Characterization of constitutive promoters for piggyBac transposon-mediated stable transgene expression in mesenchymal stem cells (MSCs)

Poly(ethylene glycol)-Based Hydrogel Microcarriers Alter Secretory Activity of Genetically Modified Mesenchymal Stromal Cells

In order to scale up culture therapeutic cells, such as mesenchymal stromal cells (MSCs), culture in suspension bioreactors using microcarriers (μCs) is preferred. However, the impact of microcarrier type on the resulting MSC secretory activity has not been investigated. In this study, two poly(ethylene glycol) hydrogel formulations with different swelling ratios (named "stiffer" and "softer") were fabricated as μC substrates to culture MSCs and MSCs genetically modified to express the interleukin-1 receptor antagonist (IL-1Ra-MSCs). Changes in cell number, secretory and angiogenic activity, and changes in MAPK signaling were evaluated when cultured on hydrogel μCs, as well as on tissue culture plastic-based Synthemax μCs. We demonstrated that culture on stiffer μCs increased secretion of IL-1Ra compared to culture on Synthemax μCs by IL-1Ra-MSCs by 1.2- to 1.6-fold, as well as their in vitro angiogenic activity, compared to culture on Synthemax μCs, while culture on both stiffer and softer μCs altered the secretion of several other factors compared to culture on Synthemax μCs. Changes in angiogenic activity corresponded with increased gene expression and secretion of hepatocyte growth factor by MSCs cultured on softer μCs by 2.5- to 6-fold compared to MSCs cultured on Synthemax μCs. Quantification of phosphoprotein signaling with the MAPK pathway revealed broad reduction of pathway activation by IL-1Ra-MSCs cultured on both stiffer and softer μCs compared to Synthemax, where phosphorylated c-Jun, ATF2, and MEK1 were reduced specifically on softer μCs. Overall, this study showed that μC surfaces can influence the secretory activity of genetically modified MSCs and identified associated changes in MAPK pathway signaling, which is a known central regulator of cytokine secretion.

Anti-Aging β-Klotho Gene-Activated Scaffold Promotes Rejuvenative Wound Healing Response in Human Adipose-Derived Stem Cells

Wound healing requires a tight orchestration of complex cellular events. Disruption in the cell-signaling events can severely impair healing. The application of biomaterial scaffolds has shown healing potential; however, the potential is insufficient for optimal wound maturation. This study explored the functional impact of a collagen-chondroitin sulfate scaffold functionalized with nanoparticles carrying an anti-aging gene β-Klotho on human adipose-derived stem cells (ADSCs) for rejuvenative healing applications. We studied the response in the ADSCs in three phases: (1) transcriptional activities of pluripotency factors (Oct-4, Nanog and Sox-2), proliferation marker (Ki-67), wound healing regulators (TGF-β3 and TGF-β1); (2) paracrine bioactivity of the secretome generated by the ADSCs; and (3) regeneration of basement membrane (fibronectin, laminin, and collagen IV proteins) and expression of scar-associated proteins (α-SMA and elastin proteins) towards maturation. Overall, we found that the β-Klotho gene-activated scaffold offers controlled activation of ADSCs' regenerative abilities. On day 3, the ADSCs on the gene-activated scaffold showed enhanced (2.5-fold) activation of transcription factor Oct-4 that was regulated transiently. This response was accompanied by a 3.6-fold increase in the expression of the anti-fibrotic gene TGF-β3. Through paracrine signaling, the ADSCs-laden gene-activated scaffold also controlled human endothelial angiogenesis and pro-fibrotic response in dermal fibroblasts. Towards maturation, the ADSCs-laden gene-activated scaffold further showed an enhanced regeneration of the basement membrane through increases in laminin (2.1-fold) and collagen IV (8.8-fold) deposition. The ADSCs also expressed 2-fold lower amounts of the scar-associated α-SMA protein with improved qualitative elastin matrix deposition. Collectively, we determined that the β-Klotho gene-activated scaffold possesses tremendous potential for wound healing and could advance stem cell-based therapy for rejuvenative healing applications.

Applications of piggyBac Transposons for Genome Manipulation in Stem Cells

Transposons are mobile genetic elements in the genome. The piggyBac (PB) transposon system is increasingly being used for stem cell research due to its high transposition efficiency and seamless excision capacity. Over the past few decades, forward genetic screens based on PB transposons have been successfully established to identify genes associated with drug resistance and stem cell-related characteristics. Moreover, PB transposon is regarded as a promising gene therapy vector and has been used in some clinically relevant stem cells. Here, we review the recent progress on the basic biology of PB, highlight its applications in current stem cell research, and discuss its advantages and challenges.

Development of a new in vitro assay system for evaluating the effects of chemicals on DNA methylation

Epigenetic toxicity, a phenomenon in which chemicals exert epigenetic effects and produce toxicity, has been attracting attention in recent years due to advances in toxicology accompanying the development of life sciences. However, it has been difficult to identify epigenetic toxicants due to the lack of a simple experimental system to evaluate epigenetic toxicity. In this study, we developed a prototype of an in vitro reporter assay system for assessing the effects of chemicals on DNA methylation using two promoters showing different degrees of DNA methylation, Agouti IAP and Daz1 promoters, and a luciferase reporter. The system successfully detected DNA demethylating activity using 5-azacytidine, a chemical having DNA demethylation activity, as a positive control chemical, and demethylation of cytosine of CpG in the promoter was confirmed by pyrosequencing analysis. Next, in order to improve the detection sensitivity of the DNA demethylating activity of this system, we tried to increase the basal level of methylation of the Daz1 promoter by pre-methylase treatment of the reporter vectors. As a result, the detection sensitivity of the system was successfully improved in cells where the basal level of methylation was indeed increased by methylase treatment. Thus, the developed assay system here is effective for the simple evaluation of chemicals that affect DNA methylation.

