Norepinephrine exacerbates renal medullary hypoxia in experimental septic acute kidney injury. Here we examined whether dexmedetomidine, an alpha 2-adrenergic agonist, can restore vasopressor responsiveness, decrease the requirement for norepinephrine and attenuate medullary hypoxia in ovine gram-negative sepsis. Sheep were instrumented with pulmonary and renal artery flow probes, and laser Doppler and oxygen-sensing probes in the renal cortex and medulla. Conscious sheep received an infusion of live Escherichia coli for 30 hours. Eight sheep in each group were randomized to receive norepinephrine, norepinephrine with dexmedetomidine, dexmedetomidine alone or saline vehicle, from 24-30 hours of sepsis. Sepsis significantly reduced the average mean arterial pressure (84 to 67 mmHg), average renal medullary perfusion (1250 to 730 perfusion units), average medullary tissue pO(2) (40 to 21 mmHg) and creatinine clearance (2.50 to 0.78 mL/Kg/min). Norepinephrine restored baseline mean arterial pressure (to 83 mmHg) but worsened medullary hypoperfusion (to 330 perfusion units) and medullary hypoxia (to 9 mmHg). Dexmedetomidine (0.5 mu g/kg/h) co-administration significantly reduced the norepinephrine dose (0.8 to 0.4 mu g/kg/min) required to restore baseline mean arterial pressure, attenuated medullary hypoperfusion (to 606 perfusion units), decreased medullary tissue hypoxia (to 29 mmHg), and progressively increased creatinine clearance (to 1.8 mL/Kg/min). Compared with vehicle time-control, dexmedetomidine given alone significantly prevented the temporal reduction in mean arterial pressure, but had no significant effects on medullary perfusion and oxygenation or creatinine clearance. Thus, in experimental septic acute kidney injury, dexmedetomidine reduced norepinephrine requirements, attenuated its adverse effects on the renal medulla, and maintained renal function.
Inflammation and tubular cell death are the hallmarks of acute kidney injury. However, the precise mechanism underlying these effects has not been fully elucidated. Here we tested whether caspase-11, an inflammatory member of the caspase family, was increased in cisplatin or ischemia-reperfusion-induced acute kidney injury. Caspase-11 knockout mice after cisplatin treatment exhibited attenuated deterioration of renal functional, reduced tubular damage, reduced macrophage and neutrophil infiltration, and decreased urinary IL-18 excretion. Mechanistically, the upregulation of caspase-11 by either cisplatin or ischemia-reperfusion cleaved gasdermin D (GSDMD) into GSDMD-N, which translocated onto the plasma membrane, thus triggering cell pyroptosis and facilitated IL-18 release in primary cultured renal tubular cells. These results were further confirmed in GSDMD knockout mice that cisplatin-induced renal morphological and functional deterioration as well as urinary IL-18 excretion were alleviated. Furthermore, deficiency of GSDMD significantly suppressed cisplatin-induced IL-18 release but not the transcription and maturation level of IL-18 in tubular cells. Thus, our study indicates that caspase-11/GSDMD dependent tubule cell pyroptosis plays a significant role in initiating tubular cell damage, urinary IL-18 excretion and renal functional deterioration in acute kidney injury.
Hypoxia promotes tubulointerstitial inflammation in the kidney. Although hypoxia inducible factor-1 alpha (HIF-1 alpha) is a master regulator of the response to hypoxia, the exact mechanisms through which HIF-1 alpha modulates the induction of tubulointerstitial inflammation are still largely unclear. We demonstrated tubulointerstitial inflammation and increased tubular HIF-1 alpha expression in murine models of ischemia/reperfusion injury and unilateral ureteral obstruction. Increased expression of HIF-1 alpha in tubular epithelial cells was associated with selective shedding of microRNA-23a (miRNA-23a)-enriched exosomes in vivo and systemic inhibition of miRNA-23a prior to ischemia/reperfusion injury attenuated tubulointerstitial inflammation. In vitro, uptake of miRNA-23a-enriched exosomes by macrophages triggered their reprogramming into a pro-inflammatory state via suppression of the ubiquitin editor A20. To confirm the effect of miRNA-23a-containing exosomes on tubulointerstitial inflammation, we exposed tubular epithelial cells to hypoxic conditions to promote the release of miRNA-23a-containing exosomes. Injection of these miRNA-23a-enriched exosomes into uninjured renal parenchyma resulted in increased inflammatory infiltration in vivo. Taken together, our studies demonstrate that the HIF-1 alpha-dependent release of miRNA-23a-enriched exosomes from hypoxic tubular epithelial cells activates macrophages to promote tubulointerstitial inflammation. Blockade of exosomemediated miRNA-23a transfer between tubular epithelial cells and macrophages may serve as a novel therapeutic approach to ameliorate tubulointerstitial inflammation.
