Ischemic Preconditioning Promotes Autophagy and Alleviates Renal Ischemia/Reperfusion Injury

Lrg1 silencing attenuates ischemia-reperfusion renal injury by regulating autophagy and apoptosis through the TGFβ1- Smad1/5 signaling pathway

BACKGROUND

Dysfunction in the processes of autophagy and apoptosis within renal tubular epithelial cells (RTEc) contributes to renal ischemia-reperfusion injury (IRI). However, the factors influencing this dysfunction remain unclear. Leucine-rich alpha-2-glycoprotein 1 (Lrg1) plays a role in the progression of diabetic nephropathy and kidney fibrosis by modulating the activin receptor-like kinase 1 (ALK1)-Smad1/5/8 and TGF-β1/Smad3 pathways, respectively. Therefore, we aimed to investigate whether Lrg1 is involved in the pathological mechanisms of renal IRI and whether its effects are related to the dysregulation of autophagy and apoptosis in RTEc.

METHODS

We conducted in vitro and in vivo experiments using CoCl2-induced hypoxic human kidney-2 (HK-2) cells and mice with renal IRI, respectively. Lrg1 was silenced using siRNA and lentiviral vectors in HK-2 cells and mouse kidneys. Rapamycin (Rapa) and methyladenine were applied to regulate autophagy in renal IRI models.

RESULTS

Increased Lrg1 expression was observed in hypoxic HK-2 cells and in the kidneys of mice with renal IRI. Silencing of Lrg1 through siRNA and lentiviral approaches restored autophagy and suppressed apoptosis in CoCl2-induced hypoxic HK-2 cells and renal IRI models. Additionally, reduced Lrg1 expression alleviated kidney damage caused by renal IRI. The downregulation of Lrg1 expression restrained the TGFβ-Smad1/5 signaling pathway in hypoxic-induced HK-2 cells and renal IRI by reducing ALK1 expression. Lastly, the enhancement of autophagy, achieved through Rapa treatment, provided protection against renal IRI in mice.

CONCLUSIONS

Our findings suggest that Lrg1 silencing can be applied as a potential therapeutic target to inhibit the TGFβ1-Smad1/5 pathway, thereby enhancing autophagy and decreasing apoptosis in patients with acute kidney injury.

Protection of Ndrg2 deficiency on renal ischemia-reperfusion injury via activating PINK1/Parkin-mediated mitophagy

BACKGROUND

Renal ischemia-reperfusion (R-I/R) injury is the most prevalent cause of acute kidney injury, with high mortality and poor prognosis. However, the underlying pathological mechanisms are not yet fully understood. Therefore, this study aimed to investigate the role of N-myc downstream-regulated gene 2 (Ndrg2) in R-I/R injury.

METHODS

We examined the expression of Ndrg2 in the kidney under normal physiological conditions and after R-I/R injury by immunofluorescence staining, real-time polymerase chain reaction, and western blotting. We then detected R-I/R injury in Ndrg2-deficient (Ndrg2-/-) mice and wild type (Ndrg2+/+) littermates in vivo, and detected oxygen and glucose deprivation and reperfusion injury (OGD-R) in HK-2 cells. We further conducted transcriptomic sequencing to investigate the role of Ndrg2 in R-I/R injury and detected levels of oxidative stress and mitochondrial damage by dihydroethidium staining, biochemical assays, and western blot. Finally, we measured the levels of mitophagy in Ndrg2+/+ and Ndrg2-/- mice after R-I/R injury or HK-2 cells in OGD-R injury.

RESULTS

We found that Ndrg2 was primarily expressed in renal proximal tubules and significantly decreased its expression 24 h after R-I/R injury. Ndrg2-/- mice exhibited significantly attenuated R-I/R injury compared to Ndrg2+/+ mice. Transcriptomics profiling showed that Ndrg2 deficiency induced perturbations of multiple signaling pathways, downregulated inflammatory responses and oxidative stress, and increased autophagy following R-I/R injury. Further studies revealed that Ndrg2 deficiency reduced oxidative stress and mitochondrial damage. Notably, Ndrg2 deficiency significantly activated phosphatase and tensin homologue on chromosome ten-induced putative kinase 1 (PINK1)/Parkin-mediated mitophagy. The downregulation of NDRG2 expression significantly increased cell viability after OGD-R injury, increased the expression of heme oxygenase-1, decreased the expression of nicotinamide adenine dinucleotide phosphate oxidase 4, and increased the expression of the PINK1/Parkin pathway.

CONCLUSION

Ndrg2 deficiency might become a therapy target for R-I/R injury by decreasing oxidative stress, maintaining mitochondrial homeostasis, and activating PINK1/Parkin-mediated mitophagy.

