Saburo Sakoda

Genome-wide association study identifies common variants at four loci as genetic risk factors for Parkinson's disease.

To identify susceptibility variants for Parkinsons disease (PD), we performed a genome-wide association study (GWAS) and two replication studies in a total of 2,011 cases and 18,381 controls from Japan. We identified a new susceptibility locus on 1q32 (P = 1.52 × 10−12) and designated this as PARK16, and we also identified BST1 on 4p15 as a second new risk locus (P = 3.94 × 10−9). We also detected strong associations at SNCA on 4q22 (P = 7.35 × 10−17) and LRRK2 on 12q12 (P = 2.72 × 10−8), both of which are implicated in autosomal dominant forms of parkinsonism. By comparing results of a GWAS performed on individuals of European ancestry, we identified PARK16, SNCA and LRRK2 as shared risk loci for PD and BST1 and MAPT as loci showing population differences. Our results identify two new PD susceptibility loci, show involvement of autosomal dominant parkinsonism loci in typical PD and suggest that population differences contribute to genetic heterogeneity in PD.

Class IV semaphorin Sema4A enhances T-cell activation and interacts with Tim-2

Semaphorins are a family of phylogenetically conserved soluble and transmembrane proteins. Although many soluble semaphorins deliver guidance cues to migrating axons during neuronal development, some members are involved in immune responses. For example, CD100 (also known as Sema4D), a class IV transmembrane semaphorin, signals through CD72 to effect nonredundant roles in immune responses in a ligand–receptor system that is distinct from any seen previously in the nervous system. Here we report that the class IV semaphorin Sema4A, which is expressed in dendritic cells and B cells, enhances the in vitro activation and differentiation of T cells and the in vivo generation of antigen-specific T cells. Treating mice with monoclonal antibodies against Sema4A blocks the development of an experimental autoimmune encephalomyelitis that is induced by an antigenic peptide derived from myelin oligodendrocyte glycoprotein. In addition, expression cloning shows that the Sema4A receptor is Tim-2, a member of the family of T-cell immunoglobulin domain and mucin domain (Tim) proteins that is expressed on activated T cells.

Plexin-A1 and its interaction with DAP12 in immune responses and bone homeostasis

Semaphorins and their receptors have diverse functions in axon guidance, organogenesis, vascularization and/or angiogenesis, oncogenesis and regulation of immune responses. The primary receptors for semaphorins are members of the plexin family. In particular, plexin-A1, together with ligand-binding neuropilins, transduces repulsive axon guidance signals for soluble class III semaphorins, whereas plexin-A1 has multiple functions in chick cardiogenesis as a receptor for the transmembrane semaphorin, Sema6D, independent of neuropilins. Additionally, plexin-A1 has been implicated in dendritic cell function in the immune system. However, the role of plexin-A1 in vivo, and the mechanisms underlying its pleiotropic functions, remain unclear. Here, we generated plexin-A1-deficient (plexin-A1−/−) mice and identified its important roles, not only in immune responses, but also in bone homeostasis. Furthermore, we show that plexin-A1 associates with the triggering receptor expressed on myeloid cells-2 (Trem-2), linking semaphorin-signalling to the immuno-receptor tyrosine-based activation motif (ITAM)-bearing adaptor protein, DAP12. These findings reveal an unexpected role for plexin-A1 and present a novel signalling mechanism for exerting the pleiotropic functions of semaphorins.

Neuromyelitis optica: Passive transfer to rats by human immunoglobulin.

Recurrent attacks of optic neuritis and myelitis are the hallmarks of both neuromyelitis optica (NMO) and multiple sclerosis (MS). NMO immunoglobulin G (NMO-IgG), which recognizes astrocytic aquaporin-4 (AQP4) water channels, is a specific serum autoantibody that distinguishes NMO from MS. The pathogenic role of the anti-AQP4 antibody (AQP4-Ab, NMO-IgG) in NMO has been speculated based on several studies in vitro. The aim of this study was to demonstrate the pathogenicity of AQP4-Ab in vivo. We obtained IgG from patients who underwent therapeutic plasmapheresis, and developed an animal model by passive transfer of IgG to rats. The active lesions of the rats exhibited pathological characteristics strikingly similar to those of NMO, marked by astrocytic loss and perivascular deposition of immunoglobulin and complements. These findings provide the first evidence of the pathogenicity of AQP4-Ab in vivo and support the therapeutic efficacy of eliminating the antibodies by plasmapheresis.

