Neurogenesis-dependent remodeling of hippocampal circuits reduces PTSD-like behaviors in adult mice.

Post-traumatic stress disorder (PTSD) is a hypermnesic condition that develops in a subset of individuals following exposure to severe trauma. PTSD symptoms are debilitating, and include increased anxiety, abnormal threat generalization, and impaired extinction. In developing treatment strategies for PTSD, preclinical studies in rodents have largely focused on interventions that target post-encoding memory processes such as reconsolidation and extinction. Instead, here we focus on forgetting, another post-encoding process that regulates memory expression. Using a double trauma murine model for PTSD, we asked whether promoting neurogenesis-mediated forgetting can weaken trauma memories and associated PTSD-relevant behavioral phenotypes. In the double trauma paradigm, consecutive aversive experiences lead to a constellation of behavioral phenotypes associated with PTSD including increases in anxiety-like behavior, abnormal threat generalization, and deficient extinction. We found that post-training interventions that elevate hippocampal neurogenesis weakened the original trauma memory and decreased these PTSD-relevant phenotypes. These effects were observed using multiple methods to manipulate hippocampal neurogenesis, including interventions restricted to neural progenitor cells that selectively promoted integration of adult-generated granule cells into hippocampal circuits. The same interventions also weakened cocaine place preference memories, suggesting that promoting hippocampal neurogenesis may represent a broadly useful approach in hypermnesic conditions such as PTSD and substance abuse disorders.

Inhibition of reactive oxygen species production accompanying alternatively activated microglia by risperidone in a mouse ketamine model of schizophrenia.

Recent studies have highlighted the potential involvement of reactive oxygen species (ROS) and microglia, a major source of ROS, in the pathophysiology of schizophrenia. In our study, we explored how the second-generation antipsychotic risperidone (RIS) affects ROS regulation and microglial activation in the hippocampus using a mouse ketamine (KET) model of schizophrenia. KET administration resulted in schizophrenia-like behaviors in male C57BL/6J mice, such as impaired prepulse inhibition (PPI) of the acoustic startle response and hyper-locomotion. These behaviors were mitigated by RIS. We found that the gene expression level of an enzyme responsible for ROS production (Nox2), which is primarily associated with activated microglia, was lower in KET/RIS-treated mice than in KET-treated mice. Conversely, the levels of antioxidant enzymes (Ho-1 and Gclc) were higher in KET/RIS-treated mice. The microglial density in the hippocampus was increased in KET-treated mice, which was counteracted by RIS. Hierarchical cluster analysis revealed three morphological subtypes of microglia. In control mice, most microglia were resting-ramified (type I, 89.7%). KET administration shifted the microglial composition to moderately ramified (type II, 44.4%) and hyper-ramified (type III, 25.0%). In KET/RIS-treated mice, type II decreased to 32.0%, while type III increased to 34.0%. An in vitro ROS assay showed that KET increased ROS production in dissociated hippocampal microglia, and this effect was mitigated by RIS. Furthermore, we discovered that a NOX2 inhibitor could counteract KET-induced behavioral deficits. These findings suggest that pharmacological inhibition of ROS production by RIS may play a crucial role in ameliorating schizophrenia-related symptoms. Moreover, modulating microglial activation to regulate ROS production has emerged as a novel avenue for developing innovative treatments for schizophrenia.

Spatiotemporal dynamics of the CD11c+ microglial population in the mouse brain and spinal cord from developmental to adult stages.

