Reduced renal prepro-epidermal growth factor mRNA and decreased EGF excretion in ARF

Predicting treatment response and clinicopathological findings in lupus nephritis with urine epidermal growth factor, monocyte chemoattractant protein-1 or their ratios

Introduction

There is a need for sensitive and specific biomarkers to predict kidney damage and therapeutic response in lupus nephritis (LN). Monocyte chemoattractant protein-1 (MCP-1) and epidermal growth factor (EGF) are cytokines with divergent roles. EGF or EGF/MCP1 ratio have been shown to correlate with prognosis in primary glomerulonephritis, but there is limited information in lupus nephritis (LN). This study evaluated the roles of MCP-1, EGF or their ratio as biomarkers of histopathology and response to treatment in LN.

Methods

This was a cross-sectional and observational study. Baseline urine MCP-1 and EGF levels in systemic lupus erythematosus (SLE) patients and controls (total n = 101) were compared, and levels were correlated with clinicopathological findings and subsequent response to treatment.

Results

MCP-1 was higher in active LN (n = 69) compared to other SLE groups and controls, whereas EGF was not different. MCP-1 correlated with disease activity (proteinuria, renal SLEDAI, classes III/IV/V, and high activity index.) By contrast, EGF correlated with eGFR, but not with proteinuria, activity index, or class III/IV/V. MCP-1 was higher, and EGF was lower in high chronicity index. EGF/MCP-1 decreased with greater clinicopathological severity. In a subgroup with proliferative LN who completed six months of induction therapy (n = 41), EGF at baseline was lower in non-responders compared to responders, whereas MCP-1 was similar. By multivariable analysis, baseline EGF was independently associated with subsequent treatment response. Area under the curve for EGF to predict response was 0.80 (0.66–0.95). EGF ≥ 65.6 ng/ mgCr demonstrated 85% sensitivity and 71% specificity for response. EGF/MCP-1 did not improve the prediction for response compared to EGF alone.

Conclusion

MCP-1 increased with disease activity, whereas EGF decreased with low GFR and chronic damage. Urine EGF may be a promising biomarker to predict therapeutic response in LN. EGF/MCP-1 did not improve the prediction of response.

Effects of Chronic Administration of Capsaicin on Biomarkers of Kidney Injury in Male Wistar Rats with Experimental Diabetes

Capsaicin is an agonist of the transient receptor potential vanilloid type 1 (TRPV1) channel, which has been related to the pathophysiology of kidney disease secondary to diabetes. This study aimed to evaluate the chronic effect of capsaicin administration on biomarkers of kidney injury in an experimental rat model of diabetes. Male Wistar rats were assigned to four groups: (1) healthy controls without diabetes (CON), (2) healthy controls plus capsaicin at 1 mg/kg/day (CON + CAPS), (3) experimental diabetes without capsaicin (DM), and (4) experimental diabetes plus capsaicin at 1 mg/kg/day (DM + CAPS). For each group, 24-h urine samples were collected to determine diuresis, albumin, cystatin C, β2 microglobulin, epidermal growth factor (EGF), alpha (1)-acid glycoprotein, and neutrophil gelatinase-associated lipocalin (NAG-L). Blood samples were drawn to measure fasting glucose. After 8 weeks, the CON + CAPS and DM + CAPS groups showed increased diuresis compared to the CON and DM groups, but the difference was significant only in the DM + CAPS group. The two-way ANOVA only showed a statistically significant effect of CAPS on the urinary EGF levels, as well as a tendency to have a significant effect in the urinary NAG-L levels. The EGF levels decreased in both CAPS-treated groups, but the change was only significant in the CON + CAPS group vs. CON group; and the NAG-L levels were lower in both CAPS-treated groups. These results show that capsaicin had a diuretic effect in healthy and diabetic rats; additionally, it increased the urinary EGF levels and tended to decrease the urinary NAG-L levels.

PPARγ maintains the metabolic heterogeneity and homeostasis of renal tubules

Background

The renal tubules, which have distant metabolic features and functions in different segments, reabsorb >99% of approximately 180 l of water and 25,000 mmol of Na ⁺ daily. Defective metabolism in renal tubules is involved in the pathobiology of kidney diseases. However, the mechanisms underlying the metabolic regulation in renal tubules remain to be defined.

Methods

We quantitatively compared the proteomes of the isolated proximal tubules (PT) and distal tubules (DT) from C57BL/6 mouse using tandem mass tag (TMT) labeling-based quantitative mass spectrometry. Bioinformatics analysis of the differentially expressed proteins revealed the significant differences between PT and DT in metabolism pathway. We also performed in vitro and in vivo assays to investigate the molecular mechanism underlying the distant metabolic features in PT and DT.

Findings

We demonstrate that the renal proximal tubule (PT) has high expression of lipid metabolism enzymes, which is transcriptionally upregulated by abundantly expressed PPARα/γ. In contrast, the renal distal tubule (DT) has elevated glycolytic enzyme expression, which is mediated by highly expressed c-Myc. Importantly, PPARγ transcriptionally enhances the protease iRhom2 expression in PT, which suppresses EGF expression and secretion and subsequent EGFR-dependent glycolytic gene expression and glycolysis. PPARγ inhibition reduces iRhom2 expression and increases EGF and GLUT1 expression in PT in mice, resulting in renal tubule hypertrophy, tubulointerstitial fibrosis and damaged kidney functions, which are rescued by 2-deoxy-d-glucose treatment.

Interpretation

These findings delineate instrumental mechanisms underlying the active lipid metabolism and suppressed glycolysis in PT and active glycolysis in DT and reveal critical roles for PPARs and c-Myc in maintaining renal metabolic homeostasis. FUND: This work was supported by the National Natural Science Foundation of China (grants 81572076 and 81873932; to Q.Z.), the Applied Development Program of the Science and Technology Committee of Chongqing (cstc2014yykfB10003; Q.Z.), the Program of Populace Creativities Workshops of the Science and Technology Committee of Chongqing (Q.Z.), the special demonstration programs for innovation and application of techniques (cstc2018jscx-mszdX0022) from the Science and Technology Committee of Chongqing (Q.Z.).

Urine epidermal growth factor, monocyte chemoattractant protein-1 or their ratio as predictors of complete remission in primary glomerulonephritis

BACKGROUND

The balance of several cytokines likely influences the resolution of glomerulonephritis. Monocyte chemoattractant protein-1(MCP-1) is a chemokine that promotes renal inflammation whereas epidermal growth factor (EGF) stimulates protective responses. Previously, high urine MCP-1(MCP-1) and low urine EGF (EGF) levels were found to be associated with tubulointerstitial fibrosis, but there is limited information on the value of these mediators as predictors of therapeutic responses or long term outcome in primary glomerulonephritis.

OBJECTIVES

To determine the performance of urine EGF, MCP-1 or their ratio at baseline as biomarkers to predict complete remission, and the relationship of these mediators with subsequent renal function 24 months later in primary glomerulonephritis.

METHODS

This is a prospective study of patients with biopsy-proven primary glomerulonephritis. Baseline urine samples were collected at biopsy before therapy. MCP-1 and EGF were analyzed by enzyme-linked immunosorbent assays and expressed as a ratio to urine creatinine (ng/mgCr) or as EGF/MCP-1 ratio (ng/ng). Proteinuria and estimated glomerular filtration rate (eGRF) were monitored after therapy. Complete remission (CR) was defined as proteinuria ≤ 0.3 g/gCr.

