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

XBP1-mediated transcriptional regulation of SLC5A1 in human epithelial cells in disease conditions

BACKGROUND

Sodium-Glucose cotransporter 1 and 2 (SGLT1/2) belong to the family of glucose transporters, encoded by SLC5A1 and SLC5A2, respectively. SGLT2 is almost exclusively expressed in the renal proximal convoluted tubule cells. SGLT1 is expressed in the kidneys but also in other organs throughout the body. Many SGLT inhibitor drugs have been developed based on the mechanism of blocking glucose (re)absorption mediated by SGLT1/2, and several have gained major regulatory agencies' approval for treating diabetes. Intriguingly these drugs are also effective in treating diseases beyond diabetes, for example heart failure and chronic kidney disease. We recently discovered that SGLT1 is upregulated in the airway epithelial cells derived from patients of cystic fibrosis (CF), a devastating genetic disease affecting greater than 70,000 worldwide.

RESULTS

In the present work, we show that the SGLT1 upregulation is coupled with elevated endoplasmic reticulum (ER) stress response, indicated by activation of the primary ER stress senor inositol-requiring protein 1α (IRE1α) and the ER stress-induced transcription factor X-box binding protein 1 (XBP1), in CF epithelial cells, and in epithelial cells of other stress conditions. Through biochemistry experiments, we demonstrated that the spliced form of XBP1 (XBP1s) acts as a transcription factor for SLC5A1 by directly binding to its promoter region. Targeting this ER stress → SLC5A1 axis by either the ER stress inhibitor Rapamycin or the SGLT1 inhibitor Sotagliflozin was effective in attenuating the ER stress response and reducing the SGLT1 level in these cellular model systems.

CONCLUSIONS

The present work establishes a causal relationship between ER stress and SGLT1 upregulation and provides a mechanistic explanation why SGLT inhibitor drugs benefit diseases beyond diabetes.

Hypothermic oxygenated perfusion attenuates DCD liver ischemia-reperfusion injury by activating the JAK2/STAT3/HAX1 pathway to regulate endoplasmic reticulum stress

BACKGROUND

Hepatic ischemia-reperfusion injury (IRI) in donation after cardiac death (DCD) donors is a major determinant of transplantation success. Endoplasmic reticulum (ER) stress plays a key role in hepatic IRI, with potential involvement of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway and the antiapoptotic protein hematopoietic-lineage substrate-1-associated protein X-1 (HAX1). In this study, we aimed to investigate the effects of hypothermic oxygenated perfusion (HOPE), an organ preservation modality, on ER stress and apoptosis during hepatic IRI in a DCD rat model.

METHODS

To investigate whether HOPE could improve IRI in DCD livers, levels of different related proteins were examined by western blotting and quantitative real-time polymerase chain reaction. Further expression analyses, immunohistochemical analyses, immunofluorescence staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and transmission electron microscopy were conducted to analyze the effects of HOPE on ER stress and apoptosis. To clarify the role of the JAK2/STAT3 pathway and HAX1 in this process, AG490 inhibitor, JAX1 plasmid transfection, co-immunoprecipitation (CO-IP), and flow cytometry analyses were conducted.

RESULTS

HOPE reduced liver injury and inflammation while alleviating ER stress and apoptosis in the DCD rat model. Mechanistically, HOPE inhibited unfolded protein responses by activating the JAK2/STAT3 pathway, thus reducing ER stress and apoptosis. Moreover, the activated JAK2/STAT3 pathway upregulated HAX1, promoting the interaction between HAX1 and SERCA2b to maintain ER calcium homeostasis. Upregulated HAX1 also modulated ER stress and apoptosis by inhibiting the inositol-requiring enzyme 1 (IRE1) pathway.

CONCLUSIONS

JAK2/STAT3-mediated upregulation of HAX1 during HOPE alleviates hepatic ER stress and apoptosis, indicating the JAK2/STAT3/HAX1 pathway as a potential target for IRI management during DCD liver transplantation.

