Intracellular accumulation of secreted proteoglycans inhibits cationic lipid-mediated gene transfer. Co-transfer of glycosaminoglycans to the nucleus

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

Lipoplex-Mediated Single-Cell Transfection via Droplet Microfluidics

While lipoplex (cationic lipid-nucleic acid complex)-mediated intracellular delivery is widely adopted in mammalian cell transfection, its transfection efficiency for suspension cells, e.g., lymphatic and hematopoietic cells, is reported at only ≈5% or even lower. Here, efficient and consistent lipoplex-mediated transfection is demonstrated for hard-to-transfect suspension cells via a single-cell, droplet-microfluidics approach. In these microdroplets, monodisperse lipoplexes for effective gene delivery are generated via chaotic mixing induced by the serpentine microchannel and co-confined with single cells. Moreover, the cell membrane permeability increases due to the shear stress exerted on the single cells when they pass through the droplet pinch-off junction. The transfection efficiency, examined by the delivery of the pcDNA3-EGFP plasmid, improves from ≈5% to ≈50% for all three tested suspension cell lines, i.e., K562, THP-1, Jurkat, and with significantly reduced cell-to-cell variation, compared to the bulk method. Efficient targeted knockout of the TP53BP1 gene for K562 cells via the CRISPR (clustered regularly interspaced short palindromic repeats)-CAS9 (CRISPR-associated nuclease 9) mechanism is also achieved using this platform. Lipoplex-mediated single-cell transfection via droplet microfluidics is expected to have broad applications in gene therapy and regenerative medicine by providing high transfection efficiency and low cell-to-cell variation for hard-to-transfect suspension cells.

Polyplex Micelles with Double-Protective Compartments of Hydrophilic Shell and Thermoswitchable Palisade of Poly(oxazoline)-Based Block Copolymers for Promoted Gene Transfection

Improving the stability of polyplex micelles under physiological conditions is a critical issue for promoting gene transfection efficiencies. To this end, hydrophobic palisade was installed between the inner core of packaged plasmid DNA (pDNA) and the hydrophilic shell of polyplex micelles using a triblock copolymer consisting of hydrophilic poly(2-ethyl-2-oxazoline), thermoswitchable amphiphilic poly(2-n-propyl-2-oxazoline) (PnPrOx) and cationic poly(L-lysine). The two-step preparation procedure, mixing the triblock copolymer with pDNA below the lower critical solution temperature (LCST) of PnPrOx, followed by incubation above the LCST to form a hydrophobic palisade of the collapsed PnPrOx segment, induced the formation of spatially aligned hydrophilic-hydrophobic double-protected polyplex micelles. The prepared polyplex micelles exhibited significant tolerance against attacks from nuclease and polyanions compared to those without hydrophobic palisades, thereby promoting gene transfection. These results corroborated the utility of amphiphilic poly(oxazoline) as a molecular thermal switch to improve the stability of polyplex gene carriers relevant for physiological applications.

Studies of proteoglycan involvement in CPP-mediated delivery

Cell-penetrating peptides (CPPs) are widely used to deliver macromolecular cargoes to intracellular sites of action. Many CPPs have been demonstrated to rely on cell surface heparan sulfate proteoglycans (HSPGs) for efficient cellular entry and delivery. In this chapter, we describe methods for the study of PG involvement in CPP uptake. We provide descriptions of how to determine whether uptake of a CPP of interest is dependent on PGs. We also provide detailed protocols for the purification of PGs by anion-exchange chromatography as well as the characterization of the HSPG core protein composition of a cell line of interest. Finally, we present methods for modulating the expression level of specific HSPG core proteins as a means to determine the core protein specificity in the uptake of a particular CPP.

ScFv antibody-induced translocation of cell-surface heparan sulfate proteoglycan to endocytic vesicles: evidence for heparan sulfate epitope specificity and role of both syndecan and glypican

