Progression Of Chronic Renal Disease Research Articles

Renal endothelin-1 and endothelin receptor type B expression in glomerular diseases with proteinuria.

The endothelin (ET) system has been studied extensively in experimental models of progressive chronic renal disease, but there is limited information regarding the ET system in renal patients. First, the expression of human ET-1, as well as ET receptor type A (ET-R(A)) and ET-R(B), was studied in 26 renal biopsies from patients with different renal diseases. Gene expression was assessed by quantitative reverse transcription-PCR. Second, ET-1 and ET-R(B) protein expression and localization were examined, by immunohistochemical analyses, among a homogeneous cohort of 16 patients with IgA nephropathy and different degrees of proteinuria. ET-R(B) mRNA expression was threefold higher among patients with higher-grade proteinuria [> or =2 g/24 h, n = 10; OD ratio (ODR), i.e., wild-type/mutant mRNA ratio, 1.81 +/- 0.3], compared with patients with lower-grade proteinuria (<2 g/24 h, n = 8; ODR, 0.63 +/- 0.1; P < 0.01) or control subjects (n = 9; ODR, 0.57 +/- 0.1; P < 0.01). ET-1 gene expression was significantly higher among patients with higher-grade proteinuria, compared with patients with lower-grade proteinuria (P < 0.01) or control subjects (P < 0.05). ET-R(A) mRNA expression was not different among the groups. Patients with higher-grade proteinuria who were receiving angiotensin-converting enzyme inhibitors exhibited significantly (P < 0.05) lower ET-1 and ET-R(B) mRNA expression, which was comparable to that of control subjects. By using immunohistochemical analyses, an association between proteinuria and expression of ET-1 and ET-R(B) in proximal tubular epithelial cells and of ET-1 in glomeruli was confirmed in the separate cohort of patients with IgA nephropathy. It is concluded that the increased ET-R(B) and ET-1 mRNA and protein expression observed in animal models of renal disease is also demonstrable among patients with renal disease and high-grade proteinuria.

Urinary cytokines: clinically useful markers of chronic renal disease progression?

Many factors that drive glomerular and tubulointerstitial fibrogenesis have been identified. These include hemodynamic factors, chemokines, inflammatory mediators, cytokines, and lipids. These strides in knowledge are important in identifying those patients at increased risk of progressive renal disease as well as in developing targets for therapeutic interventions. Identifying 'progressors' is crucial since the distribution of the slope of the glomerular filtration rate of patients with chronic kidney disease is not normal. Some patients appear to progress very rapidly, such as those with diabetes, whereas other patients fail to progress at all. Developing strategies targeted at identifying the fast from the slow progressors is therefore of paramount importance if we are to deploy resources rationally in the management of patients with chronic kidney disease. The use of urinary cytokine markers as predictors of progression of renal disease is reviewed in this paper.

Systemic administration of naked plasmid encoding hepatocyte growth factor ameliorates chronic renal fibrosis in mice

The progression of chronic renal diseases is considered as an irreversible process that eventually leads to end-stage renal failure characterized by extensive tissue fibrosis. At present, chronic renal fibrosis is incurable and the incidence of affected patients is on the rise worldwide. In this study, we demonstrate that delivery of hepatocyte growth factor (HGF) gene via systemic administration of naked plasmid vector markedly ameliorated renal fibrosis in an animal model of chronic renal disease induced by unilateral ureteral obstruction. A high level of exogenous HGF protein was detected in the obstructed kidneys following intravenous injection of naked plasmid encoding human HGF. Delivery of human HGF gene induced a sustained activation of extracellular signal-regulated kinases-1 and -2 in the obstructed kidneys. Exogenous HGF expression dramatically inhibited alpha-smooth muscle actin expression, attenuated renal interstitial accumulation and deposition of collagen I and fibronectin. In addition, exogenous HGF suppressed renal expression of pro-fibrogenic cytokine TGF-beta1 and its type I receptor in vivo. These results suggest that systemic administration of naked plasmid vector introduces a high level of exogenous HGF to the diseased kidneys, and that HGF gene transfer may provide a novel therapeutic strategy for amelioration of chronic renal fibrosis in vivo.

