Expression of Ttyh1, a member of the Tweety family in neurons in vitro and in vivo and its potential role in brain pathology

We have previously shown that Ttyh1 mRNA is expressed in neurons and its expression is up-regulated in the brain during epileptogenesis and epilepsy. In this study, we aimed to elucidate the role of Ttyh1 in neurons. We found widespread expression of Ttyh1 protein in neurons in vivo and in vitro. Ttyh1 immunoreactivity in vitro was frequently found in invaginations of dendritic spines; however, Ttyh1, seldom co-localized with synaptic markers in vivo. Silencing Ttyh1 expression with siRNA in hippocampal cultures resulted in alterations of MAP2 distribution along neurites causing it to appear in the form of chains of beads. Over-expression of Ttyh1 caused intense neuritogenesis and the formation of numerous filopodia-like protrusions. Similar protrusions were also produced in SH-SY5Y neuroblastoma cells over-expressing Ttyh1. Using a biotin-streptavidin pull-down assay and mass spectrometry, we identified proteins that can form complexes with Ttyh1 in the brain. Ttyh1 binding proteins are often expressed in the endoplasmic reticulum or the Golgi apparatus or are localized at synapses. Finally, we found increased expression of Ttyh1 in the inner molecular layer of the dentate gyrus in an animal model of epilepsy. On the basis of our findings, we propose Ttyh1 involvement in brain pathology.