Cellular gene dose and kinetics of gene expression in mouse livers transfected by high-volume tail-vein injection of naked DNA

In Vivo Tissue-Specific DNA Demethylation in Mouse Liver Through a Hydrodynamic Tail Vein Injection

A new technique called the dCas9-SunTag and scFv-TET1CD epigenome editing system has recently been developed to edit the DNA methylation status of specific genes. The transfection of an all-in-one vector containing this system into cells is feasible and induces the DNA demethylation of specific genes; however, due to the large size of the vector, difficulties are associated with its introduction into mice. We herein used a hydrodynamic tail vein injection (HTVi) to introduce the all-in-one vector into mice for in vivo epigenome editing. HTVi needs to be considered for inducing the targeted DNA demethylation of particular genes in the mouse liver.

Targeted DNA demethylation of the Fgf21 promoter by CRISPR/dCas9-mediated epigenome editing

Recently, we reported PPARα-dependent DNA demethylation of the Fgf21 promoter in the postnatal mouse liver, where reduced DNA methylation is associated with enhanced gene expression after PPARα activation. However, there is no direct evidence for the effect of site-specific DNA methylation on gene expression. We employed the dCas9-SunTag and single-chain variable fragment (scFv)-TET1 catalytic domain (TET1CD) system to induce targeted DNA methylation of the Fgf21 promoter both in vitro and in vivo. We succeeded in targeted DNA demethylation of the Fgf 21 promoter both in Hepa1-6 cells and PPARα-deficient mice, with increased gene expression response to PPARα synthetic ligand administration and fasting, respectively. This study provides direct evidence that the DNA methylation status of a particular gene may determine the magnitude of the gene expression response to activation cues.

YAP determines the cell fate of injured mouse hepatocytes in vivo

The presence of senescent, transformed or damaged cells can impair tissue function or lead to tumorigenesis; therefore, organisms have evolved quality control mechanisms to eliminate them. Here, we show that YAP activation induced by inactivation of the Hippo pathway specifically in damaged hepatocytes promotes their selective elimination by using in vivo mosaic analysis in mouse liver. These damaged hepatocytes migrate into the hepatic sinusoids, undergo apoptosis and are engulfed by Kupffer cells. In contrast, YAP activation in undamaged hepatocytes leads to proliferation. Cellular stresses such as ethanol that damage both liver sinusoidal endothelial cells and hepatocytes switch cell fate from proliferation to migration/apoptosis in the presence of activated YAP. This involves the activation of CDC42 and Rac that regulate cell migration. Thus, we suggest that YAP acts as a stress sensor that induces elimination of injured cells to maintain tissue and organ homeostasis.

Senescent and injured cells affect tissue functions and can drive tumorigenesis. Thus, efficient elimination of these cells is pivotal for tissue integrity. Here Miyamura et al. show that YAP acts as a cellular stress sensor and promotes the elimination of damaged cells to maintain tissue homeostasis.

Effects of an intravitreal injection of interleukin-35-expressing plasmid on pro-inflammatory and anti-inflammatory cytokines

In order to explore the potential effects of interleukin (IL)-35 on IL-10, transforming growth factor-β (TGF-β), interferon-γ (INF)-γ, IL-12 and IL-17, a pcDNA3.1‑IL-35 plasmid was injected into the vitreous cavity of BALB/c mice. Enzyme-linked immunosorbent assay, western blot analysis and quantitative PCR analysis were performed to confirm the successful expression of IL-35. Slit-lamp biomicroscopy, hematoxylin and eosin staining and immunofluorescence were employed to detect the status of eyes, and western blot analysis was performed to examine the expression of corneal graft rejection-related cytokines. There were no abnormalities in the eyes pre-mydriasis or post-mydriasis and no injuries to the cornea or retina following the injection of IL-35-expressing plasmid. An immunofluorescence assay detected the positive expression of IL-35 in corneal epithelial cells from IL-35‑injected mice and negative staining in the control group. Further study revealed that IL-35 enhanced the expression of IL-10 and TGF-β which reached their highest levels at 1 and 2 weeks after injection, respectively (p<0.01). Moreover, the expression of INF-γ and IL-12 was decreased significantly at 2 weeks after the injection of IL-35-expressing plasmid (p<0.05), and the expression of IL-17 was suppressed notably at 4 weeks after the injection (p<0.05). The intravitreal injection of IL-35-expressing plasmid in mice downregulates the expression of pro-inflammatory cytokines and upregulates the expression of anti-inflammatory cytokines. Thus, IL-35 may further be assessed as a potential target for the treatment of corneal graft rejection.

Efficacy and safety of Sleeping Beauty transposon-mediated gene transfer in preclinical animal studies

Sleeping Beauty (SB) transposons have been effective in delivering therapeutic genes to treat certain diseases in mice. Hydrodynamic gene delivery of integrating transposons to 5-20% of the hepatocytes in a mouse results in persistent elevated expression of the therapeutic polypeptides that can be secreted into the blood for activity throughout the animal. An alternative route of delivery is ex vivo transformation with SB transposons of hematopoietic cells, which then can be reintroduced into the animal for treatment of cancer. We discuss issues associated with the scale-up of hydrodynamic delivery to the liver of larger animals as well as ex vivo delivery. Based on our and others' experience with inefficient delivery to larger animals, we hypothesize that impulse, rather than pressure, is a critical determinant of the effectiveness of hydrodynamic delivery. Accordingly, we propose some alterations in delivery strategies that may yield efficacious levels of gene delivery in dogs and swine that will be applicable to humans. To ready hydrodynamic delivery for human application we address a second issue facing transposons used for gene delivery regarding their potential to "re-hop" from one site to another and thereby destabilize the genome. The ability to correct genetic diseases through the infusion of DNA plasmids remains an appealing goal.

