Improved biolistic transfection of hair cells

Gene therapy for hearing loss: Current status and future prospects of non-viral vector delivery systems

Current therapeutic options for hearing loss rely on hearing aids, ossiculoplasty or cochlear implants. These devices have limitations, particularly in noisy acoustic environments. Therefore, interest in exploring aetiological treatments to improve not only auditory perception but also the quality of life of those affected is increasing. Gene therapy is a promising aetiological treatment that can fully restore auditory function. The success of gene therapy relies on the efficient delivery of therapeutic genes or genetic modifications to the cells of the inner ear that are designed to repair or replace defective genes and restore normal hearing function. Two main strategies for gene therapy involve the use of recombinant viral vectors and nonviral delivery vehicles. Owing to their excellent diffusion properties and compatibility with sensory cells, recombinant viral vectors, particularly adeno-associated viruses (AAVs), have dominated gene therapy in the cochlea. However, recombinant viral vectors have several drawbacks, such as limited transgene size, immunogenicity (particularly in neonates), and potential need for repeat administration. Nonviral vectors, such as cationic lipids and polymeric nanoparticles, are potential attractive alternatives. Nonviral vectors have several advantages, including low immunogenicity and unlimited transgene size. Recent studies have demonstrated significant auditory recovery in vivo using nonviral vectors in murine models. However, nonviral vectors are not as efficient as viral vectors in transferring genetic material. An alternative to nanoparticles is the use of other methods, such as electroporation. The main advantage of electroporation is that it can be used in combination with cochlear implantation and can target surface cells, but this method has a risk of cell damage. The goal of this review is to provide valuable insights into the current state of research on nonviral vectors for inner ear gene therapy and propose the exploration of innovative and effective gene therapy strategies for the treatment of hearing loss.

TRPV6, TRPM6 and TRPM7 Do Not Contribute to Hair-Cell Mechanotransduction

Hair cells of the inner ear transduce mechanical stimuli like sound or head movements into electrical signals, which are propagated to the central nervous system. The hair-cell mechanotransduction channel remains unidentified. We tested whether three transient receptor channel (TRP) family members, TRPV6, TRPM6 and TRPM7, were necessary for transduction. TRPV6 interacted with USH1C (harmonin), a scaffolding protein that participates in transduction. Using a cysteine-substitution knock-in mouse line and methanethiosulfonate (MTS) reagents selective for this allele, we found that inhibition of TRPV6 had no effect on transduction in mouse cochlear hair cells. TRPM6 and TRPM7 each interacted with the tip-link component PCDH15 in cultured eukaryotic cells, which suggested they might be part of the transduction complex. Cochlear hair cell transduction was not affected by manipulations of Mg2+, however, which normally perturbs TRPM6 and TRPM7. To definitively examine the role of these two channels in transduction, we showed that deletion of either or both of their genes selectively in hair cells had no effect on auditory function. We suggest that TRPV6, TRPM6 and TRPM7 are unlikely to be the pore-forming subunit of the hair-cell transduction channel.

Helios(®) Gene Gun-Mediated Transfection of the Inner Ear Sensory Epithelium: Recent Updates

The transfection of vertebrate inner ear hair cells has proven to be challenging. Therefore, many laboratories attempt to use and improve different transfection methods. Each method has its own advantages and disadvantages. A particular researcher's skills in addition to available equipment and the type of experiment (in vivo or in vitro) likely determine the transfection method of choice. Biolistic delivery of exogenous DNA, mRNA, or siRNA, also known as Helios(®) Gene Gun-mediated transfection, uses the mechanical energy of compressed helium gas to bombard tissue with micron- or submicron-sized DNA or RNA-coated gold particles, which can penetrate and transfect cells in vitro or in vivo. Helios(®) Gene Gun-mediated transfection has several advantages: (1) it is simple enough to learn in a short time; (2) it is designed to overcome cell barriers even as tough as plant cell membrane or stratum corneum in the epidermis; (3) it can transfect cells deep inside a tissue such as specific neurons within a brain slice; (4) it can accommodate mRNA, siRNA, or DNA practically of any size to be delivered; and (5) it works well with various cell types including non-dividing, terminally differentiated cells that are difficult to transfect, such as neurons or mammalian inner ear sensory hair cells. The latter advantage is particularly important for inner ear research. The disadvantages of this method are: (1) low efficiency of transfection due to many variables that have to be adjusted and (2) potential mechanical damage of the tissue if the biolistic shot parameters are not optimal. This chapter provides a step-by-step protocol and critical evaluation of the Bio-Rad Helios(®) Gene Gun transfection method used to deliver green fluorescent protein (GFP)-tagged full-length cDNAs of myosin 15a, whirlin, β-actin, and Clic5 into rodent hair cells of the postnatal inner ear sensory epithelia in culture.

Using injectoporation to deliver genes to mechanosensory hair cells

Mechanosensation, the transduction of mechanical force into electrochemical signals, allows organisms to detect touch and sound, to register movement and gravity, and to sense changes in cell volume and shape. The hair cells of the mammalian inner ear are the mechanosensors for the detection of sound and head movement. The analysis of gene function in hair cells has been hampered by the lack of an efficient gene transfer method. Here we describe a method termed injectoporation that combines tissue microinjection with electroporation to express cDNAs and shRNAs in mouse cochlear hair cells. Injectoporation allows for gene transfer into dozens of hair cells, and it is compatible with the analysis of hair cell function using imaging approaches and electrophysiology. Tissue dissection and injectoporation can be carried out within a few hours, and the tissue can be cultured for days for subsequent functional analyses.

Potential of microneedle-assisted micro-particle delivery by gene guns: a review

CONTEXT

Gene guns have been used to deliver deoxyribonucleic acid (DNA) loaded micro-particle and breach the muscle tissue to target cells of interest to achieve gene transfection.

OBJECTIVE

This article aims to discuss the potential of microneedle (MN) assisted micro-particle delivery from gene guns, with a view to reducing tissue damage.

METHODS

Using a range of sources, the main gene guns for micro-particle delivery are reviewed along with the primary features of their technology, e.g. their design configurations, the material selection of the micro-particle, the driving gas type and pressure. Depending on the gene gun system, the achieved penetration depths in the skin are discussed as a function of the gas pressure, the type of the gene gun system and particle size, velocity and density. The concept of MN-assisted micro-particles delivery which consists of three stages (namely, acceleration, separation and decoration stage) is discussed. In this method, solid MNs are inserted into the skin to penetrate the epidermis/dermis layer and create holes for particle injection. Several designs of MN array are discussed and the insertion mechanism is explored, as it determines the feasibility of the MN-based system for particle transfer.

RESULTS

This review suggests that one of the problems of gene guns is that they need high operating pressures, which may result in direct or indirect tissue/cells damage. MNs seem to be a promising method which if combined with the gene guns may reduce the operating pressures for these devices and reduce tissue/cell damages.

CONCLUSIONS

There is sufficient potential for MN-assisted particle delivery systems.