Matrix Metalloproteinase-7 Is a Urinary Biomarker and Pathogenic Mediator of Kidney Fibrosis

Matrix metalloproteinase-7 (MMP-7), a secreted zinc- and calcium-dependent endopeptidase, is a transcriptional target of canonical Wnt/β-catenin signaling. Because Wnt/β-catenin is activated in diseased kidney, we hypothesized that urinary MMP-7 level may be used as a noninvasive surrogate biomarker for fibrotic lesions. To test this hypothesis, we conducted a cross-sectional study, measuring urinary MMP-7 levels in a cohort of 102 patients with CKD. Compared with normal subjects, patients with various kidney disorders had markedly elevated urinary levels of MMP-7. Furthermore, urinary MMP-7 levels closely correlated with renal fibrosis scores in patients. In mice, knockout of MMP-7 ameliorated the fibrotic lesions and expression of matrix genes induced by obstructive injury. Genetic ablation of MMP-7 also preserved E-cadherin protein expression and substantially reduced the expression of total and dephosphorylated β-catenin and the de novo expression of vimentin and fibroblast-specific protein 1 in renal tubules of obstructed kidneys. In vitro, MMP-7 proteolytically degraded E-cadherin in proximal tubular cells, leading to β-catenin liberation and nuclear translocation and induction of β-catenin target genes by a mechanism independent of Wnt ligands. Finally, pharmacologic inhibition of MMP-7 immediately after obstructive injury reduced renal fibrosis in vivo These results suggest that MMP-7 not only can serve as a noninvasive biomarker but also is an important pathogenic mediator of kidney fibrosis.

Urinary miR-21, miR-29, and miR-93: novel biomarkers of fibrosis

BACKGROUND

MicroRNAs (miRNAs) play important roles in the progression of renal fibrosis. We studied the urinary levels of miR-21, miR-29 family and miR-93, which are downstream mediators of the transforming growth factor-β(1) (TGF-β(1)), in patients with immunoglobulin A (IgA) nephropathy.

METHODS

We studied the urinary miRNA levels of 43 IgA nephropathy patients and 13 healthy controls.

RESULTS

The IgA nephropathy group had significantly lower urinary miR-29b and miR-29c, but higher miR-93 levels than controls. Proteinuria significantly correlated with urinary levels of miR-29b (r = -0.388, p = 0.003) and miR-29c (r = -0.409, p = 0.002). Glomerular filtration rate significantly correlated with urinary levels of miR-21 (r = 0.338, p = 0.028), miR-29b (r = 0.333, p = 0.031) and miR-29c (r = 0.304, p = 0.050). Urinary miR-93 level significantly correlated with glomerular scarring (r = -0.392, p = 0.010). Urinary miRNA level of SMAD3, but not TGF-β(1), correlated with urinary miR-21 (r = 0.624, p < 0.001), miR-29b (r = 0.566, p < 0.001), miR-29c (r = 0.619, p < 0.001) and miR-93 (r = 0.332, p = 0.032).

CONCLUSIONS

Urinary miR-29b and miR-29c levels correlated with proteinuria and renal function, while urinary miR-93 level correlated with glomerular scarring. More importantly, urinary levels of these miRNA targets significantly correlated with urinary SMAD3 level. Our results suggest that these miRNA targets are regulated by the TGF-β(1)/SMAD3 pathway and they may play important roles in the development of progressive renal fibrosis in IgA nephropathy.

Role of MCP-1 and RANTES in inflammation and progression to fibrosis during murine crescentic nephritis

The involvement of chemokines in inflammation is well established but their functional role in disease progression, and particularly in the development of fibrosis, is not yet understood. We have investigated the functional role that the chemokines monocyte chemotactic protein-1 (MCP-1) and RANTES play in inflammation and the progression to fibrosis during crescentic nephritis. During this disease inflammatory infiltrates are observed within glomeruli and interstitium in conjunction with increased expression of MCP-1 and RANTES and a decrease in renal function. Disease progression is marked by formation of glomerular crescents and the deposition of type I collagen. Blocking the function of MCP-1 or RANTES resulted in significant decreases in proteinuria as well as numbers of infiltrating leukocytes, indicating that both MCP-1 and RANTES play an important role in the inflammatory phase of crescentic nephritis. In particular, neutralization of MCP-1, but not RANTES, resulted in a dramatic decrease in glomerular crescent formation and deposition of type I collagen. These results highlight a novel role for MCP-1 in crescent formation and development of interstitial fibrosis and indicate that in addition to recruiting inflammatory cells this chemokine is critically involved in irreversible tissue damage.

