Takuya Yashiro

Group 2 innate lymphoid cells (ILC2s) produce large amounts of IL-5, IL-13, and amphiregulin, which are involved in the development of lung fibrosis. Activation of ILC2s is mediated by phosphorylation of STAT5. Although STAT5 has tyrosine and serine phosphorylation sites, the mechanisms responsible for phosphorylating serine residues and their significance in ILC2s remain unclear. The present study demonstrated that cyclin-dependent kinase (CDK) 8 and its paralog CDK19 (CDK8/19) were crucial for the activation of ILC2s in OVA-induced asthmatic BALB/c mice by phosphorylating serine residues of STAT5, leading to lung fibrosis. The following results were obtained: (1) The development of lung fibrosis and the number of ILC2s were significantly ameliorated by the CDK8/19 inhibitor, AS3334366, in OVA-induced asthmatic mice. Consistently, lung fibrosis did not develop in OVA-induced asthmatic ILC2-deficient (Il7rCre/+ Rorafl/fl) mice. (2) IL-33 markedly up-regulated the expression of IL-2 receptor chains, CD25 and CD132, in lung ILC2s. IL-2 significantly augmented the expression of ST2, the high-affinity receptor for IL-33. Furthermore, simultaneous stimulation with IL-33 and IL-2 resulted in the upregulation of CDK8/19 expression in ILC2s. (3) The combined treatment with IL-33 and IL-2 synergistically enhanced the proliferation and cytokine production of ILC2s. Conversely, both these effects, along with the phosphorylation of serine residues in STAT5, were suppressed by AS3334366 in a concentration-dependent manner. The present study is the first to report the involvement of CDK8/19 in the activation of ILC2s via the phosphorylation of STAT5, which led to the development of lung fibrosis.

Retinaldehyde dehydrogenase 2 encoded in the Aldh1a2 gene (RALDH2) is expressed in intestinal dendritic cells (DCs) in mesenteric lymph nodes (MLNs) and plays a crucial role in Treg development by producing retinoic acid. In the present study, we screened food ingredients and identified kaempferol, a flavonoid, as the compound that most effectively up-regulated RALDH2 expression in DCs. The development of Foxp3 ⁺ cells from OT-II-derived naïve CD4 ⁺ T cells was enhanced by a co-culture with OVA peptide-pulsed bone marrow-derived DCs (BMDCs) in the presence of kaempferol or by a pre-treatment of BMDCs with kaempferol. The involvement of the aryl hydrocarbon receptor (Ahr) in the effects of kaempferol on Aldh1a2 expression was demonstrated by in vitro experiments using siRNA and various agonistic or antagonistic compounds of AhR. AhR suppressed Aldh1a2 gene expression and kaempferol inhibited the AhR activity by functioning as an antagonist of AhR. The kaempferol treatment also increased the protein levels of PU.1 and IRF4, which are essential for transcription of the Aldh1a2 gene in DCs, and accelerated the subsequent recruitment of PU.1 to the Aldh1a2 gene. The kaempferol-induced increase in PU.1 protein levels occurred in an AhR-dependent and transcription-independent manner, whereas the kaempferol treatment transactivated the Irf4 gene in DCs. The frequency of DCs exhibiting RALDH2 activity in the MLNs of mice was increased by the intraperitoneally (i.p.) administration of an AhR antagonist or by the oral administration of astragalin, a 3- O -glucoside of kaempferol. We also observed an increase in Tregs in the Peyer’s patches of C57BL/6 mice i.p. administered kaempferol-treated BMDCs. We utilized an OVA-induced food allergy model of Balb/c mice to examine the effects of kaempferol in vivo and confirmed that the rapid decrease in body temperature and allergic diarrhea observed just after the OVA challenge were significantly suppressed in mice administered kaempferol.

NR4A3 is a transcription factor that belongs to the nuclear receptor superfamily. To reveal the roles of NR4A3 in skin diseases, we constructed contact hypersensitivity (CHS)- and imiquimod-induced psoriasis models in Nr4a3 ^-/- mice. In the CHS induced Nr4a3 ^-/- mice, ear swelling was significantly reduced, accompanied by suppressed migration of dendritic cells (DCs), in which CCR7 expression was reduced. In contrast, ear swelling in psoriasis model Nr4a3 ^-/- mice was enhanced. The expression levels of inflammatory cytokines in psoriasis skin lesions and in TLR7-ligand-stimulated DCs were increased by NR4A3 deficiency. Subcutaneous (s.c.) injection of hapten-treated Nr4a3 ^+/+ DCs induced ear swelling in Nr4a3 ^-/- mice, and s.c. injection of TLR7-ligand-stimulated Nr4a3 ^-/- DCs caused significant ear swelling. Compared with Nr4a3 ^+/+ DCs, Nr4a3 ^-/- DCs expressed lower levels of CCR7 and IRF4, and higher levels of TLR7, IRF7, IFN-β, and PU.1. Taken together, NR4A3 deficiency ameliorates CHS and exacerbates psoriasis by regulating the expression of CCR7, TLR7, and related transcription factors in DCs.