Previously published equations to estimate glomerular filtration rate (GFR) have limited accuracy in Asian populations. We aimed to develop and validate a more accurate equation for estimated GFR (eGFR) in the Chinese population, using data from 8571 adults who were referred for direct measurement of GFR by renal dynamic imaging (mGFR) at 3 representative hospitals in China. Patients from the Third Xiangya Hospital were included in our development (n = 1730) and internal validation sets (n = 1042) and patients from the other hospitals comprised the external validation set (n = 5799). We excluded patients who were prescribed medications known to influence the tubular secretion of creatinine, patients on dialysis, kidney transplant recipients, and patients with missing creatinine values or with creatinine >700 mu mol/l. We derived a novel eGFR equation by linear regression analysis and compared the performance to 12 creatinine-based eGFR equations, including previously published equations for use in Chinese or Asian populations. In the development and internal validation sets, the novel Xiangya equation had high accuracy (accuracy within 30% [P30], 79.21% and 84.33%, respectively), low bias (mean difference between mGFR and eGFR, -1.97 and -1.85 ml/min per 1.73 m(2), respectively), and high precision (interquartile range of the differences, 21.13 and 18.88 ml/min per 1.73 m(2), respectively). In external validation, the Xiangya equation had the highest P30 among all eGFR equations, with P30 <= 75% for the other 12 equations. This novel equation provides more accurate GFR estimates in Chinese adults and could replace existing eGFR equations for use in the Chinese population.
Chronic antibody-mediated rejection is the leading cause of allograft dysfunction and loss after kidney transplantation, and current immunosuppressive regimens fail to target the plasma cells that produce alloantibodies. We previously showed that treatment with the immunoproteasome inhibitor ONX 0914 prevented the expansion of plasma cells and prevented chronic allograft nephropathy and organ failure after kidney transplantation in rats, but the mechanism has remained elusive. In the current study, we confirmed a long-term reduction in alloantibody production and improvements in allograft histology in rats treated with ONX 0914 or with the broad-spectrum proteasome inhibitor bortezomib. Plasma cells from allotransplanted rats expressed immunoproteasomes at high levels. Immunoproteasome inhibition with ONX 0914 led to ubiquitin-conjugate accumulation, activation of the unfolded protein response, and induction of apoptosis in plasma cells. In addition, ONX 0914 suppressed the expression of adhesion molecules (VLA-4 and LFA-1), plasma cell survival factors (APRIL and IL-6), and IFN gamma-inducible chemokines in bone marrow, while the APRIL receptor BCMA, the IL-6 receptor, and the chemokine receptors CXCR4 and CXCR3 were down-regulated on plasma cells. Taken together, immunoproteasome inhibition blocked alloantibody production by inducing apoptosis of plasma cells through activating the unfolded protein response and suppressing plasma cell survival factors in the bone marrow.
Chronic kidney disease (CKD) has received increased attention as a leading public health problem worldwide. Globally surveillance systems for kidney disease are still lacking, especially in developing countries like China, which constitutes an obstacle to develop effective preventive strategies. China Kidney Disease Network (CK-NET) was initiated in 2014 and further developed in accordance with the national strategy of prompting Big Data application in China. One major output of CK-NET is to generate an Annual Data Report (ADR) providing resourceful information regarding kidney disease in China. Entering the second cycle of ADR, we have expanded the scope and depth of our research based on the previous ADR. There are 2 sections in the current ADR, generated from data from 2015 from various sources. Section I is based on a dataset of national hospitalized patients and describes the characteristics regarding hospitalized patients with CKD. Section II focuses on patients receiving renal replacement therapy based on 2 nationwide claims databases. There is also a chapter that focuses on patients on the waiting list for renal transplantation based on the China Organ Transplant Response System. Certain findings, including the effect of metabolic disease on the spectrum of CKD, the underdiagnoses of CKD and acute kidney injury among hospitalized patients, and the less-optimal treatment of complications among dialysis patients, will inspire the following research as well as changes in health policy. By integrating and mining national patient-level administrative or claim databases, we are able to provide a comprehensive description of the burden of CKD and end stage kidney disease in China, which could be used by multiple stakeholders with interests in kidney disease.
