Intravital imaging of neutrophil recruitment in hepatic ischemia-reperfusion injury in mice

FPR1 affects acute rejection in kidney transplantation by regulating iron metabolism in neutrophils

BACKGROUND

Acute rejection (AR) is one of the significant factors contributing to poor prognosis in patients following kidney transplantation. Neutrophils are the main cause of early host-induced tissue injury. This paper intends to investigate the possible mechanisms of neutrophil involvement in acute rejection in renal transplantation.

METHODS

Samples were analyzed for their relationship with immune cells using CIBERSORT. WGCNA was used to identify modules with high relevance to neutrophils and hub genes in the modules were extracted. The effect on neutrophil function after blocking formyl peptide receptor 1 (FPR1) was tested in vitro experiments. The effects of blocking FPR1 on neutrophil function as well as acute rejection were tested in vivo after constructing a mouse kidney transplant model.

RESULTS

The proportion of neutrophils was higher in the AR group than in the non-rejection group, and FPR1 was identified as an important gene in the regulation of acute rejection in kidney transplantation by neutrophils. At the cellular level, blocking FPR1 inhibited the activation of the ERK1/2 pathway, decreased ferrous ion content, affected the expression of iron metabolism-related proteins, and suppressed the formation of NETs. In the acute rejection model of renal transplantation, blockade of FPR1 decreased graft neutrophil infiltration and NETs content. Meanwhile, blocking FPR1 attenuated graft injury during acute rejection.

CONCLUSION

This study found that FPR1 might be an important molecule involved in neutrophils during acute rejection of kidney transplantation, explored the relationship between kidney transplantation and neutrophils, and provided potential treatment methods for clinical practice.

Ferroptosis: a new target for hepatic ischemia-reperfusion injury?

Ischemia-reperfusion injury (IRI) can seriously affect graft survival and prognosis and is an unavoidable event during liver transplantation. Ferroptosis is a novel iron-dependent form of cell death characterized by iron accumulation and overwhelming lipid peroxidation; it differs morphologically, genetically, and biochemically from other well-known cell death types (autophagy, necrosis, and apoptosis). Accumulating evidence has shown that ferroptosis is involved in the pathogenesis of hepatic IRI, and targeting ferroptosis may be a promising therapeutic approach. Here, we review the pathways and phenomena involved in ferroptosis, explore the associations and implications of ferroptosis and hepatic IRI, and discuss possible strategies for modulating ferroptosis to alleviate the hepatic IRI.

Factors predicting surgical difficulties in congenital biliary dilatation in pediatric patients

BACKGROUND

The effects of disease classification and the patient's preoperative condition on the difficulty of performing a laparotomy for pediatric congenital biliary dilatation (CBD) have not been fully elucidated.

METHODS

The present study retrospectively analyzed 46 pediatric CBD laparotomies performed at the study center between March 2010 and December 2021 and predictors of operative time. The patients were separated into a short operative time group (SOT) (≤ 360 min, n = 27) and a long operative time group (LOT) (> 360 min, n = 19).

RESULTS

The preoperative AST and ALT values were higher, and the bile duct anastomosis diameter was larger, in the LOT. Correlation analysis demonstrated that the maximum cyst diameter, preoperative neutrophil-to-lymphocyte ratio, AST, ALT, AMY, and bile duct anastomosis diameter correlated positively with operative time. Multivariate analysis identified the maximal cyst diameter, preoperative AST, and bile duct anastomosis diameter as significant factors affecting surgical time. Postoperatively, intrapancreatic stones and paralytic ileus were observed in one patient each in the SOT, and mild bile leakage was observed in one patient in the LOT.

CONCLUSIONS

The maximum cyst diameter, preoperative AST, and bile duct anastomosis diameter have the potential to predict the difficulty of performing a pediatric CBD laparotomy.

Ovarian hormones influence immune response to liver ischemia-reperfusion

Liver injury occurs after ischemia and reperfusion (IR), as seen in transplant settings. Sex hormones have been implicated in many pathophysiological mechanisms in females and this could lead to liver protection under inflammatory reperfusion conditions where an excessive immune response occurs. Despite such assumptions, this fact needs to be further investigated. To address this, female and male C57BL/6J mice (8-12 weeks old) were studied. Bilateral ovariectomy (OVX) was performed in females to decrease estradiol levels. IR was performed, and after two weeks, all animals underwent a sham control operation or IR with euthanasia at the following time points after reperfusion: 6, 12, 24, and 48 h. IR triggered an inflammatory process in the liver with recruitment of neutrophils into the parenchyma of male mice. The female sham mice were protected against liver IR presenting no alteration of aminotransferase (ALT) levels compared to males. OVX caused loss of protection, increasing hepatic injury as represented by increased ALT levels and myeloperoxidase (MPO) activity. Female sham mice showed increased Akt phosphorylation and activation, while males showed reduced Akt activation. Estradiol pretreatment recovered ALT levels after IR injury, which was associated with decreased liver injury.

Updated Views on Neutrophil Responses in Ischemia-Reperfusion Injury

Ischemia-reperfusion injury is an inevitable event during organ transplantation and represents a primary risk factor for the development of early graft dysfunction in lung, heart, liver, and kidney transplant recipients. Recent studies have implicated recipient neutrophils as key mediators of this process and also have found that early innate immune responses after transplantation can ultimately augment adaptive alloimmunity and affect late graft outcomes. Here, we discuss signaling pathways involved in neutrophil recruitment and activation after ischemia-mediated graft injury in solid organ transplantation with an emphasis on lung allografts, which have been the focus of recent studies. These findings suggest novel therapeutic interventions that target ischemia-reperfusion injury-mediated graft dysfunction in transplant recipients.

Intravital electrochemical nanosensor as a tool for the measurement of reactive oxygen/nitrogen species in liver diseases

Reactive oxygen/nitrogen species (ROS/RNS) are formed during normal cellular metabolism and contribute to its regulation, while many pathological processes are associated with ROS/RNS imbalances. Modern methods for measuring ROS/RNS are mainly based on the use of inducible fluorescent dyes and protein-based sensors, which have several disadvantages for in vivo use. Intravital electrochemical nanosensors can be used to quantify ROS/RNS with high sensitivity without exogenous tracers and allow dynamic ROS/RNS measurements in vivo. Here, we developed a method for quantifying total ROS/RNS levels in the liver and evaluated our setup in live mice using three common models of liver disease associated with ROS activation: acute liver injury with CCl4, partial hepatectomy (HE), and induced hepatocellular carcinoma (HCC). We have demonstrated using intravital electrochemical detection that any exposure to the peritoneum in vivo leads to an increase in total ROS/RNS levels, from a slight increase to an explosion, depending on the procedure. Analysis of the total ROS/RNS level in a partial hepatectomy model revealed oxidative stress, both in mice 24 h after HE and in sham-operated mice. We quantified dose-dependent ROS/RNS production in CCl4-induced injury with underlying neutrophil infiltration and cell death. We expect that in vivo electrochemical measurements of reactive oxygen/nitrogen species in the liver may become a routine approach that provides valuable data in research and preclinical studies.

