Temporal and genetic influences on protection against noise-induced hearing loss by hypoxic preconditioning in mice

The protective benefits of hypoxic preconditioning (HPC) against permanent noise-induced hearing loss (NIHL) were investigated in mice. Hypoxia induced by exposure to 8% O₂ for 4 h conferred significant protection against damaging broadband noise delivered 24-48 h later in male and female CBA/J (CBA) and CBA/CaJ mice. No protection was found in C57BL/6 (B6) mice, their B6.CAST-Cdh23^CAST (B6.CAST) congenics, or in CBAxB6 F1 hybrid mice over the same interval, suggesting that the potential for HPC depends on one or a few autosomal recessive alleles carried by CBA-related strains, and is not influenced by the Cdh23 locus. Protection against NIHL in CBA mice was associated with significant up-regulation of hypoxia-inducible factor-1α (HIF-1α) within the organ of Corti, not found in B6.CAST. In both CBA and B6.CAST mice, some hypoxia-noise intervals shorter than 24 h were associated with exacerbation of NIHL. Cellular cascades underlying the early exacerbation of NIHL by hypoxia are therefore common to both strains, and not mechanistically linked to later protection. Elucidation of the events that underlie HPC, and how these are impacted by genetics, may lead to pharmacologic approaches to mimic HPC, and may help identify individuals with elevated risk of NIHL.