Ischemic AKI Research Articles

MicroRNA-489 Induction by Hypoxia-Inducible Factor-1 Protects against Ischemic Kidney Injury.

MicroRNAs have been implicated in ischemic AKI. However, the specific microRNA species that regulates ischemic kidney injury remains unidentified. Our previous microarray analysis revealed microRNA-489 induction in kidneys of mice subjected to renal ischemia-reperfusion. In this study, we verified the induction of microRNA-489 during ischemic AKI in mice and further examined the underlying mechanisms. Hypoxia-inducible factor-1α deficiency associated with diminished microRNA-489 induction in cultured rat proximal tubular cells subjected to hypoxia and kidney tissues of mice after renal ischemia-reperfusion injury. Moreover, genomic analysis revealed that microRNA-489 is intronic in the calcitonin receptor gene, and chromatin immunoprecipitation assays showed increased binding of hypoxia-inducible factor-1 to a specific site in the calcitonin receptor gene promoter after hypoxia. Inhibition of microRNA-489 increased apoptosis in renal tubular cells after ATP depletion injury in vitro, whereas microRNA-489 mimics mediated protection. In mice, inhibition of microRNA-489 enhanced tubular cell death and ischemic AKI without significantly affecting tubular cell proliferation. Deep sequencing identified 417 mRNAs that were recruited to the RNA-induced silencing complex by microRNA-489. Of the identified mRNAs, 127 contain microRNA-489 targeting sites, and of those, 18 are involved in the cellular stress response, including the poly(ADP-ribose) polymerase 1 gene implicated in ischemic kidney injury. Sequence analysis and in vitro studies validated poly(ADP-ribose) polymerase 1 as a microRNA-489 target. Together, these results suggest that microRNA-489 is induced via hypoxia-inducible factor-1 during ischemic AKI to protect kidneys by targeting relevant genes.

Cellular and Molecular Mechanisms of AKI.

In this article, we review the current evidence for the cellular and molecular mechanisms of AKI, focusing on epithelial cell pathobiology and related cell-cell interactions, using ischemic AKI as a model. Highlighted are the clinical relevance of cellular and molecular targets that have been investigated in experimental models of ischemic AKI and how such models might be improved to optimize translation into successful clinical trials. In particular, development of more context-specific animal models with greater relevance to human AKI is urgently needed. Comorbidities that could alter patient susceptibility to AKI, such as underlying diabetes, aging, obesity, cancer, and CKD, should also be considered in developing these models. Finally, harmonization between academia and industry for more clinically relevant preclinical testing of potential therapeutic targets and better translational clinical trial design is also needed to achieve the goal of developing effective interventions for AKI.

Endothelial Krüppel-Like Factor 4 Mediates the Protective Effect of Statins against Ischemic AKI.

Endothelial cells participate in the pathophysiology of ischemic AKI by increasing the expression of cell adhesion molecules and by recruiting inflammatory cells. We previously showed that endothelial Krüppel-like factor 4 (Klf4) regulates vascular cell adhesion molecule 1 (Vcam1) expression and neointimal formation after carotid injury. In this study, we determined whether endothelial Klf4 is involved in ischemic AKI using endothelial Klf4 conditional knockout (Klf4 cKO) mice generated by breeding Tek-Cre mice and Klf4 floxed mice. Klf4 cKO mice were phenotypically normal before surgery. However, after renal ischemia-reperfusion injury, Klf4 cKO mice exhibited elevated serum levels of urea nitrogen and creatinine and aggravated renal histology compared with those of Klf4 floxed controls. Moreover, Klf4 cKO mice exhibited enhanced accumulation of neutrophils and lymphocytes and elevated expression of cell adhesion molecules, including Vcam1 and Icam1, in injured kidneys. Notably, statins ameliorated renal ischemia-reperfusion injury in control mice but not in Klf4 cKO mice. Mechanistic analyses in cultured endothelial cells revealed that statins increased KLF4 expression and that KLF4 mediated the suppressive effect of statins on TNF-α-induced VCAM1 expression by reducing NF-κB binding to the VCAM1 promoter. These results provide evidence that endothelial Klf4 is renoprotective and mediates statin-induced protection against ischemic AKI by regulating the expression of cell adhesion molecules and concomitant recruitment of inflammatory cells.

