The Lacto-Tetrapeptide Gly-Thr-Trp-Tyr, β-Lactolin, Improves Spatial Memory Functions via Dopamine Release and D1 Receptor Activation in the Hippocampus

Scope: Peptides containing tryptophan–tyrosine sequences, including the lacto-tetrapeptide glycine–threonine–tryptophan–tyrosine (GTWY) and β-lactolin, from β-lactoglobulin in whey enzymatic digestion, enhance hippocampus-dependent memory functions, which are blocked by the systemic administration of dopamine D1-like antagonist. In this study, we investigated the role of the hippocampal dopaminergic system in the memory-enhancing effect of β-lactolin. Methods and Results: The results of in vivo microdialysis revealed that oral administration of β-lactolin increased the extracellular concentration of dopamine in the hippocampus and enhanced both spatial working memory, as measured in the Y-maze test, and spatial reference memory, as measured in the novel object location test. These memory-enhancing effects of β-lactolin, but not the baseline memory functions, were impaired by the knockdown of the dopamine D1 receptor subtype in the hippocampus. β-Lactolin also enhanced object memory, as measured by the novel object recognition test. However, D1 knockdown in the hippocampus spared this memory function either with or without the administration of β-lactolin. Conclusions: The present results indicate that oral administration of β-lactolin increases dopamine release and D1 receptor signaling in the hippocampus, thereby enhancing spatial memory, but it may improve object memory via a separate mechanism.

Leucine-Histidine Dipeptide Attenuates Microglial Activation and Emotional Disturbances Induced by Brain Inflammation and Repeated Social Defeat Stress

The number of patients with mental illnesses is rapidly increasing, and daily lifestyle is closely associated with the development of symptoms. It is suggested that inflammatory molecules derived from microglia play crucial roles for the pathophysiology of depression. In the present study, we discovered that leucine–histidine (LH) dipeptide suppressed activation of primary microglia. The effects of LH dipeptide orally administered were measured using tail suspension test (TST) in mice injected with lipopolysaccharide and social interaction test in mice received social defeat stress. LH dipeptide reduced pro-inflammatory cytokines upon stimulation in microglia. Orally administered LH dipeptide was delivered to the brain and suppressed the production of pro-inflammatory cytokines in the brain and concomitant depression-like behavior in the TST. Moreover, oral administration of LH dipeptide suppressed the induction of depression- and anxiety-like behaviors induced by repeated social defeat stress. These results indicate that LH dipeptide suppressed the activation of microglia and ameliorated depression-associated emotional disturbances. Further, we found that LH dipeptide was abundant in various fermented products. Together with previous epidemiological reports that daily intake of these fermented foods is negatively associated with the incidence of psychiatric diseases, our findings suggest that food rich in LH dipeptide may improve mental health.

Improvement of PTSD-like behavior by the forgetting effect of hippocampal neurogenesis enhancer memantine in a social defeat stress paradigm

Post-traumatic stress disorder (PTSD) is a psychiatric disorder associated with memories of traumatic experiences. Recent studies have shown that the forgetting of contextual fear memory is promoted via increased adult hippocampal neurogenesis induced by neurogenesis enhancers, such as memantine (MEM) and exercise, raising the possibility that neurogenesis enhancers improve PTSD by facilitating the forgetting of traumatic memory. On the other hand, repeated exposure to social defeat (SD) stress by aggressor mice induces social avoidance behavior to the aggressor and chronic anxiety-like behavior. In this study, we assumed this SD stress paradigm as a PTSD-like model and examined the effects of treatment with neurogenesis enhancer MEM on SD stress-induced PTSD-like behavior. Male C57BL/6 mice received SD stress for 10 consecutive days and were assessed for social avoidance memory to the aggressor (memory of aggressor mice) and anxiety-like behavior using social interaction and elevated zero maze tasks. Consistent with previous studies, SD mice formed social avoidance memory and exhibited increased anxiety-like behavior. Importantly, subsequent MEM treatment (once a week for 4 weeks) significantly reduced social avoidance behavior, suggesting that MEM-treated SD mice showed forgetting of social avoidance memory. Interestingly, MEM-treated SD mice showed comparable anxiety-like behavior with control mice that were not exposed to SD stress. Moreover, MEM-treated SD mice showed no reinstatement of social avoidance memory following single re-exposure to the aggressor. Our findings suggest that neurogenesis enhancer not only enhanced the forgetting of traumatic memory but also improved PTSD (anxiety)-like behavior.

