Role of reduced manganese superoxide dismutase in ischemia-reperfusion injury: a possible trigger for autophagy and mitochondrial biogenesis?

Cold Storage Followed by Transplantation Induces Immunoproteasome in Rat Kidney Allografts: Inhibition of Immunoproteasome Does Not Improve Function

Key Points

Cold storage (CS) increases the severity of graft dysfunction in a time-dependent manner, and prolonged CS decreases animal survival. CS plus transplant increases iproeasome levels/assembly in renal allografts; IFN-γ is a potential inducer of the iproteasome. Inhibiting iproteasome ex vivo during renal CS did not confer graft protection after transplantation.

Background

It is a major clinical challenge to ensure the long-term function of transplanted kidneys. Specifically, the injury associated with cold storage (CS) of kidneys compromises the long-term function of the grafts after transplantation. Therefore, the molecular mechanisms underlying CS-related kidney injury are attractive therapeutic targets to prevent injury and improve long-term graft function. Previously, we found that constitutive proteasome function was compromised in rat kidneys after CS followed by transplantation. Here, we evaluated the role of the immunoproteasome (i proteasome), a proteasome variant, during CS followed by transplantation.

Methods

Established in vivo rat kidney transplant model with or without CS containing vehicle or iproteasome inhibitor (ONX 0914) was used in this study. The i proteasome function was performed using rat kidney homogenates and fluorescent-based peptide substrate specific to β 5i subunit. Western blotting and quantitative RT-PCR were used to assess the subunit expression/level of the i proteasome (β 5i) subunit.

Results

We demonstrated a decrease in the abundance of the β 5i subunit of the i proteasome in kidneys during CS, but β 5i levels increased in kidneys after CS and transplant. Despite the increase in β 5i levels and its peptidase activity within kidneys, inhibiting β 5i during CS did not improve graft function after transplantation.

Summary

These results suggest that the pharmacologic inhibition of immunoproteasome function during CS does not improve graft function or outcome. In light of these findings, future studies targeting immunoproteasomes during both CS and transplantation may define the role of immunoproteasomes on short-term and long-term kidney transplant outcomes.

Methane Admixture Protects Liver Mitochondria and Improves Graft Function after Static Cold Storage and Reperfusion

Mitochondria are targets of cold ischemia-reperfusion (IR), the major cause of cell damage during static cold preservation of liver allografts. The bioactivity of methane (CH₄) has recently been recognized in various hypoxic and IR conditions as having influence on many aspects of mitochondrial biology. We therefore hypothesized that cold storage of liver grafts in CH₄-enriched preservation solution can provide an increased defence against organ dysfunction in a preclinical rat model of liver transplantation. Livers were preserved for 24 h in cold histidine-tryptophan-ketoglutarate (HTK) or CH₄-enriched HTK solution (HTK-CH₄) (n = 24 each); then, viability parameters were monitored for 60 min during normothermic isolated reperfusion and perfusate and liver tissue were collected. The oxidative phosphorylation capacity and extramitochondrial Ca²⁺ movement were measured by high resolution respirometry. Oxygen and glucose consumption increased significantly while hepatocellular damage was decreased in the HTK-CH₄ grafts compared to the HTK group. Mitochondrial oxidative phosphorylation capacity was more preserved (128.8 ± 31.5 pmol/s/mL vs 201.3 ± 54.8 pmol/s/mL) and a significantly higher Ca²⁺ flux was detected in HTK-CH₄ storage (2.9 ± 0.1 mV/s) compared to HTK (2.3 ± 0.09 mV/s). These results demonstrate the direct effect of CH₄ on hepatic mitochondrial function and extramitochondrial Ca²⁺ fluxes, which may have contributed to improved graft functions and a preserved histomorphology after cold IR.

Mitochondrial Consequences of Organ Preservation Techniques during Liver Transplantation

Allograft ischemia during liver transplantation (LT) adversely affects the function of mitochondria, resulting in impairment of oxidative phosphorylation and compromised post-transplant recovery of the affected organ. Several preservation methods have been developed to improve donor organ quality; however, their effects on mitochondrial functions have not yet been compared. This study aimed to summarize the available data on mitochondrial effects of graft preservation methods in preclinical models of LT. Furthermore, a network meta-analysis was conducted to determine if any of these treatments provide a superior benefit, suggesting that they might be used on humans. A systematic search was conducted using electronic databases (EMBASE, MEDLINE (via PubMed), the Cochrane Central Register of Controlled Trials (CENTRAL) and Web of Science) for controlled animal studies using preservation methods for LT. The ATP content of the graft was the primary outcome, as this is an indicator overall mitochondrial function. Secondary outcomes were the respiratory activity of mitochondrial complexes, cytochrome c and aspartate aminotransferase (ALT) release. Both a random-effects model and the SYRCLE risk of bias analysis for animal studies were used. After a comprehensive search of the databases, 25 studies were enrolled in the analysis. Treatments that had the most significant protective effect on ATP content included hypothermic and subnormothermic machine perfusion (HMP and SNMP) (MD = −1.0, 95% CI: (−2.3, 0.3) and MD = −1.1, 95% CI: (−3.2, 1.02)), while the effects of warm ischemia (WI) without cold storage (WI) and normothermic machine perfusion (NMP) were less pronounced (MD = −1.8, 95% CI: (−2.9, −0.7) and MD = −2.1 MD; CI: (−4.6; 0.4)). The subgroup of static cold storage (SCS) with shorter preservation time (< 12 h) yielded better results than SCS ≥ 12 h, NMP and WI, in terms of ATP preservation and the respiratory capacity of complexes. HMP and SNMP stand out in terms of mitochondrial protection when compared to other treatments for LT in animals. The shorter storage time at lower temperatures, together with the dynamic preservation, provided superior protection for the grafts in terms of mitochondrial function. Additional clinical studies on human patients including marginal donors and longer ischemia times are needed to confirm any superiority of preservation methods with respect to mitochondrial function.