Peptidomic Analysis Reveals that Novel Peptide LDP2 Protects Against Hepatic Ischemia/Reperfusion Injury

BACKGROUND AND AIMS

Hepatic ischemia/reperfusion (I/R) injury has become an inevitable issue during liver transplantation, with no effective treatments available. However, peptide drugs provide promising regimens for the treatment of this injury and peptidomics has gradually attracted increasing attention. This study was designed to analyze the spectrum of peptides in injured livers and explore the potential beneficial peptides involved in I/R injury.

METHODS

C57BL/6 mice were used to establish a liver I/R injury animal model. Changes in peptide profiles in I/R-injured livers were analyzed by mass spectrometry, and the functions of the identified peptides were predicted by bioinformatics. AML12 cells were used to simulate hepatic I/R injury in vitro. After treatment with candidate liver-derived peptides (LDPs) 1-10, the cells were collected at various reperfusion times for further study.

RESULTS

Our preliminary study demonstrated that 6 h of reperfusion caused the most liver I/R injury. Peptidomic results suggested that 10 down-regulated peptides were most likely to alleviate I/R injury by supporting mitochondrial function. Most importantly, a novel peptide, LDP2, was identified that alleviated I/R injury of AML12 cells. It increased cell viability and reduced the expression of inflammation- and apoptosis-related proteins. In addition, LDP2 inhibited the expression of proteins related to autophagy.

CONCLUSIONS

Investigation of changes in the profiles of peptides in I/R-injured livers led to identification of a novel peptide, LDP2 with potential function in liver protection by inhibiting inflammation, apoptosis, and autophagy.

Musclin attenuates lipid deposition in hepatocytes through SIRT7/autophagy-mediated suppression of ER stress

Musclin, an exercise-responsive myokine, has the ability to attenuate inflammation, oxidative stress, and apoptosis in cardiomyocytes under pathogenic conditions. While the potential benefits of musclin in the cardiovascular system have been well documented, its effects on hepatic endoplasmic reticulum (ER) stress and lipid metabolism are not fully understood. The present study showed that musclin treatment reduced lipid accumulation and lipogenic protein expression in primary hepatocytes exposed to palmitate. Palmitate treatment led to an increase in markers of ER stress, which was reversed by musclin treatment. Musclin treatment increased SIRT7 expression and markers of autophagy in a dose-dependent manner. Small interfering (si) RNA of SIRT7 or 3-methyladenine (3 MA) reduced the effects of musclin on lipogenic lipid deposition in hepatocytes under hyperlipidemic conditions. These findings suggest that musclin can suppress palmitate-induced ER stress by upregulating SIRT7 and autophagy signaling, thereby alleviating lipid accumulation in primary hepatocytes. The current study provides a potential therapeutic strategy for the treatment of liver diseases characterized by lipid accumulation and ER stress, such as nonalcoholic fatty liver disease (NAFLD).

Endoplasmic reticulum stress in liver diseases

The endoplasmic reticulum (ER) is an intracellular organelle that fosters the correct folding of linear polypeptides and proteins, a process tightly governed by the ER-resident enzymes and chaperones. Failure to shape the proper 3-dimensional architecture of proteins culminates in the accumulation of misfolded or unfolded proteins within the ER, disturbs ER homeostasis, and leads to canonically defined ER stress. Recent studies have elucidated that cellular perturbations, such as lipotoxicity, can also lead to ER stress. In response to ER stress, the unfolded protein response (UPR) is activated to reestablish ER homeostasis ("adaptive UPR"), or, conversely, to provoke cell death when ER stress is overwhelmed and sustained ("maladaptive UPR"). It is well documented that ER stress contributes to the onset and progression of multiple hepatic pathologies including NAFLD, alcohol-associated liver disease, viral hepatitis, liver ischemia, drug toxicity, and liver cancers. Here, we review key studies dealing with the emerging role of ER stress and the UPR in the pathophysiology of liver diseases from cellular, murine, and human models. Specifically, we will summarize current available knowledge on pharmacological and non-pharmacological interventions that may be used to target maladaptive UPR for the treatment of nonmalignant liver diseases.