Epigenetic regulation in acute kidney injury: new light in a dark area

Epigenetic mechanisms have been implicated in the pathogenesis of renal diseases, including acute kidney injury. Mar et. al. now unravel the acetylation and methylation at histones that are associated with the transcription of key genes in AKI. Notably, histone modifications display a remarkable heterogeneity in ischemic and endotoxic AKI. Targeting epigenetic programs may offer novel strategies to protect kidneys from AKI and enhance kidney repair and recovery.

Deficiency in the Formation of 20-Hydroxyeicosatetraenoic Acid Enhances Renal Ischemia-Reperfusion Injury.

Ischemia-reperfusion (IR) injury is the most common cause of AKI. The susceptibility to develop AKI varies widely among patients. However, little is known about the genes involved. 20-Hydroxyeicosatetraenoic acid (20-HETE) has an important role in the regulation of renal tubular and vascular function and has been implicated in IR injury. In this study, we examined whether a deficiency in the renal formation of 20-HETE enhances the susceptibility of Dahl salt-sensitive (SS) rats to ischemic AKI. Transfer of chromosome 5 containing the CYP4A genes responsible for the formation of 20-HETE from the Brown Norway (BN) rat onto the SS genetic background increased renal 20-HETE levels after ischemia and reduced plasma creatinine levels (±SEM) 24 hours after IR from 3.7±0.1 to 2.0±0.2 mg/dl in an SS.5(BN)-consomic strain. Transfer of this chromosome also prevented the secondary decline in medullary blood flow and ischemia that develops 2 hours after IR in the susceptible SS strain. Blockade of the synthesis of 20-HETE with HET0016 reversed the renoprotective effects in SS.5(BN) rats. Similar results were observed in an SS.5(Lew)-congenic strain, in which a smaller region of chromosome 5 containing the CYP4A genes from a Lewis rat was introgressed onto the SS genetic background. These results indicate that 20-HETE has a protective role in renal IR injury by maintaining medullary blood flow and that a genetic deficiency in the formation of 20-HETE increases the susceptibility of SS rats to ischemic AKI.

Oat1/3 restoration protects against renal damage after ischemic AKI.

Expression of proximal tubular organic anion transporters Oat1 and Oat3 is reduced by PGE2 after renal ischemia and reperfusion (I/R) injury. We hypothesized that impaired expression of Oat1/3 is decisively involved in the deterioration of renal function after I/R injury. Therefore, we administered probenecid, which blocks proximal tubular indomethacin uptake, to abolish the indomethacin-mediated restoration of Oat1/3 regulation and its effect on renal functional and morphological outcome. Ischemic acute kidney injury (iAKI) was induced in rats by bilateral clamping of renal arteries for 45 min with 24-h follow-up. Low-dose indomethacin (1 mg/kg) was given intraperitoneally (ip) at the end of ischemia. Probenecid (50 mg/kg) was administered ip 20 min later. Indomethacin restored the expression of Oat1/3, PAH net secretion, and PGE2 clearance. Additionally, indomethacin improved kidney function as measured by glomerular filtration rate (GFR), renal perfusion as determined by corrected PAH clearance, and morphology, whereas it reduced renal cortical apoptosis and nitric oxide production. Notably, indomethacin did not affect inflammation parameters in the kidneys (e.g., monocyte chemoattractant protein-1, ED1+ cells). On the other hand, probenecid blocked the indomethacin-induced restoration of Oat1/3 and moreover abrogated all beneficial effects. Our study indicates that the beneficial effect of low-dose indomethacin in iAKI is not due to its anti-inflammatory potency, but in contrast to its restoration of Oat1/3 expression and/or general renal function. Inhibition of proximal tubular indomethacin uptake abrogates the beneficial effect of indomethacin by resetting the PGE2-mediated Oat1/3 impairment, thus reestablishing renal damage. This provides evidence for a mechanistic effect of Oat1/3 in a new model of the induction of renal damage after iAKI.

