An intracellular delivery method for siRNA by an arginine-rich peptide

RNA interference has recently become a useful research tool for the studies of gene functions, regulations, and therapies. The double-stranded RNA is utilized to induce the sequence-specific gene silencing. To achieve this goal of specific gene silencing, a proper delivery system of siRNA is highly demanded. A number of approaches for delivering siRNA have been explored over the last few years. In the present study, we demonstrated a simple peptide-based siRNA delivery system in mammalian cells. A GC-EGFP cell line stably expressing enhanced green fluorescent protein was established from stable transfection of human gastric carcinoma cells. The synthetic nona-arginine peptide, an arginine-rich intracellular delivery peptide, or called protein transduction domain peptide, could noncovalently form stable complexes with EGFP siRNA and deliver these mixtures into cells. After entry, siRNA appeared to stay in perinuclear regions within cell, and ultimately fulfilled its targeted egfp gene silencing. These data were in consonance with that RNA-induced silencing complex components could be also localized to these perinuclear regions, creating a focal point for RNA interference factories. In the future, this non-toxic peptide may be proved to be a useful tool for the delivery of exogenous siRNA in RNA interference research.     

基于核酸自组装纳米结构的siRNA药物递送研究进展

RNA干扰(RNA interference,RNAi)作为转录后调节机制,可靶向mRNA进行剪切降解从而发挥基因沉默效应.siRNA (small interference RNA)因其高效性和特异性而被广泛应用于药物研究中.目前,研究者们已开发了多种阳离子载体用于siRNA递送.但由于siRNA双链结构具有相对较强的刚性结构,且阴离子电荷密度较低,无法与阳离子载体形成稳定、致密的复合物,使得siRNA的应用仍面临诸多挑战,如细胞摄取率低、靶向特异性差、递送过程不稳定、潜在的细胞毒性以及易诱发免疫反应等.近年来,核酸自组装纳米结构由于其结构灵活且负电荷密度较高而受到广泛关注,有望实现siRNA药物的高效递送和基因沉默.本文综述了近年来基于核酸自组装纳米结构的siRNA递送的研究进展及其应用.     

A gene delivery system for insect cells mediated by arginine-rich cell-penetrating peptides

Most bioactive macromolecules, such as protein, DNA and RNA, basically cannot permeate into cells freely from outside the plasma membrane. Cell-penetrating peptides (CPPs) are a group of short peptides that possess the ability to traverse the cell membrane and have been considered as candidates for mediating gene and drug delivery into living cells. In this study, we demonstrate that three arginine-rich CPPs (SR9, HR9 and PR9) are able to form stable complexes with plasmid DNA and deliver DNA into insect Sf9 cells in a noncovalent manner. The transferred plasmid DNA containing enhanced green fluorescent protein (EGFP) and red fluorescent protein (RFP) coding regions could be expressed in cells functionally assayed at both the protein and RNA levels. Furthermore, treatment of cells with CPPs and CPP/DNA complexes resulted in a viability of 84-93% indicating these CPPs are not cytotoxic. These results suggest that arginine-rich CPPs appear to be a promising tool for insect transgenesis.     

RNA interference in pain research

Within the course of only the last few years, RNA interference (RNAi) has been established as a standard technology for investigation of protein function and target validation. The present review summarizes recent progress made in the application of RNAi in neurosciences with special emphasis on pain research. RNAi is a straightforward method to generate loss-of-function phenotypes for any gene of interest. In mammals, silencing is induced by small interfering RNAs (siRNAs), which have been shown to surpass traditional antisense molecules. Due to its high specificity, RNAi has the potential for subtype selective silencing of even closely related genes. One of the major challenges for in vivo investigations of RNAi remains efficient delivery of siRNA molecules to the relevant tissues and cells, particularly to the central nervous system. Various examples will be given to demonstrate that intrathecal application of siRNAs is a suitable approach to analyse the function of receptors or other proteins that are hypothesized to play an important role in pain signalling. Intensive efforts are currently ongoing to solve remaining problems such as the risk of off-target effects, the stability of siRNA molecules and their efficient delivery to the CNS. RNAi has thus demonstrated that it is an extremely valuable tool for the development of new analgesic drugs.     

抑制RNA沉默现象的机理及其在生物医学领域内的应用

RNA沉默在机体防御病毒入侵和调控基因表达中发挥着重要的作用,目前已成为一种有效的工具应用于基因功能研究和疾病治疗等领域.RNA沉默现象普遍存在于真核细胞中,然而在宿主与病毒漫长的进化过程中,病毒已经演化出一系列逃逸或抑制RNA沉默作用的方法和途径,使RNA沉默效果显著降低,另一方面,哺乳动物体细胞自身也存在调节RNA沉默功能从而使生命活动的调节更加精细完善.为了使RNA沉默发挥它的潜在效应,人们设计出一系列的策略针对抑制RNA沉默效应以达到弱化抑制的目的.全面总结抑制RNA沉默机制及其应用,从而使人们充分认识到使用RNA沉默技术时应考虑到存在的不利因素.     

