Urinary Post-Translationally Modified Fetuin-A Protein Is Associated with Increased Risk of Graft Failure in Kidney Transplant Recipients.

INTRODUCTION: Urinary fetuin-A has been identified as a biomarker for acute kidney injury and is proposed as a biomarker for early detection of kidney function decline. We investigated whether fetuin-A could serve as a marker of graft failure in kidney transplant recipients (KTRs). METHODS: Data of KTR with a functioning graft ≥1 year that were enrolled in the TransplantLines Food and Nutrition Biobank and cohort study were used. Graft failure was defined as the need for re-transplantation or (re-)initiation of dialysis. Urinary fetuin-A was measured using an enzyme-linked immunosorbent assay kit that detected post-translationally modified fetuin-A in the urine (uPTM-FetA). In the main analyses, 24h uPTM-FetA excretion was used. In the sensitivity analyses, we excluded the outliers in 24h uPTM-FetA excretion, and we used uPTM-FetA concentration and uPTM-FetA concentration indexed for creatinine instead of 24h uPTM-FetA excretion. RESULTS: A total of 627 KTRs (age 53 ± 13 years, 42% females) were included at 5.3 (1.9-12.2) years after transplantation. The estimated glomerular filtration rate (eGFR) was 52 ± 20 mL/min/1.73 m2 and uPTM-FetA excretion was 34 (17-74) µg/24 h. During a median follow-up of 5.3 (4.5-6.0) years after baseline measurements, 73 (12%) KTRs developed graft failure. The association of 24h uPTM-FetA excretion with increased risk of graft failure was not constant over time, with increased risk only observed after 3 years from baseline measurements, independent of potential confounders including kidney function and 24 h urinary protein excretion (hazard ratio per doubling of 24h uPTM-FetA excretion = 1.31; 95% confidence interval = 1.06-1.61). This finding was robust in the sensitivity analyses. CONCLUSIONS: Our findings suggest that uPTM-FetA can be used as a marker for early detection of graft failure in KTR. Further studies are needed to confirm our findings.

C4d, rather than C3d and C5b-9, is associated with graft loss in recurrent IgA deposition after kidney transplantation.

INTRODUCTION: Recurrent IgA deposition is common after kidney transplantation. However, it is difficult to define whether IgA deposition is innocuous or contributes to organ damage. Next, although complement is known to be involved in the pathogenesis of IgA nephropathy (IgAN), its involvement has not been studied systematically in kidney transplant recipients (KTR). METHODS: KTR with biopsy-proven native IgAN who underwent kidney biopsy after transplantation between 1995 and 2020 were included. Recurrent IgA deposition was defined as IgA deposit in the glomerulus. Staining of complement factors C4d, C3d, and C5b-9 were quantitatively evaluated using ImageScope. RESULTS: Sixty-seven KTR (85% male, 46±13 years old, 12 [6-24] months after transplantation, 58% with indication biopsy) were included in the analyses. Of them, 25 (37%) had recurrent IgA deposition. There were no clinical differences between KTR with and without recurrent IgA deposition. C3d and C5b-9 were always present in biopsies with IgA deposition, while C4d was present in 48% of the biopsies. During a median follow-up of 9.6 [4.8-14] years, 18 (27%) KTR developed death-censored graft failure. Recurrent IgA deposition was not associated with graft failure. Of the evaluated complement factors, only C4d staining was associated with graft failure in KTR with recurrent IgA deposition (Hazard ratio = 2.55, 95% confidence interval = 1.07-6.03, p = 0.034). CONCLUSIONS: Recurrent IgA deposition was not associated with graft failure in itself. C4d, when present, is strongly associated with graft loss in KTR with recurrent IgA deposition, suggesting a pathogenic role for the lectin pathway in recurrent IgAN.

Initial properdin binding contributes to alternative pathway activation at the surface of viable and necrotic cells.

Properdin, the only known positive regulator of the complement system, stabilizes the C3 convertase, thereby increasing its half-life. In contrast to most other complement factors, properdin is mainly produced extrahepatically by myeloid cells. Recent data suggest a role for properdin as a pattern recognition molecule. Here, we confirmed previous findings of properdin binding to different necrotic cells including Jurkat T cells. Binding can occur independent of C3, as demonstrated by HAP-1 C3 KO cells, excluding a role for endogenous C3. In view of the cellular source of properdin, interaction with myeloid cells was examined. Properdin bound to the surface of viable monocyte-derived pro- and anti-inflammatory macrophages, but not to DCs. Binding was demonstrated for purified properdin as well as fractionated P2, P3, and P4 properdin oligomers. Binding contributed to local complement activation as determined by C3 and C5b-9 deposition on the cell surfaces and seems a prerequisite for alternative pathway activation. Interaction of properdin with cell surfaces could be inhibited with the tick protein Salp20 and by different polysaccharides, depending on sulfation and chain length. These data identify properdin as a factor interacting with different cell surfaces, being either dead or alive, contributing to the local stimulation of complement activation.