Selenoprotein Gene mRNA Expression Evaluation During Renal Ischemia-Reperfusion Injury in Rats and Ebselen Intervention Effects

Effects of selenoproteins on many renal diseases have been reported. However, their role in renal ischemia-reperfusion (I/R) injury is unclear. The present study was performed to investigate the impact of ebselen and renal I/R injury on the expression of selenoproteins. Sprague-Dawley rats were pretreated with or without ebselen (10 mg/kg) through a daily single oral administration from 3 days before renal I/R surgery. RT-qPCR (real-time quantitative PCR) was performed to determine the mRNA expression of 25 selenoprotein genes in the renal tissues. The expression levels of two selenoproteins, including GPX3 (glutathione peroxidase 3) and DIO1 (iodothyronine deiodinase 1), were evaluated by Western blot or/and IHF (immunohistofluorescence) assays. Furthermore, renal function, renal damage, oxidative stress, and apoptosis were assessed. The results showed that in renal I/R injury, the mRNA levels of 15 selenoprotein genes (GPX1, GPX3, GPX4, DIO1, DIO2, TXNRD2, TXNRD3, SEPHS2, MSRB1, SELENOF, SELENOK, SELENOO, SELENOP, SELENOS, and SELENOT) were decreased, whereas those of eight selenoprotein genes (GPX2, GPX6, DIO3, TXNRD1, SELENOH, SELENOM, SELENOV, and SELENOW) were increased. I/R also induced a reduction in the expression levels of GPX3 and DIO1 proteins. In addition, our results indicated that ebselen reversed the changes in those selenoprotein genes, excluding SELENOH, SELENOM, SELENOP, and SELENOT, in renal I/R injury and alleviated I/R-induced renal dysfunction, tissue damage, oxidative stress, and apoptosis. To our knowledge, this is the first study to investigate the changes of 25 mammalian selenoprotein genes in renal I/R injury kidneys. The present study also provided more evidence for the roles of ebselen against renal I/R injury.

An update on the molecular mechanism and pharmacological interventions for Ischemia-reperfusion injury by regulating AMPK/mTOR signaling pathway in autophagy

AMP-activated protein kinase (5'-adenosine monophosphate-activated protein kinase, AMPK)/mammalian target of rapamycin (mTOR) is an important signaling pathway maintaining normal cell function and homeostasis in vivo. The AMPK/mTOR pathway regulates cellular proliferation, autophagy, and apoptosis. Ischemia-reperfusion injury (IRI) is secondary damage that frequently occurs clinically in various disease processes and treatments, and the exacerbated injury during tissue reperfusion increases disease-associated morbidity and mortality. IRI arises from multiple complex pathological mechanisms, among which cell autophagy is a focus of recent research and a new therapeutic target. The activation of AMPK/mTOR signaling in IRI can modulate cellular metabolism and regulate cell proliferation and immune cell differentiation by adjusting gene transcription and protein synthesis. Thus, the AMPK/mTOR signaling pathway has been intensively investigated in studies focused on IRI prevention and treatment. In recent years, AMPK/mTOR pathway-mediated autophagy has been found to play a crucial role in IRI treatment. This article aims to elaborate the action mechanisms of AMPK/mTOR signaling pathway activation in IRI and summarize the progress of AMPK/mTOR-mediated autophagy research in the field of IRI therapy.

Ischemic Preconditioning Alleviates Mouse Renal Ischemia/Reperfusion Injury by Enhancing Autophagy Activity of Proximal Tubular Cells

OBJECTIVES

Ischemia/reperfusion injury (IRI) is one of the most vital pathogenesis leading to kidney injury but lacks effective prevention and treatment strategies. This study was conducted to investigate the influences of ischemic preconditioning (IPC) on the pathological process of mouse renal IRI (RIRI) and to figure out the role of autophagy of proximal tubular cells (PTCs) in this process.

METHODS

C57BL/6J mice were randomized to three groups, i.e., sham-operated group, ischemia/reperfusion (I/R) group, and IPC + I/R group. Meanwhile, 3-methyladenine, an autophagy inhibitor, was administered when further verification was needed. Histological and functional severity of kidney injury, the autophagy and apoptosis activity of PTCs, as well as the characterization of the immune cell infiltration landscape in kidney tissues were investigated. Furthermore, HK-2 cells and primary cultured PTC were cultured to set up the hypoxic preconditioning and hypoxia/reoxygenation model for in vitro simulation and verification, and a microarray dataset derived from the Gene Expression Omnibus database was analyzed to explore the transcriptome profiles after IPC.

RESULTS

IPC could significantly attenuate I/R-induced kidney injury functionally and histologically both in the acute and recovery phase of RIRI by enhancing the autophagy activity of PTCs. Cell autophagy could regulate the release of monocyte chemoattractant protein-1, and sequentially decrease macrophages infiltration in kidney tissues in the acute phase of RIRI, thus mediating the reno-protective effect.

CONCLUSIONS

IPC could attenuate mouse RIRI-induced kidney injury. IPC-mediated activation of autophagy of PTCs plays a vital role in affording protection in RIRI-induced kidney injury.

