Messenger RNA expression of glomerular podocyte markers in the urinary sediment of acquired proteinuric diseases

Intrarenal and Urinary Glycogen Synthase Kinase-3 Beta Levels in Diabetic and Nondiabetic Chronic Kidney Disease

BACKGROUND

Renal glycogen synthase kinase-3 beta (GSK3β) overactivity has been associated with a diverse range of kidney diseases. GSK3β activity in urinary exfoliated cells was reported to predict the progression of diabetic kidney disease (DKD). We compared the prognostic value of urinary and intrarenal GSK3β levels in DKD and nondiabetic chronic kidney disease (CKD).

METHODS

We recruited 118 consecutive biopsy-proved DKD patients and 115 nondiabetic CKD patients. Their urinary and intrarenal GSK3β levels were measured. They were then followed for dialysis-free survival and rate of renal function decline.

RESULTS

DKD group had higher intrarenal and urinary GSK3β levels than nondiabetic CKD (p < 0.0001 for both), but their urinary GSK3β mRNA levels were similar. Urinary p-GSK3β level is statistically significantly correlated with the baseline estimated glomerular filtration rate (eGFR), but urinary GSK3β level by ELISA, its mRNA level, the p-GSK3β level, or the p-GSK3β/GSK3β ratio had no association with dialysis-free survival or the slope of eGFR decline. In contrast, the intrarenal pY216-GSK3β/total GSK3β ratio significantly correlated with the slope of eGFR decline (r = -0.335, p = 0.006) and remained an independent predictor after adjusting for other clinical factors.

CONCLUSION

Intrarenal and urinary GSK3β levels were increased in DKD. The intrarenal pY216-GSK3β/total GSK3β ratio was associated with the rate of progression of DKD. The pathophysiological roles of GSK3β in kidney diseases deserve further studies.

Urine podocyte mRNA loss in preterm infants and related perinatal risk factors

BACKGROUND

Preterm birth has been identified as a risk factor for development of long-term chronic kidney disease. Podocyte loss has been reported to contribute to this process in preterm animal models. However, details about podocyte loss in preterm infants and related perinatal risk factors have not been well clarified.

METHODS

Forty full-term infants and 106 preterm infants were enrolled. Urine samples were collected from full-term infants within 4-7 days of birth and preterm infants at 37-40 weeks of corrected age. Levels of urine podocin mRNA, urine protein (UP), and urine microalbumin (UMA) were measured, and the relationship between these markers was evaluated. Clinical information in these infants was collected, and potential correlates that may lead to increased podocyte loss during the perinatal period were identified using linear regression analysis.

RESULTS

Urine podocyte loss indicated by the urine podocin mRNA to creatinine ratio (UpodCR) was higher in preterm infants than in full-term infants. UpodCR was correlated with the levels of UP and UMA. Multiple linear regression analysis also showed that lower gestational age (GA) at birth and small for gestational age (SGA) were high risk factors for urine podocyte loss.

CONCLUSIONS

Increasing urine podocyte loss was identified in preterm infants. Moreover, perinatal factors were associated with podocyte loss and may be a potential direction for comprehensive research and intervention in this field. A higher resolution version of the Graphical abstract is available as Supplementary information.

Exfoliated Kidney Cells from Urine for Early Diagnosis and Prognostication of CKD: The Way of the Future?

Chronic kidney disease (CKD) is a global health issue, affecting more than 10% of the worldwide population. The current approach for formal diagnosis and prognostication of CKD typically relies on non-invasive serum and urine biomarkers such as serum creatinine and albuminuria. However, histological evidence of tubulointerstitial fibrosis is the 'gold standard' marker of the likelihood of disease progression. The development of novel biomedical technologies to evaluate exfoliated kidney cells from urine for non-invasive diagnosis and prognostication of CKD presents opportunities to avoid kidney biopsy for the purpose of prognostication. Efforts to apply these technologies more widely in clinical practice are encouraged, given their potential as a cost-effective approach, and no risk of post-biopsy complications such as bleeding, pain and hospitalization. The identification of biomarkers in exfoliated kidney cells from urine via western blotting, enzyme-linked immunosorbent assay (ELISA), immunofluorescence techniques, measurement of cell and protein-specific messenger ribonucleic acid (mRNA)/micro-RNA and other techniques have been reported. Recent innovations such as multispectral autofluorescence imaging and single-cell RNA sequencing (scRNA-seq) have brought additional dimensions to the clinical application of exfoliated kidney cells from urine. In this review, we discuss the current evidence regarding the utility of exfoliated proximal tubule cells (PTC), podocytes, mesangial cells, extracellular vesicles and stem/progenitor cells as surrogate markers for the early diagnosis and prognostication of CKD. Future directions for development within this research area are also identified.

Nephrinuria and podocytopathies

The discovery of nephrin in 1998 has launched a new era in glomerular diseases research, emphasizing its crucial role in the structure and function of the glomerular filtration barrier. In the past 20 years, substantial advances have been made in understanding podocyte structure and function as well as the discovery of several podocyte-related proteins including nephrin. The glomerular filtration barrier is comprised of podocytes, the glomerular basement membrane and endothelial cells. Podocytes, with their specialized slit diaphragm, form the essential backbone of the glomerular filtration barrier. Nephrin is a crucial structural and functional feature of the slit diaphragm that prevents plasma protein, blood cell and macromolecule leakage into the urine. Podocyte damage results in nephrin release. Podocytopathies are kidney diseases in which podocyte damage drives proteinuria, i.e., nephrotic syndrome. Many kidney diseases involve podocytopathy including congenital nephrotic syndrome of Finnish type, diffuse mesangial sclerosis, minimal change disease, focal segmental glomerulosclerosis, collapsing glomerulonephropathy, diabetic nephropathy, lupus nephropathy, hypertensive nephropathy and preeclampsia. Recently, urinary nephrin measurement has become important in the early detection of podocytopathies. In this chapter, we elaborate the main structural and functional features of nephrin as a podocyte-specific protein, pathomechanisms of podocytopathies which result in nephrinuria, highlight the most commonly used methods for detecting urinary nephrin and investigate the diagnostic, prognostic and potential therapeutic relevance of urinary nephrin in primary and secondary proteinuric kidney diseases.

Urinary sediment CCL5 messenger RNA as a potential prognostic biomarker of diabetic nephropathy

BACKGROUND

Urinary sediment messenger RNAs (mRNAs) have been shown as novel biomarkers of kidney disease. We aimed to identify targeted urinary mRNAs in diabetic nephropathy (DN) based on bioinformatics analysis and clinical validation.

METHODS

Microarray studies of DN were searched in the GEO database and Nephroseq platform. Gene modules negatively correlated with estimated glomerular filtration rate (eGFR) were identified by informatics methods. Hub genes were screened within the selected modules. In validation cohorts, a quantitative polymerase chain reaction assay was used to compare the expression levels of candidate mRNAs. Patients with renal biopsy-confirmed DN were then followed up for a median time of 21 months. End-stage renal disease (ESRD) was defined as the primary endpoint. Multivariate Cox proportional hazards regression was developed to evaluate the prognostic values of candidate mRNAs.

