Inhibition of Toll-like receptor 4 with vasoactive intestinal peptide attenuates liver ischemia-reperfusion injury

Inflammatory Mechanisms in the Pathogenesis of Pulmonary Arterial Hypertension: Recent Advances

Inflammatory processes are increasingly recognized in the pathogenesis of the vascular remodeling that characterizes pulmonary arterial hypertension (PAH). Chronic inflammation may contribute to disease progression or serve as a biomarker of PAH severity. Furthermore, inflammatory pathways may represent possible therapeutic targets for novel PAH-specific drugs beyond the currently approved therapies targeting the endothelin, nitric oxide/cyclic GMP, and prostacyclin biological pathways. The main focus of this article is to provide recent advances in the understanding of the role of inflammatory pathways in the pathogenesis of PAH from preclinical studies and current clinical data supporting chronic inflammation in PAH patients and to discuss emerging therapeutic implications. © 2021 American Physiological Society. Compr Physiol 11:1805-1829, 2021.

OTUD4 alleviates hepatic ischemia-reperfusion injury by suppressing the K63-linked ubiquitination of TRAF6

Hepatic ischemia-reperfusion (IR) injury can cause serious liver damage, leading to liver dysfunction after liver surgery, which is associated with NF-κB-mediated inflammation. The K63-linked auto-polyubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6) is essential for the activation of NF-κB. Here, we found that OTU domain-containing protein 4 (OTUD4), a deubiquitinating enzyme (DUB), interacts with TRAF6 and decreases the K63 auto-polyubiquitination of TRAF6. In addition, the data showed that NF-κB activation was impaired and inflammatory factor levels were reduced after overexpressing OTUD4 in a hypoxia/reoxygenation (HR) model and a hepatic IR model. Additionally, the liver inflammatory response and tissue damage were ameliorated in mice overexpressing OTUD4.Taken together, these results show that OTUD4 can negatively regulate NF-κB activation by suppressing the K63-linked ubiquitination of TRAF6, thus alleviating hepatic ischemia-reperfusion injury.

The role of regulatory neuropeptides and neurotrophic factors in asthma pathophysiology

In the last decade, the attention of scientists in the field of biomedicine is focused on studying the relationship between the immunological and neurogenic components of the inflammatory response and their contribution to the pathophysiology of allergic inflammation in asthma. The review is devoted to detailing the mechanism of neurogenic inflammation involving regulatory neuropeptides (substance P, vasoactive intestinal peptide, calcitonin gene-related peptide) in the pathogenesis of bronchial hyperreactivity in asthma. The role of neurotrophic growth factors (nerve growth factor, brain-derived neurotrophic factor) in the regulation of remodeling of bronchi in asthma has been analyzed. The study of neuroimmune mechanisms in the pathophysiology of asthma will it possible to find new therapeutic targets in this research area.

Role of macrophages in experimental liver injury and repair in mice

Liver macrophages make up the largest proportion of tissue macrophages in the host and consist of two dissimilar groups: Kupffer cells (KCs) and monocyte-derived macrophages (MoMø). As the liver is injured, KCs sense the injury and initiate inflammatory cascades mediated by the release of inflammatory cytokines and chemokines. Subsequently, inflammatory monocytes accumulate in the liver via chemokine-chemokine receptor interactions, resulting in massive inflammatory MoMø infiltration. When live r injury ceases, restorative macrophages, derived from recruited inflammatory monocytes (lymphocyte antigen 6 complex, locus C^hi monocytes), promote the resolution of hepatic damage and fibrosis. Consequently, a large number of studies have assessed the mechanisms by which liver macrophages exert their opposing functions at different time-points during liver injury. The present review primarily focuses on the diverse functions of macrophages in experimental liver injury, fibrosis and repair in mice and illustrates how macrophages may be targeted to treat liver disease.

