Pathogenesis Of Sepsis-associated Acute Kidney Injury Research Articles

Circ_001653 alleviates sepsis associated-acute kidney injury by recruiting BUD13 to regulate KEAP1/NRF2/HO-1 signaling pathway

BackgroundThe kidney is exceptionally vulnerable during sepsis, often resulting in sepsis-associated acute kidney injury (SA-AKI), a condition that not only escalates morbidity but also significantly raises sepsis-related mortality rates. Circular RNA circ_001653 has been previously reported to be upregulated in the serum of SA-AKI patients, while the role and underlying mechanism of circ_001653 in SA-AKI remains unknown. In this study, we aimed to explore the functional role and the molecular mechanism of circ_001653 in the pathogenesis of SA-AKI.MethodsLPS-stimulated HK-2 cells and ligation and perforation of cecum (CLP)-induced rats were used as in vitro and in vivo models of SA-AKI. The target gene expression levels were measured using qRT-PCR and western blot. Renal function (BUN, sCr, uNGAL, and uKIM-1), and renal pathological changes were detected in septic mice. TUNEL and EdU assays were conducted to measure apoptosis and proliferation rates in vitro. DCFH-DA staining was used to detect ROS levels in vitro and in vivo. Oxidative stress markers (SOD, GSH-Px, MDA, and SOD), and inflammation markers (IL-1β, IL-6, and TNF-α) were determined using commercial kits both in vitro and in vivo. Additionally, gain-and-loss-of-function assays and mechanistic experiments were conducted to explore the regulatory role of circ_001653 in SA-AKI pathogenesis.ResultsData showed that circ_001653 expression was high in LPS-stimulated HK-2 cells and CLP-induced rat renal tissue and was mainly localized in the cytoplasm. Notably, circ_001653 silencing alleviated SA-AKI by reducing apoptosis and alleviating oxidative stress and inflammation in HK-2 cells and renal tissue of rats. Mechanistically, it was found that circ_001653 alleviated SA-AKI by recruiting BUD13 to activate the KEAP1/Nrf2/HO-1 signaling pathway.ConclusionsTo summarize, our study is the first to reveal elevated expression of circ_001653 in sepsis-associated AKI, and its downregulation effectively attenuates AKI by reducing apoptosis, inflammation, and oxidative stress. Mechanistically, circ_001653 exerts its effects by recruiting BUD13 to activate the KEAP1/Nrf2/HO-1 signaling pathway. These findings suggest circ_001653 as a potential therapeutic target for the drug development of sepsis-associated AKI.

Sepsis-Associated Acute Kidney Injury: Where Are We Now?

Worldwide, sepsis is a well-recognized cause of death. Acute kidney injury (AKI) may be related to sepsis in up to 70% of AKI cases. Sepsis-associated AKI (SA-AKI) is defined as the presence of AKI according to the Kidney Disease: Improving Global Outcomes criteria in the context of sepsis. SA-AKI is categorized into early, which presents during the first 48 h of sepsis, and late, presenting between 48 h and 7 days of sepsis. SA-AKI is associated with a worse prognosis among patients with sepsis. However, there are different SA-AKI phenotypes as well as different pathophysiological pathways of SA-AKI. The aim of this review is to provide an updated synopsis of the pathogenetic mechanisms underlying the development of SA-AKI as well as to analyze its different phenotypes and prognosis. In addition, potential novel diagnostic and prognostic biomarkers as well as therapeutic approaches are discussed. A plethora of mechanisms are implicated in the pathogenesis of SA-AKI, including inflammation and metabolic reprogramming during sepsis; various types of cell death such as apoptosis, necroptosis, pyroptosis and ferroptosis; autophagy and efferocytosis; and hemodynamic changes (macrovascular and microvascular dysfunction). Apart from urine output and serum creatinine levels, which have been incorporated in the definition of AKI, several serum and urinary diagnostic and prognostic biomarkers have also been developed, comprising, among others, interleukins 6, 8 and 18, osteoprotegerin, galectin-3, presepsin, cystatin C, NGAL, proenkephalin A, CCL-14, TIMP-2 and L-FABP as well as biomarkers stemming from multi-omics technologies and machine learning algorithms. Interestingly, the presence of long non-coding RNAs (lncRNAs) as well as microRNAs (miRNAs), such as PlncRNA-1, miR-22-3p, miR-526b, LncRNA NKILA, miR-140-5p and miR-214, which are implicated in the pathogenesis of SA-AKI, may also serve as potential therapeutic targets. The combination of omics technologies represents an innovative holistic approach toward providing a more integrated view of the molecular and physiological events underlying SA-AKI as well as for deciphering unique and specific phenotypes. Although more evidence is still necessary, it is expected that the incorporation of integrative omics may be useful not only for the early diagnosis and risk prognosis of SA-AKI, but also for the development of potential therapeutic targets that could revolutionize the management of SA-AKI in a personalized manner.