Avoid being trapped by your liver: ischemia-reperfusion injury in liver transplant triggers S1P-mediated NETosis

Liver transplantation can be a life-saving treatment for end-stage hepatic disease. Unfortunately, some recipients develop ischemia-reperfusion injury (IRI) that leads to poor short- and long-term outcomes. Recent work has shown neutrophils contribute to IRI by undergoing NETosis, a form of death characterized by DNA ejection resulting in inflammatory extracellular traps. In this issue of the JCI, Hirao and Kojima et al. report that sphingosine-1-phosphate (S1P) expression induced by liver transplant-mediated IRI triggers NETosis. They also provide evidence that neutrophil expression of the carcinoembryonic antigen-related cell adhesion molecule-1 (CC1) long isoform inhibited NETosis by controlling S1P receptor-mediated autophagic flux. These findings suggest stimulating regulatory mechanisms that suppress NETosis could be used to prevent IRI.

Cardiovascular effects of immunosuppression agents

Immunosuppressive medications are widely used to treat patients with neoplasms, autoimmune conditions and solid organ transplants. Key drug classes, namely calcineurin inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and purine synthesis inhibitors, have direct effects on the structure and function of the heart and vascular system. In the heart, immunosuppressive agents modulate cardiac hypertrophy, mitochondrial function, and arrhythmia risk, while in vasculature, they influence vessel remodeling, circulating lipids, and blood pressure. The aim of this review is to present the preclinical and clinical literature examining the cardiovascular effects of immunosuppressive agents, with a specific focus on cyclosporine, tacrolimus, sirolimus, everolimus, mycophenolate, and azathioprine.

Regulation of autophagy protects against liver injury in liver surgery-induced ischaemia/reperfusion

Transient ischaemia and reperfusion in liver tissue induce hepatic ischaemia/reperfusion (I/R) tissue injury and a profound inflammatory response in vivo. Hepatic I/R can be classified into warm I/R and cold I/R and is characterized by three main types of cell death, apoptosis, necrosis and autophagy, in rodents or patients following I/R. Warm I/R is observed in patients or animal models undergoing liver resection, haemorrhagic shock, trauma, cardiac arrest or hepatic sinusoidal obstruction syndrome when vascular occlusion inhibits normal blood perfusion in liver tissue. Cold I/R is a condition that affects only patients who have undergone liver transplantation (LT) and is caused by donated liver graft preservation in a hypothermic environment prior to entering a warm reperfusion phase. Under stress conditions, autophagy plays a critical role in promoting cell survival and maintaining liver homeostasis by generating new adenosine triphosphate (ATP) and organelle components after the degradation of macromolecules and organelles in liver tissue. This role of autophagy may contribute to the protection of hepatic I/R‐induced liver injury; however, a considerable amount of evidence has shown that autophagy inhibition also protects against hepatic I/R injury by inhibiting autophagic cell death under specific circumstances. In this review, we comprehensively discuss current strategies and underlying mechanisms of autophagy regulation that alleviates I/R injury after liver resection and LT. Directed autophagy regulation can maintain liver homeostasis and improve liver function in individuals undergoing warm or cold I/R. In this way, autophagy regulation can contribute to improving the prognosis of patients undergoing liver resection or LT.