Autophagy and Oxidative Balance Mediate the Effect of Carvedilol and Glibenclamide in a Rat Model of Renal Ischemia-Reperfusion Injury

BACKGROUND: Reactive oxygen species and cytokines are the main players in the development of renal ischemia-reperfusion (I/R) injury. AIM: The current study aimed to evaluate the effects of carvedilol and/or glibenclamide and the interaction between autophagy and oxidative stress. METHODS: 50 male rats were divided into five groups: Control, IR injury (IRI), carvedilol pretreated, glibenclamide pretreated, and combined carvedilol and glibenclamide pretreated. Measurements of renal blood flow (RBF), creatinine clearance, serum blood urea nitrogen (BUN), histopathological, and immunohistochemical evaluation of autophagy marker Becl-1 in the rat kidney were performed. Beclin-1and light chain 3 (LC3) Mrna expression was detected by real time polymerase chain reaction. RESULTS: IRI was associated with significant increases in BUN, tumor necrosis factor-alpha, nuclear factor κB, and histo (H) score value of Becl-1. However, there was a significant decrease in RBF, creatinine clearance, and glutathione peroxidase compared to the control group. There was significant increase in Beclin-1 and LC3 mRNA gene expression in carvedilol, glibenclamide, and combined treatment groups as compared to IRI and control groups. Combination of carvedilol and glibenclamide significantly restored IRI changes when compared with the other pretreated groups. CONCLUSION: This study suggests that carvedilol and glibenclamide are promising reno-protective drugs to reduce renal injury induced by I/R through their antioxidant and autophagy stimulation.

Theaflavin Chemistry and Its Health Benefits

Huge epidemiological and clinical studies have confirmed that black tea is a rich source of health-promoting ingredients, such as catechins and theaflavins (TFs). Furthermore, TF derivatives mainly include theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3'-gallate (TF2B), and theaflavin-3,3'-digallate (TF3). All of these TFs exhibit extensive usages in pharmaceutics, foods, and traditional medication systems. Various indepth studies reported that how TFs modulates health effects in cellular and molecular mechanisms. The available literature regarding the pharmacological activities of TFs has revealed that TF3 has remarkable anti-inflammatory, antioxidant, anticancer, antiobesity, antiosteoporotic, and antimicrobial properties, thus posing significant effects on human health. The current manuscript summarizes both the chemistry and various pharmacological effects of TFs on human health, lifestyle or aging associated diseases, and populations of gut microbiota. Furthermore, the biological potential of TFs has also been focused to provide a deeper understanding of its mechanism of action.

The beneficial role of vitamin B12 in injury induced by ischemia/reperfusion: Beyond scavenging superoxide?

Vitamin B12 (B12) is required for cellular metabolism and DNA synthesis as a co-enzyme; it also possesses anti-reactive oxygen species (ROS) property as a superoxide scavenger. B12 deficiency has been implicated in multiple diseases such as megaloblastic anemia, and this disease can be effectively cured by supplementation of B12. Multiple studies suggest that B12 also benefits the conditions associated with excess ROS. Recently, we have reported that oral high dose B12 decreases superoxide level and renal injury induced by ischemia/reperfusion in mice. Here, we discuss potential mechanism(s) other than decreasing superoxide by which B12 executes its beneficial effects.

Total Glucosides of Paeony Inhibited Autophagy and Improved Acute Kidney Injury Induced by Ischemia-Reperfusion via the lncRNA TUG1/miR-29a/PTEN Axis

Objective

Total glucosides of paeony (TGP) has been proven to affect anti-inflammatory, immunomodulatory and hypoxia tolerance. This study investigates the effect of TGP on autophagy in acute kidney injury (AKI) induced by ischemia-reperfusion (I/R).

Methods

Rat model of AKI induced by I/R was established. Rats were administered with TGP at different doses by oral gavage. The contents of BUN, creatinine, NGAL, Kim-1 and IL-18 were detected. The levels of inflammatory factors (TNF-α, IL-1β and IL-6) and autophagy were measured. The expressions of lncRNA TUG1, miR-29a and PTEN were detected and their binding relationships were verified. I/R rat model with overexpressed TUG1 was established to explore the effect of TGP on kidney injury and autophagy. The hypoxia/reoxygenation (HR) model of HK-2 cells and the HR model of HK-2 cells overexpressing TUG1 and low-expressing PTEN were established.

Results

TGP decreased the contents of BUN, creatinine, NGAL, Kim-1 and IL-18, and reduced the levels of inflammatory factors. LncRNA TUG1 and PTEN were downregulated, and miR-29a was upregulated in kidney tissues. The binding relationships between lncRNA TUG1 and miR-29a, and miR-29a and PTEN were confirmed. TGP suppressed PTEN expression via the lncRNA TUG1/miR-29a axis. Overexpressing lncRNA TUG1 attenuated the protective effect of TGP on AKI and autophagy in HK-2 cells. TGP improved cell viability and inhibited the autophagy in HR model of HK-2 cells via lncRNA TUG1/miR-29a/PTEN axis.

Conclusion

TGP inhibited autophagy and improved AKI induced by I/R via the lncRNA TUG1/miR-29a/PTEN axis.

