Harutoshi Fujimura

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.

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.

Misregulation of miR-1 processing is associated with heart defects in myotonic dystrophy.

Myotonic dystrophy is an RNA gain-of-function disease caused by expanded CUG or CCUG repeats, which sequester the RNA binding protein MBNL1. Here we describe a newly discovered function for MBNL1 as a regulator of pre-miR-1 biogenesis and find that miR-1 processing is altered in heart samples from people with myotonic dystrophy. MBNL1 binds to a UGC motif located within the loop of pre-miR-1 and competes for the binding of LIN28, which promotes pre-miR-1 uridylation by ZCCHC11 (TUT4) and blocks Dicer processing. As a consequence of miR-1 loss, expression of GJA1 (connexin 43) and CACNA1C (Cav1.2), which are targets of miR-1, is increased in both DM1- and DM2-affected hearts. CACNA1C and GJA1 encode the main calcium- and gap-junction channels in heart, respectively, and we propose that their misregulation may contribute to the cardiac dysfunctions observed in affected persons.

Muscleblind-like 2-Mediated Alternative Splicing in the Developing Brain and Dysregulation in Myotonic Dystrophy

The RNA-mediated disease model for myotonic dystrophy (DM) proposes that microsatellite C(C)TG expansions express toxic RNAs that disrupt splicing regulation by altering MBNL1 and CELF1 activities. While this model explains DM manifestations in muscle, less is known about the effects of C(C)UG expression on the brain. Here, we report that Mbnl2 knockout mice develop several DM-associated central nervous system (CNS) features including abnormal REM sleep propensity and deficits in spatial memory. Mbnl2 is prominently expressed in the hippocampus and Mbnl2 knockouts show a decrease in NMDA receptor (NMDAR) synaptic transmission and impaired hippocampal synaptic plasticity. While Mbnl2 loss did not significantly alter target transcript levels in the hippocampus, misregulated splicing of hundreds of exons was detected using splicing microarrays, RNA-seq, and HITS-CLIP. Importantly, the majority of the Mbnl2-regulated exons examined were similarly misregulated in DM. We propose that major pathological features of the DM brain result from disruption of the MBNL2-mediated developmental splicing program.

Mitochondrial tRNAlle mutation in fatal cardiomyopathy

A patient with mitochondrial encephalomyopathy who died from progressive intractable cardiac failure at the age of 18 is reported. At the age of 4, he presented with short stature, but multiorgan disorders including deafness, focal glomerulosclerosis, epilepsy and dilated cardiomyopathy appeared later in his clinical course. Laboratory tests showed hyperlactatemia and hyperpyruvatemia. Histopathological findings demonstrated mitochondrial myopathy with ragged red fibers and focal cytochrome C oxidase-deficient fibers in skeletal and cardiac muscles. The activity of cytochrome C oxidase was 30% less than the control level in skeletal muscle. Sequencing of the entire mitochondrial tRNA genome revealed a novel point mutation in the tRNA(Ile) region (nt 4269). This A-to-G substitution was found in none of the 30 controls by screening using mispairing PCR and Ssp I digestion methods, suggesting that this new mutation was pathogenic in our case.

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.

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.

Nitric oxide via an inducible isoform of nitric oxide synthase is a possible factor to eliminate inflammatory cells from the central nervous system of mice with experimental allergic encephalomyelitis

We recently identified the inducible isoform of nitric oxide synthase (iNOS) in inflammatory lesions of the central nervous system (CNS) in mice with experimental allergic encephalomyelitis (EAE), a known animal model of multiple sclerosis (MS). In the present study, the role of excessive nitric oxide (NO) production via iNOS was investigated in mice with EAE using immunohistochemistry with antibodies to nitrotyrosine and iNOS, NADPH-diaphorase histochemistry, and the in situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) method to detect cell death, presumably through an apoptotic mechanism. NADPH-diaphorase histochemistry and immunohistochemistry for iNOS revealed an elevation of nitric oxide synthase (NOS) activity during the course of EAE, which came from iNOS. Nitrotyrosine was detected in infiltrated cells and some glial cells in the spinal cord lesions, where iNOS-positive inflammatory cells were present at the peak of EAE. The findings implied the generation of NO and peroxynitrite in the EAE lesions, which might damage structural and functional proteins. The TUNEL positive cells were mainly inflammatory ones, and most of them were located in close proximity to iNOS-positive cells, while some of them were iNOS-positive themselves. These results suggested that excessive NO via iNOS played an important role to eliminate inflammatory cells in the CNS of mice with EAE, possibly through an apoptotic mechanism.

Reduction of metallothioneins promotes the disease expression of familial amyotrophic lateral sclerosis mice in a dose-dependent manner.

We previously reported that abnormal copper release from mutated Cu, Zn‐superoxide dismutase (SOD1) proteins might be a common toxic gain‐of‐function in the pathogenesis of familial amyotrophic lateral sclerosis (FALS) [Ogawa et al. (1997) Biochem. Biophys. Res. Commun., 241, 251–257.]. In the present study, we first examined metallothioneins (MTs), known to bind copper ions and decrease oxidative toxicity, and found a twofold increase in MTs in the spinal cord of the SOD1 transgenic mice with a FALS‐linked mutation (G93A), but not in the spinal cord of wild‐type SOD1 transgenic mice. We then investigated whether the clinical course of FALS mice could be modified by the reduced expression of MTs, by crossing the FALS mice with MT‐I‐ and MT‐II‐deficient mice. FALS mice clearly reached the onset of clinical signs and death significantly earlier in response to the reduction of protein expression. These results indicated that the copper‐mediated free radical generation derived from mutant SOD1 might be related to the degeneration of motor neurons in FALS and that MTs might play a protective role against the expression of the disease.

Critical Roles of CXC Chemokine Ligand 16/Scavenger Receptor that Binds Phosphatidylserine and Oxidized Lipoprotein in the Pathogenesis of Both Acute and Adoptive Transfer Experimental Autoimmune Encephalomyelitis

The scavenger receptor that binds phosphatidylserine and oxidized lipoprotein (SR-PSOX)/CXCL16 is a chemokine expressed on macrophages and dendritic cells, while its receptor expresses on T and NK T cells. We investigated the role of SR-PSOX/CXCL16 on acute and adoptive experimental autoimmune encephalomyelitis (EAE), which is Th1-polarized T cell-mediated autoimmune disease of the CNS. Administration of mAb against SR-PSOX/CXCL16 around the primary immunization decreased disease incidence of acute EAE with associated reduced infiltration of mononuclear cells into the CNS. Its administration was also shown to inhibit elevation of serum IFN-γ level at primary immune response, as well as subsequent generation of Ag-specific T cells. In adoptive transfer EAE, treatment of recipient mice with anti-SR-PSOX/CXCL16 mAb also induced not only decreased clinical disease incidence, but also diminished traffic of mononuclear cells into the CNS. In addition, histopathological analyses showed that clinical development of EAE correlates well with expression of SR-PSOX/CXCL16 in the CNS. All the results show that SR-PSOX/CXCL16 plays important roles in EAE by supporting generation of Ag-specific T cells, as well as recruitment of inflammatory mononuclear cells into the CNS.