Critically ill patients with acute kidney injury: clinical determinants and post-mortem histology.

Acute kidney injury (AKI) requiring renal replacement therapy (RRT) in the intensive care unit (ICU) portends a poor prognosis. We aimed to better characterize predictors of survival and the mechanism of kidney failure in these patients. This was a retrospective observational study using clinical and radiological electronic health records, analysed by univariable and multivariable binary logistic regression. Histopathological examination of post-mortem renal tissue was performed. Among 157 patients with AKI requiring RRT, higher serum creatinine at RRT initiation associated with increased ICU survival [odds ratio (OR) 0.33, 95% confidence interval (CI) 0.17-0.62, P=.001]; however, muscle mass (a marker of frailty) interacted with creatinine (P=.02) and superseded creatinine as a predictor of survival (OR 0.26, 95% CI 0.08-0.82; P=.02). Achieving lower cumulative fluid balance (mL/kg) predicted ICU survival (OR 1.01, 95% CI 1.00-1.01, P<.001), as supported by sensitivity analyses showing improved ICU survival with the use of furosemide (OR 0.40, 95% CI 0.18-0.87, P=.02) and increasing net ultrafiltration (OR 0.97, 95% CI 0.95-0.99, P=.02). A urine output of >500 mL/24 h strongly predicted successful liberation from RRT (OR 0.125, 95% CI 0.05-0.35, P<.001). Post-mortem reports were available for 32 patients; clinically unrecognized renal findings were described in 6 patients, 1 of whom had interstitial nephritis. Experimental staining of renal tissue from patients with sepsis-associated AKI (S-AKI) showed glomerular loss of synaptopodin (P=.02). Confounding of creatinine by muscle mass undermines its use as a marker of AKI severity in clinical studies. Volume management and urine output are key determinants of outcome. Loss of synaptopodin implicates glomerular injury in the pathogenesis of S-AKI.

Erythropoietin promotes energy metabolism to improve LPS-induced injury in HK-2 cells via SIRT1/PGC1-α pathway.

Acute kidney injury (AKI) is one of frequent complications of sepsis with high mortality. Mitochondria is the center of energy metabolism participating in the pathogenesis of sepsis-associated AKI, and SIRT1/PGC1-α signaling pathway plays a crucial role in the modulation of energy metabolism. Erythropoietin (EPO) exerts protective functions on chronic kidney disease. We aimed to assess the effects of EPO on cell damage and energy metabolism in a cell model of septic AKI. Renal tubular epithelial cells HK-2 were treated with LPS and human recombinant erythropoietin (rhEPO). Cell viability was detected by CCK-8 and mitochondrial membrane potential was determined using JC-1 fluorescent probe. Then the content of ATP, ADP and NADPH, as well as lactic acid, were measured for the assessment of energy metabolism. Oxidative stress was evaluated by detecting the levels of ROS, MDA, SOD and GSH. Pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β, were measured with ELISA. Moreover, qRT-PCR and western blot were performed to detect mRNA and protein expressions. shSIRT1 was used to knockdown SIRT1, while EX527 and SR-18292 were applied to inhibit SIRT1 and PGC1-α, respectively, to investigate the regulatory mechanism of rhEPO on inflammatory injury and energy metabolism. In LPS-exposed HK-2 cells, rhEPO attenuated cell damage, inflammation and abnormal energy metabolism, as indicated by the elevated cell viability, the inhibited oxidative stress, cell apoptosis and inflammation, as well as the increased mitochondrial membrane potential and energy metabolism. However, these protective effects induced by rhEPO were reversed after SIRT1 or PGC1-α inhibition. EPO activated SIRT1/PGC1-α pathway to alleviate LPS-induced abnormal energy metabolism and cell damage in HK-2 cells. Our study suggested that rhEPO played a renoprotective role through SIRT1/PGC1-α pathway, which supported its therapeutic potential in septic AKI.

