ANKRD24

ANKRD24 is an ankyrin-repeat protein that organizes the stereocilia rootlet architecture of inner ear hair cells, where it is required for normal mechanosensory function and hearing (PMID:35175278). It concentrates at the stereocilia insertion point, forming a ring at the junction between the lower and upper rootlets, and surrounds and binds TRIOBP-5 within the lower rootlet where TRIOBP-5 bundles rootlet F-actin; the two proteins are mutually dependent for correct localization, as TRIOBP-5 is mislocalized in Ankrd24-null hair cells, ANKRD24 fails to localize to rootlets without TRIOBP-5, and exogenous TRIOBP-5 restores endogenous ANKRD24 to rootlets (PMID:35175278). By bridging the apical plasma membrane to the lower rootlet, ANKRD24 maintains TRIOBP-5 distribution, and its loss produces progressive hearing loss, impaired recovery after noise damage, and increased mechanical vulnerability of the hair bundle (PMID:35175278); positioning of ANKRD24 and TRIOBP-5 at this rootlet pivot point depends on the upstream factor TPRN/taperin (PMID:40471101). A homozygous frameshift variant in ANKRD24 segregates with autosomal recessive nonsyndromic sensorineural hearing loss in a consanguineous family, implicating the gene in human deafness (PMID:39434538). Independently of its rootlet role, ANKRD24 is a transcriptional target of HMGCS2 and acts in a ketone body-linked autophagic pathway, where its silencing reduces LAMP1 and LC3-II and diminishes HMGCS2-induced autophagic clearance of Tau/pTau (PMID:36442191).

1. 2022 High

   Established ANKRD24's core molecular role by showing it occupies the stereocilia rootlet pivot point and is reciprocally dependent with TRIOBP-5 for localization and rootlet F-actin organization.

   Evidence Superresolution microscopy, Ankrd24 knockout mice, and exogenous DsRed-TRIOBP-5 rescue showing mutual localization dependence

   PMID:35175278

   Open questions at the time

   • The direct binding interface and stoichiometry between ANKRD24 and TRIOBP-5 are not defined
   • Whether ANKRD24 directly contacts F-actin or only TRIOBP-5 is unresolved
   • No structural model of the rootlet ring assembly
2. 2022 High

   Connected the molecular localization to organismal function by demonstrating that ANKRD24 bridges the apical membrane to the rootlet and is required for hearing and mechanical resilience.

   Evidence Ankrd24 knockout mice with auditory functional assays and superresolution microscopy

   PMID:35175278

   Open questions at the time

   • The membrane-anchoring partner ANKRD24 uses to bridge the apical membrane is not identified
   • Mechanism by which rootlet disorganization causes progressive rather than congenital loss is unclear
3. 2023 Medium

   Placed ANKRD24 in a second pathway, downstream of HMGCS2 ketone-body signaling, where it supports autophagic clearance of Tau/pTau.

   Evidence RNA-seq identification as HMGCS2 target plus siRNA silencing with LAMP1/LC3-II western blots and TEM of autophagosomes

   PMID:36442191

   Open questions at the time

   • No direct protein interaction or reconstitution for ANKRD24 in autophagy
   • Molecular activity of ANKRD24 within the autophagic machinery is undefined
   • Relationship between the autophagy role and the stereocilia role is unknown
4. 2024 Medium

   Provided the first human disease link, implicating ANKRD24 in recessive nonsyndromic hearing loss.

   Evidence Whole exome sequencing and segregation of a homozygous frameshift variant in a consanguineous family

   PMID:39434538

   Open questions at the time

   • No functional rescue or molecular assay of the variant
   • Single family limits genotype-phenotype generalization
5. 2025 Medium

   Defined the upstream input to ANKRD24 localization, placing it (and TRIOBP-5) downstream of TPRN/taperin at the rootlet.

   Evidence TPRN-deficient mice with immunofluorescence localization of ANKRD24 and TRIOBP-5

   PMID:40471101

   Open questions at the time

   • Whether TPRN acts directly or through intermediate factors on ANKRD24 is unknown
   • Single study without biochemical interaction data

• How ANKRD24 reconciles its structural rootlet role with its autophagy function, and the direct molecular activity it carries out in either context, remains unresolved.
• No defined enzymatic or binding activity for ANKRD24 beyond TRIOBP-5 association
• No structural data
• Tissue-specific basis for dual roles unexplored