Expression and function of fibroblast growth factor (FGF) 7 during liver regeneration

BACKGROUND/AIM

Previous studies have shown that fibroblast growth factors (FGFs) are involved in the process of liver injury repair. Liver regeneration after partial hepatectomy (PH) is impaired in transgenic mice expressing dominant-negative FGFR2b in hepatocytes. Although FGF7, a ligand specifically bound to FGFR2b, is expressed by activated hepatic stellate cells (HSCs) in fibrotic livers, the expressions and functions of FGF7 and FGFR2b after PH remain unexplored. Therefore, this study sought to examine the potential role of FGF7 signaling during liver regeneration.

METHODS

We examined the expression of FGF7 and FGFR2b in normal and regenerating livers. Effects of FGF7 on hepatocytes were examined in vitro using primary hepatocyte culture with FGF7 recombinant protein and in vivo by hydrodynamic-based gene transfer method.

RESULTS

We found that FGF7 expression was increased according to the activation status of HSCs after PH. The receptor, FGFR2b, was also increased in hepatocytes during liver regeneration. In vitro treatment with FGF7 protein activated ERK1/2 and promoted proliferation of hepatocytes isolated from regenerating livers. In vivo overexpression of exogenous FGF7 could notably promote hepatic proliferation and activate MAPKs after PH.

CONCLUSION

This study suggests a role for activated HSC-expressed FGF7 in stimulating FGF signaling pathways in hepatocytes and regulating liver regeneration.

Immune activation and target organ damage are consequences of hydrodynamic treatment but not delivery of naked siRNAs in mice

Short-interfering RNAs (siRNAs), key mediators of RNA interference comprise a promising therapeutic tool, although side effects such as interferon (IFN) response are still not perfectly understood. Further, delivery to target organs is a major challenge, possibly associated with side effects including immune activation or organ damage. We investigated whether immune activation as a consequence of double-stranded RNA induced IFN response (Jak/STAT pathway activation or cytokine production) or target organ damage is induced by in vivo low-volume (LV) or high-volume (HV) hydrodynamic delivery or treatment with naked siRNA. NMRI mice were injected with naked siRNAs or saline by hydrodynamic injection (HDI) and positive control mice received polyinosinic-polycytidilic acid (poly I:C). LV (1 mL/mouse) and HV (10% of body weight) HDI were compared. After LV HDI, STAT1 and OAS1 gene expression inflammatory cytokine plasma levels and target organ injury were assessed. LV HDI induced slight alanine aminotransferase elevation and mild hepatocyte injury, whereas HV HDI resulted in high ALAT level and extensive hepatocyte necrosis. STAT1 or OAS1 was not induced by LV siRNA; however, HV saline led to a time-dependent slight increase in gene expression. Inflammatory cytokine plasma level and organ histology and functional parameters demonstrated no damage following LV HDI with or without siRNA. Our data demonstrate that naked siRNAs may be harnessed, without the induction of IFN response or immune activation, and that LV HDI is preferable, because HV HDI may cause organ damage.

Kinetics and longevity of ΦC31 integrase in mouse liver and cultured cells

The ΦC31 integrase system provides genomic integration of plasmid DNA that may be useful in gene therapy. For example, the ΦC31 system has been used in combination with hydrodynamic injection to achieve long-term expression of factor IX in mouse liver. However, a concern is that prolonged expression of ΦC31 integrase within cells could potentially stimulate chromosome rearrangements or an immune response. Western blot and immunofluorescence analyses were performed to investigate the duration of ΦC31 integrase expression in mouse liver. Integrase was expressed within 2 to 3 hr after hydrodynamic injection of a plasmid expressing ΦC31 integrase. Expression peaked between 8 and 16 hr and fell to background levels by 24-48 hr postinjection. Analysis of the amount of integrase plasmid DNA present in the liver over time suggested that the brief period of integrase expression could largely be accounted for by rapid loss of the bulk of the plasmid DNA, as well as by silencing of plasmid expression. PCR analysis of integration indicated that ΦC31 integrase carried out genomic integration of a codelivered attB-containing plasmid by 3 hr after plasmid injection. Integrase was expressed for longer times and at higher levels in transfected cultured cells compared with liver. Inhibitor studies suggested that the enzyme had a short half-life and was degraded by the 26S proteasome. The short duration of integrase expression in liver and rapid integration reaction appear to be features favorable for use in gene therapy.

