Phosphatase and tensin homolog-β-catenin signaling modulates regulatory T cells and inflammatory responses in mouse liver ischemia/reperfusion injury

The phosphatase and tensin homolog (PTEN) deleted on chromosome 10 plays an important role in regulating T cell activation during inflammatory response. Activation of β-catenin is crucial for maintaining immune homeostasis. This study investigates the functional roles and molecular mechanisms by which PTEN-β-catenin signaling promotes regulatory T cell (Treg) induction in a mouse model of liver ischemia/reperfusion injury (IRI). We found that mice with myeloid-specific phosphatase and tensin homolog knockout (PTEN^M-KO ) exhibited reduced liver damage as evidenced by decreased levels of serum alanine aminotransferase, intrahepatic macrophage trafficking, and proinflammatory mediators compared with the PTEN-proficient (floxed phosphatase and tensin homolog [PTEN^FL/FL ]) controls. Disruption of myeloid PTEN-activated b-catenin promoted peroxisome proliferator-activated receptor gamma (PPARγ)-mediated Jagged-1/Notch signaling and induced forkhead box P3 (FOXP3)1 Tregs while inhibiting T helper 17 cells. However, blocking of Notch signaling by inhibiting γ-secretase reversed myeloid PTEN deficiency-mediated protection in ischemia/reperfusion-triggered liver inflammation with reduced FOXP3⁺ and increased retinoid A receptor-related orphan receptor gamma t-mediated interleukin 17A expression in ischemic livers. Moreover, knockdown of β-catenin or PPARγ in PTEN-deficient macrophages inhibited Jagged-1/Notch activation and reduced FOXP3⁺ Treg induction, leading to increased proinflammatory mediators in macrophage/T cell cocultures. In conclusion, our findings demonstrate that PTEN-β-catenin signaling is a novel regulator involved in modulating Treg development and provides a potential therapeutic target in liver IRI. Liver Transplantation 23 813-825 2017 AASLD.

The myeloid heat shock transcription factor 1/β-catenin axis regulates NLR family, pyrin domain-containing 3 inflammasome activation in mouse liver ischemia/reperfusion injury

Heat shock transcription factor 1 (HSF1) has been implicated in the differential regulation of cell stress and disease states. β-catenin activation is essential for immune homeostasis. However, little is known about the role of macrophage HSF1-β-catenin signaling in the regulation of NLRP3 inflammasome activation during ischemia/reperfusion (I/R) injury (IRI) in the liver. This study investigated the functions and molecular mechanisms by which HSF1-β-catenin signaling influenced NLRP3-mediated innate immune response in vivo and in vitro. Using a mouse model of IR-induced liver inflammatory injury, we found that mice with a myeloid-specific HSF1 knockout (HSF1^M-KO ) displayed exacerbated liver damage based on their increased serum alanine aminotransferase levels, intrahepatic macrophage/neutrophil trafficking, and proinflammatory interleukin (IL)-1β levels compared to the HSF1-proficient (HSF1^FL/FL ) controls. Disruption of myeloid HSF1 markedly increased transcription factor X-box-binding protein (XBP1), NLR family, pyrin domain-containing 3 (NLRP3), and cleaved caspase-1 expression, which was accompanied by reduced β-catenin activity. Knockdown of XBP1 in HSF1-deficient livers using a XBP1 small interfering RNA ameliorated hepatocellular functions and reduced NLRP3/cleaved caspase-1 and IL-1β protein levels. In parallel in vitro studies, HSF1 overexpression increased β-catenin (Ser552) phosphorylation and decreased reactive oxygen species (ROS) production in bone-marrow-derived macrophages. However, myeloid HSF1 ablation inhibited β-catenin, but promoted XBP1. Furthermore, myeloid β-catenin deletion increased XBP1 messenger RNA splicing, whereas a CRISPR/CRISPR-associated protein 9-mediated XBP1 knockout diminished NLRP3/caspase-1.

CONCLUSION

The myeloid HSF1-β-catenin axis controlled NLRP3 activation by modulating the XBP1 signaling pathway. HSF1 activation promoted β-catenin, which, in turn, inhibited XBP1, leading to NLRP3 inactivation and reduced I/R-induced liver injury. These findings demonstrated that HSF1/β-catenin signaling is a novel regulator of innate immunity in liver inflammatory injury and implied the therapeutic potential for management of sterile liver inflammation in transplant recipients. (Hepatology 2016;64:1683-1698).

