Unveiling the Hidden Power of Uromodulin: A Promising Potential Biomarker for Kidney Diseases

Uromodulin, also known as Tamm-Horsfall protein, represents the predominant urinary protein in healthy individuals. Over the years, studies have revealed compelling associations between urinary and serum concentrations of uromodulin and various parameters, encompassing kidney function, graft survival, cardiovascular disease, glucose metabolism, and overall mortality. Consequently, there has been a growing interest in uromodulin as a novel and effective biomarker with potential applications in diverse clinical settings. Reduced urinary uromodulin levels have been linked to an elevated risk of acute kidney injury (AKI) following cardiac surgery. In the context of chronic kidney disease (CKD) of different etiologies, urinary uromodulin levels tend to decrease significantly and are strongly correlated with variations in estimated glomerular filtration rate. The presence of uromodulin in the serum, attributable to basolateral epithelial cell leakage in the thick ascending limb, has been observed. This serum uromodulin level is closely associated with kidney function and histological severity, suggesting its potential as a biomarker capable of reflecting disease severity across a spectrum of kidney disorders. The UMOD gene has emerged as a prominent locus linked to kidney function parameters and CKD risk within the general population. Extensive research in multiple disciplines has underscored the biological significance of the top UMOD gene variants, which have also been associated with hypertension and kidney stones, thus highlighting the diverse and significant impact of uromodulin on kidney-related conditions. UMOD gene mutations are implicated in uromodulin-associated kidney disease, while polymorphisms in the UMOD gene show a significant association with CKD. In conclusion, uromodulin holds great promise as an informative biomarker, providing valuable insights into kidney function and disease progression in various clinical scenarios. The identification of UMOD gene variants further strengthens its relevance as a potential target for better understanding kidney-related pathologies and devising novel therapeutic strategies. Future investigations into the roles of uromodulin and regulatory mechanisms are likely to yield even more profound implications for kidney disease diagnosis, risk assessment, and management.

Urinary Protein Profiling for Potential Biomarkers of Chronic Kidney Disease: A Pilot Study

Proteinuria is a risk factor for chronic kidney disease (CKD) progression and associated complications. However, there is insufficient information on individual protein components in urine and the severity of CKD. We aimed to investigate urinary proteomics and its association with proteinuria and kidney function in early-stage CKD and in healthy individuals. A 24 h urine sample of 42 individuals (21-CKD and 21-healthy individuals) was used for mass spectrometry-based proteomics analysis. An exponentially modified protein abundance index (emPAI) was calculated for each protein. Data were analyzed by Mascot software using the SwissProt database and bioinformatics tools. Overall, 298 unique proteins were identified in the cohort; of them, 250 proteins belong to the control group with median (IQR) emPAI 39.1 (19−53) and 142 proteins belong to the CKD group with median (IQR) emPAI 67.8 (49−117). The level of 24 h proteinuria positively correlated with emPAI (r = 0.390, p = 0.011). The emPAI of some urinary proteomics had close positive (ALBU, ZA2G, IGKC) and negative (OSTP, CD59, UROM, KNG1, RNAS1, CD44, AMBP) correlations (r < 0.419, p < 0.001) with 24 h proteinuria levels. Additionally, a few proteins (VTDB, AACT, A1AG2, VTNC, and CD44) significantly correlated with kidney function. In this proteomics study, several urinary proteins correlated with proteinuria and kidney function. Pathway analysis identified subpathways potentially related to early proteinuric CKD, allowing the design of prospective studies that explore their response to therapy and their relationship to long-term outcomes.

Uromodulin Regulates Murine Aquaporin-2 Activity via Thick Ascending Limb-Collecting Duct Cross-Talk during Water Deprivation

Uromodulin, a urinary protein synthesized and secreted from the thick ascending limb (TAL) of the loop of Henle, is associated with hypertension through the activation of sodium reabsorption in the TAL. Uromodulin is a potential target for hypertension treatment via natriuresis. However, its biological function in epithelial cells of the distal nephron segment, particularly the collecting duct, remains unknown. Herein, we examined the regulation of uromodulin production during water deprivation in vivo as well as the effect of uromodulin on the activity of the water channel aquaporin−2 (AQP2) in vitro and in vivo using transgenic mice. Water deprivation upregulated uromodulin production; immunofluorescence experiments revealed uromodulin adhesion on the apical surface of the collecting duct. Furthermore, the activation of AQP2 was attenuated in mice lacking uromodulin. Uromodulin enhanced the phosphorylation and apical trafficking of AQP2 in mouse collecting duct cells treated with the vasopressin analog dDAVP. The uromodulin-induced apical trafficking of AQP2 was attenuated via endocytosis inhibitor treatment, suggesting that uromodulin activates AQP2 through the suppression of endocytosis. This study provides novel insights into the cross−talk between TAL and the collecting duct, and indicates that the modulation of uromodulin is a promising approach for diuresis and hypertension treatment.

How Many Cell Types Are in the Kidney and What Do They Do?

The kidney maintains electrolyte, water, and acid-base balance, eliminates foreign and waste compounds, regulates blood pressure, and secretes hormones. There are at least 16 different highly specialized epithelial cell types in the mammalian kidney. The number of specialized endothelial cells, immune cells, and interstitial cell types might even be larger. The concerted interplay between different cell types is critical for kidney function. Traditionally, cells were defined by their function or microscopical morphological appearance. With the advent of new single-cell modalities such as transcriptomics, epigenetics, metabolomics, and proteomics we are entering into a new era of cell type definition. This new technological revolution provides new opportunities to classify cells in the kidney and understand their functions.

Associations of Serum Uromodulin and Its Genetic Variants With Blood Pressure and Hypertension in Chinese Adults

Background: Uromodulin, also named Tamm Horsfall protein, has been associated with renal function and regulation of sodium homeostasis. We aimed to examine the associations of serum uromodulin levels and its genetic variants with longitudinal blood pressure (BP) changes and hypertension incidence/risk. Methods: A total of 514 participants from the original Baoji Salt-Sensitive Study cohort were genotyped to examine the associations of genetic variations in uromodulin gene with the longitudinal BP changes and the incidence of hypertension over 8 years of follow-up. In addition, 2,210 subjects from the cohort of Hanzhong Adolescent Hypertension Study were used to investigate the relationships between serum uromodulin levels and the risk of hypertension. Results: SNPs rs12917707 and rs12708631 in the uromodulin gene were significantly associated with the longitudinal BP changes over 8 years of follow-up. SNP rs12708631 was significantly associated with the incidence of hypertension over 8 years. In addition, gene-based analyses supported the associations of uromodulin gene with the longitudinal BP changes and hypertension incidence in Baoji Salt-Sensitive Study cohort. Furthermore, serum uromodulin levels in the hypertensive subjects were lower than in the normotensive subjects (25.5 ± 1.1 vs. 34.7 ± 0.7 ng/mL). Serum uromodulin levels decreased gradually as BP levels increased (34.6, 33.2, 27.8, and 25.0 ng/mL for subjects with normotension, high-normal, grade 1 hypertension, and grade 2 hypertension, respectively). Serum uromodulin was significantly associated with the lower risk of hypertension [0.978 (0.972-0.984)] in Hanzhong Adolescent Hypertension Study cohort. Conclusion: This study shows that uromodulin is associated with blood pressure progression and development of hypertension.

