Endostatin expression in the murine model of ischaemia/reperfusion-induced acute renal failure

Proteomic aptamer analysis reveals serum markers that characterize preclinical systemic sclerosis (SSc) patients at risk for progression toward definite SSc

BACKGROUND

The study of molecular mechanisms characterizing disease progression may be relevant to get insights into systemic sclerosis (SSc) pathogenesis and to intercept patients at very early stage. We aimed at investigating the proteomic profile of preclinical systemic sclerosis (PreSSc) via a discovery/validation two-step approach.

METHODS

SOMAcan aptamer-based analysis was performed on a serum sample of 13 PreSSc (discovery cohort) according to 2001 LeRoy and Medsger criteria (characterized solely by Raynaud phenomenon plus a positive nailfold capillaroscopy and SSc-specific antibodies without any other sign of definite disease) and 8 healthy controls (HCs) age, gender, and ethnicity matched. Prospective data were available up to 4±0.6 years to determine the progression to definite SSc according to the EULAR/ACR 2013 classification criteria. In proteins with relative fluorescence units (RFU) > |1.5|-fold vs HCs values, univariate analysis was conducted via bootstrap aggregating models to determine the predicting accuracy (progression vs non-progression) of categorized baseline protein values. Gene Ontologies (GO terms) and Reactome terms of significant proteins at the adjusted 0.05 threshold were explored. Significant proteins from the discovery cohort were finally validated via ELISAs in an independent validation cohort of 50 PreSSc with clinical prospective data up to 5 years. Time-to-event analysis for interval-censored data was used to evaluate disease progression.

RESULTS

In the discovery cohort, 286 out of 1306 proteins analyzed via SomaScan, were differentially expressed versus HCs. Ten proteins were significantly associated with disease progression; analysis through GO and Reactome showed differentially enriched pathways involving angiogenesis, endothelial cell chemotaxis, and endothelial cell chemotaxis to fibroblast growth factor (FGF). In the validation cohort, endostatin (HR=10.23, CI95=2.2-47.59, p=0.003) was strongly associated with disease progression, as well as bFGF (HR=0.84, CI95=0.709-0.996, p=0.045) and PAF-AHβ (HR=0.372, CI95=0.171-0.809, p=0.013) CONCLUSIONS: A distinct protein profile characterized PreSSc from HCs and proteins associated with hypoxia, vasculopathy, and fibrosis regulation are linked with the progression from preclinical to definite SSc. These proteins, in particular endostatin, can be regarded both as markers of severity and molecules with pathogenetic significance as well as therapeutic targets.

The basement membrane in the cross-roads between the lung and kidney

The basement membrane (BM) is a specialized layer of extracellular matrix components that plays a central role in maintaining lung and kidney functions. Although the composition of the BM is usually tissue specific, the lung and the kidney preferentially use similar BM components. Unsurprisingly, diseases with BM defects often have severe pulmonary or renal manifestations, sometimes both. Excessive remodeling of the BM, which is a hallmark of both inflammatory and fibrosing diseases in the lung and the kidney, can lead to the release of BM-derived matrikines, proteolytic fragments with distinct biological functions. These matrikines can then influence disease activity at the site of liberation. However, they are also released to the circulation, where they can directly affect the vascular endothelium or target other organs, leading to extrapulmonary or extrarenal manifestations. In this review, we will summarize the current knowledge of the composition and function of the BM and its matrikines in health and disease, both in the lung and in the kidney. By comparison, we will highlight, why the BM and its matrikines may be central in establishing a renal-pulmonary interaction axis.

