Protective role of AMP-activated protein kinase-evoked autophagy on an in vitro model of ischemia/reperfusion-induced renal tubular cell injury

Environmentally relevant levels of Cd and Mo coexposure induces ferroptosis and excess ferritinophagy through AMPK/mTOR axis in duck myocardium

Cadmium (Cd) and excess molybdenum (Mo) are multiorgan toxic, but the detrimental impacts of Cd and/or Mo on poultry have not been fully clarified. Thence, a 16-week sub-chronic toxic experiment was executed with ducks to assess the toxicity of Cd and/or Mo. Our data substantiated that Cd and Mo coexposure evidently reduced GSH-Px, GSH, T-SOD, and CAT activities and elevated H2O2 and MDA concentrations in myocardium. What is more, the study suggested that Cd and Mo united exposure synergistically elevated Fe2+ content in myocardium and activated AMPK/mTOR axis, then induced ferroptosis by obviously upregulating ACSL4, PTGS2, and TFRC expression levels and downregulating SLC7A11, GPX4, FPN1, FTL1, and FTH1 expression levels. Additionally, Cd and Mo coexposure further caused excessive ferritinophagy by observably increasing autophagosomes, the colocalization of endogenous FTH1 and LC3, ATG5, ATG7, LC3II/LC3I, NCOA4, and FTH1 expression levels. In brief, this study for the first time substantiated that Cd and Mo united exposure synergistically induced ferroptosis and excess ferritinophagy by AMPK/mTOR axis, finally augmenting myocardium injure in ducks, which will offer an additional view on united toxicity between two heavy metals on poultry.

Bone Mesenchymal Stem Cells Origin Exosomes are Effective Against Sepsis-Induced Acute Kidney Injury in Rat Model

Introduction

The incidence and mortality rates of sepsis-induced acute kidney injury (SAKI) remain high, posing a substantial healthcare burden. Studies have implicated a connection between the development of SAKI and inflammation response, apoptosis, and autophagy. Moreover, evidence suggests that manipulating autophagy could potentially influence the prognosis of this condition. Notably, exosomes derived from bone mesenchymal stem cells (BMSCs-Exo) have exhibited promise in mitigating cellular damage by modulating pathways associated with inflammation, apoptosis, and autophagy. Thus, this study aims to investigate the influence of BMSCs-Exo on SAKI and the potential mechanisms that drive this impact.

Methods

The SAKI model was induced in HK-2 cells using lipopolysaccharide (LPS), while rats underwent cecal ligation and puncture (CLP) to simulate the condition. Cell viability was assessed using the CCK-8 kit, and kidney damage was evaluated through HE staining, blood urea nitrogen (BUN), and serum creatinine (SCr) measurements. Inflammatory-related RNAs and proteins were quantified via qPCR and ELISA, respectively. Apoptosis was determined through apoptosis-related protein levels, flow cytometry, and TUNEL staining. Western blot analysis was utilized to measure associated protein expressions.

Results

In vivo, BMSCs-Exo ameliorated kidney injury in CLP-induced SAKI rats, reducing inflammatory cytokine production and apoptosis levels. Fluorescence microscope observed the absorption of BMSCs-Exo by renal cells following injection via tail vein. In the SAKI rat kidney tissue, there was an upregulation of LC3-II/LC3-I, p62, and phosphorylated AMP-activated protein kinase (p-AMPK) expressions, indicating blocked autophagic flux, while phosphorylated mammalian target of rapamycin (p-mTOR) expression was downregulated. However, BMSCs-Exo enhanced LC3-II/LC3-I and p-AMPK expression, concurrently reducing p62 and p-mTOR levels. In vitro, BMSCs-Exo enhanced cell viability in LPS-treated HK-2 cells, and exerted anti-inflammation and anti-apoptosis effects which were consistent with the results in vivo. Similarly, rapamycin (Rapa) exhibited a protective effect comparable to BMSCs-Exo, albeit partially abrogated by 3-methyladenine (3-MA).

Conclusion

BMSCs-Exo mitigate inflammation and apoptosis through autophagy in SAKI, offering a promising avenue for SAKI treatment.

Mesenchymal stromal cells secretome restores bioenergetic and redox homeostasis in human proximal tubule cells after ischemic injury

BACKGROUND

Ischemia/reperfusion injury is the leading cause of acute kidney injury (AKI). The current standard of care focuses on supporting kidney function, stating the need for more efficient and targeted therapies to enhance repair. Mesenchymal stromal cells (MSCs) and their secretome, either as conditioned medium (CM) or extracellular vesicles (EVs), have emerged as promising options for regenerative therapy; however, their full potential in treating AKI remains unknown.

METHODS

In this study, we employed an in vitro model of chemically induced ischemia using antimycin A combined with 2-deoxy-D-glucose to induce ischemic injury in proximal tubule epithelial cells. Afterwards we evaluated the effects of MSC secretome, CM or EVs obtained from adipose tissue, bone marrow, and umbilical cord, on ameliorating the detrimental effects of ischemia. To assess the damage and treatment outcomes, we analyzed cell morphology, mitochondrial health parameters (mitochondrial activity, ATP production, mass and membrane potential), and overall cell metabolism by metabolomics.

RESULTS

Our findings show that ischemic injury caused cytoskeletal changes confirmed by disruption of the F-actin network, energetic imbalance as revealed by a 50% decrease in the oxygen consumption rate, increased oxidative stress, mitochondrial dysfunction, and reduced cell metabolism. Upon treatment with MSC secretome, the morphological derangements were partly restored and ATP production increased by 40-50%, with umbilical cord-derived EVs being most effective. Furthermore, MSC treatment led to phenotype restoration as indicated by an increase in cell bioenergetics, including increased levels of glycolysis intermediates, as well as an accumulation of antioxidant metabolites.

CONCLUSION

Our in vitro model effectively replicated the in vivo-like morphological and molecular changes observed during ischemic injury. Additionally, treatment with MSC secretome ameliorated proximal tubule damage, highlighting its potential as a viable therapeutic option for targeting AKI.

Urolithin A alleviates early brain injury after subarachnoid hemorrhage by regulating the AMPK/mTOR pathway-mediated autophagy

OBJECTIVE

Unfavorable outcomes in patients with subarachnoid hemorrhage (SAH) are mainly attributed to early brain injury (EBI). Reduction of neuronal death can improve the prognosis in SAH patients. Autophagy and apoptosis are critical players in neuronal death. Urolithin A (UA) is a natural compound produced by gut bacteria from ingested ellagitannins and ellagic acid. Here, we detected the role of UA in EBI post-SAH.

METHODS

We established an animal model of SAH in rats by endovascular perforation, with administration of UA, 3-methyladenine (3-MA) and Compound C. SAH grading, neurological function, brain water content, western blotting analysis of levels of proteins related to apoptosis, autophagy and pathways, blood-brain barrier (BBB) integrity, TUNEL staining, and immunofluorescence staining of LC3 were evaluated at 24h after SAH.

RESULTS

SAH induction led to neurological dysfunctions, BBB disruption, and cerebral edema at 24h post-SAH in rats, which were relieved by UA. Additionally, cortical neuronal apoptosis in SAH rats was also attenuated by UA. Moreover, UA restored autophagy level in SAH rats. Mechanistically, UA activated the AMPK/mTOR pathway. Furthermore, inhibition of autophagy and AMPK limited UA-mediated protection against EBI post-SAH CONCLUSION: UA alleviates neurological deficits, BBB permeability, and cerebral edema by inhibiting cortical neuronal apoptosis through regulating the AMPK/mTOR pathway-dependent autophagy in rats following SAH.

