Preconditioning and adenosine protect human proximal tubule cells in an in vitro model of ischemic injury

Perioperative Acute Renal Injury: Revisiting Pathophysiology

BACKGROUND

Acute renal dysfunction and subsequent acute renal failure after cardiac surgery are associated with high mortality and morbidity. Early therapeutic or preventive intervention is hampered by the lack of an early biomarker for acute renal injury. Recent studies showed that urinary neutrophil gelatinase-associated lipocalin (NGAL or lipocalin 2) is upregulated early (within 1 to 3 h) after murine renal injury and in pediatric acute renal dysfunction after cardiac surgery. The authors hypothesized that postoperative urinary NGAL concentrations are increased in adult patients developing acute renal dysfunction after cardiac surgery compared with patients without acute renal dysfunction.

METHODS

After institutional review board approval, 81 cardiac surgical patients were prospectively studied. Urine samples were collected immediately before incision and at various time intervals after surgery for NGAL analysis by quantitative immunoblotting. Acute renal dysfunction was defined as peak postoperative serum creatinine increase by 50% or greater compared with preoperative serum creatinine.

RESULTS

Sixteen of 81 patients (20%) developed postoperative acute renal dysfunction, and the mean urinary NGAL concentrations in patients who developed acute renal dysfunction were significantly higher early after surgery (after 1 h, mean ± SD, 4,195 ± 6,520 vs. 1,068 ± 2,129 ng/ml; P < 0.01) compared with patients who did not develop acute renal dysfunction. Mean urinary NGAL concentrations continued to increase and remained significantly higher at 3 and 18 h after cardiac surgery in patients with acute renal dysfunction. In contrast, urinary NGAL in patients without acute renal dysfunction decreased rapidly after cardiac surgery.

CONCLUSIONS

Patients developing postoperative acute renal dysfunction had significantly higher urinary NGAL concentrations early after cardiac surgery. Urinary NGAL may therefore be a useful early biomarker of acute renal dysfunction after cardiac surgery. These findings may facilitate the early detection of acute renal injury and potentially prevent progression to acute renal failure.

Long noncoding RNA uc007nnj.1 mediates neuronal death induced by retinal ischemia/reperfusion in mice via the miR-155-5p/Tle4 axis

BACKGROUND

Retinal ganglion cells (RGCs) apoptosis is a vital manifestation of retinal ischemia/reperfusion (I/R) injury, yet the underlying mechanisms are not well understood. The contribution of long noncoding RNAs (lncRNAs) to this cellular process is currently being explored. Based on a lncRNA chip assay, we aimed to investigate the role of lncRNA uc007nnj.1 in the pathological process of ischemia-induced RGCs apoptosis.

METHODS

Hank's balanced salt solution containing 10 µM antimycin A and 2 µM calcium ionophore for 2 h to construct an ischemic model in RGCs, and elevation of intraocular pressure to 120 mm Hg for 1 h was used to construct a mouse model of retinal I/R injury.

RESULTS

In this study, lncRNA uc007nnj.1 was highly upregulated in response to I/R injury in RGCs and mouse retinas. In addition, lncRNA uc007nnj.1 knockdown reduced retinal neuronal cell apoptosis in vitro and in vivo and significantly improved retinal function.

DISCUSSION

Mechanistically, the results demonstrated that lncRNA uc007nnj.1 acts as ceRNA competitively binding miR-155-5p, thereby enhancing the expression levels of Tle4, thus aggravating ischemia-related apoptosis in RGCs.

CONCLUSIONS

Finally, our study identifies the lncRNA uc007nnj.1/miR-155-5p/Tle4 axis as a potential target for the prevention of I/R-induced retinal neuronal death.

Human Recombinant Alkaline Phosphatase (Ilofotase Alfa) Protects Against Kidney Ischemia-Reperfusion Injury in Mice and Rats Through Adenosine Receptors

Adenosine triphosphate (ATP) released from injured or dying cells is a potent pro-inflammatory "danger" signal. Alkaline phosphatase (AP), an endogenous enzyme that de-phosphorylates extracellular ATP, likely plays an anti-inflammatory role in immune responses. We hypothesized that ilofotase alfa, a human recombinant AP, protects kidneys from ischemia-reperfusion injury (IRI), a model of acute kidney injury (AKI), by metabolizing extracellular ATP to adenosine, which is known to activate adenosine receptors. Ilofotase alfa (iv) with or without ZM241,385 (sc), a selective adenosine A_2A receptor (A_2AR) antagonist, was administered 1 h before bilateral IRI in WT, A_2AR KO (Adora2a^-/- ) or CD73^-/- mice. In additional studies recombinant alkaline phosphatase was given after IRI. In an AKI-on-chronic kidney disease (CKD) ischemic rat model, ilofotase alfa was given after the three instances of IRI and rats were followed for 56 days. Ilofotase alfa in a dose dependent manner decreased IRI in WT mice, an effect prevented by ZM241,385 and partially prevented in Adora2a^-/- mice. Enzymatically inactive ilofotase alfa was not protective. Ilofotase alfa rescued CD73^-/- mice, which lack a 5'-ectonucleotidase that dephosphorylates AMP to adenosine; ZM241,385 inhibited that protection. In both rats and mice ilofotase alfa ameliorated IRI when administered after injury, thus providing relevance for therapeutic dosing of ilofotase alfa following established AKI. In an AKI-on-CKD ischemic rat model, ilofotase alfa given after the third instance of IRI reduced injury. These results suggest that ilofotase alfa promotes production of adenosine from liberated ATP in injured kidney tissue, thereby amplifying endogenous mechanisms that can reverse tissue injury, in part through A_2AR-and non-A_2AR-dependent signaling pathways.

DsbA-L interacts with VDAC1 in mitochondrion-mediated tubular cell apoptosis and contributes to the progression of acute kidney disease

BACKGROUND

we demonstrated that disulfide-bond A oxidoreductase-like protein (DsbA-L) was involved in the progression of renal fibrosis. However, the precise function of DsbA-L in acute kidney injury (AKI), and the mechanisms involved, have yet to be elucidated.

METHODS

We illustrate the DsbA-L interacted with VDAC1 by co-IP (co-immunoprecipitation) in vitro and vivo, and found the interaction parts of them by mutation experiment. The above findings were verified by co-localization of them. In addition, we constructed the two model of PT-DsbA-L and VDAC1 KO mice to verify the function of DsbA-L and VDAC1 in models of VAN, CLP and I/R-induced AKI.

FINDINGS

The PT-DsbA-L-KO mice showed amelioration of I/R, VAN-, and CLP-induced AKI progression via the downregulation of VDAC1. Finally, we confirmed these changes in signal molecules by examining in HK-2 cells and kidney biopsies taken from patients with ischemic or acute interstitial nephritis (AIN)-induced AKI. Mechanistically, DsbA-L interacted with amino acids 9-13 and 22-27 of VDAC1 in the mitochondria of BUMPT cells to induce renal cell apoptosis and mitochondrial injury.

INTERPRETATION

This work suggested that DsbA-L, located in the proximal tubular cells, drives the progression of AKI, by directly upregulating the levels of VDAC1.Running Title: The role of DsbA-L in AKI FUNDING: National Natural Science Foundation of China, a grant from Key Project of Hunan provincial science and technology innovation, Department of Science and Technology of Hunan Province project of International Cooperation and Exchanges, Changsha Science and Technology Bureau project, Natural Science Foundation of Hunan Province, Fundamental Research Funds for the Central Universities of Central South University, Hunan Provincial Innovation Foundation For Postgraduate China Hunan Provincial Science and Technology Department.

lncRNA Ttc3-209 Promotes the Apoptosis of Retinal Ganglion Cells in Retinal Ischemia Reperfusion Injury by Targeting the miR-484/Wnt8a Axis

Purpose

Apoptosis of the retinal ganglion cells (RGCs) can cause irreversible damage to visual function after retinal ischemia reperfusion injury (RIR). Using a lncRNA chip assay, we selected lncRNA Ttc-209 and characterized its role in RGCs during ischemia reperfusion (I/R)–induced apoptosis.

