Reoxygenation-specific activation of the antioxidant transcription factor Nrf2 mediates cytoprotective gene expression in ischemia-reperfusion injury.

Tissue reoxygenation following hypoxia is associated with ischemia-reperfusion injury (IRI) and may signal the development of ischemic preconditioning, an adaptive state that is protective against subsequent IRI. Here we used microarray RNA analysis of in vivo and in vitro models of IRI to delineate the underlying molecular mechanisms. Microarray analysis of renal tissue after ischemia-reperfusion revealed a number of highly up-regulated antioxidant genes including aldehyde dehydrogenases (ALDH1A1 and ALDH1A7), glutathione S-transferases (GSTM5, GSTA2 and GSTP1), and NAD(P)H quinone oxidoreductase (NQO1). The transcription factor NF-E2-related factor-2 (Nrf2), a master regulator of this antioxidant response, is also elevated in IRI. Furthermore, microarray analysis of renal epithelial cells exposed to hypoxia/reoxygenation identified Nrf2 to be up-regulated on reoxygenation. We also reveal a reoxygenation-specific nuclear accumulation of Nrf2 protein and subsequent activation of a NQO1 promoter reporter construct. Attenuating reactive oxygen species (ROS) in reoxygenation using the antioxidant N-acetyl cysteine results in inhibition of Nrf-2 activation. mRNA levels for Nrf2-dependent genes were detected in human liver biopsy 1 h after transplantation. These results indicate that reoxygenation-dependent Nrf-2 activity facilitates ischemic preconditioning through the induction of antioxidant gene expression and that ROS may be critical in signaling this event.

Protective effects of sphingosine 1-phosphate in murine endotoxin-induced inflammatory lung injury.

Our prior in vitro studies indicate that sphingosine 1-phosphate (S1P), a phospholipid angiogenic factor, produces endothelial cell barrier enhancement through ligation of endothelial differentiation gene family receptors. We hypothesized that S1P may reduce the vascular leak associated with acute lung injury and found that S1P infusion produced a rapid and significant reduction in lung weight gain (more than 50%) in the isolated perfused murine lung. The effect of S1P was next assessed in a murine model of LPS-mediated microvascular permeability and inflammation with marked increases in parameters of lung injury at both 6 and 24 hours after intratracheal LPS. Each parameter assessed was significantly reduced by intravenous S1P (1 microM final) and in selected experiments by the S1P analogue FTY720 (0.1 mg/kg, intraperitoneally) delivered 1 hour after LPS. S1P produced an approximately 40-50% reduction in LPS-mediated extravasation of Evans blue dye albumin, bronchoalveolar lavage protein content, and lung tissue myeloperoxidase activity (reflecting phagocyte infiltration). Consistent with systemic barrier enhancement, S1P significantly decreased Evans blue dye albumin extravasation and myeloperoxidase content in renal tissues of LPS-treated mice. These studies indicate that S1P significantly decreases pulmonary/renal vascular leakage and inflammation in a murine model of LPS-mediated acute lung injury and may represent a novel therapeutic strategy for vascular barrier dysfunction.

Modification of the transcriptomic response to renal ischemia/reperfusion injury by lipoxin analog.

BACKGROUND: Lipoxins are lipoxygenase-derived eicosanoids with anti-inflammatory and proresolution bioactivities in vitro and in vivo. We have previously demonstrated that the stable synthetic LXA4 analog 15-epi-16-(FPhO)-LXA4-Me is renoprotective in murine renal ischemia/reperfusion injury, as gauged by lower serum creatinine, attenuated leukocyte infiltration, and reduced morphologic tubule injury. METHODS: We employed complementary oligonucleotide microarray and bioinformatic analyses to probe the transcriptomic events that underpin lipoxin renoprotection in this setting. RESULTS: Microarray-based analysis identified three broad categories of genes whose mRNA levels are altered in response to ischemia/reperfusion injury, including known genes previously implicated in the pathogenesis of ischemia/reperfusion injury [e.g., intercellular adhesion molecule-1 (ICAM-1), p21, KIM-1], known genes not previously associated with ischemia/reperfusion injury, and cDNAs representing yet uncharacterized genes. Characterization of expressed sequence tags (ESTs) displayed on microarrays represents a major challenge in studies of global gene expression. A bioinformatic annotation pipeline successfully annotated a large proportion of ESTs modulated during ischemia/reperfusion injury. The differential expression of a representative group of these ischemia/reperfusion injury-modulated genes was confirmed by real-time polymerase chain reaction. Prominent among the up-regulated genes were claudin-1, -3, and -7, and ADAM8. Interestingly, the former response was claudin-specific and was not observed with other claudins expressed by the kidney (e.g., claudin-8 and -6) or indeed with other components of the renal tight junctions (e.g., occludin and junctional adhesion molecule). Noteworthy among the down-regulated genes was a cluster of transport proteins (e.g., aquaporin-1) and the zinc metalloendopeptidase meprin-1 beta implicated in renal remodeling. CONCLUSION: Treatment with the lipoxin analog 15-epi-16-(FPhO)-LXA4-Me prior to injury modified the expression of many differentially expressed pathogenic mediators, including cytokines, growth factors, adhesion molecules, and proteases, suggesting a renoprotective action at the core of the pathophysiology of acute renal failure (ARF). Importantly, this lipoxin-modulated transcriptomic response included many genes expressed by renal parenchymal cells and was not merely a reflection of a reduced renal mRNA load resulting from attenuated leukocyte recruitment. The data presented herein suggest a framework for understanding drivers of kidney injury in ischemia/reperfusion and the molecular basis for renoprotection by lipoxins in this setting.