Adoptive transfer of heme oxygenase-1 (HO-1)-modified macrophages rescues the nuclear factor erythroid 2-related factor (Nrf2) antiinflammatory phenotype in liver ischemia/reperfusion injury

Macrophages are instrumental in the pathophysiology of liver ischemia/reperfusion injury (IRI). Although Nrf2 regulates macrophage-specific heme oxygenase-1 (HO-1) antioxidant defense, it remains unknown whether HO-1 induction might rescue macrophage Nrf2-dependent antiinflammatory functions. This study explores the mechanisms by which the Nrf2-HO-1 axis regulates sterile hepatic inflammation responses after adoptive transfer of ex vivo modified HO-1 overexpressing bone marrow-derived macrophages (BMMs). Livers in Nrf2-deficient mice preconditioned with Ad-HO-1 BMMs, but not Ad-β-Gal-BMMs, ameliorated liver IRI (at 6 h of reperfusion after 90 min of warm ischemia), evidenced by improved hepatocellular function (serum alanine aminotransferase [sALT] levels) and preserved hepatic architecture (Suzuki histological score). Treatment with Ad-HO-1 BMMs decreased neutrophil accumulation, proinflammatory mediators and hepatocellular necrosis/apoptosis in ischemic livers. Moreover, Ad-HO-1 transfection of Nrf2-deficient BMMs suppressed M1 (Nos2(+)) while promoting the M2 (Mrc-1/Arg-1(+)) phenotype. Unlike in controls, Ad-HO-1 BMMs increased the expression of Notch1, Hes1, phosphorylation of Stat3 and Akt in IR-stressed Nrf2-deficient livers as well as in lipopolysaccharide (LPS)-stimulated BMMs. Thus, adoptive transfer of ex vivo generated Ad-HO-1 BMMs rescued Nrf2-dependent antiinflammatory phenotype by promoting Notch1/Hes1/Stat3 signaling and reprogramming macrophages toward the M2 phenotype. These findings provide the rationale for a novel clinically attractive strategy to manage IR liver inflammation/damage.

KEAP1-NRF2 complex in ischemia-induced hepatocellular damage of mouse liver transplants

BACKGROUND & AIMS

The Keap1-Nrf2 signaling pathway regulates host cell defense responses against oxidative stress and maintains the cellular redox balance.

METHODS

We investigated the function/molecular mechanisms by which Keap1-Nrf2 complex may influence liver ischemia/reperfusion injury (IRI) in a mouse model of hepatic cold storage (20h at 4°C) followed by orthotopic liver transplantation (OLT).

RESULTS

The Keap1 hepatocyte-specific knockout (HKO) in the donor liver ameliorated post-transplant IRI, evidenced by improved hepatocellular function and OLT outcomes (Keap1 HKO→Keap1 HKO; 100% survival), as compared with controls (WT→WT; 50% survival; p<0.01). By contrast, donor liver Nrf2 deficiency exacerbated IRI in transplant recipients (Nrf2 KO→Nrf2 KO; 40% survival). Ablation of Keap1 signaling reduced macrophage/neutrophil trafficking, pro-inflammatory cytokine programs, and hepatocellular necrosis/apoptosis, while simultaneously promoting anti-apoptotic functions in OLTs. At the molecular level, Keap1 HKO increased Nrf2 levels, stimulated Akt phosphorylation, and enhanced expression of anti-oxidant Trx1, HIF-1α, and HO-1. Pretreatment of liver donors with PI3K inhibitor (LY294002) disrupted Akt/HIF-1A signaling and recreated hepatocellular damage in otherwise IR-resistant Keap1 HKO transplants. In parallel in vitro studies, hydrogen peroxide-stressed Keap1-deficient hepatocytes were characterized by enhanced expression of Nrf2, Trx1, and Akt phosphorylation, in association with decreased release of lactate dehydrogenase (LDH) in cell culture supernatants.

CONCLUSIONS

Keap1-Nrf2 complex prevents oxidative injury in IR-stressed OLTs through Keap1 signaling, which negatively regulates Nrf2 pathway. Activation of Nrf2 induces Trx1 and promotes PI3K/Akt, crucial for HIF-1α activity. HIF-1α-mediated overexpression of HO-1/Cyclin D1 facilitates cytoprotection by limiting hepatic inflammatory responses, and hepatocellular necrosis/apoptosis in a PI3K-dependent manner.

ASC/caspase-1/IL-1β signaling triggers inflammatory responses by promoting HMGB1 induction in liver ischemia/reperfusion injury

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), an adaptor protein for inflammasome receptors, is essential for inducing caspase-1 activation and the consequent secretion of interleukin-1β (IL-1β), which is associated with local inflammation during liver ischemia/reperfusion injury (IRI). However, little is known about the mechanisms by which the ASC/caspase-1/IL-1β axis exerts its function in hepatic IRI. This study was designed to explore the functional roles and molecular mechanisms of ASC/caspase-1/IL-1β signaling in the regulation of inflammatory responses in vitro and in vivo. With a partial lobar liver warm ischemia (90 minutes) model, ASC-deficient and wild-type mice (C57BL/6) were sacrificed at 6 hours of reperfusion. Separate animal cohorts were treated with an anti-IL-1β antibody or control immunoglobulin G (10 mg/kg/day intraperitoneally). We found that ASC deficiency inhibited caspase-1/IL-1β signaling and led to protection against liver ischemia/reperfusion (IR) damage, local enhancement of antiapoptotic functions, and down-regulation of high mobility group box 1 (HMGB1)-mediated, toll-like receptor 4 (TLR4)-driven inflammation. Interestingly, the treatment of ASC-deficient mice with recombinant HMGB1 re-created liver IRI. Moreover, neutralization of IL-1β ameliorated the hepatocellular damage by inhibiting nuclear factor kappa B (NF-κB)/cyclooxygenase 2 signaling in IR-stressed livers. In parallel in vitro studies, the knockout of ASC in lipopolysaccharide-stimulated bone marrow-derived macrophages depressed HMGB1 activity via the p38 mitogen-activated protein kinase pathway and led to the inhibition of TLR4/NF-κB and ultimately the depression of proinflammatory cytokine programs.

