Research Monitor

What they found

RBM24 is an RNA-binding protein that controls alternative splicing in cochlear hair cells. Exon 4 of mouse Rbm24 undergoes alternative splicing to produce two isoforms with distinct functions. Deletion of this exon causes stereocilia disorganization and progressive hair cell loss with severe hearing impairment. Critically: STRC is identified as a direct RBM24 splicing target — RBM24 regulates STRC mRNA processing, and appropriate expression levels are required for stereocilia structural integrity.

How this applies to mini-STRC

STRC expression is under splicing-level control by RBM24. This opens a hypothesis we didn’t have: instead of delivering a gene, could we modulate endogenous STRC expression by targeting RBM24? If a patient has a hypomorphic STRC mutation (partial function) rather than a null mutation, upregulating RBM24 activity or correcting its splicing targets could boost endogenous STRC to therapeutic levels without AAV delivery at all. Separate from mini-STRC, this paper also tells us that STRC mRNA structure matters — the transcript has splicing-sensitive regions that any gene therapy construct must account for.

Key numbers

• RBM24 targets: STRC among others (direct regulatory target confirmed)
• Phenotype of Rbm24 exon 4 deletion: stereocilia disorganization + hair cell loss + severe HL
• Mechanism: splicing regulation, not transcription level

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/41973913/
• DOI: https://doi.org/10.1073/pnas.2531564123

What they found

This paper reviews the current state of otoferlin (OTOF) gene therapy for infants and children with auditory neuropathy spectrum disorder (ANSD). After decades of research on hair cell regeneration, otoferlin gene therapy has emerged as the first successful inner ear gene therapy, with early clinical results demonstrating hearing restoration. The authors discuss the clinical framework for treating pediatric patients and raise the critical question of whether this early success will translate to other forms of genetic hearing loss. The paper contextualizes otoferlin gene therapy within the broader landscape of hearing loss treatment.

How this applies to mini-STRC

This is highly relevant to our program: (1) Otoferlin gene therapy is the furthest-advanced hearing loss gene therapy and serves as the regulatory and clinical precedent for all subsequent inner ear gene therapies, including mini-STRC. (2) OTOF (~6kb CDS) is similarly oversized for a single AAV, and the dual-AAV approach used for otoferlin is an important reference — though our mini-gene strategy takes a different approach to the payload problem. (3) The clinical endpoints, outcome measures, and patient selection criteria established for OTOF trials will likely inform FDA expectations for STRC gene therapy. (4) The paper’s discussion of whether success with otoferlin will replicate in other forms of genetic HL directly frames the question our program must answer. (5) Understanding the pediatric clinical framework is essential since DFNB16 patients are typically identified in childhood.

Key numbers

• Gene: OTOF (otoferlin) — ~6kb CDS, dual-AAV delivery approach
• Target population: infants and children with ANSD
• Status: early clinical success demonstrated, ongoing trials

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/41979424/
• DOI: https://doi.org/10.1097/AUD.0000000000001773

What they found

Organic nanoparticles that convert focused ultrasound into tunable light emission (blue to red) via mechanoluminescence — no implanted light source needed. The system couples reactive oxygen species-responsive chemiluminescent donors with fluorescent acceptors through energy transfer. In vitro: ultrasound triggered these nanoparticles to activate optogenetic proteins. The design principle (electronic energy gap → ROS generation → light output) is predictive and tunable, meaning specific wavelengths can be engineered for specific opsins.

Lateral connection

Our sonogenetics hypothesis requires getting light into OHCs deep in the cochlea to activate light-sensitive ion channels — without surgical implantation of an LED or fiber optic. This paper eliminates that barrier. Mechanoluminescent nanoparticles could be delivered through the round window membrane (same route as AAV), concentrate near OHCs, and then be activated externally via transcranial focused ultrasound. No implant. No surgery beyond what gene therapy already requires. The cochlea is acoustically accessible by design — it’s built to receive sound pressure.

Hypothesis suggested

Mechanoluminescent nanoparticles delivered via round window injection, combined with OHC-expressed channelrhodopsin (via AAV), could restore sound-driven OHC electromotility in DFNB16 patients without fixing STRC. External FUS transducer converts acoustic signal → nanoparticle light → opsin activation → OHC depolarization → amplification.

What could be computed

1. Acoustic modeling: FEM simulation of ultrasound propagation through skull + temporal bone to estimate intensity at OHC depth — does enough energy reach the cochlea to trigger mechanoluminescence?
2. Wavelength matching: Map available mechanoluminescent emission spectra against channelrhodopsin action spectra (ChR2 peaks at 470nm, ReaChR at 590nm) to identify optimal nanoparticle-opsin pairs.
3. Nanoparticle diffusion model: Simulate round window injection → endolymph diffusion → OHC surface concentration over time.