Ulk2 controls cortical excitatory-inhibitory balance via autophagic regulation of p62 and GABAA receptor trafficking in pyramidal neurons

Autophagy plays an essential role in intracellular degradation and maintenance of cellular homeostasis in all cells, including neurons. Although a recent study reported a copy number variation of Ulk2, a gene essential for initiating autophagy, associated with a case of schizophrenia (SZ), it remains to be studied whether Ulk2 dysfunction could underlie the pathophysiology of the disease. Here we show that Ulk2 heterozygous (Ulk2+/-) mice have upregulated expression of sequestosome-1/p62, an autophagy-associated stress response protein, predominantly in pyramidal neurons of the prefrontal cortex (PFC), and exhibit behavioral deficits associated with the PFC functions, including attenuated sensorimotor gating and impaired cognition. Ulk2+/- neurons showed imbalanced excitatory-inhibitory neurotransmission, due in part to selective down-modulation of gamma-aminobutyric acid (GABA)A receptor surface expression in pyramidal neurons. Genetically reducing p62 gene dosage or suppressing p62 protein levels with an autophagy-inducing agent restored the GABAA receptor surface expression and rescued the behavioral deficits in Ulk2+/- mice. Moreover, expressing a short peptide that specifically interferes with the interaction of p62 and GABAA receptor-associated protein, a protein that regulates endocytic trafficking of GABAA receptors, also restored the GABAA receptor surface expression and rescued the behavioral deficits in Ulk2+/- mice. Thus, the current study reveals a novel mechanism linking deregulated autophagy to functional disturbances of the nervous system relevant to SZ, through regulation of GABAA receptor surface presentation in pyramidal neurons.

Roles of multiple lipid mediators in stress and depression

Prolonged or excessive stress may induce emotional and cognitive disturbances, and is a risk factor for mental illnesses. Using rodent chronic stress models of depression, roles of multiple lipid mediators related to inflammation have been revealed in chronic stress-induced emotional alterations. Prostaglandin (PG) E2, an arachidonic acid (AA)-derived lipid mediator, and its receptor subtype EP1 mediate depression-like behavior induced by repeated social defeat stress through attenuating prefrontal dopaminergic activity. Repeated social defeat stress activates microglia through innate immune receptors, and induces PGE2 synthesis through cyclooxygenase-1, a prostaglandin synthase enriched in microglia. PGD2, another AA-derived lipid mediator, has been implicated in depression induced by chronic stress, although either pro-depressive or anti-depressive actions have been reported. Chronic stress up-regulates hippocampal expression of 5-lipoxygenase, hence synthesis of cysteinyl leukotrienes, thereby inducing depression through their receptors. Consistent with beneficial effects of n-3 fatty acids in the diet of depressive patients, resolvins—a novel class of pro-resolving lipid mediators—in the brain attenuate neuroinflammation-associated depression. These findings in animal models of depression offer lipid mediators and related molecules as novel therapeutic targets for treating depression. To translate these findings into clinics, translational biomarkers to visualize lipid mediator profiles in depressive patients need to be established.

Social defeat stress induces phosphorylation of extracellular signal-regulated kinase in the leptomeninges in mice

Aims

Animal studies using various stress models have shown that excessive environmental stress induces depression? and anxiety?like behaviors through inflammatory responses in the brain and periphery. Although the leptomeningeal cells have multiple functions related to inflammatory responses in the brain, whether environmental stress influences the leptomeninges remains unknown. In this study, we aimed to examine phosphorylation of the extracellular signal‐regulated kinase (ERK) in the leptomeninges.

