Lentivirus as a tool for lineage-specific gene manipulations

Endothelial-mesenchymal crosstalk drives osteogenic differentiation of human osteoblasts through Notch signaling

BACKGROUND

Angiogenesis and osteogenesis are closely interrelated. The interaction between endothelial and bone-forming cells, such as osteoblasts, is crucial for normal bone development and repair. Juxtacrine and paracrine mechanisms play key roles in cell differentiation towards the osteogenic direction, assuming the direct effect of endothelium on osteogenic differentiation. However, the mechanisms of this interplay have yet to be thoroughly studied.

METHODS

Isolated endothelial cells (EC) from human umbilical vein and human osteoblasts (OB) from the epiphysis of the femur or tibia were cultured in direct and indirect (separated by membrane) contact in vitro under the osteogenic differentiation conditions. Osteogenic differentiation was verified by RT-PCR, and alizarin red staining. Shotgun proteomics and RNA-sequencing were used to compare both EC and OB under different co-culture conditions to assess the mechanisms of EC-OB interplay. To verify the role of Notch signaling, experiments with Notch modulation in EC were performed by EC lentiviral transduction with further co-cultivation with OB. Additionally, the effect of Notch modulation in EC was assessed by RNA-sequencing.

RESULTS

EC have opposite effects on osteogenic differentiation depending on the co-culture conditions with OB. In direct contact, EC enhance osteogenic differentiation, but in indirect cultures, EC suppress it. Our proteotranscriptomic analysis revealed that the osteosuppressive effect is related to the action of paracrine factors secreted by EC, while the osteoinductive properties of EC are mediated by the Notch signaling pathway, which can be activated only upon a physical contact of EC with OB. Indeed, in the direct co-culture, the knockdown of Notch1 and Notch3 receptors in EC has an inhibitory effect on the OB osteogenic differentiation, whereas activation of Notch by intracellular domain of either Notch1 or Notch3 in EC has an inductive effect on the OB osteogenic differentiation.

CONCLUSION

The data indicate the dual role of the endothelium in regulating osteogenic differentiation and highlight the unique role of the Notch signaling pathway in inducing osteogenic differentiation during cell-to-cell interactions. The findings of the study emphasize the importance of intercellular communication in the regulation of osteoblast differentiation during bone development and maintenance.

Tryptophan Hydroxylase-2-Mediated Serotonin Biosynthesis Suppresses Cell Reprogramming into Pluripotent State

The monoamine neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) has important functions both in the neural system and during embryonic development in mammals. In this study, we set out to investigate whether and how endogenous serotonin affects reprogramming to pluripotency. As serotonin is synthesized from tryptophan by the rate limiting enzymes tryptophan hydroxylase-1 and -2 (TPH1 and TPH2), we have assessed the reprogramming of TPH1- and/or TPH2-deficient mouse embryonic fibroblasts (MEFs) to induced pluripotent stem cells (iPSCs). The reprogramming of the double mutant MEFs showed a dramatic increase in the efficiency of iPSC generation. In contrast, ectopic expression of TPH2 alone or in conjunction with TPH1 reverted the rate of reprogramming of the double mutant MEFs to the wild-type level and besides, TPH2 overexpression significantly suppressed reprogramming of wild-type MEFs. Our data thus suggest a negative role of serotonin biosynthesis in the reprogramming of somatic cells to a pluripotent state.

Modulation of Notch Signaling at Early Stages of Differentiation of Human Induced Pluripotent Stem Cells to Dopaminergic Neurons

Elaboration of protocols for differentiation of human pluripotent stem cells to dopamine neurons is an important issue for development of cell replacement therapy for Parkinson's disease. A number of protocols have been already developed; however, their efficiency and specificity still can be improved. Investigating the role of signaling cascades, important for neurogenesis, can help to solve this problem and to provide a deeper understanding of their role in neuronal development. Notch signaling plays an essential role in development and maintenance of the central nervous system after birth. In our study, we analyzed the effect of Notch activation and inhibition at the early stages of differentiation of human induced pluripotent stem cells to dopaminergic neurons. We found that, during the first seven days of differentiation, the cells were not sensitive to the Notch inhibition. On the contrary, activation of Notch signaling during the same time period led to significant changes and was associated with an increase in expression of genes, specific for caudal parts of the brain, a decrease of expression of genes, specific for forebrain, as well as a decrease of expression of genes, important for the formation of axons and dendrites and microtubule stabilizing proteins.

Dual Mode of Mitochondrial ROS Action during Reprogramming to Pluripotency

Essential changes in cell metabolism and redox signaling occur during the reprogramming of somatic cells into induced pluripotent stem cells (iPSCs). In this paper, using genetic and pharmacological approaches, we have investigated the role of electron transport chain (ETC) complex-I (CI) of mitochondria in the process of cell reprogramming to pluripotency. Knockdown of NADH-ubiquinone oxidoreductase core subunits S1 (Ndufs1) or subunit B10 (Ndufb10) of the CI or inhibition of this complex with rotenone during mouse embryonic fibroblast (MEF) reprogramming resulted in a significantly decreased number of induced pluripotent stem cells (iPSCs). We have found that mitochondria and ROS levels due course of the reprogramming tightly correlate with each other, both reaching peak by day 3 and significantly declining by day 10 of the process. The transient augmentation of mitochondrial reactive oxygen species (ROS) could be attenuated by antioxidant treatment, which ameliorated overall reprogramming. However, ROS scavenging after day 3 or during the entire course of reprogramming was suppressive for iPSC formation. The ROS scavenging within the CI-deficient iPSC-precursors did not improve, but further suppressed the reprogramming. Our data therefore point to distinct modes of mitochondrial ROS action during the early versus mid and late stages of reprogramming. The data further substantiate the paradigm that balanced levels of oxidative phosphorylation have to be maintained on the route to pluripotency.