Plasma endotrophin, reflecting tissue fibrosis, is associated with graft failure and mortality in KTRs: results from two prospective cohort studies.

BACKGROUND: Fibrosis is a suggested cause of graft failure and mortality among kidney transplant recipients (KTRs). Accumulating evidence suggests that collagen type VI is tightly linked to fibrosis and may be a marker of systemic fibrosis and ageing. We studied whether plasma endotrophin, a pro-collagen type VI fragment, is associated with graft failure and mortality among KTRs. METHODS: In cohort A (57% male, age 53 ± 13 years), we measured plasma endotrophin in 690 prevalent KTRs ≥1 year after transplantation. The non-overlapping cohort B included 500 incident KTRs with serial endotrophin measurements before and after kidney transplantation to assess trajectories and intra-individual variation of endotrophin. RESULTS: In cohort A, endotrophin was higher in KTRs compared with healthy controls. Concentrations were positively associated with female sex, diabetes, cardiovascular disease, markers of inflammation and kidney injury. Importantly, endotrophin was associated with graft failure {hazard ratio [HR] per doubling 1.87 [95% confidence interval (CI) 1.07-3.28]} and mortality [HR per doubling 2.59 (95% CI 1.73-3.87)] independent of potential confounders. Data from cohort B showed that endotrophin concentrations strongly decrease after transplantation and remain stable during post-transplantation follow-up [intra-individual coefficient of variation 5.0% (95% CI 3.7-7.6)]. CONCLUSIONS: Plasma endotrophin is strongly associated with graft failure and mortality among KTRs. These findings suggest a key role of abnormal extracellular matrix turnover and fibrosis in graft and patient prognosis among KTRs and highlight the need for (interventional) studies targeting the profibrotic state of KTRs. The intra-individual stability after transplantation indicates potential use of endotrophin as a biomarker and outcome measure of fibrosis. TRIAL REGISTRATION: ClinicalTrials.gov NCT02811835.

Influence of carnosine and carnosinase-1 on diabetes-induced afferent arteriole vasodilation: implications for glomerular hemodynamics.

Dysregulation in glomerular hemodynamics favors hyperfiltration in diabetic kidney disease (DKD). Although carnosine supplementation ameliorates features of DKD, its effect on glomerular vasoregulation is not known. We assessed the influence of carnosine and carnosinase-1 (CN1) on afferent glomerular arteriole vasodilation and its association with glomerular size, hypertrophy, and nephrin expression in diabetic BTBRob/ob mice. Two cohorts of mice including appropriate controls were studied: i.e., diabetic mice that received oral carnosine supplementation (cohort 1) and human (h)CN1 transgenic (TG) diabetic mice (cohort 2). The lumen area ratio (LAR) of the afferent arterioles and glomerular parameters were measured by conventional histology. Three-dimensional analysis using a tissue clearing strategy was also used. In both cohorts, LAR was significantly larger in diabetic BTBRob/ob versus nondiabetic BTBRwt/ob mice (0.41 ± 0.05 vs. 0.26 ± 0.07, P < 0.0001 and 0.42 ± 0.06 vs. 0.29 ± 0.04, P < 0.0001) and associated with glomerular size (cohort 1: r = 0.55, P = 0.001 and cohort 2: r = 0.89, P < 0.0001). LAR was partially normalized by oral carnosine supplementation (0.34 ± 0.05 vs. 0.41 ± 0.05, P = 0.004) but did not differ between hCN1 TG and wild-type BTBRob/ob mice. In hCN1 TG mice, serum CN1 concentrations correlated with LAR (r = 0.90, P = 0.006). Diabetic mice displayed decreased nephrin expression and increased glomerular hypertrophy. This was not significantly different in hCN1 TG BTBRob/ob mice (P = 0.06 and P = 0.08, respectively). In conclusion, carnosine and CN1 may affect intraglomerular pressure in an opposing manner through the regulation of afferent arteriolar tone. This study corroborates previous findings on the role of carnosine in the progression of DKD.NEW & NOTEWORTHY Dysregulation in glomerular hemodynamics favors hyperfiltration in diabetic kidney disease (DKD). Although carnosine supplementation ameliorates features of DKD, its effect on glomerular vasoregulation is not known. We assessed the influence of carnosine and carnosinase-1 (CN1) on afferent glomerular arteriole vasodilation and its association with glomerular size, hypertrophy, and nephrin expression in diabetic BTBRob/ob mice. Our results provide evidence that carnosine feeding and CN1 overexpression likely affect intraglomerular pressure through vasoregulation of the afferent arteriole.

