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Biomedical subjects

Shizuo Akira

Publications and source records attributed to Shizuo Akira.

At least 55 records · Page 3Linked to original sources
PubMed2006

Impaired postnatal development in C/EBPbeta-deficient mice.

Tail DNA genotyping of fetal and neonatal mice from C/EBPbeta heterozygous parents was performed to determine whether the decreased number of surviving C/EBPbeta mutants was caused by prenatal or postnatal death. Eighty-four 3-week-old mice born of heterozygous parents had significantly lower numbers of C/EBPbeta-deficient offspring than the expected Mendelian ratio (29.8%+/+, 65.5%+/-, 4.76%-/-, P<0.05). The genotypes of 72 fetal mice from intercrossed heterozygotes showed approximately the expected 1:2:1 Mendelian ratio (18.1% +/+, 52.8% +/-, 29.2% -/-, P>0.05). No difference in the proportions by sex could be detected in these perinates. This data indicates that C/EBPbeta-deficient mice have unknown lethal problems between the embryonic stage and weaning.

Animals↗
PubMed2006

Detection of pathogenic intestinal bacteria by Toll-like receptor 5 on intestinal CD11c+ lamina propria cells.

Toll-like receptors (TLRs) recognize distinct microbial components and induce innate immune responses. TLR5 is triggered by bacterial flagellin. Here we generated Tlr5-/- mice and assessed TLR5 function in vivo. Unlike other TLRs, TLR5 was not expressed on conventional dendritic cells or macrophages. In contrast, TLR5 was expressed mainly on intestinal CD11c+ lamina propria cells (LPCs). CD11c+ LPCs detected pathogenic bacteria and secreted proinflammatory cytokines in a TLR5-dependent way. However, CD11c+ LPCs do not express TLR4 and did not secrete proinflammatory cytokines after exposure to a commensal bacterium. Notably, transport of pathogenic Salmonella typhimurium from the intestinal tract to mesenteric lymph nodes was impaired in Tlr5-/- mice. These data suggest that CD11c+ LPCs, via TLR5, detect and are used by pathogenic bacteria in the intestinal lumen.

Animals↗
PubMed2006

Toll/IL-1R domain-containing adaptor protein (TIRAP) is a critical mediator of antibacterial defense in the lung against Klebsiella pneumoniae but not Pseudomonas aeruginosa.

Bacterial pneumonia is a leading cause of mortality and is associated with extensive neutrophil accumulation. Major pathogens associated with this disease include nonflagellated Klebsiella pneumoniae (Kp) and flagellated Pseudomonas aeruginosa (Pa). TLRs are essential for innate immune defense. TIRAP (Toll/IL-1R domain-containing adaptor protein) is an adaptor in TLR1, TLR2, TLR4, and TLR6 signaling, whereas MyD88 is an adaptor for all TLRs. However, the importance of TIRAP in pulmonary defense against Kp or Pa has not been examined. To demonstrate the role of TIRAP, TIRAP-deficient and wild-type littermates were intratracheally inoculated with Kp or Pa. We found that TIRAP(-/-) mice had substantial mortality, higher bacterial burden in the lungs, and enhanced dissemination following Kp challenge. Furthermore, Kp-induced neutrophil sequestration, histopathology, and MIP-2, TNF-alpha, IL-6, and LIX (lipopolysaccharide-induced CXC chemokine) production were attenuated in the lungs of TIRAP(-/-) mice. In contrast, TIRAP is not required for Pa-induced mortality, pulmonary bacterial burden, bacterial dissemination, neutrophil accumulation, or histopathology, yet it is necessary for MIP-2, TNF-alpha, and IL-6 production, but not LIX production. However, both Kp- and Pa-induced neutrophil influxes are MyD88 dependent. To determine the mechanisms associated with Pa-induced neutrophil accumulation, we inoculated mice with a flagellin C mutant of Pa (PaDeltafliC) or purified flagellin, a TLR5 agonist. PaDeltafliC-induced neutrophil sequestration and LIX expression are dependent on TIRAP, whereas flagellin-induced neutrophil influx and LIX expression are independent of TIRAP. These novel findings illustrate a pathogen-specific role for TIRAP in pulmonary defense and suggest that TLR5 plays an essential role for Pa-induced neutrophil influx via LIX production.

