Cabp2-Gene Therapy Restores Inner Hair Cell Calcium Currents and Improves Hearing in a DFNB93 Mouse Model

Abstract

Clinical management of auditory synaptopathies like other genetic hearing disorders is currently limited to the use of hearing aids or cochlear implants. However, future gene therapy promises restoration of hearing in selected forms of monogenic hearing impairment, in which cochlear morphology is preserved over a time window that enables intervention. This includes non-syndromic autosomal recessive hearing impairment DFNB93, caused by defects in the CABP2 gene. Calcium-binding protein 2 (CaBP2) is a potent modulator of inner hair cell (IHC) voltage-gated calcium channels Ca V 1.3. Based on disease modeling in Cabp2 –/– mice, DFNB93 hearing impairment has been ascribed to enhanced steady-state inactivation of IHC Ca V 1.3 channels, effectively limiting their availability to trigger synaptic transmission. This, however, does not seem to interfere with cochlear development and does not cause early degeneration of hair cells or their synapses. Here, we studied the potential of a gene therapeutic approach for the treatment of DFNB93. We used AAV2/1 and AAV-PHP.eB viral vectors to deliver the Cabp2 coding sequence into IHCs of early postnatal Cabp2 –/– mice and assessed the level of restoration of hair cell function and hearing. Combining in vitro and in vivo approaches, we observed high transduction efficiency, and restoration of IHC Ca V 1.3 function resulting in improved hearing of Cabp2 –/– mice. These preclinical results prove the feasibility of DFNB93 gene therapy.

Clinical management of auditory synaptopathies like other genetic hearing disorders is currently limited to the use of hearing aids or cochlear implants. However, future gene therapy promises restoration of hearing in selected forms of monogenic hearing impairment, in which cochlear morphology is preserved over a time window that enables intervention. This includes non-syndromic autosomal recessive hearing impairment DFNB93, caused by defects in the CABP2 gene. Calcium-binding protein 2 (CaBP2) is a potent modulator of inner hair cell (IHC) voltage-gated calcium channels Ca V 1.3. Based on disease modeling in Cabp2 –/– mice, DFNB93 hearing impairment has been ascribed to enhanced steady-state inactivation of IHC Ca V 1.3 channels, effectively limiting their availability to trigger synaptic transmission. This, however, does not seem to interfere with cochlear development and does not cause early degeneration of hair cells or their synapses. Here, we studied the potential of a gene therapeutic approach for the treatment of DFNB93. We used AAV2/1 and AAV-PHP.eB viral vectors to deliver the Cabp2 coding sequence into IHCs of early postnatal Cabp2 –/– mice and assessed the level of restoration of hair cell function and hearing. Combining in vitro and in vivo approaches, we observed high transduction efficiency, and restoration of IHC Ca V 1.3 function resulting in improved hearing of Cabp2 –/– mice. These preclinical results prove the feasibility of DFNB93 gene therapy.