Zinc chelator treatment in crush syndrome model mice attenuates ischemia-reperfusion-induced muscle injury due to suppressing of neutrophil infiltration

In crush syndrome, massive muscle breakdown resulting from ischemia-reperfusion muscle injury can be a life-threatening condition that requires urgent treatment. Blood reperfusion into the ischemic muscle triggers an immediate inflammatory response, and neutrophils are the first to infiltrate and exacerbate the muscle damage. Since free zinc ion play a critical role in the immune system and the function of neutrophils is impaired by zinc depletion, we hypothesized that the administration of a zinc chelator would be effective for suppressing the inflammatory reaction at the site of ischemia-reperfusion injury and for improving of the pathology of crush syndrome. A crush syndrome model was created by using a rubber tourniquet to compress the bilateral hind limbs of mice at 8 weeks. A zinc chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine (TPEN) was administered immediately after reperfusion in order to assess the anti-inflammatory effect of the chelator for neutrophils. Histopathological evaluation showed significantly less muscle breakdown and fewer neutrophil infiltration in TPEN administration group compared with control group. In addition, the expression levels of inflammatory cytokine and chemokine such as IL-6, TNFα, CXCL1, CXCL2, CXCR2, CCL2 in ischemia-reperfusion injured muscle were significantly suppressed with TPEN treatment. Less dilatation of renal tubules in histological evaluation in renal tissue and significantly better survival rate were demonstrated in TPEN treatment for ischemia-reperfusion injury in crush syndrome. The findings of our study suggest that zinc chelators contributed to the resolution of exacerbation of the inflammatory response and attenuation of muscle breakdown in the acute phase after crush syndrome. In addition, our strategy of attenuation of the acute inflammatory reaction by zinc chelators may provide a promising therapeutic strategy not only for crush syndrome, but also for other diseases driven by inflammatory reactions.

The GAG-Binding Peptide MIG30 Protects against Liver Ischemia-Reperfusion in Mice

Ischemia-reperfusion injury (IRI) drives graft rejection and is the main cause of mortality after liver transplantation. During IRI, an intense inflammatory response marked by chemokine production and neutrophil recruitment occurs. However, few strategies are available to restrain this excessive response. Here, we aimed to interfere with chemokine function during IRI in order to disrupt neutrophil recruitment to the injured liver. For this, we utilized a potent glycosaminoglycan (GAG)-binding peptide containing the 30 C-terminal amino acids of CXCL9 (MIG30) that is able to inhibit the binding of chemokines to GAGs in vitro. We observed that mice subjected to IRI and treated with MIG30 presented significantly lower liver injury and dysfunction as compared to vehicle-treated mice. Moreover, the levels of chemokines CXCL1, CXCL2 and CXCL6 and of proinflammatory cytokines TNF-α and IL-6 were significantly reduced in MIG30-treated mice. These events were associated with a marked inhibition of neutrophil recruitment to the liver during IRI. Lastly, we observed that MIG30 is unable to affect leukocytes directly nor to alter the stimulation by either CXCL8 or lipopolysaccharide (LPS), suggesting that its protective properties derive from its ability to inhibit chemokine activity in vivo. We conclude that MIG30 holds promise as a strategy to treat liver IRI and inflammation.

The Importance of CXCL1 in the Physiological State and in Noncancer Diseases of the Oral Cavity and Abdominal Organs

CXCL1 is a CXC chemokine, CXCR2 ligand and chemotactic factor for neutrophils. In this paper, we present a review of the role of the chemokine CXCL1 in physiology and in selected major non-cancer diseases of the oral cavity and abdominal organs (gingiva, salivary glands, stomach, liver, pancreas, intestines, and kidneys). We focus on the importance of CXCL1 on implantation and placentation as well as on human pluripotent stem cells. We also show the significance of CXCL1 in selected diseases of the abdominal organs, including the gastrointestinal tract and oral cavity (periodontal diseases, periodontitis, Sjögren syndrome, Helicobacter pylori infection, diabetes, liver cirrhosis, alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), HBV and HCV infection, liver ischemia and reperfusion injury, inflammatory bowel disease (Crohn’s disease and ulcerative colitis), obesity and overweight, kidney transplantation and ischemic-reperfusion injury, endometriosis and adenomyosis).

Neutrophil Extracellular Traps Regulate HMGB1 Translocation and Kupffer Cell M1 Polarization During Acute Liver Transplantation Rejection

Neutrophil extracellular traps (NETs) play important roles in hepatic ischemic reperfusion injury (IRI) and acute rejection (AR)-induced immune responses to inflammation. After liver transplantation, HMGB1, an inflammatory mediator, contributes to the development of AR. Even though studies have found that HMGB1 can promote NET formation, the correlation between NETs and HMGB1 in the development of AR following liver transplantation has not been elucidated. In this study, levels of serum NETs were significantly elevated in patients after liver transplantation. Moreover, we found that circulating levels of NETs were negatively correlated with liver function. In addition, liver transplantation and elevated extracellular HMGB1 promoted NET formation. The HMGB1/TLR-4/MAPK signaling pathway, which is initiated by HMGB1, participates in NET processes. Moreover, in the liver, Kupffer cells were found to be the main cells secreting HMGB1. NETs induced Kupffer cell M1 polarization and decreased the intracellular translocation of HMGB1 by inhibiting DNase-1. Additionally, co-treatment with TAK-242 (a TLR-4 inhibitor) and rapamycin more effectively alleviated the damaging effects of AR following liver transplantation than either drug alone.

Carabin Deficiency Aggravates Hepatic Ischemia-Reperfusion Injury Through Promoting Neutrophil Trafficking via Ras and Calcineurin Signaling

Neutrophil infiltration plays an important role in the initial phase of hepatic ischemia and reperfusion injury (HIRI). Despite many different key molecules that have been reported to meditate neutrophil trafficking in HIRI, the mechanism of this process has not been fully elucidated. In this study, we found that Carabin deficiency in myeloid cells (LysMCre : Carabinfl/fl) aggravated IRI-induced hepatic injury and apoptosis through increasing the infiltration of CD11b⁺Ly6G⁺ neutrophils. ImmGen Datasets further revealed that Carabin was expressed in bone marrow neutrophils (GM.BM) but was significantly downregulated in thio-induced peripheral neutrophils (GN.Thio.PC), which was consistently verified by comparing GM.BM and liver-infiltrating neutrophils induced by IRI. Mechanistically, up-regulation of Carabin in GM.BM in vitro reduced the expression levels of P-selectin, E-selectin, and αvβ3 integrin through inhibiting Ras-ERK and Calcineurin-NFAT signaling. Furthermore, blocking P-selectin, E-selectin, and αvβ3 integrin in LysMCre : Carabinfl/fl mice decreased the frequency and number of CD11b⁺Ly6G⁺ neutrophils and reversed hepatic ischemia−reperfusion damage. In conclusion, our results provide a new understanding of Carabin, such that it is expressed and functions not only in adaptive immune cells (T and B cells) but also in innate immune cells (neutrophils), contributing to the migration of neutrophils. These findings provide novel and promising therapeutic targets for the prevention of HIRI during liver transplantation or hepatic surgery.