Animals↗
PubMed2006

Identification of a TLR-independent pathway for Borrelia burgdorferi-induced expression of matrix metalloproteinases and inflammatory mediators through binding to integrin alpha 3 beta 1.

Borrelia burgdorferi stimulates a robust inflammatory response at sites of localization. Binding of borrelial lipoproteins to TLR-2 is one pathway important in the host response to B. burgdorferi. However, while TLR-2 is clearly important in control of infection, inflammation is actually worsened in the absence of TLR-2 or the shared TLR adapter molecule, MyD88, suggesting that there are alternative pathways regulating inflammation. Integrins are cell surface receptors that play an important role in cell to cell communications and that can activate inflammatory signaling pathways. In this study, we report for the first time that B. burgdorferi binds to integrin alpha(3)beta(1) and that binding of B. burgdorferi to this integrin results in induction of proinflammatory cytokines, chemokines, and end-effector molecules such as matrix metalloproteinases in primary human chondrocyte cells. Expression of these same molecules is not affected by the absence of MyD88 in murine articular cartilage, suggesting that the two pathways act independently in activating host inflammatory responses to B. burgdorferi. B. burgdorferi-induced alpha(3) signaling is mediated by JNK, but not p38 MAPK. In summary, we have identified a new host receptor for B. burgdorferi, integrin alpha(3)beta(1); binding of B. burgdorferi to integrin alpha(3)beta(1) results in the release of inflammatory mediators and is proposed as a TLR-independent pathway for activation of the innate immune response by the organism.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Essential role of IPS-1 in innate immune responses against RNA viruses.

IFN-beta promoter stimulator (IPS)-1 was recently identified as an adapter for retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (Mda5), which recognize distinct RNA viruses. Here we show the critical role of IPS-1 in antiviral responses in vivo. IPS-1-deficient mice showed severe defects in both RIG-I- and Mda5-mediated induction of type I interferon and inflammatory cytokines and were susceptible to RNA virus infection. RNA virus-induced interferon regulatory factor-3 and nuclear factor kappaB activation was also impaired in IPS-1-deficient cells. IPS-1, however, was not essential for the responses to either DNA virus or double-stranded B-DNA. Thus, IPS-1 is the sole adapter in both RIG-I and Mda5 signaling that mediates effective responses against a variety of RNA viruses.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Persistent expression of PDX-1 in the pancreas causes acinar-to-ductal metaplasia through Stat3 activation.

The transcription factor pancreatic and duodenal homeobox factor 1 (PDX-1) is expressed in pancreatic progenitor cells. In exocrine pancreas, PDX-1 is down-regulated during late development, while re-up-regulation of PDX-1 has been reported in pancreatic cancer and pancreatitis. To determine whether sustained expression of PDX-1 could affect pancreas development, PDX-1 was constitutively expressed in all pancreatic lineages by transgenic approaches. The transgenic pancreas was markedly small with the replacement of acinar cells by duct-like structures, accompanied by activated Stat3. Genetic ablation of Stat3 in the transgenic pancreas profoundly suppressed the metaplastic phenotype. These results provide a mechanism of pancreatic metaplasia by which persistent PDX-1 expression cell-autonomously induces acinar-to-ductal transition through Stat3 activation.

Animals↗
PubMed2006

TLR8-mediated NF-kappaB and JNK activation are TAK1-independent and MEKK3-dependent.