CD11c-positive (CD11c+) microglia have attracted considerable attention because of their potential implications in central nervous system (CNS) development, homeostasis, and disease. However, the spatiotemporal dynamics of the proportion of CD11c+ microglia in individual CNS regions are poorly understood. Here, we investigated the proportion of CD11c+ microglia in six CNS regions (forebrain, olfactory bulb, diencephalon/midbrain, cerebellum, pons/medulla, and spinal cord) from the developmental to adult stages by flow cytometry and immunohistochemical analyses using a CD11c reporter transgenic mouse line, Itgax-Venus. We found that the proportion of CD11c+ microglia in total microglia varied between CNS regions during postnatal development. Specifically, the proportion was high in the olfactory bulb and cerebellum at postnatal day P(4) and P7, respectively, and approximately half of the total microglia were CD11c+. The proportion declined sharply in all regions to P14, and the low percentage persisted over P56. In the spinal cord, the proportion of CD11c+ microglia was also high at P4 and declined to P14, but increased again at P21 and thereafter. Interestingly, the distribution pattern of CD11c+ microglia in the spinal cord markedly changed from gray matter at P4 to white matter at P21. Collectively, our findings reveal the differences in the spatiotemporal dynamics of the proportion of CD11c+ microglia among CNS regions from early development to adult stages in normal mice. These findings improve our understanding of the nature of microglial heterogeneity and its dynamics in the CNS.

The Functions and Phenotypes of Microglia in Alzheimer's Disease.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide, but therapeutic strategies to slow down AD pathology and symptoms have not yet been successful. While attention has been focused on neurodegeneration in AD pathogenesis, recent decades have provided evidence of the importance of microglia, and resident immune cells in the central nervous system. In addition, new technologies, including single-cell RNA sequencing, have revealed heterogeneous cell states of microglia in AD. In this review, we systematically summarize the microglial response to amyloid-ß and tau tangles, and the risk factor genes expressed in microglia. Furthermore, we discuss the characteristics of protective microglia that appear during AD pathology and the relationship between AD and microglia-induced inflammation during chronic pain. Understanding the diverse roles of microglia will help identify new therapeutic strategies for AD.

Identification of hyper-ramified microglia in the CA1 region of the mouse hippocampus potentially associated with stress resilience.

Recent studies have indicated that some individuals are less affected by stress, and such individuals are called resilient. This study aimed to determine whether the specific phenotype of microglia might be involved in resilience using the social defeat stress paradigm. Male C57BL/6J (B6) mice were attacked by aggressive male ICR mice for five consecutive days. After stress exposure, the social behaviour was reduced in about half of the B6 mice (vulnerable), whereas no such change was observed in the remaining half of the B6 mice (resilient). Anxiety-like behaviour was increased in vulnerable mice compared with resilient mice and non-stressed controls. However, depression-related behaviour was comparable between the three groups. The morphological characteristics of microglia in the CA1 region of the dorsal hippocampus in non-stressed controls and resilient mice differed from those in vulnerable mice. Interestingly, the voxel densities of GABAergic and glutamatergic synaptic puncta colocalized with microglia were higher in resilient mice than in non-stressed controls and vulnerable mice. Microglia were then objectively classified into three morphological types by hierarchical cluster analysis. The appearance of type I microglia resembled the so-called resting ramified microglia and represented the major population of microglia in non-stressed controls. Type II microglia exhibited a de-ramified morphology and accounted for 60% of the microglia in vulnerable mice. Type III microglia showed a hyper-ramified morphology and represented more than half of the microglia in resilient mice. These results suggest that hyper-ramified microglia in the hippocampus may be associated with stress resilience via the modulation of synaptic transmission.

Phytoestrogen genistein modulates neuron-microglia signaling in a mouse model of chronic social defeat stress.

