Urinary epidermal growth factor as a prognostic marker for the progression of Alport syndrome in children

Urine epidermal growth factor as a biomarker for kidney function recovery and prognosis in glomerulonephritis with severe kidney function impairment

BACKGROUND

Prognostication in glomerulonephritis with severe kidney function impairment is critical for evaluating the benefit-to-risk ratio of immunosuppression. We hypothesized that the urine biomarker epidermal growth factor (EGF) could have good discrimination power to identify subjects who might ultimately recover kidney function.

METHODS

We included 82 subjects with glomerulonephritis and severe kidney function impairment at admission (estimated glomerular filtration rate [eGFR] ≤ 30 mL/min/1.73m2): 58 with lupus nephritis (LN) and 24 with ANCA-associated vasculitis (AAV). Thirty-five subjects required kidney replacement therapy (KRT) at presentation. Urine epidermal growth factor was measured and corrected by urine creatinine (uEGF/Cr) and the population was analyzed by uEGF/Cr tertiles. The primary outcome was time to recovery of eGFR ≥ 30 mL/min/1.73m2 and time to recovery of kidney function with dialysis independence in those with initial KRT.

RESULTS

Forty-four (54%) participants met the primary outcome of recovery of eGFR ≥ 30 mL/min/1.73m2. The 6-month recovery rates were 93%, 57%, and 0% for participants in the highest, middle, and lowest uEGF/Cr tertile, respectively. Recovery of the kidney function was faster and led to a higher post-therapy eGFR in the highest uEGF/Cr tertile. In the ROC analysis, uEGF/Cr was a predictor of recovery with an area under the curve (AUC) of 0.92 (95% CI 0.87-0.98), and a cutoff of 2.60 ng/mg had 100% sensitivity to detect patients who recovered kidney function. In the subgroup of participants with initial KRT, the cut-off of uEGF/Cr of 2.0 ng/mg had 100% sensitivity to detect participants who recovered kidney function with dialysis independence by 6 months.

CONCLUSIONS

Urine EGF/Cr is a promising biomarker to aid in the prediction of recovery of kidney function in glomerulonephritis with severe kidney function impairment.

The association of urinary epidermal growth factors with ADPKD disease severity and progression

BACKGROUND

The epidermal growth factor receptor (EGFR) pathway is involved in kidney tissue repair and growth. Preclinical interventional data and scarce human data have suggested a role for this pathway in the pathophysiology of autosomal dominant polycystic kidney disease (ADPKD), while other data have suggested that its activation is causally linked to repair of damaged kidney tissue. We hypothesize that urinary EGFR ligands, as a reflection of EGFR activity, are associated with kidney function decline in ADPKD in the context of tissue repair following injury, and as the disease progresses as a sign of insufficient repair.

METHODS

In the present study, we measured the EGFR ligands, EGF and heparin binding-EGF (HB-EGF), in 24-h urine samples of 301 ADPKD patients and 72 age- and sex-matched living kidney donors to dissect the role of the EGFR pathway in ADPKD. During a median follow-up of 2.5 years, the association of urinary EGFR ligand excretion with annual change in estimated glomerular filtration rate (eGFR) and height-adjusted total kidney volume in ADPKD patients was analyzed using mixed-models methods, and the expression of three closely related EGFR family receptors in ADPKD kidney tissue was investigated by immunohistochemistry. Additionally, the effect of reducing renal mass (after kidney donation), was assessed to investigate whether urinary EGF matches this reduction and thus reflects the amount of remaining healthy kidney tissue.

RESULTS

At baseline, urinary HB-EGF did not differ between ADPKD patients and healthy controls (P = .6), whereas a lower urinary EGF excretion was observed in ADPKD patients [18.6 (11.8-27.8)] compared with healthy controls [51.0 (34.9-65.4) μg/24 h, P < .001]. Urinary EGF was positively associated with baseline eGFR (R = 0.54, P < .001) and a lower EGF was strongly associated with a more rapid GFR decline, even when adjusted for ADPKD severity markers (β = 1.96, P < .001), whereas HB-EGF was not. Expression of the EGFR, but not other EGFR-related receptors, was observed in renal cysts but was absent in non-ADPKD kidney tissue. Finally, unilateral nephrectomy resulted in a decrease of 46.4 (-63.3 to -17.6) % in urinary EGF excretion, alongside a decrease of 35.2 ± 7.2% in eGFR and 36.8 ± 6.9% in measured GFR (mGFR), whereas maximal mGFR (measured after dopamine induced hyperperfusion) decreased by 46.1 ± 7.8% (all P < .001).

CONCLUSIONS

Our data suggest that lower urinary EGF excretion may be a valuable novel predictor for kidney function decline in patients with ADPKD.

