Calpain2-mediated downregulation of apoptosis-inducing factors impairs mitochondrial function in noise-induced spiral ganglion neuron degeneration.

Noise-induced hearing loss can lead to degeneration of spiral ganglion neurons (SGN), resulting in impairment of auditory signalling. However, the specific mechanism is unclear. In our study, we investigated the function of mitochondrial activity following noise exposure. Findings revealed a reduction in ATP synthesis and alterations in the levels of mitochondrial electron transport chain complexes II, Ⅲ, IV and complex I subunit ND3 reduction by the seventh day post-noise exposure. These findings indicate that SGN mitochondrial dysfunction can impair SGN function. This is further demonstrated by the reduced expression of the mitochondrial marker protein Tom20 and apoptosis-inducing factor (AIF) showed inner membrane but not outer membrane resulted in changes in mitochondrial ETC complexes. And the findings of calpain 2 but not calpain 1 high expression was accompanied in AIF reduction, suggesting AIF has not yet caused SGN deaths. Calpain 2 regulated decreased expression of AIF may relieve the low function of mitochondrion in SGN after noise.