Emerging Insights Into Chronic Renal Disease Pathogenesis in Hypertension From Human and Animal Genomic Studies

The pathogenic links between elevated blood pressure and chronic kidney disease remain obscure. This article examines progress in population genetics and in animal models of hypertension and chronic kidney disease. It also provides a critique of the application of genome-wide association studies to understanding the heritability of renal function. Emerging themes identified indicate that heritable risk of chronic kidney disease in hypertension can arise from genetic variation in (1) glomerular and tubular protein handling mechanisms; (2) autoregulatory capacity of the renal vasculature; and (3) innate and adaptive immune mechanisms. Increased prevalence of hypertension-associated chronic kidney disease that occurs with aging may reflect amplification of heritable risks by normal aging processes affecting immunity and autoregulation.

Autosomal dominant tubulointerstitial kidney disease with a novel heterozygous missense mutation in the uromodulin gene: A case report

BACKGROUND

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a progressive chronic disease that is inherited in an autosomal dominant fashion. Symptoms include hyperuricemia, gout, interstitial nephritis, renal cysts, and progressive renal damage that can lead to end-stage renal disease. Mutations in the uromodulin gene (UMOD) characterize the ADTKD-UMOD clinical subtype of this disease. To date, > 100 UMOD mutations have been identified. Early diagnosis of ADTKD-UMOD is important to treat the disease, slow down disease progression, and facilitate the identification of potentially affected family members.

CASE SUMMARY

We report a 40-year-old man harboring a novel heterozygous missense mutation in UMOD (c.554G>T; p. Arg185Leu). The patient had hyperuricemia, gout, and chronic kidney disease. The same mutation was detected in his daughter, aunt and cousin.

CONCLUSION

A single nucleotide substitution in exon 3 of UMOD was responsible for the heterozygous missense mutation (c.554G>T, p.Arg185Leu).

Association of serum uromodulin with mortality and cardiovascular disease in the elderly-the Cardiovascular Health Study

BACKGROUND

Uromodulin (UMOD) is released by renal tubular cells into the serum (sUMOD) and urine. Lower urine UMOD has been linked to mortality and cardiovascular disease but much less is known about sUMOD. We evaluated the association of sUMOD with these outcomes in community-dwelling older adults.

METHODS

We measured sUMOD in a random subcohort of 933 participants enrolled in the Cardiovascular Health Study. The associations of sUMOD with all-cause mortality, incident heart failure (HF) and incident cardiovascular disease (CVD; myocardial infarction, stroke and mortality due to coronary disease or stroke) were evaluated using multivariable Cox regression, adjusting for study participants' demographics, estimated glomerular filtration rate (eGFR), albuminuria and CVD risk factors. Generalized additive models with splines were used to address the functional form of sUMOD with outcomes. Due to nonlinear associations of sUMOD with all outcomes, 2.5% of the values on either end of the sUMOD distribution were excluded from the analyses, limiting the range of sUMOD to 34.3-267.1 ng/mL.

RESULTS

The mean age was 78 ± 5 years, 40% were male, sUMOD level was 127 ± 64 ng/mL, eGFR was 63 mL/min/1.73 m2 and 42% had CKD defined as eGFR <60 mL/min/1.73 m2. Patients in the lower sUMOD quartiles had lower eGFR and higher albuminuria (P < 0.01, respectively). During a median follow-up of 9.9 years, 805 patients died, 283 developed HF and 274 developed CVD. In multivariable analysis, higher sUMOD was significantly associated with a lower hazard for mortality {hazard ratio [HR] 0.89 [95% confidence interval (CI) 0.80-0.99] per 1 standard deviation (SD) higher sUMOD}, CVD [HR 0.80 (95% CI 0.67-0.96)] and the composite endpoint [HR 0.88 (95% CI 0.78-0.99)]; the association with HF was not statistically significant [HR 0.84 (95% CI 0.70-1.01)].

CONCLUSION

Higher sUMOD is independently associated with a lower risk for mortality and CVD in older adults.

Conditional Myh9 and Myh10 inactivation in adult mouse renal epithelium results in progressive kidney disease

Actin-associated nonmuscle myosin II (NM2) motor proteins play critical roles in a myriad of cellular functions, including endocytosis and organelle transport pathways. Cell type–specific expression and unique subcellular localization of the NM2 proteins, encoded by the Myh9 and Myh10 genes, in the mouse kidney tubules led us to hypothesize that these proteins have specialized functional roles within the renal epithelium. Inducible conditional knockout (cKO) of Myh9 and Myh10 in the renal tubules of adult mice resulted in progressive kidney disease. Prior to overt renal tubular injury, we observed intracellular accumulation of the glycosylphosphatidylinositol-anchored protein uromodulin (UMOD) and gradual loss of Na⁺ K⁺ 2Cl^– cotransporter from the apical membrane of the thick ascending limb epithelia. The UMOD accumulation coincided with expansion of endoplasmic reticulum (ER) tubules and activation of ER stress and unfolded protein response pathways in Myh9&10-cKO kidneys. We conclude that NM2 proteins are required for localization and transport of UMOD and loss of function results in accumulation of UMOD and ER stress–mediated progressive renal tubulointerstitial disease. These observations establish cell type–specific role(s) for NM2 proteins in regulation of specialized renal epithelial transport pathways and reveal the possibility that human kidney disease associated with MYH9 mutations could be of renal epithelial origin.

Adult mouse renal epithelium specific knockout of Myh9 and Myh10 genes result in kidney disease.