Longitudinal monitoring of BKPyV miRNA levels in kidney transplant recipients with BKPyV-related pathology reflects viral DNA levels and remain high in viremia patients after clearance of viral DNA.

INTRODUCTION: It is unclear whether polyomavirus BK (BKPyV) microribonucleic acid (miRNA) measurement has additional diagnostic and predictive value in kidney transplant recipients (KTR) as compared to current methods of monitoring BKPyV DNA loads. PATIENTS AND METHODS: A retrospective, longitudinal study was performed in 30 KTR with BKPyV viruria (n = 10), BKPyV viremia (n = 10), or BKPyV-associated neuropathy (BKPyVAN) (n = 10). Bkv-miR-B1-3p and 5p and BKPyV DNA load were measured in urine and plasma and compared using receiver operating characteristic (ROC) curves. RESULTS: Levels of Bkv-miR-B1-3p and 5p and BKPyV DNA correlated strongly. Overall, mostly analog courses of urinary and plasma miRNA and DNA loads were observed. Areas under the ROC curves were not significantly different between miRNAs and DNA. Only, in contrast to BKPyV DNA load, BKPyV miRNA levels increased from 6 to 12 months in the viremia group, while in the BKPyVAN group, a decline was seen in both DNA and miRNA. CONCLUSIONS: In this study, we could not demonstrate an additional value of BKPyV miRNA detection compared to BKPyV DNA monitoring in the early phase after kidney transplantation. We did observe significant differences between the viremia and the BKPyVAN groups during follow-up. This study was performed with a small number of patients and therefore results should be verified in a larger patient cohort. Furthermore, future studies with larger patient groups are necessary to elucidate final clinical value of these data.

Hypercholesterolemia in Progressive Renal Failure Is Associated with Changes in Hepatic Heparan Sulfate - PCSK9 Interaction.

BACKGROUND: Dyslipidemia is an important risk factor in CKD. The liver clears triglyceride-rich lipoproteins (TRL) via LDL receptor (LDLR), LDLR-related protein-1 (LRP-1), and heparan sulfate proteoglycans (HSPGs), mostly syndecan-1. HSPGs also facilitate LDLR degradation by proprotein convertase subtilisin/kexin type 9 (PCSK9). Progressive renal failure affects the structure and activity of hepatic lipoprotein receptors, PCSK9, and plasma cholesterol. METHODS: Uninephrectomy- and aging-induced CKD in normotensive Wistar rats and hypertensive Munich-Wistar-Frömter (MWF) rats. RESULTS: Compared with 22-week-old sex- and strain-matched rats, 48-week-old uninephrectomized Wistar-CKD and MWF-CKD rats showed proteinuria, increased plasma creatinine, and hypercholesterolemia (all P<0.05), which were most apparent in hypertensive MWF-CKD rats. Hepatic PCSK9 expression increased in both CKD groups (P<0.05), with unusual sinusoidal localization, which was not seen in 22-week-old rats. Heparan sulfate (HS) disaccharide analysis, staining with anti-HS mAbs, and mRNA expression of HS polymerase exostosin-1 (Ext-1), revealed elongated HS chains in both CKD groups. Solid-phase competition assays showed that the PCSK9 interaction with heparin-albumin (HS-proteoglycan analogue) was critically dependent on polysaccharide chain length. VLDL binding to HS from CKD livers was reduced (P<0.05). Proteinuria and plasma creatinine strongly associated with plasma cholesterol, PCSK9, and HS changes. CONCLUSIONS: Progressive CKD induces hepatic HS elongation, leading to increased interaction with PCSK9. This might reduce hepatic lipoprotein uptake and thereby induce dyslipidemia in CKD. Therefore, PCSK9/HS may be a novel target to control dyslipidemia.

Machine-perfused donor kidneys as a source of human renal endothelial cells.