Duration of expression and activity of Sleeping Beauty transposase in mouse liver following hydrodynamic DNA delivery

The Sleeping Beauty (SB) transposon system can direct integration of DNA sequences into mammalian genomes. The SB system comprises a transposon and transposase that "cuts" the transposon from a plasmid and "pastes" it into a recipient genome. The transposase gene may integrate very rarely and randomly into genomes, which has led to concerns that continued expression might support continued remobilization of transposons and genomic instability. Consequently, we measured the duration of SB11 transposase expression needed for remobilization to determine whether continued expression might be a problem. The SB11 gene was expressed from the plasmid pT2/mCAGGS-Luc//UbC-SB11 that contained a luciferase expression cassette in a hyperactive SB transposon. Mice were imaged and killed at periodic intervals out to 24 weeks. Over the first 2 weeks, the number of plasmids with SB11 genes and SB11 mRNA dropped about 90 and 99.9%, respectively. Expression of the luciferase reporter gene in the transposon declined about 99% and stabilized for 5 months at nearly 1,000-fold above background. In stark contrast, transposition-supporting levels of SB11 mRNA lasted only about 4 days postinfusion. Thus, within the limits of current technology, we show that SB transposons appear to be as stably integrated as their viral counterparts.

High volume naked DNA tail-vein injection restores liver function in Fah-knock out mice

BACKGROUND

Despite pharmaceutical treatment with NTBC (2-2-nitro-4-fluoromethylbenzoyl-1,3-cyclohexanedione), a high incidence of liver malignancies occur in humans and mice suffering from hereditary tyrosinemia type 1 (HT1) caused by mutation of the fumarylacetoacetate hydrolase (fah) gene.

METHODS

To evaluate the efficacy of a definitive treatment for HT1, we transfected fah knockout mice with naked plasmid DNA using high volume tail-vein injection. This approach was chosen to reduce the occurrence of insertional mutagenesis that is frequently observed when using other (retro-)viral vectors. To prolong gene expression, the fah gene was cloned between adeno-associated virus (AAV)-specific inverted terminal repeats (ITRs).

RESULTS

All animals treated with high volume plasmid DNA injections could be successfully weaned off NTBC and survived in the long term without any further pharmacological support. Up to 50% fah positive hepatocytes were detected in livers of naked plasmid DNA-treated animals and serum liver function tests approximated those of wild-type controls.

CONCLUSIONS

Naked plasmid DNA transfection offers a promising alternative treatment for HT1. Minimizing side-effects makes this approach especially appealing.

Effect of nuclear localization and hydrodynamic delivery-induced cell division on phiC31 integrase activity

Phage φC31 integrase is a recombinase that can be expressed in mammalian cells to integrate plasmids carrying an attB sequence into the genome at specific pseudo attP locations. We demonstrate by immunofluoresence that wild-type φC31 integrase is cytoplasmic and that addition of a SV40 nuclear localization signal (NLS) localizes φC31 integrase to the nucleus. Unexpectedly, the NLS depressed integration efficiency in HeLa cells and provided no benefit when used to integrate the human Factor IX (hFIX) gene into mouse liver. Since breakdown of the nuclear membrane during mitosis could allow cytoplasmic integrase access to the chromosomes, we analyzed whether cell division was required for integration into liver cells in vivo. Hepatocytes were labeled with iododeoxyuridine to mark cells that underwent DNA replication during the week following hydrodynamic injection. Hydrodynamic delivery led to DNA replication in one-third of hepatocytes. Approximately 3 out of 4 cells having φC31 integrase-mediated stable hFIX expression did not undergo replication, indicating that cell division was not required for integrase function in liver. Therefore, although the bulk of φC31 integrase protein appears to be cytoplasmic in mammalian cells, integration can still occur in the nucleus, even without cell division.

Systemic correction of storage disease in MPS I NOD/SCID mice using the sleeping beauty transposon system

The Sleeping Beauty (SB) transposon system is a nonviral vector that directs transgene integration into vertebrate genomes. We hydrodynamically delivered SB transposon plasmids encoding human alpha-L-iduronidase (hIDUA) at two DNA doses, with and without an SB transposase gene, to NOD.129(B6)-Prkdc(scid) IDUA(tm1Clk)/J mice. In transposon-treated, nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with mucopolysaccharidosis type I (MPS I), plasma IDUA persisted for 18 weeks at levels up to several hundred-fold wild-type (WT) activity, depending on DNA dose and gender. IDUA activity was present in all examined somatic organs, as well as in the brain, and correlated with both glycosaminoglycan (GAG) reduction in these organs and level of expression in the liver, the target of transposon delivery. IDUA activity was higher in the treated males than in females. In females, omission of transposase source resulted in significantly lower IDUA levels and incomplete GAG reduction in some organs, confirming the positive effect of transposition on long-term IDUA expression and correction of the disease. The SB transposon system proved efficacious in correcting several clinical manifestations of MPS I in mice, including thickening of the zygomatic arch, hepatomegaly, and accumulation of foamy macrophages in bone marrow and synovium, implying potential effectiveness of this approach in treatment of human MPS I.

A tunable synthetic mammalian oscillator

Autonomous and self-sustained oscillator circuits mediating the periodic induction of specific target genes are minimal genetic time-keeping devices found in the central and peripheral circadian clocks. They have attracted significant attention because of their intriguing dynamics and their importance in controlling critical repair, metabolic and signalling pathways. The precise molecular mechanism and expression dynamics of this mammalian circadian clock are still not fully understood. Here we describe a synthetic mammalian oscillator based on an auto-regulated sense-antisense transcription control circuit encoding a positive and a time-delayed negative feedback loop, enabling autonomous, self-sustained and tunable oscillatory gene expression. After detailed systems design with experimental analyses and mathematical modelling, we monitored oscillating concentrations of green fluorescent protein with tunable frequency and amplitude by time-lapse microscopy in real time in individual Chinese hamster ovary cells. The synthetic mammalian clock may provide an insight into the dynamics of natural periodic processes and foster advances in the design of prosthetic networks in future gene and cell therapies.