TLR8-mediated NF-kappaB and IRF7 activation are abolished in human IRAK-deficient 293 cells and IRAK4-deficient fibroblast cells. Both wild-type and kinase-inactive mutants of IRAK and IRAK4, respectively, restored TLR8-mediated NF-kappaB and IRF7 activation in the IRAK- and IRAK4-deficient cells, indicating that the kinase activity of IRAK and IRAK4 is probably redundant for TLR8-mediated signaling. We recently found that TLR8 mediates a unique NF-kappaB activation pathway in human 293 cells and mouse embryonic fibroblasts, accompanied only by IkappaBalpha phosphorylation and not IkappaBalpha degradation, whereas interleukin (IL)-1 stimulation causes both IkappaBalpha phosphorylation and degradation. The intermediate signaling events mediated by IL-1 (including IRAK modifications and degradation and TAK1 activation) were not detected in cells stimulated by TLR8 ligands. TLR8 ligands trigger similar levels of IkappaBalpha phosphorylation and NF-kappaB and JNK activation in TAK1(-/-) mouse embryo fibroblasts (MEFs) as compared with wild-type MEFs, whereas lack of TAK1 results in reduced IL-1-mediated NF-kappaB activation and abolished IL-1-induced JNK activation. The above results indicate that although TLR8-mediated NF-kappaB and JNK activation are IRAK-dependent, they do not require IRAK modification and are TAK1-independent. On the other hand, TLR8-mediated IkappaBalpha phosphorylation, NF-kappaB, and JNK activation are completely abolished in MEKK3(-/-) MEFs, whereas IL-1-mediated signaling was only moderately reduced in these deficient MEFs as compared with wild-type cells. The differences between IL-1R- and TLR8-mediated NF-kappaB activation are also reflected at the level of IkappaB kinase (IKK) complex. TLR8 ligands induced IKKgamma phosphorylation, whereas IKKalpha/beta phosphorylation and IKKgamma ubiquitination that can be induced by IL-1 were not detected in cells treated with TLR8 ligands. We postulate that TLR8-mediated MEKK3-dependent IKKgamma phosphorylation might play an important role in the activation of IKK complex, leading to IkappaBalpha phosphorylation.

Animals↗
PubMed2006

Deficiency of interleukin-18 in mice leads to hyperphagia, obesity and insulin resistance.

Here we report the presence of hyperphagia, obesity and insulin resistance in knockout mice deficient in IL-18 or IL-18 receptor, and in mice transgenic for expression of IL-18 binding protein. Obesity of Il18-/- mice resulted from accumulation of fat tissue based on increased food intake. Il18-/- mice also had hyperinsulinemia, consistent with insulin resistance and hyperglycemia. Insulin resistance was secondary to obesity induced by increased food intake and occurred at the liver level as well as at the muscle and fat-tissue level. The molecular mechanisms responsible for the hepatic insulin resistance in the Il18-/- mice involved an enhanced expression of genes associated with gluconeogenesis in the liver of Il18-/- mice, resulting from defective phosphorylation of STAT3. Recombinant IL-18 (rIL-18) administered intracerebrally inhibited food intake. In addition, rIL-18 reversed hyperglycemia in Il18-/- mice through activation of STAT3 phosphorylation. These findings indicate a new role of IL-18 in the homeostasis of energy intake and insulin sensitivity.

Animals↗
PubMed2006

Non-cell-autonomous action of STAT3 in maintenance of neural precursor cells in the mouse neocortex.

The transcription factor STAT3 promotes astrocytic differentiation of neural precursor cells (NPCs) during postnatal development of the mouse neocortex, but little has been known of the possible role of STAT3 in the embryonic neocortex. We now show that STAT3 is expressed in NPCs of the mouse embryonic neocortex and that the JAK-STAT3 signaling pathway plays an essential role in the maintenance of NPCs by fibroblast growth factor 2. Conditional deletion of the STAT3 gene in NPCs reduced their capacity to form neurospheres in vitro, as well as promoted neuronal differentiation both in vitro and in vivo. Furthermore, STAT3 was found to maintain NPCs in the undifferentiated state in a non-cell-autonomous manner. STAT3-dependent expression of the Notch ligand Delta-like1 (DLL1) appears to account for the non-cell-autonomous effect of STAT3 on NPC maintenance, as knockdown of DLL1 by RNA interference or inhibition of Notch activation with a gamma-secretase inhibitor abrogated the enhancement of neurosphere formation by STAT3. Our results reveal a previously unrecognized mechanism of interaction between the JAK-STAT3 and DLL1-Notch signaling pathways, as well as a pivotal role for this interaction in maintenance of NPCs during early neocortical development.

Animals↗
PubMed2006

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.

Adaptor Proteins, Signal Transducing↗
PubMed2006

C/EBP homologous protein (CHOP) is crucial for the induction of caspase-11 and the pathogenesis of lipopolysaccharide-induced inflammation.

C/EBP homologous protein (CHOP)/growth arrest and DNA damage-inducible gene 153 is a C/EBP family transcription factor which is involved in endoplasmic reticulum (ER) stress-mediated apoptosis. To determine whether the ER stress-CHOP pathway is involved in the pathogenesis of the lung inflammation, mice were given LPS intratracheally. Treatment with LPS induced mRNAs for CHOP and BiP. The LPS-induced inflammation in lung, including the IL-1beta activity in bronchoalveolar lavage fluid, was attenuated in the Chop knockout mice. Caspase-11, which is needed for the activation of procaspase-1 and pro-IL-1beta, was induced by LPS treatment in the lung and primary cultured macrophages. The induction of caspase-11 by LPS was suppressed in Chop knockout mice. Caspase-11 was also induced by such ER stress inducers as thapsigargin or tunicamycin. These results show that CHOP plays a crucial role in the pathogenesis of inflammation through the induction of caspase-11.