Renal endothelial cells (ECs) play crucial roles in vasorelaxation, ultrafiltration, and selective transport of electrolytes and water, but also in leakage of the glomerular filtration barrier and inflammatory processes like complement activation and leukocyte recruitment. In addition, they are target cells for both cellular and antibody-mediated rejection in the transplanted kidney. To study the molecular and cellular processes underlying EC behavior in renal disease, well-characterized primary renal ECs are indispensible. In this report, we describe a straightforward procedure to isolate ECs from the perfusion fluid of human donor kidneys by a combination of negative selection of monocytes/macrophages, positive selection by CD31 Dynabeads, and propagation in endothelium-specific culture medium. Thus, we isolated and propagated renal ECs from 102 donor kidneys, representative of all blood groups and major human leukocyte antigen (HLA) class I and II antigens. The obtained ECs were positive for CD31 and von Willebrand factor, expressed other endothelial markers such as CD34, VEGF receptor-2, TIE2, and plasmalemmal vesicle associated protein-1 to a variable extent, and were negative for the monocyte marker CD14 and lymphatic endothelial marker podoplanin. HLA class II was either constitutively expressed or could be induced by interferon-γ. Furthermore, as a proof of principle, we showed the diagnostic value of this renal endothelial biobank in renal endothelium-specific cross-matching tests for HLA antibodies.NEW & NOTEWORTHY We describe a new and widely accessible approach to obtain human primary renal endothelial cells in a standardized fashion, by isolating from the perfusate of machine-perfused donor kidneys. Characterization of the cells showed a mixed population originating from different compartments of the kidney. As a proof of principle, we demonstrated a possible diagnostic application in an endothelium-specific cross-match. Next to transplantation, we foresee further applications in the field renal endothelial research.

Proteinuria converts hepatic heparan sulfate to an effective proprotein convertase subtilisin kexin type 9 enzyme binding partner.

Hepatic uptake of triglyceride-rich remnant lipoproteins is mediated by the low-density lipoprotein receptor, a low-density lipoprotein receptor related protein and the heparan sulfate proteoglycan, syndecan-1. Heparan sulfate proteoglycan also mediates low-density lipoprotein receptor degradation by a regulator of cholesterol homeostasis, proprotein convertase subtilisin kexin type 9 (PCSK9), thereby hampering triglyceride-rich remnant lipoproteins uptake. In this study, we investigated the effects of proteinuria on PCSK9, hepatic heparan sulfate proteoglycan and plasma triglyceride-rich remnant lipoproteins. Adriamycin-injected rats developed proteinuria, elevated triglycerides and total cholesterol (all significantly increased). Proteinuria associated with triglycerides and total cholesterol and serum PCSK9 (all significant associations) without loss of the low-density lipoprotein receptor as evidenced by immunofluorescence staining and western blotting. In proteinuric rats, PCSK9 accumulated in sinusoids, whereas in control rats PCSK9 was localized in the cytoplasm of hepatocytes. Molecular profiling revealed that the heparan sulfate side chains of heparan sulfate proteoglycan to be hypersulfated in proteinuric rats. Competition assays revealed sulfation to be a major determinant for PCSK9 binding. PCSK9 partly colocalized with hypersulfated heparan sulfate in proteinuric rats, but not in control rats. Hence, proteinuria induces hypersulfated hepatic heparan sulfate proteoglycans, increasing their affinity to PCSK9. This might impair hepatic triglyceride-rich remnant lipoproteins uptake, causing proteinuria-associated dyslipidemia. Thus, our study reveals PCSK9/heparan sulfate may be a novel target to control dyslipidemia.

An acute rise of plasma Na+ concentration associates with syndecan-1 shedding during hemodialysis.

Endothelial dysfunction (ED) contributes to the high incidence of cardiovascular events in patients undergoing hemodialysis. Syndecan-1 in the endothelial glycocalyx can be shed into the circulation, serving as a biomarker for ED. As Na+ is a trigger for glycocalyx shedding, we now tested whether hemodialysis, with higher dialysate Na+ concentrations, is associated with more syndecan-1 shedding compared with standard hemodialysis (SHD). In this crossover study in 29 patients, plasma syndecan-1 was repeatedly measured during SHD and during Hemocontrol hemodialysis (HHD), which is characterized by initially higher dialysate and plasma Na+ levels. Courses of syndecan-1 were compared with linear mixed models. Syndecan-1 shedding was assessed by area under the curve analysis. Plasma Na+ increased early after the start of SHD and HHD, with higher values during HHD (30 min: 142.3 vs. 139.9 mM, P < 0.001). Syndecan-1 increased significantly during both conditions, but the percent change was higher (42.9% vs. 19.5%) and occurred earlier (120 vs. 180 min) during HHD. Syndecan-1 levels were significantly higher at 120 min during HHD compared with SHD (P < 0.05). Overall, syndecan-1 shedding was higher during HHD compared with SHD (means: 40.4 vs. 19.0 arbitrary units, P = 0.06). Lower predialysis plasma Na+ and osmolality were associated with greater intradialytic increases in syndecan-1 levels (both groups, P = 0.001). The rise in plasma syndecan-1 levels was more pronounced and occurred earlier during hemodialysis with higher plasma Na+ levels. Although we cannot prove that the rise in plasma syndecan-1 originates from the endothelial glycocalyx, our findings are compatible with Na+-driven endothelial glycocalyx-derived syndecan-1 shedding.