Stable integration of an optimized inducible promoter system enables spatiotemporal control of gene expression throughout avian development

Precisely altering gene expression is critical for understanding molecular processes of embryogenesis. Although some tools exist for transgene misexpression in developing chick embryos, we have refined and advanced them by simplifying and optimizing constructs for spatiotemporal control. To maintain expression over the entire course of embryonic development we use an enhanced piggyBac transposon system that efficiently integrates sequences into the host genome. We also incorporate a DNA targeting sequence to direct plasmid translocation into the nucleus and a D4Z4 insulator sequence to prevent epigenetic silencing. We designed these constructs to minimize their size and maximize cellular uptake, and to simplify usage by placing all of the integrating sequences on a single plasmid. Following electroporation of stage HH8.5 embryos, our tetracycline-inducible promoter construct produces robust transgene expression in the presence of doxycycline at any point during embryonic development in ovo or in culture. Moreover, expression levels can be modulated by titrating doxycycline concentrations and spatial control can be achieved using beads or gels. Thus, we have generated a novel, sensitive, tunable, and stable inducible-promoter system for high-resolution gene manipulation in vivo.

Effect of promoter, promoter mutation and enhancer on transgene expression mediated by episomal vectors in transfected HEK293, Chang liver and primary cells

The episomal vector cannot integrate into the host cell chromosome, which has no potential risk in gene therapy. However, the low level of transgene expression driven by episomal vectors needs to be solved. In this study, we investigated the effects of enhancers, promoters and promoter variants on transgene expression levels driven by episomal vectors in HEK293, Chang liver and primary cells. Results showed that all eight cis-acting elements used could increase transfection efficiency and transient eGFP expression in transfected HEK293 and Chang liver cells. In stably transfected mammalian cells, the elongation factor-1 alpha (EF-1α) promoter and mutant-404 showed high and stable transgene expression. The mechanisms might be related to the type and quantity of transcription factor regulatory elements. Moreover, quantitative reverse transcription polymerase chain reaction analysis showed that mRNA expression levels were not directly proportional to protein expression levels. Furthermore, the EF-1α promoter conferred high transgene expression levels in primary cells, and the plasmid was also present in the episomal state. Taken together, these results provided valuable information for improving transgene expression with episomal vectors in mammalian cells.

Establishment of a megakaryoblastic cell line for conventional assessment of platelet calcium signaling

Platelet function tests utilizing agonists or patient serum are generally performed to assess platelet activation ex vivo. However, inter-individual differences in platelet reactivity and donor requirements make it difficult to standardize these tests. Here, we established a megakaryoblastic cell line for the conventional assessment of platelet activation. We first compared intracellular signaling pathways using CD32 crosslinking in several megakaryoblastic cell lines, including CMK, UT-7/TPO, and MEG-01 cells. We confirmed that CD32 was abundantly expressed on the cell surface, and that intracellular calcium mobilization and tyrosine phosphorylation occurred after CD32 crosslinking. We next employed GCaMP6s, a highly sensitive calcium indicator, to facilitate the detection of calcium mobilization by transducing CMK and MEG-01 cells with a plasmid harboring GCaMP6s under the control of the human elongation factor-1α promoter. Cells that stably expressed GCaMP6s emitted enhanced green fluorescent protein fluorescence in response to intracellular calcium mobilization following agonist stimulation in the absence of pretreatment. In summary, we have established megakaryoblastic cell lines that mimic platelets by mobilizing intracellular calcium in response to several agonists. These cell lines can potentially be utilized in high-throughput screening assays for the discovery of new antiplatelet drugs or diagnosis of disorders caused by platelet-activating substances.

Imiquimod Acts Synergistically with BMP9 through the Notch Pathway as an Osteoinductive Agent In Vitro

BACKGROUND

Autologous bone grafts used for surgical reconstruction are limited by infection or insufficient supply of host material. Experimental agents that promote differentiation of stem cells into mature bone are currently being studied for future use in the repair of bone defects. The authors hypothesized that imiquimod, a synthetic immune response modifier, increases Notch pathway gene expression and acts synergistically with bone morphogenetic protein (BMP) 9 to induce differentiation of mesenchymal stem cells toward an osteogenic phenotype.

METHODS

Alkaline phosphatase activity was used to assess the osteogenic potential of cultured mouse immortalized multipotent adipose-derived cells (iMADs) treated with 0, 4, 6, and 8 μg/ml of imiquimod with and without BMP9. Adenoviral vectors expressing human BMP9 and a dominant-negative mutant of mouse Notch1 were used to assess BMP9 and Notch blockade on osteogenic activity, respectively. Expression of Notch signaling mediators and osteogenic markers were assayed by quantitative polymerase chain reaction. Alizarin red staining was used to assess the synergism between BMP9 and imiquimod.

RESULTS

Imiquimod exposure enhanced osteogenic differentiation of iMADs by 2.8-fold (p < 0.001) and potentiated BMP9-induced osteogenic differentiation of iMADs by 1.6-fold (p < 0.001), shown by increased alkaline phosphatase activity and augmented matrix mineralization. Quantitative-real time polymerase chain reaction analysis demonstrated that imiquimod induced the expression of downstream genes (p < 0.01) of the Notch signaling pathway Hey1, Hey2, and Hes1, by increases of 9.7-, 22-, and 2.7-fold, respectively.

CONCLUSIONS

These findings identify a novel role for imiquimod to shift mesenchymal stem cells toward an osteogenic phenotype. Imiquimod may be useful clinically when scaffolds are applied to treat bone defects.

Bone Morphogenetic Protein-9-Stimulated Adipocyte-Derived Mesenchymal Progenitors Entrapped in a Thermoresponsive Nanocomposite Scaffold Facilitate Cranial Defect Repair

Due to availability and ease of harvest, adipose tissue is a favorable source of progenitor cells in regenerative medicine, but has yet to be optimized for osteogenic differentiation. The purpose of this study was to test cranial bone healing in a surgical defect model utilizing bone morphogenetic protein-9 (BMP-9) transduced immortalized murine adipocyte (iMAD) progenitor cells in a citrate-based, phase-changing, poly(polyethylene glycol citrate-co-N-isopropylacrylamide) (PPCN)-gelatin scaffold. Mesenchymal progenitor iMAD cells were transduced with adenovirus expressing either BMP-9 or green fluorescent protein control. Twelve mice underwent craniectomy to achieve a critical-sized cranial defect. The iMAD cells were mixed with the PPCN-gelatin scaffold and injected into the defects. MicroCT imaging was performed in 2-week intervals for 12 weeks to track defect healing. Histologic analysis was performed on skull sections harvested after the final imaging at 12 weeks to assess quality and maturity of newly formed bone. Both the BMP-9 group and control group had similar initial defect sizes (P = 0.21). At each time point, the BMP-9 group demonstrated smaller defect size, higher percentage defect healed, and larger percentage defect change over time. At the end of the 12-week period, the BMP-9 group demonstrated mean defect closure of 27.39%, while the control group showed only a 9.89% defect closure (P < 0.05). The BMP-9-transduced iMADs combined with a PPCN-gelatin scaffold promote in vivo osteogenesis and exhibited significantly greater osteogenesis compared to control. Adipose-derived iMADs are a promising source of mesenchymal stem cells for further studies in regenerative medicine, specifically bone engineering with the aim of potential craniofacial applications.