Vasoactive Intestinal Peptide Promotes Corneal Allograft Survival

Corneal transplantation is the most prevalent form of tissue transplantation. The success of corneal transplantation mainly relies on the integrity of corneal endothelial cells (CEnCs), which maintain graft transparency. CEnC density decreases significantly after corneal transplantation even in the absence of graft rejection. To date, different strategies have been used to enhance CEnC survival. The neuropeptide vasoactive intestinal peptide (VIP) improves CEnC integrity during donor cornea tissue storage and protects CEnCs against oxidative stress-induced apoptosis. However, little is known about the effect of exogenous administration of VIP on corneal transplant outcomes. We found that VIP significantly accelerates endothelial wound closure and suppresses interferon-γ- and tumor necrosis factor-α-induced CEnC apoptosis in vitro in a dose-dependent manner. In addition, we found that intracameral administration of VIP to mice undergoing syngeneic corneal transplantation with endothelial injury increases CEnC density and decreases graft opacity scores. Finally, using a mouse model of allogeneic corneal transplantation, we found for the first time that treatment with VIP significantly suppresses posttransplantation CEnC loss and improves corneal allograft survival.

Global MicroRNA Expression Profiling of Mouse Livers following Ischemia-Reperfusion Injury at Different Stages

Hepatic ischemia-reperfusion injury is a dynamic process consisting of two stages: ischemia and reperfusion, and triggers a cascade of physiological and biochemical events. Given the important role of microRNAs in regulating gene expression, we analyzed gene expression changes in mouse livers at sham control, ischemia stage, and reperfusion stage. We generated global expression profiles of microRNA and mRNA genes in mouse livers subjected to ischemia-reperfusion injury at the three stages, respectively. Comparison analysis showed that reperfusion injury had a distinct expression profile whereas the ischemia sample and the sham control were clustered together. Consistently, there are 69 differentially expressed microRNAs between the reperfusion sample and the sham control whereas 28 differentially expressed microRNAs between the ischemia sample and the sham control. We further identified two modes of microRNA expression changes in ischemia-reperfusion injury. Functional analysis of both the differentially expressed microRNAs in the two modes and their target mRNAs revealed that ischemia injury impaired mitochondrial function, nutrient consumption, and metabolism process. In contrast, reperfusion injury led to severe tissue inflammation that is predominantly an innate-immune response in the ischemia-reperfusion process. Our staged analysis of gene expression profiles provides new insights into regulatory mechanisms of microRNAs in mouse hepatic IR injury.

Vasoactive intestinal peptide suppresses macrophage-mediated inflammation by downregulating interleukin-17A expression via PKA- and PKC-dependent pathways

Interleukin (IL)-17A is a pro-inflammatory cytokine that markedly enhances inflammatory responses in the lungs by recruiting neutrophils and interacting with other pro-inflammatory mediators. Reducing the expression of IL-17A could attenuate inflammation in the lungs. However, whether VIP exerts its anti-inflammatory effects by regulating the expression of IL-17A has remained unclear. Here, we show that there is a remarkable increase of IL-17A in bronchoalveolar lavage fluid (BALF) and lung tissue of mice with acute lung injury (ALI). Moreover, lipopolysaccharides (LPS) stimulated elevated expression of IL-17A, which was evident by the enhanced levels of mRNA and protein observed. Furthermore, we also found that VIP inhibited LPS-mediated IL-17A expression in a time- and dose-dependent manner in an in vitro model of ALI and that this process might be mediated via the phosphokinase A (PKA) and phosphokinase C (PKC) pathways. Taken together, our results demonstrated that VIP might be an effective protector during ALI by suppressing IL-17A expression.

MiR-146b attenuates high-fat diet-induced non-alcoholic steatohepatitis in mice

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide. In this study, we investigated the role of miR-146b in the Toll-like receptor-4 signaling pathway and high-fat diet (HFD)-induced NASH in vivo and in vitro.

METHODS

The effect of miR-146b on the expression of IL-1 receptor-associated kinase 1 (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6) in RAW264.7 cells and HepG2 was studied, and the effect of miR-146b on lipid accumulation in HepG2 was also studied in vitro. The levels of IRAK1, TRAF6, NF-κB, and pro-inflammatory cytokines, as well as the histologic features and lipid accumulation in the livers of HFD-induced non-alcoholic steatohepatitis (NASH) and an miR-146b-administered HFD mouse model, were studied in vivo.