Methods

We subjected C57BL/6 male mice to a single episode of social defeat stress and analyzed the expression of phosphorylated ERK in the leptomeninges by immunohistochemistry.

Results

Social defeat stress in mice induced phosphorylation of ERK in the leptomeninges, adjacent to vascular endothelial cells and the glia limitans. This ERK phosphorylation was maintained for at least one hour after the stress.

Conclusions

This study shows the effect of environmental stress on the leptomeninges for the first time and paves the way for elucidating its functional role in stress‐induced changes in neural functions.

This study shows for the first time that social defeat stress induces phosphorylation of extracellular signal‐regulated kinase in the leptomeninges in mice. This finding paves the way for elucidating a potential role of the leptomeninges in mediating stress‐induced inflammatory signals from the periphery to the brain.

Iso-α-acids, the bitter components of beer, improve hippocampus-dependent memory through vagus nerve activation

Iso-α-acids (IAAs) are hop-derived bitter acids of beer. Epidemiologic studies suggest that moderate alcohol consumption is beneficial for cognitive function, but they do not show the ingredients in alcoholic beverages. Previously, we reported that long-term consumption of IAAs prevents inflammation and Alzheimer pathologies in mice, but their effects on cognitive function have not been evaluated. In the present study, we demonstrated that the consumption of IAAs improves spatial and object recognition memory functions not only in normal Crl:CD1(ICR) male mice but also in mice with pharmacologically induced amnesia. IAA consumption increased the total and extracellular levels of dopamine in the hippocampus of mice and Sprague-Dawley male rats, respectively. Dopamine D₁ receptor antagonist treatment and knockdown of dopamine D₁ receptor expression in the hippocampus attenuated IAA-induced spatial memory improvement. Furthermore, vagotomy attenuated the effects of IAAs in improving spatial and object recognition memory functions and increasing the total level of dopamine in the hippocampus. These results suggest that the consumption of IAAs activates dopamine D₁ receptor-signaling in the hippocampus in a vagus nerve-dependent manner and, consequently, improves spatial and object recognition memory functions. Vagal activation with food components including IAAs may be an easy and safe approach to improve cognitive functions.-Ano, Y., Hoshi, A., Ayabe, T., Ohya, R., Uchida, S., Yamada, K., Kondo, K., Kitaoka, S., Furuyashiki, T. Iso-α-acids, the bitter components of beer, improve hippocampus-dependent memory through vagus nerve activation.

mDia and ROCK Mediate Actin-Dependent Presynaptic Remodeling Regulating Synaptic Efficacy and Anxiety

Here, we show neuronal inactivation-induced presynaptic remodeling and involvement of the mammalian homolog of Diaphanous (mDia) and Rho-associated coiled-coil-containing kinase (ROCK), Rho-regulated modulators of actin and myosin, in this process. We find that social isolation induces inactivation of nucleus accumbens (NAc) neurons associated with elevated anxiety-like behavior, and that mDia in NAc neurons is essential in this process. Upon inactivation of cultured neurons, mDia induces circumferential actin filaments around the edge of the synaptic cleft, which contract the presynaptic terminals in a ROCK-dependent manner. Social isolation induces similar mDia-dependent presynaptic contraction at GABAergic synapses from NAc neurons in the ventral tegmental area (VTA) associated with reduced synaptic efficacy. Optogenetic stimulation of NAc neurons rescues the anxiety phenotype, and injection of a specific ROCK inhibitor, Y-27632, into the VTA reverses both presynaptic contraction and the behavioral phenotype. mDia-ROCK signaling thus mediates actin-dependent presynaptic remodeling in inactivated NAc neurons, which underlies synaptic plasticity in emotional behavioral responses.