Plasma syndecan-1 in hemodialysis patients associates with survival and lower markers of volume status.

Syndecan-1, a transmembrane heparan sulfate proteoglycan, associates with renal and cardiovascular functioning. We earlier reported syndecan-1 to be involved in renal tubular regeneration. We now examined plasma values of syndecan-1 in a hemodialysis cohort and its association with volume and inflammatory and endothelial markers in addition to outcome. Eighty-four prevalent hemodialysis patients were evaluated for their plasma syndecan-1 levels by ELISA before the start of hemodialysis, as well as 60, 180, and 240 min after start of dialysis. Patients were divided into sex-stratified tertiles based on predialysis plasma syndecan-1 levels. We studied the association between plasma levels of syndecan-1 and volume, inflammation, and endothelial markers and its association with cardiovascular events and all-cause mortality using Kaplan-Meier curves and Cox regression analyses with adjustments for gender, age, diabetes, and dialysis vintage. Predialysis syndecan-1 levels were twofold higher in men compared with women ( P = 0.0003). Patients in the highest predialysis plasma syndecan-1 tertile had a significantly higher ultrafiltration rate ( P = 0.034) and lower plasma values of BNP ( P = 0.019), pro-ANP ( P = 0.024), and endothelin ( P < 0.0001) compared with the two lower predialysis syndecan-1 tertiles. No significant associations with inflammatory markers were found. Cox regression analysis showed that patients in the highest syndecan-1 tertile had significantly less cardiovascular events and better survival compared with the lowest syndecan-1 tertile ( P = 0.02 and P = 0.005, respectively). In hemodialysis patients, higher plasma syndecan-1 levels were associated with lower concentrations of BNP, pro-ANP, and endothelin and with better patient survival. This may suggest that control of volume status in hemodialysis patients allows an adaptive tissue regenerative response as reflected by higher plasma syndecan-1 levels.

Dermal tissue remodeling and non-osmotic sodium storage in kidney patients.

BACKGROUND: Excess dietary sodium is not only excreted by the kidneys, but can also be stored by non-osmotic binding with glycosaminoglycans in dermal connective tissue. Such storage has been associated with dermal inflammation and lymphangiogenesis. We aim to investigate if skin storage of sodium is increased in kidney patients and if this storage is associated with clinical parameters of sodium homeostasis and dermal tissue remodeling. METHODS: Abdominal skin tissue of 12 kidney patients (5 on hemodialysis) and 12 healthy kidney donors was obtained during surgery. Skin biopsies were processed for dermal sodium measurement by atomic absorption spectroscopy, and evaluated for CD68+ macrophages, CD3+ T-cells, collagen I, podoplanin + lymph vessels, and glycosaminoglycans by qRT-PCR and immunohistochemistry. RESULTS: Dermal sodium content of kidney patients did not differ from healthy individuals, but was inversely associated with plasma sodium values (p < 0.05). Compared to controls, kidney patients showed dermal tissue remodeling by increased CD68+ macrophages, CD3+ T-cells and Collagen I expression (all p < 0.05). Also, both N- and O-sulfation of heparan sulfate glycosaminoglycans were increased (all p < 0.05), most outspoken in hemodialysis patients. Plasma and urinary sodium associates with dermal lymph vessel number (both p < 0.05), whereas loss of eGFR, proteinuria and high systolic blood pressure associated with dermal macrophage density (all p < 0.05). CONCLUSION: Kidney patients did not show increased skin sodium storage compared to healthy individuals. Results do indicate that kidney failure associates with dermal inflammation, whereas increased sodium excretion and plasma sodium associate with dermal lymph vessel formation and loss of dermal sodium storage capacity. Trial registration The cohort is registered at clinicaltrials.gov as NCT (September 6, 2017). NCT, NCT03272841. Registered 6 September 2017-Retrospectively registered, https://clinicaltrials.gov.

Carnosinase concentration, activity, and CNDP1 genotype in patients with type 2 diabetes with and without nephropathy.