New methodologies to characterize the effectiveness of the gene transfer mediated by DNA-chitosan nanoparticles

In this work three DNA-chitosan nanoparticle formulations (Np), differing in the molecular weight (MW; 150 kDa, 400 kDa, and 600 kDa) of the polysaccharide, were prepared and administered by two different administration routes: the hydrodynamics-based procedure and the intraduodenal injection. After the hydrodynamic injection, DNA-chitosan nanoparticles were predominantly accumulated in the liver, where the transgene was expressed during at least 105 days. No significant influence of MW was observed on the levels of luciferase expression. The curves of bioluminescence versus time obtained using the charge-coupled device (CCD) camera were described and divided in three phases: (i) the initial phase, (ii) the sustained release step and (iii) the decline phase (promotor inactivation, immunological and physiological processes). From these curves, which describe the transgene expression profile, the behavior of the different formulations as gene delivery systems was characterized. Therefore, the following parameters such as C_max (maximum level of detected bioluminescence), AUC (area under the bioluminescence-time curve) and MET (mean time of the transgene expression) were calculated. This approach offers the possibility of studying and comparing transgene expression kinetics among a wide variety of gene delivery systems. Finally, the intraduodenal administration of naked DNA permitted the gene transfer in a dose dependent manner quantifiable with the CCD camera within 3 days. Nevertheless, the same administration procedure of the three formulations did not improve the levels of transgene expression obtained with naked DNA. This fact could be explained by the rapid physiological turn-over of enterocytes and by the ability of chitosan nanoparticles to control the DNA release.

Systemic siRNA delivery via hydrodynamic intravascular injection

The main barrier to the use of RNAi in mammalian systems is the difficulty in delivering siRNA or shRNA to the appropriate tissues. Although progress has been made in this area, many of the technologies developed require specialized expertise and reagents that are beyond the reach of most investigators. In contrast, the hydrodynamic injection technique is simple to perform and enables highly efficient delivery of naked, unmodified siRNA to a number of tissues, especially the liver. This review describes the development of the technique and explores the possible mechanisms that enable uptake of siRNA to biological effect. Examples of the use of hydrodynamic injection in animal models of disease and for the study of gene function are presented and discussed.

Preferential delivery of the Sleeping Beauty transposon system to livers of mice by hydrodynamic injection

Nonviral, DNA-mediated gene transfer is an alternative to viral delivery systems for expressing new genes in cells and tissues. The Sleeping Beauty (SB) transposon system combines the advantages of viruses and naked DNA molecules for gene therapy purposes; however, efficacious delivery of DNA molecules to animal tissues can still be problematic. Here we describe the hydrodynamic delivery procedure for the SB transposon system that allows efficient delivery to the liver in the mouse. The procedure involves rapid, high-pressure injection of a DNA solution into the tail vein. The overall procedure takes <1 h although the delivery into one mouse requires only a few seconds. Successful injections result in expression of the transgene in 5-40% of hepatocytes 1 d after injection. Several weeks after injection, transgene expression stabilizes at approximately 1% of the level at 24 h, presumably owing to integration of the transposons into chromosomes.

N/A

N/A

Mechanism of plasmid delivery by hydrodynamic tail vein injection. II. Morphological studies

BACKGROUND

The efficient delivery of plasmid DNA (pDNA) to hepatocytes by a hydrodynamic tail vein (HTV) procedure has greatly popularized the use of naked nucleic acids. The hydrodynamic process renders onto the tissue increased physical forces in terms of increased pressures and shear forces that could lead to transient or permanent membrane damage. It can also trigger a series of cellular events to seal or reorganize the stretched membrane. Our goal was to study the uptake mechanism by following the morphological changes in the liver and correlate these with the fate of the injected plasmid DNA.

METHODS

We utilized both light microscopic (LM) and electron microscopic (EM) techniques to determine the effect of the HTV procedure on hepatocytes and non-parenchymal cells at various times after injection. The LM studies used paraffin-embedded livers with hematoxylin and eosin (H&E) staining. The immune-EM studies used antibodies labeled with sub-nanometer gold particles followed by silver enhancement to identify the location of injected pDNA at the subcellular level. The level of overall damage to liver cells was estimated based on alanine aminotransferase (ALT) release and clearance.

RESULTS

Both the LM and EM results showed the appearance of large vesicles in hepatocytes as early as 5 min post-injection. The number of vesicles decreased by 20-60 min. Plasmid DNA molecules often appeared to be associated with or inside such vesicles. DNA could also be detected in the space of Disse, in the cytoplasm and in nuclei. Non-parenchymal cells also contained DNA, but HTV-induced vesicles could not be observed in them.

CONCLUSIONS

Our studies suggest an alternative or additional pathway for naked DNA into hepatocytes besides direct entry via membrane pores. It may be difficult to prove which of these pathways lead to gene expression, but the membrane pore hypothesis alone appears insufficient to explain why expression happens preferentially in hepatocytes. Further study is needed to delineate the importance of each of these putative pathways and their interrelationship in enabling oligonucleotide (siRNA) activity and pDNA expression.

