Renal tubular Fas ligand mediates fratricide in cisplatin-induced acute kidney failure

Cisplatin nephrotoxicity: new insights and therapeutic implications

Cisplatin is an effective chemotherapeutic agent for various solid tumours, but its use is limited by adverse effects in normal tissues. In particular, cisplatin is nephrotoxic and can cause acute kidney injury and chronic kidney disease. Preclinical studies have provided insights into the cellular and molecular mechanisms of cisplatin nephrotoxicity, which involve intracellular stresses including DNA damage, mitochondrial pathology, oxidative stress and endoplasmic reticulum stress. Stress responses, including autophagy, cell-cycle arrest, senescence, apoptosis, programmed necrosis and inflammation have key roles in the pathogenesis of cisplatin nephrotoxicity. In addition, emerging evidence suggests a contribution of epigenetic changes to cisplatin-induced acute kidney injury and chronic kidney disease. Further research is needed to determine how these pathways are integrated and to identify the cell type-specific roles of critical molecules involved in regulated necrosis, inflammation and epigenetic modifications in cisplatin nephrotoxicity. A number of potential therapeutic targets for cisplatin nephrotoxicity have been identified. However, the effects of renoprotective strategies on the efficacy of cisplatin chemotherapy needs to be thoroughly evaluated. Further research using tumour-bearing animals, multi-omics and genome-wide association studies will enable a comprehensive understanding of the complex cellular and molecular mechanisms of cisplatin nephrotoxicity and potentially lead to the identification of specific targets to protect the kidney without compromising the chemotherapeutic efficacy of cisplatin.

Bombesin receptor-activated protein exacerbates cisplatin-induced AKI by regulating the degradation of SIRT2

BACKGROUND

Acute kidney injury (AKI) is a public health problem with no specific therapies in the clinic and the underlying pathogenesis of AKI remains obscure. Bombesin receptor-activated protein (BRAP, C6ORF89 protein) was initially discovered as a ligand for a previously orphan G-protein-coupled receptor bombesin-like receptor-3. At present, accepted biological effects of BRAP include cell cycle progression, wound repair and the activation of histone deacetylases. However, its role in kidney disease is unknown. In this study we have investigated the role of BRAP and underlying mechanisms involved in cisplatin (CP)-induced AKI.

METHODS

Here we used Bc004004 (homologous of C6ORF89 in mice) knockout mice and HK2 cells to investigate the effect of BRAP on AKI in vitro and in vivo. We analyzed ChIP-Seq and RNA-Seq data to search for the upstream regulators of BRAP and downstream mediators of BRAP action in AKI. Immunostaining, real-time polymerase chain reaction (PCR), co-immunoprecipitation, a dual-luciferase reporter assay and ChIP-PCR assay were applied to reveal the upstream and downstream regulation mechanism of BRAP during cisplatin-induced AKI.

RESULTS

BRAP was downregulated in mice and human kidneys with AKI. Global Bc004004 deletion alleviated tubular cell apoptosis and necroptosis in CP-induced AKI mice, whereas local overexpression of BRAP in kidneys aggravated them. Pan-caspase inhibitor Z-VAD pretreatment attenuated CP-induced blood creatinine increase and kidney injury in wild-type mice but not in BRAP -/- mice. The activation of mixed lineage kinase like-domain was magnified by Z-VAD in CP-treated mice, especially in BRAP -/- mice. The cytoprotective effect of Z-VAD was more substantial than necrostatin-1 (Nec-1, an inhibitor of necroptosis) in CP-treated human kidney proximal tubular epithelial (HK2) cells. Furthermore, Nec-1 pretreatment reduced the CP-induced cell death in BRAP overexpression HK2 cells but did not work in cells with normal BRAP levels. We determined that CP treatment activated the nuclear factor-κB subunit P65 and inhibition of P65 increased the messenger RNA (mRNA) levels of BRAP in HK2 cells. The chromatin immunoprecipitation assay and dual-luciferase reporter gene assay verified P65 binding to the C6ORF89 promoter and reduced its mRNA expression upon CP treatment. Next we found that sirtuin 2 (SIRT2) was downregulated in CP-induced AKI and BRAP levels directly impacted the protein levels of SIRT2. Our findings further confirmed that BRAP regulates the SIRT2 protein levels by affecting SIRT2's interactions with E3 ubiquitin ligase HRD1 and subsequent proteasomal degradation.

CONCLUSIONS

Our results demonstrated that BRAP played an important role in tubular cell apoptosis and necroptosis during CP-induced AKI. Safe and efficient BRAP inhibitors might be effective therapeutic options for AKI.

COVID-19 and Diabetic Nephropathy

Diabetic nephropathy is the most common condition that requires a chronic renal replacement therapy, such as hemodialysis, peritoneal dialysis, kidney transplantation, or simultaneous kidney-pancreas transplantation. Chronic kidney disease progression, that is the loss of nephrons, which causes the continuous decline of the eGFR, underlies the pathogenesis of diabetic nephropathy. During the COVID-19 pandemic, it became clear that diabetic nephropathy is amongst the independent risk factors that predicts unfavourable outcome upon SARS-CoV2 infection. While we still lack conclusive mechanistic insights into how nephrons are rapidly lost upon SARS-CoV2 infection and why patients with diabetic nephropathy are more susceptible to severe outcomes upon SARS-CoV2 infection, here, we discuss several aspects of the interface of COVID-19 with diabetic nephropathy. We identify the shortage of reliable rodent models of diabetic nephropathy, limited treatment options for human diabetic nephropathy and the lack of knowledge about virus-induced signalling pathways of regulated necrosis, such as necroptosis, as key factors that explain our failure to understand this system. Finally, we focus on immunosuppressed patients and discuss vaccination efficacy in these and diabetic patients. We conclude that more basic science and mechanistic understanding will be required both in diabetic nephropathy as well as in host immune responses to the SARS-CoV2 virus if novel therapeutic strategies are desired.

Progress and Setbacks in Translating a Decade of Ferroptosis Research into Clinical Practice

Ten years after its initial description, ferroptosis has emerged as the most intensely studied entity among the non-apoptotic forms of regulated cell death. The molecular features of ferroptotic cell death and its functional role have been characterized in vitro and in an ever-growing number of animal studies, demonstrating that it exerts either highly detrimental or, depending on the context, occasionally beneficial effects on the organism. Consequently, two contrary therapeutic approaches are being explored to exploit our detailed understanding of this cell death pathway: the inhibition of ferroptosis to limit organ damage in disorders such as drug-induced toxicity or ischemia-reperfusion injury, and the induction of ferroptosis in cancer cells to ameliorate anti-tumor strategies. However, the path from basic science to clinical utility is rocky. Emphasizing ferroptosis inhibition, we review the success and failures thus far in the translational process from basic research in the laboratory to the treatment of patients.