Dissection of Key Events in Tubular Epithelial to Myofibroblast Transition and Its Implications in Renal Interstitial Fibrosis

Myofibroblast activation is a key event playing a critical role in the progression of chronic renal disease. Emerging evidence suggests that myofibroblasts can derive from tubular epithelial cells by an epithelial to mesenchymal transition (EMT); however, the details regarding the conversion between these two cell types are poorly understood. Here we dissect the key events during the process of EMT induced by transforming growth factor-beta1. Incubation of human tubular epithelial cells with transforming growth factor-beta1 induced de novo expression of alpha-smooth muscle actin, loss of epithelial marker E-cadherin, transformation of myofibroblastic morphology, and production of interstitial matrix. Time-course studies revealed that loss of E-cadherin was an early event that preceded other alterations during EMT. The transformed cells secreted a large amount of matrix metalloproteinase-2 that specifically degraded tubular basement membrane. They also exhibited an enhanced motility and invasive capacity. These alterations in epithelial phenotypes in vitro were essentially recapitulated in a mouse model of renal fibrosis induced by unilateral ureteral obstruction. Hence, these results indicate that tubular epithelial to myofibroblast transition is an orchestrated, highly regulated process involving four key steps including: 1) loss of epithelial cell adhesion, 2) de novo alpha-smooth muscle actin expression and actin reorganization, 3) disruption of tubular basement membrane, and 4) enhanced cell migration and invasion.

Tubular‐interstitial interactions in proteinuric renal diseases

SUMMARY: Progressive chronic renal disease of all types is characterized by a relatively uniform set of tubular (atrophy, hypertrophy, hyperplasia) and interstitial (inflammatory cell infiltration, fibrosis) pathological changes, the severity of which correlates well with the degree of proteinuria and the decline in glomerular filtration. Complex and redundant pathophysiological events underlie the relationship between proteinuria, tubular injury and interstitial damage, forming potential targets for therapy. The outcome of these events is also determined by additional factors not limited to proteinuric diseases, including tissue hypoxia, complement activation and mediators produced in response to glomerular damage. In response to proteinuria and these additional factors, tubular cells are activated to produce a large number of chemoattractants, proinflammatory and profibrotic cytokines and matrix proteins, which cause, at least in part, interstitial inflammation and fibrosis. In turn, soluble products of interstitial inflammatory cells (predominantly T lymphocytes and macrophages), dendritic cells and fibroblasts are at least partially responsible for altering the phenotype of tubular cells. Abnormal tubular‐interstitial interactions may also depend on direct cell contact rather than soluble mediators, as evidenced by up‐regulation of integrins and cell adhesion molecules. Myofibroblasts, a key cell in the production of interstitial fibrosis, may arise in response to the above mediators by trans‐differentiation of fibroblasts, perivascular cells and tubular cells. In addition, tubular cells have been shown to be capable of the induced expression of the signalling molecules necessary for them to behave as antigen‐presenting cells and thereby potentially initiate interstitial inflammation through the classic interactions of cognate immunity. It is probable that several, but not all, of this bewildering number of pathophysiological events are of prime importance to the development of tubulointerstitial damage in proteinuria. The immediate challenge for investigators is to define the relative importance of these events and, thus, the most appropriate targets for new treatments.

Is there hope for preventing or slowing the progression of chronic renal disease? More support for the role of growth factors

Is there hope for preventing or slowing the progression of chronic renal disease? More support for the role of growth factors

Drug-induced acute interstitial nephritis

Drug-induced acute interstitial nephritis

Evolving strategies for renoprotection: non-diabetic chronic renal disease.

Experimental and clinical studies over the past two decades have identified several interventions for slowing the progression of chronic renal disease towards end-stage renal failure. In this paper we review the experimental and clinical evidence in support of dietary protein restriction, angiotensin-converting enzyme inhibitor therapy, control of systemic hypertension, reduction of proteinuria, treatment of hyperlipidemia and smoking cessation. We also consider potential future renoprotective therapies. Finally we propose a comprehensive strategy for achieving maximal renoprotection with available interventions and monitoring.

Angiotensin II subtype 1 receptor blockers and renal function.