Autophagy in acute kidney injury and maladaptive kidney repair

Acute kidney injury (AKI) is a major renal disease characterized by a sudden decrease in kidney function. After AKI, the kidney has the ability to repair, but if the initial injury is severe the repair may be incomplete or maladaptive and result in chronic kidney problems. Autophagy is a highly conserved pathway to deliver intracellular contents to lysosomes for degradation. Autophagy plays an important role in maintaining renal function and is involved in the pathogenesis of renal diseases. Autophagy is activated in various forms of AKI and acts as a defense mechanism against kidney cell injury and death. After AKI, autophagy is maintained at a relatively high level in kidney tubule cells during maladaptive kidney repair but the role of autophagy in maladaptive kidney repair has been controversial. Nonetheless, recent studies have demonstrated that autophagy may contribute to maladaptive kidney repair after AKI by inducing tubular degeneration and promoting a profibrotic phenotype in renal tubule cells. In this review, we analyze the role and regulation of autophagy in kidney injury and repair and discuss the therapeutic strategies by targeting autophagy.

Ferulic acid protects renal tubular epithelial cells against anoxia/reoxygenation injury mediated by AMPKα1

Anoxia/reoxygenation (A/R) injury causes dysfunction of rat renal tubular epithelial cells (NRK-52E), which is associated with excess reactive oxygen species (ROS) generation and eventually leads to apoptosis. Ferulic acid (FA), a phenolic acid, which is abundant in fruits and vegetables. FA possesses the properties of scavenging free radicals and cytoprotection against oxygen stress. In the study, the protective effects of FA against NRK-52E cells damage induced by A/R were explored and confirmed the role of AMP-activated protein kinaseα1 (AMPKα1). We found that after NRK-52E cells suffered A/R damage, FA pretreatment increased the cell viability and decreased LDH activity in culture medium in a concentration-dependent manner, the activities of endogenous antioxidant enzymes such as glutathione peroxidase, superoxide dismutase and catalase improved, intracellular ROS generation and malondialdehyde contents mitigated. In addition, pretreatment of 75 μM FA ameliorated mitochondrial dysfunction by A/R-injury and ultimately decreased apoptosis (25.3 ± 0.61 vs 12.1 ± 0.60), which was evidenced by preventing the release of cytochrome c from mitochondria to the cytoplasm. 75 μM FA pretreatment also significantly upregulated AMPKα1 expression (3.16 ± 0.18 folds) and phosphorylation (2.56 ± 0.13 folds). However, compound C, a specific AMPK inhibitor, significantly attenuated FA pretreatment's effects, as mentionedabove. These results firstly clarified that FA pretreatment attenuated NRK-52E cell damage induced by A/R via upregulating AMPKα1 expression and phosphorylation.

AMPK, metabolism, and vascular function

Adenosine monophosphate-activated protein kinase (AMPK) is a cellular energy sensor activated during energy stress that plays a key role in maintaining energy homeostasis. This ubiquitous signaling pathway has been implicated in multiple functions including mitochondrial biogenesis, redox regulation, cell growth and proliferation, cell autophagy and inflammation. The protective role of AMPK in cardiovascular function and the involvement of dysfunctional AMPK in the pathogenesis of cardiovascular disease have been highlighted in recent years. In this review, we summarize and discuss the role of AMPK in the regulation of blood flow in response to metabolic demand and the basis of the AMPK physiological anticontractile, antioxidant, anti-inflammatory, and antiatherogenic actions in the vascular system. Investigations by others and us have demonstrated the key role of vascular AMPK in the regulation of endothelial function, redox homeostasis, and inflammation, in addition to its protective role in the hypoxia and ischemia/reperfusion injury. The pathophysiological implications of AMPK involvement in vascular function with regard to the vascular complications of metabolic disease and the therapeutic potential of AMPK activators are also discussed.

MTORC1-Regulated Metabolism Controlled by TSC2 Limits Cardiac Reperfusion Injury

RATIONALE

The mTORC1 (mechanistic target of rapamycin complex-1) controls metabolism and protein homeostasis and is activated following ischemia reperfusion (IR) injury and by ischemic preconditioning (IPC). However, studies vary as to whether this activation is beneficial or detrimental, and its influence on metabolism after IR is little reported. A limitation of prior investigations is their use of broad gain/loss of mTORC1 function, mostly applied before ischemic stress. This can be circumvented by regulating one serine (S1365) on TSC2 (tuberous sclerosis complex) to achieve bidirectional mTORC1 modulation but only with TCS2-regulated costimulation.

OBJECTIVE

We tested the hypothesis that reduced TSC2 S1365 phosphorylation protects the myocardium against IR and is required for IPC by amplifying mTORC1 activity to favor glycolytic metabolism.

METHODS AND RESULTS

Mice with either S1365A (TSC2^SA; phospho-null) or S1365E (TSC2^SE; phosphomimetic) knockin mutations were studied ex vivo and in vivo. In response to IR, hearts from TSC2^SA mice had amplified mTORC1 activation and improved heart function compared with wild-type and TSC2^SE hearts. The magnitude of protection matched IPC. IPC requited less S1365 phosphorylation, as TSC2^SE hearts gained no benefit and failed to activate mTORC1 with IPC. IR metabolism was altered in TSC2^SA, with increased mitochondrial oxygen consumption rate and glycolytic capacity (stressed/maximal extracellular acidification) after myocyte hypoxia-reperfusion. In whole heart, lactate increased and long-chain acylcarnitine levels declined during ischemia. The relative IR protection in TSC2^SA was lost by lowering glucose in the perfusate by 36%. Adding fatty acid (palmitate) compensated for reduced glucose in wild type and TSC2^SE but not TSC2^SA which had the worst post-IR function under these conditions.

CONCLUSIONS

TSC2-S1365 phosphorylation status regulates myocardial substrate utilization, and its decline activates mTORC1 biasing metabolism away from fatty acid oxidation to glycolysis to confer protection against IR. This pathway is also engaged and reduced TSC2 S1365 phosphorylation required for effective IPC. Graphic Abstract: A graphic abstract is available for this article.

Role of Impaired Nutrient and Oxygen Deprivation Signaling and Deficient Autophagic Flux in Diabetic CKD Development: Implications for Understanding the Effects of Sodium-Glucose Cotransporter 2-Inhibitors

Growing evidence indicates that oxidative and endoplasmic reticular stress, which trigger changes in ion channels and inflammatory pathways that may undermine cellular homeostasis and survival, are critical determinants of injury in the diabetic kidney. Cells are normally able to mitigate these cellular stresses by maintaining high levels of autophagy, an intracellular lysosome-dependent degradative pathway that clears the cytoplasm of dysfunctional organelles. However, the capacity for autophagy in both podocytes and renal tubular cells is markedly impaired in type 2 diabetes, and this deficiency contributes importantly to the intensity of renal injury. The primary drivers of autophagy in states of nutrient and oxygen deprivation-sirtuin-1 (SIRT1), AMP-activated protein kinase (AMPK), and hypoxia-inducible factors (HIF-1α and HIF-2α)-can exert renoprotective effects by promoting autophagic flux and by exerting direct effects on sodium transport and inflammasome activation. Type 2 diabetes is characterized by marked suppression of SIRT1 and AMPK, leading to a diminution in autophagic flux in glomerular podocytes and renal tubules and markedly increasing their susceptibility to renal injury. Importantly, because insulin acts to depress autophagic flux, these derangements in nutrient deprivation signaling are not ameliorated by antihyperglycemic drugs that enhance insulin secretion or signaling. Metformin is an established AMPK agonist that can promote autophagy, but its effects on the course of CKD have been demonstrated only in the experimental setting. In contrast, the effects of sodium-glucose cotransporter-2 (SGLT2) inhibitors may be related primarily to enhanced SIRT1 and HIF-2α signaling; this can explain the effects of SGLT2 inhibitors to promote ketonemia and erythrocytosis and potentially underlies their actions to increase autophagy and mute inflammation in the diabetic kidney. These distinctions may contribute importantly to the consistent benefit of SGLT2 inhibitors to slow the deterioration in glomerular function and reduce the risk of ESKD in large-scale randomized clinical trials of patients with type 2 diabetes.