Specific, Sensitive, and Stable Reporting of Human Mesenchymal Stromal Cell Chondrogenesis

IMPACT STATEMENT

The promoter characterized in this study has been made accessible as a resource for the skeletal tissue engineering and regenerative medicine community. When combined with suitable reporter vectors, the resulting tools can be used for noninvasive and/or high-throughput screening of test conditions for stimulating chondrogenesis by candidate stem/progenitor cells. As demonstrated in this study, they can also be used with small animal imaging platforms to monitor the chondrogenic activity of implanted progenitors within orthotopic models of bone and cartilage repair.

lncRNA Rmst acts as an important mediator of BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) by antagonizing Notch-targeting microRNAs

Understanding the bone and musculoskeletal system is essential to maintain the health and quality of life of our aging society. Mesenchymal stem cells (MSCs) can undergo self-renewal and differentiate into multiple tissue types including bone. We demonstrated that BMP9 is the most potent osteogenic factors although molecular mechanism underlying BMP9 action is not fully understood. Long noncoding RNAs (lncRNAs) play important regulatory roles in many physiological and/or pathologic processes. Here, we investigated the role of lncRNA Rmst in BMP9-induced osteogenic differentiation of MSCs. We found that Rmst was induced by BMP9 through Smad signaling in MSCs. Rmst knockdown diminished BMP9-induced osteogenic, chondrogenic and adipogenic differentiation in vitro, and attenuated BMP9-induced ectopic bone formation. Silencing Rmst decreased the expression of Notch receptors and ligands. Bioinformatic analysis predicted Rmst could directly bind to eight Notch-targeting miRNAs, six of which were downregulated by BMP9. Silencing Rmst restored the expression of four microRNAs (miRNAs). Furthermore, an activating Notch mutant NICD1 effectively rescued the decreased ALP activity caused by Rmst silencing. Collectively, our results strongly suggest that the Rmst-miRNA-Notch regulatory axis may play an important role in mediating BMP9-induced osteogenic differentiation of MSCs.

Monensin may inhibit melanoma by regulating the selection between differentiation and stemness of melanoma stem cells

Melanoma is the most lethal cutaneous malignancy that threatens human lives. Poor sensitivity to chemotherapy drugs and the high rate of resistance are the bottlenecks of melanoma treatment. Thus, new chemotherapy drugs are needed. Drug repurposing is a safe, economical and timesaving way to explore new chemotherapy for diseases. Here, we investigated the possibility of repurposing the antibiotic monensin as an anti-melanoma agent. Using three human melanoma cells and two nomal human cell lines as cell models, we found that monensin is obviously toxic to human melanoma cells while safe to nomal human cells. It effectively inhibited cell proliferation and viability, while promoted apoptosis and differentiation of human melanoma cells in vitro. By establishment of an animal model of transplanted human melanoma in nude mice, we demonstrated that monensin suppressed the growth of xenografts in vivo. At the same time, we found that melanogenesis increased and the ability of sphere and cloning forming of melanoma decreased under the treatment of monensin. Further detection about differentiation and pluripotent regulations were executed. Our results suggest that monensin is a potent inhibitor of melanoma, and its anti-tumor mechanism may be through promoting the final differentiation of melanoma stem cells and inhibiting their stemness maintenance.

Transcriptomic landscape regulated by the 14 types of bone morphogenetic proteins (BMPs) in lineage commitment and differentiation of mesenchymal stem cells (MSCs)

Mesenchymal stem cells (MSCs) are ubiquitously-existing multipotent progenitors that can self-renew and differentiate into multiple lineages including osteocytes, chondrocytes, adipocytes, tenocytes and myocytes. MSCs represent one of the most commonly-used adult progenitors and serve as excellent progenitor cell models for investigating lineage-specific differentiation regulated by various cellular signaling pathways, such as bone morphogenetic proteins (BMPs). As members of TGFβ superfamily, BMPs play diverse and important roles in development and adult tissues. At least 14 BMPs have been identified in mammals. Different BMPs exert distinct but overlapping biological functions. Through a comprehensive analysis of 14 BMPs in MSCs, we demonstrated that BMP9 is one of the most potent BMPs in inducing osteogenic differentiation of MSCs. Nonetheless, a global mechanistic view of BMP signaling in regulating the proliferation and differentiation of MSCs remains to be fully elucidated. Here, we conducted a comprehensive transcriptomic profiling in the MSCs stimulated by 14 types of BMPs. Hierarchical clustering analysis classifies 14 BMPs into three subclusters: an osteo/chondrogenic/adipogenic cluster, a tenogenic cluster, and BMP3 cluster. We also demonstrate that six BMPs (e.g., BMP2, BMP3, BMP4, BMP7, BMP8, and BMP9) can induce I-Smads effectively, while BMP2, BMP3, BMP4, BMP7, and BMP11 up-regulate Smad-independent MAP kinase pathway. Furthermore, we show that many BMPs can upregulate the expression of the signal mediators of Wnt, Notch and PI3K/AKT/mTOR pathways. While the reported transcriptomic changes need to be further validated, our expression profiling represents the first-of-its-kind to interrogate a comprehensive transcriptomic landscape regulated by the 14 types of BMPs in MSCs.