RESULTS

Median follow-up was 20 months. Of all patients (n = 74), 38 patients (51.4%) subsequently achieved CR. Baseline urine EGF and EGF/MCP-1 levels were significantly higher in CR compared to Not CR. By contrast, MCP-1 was not different. High EGF (EGF > 75 ng/mgCr) was a significant predictor (OR 2.28) for CR by multivariate analysis after adjusting for proteinuria, blood pressure, baseline eGFR. In patients who completed 24 months follow-up (n = 43), baseline EGF correlated inversely with proteinuria and positively with eGFR at 24 months.

CONCLUSION

High urine EGF level is a promising biomarker of CR. Baseline EGF levels correlated with kidney function at 2 years. EGF/MCP-1 was not superior to EGF alone. Further studies are necessary to determine the role of urine EGF as a guide to therapy in primary GN.

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

BACKGROUND

Alport syndrome is a rare hereditary kidney disease manifested with progressive renal failure. Considerable variation exists in terms of disease progression among patients with Alport syndrome. Identification of patients at high risk of rapid progression remains an unmet need. Urinary epidermal growth factor (uEGF) has been shown to be independently associated with risk of progression to adverse kidney outcome in multiple independent adult chronic kidney disease (CKD) cohorts. In this study, we aim to assess if uEGF is associated with kidney impairment and its prognostic value for children with Alport syndrome.

METHODS

One hundred and seventeen pediatric patients with Alport syndrome and 146 healthy children (3-18 years old) were included in this study. uEGF was measured in duplicates in baseline urine samples using ELISA (R&D) and concentration was normalized by urine creatinine (uEGF/Cr). In patients with longitudinal follow-up data (n = 38), progression was defined as deteriorated kidney function (CKD stage increase) during follow-up period (follow-up length is about 31 months in average). The association of baseline uEGF/Cr level with estimated glomerular filtration rate (eGFR) slope and Alport syndrome patients' progression to a more advanced CKD stage during the follow-up period was used to evaluate the prognostic value of the marker.

RESULTS

We found that uEGF/creatinine (uEGF/Cr) decreases with age in pediatric patients with Alport syndrome with a significantly faster rate than in healthy children of the same age group. uEGF/Cr is significantly correlated with eGFR (r = 0.75, p < 0.001), after adjustment for age. In 38 patients with longitudinal follow-up, we observed a significant correlation between uEGF/Cr and eGFR slope (r = 0.58, p < 0.001). Patients with lower uEGF/Cr level were at increased risk of progression to a higher CKD stage. uEGF/Cr was able to distinguish progressors from non-progressors with an AUC of 0.88, versus 0.77 by eGFR and 0.81 by 24-h urinary protein (24-h UP).

CONCLUSIONS

Our study suggests that uEGF/Cr is a promising biomarker for accelerated kidney function decline in pediatric patients with Alport syndrome. It may help to identify patients at high risk of progression for targeted clinical care and improve the patients' stratification in interventional trials.

Tissue transcriptome-driven identification of epidermal growth factor as a chronic kidney disease biomarker

Chronic kidney disease (CKD) affects 8 to 16% people worldwide, with an increasing incidence and prevalence of end-stage kidney disease (ESKD). The effective management of CKD is confounded by the inability to identify patients at high risk of progression while in early stages of CKD. To address this challenge, a renal biopsy transcriptome-driven approach was applied to develop noninvasive prognostic biomarkers for CKD progression. Expression of intrarenal transcripts was correlated with the baseline estimated glomerular filtration rate (eGFR) in 261 patients. Proteins encoded by eGFR-associated transcripts were tested in urine for association with renal tissue injury and baseline eGFR. The ability to predict CKD progression, defined as the composite of ESKD or 40% reduction of baseline eGFR, was then determined in three independent CKD cohorts. A panel of intrarenal transcripts, including epidermal growth factor (EGF), a tubule-specific protein critical for cell differentiation and regeneration, predicted eGFR. The amount of EGF protein in urine (uEGF) showed significant correlation (P < 0.001) with intrarenal EGF mRNA, interstitial fibrosis/tubular atrophy, eGFR, and rate of eGFR loss. Prediction of the composite renal end point by age, gender, eGFR, and albuminuria was significantly (P < 0.001) improved by addition of uEGF, with an increase of the C-statistic from 0.75 to 0.87. Outcome predictions were replicated in two independent CKD cohorts. Our approach identified uEGF as an independent risk predictor of CKD progression. Addition of uEGF to standard clinical parameters improved the prediction of disease events in diverse CKD populations with a wide spectrum of causes and stages.

EGF receptor ligands: recent advances

Seven ligands bind to and activate the mammalian epidermal growth factor (EGF) receptor (EGFR/ERBB1/HER1): EGF, transforming growth factor-alpha (TGFA), heparin-binding EGF-like growth factor (HBEGF), betacellulin (BTC), amphiregulin (AREG), epiregulin (EREG), and epigen (EPGN). Of these, EGF, TGFA, HBEGF, and BTC are thought to be high-affinity ligands, whereas AREG, EREG, and EPGN constitute low-affinity ligands. This focused review is meant to highlight recent studies related to actions of the individual EGFR ligands, the interesting biology that has been uncovered, and relevant advances related to ligand interactions with the EGFR.

Osteogenic Protein-1: Gene Expression and Treatment in the Rat Remnant Kidney Model

Osteogenic Protein-1 (OP-1) is a bone morphogen involved in tissue repair and development. We have shown that OP-1 is downregulated during acute ischemic renal injury. Here we report the use of the rat remnant kidney model (RRKM) to evaluate changes in kidney OP-1 expression during chronic injury, and determine if treatment with recombinant human OP-1 (rhOP-1) aids in recovery from injury. Sprague—Dawley rats were subjected to kidney decapsulation (Cx) or 5/6 nephrectomy (Nx). Serum for BUN and creatinine and tissue for histology and mRNA analysis were collected at: 2, 10, and 12—14 wks post Nx. We show kidney OP-1 mRNA levels were downregulated at 2 and 12—14 wks post Nx. To determine the effect of rhOP-1 in the RRKM, rhOP-1 (0.25, 2.5 or 25 μg/kg) or vehicle (V) was injected in a second set of rats, 2 weeks after 2/3 left Nx for a total of six doses. Nx rats treated with rhOP-1 showed significantly increased tubular regeneration (increased mitotic figures, polyoid infolding, and tubular epithelial hyperplasia) in a dose dependent manner without changes in glomerular or tubular damage. rhOP-1 stimulates tubular epithelial cell regeneration, early in the repair process in a chronic renal failure model, before significant fibrosis is established.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

Value of plasmatic membrane attack complex as a marker of severity in acute kidney injury

The aim of this study was to determine if complement pathway is activated in AKI; for this purpose, we measured, through ELISA sandwich, the terminal lytic fraction of the complement system, called membrane attack complex (C5b-C9), in AKI patients compared with patients with similar clinical conditions but normal renal function. Our data showed that complement system is activated in AKI. Plasmatic MAC concentrations were significantly higher in AKI patients than in those with normal renal function; this difference is maintained independently of the AKI etiology and is proportional to the severity of AKI, measured by ADQI classification. In addition, we found that plasmatic MAC concentrations were significantly higher in patients who did not recover renal function at time of hospitalization discharge, in patients who died during the acute process, and in patients who need renal replacement therapy during hospitalization, but in this last group, the differences did not reach statistical significance. In conclusion, plasmatic MAC concentration seems valuable as a marker of AKI severity.

