DNA Targeting Sequence Improves Magnetic Nanoparticle-Based Plasmid DNA Transfection Efficiency in Model Neurons

Efficient non-viral plasmid DNA transfection of most stem cells, progenitor cells and primary cell lines currently presents an obstacle for many applications within gene therapy research. From a standpoint of efficiency and cell viability, magnetic nanoparticle-based DNA transfection is a promising gene vectoring technique because it has demonstrated rapid and improved transfection outcomes when compared to alternative non-viral methods. Recently, our research group introduced oscillating magnet arrays that resulted in further improvements to this novel plasmid DNA (pDNA) vectoring technology. Continued improvements to nanomagnetic transfection techniques have focused primarily on magnetic nanoparticle (MNP) functionalization and transfection parameter optimization: cell confluence, growth media, serum starvation, magnet oscillation parameters, etc. Noting that none of these parameters can assist in the nuclear translocation of delivered pDNA following MNP-pDNA complex dissociation in the cell’s cytoplasm, inclusion of a cassette feature for pDNA nuclear translocation is theoretically justified. In this study incorporation of a DNA targeting sequence (DTS) feature in the transfecting plasmid improved transfection efficiency in model neurons, presumably from increased nuclear translocation. This observation became most apparent when comparing the response of the dividing SH-SY5Y precursor cell to the non-dividing and differentiated SH-SY5Y neuroblastoma cells.

Electroporation-mediated gene delivery of Na+,K+ -ATPase, and ENaC subunits to the lung attenuates acute respiratory distress syndrome in a two-hit porcine model

INTRODUCTION

Acute respiratory distress syndrome (ARDS) is a common cause of organ failure with an associated mortality rate of 40%. The initiating event is disruption of alveolar-capillary interface causing leakage of edema into alveoli.

HYPOTHESIS

Electroporation-mediated gene delivery of epithelial sodium channel (ENaC) and Na+,K+ -ATPase into alveolar cells would improve alveolar clearance of edema and attenuate ARDS.

METHODS

Pigs were anesthetized and instrumented, and the superior mesenteric artery was clamped to cause gut ischemia/reperfusion injury and peritoneal sepsis by fecal clot implantation. Animals were ventilated according to ARDSnet protocol. Four hours after injury, animals were randomized into groups: (i) treatment: Na+,K+ -ATPase/ENaC plasmid (n = 5) and (ii) control: empty plasmid (n = 5). Plasmids were delivered to the lung using bronchoscope. Electroporation was delivered using eight-square-wave electric pulses across the chest. Following electroporation, pigs were monitored 48 h.

RESULTS

The Pao2/Fio2 ratio and lung compliance were higher in the treatment group. Lung wet/dry ratio was lower in the treatment group. Relative expression of the Na+,K+ -ATPase transgene was higher throughout lungs receiving treatment plasmids. Quantitative histopathology revealed a reduction in intra-alveolar fibrin in the treatment group. Bronchoalveolar lavage showed increased surfactant protein B in the treatment group. Survival was improved in the treatment group.

CONCLUSIONS

Electroporation-mediated transfer of Na+,K+ -ATPase/ENaC plasmids improved lung function, reduced fibrin deposits, decreased lung edema, and improved survival in a translational porcine model of ARDS. Gene therapy can attenuate ARDS pathophysiology in a high-fidelity animal model, suggesting a potential new therapy for patients.

Electroporation-mediated gene delivery

Electroporation has been used extensively to transfer DNA to bacteria, yeast, and mammalian cells in culture for the past 30 years. Over this time, numerous advances have been made, from using fields to facilitate cell fusion, delivery of chemotherapeutic drugs to cells and tissues, and most importantly, gene and drug delivery in living tissues from rodents to man. Electroporation uses electrical fields to transiently destabilize the membrane allowing the entry of normally impermeable macromolecules into the cytoplasm. Surprisingly, at the appropriate field strengths, the application of these fields to tissues results in little, if any, damage or trauma. Indeed, electroporation has even been used successfully in human trials for gene delivery for the treatment of tumors and for vaccine development. Electroporation can lead to between 100 and 1000-fold increases in gene delivery and expression and can also increase both the distribution of cells taking up and expressing the DNA as well as the absolute amount of gene product per cell (likely due to increased delivery of plasmids into each cell). Effective electroporation depends on electric field parameters, electrode design, the tissues and cells being targeted, and the plasmids that are being transferred themselves. Most importantly, there is no single combination of these variables that leads to greatest efficacy in every situation; optimization is required in every new setting. Electroporation-mediated in vivo gene delivery has proven highly effective in vaccine production, transgene expression, enzyme replacement, and control of a variety of cancers. Almost any tissue can be targeted with electroporation, including muscle, skin, heart, liver, lung, and vasculature. This chapter will provide an overview of the theory of electroporation for the delivery of DNA both in individual cells and in tissues and its application for in vivo gene delivery in a number of animal models.