Ectopic fat deposition (EFD) in the kidney has been shown to play a causal role in diabetic nephropathy; however, the mechanism underlying EFD remains elusive. By transcriptome analysis, we found decreased expression levels of disulfide-bond A oxidoreductase-like protein (DsbA-L) in the kidneys of diabetic mice (induced by high-fat diet plus Streptozotocin) compared with control mice. Increased expression of adipocyte differentiation-related protein and abnormal levels of collagen I, fibronectin, and phosphorylated 5 0 AMP-activated kinase (p-AMPK), adipose triglyceride lipase (p-ATGL), and HMG-CoA reductase (p-HMGCR) were also observed in diabetic mice. These alterations were accompanied by deposition of lipid droplets in the kidney, and were more pronounced in diabetic DsbA-L knockout mice. In vitro, overexpression of DsbA-L ameliorated high glucose-induced intracellular lipid droplet deposition in a human proximal tubular cell line, and DsbA-L siRNA aggravated lipid droplet deposition and reduced the levels of p-AMPK, p-ATGL, and p-HMGCR. High glucose and palmitic acid treatment enhanced the expression of interleukin-1 beta and interleukin-18; these enhancements were further increased after treatment with DsbA-L siRNA but alleviated by co-treatment with an AMPK activator. In kidney biopsy tissue from patients with diabetic nephropathy, DsbA-L expression was negatively correlated with EFD and tubular damage. Collectively, these results suggest that DsbA-L has a protective role against EFD and lipid-related kidney damage in diabetic nephropathy. Activation of the AMPK pathway is a potential mechanism underlying DsbA-L action in the kidney.
Podocyte injury is the major cause of proteinuria in primary glomerular diseases. Oxidative stress has long been thought to play a role in triggering podocyte damage; however, the underlying mechanism remains poorly understood. Here we show that the Wnt/beta-catenin pathway is involved in mediating oxidative stress-induced podocyte dysfunction. Advanced oxidation protein products, a marker and trigger of oxidative stress, were increased in the serum of patients with chronic kidney disease and correlated with impaired glomerular filtration, proteinuria, and circulating level of Wnt1. Both serum from patients with chronic kidney disease and exogenous advanced oxidation protein products induced Wnt1 and Wnt7a expression, activated beta-catenin, and reduced expression of podocyte-specific markers in vitro and in vivo. Blockade of Wnt signaling by Klotho or knockdown of beta-catenin by shRNA in podocytes abolished beta-catenin activation and the upregulation of fibronectin, desmin, matrix metalloproteinase-9, and Snail1 triggered by advanced oxidation protein products. Furthermore, conditional knockout mice with podocyte-specific ablation of beta-catenin were protected against podocyte injury and albuminuria after treatment with advanced oxidation protein products. The action of Wnt/beta-catenin was dependent on the receptor of advanced glycation end products (RAGE)-mediated NADPH oxidase induction, reactive oxygen species generation, and nuclear factor-kappa B activation. These studies uncover a novel mechanistic linkage of oxidative stress, Wnt/beta-catenin activation, and podocyte dysfunction.