The Endothelial Glycocalyx as a Target of Ischemia and Reperfusion Injury in Kidney Transplantation-Where Have We Gone So Far?

The damage of the endothelial glycocalyx as a consequence of ischemia and/or reperfusion injury (IRI) following kidney transplantation has come at the spotlight of research due to potential associations with delayed graft function, acute rejection as well as long-term allograft dysfunction. The disintegration of the endothelial glycocalyx induced by IRI is the crucial event which exposes the denuded endothelial cells to further inflammatory and oxidative damage. The aim of our review is to present the currently available data regarding complex links between shedding of the glycocalyx components, like syndecan-1, hyaluronan, heparan sulphate, and CD44 with the activation of intricate immune system responses, including toll-like receptors, cytokines and pro-inflammatory transcription factors. Evidence on modes of protection of the endothelial glycocalyx and subsequently maintenance of endothelial permeability as well as novel nephroprotective molecules such as sphingosine-1 phosphate (S1P), are also depicted. Although advances in technology are making the visualization and the analysis of the endothelial glycocalyx possible, currently available evidence is mostly experimental. Ongoing progress in understanding the complex impact of IRI on the endothelial glycocalyx, opens up a new era of research in the field of organ transplantation and clinical studies are of utmost importance for the future.

Catalytic Antioxidants in the Kidney

Reactive oxygen species and reactive nitrogen species are highly implicated in kidney injuries that include acute kidney injury, chronic kidney disease, hypertensive nephropathy, and diabetic nephropathy. Therefore, antioxidant agents are promising therapeutic strategies for kidney diseases. Catalytic antioxidants are defined as small molecular mimics of antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, and some of them function as potent detoxifiers of lipid peroxides and peroxynitrite. Several catalytic antioxidants have been demonstrated to be effective in a variety of in vitro and in vivo disease models that are associated with oxidative stress, including kidney diseases. This review summarizes the evidence for the role of antioxidant enzymes in kidney diseases, the classifications of catalytic antioxidants, and their current applications to kidney diseases.

Effect of Hyperbaric Oxygen on Tissue Damage and Expression of Adhesion Molecules and C3 in a Rat Model of Renal Ischemia-Reperfusion Injury After Kidney Transplantation

BACKGROUND The aim of this study was to investigate the protective effect and mechanism of hyperbaric oxygen (HBO) in a rat model of renal ischemia-reperfusion injury following kidney transplantation. MATERIAL AND METHODS Sprague Dawley rats were randomly divided into 3 groups (n=18): sham group, kidney transplantation group, and HBO treatment group. Six rats in each group were sacrificed at 1, 3, and 5 hours after reperfusion, and serum and renal tissue were then collected. The serum creatinine levels and histopathological changes of the renal tissue were detected. ICAM-1, VCAM-1, and C3 expression levels were also detected by immunohistochemical staining or real-time polymerase chain reaction. RESULTS Renal function was damaged in the kidney transplantation group and the HBO treatment group compared with sham group (P<0.05). Renal histopathological changes, including tubular cell swelling, tubular dilatation, and hyaline casts, were remarkably reduced in the HBO treatment group compared to the kidney transplantation group. In the immunohistochemical examination, the expression levels of ICAM-1, VCAM-1, and C3 were obviously increased in the kidney transplantation group and the HBO treatment group; moreover, the levels in the HBO treatment group were significantly lower than in the kidney transplantation group (P<0.05). In addition, the ICAM-1 and C3 mRNA levels were increased in the kidney transplantation group and HBO treatment group, but the levels of in the HBO treatment group them were significantly decreased compared to the kidney transplantation group that at 3 and 5 hours after reperfusion (P<0.05). CONCLUSIONS HBO treatment exerted a protective effect on renal function through inhibition of adhesion molecule overexpression and complement system activation in a rat model of renal ischemia-reperfusion injury after kidney transplantation.

The BK activator NS11021 partially protects rat kidneys from cold storage and transplantation-induced mitochondrial and renal injury

Kidneys from deceased donors used for transplantation are placed in cold storage (CS) solution during the search for a matched recipient. However, CS induces mitochondrial and cellular injury, which exacerbates renal graft dysfunction, highlighting the need for therapeutic interventions. Using an in vitro model of renal CS, we recently reported that pharmacological activation of the mitochondrial BK channel (mitoBK) during CS protected against CS-induced mitochondrial injury and cell death. Here, we used an in vivo syngeneic rat model of renal CS (18 hr) followed by transplantation (24 hr reperfusion) (CS+Tx) to similarly evaluate whether addition of a mitoBK activator to the CS solution can alleviate CS+Tx-induced renal injury. Western blots detected the pore-forming α subunit of the BK channel in mitochondrial fractions from rat kidneys, and mitoBK protein expression was reduced after CS+Tx compared to sham surgery. The addition of the BK activator NS11021 (3 μM) to the CS solution partially protected against CS+Tx-induced mitochondrial respiratory dysfunction, oxidative protein nitration, and cell death, but not acute renal dysfunction (SCr and BUN). In summary, the current preclinical study shows that pharmacologically targeting mitoBK channels during CS may be a promising therapeutic intervention to prevent CS+Tx-induced mitochondrial and renal injury.