The impact of transposable element activity on therapeutically relevant human stem cells

Human stem cells harbor significant potential for basic and clinical translational research as well as regenerative medicine. Currently ~ 3000 adult and ~ 30 pluripotent stem cell-based, interventional clinical trials are ongoing worldwide, and numbers are increasing continuously. Although stem cells are promising cell sources to treat a wide range of human diseases, there are also concerns regarding potential risks associated with their clinical use, including genomic instability and tumorigenesis concerns. Thus, a deeper understanding of the factors and molecular mechanisms contributing to stem cell genome stability are a prerequisite to harnessing their therapeutic potential for degenerative diseases. Chemical and physical factors are known to influence the stability of stem cell genomes, together with random mutations and Copy Number Variants (CNVs) that accumulated in cultured human stem cells. Here we review the activity of endogenous transposable elements (TEs) in human multipotent and pluripotent stem cells, and the consequences of their mobility for genomic integrity and host gene expression. We describe transcriptional and post-transcriptional mechanisms antagonizing the spread of TEs in the human genome, and highlight those that are more prevalent in multipotent and pluripotent stem cells. Notably, TEs do not only represent a source of mutations/CNVs in genomes, but are also often harnessed as tools to engineer the stem cell genome; thus, we also describe and discuss the most widely applied transposon-based tools and highlight the most relevant areas of their biomedical applications in stem cells. Taken together, this review will contribute to the assessment of the risk that endogenous TE activity and the application of genetically engineered TEs constitute for the biosafety of stem cells to be used for substitutive and regenerative cell therapies.

Monensin inhibits cell proliferation and tumor growth of chemo-resistant pancreatic cancer cells by targeting the EGFR signaling pathway

Pancreatic ductal adenocarcinoma (PDAC) is one of the most deadly malignancies with <5% five-year survival rate due to late diagnosis, limited treatment options and chemoresistance. There is thus an urgent unmet clinical need to develop effective anticancer drugs to treat pancreatic cancer. Here, we study the potential of repurposing monensin as an anticancer drug for chemo-resistant pancreatic cancer. Using the two commonly-used chemo-resistant pancreatic cancer cell lines PANC-1 and MiaPaCa-2, we show that monensin suppresses cell proliferation and migration, and cell cycle progression, while solicits apoptosis in pancreatic cancer lines at a low micromole range. Moreover, monensin functions synergistically with gemcitabine or EGFR inhibitor erlotinib in suppressing cell growth and inducing cell death of pancreatic cancer cells. Mechanistically, monensin suppresses numerous cancer-associated pathways, such as E2F/DP1, STAT1/2, NFkB, AP-1, Elk-1/SRF, and represses EGFR expression in pancreatic cancer lines. Furthermore, the in vivo study shows that monensin blunts PDAC xenograft tumor growth by suppressing cell proliferation via targeting EGFR pathway. Therefore, our findings demonstrate that monensin can be repurposed as an effective anti-pancreatic cancer drug even though more investigations are needed to validate its safety and anticancer efficacy in pre-clinical and clinical models.

A Simplified System to Express Circularized Inhibitors of miRNA for Stable and Potent Suppression of miRNA Functions

MicroRNAs (miRNAs) are an evolutionarily conserved class of small regulatory noncoding RNAs, binding to complementary target mRNAs and resulting in mRNA translational inhibition or degradation, and they play an important role in regulating many aspects of physiologic and pathologic processes in mammalian cells. Thus, efficient manipulations of miRNA functions may be exploited as promising therapeutics for human diseases. Two commonly used strategies to inhibit miRNA functions include direct transfection of chemically synthesized miRNA inhibitors and delivery of a gene vector that instructs intracellular transcription of miRNA inhibitors. While most miRNA inhibitors are based on antisense molecules to bind and sequester miRNAs from their natural targets, it is challenging to achieve effective and stable miRNA inhibition. Here we develop a user-friendly system to express circular inhibitors of miRNA (CimiRs) by exploiting the noncanonical head-to-tail backsplicing mechanism for generating endogenous circular RNA sponges. In our proof-of-principle experiments, we demonstrate that the circular forms of the hsa-miR223-binding site of human β-arrestin1 (ARRB1) 3' UTR sponge RNA (BUTR), the bulged anti-miR223 (cirBulg223) and bulged anti-miR21 (cirBulg21), exhibit more potent suppression of miRNA functions than their linear counterparts. Therefore, the engineered CimiR expression system should be a valuable tool to target miRNAs for basic and translational research.

Inflammation-induced transgene expression in genetically engineered equine mesenchymal stem cells

BACKGROUND

Osteoarthritis, a chronic and progressive degenerative joint disorder, ranks amongst the top five causes of disability. Given the high incidence, associated socioeconomic costs and the absence of effective disease-modifying therapies of osteoarthritis, cell-based treatments offer a promising new approach. Owing to their paracrine, differentiation and self-renewal abilities, mesenchymal stem cells (MSCs) have great potential for regenerative medicine, which might be further enhanced by targeted gene therapy. Hence, the development of systems allowing transgene expression, particularly when regulated by natural disease-dependent occuring substances, is of high interest.

METHODS

Bone marrow-isolated equine MSCs were stably transduced with an HIV-1 based lentiviral vector expressing the luciferase gene under control of an inducible nuclear factor κB (NFκB)-responsive promoter. Marker gene expression was analysed by determining luciferase activity in transduced cells stimulated with different concentrations of interleukin (IL)-1β or tumour necrosis factor (TNF)α.

RESULTS

A dose-dependent increase in luciferase expression was observed in transduced MSCs upon cytokine stimulation. The induction effect was more potent in cells treated with TNFα compared to those treated with IL-1β. Maximum transgene expression was obtained after 48 h of stimulation and the same time was necessary to return to baseline luciferase expression levels after withdrawal of the stimulus. Repeated cycles of induction allowed on-off modulation of transgene expression without becoming refractory to induction. The NFκB-responsive promoter retained its inducibility also in chondrogenically differentiated MSC/Luc cells.

CONCLUSIONS

The results of the present study demonstrate that on demand transgene expression from the NFκB-responsive promoter using naturally occurring inflammatory cytokines can be induced in undifferentiated and chondrogenically differentiated equine MSCs. Copyright © 2016 John Wiley & Sons, Ltd.