Common risk variants in NPHS1 and TNFSF15 are associated with childhood steroid-sensitive nephrotic syndrome

To understand the genetics of steroid-sensitive nephrotic syndrome (SSNS), we conducted a genome-wide association study in 987 childhood SSNS patients and 3,206 healthy controls with Japanese ancestry. Beyond known associations in the HLA-DR/DQ region, common variants in NPHS1-KIRREL2 (rs56117924, P=4.94E-20, odds ratio (OR) =1.90) and TNFSF15 (rs6478109, P=2.54E-8, OR=0.72) regions achieved genome-wide significance and were replicated in Korean, South Asian and African populations. Trans-ethnic meta-analyses including Japanese, Korean, South Asian, African, European, Hispanic and Maghrebian populations confirmed the significant associations of variants in NPHS1-KIRREL2 (P_meta=6.71E-28, OR=1.88) and TNFSF15 (P_meta=5.40E-11, OR=1.33) loci. Analysis of the NPHS1 risk alleles with glomerular NPHS1 mRNA expression from the same person revealed allele specific expression with significantly lower expression of the transcript derived from the risk haplotype (Wilcox test p=9.3E-4). Because rare pathogenic variants in NPHS1 cause congenital nephrotic syndrome of the Finnish type (CNSF), the present study provides further evidence that variation along the allele frequency spectrum in the same gene can cause or contribute to both a rare monogenic disease (CNSF) and a more complex, polygenic disease (SSNS).

Association of Serum Uromodulin With ESKD and Kidney Function Decline in the Elderly: The Cardiovascular Health Study

RATIONALE & OBJECTIVE

Uromodulin is released by tubular epithelial cells into the serum and lower levels are associated with more severe interstitial fibrosis and tubular atrophy. Low serum uromodulin (sUMOD) levels are associated with mortality and cardiovascular disease. However, little is known about the association of sUMOD levels with long-term kidney outcomes in older adults, a population with a high prevalence of interstitial fibrosis and tubular atrophy.

STUDY DESIGN

Case-cohort study and case-control study.

SETTING & PARTICIPANTS

Random subcohort (n=933) and additional cases of end-stage kidney disease (ESKD) and kidney function decline (≥30% decline in estimated glomerular filtration rate [eGFR]) during follow-up of the Cardiovascular Health Study (CHS).

PREDICTOR

sUMOD level.

OUTCOMES

ESKD (n=14) from the random subcohort and all additional ESKD cases from outside the random subcohort (n=39) during follow-up (10 years, case-cohort study); kidney function decline of≥30% eGFR at 9 years of follow-up in individuals with repeated eGFR assessments from the random subcohort (n=56) and additional cases (n=123). 224 participants from the random subcohort served as controls (case-control study).

ANALYTICAL APPROACH

Modified multivariable Cox regression for ESKD and multivariable logistic regression for kidney function decline. Both analyses adjusted for demographics, eGFR, urinary albumin-creatinine ratio, and other kidney disease progression risk factors.

RESULTS

Mean age of the random subcohort was 78 years, 40% were men, 15% were black. Mean sUMOD level was 127±64ng/mL and eGFR was 63±19mL/min/1.73m2. In multivariable analysis, each 1-SD higher sUMOD level was associated with 63% lower risk for ESKD (HR, 0.37; 95% CI, 0.14-0.95). In demographic-adjusted analyses of kidney function decline, each 1-SD higher sUMOD level was associated with 25% lower odds of kidney function decline (OR, 0.75; 95% CI, 0.60-0.95); after multivariable adjustment, the association was attenuated and no longer significant (OR, 0.88; 95% CI, 0.68-1.14).

LIMITATIONS

Possibility of survival bias in the kidney function decline analysis.

CONCLUSIONS

Higher sUMOD levels may identify elderly persons at reduced risk for ESKD.

Genetic Predisposition for Renal Dysfunction and Incidence of CKD in the Malmö Diet and Cancer Study

Background

Genome-wide association studies (GWAS) have identified >50 single nucleotide polymorphisms (SNP) in association with estimated glomerular filtration rate (eGFR) and chronic kidney disease (CKD) but little is known about whether the combination of these SNPs may aid in prediction of future incidence of CKD in the population.

Methods

We included 2301 participants with baseline eGFR ≥60 mL/min per 1.73 m² from the Malmö Diet and Cancer Study–Cardiovascular Cohort. The eGFR was estimated during baseline (1991–1996) and after a mean follow-up of 16.6 years using the CKD–Epidemiology Collaboration 2009 creatinine equation. We combined 53 SNPs into a genetic risk score weighted by the effect size (wGRS_CKD), and examined its association with incidence of CKD stage 3A (eGFR ≤60 mL/min per 1.73 m²).

Results

At follow-up, 453 study participants were defined as having CKD stage 3A. We observed a strong association between wGRS_CKD and eGFR at baseline (P = 6.5 × 10⁻⁸) and at the follow-up reexamination (P = 5.0 × 10⁻¹⁰). The odds ratio (OR) for incidence of CKD stage 3A was 1.25 per 1 SD increment in the wGRS_CKD (95% confidence interval [CI]: 1.12–1.39) adjusting for potential confounders (sex, age, body mass index [BMI], baseline eGFR, fasting glucose, systolic blood pressure (SBP), antihypertensive treatment, smoking, follow-up time). Adding wGRS_CKD on the top of traditional risk factors did not improve the C-statistics (P = 0.12), but the Net Reclassification-Improvement-Index was significantly improved (cNRI = 21.3%; 95% CI: 21.2–21.4; P < 0.0001).

Conclusion

wGRS_CKD was associated with a 25% increased incidence of CKD per 1 SD increment. Although the wGRS_CKD did not improve the prediction model beyond clinical risk factors per se, the information of genetic predisposition may aid in reclassification of individuals into correct risk direction.

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.

Serum uromodulin inversely associates with aortic stiffness in youth with type 1 diabetes: A brief report from EMERALD study

Youth with type 1 diabetes (T1D) carry greater cardiovascular disease (CVD) risk than their nondiabetic peers. Low serum uromodulin (SUMOD) associates with increased CVD mortality in adults. We found that T1D youth have low SUMOD. Lower SUMOD correlated with aortic stiffness, suggesting its potential as a CVD biomarker in T1D.

Genetic association in female stress urinary incontinence based on proteomic findings: a case-control study

Introduction and hypothesis

Previous studies have indicated a hereditary component of stress urinary incontinence; however, evidence on candidate genes or single-nucleotide polymorphisms (SNPs) is scarce. We hypothesize a genetic association of female stress urinary incontinence based on significant differences of the urinary and serum proteomic pattern in the identical study population.

Methods

Case-control study of 19 patients and 19 controls. We searched for known SNPs of SUI candidate genes (COL1A1, MMP1, SERPINA5, UMOD) in the database of short genetic variations and PubMed. Genomic DNA was isolated using QIAamp DNA Blood Midi Kit (Qiagen). We performed Sanger sequencing of selected exons and introns.

Results

The rs885786 SNP of the SERPINA5 gene was identified in 15 cases and 10 controls (p = 0.09). The rs6113 SNP of the SERPINA5 gene was present in 4 controls compared to 0 cases (p = 0.105). The rs4293393, rs13333226 and rs13335818 SNPs of the UMOD gene were identified in five cases and two controls (p = 0.20), the rs1800012 SNP of the COL1A1 gene in five cases versus four controls (p = 0.24) and the homozygous rs1799750 SNP of the MMP1 gene in eight cases versus five controls (p = 0.18). The combination of the rs885786 SNP of the SERPINA5 gene and rs179970 SNP of the MMP1 gene was detected in ten cases versus five controls (p = 0.072).