Intracellular small interfering RNA delivery using genetically engineered double‐stranded RNA binding protein domain

Background

A variety of synthetic carriers, such as cationic polymers and lipids, have been used as nonviral carriers for small interfering RNA (siRNA) delivery. Although siRNA polyplexes and lipoplexes exhibited good gene silencing efficiencies, they often showed serious cytotoxicities, which are not useful for clinical applications. A double‐stranded RNA binding cellular protein with highly specific siRNA binding property and noncytotoxicity was used for siRNA delivery.

Methods

A double‐stranded RNA binding domain (dsRBD) of human double‐stranded RNA activated protein kinase R was genetically produced and utilized to complex siRNA for intracellular delivery. For characterization of the siRNA/dsRBD complexes, decomplexation assay and RNase protection assay were performed. Cytotoxicity and target gene inhibition ability were also examined using human carcinoma cell lines.

Results

The recombinantly produced polypeptide dsRBD exhibited its inherent binding activity for siRNA without sequence specificity, and the siRNA/dsRBD complexes protected siRNA from degradation by ribonucleases. Green fluorescent protein (GFP) siRNA/dsRBD complexes showed prominent down‐regulation of a target GFP gene, when an endosomal escape function was supplemented by addition of a fusogenic peptide, KALA, in the formulation.

Conclusions

The results suggest that dsRBD‐based protein carriers could be successfully applied for a wide range of therapeutic siRNAs for intracellular gene inhibition without showing any cytotoxicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Transfection of "naked" siRNA results in endosomal uptake and metabolic impairment in cultured neurons

RNA interference is rapidly becoming a powerful tool for gene silencing in mammalian cells. Introduction of siRNA into primary cells, however, remains one of the major difficulties of this novel technique. Using cationic lipid-based transfection reagents satisfactory transfection results are observed in cell lines, but low transfection efficiency and cytotoxicity limit applications in primary cells, especially primary neurons. The application of "naked" siRNA has been previously used successfully in nematodes and mammals in vivo. We therefore evaluated the effects of non-cationic-lipid-based siRNA application to primary hippocampal neuron cultures. "Naked" siRNA was bound to the cell surface and was taken up into endosomes. No significant silencing effect of endogenous or reporter genes was observed, rather application of "naked" siRNA was accompanied by a moderate downregulation of metabolic activity in culture. We postulate that endosomal degradation of "naked" siRNA in neurons prevents the induction of significant RNAi-mediated mRNA-downregulation and is accompanied by a global impairment of the cell metabolism. Transfection methods circumventing the endosomal pathway therefore might prove useful for siRNA transduction of primary neurons.     

Dynamics of gene silencing by RNA interference

The large number of candidate genes identified by modern high-throughput technologies require efficient methods for generating knockout phenotypes or gene silencing in order to study gene function. RNA interference (RNAi) is an efficient method that can be used for this purpose. Effective gene silencing by RNAi depends on a number of important parameters, including the dynamics of gene expression and the RNA dose. Using mouse hepatoma cells, we detail some of the principal characteristics of RNAi as a tool for gene silencing, such as the RNA dose level, RNA complex exposure time, and the time of transfection relative to gene induction, in the context of silencing a green fluorescent protein reporter gene. Our experiments demonstrate that different levels of silencing can be attained by modulating the dose level of RNA and the time of transfection and illustrate the importance of a dynamic analysis in designing robust silencing protocols. By quantifying the kinetics of RNAi-based gene silencing, we present a model that may be used to help determine key parameters in more complex silencing experiments and explore alternative gene silencing protocols.     

Exploring cell type-specific internalizing antibodies for targeted delivery of siRNA.

A major challenge to the development of therapeutic small interfering RNAs (siRNAs) is specific and efficient in vivo delivery to target cells. Recent studies suggest that cell type-specific gene silencing in vivo can be achieved by combining siRNAs with cell type-specific affinity ligands such as monoclonal antibodies. The antibody-directed siRNA complex enters target cells through receptor endocytosis and is subsequently released to the cytosol to specifically silence target gene expression through biologically conserved RNA interference (RNAi) pathways. Antibody fragments fused with a small basic nucleic-acid-binding protein and antibody fragment-directed nanoimmunoliposomes are two examples of effective delivery vehicles in vivo. The demonstrated specificity of in vivo gene silencing and the lack of nonspecific immune activation and systemic toxicity encourage further development of therapies based on cell type-specific delivery of siRNA.     