Airway pressure release ventilation prevents ventilator-induced lung injury in normal lungs

IMPORTANCE

Up to 25% of patients with normal lungs develop acute lung injury (ALI) secondary to mechanical ventilation, with 60% to 80% progressing to acute respiratory distress syndrome (ARDS). Once established, ARDS is treated with mechanical ventilation that can paradoxically elevate mortality. A ventilation strategy that reduces the incidence of ARDS could change the clinical paradigm from treatment to prevention.

OBJECTIVES

To demonstrate that (1) mechanical ventilation with tidal volume (VT) and positive end-expiratory pressure (PEEP) settings used routinely on surgery patients causes ALI/ARDS in normal rats and (2) preemptive application of airway pressure release ventilation (APRV) blocks drivers of lung injury (ie, surfactant deactivation and alveolar edema) and prevents ARDS.

DESIGN, SETTING, AND SUBJECTS

Rats were anesthetized and tracheostomy was performed at State University of New York Upstate Medical University. Arterial and venous lines, a peritoneal catheter, and a rectal temperature probe were inserted. Animals were randomized into 3 groups and followed up for 6 hours: spontaneous breathing ventilation (SBV, n = 5), continuous mandatory ventilation (CMV, n = 6), and APRV (n = 5). Rats in the CMV group were ventilated with Vt of 10 cc/kg and PEEP of 0.5 cm H2O. Airway pressure release ventilation was set with a P(High) of 15 to 20 cm H2O; P(Low) was set at 0 cm H2O. Time at P(High) (T(High)) was 1.3 to 1.5 seconds and a T(Low) was set to terminate at 75% of the peak expiratory flow rate (0.11-0.14 seconds), creating a minimum 90% cycle time spent at P(High). Bronchoalveolar lavage fluid and lungs were harvested for histopathologic analysis at necropsy.

RESULTS

Acute lung injury/ARDS developed in the CMV group (mean [SE] PaO2/FiO2 ratio, 242.96 [24.82]) and was prevented with preemptive APRV (mean [SE] PaO2/FIO2 ratio, 478.00 [41.38]; P < .05). Airway pressure release ventilation also significantly reduced histopathologic changes and bronchoalveolar lavage fluid total protein (endothelial permeability) and preserved surfactant proteins A and B concentrations as compared with the CMV group.

CONCLUSIONS AND RELEVANCE

Continuous mandatory ventilation in normal rats for 6 hours with Vt and PEEP settings similar to those of surgery patients caused ALI. Preemptive application of APRV blocked early drivers of lung injury, preventing ARDS. Our data suggest that APRV applied early could reduce the incidence of ARDS in patients at risk.

Electroporation-mediated gene delivery to the lungs

Electroporation is a safe, efficient, and inexpensive method to transfer naked plasmid DNA into various tissues. For electroporation-mediated gene transfer to the mouse lung, a plasmid solution is delivered to the lungs via the trachea. Immediately after plasmid delivery, eight square wave pulses are delivered by two pre-gelled electrodes placed on each side of the chest. An optimal field strength in mice is 200 V/cm, with a pulse duration of 10 ms each and a 1 s interval between pulses. High level gene expression can be achieved within 24 h in all cell types in the lung with very little inflammation and no apparent trauma.

Impacts of spinosad and λ-cyhalothrin on spider communities in cabbage fields in south Texas

Spiders are a principal arthropod group that preys on numerous pests of vegetables and other crops. In this study, we determined the effects of the two most commonly used insecticides, spinosad and λ-cyhalothrin, on diversity of spiders on cabbage in south Texas. In two seasons (fall 2008 and spring 2009), we collected a total of 588 spiders belonging to 53 species in 11 families from spinosad and λ-cyhalothrin-treated cabbages and the untreated control plants. A great majority of spiders were collected from the pitfall traps (554) where only a few (34) were collected from the blower/vacuum sampling. In the insecticide-treated plots, there were significantly fewer spider individuals, species and families than in untreated fields. Spinosad had significantly less effect on spiders in total individuals, number of species and families than λ-cyhalothrin. The effects of the two insecticides were further demonstrated by the Shannon-Weiner index (H') and the hierarchical richness index (HRI). Spider diversity in the spinosad-treated plots were not significantly different from that in the untreated fields but were greater than those in λ-cyhalothrin-treated plots in both seasons when measured by H' values. In contrast, the H' values of spider's diversity in the λ-cyhalothrin-treated plots were significantly lower than spinosad-treated and untreated plots. High values of HRI for spider richness in the spinosad-treated plots suggested that spinosad had less effect on spiders than λ-cyhalothrin. We concluded that spinosad was more compatible with spiders on cabbage compared to λ-cyhalothrin and that this information should be used when developing insecticide resistance management strategies.

