Cochlear hair cell endoplasmic reticulum homeostasis and deafness. – COC-ERpathy

Hearing loss is the most frequent sensory defect in humans with a strong genetic component. We have recently shown that mutations in TMPRSS3, a type II transmembrane serine protease, induce DFNB8/10 deafness. To elucidate the role of Tmprss3 in the cochlea, we generated a mouse model for Tmprss3. Loss of function of Tmprss3, an endoplasmic reticulum (ER) protein expressed in sensory hair cells, induces a rapid and drastic degeneration of the cells at the onset of hearing, leading to profound deafness.

To decipher the molecular mechanism leading to hair cells degeneration, we compared the cochlear proteome of wild type and mutant mice by 2D gels followed by mass spectrometry. Using bioinformatics, we clustered the proteins in signalling pathway. Now, we would like to establish why hair cells are degenerating so rapidly and how to prevent this degeneration. Using complementary approaches, we will: (i) characterize the hair cell death pathway; (ii) determine if lack of Tmprss3 induces perturbation of the ER homeostasis; (iii) identify interactants of Tmprss3 and (iv) decipher the cochlear transcriptome of Tmprss3.

Notably, TMC1, mutated in DFNB7/11, and WFS1, mutated in Wolfram syndrome, are ER cochlear hair cells proteins. Thus, we will use Tmc1dn/dn mice and Wfs1E864K mice we are developing, to find out if the three proteins share a similar physiological pathway. To this end, we will (i) characterize the cochlear proteome of Tmc1dn/dn and Wfs1E864K mice; (ii) isolate the N-and C-terminal partners of Tmc1 and Wfs1 in the inner ear (iii) verify if the three proteins are able to form a complex in the ER and (iv) design effective inner ear therapeutical strategies using these models.
The proposed project, based on a particular combination of in vitro and in vivo techniques, will give us the opportunity to reveal essential molecular mechanisms that control hair cells ER homeostasis and to ascertain how perturbation of these mechanisms lead to deafness.