Mechanism of plasmid delivery by hydrodynamic tail vein injection. I. Hepatocyte uptake of various molecules

BACKGROUND

The hydrodynamic tail vein (HTV) injection of naked plasmid DNA is a simple yet effective in vivo gene delivery method into hepatocytes. It is increasingly being used as a research tool to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models. A greater understanding of its mechanism will aid these efforts and has relevance to macromolecular and nucleic acid delivery in general.

METHODS

In an attempt to explore how naked DNA enters hepatocytes the fate of a variety of molecules and particles was followed over a 24-h time frame using fluorescence microscopy. The uptake of some of these compounds was correlated with marker gene expression from a co-injected plasmid DNA. In addition, the uptake of the injected compounds was correlated with the histologic appearance of hepatocytes.

RESULTS

Out of the large number of nucleic acids, peptides, proteins, inert polymers and small molecules that we tested, most were efficiently delivered into hepatocytes independently of their size and charge. Even T7 phage and highly charged DNA/protein complexes of 60-100 nm in size were able to enter the cytoplasm. In animals co-injected with an enhanced yellow fluorescent protein (EYFP) expression vector and fluorescently labeled immunoglobulin (IgG), hepatocytes flooded with large amounts of IgG appeared permanently damaged and did not express EYFP-Nuc. Hepatocytes expressing EYFP had only slight IgG uptake. In contrast, when an EYFP expression vector was co-injected with a fluorescently labeled 200-bp linear DNA fragment, both were mostly (in 91% of the observed cells) co-localized to the same hepatocytes 24 h later.

CONCLUSIONS

The appearance of permanently damaged cells with increased uptake of some molecules such as endogenous IgG raised the possibility that a molecule could be present in a hepatocyte but its transport would not be indicative of the transport process that can lead to foreign gene expression. The HTV procedure enables the uptake of a variety of molecules (as previous studies also found), but the uptake process for some of these molecules may be associated with a more disruptive process to the hepatocytes that is not compatible with successful gene delivery.

Increased hepatic transduction with reduced systemic dissemination and proinflammatory cytokines following hydrodynamic injection of helper-dependent adenoviral vectors

Hydrodynamic injection of helper-dependent adenoviral vectors (HDAd) in mice results in increased hepatic transduction, reduced splenic and pulmonary transduction, and reduced levels of the proinflammatory cytokines IL-6 and IL-12 compared to conventional injection. These results indicate that hepatic transduction by HDAd, at least alone, does not necessarily provoke a severe innate inflammatory response. Instead, they suggest that systemic vector dissemination may play a major role in the severity of the innate inflammatory response. These results further suggest that the safety and efficacy of HDAd-mediated, liver-directed gene therapy may be improved if the vector could be preferentially, if not exclusively, targeted to liver.

Expression of foreign genes in chicks by hydrodynamics-based naked plasmid transfer in vivo

The study of gene function in vivo is considered one of the top achievements of modern biology, inasmuch as it provides tools to study gene function in the context of the whole animal. In chickens, techniques of DNA-mediated gene transfer are less advanced than in other animal or livestock models, and remain a significant challenge. The study presented here is the first to show that a hydrodynamics-based gene-transfer technique, originally developed for naked DNA transfer in mice, can be applied to chickens. Rapid injection of naked plasmids containing expression cassettes into the jugular vein of 6- to 10-day-old chicks resulted in specific expression of the transgenes. A CMV promoter-driven luciferase reporter gene was expressed at significant levels in the liver during the first 3 days post-injection with lower levels also detected in the kidney. Significantly, all injected birds showed detectable levels of luciferase expression. Similarly, injection of a plasmid containing the secreted human coagulation factor IX (hFIX) gene under the control of human alpha-1-anti-trypsin promoter resulted in detectable levels of the hFIX in the plasma during the first 2 days post-injection. The method described herein has the potential for a quick and simple route for gain and loss-of function experiments in chicken liver and kidney, as well as for studying systemic effects of secreted proteins and hormones.

Inhibition of hepatitis viral replication by siRNA

Small interfering RNA (siRNA)-mediated sequence-specific gene silencing is a powerful tool to inhibit endogenous and exogenous gene expression, and it holds great potential to prevent and eradicate viral infection, for which existing therapy is inadequate, such as HIV, hepatitis B virus (HBV) and hepatitis C virus (HCV). A number of studies have documented the effectiveness of siRNA against HBV or HCV at various regions of the viral genome in infected human hepatoma cell lines. Selected siRNA may reduce the production of viral replicons, as well as structural or non-structural proteins by > 90%. Only a few in vivo studies that demonstrated the efficacy of siRNA in the suppression of HBV replication in mice are available. Thus, reliable models of HBV and HCV infection in small animals or non-human primates are needed to evaluate the delivery and efficacy of siRNA as a therapeutic modality for viral hepatitis.