The Loss of Lam2 and Npr2-Npr3 Diminishes the Vacuolar Localization of Gtr1-Gtr2 and Disinhibits TORC1 Activity in Fission Yeast

In mammalian cells, mTORC1 activity is regulated by Rag GTPases. It is thought that the Ragulator complex and the GATOR (GAP activity towards Rags) complex regulate RagA/B as its GDP/GTP exchange factor (GEF) and GTPase-activating protein (GAP), respectively. However, the functions of components in these complexes remain elusive. Using fission yeast as a model organism, here we found that the loss of Lam2 (SPBC1778.05c), a homolog of a Ragulator component LAMTOR2, as well as the loss of Gtr1 or Gtr2 phenocopies the loss of Npr2 or Npr3, homologs of GATOR components Nprl2 or Nprl3, respectively. These phenotypes were rescued by TORC1 inhibition using pharmacological or genetic means, and the loss of Lam2, Gtr1, Gtr2, Npr2 or Npr3 disinhibited TORC1 activity under nitrogen depletion, as measured by Rps6 phosphorylation. Consistently, overexpression of GDP-locked Gtr1^S20L or GTP-locked Gtr2^Q60L, which suppress TORC1 activity in budding yeast, rescued the growth defect of Δgtr1 cells or Δgtr2 cells, respectively, and the loss of Lam2, Npr2 or Npr3 similarly diminished the vacuolar localization and the protein levels of Gtr1 and Gtr2. Furthermore, Lam2 physically interacted with Npr2 and Gtr1. These findings suggest that Lam2 and Npr2-Npr3 function together as a tether for GDP-bound Gtr1 to the vacuolar membrane, thereby suppressing TORC1 activity for multiple cellular functions.

Tor Signaling Regulates Transcription of Amino Acid Permeases through a GATA Transcription Factor Gaf1 in Fission Yeast

In the fission yeast, two Tor isoforms, Tor1 and Tor2, oppositely regulate gene expression of amino acid permeases. To elucidate the transcriptional machinery for these regulations, here we have employed the cap analysis of gene expression (CAGE), a method of analyzing expression profiles and identifying transcriptional start sites (TSSs). The loss of Tor1 decreased, and Tor2 inhibition by its temperature sensitive mutation increased, mRNA expression of isp5+, per1+, put4+ and SPBPB2B2.01. In contrast, the loss of Tor1 increased, and Tor2 inhibition decreased, the expression of cat1+. These changes were confirmed by semi-quantitative RT-PCR. These opposite effects by the loss of Tor1 and Tor2 inhibition appeared to occur evenly across multiple TSSs for the respective genes. The motif discovery analysis based on the CAGE results identified the GATA motifs as a potential cis-regulatory element for Tor-mediated regulation. In the luciferase reporter assay, the loss of Tor1 reduced, and Tor2 inhibition and nitrogen depletion increased, the activity of isp5+ promoter as well as that of a GATAAG reporter. One of the GATAAG motifs in isp5+ promoter was critical for its transcriptional activity, and a GATA transcription factor Gaf1 was critical for the activities of isp5+ promoter and the GATAAG reporter. Furthermore, Tor2 inhibition and nitrogen depletion induced nuclear localization of Gaf1 from the cytosol and its dephosphorylation. These results suggest that Tor2 inhibition, which is known to be induced by nitrogen depletion, promotes nuclear localization of Gaf1, thereby inducing isp5+ transcription through Gaf1 binding to the GATAAG motif in its promoter. Since Gaf1 was also critical for transcription of per1+ and put4+, Tor-Gaf1 signaling may coordinate transcription of multiple amino acid permeases according to nutrient availability.

Characterization of Tamoxifen as an Antifungal Agent Using the Yeast Schizosaccharomyces Pombe Model Organism