RESULTS

Bioinformatics analysis revealed four chemokines (CCL5, CXCL1, CXLC6 and CXCL12) as candidate mRNAs negatively correlated with eGFR, of which CCL5 and CXCL1 mRNA levels were upregulated in the urinary sediment of patients with DN. In addition, urinary sediment mRNA of CXCL1 was negatively correlated with eGFR (r = -0.2275, P = 0.0301) and CCL5 level was negatively correlated with eGFR (r = -0.4388, P < 0.0001) and positively correlated with urinary albumin:creatinine ratio (r = 0.2693, P = 0.0098); also, CCL5 and CXCL1 were upregulated in patients with severe renal interstitial fibrosis. Urinary sediment CCL5 mRNA was an independent predictor of ESRD [hazard ratio 1.350 (95% confidence interval 1.045-1.745)].

CONCLUSIONS

Urinary sediment CCL5 and CXCL1 mRNAs were upregulated in DN patients and associated with a decline in renal function and degree of renal interstitial fibrosis. Urinary sediment CCL5 mRNA could be used as a potential prognostic biomarker of DN.

Excretion Patterns of Urinary Sediment and Supernatant Podocyte Biomarkers in Patients with CKD

Background

Podocyte depletion causes glomerulosclerosis, and persistent podocyte loss drives progression to ESKD. Urinary sediment podocin (u-sed Pod) mRNA excretion and urinary supernatant podocalyxin (u-sup PCX) protein have been used to monitor disease activity in glomerular diseases. However, the differences in these markers among pathologies have not been investigated. We examined the roles of these markers in kidney diseases.

Methods

From January 2013 to March 2016, early morning urine samples were collected from 12 healthy controls and 172 patients with kidney disease (n=15 patients with minor glomerular abnormality with mild proteinuria and/or microscopic hematuria, n=15 with minimal change nephrotic syndrome [MCNS], n=15 with membranous nephropathy [MN], n=60 with IgA nephropathy [IgAN], n=19 with crescentic GN [Cres GN], n=10 with lupus nephritis [LN], and n=38 with other kidney diseases). We examined u-sed Pod mRNA excretion, u-sup PCX protein, and the urinary protein-creatinine ratio (u-PCR).

Results

u-sed Pod mRNA excretion was significantly correlated with u-sup PCX protein (r=0.37, P<0.001). Both u-sed Pod mRNA excretion and u-sup PCX protein were significantly correlated with u-PCR (r=0.53, P<0.001 and r=0.35, P<0.001, respectively). Interestingly, u-sed Pod mRNA excretion was significantly increased in proliferative-type GN-including IgAN with extracapillary proliferative lesions, Cres GN, and LN class IV-and significantly correlated with the rate of crescent formation, whereas u-sup PCX protein was significantly increased only in those with MN and subepithelial dense deposit-type LN compared with controls.

Conclusions

Higher u-sed Pod mRNA excretion and u-sup PCX protein were associated with proliferative-type GN, indicating podocyte detachment and subepithelial dense deposit-type GN, respectively. The results suggest that u-sed Pod mRNA excretion and u-sup PCX protein have usefulness for the diagnosis and measurement of disease activity with regard to glomerular diseases.

Increasing urinary podocyte mRNA excretion and progressive podocyte loss in kidney contribute to the high risk of long-term renal disease caused by preterm birth

Podocyte abnormalities are common mechanism driving the progression of glomerular diseases, which account for most chronic kidney diseases (CKDs). However, the role of podocyte in the mechanism of high-risk long-term CKD caused by prematurity has not been well clarified. In present study, urine samples of 86 preterm infants and 32 full-term infants were collected, and podocyte-specific podocin mRNA levels in urine pellet were applied to indicate urinary podocyte mRNA excretion. In addition, in a preterm animal rat model, preterm rats were identified by delivery 2 days early. From the age of 3 weeks-12 months, urine samples were collected to examine podocyte mRNA excretion by measuring podocyte-specific podocin mRNA levels. Kidney samples at the age of 3 weeks, 2 months, and 12 months were collected from 8, 5 and 6 preterm rats and 9, 6 and 8 full-term rats, respectively, to examine podocyte density and podocyte area by measuring the podocyte specific nuclear marker WT-1 and the podocyte specific marker synaptopodin. As results, a more than threefold increase of urinary podocyte-specific podocin mRNA excretion rate was found in preterm infants compared with full-term infants. In addition, there was negative correlation between gestational age at birth and urinary podocin mRNA excretion. In preterm rats, a reduction in the total number of differentiated podocytes in glomeruli and an increased podocyte podocin mRNA excretion rate in urine were detected at the end of kidney differentiation. Moreover, long-term follow-up data in preterm rats showed there was an increased the risk of renal disease indicated by persistent podocyte mRNA loss, proteinuria, and enlarged glomeruli. In conclusion, increasing podocyte mRNA excretion in urine and podocyte loss in kidney led by prematurity drive the progression of long-term abnormal kidney function and could potentially explain the high risk of long-term CKD in preterm infants.

Urinary podocyte markers in kidney diseases

Podocytes play an important role in the maintenance of kidney function, and they are the primary focus of many kidney diseases. Podocyte injury results in the shedding of podocyte-derived cellular fragments and podocyte-specific molecular targets into the urine, which may serve as biomarkers of kidney diseases. Intact podocytes, either viable or dead, and podocyte-derived microvesicles could be quantified in the urine by various centrifugation, visualization and culture methods. Podocyte-specific protein targets from the nucleus, cytoplasm, slit-diaphragm, glomerular capillary basement membrane, and cytoskeleton, as well as their corresponding messenger RNA (mRNA), in the urine could be quantified by western blotting, ELISA, or quantitative polymerase chain reaction. Although some of these techniques may be expensive or labor-intensive at present, they may become widely available in the future because of the improvement in technology and automation. The application of urinary podocyte markers for the diagnosis and monitoring of various kidney diseases have been explored but the published data in this area are not sufficiently systematic and lack external validation. Further research should focus on standardizing, comparing, and automizing laboratory methods, as well as defining their added value to the routine clinical tests.

Urinary mRNA Expression of Glomerular Podocyte Markers in Glomerular Disease and Renal Transplant

The research of novel markers in urinary samples, for the description of renal damage, is of high interest, and several works demonstrated the value of urinary mRNA quantification for the search of events related to renal disease or affecting the outcome of transplant kidneys. In the present pilot study, a comparison of the urine mRNA expression of specific podocyte markers among patients who had undergone clinical indication to renal transplanted (RTx, n = 20) and native (N, n = 18) renal biopsy was performed. The aim of this work was to identify genes involved in podocytes signaling and cytoskeletal regulation (NPHS1, NPHS2, SYNPO, WT1, TRPC6, GRM1, and NEUROD) in respect to glomerular pathology. We considered some genes relevant for podocytes signaling and for the function of the glomerular filter applying an alternative normalization approach. Our results demonstrate the WT1 urinary mRNA increases in both groups and it is helpful for podocyte normalization. Furthermore, an increase in the expression of TRPC6 after all kinds of normalizations was observed. According to our data, WT1 normalization might be considered an alternative approach to correct the expression of urinary mRNA. In addition, our study underlines the importance of slit diaphragm proteins involved in calcium disequilibrium, such as TRPC6.