Transcription factor nuclear factor erythroid 2 p45-related factor 2 (NRF2) ameliorates sepsis-associated acute kidney injury by maintaining mitochondrial homeostasis and improving the mitochondrial function.

Mitochondrial dysfunction has a role in sepsis-associated acute kidney injury (S-AKI), so the restoration of normal mitochondrial homeostasis may be an effective treatment strategy. Transcription factor nuclear factor erythroid 2 p45-related factor 2 (NRF2) is a main regulator of cell-redox homeostasis, and recent studies reported that NRF2 activation helped to preserve mitochondrial morphology and function under conditions of stress. However, the role of NRF2 in the process of S-AKI is still not well understood. The present study investigated whether NRF2 regulates mitochondrial homeostasis and influences mitochondrial function in S-AKI. We demonstrated activation of NRF2 in an in vitro model: lipopolysaccharide (LPS) challenge of ductal epithelial cells of rat renal tubules (NRK-52e cells), and an in vivo model: cecal ligation and puncture (CLP) of rats. Overexpression of NRF2 attenuated oxidative stress, apoptosis, and the inflammatory response; enhanced mitophagy and mitochondrial biogenesis; and mitigated mitochondrial damage in the in vitro model. In vivo experiments showed that rats treated with an NRF2 agonist had higher adenosine triphosphate (ATP) levels, lower blood urea nitrogen and creatinine levels, fewer renal histopathological changes, and higher expression of mitophagy-related proteins [PTEN-induced putative kinase 1 (PINK1), parkin RBR E3 ubiquitin protein ligase (PRKN), microtubule-associated protein 1 light chain 3 II (LC3 II)] and mitochondrial biogenesis-related proteins [peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1α) and mitochondrial transcription factor A (TFAM)]. Electron microscopy of kidney tissues showed that mitochondrial damage was alleviated by treatment with an NRF2 agonist, and the opposite response occurred upon treatment with an NRF2 antagonist. Overall, our findings suggest that mitochondria have an important role in the pathogenesis of S-AKI, and that NRF2 activation restored mitochondrial homeostasis and function in the presence of this disease. This mitochondrial pathway has the potential to be a novel therapeutic target for the treatment of S-AKI.

Research progress of microRNAs in sepsis-associated acute kidney injury

Sepsis is a life-threatening organ dysfunction syndrome caused by the host's maladjusted response to infection, and is one of the important causes of acute kidney injury (AKI). Sepsis-associated acute kidney injury (SA-AKI) has a high incidence, poor prognosis and high mortality. The pathogenesis of SA-AKI is very complex, and its pathogenesis has not been fully elucidated. Therefore, finding effective biomarkers for early diagnosis, treatment, disease development and prognosis of SA-AKI is an urgent clinical problem.

Calcium dobesilate alleviates renal dysfunction and inflammation by targeting nuclear factor kappa B (NF-κB) signaling in sepsis-associated acute kidney injury

ABSTRACT Acute kidney injury (AKI) is a serious complication of sepsis that increases mortality and the risk of progression to chronic kidney disease. Oxidative stress and apoptosis are reported to exert critical function in the pathogenesis of sepsis-associated AKI. Calcium dobesilate (CaD) was reported to play a protective role in renal diseases. Therefore, we explored the antioxidant effect and potential mechanism of CaD in lipopolysaccharide (LPS)-induced AKI in mice. We evaluated renal function (blood urea nitrogen (BUN) and serum creatinine (SCr)), histopathology, oxidative stress (superoxide dismutase (SOD) and malondialdehyde (MDA)), inflammation cytokines, and apoptosis in kidneys of mice. The effect of CaD on NF-κB signaling was evaluated by Western blot. Our findings showed that CaD alleviated renal dysfunction and kidney injury, and also reversed upregulated MDA concentration and reduced SOD enzyme activity in AKI mice. Moreover, LPS-induced inflammatory response was attenuated by CaD. CaD treatment also reduced the apoptosis evoked by LPS. Additionally, CaD downregulated phosphorylation of nuclear factor kappa B (NF-κB) signaling components in LPS mice. Conclusively, CaD alleviates renal dysfunction and inflammation by targeting NF-κB signaling in sepsis-associated AKI.