Anthelmintic mebendazole enhances cisplatin's effect on suppressing cell proliferation and promotes differentiation of head and neck squamous cell carcinoma (HNSCC)

Head and neck squamous cell carcinoma (HNSCC) is one of the most common and aggressive types of human cancers worldwide. Nearly a half of HNSCC patients experience recurrence within five years of treatment and develop resistance to chemotherapy. Thus, there is an urgent clinical need to develop safe and novel anticancer therapies for HNSCC. Here, we investigate the possibility of repurposing the anthelmintic drug mebendazole (MBZ) as an anti-HNSCC agent. Using the two commonly-used human HNSCC lines CAL27 and SCC15, we demonstrate MBZ exerts more potent anti-proliferation activity than cisplatin in human HNSCC cells. MBZ effectively inhibits cell proliferation, cell cycle progression and cell migration, and induces apoptosis of HNSCC cells. Mechanistically, MBZ can modulate the cancer-associated pathways including ELK1/SRF, AP1, STAT1/2, MYC/MAX, although the regulatory outcomes are context-dependent. MBZ also synergizes with cisplatin in suppressing cell proliferation and inducing apoptosis of human HNSCC cells. Furthermore, MBZ is shown to promote the terminal differentiation of CAL27 cells and keratinization of CAL27-derived xenograft tumors. Our results are the first to demonstrate that MBZ may exert its anticancer activity by inhibiting proliferation while promoting differentiation of certain HNSCC cancer cells. It's conceivable the anthelmintic drug MBZ can be repurposed as a safe and effective agent used in combination with other frontline chemotherapy drugs such as cisplatin in HNSCC treatment.

lncRNA H19 mediates BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) through Notch signaling

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can undergo self-renewal and differentiate into multiple lineages. Osteogenic differentiation from MSCs is a well-orchestrated process and regulated by multiple signaling pathways. We previously demonstrated that BMP9 is one of the most potent osteogenic factors. However, molecular mechanism through which BMP9 governs osteoblastic differentiation remains to be fully understood. Increasing evidence indicates noncoding RNAs (ncRNAs) may play important regulatory roles in many physiological and/or pathologic processes. In this study, we investigate the role of lncRNA H19 in BMP9-regulated osteogenic differentiation of MSCs. We demonstrated that H19 was sharply upregulated at the early stage of BMP9 stimulation of MSCs, followed by a rapid decease and gradual return to basal level. This process was correlated with BMP9-induced expression of osteogenic markers. Interestingly, either constitutive H19 expression or silencing H19 expression in MSCs significantly impaired BMP9-induced osteogenic differentiation in vitro and in vivo, which was effectively rescued by the activation of Notch signaling. Either constitutive H19 expression or silencing H19 expression led to the increased expression of a group of miRNAs that are predicted to target Notch ligands and receptors. Thus, these results indicate that lncRNA H19 functions as an important mediator of BMP9 signaling by modulating Notch signaling-targeting miRNAs. Our findings suggest that the well-coordinated biphasic expression of lncRNA H19 may be essential in BMP9-induced osteogenic differentiation of MSCs, and that dysregulated H19 expression may impair normal osteogenesis, leading to pathogenic processes, such as bone tumor development.

Characterization of retroviral infectivity and superinfection resistance during retrovirus-mediated transduction of mammalian cells

Retroviral vectors including lentiviral vectors are commonly used tools to stably express transgenes or RNA molecules in mammalian cells. Their utilities are roughly divided into two categories, stable overexpression of transgenes and RNA molecules, which requires maximal transduction efficiency, or functional selection with retrovirus (RV)-based libraries, which takes advantage of retroviral superinfection resistance. However, the dynamic features of RV-mediated transduction are not well characterized. Here, we engineered two murine stem cell virus-based retroviral vectors expressing dual fluorescence proteins and antibiotic markers, and analyzed virion production efficiency and virion stability, dynamic infectivity and superinfection resistance in different cell types, and strategies to improve transduction efficiency. We found that the highest virion production occurred between 60 and 72 h after transfection. The stability of the collected virion supernatant decreased by >60% after 3 days in storage. We found that RV infectivity varied drastically in the tested human cancer lines, while low transduction efficiency was partially overcome with increased virus titer, prolonged infection duration and/or repeated infections. Furthermore, we demonstrated that RV receptors PIT1 and PIT2 were lowly expressed in the analyzed cells, and that PIT1 and/or PIT2 overexpression significantly improved transduction efficiency in certain cell lines. Thus, our findings provide resourceful information for the optimal conditions of retroviral-mediated gene delivery.

Dynamic silencing of somatic L1 retrotransposon insertions reflects the developmental and cellular contexts of their genomic integration

Background

The ongoing mobilization of mammalian transposable elements (TEs) contributes to natural genetic variation. To survey the epigenetic control and expression of reporter genes inserted by L1 retrotransposition in diverse cellular and genomic contexts, we engineered highly sensitive, real-time L1 retrotransposon reporter constructs.

Results

Here we describe different patterns of expression and epigenetic controls of newly inserted sequences retrotransposed by L1 in various somatic cells and tissues including cultured human cancer cells, mouse embryonic stem cells, and tissues of pseudofounder transgenic mice and their progeny. In cancer cell lines, the newly inserted sequences typically underwent rapid transcriptional gene silencing, but they lacked cytosine methylation even after many cell divisions. L1 reporter expression was reversible and oscillated frequently. Silenced or variegated reporter expression was strongly and uniformly reactivated by treatment with inhibitors of histone deacetylation, revealing the mechanism for their silencing. By contrast, de novo integrants retrotransposed by L1 in pluripotent mouse embryonic stem (ES) cells underwent rapid silencing by dense cytosine methylation. Similarly, de novo cytosine methylation also was identified at new integrants when studied in several distinct somatic tissues of adult founder mice. Pre-existing L1 elements in cultured human cancer cells were stably silenced by dense cytosine methylation, whereas their transcription modestly increased when cytosine methylation was experimentally reduced in cells lacking DNA methyltransferases DNMT1 and DNMT3b. As a control, reporter genes mobilized by piggyBac (PB), a DNA transposon, revealed relatively stable and robust expression without apparent silencing in both cultured cancer cells and ES cells.

Conclusions

We hypothesize that the de novo methylation marks at newly inserted sequences retrotransposed by L1 in early pre-implantation development are maintained or re-established in adult somatic tissues. By contrast, histone deacetylation reversibly silences L1 reporter insertions that had mobilized at later timepoints in somatic development and differentiation, e.g., in cancer cell lines. We conclude that the cellular contexts of L1 retrotransposition can determine expression or silencing of newly integrated sequences. We propose a model whereby reporter expression from somatic TE insertions reflects the timing, molecular mechanism, epigenetic controls and the genomic, cellular and developmental contexts of their integration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13100-017-0091-2) contains supplementary material, which is available to authorized users.

