國澤 和生

Background and Purpose Alterations in tryptophan‐kynurenine (TRP‐KYN) pathway are implicated in major depressive disorder (MDD). α7 nicotinic acetylcholine (α7nACh) receptor regulates the hypothalamic–pituitary–adrenal (HPA) axis. We have shown that deficiency of kynurenine 3‐monooxygenase (KMO) induces depression‐like behaviour via kynurenic acid (KYNA; α7nACh antagonist). In this study, we investigated the involvement of the TRP‐KYN pathway in stress‐induced behavioural changes and the regulation of the HPA axis. Experimental Approach Mice were exposed to chronic unpredictable mild stress (CUMS) and subjected to behavioural tests. We measured TRP‐KYN metabolites and the expression of their enzymes in the hippocampus. KMO heterozygous mice were used to investigate stress vulnerability. We also evaluated the effect of nicotine (s.c.) on CUMS‐induced behavioural changes and an increase in serum corticosterone (CORT) concentration. Key Results CUMS decreased social interaction time but increased immobility time under tail suspension associated with increased serum corticosterone concentration. CUMS increased KYNA levels via KMO suppression with microglial decline in the hippocampus. Kmo^+/− mice were vulnerable to stress: they exhibited social impairment and increased serum corticosterone concentration even after short‐term CUMS. Nicotine attenuated CUMS‐induced behavioural changes and increased serum corticosterone concentration by inhibiting the increase in corticotropin‐releasing hormone. Methyllycaconitine (α7nACh antagonist) inhibited the attenuating effect of nicotine. Conclusions and Implications CUMS‐induced behavioural changes and the HPA axis dysregulation could be induced by the increased levels of KYNA via KMO suppression. KYNA plays an important role in the pathophysiology of MDD as an α7nACh antagonist. Therefore, α7nACh receptor is an attractive therapeutic target for MDD.

Abstract Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, social deficits, and cognitive impairments. Maternal use of valproic acid (VPA) during pregnancy is associated with an increased risk of ASD in offspring. The prevailing pathophysiological hypothesis for ASD involves excitation/inhibition (E/I) imbalances and serotonergic dysfunction. Here, we investigated the association between glutamatergic-serotonergic neuronal interactions and ASD-like behaviors in mice exposed to prenatal VPA. Prenatal VPA exposure induced excessive repetitive self-grooming behavior and impaired social behavior and object recognition memory in young adult period. Prenatal VPA mice showed hyper-glutamatergic function (increase in basal extracellular glutamate levels and CaMKII phosphorylation) and hypo-serotonergic function (decrease in 5-hydroxyindoleacetic acid and stimulation-induced serotonin [5-HT] release, but an increase in 5-HT transporter expression) in the prefrontal cortex. Treatment with a low-affinity NMDA receptor antagonist (memantine), a selective 5-HT reuptake inhibitor (fluoxetine), and a 5-HT_1A receptor agonist (tandospirone) attenuated both the increase in CaMKII phosphorylation and ASD-like behavior of prenatal VPA mice. Opto-genetic activation of the serotonergic neuronal system attenuated impairments in social behavior and object recognition memory in prenatal VPA mice. WAY-100635—a 5-HT_1A receptor antagonist—antagonized the effect of fluoxetine on impaired social behavior and object recognition memory. These results suggest that E/I imbalance and ASD-like behavior are associated with hypo-serotonergic receptor signaling through 5-HT_1A receptors in prenatal VPA mice.