CONCLUSION

ASC-mediated caspase-1/IL-1β signaling promotes HMGB1 to produce a TLR4-dependent inflammatory phenotype and leads to hepatocellular injury. Hence, ASC/caspase-1/IL-1β signaling mediates the inflammatory response by triggering HMGB1 induction in hepatic IRI. Our findings provide a rationale for a novel therapeutic strategy for managing liver injury due to IR.

β-catenin regulates innate and adaptive immunity in mouse liver ischemia-reperfusion injury

Dendritic cells (DCs) are critical mediators of immune responses that integrate signals from the innate immune system to orchestrate adaptive host immunity. This study was designed to investigate the role and molecular mechanisms of STAT3-induced β-catenin in the regulation of DC function and inflammatory responses in vitro and in vivo. STAT3 induction in lipopolysaccharide (LPS)-stimulated mouse bone marrow-derived DCs (BMDCs) triggered β-catenin activation by way of GSK-3β phosphorylation. The activation of β-catenin inhibited phosphatase and tensin homolog delete on chromosome 10 (PTEN) and promoted the phosphoinositide 3-kinase (PI3K)/Akt pathway, which in turn down-regulated DC maturation and function. In contrast, knockdown of β-catenin increased PTEN/TLR4 (Toll-like receptor 4), interferon regulatory factor-3 (IRF3), nuclear factor kappa B (NF-κB) activity, and proinflammatory cytokine programs in response to LPS stimulation. In a mouse model of warm liver ischemia and reperfusion injury (IRI), disruption of β-catenin signaling increased the hepatocellular damage, enhanced hepatic DC maturation/function, and PTEN/TLR4 local inflammation in vivo.

CONCLUSION

These findings underscore the role of β-catenin to modulate DC maturation and function at the innate-adaptive interface. Activation of β-catenin triggered PI3K/Akt, which in turn inhibited TLR4-driven inflammatory response in a negative feedback regulatory mechanism. By identifying the molecular pathways by which β-catenin regulates DC function, our findings provide the rationale for novel therapeutic approaches to manage local inflammation and injury in IR-stressed liver.

PTEN-mediated Akt/β-catenin/Foxo1 signaling regulates innate immune responses in mouse liver ischemia/reperfusion injury

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) regulates innate immune responses inversely with phosphoinositide 3-kinase (PI3K) and its direct downstream target gene, Akt. The Forkhead box O (Foxo) transcription factors are essential in the regulation of tissue development, immune homeostasis, and cell survival. This study was designed to investigate the role of PTEN-mediated Akt/β-catenin/Foxo1 signaling in the regulation of in vivo and in vitro innate immune responses in a mouse model of hepatic inflammatory injury induced by 90 minutes of liver partial warm ischemia followed by 6 hours of reperfusion. We found that knockdown of PTEN with small interfering RNA (siRNA) promoted Akt/β-catenin/Foxo1 signaling, leading to resistance against liver ischemia/reperfusion (IR) damage, local enhancement of antiapoptotic function, and downregulation of innate Toll-like receptor 4 (TLR4) expression. A specific PI3K blockade inhibited Akt/β-catenin signaling, increased Foxo1-mediated TLR4-driven local inflammation, and recreated cardinal features of liver IR injury. Moreover, knockdown of PTEN in lipopolysaccharide-stimulated mouse bone marrow-derived macrophages enhanced β-catenin activity, which in turn provided a negative regulatory feedback to the Foxo1 function, leading to the inhibition of TLR4 and NF-κB, with ultimate depression of proinflammatory cytokine programs in vitro.

CONCLUSION

Our novel findings identify the PTEN-mediated Akt/β-catenin/Foxo1 axis as a key regulator of innate inflammatory response in the mouse liver. By identifying molecular mechanisms of PTEN-mediated Akt/β-catenin/Foxo1 signaling in TLR4 innate immune regulation, our study provides a rationale for therapeutic approaches to manage inflammation injury in IR-stressed liver.

Disruption of Type-I IFN pathway ameliorates preservation damage in mouse orthotopic liver transplantation via HO-1 dependent mechanism