Conclusions

We found nonsignificant trends toward associations of SNPs on the SERPINA5, UMOD and MMP1 gene and SUI.

Electronic supplementary material

The online version of this article (10.1007/s00192-019-03878-0) contains supplementary material, which is available to authorized users.

Serum Uromodulin Predicts Less Coronary Artery Calcification and Diabetic Kidney Disease Over 12 Years in Adults With Type 1 Diabetes: The CACTI Study

OBJECTIVE

Novel biomarkers are needed to better predict coronary artery calcification (CAC), a marker of subclinical atherosclerosis, and diabetic kidney disease (DKD) in type 1 diabetes. We evaluated the associations between serum uromodulin (SUMOD [a biomarker associated with anti-inflammatory and renal protective properties]), CAC progression, and DKD development over 12 years.

RESEARCH DESIGN AND METHODS

Participants (n = 527, 53% females) in the Coronary Artery Calcification in Type 1 Diabetes (CACTI) study were examined during 2002-2004, at a mean age of 39.6 ± 9.0 years and a median duration of diabetes of 24.8 years. Urine albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) determined by the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine equation were measured at baseline and after a mean follow-up period of 12.1 ± 1.5 years. Elevated albumin excretion was defined as ACR ≥30 mg/g, rapid GFR decline (>3 mL/min/1.73 m²/year), and impaired GFR as eGFR <60 mL/min/1.73 m². SUMOD was measured on stored baseline plasma samples (Meso Scale Discovery). CAC was measured using electron beam computed tomography. CAC progression was defined as a change in the square root-transformed CAC volume of ≥2.5.

RESULTS

Higher baseline SUMOD level conferred lower odds of CAC progression (odds ratio 0.68; 95% CI 0.48-0.97), incident elevated albumin excretion (0.37; 0.16-0.86), rapid GFR decline (0.56; 0.35-0.91), and impaired GFR (0.44; 0.24-0.83) per 1 SD increase in SUMOD (68.44 ng/mL) after adjustment for baseline age, sex, systolic blood pressure, LDL cholesterol, and albuminuria/GFR. The addition of SUMOD to models with traditional risk factors also significantly improved the prediction performance for CAC progression and incident DKD.

CONCLUSIONS

Higher baseline SUMOD level predicted lower odds of both CAC progression and incident DKD over 12 years in adults with type 1 diabetes.

Proteomic Evidence of Biological Aging in a Child with a Compound Heterozygous ZMPSTE24 Mutation

BACKGROUND

Progeria-like syndromes offer a unique insight into aging. Here the case of a boy affected with mandibuloacral dysplasia and compound heterozygous mutations in ZMPSTE24 is presented.

METHODS

Capillary electrophoresis-mass spectroscopy is used for proteome analysis to analyze peptides previously found to be differentially regulated in chronic kidney disease (273 peptides defining the CKD273 classifier), coronary artery disease (238 peptides defining the CAD238 classifier), and aging (116 peptides defining the AGE116 classifier).

RESULTS

No evidence of renal disease is identified. Although the boy has no overt cardiovascular disease other than a raised carotid intima media thickness relative to his age, a proteomic classifier for the diagnosis of coronary artery disease is mildly raised. The biological age based on the proteomic AGE116 classifier is 24 years compared to the chronological ages of 5 and 10 years. In contrast, a control group of healthy children has a significantly lower (p < 0.0001) calculated mean age of 13.

CONCLUSION

Urinary proteomic analysis is effective in confirming advanced biological age and to identify early evidence of renal or cardiovascular damage. This case highlights the value of proteomic approaches in aging research and may represent a method for non-invasive monitoring of the effects of early aging.

Nonmuscle myosin 2 proteins encoded by Myh9, Myh10, and Myh14 are uniquely distributed in the tubular segments of murine kidney

The diverse epithelial cell types of the kidneys are segregated into nephron segments and the collecting ducts in order to endow each tubular segment with unique functions. The rich diversity of the epithelial cell types is highlighted by the unique membrane channels and receptors expressed within each nephron segment. Our previous work identified a critical role for Myh9 and Myh10 in mammalian endocytosis. Here, we examined the expression patterns of Nonmuscle myosin 2 (NM2) heavy chains encoded by Myh9, Myh10, and Myh14 in mouse kidneys as these genes may confer unique nephron segment‐specific membrane transport properties. Interestingly, we found that each segment of the renal tubules predominately expressed only two of the three NM2 isoforms, with isoform‐specific subcellular localization, and different levels of expression within a nephron segment. Additionally, we identify Myh14 to be restricted to the intercalated cells and Myh10 to be restricted to the principal cells within the collecting ducts and connecting segments. We speculate that the distinct expression pattern of the NM2 proteins likely reflects the diversity of the intracellular trafficking machinery present within the different renal tubular epithelial segments.

A review on autosomal dominant tubulointerstitial kidney disease

In recent years there has been a reclassification of hereditary tubulointerstitial renal diseases. The old concepts of nephronoptisis or medullary cystic disease have been reordered based on the discovery of new genes. The 2015 KDIGO guidelines proposed a unification of terminology, diagnostic criteria and monitoring. So far 4genes causing autosomal dominant tubulointerstitial kidney disease have been described: MUC1, UMOD, HNF1B and REN. Although the mutation in each of them causes distinctive features in how they present, all have in common the progressive tubulointerstitial damage and renal fibrosis. In this article, we present a review of the guidelines and the literature, and some practical recommendations for dealing with this disease.

Cell-Type-Specific Gene Programs of the Normal Human Nephron Define Kidney Cancer Subtypes

Comprehensive transcriptome studies of cancers often rely on corresponding normal tissue samples to serve as a transcriptional reference. In this study, we performed in-depth analyses of normal kidney tissue transcriptomes from the TCGA and demonstrate that the histological variability in cellularity, inherent in the kidney architecture, lead to considerable transcriptional differences between samples. This should be considered when comparing expression profiles of normal and cancerous kidney tissues. We exploited these differences to define renal-cell-specific gene signatures and used these as a framework to analyze renal cell carcinoma (RCC) ontogeny. Chromophobe RCCs express FOXI1-driven genes that define collecting duct intercalated cells, whereas HNF-regulated genes, specific for proximal tubule cells, are an integral part of clear cell and papillary RCC transcriptomes. These networks may be used as a framework for understanding the interplay between genomic changes in RCC subtypes and the lineage-defining regulatory machinery of their non-neoplastic counterparts.