RESULTS

After miR-146b administration, TRAF6 and IRAK1 mRNA and protein levels in macrophages after lipopolysaccharide administration and in HepG2 cells after oleic acid (OA) administration were significantly decreased in 146b group compared with control group (P < 0.001). The lipid accumulation in HepG2 cells exposed to OA was also decreased by inactivation of IRAK1 and TRAF6, then downregulation of the downstream molecules (NF-κB) and upregulation of the tension homolog deleted on chromosome 10 (PTEN) level. In vivo, after administration of miR-146b, TRAF6 and IRAK1 mRNA and protein levels as well as TNF-α and IL-6 mRNA and protein levels were decreased, and hematoxylin and eosin staining showed that the 146b group had low average adipose cell cross-sectional areas compared with control group.

CONCLUSION

MiR-146b ameliorated HFD-induced NASH by directly suppressing IRAK1 and TRAF6.

The microRNA-146a/b attenuates acute small-for-size liver graft injury in rats

BACKGROUND & AIMS

A critical role of the Toll-like receptor (TLR)-4 and its downstream mediators in the pathogenesis of small-for-size liver graft injury has been documented. Recently, the microRNA-146 (miR-146) was identified as a potent negative regulator of the TLR4 signalling pathway. In this study, the role of miR-146a and miR-146b in the attenuation of TLR-4 signalling and small-for-size liver graft injury was investigated.

METHODS

The expression levels of miR-146a and miR-146b during small-for-size liver graft injury were studied in vivo. In addition, the effects of miR-146a and miR-146b on the expression of IRAK1 and TRAF6 in the rat macrophage cell line NR8383 and rat liver kupffer cells were studied in vitro. The in vivo effect of miR-146a and miR-146b on small-for-size liver graft injury was studied by the tail vein injection of miR-146a mimics and miR-146b mimics.

RESULTS

The levels of miR-146a and miR-146b decreased with a small-for-size liver graft. MiR-146a and miR-146b inhibited IRAK1 and TRAF6 expression by binding to the 3'UTR of IRAK1 or TRAF6, respectively, in the rat macrophage cell line NR8383. The administration of miR-146a mimics and miR-146b mimics prevented liver graft injury in small-for-size liver graft injury via the inactivation of IRAK1 and TRAF6 in vivo.

CONCLUSIONS

miR-146a and miR-146b prevent liver injury in small-for-size liver graft injury via the inactivation of IRAK1 and TRAF6.

Significance of changes in Toll-like receptor 4 and TRAF6 expression in intestinal ischemic injury in rats

AIM: To investigate the changes in the expression of Toll-like receptor 4 (TLR4) and tumor necrosis factor receptor associated-factor 6 (TRAF6) in intestinal ischemic injury in rats and to analyze their significance.

METHODS: Thirty-two adult male SD rats were randomly and equally divided into four groups: a sham operation group, and 1-, 3- and 6-h ischemia groups. Superior mesenteric artery ligation was performed in SD rats to induce intestinal ischemia. Real-time quantitative PCR (qPCR) and Western blot were carried out to detect the expression of TLR4 and TRAF6 in intestinal tissues. Meanwhile, the level of myeloperoxidase (MPO) was measured.

RESULTS: Compared with the sham operation group (20.65 U/L ± 6.88 U/L), MPO level was slightly elevated in the intestine in the 1-h ischemia group (23.27 U/L ± 3.00 U/L), but significantly increased in the 3-h (35.73 U/L ± 5.04 U/L, P < 0.01) and 6-h ischemia groups (51.79 U/L ± 2.27 U/L, P < 0.01). TLR4 expression gradually increased in the three ischemia groups (P < 0.01), while TRAF6 expression decreased in the intestine in the 1-h ischemia group, but rapidly increased in the 3- and 6-h groups (P < 0.05).

CONCLUSION: TLR4 and TRAF6 may be involved in regulating intestinal damage and inflammatory processes in rats with intestinal ischemic injury.

miR-146a ameliorates liver ischemia/reperfusion injury by suppressing IRAK1 and TRAF6