Ischemia/reperfusion injury (IRI) remains unresolved problem in clinical organ transplantation. We analyzed the role of Type-I interferon (IFN) pathway in a clinically relevant murine model of extended hepatic cold preservation followed by orthotopic liver transplantation (OLT). Livers from Type-I IFN receptor (IFNAR) knockout (KO) or wild-type (WT) mice (C57/BL6) were harvested, preserved at 4°C in UW solution for 20 h and transplanted to groups of syngeneic IFNAR KO or WT recipients. Liver graft but not recipient IFNAR deficiency was required to consistently ameliorate IRI in OLTs. Indeed, disruption of Type-I IFN signaling decreased serum alanine aminotransferase (sALT) levels (p < 0.001), diminished Suzuki's score of histological OLT damage (p < 0.01) and improved 14-day survival (from 42%[5/12] in WT to 92%[11/12] in IFNAR KO; p < 0.05). Unlike in WT group, IFNAR deficiency attenuated OLT expression of TNF-α, IL-1β, IL-6, MCP-1, CXCL-10, ICAM-1; diminished infiltration by macrophages/PMNs; and enhanced expression of antioxidant HO-1/Nrf2. The frequency of TUNEL+ apoptotic cells and caspase-3 activity/expression selectively decreased in IFNAR KO group. Small interfering (si)RNA-directed targeting of HO-1 restored cardinal features of liver IRI in otherwise resistant IFNAR-deficient OLTs. Thus, intact Type-I IFN signaling is required for hepatic IRI, whereas HO-1 is needed for cytoprotection against innate immunity-dominated organ preservation damage in IFNAR-deficient liver transplants.

Activation of cyclic adenosine monophosphate-dependent protein kinase a signaling prevents liver ischemia/reperfusion injury in mice

Hepatic ischemia/reperfusion injury (IRI) occurs in multiple clinical settings, including liver transplantation. The cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) pathway inhibits hepatocellular apoptosis and regulates toll-like receptor 4-triggered inflammation responses in vitro. Here we examined the function and therapeutic potential of cAMP-PKA activation in a murine (C57/BL6) model of liver warm ischemia (90 minutes) followed by reperfusion. Liver IRI triggered cAMP-PKA activation, whereas the administration of its specific inhibitor, H89, exacerbated hepatocellular damage. Conversely, forskolin therapy, which activates PKA by elevating cAMP levels, protected livers from IRI; this was evidenced by diminished serum alanine aminotransferase levels and well-preserved tissue architecture. Liver protection due to cAMP-PKA stimulation was accompanied by diminished neutrophil and macrophage infiltration/activation, reduced hepatocyte necrosis/apoptosis, and increased cAMP response element-binding protein (CREB) expression and augmented interleukin-10 (IL-10) expression. The neutralization of IL-10 restored liver damage in otherwise ischemia/reperfusion-resistant, forskolin-treated mice. In vitro, cAMP-PKA activation diminished macrophage tumor necrosis factor α, IL-6, and IL-12 in an IL-10-dependent manner and prevented necrosis/apoptosis in primary mouse hepatocyte cultures. Our novel findings in a mouse model of liver IRI document the importance of cAMP-PKA signaling in hepatic homeostasis and cytoprotection in vivo. The activation of cAMP-PKA signaling differentially regulates local inflammation and prevents hepatocyte death, and this provides a rationale for novel therapeutic approaches to combating liver IRI in transplant recipients.

HO-1-STAT3 axis in mouse liver ischemia/reperfusion injury: regulation of TLR4 innate responses through PI3K/PTEN signaling

BACKGROUND & AIMS

Signal transducer and activator of transcription 3 (STAT3), a key mediator of anti-inflammatory cytokine signaling, is essential for heme oxygenase-1 (HO-1)-induced cytoprotection. The phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog delete on chromosome 10 (PTEN) pathways regulate diverse innate immune responses. This study was designed to investigate the role of STAT3 in the regulation of PI3K/PTEN cascade after HO-1 induction in a mouse model of innate immune-dominated liver ischemia/reperfusion injury (IRI).

METHODS

Partial warm ischemia was produced in the left and middle hepatic lobes of C57BL/6 mice for 90 min, followed by 6h of reperfusion.

RESULTS

Mice subjected to Ad-HO-1 transfer were resistant to liver IRI, and this cytoprotective effect correlated with increased intrahepatic PI3K/Akt and diminished PTEN expression. In contrast, mice undergoing adjunctive Ad-HO-1 treatment and STAT3 knockdown (siRNA) remained susceptible to IR-mediated local inflammatory response and hepatocellular damage. Consistent with decreased cell apoptosis and inhibited TLR4 expression after PI3K/Akt activation, treatment with specific PI3k inhibitor increased local inflammation and recreated liver IRI despite Ad-HO-1 gene transfer. Parallel in vitro studies with bone marrow derived-macrophages have confirmed that HO-1-STAT3 axis-induced PI3K/Akt negatively regulated PTEN expression in TLR4-dependent fashion.

CONCLUSIONS

These findings underscore the role of HO-1 induced STAT3 in modulating PI3K/PTEN in liver IRI cascade. Activating PI3K/Akt provides negative feedback mechanism for TLR4-driven inflammation. Identifying molecular pathways of STAT3 modulation in the innate immune system provides the rationale for novel therapeutic approaches for the management of liver inflammation and IRI in transplant patients.

