Induction of Zf9 in the kidney following early ischemia/reperfusion

Lineage Tracing and Single-Nucleus Multiomics Reveal Novel Features of Adaptive and Maladaptive Repair after Acute Kidney Injury

SIGNIFICANCE STATEMENT

Understanding the mechanisms underlying adaptive and maladaptive renal repair after AKI and their long-term consequences is critical to kidney health. The authors used lineage tracing of cycling cells and single-nucleus multiomics (profiling transcriptome and chromatin accessibility) after AKI. They demonstrated that AKI triggers a cell-cycle response in most epithelial and nonepithelial kidney cell types. They also showed that maladaptive proinflammatory proximal tubule cells (PTCs) persist until 6 months post-AKI, although they decreased in abundance over time, in part, through cell death. Single-nucleus multiomics of lineage-traced cells revealed regulatory features of adaptive and maladaptive repair. These included activation of cell state-specific transcription factors and cis-regulatory elements, and effects in PTCs even after adaptive repair, weeks after the injury event.

BACKGROUND

AKI triggers a proliferative response as part of an intrinsic cellular repair program, which can lead to adaptive renal repair, restoring kidney structure and function, or maladaptive repair with the persistence of injured proximal tubule cells (PTCs) and an altered kidney structure. However, the cellular and molecular understanding of these repair programs is limited.

METHODS

To examine chromatin and transcriptional responses in the same cell upon ischemia-reperfusion injury (IRI), we combined genetic fate mapping of cycling ( Ki67+ ) cells labeled early after IRI with single-nucleus multiomics-profiling transcriptome and chromatin accessibility in the same nucleus-and generated a dataset of 83,315 nuclei.

RESULTS

AKI triggered a broad cell cycle response preceded by cell type-specific and global transcriptional changes in the nephron, the collecting and vascular systems, and stromal and immune cell types. We observed a heterogeneous population of maladaptive PTCs throughout proximal tubule segments 6 months post-AKI, with a marked loss of maladaptive cells from 4 weeks to 6 months. Gene expression and chromatin accessibility profiling in the same nuclei highlighted differences between adaptive and maladaptive PTCs in the activity of cis-regulatory elements and transcription factors, accompanied by corresponding changes in target gene expression. Adaptive repair was associated with reduced expression of genes encoding transmembrane transport proteins essential to kidney function.

CONCLUSIONS

Analysis of genome organization and gene activity with single-cell resolution using lineage tracing and single-nucleus multiomics offers new insight into the regulation of renal injury repair. Weeks to months after mild-to-moderate IRI, maladaptive PTCs persist with an aberrant epigenetic landscape, and PTCs exhibit an altered transcriptional profile even following adaptive repair.

Downregulation of krüppel-like factor 6 expression modulates extravillous trophoblast cell behavior by increasing reactive oxygen species

INTRODUCTION

Placental extravillous trophoblasts play a crucial role in the establishment of a healthy pregnancy. Reactive oxygen species (ROS) may contribute to their differentiation and function as mediators in signaling processes or might cause oxidative stress resulting in trophoblast dysfunction. The krüppel-like transcription factor 6 (KLF6) regulates many genes involved in essential cell processes where ROS are also involved. However, whether KLF6 regulates ROS levels has not been previously investigated.

MATERIALS AND METHODS

KLF6 was silenced by siRNAs in HTR8-SV/neo cells, an extravillous trophoblast model. Total and mitochondrial ROS levels, as well as mitochondrial membrane potential and apoptosis were analyzed by flow cytometry. The expression of genes and proteins of interest were analyzed by qRT-PCR and Western blot, respectively. Cell response to oxidative stress, proliferation, viability, morphology, and migration were evaluated.

RESULTS

KLF6 downregulation led to an increase in ROS and NOX4 mRNA levels, accompanied by reduced cell proliferation and increased p21 protein expression. Catalase activity, 2-Cys peroxiredoxin protein levels, Nrf2 cytoplasmic localization and hemoxygenase 1 expression, as well as mitochondrial membrane potential and cell apoptosis were not altered suggesting that ROS increase is not associated with cellular damage. Instead, KLF6 silencing induced cytoskeleton modifications and increased cell migration in a ROS-dependent manner.