Cellular uptake of several viruses and polybasic macromolecules requires the expression of cell-surface heparan sulfate proteoglycan (HSPG) through as yet ill defined mechanisms. We unexpectedly found that among several cell-surface-binding single chain variable fragment (scFv) anti-HS antibody (alphaHS) clones, only one, AO4B08, efficiently translocated macromolecular cargo to intracellular vesicles through induction of HSPG endocytosis. Interestingly, AO4B08-induced PG internalization was strictly dependent on HS 2-O-sulfation and appeared independent of intact N-sulfation. AO4B08 and human immunodeficiency virus (HIV)-Tat, i.e. a well known cell-penetrating peptide, were shown to compete for the internalizing PG population. To obtain a more detailed characterization of this pathway, we have developed a procedure for the isolation of endocytic vesicles by conjugating AO4B08 with superparamagnetic nanoparticles. [(35)S]sulfate-labeled HSPG was found to accumulate in isolated, AO4B08-containing vesicles, providing the first biochemical evidence for intact HSPG co-internalization with its ligand. Further analysis revealed the existence of both syndecan, i.e. a transmembrane HSPG, and glycosyl-phosphatidyl-inositol-anchored glypican in purified vesicles. Importantly, internalized syndecan and glypican were found to co-localize in AO4B08-containing vesicles. Our data establish HSPGs as true internalizing receptors of macromolecular cargo and indicate that the sorting of cell-surface HSPG to endocytic vesicles is determined by a specific HS epitope that can be carried by both syndecan and glypican core protein.

Glycosaminoglycan-resistant and pH-sensitive lipid-coated DNA complexes produced by detergent removal method

Cationic polymers are efficient gene delivery vectors in in vitro conditions, but these carriers can fail in vivo due to interactions with extracellular polyanions, i.e. glycosaminoglycans (GAG). The aim of this study was to develop a stable gene delivery vector that is activated at the acidic endosomal pH. Cationic DNA/PEI complexes were coated by 1,2-dioleylphosphatidylethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS) (3:2 mol/mol) using two coating methods: detergent removal and mixing with liposomes prepared by ethanol injection. Only detergent removal produced lipid-coated DNA complexes that were stable against GAGs, but were membrane active at low pH towards endosome mimicking liposomes. In relation to the low cellular uptake of the coated complexes, their transfection efficacy was relatively high. PEGylation of the coated complexes increased their cellular uptake but reduced the pH-sensitivity. Detergent removal was thus a superior method for the production of stable, but acid activatable, lipid-coated DNA complexes.

Cell-penetrating peptides: from molecular mechanisms to therapeutics

The recent discovery of new potent therapeutic molecules which do not reach the clinic due to poor delivery and low bioavailability have made the delivery of molecules a keystone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including CPPs (cell-penetrating peptides), which represent a new and innovative concept to bypass the problem of bioavailability of drugs. CPPs constitute very promising tools and have been successfully applied for in vivo. Two CPP strategies have been described to date; the first one requires chemical linkage between the drug and the carrier for cellular drug internalization, and the second is based on the formation of stable complexes with drugs, depending on their chemical nature. The Pep and MPG families are short amphipathic peptides, which form stable nanoparticles with proteins and nucleic acids respectively. MPG- and Pep-based nanoparticles enter cells independently of the endosomal pathway and efficiently deliver cargoes, in a fully biologically active form, into a large variety of cell lines, as well as in animal models. This review focuses on the structure-function relationship of non-covalent MPG and Pep-1 strategies, and their requirement for cellular uptake of biomolecules and applications in cultured cells and animal models.

Delivery of proteins and nucleic acids using a non-covalent peptide-based strategy

The recent discovery of new potent therapeutic molecules which do not reach the clinic due to poor delivery and low bioavailability have made of delivery a key stone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including cell-penetrating peptides (CPPs), which have been successfully applied for in vivo delivery of biomolecules and constitute very promising tools. Distinct families of CPPs have been described; some require chemical linkage between the drug and the carrier for cellular drug internalization while others like Pep-and MPG-families, form stable complexes with drugs depending on their chemical nature. Pep and MPG are short amphipathic peptides, which form stable nanoparticles with proteins and nucleic acids respectively. MPG and Pep based nanoparticles enter cells independently of the endosomal pathway and efficiently deliver cargoes in a fully biologically active form into a large variety of cell lines as well as in animal models. This review will focus on the mechanisms of non-covalent MPG and Pep-1 strategies and their applications in cultured cells and animal models.