Detection of urinary podocytes by flow cytometry in idiopathic membranous nephropathy

Idiopathic membranous nephropathy (iMN) is considered an immune-mediated disease where circulating autoantibodies against podocyte targets (mainly the PLA₂R) cause the deposition of in-situ subepithelial immune-complexes. The consequent podocyte damage may cause cell detachment in urine (Podocyturia-PdoU). PdoU has been assessed in different kidney diseases, but limited data are available in iMN. In this study all patients with a diagnosis of iMN between 15/12/1999-16/07/2014 were tested for PLA₂R antibodies (Ab anti-PLA₂R, ELISA kit) and PdoU by flow cytometry with anti-podocalyxin antibody. A semi-quantitative PdoU score was defined according to the percentage of podocalyxin positive cells normalized to the total volume of sample and set relative to the urine creatinine measured in the supernatant. PdoU was positive in 17/27 patients (63%; 1+ score in 6/27-22.2%, 2+ in 4/27-14.8%, 3+ in 2/27-7.4%, 4+ in 5/27-18.5%). Only 2/7 patients with complete remission showed a positive PdoU (1+) while all six patients without remission have significant PdoU. PdoU+ was statistically correlated with the absence of remission and Ab anti-PLA₂R + (p < 0.05) but PdoU, analysed as a continuous variable, showed a non-linear correlation with proteinuria or PLA₂R antibody levels also in the cohort of patients with two available PdoU tests. In conclusion, PdoU could be detected in iMN and seems to be associated with commonly considered markers of disease activity (proteinuria and Ab anti-PLA₂R) with a non-linear correlation. Despite data should be confirmed in large and prospective cohorts, according to the podocyte depletion hypothesis PdoU may represent an early marker of immunological activation with potential prognostic utility.

Research Progress in Acute Hypertensive Renal Injury by "in Vivo Cryotechnique"

Arterial hypertension has a large prevalence in the general population and as a major hypertensive target organ, the involvement of kidney is usually hard to avoid and gradually develops into chronic kidney disease (CKD). Acute hypertension is defined as a blood pressure greater than 180/120, also known as hypertensive emergency (HE). In acute severe hypertension, the pathophysiology damage to the kidney tends to worsen on the basis of chronic damage, and accounts for more significant mortality. However, the mechanisms of renal injury induced by acute hypertension remain unclear. This review summarizes the clinical and histopathological features of hypertensive renal injury by using "in vivo cyrotechnique" and focusses on the interplay of distinct systemic signaling pathways, which drive glomerular podocyte injury. A thorough understanding of the cellular and molecular mechanisms of kidney damage and repair in hypertension will provide significant insight into the development of new research methods and therapeutic strategies for global CKD progression.

Podocyte hypertrophic stress and detachment precedes hyperglycemia or albuminuria in a rat model of obesity and type2 diabetes-associated nephropathy

Type2 diabetes-associated nephropathy is the commonest cause of renal failure. Mechanisms responsible are controversial. Leptin-deficient hyperphagic Zucker (fa/fa) rats were modeled to test the hypothesis that glomerular enlargement drives podocyte hypertrophic stress leading to accelerated podocyte detachment, podocyte depletion, albuminuria and progression. By 6weeks, prior to development of either hyperglycemia or albuminuria, fa/fa rats were hyperinsulinemic with high urinary IGF1/2 excretion, gaining weight rapidly, and had 1.6-fold greater glomerular volume than controls (P < 0.01). At this time the podocyte number per glomerulus was not yet reduced although podocytes were already hypertrophically stressed as shown by high podocyte phosphor-ribosomal S6 (a marker of mTORC1 activation), high urinary pellet podocin:nephrin mRNA ratio and accelerated podocyte detachment (high urinary pellet podocin:aquaporin2 mRNA ratio). Subsequently, fa/fa rats became both hyperglycemic and albuminuric. 24 hr urine albumin excretion correlated highly with decreasing podocyte density (R2 = 0.86), as a consequence of both increasing glomerular volume (R2 = 0.70) and decreasing podocyte number (R2 = 0.63). Glomerular podocyte loss rate was quantitatively related to podocyte detachment rate measured by urine pellet mRNAs. Glomerulosclerosis occurred when podocyte density reached <50/106um3. Reducing food intake by 40% to slow growth reduced podocyte hypertrophic stress and "froze" all elements of the progression process in place, but had small effect on hyperglycemia. Glomerular enlargement caused by high growth factor milieu starting in pre-diabetic kidneys appears to be a primary driver of albuminuria in fa/fa rats and thereby an under-recognized target for progression prevention. Progression risk could be identified prior to onset of hyperglycemia or albuminuria, and monitored non-invasively by urinary pellet podocyte mRNA markers.

Human podocyte injury in the early course of hypertensive renal injury

BACKGROUND

Hypertension is prevalent in the general population and is regarded as the second leading cause of renal damage and dysfunction, outnumbered only by diabetes. However, the mechanisms remain unclear.

AIM

To investigate podocyte injury induced by hypertension in the early course without massive proteinuria or renal dysfunction.

METHODS

The hypertension group comprised 18 patients with hypertension accompanied by microalbuminuria, diagnosed with hypertensive renal injury according to biopsy results. For a comparison of pathological changes in renal tissue, control group 1 comprised 10 healthy volunteers, and control group 2 comprised 16 patients who underwent surgery for renal trauma.

RESULTS

The hypertension group had significantly higher blood pressure (P = 0.000) and microalbuminuria (P = 0.000) compared with control group 1. In the hypertension group, urinary podocytes were detected following positive staining of podocyte-specific nephrin and/or CD2-associated protein (CD2AP) in urine sediment. Podocyte foot process fusion and a significant decrease in nephrin and/or CD2AP expression in glomeruli were observed in the hypertension group compared with control group 2. This indicated that hypertension caused podocyte injury and detachment from the glomerular basement membrane, which was consistent with urinary detection of podocytes.

CONCLUSION

Our results suggest that podocyturia appears early in the course of hypertensive renal injury, and may be a sensitive marker for early prediction of hypertensive renal injury.

Urine markers of podocyte dysfunction: a review of podocalyxin and nephrin in selected glomerular diseases

Urinary podocalyxin and nephrin are urine markers of podocyte dysfunction that may reflect the integrity of kidney's filtration barrier. Studies on their respective roles in glomerular diseases are still underway. However, the isolated and unsystematic manner in which they are being studied does not permit proper identification of their roles in each glomerular disease. As such, there is little or no appreciation of what research has already achieved and what remains to be achieved as the research direction is not clearly defined. We explored the recent studies and outlined the major findings regarding the value of both biomarkers in each of the three glomerular disease entities. Our review covered diabetic nephropathy, membranous nephropathy and IgA nephropathy.

Urinary podocyte and TGF-β1 mRNA as markers for disease activity and progression in anti-glomerular basement membrane nephritis

Background

Podocyte depletion causes glomerulosclerosis, with persistent podocyte loss being a major factor driving disease progression. Urinary podocyte mRNA is potentially useful for monitoring disease progression in both animal models and in humans. To determine whether the same principles apply to crescentic glomerular injury, a rat model of anti-glomerular basement membrane (anti-GBM) nephritis was studied in parallel with a patient with anti-GBM nephritis.

Methods

Podocyte loss was measured by Wilms' Tumor 1-positive podocyte nuclear counting and density, glomerular epithelial protein 1 or synaptopodin-positive podocyte tuft area and urinary podocyte mRNA excretion rate. Glomerulosclerosis was evaluated by Azan staining and urinary transforming growth factor (TGF)-β1 mRNA excretion rate.