Methods

We created an ischemic model of RGCs by applying Hank's balanced salt solution containing 10 µM antimycin A and 2 µM calcium ionophore for 2 hours. RIR was induced in mice by elevating the intraocular pressure to 120 mm Hg for 1 hour by cannulation of the cornea; this was followed by reperfusion. Real-time quantitative PCR was used to detect the expression levels of long noncoding RNA (lncRNA), microRNA (miRNA), and target gene mRNA. Western blotting, flow cytometry, immunofluorescent staining, and TUNEL assays were performed to detect cell apoptosis. Dual-luciferase reporter assays and FISH were used to identify endogenous competitive RNA (ceRNA) mechanisms that link lncRNAs, miRNAs, and target genes. We also used scotopic electroretinography examinations to evaluate visual function in treated mice.

Results

lncRNA Ttc3-209 was significantly upregulated after I/R injury and played a proapoptotic role in RGCs during I/R-induced apoptosis. Mechanistically, lncRNA Ttc3-209 is a ceRNA that competitively binds to miR-484 and upregulates the translation of its target (Wnt8a mRNA), thus promoting apoptosis in RGCs.

Conclusions

Reducing the expression of lncRNA Ttc3-209 had a protective effect against apoptosis in RGCs. This may provide a new therapeutic option for the prevention of RGC apoptosis in response to RIR injury.

Mbd2 Mediates Retinal Cell Apoptosis by Targeting the lncRNA Mbd2-AL1/miR-188-3p/Traf3 Axis in Ischemia/Reperfusion Injury

Recent studies reported that DNA methylation was involved in retinal cell death. Methyl-CpG binding domain protein 2 (Mbd2) is one of the DNA methylation readers. Its role and mechanism of regulation remain unclear. The ischemia/reperfusion (I/R) model in mice primary culture retinal ganglion cells (RGCs) and Mbd2 knockout (Mbd2-KO) mice was used in the current study. We demonstrated that Mbd2 mediates RGC apoptosis caused by I/R injury. Mechanistically, the data suggested that Mbd2 upregulated Mbd2-associated long noncoding RNA 1 (Mbd2-AL1) via demethylation of its promoter. Furthermore, Mbd2-AL1 sponged microRNA (miR)-188-3p, thus preventing tumor necrosis factor (TNF) receptor-associated factor 3 (Traf3) downregulation and inducing RGC apoptosis. This was further demonstrated by the fact that inhibition of miR-188-3p diminished the anti-apoptosis role of Mbd2-AL1 small interfering RNA (siRNA). Finally, it showed that the apoptosis of retinal cells was attenuated, and the visual function was preserved in Mbd2-KO mice, which were associated with the Mbd2-AL1/miR-188-3p/Traf3 axis. Our present study revealed the role of Mbd2 in RGC apoptosis, which may provide a novel therapeutic strategy for retinal ischemic diseases.

miRNA transfection via poly(amidoamine)-based delivery vector prevents hypoxia/reperfusion-induced cardiomyocyte apoptosis

Aim: Myocardial infarction is a tissue injury that leads to apoptosis of cardiomyocytes. This can be prevented by using miRNAs, but its delivery to cardiomyocytes is a major hurdle. We aimed to deliver miRNAs using poly(amidoamine)-histidine (PAMAM-His) nanocarriers to prevent apoptosis. Materials & methods: The PAMAM-His nanoparticles were synthesized and assessed for their transfection efficiency of miRNAs to prevent apoptosis in hypoxia/reperfusion-induced H9c2 as well as primary cultured cardiomyocytes. Results & conclusion: miRNAs-nanoparticle complexes exerted a significant antiapoptotic effect on the H9c2 and primary rat ventricular cardiomyocytes. Enhanced expression of antiapoptotic genes and decreased expression of proapoptotic genes were observed. PAMAM-His nanoparticles effectively delivered miRNAs to the cardiomyocytes and prevented the hypoxia/reperfusion-induced apoptosis critical in myocardial infarctions.

p53-cyclophilin D mediates renal tubular cell apoptosis in ischemia-reperfusion-induced acute kidney injury

Ischemia-reperfusion (I/R)-induced acute kidney injury (I/R-AKI) favors mitochondrial permeability transition pore (mPTP) opening and subsequent cell death. Cyclophilin D (CypD) is an essential component of the mPTP, and recent findings have implicated the p53-CypD complex in cell death. To evaluate the role of p53-CypD after I/R-AKI, we tested the hypothesis that the p53-CypD complex mediates renal tubular cell apoptosis in I/R-AKI via mPTP opening. Expression of p53 and cleaved caspase-3 was significantly increased in rats subjected to I/R-AKI compared with normal controls and sham-operated controls. The underlying mechanisms were determined using an in vitro model of ATP depletion. Inhibition of mPTP opening using the CypD inhibitor cyclosporin A or siRNA for p53 in ATP-depleted HK-2 cells prevented mitochondrial membrane depolarization and reduced apoptosis. Furthermore, p53 bound to CypD in ATP-depleted HK-2 cells. These results suggest that the p53-CypD complex mediates renal tubular cell apoptosis in I/R-AKI via mPTP opening.

Salvianolic acid A ameliorates renal ischemia/reperfusion injury by activating Akt/mTOR/4EBP1 signaling pathway

Salvianolic acid A (Sal A) has been shown to prevent and treat ischemic cardiovascular, as well as cerebral vascular diseases. However, little is known about Sal A in renal ischemia/reperfusion (I/R) injury. In this study, a renal I/R injury model in rats and a hypoxia/reoxygenation (H/R) model to damage proximal renal tubular cells (HK-2) were used to assess whether Sal A halts the development and progression of renal I/R injury. As compared with vehicle treatment, Sal A significantly attenuated kidney injury after renal I/R injury, accompanied by decreases in plasma creatinine, blood urea nitrogen levels, the number of apoptosis-positive tubular cells, and kidney oxidative stress. Sal A also activated phosphorylated protein kinase B (p-Akt) and phosphorylated-mammalian target of rapamycin (p-mTOR) compared with vehicle-treated I/R injury rats. In H/R-injured HK-2 cells, Sal A can reduce the levels of reactive oxygen species in a dose-related manner. Similar to the results from in vivo experiments, in vitro Sal A also increased the protein expression of phosphorylated-eukaryotic initiation factor 4E binding protein 1 (p-4EBP1) compared with vehicle. Furthermore, the cytoprotective activity of Sal A was inhibited by LY294002 and rapamycin. These findings indicate that Sal A can ameliorate renal I/R injury and promote tubular cell survival partly via the Akt/mTOR/4EBP1pathway. Sal A could be a candidate compound to prevent ischemic tissue damage.

Protective effect of hydroxysafflor yellow A against acute kidney injury via the TLR4/NF-κB signaling pathway

This study aimed to evaluate the protective effect of hydroxysafflor yellow A (HSYA) on ischemia/reperfusion (I/R)-induced acute kidney injury via the TLR4/NF-κB pathway, both in vitro and in vivo. Rats were subjected to removal of the right kidney and I/R injury to the left kidney. Rats subjected to renal I/R injury were treated with HSYA at 0.5 h prior to I/R injury. Renal function, histopathological analysis, and cells apoptosis were measured in vivo. In vitro, proximal renal tubular cells (HK-2) were subjected to hypoxia/reoxygenation (H/R). Apoptotic cell death and inflammatory cytokines, Toll-like receptor 4 (TLR4), and nuclear factor (NF)-κB expression were determined. Treatment of I/R rats with HSYA markedly reduced the levels of serum creatinine and blood urea nitrogen, attenuated renal cell apoptosis, alleviated changes in renal tissue morphology, and reduced IL-1β, TNF-α, and caspase-3 release. In vitro, HSYA effectively decreased NF-κB p65 and inflammatory cytokines, such as IL-1β, TNF-α, and IL-6. Thus, HSYA can protect renal function from I/R injury by ameliorating acute kidney injury and partly by promoting tubular cell survival via the TLR4/NF-κB pathway. These results suggest that HSYA can be used to prevent I/R-induced acute kidney injury.

Phosphorylation of vasodilator-stimulated phosphoprotein contributes to myocardial ischemic preconditioning

Ischemic preconditioning (IP) is a well-known strategy to protect organs against cell death following ischemia. The previous work has shown that vasodilator-stimulated phosphoprotein (VASP) is involved in cytoskeletal reorganization and that it holds significant importance for the extent of myocardial ischemia reperfusion injury. Yet, the role of VASP during myocardial IP is, to date, not known. We report here that VASP phosphorylation at serine¹⁵⁷ and serine²³⁹ is induced during hypoxia in vitro and during IP in vivo. The preconditioning-induced VASP phosphorylation inactivates the GP IIb/IIIa integrin receptor on platelets, which results in the reduced formation of organ compromising platelet neutrophil complexes. Experiments in chimeric mice confirmed the importance of VASP phosphorylation during myocardial IP. When studying this in VASP^-/- animals and in an isolated heart model, we were able to confirm the important role of VASP on myocardial IP. In conclusion, we were able to show that IP-induced VASP phosphorylation in platelets is a protective mechanism against the deleterious effects of ischemia.