Development of a generic transient transfection process at 100 L scale

We have developed a generic transient transfection process at 100 L scale, using HEK293-EBNA cells and PEI as the transfection reagent for the production of recombinant IgG. The process, including large-scale plasmid preparation, expression at bioreactor scale, capture, purification and, if necessary, endotoxin removal allows reproducible production of more than 0.5 g IgG for in vitro and in vivo studies. We compared the performance of two HEK cell lines, investigated the effect of conditioned medium, optimized the DNA:PEI ratio and implemented a feed strategy to prolong the culture time to increase product yield. The transient transfection protocol developed enables a closed process from seeding culture to protein capture. The challenge of performing a medium exchange before transfection at large scale is solved by applying a continuous centrifugation step between the seeding bioreactor and the production bioreactor. After 7-8 days the harvest and capture is performed in a one-step operation using a Streamline expanded bed chromatography system. Following a polishing step the purified antibody is transferred to the final formulation buffer. The method has shown to be reproducible at 10, 50, and 100 L scale expressing between 5 and 8 mg L(-1) IgG.

Identification of proteins released by mammalian cells that mediate DNA internalization through proteoglycan-dependent macropinocytosis

Naked DNA plasmid represents the simplest vehicle for gene therapy and DNA-based vaccination purposes; however, the molecular mechanisms of DNA uptake in mammalian cells are poorly understood. Here, we show that naked DNA uptake occurs via proteoglycan-dependent macropinocytosis, thus challenging the concept of a specific DNA-internalizing receptor. Cells genetically deficient in proteoglycans, which constitute a major source of cell-surface polyanions, exhibited substantially decreased uptake of likewise polyanionic DNA. The apparent paradox was explained by the action of DNA-transporting proteins present in conditioned medium. Complexes between these proteins and DNA require proteoglycans for cellular entry. Mass spectrometry analysis of cell medium components identified several proteins previously shown to associate with DNA and to participate in membrane transport of macromolecular cargo. The major pathway for proteoglycan-dependent DNA uptake was macropinocytosis, whereas caveolae-dependent and clathrin-dependent pathways were not involved, as determined by using caveolin-1 knock-out cells, dominant-negative constructs for dynamin and Eps15, and macropinocytosis-disruptive drugs, as well as confocal fluorescence co-localization studies. Importantly, a significant fraction of internalized DNA was translocated to the nucleus for expression. Our results provide novel insights into the mechanism of DNA uptake by mammalian cells and extend the emerging role of proteoglycans in macromolecular transport.

First step of the cell-penetrating peptide mechanism involves Rac1 GTPase-dependent actin-network remodelling

BACKGROUND INFORMATION

Application of CPPs (cell-penetrating peptides) constitutes a promising strategy for the intracellular delivery of therapeutic molecules. The non-covalent approach based on the amphipathic peptide MPG has been successfully used to improve the delivery of biologically active macromolecules, both in cellulo and in vivo, through a mechanism independent of the endosomal pathway and mediated by the membrane potential.

RESULTS

In the present study, we have investigated the first step of the cellular uptake mechanism of MPG and shown that both MPG and MPG-cargo complexes interact with the extracellular matrix through the negatively charged heparan sulfate proteoglycans. We demonstrated that initiation of cellular uptake constitutes a highly dynamic mechanism where the binding of MPG or the MPG-cargo to the extracellular matrix is rapidly followed by a remodelling of the actin network associated with the activation of the GTPase Rac1. We suggest that MPG-induced clustering of the glycosaminoglycan platform constitutes the 'onset' of the cellular uptake mechanism, thereby increasing membrane dynamics and membrane fusion processes. This process favours cell entry of MPG or MPG-DNA complexes, which is further controlled by the ability of MPG to induce a local membrane destabilization.

CONCLUSIONS

Although CPPs are taken up through different pathways and mechanisms, the initial step involves electrostatic interactions with the glycosaminoglycan platform, and the dynamics of associated membrane microdomains can be generalized to most non-viral delivery systems.

Polyplex-mediated gene transfer and cell cycle: effect of carrier on cellular uptake and intracellular kinetics, and significance of glycosaminoglycans

BACKGROUND

Here we report on studies that probe whether the intracellular kinetics of plasmid DNA (pDNA) and cell surface glycosaminoglycans (GAGs) are modified during the cell cycle in a way that can be correlated with changes in gene transfer efficiency with poly(ethyleneimine) (PEI) and poly-L-lysine (PLL) polyplexes.

METHODS

Synchronized D407 retinal cells were transfected with PEI and PLL polyplexes using a luciferase reporter. The free and/or loosely complexed nuclear pDNA was determined by real-time PCR, and compared with transgene expression, the rate of pinocytosis by FITC-dextran uptake and the content of cell surface GAGs.