Microglia, resident immune cells in the brain, are shown to mediate the crosstalk between psychological stress and depression. Interestingly, increasing evidence indicates that sex hormones, particularly estrogen, are involved in the regulation of immune system. In this study, we aimed to understand the potential effects of chronic social defeat stress (CSDS) and genistein (GEN), an estrogenic compound of the plant origin, on neuron-microglia interactions in the mouse hippocampus. The time spent in the avoidance zone in the social interaction test was increased by CSDS 1 day after the exposure, while the avoidance behavior returned to control levels 14 days after the CSDS exposure. Similar results were obtained from the elevated plus-maze test. However, the immobility time in the forced swim test was increased by CSDS 14 days after the exposure, and the depression-related behavior was in part alleviated by GEN. The numerical densities of microglia in the hippocampus were increased by CSDS, and they were decreased by GEN. The voxel densities of synaptic structures and synaptic puncta colocalized with microglia were decreased by CSDS, and they were increased by GEN. Neither CSDS nor GEN affected the gene expressions of major pro-inflammatory cytokines. Conversely, the expression levels of genes related to neurotrophic factors were decreased by CSDS, and they were partially reversed by GEN. These findings show that GEN may in part alleviate stress-related symptoms, and the effects of GEN may be associated with the modulation of neuron-microglia signaling via chemokines and neurotrophic factors in the hippocampus.

Subclass imbalance of parvalbumin-expressing GABAergic neurons in the hippocampus of a mouse ketamine model for schizophrenia, with reference to perineuronal nets.

Impairments of parvalbumin-expressing GABAergic neurons (PV+ neurons) and specialized extracellular structures called perineuronal nets (PNNs) have been found in schizophrenic patients. In this study, we examined potential alterations in four subclasses of PV+ neurons colocalized with PNNs in the hippocampus of a mouse ketamine model for schizophrenia. Because biosynthesis of human natural killer-1 (HNK-1) is shown to be associated with the risk of schizophrenia, here we used mouse monoclonal Cat-315 antibody, which recognizes HNK-1 glycans on PNNs. Once-daily intraperitoneal injections of ketamine for seven consecutive days induced hyper-locomotor activity in the open field tests. The prepulse inhibition (PPI) test showed that PPI scores declined in ketamine-treated mice compared to vehicle-treated mice. The densities of PV+ neurons and Cat-315+ PNNs declined in the CA1 region of ketamine-treated mice. Interestingly, the density of Cat-315+/PV+ neurons was lower in ketamine-treated mice than in vehicle-treated mice, whereas the density of Cat-315-/PV+ neurons was not affected by ketamine. Among the four subclasses of PV+ neurons, the densities of Cat-315+/PV+ basket cells and Cat-315-/PV+ axo-axonic cells were lower in ketamine-treated mice than in vehicle-treated mice, while the densities of Cat-315-/PV+ basket cells and Cat-315+/PV+ axo-axonic cells were not affected by ketamine. Taken together, PNNs may not play a simple neuroprotective role against ketamine. Because different subclasses of PV+ neurons are considered to play distinct roles in the hippocampal neuronal network, the ketamine-induced subclass imbalance of PV+ neurons may result in abnormal network activity, which underlies the pathophysiology of schizophrenia.

Sequential Inward Bending of Arterial Bifurcations is Associated with Intracranial Aneurysm Formation.

OBJECTIVE: To investigate the association between vascular morphology and the development of intracranial aneurysms (IAs), the morphological changes of intracranial arteries after IA induction were examined using a rodent model. METHODS: The vascular morphology of the circle of Willis in rats was visualized at 1 week and at 3 months after IA induction using 7-T magnetic resonance imaging. The following 2 angle parameters were defined: the angle between the parent artery and the daughter arteries (PD angle), and the widening of the daughter arteries (DD angle). The correlations of the angle parameters with IA size and with the number of macrophages infiltrated in the IA wall by immunohistochemistry were examined. RESULTS: Magnetic resonance imaging showed bending of the arteries over time around the predilection site for IAs. The PD angle increased significantly 1 week after IA induction (P < 0.05) and correlated with IA size (P < 0.01). The DD angle did not increase after 1 week, but increased 3 months after IA induction (P < 0.01). The PD angle 1 week after surgery also correlated with the number of infiltrated macrophages in aneurysmal walls (P = 0.01). CONCLUSIONS: Sequential inward bending of arterial bifurcations occurred after IA induction in the rat model. The degree of arterial bending correlated with IA development and inflammation in the IA wall, suggesting that the vascular morphology may be strongly associated with IA development through a proinflammatory mechanism.

