Current cochlear gene therapies use ubiquitous promoters (CAG, CMV) that express in all cell types. The ARBITER workflow (Zhao et al. 2025) identified synthetic enhancers that drive expression exclusively in outer hair cells, with zero leakage into IHCs or vestibular cells.
ARBITER (AAV-Reporter-Based In vivo Transcriptional Enhancer Reconstruction) is a systematic workflow for identifying cell-type-specific enhancers. Starting from conserved non-coding elements (CNEs) near hearing loss genes, the pipeline tests reporter constructs in vivo, dissects critical modules, and reassembles them into optimized synthetic enhancers.
High-dose AAV-ie-B8-Slc26a5 (5e10 gc) restored prestin expression in OHCs to wild-type comparable levels, particularly in the apical cochlea.
ABR thresholds and wave 1 amplitudes/latencies at 16 kHz were completely rescued to wild-type levels.
Critically, no prestin mislocalization was observed in IHCs or vestibular hair cells, unlike the CAG promoter which caused ectopic expression in both.
Stereocilin is an OHC-specific protein. Current STRC gene therapy research (Iranfar 2026) uses generic promoters. Applying the ARBITER workflow to find STRC-specific enhancers could improve targeting precision and potentially increase therapeutic expression levels.
The key question: do conserved non-coding elements near the STRC locus contain enhancer activity? Given that STRC (like Slc26a5) is OHC-specific, there is reason to expect dedicated regulatory elements exist.
A compact enhancer like B8 (~600 bp) combined with our recommended shorter mini-STRC (3,228 bp) fits comfortably within a single AAV vector: ~600 + 3,228 = 3,828 bp. This leaves 872 bp of headroom for UTRs, polyA, and optimized regulatory elements, enabling a single-vector, OHC-targeted STRC gene therapy.
Zhao et al. (2025) "Deciphering the enhancers of hearing loss genes enables targeted and effective gene therapy." Neuron.