Control by membrane order of voltage-induced permeabilization, loading and gene transfer in mammalian cells

Importance of the electrophoresis and pulse energy for siRNA-mediated gene silencing by electroporation in differentiated primary human myotubes

BACKGROUND

Electrotransfection is based on application of high-voltage pulses that transiently increase membrane permeability, which enables delivery of DNA and RNA in vitro and in vivo. Its advantage in applications such as gene therapy and vaccination is that it does not use viral vectors. Skeletal muscles are among the most commonly used target tissues. While siRNA delivery into undifferentiated myoblasts is very efficient, electrotransfection of siRNA into differentiated myotubes presents a challenge. Our aim was to develop efficient protocol for electroporation-based siRNA delivery in cultured primary human myotubes and to identify crucial mechanisms and parameters that would enable faster optimization of electrotransfection in various cell lines.

RESULTS

We established optimal electroporation parameters for efficient siRNA delivery in cultured myotubes and achieved efficient knock-down of HIF-1α while preserving cells viability. The results show that electropermeabilization is a crucial step for siRNA electrotransfection in myotubes. Decrease in viability was observed for higher electric energy of the pulses, conversely lower pulse energy enabled higher electrotransfection silencing yield. Experimental data together with the theoretical analysis demonstrate that siRNA electrotransfer is a complex process where electropermeabilization, electrophoresis, siRNA translocation, and viability are all functions of pulsing parameters. However, despite this complexity, we demonstrated that pulse parameters for efficient delivery of small molecule such as PI, can be used as a starting point for optimization of electroporation parameters for siRNA delivery into cells in vitro if viability is preserved.

CONCLUSIONS

The optimized experimental protocol provides the basis for application of electrotransfer for silencing of various target genes in cultured human myotubes and more broadly for electrotransfection of various primary cell and cell lines. Together with the theoretical analysis our data offer new insights into mechanisms that underlie electroporation-based delivery of short RNA molecules, which can aid to faster optimisation of the pulse parameters in vitro and in vivo.

Development of novel HPV therapeutic vaccine constructs based on engineered exosomes and tumor cell lysates

AIMS

Human papillomavirus (HPV) infections are highly prevalent globally. While preventive HPV vaccines exist, therapeutic vaccines are needed to treat existing HPV lesions and malignancies. This study evaluated the immunostimulatory and anti-tumor effects of three therapeutic vaccine candidates based on the recombinant protein, tumor cell lysate (TCL), and engineered exosome (Exo) harboring the heat shock protein 27 (Hsp27)-E7 fusion construct in mouse model.

MAIN METHODS

At first, the recombinant Hsp27-E7 protein was generated in E. coli expression system. Then, tumor cell lysates-based and engineered exosomes-based vaccine constructs harboring green fluorescent protein (GFP) and Hsp27-E7 were produced using lentiviral system. Finally, their immunological and antitumor effects were investigated in both prophylactic and therapeutic experiments.

KEY FINDINGS

Our data showed that the recombinant Hsp27-E7 protein, TCL-Hsp27-E7 and Exo-Hsp27-E7 regimens can induce the highest level of IFN-γ, TNF-α and Granzyme B, respectively. The percentage of tumor-free mice was identical for three vaccine strategies (survival rate: 75 %) in both prophylactic and therapeutic experiments. Generally, the TCL-Hsp27-E7, Exo-Hsp27-E7 and recombinant Hsp27-E7 protein regimens induced effective immune responses toward Th1 and CTL activity, and subsequently antitumor effects in mouse model.

SIGNIFICANCE

Regarding to higher Granzyme B secretion, lower tumor growth and more safety, the Exo-Hsp27-E7 regimen can be considered as the most promising HPV vaccination strategy.