Energy-stress-mediated AMPK activation inhibits ferroptosis

Energy stress depletes ATP and induces cell death. Here, we identify an unexpected inhibitory role of energy stress on ferroptosis, a form of regulated cell death induced by iron-dependent lipid peroxidation. We found that ferroptotic cell death and lipid peroxidation can be inhibited by treatments that induce or mimic energy stress. Inactivation of AMP-activated protein kinase (AMPK), a sensor of cellular energy status, largely abolishes the protective effects of energy stress on ferroptosis in vitro and on ferroptosis-associated renal ischemia/reperfusion injury in vivo. Cancer cells with high basal AMPK activation are resistant to ferroptosis, and AMPK inactivation sensitizes these cells to ferroptosis. Functional and lipidomic analyses further link AMPK regulation of ferroptosis to AMPK-mediated phosphorylation of acetyl-CoA carboxylase (ACC) and polyunsaturated fatty acid biosynthesis. Together, our study demonstrates that energy stress inhibits ferroptosis partly through AMPK, and reveals an unexpected coupling between ferroptosis and AMPK-mediated energy stress signaling.

AMPK activation suppresses mTOR/S6K1 phosphorylation and induces leucine resistance in rats with sepsis

Although it has been known that protein synthesis is suppressed in sepsis, which cannot be corrected by leucine supplement (also known as leucine resistance), the molecular signaling mechanism remains unclear. This study aimed to investigate the AMP-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR) pathway in sepsis-induced leucine resistance and its upstream signals, and to seek a way to correct leucine resistance in sepsis. Sepsis was produced by cecal ligation and puncture (CLP) model in rat. Both septic rats and sham operation rat received total parenteral nutrition (TPN) with or without leucine for 24 h, and then protein synthesis and AMPK/mTOR and protein kinase B (PKB) were tested. In vitro C2C12 cells were treated with or without leucine, and we tested the AMPK/mTOR pathway and protein synthesis. We blocked AMPK by compound C and stimulated it by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) individually. The results showed that AMPK was highly phosphorylated and suppressed mTOR/S6K1 activation in CLP rats. In vitro when AMPK was activated by AICAR, protein synthesis was suppressed and leucine resistance was observed. High phosphorylation of AMPK was accompanied by PKB inactivation in CLP rats. When PKB was blocked, both AMPK activation and leucine resistance were observed. In CLP rats, nutrition support with intensive insulin therapy reversed leucine resistance by activating PKB and suppressing AMPK phosphorylation. These findings suggest that high phosphorylation of AMPK induced by PKB inactivation in sepsis suppresses mTOR, S6K1 phosphorylation, and protein synthesis and leads to leucine resistance. Intensive insulin treatment can reverse leucine resistance by suppressing AMPK activation through activation of PKB.

Effect of ATM on inflammatory response and autophagy in renal tubular epithelial cells in LPS-induced septic AKI

The aim of the present study was to explore the role of ataxia-telangiectasia mutated (ATM) in lipopolysaccharide (LPS)-induced in vitro model of septic acute kidney injury (AKI) and the association between ATM, tubular epithelial inflammatory response and autophagy. The renal tubular epithelial cell HK-2 cell line was cultured and passaged, with HK-2 cell injury induced by LPS. The effects of LPS on HK-2 cell morphology, viability, ATM expression and inflammation were observed. Lentiviral vectors encoding ATM shRNA were constructed to knock down ATM expression in HK-2 cells. The efficiency of ATM knockdown in HK-2 cells was detected by western blot analysis and reverse transcription-quantitative PCR (RT-qPCR). HK-2 cells transfected with the ATM shRNA lentivirus were used for subsequent experiments. Following ATM knockdown, corresponding controls were set up, and the effects of ATM on inflammation and autophagy were detected in HK-2 cells using RT-qPCR, western blotting and ELISA. After LPS stimulation, the HK-2 cells were rounded into a slender or fusiform shape with poorly defined outlines. LPS treatment reduced cell viability in a partly dose-dependent manner. LPS increased the expression of tumor necrosis factor-α, interleukin (IL)-1β and IL-6, with the levels reaching its highest value at 10 µg/ml. IL-6 and IL-1β expression increased with increasing LPS concentration. These findings suggest that LPS reduced HK-2 cell viability whilst increasing the expression of inflammatory factors. Following transfection with ATM shRNA, expression levels of key autophagy indicators microtubule associated protein 1 light chain 3α I/II ratio and beclin-1 in the two ATM shRNA groups were also significantly reduced compared with the NC shRNA group. In summary, downregulation of ATM expression in HK-2 cells reduced LPS-induced inflammation and autophagy in sepsis-induced AKI in vitro, suggesting that LPS may induce autophagy in HK-2 cells through the ATM pathway leading to the upregulation of inflammatory factors.

Advances on Cell Autophagy and Its Potential Regulatory Factors in Renal Ischemia-Reperfusion Injury

Ischemia-reperfusion injury is a major reason for acute kidney injury and various kidney diseases. Autophagy plays an important role during renal ischemia-reperfusion injury (RIRI), but it remains controversial whether autophagy contributes to cell survival or ischemia-reperfusion-induced cell death. In the review, we summarized the function of autophagy in the progression of acute ischemic kidney injury, as well as its related molecular mechanisms. While analyzing the opposite roles of autophagy in RIRI, it was concluded that the protective or detrimental function of autophagy was depending on the timing and amount of the activation of cell autophagy. We also summarized the regulatory agents, including active compounds, proteins, or microRNAs (miRNAs), which regulated the cell autophagy during renal acute ischemic kidney injury process. This explained why the opposite conclusion occurred when cell autophagy was studied in the RIRI models from different researchers. Therefore, the article provided a hypothesis to control cell autophagy at the appropriate timing and intensity so as to alleviate renal injury and sustain cell survival of the renal cell.

SIRT3 Protects Against Acute Kidney Injury via AMPK/mTOR-Regulated Autophagy

Acute kidney injury (AKI), which involves the loss of kidney function caused by damage to renal tubular cells, is an important public health concern. We previously showed that sirtuin (SIRT)3 protects the kidneys against mitochondrial damage by inhibiting the nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasome, attenuating oxidative stress, and downregulating proinflammatory cytokines. In this article, we investigated the role of autophagy, mediated by a mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK), in the protective effect of SIRT3, against sepsis-induced AKI, in a mouse model of cecal ligation and puncture (CLP). The AKI in CLP mice was associated with the upregulation of autophagy markers; this effect was abolished in SIRT3^- mice in parallel with the downregulation of phospho (p)-AMPK and the upregulation of p-mTOR. Pretreatment with the autophagy inhibitor 3-methyladenine (3-MA) or AMPK inhibitor compound isotonic saline (C), exacerbated AKI. SIRT3 overexpression promoted autophagy, upregulated p-AMPK and downregulated p-mTOR in CLP mice, attenuating sepsis-induced AKI, tubular cell apoptosis, and inflammatory cytokine accumulation in the kidneys. The blockage of autophagy induction largely abolished the protective effect of SIRT3 in sepsis-induced AKI. These findings indicate that SIRT3 protects against CLP-induced AKI by inducing autophagy through regulation of the AMPK/mTOR pathway.

