Mechanism of injury in uromodulin-associated kidney disease

The use of diagnostic tools for pediatric AKI: applying the current evidence to the bedside

Given the known deleterious consequences of acute kidney injury (AKI), exciting recent research efforts have focused on developing strategies for the earlier recognition of AKI in the pediatric population. Recognizing the limitations of serum creatinine, investigators have focused on the study of novel biomarkers and practical bedside tools for identifying patients at risk for AKI prior to a rise in serum creatinine. In PubMed, there are presently over 30 original research papers exploring the use of pediatric AKI risk prediction tools in just the last 2 years. The following review highlights the most recent advances in the literature regarding opportunities to refine our ability to detect AKI early. Importantly, this review discusses how prediction tools including novel urine and serum biomarkers, practical risk stratification tests, renal functional reserve, and electronic medical record alerts may ultimately be applied to routine clinical practice.

Study of the relationship between urinary level of uromodulin, renal involvement and disease activity in patients with systemic lupus erythrematosus

Systemic lupus erythematosus (SLE) is a multifactorial chronic inflammatory autoimmune connective tissue disease. Lupus nephritis (LN) is a common and serious complication of SLE which can progress to end-stage renal disease. Renal biopsy is the gold standard in the diagnosis and classification of LN, but since it is an invasive procedure, it is neither desirable nor applicable for all cases. This has led to the search for an alternative, noninvasive, site-specific, and immune process-related biomarkers. Uromodulin (Tamm-Horsfall glycoprotein) is the most abundant urinary protein expressed exclusively by the thick ascending limb cells and released into urine of healthy controls. Studies showed that it may act as a danger signaling molecule eliciting an inflammatory response following conditions that damage the nephron integrity and leading to uromodulin release into the interstitial space. This study aimed to assess uromodulin as a screening biomarker of tubulointerstitial involvement in patients with SLE and to elucidate its correlation with disease activity and progression. The study was conducted on 70 patients divided into two groups: control group (Group I) consisted of 20 apparently healthy volunteers of comparable age and sex to the patients' group, and 50 SLE patients (Group II) diagnosed according to the 2012 Systemic Lupus Collaborating Clinics (SLICC) classification criteria. Group II was further subdivided into 23 patients without manifestations of LN (Group II A) and 27 patients with manifestations of LN (Group II B). Urinary uromodulin level showed statistically significant difference among the studied groups, being lowest among the LN patients with a mean value 5.6 ± 3.4, in SLE patients without nephritis 9.9 ± 5.2 and 12.9 ± 4.6 in the control group. Urinary uromodulin also correlated positively with estimated glome- rular filtration rate. A negative correlation was found between urinary uromodulin and serum creatinine, 24 h urinary proteins and SLICC renal activity score. No statistically significant correlation was found between urinary uromo- dulin and SLE disease activity index. Thus, decreasing urinary uromodulin levels can be a marker for renal involvement and tubulo- interstitial nephritis in active SLE patients and a marker for chronic kidney disease and nephron loss in the absence of activity markers.

Serum uromodulin-a marker of kidney function and renal parenchymal integrity

Background

An ELISA to analyse uromodulin in human serum (sUmod) was developed, validated and tested for clinical applications.

Methods

We assessed sUmod, a very stable antigen, in controls, patients with chronic kidney disease (CKD) stages 1-5, persons with autoimmune kidney diseases and recipients of a renal allograft by ELISA.

Results

Median sUmod in 190 blood donors was 207 ng/mL (women: men, median 230 versus 188 ng/mL, P = 0.006). sUmod levels in 443 children were 193 ng/mL (median). sUmod was correlated with cystatin C (rs = -0.862), creatinine (rs = -0.802), blood urea nitrogen (BUN) (rs = -0.645) and estimated glomerular filtration rate (eGFR)-cystatin C (rs  =  0.862). sUmod was lower in systemic lupus erythematosus-nephritis (median 101 ng/mL), phospholipase-A2 receptor- positive glomerulonephritis (median 83 ng/mL) and anti-glomerular basement membrane positive pulmorenal syndromes (median 37 ng/mL). Declining sUmod concentrations paralleled the loss of kidney function in 165 patients with CKD stages 1-5 with prominent changes in sUmod within the 'creatinine blind range' (71-106 µmol/L). Receiver-operating characteristic analysis between non-CKD and CKD-1 was superior for sUmod (AUC 0.90) compared with eGFR (AUC 0.39), cystatin C (AUC 0.39) and creatinine (AUC 0.27). sUmod rapidly recovered from 0 to 62 ng/mL (median) after renal transplantation in cases with immediate graft function and remained low in delayed graft function (21 ng/mL, median; day 5-9: relative risk 1.5-2.9, odds ratio 1.5-6.4). Immunogold labelling disclosed that Umod is transferred within cytoplasmic vesicles to both the apical and basolateral plasma membrane. Umod revealed a disturbed intracellular location in kidney injury.