Targeting Mitochondria during Cold Storage to Maintain Proteasome Function and Improve Renal Outcome after Transplantation

Kidney transplantation is the preferred treatment for end-stage kidney disease (ESKD). Compared to maintenance dialysis, kidney transplantation results in improved patient survival and quality of life. Kidneys from living donors perform best; however, many patients with ESKD depend on kidneys from deceased donors. After procurement, donor kidneys are placed in a cold-storage solution until a suitable recipient is located. Sadly, prolonged cold storage times are associated with inferior transplant outcomes; therefore, in most situations when considering donor kidneys, long cold-storage times are avoided. The identification of novel mechanisms of cold-storage-related renal damage will lead to the development of new therapeutic strategies for preserving donor kidneys; to date, these mechanisms remain poorly understood. In this review, we discuss the importance of mitochondrial and proteasome function, protein homeostasis, and renal recovery during stress from cold storage plus transplantation. Additionally, we discuss novel targets for therapeutic intervention to improve renal outcomes.

The Effects of Meldonium on the Renal Acute Ischemia/Reperfusion Injury in Rats

Acute renal ischemia/reperfusion (I/R) injury is a clinical condition that is challenging to treat. Meldonium is an anti-ischemic agent that shifts energy production from fatty acid oxidation to less oxygen-consuming glycolysis. Thus, in this study we investigated the effects of a four-week meldonium pre-treatment (300 mg/kg b.m./day) on acute renal I/R in male rats (Wistar strain). Our results showed that meldonium decreased animal body mass gain, food and water intake, and carnitine, glucose, and lactic acid kidney content. In kidneys of animals subjected to I/R, meldonium increased phosphorylation of mitogen-activated protein kinase p38 and protein kinase B, and increased the expression of nuclear factor erythroid 2-related factor 2 and haeme oxygenase 1, causing manganese superoxide dismutase expression and activity to increase, as well as lipid peroxidation, cooper-zinc superoxide dismutase, glutathione peroxidase, and glutathione reductase activities to decrease. By decreasing the kidney Bax/Bcl2 expression ratio and kidney and serum high mobility group box 1 protein content, meldonium reduced apoptotic and necrotic events in I/R, as confirmed by kidney histology. Meldonium increased adrenal noradrenaline content and serum, adrenal, hepatic, and renal ascorbic/dehydroascorbic acid ratio, which caused complex changes in renal lipidomics. Taken together, our results have confirmed that meldonium pre-treatment protects against I/R-induced oxidative stress and apoptosis/necrosis.

HO-1 mitigates acute kidney injury and subsequent kidney-lung cross-talk

Ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI), which contributes to the development of chronic kidney disease (CKD). IRI-induced AKI releases proinflammatory cytokines (e.g. IL-1β, TNF-α, IL-6) that induce a systemic inflammatory response, resulting in proinflammatory cells recruitment and remote organ damage. AKI is associated with poor outcomes, particularly when extrarenal complications or distant organ injuries occur. Acute lung injury (ALI) is a major remote organ dysfunction associated with AKI. Hence, kidney-lung cross-talk remains a clinical challenge, especially in critically ill population. The stress-responsive enzyme, heme oxygenase-1 (HO-1) is largely known to protect against renal IRI and may be preventively induced using hemin prior to renal insult. However, the use of hemin-induced HO-1 to prevent AKI-induced ALI remains poorly investigated. Mice received an intraperitoneal injection of hemin or sterile saline 1 day prior to surgery. Twenty-four hours later, mice underwent bilateral renal IRI for 26 min or sham surgery. After 4 or 24 h of reperfusion, mice were sacrificed. Hemin-induced HO-1 improved renal outcomes after IRI (i.e. fewer renal damage, renal inflammation, and oxidative stress). This protective effect was associated with a dampened systemic inflammation (i.e. IL-6 and KC). Subsequently, mitigated lung inflammation was found in hemin-treated mice (i.e. neutrophils influx and lung KC). The present study demonstrates that hemin-induced HO-1 controls the magnitude of renal IRI and the subsequent AKI-induced ALI. Therefore, targeting HO-1 represents a promising approach to prevent the impact of renal IRI on distant organs, such as lung.

Molecular Interactions Between Reactive Oxygen Species and Autophagy in Kidney Disease

Reactive oxygen species (ROS) are highly reactive signaling molecules that maintain redox homeostasis in mammalian cells. Dysregulation of redox homeostasis under pathological conditions results in excessive generation of ROS, culminating in oxidative stress and the associated oxidative damage of cellular components. ROS and oxidative stress play a vital role in the pathogenesis of acute kidney injury and chronic kidney disease, and it is well documented that increased oxidative stress in patients enhances the progression of renal diseases. Oxidative stress activates autophagy, which facilitates cellular adaptation and diminishes oxidative damage by degrading and recycling intracellular oxidized and damaged macromolecules and dysfunctional organelles. In this review, we report the current understanding of the molecular regulation of autophagy in response to oxidative stress in general and in the pathogenesis of kidney diseases. We summarize how the molecular interactions between ROS and autophagy involve ROS-mediated activation of autophagy and autophagy-mediated reduction of oxidative stress. In particular, we describe how ROS impact various signaling pathways of autophagy, including mTORC1-ULK1, AMPK-mTORC1-ULK1, and Keap1-Nrf2-p62, as well as selective autophagy including mitophagy and pexophagy. Precise elucidation of the molecular mechanisms of interactions between ROS and autophagy in the pathogenesis of renal diseases may identify novel targets for development of drugs for preventing renal injury.

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.

