Yasuko Yamamoto

Predicted expansion of the claudin multigene family

ZO‐1 and Claudin‐26 colocalize by fluorescence microscopy (View interaction)

Presence of B cell progenitors in the thymus.

We characterize B cell progenitors in the thymus. Although mature thymic B cells are surface Ig+, B220(high), but CD43-, B cell progenitors in the thymus were found to be slg-, B220(med), and CD43+. Most progenitors showed rearranged Ig D-J and V-D-J patterns when DNA from sorted B cell progenitors was amplified by PCR, blotted, and probed. When B cell progenitors were purified from the thymus and injected intrathymically into Ig heavy chain (Igh) allotype-disparate recipients, B cells bearing donor-type Igh6 were detected in the thymus but not in the periphery. Thymic B cells generated from these progenitors were CD5+ cells, although there was a broad range of expression of CD5 molecules. Furthermore, B cells purified from thymus that had been inoculated with B cell progenitors were able to differentiate into Ab-forming cells under the influence of CD40 ligand plus IL-10, and secreted IgM with donor Igh6 allotype. We thus clarified the existence of B cell progenitors in the thymus and also characterized the surface markers and their developmental functions.

Studies on Tissue and Cellular Distribution of Indoleamine 2,3-Dioxygenase 2 The Absence of IDO1 Upregulates IDO2 Expression in the Epididymis

Indoleamine 2,3-dioxygenase 1 (IDO1) catabolizes tryptophan to kynurenine at the first step of tryptophan metabolism. Recently, in addition to IDO1, a new isoform called IDO2 was identified. In this study, we examined the tissue expression pattern of IDO2 mRNA and the cellular localization of expressed IDO2 protein in mice. IDO1 mRNA expression was observed in the colon and epididymis, whereas IDO2 mRNA expression was found in the cerebral cortex, liver, kidney, and epididymis. Immunohistochemical analysis revealed that IDO2 protein was exclusively expressed on the hepatocytes, interlobular bile ducts, neuronal cells of the cerebrum cortex, Purkinje cells of the cerebellum cortex, lamina epithelialis, proximal convoluted tubule, and the collecting tubule of the kidney. In the epididymis, IDO1 protein expression was restricted to the caput, whereas IDO2 protein expression was observed on the caput, corpus, and cauda. Both IDO proteins were expressed on the caput, but both showed a different protein expression pattern in the segments. Immunohistochemical analysis in IDO1−/− mouse epididymis showed that IDO2 protein was extensively upregulated due to the loss of IDO1 expression.

Remarkable Role of Indoleamine 2,3-Dioxygenase and Tryptophan Metabolites in Infectious Diseases: Potential Role in Macrophage-Mediated Inflammatory Diseases

Indoleamine 2,3-dioxygenase 1 (IDO1), the L-tryptophan-degrading enzyme, plays a key role in the immunomodulatory effects on several types of immune cells. Originally known for its regulatory function during pregnancy and chronic inflammation in tumorigenesis, the activity of IDO1 seems to modify the inflammatory state of infectious diseases. The pathophysiologic activity of L-tryptophan metabolites, kynurenines, is well recognized. Therefore, an understanding of the regulation of IDO1 and the subsequent biochemical reactions is essential for the design of therapeutic strategies in certain immune diseases. In this paper, current knowledge about the role of IDO1 and its metabolites during various infectious diseases is presented. Particularly, the regulation of type I interferons (IFNs) production via IDO1 in virus infection is discussed. This paper offers insights into new therapeutic strategies in the modulation of viral infection and several immune-related disorders.

l-Tryptophan–Kynurenine Pathway Metabolites Regulate Type I IFNs of Acute Viral Myocarditis in Mice