BacMam Delivery of a Protective Gene to Reduce Renal Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury remains the primary contributor to delayed graft function in kidney transplantation. The beneficial application of manganese superoxide dismutase (sod), delivered by a BacMam vector, against renal I/R injury has not been evaluated previously. Therefore, this study overexpressed sod-2 in proximal tubular epithelial (HK-2) cells and porcine kidney organs during simulated renal I/R injury. Incubation of HK-2 cells with antimycin A and 2-deoxyglucose resulted in a significant decrease in intracellular adenosine triphosphate (ATP) levels; following reperfusion, ATP levels significantly increased over time in cells overexpressing sod-2. In addition, lactate dehydrogenase (LDH) release declined over 72 h in BacMam-transduced injured cells. Ex vivo delivery of sod-2 significantly increased ATP levels in organs after 24 h of cold perfusion. In vitro and ex vivo results suggested that BacMam transduction successfully delivered sod-2, which reduced injury associated with I/R, by improving ATP cell content and decreasing LDH release with a subsequent increase in kidney tissue viability. These data provide further evidence for the potential application of BacMam as a gene delivery system for attenuating injury after cold preservation.

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

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

Renalase contributes to the renal protection of delayed ischaemic preconditioning via the regulation of hypoxia-inducible factor-1α

Ischaemic preconditioning (IPC) attenuates acute kidney injury (AKI) from renal ischaemia reperfusion. Renalase, an amine oxidase secreted by the proximal tubule, not only degrades circulating catecholamines but also protects against renal ischaemia reperfusion injury. Here, it has been suggested that the renoprotective effect of renal IPC is partly mediated by renalase. In a model of brief intermittent renal IPC, the increased cortex renalase expression was found to last for 48 hrs. IPC significantly reduced renal tubular inflammation, necrosis and oxidative stress following renal ischaemia reperfusion injury. Such effects were attenuated by blocking renalase with an anti-renalase monoclonal antibody. We further demonstrated that renalase expression was up-regulated by hypoxia in vitro via an hypoxia-inducible factor (HIF)-1α mechanism. The IPC-induced up-regulation of renalase in vivo was also reduced by pre-treatment with an HIF-1α inhibitor, 3-(5′-Hydroxymethyl-2′-furyl)-1-benzyl indazole. In summary, the renoprotective effect of IPC is partly dependent on the renalase expression, which may be triggered by hypoxia via an HIF-1α mechanism. Endogenous renalase shows potential as a therapeutic agent for the prevention and treatment of AKI.

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.

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

Ischemia/reperfusion (I/R) injury is a common cause of injury to target organs such as brain, heart, and kidneys. Renal injury from I/R, which may occur in renal transplantation, surgery, trauma, or sepsis, is known to be an important cause of acute kidney injury. The detailed molecular mechanism of renal I/R injury is still not fully clear. Here, we investigate the role of AMP-activated protein kinase (AMPK)-evoked autophagy in the renal proximal tubular cell death in an in vitro I/R injury model. To mimic in vivo renal I/R injury, LLC-PK1 cells, a renal tubular cell line derived from pig kidney, were treated with antimycin A and 2-deoxyglucose to mimic ischemia injury followed by reperfusion with growth medium. This I/R injury model markedly induced apoptosis and autophagy in LLC-PK1 cells in a time-dependent manner. Autophagy inhibitor 3-methyladenine (3MA) significantly enhanced I/R injury-induced apoptosis. I/R could also up-regulate the phosphorylation of AMPK and down-regulate the phosphorylation of mammalian target of rapamycin (mTOR). Cells transfected with small hairpin RNA (shRNA) for AMPK significantly increased the phosphorylation of mTOR as well as decreased the induction of autophagy followed by enhancing cell apoptosis during I/R. Moreover, the mTOR inhibitor RAD001 significantly enhanced autophagy and attenuated cell apoptosis during I/R. Taken together, these findings suggest that autophagy induction protects renal tubular cell injury via an AMPK-regulated mTOR pathway in an in vitro I/R injury model. AMPK-evoked autophagy may be as a potential target for therapeutic intervention in I/R renal injury.

TIM family proteins promote the lysosomal degradation of the nuclear receptor NUR77

T cell immunoglobulin and mucin domain (TIM) proteins are cell-surface signaling receptors in T cells and scavenger receptors in antigen-presenting cells and kidney tubular epithelia. Here, we demonstrated a function for TIM proteins in mediating the degradation of NUR77, a nuclear receptor implicated in apoptosis and cell survival. TIM proteins interacted with and mediated the lysosomal degradation of NUR77 in a phosphoinositide 3-kinase-dependent pathway. We also showed dynamic cycling of TIM-1 to and from the cell surface through clathrin-dependent constitutive endocytosis. Blocking this process or mutating the phosphatidylserine-binding pocket in TIM-1 abrogated TIM-1-mediated degradation of NUR77. In an in vitro model of kidney injury, silencing TIM-1 increased NUR77 abundance and decreased epithelial cell survival. These results show that TIM proteins may affect immune cell function and the response of the kidney to injury.

Proximal tubule sphingosine kinase-1 has a critical role in A1 adenosine receptor-mediated renal protection from ischemia

Renal ischemia reperfusion injury is a major cause of acute kidney injury. We previously found that renal A1 adenosine receptor (A1AR) activation attenuated multiple cell death pathways including necrosis, apoptosis and inflammation. Here, we tested whether induction of cytoprotective sphingosine kinase (SK)-1 and sphingosine-1 phosphate (S1P) synthesis might be the mechanism of protection. A selective A1AR agonist (CCPA) increased the synthesis of S1P and selectively induced SK-1 in mouse kidney and HK-2 cells. This agonist failed to protect SK1-knockout but protected SK2-knockout mice against renal ischemia reperfusion injury indicating a critical role of SK1 in A1AR-mediated renal protection. Inhibition of SK prevented A1AR-mediated defense against necrosis and apoptosis in HK-2 cells. A selective S1P1R antagonist (W146) and global in vivo gene knockdown of S1P1Rs with small interfering RNA completely abolished the renal protection provided by CCPA. Mice selectively deficient in renal proximal tubule S1P1Rs (S1P1Rflox/flox PEPCKCre/−) were not protected against renal ischemia reperfusion injury by CCPA. Mechanistically, CCPA increased nuclear translocation of hypoxia inducible factor-1α in HK-2 cells and selective hypoxia inducible factor-1α inhibition blocked A1AR-mediated induction of SK1. Thus, proximal tubule SK-1 has a critical role in A1AR-mediated protection against renal ischemia reperfusion injury.

Equilibrative nucleoside transporter 1 (ENT1) regulates postischemic blood flow during acute kidney injury in mice

A complex biologic network regulates kidney perfusion under physiologic conditions. This system is profoundly perturbed following renal ischemia, a leading cause of acute kidney injury (AKI) - a life-threatening condition that frequently complicates the care of hospitalized patients. Therapeutic approaches to prevent and treat AKI are extremely limited. Better understanding of the molecular pathways promoting postischemic reflow could provide new candidate targets for AKI therapeutics. Due to its role in adapting tissues to hypoxia, we hypothesized that extracellular adenosine has a regulatory function in the postischemic control of renal perfusion. Consistent with the notion that equilibrative nucleoside transporters (ENTs) terminate adenosine signaling, we observed that pharmacologic ENT inhibition in mice elevated renal adenosine levels and dampened AKI. Deletion of the ENTs resulted in selective protection in Ent1-/- mice. Comprehensive examination of adenosine receptor-knockout mice exposed to AKI demonstrated that renal protection by ENT inhibitors involves the A2B adenosine receptor. Indeed, crosstalk between renal Ent1 and Adora2b expressed on vascular endothelia effectively prevented a postischemic no-reflow phenomenon. These studies identify ENT1 and adenosine receptors as key to the process of reestablishing renal perfusion following ischemic AKI. If translatable from mice to humans, these data have important therapeutic implications.