Thrombomodulin-mediated Inhibition of Neutrophil Extracellular Trap Formation Alleviates Hepatic Ischemia/Reperfusion Injury by Blocking TLR4 in Rats Subjected to Liver Transplantation

BACKGROUND

Hepatic ischemia/reperfusion injury (IRI) is an unavoidable outcome of liver transplantation, during which neutrophil extracellular traps (NETs) may play a critical role in the IRI-induced immune response to inflammation. The purpose of this study was to identify the function of recombinant human thrombomodulin (rTM) in the remission of hepatic IRI after liver transplantation and elucidate the specific mechanism.

METHODS

NET formation was detected in the serum of liver transplantation patients and rats following liver transplantation. Hematoxylin-eosin (HE) staining, terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining, immunohistochemistry and immunofluorescence were used to assess the effect of rTM on NET formation in vitro and in vivo.

RESULTS

We found that rTM markedly inhibited neutrophil formation in NETs, reduced apoptosis in hepatocytes, alleviated rat hepatic IRI and improved liver function. In vitro, rTM inhibited neutrophil formation in NETs, and lipopolysaccharide (LPS) (a Toll-like receptor (TLR)-4 agonist) reversed the inhibitory effect of rTM on NET formation. rTM blocked TLR-4 and the downstream extracellular signal-regulated kinase (ERK)/c-Jun NH2 terminal kinase (JNK) and nicotinamide adenine dinucleotide phosphate (NADPH)/ROS/peptidylarginine deiminase 4 (PAD4) signaling pathways to protect against hepatic IRI and inhibit NET formation. In addition, we demonstrated that combined treatment with rTM and an NADPH oxidative inhibitor had a better effect than either treatment alone.

CONCLUSIONS

NETs are a potential therapeutic target in hepatic IRI, and rTM could be used to prevent IR-induced hepatic injury. In addition, cotargeting NETosis-related signaling pathways might be a novel therapeutic strategy for hepatic IRI treatment.

Dexmedetomidine hydrochloride inhibits hepatocyte apoptosis and inflammation by activating the lncRNA TUG1/miR-194/SIRT1 signaling pathway

BACKGROUND

Liver injury seriously threatens the health of people. Meanwhile, dexmedetomidine hydrochloride (DEX) can protect against liver injury. However, the mechanism by which Dex mediates the progression of liver injury remains unclear. Thus, this study aimed to investigate the function of DEX in oxygen and glucose deprivation (OGD)-treated hepatocytes and its underlying mechanism.

METHODS

In order to investigate the function of DEX in liver injury, WRL-68 cells were treated with OGD. Cell viability was measured by MTT assay. Cell apoptosis was detected by flow cytometry. Inflammatory cytokines levels were measured by ELISA assay. The interaction between miR-194 and TUG1 or SIRT1 was detected by dual-luciferase reporter. Gene and protein levels were measured by qPCR or western blotting.

RESULTS

DEX notably reversed OGD-induced inflammation and apoptosis in WRL-68 cell. Meanwhile, the effect of OGD on TUG1, SIRT1 and miR-194 expression in WRL-68 cells was reversed by DEX treatment. However, TUG1 knockdown or miR-194 overexpression reversed the function of DEX in OGD-treated WRL-68 cells. Moreover, TUG1 could promote the expression of SIRT1 by sponging miR-194. Furthermore, knockdown of TUG1 promoted OGD-induced cell growth inhibition and inflammatory responses, while miR-194 inhibitor or SIRT1 overexpression partially reversed this phenomenon.

CONCLUSIONS

DEX could suppress OGD-induced hepatocyte apoptosis and inflammation by mediation of TUG1/miR-194/SIRT1 axis. Therefore, this study might provide a scientific basis for the application of DEX on liver injury treatment.

Live Intravital Intestine with Blood Flow Visualization in Neonatal Mice Using Two-photon Laser Scanning Microscopy

This protocol describes a novel technique to investigate the microcirculation dynamics underlying the pathology in the small intestine of neonatal mice using two-photon laser-scanning microscopy (TPLSM). Recent technological advances in multi-photon microscopy allow intravital analysis of different organs such as the liver, brain and intestine. Despite these advances, live visualization and analysis of the small intestine in neonatal rodents remain technically challenging. We herein provide a detailed description of a novel method to capture high resolution and stable images of the small intestine in neonatal mice as early as postnatal day 0. This imaging technique allows a comprehensive understanding of the development and blood flow dynamics in small intestine microcirculation.

Protective effects of Ginkgo Biloba Dropping Pills against liver ischemia/reperfusion injury in mice

BACKGROUND

Liver ischemia/reperfusion (I/R) injury is an inevitable pathological phenomenon in various clinical conditions, such as liver transplantation, resection surgery, or shock, which is the major cause of morbidity and mortality after operation. Ginkgo Biloba Dropping Pill (GBDP) is a unique Chinese Ginkgo Biloba leaf extract preparation that exhibits a variety of beneficial biological activities. The aim of this study is to investigate the protective effects of GBDP on the liver I/R injury both in the in vitro and in vivo.

METHODS

Hypoxia/reoxygenation (H/R) experiments were performed in alpha mouse liver 12 (AML-12) cells and primary hepatocytes, which were pretreated with GBDP (60 or 120 µg/mL) followed by incubation in a hypoxia chamber. Cell viability was detected by 3-(4,5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) assay. Annexin V staining as well as western blot analysis of apoptosis-related proteins was performed to detect the protective effect of GBDP on cell apoptosis induced by H/R injury. C57BL/6 mice were used to establish the liver I/R injury model, and were pretreated with GBDP (100 or 200 mg/kg/day, i.g.) for two weeks. The liver damage was evaluated by detection of plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST), as well as histopathological examinations. Liver inflammation was determined by detecting the secretion of pro-inflammatory cytokines and neutrophil infiltration through enzyme-linked immunosorbent assay (ELISA) and myeloperoxidase (MPO) immunohistochemistry staining. Finally, Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick and labeling (TUNEL) staining and western blot analysis of apoptosis-related proteins were used to investigate the anti-apoptotic effect of GBDP in mice.

RESULTS

In the in vitro study, GBDP pretreatment improved the cell viability of AML-12 cells in the H/R injury model. Similarly, the same result was found in the primary hepatocytes isolated from C57BL/6 mice. Moreover, GBDP decreased the number of apoptotic cells and reduced the expression of apoptosis-related proteins induced by H/R injury. In the in vivo study, oral administration of GBDP ameliorated liver injury evidenced by a significant decline in the levels of ALT and AST. Furthermore, the result of hematoxylin and eosin (H&E) staining showed that GBDP reduced the size of necrosis area in the liver tissue. In addition, the decreased infiltration of neutrophils and secretion of pro-inflammatory cytokines indicated that GBDP may play an anti-inflammatory effect. More importantly, GBDP reduced TUNEL-positive cells and the expression of apoptosis-related proteins in the liver indicating GBDP has anti-apoptotic effects.

