Ischemia-reperfusion induces G-CSF gene expression by renal medullary thick ascending limb cells in vivo and in vitro

CD44 expression in renal tubular epithelial cells in the kidneys of rats with cyclosporine-induced chronic kidney disease

Renal tubular epithelial cell (TEC) injury is the most common cause of drug-induced kidney injury (DIKI). Although TEC regeneration facilitates renal function and structural recovery following DIKI, maladaptive repair of TECs leads to irreversible fibrosis, resulting in chronic kidney disease (CKD). CD44 is specifically expressed in TECs during maladaptive repair in several types of rat CKD models. In this study, we investigated CD44 expression and its role in renal fibrogenesis in a cyclosporine (CyA) rat model of CKD. Seven-week-old male Sprague-Dawley rats fed a low-salt diet were subcutaneously administered CyA (0, 15, or 30 mg/kg) for 28 days. CD44 was expressed in atrophic, dilated, and hypertrophic TECs in the fibrotic lesions of the CyA groups. These TECs were collected by laser microdissection and evaluated by microarray analysis. Gene ontology analysis suggested that these TECs have a mesenchymal phenotype, and pathway analysis identified CD44 as an upstream regulator of fibrosis-related genes, including fibronectin 1 (Fn1). Immunohistochemistry revealed that epithelial and mesenchymal markers of TECs of fibrotic lesions were downregulated and upregulated, respectively, and that these TECs were surrounded by a thickened basement membrane. In situ hybridization revealed an increase in Fn1 mRNA in the cytoplasm of TECs of fibrotic lesions, whereas fibronectin protein was localized in the stroma surrounding these tubules. Enzyme-linked immunosorbent assay revealed increased serum CD44 levels in CyA-treated rats. Collectively, these findings suggest that CD44 contributes to renal fibrosis by inducing fibronectin secretion in TECs exhibiting partial epithelial-mesenchymal transition and highlight the potential of CD44 as a biomarker of renal fibrosis.

Role of CD44 expressed in renal tubules during maladaptive repair in renal fibrogenesis in an allopurinol-induced rat model of chronic kidney disease

The kidney is a major target organ for the adverse effects of pharmaceuticals; renal tubular epithelial cells (TECs) are particularly vulnerable to drug-induced toxicity. TECs have regenerative capacity; however, maladaptive repair of TECs after injury leads to renal fibrosis, resulting in chronic kidney disease (CKD). We previously reported the specific expression of CD44 in failed-repair TECs of rat CKD model induced by ischemia reperfusion injury. Here, we investigated the pathophysiological role of CD44 in renal fibrogenesis in allopurinol-treated rat CKD model. Dilated or atrophic TECs expressing CD44 in fibrotic areas were collected by laser microdissection and subjected to microarray analysis. Gene ontology showed that extracellular matrix (ECM)-related genes were upregulated and differentiation-related genes were downregulated in dilated/atrophic TECs. Ingenuity Pathway Analysis identified CD44 as an upstream regulator of fibrosis-related genes, including Fn1, which encodes fibronectin. Immunohistochemistry demonstrated that dilated/atrophic TECs expressing CD44 showed decreases in differentiation markers of TECs and clear expression of mesenchymal markers during basement membrane attachment. In situ hybridization revealed an increase in Fn1 mRNA in the cytoplasm of dilated/atrophic TECs, whereas fibronectin was localized in the stroma around these TECs, supporting the production/secretion of ECM by dilated/atrophic TECs. Overall, these data indicated that dilated/atrophic TECs underwent a partial epithelial-mesenchymal transition (pEMT) and that CD44 promoted renal fibrogenesis via induction of ECM production in failed-repair TECs exhibiting pEMT. CD44 was detected in the urine and serum of APL-treated rats, which may reflect the expression of CD44 in the kidney.

Neutrophil diversity and plasticity: Implications for organ transplantation

Neutrophils, as the first defenders against external microbes and stimuli, are highly active and finely regulated innate immune cells. Emerging evidence has challenged the conventional dogma that neutrophils are a homogeneous population with a short lifespan that promotes tissue damage. Recent findings on neutrophil diversity and plasticity in homeostatic and disease states have centered on neutrophils in the circulation. In contrast, a comprehensive understanding of tissue-specialized neutrophils in health and disease is still lacking. This article will first discuss how multiomics advances have contributed to our understanding of neutrophil heterogeneity and diversification in resting and pathological settings. This discussion will be followed by a focus on the heterogeneity and role of neutrophils in solid organ transplantation and how neutrophils may contribute to transplant-related complications. The goal of this article is to provide an overview of the research on the involvement of neutrophils in transplantation, with the aim that this may draw attention to an underappreciated area of neutrophil research.

