The effect of cell division on the cellular dynamics of microinjected DNA and dextran

Microfluidic Mechanoporation: Current Progress and Applications in Stem Cells

Intracellular delivery, the process of transporting substances into cells, is crucial for various applications, such as drug delivery, gene therapy, cell imaging, and regenerative medicine. Among the different approaches of intracellular delivery, mechanoporation stands out by utilizing mechanical forces to create temporary pores on cell membranes, enabling the entry of substances into cells. This method is promising due to its minimal contamination and is especially vital for stem cells intended for clinical therapy. In this review, we explore various mechanoporation technologies, including microinjection, micro-nano needle arrays, cell squeezing through physical confinement, and cell squeezing using hydrodynamic forces. Additionally, we highlight recent research efforts utilizing mechanoporation for stem cell studies. Furthermore, we discuss the integration of mechanoporation techniques into microfluidic platforms for high-throughput intracellular delivery with enhanced transfection efficiency. This advancement holds potential in addressing the challenge of low transfection efficiency, benefiting both basic research and clinical applications of stem cells. Ultimately, the combination of microfluidics and mechanoporation presents new opportunities for creating comprehensive systems for stem cell processing.

Knockout of the lysosomal membrane protein, LAMP2C, improves transient gene expression in HEK293 cells via increased intracellular plasmid availability

Plasmid-based transfection can be used in many applications such as transient gene expression (TGE)-based therapeutic protein production. These applications preferentially require maximization of intracellular plasmid availability. Here, we applied a lysosome engineering approach to alleviate lysosome-mediated nucleic acid degradation and enhance the TGE in mammalian cells. By knocking out the lysosomal membrane protein LAMP2C, which is known to be the main player in RNautophagy/DNautophagy (RDA), we significantly improved transient fluorescent protein expression in HEK293 cells by improving the retention rate of transfected plasmids; however, this effect was not observed in CHO cells. Additional knockout of a lysosomal membrane transporter and another RDA player, SIDT2, was ineffective, regardless of the presence of LAMP2C. LAMP2C knockout enhanced TGE-based mAb production in HEK293 cells by up to 2.82-fold increase in specific mAb productivity. Taken together, these results demonstrate that HEK293 cells can be engineered to improve the usage of the transfected plasmid via knockout of the lysosomal membrane protein LAMP2C and provide efficient host cells in TGE systems for therapeutic protein production.

Nuclear Entry of DNA and Transgene Expression in Dividing and Non-dividing Cells

Introduction

Plasmid DNA (pDNA) must be delivered into the nucleus for transgene expression in mammalian cells. The entry may happen passively during the nuclear envelope breakdown and reformation in dividing cells or actively through the nuclear pore complexes. The goal of this study was to investigate the relative importance of these two pathways for pDNA nuclear entry and subsequent gene expression.

Methods

To measure nuclear entry of pDNA encoding enhanced green florescence protein (EGFP) in electrotransfected cells, we developed a sensitive technique for quantitative analysis of pDNA in the nuclei, based on a hybridization probe for pDNA detection at the single molecule level and automatic image analysis. In matched experiments, we used an mRNA targeted hybridization probe to quantify reporter mRNA expression per cell, and flow cytometry to quantify expression of EGFP.

Results

We discovered two distinct patterns of pDNA distribution in the nuclei: punctate and diffuse, which were dominant in arrested and unarrested cells, respectively. The cell cycle arrest decreased diffuse pDNA and increased punctate pDNA. Its net effect was a decrease in the total intranuclear pDNA. Additionally, the cell cycle arrest increased the reporter mRNA synthesis but had no substantial impact on reporter protein expression.

Conclusion

Results from the study demonstrated that the efficient nuclear entry of pDNA during cell division did not necessarily lead to a high level of transgene expression. They also suggested that the punctate pDNA was more transcriptionally active than diffuse pDNA in the nuclei. These data will be useful in future studies for understanding mechanisms of nonviral gene delivery.

Potentials of a Plasma-Aerosol System for Wound Healing Advanced by Drug Introduction: An In Vitro Study

Cold plasmas have found their application in a wide range of biomedical fields by virtue of their high chemical reactivity. In the past decades, many attempts have been made to use cold plasmas in wound healing, and within this field, many studies have focused on plasma-induced cell proliferation mechanisms. In this work, one step further has been taken to demonstrate the advanced role of plasma in wound healing. To this end, the simultaneous ability of plasma to induce cell proliferation and permeabilize treated cells has been examined in the current study. The driving force was to advance the wound healing effect of plasma with drug delivery. On this subject, we demonstrate in vitro the healing effect of Ar, Ar+N₂ plasma, and their aerosol counterparts. A systematic study has been carried out to study the role of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in cell adhesion, signaling, differentiation, and proliferation. An additional investigation was also performed to study the permeabilization of cells and the delivery of the modeled drug carrier fluorescein isothiocyanate (FITC) labeled dextran into cells upon plasma treatment. Short 35 s plasma treatments were found to promote fibroblast adhesion, migration, signaling, proliferation, and differentiation by means of reactive oxygen and nitrogen species (RONS) created by plasma and deposited into the cell environment. The impact of the plasma downstream products NO₂^- and NO₃^- on the expressions of the focal adhesion's genes, syndecans, and collagens was observed to be prominent. On the other hand, the differentiation of fibroblasts to myofibroblasts was mainly initiated by ROS produced by the plasma. In addition, the ability of plasma to locally permeabilize fibroblast cells was demonstrated. During proliferative cell treatment, plasma can simultaneously induce cell membrane permeabilization (d ∼ 7.3 nm) by the species OH and H₂O₂. The choice for a plasma or a plasma-aerosol configuration thus allows the possibility to change the spatial chemistry of drug delivery molecules and thus to locally deliver drugs. Accordingly, this study offers a pivotal step toward plasma-assisted wound healing advanced by drug delivery.

Maintaining soluble protein homeostasis between nuclear and cytoplasmic compartments across mitosis

The nuclear envelope (NE) is central to the architecture of eukaryotic cells, both as a physical barrier separating the nucleus from the cytoplasm and as gatekeeper of selective transport between them. However, in open mitosis, the NE fragments to allow for spindle formation and segregation of chromosomes, resulting in intermixing of nuclear and cytoplasmic soluble fractions. Recent studies have shed new light on the mechanisms driving reinstatement of soluble proteome homeostasis following NE reformation in daughter cells. Here, we provide an overview of how mitotic cells confront this challenge to ensure continuity of basic cellular functions across generations and elaborate on the implications for the proteasome - a macromolecular machine that functions in both cytoplasmic and nuclear compartments.

