Transcription Co-Factor LBH Is Necessary for Maintenance of Stereocilia Bundles and Survival of Cochlear Hair Cells

Hearing loss affects ~10% of adults worldwide and is irreversible. Most sensorineural hearing loss is caused by progressive loss of mechanosensitive hair cells (HCs) in the cochlea of the inner ear. The molecular mechanisms underlying HC maintenance and loss are largely unknown. Our previous cell-specific transcriptome analysis showed that Limb-Bud-and-Heart (LBH), a transcription co-factor implicated in development, is abundantly expressed in outer hair cells (OHCs). We used Lbh-null mice to identify its role. Surprisingly, Lbh deletion did not affect differentiation and early development of HCs, as nascent HCs in Lbh knockout mice had normal looking stereocilia bundles. Whole-cell recording showed that the stereocilia bundle was mechanosensitive and OHCs exhibited the characteristic electromotility. However, Lbh-null mice displayed progressive hearing loss, with stereocilia bundle degeneration and OHC loss as early as postnatal day 12. Cell-specific RNA-seq and bioinformatic analyses identified Spp1, Six2, Gps2, Ercc6, Snx6 as well as Plscr1, Rarb, Per2, Gmnn and Map3k5 among the top five transcription factors up- or down-regulated in Lbh-null OHCs. Furthermore, this analysis showed significant gene enrichment of biological processes related to transcriptional regulation, cell cycle, DNA damage/repair and autophagy. In addition, Wnt and Notch pathway-related genes were found to be dysregulated in Lbh-deficient OHCs. We speculate that LBH may promote maintenance of HCs and stereocilia bundles by regulating Notch and Wnt signaling activity. Our study implicates, for the first time, loss of LBH function in progressive hearing loss, and demonstrates a critical requirement of LBH in promoting HC survival.