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A functional study of plasma-membrane calcium-pump isoform 2 mutants causing digenic deafness
R Ficarella1, F Di Leva, M Bortolozzi
1Telethon Institute of Genetics and Medicine, 80131 Naples, Italy.
Summary
Mutations in the plasma-membrane calcium-pump isoform 2 (PMCA2) gene cause deafness by impairing calcium ion (Ca2+) export from hair cells. The G293S mutation in PMCA2 and cadherin 23 mutations exacerbate hearing loss.
Area of Science:
- Otolaryngology
- Genetics
- Cell Biology
Background:
- Calcium ion (Ca2+) homeostasis is critical for hair cell function in the inner ear.
- The plasma-membrane calcium-pump isoform 2 (PMCA2) and its w/a splicing variant are essential for Ca2+ extrusion from hair cell stereocilia.
- Mutations in PMCA2, such as G283S in deafwaddler mice, lead to deafness.
Purpose of the Study:
- To investigate the functional consequences of a novel PMCA2 mutation (G293S) identified in a human family with deafness.
- To examine the role of cadherin 23 mutations in modulating hearing loss in conjunction with PMCA2 mutations.
- To characterize the activity of the PMCA2 w/a isoform and the impact of mutations on Ca2+ transients in hair cells.
Main Methods:
- Genetic screening for PMCA2 and cadherin 23 mutations in a human family.
- Overexpression of PMCA2 isoforms in Chinese Hamster Ovary (CHO) cells.
- Assessment of Ca2+ transients using InsP3-induced Ca2+ release in CHO cells.
- Calcium imaging in organotypic cultures of vestibular hair cells from mouse models.
Main Results:
- A novel deafness-inducing PMCA2 mutation (G293S) was identified in a human family.
- A cadherin 23 mutation (T1999S) was found in an affected individual, suggesting a synergistic effect on hearing loss.
- The PMCA2 w/a isoform showed limited activation, and mutations G293S and G283S impaired Ca2+ transient dissipation in cell models.
- Compromised Ca2+ transient dissipation and reduced mechanoelectrical transduction channel sensitivity were observed in hair cells from PMCA2-deficient mice.
Conclusions:
- The PMCA2 w/a isoform plays a crucial role in hair cell Ca2+ clearance, and its dysfunction due to mutations leads to hearing impairment.
- Cadherin 23 mutations can exacerbate hearing loss in individuals with PMCA2 mutations.
- These findings highlight the importance of PMCA2 and cadherin 23 in maintaining auditory function and provide insights into the genetic basis of deafness.
