Rapamycin protection of livers from ischemia and reperfusion injury is dependent on both autophagy induction and mammalian target of rapamycin complex 2-Akt activation

Huang Lian Jie Du decoction attenuates inflammation in septic rats by activating autophagy and altering the intestinal microbiome

Aims

The aim of this study was to investigate the protective effect of HLJDD on septic rats and the underlying mechanisms.

Materials and methods

Adult male Sprague-Dawley (SD) adult rats (150-180 g) were randomly divided into the following 5 groups (n = 7 per group): the Sham group, caecal ligation and puncture (CLP) group, HLJDD + CLP (Huang Lian Jie Du Decoction, HLJDD) group (1 g/mL/100 g), HLJDD + Rap + CLP (H. Rap) group (Rap: 3 mg/kg), and HLJDD+3-MA + CLP (H. 3-MA) group (3-MA: 30 mg/kg). Rapamycin (Rap) and 3-methyladenosine (3-MA) were used to activate and inhibit autophagy, respectively. HLJDD was purchased from Beijing Tong Ren Tang Guiyang Branch and verified by experts as a genuine product. We used CLP to establish an animal model of sepsis in the last four groups. Survival was analysed by the Kaplan‒Meier method. Then, we examined autophagy-related genes (Atgs) and proteins using real-time PCR and Western blotting, respectively. The microstructure of the ileum and the number of autophagosomes were observed by transmission electron microscopy (TEM). Analyses of HE-stained pathological ileum and inflammatory factor levels were examined to assess the extent of septic injury. The effect of HLJDD on the gut microbiota was analysed by 16S rRNA gene sequencing of faeces.

Results

In this study, we identified the protective effects of HLJDD on mortality and inflammation in septic rats. Several key proteins, including LC3-II, Beclin-1 and p62, were examined and showed that HLJDD could effectively reverse the sepsis-induced decrease in autophagy. TEM was performed and the expression of Atgs was assessed to evaluate fluctuations in autophagy. Then, we examined the intestinal tight junction protein zona occludens (ZO-1), lipopolysaccharide (LPS) and inflammatory factors, and found that HLJDD effectively alleviated the increase in ZO-1 gene expression, the level of LPS and serum level of inflammatory factors caused by sepsis. These results were consistent with those obtained from pathological sectioning and TEM analysis. Moreover, autophagy activation effectively ameliorated sepsis, and autophagy inhibition exacerbated the systemic symptoms caused by infection. By examining the expression of key proteins upstream of the autophagy pathway, we found that HLJDD inhibited mTOR via the MAPK/PI3K signalling pathway to promote autophagy in septic rats. 16S rRNA sequencing revealed that HLJDD significantly affected the diversity and physiological function of the gut microbiota in septic rats.

Conclusions

The results of this study indicate that autophagy activation is a potential mechanism underlying the protective effect of HLJDD on the intestine in septic rats.

Quercetin, a natural flavonoid, protects against hepatic ischemia-reperfusion injury via inhibiting Caspase-8/ASC dependent macrophage pyroptosis

INTRODUCTION

Hepatic ischemia-reperfusion injury (IRI) is an inevitable adverse event following liver surgery, leading to liver damage and potential organ failure. Despite advancements, effective interventions for hepatic IRI remain elusive, posing a significant clinical challenge. The innate immune response significantly contributes to the pathogenesis of hepatic IRI by promoting an inflammatory cytotoxic cycle. We have reported that blocking GSDMD-induced pyroptosis in innate immunity cells protected hepatic IRI from inflammatory injury. However, the search for effective pyroptosis inhibitors continues.

OBJECTIVES

This study aims to evaluate whether quercetin, a natural flavonoid, can inhibit GSDMD-induced pyroptosis and mitigate hepatic IRI.

METHODS

We established the hepatic IRI murine model and cellular pyroptosis model to evaluate the efficacy of quercetin.

RESULTS

Quercetin effectively alleviated hepatic IRI-induced tissue necrosis and inflammation. We found that during hepatic IRI, the cleavage of GSDMD occurred in hepatic macrophages, but not in other non-parenchymal cells. Quercetin inhibited the cleavage of GSDMD in macrophages. Moreover, we found that quercetin blocked the ASC assembly to inhibit the formation of NLRP3 inflammasomes and AIM2 inflammasomes, suppressing macrophage pyroptosis. Co-immunoprecipitation experiments confirmed that quercetin inhibited the interaction between ASC and Caspase-8, which is the mechanism of ASC complex and inflammasome formation. Overexpression of Caspase-8 abolished the anti-pyroptosis effect of quercetin in NLRP3 and AIM2 inflammasome signaling. Furthermore, we found that the hepatoprotective activity of quercetin was reduced in myelocytic GSDMD-deficient mice.

CONCLUSION

Our findings suggest that quercetin has beneficial effects on hepatic IRI. Quercetin could attenuate hepatic IRI and target inhibition of macrophage pyroptosis via blocking Caspase-8/ASC interaction. We recommend that quercetin might serve as a targeted approach for the prevention and personalized treatment of hepatic IRI in perioperative patients.

Exploring the therapeutic potential of regulatory T cell in rheumatoid arthritis: Insights into subsets, markers, and signaling pathways

Rheumatoid arthritis (RA) is a complex autoimmune inflammatory rheumatic disease characterized by an imbalance between immunological reactivity and immune tolerance. Regulatory T cells (Tregs), which play a crucial role in controlling ongoing autoimmunity and maintaining peripheral tolerance, have shown great potential for the treatment of autoimmune inflammatory rheumatic diseases such as RA. This review aims to provide an updated summary of the latest insights into Treg-targeting techniques in RA. We focus on current therapeutic strategies for targeting Tregs based on discussing their subsets, surface markers, suppressive function, and signaling pathways in RA.

Mechanistic target of rapamycin complex 1 orchestrates the interplay between hepatocytes and Kupffer cells to determine the outcome of immune-mediated hepatitis

The cell-cell interaction between hepatocytes and Kupffer cells (KCs) is crucial for maintaining liver homeostasis, and the loss of KCs and hepatocytes is known to represent a common pathogenic phenomenon in autoimmune hepatitis. Until now, the mechanisms of cell-cell interaction between hepatocytes and KCs involved in immune-mediated hepatitis remains unclear. Here we dissected the impact of activated mTORC1 on the cell-cell interaction of KCs and hepatocyte in immune-mediated hepatitis. In the liver from patients with AIH and mice administrated with Con-A, mTORC1 was activated in both KCs and hepatocytes. The activated mTORC1 signal in hepatocytes with Con-A challenge caused a markedly production of miR-329-3p. Upregulated miR-329-3p inhibited SGMS1 expression in KCs through paracrine, resulting in the death of KCs. Most of maintained KCs were p-S6 positive and distributed in hepatocyte mTORC1 negative area. The activation of mTORC1 enabled KCs expressed complement factor B (CFB) to enhance the complement alternative system, which produced more complement factors to aggravate liver injury. Our findings remonstrate a heterogeneous role of mTORC1 in specific cell type for maintaining tolerogenic liver environment, and will form the basis for the development of new interventions against immune-mediated hepatitis.

Ubiquitin ligase E3 HUWE1/MULE targets transferrin receptor for degradation and suppresses ferroptosis in acute liver injury

Hepatic ischemia followed by reperfusion (I/R), a major clinical problem during liver surgical procedures, can induce liver injury with severe cell death including ferroptosis which is characterized by iron-dependent accumulation of lipid peroxidation. The HECT domain-containing ubiquitin E3 ligase HUWE1 (also known as MULE) was initially shown to promote apoptosis. However, our preliminary study demonstrates that high expression of HUWE1 in the liver donors corelates with less injury and better hepatic function after liver transplantation in patients. Thus, we investigate the role of HUWE1 in acute liver injury, and identify HUWE1 as a negative ferroptosis modulator through transferrin receptor 1(TfR1). Deficiency of Huwe1 in mice hepatocytes (HKO) exacerbated I/R and CCl4-induced liver injury with more ferroptosis occurrence. Moreover, Suppression of Huwe1 remarkably enhances cellular sensitivity to ferroptosis in primary hepatocytes and mouse embryonic fibroblasts. Mechanistically, HUWE1 specifically targets TfR1 for ubiquitination and proteasomal degradation, thereby regulates iron metabolism. Importantly, chemical and genetic inhibition of TfR1 dramatically diminishes the ferroptotic cell death in Huwe1 KO cells and Huwe1 HKO mice. Therefore, HUWE1 is a potential protective factor to antagonize both aberrant iron accumulation and ferroptosis thereby mitigating acute liver injury. These findings may provide clinical implications for patients with the high-expression Huwe1 alleles.