Optimization of piggyBac Transposon System Electrotransfection in Sheep Fibroblasts

Electroporation is a non-viral mediated transfection technique, which has the advantages of being harmless, easy to operate, and less expensive. This transfection method can be used for almost all cell types and has gradually become the preferred transfection method for mammalian gene editing. However, further improvements are needed in electroporation efficiency. There is no universal standard electrotransfection step for different types of cells, and the inappropriate electroporation parameters will result in a low transfection efficiency and high cell mortality. Here, we systematically optimized the electrotransfection parameters of piggyBac transposon system into sheep fetal fibroblasts for the first time. We found that the cell transfection efficiency and cell viability could be improved by using traditional cell culture medium DMEM/F12 as an electroporation buffer, and simultaneously using the square-wave pulsing program of 200 V, 2 pulses, 20 ms length, and 20 μg DNA (3 μg/μL) in 4 mm cuvette, and the transfection efficiency and cell viability could eventually reach 78.0% and 40.9%, respectively. The purpose of this study is to provide a method reference and theoretical basis for the plasmid electrotransfection in mammal cells.

The impact of impaired DNA mobility on gene electrotransfer efficiency: analysis in 3D model

Background

Gene electrotransfer is an established method that enables transfer of DNA into cells with electric pulses. Several studies analyzed and optimized different parameters of gene electrotransfer, however, one of main obstacles toward efficient electrotransfection in vivo is relatively poor DNA mobility in tissues. Our aim was to analyze the effect of impaired mobility on gene electrotransfer efficiency experimentally and theoretically. We applied electric pulses with different durations on plated cells, cells grown on collagen layer and cells embedded in collagen gel (3D model) and analyzed gene electrotransfer efficiency. In order to analyze the effect of impaired mobility on gene electrotransfer efficiency, we applied electric pulses with different durations on plated cells, cells grown on collagen layer and cells embedded in collagen gel (3D model) and analyzed gene electrotransfer efficiency.

Results

We obtained the highest transfection in plated cells, while transfection efficiency of embedded cells in 3D model was lowest, similarly as in in vivo. To further analyze DNA diffusion in 3D model, we applied DNA on top or injected it into 3D model and showed, that for the former gene electrotransfer efficiency was similarly as in in vivo. The experimental results are explained with theoretical analysis of DNA diffusion and electromobility.

Conclusion

We show, empirically and theoretically that DNA has impaired electromobility and especially diffusion in collagen environment, where the latter crucially limits electrotransfection. Our model enables optimization of gene electrotransfer in in vitro conditions.

Post-pulse addition of trans-cyclohexane-1,2-diol improves electrotransfer mediated gene expression in mammalian cells

Electric field mediated gene transfer is facing a problem in expression yield due to the poor transfer across the nuclear envelope. Trans-cyclohexane-1,2-diol (TCHD) was shown to significantly increase chemically mediated transfection by collapsing the permeability barrier of the nuclear pore complex. We indeed observed a significant increase in expression by electrotransfer when cells are treated post pulse by a low non toxic concentration of TCHD. This was obtained for different pulsing conditions, cell strains and plasmid constructs. An interesting improvement in cell viability can be obtained. This can significantly enhance the non-viral gene electrical delivery.

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Trans-cyclohexane-1,2-diol (TCHD) collapses the permeability barrier of the nuclear pore complex.

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TCHD improves expression in gene electrotransfer.

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Post pulse TCHD addition is the most effective protocol.

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TCHD does not affect the cell viability when coupled to electrotransfer.

Comparison of flow cytometry, fluorescence microscopy and spectrofluorometry for analysis of gene electrotransfer efficiency

In this study, we compared three different methods used for quantification of gene electrotransfer efficiency: fluorescence microscopy, flow cytometry and spectrofluorometry. We used CHO and B16 cells in a suspension and plasmid coding for GFP. The aim of this study was to compare and analyse the results obtained by fluorescence microscopy, flow cytometry and spectrofluorometry and in addition to analyse the applicability of spectrofluorometry for quantifying gene electrotransfer on cells in a suspension. Our results show that all the three methods detected similar critical electric field strength, around 0.55 kV/cm for both cell lines. Moreover, results obtained on CHO cells showed that the total fluorescence intensity and percentage of transfection exhibit similar increase in response to increase electric field strength for all the three methods. For B16 cells, there was a good correlation at low electric field strengths, but at high field strengths, flow cytometer results deviated from results obtained by fluorescence microscope and spectrofluorometer. Our study showed that all the three methods detected similar critical electric field strengths and high correlations of results were obtained except for B16 cells at high electric field strengths. The results also demonstrated that flow cytometry measures higher values of percentage transfection compared to microscopy. Furthermore, we have demonstrated that spectrofluorometry can be used as a simple and consistent method to determine gene electrotransfer efficiency on cells in a suspension.