The TRPM6/EGF pathway is downregulated in a rat model of cisplatin nephrotoxicity

Cisplatin-induced hypomagnesemia is described in humans and rats, but the underlying mechanisms are still unclear. Recent studies have shown that epidermal growth factor (EGF) stimulates Mg²⁺ re-absorption in the distal convoluted tubule via the Mg²⁺ channel TRPM6. This study investigates the role of TRPM Mg²⁺ channels, claudines, and EGF in the Mg²⁺ homeostasis in a rat model of cisplatin-induced nephrotoxicity. Wistar rats were given 2.5 mg/kg cisplatin per week for 3 weeks and were euthanized 4 or 9 weeks after the first administration. The cisplatin treatment significantly increased the fractional excretion of Mg²⁺. Real-time RT-PCR and/or Western blots were performed to assess the renal expression TRPM6, TRPM7, claudin-16, claudin-19, EGF, EGF receptor (EGFR) and EGFR-pathway components. The renal mRNA expression of TRPM6 and EGF showed a significant decrease after cisplatin treatment, while the TRPM7, claudin-16 and EGFR expressions remained stable. The claudin-19 mRNA expression was significantly upregulated after cisplatin treatment. Western blotting confirmed the mRNA expression data for the claudins, but an showed upregulation of EGFR only at week 9. The role of the EGFR pathway, involving Pi3-AKT-Rac1, in cisplatin-induced nephropathy, could not be substantiated in further detail. This study shows that cisplatin treatment results in EGF and TRPM6 downregulation in the rat kidney, causing renal Mg²⁺ loss. Our results are in line with the hypothesis that EGF influences the renal expression or activation of TRPM6 and plays a significant role in Mg²⁺ loss in medication-induced nephropathy.

Delayed relief of ureteral obstruction is implicated in the long-term development of renal damage and arterial hypertension in patients with unilateral ureteral injury

PURPOSE

A delay in the diagnosis and treatment of iatrogenic obstructive ureteral injury is the most important prognostic factor for worse results in terms of lesion repair and renal function recovery. The role of the time of relief in determining the onset of renal failure and arterial hypertension in patients with obstructive ureteral injury was evaluated. In addition, we analyzed the prognostic value of the ratio of urinary epidermal growth factor-to-monocyte chemotactic peptide-1 in predicting long-term renal function deterioration.

MATERIALS AND METHODS

A total of 76 patients with obstructive ureteral injury and treated with reconstructive procedures were prospectively enrolled in the study. The ratio of epidermal growth factor-to-monocyte chemotactic peptide-1 was evaluated 4 weeks after the relief of obstruction. After a median followup of 60.8 months, estimated creatinine clearance and (99m)technetium-mercaptoacetyltriglycine scan were evaluated.

RESULTS

Within 2 weeks of the obstructive ureteral injury 36 patients underwent surgery for relief of obstruction while in the remaining 40 patients the surgery was performed after more than 2 weeks. Significant differences between the 2 groups were observed regarding mean mercaptoacetyltriglycine clearance of the obstructed kidney (p <0.0001), estimated creatinine clearance (p <0.001) and ratio of epidermal growth factor-to-monocyte chemotactic peptide-1 (p <0.0001). There was a direct correlation between mercaptoacetyltriglycine clearance and epidermal growth factor-to-monocyte chemotactic peptide-1 (rs = 0.78, p <0.0001). Patients with a time of relief greater than 2 weeks had a higher incidence of postoperative hypertension. On logistic regression the time of relief was the only significant variable predicting renal function deterioration (OR 1.49, p = 0.01).

CONCLUSIONS

Patients who experience delayed relief of obstructive ureteral injury have decreased long-term renal function as suggested by the lower values of estimated creatinine clearance and mercaptoacetyltriglycine clearance, and are at risk for hypertension or exacerbation of preexisting hypertension.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Comparison of the course of biomarker changes and kidney injury in a rat model of drug-induced acute kidney injury

OBJECTIVE

To aid in evaluating the performance of biomarkers, we measured kidney injury biomarkers in rat models of drug-induced acute kidney injury.

METHODS AND RESULTS

Rats were treated with site-specific nephrotoxins, puromycin, gentamicin, cisplatin, or 2-bromoethylamine. Fifteen biomarkers (β-2-microglobulin, calbindin, clusterin, cystatin-C, KIM-1, GST-α, GST-μ, NGAL, osteopontin, EGF, TIMP-1, VEGF, albumin, RPA-1, and urinary total protein) were examined in comparison with BUN, serum creatinine, and NAG. Some biomarkers, which were different depending in each nephrotoxin, showed ability to detect the prodromal stage of drug-induced kidney injury. Characteristic changing patterns of biomarkers were also found depending on the specific lesion site in the kidney.

CONCLUSION

These data suggested that establishment of a suitable biomarker panel would facilitate detection of site-specific kidney injury with high sensitivity.

Soluble HB-EGF induces epithelial-to-mesenchymal transition in inner medullary collecting duct cells by upregulating Snail-2

Animal models of acute renal injury suggest that the epidermal growth factor receptor (EGFR) axis may have a beneficial role in the recovery from acute renal injury, but recent reports describe detrimental effects of EGFR activation in chronic renal injury. Expression of the EGFR ligand heparin-binding EGF-like growth factor (HB-EGF) increases following renal injury, but the effects of this sustained upregulation have not been well studied. Here, stable overexpression of soluble HB-EGF (sHB-EGF) in mouse inner medullary collecting duct (IMCD) cells led to marked phenotypic changes: sHB-EGF-expressing cells demonstrated a fibroblast-like morphology, did not form epithelial sheets, exhibited cytoplasmic projections, decreased expression of epithelial markers, and increased expression of fibroblast-specific protein-1. They also demonstrated anchorage-independent growth and formed tumors when injected subcutaneously into nude mice. Quantitative RT-PCR and a luciferase reporter assay suggested that sHB-EGF repressed transcription of E-cadherin, and a concomitant TGF-beta-independent upregulation of the E-cadherin repressor Snail-2 was observed. Stable downregulation of Snail-2 in sHB-EGF-overexpressing cells restored epithelial characteristics (E-cadherin and cytokeratin expression) but did not alter their anchorage-independent growth. In summary, sustained exposure to sHB-EGF induces epithelial-to-mesenchymal transition of IMCD cells, in part by upregulating the E-cadherin transcriptional repressor Snail-2.

The role of the EGF family of ligands and receptors in renal development, physiology and pathophysiology

Mammalian kidney expresses all of the members of the ErbB family of receptors and their respective ligands. Studies support a role for ErbB family receptor activation in kidney development and differentiation. Under physiologic conditions, EGFR activation appears to play an important role in the regulation of renal hemodynamics and electrolyte handling by the kidney, while in different pathophysiologic states, EGFR activation may mediate either beneficial or detrimental effects to the kidney. This article provides an overview of the expression profile of the ErbB family of ligands and receptors in the mammalian kidney and summarizes known physiological and pathophysiological roles of EGFR activation in the organ.