The Effects of Rapamycin on the Intestinal Graft in a Rat Model of Cold Ischemia Perfusion and Preservation

Attenuating the rheological and structural consequences of intestinal ischemia-reperfusion-injury (IRI) is important in transplant proceedings. Preconditioning is an often-proposed remedy. This technique uses physical or pharmacological methods to manipulate key ischemia pathways, such as oxidation, inflammation, and autophagy, prior to ischemia. This study determined the time-dependent effects of Rapamycin preconditioning on small-bowel grafts undergoing cold ischemia perfusion and preservation. Our main parameters were mucosa and cell injury and autophagy. A total of 30 male Wistar rats were divided into 5 groups: sham, preservation-control, and 3 treated groups (Rapamycin administered either 0, 30, or 60 min prior to perfusion). After perfusion, the intestines were placed in chilled IGL-1 solution for 12 h. Thereafter, they were reperfused. Histology and bioanalysis (LDH and lactate) were used to ascertain intestinal injury while immunohistochemistry was used for measuring changes in autophagy markers (Beclin-1, LC3B, and p62 proteins). The results show no significant difference amongst the groups after vascular perfusion. However, intestinal injury findings and autophagy changes demonstrate that administering Rapamycin 30 min or 60 min prior was protective against adverse cold ischemia and reperfusion of the intestinal graft. These findings show that Rapamycin is protective against cold ischemia of the small intestine, especially when administered 30 min before the onset.

Ellagic acid Alleviates hepatic ischemia-reperfusion injury in C57 mice via the Caspase-1-GSDMD pathway

BACKGROUND

Ellagic acid (EA) has improving function against oxidative damage and inflammatory reaction in many disorders. Hepatic ischemia-reperfusion injury (IRI) is a common pathophysiological phenomenon in the veterinary clinic. In the present study, the protective effects of EA pretreatment against hepatic IRI-induced injury and the underlying mechanisms were investigated.

RESULTS

We found that pyroptosis is involved in hepatic IRI, which is manifested in increasing the expression of pyroptosis-related genes and promoting the expression of active caspase-1, thereby cleaving GSDMD-N to cause pyroptosis, and caspase-1-/- mice were used to verify this conclusion. In addition, we found that EA protects against hepatic IRI by inhibiting pyroptosis, including reducing the activity of caspase-1 and its expression in the liver, inhibiting the lysis of GSDMD-N, and reducing the levels of IL-18 and IL-1β.

CONCLUSIONS

The present results have demonstrated that prophylactic administration of EA ameliorated hepatic IRI by inhibiting pyroptosis induced in hepatic ischemia-reperfusion in vivo through the caspase-1-GSDMD axis, providing a potential therapeutic option prevent hepatic IRI in pets.

Metabonomics Study on the hepatoprotective effect mechanism of polysaccharides from different processed products of Angelica Sinensis on the layer chickens based on UPLC-Q/TOF-MS/MS, multivariate statistical analysis and conjoint analysis

Chicken colibacillosis is one of the most severe diseases in the poultry industry. Ceftiofur sodium (CS) is often used to treat it in clinical practice and lipopolysaccharide (LPS) accumulates in the chicken's body. Previous experimental studies found that CS combined with LPS could induce liver injury in layer chickens, and polysaccharides from charred Angelica sinensis(CASP) had a better hepatoprotective effect than polysaccharides from unprocessed Angelica sinensis(UASP). However, the intervention mechanism was unclear. Thus, UPLC–Q/TOF–MS/MS‐based metabonomics and transcriptomics were used in this study to clarify the hepatoprotective effect mechanism of CASP and UASP in layer chickens. Transcriptomics and enzyme‐linked immunosorbent assay were used for biological verification of some critical mutual metabolic pathways screened with metabonomics. The comprehensive analysis results showed that in a layer chicken liver injury model built with LPS and CS, 12 critical metabolic pathways were disturbed, involving 10 important differential metabolites. The hepatoprotective effect mechanism of CASP is related to the arachidonic acid metabolism and mTOR signaling pathways, involving nine important differential metabolites. In contrast, the hepatoprotective effect mechanism of UASP is related to the arachidonic acid metabolism pathway, involving six important differential metabolites.

Augmenter of liver regeneration-mediated mitophagy protects against hepatic ischemia/reperfusion injury

Augmenter of liver regeneration (ALR) is an anti-apoptotic protein found mainly in mitochondria. It protects hepatocytes from ischemia-reperfusion (I/R) injury, but the underlying mechanism is not clear. We found that in rats, delivery of the ALR gene alleviated hepatic I/R injury during orthotopic liver transplantation as evidenced by reduced serum aminotransferase, oxidative stress and apoptosis, and increased expression of autophagy markers. In an in vitro hypoxia/reoxygenation (H/R) model, overexpression of the ALR gene activated autophagy and relieved defective mitophagy via the PINK1/Parkin pathway. Mechanistically, ALR transfection induced the expression of mitofusin 2 (Mfn2) in the H/R model, which led to PINK1 accumulation and mitochondrial translocation of Parkin. Deletion of Mfn2 abolished mitophagy activation induced by ALR transfection, promoted mitochondrial dysfunction, and eventually increased cell apoptosis. Mfn2 administration prevented the inhibition of mitophagy in ALR-knockout (KO) cells, thus attenuated mitochondrial dysfunction and cell apoptosis. In heterozygous ALR-knockout mice treated with a warm I/R injury, marked aggravation of liver injury was associated with mitophagy inhibition and reduction in Mfn2 expression. Taken together, our results confirm that ALR accelerated Parkin translocation and mitophagy via Mfn2, and protected hepatocytes from I/R-induced injury. Our findings provide a novel rationale for the treatment of hepatic I/R injury.

Rimonabant ameliorates hepatic ischemia/reperfusion injury in rats: Involvement of autophagy via modulating ERK- and PI3K/AKT-mTOR pathways

Hepatic ischemia/reperfusion (HIR), which can result in severe liver injury and dysfunction, is usually associated with autophagy and endocannabinoid system derangements. Whether or not the modulation of the autophagic response following HIR injury is involved in the hepatoprotective effect of the cannabinoid receptor 1(CB1R) antagonist rimonabant remains elusive and is the aim of the current study. Rats pre-treated with rimonabant (3 mg/kg) or vehicle underwent 30 min hepatic ischemia followed by 6 hrs. reperfusion. Liver injury was evaluated by serum ALT, AST, bilirubin (total and direct levels) and histopathological examination. The inflammatory, profibrotic and oxidative responses were investigated by assessing hepatic tumor necrosis factor α (TNFα), nuclear factor kappa B (NF-κB), transforming growth factor (TGF-β), lipid peroxidation and reduced glutathione. The hepatic levels of CB1R and autophagic markers p62, Beclin-1, and LC3 as well as the autophagic signaling inhibitors ERK1/2, PI3K, Akt and mTOR were also determined. Rimonabant significantly attenuated HIR-induced increases in hepatic injury, inflammation, profibrotic responses and oxidative stress and improved the associated pathological features. Rimonabant modulated the expression of p62, Beclin-1, and LC3, down-regulated CB1R, and dcreased pERK1/2, PI3K, Akt, and mTOR activities. The current study suggests that rimonabant can protect the liver from IR injury at least in part by inducing autophagy, probably by modulating ERK- and/or PI3K/AKT-mTOR signaling.

Characterizing Autophagy in the Cold Ischemic Injury of Small Bowel Grafts: Evidence from Rat Jejunum

Cold ischemic injury to the intestine during preservation remains an unresolved issue in transplantation medicine. Autophagy, a cytoplasmic protein degradation pathway, is essential for metabolic adaptation to starvation, hypoxia, and ischemia. It has been implicated in the cold ischemia (CI) of other transplantable organs. This study determines the changes in intestinal autophagy evoked by cold storage and explores the effects of autophagy on ischemic grafts. Cold preservation was simulated by placing the small intestines of Wistar rats in an IGL-1 (Institute George Lopez) solution at 4 °C for varying periods (3, 6, 9, and 12 h). The extent of graft preservation injury (mucosal and cellular injury) and changes in autophagy were measured after each CI time. Subsequently, we determined the differences in apoptosis and preservation injury after activating autophagy with rapamycin or inhibiting it with 3-methyladenine. The results revealed that ischemic injury and autophagy were induced by cold storage. Autophagy peaked at 3 h and subsequently declined. After 12 h of storage, autophagic expression was reduced significantly. Additionally, enhanced intestinal autophagy by rapamycin was associated with less tissue, cellular, and apoptotic damage during and after the 12-h long preservation. After reperfusion, grafts with enhanced autophagy still presented with less injury. Inhibiting autophagy exhibited the opposite trend. These findings demonstrate intestinal autophagy changes in cold preservation. Furthermore, enhanced autophagy was protective against cold ischemia-reperfusion damage of the small bowels.