A Comparison between Endostatin and Conventional Biomarkers on 30-Day Mortality and Renal Replacement Therapy in Unselected Intensive Care Patients

Endostatin may predict mortality and kidney impairment in general populations as well as in critically ill patients. We decided to explore the possible role of endostatin as a predictor of 30-day mortality, acute kidney injury (AKI), and renal replacement therapy (RRT) in a cohort of unselected intensive care unit (ICU) patients. Endostatin and creatinine in plasma were analyzed and SAPS3 was determined in 278 patients on ICU arrival at admission to a Swedish medium-sized hospital. SAPS3 had the highest predictive value, 0.85 (95% C.I.: 0.8–0.90), for 30-day mortality. Endostatin, in combination with age, predicted 30-day mortality by 0.76 (95% C.I.: 0.70–0.82). Endostatin, together with age and creatinine, predicted AKI with 0.87 (95% C.I.: 0.83–0.91). Endostatin predicted AKI with [0.68 (0.62–0.74)]. Endostatin predicted RRT, either alone [0.82 (95% C.I.: 0.72–0.91)] or together with age [0.81 (95% C.I.: 0.71–0.91)]. The predicted risk for 30-day mortality, AKI, or RRT during the ICU stay, predicted by plasma endostatin, was not influenced by age. Compared to the complex severity score SAPS3, circulating endostatin, combined with age, offers an easily managed option to predict 30-day mortality. Additionally, circulating endostatin combined with creatinine was closely associated with AKI development.

Endostatin in Renal and Cardiovascular Diseases

Endostatin, a protein derived from the cleavage of collagen XVIII by the action of proteases, is an endogenous inhibitor known for its ability to inhibit proliferation and migration of endothelial cells, angiogenesis, and tumor growth. Angiogenesis is defined as the formation of new blood vessels from pre-existing vasculature, which is crucial in many physiological processes, such as embryogenesis, tissue regeneration, and neoplasia.

SUMMARY

Increasing evidence shows that dysregulation of angiogenesis is crucial for the pathogenesis of renal and cardiovascular diseases. Endostatin plays a pivotal role in the regulation of angiogenesis. Recent studies have provided evidence that circulating endostatin increases significantly in patients with kidney and heart failure and may also contribute to disease progression.

KEY MESSAGE

In the current review, we summarize the latest findings on preclinical and clinical studies analyzing the impact of endostatin on renal and cardiovascular diseases.

Validation of an enzyme-linked immunosorbent assay (ELISA) for quantification of endostatin levels in mice as a biomarker of developing glomerulonephritis

Endostatin, the C-terminal fragment of type XVIII collagen, was shown to be one of the most potent endothelial cell-specific inhibitors of angiogenesis. As altered circulating endostatin concentration is associated with impaired kidney function, new tools for measuring endostatin in rodents may be helpful to further investigate and understand its role within kidney disease progression. A novel and commercially available ELISA for the quantification of mouse and rat endostatin was developed and validated according to international quality guidelines including the parameters specificity, robustness, accuracy, dilution linearity, precision, limit of detection (LOD) and lower limit of quantification (LLOQ). Endostatin and blood urea nitrogen (BUN) concentration were measured in mice with a glomerulonephritis phenotype. The validation revealed that within the range of 0.5–32 nmol/L the immunoassay is robust and highly specific for the measurement of rodent endostatin with high sensitivity (LOD 0.24 nmol/L, LLOQ 0.5 nmol/L) and good reproducibility (intra- and inter-assay CV <10%). Also accuracy and dilution linearity were within the range of acceptance. BCL2 transgenic and ETV6/RUNX1;BCL2 double transgenic mice develop a glomerulonephritis phenotype over time, which was displayed by staining of kidney sections. Even before full manifestation of disease serum endostatin concentration rises significantly, whereas BUN levels just slightly increase. This newly developed and commercially available ELISA provides a reliable and accurate tool for the quantification of mouse and rat endostatin and may give new perspectives in the investigation of the role of endostatin as an important and early biomarker for reduced kidney function. Measurement of endostatin concentration is recommended to be used as a superior biomarker for chronic kidney disease compared to BUN.