This study assessed if serum carnosinase (CNDP1) activity and concentration in patients with type 2 diabetes mellitus (T2D) with diabetic nephropathy (DN) differs from those without nephropathy. In a cross-sectional design 127 patients with T2D with DN ((CTG)5 homozygous patients n = 45) and 145 patients with T2D without nephropathy ((CTG)5 homozygous patients n = 47) were recruited. Univariate and multivariate regression analyses were performed to predict factors relevant for serum CNDP1 concentration. CNDP1 (CTG)5 homozygous patients with T2D with DN had significantly lower CNDP1 concentrations (30.4 ± 18.3 vs 51.2 ± 17.6 µg/ml, p < 0.05) and activity (1.25 ± 0.5 vs 2.53 ± 1.1 µmol/ml/h, p < 0.05) than those without nephropathy. This applied for patients with DN on the whole, irrespective of (CTG)5 homozygosity. In the multivariate regression analyses, lower serum CNDP1 concentrations correlated with impaired renal function and to a lesser extend with the CNDP1 genotype (95% CI of regression coefficients: eGFR: 0.10-1.94 (p = 0.001); genotype: - 0.05 to 5.79 (p = 0.055)). Our study demonstrates that serum CNDP1 concentrations associate with CNDP1 genotype and renal function in patients with T2D. Our data warrant further studies using large cohorts to confirm these findings and to delineate the correlation between low serum CNDP1 concentrations and renal function deterioration in patients with T2D.

Identification and characterisation of carnostatine (SAN9812), a potent and selective carnosinase (CN1) inhibitor with in vivo activity.

Carnosinase 1 (CN1) has been postulated to be a susceptibility factor for developing diabetic nephropathy (DN). Although its major substrate, carnosine, is beneficial in rodent models of DN, translation of these findings to humans has been hampered by high CN1 activity in human serum resulting in rapid degradation of carnosine. To overcome this hurdle, we screened a protease-directed small-molecule library for inhibitors of human recombinant CN1. We identified SAN9812 as a potent and highly selective inhibitor of CN1 activity with a Ki of 11 nM. It also inhibited CN1 activity in human serum and serum of transgenic mice-overexpressing human CN1. Subcutaneous administration of 30 mg/kg SAN9812 led to a sustained reduction in circulating CN1 activity in human CN1 transgenic (TG) mice. Simultaneous administration of carnosine and SAN9812 increased carnosine levels in plasma and kidney by up to 100-fold compared to treatment-naïve CN1-overexpressing mice. To our knowledge, this is the first study reporting on a potent and selective CN1 inhibitor with in vivo activity. SAN9812, also called carnostatine, may be used to increase renal carnosine concentration as a potential therapeutic modality for renal diseases linked to glycoxidative conditions.

Endothelial heparan sulfate deficiency reduces inflammation and fibrosis in murine diabetic nephropathy.

Inflammation plays a vital role in the development of diabetic nephropathy, but the underlying regulatory mechanisms are only partially understood. Our previous studies demonstrated that, during acute inflammation, endothelial heparan sulfate (HS) contributes to the adhesion and transendothelial migration of leukocytes into perivascular tissues by direct interaction with L-selectin and the presentation of bound chemokines. In the current study, we aimed to assess the role of endothelial HS on chronic renal inflammation and fibrosis in a diabetic nephropathy mouse model. To reduce sulfation of HS specifically in the endothelium, we generated Ndst1 f/f Tie2Cre + mice in which N-deacetylase/N-sulfotransferase-1 (Ndst1), the gene that initiates HS sulfation modifications in HS biosynthesis, was expressly ablated in endothelium. To induce diabetes, age-matched male Ndst1 f/f Tie2Cre - (wild type) and Ndst1 f/f Tie2Cre + mice on a C57Bl/6J background were injected intraperitoneally with streptozotocin (STZ) (50 mg/kg) on five consecutive days (N = 10-11/group). Urine and plasma were collected. Four weeks after diabetes induction the animals were sacrificed and kidneys were analyzed by immunohistochemistry and qRT-PCR. Compared to healthy controls, diabetic Ndst1 f/f Tie2Cre - mice showed increased glomerular macrophage infiltration, mannose binding lectin complement deposition and glomerulosclerosis, whereas these pathological reactions were prevented significantly in the diabetic Ndst1 f/f Tie2Cre + animals (all three p < 0.01). In addition, the expression of the podocyte damage marker desmin was significantly higher in the Ndst1 f/f Tie2Cre - group compared to the Ndst1 f/f Tie2Cre + animals (p < 0.001), although both groups had comparable numbers of podocytes. In the cortical tubulo-interstitium, similar analyses show decreased interstitial macrophage accumulation in the diabetic Ndst1 f/f Tie2Cre + animals compared to the diabetic Ndst1 f/f Tie2Cre - mice (p < 0.05). Diabetic Ndst1 f/f Tie2Cre + animals also showed reduced interstitial fibrosis as evidenced by reduced density of αSMA-positive myofibroblasts (p < 0.01), diminished collagen III deposition (p < 0.001) and reduced mRNA expression of collagen I (p < 0.001) and fibronectin (p < 0.001). Our studies indicate a pivotal role of endothelial HS in the development of renal inflammation and fibrosis in diabetic nephropathy in mice. These results suggest that HS is a possible target for therapy in diabetic nephropathy.