EP4 receptor-associated protein regulates gluconeogenesis in the liver and is associated with hyperglycemia in diabetic mice.

Prostaglandin E2 receptor 4-associated protein (EPRAP) is a key molecule in suppressing inflammatory responses in macrophages. EPRAP is expressed not only in macrophages but also in hepatocytes; however, the role of EPRAP in hepatocytes has not yet been defined. To examine the physiological role of hepatic EPRAP in mice, we performed the glucose tolerance test and the hyperinsulinemic-euglycemic clamp in high-fat sucrose diet (HFSD)-fed wild-type (WT) and Eprap null mice. We evaluated the contribution of EPRAP to gluconeogenesis by pyruvate tolerance test and primary hepatocyte experiments. Furthermore, lentivirus-expressing Eprap-specific small-hairpin RNA was injected in db/ db mice. HFSD-fed Eprap null mice had significantly lower blood glucose levels than HFSD-fed WT mice. Eprap null mice also had low glucose levels after fasting or pyruvic acid injection. Moreover, primary hepatocytes from Eprap-deficient mice showed decreased glucose production and lower expression of the Phosphoenol pyruvate carboxykinase and Glucose 6-phosphatase genes. Lentivirus-mediated hepatic Eprap suppression decreased glucose levels and the expression of gluconeogenic genes in db/ db mice. We conclude that EPRAP regulates gluconeogenesis in hepatocytes and is associated with hyperglycemia in diabetic mice. Our data suggest that suppression of EPRAP could be a novel strategy for the treatment of diabetes.

The Japanese Angelica acutiloba root and yokukansan increase hippocampal acetylcholine level, prevent apoptosis and improve memory in a rat model of repeated cerebral ischemia.

ETHNOPHARMACOLOGICAL RELEVANCE: Japanese Angelica acutiloba root (Angelica root) is included in several Kampo medicines including Yokukansan (YKS). Angelica root and YKS are used for the treatment of a variety of psychological and neurodegenerative disorders. Development of safe and effective therapeutic agents against cerebrovascular disorders will improve the treatment of patients with dementia. AIM OF THE STUDY: The effect of Angelica root and YKS on ischemia-impaired memory has not yet been fully investigated. The present study investigated whether Angelica root is also involved in memory improving and neuroprotective effect of YKS in a model of cerebrovascular ischemia. MATERIALS AND METHODS: Male Wistar rats grouped into sham rats received saline, and other three groups subjected to repeated cerebral ischemia induced by 4-vessel occlusion (4-VO), received a 7-day oral administration of either saline, Angelica root or YKS. Memory was evaluated by eight-arm radial maze task. Acetylcholine release (ACh) in the dorsal hippocampus was investigated by microdialysis-HPLC. Apoptosis was determined by terminal deoxynucleotidyl transferase (TdT)-mediated fluorescein-deoxyuridine triphosphate (dUTP) nick-end labeling. RESULTS: Ischemia induced apoptosis, reduced release of ACh, and impaired the memory (increased error choices and decreased correct choices). Angelica root and YKS improved the memory deficits, upregulated the release of ACh and prevented 4-VO-induced hippocampal apoptosis. CONCLUSION: The dual ACh-increasing and neuroprotective effect of Angelica root could make it a promising therapeutic agent useful for the treatment of symptoms of cerebrovascular dementia. Angelica root could be one of the components contributing to the memory-improving and neuroprotective effects of YKS.

Imaging mass spectroscopy delineates the thinned and thickened walls of intracranial aneurysms.