RESULTS

The amount of free and/or loosely complexed nuclear pDNA between cell cycle phases varied approximately 4-20 times (G1 < S < G2/M). Both carriers delivered pDNA in a similar way into the nucleus (PLL vs. PEI < or = 3.5-fold), but PEI was approximately 10-100 times more efficient in gene expression than PLL (G1 < G2/M < S). The rate of pinocytosis increased up to 70-fold from G1 to middle S phase. Cell surface heparan and chondroitin sulfate increased 50-80%, and hyaluronan decreased 50% when the cells went from G1 through S to G2/M.

CONCLUSIONS

The data obtained indicates that no single parameter (pinocytosis, cell surface GAGs, nuclear uptake) solely accounts for the differential pDNA uptake or expression during cell cycle, and that the main difference in PLL- and PEI-mediated transfections seems to be at the nuclear level.

Characterization of gene delivery in vitro and in vivo by the arginine peptide system

We have reported previously that a basic peptide, arginine peptide, can be used as an efficient system for delivery of foreign genes. In this work, to better understand the mechanism of arginine peptide-mediated gene delivery, we further evaluated the process of cellular uptake and nuclear localization of the peptide/DNA complex. To investigate the effect of cellular proteoglycans on arginine peptide/DNA complexes, interactions between polyanionic glycosaminoglycans (GAGs) and peptide/DNA complexes were examined by the ethidium bromide interaction assay. Sulfated GAGs were found to relax the complexed DNA at low peptide/DNA charge ratios. Condensed peptide/DNA complexes facilitate cellular uptake, but their mechanism of uptake is poorly understood. Studies of various endocytosis inhibitors suggested that the peptide/DNA complex internalization involved the caveolar-related endocytosis pathway. A critical step in the gene delivery is the cytosol-to-nucleus transport of exogenous DNA following initial complex uptake. Nuclear localization of peptide/DNA complex was confirmed by confocal laser scanning microscopic observation. Further, we show that transfections with peptides result in an early accumulation of plasmid DNA in the nucleus of growth-arrested cells, which suggest nuclear transport. To assess the potential for arginine peptide as an agent for therapeutic gene delivery, in vivo complexed DNA transduction studies were performed. Mice were injected subcutaneously with the reporter gene beta-galactosidase, resulting in high levels of gene expression in dermal tissue.

Formation and intracellular trafficking of lipoplexes and polyplexes

Cationic lipid/DNA lipoplexes and cationic polymer/DNA polyplexes represent an attractive alternative to viral vectors for cell transfection in vitro and in vivo but still suffer from a relatively low efficiency. Optimization of their transfection efficiency may be attempted by using a trial and error approach consisting of synthesizing and testing a large number of derivatives. On the other hand, rational design of highly efficient cationic lipids and polymers requires a deeper understanding of the interactions between the vector and the DNA as well as the cellular pathways and mechanisms involved in DNA entry into the cell and ultimately the nucleus. In the present review, the pathways and mechanisms involved in lipoplex- and polyplex-mediated transfection are comparatively addressed and unresolved questions are highlighted.

Dioleoyl phosphatidylethanolamine and PEG-lipid conjugates modify DNA delivery mediated by 1,4-dihydropyridine amphiphiles

Complexes of amphiphilic cationic 1,4-dihydropyridines with DNA (lipoplexes) can be used for nonviral gene delivery. In order to achieve serum-resistant transfection system, DOPE and PEG-lipid conjugates were used to modify 1,4-dihydropyridine amphiphile DHP-12 complexes with DNA. The ability to bind DNA was examined by ethidium bromide displacement assay. Cellular uptake, transfection efficacy and intracellular trafficking of the lipoplexes were assessed using FACS, betagalactosidase gene transfection and confocal laser microscopy, respectively. Cytotoxicity was determined by MTT assay. DHP-12 lipoplexes that included DOPE showed enhanced cell uptake and transfection efficacy both in the absence and presence of serum. PEG-lipid conjugates, in contrast, impaired transfection. In conclusion, combination of DHP-12 with DOPE appears to be a promising transfection system.

