Adenosine A2B receptor: A pathogenic factor and a therapeutic target for sensorineural hearing loss

FASEB J. 2020 Dec;34(12):15771-15787. doi: 10.1096/fj.202000939R. Epub 2020 Nov 1.

Abstract

Over 466 million people worldwide are diagnosed with hearing loss (HL). About 90% of HL cases are sensorineural HL (SNHL) with treatments limited to hearing aids and cochlear implants with no FDA-approved drugs. Intriguingly, ADA-deficient patients have been reported to have bilateral SNHL, however, its underlying cellular and molecular basis remain unknown. We report that Ada-/- mice, phenocopying ADA-deficient humans, displayed SNHL. Ada-/- mice cochlea with elevated adenosine caused substantial nerve fiber demyelination and mild hair cell loss. ADA enzyme therapy in these mice normalized cochlear adenosine levels, attenuated SNHL, and prevented demyelination. Additionally, ADA enzyme therapy rescued SNHL by restoring nerve fiber structure in Ada-/- mice post two-week drug withdrawal. Moreover, elevated cochlear adenosine in untreated mice was associated with enhanced Adora2b gene expression. Preclinically, ADORA2B-specific antagonist treatment in Ada-/- mice significantly improved HL, nerve fiber density, and myelin compaction. We also provided genetic evidence that ADORA2B is detrimental for age-related SNHL by impairing cochlear myelination in WT aged mice. Overall, understanding purinergic molecular signaling in SNHL in Ada-/- mice allows us to further discover that ADORA2B is also a pathogenic factor underlying aged-related SNHL by impairing cochlear myelination and lowering cochlear adenosine levels or blocking ADORA2B signaling are effective therapies for SNHL.

Keywords: ADA-deficiency; adenosine deaminase deficiency; aging; myelin protein zero; myelination.