Heparin-binding epidermal growth factor and Src family kinases in proliferation of renal epithelial cells

Our recent studies have shown that proliferation of renal proximal tubular cells (RPTC) in the absence of growth factors requires activation of the epidermal growth factor (EGF) receptor. We sought to identify the endogenous EGF receptor ligand and investigate the mechanism(s) by which RPTC proliferate in different models. RPTC expressed both pro- and cleaved forms of heparin-binding epidermal growth factor (HB-EGF) and several metalloproteinases (MMP-2, -3, -9, and ADAM10, ADAM17) that have been reported to cleave HB-EGF. Treatment of RPTC with CRM 197, an inhibitor of HB-EGF binding to the EGF receptor, or downregulation of HB-EGF with small interfering RNA inhibited RPTC proliferation following plating. Furthermore, GM6001 (pan-MMP inhibitor), tumor-necrosis factor protease inhibitor-1 (TAPI-1; MMP and ADAM17 inhibitor), and GW280264X (ADAM10 and -17 inhibitor), but not GI254023X (ADAM10 inhibitor), attenuated the proliferation after plating. Although EGF receptor activation is required for RPTC proliferation after oxidant injury, CRM197, GM6001, and TAPI-1 did not block this response. In contrast, inhibition of Src with PP1 blocked EGF receptor activation and RPTC proliferation after oxidant injury. In addition, PP1 treatment attenuated HB-EGF-enhanced RPTC proliferation. We suggest that RPTC proliferation after plating is mediated by HB-EGF produced through an autocrine/paracrine mechanism and RPTC proliferation following oxidant injury is mediated by Src without involvement of HB-EGF.

Dedifferentiation and proliferation of surviving epithelial cells in acute renal failure

In contrast to the heart or brain, the kidney can completely recover from an ischemic or toxic insult that results in cell death. During recovery from ischemia/reperfusion injury, surviving tubular epithelial cells dedifferentiate and proliferate, eventually replacing the irreversibly injured tubular epithelial cells and restoring tubular integrity. Repair of the kidney parallels kidney organogenesis in the high rate of DNA synthesis and apoptosis and in patterns of gene expression. As has been shown by proliferating cell nuclear antigen and 5-bromo 2'-deoxyuridine labeling studies and, in unpublished studies, by counting mitotic spindles identified by labeling with antitubulin antibody, the proliferative response is rapid and extensive, involving many of the remaining cells of the proximal tubule. This extensive proliferative capacity is interpreted to reflect the intrinsic ability of the surviving epithelial cell to adapt to the loss of adjacent cells by dedifferentiating and proliferating. Adhesion molecules likely play important roles in the regulation of renal epithelial cell migration, proliferation, and differentiation, as do cytokines and chemokines. Better understanding of all of the characteristics resulting in dedifferentiation and proliferation of the proximal tubule epithelial cell and cell-cell and cell-matrix interactions important for this repair function will lead to novel approaches to therapies designed to facilitate the processes of recovery in humans.

Erythropoietin enhances recovery after cisplatin-induced acute renal failure in the rat

BACKGROUND

Erythropoietin (Epo) is a growth factor whose synthesis mainly takes place in the kidney. Epo has been shown to support the growth not only of erythroid progenitor cells but also of certain other cell types. We attempted to establish whether Epo enhances the recovery from acute renal failure induced by cisplatin.

METHODS

Sprague-Dawley rats were randomized into three groups. In the cisplatin group, animals received one intraperitoneal injection of cisplatin (6 mg/kg) and a daily injection of placebo for 9 days. In the cisplatin+Epo group, animals received intrapertoneal cisplatin and a daily injection of Epo (100 IU/kg) for 9 days. In the control group, animals received both placebo preparations alone. Para-aminohippuric acid and inulin clearances were determined after 4 and 9 days to evaluate renal blood flow and glomerular filtration rate. In addition, light microscopy and immunohistochemistry examinations were performed, and in situ proliferating cell nuclear antigen (PCNA) staining was done to estimate the degree of renal tubular cell regenerative activity. The potential role of epithelial growth factor (EGF) was evaluated by semi-quantitative assessment of EGF immunostaining.

RESULTS

Renal blood flow and glomerular filtration rate decreased significantly in cisplatin and cisplatin+Epo groups versus control group at day 4. However, at day 9, they both were significantly greater in cisplatin+Epo-treated animals than in rats that had received cisplatin alone. Tubular cell regeneration was significantly enhanced at day 4 in cisplatin+Epo group, compared with cisplatin and control groups respectively. EGF immunostaining was not significantly different between the three groups.

CONCLUSION

Epo significantly enhanced the rate of recovery from acute renal failure induced by cisplatin. PCNA staining indicated that Epo might act directly via stimulation of tubular cell regeneration.

Mrna expression of transforming growth factor-alpha and the EGF receptor following nephrotoxic renal injury

We studied gene expression for transforming growth factor (TGF)-alpha, epidermal growth factor (EGF), heparin binding (HB) EGF, and the EGF receptor following acute renal failure induced by mercuric chloride administration to gain insight into potential mechanisms of renal repair. Twenty four hours after HgCl2, 2 mg/kg, creatinine increased from 0.3+/-0.01 mg/dl in controls to 2.2+/-0.26 mg/dl in injured rats (n = 5, p < 0.01). Similar changes were observed after 3 days. Messenger RNA expression for EGF was decreased at 24 hours in HgCl2 treated rats and remained depressed for at least 3 days. On the other hand steady state mRNA for TGF-alpha increased nearly 2 fold at day 3 in HgCl2 treated rats 4 mg/kg. Heparin binding EGF was increased early, by day one in injured kidneys and gene expression for the EGF receptor was increased as well. Immunohistochemistry documented an increase in expression of TGF-alpha in injured kidneys at distal nephron sites. These studies suggest that TGF-alpha along with HB EGF may be important ligands for the EGF receptor during repair from renal injury.

Identification of a novel kidney-specific gene downregulated in acute ischemic renal failure

To gain further insights into the molecular mechanisms involved in acute renal failure, we have isolated a new gene from rat and human, named KSP32 (kidney-specific protein with a molecular mass of 32 kDa). KSP32 encodes a novel gene that shows little homology to other mammalian proteins. It, however, shares extensive homology with several proteins found in the nematode Caenorhabditis elegans and plants. The expression of KSP32 mRNA is highly restricted to kidney. In situ hybidization analysis revealed that the expression of KSP32 mRNA was prominent in the boundary of kidney cortex and outer medulla, exhibiting a raylike formation extending from the medulla into the cortex. Finally, KSP32 mRNA was dramatically downregulated in rat following induction of acute ischemic renal failure. Rapid loss of KSP32 mRNA expression was observed beginning at approximately 5 h following renal injury and mRNA levels remained depressed for at least 96 h. Both KSP32 mRNA levels as well as renal function recovered 14 days after injury. Administration of an endothelin receptor antagonist (SB-209670), known to restore renal function, significantly increased KSP32 expression.