DISCUSSION

Present data reveal a novel role of KLF6 on ROS balance and signaling demonstrating that KLF6 downregulation induces an increase in ROS levels that contribute to extravillous trophoblast cell migration.

Two Sides of the Same Coin: The Roles of KLF6 in Physiology and Pathophysiology

The Krüppel-like factors (KLFs) family of proteins control several key biological processes that include proliferation, differentiation, metabolism, apoptosis and inflammation. Dysregulation of KLF functions have been shown to disrupt cellular homeostasis and contribute to disease development. KLF6 is a relevant example; a range of functional and expression assays suggested that the dysregulation of KLF6 contributes to the onset of cancer, inflammation-associated diseases as well as cardiovascular diseases. KLF6 expression is either suppressed or elevated depending on the disease, and this is largely due to alternative splicing events producing KLF6 isoforms with specialised functions. Hence, the aim of this review is to discuss the known aspects of KLF6 biology that covers the gene and protein architecture, gene regulation, post-translational modifications and functions of KLF6 in health and diseases. We put special emphasis on the equivocal roles of its full-length and spliced variants. We also deliberate on the therapeutic strategies of KLF6 and its associated signalling pathways. Finally, we provide compelling basic and clinical questions to enhance the knowledge and research on elucidating the roles of KLF6 in physiological and pathophysiological processes.

Role of promoting inflammation of Krüppel-like factor 6 in acute kidney injury

Background

Krüppel-like factor 6 (KLF6) is a transcription factor that participate in various pathophysiological processes, but its contribution in ischemia acute kidney injury (AKI) is lacking so far. The study aimed to investigate the expression and the role of KLF6 in kidney ischemia–reperfusion (IR) injury.

Method

Microarray data were collected from GSE58438 and GSE52004. The rat IR model was established to evaluate the mRNA and protein expression of KLF6 and inflammatory cytokines in serum and kidney tissues. SiRNA-KLF6 was transfected with HK-2 cells, and then a cell-based hypoxia-reoxygenation (HR) model was established.

Results

Bioinformatics showed KLF6 mRNA in kidney tissue is up-regulated in 3 h after IR in rat kidney, which involved in cell activation, leukocyte activation, and response to hydrogen peroxide after IR. The rat IR model results showed that KLF6 expression was peaking at 6 h, and the expression of pro-inflammatory cytokines MCP-1 and TNF-α was increased both in serum and kidney tissues, while anti-inflammatory cytokine IL-10 was decreased after IR. Furthermore, in vitro results showed that KLF6 knock-down reduced the pro-inflammatory cytokines expression.

Conclusion

These results suggest that (1) KLF6 might be a novel biomarker for early diagnosis of AKI and (2) KLF6 may play a role in promoting inflammation in AKI.

TGF-β-mediated NADPH oxidase 4-dependent oxidative stress promotes colistin-induced acute kidney injury

Background

Colistin (polymyxin E) is an important constituent of the polymyxin class of cationic polypeptide antibiotics. Intrarenal oxidative stress can contribute to colistin-induced nephrotoxicity. Nicotinamide adenine dinucleotide 3-phosphate oxidases (Noxs) are important sources of reactive oxygen species. Among the various types of Noxs, Nox4 is predominantly expressed in the kidney.

Objectives

We investigated the role of Nox4 and benefit of Nox4 inhibition in colistin-induced acute kidney injury using in vivo and in vitro models.

Methods

Human proximal tubular epithelial (HK-2) cells were treated with colistin with or without NOX4 knockdown, or GKT137831 (most specific Nox1/4 inhibitor). Effects of Nox4 inhibition on colistin-induced acute kidney injury model in Sprague-Dawley rats were examined.

Results

Nox4 expression in HK-2 cells significantly increased following colistin exposure. SB4315432 (transforming growth factor-β1 receptor I inhibitor) significantly inhibited Nox4 expression in HK-2 cells. Knockdown of NOX4 transcription reduced reactive oxygen species production, lowered the levels of pro-inflammatory markers (notably mitogen-activated protein kinases) implicated in colistin-induced nephrotoxicity and attenuated apoptosis by altering Bax and caspase 3/7 activity. Pretreatment with GKT137831 replicated these effects mediated by downregulation of mitogen-activated protein kinase activities. In a rat colistin-induced acute kidney injury model, administration of GKT137831 resulted in attenuated colistin-induced acute kidney injury as indicated by attenuated impairment of glomerulus function, preserved renal structures, reduced expression of 8-hydroxyguanosine and fewer apoptotic cells.