Animals↗
PubMed2006

Negative regulation of interferon-regulatory factor 3-dependent innate antiviral response by the prolyl isomerase Pin1.

Recognition of double-stranded RNA activates interferon-regulatory factor 3 (IRF3)-dependent expression of antiviral factors. Although the molecular mechanisms underlying the activation of IRF3 have been studied, the mechanisms by which IRF3 activity is reduced have not. Here we report that activation of IRF3 is negatively regulated by the peptidyl-prolyl isomerase Pin1. After stimulation by double-stranded RNA, induced phosphorylation of the Ser339-Pro340 motif of IRF3 led to its interaction with Pin1 and finally polyubiquitination and then proteasome-dependent degradation of IRF3. Suppression of Pin1 by RNA interference or genetic deletion resulted in enhanced IRF-3-dependent production of interferon-beta, with consequent reduction of virus replication. These results elucidate a previously unknown mechanism for controlling innate antiviral responses by negatively regulating IRF3 activity via Pin1.

Animals↗
PubMed2006

TAK1 is a master regulator of epidermal homeostasis involving skin inflammation and apoptosis.

Transforming growth factor beta-activated kinase 1 (TAK1) functions downstream of inflammatory cytokines to activate c-Jun N-terminal kinase (JNK) as well as NF-kappaB in several cell types. However, the functional role of TAK1 in an in vivo setting has not been determined. Here we have demonstrated that TAK1 is the major regulator of skin inflammation as well as keratinocyte death in vivo. Epidermal-specific deletion of TAK1 causes a severe inflammatory skin condition by postnatal day 6-8. The mutant skin also exhibits massive keratinocyte death. Analysis of keratinocytes isolated from the mutant skin revealed that TAK1 deficiency results in a striking increase in apoptosis in response to tumor necrosis factor (TNF). TAK1-deficient keratinocytes cannot activate NF-kappaB or JNK upon TNF treatment. These results suggest that TNF induces TAK1-deficient keratinocyte death because of the lack of NF-kappaB (and possibly JNK)-mediated cell survival signaling. Finally, we have shown that deletion of the TNF receptor can largely rescue keratinocyte death as well as inflammatory skin condition in epidermal-specific TAK1-deficient mice. Our results demonstrate that TAK1 is a master regulator of TNF signaling in skin and regulates skin inflammation and keratinocyte death.

Animals↗
PubMed2006

Roles of caspase-8 and caspase-10 in innate immune responses to double-stranded RNA.

Upon viral infection, host cells trigger antiviral immune responses by inducing type I IFN and inflammatory cytokines. dsRNA generated during viral replication is recognized by the cytoplasmic RNA helicases retinoic acid-inducible gene I and melanoma differentiation-associated gene 5, which interact with an adaptor, IFN-beta promoter stimulator-1, to activate the transcription factors NF-kappaB and IFN regulatory factor 3. In this article we demonstrate that caspase-8 and caspase-10 are involved in these pathways. Both caspases were cleaved during dsRNA stimulation, and overexpression of a cleaved form of these caspases activated NF-kappaB. Knockdown of caspase-10 or caspase-8 in a human cell line resulted in the reduction of inflammatory cytokine production. Cells derived from caspase-8-deficient mice also showed reduced expression of inflammatory cytokines as well as NF-kappaB activation. Furthermore, the Fas-associated death domain protein interacted with these two caspases and IFN-beta promoter stimulator 1. These results indicate that caspase-8 and caspase-10 are essential components that mediate NF-kappaB-dependent inflammatory responses in antiviral signaling.

Adaptor Proteins, Signal Transducing↗
PubMed2006

IkappaB kinase-alpha is critical for interferon-alpha production induced by Toll-like receptors 7 and 9.