Association of kidney fibrosis with urinary peptides: a path towards non-invasive liquid biopsies?

Chronic kidney disease (CKD) is a prevalent cause of morbidity and mortality worldwide. A hallmark of CKD progression is renal fibrosis characterized by excessive accumulation of extracellular matrix (ECM) proteins. In this study, we aimed to investigate the correlation of the urinary proteome classifier CKD273 and individual urinary peptides with the degree of fibrosis. In total, 42 kidney biopsies and urine samples were examined. The percentage of fibrosis per total tissue area was assessed in Masson trichrome stained kidney tissues. The urinary proteome was analysed by capillary electrophoresis coupled to mass spectrometry. CKD273 displayed a significant and positive correlation with the degree of fibrosis (Rho = 0.430, P = 0.0044), while the routinely used parameters (glomerular filtration rate, urine albumin-to-creatinine ratio and urine protein-to-creatinine ratio) did not (Rho = -0.222; -0.137; -0.070 and P = 0.16; 0.39; 0.66, respectively). We identified seven fibrosis-associated peptides displaying a significant and negative correlation with the degree of fibrosis. All peptides were collagen fragments, suggesting that these may be causally related to the observed accumulation of ECM in the kidneys. CKD273 and specific peptides are significantly associated with kidney fibrosis; such an association could not be detected by other biomarkers for CKD. These non-invasive fibrosis-related biomarkers can potentially be implemented in future trials.

Urine Fibrosis Markers and Risk of Allograft Failure in Kidney Transplant Recipients: A Case-Cohort Ancillary Study of the FAVORIT Trial

BACKGROUND

Kidney tubulointerstitial fibrosis marks risk for allograft failure in kidney transplant recipients, but is poorly captured by estimated glomerular filtration rate (eGFR) or urine albumin-creatinine ratio (ACR). Whether urinary markers of tubulointerstitial fibrosis can noninvasively identify risk for allograft failure above and beyond eGFR and ACR is unknown.

STUDY DESIGN

Case-cohort study.

SETTING & PARTICIPANTS

The FAVORIT (Folic Acid for Vascular Outcome Reduction in Transplantation) Trial was a randomized double-blind trial testing vitamin therapy to lower homocysteine levels in stable kidney transplant recipients. We selected a subset of participants at random (n=491) and all individuals with allograft failure during follow-up (cases; n=257).

PREDICTOR

Using spot urine specimens from the baseline visit, we measured 4 urinary proteins known to correlate with tubulointerstitial fibrosis on biopsy (urine α1-microglobulin [A1M], monocyte chemoattractant protein 1 [MCP-1], and procollagen type III and type I amino-terminal amino pro-peptide).

OUTCOME

Death-censored allograft failure.

RESULTS

In models adjusted for demographics, chronic kidney disease risk factors, eGFR, and ACR, higher concentrations of urine A1M (HR per doubling, 1.73; 95% CI, 1.43-2.08) and MCP-1 (HR per doubling, 1.60; 95% CI, 1.32-1.93) were strongly associated with allograft failure. When additionally adjusted for concentrations of other urine fibrosis and several urine injury markers, urine A1M (HR per doubling, 1.76; 95% CI, 1.27-2.44]) and MCP-1 levels (HR per doubling, 1.49; 95% CI, 1.17-1.89) remained associated with allograft failure. Urine procollagen type III and type I levels were not associated with allograft failure.

LIMITATIONS

We lack kidney biopsy data, BK titers, and HLA antibody status.

CONCLUSIONS

Urine measurement of tubulointerstitial fibrosis may provide a noninvasive method to identify kidney transplant recipients at higher risk for future allograft failure, above and beyond eGFR and urine ACR.

Accelerated renal fibrosis in cardiorenal syndrome is associated with long-term increase in urine neutrophil gelatinase-associated lipocalin levels

BACKGROUND

Cardiac events are the main cause of death among patients with end-stage renal failure. Even a mild renal disease is currently considered a major risk factor for cardiovascular complications following myocardial infarction (MI). The aim of the present study was to detect histological, sera and urine characteristics of kidney injury in cardiorenal syndrome (CRS) compared to chronic kidney disease (CKD) with an intact cardiac function.