MCP-1 and EGF renal expression and urine excretion in human congenital obstructive nephropathy

BACKGROUND

Obstructive nephropathy is characterized at the histologic level by tubular atrophy and interstitial monocyte infiltration. The molecular mechanisms underlying these histologic changes are still poorly defined. Epidermal growth factor (EGF) produced by tubular cells seems to play a pivotal role in the modulation of tubular cell growth, while monocyte chemotactic peptide-1 (MCP-1) is a powerful and specific chemotactic and activating factor for monocytes.

METHODS

Twenty-four patients with congenital ureteropelvic junction obstruction [UPJO; 10 with recurrent urinary tract infection (UTI) and 10 with no UTI] and 15 healthy children were studied. Diagnosis was made by renal ultrasound, intravenous pielography, and MAG3 scan. Urinary samples were collected before and after surgery. In 10 patients, urine was also collected directly from the affected pelvis at the time of surgery. Urinary EGF and MCP-1 levels were measured by enzyme-linked immunosorbent assay. MCP-1 and EGF gene expression were evaluated by in situ hybridization in 15 biopsies from congenital UPJO and in 10 normal kidneys.

RESULTS

In normal kidneys, there was a high expression of EGF mRNA, whereas MCP-1 mRNA was undetectable. MCP-1 gene expression was strikingly increased at the tubulointerstitial level in UPJO biopsies compared with controls and was directly correlated with the extent of monocyte infiltration. In addition, UPJO kidney sections showed a marked reduction in EGF gene expression that was directly correlated with the degree of tubular damage. EGF urine concentration was significantly reduced in UPJO when compared with control and directly correlated with its renal gene expression. On the other hand, the MCP-1 urine concentration was strikingly increased in UPJO patients. It is noteworthy that a significant and inverse correlation was observed between the MCP-1 concentration in the urine collected from the obstructed pelvis and the MAG3 clearance of the obstructed kidney (r = -0.76). The presence of recurrent UTI was associated with a significantly higher MCP-1 excretion and a slight reduction in EGF urine concentration. The surgical correction of UPJO was followed by an improvement of renal function together with a significant reduction in MCP-1 excretion and a marked increase in EGF urine concentrations. Interestingly, EGF urine concentration measured before surgery was significantly correlated with the difference between the MAG3 clearance of the obstructed kidney before and after surgery.

CONCLUSIONS

MCP-1 and EGF seem to be involved in the pathogenesis of tubulointerstitial damage in congenital obstructive nephropathy, and their urine excretion may represent a powerful prognostic marker in this form of renal disease.

Expression of apoptosis regulatory proteins in tubular epithelium stressed in culture or following acute renal failure

BACKGROUND

While tubular cell death is a characteristic of acute renal failure (ARF), the molecular mechanisms that modulate this cell death are unclear. Cell fate in acute renal failure hinges on a balance of survival and mortality factors in a changing environment. We further explored this issue by studying selected cell death-related proteins in experimental renal failure.

METHOD

The expression of genes that promote (c-myc, Bax, BclxS) or protect (Bcl2, BclxL) from cell death was studied by Northern blot, Western blot, and immunohistochemistry in murine kidneys following ARF induced by folic acid or in renal tubular epithelial cells (MCT) stressed in culture.

RESULTS

Renal mRNA levels encoding for c-myc and BclxL were elevated in ARF while the Bcl2/Bax ratio was decreased (Bcl2 decreased and Bax increased; P < 0.05). Protein levels of BclxL increased and Bcl2 protein decreased. Expression of tumor necrosis factor (TNF-alpha), a mediator of ARF, was also increased. Immunohistochemistry further demonstrated that BclxL was increased in some tubuli and absent in others, while Bcl2 expression decreased diffusely. Bax staining was also patchy among tubuli and individual cells in the tubular wall and lumen. As a relative deficit of survival factors is present in ARF, MCT epithelium were deprived of serum survival factors. This resulted in apoptosis, decreased Bcl2/Bax and BclxL/Bax ratios (P < 0.05) and sensitization to TNF-alpha-induced apoptosis (P < 0.05). The latter was prevented by enforced overexpression of BclxL (P < 0.01). TNF-alpha increased the mRNA levels encoding for c-myc and decreased BclxL expression. Neither MCT cells nor the kidney expressed BclxS.

CONCLUSIONS

A relative deficit of survival factors likely contributes to changes in levels of BclxL and Bax in ARF. These deficits predispose to cell death induced by persistent lethal factors such as TNF-alpha that is increased in ARF and a potential source of increased c-myc, a downstream facilitator of cell death. These findings implicate members of the Bcl2 family of proteins as regulators of tubular cell death in ARF and single them out as potential therapeutic targets.

Protection from toxicant-mediated renal injury in the rat with anti-CD54 antibody

BACKGROUND

The benefit of the potent chemotherapeutic agent cisplatin in treating neoplasms is limited by nephrotoxicity. We tested the hypothesis that CD54 [intercellular adhesion molecule-1 (ICAM-1)] is an important mediator in cisplatin-mediated renal failure.

METHODS

The effect of a monoclonal anti-CD54 antibody was evaluated in a rat model of cisplatin toxicity. Renal function, histopathology, renal myeloperoxidase activity, and mortality were determined in the anti-CD54 and placebo groups.

RESULTS

Renal CD54 mRNA expression was markedly increased by 24 hours after exposure to cisplatin in mice. An improvement in renal function, mortality, and histological abnormalities was evident in animals exposed to cisplatin and treated with anti-CD54 antibody (mAb). Seven days after the administration of cisplatin, the mean creatinine was 0.65+/-0.05 mg/dl in the rats that received anti-CD54 mAb and 4.76+/-1.42 in control animals (P<0.02). Mortality was lower in experimental animals (0 vs. 29% in control rats seven days following cisplatin, P<0.04). Histological evidence of cell injury was markedly attenuated (P<0.04) in the treated compared with the control rats.

CONCLUSION

CD54 may be critical in the pathophysiology of renal injury following cisplatin, perhaps by its effects on leukocyte-endothelial interactions.

Lessons learned from ischemic and cisplatin-induced nephrotoxicity in animals

Following ischemic or nephrotoxic injury, the regenerating kidney assumes an earlier developmental stage and a less mature phenotype. Recovery involves the activation of a group of genes, including protooncogenes and growth factor genes that initiate and sustain cell growth. Inflammation also plays an important role in the recovery process as several of the changes in gene expression implicate the participation of the inflammatory cascade. Many of the changes in gene expression may eventually be reflected in the urine of the damaged kidney. By exploiting these changes in urine composition as a consequence of injury it should be possible to detect evidence of biologic effects of exposure and may yield predictions of eventual risk of serious damage to kidney.

Cell cycle events during renal injury

Recovery from ischemic and nephrotoxic acute renal failure requires replacement of damaged tubule cells in order to restore the morphological and functional integrity of the renal epithelium. A more thorough understanding of the renal stress response and its molecular interactions with the cell cycle machinery will be important areas of biomarker research in nephrotoxicity. Many of these molecular targets should be detectable hopefully without resorting the invasive techniques.