The interrupted cross-talk of inflammatory and oxidative stress trajectories signifies the effect of artesunate against hepatic ischemia/reperfusion-induced inflammasomopathy

The antimalarial drug artesunate (Art) has proven its beneficial effects against ischemia/reperfusion (I/R) injury in diverse organs, but its potential role against hepatic I/R is still obscure. This study, hence, examined whether treatment with Art alone or in combination with rapamycin (Rapa), an mTOR inhibitor, can ameliorate hepatic I/R injury via targeting the NLRP3 inflammasome signaling pathway. Rats were divided into hepatic sham- and I/R-operated rats. The latter were either left untreated (I/R group) or treated with Art, Rapa, or their combination. On the molecular level, all treatment regimens succeeded to hinder inflammasome assembly and activation, assessed as NLRP3, ASC, cleaved caspase-1, caspase-11, N-terminal cleaved gasdermin-D (GSDMD-N), IL-1β, and IL-18. This effect was associated by the inhibition in the harmful signaling pathways HMGB1/RAGE and TLR4/MyD88/TRAF6 to inactivate the transcription factor NF-κB and the production of its pro-inflammatory cytokines IL-1β, IL-18, IL-6, and TNF-α. Additionally, this effect entailed the inhibition of ICAM-1/MPO/ROS cascade, which in turn hampered cell demise induced by apoptosis, manifested as correction of the imbalanced Bcl2/Bax, as well as pyroptosis (LDH, cleaved caspase-1, caspase-11, GSDMD-N, IL-1β, and IL-18), and necrosis. The corrected pathways were reflected on the improved liver function (serum ALT, AST, and LDH) and microscopical hepatic architecture. Noteworthy, the effect of Art on all parameters exceeded significantly that of Rapa and even improved the effect of the latter in the combination group. In conclusion, our results suggest novel roles for Art in abating functional and structural I/R-induced hepatic abnormalities via several traversing cross-talking pathways that succeeded to abate NLRP3 inflammasome and cell death.

Blocking GSDMD processing in innate immune cells but not in hepatocytes protects hepatic ischemia-reperfusion injury

Pyroptosis, a proinflammatory form of programmed cell death, plays important roles in the pathogenesis of many diseases. Inflammasome activation, which has been shown in hepatic ischemia-reperfusion injury (IRI), is demonstrated to be closely associated with pyroptosis, indicating that pyroptosis may occur and perform functions in hepatic IRI. However, there is no direct evidence showing the function of pyroptosis in hepatic IRI. In this study, by detecting the pyroptosis markers, we showed that pyroptosis may be induced during hepatic IRI. Furthermore, by adopting caspase-1 inhibitors, we showed that inhibition of pyroptosis could significantly ameliorate liver injury and suppress inflammatory response during hepatic IRI. Interestingly, caspase-1 inhibitors have no protective effects on in vitro hepatocytes under hypoxic reoxygenation condition. To investigate pyroptosis induced in which specific cell types may affect hepatic IRI, we generated hepatocyte-specific Gsdmd-knockout (Hep-Gsdmd-/-) and myeloid-specific Gsdmd-knockout (LysmCre+Gsdmdf/f) mice. Functional experiments showed that compared to control mice (Gsdmdf/f), there were alleviated liver injury and inflammation in LysmCre+Gsdmdf/f mice, but not in AlbCre+Gsdmdf/f mice. In parallel in vitro studies, cytokine expression and production decreased in bone-marrow-derived macrophages and Kupffer cells from LysmCre+Gsdmdf/f mice compared to their controls. Our findings demonstrated that pyroptosis in innate immune cells aggravates hepatic IRI and implied that hepatic IRI could be protected by blocking pyroptosis, which may become a potential therapeutic target in the clinic.

Remote Ischemic Preconditioning induces Cardioprotective Autophagy and Signals through the IL-6-Dependent JAK-STAT Pathway

Autophagy is a cellular process by which mammalian cells degrade and assist in recycling damaged organelles and proteins. This study aimed to ascertain the role of autophagy in remote ischemic preconditioning (RIPC)-induced cardioprotection. Sprague Dawley rats were subjected to RIPC at the hindlimb followed by a 30-min transient blockade of the left coronary artery to simulate ischemia reperfusion (I/R) injury. Hindlimb muscle and the heart were excised 24 h post reperfusion. RIPC prior to I/R upregulated autophagy in the rat heart at 24 h post reperfusion. In vitro, autophagy inhibition or stimulation prior to RIPC, respectively, either ameliorated or stimulated the cardioprotective effect, measured as improved cell viability to mimic the preconditioning effect. Recombinant interleukin-6 (IL-6) treatment prior to I/R increased in vitro autophagy in a dose-dependent manner, activating the Janus kinase/signal transducers and activators of transcription (JAK-STAT) pathway without affecting the other kinase pathways, such as p38 mitogen-activated protein kinases (MAPK), and glycogen synthase kinase 3 Beta (GSK-3β) pathways. Prior to I/R, in vitro inhibition of the JAK-STAT pathway reduced autophagy upregulation despite recombinant IL-6 pre-treatment. Autophagy is an essential component of RIPC-induced cardioprotection that may upregulate autophagy through an IL-6/JAK-STAT-dependent mechanism, thus identifying a potentially new therapeutic option for the treatment of ischemic heart disease.

Rapamycin Is Not Protective against Ischemic and Cisplatin-Induced Kidney Injury

Autophagy plays an important role in the pathogenesis of acute kidney injury (AKI). Although autophagy activation was shown to be associated with an increased lifespan and beneficial effects in various pathologies, the impact of autophagy activators, particularly, rapamycin and its analogues on AKI remains obscure. In our study, we explored the effects of rapamycin treatment in in vivo and in vitro models of ischemic and cisplatin-induced AKI. The impact of rapamycin on the kidney function after renal ischemia/reperfusion (I/R) or exposure to the nephrotoxic agent cisplatin was assessed by quantifying blood urea nitrogen and serum creatinine and evaluating the content of neutrophil gelatinase-associated lipocalin, a novel biomarker of AKI. In vitro experiments were performed on the primary culture of renal tubular cells (RTCs) that were subjected to oxygen-glucose deprivation (OGD) or incubated with cisplatin under various rapamycin treatment protocols. Cell viability and proliferation were estimated by the MTT assay and real-time cell analysis using an RTCA iCELLigence system. Although rapamycin inhibited mTOR (mammalian target of rapamycin) signaling, it failed to enhance the autophagy and to ameliorate the severity of AKI caused by ischemia or cisplatin-induced nephrotoxicity. Experiments with RTCs demonstrated that rapamycin exhibited the anti-proliferative effect in primary RTCs cultures but did not protect renal cells exposed to OGD or cisplatin. Our study revealed for the first time that the mTOR inhibitor rapamycin did not prevent AKI caused by renal I/R or cisplatin-induced nephrotoxicity and, therefore, cannot be considered as an ideal mimetic of the autophagy-associated nephroprotective mechanisms (e.g., those induced by caloric restriction), as it had been suggested earlier. The protective action of such approaches like caloric restriction might not be limited to mTOR inhibition and can proceed through more complex mechanisms involving alternative autophagy-related targets. Thus, the use of rapamycin and its analogues for the treatment of various AKI forms requires further studies in order to understand potential protective or adverse effects of these compounds in different contexts.

Therapeutic targets for liver regeneration after acute severe injury: a preclinical overview

Introduction: Liver transplantation is the only viable treatment with a proven survival benefit for acute liver failure (ALF). Donor organ shortage is, however, a major hurdle; hence, alternative approaches that enable liver regeneration and target acute severe hepatocellular damage are necessary.Areas covered: This article sheds light on therapeutic targets for liver regeneration and considers their therapeutic potential. ALF following extensive hepatocyte damage and small-for-size syndrome (SFSS) are illuminated for the reader while the molecular mechanisms of liver regeneration are assessed in accordance with relevant therapeutic strategies. Furthermore, liver background parameters and predictive biomarkers that might associate with liver regeneration are reviewed.Expert opinion: There are established and novel experimental strategies for liver regeneration to prevent ALF resulting from SFSS. Granulocyte-colony stimulating factor (G-CSF) is a promising agent targeting liver regeneration after acute severe injury. Autophagy and hepatocyte senescence represent attractive new targets for liver regeneration in acute severe hepatic injury. Liver support strategies, including tissue engineering, constitute novel regenerative means; the success of this is dependent on stem cell research advances. However, there is no firm clinical evidence that these supportive strategies may alleviate hepatocellular damage until liver transplantation becomes available or successful self-liver regeneration occurs.

Transcriptional changes during hepatic ischemia-reperfusion in the rat

There are few effective targeted strategies to reduce hepatic ischemia-reperfusion (IR) injury, a contributor to poor outcomes in liver transplantation recipients. It has been proposed that IR injury is driven by the generation of reactive oxygen species (ROS). However, recent studies implicate other mediators of the injury response, including mitochondrial metabolic dysfunction. We examined changes in global gene expression after transient hepatic ischemia and at several early reperfusion times to identify potential targets that could be used to protect against IR injury. Male Wistar rats were subjected to 30 minutes of 70% partial warm ischemia followed by 0, 0.5, 2, or 6 hours of reperfusion. RNA was extracted from the reperfused and non-ischemic lobes at each time point for microarray analysis. Identification of differentially expressed genes and pathway analysis were used to characterize IR-induced changes in the hepatic transcriptome. Changes in the reperfused lobes were specific to the various reperfusion times. We made the unexpected observation that many of these changes were also present in tissue from the paired non-ischemic lobes. However, the earliest reperfusion time, 30 minutes, showed a marked increase in the expression of a set of immediate-early genes (c-Fos, c-Jun, Atf3, Egr1) that was exclusive to the reperfused lobe. We interpreted these results as indicating that this early response represented a tissue autonomous response to reperfusion. In contrast, the changes that occurred in both the reperfused and non-ischemic lobes were interpreted as indicating a non-autonomous response resulting from hemodynamic changes and/or circulating factors. These tissue autonomous and non-autonomous responses may serve as targets to ameliorate IR injury.