The activity of IDO that catalyzes the degradation of tryptophan (Trp) into kynurenine (Kyn) increases after diseases caused by different infectious agents. Previously, we demonstrated that IDO has an important immunomodulatory function in immune-related diseases. However, the pathophysiological role of IDO following acute viral infection is not fully understood. To investigate the role of IDO in the l-Trp–Kyn pathway during acute viral myocarditis, mice were infected with encephalomyocarditis virus, which induces acute myocarditis. We used IDO-deficient (IDO−/−) mice and mice treated with 1-methyl-d,l-Trp (1-MT), an inhibitor of IDO, to study the importance of Trp–Kyn pathway metabolites. Postinfection with encephalomyocarditis virus infection, the serum levels of Kyn increased, whereas those of Trp decreased, and IDO activity increased in the spleen and heart. The survival rate of IDO−/− or 1-MT–treated mice was significantly greater than that of IDO+/+ mice. Indeed, the viral load was suppressed in the IDO−/− or 1-MT–treated mice. Furthermore, the levels of type I IFNs in IDO−/− mice and IDO−/− bone marrow-transplanted IDO+/+ mice were significantly higher than those in IDO+/+ mice, and treatment of IDO−/− mice with Kyn metabolites eliminated the effects of IDO−/− on the improved survival rates. These results suggest that IDO has an important role in acute viral myocarditis. Specifically, IDO increases the accumulation of Kyn pathway metabolites, which suppress type I IFNs production and enhance viral replication. We concluded that inhibition of the Trp–Kyn pathway ameliorates acute viral myocarditis.

L-Tryptophan-kynurenine pathway enzymes are therapeutic target for neuropsychiatric diseases: Focus on cell type differences

ABSTRACT The kynurenine pathway (KP) is the major route for tryptophan (TRP) metabolism in most mammalian tissues. The KP metabolizes TRP into a number of neuroactive metabolites, such as kynurenine (KYN), kynurenic acid (KYNA), 3‐hydroxykynurenine (3‐HK), and quinolinic acid (QUIN). Elevated metabolite concentrations in the central nervous system are associated with the pathophysiology of several inflammation‐related neuropsychiatric diseases. During an inflammatory response, the initial KP metabolic step is primarily regulated by indoleamine 2,3‐dioxygenase 1 (IDO1), which produces KYN from TRP. Following this initial step, the KP has 2 distinct branches; one branch is regulated by kynurenine 3‐monooxygenase (KMO) and is primarily responsible for the 3‐HK and QUIN production, and the other branch is regulated by kynurenine aminotransferase (KAT), which produces KYNA, an N‐methyl‐d‐aspartate receptor and alpha‐7‐nicotinic acetylcholine receptor antagonist. Unbalanced KP metabolism has been demonstrated in distinct neuropsychiatric diseases; thus, understanding the mechanisms that regulate KP enzyme expression and activity is important. These enzymes are expressed by specific cell types, and the induction of enzyme expression by inflammatory stimuli also shows cell type specificity. This review provides an overview and discusses the current understanding of the influence of KP enzyme expression and activity in different cell types on the pathophysiological mechanisms of specific neuropsychiatric diseases. Moreover, the potential use of KP enzyme inhibition as a therapeutic strategy for treating neurological diseases is briefly discussed. This article is part of the Special Issue entitled ‘The Kynurenine Pathway in Health and Disease’. HIGHLIGHTSThe kynurenine pathway (KP) is associated with neurological diseases because several KP metabolites are neuroactive.The KP enzymes show cell‐type specific expression.KP manipulation by KP enzyme inhibition is a potential therapeutic strategy for neurological diseases.

Inhibition of increased indoleamine 2,3-dioxygenase activity attenuates Toxoplasma gondii replication in the lung during acute infection.

The regulation of local L-tryptophan concentrations by tryptophan-degrading enzyme, indoleamine 2,3-dioxygenase (IDO) induced by various stimuli such as interferon-γ (IFN-γ) is one of the key mechanisms in antimicrobial effect. Recently, IDO is also focused on an immunosuppressive mechanism shared by several different immune cell types. Here, we show that inhibition of increased IDO activity maybe involved in the antiparasitic mechanism during Toxoplasma gondii (T. gondii) infection in vivo. In this study, we investigated the role of IDO by using IDO-gene-deficient (IDO KO) mice and by administering a competitive enzyme inhibitor, 1-methyl-D,L-tryptophan (1MT), to wild-type mice following T. gondii infection. Although depletion of lung l-tryptophan did not occur in IDO KO mice after T. gondii infection, the increased mRNA expression of T. gondii surface antigen gene 2 (SAG2) and the inflammatory cytokines in the lung were drastically reduced in the IDO KO mice following infection. We also found that complete depletion of lung l-tryptophan was observed in wild-type mice after infection, but not in mice treated with 1MT. At the same time, 1MT suppressed the increased mRNA expression of SAG2. Taken together, we observed that the inflammatory damage was significantly decreased by the administration of 1MT in the lung after infection. Inhibition of the IDO activity or the elimination of IDOs substrate may be an effective therapy against microbial diseases.