Genome-wide mRNA profiling identifies X-box-binding protein 1 (XBP1) as an IRE1 and PUMA repressor

Accumulation of misfolded proteins in ER activates the unfolded protein response (UPR), a multifunctional signaling pathway that is important for cell survival. The UPR is regulated by three ER transmembrane sensors, one of which is inositol-requiring protein 1 (IRE1). IRE1 activates a transcription factor, X-box-binding protein 1 (XBP1), by removing a 26-base intron from XBP1 mRNA that generates spliced XBP1 mRNA (XBP1s). To search for XBP1 transcriptional targets, we utilized an XBP1s-inducible human cell line to limit XBP1 expression in a controlled manner. We also verified the identified XBP1-dependent genes with specific silencing of this transcription factor during pharmacological ER stress induction with both an N-linked glycosylation inhibitor (tunicamycin) and a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) (thapsigargin). We then compared those results to the XBP1s-induced cell line without pharmacological ER stress induction. Using next‐generation sequencing followed by bioinformatic analysis of XBP1-binding motifs, we defined an XBP1 regulatory network and identified XBP1 as a repressor of PUMA (a proapoptotic gene) and IRE1 mRNA expression during the UPR. Our results indicate impairing IRE1 activity during ER stress conditions accelerates cell death in ER-stressed cells, whereas elevating XBP1 expression during ER stress using an inducible cell line correlated with a clear prosurvival effect and reduced PUMA protein expression. Although further studies will be required to test the underlying molecular mechanisms involved in the relationship between these genes with XBP1, these studies identify a novel repressive role of XBP1 during the UPR.

Current State of Preeclampsia Mouse Models: Approaches, Relevance, and Standardization

Preeclampsia (PE) is a multisystemic, pregnancy-specific disorder and a leading cause of maternal and fetal death. PE is also associated with an increased risk for chronic morbidities later in life for mother and offspring. Abnormal placentation or placental function has been well-established as central to the genesis of PE; yet much remains to be determined about the factors involved in the development of this condition. Despite decades of investigation and many clinical trials, the only definitive treatment is parturition. To better understand the condition and identify potential targets preclinically, many approaches to simulate PE in mice have been developed and include mixed mouse strain crosses, genetic overexpression and knockout, exogenous agent administration, surgical manipulation, systemic adenoviral infection, and trophoblast-specific gene transfer. These models have been useful to investigate how biological perturbations identified in human PE are involved in the generation of PE-like symptoms and have improved the understanding of the molecular mechanisms underpinning the human condition. However, these approaches were characterized by a wide variety of physiological endpoints, which can make it difficult to compare effects across models and many of these approaches have aspects that lack physiological relevance to this human disorder and may interfere with therapeutic development. This report provides a comprehensive review of mouse models that exhibit PE-like symptoms and a proposed standardization of physiological characteristics for analysis in murine models of PE.

Assisted Reproductive Techniques and Genetic Manipulation in the Common Marmoset

Genetic modification of nonhuman primate (NHP) zygotes is a useful method for the development of NHP models of human diseases. This review summarizes the recent advances in the development of assisted reproductive and genetic manipulation techniques in NHP, providing the basis for the generation of genetically modified NHP disease models. In this study, we review assisted reproductive techniques, including ovarian stimulation, in vitro maturation of oocytes, in vitro fertilization, embryo culture, embryo transfer, and intracytoplasmic sperm injection protocols in marmosets. Furthermore, we review genetic manipulation techniques, including transgenic strategies, target gene knock-out and knock-in using gene editing protocols, and newly developed gene-editing approaches that may potentially impact the production of genetically manipulated NHP models. We further discuss the progress of assisted reproductive and genetic manipulation techniques in NHP; future prospects on genetically modified NHP models for biomedical research are also highlighted.

LMNA Mutations G232E and R482L Cause Dysregulation of Skeletal Muscle Differentiation, Bioenergetics, and Metabolic Gene Expression Profile

Laminopathies are a family of monogenic multi-system diseases resulting from mutations in the LMNA gene which include a wide range of neuromuscular disorders. Although lamins are expressed in most types of differentiated cells, LMNA mutations selectively affect only specific tissues by mechanisms that remain largely unknown. We have employed the combination of functional in vitro experiments and transcriptome analysis in order to determine how two LMNA mutations associated with different phenotypes affect skeletal muscle development and metabolism. We used a muscle differentiation model based on C2C12 mouse myoblasts genetically modified with lentivirus constructs bearing wild-type human LMNA (WT-LMNA) or R482L-LMNA/G232E-LMNA mutations, linked to familial partial lipodystrophy of the Dunnigan type and muscular dystrophy phenotype accordingly. We have shown that both G232E/R482L-LMNA mutations cause dysregulation in coordination of pathways that control cell cycle dynamics and muscle differentiation. We have also found that R482/G232E-LMNA mutations induce mitochondrial uncoupling and a decrease in glycolytic activity in differentiated myotubes. Both types of alterations may contribute to mutation-induced muscle tissue pathology.