The mechanism of naked DNA uptake and expression

The administration of naked nucleic acids into animals is increasingly being used as a research tool to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models (Herweijer and Wolff, 2003; Hodges and Scheule, 2003). It is also being used in several human clinical trials for genetic vaccines, Duchenne muscular dystrophy, peripheral limb ischemia, and cardiac ischemia (Davis et al., 1996; Romero et al., 2002; Tsurumi et al., 1997). Naked DNA is an attractive non-viral vector because of its inherent simplicity and because it can easily be produced in bacteria and manipulated using standard recombinant DNA techniques. It shows very little dissemination and transfection at distant sites following delivery and can be readministered multiple times into mammals (including primates) without inducing an antibody response against itself (i.e., no anti-DNA antibodies generated) (Jiao et al., 1992). Also, contrary to common belief, long-term foreign gene expression from naked plasmid DNA (pDNA) is possible even without chromosome integration if the target cell is postmitotic (as in muscle) or slowly mitotic (as in hepatocytes) and if an immune reaction against the foreign protein is not generated (Herweijer et al., 2001; Miao et al., 2000; Wolff et al., 1992; Zhang et al., 2004). With the advent of intravascular and electroporation techniques, its major restriction--poor expression levels--is no longer limiting and levels of foreign gene expression in vivo are approaching what can be achieved with viral vectors. Direct in vivo gene transfer with naked DNA was first demonstrated when efficient transfection of myofibers was observed following injection of mRNA or pDNA into skeletal muscle (Wolff et al., 1990). It was an unanticipated finding in that the use of naked nucleic acids was the control for experiments designed to assess the ability of cationic lipids to mediate expression in vivo. Subsequent studies also found foreign gene expression after direct injection in other tissues such as heart, thyroid, skin, and liver (Acsadi et al., 1991; Hengge et al., 1996; Kitsis and Leinwand, 1992; Li et al., 1997; Sikes and O'Malley 1994; Yang and Huang, 1996). However, the efficiency of gene transfer into skeletal muscle and these other tissues by direct injection is relatively low and variable, especially in larger animals such as nonhuman primates (Jiao et al., 1992). After our laboratory had developed novel transfection complexes of pDNA and amphipathic compounds and proteins, we sought to deliver them to hepatocytes in vivo via an intravascular route into the portal vein. Our control for these experiments was naked pDNA and we were once again surprised that this control group had the highest expression levels (Budker et al., 1996; Zhang et al., 1997). High levels of expression were achieved by the rapid injection of naked pDNA in relatively large volumes via the portal vein, the hepatic vein, and the bile duct in mice and rats. The procedure also proved effective in larger animals such as dogs and nonhuman primates (Eastman et al., 2002; Zhang et al., 1997). The next major advance was the demonstration that high levels of expression could also be achieved in hepatocytes in mice by the rapid injection of naked DNA in large volumes simply into the tail vein (Liu et al., 1999; Zhang et al., 1999). This hydrodynamic tail vein (HTV) procedure is proving to be a very useful research tool not only for gene expression studies, but also more recently for the delivery of small interfering RNA (siRNA) (Lewis et al., 2002; McCaffrey et al., 2002). The intravascular delivery of naked pDNA to muscle cells is also attractive particularly since many muscle groups would have to be targeted for intrinsic muscle disorders such as Duchenne muscular dystrophy. High levels of gene expression were first achieved by the rapid injection of naked DNA in large volumes via an artery route with both blood inflow and outflow blocked surgically (Budker et al., 1998; Zhang et al., 2001). Intravenous routes have also been shown to be effective (Hagstrom et al., 2004; Liang et al., 2004; Liu et al., 2001). For limb muscles, the ability to use a peripheral limb vein for injection and a proximal, external tourniquet to block blood flow renders the procedure to be clinically viable. This review concerns itself with the mechanism by which naked DNA is taken up by cells in vivo. A greater understanding of the mechanisms involved in the uptake and expression of naked DNA, and thus connections between postulated mechanisms and expression levels, is emphasized. Inquiries into the mechanism not only aid these practical efforts, but are also interesting on their own account with relevance to viral transduction and cellular processes. The delivery to hepatocytes is first discussed given the greater information available for this process, and then uptake by myofibers is discussed.

Liver-targeted gene therapy by SV40-based vectors using the hydrodynamic injection method

Efficient reconstitution of defective genes in hepatocytes could be used to treat various liver and systemic diseases through gene therapy. To explore the potential of SV40-based vectors in liver gene therapy, we constructed SV/luc, an SV40 T-antigen replacement transduction vector, that was propagated on COS and COT cells, which supply the SV40 T-antigen in trans. For liver targeting, BALB/C mice were injected via the tail vein with SV/luc stocks containing 3 x 10(6) to 10(8) transducing units in a volume of 1-2 ml. Luciferase activity was monitored with a light-detection cooled charged-coupled device (CCCD) camera, which enables continuous in vivo measurement of luc expression. The SV40 vector proved to be efficient in gene delivery to the liver, leading to long-term (> or =107 days) transgene expression in hepatocytes. Optimal results were obtained with 3 x 10(6) to 3 x 10(7) transducing units. The hydrodynamic vector delivery method caused transient liver inflammatory changes, with full recovery within days. Low levels of SV40-neutralizing antibodies were detected in the sera of treated mice; however, there was no indication of vector or transgene-specific cellular immune responses. Vectors packaged in vitro, using recombinant capsid proteins and plasmid DNA, were also effective in liver transduction. These results suggest that SV40 vectors may be useful for liver gene therapy.