Sotrastaurin, a protein kinase C inhibitor, ameliorates ischemia and reperfusion injury in rat orthotopic liver transplantation

Sotraustaurin (STN), a small molecule, targeted protein kinase C (PKC) inhibitor that prevents T-lymphocyte activation via a calcineurin-independent pathway, is currently being tested in Phase II renal and liver transplantation clinical trials. We have documented the key role of activated T cells in the inflammation cascade leading to liver ischemia/reperfusion injury (IRI). This study explores putative cytoprotective functions of STN in a clinically relevant rat model of hepatic cold ischemia followed by orthotopic liver transplantation (OLT). Livers from Sprague-Dawley rats were stored for 30 h at 4°C in UW solution, and then transplanted to syngeneic recipients. STN treatment of liver donors/recipients or recipients only prolonged OLT survival to >90% (vs. 40% in controls), decreased hepatocellular damage and improved histological features of IRI. STN treatment decreased activation of T cells, and diminished macrophage/neutrophil accumulation in OLTs. These beneficial effects were accompanied by diminished apoptosis, NF-κB/ERK signaling, depressed proapoptotic cleaved caspase-3, yet upregulated antiapoptotic Bcl-2/Bcl-xl and hepatic cell proliferation. In vitro, STN decreased PKCθ/IκBα activation and IL-2/IFN-γ production in ConA-stimulated spleen T cells, and diminished TNF-α/IL-1β in macrophage-T cell cocultures. This study documents positive effects of STN on liver IRI in OLT rat model that may translate as an additional benefit of STN in clinical liver transplantation.

Native macrophages genetically modified to express heme oxygenase 1 protect rat liver transplants from ischemia/reperfusion injury

We investigated whether native macrophages overexpressing heme oxygenase 1 (HO-1) could protect rat orthotopic liver transplant (OLT) against cold ischemia/reperfusion injury (IRI). Livers from Sprague-Dawley rats were stored at 4°C in University of Wisconsin solution for 24 hours, and then they were transplanted into syngeneic recipients. Bone marrow-derived macrophages (BMMs) that were transfected ex vivo with heme oxygenase 1 adenovirus (Ad-HO-1), β-galactosidase adenovirus (Ad-β-gal), or HO-1 small interfering RNA (siRNA) were infused directly into the OLT before reperfusion. Controls were OLT conditioned with unmodified or scrambled siRNA-transfected cells. The transfer of Ad-HO-1/BMMs increased the survival of OLT to 100% (versus 40%-50% for controls) and decreased serum alanine aminotransferase levels and histological features of hepatocellular damage. In contrast, an infusion of macrophages transfected with HO-1 siRNA/Ad-β-gal failed to affect IRI. Gene therapy-induced HO-1 suppressed toll-like receptor 4 expression, decreased expression of proinflammatory tumor necrosis factor α, interleukin-1β, monocyte chemoattractant protein 1, and chemokine (C-X-C motif) ligand 10, and attenuated endothelial intercellular cell adhesion molecule 1 expression with resultant diminished OLT leukocyte sequestration. Although Ad-HO-1/BMMs decreased the frequency of apoptotic cells positive for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and ameliorated caspase-3 activity, the expression of interleukin-10 and antiapoptotic B cell lymphoma 2/B cell lymphoma extra large increased in well-functioning OLT. Thus, the transfer of native macrophages transfected ex vivo with HO-1 can rescue rat iso-OLT from IRI. Our study validates a novel and clinically attractive concept: native macrophages transfected ex vivo with the antioxidant HO-1 can be applied at the time of transplantation to mitigate otherwise damaging antigen-independent liver inflammation and injury resulting from the peritransplant harvesting insult. If this new, refined strategy is proven to be effective in allo-OLT recipients, it should be considered in clinical settings to increase the supply of usable donor organs and ultimately improve the overall success of liver transplantation.

T-cell immunoglobulin mucin-3 determines severity of liver ischemia/reperfusion injury in mice in a TLR4-dependent manner

BACKGROUND & AIMS

T-cell immunoglobulin mucin (TIM) genes are expressed by T cells and regulate host immunity and tolerance. CD4(+) T cells mediate innate immunity-dominated liver ischemia-reperfusion injury (IRI) by unknown mechanisms. TIM-1 is involved in liver IRI, which is activated in part by the Toll-like receptor (TLR)4; we investigated the role of TIM-3 and TLR4 in IRI.

METHODS

Using an antibody against TIM-3 (anti-TIM-3), we studied TIM-3 signaling in mice following partial warm liver ischemia and reperfusion.

RESULTS

Mice given anti-TIM-3 had more liver damage than controls. Histological studies revealed that anti-TIM-3 increased hepatocellular damage and local neutrophil infiltration, facilitated local accumulation of T cells and macrophages, and promoted liver cell apoptosis. Intrahepatic neutrophil activity; induction of proinflammatory cytokines and chemokines; and expression of cleaved caspase-3, nuclear factor-κB, and TLR4 all increased in mice given anti-TIM-3. Administration of anti-TIM-3 followed by anti-galectin-9 (Gal-9 is a TIM-3 ligand) increased production of interferon-γ by concanavalin A (ConA)-stimulated spleen T cells and expression of tumor necrosis factor-α and interleukin-6 in ConA-stimulated macrophages co-cultured with T cells. Anti-TIM-3 did not affect liver IRI in TLR4-deficient mice.