Conclusions

Collectively, these findings identify Nox4 as a key source of reactive oxygen species responsible for kidney injury in colistin-induced nephrotoxicity and highlight a novel potential way to treat drug-related nephrotoxicity.

Low oxygen tension induces Krüppel-Like Factor 6 expression in trophoblast cells

The transcription factor Krüppel-Like Factor 6 (KLF6) has important roles in cell differentiation, angiogenesis, apoptosis, and proliferation. Furthermore, there is evidence that KLF6 is required for proper placental development. While oxygen is a critical mediator of trophoblast differentiation and function, the involvement of oxygen in the regulation of KLF6 expression remains unexplored. In the present study we examined the expression of KLF6 in placental tissue from uncomplicated and preeclamptic pregnancies, the latter often characterized by an inadequately perfused placenta. We also determined the effect of hypoxia and the involvement of Hypoxia-Inducible Factor 1α (HIF-1α) on the expression of KLF6 in cultured trophoblast cells and placental tissues. Results revealed that villous, interstitial and endovascular extravillous cytotrophoblasts from placentas from normal and preeclamptic pregnancies express KLF6. In addition, KLF6 immunoreactivity was higher in the placental bed of preeclamptic pregnancies than in those of uncomplicated pregnancies. We demonstrated that hypoxia induced an early and transient increase in KLF6 protein levels in HTR8/SVneo extravillous cytotrophoblast cells and in placental explants. Reoxygenation returned KLF6 protein to basal levels. Moreover, hypoxia-induced up-regulation of KLF6 expression was dependent on HIF-1α as revealed by siRNA knockdown in HTR8/SVneo cells. These results indicate that KLF6 may mediate some of the effects of hypoxia in placental development. The regulation of KLF6 protein levels by oxygen has significant implications for understanding its putative role in diseases affected by tissue hypoxia.

Krüppel -like factor 8 is a stress-responsive transcription factor that regulates expression of HuR

BACKGROUND/AIMS

HuR is an RNA-binding protein that regulates the post-transcriptional life of thousands of cellular mRNAs and promotes cell survival. HuR is expressed as two mRNA transcripts that are differentially regulated by cell stress. The goal of this study is to define factors that promote transcription of the longer alternate form.

METHODS

Effects of transcription factors on HuR expression were determined by inhibition or overexpression of these factors followed by competitive RT-PCR, gel mobility shift, and chromatin immunoprecipitation. Transcription factor expression patterns were identified through competitive RT-PCR and Western analysis. Stress responses were assayed in thapsigargin-treated proximal tubule cells and in ischemic rat kidney.

RESULTS

A previously described NF-κB site and a newly identified Sp/KLF factor binding site were shown to be important for transcription of the long HuR mRNA. KLF8, but not Sp1, was shown to bind this site and increase HuR mRNA levels. Cellular stress in cultured or native proximal tubule cells resulted in a rapid decrease of KLF8 levels that paralleled those of the long HuR mRNA variant.

CONCLUSIONS

These results demonstrate that KLF8 can participate in regulating expression of alternate forms of HuR mRNA along with NF-κB and other factors, depending on cellular contexts.

Pathogenesis of renal failure in multiple myeloma: any role of contrast media?

The spectrum of kidney disease-associated monoclonal immunoglobulin and plasma cell malignancies is remarkably broad and encompasses nearly all nephropathologic entities. Multiple myeloma with kidney impairment at presentation is a medical emergency since the recovery of kidney function is associated with survival benefits. In most cases, kidney impairment may be the first clinical manifestation of malignant plasma cell dyscrasias like multiple myeloma and light chain amyloidosis. Multiple myeloma per se cannot be considered a main risk factor for developing acute kidney injury following intravascular administration of iodinated contrast media. The risk is increased by comorbidities such as chronic kidney disease, diabetes, hypercalcemia, dehydration, and use of nephrotoxic drugs. Before the administration of contrast media, the current recommended laboratory tests for assessing kidney function are serum creatinine measurement and the estimation of glomerular filtration rate by using the CKD-EPI equation. The assessment of Bence Jones proteinuria is unnecessary for evaluating the risk of kidney failure in patients with multiple myeloma, since this test cannot be considered a surrogate biomarker of kidney function.