Conditional knockout of proximal tubule mitofusin 2 accelerates recovery and improves survival after renal ischemia.

Proximal tubule (PT) cells are critical targets of acute ischemic injury. Elimination of the mitochondrial fusion protein mitofusin 2 (Mfn2) sensitizes PT cells to apoptosis in vitro. However, the role of PT Mfn2 in ischemic AKI in vivo is unknown. To test its role, we evaluated the effects of conditional KO of PT Mfn2 (cKO-PT-Mfn2) on animal survival after transient bilateral renal ischemia associated with severe AKI. Forty-eight hours after ischemia, 28% of control mice survived compared with 86% of cKO-PT-Mfn2 animals (P<0.001 versus control). Although no significant differences in histologic injury score, apoptosis, or necrosis were detected between genotypes, cKO-PT-Mfn2 kidneys exhibited a 3.5-fold increase in cell proliferation restricted to the intrarenal region with Mfn2 deletion. To identify the signals responsible for increased proliferation, primary PT cells with Mfn2 deficiency were subjected to stress by ATP depletion in vitro. Compared with normal Mfn2 expression, Mfn2 deficiency significantly increased PT cell proliferation and persistently activated extracellular signal-regulated kinase 1/2 (ERK1/2) during recovery from stress. Furthermore, stress and Mfn2 deficiency decreased the interaction between Mfn2 and Ras detected by immunoprecipitation, and purified Mfn2 dose-dependently decreased Ras activity in a cell-free assay. Ischemia in vivo also reduced the Mfn2-RAS interaction and increased both RAS and p-ERK1/2 activity in the renal cortical homogenates of cKO-PT-Mfn2 mice. Our results suggest that, in contrast to its proapoptotic effects in vitro, selective PT Mfn2 deficiency accelerates recovery of renal function and enhances animal survival after ischemic AKI in vivo, partly by increasing Ras-ERK-mediated cell proliferation.

Stanniocalcin-1 inhibits renal ischemia/reperfusion injury via an AMP-activated protein kinase-dependent pathway.

AKI is associated with increased morbidity, mortality, and cost of care, and therapeutic options remain limited. Reactive oxygen species are critical for the genesis of ischemic AKI. Stanniocalcin-1 (STC1) suppresses superoxide generation through induction of uncoupling proteins (UCPs), and transgenic overexpression of STC1 inhibits reactive oxygen species and protects from ischemia/reperfusion (I/R) kidney injury. Our observations revealed high AMP-activated protein kinase (AMPK) activity in STC1 transgenic kidneys relative to wild-type (WT) kidneys; thus, we hypothesized that STC1 protects from I/R kidney injury through activation of AMPK. Baseline activity of AMPK in the kidney correlated with the expression of STCs, such that the highest activity was observed in STC1 transgenic mice followed (in decreasing order) by WT, STC1 knockout, and STC1/STC2 double-knockout mice. I/R in WT kidneys increased AMPK activity and the expression of STC1, UCP2, and sirtuin 3. Inhibition of AMPK by administration of compound C before I/R abolished the activation of AMPK, diminished the expression of UCP2 and sirtuin 3, and aggravated kidney injury but did not affect STC1 expression. Treatment of cultured HEK cells with recombinant STC1 activated AMPK and increased the expression of UCP2 and sirtuin 3, and concomitant treatment with compound C abolished these responses. STC1 knockout mice displayed high susceptibility to I/R, whereas pretreatment of STC1 transgenic mice with compound C restored the susceptibility to I/R kidney injury. These data suggest that STC1 is important for activation of AMPK in the kidney, which mediates STC1-induced expression of UCP2 and sirtuin 3 and protection from I/R.

N-Octanoyl dopamine transiently inhibits T cell proliferation via G1 cell-cycle arrest and inhibition of redox-dependent transcription factors.

