Age related changes in gene expression within the cochlea of C57BL/6J mice.

Abstract

Hearing loss as a unique symptom is highly prevalent in the elderly and while there exists several pathologies that would result in age related hearing loss (ARHL), most agree it is multifactorial with environmental, metabolic and genetic components. However, no research to date has discovered a definitive genetic cause. This paper describes the use of microarray to address this issue. The left cochlea of laboratory aged C57BL6J mice at 4, 15 and 45 weeks was extracted from pooled, agematched animals and the RNA extracted for use in microarray analysis. The contralateral cochlea was also removed and used for immunohistochemical analysis. Microarray revealed 116 genes to be up or down regulated between young and old animals, the most prominent being prolactin (108.2 fold increase) and growth hormone (43.94 fold increase). The prolactin inhibitor calcitonin was also down regulated over 2 fold. Immunohistochemistry revealed prolactin to be weakly expressed within the spiral ganglion, whilst its receptor was widely distributed throughout the cochlea. This is the first study demonstrating the cochlea as a site for extrapituitary prolactin expression and that this expression is related to age. Combined with the widespread distribution of prolactin receptor, there may be implications for prolactin's role in ARHL.