CONCLUSIONS

Our findings elucidated that GBDP has potential effects for protecting against liver I/R injury characterized by its anti-apoptotic, anti-necrotic, and anti-inflammatory properties, which would promisingly make contributions to the exploration of therapeutic strategies in the liver I/R injury.

The role of neutrophil extracellular traps and TLR signaling in skeletal muscle ischemia reperfusion injury

Ischemia reperfusion (IR) injury results in devastating skeletal muscle fibrosis. Here, we recapitulate this injury with a mouse model of hindlimb IR injury which leads to skeletal muscle fibrosis. Injury resulted in extensive immune infiltration with robust neutrophil extracellular trap (NET) formation in the skeletal muscle, however, direct targeting of NETs via the peptidylarginine deiminase 4 (PAD4) mechanism was insufficient to reduce muscle fibrosis. Circulating levels of IL-10 and TNFα were significantly elevated post injury, indicating toll-like receptor (TLR) signaling may be involved in muscle injury. Administration of hydroxychloroquine (HCQ), a small molecule inhibitor of TLR7/8/9, following injury reduced NET formation, IL-10, and TNFα levels and ultimately mitigated muscle fibrosis and improved myofiber regeneration following IR injury. HCQ treatment decreased fibroadipogenic progenitor cell proliferation and partially inhibited ERK1/2 phosphorylation in the injured tissue, suggesting it may act through a combination of TLR7/8/9 and ERK signaling mechanisms. We demonstrate that treatment with FDA-approved HCQ leads to decreased muscle fibrosis and increased myofiber regeneration following IR injury, suggesting short-term HCQ treatment may be a viable treatment to prevent muscle fibrosis in ischemia reperfusion and traumatic extremity injury.

Live Imaging of Innate and Adaptive Immune Responses in the Liver

Immune response in the liver is determined by the spatial organization and cellular dynamics of hepatic immune cells. The liver vasculature accommodates abundant tissue-resident innate immune cells, such as Kupffer cells, natural killer cells, and natural killer T cells, to ensure efficient intravascular immunosurveillance. The fenestrated sinusoids also allow direct contact between circulating T cells and non-canonical antigen-presenting cells, such as hepatocytes, to instruct adaptive immune responses. Distinct cellular behaviors are exploited by liver immune cells to exert proper functions. Intravital imaging enables real-time visualization of individual immune cell in living animals, representing a powerful tool in dissecting the spatiotemporal features of intrahepatic immune cells during steady state and liver diseases. This review summarizes current advances in liver immunology prompted by in vivo imaging, with a particular focus on liver-resident innate immune cells and hepatic T cells.

Platelets Boost Recruitment of CD133+ Bone Marrow Stem Cells to Endothelium and the Rodent Liver-The Role of P-Selectin/PSGL-1 Interactions

We previously demonstrated that clinical administration of mobilized CD133⁺ bone marrow stem cells (BMSC) accelerates hepatic regeneration. Here, we investigated the potential of platelets to modulate CD133⁺BMSC homing to hepatic endothelial cells and sequestration to warm ischemic livers. Modulatory effects of platelets on the adhesion of CD133⁺BMSC to human and mouse liver-sinusoidal- and micro- endothelial cells (EC) respectively were evaluated in in vitro co-culture systems. CD133⁺BMSC adhesion to all types of EC were increased in the presence of platelets under shear stress. This platelet effect was mostly diminished by antagonization of P-selectin and its ligand P-Selectin-Glyco-Ligand-1 (PSGL-1). Inhibition of PECAM-1 as well as SDF-1 receptor CXCR4 had no such effect. In a model of the isolated reperfused rat liver subsequent to warm ischemia, the co-infusion of platelets augmented CD133⁺BMSC homing to the injured liver with heightened transmigration towards the extra sinusoidal space when compared to perfusion conditions without platelets. Extravascular co-localization of CD133⁺BMSC with hepatocytes was confirmed by confocal microscopy. We demonstrated an enhancing effect of platelets on CD133⁺BMSC homing to and transmigrating along hepatic EC putatively depending on PSGL-1 and P-selectin. Our insights suggest a new mechanism of platelets to augment stem cell dependent hepatic repair.

Anti-Inflammatory and Antioxidant Effect of Eucommia ulmoides Polysaccharide in Hepatic Ischemia-Reperfusion Injury by Regulating ROS and the TLR-4-NF-κB Pathway

Eucommia ulmoides polysaccharide (EUP) has been shown to have anti-inflammatory and antioxidant effects. However, the mechanism underlying these effects has rarely been reported, and whether EUP can reduce liver injury in hepatic ischemia-reperfusion injury (HIRI) has not been reported. In this study, 40 Sprague-Dawley (SD) rats were randomly divided into 5 groups: the sham group, ischemia-reperfusion (I/R) group, and three EUP pretreatment groups (320 mg/kg, 160 mg/kg, and 80 mg/kg). SD rats were pretreated with EUP by gavage once a day prior to I/R injury for 10 days. Except for the sham group, blood flow in the middle and left liver lobes was blocked in all the other groups, resulting in 70% liver ischemia, and the ischemia and reperfusion times were 1 h and 4 h, respectively. Ischemic liver tissue and serum were obtained to detect biochemical markers and liver histopathological damage. Compared with the I/R group, after EUP pretreatment, serum alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α, and interleukin-1β levels were significantly decreased, malondialdehyde levels in liver tissues were significantly decreased, superoxide dismutase levels were significantly increased, and the area of liver necrosis was notably reduced. To understand the specific mechanism involved, we determined the levels of Toll-like receptor- (TLR-) 4-nuclear factor-kappaB (NF-κB) pathway-associated proteins in vivo and in vitro. The data showed that EUP can reduce liver damage by decreasing ROS levels and inhibiting TLR-4-NF-κB pathway activation and may be a promising drug in liver surgery to prevent HIRI.

OX40 expression in neutrophils promotes hepatic ischemia/reperfusion injury

Neutrophils play critical roles during the initial phase of hepatic ischemia/reperfusion injury (HIRI). However, the regulation of neutrophil activation, infiltration, and proinflammatory cytokine secretion has not been fully elucidated. In this study, we revealed that OX40 was expressed by neutrophils, its expression in neutrophils was time-dependently upregulated following HIRI, and Ox40 knockout markedly alleviated liver injury. Compared with wild-type neutrophils, the adoptive transfer of Ox40-/- neutrophils decreased HIRI in neutrophil-depleted Rag2/Il2rg-/- or Ox40-/- mice. Moreover, consistently, the in vitro experiments showed that Ox40 not only prolonged neutrophil survival but also promoted proinflammatory cytokines, ROS production, and even neutrophil chemotaxis. Further investigation demonstrated that the knockout of Ox40 in neutrophils inhibited NF-κB signaling via the TRAF1/2/4 and IKKα/IKKβ/IκBα pathways. OX40L and OX86 stimulation could enhance neutrophil activation and survival in vitro and in vivo. In conclusion, our study provides a new understanding of OX40, which is expressed not only in adaptive immune cells but also in innate immune cells, i.e., neutrophils, contributing to the activation and survival of neutrophils. These findings provide a novel potential therapeutic target for the prevention of HIRI during liver transplantation or hepatic surgery.