Polyanions and the proteome

The behavior of the proteome reflects spatial and temporal organization both within and without cells. We propose that various macromolecular entities possessing polyanionic character such as proteoglycans, lipid bilayer surfaces, microtubules, microfilaments, and polynucleotides may provide a functional network that mediates a variety of cellular phenomena. The interaction of proteins with this array of polyanions is characterized by a lower degree of specificity than seen with most commonly recognized macromolecular interactions. In this commentary, potential roles for this polyanion network in diverse functions such as protein/protein interactions, protein folding and stabilization, macromolecular transport, and various disease processes are all considered, as well as the use of polyanions as therapeutic agents. The role of small polyanions in the regulation of protein/polyanion interactions is also postulated. We provide preliminary experimental analysis of the extent to which proteins interact with polyanions inside cells using a combination of two-dimensional chromatographic and electrophoretic methods and antibody arrays. We conclude that many hundreds to thousands of such interactions are present in cells and argue that future understanding of the proteome will require that the "polyanion world" be taken into account.

The Human Antimicrobial Peptide LL-37 Transfers Extracellular DNA Plasmid to the Nuclear Compartment of Mammalian Cells via Lipid Rafts and Proteoglycan-dependent Endocytosis

Antimicrobial peptides, such as LL-37, are found both in nonvertebrates and vertebrates, where they represent important components of innate immunity. Bacterial infections at epithelial surfaces are associated with substantial induction of LL-37 expression, which allows efficient lysis of the invading microbes. Peptide-mediated lysis results in the release of bacterial nucleic acids with potential pathobiological activity in the host. Here, we demonstrate that LL-37 targets extracellular DNA plasmid to the nuclear compartment of mammalian cells, where it is expressed. DNA transfer occurred at physiological LL-37 concentrations that killed bacterial cells, whereas virtually no cytotoxic or growth-inhibitory effects were observed in mammalian cells. Furthermore, LL-37 protected DNA from serum nuclease degradation. LL-37.DNA complex uptake was a saturable time- and temperature-dependent process and was sensitive to cholesterol-depleting agents that are known to disrupt lipid rafts and caveolae, as shown by flow cytometry. Confocal fluorescence microscopy studies showed localization of internalized DNA to compartments stained by cholera toxin B, a marker of lipid rafts, but failed to demonstrate any co-localization of internalized DNA with caveolin-positive endocytotic vesicles. Moreover, LL-37-mediated plasmid uptake and reporter gene expression were strictly dependent on cell surface proteoglycans. We conclude that the human antimicrobial peptide LL-37 binds to, protects, and efficiently targets DNA plasmid to the nuclei of mammalian cells through caveolae-independent membrane raft endocytosis and cell surface proteoglycans.

Compositional effects of cationic lipid/DNA delivery systems on transgene expression in cell culture

Studies of the contribution of various physical properties of cationic lipid/DNA complexes (CLDCs) to their observed transgene expression in vitro were conducted using cationic liposomes composed of the cationic lipids 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and dimethyldioctadecylammonium bromide (DDAB), with or without equimolar amounts of cholesterol (CHOL) or 1,2-dioleoylphosphatidylethanolamine (DOPE). The relative degree of luciferase expression by CLDCs is dependent on a complex relationship between net charge of the CLDC as well as previously reported properties, such as membrane fluidity and curvature of the cationic bilayer. Assessments were made of the role of these physical properties on CLDC stability in the extracellular medium, the extent of DNA cellular association, and membrane disruption activity. The efficiency of luciferase expression from negatively charged CLDCs is greatly improved by incorporation of DOPE. This result correlates with enhanced resistance to inhibition of gene delivery by heparan sulfate, increased cellular association of DNA, and enhanced membrane disruption activity. Luciferase expression by positively charged CLDCs is greatly reduced by incorporating equimolar amounts of CHOL and DOPE. This result occurs is in spite of increased resistance to heparan sulfate-mediated inhibition of gene delivery, increased DNA cellular association, and enhanced membrane disruption activity. The observed CLDC compositional effects on luciferase expression along with observed effects on the delivery process suggest that a better understanding of the kinetics and specific routes of gene delivery is necessary.