METHODS

We employed a rat model for CRS, in which an acute MI (AMI) was induced 4 weeks after establishment of subtotal nephrectomy. Four weeks later, left ventricular function was assessed by echocardiography and changes in renal performance were examined using histological and biochemical parameters.

RESULTS

Increased interstitial fibrosis as well as renal inflammation were observed in renal sections derived from CRS rats, compared to subtotal nephrectomy (CKD)-only animals. Moreover, we found that even though AMI on the background of CKD was not associated with a further decrease in creatinine clearance or a further increase in sera BUN levels compared to CKD only, a significant long-term elevation in urine neutrophil gelatinase-associated lipocalin (Ngal) levels was detectable post-MI induction.

CONCLUSIONS

AMI in the CKD setting is associated with accelerated renal fibrosis and long-term elevated urine Ngal values, suggesting that cardiac dysfunction contributes to accelerated intrinsic kidney injury in CKD. The data indicate that elevated urine Ngal may potentially serve as an early non-invasive laboratory parameter for a left ventricular dysfunction-related renal injury.

Soluble klotho as a marker of renal fibrosis and podocyte injuries in human kidneys

Klotho deficiency is relevant to renal fibrosis and podocyte injury in vivo and in vitro. We examined whether histological findings of renal biopsy specimens were associated with the levels of soluble klotho in humans. We investigated renal biopsy specimens of 67 patients and detailed microscopic findings were reviewed. Soluble serum/urinary klotho and urinary angiotensinogen were assessed by enzyme-linked immunosorbent assays, and tissue klotho expression was assessed by immunohistochemical staining. The median age of the study participants was 35.6 years. High serum klotho levels (≥14 pg/mL) were associated with decreased odds ratios (ORs) of interstitial fibrosis (OR = 0.019, P = 0.003) and segmental sclerosis (OR = 0.190, P = 0.022) in multivariable logistic regression analysis. Patients with a lower urinary klotho-to-creatinine ratio (UKCR) were significantly more likely to have diffuse foot process effacement (OR = 0.450, P = 0.010). The area under the receiver-operating characteristic curve (AUC) of serum klotho for predicting interstitial fibrosis was 0.920 (95% CI, 0.844–0.996), and the best cut-off value of serum klotho was 138.1 pg/mL. The AUC of UKCR for predicting diffuse foot process effacement was 0.754 (95% CI, 0.636–0.872), and the best cut-off value of UKCR was 96.7 pg/mgCr. Urinary angiotensinogen-to-creatinine ratio was not associated with serum klotho, UKCR, or any pathological finding. Our data suggested that soluble serum and urinary klotho levels represent a potential biomarker to predict renal fibrosis and podocyte injury in humans.

Renal protective effects of blocking the intrarenal renin-angiotensin system: angiotensin II type I receptor antagonist compared with angiotensin-converting enzyme inhibitor

The present study compared renoprotective effects of angiotensin II type I receptor antagonist (AT1RA) with angiotensin converting enzyme inhibitor (ACEI), and their influence on the renin-angiotensin-system (RAS). Experimental nephrotic syndrome was induced in SD rats by repeated peritoneal injections of puromycin. Twenty-eight rats were randomly divided into four groups: normal control, nephrotic control, ACEI-treated, and AT1RA-treated groups. Serum, urine, and renal tissue were collected for study at the end of 12 weeks. Compared with those of the nephrotic control group, urinary protein was less and renal function was better in both treated groups. The glomerular and interstitial damage indexes of both ACEI- and AT1RA-treated rats were lower than those of nephrotic control rats, with no significant difference observed between the two treated groups. Local renal ACE activity and angiotensin II concentration were elevated in nephrotic rats (p< 0.01). However, there is no significant difference in circulating RAS, renal tissue renin, and aldosterone between the normal control and nephrotic control rats. As expected, enalapril inhibited the local renal ACE activity and significantly decreased angiotensin II (p< 0.01). Intrarenal ACE activity and angiotensin concentration returned to normal levels after treatment with irbesartan (p< 0.01). In conclusion, AT1RA and ACEI have comparable renal protective effects, and these protective effects were associated with the inhibition of intrarenal ANG II.