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/41974592/
• DOI: https://doi.org/10.1021/jacs.5c22630

What they found

TMEM145 is a newly identified transmembrane protein that forms the core of TM-ACs (tectorial membrane attachment crowns) on outer hair cell stereocilia. Without TMEM145, stereocilin is lost from OHC stereocilia, the hair bundle physically disconnects from the tectorial membrane, and profound hearing loss results. TMEM145 appears to act as an anchor or scaffold that retains stereocilin at the stereocilia tip — not just a passenger in the complex.

How this applies to mini-STRC

This changes the structural model for mini-STRC design. Stereocilin doesn’t sit at the TM-AC alone — it depends on TMEM145 for localization. Mini-STRC (residues 700–1775) must preserve the TMEM145-binding interface, or the truncated protein will express but fail to localize correctly. This is the critical test: does the truncated region contain the TMEM145 interaction domain? Computational priority: AlphaFold-Multimer model of STRC-TMEM145 complex, then map which STRC residues form the interface, then verify those residues fall within our 700–1775 window.

Key numbers

• Without TMEM145: stereocilin lost from OHC stereocilia entirely
• Result: hair bundle disconnects from tectorial membrane → profound HL
• TMEM145 is transmembrane (OHC-expressed), stereocilin is extracellular

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/41923617/
• DOI: https://doi.org/10.1016/j.neuron.2026.03.007

What they found

Cryo-EM structure of PCDH15 — the lower tip link protein that connects stereocilia and gates mechanotransduction channels. PCDH15 forms parallel cis-dimers arranged as a right-handed double helix. This specific oligomeric architecture is required for tip link function: mutations that disrupt dimerization impair mechanotransduction even when the protein is expressed and present. Architecture = function, not just presence.

How this applies to mini-STRC

Stereocilin and PCDH15 are both extracellular proteins that form load-bearing connections between stereocilia structures. The PCDH15 finding generalizes: in the hair bundle, extracellular connector proteins don’t just need to be present — they need to self-assemble into precise supramolecular structures. Mini-STRC must therefore preserve not only folding stability but oligomerization capacity. The truncation at residues 700–1775 may disrupt self-assembly domains that exist outside this window. Computationally: predict STRC oligomeric state with AlphaFold-Multimer, identify self-assembly interfaces, verify they fall within the mini-STRC window.

Key numbers

• PCDH15 architecture: right-handed double helix parallel cis-dimer
• Dimerization domain mutations: impair mechanotransduction even with normal expression levels
• Technique: cryo-EM

Links

• bioRxiv: https://biorxiv.org/content/10.64898/2026.03.02.709101
• DOI: https://doi.org/10.64898/2026.03.02.709101

What they found

SLC26A4 mutations are the second most common cause of hereditary hearing loss in many Asian countries (DFNB4). The authors demonstrated that postnatal AAV-mediated Slc26a4 gene therapy can improve hearing and preserve structural integrity of the inner ear in an animal model. Critically, they identified a therapeutic window for intervention — establishing that timing of gene delivery matters for efficacy. The study targeted the endolymphatic sac and cochlear lateral wall, showing these are viable sites for effective gene therapy intervention in DFNB4.

How this applies to mini-STRC

This is directly informative for our mini-STRC program in several ways: (1) It demonstrates postnatal gene therapy feasibility for a different hereditary hearing loss gene, validating the general approach. (2) The identification of a critical therapeutic window is important — we should consider whether STRC/DFNB16 has a similar window where intervention must occur before irreversible hair cell damage. (3) Their targeting of specific cochlear structures (endolymphatic sac, lateral wall) contrasts with our need to target outer hair cells specifically, but the delivery methodology and surgical approach may be informative. (4) As another oversized-gene adjacent program (SLC26A4 is ~2.3kb CDS, fitting AAV), their regulatory/preclinical path provides a reference for DFNB16 IND strategy.

Key numbers

• Gene: SLC26A4 (pendrin) — second most common cause of hereditary HL in Asian populations
• Target structures: endolymphatic sac and cochlear lateral wall
• Finding: critical therapeutic window identified for postnatal intervention

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/41701544/
• DOI: https://doi.org/10.1172/JCI193812

What they found

First proof-of-concept STRC gene therapy in Strc-/- mice. Dual AAV (PHP.B serotype) delivering split STRC injected at P1. Confirmed STRC protein at OHC stereocilia tips, structural restoration, and partial hearing recovery.

Key numbers

• Injection age: P1 (postnatal day 1) — NEONATAL ONLY
• OHC transduction: 59% of OHC bundles showed distinct STRC localization
• Hearing recovery: 50-60 dB improvement in best responders; thresholds as low as 30 dB
• Bundle morphology: 61-65% of bundles showed normal organization and top connectors
• TM attachment: Restored — attachment crowns reformed after STRC delivery

Critical finding on TM re-attachment

Even in full STRC knockout mice, where TM imprints were ABSENT (Verpy 2011), gene therapy at P1 successfully restored TM-OHC attachment crowns.

This means: TM contact can reform when STRC is provided, even starting from zero. The TM retains the structural capacity to embed stereocilia tips if STRC is present.