Claudin-21 Has a Paracellular Channel Role at Tight Junctions

ABSTRACT Claudin protein family members, of which there are at least 27 in humans and mice, polymerize to form tight junctions (TJs) between epithelial cells, in a tissue- and developmental stage-specific manner. Claudins have a paracellular barrier function. In addition, certain claudins function as paracellular channels for small ions and/or solutes by forming selective pores at the TJs, although the specific claudins involved and their functional mechanisms are still in question. Here we show for the first time that claudin-21, which is more highly expressed in the embryonic than the postnatal stages, acts as a paracellular channel for small cations, such as Na+, similar to the typical channel-type claudins claudin-2 and -15. Claudin-21 also allows the paracellular passage of larger solutes. Our findings suggest that claudin-21-based TJs allow the passage of small and larger solutes by both paracellular channel-based and some additional mechanisms.

Depressive symptoms as a side effect of Interferon-α therapy induced by induction of indoleamine 2,3-dioxygenase 1.

Depression is known to occur frequently in chronic hepatitis C viral (HCV) patients receiving interferon (IFN)-α therapy. In this study, we investigated whether indoleamine 2,3-dioxygenase1 (IDO1)-mediated tryptophan (TRP) metabolism plays a critical role in depression occurring as a side effect of IFN-α therapy. Increases in serum kynurenine (KYN) and 3-hydroxykynurenine (3-HK) concentrations and in the ratios of KYN/TRP and 3-HK/kynurenic acid (KA) were much larger in depressive HCV patients than in non-depressed patients following therapy. Furthermore, transfection of a plasmid continuously expressing murine IFN-γ into normal mice significantly increased depression-like behavior. IFN-γ gene transfer also resulted in a decrease in serum TRP levels in the mice while KYN and 3-HK levels were significantly increased in both serum and frontal cortex. Genetic deletion of IDO1 in mice abrogated both the increase in depression-like behavior and the elevation in TRP metabolites’ levels, and the turnover of serotonin in the frontal cortex after IFN-γ gene transfer. These results indicate that the KYN pathway of IDO1-mediated TRP metabolism plays a critical role in depressive symptoms associated with IFN-α therapy.

Effects of Various Phytochemicals on Indoleamine 2,3-Dioxygenase 1 Activity: Galanal Is a Novel, Competitive Inhibitor of the Enzyme

Indoleamine 2,3-dioxygenase (IDO) 1, that catalyzes the first and rate-limiting step in the degradation of L-tryptophan, has an important immunomodulatory function. The activity of IDO1 increases in various inflammatory diseases, including tumors, autoimmune diseases, and different kinds of inflammation. We evaluated the suppressive effect of plant extracts or phytochemicals on IDO1 induction and activity; sixteen kinds of plants extracts and fourteen kinds of phytochemicals were examined. As a result, the methanol extracts of Myoga flower buds, which are traditional Japanese foods, and labdane-type diterpene galanal derived from Myoga flowers significantly suppressed IDO1 activity. The Lineweaver-Burk plot analysis indicated that galanal is a competitive inhibitor. Galanal attenuated L-kynurenine formation with an IC50 value of 7.7 µM in the assay system using recombinant human IDO1, and an IC50 value of 45 nM in the cell-based assay. Further, mechanistic analysis revealed that galanal interfered with the transcriptional function of the nuclear factor-κB and the interferon-γ signaling pathway. These effects of galanal are important for immune response. Because the inhibitory effect of galanal on IDO1 activity was stronger than that of 1-methyl tryptophan, a tryptophan analog, galanal may have great potential as the novel drug for various immune-related diseases.