Expression of the inducible isoform of nitric oxide synthase in the central nervous system of mice correlates with the severity of actively induced experimental allergic encephalomyelitis.

A cytokine-mediated excessive increase in nitric oxide (NO) by macrophages or glial cells via an inducible isoform of NO synthase (iNOS) has been proposed to play an important role in demyelinating diseases. To further investigate the role of iNOS in demyelination, experimental allergic encephalomyelitis (EAE), a known animal model of multiple sclerosis (MS) in mice, was chosen in this study. A semiquantitative reverse transcriptase-polymerase chain reaction (RT/PCR) analysis revealed an increase in the mRNA levels of iNOS and cytokines known to induce iNOS or inflammatory cytokines (interleukin (IL)-1 alpha, IL-1 beta, IL-2, IL-6, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and TNF-beta) in the spinal cord corresponding to the severity of the disease without significant change in the mRNA levels of immunoregulatory cytokines (IL-4, IL-10 and transforming growth factor (TGF)-beta) during the course of EAE. An immunohistochemical examination of the spinal cord using an iNOS-specific antibody showed iNOS-positive cells to be mainly inflammatory cells with a higher frequency of iNOS-positive cells at the peak of EAE than in the early phase. These iNOS-positive cells at the peak appeared to be composed of infiltrating macrophages and most of them were located in the necrotic area. These results suggested that cytokine-induced excessive NO via iNOS by macrophages caused tissue damage in the central nervous system in EAE.

Role of the prefrontal cortex in human balance control

Although recent studies have demonstrated cortical involvement in human balance control, there is insufficient information regarding the regions of the cerebral cortex that contribute to human balance control and their mechanism of action. Using a functional near-infrared spectroscopic system, we investigated perturbation-related cortical activation. External perturbations were provided with and without the preceding auditory warning signals 2 s before the perturbation. Statistical analysis by applying the general linear model showed significant activation in the prefrontal cortex, including the dorsolateral prefrontal cortex and frontal eye field after external perturbation, regardless of the preceding auditory warning signals. A time-line analysis revealed similar temporal profiles for prefrontal activation in 2 different conditions. Based on the contrast between the 2 conditions, we detected enhanced activation in the right posterior parietal cortex and supplementary motor area in the condition where the auditory warning signals were provided. We presumed that prefrontal involvement may be relevant to adequate allocation of visuospatial attention. Our results may facilitate the understanding of cortical mechanisms for balance control in humans and the underlying pathophysiology of falls.

Cognitive function in amyotrophic lateral sclerosis

Cognitive function in patients with amyotrophic lateral sclerosis (ALS) has drawn recent attention. However, the pathogenesis of cognitive dysfunction in patients with ALS remains uncertain. To explore the underlying mechanism for cognitive dysfunction further, we studied 26 patients with ALS (15 male and 11 female; age from 36 to 67 years) by using neuropsychological batteries, magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT). We also evaluated these patients and an additional 26 age- and sex-matched normal controls using neuropsychological batteries with special attention to the frontal lobe function. On the basis of neuropsychological examination, we classified patients into three groups using cluster analysis. Age, education level and severity were comparable across these subgroups. Neuropathologic examination was subsequently carried out in six patients. Patients in Group 1 and 2 had low scores on all measures compared to patients in Group 3 and normal controls. Patients in Group 1 and 2 had frontal atrophy on MRI and reduced isotope uptake in the frontal region on SPECT, which was more evident in patients in Group 1. On neuropathologic examination, patients in Group 1 showed spongy degeneration and neuronal loss in the frontal lobe. Patients in Group 3 showed no notable pathology in the frontal region. The gradient distribution of the scores for attention and executive function, as well as SPECT findings suggested the presence of a continuum of cognitive disability in patients with ALS corresponding to the pathologic process in the frontal lobe ranging from significant impairment to normality. We, therefore, believe that inattention and executive dysfunction alternatives may evolve in patients with ALS corresponding to the pathologic process in the frontal lobe.