Calcium alleviates fluoride-induced kidney damage via FAS/FASL, TNFR/TNF, DR5/TRAIL pathways in rats

Long-term excessive intake of fluoride (F) can cause osseous and non-osseous damage. The kidney is the main fluoride excretion organ of the body. This study aimed to explore whether dietary calcium (Ca) supplementation can alleviate kidney damage caused by fluorosis and to further investigate the effects of Ca on the mitigation mechanism of renal cell apoptosis triggered by F. We evaluated the histopathological structure, renal function indicators, and gene and protein expression levels of death receptor-mediated apoptosis pathways in Sprague Dawley (SD) rats treated with sodium fluoride (NaF) and/or calcium carbonate (CaCO₃) for 120 days. The results showed that 100 mg/L NaF induced kidney histopathological injury and apoptosis, increased the concentrations of Creatinine (CRE), uric acid (UA), blood urea nitrogen (BUN), potassium (K), phosphorus (P) and F (p < 0.05), and decrease the level of serum magnesium (Mg) (p < 0.05). Moreover, NaF increased the mRNA and protein expression levels of Fas cell surface death receptor (FAS), tumor necrosis factor (TNF), TNF-related apoptosis-inducing ligand (TRAIL), Caspase 8, Caspase 3 and poly ADP-ribose polymerase (PARP) (p < 0.01), which finally activated the death receptor pathway. Inversely, Ca supplementation reversed the decrease of CRE, BUN, UA, F and P levels induced by F, alleviated histopathological damage and apoptosis, and reduced the gene and protein expression levels of death receptor pathway-related markers. In conclusion, 1% Ca alleviates F-induced kidney apoptosis through FAS/FASL, TNFR/TNF, DR5/TRAIL signaling pathways.

Possible protective effect of pantoprazole against cisplatin-induced nephrotoxicity in head and neck cancer patients: a randomized controlled trial

Cisplatin is used to treat solid malignancies including head and neck cancer. However, nephrotoxicity limits its use. In this study, we looked for a possible protective effect of pantoprazole against cisplatin-induced nephrotoxicity. We used novel biomarkers for early detection of nephrotoxicity. Sixty chemotherapy naïve head and neck cancer patients completed the study. Following complete history taking and thorough clinical examination, patients were randomly divided into three groups: 20 patients in each. Group I (control group) received cisplatin without pantoprazole, groups II and III received pantoprazole 80 mg and 40 mg, respectively, concurrently with cisplatin. Blood and urine samples were collected at baseline, and 48 h after the first and third cycles of cisplatin administration. Assessment of serum creatinine and soluble FasL (sFasL), as well as urinary neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) was performed. Nephrotoxicity was detected in 6 patients in group I, none in group II and 3 patients in group III. Serum creatinine significantly increased at the end of treatment in group I compared to groups II and III. Group I also had significantly higher urinary KIM-1 and NGAL and serum sFasL compared to groups II and III after the first and third cycles. On the contrary, there was no significant difference between groups II and III. Pantoprazole prevented the increase in acute kidney injury biomarkers in cisplatin-treated patients. Therefore, it is a promising agent in reducing cisplatin-induced nephrotoxicity.Trial registration Clinical Trials.gov identifier: NCT04217512, registered in January 2020 " retrospectively registered".

Ferroptosis and Necroptosis in the Kidney

In the last decade, the role of apoptosis in the pathophysiology of acute kidney injury (AKI) and AKI to chronic kidney disease (CKD) progression has been revisited as our understanding of ferroptosis and necroptosis has emerged. A growing body of evidence, reviewed here, ascribes a central pathophysiological role for ferroptosis and necroptosis to AKI, nephron loss, and acute tubular necrosis. We will introduce concepts to the non-cell-autonomous manner of kidney tubular injury during ferroptosis, a phenomenon that we refer to as a "wave of death." We hypothesize that necroptosis might initiate cell death propagation through ferroptosis. The remaining necrotic debris requires effective removal processes to prevent a secondary inflammatory response, referred to as necroinflammation. Open questions include the differences in the immunogenicity of ferroptosis and necroptosis, and the specificity of necrostatins and ferrostatins to therapeutically target these processes to prevent AKI-to-CKD progression and end-stage renal disease.

Antioxidant and anti-apoptotic effects of vitexilactone on cisplatin-induced nephrotoxicity in rats

Cisplatin (CP) is an antineoplastic drug; however, owing to its nephrotoxicity, its clinical use is limited. We investigated whether vitexilactone (vitex) is a safe and effective treatment for CP induced kidney injury. We allocated Sprague-Dawley rats into six groups: control group, low dose-high dose vitex groups (40 and 80 mg/kg vitex for 6 days before administration of CP), CP group (single 6 mg/kg dose on day 6) and CP + low dose vitex-CP + high dose vitex group (40 and 80 mg/kg vitex for 6 days, and a single 6 mg/kg dose of CP on day 6. Rats were euthanized 5 days after CP treatment. After exposure to CP and/or vitex, total oxidative stress and total antioxidant status were assessed. The histology of the kidney was examined using hematoxylin and eosin, and periodic acid-Schiff. We used immunohistochemical and fluorescence staining to detect expression of caspase-3. We also measured blood urea nitrogen, uric acid and creatinine levels. Nephroprotective effects of vitex were associated with decreased serum toxicity markers and increased antioxidant activity. Vitex also reduced the expression of the apoptosis marker, caspase-3. Treatment with CP increased blood urea nitrogen, uric acid, creatinine levels and total antioxidant status, and decreased total antioxidant status compared to the control group. Use of vitex for protection from CP induced nephrotoxicity appears to be a safe and efficacious alternative for treatment of kidney injury.

Protective effect of anisodamine in rats with glycerol-induced acute kidney injury

Background

Anisodamine is used for the treatment of reperfusion injury in various organs. In this study, we investigated the effectiveness and mechanisms of action of anisodamine in promoting recovery from glycerol-induced acute kidney injury (AKI).

Methods

We compared the protective effects of atropine and anisodamine in the rat model of glycerol-induced AKI. We examined signaling pathways involved in oxidative stress, inflammation and apoptosis, as well as expression of kidney injury molecule-1 (KIM-1). Renal injury was assessed by measuring serum creatinine and urea, and by histologic analysis. Rhabdomyolysis was evaluated by measuring creatine kinase levels, and oxidative stress was assessed by measuring malondialdehyde (MDA) and superoxide dismutase (SOD) levels in kidney tissues. Inflammation was assessed by quantifying interleukin 6 (IL-6) and CD45 expression. Apoptosis and necrosis were evaluated by measuring caspase-3 (including cleaved caspase 3) and RIP3 levels, respectively.

Results

Glycerol administration resulted in a higher mean histologic damage score, as well as increases in serum creatinine, urea, creatine kinase, reactive oxygen species (ROS), MDA, IL-6, caspase-3 and KIM-1 levels. Furthermore, glycerol reduced kidney tissue SOD activity. All of these markers were significantly improved by anisodamine and atropine. However, the mean histologic damage score and levels of urea, serum creatinine, creatine kinase, ROS and IL-6 were lower in the anisodamine treatment group compared with the atropine treatment group.

Conclusion

Pretreatment with anisodamine ameliorates renal dysfunction in the rat model of glycerol-induced rhabdomyolytic kidney injury by reducing oxidative stress, the inflammatory response and cell death.

Design, synthesis and evaluation of PD176252 analogues for ameliorating cisplatin-induced nephrotoxicity

Cisplatin is a clinical chemotherapy drug for cancers; however, its remarkably high kidney toxicity and other toxicities pose a danger to patients. As the small molecule inhibitor of GRPR, PD176252 can inhibit the growth and proliferation of various cancer cells, but the characteristics of high toxicity and poor water solubility has limited its use as a drug. When we studied PD176252 for the reduction of toxicity of cisplatin, we modified its structure to synthesize 16 analogues. Surprisingly, the analogues showed reduced cisplatin-induced renal toxicity, and unlike PD176252, the analogues 5d and 5m were almost non-toxic to the normal HK2 cells. Furthermore, the analogue 5d and PD176252 were subjected to cisplatin-induced inflammatory response in vitro. The results showed that 5d was able to better prevent this condition by effectively inhibiting its inflammatory response. Thus, this study will help in clinically reducing the side effects of cisplatin.

