Expression of prosaposin and its G protein-coupled receptor (GPR) 37 in mouse cochlear and vestibular nuclei

Prosaposin is a precursor of lysosomal hydrolases activator proteins, saposins, and also acts as a secretory protein that is not processed into saposins. Prosaposin elicits neurotrophic function via G protein-coupled receptor (GPR) 37, and prosaposin deficiency causes abnormal vestibuloauditory end-organ development. In this study, immunohistochemistry was used to examine prosaposin and GPR37 expression patterns in the mouse cochlear and vestibular nuclei. Prosaposin immunoreactivity was observed in neurons and glial cells in both nuclei. GPR37 immunoreactivity was observed in only some neurons, and its immunoreactivity in the vestibular nucleus was weaker than that in the cochlear nucleus. This study suggests a possibility that prosaposin deficiency affects not only the end-organs but also the first center of the vestibuloauditory system.