8.A.122. The Vesicular Membrane Neurensin/TMEM74 (Neurensin/TMEM74) Family
Nuerensins may play important roles in neural organelle transport, transduction of nerve signals and nerve growth, and may also play a role in neurite extension. The homologous transmembrane protein 74 (TMEM74), which contains two putative transmembrane domains and exhibits high levels of mRNA in the brain, is closely associated with the pathogenesis of anxiety disorders (Shao et al. 2019). TMEM74 is decreased in the serum of patients with anxiety and the basolateral amygdaloid nucleus (BLA) in chronic stress mice. Genetic deletion of Tmem74 or selective knockdown of Tmem74 in BLA pyramidal neurons resulted in anxiety-like behaviors in mice. Whole-cell recordings in BLA pyramidal neurons revealed lower hyperpolarization-activated cation current (Ih) and greater input resistance and excitability in Tmem74(-/-) neurons than in wild-type neurons. Accordingly, surface expression of hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels was also lower in the BLA of Tmem74(-/-) mice. The Ih current blocker ZD7288 mimicked these effects in BLA pyramidal neurons in wild-type mice but not in Tmem74(-/-) mice. Consistent with the improvement in anxiety-like behaviors, Tmem74 overexpression restored HCN1 channel trafficking and pyramidal neuron excitability in the BLA of Tmem74(-/-) and chronic stress mice. Interactions between Tmem74 and HCN1 are physiologically relevant, and TMS1 is essential for the cellular membrane localization of Tmem74 to enhance Ih. Thus, Tmem74 coupling with HCN1 acts as a critical component in the pathophysiology of anxiety and is a potential target for new treatments of anxiety disorders (Shao et al. 2019).