Summary: Researchers have identified a connection between age-related hearing loss and a decline in cholesterol levels within the inner ear. This reduction particularly affects outer hair cells (OHCs), specialized sensory cells that amplify sound. The findings suggest that replacing lost cholesterol with cholesterol-like plant compounds could preserve OHC function and slow or prevent some forms of hearing decline.
In animal experiments, mice that received dietary phytosterols—plant-derived compounds structurally similar to cholesterol—showed restoration of OHC function after cholesterol loss was induced. If similar effects occur in humans, broadly available phytosterol supplements may offer a convenient strategy to reduce or delay age-related hearing loss, though human trials will be required to confirm safety and efficacy.
Key Facts:
- Age-related hearing loss may be linked to reduced cholesterol levels within sensory cells of the inner ear.
- Cholesterol supports the mechanical stretch response of outer hair cells, a critical process for sound amplification.
- In mice, dietary phytosterols were able to substitute for lost cholesterol and help preserve outer hair cell function.
Source: PLOS
Research teams led by María Eugenia Gomez-Casati (Institute of Pharmacology, School of Medicine, University of Buenos Aires-CONICET), Mauricio Martin (Institute of Medical Research Mercedes), and Martín Ferreyra (INIMEC-CONICET-UNC, National University of Córdoba) in Argentina report that age-related hearing loss is associated with decreased cholesterol in the inner ear.
Published August 24 in the open-access journal PLOS Biology, the experiments demonstrate that phytosterol supplementation can compensate for cholesterol loss and prevent sensory dysfunction in a mouse model. The study provides proof-of-principle evidence linking cholesterol homeostasis in the cochlea to auditory function and suggests a potential avenue for preventive or therapeutic approaches.
Outer hair cells (OHCs) are specialized sensory cells in the cochlea that actively amplify incoming sound by changing their length in response to stimulation. This electromechanical response is essential for sensitive hearing and sharp frequency discrimination. With aging, however, OHCs can lose the capacity to change shape effectively, reducing sound amplification and contributing to age-related hearing loss.
Cholesterol plays a central role in membrane structure and function and is particularly important for the mechanical properties and protein organization of OHC membranes. Since brain cholesterol has been observed to decline with age, the authors hypothesized that a similar cholesterol deficit in cochlear OHCs could underlie functional decline and hearing impairment.
To test this idea, the researchers measured levels of the enzyme cholesterol 24‑hydroxylase (CYP46A1) in OHCs, an enzyme that promotes cholesterol turnover and clearance. They found increased CYP46A1 expression and lower cholesterol content in the inner ears of older mice compared to younger animals. To demonstrate causality, they pharmacologically activated CYP46A1 in young mice using the antiretroviral drug efavirenz, which led to reduced OHC cholesterol, decreased prestin immunolabeling (prestin is the motor protein critical for OHC electromotility), and measurable declines in auditory function as reflected by elevated distortion product otoacoustic emission (DPOAE) thresholds.
Because cholesterol itself does not readily cross from blood into the brain and inner ear, the team turned to phytosterols—plant sterols that resemble cholesterol chemically and can access neural tissues. Young mice treated concurrently with efavirenz and a three-week dietary regimen of phytosterols showed improved OHC function compared with drug-only animals, indicating that phytosterols can at least partly substitute for lost cholesterol and restore aspects of cochlear performance.
Phytosterols are commonly found in dietary supplements and certain foods. The researchers emphasize that while their results are promising, additional experiments are necessary: specifically, studies that directly test phytosterol effects in aged animal models and carefully controlled clinical trials in humans will be required before recommending phytosterol supplementation as a treatment for age-related hearing loss.
The authors summarize their conclusions as follows: aging reduces cholesterol in cochlear sensory cells; pharmacological activation of CYP46A1 replicates this cholesterol loss and impairs OHC function; and phytosterol supplementation can partly reverse those defects. These findings highlight cholesterol homeostasis in the inner ear as a novel target for strategies aimed at preventing or delaying hearing decline.
About this hearing loss research news
Author: Claire Turner
Source: PLOS
Contact: Claire Turner – PLOS
Image: The image is credited to Neuroscience News
Original Research: Open access. “Phytosterols reverse antiretroviral-induced hearing loss, with potential implications for cochlear aging” by Sodero AO et al., PLOS Biology.
Abstract
Phytosterols reverse antiretroviral-induced hearing loss, with potential implications for cochlear aging
Cholesterol contributes to neuronal membrane integrity, supports membrane protein clustering and function, and facilitates proper signal transduction. Extensive evidence has shown that cholesterol imbalances in the central nervous system occur during aging and in the development of neurodegenerative diseases. In this study, the authors characterize cholesterol homeostasis in the inner ear of young and aged mice as a previously underexplored factor in the prevention and treatment of hearing loss.
Their results demonstrate that cholesterol levels in the inner ear decline with age, accompanied by increased expression of the cholesterol 24‑hydroxylase enzyme (CYP46A1), the primary enzyme responsible for cholesterol turnover in the brain. Pharmacological activation of CYP46A1 with the antiretroviral drug efavirenz reduced cholesterol in OHCs, caused a reduction in prestin immunolabeling, and produced elevated DPOAE thresholds—consistent with impaired OHC-mediated amplification. Dietary supplementation with phytosterols, plant sterols with structural similarity to cholesterol, mitigated the auditory deficits induced by efavirenz.
Taken together, these findings emphasize the importance of cholesterol homeostasis in the inner ear and point to phytosterol supplementation as a promising experimental strategy to prevent or delay aspects of cochlear aging and age-related hearing loss. Further validation in aged animal models and clinical investigations will be needed to determine the translational potential of this approach.