron microscopy in tissues

Correlative microscopy has meant different things over the years; currently, this term refers to imaging the same exact structures with two or more imaging modalities. This commonly involves combining fluorescence and electron microscopy. Much of the recent work related to correlative microscopy has been done using cell culture models. However, many biological questions cannot be addressed in these models, but require instead the 3-dimensional organization of cells found in tissues. Herein, we discuss some of the issues related to correlative microscopy of tissues including the major reporter systems presently available for correlative microscopy. We present data from our own work in which we have focused on the use of ultrathin cryosections of tissues as the substrate for immunolabeling to combine immunofluorescence and electron microscopy of the same sub-cellular structures.

Expression of flotillins in the human placenta: potential implications for placental transcytosis

A proteomics survey of human placental syncytiotrophoblast (ST) apical plasma membranes revealed peptides corresponding to flotillin-1 (FLOT1) and flotillin-2 (FLOT2). The flotillins belong to a class of lipid microdomain-associated integral membrane proteins that have been implicated in clathrin- and caveolar-independent endocytosis. In the present study, we characterized the expression of the flotillin proteins within the human placenta. FLOT1 and FLOT2 were coexpressed in placental lysates and BeWo human trophoblast cells. Immunofluorescence microscopy of first-trimester and term placentas revealed that both proteins were more prominent in villous endothelial cells and cytotrophoblasts (CTs) than the ST. Correspondingly, forskolin-induced fusion in BeWo cells resulted in a decrease in FLOT1 and FLOT2, suggesting that flotillin protein expression is reduced following trophoblast syncytialization. The flotillin proteins co-localized with a marker of fluid-phase pinocytosis, and knockdown of FLOT1 and/or FLOT2 expression resulted in decreased endocytosis of cholera toxin B subunit. We conclude that FLOT1 and FLOT2 are abundantly coexpressed in term villous placental CTs and endothelial cells, and in comparison, expression of these proteins in the ST is reduced. These findings suggest that flotillin-dependent endocytosis is unlikely to be a major pathway in the ST, but may be important in the CT and endothelium.

Expression of myoferlin in human airway epithelium and its role in cell adhesion and zonula occludens-1 expression

Background

Normal airway epithelial barrier function is maintained by cell-cell contacts which require the translocation of adhesion proteins at the cell surface, through membrane vesicle trafficking and fusion events. Myoferlin and dysferlin, members of the multiple-C2-domain Ferlin superfamily, have been implicated in membrane fusion processes through the induction of membrane curvature. The objectives of this study were to examine the expression of dysferlin and myoferlin within the human airway and determine the roles of these proteins in airway epithelial homeostasis.

Methods

The expression of dysferlin and myoferlin were evaluated in normal human airway sections by immunohistochemistry, and primary human airway epithelial cells and fibroblasts by immuno blot. Localization of dysferlin and myoferlin in epithelial cells were determined using confocal microscopy. Functional outcomes analyzed included cell adhesion, protein expression, and cell detachment following dysferlin and myoferlin siRNA knock-down, using the human bronchial epithelial cell line, 16HBE.

Results

Primary human airway epithelial cells express both dysferlin and myoferlin whereas fibroblasts isolated from bronchi and the parenchyma only express myoferlin. Expression of dysferlin and myoferlin was further localized within the Golgi, cell cytoplasm and plasma membrane of 16HBE cells using confocal micrscopy. Treatment of 16HBE cells with myoferlin siRNA, but not dysferlin siRNA, resulted in a rounded cell morphology and loss of cell adhesion. This cell shedding following myoferlin knockdown was associated with decreased expression of tight junction molecule, zonula occludens-1 (ZO-1) and increased number of cells positive for apoptotic markers Annexin V and propidium iodide. Cell shedding was not associated with release of the innate inflammatory cytokines IL-6 and IL-8.

Conclusions/Significance

This study demonstrates the heterogeneous expression of myoferlin within epithelial cells and fibroblasts of the respiratory airway. The effect of myoferlin on the expression of ZO-1 in airway epithelial cells indicates its role in membrane fusion events that regulate cell detachment and apoptosis within the airway epithelium.

A placental sub-proteome: the apical plasma membrane of the syncytiotrophoblast

As a highly vascularized tissue, the placenta mediates gas and solute exchange between maternal and fetal circulations. In the human placenta, the interface with maternal blood is a unique epithelial structure known as the syncytiotrophoblast. Previously we developed a colloidal-silica based method to generate highly enriched preparations of the apical plasma membrane of the syncytiotrophoblast. Using similar preparations, a proteomics assessment of this important sub-proteome has identified 340 proteins as part of this apical membrane fraction. The expression of 38 of these proteins was previously unknown in the human placental syncytiotrophoblast. Together with previous studies, the current proteomic database expands our knowledge of the proteome of the syncytiotrophoblast apical plasma membrane from normal placentas to include more than 500 proteins. This database is a valuable resource for future comparisons to diseased placentas. Additionally, this data set provides a basis for further experimental studies of placenta and trophoblast function.