Mas Receptor Blockade Promotes Renal Vascular Response to Ang II after Partial Kidney Ischemia/Reperfusion in a Two-Kidney-One-Clip Hypertensive Rats Model

BACKGROUND

Partial kidney ischemia-reperfusion (IR) injury is the principal cause of acute kidney injury. The renin-angiotensin system (RAS) and hypertension also may be influenced by renal IR injury. In two models of partial renal IR with and without ischemia preconditioning (IPC) and using Mas receptor (MasR) blockade, A779 or its vehicle, the renal vascular responses to angiotensin II (Ang II) administration in two-kidney-one-clip (2K1C) hypertensive rats were determined.

METHODS

Thirty-seven 2K1C male Wistar rats with systolic blood pressure ≥150 mmHg were randomly divided into three groups; sham, IR, and IPC + IR. The animals in the sham group underwent surgical procedures except partial IR. The rats in the IR group underwent 45 min partial kidney ischemia, and the animals in the IPC + IR group underwent two 5 min cycles of partial kidney ischemia followed by 10 min reperfusion and partial kidney ischemia for 45 min. The renal vascular responses to graded Ang II (30, 100, 300, and 1000 ng kg-1.min-1) infusion using A779 or its vehicle were measured at constant renal perfusion pressure.

RESULTS

Four weeks after 2K1C implementation, the intravenous infusion of graded Ang II resulted in dose-related increases in mean arterial pressure (MAP) (P dose < 0.0001) that was not different significantly between the groups. No significant differences were detected between the groups in renal blood flow (RBF) or renal vascular resistance (RVR) responses to Ang II infusion when MasR was not blocked. However, by MasR blockade, these responses were increased in IR and IPC + IR groups that were significantly different from the sham group (P < 0.05). For example, infusion of Ang II at dose 1000 ng kg-1.min-1 resulted in decreased RBF percentage change (RBF%) from the baseline to 17.5 ± 1.9%, 39.7 ± 3.8%, and 31.0 ± 3.4% in sham, IR, and IPC + IR, respectively.

CONCLUSION

These data revealed the important role of MasR after partial kidney IR in the responses of RBF and RVR to Ang II administration in 2K1C hypertensive rats.

Novel biomarkers for post-contrast acute kidney injury identified from long non-coding RNA expression profiles

Background: Post-contrast acute kidney injury (PC-AKI) is a severe complication of cardiac catheterization. Emerging evidence indicated that long non-coding RNAs (lncRNAs) could serve as biomarkers for various diseases. However, the lncRNA expression profile and potential biomarkers in PC-AKI remain unclear. This study aimed to investigate novel lncRNA biomarkers for the early detection of PC-AKI. Methods: lncRNA profile in the kidney tissues of PC-AKI rats was evaluated through RNA sequencing. Potential lncRNA biomarkers were identified through human-rat homology analysis, kidney and blood filtering in rats and verified in 112 clinical samples. The expression patterns of the candidate lncRNAs were detected in HK-2 cells and rat models to evaluate their potential for early detection. Results: In total, 357 lncRNAs were found to be differentially expressed in PC-AKI. We identified lnc-HILPDA and lnc-PRND were conservative and remarkably upregulated in both kidneys and blood from rats and the blood of PC-AKI patients; these lncRNAs can precisely distinguish PC-AKI patients (area under the curve (AUC) values of 0.885 and 0.875, respectively). The combination of these two lncRNAs exhibited improved accuracy for predicting PC-AKI, with 100% sensitivity and 83.93% specificity. Time-course experiments showed that the significant difference was first noted in the blood of PC-AKI rats at 12 h for lnc-HILPDA and 24 h for lnc-PRND. Conclusion: Our study revealed that lnc-HILPDA and lnc-PRND may serve as the novel biomarkers for early detection and profoundly affect the clinical stratification and strategy guidance of PC-AKI.

Overexpression of SP1 restores autophagy to alleviate acute renal injury induced by ischemia-reperfusion through the miR-205/PTEN/Akt pathway

Background

Acute kidney injury (AKI) is a major kidney disease with poor clinical outcome. SP1, a well-known transcription factor, plays a critical role in AKI and subsequent kidney repair through the regulation of various cell biologic processes. However, the underlying mechanism of SP1 in these pathological processes remain largely unknown.

Methods

An in vitro HK-2 cells with anoxia-reoxygenation injury model (In vitro simulated ischemic injury disease) and an in vivo rat renal ischemia-reperfusion injury model were used in this study. The expression levels of SP1, miR-205 and PTEN were detected by RT-qPCR, and the protein expression levels of SP1, p62, PTEN, AKT, p-AKT, LC3II, LC3I and Beclin-1 were assayed by western blot. Cell proliferation was assessed by MTT assay, and the cell apoptosis was detected by flow cytometry. The secretions of IL-6 and TNF-α were detected by ELISA. The targeted relationship between miR-205 and PTEN was confirmed by dual luciferase report assay. The expression and positioning of LC-3 were observed by immunofluorescence staining. TUNEL staining was used to detect cell apoptosis and immunohistochemical analysis was used to evaluate the expression of SP1 in renal tissue after ischemia-reperfusion injury in rats.

Results

The expression of PTEN was upregulated while SP1 and miR-205 were downregulated in renal ischemia-reperfusion injury. Overexpression of SP1 protected renal tubule cell against injury induced by ischemia-reperfusion via miR-205/PTEN/Akt pathway mediated autophagy. Overexpression of SP1 attenuated renal ischemia-reperfusion injury in rats.

