Otoprotective effects of mouse nerve growth factor in DBA/2J mice with early-onset progressive hearing loss.

As it displays progressive hair-cell loss and degeneration of spiral ganglion neurons (SGNs) characterized by early-onset progressive hearing loss (ePHL), DBA/2J is an inbred mouse strain widely used in hearing research. Mouse nerve growth factor (mNGF), as a common exogenous nerve growth factor (NGF), has been studied extensively for its ability to promote neuronal survival and growth. To determine whether mNGF can ameliorate progressive hearing loss (PHL) in DBA/2J mice, saline or mNGF was given to DBA/2J mice of either sex by daily intramuscular injection from the 1st to the 9th week after birth. At 5, 7, and 9 weeks of age, in comparison with vehicle groups, mNGF groups experienced decreased auditory-evoked brainstem response (ABR) thresholds and increased distortion product otoacoustic emission (DPOAE) amplitudes, the prevention of hair cell loss, and the inhibition of apoptosis of SGNs. Downregulation of Bak/Bax and Caspase genes and proteins in cochleae of mice receiving the mNGF treatment was detected by real-time PCR, Western blot, and immunohistochemistry. This suggests that the Bak-dependent mitochondrial apoptosis pathway may be involved in the otoprotective mechanism of mNGF in progressive hearing loss of DBA/2J mice. Our results demonstrate that mNGF can act as an otoprotectant in the DBA/2J mice for the early intervention of PHL and, thus, could become of great value in clinical applications.