Kidney injury enhances renal G-CSF expression and modulates granulopoiesis and human neutrophil CD177 in vivo

Kidney injury significantly increases overall mortality. Neutrophilic granulocytes (neutrophils) are the most abundant human blood leukocytes. They are characterized by a high turnover rate, chiefly controlled by granulocyte colony stimulating factor (G‐CSF). The role of kidney injury and uremia in regulation of granulopoiesis has not been reported. Kidney transplantation, which inherently causes ischemia–reperfusion injury of the graft, elevated human neutrophil expression of the surface glycoprotein CD177. CD177 is among the most G‐CSF‐responsive neutrophil genes and reversibly increased on neutrophils of healthy donors who received recombinant G‐CSF. In kidney graft recipients, a transient rise in neutrophil CD177 correlated with renal tubular epithelial G‐CSF expression. In contrast, CD177 was unaltered in patients with chronic renal impairment and independent of renal replacement therapy. Under controlled conditions of experimental ischemia–reperfusion and unilateral ureteral obstruction injuries in mice, renal G‐CSF mRNA and protein expression significantly increased and systemic neutrophilia developed. Human renal tubular epithelial cell G‐CSF expression was promoted by hypoxia and proinflammatory cytokine interleukin 17A in vitro. Clinically, recipients of ABO blood group‐incompatible kidney grafts developed a larger rise in neutrophil CD177. Their grafts are characterized by complement C4d deposition on the renal endothelium, even in the absence of rejection. Indeed, complement activation, but not hypoxia, induced primary human endothelial cell G‐CSF expression. Our data demonstrate that kidney injury induces renal G‐CSF expression and modulates granulopoiesis. They delineate differential G‐CSF regulation in renal epithelium and endothelium. Altered granulopoiesis may contribute to the systemic impact of kidney injury.

Bioactive Compounds for the Treatment of Renal Disease

Kidney diseases including acute kidney injury and chronic kidney disease are among the largest health issues worldwide. Dialysis and kidney transplantation can replace a significant portion of renal function, however these treatments still have limitations. To overcome these shortcomings, a variety of innovative efforts have been introduced, including cell-based therapies. During the past decades, advances have been made in the stem cell and developmental biology, and tissue engineering. As part of such efforts, studies on renal cell therapy and artificial kidney developments have been conducted, and multiple therapeutic interventions have shown promise in the pre-clinical and clinical settings. More recently, therapeutic cell-secreting secretomes have emerged as a potential alternative to cell-based approaches. This approach involves the use of renotropic factors, such as growth factors and cytokines, that are produced by cells and these factors have shown effectiveness in facilitating kidney function recovery. This review focuses on the renotropic functions of bioactive compounds that provide protective and regenerative effects for kidney tissue repair, based on the available data in the literature.

Cutaneous exposure to lewisite causes acute kidney injury by invoking DNA damage and autophagic response

Lewisite (2-chlorovinyldichloroarsine) is an organic arsenical chemical warfare agent that was developed and weaponized during World Wars I/II. Stockpiles of lewisite still exist in many parts of the world and pose potential environmental and human health threat. Exposure to lewisite and similar chemicals causes intense cutaneous inflammatory response. However, morbidity and mortality in the exposed population is not only the result of cutaneous damage but is also a result of systemic injury. Here, we provide data delineating the pathogenesis of acute kidney injury (AKI) following cutaneous exposure to lewisite and its analog phenylarsine oxide (PAO) in a murine model. Both agents caused renal tubular injury, characterized by loss of brush border in proximal tubules and tubular cell apoptosis accompanied by increases in serum creatinine, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1. Interestingly, lewisite exposure enhanced production of reactive oxygen species (ROS) in the kidney and resulted in the activation of autophagic and DNA damage response (DDR) signaling pathways with increased expression of beclin-1, autophagy-related gene 7, and LC-3A/B-II and increased phosphorylation of γ-H2A.X and checkpoint kinase 1/2, respectively. Terminal deoxyribonucleotide-transferase-mediated dUTP nick-end labeling-positive cells were detected in renal tubules along with enhanced proapoptotic BAX/cleaved caspase-3 and reduced antiapoptotic BCL2. Scavenging ROS by cutaneous postexposure application of the antioxidant N-acetyl-l-cysteine reduced lewisite-induced autophagy and DNA damage. In summary, we provide evidence that topical exposure to lewisite causes AKI. The molecular mechanism underlying these changes involves ROS-dependent activation of autophagy and DDR pathway associated with the induction of apoptosis.

Can neutrophil-lymphocyte ratio be independent risk factor for predicting acute kidney injury in patients with severe sepsis?

AIM

Neutrophil-lymphocyte ratio (NLR) is an easily calculated, sensitive, and accurate marker for prognosis and diagnosing sepsis, cardiovascular disease and cancer. As sepsis and septic shock are main causes of acute kidney injury (AKI) intensive care unit (ICU), we investigated whether NLR is an early predictor of AKI in patients with severe sepsis. We compared NLR's predictive power with that of other inflammation-related variables.

METHODS

Between December 2011 and November 2013, we enrolled 118 consecutive cases with severe sepsis admitted to ICU in this retrospective study. Levels of C-reactive protein (CRP), NLR, and white blood cell count (WBC) were recorded on admission and patients' renal function was monitored for seven consecutive days.

RESULTS

The rate of AKI occurrence 7 days after enrollment was 57.6%. NLR levels were higher in the AKI group (Group 1) than in the non-AKI group (Group 2) on the day of ICU admission (p<0.001). AKI development was independently associated with NLR, Acute Physiology and Chronic Health Evaluation II (APACHE II) and duration of invasive mechanical ventilation (MV) in multivariate logistic regression analysis. The area under the receiver-operating characteristic (ROC) curve of NLR for predicting AKI was 0.986, which was superior to WBC and CRP (p<0.05). The cut-off value of 10.15 for NLR had the highest validity for predicting AKI in patients with severe sepsis. The sensitivity, specificity, negative-predictive value (NPV), and positive-predictive value (PPV), for this cut-off value was 90.2%, 92.9%, 90.4%, and 92.7%, respectively.