Conclusions

SP1 overexpression restored autophagy to alleviate acute renal injury induced by ischemia-reperfusion through the miR-205/PTEN/Akt pathway.

Theaflavin ameliorates renal ischemia/reperfusion injury by activating the Nrf2 signalling pathway in vivo and in vitro

Studies have demonstrated that oxidaive stress-induced apoptosis may be the main pathogenic mechanism of renal ischemia/reperfusion (I/R) injury. Theaflavin, a polyphenolic compound extracted from black tea, has been proven to exert strong antioxidant biological function. The objective of the present study was to investigate the potential role of theaflavin on renal I/R injury and its potential molecular mechanism both in vitro and in vivo. C57/BL6 J mice were used to create a model of I/R injury wherein mice were ligated with bilateral renal pedicles for 45 min, and then reperfused for 24 h. A hypoxia/reoxygenation (H/R) model of TCMK-1 cells was used to simulate I/R in vitro. Theaflavin were administered to the treatment group first and then established the model. Kidney Injury Molecule-1 (KIM-1), serum creatinine, urea nitrogen, and 24-h urinary protein levels were evaluated and changes in mitochondrial membrane potential and the ultrastructure of mitochondria were observed. Cell viability, oxidative stress damage, and apoptosis were assessed. The expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target genes HO-1 and NQO1 were evaluated. Our results revealed that pretreatment with theaflavin significantly inhibited I/R- and H/R-induced renal injury and cell apoptosis. Theaflavin improved mitochondrial dysfunction by attenuating mitochondrial damage and promoting mitochondrial membrane potential. Theaflavin pretreatment significantly reduced malondialdehyde content, while enhancing superoxide dismutase activity in vivo and in vitro. It also reduced oxidative stress and apoptosis mainly by upregulating Nrf2 and its downstream targets in TCMK-1 cells. Thus, theaflavin exerted a protective effect against renal I/R injury by inhibiting oxidative stress and apoptosis via activation of the Nrf2-NQO1/HO-1 pathway as well as correcting mitochondrial dysfunction, thereby presenting its potential as a clinical therapeutic in cases of acute kidney injury.

Activation of sirtuin1 protects against ischemia/reperfusion-induced acute kidney injury

Sirtuin1 (SIRT1), a class III histone deacetylase, exerts a protective role against kidney injury. However, its functions in renal ischemia/reperfusion (I/R) injury remains unclear as yet. In this study, we established acute kidney injury (AKI) rat model through renal ischemia and reperfusion, and the role of SIRT1 in I/R-induced AKI was investigated both in vivo and in vitro. In in vivo study, SIRT1 was expressed in tubular epithelial cells (TECs) and its expression was upregulated after I/R treatment. Meanwhile, our in vitro experiment confirmed that the expression of SIRT1 was also elevated in human renal proximal tubular epithelial (HK2) cells treated with hypoxia and reoxygenation (H/R). Notably, activation of SIRT1 by resveratrol (Res, an activator of SIRT1) could significantly ameliorate renal function and reduce the TECs apoptosis in rats. Likewise, Res intervention also reduced the apoptosis and the production of reactive oxygen species in HK2 cells. Furthermore, we found that the autophagy level was upregulated in I/R injury, which could be raised further through resveratrol intervention; and chloroquine (CQ, an autophagy inhibitor) did reverse these protective effects of SIRT1 activation. Taken together, our results suggest that SIRT1 plays a protective role by autophagy induction in I/R- induced AKI. Its role might serve as a preventive approach in I/R-associated AKI.

Inhibition of Disruptor of Telomeric Silencing 1-Like Alleviated Renal Ischemia and Reperfusion Injury-Induced Fibrosis by Blocking PI3K/AKT-Mediated Oxidative Stress

Background

Ischemia/reperfusion (I/R) injury is a major cause of acute kidney injury, usually occurs during renal surgeries, and may eventually lead to chronic kidney diseases. However, effective therapeutic targets for renal I/R injury remain limited.

Purpose

In the present study, we investigated whether inhibition of disruptor of telomeric silencing 1-like (Dot1l) could alleviate renal I/R in vivo and in vitro, as well as the potential mechanisms involved in this process.

Methods

Sprague–Dawley rats were subjected to right renal ischemia for 45 mins and reperfusion for 0, 7, or 14 days with and without the Dot1l inhibitor EPZ004777. In addition, human renal proximal tubular epithelial cell line human kidney-2 cells were subjected to the hypoxia/reoxygenation (H/R) process (ie, 3 hrs hypoxia, 12 hrs and 24 hrs reoxygenation), with or without Dot1l inhibitor or genetic knockdown.

Results

Inhibition of Dot1l through EPZ004777 or genetic knockdown reduced the expression of alpha-smooth muscle actin, vimentin, and fibronectin in I/R- and H/R-induced injury. Moreover, H/R-induced fibrosis depended on oxidative stress in vitro. In addition, I/R- and H/R-induced generation of reactive oxygen species (ROS) was attenuated by EPZ004777 or small interfering RNA for Dot1l. Furthermore, the elevation of ROS induced by Dot1l was regulated via phosphatidylinositol 3-kinase (PI3K) and serine-threonine protein kinase (AKT) phosphorylation in vivo and in vitro.