Epidermal growth factor accelerates recovery of LLC-PK1 cells following oxidant injury

In renal tubular epithelial cells, oxidant injury results in several metabolic alterations including ATP depletion, decreased Na+K+ATPase activity, and altered intracellular sodium and potassium content. To investigate the recovery of LLC-PK1 cells following oxidant injury and to determine if recovery can be accelerated, we induced oxidant stress in LLC-PK1 cells with 500 microM hydrogen peroxide for 60 min. Identical cohorts of oxidant-stressed cells were incubated in recovery medium without epidermal growth factor (EGF) or recovery medium containing 25 ng EGF per ml. ATP levels, Na+K+ATPase activity in whole cells, Na+K+ATPase activity in disrupted cells, and intracellular sodium and potassium ion content were determined at 0, 5, 24, 48, and 72 h following oxidant injury in each cohort of cells. In oxidant-stressed cells recovering in medium without EGF, ATP levels, Na+K+ATPase activity, and intracellular ion content improved but continued to remain substantially lower than control values at all time points following oxidant stress. In cells recovering in medium with EGF, ATP levels, Na+K+ATPase activity, and the intracellular potassium-to-sodium ratio were significantly higher at nearly all time points than values in cells recovering in medium alone. In cells recovering with added EGF, Na+K+ATPase activity had improved to control levels, whereas ATP levels and intracellular ion content approached control values by 72 h following oxidant stress. We conclude that oxidant-mediated ATP depletion, altered Na+K+ATPase activity, and intracellular ion content remain depressed for several d following oxidant stress and that EGF accelerated recovery of LLC-PK1 cells from oxidant injury.

Involvement of macromolecule synthesis, endonuclease activation and c-fos expression in cisplatin-induced apoptosis of mouse proximal tubule cells

We have previously demonstrated that cisplatin-induced nephrotoxicity is associated with the induction of apoptosis using mouse renal cells derived from the terminal proximal tubule (S3) which is the major target site of cisplatin-induced injury. The purpose of this study was to elucidate the intracellular mechanisms leading to the cisplatin-induced apoptosis of S3 cells. Actinomycin D (an inhibitor of RNA synthesis), cycloheximide (an inhibitor of protein synthesis) and aurintricarboxylic acid (an endonuclease inhibitor) reduced the extent of DNA fragmentation, a biochemical parameter of apoptosis, in cisplatin-treated S3 cells. Furthermore, cisplatin-induced apoptosis of S3 cells was accompanied by an increase in the level of c-fos mRNA expression, which is inhibited by pretreatment of the cells with actinomycin D, but not with cycloheximide or aurintricarboxylic acid. In contrast, outer medullary collecting duct cells treated with cisplatin exhibited morphological changes characteristic of apoptosis and an increase in the level of c-fos mRNA expression, but no increase in the extent of DNA fragmentation. In conclusion, the synthesis of macromolecules such as RNA and protein, endonuclease activation and c-fos expression appear to be involved in the intracellular pathways leading to the induction of apoptosis in cisplatin-treated S3 cells. In addition, the response to cisplatin may be different in different cells.

Renal epidermal growth factor precursor: proteolytic processing in an in vitro cell-free system

The enzymatic processing of the membrane-bound renal epidermal growth factor precursor (proEGF) could be an important step in the control of nephrogenic repair consecutive to kidney insult. The enzyme machinery responsible for that processing was examined in a cell-free system consisting of renal membranes isolated from kidney homogenates by differential centrifugation, and incubated in vitro. After a 24-h incubation at 37 degrees C, 6-14% of membrane-bound proEGF was processed and soluble products with EGF immunoreactivity were released. As revealed by HPLC and Western blotting analysis, the products of proEGF proteolysis consisted of 6 kDa EGF (the molecular weight of mature EGF) and two polypeptides with molecular weights around 45 kDa. Interestingly the 45 kDa EGF forms, like the 6 kDa EGF, exhibited mitogenic activity toward growth-arrested NRK-52E renal cell line. The kinetic study of proEGF degradation gave data consistent with the 45 kDa product(s) being processing intermediate(s) between proEGF and 6 kDa EGF. The enzymatic activity responsible for proEGF nicking was inhibited by divalent heavy metal ions (Cu2+ or Zn2+) and several protease inhibitors (aprotinin, PMSF, leupeptin, soybean trypsin inhibitor), suggesting that proEGF is processed by kallikrein-like serine proteases present in the membrane preparations. Along with previous studies, the current observations suggest that renal kallikreins might play a role in renal tubular regeneration by promoting the release of soluble EGF in renal tissue.

Production of heparin binding epidermal growth factor-like growth factor in the early phase of regeneration after acute renal injury. Isolation and localization of bioactive molecules

We have recently reported that heparin-binding epidermal growth factor-like growth factor (HB-EGF) mRNA is induced in the rat kidney after acute ischemic injury. The present studies were designed to investigate whether bioactive HB-EGF protein is also produced in response to renal injury induced by either ischemia/reperfusion or aminoglycosides. Heparin-binding proteins were purified from kidney homogenates by heparin affinity column chromatography using elution with a 0.2-2.0 M gradient of NaCl. A single peak of proteins that eluted at 1.0-1.2 M NaCl was detected in the postischemic kidney within 6 h of injury. This eluate fraction stimulated DNA synthesis in quiescent Balb/c3T3, RIE, and NRK-52E cell lines, all of which are responsive to the epidermal growth factor family of mitogenic proteins. The EGF receptor of A431 cells was also tyrosine phosphorylated by this eluate peak. Furthermore, immunoblotting with a polyclonal antibody against rat HB-EGF indicated that the eluate peak contained immunoreactive proteins of 22 and 29 kD mol wt, consistent with the reported sizes of the secreted form and membrane anchored form of HB-EGF, respectively. Immunohistochemical studies revealed that HB-EGF was produced predominantly in distal tubules in kidneys injured either by ischemia/reperfusion or aminoglycoside administration. We also found that during metanephric development immunoreactive HB-EGF was detected in the ureteric bud as early as E14.5 and persisted in structures arising from the ureteric bud throughout embryogenesis. These results suggest that in response to acute injury, HB-EGF is produced predominantly in distal tubules and that endogenous HB-EGF may be an important growth factor involved in renal epithelial cell repair, proliferation, and regeneration in the early stages of recovery after acute renal injury, as well as in nephrogenesis.

Ischemic-reperfusion injury in the kidney: overexpression of colonic H+-K+-ATPase and suppression of NHE-3