For adult treatment, this is cautiously positive — but untested.

Age limitation (explicit from paper)

“Because injection in adult mouse cochleas is technically challenging, we focused on vector delivery during the first postnatal week, and whether dual vector delivery of STRC into mature cochleas is a viable treatment option remains to be determined.”

This is the critical open question. No adult data exists.

Comparison to Iranfar 2026

Iranfar (CTM 2026) is a more recent replication using AAV9-PHP.eB with similar results. Both papers demonstrate neonatal STRC restoration. Neither tests adult.

Relevance to Misha

The TM re-attachment finding is encouraging: even full KO cochlea can reform TM contact. Misha’s partial STRC likely maintained more TM contact than KO. His cochlea is probably in a BETTER state for rescue than the KO mice that were treated.

The gap: no one has tried delivery at P30+, P60+, or adult in STRC-null mice. This is the experiment the field needs — and the data Misha’s program needs.

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/34910522/
• PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC8673757/
• DOI: https://doi.org/10.1126/sciadv.abi7629

What they found

First direct measurement of HTC spring contribution to OHC hair bundle stiffness using non-contact acoustic FM-AFM. Measured at P9–P15 in Strc-/-, Strc+/-, and Strc-/-/Tecta-/- mice, isolating the specific contribution of horizontal top connectors.

Key numbers (directly from paper)

Condition	OHC bundle stiffness	IHC bundle stiffness
With HTCs (Strc+/−/Tecta−/−)	5.12 ± 0.46 pN/nm	2.34 ± 0.64 pN/nm
Without HTCs (Strc−/−/Tecta−/−)	2.05 ± 0.15 pN/nm	2.74 ± 0.50 pN/nm

• Reduction: ~60% in OHC bundle stiffness without HTCs
• IHC stiffness is UNCHANGED — HTCs are OHC-specific, IHC are unaffected
• Measurements at P13–P15 (post HTC maturation)

Unit conversion for model

• 5.12 pN/nm = 5.12 mN/m (per bundle, ~20 stereocilia)
• HTC contribution: 5.12 − 2.05 = 3.07 mN/m per bundle
• Per stereocilium: ~0.154 mN/m
• Per HTC link (19 links in 20-stereocilia chain): ~0.16 mN/m per link

This is ~5.7× larger than my original k_HTC estimate (0.028 mN/m). Model needs recalibration with these values.

Developmental timeline

Top connector maturation coincides with hearing onset (P12–P15). Significant increase in OHC (not IHC) stiffness from P12→P15 = HTC maturation window. No adult measurements — limitation of the study.

Relevance to model

Provides ground-truth calibration for k_HTC in stereocilia_bundle_mechanics.py. The 60% reduction figure is confirmed with direct measurement, not inferred. Critical: IHC stiffness unchanged = tip-link parameters remain valid for HTC-free state.

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/30801007/
• PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC6382404/
• DOI: https://doi.org/10.1126/sciadv.aat9934

What they found

Extended characterization of Strc-/- mouse cochlea at multiple ages including late (5 months). Critical data on tectorial membrane morphology and OHC structural/survival status over time.

Key findings — OHC survival timeline

Age	Finding
P9	Bundle structurally and functionally NORMAL
P10	First morphological anomalies in some OHCs
P14	Stereocilia still connected by tip links
P15	Tip links begin disappearing
P60	”Almost all OHC stereocilia fully disconnected from each other”
5 months	BASAL region: “only rare OHC hair bundles, all with scarce and shortened stereocilia”
5 months	APICAL region: “OHC loss NOT increased compared to control mice”

Critical distinction: basal (high-freq) OHCs degrade faster than apical (low-freq). At 5 months: apical OHCs largely preserved, basal OHCs significantly damaged.

Key findings — Tectorial membrane

TM imprints ABSENT throughout development and adulthood in Strc-/- mice:

“Stereocilia imprints on the lower surface of the tectorial membrane were not observed in Strc-/- mice”

This means: without STRC, the TM-OHC attachment crowns never form — not that they form and then degrade. The TM never embeds the OHC stereocilia tips.

However:

• Hensen’s stripe present and unaffected
• TM remains attached to spiral limbus normally
• TM gross structure maintained

Critical implication for Misha

Misha has PARTIAL STRC (VUS allele produces some protein). His TM likely DID form partial attachment crowns and imprints at birth. Unlike the full KO, he had some OHC-TM coupling. His question is not “did TM contact ever exist” (it probably did, partially) but “is it maintained at age 5?”

The apical vs basal gradient matters for Misha specifically:

• Left ear (milder, ~40-50 dB) → more apical involvement → better preserved OHCs
• Right ear (worse, ~50-65 dB) → more basal damage → more degradation

Links

• PubMed: https://pubmed.ncbi.nlm.nih.gov/21165971/
• PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC3375590/
• DOI: https://doi.org/10.1002/cne.22509