Shock waves associated with electric pulses affect cell electro-permeabilization

New features of cell electro-permeabilization are obtained by using high field (several tens of kV/cm) with short (sub-microsecond, nanosecond) pulse duration. Arcing appears as a main safety problem when air gaps are present between electrodes. A new applicator design was chosen to obtain a closed chamber where high field pulses could be delivered in a safe way with very short pulse duration. The safety issue of the system was validated under millisecond, microsecond and nanosecond pulses. The closed chamber applicator was then checked for its use under classical electro-mediated permeabilization and electro-gene transfer (EGT). A 20 times decrease in gene expression was observed compared with classical open chambers. It was experimentally observed that shock waves were present under the closed chamber configuration of the applicator. This was not the case with an open chamber design. Electropulsation chamber design plays a role on pulsing conditions and in the efficiency of gene electro transfer.

Electrically controlled membranes exploiting Cassie-Wenzel wetting transitions

We report electrically controlled membranes which become permeable when an electrical field is exerted on a droplet deposited on the membrane. Micro-porous polycarbonate membranes are obtained with the breath-figures assembly technique, using micro-scaled stainless steel gauzes as supports. The membranes demonstrate pronounced Cassie-Baxter wetting. Air cushions trapped by the droplet prevent water penetration through the membrane. We demonstrate two possibilities for controlling the permeability of the membrane, namely contact and non-contact scenarios. When an electrical field is exerted on a droplet deposited on the membrane, the triple-line is de-pinned and the wetting transition occurs in the non-contact scheme. Thus, the membrane becomes permeable. The contact scheme of the permeability control is based on the electrowetting phenomenon.

Strategies for efficient transfection of CHO-cells with plasmid DNA

Stable cell lines of Chinese hamster ovary (CHO) cells are the predominant source of commercial -biopharmaceutical proteins. Because making suitable CHO cell lines is time-consuming and costly, -preliminary experiments with transient expression are usually performed to optimize as many protein -production parameters as possible. Here, we describe protocols for optimizing expression in transient expression experiments and isolating stable CHO cell lines using two types of self-made reagents, namely, lipoplexes and polyplexes.

Effect of Mg ions on efficiency of gene electrotransfer and on cell electropermeabilization

Gene electrotransfer is a promising nonviral method that enables DNA to be transferred into living cells with electric pulses. However, there are many parameters that determine gene electrotransfer efficiency. One of the steps involved in gene electrotransfer is interaction of DNA with the cell membrane. Divalent cations in the electroporative media can influence the anchoring of DNA to the cell membrane and by that gene electrotransfer efficiency. Here we report the effect of different concentrations of Mg2+ on electropermeabilization for small molecule (propidium iodide), gene electrotransfer and viability of the cells. We also used TOTO-1 dye to visualize DNA-cell membrane interaction for different [Mg]. For this purpose, we used different electroporative media with increasing [Mg]. Our study shows that higher [Mg] lead to higher electropermeabilization for propidium iodide and higher viability, while causing lower gene electrotransfer efficiency. Because we observed higher TOTO-1 labeled DNA at cell surface when using higher [Mg], we suggest that Mg2+ ions can bind DNA at cell surface at such strength that cannot pass into the cell during application of electric pulses, which can lead to lower gene transfection. There may also be other mechanisms involved, since there are many steps of gene electrotransfer on which Mg2+ ions can have an effect on. Our results also imply that membrane permeability changes are not sufficient for an efficient gene electrotransfer.

Comparison of red blood cell membrane microstructure after different physicochemical influences: atomic force microscope research

PURPOSE

After the influence of different actions on the blood, the erythrocytes may change their macrostructure. At the same time, the microstructure of cell membrane will be changed as well. This study provides the results of comparison of red blood cell membrane microstructure after they have been affected by different factors.

MATERIALS AND METHODS

Images and spatial profiles of the cell surface were obtained by atomic force microscope. It was proposed to use spatial Fourier transform to decompose the initial complex profile into series of simple ones. This made it possible to compare surface parameters after exposure of red blood cells to different external actions.

RESULTS

Quantitative differences between membrane profile harmonic composition parameters (amplitude and spatial period) after physical impact (impulse electrical field, osmotic swelling) and after chemical impact (the fixing fluid glutaraldehyde and the drug Esmeron) were experimentally confirmed.