Microinjection-based CRISPR/Cas9 mutagenesis in the decapoda crustaceans, Neocaridina heteropoda and Eriocheir sinensis

CRISPR/Cas9 technology has been applied to many arthropods. However, application of this technology to crustaceans remains limited due to the unique characteristics of embryos. Our group has developed a microinjection system to introduce the CRISPR/Cas9 system into Neocaridina heteropoda embryos (one-cell stage). Using the developed method, we mutated the target gene Nh-scarlet (N. heteropoda scarlet), which functions in eye development and pigmentation. The results showed that both eye color and shape were altered in individuals in which Nh-scarlet was knocked out. Furthermore, this system was also successfully applied to another decapod crustacean, Eriocheir sinensis. DNA sequencing revealed that the zoeae with red eyes had an edited version of Es-scarlet. This study provides a stable microinjection method for freshwater crustaceans, and will contribute to functional genomics studies in various decapods.

Transfected plasmid DNA is incorporated into the nucleus via nuclear envelope reformation at telophase

DNA transfection is an important technology in life sciences, wherein nuclear entry of DNA is necessary to express exogenous DNA. Non-viral vectors and their transfection reagents are useful as safe transfection tools. However, they have no effect on the transfection of non-proliferating cells, the reason for which is not well understood. This study elucidates the mechanism through which transfected DNA enters the nucleus for gene expression. To monitor the behavior of transfected DNA, we introduce plasmid bearing lacO repeats and RFP-coding sequences into cells expressing GFP-LacI and observe plasmid behavior and RFP expression in living cells. RFP expression appears only after mitosis. Electron microscopy reveals that plasmids are wrapped with nuclear envelope (NE)‒like membranes or associated with chromosomes at telophase. The depletion of BAF, which is involved in NE reformation, delays plasmid RFP expression. These results suggest that transfected DNA is incorporated into the nucleus during NE reformation at telophase.

Streamlined Human Cell-Based Recombinase-Mediated Cassette Exchange Platform Enables Multigene Expression for the Production of Therapeutic Proteins

A platform, based on targeted integration of transgenes using recombinase-mediated cassette exchange (RMCE) coupled with CRISPR/Cas9, is increasingly being used for the development of mammalian cell lines that produce therapeutic proteins, because of reduced clonal variation and predictable transgene expression. However, low efficiency of the RMCE process has hampered its application in multicopy or multisite integration of transgenes. To improve RMCE efficiency, nuclear transport of RMCE components such as site-specific recombinase and donor plasmid was accelerated by incorporation of nuclear localization signal and DNA nuclear-targeting sequence, respectively. Consequently, the efficiency of RMCE in dual-landing pad human embryonic kidney 293 (HEK293) cell lines harboring identical or orthogonal pairs of recombination sites at two well-known human safe harbors (AAVS1 and ROSA26 loci), increased 6.7- and 8.1-fold, respectively. This platform with enhanced RMCE efficiency enabled simultaneous integration of transgenes at the two sites using a single transfection without performing selection and enrichment processes. The use of a homotypic dual-landing pad HEK293 cell line capable of incorporating the same transgenes at two sites resulted in a 2-fold increase in the transgene expression level compared to a single-landing pad HEK293 cell line. In addition, the use of a heterotypic dual-landing pad HEK293 cell line, which can incorporate transgenes for a recombinant protein at one site and an effector transgene for cell engineering at another site, increased recombinant protein production. Overall, a streamlined RMCE platform can be a versatile tool for mammalian cell line development by facilitating multigene expression at genomic safe harbors.

Physical and mechanical cues affecting biomaterial-mediated plasmid DNA delivery: insights into non-viral delivery systems

BACKGROUND

Whilst traditional strategies to increase transfection efficiency of non-viral systems aimed at modifying the vector or the polyplexes/lipoplexes, biomaterial-mediated gene delivery has recently sparked increased interest. This review aims at discussing biomaterial properties and unravelling underlying mechanisms of action, for biomaterial-mediated gene delivery. DNA internalisation and cytoplasmic transport are initially discussed. DNA immobilisation, encapsulation and surface-mediated gene delivery (SMD), the role of extracellular matrix (ECM) and topographical cues, biomaterial stiffness and mechanical stimulation are finally outlined.

MAIN TEXT

Endocytic pathways and mechanisms to escape the lysosomal network are highly variable. They depend on cell and DNA complex types but can be diverted using appropriate biomaterials. 3D scaffolds are generally fabricated via DNA immobilisation or encapsulation. Degradation rate and interaction with the vector affect temporal patterns of DNA release and transgene expression. In SMD, DNA is instead coated on 2D surfaces. SMD allows the incorporation of topographical cues, which, by inducing cytoskeletal re-arrangements, modulate DNA endocytosis. Incorporation of ECM mimetics allows cell type-specific transfection, whereas in spite of discordances in terms of optimal loading regimens, it is recognised that mechanical loading facilitates gene transfection. Finally, stiffer 2D substrates enhance DNA internalisation, whereas in 3D scaffolds, the role of stiffness is still dubious.

CONCLUSION

Although it is recognised that biomaterials allow the creation of tailored non-viral gene delivery systems, there still are many outstanding questions. A better characterisation of endocytic pathways would allow the diversion of cell adhesion processes and cytoskeletal dynamics, in order to increase cellular transfection. Further research on optimal biomaterial mechanical properties, cell ligand density and loading regimens is limited by the fact that such parameters influence a plethora of other different processes (e.g. cellular adhesion, spreading, migration, infiltration, and proliferation, DNA diffusion and release) which may in turn modulate gene delivery. Only a better understanding of these processes may allow the creation of novel robust engineered systems, potentially opening up a whole new area of biomaterial-guided gene delivery for non-viral systems.

