Increased Sensitivity to Noise-Induced Hearing Loss by Blockade of Endogenous PI3K/Akt Signaling

The PI3K/Akt signaling pathway is involved in mediating survival of sensory hair cells. Here, we investigated the involvement of PI3K/Akt in noise-induced hearing loss in both temporary and permanent threshold shift noise models. The PI3K regulatory subunit p85 alpha and phosphorylation of Akt on serine 473 (p-Akt S473) are downregulated in sensory hair cells, including both outer and inner hair cells, and supporting cells of the mouse organ of Corti 1 h after exposure to permanent-threshold-shift-inducing noise (PTS noise), but not with temporary-threshold-shift-inducing noise (TTS noise). In contrast, the PI3K catalytic subunit p110 alpha and phosphorylation of Akt on threonine 308 (p-Akt T308) do not change with PTS or TTS noise. Additionally, mice pretreated with p85 alpha small interfering RNA (siRNA) have decreased expression of p-Akt1 (S473) in their sensory hair cells and increased sensitivity to TTS noise-induced hearing loss. Finally, Akt1-knockout mice also have enhanced sensitivity to TTS noise-induced hearing loss. In conclusion, this study suggests that endogenous PI3K/Akt signaling is an intrinsic protective mechanism of the inner ear. Blockade of PI3K/Akt signaling pathways increases sensitivity to TTS noise-induced hearing loss.