Blood pressure reduction is the most significant factor in delaying onset and progression of renal disease. Blockade of the renin-angiotensin system (RAS) using angiotensin-converting enzyme inhibitors (ACEIs) delays renal disease progression. More recently, agents that block the RAS by preventing angiotensin II from binding to its subtype 1 receptor (ARBs) have been developed in an effort to prevent deleterious consequences of pathologic levels of angiotensin II and to reduce the adverse effects of RAS blockade associated with ACEIs. Human studies with a variety of ARBs have clearly demonstrated the antihypertensive and antiproteinuric efficacy of these agents in patients with progressive renal diseases. Moreover, the effects of ARBs are similar or identical to those of ACEIs. Ongoing long-term clinical trials are designed to determine whether ARBs also preserve renal function similar to ACEIs. Specifically, the role of ARBs in patients with hypertension and type 2 diabetes is being evaluated in 3 large trials, including Appropriate Blood Pressure Control in Diabetes-Part 2 With Valsartan, the Losartan Renal Protection Study, and the Irbesartan Diabetic Nephropathy Trial. Definitive evidence of the long-term protective effects of ARBs in chronic progressive renal disease is expected from these important studies.

The role of the tubular epithelial cell in renal fibrogenesis

Changes in the tubulointerstitial compartment play an important role in the progression of chronic renal disease to endstage renal failure. These changes consist of interstitial inflammation and subsequent fibrosis. The tubular epithelial cell plays a key role in the formation of interstitial inflammation. Stimulated by proteinuria and morphokines in the tubular fluid, the tubular epithelial cell responds by synthesizing chemokines, which, in turn, results in the influx of inflammatory mononuclear cells. Increased tubular expression of adhesion molecules, such as intercellular adhesion molecule (ICAM)-1 and vascular adhesion molecule (VCAM)-1, as well as major histocompatibility complex (MHC) class II antigens, in conjunction with costimulatory molecules, may have additional effects. However, the tubular epithelial cell does not only mediate interstitial inflammation, it also stimulates interstitial fibroblasts via the secretion of cytokines such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF)-2, and transforming growth factor (TGF)-β. Furthermore, tubular epithelial cells have the capacity to participate in the synthesis of extracellular matrix either directly or indirectly via their transformation into mesenchymal-like fibroblasts. This process of epithelial-mesenchymal transformation (EMT) depends on cytokines such as TGF-β1 and epidermal growth factor (EGF), as well as disruption of the tubular basement membrane (TBM). The contribution of epithelial cell apoptosis to tubular atrophy is actively under investigation.

Role of hypertension in the progression of chronic renal disease.

Hypertension leads to renal disease through a series of mechanisms that seem to be exaggerated in African-Americans, who have a higher prevalence of both hypertension and end-stage renal disease than whites. Renal disease itself leads to hypertension, which in turn can contribute to progression of renal disease. Although there are numerous mechanisms involved in the process of renal disease progression, the renin-angiotensin system plays a major role as determined by the beneficial response to angiotensin I-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (AT II blockers) of reduced rate of progression in a variety of clinical and experimental renal diseases. Macromolecular trafficking across the glomerulus leading to proteinuria plays a significant role in progression of chronic renal disease. Reversal of this abnormality and reduced stress on capillary walls may be the major mechanisms of beneficial action of ACEIs and AT II blockers in halting renal disease progression.

Update in podocyte biology.

Knowledge of podocyte biology is growing rapidly. Podocytes are crucially involved in most hereditary diseases affecting the glomerulus, which all exhibit podocyte-specific defects, that is, foot process effacement and protein leakage. Efforts to understand molecular mechanisms causing these derangements are increasingly successful and will allow a better targeting of interventions to halt the progression of chronic renal disease.

Up-regulation of endoglin, a TGF-beta-binding protein, in rats with experimental renal fibrosis induced by renal mass reduction.

