Kenji Chiba

Migration of CD4 T Cells and Dendritic Cells toward Sphingosine 1-Phosphate (S1P) Is Mediated by Different Receptor Subtypes: S1P Regulates the Functions of Murine Mature Dendritic Cells via S1P Receptor Type 3

Dendritic cells (DCs) and lymphocytes are known to show a migratory response to the phospholipid mediator, sphingosine 1-phosphate (S1P). However, it is unclear whether the same S1P receptor subtype mediates the migration of lymphocytes and DCs toward S1P. In this study, we investigated the involvement of S1P receptor subtypes in S1P-induced migration of CD4 T cells and bone marrow-derived DCs in mice. A potent S1P receptor agonist, the (S)-enantiomer of FTY720-phosphate [(S)-FTY720-P], at 0.1 nM or higher and a selective S1P receptor type 1 (S1P1) agonist, SEW2871, at 0.1 μM or higher induced a dose-dependent down-regulation of S1P1. The pretreatment with these compounds resulted in a significant inhibition of mouse CD4 T cell migration toward S1P. Thus, it is revealed that CD4 T cell migration toward S1P is highly dependent on S1P1. Mature DCs, when compared with CD4 T cells or immature DCs, expressed a relatively higher level of S1P3 mRNA. S1P at 10–1000 nM induced a marked migration and significantly enhanced the endocytosis of FITC-dextran in mature but not immature DCs. Pretreatment with (S)-FTY720-P at 0.1 μM or higher resulted in a significant inhibition of S1P-induced migration and endocytosis in mature DCs, whereas SEW2871 up to 100 μM did not show any clear effect. Moreover, we found that S1P-induced migration and endocytosis were at an extremely low level in mature DCs prepared from S1P3-knockout mice. These results indicate that S1P regulates migration and endocytosis of murine mature DCs via S1P3 but not S1P1.

Involvement of Neuroinflammation during Brain Development in Social Cognitive Deficits in Autism Spectrum Disorder and Schizophrenia

Development of social cognition, a unique and high-order function, depends on brain maturation from childhood to adulthood in humans. Autism spectrum disorder (ASD) and schizophrenia have similar social cognitive deficits, although age of onset in each disorder is different. Pathogenesis of these disorders is complex and contains several features, including genetic risk factors, environmental risk factors, and sites of abnormalities in the brain. Although several hypotheses have been postulated, they seem to be insufficient to explain how brain alterations associated with symptoms in these disorders develop at distinct developmental stages. Development of ASD appears to be related to cerebellar dysfunction and subsequent thalamic hyperactivation in early childhood. By contrast, schizophrenia seems to be triggered by thalamic hyperactivation in late adolescence, whereas hippocampal aberration has been possibly initiated in childhood. One of the possible culprits is metal homeostasis disturbances that can induce dysfunction of blood-cerebrospinal fluid barrier. Thalamic hyperactivation is thought to be induced by microglia-mediated neuroinflammation and abnormalities of intracerebral environment. Consequently, it is likely that the thalamic hyperactivation triggers dysregulation of the dorsolateral prefrontal cortex for lower brain regions related to social cognition. In this review, we summarize the brain aberration in ASD and schizophrenia and provide a possible mechanism underlying social cognitive deficits in these disorders based on their distinct ages of onset.