Probing the role of nuclear-envelope invaginations in the nuclear-entry route of lipofected DNA by multi-channel 3D confocal microscopy

Nuclear breakdown was found to be the dominant route for DNA entry into the nucleus in actively dividing cells. The possibility that alternative routes contribute to DNA entry into the nucleus, however, cannot be ruled out. Here we address the process of lipofection by monitoring the localization of fluorescently-labelled DNA plasmids at the single-cell level by confocal imaging in living interphase cells. As test formulation we choose the cationic 3β-[N-(N,N-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol) and the zwitterionic helper lipid dioleoylphosphatidylethanolamine (DOPE) with plasmidic DNA pre-condensed by means of protamine. By exploiting the spectral shift of the fluorescent dye FM4-64 (N-(3-triethylammoniumpropyl)-4-(p-diethylaminophenylhexatrienyl)-pyridinium 2Br) we monitor the position of the nuclear envelope (NE), while concomitantly imaging the whole nucleus (by Hoechst) and the DNA (by Cy3 fluorophore) in a multi-channel 3D confocal imaging experiment. Reported results show that DNA clusters are typically associated with the NE membrane in the form of tubular invaginations spanning the nuclear environment, but not completely trapped within the NE invaginations, i.e. the DNA may use these NE regions as entry-points towards the nucleus. These observations pave the way to investigating the molecular details of the postulated processes for a better exploitation of gene-delivery vectors, particularly for applications in non-dividing cells.

Single-cell transfection technologies for cell therapies and gene editing

Advances in gene editing and cell therapies have recently led to outstanding clinical successes. However, the lack of a cost-effective manufacturing process prevents the democratization of these innovative medical tools. Due to the common use of viral vectors, the step of transfection in which cells are engineered to gain new functions, is a major bottleneck in making safe and affordable cell products. A promising opportunity lies in Single-Cell Transfection Technologies (SCTTs). SCTTs have demonstrated higher efficiency, safety and scalability than conventional transfection methods. They can also feature unique abilities such as substantial dosage control over the cargo delivery, single-cell addressability and integration in microdevices comprising multiple monitoring modalities. Unfortunately, the potential of SCTTs is not fully appreciated: they are most often restricted to research settings with little adoption in clinical settings. To encourage their adoption, we review and compare recent developments in SCTTs, and how they can enable selected clinical applications. To help bridge the gap between fundamental research and its translation to the clinic, we also describe how Good Manufacturing Practices (GMP) can be integrated in the design of SCTTs.

Peptides as a material platform for gene delivery: Emerging concepts and converging technologies

Successful gene therapies rely on methods that safely introduce DNA into target cells and enable subsequent expression of proteins. To that end, peptides are an attractive materials platform for DNA delivery, facilitating condensation into nanoparticles, delivery into cells, and subcellular release to enable protein expression. Peptides are programmable materials that can be designed to address biocompatibility, stability, and subcellular barriers that limit efficiency of non-viral gene delivery systems. This review focuses on fundamental structure-function relationships regarding peptide design and their impact on nanoparticle physical properties, biologic activity, and biocompatibility. Recent peptide technologies utilize multi-dimensional structures, non-natural chemistries, and combinations of peptides with lipids to achieve desired properties and efficient transfection. Advances in DNA cargo design are also presented to highlight further opportunities for peptide-based gene delivery. Modern DNA designs enable prolonged expression compared to traditional plasmids, providing an additional component that can be synergized with peptide carriers for improved transfection. Peptide transfection systems are poised to become a flexible and efficient platform incorporating new chemistries, functionalities, and improved DNA cargos to usher in a new era of gene therapy.

Non-viral transfection vectors: are hybrid materials the way forward?

Transfection is a process by which oligonucleotides (DNA or RNA) are delivered into living cells. This allows the synthesis of target proteins as well as their inhibition (gene silencing). However, oligonucleotides cannot cross the plasma membrane by themselves; therefore, efficient carriers are needed for successful gene delivery. Recombinant viruses are among the earliest described vectors. Unfortunately, they have severe drawbacks such as toxicity and immunogenicity. In this regard, the development of non-viral transfection vectors has attracted increasing interests, and has become an important field of research. In the first part of this review we start with a tutorial introduction into the biological backgrounds of gene transfection followed by the classical non-viral vectors (cationic organic carriers and inorganic nanoparticles). In the second part we highlight selected recent reports, which demonstrate that hybrid vectors that combine key features of classical carriers are a remarkable strategy to address the current challenges in gene delivery.

Towards development of plasmacytoma cells-based expression systems utilizing alphavirus vectors: An NS0-VEE model

Plasmacytoma (myeloma) cells have a large protein expression capacity, although their industrial use is confined to stable expression systems. Vectors derived from genomes of viruses from the genus Alphavirus allow obtaining of high yields of target proteins but their use is limited to transient expression. Little information has been published to date on attempts to combine the myeloma cells as hosts with alphaviruses as expression vectors. A plasmid construct which allows rescue of a model alphavirus Venezuelan equine encephalitis virus (VEE) upon transfection of a cell culture was created. Mutations in the capsid and nsP2 genes allow for less cytopathogenic propagation of the virus. A cDNA-copy of the genome was placed in a plasmid under the control of the CMV promoter for virus rescue following DNA transfection. Parameters for the virus rescue by electroporating of the infectious clone in murine myeloma cells (NS0) were optimized. The highest FFU counts (1.2 × 10⁵ FFU per 10 ug DNA) were produced with 2 pulses (voltage 250 V, capacitance 960 u F) and the best electroporation buffer was selected from eight buffers. Self-sustained VEE infection was established in NS0 cultures with high titers (8 × 10⁸ FFU/ml) of the virus, despite a fraction of infected cells dying during 5-days observation. Further development of the NS0-VEE expression system may require addressing of apoptosis induced by VEE.