In type 2 cardiorenal syndrome, chronic heart failure is thought to cause or promote chronic kidney disease; however, the underlying mechanisms remain poorly understood. We investigated the role of Wnt signaling in heart and kidney injury in a mouse model of cardiac hypertrophy and heart failure induced by transverse aortic constriction (TAC). At 8 weeks after TAC, cardiac hypertrophy, inflammation, and fibrosis were prominent, and echocardiography confirmed impaired cardiac function. The cardiac lesions were accompanied by upregulation of multiple Wnt ligands and activation of beta-catenin, as well as activation of the renin-angiotensin system (RAS). Wnt3a induced multiple components of the RAS in primary cardiomyocytes and cardiac fibroblasts in vitro. TAC also caused proteinuria and kidney fibrosis, accompanied by klotho depletion and beta-catenin activation in the kidney. Pharmacologic blockade of beta-catenin with a small molecule inhibitor or the RAS with losartan ameliorated cardiac injury, restored heart function, and mitigated the renal lesions. Serum from TAC mice was sufficient to activate beta-catenin and trigger tubular cell injury in vitro, indicating a role for circulating factors. Multiple inflammatory cytokines were upregulated in the circulation of TAC mice, and tumor necrosis factor-alpha was able to inhibit klotho, induce beta-catenin activation, and cause tubular cell injury in vitro. These studies identify Wnt/beta-catenin signaling as a common pathogenic mediator of heart and kidney injury in type 2 cardiorenal syndrome after TAC. Targeting this pathway could be a promising therapeutic strategy to protect both organs in cardiorenal syndrome.
The G1 cell cycle inhibitors tissue inhibitor metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7) have been identified as novel biomarkers for the prediction of moderate to severe acute kidney injury (AKI) risk. However, the prognostic value of [TIMP2]center dot[IGFBP7] in predicting adverse outcomes in intensive care unit (ICU) patients with AKI was not previously described. To evaluate this, we conducted a cohort study, measuring [TIMP2]center dot[IGFBP7] levels in critically ill patients admitted to the ICU and classified the patients as NephroCheck (NC) (+) or NC (-) according to [TIMP-2]center dot[IGFBP7] values and AKI (+) or AKI (-) according to Kidney Disease: Improving Global Outcomes (KDIGO) criteria. We then evaluated the incidence of continuous renal replacement therapy initiation, all-cause mortality and a composite endpoint of both in the four groups. Baseline [TIMP-2]center dot[IGFBP7] values were available for 719 patients, of whom 239 developed AKI and 151 met the composite endpoint. Compared to NC (-)/AKI (+) patients, NC (+)/AKI (+) patients had a significant risk of ICU mortality and the composite endpoint. Kaplan-Meier curves showed that the survival estimate for the composite endpoint of NC (+)/AKI (+) patients was 34.4%; significantly worse than NC (-)/AKI (+) patients (67.4%). Multivariate analyses showed strong association between NC positivity and the composite endpoint. The inflammatory marker, procalcitonin, was an additional prognostic biomarker to compare and confirm the incremental value of NephroCheck. No association between procalcitonin and the composite endpoint was found, especially in patients with AKI, suggesting that NephroCheck may be more kidney specific. Thus, the [TIMP-2]center dot[IGFBP7] values can serve to identify patients with AKI at increased risk for adverse outcomes in the ICU.
Mitochondria are critical in determining a cell's energy homeostasis and fate, and mitochondrial dysfunction has been implicated in the pathogenesis of chronic kidney disease (CKD). We sought to identify causative mitochondrial microRNAs. A microarray screen of kidney tissue from healthy mice identified 97 microRNAs that were enriched in the mitochondrial fraction. We focused on microRNA-214-3p (miR-214) because of a very high ratio of mitochondrial to cytoplasmic expression in the kidney compared to other organs. Tubular expression of miR-214 was more abundant in kidney tissue from patients with CKD than from healthy controls, and was positively correlated with the degree of proteinuria and kidney fibrosis. Expression of miR-214 was also increased in the kidney of mouse models of CKD induced by obstruction, ischemia/reperfusion, and albumin overload. Proximal tubule-specific deletion of miR-214 attenuated apoptosis, inflammation, fibrosis, and mitochondrial damage in these CKD models. Pharmacologic inhibition of miR-214 had a similar effect in the albumin overload model of CKD. In vitro, overexpressing miR-214 in proximal tubular cell lines induced apoptosis and disrupted mitochondrial oxidative phosphorylation, while miR-214 expression was upregulated in response to a variety of insults. The mitochondrial genes mt-Nd6 and mt-Nd4l were identified as the specific targets of miR-214 in the kidney. Together, these results demonstrate a pathogenic role of miR-214 in CKD through the disruption of mitochondrial oxidative phosphorylation, and suggest the potential for miR-214 to serve as a therapeutic target and diagnostic biomarker for CKD.