Pretreatment strategy with adenosine A2A receptor agonist attenuates reperfusion injury in a preclinical porcine lung transplantation model

OBJECTIVE

Adenosine A(2A) receptor activation after lung transplantation attenuates ischemia-reperfusion injury by reducing inflammation. However, the effect of adenosine A(2A) receptor activation in donor lungs before transplant remains ill defined. This study compares the efficacy of 3 different treatment strategies for adenosine A(2A) receptor agonist in a clinically relevant porcine lung transplantation model.

METHODS

Mature porcine lungs underwent 6 hours of cold ischemia before allotransplantation and 4 hours of reperfusion. Five groups (n = 6/group) were evaluated on the basis of treatment with ATL-1223, a selective adenosine A(2A) receptor agonist: thoracotomy alone (sham), transplant alone (ischemia-reperfusion), donor pretreatment via ATL-1223 bolus (ATL-D), recipient treatment via ATL-1223 infusion (ATL-R), and a combination of both ATL-1223 treatments (ATL-D/R). Lung function and injury were compared.

RESULTS

Blood oxygenation was significantly higher among ATL-D, ATL-R, and ATL-D/R groups versus ischemia-reperfusion (392.0 ± 52.5, 428.9 ± 25.5, and 509.4 ± 25.1 vs 77.2 ± 17.0 mm Hg, respectively, P < .001). ATL-1223-treated groups had lower pulmonary artery pressures (ATL-D = 30.5 ± 1.8, ATL-R = 30.2 ± 3.3, and ATL-D/R = 29.3 ± 4.5 vs IR = 45.2 ± 2.1 mm Hg, P < .001) and lower mean airway pressures versus ischemia-reperfusion (ATL-D = 9.1 ± 0.8, ATL-R = 9.1 ± 2.6, and ATL-D/R = 9.6 ± 1.3 vs IR = 21.1 mm Hg, P < .001). Likewise, ATL-1223-treated groups had significantly lower lung wet/dry weight, proinflammatory cytokine expression, and lung injury scores by histology compared with ischemia-reperfusion. All parameters of lung function and injury in ATL-1223-treated groups were similar to sham (all P > .05).

CONCLUSIONS

Pretreatment of donor lungs with ATL-1223 was as efficacious as other treatment strategies in protecting against ischemia-reperfusion injury. If necessary, supplemental treatment of recipients with ATL-1223 may provide additional protection. These results support the development of pharmacologic A(2A)R agonists for use in human clinical trials for lung transplantation.

Caloric restriction mimetic 2-deoxyglucose antagonizes doxorubicin-induced cardiomyocyte death by multiple mechanisms

Caloric restriction (CR) is a dietary intervention known to enhance cardiovascular health. The glucose analog 2-deoxy-D-glucose (2-DG) mimics CR effects in several animal models. However, whether 2-DG is beneficial to the heart remains obscure. Here, we tested the ability of 2-DG to reduce cardiomyocyte death triggered by doxorubicin (DOX, 1 μm), an antitumor drug that can cause heart failure. Treatment of neonatal rat cardiomyocytes with 0.5 mm 2-DG dramatically suppressed DOX cytotoxicity as indicated by a decreased number of cells that stained positive for propidium iodide and reduced apoptotic markers. 2-DG decreased intracellular ATP levels by 17.9%, but it prevented DOX-induced severe depletion of ATP, which may contribute to 2-DG-mediated cytoprotection. Also, 2-DG increased the activity of AMP-activated protein kinase (AMPK). Blocking AMPK signaling with compound C or small interfering RNA-mediated knockdown of the catalytic subunit markedly attenuated the protective effects of 2-DG. Conversely, AMPK activation by pharmacological or genetic approach reduced DOX cardiotoxicity but did not produce additive effects when used together with 2-DG. In addition, 2-DG induced autophagy, a cellular degradation pathway whose activation could be either protective or detrimental depending on the context. Paradoxically, despite its ability to activate autophagy, 2-DG prevented DOX-induced detrimental autophagy. Together, these results suggest that the CR mimetic 2-DG can antagonize DOX-induced cardiomyocyte death, which is mediated through multiple mechanisms, including the preservation of ATP content, the activation of AMPK, and the inhibition of autophagy.

Selective renal overexpression of human heat shock protein 27 reduces renal ischemia-reperfusion injury in mice

We have previously shown that exogenous and endogenous A(1) adenosine receptor (A(1)AR) activation protected against renal ischemia-reperfusion (IR) injury in mice by induction and phosphorylation of heat shock protein 27 (HSP27). With global overexpression of HSP27 in mice, however, there was a paradoxical increase in systemic inflammation with increased renal injury after an ischemic insult due to increased NK1.1 cytotoxicity. In this study, we hypothesized that selective renal expression of HSP27 in mice would improve renal function and reduce injury after IR. Mice were subjected to renal IR injury 2 days after intrarenal injection of saline or a lentiviral construct encoding enhanced green fluorescent protein (EGFP) or human HSP27 coexpressing EGFP (EGFP-huHSP27). Mice with kidney-specific reconstitution of huHSP27 had significantly lower plasma creatinine, renal necrosis, apoptosis, and inflammation as demonstrated by decreased proinflammatory cytokine mRNA induction and neutrophil infiltration. In addition, there was better preservation of the proximal tubule epithelial filamentous (F)-actin cytoskeleton in the huHSP27-reconstituted groups than in the control groups. Furthermore, huHSP27 overexpression led to increased colocalization with F-actin in renal proximal tubules. Taken together, these findings have important clinical implications, as they imply that kidney-specific expression of HSP27 through lentiviral delivery is a viable therapeutic option in attenuating the effects of renal IR.

Protection against acute kidney injury via A(1) adenosine receptor-mediated Akt activation reduces liver injury after liver ischemia and reperfusion in mice

Hepatic ischemia reperfusion (IR) injury causes acute kidney injury (AKI). However, the contribution of AKI to the pathogenesis of liver IR injury is unclear. Furthermore, controversy still exists regarding the role of A(1) adenosine receptors (A(1)ARs) in AKI. In this study, we determined whether exogenous and endogenous A(1)AR activation protects against AKI with subsequent liver protection after hepatic IR in mice. We found that after hepatic IR A(1) knockout (KO) mice and A(1)AR antagonist-treated A(1) wild-type (WT) mice developed worse AKI and liver injury compared with vehicle-treated A(1)WT mice. Moreover, a selective A(1)AR agonist protected against hepatic IR-induced AKI and liver injury in A(1)WT mice. Renal A(1)AR-mediated kidney protection plays a crucial role in protecting the liver after IR because: 1) selective unilateral renal lentiviral overexpression of human A(1)ARs [enhanced green fluorescent protein (EGFP)-huA(1)AR] in A(1)KO mice protected against both kidney and liver injury sustained after liver IR, 2) removal of the EGFP-huA(1)AR lentivirus-injected kidney from A(1)KO mice abolished both renal and hepatic protection after liver IR, and 3) bilateral nephrectomy before hepatic ischemia abolished the protective effects of A(1)AR activation in A(1)WT mice. Finally, inhibition of Akt, but not extracellular signal-regulated kinase mitogen-activated protein kinase, prevented the kidney and liver protection afforded by A(1)AR agonist treatment. Taken together, we show that endogenous and exogenous activation of renal A(1)ARs protect against liver and kidney injury after liver IR in vivo via pathways involving Akt activation.

Selective intrarenal human A1 adenosine receptor overexpression reduces acute liver and kidney injury after hepatic ischemia reperfusion in mice

Acute kidney injury (AKI) is frequent after liver ischemia reperfusion (IR) can potentiate liver injury and is often complicated by subsequent multiorgan dysfunction syndrome. AKI because of liver IR is characterized by early renal endothelial cell apoptosis and impaired vascular integrity with subsequent neutrophil infiltration, proximal tubule necrosis/inflammation, and filamentous (F) actin disintegration. We tested whether selective renal overexpression of human A(1) adenosine receptors (huA(1)AR) protects against both liver and kidney injury sustained after liver IR. Mice were subjected to liver IR or to sham surgery 48 h after unilateral intrarenal injection of lentivirus encoding enhanced green fluorescent protein (EGFP) or EGFP-huA(1)AR. Intrarenal lentiviral gene delivery caused a robust transgene expression in the injected kidney without significant expression in the contralateral kidney or in the liver. Mice injected with EGFP-huA(1)AR lentivirus were protected against hepatic IR-induced liver and kidney injury with reduced necrosis, inflammation, and apoptosis, and better preserved F-actin and vascular permeability compared with mice injected with EGFP lentivirus. Importantly, we show that removing the EGFP-huA(1)AR lentivirus-injected kidney before hepatic ischemia abolished both renal and hepatic protection after liver IR showing that the overexpression of huA(1)AR in the injected kidney has a crucial role in protecting the kidney and liver after liver IR. Therefore, our findings show that protecting the kidney reduces liver IR injury and selective overexpression of cytoprotective A(1)ARs in the kidney leads to protection of both liver and kidney after hepatic IR.