OBJECT: The wall thickness of intracranial aneurysms (IAs) is heterogeneous. Although thinning of the IA wall is thought to contribute to IA rupture, the underlying mechanism remains poorly understood. Recently, imaging mass spectroscopy (IMS) has been used to reveal the distribution of phospholipids in vascular diseases. To investigate the feature of phospholipid composition of IA walls, we conducted IMS in a rat model of experimentally induced IA. MATERIAL AND METHODS: IAs were surgically induced in 7-week-old male rats and analyzed by IMS in negative-ion mode. RESULTS: A molecule at m/z 885.5 was more abundant in the thickened wall than in the thinned wall (P = 0.03). Multiple-stage mass spectroscopy revealed the molecule to be phosphatidylinositol containing stearic acid and arachidonic acid (PI 18:0/20:4). Immunohistochemistry indicated that vascular smooth muscle cells (SMCs) in the thickened wall had dedifferentiated phenotypes. To investigate the relationship between accumulation of PI (18:0/20:4) and phenotypic changes in SMCs, we subjected primary mouse aortic SMCs to liquid chromatography-tandem mass spectrometry. Notably, dedifferentiated SMCs had 1.3-fold more PI (18:0/20:4) than partly differentiated SMCs. CONCLUSIONS: Our study demonstrated the heterogeneity in phospholipid composition of the aneurysmal walls using experimentally induced IAs. PI (18:0/20:4) accumulated at high levels in the thickened aneurysmal wall where synthetic dedifferentiated SMCs exist, suggesting that this phospholipid may be involved in the phenotypic switching of medial SMCs in the IA wall.

Deficiency in EP4 Receptor-Associated Protein Ameliorates Abnormal Anxiety-Like Behavior and Brain Inflammation in a Mouse Model of Alzheimer Disease.

Microglia are thought to play key roles in the progression of Alzheimer disease (AD). Overactivated microglia produce proinflammatory cytokines, such as tumor necrosis factor-α, which appear to contribute to disease progression. Previously, we reported that prostaglandin E2 type 4 receptor-associated protein (EPRAP) promotes microglial activation. We crossed human amyloid precursor protein transgenic mice from strain J20+/- onto an EPRAP-deficient background to determine the role of EPRAP in AD. Behavioral tests were performed in 5-month-old male J20+/-EPRAP+/+ and J20+/-EPRAP-/- mice. EPRAP deficiency reversed the reduced anxiety of J20+/- mice but did not affect hyperactivity. No differences in spatial memory were observed between J20+/-EPRAP+/+ and J20+/-EPRAP-/- mice. In comparison with J20+/-EPRAP+/+, J20+/-EPRAP-/- mice exhibited less microglial accumulation and reductions in the Cd68 and tumor necrosis factor-α mRNAs in the prefrontal cortex and hippocampus. No significant differences were found between the two types of mice in the amount of amyloid-ß 40 or 42 in the cortex and hippocampus. J20+/-EPRAP-/- mice reversed the reduced anxiety-like behavior and had reduced microglial activation compared with J20+/-EPRAP+/+ mice. Further research is required to identify the role of EPRAP in AD, but our results indicate that EPRAP may be related to behavioral and psychological symptoms of dementia and inflammation in patients with AD.

Dipeptidyl Peptidase-4 Inhibitor Anagliptin Prevents Intracranial Aneurysm Growth by Suppressing Macrophage Infiltration and Activation.