Recently, we developed a nonhemodynamic dopamine derivative, NOD, which has profound anti-inflammatory effects in vitro. As NOD also protects rats from ischemic AKI, the present study tested whether NOD is able to modulate cellular immunity for potential use as a T cell-suppressive agent. To this end, T cells were stimulated by anti-CD3/CD28 or PMA/ionomycin in the presence or absence of different concentrations of NOD. T cell proliferation, activation markers, intracellular cytokine expression, and activation of transcription factors were assessed. Whereas T cell proliferation was inhibited significantly by NOD at Day 3, proliferation was restored at Day 7 or later depending on the NOD concentration used. Inhibition of proliferation was reflected by a diminished CD25 expression and switch from naive to memory T cells. Early TCR activation events were unaffected, yet NF-κB and AP-1 were strongly inhibited by NOD. The inhibitory effect of NOD seemed to be dependent on its redox activity, as NOT, a redox-inactive NOD derivate, did not influence proliferation. NOD displayed synergistic effects with CNIs on T cell proliferation. Our data demonstrate that NOD displays T cell-suppressive activity. In keeping with its anti-inflammatory action and its beneficial effect on ischemia-induced AKI, NOD may be an interesting drug candidate to prevent CNI-related side-effects.

MicroRNA-24 antagonism prevents renal ischemia reperfusion injury.

Ischemia-reperfusion (I/R) injury of the kidney is a major cause of AKI. MicroRNAs (miRs) are powerful regulators of various diseases. We investigated the role of apoptosis-associated miR-24 in renal I/R injury. miR-24 was upregulated in the kidney after I/R injury of mice and in patients after kidney transplantation. Cell-sorting experiments revealed a specific miR-24 enrichment in renal endothelial and tubular epithelial cells after I/R induction. In vitro, anoxia/hypoxia induced an enrichment of miR-24 in endothelial and tubular epithelial cells. Transient overexpression of miR-24 alone induced apoptosis and altered functional parameters in these cells, whereas silencing of miR-24 ameliorated apoptotic responses and rescued functional parameters in hypoxic conditions. miR-24 effects were mediated through regulation of H2A histone family, member X, and heme oxygenase 1, which were experimentally validated as direct miR-24 targets through luciferase reporter assays. In vitro, adenoviral overexpression of miR-24 targets lacking miR-24 binding sites along with miR-24 precursors rescued various functional parameters in endothelial and tubular epithelial cells. In vivo, silencing of miR-24 in mice before I/R injury resulted in a significant improvement in survival and kidney function, a reduction of apoptosis, improved histologic tubular epithelial injury, and less infiltration of inflammatory cells. miR-24 also regulated heme oxygenase 1 and H2A histone family, member X, in vivo. Overall, these results indicate miR-24 promotes renal ischemic injury by stimulating apoptosis in endothelial and tubular epithelial cell. Therefore, miR-24 inhibition may be a promising future therapeutic option in the treatment of patients with ischemic AKI.

Tubular p53 Regulates Multiple Genes to Mediate AKI

A pathogenic role of p53 in AKI was suggested a decade ago but remains controversial. Indeed, recent work indicates that inhibition of p53 protects against ischemic AKI in rats but exacerbates AKI in mice. One intriguing possibility is that p53 has cell type-specific roles in AKI. To determine the role of tubular p53, we generated two conditional gene knockout mouse models, in which p53 is specifically ablated from proximal tubules or other tubular segments, including distal tubules, loops of Henle, and medullary collecting ducts. Proximal tubule p53 knockout (PT-p53-KO) mice were resistant to ischemic and cisplatin nephrotoxic AKI, which was indicated by the analysis of renal function, histology, apoptosis, and inflammation. However, other tubular p53 knockout (OT-p53-KO) mice were sensitive to AKI. Mechanistically, AKI associated with the upregulation of several known p53 target genes, including Bax, p53-upregulated modulator of apoptosis-α, p21, and Siva, and this association was attenuated in PT-p53-KO mice. In global expression analysis, ischemic AKI induced 371 genes in wild-type kidney cortical tissues, but the induction of 31 of these genes was abrogated in PT-p53-KO tissues. These 31 genes included regulators of cell death, metabolism, signal transduction, oxidative stress, and mitochondria. These results suggest that p53 in proximal tubular cells promotes AKI, whereas p53 in other tubular cells does not.