Expression changes of autophagy-related proteins in AKI patients treated with CRRT and their effects on prognosis of adult and elderly patients

Background

Sepsis is one of the common death factors in intensive care unit, which refers to the systemic inflammatory response syndrome caused by infection. It has many complications such as acute renal injury, shock, multiple organ dysfunction, and failure. The mortality of acute renal injury is the highest among the complications, which is a serious threat to the safety of patients and affects the quality of life. This study aimed to observe the changes in autophagy-related protein expressions in patients with acute kidney injury (AKI) after continuous renal replacement therapy (CRRT) and their impacts on prognosis.

Methods

207 AKI patients visiting the Emergency Department of The First People's Hospital of Xuzhou from January 2014 to February 2018 were recruited and treated with CRRT. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was applied to detect the expression of autophagy-related genes, including light chain 3 type II (LC3-II), autophagy-related 5 (Atg-5) and Beclin-1, in the monocytes of the patient's peripheral blood before and after treatment. The levels of inflammatory mediators interleukin (IL)-1β and IL-6 were determined via enzyme-linked immunosorbent assay before and after treatment. The patient's serum creatinine (Scr) level before and after treatment was measured using a full-automatic biochemistry analyser. Moreover, the treatment effect was graded after CRRT, and the relationship between the prognosis of patients and the autophagy-related proteins was observed.

Results

The Scr levels in the patients were significantly decreased after treatment with CRRT. Before treatment, the IL-1β and IL-6 blood levels were high in the patients, while the amounts were significantly reduced after CRTT. The expressions of LC3-II, Atg-5 and Beclin-1 in the monocytes of patients after treatment were significantly decreased compared with those before treatment. Compared with those in survived patients, the expression of autophagy-related proteins was significantly elevated in in patients died after one to three weeks after the treatment. IL-1β, IL-6, LC3-II and Beclin-1, but not Atg-5 values were significantly correlated with Scr.

Conclusion

The expression of LC3-II, Atg-5 and Beclin-1 in the monocytes of patients may change prominently after treatment with CRRT, so they are expected to be regarded as new prognostic indicators for AKI patients.

Defining the short-term effects of pharmacological 5'-AMP activated kinase modulators on mitochondrial polarization, morphology and heterogeneity

Background

Under aerobic growth conditions, mitochondria are the major producers of cellular ATP and crucial for the proper performance of organs and tissues. This applies especially to cells with high energy demand, such as the renal proximal tubule epithelium. Mitochondrial dysfunction contributes to the pathology of human health conditions, including various kidney diseases. The improvement of mitochondrial function ameliorates some of these pathologies. This can potentially be achieved with pharmacological compounds. For example, long-term treatment with activators of 5'-AMP activated kinase (AMPK) enhances mitochondrial biogenesis. However, pharmacological damage control during acute cell injury requires that the short-term effects of these compounds and the impact on healthy cells are also understood. It was our objective to define the changes elicited by established modulators of AMPK activity in healthy renal proximal tubule cells.

Methods

Our work combines confocal microscopy with quantitative image analysis, 3D image reconstruction and Western blotting to provide novel insights into the biology of mitochondria. Specifically, we evaluated the effects of pharmacological AMPK modulators (compound C, AICAR, phenformin, resveratrol) on mitochondrial polarization, morphology and heterogeneity. Microscopic studies generated information at the single cell and subcellular levels. Our research focused on LLC-PK1 cells that are derived from the renal proximal tubule. Mitochondrial heterogeneity was also examined in MCF7 breast cancer cells.

Results

Pharmacological agents that affect AMPK activity in renal proximal tubule cells can alter mitochondrial organization and the electrochemical potential across the inner mitochondrial membrane. These changes were compound-specific. Short-term incubation with the AMPK inhibitor compound C caused mitochondrial hyperpolarization. This was accompanied by mitochondrial fragmentation. By contrast, AMPK activators AICAR, phenformin and resveratrol had little impact. We further show that the biological properties of mitochondria are determined by their subcellular location. Mitochondria at the cell periphery displayed higher MitoTracker/Tom70 values as compared to organelles located in the vicinity of the nucleus. This was not limited to renal proximal tubule cells, but also observed in MCF7 cells. Pharmacological AMPK modulators altered these location-dependent properties in a compound-specific fashion. While the region-dependent differences were enhanced with phenformin, they were ameliorated by resveratrol.

Discussion

We evaluated the rapid changes in mitochondrial characteristics that are induced by pharmacological AMPK modulators. Our research supports the concept that pharmacological agents that target AMPK can rearrange mitochondrial networks at the single cell level. Collectively, these insights are relevant to the development of proper strategies for the short-term adjustment of mitochondrial performance.

AMPK: Potential Therapeutic Target for Ischemic Stroke

5'-AMP-activated protein kinase (AMPK), a member of the serine/threonine (Ser/Thr) kinase group, is universally distributed in various cells and organs. It is a significant endogenous defensive molecule that responds to harmful stimuli, such as cerebral ischemia, cerebral hemorrhage, and, neurodegenerative diseases (NDD). Cerebral ischemia, which results from insufficient blood flow or the blockage of blood vessels, is a major cause of ischemic stroke. Ischemic stroke has received increased attention due to its '3H' effects, namely high mortality, high morbidity, and high disability. Numerous studies have revealed that activation of AMPK plays a protective role in the brain, whereas its action in ischemic stroke remains elusive and poorly understood. Based on existing evidence, we introduce the basic structure, upstream regulators, and biological roles of AMPK. Second, we analyze the relationship between AMPK and the neurovascular unit (NVU). Third, the actions of AMPK in different phases of ischemia and current therapeutic methods are discussed. Finally, we evaluate existing controversy and provide a detailed analysis, followed by ethical issues, potential directions, and further prospects of AMPK. The information complied here may aid in clinical and basic research of AMPK, which may be a potent drug candidate for ischemic stroke treatment in the future.

Metformin Improves Neurologic Outcome Via AMP-Activated Protein Kinase-Mediated Autophagy Activation in a Rat Model of Cardiac Arrest and Resuscitation

BACKGROUND

Sudden cardiac arrest (CA) often results in severe injury to the brain, and neuroprotection after CA has proved to be difficult to achieve. Herein, we sought to investigate the effects of metformin pretreatment on brain injury secondary to CA and cardiopulmonary resuscitation.

METHODS AND RESULTS

Rats were subjected to 9-minute asphyxial CA after receiving daily metformin treatment for 2 weeks. Survival rate, neurologic deficit scores, neuronal loss, AMP-activated protein kinase (AMPK), and autophagy activation were assessed at indicated time points within the first 7 days after return of spontaneous circulation. Our results showed that metformin pretreatment elevated the 7-day survival rate from 55% to 85% and significantly reduced neurologic deficit scores. Moreover, metformin ameliorated CA-induced neuronal degeneration and glial activation in the hippocampal CA1 region, which was accompanied by augmented AMPK phosphorylation and autophagy activation in affected neuronal tissue. Inhibition of AMPK or autophagy with pharmacological inhibitors abolished metformin-afforded neuroprotection, and augmented autophagy induction by metformin treatment appeared downstream of AMPK activation.

CONCLUSIONS

Taken together, our data demonstrate, for the first time, that metformin confers neuroprotection against ischemic brain injury after CA/cardiopulmonary resuscitation by augmenting AMPK-dependent autophagy activation.

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.