The central process in chronic renal failure is the progressive accumulation of extracellular matrix in the glomeruli and in the tubulo-interstitial space, resulting in renal fibrosis. Transforming growth factor-beta1 (TGF-beta1) up-regulation plays a major role in the genesis of renal fibrosis. Endoglin is a membrane glycoprotein that binds TGF-beta1 and TGF-beta3 with high affinity. An increased level of endoglin immunostaining has been demonstrated previously in biopsies from patients with chronic progressive renal disease. We have assessed the expression of endoglin in the rat 5/6th renal mass reduction (RMR) model. One, 3 and 5 months after RMR, mean arterial pressure and renal function were measured, animals were sacrificed, renal fibrosis was evaluated quantitatively and the expression of endoglin was assessed by western blot, northern blot and immunohistochemistry. RMR induced a progressive increase in mean arterial pressure and urinary protein excretion. Renal corpuscular area, and mesangial and interstitial fibrosis increased with time after RMR. Immunohistochemical staining for endoglin demonstrated its expression mainly on the endothelial surface of major vessels. In kidneys 1 and 3 months after RMR, the expression of endoglin in renal corpuscles was limited to Bowman's parietal epithelium. In rats 5 months after RMR, the immunoexpression in glomerular endothelium was more marked. Northern blot analysis revealed that rats with RMR showed an increase in the expression of mRNA for endoglin, only at 5 months after RMR. Western blot analysis gave a different time course: a marked increase in the first month, a decrease in the 3rd month and a further increase in the 5th month after RMR. The present study demonstrates increased endoglin expression in rats with severe hypertension and renal damage. This increased endoglin expression coincides with the period of higher renal damage and renal dysfunction.

Tubulointerstitial renal disease

Tubulointerstitial damage, in progressive chronic renal disease of all types, arises because of a complex interplay between factors in the tubular lumen, tubular epithelial cells, peritubular capillaries, resident and infiltrating interstitial cells and extracellular matrix. Particularly in proteinuric renal disease, tubular epithelial cells play a central role in orchestrating these events. In response to mediators arising systemically, in the tubular lumen or from other renal cells, tubular epithelial cells undergo a complex series of structural and functional changes and produce a bewildering number of soluble and fixed mediators, which in turn lead to interstitial inflammation and fibrosis. Knowledge of these interactions has increased exponentially over the past decade, and has defined a number of new targets for treatment. Both expansion and consolidation of this knowledge is needed to determine which of these targets holds the most promise for future treatment.

Progression of chronic renal disease.

Progressive chronic renal disease is characterized histologically by the accumulation of extracellular matrix proteins within the renal interstitium and progressive tubular atrophy. A number of kidney diseases and their progression to end-stage renal failure are driven by the intercrine, autocrine, paracrine, and endocrine effects of angiotensin II. Growth factors appear to have an important role in the development and progression of diabetic nephropathy. Substantial evidence indicates that induction of transforming growth factor beta (TGF-beta) is mediated by high levels of glucose. TGF-beta is pivotal for the hypertrophy of mesangial and tubular cells. Other factors such as hypertension, protein glycation products, and other mediators may further amplify the synthesis of TGF-beta and/or the expression of its receptors in the diabetic state. Other cytokines, such as tumor necrosis factor alpha also contribute to the progression of chronic renal disease. The overall picture derived from several studies of chronic renal disease suggests that treatment of the progression of the renal fibrosis may require the use of several strategies to prevent the advent of end-stage renal disease.

Mechanisms underlying renoprotection during renin-angiotensin system blockade.

Potential determinants of chronic renal disease (CRD) progression were studied in male Munich-Wistar rats subjected to 5/6 nephrectomy and treated with candesartan (Csn; n = 30) or enalapril (Ena; n = 27) from 5 wk postsurgery. Despite control of systolic blood pressure (SBP; 24 wk: Csn = 143 +/- 9; Ena = 148 +/- 8 mmHg), urinary protein excretion rates (U(pr)V) increased over 24 wk (Csn = 92 +/- 10; Ena = 99 +/- 8mg/day). Glomerulosclerosis scores (GS) at 24 wk were similar for Csn (42 +/- 7%) vs. Ena (42 +/- 4%), values close to those of untreated controls at 12 wk (43 +/- 4%). At 24 wk, SBP and UprV correlated strongly with GS, together accounting for 72% of the variance in GS. Renal cortex mRNA levels (determined by competitive RT-PCR) for transforming growth factor (TGF)-beta1 and monocyte chemoattractant protein (MCP)-1 were elevated in Csn and Ena at 12 wk and remained higher at 24 wk vs. sham. Strong correlations were evident among TGF-beta1, MCP-1, and interleukin-1beta and renal injury at 24 wk. Cns and Ena are thus equally effective renoprotective agents in this model. During renin-angiotensin system inhibition, renoprotection is dependent on control of both SBP and UprV. Incomplete suppression of renal cytokine gene expression may also contribute to CRD progression.