Cytoprotective effects of adenosine and inosine in an in vitro model of acute tubular necrosis

BACKGROUND AND PURPOSE

We have established an in vitro model of acute tubular necrosis in rat kidney tubular cells, using combined oxygen-glucose deprivation (COGD) and screened a library of 1280 pharmacologically active compounds for cytoprotective effects.

EXPERIMENTAL APPROACH

We used in vitro cell-based, high throughput, screening, with cells subjected to COGD using hypoxia chambers, followed by re-oxygenation. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and the Alamar Blue assay measured mitochondrial respiration and the lactate dehydrogenase assay was used to indicate cell death. ATP levels were measured using a luminometric assay.

KEY RESULTS

Adenosine markedly reduced cellular injury, with maximal cytoprotective effect at 100 microM and an EC(50) value of 14 microM. Inosine was also found to be cytoprotective. The selective A(3) adenosine receptor antagonist MRS 1523 attenuated the protective effects of adenosine and inosine, while an A(3) adenosine receptor agonist provided a partial protective effect. Adenosine deaminase inhibition attenuated the cytoprotective effect of adenosine but not of inosine during COGD. Inhibition of adenosine kinase reduced the protective effects of both adenosine and inosine during COGD. Pretreatment of the cells with adenosine or inosine markedly protected against the fall in cellular ATP content in the cells subjected to COGD.

CONCLUSIONS AND IMPLICATIONS

The cytoprotection elicited by adenosine and inosine in a model of renal ischaemia involved both interactions with cell surface adenosine receptors on renal tubular epithelial cells and intracellular metabolism and conversion of adenosine to ATP.

Dexamethasone ameliorates renal ischemia-reperfusion injury

In the setting of renal ischemia-reperfusion injury (IRI), the effect and mechanism of action of glucocorticoids are not well understood. In rat renal IRI, a single dose of dexamethasone administered before ischemia, or at the onset of reperfusion, ameliorated biochemical and histologic acute kidney injury after 24 h. Dexamethasone upregulated Bcl-xL, downregulated ischemia-induced Bax, inhibited caspase-9 and caspase-3 activation, and reduced apoptosis and necrosis of proximal tubular cells. In addition, dexamethasone decreased the number of infiltrating neutrophils and ICAM-1. We observed the protective effect of dexamethasone in neutrophil-depleted mice, suggesting a neutrophil-independent mechanism. In vitro, dexamethasone protected human kidney proximal tubular (HK-2) cells during serum starvation and IRI-induced apoptosis, but inhibition of MEK 1/2 abolished its anti-apoptotic effects in these conditions. Dexamethasone stimulated rapid and transient phosphorylation of ERK 1/2, which required the presence of the glucocorticoid receptor and was independent of transcriptional activity. In summary, in the setting of renal ischemia-reperfusion injury, dexamethasone directly protects against kidney injury by a receptor-dependent, nongenomic mechanism.

Attenuation of renal ischemia-reperfusion injury by postconditioning involves adenosine receptor and protein kinase C activation

SUMMARY

Significant organ injury occurs after transplantation and reflow (i.e., reperfusion injury). Postconditioning (PoC), consisting of alternating periods of reperfusion and re-occlusion at onset of reperfusion, attenuates reperfusion injury in organs including heart and brain. We tested whether PoC attenuates renal ischemia-reperfusion (I/R) injury in the kidney by activating adenosine receptors (AR) and protein kinase C (PKC). The single kidney rat I/R model was used. Groups: (1) sham: time-matched surgical protocol only. In all others, the left renal artery (RA) was occluded for 45 min and reperfused for 24 h. (2) CONTROL: I/R with no intervention at R. All antagonists were administered 5 min before reperfusion. (3) PoC: I/R + four cycles of 45 s of R and 45 s of re-occlusion before full R. (4) PoC + ARi: PoC plus the AR antagonist 8-rho-(sulfophenyl) theophylline (8-SPT). (5) PoC + PKCi: PoC plus the PKC antagonist chelerythrine (Che). In shams, plasma blood urea nitrogen (BUN mg/dl) at 24 h averaged 23.2 +/- 5.3 and creatinine (Cr mg/dl) averaged 1.28 +/- 0.2. PoC reduced BUN (87.2 +/- 10 in CONTROL vs. 38.8 +/- 9, P = 0.001) and Cr (4.2 +/- 0.6 in CONTROL vs. 1.5 +/- 0.2, P < 0.001). 8-SPT and Che reversed renal protection indices after PoC. I/R increased apoptosis, which was reduced by PoC, which was reversed by 8-SPT and Che. Postconditioning attenuates renal I/R injury by adenosine receptor activation and PKC signaling.

The role of plasminogen activator inhibitor 1 in renal and cardiovascular diseases

The 50 kDa glycoprotein plasminogen activator inhibitor 1 (PAI-1) is the major physiological inhibitor of tissue-type and urokinase-type plasminogen activator. These two molecules convert inactive plasminogen into its fibrin-degrading form, plasmin. Plasma and tissue concentrations of PAI-1 are extremely low under normal circumstances but increase under pathologic conditions. This increase is mediated by many factors, including reactive oxygen species. Increased PAI-1 activity is associated with an increased risk of ischemic cardiovascular events and tissue fibrosis. Whereas the antifibrinolytic property of PAI-1 derives mainly from its inhibition of serine proteases, its profibrotic actions seem to derive from a capacity to stimulate interstitial macrophage recruitment and increase transcription of profibrotic genes, as well as from inhibition of serine proteases. Despite studies in mice that lack or overexpress PAI-1, the biological effects of this molecule in humans remain incompletely understood because of the complexity of the PAI-1-plasminogen-activator-plasmin system. The cardioprotective and renoprotective properties of some currently available drugs might be attributable in part to inhibition of PAI-1. The development of an orally active, high-affinity PAI-1 inhibitor will provide a potentially important pharmacological tool for further investigation of the role of PAI-1 and might offer a novel therapeutic strategy in renal and cardiovascular diseases.

Kidney-specific reconstitution of the A1 adenosine receptor in A1 adenosine receptor knockout mice reduces renal ischemia-reperfusion injury

Genetic deletion of the adenosine A1 receptor (A1AR) increased renal injury following ischemia-reperfusion injury suggesting that receptor activation is protective in vivo. Here we tested this hypothesis by expressing the human-A(1)AR in A(1)AR knockout mice. Renal ischemia-reperfusion was induced in knockout mice 2 days after intrarenal injection of saline or a lentivirus encoding enhanced green fluorescent protein (EGFP) or EGFP-human-A(1)AR. We found that the latter procedure induced a robust expression of the reporter protein in the kidneys of knockout mice. Mice with kidney-specific human-A(1)AR reconstitution had significantly lower plasma creatinine, tubular necrosis, apoptosis, and tubular inflammation as evidenced by decreased leukocyte infiltration, pro-inflammatory cytokine, and intercellular adhesion molecule-1 expression in the kidney following injury compared to mice injected with saline or the control lentivirus. Additionally, there were marked disruptions of the proximal tubule epithelial filamentous (F)-actin cytoskeleton in both sets of control mice upon renal injury, whereas the reconstituted mice had better preservation of the renal tubule actin cytoskeleton, which co-localized with the human-A(1)ARs. Consistent with reduced renal injury, there was a significant increase in heat shock protein-27 expression, also co-localizing with the preserved F-actin cytoskeleton. Our findings suggest that selective expression of cytoprotective A(1)ARs in the kidney can attenuate renal injury.

