Publications

Mast cells (MCs) mature locally, thus possessing tissue-dependent phenotypes for their critical roles in both protective immunity against pathogens and the development of allergy or inflammation. We previously reported that MCs highly express P2X7, a receptor for extracellular ATP, in the colon but not in the skin. The ATP-P2X7 pathway induces MC activation and consequently exacerbates the inflammation. Here, we identified the mechanisms by which P2X7 expression on MCs is reduced by fibroblasts in the skin, but not in the other tissues. The retinoic-acid-degrading enzyme Cyp26b1 is highly expressed in skin fibroblasts, and its inhibition resulted in the upregulation of P2X7 on MCs. We also noted the increased expression of P2X7 on skin MCs and consequent P2X7- and MC-dependent dermatitis (so-called retinoid dermatitis) in the presence of excessive amounts of retinoic acid. These results demonstrate a unique skin-barrier homeostatic network operating through Cyp26b1-mediated inhibition of ATP-dependent MC activation by fibroblasts.

IκBζ, encoded by Nfibiz , is a nuclear IκB-like protein harboring ankyrin repeats. IκBζ has been shown to regulate IL-6 production in macrophages and Th17 development in T cells. However, the role of IκBζ in natural killer (NK) cells has not be understood. In the present study, we found that the expression of IκBζ was rapidly induced in response to IL-18 in NK cells, but not in T cells. Analysis of Nfkbiz −/− mice revealed that IκBζ was essential for the production of IFN-γ production and cytotoxic activity in NK cells in response to IL-12 and/or IL-18 stimulation. IL-12/IL-18–mediated gene induction was profoundly impaired in Nfkbiz −/− NK cells. Whereas the phosphorylation of STAT4 was normally induced by IL-12 stimulation, STAT4 was not recruited to the Ifng gene regions in Nfkbiz −/− NK cells. Acetylation of histone 3 K9 on Ifng regions was also abrogated in Nfkbiz −/− NK cells. IκBζ was recruited on the proximal promoter region of the Ifng gene, and overexpression of IκBζ together with IL-12 activated the Ifng promoter. Furthermore, Nfkbiz −/− mice were highly susceptible to mouse MCMV infection. Taken together, these results demonstrate that IκBζ is essential for the activation of NK cells and antiviral host defense responses.

Epidemiological studies have suggested that the long-term use of nonsteroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX) activity moderates the onset or progression of Alzheimer’s disease (AD). Thus it has been suggested that prostaglandin E2 (PGE2), a major end-product of COX, may play a pathogenic role in AD, but the involvement of PGE synthase (PGES), a terminal enzyme downstream from COX, has not been fully elucidated. To examine the involvement in AD pathology of microsomal PGES-1 (mPGES-1), a PGES enzyme, we here prepared primary cerebral neuronal cells from the cerebri of wild-type and mPGES-1-deficient mice and then treated them with β-amyloid (Aβ) fragment 31–35 (Aβ31–35), which represents the shortest sequence of native Aβ peptide required for neurotoxicity. Treatment of wild-type neuronal cells with Aβ31–35 induced mPGES-1 gene expression and PGE2 production, followed by significant apoptotic cell death, but apoptosis was not induced in mPGES-1-deficient cells. Furthermore, the combined treatment of Aβ31–35 and PGE2 induced apoptosis in mPGES-1-deficient neuronal cells. These results indicated that mPGES-1 is induced during Aβ-mediated neuronal cell death and is involved in Aβ-induced neurotoxicity associated with AD pathology.