Basic peptide system for efficient delivery of foreign genes

Certain peptides containing high percentage of cationic amino acids are known to efficiently translocate through the cell membrane. This principle was previously exploited for delivery of variety proteins. We had observed that various basic peptides of earlier studies, though not specifically use for gene delivery, contain DNA or RNA binding domains. In the present study, we reported on arginine peptides, which form DNA complexes that efficiently transfect various cell lines. The transfection abilities of the peptides were observed by green fluorescent protein (GFP) and beta-galactosidase gene expression in 293T, HeLa, Jurkat, and COS-7 cells. We found superior transfection activity of arginine peptides compared with commercially available efficient transfection agents. The expression of marker genes induced by arginine peptides was partially inhibited in the presence of heparan sulfate, chondroitin sulfate B and C, or both heparinase III and chondroitinase ABC. The transfection proficiency of these peptides was affected by endosomotropic reagent as well as low temperature (4 degrees C). Finally, we have investigated the potential of arginine peptides as a delivery agent for gene therapy, by attempting to deliver herpes simplex virus thymidine kinase (HSV-TK) gene into tumor cells. HSV-TK transfected tumor cells exhibited sensitivity to the antiviral drug ganciclovir (GCV), leading to cell death. Taken together, these data demonstrate that arginine peptide is proficient for transfection, indicating its potentially benefit to studies in gene therapy and gene delivery in a range of model organisms.

Heparan sulfate proteoglycan as a plasma membrane carrier

The plasma membrane defines the border of living cells and provides a barrier to extracellular components. Advances in molecular biology have resulted in the development of novel therapeutic strategies (e.g. gene therapy and cellular protein delivery) which rely on the entry of charged macromolecules into the intracellular compartment. Recent reports demonstrate an intriguing role for heparan sulfate proteoglycans in cellular internalization of viruses, basic peptides and polycation-nucleic-acid complexes and the possibility that they have important implications for gene transfer and protein delivery to mammalian cells. This review focuses on heparan sulfate proteoglycan as a plasma membrane carrier.

Cell transfection in vitro and in vivo with nontoxic TAT peptide-liposome-DNA complexes

Liposomes modified with TAT peptide (TATp-liposomes) showed fast and efficient translocation into the cell cytoplasm with subsequent migration into the perinuclear zone. TATp-liposomes containing a small quantity ( Collapse

Key Words

• gene delivery‖green fluorescent protein‖intracellular trafficking

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MESH Headings

• 3T3 Cells
• Animals
• DNA/genetics
• Freeze Fracturing
• Gene Products, tat/genetics
• Humans
• Liposomes
• Mice
• Microscopy, Electron
• Transfection
• Tumor Cells, Cultured

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Affiliation(s)

Vladimir P Torchilin Department of Pharmaceutical Sciences, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA.
Tatyana S Levchenko
Ram Rammohan
Natalia Volodina
Brigitte Papahadjopoulos-Sternberg
Gerard G M D'Souza

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Nitric oxide-dependent processing of heparan sulfate in recycling S-nitrosylated glypican-1 takes place in caveolin-1-containing endosomes

We have previously demonstrated intracellular degradation of the heparan sulfate side chains in recycling glypican-1 by heparanase and by deaminative cleavage at N-unsubstituted glucosamine with nitric oxide derived from intrinsic nitrosothiols (see Ding, K., Mani, K., Cheng, F., Belting, M. and Fransson, L.-A. (2002) J. Biol. Chem. 277, 33353-33360). To determine where and in what order events take place, we have visualized, by using confocal laser-scanning immunofluorescence microscopy, glypican-1 variants in unperturbed cells or arrested at various stages of processing. In unperturbed proliferating cells, glypican-1 was partly S-nitrosylated. Intracellular glypican-1 was enriched in endosomes, colocalized significantly with GM-1 ganglioside, caveolin-1, and Rab9-positive endosomes, and carried side chains rich in N-unsubstituted glucosamine residues. However, such residues were scarce in cell surface glypican-1. Brefeldin A-arrested glypican-1, which was non-S-nitrosylated and carried side chains rich in N-unsubstituted glucosamines, colocalized extensively with caveolin-1 but not with Rab9. Suramin, which inhibits heparanase, induced the appearance of S-nitrosylated glypican-1 in caveolin-1-rich compartments. Inhibition of deaminative cleavage did not prevent heparanase from generating heparan sulfate oligosaccharides that colocalized strongly with caveolin-1. Growth-quiescent cells displayed extensive NO-dependent deaminative cleavage of heparan sulfate-generating anhydromannose-terminating fragments that were partly associated with acidic vesicles. Proliferating cells generated such fragments during polyamine uptake. We conclude that recycling glypican-1 that is associated with caveolin-1-containing endosomes undergoes sequential N-desulfation/N-deacetylation, heparanase cleavage, S-nitrosylation, NO release, and deaminative cleavage of its side chains in conjunction with polyamine uptake.