Protective Role of mTOR in Liver Ischemia/Reperfusion Injury: Involvement of Inflammation and Autophagy

Liver ischemia/reperfusion (IR) injury is a common phenomenon after liver resection and transplantation, which often results in liver graft dysfunction such as delayed graft function and primary nonfunction. The mammalian target of rapamycin (mTOR) is an evolutionarily highly conserved serine/threonine protein kinase, which coordinates cell growth and metabolism through sensing environmental inputs under physiological or pathological conditions, involved in the pathophysiological process of IR injury. In this review, we mainly present current evidence of the beneficial role of mTOR in modulating inflammation and autophagy under liver IR to provide some evidence for the potential therapies for liver IR injury.

Spermidine ameliorates liver ischaemia-reperfusion injury through the regulation of autophagy by the AMPK-mTOR-ULK1 signalling pathway

BACKGROUND

Hepatic ischaemia-reperfusion (IR) injury is a common clinical challenge lacking effective therapy. The aim of this study was to investigate whether spermidine has protective effects against hepatic IR injury through autophagy.

METHODS

Liver ischaemia reperfusion was induced in male C57BL/6 mice. Then, liver function, histopathology, cytokine production and immunofluorescence were evaluated to assess the impact of spermidine pre-treatment on IR-induced liver injury. Autophagosome formation was observed by transmission electron microscopy. Western blotting was used to explore the underlying mechanism and its relationship with autophagy, and TUNEL staining was conducted to determine the relationship between apoptosis and autophagy in the ischaemic liver.

RESULTS

The results of the transaminase assay, histopathological examination, and pro-inflammatory cytokine production and immunofluorescence evaluations demonstrated that mice pre-treated with spermidine showed significantly preserved liver function. Further experiments demonstrated that mice administered spermidine before the induction of IR exhibited increased autophagy via the AMPK-mTOR-ULK1 pathway, and TUNEL staining revealed that spermidine attenuated IR-induced apoptosis in the liver.

CONCLUSIONS

Our results provide the first line of evidence that spermidine provides protection against IR-induced injury in the liver by regulating autophagy through the AMPK-mTOR-ULK1 signalling pathway. These results suggest that spermidine may be beneficial for hepatic IR injury.

De-bugging the system: could antibiotics improve liver transplant outcomes?

Organ transplantation is now a preferred treatment for end-stage organ failure. Among the challenges for ensuring excellent clinical outcomes for transplant recipients is good initial allograft function at the time of organ implantation. This is determined in part by the functional status of the donor and donor organ, functional status of the recipient, and conduct of the operative procedure. Despite optimization of these variables, organ transplantation is still often plagued by substantial initial dysfunction, variably referred to as slow or delayed graft function, or in the most extreme cases, primary graft nonfunction necessitating urgent regrafting. In this issue of the JCI, Nakamura, Kageyama, Ito, Hirao, and colleagues investigate a potential role for the recipient's microbiome in determining graft function after liver transplantation and demonstrate the benefits of antibiotic pretreatment in both a mouse model and in human patients.

Antibiotic pretreatment alleviates liver transplant damage in mice and humans

Although modifications of gut microbiota with antibiotics (Abx) influence mouse skin and cardiac allografts, its role in orthotopic liver transplantation (OLT) remains unknown. We aimed to determine whether and how recipient Abx pretreatment may affect hepatic ischemia-reperfusion injury (IRI) and OLT outcomes. Mice (C57BL/6) with or without Abx treatment (10 days) were transplanted with allogeneic (BALB/c) cold-stored (18 hours) livers, followed by liver and blood sampling (6 hours). We divided 264 human OLT recipients on the basis of duration of pre-OLT Abx treatment into control (Abx-free/Abx <10 days; n = 108) and Abx treatment (Abx ≥10days; n = 156) groups; OLT biopsy (Bx) samples were collected 2 hours after OLT (n = 52). Abx in mice mitigated IRI-stressed OLT (IRI-OLT), decreased CCAAT/enhancer-binding protein homologous protein (CHOP) (endoplasmic reticulum [ER] stress), enhanced LC3B (autophagy), and inhibited inflammation, whereas it increased serum prostaglandin E2 (PGE2) and hepatic PGE2 receptor 4 (EP4) expression. PGE2 increased EP4, suppressed CHOP, and induced autophagosome formation in hepatocyte cultures in an EP4-dependent manner. An EP4 antagonist restored CHOP, suppressed LC3B, and recreated IRI-OLT. Remarkably, human recipients of Abx treatment plus OLT (Abx-OLT), despite severe pretransplantation clinical acuity, had higher EP4 and LC3B levels but lower CHOP levels, which coincided with improved hepatocellular function (serum aspartate aminotransferase/serum aspartate aminotransferase [sALT/sAST]) and a decreased incidence of early allograft dysfunction (EAD). Multivariate analysis identified "Abx-free/Abx <10 days" as a predictive factor of EAD. This study documents the benefits of Abx pretreatment in liver transplant recipients, identifies ER stress and autophagy regulation by the PGE2/EP4 axis as a homeostatic underpinning, and points to the microbiome as a therapeutic target in OLT.

Combined ischemic and rapamycin preconditioning alleviated liver ischemia and reperfusion injury by restoring autophagy in aged mice

Old livers are more damaged by hepatic ischemia and reperfusion (IR) injury than young livers. The aim of this study was to investigate the effects of ischemic and rapamycin preconditioning on IR injury in old livers. Young (8-week-old) and aged (60-week-old) mice were subjected to IR or a sham control procedure. The aged mice were randomly divided into six groups: IR (CON), IR with ischemic preconditioning (IPC), IR with rapamycin preconditioning (RAPA), IR with combined ischemic and rapamycin preconditioning (IPC + RAPA), IR with 3-methyladenine (3-MA), IR with combined ischemic and rapamycin preconditioning with 3-MA pretreatment (IPC + RAPA+3-MA). Liver injury was evaluated 6 h after reperfusion. Hepatocellular autophagy induction was also analyzed by western blotting. The results revealed that aged mice had aggravated liver IR injury as compared to young mice. In aged mice following IR, IPC + RAPA but not IPC or RAPA alleviated liver injury, as evidenced by lower levels of serum ALT, improved preservation of liver architecture with lower Suzuki scores, and decreased caspase-3 activity compared with CON. In addition, western blot analysis revealed increased LC3B II but decreased p62 protein expression levels in the IPC + RAPA group, indicating that autophagic flux was restored by combined ischemic and rapamycin preconditioning. Furthermore, autophagy inhibition by the inhibitor 3-MA abrogated the protective role in the IPC + RAPA group, while no significant effects were observed in the CON group. In conclusions, our results demonstrated that combined ischemic and rapamycin preconditioning protected old livers against IR injury, which was likely attributed to restored autophagy activation.

Inhibition of Autophagy Attenuated Intestinal Injury After Intestinal I/R via mTOR Signaling

BACKGROUND

Intestinal ischemia/reperfusion (I/R) is a grave condition related to high morbidity and mortality. Autophagy, which can induce a new cell death named type II programmed cell death, has been reported in some intestinal diseases, but little is known in I/R-induced intestinal injury. In this study, we aimed to explore the role of autophagy in intestinal injury induced by I/R and its potential mechanisms.

MATERIALS AND METHODS

The rats pretreated with rapamycin or 3-methyladenine had intestinal I/R injury. After reperfusion, intestinal injury was measured by Chiu's score, intestinal mucosal wet-to-dry ratio, and lactic acid level. Intestinal mucosal oxidative stress level was measured by malondialdehyde and superoxide dismutase. Autophagosome, LC3, and p62 were detected to evaluate autophagy level. Mammalian target of rapamycin (mTOR) was detected to explore potential mechanism.

RESULTS

Chiu's score, intestinal mucosal wet-to-dry ratio, lactic acid level, malondialdehyde level, autophagosomes, and LC3-II/LC3-I were significantly increased, and superoxide dismutase level and expression of p62 were significantly decreased in intestinal mucosa after intestinal ischemia/reperfusion. Pretreatment with rapamycin significantly aggravated intestinal injury evidenced by increased Chiu's score, intestinal mucosal wet-to-dry ratio and lactic acid level, increased autophagy level evidenced by increased autophagosomes and LC3-II/LC3-I and decreased expression of p62, and downregulated expression of p-mTOR/mTOR. On the contrary, pretreatment with 3-methyladenine significantly attenuated intestinal injury and autophagy level and upregulated expression of p-mTOR/mTOR.

CONCLUSIONS

In summary, autophagy was significantly enhanced in intestinal mucosa after intestinal ischemia/reperfusion, and inhibition of autophagy attenuated intestinal injury induced by I/R through activating mTOR signaling.