Conclusion

Inhibition of Dot1l alleviated renal fibrosis by preventing the generation of ROS via the PI3K/AKT pathway. These results indicate that inhibitor of Dot1l could be a potential therapeutic target for renal I/R injury.

Propofol Attenuates Hypoxia/Reoxygenation-Induced Apoptosis and Autophagy in HK-2 Cells by Inhibiting JNK Activation

PURPOSE

The aim of this study was to investigate whether propofol could attenuate hypoxia/reoxygenation-induced apoptosis and autophagy in human renal proximal tubular cells (HK-2) by inhibiting JNK activation.

MATERIALS AND METHODS

HK-2 cells were treated with or without propofol or JNK inhibitor SP600125 for 1 hour and then subjected to 15 hours of hypoxia and 2 hours of reoxygenation (H/R). Cell viability and LDH release were measured with commercial kits. Cell apoptosis was evaluated by flow cytometry. The expressions of p-JNK, cleaved-caspase-3, Bcl-2, and autophagy markers LC3 and p62 were measured by Western blot or immunofluorescence.

RESULTS

HK-2 cells exposed to H/R insult showed higher cell injury (detected by increased LDH release and decreased cell viability), increased cell apoptosis index and expression of cleaved-caspase-3, a decrease in the expression of Bcl-2 accompanied by increased expression of p-JNK and LC3II, and a decrease in expression of p62. All of these alterations were attenuated by propofol treatment. Similar effects were provoked upon treatment with the JNK inhibitor SP600125. Moreover, the protective effects were more obvious with the combination of propofol and SP600125.

CONCLUSION

These results suggest that propofol could attenuate hypoxia/reoxygenation induced apoptosis and autophagy in HK-2 cells, probably through inhibiting JNK activation.

Inhibition of PRMT5 Attenuates Oxidative Stress-Induced Pyroptosis via Activation of the Nrf2/HO-1 Signal Pathway in a Mouse Model of Renal Ischemia-Reperfusion Injury

Background

Extensive evidence has demonstrated that oxidative stress, pyroptosis, and proinflammatory programmed cell death are related to renal ischemia/reperfusion (I/R) injury. However, the underlying mechanism remains to be illustrated. Protein arginine methylation transferase 5 (PRMT5), which mediates arginine methylation involved in the regulation of epigenetics, exhibits a variety of biological functions and essential roles in diseases. The present study investigated the role of PRMT5 in oxidative stress and pyroptosis induced by I/R injury in a mouse model and in a hypoxia/reoxygenation (H/R) model of HK-2 cells.

Methods

C57 mice were used as an animal model. All mice underwent right nephrectomy, and the left renal pedicles were either clamped or not. Renal I/R injury was induced by ligating the left renal pedicle for 30 min followed by reperfusion for 24 h. HK-2 cells were exposed to normal conditions or stimulation through H/R. EPZ015666(EPZ)—a selective potent chemical inhibitor—and small interfering RNA (siRNA) were administered to suppress the function and expression of PRMT5. The levels of urea nitrogen and creatinine in the serum and renal tissue injury were assessed. Immunohistochemistry, western blotting, and reverse transcription-polymerase chain reaction were used to evaluate pyroptosis-related proteins including nod-like receptor protein-3, ASC, caspase-1, caspase-11, GSDMD-N, and interleukin-1β. Cell apoptosis and cell viability were detected through flow cytometry, and the levels of reactive oxygen species (ROS) and hydrogen peroxide (H₂O₂) were measured. Ki-67 was used to assess the proliferation of renal tubular epithelium. In addition, the activity of malondialdehyde and superoxide dismutase was determined.

Results

I/R or H/R induced an increase in the expression of PRMT5. Inhibition of PRMT5 by EPZ alleviated oxidative stress and I/R- or H/R-induced pyroptosis. In renal tissue, the application of EPZ promoted the proliferation of tubular epithelium. In addition, H/R-induced pyroptosis in HK-2 cells was dependent on oxidative stress in vitro. Administration of either EPZ or siRNA led to decreased expression of pyroptosis-related proteins. Inhibition of PRMT5 also attenuated the I/R- or H/R-induced oxidative stress in vivo and in HK-2 cells, respectively. It also resulted in a distinct decrease in the levels of malondialdehyde and H₂O₂, and an apparent increase in superoxide dismutase activity in mouse renal tissue. Moreover, it led to a significant decrease in the levels of ROS and H₂O₂ in HK-2 cells. When activated, NF-E2-related factor/heme oxygenase-1 (Nrf2/HO-1)—a key regulator of various cytoprotective proteins that withstand oxidative damage—can decrease the generation of ROS. Nrf2/HO-1 was downregulated during I/R in tissues and H/R in HK-2 cells, and this effect was reversed by the PRMT5 inhibitor. Furthermore, the expressions of Nrf2 and HO-1 proteins were markedly upregulated by EPZ or siRNA against PRMT5.