Ischemic renal injury is associated with changes in the expression of a number of genes. Although pH regulation is undoubtedly important during the recovery from ischemia, the expression of acid-base transporters during acute ischemic renal failure has not been studied. In the present study, levels of mRNA encoding the colonic H+-K+-ATPase and four isoforms of the Na+/H+ exchanger (NHE-1, NHE-2, NHE-3 and NHE-4) were measured by quantitative Northern analysis in rat renal cortex and medulla following ischemia-reperfusion injury. Rats were subjected to 30 minutes of renal artery occlusion and then sacrificed either 12 or 24 hours after the occlusion was released. The most striking changes followed 30 minutes of occlusion and 12 hours of reperfusion and involved the mRNA for NHE-3 (involved in HCO3- reabsorption in proximal tubule and thick limb) and colonic H+-K+-ATPase (involved in HCO3- reabsorption in collecting duct). These changes were: (1) a approximately 75% decrease in NHE-3 mRNA in both cortex and medulla; and (2) an approximately 8-fold increase in colonic H+-K+-ATPase mRNA in the cortex. At 12 hours of reperfusion, there was a 66% reduction in the Na+/H+ exchanger (NHE-3) activity as assayed by acid-stimulated 22Na+ influx into brush border membrane vesicles (P < 0.01). After 24 hours of reperfusion, NHE-3 mRNA remained suppressed while cortical colonic H+-K+-ATPase mRNA declined to only twice the control level. Medullary colonic H+-K+-ATPase mRNA did not change significantly. Gastric H+-K+-ATPase mRNA in cortex or medulla remained the same at 0, 12, and 24 hours after reperfusion. Cortical NHE-1 increased mildly at 12 and 24 hours of reperfusion whereas a moderate decrease in NHE-2 and NHE-4 mRNAs was observed in cortex and medulla after both 12 and 24 hours of reperfusion. We suggest that overexpression of colonic H+-K+-ATPase in the early phase of renal reperfusion injury may be responsible for compensatory reabsorption of increased HCO3- load resulting from suppression of NHE-3. This was supported by a fourfold increase in colonic H+-K+-ATPase mRNA in rats treated with acetazolamide, which causes renal HCO3-wasting. Rapid decline in colonic H+-K+-ATPase expression at 24 hours after reperfusion is likely due to reduced HCO3- delivery to distal tubules resulting from decreased GFR. Overexpression of H+-K+-ATPase may be vital to acid-base homeostasis in the early phase of acute ischemic renal failure.

Delayed graft function in renal transplantation: etiology, management and long-term significance

PURPOSE

In cadaveric renal transplantation a period of delayed graft function postoperatively is not uncommon and often associated with a poor outcome. We reviewed the biology of reperfusion injury and delayed graft function in renal transplantation, as well as its prevention, management and long-term effects.

MATERIALS AND METHODS

The medical literature covering acute tubular necrosis, delayed graft function in renal transplantation and immunology of ischemia reperfusion injury was reviewed.

RESULTS

Delayed graft function is clearly associated with poor allograft survival, and is caused by an interaction of ischemic and immunological factors. Technical and pharmacological maneuvers can improve early function rates. The response to ischemic injury is complex, and may increase graft immunogenicity and promote the chronic proliferative changes seen in chronic allograft nephropathy.

CONCLUSIONS

Improvement in early renal function should be a primary goal in renal transplantation to enhance early and long-term results. Basic research into the injury response may yield insights into renal pathophysiology.

Expression of epidermal growth factor and its receptor in normal and diseased human kidney: an immunohistochemical and in situ hybridization study

The kidney is one of the major sites of EGF production and there it seems to play several biological functions, such as modulation of cell growth, renal repair following injury, regulation of cellular metabolism and glomerular haemodinamics. The present study was first aimed at localizing EGF and its receptor (R) in normal human kidney by immunohistochemical and in situ hybridization techniques. Then, the distribution of the growth factor and its R was explored in biopsy specimens from eight patients with acute tubulointerstitial damage. In the normal human kidney, both EGF immunoreactivity and EGF mRNA were localized in tubular profiles corresponding to Henle's loop and, although to a lesser intensity, to distal convoluted tubule. EGF immunostaining was remarkable mainly at the apical surface of tubular cells. EGF-R protein expression was detected in glomerular endothelial cells, in peritubular capillaries and arteriolar walls, as well as along the thick ascending limb of Henle's lop and distal convoluted tubule, where it colocalized with Tamm-Horsfall protein. Immunohistochemical analysis of tubular profiles revealed that EGF-R was located especially along the basolateral membrane of tubular cells and within the basal part of cytoplasm. Endogenous alkaline phosphatase and CHIP28 positive tubules did not show any signal for EGF and its receptor. Kidneys with acute tubulointerstitial injury exhibited a dramatic decrease of EGF expression, whereas EGF-R showed only minor modifications. Interestingly, EGF-R was localized to both apical and antiluminal membranes of positive tubular cells. It is concluded that EGF-EGF receptor loop may be relevant in the pathogenesis of acute tubulointerstitial damage and recovery from tubular injury, while its role in the physiological renewal of the urothelium remains speculative.

Renal expression of a transforming growth factor-alpha transgene accelerates the progression of inherited, slowly progressive polycystic kidney disease in the mouse

Polycystic kidney disease (PKD) is a prevalent inherited disease in human beings. The pathogenesis of PKD is as yet unclear. The epidermal growth factor family of proteins has been implicated in PKD based largely on in vitro data. To determine whether these growth factors contribute to the progression of inherited PKD in vivo, we crossed mice with a transgene for human transforming growth factor-alpha (TGF-alpha, a member of the epidermal growth factor (EGF) family) and mice with the pcy gene (which causes a slowly progressive form of PKD very similar to human autosomal dominant PKD). Renal expression of the TGF-alpha transgene in cystic mice (homozygous for the pcy gene) accelerated the development of PKD as shown by an increased kidney weight as a percent of body weight and an increased volume density of renal cysts at 8.5 weeks of age. However, renal expression of the TGF-alpha transgene did not appear to precociously initiate cyst development (at 6.5 weeks), nor did it cause an increase in the final degree of renal enlargement (at 29 weeks). Thus TGF-alpha accelerated the enlargement of cysts once initiated. At 8.5 weeks of age, renal expression of the TGF-alpha mRNA correlated positively with the amount of renal enlargement. At all time points studied, cystic kidneys exhibited increased expression of c-myc mRNA as compared with phenotypic normal kidneys, consistent with PKD being a hyperplastic disease of renal tubules. However, the renal expression of c-myc in 8.5 week cystic kidneys, with or without the transgene, did not correlate with the degree of renal enlargement. The results of this study suggest that EGF-like proteins may accelerate the progression of inherited renal cystic disease. However, the final degree of cystic change is dictated by the primary disease process rather than by the continued presence of growth factor.

Response of the intrarenal insulin-like growth factor-I axis to acute ischemic injury and treatment with growth hormone and epidermal growth factor

We previously reported that following bilateral acute tubular necrosis (ATN) profound changes in the intrarenal insulin-like growth factor-I axis occurs which are unrelated to altered nutritional intake. In this current report we studied rats with unilateral ATN to assess whether these changes reflect a response to acute injury or the accompanying uremia. Compared to the contralateral kidney, the injured kidney showed an increase in IGF-I receptor number without a change in IGF-I receptor mRNA levels, a decrease in IGF-I mRNA and IGF-I protein levels, a decrease in growth hormone (GH) receptor mRNA abundance and receptor binding. There was also a decrease in IGF binding protein-2, -3 and -5 mRNA levels together with a fall in protein products. Since this unilateral ATN model excludes the influence of uremia and reduced nutritional intake, we surmised that these changes reflect a direct response to injury. Next, because of the reduced GH receptor binding noted above and the reported decrease in epidermal growth factor (EGF) expression in ATN, we tested the thesis that the low kidney IGF-I mRNA levels in ATN are partly due to a relative or absolute deficiency of these hormones. Administration of EGF or GH promptly increased ATN kidney IGF-I mRNA levels to control kidney values, lending support to the thesis. The response to EGF also suggests that the salutary effect of EGF treatment in ATN may partly be mediated by stimulating IGF-I production.