The Toll-like receptor (TLR) family has important roles in microbial recognition and dendritic cell activation. TLRs 7 and 9 can recognize nucleic acids and trigger signalling cascades that activate plasmacytoid dendritic cells to produce interferon-alpha (IFN-alpha) (refs 7, 8). TLR7/9-mediated dendritic cell activation is critical for antiviral immunity but also contributes to the pathogenesis of systemic lupus erythematosus, a disease in which serum IFN-alpha levels are elevated owing to plasmacytoid dendritic cell activation. TLR7/9-induced IFN-alpha induction depends on a molecular complex that contains a TLR adaptor, MyD88, and IFN regulatory factor 7 (IRF-7) (refs 10-14), but the underlying molecular mechanisms are as yet unknown. Here we show that IkappaB kinase-alpha (IKK-alpha) is critically involved in TLR7/9-induced IFN-alpha production. TLR7/9-induced IFN-alpha production was severely impaired in IKK-alpha-deficient plasmacytoid dendritic cells, whereas inflammatory cytokine induction was decreased but still occurred. Kinase-deficient IKK-alpha inhibited the ability of MyD88 to activate the Ifna promoter in synergy with IRF-7. Furthermore, IKK-alpha associated with and phosphorylated IRF-7. Our results identify a role for IKK-alpha in TLR7/9 signalling, and highlight IKK-alpha as a potential target for manipulating TLR-induced IFN-alpha production.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Oral and intraperitoneal administration of phosphorothioate oligodeoxynucleotides leads to control of Cryptosporidium parvum infection in neonatal mice.

BACKGROUND: Neonates are particularly vulnerable to infections, in part because of the incomplete development of their immune system. Recent advances in immunostimulatory treatments based on conserved microbial components led us to assess the potential of oligodeoxynucleotides (ODNs) for decreasing the sensitivity of neonates to Cryptosporidium parvum infection. METHODS: Neonate mice were treated orally or intraperitoneally (ip) with CpG ODNs or non-CpG ODNs 24 h before C. parvum infection, and parasite load and cytokine up-regulation were evaluated. RESULTS: CpG ODN 1668 and non-CpG ODN 1668 administered orally, as well as CpG ODN 1668 administered ip, induced an 80%-95% decrease in intestinal parasite load 6 days after infection. Intraperitoneal and oral pretreatment with CpG ODN 1668 led to a strong initial up-regulation of cytokines and CD69 messenger RNA in the intestine and a decrease in parasite load by a Toll-like receptor 9 (TLR9)-dependent mechanism. By contrast, oral administration of non-CpG ODN 1668 decreased parasite load by a TLR9-independent mechanism. CONCLUSION: The control of neonatal C. parvum infection by ip or oral administration of ODNs is feasible by 2 different mechanisms: (1) the well-known interaction involving CpG/TLR9, leading to the production of cytokines and lymphocyte activation, and (2) a new unknown mechanism that is independent of TLR9 and effective orally.

Adjuvants, Immunologic↗
PubMed2006

Differential roles of MDA5 and RIG-I helicases in the recognition of RNA viruses.

The innate immune system senses viral infection by recognizing a variety of viral components (including double-stranded (ds)RNA) and triggers antiviral responses. The cytoplasmic helicase proteins RIG-I (retinoic-acid-inducible protein I, also known as Ddx58) and MDA5 (melanoma-differentiation-associated gene 5, also known as Ifih1 or Helicard) have been implicated in viral dsRNA recognition. In vitro studies suggest that both RIG-I and MDA5 detect RNA viruses and polyinosine-polycytidylic acid (poly(I:C)), a synthetic dsRNA analogue. Although a critical role for RIG-I in the recognition of several RNA viruses has been clarified, the functional role of MDA5 and the relationship between these dsRNA detectors in vivo are yet to be determined. Here we use mice deficient in MDA5 (MDA5-/-) to show that MDA5 and RIG-I recognize different types of dsRNAs: MDA5 recognizes poly(I:C), and RIG-I detects in vitro transcribed dsRNAs. RNA viruses are also differentially recognized by RIG-I and MDA5. We find that RIG-I is essential for the production of interferons in response to RNA viruses including paramyxoviruses, influenza virus and Japanese encephalitis virus, whereas MDA5 is critical for picornavirus detection. Furthermore, RIG-I-/- and MDA5-/- mice are highly susceptible to infection with these respective RNA viruses compared to control mice. Together, our data show that RIG-I and MDA5 distinguish different RNA viruses and are critical for host antiviral responses.

Animals↗