Mice that overexpress human heat shock protein 27 have increased renal injury following ischemia reperfusion

We previously showed that activation of the A1 adenosine receptor protected the kidney against ischemia-reperfusion injury by induction and phosphorylation of heat shock protein 27 (HSP27). Here, we used mice that overexpress human HSP27 (huHSP27) to determine if kidneys from these mice were protected against injury. Proximal tubule cells cultured from the transgenic mice had increased resistance to peroxide-induced necrosis compared to cells from wild-type mice. However, after renal ischemic injury, HSP27 transgenic mice had decreased renal function compared to wild-type mice, along with increased renal expression of mRNAs of pro-inflammatory cytokines (TNF-alpha, ICAM-1, MCP-1) and increased plasma and kidney keratinocyte-derived cytokine. Following ischemic injury, neutrophils infiltrated the kidneys earlier in the transgenic mice. Flow cytometric analysis of lymphocyte subsets showed that those isolated from the kidneys of transgenic mice had increased CD3(+), CD4(+), CD8(+), and NK1.1(+) cells 3 h after injury. When splenocytes or NK1.1(+) cells were isolated from transgenic mice and adoptively transferred into wild-type mice there was increased renal injury. Further, depletion of lymphocytes by splenectomy or neutralization of NK1.1(+) cells resulted in improved renal function in the transgenic mice following reperfusion. Our study shows that induction of HSP27 in renal tubular cells protects against necrosis in vitro, but its systemic increase counteracts this protection by exacerbating renal and systemic inflammation in vivo.

The reno-vascular A2B adenosine receptor protects the kidney from ischemia

BACKGROUND

Acute renal failure from ischemia significantly contributes to morbidity and mortality in clinical settings, and strategies to improve renal resistance to ischemia are urgently needed. Here, we identified a novel pathway of renal protection from ischemia using ischemic preconditioning (IP).

METHODS AND FINDINGS

For this purpose, we utilized a recently developed model of renal ischemia and IP via a hanging weight system that allows repeated and atraumatic occlusion of the renal artery in mice, followed by measurements of specific parameters or renal functions. Studies in gene-targeted mice for each individual adenosine receptor (AR) confirmed renal protection by IP in A1(-/-), A2A(-/-), or A3AR(-/-) mice. In contrast, protection from ischemia was abolished in A2BAR(-/-) mice. This protection was associated with corresponding changes in tissue inflammation and nitric oxide production. In accordance, the A2BAR-antagonist PSB1115 blocked renal protection by IP, while treatment with the selective A2BAR-agonist BAY 60-6583 dramatically improved renal function and histology following ischemia alone. Using an A2BAR-reporter model, we found exclusive expression of A2BARs within the reno-vasculature. Studies using A2BAR bone-marrow chimera conferred kidney protection selectively to renal A2BARs.

CONCLUSIONS

These results identify the A2BAR as a novel therapeutic target for providing potent protection from renal ischemia.

Morphine dependence protects rat kidney against ischaemia-reperfusion injury

Ischaemic preconditioning (IPC) protects the heart and kidneys against ischaemia-reperfusion (I/R) injury. It has been shown that opioid receptor activation can mimic cardiac IPC. In a kidney model of I/R, a single dose of morphine failed to mimic IPC. The aim of the present study was to determine the role of chronic morphine (dependence) in protection against renal I/R injury. Male Wistar rats were treated with increasing doses of morphine (20-30 mg/kg per day, s.c., for 5 days) to develop morphine dependence (MD). Three weeks before the I/R procedure, the right kidney was removed. Ischaemia-reperfusion injury was induced by clamping the left renal artery for 45 min, followed by 24 h reperfusion. Some MD rats were pretreated with naloxone (5 mg/kg, s.c.). Twenty-four hours later, creatinine and sodium concentrations were measured in serum and urine, then creatinine clearance (CCr) and the fractional excretion of sodium (FE(Na)) were calculated. Blood urea nitrogen (BUN) was measured only in serum samples. Kidneys were also assessed histologically for evidence of tissue injury. In the present study, MD decreased tissue injury (histological score), serum creatinine and BUN levels, increased CCr and decreased FE(Na) after I/R. Pretreatment with naloxone attenuated the protective effects of MD. Morphine dependence did not have any significant effect on urine volume. In conclusion, it seems that morphine dependence protects the kidney against I/R injury via opioid receptor-dependent pathways. Further studies are required to clearly determine the mechanisms involved.

Short- and long-term A3 adenosine receptor activation inhibits the Na+/H+ exchanger NHE3 activity and expression in opossum kidney cells

The renal function of the A(3) adenosine receptor (A3AR) is poorly characterized. In this study, we report that the A3AR-selective agonist, 1-[2-chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purine-9-yl]-1-deoxy-N-methyl-b-D-ribofuranuronamide (2-Cl-IBMECA) regulates the Na+/H+ exchanger-3 (NHE3) in a dose- and time-dependent fashion. In opossum kidney (OK) cells, 2-Cl-IBMECA at high (10(-6) M) and low (10(-8) M) dose inhibits NHE3 by a multiphasic time course with an acute phase of NHE3 inhibition from 15 min to 1 h, followed by a chronic phase of NHE3 inhibition from 24 to 48 h. Pre-incubation with either the selective A3AR-antagonist MRS1523 (10(-7) M) or the protein kinase C inhibitor, Calphostin C (10(-8) M) completely blocked 10(-6) M 2-Cl-IBMECA-induced acute (15 min) and chronic (24 h) phases of NHE3 inhibition. In contrast, the acute inhibitory phase (15 min) of 10(-8) M 2-Cl-IBMECA was completely prevented only when Calphostin C (10(-8) M) was added in conjunction with the protein kinase A inhibitor, H89 (10(-7) M). Acute (15 or 30 min depending on the A3AR-agonist concentration) A3AR-dependent inhibition of NHE3 activity was accompanied by decrease in cell surface NHE3 protein with no change in total NHE3 antigen. Chronic (24 h) A3AR-mediated down-regulation of NHE3 was associated with reduction of surface NHE3, decreased total NHE3 protein (70%) and a paradoxical rise of NHE3 RNA (40%). In summary, these results indicate that A3AR directly regulates NHE3 at multiple levels in a complex pattern. A3AR-dependent short- and long-term inhibition of NHE3 may be a fundamental mechanism of net sodium and fluid balance.

Endogenous A1 adenosine receptors protect against hepatic ischemia reperfusion injury in mice

Hepatic ischemia reperfusion (IR) injury is a major clinical problem during the perioperative period and occurs frequently after major hepatic resection or liver transplantation. Exogenous and endogenous A(1) adenosine receptor (A(1)AR) activation protects against renal IR injury. In this study, we questioned whether exogenous and endogenous A(1)AR activation protects against hepatic IR injury in vivo. A(1)AR wild-type (WT) or knockout mice were subjected to 60 minutes of partial hepatic IR. Some animals were treated with a selective A(1)AR agonist, 2-chloro-N(6)-cyclopentyladenosine (CCPA; 0.1 mg/kg), or a selective A(1)AR antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.4 mg/kg), 15 minutes before hepatic ischemia. Twenty-four hours after hepatic IR, the A(1) knockout mice and DPCPX-treated A(1) wild-type (A(1)WT) mice developed significantly worse liver injury (alanine aminotransferase, liver necrosis, neutrophil infiltration, and apoptosis) compared to A(1)AR WT mice. However, the selective A(1)AR agonist CCPA failed to protect against hepatic IR injury in A(1)WT mice. Our results show that the endogenous A(1)ARs protect against hepatic IR injury in vivo by primarily reducing apoptosis and necrosis with subsequent reductions in proinflammatory neutrophil infiltration. However, in contrast to the kidneys, in which exogenous A(1)AR activation protected against IR injury, exogenous A(1)AR activation failed to protect against liver injury after IR. We conclude that endogenous A(1)AR activation prevents worsened murine liver IR injury primarily by reducing necrotic and apoptotic cell death. Harnessing the mechanisms of cytoprotection with endogenous A(1)AR activation may lead to new therapies for perioperative hepatic IR injury.

