Impaired Development of the Medial Olivocochlear System in a KCNQ4-Deficient Mouse Model

Area of Science:

• Neuroscience
• Otolaryngology
• Cell Biology

Background:

• The medial olivocochlear (MOC) efferent system regulates outer hair cell (OHC) function and cochlear protection.
• KCNQ4 potassium channels are crucial for OHC repolarization; their loss causes hearing impairment.
• The role of KCNQ4 in efferent synapse development and organization remains unclear.

Purpose of the Study:

• To investigate the impact of KCNQ4 deficiency on the development and organization of cochlear efferent synapses.
• To analyze structural and molecular changes in efferent boutons associated with KCNQ4 loss.

Main Methods:

• Confocal immunofluorescence microscopy was used to examine efferent innervation in the organ of Corti of Kcnq4 knockout (KO) and wild-type (WT) mice.
• Morphometric analysis quantified synaptic vesicle number, volume, and bouton organization.
• Quantitative PCR (qPCR) and protein expression analysis assessed key molecular components of the synapse.

Main Results:

• KCNQ4 deficiency caused delayed maturation of MOC terminals on OHCs, with persistent lateral displacement.
• KO mice exhibited reduced synaptic vesicle number and volume in efferent boutons.
• Downregulation of α10 nAChR, BK, and SK2 transcripts was observed, with altered BK protein expression and synaptic organization, alongside age-dependent upregulation of calbindin and calretinin.

Conclusions:

• KCNQ4 is essential for the proper maturation and maintenance of cochlear efferent synapses on OHCs.
• KCNQ4 dysfunction leads to structural and molecular alterations at the efferent synapse, affecting synaptic plasticity and homeostasis.
• These findings highlight KCNQ4's critical role in auditory synapse integrity and function.