Melatonin alleviates asphyxial cardiac arrest-induced cerebellar Purkinje cell death by attenuation of oxidative stress

Although multiple reports using animal models have confirmed that melatonin appears to promote neuroprotective effects following ischemia/reperfusion-induced brain injury, the relationship between its protective effects and activation of autophagy in Purkinje cells following asphyxial cardiac arrest and cardiopulmonary resuscitation (CA/CPR) remains unclear. Rats used in this study were randomly assigned to 6 groups as follows; vehicle-treated sham operated group, vehicle-treated asphyxial CA/CPR operated group, melatonin-treated sham operated group, melatonin-treated asphyxial CA/CPR operated group, PDOT (a MT2 melatonin receptor antagonist) plus (+) melatonin-treated sham operated group and PDOT+melatonin-treated asphyxial CA/CPR operated group. Melatonin (20 mg/kg, i.p., 4 times before CA and 3 times after CA) treatment significantly improved survival rate and neurological deficit compared with the vehicle-treated asphyxial CA/CPR rats (survival rates ≥40% vs 10%), showing that melatonin treatment exhibited protective effect against asphyxial CA/CPR-induced Purkinje cell death. The protective effect of melatonin against CA/CPR-induced Purkinje cell death paralleled a remarkable attenuation of autophagy-like processes (Beclin-1, Atg7 and LC3), as well as a dramatic reduction in superoxide anion radical (O₂·-), intense enhancements of CuZn superoxide dismutase (SOD1) and MnSOD (SOD2) expressions. Furthermore, the protective effect was notably reversed by treatment with PDOT, which is a selective MT2 antagonist. In brief, melatonin conferred neuroprotection against asphyxial CA/CPR-induced Purkinje cell death via inhibiting autophagic activation by reducing expressions of O₂·- and increasing expressions of antioxidant enzymes, and suggests that MT2 is involved in neuroprotective effect of melatonin against Purkinje cell death caused by asphyxial CA/CPR.

Cold Storage Increases Albumin and Advanced Glycation-End Product-Albumin Levels in Kidney Transplants: A Possible Cause for Exacerbated Renal Damage

Prolonged cold storage (CS) of kidneys is associated with poor renal outcome after transplantation (Tx). We recently showed that in rats (Lewis), proteasome and renal function were severely compromised in kidney transplants subjected to CS (CS/Tx) as compared with those without CS exposure (autotransplanted [ATx]).

A Cycle of Altered Proteasome and Reactive Oxygen Species Production in Renal Proximal Tubular Cells

Aims

An intricate relationship exists between the mitochondrial function and proteasome activity. Our recent report showed in a rat model of renal transplantation that mitochondrial dysfunction precedes compromised proteasome function and this results in a vicious cycle of mitochondrial injury and proteasome dysfunction. In this study, we studied whether reactive oxygen species (ROS) has a role in proteasome alteration in renal cells and vice versa.

Methods

We used the genomic and pharmacologic approach on rat normal kidney proximal tubular (NRK) cell lines. First, we knocked down β5 or Rpt6 subunit of the proteasome using small interfering RNA (siRNA) in NRK cells. We also treated NRK cells with Bortezomib, a proteasome inhibitor, and peroxynitrite (a potent ROS).

Results

Studies with RNA interference showed increased mitochondrial ROS following knockdown of β5 or Rpt6 subunit in NRK cells. Similarly, pharmacological inhibition of the proteasome in NRK cells using Bortezomib also showed an increase of mitochondrial ROS in a dose-dependent manner. Next, exposing NRK cells to different concentrations of peroxynitrite provided evidence that the higher levels of peroxynitrite exposure decreased the key subunits (β5 and α3) of the proteasome in NRK cells.

Conclusion

Our results suggest that proteasome inhibition/downregulation increases ROS, which then impairs proteasome subunits in renal proximal tubular cells.

Renal cold storage followed by transplantation impairs proteasome function and mitochondrial protein homeostasis

Identifying pathways related to renal cold storage (CS) that lead to renal damage after transplantation (Tx) will help us design novel pathway-specific therapies to improve graft outcome. Our recent report showed that mitochondrial function was compromised after CS alone, and this was exacerbated when CS was combined with Tx (CS/Tx). The goal of this study was to determine whether the proteasome exacerbates mitochondrial dysfunction after CS/Tx. We exposed the kidneys of male Lewis rats (in vivo) and rat renal proximal tubular (NRK) cells (in vitro) to CS/Tx or rewarming (CS/RW), respectively. To compare CS-induced effects, in vivo kidney Tx without CS exposure (autotransplantation; ATx) was also used. Our study provides the first evidence that the chymotrypsin-like (ChT-L) peptidase activity of the proteasome declined only after CS/Tx or CS/RW, but not after CS or ATx. Interestingly, key mitochondrial proteins involved with respiration [succinate dehydrogenase complex, subunit A (SDHA), a complex II subunit, and ATP5B, an ATP synthase/complex V subunit] were detected in the detergent-insoluble fraction after CS/Tx or CS/RW, with compromised complex V activity. Pharmacological inhibition of ChT-L activity in NRK cells decreased the activity of mitochondrial complexes I, II, and V and also increased the levels of SDHA and ATP5B in the insoluble fraction. On the other hand, inhibiting mitochondrial respiration in NRK cells with antimycin A compromised ChT-L function and increased the amounts of SDHA and ATP5B in the insoluble fraction. Our results suggest that mitochondrial respiratory dysfunction during CS precedes compromised ChT-L function after CS/Tx and proteasome dysfunction further alters mitochondrial protein homeostasis and decreases respiration in the kidneys after CS/Tx. Therefore, therapeutics that preserve mitochondrial and proteasome function during CS may provide beneficial outcomes following transplantation.