Voices from the dead: The complex vocabulary and intricate grammar of dead cells

Of the roughly one million cells per second dying throughout the body, the vast majority dies by apoptosis, the predominant form of regulated cell death in higher organisms. Long regarded as mere waste, apoptotic cells are now recognized as playing a prominent and active role in homeostatic maintenance, especially resolution of inflammation, and in the sculpting of tissues during development. The activities associated with apoptotic cells are continually expanding, with more recent studies demonstrating their ability to modulate such vital functions as proliferation, survival, differentiation, metabolism, migration, and angiogenesis. In each case, the role of apoptotic cells is active, exerting their effects via new activities acquired during the apoptotic program. Moreover, the capacity to recognize and respond to apoptotic cells is not limited to professional phagocytes. Most, if not all, cells receive and integrate an array of signals from cells dying in their vicinity. These signals comprise a form of biochemical communication. As reviewed in this chapter, this communication is remarkably sophisticated; each of its three critical steps-encoding, transmission, and decoding of the apoptotic cell's "message"-is endowed with exquisite robustness. Together, the abundance and intricacy of the variables at each step comprise the vocabulary and grammar of the language by which dead cells achieve their post-mortem voice. The combinatorial complexity of the resulting communication network permits dying cells, through the signals they emit and the responses those signals elicit, to partake of an expanded role in homeostasis, acting as both sentinels of environmental change and agents of adaptation.

Immunopathogenesis of Acute Kidney Injury

Pathophysiologically, the classification of acute kidney injury (AKI) can be divided into three categories: (1) prerenal, (2) intrinsic, and (3) postrenal. Emerging evidence supports the involvement of renal tubular epithelial cells and the innate and adaptive arms of the immune system in the pathogenesis of intrinsic AKI. Pro-inflammatory damage-associated molecular patterns, pathogen-associated molecular patterns, hypoxia inducible factors, toll-like receptors, complement system, oxidative stress, adhesion molecules, cell death, resident renal dendritic cells, neutrophils, T and B lymphocytes, macrophages, natural killer T cells, cytokines, and secreted chemokines contribute to the immunopathogenesis of AKI. However, other immune cells and pathways such as M2 macrophages, regulatory T cells, progranulin, and autophagy exhibit anti-inflammatory properties and facilitate kidney tissue repair after AKI. Thus, therapies for AKI include agents such as anti-inflammatory (e.g., recombinant alkaline phosphatase), antioxidants (iron chelators), and apoptosis inhibitors. In preclinical toxicity studies, drug-induced kidney injury can be seen after exposure to a nephrotoxicant test article due to immune mechanisms and dysregulation of innate, and/or adaptive cellular immunity. The focus of this review will be on intrinsic AKI, as it relates to the immune and renal systems cross talks focusing on the cellular and pathophysiologic mechanisms of AKI.

Cisplatin-induced oxidative stress stimulates renal Fas ligand shedding

Acute kidney injury (AKI), a significant complication of cisplatin chemotherapy is associated with reactive oxygen species (ROS)-dependent renal cell death, but the cellular targets of ROS in cisplatin nephrotoxicity are not fully resolved. Here, we investigated cisplatin-induced oxidative renal damage and tested the hypothesis that ROS-dependent shedding of death activator Fas ligand (FasL) occurs in cisplatin nephropathy. We show that intraperitoneal injection of sulfobutyl ether-β-cyclodextrin (Captisol™)-solubilized cisplatin elevated the level of lipid peroxidation product malondialdehyde in mouse kidneys and urinary concentration of oxidative DNA damage biomarker 8-hydroxy-2'-deoxyguanosine. Cisplatin increased mouse kidney-to-body weight ratio and the plasma or urinary levels of predictive biomarkers of AKI, including creatinine, blood urea nitrogen, microalbumin, neutrophil gelatinase-associated lipocalin, and cystatin C. Histological analysis and dUTP nick end labeling of kidney sections indicated tubular injury and renal apoptosis, respectively in cisplatin-treated mice. Whereas the plasma concentration of soluble FasL (sFasL) was unaltered, urinary sFasL was increased ∼4-fold in cisplatin-treated mice. Real-time quantitative live-cell imaging and lactate dehydrogenase assay showed that cisplatin stimulated caspase 3/7 activation and cytotoxicity in a human proximal tubule epithelial cell line which were attenuated by inhibitors of the FasL/Fas system and poly [ADP-ribose] polymerase-1. Moreover, TEMPOL, an intracellular free radical scavenger mitigated cisplatin-induced renal oxidative stress and injury, AKI biomarker and urinary sFasL elevation, and proximal tubule cell death. Our findings indicate that cisplatin-induced oxidative stress triggers the shedding of membrane-bound FasL to sFasL in the kidney. We demonstrate that cisplatin elicits nephrotoxicity by promoting FasL/Fas-dependent oxidative renal tubular cell death.

Necrostatin-1 Attenuates Cisplatin-Induced Nephrotoxicity Through Suppression of Apoptosis and Oxidative Stress and Retains Klotho Expression

Aim: Cisplatin is an effective chemotherapeutic drug, but the application in clinical is greatly limited by its nephrotoxicity. Necrostatin-1 (Nec-1), an inhibitor of RIP1 kinase, has been reported to inhibit RIP-mediated necroptosis. The aim of this study is to detect the protective effects of Nec-1 on the nephrotoxicity of cisplatin and to investigate its renoprotection mechanism. Methods: 8-week-old male C57BL/6 mice were randomly assigned into four groups: Control, Nec-1, Cisplatin, and Cisplatin+Nec-1. Mice were treated with cisplatin with or without Nec-1 pre-treatment. Renal function, histological changes, necroptosis, and apoptotic markers were investigated. NFκB pathway related proteins, proinflammatory cytokines, oxidative stress markers, renal Klotho, and autophagy-related proteins levels were also examined. Results: Renal function and histological data displayed that the treatment with Nec-1 significantly attenuates cisplatin-induced renal damage. The expression of RIPK1/RIPK3/MLKL were significantly enhanced in cisplatin group as compared to the control group (p < 0.05) and was significantly reduced by pre-treatment of Nec-1 (p < 0.05). The level of stress and apoptosis-related protein, including p-JNK, p-c-Jun, p-p38, Bax/Bcl-2 ratio, and caspase-3 showed the similar trend. Pre-treatment with Nec-1 inhibit NFκB signaling, reduced proinflammatory cytokines and oxidative stress, up-regulated renal Klotho, and autophagy-related proteins levels. Conclusion: Our results suggest that Nec-1 could be a potential therapeutic drug against the cisplatin-induced nephrotoxicity through its anti-necroptosis, anti-apoptotic, anti-inflammatory anti-oxidant and retain Klotho expression and activate autophagy effects in the kidney.

Cisplatin-induced renal inflammation is ameliorated by cilastatin nephroprotection

Background

Cisplatin is a potent chemotherapeutic drug whose nephrotoxic effect is a major complication and a dose-limiting factor for antitumoral therapy. There is much evidence that inflammation contributes to the pathogenesis of cisplatin-induced nephrotoxicity. We found that cilastatin, a renal dehydropeptidase-I inhibitor, has protective effects in vitro and in vivo against cisplatin-induced renal damage by inhibiting apoptosis and oxidation. Here, we investigated the potential use of cilastatin to protect against cisplatin-induced kidney injury and inflammation in rats.