Sulfuretin protects hepatic cells through regulation of ROS levels and autophagic flux

Palmitate (PA) exposure induces stress conditions featuring ROS accumulation and upregulation of p62 expression, resulting in autophagic flux blockage and cell apoptosis. Sulfuretin (Sul) is a natural product isolated from Rhus verniciflua Stokes; the cytoprotective effect of Sul on human hepatic L02 cells and mouse primary hepatocytes under PA-induced stress conditions was investigated in this study. Sul induced mitophagy by activation of p-TBK1 and LC3 and produced a concomitant decline in p62 expression. Autophagosome formation and mitophagy were assessed by the sensitive dual fluorescence reporter mCherry-EGFP-LC3B, and mitochondrial fragmentation was analyzed using MitoTracker Deep Red FM. A preliminary structure-activity relationship (SAR) for Sul was also investigated, and the phenolic hydroxyl group was found to be pivotal for maintaining the cytoprotective bioactivity of Sul. Furthermore, experiments using flow cytometry and western blots revealed that Sul reversed the cytotoxic effect stimulated by the autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ), and its cytoprotective effect was almost eliminated when the autophagy-related 5 (Atg5) gene was knocked down. These studies suggest that, in addition to its antioxidative effects, Sul stimulates mitophagy and restores impaired autophagic flux, thus protecting hepatic cells from apoptosis, and that Sul has potential future medical applications for hepatoprotection.

Vinyl chloride-induced interaction of nonalcoholic and toxicant-associated steatohepatitis: Protection by the ALDH2 activator Alda-1

Vinyl chloride (VC), an abundant environmental contaminant causes steatohepatitis at high levels, but is considered safe at lower (i.e., sub-OSHA) levels. However, we have previously shown that even lower VC levels exacerbate experimental nonalcoholic fatty liver disease (NAFLD) caused by high-fat diet (HFD). Mitochondrial oxidative injury and subsequent metabolic dysfunction appeared to play key roles in mediating this interaction. Mitochondrial aldehyde dehydrogenase 2 (ALDH2) serves as a key line of defense against endogenous and exogenous reactive aldehydes. The current study therefore tests the hypothesis that allosteric activation of ALDH2 with Alda-1 will protect against VC-enhanced NAFLD. Mice were exposed to low VC concentrations (<1 ppm), or room air for 6 h/day, 5 days/week for 12 weeks, while on HFD or low-fat control diet (LFD). Some mice received Alda-1 (20 mg/kg i.p., 3 × /week) for the last 3 weeks of diet/VC exposure. Indices of liver injury, oxidative stress, metabolic and mitochondrial (dys)function were measured. As observed previously, low-dose VC did not cause liver injury in control mice; while liver injury caused by HFD was enhanced by VC. VC decreased hepatic ALDH2 activity of mice fed HFD. Alda-1 attenuated oxidative stress, liver injury, and dysmetabolism in mice exposed to HFD+VC under these conditions. Importantly, alterations in mitochondrial function caused by VC and HFD were diminished by Alda-1. Previous studies have indicated that liver injury caused by HFD is mediated, at least in part, by enhanced mitochondrial autophagy (mitophagy). Here, Alda-1 suppressed PINK1/PARKIN-mediated mitophagy. Taken together, these results support the hypothesis that ALDH2 is a critical defense against mitochondrial injury caused by VC in experimental NAFLD. The ALDH2 activator Alda-1 conferred protection against liver damage under these conditions, most likely via increasing clearance of aldehydes and preserving mitochondrial respiratory function.

•

VC, combined with HFD impairs ALDH2 function, causing an accumulation of endogenous aldehydes and oxidative stress in vivo.

•

VC metabolite chloroacetaldehyde directly blocks ALDH2 activity in vitro.

•

Alda-1 treatment reverses pre-established liver injury, oxidative stress and metabolic dysregulation caused by VC and HFD.

•

Alda-1 increases overall autophagy caused by VC+HFD, but decreases mitophagy, likely to preserve mitochondrial function.

Snapshot: Implications for mTOR in Aging-related Ischemia/Reperfusion Injury

Aging may aggravate the damage and dysfunction of different components of multiorgan and thus increasing multiorgan ischemia/reperfusion (IR) injury. IR injury occurs in many organs and tissues, which is a major cause of morbidity and mortality worldwide. The kinase mammalian target of rapamycin (mTOR), an atypical serine/threonine protein kinase, involves in the pathophysiological process of IR injury. In this review, we first briefly introduce the molecular features of mTOR, the association between mTOR and aging, and especially its role on autophagy. Special focus is placed on the roles of mTOR during ischemic and IR injury. We then clarify the association between mTOR and conditioning phenomena. Following this background, we expand our discussion to potential future directions of research in this area. Collectively, information reviewed herein will serve as a comprehensive reference for the actions of mTOR in IR injury and may be significant for the design of future research and increase the potential of mTOR as a therapeutic target.

Comprehensive circRNA expression profile during ischemic postconditioning attenuating hepatic ischemia/reperfusion injury

Ischemic postconditioning (IPO) attenuates hepatic ischemia/reperfusion (I/R) injury. The aim of this study was to explore the role of circular RNAs (circRNAs) in the protective mechanism of IPO. In this study, microarray hybridization analysis was performed to determine the circRNA expression profile. Briefly, a total of 1599 dysregulated circRNAs were detected. The competitive endogenous RNA (ceRNA) network, including 6 circRNAs, 47 miRNAs and 90 mRNAs, indicated that the potential “housekeeping” function of circRNAs is dysregulated in hepatic I/R injury. Based on the validation results of selected circRNAs, miRNAs and mRNAs following qRT-PCR amplification, the mmu_circRNA_005186-miR-124-3p-Epha2 pathway was constructed. Dual-luciferase reporter analysis showed that miR-124-3p interacted directly with mmu_circRNA_005186 and Epha2 through the predicted binding sites, which suggested that mmu_circRNA_005186, serving as a miRNA sponge for miR-124-3p, regulated the expression of Epha2. Functionally, we explored the mechanism of mmu_circRNA_005186 in LPS-treated RAW264.7 cells which simulated the inflammation in hepatic I/R injury. We found that mmu_circRNA_005186 silencing attenuated the LPS-induced inflammation and was associated with miR-124-3p upregulation and Epha2 downregulation. Our study is the first to show that circRNAs are closely related to hepatic I/R injury and IPO and suggests that targeting mmu_circRNA_005186-miR-124-3p-Epha2 pathway might attenuate hepatic I/R injury.

Rapamycin treatment increases hippocampal cell viability in an mTOR-independent manner during exposure to hypoxia mimetic, cobalt chloride

BACKGROUND

Cobalt chloride (CoCl2) induces chemical hypoxia through activation of hypoxia-inducible factor-1 alpha (HIF-1α). Mammalian target of rapamycin (mTOR) is a multifaceted protein capable of regulating cell growth, angiogenesis, metabolism, proliferation, and survival. In this study, we tested the efficacy of a well-known mTOR inhibitor, rapamycin, in reducing oxidative damage and increasing cell viability in the mouse hippocampal cell line, HT22, during a CoCl2-simulated hypoxic insult.

RESULTS

CoCl2 caused cell death in a dose-dependent manner and increased protein levels of cleaved caspase-9 and caspase-3. Rapamycin increased viability of HT22 cells exposed to CoCl2 and reduced activation of caspases-9 and -3. Cells exposed to CoCl2 displayed increased reactive oxygen species (ROS) production and hyperpolarization of the mitochondrial membrane, both of which rapamycin successfully blocked. mTOR protein itself, along with its downstream signaling target, phospho-S6 ribosomal protein (pS6), were significantly inhibited with CoCl2 and rapamycin addition did not significantly lower expression further. Rapamycin promoted protein expression of Beclin-1 and increased conversion of microtubule-associated protein light chain 3 (LC3)-I into LC3-II, suggesting an increase in autophagy. Pro-apoptotic protein, Bcl-2 associated × (Bax), exhibited a slight, but significant decrease with rapamycin treatment, while its anti-apoptotic counterpart, B cell lymphoma-2 (Bcl-2), was to a similar degree upregulated. Finally, the protein expression ratio of phosphorylated mitogen-activated protein kinase (pMAPK) to its unphosphorylated form (MAPK) was dramatically increased in rapamycin and CoCl2 co-treated cells.

CONCLUSIONS

Our results indicate that rapamycin confers protection against CoCl2-simulated hypoxic insults to neuronal cells. This occurs, as suggested by our results, independent of mTOR modification, and rather through stabilization of the mitochondrial membrane with concomitant decreases in ROS production. Additionally, inhibition of caspase-9 and -3 activation and stimulation of protective autophagy reduces cell death, while a decrease in the Bax/Bcl-2 ratio and an increase in pMAPK promotes cell survival during CoCl2 exposure. Together these results demonstrate the therapeutic potential of rapamycin against hypoxic injury and highlight potential pathways mediating the protective effects of rapamycin treatment.