Immortalized Mouse Achilles Tenocytes Demonstrate Long-Term Proliferative Capacity While Retaining Tenogenic Properties

Investigating the cellular processes underlying tendon healing can allow researchers to improve long-term outcomes after injury. However, conducting meaningful studies to uncover the injury healing mechanism at cellular and molecular levels remains challenging. This is due to the inherent difficulty in isolating, culturing, and expanding sufficient primary tenocytes, due to their limited proliferative capacity and short lifespan. In this study, we sought to establish a novel line of immortalized mouse Achilles tenocytes (iMATs) with primary tenocyte properties, but increased proliferative capacity suitable for extensive in vitro experimentation. We show that isolated primary mouse Achilles tenocytes (pMATs) can be effectively immortalized using a piggyBac transposon expressing SV40 large T antigen flanked by FLP recombination target site (FRT). The resulting iMATs exhibit markedly greater proliferation and survival, which can be reversed with FLP recombinase. Furthermore, iMATs express the same set of tendon-specific markers as that of primary cells, although in lower levels, and respond similarly to exogenous stimulation with bone morphogenetic protein 13 (BMP13) as has been previously reported with pMATs. Taken together, our results suggest that iMATs acquire long-term proliferative capacity while maintaining tenogenic properties. We believe that iMATs are a suitable model for studying not only the native cellular processes involved in injury and healing, but also potential therapeutic agents that may augment the stability of tendon repair.

The Functionality of Minimal PiggyBac Transposons in Mammalian Cells

Minimal piggyBac vectors are a modified single-plasmid version of the classical piggyBac delivery system that can be used for stable transgene integration. These vectors have a truncated terminal domain in the delivery cassette and thus, integrate significantly less flanking transposon DNA into host cell chromatin than classical piggyBac vectors. Herein, we test various characteristics of this modified transposon. The integration efficiency of minimal piggyBac vectors was inversely related to the size of both the transposon and the entire plasmid, but inserts as large as 15 kb were efficiently integrated. Open and super-coiled vectors demonstrated the same integration efficiency while DNA methylation decreased the integration efficiency and silenced the expression of previously integrated sequences in some cell types. Importantly, the incidence of plasmid backbone integration was not increased above that seen in nontransposon control vectors. In BALB/c mice, we demonstrated prolonged expression of two transgenes (intracellular mCherry and secretable Gaussia luciferase) when delivered by the minimal piggyBac that resulted in a more sustained antibody production against the immunogenic luciferase than when delivered by a transient (nontransposon) vector plasmid. We conclude that minimal piggyBac vectors are an effective alternative to other integrative systems for stable DNA delivery in vitro and in vivo.

Bone morphogenetic protein 9 (BMP9) induces effective bone formation from reversibly immortalized multipotent adipose-derived (iMAD) mesenchymal stem cells

Regenerative medicine and bone tissue engineering using mesenchymal stem cells (MSCs) hold great promise as an effective approach to bone and skeletal reconstruction. While adipose tissue harbors MSC-like progenitors, or multipotent adipose-derived cells (MADs), it is important to identify and characterize potential biological factors that can effectively induce osteogenic differentiation of MADs. To overcome the time-consuming and technically challenging process of isolating and culturing primary MADs, here we establish and characterize the reversibly immortalized mouse multipotent adipose-derived cells (iMADs). The isolated mouse primary inguinal MAD cells are reversibly immortalized via the retrovirus-mediated expression of SV40 T antigen flanked with FRT sites. The iMADs are shown to express most common MSC markers. FLP-mediated removal of SV40 T antigen effectively reduces the proliferative activity and cell survival of iMADs, indicating the immortalization is reversible. Using the highly osteogenic BMP9, we find that the iMADs are highly responsive to BMP9 stimulation, express multiple lineage regulators, and undergo osteogenic differentiation in vitro upon BMP9 stimulation. Furthermore, we demonstrate that BMP9-stimulated iMADs form robust ectopic bone with a thermoresponsive biodegradable scaffold material. Collectively, our results demonstrate that the reversibly immortalized iMADs exhibit the characteristics of multipotent MSCs and are highly responsive to BMP9-induced osteogenic differentiation. Thus, the iMADs should provide a valuable resource for the study of MAD biology, which would ultimately enable us to develop novel and efficacious strategies for MAD-based bone tissue engineering.

A thermoresponsive polydiolcitrate-gelatin scaffold and delivery system mediates effective bone formation from BMP9-transduced mesenchymal stem cells

Successful bone tissue engineering requires at the minimum sufficient osteoblast progenitors, efficient osteoinductive factors, and biocompatible scaffolding materials. We previously demonstrated that bone morphogenetic protein 9 (BMP9) is one of the most potent factors in inducing osteogenic differentiation of mesenchymal stem cells (MSCs). Here, we investigated the potential use of a biodegradable citrate-based thermosensitive macromolecule, poly(polyethyleneglycol citrate-co-N-isopropylacrylamide) (PPCN) mixed with gelatin (PPCNG) as a scaffold for the delivery of BMP9-stimulated MSCs to promote localized bone formation. The addition of gelatin to PPCN effectively enhanced the cell adhesion and survival properties of MSCs entrapped within the gel in 3D culture. Using the BMP9-transduced MSC line immortalized mouse embryonic fibroblasts (iMEFs), we found that PPCNG facilitated BMP9-induced osteogenic differentiation of iMEFs in vivo and promoted the formation of well-ossified and vascularized trabecular bone-like structures in a mouse model of ectopic bone formation. Histologic evaluation revealed that vascularization of the bony masses retrieved from the iMEFs  +  PPCNG group was significantly more pronounced than that of the direct cell injection group. Accordingly, vascular endothelial growth factor (VEGF) expression was shown to be significantly higher in the bony masses recovered from the iMEFs  +  PPCNG group. Taken together, our results suggest that PPCNG may serve as a novel biodegradable and injectable scaffold and carrier for gene and cell-based bone tissue engineering.