Methods

Male Wistar rats were divided into four groups: control, cilastatin-control, cisplatin and cilastatin-cisplatin. Nephrotoxicity was assessed 5 days after administration of cisplatin based on blood urea nitrogen, creatinine, glomerular filtration rate (GFR), kidney injury molecule (KIM)-1 and renal morphology. Inflammation was measured using the electrophoretic mobility shift assay, immunohistochemical studies and evaluation of inflammatory mediators.

Results

Compared with the control rats, cisplatin-administered rats were affected by significant proximal tubule damage, decreased GFR, increased production of inflammatory mediators and elevations in urea, creatinine and tissue KIM-1 levels. Cilastatin prevented these changes in renal function and ameliorated histological damage in cisplatin-administered animals. Cilastatin also reduced pro-inflammatory cytokine levels, activation of nuclear factor-κB and CD68-positive cell concentrations.

Conclusions

Cilastatin reduces cisplatin-induced nephrotoxicity, which is associated with decreased inflammation in vivo. Although the exact role of decreased inflammation in nephroprotection has not been fully elucidated, treatment with cilastatin could be a novel strategy for the prevention of cisplatin-induced acute kidney injury.

The in vivo evidence for regulated necrosis

Necrosis is a hallmark of several widespread diseases or their direct complications. In the past decade, we learned that necrosis can be a regulated process that is potentially druggable. RIPK3- and MLKL-mediated necroptosis represents by far the best studied pathway of regulated necrosis. During necroptosis, the release of damage-associated molecular patterns (DAMPs) drives a phenomenon referred to as necroinflammation, a common consequence of necrosis. However, most studies of regulated necrosis investigated cell lines in vitro in a cell autonomous manner, which represents a non-physiological situation. Conclusions based on such work might not necessarily be transferrable to disease states in which synchronized, non-cell autonomous effects occur. Here, we summarize the current knowledge of the pathophysiological relevance of necroptosis in vivo, and in light of this understanding, we reassess the morphological classification of necrosis that is generally used by pathologists. Along these lines, we discuss the paucity of data implicating necroptosis in human disease. Finally, the in vivo relevance of non-necroptotic forms of necrosis, such as ferroptosis, is addressed.

Assessment of In Vivo Kidney Cell Death: Acute Kidney Injury

The kidney has been studied as an organ to investigate cell death in vivo for a number of reasons. The unique vasculature that does not contain collateral vessels favors the kidney over other organs for the investigation of ischemia-reperfusion injury. Unilateral uretic obstruction has become the most prominently studied model for fibrosis with impact far beyond postrenal kidney injury. In addition, the tubular elimination mechanisms render the kidney susceptible to toxicity models, such as cisplatin-induced acute kidney injury. During trauma of skeletal muscles, myoglobulin deposition causes tubular cell death in the model of rhabdomyolysis-induced acute kidney injury. Here, we introduce these clinically relevant in vivo models of acute kidney injury (AKI) and critically review the protocols we use to effectively induce them.

Wogonin protects against cisplatin-induced acute kidney injury by targeting RIPK1-mediated necroptosis

Acute kidney injury (AKI), characterized by aggressive inflammatory responses and destruction of renal resident cells, can cause abrupt kidney dysfunction. To date, effective therapy for AKI is lacking. In this study, we evaluated the renoprotective effect of wogonin, an herbal active compound, using a cisplatin-induced AKI mouse model. In vivo results show that wogonin substantially suppressed the increased levels of serum creatinine and blood urea nitrogen (BUN) almost to the normal level. Wogonin also attenuated tubular damage, shown by PAS staining, electron microscopy and molecular analysis of KIM-1. In addition, wogonin suppressed kidney inflammation as indicated by a >60% decrease in macrophage infiltration, a >50% reduction in inflammatory cytokine production and inhibited NF-κB activation in the injured kidney. Mechanistically, molecular docking results show that wogonin effectively inhibited RIPK1 by occupying the ATP-binding pocket of the enzyme, which is a key regulator of necroptosis. Moreover, inhibition of RIPK1, or RIPK3, reversed the protective effects of wogonin in cisplatin-treated HK2 cells, indicating wogonin works in a RIPK1/RIPK3-dependent manner. Surprisingly, wogonin enhanced the anti-proliferative effect of cisplatin on human hepatoma HepG2 cells. Thus, our findings suggest wogonin may be a renoprotective adjuvant for cisplatin-based anticancer therapy.

Neuropeptide Y protects kidney against cisplatin-induced nephrotoxicity by regulating p53-dependent apoptosis pathway

Cisplatin is a platinum-based chemotherapeutic drug for treating various types of cancers. However, the use of cisplatin is limited by its negative effect on normal tissues, particularly nephrotoxicity. Various mechanisms such as DNA adduct formation, mitochondrial dysfunction, oxidative stress, and apoptosis are involved in the adverse effect induced by cisplatin treatment. Several studies have suggested that neuropeptide Y (NPY) is involved in neuroprotection as well as restoration of bone marrow dysfunction from chemotherapy induced nerve injury. However, the role of NPY in chemotherapy-induced nephrotoxicity has not been studied. Here, we show that NPY rescues renal dysfunction by reducing the expression of pro-apoptotic proteins in cisplatin induced nephrotoxicity through Y1 receptor, suggesting that NPY can protect kidney against cisplatin nephrotoxicity as a possible useful agent to prevent and treat cisplatin-induced nephrotoxicity. [BMB Reports 2016; 49(5): 288-292]

Nonapoptotic cell death in acute kidney injury and transplantation

Acute tubular necrosis causes a loss of renal function, which clinically presents as acute kidney failure (AKI). The biochemical signaling pathways that trigger necrosis have been investigated in detail over the past 5 years. It is now clear that necrosis (regulated necrosis, RN) represents a genetically driven process that contributes to the pathophysiology of AKI. RN pathways such as necroptosis, ferroptosis, parthanatos, and mitochondrial permeability transition-induced regulated necrosis (MPT-RN) may be mechanistically distinct, and the relative contributions to overall organ damage during AKI in living organisms largely remain elusive. In a synchronized manner, some necrotic programs induce the breakdown of tubular segments and multicellular functional units, whereas others are limited to killing single cells in the tubular compartment. Importantly, the means by which a renal cell dies may have implications for the subsequent inflammatory response. In this review, the recent advances in the field of renal cell death in AKI and key enzymes that might serve as novel therapeutic targets will be discussed. As a consequence of the interference with RN, the immunogenicity of dying cells in AKI in renal transplants will be diminished, rendering inhibitors of RN indirect immunosuppressive agents.

Resveratrol attenuates acute kidney injury by inhibiting death receptor‑mediated apoptotic pathways in a cisplatin‑induced rat model

Acute kidney injury is a clinical syndrome characterized by a loss of renal function and acute tubular necrosis. Resveratrol exerts a wide range of pharmacological effects based on its anti-inflammatory, antioxidant and cytoprotective properties. The present study aimed to evaluate whether resveratrol attenuates acute kidney injury in a cisplatin-induced rat model and to investigate the potential mechanisms involved. Rats were randomly divided into four treatment groups: Control, cisplatin, resveratrol, and cisplatin plus resveratrol. Rats exposed to cisplatin displayed acute kidney injury, identified by analysis of renal function and histopathological observation. Resveratrol significantly ameliorated the increased serum creatinine, blood urea nitrogen, renal index and histopathological damage induced by cisplatin. Furthermore, compared with untreated control animals, cisplatin lead to significantly increased expression of Fas ligand, tumor necrosis factor-α (TNF-α), caspase-8 and Bcl-2 associated protein X apoptosis regulator (Bax), and decreased expression of anti-apoptosis regulators, BH3 interacting domain death agonist (BID) and B cell lymphoma 2 apoptosis regulator (Bcl-2). Administration of resveratrol significantly reversed the cisplatin-induced alteration in these apoptosis-associated proteins. In conclusion, these findings suggest that resveratrol attenuates cisplatin-induced acute kidney injury through inactivation of the death receptor-mediated apoptotic pathway, and may provide a new therapeutic strategy to ameliorate the process of acute kidney injury.