Association of plasma somatostatin with disease severity and progression in patients with autosomal dominant polycystic kidney disease.

BACKGROUND: Somatostatin (SST) inhibits intracellular cyclic adenosine monophosphate (cAMP) production and thus may modify cyst formation in autosomal dominant polycystic kidney disease (ADPKD). We investigated whether endogenous plasma SST concentration is associated with disease severity and progression in patients with ADPKD, and whether plasma SST concentrations change during treatment with a vasopressin V2 receptor antagonist or SST analogue. METHODS: In this observational study, fasting concentrations of SST were measured in 127 ADPKD patients (diagnosed upon the revised Ravine criteria) by ELISA. cAMP was measured in 24 h urine by Radio Immuno Assay. Kidney function was measured (mGFR) as 125I-iothalamate clearance, and total kidney volume was measured by MRI volumetry and adjusted for height (htTKV). Disease progression was expressed as annual change in mGFR and htTKV. Additionally, baseline versus follow-up SST concentrations were compared in ADPKD patients during vasopressin V2 receptor antagonist (tolvaptan) (n = 27) or SST analogue (lanreotide) treatment (n = 25). RESULTS: In 127 ADPKD patients, 41 ± 11 years, 44% female, eGFR 73 ± 32 ml/min/1.73m2, mGFR 75 ± 32 ml/min/1.73m2 and htTKV 826 (521-1297) ml/m, SST concentration was 48.5 (34.3-77.8) pg/ml. At baseline, SST was associated with urinary cAMP, mGFR and htTKV (p = 0.02, p = 0.004 and p = 0.02, respectively), but these associations lost significance after adjustment for age and sex or protein intake (p = 0.09, p = 0.06 and p = 0.15 respectively). Baseline SST was not associated with annual change in mGFR, or htTKV during follow-up (st. ß = - 0.02, p = 0.87 and st. ß = - 0.07, p = 0.54 respectively). During treatment with tolvaptan SST levels remained stable 38.2 (23.8-70.7) pg/mL vs. 39.8 (31.2-58.5) pg/mL, p = 0.85), whereas SST levels decreased significantly during treatment with lanreotide (42.5 (33.2-55.0) pg/ml vs. 29.3 (24.8-37.6), p = 0.008). CONCLUSIONS: Fasting plasma SST concentration is not associated with disease severity or progression in patients with ADPKD. Treatment with lanreotide caused a decrease in SST concentration. These data suggest that plasma SST cannot be used as a biomarker to assess prognosis in ADPKD, but leave the possibility open that change in SST concentration during lanreotide treatment may reflect therapy efficacy.

Accumulation of worn-out GBM material substantially contributes to mesangial matrix expansion in diabetic nephropathy.

Thickening of the glomerular basement membrane (GBM) and expansion of the mesangial matrix are hallmarks of diabetic nephropathy (DN), generally considered to emerge from different sites of overproduction: GBM components from podocytes and mesangial matrix from mesangial cells. Reevaluation of 918 biopsies with DN revealed strong evidence that these mechanisms are connected to each other, wherein excess GBM components fail to undergo degradation and are deposited in the mesangium. These data do not exclude that mesangial cells also synthesize components that contribute to the accumulation of matrix in the mesangium. Light, electron microscopic, immunofluorescence, and in situ hybridization studies clearly show that the thickening of the GBM is due not only to overproduction of components of the mature GBM (α3 and α5 chains of collagen IV and agrin) by podocytes but also to resumed increased synthesis of the α1 chain of collagen IV and of perlecan by endothelial cells usually seen during embryonic development. We hypothesize that these abnormal production mechanisms are caused by different processes: overproduction of mature GBM-components by the diabetic milieu and regression of endothelial cells to an embryonic production mode by decreased availability of mediators from podocytes.

Urinary collagen degradation products as early markers of progressive renal fibrosis.