CONCLUSIONS

Such experimental and theoretical approach may lay down the foundations of mechanisms of different factors' effect on red blood cells both in research and in clinics.

Electro-mediated gene transfer and expression are controlled by the life-time of DNA/membrane complex formation

BACKGROUND

Electroporation is a physical method used to transfer molecules into cells and tissues. Clinical applications have been developed for antitumor drug delivery. Clinical trials of gene electrotransfer are under investigation. However, knowledge about how DNA enters cells is not complete. By contrast to small molecules that have direct access to the cytoplasm, DNA forms a long lived complex with the plasma membrane and is transferred into the cytoplasm with a considerable delay.

METHODS

To increase our understanding of the key step of DNA/membrane complex formation, we investigated the dependence of DNA/membrane interaction and gene expression on electric pulse polarity and repetition frequency.

RESULTS

We observed that both are affected by reversing the polarity and by increasing the repetition frequency of pulses. The results obtained in the present study reveal the existence of two classes of DNA/membrane interaction: (i) a metastable DNA/membrane complex from which DNA can leave and return to external medium and (ii) a stable DNA/membrane complex, where DNA cannot be removed, even by applying electric pulses of reversed polarity. Only DNA belonging to the second class leads to effective gene expression.

CONCLUSIONS

The life-time of DNA/membrane complex formation is of the order of 1 s and has to be taken into account to improve protocols of electro-mediated gene delivery.

A multi-channel electroporation microchip for gene transfection in mammalian cells

We developed a multi-channel electroporation microchip made of polydimethylsiloxane (PDMS) and glass for gene transfer in mammalian cells. This chip produces multiple electric field gradients in a single microchip by varying the lengths of the microchannels from 2 to 4 cm. Electric fields of 0.65, 0.57, 0.49, 0.41, and 0.33 kV/cm were simultaneously produced in a single chip when the voltage of 1.3 kV was applied. We transferred enhanced green fluorescent protein genes (pEGFP) into HEK-293 and CHO cells, which were cultured within the microchannels. The feasibility of our device was demonstrated because it was able to produce five different transfection rates and survival rates at different electric fields produced in a single microchip. This system is expected to optimize the experimental conditions in gene transfection research more easily and faster than conventional electroporation methods.

Mechanism of Lysophosphatidylcholine-Induced Lysosome Destabilization

Lysosomal destabilization is critical for the organelle and living cells. Phospholipase A(2 )(PLA(2)) was shown to be able to destabilize lysosomes under some conditions. By what mechanism the enzyme affects lysosomal stability is not fully studied. In this study, we investigated the effects of lysophosphatidylcholine (lysoPC), a PLA(2)-produced lipid metabolite, on lysosomal ion permeability, osmotic sensitivity and stability. By measuring lysosomal beta-hexosaminidase free activity, membrane potential, proton leakage and their enzyme latency loss in hypotonic sucrose medium, we established that lysoPC could increase the lysosomal permeability to both potassium ions and protons and enhance lysosomal osmotic sensitivity. These changes in lysosomal membrane properties promoted entry of potassium ions into lysosomes via K(+)/H(+) exchange. The resultant osmotic imbalance across the membranes led to losses of lysosomal integrity. The enhancement of lysosomal osmotic sensitivity caused the lysosomes to become more liable to destabilization in osmotic shock. These results suggest that lysoPC may play a key role in PLA(2)-induced lysosomal destabilization.

Electrical and thermal characterization of nanochannels between a cell and a silicon based micro-pore

Micro and nano fabrication techniques have facilitated the production of new devices for manipulation of single cells on a chip, such as the planar micro-pore electroporation technology. To characterize this technology we have studied the seal that forms at the interface between an individual cell and the micro-pore, in which the cell normally resides, as a function of an electrical field applied across the cell and temperature. Mathematical analysis of non-electroporative electrical fields in experiments with Madin-Darby canine kidney (MDCK) cells suggests that nanoscale channels form between the exterior of the cell and the pore wall. The results indicate that the electrical currents through these channels need to be considered when using planar micro-pores in general and performing micro-pore electroporation in particular. Our results show that the size of these channels is strongly temperature dependent and the cell to pore wall distance can increase by as much as 60% when the temperature of the system is lowered from 35 to 0( composite function)C. Temperature appears to be an important factor in the use of devices for cells on a chip and our results suggest that physiological temperatures should yield better seal formation, thus improved feedback sensitivity, than the traditional use of room temperature in planar micro-pore electroporation devices.