Excess sphingomyelin disturbs ATG9A trafficking and autophagosome closure

Sphingomyelin is an essential cellular lipid that traffics between plasma membrane and intracellular organelles until directed to lysosomes for SMPD1 (sphingomyelin phosphodiesterase 1)-mediated degradation. Inactivating mutations in the SMPD1 gene result in Niemann-Pick diseases type A and B characterized by sphingomyelin accumulation and severely disturbed tissue homeostasis. Here, we report that sphingomyelin overload disturbs the maturation and closure of autophagic membranes. Niemann-Pick type A patient fibroblasts and SMPD1-depleted cancer cells accumulate elongated and unclosed autophagic membranes as well as abnormally swollen autophagosomes in the absence of normal autophagosomes and autolysosomes. The immature autophagic membranes are rich in WIPI2, ATG16L1 and MAP1LC3B but display reduced association with ATG9A. Contrary to its normal trafficking between plasma membrane, intracellular organelles and autophagic membranes, ATG9A concentrates in transferrin receptor-positive juxtanuclear recycling endosomes in SMPD1-deficient cells. Supporting a causative role for ATG9A mistrafficking in the autophagy defect observed in SMPD1-deficient cells, ectopic ATG9A effectively reverts this phenotype. Exogenous C12-sphingomyelin induces a similar juxtanuclear accumulation of ATG9A and subsequent defect in the maturation of autophagic membranes in healthy cells while the main sphingomyelin metabolite, ceramide, fails to revert the autophagy defective phenotype in SMPD1-deficient cells. Juxtanuclear accumulation of ATG9A and defective autophagy are also evident in tissues of smpd1-deficient mice with a subsequent inability to cope with kidney ischemia-reperfusion stress. These data reveal sphingomyelin as an important regulator of ATG9A trafficking and maturation of early autophagic membranes.

Epoxyeicosatrienoic acid analogue mitigates kidney injury in a rat model of radiation nephropathy

Arachidonic acid is metabolized to epoxyeicosatrienoic acids (EETs) by CYP epoxygenases, and EETs are kidney protective in multiple pathologies. We determined the ability of an EET analogue, EET-A, to mitigate experimental radiation nephropathy. The kidney expression of the EET producing enzyme CYP2C11 was lower in rats that received total body irradiation (TBI rat) compared with non-irradiated control. At 12 weeks after TBI, the rats had higher systolic blood pressure and impaired renal afferent arteriolar function compared with control, and EET-A or captopril mitigated these abnormalities. The TBI rats had 3-fold higher blood urea nitrogen (BUN) compared with control, and EET-A or captopril decreased BUN by 40-60%. The urine albumin/creatinine ratio was increased 94-fold in TBI rats, and EET-A or captopril attenuated that increase by 60-90%. In TBI rats, nephrinuria was elevated 30-fold and EET-A or captopril decreased it by 50-90%. Renal interstitial fibrosis, tubular and glomerular injury were present in the TBI rats, and each was decreased by EET-A or captopril. We further demonstrated elevated renal parenchymal apoptosis in TBI rats, which was mitigated by EET-A or captopril. Additional studies revealed that captopril or EET-A mitigated renal apoptosis by acting on the p53/Fas/FasL (Fas ligand) apoptotic pathway. The present study demonstrates a novel EET analogue-based strategy for mitigation of experimental radiation nephropathy by improving renal afferent arteriolar function and by decreasing renal apoptosis.

Loss of α(E)-catenin promotes Fas mediated apoptosis in tubular epithelial cells

The aging kidney undergoes structural and functional alterations which make it more susceptible to drug-induced acute kidney injury (AKI). Previous studies in our lab have shown that the expression of α(E)-catenin is decreased in aged kidney and loss of α(E)-catenin potentiates AKI-induced apoptosis, but not necrosis, in renal tubular epithelial cells (NRK-52E cells). However, the specific apoptotic pathway underlying the increased AKI-induced cell death is not yet understood. In this study, cells were challenged with nephrotoxicant cisplatin to induce AKI. A ~5.5-fold increase in Fas expression in C2 (stable α(E)-catenin knockdown) relative to NT3 (non-targeted control) cells was seen. Increased caspase-8 and -9 activation was induced by cisplatin in C2 as compared to NT3 cells. In addition, decreased Bcl-2 expression and increased BID cleavage and cytochrome C release were detected in C2 cells after cisplatin challenge. Treating the cells with cisplatin, in combination with a Bcl-2 inhibitor, decreased the viability of NT3 cells to the same level as C2 cells after cisplatin. Furthermore, caspase-3/-7 activation is blocked by Fas, caspase-8, caspase-9 and pan-caspase inhibitors. These inhibitors also completely abolished the difference in viability between NT3 and C2 cells in response to cisplatin. These results demonstrate a Fas-mediated apoptotic signaling pathway that is enhanced by the age-dependent loss of α(E)-catenin in renal tubule epithelial cells.

Tubular cross talk in acute kidney injury: a story of sense and sensibility

The mammalian kidney is an organ composed of numerous functional units or nephrons. Beyond the filtering glomerulus of each nephron, various tubular segments with distinct populations of epithelial cells sequentially span the kidney from cortex to medulla. The highly organized folding of the tubules results in a spatial distribution that allows intimate contact between various tubular subsegments. This unique arrangement can promote a newly recognized type of horizontal epithelial-to-epithelial cross talk. In this review, we discuss the importance of this tubular cross talk in shaping the response of the kidney to acute injury in a sense and sensibility model. We propose that injury-resistant tubules such as S1 proximal segments and thick ascending limbs (TAL) can act as "sensors" and thus modulate the responsiveness or "sensibility" of the S2-S3 proximal segments to injury. We also discuss new findings that highlight the importance of tubular cross talk in regulating homeostasis and inflammation not only in the kidney, but also systemically.

Major pathways of polymyxin-induced apoptosis in rat kidney proximal tubular cells

Identifying the pathways involved in the apoptotic cell death that is associated with polymyxin-induced nephrotoxicity is crucial for the development of strategies to ameliorate this dose-limiting side effect and for the development of novel safer polymyxins. The primary aim of this study was to identify the major pathways which lead to polymyxin-induced apoptosis in cultured rat kidney proximal tubular cells (NRK-52E). Caspase-3, -8, and -9 were activated by polymyxin B treatment in a concentration-dependent manner. Concentration- and time-dependent expression of FasL and deformation of mitochondrial morphology were revealed following polymyxin B treatment. The proportion of cells with filamentous mitochondria (regular morphology) following an 8-h treatment with 1.0 mM polymyxin B was 56.2% ± 9.7% (n = 3). This was decreased to 30.7% ± 7.5% when the polymyxin B concentration was increased to 2.0 mM. The mitochondrial membrane potential (Δψm) decreased to 14.1% ± 2.9% in the cells treated with 1.0 mM polymyxin B for 24 h (n = 3) compared to that in the untreated control group. Concomitantly, concentration- and time-dependent production of mitochondrial superoxide was also observed. This study is the first to have demonstrated that polymyxin-induced apoptosis is mediated through both the death receptor and mitochondrial pathways in cultured renal tubular cells. It provides key information not only for the amelioration of polymyxin-induced nephrotoxicity but also for the discovery of novel safer polymyxin-like antibiotics against Gram-negative "superbugs."