Inhibition of autophagy with 3-methyladenine is protective in a lethal model of murine endotoxemia and polymicrobial sepsis

Here, the regulatory role of autophagy is examined in both an LPS-induced lethal endotoxic shock mouse model and cecal ligation and puncture (CLP) mouse model. Autophagy-inhibitor 3-methyladenine (3-MA) and autophagy-enhancer rapamycin were administrated to mice challenged with LPS or CLP. Animals challenged with LPS or CLP combined with 3-MA displayed increased survival after endotoxemia, but LPS combined with rapamycin worsened the endotoxic shock of the mice. Among the different organs studied, the lungs and intestines exhibited significant differences among LPS alone, LPS combined with 3-MA and LPS combined with rapamycin. LPS combined with 3-MA attenuated the inflammatory damages of these organs as compared with LPS alone. In contrast, LPS combined with rapamycin increased damage in these organs. Consistently, serum inflammatory mediators TNF-α and IL-6 were decreased by the treatment of LPS combined with 3-MA as compared with LPS alone, while administration of LPS combined with rapamycin increased the serum TNF-α and IL-6 levels. Similar results were found in mouse bone marrow-derived macrophages exposed to LPS. Moreover, the regulatory effect of autophagy to endotoxic shock is dependent on the TLR4 signaling pathway. Our results demonstrate the central role of autophagy in the regulation of endotoxic shock and its potential modulation for endotoxic shock treatment.

Autophagy: novel applications of nonsteroidal anti-inflammatory drugs for primary cancer

In eukaryotic cells, autophagy is a process associated with programmed cell death. During this process, cytoplasmic proteins and organelles are engulfed by double-membrane autophagosomes, which then fuse with lysosomes to form autolysosomes. These autolysosomes then degrade their contents to recycle the cellular components. Autophagy has been implicated in a wide variety of physiological and pathological processes that are closely related to tumorigenesis. In recent years, an increasing number of studies have indicated that nonsteroidal anti-inflammatory drugs, such as celecoxib, meloxicam, sulindac, aspirin, sildenafil, rofecoxib, and sodium salicylate, have diverse effects in cancer that are mediated by the autophagy pathway. These nonsteroidal anti-inflammatory drugs can modulate tumor autophagy through the PI3K/Akt/mTOR, MAPK/ERK1/2, P53/DRAM, AMPK/mTOR, Bip/GRP78, CHOP/ GADD153, and HGF/MET signaling pathways and inhibit lysosome function, leading to p53-dependent G1 cell-cycle arrest. In this review, we summarize the research progress in autophagy induced by nonsteroidal anti-inflammatory drugs and the molecular mechanisms of autophagy in cancer cells to provide a reference for the potential benefits of nonsteroidal anti-inflammatory drugs in cancer chemotherapy.

Autophagy: A new treatment strategy for MSC-based therapy in acute kidney injury (Review)

Acute kidney injury (AKI) is a common and serious medical condition associated with poor health outcomes. Autophagy is a conserved multistep pathway that serves a major role in many biological processes and diseases. Recent studies have demonstrated that autophagy is induced in proximal tubular cells during AKI. Autophagy serves a pro‑survival or pro‑death role under certain conditions. Furthermore, mesenchymal stem cells (MSCs) have therapeutic potential in the repair of renal injury. This review summarizes the recent progress on the role of autophagy in AKI and MSCs‑based therapy for AKI. Further research is expected to prevent and treat acute kidney injury.

Necrostatin-1 attenuates sepsis-associated acute kidney injury by promoting autophagosome elimination in renal tubular epithelial cells

The aim of the present study was to investigate the protective effect of necrostatin‑1 (Nec‑1) in sepsis‑associated acute kidney injury (SA‑AKI). An SA‑AKI mouse model was established through an intraperitoneal injection of lipopolysaccharide (LPS), and Nec‑1 was administered to the mice prior to the establishment of SA‑AKI. Renal function and histological changes were evaluated, and the expression levels of microtubule‑associated protein light chain 3‑II (LC3‑II) and p62, as markers of autophagic flux, were detected. Autophagosomes and autolysosomes in renal tubular epithelial cells were also identified using electron microscopy. Pretreatment with Nec‑1 could attenuate the LPS‑induced increases in the concentrations of blood urea nitrogen (LPS+Nec‑1 vs. LPS group, 14.15±4.14 mmol/l vs. 32.54±5.46 mmol/l, respectively; P<0.001) and serum creatinine (11.50±1.67 µmol/l vs. 30.08±4.18 µmol/l, respectively; P<0.001). However, there were no significant differences in the rate of renal tubular epithelial cell necrosis between the groups. In the renal tissues of SA‑AKI mice, protein analysis showed that the LC3‑II and p62 proteins were increased, while a reverse transcription‑quantitative Reverse transcription‑polymerase chain reaction analysis detected no increase in LC3‑II or p62 mRNA. Additionally, a high number of autophagosomes, but not of autolysosomes, were observed by electron microscopy. When mice were pretreated with Nec‑1, the levels of LC3‑II and p62 decreased, and a large number of autolysosomes were observed by electron microscopy in the Nec‑1 pretreatment group. These results indicated that Nec‑1 improved autophagosome elimination, a process that is impaired by LPS, in renal tubular epithelial cells. This potentially enabled Nec‑1 to prevent SA‑AKI. Furthermore, the findings suggested that the protective effect of Nec‑1 may not have involved the inhibition of necroptosis, but may have occurred through the promotion of autophagosome elimination in renal tubular epithelial cells.

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.

Cell-specific regulation of iNOS by AMP-activated protein kinase in primary rat hepatocytes

BACKGROUND

AMP-activated protein kinase (AMPK) regulates several metabolic pathways in hepatocytes that are critical to the hepatic response to sepsis and shock. Induction of nitric oxide synthesis is an important response to sepsis, inflammation and shock and many of the stimuli that upregulate inducible nitric oxide synthase (iNOS) also activate AMPK. AMPK inhibits nitric oxide (NO) production in skeletal and cardiac muscle cells, but the role of AMPK in regulating iNOS expression in hepatocytes has not been determined.

MATERIALS AND METHODS

Primary cultured rat hepatocytes were preincubated with an AMPK inhibitor, AMPK activators, or transfected with AMPK siRNA before being treated with the proinflammatory cytokines interleukin-1β (IL-1β) and interferon-γ (IFNγ). The hepatocyte cell lysate and culture supernatants were collected for Western blot analysis and Griess assay.

RESULTS

IL-1β and IFNγ markedly upregulated iNOS expression and AMPK phosphorylation. IL-1β + IFNγ-induced NO production and iNOS expression were significantly decreased in hepatocytes treated with the AMPK inhibitor compound C and AMPK knockdown by AMPK siRNA. Cytokine-induced iNOS expression was increased by AMPK activators 1-oxo-2-(2H-pyrrolium-1-yl)-1H-inden-3-olate, AMPK signaling activator III and AICA-riboside. Compound C upregulated Akt and c-Jun N-terminal kinase phosphorylation but decreased IκBα phosphorylation. AICA-riboside exerted opposite effects on these signaling pathways in hepatocytes.

CONCLUSIONS

In contrast to other cell types, AMPK increased IL-1β + IFNγ-induced NO production and iNOS expression through the Akt, c-Jun N-terminal kinase, and NF-κΒ signaling pathways in primary hepatocytes. These data suggest that AMPK-altering medications used clinically may have subsequent effects on iNOS expression and proinflammatory signaling pathways.

Determination of optimized oxygen partial pressure to maximize the liver regenerative potential of the secretome obtained from adipose-derived stem cells

BACKGROUND

A hypoxic-preconditioned secretome from stem cells reportedly promotes the functional and regenerative capacity of the liver more effectively than a control secretome. However, the optimum oxygen partial pressure (pO₂) in the cell culture system that maximizes the therapeutic potential of the secretome has not yet been determined.

