The plasma membrane calcium pump in the hearing process: physiology and pathology

Area of Science:

• Biochemistry
• Cell Biology
• Genetics

Background:

• Mammalian cells utilize four plasma membrane Ca(2+) ATPases (PMCAs) for calcium extrusion.
• PMCA2, particularly its variants, plays a critical role in the specialized environment of the inner ear's hair cells.
• Alternative splicing generates diverse PMCA isoforms with distinct functional properties.

Purpose of the Study:

• To investigate the role of PMCA2 variants in the inner ear and their contribution to hearing.
• To understand the molecular mechanisms underlying hearing loss associated with PMCA2 defects.

Main Methods:

• Analysis of PMCA alternative splicing patterns.
• Functional characterization of PMCA2 variants in cellular models.
• Molecular analysis of mutations in PMCA2 associated with deafness in humans and mice.

Main Results:

• A specific PMCA2 variant, truncated and with an N-terminal insert, is localized to inner ear stereocilia.
• This variant exports Ca(2+) less efficiently than full-length PMCA2, impacting mechano-electrical transduction.
• Defects in this PMCA2 variant, or in cadherin 23, lead to hearing loss phenotypes.

Conclusions:

• The PMCA2 pump's function in stereocilia is essential for maintaining auditory function.
• Molecular analysis reveals that PMCA2 defects affecting its basal Ca(2+) export capability underlie certain forms of deafness.
• These findings highlight the intricate relationship between calcium homeostasis and hearing.