Nuclear targeting of macromolecular polyanions by an HIV-Tat derived peptide. Role for cell-surface proteoglycans

New therapies based on gene transfer and protein delivery require a better understanding of the basic mechanisms of macromolecular membrane transport. We have studied cellular uptake of macromolecular polyanions, i.e. DNA and glycosaminoglycans, and a polybasic HIV-Tat derived peptide (GRKKRRQRRRPPQC) using fluorescence assisted cell sorting and confocal fluorescence microscopy. The transactivator of HIV transcription (Tat) peptide stimulated cellular uptake of both DNA and heparan sulfate in a time-, concentration-, and temperature-dependent manner. Peptide-polyanion complexes accumulated in large, acidic, cytoplasmic vesicles formed de novo. This was followed by transfer of polyanion into the nuclear compartment and subsequent disappearance of the endolysosomal vesicles. In the absence of polyanion the Tat peptide displayed rapid accumulation in the nuclear compartment. However, in the presence of polyanion the peptide was almost exclusively retained in cytoplasmic vesicles. Cell-surface proteoglycans played a pivotal role in the uptake of complexes exhibiting a relatively high peptide to polyanion ratio, corresponding to a net positive charge of the complexes. Uptake of polyanions per se or complexes with a relatively low peptide to polyanion ratio was favored by proteoglycan deficiency in the recipient cells, indicating the existence of distinct transport mechanisms. Moreover, expression of full-length HIV-Tat as well as exogenous addition of HIV-Tat peptide resulted in cellular accumulation of endogenous proteoglycans. We conclude that an HIV-Tat derived peptide efficiently targets extraneous DNA and glycosaminoglycans to the nuclear compartment and that proteoglycans serve a regulatory role in these processes, which may have implications for directed gene and drug delivery in vivo.

Extracellular and intracellular factors influencing gene transfection mediated by 1,4-dihydropyridine amphiphiles

Double-charged 1,4-dihydropyridine (1,4-DHP) amphiphiles have been shown to condense DNA and efficiently transfect it into cells in vitro [Hyvönen et al., Biochim. Biophys. Acta 1509 (2000) 451]. Alkyl chain length and buffering capacity at endosomal pH range (5.0-7.4) affected complexation and transfection activity. In this study we examined how those chemical modifications of amphiphile-DNA complexes (amphiplexes) affect their interactions with extracellular polyanions (glycosaminoglycans, albumin) and lipid bilayers, their cellular uptake and intracellular distribution. To evaluate cellular uptake, CV1-P cells were incubated with labeled DNA-amphiphile complexes and analyzed by flow cytometry. Confocal laser fluorescence microscopy was used to investigate the intracellular distribution of amphiplexes. The results showed that biophysical properties of compounds can be changed by slight structural modifications. These factors determine the intracellular kinetics and transfection efficacy of the compounds. Some extracellular glycosaminoglycans and serum interfere with 1,4-DHP-amphiphile-mediated transfection by destabilizing the amphiplexes. Neither high cellular uptake, membrane destabilizing activity nor buffering capacity alone is adequate for high transfection efficacy. The activity results from complex interplay of various factors that determine intracellular kinetics and, consequently, transfection.

High-level and high-throughput recombinant protein production by transient transfection of suspension-growing human 293-EBNA1 cells

A scalable transfection procedure using polyethylenimine (PEI) is described for the human embryonic kidney 293 cell line grown in suspension. Green fluorescent protein (GFP) and human placental secreted alkaline phosphatase (SEAP) were used as reporter genes to monitor transfection efficiency and productivity. Up to 75% of GFP-positive cells were obtained using linear or branched 25 kDa PEI. The 293 cell line and two genetic variants, either expressing the SV40 large T-antigen (293T) or the Epstein-Barr virus (EBV) EBNA1 protein (293E), were tested for protein expression. The highest expression level was obtained with 293E cells using the EBV oriP-containing plasmid pCEP4. We designed the pTT vector, an oriP-based vector having an improved cytomegalovirus expression cassette. Using this vector, 10- and 3-fold increases in SEAP expression was obtained in 293E cells compared with pcDNA3.1 and pCEP4 vectors, respectively. The presence of serum had a positive effect on gene transfer and expression. Transfection of suspension-growing cells was more efficient with linear PEI and was not affected by the presence of medium conditioned for 24 h. Using the pTT vector, >20 mg/l of purified His-tagged SEAP was recovered from a 3.5 l bioreactor. Intracellular proteins were also produced at levels as high as 50 mg/l, representing up to 20% of total cell proteins.