Because nontuberculous mycobacterial pulmonary disease is a considerable health burden, a simple and clinically applicable analytical protocol enabling the identification of subspecies and drug-resistant disease is required to determine the treatment strategy. We aimed to develop a simplified workflow consisting only of direct sequencing of mycobacterial growth indicator tube cultures (MGIT-seq). In total, 138 patients were prospectively enrolled between April 2021 and May 2022, and culture-positive MGIT broths were subjected to sequencing using MinION, a portable next-generation sequencer. Sequence analysis was conducted to identify species using core genome multilocus sequence typing and to predict macrolide and amikacin (AMK) resistance based on previously reported mutations in rrl, rrs, and erm(41). The results were compared to clinical tests for species identification and drug susceptibility. A total of 116 patients with positive MGIT cultures were included in the analysis. MGIT-seq yielded 99.1% accuracy in species-level identification and identified 98 isolates (84.5%) at the subspecies level. Macrolide and AMK resistance were detected in 19.4% and 1.9% of Mycobacterium avium complex (MAC) and Mycobacterium abscessus isolates. The predicted macrolide and AMK resistance was consistent with the results of conventional drug susceptibility tests, with specificities of 97.6% and 100.0%, respectively. Direct MGIT-seq has achieved comprehensive identification and drug resistance detection of nontuberculous mycobacteria, which could be applicable to determine the treatment strategy by a single test in clinical practice.

Antigen-presenting cells (APCs) can induce T cell activation as well as T cell tolerance. The molecular mechanisms by which APCs regulate this critical decision of the immune system are not well understood. Here we show that Stat3 signaling plays a critical role in the induction of antigen-specific T cell tolerance. Targeted disruption of Stat3 signaling in APCs resulted in priming of antigen-specific CD4+ T cells in response to an otherwise tolerogenic stimulus in vivo. Furthermore, APCs devoid of Stat3 effectively break antigen-specific T cell anergy in vitro. Conversely, increased Stat3 activity in APCs led to impaired antigen-specific T cell responses. Stat3 signaling provides, therefore, a novel molecular target for manipulation of immune activation/tolerance, a central decision with profound implications in autoimmunity, transplantation, and cancer immunotherapy.

No abstract is provided for this article.

No abstract is provided for this article.

No abstract is provided for this article.

Secondary bacterial infection is a common sequela to viral infection and is associated with increased lethality and morbidity. However, the underlying mechanisms remain poorly understood. We show that the TLR3/MDA5 agonist poly I:C or viral infection dramatically augments signaling via the NLRs Nod1 and Nod2 and enhances the production of proinflammatory cytokines. Enhanced Nod1 and Nod2 signaling by poly I:C required the TLR3/MDA5 adaptors TRIF and IPS-1 and was mediated by type I IFNs. Mechanistically, poly I:C or IFN-β induced the expression of Nod1, Nod2, and the Nod-signaling adaptor Rip2. Systemic administration of poly I:C or IFN-β or infection with murine norovirus-1 promoted inflammation and lethality in mice superinfected with E. coli, which was independent of bacterial burden but attenuated in the absence of Nod1/Nod2 or Rip2. Thus, crosstalk between type I IFNs and Nod1/Nod2 signaling promotes bacterial recognition, but induces harmful effects in the virally infected host.

Various receptors on cell surface recognize specific extracellular molecules and trigger signal transduction altering gene expression in the nucleus. Gain or loss-of-function mutations of one molecule have shown to affect alternative signaling pathways with a poorly understood mechanism. In Toll-like receptor (TLR) 4 signaling, which branches into MyD88- and TRAM-dependent pathways upon lipopolysaccharide (LPS) stimulation, we investigated the gain or loss-of-function mutations of MyD88. We predict, using a computational model built on the perturbation-response approach and the law of mass conservation, that removal and addition of MyD88 in TLR4 activation, enhances and impairs, respectively, the alternative TRAM-dependent pathway through signaling flux redistribution (SFR) at pathway branches. To verify SFR, we treated MyD88-deficient macrophages with LPS and observed enhancement of TRAM-dependent pathway based on increased IRF3 phosphorylation and induction of Cxcl10 and Ifit2. Furthermore, increasing the amount of MyD88 in cultured cells showed decreased TRAM binding to TLR4. Investigating another TLR4 pathway junction, from TRIF to TRAF6, RIP1 and TBK1, the removal of MyD88-dependent TRAF6 increased expression of TRAM-dependent Cxcl10 and Ifit2. Thus, we demonstrate that SFR is a novel mechanism for enhanced activation of alternative pathways when molecules at pathway junctions are removed. Our data suggest that SFR may enlighten hitherto unexplainable intracellular signaling alterations in genetic diseases where gain or loss-of-function mutations are observed.