Short-chain fatty acids (SCFAs) are produced by the intestinal microbiota during the fermentation of dietary fibers as secondary metabolites. Several recent studies reported that SCFAs modulate the development and function of immune-related cells. However, the molecular mechanisms by which SCFAs regulate mast cells (MCs) remain unclear. In the current study, we analyzed the function and gene expression of mouse MCs in the presence of SCFAs in vitro and in vivo. We found that the oral administration of valerate or butyrate ameliorated passive systemic anaphylaxis and passive cutaneous anaphylaxis in mice. The majority of SCFAs, particularly propionate, butyrate, valerate, and isovalerate, suppressed the IgE-mediated degranulation of bone marrow–derived MCs, which were eliminated by the Gi protein inhibitor pertussis toxin and by the knockdown of Gpr109a. A treatment with the HDAC inhibitor trichostatin A also suppressed IgE-mediated MC activation and reduced the surface expression level of FcεRI on MCs. Acetylsalicylic acid and indomethacin attenuated the suppressive effects of SCFAs on degranulation. The degranulation degree was significantly reduced by PGE2 but not by PGD2. Furthermore, SCFAs enhanced PGE2 release from stimulated MCs. The SCFA-mediated amelioration of anaphylaxis was exacerbated by COX inhibitors and an EP3 antagonist, but not by an EP4 antagonist. The administration of niacin, a ligand of GPR109A, alleviated the symptoms of passive cutaneous anaphylaxis, which was inhibited by cyclooxygenase inhibitors and the EP3 antagonist. We conclude that SCFAs suppress IgE-mediated activation of MCs in vivo and in vitro involving GPR109A, PGE2, and epigenetic regulation.

In the present study, we evaluated the effects of kaempferol on bone marrow-derived mast cells (BMMCs). Kaempferol treatment significantly and dose-dependently inhibited IgE-induced degranulation, and cytokine production of BMMCs under the condition that cell viability was maintained. Kaempferol downregulated the surface expression levels of FcεRI on BMMCs, but the mRNA levels of FcεRIα, β, and γ-chains were not changed by kaempferol treatment. Furthermore, the kaempferol-mediated downregulation of surface FcεRI on BMMCs was still observed when protein synthesis or protein transporter was inhibited. We also found that kaempferol inhibited both LPS- and IL-33-induced IL-6 production from BMMCs, without affecting the expression levels of their receptors, TLR4 and ST2. Although kaempferol treatment increased the protein amount of NF-E2-related factor 2 (NRF2)—a master transcription factor of antioxidant stress—in BMMCs, the inhibition of NRF2 did not alter the suppressive effect of kaempferol on degranulation. Finally, we found that kaempferol treatment increased the levels of mRNA and protein of a phosphatase SHIP1 in BMMCs. The kaempferol-induced upregulation of SHIP1 was also observed in peritoneal MCs. The knockdown of SHIP1 by siRNA significantly enhanced IgE-induced degranulation of BMMCs. A Western blotting analysis showed that IgE-induced phosphorylation of PLCγ was suppressed in kaempferol-treated BMMCs. These results indicate that kaempferol inhibited the IgE-induced activation of BMMCs by downregulating FcεRI and upregulating SHIP1, and the SHIP1 increase is involved in the suppression of various signaling-mediated stimulations of BMMCs, such as those associated with TLR4 and ST2.

Various gut bacteria, including Lactobacillus plantarum , possess several enzymes that produce hydroxy fatty acids (FAs), oxo FAs, conjugated FAs, and partially saturated FAs from polyunsaturated FAs as secondary metabolites. Among these derivatives, we identified 10-oxo- cis -6, trans -11-octadecadienoic acid (γKetoC), a γ-linolenic acid-derived enon FA, as the most effective immunomodulator, which inhibited the antigen-induced immunoactivation and the LPS-induced production of inflammatory cytokines. The treatment with γKetoC markedly increased the protein level of NRF2, a master transcription factor for antioxidant responses, and the mRNA level of Hmox1 , a target gene of NRF2, in bone marrow-derived dendritic cells (BMDCs). Although γKetoC significantly suppressed the LPS-induced activation of control BMDCs, particularly the secretion of IL-12/23p40, the suppressive effects of γKetoC were reduced in Nrf2 ^-/- BMDCs. GW9508, an agonist of GPR40/GPR120, inhibited the release of cytokines from LPS-stimulated BMDCs without activating the NRF2 pathway. We evaluated the role of NRF2 in the anti-inflammatory effects of γKetoC in a dextran sodium sulfate-induced colitis model. The oral administration of γKetoC significantly reduced body weight loss, improved stool scores, and attenuated atrophy of the colon, in wild-type C57BL/6J and Nrf2 ^+/- (C57BL/6N) mice with colitis. In contrast, the pathology of colitis was deteriorated in Nrf2 ^-/- mice even with the administration of γKetoC. Collectively, the present results demonstrated the involvement of the NRF2 pathway in γKetoC-mediated anti-inflammatory responses.