Pathophysiological contributions of fucosyltransferases in renal ischemia reperfusion injury.

Ischemia reperfusion injury (IRI) is a major cause of delayed graft function. Recent studies have shown that selectins play an important role in IRI. Selectins bind to sialylated and fucosylated sLe(x) receptors, and two enzymes, fucosyltransferase IV (FucT-IV) and VII (FucT-VII), are important in the function of these receptors. We hypothesized that fucosyltransferase (FucT) enzymes were important pathophysiologic mediators of renal IRI. We therefore evaluated renal IRI in mice deficient in FucT-IV, FucT-VII, and both FucT-IV and FucT-VII and compared their renal function, tubular injury, selectin ligand expression, and neutrophil infiltration to those in wild-type control mice. Bilateral 30-min renal IRI was performed, and the results demonstrated that mice deficient in both FucT-IV/FucT-VII were significantly protected from renal IRI at 24 and 48 h compared with wild-type control mice. FucT-IV-deficient mice showed only modest protection from renal injury at 24 h. However, FucT-VII-deficient mice had similar injury as wild-type mice. Histological analysis of kidney tissue postischemia revealed that mice deficient in both FucT-IV and FucT-VII had significantly reduced tubular injury compared with wild-type mice. Selectin ligand expression increased postischemia in wild-type, but not FucT-IV/FucT-VII-deficient, mice. Neutrophil infiltration in postischemic kidneys of FucT-IV/FucT-VII-deficient mice was also attenuated. These data demonstrate that fucosyltransferases are important in the pathogenesis of renal IRI and are potential therapeutic targets.

15-Epi-16-(para-fluorophenoxy)-lipoxin A(4)-methyl ester, a synthetic analogue of 15-epi-lipoxin A(4), is protective in experimental ischemic acute renal failure.

Lipoxins are endogenous lipoxygenase-derived eicosanoids, generated during inflammatory, hypersensitivity, and vascular events, that display vasodilatory, antiinflammatory, and pro-resolution activity. Here, we evaluated the efficacy of 15-epi-16-(para-fluorophenoxy)-lipoxin A(4)-methyl ester (15-epi-16-(FPhO)-LXA(4)-Me), a stable synthetic analogue of aspirin-triggered 15-epi-lipoxin A(4) in ischemic acute renal failure (ARF) in NIH Swiss mice. ARF was induced by 30-min crossclamping of renal pedicles and was associated with elevated serum creatinine, morphologic injury, polymorphonuclear leukocyte (PMN) recruitment, and increased mRNA levels for adhesion molecules (intercellular adhesion molecule-1 [ICAM-1] and vascular cell adhesion molecule-1 [VCAM-1]), chemokines (growth regulated oncogene-1 [GRO1]), and cytokines (interleukin-1beta [IL-1beta] and IL-6) after 24-h reperfusion. A single bolus of 15-epi-16-(FPhO)-LXA(4)-Me afforded striking functional (mean +/- SEM creatinine in mg/dl: sham-operated, 0.77 +/- 0.04; ARF + vehicle, 2.49 +/- 0.19; ARF + 15-epi-16-(FPhO)-LXA(4)-Me, 0.75 +/- 0.12; P < 0.001) and morphologic protection and reduced PMN infiltration. Treatment with 15-epi-16-(FPhO)-LXA(4)-Me was also associated with lower IL-1beta, IL-6, and GRO1 mRNA levels, whereas ICAM-1 and VCAM-1 mRNA levels were unchanged. Compatible with these results, LXA(4) blunted chemoattractant-stimulated PMN migration across HK-2 renal epithelial cell monolayers in vitro, but it did not inhibit cytokine-induced HK-2 ICAM-1 expression or adhesiveness for PMN. Interestingly 15-epi-16-(FPhO)-LXA(4)-Me-treated animals also displayed increased renal mRNA levels for suppressors of cytokine signaling-1 (SOCS-1) and SOCS-2, but not CIS-1, endogenous inhibitors of cytokine-elicited Jak/Stat-signaling pathways. These results indicate that 15-epi-16-(FPhO)-LXA(4)-Me is protective in renal ischemia reperfusion injury in vivo, at least partially by modulating cytokine and chemokine expression and PMN recruitment, and provides a rationale for further exploration of the efficacy of LXA(4) structural analogues in ischemic ARF and other renal diseases.