Received for publication September 14, 2007.
Revised January 15, 2008.
Accepted for publication January 15, 2008.

Salicylate Alters Expression of Calcium Response Transcription Factor 1 (CaRF1) in the Cochlea: Implications for BDNF Transcriptional Regulation

Abstract

Brain-derived neurotrophic factor (BDNF) is a key neurotrophin whose expression is altered in response to neurological activity, influencing both short- and long-term synaptic changes. The BDNF gene consists of eight upstream exons (I-VII), each of which has a distinct promoter, and can be independently spliced to the ninth coding exon (IX). We recently showed that the expression of BDNF exon IV in the cochlea is altered following exposure to salicylate, an ototoxic drug that in high doses is able to induce hearing loss and tinnitus. These changes were a crucial trigger for plasticity changes in the central auditory system. BDNF exon IV expression is regulated via interaction between calcium response elements CaRE1, CaRE2 and CaRE3/Cre (CaREs) that are bound by the transcription factors CaRF1, USF1/2 and CREB, respectively. To determine if the salicylate induced changes in cochlear BDNF exon IV expression include a differential use of the CaRE binding proteins, we studied the level of the corresponding binding-proteins in the spiral ganglion neurons prior to and following systemic application of concentrated salicylate using in situ hybridization and RT-PCR. BDNF exon IV and CaRF1 expression were upregulated following application of salicylate, while USF1/2 and CREB mRNA expression remained unaffected. The changes in BDNF exon IV and CaRF1 expression were also dose-dependent. The data show Ca²⁺ and CaRF1 as messengers of trauma (salicylate)-induced altered BDNF levels in the cochlea. Furthermore, they also provide the first evidence that a differential regulation of BDNF transcription factors might participate in BDNF-mediated plasticity changes.

Key words: Calcium (Votage-Gated Channels), CREB, DNA binding sites, In situ hybridization, Regulation of gene expression, Regulation - transcriptional, Synaptic plasticity