CONCLUSION

NLR is superior to CRP, and WBC for predicting the development of AKI in patients with severe sepsis.

Reactive oxygen species and IRF1 stimulate IFNα production by proximal tubules during ischemic AKI

We previously reported that expression of the transcription factor interferon regulatory factor 1 (IRF1) is an early, critical maladaptive signal expressed by renal tubules during murine ischemic acute kidney injury (AKI). We now show that IRF1 mediates signals from reactive oxygen species (ROS) generated during ischemic AKI and that these signals ultimately result in production of α-subtypes of type I interferons (IFNαs). We found that genetic knockout of the common type I IFN receptor (IFNARI-/-) improved kidney function and histology during AKI. There are major differences in the spatial-temporal production of the two major IFN subtypes, IFNβ and IFNαs: IFNβ expression peaks at 4 h, earlier than IFNαs, and continues at the same level at 24 h; expression of IFNαs also increases at 4 h but continues to increase through 24 h. The magnitude of the increase in IFNαs relative to baseline is much greater than that of IFNβ. We show by immunohistology and study of isolated cells that IFNβ is produced by renal leukocytes and IFNαs are produced by renal tubules. IRF1, IFNαs, and IFNARI were found on the same renal tubules during ischemic AKI. Furthermore, we found that ROS induced IFNα expression by renal tubules in vitro. This expression was inhibited by small interfering RNA knockdown of IRF1. Overexpression of IRF1 resulted in the production of IFNαs. Furthermore, we found that IFNα stimulated production of maladaptive proinflammatory CXCL2 by renal tubular cells. Altogether our data support the following autocrine pathway in renal tubular cells: ROS > IRF1 > IFNα > IFNARI > CXCL2.

Acid stress increases gene expression of proinflammatory cytokines in Madin-Darby canine kidney cells

Metabolic acidosis is thought to exacerbate chronic kidney disease in part by stimulating the release of potentially injurious substances. To define the genes whose expression is affected by exposure to an acidic milieus, we examined the effect of exposure of MDCK cells to pH 7.4 and pH 7.0 for 24 h on gene expression using a canine derived microarray. Exposure to this pH stress for 24 h led to increased expression of 278 genes (2.2% of the transcriptome) by at least 2-fold and 60 of these (21%) were upregulated by >3-fold. On the other hand, 186 genes (1.5% of the transcriptome) were downregulated by at least 2-fold and 16 of these (9%) were downregulated by 3-fold or more. Ten percent of the genes upregulated by at least threefold encode proinflammatory cytokine proteins, including colony stimulating factor 2, chemokine ligand 7, chemokine ligand 20, chemokine ligand 8, and interleukin-1α. Two others encode metallopeptidases. The most highly upregulated gene encodes a protein, lubricin, shown to be important in preventing cartilage damage and in tissue injury or repair. Upregulation of four genes was confirmed by quantitative PCR. Housekeeping genes were not increased. To examine the effect of decreasing medium pH, we measured intracellular pH (pHi) using 2,7-bis (2-carboxyethyl)5-carboxyfluorescein. With extracellular pH (pHo) of 7.0, pHi fell and remained depressed. These findings suggest that a pH stress alone can increase renal expression of proinflammatory and other genes that contribute to renal injury.

Cytokine production increases and cytokine clearance decreases in mice with bilateral nephrectomy

BACKGROUND

Serum cytokines are increased in patients with acute kidney injury (AKI) and predict increased mortality. It is widely assumed that increased renal production of cytokines is the source of increased serum cytokines; the role of extra-renal cytokine production and impaired renal cytokine clearance is less well studied. We hypothesized that cytokine production in AKI was mononuclear phagocyte dependent, independent of production by the kidneys, and that serum cytokine clearance would be impaired in AKI.

METHODS

Bilateral nephrectomy was used as a model of AKI to assess cytokine production independent of kidney cytokine production. Mononuclear phagocytes were depleted utilizing intravenous (IV) administration of liposome-encapsulated clodronate (LEC). Twenty-three serum cytokines were determined utilizing a multiplex cytokine kit. Proteins for cytokines were determined in the spleen and liver by enzyme-linked immunosorbent assay. Recombinant cytokines were injected by IV into mice with bilateral nephrectomy to determine the effect of absent kidney function on serum cytokine clearance.

RESULTS

Serum interleukin (IL)-6, chemokine (C-X-C motif) ligand 1 (CXCL1), IL-10, IL-1β, monocyte chemotactic protein 1 (MCP-1), IL-5 and eotaxin were increased in the serum of mice after bilateral nephrectomy and were reduced with LEC. Serum IL-12p40 and regulated upon activation, normal T-cell expressed, and secreted (RANTES) were increased after bilateral nephrectomy and were further increased with LEC. Spleen IL-6, CXCL1, IL-10 and IL-1β and liver IL-6 and IL-10 were increased after bilateral nephrectomy. After IV injection, IL-6, CXCL1, IL-10 and IL-1β had a prolonged serum cytokine appearance in mice with bilateral nephrectomy versus sham operation.

CONCLUSIONS

Increased mononuclear phagocyte production and impaired renal clearance contribute to serum cytokine accumulation in AKI, independent of kidney injury. The effect of AKI on cytokine production and clearance may contribute to the increased mortality of patients with AKI.

