¹University of Toyama, Department of Pharmaceutical Therapy & Neuropharmacology, Faculty of Pharmaceutical Sciences, Toyama, Japan, ²Jichi Medical University, Divison of Neurological Gene Therapy, Open Innovation Center, Shimotsuke, Japan, ³The University of Tokyo, Center for Gene and Cell Therapy, The Institute of Medical Science, Tokyo, Japan

Background: The number of patients with depression is increasing worldwide; however, current antidepressants need over two weeks for their effect. Around 30% of patients exhibit treatment resistance. Novel therapeutic strategies are required for these problems. Mutation in ODZ4, which encodes the Teneurin-4 (Tenm-4) protein, has been reported as a risk factor for mental disorders such as bipolar disorder and schizophrenia, accompanied by depressive syndrome. In addition, Tenm-4 could induce changes in synapse formation, axon guidance, or cell differentiation in oligodendrocytes. The prefrontal cortex (PFC) is involved in the regulation of depressive behaviors.

Aims & Objectives: To reveal the relation of Tenm-4 with mental disorders, we generated PFC-specific knockdown (Tenm-4KD) mice and evaluated behavior phenotypes. To investigate neuropathological changes in PFC caused by Tenm4KD, the change in the amount of myelin sheath was evaluated with immunohistochemistry.

Method: We generated prefrontal Tenm-4KD mice with adeno-associated virus injection male C57BL6/J (6-7 week-old) with (Tenm-4KD, and Mock as control) vectors integrated with the CRISPR-Cas9 system. Four weeks after the AAV injection, behavioral tests, including the sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST), were conducted to assess depression-like behaviors. Additionally, aripiprazole (APZ), a dopamine D2/3 partial agonist and serotonin 5-HT1A partial agonist/5-HT2A antagonist, was administered to evaluate its antidepressant effects. Myelin alterations in the PFC were analyzed using immunofluorescence staining for myelin basic protein (MBP).

Results: Tenm4KD mice exhibited significant reductions in sucrose preference (Tenm4KD mice=72.1% vs. Mock mice=85.8%, p < 0.05) in SPT. Tenm4KD mice showed increased immobility time in TST (164.7 sec vs. 130.1 sec, p < 0.05) and FST (218.7 sec vs. 179.2 sec, p < 0.01) compared to Mock mice. APZ treatment restored sucrose preference (80.5% vs. 58.6%, p < 0.05) in Tenm4KD mice compared to saline treatment. Furthermore, MBP staining revealed a significant reduction in myelin she in the PFC of Tenm4KD mice.

Discussion & Conclusions: These results suggest that PFC-specific Tenm4KD induces depression-like behaviors without affecting locomotor activity or recognition memory. The reversal of these behaviors after administration with APZ was recovered, therefore Tenm-4KD could involve dysfunction of dopamine and/or serotonin nervous. Additionally, the observed myelin reduction indicates that Tenm-4 deficiency would contribute to depression pathophysiology through glial dysfunction. Our results suggest PFC-specific Tenm-4KD mice could be a novel model for depression leading to the development of new antidepressant strategies.