Specific intestinal bacteria modulate immunoresponses through various pathways, and several probiotic bacteria have been identified as immunostimulants by screening. In the present study, we evaluated the immunomodulating effects of Bacillus coagulans SANK70258 ( B. coagulans SANK70258), a spore-forming and lactic acid-producing bacterium usable as food supplement for human and animals. We found that treatment of mouse splenocytes with γ-ray irradiated B. coagulans SANK70258 induced high amount of IFN-γ in comparison with 7 kinds of typical lactic acid bacteria. Further analyses using splenocytes revealed that NK cell is a major source of IFN-γ, and B . coagulans SANK70258-induced IFN-γ production was inhibited by neutralization of IL-12 or IL-23, depletion of CD11c ⁺ cells, and inhibition of NFκB. B. coagulans SANK70258 also induced release of IFN-γ from activated CD8 ⁺ T cells, and increased expression of chemokine receptors in CD8 ⁺ T cells. B. coagulans SANK70258-treatment induced production of cytokines from bone marrow-derived dendritic cells, which is reduced by knockdown of Tlr2 and Nod2. B. coagulans SANK70258-treatment also induced IgA production from Peyer’s patch cells with high level among tested lactic bacteria. The oral intake of γ-ray irradiated B. coagulans SANK70258 significantly increased intestinal IgA levels and IgA-expressing B cells in the Peyer’s patch of mice. Taken together, we conclude that B. coagulans SANK70258 possesses high activity as immunostimulant inducing production of IFN-γ and IgA.

In the present study, we evaluated the effects of kaempferol on bone marrow-derived mast cells (BMMCs). Kaempferol treatment significantly and dose-dependently inhibited IgE-induced degranulation, and cytokine production of BMMCs under the condition that cell viability was maintained. Kaempferol downregulated the surface expression levels of FcεRI on BMMCs, but the mRNA levels of FcεRIα, β, and γ-chains were not changed by kaempferol treatment. Furthermore, the kaempferol-mediated downregulation of surface FcεRI on BMMCs was still observed in the presence of a protein-synthesis inhibitor. These results suggest that kaempferol reduced the surface FcεRI on BMMCs, independently of transcription and translation. We also found that kaempferol inhibited both LPS- and IL-33-induced IL-6 production from BMMCs, without affecting the expression levels of their receptors, TLR4 and ST2. Although kaempferol treatment increased the protein amount of NRF2, a master transcription factor of antioxidant stress, in BMMCs, inhibition of NRF2 did not alter the suppressive effect of kaempferol on degranulation. Finally, we observed that kaempferol treatment increased the levels of mRNA and protein of a phosphatase SHIP1 in BMMCs. These results indicate that kaempferol inhibited the IgE-induced activation of BMMCs by downregulating FcεRI and upregulating SHIP1, and the SHIP1 increase is involved in the suppression of various signaling-mediated stimulations of BMMCs, such as those associated with TLR4 and ST2.

Short chain fatty acids (SCFAs) were recently shown to modulate the development and functions of immune-related cells. However, the molecular mechanisms by which SCFAs regulate mast cells (MCs) are not fully understood. We found that the oral administration of valerate or butyrate ameliorated passive systemic anaphylaxis in mice. Butyrate and valerate suppressed the IgE-mediated degranulation of bone marrow-derived MCs, which were eliminated by pertussis toxin and by the knockdown of Gpr109a . A treatment with trichostatin A suppressed IgE-mediated MC activation and reduced the surface expression level of FcεRI on MCs. Acetylsalicylic acid and indomethacin attenuated the suppressive effects of SCFAs on degranulation. The degranulation degree was significantly decreased by the treatment with PGE ₂ whose release from MCs was markedly enhanced by SCFAs. The SCFA-mediated amelioration of anaphylaxis was exacerbated by COX inhibitors and an EP3 antagonist. The administration of niacin, a ligand of GPR109A, alleviated the symptoms of passive cutaneous anaphylaxis, which was inhibited by COX inhibitors and the EP3 antagonist. Key Messages: Short chain fatty acids (SCFAs), particularly butyrate and valerate, suppress the IgE-mediated activation of mast cells (MCs) in vivo and in vitro . SCFAs enhance the release of PGE ₂ from MCs, which inhibits the IgE-mediated activation of MCs. Niacin, a ligand of GPR109A, ameliorates IgE-dependent anaphylaxis. The administration of COX inhibitors or an antagonist of PGE ₂ receptor 3 (EP3) inhibited the suppressive effects of butyrate and niacin on IgE-dependent anaphylaxis.