Transfection and expression of plasmid DNA in plant cells by an arginine-rich intracellular delivery peptide without protoplast preparation

The delivery and expression of exogenous genes in plant cells have been of particular interest for plant research and biotechnology. Here, we present results demonstrating a simple DNA transfection system in plants. Short arginine-rich intracellular delivery peptide, a protein transduction domain, was capable of delivering plasmid DNA into living plant cells non-covalently. This peptide-mediated DNA delivery conferred several advantages, such as nuclear targeting, non-toxic effect, and ease of preparation without protoplast formulation. Thus, this novel technology shall provide a powerful tool to investigate gene function in vivo, and lay the foundation for the production of transgenic plants in future.     

siRNA delivery by a transferrin-associated lipid-based vector: a non-viral strategy to mediate gene silencing

BACKGROUND: RNA interference provides a powerful technology for specific gene silencing. Therapeutic applications of small interfering RNA (siRNA) however require efficient vehicles for stable complexation, protection, and extra- and intracellular delivery of these nucleic acids. Here, we evaluated the potential of transferrin (Tf)-associated liposomes for siRNA complexation and gene silencing. METHODS: Cationic liposomes composed of DOTAP : Cholesterol associated with or without transferrin (Tf) were complexed with siRNA at different lipid/siRNA charge ratios. Complexation and protection of siRNA from enzymatic degradation was assessed with the PicoGreen intercalation assay and gel electrophoresis. Cellular internalization of these siRNA Tf-lipoplexes was detected by confocal microscopy. Luciferase assay, immunoblot and fluorescence-activated cell sorting (FACS) analysis were used to evaluate reporter gene silencing in Huh-7 hepatocarcinoma and U-373 glioma cells. c-Jun knockdown in HT-22 cells was evaluated by quantitative real-time polymerase chain reaction (RT-PCR). Cytotoxicity of the siRNA complexes was assessed by Alamar blue, lactate dehydrogenase and MTT assays. RESULTS: Complexation of siRNA with the cationic liposomes in the presence of Tf results in the formation of stable particles and prevents serum-mediated degradation. Confocal microscopy showed fast cellular internalization of the Tf-lipoplexes via endocytosis. In the GFP glioma cells Tf-lipoplexes showed enhanced gene silencing at minimum toxicity in comparison to Tf-free lipoplexes. Targeting luciferase in the hepatocarcinoma cell line resulted in more than 70% reduction of luciferase activity, while in HT-22 cells 50% knockdown of endogenous c-Jun resulted in a significant protection from glutamate-mediated toxicity. CONCLUSIONS: Cationic liposomes associated with Tf form stable siRNA lipoplexes with reduced toxicity and enhanced specific gene knockdown activity compared to conventional lipoplexes. Thus, such formulations may constitute efficient delivery systems for therapeutic siRNA applications.     

Construction of a vector generating both siRNA and a fluorescent reporter: a siRNA study in cultured neurons

RNA interference is an important tool for gene silencing. However, its application to primary cultured cells has been limited by low transfection efficiencies. In this work we developed a vector which encodes both siRNA and red fluorescent protein. Using this vector we could markedly suppress green fluorescent protein (GFP) and bim an endogenous gene. Primary cultured cortical neurons transfected with siRNA against doublecortin showed that doublecortin expression was significantly inhibited in nearly all the transfected neurons. This vector identifies the transfected cells and should be useful for loss-of-gene function studies in neurons.     

RNA silencing in fungi: mechanisms and applications

Two RNA silencing-related phenomena, quelling and meiotic silencing by unpaired DNA (MSUD) have been identified in the fungus Neurospora crassa. Similar to the case with the siRNA and miRNA pathways in Drosophila, different sets of protein components including RNA-dependent RNA polymerase, argonaute and dicer, are used in the quelling and MSUD pathways. Orthologs of the RNA silencing components are found in most, but not all, fungal genomes currently available in the public databases, indicating that the majority of fungi possess the silencing machinery. Advantage and disadvantage of RNA silencing as a tool to explore gene function in fungi are discussed.     

不同长度茎部shRNA表达载体构建与鉴定

本研究针对同一目的基因设计构建不同茎部长度的shRNA表达载体,并对其在细胞及胚胎水平的干扰效应做一比较。以绿色荧光蛋白基因为沉默效应的靶基因,设计茎部长度分别为21bp、27bp、29bp的干扰片段,退火后连入带有H6启动子的真核表达载体psiSTRIKE中(分别命名为EGFP-21siRNA、EGFP-27siRNA和EGFP-29siRNA),将构建成功的载体以脂质体法转染小鼠胚胎成纤维细胞,利用荧光定量PCR对其荧光表达进行精确定量。不同茎部长度的shRNA载体均使绿色荧光蛋白基因表达降低,茎部为29bp时比21bp、27bp表现出更明显的沉默效应。细胞水平沉默效应的初步验证,为筛选适合小鼠个体水平的最佳发夹结构奠定了基础。