The auditory phenotype of children harboring mutations in the prestin gene

Prestin in Human Perilymph, Cerebrospinal Fluid, and Blood as a Biomarker for Hearing Loss

OBJECTIVE

Determining the concentration of prestin in human blood, cerebrospinal fluid (CSF), and perilymph (PL), and evaluating its suitability as a clinical biomarker for sensori-neural hearing loss (SNHL).

STUDY DESIGN

Human blood, CSF, and PL samples were intraoperatively collected from 42 patients with tumors of the internal auditory canal or with intracochlear tumors undergoing translabyrinthine or middle fossa tumor removal. Prestin concentration was measured using enzyme-linked immunosorbent assay and linear regression analyses were performed to investigate its associations with audiological as well as vestibular test results.

SETTING

Tertiary referral center.

RESULTS

The median prestin concentration in blood samples of the 42 study participants (26 women, mean ± standard deviation age, 52.7 ± 12.5 years) was 1.32 (interquartile range, IQR, 0.71-1.99) ng/mL. CSF prestin levels were significantly higher with 4.73 (IQR, 2.45-14.03) ng/mL (P = .005). With 84.74 (IQR, 38.95-122.00) ng/mL, PL prestin concentration was significantly higher compared to blood (P = .01) and CSF (P = .03) levels. Linear regression analyses showed significant associations of CSF prestin concentration with preoperative hearing levels (pure-tone average and word recognition; P = .008, R2 = 0.1894; P = .03, R2 = 0.1857), but no correlations with blood or PL levels.

CONCLUSION AND RELEVANCE

This study's findings highlight the volatile nature of prestin levels and provide the first insights into this potential biomarker's concentrations in body fluids apart from blood. Future investigations should comprehensively assess human prestin levels with different etiologies of SNHL, prestin's natural homeostasis and systemic circulation, and its temporal dynamics after cochlear trauma. Finally, clinically approved detection kits for prestin are urgently required prior to considering a potential translational implementation of this diagnostic technique.

The pathogenic roles of the p.R130S prestin variant in DFNB61 hearing loss

DFNB61 is a recessively inherited nonsyndromic hearing loss caused by mutations in SLC26A5, the gene that encodes the voltage-driven motor protein, prestin. Prestin is abundantly expressed in the auditory outer hair cells that mediate cochlear amplification. Two DFNB61-associated SLC26A5 variants, p.W70X and p.R130S, were identified in patients who are compound heterozygous for these nonsense and missense changes (SLC26A5W70X/R130S ). Our recent study showed that mice homozygous for p.R130S (Slc26a5R130S/R130S ) suffer from hearing loss that is ascribed to significantly reduced motor kinetics of prestin. Given that W70X-prestin is nonfunctional, compound heterozygous Slc26a5R130S/- mice were used as a model for human SLC26A5W70X/R130S . By examining the pathophysiological consequences of p.R130S prestin when it is the sole allele for prestin protein production, we determined that this missense change results in progressive outer hair cell loss in addition to its effects on prestin's motor action. Thus, this study defines the pathogenic roles of p.R130S prestin and identifies a limited time window for potential clinical intervention. KEY POINTS: The voltage-driven motor protein, prestin, is encoded by SLC26A5 and expressed abundantly in cochlear outer hair cells (OHCs). The importance of prestin for normal hearing was demonstrated in mice lacking prestin; however, none of the specific SLC26A5 variants identified to date in human patients has been experimentally demonstrated to be pathogenic. In this study we used both cell lines and a mouse model to define the pathogenic role of compound heterozygous p.W70X (c.209G>A) and p.R130S (c.390A>C) SLC26A5 variants identified in patients with moderate to profound hearing loss. As in patients, mice carrying one copy of p.R130S Slc26a5 showed OHC dysfunction and progressive degeneration, which results in congenital progressive hearing loss. This is the first functional study reporting pathogenic SLC26A5 variants and pointing to the presence of a therapeutic time window for potential clinical interventions targeting the affected OHCs before they are lost.

The pathogenic roles of the p.R130S prestin variant in DFNB61 hearing loss

DFNB61 is a recessively inherited nonsyndromic hearing loss caused by mutations in SLC26A5 , the gene that encodes the voltage-driven motor protein, prestin. Prestin is abundantly expressed in the auditory outer hair cells that mediate cochlear amplification. Two DFNB61-associated SLC26A5 variants, p.W70X and p.R130S, were identified in patients who are compound heterozygous for these nonsense and missense changes ( SLC26A5 W70X/R130S ). Our recent study showed that mice homozygous for p.R130S ( Slc26a5 R130S/R130S ) suffer from hearing loss that is ascribed to significantly reduced motor kinetics of prestin. Given that W70X-prestin is nonfunctional, compound heterozygous Slc26a5 R130S/- mice were used as a model for human SLC26A5 W70X/R130S . By examining the pathophysiological consequences of p.R130S prestin when it is the sole allele for prestin protein production, we determined that this missense change results in progressive outer hair cell loss in addition to its effects on prestin's motor action. Thus, this study fully defines the pathogenic roles for the p.R130S prestin, which points to the presence of a limited time window for potential clinical intervention.

Blood Prestin Levels in Normal Hearing and in Sensorineural Hearing Loss: A Scoping Review

Supplemental Digital Content is available in the text.

Objectives:

Recently, it has been hypothesized that blood prestin concentration levels may reflect cochlear damage and thus serve as an easily measurable, early sensorineural hearing loss (HL) biomarker. This is a scoping review aiming to identify and critically appraise current evidence on prestin blood levels and their temporal variation in rodents and humans with normal hearing and with sensorineural HL.

Design:

This study was designed and held according to PRISMA Extension for Scoping Reviews (PRISMA-ScR) guidelines. With no limitation with regards to study type, animal and human studies focusing on prestin blood levels in normal hearing and in sensorineural HL were sought in major databases such as Medline, Central Scopus, PROSPERO, and Clinicaltrials.gov. Results were then hand-searched. A data charting form was developed including the parameters of interest.

Results:

Seven studies focusing on measuring prestin blood levels by means of ELISA in rodents and human subjects with normal hearing and noise-induced, drug-induced, or idiopathic sudden HL were found eligible and were included in the analysis. According to these proof-of-concept studies, prestin can be detected in the circulation of subjects with no HL; however, normal ranges remain unclear. After cochlear damage, blood prestin levels seem to initially rise and then return to near or below baseline. The degree of their change relates with subjects’ degree of HL, damaged cochlear region and recovery. Prestin blood levels and their temporal variation seem to correlate with cochlear damage; however, methodological weaknesses, such as small sample size, lack of detailed phenotyping, insufficient exclusion of confounding factors, and short follow-up, do not allow for robust conclusions.

Conclusions:

Current findings support the value of studying blood prestin levels in normal hearing and HL and highlight a need for larger-scale longitudinal research.

Outer Hair Cells and Electromotility

Outer hair cells (OHCs) of the mammalian cochlea behave like actuators: they feed energy into the cochlear partition and determine the overall mechanics of hearing. They do this by generating voltage-dependent axial forces. The resulting change in the cell length, observed by microscopy, has been termed "electromotility." The mechanism of force generation OHCs can be traced to a specific protein, prestin, a member of a superfamily SLC26 of transporters. This short review will identify some of the more recent findings on prestin. Although the tertiary structure of prestin has yet to be determined, results from the presence of its homologs in nonmammalian species suggest a possible conformation in mammalian OHCs, how it can act like a transport protein, and how it may have evolved.