Extracellular glycosaminoglycans modify cellular trafficking of lipoplexes and polyplexes

It has been shown that extracellular glycosaminoglycans (GAGs) limit the gene transfer by cationic lipids and polymers. The purpose of this study was to clarify how interactions with anionic GAGs (hyaluronic acid and heparan sulfate) modify the cellular uptake and distribution of lipoplexes and polyplexes. Experiments on cellular DNA uptake and GFP reporter gene expression showed that decreased gene expression can rarely be explained by lower cellular uptake. In most cases, the cellular uptake is not changed by GAG binding to the lipoplexes or polyplexes. Reporter gene expression is decreased or blocked by heparan sulfate, but it is increased by hyaluronic acid; this suggests that intracellular factors are involved. Confocal microscopy experiments demonstrated that extracellular heparan sulfate and hyaluronic acid are taken into cells both with free and DNA-associated carriers. We conclude that extracellular GAGs may alter both the cellular uptake and the intracellular behavior of the DNA complexes.

The potential role of proteoglycans in cationic lipid-mediated gene delivery. Studies of the interaction of cationic lipid-DNA complexes with model glycosaminoglycans

Recent evidence supports a role for proteoglycans in polycation-mediated gene delivery. Therefore, the interaction of glycosaminoglycans with cationic lipid-DNA complexes (CLDCs) has been characterized using a combination of biophysical approaches. At low ionic strength, CLDCs bind to heparin-derivatized Sepharose particles, with the ratio of cationic lipid to DNA controlling the binding. Incorporation of the helper lipids cholesterol or 1,2-dioleoyl-phosphatidylethanolamine increases the amount of bound CLDC. Heparin also induces the aggregation of CLDCs, with cholesterol reducing this effect. Isothermal titration calorimetry demonstrates an endothermic heat for the binding of heparin to CLDCs at low ionic strength, whereas circular dichroism studies suggest a heparin-stimulated release of DNA from CLDCs at a greater than 20-fold charge excess. Increasing the ionic strength to 0.11 reduces CLDC binding to heparin beads, and greatly enhances the release of DNA from CLDCs by heparin. The ability of the cell surface glycosaminoglycan heparan sulfate to release DNA from CLDCs is more sensitive than heparin to the incorporation of the cholesterol or 1,2-dioleoyl-phosphatidylethanolamine. Titration calorimetry reveals an exothermic heat for the interaction glycosaminoglycans with CLDCs at higher ionic strength. These results are consistent with the direct involvement of proteoglycans in transfection.

Mechanism of lipoplex gene delivery in mouse lung: binding and internalization of fluorescent lipid and DNA components

We introduce a lung inflation-fixation protocol to examine the distribution and gene transfer efficiency of fluorescently tagged lipoplexes using fluorescence confocal microscopy within thick lung tissue sections. Using this technique, we tested the hypothesis that factors related to lipoplex distribution were the predominant reason that intravenous (i.v.) administration of lipoplex was superior to intratracheal (i.t.) administration for gene transfer in the murine lung. Lipoplex distribution was analyzed using digitized images of overlapping fields, reconstructed to view an entire lung lobe. Intravenously administered lipoplexes were confined to the capillary network and homogenously distributed throughout the lung lobe. In contrast, i.t. administration resulted in regional distribution of lipoplex, concentrated around bronchioles and distal airways. Not all the bronchioles were stained with lipoplex, suggesting that the airway-administered solution became channeled through certain bronchiolar pathways. A fluorescent oligonucleotide was used as a marker for cytoplasmic release of nucleic acids. Quantification of the resulting fluorescent nuclei was used to define the relationship between cytoplasmic release of nucleic acids and gene expression. Endothelial cells were stained after i.v. administration, and epithelial cells were stained after i.t. administration. The delivery of nucleic acids was also more homogeneous with i.v. administration of lipoplex than with i.t. administration. After i.t. administration, it was notable that high concentrations of fluorescent nuclei correlated with low GFP expression. This suggested that toxicity was associated with high local concentrations of cationic lipoplexes. The ratio of GFP-expressing cells to fluorescent nuclei indicated that capillary endothelial cells were more efficient in gene expression per delivery event than were pulmonary epithelial cells. Thus, the greater gene expression efficiency of i.v. administered lipoplexes was due not only to the initial distribution but also to the greater efficiency of the vascular endothelial cells to appropriately traffic and express the foreign gene.