Dysregulation of Notch signaling in cardiac mesenchymal cells of patients with tetralogy of Fallot

BACKGROUND

Tetralogy of Fallot (TF) is a severe congenital defect of heart development. Fine-tuned sequential activation of Notch signaling genes is responsible for proper heart chamber development. Mutations in Notch genes have been associated with TF. The aim of this study was to analyze the activity of the Notch pathway in cardiac mesenchymal cells derived from ventricular tissue of TF patients.

METHODS

Cardiac mesenchymal cells were isolated from 42 TF patients and from 14 patients with ventricular septal defects (VSDs), used as a comparison group. The Notch pathway was analyzed by estimating the expression of Notch-related genes by qPCR. Differentiation and proliferation capacity of the cells was estimated.

RESULTS

The TF-derived cells demonstrated a dysregulated pattern of Notch-related gene expression comparing to VSD-derived cells. Correlation of Notch signaling activation level by HEY1/HES1 expression level with proliferation and cardiogenic-like differentiation of cardiac mesenchymal cells was observed but not with clinical parameters nor with the age of the patients.

CONCLUSIONS

The data suggest a contribution of dysregulated Notch signaling to the pathogenesis of tetralogy of Fallot and importance of Notch signaling level for the functional state of cardiac mesenchymal cells, which could be critical considering these cells for potential cell therapy approaches.

Human AlphoidtetO Artificial Chromosome as a Gene Therapy Vector for the Developing Hemophilia A Model in Mice

Human artificial chromosomes (HACs), including the de novo synthesized alphoid^tetO-HAC, are a powerful tool for introducing genes of interest into eukaryotic cells. HACs are mitotically stable, non-integrative episomal units that have a large transgene insertion capacity and allow efficient and stable transgene expression. Previously, we have shown that the alphoid^tetO-HAC vector does not interfere with the pluripotent state and provides stable transgene expression in human induced pluripotent cells (iPSCs) and mouse embryonic stem cells (ESCs). In this study, we have elaborated on a mouse model of ex vivo iPSC- and HAC-based treatment of hemophilia A monogenic disease. iPSCs were developed from FVIII^Y/− mutant mice fibroblasts and FVIII cDNA, driven by a ubiquitous promoter, was introduced into the alphoid^tetO-HAC in hamster CHO cells. Subsequently, the therapeutic alphoid^tetO-HAC-FVIII was transferred into the FVIII^Y/– iPSCs via the retro-microcell-mediated chromosome transfer method. The therapeutic HAC was maintained as an episomal non-integrative vector in the mouse iPSCs, showing a constitutive FVIII expression. This study is the first step towards treatment development for hemophilia A monogenic disease with the use of a new generation of the synthetic chromosome vector—the alphoid^tetO-HAC.

Genetic tool for fate mapping of Oct4 (Pou5f1)-expressing cells and their progeny past the pluripotency stage

Background

Methods based on site-specific recombinases are widely used in studying gene activities in vivo and in vitro. In these studies, constitutively active or inducible variants of these recombinases are expressed under the control of either lineage-specific or ubiquitous promoters. However, there is a need for more advanced schemes that combine these features with possibilities to choose a time point from which lineage tracing starts in an autonomous fashion. For example, the key mammalian germline gatekeeper gene Oct4 (Pou5f1) is expressed in the peri-implantation epiblast which gives rise to all cells within embryos. Thus the above techniques are hardly applicable to Oct4 tracing past the epiblast stage, and the establishment of genetic tools addressing such a limitation is a highly relevant pursuit.

Methods

The CRISPR/Cas9 tool was used to manipulate the genome of mouse embryonic stem cells (ESCs), and various cell culture technics—to maintain and differentiate ESCs to neural cell, lentivirus-based reprogramming technique—to generate induced pluripotent stem cells (iPSCs).

Results

In this paper, we have developed a two-component genetic system (referred to as O4S) that allows tracing Oct4 gene activity past the epiblast stage of development. The first component represents a knock-in of an ubiquitous promoter-driven inducible Cre, serving as a stop signal for downstream tdTomato. Upon activation of Cre activity with 4-hydroxytamoxifen (4-OHT) at any given time point, the recombinase excises a stop signal and poses the second component of the system—the FlpO recombinase, knocked into 3’UTR of Oct4, to be expressed upon activation of the latter gene. Oct4-driven expression of FlpO, in turn, triggers the tdTomato expression and thus, permanently marks Oct4⁺ cells and their progeny. We have validated the O4S system in cultured ESCs and shown that it is capable, for example, to timely capture an activation of Oct4 gene during the reprogramming of somatic cells into iPSCs.

Conclusions

The developed O4S system can be used to detect Oct4 activation event, both permanent and transient, in somatic cell types outside the germline. The approach can be equally adjusted to other genes, provided the first component of the system is placed under transcriptional control of these genes, thus, making it a valuable tool for cell fate mapping in mice.