Volatile Anesthetics and AKI

AKI is a major clinical problem with extremely high mortality and morbidity. Kidney hypoxia or ischemia-reperfusion injury inevitably occurs during surgery involving renal or aortic vascular occlusion and is one of the leading causes of perioperative AKI. Despite the growing incidence and tremendous clinical and financial burden of AKI, there is currently no effective therapy for this condition. The pathophysiology of AKI is orchestrated by renal tubular and endothelial cell necrosis and apoptosis, leukocyte infiltration, and the production and release of proinflammatory cytokines and reactive oxygen species. Effective management strategies require multimodal inhibition of these injury processes. Despite the past theoretical concerns about the nephrotoxic effects of several clinically utilized volatile anesthetics, recent studies suggest that modern halogenated volatile anesthetics induce potent anti-inflammatory, antinecrotic, and antiapoptotic effects that protect against ischemic AKI. Therefore, the renal protective properties of volatile anesthetics may provide clinically useful therapeutic intervention to treat and/or prevent perioperative AKI. In this review, we outline the history of volatile anesthetics and their effect on kidney function, briefly review the studies on volatile anesthetic-induced renal protection, and summarize the basic cellular mechanisms of volatile anesthetic-mediated protection against ischemic AKI.

IL-11 Is Required for A1 Adenosine Receptor–Mediated Protection against Ischemic AKI

A1 adenosine receptor activation ameliorates ischemic AKI through the induction of renal proximal tubular sphingosine kinase-1. However, systemic adverse effects may limit A1 adenosine receptor-based therapy for ischemic AKI, indicating a need to identify alternative therapeutic targets within this pathway. Here, we evaluated the function of renal proximal tubular IL-11, a clinically approved hematopoietic cytokine, in A1 adenosine receptor-mediated induction of sphingosine kinase-1 and renal protection. Treatment of human proximal tubule epithelial (HK-2) cells with a selective A1 adenosine receptor agonist, chloro-N(6)-cyclopentyladenosine (CCPA), induced the expression of IL-11 mRNA and protein in an extracellular signal-regulated kinase-dependent manner, and administration of CCPA in mice induced renal synthesis of IL-11. Pretreatment with CCPA protected against renal ischemia-reperfusion injury in wild-type mice, but not in IL-11 receptor-deficient mice. Administration of an IL-11-neutralizing antibody abolished the renal protection provided by CCPA. Similarly, CCPA did not induce renal IL-11 expression or protect against renal ischemia-reperfusion injury in mice lacking the renal proximal tubular A1 adenosine receptor. Finally, treatment with CCPA induced sphingosine kinase-1 in HK-2 cells and wild-type mice, but not in IL-11 receptor-deficient or renal proximal tubule A1 adenosine receptor-deficient mice. Taken together, these results suggest that induction of renal proximal tubule IL-11 is a critical intermediary in A1 adenosine receptor-mediated renal protection that warrants investigation as a novel therapeutic target for the treatment of ischemic AKI.

Renalase Protects against Ischemic AKI

Elevated levels of plasma catecholamines accompany ischemic AKI, possibly contributing the inflammatory response. Renalase, an amine oxidase secreted by the proximal tubule, degrades circulating catecholamines and reduces myocardial necrosis, suggesting that it may protect against renal ischemia reperfusion injury. Here, mice subjected to renal ischemia reperfusion injury had significantly lower levels of renalase in the plasma and kidney compared with sham-operated mice. Consistent with this, plasma NE levels increased significantly after renal ischemia reperfusion injury. Furthermore, renal tubular inflammation, necrosis, and apoptosis were more severe and plasma catecholamine levels were higher in renalase-deficient mice subjected to renal ischemia reperfusion compared with wild-type mice. Administration of recombinant human renalase reduced plasma catecholamine levels and ameliorated ischemic AKI in wild-type mice. Taken together, these data suggest that renalase protects against ischemic AKI by reducing renal tubular necrosis, apoptosis, and inflammation, and that plasma renalase might be a biomarker for AKI. Recombinant renalase therapy may have potential for the prevention and treatment of AKI.