A critical role of the Toll-like receptor(TLR) and its downstream molecules, including IL-1 receptor-associated kinase 1(IRAK1) and tumor necrosis factor receptor- associated factor 6(TRAF6), in the pathogenesis of liver ischemia/reperfusion (I/R) injury has been documented. Recently a microRNA, miR-146a, was identified as a potent negative regulator of the TLR signaling pathway. In this study, we investigated the role of miR-146a to attenuate TLR signaling and liver I/R injury in vivo and in vitro. miR-146a was decreased in mice Kupffer cells following hepatic I/R, whereas IRAK1 and TRAF6 increased. Overexpression of miR-146a directly decreased IRAK1 and TRAF6 expression and attenuated the release of proinflammatory cytokines through the inactivation of NF-κB P65 in hypoxia/reoxygenation (H/R)-induced macrophages, RAW264.7 cells. Knockdown experiments demonstrated that IRAK1 and TRAF6 are two potential targets for reducing the release of proinflammatory cytokines. Moreover, co-culture assays indicated that miR-146a decreases the apoptosis of hepatocytes after H/R. In vivo administration of Ago-miR-146a, a stable version of miR-146a in vivo, protected against liver injury in mice after I/R via inactivation of the TLR signaling pathway. We conclude that miR-146a ameliorates liver ischemia/reperfusion injury in vivo and hypoxia/reoxygenation injury in vitro by directly suppressing IRAK1 and TRAF6.

Molecular mechanism and therapeutic modulation of high mobility group box 1 release and action: an updated review

High mobility group box 1 (HMGB1) is an evolutionarily conserved protein, and is constitutively expressed in virtually all types of cells. Infection and injury converge on common inflammatory responses that are mediated by HMGB1 secreted from immunologically activated immune cells or passively released from pathologically damaged cells. Herein we review the emerging molecular mechanisms underlying the regulation of pathogen-associated molecular patterns (PAMPs)-induced HMGB1 secretion, and summarize many HMGB1-targeting therapeutic strategies for the treatment of infection- and injury-elicited inflammatory diseases. It may well be possible to develop strategies that specifically attenuate damage-associated molecular patterns (DAMPs)-mediated inflammatory responses without compromising the PAMPs-mediated innate immunity for the clinical management of infection- and injury-elicited inflammatory diseases.

Inhibition of the phosphoinositide 3-kinase pathway decreases innate resistance to lipopolysaccharide toxicity in TLR4 deficient mice

Background

Upon lipopolysaccharide (LPS) stimulation, activation of both the Toll-like receptor 4 (TLR4) and phosphoinositide 3-kinase (PI3K) pathways serves to balance proinflammatory and anti-inflammatory responses. Although the antagonist to TLR4 represents an emerging promising target for the treatment of sepsis; however, the role of the PI3K pathway under TLR4-null conditions is not well understood. This goal of this study was to investigate the effect of inhibition of PI3K on innate resistance to LPS toxicity in a murine model.

Results

The overall survival of the cohorts receiving intraperitoneal injections of 100, 500, or 1000 μg LPS from Escherichia coli serotype 026:B6 after 7 d was 100%, 10%, and 10%, respectively. In contrast, no mortality was noted after 500-μg LPS injection in Tlr4^-/- mice. When the PI3K inhibitor LY294002 was injected (1 mg/25 g body weight) 1 h prior to the administration of LPS, the overall survival of the Tlr4^-/- mice was 30%. In the Tlr4^-/- mice, the LPS injection induced no NF-κB activation but an increased Akt phosphorylation in the lung and liver, when compared to that of the C57BL/6 mice. Injection of 500 μg LPS led to a significant induction in O₂^- detected by electron paramagnetic resonance (EPR) spin trapping spectroscopy in the lung and liver at 3 and 6 h in C57BL/6 but not Tlr4^-/- mice. Addition of LY294002 only significantly increased the O₂^- level in the lung and liver of the Tlr4^-/- mice but not in the C57BL/6 mice following 500-μg LPS injection. In addition, the serum IL-1β and IL-2 levels were more elevated in C57BL/6 mice than in Tlr4^-/- mice. Notably, IL-1β and IL-2 were significantly increased in Tlr4^-/- mice but not in the C57BL/6 mice when the PI3K pathway was inhibited by LY294002 prior to LPS injection.

Conclusions

In this study, we demonstrate that innate resistance to LPS toxicity in Tlr4^-/- mice is impaired by inhibition of the PI3K pathway, with a corresponding increase in mortality and production of tissue O₂^- and inflammatory cytokines.