Uromodulin associates with cardiorenal function in patients with hypertension and cardiovascular disease

OBJECTIVE

Common genetic variants in the gene encoding uromodulin (UMOD) have been associated with renal function, blood pressure (BP) and hypertension. We investigated the associations between an important single nucleotide polymorphism (SNP) in UMOD, that is rs12917707-G>T, and estimated glomerular filtration rate (eGFR), BP and cardiac organ damage as determined by echocardiography in patients with arterial hypertension.

METHODS

A cohort of 1218 treated high-risk patients (mean age 58.5 years, 83% men) with documented cardiovascular disease (81% with coronary heart disease) was analysed.

RESULTS

The mean values for 24-h SBP and DBP were 124.7 ± 14.7 and 73.9 ± 9.4 mmHg; mean eGFR was 77.5 ± 18.3 ml/min per 1.73 m, mean left ventricular ejection fraction was 59.3 ± 9.9% and mean left ventricular mass index in men and women was 53.9 ± 23.2 and 54.9 ± 23.7 g/m with 50.4% of patients having left ventricular hypertrophy. A significant association between rs12917707 and eGFR was observed with T-allele carriers showing significantly higher eGFR values (+2.6 ml/min per 1.73 m, P = 0.006) than noncarriers. This SNP associated also with left atrial diameter (P = 0.007); homozygous carriers of the T-allele had smaller left atrial diameter (-1.5 mm) than other genotype groups (P = 0.040). No significant associations between rs12917707 and other cardiac or BP phenotypes were observed.

CONCLUSIONS

These findings extend the previously documented role of UMOD for renal function also to treated high-risk patients with arterial hypertension and reveal a novel association with left atrial remodelling and thus a potential cardiorenal link modulated by UMOD.

Blood HER2 and Uromodulin as Causal Mediators of CKD

Many biomarkers have been epidemiologically linked with CKD; however, the possibility that such associations are due to reverse causation or confounding limits the utility of these biomarkers. To overcome this limitation, we used a Mendelian randomization (MR) approach to identify causal mediators of CKD. We performed MR by first identifying genetic determinants of 227 serum protein biomarkers assayed in 4147 participants of the Outcome Reduction with Initial Glargine Intervention (ORIGIN) trial who had early or prediabetes, and assessing the effects of these biomarkers on CKD in the CKD genetics consortium (n=117,165; 12,385 cases) using the inverse-variance weighted (fixed-effects) method. We then estimated the relationship between the serum concentration of each biomarker identified and incident CKD in ORIGIN participants. MR identified uromodulin (UMOD) and human EGF receptor 2 (HER2) as novel, causal mediators of CKD (UMOD: odds ratio [OR], 1.30 per SD; 95% confidence interval [95% CI], 1.25 to 1.35; P<5×10^-20; HER2: OR, 1.30 per SD; 95% CI, 1.14 to 1.48; P=8.0×10^-5). Consistent with these findings, blood HER2 concentration associated with CKD events in ORIGIN participants (OR, 1.07 per SD; 95% CI, 1.01 to 1.13; P=0.01). Additional exploratory MR analyses identified angiotensin-converting enzyme (ACE) as a regulator of HER2 levels (β=0.13 per SD; 95% CI, 0.08 to 0.16; P=2.5×10^-7). This finding was corroborated by an inverse relationship between ACE inhibitor use and HER2 levels. Thus, UMOD and HER2 are independent causal mediators of CKD in humans, and serum HER2 levels are regulated in part by ACE. These biomarkers are potential therapeutic targets for CKD prevention.

Identification of a novel UMOD mutation (c.163G>A) in a Brazilian family with autosomal dominant tubulointerstitial kidney disease

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is characterized by autosomal dominant inheritance, progressive chronic kidney disease, and a bland urinary sediment. ADTKD is most commonly caused by mutations in the UMOD gene encoding uromodulin (ADTKD-UMOD). We herein report the first confirmed case of a multi-generational Brazilian family with ADTKD-UMOD, caused by a novel heterozygous mutation (c.163G>A, GGC→AGC, p.Gly55Ser) in the UMOD gene. Of 41 family members, 22 underwent genetic analysis, with 11 individuals found to have this mutation. Three affected individuals underwent hemodialysis, one peritoneal dialysis, and one patient received a kidney transplant from a family member later found to be genetically affected. Several younger individuals affected with the mutation were also identified. Clinical characteristics included a bland urinary sediment in all tested individuals and a kidney biopsy in one individual showing tubulointerstitial fibrosis. Unlike most other reported families with ADTKD-UMOD, neither gout nor hyperuricemia was found in affected individuals. In summary, we report a novel UMOD mutation in a Brazilian family with 11 affected members, and we discuss the importance of performing genetic testing in families with inherited kidney disease of unknown cause.

Genomic medicine for kidney disease

Technologies such as next-generation sequencing and chromosomal microarray have advanced the understanding of the molecular pathogenesis of a variety of renal disorders. Genetic findings are increasingly used to inform the clinical management of many nephropathies, enabling targeted disease surveillance, choice of therapy, and family counselling. Genetic analysis has excellent diagnostic utility in paediatric nephrology, as illustrated by sequencing studies of patients with congenital anomalies of the kidney and urinary tract and steroid-resistant nephrotic syndrome. Although additional investigation is needed, pilot studies suggest that genetic testing can also provide similar diagnostic insight among adult patients. Reaching a genetic diagnosis first involves choosing the appropriate testing modality, as guided by the clinical presentation of the patient and the number of potential genes associated with the suspected nephropathy. Genome-wide sequencing increases diagnostic sensitivity relative to targeted panels, but holds the challenges of identifying causal variants in the vast amount of data generated and interpreting secondary findings. In order to realize the promise of genomic medicine for kidney disease, many technical, logistical, and ethical questions that accompany the implementation of genetic testing in nephrology must be addressed. The creation of evidence-based guidelines for the utilization and implementation of genetic testing in nephrology will help to translate genetic knowledge into improved clinical outcomes for patients with kidney disease.

Genome-Wide Analysis Studies and Chronic Kidney Disease

In recent years, the very high worldwide prevalence of chronic kidney disease (CKD) has led some authors to talk of an "epidemic." The progression of CKD varies considerably among individuals despite similar aetiologies, optimal blood pressure, and glycaemic control. Over the last decade, through genome-wide association studies (GWAS), more than 50 genetic loci have been identified in association with CKD. Understanding the genetic basis of CKD could provide a better knowledge of the biology of the involved pathways, thus potentially leading to novel tools for the diagnosis, prevention, and therapy of CKD. In this review, we will analyse the role of GWAS in the study of CKD.

[Uromodulin gene polymorphisms in patients with cast nephropathy in multiple myeloma]

AIM

To investigate the nature of mutations in exons 4 and 5 of the uromodulin (UM) gene, including in the area encoding the domain of 8 cysteines (D8C), in patients with multiple myeloma (MM) with the secretion of monoclonal light chains (LC) in cast nephropathy (CN) and without kidney injury.