Proteomic and functional analyses of protein-DNA complexes during gene transfer

One of the barriers to successful nonviral gene delivery is the crowded cytoplasm, which plasmids need to actively traverse for gene expression. Relatively little is known about how this process occurs, but our lab and others have shown that the microtubule network and motors are required for plasmid movement to the nucleus. To further investigate how plasmids exploit normal physiological processes to transfect cells, we have taken a proteomics approach to identify the proteins that comprise the plasmid-trafficking complex. We have developed a live cell DNA-protein pull-down assay to isolate complexes at certain time points post-transfection (15 minutes to 4 hours) for analysis by mass spectrometry (MS). Plasmids containing promoter sequences bound hundreds of unique proteins as early as 15 minutes post-electroporation, while a plasmid lacking any eukaryotic sequences failed to bind many of the proteins. Specific proteins included microtubule-based motor proteins (e.g., kinesin and dynein), proteins involved in protein nuclear import (e.g., importin 1, 2, 4, and 7, Crm1, RAN, and several RAN-binding proteins), a number of heterogeneous nuclear ribonucleoprotein (hnRNP)- and mRNA-binding proteins, and transcription factors. The significance of several of the proteins involved in protein nuclear localization and plasmid trafficking was determined by monitoring movement of microinjected fluorescently labeled plasmids via live cell particle tracking in cells following protein knockdown by small-interfering RNA (siRNA) or through the use of specific inhibitors. While importin β1 was required for plasmid trafficking and subsequent nuclear import, importin α1 played no role in microtubule trafficking but was required for optimal plasmid nuclear import. Surprisingly, the nuclear export protein Crm1 also was found to complex with the transfected plasmids and was necessary for plasmid trafficking along microtubules and nuclear import. Our results show that various proteins involved in nuclear import and export influence intracellular trafficking of plasmids and subsequent nuclear accumulation.

Insertion of a nuclear factor kappa B DNA nuclear-targeting sequence potentiates suicide gene therapy efficacy in lung cancer cell lines

Lung cancer currently causes the majority of cancer-related deaths worldwide and new treatments are in high demand. Gene therapy could be a promising treatment but currently lacks sufficient efficiency for clinical use, primarily due to limited cellular and nuclear DNA delivery. In the present study, we investigated whether it was possible to exploit the endogenous nuclear-shuttling activity by the nuclear factor kappa B (NFκB) system, which is highly prominent in many cancers as well as lung cancer. We observed that insertion of a DNA nuclear-targeting sequence (DTS) recognized by NFκB could improve plasmid nuclear delivery and enhance the therapeutic effect of a validated transcriptionally cancer-targeted suicide gene therapy system. A clear correlation between the number of inserted NFκB-binding sites and the therapeutic effect of the suicide system was observed in both small cell lung cancer (SCLC) and non-SCLC cell lines. The effect was observed to be due to elevated nuclear translocation of the suicide gene-encoding plasmids. The results show that a significant improvement of gene therapeutic efficiency can be obtained by increasing the intracellular trafficking of therapeutic DNA. This is to our knowledge the first time a DTS strategy has been implemented for suicide gene therapy.

Highly acetylated tubulin permits enhanced interactions with and trafficking of plasmids along microtubules

Microtubule-based transport is required for plasmid translocation to the nucleus during transfections, and having stable structures could enhance this movement. In previous studies in which the cytoskeleton was disrupted, we found that populations of microtubules remain that are stable and highly acetylated. By increasing the levels of acetylated tubulin through inhibition of the tubulin deacetylase HDAC6, we observe more rapid plasmid nuclear localization of transfected plasmids and greater levels of gene transfer. In this study, we sought to understand plasmid movement in cells with enhanced tubulin acetylation. Using variations of a microtubule spin down assay, we found that plasmids bound to hyper-acetylated microtubules to a greater degree than they did to unmodified microtubules. To determine if microtubule acetylation also affects cytoplasmic trafficking, plasmid movement was evaluated in real time by particle tracking in cells with varying levels of acetylated microtubules. We found that plasmids display greater net rates of movement, spend more time in productive motion and display longer runs of continuous motion in cells with highly acetylated microtubules compared to those with fewer modifications. These results all suggest that plasmid movement is enhanced along highly acetylated microtubules, reducing the time spent in the cytoplasm prior to nuclear import. Taken together, these findings provide a foundation for determining how modulation of microtubule acetylation can be used as a means to increase intracellular trafficking of plasmids and enhance gene therapy.

