Canalostomy is an ideal surgery route for inner ear gene delivery in big animal model

Minimizing hearing loss: A novel surgical approach for round window exposure in miniature pigs

BACKGROUND

A delicate operation for exposing the round window without affecting the hearing function is critical for auditory research. Despite the different surgical approaches proposed for miniature pigs, hearing protection during operation is still challenging. The efficient solution to this problem is significant for accurate auditory research.

NEW METHOD

Eight healthy Diannan miniature pigs, aged three months and of both sexes, with normal hearing, were utilized. Three pigs were employed for anatomical studies. Based on the findings from these anatomical investigations, we propose the facial nerve medial approach designed to expose the round window while preserving hearing function in the porcine model. The remaining five pigs were used to verify the surgical approach and hearing function.

RESULTS

The anatomy study confirmed that the lateral side of the round window was the genu of the facial nerve. Removing the medial wall of the genu part of the facial nerve canal allows access to the tympanic cavity and exposes the round window. The facial nerve medial approach effectively exposed the round window in vivo, with no significant change in auditory brainstem response threshold immediately post-operation.

COMPARISON WITH EXISTING METHODS

The facial nerve medial approach to exposing the round window preserved the sound transmission structures of the ear, maintaining hearing function post-operation.

CONCLUSIONS

The facial nerve medial approach with a retroauricular incision allows access to the tympanic cavity and exposes the round window without impacting hearing, making it ideal for accurate auditory research in miniature pigs.

Transduction Efficiency and Immunogenicity of Viral Vectors for Cochlear Gene Therapy: A Systematic Review of Preclinical Animal Studies

Background: Hearing impairment is the most frequent sensory deficit, affecting 466 million people worldwide and has been listed by the World Health Organization (WHO) as one of the priority diseases for research into therapeutic interventions to address public health needs. Inner ear gene therapy is a promising approach to restore sensorineural hearing loss, for which several gene therapy applications have been studied and reported in preclinical animal studies. Objective: To perform a systematic review on preclinical studies reporting cochlear gene therapy, with a specific focus on transduction efficiency. Methods: An initial PubMed search was performed on April 1st 2021 using the PRISMA methodology. Preclinical in vivo studies reporting primary data regarding transduction efficiency of gene therapy targeting the inner ear were included in this report. Results: Thirty-six studies were included in this review. Transduction of various cell types in the inner ear can be achieved, according to the viral vector used. However, there is significant variability in the applied vector delivery systems, including promoter, viral vector titer, etc. Conclusion: Although gene therapy presents a promising approach to treat sensorineural hearing loss in preclinical studies, the heterogeneity of methodologies impedes the identification of the most promising tools for future use in inner ear therapies.

Gene therapy via canalostomy approach preserves auditory and vestibular functions in a mouse model of Jervell and Lange-Nielsen syndrome type 2

Mutations in voltage-gated potassium channel KCNE1 cause Jervell and Lange-Nielsen syndrome type 2 (JLNS2), resulting in congenital deafness and vestibular dysfunction. We conducted gene therapy by injecting viral vectors using the canalostomy approach in Kcne1^−/− mice to treat both the hearing and vestibular symptoms. Results showed early treatment prevented collapse of the Reissner’s membrane and vestibular wall, retained the normal size of the semicircular canals, and prevented the degeneration of inner ear cells. In a dose-dependent manner, the treatment preserved auditory (16 out of 20 mice) and vestibular (20/20) functions in mice treated with the high-dosage for at least five months. In the low-dosage group, a subgroup of mice (13/20) showed improvements only in the vestibular functions. Results supported that highly efficient transduction is one of the key factors for achieving the efficacy and maintaining the long-term therapeutic effect. Secondary outcomes of treatment included improved birth and litter survival rates. Our results demonstrated that gene therapy via the canalostomy approach, which has been considered to be one of the more feasible delivery methods for human inner ear gene therapy, preserved auditory and vestibular functions in a dose-dependent manner in a mouse model of JLNS2.

Jervell and Lange-Nielsen syndrome is characterised by congenital deafness and vestibular dysfunction, and is caused by mutations in KCNE1 or KCNQ1. Here, the authors show that gene therapy via canalostomy at early postnatal stage can preserve the morphology of inner ear and auditory and vestibular functions in a mouse model of human JLNS2.

Viewing the current situation of pig model application in China's medical field from the application and funding of NSFC

Background

The National Natural Science Foundation of China (NSFC) is an important part of China’s innovation system. In the last decade, the pig has become more and more widely used in the field of medical science, especially in otology research.

Objective

By analyzing and summarizing the funding information over recent years, we intend to identify the characteristics and trends of funding for research using pig models and provide references for future development.

Material and methods

This is a comprehensive analysis of features in funding for research projects involving pig models by the NSFC in the past 10 years, with a focus on projects in the field of otolaryngology/head and neck surgery.

Results

Both the number and amount of funding provided by the NSFC for research involving pig models are on the rise with each passing year. Researchers at the PLA General Hospital have completed a number of studies using miniature pigs in cochlear morphology, electrophysiology, cochlear implantation, cochlear transcription analysis, gene therapy, inner ear disease modeling and Eustachian tube pathology modeling.

Conclusion

Pigs as an ideal large mammal model are well suited in the current national basic research strategy in China, and can help further strengthen China’s leading position in basic research in the world.

Transcript Profiles of Stria Vascularis in Models of Waardenburg Syndrome

Background

Waardenburg syndrome is an uncommon genetic condition characterized by at least some degree of congenital hearing loss and pigmentation deficiencies. However, the genetic pathway affecting the development of stria vascularis is not fully illustrated.

Methods

The transcript profile of stria vascularis of Waardenburg syndrome was studied using Mitf-M mutant pig and mice models. Therefore, GO analysis was performed to identify the differential gene expression caused by Mitf-M mutation.

Results

There were 113 genes in tyrosine metabolism, melanin formation, and ion transportations showed significant changes in pig models and 191 genes in mice models. In addition, there were some spice's specific gene changes in the stria vascularis in the mouse and porcine models. The expression of tight junction-associated genes, including Cadm1, Cldn11, Pcdh1, Pcdh19, and Cdh24 genes, were significantly higher in porcine models compared to mouse models. Vascular-related and ion channel-related genes in the stria vascularis were also shown significantly difference between the two species. The expression of Col2a1, Col3a1, Col11a1, and Col11a2 genes were higher, and the expression of Col8a2, Cd34, and Ncam genes were lower in the porcine models compared to mouse models.

Conclusions

Our data suggests that there is a significant difference on the gene expression and function between these two models.

Gene therapy development in hearing research in China

Sensorineural hearing loss, the most common form of hearing impairment, is mainly attributable to genetic mutations or acquired factors, such as aging, noise exposure, and ototoxic drugs. In the field of gene therapy, advances in genetic and physiological studies and profound increases in knowledge regarding the underlying mechanisms have yielded great progress in terms of restoring the auditory function in animal models of deafness. Nonetheless, many challenges associated with the translation from basic research to clinical therapies remain to be overcome before a total restoration of auditory function can be expected. In recent years, Chinese research teams have promoted various developmental efforts in this field, including gene sequencing to identify additional potential loci that cause deafness, studies to elucidate the underlying molecular mechanisms, and research to optimize vectors and delivery routes. In this review, we summarize the state of the field and focus mainly on the progress of gene therapy in animal model studies and the optimization of therapeutic strategies in China.