Intraindividual variations of urinary biomarkers in hospitalized children with glomerular diseases: a prospective observational study

This study aimed to assess the intraindividual variations of urinary biomarkers in hospitalized children with glomerular diseases. Hospitalized children with glomerular diseases participated in the study. For each patient, an overnight (9:00 p.m.-7:00 a.m.) urine was collected, followed by a 24-h urine (classified into four distinct periods: morning 7:00 a.m.-12:00 p.m., afternoon 12:00 p.m.-4:00 p.m., evening 4:00 p.m.-9:00 p.m., and overnight 9:00 p.m.-7:00 a.m.). The concentrations of protein, albumin, N-acetyl-beta-D-glucosaminidase, and epidermal growth factor (EGF) were measured and normalized by three correction factors (creatinine, osmolality, or specific gravity, respectively). Additionally, the 2nd overnight urine sample was grouped into different aliquots according to centrifugation, additives, storage temperature, or delayed processing. Twenty (14 boys, 6 girls) children were enrolled, with an average age of 11.3 years. Among the three correction factors, creatinine-normalized biomarkers provided the best agreements among different periods over 24 h. There were significant diurnal variations during 24 h in the concentrations of urinary protein, albumin, N-acetyl-beta-D-glucosaminidase, and EGF (p = 0.001, p = 0.003, p = 0.003, and p = 0.003, respectively). Evening urine overestimated 24-h urinary protein and albumin, while overnight urine underestimated 24-h urinary albumin. Urinary EGF showed low variability within a day or between the 2 days (coefficients of variation 10.2% and 10.6%, respectively) and excellent agreements (intraclass correlation coefficients > 0.9) with 24-h urinary concentration. Furthermore, urinary EGF was not affected by centrifugation, additives, storage temperature, or delayed processing of urine samples (all p > 0.05).  Conclusion: Given the diurnal variations of urinary biomarkers, urine samples should be collected during the same time period in clinical practice if possible. The results also extend the evidence for urinary EGF as a relatively stable biomarker applied in the future clinical practice. What is Known: • Urinary biomarkers have been widely used or discussed in making diagnoses and therapy regimens and estimating the prognosis of pediatric glomerular diseases. It remains unclear whether their levels would be affected by the time of sample collection, processing methods, and storage conditions in hospitalized children with glomerular diseases. What is New: • The levels of both commonly used biomarkers and novel biomarkers exhibited diurnal variations in hospitalized children with glomerular diseases. • Our results extend the evidence for urinary EGF as a relatively stable biomarker applied in the future clinical practice.

Combining robust urine biomarkers to assess chronic kidney disease progression

BACKGROUND

Urinary biomarkers may improve the prediction of chronic kidney disease (CKD) progression. Yet, data reporting the applicability of most commercial biomarker assays to the detection of their target analyte in urine together with an evaluation of their predictive performance are scarce.

METHODS

30 commercial assays (ELISA) were tested for their ability to quantify the target analyte in urine using strict (FDA-approved) validation criteria. In an exploratory analysis, LASSO (Least Absolute Shrinkage and Selection Operator) logistic regression analysis was used to identify potentially complementary biomarkers predicting fast CKD progression, determined as the ⁵¹CrEDTA clearance-based measured glomerular filtration rate (mGFR) decline (>10% per year) in a subsample of 229 CKD patients (mean age, 61 years; 66% men; baseline mGFR, 38 mL/min) from the NephroTest prospective cohort.

FINDINGS

Among the 30 assays, directed against 24 candidate biomarkers, encompassing different pathophysiological mechanisms of CKD progression, 16 assays fulfilled the FDA-approved criteria. LASSO logistic regressions identified a combination of five biomarkers including CCL2, EGF, KIM1, NGAL, and TGF-α that improved the prediction of fast mGFR decline compared to the kidney failure risk equation variables alone: age, gender, mGFR, and albuminuria. Mean area under the curves (AUC) estimated from 100 re-samples was higher in the model with than without these biomarkers, 0.722 (95% confidence interval 0.652-0.795) vs. 0.682 (0.614-0.748), respectively. Fully-adjusted odds-ratios (95% confidence interval) for fast progression were 1.87 (1.22, 2.98), 1.86 (1.23, 2.89), 0.43 (0.25, 0.70), 1.10 (0.71, 1.83), 0.55 (0.33, 0.89), and 2.99 (1.89, 5.01) for albumin, CCL2, EGF, KIM1, NGAL, and TGF-α, respectively.

INTERPRETATION

This study provides a rigorous validation of multiple assays for relevant urinary biomarkers of CKD progression which combination may improve the prediction of CKD progression.

FUNDING

This work was supported by Institut National de la Santé et de la Recherche Médicale, Université de Paris, Assistance Publique Hôpitaux de Paris, Agence Nationale de la Recherche, MSDAVENIR, Pharma Research and Early Development Roche Laboratories (Basel, Switzerland), and Institut Roche de Recherche et Médecine Translationnelle (Paris, France).

