Viral-mediated Ntf3 overexpression disrupts innervation and hearing in nondeafened guinea pig cochleae

Abstract

Synaptopathy in the cochlea occurs when the connection between inner hair cells and the auditory nerve is disrupted, leading to impaired hearing and nerve degeneration. Experiments using transgenic mice have shown that overexpression of NT3 by supporting cells repairs synaptopathy caused by overstimulation. To accomplish such therapy in the clinical setting, it would be necessary to activate the neurotrophin receptor on auditory neurons by other means. Here we test the outcome of NT3 overexpression using viral-mediated gene transfer into the perilymph versus the endolymph of the normal guinea pig cochlea. We inoculated two different Ntf3 viral vectors, adenovirus (Adv) or adeno-associated virus (AAV) into the perilymph, to facilitate transgene expression in the mesothelial cells and cochlear duct epithelium, respectively. We assessed outcomes by comparing Auditory brainstem response (ABR) thresholds prior to that at baseline to thresholds at 1 and 3 weeks after inoculation, and then performed histologic evaluation of hair cells, nerve endings, and synaptic ribbons. We observed hearing threshold shifts as well as disorganization of peripheral nerve endings and disruption of synaptic connections between inner hair cells and peripheral nerve endings with both vectors. The data suggest that elevation of NT3 levels in the cochlear fluids can disrupt innervation and degrade hearing.

Translating animal models to human therapeutics in noise-induced and age-related hearing loss

“…At this trauma-treatment interval, the neural degeneration likely includes only the synapse itself and the unmyelinated dendritic portion of the ANF within the organ of Corti (Liberman et al, 2015). Although some have reported that virally driven NT-3 overexpression can disrupt the normal innervation patterns in an undamaged cochlea (Lee et al, 2016), we have seen no signs of this in our experiments (Hashimoto et al, 2019). At longer traumatreatment intervals (i.e.…”

Potential of Gene and Cell Therapy for Inner Ear Hair Cells

“…By contrast, despite its higher incidence and the economic consequences, there has been little success in preventing hearing loss caused by acoustic overexposure. Neurotrophin 3 [ 51 ], with the potential to resolve the synaptopathy caused by overstimulation, may be a candidate, but noninvasive methods to deliver the Nt3 gene to the cochlea before acoustic ototoxicity should be investigated before extensive gene therapy studies are conducted. Recently, inhibition of AMP-activated protein kinase (AMPK) by siRNA has shown a protective effect against acoustic overexposure in mouse [ 52 ], suggesting the alternative target for a therapeutic approach.…”

“…If so, it will likely require support from other techniques, such as the damage-free injection of the required growth factors or inhibitors into the cochlea using, for example, a mini-osmotic pump. Innervating the cells with nerve fibers is also necessary for a positive functional outcome and might be feasible using neurotrophin gene therapy [ 51 , 88 – 90 ], which has already been widely tested in nerve regeneration and growth.…”

Profound analgesia is associated with a truncated peptide resulting from tissue specific alternative splicing of DRG CA8-204 regulated by an exon-level cis-eQTL

“…SN (sciatic nerve) injections of viral particles was followed using a previously prescribed procedure [7]. We have used V5 and FLAG tags due to their small size as tags, and data that have shown these tags lack effects in neurobehavioral studies [5, 6, 38–40]. Preceding the SN exposure, 1.5 μl of 1.0E13 genome copies/ml of viral particles were injected into the sciatic nerve through a 35-gauge NanoFil needle using a NanoFil syringe (World Precision Instruments, Sarasota, FL).…”