Conclusion

PRMT5 is involved in ischemia- and hypoxia-induced oxidative stress and pyroptosis in vitro and in vivo. Inhibition of PRMT5 may ameliorate renal I/R injury by suppressing oxidative stress and pyroptosis via the activation of the Nrf2/HO-1 pathway, as well as promoting the proliferation of tubular epithelium. Therefore, PRMT5 may be a promising therapeutic target.

Berberine protects steatotic donor undergoing liver transplantation via inhibiting endoplasmic reticulum stress-mediated reticulophagy

Steatotic livers are more susceptible to ischemia/reperfusion injury, and increase the risk of primary graft non-function after liver transplantation. The protective effects of berberine have been described in various liver pathological models. However, it is unknown if berberine exerts its beneficial action in steatotic donors undergoing liver transplantation. In the present study, male Wistar rats were fed with high-fat diet (HFD) for 12 weeks to induce moderate steatotic liver. Then orthotropic liver transplantation was constructed. Berberine (200 mg/kg/d) was given intragastrically one week before liver transplantation. Thapsigargin (TG) (0.2 mg/kg) was administrated intravenously 24 h before liver transplantation. Liver function, oxidative stress, and inflammatory cytokine were detected by biochemical or histopathological analysis. The morphology of autophagosomes and endoplasmic reticulum (ER) was observed by transmission electron microscopy. The expression of CHOP, BIP, the phosphorylation of PERK, LC3-II/I, Beclin-1, and p62 were determined by Western blot assay. The co-localization of endoplasmic reticulum marker (KDEL) and autophagic protein (LC3B) was analyzed by immunofluorescence microscopy. The level of reticulophagy hallmark (FAM134B) was determined by immunohistochemistry. Compared with HFD + LT group, berberine ameliorated hepatocellular damage, decreased the oxidative stress level and inflammatory cytokine release. Simultaneously, berberine inhibited the expression of both endoplasmic reticulum stress parameters and autophagy-related proteins. Additionally, the co-localization of endoplasmic reticulum marker and LC3B was also reduced in HFD + BBR + LT group. berberine down-regulated the level of FAM134B. TG reversed the beneficial effects of berberine. Our study revealed that berberine exerts protective effects on steatotic livers undergoing transplantation by inhibiting endoplasmic reticulum stress-mediated reticulophagy.

Impact statement

Berberine is isolated from traditional Chinese medicine plants and has dramatically therapeutic potential against inflammation, diarrhea, and diabetes. But the benefits of BBR on steatotic grafts after liver transplantation remain poorly understood. Our findings might help explain the mechanism of berberine in protecting steatotic livers undergoing transplantation and give advantageous insights that berberine has potential as a suitable candidate for preventing hepatic injury after steatotic liver transplantation by inhibiting ER stress-mediated reticulophagy.

Biphasic effects of autophagy on decompression bubble-induced endothelial injury

Endothelial dysfunction induced by bubbles plays an important role in decompression sickness (DCS), but the mechanism of which has not been clear. The present study was to investigate the role of autophagy in bubble‐induced endothelial injury. Human umbilical vein endothelial cells (HUVECs) were treated with bubbles, autophagy markers and endothelial injury indices were determined, and relationship strengths were quantified. Effects of autophagy inhibitor 3‐methyladenine (3‐MA) were observed. Bubble contact for 1, 5, 10, 20 or 30 minutes induced significant autophagy with increases in LC3‐II/I ratio and Beclin‐1, and a decrease in P62, which correlated with bubble contact duration. Apoptosis rate, cytochrome C and cleaved caspase‐3 increased, and cell viability decreased following bubble contact for 10, 20 or 30 minutes, but not for 1 or 5 minutes. Injuries in HUVECs were correlated with LC3‐II/I ratio and partially reversed by 3‐MA in 10, 20 or 30 minutes contact, but worsened in 1 or 5 minutes. Bubble pre‐conditioning for 1 minutes resulted in increased cell viability and decreased apoptosis rate compared with no pre‐conditioning, and 30‐minutes pre‐conditioning induced opposing changes, all of which were inhibited by 3‐MA. In conclusion, autophagy was involved and played a biphasic role in bubble‐induced endothelial injury.

Aged kidneys are refractory to autophagy activation in a rat model of renal ischemia-reperfusion injury

Background

Ischemia-reperfusion (I/R) injury is the most common cause of acute kidney injury (AKI). Numerous therapeutic approaches for I/R injury have been studied, including autophagy, particularly in animal models of renal I/R injury derived from young or adult animals. However, the precise role of autophagy in renal ischemia-reperfusion in the aged animal model remains unclear. The purpose of this study was to demonstrate whether autophagy has similar effects on renal I/R injury in young and aged rats.