SUBJECTS AND METHODS

The investigation enrolled 24 patients in MM remission, who were observed to have monoclonal LC secretion at onset. Group 1 included 14 patients with CN; Group 2 consisted of 10 patients with normal renal function (a comparison group). The compared groups did not differ in the number of serum and urinary monoclonal LCs. Genomic DNA was extracted from the peripheral blood samples of patients. The nucleotide sequence of exons 4 and 5 of the UM gene was determined by the Sanger method.

RESULTS

No differences were found in the frequency of polymorphisms depending on the severity of kidney injury. The missense mutation p.142R>R/Q in the UM gene, which had not been previously described, was discovered.

CONCLUSION

The patients with MM were not found to have statistically significant differences in the frequency and nature of polymorphisms of exons 4 and 5 in the UM gene, including in the area encoding D8C, in CN without kidney injury.

Elevated UMOD methylation level in peripheral blood is associated with gout risk

Uromodulin (UMOD) encodes an uromodulin glycoprotein, and its mutation results in uromodulin glycoprotein dysfunction and the occurrence of gout. The aim of our study was to assess whether UMOD methylation could predict the risk of gout. A total of 89 sporadic gout cases and 103 age and gender-matched healthy controls were recruited in this study. UMOD methylation level was determined by quantitative methylation-specific PCR (qMSP) in peripheral blood, and the percentage of methylated reference (PMR) was described to represent the methylation level. Our results showed that UMOD methylation was significantly higher in gout cases than controls (median: 1.45 versus 0.75, P < 0.001). The area under curve (AUC) of UMOD methylation in gout was 0.764 (P = 2.90E-10) with a sensitivity of 65.2% and a specificity of 88.3%. UMOD methylation level was shown to be significantly correlated with the serum level of uric acid (UA) (r = −0.208, P = 0.035). Besides, the luciferase reporter assay showed that UMOD CpG island region was able to upregulate gene expression (fold change = 2, P = 0.004). In conclusion, UMOD methylation assessment might be used to predict the occurrence of gout.

Urinary glycated uromodulin in diabetic kidney disease

Advanced glycation end-products (AGEs) form during oxidative stress, which is increased in diabetes mellitus (DM). Uromodulin is a protein with a renal protective effect, and may be subject to glycation. The implications of uromodulin glycation and AGEs in the urine are not understood. Here, immunoprecipitation and liquid chromatography–mass spectrometry identified glycated uromodulin (glcUMOD) in the urine of 62.5% of patients with diabetic kidney disease (DKD), 20.0% of patients with non-diabetic chronic kidney disease (CKD), and no DM patients with normal renal function or healthy control participants; a finding replicated in a larger cohort of 84 patients with CKD in a case–control study (35 with DM, 49 without). Uromodulin forms high molecular weight polymers that associate with microvesicles and exosomes. Differential centrifugation identified uromodulin in the supernatant, microvesicles, and exosomes of the urine of healthy participants, but only in the supernatant of samples from patients with DKD, suggesting that glycation influences uromodulin function. Finally, the diagnostic and prognostic utility of measuring urinary glcUMOD concentration was examined. Urinary glcUMOD concentration was substantially higher in DKD patients than non-diabetic CKD patients. Urinary glcUMOD concentration predicted DKD status, particularly in patients with CKD stages 1–3a aged <65 years and with urine glcUMOD concentration ≥9,000 arbitrary units (AU). Urinary uromodulin is apparently glycated in DKD and forms AGEs, and glcUMOD may serve as a biomarker for DKD.

Cysteines as Redox Molecular Switches and Targets of Disease

Thiol groups can undergo numerous modifications, making cysteine a unique molecular switch. Cysteine plays structural and regulatory roles as part of proteins or glutathione, contributing to maintain redox homeostasis and regulate signaling within and amongst cells. Not surprisingly therefore, cysteines are associated with many hereditary and acquired diseases. Mutations in the primary protein sequence (gain or loss of a cysteine) are most frequent in membrane and secretory proteins, correlating with the key roles of disulfide bonds. On the contrary, in the cytosol and nucleus, aberrant post-translational oxidative modifications of thiol groups, reflecting redox changes in the surrounding environment, are a more frequent cause of dysregulation of protein function. This essay highlights the regulatory functions performed by protein cysteine residues and provides a framework for understanding how mutation and/or (in)activation of this key amino acid can cause disease.

A mouse model for inherited renal fibrosis associated with endoplasmic reticulum stress

Renal fibrosis is a common feature of renal failure resulting from multiple etiologies, including diabetic nephropathy, hypertension and inherited renal disorders. However, the mechanisms of renal fibrosis are incompletely understood and we therefore explored these by establishing a mouse model for a renal tubular disorder, referred to as autosomal dominant tubulointerstitial kidney disease (ADTKD) due to missense uromodulin (UMOD) mutations (ADTKD-UMOD). ADTKD-UMOD, which is associated with retention of mutant uromodulin in the endoplasmic reticulum (ER) of renal thick ascending limb cells, is characterized by hyperuricemia, interstitial fibrosis, inflammation and renal failure, and we used targeted homologous recombination to generate a knock-in mouse model with an ADTKD-causing missense cysteine to arginine uromodulin mutation (C125R). Heterozygous and homozygous mutant mice developed reduced uric acid excretion, renal fibrosis, immune cell infiltration and progressive renal failure, with decreased maturation and excretion of uromodulin, due to its retention in the ER. The ER stress marker 78 kDa glucose-regulated protein (GRP78) was elevated in cells expressing mutant uromodulin in heterozygous and homozygous mutant mice, and this was accompanied, both in vivo and ex vivo, by upregulation of two unfolded protein response pathways in primary thick ascending limb cells from homozygous mutant mice. However, this did not lead to an increase in apoptosis in vivo. Thus, we have developed a novel mouse model for renal fibrosis, which will be a valuable resource to decipher the mechanisms linking uromodulin mutations with ER stress and renal fibrosis.

Summary: A mouse model for renal fibrosis caused by uromodulin mutations reveals roles for ER stress and the unfolded protein response.