Extracellular nucleotides from dying cells act as molecular signals to promote wound repair in renal tubular injury

Acute kidney injury (AKI) often correlates with poor prognosis and is followed by various severe unfavorable systemic outcomes. It is important to understand the pathophysiology of AKI for the development of novel therapeutic approaches toward promoting renal regeneration after injury. Recent studies have indicated that AKI-induced tubular cell death plays an active role in the onset of tissue regeneration; however, the mechanisms underlying renal tubular repair after injury have yet to be understood. In the present study, we explored molecules that might serve as "danger" signals in mediating tubular regeneration. Kidneys of rats systemically administered the nephrotoxicant cisplatin (to induce AKI) exhibited massive cell proliferation. The proportion of proliferating cells in the total cell distribution was highest in the outer stripe of the outer medulla coincided with where the tubular damage was the most severe in this study. This finding suggests that soluble factors may have been released from damaged cells to stimulate the proliferation of neighboring tubular epithelial cells. In elucidating the mechanism of dying cell-to-surviving cell communication using normal rat kidney NRK-52E epithelial cells, we found a significant increase in ATP levels in supernatants of these cells after the induction of cell death using ultraviolet irradiation. Furthermore, treatment of conditioned supernatants with apyrase or suramin, which inhibits purinergic signaling, resulted in significant decreases in cell proliferation and migration activities. These results demonstrate a novel role for extracellular nucleotides, probably as danger signals in aggravating tubular regeneration after AKI.

Immune cells in experimental acute kidney injury

Acute kidney injury (AKI) prolongs hospital stay and increases mortality in various clinical settings. Ischaemia-reperfusion injury (IRI), nephrotoxic agents and infection leading to sepsis are among the major causes of AKI. Inflammatory responses substantially contribute to the overall renal damage in AKI. Both innate and adaptive immune systems are involved in the inflammatory process occurring in post-ischaemic AKI. Proinflammatory damage-associated molecular patterns, hypoxia-inducible factors, adhesion molecules, dysfunction of the renal vascular endothelium, chemokines, cytokines and Toll-like receptors are involved in the activation and recruitment of immune cells into injured kidneys. Immune cells of both the innate and adaptive immune systems, such as neutrophils, dendritic cells, macrophages and lymphocytes contribute to the pathogenesis of renal injury after IRI, and some of their subpopulations also participate in the repair process. These immune cells are also involved in the pathogenesis of nephrotoxic AKI. Experimental studies of immune cells in AKI have resulted in improved understanding of the immune mechanisms underlying AKI and will be the foundation for development of novel diagnostic and therapeutic targets. This Review describes what is currently known about the function of the immune system in the pathogenesis and repair of ischaemic and nephrotoxic AKI.

Pathophysiology of cisplatin-induced acute kidney injury

Cisplatin and other platinum derivatives are the most widely used chemotherapeutic agents to treat solid tumors including ovarian, head and neck, and testicular germ cell tumors. A known complication of cisplatin administration is acute kidney injury (AKI). The nephrotoxic effect of cisplatin is cumulative and dose-dependent and often necessitates dose reduction or withdrawal. Recurrent episodes of AKI may result in chronic kidney disease. The pathophysiology of cisplatin-induced AKI involves proximal tubular injury, oxidative stress, inflammation, and vascular injury in the kidney. There is predominantly acute tubular necrosis and also apoptosis in the proximal tubules. There is activation of multiple proinflammatory cytokines and infiltration of inflammatory cells in the kidney. Inhibition of the proinflammatory cytokines TNF-α or IL-33 or depletion of CD4+ T cells or mast cells protects against cisplatin-induced AKI. Cisplatin also causes endothelial cell injury. An understanding of the pathogenesis of cisplatin-induced AKI is important for the development of adjunctive therapies to prevent AKI, to lessen the need for dose decrease or drug withdrawal, and to lessen patient morbidity and mortality.

Klotho has dual protective effects on cisplatin-induced acute kidney injury

Klotho protects the kidney from ischemia-reperfusion injury, but its effect on nephrotoxins is unknown. Here we determined whether Klotho protects the kidney from cisplatin toxicity. Cisplatin increased plasma creatinine and induced tubular injury, which were exaggerated in Klotho haplosufficient (Kl/+) and ameliorated in transgenic Klotho overexpressing (Tg-Kl) mice. Neutrophil gelatinase-associated lipocalin and active caspase-3 protein and the number of apoptotic cells in the kidney were higher in Kl/+ and lower in Tg-Kl compared with wild-type mice. Klotho suppressed basolateral uptake of cisplatin by the normal rat kidney cell line (NRK), an effect similar to cimetidine, a known inhibitor of organic cation transport (OCT). A decrease in cell surface and total OCT2 protein and OCT activity by Klotho was mimicked by β-glucuronidase. The Klotho effect was attenuated by β-glucuronidase inhibition. On the other hand, OCT2 mRNA was reduced by Klotho but not by β-glucuronidase. Moreover, cimetidine inhibited OCT activity but not OCT2 expression. Unlike cimetidine, Klotho reduced cisplatin-induced apoptosis from either the basolateral or apical side and even when added after NRK cells were already loaded with cisplatin. Thus, Klotho protects the kidney against cisplatin nephrotoxicity by reduction of basolateral uptake of cisplatin by OCT2 and a direct anti-apoptotic effect independent of cisplatin uptake. Klotho may be a useful agent to prevent and treat cisplatin-induced nephrotoxicity.

RIPK3-mediated necroptosis promotes donor kidney inflammatory injury and reduces allograft survival

Kidney transplant injury occurs with ischemia and alloimmunity. Members of the receptor interacting protein kinase family (RIPK1,3) are key regulators of "necroptosis," a newly recognized, regulated form of necrosis. Necroptosis and apoptosis death appear to be counterbalanced as caspase-8 inhibition can divert death from apoptosis to necrosis. Inhibition of necroptosis in donor organs to limit injury has not been studied in transplant models. In this study, necroptosis was triggered in caspase inhibited tubular epithelial cells (TEC) exposed to tumor necrosis factor alpha in vitro, while RIPK1 inhibition with necrostatin-1 or use of RIPK3(-/-) TEC, prevented necroptosis. In vivo, short hairpin RNA silencing of caspase-8 in donor B6 mouse kidneys increased necroptosis, enhanced high-mobility group box 1 release, reduced renal function and accelerated rejection when transplanted into BALB/c recipients. Using ethidium homodimer perfusion to assess necrosis in vivo, necrosis was abrogated in RIPK3(-/-) kidneys postischemia. Following transplantation, recipients receiving RIPK3(-/-) kidneys had longer survival (p = 0.002) and improved renal function (p = 0.03) when compared to controls. In summary, we show for the first time that RIPK3-mediated necroptosis in donor kidneys can promote inflammatory injury, and has a major impact on renal ischemia-reperfusion injury and transplant survival. We suggest inhibition of necroptosis in donor organs may similarly provide a major clinical benefit.