Carbamazepine promotes specific stimuli-induced NLRP3 inflammasome activation and causes idiosyncratic liver injury in mice

The occurrence of idiosyncratic drug-induced liver injury (IDILI) is a leading cause of post-marketing safety warnings and withdrawals of drugs. Carbamazepine (CBZ), widely used as an antiepileptic agent, could cause rare but severe idiosyncratic liver injury in humans. Although recent studies have shown that inflammasome is implicated in CBZ-induced hepatocellular injury in vitro, the precise pathogenesis of hepatotoxicity remains largely unexplored. Here we report that CBZ causes idiosyncratic liver injury through promoting specific stimuli-induced NLRP3 inflammasome activation. CBZ (40 μM) enhances NLRP3 inflammasome activation triggered by adenosine triphosphate (ATP) or nigericin, rather than SiO₂, monosodium urate crystal or intracellular lipopolysaccharide (LPS). In addition, CBZ has no effect on NLRC4 or AIM2 inflammasome activation. Mechanistically, synergistic induction of mitochondrial reactive oxygen species (mtROS) is a crucial event in the enhancement effect of CBZ on ATP- or nigericin-induced NLRP3 inflammasome activation. Moreover, the "C=C" on the seven-membered ring and "C=O" on the nitrogen of CBZ may be contribute to NLRP3 inflammasome hyperactivation and hepatotoxicity. Notably, in vivo data indicate that CBZ (50 mg/kg) causes liver injury in an LPS (2 mg/kg)-mediated susceptibility mouse model of IDILI, accompanied by an increase in caspase-1 activity and IL-1β production, whereas the combination of CBZ and LPS does not exhibit the effect in NLRP3-knockout mice. In conclusion, CBZ specifically promotes ATP- or nigericin-induced NLRP3 inflammasome activation and causes idiosyncratic liver injury. Our findings also suggest that CBZ may be avoided in patients with NLRP3 inflammasome activation-related diseases that are triggered by ATP or nigericin, which may be risk factors for IDILI.

Mesenchymal Stem Cells Ameliorate Hepatic Ischemia/Reperfusion Injury via Inhibition of Neutrophil Recruitment

Ischemia/reperfusion injury (IRI) remains a major problem in organ transplantation, which represents the main cause of graft dysfunction posttransplantation. Hepatic IRI is characterized by an excessive inflammatory response within the liver. Mesenchymal stem cells (MSCs) have been shown to be immunomodulatory cells and have the therapeutic action on IRI in several organs. However, the mechanism of regulatory effect of MSCs on IRI remains unclear. In the present study, we examined the impact of MSCs on hepatic inflammatory response such as neutrophil influx and liver damage in a rat model of 70% hepatic IRI. Treatment with MSCs protected rat against hepatic IRI, with significantly decreased serum levels of liver enzymes, attenuated hepatic neutrophil infiltration, reduced expression of apoptosis-associated proteins, and ameliorated liver pathological injury. MSCs also significantly enhanced the intracellular activation of p38 MAPK phosphorylation, which led to decreased expression of CXCR2 on the surface of neutrophils. In addition, MSCs significantly diminished neutrophil chemoattractant CXCL2 production by inhibiting NF-κB p65 phosphorylation in macrophages. These results demonstrate that MSCs significantly ameliorate hepatic IRI predominantly through its inhibitory effect on hepatic neutrophil migration and infiltration.

TXNIP knockdown alleviates hepatocyte ischemia reperfusion injury through preventing p38/JNK pathway activation

Hepatic ischemia and reperfusion (I/R) injury is a major cause of liver damage during liver transplantation, resection surgery, shock, and trauma. It has been reported that TXNIP expression was upregulated in a rat model of hepatic I/R injury. However, the role of TXNIP in the hepatic I/R injury is little known. In our study, we investigated the biological role of TXNIP and its potential molecular mechanism in the human hepatic cell line (HL7702 cells). Using oxygen-glucose deprivation and reoxygenation (OGD/R) to create a cell model of hepatic I/R injury, we found that the mRNA and protein expression levels of TXNIP were upregulated in HL7702 cells exposed to OGD/R. TXNIP overexpression remarkably promoted OGD/R-induced cell apoptosis and lactate dehydrogenase (LDH) release, both of which were significantly decreased by TXNIP knockdown. The production of malondialdehyde (MDA) was also increased by TXNIP overexpression, but was reduced by TXNIP knockdown. Moreover, TXNIP overexpression significantly upregulated the phosphorylation of p38 and JNK, which was remarkably inhibited by TXNIP knockdown. Additionally, p38-specific inhibitor SB203580 abrogated the effect of TXNIP overexpression on OGD/R-induced cell injury. Taken together, these results indicated that TXNIP knockdown alleviated hepatocyte I/R injury through preventing p38/JNK pathway activation. Thus, TXNIP might offer a novel potential therapeutic target for the treatment of hepatic I/R injury.

Intravital imaging with two-photon microscopy reveals cellular dynamics in the ischeamia-reperfused rat heart

Recent advances in intravital microscopy have provided insight into dynamic biological events at the cellular level in both healthy and pathological tissue. However, real-time in vivo cellular imaging of the beating heart has not been fully established, mainly due to the difficulty of obtaining clear images through cycles of cardiac and respiratory motion. Here we report the successful recording of clear in vivo moving images of the beating rat heart by two-photon microscopy facilitated by cardiothoracic surgery and a novel cardiac stabiliser. Subcellular dynamics of the major cardiac components including the myocardium and its subcellular structures (i.e., nuclei and myofibrils) and mitochondrial distribution in cardiac myocytes were visualised for 4-5 h in green fluorescent protein-expressing transgenic Lewis rats at 15 frames/s. We also observed ischaemia/reperfusion (I/R) injury-induced suppression of the contraction/relaxation cycle and the consequent increase in cell permeability and leukocyte accumulation in cardiac tissue. I/R injury was induced in other transgenic mouse lines to further clarify the biological events in cardiac tissue. This imaging system can serve as an alternative modality for real time monitoring in animal models and cardiological drug screening, and can contribute to the development of more effective treatments for cardiac diseases.