Acute and delayed renal protection against renal ischemia and reperfusion injury with A1adenosine receptors

We showed previously that activation of A1adenosine receptors (AR) protects against renal ischemia-reperfusion (IR) injury in rats and mice. In the heart, transient A1AR activation produces biphasic protective effects: acute protection wanes after several hours but protective effects return 24–72 h later (second window of protection). In this study, we determined whether A1AR activation produces delayed renal protection and elucidated the mechanisms of acute and delayed renal protection. A1AR wild-type mice were subjected to 30-min renal ischemia and 24 h of reperfusion to produce acute renal failure. Pretreatment with a selective A1AR agonist 2-chloro- N6-cyclopentyladenosine (CCPA; 0.1 mg/kg bolus ip) either 15 min or 24 h before renal ischemia protected against renal IR injury and reduced renal corticomedullary necrosis, apoptosis, and inflammation. Transient A1AR activation led to phosphorylation of extracellular signal-regulated protein kinase mitogen-activated protein kinase (ERK MAPK), Akt, and heat shock protein 27 (HSP27). Moreover, induction of HSP27 and Akt occurred with CCPA treatment. Inhibition of PKC with chelerythrine prevented acute but not delayed renal protection with A1AR activation. Moreover, deletion of PI3Kγ or inhibition of Akt, but not inhibition of ERK, prevented delayed and acute renal protection with A1AR activation. Inhibition of Gi/owith pertussis toxin obliterated both acute and delayed A1AR-mediated renal protection. In contrast to renal protection with delayed ischemic preconditioning, nitric oxide synthase activity was not induced with delayed A1AR-mediated renal protection. Therefore, transient activation of renal A1AR led to acute as well as delayed protective effects against renal IR injury via distinct signaling pathways.

Additive protection against lung ischemia-reperfusion injury by adenosine A2A receptor activation before procurement and during reperfusion

OBJECTIVE

Adenosine A2A receptor activation during reperfusion improves lung ischemia-reperfusion injury. In this study we sought to determine whether pretreatment of rabbits with a potent and selective adenosine A2A receptor agonist, ATL-313, before transplantation or whether adding ATL-313 to the preservation solution results in equivalent or additional protection compared with ATL-313 added during reperfusion.

METHODS

An isolated, ventilated, ex vivo blood-perfused rabbit lung model was used. All groups underwent 2 hours of reperfusion after 18 hours of cold ischemia (4 degrees C). ATL-313 was administered 1 hour before ischemia intravenously, with the preservation solution, and/or during reperfusion.

RESULTS

Both pretreatment of donor animals with ATL-313 or adding ATL-313 just during reperfusion improved pulmonary function, but significantly greater improvement was observed when pretreatment and treatment during reperfusion were combined (all P < .05). Myeloperoxidase levels, bronchoalveolar lavage tumor necrosis factor alpha levels, and pulmonary edema were all maximally decreased in the combined treatment group. The administration of an equimolar amount of the potent and highly selective adenosine 2A receptor antagonist, ZM 241385, along with ATL-313, resulted in the loss of protection conferred by ATL-313.

CONCLUSIONS

Adenosine A2A receptor activation with ATL-313 results in the greatest protection against lung ischemia-reperfusion injury when given before ischemia and during reperfusion. Improved pulmonary function observed with adenosine A2A receptor activation was correlated with decreased bronchoalveolar lavage tumor necrosis factor alpha and decreased lung myeloperoxidase. The loss of protection observed with the concurrent administration of the adenosine A2A receptor antagonist, ZM 241385, supports that the mechanism of ATL-313 protection is specifically mediated via adenosine A2A receptor activation.

Renal tubule necrosis and apoptosis modulation by A1 adenosine receptor expression

We have shown that A1 adenosine receptors (A1ARs) are cytoprotective against renal tubular necrosis and apoptosis both in vivo and in vitro. To study the role of A1AR numbers on renal epithelial cell survival, we stably overexpressed the human A1 receptor in a porcine renal tubule cell line and utilized primary cultures of proximal tubules obtained from A1AR knockout mice. Receptor-overexpressing cells were protected against peroxide-induced necrosis and tumor necrosis factor-alpha/cycloheximide-induced apoptosis. Conversely, cultured proximal tubule cells from receptor knockout mice showed more necrotic and apoptotic cell loss than corresponding cells from wild-type mice. Overexpression of the receptor resulted in a significantly higher baseline expression of both total and phosphorylated heat-shock protein (HSP)27; the latter due to A1 receptor enhancement of p38 and AP2 mitogen-activated protein kinase activities. The resistance to cell death in the porcine cells was reversed by selective A1 receptor antagonism and by a selective inhibitor of HSP synthesis. Receptor activation in wild-type mice in vivo led to increased total and phosphorylated HSP27, whereas receptor knockout mice showed decreased baseline and adenosine-mediated HSP phosphorylation. These studies show that endogenous A1AR activation produces cytoprotective effects in renal proximal tubules by modulating HSP27 signaling pathways.

Protective role of ecto-5'-nucleotidase (CD73) in renal ischemia

Acute renal failure from ischemia significantly contributes to cardiovascular morbidity and mortality. Extracellular adenosine has been implicated as an anti-inflammatory metabolite particularly during conditions of limited oxygen availability (e.g., ischemia). Because ecto-5'-nucleotidase (CD73) is rate limiting for extracellular adenosine generation, this study examined the contribution of CD73-dependent adenosine production to ischemic preconditioning (IP) of the kidneys. After the initial observation that murine CD73 transcript, protein, and function are induced by renal IP, its role in IP-mediated kidney protection was studied. In fact, increases in renal adenosine concentration with IP are attenuated in cd73(-/-) mice. Moreover, pharmacologic inhibition of CD73 or its targeted gene deletion abolished renal protection by IP as measured by clearance studies, plasma electrolytes, and renal tubular destruction, and reconstitution of cd73(-/-) mice with soluble 5'-nucleotidase resulted in complete restoration of renal protection by IP. Finally, renal injury after ischemia was attenuated by intraperitoneal treatment of wild-type mice with soluble 5'-nucleotidase to a similar degree as by IP. Taken together, these data reveal what is believed to be a previously unrecognized role of CD73 in renal protection from ischemia and suggest treatment with soluble 5'-nucleotidase as a novel therapeutic approach in the treatment of renal diseases that are precipitated by limited oxygen availability.

Apoptosis antagonizing transcription factor protects renal tubule cells against oxidative damage and apoptosis induced by ischemia-reperfusion

Apoptosis antagonizing transcription factor (AATF) is a leucine zipper domain-containing protein that has antiapoptotic properties. AATF is expressed in several organs and tissues, including the kidney. AATF may participate in inhibition of proapoptotic pathways and/or activation of antiapoptotic pathways. Ischemia/reperfusion-induced renal injury (IRI) is clinically important because it typically damages renal tubular epithelial cells and glomerular cells and is the most common cause of acute renal failure. It now is reported that AATF is expressed in human kidney proximal tubule (HK-2) cells and in mouse primary renal tubule epithelial cells. Levels of AATF expression were altered significantly in these cells in a well-established in vitro model of renal IRI. In transfected HK-2 cells, RNA interference-mediated silencing of AATF exacerbated whereas overexpression of the full-length AATF ameliorated mitochondrial dysfunction, accumulation of superoxide and peroxynitrite, lipid peroxidation, caspase-3 activation, and apoptotic death that were induced by IRI. In primary renal tubule epithelial cells, overexpression of AATF mediated by recombinant adeno-associated virus (AAV) vectors resulted in significant antiapoptotic activity, whereas knockdown of AATF by small interference RNA led to exacerbated cell death after IRI. These results identify AATF as a novel cytoprotective factor against oxidative and apoptotic damage in renal tubular cells. AATF may represent a potential candidate for therapeutic application in IRI.

Use of a hanging-weight system for isolated renal artery occlusion during ischemic preconditioning in mice

Renal failure from ischemia contributes to morbidity and mortality. Ischemic preconditioning (IP) represents a powerful strategy for kidney protection, and recent advances in transgenic mice may help elucidate its molecular mechanisms. However, murine IP is technically challenging and experimental details significantly influence results. Thus we developed a novel model for renal IP using a hanging-weight system for isolated renal artery occlusion. In contrast to previous models, this technique eliminates the need for clamping the vascular pedicle (artery/vein). In fact, assessment of renal injury after different time periods of ischemia (10-60 min) revealed highly reproducible increases in plasma creatinine and potassium levels, while creatinine clearance, urinary flow and potassium/sodium excretion were significantly attenuated. Using different numbers of IP cycles, we found maximal protection with four cycles of 4 min of ischemia-reperfusion. In contrast, no significant renal protection was observed with IP of the vascular pedicle. To assess transcriptional responses in this model, we isolated RNA from preconditioned kidneys and found time-dependent induction of erythropoietin mRNA and plasma levels with IP. Taken together, this model provides highly reproducible renal injury and protection by IP, thus minimizing variability associated with previous techniques based on clamping of the renal pedicle. Further studies on renal ischemia/IP in mice may consider this technique.