METHODS

We first determined the cellular alterations in adipose tissue-derived stem cells (ASCs) cultured under different pO₂ (21%, 10%, 5%, and 1%). Subsequently, partially hepatectomized mice were injected with the secretome of ASCs cultured under different pO₂, and then sera and liver specimens were obtained for analyses.

RESULTS

Of all AML12 cells cultured under different pO₂, the AML12 cells cultured under 1% pO₂ showed the highest mRNA expression of proliferation-associated markers (IL-6, HGF, and VEGF). In the cell proliferation assay, the AML12 cells cultured with the secretome of 1% pO₂ showed the highest cell proliferation, followed by the cells cultured with the secretome of 21%, 10%, and 5% pO₂, in that order. When injected into the partially hepatectomized mice, the 1% pO₂ secretome most significantly increased the number of Ki67-positive cells, reduced serum levels of proinflammatory mediators (IL-6 and TNF-α), and reduced serum levels of liver transaminases. In addition, analysis of the liver specimens indicated that injection with the 1% pO₂ secretome maximized the expression of the intermediate molecules of the PIP3/Akt and IL-6/STAT3 signaling pathways, all of which are known to promote liver regeneration.

CONCLUSIONS

The data of this study suggest that the secretome of ASCs cultured under 1% pO₂ has the highest liver reparative and regenerative potential of all the secretomes tested here.

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.

Preconditioning mice with activators of AMPK ameliorates ischemic acute kidney injury in vivo

This study had two objectives: 1) to determine whether preconditioning cultured proximal tubular cells (PTCs) with pharmacological activators of AMP-activated protein kinase (AMPK) protects these cells from apoptosis induced by metabolic stress in vitro and 2) to assess the effects of preconditioning mice with these agents on the severity of ischemic acute renal kidney injury (AKI) in vivo. We demonstrate that preconditioning PTCs with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) or A-769662 reduces apoptosis of PTCs induced by subsequent stress. We also show that the reduction in cell death during metabolic stress associated with pretreatment by AMPK activators is associated with an increase in the cytosolic level of ATP, which is mediated by an increase in the rate of glycolysis. In addition, we provide evidence that the effect of AMPK activators on glycolysis is mediated, at least in part, by an increased uptake of glucose, and by the induction of hexokinase II (HK II) expression. Our data also show that the increased in HK II expression associated with preconditioning with AMPK activators is mediated by the activation (phosphorylation) of the cAMP-response element binding protein (CREB). We also provide entirely novel evidence that that A-79662 is substantially more effective than AICAR in mediating these alterations in PTCs in vitro. Finally, we demonstrate that preconditioning mice with AICAR or A-769662 substantially reduces the severity of renal dysfunction and tubular injury in a model of ischemic AKI in vivo and that the efficacy of AICAR and A-768662 in ameliorating ischemic AKI in vivo is comparable.

Brazilin exerts protective effects against renal ischemia-reperfusion injury by inhibiting the NF-κB signaling pathway

Renal ischemia-reperfusion (I/R) injury is associated with high morbidity and mortality as there is currently no available effective therapeutic strategy with which to treat this injury. Thus, the aim of this study was to investigate the potential protective effects of brazilin, a major active component of the Chinese medicine Caesalpinia sappan L., against renal I/R injury in vitro and in vivo. Rats were subjected to removal of the right kidney and I/R injury to the left kidney (ischemia for 45 min followed by reperfusion for 24 h). Treatment with brazilin (30 mg/kg, administered intravenously at 30 min prior to ischemia) led to the reversal of I/R-induced changes in serum creatinine (Scr) and blood urea nitrogen (BUN) levels, and also attenuated the histopathological damage induced by I/R. Furthermore, TUNEL assay revealed that brazilin reduced cell necrosis, and significantly decreased the expression of tumor necrosis factor (TNF)-α and interleukin (IL)-1β in renal tissue. Moreover, HK-2 cells were used in order to elucidate the mechanisms responsible for the protective effects of brazilin. The levels of phosphorylated IκBα and the nuclear translocation of nuclear factor-κB (NF-κB) were all evidently decreased by brazilin. These findings suggested that pre-treatment with brazilin protects against I/R-induced renal damage and suppresses the inflammatory response by inhibiting the activation of the NF-κB signaling pathway.

Autophagy in sepsis: Degradation into exhaustion?

Autophagy is one of the innate immune defense mechanisms against microbial challenges. Previous in vitro and in vivo models of sepsis demonstrated that autophagy was activated initially in sepsis, followed by a subsequent phase of impairment. Autophagy modulation appears to be protective against multiple organ injuries in these murine sepsis models. This is achieved in part by preventing apoptosis, maintaining a balance between the productions of pro- and anti-inflammatory cytokines, and preserving mitochondrial functions. This article aims to discuss the role of autophagy in sepsis and the therapeutic potential of autophagy enhancers.

Heme oxygenase‑1 protects H2O2‑insulted glomerular mesangial cells from excessive autophagy

Increasing evidence has demonstrated that the activation of heme oxygenase (HO)‑1 reduces autophagy stimulated by oxidative stress injury, in which the supraphysiological production of reactive oxygen species (ROS) is detected. However, the potential mechanism underlying this effect remains unclear. The present study aimed to investigate the function of HO‑1 activation in the regulation of autophagy in glomerular mesangial cells subjected to H2O2‑induced oxidative stress injury. The results demonstrated that the HO‑1 agonist, hemin, reduces the LC3 protein level, which was enhanced by H2O2 treatment. Furthermore, hemin‑activated HO‑1 may function as a regulator of oxidative stress‑induced autophagy in a dose‑dependent manner. Pharmacological activation of c‑Jun N‑terminal kinase (JNK) inhibited the effect of hemin, indicating that the JNK signaling pathway is associated with the mechanism of HO‑1 in impeding excessive autophagy. In addition to successfully alleviating H2O2‑induced oxidative stress and cellular apoptosis, hemin‑activated HO‑1 may provide cytoprotection against rapamycin, a specific autophagy agonist. The present result suggested the inhibitory action of HO‑1 in the avoidance of a potentially enhanced linkage between autophagy and apoptosis, particularly in the setting of excessive ROS. Therefore, enhancing the intracellular activity of HO‑1 may assist the crosstalk between oxidative stress, autophagy and apoptosis, and represent a novel therapeutic strategy for renal ischemic disease.

New Insights into the Role of Autophagy in Ovarian Cryopreservation by Vitrification

Ovarian cryopreservation by vitrification is a highly useful method for preserving female fertility during radiotherapy and chemotherapy. However, cryoinjury, osmotic stress during vitrification, and ischemia/reperfusion during transplantation lead to loss of ovarian follicles. Ovarian follicle loss may be partially reduced by several methods; however, studies regarding the mechanism of ovarian follicle loss have only investigated cell apoptosis, which consists of type I programmed cell death. Autophagy is type II programmed cell death, and cell homeostasis is maintained by autophagy during conditions of stress. The role of autophagy during cryopreservation by vitrification has rarely been reported. The potential role of autophagy during ovarian cryopreservation by vitrification is reviewed in this article.