BACKGROUND: Chronic inflammation plays a key role in the pathogenesis of intracranial aneurysms (IAs). DPP-4 (dipeptidyl peptidase-4) inhibitors have anti-inflammatory effects, including suppressing macrophage infiltration, in various inflammatory models. We examined whether a DPP-4 inhibitor, anagliptin, could suppress the growth of IAs in a rodent aneurysm model. METHODS AND RESULTS: IAs were surgically induced in 7-week-old male Sprague Dawley rats, followed by oral administration of 300 mg/kg anagliptin. We measured the morphologic parameters of aneurysms over time and their local inflammatory responses. To investigate the molecular mechanisms, we used lipopolysaccharide-treated RAW264.7 macrophages. In the anagliptin-treated group, aneurysms were significantly smaller 2 to 4 weeks after IA induction. Anagliptin inhibited the accumulation of macrophages in IAs, reduced the expression of MCP-1 (monocyte chemotactic protein 1), and suppressed the phosphorylation of p65. In lipopolysaccharide-stimulated RAW264.7 cells, anagliptin treatment significantly reduced the production of tumor necrosis factor α, MCP-1, and IL-6 (interleukin 6) independent of GLP-1 (glucagon-like peptide 1), the key mediator in the antidiabetic effects of DPP-4 inhibitors. Notably, anagliptin activated ERK5 (extracellular signal-regulated kinase 5), which mediates the anti-inflammatory effects of statins, in RAW264.7 macrophages. Preadministration with an ERK5 inhibitor blocked the inhibitory effect of anagliptin on MCP-1 and IL-6 expression. Accordingly, the ERK5 inhibitor also counteracted the suppression of p65 phosphorylation in vitro. CONCLUSIONS: A DPP-4 inhibitor, anagliptin, prevents the growth of IAs via its anti-inflammatory effects on macrophages.

Behavioral abnormalities and reduced norepinephrine in EP4 receptor-associated protein (EPRAP)-deficient mice.

EP4 receptor-associated protein (EPRAP) is a newly identified molecule that regulates macrophage activation. We recently demonstrated the presence of EPRAP in the mice brain; however, little is known about the function of EPRAP in this tissue. Therefore, we investigated the role of EPRAP in behavior and emotion using behavioral analysis in mice. In this study, we subjected EPRAP-deficient (KO) mice and wild-type C57BL/6 (WT) mice to a battery of behavioral tests. EPRAP-KO mice tended to have shorter latencies to fall in the wire hang test, but had normal neuromuscular strength. EPRAP-KO mice exhibited elevated startle responses and reduced pre-pulse inhibition. Compared with WT mice, EPRAP-KO mice increased depression-like behavior in the forced swim test. These abnormal behaviors partially mimic symptoms of depression, attention deficit hyperactivity disorder (ADHD) and schizophrenia. Methylphenidate administration increased locomotor activity less in EPRAP-KO mice than in WT mice. Finally, levels of norepinephrine were reduced in the EPRAP-KO mouse brain. These behavioral abnormalities in EPRAP-KO mice may result from the dysfunction of monoamines, in particular, norepinephrine. Our results suggest that EPRAP participates in the pathogenesis of various behavioral disorders.

EP4 Receptor-Associated Protein in Macrophages Protects against Bleomycin-Induced Pulmonary Inflammation in Mice.

Excessive activation of inflammatory macrophages drives the pathogenesis of many chronic diseases. EP4 receptor-associated protein (EPRAP) has been identified as a novel, anti-inflammatory molecule in macrophages. In this study, we investigated the role of EPRAP using a murine model of bleomycin (BLM)-induced pulmonary inflammation. When compared with wild-type mice, EPRAP-deficient mice exhibited significantly higher mortality, and increased accumulation of macrophages and proinflammatory molecules in the lung 7 d post-BLM administration. Accordingly, the levels of phosphorylated p105, MEK1/2, and ERK1/2 were elevated in EPRAP-deficient alveolar macrophages following BLM administration. In contrast, macrophage-specific EPRAP overexpression decreased the production of proinflammatory cytokines and chemokines, suggesting that EPRAP in macrophages plays a key role in attenuating BLM-induced pulmonary inflammation. As EPRAP is phosphorylated after translation, we examined the role of posttranslational modifications in cellular inflammatory activation using mouse embryo fibroblasts (MEFs) expressing mutant EPRAP proteins. Expression of mutant EPRAP, in which serine-108 and serine-608 were replaced with alanine (EPRAP S108A/S608A), markedly suppressed TNF-α production in LPS-treated MEFs. Conversely, the serine phosphatase 2A (PP2A) inhibitor, cantharidic acid, increased LPS-induced TNF-α production in MEFs expressing wild-type EPRAP, but not in MEFs expressing EPRAP S108A/S608A. Immunoprecipitation analyses demonstrated that EPRAP associated with PP2A in both MEFs and alveolar macrophages from BLM-treated mice. Our data suggest that PP2A dephosphorylates EPRAP, which may be a crucial step in exertion of its anti-inflammatory properties. For these reasons, we believe the EPRAP-PP2A axis in macrophages holds the key to treating chronic inflammatory disorders.