Immunohistochemical analysis of molecular events in tubulo-interstitial fibrosis in a mouse model of diffuse mesangial sclerosis (ICGN strain)

Diffuse mesangial sclerosis (DMS) is one of the hereditary glomerular diseases and histologically characterized by severe glomerulosclerosis and subsequent tubulo-interstitial fibrosis (TIF). In DMS patients, renal dysfunction correlates well with TIF, rather than with glomerular lesions. Thus, molecular mechanisms whereby TIF in DMS progresses should be addressed. Previously, we found that nephrotic ICGN mice manifest DMS-like lesions and develop renal dysfunction in accordance with onset of TIF. In the present study, we investigated fibrogenic events involved in the progression of TIF after DMS manifestation, using the DMS mouse model. Immunohistochemistry revealed that expression of transforming growth factor-beta (TGF-beta) was rare in the interstitial cells of the nephrotic mice at the early-stage of DMS, while the TGF-beta expression became evident in the late-stage DMS mice. Platelet-derived growth factor (PDGF) was mildly expressed in the distal tubules of the early-stage DMS mice, whereas the PDGF expression markedly increased at the late-stage of DMS. As a result, alpha-actin-positive myofibroblastic cells were found dominant in the interstitial spaces of the late-stage DMS mice. Finally, TIF became severe in accordance with the overexpressions of these molecules. Our results suggest that in our murine model: 1) persistent proteinuria leads to over-expression of TGF-beta and PDGF in non-glomerular areas; 2) these cytokines provoke interstitial myofibroblast accumulation; and 3) the myofibroblasts produce fibrotic matrix proteins in the interstitial spaces. This process may possibly contribute to the development of TIF in DMS patients.

[Clinical implication of urine test for markers of endothelial dysfunction and angiogenesis factors in assessment of tubulointerstitial fibrosis in chronic glomerulonephritis]

AIM

To evaluate contribution of endothelial dysfunction and impairment of endothelial proliferation/ regeneration to mechanisms of development of tubulointerstitial fibrosis (TIF) in chronic glomerulonephritis (CGN) basing on urinary levels of markers of endothelial activation/impairment and angiogenesis factors.

MATERIAL AND METHODS

A total of 67 CGN patients entered the study: 19 patients with moderate urinary syndrome (group 1), 37 patients with nephrotic syndrome (group 2), 11 patients with nephrotic syndrome and persistent renal failure (RF). A control group consisted of 12 healthy subjects. The examination covered excretion with urine of Willebrand factor (WF), plasminogen activator inhibitor I (PAL-I), fibrin degradation products (FDP), vascular endothelial growth factor (VEGF). These values were compared with severity of fibrous changes in renal interstitium estimated by biopsy morphometry.

RESULTS

CGN patients had signs of affection of parietal effects of vascular endothelium. In particular, increased excretion of functionally active WF, PAI-I and FDP correlating with activity/severity of CGN. The changes were especially noticeable in patients with progressive forms of CGN (with NS and RF). Patients with morphologically verified TIF (interstitial area more than 20%) excretion of endothelial dysfunction markers was higher than in CGN patients free of TIF In a progressive course of nephritis endothelial dysfunction deteriorates by endothelial proliferation/regeneration impairment as shown by reduced urinary excretion of angiogenic factor VEGF and parallel elevation of functionally active WF in urine of patients with severe forms of CGN. Combined contribution of endothelial dysfunction and angiogenesis impairment to mechanisms of TIF development is seen from these values relations with severity of creatinemia and fibrous alterations in tubulointerstitial tissues of the kidney.

CONCLUSION

The results point to participation of endothelium in mechanisms promoting development of TIF and RF in CGN both in terms of endothelial dysfunction and impairment of endothelial repair capacity. Clinicomorphological comparisons confirm the significance of WF, PAI-I and VEGF in assessment of local-renal endothelial changes and severity of fibrosis in renal tissue in CGN. Due to availability of the study material, perspectives of fibrogenesis monitoring in the kidneys with the tests appear which is essential for making prognosis and treatment policy in CGN patients.

Elevated Serum and Urinary Secreted Protein Acidic and Rich in Cysteine Levels are Novel Biomarkers of Kidney Fibrosis Severity

BACKGROUND

Interstitial fibrosis is the primary determinant of the progression of chronic kidney disease (CKD), and noninvasive identification of interstitial fibrosis is a major challenge. We aimed to explore the diagnostic value of secreted protein acidic and rich in cysteine (SPARC) in serum and urine in kidney fibrosis.

METHODS

Single-cell transcriptome analysis was used to measure SPARC expression in healthy reference kidneys and those of patients with CKD. A total of 674 patients with CKD who underwent renal biopsy served as the training cohort (n = 322) and the validation cohort (n = 352). Serum and urinary SPARC levels were measured at the time of kidney biopsy. In vivo and in vitro models of kidney fibrosis were also used to confirm the role of SPARC.