Recent Advances in Urinary Peptide and Proteomic Biomarkers in Chronic Kidney Disease: A Systematic Review

Biomarker development, improvement, and clinical implementation in the context of kidney disease have been a central focus of biomedical research for decades. To this point, only serum creatinine and urinary albumin excretion are well-accepted biomarkers in kidney disease. With their known blind spot in the early stages of kidney impairment and their diagnostic limitations, there is a need for better and more specific biomarkers. With the rise in large-scale analyses of the thousands of peptides in serum or urine samples using mass spectrometry techniques, hopes for biomarker development are high. Advances in proteomic research have led to the discovery of an increasing amount of potential proteomic biomarkers and the identification of candidate biomarkers for clinical implementation in the context of kidney disease management. In this review that strictly follows the PRISMA guidelines, we focus on urinary peptide and especially peptidomic biomarkers emerging from recent research and underline the role of those with the highest potential for clinical implementation. The Web of Science database (all databases) was searched on 17 October 2022, using the search terms "marker *" OR biomarker * AND "renal disease" OR "kidney disease" AND "proteome *" OR "peptid *" AND "urin *". English, full-text, original articles on humans published within the last 5 years were included, which had been cited at least five times per year. Studies based on animal models, renal transplant studies, metabolite studies, studies on miRNA, and studies on exosomal vesicles were excluded, focusing on urinary peptide biomarkers. The described search led to the identification of 3668 articles and the application of inclusion and exclusion criteria, as well as abstract and consecutive full-text analyses of three independent authors to reach a final number of 62 studies for this manuscript. The 62 manuscripts encompassed eight established single peptide biomarkers and several proteomic classifiers, including CKD273 and IgAN237. This review provides a summary of the recent evidence on single peptide urinary biomarkers in CKD, while emphasizing the increasing role of proteomic biomarker research with new research on established and new proteomic biomarkers. Lessons learned from the last 5 years in this review might encourage future studies, hopefully resulting in the routine clinical applicability of new biomarkers.

Urinary epidermal growth factor reflects vascular health in boys with either obesity or type 1 diabetes. A role for renin, or beyond?

An increased blood pressure is a known comorbidity of both type 1 diabetes (T1DM) and obesity in children. Increasing evidence suggests a subtle interplay between epidermal growth factor (EGF) and renin along the juxtaglomerular system, regulating the impact of blood pressure on kidney health and the cardiovascular system. In this study, we investigated the relation between urinary EGF, serum renin and blood pressure in children with obesity or T1DM. 147 non-obese children with T1DM and 126 children with obesity, were included. Blood pressure was measured and mean arterial pressure (MAP) and the pulse pressure (PP) were calculated. Serum renin and urinary EGF levels were determined with a commercial ELISA kit. Partial Spearman rank correlation coefficients and multiple linear regression models were used to study the association between renin, the urinary EGF/urinary creatinine ratio and blood pressure parameters. The urinary EGF/urinary creatinine ratio is correlated with the SBP and the MAP in boys with obesity as well as in boys with T1DM. Multiple regression analysis showed that sex and pulse pressure in male subjects were found to be independently associated with renin. Sex, the presence of diabetes, age, the glomerular filtration rate and both pulse pressure and mean arterial pressure in male subjects were independently associated with urinary EGF/urinary creatinine. In conclusion, in boys with either obesity or diabetes, pulse pressure and mean arterial pressure are negatively associated with the functional integrity of the nephron, which is reflected by a decreased expression of urinary EGF.

Urinary epidermal growth factor predicts complete remission of proteinuria in Chinese children with IgA nephropathy

BACKGROUND

This study investigated the association between urinary epidermal growth factor (EGF) and complete remission (CR) of proteinuria in children with IgA nephropathy (IgAN).

METHODS

We included 108 patients from the Registry of IgA Nephropathy in Chinese Children. The urinary EGF at the baseline and follow-up were measured and normalized by urine creatinine (expressed as uEGF/Cr). The person-specific uEGF/Cr slopes were estimated using linear mixed-effects models for the subset of patients with longitudinal data of uEGF/Cr. Cox models were used to analyze the associations of baseline uEGF/Cr and uEGF/Cr slope with CR of proteinuria.

RESULTS

Patients with high baseline uEGF/Cr were more likely to achieve CR of proteinuria (adjusted HR 2.24, 95% CI: 1.05-4.79). The addition of high baseline uEGF/Cr on the traditional parameters significantly improved the model fit for predicting CR of proteinuria. In the subset of patients with longitudinal data of uEGF/Cr, high uEGF/Cr slope was associated with a higher likelihood of CR of proteinuria (adjusted HR 4.03, 95% CI: 1.02-15.88).