Transgelin Up-Regulation in Obstructive Nephropathy

Fibrosis is a complex and multifactorial process, affecting the structure and compromising the function of several organs. Among those, renal fibrosis is an important pathological change, eventually leading to renal failure. Proteomic analysis of the renal parenchyma in the well-established rat model of unilateral ureteral obstruction (UUO model) suggested that transgelin was up-regulated during the development of fibrosis. Transgelin up-regulation was confirmed both at the protein and at the mRNA level. It was observed that at early stages of fibrosis transgelin was mainly expressed in the interstitial compartment and, more specifically, in cells surrounding the glomeruli. Subsequently, it was confirmed that transgelin expressing cells were activated fibroblasts, based on their extensive co-expression of α-SMA and their complete lack of co-distribution with markers of other cell types (endothelial, epithelial and cells of the immune system). These periglomerular fibroblasts exhibited staining for transgelin mainly cytoplasmic but occasionally nuclear as well. In addition, transgelin expression in periglomerular fibroblasts was absent in renal fibrosis developed in a hypertensive model, compared to the UUO model. Promoter analysis indicated that there are several conserved motifs for transcription factor binding. Among those, Kruppel-like factor 6 was found to be up-regulated in transgelin positive periglomerular activated fibroblasts, suggesting a possible involvement in the mechanism of transgelin up-regulation. These data strongly suggest that transgelin is up-regulated in the obstructive nephropathy and could be used as a novel marker for renal fibrosis in the future.

Deleting the TGF-β receptor attenuates acute proximal tubule injury

TGF-β is a profibrotic growth factor in CKD, but its role in modulating the kidney's response to AKI is not well understood. The proximal tubule epithelial cell, which is the main cellular target of AKI, expresses high levels of both TGF-β and its receptors. To determine how TGF-β signaling in this tubular segment affects the response to AKI, we selectively deleted the TGF-β type II receptor in the proximal tubules of mice. This deletion attenuated renal impairment and reduced tubular apoptosis in mercuric chloride-induced injury. In vitro, deficiency of the TGF-β type II receptor protected proximal tubule epithelial cells from hydrogen peroxide-induced apoptosis, which was mediated in part by Smad-dependent signaling. Taken together, these results suggest that TGF-β signaling in the proximal tubule has a detrimental effect on the response to AKI as a result of its proapoptotic effects.

Transactivation of inducible nitric oxide synthase gene by Kruppel-like factor 6 regulates apoptosis during influenza A virus infection

Influenza A virus (flu) is a respiratory tract pathogen causing high morbidity and mortality among the human population. NO is a cellular mediator involved in tissue damage through its apoptosis of target cells and resulting enhancement of local inflammation. Inducible NO synthase (iNOS) is involved in the production of NO following infection. Although NO is a key player in the development of exaggerated lung disease during flu infection, the underlying mechanism, including the role of NO in apoptosis during infection, has not been reported. Similarly, the mechanism of iNOS gene induction during flu infection is not well defined in terms of the host transactivator(s) required for iNOS gene expression. In the current study, we identified Kruppel-like factor 6 (KLF6) as a critical transcription factor essential for iNOS gene expression during flu infection. We also underscored the requirement for iNOS in inducing apoptosis during infection. KLF6 gene silencing in human lung epithelial cells resulted in the drastic loss of NO production, iNOS promoter-specific luciferase activity, and expression of iNOS mRNA following flu infection. Chromatin immunoprecipitation assay revealed a direct interaction of KLF6 with iNOS promoter during in vitro and in vivo flu infection of human lung cells and mouse respiratory tract, respectively. A significant reduction in flu-mediated apoptosis was noted in KLF6-silenced cells, cells treated with iNOS inhibitor, and primary murine macrophages derived from iNOS knockout mice. A similar reduction in apoptosis was noted in the lungs following intratracheal flu infection of iNOS knockout mice.