Tamoxifen, a selective estrogen receptor modulator used for managing breast cancer, is known to have antifungal activity. However, its molecular mechanism remains unknown. Using the fission yeast Schizosaccharomyces pombe as a model organism, we have explored the mechanism involved in antifungal action of tamoxifen. Since tamoxifen was shown to inhibit the binding of calmodulin to calcineurin in fungi, we first examined involvement of these molecules and found that overexpression of a catalytic subunit of calcineurin and its constitutively active mutant as well as calmodulin increases tamoxifen sensitivity. Since terbinafine and azoles inhibit enzymes for ergosterol biosynthesis, Erg1 and Erg11, for their antifungal actions, we also examined involvement of these molecules. Overexpression of Erg1 and Erg11 reduced the sensitivity to terbinafine and azoles, respectively, but increased tamoxifen sensitivity, suggesting that ergosterol biosynthesis is differently related to the action of tamoxifen and those of terbinafine and azoles. To elucidate molecules involved in tamoxifen action, we performed a genome-wide screen for altered sensitivity to tamoxifen using a fission yeast gene deletion library, and identified various hypersensitive and resistant mutants to this drug. Notably, these mutants are rarely overlapped with those identified in similar genetic screens with currently used antifungals, suggesting a novel mode of antifungal action. Furthermore, tamoxifen augmented antifungal actions of terbinafine and azoles, suggesting synergetic actions between these drugs. Therefore, our findings suggest that calmodulin-calcineurin pathway and ergosterol biosynthesis are related to antifungal action of tamoxifen, and propose novel targets for antifungal development as well as combined therapy with tamoxifen for fungal diseases.

Constitutive Tor2 Activity Promotes Retention of the Amino Acid Transporter Agp3 at Trans-Golgi/Endosomes in Fission Yeast

Amino acid transporters are located at specific subcellular compartments, and their localizations are regulated by the extracellular availability of amino acids. In yeast, target of rapamycin (TOR) activation induces the internalization of amino acid transporters located at the plasma membrane. However, whether and how TOR signaling regulates other amino acid transporters located at intracellular compartments remains unknown. Here, we demonstrate that in the fission yeast, the TOR inhibitor Torin-1 induces the transfer of several yellow fluorescent protein (YFP)-fused intracellular amino acid transporters, including Agp3, Isp5, Aat1, and Put4, from trans-Golgi/endosomes into the vacuoles. By contrast, the localizations of YFP-fused Can1, Fnx1, and Fnx2 transporter proteins were unaffected upon Torin-1 treatment. There are two TOR isoforms in fission yeast, Tor1 and Tor2. Whereas tor1 deletion did not affect the Torin-1-induced transfer of Agp3-YFP, Tor2 inhibition using a temperature-sensitive mutant induced the transfer of Agp3-YFP to the vacuolar lumen, similar to the effects of Torin-1 treatment. Tor2 inhibition also induced the transfer of the YFP-fused Isp5, Aat1, and Put4 transporter proteins to the vacuoles, although only partial transfer of the latter two transporters was observed. Under nitrogen depletion accompanied by reduced Tor2 activity, Agp3-YFP was transferred from the trans-Golgi/endosomes to the plasma membrane and then to the vacuoles, where it was degraded by the vacuolar proteases Isp6 and Psp3. Mutants with constitutively active Tor2 showed delayed transfer of Agp3-YFP to the plasma membrane upon nitrogen depletion. Cells lacking Tsc2, a negative regulator of Tor2, also showed a delay in this process in a Tor2-dependent manner. Taken together, these findings suggest that constitutive Tor2 activity is critical for the retention of amino acid transporters at trans-Golgi/endosomes. Moreover, nitrogen depletion suppresses Tor2 activity through Tsc2, thereby promoting the surface expression of these transporters.

Azoles activate Atf1-mediated transcription through MAP kinase pathway for antifungal effects in fission yeast