CONCLUSION

TIM-3 blockade exacerbated local inflammation and liver damage, indicating the importance of TIM-3-Gal-9 signaling in maintaining hepatic homeostasis. TIM-3-TLR4 cross-regulation determined the severity of liver IRI in TLR4-dependent manner; these findings provide important information about the modulation of innate vs adaptive responses in patients that received liver transplants. Negative co-stimulation signaling by hepatic T-cells might be developed to minimize innate immunity-mediated liver tissue damage.

Programmed death-1/B7-H1 negative costimulation protects mouse liver against ischemia and reperfusion injury

Programmed death-1 (PD-1)/B7-H1 costimulation acts as a negative regulator of host alloimmune responses. Although CD4 T cells mediate innate immunity-dominated ischemia and reperfusion injury (IRI) in the liver, the underlying mechanisms remain to be elucidated. This study focused on the role of PD-1/B7-H1 negative signaling in liver IRI. We used an established mouse model of partial liver warm ischemia (90 minutes) followed by reperfusion (6 hours). Although disruption of PD-1 signaling after anti-B7-H1 monoclonal antibody treatment augmented hepatocellular damage, its stimulation following B7-H1 immunoglobulin (B7-H1Ig) fusion protected livers from IRI, as evidenced by low serum alanine aminotransferase levels and well-preserved liver architecture. The therapeutic potential of B7-H1 engagement was evident by diminished intrahepatic T lymphocyte, neutrophil, and macrophage infiltration/activation; reduced cell necrosis/apoptosis but enhanced anti-necrotic/apoptotic Bcl-2/Bcl-xl; and decreased proinflammatory chemokine/cytokine gene expression in parallel with selectively increased interleukin (IL)-10. Neutralization of IL-10 re-created liver IRI and rendered B7-H1Ig-treated hosts susceptible to IRI. These findings were confirmed in T cell-macrophage in vitro coculture in which B7-H1Ig diminished tumor necrosis factor-α/IL-6 levels in an IL-10-dependent manner. Our novel findings document the essential role of the PD-1/B7-H1 pathway in liver IRI.

CONCLUSION

This study is the first to demonstrate that stimulating PD-1 signals ameliorated liver IRI by inhibiting T cell activation and Kupffer cell/macrophage function. Harnessing mechanisms of negative costimulation by PD-1 upon T cell-Kupffer cell cross-talk may be instrumental in the maintenance of hepatic homeostasis by minimizing organ damage and promoting IL-10-dependent cytoprotection.

Interaction between the intermediary electron acceptor (pheophytin) and a possible plastoquinone-iron complex in photosystem II reaction centers

Photoreduction of the intermediary electron acceptor, pheophytin (Pheo), in photosystem II reaction centers of spinach chloroplasts or subchloroplast particles (TSF-II and TSF-IIa) at 220 K and redox potential E(h) = -450 mV produces an EPR doublet centered at g = 2.00 with a splitting of 52 G at 7 K in addition to a narrow signal attributed to Pheo([unk]) (g = 2.0033, DeltaH approximately 13 G). The doublet is eliminated after extraction of lyophilized TSF-II with hexane containing 0.13-0.16% methanol but is restored by reconstitution with plastoquinone A (alone or with beta-carotene) although not with vitamin K(1). TSF-II and TSF-IIa are found to contain approximately 2 nonheme Fe atoms per reaction center. Incubation with 0.55 M LiClO(4) plus 2.5 mM o-phenanthroline (but not with 0.55 M LiClO(4) alone) decreases this value to approximately 0.6 and completely eliminates the EPR doublet, but photoreduction of Pheo is not significantly affected. Partial restoration of the doublet (about 25%) was achieved by subsequent incubation with 0.2 mM Fe(2+), but not with either Mn(2+) or Mg(2+). The Fe removal results in the development of a photoinduced EPR signal (g = 2.0044 +/- 0.0003, DeltaH = 9.2 +/- 0.5 G) at E(h) = 50 mV, which is not observed after extraction with 0.16% methanol in hexane. It is ascribed to plastosemiquinone no longer coupled to Fe in photosystem II reaction centers. The results show that a complex of plastoquinone and Fe can act as the stable "primary" electron acceptor in photosystem II reaction centers and that the interaction of its singly reduced form with the reduced intermediary acceptor, Pheo([unk]), is responsible for the EPR doublet.

Redox titration of fluorescence yield of photosystem II

The variable fluorescence yield of photosystem II is dependent on the redox state of the fluorescence quencher molecule or the primary electron acceptor of the system. We have carried out redox titrations of fluorescence yield of a photochemically active photosystem-II reaction-center particle and have measured the redox potential of the photosystem-II primary acceptor.During reductive titrations using dithionite as the reductant, only a single quenching transition was observed. For instance, at pH 7.0, the midpoint potential of the fluorescence transition is -325 mV, and those at a pH between 6.0 and 7.5 are consistent with a pH dependence of about 60 mV/pH unit. At a given pH, the midpoint potential of the transition closely corresponds to that of the most negative transition previously measured in unfractionated chloroplasts (both by chemical reductive titration). Oxidative titrations using ferricyanide as the oxidant yielded hysteresis in the titration curves.Similar changes in fluorescence yield were observed in redox titrations by electrochemical reduction or oxidation. Electrochemical reductive and oxidative titrations yielded reversible transitions, contrary to the hysteresis observed during chemical oxidative titration. From coulometric-titration data, we have estimated that most likely one electron is involved in the redox transition of the fluorescence-quencher or primary-electron-acceptor molecule of photosystem II. These findings are consistent with the current proposal that a membrane-bound plastoquinone functions as the primary acceptor of photosystem II.