Dual effect of hemin on renal ischemia-reperfusion injury

Acute kidney injury (AKI) is a major public health concern, which is contributing to serious hospital complications, chronic kidney disease (CKD) and even death. Renal ischemia-reperfusion injury (IRI) remains a leading cause of AKI. The stress-responsive enzyme, heme oxygenase-1 (HO-1) mediates protection against renal IRI and may be preventively induced using hemin prior to renal insult. This HO-1 induction pathway called hemin preconditioning is largely known to be effective. Therefore, HO-1 might be an interesting therapeutic target in case of predictable AKI (e.g. partial nephrectomy or renal transplantation). However, the use of hemin to mitigate established AKI remains poorly characterized. Mice underwent bilateral renal IRI for 26 min or sham surgery. After surgical procedure, animals were injected either with hemin (5 mg/kg) or vehicle. Twenty-four hours later, mice were sacrificed. Despite strong HO-1 induction, hemin-treated mice exhibited significant renal damage and oxidative stress as compared to vehicle-treated mice. Interestingly, higher dose of hemin is associated with more severe IRI-induced AKI in a dose-dependent relation. To determine whether hemin preconditioning remains efficient to dampen postoperative hemin-amplified IRI-induced AKI, we pretreated mice either with hemin (5 mg/kg) or vehicle 24 h prior to surgical procedure. Then, all mice (hemin- and vehicle-pretreated) received postoperative injection of hemin (5 mg/kg) to amplify IRI-induced AKI. In comparison to vehicle, prior administration of hemin to renal IRI mitigated hemin-amplified IRI-induced AKI as attested by fewer renal damage, inflammation and oxidative stress. In conclusion, hemin may have a dual effect on renal IRI, protective or deleterious, depending on the timing of its administration.

Pioglitazone Protects Against Renal Ischemia-Reperfusion Injury via the AMP-Activated Protein Kinase-Regulated Autophagy Pathway

Renal ischemia-reperfusion injury (IRI) is a major cause of acute renal failure. Our previous studies have shown that pioglitazone, a peroxisome proliferators-activated receptor (PPAR)-γ agonist used in type 2 diabetes, protects against renal IRI; however, the molecular mechanism underlying the renoprotective effects of pioglitazone is still unclear. In this study, we investigated the role of AMP-activated protein kinase (AMPK)-regulated autophagy in renoprotection by pioglitazone in IRI. To investigate whether pioglitazone protects renal cells from IRI, an in vivo renal IRI model was used. Cell apoptosis in the kidneys was determined by TUNEL staining. Western blotting was used to determine the expression of AMPK, autophagy-related proteins, and caspase-3/8 proteins in the kidneys. In a rat model of IRI, pioglitazone decreased the increased serum creatinine and urea nitrogen, improved renal histological score, and decreased the cell injury. Pioglitazone also increased AMPK phosphorylation, inhibited p62 and cleaved caspase-3/8 proteins, and activated autophagy-related proteins LC3 II and Beclin-1 in the kidneys of IRI rats. Moreover, GW9662, as a selective inhibitor of PPAR-γ, inhibited the protective effects of pioglitazone. These results suggest that pioglitazone exerts its protective effects in renal IRI via activation of an AMPK-regulated autophagy signaling pathway.

Autophagy and mitochondrial biogenesis impairment contribute to age-dependent liver injury in experimental sepsis: dysregulation of AMP-activated protein kinase pathway

Age is an independent risk factor of multiple organ failure in patients with sepsis. However, the age-related mechanisms of injury are not known. AMPK is a crucial regulator of energy homeostasis, which controls mitochondrial biogenesis by activation of peroxisome proliferator-activated receptor-γ coactivator-α (PGC-1α) and disposal of defective organelles by autophagy. We investigated whether AMPK dysregulation might contribute to age-dependent liver injury in young (2-3 mo) and mature male mice (11-13 mo) subjected to sepsis. Liver damage was higher in mature mice than in young mice and was associated with impairment of hepatocyte mitochondrial function, structure, and biogenesis and reduced autophagy. At molecular analysis, there was a time-dependent nuclear translocation of the active phosphorylated catalytic subunits AMPKα1/α2 and PGC-1α in young, but not in mature, mice after sepsis. Treatment with the AMPK activator 5-amino-4-imidazolecarboxamide riboside-1-β-d-ribofuranoside (AICAR) improved liver mitochondrial structure in both age groups compared with vehicle. In loss-of-function studies, young knockout mice with systemic deficiency of AMPKα1 exhibited greater liver injury than did wild-type mice after sepsis. Our study suggests that AMPK is important for liver metabolic recovery during sepsis. Although its function may diminish with age, pharmacological activation of AMPK may be of therapeutic benefit.-Inata, Y., Kikuchi, S., Samraj, R. S., Hake, P. W., O'Connor, M., Ledford, J. R., O'Connor, J., Lahni, P., Wolfe, V., Piraino, G., Zingarelli, B. Autophagy and mitochondrial biogenesis impairment contribute to age-dependent liver injury in experimental sepsis: dysregulation of AMP-activated protein kinase pathway.

Renal Mitochondrial Response to Low Temperature in Non-Hibernating and Hibernating Species

SIGNIFICANCE

Therapeutic hypothermia is commonly applied to limit ischemic injury in organ transplantation, during cardiac and brain surgery and after cardiopulmonary resuscitation. In these procedures, the kidneys are particularly at risk for ischemia/reperfusion injury (IRI), likely due to their high rate of metabolism. Although hypothermia mitigates ischemic kidney injury, it is not a panacea. Residual mitochondrial failure is believed to be a key event triggering loss of cellular homeostasis, and potentially cell death. Subsequent rewarming generates large amounts of reactive oxygen species that aggravate organ injury. Recent Advances: Hibernators are able to withstand periods of profoundly reduced metabolism and body temperature ("torpor"), interspersed by brief periods of rewarming ("arousal") without signs of organ injury. Specific adaptations allow maintenance of mitochondrial homeostasis, limit oxidative stress, and protect against cell death. These adaptations consist of active suppression of mitochondrial function and upregulation of anti-oxidant enzymes and anti-apoptotic pathways.