Cut-off phenomenon in the protective effect of alcohols against lysophosphatidylcholine-induced calcium overload

We studied the effect of chain length on the protective effect of alcohols against lysophosphatidylcholine (LPC)-induced Ca2+ overload in neonatal rat cardiomyocytes. We previously found that ethanol retards Ca2+ elevation. Cells were loaded with the Ca2+-sensitive fluorophore fura-2, and changes in fluorescence were followed. The addition of 10 microM LPC increased Ca2+, which reached a plateau after an 8-10 min delay. The presence of 88 mM n-propanol, n-butanol, tert-butanol, or 2,2-dimethylpropanol significantly increased the delay by 94-213%. However, n-pentanol at 2 mM or 88 mM had no protective effect. Among n-alcohols, the increase in lag time was inversely proportional to the length of the carbon chain. Chain length, rather than molecular weight determines the effect, because 2,2-dimethylpropanol had a protective effect. The influence of alcohols on LPC micelle formation was estimated from the increase in octadecyl rhodamine B fluorescence; the increase by n-alcohols was directly proportional to chain length, indicating that micelle formation was not involved in the extension of lag time. The absence of the protective effect when the alcohol aliphatic chain exceeds four carbons suggests that the effect of ethanol may be mediated via a small lipophilic pocket on a protein, or to lateral pressure perturbation in the membrane.

The effects of organic pesticides on inner membrane permeability in Escherichia coli ML35

We have tested whether some pesticides might cause inner membrane leakage in ML35 Escherichia coli cells, which express beta-galactosidase (lacZ; EC 3.2.1.23) constitutively but lack the permease (lacY) required for substrate entry. The activity of beta-galactosidase (indicative of substrate leakage through the inner membrane) was increased by various concentrations of pesticides, including the organometallic fungicides maneb and mancozeb, the insecticide Thiodan, and the herbicide Ally, as well as by antibiotics such as ampicillin, gramicidin D, and the calcium ionophore A23187. The enzyme activity was increased by up to approximately 30% when the E. coli ML35 strain was exposed to various concentrations (between 50 and 250 ppm) of both fungicides. Thiodan had only a slight effect on beta-galactosidase activity (increase of 12.8%), whereas, among the antibiotics, the calcium ionophore at 20 microg/ml caused a significant increase in enzyme activity by up to 61.8%. This effect is similar to that of sodium dodecyl sulfate, used as positive control ( approximately 70% increase). Accumulation of maneb and mancozeb by bacterial cells was also studied taking advantage of their metal content and using atomic absorption spectrophotometry. In parallel with the increase in enzyme activity, both fungicides accumulated in the cells as a function of their concentration. Time course experiments (3, 6, and 9 h) of fungicide accumulation and of bacterial growth at various pesticide concentrations were also carried out. Maneb seems to inhibit the bacterial growth better than mancozeb. In addition, maneb uptake increases with time up to 9 h at all tested concentrations, whereas the accumulation of mancozeb is similar at all the exposure times tested. This indicates a different uptake and/or metabolizing strategy by E. coli cells for the two fungicides.

Setting optimal parameters for in vitro electrotransfection of B16F1, SA1, LPB, SCK, L929 and CHO cells using predefined exponentially decaying electric pulses

To achieve the maximal introduction of plasmid DNA into cells and, at the same time, to prevent undesirable cell deaths, electrotransfection conditions should be determined for every single cell type individually. In the present study, we determined the optimal electrotransfection parameters for in vitro transfection of B16F1, SA1, LPB, SCK, L929 and CHO cells. Some of these varying parameters were electric field strength, number of applied pulses and their duration, osmolarity of electroporation buffer, plasmid DNA concentration and temperature at which the electroporation was carried out. The maximal transfection rates at optimal electrotransfection parameters in B16F1, SA1, LPB, SCK, L929 and CHO were 85%, 40%, 60%, 1%, 40% and 65%, respectively. The obtained results confirmed that the electroporation is a useful procedure for an in vitro transfection of the majority of mammalian cells. The method, if optimized, may generate reproducibly high proportion of transfected cells among the cell types that are sensitive to electric field action. Thus, the determined parameters could serve for the subsequent implementations of this method.