Spectral and kinetic evidence for two early electron acceptors in photosystem I

Triton-fractionated photosystem-I particles poised at -625 mV, where the two bound iron-sulfur proteins are reduced, have been studied by optical and electron paramagnetic resonance spectroscopies from 293 to 5 K. At 5-9 K, these particles exhibit two decay components with lifetimes of 1.3 and 130 msec in the laser pulse-induced absorption and electron paramagnetic resonance signal changes. Spectral properties of the 130-msec decay component reflect the charge separation between P-700 and some iron-sulfur center having a broad optical absorbance in the 400- to 550-nm region and a previously reported electron paramagnetic resonance signal with g = 1.78, 1.88, and 2.08. Spectral properties of the 1-msec decay component indicate photoinduced charge separation between P-700 and a chlorophyll a dimer having absorption bands at 420, 450, and 700 nm. It is assumed that these two acceptors participate in the electron transfer from P-700(*) to the bound iron-sulfur proteins.

Oxidation-reduction potentials of bound iron-sulfur proteins of photosystem I

Digitonin - fractionated photosystem - I subchloroplasts were titrated potentiometrically between -450 and -610 mV at pH 10. Examination of the titrated subchloroplasts by low-temperature (13 degrees K) electron paramagnetic resonance spectroscopy revealed resonances centered at values of 2.05, 1.94, 1.92, 1.89, and 1.86 on the g-factor scale. The peak heights depended on the potentials at which the chloroplasts were poised. The resonances of at least three iron-sulfur centers can be recognized: one with lines at g = 2.05 and 1.94; one with lines at g = 2.05, 1.92, and 1.89; and one for which only a line at g = 1.86 has been resolved. The midpoint potentials of the iron-sulfur species fall into two distinctly separate regions: the titration profile of the g = 1.94 signal, the first segment of the g = 2.05 plot, and the rise phase of the g = 1.86 signal had a value of -530 +/- 5 mV; the upper segment of the g = 2.05 plot, the decrease phase of the g = 1.86 signal, and the g = 1.89 profile had a midpoint potential estimated to be [unk] -580 mV. The oxidation-reduction reaction of each of the bound iron-sulfur species, as represented by the changes of the electron paramagnetic resonance spectra, was reversible and apparently involved a two-electron change.Titration at pH 9 could only be carried to -560 mV, and essentially only the first half of the titration behavior as found at pH 10 was seen. At any given potential more positive than -560 mV, the part of the iron-sulfur protein that was not reduced electrochemically could be reduced photochemically, but only to the maximum extent reduced electrochemically at -560 mV. Whereas, chloroplasts illuminated at room temperature and then frozen while still being illuminated developed a signal similar to that produced by electrochemical reduction at -610 mV, illumination at 77 degrees K did not bring about photoreduction beyond that accomplished electrochemically at about -560 mV.Dithionite alone in the dark and under anaerobic conditions brought about a partial reduction to the extent of the first electrochemical reduction step. Dithionite plus illumination at room temperature or dithionite plus methyl viologen in the dark produced the maximum signal. Electron paramagnetic resonance spectra due to either light or electrochemically reduced iron-sulfur proteins showed no detectable decay for at least 3 days when samples were stored in the dark at 77 degrees K.

Blockade of Janus kinase-2 signaling ameliorates mouse liver damage due to ischemia and reperfusion

Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling is one of the major pathways for cytokine signal transduction. However, the role of the JAK/STAT pathway in liver ischemia/reperfusion is not clear. This study focuses on Janus kinase-2 (JAK2), which functions upstream of signal transducer and activator of transcription 1 (STAT1) in JAK/STAT, and its role in the mechanism of liver ischemia/reperfusion injury (IRI). Partial warm ischemia was produced in the hepatic lobes of C57BL/6 mice for 90 minutes, and this was followed by 6 hours of reperfusion. Mice were treated with a JAK2 inhibitor (tyrphostin AG490; 40 mg/kg intraperitoneally) or vehicle 60 minutes prior to ischemic insult. JAK2 blockade resulted in a significant reduction of hepatocyte apoptosis and liver injury. Macrophage and neutrophil infiltration, as assessed by immunohistochemistry, was markedly decreased in AG490-treated livers in comparison with controls. The expression of pro-inflammatory cytokines [tumor necrosis factor alpha, interleukin 6 (IL-6), and IL-1beta] and chemokines [chemokine (C-X-C motif) ligand 10 (CXCL-10) and CXCL-2] was also significantly reduced in the AG490-treated group in comparison with controls. AG490-treated livers showed fewer cells positive for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and reduced cleaved caspase-3 protein expression in parallel with increased B-cell lymphoma extra large expression. We employed AG490 (75 mM) in primary bone marrow-derived macrophage (BMM) and hepatoma cell (CRL1830) cultures, which were both stimulated with lipopolysaccharide (LPS; 10 ng/mL). In BMM cultures, AG490 depressed otherwise LPS-induced pro-inflammatory gene expression programs (IL-6, IL-12p40, IL-1beta, CXCL-10, and inducible nitric oxide synthase). In hepatoma cells, AG490 reduced cleaved caspase-3 expression. Moreover, JAK2 blockade inhibited STAT1 and STAT3 phosphorylation. This is the first report documenting that JAK2 signaling is essential in the pathophysiology of liver IRI, as its selective blockage ameliorated the disease process and protected livers from inflammation and apoptosis.