Dose-dependent mechanism of Notch action in promoting osteogenic differentiation of mesenchymal stem cells

Osteogenic differentiation is a tightly regulated process realized by progenitor cell osteoblasts. Notch signaling pathway plays a critical role in skeletal development and bone remodeling. Controversial data exist regarding the role of Notch activation in promoting or preventing osteogenic differentiation. This study aims to investigate the effect of several Notch components and their dosage on osteogenic differentiation of mesenchymal stem cells of adipose tissue. Osteogenic differentiation was induced in the presence of either of Notch components (NICD, Jag1, Dll1, Dll4) dosed by lentiviral transduction. We show that osteogenic differentiation was increased by NICD and Jag1 transduction in a dose-dependent manner; however, a high dosage of both NICD and Jag1 decreased the efficiency of osteogenic differentiation. NICD dose-dependently increased activity of the CSL luciferase reporter but a high dosage of NICD caused a decrease in the activity of the reporter. A high dosage of both Notch components NICD and Jag1 induced apoptosis. In co-culture experiments where only half of the cells were transduced with either NICD or Jag1, only NICD increased osteogenic differentiation according to the dosage, while Jag1-transduced cells differentiated almost equally independently on dosage. In conclusion, activation of Notch promotes osteogenic differentiation in a tissue-specific dose-dependent manner; both NICD and Jag1 are able to increase osteogenic potential but at moderate doses only and a high dosage of Notch activation is detrimental to osteogenic differentiation. This result might be especially important when considering possibilities of using Notch activation to promote osteogenesis in clinical applications to bone repair.

Hypertensive disorders of pregnancy: Strategy to develop clinical peptide biomarkers for more accurate evaluation of the pathophysiological status of this syndrome

Hypertensive disorders of pregnancy (HDP) is the most common and widely known as serious complication of pregnancy. As this syndrome is a major leading cause of maternal, fetal, and neonatal morbidity/mortality worldwide, many studies have sought to identify candidate molecules as potential disease biomarkers (DBMs) for use in clinical examinations. Accumulating evidence over the past 2 decades that the many proteolytic peptides appear in human humoral fluids, including peripheral blood, in association with an individual's health condition. This review provides the potential utility of peptidomic analysis for monitoring for pathophysiological status in HDP, and presents an overview of current status of peptide quantification technology. Especially, the technical limitations of the methods used for DBM discovery in the blood are discussed.

Hemochorial placentation: development, function, and adaptations

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

hnRNP-K Targets Open Chromatin in Mouse Embryonic Stem Cells in Concert with Multiple Regulators

The transcription factor Oct4 plays a key regulatory role in the induction and maintenance of cellular pluripotency. In this article, we show that ubiquitous and multifunctional poly(C) DNA/RNA-binding protein hnRNP-K occupies Oct4 (Pou5f1) enhancers in embryonic stem cells (ESCs) but is dispensable for the initiation, maintenance, and downregulation of Oct4 gene expression. Nevertheless, hnRNP-K has an essential cell-autonomous function in ESCs to maintain their proliferation and viability. To better understand mechanisms of hnRNP-K action in ESCs, we have performed ChIP-seq analysis of genome-wide binding of hnRNP-K and identified several thousands of hnRNP-K target sites that are frequently co-occupied by pluripotency-related and common factors (Oct4, TATA-box binding protein, Sox2, Nanog, Otx2, etc.), as well as active histone marks. Furthermore, hnRNP-K localizes exclusively within open chromatin, implying its role in the onset and/or maintenance of this chromatin state. Stem Cells 2019;37:1018-1029.

Trophoblast-Specific Expression of Hif-1α Results in Preeclampsia-Like Symptoms and Fetal Growth Restriction

The placenta is an essential organ that is formed during pregnancy and its proper development is critical for embryonic survival. While several animal models have been shown to exhibit some of the pathological effects present in human preeclampsia, these models often do not represent the physiological aspects that have been identified. Hypoxia-inducible factor 1 alpha (Hif-1α) is a necessary component of the cellular oxygen-sensing machinery and has been implicated as a major regulator of trophoblast differentiation. Elevated levels of Hif-1α in the human placenta have been linked to the development of pregnancy-associated disorders, such as preeclampsia and fetal growth restriction. As oxygen regulation is a critical determinant for placentogenesis, we determined the effects of constitutively active Hif-1α, specifically in trophoblasts, on mouse placental development in vivo. Our research indicates that prolonged expression of trophoblast-specific Hif-1α leads to a significant decrease in fetal birth weight. In addition, we noted significant physiological alterations in placental differentiation that included reduced branching morphogenesis, alterations in maternal and fetal blood spaces, and failure to remodel the maternal spiral arteries. These placental alterations resulted in subsequent maternal hypertension with parturitional resolution and maternal kidney glomeruloendotheliosis with accompanying proteinuria, classic hallmarks of preeclampsia. Our findings identify Hif-1α as a critical molecular mediator of placental development and indicate that prolonged expression of Hif-1α, explicitly in placental trophoblasts causes maternal pathology and establishes a mouse model that significantly recapitulates the physiological and pathophysiological characteristics of preeclampsia with fetal growth restriction.

Transfer of Synthetic Human Chromosome into Human Induced Pluripotent Stem Cells for Biomedical Applications

Alphoid^tetO-type human artificial chromosome (HAC) has been recently synthetized as a novel class of gene delivery vectors for induced pluripotent stem cell (iPSC)-based tissue replacement therapeutic approach. This HAC vector was designed to deliver copies of genes into patients with genetic diseases caused by the loss of a particular gene function. The alphoid^tetO-HAC vector has been successfully transferred into murine embryonic stem cells (ESCs) and maintained stably as an independent chromosome during the proliferation and differentiation of these cells. Human ESCs and iPSCs have significant differences in culturing conditions and pluripotency state in comparison with the murine naïve-type ESCs and iPSCs. To date, transferring alphoid^tetO-HAC vector into human iPSCs (hiPSCs) remains a challenging task. In this study, we performed the microcell-mediated chromosome transfer (MMCT) of alphoid^tetO-HAC expressing the green fluorescent protein into newly generated hiPSCs. We used a recently modified MMCT method that employs an envelope protein of amphotropic murine leukemia virus as a targeting cell fusion agent. Our data provide evidence that a totally artificial vector, alphoid^tetO-HAC, can be transferred and maintained in human iPSCs as an independent autonomous chromosome without affecting pluripotent properties of the cells. These data also open new perspectives for implementing alphoid^tetO-HAC as a gene therapy tool in future biomedical applications.