Depletion of macrophages and dendritic cells in ischemic acute kidney injury

BACKGROUND

Inflammation is thought to play a role in ischemic acute kidney injury (AKI). We have demonstrated that macrophage and dendritic cell depletion, using liposome-encapsulated clodronate (LEC), is protective against ischemic AKI.

METHODS

To determine whether macrophages or dendritic cells or both play a role in ischemic AKI, we performed ischemic AKI in CD11b-DTR mice that have a diphtheria toxin (DT)-induced depletion of CD11b cells (macrophages) and CD11c-DTR mice that have a DT-induced depletion of CD11c cells (dendritic cells).

RESULTS

While LEC-treated animals had a significant functional protection from AKI, CD11b-DTR and CD11c-DTR mice were not protected against AKI despite a similar degree of renal macrophage and dendritic cell depletion. Proinflammatory cytokines are known to play a role in ischemic AKI. To determine the possible reasons for the lack of protection in CD11b-DTR and CD11c-DTR mice compared to LEC-treated mice, 32 cytokines/chemokines were measured in these mice. Of the cytokines/chemokines measured, IL-6, MCP-1, GMCSF, IL-1β and CXCL1 (also known as IL-8 in humans or KC in mice) showed significant differences in the LEC-treated, CD11b-DTR and CD11c-DTR mice. MCP-1 and CXCL1 (known mediators of AKI), and also GMCSF and IL-1β were increased in AKI and decreased in LEC-treated AKI but not AKI in CD11b-DTR or CD11c-DTR mice.

CONCLUSIONS

These findings suggest that LEC-mediated protection from AKI is not simply mediated by depletion of renal macrophage or dendritic cell subpopulations. Protection against AKI in LEC-treated compared to CD11b-DTR or CD11c-DTR mice may be partially explained by differences in proinflammatory cytokine profiles.

Mobilisation of hematopoietic CD34+ precursor cells in patients with acute stroke is safe--results of an open-labeled non randomized phase I/II trial

Background

Regenerative strategies in the treatment of acute stroke may have great potential. Hematopoietic growth factors mobilize hematopoietic stem cells and may convey neuroprotective effects. We examined the safety, potential functional and structural changes, and CD34⁺ cell–mobilization characteristics of G-CSF treatment in patients with acute ischemic stroke.

Methods and Results

Three cohorts of patients (8, 6, and 6 patients per cohort) were treated subcutaneously with 2.5, 5, or 10 µg/kg body weight rhG-CSF for 5 consecutive days within 12 hrs of onset of acute stroke. Standard treatment included IV thrombolysis. Safety monitoring consisted of obtaining standardized clinical assessment scores, monitoring of CD34⁺ stem cells, blood chemistry, serial neuroradiology, and neuropsychology. Voxel-guided morphometry (VGM) enabled an assessment of changes in the patients' structural parenchyma. 20 patients (mean age 55 yrs) were enrolled in this study, 5 of whom received routine thrombolytic therapy with r-tPA. G-CSF treatment was discontinued in 4 patients because of unrelated adverse events. Mobilization of CD34⁺ cells was observed with no concomitant changes in blood chemistry, except for an increase in the leukocyte count up to 75,500/µl. Neuroradiological and neuropsychological follow-up studies did not disclose any specific G-CSF toxicity. VGM findings indicated substantial atrophy of related hemispheres, a substantial increase in the CSF space, and a localized increase in parenchyma within the ischemic area in 2 patients.

Conclusions

We demonstrate a good safety profile for daily administration of G-CSF when begun within 12 hours after onset of ischemic stroke and, in part in combination with routine IV thrombolysis. Additional analyses using VGM and a battery of neuropsychological tests indicated a positive functional and potentially structural effect of G-CSF treatment in some of our patients.

Trial Registration

German Clinical Trial Register DRKS 00000723

Early interleukin 6 production by leukocytes during ischemic acute kidney injury is regulated by TLR4

Although leukocytes infiltrate the kidney during ischemic acute kidney injury (AKI) and release interleukin 6 (IL6), their mechanism of activation is unknown. Here, we tested whether Toll-like receptor 4 (TLR4) on leukocytes mediated this activation by interacting with high-mobility group protein B1 (HMGB1) released by renal cells as a consequence of ischemic kidney injury. We constructed radiation-induced bone marrow chimeras using C3H/HeJ and C57BL/10ScNJ strains of TLR4 (-/-) mice and their respective TLR4 (+/+) wild-type counterparts and studied them at 4 h after an ischemic insult. Leukocytes adopted from TLR4 (+/+) mice infiltrated the kidneys of TLR4 (-/-) mice, and TLR4 (-/-) leukocytes infiltrated the kidneys of TLR4 (+/+) mice but caused little functional renal impairment in each case. Maximal ischemic AKI required both radiosensitive leukocytes and radioresistant renal parenchymal and endothelial cells from TLR4 (+/+) mice. Only TLR4 (+/+) leukocytes produced IL6 in vivo and in response to HMGB1 in vitro. Thus, following infiltration of the injured kidney, leukocytes produce IL6 when their TLR4 receptors interact with HMGB1 released by injured renal cells. This underscores the importance of TLR4 in the pathogenesis of ischemic AKI.