CONCLUSIONS

Urinary EGF may be a useful noninvasive biomarker for predicting and monitoring CR of proteinuria in children with IgAN.

IMPACT

High levels of baseline uEGF/Cr (>21.45 ng/mg) could serve as an independent predictor for CR of proteinuria. The addition of baseline uEGF/Cr on the traditional clinical pathological parameters significantly improved the fitting ability for the prediction of CR of proteinuria. Longitudinal data of uEGF/Cr were also independently associated with CR of proteinuria. Our study provides evidence that urinary EGF may be a useful noninvasive biomarker in the prediction of CR of proteinuria as well as monitoring therapeutic response, thus guiding treatment strategies in clinical practice for children with IgAN.

The Michigan O'Brien Kidney Research Center: transforming translational kidney research through systems biology

Research on kidney diseases is being transformed by the rapid expansion and innovations in omics technologies. The analysis, integration, and interpretation of big data, however, have been an impediment to the growing interest in applying these technologies to understand kidney function and failure. Targeting this urgent need, the University of Michigan O'Brien Kidney Translational Core Center (MKTC) and its Administrative Core established the Applied Systems Biology Core. The Core provides need-based support for the global kidney community centered on enabling incorporation of systems biology approaches by creating web-based, user-friendly analytic and visualization tools, like Nephroseq and Nephrocell, guiding with experimental design, and processing, analysis, and integration of large data sets. The enrichment core supports systems biology education and dissemination through workshops, seminars, and individualized training sessions. Meanwhile, the Pilot and Feasibility Program of the MKTC provides pilot funding to both early-career and established investigators new to the field, to integrate a systems biology approach into their research projects. The relevance and value of the portfolio of training and services offered by MKTC are reflected in the expanding community of young investigators, collaborators, and users accessing resources and engaging in systems biology-based kidney research, thereby motivating MKTC to persevere in its mission to serve the kidney research community by enabling access to state-of-the-art data sets, tools, technologies, expertise, and learning opportunities for transformative basic, translational, and clinical studies that will usher in solutions to improve the lives of people impacted by kidney disease.

Potential Renal Damage Biomarkers in Alport Syndrome—A Review of the Literature

Alport syndrome (AS) is the second most common cause of inherited chronic kidney disease. This disorder is caused by genetic variants on COL4A3, COL4A4 and COL4A5 genes. These genes encode the proteins that constitute collagen type IV of the glomerular basement membrane (GBM). The heterodimer COL4A3A4A5 constitutes the majority of the GBM, and it is essential for the normal function of the glomerular filtration barrier (GFB). Alterations in any of collagen type IV constituents cause disruption of the GMB structure, allowing leakage of red blood cells and albumin into the urine, and compromise the architecture of the GFB, inducing inflammation and fibrosis, thus resulting in kidney damage and loss of renal function. The advances in DNA sequencing technologies, such as next-generation sequencing, allow an accurate diagnose of AS. Due to the important risk of the development of progressive kidney disease in AS patients, which can be delayed or possibly prevented by timely initiation of therapy, an early diagnosis of this condition is mandatory. Conventional biomarkers such as albuminuria and serum creatinine increase relatively late in AS. A panel of biomarkers that might detect early renal damage, monitor therapy, and reflect the prognosis would have special interest in clinical practice. The aim of this systematic review is to summarize the biomarkers of renal damage in AS as described in the literature. We found that urinary Podocin and Vascular Endothelial Growth Factor A are important markers of podocyte injury. Urinary Epidermal Growth Factor has been related to tubular damage, interstitial fibrosis and rapid progression of the disease. Inflammatory markers such as Transforming Growth Factor Beta 1, High Motility Group Box 1 and Urinary Monocyte Chemoattractant Protein- 1 are also increased in AS and indicate a higher risk of kidney disease progression. Studies suggest that miRNA-21 is elevated when renal damage occurs. Novel techniques, such as proteomics and microRNAs, are promising.

Proteomic and metabolomic profiling of urine uncovers immune responses in patients with COVID-19

The utility of the urinary proteome in infectious diseases remains unclear. Here, we analyzed the proteome and metabolome of urine and serum samples from patients with COVID-19 and healthy controls. Our data show that urinary proteins effectively classify COVID-19 by severity. We detect 197 cytokines and their receptors in urine, but only 124 in serum using TMT-based proteomics. The decrease in urinary ESCRT complex proteins correlates with active SARS-CoV-2 replication. The downregulation of urinary CXCL14 in severe COVID-19 cases positively correlates with blood lymphocyte counts. Integrative multiomics analysis suggests that innate immune activation and inflammation triggered renal injuries in patients with COVID-19. COVID-19-associated modulation of the urinary proteome offers unique insights into the pathogenesis of this disease. This study demonstrates the added value of including the urinary proteome in a suite of multiomics analytes in evaluating the immune pathobiology and clinical course of COVID-19 and, potentially, other infectious diseases.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Alport Syndrome: A Primer for Clinicians