Immortalized murine fibroblast cell lines are refractory to reprogramming to pluripotent state

To date different cell types of various mammalian species have been reprogrammed to induced pluripotent stem cells (iPSCs) using Yamanaka's cocktail of transcription factors (Oct4, Klf4, Sox2, and cMyc). It has been shown that several primary human cancer cell lines could be reprogrammed to iPSCs. We sought if immortalized mouse fibroblast cell lines could also be reprogrammed to iPSCs. The approach of generating iPSCs from such cells should be valuable in different experimental settings as it allows clonally derive cell lines carrying mutations whose impact on reprogramming could be next evaluated. Therefore, we investigated reprogramming of widely used immortalized cell lines (NIH3T and STO), as well as of de novo immortalized fibroblast line (tKM) with the use of highly effective lentiviral polycistronic OKSM expression system. Our reprogramming experiments have shown that in contrast to mouse embryonic fibroblasts (MEFs), none of the immortalized cell lines can be reprogrammed to pluripotent state. Contrary to colonies derived from MEFs, those derived from the immortalized cells lines (1) developed much later, (2) contained large round cells, not typical for iPSCs, and (3) were negative for trusted markers of matured iPSCs, Nanog and SSEA1. Immortalized cell lines NIH3T and STO are known to be mostly aneuploid, whereas tKM population includes cells with normal karyotype, however, neither cell type can be reprogrammed. Thus our data argue that aneuploidy per se is not a reason for the observed refractoriness of mouse immortalized cells to reprogramming to pluripotent state.

Placenta-specific gene manipulation using lentiviral vector and its application

The placenta is an essential organ for embryo development in the uterus of eutherian mammals. Large contributions in unveiling molecular mechanisms and physiological functions underlying placental formation were made by analyzing mutant and transgenic animals. However, it had been difficult to elucidate whether the placental defects observed in such animals originate from the placenta itself or from the fetus, as both placental and fetal genomes are modified. Therefore strategies to modify the placental genome without affecting the "fetal genome" had been needed. Through the ingenious use of lentiviral (LV) vectors, placenta-specific modification is now possible. Lentivirus is a genus of retroviruses that use reverse-transcriptase to convert its single-strand RNA genome to double-strand DNA and integrate into the host genome. Previous studies showed that when LV vectors were used to transduce embryos at the 2-cell stage, the viral genome is systemically introduced into host genome. Interestingly, by delaying the timing of transduction to the blastocyst stage, the transgene is expressed specifically in the placenta as a consequence of trophectoderm-specific viral transduction. This review summarizes the development of the LV vector-mediated placenta-specific gene manipulation technology and its application in placental research over the past decade. A perspective for future application of LV vectors to further placenta research, especially in combination with next generation genome editing technologies, is also presented.

Placenta-specific gene manipulation in rabbits

Lentiviral gene constructs can be efficiently and specifically delivered to trophoblast cell lineages in rodents. In vivo genetic manipulation of trophoblast cell lines enables functional and developmental studies in the placenta. In this report we show that genetic modification can be produced in the extraembryonic tissues of rabbits by lentiviral gene constructs. When 8-16 cell stage embryos were injected with lentiviral particles, strong reporter gene expression resulted in the rabbit placenta. The expression pattern displayed some mosaicism. A strikingly high degree of mosaic GFP expression was detected in some parts of the yolk sac, which is a hypoblast-derived tissue. Whereas expression of the reporter gene construct was detected in placentas and yolk sacs, fetuses never expressed the transgene. As rabbits are an ideal model for functional studies in the placenta, our method would open new possibilities in rabbit biotechnology and placentation studies.

Mechanisms of Smooth Muscle Cell Differentiation Are Distinctly Altered in Thoracic Aortic Aneurysms Associated with Bicuspid or Tricuspid Aortic Valves

Cellular and molecular mechanisms of thoracic aortic aneurysm are not clear and therapeutic approaches are mostly absent. Thoracic aortic aneurysm is associated with defective differentiation of smooth muscle cells (SMC) of aortic wall. Bicuspid aortic valve (BAV) comparing to tricuspid aortic valve (TAV) significantly predisposes to a risk of thoracic aortic aneurysms. It has been suggested recently that BAV-associated aortopathies represent a separate pathology comparing to TAV-associated dilations. The only proven candidate gene that has been associated with BAV remains NOTCH1. In this study we tested the hypothesis that Notch-dependent and related TGF-β and BMP differentiation pathways are differently altered in aortic SMC of BAV- vs. TAV-associated aortic aneurysms. SMC were isolated from aortic tissues of the patients with BAV- or TAV-associated aortic aneurysms and from healthy donors used as controls. Gene expression was verified by qPCR and Western blotting. For TGF-β induced differentiation SMC were treated with the medium containing TGF-β1. To induce proosteogenic signaling we cultured SMC in the presence of specific osteogenic factors. Notch-dependent differentiation was induced via lentiviral transduction of SMC with activated Notch1 domain. MYOCD expression, a master gene of SMC differentiation, was down regulated in SMC of both BAV and TAV patients. Discriminant analysis of gene expression patterns included a set of contractile genes specific for SMC, Notch-related genes and proosteogenic genes and revealed that control cells form a separate cluster from both BAV and TAV group, while BAV- and TAV-derived SMC are partially distinct with some overlapping. In differentiation experiments TGF-β caused similar patterns of target gene expression for BAV- and TAV derived cells while the induction was higher in the diseased cells than in control ones. Osteogenic induction caused significant change in RUNX2 expression exclusively in BAV group. Notch activation induced significant ACTA2 expression also exclusively in BAV group. We show that Notch acts synergistically with proosteogenic factors to induce ACTA2 transcription and osteogenic differentiation. In conclusion we have found differences in responsiveness of SMC to Notch and to proosteogenic induction between BAV- and TAV-associated aortic aneurysms.