Upregulation of Krüppel-like factor 6 in the mouse hippocampus after pilocarpine-induced status epilepticus

Krüppel-like factor 6 (KLF6) is a transcriptional regulator involved in a broad range of cellular processes. To date, however, the expression of KLF6 in brains with pathophysiological conditions, such as epilepsy, has not been reported. Therefore, the present study investigated the temporal pattern of KLF6 expression in the mouse hippocampus and identified cell types expressing KLF6 after pilocarpine-induced status epilepticus (SE). Seizures were induced by administrating pilocarpine hydrochloride (280 mg/kg, i.p.) 30 min after an injection of atropine methyl nitrate (3 mg/kg, i.p.). Pilocarpine- and saline-injected animals were sacrificed 1, 3, 7, 14, or 28 days after the onset of SE. Immunohistochemistry showed that the proportion of KLF6-positive cells increased in the hippocampus 1 day after SE onset, peaked at 3 days after SE, and then gradually decreased until 28 days after SE, consistent with the results from our immunoblot analysis. Cells expressing increased levels of KLF6 following pilocarpine-induced SE also expressed GFAP and Ox-42, markers for astrocytes and microglia, respectively. Quantitative analysis revealed that astrocytes were the major type of KLF6-expressing glial cells. These cells also expressed heat shock protein 47 (HSP47), a collagen-specific molecular chaperone. This is the first report showing that KLF6 is inducible in the hippocampus and may be associated with glial responses, especially HSP47-related tissue remodeling after pilocarpine-induced SE.

The roles of Kruppel-like factor 6 and peroxisome proliferator-activated receptor-γ in the regulation of macrophage inflammatory protein-3α at early onset of diabetes

Macrophage inflammatory protein-3 alpha (MIP-3α) is known to be upregulated early in the development of diabetic nephropathy (DN). However, the transcriptional regulation of MIP-3α is unknown. We previously demonstrated that the transcription factors KLF6 and PPAR-γ play key roles in regulating renal fibrotic and inflammatory responses to factors inherent in diabetes mellitus. Hence we determined the role of these transcription factors in regulating MIP-3α expression. HK-2 cells and STZ-induced diabetic rats were used. siRNAs, over-expressing constructs and CHIP promoter binding assays were used to determine the role of KLF6 and PPAR-γ in MIP-3α transcriptional regulation. KLF6 overexpression increased MIP-3α which was inhibited by concurrent exposure to PPAR-γ agonists. PPAR-γ agonists attenuated high glucose-induced MIP-3α secretion. Furthermore, MIP-3α secretion was up-regulated in PPAR-γ silenced cells, suggesting both KLF6 and PPAR-γ antagonistically regulate high glucose-induced MIP-3α secretion. The CHIP promoter binding assay confirmed that PPAR-γ binds to the MIP-3α promoter and negatively regulates MIP-3α expression. PPAR-γ agonists increased the binding activity of the PPAR-γ-MIP-3α promoter. In contrast, promoter binding activity decreased in KLF6 over-expressing cells. PPAR-γ decreased in KLF6 over-expressing cells and increased in KLF6 silenced cells, while PPAR-γ siRNA had no effect on KLF6 expression, suggesting that KLF6 acted upstream of PPAR-γ in the regulation of MIP-3α. In diabetic rats, renal MIP-3α and the macrophage marker ED-1 expression increased, which was inhibited by exposure to PPAR-γ agonists. The recognition of MIP-3α as a significant pathogenic mediator in diabetic nephropathy reaffirms the increasingly recognized role of inflammation in the progression of DN. Targeting pro-inflammatory chemokine MIP-3α and its signaling pathways will provide novel strategy to treat diabetic kidney disease.

Transcription factors Krüppel-like factor 6 and peroxisome proliferator-activated receptor-{gamma} mediate high glucose-induced thioredoxin-interacting protein