Rapamycin Alternatively Modifies Mitochondrial Dynamics in Dendritic Cells to Reduce Kidney Ischemic Reperfusion Injury

Dendritic cells (DCs) are unique immune cells that can link innate and adaptive immune responses and Immunometabolism greatly impacts their phenotype. Rapamycin is a macrolide compound that has immunosuppressant functions and is used to prevent graft loss in kidney transplantation. The current study evaluated the therapeutic potential of ex-vivo rapamycin treated DCs to protect kidneys in a mouse model of acute kidney injury (AKI). For the rapamycin single (S) treatment (Rapa-S-DC), Veh-DCs were treated with rapamycin (10 ng/mL) for 1 h before LPS. In contrast, rapamycin multiple (M) treatment (Rapa-M-DC) were exposed to 3 treatments over 7 days. Only multiple ex-vivo rapamycin treatments of DCs induced a persistent reprogramming of mitochondrial metabolism. These DCs had 18-fold more mitochondria, had almost 4-fold higher oxygen consumption rates, and produced more ATP compared to Veh-DCs (Veh treated control DCs). Pathway analysis showed IL10 signaling as a major contributing pathway to the altered immunophenotype after Rapamycin treatment compared to vehicle with significantly lower cytokines Tnfa, Il1b, and Il6, while regulators of mitochondrial content Pgc1a, Tfam, and Ho1 remained elevated. Critically, adoptive transfer of rapamycin-treated DCs to WT recipients 24 h before bilateral kidney ischemia significantly protected the kidneys from injury with a significant 3-fold improvement in kidney function. Last, the infusion of DCs containing higher mitochondria numbers (treated ex-vivo with healthy isolated mitochondria (10 µg/mL) one day before) also partially protected the kidneys from IRI. These studies demonstrate that pre-emptive infusion of ex-vivo reprogrammed DCs that have higher mitochondria content has therapeutic capacity to induce an anti-inflammatory regulatory phenotype to protect kidneys from 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.

Suppression of microRNA‑27a protects against liver ischemia/reperfusion injury by targeting PPARγ and inhibiting endoplasmic reticulum stress

Liver ischemia‑reperfusion (I/R) injury is an important clinical issue related to liver transplantation. Recent studies suggest that microRNAs are implicated in various biological and pathological processes, including liver I/R injury. This study aimed to investigate the role and potential mechanism of miR‑27a during liver I/R injury. A liver I/R model was induced via 60 min of ischemia and reperfusion for 6 h in rats. Cells were transfected with miR‑27a mimics or the miR‑27a inhibitor to examine the effect of miR‑27a on liver I/R. Apoptotic cells were detected by flow cytometry and TUNEL staining. The expression of miR‑27a was measured by real‑time PCR. The expression of peroxisome proliferator‑activated receptor γ (PPARγ); gastrin‑releasing peptide 78 (GRP78) and C/EBP homologous protein (CHOP) were detected by western blot analysis. The results showed that miR‑27a was significantly upregulated during I/R injury in vivo and in vitro. In addition, miR‑27a inhibitors attenuated hypoxia/reoxygenation (H/R)‑induced oxidative stress, endoplasmic reticulum stress (ERS) and apoptosis in AML12 cells. By contrast, miR‑27a mimics promoted hypoxia/reoxygenation‑induced ERS, and apoptosis. Furthermore, PPARγ was identified as a target gene of miR‑27a using bioinformatic analysis and a dual‑luciferase reporter assay. Knockdown of PPARγ significantly abrogated the inhibitory effect of miR‑27a inhibitors on the ERS pathway. Moreover, the miR‑27a antagomir attenuated liver I/R injury in rats, a finding manifested by reduced ALT/AST, hepatocyte apoptosis, oxidative stress and inhibition of the ERS pathway. Taken together, these findings demonstrate that suppression of miR‑27a protects against liver I/R injury by targeting PPARγ and by inhibiting the ERS pathway.

Rapamycin Rescues Endoplasmic Reticulum Stress-Induced Dry Eye Syndrome in Mice

Purpose

To investigate whether rapamycin protects tear production and the ocular surface during endoplasmic reticulum (ER) stress-induced dry eye syndrome in mice.