Plasma endostatin predicts kidney outcomes in patients with type 2 diabetes

Novel biomarkers are needed to predict kidney function decline in patients with type 2 diabetes, especially those with preserved glomerular filtration rate (GFR). There are limited data on the association of markers of endothelial dysfunction with longitudinal GFR decline. We used banked specimens from a nested case-control study in the Action to Control Cardiovascular Disease (ACCORD) trial (n=187 cases: 187 controls) and from a diverse contemporary cohort of type 2 diabetic patients from the Mount Sinai BioMe Biobank (n=871) to assess the association of plasma endostatin and kidney outcomes. We measured plasma endostatin at enrollment and examined its association with a composite kidney outcome of sustained 40% decline in estimated GFR or end-stage renal disease. Baseline plasma endostatin levels were higher in participants with the composite outcome. Each log2 increment in plasma endostatin was associated with approximately 2.5-fold higher risk of the kidney outcome (adjusted odds ratio [OR] 2.5; 95% confidence interval [CI] 1.5-4.3 in ACCORD and adjusted hazard ratio [HR] 2.6; 95% CI 1.8-3.8 in BioMe). Participants in the highest vs. lowest quartile of plasma endostatin had approximately four-fold higher risk for the kidney outcome (adjusted OR 3.6; 95% CI 1.8-7.3 in ACCORD and adjusted HR 4.4; 95% CI 2.3-8.5 in BioMe). The AUC for the kidney outcome improved from 0.74 to 0.77 in BioMe with the addition of endostatin to a base clinical model. Plasma endostatin was strongly associated with kidney outcomes in type 2 diabetics with preserved eGFR and improved risk discrimination over traditional predictors.

Derivation and validation of plasma endostatin for predicting renal recovery from acute kidney injury: a prospective validation study

BACKGROUND

Acute kidney injury (AKI) is associated with high morbidity and mortality in surgical patients. Nonrecovery from AKI may increase mortality and early risk stratification seems key to improving clinical outcomes. The aim of the current study was to explore and validate the value of endostatin for predicting failure to recover from AKI.

METHODS

We conducted a prospective cohort study of 198 patients without known chronic kidney disease who underwent noncardiac major surgery and developed new-onset AKI in the first 48 h after admission to the ICU. The biomarkers of plasma endostatin, neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C were detected immediately after AKI diagnosis. The primary endpoint was nonrecovery from AKI (within 7 days). Cutoff values of the biomarkers for predicting nonrecovery were determined in a derivation cohort (105 AKI patients). Predictive accuracy was then analyzed in a validation cohort (93 AKI patients).

RESULTS

Seventy-six of 198 (38.4%) patients failed to recover from AKI onset, with 41 in the derivation cohort and 35 in the validation cohort. Compared with NGAL and cystatin C, endostatin showed a better prediction for nonrecovery, with an area under the receiver operating characteristic curve (AUC) of 0.776 (95% confidence interval (CI) 0.654-0.892, p < 0.001) and an optimal cutoff value of 63.7 ng/ml. The predictive ability for nonrecovery was greatly improved by the prediction model combining endostatin with clinical risk factors of Sequential Organ Failure Assessment (SOFA) score and AKI classification, with an AUC of 0.887 (95% CI 0.766-0.958, p < 0.001). The value of the endostatin-clinical risk prediction model was superior to the NGAL-clinical risk and cystatin C-clinical risk prediction models in predicting failure to recover from AKI, which was supported by net reclassification improvement and integrated discrimination improvement. Further, the endostatin-clinical risk prediction model achieved sensitivity and specificity of 94.6% (76.8-99.1) and 72.7% (57.2-85.0), respectively, when validated in the validation cohort.

CONCLUSION

Plasma endostatin shows a useful value for predicting failure to recover from AKI. The predictive ability can be greatly improved when endostatin is combined with the SOFA score and AKI classification.

Assessment of plasma endostatin to predict acute kidney injury in critically ill patients

BACKGROUND

We evaluated whether plasma endostatin predicts acute kidney injury (AKI), need for renal replacement therapy (RRT), or death.

METHODS

Prospective, observational, multicenter study from 1 September 2011 to 1 February 2012 with data from 17 intensive care units (ICUs) in Finland.