Autophagy in acute kidney injury

Autophagy is a conserved multistep pathway that degrades and recycles damaged organelles and macromolecules to maintain intracellular homeostasis. The autophagy pathway is upregulated under stress conditions including cell starvation, hypoxia, nutrient and growth-factor deprivation, endoplasmic reticulum stress, and oxidant injury, most of which are involved in the pathogenesis of acute kidney injury (AKI). Recent studies demonstrate that basal autophagy in the kidney is vital for the normal homeostasis of the proximal tubules. Deletion of key autophagy proteins impaired renal function and increased p62 levels and oxidative stress. In models of AKI, autophagy deletion in proximal tubules worsened tubular injury and renal function, highlighting that autophagy is renoprotective in models of AKI. In addition to nonselective sequestration of autophagic cargo, autophagy can facilitate selective degradation of damaged organelles, particularly mitochondrial degradation through the process of mitophagy. Damaged mitochondria accumulate in autophagy-deficient kidneys of mice subjected to ischemia-reperfusion injury, but the precise mechanisms of regulation of mitophagy in AKI are not yet elucidated. Recent progress in identifying the interplay of autophagy, apoptosis, and regulated necrosis has revived interest in examining shared pathways/molecules in this crosstalk during the pathogenesis of AKI. Autophagy and its associated pathways pose potentially unique targets for therapeutic interventions in AKI.

β-Guanidinopropionic acid extends the lifespan of Drosophila melanogaster via an AMP-activated protein kinase-dependent increase in autophagy

Previous studies have demonstrated that AMP‐activated protein kinase (AMPK) controls autophagy through the mammalian target of rapamycin (mTOR) and Unc‐51 like kinase 1 (ULK1/Atg1) signaling, which augments the quality of cellular housekeeping, and that β‐guanidinopropionic acid (β‐GPA), a creatine analog, leads to a chronic activation of AMPK. However, the relationship between β‐GPA and aging remains elusive. In this study, we hypothesized that feeding β‐GPA to adult Drosophila produces the lifespan extension via activation of AMPK‐dependent autophagy. It was found that dietary administration of β‐GPA at a concentration higher than 900 mm induced a significant extension of the lifespan of Drosophila melanogaster in repeated experiments. Furthermore, we found that Atg8 protein, the homolog of microtubule‐associated protein 1A/1B‐light chain 3 (LC3) and a biomarker of autophagy in Drosophila, was significantly upregulated by β‐GPA treatment, indicating that autophagic activity plays a role in the effect of β‐GPA. On the other hand, when the expression of Atg5 protein, an essential protein for autophagy, was reduced by RNA interference (RNAi), the effect of β‐GPA on lifespan extension was abolished. Moreover, we found that AMPK was also involved in this process. β‐GPA treatment significantly elevated the expression of phospho‐T172‐AMPK levels, while inhibition of AMPK by either AMPK‐RNAi or compound C significantly attenuated the expression of autophagy‐related proteins and lifespan extension in Drosophila. Taken together, our results suggest that β‐GPA can induce an extension of the lifespan of Drosophila via AMPK‐Atg1‐autophagy signaling pathway.

Aloperine Protects Mice against Ischemia-Reperfusion (IR)-Induced Renal Injury by Regulating PI3K/AKT/mTOR Signaling and AP-1 Activity

Aloperine is a quinolizidine alkaloid extracted from the leaves of Sophora plants. It has been recognized with the potential to treat inflammatory and allergic diseases as well as tumors. In this report, we demonstrate that pretreatment with aloperine provided protection for mice against ischemia-reperfusion (IR)-induced acute renal injury as manifested by the attenuated inflammatory infiltration, reduced tubular apoptosis, and well-preserved renal function. Mechanistic studies revealed that aloperine selectively repressed IL-1β and IFN-γ expression by regulating PI3K/Akt/mTOR signaling and NF-κB transcriptional activity. However, aloperine did not show a perceptible impact on IL-6 and TGF-β expression and the related Jak2/Stat3 signaling. It was also noted that aloperine regulates AP-1 activity, through which it not only enhances SOD expression to increase reactive oxygen species (ROS) detoxification but also promotes the expression of antiapoptotic Bcl-2, thereby preventing tubular cells from IR-induced apoptosis. Collectively, our data suggest that administration of aloperine prior to IR insults, such as renal transplantation, could be a viable approach to prevent IR-induced injuries.

Blocking autophagy enhances meloxicam lethality to hepatocellular carcinoma by promotion of endoplasmic reticulum stress

OBJECTIVES

Meloxicam, a selective cyclooxygenase-2 (COX-2) inhibitor, has been demonstrated to exert anti-tumour effects against various malignancies. However, up to now, mechanisms involved in meloxicam anti-hepatocellular carcinoma effects have remained unclear.

MATERIALS AND METHODS

Cell viability and apoptosis were assessed by CCK-8 and flow cytometry. Endoplasmic reticulum (ER) stress and autophagy-associated molecules were analysed by western blotting and immunofluorescence assay. GRP78 and Atg5 knock-down by siRNA or chemical inhibition was used to investigate cytotoxic effects of meloxicam treatment on HCC cells.

RESULTS

We found that meloxicam led to apoptosis and autophagy in HepG2 and Bel-7402 cells via a mechanism that involved ER stress. Up-regulation of GRP78 signalling pathway from meloxicam-induced ER stress was critical for activation of autophagy. Furthermore, autophagy activation attenuated ER stress-related cell death. Blocking autophagy by 3-methyladenine (3-MA) or Atg5 siRNA knock-down enhanced meloxicam lethality for HCC by activation of ER stress-related apoptosis. In addition, GRP78 seemed to lead to autophagic activation via the AMPK-mTOR signalling pathway. Blocking AMPK with a chemical inhibitor inhibited autophagy suggesting that meloxicam-regulated autophagy requires activation of AMPK.

CONCLUSIONS

Our results revealed that both ER stress and autophagy were involved in cell death evoked by meloxicam in HCC cells. This inhibition of autophagy to enhance meloxicam lethality, suggests a novel therapeutic strategy against HCC.

P-Glycoprotein Induction Ameliorates Colistin Induced Nephrotoxicity in Cultured Human Proximal Tubular Cells

The pathogenesis of colistin induced nephrotoxicity is poorly understood. Currently there are no effective therapeutic or prophylactic agents available. This study was aimed to determine the mechanism of colistin induced nephrotoxicity and to determine whether P-glycoprotein (P-gp) induction could prevent colistin induced nephrotoxicity. Colistin induced cell toxicity in cultured human proximal tubular cells in both dose and time dependent manner. Colistin provoked ROS in a dose dependent manner as measured by DCF-DA. To investigate apoptosis, caspase 3/7 activity was determined. Caspase 3/7 activity was increased dose dependently (25, 50, 100 μg/ml) at 6 h. Autophagosome formation was assessed by measuring LC3- II/LC3-I ratio. The ratio of LC3-II to LC3- I was increased at 2 h (25 μg/ml). Suppression of autophagosome formation increased colistin induced nephrotoxicity. The expression of P-gp and the cell toxicity was determined in colistin with or without dexamethasone (P-gp inducer) and verapamil (selective P-gp inhibitor). Colistin itself suppressed the expression of P-gp. P-gp expression and activity decreased colistin induced nephrotoxicity with dexamethasone treatment. In addition induced P-gp transporter was shown to improve the efflux effect on colistin treated HK2 cell line, which was demonstrated by calcein-AM fluorescence accumulation assay. The increased activity could be blocked by N-acetylcysteine. In conclusion, colistin induces nephrotoxicity by suppressing P-gp. Induction of P-gp could ameliorate colistin induced nephrotoxicity by decreasing apoptosis.