CRITICAL ISSUES

Unraveling the precise molecular mechanisms that allow hibernators to cycle through torpor and arousal without precipitating organ injury may translate into novel pharmacological approaches to limit IRI in patients.

FUTURE DIRECTIONS

Although the precise signaling routes involved in natural hibernation are not yet fully understood, torpor-like hypothermic states with increased resistance to ischemia/reperfusion can be induced pharmacologically by 5'-adenosine monophosphate (5'-AMP), adenosine, and hydrogen sulfide (H₂S) in non-hibernators. In this review, we compare the molecular effects of hypothermia in non-hibernators with natural and pharmacologically induced torpor, to delineate how safe and reversible metabolic suppression may provide resistance to renal IRI. Antioxid. Redox Signal. 27, 599-617.

Specific expression of heme oxygenase-1 by myeloid cells modulates renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) is a major risk factor for delayed graft function in renal transplantation. Compelling evidence exists that the stress-responsive enzyme, heme oxygenase-1 (HO-1) mediates protection against IRI. However, the role of myeloid HO-1 during IRI remains poorly characterized. Mice with myeloid-restricted deletion of HO-1 (HO-1^M-KO), littermate (LT), and wild-type (WT) mice were subjected to renal IRI or sham procedures and sacrificed after 24 hours or 7 days. In comparison to LT, HO-1^M-KO exhibited significant renal histological damage, pro-inflammatory responses and oxidative stress 24 hours after reperfusion. HO-1^M-KO mice also displayed impaired tubular repair and increased renal fibrosis 7 days after IRI. In WT mice, HO-1 induction with hemin specifically upregulated HO-1 within the CD11b⁺ F4/80^lo subset of the renal myeloid cells. Prior administration of hemin to renal IRI was associated with significant increase of the renal HO-1⁺ CD11b⁺ F4/80^lo myeloid cells in comparison to control mice. In contrast, this hemin-mediated protection was abolished in HO-1^M-KO mice. In conclusion, myeloid HO-1 appears as a critical protective pathway against renal IRI and could be an interesting therapeutic target in renal transplantation.

Mitochondria-Targeted Antioxidants: Future Perspectives in Kidney Ischemia Reperfusion Injury

Kidney ischemia/reperfusion injury emerges in various clinical settings as a great problem complicating the course and outcome. Ischemia/reperfusion injury is still an unsolved puzzle with a great diversity of investigational approaches, putting the focus on oxidative stress and mitochondria. Mitochondria are both sources and targets of ROS. They participate in initiation and progression of kidney ischemia/reperfusion injury linking oxidative stress, inflammation, and cell death. The dependence of kidney proximal tubule cells on oxidative mitochondrial metabolism makes them particularly prone to harmful effects of mitochondrial damage. The administration of antioxidants has been used as a way to prevent and treat kidney ischemia/reperfusion injury for a long time. Recently a new method based on mitochondria-targeted antioxidants has become the focus of interest. Here we review the current status of results achieved in numerous studies investigating these novel compounds in ischemia/reperfusion injury which specifically target mitochondria such as MitoQ, Szeto-Schiller (SS) peptides (Bendavia), SkQ1 and SkQR1, and superoxide dismutase mimics. Based on the favorable results obtained in the studies that have examined myocardial ischemia/reperfusion injury, ongoing clinical trials investigate the efficacy of some novel therapeutics in preventing myocardial infarct. This also implies future strategies in preventing kidney ischemia/reperfusion injury.

ZYZ451 protects cardiomyocytes from hypoxia-induced apoptosis via enhancing MnSOD and STAT3 interaction

3,5-dimethoxy-4-(2-amino-3-prop-2-ynylsulfanyl-propionyl)-benzoic acid 4-guanidino-butyl ester (ZYZ451) was found to be an excellent cardio-protective agent in the previous research in our lab. However, its potent therapeutic effects on myocardial infarction and the underlying mechanism remain elusive. In the present study, we demonstrate that ZYZ451 protects neonatal rat ventricular cardiomyocytes (NRVCs) from hypoxia-induced apoptosis via increasing manganese-containing superoxide dismutase (MnSOD) activity and inhibiting mitochondrial reactive oxidative species (mitoROS) production. MnSOD knockdown impairs the anti-apoptotic effects of ZYZ451. We report here for the first time that signal transducer and activator of transcription 3 (STAT3), an important nuclear transcriptional factor also identified in mitochondria, co-localizes with MnSOD and interacts with it, as determined by using methods of co-immunofluorescence and co-immunoprecipitation. Knockdown of STAT3 rather than inhibition of STAT3 phosphorylation results in a significant reduction in MnSOD activity. Furthermore, interaction between MnSOD and STAT3 is diminished in STAT3 deficient H9C2 cells. Its novel subcellular localization and interaction with MnSOD suggest that STAT3 may be involved in regulation of MnSOD activity beyond its transcriptional potential. Consistent with the results in vitro, ZYZ451 reduces myocardial infarct size as well as cardiomyocytes apoptosis, inhibits lactate dehydrogenase (LDH) and malondialchehyche (MDA) release, and restores MnSOD activity in peri-infarct hearts. These benefits appear to be attributed to the enhanced interaction between STAT3 and MnSOD. These findings shed a light on a new role of STAT3 in oxidative stress and suggest that ZYZ451 is likely an effective cardio-protective agent.

