Diverse cellular and environmental stresses can activate the heat shock response, an evolutionarily conserved mechanism to protect
proteins from denaturation. Stressors activate
heat shock transcription factor 1 (HSF1), which binds to heat shock elements in the genes for
heat shock proteins, leading to rapid induction of these important
molecular chaperones. Both heat and noise stress are known to activate the heat shock response in the cochlea and
protect it from subsequent noise
trauma. However, the contribution of HSF1 to induction of
heat shock proteins following noise
trauma has not been investigated at the molecular level. We evaluated the role of HSF1 in the cochlea following noise stress by examining induction of
heat shock proteins in Hsf1 ( +/- ) control and Hsf1 ( -/- ) mice. Heat stress rapidly induced expression of Hsp25, Hsp47,
Hsp70.1, Hsp70.3, Hsp84, Hsp86, and Hsp110 in the cochleae of wild-type and Hsf1 ( +/- ) mice, but not in Hsf1 ( -/- ) mice, confirming the essential role of HSF1 in mediating the heat shock response. Exposure to broadband noise (2-20 kHz) at 106 dB SPL for 2 h produced partial
hearing loss. Maximal induction of
heat shock proteins occurred 4 h after the noise. In comparison to heat stress, noise stress resulted in lower induced levels of Hsp25,
Hsp70.1, Hsp70.3, Hsp86, and Hsp110 in Hsf1 ( +/- ) mice. Induction of these
heat shock proteins was attenuated, but not completely eliminated, in Hsf1 ( -/- ) mice. These same noise exposure conditions induced genes for several immediate early
transcription factors and maximum induction occurred earlier than for
heat shock proteins. Thus, additional signaling pathways and transcriptional regulators that are activated by noise probably contribute to induction of
heat shock proteins in the cochlea.