Two-photon Intravital Imaging of Leukocytes During the Immune Response in Lipopolysaccharide-treated Mouse Liver

Sepsis is a type of severe infection that can cause organ failure and tissue damage. Although the mortality and morbidity rates associated with sepsis are extremely high, no direct treatment or organ-related mechanism has been examined in detail in real time. The liver is the key organ that manages toxins and infections in the human body. Herein, we aimed to perform intravital imaging of mouse liver after induction of endotoxemia in order to track the motility of immune cells, such as neutrophils and liver capsular macrophages (LCMs). Accordingly, we designed a novel surgical method for exposure of the liver with minimally invasive surgery. Mice were intraperitoneally injected with lipopolysaccharide (LPS), a common endotoxin. Using our novel surgical approach for exposure and intravital imaging of the mouse liver, we found that neutrophil recruitment in LPS-treated LysM-green fluorescent protein (GFP) mouse liver was increased compared with that in phosphate-buffered saline-treated liver. After LPS treatment, the number of neutrophils increased significantly with time. Additionally, using CX3Cr1-GFP mice, we successfully visualized liver resident macrophages called LCMs. Therefore, to investigate the efficacy of new reagents to control immune mobility in vivo, determining the motility and morphology of neutrophils and LCMs in the liver may allow us to identify therapeutic effect in organ failure and tissue damage caused by leukocytes activation in sepsis.

Intravital Microscopic Evaluation of the Effects of a CXCR2 Antagonist in a Model of Liver Ischemia Reperfusion Injury in Mice

Background

Ischemia-reperfusion (IR) is a major contributor to graft rejection after liver transplantation. During IR injury, an intense inflammatory process occurs in the liver. Neutrophils are considered central players in the events that lead to liver injury. CXC chemokines mediate hepatic inflammation following reperfusion. However, few studies have demonstrated in real-time the behavior of recruited neutrophils. We used confocal intravital microscopy (IVM) to image neutrophil migration in the liver and to analyze in real-time parameters of neutrophil recruitment in the inflamed tissue in animals treated or not with reparixin, an allosteric antagonist of CXCR1/2 receptors.

Materials and methods

WT and LysM-eGFP mice treated with reparixin or saline were subjected to 60 min of ischemia followed by different times of reperfusion. Mice received Sytox orange intravenously to show necrotic DNA in IVM. The effect of reparixin on parameters of local and systemic reperfusion-induced injury was also investigated.

Results

IR induced liver injury and inflammation, as evidenced by high levels of alanine aminotransferase and myeloperoxidase activity, chemokine and cytokine production, and histological outcome. Treatment with reparixin significantly decreased neutrophil influx. Moreover, reparixin effectively suppressed the increase in serum concentrations of TNF-α, IL-6, and CCL3, and the reperfusion-associated tissue damage. The number of neutrophils in the liver increased between 6 and 24 h of reperfusion, whereas the distance traveled, velocity, neutrophil size and shape, and cluster formation reached a maximum 6 h after reperfusion and then decreased gradually. In vivo imaging revealed that reparixin significantly decreased neutrophil infiltration and movement and displacement of recruited cells. Moreover, neutrophils had a smaller size and less elongated shape in treated mice.

Conclusion

Imaging of the liver by confocal IVM was successfully implemented to describe neutrophil behavior in vivo during liver injury by IR. Treatment with reparixin decreased not only the recruitment of neutrophils in tissues but also their activation state and capacity to migrate within the liver. CXCR1/2 antagonists may be a promising therapy for patients undergoing liver transplantation.

Neutrophils: a cornerstone of liver ischemia and reperfusion injury

Ischemia-reperfusion injury (IRI) is the main cause of morbidity and mortality due to graft rejection after liver transplantation. During IRI, an intense inflammatory process occurs in the liver. This hepatic inflammation is initiated by the ischemic period but occurs mainly during the reperfusion phase, and is characterized by a large neutrophil recruitment to the liver. Production of cytokines, chemokines, and danger signals results in activation of resident hepatocytes, leukocytes, and Kupffer cells. The role of neutrophils as the main amplifiers of liver injury in IRI has been recognized in many publications. Several studies have shown that elimination of excessive neutrophils or inhibition of their function leads to reduction of liver injury and inflammation. However, the mechanisms involved in neutrophil recruitment during liver IRI are not well known. In addition, the molecules necessary for this type of migration are poorly defined, as the liver presents an atypical sinusoidal vasculature in which the classical leukocyte migration paradigm only partially applies. This review summarizes recent advances in neutrophil-mediated liver damage, and its application to liver IRI. Basic mechanisms of activation of neutrophils and their unique mechanisms of recruitment into the liver vasculature are discussed. In particular, the role of danger signals, adhesion molecules, chemokines, glycosaminoglycans (GAGs), and metalloproteinases is explored. The precise definition of the molecular events that govern the recruitment of neutrophils and their movement into inflamed tissue may offer new therapeutic alternatives for hepatic injury by IRI and other inflammatory diseases of the liver.

Intravital imaging of neutrophil recruitment in intestinal ischemia-reperfusion injury

BACKGROUND

Neutrophils are known to be key players in innate immunity. Activated neutrophils induce local inflammation, which results in pathophysiologic changes during intestinal ischemia-reperfusion injury (IRI). However, most studies have been based on static assessments, and few have examined real-time intravital neutrophil recruitment. We herein report a method for imaging and evaluating dynamic changes in the neutrophil recruitment in intestinal IRI using two-photon laser scanning microscopy (TPLSM).

METHODS

LysM-eGFP mice were subjected to 45 min of warm intestinal ischemia followed by reperfusion. Mice received an intravenous injection of tetramethylrhodamine isothiocyanate-labeled albumin to visualize the microvasculature. Using a time-lapse TPLSM technique, we directly observed the behavior of neutrophils in intestinal IRI.

RESULTS

We were able to image all layers of the intestine without invasive surgical stress. At low-magnification, the number of neutrophils per field of view continued to increase for 4 h after reperfusion. High-magnification images revealed the presence or absence of blood circulation. At 0-2 h after reperfusion, rolling and adhesive neutrophils increased along the vasculature. At 2-4 h after reperfusion, the irregularity of crypt architecture and transmigration of neutrophils were observed in the lamina propria. Furthermore, TPLSM imaging revealed the villus height, the diameters of the crypt, and the number of infiltrating neutrophils in the crypt. In the IRI group, the villus height 4 h after reperfusion was significantly shorter than in the control group.

CONCLUSIONS

TPLSM imaging revealed the real-time neutrophil recruitment in intestinal IRI. Z-stack imaging was useful for evaluating pathophysiological changes in the intestinal wall.

Neutrophil extracellular traps in acrolein promoted hepatic ischemia reperfusion injury: Therapeutic potential of NOX2 and p38MAPK inhibitors

Neutrophil is a significant contributor to ischemia reperfusion (IR) induced liver tissue damage. However, the exact role of neutrophils in IR induced innate immune activation and liver damage is not quite clear. Our study sheds light on the role of chronic oxidative stress end products in worsening the IR inflammatory process by neutrophil recruitment and activation following liver surgery. We employed specific inhibitors for molecular targets-NOX2 (NADPH oxidase 2) and P38 MAPK (Mitogen activated protein kinase) signal to counteract neutrophil activation and neutrophil extracellular trap (NET) release induced liver damage in IR injury. We found that acrolein initiated neutrophil chemotaxis and induced NET release both in vitro and in vivo. Acrolein exposure caused NET induced nuclear and mitochondrial damage in HepG2 cells as well as aggravated the IR injury in rat liver. Pretreatment with F-apocynin and naringin, efficiently suppressed acrolein induced NET release in vitro. Notably, it suppressed the expression of inflammatory cytokines, P38MAPK-ERK activation, and apoptotic signals in rat liver exposed to acrolein and subjected to IR. Moreover, this combination effectively attenuated acrolein induced NET release and hepatic IR injury. In the current study we have shown that the acrolein accumulation in liver due to chronic stress, is responsible for neutrophil recruitment and its activation leading to NET induced liver damage during surgery. Our study shows that therapeutic targeting of NOX2 and P38MAPK signaling in patients with chronic hepatic disorders would improve post operative hepatic function and survival.