RESULTS

Increased SPARC expression was detected in kidney fibrosis tissues. Higher serum SPARC levels were associated with increased severity of kidney fibrosis. Moreover, the area under the receiver operating characteristic curve (AUC-ROC) (AUC 0.86) was greater for the serum SPARC level than for the urinary SPARC level and estimated glomerular filtration rate (eGFR). The combination of the serum and urinary SPARC levels and eGFR increased the AUC-ROC for predicting kidney fibrosis from 0.86 to 0.90. The diagnostic performance of serum or urinary SPARC levels was consistent in the validation cohort. In vivo and in vitro models of kidney fibrosis also confirmed the upregulation of SPARC expression.

CONCLUSIONS

Serum and urinary SPARC levels may be potential biomarkers for kidney fibrosis and may be useful for noninvasive diagnosis.

[Urinary fibronectin as an indicator of kidney fibrosis in nephritis]

AIM

To investigate clinicomorphological relationships between elevated urinary excretion of fibronectin (FN) and development of fibrosis in the kidney in patients with lupus nephritis (LN) and chronic glomerulonephritis (CGN).

MATERIALS AND METHODS

Urinary FN excretion was measured at radial immunodiffusion in 54 LN patients. Of them, 15 patients had inactive LN, 39 patients had active LN varying in clinical forms. Urinary FN was also measured by passive hemagglutination in 36 CGN patients (11 inactive CGN and 25 active CGN cases). Biopsy specimens were obtained from 49 patients with active nephritis (43 with CGN and 6 with LN). FN deposits were studied immunohistochemically and morphometrically with determination of relative fibrosis area.

RESULTS

Urinary FN excretion in patients with nephritis was higher than in healthy controls. In active CGN and LN the levels of FN were significantly higher than in inactive CGN and LN. The highest FN urinary concentrations were registered in patients with severe CGN and LN, especially in the presence of renal failure and arterial hypertension. Among them, the highest individual values were observed in patients with rapidly progressive nephritis. No positive correlations were found between the degree of the urinary FN excretion increment and degree of proteinuria. This suggests local-renal origin of most urinary FN. Morphologically, FN deposits were revealed in 73% of the biopsies. In most of the patients with severe nephritis both in CGN and LN there was a diffuse distribution of FN in the glomerules and interstitium. A correlation with a morphological nephritis type was absent, but existed between FN presence in the renal biopsies and relative area of interstitium (fibrosis).

CONCLUSION

FN excreted in high amounts with urine in nephritis originates from the kidneys and reflects severity of fibrogenesis in the kidney.

Development of a multiple urinary biomarker model to predict the tubulointerstitial fibrosis area in patients with primary IgA Nephropathy

BACKGROUND

Previous studies highlighted the utility of individual urinary biomarkers in the prediction of interstitial fibrosis in IgA Nephropathy patients. However, it´s uncertain which biomarker or combination of biomarkers provides a more accurate estimation of renal interstitial fibrosis Surface. Herein, we measured the urinary excretion of a set of seven tubular injury biomarkers in a group of patients with primary IgA Nephropathy and analyzed their utility as non-invasive estimators of interstitial fibrosis area found on kidney biopsy.

METHODS

Two hundred forty-seven adults with primary IgA Nephropathy diagnosed by kidney biopsy and a control group of 50 healthy control were included. The urinary excretion of EGF, MCP-1, NGAL, KIM-1, L-FABP, β2-microglobulin and DKK-3 was measured in urine samples collected at the day of the renal biopsy. Estimated glomerular filtration rate was measured by the CKD-EPI formula. Interstitial fibrosis area was quantified using a quantitative morphometric procedure and graded according to Oxford Classification. Predictive multivariate models were developed to predict the interstitial fibrosis surface.

RESULTS

Patients with primary IgA Nephropathy showed significantly higher urinary levels of DKK-3, L-FABP and β2-microglobulin, and lower EGF levels than healthy controls. Interstitial fibrosis was negatively correlated with urinary EGF levels and positively with age, proteinuria, eGFR and urinary DKK-3, L-FABP and β2-microglobulin. The best model to predict interstitial fibrosis area accounted for > 60% of its variability and included age, eGFR, proteinuria, DKK-3, EGF, L-FABP and β2-microglobulin.

CONCLUSIONS

Our study provides a model to estimate the IFS in IgA Nephropathy which could be useful to monitor the progression of chronic kidney injury.