Expression and trafficking of placental microRNAs at the feto-maternal interface

During pregnancy, placental trophoblasts at the feto-maternal interface produce a broad repertoire of microRNA (miRNA) species. These species include miRNA from the primate-specific chromosome 19 miRNA cluster (C19MC), which is expressed nearly exclusively in the placenta. Trafficking of these miRNAs among the maternal, placental, and fetal compartments is unknown. To determine miRNA expression and trafficking patterns during pregnancy, we sequenced miRNAs in triads of human placenta and of maternal and fetal blood and found large subject-to-subject variability, with C19MC exhibiting compartment-specific expression. We therefore created humanized mice that transgenically express the entire 160-kb human C19MC locus or lentivirally express C19MC miRNA members selectively in the placenta. C19MC transgenic mice expressed a low level of C19MC miRNAs in diverse organs. When pregnant, female C19MC mice exhibited a strikingly elevated (>40-fold) expression of C19MC miRNA in the placenta, compared with other organs, that resembled C19MC miRNAs patterns in humans. Our mouse models showed that placental miRNA traffic primarily to the maternal circulation and that maternal miRNA can traffic to the placenta and even into the fetal compartment. These findings define an extraordinary means of nonhormonal, miRNA-based communication between the placenta and feto-maternal compartments.-Chang, G., Mouillet, J.-F., Mishima, T., Chu, T., Sadovsky, E., Coyne, C. B., Parks, W. T., Surti, U., Sadovsky, Y. Expression and trafficking of placental microRNAs at the feto-maternal interface.

Ex vivo Trophoblast-specific Genetic Manipulation Using Lentiviral Delivery

In this protocol report, we describe a lentiviral gene delivery technique for genetic modification of the rat trophoblast cell lineage. Lentiviral packaged gene constructs can be efficiently and specifically delivered to the trophoblast cell lineage of the blastocyst. The consequences of 'gain-of-function' and 'loss-of-function' blastocyst manipulations can be evaluated with in vitro outgrowth assays or following transfer to pseudopregnant rats.

Determinants of effective lentivirus-driven microRNA expression in vivo

Manipulation of microRNA (miRNA) levels, including overexpression of mature species, has become an important biological tool, even motivating miRNA-based therapeutics. To assess key determinants of miRNA overexpression in a mammalian system in vivo, we sought to bypass the laborious generation of a transgenic animal by exploiting placental trophoblast-specific gene manipulation using lentiviral vectors, which has been instrumental in elucidating trophoblast biology. We examined the impact of several key components of miRNA stem loops and their flanking sequences on the efficiency of mature miRNA expression in vivo. By combining established and novel approaches for miRNA expression, we engineered lentivirus-driven miRNA expression plasmids, which we tested in the mouse placenta. We found that reverse sense inserts minimized single-strand splicing and degradation, and that maintaining longer, poly-A-containing arms flanking the miRNA stem-loop markedly enhanced transgenic miRNA expression. Additionally, we accomplished overexpression of diverse mammalian, drosophila, or C. elegans miRNAs, either based on native context or using a “cassette” replacement of the mature miRNA sequence. Together, we have identified primary miRNA sequences that are paramount for effective expression of mature miRNAs, and validated their role in mice. Principles established by our findings may guide the design of efficient miRNA vectors for in vivo use.

Notch-dependent EMT is attenuated in patients with aortic aneurysm and bicuspid aortic valve

Bicuspid aortic valve is the most common congenital heart malformation and the reasons for the aortopathies associated with bicuspid aortic valve remain unclear. NOTCH1 mutations are associated with bicuspid aortic valve and have been found in individuals with various left ventricular outflow tract abnormalities. Notch is a key signaling during cardiac valve formation that promotes the endothelial-to-mesenchymal transition. We address the role of Notch signaling in human aortic endothelial cells from patients with bicuspid aortic valve and aortic aneurysm. Aortic endothelial cells were isolated from tissue fragments of bicuspid aortic valve-associated thoracic aortic aneurysm patients and from healthy donors. Endothelial-to-mesenchymal transition was induced by activation of Notch signaling. Effectiveness of the transition was estimated by loss of endothelial and gain of mesenchymal markers by immunocytochemistry and qPCR. We show that aortic endothelial cells from the patients with aortic aneurysm and bicuspid aortic valve have down regulated Notch signaling and fail to activate Notch-dependent endothelial-to-mesenchymal transition in response to its stimulation by different Notch ligands. Our findings support the idea that bicuspid aortic valve and associated aortic aneurysm is associated with dysregulation of the entire Notch signaling pathway independently on the specific gene mutation.