From juvenile hyperuricaemia to dysfunctional uromodulin: an ongoing metamorphosis

Familial juvenile hyperuricaemic nephropathy (FJHN) is a diagnosis that is easily missed. It has taken a long time to clarify the pathophysiology and prevalence of this disease entity which has been shown to be genetically identical to medullary cystic kidney disease (MCKD) type II. The initial suspicion that uric acid was the noxious agent has been replaced by the recognition that a mutant uromodulin (UMOD) is the real culprit-although the exact mechanisms of pathogenicity remain uncertain. The mutation has been traced to the UMOD gene in chromosome 16. The disease is characterised by the classic triad of autosomal dominant inheritance, progressive renal failure beginning in the third to fifth decade of life and gout. Phenotypically similar but genotypically distinct entities have been described over the last 10 years, making a clinical diagnosis difficult. These include mutations in the renin, hepatocyte nuclear factor 1-β and mucin 1 genes. UMOD-associated kidney disease has been proposed as a logical diagnostic label to replace FJHN, but given all these other mutations, an over-arching diagnostic term of 'autosomal dominant tubulointerstitial kidney disease' (ADTKD) has been recently adopted. Allopurinol has been suggested as a therapeutic agent, but unfortunately this was based on non-randomised uncontrolled trials with small patient numbers.

Potential serum and urine biomarkers in patients with lupus nephritis and the unsolved problems

Lupus nephritis (LN) is one of the most frequent and serious complications in the patients with systemic lupus erythematosus. Autoimmune-mediated inflammation in both renal glomerular and tubulointerstitial tissues is the major pathological finding of LN. In clinical practice, the elevated anti-dsDNA antibody titer concomitant with reduced complement C3 and C4 levels has become the predictive and disease-activity surrogate biomarkers in LN. However, more and more evidences suggest that autoantibodies other than anti-dsDNA antibodies, such as anti-nucleosome, anti-C1q, anti-C3b, anti-cardiolipin, anti-endothelial cell, anti-ribonuclear proteins, and anti-glomerular matrix (anti-actinin) antibodies, may also involve in LN. Researchers have demonstrated that the circulating preformed and in situ-formed immune complexes as well as the direct cytotoxic effects by those cross-reactive autoantibodies mediated kidney damage. On the other hand, many efforts had been made to find useful urine biomarkers for LN activity via measurement of immune-related mediators, surface-enhanced laser desorption/ionization time-of-flight mass spectrometry proteomic signature, and assessment of mRNA and exosomal-derived microRNA from urine sediment cell. Our group had also devoted to this field with some novel findings. In this review, we briefly discuss the possible mechanisms of LN and try to figure out the potential serum and urine biomarkers in LN. Finally, some of the unsolved problems in this field are discussed.

Identification of ageing-associated naturally occurring peptides in human urine

To assess normal and pathological peptidomic changes that may lead to an improved understanding of molecular mechanisms underlying ageing, urinarypeptidomes of 1227 healthy and 10333 diseased individuals between 20 and 86 years of age were investigated. The diseases thereby comprised diabetes mellitus, renal and cardiovascular diseases. Using age as a continuous variable, 116 peptides were identified that significantly (p < 0.05; |ρ|≥0.2) correlated with age in the healthy cohort. The same approach was applied to the diseased cohort. Upon comparison of the peptide patterns of the two cohorts 112 common age-correlated peptides were identified. These 112 peptides predominantly originated from collagen, uromodulin and fibrinogen. While most fibrillar and basement membrane collagen fragments showed a decreased age-related excretion, uromodulin, beta-2-microglobulin and fibrinogen fragments showed an increase. Peptide-based in silico protease analysis was performed and 32 proteases, including matrix metalloproteinases and cathepsins, were predicted to be involved in ageing. Identified peptides, predicted proteases and patient information were combined in a systems biology pathway analysis to identify molecular pathways associated with normal and/or pathological ageing. While perturbations in collagen homeostasis, trafficking of toll-like receptors and endosomal pathways were commonly identified, degradation of insulin-like growth factor-binding proteins was uniquely identified in pathological ageing.

Urinary proteomic pattern in female stress urinary incontinence: a pilot study

Introduction and hypothesis

Previous studies aiming to identify specific pre-defined urine protein biomarkers for stress urinary incontinence (SUI) have not identified clinically important differences. The hypothesis of our study was that the global distribution of urinary proteins, the proteome, differs between women with and those without SUI.

Methods

In this age-matched case–control study, we compared the urinary proteome of 20 women with SUI and 20 controls. Proteins were identified by applying high-performance liquid chromatography separation and tandem mass spectrometry detection. Data analysis was performed using Mascot 2.4.1 embedded in ProteinScape 3.1.

Results

We identified 828 different proteins. The concentration of six of those showed a significant difference between urine samples of SUI patients and those of controls (q value < 0.25). Four proteins showed a higher abundance in SUI samples compared with controls: plasma serine protease inhibitor (logFC 1.11), leucine-rich alpha-2-glycoprotein (logFC 3.91), lysosomal alpha-glucosidase (logFC 1.24), and peptidyl-prolyl cis- trans isomerase A (logFC 1.96). We identified two proteins in lower abundance in SUI samples compared with controls: uromodulin (logFC −4.87) and TALPID3 (logFC −1.99).

Conclusions

Overexpression of plasma serine protease inhibitor, leucine-rich alpha-2-glycoprotein, lysosomal alpha-glucosidase, and peptidyl-prolyl cis- trans isomerase A, and lower expression of uromodulin and TALPID3, in urine may be associated with female SUI.

Electronic supplementary material

The online version of this article (doi:10.1007/s00192-016-3033-5) contains supplementary material, which is available to authorized users

Plasma Uromodulin Correlates With Kidney Function and Identifies Early Stages in Chronic Kidney Disease Patients

Uromodulin, released from tubular cells of the ascending limb into the blood, may be associated with kidney function. This work studies the relevance of plasma uromodulin as a biomarker for kidney function in an observational cohort of chronic kidney disease (CKD) patients and subjects without CKD (CKD stage 0). It should be further evaluated if uromodulin allows the identification of early CKD stages.Plasma uromodulin, serum creatinine, cystatin C, blood-urea-nitrogen (BUN) concentrations, and estimated glomerular filtration rate (eGFR CKD-EPIcrea-cystatin) were assessed in 426 individuals of whom 71 were CKD stage 0 and 355 had CKD. Besides descriptive statistics, univariate correlations between uromodulin and biomarkers/eGFR were calculated using Pearson-correlation coefficient. Multiple linear regression modeling was applied to establish the association between uromodulin and eGFR adjusted for demographic parameters and pharmacologic treatment. Receiver-operating-characteristic (ROC) analysis adjusted for demographic parameters was performed to test if uromodulin allows differentiation of subjects with CKD stage 0 and CKD stage I.Mean uromodulin plasma levels were 85.7 ± 60.5 ng/mL for all CKD stages combined. Uromodulin was correlated with all biomarkers/eGFR in univariate analysis (eGFR: r = 0.80, creatinine: r = -0.76, BUN: r = -0.72, and cystatin C: r = -0.79). Multiple linear regression modeling showed significant association between uromodulin and eGFR (coefficient estimate β = 0.696, 95% confidence interval [CI] 0.603-0.719, P < 0.001). In ROC analysis uromodulin was the only parameter that significantly improved a model containing demographic parameters to differentiate between CKD 0° and I° (area under the curve [AUC] 0.831, 95% CI 0.746-0.915, P = 0.008) compared to creatinine, cystatin C, BUN, and eGFR (AUC for creatinine: 0.722, P = 0.056, cystatin C: 0.668, P = 0.418, BUN: 0.653, P = 0.811, and eGFR: 0.634, P = 0.823).Plasma uromodulin serves as a robust biomarker for kidney function and uniquely allows the identification of early stages of CKD. As a marker of tubular secretion it might represent remaining nephron mass and therefore intrinsic "kidney function" rather than just glomerular filtration, the latter only being of limited value to represent kidney function as a whole. It therefore gives substantial information on the renal situation in addition to glomerular filtration and potentially solves the problem of creatinine-blind range of CKD, in which kidney impairment often remains undetected.