Azole antifungals directly inhibit enzymes for ergosterol biosynthesis, and this direct action is thought to underlie antifungal actions of these drugs. Recent studies showed that azoles alter expression of genes for various cellular functions. However, transcription factors regulated by azoles and their roles in antifungal actions remain poorly characterized. Using luciferase assay, we found that miconazole increased luciferase activity under the promoter containing the cAMP response element (CRE) motif. This azole-induced activation of CRE reporter was abolished in Atf1-deficient cells, suggesting that azoles induce Atf1 activation. As Atf1 is activated by stress-activated MAP kinase Sty1 upon various stressors, we examined its involvement. Azoles increased phosphorylation of Sty1 for its activation, and Sty1 deletion impaired azole-induced CRE reporter activation. In contrast, deletion of Pyp1, a tyrosine phosphatase which negatively regulates Sty1, increased CRE reporter activation. In addition, cells deficient in Atf1 and stress-activated MAP kinase pathway showed resistance to azoles, whereas cells lacking Pyp1 increased azole susceptibility, suggesting a critical role for azole-induced activation of MAP kinase-Atf1 pathway in antifungal actions of azoles. Collectively, these results suggest that azoles activate stress-activated MAP kinase pathway, thereby facilitating Atf1-mediated transcription for antifungal effects.

The combined effect of clothianidin and environmental stress on the behavioral and reproductive function in male mice

Neonicotinoids, some of the most widely used pesticides in the world, act as agonists to the nicotinic acetylcholine receptors (nAChRs) of insects, resulting in death from abnormal excitability. Neonicotinoids unexpectedly became a major topic as a compelling cause of honeybee colony collapse disorder, which is damaging crop production that requires pollination worldwide. Mammal nAChRs appear to have a certain affinity for neonicotinoids with lower levels than those of insects; there is thus rising concern about unpredictable adverse effects of neonicotinoids on vertebrates. We hypothesized that the effects of neonicotinoids would be enhanced under a chronic stressed condition, which is known to alter the expression of targets of neonicotinoids, i.e., neuronal nAChRs. We performed immunohistochemical and behavioral analyses in male mice actively administered a neonicotinoid, clothianidin (CTD; 0, 10, 50 and 250 mg/kg/day), for 4 weeks under an unpredictable chronic stress procedure. Vacuolated seminiferous epithelia and a decrease in the immunoreactivity of the antioxidant enzyme glutathione peroxidase 4 were observed in the testes of the CTD+stress mice. In an open field test, although the locomotor activities were not affected, the anxiety-like behaviors of the mice were elevated by both CTD and stress. The present study demonstrates that the behavioral and reproductive effects of CTD become more serious in combination with environmental stress, which may reflect our actual situation of multiple exposure.

CCAAT/enhancer-binding protein delta/miR135a/thrombospondin 1 axis mediates PGE2-induced angiogenesis in Alzheimer's disease

In Alzheimer's disease (AD), large populations of endothelial cells undergo angiogenesis due to brain hypoxia and inflammation. Substantial evidence from epidemiologic, pathologic, and clinical reports suggests that vascular factors are critical for the pathogenesis of AD. However, the precise mechanistic correlation between inflammation and angiogenesis in AD has not been well elucidated. Prostaglandin E2 (PGE2), a key factor of the inflammatory response, has been known to promote angiogenesis. In this study, we demonstrated that PGE2 acts through EP4 receptor and protein kinase A to modulate CCAAT/enhancer-binding protein delta (CEBPD) abundance in astrocytes. Attenuated vessel formation was observed in the brains of AppTg/Cebpd(-/-) mice. We showed that miR135a was responsive to the induction of CEBPD and further negatively regulated thrombospondin 1 (THBS1) transcription by directly targeting its 3'-untranslated region (3'UTR) in astrocytes. Furthermore, conditioned media from astrocytes expressing miR135a promoted Human umbilical vein endothelial cells (HUVECs) tube-like formation, which correlated with the effects of PGE2 on angiogenesis. Our results indicated that CEBPD contributes to the repression of THBS1 transcription by activating the expression of miR135a in astrocytes following PGE2 treatment. We provided new evidence that astrocytic CEBPD increases angiogenesis during AD pathogenesis. This discovery supports the negative influence of CEBPD activation in astrocytes with respect to AD pathogenesis and implies that the CEBPD/miR135a/THBS1 axis could be a therapeutic target of AD.