The hydrodynamics-based procedure for controlling the pharmacokinetics of gene medicines at whole body, organ and cellular levels

Hydrodynamics-based gene delivery, involving a large-volume and high-speed intravenous injection of naked plasmid DNA (pDNA), gives a significantly high level of transgene expression in vivo. This has attracted a lot of attention and has been used very frequently as an efficient, simple and convenient transfection method for laboratory animals. Until recently, however, little information has been published on the pharmacokinetics of the injected DNA molecules and of the detailed mechanisms underlying the efficient gene transfer. We and other groups have very recently demonstrated that the mechanism for the hydrodynamics-based gene transfer would involve, in part, the direct cytosolic delivery of pDNA through the cell membrane due to transiently enhanced permeability. Along with the findings in our series of studies, this article reviews the cumulative reports and other intriguing information on the controlled pharmacokinetics of naked pDNA in the hydrodynamics-based gene delivery. In addition, we describe various applications reported so far, as well as the current attempts and proposals to develop novel gene medicines for future gene therapy using the concept of the hydrodynamics-based procedure. Furthermore, the issues associated with the clinical feasibility of its seemingly invasive nature, which is probably the most common concern about this hydrodynamics-based procedure, are discussed along with its future prospects and challenges.

Gene Expression in Primary Cultured Mouse Hepatocytes with a Cationic Liposomal Vector, TFL-3: Comparison with Rat Hepatocytes

We recently reported that a cationic liposomal vector, TFL-3, could be used to achieve significant gene expression in primary cultured rat hepatocytes (Nguyen et al., Biol. Pharm. Bull., 26, 880-885 (2003)). A combination of hepatocyte transplantation and hepatocyte-targeted gene transfer represents a potentially important strategy for expanding treatment options for liver disease. A widely applied approach to support cross-species is necessary before human applications can be realized. Therefore, in this study, we examined the utility of TFL-3 in another species of rodent hepatocytes, namely mouse hepatocytes. Gene expression in mouse hepatocytes by TFL-3 was successful and the level was higher than those in rat hepatocytes that we recently reported on. Interestingly, it appears that both the degree and rate of gene expression were dependent on the incubation time prior to lipofection as well as on the density of cells per dish, but these parameters were independent of the amount of pDNA associated with the cells. These significantly suggest that the culture time prior to and following lipofection, which are related to the biological condition of the cells, may be one of major factors that affect gene expression in hepatocytes and non- or less dividing cells.

Hydrodynamic Delivery

Hydrodynamic delivery has emerged as a near-perfect method for intracellular DNA delivery in vivo. For gene delivery to parenchymal cells, only essential DNA sequences need to be injected via a selected blood vessel, eliminating safety concerns associated with current viral and synthetic vectors. When injected into the bloodstream, DNA is capable of reaching cells in the different tissues accessible to the blood. Hydrodynamic delivery employs the force generated by the rapid injection of a large volume of solution into the incompressible blood in the circulation to overcome the physical barriers of endothelium and cell membranes that prevent large and membrane-impermeable compounds from entering parenchymal cells. In addition to the delivery of DNA, this method is useful for the efficient intracellular delivery of RNA, proteins, and other small compounds in vivo. This review discusses the development, current application, and clinical potential of hydrodynamic delivery.

Phenotypic correction and long-term expression of factor VIII in hemophilic mice by immunotolerization and nonviral gene transfer using the Sleeping Beauty transposon system

Hemophilia A is a lead candidate for treatment by gene therapy because small increments in the missing secreted protein product, coagulation factor VIII (FVIII), would result in substantial clinical amelioration. Clinically relevant therapy might be achieved by stably delivering a human FVIII cDNA to correct the bleeding disorder. We used the Sleeping Beauty (SB) transposon, delivered as naked plasmid DNA by tail-vein injection, to integrate B-domain-deleted FVIII genes into the chromosomes of hemophilia A mice and correct the phenotype. Since FVIII protein is a neoantigen to these mice, sustaining therapeutic plasma FVIII levels was problematic due to inhibitory antibody production. We circumvented this problem by tolerizing 82% of neonates by a single facial-vein injection of recombinant FVIII within 24 hours of birth (the remaining 18% formed inhibitors). Achievement of high-level (10%-100% of normal) FVIII expression and phenotypic correction required co-injection of an SB transposase-expressing plasmid to facilitate transgene integration in immunotolerized animals. Linker-mediated polymerase chain reaction was used to clone FVIII transposon insertion sites from liver genomic DNA, providing molecular evidence of transposition. Thus, SB provides a nonviral means for sustained FVIII gene delivery in a mouse model of hemophilia A if the immune response is prevented.

Long-term Transgene Expression from Plasmid DNA Gene Therapy Vectors Is Negatively Affected by CpG Dinucleotides

CpG-reduced, CMV-based plasmid DNA constructs encoding human alpha-galactosidase A and factor IX were injected into C57Bl/6, BALB/c, and CD1 mice using hydrodynamics-based delivery of plasmid DNA (pDNA), and gene expression was monitored for 6 months. Linearized and supercoiled pDNAs were compared for their abilities to support long-term expression and to generate immune responses to the transgene product. In all mouse strains supercoiled CpG-reduced pDNA encoding alpha-galactosidase A and factor IX generated higher and more sustained levels of circulating gene product than their supercoiled CpG-replete analogs. Linearizing supercoiled CpG-reduced pDNA did not significantly increase levels of circulating gene product beyond levels supercoiled CpG-reduced pDNA could achieve. Linearizing supercoiled CpG-replete pDNA vectors significantly increased expression compared to their supercoiled CpG-replete analogs, but the increase was short-lived or subtherapeutic. Regardless of vector, liver depot expression did not elicit significant antibody responses to human alpha-galactosidase A or factor IX. Taken together, these data suggest that a clinically acceptable hydrodynamics-based approach targeting the liver combined with CpG-reduced pDNA vectors may represent a viable option for individuals with hemophilia, a lysosomal storage disease, or other disease in which prolonged depot expression of a therapeutic protein from the liver is desirable.