Heme oxygenase-1 induction contributes to renoprotection by G-CSF during rhabdomyolysis-associated acute kidney injury

Granulocyte colony-stimulating factor (G-CSF) is renoprotective during acute kidney injury (AKI) induced by ischemia and cisplatin nephrotoxicity; however, the underlying mechanism is not entirely clear. Rhabdomyolysis is another important clinical cause of AKI, due to the release of nephrotoxins (e.g., heme) from disrupted muscles. The current study has determined the effects of G-CSF on rhabdomyolysis-associated AKI using in vivo and in vitro models. In C57BL/6 mice, intramuscular injection of glycerol induced AKI, which was partially prevented by G-CSF pretreatment. Consistently, glycerol-induced renal tissue damage was ameliorated by G-CSF. In addition, animal survival following the glycerol injection was improved from ∼30 to ∼70% by G-CSF. In cultured renal tubular cells, hemin-induced apoptosis was also suppressed by G-CSF. Interestingly, G-CSF induced heme oxygenase-1 (HO-1, a critical enzyme for heme/hemin degradation and detoxification) in both cultured tubular cells and mouse kidneys. Blockade of HO-1 with protoporphyrin IX zinc(II) (ZnPP) could largely diminish the protective effects of G-CSF. Together, these results demonstrated the renoprotective effects of G-CSF in rhabdomyolysis-associated AKI. Notably, G-CSF may directly protect against tubular cell injury under the disease condition by inducing HO-1.

Bcl3 prevents acute inflammatory lung injury in mice by restraining emergency granulopoiesis

Granulocytes are pivotal regulators of tissue injury. However, the transcriptional mechanisms that regulate granulopoiesis under inflammatory conditions are poorly understood. Here we show that the transcriptional coregulator B cell leukemia/lymphoma 3 (Bcl3) limits granulopoiesis under emergency (i.e., inflammatory) conditions, but not homeostatic conditions. Treatment of mouse myeloid progenitors with G-CSF--serum concentrations of which rise under inflammatory conditions--rapidly increased Bcl3 transcript accumulation in a STAT3-dependent manner. Bcl3-deficient myeloid progenitors demonstrated an enhanced capacity to proliferate and differentiate into granulocytes following G-CSF stimulation, whereas the accumulation of Bcl3 protein attenuated granulopoiesis in an NF-κB p50-dependent manner. In a clinically relevant model of transplant-mediated lung ischemia reperfusion injury, expression of Bcl3 in recipients inhibited emergency granulopoiesis and limited acute graft damage. These data demonstrate a critical role for Bcl3 in regulating emergency granulopoiesis and suggest that targeting the differentiation of myeloid progenitors may be a therapeutic strategy for preventing inflammatory lung injury.

Mesenchymal stem cells in renal function recovery after acute kidney injury: use of a differentiating agent in a rat model

Acute kidney injury (AKI) is a major health care condition with limited current treatment options. Within this context, stem cells may provide a clinical approach for AKI. Moreover, a synthetic compound previously developed, hyaluronan monoesters with butyric acid (HB), able to induce metanephric differentiation, formation of capillary-like structures, and secretion of angiogenic cytokines, was tested in vitro. Thereafter, we investigated the effects of human mesenchymal stem cells from fetal membranes (FMhMSCs), both treated and untreated with HB, after induction of ischemic AKI in a rat model. At reperfusion following 45-min clamping of renal pedicles, each rat was randomly assigned to one of four groups: CTR, PBS, MSC, and MSC-HB. Renal function at 1, 3, 5, and 7 days was assessed. Histological samples were analyzed by light and electron microscopy and renal injury was graded. Cytokine analysis on serum samples was performed. FMhMSCs induced an accelerated renal functional recovery, demonstrated by biochemical parameters and confirmed by histology showing that histopathological alterations associated with ischemic injury were less severe in cell-treated kidneys. HB-treated rats showed a minor degree of inflammation, both at cytokine and TEM analyses. Better functional and morphological recovery were not associated to stem cells' regenerative processes, but possibly suggest paracrine effects on microenvironment that induce retrieval of renal damaged tissues. These results suggest that FMhMSCs could be useful in the treatment of AKI and the utilization of synthetic compounds could enhance the recovery induction ability of cells.

Toll-like receptor 4 regulates early endothelial activation during ischemic acute kidney injury

Ischemic acute kidney injury (AKI) triggers an inflammatory response which exacerbates injury that requires increased expression of endothelial adhesion molecules. To study this further, we used in situ hybridization, immunohistology, and isolated endothelial cells, and found increased Toll-like receptor 4 (TLR4) expression on endothelial cells of the vasa rectae of the inner stripe of the outer medulla of the kidney 4 h after reperfusion. This increase was probably due to reactive oxygen species, known to be generated early during ischemic AKI, because the addition of hydrogen peroxide increased TLR4 expression in MS1 microvascular endothelial cells in vitro. Endothelial TLR4 may regulate adhesion molecule (CD54 and CD62E) expression as they were increased on endothelia of wild-type but not TLR4 knockout mice in vivo. Further, the addition of high-mobility group protein B1, a TLR4 ligand released by injured cells, increased adhesion molecule expression on endothelia isolated from wild-type but not TLR4 knockout mice. TLR4 was localized to proximal tubules in the cortex and outer medulla after 24 h of reperfusion. Thus, at least two different cell types express TLR4, each of which contributes to renal injury by temporally different mechanisms during ischemic AKI.