Hints to the diagnosis of uromodulin kidney disease

Background

Uromodulin kidney disease (UKD) is an inherited kidney disease caused by a uromodulin (UMOD) gene mutation. The UMOD gene encodes the Tamm–Horsfall protein (THP), which is the most abundant protein in healthy human urine. Because of its rarity, the incidence of UKD has not been fully elucidated. The purpose of the present study is to clarify the frequency of UKD among patients who underwent renal biopsy.

Methods

Immunostaining for THP was performed for patients <50 years of age with renal insufficiency and hyperuricemia without overt urinalysis abnormality from renal biopsy databases. Serum and urinary THP concentrations were evaluated in available individuals.

Results

Fifteen patients were selected for immunostaining from a total of 3787 patients. In three independent patients, abnormal THP accumulation in renal tubular cells was observed. A novel missense A247P UMOD mutation was detected in two of the three patients, including one having a typical family history of familial juvenile hyperuricemic nephropathy. Serum and urinary THP concentrations of all available patients with UMOD A247P mutation were significantly lower than those of controls.

Conclusions

In the present study, UKD was detected in <1 in 1000 subjects who underwent renal biopsies. However, in subjects meeting all of the above criteria, abnormal THP accumulation was detected in 20% (3/15), suggesting that renal biopsy with immunostaining for THP is a good tool for diagnosing UKD. Also, low serum THP concentration detected in the present subjects might be a good diagnostic marker or important in understanding the pathogenesis of UKD.

A roadmap for the genetic analysis of renal aging

Several studies show evidence for the genetic basis of renal disease, which renders some individuals more prone than others to accelerated renal aging. Studying the genetics of renal aging can help us to identify genes involved in this process and to unravel the underlying pathways. First, this opinion article will give an overview of the phenotypes that can be observed in age-related kidney disease. Accurate phenotyping is essential in performing genetic analysis. For kidney aging, this could include both functional and structural changes. Subsequently, this article reviews the studies that report on candidate genes associated with renal aging in humans and mice. Several loci or candidate genes have been found associated with kidney disease, but identification of the specific genetic variants involved has proven to be difficult. CUBN, UMOD, and SHROOM3 were identified by human GWAS as being associated with albuminuria, kidney function, and chronic kidney disease (CKD). These are promising examples of genes that could be involved in renal aging, and were further mechanistically evaluated in animal models. Eventually, we will provide approaches for performing genetic analysis. We should leverage the power of mouse models, as testing in humans is limited. Mouse and other animal models can be used to explain the underlying biological mechanisms of genes and loci identified by human GWAS. Furthermore, mouse models can be used to identify genetic variants associated with age-associated histological changes, of which Far2, Wisp2, and Esrrg are examples. A new outbred mouse population with high genetic diversity will facilitate the identification of genes associated with renal aging by enabling high-resolution genetic mapping while also allowing the control of environmental factors, and by enabling access to renal tissues at specific time points for histology, proteomics, and gene expression.

Next generation sequencing search for uromodulin gene variants related with impaired renal function

Uromodulin gene (UMOD) mutations have been linked to rare forms of mendelian dominant medullary cystic kidney disease and familial hyperuricemia. In addition, common single nucleotide polymorphisms in the UMOD promoter have been associated with the risk for impaired renal function and chronic kidney disease. Our main purpose was to identify UMOD variants related with impaired renal function in an elderly population. The UMOD gene was next generation sequenced in a total of 100 healthy individuals with normal or reduced renal function [measured as the rate of estimated glomerular filtration (eGFR)]. The identified missense changes and the common promoter rs12917707 polymorphism were determined in individuals with reduced (n = 88) and normal (n = 442) eGFR values. Allele and genotype frequencies were compared between the groups. We only identified a rare UMOD misense change, p.V458L, and the rare leu allele was significantly more frequent in a cohort of individuals with reduced (eGFR < 60) compared to normal eGFR (P = 0.02). The common rs12917707 polymorphism previously linked to renal function and kidney disease was not associated with impaired filtration rate in our cohort. We found a significant effect of the rare p.V458L variant on the value of estimated glomerular filtration. This finding deserves further validation in larger cohorts.

Nephrosclerosis: update on a centenarian

Nephrosclerosis is an umbrella term defining changes in all compartments of the kidney, changes caused by hypertension and by ageing. Among other lesions, arteriolosclerosis and arteriolohyalinosis play a major role in inducing glomerular ischaemic shrinking and sclerosis along with glomerulomegaly and focal-segmental glomerulosclerosis (FSGS). These lesions are accompanied by tubulointerstitial inflammation and fibrosis that predict the decline of renal function. Nephrosclerosis is a major cause of renal insufficiency in blacks of African descent with a severe, early form of renovasculopathy and a rapid course to renal failure with predominant lesions of FSGS. It seems that in blacks, separate genetic factors independently lead to vascular lesions and to hypertension with a different time-scale of their onset and of their progression, nephroangiosclerosis preceding the onset of hypertension. Conversely, true and histologically identified nephrosclerosis in white Europeans rarely leads to end-stage renal disease in the absence of malignant hypertension. Various animal models demonstrate that renal vascular lesions may exist in the absence of hypertension. These experiments also point to a major role of angiotensin II and of a number of independent and overlapping cellular and molecular pathways in a cascade of inflammatory events that end in renal fibrosis. Two pathophysiologic mechanisms are at work in inducing glomerular lesions and tubulointerstitial fibrosis: a loss of autoregulation of the renal blood flow caused by an arteriolohyalinosis of the glomerular afferent arteriole and ischaemia that fosters the generation of hypoxia inducible-fibrosing factors. Not all antihypertensive drugs equally protect the kidney from nephrosclerosis. Angiotensin II antagonists exert a favourable effect on hyperfiltration. Conversely, dihydropyridine calcium-channel blockers and vasodilators do not withstand the derangement of renal autoregulation.