Results

In the rat model, sequential kidney biopsies revealed that after a threshold of 30% podocyte loss, the degree of glomerulosclerosis was linearly associated with the degree of podocyte depletion, compatible with podocyte depletion driving the sclerotic process. Urinary podocyte mRNA correlated with the rate of glomerular podocyte loss. In treatment studies, steroids prevented glomerulosclerosis in the anti-GBM model in contrast to angiotensin II inhibition, which lacked a protective effect, and urinary podocyte and TGF-β1 mRNA markers more accurately reflected both the amount of podocyte depletion and the degree of glomerulosclerosis compared with proteinuria under both scenarios. In a patient successfully treated for anti-GBM nephritis, urinary podocyte and TGB-β1 mRNA reflected treatment efficacy.

Conclusion

These results emphasize the role of podocyte depletion in anti-GBM nephritis and suggest that urinary podocyte and TGF-β1 mRNA could serve as markers of disease progression and treatment efficacy.

Urinary sediment mRNA level of extracellular matrix molecules in adult nephrotic syndrome

BACKGROUND

Glomerular and tubulointerstitial fibrosis play important roles in the progression of chronic kidney disease. We determine whether urinary mRNA levels of extracellular matrix proteins reflect the degree of kidney fibrosis and predict renal function decline in adult nephrotic patients.

METHODS

We studied 56 adult nephrotic patients and 20 controls. Urinary mRNA levels of collagen I A1 chain (COL1A1), collagen IV A3 chain (COL4A3), and fibronectin were measured.

RESULTS

Urinary sediment mRNA levels of COL1A1 and fibronectin were significantly higher in nephrotic patients as compared to the control, irrespective to the pathological diagnosis. Urinary COL1A1 mRNA level correlates with proteinuria, glomerular and interstitial fibrosis, and inversely with estimated glomerular filtration rate (GFR); urinary fibronectin mRNA level significantly correlates with glomerular and interstitial fibrosis, and inversely with estimated GFR. After 42.4 ± 12.6 months follow-up, the rate of GFR decline inversely correlates with urinary mRNA level of COL1A1 (r = -0.273, p = 0.044). Multivariate analysis confirmed that urinary COL1A1 mRNA level is an independent predictor of serum creatinine doubling or progressing to end stage renal disease; for each 10-fold increase in urinary COL1A1 mRNA level, there is 15.1% excess in risk (95% confidence interval, 1.9% to 30.4%, p=0.022).

CONCLUSIONS

Urinary COL1A1 mRNA level is elevated in nephrotic patients irrespective to the pathological diagnosis, and it correlates with proteinuria, histological scarring, and inversely with renal function. Furthermore, urinary COL1A1 mRNA level predicts renal function loss during follow-up. Our results suggest that urinary COL1A1 mRNA level may be used for risk stratification of adult nephrotic syndrome.

A Systems Biology Overview on Human Diabetic Nephropathy: From Genetic Susceptibility to Post-Transcriptional and Post-Translational Modifications

Diabetic nephropathy (DN), a microvascular complication occurring in approximately 20-40% of patients with type 2 diabetes mellitus (T2DM), is characterized by the progressive impairment of glomerular filtration and the development of Kimmelstiel-Wilson lesions leading to end-stage renal failure (ESRD). The causes and molecular mechanisms mediating the onset of T2DM chronic complications are yet sketchy and it is not clear why disease progression occurs only in some patients. We performed a systematic analysis of the most relevant studies investigating genetic susceptibility and specific transcriptomic, epigenetic, proteomic, and metabolomic patterns in order to summarize the most significant traits associated with the disease onset and progression. The picture that emerges is complex and fascinating as it includes the regulation/dysregulation of numerous biological processes, converging toward the activation of inflammatory processes, oxidative stress, remodeling of cellular function and morphology, and disturbance of metabolic pathways. The growing interest in the characterization of protein post-translational modifications and the importance of handling large datasets using a systems biology approach are also discussed.

Urinary mRNA levels of ELR-negative CXC chemokine ligand and extracellular matrix in diabetic nephropathy

BACKGROUND

Inflammation and fibrosis play important roles in the progression of diabetic nephropathy. We determine the urinary mRNA levels of ELR-CXC chemokine ligand and extracellular matrix in diabetic nephropathy.

METHODS

We studied 26 patients with biopsy-proven diabetic nephropathy, 15 with hypertensive nephrosclerosis and 10 healthy controls. Urinary mRNA levels of CXCL9, CXCL10, CXCL11, collagen I A1 chain, collagen IV A3 chain and fibronectin were measured. Patients were followed for 36.9 ± 7.4 months to determine the rate of glomerular filtration rate (GFR) decline.

RESULTS

Urinary mRNA levels of CXCL10 and CXCL11 are decreased, and those of collagen I A1 chain and fibronectin are increased in diabetic nephropathy. Baseline estimated GFR correlates with urinary mRNA level of CXCL9 (r = 0.583, p = 0.002) and CXCL11 (r = 0.703, p < 0.0001), respectively. The rate of GFR decline significantly correlates with urinary CXCL9 (r = -0.618, p = 0.0008) and CXCL11 mRNA levels (r = -0.726, p < 0.0001). Multivariate linear regression analysis confirms that urinary CXCL9 mRNA level is independently associated with the rate of GFR decline, while the correlation with urinary CXCL11 mRNA level has borderline significance.

CONCLUSION

Urinary CXCL9 and CXCL11 mRNA levels correlate with baseline renal function. The rate of renal function decline correlates with urinary CXCL9 mRNA level. Our results suggest that urinary CXCL9 mRNA levels may be used for risk stratification of diabetic nephropathy.

Urine podocyte mRNAs mark disease activity in IgA nephropathy

BACKGROUND

Podocyte depletion is a major mechanism driving glomerulosclerosis. We and others have previously projected from model systems that podocyte-specific mRNAs in the urine pellet might serve as glomerular disease markers. We evaluated IgA nephropathy (IgAN) to test this concept.

METHODS

From 2009 to 2013, early morning voided urine samples and kidney biopsies from IgAN patients (n = 67) were evaluated in comparison with urine samples from healthy age-matched volunteers (n = 28). Urine podocyte (podocin) mRNA expressed in relation to either urine creatinine concentration or a kidney tubular marker (aquaporin 2) was tested as markers.

RESULTS

Urine podocyte mRNAs were correlated with the severity of active glomerular lesions (segmental glomerulosclerosis and acute extracapillary proliferation), but not with non-glomerular lesions (tubular atrophy/interstitial fibrosis) or with clinical parameters of kidney injury (serum creatinine and estimated glomerular filtration rate), or with degree of accumulated podocyte loss at the time of biopsy. In contrast, proteinuria correlated with all histological and clinical markers. Glomerular tuft podocyte nuclear density (a measure of cumulative podocyte loss) correlated with tubular atrophy/interstitial fibrosis, estimated-glomerular filtration rate and proteinuria, but not with urine podocyte markers. In a subset of the IgA cohort (n = 19, median follow-up period = 37 months), urine podocyte mRNAs were significantly decreased after treatment, in contrast to proteinuria which was not significantly changed.

CONCLUSIONS

Urine podocyte mRNAs reflect active glomerular injury at a given point in time, and therefore provide both different and additional clinical information that can complement proteinuria in the IgAN decision-making paradigm.

Urinary podocyte excretion and proteinuria in patients treated with antivascular endothelial growth factor therapy for solid tumor malignancies

BACKGROUND

Urinary podocyte excretion (podocyturia) may function as a more specific marker of ongoing glomerular damage. This study sought to analyze the relationship between proteinuria and podocyturia in cancer patients treated with antivascular endothelial growth factor (anti-VEGF) agents.