Cellular maintenance and repair of the kidney

The mammalian kidney is a highly complex organ that requires the precise structural arrangement of multiple cell types for effective function. The need to filter large volumes of plasma at the glomerulus followed by active reabsorption of nearly 99% of that filtrate by the tubules creates vulnerability in both compartments for cell injury. Thus maintenance of cell viability and replacement of those cells that are lost are essential for functional stability of the kidney. This review addresses our current understanding of how cells from the glomerular, tubular, and interstitial compartments arise during development and the manner in which they may be regenerated in the adult organ. In addition, we discuss the data regarding the role of organ-specific and bone marrow-derived stem and progenitor cells in the replacement/repair process, as well as the potential for ex vivo programming of stem cells toward a renal lineage.

Stem cell therapy for the kidney?

The kidney has a remarkable capacity to regenerate after injury, as it is not a terminally differentiated organ. This regenerative potential is somehow incomplete, however, and as the insult continues, progressive and irreversible scarring results in chronic renal disease. Dialysis and organ transplantation are nonspecific and incomplete methods of renal replacement therapy. Stem cells may provide a more efficacious method for both prevention and amelioration of renal disease of many etiologies. Although many reports have claimed the existence of renal-specific stem or progenitor cells isolated and characterized by various methods, the results have been diverse and debatable. The bone marrow stem cells seem to play a minor role in renal regeneration after acute ischemia in mice through transdifferentiation and cell fusion, but their immediate paracrine effects result in considerable improvements in renal function. Therefore, as in stem cell therapy for the heart, bone marrow-derived stem cells show promise in regeneration of the kidney. Although more research is needed in the basic science of renal regeneration, clinical research in animals has demonstrated the versatility of stem cell therapy. The first phase of clinical trials of bone marrow mesenchymal cells in protection against acute kidney injury may begin shortly. This will enable further exploration of stem cell therapy in renal patients with multiple comorbidities.

IRF-1 promotes inflammation early after ischemic acute kidney injury

Acute renal ischemia elicits an inflammatory response that may exacerbate acute kidney injury, but the regulation of the initial signals that recruit leukocytes is not well understood. Here, we found that IFN regulatory factor 1 (IRF-1) was a critical, early proinflammatory signal released during ischemic injury in vitro and in vivo. Within 15 min of reperfusion, proximal tubular cells of the S3 segment produced IRF-1, which is a transcription factor that activates proinflammatory genes. Transgenic knockout of IRF-1 ameliorated the impairment of renal function, morphologic injury, and inflammation after acute ischemia. Bone marrow chimera experiments determined that maximal ischemic injury required IRF-1 expression by both leukocytes and radioresistant renal cells, the latter identified as S3 proximal tubule cells in the outer medulla by in situ hybridization and immunohistochemistry. In vitro, reactive oxygen species, generated during ischemia/reperfusion injury, stimulated expression of IRF-1 in an S3 proximal tubular cell line. Taken together, these data suggest that IRF-1 gene activation by reactive oxygen species is an early signal that promotes inflammation after ischemic renal injury.

Acute inactivation of the VHL gene contributes to protective effects of ischemic preconditioning in the mouse kidney

BACKGROUND/AIMS

The von Hippel-Lindau (VHL) protein functions as an E3 ubiquitin ligase, controlling the stability of hypoxia-inducible factor (HIF). Preinduction of HIF-1alpha before pathological insult activates a self-defense mechanism and suppresses further aggravation of organ or cellular injury by ischemia. We investigated whether acute inactivation of the VHL gene might play a role in the response of mice to ischemic renal injury.

METHODS

We generated tamoxifen-inducible conditional VHL knockout (VHL-KO) mice to inactivate the VHL gene in an acute manner during renal ischemia-reperfusion injury (IRI) induced by bilateral clamping of kidney arteries. Renal IRI is characterized by renal dysfunction and tubular damage.

RESULTS

After the procedure of IRI, blood urea nitrogen (BUN) and creatinine (CRN) levels in control mice were significantly higher (BUN, 138.10 +/- 13.03 mg/dl; CRN, 0.72 +/- 0.16 mg/dl) than in VHL-KO mice (BUN, 52.12 +/- 6.61 mg/dl; CRN, 0.24 +/- 0.04 mg/dl; BUN: p < 0.05; CRN: p < 0.05). Histologically, tubular injury scores were higher in control mice than in VHL-KO mice (p < 0.05).

CONCLUSION

We suggest that the acute inactivation of the VHL gene contributes to protective effects of ischemic preconditioning in renal tubules of the mouse.

Pulmonary complications after acute kidney injury

The development of respiratory failure in patients with AKI is a particularly devastating consequence that greatly increases patient mortality. When respiratory failure and AKI occur together, the mortality is greater than 80%. A clear understanding of the mechanisms leading to respiratory failure is of great clinical relevance to patients with AKI in order to prevent and treat this life-threatening complication. Pulmonary edema leading to respiratory failure has been a recognized complication of kidney failure since 1901. Remarkably, the pathogenesis of this complication remains elusive, despite over 100 years of clinical and experimental debate in the literature. A review of this literature suggests that there are 4 causes of pulmonary edema leading to respiratory failure in patients with AKI: (1) volume overload (cardiogenic edema), (2) left ventricular dysfunction (cardiogenic edema), (3) increased lung capillary permeability (noncardiogenic edema), and (4) acute lung injury (noncardiogenic edema with inflammation). In this review, these mechanisms are presented in historical context including the original descriptions of pathology and pathophysiology, recent epidemiologic data, and experimental studies in animals. Although volume overload is a well-accepted mechanism of pulmonary edema in patients with AKI, the purpose of this review was to highlight the evidence showing that noncardiogenic edema and acute lung injury also occur. By recognizing that the pulmonary complications of AKI are not simply from volume overload, specific treatment strategies may be discovered and used to improve outcomes in patients with the ominous and life threatening combination of AKI and respiratory failure.