Intravital Imaging of Neutrophil Recruitment Reveals the Efficacy of FPR1 Blockade in Hepatic Ischemia-Reperfusion Injury

Neutrophils are considered responsible for the pathophysiological changes resulting from hepatic ischemia-reperfusion (I/R) injury, which is a complication of trauma, shock, liver resection, and transplantation. Recently, evidence is accumulating that formyl-peptide receptor (FPR) signaling constitutes an important danger signal that guides neutrophils to sites of inflammation. This study aimed to investigate dynamic neutrophil recruitment using two-photon laser-scanning microscopy (TPLSM) in response to FPR1 blockade during hepatic I/R. LysM-eGFP mice were subjected to partial warm hepatic I/R. They were pretreated with an FPR1 antagonist, cyclosporine H (CsH), or formyl peptide, fMLF. Liver was imaged after hepatic laser irradiation or I/R using the TPLSM technique. CsH treatment alleviated hepatic I/R injury, as evidenced by decreased serum transaminase levels, reduced hepatocyte necrosis/apoptosis, and diminished inflammatory cytokine, chemokine, and oxidative stress. In contrast, systemic administration of fMLF showed few effects. Time-lapse TPLSM showed that FPR1 blockade inhibited the accumulation of neutrophils in the necrotic area induced by laser irradiation in vivo. In the CsH-treated I/R group, the number and crawling velocity of neutrophils in the nonperfused area were lower than those in the control group. Meanwhile, FPR1 blockade did not affect monocyte/macrophage recruitment. Hepatic I/R promoted the retention of neutrophils and their active behavior in the spleen, whereas CsH treatment prevented their changes. Intravital TPLSM revealed that formyl-peptide-FPR1 signaling is responsible for regulating neutrophil chemotaxis to allow migration into the necrotic area in hepatic I/R. Our findings suggest effective approaches for elucidating the mechanisms of immune cell responses in hepatic I/R.

Visualizing liver anatomy, physiology and pharmacology using multiphoton microscopy

Multiphoton microscopy (MPM) has become increasingly popular and widely used in both basic and clinical liver studies over the past few years. This technology provides insights into deep live tissues with less photobleaching and phototoxicity, which helps us to better understand the cellular morphology, microenvironment, immune responses and spatiotemporal dynamics of drugs and therapeutic cells in the healthy and diseased liver. This review summarizes the principles, opportunities, applications and limitations of MPM in hepatology. A key emphasis is on the use of fluorescence lifetime imaging (FLIM) to add additional quantification and specificity to the detection of endogenous fluorescent species in the liver as well as exogenous molecules and nanoparticles that are applied to the liver in vivo. We anticipate that in the near future MPM-FLIM will advance our understanding of the cellular and molecular mechanisms of liver diseases, and will be evaluated from bench to bedside, leading to real-time histology of human liver diseases.

Intravital Multiphoton Imaging of the Kidney: Tubular Structure and Metabolism

Multiphoton microscopy (MPM) allows the visualization of dynamic pathophysiological events in real time in live animals. Intravital imaging can be applied to investigate novel mechanisms and treatments of different forms of kidney disease as well as improve our understanding of normal kidney physiology. Using rodent models, in conjunction with endogenous fluorescence and infused exogenous fluorescent dyes, measurement can be made of renal processes such as glomerular permeability, juxtaglomerular apparatus function, interactions of the tubulointerstitium, tubulovascular interactions, vascular flow rate, and the renin-angiotensin-aldosterone system. Subcellular processes including mitochondrial dynamics, reactive oxygen species production, cytosolic ion concentrations, and death processes of apoptosis and necrosis can also be seen and measured by MPM. The current methods chapter presents an overview of MPM with a focus on techniques for intravital kidney imaging and gives examples of instances where intravital MPM has been utilized to study renal pathophysiology. Suggestions are provided for MPM methods within the confines of intravital microscopy and selected kidney structure. MPM is undoubtedly a powerful new technique for application in experimental nephrology, and we believe it will continue to create new paradigms for understanding and treating kidney disease.

Immunology in the liver--from homeostasis to disease

The liver is a central immunological organ with a high exposure to circulating antigens and endotoxins from the gut microbiota, particularly enriched for innate immune cells (macrophages, innate lymphoid cells, mucosal-associated invariant T (MAIT) cells). In homeostasis, many mechanisms ensure suppression of immune responses, resulting in tolerance. Tolerance is also relevant for chronic persistence of hepatotropic viruses or allograft acceptance after liver transplantation. The liver can rapidly activate immunity in response to infections or tissue damage. Depending on the underlying liver disease, such as viral hepatitis, cholestasis or NASH, different triggers mediate immune-cell activation. Conserved mechanisms such as molecular danger patterns (alarmins), Toll-like receptor signalling or inflammasome activation initiate inflammatory responses in the liver. The inflammatory activation of hepatic stellate and Kupffer cells results in the chemokine-mediated infiltration of neutrophils, monocytes, natural killer (NK) and natural killer T (NKT) cells. The ultimate outcome of the intrahepatic immune response (for example, fibrosis or resolution) depends on the functional diversity of macrophages and dendritic cells, but also on the balance between pro-inflammatory and anti-inflammatory T-cell populations. As reviewed here, tremendous progress has helped to understand the fine-tuning of immune responses in the liver from homeostasis to disease, indicating promising targets for future therapies in acute and chronic liver diseases.

Dynamic weight bearing is an efficient and predictable method for evaluation of arthritic nociception and its pathophysiological mechanisms in mice

The assessment of articular nociception in experimental animals is a challenge because available methods are limited and subject to investigator influence. In an attempt to solve this problem, the purpose of this study was to establish the use of dynamic weight bearing (DWB) as a new device for evaluating joint nociception in an experimental model of antigen-induced arthritis (AIA) in mice. AIA was induced in Balb/c and C57BL/6 mice, and joint nociception was evaluated by DWB. Western Blotting and real-time PCR were used to determine protein and mRNA expression, respectively. DWB detected a dose- and time-dependent increase in joint nociception during AIA and was able to detect the dose-response effects of different classes of analgesics. Using DWB, it was possible to evaluate the participation of spinal glial cells (microglia and astrocytes) and cytokines (IL-1β and TNFα) for the genesis of joint nociception during AIA. In conclusion, the present results indicated that DWB is an effective, objective and predictable test to study both the pathophysiological mechanisms involved in arthritic nociception in mice and for evaluating novel analgesic drugs against arthritis.