RhoE is regulated by cyclic AMP and promotes fusion of human BeWo choriocarcinoma cells

Fusion of placental villous cytotrophoblasts with the overlying syncytiotrophoblast is essential for the maintenance of successful pregnancy, and disturbances in this process have been implicated in pathological conditions such as pre-eclampsia and intra-uterine growth retardation. In this study we examined the role of the Rho GTPase family member RhoE in trophoblast differentiation and fusion using the BeWo choriocarcinoma cell line, a model of villous cytotrophoblast fusion. Treatment of BeWo cells with the cell permeable cyclic AMP analogue dibutyryl cyclic AMP (dbcAMP) resulted in a strong upregulation of RhoE at 24h, coinciding with the onset of fusion. Using the protein kinase A (PKA)-specific cAMP analogue N⁶-phenyl-cAMP, and a specific inhibitor of PKA (14–22 amide, PKI), we found that upregulation of RhoE by cAMP was mediated through activation of PKA signalling. Silencing of RhoE expression by RNA interference resulted in a significant decrease in dbcAMP-induced fusion. However, expression of differentiation markers human chorionic gonadotrophin and placental alkaline phosphatase was unaffected by RhoE silencing. Finally, we found that RhoE upregulation by dbcAMP was significantly reduced under hypoxic conditions in which cell fusion is impaired. These results show that induction of RhoE by cAMP is mediated through PKA and promotes BeWo cell fusion but has no effect on functional differentiation, supporting evidence that these two processes may be controlled by separate or diverging pathways.

GREG cells, a dysferlin-deficient myogenic mouse cell line

The dysferlinopathies (e.g. LGMD2b, Myoshi myopathy) are progressive, adult-onset muscle wasting syndromes caused by mutations in the gene coding for dysferlin. Dysferlin is a large (~200kDa) membrane-anchored protein, required for maintenance of plasmalemmal integrity in muscle fibers. To facilitate analysis of dysferlin function in muscle cells, we have established a dysferlin-deficient myogenic cell line (GREG cells) from the A/J mouse, a genetic model for dysferlinopathy. GREG cells have no detectable dysferlin expression, but proliferate normally in growth medium and fuse into functional myotubes in differentiation medium. GREG myotubes exhibit deficiencies in plasma membrane repair, as measured by laser wounding in the presence of FM1-43 dye. Under the wounding conditions used, the majority (~66%) of GREG myotubes lack membrane repair capacity, while no membrane repair deficiency was observed in dysferlin-normal C2C12 myotubes, assayed under the same conditions. We discuss the possibility that the observed heterogeneity in membrane resealing represents genetic compensation for dysferlin deficiency.

Ferlins: regulators of vesicle fusion for auditory neurotransmission, receptor trafficking and membrane repair

Ferlins are a family of multiple C2 domain proteins with emerging roles in vesicle fusion and membrane trafficking. Ferlin mutations are associated with muscular dystrophy (dysferlin) and deafness (otoferlin) in humans, and infertility in Caenorhabditis elegans (Fer-1) and Drosophila (misfire), demonstrating their importance for normal cellular functioning. Ferlins show ancient origins in eukaryotic evolution and are detected in all eukaryotic kingdoms, including unicellular eukaryotes and apicomplexian protists, suggesting origins in a common ancestor predating eukaryotic evolutionary branching. The characteristic feature of the ferlin family is their multiple tandem cytosolic C2 domains (five to seven C2 domains), the most of any protein family, and an extremely rare feature amongst eukaryotic proteins. Ferlins also bear a unique nested DysF domain and small conserved 60-70 residue ferlin-specific sequences (Fer domains). Ferlins segregate into two subtypes based on the presence (type I ferlin) or absence (type II ferlin) of the DysF and FerA domains. Ferlins have diverse tissue-specific and developmental expression patterns, with ferlin animal models united by pathologies arising from defects in vesicle fusion. Consistent with their proposed role in vesicle trafficking, ferlin interaction partners include cytoskeletal motors, other vesicle-associated trafficking proteins and transmembrane receptors or channels. Herein we summarize the research history of the ferlins, an intriguing family of structurally conserved proteins with a preserved ancestral function as regulators of vesicle fusion and receptor trafficking.

Placental dysferlin expression is reduced in severe preeclampsia

Dysferlin (DYSF) and myoferlin (MYOF), members of the ferlin family of membrane proteins, are co-expressed in human placental syncytiotrophoblast (STB). Although the role of these ferlin proteins in the placenta has yet to be established, it has been suggested that DYSF and MYOF may contribute to the stability of the apical STB plasma membrane. The release of STB-derived cellular debris increases in the setting of preeclampsia (PE), suggesting relative destabilization of the hemochorial interface. To test whether PE was associated with alterations in placental expression of DYSF and/or MYOF, a cross-sectional study was performed using specimens of villous placenta collected form women with severe PE (n=10) and normotensive controls (n=10). DYSF and MYOF expression were examined using quantitative real-time RT-PCR, immunoblotting, and immunofluorescence labeling of tissue specimens. Placental DYSF expression was 57% lower at the mRNA level (p=0.03) and 38% lower at the protein level (p=0.026) in severe PE as compared to normotensive subjects. There were no differences in placental MYOF protein or mRNA expression between these groups. No appreciable changes in the distribution of DYSF or MYOF within placental villi was observed in PE relative to control specimens. We conclude that DYSF expression is reduced in severe PE relative to gestational age-matched controls. As DYSF has a role in membrane repair, these data suggest a role for DYSF in the stability of the apical STB plasma membrane and may account, at least in part, for the increased shedding of microparticles from this membrane in PE.