TMTC4 is a hair cell-specific human deafness gene

Area of Science:

• Genetics
• Otolaryngology
• Cell Biology

Background:

• Transmembrane and tetratricopeptide repeat 4 (Tmtc4) is identified as a deafness gene in mouse models.
• Tmtc4 knockout (KO) mice exhibit rapid, progressive postnatal hearing loss linked to unfolded protein response (UPR) overactivation.
• The specific cellular mechanisms and human relevance of Tmtc4 in cochlear function were previously unclear.

Purpose of the Study:

• To investigate the role of Tmtc4 as a hair cell-specific gene contributing to hearing loss.
• To determine the relevance of Tmtc4 variants in human progressive hearing loss.
• To elucidate the cellular basis of Tmtc4-associated hearing impairment and its link to the UPR.

Main Methods:

• Generation of a hair cell-specific conditional Tmtc4 KO mouse model.
• Phenotypic analysis of hearing loss in Tmtc4-deficient mice.
• Segregation analysis of Tmtc4 variants in a human family with progressive hearing loss.
• In vitro studies using lymphoblastoid and HEK293 cells to assess UPR sensitivity to apoptosis.

Main Results:

• The hair cell-specific conditional Tmtc4 KO mouse model recapitulated the hearing loss phenotype of the constitutive KO model, confirming Tmtc4's role in cochlear hair cells.
• Human TMTC4 variants were identified and segregated with adult-onset progressive hearing loss within a family.
• Human TMTC4 variants demonstrated increased UPR hypersensitivity to apoptosis in cellular models.

Conclusions:

• TMTC4 is confirmed as a causative gene for progressive hearing loss in humans.
• The findings highlight the critical role of TMTC4 in maintaining cochlear function and preventing UPR-induced apoptosis.
• This study further implicates the unfolded protein response (UPR) pathway in the pathogenesis of progressive hearing loss.