Alda-1 Ameliorates Liver Ischemia-Reperfusion Injury by Activating Aldehyde Dehydrogenase 2 and Enhancing Autophagy in Mice

Aldehyde dehydrogenase 2 (ALDH2) is a key enzyme for metabolism of reactive aldehydes, but its role during liver ischemia-reperfusion injury (IRI) remains unclear. In the present study, we investigated the effects of the ALDH2 activator, Alda-1, in liver IRI and elucidated the underlying mechanisms. Mice were pretreated with Alda-1 and subjected to a 90 min hepatic 70% ischemia model, and liver tissues or serum samples were collected at indicated time points after reperfusion. We demonstrated that Alda-1 pretreatment had a hepatoprotective role in liver IRI as evidenced by decreased liver necrotic areas, serum ALT/AST levels, and liver inflammatory responses. Mechanistically, Alda-1 treatment enhanced ALDH2 activity and subsequently reduced the accumulation of reactive aldehydes and toxic protein adducts, which result in decreased hepatocyte apoptosis and mitochondrial dysfunction. We further demonstrated that Alda-1 treatment could activate AMPK and autophagy and that AMPK activation was required for Alda-1-mediated autophagy enhancement. These findings collectively indicate that Alda-1-mediated ALDH2 activation could be a promising strategy to improve liver IRI by clearance of reactive aldehydes and enhancement of autophagy.

Rapamycin induces the expression of heme oxygenase-1 and peroxyredoxin-1 in normal hepatocytes but not in tumorigenic liver cells

Rapamycin (sirolimus) is employed as an immunosuppressant following liver transplant, to inhibit the re-growth of cancer cells following liver resection for hepatocellular carcinoma (HCC), and for the treatment of advanced HCC. Rapamycin also induces the expression of antioxidant enzymes in the liver, suggesting that pretreatment with the drug could provide a potential strategy to reduce ischemia reperfusion injury following liver surgery. The aim of this study was to further investigate the actions of rapamycin in inducing expression of the antioxidant enzymes heme oxygenase-1 (HO-1) and peroxiredoxin-1 (Prx-1) in normal liver and in tumorigenic liver cells. A rat model of segmental hepatic ischemia and reperfusion, cultured freshly-isolated rat hepatocytes, and tumorigenic H4IIE rat liver cells in culture were employed. Expression of HO-1 and Prx-1 was measured using quantitative PCR and western blot. Rapamycin pre-treatment of normal liver in vivo or normal hepatocytes in vitro led to a substantial induction of mRNA encoding HO-1 and Prx-1. The dose-response curve for the action of rapamycin on mRNA expression was biphasic, showing an increase in expression at 0 - 0.1 μM rapamycin but a decrease from maximum at concentrations greater than 0.1 μM. By contrast, in H4IIE cells, rapamycin inhibited the expression of HO-1 and Prx-1 mRNA. Oltipraz, an established activator of transcription factor Nrf2, caused a large induction of HO-1 and Prx-1 mRNA. The dose response curve for the inhibition by rapamycin of HO-1 and Prx-4 mRNA expression, determined in the presence of oltipraz, was monophasic with half maximal inhibition at about 0.01 μM. It is concluded that, at concentrations comparable to those used clinically, pre-treatment of the liver with rapamycin induces the expression of HO-1 and Prx-1. However, the actions of rapamycin on the expression of these two antioxidant enzymes in normal hepatocytes are complex and, in tumorigenic liver cells, differ from those in normal hepatocytes. Further studies are warranted to evaluate preconditioning the livers of patients subject to liver resection or liver transplant with rapamycin as a viable strategy to reduce IR injury following liver surgery.

Regulatory effect of immunosuppressive agents in mice with renal ischemia reperfusion injury

This study was designed to investigate the regulatory effect of rapamycin in mice with renal ischemia-reperfusion injury. A total of 100 mice were randomly divided into normal control, sham operation, model and experimental groups with 25 rats in each group. Mice in the experimental group were subjected to rapamycin gavage. Mice in each group were sacrificed 24 h after operation. Then, blood, spleen and left kidney were collected. PAS staining was used for semi-quantitative analysis of renal pathological injury. Serum creatinine (SCr) and blood urea nitrogen (BUN) levels were measured. TUNEL method was used to detect cell apoptosis. Flow cytometry was used to detect the percentage of NKT cells. The expression of CXC chemokine ligand 10 (CXCL10), hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) mRNA were detected by RT-qPCR. Semi-quantitative scoring of renal pathological injury showed that pathological injury score of the experimental group was significantly lower than that of the model group (p<0.05). Serum levels of SCr and BUN in the experimental group was compared to those in the model group (p<0.05). The number of apoptotic cells in the experimental group was compared to that of the model group (p<0.05). The percentage of NKT cells in the experimental group was compared to that of the model group (p<0.05). The percentage of NKT cells was significantly higher in the kidney and peripheral blood of the experimental group than that in the model group (p<0.05). The expression levels of HIF-1α and VEGF mRNA in the model and experimental groups were significantly lower in the experimental group than those in the model group (p<0.05). The expression levels of CXCL10 mRNA in the model and experimental groups were significantly higher in the experimental group than those in the model group (p<0.05). The results indicated that rapamycin can significantly upregulate the expression level of CXCL9 and promote the accumulation of NKT cells in kidney from spleen through peripheral blood. Rapamycin can also inhibit the HIF-1α expression level and protect renal ischemia-reperfusion injury.

Heme oxygenase-1 regulates sirtuin-1-autophagy pathway in liver transplantation: From mouse to human

Liver ischemia-reperfusion injury (IRI) represents a major risk factor of early graft dysfunction and a key obstacle to expanding the donor pool in orthotopic liver transplantation (OLT). Although graft autophagy is essential for resistance against hepatic IRI, its significance in clinical OLT remains unknown. Despite recent data identifying heme oxygenase-1 (HO-1) as a putative autophagy inducer, its role in OLT and interactions with sirtuin-1 (SIRT1), a key autophagy regulator, have not been studied. We aimed to examine HO-1-mediated autophagy induction in human OLT and in a murine OLT model with extended (20 hours) cold storage, as well as to analyze the requirement for SIRT1 in autophagy regulation by HO-1. Fifty-one hepatic biopsy specimens from OLT patients were collected under an institutional review board protocol 2 hours after portal reperfusion, followed by Western blot analyses. High HO-1 levels correlated with well-preserved hepatocellular function and enhanced SIRT1/LC3B expression. In mice, HO-1 overexpression by genetically modified HO-1 macrophage therapy was accompanied by decreased OLT damage and increased SIRT1/LC3B expression, whereas adjunctive inhibition of SIRT1 signaling diminished HO-1-mediated hepatoprotection and autophagy induction. Our translational study confirms the clinical relevance of HO-1 cytoprotection and identifies SIRT1-mediated autophagy pathway as a new essential regulator of HO-1 function in IR-stressed OLT.

Stat3-Atg5 signal axis inducing autophagy to alleviate hepatic ischemia-reperfusion injury

In performing our experiment, impaired autophagy increased hepatocellular damage during the reperfusion period. It was demonstrated by the effect of blocking autophagy using bafilomycin A1 or knocking Atg5 gene out reduces the anti-apoptotic effect of Stat3. Here we focus on the role of signal transducer and activator of transcription 3 (Stat3) in regulating autophagy to alleviate hepatic IRI. We found that Stat3 was up-regulated during hepatic IRI and was associated with an activation of the autophagic signaling pathway. This increased Stat3 expression, which was allied with high autophagic activity, alleviated liver damage to IR, an effect which was abrogated by Stat3 epletion as demonstrated in both in vivo and in vitro methods. The levels of Atg5 protein were decreased when Stat3 was inhibited by HO 3867 or siStat3. We conclude that Stat3 appeared to exert a pivotal role in hepatic IRI, by activating autophagy to alleviate hepatic IRI, and Atg5 was required for this process. The identification of this novel pathway, that links expression levels of Stat3 with Atg5-mediated autophagy, may provide new insights for the generation of novel protective therapies directed against hepatic IRI.

Biochemical targets of drugs mitigating oxidative stress via redox-independent mechanisms

Acute or chronic oxidative stress plays an important role in many pathologies. Two opposite approaches are typically used to prevent the damage induced by reactive oxygen and nitrogen species (RONS), namely treatment either with antioxidants or with weak oxidants that up-regulate endogenous antioxidant mechanisms. This review discusses options for the third pharmacological approach, namely amelioration of oxidative stress by 'redox-inert' compounds, which do not inactivate RONS but either inhibit the basic mechanisms leading to their formation (i.e. inflammation) or help cells to cope with their toxic action. The present study describes biochemical targets of many drugs mitigating acute oxidative stress in animal models of ischemia-reperfusion injury or N-acetyl-p-aminophenol overdose. In addition to the pro-inflammatory molecules, the targets of mitigating drugs include protein kinases and transcription factors involved in regulation of energy metabolism and cell life/death balance, proteins regulating mitochondrial permeability transition, proteins involved in the endoplasmic reticulum stress and unfolded protein response, nuclear receptors such as peroxisome proliferator-activated receptors, and isoprenoid synthesis. The data may help in identification of oxidative stress mitigators that will be effective in human disease on top of the current standard of care.

Isoflurane Preconditioning Alleviated Murine Liver Ischemia and Reperfusion Injury by Restoring AMPK/mTOR-Mediated Autophagy

BACKGROUND

Isoflurane has a pharmacological preconditioning effect against ischemia injury in the heart, kidney, and brain, but whether and how isoflurane preconditioning protects livers against ischemia and reperfusion (IR) injury is unclear.

