Deletion of Tmtc4 activates the unfolded protein response and causes postnatal hearing loss
Jiang Li, Omar Akil, Stephanie L. Rouse, Conor W. McLaughlin, Ian R. Matthews, Lawrence R. Lustig, Dylan K. Chan, Elliott H. Sherr
Jiang Li, Omar Akil, Stephanie L. Rouse, Conor W. McLaughlin, Ian R. Matthews, Lawrence R. Lustig, Dylan K. Chan, Elliott H. Sherr
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Research Article Cell biology Otology

Deletion of Tmtc4 activates the unfolded protein response and causes postnatal hearing loss

Abstract

Hearing loss is a significant public health concern, affecting over 250 million people worldwide. Both genetic and environmental etiologies are linked to hearing loss, but in many cases the underlying cellular pathophysiology is not well understood, highlighting the importance of further discovery. We found that inactivation of the gene Tmtc4 (transmembrane and tetratricopeptide repeat 4), which was broadly expressed in the mouse cochlea, caused acquired hearing loss in mice. Our data showed Tmtc4 enriched in the endoplasmic reticulum, and that it functioned by regulating Ca2+ dynamics and the unfolded protein response (UPR). Given this genetic linkage of the UPR to hearing loss, we demonstrated a direct link between the more common noise-induced hearing loss (NIHL) and the UPR. These experiments suggested a novel approach to treatment. We demonstrated that the small-molecule UPR and stress response modulator ISRIB (integrated stress response inhibitor), which activates eIF2B, prevented NIHL in a mouse model. Moreover, in an inverse genetic complementation approach, we demonstrated that mice with homozygous inactivation of both Tmtc4 and Chop had less hearing loss than knockout of Tmtc4 alone. This study implicated a novel mechanism for hearing impairment, highlighting a potential treatment approach for a broad range of human hearing loss disorders.

Authors

Jiang Li, Omar Akil, Stephanie L. Rouse, Conor W. McLaughlin, Ian R. Matthews, Lawrence R. Lustig, Dylan K. Chan, Elliott H. Sherr

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Figure 5

TMTC4 coimmunoprecipitation with ER membrane proteins.

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TMTC4 coimmunoprecipitation with ER membrane proteins. (A) Nonnuclear wh...
(A) Nonnuclear whole-cell lysates from HEK cells with stably incorporated TMTC4-c-Myc vector (HEK-TMTC4) or empty plasmid (HEK) were assayed with antibodies against ER proteins (SERCA2b, calnexin) or TMTC4, showing that all 3 proteins were present in transfected HEK cells and that the TMTC4 antibody did not stain nonspecifically in mock-transfected cells. These extracts from TMTC4-c-Myc stably transfected cells were then incubated with agarose beads linked with antibodies against c-Myc or to beads alone (Beads). Bound proteins were purified and the “pull down” fraction stained with the aforementioned antibodies against TMTC4 and ER proteins, showing that SERCA2b and calnexin are copurified upon c-Myc pull down. Images are representative of 3 experiments. (B) Human fetal brain lysate was used to assess endogenous TMTC4 interactions. Pull down fractions were isolated using beads linked to antibody against SERCA2b, calnexin, or beads alone without linked antibodies (Beads), and probed with antibody against TMTC4. Endogenous TMTC4 was found to coimmunoprecipitate strongly with SERCA2b and weakly with calnexin. Images are representative of 3 experiments.