RESULTS

A total of 1112 patients were analyzed. We measured plasma endostatin within 2 h of ICU admission. Early AKI (KDIGO stage within 12 h of ICU admission) was found in 20% of the cohort, and 18% developed late AKI (KDIGO criteria > 12 h from ICU admission). Median (IQR) admission endostatin was higher in the early AKI group, 29 (19.1, 41.9) ng/ml as compared to 22.4 (16.1, 30.1) ng/ml for the late AKI group, and 18 (14.0, 23.6) ng/ml for non-AKI patients (P < 0.001). Endostatin level increased with increasing KDIGO stage. Significantly higher endostatin levels were found in patients with sepsis as compared to those without. Predictive properties for AKI, RRT, and mortality were low with corresponding areas under the receiver operating characteristic curve (AUC) of 0.62, 0.67, and 0.59. Sensitivity analyses among patients with chronic kidney disease or sepsis did not improve the predictive ability of endostatin. Adding endostatin to a clinical AKI prediction model (illness severity score, urine output, and age) insignificantly changed the AUC from 0.67 to 0.70 (P = 0.14).

CONCLUSIONS

Endostatin increases with AKI severity but has limited value as a predictor of AKI, RRT and 90-day mortality in patients admitted to ICU. Moreover, endostatin does not improve AKI risk prediction when added to a clinical risk model.

Endostatin in chronic kidney disease: Associations with inflammation, vascular abnormalities, cardiovascular events and survival

BACKGROUND AND AIMS

Endostatin, generated from collagen XVIII, and endorepellin, possess dual activity as modifiers of both angiogenesis and endothelial cell autophagy. Plasma endostatin levels are elevated in a large number of diseases, and may reflect endothelial cell dysfunction. Few data on endostatins are available for patients with chronic kidney disease (CKD). We tested whether serum endostatin values are predictive for all-cause mortality and cardiovascular events (CVEs) in a CKD population.

MATERIALS AND METHOD

A total of 519 CKD pre-dialysis patients were included. Baseline plasma endostatin levels were measured in all patients. All included patients were followed-up (time-to-event analysis) until occurrence of death, fatal or nonfatal CVEs. Fatal and nonfatal CVE including death, stroke, and myocardial infarction were recorded prospectively

RESULTS

The mean age of the patients was 52.2±12.3years. There were 241 (46.4%) males, 111 (21.4%) had diabetes, 229 (44.1%) were smokers and 103 (19.8%) had a previous CVE. After a median follow-up of 46months, 46 patients died and 172 had a new CVE. In the univariable Cox survival analysis, higher endostatin levels were associated with a higher risk for both outcomes. However, after adjusting for traditional (age, gender, smoking status, diabetes, systolic blood pressure, HDL and total cholesterol) and renal-specific (eGFR, proteinuria and hsCRP) risk factors, endostatin levels remained associated only with the CVE outcome (HR=1.88, 95% CI 1.37-2.41 for a 1 SD increase in log endostatin values).

CONCLUSION

Endostatin levels are independently associated with incident CVE in CKD patients, but show limited prediction abilities for all-cause mortality and CVE above traditional and renal-specific risk factors.

Matrix Metalloproteinase-9 and Graft Preservation Injury in Clinical Renal Transplantation

BACKGROUND

Deleterious effects of matrix metalloproteinase-9 (MMP-9) have been established in experimental renal ischemia-reperfusion models but not in clinical renal transplantation thus far.

METHODS

We studied MMP-9 and its physiological inhibitor tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) in 45 consecutive patients of a larger trial in renal transplantation: perioperative anti-thymocyte globulin (group A, n = 15), perioperative basiliximab (group B, n = 16), and conventional triple therapy (group C, n = 14). In addition to systemic blood samples, local blood samples were obtained simultaneously at 1 and 5 minutes after reperfusion from iliac artery and graft vein for calculation of transrenal changes. Because anti-thymocyte globulin activates inflammation, group A was analyzed separately. Groups B and C were pooled (group BC).