Alport syndrome is a genetic and hereditary disease, caused by mutations in the type IV collagen genes COL4A3, COL4A4 and COL4A5, that affects the glomerular basement membrane of the kidney. It is a rare disease with an underestimated prevalence. Genetic analysis of population cohorts has revealed that it is the second most common inherited kidney disease after polycystic kidney disease. Renal involvement is the main manifestation, although it may have associated extrarenal manifestations such as hearing loss or ocular problems. The degree of expression of the disease changes according to the gene affected and other factors, known or yet to be known. The pathophysiology is not yet fully understood, although some receptors, pathways or molecules are known to be linked to the disease. There is also no specific treatment for Alport syndrome; the most commonly used are renin–angiotensin–aldosterone system inhibitors. In recent years, diagnosis has come a long way, thanks to advances in DNA sequencing technologies such as next-generation sequencing (NGS). Further research at the genetic and molecular levels in the future will complete the partial vision of the pathophysiological mechanism that we have, and will allow us to better understand what is happening and how to solve it.

The lupus nephritis management renaissance

Over the past year, and for the first time ever, the US Food and Drug Administration approved 2 drugs specifically for the treatment of lupus nephritis (LN). As the lupus community works toward understanding how to best use these new therapies, it is also an ideal time to begin to rethink the overall management strategy of LN. In addition to new drugs, this must include how to use kidney biopsies for management and not just diagnosis, how molecular technologies can be applied to interrogate biopsies and how such data can impact management, and how to incorporate LN biomarkers into management paradigms. Herein, we will review new developments in these areas of LN and put them into perspective for disease management now and in the future.

Urine Biomarkers of Kidney Tubule Health, Injury, and Inflammation are Associated with Progression of CKD in Children

BACKGROUND

Novel urine biomarkers may improve identification of children at greater risk of rapid kidney function decline, and elucidate the pathophysiology of CKD progression.

METHODS

We investigated the relationship between urine biomarkers of kidney tubular health (EGF and α-1 microglobulin), tubular injury (kidney injury molecule-1; KIM-1), and inflammation (monocyte chemoattractant protein-1 [MCP-1] and YKL-40) and CKD progression. The prospective CKD in Children Study enrolled children aged 6 months to 16 years with an eGFR of 30-90ml/min per 1.73m². Urine biomarkers were assayed a median of 5 months [IQR: 4-7] after study enrollment. We indexed the biomarker to urine creatinine by dividing the urine biomarker concentration by the urine creatinine concentration to account for the concentration of the urine. The primary outcome was CKD progression (a composite of a 50% decline in eGFR or kidney failure) during the follow-up period.

RESULTS

Overall, 252 of 665 children (38%) reached the composite outcome over a median follow-up of 6.5 years. After adjustment for covariates, children with urine EGF concentrations in the lowest quartile were at a seven-fold higher risk of CKD progression versus those with concentrations in the highest quartile (fully adjusted hazard ratio [aHR], 7.1; 95% confidence interval [95% CI], 3.9 to 20.0). Children with urine KIM-1, MCP-1, and α-1 microglobulin concentrations in the highest quartile were also at significantly higher risk of CKD progression versus those with biomarker concentrations in the lowest quartile. Addition of the five biomarkers to a clinical model increased the discrimination and reclassification for CKD progression.

CONCLUSIONS

After multivariable adjustment, a lower urine EGF concentration and higher urine KIM-1, MCP-1, and α-1 microglobulin concentrations were each associated with CKD progression in children.

The next generation: Urinary epidermal growth factor is associated with an early decline in kidney function in children and adolescents with type 1 diabetes mellitus

AIMS

Micro-albuminuria is considered an early clinical sign of diabetes nephropathy, however, early decrease of glomerular filtration can be present years before the presence of microalbuminuria. In this study, we explored whether urinary epidermal growth factor (uEGF) might serve as an early marker of diabetes nephropathy compared to microalbuminuria in children and adolescents.

METHODS

Children with type 1 diabetes mellitus (n = 158) and healthy controls (n = 40) were included in this study. Serum and urine samples were collected three times with an interval of at least one month to determine creatinine (serum and urine), epidermal growth factor and albumin (urine). Demographic data and routine lab values were extracted out of the electronic patient files.

RESULTS

uEGF was significantly lower in children with T1DM compared to healthy controls (p = 0.032). A relatively lower glomerular filtration rate (eGFR) was associated with a decreased uEGF (p < 0.001). uEGF was independently associated with eGFR in a multivariate analysis.

CONCLUSION

This study provides evidence that uEGF can serve as an early marker of diabetes nephropathy in children and adolescents.