Two independent pathways of regulated necrosis mediate ischemia-reperfusion injury

Regulated necrosis (RN) may result from cyclophilin (Cyp)D-mediated mitochondrial permeability transition (MPT) and receptor-interacting protein kinase (RIPK)1-mediated necroptosis, but it is currently unclear whether there is one common pathway in which CypD and RIPK1 act in or whether separate RN pathways exist. Here, we demonstrate that necroptosis in ischemia-reperfusion injury (IRI) in mice occurs as primary organ damage, independent of the immune system, and that mice deficient for RIPK3, the essential downstream partner of RIPK1 in necroptosis, are protected from IRI. Protection of RIPK3-knockout mice was significantly stronger than of CypD-deficient mice. Mechanistically, in vivo analysis of cisplatin-induced acute kidney injury and hyperacute TNF-shock models in mice suggested the distinctness of CypD-mediated MPT from RIPK1/RIPK3-mediated necroptosis. We, therefore, generated CypD-RIPK3 double-deficient mice that are viable and fertile without an overt phenotype and that survived prolonged IRI, which was lethal to each single knockout. Combined application of the RIPK1 inhibitor necrostatin-1 and the MPT inhibitor sanglifehrin A confirmed the results with mutant mice. The data demonstrate the pathophysiological coexistence and corelevance of two separate pathways of RN in IRI and suggest that combination therapy targeting distinct RN pathways can be beneficial in the treatment of ischemic injury.

Programmed necrosis in acute kidney injury

Programmed cell death (PCD) had been widely used synonymously to caspase-mediated apoptosis until caspase-independent cell death was described. Identification of necrosis as a regulated process in ischaemic conditions has recently changed our understanding of PCD. At least three pathways of programmed necrosis (PN) have been identified. First, receptor-interacting protein kinase 3 (RIP3)-dependent necroptosis causes organ failure following stroke, myocardial infarction and renal ischaemia/reperfusion injury. Necroptosis can be mediated either by a large intracellular caspase-8-containing signalling complex called the ripoptosome or by the RIP1-/RIP3-containing necroptosome and is controlled by a caspase-8/FLICE inhibitory protein(long) heterodimer at least in the latter case. Second, mitochondrial permeability transition mediates apoptotic or necrotic stimuli and depends on the mitochondrial protein cyclophilin D. The third PN pathway involves the poly(ADP-ribose) polymerase-calpain axis that contributes to acute kidney injury (AKI). Preclinical interference with the PN pathways therefore raises expectations for the future treatment of ischaemic conditions. In this brief review, we aim to summarize the clinically relevant PCD pathways and to transfer the basic science data to settings of AKI. We conclude that pathologists were quite right to refer to ischaemic kidney injury as 'acute tubular necrosis'.

The RIP1-kinase inhibitor necrostatin-1 prevents osmotic nephrosis and contrast-induced AKI in mice

The pathophysiology of contrast-induced AKI (CIAKI) is incompletely understood due to the lack of an appropriate in vivo model that demonstrates reduced kidney function before administration of radiocontrast media (RCM). Here, we examine the effects of CIAKI in vitro and introduce a murine ischemia/reperfusion injury (IRI)-based approach that allows induction of CIAKI by a single intravenous application of standard RCM after injury for in vivo studies. Whereas murine renal tubular cells and freshly isolated renal tubules rapidly absorbed RCM, plasma membrane integrity and cell viability remained preserved in vitro and ex vivo, indicating that RCM do not induce apoptosis or regulated necrosis of renal tubular cells. In vivo, the IRI-based CIAKI model exhibited typical features of clinical CIAKI, including RCM-induced osmotic nephrosis and increased serum levels of urea and creatinine that were not altered by inhibition of apoptosis. Direct evaluation of renal morphology by intravital microscopy revealed dilation of renal tubules and peritubular capillaries within 20 minutes of RCM application in uninjured mice and similar, but less dramatic, responses after IRI pretreatment. Necrostatin-1 (Nec-1), a specific inhibitor of the receptor-interacting protein 1 (RIP1) kinase domain, prevented osmotic nephrosis and CIAKI, whereas an inactive Nec-1 derivate (Nec-1i) or the pan-caspase inhibitor zVAD did not. In addition, Nec-1 prevented RCM-induced dilation of peritubular capillaries, suggesting a novel role unrelated to cell death for the RIP1 kinase domain in the regulation of microvascular hemodynamics and pathophysiology of CIAKI.

Clinical use of biomarkers for toxicant-induced acute kidney injury

Toxicant-induced acute kidney injury (ToxAKI) causes substantial morbidity and retards drug development. ToxAKI is relatively underexplored compared with ischemia–reperfusion injury in clinical biomarker studies. We highlight the rationale for novel AKI biomarkers in management of ToxAKI, and review the contemporary evidence supporting their clinical use. Directly-acting nephrotoxins, such as cisplatin, aminoglycosides, vancomycin and radiocontrast, remain widely used and highlight how novel biomarkers can either improve the detection of changes in glomerular filtration rate or directly signal cellular injury and structural damage. Serum cystatin C has already improved clinical risk prediction and drug dosing although its clinical use for early diagnosis awaits validation. The use of novel functional and structural biomarkers to stage ToxAKI and aid prognosis requires robust validation and better understanding of the relationship between biomarkers, morbidity and mortality. Biomarkers that illustrate the probable mechanisms and phase of ToxAKI may guide mechanism-specific diagnosis and therapy.

Bee Venom Mitigates Cisplatin-Induced Nephrotoxicity by Regulating CD4(+)CD25(+)Foxp3(+) Regulatory T Cells in Mice

Cisplatin is used as a potent anticancer drug, but it often causes nephrotoxicity. Bee venom (BV) has been used for the treatment of various inflammatory diseases, and its renoprotective action was shown in NZB/W mice. However, little is known about whether BV has beneficial effects on cisplatin-induced nephrotoxicity and how such effects might be mediated. In the present study, the BV-injected group showed a significant increase in the population of Tregs in spleen. Although there was no significant difference in the numbers of Tregs 3 days after cisplatin injection between the BV- and PBS-injected groups, more migration of Tregs into the kidney was observed 6 hours after cisplatin administration in BV group than in PBS group. In addition, BV-injected mice showed reduced levels of serum creatinine, blood urea nitrogen, renal tissue damage, proinflammatory cytokines, and macrophage infiltration into the kidney 3 days after cisplatin administration. These renoprotective effects were abolished by the depletion of Tregs. The anticancer effect of repeated administrations of cisplatin was not affected by BV injection. These results suggest that BV has protective effects on cisplatin-induced nephrotoxicity in mice, at least in part, through the regulation of Tregs without a big influence on the antitumor effects of cisplatin.

Investigating mechanisms of chronic kidney disease in mouse models

Animal models of chronic kidney disease (CKD) are important experimental tools that are used to investigate novel mechanistic pathways and to validate potential new therapeutic interventions prior to pre-clinical testing in humans. Over the past several years, mouse CKD models have been extensively used for these purposes. Despite significant limitations, the model of unilateral ureteral obstruction (UUO) has essentially become the high-throughput in vivo model, as it recapitulates the fundamental pathogenetic mechanisms that typify all forms of CKD in a relatively short time span. In addition, several alternative mouse models are available that can be used to validate new mechanistic paradigms and/or novel therapies. Here, we review several models-both genetic and experimentally induced-that provide investigators with an opportunity to include renal functional study end-points together with quantitative measures of fibrosis severity, something that is not possible with the UUO model.

Renal function and genetic polymorphisms in pediatric heart transplant recipients

BACKGROUND

Common genetic variations influence rejection, infection, drug metabolism, and side effect profiles after pediatric heart transplantation. Reports in adults suggest that genetic background may influence post-transplant renal function. In this multicenter study, we investigated the association of genetic polymorphisms (GPs) in a panel of candidate genes on renal function in 453 pediatric heart transplant recipients.

METHODS

We performed genotyping for functional GPs in 19 candidate genes. Renal function was determined annually after transplantation by calculation of the estimated glomerular filtration rate (eGFR). Mixed-effects and Cox proportional hazard models were used to assess recipient characteristics and the effect of GPs on longitudinal eGFR and time to eGFR < 60 mL/min/1.73m(2).