The local and systemic inflammatory transcriptome after acute kidney injury

Studies in humans and animal models have demonstrated that acute kidney injury (AKI) has a significant effect on the function of extrarenal organs. The combination of AKI and lung dysfunction is associated with 80% mortality; the lung, because of its extensive capillary network, is a prime target for AKI-induced effects. The study presented here tested the hypothesis that AKI leads to a vigorous inflammatory response and produces distinct genomic signatures in the kidney and lung. In a murine model of ischemic AKI, prominent global transcriptomic changes and histologic injury in both kidney and lung tissues were identified. These changes were evident at both early (6 h) and late (36 h) timepoints after 60-min bilateral kidney ischemia and were more prominent than similar timepoints after sham surgery or 30 min of ischemia. The inflammatory transcriptome (109 genes) of both organs changed with marked similarity, including the innate immunity genes Cd14, Socs3, Saa3, Lcn2, and Il1r2. Functional genomic analysis of these genes suggested that IL-10 and IL-6 signaling was involved in the distant effects of local inflammation, and this was supported by increased serum levels of IL-10 and IL-6 after ischemia-reperfusion. In summary, this is the first comprehensive analysis of concomitant inflammation-associated transcriptional changes in the kidney and a remote organ during AKI. Functional genomic analysis identified potential mediators that connect local and systemic inflammation, suggesting that this type of analysis may be a useful discovery tool for novel biomarkers and therapeutic drug development.

Mobilized bone marrow progenitor cells serve as donors of cytoprotective genes for cardiac repair

We proposed here that mobilized progenitor cells (MPCs) from the bone marrow are special cell types which carry cytoprotective proteins for cardiac repair following ischemia. Myocardial ischemia was induced by ligation of the left anterior descending coronary artery (LAD) in mice. Progenitor cells in peripheral blood were analyzed by fluorescence-activated cell sorting (FACS). The expression of cytoprotective genes was assayed by ELISA, RT-PCR, and/or real-time PCR. G-CSF was markedly up-regulated in the ischemic myocardium. A good correlation was observed between serum G-CSF and progenitor cells in circulation following LAD ligation. MPCs overexpressed cardiac transcription factor, GATA-4, and anti-apoptotic factor, Bcl-2, besides expression of the surface markers of bone marrow stem cells (BMSCs). Transplantation of cultured MPCs into the ischemic border area significantly improved cardiac function by reducing infarction size. More importantly, MPCs significantly protected cardiomyocytes against apoptosis when co-cultured with cardiomyocytes. The cardiac protection by MPCs was blocked by Bcl-2 neutralizing antibody and GATA-4 siRNA. In contrast, transfection of BMSCs with GATA-4 provided increased protection of myocytes against apoptosis. It is concluded that MPCs are highly cytoprotective and carry protective genes responsible for cardiac repair.

Endotoxin and cisplatin synergistically induce renal dysfunction and cytokine production in mice

A major toxicity of the cancer chemotherapeutic agent cisplatin is acute renal failure. Sepsis is a common cause of acute renal failure in humans and patients who receive cisplatin are at increased risk for sepsis. Accordingly, this study examined the interactions between cisplatin and endotoxin in vivo with respect to renal function and cytokine production. Mice were treated with either a single dose of cisplatin or two doses of LPS administered 24 h apart, or both agents in combination. Administration of 10 mg/kg cisplatin had no effect on blood urea nitrogen or creatinine levels throughout the course of the study. LPS resulted in a modest rise in blood urea nitrogen at 24 and 48 h, which returned to normal by 72 h. In contrast, mice treated with both cisplatin and LPS developed severe renal failure and an increase in mortality. Urine, but not serum, TNF-alpha levels showed a synergistic increase by cisplatin and LPS. Urinary IL-6, MCP-1, KC, and GM-CSF also showed a synergistic increase with cisplatin+LPS treatment. The renal dysfunction induced by cisplatin+LPS was completely dependent on TLR4 signaling and partially dependent on TNF-alpha production. Increased cytokine production was associated with a moderate increase in infiltrating leukocytes which was not different between cisplatin+LPS and LPS alone. These results indicate that cisplatin and LPS act synergistically to produce nephrotoxicity which may involve proinflammatory cytokine production.

How Does G-CSF Act on the Kidney during Acute Tubular Injury?

Recent findings in stem cell research have demonstrated multi-lineage plasticity of bone marrow cells, and also the contribution of hematopoietic bone marrow stem cells to the regeneration of injured organs including the kidney. These findings suggested the possibility of the use of granulocyte colony-stimulating factor (G-CSF) as a therapeutic option to regenerate injured organs. Recently, several studies regarding the effect of G-CSF on renal function have been reported in mouse models of acute renal failure. This series of experiments provided potentially important information regarding the treatment of patients with renal injury. This review summarizes the possible actions of G-CSF on the kidney, especially during acute tubular injury caused by toxic or ischemic insults.