Long Non-coding RNA MEG3 Promotes Renal Tubular Epithelial Cell Pyroptosis by Regulating the miR-18a-3p/GSDMD Pathway in Lipopolysaccharide-Induced Acute Kidney Injury.

Background and Objective: Acute kidney injury (AKI) is a complication of sepsis. Pyroptosis of gasdermin D (GSDMD)-mediated tubular epithelial cells (TECs) play important roles in pathogenesis of sepsis-associated AKI. Long non-coding RNA (lncRNA) maternally expressed gene 3 (MEG3), an imprinted gene involved in tumorigenesis, is implicated in pyroptosis occurring in multiple organs. Herein, we investigated the role and mechanisms of MEG3 in regulation of TEC pyroptosis in lipopolysaccharide (LPS)-induced AKI.Materials and Methods: Male C57BL/6 mice and primary human TECs were treated with LPS for 24 h to establish the animal and cell models, respectively, of sepsis-induced AKI. Renal function was assessed by evaluation of serum creatinine and urea levels. Renal tubule injury score was assessed by Periodic acid-Schiff staining. Renal pyroptosis was assessed by evaluating expression of caspase-1, GSDMD, and inflammatory factors IL-1β and IL-18. Cellular pyroptosis was assessed by analyzing the release rate of LDH, expression of IL-1β, IL-18, caspase-1, and GSDMD, and using EtBr and EthD2 staining. MEG3 expression in renal tissues and cells was detected using RT-qPCR. The molecular mechanisms of MEG3 in LPS-induced AKI were assessed through bioinformatics analysis, RNA-binding protein immunoprecipitation, dual luciferase reporter gene assays, and a rescue experiment.Results: Pyroptosis was detected in both LPS-induced animal and cell models, and the expression of MEG3 in these models was significantly up-regulated. MEG3-knockdown TECs treated with LPS showed a decreased number of pyroptotic cells, down-regulated secretion of LDH, IL-1β, and IL-18, and decreased expression of GSDMD, compared with those of controls; however, there was no difference in the expression of caspase-1 between MEG3 knockdown cells and controls. Bioinformatics analysis screened out miR-18a-3P, and further experiments demonstrated that MEG3 controls GSDMD expression by acting as a ceRNA for miR-18a-3P to promote TECs pyroptosis.Conclusion: Our study demonstrates that lncRNA MEG3 promoted renal tubular epithelial pyroptosis by regulating the miR-18a-3p/GSDMD pathway in LPS-induced AKI.

Galectin-3 in septic acute kidney injury: a translational study

BackgroundGalectin-3 (Gal-3) is a pleiotropic glycan-binding protein shown to be involved in sepsis and acute kidney injury (AKI). However, its role has never been elucidated in sepsis-associated AKI (S-AKI). We aimed to explore Gal-3’s role and its potential utility as a therapeutic target in S-AKI.MethodsIn 57 patients admitted to the intensive care unit (ICU) with sepsis, serum Gal-3 was examined as a predictor of ICU mortality and development of AKI. In a rat model of S-AKI induced by cecal ligation and puncture (CLP), 7-day mortality and serum Gal-3, Interleukin-6 (IL-6), and creatinine were examined at 2, 8, and 24 hours (h) post-CLP. Two experimental groups received the Gal-3 inhibitor modified citrus pectin (P-MCP) at 400 mg/kg/day and 1200 mg/kg/day, while the control group received water only (n = 18 in each group).ResultsAmong 57 patients, 27 developed AKI and 8 died in the ICU. Serum Gal-3 was an independent predictor of AKI (OR = 1.2 [95% CI 1.1–1.4], p = 0.01) and ICU mortality (OR = 1.4 [95% CI 1.1–2.2], p = 0.04) before and after controlling for age, AKI, and acute physiology and chronic health evaluation (APACHE II) score. In the CLP rat experiment, serum Gal-3 peaked earlier than IL-6. Serum Gal-3 was significantly lower in both P-MCP groups compared to control at 2 h post-CLP (400 mg: p = 0.003; 1200 mg: p = 0.002), and IL-6 was significantly lower in both P-MCP groups at all time points with a maximum difference at 24 h post-CLP (400 mg: p = 0.015; 1200 mg: p = 0.02). In the Gal-3 inhibitor groups, 7-day mortality was significantly reduced from 61% in the control group to 28% (400 mg P-MCP: p = 0.03) and 22% (1200 mg P-MCP: p = 0.001). Rates of AKI per RIFLE criteria were significantly reduced from 89% in the control group to 44% in both P-MCP groups (400 mg: p = 0.007; 1200 mg: p = 0.007).ConclusionsThis translational study demonstrates the importance of Gal-3 in the pathogenesis of S-AKI, and its potential utility as a therapeutic target.Graphic abstract