Benefit of valproic acid in suppressing disease progression of ALS model mice.

Valproic acid (VPA) has long been used as an antiepileptic drug and recently as a mood stabilizer, and evidence is increasing that VPA exerts neuroprotective effects through changes in a variety of intracellular signalling pathways including upregulation of Bcl‐2 protein with an antiapoptotic property and inhibiting glycogen synthase kinase 3‐β, which is considered to promote cell survival. Although the neuroprotective effects of VPA have been demonstrated in a murine model of human immunodeficiency virus‐1 encephalitis, there have been no reports on the effect of VPA in chronic progressing neurodegenerative disease models including amyotrophic lateral sclerosis (ALS). ALS is a devastating disease selectively affecting motoneurons, and its disease model mice bear a close resemblance to ALS symptomatically and pathologically. First, we used an organotypic slice culture using mouse spinal cord, and showed that VPA protected spinal motoneurons against death from glutamate toxicity in vitro. Then, we treated ALS model mice with VPA at the dose effective level for epileptic model mice after 45 days of age (pre‐onset treatment) or the day of the disease onset (post‐onset treatment). We found a significant prolongation of the disease duration in ALS model mice in both methods of treatment. Considering the long usage of VPA for epileptic patients with good tolerance and safety, these data strongly support the clinical application of VPA for ALS treatment.

Neuroaxonal Dystrophy Caused by Group VIA Phospholipase A2 Deficiency in Mice: A Model of Human Neurodegenerative Disease

Calcium-independent group VIA phospholipase A2 (iPLA2β) is considered to play a role in signal transduction and maintenance of homeostasis or remodeling of membrane phospholipids. A role of iPLA2β has been suggested in various physiological and pathological processes, including immunity, chemotaxis, and cell death, but the details remain unclear. Accordingly, we investigated mice with targeted disruption of the iPLA2β gene. iPLA2β−/− mice developed normally and grew to maturity, but all showed evidence of severe motor dysfunction, including a hindlimb clasping reflex during tail suspension, abnormal gait, and poor performance in the hanging wire grip test. Neuropathological examination of the nervous system revealed widespread degeneration of axons and/or synapses, accompanied by the presence of numerous spheroids (swollen axons) and vacuoles. These findings provide evidence that impairment of iPLA2β causes neuroaxonal degeneration, and indicate that the iPLA2β−/− mouse is an appropriate animal model of human neurodegenerative diseases associated with mutations of the iPLA2β gene, such as infantile neuroaxonal dystrophy and neurodegeneration with brain iron accumulation.

IL-6 plays a crucial role in the induction phase of myelin oligodendrocyte glycoprotein 35–55 induced experimental autoimmune encephalomyelitis

We investigated the role of IL-6 in myelin oligodendrocyte glycoprotein (MOG) peptide induced experimental autoimmune encephalomyelitis (EAE) using IL-6-deficient mice and found that IL-6-deficient mice were resistant to active induction of EAE, but that the treatment of those mice with IL-6 during the preclinical phase caused typical EAE. We also found that both wild-type and IL-6-deficient mice were resistant to passive transfer of EAE by lymphocytes from IL-6-deficient mice, but that passive transfer of lymphocytes from wild-type mice induced typical EAE in IL-6-deficient mice. Histological abnormalities of the central nervous system (CNS) in those IL-6-deficient mice with EAE were similar to those in wild-type mice with EAE. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed no difference in the production of inflammatory cytokines such as IL-1beta, IL-2, TNF-alpha, and IFN-gamma in the CNS of IL-6-deficient mice with EAE as compared to the CNS of wild-type mice with EAE. These results indicated that IL-6 might be an important factor in the induction phase, but might have little influence on the effector phase of EAE. We further estimated the production of cytokines in MOG-stimulated lymph node (LN) cells by enzyme-linked immunosorbent assay. Increased IL-4 and IL-10 production and reduced IL-2 and IFN-gamma production were observed in LN cells from IL-6-deficient mice as compared to LN cells from wild-type mice. These results suggested that a shift of T cell responses from Thl to Th2 might explain the resistance of IL-6-deficient mice to EAE. Taken together, IL-6 may play a crucial role in the induction phase of EAE by modulating Th1/Th2 balance.