Neonatal oxygen increases sensitivity to influenza A virus infection in adult mice by suppressing epithelial expression of Ear1

Oxygen exposure in premature infants is a major risk factor for bronchopulmonary dysplasia and can impair the host response to respiratory viral infections later in life. Similarly, adult mice exposed to hyperoxia as neonates display alveolar simplification associated with a reduced number of alveolar epithelial type II cells and exhibit persistent inflammation, fibrosis, and mortality when infected with influenza A virus. Because type II cells participate in innate immunity and alveolar repair, their loss may contribute to oxygen-mediated sensitivity to viral infection. A genomewide screening of type II cells identified eosinophil-associated RNase 1 (Ear1). Ear1 was also detected in airway epithelium and was reduced in lungs of mice exposed to neonatal hyperoxia. Electroporation-mediated gene delivery of Ear1 to the lung before infection successfully reduced viral replication and leukocyte recruitment during infection. It also diminished the enhanced morbidity and mortality attributed to neonatal hyperoxia. These findings demonstrate that novel epithelial expression of Ear1 functions to limit influenza A virus infection, and its loss contributes to oxygen-associated epithelial injury and fibrosis after infection. People born prematurely may have defects in epithelial innate immunity that increase their risk for respiratory viral infections.

SIRT1 protects against emphysema via FOXO3-mediated reduction of premature senescence in mice

Chronic obstructive pulmonary disease/emphysema (COPD/emphysema) is characterized by chronic inflammation and premature lung aging. Anti-aging sirtuin 1 (SIRT1), a NAD+-dependent protein/histone deacetylase, is reduced in lungs of patients with COPD. However, the molecular signals underlying the premature aging in lungs, and whether SIRT1 protects against cellular senescence and various pathophysiological alterations in emphysema, remain unknown. Here, we showed increased cellular senescence in lungs of COPD patients. SIRT1 activation by both genetic overexpression and a selective pharmacological activator, SRT1720, attenuated stress-induced premature cellular senescence and protected against emphysema induced by cigarette smoke and elastase in mice. Ablation of Sirt1 in airway epithelium, but not in myeloid cells, aggravated airspace enlargement, impaired lung function, and reduced exercise tolerance. These effects were due to the ability of SIRT1 to deacetylate the FOXO3 transcription factor, since Foxo3 deficiency diminished the protective effect of SRT1720 on cellular senescence and emphysematous changes. Inhibition of lung inflammation by an NF-κB/IKK2 inhibitor did not have any beneficial effect on emphysema. Thus, SIRT1 protects against emphysema through FOXO3-mediated reduction of cellular senescence, independently of inflammation. Activation of SIRT1 may be an attractive therapeutic strategy in COPD/emphysema.

Gene therapy for ALI/ARDS

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are characterized by acute respiratory failure and are associated with diverse disorders. Gene therapy is a potentially powerful approach to treat diseases related to ALI/ARDS, and numerous viral and nonviral methods for gene delivery to the lung have been developed. Discussed are recent advances in the development of more efficient viral and nonviral gene transfer systems, and the current status of gene therapy applied to ALI/ARDS-associated pulmonary diseases is reviewed. With the development of more efficient gene therapy vectors, gene therapy is a promising strategy for clinical application.

Cyclic stretch of alveolar epithelial cells alters cytoskeletal micromechanics

Cytoplasmic transport of large molecules such as plasmid DNA (pDNA) has been shown to increase when cells are subjected to mild levels of cyclic stretch for brief periods. In the case of pDNA, this is in part due to the increased active transport of pDNA along stabilized, acetylated microtubules in the cytoplasm, whose levels are increased in response to stretch. It also has been shown that disruption of the dense actin network leads to increased pDNA and macromolecule diffusion as well. We hypothesize that stretch not only increases active transport of pDNA but also, similar to actin disrupting drugs, decreases cytoplasmic stiffness leading to a less restive pathway for macromolecules to diffuse. To test this we used particle tracking microrheology to measure cytoplasmic mechanics. We conclude that while cyclic stretch transiently decreases cytoplasmic stiffness and increases diffusivity, stretch-independent modulation of the levels of acetylated, stable microtubules has no effect on cytoplasmic stiffness. Furthermore, stretching cells that have maximally acetylated microtubules increases cytoplasmic trafficking of pDNA, without increasing levels of acetylated microtubules. These findings suggest that stretch-enhanced gene transfer may occur by two independent mechanisms: increased levels of acetylated microtubules for directed active transport, and reduced cytoplasmic stiffness for increased diffusion.