Methods

Tunicamycin was injected intraperitoneally in BALB/c mice without or with rapamycin (TM or RM5 group). Peritoneal injection of PBS performed in vehicle group. Group without injection served as control. Blinking rate, fluorescein staining score (FSS), and phenol red thread tear production test were measured at 4 days, 1 week, and 2 weeks after treatment. Levels of inflammatory and angiogenic cytokines were measured by ELISA.

Results

Blinking rate and FSS were elevated, and tear production was decreased in TM group compared with controls (P < 0.05 for all), which was ameliorated by rapamycin at 1 and 2 weeks. Levels of inflammatory and angiogenic cytokines in the cornea and lacrimal glands were higher in the TM group than controls, and lower in the RM5 group than the TM group at 1 and 2 weeks (P < 0.05 for all).

Conclusion

Rapamycin protected tear production and the ocular surface against this dry eye syndrome by ameliorating ER stress-induced vascular damage and inflammation of lacrimal glands and the ocular surface.

BMSCs protect against renal ischemia-reperfusion injury by secreting exosomes loaded with miR-199a-5p that target BIP to inhibit endoplasmic reticulum stress at the very early reperfusion stages

Bone marrow-derived mesenchymal stem cells (BMSCs) have been recently reported to play a variety of vital roles in organ and tissue damage repair, mainly via potent paracrine activity, including secreting extracellular vesicles, such as exosomes, that serve as mediators facilitating intercellular communication and reprogramming recipient cells by delivering their contents to target cells. However, the underlying mechanisms are diverse and complex, and the influencing characteristics have rarely been studied. Accordingly, we designed this study to explore the time dependence of the effects of exosomes derived from BMSCs (BMexos) on renal ischemia-reperfusion (I/R) injury and the underlying mechanisms associated with the reperfusion time. Impressively, our study is the first to find that BMexos protected against renal I/R injury in vitro and in vivo at the very early reperfusion stages, especially 4-8 h after reperfusion in vitro and 8-16 h after reperfusion in vivo. Interestingly, we simultaneously found that endoplasmic reticulum (ER) stress was significantly suppressed following the administration of BMexos in vitro and in vivo with a similar time dependence. Additionally, we discovered that miR-199a-5p, which was abundant in the BMSCs, was transferred into renal tubular epithelial cells (NRK-52E) in a time-dependent manner and significantly inhibited I/R-induced ER stress by targeting binding immunoglobulin protein (BIP). Cocultivation with miR-199a-5p-overexpressing BMSCs amplified the suppression of ER stress and further protected against I/R injury. However, coculture with miR-199a-5p-knockdown BMSCs obviously increased ER stress and reversed the BMexos-induced protection, and silencing BIP by small interfering RNA-1098 in NRK-52E inhibited these effects. This study provides evidence that administering BMexos at the very early reperfusion stages significantly protects against renal I/R injury, and ER stress is closely linked to this protection. These results suggest a novel therapeutic strategy during the very early reperfusion stages of renal I/R injury.-Wang, C., Zhu, G., He, W., Yin, H., Lin, F., Gou, X., Li, X. BMSCs protect against renal ischemia-reperfusion injury by secreting exosomes loaded with miR-199a-5p that target BIP to inhibit endoplasmic reticulum stress at the very early reperfusion stages.

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.