Understanding liver immunology using intravital microscopy

The liver has come a long way since it was considered only a metabolic organ attached to the gastrointestinal tract. The simultaneous ascension of immunology and intravital microscopy evidenced the liver as a central axis in the immune system, controlling immune responses to local and systemic agents as well as disease tolerance. The multiple hepatic cell populations are organized in a vascular environment that promotes intimate cellular interactions, including initiation of innate and adaptive immune responses, rapid leukocyte recruitment, pathogen clearance and production of a variety of immune mediators. In this review, we focus on the advances in liver immunology supported by intravital microscopy in diseases such as isquemia/reperfusion, acute liver injury and infections.

Damage-associated molecular pattern-activated neutrophil extracellular trap exacerbates sterile inflammatory liver injury

Innate immunity plays a crucial role in the response to sterile inflammation such as liver ischemia/reperfusion (I/R) injury. The initiation of liver I/R injury results in the release of damage-associated molecular patterns, which trigger an innate immune and inflammatory cascade through pattern recognition receptors. Neutrophils are recruited to the liver after I/R and contribute to organ damage and innate immune and inflammatory responses. Formation of neutrophil extracellular traps (NETs) has been recently found in response to various stimuli. However, the role of NETs during liver I/R injury remains unknown. We show that NETs form in the sinusoids of ischemic liver lobes in vivo. This was associated with increased NET markers, serum level of myeloperoxidase-DNA complexes, and tissue level of citrullinated-histone H3 compared to control mice. Treatment with peptidyl-arginine-deiminase 4 inhibitor or DNase I significantly protected hepatocytes and reduced inflammation after liver I/R as evidenced by inhibition of NET formation, indicating the pathophysiological role of NETs in liver I/R injury. In vitro, NETs increase hepatocyte death and induce Kupffer cells to release proinflammatory cytokines. Damage-associated molecular patterns, such as High Mobility Group Box 1 and histones, released by injured hepatocytes stimulate NET formation through Toll-like receptor (TLR4)- and TLR9-MyD88 signaling pathways. After neutrophil depletion in mice, the adoptive transfer of TLR4 knockout or TLR9 knockout neutrophils confers significant protection from liver I/R injury with a significant decrease in NET formation. In addition, we found inhibition of NET formation by the peptidyl-arginine-deiminase 4 inhibitor and that DNase I reduces High Mobility Group Box 1 and histone-mediated liver I/R injury.

CONCLUSION

Damage-associated molecular patterns released during liver I/R promote NET formation through the TLR signaling pathway. Development of NETs subsequently exacerbates organ damage and initiates inflammatory responses during liver I/R.

Six-color intravital two-photon imaging of brain tumors and their dynamic microenvironment

The majority of intravital studies on brain tumor in living animal so far rely on dual color imaging. We describe here a multiphoton imaging protocol to dynamically characterize the interactions between six cellular components in a living mouse. We applied this methodology to a clinically relevant glioblastoma multiforme (GBM) model designed in reporter mice with targeted cell populations labeled by fluorescent proteins of different colors. This model permitted us to make non-invasive longitudinal and multi-scale observations of cell-to-cell interactions. We provide examples of such 5D (x,y,z,t,color) images acquired on a daily basis from volumes of interest, covering most of the mouse parietal cortex at subcellular resolution. Spectral deconvolution allowed us to accurately separate each cell population as well as some components of the extracellular matrix. The technique represents a powerful tool for investigating how tumor progression is influenced by the interactions of tumor cells with host cells and the extracellular matrix micro-environment. It will be especially valuable for evaluating neuro-oncological drug efficacy and target specificity. The imaging protocol provided here can be easily translated to other mouse models of neuropathologies, and should also be of fundamental interest for investigations in other areas of systems biology.

Tumor necrosis factor α (TNF-α) receptor-I is required for TNF-α-mediated fulminant virus hepatitis caused by murine hepatitis virus strain-3 infection

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TNFR1^−/− mice displayed a dramatic decrease in tissue necrosis and cell apoptosis in the MHV-3 infected spleens and livers.

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TNFR1 deficiency directly impeded FGL2 secretion as well as reduced Fas and FasL expression in MHV-3 infected livers.

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TNFR1 deficiency impeded neutrophils, which produce proinflammatory factors and FGL2 directly, infiltration into liver and spleen.

TNF-α plays an essential role in the pathogenesis of fulminant virus hepatitis (FH) caused by infection with murine hepatitis virus strain-3 (MHV-3). However, the specific TNF-α receptors (TNFR) involved in this disease and how they mediate this effect are uncertain. Here, we showed that the expression of TNFR1 and TNFR2 in the liver and spleen was triggered by MHV-3. However, only TNFR1^−/− mice were resistant to MHV-3 mediated FH, as displayed by a dramatic decrease in tissue necrosis and cell apoptosis in the infected spleens and livers from TNFR1^−/− mice, as well as prolonged survival in these mice compared to wild type littermate controls. Mechanistically, TNFR1 deficiency directly impeded the serum and tissue levels of fibrinogen-like protein 2 (FGL2), a virus-induced procoagulant molecule that promotes cell apoptosis. Additionally, the expression of apoptosis-associated molecules, Fas and Fas ligand (FasL) in the infected organs from TNFR1^−/− mice were also decreased. Moreover, the infiltration of neutrophils rather than Foxp3⁺ regulatory T cells, which produce proinflammatory factors and FGL2 directly, into the infected liver and spleen tissues was also decreased in TNFR1^−/− mice. These combined results indicate that signaling through TNFR1 plays an essential role in the pathogenesis of FH caused by MHV-3 infection, and interruption of this signaling pathway could be useful for clinical therapy.

Interleukin-4 deficiency protects mice from acetaminophen-induced liver injury and inflammation by prevention of glutathione depletion

OBJECTIVE

Interleukin-4 (IL-4) is a multifunctional cytokine involved in many diseases such as autoimmune hepatitis and idiosyncratic drug reactions. However, its role in acetaminophen (APAP)-induced liver injury remains unclear. Our objective was to evaluate the contribution of IL-4 to the pathogenesis of APAP-induced liver injury.

METHODS

Balb/C (WT) and IL-4 knockout (IL-4(-/-)) mice were orally overdosed with APAP. After 24 h, survival percentage, biochemical and morphological markers of liver injury, and tissue inflammation were assessed.

RESULTS

IL-4(-/-) mice were protected from APAP toxicity. Intravital confocal microscopy, tissue histology and serum ALT levels showed significantly less liver injury and inflammation than in the WT group, which may explain the increased survival rate of IL-4(-/-) mice. In addition, IL-4(-/-) mice had decreased production of tumor necrosis factor α, CXCL1 and interleukin-1β in the liver, but not in a remote site such as the lungs. Hepatic macrophage activation was markedly reduced in IL-4-deficient mice. In addition, glutathione depletion-a primary cause of APAP-mediated injury-was significantly attenuated in IL-4(-/-) mice.

CONCLUSIONS

Taken together, our data demonstrate that IL-4(-/-) mice are protected from APAP-induced liver injury due to reduced depletion of glutathione, which prevented liver damage and tissue inflammation.