Mechanisms of unprimed and dexamethasone-primed nonviral gene delivery to human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are under intense study for applications of cell and gene therapeutics because of their unique immunomodulatory and regenerative properties. Safe and efficient genetic modification of hMSCs could increase their clinical potential by allowing functional expression of therapeutic transgenes or control over behavior and differentiation. Viral gene delivery is efficient, but suffers from safety issues, while nonviral methods are safe, but highly inefficient, especially in hMSCs. Our lab previously demonstrated that priming cells before delivery of DNA complexes with dexamethasone (DEX), an anti‐inflammatory glucocorticoid drug, significantly increases hMSC transfection success. This work systematically investigates the mechanisms of hMSC transfection and DEX‐mediated enhancement of transfection. Our results show that hMSC transfection and its enhancement by DEX are decreased by inhibiting classical intracellular transport and nuclear import pathways, but DEX transfection priming does not increase cellular or nuclear internalization of plasmid DNA (pDNA). We also show that hMSC transgene expression is largely affected by pDNA promoter and enhancer sequence changes, but DEX‐mediated enhancement of transfection is unaffected by any pDNA sequence changes. Furthermore, DEX‐mediated transfection enhancement is not the result of increased transgene messenger RNA transcription or stability. However, DEX‐priming increases total protein synthesis by preventing hMSC apoptosis induced by transfection, resulting in increased translation of transgenic protein. DEX may also promote further enhancement of transgenic reporter enzyme activity by other downstream mechanisms. Mechanistic studies of nonviral gene delivery will inform future rationally designed technologies for safe and efficient genetic modification of clinically relevant cell types.

Intracellular delivery of colloids: Past and future contributions from microinjection

The manipulation of single cells and whole tissues has been possible since the early 70's, when semi-automatic injectors were developed. Since then, microinjection has been used to introduce an ever-expanding range of colloids of up to 1000 nm in size into living cells. Besides injecting nucleic acids to study transfection mechanisms, numerous cellular pathways have been unraveled through the introduction of recombinant proteins and blocking antibodies. The injection of nanoparticles has also become popular in recent years to investigate toxicity mechanisms and intracellular transport, and to conceive semi-synthetic cells containing artificial organelles. This article reviews colloidal systems such as proteins, nucleic acids and nanoparticles that have been injected into cells for different research aims, and discusses the scientific advances achieved through them. The colloids' intracellular processing and ultimate fate are also examined from a drug delivery perspective with an emphasis on the differences observed for endocytosed versus microinjected material.

Cytoplasmic transport and nuclear import of plasmid DNA

Productive transfection and gene transfer require not simply the entry of DNA into cells and subsequent transcription from an appropriate promoter, but also a number of intracellular events that allow the DNA to move from the extracellular surface of the cell into and through the cytoplasm, and ultimately across the nuclear envelope and into the nucleus before any transcription can initiate. Immediately upon entry into the cytoplasm, naked DNA, either delivered through physical techniques or after disassembly of DNA-carrier complexes, associates with a large number of cellular proteins that mediate subsequent interactions with the microtubule network for movement toward the microtubule organizing center and the nuclear envelope. Plasmids then enter the nucleus either upon the mitotic disassembly of the nuclear envelope or through nuclear pore complexes in the absence of cell division, using a different set of proteins. This review will discuss our current understanding of these pathways used by naked DNA during the transfection process. While much has been elucidated on these processes, much remains to be discerned, but with the development of a number of model systems and approaches, great progress is being made.

Resolving Subcellular miRNA Trafficking and Turnover at Single-Molecule Resolution

Regulation of microRNA (miRNA) localization and stability is critical for their extensive cytoplasmic RNA silencing activity and emerging nuclear functions. Here, we have developed single-molecule fluorescence-based tools to assess the subcellular trafficking, integrity, and activity of miRNAs. We find that seed-matched RNA targets protect miRNAs against degradation and enhance their nuclear retention. While target-stabilized, functional, cytoplasmic miRNAs reside in high-molecular-weight complexes, nuclear miRNAs, as well as cytoplasmic miRNAs targeted by complementary anti-miRNAs, are sequestered stably within significantly lower-molecular-weight complexes and rendered repression incompetent. miRNA stability and activity depend on Argonaute protein abundance, whereas miRNA strand selection, unwinding, and nuclear retention depend on Argonaute identity. Taken together, our results show that miRNA degradation competes with Argonaute loading and target binding to control subcellular miRNA abundance for gene silencing surveillance. Probing single cells for miRNA activity, trafficking, and metabolism promises to facilitate screening for effective miRNA mimics and anti-miRNA drugs.

Rational Development of A Polycistronic Plasmid with A CpG-Free Bacterial Backbone as A Potential Tool for Direct Reprogramming

Objective

Induced pluripotent stem cells are generated from somatic cells by direct reprogramming. These reprogrammed pluripotent cells have different applications in biomedical fields such as regenerative medicine. Although viral vectors are widely used for efficient reprogramming, they have limited applications in the clinic due to the risk for immunogenicity and insertional mutagenesis. Accordingly, we designed and developed a small, non-integrating plasmid named pLENSO/Zeo as a 2A-mediated polycistronic expression vector.

Materials and Methods

In this experimental study, we developed a single plasmid which includes a single expression cassette containing open reading frames of human LIN28, NANOG, SOX2 and OCT4 along with an EGFP reporter gene. Each reprogramming factor is separated by an intervening sequence that encodes a 2A self-processing peptide. The reprogramming cassette is located downstream of a CMV promoter. The vector is easily propagated in the E. coli GT115 strain through a CpG-depleted vector backbone. We evaluated the stability of the constructed vector bioinformatically, and its ability to stoichiometric expression of the reprogramming factors using quantitative molecular methods analysis after transient transfection into HEK293 cells.

Results

In the present study, we developed a nonviral episomal vector named pLENSO/ Zeo. Our results demonstrated the general structural stability of the plasmid DNA. This relatively small vector showed concomitant, high-level expression of the four reprogramming factors with similar titers, which are considered as the critical parameters for efficient and consistent reprogramming.

Conclusion

According to our experimental results, this stable extrachromosomal plasmid expresses reliable amounts of four reprogramming factors simultaneously. Consequently, these promising results encouraged us to evaluate the capability of pLENSO/Zeo as a simple and feasible tool for generation of induced pluripotent stem cells from primary cells in the future.