Abstract Stressful life events contribute to the onset of major depressive disorder (MDD). We recently demonstrated abnormalities in ubiquitination in the pathophysiology of MDD. However, the underlying molecular mechanisms remain unclear. We investigated the involvement of the ubiquitination system‐mediated glutamatergic dysfunction in social impairment induced by chronic social defeat stress (CSDS). Adult C57BL/6J mice were exposed to aggressor ICR male mice for 10 consecutive days. Social impairment was induced by CSDS in the social interaction test 1 days after the last stress exposure. In terms of brain microdialysis, CSDS reduced depolarization‐evoked glutamate release in the prefrontal cortex (PFC), which was reversed by a glutamate transporter 1 (GLT‐1) inhibitor. Interestingly, the expression of ubiquitinated, but not total GLT‐1, was decreased in the PFC of mice exposed to CSDS. The expression of neural precursor cells expressing developmentally downregulated gene 4‐like (Nedd4L: E3 ligase for GLT‐1), and ubiquitin‐conjugating enzyme E2D2 (Ube2d2: E2 ubiquitin‐conjugating enzyme for Nedd4L) was also reduced in CSDS mice. Furthermore, the downregulation of the Nedd4L‐GLT‐1 ubiquitination pathway decreased SIT ratio, but up‐regulation increased it even in non‐CSDS mice. Taken together, the decrease in GLT‐1 ubiquitination may reduce the release of extracellular glutamate induced by high‐potassium stimulation, which may lead to social impairment, while we could not find differences in GLT‐1 ubiquitination between susceptible and resistant CSDS mice. In conclusion, GLT‐1 ubiquitination could play a crucial role in the pathophysiology of MDD and is an attractive target for the development of novel antidepressants.

Indoleamine 2,3-dioxygenase 2 (IDO2) is an enzyme of the tryptophan-kynurenine pathway that is constitutively expressed in the brain. To provide insight into the physiological role of IDO2 in the brain, behavioral and neurochemical analyses in IDO2 knockout (KO) mice were performed. IDO2 KO mice showed stereotyped behavior, restricted interest and social deficits, traits that are associated with behavioral endophenotypes of autism spectrum disorder (ASD). IDO2 was colocalized immunohistochemically with tyrosine-hydroxylase-positive cells in dopaminergic neurons. In the striatum and amygdala of IDO2 KO mice, decreased dopamine turnover was associated with increased α-synuclein level. Correspondingly, levels of downstream dopamine D1 receptor signaling molecules such as brain-derived neurotrophic factor and c-Fos positive proteins were decreased. Furthermore, decreased abundance of ramified-type microglia resulted in increased dendritic spine density in the striatum of IDO2 KO mice. Both chemogenetic activation of dopaminergic neurons and treatment with methylphenidate, a dopamine reuptake inhibitor, ameliorated the ASD-like behavior of IDO2 KO mice. Sequencing analysis of exon regions in IDO2 from 309 ASD samples identified a rare canonical splice site variant in one ASD case. These results suggest that the IDO2 gene is, at least in part, a factor closely related to the development of psychiatric disorders.

BACKGROUND AND PURPOSE: High salt (HS) intake has been associated with hypertension and cognitive impairment. It is well known that the angiotensin II (Ang II)-AT1 receptor and prostaglandin E2 (PGE2)-EP1 receptor systems are involved in hypertension and neurotoxicity. However, the involvement of these systems in HS-mediated hypertension and emotional and cognitive impairments remains unclear. EXPERIMENTAL APPROACH: Mice were loaded with HS solution (2% NaCl drinking water) for 12 weeks, and blood pressure was monitored. Subsequently, effects of HS intake on emotional and cognitive function and tau phosphorylation in the prefrontal cortex (PFC) and hippocampus (HIP) were investigated. The involvement of Ang II-AT1 and PGE2-EP1 systems in HS-induced hypertension and neuronal and behavioural impairments was examined by treatment with losartan, an AT1 receptor blocker (ARB), or EP1 gene knockout. KEY RESULTS: We demonstrate that hypertension and impaired social behaviour and object recognition memory following HS intake may be associated with tau hyperphosphorylation, decreased phosphorylation of Ca2+ /calmodulin-dependent protein kinase II (CaMKII), and postsynaptic density protein 95 (PSD95) expression in the PFC and HIP of mice. These changes were blocked by pharmacological treatment with losartan or EP1 receptor gene knockout. CONCLUSIONS AND IMPLICATIONS: Our findings suggest that the interaction of Ang II-AT1 receptor and PGE2-EP1 receptor systems could be novel therapeutic targets for hypertension-induced cognitive impairment.