Primary Murine Myotubes as a Model for Investigating Muscular Dystrophy

Muscular dystrophies caused by defects in various genes are often associated with impairment of calcium homeostasis. Studies of calcium currents are hampered because of the lack of a robust cellular model. Primary murine myotubes, formed upon satellite cell fusion, were examined for their utilization as a model of adult skeletal muscle. We enzymatically isolated satellite cells and induced them to differentiation to myotubes. Myotubes displayed morphological and physiological properties resembling adult muscle fibers. Desmin and myosin heavy chain immunoreactivity in the differentiated myotubes were similar to the mature muscle cross-striated pattern. The myotubes responded to electrical and chemical stimulations with sarcoplasmic reticulum calcium release. Presence of L-type calcium channels in the myotubes sarcolemma was confirmed via whole-cell patch-clamp technique. To assess the use of myotubes for studying functional mutation effects lentiviral transduction was applied. Satellite cells easily underwent transduction and were able to retain a positive expression of lentivirally encoded GFP up to and after the formation of myotubes, without changes in their physiological and morphological properties. Thus, we conclude that murine myotubes may serve as a fruitful cell model for investigating calcium homeostasis in muscular dystrophy and the effects of gene modifications can be assessed due to lentiviral transduction.

Various lamin A/C mutations alter expression profile of mesenchymal stem cells in mutation specific manner

Various mutations in LMNA gene, encoding for nuclear lamin A/C protein, lead to laminopathies and contribute to over ten human disorders, mostly affecting tissues of mesenchymal origin such as fat tissue, muscle tissue, and bones. Recently it was demonstrated that lamins not only play a structural role providing communication between extra-nuclear structures and components of cell nucleus but also control cell fate and differentiation. In our study we assessed the effect of various LMNA mutations on the expression profile of mesenchymal multipotent stem cells (MMSC) during adipogenic and osteogenic differentiation. We used lentiviral approach to modify human MMSC with LMNA-constructs bearing mutations associated with different laminopathies--G465D, R482L, G232E, R527C, and R471C. The impact of various mutations on MMSC differentiation properties and expression profile was assessed by colony-forming unit analysis, histological staining, expression of the key differentiation markers promoting adipogenesis and osteogenesis followed by the analysis of the whole set of genes involved in lineage-specific differentiation using PCR expression arrays. We demonstrate that various LMNA mutations influence the differentiation efficacy of MMSC in mutation-specific manner. Each LMNA mutation promotes a unique expression pattern of genes involved in a lineage-specific differentiation and this pattern is shared by the phenotype-specific mutations.

Aggregate-prone desmin mutations impair mitochondrial calcium uptake in primary myotubes

Desmin, being a major intermediate filament of mature muscle cell, interacts with mitochondria within the cell and participates in mitochondria proper localization. The goal of the present study was to assess the effect of aggregate-prone and non-aggregate-prone desmin mutations on mitochondrial calcium uptake. Primary murine satellite cells were transduced with lentiviruses carrying desmin in wild type or mutant form, and were induced to differentiate into myotubes. Four mutations resulting in different degree of desmin aggregates formation were analyzed. Tail domain mutation Asp399Tyr has the mildest impact on desmin filament polymerization, rod domain mutation Ala357Pro causes formation of large aggregates composed of filamentous material, and Leu345Pro and Leu370Pro are considered to be the most severest in their impact on desmin polymerization and structure. For mitochondrial calcium measurement cells were loaded with rhod 2-AM. We found that aggregate-prone mutations significantly decreased [Ca(2+)]mit, whereas non-aggregate-prone mutations did not decrease [Ca(2+)]mit. Moreover aggregate-prone desmin mutations resulted in increased resting cytosolic [Ca(2+)]. However this increase was not accompanied by any alterations in sarcoplasmic reticulum calcium release. We suggest that the observed decline in [Ca(2+)]mit was due to desmin aggregate accumulation resulting in the loss of desmin mitochondria interactions.

Important aspects of placental-specific gene transfer

The placenta is a unique and highly complex organ that develops only during pregnancy and is essential for growth and survival of the developing fetus. The placenta provides the vital exchange of gases and wastes, the necessary nutrients for fetal development, acts as immune barrier that protects against maternal rejection, and produces numerous hormones and growth factors that promote fetal maturity to regulate pregnancy until parturition. Abnormal placental development is a major underlying cause of pregnancy-associated disorders that often result in preterm birth. Defects in placental stem cell propagation, growth, and differentiation are the major factors that affect embryonic and fetal well-being and dramatically increase the risk of pregnancy complications. Understanding the processes that regulate placentation is important in determining the underlying factors behind abnormal placental development. The ability to manipulate genes in a placenta-specific manner provides a unique tool to analyze development and eliminates potentially confounding results that can occur with traditional gene knockouts. Trophoblast stem cells and mouse embryos are not overly amenable to traditional gene transfer techniques. Most viral vectors, however, have a low infection rate and often lead to mosaic transgenesis. Although the traditional method of embryo transfer is intrauterine surgical implantation, the methodology reported here, combining lentiviral blastocyst infection and nonsurgical embryo transfer, leads to highly efficient and placental-specific gene transfer. Numerous advantages of our optimized procedures include increased investigator safety, a reduction in animal stress, rapid and noninvasive embryo transfer, and higher a rate of pregnancy and live birth.