Quercetin attenuates renal ischemia/reperfusion injury via an activation of AMP-activated protein kinase-regulated autophagy pathway

Renal ischemia/reperfusion (I/R) is a major cause of acute renal failure. Quercetin, a flavonoid antioxidant, presents in many kinds of food. The molecular mechanism of quercetin on renal protection during I/R is still unclear. Here, we investigated the role of AMP-activated protein kinase (AMPK)-regulated autophagy in renal protection by quercetin. To investigate whether quercetin protects renal cells from I/R-induced cell injury, an in vitro model of I/R and an in vivo I/R model were used. Cell apoptosis was determined by propidium iodide/annexin V staining. Western blotting and immunofluorescence were used to determine the autophagy. AMPK expression was inhibited with appropriate short hairpin RNA (shRNA). In cultured renal tubular cell I/R model, quercetin decreased the cell injury, up-regulated the AMPK phosphorylation, down-regulated the mammalian target of rapamycin (mTOR) phosphorylation and activated autophagy during I/R. Knockdown of AMPK by shRNA transfection decreased the quercetin-induced autophagy but did not affect the mTOR phosphorylation. In I/R mouse model, quercetin decreased the increased serum creatinine level and altered renal histological score. Quercetin also increased AMPK phosphorylation, inhibited the mTOR phosphorylation and activated autophagy in the kidneys of I/R mice. These results suggest that quercetin activates an AMPK-regulated autophagy signaling pathway, which offers a protective effect in renal I/R injury.

Antioxidant supplement inhibits skeletal muscle constitutive autophagy rather than fasting-induced autophagy in mice

In this study, we tested the hypothesis that NAC administration leads to reduced oxidative stress and thus to decreased expression of autophagy markers in young mice. Our results reveal that NAC administration results in reduced muscle mRNA levels of several autophagy markers, including Beclin-1, Atg7, LC3, Atg9, and LAMP2. However, NAC supplement fails to block the activation of skeletal muscle autophagy in response to fasting, because fasting significantly increases the mRNA level of several autophagy markers and LC3 lipidation. We further examined the effects of NAC administration on mitochondrial antioxidant capacity in fed and 24-hour fasted mice. Our results clearly show that NAC administration depresses the expression of manganese superoxide dismutase (MnSOD) and TP53-induced glycolysis and apoptosis regulator (TIGAR), both of which play a predominant antioxidant role in mitochondria by reducing ROS level. In addition, we found no beneficial effect of NAC supplement on muscle mass but it can protect from muscle loss in response to fasting. Collectively, our findings indicate that ROS is required for skeletal muscle constitutive autophagy, rather than starvation-induced autophagy, and that antioxidant NAC inhibits constitutive autophagy by the regulation of mitochondrial ROS production and antioxidant capacity.

Mitochondrial dysfunction and mitophagy: the beginning and end to diabetic nephropathy?

Diabetic nephropathy (DN) is a progressive microvascular complication arising from diabetes. Within the kidney, the glomeruli, tubules, vessels and interstitium are disrupted, ultimately impairing renal function and leading to end-stage renal disease (ESRD). Current pharmacological therapies used in individuals with DN do not prevent the inevitable progression to ESRD; therefore, new targets of therapy are urgently required. Studies from animal models indicate that disturbances in mitochondrial homeostasis are central to the pathogenesis of DN. Since renal proximal tubule cells rely on oxidative phosphorylation to provide adequate ATP for tubular reabsorption, an impairment of mitochondrial bioenergetics can result in renal functional decline. Defects at the level of the electron transport chain have long been established in DN, promoting electron leakage and formation of superoxide radicals, mediating microinflammation and contributing to the renal lesion. More recent studies suggest that mitochondrial-associated proteins may be directly involved in the pathogenesis of tubulointerstitial fibrosis and glomerulosclerosis. An accumulation of fragmented mitochondria are found in the renal cortex in both humans and animals with DN, suggesting that in tandem with a shift in dynamics, mitochondrial clearance mechanisms may be impaired. The process of mitophagy is the selective targeting of damaged or dysfunctional mitochondria to autophagosomes for degradation through the autophagy pathway. The current review explores the concept that an impairment in the mitophagy system leads to the accelerated progression of renal pathology. A better understanding of the cellular and molecular events that govern mitophagy and dynamics in DN may lead to improved therapeutic strategies.

The use of the Cre/loxP system to study oxidative stress in tissue-specific manganese superoxide dismutase knockout models

SIGNIFICANCE

Respiring mitochondria are a significant site for reactions involving reactive oxygen and nitrogen species that contribute to irreversible cellular, structural, and functional damage leading to multiple pathological conditions. Manganese superoxide dismutase (MnSOD) is a critical component of the antioxidant system tasked with protecting the oxidant-sensitive mitochondrial compartment from oxidative stress. Since global knockout of MnSOD results in significant cardiac and neuronal damage leading to early postnatal lethality, this approach has limited use for studying the mechanisms of oxidant stress and the development of disease in specific tissues lacking MnSOD. To circumvent this problem, a number of investigators have employed the Cre/loxP system to precisely knockout MnSOD in individual tissues.

RECENT ADVANCES

Multiple tissue and organ-specific Cre-expressing mice have been generated, which greatly enhance the specificity of MnSOD knockout in tissues and organ systems that were once difficult, if not impossible to study.

CRITICAL ISSUES

Evaluating the contribution of MnSOD deficiency to oxidant-mediated mitochondrial damage requires careful consideration of the promoter system used for creating the tissue-specific knockout animal, in addition to the collection and interpretation of multiple indices of oxidative stress and damage.

FUTURE DIRECTIONS

Expanded use of well-characterized tissue-specific promoter elements and inducible systems to drive the Cre/loxP recombinational events will lead to a spectrum of MnSOD tissue knockout models, and a clearer understanding of the role of MnSOD in preventing mitochondrial dysfunction in human disease.