Effect of ethanol on lipid-mediated transfection of primary cortical neurons

Successful introduction of nucleic acids into mammalian neurons has revolutionized the analyses of gene regulation and cellular function. Various methods, including viral infection, have been developed to introduce plasmid DNA into primary neuronal cultures. However, transfection of primary cultures of neurons using the calcium phosphate precipitation method and electroporation have been comparatively inefficient. In this paper, we describe a method to successfully transfect cultured fetal cortical neurons using a cationic lipid reagent, lipofectamine. Cells were cultured in the absence and presence of 50 mM ethanol. To monitor transfection of neurons, we employed three mammalian expression vectors containing Renilla luciferase and/or firefly luciferase, or the beta-galactosidase reporter gene. Fetal cortical neurons were isolated and cultured in the absence or presence of 50 mM ethanol, for two days. On day 3, neurons were washed, fed with serum-free medium, and transfected with the DNA-lipofectamine complex. After two hours, cells were washed, fed complete medium lacking or containing 50 mM ethanol and cultured for two additional days with a change of medium after 24 h. Cultures were terminated 48 h after transfection. Cells were either stained for beta-galactosidase activity using X-gal or lysed to prepare cell extracts to assay for luciferase activity using a luminometer. When neurons were cotransfected, Renilla luciferase was used as an internal control to normalize the expression of the firefly luciferase reporter gene. Analysis of results showed that expression of the reporter gene, firefly luciferase, was approximately 2.5 times greater in ethanol treated neuronal cultures than for neurons cultured in the absence of ethanol. An increased number of neurons expressing beta-galactosidase was also observed in ethanol-treated neurons. These data suggest that perhaps ethanol treatment of fetal cortical neurons improved the DNA uptake and/or increased the expression of the reporter genes.

High-efficiency gene electrotransfer into skeletal muscle: description and physiological applicability of a new pulse generator

Efficiency and reproducibility of gene electrotransfer depend on the electrical specifications provided by the pulse generator, such as pulse duration, pulse number, pulse frequency, pulse combination, and current intensity. Here, we describe the performances of GET42, a pulse generator specifically designed for gene electrotransfer into skeletal muscle. Expression of beta-galactosidase in the Tibialis anterior muscle of Sprague-Dawley male rats was increased 250-fold by GET42 compared to DNA injection alone. Combination of high and low current intensity pulses further increased transfection efficiency (400-fold compared to DNA injection without electrotransfer). Varying degrees of muscle necrosis were observed after gene electrotransfer. Nevertheless, muscle necrosis was dramatically reduced after optimization of cumulated pulse duration without significant reduction in transfection efficiency. Physiological applicability was illustrated by the analysis of cytochrome c promoter transactivation. In conclusion, GET42 has proven to be a reliable and efficient pulse generator for gene electrotransfer experiments, and provides a powerful mean to study in vivo the regulation of gene expression.

Improvement of DNA transfection with cationic liposomes

The increasing use of cationic liposomes as vectors for DNA transfection of eukaryotic cells is due to its high efficiency and reproducibility. After the interaction of the DNA cationic-liposome complexes (DNA-CLC) with the plasma membrane, the entry into the cells delivers the DNA-CLC to the endosome-lysosome pathway where some of the DNA-CLC are degraded. The non-degraded DNA that escapes to the cytoplasm, still has to transverse the nuclear membrane to be transcribed and then translated. To improve the efficiency of the whole process, we can manipulate the DNA (sequences, promoters, enhancers, nuclear localisation signals, etc), the DNA-CLC (lipids) or the plasmatic, endosomal and/or nuclear cellular membranes (ultrasound, electroporation, Ca++, pH of the endosomes, mitosis, fusogenic peptides, nuclear localisation signals, etc). Most of these methods have been generally used individually but in combination, may greatly improve the efficiency and reproducibility of in vitro transfection. While much of this work remains yet to be done and present results further explored, the application of these efforts is essential to the future development of new gene therapy strategies.