Perspectives in systems nephrology

Chronic kidney diseases (CKD) are a major health problem affecting approximately 10% of the world’s population and posing increasing challenges to the healthcare system. While CKD encompasses a broad spectrum of pathological processes and diverse etiologies, the classification of kidney disease is currently based on clinical findings or histopathological categorizations. This descriptive classification is agnostic towards the underlying disease mechanisms and has limited progress towards the ability to predict disease prognosis and treatment responses. To gain better insight into the complex and heterogeneous disease pathophysiology of CKD, a systems biology approach can be transformative. Rather than examining one factor or pathway at a time, as in the reductionist approach, with this strategy a broad spectrum of information is integrated, including comprehensive multi-omics data, clinical phenotypic information, and clinicopathological parameters. In recent years, rapid advances in mathematical, statistical, computational, and artificial intelligence methods enable the mapping of diverse big data sets. This holistic approach aims to identify the molecular basis of CKD subtypes as well as individual determinants of disease manifestation in a given patient. The emerging mechanism-based patient stratification and disease classification will lead to improved prognostic and predictive diagnostics and the discovery of novel molecular disease-specific therapies.

Association Between Urinary Epidermal Growth Factor and Renal Prognosis in Lupus Nephritis

OBJECTIVE

To evaluate the role of urinary epidermal growth factor (EGF) as a biomarker of chronic kidney damage in lupus nephritis (LN).

METHODS

A proteomics approach was used to identify urinary EGF as a biomarker of interest in a discovery cohort of patients with LN. The expression of urinary EGF was characterized in 2 large multiethnic LN cohorts, and the association between urinary EGF levels at the time of flare and kidney outcomes was evaluated in a subset of 120 patients with long-term follow-up data. For longitudinal studies, the expression of urinary EGF over time was determined in 2 longitudinal cohorts of patients with LN from whom serial urine samples were collected.

RESULTS

Discovery analysis showed the urinary EGF levels as being low in patients with active LN (median peptide count 8.4, interquartile range [IQR] 2.8-12.3 in patients with active LN versus median 48.0, IQR 45.3-64.6 in healthy controls). The peptide sequence was consistent with that of proEGF, and this was confirmed by immunoblotting. The discovery findings were verified by enzyme-linked immunosorbent assay. Patients with active LN had a significantly lower level of urinary EGF compared to that in patients with active nonrenal systemic lupus erythematosus (SLE), patients with inactive SLE, and healthy kidney donors (each P < 0.05). The urinary EGF level was inversely correlated with the chronicity index of histologic features assessed in kidney biopsy tissue (Spearman's r = -0.67, P < 0.001). Multivariate survival analysis showed that the urinary EGF level was associated with time to doubling of the serum creatinine level (DSCr), a marker of future end-stage kidney disease (ESKD) (hazard ratio 0.88, 95% confidence interval 0.77-0.99, P = 0.045). Patients whose LN symptoms progressed to DSCr and those who experienced progression to ESKD had a lower urinary EGF level at the time of flare, and urinary EGF levels decreased over the 12 months following flare. All patients who experienced progression to ESKD were identified based on a urinary EGF cutoff level of <5.3 ng/mg.

CONCLUSION

Urinary EGF levels are correlated with histologic kidney damage in patients with LN. Low urinary EGF levels at the time of flare and decreasing urinary EGF levels over time are associated with adverse long-term kidney outcomes.

Biopsy or Biomarker? Children With Minimal Change Disease Have a Distinct Profile of Urinary Epidermal Growth Factor

Background: In this study, the profile of urinary EGF excretion (uEGF/uCreat) was mapped in children presenting with prolonged proteinuria or with nephrotic syndrome refractory to or dependent of steroids. We investigated whether uEGF/uCreat could be linked to the underlying biopsy result, taking into account its response to immunosuppressive medication and to ACE inhibition, as well as genetic predisposition. Methods: Ninety-eight pediatric patients with initial presentation of nephrotic syndrome or prolonged proteinuria were included in this study, along with 49 healthy controls and 20 pediatric Alport patients. All patients had a normal kidney function and were normotensive during the course of the study, whether or not under ACE inhibition. In repeated urine samples, uEGF was measured and concentration was normalized by urine creatinine. In order to compare diagnosis on kidney biopsy, genetic predisposition and response of uEGF/uCreat to immunosuppression and to ACE inhibition, uEGF/uCreat is studied in a linear mixed effects model. Results: Patients with Minimal Change Disease (MCD) showed a significantly different profile of uEGF/uCreat in comparison to healthy children, as well as compared to patients with Focal Segmental Glomerulosclerosis (FSGS) or another glomerulopathy on kidney biopsy. The response of uEGF/uCreat to ACE inhibition was absent in minimal change disease and contrasted with an impressive beneficial effect of ACE inhibition on uEGF/uCreat in FSGS and other proteinuric glomerulopathies. Absence of a genetic predisposition was also associated with a significantly lower uEGF/uCreat. Conclusions: Despite preserved kidney function, children with a proteinuric or nephrotic glomerular disease on kidney biopsy show a significantly lower uEGF/uCreat, indicative of early tubulo-interstitial damage, which appears reversible under ACE inhibition in any underlying glomerulopathy except in minimal change disease. In view of the distinct profile of uEGF/uCreat in minimal change disease compared to other glomerulopathies, and the link between genetic predisposition and uEGF/uCreat, our study suggests that uEGF/uCreat can be a helpful tool to decide on the need for a renal biopsy in order to differentiate minimal change disease from other proteinuric glomerular diseases.