Liposome-mediated transfection

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology. Cationic liposomes are the most widely used class of carrier for transfection and a number of products are available commercially: Lipofectin (a 1:1 mixture of DOTMA [N-[1(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride] and DOPE [dioleoyl phosphatidylethanolamine]), Transfectam, and DOTAP [1,2-dioleoyloxy-3-trimethylammonium propane]:DOPE. However, all these reagents are costly; it can be less expensive to purchase purified lipids and formulate homemade transfection reagents by adding equimolar amounts of each lipid suspended in chloroform, mixing, and drying under inert gas. The reagents can be stored until they are reconstituted in an appropriate buffer. Although each manufacturer provides detailed instructions for the use of its reagent, the following general steps are used for essentially all formulations; times, concentrations, and volumes might differ slightly. The following volumes are sufficient for transfecting a 35-mm dish or one well of a six-well dish.

Preparing injection pipettes on a PUL-1 micropipette puller

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology, and direct delivery of genetic material by microinjection remains a reliable means of transfection. Needles for microinjection can either be pulled from glass capillaries on a pipette puller or be purchased premade. When pulling needles, variables such as filament design, heat, pull strength (tension), and delay time between heating and pulling must be addressed. The heat setting affects the length and the tip size of the needle; high heat will typically produce longer needles and finer tips. The pull strength will also affect length and tip size, with greater pull strength producing longer tapered needles with finer tips. Finally, shorter delay times between heating and pulling can result in longer tapers and finer needles; if the delay is too short, the glass forms fibers resembling glass wool rather than usable needles. The advantage of pulling needles in the laboratory is that a variety of different needle types can be pulled, depending on the samples and the cells being injected. The PUL-1 micropipette puller is a robust and inexpensive machine that can be found in many laboratories around the world. New machines are no longer being manufactured, although used ones can still be purchased.

Dendrimer-mediated transfection

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology. Polymer-based systems can be used to transfect cells, some of which rely on one type of molecule, whereas others contain a mixture of polymers and lipids. Reagents such as SuperFect or PolyFect use activated dendrimers, which are positively charged and resemble snowflakes in structure. One advantage of using dendrimer-based reagents is that they appear to be less sensitive than liposomal reagents to the presence of serum during transfection. Thus, they could be a better choice for cells that show greater dependence on the continual presence of serum (to avoid initiation of stress responses or induction of differentiation). This protocol describes a procedure for dendrimer-mediated transfection.

DNA sample preparation and loading sample into pipettes for microinjection of cells

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology, and direct delivery of genetic material by microinjection remains a reliable means of transfection. This protocol describes in general the preparation and loading of plasmid DNA for microinjections. Plasmid DNA can be purified by traditional means such as cesium chloride density ultracentrifugation, or by commercially available resin-based purification kits. The resulting preparation can then be delivered into microinjection needles either by backfilling or by a forward-filling approach.

Plating cells for microinjection

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology, and direct delivery of genetic material by microinjection remains a reliable means of transfection. This protocol describes the general procedures needed to culture cells for microinjection. Coverslips need to be marked so that microinjected cells can be identified at desired time points after injection. Coverslips can be etched by the user, as described here, or pre-etched coverslips can be purchased. Once the coverslips have been etched and sterilized, cells can be plated onto them and allowed to grow.

Progress and prospects: nuclear import of nonviral vectors

The nuclear envelope represents a key barrier to successful nonviral transfection and gene therapy both in vitro and in vivo. Although the main purpose of the nuclear envelope is to partition the cell to maintain cytoplasmic components in the cytoplasm and nuclear components, most notably genomic DNA, in the nucleus, this function poses a problem for transfections in which exogenous DNA is delivered into the cytoplasm. After delivery to the cytoplasm, nucleic acids rapidly become complexed with cellular proteins that mediate interactions with the cellular machinery for trafficking. Thus, it is these proteins that, in essence, control the nuclear import of DNA, and we must also understand their activities in cells. In this review, we will discuss the principles of nuclear import of proteins and DNA-protein complexes, as well as the various approaches that investigators have used to improve nuclear targeting of plasmids. These approaches include complexation of plasmids with peptides, native and engineered proteins, ligands and polymers, as well as the inclusion of transcription factor-binding sites for general and cell-specific delivery.

KEYWORDS

nonviral gene transfermid R:plasmidmid R:nuclear pore complexmid R:importinmid R:nuclear localization signalmid R:karyopherin.