Major depressive disorder (MDD) is a common and serious psychiatric disease that involves brain inflammation. Bifidobacterium breve is commonly used as a probiotic and was shown to improve colitis and allergic diseases by suppressing the inflammatory response. Heat-sterilized B. breve has beneficial effects on inflammation. We hypothesize, therefore, that this probiotic might reduce depression symptoms. We tested this is a mouse model of social defeat stress. C57BL/6J mice exposed to chronic social defeat stress (CSDS) for five consecutive days developed a mild depression-like behavior characterized by a social interaction impairment. CSDS also altered the gut microbiota composition, such as increased abundance of Bacilli, Bacteroidia, Mollicutes, and Verrucomicrobiae classes and decreased Erysipelotrichi class. The prophylactic effect of heat-sterilized B. breve as a functional food ingredient was evaluated on the depression-like behavior in mice. The supplementation started two weeks before and lasted two weeks after the last exposure to CSDS. Two weeks after CSDS, the mice showed deficits in social interaction and increased levels of inflammatory cytokines, including interleukin-1β (IL-1β) in the prefrontal cortex (PFC) and hippocampus (HIP). Heat-sterilized B. breve supplementation significantly prevented social interaction impairment, suppressed IL-1β increase in the PFC and HIP, and modulated the alteration of the gut microbiota composition induced by CSDS. These findings suggest that heat-sterilized B. breve prevents depression-like behavior and IL-1β expression induced by CSDS through modulation of the gut microbiota composition in mice. Therefore, heat-sterilized B. breve used as an ingredient of functional food might prevent MDD.

Successful completion of daily activities relies on the ability to select the relevant features of the environment for memory and recall. Disruption to these processes can lead to various disorders, such as attention-deficit hyperactivity disorder (ADHD). Dopamine is a neurotransmitter implicated in the regulation of several processes, including attention. In addition to the higher-order brain function, dopamine is implicated in the regulation of adult neurogenesis. Previously, we generated mice lacking Shati, an N-acetyltransferase-8-like protein on a C57BL/6J genetic background (Shati/Nat8l-/- ). These mice showed a series of changes in the dopamine system and ADHD-like behavioral phenotypes. Therefore, we hypothesized that deficiency of Shati/Nat8l would affect neurogenesis and attentional behavior in mice. We found aberrant morphology of neurons and impaired neurogenesis in the dentate gyrus of Shati/Nat8l-/- mice. Additionally, research has suggested that impaired neurogenesis might be because of the reduction of dopamine in the hippocampus. Galantamine (GAL) attenuated the attentional impairment observed in the object-based attention test via increasing the dopamine release in the hippocampus of Shati/Nat8l-/- mice. The α7 nicotinic acetylcholine receptor antagonist, methyllycaconitine, and dopamine D1 receptor antagonist, SCH23390, blocked the ameliorating effect of GAL on attentional impairment in Shati/Nat8l-/- mice. These results suggest that the ameliorating effect of GAL on Shati/Nat8l-/- attentional impairment is associated with activation of D1 receptors following increased dopamine release in the hippocampus via α7 nicotinic acetylcholine receptor. In summary, Shati/Nat8l is important in both morphogenesis and neurogenesis in the dentate gyrus and attention, possible via modulation of dopaminergic transmission.

Myelinated axons segregate the axonal membrane into four defined regions: the node of Ranvier, paranode, juxtaparanode, and internode. The paranodal junction consists of specific component proteins, such as neurofascin155 (NF155) on the glial side, and Caspr and Contactin on the axonal side. Although paranodal junctions are thought to play crucial roles in rapid saltatory conduction and nodal assembly, the role of their interaction with neurons is not fully understood. In a previous study, conditional NF155 knockout in oligodendrocytes led to disorganization of the paranodal junctions. To examine if disruption of paranodal junctions affects neuronal gene expression, we prepared total RNA from the retina of NF155 conditional knockout, and performed expression analysis. We found that the expression level of 433 genes changed in response to paranodal junction ablation. Interestingly, expression of aquaporin 3 (AQP3) was significantly reduced in NF155 conditional knockout mice, but not in cerebroside sulfotransferase knockout (CST-KO) mice, whose paranodes are not originally formed during development. Copy number variations have an important role in the etiology of schizophrenia (SCZ). We observed rare duplications of AQP3 in SCZ patients, suggesting a correlation between abnormal AQP3 expression and SCZ. To determine if AQP3 over-expression in NF155 conditional knockout mice influences neuronal function, we performed adeno-associated virus (AAV)-mediated over-expression of AQP3 in the motor cortex of mice and found a significant increase in caspase 3-dependent neuronal apoptosis in AQP3-transduced cells. This study may provide new insights into therapeutic approaches for SCZ by regulating AQP3 expression, which is associated with paranodal disruption.