Transgene expression efficiency from plasmid DNA delivered as a complex with histone H3

Impacts of Nucleosome Positioning Elements and Pre-Assembled Chromatin States on Expression and Retention of Transgenes

BACKGROUND/OBJECTIVES

Transgene applications, ranging from gene therapy to the development of stable cell lines and organisms, rely on maintaining the expression of transgenes. To date, the use of plasmid-based transgenes has been limited by the loss of their expression shortly after their delivery into the target cells. The short-lived expression of plasmid-based transgenes has been largely attributed to host-cell-mediated degradation and/or silencing of transgenes. The development of chromatin-based strategies for gene delivery has the potential to facilitate defining the requirements for establishing epigenetic states and to enhance transgene expression for numerous applications.

METHODS

To assess the impact of "priming" plasmid-based transgenes to adopt accessible chromatin states to promote gene expression, nucleosome positioning elements were introduced at promoters of transgenes, and vectors were pre-assembled into nucleosomes containing unmodified histones or mutants mimicking constitutively acetylated states at residues 9 and 14 of histone H3 or residue 16 of histone H4 prior to their introduction into cells, then the transgene expression was monitored over time.

RESULTS

DNA sequences capable of positioning nucleosomes could positively impact the expression of adjacent transgenes in a distance-dependent manner in the absence of their pre-assembly into chromatin. Intriguingly, the pre-assembly of plasmids into chromatin facilitated the prolonged expression of transgenes relative to plasmids that were not pre-packaged into chromatin. Interactions between pre-assembled chromatin states and nucleosome positioning-derived effects on expression were also assessed and, generally, nucleosome positioning played the predominant role in influencing gene expression relative to priming with hyperacetylated chromatin states.

CONCLUSIONS

Strategies incorporating nucleosome positioning elements and the pre-assembly of plasmids into chromatin prior to nuclear delivery can modulate the expression of plasmid-based transgenes.

A comprehensive review on histone-mediated transfection for gene therapy

Histone has been considered to be an effective carrier in non-viral gene delivery due to its unique properties such as efficient DNA binding ability, direct translocation to cytoplasm and favorable nuclear localization ability. Meanwhile, the rapid development of genetic engineering techniques could facilitate the construction of multifunctional fusion proteins based on histone molecules to further improve the transfection efficiency. Remarkably, histone has been demonstrated to achieve gene transfection in a synergistic manner with cationic polymers, affording to a significant improvement of transfection efficiency. In the review, we highlighted the recent developments and future trends in gene delivery mediated by histones or histone-based fusion proteins/peptides. This review also discussed the mechanism of histone-mediated gene transfection and provided an outlook for future therapeutic opportunities in the viewpoint of transfection efficacy and biosafety.

Genipin-Cross-Linked Thermophilic Histone-Polyethylenimine as a Hybrid Gene Carrier

A hybrid gene carrier, HGP, has been successfully constructed through the genipin-mediated cross-linking of thermophilic histone and PEI25K. The thermophilic histone gene GK2215 was cloned from Geobacillus kastophilus HTA426 and overexpressed in Escherichia coli BL21. The thermophilic histone was systematically characterized and then cross-linked with PEI25K by genipin to obtain HGP. Notably, HGP exhibited superior transfection efficiency due to the synergistic effects between these two components: PEI25K mainly contributed to the condensation and transfer of pDNA, while thermophilic histone could enhance the endosomal escape and further nuclear location to achieve high gene expression. Meanwhile, HGP showed much lower cytotoxicity and hemolytic activity than PEI25K due to the introduction of nontoxic thermophilic histone. In addition, a strong intrinsic red fluorescence could be obviously observed in HGP. In conclusion, the protein-polymer hybrid carrier could potentially be used as a theranostic delivery system for achieving both efficient gene therapy and in vivo imaging.

A protein–polymer hybrid gene carrier based on thermophilic histone and polyethylenimine

Protein–polymer hybrid gene carrier with high transfection efficiency and low cytotoxicity.

Enhanced transgene expression from chromatinized plasmid DNA in mouse liver

Plasmid DNA was chromatinized with core histones (H2A, H2B, H3, and H4) in vitro and was delivered into mouse liver by hydrodynamics-based administration. Transgene expression from the chromatinized plasmid DNA was more efficient than that from plasmid DNA delivered in the naked form. The use of acetylation-enriched histones isolated from cells treated with a histone deacetylase inhibitor (trichostatin A) seemed to be more effective. These results indicated that chromatinized plasmid DNA is useful for efficient transgene expression in vivo.

[MITO-Porter; a cutting-edge technology for mitochondrial gene therapy]

Gene therapy is an attractive strategy, for not only targeting nuclear genome, but the mitochondrial genome as well. Human mitochondrial DNA (mtDNA) encodes 13 subunits of the electron transport chain, 22 tRNAs, and 2 rRNAs and their mutations cause a wide range of mitochondrial diseases. Each cell contains hundreds to thousands of mtDNAs, and in the case of a diseased cell, the mitochondrion possesses both mutant mtDNA and wild-type mtDNA. It is generally accepted that the disease phenotype appears when the proportion of the pathogenic mutant mtDNA exceeds a certain threshold. Therefore, the suppression of mutant mtDNA or supplementing wild-type mtDNA will control the onset of mitochondrial disease. To achieve the transfection of an exogenous therapeutic gene to the mitochondrial matrix where mtDNA is transcribed and translated, it is necessary to transfer cargos through mitochondrial outer and inner membranes. Several methods have been examined for mitochondrial transfection, but a universal, wide-ranging transfection technique has yet not been established. We recently developed a mitochondrial targeting delivery system, namely the MITO-Porter. The MITO-Porter is liposomal nanocarrier with a mitochondrial fusogenic lipid composition. We reported that the MITO-Porter could deliver chemical compounds and proteins to the mitochondrial matrix via membrane fusion. In this review, we report (1) on the pharmacological enhancement of lecithinized superoxide dismutase (PC-SOD) using MITO-Porter, (2) the transcription activation of exogenous DNA by mitochondrial transcription factor A (TFAM), and (3) perspectives on a mitochondrial targeting device.