Age-related hearing loss (ARHL) is a threat to future human wellbeing. Multiple factors contributing to the terminal auditory decline have been identified; but a unified understanding of ARHL-or the homeostatic maintenance of hearing before its breakdown-is missing. We here present an in-depth analysis of homeostasis and ageing in the antennal ears of the fruit fly Drosophila melanogaster. We show that Drosophila, just like humans, display ARHL. By focusing on the phase of dynamic stability prior to the eventual hearing loss we discovered a set of evolutionarily conserved homeostasis genes. The transcription factors Onecut (closest human orthologues: ONECUT2, ONECUT3), Optix (SIX3, SIX6), Worniu (SNAI2) and Amos (ATOH1, ATOH7, ATOH8, NEUROD1) emerged as key regulators, acting upstream of core components of the fly's molecular machinery for auditory transduction and amplification. Adult-specific manipulation of homeostatic regulators in the fly's auditory neurons accelerated-or protected against-ARHL.

Across their lives, biological sensors maintain near-constant functional outputs despite countless exogenous and endogenous perturbations. This sensory homeostasis is the product of multiple dynamic equilibria, the breakdown of which contributes to age-related decline. The mechanisms of homeostatic maintenance, however, are still poorly understood. The ears of vertebrates and insects are characterized by exquisite sensitivities but also by marked functional vulnerabilities. Being under the permanent load of thermal and acoustic noise, auditory transducer channels exemplify the homeostatic challenge. We show that (1) NompC-dependent mechanotransducers in the ear of the fruit fly Drosophila melanogaster undergo continual replacement with estimated turnover times of 9.1 hr; (2) a de novo synthesis of NompC can restore transducer function in the adult ears of congenitally hearing-impaired flies; (3) key components of the auditory transduction chain, including NompC, are under activity-dependent transcriptional control, likely forming a transducer-operated mechanosensory gain control system that extends beyond hearing organs.

No abstract

AbstractThe widespread loss of hearing is one of the major threats to future wellbeing in ageing human societies. Amongst its various forms, age-related hearing loss (ARHL) carries the vast bulk of the global disease burden. The causes for the terminal decline of auditory function, however, are as unknown as the mechanisms that maintain sensitive hearing before its breakdown. We here present an in-depth analysis of maintenance and ageing in the auditory system of the fruit fly Drosophila melanogaster. We show that Drosophila, just like humans, display ARHL and that their auditory life span is homeostatically supported by a set of evolutionarily conserved transcription factors. The transcription factors Onecut (closest human orthologues: ONECUT2, ONECUT3), Optix (SIX3, SIX6), Worniu (SNAI2) and Amos (ATOH1, ATOH7, NEUROD1) emerged as key regulators acting upstream of core sensory genes, including components of the fly’s molecular machinery for auditory transduction and amplification.