The MluI cell cycle box (MCB) motifs, but not damage-responsive elements (DREs), are responsible for the transcriptional induction of the rhp51+ gene in response to DNA replication stress

DNA replication stress induces the transcriptional activation of rhp51+, a fission yeast recA homolog required for repair of DNA double strand breaks. However, the mechanism by which DNA replication stress activates rhp51+ transcription is not understood. The promoter region of rhp51+ contains two damage-responsive elements (DREs) and two MluI cell cycle box (MCB) motifs. Using luciferase reporter assays, we examined the role of these elements in rhp51+ transcription. The full-length rhp51+ promoter and a promoter fragment containing MCB motifs only, but not a fragment containing DREs, mediated transcriptional activation upon DNA replication stress. Removal of the MCB motifs from the rhp51+ promoter abolished the induction of rhp51+ transcription by DNA replication stress. Consistent with a role for MCB motifs in rhp51+ transcription activation, deletion of the MBF (MCB-binding factor) co-repressors Nrm1 and Yox1 precluded rhp51+ transcriptional induction in response to DNA replication stress. Using cells deficient in checkpoint signaling molecules, we found that the Rad3-Cds1/Chk1 pathway partially mediated rhp51+ transcription in response to DNA replication stress, suggesting the involvement of unidentified checkpoint signaling pathways. Because MBF is critical for G1/S transcription, we examined how the cell cycle affected rhp51+ transcription. The transcription of rhp51+ and cdc18+, an MBF-dependent G1/S gene, peaked simultaneously in synchronized cdc25-22 cells. Furthermore, DNA replication stress maintained transcription of rhp51+ similarly to cdc18+. Collectively, these results suggest that MBF and its regulators mediate rhp51+ transcription in response to DNA replication stress, and underlie rhp51+ transcription at the G1/S transition.

[Roles of inflammation-related molecules in emotional changes induced by repeated stress]

Stress is a risk factor for psychiatric disorders. Studies using rodent stress models have shown critical roles for inflammation-related molecules in stress-induced behavioral changes. Under chronic mild stress, IL-1beta through IL-1 receptor type 1 (IL-1RI) in the brain activates the hypothalamic-pituitary-adrenal axis, thereby stimulating glucocorticoid release, which in turn decreases motivation to obtain reward. IL-1beta can also suppress proliferation of neural progenitor cells directly through IL-1RI and/or indirectly through glucocorticoid. In repeated social defeat stress, endothelial IL-1RI is involved in stress-induced upregulation of inflammation-related molecules and elevated anxiety. Prostaglandin (PG) E2 and its receptor EP1 mediate elevated anxiety and social avoidance induced by repeated social defeat through attenuating a stress-coping action of the meso-prefrontal dopaminergic pathway. IL-1beta and PGE2 are thought to be released from microglia activated by repeated stress. Whereas the mechanism for stress-induced microglial activation remains elusive, it has been reported that repeated stress induces migration of peripheral macrophages into the brain in a manner dependent on IL-1RI and multiple chemokines, which are also critical for stress-induced elevated anxiety. These findings reveal multiple actions of inflammation-related molecules in the brain and the crosstalk between neurons and microglia as well as that between the brain and the periphery in rodent stress models.

EphA4-dependent axon retraction and midline localization of Ephrin-B3 are disrupted in the spinal cord of mice lacking mDia1 and mDia3 in combination

mDia is an actin nucleator and polymerization factor regulated by the small GTPase Rho and consists of three isoforms. Here, we found that mice lacking mDia1 and mDia3, two isoforms expressed in the brain, in combination (mDia-DKO mice) show impaired left-right limb coordination during locomotion and aberrant midline crossing of axons of corticospinal neurons and spinal cord interneurons. Given that mice lacking Ephrin-B3-EphA4 signaling show a similar impairment in locomotion, we examined whether mDia is involved in Ephrin-B3-EphA4 signaling for axon repulsion. In primary cultured neurons, mDia deficiency impairs growth cone collapse and axon retraction induced by chemo-repellants including EphA ligands. In mDia-DKO mice, the Ephrin-B3-expressing midline structure in the spinal cord is disrupted, and axons aberrantly cross the spinal cord midline preferentially through the region devoid of Ephrin-B3. Therefore, mDia plays multiple roles in the proper formation of the neural network in vivo.