BACKGROUND: Renal fibrogenesis is associated with increased ECM remodeling and release of collagen fragments in urine in progressive renal disease. We investigated the diagnostic value of urinary collagen degradation products in a proteinuria-driven fibrosis rat model with and without anti-fibrotic S1P-receptor modulator FTY720 treatment. METHODS: Proteinuria was induced in male Wistar rats by Adriamycin (ADR) injection (n = 16). Healthy rats served as controls (n = 12). Six weeks post-injection, all underwent renal biopsy, and FTY720-treatment started in ADR-rats (n = 8) and controls (n = 6). Others remained untreated. Rats were sacrificed after 12 weeks. Collagen type I (C1M) and III (C3M) degradation fragments were measured in blood and urine using ELISA. Kidneys were stained for various inflammatory and fibrotic markers. RESULTS: Six weeks post-injection proteinuria increased (versus controls, P < 0.001) and although no accumulation of interstitial renal collagen type III (iColl3) was observed at this time, urinary C3M (uC3M) and C1M (uC1M) were significantly increased (both P < 0.001). At 12 weeks, uC3M (P < 0.001) and uC1M (P < 0.01) further increased in ADR-rats versus controls, just as fibronectin, PDGF-ß receptor, hyaluronan (all P < 0.01), iColl3, PAS, myofibroblasts, macrophages and T-cells (all P < 0.05). FTY720-treatment reduced accumulation of immune cells, α-SMA+ myofibroblasts and PAS-score, but not iColl3 and uC3M. Correlation analyses indicated that uC3M and uC1M reflected and predicted tubulointerstitial fibrogenesis. CONCLUSIONS: These data displayed urinary collagen breakdown products as sensitive early markers of interstitial fibrosis, preceding histological fibrotic changes, which might replace the invasive renal biopsy procedure to assess fibrosis. Anti-fibrotic FTY720 intervention reduced some fibrotic markers without affecting collagen type III metabolism.

The bittersweet taste of tubulo-interstitial glycans.

Recently, interesting work was published by Farrar et al. [1] showing the interaction of fucosylated glycoproteins on stressed tubular epithelial cells with collectin-11 leading to complement activation via the lectin route of complement. This elegant work stimulated us to evaluate the dark side (bittersweet taste) of tubulo-interstitial glycans in kidney tissue damage. As will be discussed, glycans not only initiate tubular complement activation but also orchestrate tubulo-interstitial leucocyte recruitment and growth factor responses. In this review we restrict ourselves to tubulo-interstitial damage mainly by proteinuria, ischaemia-reperfusion injury and transplantation, and we discuss the involvement of endothelial and tubular glycans in atypical and Escherichia coli-mediated haemolytic uraemic syndrome. As will be seen, fucosylated, mannosylated, galactosylated and sialylated oligosaccharide structures along with glycosaminoglycans comprise the most important glycans related to kidney injury pathways. Up to now, therapeutic interventions in these glycan-mediated injury pathways are underexplored and warrant further research.

Sodium restriction potentiates the renoprotective effects of combined vitamin D receptor activation and angiotensin-converting enzyme inhibition in established proteinuric nephropathy.

BACKGROUND: Renin-angiotensin-aldosterone system (RAAS) blockade provides renoprotective effects in chronic kidney disease (CKD); yet progressive renal function loss remains common. Dietary sodium restriction potentiates the renoprotective effects of RAAS blockade. Vitamin D receptor activator (VDRA) treatment reduces proteinuria, inflammation and fibrosis, but whether these effects depend on sodium intake has not been studied. We hypothesized that the renoprotective effects of VDRA treatment, with or without RAAS blockade, are modulated by sodium intake. METHODS: Six weeks after the induction of adriamycin nephrosis in Wistar rats, i.e. with established proteinuria, animals were treated with the VDRA paricalcitol, lisinopril, the combination, or vehicle; each treatment was given during either a high- (2% NaCl) or a low-sodium (0.05% NaCl) diet for 6 weeks. We assessed proteinuria, blood pressure, renal macrophage accumulation and renal expression of the pre-fibrotic marker alpha-smooth muscle actin (α-SMA) at the end of the treatment. RESULTS: Both paricalcitol and lisinopril individually, as well as in combination, reduced proteinuria and glomerular and interstitial inflammation during a low-sodium diet, but not during a high-sodium diet. All interventions also reduced focal glomerulosclerosis and interstitial expression of α-SMA during the low-sodium diet, while similar trends were observed during the high-sodium diet. The renoprotective effects of paricalcitol were not accompanied by blood pressure reduction. As proteinuria was already abolished by lisinopril during the low-sodium diet, the addition of paricalcitol had no further effect on proteinuria or downstream inflammatory or pre-fibrotic changes. CONCLUSION: The renoprotective effects of the VDRA paricalcitol are blood pressure independent but do depend on dietary sodium status. The combination of RAAS blockade, dietary sodium restriction and VDRA may be a promising intervention to further retard renal function loss in CKD.