Stem cells in kidney regeneration following acute renal injury

Acute renal failure has 50-80% mortality. Currently, treatment options for this life-threatening disease are limited. Stem cells offer an exciting potential for kidney regeneration. This review discusses pathogenesis of acute renal failure resulting from ischemia-reperfusion injury and the role of stem cells in reversing or mitigating this disorder. Specifically, the issues of differentiation of kidney cells from embryonic stem cells and bone marrow stem cells, and whether adult kidney stem/progenitor cells exist in the postnatal kidney are discussed. Evidence to support the conclusion that intra-renal cells, including surviving tubular epithelial cells and potential renal stem/progenitor cells, are the main source for renal regeneration is provided. Future research in selecting the type(s) of stem cells and optimizing the dose, frequency and route of administration of the cells will be fundamental in successful cell replacement therapy in acute renal failure. Methods for enhancing endogenous renal cell proliferation and differentiation for renal repair continue to be important research directions.

Keratinocyte-derived chemokine is an early biomarker of ischemic acute kidney injury

Renal ischemia-reperfusion injury (IRI) is the leading cause of acute kidney injury [AKI; acute renal failure (ARF)] in native kidneys and delayed graft function in deceased donor kidney transplants. Serum creatinine rises late after renal IRI, which results in delayed diagnosis. There is an important need to identify novel biomarkers for early diagnosis and prognosis in renal IRI. Given the inflammatory pathophysiology of renal IRI, we used a protein array to measure 18 cytokines and chemokines in a mouse model of renal IRI at 3, 24, and 72 h postischemia. A rise in renal keratinocyte-derived chemokine (KC) was the earliest and most consistent compared with other molecules, with 3-h postischemia values being 9- and 13-fold greater than sham and normal animals, respectively. Histological changes were evident within 1 h of IRI but serum creatinine only increased 24 h after IRI. With the use of an ELISA, KC levels in serum and urine were highest 3 h postischemia, well before a significant rise in serum creatinine. The human analog of KC, Gro-alpha, was markedly elevated in urine from humans who received deceased donor kidney transplants that required dialysis, compared with deceased donor kidney recipients with good graft function and live donor recipients with minimal ischemia. Measurement of KC and its human analog, Gro-alpha, could serve as a useful new biomarker for ischemic ARF.

Adult stem cells in the repair of the injured renal tubule

The capacity of the kidney to regenerate functional tubules following episodes of acute injury is an important determinant of patient morbidity and mortality in the hospital setting. After severe injury or repeated episodes of injury, kidney recovery can be significantly impaired or even fail completely. Although significant advances have been made in the clinical management of such cases, there is no specific therapy that can improve the rate or effectiveness of the repair process. Recent studies have indicated that adult stem cells, either in the kidney itself or derived from the bone marrow, could participate in this repair process and might therefore be utilized clinically to treat acute renal failure. This review will focus on our current understanding of these stem cells, the controversies surrounding their in vivo capacity to repopulate the renal tubule, and further investigations that will be required before stem cell therapy can be considered for use in the clinical setting.

Maladaptive role of IL-6 in ischemic acute renal failure

The role of IL-6 was investigated in murine ischemic acute renal failure. The renal pedicles were clamped for 17 min, and the mice were studied at various times after reperfusion. We found that serum IL-6 increased after murine ischemic renal injury. This increase was associated with increased IL-6 mRNA in the ischemic kidney but not in the contralateral kidney or the liver. Maximal IL-6 production occurred at 4 to 8 h and decreased to baseline by 24 h. Reperfusion of the kidney was required for IL-6 production. In situ hybridization and immunohistochemistry showed that macrophages infiltrated areas adjacent to the vascular bundles in the outer medulla within hours of reperfusion and showed that these macrophages produced IL-6 mRNA. For understanding how macrophages were stimulated to produce IL-6, an in vitro model in which S3 proximal tubular cells were injured by reactive oxygen species was set up. These injured cells released molecules that activated macrophages to produce IL-6 in vitro. IL-6 that was produced in response to renal ischemia was maladaptive because transgenic knockout of IL-6 ameliorated renal injury as measured by serum creatinine and histology. IL-6 transgenic knockout mice were lethally irradiated, and their bone marrow was reconstituted with wild-type IL-6 cells. Such bone marrow transfers abolished the protective effects of transgenic IL-6 knockout. It is concluded that macrophages infiltrate the area of the vascular bundles of the outer medulla, these macrophages produce IL-6, and this IL-6 exacerbates ischemic murine acute renal failure.

The diagnosis of acute renal failure in intensive care: mongrel or pedigree?

Acute renal failure is common in the intensive care unit; it is well recognised that patients who develop acute renal failure have a high mortality rate. While there have been improvements in the management of acute renal failure, the mortality remains high. Acute renal failure is easily diagnosed biochemically and clinically but it is not a single disease entity. It is a syndrome that affects a very heterogeneous population. Studies of acute renal failure and of the impact of renal replacement therapy in intensive care are usually inconclusive, which may be the natural consequence of studying a syndrome. This article focuses on the more uncertain features of acute renal failure, the problems of investigating acute renal failure as a disease and the difficulties of applying the results of a study of a heterogeneous population to the management of individuals.