Genetic variation in dysbindin (DTNBP1: dystrobrevin-binding protein 1) has recently been shown to be associated with schizophrenia. The dysbindin gene is located at chromosome 6p22.3, one of the most promising susceptibility loci in schizophrenia linkage studies. We attempted to replicate this association in a Japanese sample of 670 patients with schizophrenia and 588 controls. We found a nominally significant association with schizophrenia for four single nucleotide polymorphisms and stronger evidence for association in a multi-marker haplotype analysis (P = 0.00028). We then explored functions of dysbindin protein in primary cortical neuronal culture. Overexpression of dysbindin induced the expression of two pre-synaptic proteins, SNAP25 and synapsin I, and increased extracellular basal glutamate levels and release of glutamate evoked by high potassium. Conversely, knockdown of endogenous dysbindin protein by small interfering RNA (siRNA) resulted in the reduction of pre-synaptic protein expression and glutamate release, suggesting that dysbindin might influence exocytotic glutamate release via upregulation of the molecules in pre-synaptic machinery. The overexpression of dysbindin increased phosphorylation of Akt protein and protected cortical neurons against neuronal death due to serum deprivation and these effects were blocked by LY294002, a phosphatidylinositol 3-kinase (PI3-kinase) inhibitor. SiRNA-mediated silencing of dysbindin protein diminished Akt phosphorylation and facilitated neuronal death induced by serum deprivation, suggesting that dysbindin promotes neuronal viability through PI3-kinase-Akt signaling. Genetic variants associated with impairments of these functions of dysbindin could play an important role in the pathogenesis of schizophrenia.

Disrupted-in-schizophrenia 1 (DISC1), identified in a pedigree with a familial psychosis with the chromosome translocation (1:11), is a putative susceptibility gene for psychoses such as schizophrenia and bipolar disorder. Although there are a number of patients with major depressive disorder (MDD) in the family members with the chromosome translocation, the possible association with MDD has not yet been studied. We therefore performed an association study of the DISC1 gene with MDD and schizophrenia. We found that Cys704 allele of the Ser704Cys single-nucleotide polymorphism (SNP) was associated with an increased risk of developing MDD (P=0.005, odds ratio=1.46) and stronger evidence for association in a multi-marker haplotype analysis containing this SNP (P=0.002). We also explored possible impact of Ser704Cys on brain morphology in healthy volunteers using MR imaging. We found a reduction in gray matter volume in cingulate cortex and a decreased fractional anisotropy in prefrontal white matter of individuals carrying the Cys704 allele compared with Ser/Ser704 subjects. In primary neuronal culture, knockdown of endogenous DISC1 protein by small interfering RNA resulted in the suppression of phosphorylation of ERK and Akt, whose signaling pathways are implicated in MDD. When effects of sDISC1 (Ser704) and cDISC1 (Cys704) proteins were examined separately, phosphorylation of ERK was greater in sDISC1 compared with cDISC1. A possible biological mechanism of MDD might be implicated by these convergent data that Cys704 DISC1 is associated with the lower biological activity on ERK signaling, reduced brain gray matter volume and an increased risk for MDD.

Very little is known about the contribution of a low affinity neurotrophin receptor, p75, to neurotransmitter release. Here we show that nerve growth factor (NGF) induced a rapid release of glutamate and an increase of Ca 2؉ in cerebellar neurons through a p75-dependent pathway. The NGF-induced release occurred even in the presence of the Trk inhibitor K252a. The release caused by NGF but not brain-derived neurotrophic factor was enhanced in neurons overexpressing p75. Further, after transfection of p75-small interfering RNA, which downregulated the endogenous p75 expression, the NGF-induced release was inhibited, suggesting that the NGFinduced glutamate release was through p75. We found that the NGF-increased Ca 2؉ was derived from the ryanodine-sensitive Ca 2؉ receptor and that the NGF-increased Ca 2؉ was essential for the NGF-induced glutamate release. Furthermore, scyphostatin, a sphingomyelinase inhibitor, blocked the NGF-dependent Ca 2؉ increase and glutamate release, suggesting that a ceramide produced by sphingomyelinase was required for the NGF-stimulated Ca 2؉ increase and glutamate release. This action of NGF only occurred in developing neurons whereas the brain-derived neurotrophic factor-mediated Ca 2؉ increase and glutamate release was observed at the mature neuronal stage. Thus, we demonstrate that NGF-mediated neurotransmitter release via the p75-dependent pathway has an important role in developing neurons.