The Prodomain-Containing BMP9 Produced from a Stable Line Effectively Regulates the Differentiation of Mesenchymal Stem Cells

BACKGROUND

BMPs play important roles in regulating stem cell proliferation and differentiation. Using adenovirus-mediated expression of the 14 types of BMPs we demonstrated that BMP9 is one of the most potent BMPs in inducing osteogenic differentiation of mesenchymal stem cells (MSCs), which was undetected in the early studies using recombinant BMP9 proteins. Endogenous BMPs are expressed as a precursor protein that contains an N-terminal signal peptide, a prodomain and a C-terminal mature peptide. Most commercially available recombinant BMP9 proteins are purified from the cells expressing the mature peptide. It is unclear how effectively these recombinant BMP9 proteins functionally recapitulate endogenous BMP9.

METHODS

A stable cell line expressing the full coding region of mouse BMP9 was established in HEK-293 cells by using the piggyBac transposon system. The biological activities and stability of the conditioned medium generated from the stable line were analyzed.

RESULTS

The stable HEK-293 line expresses a high level of mouse BMP9. BMP9 conditioned medium (BMP9-cm) was shown to effectively induce osteogenic differentiation of MSCs, to activate BMP-R specific Smad signaling, and to up-regulate downstream target genes in MSCs. The biological activity of BMP9-cm is at least comparable with that induced by AdBMP9 in vitro. Furthermore, BMP9-cm exhibits an excellent stability profile as its biological activity is not affected by long-term storage at -80ºC, repeated thawing cycles, and extended storage at 4ºC.

CONCLUSIONS

We have established a producer line that stably expresses a high level of active BMP9 protein. Such producer line should be a valuable resource for generating biologically active BMP9 protein for studying BMP9 signaling mechanism and functions.

Conservative site-specific and single-copy transgenesis in human LINE-1 elements

Genome engineering of human cells plays an important role in biotechnology and molecular medicine. In particular, insertions of functional multi-transgene cassettes into suitable endogenous sequences will lead to novel applications. Although several tools have been exploited in this context, safety issues such as cytotoxicity, insertional mutagenesis and off-target cleavage together with limitations in cargo size/expression often compromise utility. Phage λ integrase (Int) is a transgenesis tool that mediates conservative site-specific integration of 48 kb DNA into a safe harbor site of the bacterial genome. Here, we show that an Int variant precisely recombines large episomes into a sequence, term edattH4X, found in 1000 human Long INterspersed Elements-1 (LINE-1). We demonstrate single-copy transgenesis through attH4X-targeting in various cell lines including hESCs, with the flexibility of selecting clones according to transgene performance and downstream applications. This is exemplified with pluripotency reporter cassettes and constitutively expressed payloads that remain functional in LINE1-targeted hESCs and differentiated progenies. Furthermore, LINE-1 targeting does not induce DNA damage-response or chromosomal aberrations, and neither global nor localized endogenous gene expression is substantially affected. Hence, this simple transgene addition tool should become particularly useful for applications that require engineering of the human genome with multi-transgenes.

Antibiotic monensin synergizes with EGFR inhibitors and oxaliplatin to suppress the proliferation of human ovarian cancer cells

Ovarian cancer is the most lethal gynecologic malignancy with an overall cure rate of merely 30%. Most patients experience recurrence within 12–24 months of cure and die of progressively chemotherapy-resistant disease. Thus, more effective anti-ovarian cancer therapies are needed. Here, we investigate the possibility of repurposing antibiotic monensin as an anti-ovarian cancer agent. We demonstrate that monensin effectively inhibits cell proliferation, migration and cell cycle progression, and induces apoptosis of human ovarian cancer cells. Monensin suppresses multiple cancer-related pathways including Elk1/SRF, AP1, NFκB and STAT, and reduces EGFR expression in ovarian cancer cells. Monensin acts synergistically with EGFR inhibitors and oxaliplatin to inhibit cell proliferation and induce apoptosis of ovarian cancer cells. Xenograft studies confirm that monensin effectively inhibits tumor growth by suppressing cell proliferation through targeting EGFR signaling. Our results suggest monensin may be repurposed as an anti-ovarian cancer agent although further preclinical and clinical studies are needed.

A Novel Organ Culture Model of Mouse Intervertebral Disc Tissues

The intervertebral disc (IVD) is a fibrocartilaginous joint between two vertebral bodies. An IVD unit consists of a gelatinous central nucleus pulposus, encased by the annulus fibrosus, which is sandwiched between cartilaginous endplates (EPs). The IVD homeostasis can be disrupted by injuries, ageing and/or genetic predispositions, leading to degenerative disc disorders and subsequent lower back pain. The complex structure and distinct characteristics of IVDs warrant the establishment of robust in vitro IVD organ culture for studying the etiology and treatment of disc degeneration. Here, we isolate mouse lumbar IVDs and culture the minimal IVD units in submersion or suspension medium supplemented with 2% bovine serum or 10% fetal bovine serum (FBS). We find the minimal IVD units remain healthy for up to 14 days when cultured in submersion culture supplemented with 10% FBS. New bone formation in the EPs of the cultured IVDs can be assessed with calcein labeling. Furthermore, the cultured IVDs can be effectively transduced by recombinant adenovirus, and transgene expression lasts for 2 weeks. Thus, our findings demonstrate that the optimized IVD organ culture system can be used to study IVD biology and screen for biological factors that may prevent, alleviate and/or treat disc degeneration.