Diabetes and Hypertension

The incidence of hypertension is increased in individuals with diabetes mellitus. This is especially true in patients with type 2 diabetes. In these patients high blood pressure is common at the time of diagnosis of diabetes, but the development of diabetes is often preceded by a period during which hyperinsulinemia and insulin resistance is already present. Diabetes represents by itself a major risk of cardiovascular morbidity and mortality. This risk is considerably enhanced by the co-existence of hypertension. One of the main complications of type 2 diabetes is nephropathy, which manifests initially by microalbuminuria, then by clinical proteinuria, leading to a progressive chronic renal failure and end-stage renal disease. Microalbuminuria is considered today as an indicator of renal endothelial dysfunction as well as an independent predictor of the cardiovascular risk. During recent years a number of studies have shown that tight blood pressure control is essential in diabetic patients in order to provide maximal protection against cardiovascular events and the deterioration of renal function. Of note, there is recent evidence indicating that blockade of the renin-angiotensin system with angiotensin II antagonists has marked nephroprotective effects in patients with hypertension and type 2 diabetes, both at early and late stages of renal disease.

Renal expression of aminopeptidase A in rats with two-kidney, one-clip hypertension.

Angiotensin II (ANG II) is a major factor involved in the progression of chronic renal disease. Although the generation of this vasoactive peptide has been investigated in great detail, only a few studies have hitherto addressed the metabolism of ANG II into fragments such as angiotensin III and IV (ANG III, IV) which may exert physiological effects independent of ANG II. Aminopeptidase A (APA) is the major enzyme degrading ANG II. The aim of the current study was to evaluate glomerular APA expression in rats with two-kidney, one-clip hypertension. The left renal artery was restricted with a 0.2-mm silver clip. Kidneys were harvested 1 and 4 weeks after surgery. APA enzyme and protein expression was evaluated in kidney sections. Total APA enzyme activity and mRNA expression was assessed in isolated glomeruli. Degradation of exogenous ANG II by isolated glomeruli was measured with reverse-phase high-performance liquid chromatography. APA enzyme activity, protein, and mRNA expression were stimulated in the clipped kidney 1 week after surgery compared with the contralateral kidney or normal controls. In contrast, 4 weeks after clipping APA activity and expression was higher in the contralateral kidney. In parallel to these findings, degradation of ANG II was greatest in isolated glomeruli obtained from the clipped kidney after 1 week. However, preparations from the contralateral kidney 4 weeks after surgery were more active in the metabolism of exogenous ANG II. The present study provides evidence that APA is complexly regulated in in vivo situations with an activated local renin-ANG II system. ANG II appears to play a direct role in this regulation. However, since conversion of ANG II to ANG III by APA is the initial step leading to the formation of ANG IV which may exert detrimental effects not mediated through classical ANG II receptors, a local increase in APA activity may contribute to the progression of chronic renal disease even during complete AT(1)-receptor blockade.

Identification and characterization of a glomerular-specific promoter from the human nephrin gene.

Podocytes are highly specialized cells that make up a major portion of the glomerular filtration barrier in the kidney. They are also believed to play a pivotal role in the progression of chronic renal disease due to diverse causes that include diabetes (3, 20, 24) and aging (1, 7). Despite the importance of podocytes for kidney function and disease, studies of this cell type have been hindered due to a lack of model systems. Recently, the gene responsible for congenital Finnish nephropathy was identified and named nephrin (13). Nephrin expression is restricted to slit diaphragms of podocytes (11, 30). Infants with congenital Finnish nephropathy develop massive proteinuria and subsequent kidney failure due to podocyte injury. We have identified a 1.25-kb DNA fragment from the human nephrin promoter and 5'-flanking region that is capable of directing podocyte-specific expression in transgenic mice; this represents the first glomerular-specific promoter to be identified. Use of this transgene will facilitate studies of the podocyte in vivo and allow the identification of transacting factors that are required for podocyte-specific expression.

Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways

Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways.BackgroundHepatocyte growth factor (HGF) has been shown to promote tubule repair and renal regeneration following acute injury; however, whether HGF also modulates the development and progression of chronic renal diseases that are characterized by progressive tissue fibrosis is uncertain. To examine this question, this study investigated the functional consequence of blocking endogenous HGF signaling in vivo in a model of chronic renal disease. The effects of HGF on the processes of matrix synthesis and degradation in cultured renal epithelial cells were also examined.MethodsThe level of activity of the HGF/c-met axis was examined in rats following 5/6 nephrectomy at multiple time points. To determine the effects of HGF in modulating chronic renal injury, HGF action was blocked in remnant kidney rats using an anti-HGF antibody. The effects of HGF on extracellular matrix (ECM) synthesis and degradation were examined in renal epithelial cells by 35S-methionine labeling, Western blotting, and zymographic analysis.ResultsAn increase in renal and systemic production of HGF coupled with an increase in renal c-met was observed in rats with remnant kidneys. When HGF action was blocked by the administration of an anti-HGF antibody, rats experienced a rapid decrease in glomerular filtration rate and increased renal fibrosis. Kidney sections from the antibody-treated rats displayed a marked increase in ECM accumulation and in α-smooth muscle actin-positive cells in both the interstitium and tubular epithelium. In vitro studies revealed that HGF reduced net ECM accumulation by human proximal tubule cells (HKC), and this effect was abolished by incubating cells with an anti-HGF antibody. HGF did not alter the ECM synthetic rate in HKC cells. Rather, it markedly increased collagenase such as matrix metalloproteinase-9 (MMP-9) protein expression, as evidenced by Western blotting and zymographic analysis. HGF also decreased the expression of tissue inhibitors of matrix metalloproteinase-1 (TIMP-1) and TIMP-2, the endogenous inhibitors of MMPs.ConclusionThese results suggest that HGF is a potent antifibrogenic factor both in vitro and in vivo. Endogenous activation of HGF tends to preserve kidney structure and function in rats with chronic renal disease by activating matrix degradation pathways. Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways. Hepatocyte growth factor (HGF) has been shown to promote tubule repair and renal regeneration following acute injury; however, whether HGF also modulates the development and progression of chronic renal diseases that are characterized by progressive tissue fibrosis is uncertain. To examine this question, this study investigated the functional consequence of blocking endogenous HGF signaling in vivo in a model of chronic renal disease. The effects of HGF on the processes of matrix synthesis and degradation in cultured renal epithelial cells were also examined. The level of activity of the HGF/c-met axis was examined in rats following 5/6 nephrectomy at multiple time points. To determine the effects of HGF in modulating chronic renal injury, HGF action was blocked in remnant kidney rats using an anti-HGF antibody. The effects of HGF on extracellular matrix (ECM) synthesis and degradation were examined in renal epithelial cells by 35S-methionine labeling, Western blotting, and zymographic analysis. An increase in renal and systemic production of HGF coupled with an increase in renal c-met was observed in rats with remnant kidneys. When HGF action was blocked by the administration of an anti-HGF antibody, rats experienced a rapid decrease in glomerular filtration rate and increased renal fibrosis. Kidney sections from the antibody-treated rats displayed a marked increase in ECM accumulation and in α-smooth muscle actin-positive cells in both the interstitium and tubular epithelium. In vitro studies revealed that HGF reduced net ECM accumulation by human proximal tubule cells (HKC), and this effect was abolished by incubating cells with an anti-HGF antibody. HGF did not alter the ECM synthetic rate in HKC cells. Rather, it markedly increased collagenase such as matrix metalloproteinase-9 (MMP-9) protein expression, as evidenced by Western blotting and zymographic analysis. HGF also decreased the expression of tissue inhibitors of matrix metalloproteinase-1 (TIMP-1) and TIMP-2, the endogenous inhibitors of MMPs. These results suggest that HGF is a potent antifibrogenic factor both in vitro and in vivo. Endogenous activation of HGF tends to preserve kidney structure and function in rats with chronic renal disease by activating matrix degradation pathways.