METHODS

Mice were randomly divided into an isoflurane preconditioning (ISO) group and control group, receiving 1.5% isoflurane or carrier gas for 40 minutes, respectively (n = 8/group). A partial warm liver IR model was used, and liver injury was evaluated. Primary hepatocytes were pretreated with 1.5% isoflurane for 2 hours before the induction of cell death by hydrogen peroxide. Cell death and survival were evaluated with the lactate dehydrogenase and cell counting kit-8 assay. Autophagy and regulatory molecules in stressed livers and hepatocytes were analyzed by Western blot (n = 6/group). An autophagy inhibitor (3-methyladenine [3-MA]) and 5' adenosine monophosphate-activated protein kinase (AMPK) inhibitor (dorsomorphin) were administered in vivo (n = 8/group) and in vitro (n = 6/group).

RESULTS

Compared to that observed in the control group, mice in the ISO group showed reduced liver injury (alanine aminotransferase [ALT] levels, control versus ISO group, 8285 ± 769 vs 4896 ± 917 U/L, P < .001) and enhanced hepatocellular antiapoptosis in livers after IR. Furthermore, liver autophagy was restored by ISO as indicated by elevated LC3B II protein levels accompanied with increased p62 degradation. The in vitro study of primary hepatocytes also found that ISO effectively attenuated hepatocyte cell death induced by hydrogen peroxide. In addition, 3-MA pretreatment showed no significant influence in the control group, but abrogated the protective role of ISO both in stressed livers (ALT levels, phosphate-buffered saline + ISO versus 3-MA + ISO group, 5081 ± 294 vs 8663 ± 607 U/L, P < .001) and in hepatocytes. Finally, signaling pathway analysis demonstrated that AMPK was activated by ISO. Pretreatment with an AMPK inhibitor also abrogated liver protection by ISO (ALT levels, phosphate-buffered saline + ISO versus dorsomorphin [DOR] + ISO group, 5081 ± 294 vs 8710 ± 500 U/L, P < .001), with no significant effect in control mice.

CONCLUSIONS

Our results indicate that isoflurane preconditioning attenuates liver IR injury via AMPK/mTOR-mediated hepatocellular autophagy restoration. Our findings provide a novel potential therapeutic strategy for managing liver IR injury.

The triterpenoid CDDO-imidazolide ameliorates mouse liver ischemia-reperfusion injury through activating the Nrf2/HO-1 pathway enhanced autophagy

Nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated induction of antioxidants has been implicated to have protective roles in ischemia-reperfusion (I/R) injury in many animal models. However, the in vivo effects of CDDO-imidazole (CDDO-Im) (1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl] imidazole), a Nrf2 activator, in hepatic I/R injury is lacking and its exact molecular mechanisms are still not very clear. The goals of this study were to determine whether CDDO-Im can prevent liver injury induced by I/R in the mouse, and to elucidate the molecular target of drug action. Mice were randomly equally divided into two groups and administered intraperitoneally with either DMSO control or CDDO-Im (2 mg/kg) 3 h before subjected to 90-min hepatic 70% ischemia followed by reperfusion. Subsequently, the Liver and blood samples of these mice were collected to evaluate liver injury. CDDO-Im pretreatment markedly improve hepatic I/R injury by attenuating hepatic necrosis and apoptosis, reducing reactive oxygen species (ROS) levels and inflammatory responses, and ameliorating mitochondrial dysfunction. Mechanistically, by using Nrf2 Knockout mice and hemeoxygenase 1 (HO-1) inhibitor, we found that these CDDO-Im protection effects are attributed to enhanced autophagy, which is mediated by activating Nrf2/HO-1 pathway. By accelerating autophagy and clearance of damaged mitochondria, CDDO-Im reduced the mtDNA release and ROS overproduction, and in turn decreased damage-associated molecular patterns induced inflammatory responses and the following secondary liver injury. These results indicate that by enhancing autophagy, CDDO-Im-mediated activation of Nrf2/HO-1 signaling could be a novel therapeutic strategy to minimize the adverse effects of hepatic I/R injury.

Stimulation of autophagy prevents intestinal mucosal inflammation and ameliorates murine colitis

BACKGROUND AND PURPOSE

Defective autophagy contributes to the pathogenesis of inflammatory disorders such as inflammatory bowel disease and there are interactions between autophagy and inflammation. Here we have analysed the effects of autophagy stimulators on murine colitis.

EXPERIMENTAL APPROACH

Mice were treated with intrarectal administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) (3.5 mg·20 g^-1 ) and body weight was measured daily. Histological damage was scored 2 or 4 days after treatment. Some mice received trehalose (3% in drinking water 3 weeks before TNBS administration) or a daily administration of rapamycin (1.25 mg·kg^-1 , i.p.), betanin (1 g·kg^-1 , i.p.) or betanin + 3-methyladenine (3MA) (10 mg·kg^-1 , i.p.). Protein levels of p-mTOR, p62, LC3, BCL10, NFκB, IκBα and p-IκBα in mucosa were determined by Western blots and mRNA expression of TNFα, IL1β, IL6, IL10, COX2, CCR7, CD11c, inducible NOS and CD86 by qRT-PCR.

KEY RESULTS

Impaired autophagy associated with body weight loss and intestinal damage was detected in the mucosa of TNBS-treated mice. Administration of trehalose, rapamycin or betanin prevented the impaired autophagic flux induced by TNBS and decreased mucosal protein levels of BCL10, p-IκBα and NFκB-p65 and the expression of pro-inflammatory cytokines and M1 macrophage markers. Blockade of autophagosome formation by treatment with 3MA, prevented the reduction in protein levels of p62, BCL10, p-IκBα and NFκB-p65 induced by betanin in TNBS-treated mice and weakened the protective effects of betanin on murine colitis.

CONCLUSIONS AND IMPLICATIONS

Pharmacological stimulation of mucosal autophagy reduced intestinal inflammation and improved murine colitis.

Innate Immune Regulations and Liver Ischemia-Reperfusion Injury

Liver ischemia reperfusion activates innate immune system to drive the full development of inflammatory hepatocellular injury. Damage-associated molecular patterns (DAMPs) stimulate myeloid and dendritic cells via pattern recognition receptors (PRRs) to initiate the immune response. Complex intracellular signaling network transduces inflammatory signaling to regulate both innate immune cell activation and parenchymal cell death. Recent studies have revealed that DAMPs may trigger not only proinflammatory but also immune regulatory responses by activating different PRRs or distinctive intracellular signaling pathways or in special cell populations. Additionally, tissue injury milieu activates PRR-independent receptors which also regulate inflammatory disease processes. Thus, the innate immune mechanism of liver ischemia-reperfusion injury involves diverse molecular and cellular interactions, subjected to both endogenous and exogenous regulation in different cells. A better understanding of these complicated regulatory pathways/network is imperative for us in designing safe and effective therapeutic strategy to ameliorate liver ischemia-reperfusion injury in patients.

Differential autophagic effects of vital dyes in retinal pigment epithelial ARPE-19 and photoreceptor 661W cells

Indocyanine green (ICG) and brilliant blue G (BBG) are commonly used vital dyes to remove internal limiting membrane (ILM) in vitreoretinal surgery. The vital dyes have shown cytotoxic effects in ocular cells. Autophagy is a stress responsive pathway for either protecting cells or promoting cell death. However, the role of autophagy in ocular cells in response to the vital dyes remains unknown. In this study, we found that ICG and BBG reduced cell viability in both human retinal pigment epithelial ARPE-19 and mouse photoreceptor 661W cells. ICG and BBG induced lipidated GFP-LC3-II and LC3-II in ARPE-19 and 661W cells. Combination treatment with the autophagy inhibitor chloroquine indicated that ICG and BBG reduced autophagic flux in ARPE-19 cells, whereas the vital dyes induced autophagic flux in 661W cells. Moreover, genetic and pharmacological ablation of autophagy enhanced vital dyes-induced cytotoxicity in ocular cells. Dietary supplements, including resveratrol, lutein, and CoQ10, induced autophagy and diminished the cytotoxic effects of ICG and BBG in ocular cells. These results suggest that autophagy may protect ARPE-19 and 661W cells from vital dyes-induced damage.

mTOR activation protects liver from ischemia/reperfusion-induced injury through NF-κB pathway

Hepatic steatosis renders liver more vulnerable to ischemia/reperfusion injury (IRI), which commonly occurs in transplantation, trauma, and liver resection. The underlying mechanism is not fully characterized. We aimed to clarify the role of mechanistic target of rapamycin (mTOR) signaling in hepatic ischemia/reperfusion injury (HIRI) in normal and steatotic liver using Alb-TSC1^-/- (AT) and Alb-mTOR^-/- (Am) transgenic mice. Steatotic liver induced by high-fat diet was more vulnerable to IRI. Activation of hepatic mTOR in AT mice decreased lipid accumulation attenuated HIRI as measured by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, circulating levels of alanine aminotransferase and lactate dehydrogenase, and inflammatory mediators such as monocyte chemoattractant protein 1 (MCP-1), TNF-α, and IL-6 and hepatic cleaved caspase 3 in mice fed either a normal chow diet or a high-fat diet. The effects of mTOR activation on hepatic cleaved caspase 3 were reversed by rapamycin, an inhibitor of mTOR signaling. Inhibition of hepatic mTOR in Am mice increased hepatic lipid deposition and HIRI. The increment in hepatic susceptibility to IRI was significantly attenuated by pretreatment with IKKβ inhibitor. Further, suppression of mTOR facilitated nuclear translocation of NF-κB p65. In conclusion, our study suggests that mTOR activity in hepatocytes decreases hepatic vulnerability to injury through a mechanism dependent on NF-κB proinflammatory cytokine signaling pathway in both normal and steatotic liver.-Li, Z., Zhang, J., Mulholland, M., Zhang, W. mTOR activation protects liver from ischemia/reperfusion-induced injury through NF-κB pathway.