Baicalin attenuates liver hypoxia/reoxygenation injury by inducing autophagy

The aim of the present study was to explore the effect of baicalin on liver hypoxia/reoxygenation (H/R) injury and the possible mechanism involved. A cellular H/R model was established and cells were treated with 50, 100 and 200 µmol/l baicalin. Following reoxygenation for 6 h, cell viability, lactate dehydrogenase (LDH), B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), caspase 3 and cleaved caspase 3 were assessed. Furthermore, levels of endoplasmic reticulum stress markers binding of immunoglobulin protein (BIP) and CCAAT/enhancer-binding protein homologous protein (CHOP) and autophagy markers microtubule-associated proteins 1A/1B light chain 3B (LC3) and beclin 1 were measured. To confirm the involvement of autophagy in baicalin-mediated attenuation of H/R injury, the autophagy inhibitor 3-methyladenine (3-MA) was administered. The results revealed that baicalin administration increased cell viability and decreased LDH levels, most notably at a dosage of 100 µmol/l. Baicalin pretreatment also downregulated the expression of caspase 3, cleaved caspase 3 and Bax, while upregulating the expression of Bcl-2. Furthermore, BIP and CHOP were decreased while LC3 and beclin-1 were significantly increased by baicalin pretreatment. Inhibiting autophagy using 3-MA, resulted in a significant decrease in LC3-II, beclin-1 and LDH, as well as increase in the expression of BIP, CHOP, caspase 3, cleaved caspase 3 and Bax. Bcl-2 and cell viability were also decreased. In conclusion, the results of the present study indicate that baicalin exerts a protective effect on liver H/R injury and this may be achieved via the induction of autophagy.

cGAS-mediated autophagy protects the liver from ischemia-reperfusion injury independently of STING

Liver ischemia-reperfusion (I/R) injury occurs through induction of oxidative stress and release of damage-associated molecular patterns (DAMPs), including cytosolic DNA released from dysfunctional mitochondria or from the nucleus. Cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase (cGAS) is a cytosolic DNA sensor known to trigger stimulator of interferon genes (STING) and downstream type 1 interferon (IFN-I) pathways, which are pivotal innate immune system responses to pathogen. However, little is known about the role of cGAS/STING in liver I/R injury. We subjected C57BL/6 (WT), cGAS knockout (cGAS^-/-), and STING-deficient (STING^gt/gt) mice to warm liver I/R injury and that found cGAS^-/- mice had significantly increased liver injury compared with WT or STING^gt/gt mice, suggesting a protective effect of cGAS independent of STING. Liver I/R upregulated cGAS in vivo and also in vitro in hepatocytes subjected to anoxia/reoxygenation (A/R). We confirmed a previously published finding that hepatocytes do not express STING under normoxic conditions or after A/R. Hepatocytes and liver from cGAS^-/- mice had increased cell death and reduced induction of autophagy under hypoxic conditions as well as increased apoptosis. Protection could be restored in cGAS^-/- hepatocytes by overexpression of cGAS or by pretreatment of mice with autophagy inducer rapamycin. Our findings indicate a novel protective role for cGAS in the regulation of autophagy during liver I/R injury that occurs independently of STING. NEW & NOTEWORTHY Our studies are the first to document the important role of cGAS in the acute setting of sterile injury induced by I/R. Specifically, we provide evidence that cGAS protects liver from I/R injury in a STING-independent manner.

Negative feedback loop of autophagy and endoplasmic reticulum stress in rapamycin protection against renal ischemia-reperfusion injury during initial reperfusion phase

Rapamycin, an immunosuppressant, is widely used in patients with kidney transplant. However, the therapeutic effects of rapamycin remain controversial. Additionally, previous studies have revealed deleterious effects of rapamycin predominantly when administered for ≥24 h. Few studies, however, have focused on the short-term effects of rapamycin administered only during the initial reperfusion phase. As such, we designed this study to explore the potential effects and mechanisms of rapamycin under a specific therapeutic regimen in which rapamycin is mixed in the perfusate during the initial reperfusion phase (within 24 h). Interestingly, we found that rapamycin maintained renal function and attenuated ischemia-reperfusion (I/R)-induced apoptosis in vivo and in vitro during the initial reperfusion phase, especially at 8 h after reperfusion. Simultaneously, rapamycin activated autophagy and inhibited endoplasmic reticulum (ER) stress and 3 pathways of unfolding protein response: ATF6, PERK, and IRE1α. Interestingly, we further found that the protective effects of rapamycin were suppressed when autophagy was inhibited by chloroquine and 3-methyladenine or when ER stress was induced by thapsigargin. Moreover, in terms of the regulatory effects of rapamycin, a negative-feedback loop between autophagy and ER stress occurred, with autophagy inhibiting ER stress and increased ER stress promoting autophagy during the initial reperfusion phase of renal I/R injury. Our study provides evidence that immediate reperfusion with rapamycin during the initial reperfusion phase repairs renal function and reduces apoptosis via activating autophagy, which could further inhibit ER stress. These results suggest a novel treatment modality for application during the initial reperfusion phase of renal I/R injury caused by kidney transplantation.-Li, X., Zhu, G., Gou, X., He, W., Yin, H., Yang, X., Li, J. Negative feedback loop of autophagy and endoplasmic reticulum stress in rapamycin protection against renal ischemia-reperfusion injury during initial reperfusion phase.