Conclusions

We conclude that sUmod is a novel sensitive kidney-specific biomarker linked to the structural integrity of the distal nephron and to renal function.

Plasma biomarkers improve prediction of diabetic kidney disease in adults with type 1 diabetes over a 12-year follow-up: CACTI study

Background

The objective of the study was to determine whether plasma biomarkers of kidney injury improve the prediction of diabetic kidney disease (DKD) in adults with type 1 diabetes (T1D) over a period of 12 years.

Methods

Participants (n = 527, 53% females) in the Coronary Artery Calcification in T1D (CACTI) Study were examined during 2002-04, at a mean (± standard deviation) age of 39.6 ± 9.0 years with 24.8 years as the median duration of diabetes. Urine albumin-to-creatinine (ACR) and estimated glomerular filtration rate (eGFR) by CKD-EPI (chronic kidney disease epidemiology collaboration) creatinine were measured at the baseline and after mean follow-up of 12.1 ± 1.5 years. Albuminuria was defined as ACR ≥30 mg/g and impaired GFR as eGFR <60 mL/min/1.73 m2. Kidney injury biomarkers (Meso Scale Diagnostics) were measured on stored baseline plasma samples. A principal component analysis (PCA) identified two components: (i) kidney injury molecule-1, calbindin, osteoactivin, trefoil factor 3 and vascular endothelial growth factor; and (ii) β-2 microglobulin, cystatin C, neutrophil gelatinase-associated lipocalin and osteopontin that were used in the multivariable regression analyses.

Results

Component 2 of the PCA was associated with increase in log modulus ACR [β ± standard error (SE): 0.16 ± 0.07, P = 0.02] and eGFR (β ± SE: -2.56 ± 0.97, P = 0.009) over a period of 12 years after adjusting for traditional risk factors (age, sex, HbA1c, low-density lipoprotein cholesterol and systolic blood pressure and baseline eGFR/baseline ACR). Only Component 2 of the PCA was associated with incident-impaired GFR (odds ratio 2.08, 95% confidence interval 1.18-3.67, P = 0.01), adjusting for traditional risk factors. The addition of Component 2 to traditional risk factors significantly improved C-statistics and net-reclassification improvement for incident-impaired GFR (ΔAUC: 0.02 ± 0.01, P = 0.049, and 29% non-events correctly reclassified, P < 0.0001).

Conclusions

Plasma kidney injury biomarkers can help predict development of DKD in T1D.

Preoperative levels of urinary uromodulin predict acute kidney injury after pediatric cardiopulmonary bypass surgery

BACKGROUND

Acute kidney injury (AKI) is a common complication of cardiopulmonary bypass surgery (CPB) in children. Several promising postoperative AKI biomarkers have been identified, but no preoperative biomarkers are available. We evaluated the association of urinary uromodulin (uUMOD) with postoperative AKI.

METHODS

One hundred and one children undergoing CPB were enrolled. Urine was collected prior to CPB, and AKI was defined as ≧50% increase in serum creatinine from preoperative baseline within 48 h of surgery.

RESULTS

Forty-seven patients (47%) developed AKI, and 92% of participants in the lowest quartile of preoperative uUMOD concentrations developed AKI compared with 8% in the highest quartile. Patients with preoperative uUMOD levels in the lowest quartile had 132.3× increased risk of postoperative AKI versus the highest quartile. Raw uUMOD levels were significantly lower in patients with AKI vs. no AKI. Significance was unchanged after correcting uUMOD levels for urinary creatinine. Receiver operating characteristic analysis showed preoperative uUMOD strongly predicted postoperative AKI, with area under the curve (AUC) 0.90. Stepwise logistic regression analysis revealed a model combining uUMOD, and bypass time predicted AKI at p<0.001. Neither Risk Adjustment for Congenital Heart Surgery 1 (RACHS) score nor age improved the model's ability to predict AKI. Independent analysis demonstrated that while bypass time was associated with AKI, the predictive ability of bypass time (AUC 0.77) was less than that of preoperative uUMOD levels (AUC 0.9).

CONCLUSIONS

Children with lowest preoperative levels of uUMOD have greatly increased risk of AKI post-CPB. If uUMOD were used to risk-stratify patients undergoing CPB, clinical measures could be taken to minimize AKI development.