We demonstrated recently that thioredoxin-interacting protein (Txnip) and the transcription factor Krüppel-like factor 6 (KLF6) were up-regulated in both in vivo and in vitro models of diabetic nephropathy, thus promoting renal injury. Conversely, peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists have been shown to be renoprotective. Hence, this study was undertaken to determine whether Txnip expression is regulated by the transcription factors KLF6 and PPAR-gamma. By using siRNAs and overexpressing constructs, the role of KLF6 and PPAR-gamma in Txnip transcriptional regulation was determined in human kidney proximal tubule cells and in streptozocin-induced diabetes mellitus in Sprague-Dawley rats, in vitro and in vivo models of diabetic nephropathy, respectively. KLF6 overexpression increased Txnip expression and promoter activity, which was inhibited by concurrent exposure to PPAR-gamma agonists. In contrast, reduced expression of KLF6 by siRNA or exposure to PPAR-gamma agonists attenuated high glucose-induced Txnip expression and promoter activity. KLF6-Txnip promoter binding was decreased in KLF6-silenced cells, whereas PPAR-gamma agonists increased PPAR-gamma-Txnip promoter binding. Indeed, silencing of KLF6 increased PPAR-gamma expression, suggesting endogenous regulation of PPAR-gamma expression by KLF6. Moreover, renal KLF6 and Txnip expression increased in rats with diabetes mellitus and was inhibited by PPAR-gamma agonist treatment; however, KLF6 expression did not change in HK-2 cells exposed to PPAR-gamma agonists. Hence, Txnip expression and promoter activity are mediated via divergent effects of KLF6 and PPAR-gamma transcriptional regulation.

Frataxin deficiency causes upregulation of mitochondrial Lon and ClpP proteases and severe loss of mitochondrial Fe-S proteins

Friedreich ataxia (FRDA) is a rare hereditary neurodegenerative disease characterized by progressive ataxia and cardiomyopathy. The cause of the disease is a defect in mitochondrial frataxin, an iron chaperone involved in the maturation of Fe-S cluster proteins. Several human diseases, including cardiomyopathies, have been found to result from deficiencies in the activity of specific proteases, which have important roles in protein turnover and in the removal of damaged or unneeded protein. In this study, using the muscle creatine kinase mouse heart model for FRDA, we show a clear progressive increase in protein levels of two important mitochondrial ATP-dependent proteases, Lon and ClpP, in the hearts of muscle creatine kinase mutants. These proteases have been shown to degrade unfolded and damaged proteins in the matrix of mitochondria. Their upregulation, which was triggered at a mid-stage of the disease through separate pathways, was accompanied by an increase in proteolytic activity. We also demonstrate a simultaneous and significant progressive loss of mitochondrial Fe-S proteins with no substantial change in their mRNA level. The correlative effect of Lon and ClpP upregulation on loss of mitochondrial Fe-S proteins during the progression of the disease may suggest that Fe-S proteins are potential targets of Lon and ClpP proteases in FRDA.

Role of Kruppel-like factor 6 in transforming growth factor-beta1-induced epithelial-mesenchymal transition of proximal tubule cells

Krüppel-like factor 6 (KLF6) is a DNA-binding protein containing a triple zinc-fingered motif and plays a key role in the regulation of cell proliferation, differentiation, and development. More recently it has been implicated in hepatic fibrosis via its binding to the transforming growth factor (TGF)-beta control element. In the kidney, epithelial-mesenchymal transition (EMT) is a major contributor to the pathogenesis of renal fibrosis, with TGF-beta1 being a key mediator of EMT. The present study aimed to determine the role of KLF6 and TGF-beta1 in EMT in proximal tubule cells. To determine the relevance in clinical disease, KLF6 was measured in kidneys of streptozotocin-induced diabetic Ren-2 rats and in cells exposed to high (30 mM) glucose. TGF-beta1 was confirmed to induce EMT by morphological change, loss of E-cadherin, and gain in vimentin expression. KLF6 mRNA expression was concomitantly measured. To determine the role of KLF6 in EMT, the above markers of EMT were determined in KLF6-silenced (small interfering RNA) and KLF6-overexpressing proximal tubule cells. KLF6 overexpression significantly promoted a phenotype consistent with EMT. High glucose induced KLF6 in proximal tubule cells (P < 0.05). This increase in KLF6 in response to high glucose was TGF-beta1 mediated. In an in vivo model of diabetic nephropathy KLF6 increased at week 8 (P < 0.05). KLF6 plays a permissive role in TGF-beta1-induced EMT in proximal tubule cells. Its upregulation in in vivo models of diabetic nephropathy suggests it as a potential therapeutic target.