CAAT/enhancer binding protein-homologous protein deficiency attenuates liver ischemia/reperfusion injury in mice

Ischemia/reperfusion injury (IRI) is one of the main causes of liver dysfunction after liver surgery. Involvement of endoplasmic reticulum (ER) stress in various diseases has been demonstrated, and CAAT/enhancer binding protein-homologous protein (CHOP) is a transcriptional regulator that is induced by ER stress. It is also a key regulator of ER stress-mediated apoptosis. The aim of this study was to investigate the role of CHOP in liver IRI. Wild type (WT) and CAAT/enhancer binding protein-homologous protein knockout (CHOP-/-) mice were subjected to 70% liver warm ischemia/reperfusion for 60 minutes. At different times after reperfusion, liver tissues and blood samples were collected for evaluation. Induction of ER stress including CHOP expression was ascertained. Liver damage was evaluated based on serum liver enzymes, liver histology, and neutrophil infiltration. Hepatocyte death including apoptosis was assessed. Liver warm IRI induced ER stress in both WT and CHOP-/- mice. In addition, CHOP expression was up-regulated in WT mice. At 6 hours after reperfusion, liver damage was attenuated in CHOP-/- mice. On the basis of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining, apoptotic and necrotic cells were significantly reduced in CHOP-/- mice. CHOP deficiency also reduced the cleavage of caspase 3 and expression of the proapoptotic protein B cell lymphoma 2-associated X protein. Liver IRI induces CHOP expression, and CHOP deficiency attenuates liver IRI by inhibiting apoptosis. Elucidation of the function of CHOP in liver IRI may contribute to further investigation for a therapy against liver IRI associated with the ER stress pathway. Liver Transplantation 24 645-654 2018 AASLD.

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.

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.

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.

New Insights in Cardiac Calcium Handling and Excitation-Contraction Coupling

Excitation-contraction (EC) coupling denotes the conversion of electric stimulus in mechanic output in contractile cells. Several studies have demonstrated that calcium (Ca²⁺) plays a pivotal role in this process. Here we present a comprehensive and updated description of the main systems involved in cardiac Ca²⁺ handling that ensure a functional EC coupling and their pathological alterations, mainly related to heart failure.

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.

Pharmacological Modulators of Endoplasmic Reticulum Stress in Metabolic Diseases

The endoplasmic reticulum (ER) is the principal organelle responsible for correct protein folding, a step in protein synthesis that is critical for the functional conformation of proteins. ER stress is a primary feature of secretory cells and is involved in the pathogenesis of numerous human diseases, such as certain neurodegenerative and cardiometabolic disorders. The unfolded protein response (UPR) is a defense mechanism to attenuate ER stress and maintain the homeostasis of the organism. Two major degradation systems, including the proteasome and autophagy, are involved in this defense system. If ER stress overwhelms the capacity of the cell's defense mechanisms, apoptotic death may result. This review is focused on the various pharmacological modulators that can protect cells from damage induced by ER stress. The possible mechanisms for cytoprotection are also discussed.