Role of Cell Membrane-Vector Interactions in Successful Gene Delivery

Cationic polymers have been investigated as nonviral vectors for gene delivery due to their favorable safety profile when compared to viral vectors. However, nonviral vectors are limited by poor efficacy in inducing gene expression. The physicochemical properties of cationic polymers enabling successful gene expression have been investigated in order to improve expression efficiency and safety. Studies over the past several years have focused on five possible rate-limiting processes to explain the differences in gene expression: (1) endosomal release, (2) transport within specific intracellular pathways, (3) protection of DNA from nucleases, (4) transport into the nucleus, and (5) DNA release from vectors. However, determining the relative importance of these processes and the vector properties necessary for optimization remain a challenge to the field. In this Account, we describe over a decade of studies focused on understanding the interaction of cationic polymer and cationic polymer/oligonucleotide (polyplex) interactions with model lipid membranes, cell membranes, and cells in culture. In particular, we have been interested in how the interaction between cationic polymers and the membrane influences the intracellular transport of intact DNA to the nucleus. Recent advances in microfluidic patch clamp techniques enabled us to quantify polyplex cell membrane interactions at the cellular level with precise control over material concentrations and exposure times. In attempting to relate these findings to subsequent intracellular transport of DNA and expression of protein, we needed to develop an approach that could distinguish DNA that was intact and potentially functional for gene expression from the much larger pool of degraded, nonfunctional DNA within the cell. We addressed this need by developing a FRET oligonucleotide molecular beacon (OMB) to monitor intact DNA transport. The research highlighted in this Account builds to the conclusion that polyplex transported DNA is released from endosomes by free cationic polymer intercalated into the endosomal membrane. This cationic polymer initially interacts with the cell plasma membrane and appears to reach the endosome by lipid cycling mechanisms. The fraction of cells displaying release of intact DNA from endosomes quantitatively predicts the fraction of cells displaying gene expression for both linear poly(ethylenimine) (L-PEI; an effective vector) and generation five poly(amidoamine) dendrimer (G5 PAMAM; an ineffective vector). Moreover, intact OMB delivered with G5 PAMAM, which normally is confined to endosomes, was released by the subsequent addition of L-PEI with a corresponding 10-fold increase in transgene expression. These observations are consistent with experiments demonstrating that cationic polymer/membrane partition coefficients, not polyplex/membrane partition coefficients, predict successful gene expression. Interestingly, a similar partitioning of cationic polymers into the mitochondrial membranes has been proposed to explain the cytotoxicity of these materials. Thus, the proposed model indicates the same physicochemical property (partitioning into lipid bilayers) is linked to release from endosomes, giving protein expression, and to cytotoxicity.

DNA uptake, intracellular trafficking and gene transfection after ultrasound exposure

Ultrasound has been studied as a promising tool for intracellular gene delivery. In this work, we studied gene transfection of a human prostate cancer cell line exposed to megahertz pulsed ultrasound in the presence of contrast agent and assessed the efficiency of fluorescently labelled DNA delivery into cell nuclei, which is necessary for gene transfection. At the sonication conditions studied, ~30% of cells showed DNA uptake 30min after sonication, but that fraction decreased over time to ~10% of cells after 24h. Most cells containing DNA had DNA in their nuclei, but the amount varied significantly. Transfection efficiency peaked at ~10% at 8h post sonication. Among those cells containing DNA, ~30% of DNA was localized in the cell nuclei, ~30% was in autophagosomes/autophagolysosomes and the remainder was "free" in the cytoplasm 30min after sonication. At later times up to 24h, ~30% of DNA continued to be found in the nuclei and most or all of the rest of the DNA was in autophagosomes/autophagolysosomes. These results demonstrate that ultrasound can deliver DNA into cell nuclei shortly after sonication and that the rest of the DNA can be cleared by autophagosomes/autophagolysosomes.

Cationic Polymer Intercalation into the Lipid Membrane Enables Intact Polyplex DNA Escape from Endosomes for Gene Delivery

Developing improved cationic polymer-DNA polyplexes for gene delivery requires improved understanding of DNA transport from endosomes into the nucleus. Using a FRET-capable oligonucleotide molecular beacon (OMB), we monitored the transport of intact DNA to cell organelles. We observed that for effective (jetPEI) and ineffective (G5 PAMAM) vectors, the fraction of cells displaying intact OMB in the cytosol (jetPEI ≫ G5 PAMAM) quantitatively predicted the fraction expressing transgene (jetPEI ≫ G5 PAMAM). Intact OMB delivered with PAMAM and confined to endosomes could be released to the cytosol by the subsequent addition of L-PEI, with a corresponding 10-fold increase in transgene expression. These results suggest that future vector development should optimize vectors for intercalation into, and destabilization of, the endosomal membrane. Finally, the study highlights a two-step strategy in which the pDNA is loaded in cells using one vector and endosomal release is mediated by a second agent.

Exploring the role of polymer structure on intracellular nucleic acid delivery via polymeric nanoparticles

Intracellular nucleic acid delivery has the potential to treat many genetically-based diseases, however, gene delivery safety and efficacy remains a challenging obstacle. One promising approach is the use of polymers to form polymeric nanoparticles with nucleic acids that have led to exciting advances in non-viral gene delivery. Understanding the successes and failures of gene delivery polymers and structures is the key to engineering optimal polymers for gene delivery in the future. This article discusses the polymer structural features that enable effective intracellular delivery of DNA and RNA, including protection of nucleic acid cargo, cellular uptake, endosomal escape, vector unpacking, and delivery to the intracellular site of activity. The chemical properties that aid in each step of intracellular nucleic acid delivery are described and specific structures of note are highlighted. Understanding the chemical design parameters of polymeric nucleic acid delivery nanoparticles is important to achieving the goal of safe and effective non-viral genetic nanomedicine.

Integrating mitosis, toxicity, and transgene expression in a telecommunications packet-switched network model of lipoplex-mediated gene delivery

Gene delivery systems transport exogenous genetic information to cells or biological systems with the potential to directly alter endogenous gene expression and behavior with applications in functional genomics, tissue engineering, medical devices, and gene therapy. Nonviral systems offer advantages over viral systems because of their low immunogenicity, inexpensive synthesis, and easy modification but suffer from lower transfection levels. The representation of gene transfer using models offers perspective and interpretation of complex cellular mechanisms,including nonviral gene delivery where exact mechanisms are unknown. Here, we introduce a novel telecommunications model of the nonviral gene delivery process in which the delivery of the gene to a cell is synonymous with delivery of a packet of information to a destination computer within a packet-switched computer network. Such a model uses nodes and layers to simplify the complexity of modeling the transfection process and to overcome several challenges of existing models. These challenges include a limited scope and limited time frame, which often does not incorporate biological effects known to affect transfection. The telecommunication model was constructed in MATLAB to model lipoplex delivery of the gene encoding the green fluorescent protein to HeLa cells. Mitosis and toxicity events were included in the model resulting in simulation outputs of nuclear internalization and transfection efficiency that correlated with experimental data. A priori predictions based on model sensitivity analysis suggest that increasing endosomal escape and decreasing lysosomal degradation, protein degradation, and GFP-induced toxicity can improve transfection efficiency by three-fold. Application of the telecommunications model to nonviral gene delivery offers insight into the development of new gene delivery systems with therapeutically relevant transfection levels.