The proprotein convertase furin is required for trophoblast syncytialization

The multinucleated syncytial trophoblast, which forms the outermost layer of the placenta and serves multiple functions, is differentiated from and maintained by cytotrophoblast cell fusion. Deficiencies in syncytial trophoblast differentiation or maintenance likely contribute to intrauterine growth restriction and pre-eclampsia, two common gestational diseases. The cellular and molecular mechanisms governing trophoblast syncytialization are poorly understood. We report here that the proprotein convertase furin is highly expressed in syncytial trophoblast in the first trimester human placentas, and expression of furin in the syncytiotrophoblast is significantly lower in the placentas from pre-eclamptic patients as compared with their gestational age-matched control placentas. Using multiple experimental models including induced fusion of choriocarcinoma BeWo cells and spontaneous fusion of primary cultured cytotrophoblast cells or placental explants, we demonstrate that cytotrophoblast cell fusion and syncytialization are accompanied by furin expression. Furin-specific siRNAs or inhibitors inhibit cell fusion in BeWo cells, as well as trophoblast syncytialization in human placental explants. Furthermore, type 1 IGF receptor (IGF1R) is indicated in this study as a substrate of furin, and processing of IGF1R by furin is an essential mechanism for syncytialization. Finally, using lentivirus-mediated RNAi targeting to mouse trophectoderm, we demonstrate that furin function is required for the development of syncytiotrophoblast structure in the labyrinth layer, as well as for normal embryonic development.

Lineage conversion of murine extraembryonic trophoblast stem cells to pluripotent stem cells

In mammals, the first cell fate decision is initialized by cell polarization at the 8- to 16-cell stage of the preimplantation embryo. At this stage, outside cells adopt a trophectoderm (TE) fate, whereas the inside cell population gives rise to the inner cell mass (ICM). Prior to implantation, transcriptional interaction networks and epigenetic modifications divide the extraembryonic and embryonic fate irrevocably. Here, we report that extraembryonic trophoblast stem cell (TSC) lines are converted to induced pluripotent stem cells (TSC-iPSCs) by overexpressing Oct4, Sox2, Klf4, and cMyc. Methylation studies and gene array analyses indicated that TSC-iPSCs had adopted a pluripotent potential. The rate of conversion was lower than those of somatic reprogramming experiments, probably due to the unique genetic network controlling extraembryonic lineage fixation. Both in vitro and in vivo, TSC-iPSCs differentiated into tissues representing all three embryonic germ layers, indicating that somatic cell fate could be induced. Finally, TSC-iPSCs chimerized the embryo proper and contributed to the germ line of mice, indicating that these cells had acquired full somatic differentiation potential. These results lead to a better understanding of the molecular processes that govern the first lineage decision in mammals.

Noninvasive monitoring of placenta-specific transgene expression by bioluminescence imaging

Background

Placental dysfunction underlies numerous complications of pregnancy. A major obstacle to understanding the roles of potential mediators of placental pathology has been the absence of suitable methods for tissue-specific gene manipulation and sensitive assays for studying gene functions in the placentas of intact animals. We describe a sensitive and noninvasive method of repetitively tracking placenta-specific gene expression throughout pregnancy using lentivirus-mediated transduction of optical reporter genes in mouse blastocysts.

Methodology/Principal Findings

Zona-free blastocysts were incubated with lentivirus expressing firefly luciferase (Fluc) and Tomato fluorescent fusion protein for trophectoderm-specific infection and transplanted into day 3 pseudopregnant recipients (GD3). Animals were examined for Fluc expression by live bioluminescence imaging (BLI) at different points during pregnancy, and the placentas were examined for tomato expression in different cell types on GD18. In another set of experiments, blastocysts with maximum photon fluxes in the range of 2.0E+4 to 6.0E+4 p/s/cm²/sr were transferred. Fluc expression was detectable in all surrogate dams by day 5 of pregnancy by live imaging, and the signal increased dramatically thereafter each day until GD12, reaching a peak at GD16 and maintaining that level through GD18. All of the placentas, but none of the fetuses, analyzed on GD18 by BLI showed different degrees of Fluc expression. However, only placentas of dams transferred with selected blastocysts showed uniform photon distribution with no significant variability of photon intensity among placentas of the same litter. Tomato expression in the placentas was limited to only trophoblast cell lineages.

Conclusions/Significance

These results, for the first time, demonstrate the feasibility of selecting lentivirally-transduced blastocysts for uniform gene expression in all placentas of the same litter and early detection and quantitative analysis of gene expression throughout pregnancy by live BLI. This method may be useful for a wide range of applications involving trophoblast-specific gene manipulations in utero.

Pravastatin induces placental growth factor (PGF) and ameliorates preeclampsia in a mouse model

Preeclampsia is a relatively common pregnancy-related disorder. Both maternal and fetal lives will be endangered if it proceeds unabated. Recently, the placenta-derived anti-angiogenic factors, such as soluble fms-like tyrosine kinase-1 (sFLT1) and soluble endoglin (sENG), have attracted attention in the progression of preeclampsia. Here, we established a unique experimental model to test the role of sFLT1 in preeclampsia using a lentiviral vector-mediated placenta-specific expression system. The model mice showed hypertension and proteinuria during pregnancy, and the symptoms regressed after parturition. Intrauterine growth restriction was also observed. We further showed that pravastatin induced the VEGF-like angiogenic factor placental growth factor (PGF) and ameliorated the symptoms. We conclude that our experimental preeclamptic murine model phenocopies the human case, and the model identifies low-dose statins and PGF as candidates for preeclampsia treatment.