Materials and methods

All rats were divided into two age groups (3 months and 24 months) with each group being further divided into four subgroups (sham, I/R, I/R+Rap (rapamycin, an activator of autophagy), I/R+3-MA (3-methyladenine, an inhibitor of autophagy)). The I/R+Rap and I/R+3-MA groups were intraperitoneally injected with rapamycin and 3-MA prior to ischemia. We then measured serum levels of urea nitrogen, creatinine and assessed damage in the renal tissue. Immunohistochemistry was used to assess LC3-II and caspase-3, and Western blotting was used to evaluate the autophagy-related proteins LC3-II, Beclin-1 and P62. Apoptosis and autophagosomes were evaluated by TUNEL and transmission electron microscopy, respectively.

Results

Autophagy was activated in both young and aged rats by I/R and enhanced by rapamycin, although the level of autophagy was lower in the aged groups. In young rats, the activation of autophagy markedly improved renal function, reduced apoptosis in the renal tubular epithelial cells and the injury score in the renal tissue, thereby exerting protective effects on renal I/R injury. However, this level of protection was not present in aged rats.

Conclusion

Our data indicated that the activation of autophagy was ineffective in aged rat kidneys. These discoveries may have major implications in that severe apoptosis in aged kidneys might be refractory to antiapoptotic effect induced by the activation of autophagy.

Barriers and Advances in Kidney Preservation

Despite the fact that a significant fraction of kidney graft dysfunctions observed after transplantation is due to ischemia-reperfusion injuries, there is still no clear consensus regarding optimal kidney preservation strategy. This stems directly from the fact that as of yet, the mechanisms underlying ischemia-reperfusion injury are poorly defined, and the role of each preservation parameter is not clearly outlined. In the meantime, as donor demography changes, organ quality is decreasing which directly increases the rate of poor outcome. This situation has an impact on clinical guidelines and impedes their possible harmonization in the transplant community, which has to move towards changing organ preservation paradigms: new concepts must emerge and the definition of a new range of adapted preservation method is of paramount importance. This review presents existing barriers in transplantation (e.g., temperature adjustment and adequate protocol, interest for oxygen addition during preservation, and clear procedure for organ perfusion during machine preservation), discusses the development of novel strategies to overcome them, and exposes the importance of identifying reliable biomarkers to monitor graft quality and predict short and long-term outcomes. Finally, perspectives in therapeutic strategies will also be presented, such as those based on stem cells and their derivatives and innovative models on which they would need to be properly tested.

FGF10 Protects Against Renal Ischemia/Reperfusion Injury by Regulating Autophagy and Inflammatory Signaling

Ischemia-reperfusion (I/R) is a common cause of acute kidney injury (AKI), which is associated with high mortality and poor outcomes. Autophagy plays important roles in the homeostasis of renal tubular cells (RTCs) and is implicated in the pathogenesis of AKI, although its role in the process is complex and controversial. Fibroblast growth factor 10 (FGF10), a multifunctional FGF family member, was reported to exert protective effect against cerebral ischemia injury and myocardial damage. Whether FGF10 has similar beneficial effect, and if so whether autophagy is associated with the potential protective activity against AKI has not been investigated. Herein, we report that FGF10 treatment improved renal function and histological integrity in a rat model of renal I/R injury. We observed that FGF10 efficiently reduced I/R-induced elevation in blood urea nitrogen, serum creatinine as well as apoptosis induction of RTCs. Interestingly, autophagy activation following I/R was suppressed by FGF10 treatment based on the immunohistochemistry staining and immunoblot analyses of LC3, Beclin-1 and SQSTM1/p62. Moreover, combined treatment of FGF10 with Rapamycin partially reversed the renoprotective effect of FGF10 suggesting the involvement of mTOR pathway in the process. Interestingly, FGF10 also inhibited the release of HMGB1 from the nucleus to the extracellular domain and regulated the expression of inflammatory cytokines such as TNF-α, IL-1β and IL-6. Together, these results indicate that FGF10 could alleviate kidney I/R injury by suppressing excessive autophagy and inhibiting inflammatory response and may therefore have the potential to be used for the prevention and perhaps treatment of I/R-associated AKI.

Activation of autophagy contributes to the renoprotective effect of postconditioning on acute kidney injury and renal fibrosis

Ischemia/Reperfusion injury contributes to acute kidney injury (AKI) and subsequent chronic kidney disease (CKD) including renal fibrosis. Autophagy is a cytoplasmic components degradation pathway that has complex function in the development of various diseases such as fibrosis in kidney. Our previous work demonstrated that postconditioning (POC) showed excellent therapeutic effect on renal fibrosis via inhibiting the overproduction of reactive oxygen species (ROS) after reperfusion. But the connection of autophagy and POC in the renoprotective effect remains unclear. Here, we defined the relevance of autophagy and POC in the protective effect on AKI and subsequent renal fibrosis. We found that at two days after I/R injury, POC largely reduced renal tubular epithelial cell apoptosis and improved renal function; autophagy was significantly activated in kidneys of the POC rats. At two months after reperfusion, the I/R injury rats displayed severe renal fibrosis and epithelial-mesenchymal transition (EMT), whereas these were remarkably attenuated in the POC treated rats. Overall, our results demonstrated that POC could reduce renal damage and attenuate the degree of EMT after I/R injury via enhanced activation of autophagy.