Identifying Intracellular pDNA Losses From a Model of Nonviral Gene Delivery

Nonviral gene delivery systems are a type of nanocommunication system that transmit plasmid packets (i.e., pDNA packets) that are programmed at the nanoscale to biological systems at the microscopic cellular level. This engineered nanocommunication system suffers large pDNA losses during transmission of the genetically encoded information, preventing its use in biotechnological and medical applications. The pDNA losses largely remain uncharacterized, and the ramifications of reducing pDNA loss from newly designed gene delivery systems remain difficult to predict. Here, the pDNA losses during primary and secondary transmission chains were identified utilizing a MATLAB model employing queuing theory simulating delivery of pEGFPLuc transgene to HeLa cells carried by Lipofectamine 2000 nonviral DNA carrier. Minimizing pDNA loss during endosomal escape of the primary transmission process results in increased number of pDNA in the nucleus with increased transfection, but with increased probability of cell death. The number of pDNA copies in the nucleus and the amount of time the pDNAs are in the nucleus directly correlates to improved transfection efficiency. During secondary transmission, pDNAs are degraded during distribution to daughter cells. Reducing pDNA losses improves transfection, but a balance in quantity of nuclear pDNA, mitosis, and toxicity must be considered in order to achieve therapeutically relevant transfection levels.

Enhancement of transfection efficiency with NLS and SPB-NLS

Low positive cell screening efficiency severely hinders the development of transgenic animals. The major rate-limiting step of positive cell screening is DNA entering the nucleus, particularly for large DNA molecules. To enhance the transport of large DNA molecules into the nucleus, particularly for the production of transgenic animals, nuclear localization sequence (NLS) peptides and the peptide derivative succinimidyl-[4-(psoralen-8-yloxy)]-butyrate (SPB)-NLS were synthesized to mediate transfection in vitro. To investigate the function of NLS and SPB-NLS in vitro, the expression levels of growth hormone (GH) mRNA and green fluorescent protein (GFP) protein were analyzed following transfection mediated by NLS and SPB-NLS. The results demonstrated that the expression of GH mRNA was significantly higher in the NLS (increased by 69%) and SPB-NLS (330%) groups than that in the liposome/pGN group. Similarly, GFP expression was found to be higher in the SPB-NLS group than that in the liposome group, while the expression in the NLS group was lower than that in the liposome group. Further analysis demonstrated that SPB-NLS enhanced the expression of insulin-like growth factor 1 in hard-to-transfect goat mammary epithelia cells. The results of the microscopy analysis revealed that transfected DNA entered the nucleus via the nuclear pores, facilitated by NLS. Analysis of the cell cycle demonstrated that the cytotoxic effects of NLS and SPB-NLS were low. In conclusion, the results of the present study demonstrate that SPB-NLS acts as a transfection-enhancing agent and may be used both to enhance nuclear delivery and for the development of genetically modified animals.

In vitro efficient transfection by CM₁₈-Tat₁₁ hybrid peptide: a new tool for gene-delivery applications

Cell penetrating peptides (CPPs) are actively researched as non-viral molecular carriers for the controlled delivery of nucleic acids into cells, but widespread application is severely hampered by their trapping into endosomes. Here we show that the recently introduced endosomolytic CM₁₈-Tat₁₁ hybrid peptide (KWKLFKKIGAVLKVLTTG-YGRKKRRQRRR, residues 1-7 of Cecropin-A, 2-12 of Melittin, and 47-57 of HIV-1 Tat protein) can be exploited to obtain a self-assembled peptide-DNA vector which maintains the CM₁₈-Tat₁₁ ability to enter cells and destabilize vesicular membranes, concomitantly yielding high DNA transfection efficiency with no detectable cytotoxic effects. Different peptide-DNA stoichiometric ratios were tested to optimize vector size, charge, and stability characteristics. The transfection efficiency of selected candidates is quantitatively investigated by the luciferase-reporter assay. Vector intracellular trafficking is monitored in real time and in live cells by confocal microscopy. In particular, fluorescence resonant energy transfer (FRET) between suitably-labeled peptide and DNA modules was exploited to monitor complex disassembly during endocytosis, and this process is correlated to transfection timing and efficiency. We argue that these results can open the way to the rational design and application of CM₁₈-Tat₁₁–based systems for gene-delivery purposes.

Trends in polymeric delivery of nucleic acids to tumors

Delivery of nucleic acids to tumors has received extensive attention in the past few decades since these molecules are capable of treating disease by modulating the source of abnormalities. Although high efficiency and low toxicity of numerous delivery systems for nucleic acids have been approved frequently with in vitro assays, contradictions have been observed in many cases between these results and what has occurred in the dynamic in vivo situation. Filling this gap seems to be crucial for further preclinical development of such systems. In this paper, we discuss various barriers which polymeric DNA or siRNA nanoparticles encounter upon systemic administration with an aim to assist in designing more relevant in vitro assays. Furthermore, individual considerations concerning delivery of DNA and siRNA have been addressed.

Polyplex exposure inhibits cell cycle, increases inflammatory response, and can cause protein expression without cell division

We sought to evaluate the relationship between cell division and protein expression when using commercial poly(ethylenimine) (PEI)-based polyplexes. The membrane dye PKH26 was used to assess cell division, and cyan fluorescent protein (CFP) was used to monitor protein expression. When analyzed at the whole population level, a greater number of cells divided than expressed protein, regardless of the level of protein expression observed, giving apparent consistency with the hypothesis that protein expression requires cells to pass through mitosis in order for the transgene to overcome the nuclear membrane. However, when the polyplex-exposed population was evaluated for the amount of division in the protein-expressing subpopulation, it was observed that substantial amounts of expression had occurred in the absence of division. Indeed, in HeLa S3 cells, this represented the majority of expressing cells. Of interest, the doubling time for both cell lines was slowed by ~2-fold upon exposure to polyplexes. This change was not altered by the origin of the plasmid DNA (pDNA) transgene promoter (cytomegalovirus (CMV) or elongation factor-1 alpha (EF1α)). Gene expression arrays in polyplex-exposed HeLa S3 cells showed upregulation of cell cycle arrest genes and downregulation of genes related to mitosis. Chemokine, interleukin, and toll-like receptor genes were also upregulated, suggesting activation of proinflammatory pathways. In summary, we find evidence that a cell division-independent expression pathway exists, and that polyplex exposure slows cell division and increases inflammatory response.