TqPCR: A Touchdown qPCR Assay with Significantly Improved Detection Sensitivity and Amplification Efficiency of SYBR Green qPCR

The advent of fluorescence-based quantitative real-time PCR (qPCR) has revolutionized the quantification of gene expression analysis in many fields, including life sciences, agriculture, forensic science, molecular diagnostics, and medicine. While SYBR Green-based qPCR is the most commonly-used platform due to its inexpensive nature and robust chemistry, quantifying the expression of genes with low abundance or RNA samples extracted from highly restricted or limited sources can be challenging because the detection sensitivity of SYBR Green-based qPCR is limited. Here, we develop a novel and effective touchdown qPCR (TqPCR) protocol by incorporating a 4-cycle touchdown stage prior to the quantification amplification stage. Using the same cDNA templates, we find that TqPCR can reduce the average Cq values for Gapdh, Rps13, and Hprt1 reference genes by 4.45, 5.47, and 4.94 cycles, respectively, when compared with conventional qPCR; the overall average Cq value reduction for the three reference genes together is 4.95. We further find that TqPCR can improve PCR amplification efficiency and thus increase detection sensitivity. When the quantification of Wnt3A-induced target gene expression in mesenchymal stem cells is analyzed, we find that, while both conventional qPCR and TqPCR can detect the up-regulation of the relatively abundant target Axin2, only TqPCR can detect the up-regulation of the lowly-expressed targets Oct4 and Gbx2. Finally, we demonstrate that the MRQ2 and MRQ3 primer pairs derived from mouse reference gene Tbp can be used to validate the RNA/cDNA integrity of qPCR samples. Taken together, our results strongly suggest that TqPCR may increase detection sensitivity and PCR amplification efficiency. Overall, TqPCR should be advantageous over conventional qPCR in expression quantification, especially when the transcripts of interest are lowly expressed, and/or the availability of total RNA is highly restricted or limited.

Sustained high level transgene expression in mammalian cells mediated by the optimized piggyBac transposon system

Sustained, high level transgene expression in mammalian cells is desired in many cases for studying gene functions. Traditionally, stable transgene expression has been accomplished by using retroviral or lentiviral vectors. However, such viral vector-mediated transgene expression is often at low levels and can be reduced over time due to low copy numbers and/or chromatin remodeling repression. The piggyBac transposon has emerged as a promising non-viral vector system for efficient gene transfer into mammalian cells. Despite its inherent advantages over lentiviral and retroviral systems, piggyBac system has not been widely used, at least in part due to their limited manipulation flexibilities. Here, we seek to optimize piggyBac-mediated transgene expression and generate a more efficient, user-friendly piggyBac system. By engineering a panel of versatile piggyBac vectors and constructing recombinant adenoviruses expressing piggyBac transposase (PBase), we demonstrate that adenovirus-mediated PBase expression significantly enhances the integration efficiency and expression level of transgenes in mesenchymal stem cells and osteosarcoma cells, compared to that obtained from co-transfection of the CMV-PBase plasmid. We further determine the drug selection timeline to achieve optimal stable transgene expression. Moreover, we demonstrate that the transgene copy number of piggyBac-mediated integration is approximately 10 times higher than that mediated by retroviral vectors. Using the engineered tandem expression vector, we show that three transgenes can be simultaneously expressed in a single vector with high efficiency. Thus, these results strongly suggest that the optimized piggyBac system is a valuable tool for making stable cell lines with sustained, high transgene expression.

Canonical Wnt signaling acts synergistically on BMP9-induced osteo/odontoblastic differentiation of stem cells of dental apical papilla (SCAPs)

Dental pulp/dentin regeneration using dental stem cells combined with odontogenic factors may offer great promise to treat and/or prevent premature tooth loss. Here, we investigate if BMP9 and Wnt/β-catenin act synergistically on odontogenic differentiation. Using the immortalized SCAPs (iSCAPs) isolated from mouse apical papilla tissue, we demonstrate that Wnt3A effectively induces early osteogenic marker alkaline phosphatase (ALP) in iSCAPs, which is reduced by β-catenin knockdown. While Wnt3A and BMP9 enhance each other's ability to induce ALP activity in iSCAPs, silencing β-catenin significantly diminishes BMP9-induced osteo/odontogenic differentiation. Furthermore, silencing β-catenin reduces BMP9-induced expression of osteocalcin and osteopontin and in vitro matrix mineralization of iSCAPs. In vivo stem cell implantation assay reveals that while BMP9-transduced iSCAPs induce robust ectopic bone formation, iSCAPs stimulated with both BMP9 and Wnt3A exhibit more mature and highly mineralized trabecular bone formation. However, knockdown of β-catenin in iSCAPs significantly diminishes BMP9 or BMP9/Wnt3A-induced ectopic bone formation in vivo. Thus, our results strongly suggest that β-catenin may play an important role in BMP9-induced osteo/ondontogenic signaling and that BMP9 and Wnt3A may act synergistically to induce osteo/odontoblastic differentiation of iSCAPs. It's conceivable that BMP9 and/or Wnt3A may be explored as efficacious biofactors for odontogenic regeneration and tooth engineering.

A simplified and versatile system for the simultaneous expression of multiple siRNAs in mammalian cells using Gibson DNA Assembly

RNA interference (RNAi) denotes sequence-specific mRNA degradation induced by short interfering double-stranded RNA (siRNA) and has become a revolutionary tool for functional annotation of mammalian genes, as well as for development of novel therapeutics. The practical applications of RNAi are usually achieved by expressing short hairpin RNAs (shRNAs) or siRNAs in cells. However, a major technical challenge is to simultaneously express multiple siRNAs to silence one or more genes. We previously developed pSOS system, in which siRNA duplexes are made from oligo templates driven by opposing U6 and H1 promoters. While effective, it is not equipped to express multiple siRNAs in a single vector. Gibson DNA Assembly (GDA) is an in vitro recombination system that has the capacity to assemble multiple overlapping DNA molecules in a single isothermal step. Here, we developed a GDA-based pSOK assembly system for constructing single vectors that express multiple siRNA sites. The assembly fragments were generated by PCR amplifications from the U6-H1 template vector pB2B. GDA assembly specificity was conferred by the overlapping unique siRNA sequences of insert fragments. To prove the technical feasibility, we constructed pSOK vectors that contain four siRNA sites and three siRNA sites targeting human and mouse β-catenin, respectively. The assembly reactions were efficient, and candidate clones were readily identified by PCR screening. Multiple β-catenin siRNAs effectively silenced endogenous β-catenin expression, inhibited Wnt3A-induced β-catenin/Tcf4 reporter activity and expression of Wnt/β-catenin downstream genes. Silencing β-catenin in mesenchymal stem cells inhibited Wnt3A-induced early osteogenic differentiation and significantly diminished synergistic osteogenic activity between BMP9 and Wnt3A in vitro and in vivo. These findings demonstrate that the GDA-based pSOK system has been proven simplistic, effective and versatile for simultaneous expression of multiple siRNAs. Thus, the reported pSOK system should be a valuable tool for gene function studies and development of novel therapeutics.