Integrated multi-omics approaches to improve classification of chronic kidney disease

Chronic kidney diseases (CKDs) are currently classified according to their clinical features, associated comorbidities and pattern of injury on biopsy. Even within a given classification, considerable variation exists in disease presentation, progression and response to therapy, highlighting heterogeneity in the underlying biological mechanisms. As a result, patients and clinicians experience uncertainty when considering optimal treatment approaches and risk projection. Technological advances now enable large-scale datasets, including DNA and RNA sequence data, proteomics and metabolomics data, to be captured from individuals and groups of patients along the genotype-phenotype continuum of CKD. The ability to combine these high-dimensional datasets, in which the number of variables exceeds the number of clinical outcome observations, using computational approaches such as machine learning, provides an opportunity to re-classify patients into molecularly defined subgroups that better reflect underlying disease mechanisms. Patients with CKD are uniquely poised to benefit from these integrative, multi-omics approaches since the kidney biopsy, blood and urine samples used to generate these different types of molecular data are frequently obtained during routine clinical care. The ultimate goal of developing an integrated molecular classification is to improve diagnostic classification, risk stratification and assignment of molecular, disease-specific therapies to improve the care of patients with CKD.

Urinary Epidermal Growth Factor as a Marker of Disease Progression in Children With Nephrotic Syndrome

INTRODUCTION

Childhood-onset nephrotic syndrome has a variable clinical course. Improved predictive markers of long-term outcomes in children with nephrotic syndrome are needed. This study tests the association between baseline urinary epidermal growth factor (uEGF) excretion and longitudinal kidney function in children with nephrotic syndrome.

METHODS

The study evaluated 191 participants younger than 18 years enrolled in the Nephrotic Syndrome Study Network, including 118 with their first clinically indicated kidney biopsy (68 minimal change disease; 50 focal segmental glomerulosclerosis) and 73 with incident nephrotic syndrome without a biopsy. uEGF was measured at baseline for all participants and normalized by the urine creatinine (Cr) concentration. Renal epidermal growth factor (EGF) mRNA was measured in the tubular compartment microdissected from kidney biopsy cores from a subset of patients. Linear mixed models were used to test if baseline uEGF/Cr and EGF mRNA expression were associated with change in estimated glomerular filtration rate (eGFR) over time.

RESULTS

Higher uEGF/Cr at baseline was associated with slower eGFR decline during follow-up (median follow-up = 30 months). Halving of uEGF/Cr was associated with a decrease in eGFR slope of 2.0 ml/min per 1.73 m2 per year (P < 0.001) adjusted for age, race, diagnosis, baseline eGFR and proteinuria, and APOL1 genotype. In the biopsied subgroup, uEGF/Cr was correlated with EGF mRNA expression (r = 0.74; P < 0.001), but uEGF/Cr was retained over mRNA expression as the stronger predictor of eGFR slope after multivariable adjustment (decrease in eGFR slope of 1.7 ml/min per 1.73 m2 per year per log2 decrease in uEGF/Cr; P < 0.001).

CONCLUSION

uEGF/Cr may be a useful noninvasive biomarker that can assist in predicting the long-term course of kidney function in children with incident nephrotic syndrome.

Urinary prostaglandin E2 is a biomarker of early adaptive hyperfiltration in solitary functioning kidney

INTRODUCTION

Hyperfiltration is a major contributor to progression of chronic kidney disease (CKD) in diabetes, obesity and in individuals with solitary functioning kidney (SFK). We have proposed hyperfiltration-induced injury as a continuum of overlapping glomerular changes caused by increased biomechanical forces namely, fluid flow shear stress (FFSS) and tensile stress. We have shown that FFSS is elevated in animals with SFK and, it upregulates prostaglandin E₂ (PGE₂), cyclooxygenase-2 and PGE₂ receptor EP2 in cultured podocytes and in uninephrectomized mice. We conceptualized urinary PGE₂ as a biomarker of early effects of hyperfiltration-induced injury preceding microalbuminuria in individuals with SFK. We studied children with SFK to validate our hypothesis.

