Modeling and Preventing Progressive Hearing Loss in Usher Syndrome III

Abstract

Usher syndrome type III (USH3) characterized by progressive loss of vision and hearing is caused by mutations in the clarin-1 gene (CLRN1). Clrn1 knockout (KO) mice develop hair cell defects by postnatal day 2 (P2) and are deaf by P21-P25. Early onset profound hearing loss in KO mice and lack of information about the cochlear cell type that requires Clrn1 expression pose challenges to therapeutic investigation. We generated KO mice harboring a transgene, TgAC1, consisting of Clrn1-UTR (Clrn1 cDNA including its 5′ and 3′ UTR) under the control of regulatory elements (Atoh1 3′ enhancer/β-globin basal promoter) to direct expression of Clrn1 in hair cells during development and down regulate it postnatally. The KO-TgAC1 mice displayed delayed onset progressive hearing loss associated with deterioration of the hair bundle structure, leading to the hypothesis that hair cell expression of Clrn1 is essential for postnatal preservation of hair cell structure and hearing. Consistent with that hypothesis, perinatal transfection of hair cells in KO-TgAC1 mice with a single injection of AAV-Clrn1-UTR vector showed correlative preservation of the hair bundle structure and hearing through adult life. Further, the efficacy of AAV-Clrn1 vector was significantly attenuated, revealing the potential importance of UTR in gene therapy.

Clarin-1 gene transfer rescues auditory synaptopathy in model of Usher syndrome

“…Clarin-1, a tetraspan protein defective in Usher syndrome type IIIA (deaf-blindness), has been reported to be involved in hair bundle morphogenesis (7,8,32). We show here that a deletion of clarin-1 leads to a lower Ca 2+ efficiency of exocytosis in IHCs, probably due to abnormal clustering of Ca 2+ channels in the active zones of the ribbon.…”

“…These features closely match the progressiveness of hearing loss in USH3A patients. Progressive hearing loss has also been reported for Clrn1 -/-total knockout mice in which clarin-1 was transiently expressed in the hair cells, under the control of the Atoh1 promoter, between E12.5 and P3; these mice were referred to as KO-TgAC1 mice (32). Interestingly, a single cochlear injection of AAV2/8-Clrn1 (isoform 2) into KO-TgAC1 mice or our conditional Clrn1 ex4fl/fl Myo15-Cre +/-mice durably preserved the hair cells and hearing.…”

Targeted Allele Suppression Prevents Progressive Hearing Loss in the Mature Murine Model of Human TMC1 Deafness

“…Auditory thresholds in RNAi-treated Tmc1 Bth/+ mice were elevated relative to those in wild-type mice, indicating incomplete rescue of auditory function. Although low transduction efficiency following viral delivery has been a common explanation for variable hearing outcomes following cochlear gene therapy, 7,9,11,12,14,15,27 we noted that a single injection of AAV2/9 at P15-P16 using the RWM+CF approach resulted in virtually complete transduction of all IHCs throughout the cochlea. Thus, other factors may have impacted our results, including degree of allele suppression and ongoing, irreversible HC damage.…”

“…7 Other reports have also described successful auditory and/or balance restoration following intra-cochlear gene therapy in neonatal mouse models of genetic deafness. [7][8][9][10][11][12][13][14][15][16][17][18] These outcomes represent important advances; however, the neonatal murine inner ear is only partially developed and undergoes structural maturation until the onset of hearing at post-natal day (P) 14 and P15. 19 At P1-P2, it is temporally equivalent to the human cochlea prior to 26 weeks gestational age, 20 suggesting that translation of neonatal murine studies to human subjects would require in utero intervention.…”

Usher syndrome: reason for combined hearing and vision loss

“…CLRN1 encodes clarin-1, a protein crucial for the development and maintenance of the retina and inner ear. 11,12 US type IV, X-linked inheritance, but phenotype is similar to that of type II. 13 Early detection of US with an accurate diagnosis is crucial and it is generally performed through hearing, balance, and vision tests.…”