Peroxynitrite induced mitochondrial biogenesis following MnSOD knockdown in normal rat kidney (NRK) cells

Superoxide is widely regarded as the primary reactive oxygen species (ROS) which initiates downstream oxidative stress. Increased oxidative stress contributes, in part, to many disease conditions such as cancer, atherosclerosis, ischemia/reperfusion, diabetes, aging, and neurodegeneration. Manganese superoxide dismutase (MnSOD) catalyzes the dismutation of superoxide into hydrogen peroxide which can then be further detoxified by other antioxidant enzymes. MnSOD is critical in maintaining the normal function of mitochondria, thus its inactivation is thought to lead to compromised mitochondria. Previously, our laboratory observed increased mitochondrial biogenesis in a novel kidney-specific MnSOD knockout mouse. The current study used transient siRNA mediated MnSOD knockdown of normal rat kidney (NRK) cells as the in vitro model, and confirmed functional mitochondrial biogenesis evidenced by increased PGC1α expression, mitochondrial DNA copy numbers and integrity, electron transport chain protein CORE II, mitochondrial mass, oxygen consumption rate, and overall ATP production. Further mechanistic studies using mitoquinone (MitoQ), a mitochondria-targeted antioxidant and L-NAME, a nitric oxide synthase (NOS) inhibitor demonstrated that peroxynitrite (at low micromolar levels) induced mitochondrial biogenesis. These findings provide the first evidence that low levels of peroxynitrite can initiate a protective signaling cascade involving mitochondrial biogenesis which may help to restore mitochondrial function following transient MnSOD inactivation.

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MnSOD knockdown in NRK cells results in a transient loss of MnSOD activity, increased nitrotyrosine and mitochondrial superoxide.

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MnSOD knockdown in NRK cells results in a transient induction of mitochondrial biogenesis.

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Nitric oxide synthase inhibition and Mitoquinone blocks mitochondrial biogenesis after MnSOD knockdown.

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Low doses of peroxynitrite induce biogenesis in NRK cells.

Oxidative stress-induced autophagy: role in pulmonary toxicity

Autophagy is an evolutionarily conserved catabolic process important in regulating the turnover of essential proteins and in elimination of damaged organelles and protein aggregates. Autophagy is observed in the lung in response to oxidative stress generated as a consequence of exposure to environmental toxicants. Whether autophagy plays role in promoting cell survival or cytotoxicity is unclear. In this article recent findings on oxidative stress-induced autophagy in the lung are reviewed; potential mechanisms initiating autophagy are also discussed. A better understanding of autophagy and its role in pulmonary toxicity may lead to the development of new strategies to treat lung injury associated with oxidative stress.

Ischaemia-reperfusion injury: a major protagonist in kidney transplantation

Ischaemia-reperfusion injury (IRI) is a frequent event in kidney transplantation, particularly when the kidney comes from a deceased donor. The brain death is usually associated with generalized ischaemia due to a hyperactivity of the sympathetic system. In spite of this, most donors have profound hypotension and require administration of vasoconstrictor agents. Warm ischaemia after kidney vessels clamping and the cold ischaemia after refrigeration also reduce oxygen and nutrients supply to tissues. The reperfusion further aggravates the state of oxidation and inflammation created by ischaemia. IRI first attacks endothelial cells and tubular epithelial cells. The lesions may be so severe that they lead to acute kidney injury (AKI) and delayed graft function (DGF), which can impair the graft survival. The unfavourable impact of DGF is worse when DGF is associated with acute rejection. Another consequence of IRI is the activation of the innate immunity. Danger signals released by dying cells alarm Toll-like receptors that, through adapter molecules and a chain of kinases, transmit the signal to transcription factors which encode the genes regulating inflammatory cells and mediators. In the inflammatory environment, dendritic cells (DCs) intercept the antigen, migrate to lymph nodes and present the antigen to immunocompetent cells, so activating the adaptive immunity and favouring rejection. Attempts to prevent IRI include optimal management of donor and recipient. Calcium-channel blockers, l-arginine and N-acetylcysteine could obtain a small reduction in the incidence of post-transplant DGF. Fenoldopam, Atrial Natriuretic Peptide, Brain Natriuretic Peptide and Dopamine proved to be helpful in reducing the risk of AKI in experimental models, but there is no controlled evidence that these agents may be of benefit in preventing DGF in kidney transplant recipients. Other antioxidants have been successfully used in experimental models of AKI but only a few studies of poor quality have been made in clinical transplantation with a few of these agents and we still lack of unambiguous demonstration that pre-treatment with these antioxidants can attenuate the impact of IRI in kidney transplantation. Interference with the signals leading to activation of innate immunity, inactivation of complement or manipulation of DCs is a promising therapeutic option for the near future.

Autophagy in acute kidney injury

Acute kidney injury is a major kidney disease associated with poor clinical outcomes. The pathogenesis of acute kidney injury is multifactorial and is characterized by tubular cell injury and death. Recent studies have shown autophagy induction in proximal tubular cells during acute kidney injury. The regulatory mechanisms of tubular cell autophagy are poorly understood; however, some recent findings have set up a foundation for further investigation. Although autophagy may promote cell death under certain experimental conditions, pharmacologic and autophagy-related gene knockout studies have established a renoprotective role for autophagy in acute kidney injury. The mechanisms by which autophagy protects cells from injury and how, possibly, its pro-survival role switches to pro-death under certain conditions are discussed. Further research is expected to help us understand the regulatory network of tubular cell autophagy, define its precise roles in the specific context of acute kidney injury, and identify autophagy-targeting strategies for the prevention and treatment of acute kidney injury.