The abnormal expression and function of myelin-related proteins contribute to nervous system dysfunction associated with neuropsychiatric disorders; however, the underlying mechanism of this remains unclear. We found here that breast carcinoma amplified sequence 1 (BCAS1), a basic protein abundant in the brain, was expressed specifically in oligodendrocytes and Schwann cells, and that its expression level was decreased by demyelination. This suggests that BCAS1 is a novel myelin-associated protein. BCAS1 knockout mice displayed schizophrenia-like behavioral abnormalities and a tendency toward reduced anxiety-like behaviors. Moreover, we found that the loss of BCAS1 specifically induced hypomyelination and the expression of inflammation-related genes in the brain. These observations provide a novel insight into the functional link between oligodendrocytes and inflammation and/or abnormal behaviors.

Little is known about the role of the integrin-associated protein (IAP, or CD47) in neuronal development and its function in the central nervous system. We investigated neuronal responses in IAP-overexpressing cortical neurons using a virus-gene transfer system. We found that dendritic outgrowth was significantly enhanced in IAP (form 4)-transfected neurons. Furthermore, synaptic proteins including synaptotagmin, syntaxin, synapsin I, and SNAP25 (25-kDa synaptosomal associated protein) were up-regulated. In accordance with this finding, the release of the excitatory transmitter glutamate and the frequencies of Ca 2؉ oscillations (glutamate-mediated synaptic transmission) were increased. Interestingly, the overexpression of IAP activated mitogen-activated protein kinase (MAPK), and this activation was required for the IAP-dependent biological effects. After down-regulation of the endogenous IAP by small interfering RNA, MAPK activity, synaptic protein levels, and glutamate release decreased. These observations suggest that the IAP plays important roles in dendritic outgrowth and synaptic transmission in developing cortical neurons through the activation of MAPK.Growing evidence has suggested that cell adhesion proteins and associated proteins such as the neural cell adhesion molecule, cadherin, and integrins play an important role in the formation, maintenance, and function of synapses (1, 2). Integrin forms heterodimers of ␣-and ␤-subunits linked to the actin cytoskeleton (3, 4). Recently, Chan et al. (5) showed that many different integrins, including ␣ 3 and ␣ 5 , are expressed in the brain and are associated with synapses. In contrast, little is known about integrin-associated protein (IAP) 1 -dependent regulation in neuronal function, although IAP physically associates with integrins including ␣ 2 ␤ 1 , ␣ V ␤ 3 , and ␣ IIb ␤ 3 (6 -8).The function of IAP in non-neuronal cell populations has been well studied. For example, IAP plays an essential role in host defense by participating in the migration and activation of leukocytes in response to bacterial infection (9). IAP is a receptor for the C-terminal cell-binding domain of thrombospondin (10). Thrombospondin stimulates the integrin-dependent adhesion, spreading, and motility of endothelial cells, leukocytes, and smooth muscle cells (10, 11). Furthermore, IAP is a ligand for the transmembrane signal-regulatory protein (12) and is involved in macrophage function. In platelets, a peptide from the C-terminal cell-binding domain of thrombospondin induces aggregation (13) and spreading on immobilized fibrinogen or collagen (7). There is some evidence that IAP is involved in neuronal function. Memory retention and long-term potentiation were reduced in IAP-deficient mice (14). Monoclonal antibody to IAP significantly impaired memory retention and reduced the amplitude of long-term potentiation in dentate gyrus neurons (15). However, little is known as to the possible effects of IAP on neuronal development and function at the molecular level.In the present study, ...