Rapamycin suppresses hypoxia/reoxygenation-induced islet injury by up-regulation of miR-21 via PI3K/Akt signalling pathway

OBJECTIVES

Increasing evidences indicate that microRNAs may play a critical role in the regulation of hypoxia/reoxygenation (H/R) injury, and their expression is associated with mTORC activity. We propose that rapamycin modulates H/R-induced islets injury by regulating microRNA expression.

MATERIALS AND METHODS

We investigated whether rapamycin treatment could alter the expression profile of miRNAs in islets. Furthermore, we assessed the islet apoptosis and function after H/R or syngeneic islet transplantation.

RESULTS

We found that rapamycin treatment significantly decreased H/R-induced islet apoptosis, and improved islet function in vivo and in vitro, and that miR-21 gene transcription is controlled by rapamycin. When the PI3k/Akt signalling pathways was blocked by wortmannin, the up-regulative effects of rapamycin on miR-21 expression were inhibited in vitro. Furthermore, our study clearly demonstrates that miR-21 is essential for the rapamycin-mediated protection islets against H/R injury.

DISCUSSION

Our findings indicate that up-regulation of miR-21 function in islets by treatment with rapamycin or overexpression of the miR-21 could represent a potential new therapy for the treatment of H/R injury.

CONCLUSION

The results of this study clearly suggest that rapamycin exerts its inhibitory effects on islets H/R injury by inducing miR-21 expression via PI3K/Akt.

Targeting endoplasmic reticulum stress in liver disease

INTRODUCTION

The accumulation of unfolded protein in the endoplasmic reticulum (ER) initiates an unfolded protein response (UPR) via three signal transduction cascades, which involve protein kinase RNA-like ER kinase (PERK), inositol requiring enzyme-1α (IRE1α) and activating transcription factor-6α (ATF6α). An ER stress response is observed in nearly all physiologies related to acute and chronic liver disease and therapeutic targeting of the mechanisms implicated in UPR signaling have attracted considerable attention.

AREAS COVERED

This review focuses on the correlation between ER stress and liver disease and the possible targets which may drive the potential for novel therapeutic intervention. Expert Commentary: We describe pathways which are involved in UPR signaling and their potential correlation with various liver diseases and underlying mechanisms which may present opportunities for novel therapeutic strategies are discussed.

Akt: A Therapeutic Target in Hepatic Ischemia-Reperfusion Injury

BACKGROUND

Liver transplantation is the second most common transplant procedure in the United States. A leading cause of post-transplantation organ dysfunction is I/R injury. During I/R injury, the serine/threonine kinase Akt is activated, stimulating downstream mediators to promote cellular survival. Due to the cellular effects of Akt, therapeutic manipulation of the Akt pathway can help reduce cellular damage during hepatic I/R that occurs during liver transplantation.

OBJECTIVE

A full description of therapeutic options available that target Akt to reduce hepatic I/R injury has not been addressed within the literature. The purpose of this review is to illuminate advances in the manipulation of Akt that can be used to therapeutically target I/R injury in the liver.

METHODS

An in depth literature review was performed using the Scopus and PubMed databases. A total of 75 published articles were utilized for this manuscript. Terminology searched includes a combination of "hepatic ischemia/reperfusion injury", "Akt/PKB", "preconditioning" and "postconditioning."

RESULTS

Four principal methods that reduce I/R injury include hepatic pre- and postconditioning, pharmacological intervention and future miRNA/gene therapy. Discussed therapies used serum alanine aminotransferase levels, liver histology and phosphorylation of downstream mediators to confirm the Akt protective effect.

CONCLUSION

The activation of Akt from the reviewed therapies has resulted in predictable reduction in hepatocyte damage using the previously mentioned measurements. In a clinical setting, these therapies could potentially be used in combination to achieve better outcomes in hepatic transplant patients. Evidence supporting reduced I/R injury through Akt activation warrants further studies in human clinical trials.

Activation of Autophagy by Everolimus Confers Hepatoprotection Against Ischemia-Reperfusion Injury

As the criteria for liver donation have been extended to include marginal donors, liver grafts are becoming particularly vulnerable to hepatic ischemia-reperfusion injury (IRI). However, no specific measures have been validated to ameliorate hepatic IRI. In this article, we explored whether everolimus has protective effects against hepatic IRI in relation with autophagy. The effects of everolimus were investigated in both in vitro and in vivo hepatic IRI models. Mouse hepatocyte AML12 cells and BALB/c mice were utilized for the establishment of each model. In the IRI-induced AML12 cells, everolimus treatment increased the expressions of autophagic markers (microtubule-associated protein 1 light chain 3 and p62) and decreased pro-apoptotic proteins (cleaved caspase 3 and cleaved poly-ADP ribose polymerase). The blockage of autophagy, using either bafilomycin A1 or si-autophagy-related protein 5, abrogated these anti-apoptosis effects of everolimus. Subsequently, everolimus administration to the hepatic IRI-induced mice provided hepatoprotective effects in terms of (1) decreasing the expressions of pro-apoptotic proteins, (2) inhibiting the release of pro-inflammatory cytokines (IL-6 and tumor necrosis factor-α), (3) reducing elevated liver enzymes (aspartate transaminase, alanine transaminase, and ammonia), and (4) restoring liver histopathology. These findings suggest that everolimus protects the liver against hepatic IRI by way of activating autophagy, and thus could be a potential therapeutic agent for hepatic IRI.

The Dichotomy of Endoplasmic Reticulum Stress Response in Liver Ischemia-Reperfusion Injury

Endoplasmic reticulum (ER) stress plays critical roles in the pathogenesis of liver ischemia-reperfusion injury (IRI). As ER stress triggers an adaptive cellular response, the question of what determines its functional outcome in liver IRI remains to be defined. In a murine liver partial warm ischemia model, we studied how transient (30 minutes) or prolonged (90 minutes) liver ischemia regulated local ER stress response and autophagy activities and their relationship with liver IRI. Effects of chemical chaperon 4-phenylbutyrate (4-PBA) or autophagy inhibitor 3-methyladenine (3-MA) were evaluated. Our results showed that although the activating transcription factor 6 branch of ER stress response was induced in livers by both types of ischemia, liver autophagy was activated by transient, but inhibited by prolonged, ischemia. Although 3-MA had no effects on liver IRI after prolonged ischemia, it significantly increased liver IRI after transient ischemia. The 4-PBA treatment protected livers from IRI after prolonged ischemia by restoring autophagy flux, and the adjunctive 3-MA treatment abrogated its liver protective effect. The same 4-PBA treatment, however, increased liver IRI and disrupted autophagy flux after transient ischemia. Although both types of ischemia activated 5' adenosine monophosphate-activated protein kinase and inactivated protein kinase B (Akt), prolonged ischemia also resulted in downregulations of autophagy-related gene 3 and autophagy-related gene 5 in ischemic livers. These results indicate a functional dichotomy of ER stress response in liver IRI via its regulation of autophagy. Transient ischemia activates autophagy to protect livers from IRI, whereas prolonged ischemia inhibits autophagy to promote the development of liver IRI.

Rapamycin Attenuates Mouse Liver Ischemia and Reperfusion Injury by Inhibiting Endoplasmic Reticulum Stress

The roles of endoplasmic reticulum (ER) stress in liver ischemia and reperfusion injury (IRI) have been well recognized. However, the impact of rapamycin (Rapa), a broadly used immunosuppressive agent in human liver transplantation, on ER stress during IRI remains unclear. This study was designed to investigate the roles of Rapa in the regulation of ER stress in vivo and in vitro. In a mouse liver partial warm ischemia and reperfusion mode, we demonstrated that Rapa markedly protected livers from IRI, as evidenced by serum alanine aminotransferase (sALT) levels and liver histology. Then we also confirmed the protection of Rapa from thapsigargin (Tg)-induced cell death in primary hepatocytes. Both in vivo and in vitro experiments showed that the ER stress markers were markedly up-regulated by IRI and Tg treatment, whereas they were down-regulated by Rapa pretreatment, as monitored by Western blot at the protein levels and by quantitative reverse transcription polymerase chain reaction (RT-PCR) at the messenger RNA (mRNA) levels. In addition, it was also revealed that Rapa was able to remarkably inhibit the mammalian target of rapamycin (mTOR) pathway and enhance autophagy both in IR-stressed livers and Tg-treated primary hepatocytes. Thus, these results suggest that Rapa protects livers from IRI through inhibiting the ER stress pathway.