First Report of Familial Juvenile Hyperuricemic Nephropathy (FJHN) in Iran Caused By a Novel De Novo Mutation (E197X) in UMOD

Uromodulin (UMOD) gene mutation causes autosomal dominant Uromodulin-Associated Kidney Disease (UAKD), which in turn leads to end-stage renal disease. This is the first case report of a family with UAKD caused by a novel de novo mutation (E197X) in the UMOD gene. This case is a 28-year-old man with severely reduced kidney function [1]. No similar case was reported in his family history. This report highlights and reminds the importance of genetic screening in young patients involving kidney dysfunction, as the UAKD and some other kidney genetic diseases may be late-onset.

Tamm-Horsfall protein-deficient thick ascending limbs promote injury to neighboring S3 segments in an MIP-2-dependent mechanism

Tamm-Horsfall protein (THP) is a glycoprotein expressed exclusively in thick ascending limbs (TAL) of the kidney. We recently described a novel protective role of THP against acute kidney injury (AKI) via downregulation of inflammation in the outer medulla. Our current study investigates the mechanistic relationships among the status of THP, inflammation, and tubular injury. Using an ischemia-reperfusion model in wild-type and THP-/- mice, we demonstrate that it is the S3 proximal segments but not the THP-deficient TAL that are the main targets of tubular injury during AKI. The injured S3 segments that are surrounded by neutrophils in THP-/- mice have marked overexpression of neutrophil chemoattractant MIP-2 compared with wild-type counterparts. Neutralizing macrophage inflammatory protein-2 (MIP-2) antibody rescues S3 segments from injury, decreases neutrophil infiltration, and improves kidney function in THP-/- mice. Furthermore, using immunofluorescence volumetric imaging of wild-type mouse kidneys, we show that ischemia alters the intracellular translocation of THP in the TAL cells by partially shifting it from its default apical surface domain to the basolateral domain, the latter being contiguous to the basolateral surface of S3 segments. Concomitant with this is the upregulation, in the basolateral surface of S3 segments, of the scavenger receptor SRB-1, a putative receptor for THP. We conclude that TAL affects the susceptibility of S3 segments to injury at least in part by regulating MIP-2 expression in a THP-dependent manner. Our findings raise the interesting possibility of a direct role of basolaterally released THP on regulating inflammation in S3 segments.

A case of familial juvenile hyperuricemic nephropathy with novel uromodulin gene mutation, a novel heterozygous missense mutation in Korea

Familial Juvenile hyperuricemic nephropathy (FJHN, OMIM #162000) is a rare autosomal dominant disorder characterized by hyperuricemia with renal uric acid under-excretion, gout and chronic kidney disease. In most but not all families with FJHN, genetic studies have revealed mutations in the uromodulin (UMOD) gene located on chromosome 16p11-p13. We here described a novel heterozygous missense mutation (c.1382C>A causing p.Ala461Glu) in an affected 16-year-old male with hyperuricemia, gout and chronic kidney disease. His father was also affected and the UMOD mutation was found to segregate with the disease. There has been only one case report of Korean family with FJHN, which has not been diagnosed by genetic study. This is the first report of genetically diagnosed FJHN in Korea.

The classification of renal cystic diseases and other congenital malformations of the kidney and urinary tract

CONTEXT

Renal cystic diseases and congenital abnormalities of the kidney and urinary tract comprise a heterogeneous group of lesions whose pathogenesis has eluded physicians for centuries. Recent advances in molecular and genetic understanding of these diseases may provide the solution to this riddle.

OBJECTIVE

The formulation of an effective classification system for these disorders has been elusive but is needed to introduce order while providing a conceptual framework for diagnosis.

DATA SOURCES

This review discusses the evolution, beginning in the 19th century, of postulates regarding the pathogenesis of cystic and developmental renal diseases. Selected classification systems proffered during this period are discussed in pursuit of an ideal classification schema that would account for morphologic features and their clinical importance, with logical links to pathogenesis and treatment. Although this remains an elusive target, its general outline is becoming clearer. A classification approach favored by the author is presented, which incorporates many of the strengths contained in several previous classifications.

CONCLUSIONS

Genetic-and molecular-based postulates regarding the pathogenesis of the renal cystic and developmental diseases have implicated mutated master genes and the modification of genes that are crucial in renal development and genes that are central to the sensory effects of the renal tubular primary cilium on cell physiology. These scientific advances provide pathogenetic links between morphologically and genetically distinct entities and certain cystic and neoplastic entities, associations that seemed implausible not long ago. These advances may eventually provide the basis for future classification systems while suggesting targets for therapeutic approaches in the prevention and treatment of these diseases.