EP4 Receptor-Associated Protein in Microglia Promotes Inflammation in the Brain.

Microglial cells play a key role in neuronal damage in neurodegenerative disorders. Overactivated microglia induce detrimental neurotoxic effects through the excess production of proinflammatory cytokines. However, the mechanisms of microglial activation are poorly understood. We focused on prostaglandin E2 type 4 receptor-associated protein (EPRAP), which suppresses macrophage activation. We demonstrated that EPRAP exists in microglia in the brain. Furthermore, EPRAP-deficient mice displayed less microglial accumulation, and intraperitoneal administration of lipopolysaccharide (LPS) led to reduced expression of tumor necrosis factor-α and monocyte chemoattractant protein-1 mRNA in the brains of EPRAP-deficient mice. Consistently, EPRAP-deficient microglia showed a marked decrease in the production of tumor necrosis factor-α and monocyte chemoattractant protein-1 induced by LPS treatment compared with wild-type controls. In addition, EPRAP deficiency decreased microglial activation and neuronal cell death induced by intraventricular injection of kainic acid. EPRAP deficiency impaired the LPS-induced phosphorylation of c-jun N-terminal kinase and p38 mitogen-activated protein kinase in microglia. The phosphorylation levels of mitogen-activated protein kinase kinase 4-which phosphorylates c-jun N-terminal kinase and p38 mitogen-activated protein kinase-were also decreased in EPRAP-deficient microglia after LPS stimulation. Although EPRAP in macrophages plays a role in the attenuation of inflammation, EPRAP promotes proinflammatory activation of microglia through mitogen-activated protein kinase kinase 4-mediated signaling and may be key to the deteriorating neuronal damage brought on by brain inflammation.

EP4 Receptor-Associated Protein in Macrophages Ameliorates Colitis and Colitis-Associated Tumorigenesis.

Prostaglandin E2 plays important roles in the maintenance of colonic homeostasis. The recently identified prostaglandin E receptor (EP) 4-associated protein (EPRAP) is essential for an anti-inflammatory function of EP4 signaling in macrophages in vitro. To investigate the in vivo roles of EPRAP, we examined the effects of EPRAP on colitis and colitis-associated tumorigenesis. In mice, EPRAP deficiency exacerbated colitis induced by dextran sodium sulfate (DSS) treatment. Wild-type (WT) or EPRAP-deficient recipients transplanted with EPRAP-deficient bone marrow developed more severe DSS-induced colitis than WT or EPRAP-deficient recipients of WT bone marrow. In the context of colitis-associated tumorigenesis, both systemic EPRAP null mutation and EPRAP-deficiency in the bone marrow enhanced intestinal polyp formation induced by azoxymethane (AOM)/DSS treatment. Administration of an EP4-selective agonist, ONO-AE1-329, ameliorated DSS-induced colitis in WT, but not in EPRAP-deficient mice. EPRAP deficiency increased the levels of the phosphorylated forms of p105, MEK, and ERK, resulting in activation of stromal macrophages in DSS-induced colitis. Macrophages of DSS-treated EPRAP-deficient mice exhibited a marked increase in the expression of pro-inflammatory genes, relative to WT mice. By contrast, forced expression of EPRAP in macrophages ameliorated DSS-induced colitis and AOM/DSS-induced intestinal polyp formation. These data suggest that EPRAP in macrophages functions crucially in suppressing colonic inflammation. Consistently, EPRAP-positive macrophages were also accumulated in the colonic stroma of ulcerative colitis patients. Thus, EPRAP may be a potential therapeutic target for inflammatory bowel disease and associated intestinal tumorigenesis.

