Age-related declines to serum prestin levels in humans.

Measurement of the motor protein prestin offers a novel approach to assessing outer hair cell (OHC) status using serological techniques. Motivated by our prior work showing reduced serum prestin levels in healthy young adults at-risk for noise damage, the current study examined serum prestin levels, measured from circulating blood, across the age span from 18 to 82 years old. Results suggest that serum prestin levels negatively correlate with age, with young adults having higher levels of circulating serum in the blood than older adults. Group-level analyses showed minimal differences in prestin levels between 18 and 29, 30-39, and 40-49 year olds, but significant reductions in the 50+ years-old age group compared to the three younger groups, even though all groups significantly differed from each other in audiometric thresholds and distortion product otoacoustic emissions signal-to-noise ratio. Serum prestin levels declined with increasing levels of hearing loss, with a statistically significant relationship emerging between prestin and low-frequency hearing thresholds (0.25-2 kHz) but a weaker non-significant relationship for high-frequency hearing thresholds (3-8 kHz). This differential pattern between low- and high- frequency thresholds is consistent with the basal-to-apical progression of OHC loss with age. Findings support the idea that serum prestin is the product of residual OHCs in the less age-affected apical regions. Moreover, when entered in a regression model with audiometric thresholds, age was a stronger predictor than pure tone hearing threshold level for predicting serum prestin levels.