P53 Is Renoprotective after Ischemic Kidney Injury by Reducing Inflammation

In the rat, p53 promotes tubular apoptosis after ischemic AKI. Acute pharmacologic inhibition of p53 is protective in this setting, but chronic inhibition enhances fibrosis, demonstrating that the role of p53 in ischemic AKI is incompletely understood. Here, we investigated whether genetic absence of p53 is also protective in ischemic AKI. Surprisingly, p53-knockout mice (p53(-/-)) had worse kidney injury, compared with wild-type mice, and exhibited increased and prolonged infiltration of leukocytes after ischemia. Acute inhibition of p53 with pifithrin-α in wild-type mice mimicked the observations in p53(-/-) mice. Chimeric mice that lacked p53 in leukocytes sustained injury similar to p53(-/-) mice, suggesting an important role for leukocyte p53 in ischemic AKI. Compared with wild-type mice, a smaller proportion of macrophages in the kidneys of p53(-/-) and pifithrin-α-treated mice after ischemic injury were the anti-inflammatory M2 phenotype. Ischemic kidneys of p53(-/-) and pifithrin-α-treated mice also showed reduced expression of Kruppel-like factor-4. Finally, models of peritonitis in p53(-/-) and pifithrin-α-treated mice confirmed the anti-inflammatory role of p53 and its effect on the polarization of macrophage phenotype. In summary, in contrast to the rat, inflammation characterizes ischemic AKI in mice; leukocyte p53 is protective by reducing the extent and duration of this inflammation and by promoting the anti-inflammatory M2 macrophage phenotype.

Lung Endothelial Cell Apoptosis During Ischemic Acute Kidney Injury

Kidney ischemia-reperfusion injury (IRI) activates cellular and soluble mediators that drive lung inflammatory cascades, tumor necrosis factor receptor 1 (TNFR1)-mediated programmed cell death, and microvascular barrier dysfunction, leading to acute lung injury. We hypothesized that lung microvascular endothelial cells (ECs), with their integral role in maintaining the lung-semipermeable barrier, were key cellular targets of TNFR1-mediated apoptosis during ischemic AKI. Male C57/BL6 mice and Sprague-Dawley rats underwent 60 min of bilateral renal pedicle occlusion (IRI) or sham laparotomy (sham) and were killed at 4 or 24 h. Colocalization with TUNEL, DAPI, and CD34 was performed to identify EC-specific apoptosis. Mouse ECs (CD45/CD31) isolated with novel tissue digestion techniques and magnetic microbead sorting underwent quantitative real-time polymerase chain reaction SuperArray analysis with 84 apoptosis-related genes. In parallel, rat lung microvascular ECs grown to confluence were treated with serum from rats obtained following sham or kidney IRI. Rat lung microvascular ECs treated +/- etanercept, a TNF-α/TNFR1 signaling inhibitor, underwent custom real-time polymerase chain reaction analysis for proapoptotic and TNF superfamily transcriptional events, and apoptosis was identified with caspase 3 and poly(ADP-ribose) polymerase activity assays. In vivo, TUNEL-positive cells colocalized with CD34 in whole-lung tissue and isolated lung ECs demonstrated a proapoptotic transcriptome during ischemic AKI. In vitro, ischemic AKI incited proapoptotic (FasL, Dapk1, Bcl10) and TNF superfamily (TNFR1, TNFR2, TNF-α) gene activation and increased caspase 3 and poly(ADP-ribose) polymerase activity at 24 h versus sham. Compared with vehicle, treatment of rat lung microvascular ECs with etanercept inhibited proinflammatory gene activation (E-selectin, intercellular adhesion molecule 1, interleukin 6, RhoB) and apoptosis during ischemic AKI. Ischemic AKI drives distinct proinflammatory and proapoptotic changes in the pulmonary EC transcriptome with TNFR1-dependent caspase activation and programmed cell death. Further investigation of potential EC mechanisms of kidney-lung crosstalk during AKI may identify potential therapeutic targets for this deadly disease.

