Background: Age-related hearing loss (ARHL) is a common sensory disorder predominantly affecting older individuals, primarily caused by progressive degeneration of cochlear. While the toll-like receptor 4 (TLR-4)/nuclear factor kappa-B (NF-κB) signaling pathway plays a crucial role in inflammation, its precise role in cochlear inflammation and ARHL remains to be elucidated. Therefore, this study explored the role of TLR-4/NF-κB signaling axis in cochlear inflammation and its impact on ARHL pathogenesis.

Methods: HEI-OC1 cells were treated with lipopolysaccharide (LPS) to establish an inflammatory model, with TLR-4 and NF-κB inhibitors used as interventions. Similarly, male C57BL/6 mice (8 weeks and 24 months old) were treated with LPS to induce an ARHL model. Cellular viability and apoptosis rate were assessed using the cell counting kit-8 (CCK-8) assay. Furthermore, hearing function was determined using distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR). Finally, the expression levels of TLR-4, NF-κB, and pro-inflammatory cytokines were assessed using quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and enzyme-linked immunosorbent assay (ELISA).

Results: In vitro experiments revealed that TLR-4 and NF-κB inhibitors significantly restored cell viability and reduced LPS-induced apoptosis (p < 0.05). LPS treatment activated TLR-4/NF-κB signaling pathway and increased interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) expression levels, while these effects were suppressed through TLR-4 inhibition (p < 0.05). In vivo experiments showed that LPS-treated mice exhibited significant hearing impairment, which was alleviated through TLR-4 inhibitor (p < 0.05). Histopathological analysis revealed that LPS induced cochlear inflammation and cell damage, whereas TLR-4 inhibition mitigated these pathological changes. Furthermore, suppression of the TLR-4/NF-κB pathway significantly reduced the expression of pro-inflammatory cytokines in cochlear tissues, thereby alleviating inflammatory responses (p < 0.05).

Conclusion: The TLR-4/NF-κB pathway plays a crucial role in LPS-induced cochlear inflammation and ARHL progression. Inhibition of this pathway effectively alleviates age-related hearing loss by attenuating cochlear inflammation and protecting cochlear cells from apoptosis.