METHODS

Thirty-seven patients treated with anti-VEGF medications were analyzed in a single-institution, cross-sectional study. Podocyte cultures were performed on random urine collections (50-100 ml), and podocytes were identified by positive podocin staining. The corresponding urine samples were analyzed for protein and creatinine (Cr) measurements.

RESULTS

Proteinuria ≥0.5 g/g Cr was found in 30% of the patients (median, 0.12; interquartile range, 0.04-0.86), and 62% had podocyturia. There was a significant difference in the amount of podocyturia between patients with proteinuria ≥0.5 g/g Cr and those with a value <0.5 g/g Cr (median podocyturia, 1.08 cells/mg Cr, range, 0-14.55 vs. 0.03 cells/mg Cr, range, 0-1.64, respectively; p < 0.001). A statistically significant correlation was observed between the cumulative dose of bevacizumab and both proteinuria (r = 0.48, p = 0.004) and podocyturia (r = 0.34, p = 0.045) as well as between proteinuria and podocyturia (r = 0.63, p < 0.001), suggesting that these are mechanistically related.

DISCUSSION

Ongoing podocyte loss may be mechanistically related to the onset and severity of proteinuria in patients treated with anti-VEGF agents.

Urinary mRNA in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a relapsing autoimmune disease with clinical manifestations that affect multiple organ systems. Lupus nephritis is recognized as one of the most severe organ involvements in SLE and affects half of the lupus patients. Notably, lupus nephritis is characterized by intrarenal lymphocyte activation and inflammation. Since most of the cytokines exert their effects in a paracrine fashion, measuring their expression at the site of pathology should be of biological relevance. Although kidney biopsy is widely used to determine the histology and severity of lupus nephritis, this invasive procedure has its own risk and is not practical for serial monitoring. In the past decade, extraction and quantification of messenger RNA (mRNA) from urinary sediment has emerged as a robust laboratory technique. Quantification of mRNA expression in urinary sediment has been tested as a noninvasive means to assess the disease activity of SLE patients. Available published evidence, however, is limited to small-scale studies. Based on the result of these studies, a number of cytokine and transcript factor genes have been found to have potential for the differentiation between active and inactive SLE, between proliferative and membranous types of lupus nephritis, assessment of the systemic lupus activity or histological activity of kidney biopsy specimen, monitoring of treatment response in active lupus nephritis, or detection of lupus disease flare in clinically quiescent patients. Being a simple and noninvasive method, urinary mRNA level deserves further studies to validate its role in risk stratification and monitoring of therapeutic response in patients with lupus nephritis.

ELISA analysis of urinary nephrin and podocalyxin standardized by aquaporin-2 in adult patients with nephrotic syndrome

OBJECTIVE

To investigate urinary nephrin and podocalyxin standardized by aquaporin (AQP)-2 using the enzyme-linked immunosorbent assay (ELISA) method in adult nephrotic syndrome (NS) patients.

METHODS

In 107 adult NS patients (27 proliferative nephritis, 77 non-proliferative, and 3 amyloidosis) undergoing renal biopsy, urinary nephrin, podocalyxin and AQP2 were measured by ELISA. Urinary nephrin and podocalyxin were standardized by AQP2 (neph/AQP and PCX/AQP) and values were compared with 11 healthy controls.

RESULTS

Urinary neph/AQP correlated positively to PCX/AQP (r = 0.51, p < 0.001). Urinary neph/AQP and PCX/AQP were lower in controls than NS patients. Both proliferative and non-proliferative NS patients excreted high urinary neph/AQP and PCX/AQP without a significant difference between them (p > 0.05). Patients with focal segmental glomerular sclerosis (FSGS) excreted higher urinary neph/AQP (p = 0.09) and PCX/AQP (p < 0.05) compared to the other patients. Urinary neph/AQP and PCX/AQP were increased in the immunoglobulin M nephropathy patients. Amyloidosis patients excreted lower neph/AQP and PCX/AQP. The sensitivity was 0.87 and specificity 0.37 when the neph/AQP borderline value of 0.16 was adopted [area under the curve (AUC) = 0.61]. The sensitivity was 0.74 and specificity 0.61 when the PCX/AQP borderline value was 3.06 (AUC = 0.69).

CONCLUSIONS

Urinary neph/AQP and PCX/AQP are increased in NS patients, with FSGS patients showing the highest levels. To distinguish FSGS from other NS forms, the measurement of urinary PCX/AQP may be a practical method, and superior to neph/AQP.

Dipping your feet in the water: podocytes in urine

Podocyte injury and loss plays an important role in the pathogenesis and progression of many kidney diseases. Studies have shown that podocyte-related markers and products can be detected in the urine of patients with glomerular diseases such as focal segmental glomerulosclerosis, IgA nephropathy, lupus nephritis, diabetic nephropathy and pre-eclampsia. Therefore, detecting the loss of podocytes in the urine provides a useful noninvasive technique of gathering information about the disease type and/or activity of glomerular diseases. Currently, urine podocyte-related protein markers, mRNA, microRNA and exosomes have been used with varying degrees of success to study glomerular diseases. The determination of urinary podocyte loss may become an important noninvasive tool in the evaluation of glomerular diseases.

A compendium of urinary biomarkers indicative of glomerular podocytopathy

It is well known that glomerular podocyte injury and loss are present in numerous nephropathies and that the pathophysiologic consecution of disease hinges upon the fate of the podocyte. While multiple factors play a hand in glomerulopathy progression, basic logic lends that if one monitors the podocyte's status, that may reflect the status of disease. Recent investigations have focused on what one can elucidate from the noninvasive collection of urine, and have proven that certain, specific biomarkers of podocytes can be readily identified via varying techniques. This paper has brought together all described urinary biomarkers of podocyte injury and is made to provide a concise summary of their utility and testing in laboratory and clinical theatres. While promising in the potential that they hold as tools for clinicians and investigators, the described biomarkers require further comprehensive vetting in the form of larger clinical trials and studies that would give their value true weight. These urinary biomarkers are put forth as novel indicators of glomerular disease presence, disease progression, and therapeutic efficacy that in some cases may be more advantageous than the established parameters/measures currently used in practice.

CD2AP mRNA in urinary exosome as biomarker of kidney disease

AIMS

Podocyte injury plays an important role in the pathogenesis of kidney disease. Urinary exosomes are microvesicles released by tubular epithelial cells and podocytes containing information of their originated cells. This study investigated for the first time whether podocyte related mRNA in urinary exosome could serve as novel biomarkers for kidney disease.

METHODS

Urine samples were collected from 32 patients of kidney disease who underwent kidney biopsy and 7 controls. CD2AP, NPHS2 and synaptopodin were detected by real-time RT-PCR on RNA isolated from urinary exosome.

RESULTS

The pellet microvesicles were positively stained with exosome and podocyte marker, AQP2, CD9 and nephrin. CD2AP mRNA was lower (p=0.008) in kidney disease patients compared with controls and decreased with the increasing severity of proteinuria (p=0.06). CD2AP correlated with serum creatinine (r=-0.373, p=0.035), BUN (r=-0.445, p=0.009) and eGFR (r=0.351, p=0.046). Neither NPHS2 nor synaptopodin correlated with parameters of renal function. CD2AP mRNA correlated negatively with 24 hour urine protein (r=-0.403, p=0.022), severity of tubulointerstitial fibrosis (r=-0.394, p=0.026) and glomerulosclerosis (r=-0.389, p=0.031) and could discriminate kidney disease from controls with AUC of 0.821 (p=0.008).