Kidney-Lung Crosstalk During Ischemic AKI: Is the T Cell the Missing Link?

Introduction: Kidney IRI induces TNF-mediated lung apoptosis which contributes to microvascular injury. T lymphocyte trafficking and activation play a critical role in mediating the local immune response during kidney ischemia-reperfusion injury (IRI), and we have previously shown CD3+ T lymphocyte activation and trafficking to the lungs during ischemic AKI. Utilizing T cell-deficitent (Tnu/nu) mice and adoptive transfer experiments, we investigated the specific role of T lymphocytes in mediating pulmonary apoptosis during kidney IRI.

Acute renal venous obstruction is more detrimental to the kidney than arterial occlusion: implication for murine models of acute kidney injury

In this study, we compared the traditional murine model with renal pedicle clamp with models that clamped the renal artery or vein alone as well as to a whole body ischemia-reperfusion injury (WBIRI) model. Male C57BL/6J mice underwent either clamping of the renal artery, vein, or both (whole pedicle) for 30 or 45 min followed by reperfusion, or 10 min of cardiac arrest followed by resuscitation up to 24 h. After 30 min of ischemia, the mice with renal vein clamping showed the mostly increased serum creatinine and the most severe renal tubule injury. After 45 min of ischemia, all mice with renal vasculature clamping had a comparable increase in serum creatinine but the renal tubule injury was most severe in renal artery-clamped mice. Renal arterial blood flow was most decreased in mice with a renal vein clamp compared with a renal artery or pedicle clamp. A 30-or 45-min renal ischemia time led to a significant increase in the protein level of interleukin-6, keratinocyte-derived chemokine (KC), and granular colony-stimulating factor in the ischemic kidney, but the KC was the highest in the renal pedicle-clamped kidney and the lowest in the renal vein-clamped kidney. Of note, 10 min of WBIRI led to kidney dysfunction and structural injury, although less than longer time clamping of isolated renal vasculature. Our data demonstrate important differences in ischemic AKI models. Understanding these differences is important in designing future experimental studies in mice as well as clinical trials in humans.

Thyroid hormones and the gut.

A pathogenic role of p53 in AKI was suggested a decade ago but remains controversial. Indeed, recent work indicates that inhibition of p53 protects against ischemic AKI in rats but exacerbates AKI in mice. One intriguing possibility is that p53 has cell type-specific roles in AKI. To determine the role of tubular p53, we generated two conditional gene knockout mouse models, in which p53 is specifically ablated from proximal tubules or other tubular segments, including distal tubules, loops of Henle, and medullary collecting ducts. Proximal tubule p53 knockout (PT-p53-KO) mice were resistant to ischemic and cisplatin nephrotoxic AKI, which was indicated by the analysis of renal function, histology, apoptosis, and inflammation. However, other tubular p53 knockout (OT-p53-KO) mice were sensitive to AKI. Mechanistically, AKI associated with the upregulation of several known p53 target genes, including Bax, p53-upregulated modulator of apoptosis-<i>α</i>, p21, and Siva, and this association was attenuated in PT-p53-KO mice. In global expression analysis, ischemic AKI induced 371 genes in wild-type kidney cortical tissues, but the induction of 31 of these genes was abrogated in PT-p53-KO tissues. These 31 genes included regulators of cell death, metabolism, signal transduction, oxidative stress, and mitochondria. These results suggest that p53 in proximal tubular cells promotes AKI, whereas p53 in other tubular cells does not.