Porphyromonas gingivalis is a Gram-negative anaerobe considered to be a major periodontal pathogen. TLR2 plays a central role in the response to P. gingivalis infection in vivo. In its absence there is a weak inflammatory response; however, bacteria are cleared rapidly compared with wild-type mice. We examined the role of the TLR adaptor proteins MyD88 and TLR/IL-1R–domain-containing adaptor-inducing IFN-β in the inflammatory response to P. gingivalis in vivo and in the ability to clear the bacterial infection. Proinflammatory cytokine production in response to P. gingivalis infection depends on TLR2, but it does not require MyD88 or TLR/IL-1R–domain-containing adaptor-inducing IFN-β. In contrast, the generation of intracellular toxic oxygen species and the ultimate clearance of P. gingivalis infection depend critically on MyD88, independent of TLR2. Thus, robust cytokine production and bacterial clearance are independent events mediated by distinct signaling pathways following infection with P. gingivalis.

TGF-β-activated kinase 1 (TAK1), a member of the MAPKKK family, is thought to be a key modulator of the inducible transcription factors NF-κB and AP-1 and, therefore, plays a crucial role in regulating the genes that mediate inflammation. Although in vitro biochemical studies have revealed the existence of a TAK1 complex, which includes TAK1 and the adapter proteins TAB1 and TAB2, it remains unclear which members of this complex are essential for signaling. To analyze the function of TAK1 in vivo, we have deleted the Tak1 gene in mice, with the resulting phenotype being early embryonic lethality. Using embryonic fibroblasts lacking TAK1, TAB1, or TAB2, we have found that TNFR1, IL-1R, TLR3, and TLR4-mediated NF-κB and AP-1 activation are severely impaired in Tak1 m/m cells, but they are normal in Tab1 -/- and Tab2 -/- cells. In addition, Tak1 m/m cells are highly sensitive to TNF-induced apoptosis. TAK1 mediates IKK activation in TNF-α and IL-1 signaling pathways, where it functions downstream of RIP1–TRAF2 and MyD88–IRAK1–TRAF6, respectively. However, TAK1 is not required for NF-κB activation through the alternative pathway following LT-β signaling. In the TGF-β signaling pathway, TAK1 deletion leads to impaired NF-κB and c-Jun N-terminal kinase (JNK) activation without impacting Smad2 activation or TGF-β-induced gene expression. Therefore, our studies suggests that TAK1 acts as an upstream activating kinase for IKKβ and JNK, but not IKKα, revealing an unexpectedly specific role of TAK1 in inflammatory signaling pathways.

Although ubiquitin is thought to be important for the autophagic sequestration of invading bacteria (also called xenophagy), its precise role remains largely enigmatic. Here we determined how ubiquitin is involved in this process. After invasion, ubiquitin is conjugated to host cellular proteins in endosomes that contain Salmonella or transfection reagent–coated latex (polystyrene) beads, which mimic invading bacteria. Ubiquitin is recognized by the autophagic machinery independently of the LC3–ubiquitin interaction through adaptor proteins, including a direct interaction between ubiquitin and Atg16L1. To ensure that invading pathogens are captured and degraded, Atg16L1 targeting is secured by two backup systems that anchor Atg16L1 to ubiquitin-decorated endosomes. Thus, we reveal that ubiquitin is a pivotal molecule that connects bacteria-containing endosomes with the autophagic machinery upstream of LC3.