Using best subset regression to identify clinical characteristics and biomarkers associated with sepsis-associated acute kidney injury.

Sepsis-associated acute kidney injury (AKI) is a complex clinical disorder associated with inflammation, endothelial dysfunction, and dysregulated coagulation. With standard regression methods, collinearity among biomarkers may lead to the exclusion of important biological pathways in a single final model. Best subset regression is an analytic technique that identifies statistically equivalent models, allowing for more robust evaluation of correlated variables. Our objective was to identify common clinical characteristics and biomarkers associated with sepsis-associated AKI. We enrolled 453 septic adults within 24 h of intensive care unit admission. Using best subset regression, we evaluated for associations using a range of models consisting of 1-38 predictors (composed of clinical risk factors and plasma and urine biomarkers) with AKI as the outcome [defined as a serum creatinine (SCr) increase of ≥0.3 mg/dL within 48 h or ≥1.5× baseline SCr within 7 days]. Two hundred ninety-seven patients had AKI. Five-variable models were found to be of optimal complexity, as the best subset of five- and six-variable models were statistically equivalent. Within the subset of five-variable models, 46 permutations of predictors were noted to be statistically equivalent. The most common predictors in this subset included diabetes, baseline SCr, angiopoetin-2, IL-8, soluble tumor necrosis factor receptor-1, and urine neutrophil gelatinase-associated lipocalin. The models had a c-statistic of ∼0.70 (95% confidence interval: 0.65-0.75). In conclusion, using best subset regression, we identified common clinical characteristics and biomarkers associated with sepsis-associated AKI. These variables may be especially relevant in the pathogenesis of sepsis-associated AKI.

Long Noncoding RNA TCONS_00016406 Attenuates Lipopolysaccharide-Induced Acute Kidney Injury by Regulating the miR-687/PTEN Pathway.

Acute kidney injury (AKI) is a common and serious complication of sepsis accompanied by kidney dysfunction resulting from various etiologies and pathophysiological processes. Unfortunately, there is currently no ideal therapeutic strategy for AKI. Numerous studies have confirmed that long noncoding RNAs (lncRNAs) play important regulatory roles in the pathogenesis of sepsis-associated AKI. In this study, lncRNA TCONS_00016406 (termed lncRNA 6406), a novel lncRNA identified by using TargetScan, was significantly downregulated in the kidney tissues of mice with sepsis-associated AKI. This study aimed to explore the role of lncRNA 6406 in lipopolysaccharide (LPS)-induced AKI and its potential molecular mechanism. The models of sepsis-induced AKI (called LPS-induced AKI models) in mice and cell lines were established with male C57BL/6 mice and renal tubular epithelial (PTEC) cells, respectively. Twenty-four hours after LPS administration, kidneys and cell samples were collected after various treatments to examine the alterations in the lncRNA 6406 levels and to evaluate the effects on LPS-induced inflammation, oxidative stress, and apoptosis through real-time PCR (RT-PCR) analysis, western blotting, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. The results revealed that lncRNA 6406 could significantly attenuate LPS-induced AKI, as shown by the alleviation of inflammation, the suppression of oxidative stress and the inhibition of apoptosis. Mechanistically, a luciferase reporter assay and additional research showed that lncRNA 6406 functioned as a ceRNA to sponge miRNA-687, thereby modulating LPS-stimulated AKI by targeting the miR-687/PTEN axis; thus, this study presents a novel therapeutic strategy or sepsis-associated AKI.