Prostaglandin E receptor EP1 forms a complex with dopamine D1 receptor and directs D1-induced cAMP production to adenylyl cyclase 7 through mobilizing G(βγ) subunits in human embryonic kidney 293T cells

The mechanism underlying the crosstalk between multiple G protein-coupled receptors remains poorly understood. We previously reported that prostaglandin E receptor EP1 facilitates dopamine D1 receptor signaling in striatal slices and promotes behavioral responses induced by D1 receptor agonists. Here, using human embryonic kidney (HEK)-293T cells expressing D1 and EP1, we have analyzed the mechanism underlying EP1-mediated facilitation of D1 receptor signaling. Fluorescent immunostaining showed that EP1 and D1 receptors are partly colocalized in the cells, and coprecipitation experiments revealed a molecular complex of EP1 and D1 receptors. Treatment of the cells with 17S,17,20-dimethyl-2,5-ethano-6-oxo-PGE₁ (ONO-DI-004), an EP1-selective agonist, enhanced cAMP production induced by D1 agonists (±)-6-chloro-2,3,4,5-tetrahydro-1-phenyl-1H-3-benzazepine hydrobromide (SKF-81297) and 6-chloro-2,3,4,5-tetrahydro-1-(3-methylphenyl)-3-(2-propenyl)-1H-3-benzazepine-7,8-diol hydrobromide (SKF-83822). Although this facilitative effect of EP1 stimulation was not affected by pharmacologic blockade of EP1-induced Ca²⁺ increase, it was blocked by overexpression of G(tα) as a G(βγ) scavenger. Consistently, depletion of adenylyl cyclase (AC) 7, a G(βγ)-sensitive AC isoform, abolished the facilitative action of EP1 on D1-induced cAMP production. Notably, neither G(tα) overexpression nor AC7 depletion affected cAMP production induced by D1 stimulation alone. In contrast, depletion of AC6, another AC isoform, reduced cAMP production induced by D1 stimulation alone, but spared its facilitation by EP1 stimulation. Collectively, these data suggest that, through complex formation with D1, EP1 signaling directs the D1 receptor through G(βγ) to be coupled to AC7, an AC isoform distinct from those used by the D1 receptor alone, in HEK-293T cells.

[Roles of altered striatal function in major depression]

Major depression, a psychiatric disorder characterized by depressive mood and loss of interest and pleasure, is a leading cause of disability and suicide in developed countries. However, the mechanisms that underlie major depression remain to be elucidated. Clinical studies on patients with major depression have shown abnormalities in multiple brain areas, each of which can account for a distinct symptom or endophenotype. Notably, the striatum in healthy control subjects responds to positive emotional stimuli and to positive feedback signals during cognitive tasks, but these striatal responses are greatly reduced in depressive patients. Given the role of the striatum in behavioral learning with positive reinforcers, abnormalities as such suggest that impairment in reward processing and/or reinforcement learning in major depression is the basis of anhedonia and reduced psychomotor activity. In animal studies, stress -a risk factor for major depression- is frequently used to induce behavioral depression. Repeated social defeat stress increases the excitability of dopamine neurons and subsequent CREB-mediated transcription in the nucleus accumbens shell, leading to behavioral depression. Surprisingly, this pathway seems not to be involved in behavioral depression caused by prolonged social isolation, suggesting distinct mechanisms underlying the two stressful contexts. In contrast, ΔFosB-mediated gene expression in the nucleus accumbens shell confers resilience to stress. Repeated social defeat stress induces accumbal ΔFosB expression in a stress-resilient subset of individuals, whereas prolonged social isolation decreases this expression, leading to stress susceptibility. In addition to emotional changes, chronic stress also alters the mode of instrumental behavior from goal-directed to habitual responding, with consistent morphological changes in striatal subregions responsible for the corresponding behavioral modes. Therefore, these clinical and preclinical findings suggest that striatal abnormalities play a role in emotional and cognitive changes associated with major depression.