The emerging role of T cell immunoglobulin mucin-1 in the mechanism of liver ischemia and reperfusion injury in the mouse

The T cell immunoglobulin and mucin domain-containing molecules (TIM) protein family, which is expressed by T cells, plays a crucial role in regulating host adaptive immunity and tolerance. However, its role in local inflammation, such as innate immunity-dominated organ ischemia-reperfusion injury (IRI), remains unknown. Liver IRI occurs frequently after major hepatic resection or liver transplantation. Using an antagonistic anti-TIM-1 antibody (Ab), we studied the role of TIM-1 signaling in the model of partial warm liver ischemia followed by reperfusion. Anti-TIM-1 Ab monotherapy ameliorated the hepatocellular damage and improved liver function due to IR, as compared with controls. Histological examination has revealed that anti-TIM-1 Ab treatment decreased local neutrophil infiltration, inhibited sequestration of T lymphocytes, macrophages, TIM-1 ligand-expressing TIM-4(+) cells, and reduced liver cell apoptosis. Intrahepatic neutrophil activity and induction of proinflammatory cytokines/chemokines were also reduced in the treatment group. In parallel in vitro studies, anti-TIM-1 Ab suppressed interferon-gamma (IFN-gamma) production in concanavalin A (conA)-stimulated spleen T cells, and diminished tumor necrosis factor alpha (TNF-alpha)/interleukin (IL)-6 expression in a macrophage/spleen T cell coculture system. This is the first study to provide evidence for the novel role of TIM-1 signaling in the mechanism of liver IRI. TIM-1 regulates not only T for the role of cell activation but may also affect macrophage function in the local inflammation response. These results provide compelling data for further investigation of TIM-1 pathway in the mechanism of IRI, to improve liver function, expand the organ donor pool, and improve the overall success of liver transplantation.

The parameters of electron cyclotron resonance/radio-frequency hybrid hydrogen plasma adjusted by substrate arrangements

Hybrid hydrogen plasma was formed by biasing 13.56 MHz radio-frequency (rf) power on a substrate immersed in 2.45 GHz microwave electron cyclotron resonance (ECR) plasma. The influences of the substrate configuration on plasma characteristics were investigated. With increasing rf self-bias voltage, electron temperature, T(e), increases obviously in the case of the single-electrode substrate, whereas a slight change in T(e) was observed with the double-electrode substrate condition. Electron density rises almost with a same magnitude under both two substrate conditions. It exhibited that electron energy and density in ECR-rf hybrid mode could be adjusted independently by controlling rf discharge with favorable substrate configurations.

The antioxidant drink “effective microorganism-X (EM-X)” pre-treatment attenuates the loss of nigrostriatal dopaminergic neurons in 6-hydroxydopamine-lesion rat model of Parkinson’s disease

There is continued interest in the assessment and potential use of antioxidants as neuroprotective agents in diseases associated with increased oxidative stress, such as Parkinson's disease. The neuroprotective effect of a natural antioxidant drink, EM-X (a ferment derivative of unpolished rice, papaya and seaweeds with effective microorganisms), was investigated using the 6-hydroxydopamine (6-OHDA)-lesion rat model of Parkinson's disease. The nigrostriatal dopaminergic neurons were unilaterally lesioned with 6-OHDA (8 μg) in rats that were treated with a 10-times diluted EM-X drink (dilEM-X), standard EM-X drink (stdEM-X) or tap water for 4 days. Seven days post lesion, the integrity (no. of tyrosine hydroxylase positive cells (TH+ cells) in the substantia nigra pars compacta (SNpc)) and functionality (dopamine and its metabolites DOPAC and HVA content in the striata) of nigrostriatal dopaminergic neurons were assessed. In the vehicle-treated rats, infusion of 8 μg of 6-OHDA significantly reduced the number of TH+ cells in the SNpc as well as the levels of dopamine, DOPAC and HVA in the striata on the lesion side. The loss of TH+ cells, dopamine and HVA, but not the DOPAC levels, was significantly attenuated by stdEM-X pretreatment, but not by the dilEM-X pretreatment. There were no significant changes in the TH+ cells, or in the monoamine levels with the EM-X pretreatment per se, except for a small but significant fall in the levels of dopamine with the stdEM-X. The evidence presented supports the potential neuroprotective effects of stdEM-X drink, although its effect on dopamine levels needs further investigation.