Noncoding DNA in lipofection of HeLa cells-a few insights

In cationic carrier-mediated gene delivery, the disproportional relationship between the quantity of delivered DNA and the amount of encoded protein produced is a well-known phenomenon. The numerous intracellular barriers which need to be overcome by pDNA to reach the nucleoplasm play a major role in it. In contrast to what one would expect, a partial replacement of coding pDNA by noncoding DNA does not lead to a decrease in transfection efficiency. The mechanism underlying this observation is still unclear. Therefore, we investigated which constituents of the transfection process might contribute to this phenomenon. Our data reveal that the topology of the noncoding plasmid DNA plays a major role. Noncoding pDNA can be used only in a supercoiled form to replace coding pDNA in Lipofectamine lipoplexes, without a loss in transfection levels. When noncoding pDNA is linearized or partly digested, it diminishes the transfection potential of coding pDNA, as does noncoding salmon DNA. The difference in transfection efficiencies could not be attributed to diverse physicochemical characteristics of the Lipofectamine lipoplexes containing different types of noncoding DNA or to the extent of their internalization. At the level of endosomal release, however, nucleic acid release from the endosomal compartment proceeds faster when lipoplexes contain noncoding salmon DNA. Since the half-life of pDNA in the cytosol hardly exceeds 90 min, it is conceivable that prolonged release of coding pDNA from complexes carrying supercoiled noncoding pDNA may explain its positive effect on transfection, while this depot effect does not exist when noncoding salmon DNA is used.

Importin-7 mediates nuclear trafficking of DNA in mammalian cells

Eukaryotic cells have the ability to uptake and transport endogenous and exogenous DNA in their nuclei, however little is known about the specific pathways involved. Here we show that the nuclear transport receptor importin 7 (imp7) supports nuclear import of supercoiled plasmid DNA and human mitochondrial DNA in a Ran and energy-dependent way. The imp7-dependent pathway was specifically competed by excess DNA but not by excess of maltose-binding protein fused with the classical nuclear localizing signal (NLS) or the M9 peptides. Transport of DNA molecules complexed with poly-l-lysine was impaired in intact cells depleted of imp7, and DNA complexes remained localized in the cytoplasm. Poor DNA nuclear import in cells depleted of imp7 directly correlated with lower gene expression levels in these cells compared to controls. Inefficient nuclear import of transfected DNA induced greater upregulation of the interferon pathway, suggesting that rapid DNA nuclear import may prevent uncontrolled activation of the innate immune response. Our results provide evidence that imp7 is a non-redundant component of an intrinsic pathway in mammalian cells for efficient accumulation of exogenous and endogenous DNA in the nucleus, which may be critical for the exchange of genetic information between mitochondria and nuclear genomes and to control activation of the innate immune response.

Non-viral gene therapy for spinal cord regeneration

Spinal cord injury (SCI) normally results in life-long disabilities and a broad range of secondary complications. Advances in therapeutic delivery during the past few decades offer hope for such victims. However, the limited functional improvement shown in in vivo studies hinders effective therapeutic application in clinical practice. Recent studies showed that gene vectors can transfect cells present in the lesion of an injured spinal cord (endogenous cells) and thereby produce therapeutic molecules with long-lasting biological effects that promote neural tissue regeneration. In this article we review recent advances in non-viral gene delivery into neural cells and their use for gene therapy in SCI.

Intracellular partitioning of cell organelles and extraneous nanoparticles during mitosis

The nucleocytoplasmic partitioning of nanoparticles as a result of cell division is highly relevant to the field of nonviral gene delivery. We reviewed the literature on the intracellular distribution of cell organelles (the endosomal vesicles, Golgi apparatus, endoplasmic reticulum and nucleus), foreign macromolecules (dextrans and plasmid DNA) and inorganic nanoparticles (gold, quantum dot and iron oxide) during mitosis. For nonviral gene delivery particles (lipid- or polymer-based), indirect proof of nuclear entry during mitosis is provided. We also describe how retroviruses and latent DNA viruses take advantage of mitosis to transfer their viral genome and segregate their episomes into the host daughter nuclei. Based on this knowledge, we propose strategies to improve nonviral gene delivery in dividing cells with the ultimate goal of designing nonviral gene delivery systems that are as efficient as their viral counterparts but non-immunogenic, non-oncogenic and easy and inexpensive to prepare.

A new approach to manipulate the fate of single neural stem cells in tissue

A challenge in the field of neural stem cell biology is the mechanistic dissection of single stem cell behavior in tissue. Although such behavior can be tracked by sophisticated imaging techniques, current methods of genetic manipulation do not allow researchers to change the level of a defined gene product on a truly acute time scale and are limited to very few genes at a time. To overcome these limitations, we established microinjection of neuroepithelial/radial glial cells (apical progenitors) in organotypic slice culture of embryonic mouse brain. Microinjected apical progenitors showed cell cycle parameters that were indistinguishable to apical progenitors in utero, underwent self-renewing divisions and generated neurons. Microinjection of single genes, recombinant proteins or complex mixtures of RNA was found to elicit acute and defined changes in apical progenitor behavior and progeny fate. Thus, apical progenitor microinjection provides a new approach to acutely manipulating single neural stem and progenitor cells in tissue.

