Audiological characterization of X-linked mouse model

Alport Syndrome (AS) is a group of hereditary diseases caused by mutations in COL4A3, COL4A4, COL4A5 genes, these codify for polypeptidic chains of collagen type IV (respectively alpha3. alpha 4. alpha 5- a345), this network results the major collagenous constituent of the mature mammalian basement membrane (BM) of kidney (renal glomerulus), inner ear and eye. The molecular defect includes the synthesis, assembly, deposition, or function of the alpha3. alpha 4. alpha 5. The diagnosis of AS is established in a proband with a pathogenic variant(s) in COL4A3, COL4A4, or COL4A5 identified on molecular genetic testing. Clinically AS has a spectrum of phenotypes extending from isolated hematuria with no/slow progression over years to progressive renal disease up to ESRD, furthermore sensorineural hearing loss (SNHL) and anterior ocular lenticonus are frequent extra-renal findings Several animal models of AS have been used to study the syndrome. Transgenic mouse and rat models are the best models for AS research. In this study, we present the audiological features of X-linked mouse model using the CRISPR/Cas9 system via a very comprehensive protocol for assessment of hearing threshold. We investigated five mice of 4-month-old: two X-linked Alport mice and three healthy wild type mice (WT - C57BL/6J). The protocol for assessment of hearing threshold includes: Auditory Brainstem Response (ABR), Electrocochleography (EcoG), Cochlear microphonic potentials (CM), Otoacustic emissions (OAEs). We evaluated the experimental audiological protocol at baseline (T0) and 24-hour after noise exposure (T1). At T0 we found no differences between WT mice and X-linked Alport mice of same age in terms of hearing threshold (WT: 35 dB ± 5, Alport: 40 dB respectively). At T1 we outlined threshold shift of X-linked Alport mice after exposure to loud sounds, conversely WT mice didn't suffer any changes in hearing threshold. After brief noise exposure, X-linked Alport mice exhibited a dramatic worsening of their hearing threshold independently from the age, as if they were more prone to damage of the cochlear structure.