RESULTS

Mean age at transplantation was 6.2 ± 6.1 years. Mean follow-up was 5.1 ± 2.5 years. Older age at transplant and black race were independently associated with post-transplant renal dysfunction. Univariate analyses showed FASL (C-843T) T allele (p = 0.014) and HO-1 (A326G) G allele (p = 0.0017) were associated with decreased renal function. After adjusting for age and race, these associations were attenuated (FASL, p = 0.075; HO-1, p = 0.053). We found no associations of other GPs with post-transplant renal function, including GPs in TGFβ1, CYP3A5, ABCB1, and ACE.

CONCLUSIONS

In this multicenter, large, sample of pediatric heart transplant recipients, we found no strong associations between GPs in 19 candidate genes and post-transplant renal function. Our findings contradict reported associations of CYP3A5 and TGFβ1 with renal function and suggest that genotyping for these GPs will not facilitate individualized immunosuppression for the purpose of protecting renal function after pediatric heart transplantation.

Dichotomy between RIP1- and RIP3-mediated necroptosis in tumor necrosis factor-α-induced shock

Tumor necrosis factor receptor (TNFR) signaling may result in survival, apoptosis or programmed necrosis. The latter is called necroptosis if the receptor-interacting protein 1 (RIP1) inhibitor necrostatin-1 (Nec-1) or genetic knockout of RIP3 prevents it. In the lethal mouse model of TNFα-mediated shock, addition of the pan-caspase inhibitor zVAD-fmk (zVAD) accelerates time to death. Here, we demonstrate that RIP3-deficient mice are protected markedly from TNFα-mediated shock in the presence and absence of caspase inhibition. We further show that the fusion protein TAT-crmA, previously demonstrated to inhibit apoptosis, also prevents necroptosis in L929, HT29 and FADD-deficient Jurkat cells. In contrast to RIP3-deficient mice, blocking necroptosis by Nec-1 or TAT-crmA did not protect from TNFα/zVAD-mediated shock, but further accelerated time to death. Even in the absence of caspase inhibition, Nec-1 application led to similar kinetics. Depletion of macrophages, natural killer (NK) cells, granulocytes or genetic deficiency for T lymphocytes did not influence this model. Because RIP3-deficient mice are known to be protected from cerulein-induced pancreatitis (CIP), we applied Nec-1 and TAT-crmA in this model and demonstrated the deterioration of pancreatic damage upon addition of these substances. These data highlight the importance of separating genetic RIP3 deficiency from RIP1 inhibition by Nec-1 application in vivo and challenge the current definition of necroptosis.

Recognition-dependent signaling events in response to apoptotic targets inhibit epithelial cell viability by multiple mechanisms: implications for non-immune tissue homeostasis

Apoptosis allows for the removal of damaged, aged, and/or excess cells without harm to surrounding tissue. To accomplish this, cells undergoing apoptosis acquire new activities that enable them to modulate the fate and function of nearby cells. We have shown that receptor-mediated recognition of apoptotic versus necrotic target cells by viable kidney proximal tubular epithelial cells (PTEC) modulates the activity of several signaling pathways critically involved in regulation of proliferation and survival. Generally, apoptotic and necrotic targets have opposite effects with apoptotic targets inhibiting and necrotic targets stimulating the activity of these pathways. Here we explore the consequences of these signaling differences. We show that recognition of apoptotic targets induces a profound decrease in PTEC viability through increased responder cell death and decreased proliferation. In contrast, necrotic targets promote viability through decreased death and increased proliferation. Both target types mediate their effects through a network of Akt-dependent and -independent events. Apoptotic targets modulate Akt-dependent viability in part through a reduction in cellular β-catenin and decreased inactivation of Bad. In contrast, Akt-independent modulation of viability occurs through activation of caspase-8, suggesting that death receptor-dependent pathways are involved. Apoptotic targets also activate p38, which partially protects responders from target-induced death. The response of epithelial cells varies depending on their tissue origin. Some cell lines, like PTEC, demonstrate decreased viability, whereas others (e.g. breast-derived) show increased viability. By acting as sentinels of environmental change, apoptotic targets allow neighboring cells, especially non-migratory epithelial cells, to monitor and potentially adapt to local stresses.

Rip1 (receptor-interacting protein kinase 1) mediates necroptosis and contributes to renal ischemia/reperfusion injury

Loss of kidney function in renal ischemia/reperfusion injury is due to programmed cell death, but the contribution of necroptosis, a newly discovered form of programmed necrosis, has not been evaluated. Here, we identified the presence of death receptor-mediated but caspase-independent cell death in murine tubular cells and characterized it as necroptosis by the addition of necrostatin-1, a highly specific receptor-interacting protein kinase 1 inhibitor. The detection of receptor-interacting protein kinase 1 and 3 in whole-kidney lysates and freshly isolated murine proximal tubules led us to investigate the contribution of necroptosis in a mouse model of renal ischemia/reperfusion injury. Treatment with necrostatin-1 reduced organ damage and renal failure, even when administered after reperfusion, resulting in a significant survival benefit in a model of lethal renal ischemia/reperfusion injury. Unexpectedly, specific blockade of apoptosis by zVAD, a pan-caspase inhibitor, did not prevent the organ damage or the increase in urea and creatinine in vivo in renal ischemia/reperfusion injury. Thus, necroptosis is present and has functional relevance in the pathophysiological course of ischemic kidney injury and shows the predominance of necroptosis over apoptosis in this setting. Necrostatin-1 may have therapeutic potential to prevent and treat renal ischemia/reperfusion injury.

Mice with defective Fas ligand are protected from crescentic glomerulonephritis

Fas ligand is a well-known inducer of apoptosis in cells expressing its receptor Fas; it also prevents autoimmunity by inducing apoptosis of activated T cells. However, Fas ligand also mediates non-apoptotic functions involving inflammatory cell migration and cytokine responses. We sought here to study the role of Fas ligand in nephrotoxic nephritis, a model of crescentic glomerulonephritis, using generalized lymphoproliferative disorder (GLD) mice on a C57BL/6 background, which have defective Fas ligand and display only mild autoimmunity. These mice were significantly protected from glomerular crescent formation, glomerular thrombosis, renal impairment, and albuminuria 15 days after the induction of glomerulonephritis in comparison with wild-type mice. There were a reduced number of apoptotic cells in the glomeruli of nephritic GLD mice but no defect in their antibody responses or splenocyte proliferation at 15 days following the induction of glomerulonephritis. Bone marrow transplantation from wild-type mice restored disease susceptibility to GLD mice; however, wild-type mice were not protected when transplanted with bone marrow from GLD mice. Mesangial cells express Fas ligand in vitro, and these cells isolated from GLD mice produced lower amounts of monocyte chemoattractive protein-1 following interleukin-1 stimulation compared with cells from wild-type mice. Thus, Fas ligand-defective mice are protected from nephrotoxic nephritis, a disease in which both circulating and intrinsic renal cells appear to have a role.

Am I my brother's keeper?: fratricide in the kidney

Experimental acute kidney injury (AKI) is accompanied by the death of renal tubule epithelial cells, necrosis and apoptosis of the terminal portion of the proximal tubule, and apoptosis in the distal nephron. While immune competent cells invading the kidney play a role in such cell death, intervention in these processes only partially ameliorates the extent of cell death. Given the results of Linkermann et al. in this issue of KI, an epithelium-derived component of immune mediated cell death must now be strongly considered.