Prostaglandin D 2 signaling mediated by the CRTH2 receptor is involved in MK-801-induced cognitive dysfunction

Timapiprant, a prostaglandin D2 receptor antagonist, ameliorates pathology in a rat Alzheimer's model

We investigated the relevance of the prostaglandin D2 pathway in Alzheimer's disease, because prostaglandin D2 is a major prostaglandin in the brain. Thus, its contribution to Alzheimer's disease merits attention, given the known impact of the prostaglandin E2 pathway in Alzheimer's disease. We used the TgF344-AD transgenic rat model because it exhibits age-dependent and progressive Alzheimer's disease pathology. Prostaglandin D2 levels in hippocampi of TgF344-AD and wild-type littermates were significantly higher than prostaglandin E2. Prostaglandin D2 signals through DP1 and DP2 receptors. Microglial DP1 receptors were more abundant and neuronal DP2 receptors were fewer in TgF344-AD than in wild-type rats. Expression of the major brain prostaglandin D2 synthase (lipocalin-type PGDS) was the highest among 33 genes involved in the prostaglandin D2 and prostaglandin E2 pathways. We treated a subset of rats (wild-type and TgF344-AD males) with timapiprant, a potent highly selective DP2 antagonist in development for allergic inflammation treatment. Timapiprant significantly mitigated Alzheimer's disease pathology and cognitive deficits in TgF344-AD males. Thus, selective DP2 antagonists have potential as therapeutics to treat Alzheimer's disease.

Lipocalin-type prostaglandin D synthase regulates light-induced phase advance of the central circadian rhythm in mice

We previously showed that mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) exhibit attenuated light-induced phase shift. To explore the underlying mechanisms, we performed gene expression analysis of laser capture microdissected suprachiasmatic nuclei (SCNs) and found that lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is involved in the impaired response to light stimulation in the late subjective night in PACAP-deficient mice. L-PGDS-deficient mice also showed impaired light-induced phase advance, but normal phase delay and nonvisual light responses. Then, we examined the receptors involved in the response and observed that mice deficient for type 2 PGD₂ receptor DP2/CRTH2 (chemoattractant receptor homologous molecule expressed on Th2 cells) show impaired light-induced phase advance. Concordant results were observed using the selective DP2/CRTH2 antagonist CAY10471. These results indicate that L-PGDS is involved in a mechanism of light-induced phase advance via DP2/CRTH2 signaling.

Kawaguchi et al. show that mice deficient in lipocalin-type prostaglandin (PG) D synthase (L-PGDS) exhibit impaired light-induced phase advance, but normal phase delay and nonvisual light responses. This study suggests the role of L-PGDS for the light-induced phase advance possibly via a chemoattractant receptor DP2/CRTH2.

Ketamine Affects the Expression of ErbB4 in the Hippocampus and Prefrontal Cortex of Rats

Schizophrenia is a severe chronic neuropsychiatric disorder, and its exact pathogenesis remains unclear. This study investigated the effect of ketamine on the expression of ErbB4 (considered a schizophrenia candidate gene) in the hippocampus and prefrontal cortex of rats. Rats were randomly divided into four groups: control, low-dose, medium-dose and high-dose groups. The low-dose, medium-dose and high-dose groups were intraperitoneally injected with 15 mg/kg, 30 mg/kg and 60 mg/kg ketamine, respectively, twice a day (9:00 a.m. and 9:00 p.m.); the control group was administered normal saline. The treatment lasted 7 days. After treatment, rats were euthanized, and their brain tissues were collected and then analyzed by immunohistochemistry. The results of immunohistochemistry staining demonstrated that the ErbB4 protein was expressed exclusively in the CA3 region of the hippocampus and the Cg1 region of the prefrontal cortex. Ketamine administration significantly decreased the expression of ErbB4 in a dose-dependent manner. The high-dose ketamine treatment was found to be optimal for establishing a rat model for schizophrenia. Ketamine induced symptoms similar to schizophrenia in humans. The ketamine-induced rat model for schizophrenia constructed in this study provides novel insights to better understand the pathogenic mechanisms of schizophrenia and aid in drug discovery.

The therapeutic potential of CRTH2/DP2 beyond allergy and asthma

Prostaglandin (PG) D₂ has been in the focus of research for quite a long time, but its biological effects and its roles in human disease are still not fully characterized. When in 2001 a second major PGD₂ receptor termed chemoattractant receptor homologue expressed on Th2 cells (CRTH2; alternative name DP2) was discovered, diverse investigations started to shed more light on the complex and often controversial actions of the prostaglandin. With various immunomodulating effects, such as induction of migration, activation, and cytokine release of leukocytes observed both in vivo and in vitro, CRTH2 has emerged as a promising target for the treatment of allergic diseases. However, with more and more research being performed on CRTH2, it has also become clear that its biological actions are far more diverse than expected at the beginning. In this review, we aim to summarize the roles that PGD₂ - and CRTH2 in particular - might play in diseases of the central nervous system, kidney, intestine, lung, hair and skin, bone and cartilage, and in cancer. Based on current data we propose that blocking CRTH2 might be a potential therapeutic approach to numerous conditions beyond classical allergic diseases and asthma.

Critical involvement of the orbitofrontal cortex in hyperlocomotion induced by NMDA receptor blockade in mice

Glutamatergic N-methyl-d-aspartate (NMDA) receptors play critical roles in several neurological and psychiatric diseases. Blockade by noncompetitive NMDA receptor antagonist leads to psychotomimetic effects; however, the brain regions responsible for the effects are not well understood. Here, we determined the specific brain regions responsive to MK-801, a noncompetitive NMDA receptor antagonist, by mapping Arc expression as an indicator of neuronal activity using Arc::dVenus reporter mice. MK-801 increased dVenus expression predominantly in the orbitofrontal cortex (OFC) and, as expected, induced a marked hyperlocomotion. Local OFC lesions selectively attenuated the early phase (0-30 min) of MK-801-induced hyperlocomotion. Further, clozapine, an atypical antipsychotic, effectively attenuated both the MK-801-induced dVenus expression in the OFC and hyperlocomotion. These results suggest that the OFC may be critically involved in NMDA receptor-mediated psychotic-like behavioral abnormalities.