Low-Density Lipoprotein (LDL) Receptor/Transferrin Fusion Protein:In VivoProduction and Functional Evaluation as a Potential Therapeutic Tool for Lowering Plasma LDL Cholesterol

A soluble form of human low-density lipoprotein receptor (LDL-R) fused in frame with rabbit transferrin (LDL-Rs(hu)/Tf(rab)) is assessed in vivo as a therapeutic tool for lowering plasma LDL cholesterol. The cDNA encoding LDL-Rs(hu)/Tf(rab) is expressed in mice, using a hydrodynamics-based gene transfer procedure. The transgene is transcribed in the liver of transduced animals and the corresponding protein is secreted into the bloodstream. Circulating LDL-Rs(hu)/Tf(rab) binds LDL specifically, thus indicating that it is correctly processed through the cellular compartments in vivo. More importantly, the expression of LDL-Rs(hu)/Tf(rab) allows the removal of injected human (125)I-labeled LDL ((123)I-LDL) from the bloodstream of transduced CD1 mice, which show faster LDL plasma clearance, anticipating by approximately 90 min the same clearance value observed in control animals. A similar effect is observed in transduced LDL-R(-/-) mice, in which the clearance of injected human LDL depends solely on the presence of circulating LDL-Rs(hu) /Tf(rab). In these animals the extent of plasma LDL clearance is directly related to the concentration of LDL-Rs(hu)/Tf(rab) in the blood. Finally, LDL-Rs(hu)/Tf(rab) does not alter the pattern of LDL organ distribution: in transduced animals, as well as in control animals, liver and bladder are the predominantly labeled organs after (123)I-LDL injection. However, LDL-Rs(hu)/Tf(rab) has a quantitative effect on LDL tissue deposition: in treated animals LDL-Rs(hu)/Tf(rab) determines an increase in radioactivity in the liver at early times after (123)I-LDL injection and a progressive labeling of the bladder, starting 20 min after injection.

Overexpression of activin beta(C) or activin beta(E) in the mouse liver inhibits regenerative deoxyribonucleic acid synthesis of hepatic cells

Activins are dimeric growth factors composed of beta-subunits, four of which have been isolated so far. Whereas activin beta(A) and beta(B) are expressed in many tissues, the expression of activin beta(C) and beta(E) is confined to the liver. To date no biological role or activity has been assigned to activins formed from beta(C) or beta(E) subunits (activin C and E). Because activin A (beta(A)beta(A)), among its various functions in other tissues, appears to be a negative regulator of liver growth, we hypothesized a similar role for activin C and E. Using a nonviral gene transfer system we specifically delivered genes encoding activin beta(C), beta(E), or beta(A) to the mouse liver. The mRNA analysis and reporter gene coexpression both indicated a reproducible temporal and spatial transgene expression pattern. The effects of activin overexpression were studied in the context of a regenerative proliferation of hepatic cells, a result of the tissue damage associated with the hydrodynamics based gene transfer procedure. Activin beta(C), beta(E), or beta(A) expression, all temporarily inhibited regenerative DNA synthesis of hepatocytes and nonparenchymal cells, though to a varying degree. This first report of a biological activity of activin C and E supports an involvement in liver tissue homeostasis and further emphasizes the role of the growing activin family in liver physiology.

Inhibition of hepatitis B virus replication in vivo by nucleoside analogues and siRNA

BACKGROUND & AIMS

Hepatitis B virus (HBV) causes acute and chronic infections that may result in severe liver diseases. Animal models to study new treatment options in vivo have several drawbacks. Therefore, we were interested to establish a new small animal model in which HBV replication and especially new treatment options can be studied easily.

METHODS

Naked DNA of an HBV replication competent vector was transferred via tail vein into NMRI mice. HBV replication was studied in serum and liver of the animals. HBV replication was modulated by treatment through siRNA and nucleoside analogues.

RESULTS

Tail vein transfer of a HBV replication competent construct resulted in expression of HBV-specific transcripts in the liver, and up to 10% of hepatocytes became HBc- and HBsAg-positive. HBeAg, HBsAg, and viral DNA could be detected in the serum of the animals, followed by the induction of HBV-specific cellular immune responses. Nucleoside treatment of the mice resulted in reduced polymerase activity in the liver. Additionally, siRNA transfer in the animals led to a significant reduction of HBsAg and/or eventually HBeAg expression, which was dependent on the localization of the complementary sequence in the HBV genome.

CONCLUSIONS

We have established a mouse model to study HBV replication and to investigate new and existing treatment approaches in vivo. Interestingly, siRNA seems a promising innovative treatment option to inhibit specifically HBV replication in vivo.