RESULTS

Anti-thymocyte globulin infusion caused a robust rise of MMP-9 in the systemic circulation in group A. No significant transrenal difference of MMP-9 or TIMP-1 occurred in either group during graft reperfusion. In group BC, strong transrenal release of MMP-9 at 1 minute after reperfusion correlated with cold ischemia time (R = 0.66, P = .0001) and was associated with delayed graft function (P = .052).

CONCLUSIONS

Renal production of MMP-9 on graft reperfusion is associated with cold ischemia time and emergence of delayed graft function. MMP inhibition may offer a means to reduce reperfusion injury in renal transplantation.

Plasma endostatin may improve acute kidney injury risk prediction in critically ill patients

Background

Breakdown of renal endothelial, tubular and glomerular matrix collagen plays a major role in acute kidney injury (AKI) development. Such collagen breakdown releases endostatin into the circulation. The aim of this study was to compare the AKI predictive value of plasma endostatin with two previously suggested biomarkers of AKI, cystatin C and neutrophil gelatinase-associated lipocalin (NGAL).

Methods

We studied 93 patients without kidney disease who had a first plasma sample obtained within 48 h of ICU admission. We identified risk factors for AKI within the population and designed a predictive model. The individual ability and net contribution of endostatin, cystatin C and NGAL to predict AKI were evaluated by the area under the receiver operating characteristics curve (AUC), likelihood-ratio test, net reclassification improvement (NRI) and integrated discrimination improvement (IDI).

Results

In total, 21 (23 %) patients experienced AKI within 72 h. A three-parameter model (age, illness severity score and early oliguria) predicted AKI with an AUC of 0.759 (95 % CI 0.646–0.872). Adding endostatin to the predictive model significantly (P = 0.04) improved the AUC to 0.839 (95 % CI 0.752–0.925). In addition, endostatin significantly improved risk prediction using the likelihood-ratio test (P = 0.005), NRI analysis (0.27; P = 0.04) and IDI analysis (0.07; P = 0.04). In contrast, adding cystatin C or NGAL to the three-parameter model did not improve risk prediction in any of the four analyses.

Conclusions

In this cohort of critically ill patients, plasma endostatin improved AKI prediction based on clinical risk factors, while cystatin C and NGAL did not.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0108-x) contains supplementary material, which is available to authorized users.

Predictive Value of Endostatin in Chronic Heart Failure Patients with Poor Kidney Function

Objectives: Increased circulating endostatin levels have been demonstrated in progressive cardiovascular (CV) and renal disorders. We investigated the predictive value of endostatin in patients with chronic heart failure (HF) and the association between endostatin and renal function. Methods: The interaction between serum endostatin, estimated glomerular filtration rate (eGFR) and predefined endpoints, including the primary endpoint (CV death, nonfatal myocardial infarction, nonfatal stroke; n = 397), all-cause mortality (n = 410), CV death (n = 335) or the coronary endpoint (n = 317), was evaluated in 1,390 patients >60 years of age with ischemic systolic HF in the Controlled Rosuvastatin Multinational Trial in HF (CORONA) population, who were randomly assigned to 10 mg rosuvastatin or placebo. Results: In the population as a whole, endostatin added no predictive information after full multivariable adjustment including eGFR and N-terminal pro-brain natriuretic peptide. Serum endostatin was strongly correlated with eGFR (r = 0.59, p < 0.001). After full multivariable adjustment, an association between high serum endostatin and increased risk of all-cause mortality and decreased risk of the primary and coronary endpoints was seen in HF patients with impaired and preserved renal function, respectively. Conclusions: Endostatin added no predictive information regarding the adverse outcome in patients with chronic systolic HF of ischemic etiology. An increased risk of all-cause mortality was seen in patients with decreased renal function. i 2014 S. Karger AG, Basel

Basement membrane zone collagens XV and XVIII/proteoglycans mediate leukocyte influx in renal ischemia/reperfusion