Induction of proapoptotic Daxx following ischemic acute kidney injury

Transcriptome profiling has shown that the pro-apoptotic death-domain-associated protein Daxx is rapidly induced in the kidney of animals following ischemic injury. Here we found that Daxx protein was increased 5-fold in tubule cells in both animal and human models of ischemic acute kidney injury. Further there was upregulation of its primary interacting partner, Fas and phosphorylation of its primary downstream activator (JNK) in parallel to Daxx induction. In cultured tubule cells, partial ATP depletion resulted in a rapid induction of Daxx, Fas, JNK phosphorylation and apoptosis. Antisense oligonucleotides to Daxx and specific JNK inhibitors blunted the apoptotic response to ATP depletion. These studies indicate that Daxx may play an unrecognized role in the early apoptotic response to ischemic renal injury.

Proteomics for biomarker discovery in acute kidney injury

Acute kidney injury (AKI), previously referred to as acute renal failure, represents a common and devastating problem in clinical medicine. Despite significant improvements in therapeutics, the mortality and morbidity associated with AKI remain high. A major reason for this is the lack of early markers for AKI, and hence an unacceptable delay in initiating therapy. Fortunately, the application of innovative technologies such as functional genomics and proteomics to human and animal models of AKI has uncovered several novel biomarkers and therapeutic targets. The most promising of these are chronicled in this review. These include the identification of biomarker panels in plasma (neutrophil gelatinase-associated lipocalin and cystatin C) and urine (neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, interleukin-18, cystatin C, alpha1-microglobulin, Fetuin-A, Gro-alpha, and meprin). It is likely that the AKI panels will be useful for timing the initial insult, and assessing the duration and severity of AKI. It is also probable that the AKI panels will distinguish between the various etiologies of AKI and predict clinical outcomes. It will be important in future studies to validate the sensitivity and specificity of these biomarker panels in clinical samples from large cohorts and from multiple clinical situations. Such studies will be facilitated markedly by the development of commercial tools for the reproducible measurement of biomarkers across different laboratories.

Mechanistic biomarkers for cytotoxic acute kidney injury

Acute kidney injury is a common condition and is associated with a high mortality rate. It has been recognised that routinely used measures of renal function, such as levels of blood urea nitrogen and serum creatinine, increase significantly only after substantial kidney injury occurs and then with a time delay. Insensitivity of such tests delays the diagnosis in humans, making it particularly challenging to administer putative therapeutic agents in a timely fashion. Furthermore, this insensitivity affects the evaluation of toxicity in preclinical studies by allowing drug candidates, which have low, but nevertheless important, nephrotoxic side effects in animals, to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. This review presents the current status of sensitive and specific biomarkers to detect preclinical and clinical renal injury and summarises the techniques used to quantitate these biomarkers in biological fluids.

Timing of morphologic and apoptotic changes in the sheep fetal kidney in response to bladder outflow obstruction

PURPOSE

Posterior urethral valves are the main cause of bladder outflow obstruction in human fetuses. Thirty per cent of boys with valves develop end-stage renal disease, despite intervention in the postnatal period. The timing and mechanisms of renal damage in bladder outflow obstruction are unknown. We investigated the timing of changes in morphology and apoptosis in the fetal sheep kidney in response to obstruction.

MATERIALS AND METHODS

Thirty-three fetal lambs at day 70 of gestation underwent surgical creation of bladder outflow obstruction. Twenty-nine fetal lambs had sham surgery. Fetal kidneys were collected 2, 5, 10, 20 and 30 days after surgery. Renal histology was examined. Real-time PCR was used to quantify the renal cortical expression of the pro-apoptotic gene Bax and anti-apoptotic gene Bcl-X. The TUNEL technique was used to assess regional renal apoptosis in response to obstruction.

RESULTS

Changes in renal morphology were evident as early as 2 days after surgery in fetuses with bladder outflow obstruction, and progressed over 20-30 days to cystic renal dysplasia. Bladder outflow obstruction increased the renal cortical expression of Bax relative to Bcl-X. Tubular apoptosis peaked after 2 days of obstruction. Blastemal apoptosis peaked after 5 days of obstruction.

CONCLUSIONS

Changes in pro- and anti-apoptotic gene expression in the fetal renal cortex, and alterations in the number of apoptotic cells and renal morphology are evident soon after the onset of bladder outflow obstruction. These findings suggest that damage to the developing fetal kidney begins to occur at the onset of obstruction. Attempts to preserve renal function by antenatal interventions may best be achieved by early treatment.