Improved CRISPR-Cas9 will bring precision gene therapy to deafness

Recently, a joint team of researchers from Harvard Medical School and Boston Children's Hospital helped mice retain hearing by accurately identifying and correcting deaf mutations in the inner ear model using an optimized CRISPR-Cas9 gene editing systemThe completion of this proof-of-concept is expected to provide safe gene editing therapy for many people with hereditary deafnessThe results of the study were published in the academic journal Nature-MedicineBeethoven micedeep in our ears, known as the inner ear, and have a class of "hair cells" that are distributed on the surface of the inner ear and are shaped like a clump of mane and play an important role in hearingA team led by Jeffrey Holt, professor of otolaryngology, and David Corey, a professor of translational medicine science, have found in the past that hair cells can perform the function of transmitting auditory signals without a protein called TMC1When the gene that encodes the TMC1 protein mutates, the hair cells gradually degrade and die, leading to hearing lossSome genetic deaf patients begin to lose hearing at the age of 10 to 15 and lose their hearing completely by the age of 25, precisely because of the TMC1 gene mutationProfessor David Corey (left) and Professor Jeffrey Holt (right) (pictured)scientists to discover the TMC1 gene, using the same mutation to build a disease model in mice, hoping to use the disease to be used to study the treatment of the diseaseThese genetically mutated mice gradually lose their hearing after birth and become completely deaf in their "young adults." Scientists named the disease model "Beethoven mouse" because they exhibited a course similar to the performing hearing loss experienced by the great musician BeethovenBut, by the way, the real cause of Beethoven's deafness remains inconclusiveto accurately find one in 3 billionlike deaf patients with TMC1 mutations, the Tmc1 gene in Beethoven's mice made only a "little" error: in two copies of the gene from both parents, a Tmc1 mutation would be deaf;want to correct DNA errors through gene therapy, which, in the words of the researchers, means that their gene-editing system needs to successfully find the wrong letter in the 3 billion base letters in the mouse genomein order to pinpoint the wrong copy of the gene in Beethoven's mice without affecting the normal gene, the team refined the classic CRISPR-Cas9 system to optimize the guided molecule gRNA and the endoenzyme Cas9, respectively Preliminary tests in cell experiments showthat that the optimized CRISPR-Cas9 tool can accurately distinguish the mutant version from the normal version in two copies of the Tmc1 gene then, the researchers delivered gene therapy to the inner ear of mice using adeno-related viruses (AAVs) vectors the gene-editing treatment after the birth of Beethoven mice and assessthe effects of thetherapy on disease development within the next few weeks (Photo: Supplied) The results of DNA analysis showed that gene editing activity was limited to the inner ear cells in Beethoven mice The same "treatment" for normal mice, withno or no editing changes detected in the inner ear cells, showed that the treatment did not interfere with normal genetic function, further demonstrating the specificity of the tool researchers looked under a microscope at hair cells in the inner ear of mice Unsurprisingly, in untreated Beethoven mice, hair cells gradually disappeared as the structure deteriorated, whereas after treatment, the normal number of hair cells were retained, structurally or almost complete normal hair cells, the hair cells of Beethoven mice when they were not treated, and treated hair cells (Photo: Carl Nist-Lund and Jeffrey Holt) the structure of the inner ear hair cells can really improve hearing when they are saved? The scientists examined the hearing of the mice using the "hearing brain stem response " (ABR) This test examines the response of brain waves with different intensity sound stimuli, meaning that auditory cells in the inner ear capture the sound and transmit the signal to the brain This is also a common method of hearing screening in newborns without treatment, Beethoven mice usually begin to react less to high-frequency sounds at 1 month old and become completely deaf at 6 months old In contrast, mice that received gene-editing therapy shortly after birth had little difference in hearing between healthy mice at 2 months of age; by 6 months of age, hearing for low-frequency sounds remained normal, and some even responded to healthy mice with high-frequency sounds Even more encouraging is that a portion of the treated Beethoven mice have maintained a steady hearing for nearly a year after that! treated Beethoven mice can hear sounds as low as 30 decibels as normal mice, equivalent to the sound of our whispers (Photo: Source: Supplied) the performance of this therapy is worth mentioning in terms of safety, which is of great concern to people After the scientists administered the therapy to mice that did not carry the defective gene, the mice did not suffer any hearing loss as a result at the end of the study, to test the treatment's potential in genetically deaf patients, scientists conducted experiments on a series of human cell lines that carry TMC1 mutations DNA analysis showed that only the mutant copy would be edited and the normal copy in the same cell would not be affected the newly-optimized CRISPR-Cas9 specific targeting of individual base mutations in human TMC1 mutant cells (Photo: Source: Supplied) From these results, the new CRISPR-Cas9 tool brought by the research team "significantly improves the effectiveness and safety of standard gene editing techniques." But they also caution that even highly accurate gene-editing therapies like this still need to be done before they can be used in humans because this method can target a single point mutation, the benefits will not only be in the inherited deaf patients caused by the TMC1 mutation, 15 genetic deafening diseases caused by other auditory gene single mutations are also expected to be treated in this way Such progress is certainly to be expected! "We believe that these results open the door to a range of genetic diseases caused by single-copy defects in genes that can be used to develop targeted treatments on that basis Professor Holt said, "It's really precise treatment Beethoven himself had not heard "Ode to Joy" in his own eyes, and precise gene-editing therapy was approaching the goal of curing the disease, bringing a happy song to many deaf people Reference s.1 Bence Gyorgy et al., (2019) Allele-specific gene editing sin-for-sina model of dominant progressive hearing loss Nature Medicine DOI: 10.1038/s41591-019-0500-9 Nature Genetic , B et al (2018) TMC1 forms the pore of mechano translairion channels in inner inner lehair hair cells Neuron The Hearing Molecule Retrieved Jul 4, 2019 from https://hms.harvard.edu/news/saving-beethoven Retrieved Jul 5, 2019, from https://