Collagen type XV and XVIII are proteoglycans found in the basement membrane zones of endothelial and epithelial cells, and known for their cryptic anti-angiogenic domains named restin and endostatin, respectively. Mutations or deletions of these collagens are associated with eye, muscle and microvessel phenotypes. We now describe a novel role for these collagens, namely a supportive role in leukocyte recruitment. We subjected mice deficient in collagen XV or collagen XVIII, and their compound mutant, as well as the wild-type control mice to bilateral renal ischemia/reperfusion, and evaluated renal function, tubular injury, and neutrophil and macrophage influx at different time points after ischemia/reperfusion. Five days after ischemia/reperfusion, the collagen XV, collagen XVIII and the compound mutant mice showed diminished serum urea levels compared to wild-type mice (all p<0.05). Histology showed reduced tubular damage, and decreased inflammatory cell influx in all mutant mice, which were more pronounced in the compound mutant despite increased expression of MCP-1 and TNF-α in double mutant mice compared to wildtype mice. Both type XV and type XVIII collagen bear glycosaminoglycan side chains and an in vitro approach with recombinant collagen XVIII fragments with variable glycanation indicated a role for these side chains in leukocyte migration. Thus, basement membrane zone collagen/proteoglycan hybrids facilitate leukocyte influx and tubular damage after renal ischemia/reperfusion and might be potential intervention targets for the reduction of inflammation in this condition.

Peritubular capillary rarefaction: a new therapeutic target in chronic kidney disease

Chronic kidney disease (CKD) has reached worldwide epidemic proportions and desperately needs new therapies. Peritubular capillary (PTC) rarefaction, together with interstitial fibrosis and tubular atrophy, is one of the major hallmarks of CKD and predicts renal outcome in patients with CKD. PTC endothelial cells (ECs) undergo apoptosis during CKD, leading to capillary loss, tissue hypoxia, and oxidative stress. Although the mechanisms of PTC rarefaction are not well understood, the process of PTC rarefaction depends on multiple events that occur during CKD. These events, which lead to an antiangiogenic environment, include deprivation of EC survival factors, increased production of vascular growth inhibitors, malfunction of ECs, dysfunction of endothelial progenitor cells, and loss of EC integrity via pericyte detachment from the vasculature. In this review, we focus on major factors regulating angiogenesis and EC survival and describe the roles of these factors in PTC rarefaction during CKD and possible therapeutic applications.

Screening plasma miRNAs as biomarkers for renal ischemia-reperfusion injury in rats

Background

Acute kidney injury is a common clinical comorbidity and early diagnosis is crucial for improving prognosis, but there is still no ideal biomarker for early diagnosis.

Material/Methods

miRNA microarray was used for detecting miRNA in kidney subjected to renal ischemia-reperfusion injury 12 h after reperfusion. Real-time PCR was performed to validate the results of microarray. miRNAs in the ischemia group were twice as high as in the sham group. Kidney-enriched miR-10a, miR-192, and miR-194 were detected in rat plasma to screen potential biomarkers for renal ischemia-reperfusion injury. Aberrant expressed miRNA in plasma at 12 h were further detected at 1 h, 2 h, 6 h, 12 h, and 24 h to observe the changing trend of these miRNAs and were compared to blood urea nitrogen and serum creatinine.

Results

Thirty-six miRNAs were aberrantly expressed in kidney of rats with renal ischemia-reperfusion injury, among which 15 miRNAs had a 2-fold greater change. Results of real-time PCR were generally in accordance with microarray results. Levels of the 15 miRNAs differentially expressed in injured kidney were not significantly different from those in sham kidney. However, miR-10a, miR-192, and miR-194 were significantly increased in plasma of rats with renal ischemia-reperfusion injury, among which miR-10a was elevated within 1 h after reperfusion, whereas miR-192 and miR-194 were elevated at 6 h after injury. Blood urea nitrogen was increased at 12 h and serum creatinine was increased at 6 h after injury.

