Characterization of the Expression and Role of Striatin-Interacting Protein 2 in Mouse Cochlea.

Hypothesis: In this study, we aimed to examine the cochlear expression pattern and function of Striatin-interacting protein 2 (STRIP2) by using animal models.

Background: Sensorineural hearing loss often results from genetic defects in hair cell (HC) development and function. STRIP2 is a part of the striatin-interacting phosphatase and kinase (STRIPAK) complex, which plays important regulatory roles in cell fate determination, proliferation, cytoskeletal organization, and cell morphology. A recent study revealed Strip2 as the candidate gene that regulates positive selection in HC lineages. However, its role in the inner ear has not been identified.

Methods: Strip2 knockout mouse model was used to examine the cochlear expression pattern and function of STRIP2. Auditory brainstem response test was used to evaluate the hearing function of mice. Immunostaining and scanning electron microscope were used to study hair cells, synapses, and stereocilia of cochlea.

Results: Immunostaining showed that cytoplasmic STRIP2 expression in hair cells increased from postnatal day (P) 3 to P14. Despite having normal hearing thresholds, hair cell numbers, and stereocilia morphology until P90, the deletion of Strip2 resulted in a mild reduction in ribbon synapse density, suggesting a late onset of cochlear synaptic defects.

Conclusion: Our results revealed that STRIP2 was abundantly expressed in hair cells; however, the hearing function of Strip2-/- mice was comparable to that of control mice until P90, and a mild decrease in ribbon synapse number was detected at P60 and P90. Further studies on STRIP2 and its associated complexes will provide new insights into the pathways involved in inner ear development and function.