The Role of Cardiolipin in Cardiovascular Health

Cardiolipin (CL), the signature phospholipid of mitochondrial membranes, is crucial for both mitochondrial function and cellular processes outside of the mitochondria. The importance of CL in cardiovascular health is underscored by the life-threatening genetic disorder Barth syndrome (BTHS), which manifests clinically as cardiomyopathy, skeletal myopathy, neutropenia, and growth retardation. BTHS is caused by mutations in the gene encoding tafazzin, the transacylase that carries out the second CL remodeling step. In addition to BTHS, CL is linked to other cardiovascular diseases (CVDs), including cardiomyopathy, atherosclerosis, myocardial ischemia-reperfusion injury, heart failure, and Tangier disease. The link between CL and CVD may possibly be explained by the physiological roles of CL in pathways that are cardioprotective, including mitochondrial bioenergetics, autophagy/mitophagy, and mitogen activated protein kinase (MAPK) pathways. In this review, we focus on the role of CL in the pathogenesis of CVD as well as the molecular mechanisms that may link CL functions to cardiovascular health.

Melatonin modulates endoplasmic reticulum stress and Akt/GSK3-beta signaling pathway in a rat model of renal warm ischemia reperfusion

Melatonin (Mel) is widely used to attenuate ischemia/reperfusion (I/R) injury in several organs. Nevertheless, the underlying mechanisms remain unclear. This study was conducted to explore the effect of Mel on endoplasmic reticulum (ER) stress, Akt and MAPK cascades after renal warm I/R. Eighteen Wistar rats were randomized into three groups: Sham, I/R, and Mel + I/R. The ischemia period was 60 min followed by 120 min of reperfusion. Mel (10 mg/kg) was administrated 30 min prior to ischemia. The creatinine clearance, MDA, LDH levels, and histopathological changes were evaluated. In addition, Western blot was performed to study ER stress and its downstream apoptosis as well as phosphorylation of Akt, GSK-3β, VDAC, ERK, and P38. Mel decreased cytolysis and lipid peroxidation and improved renal function and morphology compared to I/R group. Parallely, it significantly reduced the ER stress parameters including GRP 78, p-PERK, XBP 1, ATF 6, CHOP, and JNK. Simultaneously, p-Akt level was significantly enhanced and its target molecules GSK-3β and VDAC were inhibited. Furthermore, the ERK and P38 phosphorylation were evidently augmented after Mel administration in comparison to I/R group. In conclusion, Mel improves the recovery of renal function by decreasing ER stress and stimulating Akt pathway after renal I/R injury.

Traumatic Brain Injury-Induced Neuronal Apoptosis is Reduced Through Modulation of PI3K and Autophagy Pathways in Mouse by FTY720

FTY720 is a synthetic compound produced by modification of metabolite from Isaria sinclairii. It is a novel type of immunosuppressive agent inhibiting lymphocyte egress from secondary lymphoid tissues, thereby causing peripheral lymphopenia. Growing evidences have suggested that apoptosis and autophagy were involved in the secondary brain injury after traumatic brain injury (TBI) although FTY720 exerted neuroprotective effects in a variety of neurological diseases except TBI. The present study was aimed to investigate the role of FTY720 in a mouse model of TBI. In experiment 1, ICR mice were divided into four groups: sham group, TBI group, TBI + vehicle group, and TBI + FTY720 group. And the injured cerebral cortex (including both contused and penumbra) was used for analysis. We found that FTY720 administration after TBI improved neurobehavioral function, alleviated brain edema, accompanied by modulation of apoptotic indicators such as Bcl-2, Bcl-xL, Bax, and cytochrome c. In experiment 2, ICR mice were also divided into four groups: sham group, TBI + vehicle group, TBI + FTY720 group, and TBI + FTY720 + inhibitors group. And the injured cerebral cortex (including both contused and penumbra) was used for analysis. We found that FTY720 increased the expression of phospho-protein kinase B (AKT) and some autophagy markers such as LC3 and Beclin 1. In addition, the apoptosis inhibition effect of FTY720 was partly abrogated by the phosphatidylinositide 3-kinases (PI3K)/AKT pathway inhibitor LY294002 and autophagy inhibitor 3-methyladenine. Collectively, our data provide the first evidence that FTY720 exerted neuroprotective effects after TBI, at least in part, through the activation of PI3K/AKT pathway and autophagy.

Ischemic conditioning-induced endogenous brain protection: Applications pre-, per- or post-stroke

In the area of brain injury and neurodegenerative diseases, a plethora of experimental and clinical evidence strongly indicates the promise of therapeutically exploiting the endogenous adaptive system at various levels like triggers, mediators and the end-effectors to stimulate and mobilize intrinsic protective capacities against brain injuries. It is believed that ischemic pre-conditioning and post-conditioning are actually the strongest known interventions to stimulate the innate neuroprotective mechanism to prevent or reverse neurodegenerative diseases including stroke and traumatic brain injury. Recently, studies showed the effectiveness of ischemic per-conditioning in some organs. Therefore the term ischemic conditioning, including all interventions applied pre-, per- and post-ischemia, which spans therapeutic windows in 3 time periods, has recently been broadly accepted by scientific communities. In addition, it is extensively acknowledged that ischemia-mediated protection not only affects the neurons but also all the components of the neurovascular network (consisting of neurons, glial cells, vascular endothelial cells, pericytes, smooth muscle cells, and venule/veins). The concept of cerebroprotection has been widely used in place of neuroprotection. Intensive studies on the cellular signaling pathways involved in ischemic conditioning have improved the mechanistic understanding of tolerance to cerebral ischemia. This has added impetus to exploration for potential pharmacologic mimetics, which could possibly induce and maximize inherent protective capacities. However, most of these studies were performed in rodents, and the efficacy of these mimetics remains to be evaluated in human patients. Several classical signaling pathways involving apoptosis, inflammation, or oxidation have been elaborated in the past decades. Newly characterized mechanisms are emerging with the advances in biotechnology and conceptual renewal. In this review we are going to focus on those recently reported methodological and mechanistic discoveries in the realm of ischemic conditioning. Due to the varied time differences of ischemic conditioning in different animal models and clinical trials, it is important to define optimal timing to achieve the best conditioning induced neuroprotection. This brings not only an opportunity in the treatment of stroke, but challenges as well, as data is just becoming available and the procedures are not yet optimized. The purpose of this review is to shed light on exploiting these ischemic conditioning modalities to protect the cerebrovascular system against diverse injuries and neurodegenerative disorders.

Endoplasmic reticulum chaperone GRP78 is involved in autophagy activation induced by ischemic preconditioning in neural cells

Background

Our previous finding showed that brain ischemic preconditioning mediates neuroprotection through endoplasmic reticulum (ER) stress-induced autophagy. This study was aimed at exploring the role of ER chaperone GRP78 in IPC induced autophagy activation in neural cells.

Results

Ischemic preconditioning (IPC) and oxygen glucose deprivation (OGD) models were established in rat pheochromocytoma (PC12) cells and primary cultured murine cortical neurons. IPC exerted neuroprotection against subsequent OGD injury in both PC12 cells and primary cortical neurons. IPC increased GRP78 expression and activated autophagy, as evidenced by upregulated LC3 and Beclin1, increased autophagic flux and formation of autophagosomes. BAPTA(dibromo-1,2-bis(aminophenoxy)ethane N,N,N9,N9 - tetra acetic acid, 0.125-2 μM) and small interfering RNA targeted GRP78 abrogated IPC induced neuroprotection and decreased the expression of GRP78, LC3II/LC3I and Beclin1. In contrast, lentiviral vector mediated GRP78 overexpression (LV-GRP78) strengthened resistance of PC12 cells to OGD injury and increased LC3 and Beclin1 expression. Moreover, knockdown of GRP78 in stable GRP78 overexpressing PC12 cells abolished the upregulation of LC3II/LC3I. GRP78 might activate autophagy through AMPK - mTOR pathway.

Conclusion

These results suggest that IPC- induced GRP78 upregulation is involved in autophagy activation, and hence exerts protection against ischemic injury in neural cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0112-3) contains supplementary material, which is available to authorized users.