Conclusions

Plasma miR-10a, miR-192, and miR-194 were potential biomarkers for renal ischemia reperfusion injury in rats, and miR-10a might be the most promising plasma biomarker for renal injury because of its elevation within 1 h after renal injury, as well as renal specificity.

Association between circulating endostatin, hypertension duration, and hypertensive target-organ damage

Our aim is to study associations between circulating endostatin, hypertension duration, and hypertensive target-organ damage. Long-term hypertension induces cardiovascular and renal remodeling. Circulating endostatin, a biologically active derivate of collagen XVIII, has been suggested to be a relevant marker for extracellular matrix turnover and remodeling in various diseases. However, the role of endostatin in hypertension and hypertensive target-organ damage is unclear. Serum endostatin was measured in 2 independent community-based cohorts: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS; women 51%; n = 812; mean age, 75 years) and the Uppsala Longitudinal Study of Adult Men (ULSAM; n=785; mean age, 77.6 years). Retrospective data on blood pressure measurements and antihypertensive medication (PIVUS >5 years, ULSAM >27 years), and cross-sectional data on echocardiographic left ventricular mass, endothelial function (endothelium-dependent vasodilation assessed by the invasive forearm model), and urinary albumin/creatinine ratio were available. In PIVUS, participants with ≥ 5 years of history of hypertension portrayed 0.42 SD (95% confidence interval, 0.23-0.61; P<0.001) higher serum endostatin, compared with that of normotensives. This association was replicated in ULSAM, in which participants with 27 years hypertension duration had the highest endostatin (0.57 SD higher; 95% confidence interval, 0.35-0.80; P<0.001). In addition, higher endostatin was associated with higher left ventricular mass, worsened endothelial function, and higher urinary albumin/creatinine ratio (P<0.03 for all) in participants with prevalent hypertension. Circulating endostatin is associated with the duration of hypertension, and vascular, myocardial, and renal indices of hypertensive target-organ damage. Further studies are warranted to assess the prognostic role of endostatin in individuals with hypertension.

Models for studies of proteoglycans in kidney pathophysiology

Proteoglycans (PGs) impact many aspects of kidney health and disease. Models that permit genetic dissection of PG core protein and glycosaminoglycan (GAG) function have been instrumental to understanding their roles in the kidney. Matrix-associated PGs do not serve critical structural roles in the organ, nor do they contribute significantly to the glomerular barrier under normal conditions, but their abnormal expression influences fibrosis, inflammation, and progression of kidney disease. Most core proteins are dispensable for nephrogenesis (glypican-3 being an exception) and for maintenance of function in adult life, but their loss alters susceptibility to experimental kidney injury. In contrast, kidney development is exquisitely sensitive to GAG expression and fine structure as evidenced by the severe phenotypes of mutants for genes involved in GAG biosynthesis. This article reviews PG expression in normal kidney and the abnormalities caused by their disruption in mice and man.

Differential expression of proteoglycans in tissue remodeling and lymphangiogenesis after experimental renal transplantation in rats

Background

Chronic transplant dysfunction explains the majority of late renal allograft loss and is accompanied by extensive tissue remodeling leading to transplant vasculopathy, glomerulosclerosis and interstitial fibrosis. Matrix proteoglycans mediate cell-cell and cell-matrix interactions and play key roles in tissue remodeling. The aim of this study was to characterize differential heparan sulfate proteoglycan and chondroitin sulfate proteoglycan expression in transplant vasculopathy, glomerulosclerosis and interstitial fibrosis in renal allografts with chronic transplant dysfunction.

Methods

Renal allografts were transplanted in the Dark Agouti-to-Wistar Furth rat strain combination. Dark Agouti-to-Dark Agouti isografts and non-transplanted Dark Agouti kidneys served as controls. Allograft and isograft recipients were sacrificed 66 and 81 days (mean) after transplantation, respectively. Heparan sulfate proteoglycan (collXVIII, perlecan and agrin) and chondroitin sulfate proteoglycan (versican) expression, as well as CD31 and LYVE-1 (vascular and lymphatic endothelium, respectively) expression were (semi-) quantitatively analyzed using immunofluorescence.