Vasoactive intestinal peptide attenuates liver ischemia/reperfusion injury in mice via the cyclic adenosine monophosphate-protein kinase a pathway

Hepatic ischemia/reperfusion injury (IRI), an exogenous, antigen-independent, local inflammation response, occurs in multiple clinical settings, including liver transplantation, hepatic resection, trauma, and shock. The nervous system maintains extensive crosstalk with the immune system through neuropeptide and peptide hormone networks. This study examined the function and therapeutic potential of the vasoactive intestinal peptide (VIP) neuropeptide in a murine model of liver warm ischemia (90 minutes) followed by reperfusion. Liver ischemia/reperfusion (IR) triggered an induction of gene expression of intrinsic VIP; this peaked at 24 hours of reperfusion and coincided with a hepatic self-healing phase. Treatment with the VIP neuropeptide protected livers from IRI; this was evidenced by diminished serum alanine aminotransferase levels and well-preserved tissue architecture and was associated with elevated intracellular cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling. The hepatocellular protection rendered by VIP was accompanied by diminished neutrophil/macrophage infiltration and activation, reduced hepatocyte necrosis/apoptosis, and increased hepatic interleukin-10 (IL-10) expression. Strikingly, PKA inhibition restored liver damage in otherwise IR-resistant VIP-treated mice. In vitro, VIP not only diminished macrophage tumor necrosis factor α/IL-6/IL-12 expression in a PKA-dependent manner but also prevented necrosis/apoptosis in primary mouse hepatocyte cultures. In conclusion, our findings document the importance of VIP neuropeptide-mediated cAMP-PKA signaling in hepatic homeostasis and cytoprotection in vivo. Because the enhancement of neural modulation differentially regulates local inflammation and prevents hepatocyte death, these results provide the rationale for novel approaches to managing liver IRI in transplant patients.

Down-regulation of microRNA-146a in the early stage of liver ischemia-reperfusion injury

BACKGROUND

MicroRNAs (miRNAs), 21-23-nucleotide noncoding RNAs, act as regulators of gene expression transcriptionally. MicroRNA-146a(miR-146a) has been demonstrated to be one of the key molecules in oncogenesis and inflammatory responses. Few data describe the expression of miR-146a in liver ischemia-reperfusion (IR) injury. The present study sought to explore the relationship of miR-146a to Toll-like receptor 4 (TLR4) signaling pathways in a rat model of warm IR injury.

METHODS

The expression of miR-146a was detected by real-time reverse-transcriptase polymerase chain reaction using a partial warm hepatic IR injury model. The expression of TLR4, tumor necrosis factor receptor-associated factor 6 (TRAF6), and interleukin-1 receptor-associated kinase (IRAK 1) protein was assessed by Western blotting as well as the signaling pathways induced by TLR4.

RESULTS

The expression of hepatic miR-146a was down-regulated in IR injury during the 24 hours after reperfusion, reaching the lowest level at 6 hours after reperfusion. Increases in TLR4, TRAF6, and IRAK1 were accompanied by decreased miR-146a during the 24 hours after reperfusion, peaking at 6 hours. Immunohistochemistry showed cytoplasmic expression of cells positive for TLR4, and nuclear expression of cells positive for nuclear factor κB p65 and c-jun to be increased among IR groups after reperfusion.

CONCLUSION

miR-146a was down-regulated in the early stage of liver IR injury.

Immunological variation between inbred laboratory mouse strains: points to consider in phenotyping genetically immunomodified mice

Inbred laboratory mouse strains are highly divergent in their immune response patterns as a result of genetic mutations and polymorphisms. The generation of genetically engineered mice (GEM) has, in the past, used embryonic stem (ES) cells for gene targeting from various 129 substrains followed by backcrossing into more fecund mouse strains. Although common inbred mice are considered "immune competent," many have variations in their immune system-some of which have been described-that may affect the phenotype. Recognition of these immune variations among commonly used inbred mouse strains is essential for the accurate interpretation of expected phenotypes or those that may arise unexpectedly. In GEM developed to study specific components of the immune system, accurate evaluation of immune responses must take into consideration not only the gene of interest but also how the background strain and microbial milieu contribute to the manifestation of findings in these mice. This article discusses points to consider regarding immunological differences between the common inbred laboratory mouse strains, particularly in their use as background strains in GEM.