METHODS

Urine samples from children with SFK and controls were analyzed for PGE₂, albumin (glomerular injury biomarker) and epidermal growth factor (EGF, tubular injury biomarker). Age, gender, and Z-scores for height, weight, BMI, and blood pressure were obtained.

RESULTS

Children with SFK were comparable to controls except for lower BMI Z-scores. The median values were elevated in SFK compared to control for urine PGE₂ [9.1 (n = 57) vs. 5.7 (n = 72), p = 0.009] ng/mgCr and albumin [7.6 (n = 40) vs. 7.0 (n = 41), p = 0.085] μg/mgCr, but not for EGF [20098 (n = 44) vs. 18637 (n = 44), p = 0.746] pg/mgCr. Significant increase in urinary PGE₂ (p = 0.024) and albumin (p = 0.019) but not EGF (p = 0.412) was observed using additional regression modeling. These three urinary analytes were independent of each other.

CONCLUSION

Increased urinary PGE₂ from elevated SNGFR and consequently increased FFSS during early stage of CKD precedes overt microalbuminuria and is a biomarker for early hyperfiltration-induced injury in individuals with SFK.

Evolving Clinical Applications of Tissue Transcriptomics in Kidney Disease

Nephrotic syndrome is classically categorized by the histopathology with examples including focal segmental glomerulosclerosis (FSGS) and minimal change disease. Pediatric patients are also classified by whether their nephrotic syndrome is sensitive to, dependent on, or resistant to steroids. However, this traditional classification system overlooks the frequent clinical conundrum when, for example, one patient with FSGS responds briskly to steroids, and another quickly progresses to end stage kidney disease despite therapy. Two patients may have similar histopathologic appearances on kidney biopsy but entirely different clinical characteristics, rates of progression, and treatment responses. Transcriptional regulation of gene activation and posttranscriptional processing of mRNA may drive the unique and heterogeneous phenotypes which are incompletely understood in kidney disease and are a recent focus of research. Gene expression profiles provide insight on active transcriptional programs in tissues, are being used to understand biologic mechanisms of progressive chronic kidney disease, and may help to identify patients with shared mechanisms of kidney damage. This mini-review discusses clinically relevant techniques of bulk tissue and single cell transcriptomics, as well as strengths and limitations of each methodology. Further, we summarize recent examples in kidney research achieved through transcriptomics. This review offers an outlook on the role of transcriptomics in an integrative systems biology model with the goal of defining unique disease subgroups, finding targets for drug development, and aligning the right drug with the right patient.

Dysregulated Expression of microRNA-21 and Disease-Related Genes in Human Patients and in a Mouse Model of Alport Syndrome

Alport syndrome is a genetic disease caused by mutations in type IV collagen and is characterized by progressive kidney disease. The Col4α3^-/- mouse model recapitulates the main features of human Alport syndrome. Previously, it was reported that kidney microRNA-21 (miR-21) expression is significantly increased in Col4α3^-/- mice, and administration of anti-miR-21 oligonucleotides (anti-miR-21) attenuates kidney disease progression in Col4α3^-/- mice, indicating that miR-21 is a viable therapeutic target for Alport syndrome. However, the expression pattern of miR-21 in the kidneys of patients with human Alport syndrome has not been evaluated. Paraffin-embedded kidney specimens were obtained from 27 patients with Alport syndrome and from 10 normal controls. They were evaluated for miR-21 expression and for in situ hybridization and mRNA expression by quantitative polymerase chain reaction. In addition, anti-miR-21 was administrated to Col4α3^-/- mice at different stages of disease, and changes in proteinuria, kidney function, and survival were monitored. Transcriptomic analysis of mouse kidney was conducted using RNA sequencing. miR-21 expression was significantly elevated in kidney specimens from patients with Alport syndrome compared to normal controls. Elevated renal miR-21 expression positively correlated with 24 h urine protein, serum blood urea nitrogen, serum creatinine, and severity of kidney pathology. On histological evaluation, high levels of miR-21 were localized to damaged tubular epithelial cells and glomeruli. Kidney specimens from both humans and mice with Alport syndrome exhibited abnormal expression of genes involved in kidney injury, fibrosis, inflammation, mitochondrial function, and lipid metabolism. Administration of anti-miR-21 to Alport mice resulted in slowing of kidney function decline, partial reversal of abnormal gene expression associated with disease pathology, and improved survival. Increased levels of miR-21 in human Alport kidney samples showed a correlation with kidney disease severity measured by proteinuria, biomarkers of kidney function, and kidney histopathology scores. These human data, combined with the finding that a reduction of miR-21 in Col4α3^-/- mice improves kidney phenotype and survival, support miR-21 as a viable therapeutic target for the treatment of Alport syndrome.