Decreased urinary epidermal growth factor in children with acute renal failure: epidermal growth factor/creatinine ratio not a reliable parameter for urinary epidermal growth factor excretion

To verify some animal experimental results in humans, we have studied urinary epidermal growth factor (EGF) excretion in normal children as well as children with acute renal failure (ARF). Urinary EGF excretion was expressed as a ratio of urinary EGF to urinary creatinine concentration (EGF/Cr) for random and 24-h urine, and a daily total urinary EGF for 24-h urine. The highest urinary EGF/Cr in children was found at 1 mo to 3 y of age. There was a highly significant correlation between random urine EGF/Cr and 24-h urine EGF/Cr (r = 0.92, p < 0.001), whereas no correlation of urinary EGF/Cr with daily total urine EGF was found. During the course of ARF, a decline in urinary EGF/Cr from the period before peak serum creatinine to the period after the declination of serum creatinine was noted (p = 0.013, n = 13, by repeated measure analysis), with a constant low daily total urine EGF (p value not significant). However, a rise in both urinary EGF/Cr and daily total urine EGF was found between the period of serum creatinine decline and the period of completely normal serum creatinine (p < 0.001). Serum EGF remained unchanged throughout the course of ARF. These results suggest 1) the possible role of EGF in renal growth or maturation during the first 2 or 3 y of life, 2) the possible renal origin of human urinary EGF, and 3) decreased urinary EGF excretion in children with ARF. In particular, EGF/Cr is not a reliable indicator for the expression of actual urinary EGF excretion in ARF. Instead of urinary EGF/Cr, urinary EGF concentration may be used to predict the daily total urinary EGF excretion during ARF. These results provide the pattern of urinary EGF excretion during ARF in children and may be of help for further clinical studies.

DNA synthesis is dissociated from the immediate-early gene response in the post-ischemic kidney

The response of the kidney to ischemic injury includes increased DNA synthesis, which is preceded by rapid and brief expression of the c-fos proto-oncogene. While the timing of these two events would suggest that c-Fos participates in an immediate-early gene program leading to proliferation, no direct test of this hypothesis exists. The purpose of these studies was (1) to determine whether c-fos is expressed as part of a typical immediate-early (IE) gene response, which would require co-expression of c-jun and sensitivity to cycloheximide, and (2) to determine whether the cells expressing c-Fos are the same as those undergoing DNA synthesis. Northern analysis was performed on renal mRNA at different times following release of a 50 minute period of renal hilar clamping. c-jun and c-fos mRNA were rapidly and briefly expressed following renal ischemia and their expression was superinduced by cycloheximide in a manner typical of an immediate-early gene response. 3H-thymidine autoradiography performed on semi-thin sections from intravascularly perfusion fixed kidneys 24 hours following induction of ischemia showed labeled nuclei in cells lining the damaged proximal tubules of the outer stripe of the outer medulla, as well as proximal tubules in the cortex and interstitial cells throughout the kidney. However, immunohistochemical localization of c-Fos and c-Jun protein occurred predominantly in nuclei of the thick ascending limb, distal tubule and collecting duct cells. The studies demonstrate that c-fos and c-jun are expressed following renal ischemia as a typical immediate-early gene response, but they are expressed in cells that do not enter the cell cycle. The failure of the cells to enter the cell cycle may depend on the co-expression of jun-B and jun-D, which suppress the mitogenic activity of c-Jun in other cells. The data suggest that the IE response following renal ischemia is part of the stress response, which is antiproliferative rather than proliferative. The role of the stress response during renal ischemia and the fate of the cells undergoing it are unknown.

Induction of heparin-binding epidermal growth factor-like growth factor mRNA in rat kidney after acute injury

Previous studies have suggested that EGF or other members of the EGF family of mitogenic proteins are involved in proliferation of renal tubular epithelial cells occurring during recovery from injury to the kidney. The present studies examined whether expression of mRNA for the recently identified heparin-binding EGF-like growth factor (HB-EGF) is regulated in response to renal injury induced by either ischemia/reperfusion or mercuric chloride. Increased expression of HB-EGF mRNA was demonstrated in the post-ischemic kidney within 45 min of unilateral ischemia/reperfusion in the rat. Induction of HB-EGF mRNA occurred only when ischemia was followed by reperfusion, and was not eliminated by removal of blood cells from the post-ischemic kidney by saline perfusion. In situ hybridization with 35S-labeled antisense riboprobes of HB-EGF indicated that compared with control, there was increased HB-EGF mRNA expression in the 6 h post-ischemic kidney in the inner cortex and outer medulla in a patchy distribution, with the greatest expression in the inner stripe of the outer medulla. Expression occurred primarily in tubular epithelial cells. Recombinant human HB-EGF stimulated [3H]-thymidine incorporation in both primary cultures of rabbit proximal tubule cells and NRK 52E normal rat kidney epithelial cells, with potency similar to that of EGF. Induction of HB-EGF mRNA was observed in tubules freshly isolated from rat renal cortex or outer medulla when the tubules were subjected to reoxygenation after incubation in anoxic conditions. The nephrotoxin, mercuric chloride, also caused induction of HB-EGF mRNA both in vivo and in isolated rat cortical tubules. The anoxia/reoxygenation-induced expression of HB-EGF mRNA in isolated tubules was inhibited by the free radical scavengers, di- and tetra-methylthiourea, indicating involvement of reactive oxygen species. These findings indicate that HB-EGF mRNA is inducible in the kidney in vivo by acute tubular injury and suggest that HB-EGF may act as an autocrine/paracrine growth factor involved in proliferation of tubular epithelial cells and repair of the kidney.

Insulin-like growth factor improves renal architecture of fetal kidneys with complete ureteral obstruction

Others have previously demonstrated that the administration of insulin-like growth factor-I accelerates recovery from ischemic acute tubular necrosis in the rat kidney. We investigated the effect of insulin-like growth factor-I on the histology of unilaterally obstructed kidneys in the pouch young of the North American opossum, Didelphis virginiana. In this model complete unilateral ureteral obstruction reliably induces statistically significant degrees of caliceal dilatation, tubular cystic change, and cortical and medullary fibrosis in kidneys examined 1 week after the creation of complete obstruction. Cortical and medullary inflammation is also increased after 1 week of obstruction in this model but not to a degree that is statistically different than control (sham operated) animals. We administered insulin-like growth factor-I to opossum pups with complete unilateral obstruction created at a length of 5 cm. (age 25 days, human equivalent 18 to 20 weeks). Insulin-like growth factor-I (400 mcg/kg.) was injected subcutaneously on the day of operation and again on days 2 and 4 postoperatively. The animals were sacrificed 1 week after obstruction and the formalin fixed, paraffin embedded kidneys were assessed histologically. In the obstructed kidney insulin-like growth factor-I ameliorated the development of fibrosis (cortical and medullary) and caliceal dilatation such that these characteristics did not differ significantly from those of sham operated animals. Tubular cystic change in the obstructed kidneys was also decreased by insulin-like growth factor-I administration but not to significant levels. Insulin-like growth factor-I treatment in obstructed animals resulted in significantly more inflammation (cortical and medullary) than in the sham operated animals. We also administered insulin-like growth factor-I to normal pups with no other intervention. These insulin-like growth factor-I treated pups did not differ from sham pups for any characteristic studied. Our study suggests that there is protective effect of insulin-like growth factor-I on renal architecture when administered in the setting of experimental fetal ureteral obstruction.