Par-4 is a novel mediator of renal tubule cell death in models of ischemia-reperfusion injury

Prostate apoptosis response-4 (Par-4) is a leucine zipper protein linked to apoptotic cell death in prostate cancer and neuronal tissues. The leucine zipper domain of Par-4 (Leu.zip) mediates protein-protein interactions that are essential for sensitization of cells to apoptosis, and overexpression of Leu.zip blocks Par-4 activity in a dominant negative fashion. Ischemia-reperfusion-induced renal injury (IRI) is clinically important because it typically damages renal tubular epithelial cells and glomerular cells, and it is the most common cause of acute renal failure (ARF). We now report that Par-4 is expressed in renal tubule cells and that aberrant expression of Par-4 activity plays a crucial role in activating apoptotic pathways in well-characterized models of renal IRI. Increased levels of Par-4 were observed following chemical ischemia-reperfusion in HK-2 cells in vitro and in mouse renal tubular cells following bilateral clamping of renal pedicles in vivo. Inhibition of Par-4 expression by specific par-4 antisense oligonucleotides largely prevented HK-2 cell apoptosis induced by IRI. Overexpression of Par-4 in these cells exacerbated mitochondrial dysfunction and caspase activation and conferred increased sensitivity to IRI-induced apoptosis. Expression of Leu.zip, a dominant negative regulator of Par-4, largely prevented mitochondrial dysfunction and caspase activation and significantly inhibited IRI-induced apoptosis in HK-2 cells. In addition, transfection of Par-4 increased while transfection of Leu.zip decreased necrosis in HK-2 cells following prolonged IRI. These results identify Par-4 as a novel and early mediator of renal tubule cell injury following IRI and provide a potential target for developing new therapeutic strategies for renal IRI and ARF.

Decreased capacity of immune cells to cause tissue injury mediates kidney ischemic preconditioning

Ischemic preconditioning (IP) is a well-established phenomenon, and the underlying mechanisms of IP are thought to involve adaptive changes within the injured tissue. Because one of the main functions of immune cells is to harbor memory, we hypothesized that circulating immune cells could mediate IP by responding to an initial ischemia reperfusion injury (IRI) and then mediate decreased injury after a second IRI event. C57BL/6 mice underwent 30 min of bilateral renal clamping or sham operation. At 5 days after ischemia, purified leukocytes from spleen were adoptively transferred into T cell-deficient (nu/nu) mice. After 1 wk, these mice underwent 30 min of renal IRI. The nu/nu mice receiving leukocytes from ischemic wild-type mice had significantly reduced renal injury compared with nu/nu mice receiving leukocytes from sham-operated, wild-type mice. Infiltration of neutrophil and macrophage in postischemic kidney did not correlate with the protection. No difference in kidney C3d or IgG deposition was detected between groups. Given that inducible NO synthase (iNOS) has been implicated in IP, leukocytes from ischemic or sham-operated, iNOS-deficient mice were transferred into nu/nu mice. Effects similar to those of wild-type transfer of ischemic leukocytes were demonstrated; thus, iNOS was not mediating the IP effect of leukocytes. This is the first evidence that immune cells are primed after renal IRI and thereby lose the capacity to cause kidney injury during a second episode of IRI. This finding may also be relevant for elucidating the mechanisms underlying cross-talk between injured kidney and distant organs.

Purinergic signaling and kinase activation for survival in pulmonary oxidative stress and disease

Stimulus-induced release of endogenous ATP into the extracellular milieu has been shown to occur in a variety of cells, tissues, and organs. Extracellular ATP can propagate signals via P2 receptors that are essential for growth and survival of cells. Abundance of P2 receptors, their multiple isoforms, and their ubiquitous distribution indicate that they transmit vital signals. Pulmonary epithelium and endothelium are rich in both P2X and P2Y receptors. ATP release from lung tissue and cells occurs upon stimulation both in vivo and in vitro. Extracellular ATP can activate signaling cascades composed of protein kinases including extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K). Here we summarize progress related to release of endogenous ATP and nucleotide signaling in pulmonary tissues upon exposure to oxidant stress. Hypoxic, hyperoxic, and ozone exposures cause a rapid increase of extracellular ATP in primary pulmonary endothelial and epithelial cells. Extracellular ATP is critical for survival of these cells in high oxygen and ozone concentrations. The released ATP, upon binding to its specific receptors, triggers ERK and PI3K signaling and renders cells resistant to these stresses. Impairment of ATP release and transmission of such signals could limit cellular survival under oxidative stress. This may further contribute to disease pathogenesis or exacerbation.

Plasminogen activator inhibitor-1 and diabetic nephropathy

Diabetic nephropathy is characterized by excessive accumulation of extracellular matrix (ECM) in the kidney. Decreased ECM degradation as well as increased ECM synthesis plays an important role in ECM remodeling that favours tissue fibrosis. Plasminogen activator (PA)/plasmin/PA inhibitor (PAI) system is involved in ECM degradation and PAI-1 plays a critical role in ECM remodeling in the kidney. Normal human kidneys do not express PAI-1 but PAI-1 is overexpressed in pathologic conditions associated with renal fibrosis including diabetic nephropathy. Reactive oxygen species mediate PAI-1 up-regulation in renal cells cultured under high glucose, hypoxia, and TGF-beta1. Recent studies utilizing PAI-1 deficient mice suggest that PAI-1 induce ECM deposition in diabetic kidney through increased ECM synthesis by TGF-beta1 up-regulation as well as through decreased ECM degradation by suppression of plasmin and MMP-2 activity.

Effect of adenosine triphosphate in renal ischemic injury: involvement of NF-kappaB

Renal ischemic/reperfusion injury in vivo results in a significant increase of acute renal failure (ARF) and death. Nevertheless, there are many limitations in using in vivo models of renal ischemic injury to elucidate the detailed mechanisms of renal injury. Adenosine triphosphate (ATP), an extracellular signal, has been shown to be an important factor in regulation of epithelial cell function. Thus, the present study was performed to establish in vitro ischemic model using primary cultured rabbit renal proximal tubule cells (PTCs) and to examine the effect of ATP in this model. We established an in vitro model of ischemic injury, causing severe depletion of intracellular ATP by using the combination of a mitochondrial respiration inhibitor (antimycin A), non-metabolizable glucose analog (2-deoxyglucose), and calcium ionophore (A23187) in PTCs. Indeed, this ischemic injury significantly increased LDH release, a marker of structural damage, and ATP blocked ischemic injury-induced LDH release. 2-Methylthio-ATP and ATP-gamma-S (P2Y purinoceptor agonists) also blocked ischemic injury-induced LDH release, whereas AMP-CPP (P2X purinoceptor agonist) did not block it. In experiments to examine the relationship between ischemic injury and NF-kappaB activation, ischemic injury increased NF-kappaB translocation, DNA binding activity, and CAT activity. On the other hand, ATP, ATP-gamma-S, or 2-methylthio-ATP protected ischemic injury-induced NF-kappaB activation. These results suggest that the protective effect of ATP on ischemic injury is, in part, related to inhibition of NF-kappaB activation via P2Y receptor in PTCs.

Hematologic and biochemical effects of the Gradiflow in an ex vivo ovine model

The Gradiflow (Life Therapeutics, Frenchs Forest, Australia) system is a novel electrophoretic technique that uses the dual characteristics of size and charge to separate target macromolecules from complex biological solutions. The system has the potential to selectively remove a range of moieties from blood and plasma in an in vivo system such as hemodialysis or, alternatively, in an in vitro setting such as a blood bank. In this study, the safety of a scaled down Gradiflow prototype device with a membrane surface area of 16 cm2 was investigated using an ex vivo ovine model. Physiologic, hematologic, and biochemical parameters were assessed in 12 sheep: 6 animals treated using the Gradiflow and 6 controls. The effects of the Gradiflow procedure on both whole blood and plasma were analyzed. The Gradiflow procedure was well tolerated, and the application of an electrical potential or exposure to the Gradiflow membrane did not cause any significant changes in the parameters measured. Hemoglobin levels remained stable in all groups during the 4-hour experiment. An early neutropenia was observed in all groups, although this appeared to be more pronounced with exposure to a plasma filter; the presence of the Gradiflow component had no separate influence. One sheep in the plasma group experienced septic shock, caused by Staphylococcus contamination of the separation membrane. Overall, the results indicate that there were no gross physiologic, hematologic, or biochemical adverse reactions to the ex vivo Gradiflow procedure.