CONCLUSIONS

Urinary exosome mRNA of CD2AP might be a non-invasive tool for detecting both renal function and fibrosis of kidney disease.

Messenger RNA levels of podocyte-associated proteins in subjects with different degrees of glucose tolerance with or without nephropathy

BACKGROUND

To investigate gene expression of podocyte-specific proteins in urine of diabetes and prediabetes subjects and the association of these proteins with albuminuria.

METHODS

Fifteen controls, 19 prediabetes, and 67 diabetes subjects were included. Messenger RNA of nephrin, podocin, podocalyxin, synaptopodin, TRPC6, alpha-actinin-4, and TGF-β1 were measured using RT-PCR. Podocyte marker expression was correlated with albuminuria, glycemic control, and renal function. The diagnostic performance of the genes used to detect increased albuminuria was assessed using ROC curves and Poisson regressions.

RESULTS

Podocyte marker expression was significantly higher in diabetic subjects. Urinary nephrin was correlated with increasing levels of albuminuria; risk of albuminuria increased by 20% for every one-unit increase in the log10 of nephrin mRNA. Nephrinuria was found in 53%, 71%, and 90% of normo-, micro-, and macroalbuminuric diabetes subjects, respectively (p = 0.023). Urinary nephrin, podocalyxin, TRPC6, podocin, and alpha actinin-4 were correlated with glycemic control and albuminuria but not with renal function.

CONCLUSIONS

Diabetes subjects had higher urinary mRNA levels of podocyte proteins than nondiabetic subjects, even the normoalbuminuric patients. Nephrinuria was correlated with diabetic nephrophathy stage and predicted pathological albuminuria. Urinary mRNA levels of podocyte markers of prediabetic subjects did not differ from controls.

Urine podocyte mRNAs, proteinuria, and progression in human glomerular diseases

Model systems demonstrate that progression to ESRD is driven by progressive podocyte depletion (the podocyte depletion hypothesis) and can be noninvasively monitored through measurement of urine pellet podocyte mRNAs. To test these concepts in humans, we analyzed urine pellet mRNAs from 358 adult and pediatric kidney clinic patients and 291 controls (n=1143 samples). Compared with controls, urine podocyte mRNAs increased 79-fold (P<0.001) in patients with biopsy-proven glomerular disease and a 50% decrease in kidney function or progression to ESRD. An independent cohort of patients with Alport syndrome had a 23-fold increase in urinary podocyte mRNAs (P<0.001 compared with controls). Urinary podocyte mRNAs increased during active disease but returned to baseline on disease remission. Furthermore, urine podocyte mRNAs increased in all categories of glomerular disease evaluated, but levels ranged from high to normal, consistent with individual patient variability in the risk for progression. In contrast, urine podocyte mRNAs did not increase in polycystic kidney disease. The association between proteinuria and podocyturia varied markedly by glomerular disease type: a high correlation in minimal-change disease and a low correlation in membranous nephropathy. These data support the podocyte depletion hypothesis as the mechanism driving progression in all human glomerular diseases, suggest that urine pellet podocyte mRNAs could be useful for monitoring risk for progression and response to treatment, and provide novel insights into glomerular disease pathophysiology.

Temporal and spatial expression of podocyte-associated molecules are accompanied by proteinuria in IgA nephropathy rat model

We used a rat model to assess the role of nephrin, podocin, and desmin in the pathogenesis of IgA nephropathy (IgAN). A rat IgAN model was established by administration of BSA, CCl(4), and lipopolysaccharide (LPS) and compared with healthy control rats. Urinary protein, urine red blood cells, and biochemical parameters were measured for 12 weeks. Renal morphology and ultrastructure were examined by light and electron microscopy. Immunofluorescence was used to assess IgA deposition in the glomeruli and to measure expression of nephrin, podocin, and desmin. Real-time quantitative PCR was used to measure expression of nephrin, podocin, and desmin mRNAs. IgAN rats developed proteinuria at week-6 and this worsened over time. Pathological changes were evident under light microscopy at week-8 and under electron microscopy at week-4. Immunofluorescence analysis showed deposition of IgA in the kidneys of IgAN rats, but not control rats. IgAN rats had increased expression of glomerular podocin, nephrin, and desmin mRNAs and proteins at week-4. The expression of nephrin, podocin and desmin proteins and the expression of podocin and desmin mRNAs preceded the increase in urinary protein. Taken together, our study of a rat model of IgAN indicates that changes in the expression and distribution of nephrin, podocin, and desmin precede and may cause foot process fusion and proteinuria.

Quantitative polymerase chain reaction-based analysis of podocyturia is a feasible diagnostic tool in preeclampsia

Preeclampsia is a significant cause of maternal and fetal morbidity and mortality worldwide. A clinically useful screening test that can predict development of preeclampsia at an early stage is urgently needed. The detection of podocyturia by immunohistochemistry after cell culture has been noted as a reliable marker for preeclampsia. However, this method is laborious and carries the risk of cell culture contamination. The aim of this study was to investigate the diagnostic value of quantitative polymerase chain reaction as a rapid method to detect preeclampsia. Clean-catch urine samples were collected from preeclamptic (n=35), healthy pregnant (n=34), and healthy nonpregnant (n=12) women. Furthermore, a control group of women with gestational hypertension (n=5) was included. Quantitative polymerase chain reaction analysis was performed for podocyte-specific markers. Receiver operating characteristic curve analyses were performed. Significantly elevated mRNA levels of nephrin, podocin, and vascular endothelial growth factor were detected in preeclamptic women compared with healthy pregnant and healthy nonpregnant controls. In addition, significantly elevated levels of nephrin mRNA were detected in urine of preeclamptic women compared with women with gestational hypertension. A positive correlation (ρ=0.82; P<0.0001) was observed between nephrin and vascular endothelial growth factor mRNA levels in preeclamptic women. Receiver operating characteristic curve analyses demonstrated a strong ability of this method to discriminate between the different study groups. Quantitative polymerase chain reaction analysis of podocyte-specific molecules in urine samples is a rapid and reliable method to quantify podocyturia. We demonstrate that this method distinguishes preeclamptic patients from healthy controls and women with gestational hypertension. This method may be a tool for the detection of preeclampsia at an earlier stage, thereby preventing maternal and fetal morbidity and mortality.

Urine podocin:nephrin mRNA ratio (PNR) as a podocyte stress biomarker

BACKGROUND

Proteinuria and/or albuminuria are widely used for noninvasive assessment of kidney diseases. However, proteinuria is a nonspecific marker of diverse forms of kidney injury, physiologic processes and filtration of small proteins of monoclonal and other pathologic processes. The opportunity to develop new glomerular disease biomarkers follows the realization that the degree of podocyte depletion determines the degree of glomerulosclerosis, and if persistent, determines the progression to end-stage kidney disease (ESKD). Podocyte cell lineage-specific mRNAs can be recovered in urine pellets of model systems and in humans. In model systems, progressive glomerular disease is associated with decreased nephrin mRNA steady-state levels compared with podocin mRNA. Thus, the urine podocin:nephrin mRNA ratio (PNR) could serve as a useful progression biomarker. The use of podocyte-specific transcript ratios also circumvents many problems inherent to urine assays.