Findings

Arteries with transplant vasculopathy and sclerotic glomeruli in allografts displayed pronounced neo-expression of collXVIII and perlecan. In contrast, in interstitial fibrosis expression of the chondroitin sulfate proteoglycan versican dominated. In the cortical tubular basement membranes in both iso- and allografts, induction of collXVIII was detected. Allografts presented extensive lymphangiogenesis (p<0.01 compared to isografts and non-transplanted controls), which was associated with induced perlecan expression underneath the lymphatic endothelium (p<0.05 and p<0.01 compared to isografts and non-transplanted controls, respectively). Both the magnitude of lymphangiogenesis and perlecan expression correlated with severity of interstitial fibrosis and impaired graft function.

Interpretation

Our results reveal that changes in the extent of expression and the type of proteoglycans being expressed are tightly associated with tissue remodeling after renal transplantation. Therefore, proteoglycans might be potential targets for clinical intervention in renal chronic transplant dysfunction.

Biomarkers in renal transplantation ischemia reperfusion injury

Ischemia reperfusion injury (IRI) is a choreographed process leading to delayed graft function (DGF) and reduced long-term patency of the transplanted organ. Early identification of recipients of grafts at risk would allow modification of the posttransplant management, and thereby potentially improve short- and long-term outcomes. The recently emerged "omics" technologies together with bioinformatics workup have allowed the integration and analysis of IRI-associated molecular profiles in the context of DGF. Such a systems biological approach promises qualitative information about interdependencies of complex processes such as IRI regulation, rather than offering descriptive tables of differentially regulated features on a transcriptome, proteome, or metabolome level leaking the functional, biological framework. In deceased-donor kidney transplantation as the primary causative factor resulting in IRI and DGF, a distinct signature and choreography of molecular events in the graft before harvesting seems to be associated with subsequent DGF. A systems biological assessment of these molecular changes suggests that processes along inflammation are of pivotal importance for the early stage of IRI. The causal proof of this association has been tested by a double-blinded, randomized, controlled trial of steroid or placebo infusion into deceased donors before the organs were harvested. Thorough systems biological analysis revealed a panel of biomarkers with excellent discrimination. In summary, integrated analysis of omics data has brought forward biomarker candidates and candidate panels that promise early assessment of IRI. However, the clinical utility of these markers still needs to be established in prospective trials in independent patient populations.

MMP9 and SCF protect from apoptosis in acute kidney injury

Apoptosis of tubular epithelial cells is a hallmark of acute kidney injury (AKI), but the cellular events preceding apoptosis in this setting are incompletely understood. Because matrix metalloproteinase 9 (MMP9) degrades matrix components involved in cell survival, we studied the role of MMP9 in AKI. In the mouse model of folic acid-induced AKI, we observed a marked increase of MMP9 activity in the S3 segment of the proximal tubule (S3PT), correlating with the apoptotic phase. MMP9 deficiency increased apoptosis and the severity of renal lesions and substantially delayed recovery of renal function. MMP9-/- mice exhibited significant apoptosis in the S3PT and the intercalated cells of the collecting duct (I-CD), whereas wild-type mice exhibited none in these segments. Stem cell factor (SCF), an MMP9 substrate, was identified in the S3PT, and its receptor, c-Kit, was expressed in both the S3PT and I-CD. MMP9 released the soluble form of SCF (sSCF) from kidney cells in vivo and in vitro. In addition, SCF inhibited apoptosis of tubular cells in vitro, rescued MMP9-/- S3PT and I-CD from apoptosis in vivo, and improved renal function. An ischemia-reperfusion model of AKI produced similar results. In patients with AKI, urinary sSCF increased with acute tubular necrosis but not with prerenal azotemia. In conclusion, these data show that MMP9 protects the S3 segment of the proximal tubule and the I-CD from apoptosis in AKI, most likely by releasing sSCF.