Nuclear inclusion of nontargeted and chromatin-targeted polystyrene beads and plasmid DNA containing nanoparticles

The nuclear membrane is one of the major cellular barriers in the delivery of plasmid DNA (pDNA). Cell division has a positive influence on the expression efficiency since, at the end of mitosis, pDNA or pDNA containing complexes near the chromatin are probably included by a random process in the nuclei of the daughter cells. However, very little is known about the nuclear inclusion of nanoparticles during cell division. Using the Xenopus nuclear envelope reassembly (XNER) assay, we found that the nuclear enclosure of nanoparticles was dependent on size (with 100 and 200 nm particles being better included than the 500 nm ones) and charge (with positively charged particles being better included than negatively charged or polyethyleneglycolated (PEGylated) ones) of the beads. Also, coupling chromatin-targeting peptides to the polystyrene beads or pDNA complexes improved their inclusion by 2- to 3-fold. Upon microinjection in living HeLa cells, however, nanoparticles were never observed in the nuclei of cells postdivision but accumulated in a specific perinuclear region, which was identified as the lysosomal compartment. This indicates that nanoparticles can end up in the lysosomes even when they were not delivered through endocytosis. To elucidate if the chromatin binding peptides also have potential in living cells, this additional barrier first has to be tackled, since it prevents free particles from being present near the chromatin at the moment of cell division.

Quantitative analysis of condensation/decondensation status of pDNA in the nuclear sub-domains by QD-FRET

Recent studies indicate that controlling the nuclear decondensation and intra-nuclear localization of plasmid DNA (pDNA) would result in an increased transfection efficiency. In the present study, we established a technology for imaging the nuclear condensation/decondensation status of pDNA in nuclear subdomains using fluorescence resonance energy transfer (FRET) between quantum dot (QD)-labeled pDNA as donor, and rhodamine-labeled polycations as acceptor. The FRET-occurring pDNA/polycation particle was encapsulated in a nuclear delivery system; a tetra-lamellar multifunctional envelope-type nano device (T-MEND), designed to overcome the endosomal membrane and nuclear membrane via step-wise fusion. Nuclear subdomains (i.e. heterochromatin and euchromatin) were distinguished by Hoechst33342 staining. Thereafter, Z-series of confocal images were captured by confocal laser scanning microscopy. pDNA in condensation/decondensation status in heterochromatin or euchromatin were quantified based on the pixel area of the signals derived from the QD and rhodamine. The results obtained indicate that modulation of the supra-molecular structure of polyrotaxane (DMAE-ss-PRX), a condenser that is cleaved in a reductive environment, conferred euchromatin-preferred decondensation. This represents the first demonstration of the successful control of condensation/decondensation in specific nuclear sub-domain via the use of an artificial DNA condenser.

Construction of cell penetrating peptide vectors with N-terminal stearylated nuclear localization signal for targeted delivery of DNA into the cell nuclei

Cellular uptake and nuclear localization are two barriers to gene delivery. Here, we designed new gene delivery carriers with an N-terminal stearylated (STR) nuclear localization signal (NLS), PKKKRKV, present in the Simian Virus 40 large T antigen with the aim to overcome limitations, such as cell membrane and nuclear pores, offering attractive possibilities to enhance gene delivery. Four vectors with different structures of N-stearylated nuclear localization signal-octaarginine peptide (STR-PKKKRKV-R(8) or STR-NLS-R(8), STR-VKRKKKP-R(8) or STR-reverse NLS-R(8), PKKKRKV-R(8) or NLS-R(8), and VKRKKKP-R(8) or reverse NLS-R(8)) were compared. The gene expression mediated by these vectors in dividing and non-dividing cells (both in 293T and HeLa cell lines) was investigated. The most efficient N/P ratio was 4 for STR-PKKKRKV-R(8,) STR-VKRKKKP-R(8,) and 0.25 for PKKKRKV-R(8), VKRKKKP-R(8.) The maximum transfection activity of these vehicles (VKRKKKP-R(8)) was up to 80% as effective as jetPEI™ and the vehicles did not exhibit cytotoxicity. Interestingly, N-stearylated peptides presented lower transfection activity compared to peptides without N-stearylation at lower N/P ratios (0.25 to 1). Confocal study showed that the vectors could effectively promote the nuclear translocation.

Diffusion of large molecules into assembling nuclei revealed using an optical highlighting technique

The nuclear envelope (NE) defines the nuclear compartment, and nuclear pore complexes (NPCs) on the NE form aqueous passages through which small water-soluble molecules can passively diffuse. It is well known that proteins smaller than 50 kDa can diffuse though NPCs, whereas proteins larger than 60 kDa rarely enter by passive diffusion. Little, however, is known about how this size cutoff develops as the NE reassembles and the nucleus expands. In 1987, a well-known study identified an efficient mechanism by which large diffusing proteins (> 60 kDa) were excluded from the reassembling nucleus after mitosis. Since then, it has been generally accepted that after mitosis, newly formed nuclei completely exclude all proteins except those that are initially bound to the mitotic chromosomes and those that are selectively imported through NPCs. Here, the tetrameric complex of the photoconvertible fluorescent protein KikGR ( approximately 103 kDa) was optically highlighted in the cytoplasm and followed to examine its entry into nuclei. Remarkably, highlighted complexes efficiently entered newly assembled nuclei during an approximately 20-min period after the completion of cytokinesis. Because KikGR contains no known nuclear-localization or chromosome-binding sequences, our results indicate the diffusion barrier is less restrictive during nuclear reassembly.

Chromatin tethering and retroviral integration: recent discoveries and parallels with DNA viruses

Permanent integration of the viral genome into a host chromosome is an essential step in the life cycles of lentiviruses and other retroviruses. By archiving the viral genetic information in the genome of the host target cell and its progeny, integrated proviruses prevent curative therapy of HIV-1 and make the development of antiretroviral drug resistance irreversible. Although the integration reaction is known to be catalyzed by the viral integrase (IN), the manner in which retroviruses engage and attach to the chromatin target is only now becoming clear. Lens epithelium-derived growth factor (LEDGF/p75) is a ubiquitously expressed nuclear protein that binds to lentiviral IN protein dimers at its carboxyl terminus and to host chromatin at its amino terminus. LEDGF/p75 thus tethers ectopically expressed IN to chromatin. It also protects IN from proteosomal degradation and can stimulate IN catalysis in vitro. HIV-1 infection is inhibited at the integration step in LEDGF/p75-deficient cells, and the characteristic lentiviral preference for integration into active genes is also reduced. A model in which LEDGF/p75 acts to tether the viral preintegration complex to chromatin has emerged. Intriguingly, similar chromatin tethering mechanisms have been described for other retroelements and for large DNA viruses. Here we review the evidence supporting the LEDGF/p75 tethering model and consider parallels with these other viruses.