The Prostaglandin E2 Receptor EP4 Regulates Obesity-Related Inflammation and Insulin Sensitivity.

With increasing body weight, macrophages accumulate in adipose tissue. There, activated macrophages secrete numerous proinflammatory cytokines and chemokines, giving rise to chronic inflammation and insulin resistance. Prostaglandin E2 suppresses macrophage activation via EP4; however, the role of EP4 signaling in insulin resistance and type 2 diabetes mellitus remains unknown. In this study, we treated db/db mice with an EP4-selective agonist, ONO-AE1-329, for 4 weeks to explore the role of EP4 signaling in obesity-related inflammation in vivo. Administration of the EP4 agonist did not affect body weight gain or food intake; however, in the EP4 agonist-treated group, glucose tolerance and insulin resistance were significantly improved over that of the vehicle-treated group. Additionally, administration of the EP4 agonist inhibited the accumulation of F4/80-positive macrophages and the formation of crown-like structures in white adipose tissue, and the adipocytes were significantly smaller. The treatment of the EP4 agonist increased the number of anti-inflammatory M2 macrophages, and in the stromal vascular fraction of white adipose tissue, which includes macrophages, it markedly decreased the levels of proinflammatory cytokines and chemokines. Further, EP4 activation increased the expression of adiponectin and peroxidase proliferator-activated receptors in white adipose tissue. Next, we examined in vitro M1/M2 polarization assay to investigate the impact of EP4 signaling on determining the functional phenotypes of macrophages. Treatment with EP4 agonist enhanced M2 polarization in wild-type peritoneal macrophages, whereas EP4-deficient macrophages were less susceptible to M2 polarization. Notably, antagonizing peroxidase proliferator-activated receptor δ activity suppressed EP4 signaling-mediated shift toward M2 macrophage polarization. Thus, our results demonstrate that EP4 signaling plays a critical role in obesity-related adipose tissue inflammation and insulin resistance by regulating macrophage recruitment and polarization. The activation of EP4 signaling holds promise for treating obesity and type 2 diabetes mellitus.

Expression of Vasohibin-1 in Human Carotid Atherosclerotic Plaque.

AIM: In patients with carotid plaque, intraplaque hemorrhage arising from ruptured neovascular vessels within the neointima is an important cause of stroke. The expression of Vasohibin-1 (VASH1), a negative feedback regulator of angiogenesis, occurs in the microvessel endothelial cells of various solid tumors and the arterial wall. However, the roles of VASH1 in the pathogenesis of atherosclerotic diseases remain unclear. The present study aimed to clarify the relevance of the VASH1 expression and plaque instability in human carotid plaques. METHODS: We used quantitative real-time PCR and immunostaining to examine 12 atheromatous plaque specimens obtained via carotid endarterectomy. The distal areas of specimens lacking macroscopic atherosclerotic lesions served as controls. RESULTS: Compared with that observed in the controls, the VASH1 gene expression increased significantly in the atheromatous plaque (p=0.018). Moreover, the VASH1 mRNA levels correlated positively with those of VEGFA, CD31 and VCAM1 (r=0.788, p=0.004; r=0.99, p ＜ 0.001; r=0.94, p ＜ 0.001, respectively). Finally, the immunohistochemical analyses revealed the VASH1 expression in the neointimal microvessel endothelial cells of carotid plaque. CONCLUSIONS: The VASH1 expression levels in atheroma reflect both enhanced neovascularization and the inflammatory burden. Therefore, the VASH1 level may be a novel biomarker for evaluating plaque instability in patients with carotid arteriosclerosis and predicting ischemic stroke.