ILDR1 deficiency causes degeneration of cochlear outer hair cells and disrupts the structure of the organ of Corti: a mouse model for human DFNB42

Immunoglobulin-like domain containing receptor 1 (ILDR1) is a poorly characterized gene that was first identified in lymphoma cells. Mutations in ILDR1 are responsible for DFNB42, but the pathogenesis of hearing loss caused by ILDR1 mutations remains to be elucidated. To explore the role of ILDR1 in hearing, we created Ildr1 knockout mice. In heterozygous mice, ILDR1 expression was found in outer hair cells (OHCs) and inner hair cells (IHCs) of the organ of Corti. ILDR1-deficient mice are profoundly deaf by postnatal day 21 (P21). No significant difference was observed in the supporting cells and IHCs of ILDR1-deficient mice, but progressive degeneration of OHCs occurred at P15 and disruption of the tunnel running through the organ of Corti was noticeable at P21. By P28, there were no OHCs visible in any of the turns of the organ of Corti, and the tunnel of the organ of Corti was entirely destroyed. ILDR1 deficiency affects expression of tricellulin in vivo, and this provides a possible explanation to hearing loss. To further elucidate the mechanism of deafness related to ILDR1 deficiency, we pursued a differential proteomic approach to comprehensively assess differential protein expression in the cochleae of Ildr1(+/-) and Ildr1(-/-) mice at P21. Altogether, 708 proteins were up-regulated (fold change >1.5) and 114 proteins were down-regulated (fold change <0.5) in the Ildr1(-/-) mice compared with Ildr1(+/-) mice. Gene ontology classification indicated that a number of differentially expressed proteins are involved in cell adhesion, protein and vesicle-mediated transport, cell death, membrane organization, and cellular homeostasis. A few of these proteins are closely related to hearing development. Taken together, our data suggest that ILDR1 is important for the survival of OHCs and provide novel insights into the pathogenesis of human deafness DFNB42 deafness.