METHODS

To test this hypothesis, the human diphtheria toxin receptor (hDTR) rat model of progression was used to evaluate potentially useful urine mRNA biomarkers. We compared histologic progression parameters (glomerulosclerosis score, interstitial fibrosis score and percent of podocyte depletion) with clinical biomarkers [serum creatinine, systolic blood pressure (BP), 24-h urine volume, 24-h urine protein excretion and the urine protein:creatinine ratio(PCR)] and with the novel urine mRNA biomarkers.

RESULTS

The PNR correlated with histologic outcome as well or better than routine clinical biomarkers and other urine mRNA biomarkers in the model system with high specificity and sensitivity, and a low coefficient of assay variation.

CONCLUSIONS

We concluded that the PNR, used in combination with proteinuria, will be worth testing for its clinical diagnostic and decision-making utility.

Genomic biomarkers for chronic kidney disease

Chronic kidney disease (CKD) remains a major challenge in nephrology and for public health care, affecting 14% to 15% of the adult US population and consuming significant health care resources. In the next 20 years, the number of patients with end stage renal disease is projected to increase by 50%. Ideal biomarkers that allow early identification of CKD patients at high risk of progression are urgently needed for early and targeted treatment to improve patient care. Recent success of integrating molecular approaches for personalized management of neoplastic diseases, including diagnosis, staging, prognosis, treatment selection, and monitoring, has strongly encouraged kidney researchers to pursue molecular definitions of patients with kidney disease. Challenges for molecular marker identification in CKD are a high degree of cellular heterogeneity of the kidney and the paucity of human tissue availability for molecular studies. Despite these limitations, potential molecular biomarker candidates have been uncovered at multiple levels along the genome--phenome continuum. Here we will review the identification and validation of potential genomic biomarker candidates of CKD and CKD progression in clinical studies. The challenges in predicting CKD progression, as well as the promises and opportunities resulting from a molecular definition of CKD will be discussed.

Novel insights into the relationship between glomerular pathology and progressive kidney disease

Both glomerular and tubulointerstitial damage are important factors in the pathophysiology and progression of nephropathy. Glomerular injury is associated with tubulointerstitial inflammation, and many studies show that tubulointerstitial changes correlate well with progressive renal functional decline. Strong evidence supports the concept that once established, proteinuric glomerular injury can cause tubular injury. This review briefly summarizes the pathophysiological consequences of glomerular damage that are responsible for tubulointerstitial injury. It further focuses on tubule-derived renal injury biomarkers that may be used to monitor the progression of kidney disease. This monitoring is predicted to become increasingly useful as novel therapeutic interventions preventing progressive renal damage are introduced. In particular, biomarkers of kidney dysfunction, such as urinary podocytes, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, hematopoietic growth factor-inducible neurokinin 1, or periostin, might be useful in the diagnosis or detection of early nephropathy and risk assessment of kidney disease. However, these biomarkers require further study before they are used in routine screening or in guiding patient therapy.

Angiotensin II-dependent persistent podocyte loss from destabilized glomeruli causes progression of end stage kidney disease

Podocyte depletion is a major mechanism driving glomerulosclerosis. Progression is the process by which progressive glomerulosclerosis leads to end stage kidney disease (ESKD). In order to determine mechanisms contributing to persistent podocyte loss, we used a human diphtheria toxin transgenic rat model. After initial diphtheria toxin-induced podocyte injury (over 30% loss in 4 weeks), glomeruli became destabilized, resulting in continued autonomous podocyte loss causing global podocyte depletion (ESKD) by 13 weeks. This was monitored by urine mRNA analysis and by quantitating podocytes in glomeruli. Similar patterns of podocyte depletion were found in the puromycin aminonucleoside and 5/6 nephrectomy rat models of progressive end-stage disease. Angiotensin II blockade (combined enalapril and losartan) restabilized the glomeruli, and prevented continuous podocyte loss and progression to ESKD. Discontinuing angiotensin II blockade resulted in recurrent glomerular destabilization, podocyte loss, and progression to ESKD. Reduction in blood pressure alone did not reduce proteinuria or prevent podocyte loss from destabilized glomeruli. The protective effect of angiotensin II blockade was entirely accounted for by reduced podocyte loss. Thus, an initiating event resulting in a critical degree of podocyte depletion can destabilize glomeruli and initiate a superimposed angiotensin II-dependent podocyte loss process that accelerates progression resulting in eventual global podocyte depletion and ESKD. These events can be monitored noninvasively in real-time through urine mRNA assays.

Quantitative and qualitative urinary cellular patterns correlate with progression of murine glomerulonephritis

The kidney is a nonregenerative organ composed of numerous functional nephrons and collecting ducts (CDs). Glomerular and tubulointerstitial damages decrease the number of functional nephrons and cause anatomical and physiological alterations resulting in renal dysfunction. It has recently been reported that nephron constituent cells are dropped into the urine in several pathological conditions associated with renal functional deterioration. We investigated the quantitative and qualitative urinary cellular patterns in a murine glomerulonephritis model and elucidated the correlation between cellular patterns and renal pathology.

Urinary cytology and renal histopathology were analyzed in BXSB/MpJ (BXSB; glomerulonephritis model) and C57BL/6 (B6; control) mice. Urinary cytology revealed that the number of urinary cells in BXSB mice changed according to the histometric score of glomerulonephritis and urinary albumin; however, no correlation was detected for the levels of blood urea nitrogen and creatinine. The expression of specific markers for podocytes, distal tubules (DTs), and CDs was detected in BXSB urine. Cells immunopositive for Wilms tumor 1 (podocyte marker) and interleukin-1 family, member 6 (damaged DT and CD marker) in the kidney significantly decreased and increased in BXSB versus B6, respectively. In the PCR array analysis of inflammatory cytokines and chemokines, Il10, Cxcl2, C3, and Il1rn showed relatively higher expression in BXSB kidneys than in B6 kidneys. In particular, the highest expression of C3 mRNA was detected in the urine from BXSB mice. Furthermore, C3 protein and mRNA were localized in the epithelia of damaged nephrons.

These findings suggest that epithelial cells of the glomerulus, DT, and CD are dropped into the urine, and that these patterns are associated with renal pathology progression. We conclude that evaluation of urinary cellular patterns plays a key role in the early, noninvasive diagnosis of renal disease.

The emerging role of biomarkers in diabetic and hypertensive chronic kidney disease

Currently used measures to assess kidney function and injury are largely inadequate. Markers such as serum creatinine, formulas to estimate glomerular filtration rate, cystatin C, and proteinuria largely identify an underlying disease process that is well established. Thus, there has been a recent effort to identify new biomarkers that reflect kidney function, early injury, and/or repair that ultimately can relate to progression or regression of damage. Several biomarkers emerged recently that are able to detect kidney damage earlier than is currently possible with traditional biomarkers such as serum creatinine and proteinuria. Identification of urine biomarkers has proven to be beneficial in recent years because of ease of handling, stability, and the ability to standardize the various markers to creatinine or other peptides generally already present in the urine. Recent markers such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), and podocin have garnered a lot of attention. The emergence of these and other biomarkers is largely because of the evolution of novel genomic and proteomic applications in investigations of acute kidney injury and chronic kidney disease. In this article, we focus on the applications of these biomarkers in disease.