Protective Role of AMPK in Sepsis‐Associated AKI

Acute kidney injury (AKI) significantly contributes to the morbidity and the mortality in critically ill patients. AKI is also an independent risk factor for developing and progression of chronic kidney disease. Effective therapeutic strategies for AKI are limited due to incomplete understanding its pathogenesis. In most eukaryotic cells, AMP‐activated protein kinase (AMPK) functions as a principle sensory protein, which monitors the cellular energy status and mediates metabolic adaptation through increasing ATP level and regulating mitochondrial hemostasis. Sepsis is the most common cause of AKI. Using a mouse s‐AKI model induced by cecal ligation and puncture (CLP), we investigated the role of AMPK in the pathogenesis of sepsis‐associated AKI (s‐AKI) and its underlying mechanisms.The GFR was measured by FITC inulin clearance method. At 24 hours post‐injury, the GFR was significantly reduced in CLP mice (345±19 vs. 155±35 uL/min; p=0.004). Treatments with AICAR (an AMPK activator) 24 hours prior to CLP significantly improved the GFR. Additionally, mitochondrial function was evaluated using Seahorse. A significantly increased maximum respiration rate observed in CLP mice was abolished by Pre‐treatment with AICAR. Moreover, mitochondrial DNA copy number and expression of PGC1α, a master regulator of mitochondrial biogenesis were initially increased at 4h’ post CLP injury; then significantly decreased at 24h’ post‐injury, suggesting mitochondrial volume and mitochondrial biogenesis were increased shortly after the injury but eventually dropped. Pre‐treatment with AICAR prevented these alterations at both 4 and 24 hours post CLP. Finally, an elevation of glycolysis, a less efficient pathway compared to oxidative phosphorylation, was observed in response to CLP. This elevation of glycolysis was prevented in mice pre‐treated with AICAR, suggesting activation of AMPK may prevent CLP‐induced alteration of mitochondrial metabolism. Increased glycolysis was not seen at 4h’ post CLP surgery (Figure 1).Our findings provide novel evidence supporting the critical role of activation of AMPK signaling pathway in preventing development and/or progression of AKI induced by sepsis. Activation of AKI may prevent renal dysfunction in s‐AKI through regulating mitochondrial function, biogenesis, and metabolism. AMPK and its signaling pathway may serve as novel therapeutic targets in s‐AKI.Support or Funding InformationNIH R01DK107852VA Merit Review BX002175NIH R03 DK101841This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hydrogen Sulfide Attenuates LPS-Induced Acute Kidney Injury by Inhibiting Inflammation and Oxidative Stress.

In order to investigate the protective mechanism of hydrogen sulfide (H2S) in sepsis-associated acute kidney injury (SA-AKI), ten AKI patients and ten healthy controls were enrolled. In AKI patients, levels of creatinine (Cre), urea nitrogen (BUN), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), and myeloperoxidase (MPO) activity as well as concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2) were significantly increased compared with those of controls. However, plasma level of H2S decreased and was linearly correlated with levels of Cre and BUN. After that, an AKI mouse model by intraperitoneal lipopolysaccharide (LPS) injection was constructed for in vivo study. In AKI mice, H2S levels decreased with the decline of 3-MST activity and expression; similar changes were observed in other indicators mentioned above. However, the protein expressions of TLR4, NLRP3, and caspase-1 in mice kidney tissues were significantly increased 6 h after LPS injection. NaHS could improve renal function and kidney histopathological changes, attenuate LPS-induced inflammation and oxidative stress, and inhibit expressions of TLR4, NLRP3, and caspase-1. Our study demonstrated that endogenous H2S is involved in the pathogenesis of SA-AKI, and exogenous H2S exerts protective effects against LPS-induced AKI by inhibiting inflammation and oxidative stress via the TLR4/NLRP3 signaling pathway.