Conditionally immortalized human podocyte cell lines established from urine

Evidence suggests that loss of podocytes into urine contributes to development of glomerular diseases; shed podocytes are frequently viable and proliferate in culture conditions. To determine the phenotypic characteristics of viable urinary cells derived from human subjects, we established long-term urinary cell culture from two patients with focal segmental glomerulosclerosis and two healthy volunteers, via transformation with the thermosensitive SV40 large T antigen (U19tsA58) together with human telomerase (hTERT). Characterization of arbitrarily selected two clonal cell lines from each human subject was carried out. mRNA expression for the podocyte markers synaptopodin, nestin, and CD2AP were detected in all eight clones. Podocin mRNA was absent from all eight clones. The expression of nephrin, Wilms' tumor 1 (WT1), and podocalyxin mRNA varied among the clones, which may be due to transformation and/or cloning. These results suggest that podocyte cell lines can be established consistently from human urine. The generation of podocyte cell lines from urine of patients and healthy volunteers is novel and will help to advance studies of podocyte cell biology. Further improvements in the approaches to cell transformation and/or cell culture techniques are needed to allow cultured podocytes to fully reproduce in vivo characteristics.

Urine podocyte mRNAs mark progression of renal disease

Because loss of podocytes associates with glomerulosclerosis, monitoring podocyte loss by measuring podocyte products in urine may be clinically useful. To determine whether a single episode of podocyte injury would cause persistent podocyte loss, we induced limited podocyte depletion using a diphtheria toxin receptor (hDTR) transgenic rat. We monitored podocyte loss by detecting nephrin and podocin mRNA in urine particulates with quantitative reverse transcriptase-PCR. Aquaporin 2 mRNA served as a kidney reference gene to account for variable kidney contribution to RNA amount and quality. We found that a single injection of diphtheria toxin resulted in an initial peak of proteinuria and podocyte mRNAs (podocin and nephrin) followed 8 d later by a second peak of proteinuria and podocyte mRNAs that were podocin positive but nephrin negative. Proteinuria that persisted for months correlated with podocin-positive, nephrin-negative mRNAs in urine. Animals with persistent podocyte mRNA in urine progressed to ESRD with global podocyte depletion and interstitial scarring. Podocytes in ectatic tubules expressed podocalyxin and podocin proteins but not nephrin, compatible with detached podocytes' having an altered phenotype. Parallel human studies showed that biopsy-proven glomerular injury associated with increased urinary podocin:aquaporin 2 and nephrin:aquaporin 2 molar ratios. We conclude that a single episode of podocyte injury can trigger glomerular destabilization, resulting in persistent podocyte loss and an altered phenotype of podocytes recovered from urine. Podocyte mRNAs in urine may be a useful clinical tool for the diagnosis and monitoring of glomerular diseases.

Podocyte loss in human hypertensive nephrosclerosis

BACKGROUND

Podocyte injury probably plays important roles in the pathogenesis of hypertensive nephropathy, but human data are limited. We studied glomerular podocyte count and intrarenal expression of podocyte-associated molecules in patients with hypertensive nephrosclerosis.

METHODS

We studied 41 consecutive patients with biopsy-proven hypertensive nephropathy, 10 cadaveric kidney donors, and 9 healthy subjects. Intrarenal and urinary mRNA expression of podocyte-associated molecules was quantified and podocyte number was determined by stereological method.

RESULTS

Intrarenal mRNA expression levels of nephrin, podocin, and synaptopodin were lower, and urinary mRNA expression levels were higher in patients with hypertensive nephropathy than controls. Glomerular podocyte number was significantly lower in patients with hypertensive nephrosclerosis than kidney donors (545 +/- 237 vs. 773 +/- 296 per glomeruli, P < 0.02). Podocyte density and intrarenal gene expression of podocyte-associated molecules significantly correlated with estimated glomerular filtration rate (GFR) and inversely correlated with blood pressure and the degree of renal fibrosis. Intrarenal gene expression of nephrin significantly correlated with change in renal function decline.

CONCLUSION

This study demonstrates a decrease in podocyte number and intrarenal gene expression of podocyte-associated molecules in patients with hypertensive nephrosclerosis. We observed correlations between glomerular podocyte density and intrarenal expression of podocyte-associated molecules with renal function and the degree of renal fibrosis, suggesting podocyte loss may play an important role in the pathogenesis of hypertensive nephrosclerosis.

Glomerular epithelial cells in the urine: what has to be done to make them worthwhile?

The significance of the native urine sediment in the differential of glomerular diseases needs no further comment. However, the question arises whether it could be useful to develop a more specific diagnostic approach to identify the origin of renal epithelial cells that can be detected in the urine sediments as well. Especially the detection of podocytes in the urine could be a valuable noninvasive method to get information about the disease activity or disease type and could be used as a follow-up after a biopsy in an outpatient setting. So far, there are only a few studies that analyzed the clinical relevance of renal epithelial cells in the urine systematically or prospectively. The reason for this could be the nature of the material since it will remain unclear whether detachment and changes in the urine milieu have a direct effect on the expression of marker proteins on the detected cells. Dedifferentiation or transdifferentiation of cells that goes along with changed marker expression is certainly also part of the underlying disease process. This review summarizes the available information on marker proteins that have been successfully used in the diagnostic of "podocytes" in the urine. Furthermore, it gives an overview of marker expression on podocytes in situ in development and disease and examines the role of glomerular epithelial shedding in the urine at the interface of basic science and clinical medicine.

Expression of mRNA for functional molecules in urinary sediment in glomerulonephritis

Recent studies have suggested that gene expression studies using urinary sediment might be a non-invasive approach to assessing activity and pathogenesis in glomerulonephritis. However, little information is available regarding the mRNA expression patterns of functional molecules, such as T-bet, GATA-3, FOXP3, and retinoic acid-inducible gene-I (RIG-I), in urinary sediment, from patients with immunocomplex-mediated glomerulonephritis. Fourteen lupus nephritis (LN) patients, 13 IgA nephropathy (IgAN) patients, and 12 healthy controls were enrolled in the study. The mRNA expressions of T-bet, GATA-3, FOXP3 and RIG-I in urinary sediment were measured using real time quantitative polymerase chain reaction. We also studied the expression of RIG-I in kidney tissue specimens obtained from LN and IgAN patients. Significant differences in the expression patterns of GATA-3, FOXP3 and RIG-I, and marginal differences in T-bet expression, were observed between the three study groups. Immunofluorescent staining for RIG-I was observed in the tissue specimens from the LN patients, but not in those from the IgAN patients. The mRNA expression patterns of T-bet, GATA-3, FOXP3 and RIG-I in urinary sediment differ according to diagnostic category. These results suggest that the measurement of these target gene expressions might be a useful, non-invasive method for clinical monitoring and studying of pathogenesis in glomerulonephritis.

Lack of association between NPHS2 gene polymorphisms and sporadic IgA nephropathy

AIM

IgA nephropathy (IgAN) is the most common primary form of glomerulonephritis worldwide. In the present study, the genetic structure of the NPHS2 gene was studied to verify if podocin plays a role in the pathogenesis of IgAN.

METHODS

Clinical characteristics and DNA samples were collected from 26 Chinese children with sporadic IgAN. A direct sequencing was performed after polymerase chain reaction amplification to all the eight exons of the NPHS2 gene.

RESULTS

Three synonymous variants as known polymorphisms (954T-->C homozygous, 1038A-->G heterozygous and homozygous) were found in 3, 4 and 1 patients, respectively. There was no significant difference in the genotypic and allelic frequencies of 954T > C and 1038A > G polymorphisms between the patients and normal controls.

CONCLUSION

No significant difference in the genotypic and allelic frequencies of the identified 954T > C and 1038A > G polymorphisms between the patients and normal controls was found.